UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Treatment and disposal of secondary sewage effluent through snowmaking Zapf-Gilje, Reidar 1985

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1985_A1 Z36.pdf [ 8.98MB ]
Metadata
JSON: 831-1.0062722.json
JSON-LD: 831-1.0062722-ld.json
RDF/XML (Pretty): 831-1.0062722-rdf.xml
RDF/JSON: 831-1.0062722-rdf.json
Turtle: 831-1.0062722-turtle.txt
N-Triples: 831-1.0062722-rdf-ntriples.txt
Original Record: 831-1.0062722-source.json
Full Text
831-1.0062722-fulltext.txt
Citation
831-1.0062722.ris

Full Text

TREATMENT AND DISPOSAL OF SECONDARY SEWAGE EFFLUENT THROUGH SNOWMAKING by REIDAR ZAPF-GILJE, P.Eng. M.A.Sc. University of B r i t i s h Columbia, 1979 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n THE FACULTY OF GRADUATE STUDIES (Department of C i v i l Engineering) We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA June 1985 © Reidar Z a p f - G i l j e , 1985 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the head of my department or by h i s or her representatives. I t i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of CJAIIJI £ K The University of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 )E-6 (.3/81) ABSTRACT When secondary sewage e f f l u e n t I s converted to snow, the n u t r i e n t s and r e s i d u a l organics become concentrated i n the e a r l y meltwater discharge through melt-freeze processes w i t h i n the snow-pack. The e a r l y season melt comes o f f r e l a t i v e l y s l o w l y . P r o v i d i n g the s o i l can absorb the e a r l y melt, the bulk of the n u t r i e n t s w i l l be removed even i f l a t e r season melt rates exceeds the s o i l ' s i n f i l -t r a b i l i t y . T h is could provide an inexpensive method f o r n u t r i e n t removal from secondary sewage e f f l u e n t s . Laboratory experiments showed that the degree of i m p u r i t y c o n c e n t r a t i o n was l a r g e l y independent of the number of d i u r n a l melt-freeze c y c l e s , snow depth, snow temperature and i n i t i a l concentra-t i o n of impurity i n the snow. As a r e s u l t , the removal of imp u r i -t i e s from a snowpack can be expressed i n terms of the cumulative melt discharge. A simple exponential decay process was found to des c r i b e the i m p u r i t y removal w e l l f o r most cases. The f i r s t 20% of the melt removed, on the average, 65% of the phosphorus and 86% of the n i t r o g e n from snow made from sewage e f f l u e n t ; and 92% of the potassium c h l o r i d e from snow made from potassium c h l o r i d e s o l u t i o n . S t r i p p i n g of ammonia during snow production and me l t i n g increased the o v e r a l l n i t r o g e n removal to about 90%. A f i e l d i n v e s t i g a t i o n of s a l t movement through a n a t u r a l snowpack confirmed the l a b o r a t o r y r e s u l t s . - i i -TABLE OF CONTENTS Page ABSTRACT i i LIST OF TABLES i v LIST OF FIGURES v ACKNOWLEDGEMENTS v i i CHAPTER 1 - INTRODUCTION 1 CHAPTER 2 - BACKGROUND 2.1. Snow C r y s t a l Formation 5 2.2. Snow C r y s t a l Me tamo r phi sm 16 2.3. Snowmelt E s t i m a t i o n 22 2.4. Water Movement Through Snow 27 2.5. Impurity Movement Through Snow 37 2.6 Impurity Removal Hypothesis 59 CHAPTER 3 - MATERIALS AND METHODS 3.1. Experimental Program 64 3.2. Experimental Equipment 66 3.3. Experimental Procedures 69 3.4. Measurements 72 3.5. Sources of E r r o r 74 CHAPTER 4 - RESULTS AND DISCUSSION 4.1. Pre-Experiment Tests 76 4.2. Impurity Removal During M e l t i n g 77 4.3. R e s i d u a l Snow C h a r a c t e r i s t i c s 99 4.4. Impurity Changes During Snow Production and Storage 106 4.5. F i e l d Experiment 107 4.6. Summary 114 CHAPTER 5 - MODEL FOR PREDICTION OF RUNOFF RATES AND QUALITY 118 CHAPTER 6 - CONCLUSIONS AND RECOMMENDATIONS 121 REFERENCES 126 APPENDIX A - A d d i t i o n a l Results APPENDIX B - Pre-Experiment Tests APPENDIX C - Freezing of Water Droplets APPENDIX D - Design Model Documentation and Computer Code APPENDIX E - Photos of Experiments APPENDIX F - D a i l y Weather Records - i i i -LIST OF TABLES Page 3.1 O u t l i n e of Experiments 65 3.2 Laboratory A n a l y s i s of Sewage E f f l u e n t Samples 65 4.1 Potassium Chloride Removals Observed During the P r e l i m i n a r y Experiments 78 4.2 Potassium Chloride Removals f o r the Baseline Experiments 78 4.3 Impurity Removals Observed During M e l t i n g of Secondary Sewage E f f l u e n t Snow Under B a s e l i n e Conditions 87 4.4 R e s t r i c t e d Exponential Regression of Impurity Removals w i t h Respect to the Cumulative Meltwater F r a c t i o n 87 4.5 Mean Deviations of Observed Potassium Chloride Removals 100 4.6 Observed Changes i n Impurity Concentrations During Laboratory Production of Sewage E f f l u e n t Snow 100 4.7 Impurity Mass Balances Estimated from Melt and Residual Snow Measurements 108 4..8 Impurity Removals From a N a t u r a l Snowpack I r r i g a t e d With B r i n e 108 - i v -LIST OF FIGURES Page 1.1 Di s p o s a l of Sewage E f f l u e n t Through Snowmaking 2 2.1 Grain P u r i f i c a t i o n by Curvature Induced Metamorphism .. 62 2.2 Impurity Concentration by Freeze E x t r a c t i o n of Water from Snowmelt 62 3.1 Laboratory Melt Column 68 4.1 Potassium Chloride Removals f o r Various Solute Strengths, Snow Temperatures and Melt Modes 80 4.2 Removal of Potassium Chloride From Shallow Snowpacks Under Ambient Melt Conditions 80 4.3 E f f e c t s of Melt Mode and Impurity A p p l i c a t i o n on the Removal of S a l t For B a s e l i n e Conditions 83 4.4 E f f e c t s of Snow Depth and Solute Strength on Continuous Melt Concentration of Potassium C h l o r i d e 83 4.5 Mean Removal of Potassium Chloride f o r Various Solute Strengths, Snow Depths, Temperatures and Melt Modes ... 85 4.6 E f f e c t of Snow Wetness on Potassium Chloride Removal Under Continuous Melt Conditions 85 4.7 Removal of Sewage E f f l u e n t I m p u r i t i e s Under Continuous Melt Conditions 89 4.8 Removal of T o t a l Organic Carbon Under Continuous Melt Conditions 89 4.9 Sewage E f f l u e n t I m p u r i t i e s Removal Under Melt-Freeze Co n d i t i o n s 90 4.10 T o t a l Organic Carbon Removal Under Melt-Freeze C o n d i t i o n 90 4.11 C o n d u c t i v i t y and T o t a l K j e l d a h l Nitrogen Removals Under Melt-Freeze and Continuous Melt Conditions 91 4.12 T o t a l Phosporus Removal Under Melt-Freeze and Continuous Melt Conditions 91 4.13 N i t r a t e Removal Under Melt-Freeze and Continuous Melt Conditions 92 - v -Page 4.14 T o t a l Organic Carbon Removal Under Melt-Freeze and Continous Melt Conditions 92 4.15 Average Removals of Sewage E f f l u e n t I m p u r i t i e s f o r Continuous Melt and Melt-Freeze 94 4.16 Impurity M i g r a t i o n Through Snow as Observed During the P r e l i m i n a r y Experiments 94 4.17 Impurity Concentrations i n Top 15 cm of Residual Snow Based on C o n d u c t i v i t y Measurements 103 4.18 Meltwater Discharge Rates Observed During Continuous M e l t i n g of Sewage E f f l u e n t and Potassium C h l o r i d e Baseline Experiments 103 4.19 Impurity Removals From a Brine I r r i g a t e d Snowpack I l l 4.20 Impurity P r o f i l e s Observed During F i e l d Experiment .... I l l - v i -ACKNOWLEDGEMENTS The author thank Drs. S.O. Russ e l l , D.S. Mavinic and W.K. Oldham f o r t h e i r invaluable assistance during the research and thesis preparation, and Dr. J . de Vries for his advice on porous media physics. The author i s also thankful f o r the laboratory assistance received from Susan Jasper and Susan Liptak and for the excellent manuscript typing by Carol Lore and K e l l y Lamb. The author was supported by a NSERC postgraduate scholarship throughout the research period. The research was also supported i n part by Dr. S.O. Ru s s e l l and, Dr. D.S. Mavinic's Research Grants. This work could not have been conducted without the moral support and i n s p i r a t i o n given by L e i f and Margery. - v i i -1. 1. INTRODUCTION Many sm a l l communities face s e r i o u s e f f l u e n t d i s p o s a l r e s t r i c -t i o n i n the winter. Some s i t e s do not meet the reg u l a t o r y r e q u i r e -ments f o r d i s p o s a l of even high q u a l i t y d i s i n f e c t e d sewage e f f l u e n t . Ski r e s o r t s , f o r example, u s u a l l y l a c k s u f f i c i e n t s o i l cover f o r ground d i s p o s a l of e f f l u e n t , and surface water discharge i s u s u a l l y not f e a s i b l e i n the winter because of the low creek flows . Other communities that experience c o l d weather l i m i t a t i o n s of conventional d i s p o s a l technology include those using spray i r r i g a t i o n . The short Canadian i r r i g a t i o n season means storage of sewage generated during the r e s t of the year at a high c o s t . Conversion of secondary, d i s i n f e c t e d e f f l u e n t to snow could provide a p r a c t i c a l d i s p o s a l a l t e r n a t i v e f o r some of these commu-n i t i e s . I t i s a unique d i s p o s a l method that makes use of the n a t u r a l winter c o n d i t i o n s to remove d i s s o l v e d i m p u r i t i e s , such as n u t r i e n t s and r e s i d u a l organic matter, from the e f f l u e n t . These d i s s o l v e d i m p u r i t i e s become concentrated i n the e a r l y melt by melt freeze a c t i o n w i t h i n the e f f l u e n t snowpack (Figu r e 1.1). With a s o i l of s u i t a b l e p e r m e a b i l i t y , the e a r l y meltwater (which comes o f f s l o w l y ) would i n f i l t r a t e the s o i l l e a v i n g a p u r i f i e d snowpack f o r l a t e r s p r i n g melt, some of which would i n f i l t r a t e and some of which would run o f f . The snowmaking d i s p o s a l method has been explored a t a few s k i r e s o r t s over the past decade (Wright-McLaughlin Engineers, 1975; Ontario M i n i s t r y of the Environment, 1982; SIGMA Engineering, 1982). Grab samples of the snow and surface runoff i n d i c a t e d that e f f l u e n t Ammonia stripping Disinfection Snowpack P ,H Infiltration T , . Nutrient uptake •' , Groundwater Figure l.i - Disposal of Sewage Effluent through Snowmaking. 3. i m p u r i t i e s were removed from the snow. The i n v e s t i g a t o r s a l l concluded that the snow d i s p o s a l method appeared very promising and they recommended f u r t h e r and b e t t e r c o n t r o l l e d experiments l e a d i n g to f u l l - s c a l e o p e r a t i o n s . The e f f l u e n t snow d i s p o s a l system may be considered as a winter a p p l i c a t i o n of the conventional spray i r r i g a t i o n d i s p o s a l system. I t i s a two-step process which; (1) concentrates i m p u r i t i e s i n t o the ground by melt-freeze a c t i o n ; and (2) r e t a i n s the i m p u r i t i e s by s o i l s o r p t i o n , p l a n t uptake, and biodegradation. The e f f l u e n t renovation by the e s o i l i s s i m i l a r to that of other ground d i s p o s a l systems. Considerable research i n f o r m a t i o n i s a v a i l a b l e on t h i s s u b j e c t (Metcalf and Eddy, 1979), whereas the mechanism of movement of i m p u r i t i e s through snow i s l a r g e l y unknown. This research has there f o r e concentrated on the snow processes and does not address e f f l u e n t r e n o v a t i o n by the s o i l and v e g e t a t i o n system. The main o b j e c t i v e s of t h i s research were to gain a q u a l i t a t i v e and q u a n t i t a t i v e understanding of the phenomena by which i m p u r i t i e s i n snow become concentrated during the melting, process; and to develop the c a p a b i l i t y of e s t i m a t i n g the i m p u r i t y c o n c e n t r a t i o n i n the runoff from a melting snowpack made of sewage e f f l u e n t . This i n v o l v e d an extensive review of the l i t e r a t u r e i n a number of r e l a t e d f i e l d s and some simple experiments with f r e e z i n g of dye and s a l t s o l u t i o n s , from which a conceptual model d e s c r i b i n g the process of impurity c o n c e n t r a t i o n and mi g r a t i o n through snow was formed. The experimental research program was based on t h i s model. I t invo l v e d c o n t r o l l e d experiments on the melting of l a b o r a t o r y 4. produced snow, made from a s o l u t i o n of KC1, and using c o n d u c t i v i t y as an i n d i c a t o r of the impurity concentration; l a b o r a t o r y e x p e r i -ments usi n g snow made from sewage e f f l u e n t s ; l a b o r a t o r y and f i e l d experiments with brine s o l u t i o n s added to the surface of man-made and n a t u r a l snow; development of a r e l a t i o n s h i p between the cumu-l a t i v e snowmelt f r a c t i o n and the amount of i m p u r i t i e s removed from the snowpack; and the development of a computer model f o r the p r e d i c t i o n of the runoff rates and concentrations from a sewage e f f l u e n t snowpack. Background l i t e r a t u r e and the i m p u r i t y removal hypothesis which was developed from t h i s i n f o r m a t i o n , are presented i n Chapter 2. The experimental design i s o u t l i n e d i n Chapter 3. Chapter 4 presents r e s u l t s and discusses them In the l i g h t of the impurity removal hypothesis. Chapter 5 O u t l i n e s a proposed design model, and presents sample c a l c u l a t i o n s f o r a t y p i c a l d i s p o s a l s i t e . A d e t a i l e d model d e s c r i p t i o n i s presented i n Appendix D. Appendix A contains a d d i t i o n a l experimental r e s u l t s . Appendix B discusses the e a r l y t e s t s conducted during f o r m u l a t i o n of the research program. Appendix C summarizes the r e s u l t s from some simple t e s t s performed f o r i n v e s t i g a t i o n of i m p u r i t y d i s t r i b u t i o n during f r e e z i n g of i n d i -v i d u a l water d r o p l e t s . Appendix E presents photos of experimental equipment, and describes procedures used. D a i l y weather records of the f i e l d experiment period can be found i n Appendix F. 5. 2. BACKGROUND D i s p o s a l of sewage e f f l u e n t through snowmaking has been explored i n only a few f i e l d t e s t s during the l a s t decade (Wright-McLaughlin Engineers (1975); Ontario M i n i s t r y of the Environment, 1982; and SIGMA Engineering, 1982). The t e s t s have been conducted by engineering c o n s u l t a n t s and the r e s u l t s published i n p r o j e c t r e p o r t s . The reports conclude that e f f l u e n t snowpacks are p u r i f i e d w i t h time, but o f f e r few explanations of the processes by which the i m p u r i t i e s may have been removed. The main purpose of the present research was to g a i n an under-standing of the processes of impurity c o n c e n t r a t i o n and m i g r a t i o n through snow, and to develop procedures to estimate the runoff q u a l i t y from a mel t i n g snowpack made from sewage e f f l u e n t . P r i o r to any experiments, the a v a i l a b l e l i t e r a t u r e from r e l e v a n t r e l a t e d f i e l d s such as c r y s t a l formation, c o l l o i d science, chemistry, meteorology, and snow hydrology was reviewed. Ideas and concepts drawn from t h i s review were synthesized i n t o a hypothesis d e s c r i b i n g the processes of i m p u r i t y c o n c e n t r a t i o n and removal from snow. In t h i s chapter the r e l e v a n t l i t e r a t u r e i s reviewed and the im p u r i t y removal hypothesis i s presented. 2.1. Snow C r y s t a l Formation  Atmospheric Snow The formation of snow i n the atmosphere i s p a r t of the p r e c i p i t a t i o n process. When warm, moist a i r i s forced to r i s e , i t i s cooled by a d i a b a t i c expansion. The c o o l e r a i r can hold l e s s water vapour and hence small d r o p l e t s (10-40 um) condense onto 6. a e r o s o l p a r t i c l e s (condensation n u c l e i of 0.01 to 1 um) to form clouds. Only a very small f r a c t i o n of the a e r o s o l p a r t i c l e s are a c t i v e f r e e z i n g n u c l e i . T h e i r f r e e z i n g p o t e n t i a l i n c r e a s e s w i t h decreasing temperature. I t follows then, that clouds, at ambient temperatures below f r e e z i n g , c o n t a i n a mixture of i c e c r y s t a l s and supercooled water d r o p l e t s . The r e l a t i v e d i s t r i b u t i o n depends on the temperature and the amount of a c t i v e i c e n u c l e i present. Typic-a l l y , only one i n a m i l l i o n d r o p l e t s freezes at -10°C. A l l d r o p l e t s freeze spontaneously a t temperatures below -40°C. The i c e c r y s t a l i s the i n i t i a l stage of the forming snow c r y s t a l . I t i s u s u a l l y l e s s than 75 um i n diameter w i t h a simple c r y s t a l shape (hexagonal p l a t e ) . The i c e c r y s t a l continues to grow by vapour d e p o s i t i o n (sublimation) to form a snow c r y s t a l . The snow c r y s t a l i s a large (>300 um) i n d i v i d u a l p a r t i c l e w i t h o f t e n i n t r i c a t e shape ( s t e l l a r , d e n d r i t i c , p l a t e s , e t c . ) . The shape i s determined by the temperature during s u b l i m a t i o n . I f snow c r y s t a l s f a l l through regions of supercooled d r o p l e t s , riming occurs as the dr o p l e t s freeze onto the snow c r y s t a l upon contact. This t y p i c a l l y occurs a t -5 to -20°C and r e s u l t s i n a rimed snow c r y s t a l and, i n the case of extreme r i m i n g , a snow p e l l e t w i l l be formed ( g r a u p e l ) . F i n a l l y , snow c r y s t a l s may c o l l i d e and form l a r g e snow f l a k e s by adhesion (1 mm to 10 mm). The snow c r y s t a l s viewed at the ground may be f a r from the o r i g i n a l s i z e and shape. As the snow c r y s t a l s f a l l through the atmosphere, they change by metamorphism and mechanical abrasion. I f snow f a l l s through lower, warmer atmospheric l a y e r s , complete meta-morphism and m e l t i n g may occur, r e s u l t i n g i n r a i n . Strong winds may break up the snow c r y s t a l s to fragments. 7. Ice N u c l e a t i o n : Ice forming n u c l e i are a e r o s o l p a r t i c l e s which create i c e c r y s t a l s e i t h e r by contact, causing d i r e c t f r e e z i n g of d r o p l e t s , or by f r e e z i n g water vapour onto n u c l e i p a r t i c l e s . This i s the most common form of i c e n u c l e a t i o n and i s r e f e r r e d to as heterogeneous n u c l e a t i o n . Homogeneous n u c l e a t i o n occurs instantaneously below -40°C at which temperature minute i c e c r y s t a l s are formed by chance o r g a n i z a t i o n of water molecules. These minute c r y s t a l s a ct as n u c l e i f o r f u r t h e r i c e formation. Heterogenous i c e n u c l e a t i o n i s extremely complex. In general, the n u c l e i form i c e c r y s t a l s by immersion, contact or d e p o s i t i o n . Immersion r e f e r s to the case where the d r o p l e t nucleus causes the dro p l e t to freeze at a temperature determined by the nature of the nucleus. Contact n u c l e a t i o n i s the process by which the d r o p l e t freezes upon contact with an i c e nucleus. A d e p o s i t i o n nucleus i s a p a r t i c l e upon which vapour d e p o s i t s and f r e e z e s . P i t t e r and Pruppacher (1973) found that contact n u c l e a t i o n f r o z e d r o p l e t s (32.5 ym d i a . ) at temperatures 10°C warmer than the temperatures r e q u i r e d to freeze s i m i l a r s i z e d d r o p l e t s by immersion n u c l e a t i o n . Ice-forming n u c l e i are c h a r a c t e r i z e d by a p a r t i c u l a r a c t i v a t i o n temperature f o r i n i t i a t i o n of i c e formation which depends l a r g e l y on the chemical composition of the p a r t i c l e . E f f e c t i v e i c e n u c l e i are a c t i v e i n the range of -5 to -10°C. Those a c t i v e at temperatures below -20°C are c l a s s i f i e d as poor i c e n u c l e i (Male and Gray, 1981) . 8. Dust from the earth's surface i s the major source of i c e n u c l e i present i n the atmosphere. Clay p a r t i c l e s are the most common and most a c t i v e ice-forming agent. Other important sources are a i r p o l l u t i o n , s a l t and a l s o minute i c e p a r t i c l e s produced by d r o p l e t s p l i n t e r i n g and wind abrasion. The number of a c t i v e i c e n u c l e i Increases one order of magnitude f o r each 4°C decrease i n temperature. C r y s t a l Growth: Ice c r y s t a l s , surrounded by water d r o p l e t s , grow by d e p o s i t i o n of water vapour. Sublimation i n v o l v e s t r a n s f e r of water molecules from the d r o p l e t s to the i c e c r y s t a l faces because the Ice surface vapour pressure i s l e s s than that of the water surface. This process of p r e f e r e n t i a l growth of i c e c r y s t a l s i n clouds i s sometimes r e f e r r e d to as the "Bergeron mechanism" and forms the b a s i s of p r e c i p i t a t i o n formation theory at temperate l a t i t u d e s (Male and Gray, 1981). Sublimation r e s u l t s i n c r y s t a l growth of a v a r i e t y of hexagonal forms. The f i n a l form depends on the r e l a t i v e rates of growth along the b a s a l plane (hexagonal a-axis) and the p r i n c i p a l a x i s ( c - a x i s ) of the c r y s t a l . The i n i t i a l b a s i c shape i s temperature dependent, whereas secondary c r y s t a l f e a t u r e s depends on moisture c o n t r o l l e d growth r a t e s . Riming i s the growth of snow c r y s t a l s by adhesion and subse-quent f r e e z i n g of water d r o p l e t s onto the c r y s t a l ' s surface. The adhesion e f f i c i e n c y i s cl o s e to u n i t y , meaning that nearly a l l drop-9 . l e t s t h a t c o l l i d e w i t h snow c r y s t a l s w i l l f reeze to i t s surface. The onset of riming i s mass dependent and u s u a l l y s t a r t s at 200-300 um d i a . f o r hexagonal p l a t e s and d e n d r i t e s . Riming increases the snow c r y s t a l ' s d e n s i t y and hence the f a l l v e l o c i t y . Extreme riming produces graupels and h a i l s t o n e s . P i t t e r and Pruppacher's (1973) wind tunn e l i n v e s t i g a t i o n of f r e e z i n g of small water d r o p l e t s i n d i c a t e d that secondary, minute i c e p a r t i c l e s are ejected during f r e e z i n g of cloud d r o p l e t s through s p l i n t e r i n g or s h a t t e r i n g . These p a r t i c l e s may act as i c e n u c l e i f o r new i c e c r y s t a l formation. I t i s p o s s i b l e , t h e r e f o r e , that r i m i n g may induce increased formation of i c e c r y s t a l s . Aggregation i s the adhesion of snow c r y s t a l s upon c o l l i s i o n . The c o l l i s i o n e f f i c i e n c y depends on temperature and the strength and d i r e c t i o n of the e l e c t r i c f i e l d of the c r y s t a l . T y p i c a l values l i e between 0.1 and 1.0. The snow c r y s t a l s may adhere by i n t e r l o c k i n g , r i m i n g , vapour d e p o s i t i o n and s i n t e r i n g . The maximum snowflake s i z e occurs at 0°C when the adhesion forces are the l a r g e s t . Machine-Produced Snow The physics of machine snow production has received only l i m i t e d i n v e s t i g a t i o n . Studies r e f e r r e d to i n t h i s s e c t i o n present u s e f u l i n f o r m a t i o n but statements of n u c l e a t i o n and d r o p l e t f r e e z i n g appear to c o n t r a d i c t snow formation physics as discussed and referenced i n the previous s e c t i o n . The d i s c u s s i o n below i s based on the general physics of snow formation and on p r a c t i c a l informa-t i o n reported by " a r t i f i c i a l " snow production i n v e s t i g a t i o n s . Machine snow i s produced by i n j e c t i n g a mixture of compressed 10. a i r and water i n t o a sub-zero atmosphere. The a i r turbulence shears the water into droplets which are subsequently cooled by adiabatic expansion at the nozzle, and by convective and l a t e n t heat loss during the droplet t r a j e c t o r y . The r e l a t i v e importance of the two cooling mechanisms depends on the snowmaking system and i t s operation. Typical laboratory set-ups have a l i m i t e d t r a j e c t o r y length (2.5m f o r t h i s research) and are therefore operated at a high air-water r a t i o to provide s u f f i c i e n t cooling for freezing by adiabatic expansion. For lower air-water r a t i o s , t y p i c a l of f i e l d operations, the heat loss to the atmosphere i s dominant. Heat Transfer: The cooling of droplets r e s u l t s from 1) adiabatic expansion of a i r , and 2) convective and latent heat transfer to the ambient a i r during t r a v e l . The adiabatic cooling e f f i c i e n c y depends on the nozzle design. Most manufacturers report a close to sonic a i r d i s -charge v e l o c i t y , r e s u l t i n g i n a temperature at the nozzle of about -50°F (-45.6°C) for i n l e t pressure of 100 psig (690 kPa). O'Byrne and Haynes (1973) designed a supersonic, external-mixing nozzle that could achieve a i r discharges of -160°F (-107°C) with exit Mach numbers of 1.4 to 1.6 (noise l e v e l of 105 db). As f o r the import-ance of the adiabatic expansion of a i r for the making of machine snow, Chen and Kevorkian (1971) estimated that i t s contribution i s only 1.4% for a t y p i c a l f i e l d operation of 10 gpm (37.8 1/min) water and 100 sem (2.83 m3/min) a i r at 100 psig (690 kPa) . This means that f i e l d production of machine snow depends mainly on transfer of heat to the surrounding ambient a i r . The c o o l i n g of the d r o p l e t s , as they t r a v e l through the a i r , occurs by convective heat l o s s and t r a n s f e r of l a t e n t heat of evaporation. The rat e of heat l o s s i s p r o p o r t i o n a l to the d r o p l e t s i z e , i . e . s m a l l e r drops experience higher heat l o s s due to t h e i r l a r g e r area to volume r a t i o . The convective heat t r a n s f e r i s a l s o p r o p o r t i o n a l to the r a t e of a i r exchange at the s i t e ( i . e . wind and updraft c o n d i t i o n s ) . Chen and Kevorkian (1971) found that the surrounding ambient a i r temperature increased q u i c k l y to 0°C during calm c o n d i t i o n s , preventing f u r t h e r snowmaking. They estimated t h a t the mass of a i r r e q u i r e d f o r s u f f i c i e n t c o o l i n g (~15,000 scfm @ 18°F or 33,000 scfm @ 30°F) (425 m3/min @ -7.8°C or 935 m3/min @ -0.5°C) could be s u p p l i e d by moderate winds. Droplet S i z e : The a i r - w a t e r r a t i o of the snowgun determines the d r o p l e t s i z e . Higher r a t i o s create more turbulence and hence increased shear s t r e s s on the water phase, r e s u l t i n g i n smaller d r o p l e t s . Chen and Kevorkian (1968) reported that t y p i c a l f i e l d operations of 2 to 32 U.S. gpm (9.1 to 145.6 1/min) water and 125 scfm (3.54 m3/min) of a i r at 30-100 p s i g (207-690 kPa) produced d r o p l e t s ranging from one hundred to s e v e r a l hundred um mean volume diameter (MVD) 1. By c o n t r a s t , the high energy input of l a b o r a t o r y snowmaking systems Diameter of a sphere w i t h a volume equal to the mean volume of the water d r o p l e t . 12. typically produce mist-like droplets of 10 to 30 ym for air-water ratios 2-3 orders of magnitude greater than those of f i e l d systems. The water flow rate of the snowmaking system used i n the present research was 0.1 to 0.2 US gpm (0.38-0.76 1/min). The size of the snowgun droplets largely governs how the resulting machine snow is formed and thus the quality of the snow. Effective f i e l d operations produce droplets sufficiently large for deposit in the desired area with minimal loss due to wind. On the other hand, the droplet should be small in order to maximize the ambient air cooling during i t s trajectory. Chen and Kevorkian (1971) suggest that a droplet size of 200-700 ym w i l l provide s u f f i -cient ambient air residence time for freezing (~ 15 sec) and have a terminal velocity sufficiently large to prevent loss of snow by wind drif t i n g . Ice Nucleation: Nucleation of man-made snow crystals i s part of the general nucleation process of freezing of droplets. However, homogeneous nucleation may be more important i n this case. It i s conceivable that homogeneous nucleation may be the dominating mechanism for high air/water snowmaking operations where adiabatic cooling dominates (laboratory systems) whereas, heterogeneous nucleation plays a significant role for f i e l d systems, with an ambient a i r residence time of several seconds. The importance of the heterogenous nuclea-tion increases with decreasing air temperatures. The ice nuclei are supplied by the aerosol present in the compressed air, and in the ambient a i r . A secondary source of nuclei may also be produced by the r i m i n g process during the t r a j e c t o r y . As discussed e a r l i e r , minute i c e c r y s t a l s may be ejected during f r e e z i n g of d r o p l e t s onto snow c r y s t a l s . A common method of i n c r e a s i n g the e f f i c i e n c y of a l a r g e s c a l e snowmaking system i s to use an a u x i l i a r y small ( l a b o r a t o r y scale) snowgun to blow across the l a r g e gun's t r a j e c t o r y . The s m a l l gun i s operated at a high a i r - w a t e r r a t i o r e s u l t i n g i n small d r o p l e t s , high heat l o s s and high c o n c e n t r a t i o n of i c e n u c l e i . C r y s t a l Growth: Machine produced snow c r y s t a l s grow p r i m a r i l y by riming and aggregation. Vapour d e p o s i t i o n growth i s minimal due to the c r y s t a l s ' s h o r t residence time i n the atmosphere. Both r i m i n g and aggregation depend on contact by c o l l i s i o n . Droplets c o l l i d i n g w i t h l a r g e r snow c r y s t a l s adhere by f r e e z i n g onto the c r y s t a l s u r f ace. C o l l i d i n g snow c r y s t a l s aggregate mainly by r i m i n g . The aggregation e f f i c i e n c y of machine produced snow i s most l i k e l y lower than that of atmospheric snow, since adhesion mechanisms such as i n t e r l o c k i n g , vapour d e p o s i t i o n , and s i n t e r i n g have l e s s o p p o r t u n i t y to occur. The growth of snow c r y s t a l s i s important to the o v e r a l l e f f i c i e n c y of a snowmaking process. The growth i s l i m i t e d by the c o n c e n t r a t i o n of a c t i v e i c e n u c l e i , the a i r residence time, and the d r o p l e t temperature. Male and Gray (1981) suggest t h a t a 250 um atmospheric snow c r y s t a l may grow to a 1-2 mm graupel i n 10-20 min. Machine produced snow c r y s t a l s , however, t y p i c a l l y have a residence time 1-2 orders of magnitude l e s s and t h e i r growth w i l l t h e r e f o r e be c o n s i d e r a b l y l e s s than atmospheric snow. O'Byrne and Haynes (1973) using a supersonic, e x t e r n a l - m i x i n g snowgun operated at 120 cfm a i r (3.40 m 3/min), at 110 p s i g (758 kPa), reported i n c r e a s i n g snow c r y s t a l s i z e w i t h i n c r e a s i n g water flow r a t e s from 60 um MVD f o r 7. US gpm (29.5 1/min) to 500 um f o r 9.1 US gpm (34.4 1/min). Lower a i r - w a t e r r a t i o s a l s o r e s u l t e d i n higher d e n s i t i e s of snow (range: 400-750 kg/m3) and increased snow production (range: 0.8-3.8 cm/hr) Laboratory snowmaking can be l i m i t e d by the c o l d chamber dimensions. The l i m i t e d ambient a i r a v a i l a b l e as heat sink and the very much shortened t r a j e c t o r y path d i c t a t e s a high a i r - w a t e r r a t i o o p e r a tion. The r e s u l t i n g high turbulence shears the water i n t o a f i n e d r o p l e t mist of 10-30 um MVD. I t i s conceivable that i n s t a n t -aneous and complete f r e e z i n g may occur at the nozzle when operated a t a high a i r - w a t e r r a t i o . However, the snow i s more l i k e l y to be produced by d e p o s i t i o n and subsequent f r e e z i n g of supercooled d r o p l e t s onto the c o l d chamber w a l l . This snow formation process may be explained by the f o l l o w i n g s c e n a r i o . Homogeneous n u c l e a t i o n and d r o p l e t supercooling occur at the nozzle but the very short t r a j e c t o r y ( f r a c t i o n s of a second) i s i n s u f f i c i e n t f o r f r e e z i n g , thus r e s u l t i n g i n the formation of non-p r e c i p i t a t e d rime snow. This snow formation process i s i d e n t i c a l t the riming on tre e s and other s t r u c t u r e s exposed to winds c a r r y i n g supercooled cloud d r o p l e t s (LaChapelle, 1971). The rime feathers grow from a s m a l l p o i n t and widen i n t o the wind, developing a t r i -angular and sometimes branching shape as shown i n Photo E-6, Appendix E. 15. Snow C r y s t a l C l a s s i f i c a t i o n The term "snow" covers a large v a r i e t y of snow c r y s t a l s formed under d i f f e r e n t conditions. It i s desirable to have a standard c l a s s i f i c a t i o n system by which a l l types of snow and t h e i r formation processes can be s c i e n t i f i c a l l y recorded. Two c l a s s i f i c a t i o n systems are routinely used f o r recording atmospheric snow character-i s t i c s : The International C l a s s i f i c a t i o n of Soli d P r e c i p i t a t i o n and the c l a s s i f i c a t i o n proposed by Magono and Lee (Male and Gray, 1981). C l a s s i f i c a t i o n of machine produced snow has not been standardized. The c r y s t a l structure of i c e i s described by four i n t r i n s i c axes, three a-axes and one c-axis. The a-axes l i e i n the basal plan. The c-axis, also c a l l e d the p r i n c i p a l axis, i s perpendicular to the hexagonal basal plane. Growth i n the basal plane re s u l t s i n f l a t , hexagonal p l a t e l i k e c r y s t a l s whereas growth along the p r i n c i -pal axis produces column-like structures. F i e l d and laboratory observations have demonstrated that the r e l a t i v e growth along the a-and c-axes are con t r o l l e d by temperature and degree of supersatura-t i o n of water vapour i n the atmosphere. As the a i r temperature decreases from 0°C to -25°C, the dominating growth d i r e c t i o n changes from a-axis to c-axis and back to a-axis. When observing newly f a l l e n snow, one should keep i n mind that the snow c r y s t a l morpho-logy may not just be a simple product of i c e c r y s t a l formation. It may have been greatly modified by complex processes during i t s complex l i f e h istory (Male and Gray, 1981). The International c l a s s i f i c a t i o n system divides the i c e p a r t i c l e s Into 10 major categories which can be augmented by four a d d i t i o n a l c h a r a c t e r i s t i c s . This system allows most snow c r y s t a l s to be c l a s s i f i e d i n a broad sense, but i t has led to much m i s c l a s s i -16. f i c a t i o n of so-called " I r r e g u l a r " i c e p a r t i c l e s . The more de t a i l e d c l a s s i f i c a t i o n system, developed by Magono and Lee i n 1966, has 80 main categories, which i s s u f f i c i e n t to c l a s s i f y almost a l l c r y s t a l types. Ice p e l l e t s , s l e e t and hailstones not included i n t h i s system c l a s s i f i c a t i o n may be described by the International Standard. Machine produced snow cannot be f u l l y described by eit h e r of the above mentioned c l a s s i f i c a t i o n systems. The machine snow consists generally of high density, rimed i c e c r y s t a l s . A possible c l a s s i f i c a t i o n system for man-made snow should include: operational conditions, basic shape, secondary growth, moisture content, and mean volume diameter. 2.2. Snow C r y s t a l Metamorphism Af t e r snow has been deposited, the c r y s t a l ' s shape i s modified by metamorphism. The fresh snow c r y s t a l s have i n t r i c a t e and unstable structures of high s p e c i f i c surface area and thus high surface free energy. Temperature and pressure conditions transform the c r y s t a l s towards a state of equilibrium by reducing t h e i r s p e c i f i c surface area. The rate of the metamorphism depends on the snow temperature, whereas the dominating metamorphic mechanism i s dependent on the temperature gradient. Snow c r y s t a l s i n dry snowpacks are metamorphosed by temperature gradient driven vapour transfer. Under isothermal conditions, the temperature gradient i s induced by the c r y s t a l s ' curvature. Meta-morphism i n wet snowpacks occur by melt-freeze and grain coarsening action. Melt-freeze metamorphism produces large p o l y c r y s t a l l i n e 17. c l u s t e r s by daytime melt of small grains and subsequent bonding of the remaining coarse grains i n cl u s t e r s during r e f r e e z i n g . Grain coarsening of isothermal snow r e s u l t i n p r e f e r e n t i a l growth pf large p a r t i c l e s at the expense of smaller ones. The growth i s driven by thermal gradients induced by the ice-water i n t e r f a c e curvature. Machine produced snow undergoes the same metamorphic processes and consequently forms the same metamorphic snow products as those produced from atmospheric snow. However, the machine snow has lower surface free energy than natural snow, due to the rapid f r e e z i n g of the water droplets; thus, i t reaches so-called spring, "corn snow" condition sooner. Equi-Temperature Metamorphism In terms of thermodynamics, newly formed snow c r y s t a l s have very unstable structures. The large s p e c i f i c surface area of these c r y s t a l s i s due to the intermolecular a t t r a c t i o n r e s u l t i n g from the high p o t e n t i a l energy. This i s the surface free energy (or Gibbs Free Energy) of the c r y s t a l . The natural tendency of thermodynamic processes i s to reduce the Gibbs Free Energy to a minimum. In the case of snow metamorphism, mass and energy trans f e r through phase changes reduce the s p e c i f i c surface area of a newly formed c r y s t a l towards the minimum, that of a sphere. This process i s also some-times known as destructive metamorphism, since i t destroys the o r i g i n a l shape of the snow c r y s t a l . It i s most rapid at tempera-tures close to 0°C and i s v i r t u a l l y non-existent at -40°C. Under constant temperature, pressure and surface energy, the Gibbs Free Energy can only be reduced by a decrease of the 18. particle's specific surface area. (Refer to Langham, 1981 for derivation of the Gibbs Free Energy equation for a snow system.) The particle's specific surface area i s reduced by mass transfer of vapour from convex areas of higher to concave areas of lower vapour pressure, resulting i n rounding of anticlastic particles. By the same reasoning, several particles may be bonded together by vapour transfer from crystal points to the necks. This process i s called sintering and reduces the specific surface area of a group of particles. Equi-temperature vapour pressure gradients also form between particles of different size (and curvature). The resulting sublima-tion causes large particles to grow at the expense of small particles. Temperature-Gradient Metamorphism The vapour pressure over an ice surface i s proportional to the temperature of the surface. This implies that, for a given tempera-ture gradient across the snowpack, a corresponding vapour pressure gradient w i l l exist. The vapour pressure gradient can be calculated by the Clausius-Clapeyron equation. The resulting vapour flow from high to low temperature regions in the snowpack is not well understood. Yoshida and others (Langham, 1981) suggested that the vapour i s transferred from grain to grain through successive phase changes. In other words, the vapour i s deposited as ice on an adjacent and colder crystal, while ice on the other side of the same crystal is removed as vapour (hand-to-hand). It i s also possible that the vapour i s transferred 19. through the pore channels d i r e c t l y . Once side channels have been saturated with vapour, the mass transfer would proceed rapidly by displacement of vapour molecules ( i . e . one molecule added at one end displaces a molecule at the other). The amount of temperature gradient induced mass transf e r i s small because of the high latent heat of sublimation. This process i s often c a l l e d constructive metamorphism since i t r e s u l t s i n growth of snow c r y s t a l s . The new c r y s t a l s have an e n t i r e l y d i f f e r e n t structure. They may take the shape of cups, s c r o l l s or columns depending on the l o c a l conditions during growth. However, these sublimation produced c r y s t a l s are a l l characterized by a layered structure that looks l i k e a stepped c r y s t a l surface. The rate of temperature-gradient metamorphism depends on a l t i t u d e and snowstructure but i s only s i g n i f i c a n t for temperature gradients steeper than 0.1°C per centimeter (LaChapelle, 1973). Larger c r y s t a l s generally form for large temperature gradients. The rate of metamorphism increases with increasing vapour pressure gradients. Also, the vapour gradient i s steeper for a given temper-ature gradient at higher temperatures than i t i s at lower ones. Hoar c r y s t a l s may form anywhere i n the snowpack where tempera-ture gradients e x i s t . However, due to ground heat f l u x , the snow near the bottom of the pack changes most r a p i d l y . It i s not uncommon that the e n t i r e lower layer of the snowpack has been re d i s t r i b u t e d through the vapour phase as depth hoar c r y s t a l s . Surface hoarfrost i s formed by sublimation of atmospheric water vapour to form ice c r y s t a l s , when nocturnal r a d i a t i o n cools the surface below the dew-point temperature of the a i r . 20. Melt-Freeze Metamorphism D i u r n a l snow temperature f l u c t u a t i o n s melt snow i n the daytime and r e f r e e z e i t at n i g h t . This process Is e s p e c i a l l y a c t i v e during the s p r i n g . The r e s u l t i n g melt-freeze metamorphism b u i l d s p o l y -granular c l u s t e r s c o n s i s t i n g of l a r g e , coarse grains bonded together by r e f r o z e n meltwater. Grains and bonds of smaller r a d i i of curva-ture have a s l i g h t l y lower melting point than l a r g e r ones, r e s u l t i n g i n p r e f e r e n t i a l m e l t i n g of the former. The meltwater produced w i l l bond the remaining l a r g e r grains i n c l u s t e r s upon r e f r e e z i n g . The meltwater w i l l a l s o c o n t r i b u t e to the g r a i n coarsening process discussed below. G r a i n coarsening i s the r e s u l t of metamorphism of wet, i s o -thermal snowpacks experiencing no net m e l t i n g . In t h i s case, g r a i n s grow by mass tr a n s p o r t of water from small to l a r g e g r a i n s due to the temperature d i f f e r e n c e s at the g r a i n boundaries. Smaller p a r t i c l e s have lower temperatures due to the smaller curvature of the ice-water i n t e r f a c e . The r e s u l t i n g heat f l u x , from large to small p a r t i c l e s , melts the s m a l l ones and r e f r e e z e s the meltwater on the l a r g e r p a r t i c l e s . The r a t e of g r a i n coarsening increases with the degree of s a t u r a t i o n of the snow. The c a p i l l a r y t e n s i o n of "dry" snow (< 7% free water) reduces the curvature induced s t r e s s e s r e s u l t i n g i n smaller temperature d i f f e r e n c e s and thus reduces thermally d r i v e n g r a i n growth (Colbeck, 1979). Raymond and Tusima (1979) suggest that the melt r a t e of very small p a r t i c l e s under saturated c o n d i t i o n s i s independent of the g r a i n s i z e d i s t r i b u t i o n and has an approximate value of 1 0 - 2 mm3/hr. 21. They also concluded that impurities reduce the grain coarsening process by lowering the temperature difference at the grain bound-a r i e s (a r e s u l t of d i l u t e solute concentration i n l o c a l regions of melt and high concentration i n regions of f r e e z i n g ) . Stress-Induced Metamorphism Variations i n s t r e s s , and consequently i n Gibbs free energy, occur i n c r y s t a l matrices of snowpack laye r s . These v a r i a t i o n s produce mass transfer between c r y s t a l s i n snowpacks of high d e n s i t i e s . Mass i s transferred by volume d i f f u s i o n through the i c e l a t t i c e to the contact areas of the c r y s t a l s (high stress zones). The e f f e c t i v e intergranular stress deforms some c r y s t a l s . Crystals not deformed gain e l a s t i c energy (which increases the free energy) and subsequently melt, inducing p r e f e r e n t i a l growth of the deformed c r y s t a l s . C r y s t a l l a t t i c e defects increase the free energy of a snow c r y s t a l . This r e s u l t s i n thermally driven grain growth as above. The d i s l o c a t i o n energy of defective p a r t i c l e s cause a s l i g h t increase i n their temperature and thus l o c a l melting and subsequent refree z i n g on non-defective p a r t i c l e s . C l a s s i f i c a t i o n of Metamorphosed Snow C l a s s i f i c a t i o n of metamorphosed snow Is somewhat simpler because i t has fewer d i s t i n c t l y d i f f e r e n t c r y s t a l forms to consider than does pr e c i p i t a t e d snow. The metamorphism of snow i s an ongoing process towards the f i n a l end product which i s g l a c i e r i c e . The various types of metamorphosed snow are simply stages i n the ongoing process. Sommerfeld and LaChapelle (1970) proposed a c l a s s i f i c a t i o n 22. system based on the mechanism and state of the metamorphic process. This system i s more complete than e a r l i e r ones and i s widely used. 2.3 Snowmelt Estimation Direct a p p l i c a t i o n of rigorous snowmelt physics f o r p r e d i c t i o n of runoff i s not yet p r a c t i c a l , since many of the energy components cannot yet be routinely measured i n the f i e l d . Flood forecasters, therefore, have applied empirical r e l a t i o n s h i p s for d e s c r i p t i o n of the snowmelt process, making various approximations. Most empirical snowmelt models use the a i r temperature as an index of the energy a v a i l a b l e f o r melt because a i r temperature data are widely a v a i l a b l e . Good c o r r e l a t i o n has been achieved i n some cases between temperature index and ph y s i c a l l y based snowmelt estimation (Male and Gray, 1981). The most commonly used temperature index expression f o r predic-t i o n of snowmelt, M(mm/d) i s : M = M £ (T. - T ) + 0.0126 P (1) f i b where: M snowmelt (mm/d) Mf = melt factor (mm/°C d) T. = l index a i r temperature T b = base temperature P r a i n f a l l (mm/day) The temperature index, T^, i s usually represented by the maximum or mean a i r temperature. The base temperature, T^, i s usually set at 0°C. However, d i f f e r e n t forecasters use T. or T, I b for melt corrections of open versus forested s i t e s . Quick and Pipes (1976) use the maximum a i r temperatures to c a l c u l a t e melt generated by open s i t e s and the mean temperature for forested s i t e s . The US Army Corps of Engineers (1956) on the other hand adjusts T, for b open (-2.8 °C) and forested s i t e s (+5.6 °C). The melt factor, M^ , i s basin s p e c i f i c and also v a r i e s annually and seasonally. The US Army Corps of Engineers recommends that the melt factor be determined over several years at d i f f e r e n t points throughout the snow basin of i n t e r e s t . A large v a r i a t i o n i n has been reported over several years of operation at three d i f f e r e n t snow laboratories with an average melt f a c t o r value of 1.74 mm/°C d for T^ = maximum temperature and T^ = 0°C. The large v a r i a t i o n reported i s not s u r p r i s i n g since the a i r temperature i s only one f a c t o r i n f l u e n c i n g the melt rate. Other factors such as wind, humidity, solar r a d i a t i o n , and albedo are not d i r e c t l y r e l a t e d to the a i r temperature. For watersheds, where melt may occur throughout the winter months, a seasonal adjustment of the melt factor i s appropriate. Anderson (1973) suggests that the seasonal v a r i a t i o n follow a time curve with the maximum and minimum coinciding with the summer and winter s o l s t i c e r e s p e c t i v e l y . Anderson reported maximum melt rate values of 1.32 to 3.60 mm/°C d. The maximum melt factors were found to be 2-12 times the minimum, l a r g e l y depending on the degree of forest cover of the basin. 24. Snowmelt runoff may be delayed by i n t e r n a l energy changes and water t r a n s m i s s i o n . Frozen snowpacks must be warmed up to 0°C before any melt can be r e l e a s e d . This i s often a d i u r n a l process where daytime heat input i s l o s t through night-time longwave r a d i a t i o n . The US Army Corps of Engineers (1956) use a " c o l d content" concept. They d e f i n e the c o l d content of a snowpack as the heat r e q u i r e d per u n i t area to r a i s e the temperature of the pack to 0°C. P r e c i s e surface f l u x measurements are r e q u i r e d f o r e s t i m a t i o n of the transmission time f o r the meltwater to reach the base of the snowpack. These f l u x e s are d i f f i c u l t to estimate f o r unsaturated c o n d i t i o n s , and since the meltwater transmission time's c o n t r i b u -t i o n to the t o t a l meltwater r e t e n t i o n i s n e g l i g i b l e , i t u s u a l l y i s ignored. The c a p i l l a r y b a s a l l a y e r may cause some delay of the f i r s t melt discharged from the pack. Later melt reaching the top of the b a s a l l a y e r w i l l merely d i s p l a c e an equal amount of water from the bottom. T y p i c a l basal l a y e r thickness i s about-3-5 cm, s t o r i n g about 1 cm of water. The t h i c k n e s s i s r e l a t e d to the pore s i z e of the snow. For i l l u s t r a t i o n , the snowpack may be considered as two r e s e r -v o i r s i n s e r i e s . Once the energy r e s e r v o i r i s f i l l e d ( i . e . snow-pack has reached 0°C throughout), water s t a r t s f l o w i n g i n t o the b a s a l l a y e r r e s e r v o i r . The t o t a l runoff r e t e n t i o n i s the time i t takes to f i l l the two r e s e r v o i r s ( n e g l e c t i n g the water tran s m i s s i o n t i m e ) . 25. The mean a i r temperature i s a good index of energy a v a i l a b l e for melt for densely forested s i t e s where longwave r a d i a t i o n heat transf e r dominates. However, i t i s not a r e l i a b l e index f o r open s i t e s because shortwave r a d i a t i o n , convective, and latent heat exchanges are not d i r e c t l y r e l a t e d to a i r temperature but may vary considerably, depending on l o c a l weather conditions. In p a r t i c u l a r , the simple temperature index method may seriously underestimate the melt rate when the humidity, solar r a d i t i o n and minimum temperature are high ( t y p i c a l spring c o n d i t i o n s ) . UBC Watershed Model: The snowmelt formulation for open s i t e s by Quick and Pipes (1976) used the following r e f i n e d temperature index equation: T = T + f T . (2) i max e min T , + T./f f = _ E i £ 1 _ L m r d + V f t ( } where: T^ = d a i l y temperature index, °C T = maximum d a i l y a i r temperature, °C max T . = minimum d a i l y a i r temperature, °C mm f = energy p a r t i t i o n m u l t i p l i e r f = d a i l y temperature range factor, usually taken as 2 T, = T - T . d max mm r = reference dewpoint = 10°C 26. The mean a i r temperature i s used as an index of the convective heat transfer f o r forested s i t e s . For open s i t e s , however, Quick. & Pipes use the maximum temperature to allow for the higher solar r a d i a t i o n input. The net radiant energy i s represented by the d a i l y temperature range. This energy i s assumed to produce melt i f the minimum a i r temperature i s above free z i n g and sublimation i f i t i s below. The underlying assumption i s that the minimum temperature i s a good estimate of the dew point and therefore represents the vapour pressure of the a i r . A negative temperature index estimates the energy d e f i c i t of the snowpack. This index i s based on mean a i r temperatures below freezing and a d a i l y decay of 30%. (T ,). = T + (T ,). . • 0.7 (4) ni'k mean v n i k-1 for T < 0 mean where: T ^ = d a i l y negative temperature index, °C T = daily mean a i r temperature, °C mean k = timestep, days Quick and Pipes (1976) assume the water holding capacity of the snow to be 7%. The d a i l y snowmelt due to convective and r a d i t i o n energy transfer i s computed by the standard empirical equation (1) where: = d a i l y negative temperature index, T n i M f = f • M s mean M mean = annual mean melt f a c t o r = 2 mm/°Od f = monthly s o l a r r a d i a t i o n adjustment f a c t o r s f o r B r i t i s h Columbia s = 0.36, 0.64, 1, 1.36, 1.52, 1.64, 1.52, 1.36, 1, 0.64, 0.36, 0.26 f o r January through December r e s p e c t i v e l y . The values f o r the mean melt and the seasonal adjustment f a c t o r were based on s e v e r a l years of snowpillow and streamflow data f o r southern B r i t i s h Columbia. Melt produced by condensation I s estimated as a f r a c t i o n of the mean annual melt f a c t o r m u l t i p l i e d by the d a i l y minimum a i r tempera-tur e . 2.4. Water Movement Through Snow The r e c e n t l y developed theory of water flow through snow i s based on porous media hydrology. I t i s r e s t r i c t e d to v e r t i c a l flow through i s o t h e r m a l , mature snowcovers. Flow through h e a v i l y l a y e r e d packs can only be determined i f the e q u i v a l e n t , a n i s o t r o p i c perme-a b i l i t i e s of the snowpack can be estimated. Colbeck (1972, 1974, 1974b, 1975, 1978) d i s t i n g u i s h e s between v e r t i c a l flow and l a t e r a l b a s a l flow i n a snowcover. The v e r t i c a l flow i s governed by unsaturated, g r a v i t y dominated Darcian c o n d i t i o n s . L a t e r a l b a s a l flow w i l l occur i f the melt r a t e exceeds the i n f i l t r a b i l i t y of the underlying ground. The l a t e r a l flow runs along the snow-ground i n t e r f a c e i n a saturated slush-zone and i s considered to s a t i s f y Darcy's law f o r small to moderate slopes. 28. Snowcover as a Porous Medium The flow of water through snowcovers i s one of the l e a s t under-stood aspects of snow hydrology. The d i f f i c u l t i e s are mainly due to the complex nature of snowcovers r e s u l t i n g from v a r i e d snow forma-t i o n , d e p o s i t i o n and metamorphic c o n d i t i o n s . Snowpacks are formed by a s e r i e s of i n d i v i d u a l s n o w f a l l s . M e l t - f r e e z e processes may form i c e l a y e r s and melt channels through-out the pack. The presence of l i q u i d water causes r a p i d g r a i n growth at the expense of smaller g r a i n s . The r e s u l t i n g mature snow-pack i s coarse grained (1-2 mm), s t r a t i f i e d and heterogeneous. As the snowpack meltout progresses, the g r a i n s i z e i n c r e a s e s , and the i c e lenses degrade, thus r e s u l t i n g i n r a p i d increase i n the me l t r a t e . The s m a l l - s c a l e aspects of water movement through snowcovers has been i n v e s t i g a t e d by Wakama, and de Quervain (1973). T h e i r work on water f i l m versus pore channel flow i s i n t e r e s t i n g , and has rami-f i c a t i o n s regarding the understanding of snow h y d r a u l i c s . As i n hydrogeology, however, t h i s microscopic approach has not l e d to a q u a n t i t a t i v e s o l u t i o n . The a c t u a l geometry and r e s u l t i n g flow p a t t e r n of a t y p i c a l s o i l specimen i s too complex to be described i n microscopic d e t a i l . The Darcian approach replaces the a c t u a l s o i l specimen with an equivalent homogeneous porous medium f o r which macroparameters, such as h y d r a u l i c c o n d u c t i v i t y , can be defined (Freeze and Cherry (1979), H i l l e l l (1981)). For snowcovers, Colbeck (1972) concluded that flow averaging takes place over an area which 29. i s s m a l l compared to the a r e a l extent of the cover. He suggests th a t the e q u i v a l e n t snowpack specimen should have an area of about z 2 , where z i s the depth of the snowcover (1978). For h e a v i l y layered snowcovers, Colbeck (1975) recommends r e p l a c i n g the n a t u r a l pack w i t h a homogeneous but a n i s o t r o p i c medium of e q u i v a l e n t p r o p e r t i e s . In t h i s approach, one-dimensional flow concept represents the stepwise, two-dimensional flow past each l a y e r . The behaviour of the homogeneous a n i s o t r o p i c m a t e r i a l i s equal to the l a y e r e d snowpack f o r a s c a l e l a r g e enough to average the f l u c t u a t i o n s of the flow f i e l d . Lack of snowpack s t r a t i g r a p h y i n f o r m a t i o n i s the most se r i o u s l i m i t a t i o n of t h i s theory. The s i t u a t i o n i s f u r t h e r complicated by the continuous metamorphism i n the presence of water, r e s u l t i n g i n g r a i n growth and i c e l a y e r d e s t r u c t i o n . However, the theory does provide a basis f o r f l u x e v a l u a t i o n f o r s i t u a t i o n s where the snowpack p r o p e r t i e s are known. The q u a n t i t a t i v e theory of flow described above i s at present r e s t r i c t e d to mature, isot h e r m a l snowpacks. Water i n f i l t r a t i n g c o l d snowpacks blocks the pore channels upon r e f r e e z i n g as w e l l as chang-i n g the water and thermal contents of the pack. Colbeck (1972, 1974a) concluded that rigorous a n a l y s i s of water flow through snow at temperatures below f r e e z i n g i s not p o s s i b l e because of these c o m p l i c a t i o n s . In a d d i t i o n , Colbeck's v e r t i c a l flow theory has not been t e s t e d f o r f r e s h l y wetted snowcovers and thus there i s some doubt about i t s a p p l i c a b i l i t y to these c o n d i t i o n s . As the water f i r s t i n f i l t r a t e s the snowcover, i t i s held by the c a p i l l a r i t y i n between the smaller 30. g r a i n s . In the presence of water, the smaller g r a i n s q u i c k l y melt a t the expense of growth of the l a r g e r ones, r e s u l t i n g i n a r a p i d r e l e a s e of water. Machine produced snow has more uniform c h a r a c t e r i s t i c s than atmospheric snow. In a d d i t i o n , snow s t r a t i f i c a t i o n w i l l be much reduced s i n c e a t y p i c a l e f f l u e n t d i s p o s a l system w i l l produce deep packs over a r e l a t i v e l y short time p e r i o d . The r e s u l t i s th a t e f f l u e n t snowpacks are expected to be more homogeneous and have fewer l a y e r s than n a t u r a l packs. The v e r t i c a l flow theory, there-f o r e , may be a p p l i e d to machine snow columns of smaller area-depth s c a l e than suggested by Colbeck. V e r t i c a l Flow The v e r t i c a l f l u x of water through a mature, m e l t i n g and i s o -thermal snowpack can be described by a one-dimensional, unsaturated, Darcian a n a l y s i s . U n f o r t u n a t e l y , t h i s a n a l y s i s cannot be a p p l i e d to col d snowpacks. The problems are associated w i t h : (1) changing water content of the snow as a r e s u l t of m e l t i n g and f r e e z i n g ; (2) es t i m a t i n g the saturated h y d r a u l i c c o n d u c t i v i t y (because of g r a i n coarsening); (3) pore geometry deformation i n response to v a r i a t i o n i n c a p i l l a r y t e n s i o n (Colbeck and Anderson, 1982). However, isot h e r m a l m e l t i n g snowcovers are g e n e r a l l y coarse-grained and thus dominated by g r a v i t y d r i v e n flow. Colbeck (1974) showed th a t pressure g r a d i e n t s are only s i g n i f i c a n t a t very low water f l u x e s , and at the leading edge of the meltwater advance. Wankiewicz (1978) found a pressure g r a d i e n t at the bottom few centimeters of the pack. This c a p i l l a r y f r i n g e and t r a n s i t i o n zone i s a f u n c t i o n of the pore geometry of the snow and the underlying s o i l , and of the s o i l moisture content. F r e e l y d r a i n i n g , mature snowcovers g e n e r a l l y have a free-water content of only 2-10% by volume and hence a l a r g e a i r content. The a i r i s mostly continuous throughout the pores and therefore f r e e to move as i t i s d i s p l a c e d by the water. I t i s t h e r e f o r e reasonable to assume that the a i r and water f l u x e s are balanced at any point i n space and time. The f o l l o w i n g development of the flow equation f o r v e r t i c a l and h o r i z o n t a l flow of water through snow i s based on Colbeck (1972, 1974a, 1976) and Colbeck and Anderson (1982). The Darcy equation f o r unsaturated, v e r t i c a l , and one-dimensional flow i s : a ip a xp <*z = "*<e> ^ + J f - ) (5) where: v e r t i c a l water f l u x , m/s K ( 9 ) unsaturated h y d r a u l i c c o n d u c t i v i t y , m/s 3T|I £ 3z pressure p o t e n t i a l g r a d i e n t , m/m pressure p o t e n t i a l , m = J/N g r a v i t y p o t e n t i a l , m = J/N g g r a v i t a t i o n a l p o t e n t i a l g r a d i e n t , m/m 3z 32. For the case of g r a v i t y dominated f l o w , the f l u x i s equal to the h y d r a u l i c c o n d u c t i v i t y of the porous medium. q = -K(9) = k(6) (6) z M where: k(6) = unsaturated p e r m e a b i l i t y , ra2 . p = den s i t y of water = 1000 kg/m3 & 0°C g = g r a v i t a t i o n a l constant = 9.81 m/s2 H M.S.L. u = dynamic v i s c o s i t y = 1.798 x 10~ 3 kg/ms G 0°C Colbeck and Anderson (1982) suggests the power law as the most convenient r e l a t i o n s h i p f o r saturated and unsaturated perme-a b i l i t i e s . They found that n = 3 produced good c o r r e l a t i o n w i t h f i e l d data and Shimizu's equation k(6) = k S g n (7) where S i s the e f f e c t i v e water s a t u r a t i o n defined as: e S - S . s e • r ^ i r r ( 8 ) wi and k = i n t r i n s i c p e r m e a b i l i t y , m2 S = water content as a f r a c t i o n of pore volume w S . = r e s i d u a l water content ( u s u a l l y 5-6% of pore volume) wi Combining equations ( 6 ) , (7) and (8) gives the f o l l o w i n g expression f o r the f l u x : = - a kS 3 (9) where a = u The conservation of mass for the l i q u i d phase applied to a elemental volume of snowcover i s : 9q dS where i s the e f f e c t i v e porosity ( i . e . the f r a c t i o n of pore volume a v a i l a b l e f o r flow) which may be estimated by: M = M(l - S .) (11) e wi ' Equations (9), (10) and (11) can be combined to give the following equation f o r the v e r t i c a l water flux through a snowcover. 3 C a k )./3 ^2/3 ! ! i » ( 1 2 ) This equation can be solved by the Method of C h a r a c t e r i s t i c s , which gives the rate of flow f o r f i x e d values of the flux (Colbeck, 1972): 34. 4f| = 3 ( a k ) l ' 3 S " I q 2 / 3 (13) dt'q e ^z ^z Equation (13) p r e d i c t s that the movement of a fr o n t increases i n d i r e c t p r o p o r t i o n to q 2 / 3 . Observation, by Colbeck and Davidson (1973), of d i u r n a l meltwaves i n long, repacked snow columns confirmed the t h e o r e t i c a l p r e d i c t i o n . They concluded that slower moving, smaller f l u x e s generated by moving melt are overtaken by f a s t e r moving f l u x e s generated l a t e r i n the day, forming a l e a d i n g edge of the meltwater wave as the two fl u x e s i n t e r s e c t . Colbeck and Anderson (1982) a l s o checked h i s proposed g r a v i t y flow theory using data from snow l y s i m e t e r s i n C a l i f o r n i a and Vermont to c a l c u l a t e the i n t r i n s i c p e r m e a b i l i t y c o e f f i c i e n t s . They found that the p e r m e a b i l i t i e s v a r i e d w i t h d e n s i t y as p r e d i c t e d by Shimizu's expression f or f i n e - g r a i n e d , dry snow p e r m e a b i l i t i e s . The estimated p e r m e a b i l i t i e s ranged from 1.4 x 10~ 9 to 3.8 x I O - 9 m2. Wankiewicz (1979) gives a pe r m e a b i l i t y range of 2-20 x 10~ 9 m2 for dry, newly f a l l e n snow to coarse, s p r i n g snow. L a t e r a l Flow L a t e r a l overland flow occurs when the mel t r a t e reaching the ground exceeds the i n f i l t r a b i l i t y . Colbeck (1974b) proposes that the saturated flow through the slush-zone can be described by Darcy's law f o r small slope angles, ( g , r a d ) . q = - K -r± = - a k 3 (14) x x 3x x where x i s the axi s along the ground i n the flow d i r e c t i o n and g i s the slope angle expressed i n r a d i a n s . The i n t r i n s i c perme-a b i l i t y , k^, i s assumed to represent the saturated c o n d i t i o n s although complete s a t u r a t i o n may not occur because of entrapment of a i r bubbles ( s a t i a t e d p e r m e a b i l i t y ) . Shimizu (1970) r e l a t e s the pe r m e a b i l i t y of snow to g r a i n s i z e and snow d e n s i t y . 1 Applying mass conservation to the saturated l a y e r g i v e s : ^ + »!if • 1 ci5) where I ( x , t ) = net flow i n t o the saturated l a y e r (melt l e s s i n f i l t r a t i o n ) h ( x,t) = saturated l a y e r t h i c k n e s s The equation governing the l a t e r a l flow along the basal l a y e r i s thus obtained by combining equations (14) and (15). . „ 9h , 8 2h ^ 8h T x B 3x x ~Tx Tt = 1 ( l b ) k = 0.077 d 2 exp[-7.8(p /p )] where p i s the density of snow, p i s the d e n s i t y of w a t e r S a n ^ d i s the mean g r a i n diameter. If the increase of h i n the x - d i r e c t i o n i s small compared to the slope, B, then the second d e r i v a t i v e of h with respect to x i s ne g l i b l e . The flow then reduces to: 9 h 9 x I -3t ( 1 7 ) Colbeck solves this equation using a coordinate system that moves with the average p a r t i c l e v e l o c i t y , 1x/n' "^ie t o C a l discharge per unit width i s determined by integr a t i n g equation (10) over time, At, i t takes for an average p a r t i c l e to t r a v e l the length of the saturated layer, L. Short-term v a r i a t i o n of I w i l l be diffused i f the t r a n s i t time, At, through the saturated layer i s large. However, shallow snow-packs with subsnow channels or streams w i l l maintain the d i u r n a l melt cycle s . In summary, the two-step v e r t i c a l - l a t e r a l flow model developed by Colbeck i s ph y s i c a l l y based, yet r e l a t i v e l y simple to use, i n forecasting meltwater routing for small watersheds. At L ( 1 8 ) q /n x 37. 2.5. Impurity Movement Through Snow The p r e f e r e n t i a l movement of i m p u r i t i e s through snow i s a r e s u l t of the r e j e c t i o n of i m p u r i t i e s from the s o l i d phase during r e - f r e e z i n g of meltwater. This s e c t i o n summarizes previous i n v e s t i -g a t i o n s of i m p u r i t y c o n c e n t r a t i o n and m i g r a t i o n i n i c e and snow. The summary incl u d e s i n v e s t i g a t i o n s of: a c i d snow; wastewater c o n c e n t r a t i o n by f r e e z i n g ; e f f l u e n t snow d i s p o s a l ; and f e r t i l i z e r -on-snow. Concentration by Fre e z i n g Soluble i m p u r i t i e s are r e j e c t e d from the forming i c e during r e f r e e z i n g . The r e j e c t i o n e f f i c i e n c y decreases with i n c r e a s i n g f r e e z i n g r a t e s , and i s higher f o r non-ionic than i o n i c s o l u t i o n s . The very high r e j e c t i o n e f f i c i e n c i e s reported i n the l i t e r a t u r e (99.9+%) suggest that s o l u b l e i m p u r i t i e s impose a considerable s t r a i n on the i c e l a t t i c e . However, l i t t l e i s known about how i m p u r i t i e s are incorporated i n the i c e s t r u c t u r e . Bulk entrapment of i m p u r i t i e s may occur when the f r e e z i n g r a t e i s much grea t e r than the r a t e of s o l u t e t r a n s f e r away from the i n t e r f a c e . The r e s u l t i n g c o n s t i t u t i o n a l s u p e r c o o l i n g 1 produces an unstable f r e e z i n g f r o n t from which spikes and den d r i t e s grow i n t o the l i q u i d and trap pockets of concentrated s o l u t e . C o n s t i t u t i o n a l supercooling occurs when the temperature at the phase boundary of a h i g h l y concentrated f r e e z i n g s o l u t i o n i s below the e q u i l i b r i u m l i q u i d temperature (Hobbs, 1974, p. 606). 38. The rate of solute incorporation i n t o i c e i s determined by the d i s t r i b u t i o n c o e f f i c i e n t , k Q, which i s defined as (Terwillinger and D i z i o , 1970): C„(i) where C ( i ) = i n t e r f a c e solute concentration i n s o l i d C ( i ) - i n t e r f a c e solute concentration i n l i q u i d . L i The d i s t r i b u t i o n c o e f f i c i e n t i s a measure of the i c e l a t t i c e d i s t o r -t i o n imposed by a solute. The presence of a solute weakens the molecular binding and increases the intermolecular distances. Consequently, the melting point i s lowered. For small thermal gradients or high rate of solute transport ( r e s u l t i n g i n zero concentration gradient i n the solution) k^ i s equal to the thermo-dynamic equilibrium c o e f f i c i e n t , k Q . In practice, thermodynamic equilibrium i s seldom reached and thus k^ > k Q. The d i f f u s i o n of NaCl i n water, for example, i s 2-3 orders of magnitude les s than the thermal d i f f u s i v i t y of i c e and water. Hence, part of the solute rejected at the freezing front accumulates In a solute r i c h boundary layer at the i n t e r f a c e . The concentration and thickness of the s o l u t e - r i c h layer depend on the rate of freezing, the d i s t r i b u t i o n c o e f f i c i e n t , and the d i f f u s i o n c o e f f i c i e n t of the solute. The enriched solute boundary layer may lead to c o n s t i t u t i o n a l supercooling. This occurs when the actual temperature d i s t r i b u t i o n across the boundary layer i s lower than the s o l i d i f i c a t i o n tempera-39. t u r e . The s o l i d i f i c a t i o n temperature increases sharply from the i n t e r f a c e to the bulk s o l u t i o n as a r e s u l t of the steep concentra-t i o n gradient ( T e r w i l l i n g e r and D i z i o , 1970). C o n s t i t u t i o n a l supercooling produces an unstable s i t u a t i o n . Any i r r e g u l a r i t y at the i c e i n t e r f a c e , reaching ahead of the general f r e e z i n g f r o n t , i s exposed to greater supercooling and thus a c c e l e r -ated growth r e s u l t s . The growth may take the form of c e l l s , spikes and, f o r extensive s u p e r c o o l i n g , d e n d r i t e s . The h i g h l y concentrated s o l u t i o n that develops between these a c c e l e r a t e d growth zones may become trapped i n the s o l i d (Gross, 1968). The d i s t r i b u t i o n c o e f f i c i e n t does not apply to these bulk entrapment c o n d i t i o n s . Since the solute c o n c e n t r a t i o n immediately adjacent to the i n t e r f a c e i s impossible to measure, an e f f e c t i v e d i s t r i b u t i o n c o e f f i c i e n t , k , i s used: C (20) where C = s o l u t e c o n c e n t r a t i o n of the i c e s C = s o l u t e c o n c e n t r a t i o n of the bulk s o l u t i o n , o The e f f e c t i v e d i s t r i b u t i o n c o e f f i c i e n t i s estimated from e x p e r i -mental data. I t i s a f u n c t i o n of sample length f o r non-steady s t a t e c o n d i t i o n s . The steady s t a t e value of ^-eff equals u n i t y , provided there i s no convection. Gross (1968) and Hobbs (1974) described r e d i s t r i b u t i o n of i o n i c i m p u r i t i e s during f r e e z i n g of s o l u t i o n s . The same processes exclude 40. suspended c o l l o i d a l m a t e r i a l and organic s o l u t e s from the i c e . Work by Baker (1967a, 1967b) and Malo and Baker (1968) i n d i c a t e that non-ionized s o l u t e s are r e j e c t e d more r e a d i l y from the i c e than are i o n s . They al s o concluded that the separation e f f i c i e n c y of the non-ionized s o l u t e s i s reduced i f i o n i z e d s o l u t e s are a l s o present i n the f r e e z i n g s o l u t i o n . Treated e f f l u e n t a l s o contains suspended m a t e r i a l . These i n s o l u b l e p a r t i c l e s r e s i s t i n c o r p o r a t i o n i n t o the i c e phase by the mechanism described below. C o l l o i d a l m a t e r i a l may therefore be concentrated i n the snowpack and discharged during the f i r s t melt-water f r a c t i o n along with the s o l u t e s . Larger p a r t i c l e s , however, w i l l be f i l t e r e d by the snow and accumulate at the surface of the snow. P a r t i c l e segregation, induced by i c e , has been studied by s o i l p h y s i c i s t s . Corte (1962) observed that the r e j e c t i o n e f f i c i e n c y increased with decreasing f r e e z i n g r a t e , decreasing p a r t i c l e s i z e , i n c r e a s i n g surface area and surface i r r e g u l a r i t i e s . G i l p i n (1979, 1980) combined previous t h e o r i e s to e x p l a i n the r e j e c t i o n of p a r t i c l e s by an advancing i c e f r o n t . His model i s based on the existence of a l i q u i d - l i k e l a y e r around the p a r t i c l e s . An approaching i c e f r o n t w i l l compress the f i l m a t the p o i n t of contact c r e a t i n g a viscous pressure drop. The pressure drop r e s u l t s i n a flow of water i n t o the contact r e g i o n of the f i l m which e f f e c t i v e l y pushes the p a r t i c l e ahead of the f r o n t . 41. Migration i n Ice As mentioned i n the previous section, very l i t t l e solute i s incorporated d i r e c t l y into the i c e l a t t i c e (kp = 10~ 5 to 1 0 - 3 ) . High impurity content i n i c e i s a re s u l t of bulk entrapment of highly concentrated solute under unstable f r e e z i n g front conditions. The high s a l t content of sea i c e i s an example of bulk entrapment. The solute associated with the s o l i d i c e structure may d i f f u s e through the s o l i d but at very slow rates (Gross, 1968). The mechan-isms of the migration of i n d i v i d u a l ions and molecules are not we l l understood (Drost-Hansen, 1967). The p u r i f i c a t i o n of i n d i v i d u a l i c e grains are, instead, a r e s u l t of gr a i n boundary migration, induced by either curvature or pressure. Glen et a l . (1977), studying temperate g l a c i e r s , suggest that r e c r y s t a l l i z a t i o n during g l a c i e r deformation provides an opportunity for the impurities to reach the grain boundaries. Pressure induced thermal gradients r e s u l t i n release of impurities at point of melt, and subsequent freeze concentration of Impurities i n the cold zones. Continuous r e c r y s t a l l i z a t i o n therefore, w i l l bring the impurities out of the i c e structure to the surface of i n d i v i d u a l grains, where they are available for transport by water. Sea i c e contains s a l t i n i n t e r c r y s t a l l i n e l a y e r s , c a p i l l a r i e s and closed pockets of various forms. The nature and rate of brine migration depends on the form of the i n c l u s i o n s . Doronin and Kheisin (1977) developed a p h y s i c a l l y based equation describing the migration of a brine pocket i n i c e . The equation predicts a down-ward migration rate of 18 cm/month for a temperature gradient .-of 10°C/m of i c e , which compares w e l l with observations made i n the A r c t i c and the A n t a r c t i c . 42. The brine c e l l s move towards higher temperature regions by a melt-freeze process. F r e e z i n g p o i n t depression produces a higher s a l t concentration at the cold region of the c e l l than at the warm end. The c o n c e n t r a t i o n d i f f e r e n t i a l i s reduced by d i f f u s i o n and p o s s i b l y density-induced convection. The thermodynamic e q u i l i b r i u m i s r e s t o r e d by m e l t i n g a t the higher temperature zone; t h i s d i l u t e s the brine and causes freeze concentration of the brine at the co l d end. Temperature gradient d r i v e n m i g r a t i o n of p a r t i c l e s i n s o l i d i c e has been described i n a s i m i l a r manner. Romkens and M i l l e r (1973) suggest that p a r t i c l e s may be enclosed by brine pockets and thus move towards the higher temperature r e g i o n ; t h i s induces melt i n the warm end and subsequent f r e e z i n g at the co l d end. They al s o proposed another model which i s based on e l e c t r i c a l double l a y e r e f f e c t s and viscous flow of water. Both models were found to produce q u a l i t a t i v e agreement w i t h experimental r e s u l t s . The rate of mi g r a t i o n f o r 10-20 um p a r t i c l e s was observed to be about 10 um/hr f o r a temperature gr a d i e n t of 1.55°C/cm. Thermal gradient d r i v e n p a r t i c l e m i g r a t i o n , t h e r e f o r e , i s l i k e l y i n s i g n i f i -cant f o r p a r t i c l e c o n c e n t r a t i o n i n snowcovers when compared to the metamorphic processes. Only during nocturnal c o l d s p e l l s w i l l the temperature gradient i n the surface l a y e r of a snowpack approach the gradient used i n Romkens and M i l l e r s ' l a b o r a t o r y experiment. 43. Solute Transport i n Snow Mass t r a n s p o r t through porous media i s governed by the ad v e c t i o n - d i s p e r s i o n equation (equation (28)). A n a l y t i c a l s o l u t i o n s are l i m i t e d to simple, one-dimensional, steady-state s i t u a t i o n s . Tran s i e n t , unsaturated, one-dimensional solute transport can be solved by numerical methods, only i f the porous medium i s i s o t r o p i c , homogeneous and i n e r t , and i f the water movement i s isothermal and d r i v e n by h y d r a u l i c g r a d i e n t only ( B r e s l e r , 1973). Unfortunately, solute transport through snow v i o l a t e s most of these r e s t r i c t i o n s . The c o n s t a n t l y changing water content, pore geometry, c r y s t a l s i z e and shape, and solute d i s t r i b u t i o n are a l l a r e s u l t of the h i g h l y unstable nature of snow as a porous medium. A r i g o r o u s , p h y s i c a l l y based approach f o r q u a n t i t a t i v e e s t i m a t i o n of so l u t e t r a n s p o r t through snowcovers, i s t h e r e f o r e not p o s s i b l e . Solutes are transported by advection and hydrodynamic d i s p e r -s i o n through porous media. The mean p o s i t i o n of the s o l u t e plume moves at the average i n t e r s t i t i a l v e l o c i t y , through a nonreactive medium, w h i l e d i s p e r s i o n r e s u l t s i n a gradual spreading of the solute f r o n t . Hydrodynamic d i s p e r s i o n i s a r e s u l t of molecular d i f f u s i o n and mechanical d i s p e r s i o n . D i f f u s i o n t r a n s p o r t s molecules from areas of high to areas of low concentration due to thermal-k i n e t i c g r a d i e n t s . The process of mechanical d i s p e r s i o n occurs as a r e s u l t of l o c a l v e l o c i t y v a r i a t i o n s induced by the microscopic pore geometry. This d i s p e r s i o n process i s h i g h l y dependent on the pore geometry and increases w i t h i n c r e a s i n g water flow. The r e l a t i v e importance of d i f f u s i o n and d i s p e r s i o n i s c h a r a c t e r i z e d by the 44. P e c l e t number 1 (Freeze and Cherry, 1979). Solute d i s p e r s i o n through snow i s dominated by the mechanical process f o r melt f l u x e s through r i p e snowpacks (> 10~ 6 m/s). Molecular d i f f u s i o n i s more important f o r low flows o c c u r r i n g e s p e c i a l l y during nighttime. D i f f u s i o n may e f f e c t i v e l y r e d i s t r i b u t e the s o l u t e f r o n t under such c o n d i t i o n s (Colbeck and Anderson, 1982). In f a c t , molecular d i f f u s i o n during low ( o r no) flow reduces the l o c a l s o l ute concentration d i f f e r e n c e s of heterogeneous snow-packs and thus inc r e a s e s the a v a i l a b i l i t y of the s o l u t e s f o r advective t r a n s p o r t . D i f f u s i o n w i l l a l s o cause l a t e r a l spread of the s o l u t e s during v e r t i c a l i n f i l t r a t i o n through l a y e r s that have undergone l e s s g r a i n p u r i f i c a t i o n . The r a t e of r e d i s t r i b u t i o n by d i f f u s i o n i n c r e a s e s w i t h i n c r e a s i n g water content and c o n c e n t r a t i o n g r a d i e n t . Colbeck (1977) developed a s i m p l i f i e d , a n a l y t i c a l model f o r unsaturated, t r a n s i e n t , one-dimensional flow c o n d i t i o n s based on work by B r e s l e r (1973) and Bear (1972). The proposed model i s mainly of academic i n t e r e s t , s i n c e the imposed r e s t r i c t i o n s are too severe for p r a c t i c a l a p p l i c a t i o n to solute movement through s e v e r a l snowpacks. Colbeck suggests t h a t the s i m p l i f i e d model may be u s e f u l for the p r e d i c t i o n of t r a c e r movement through r i p e , deep g l a c i e r s n o w f i e l d s . He derived h i s equation f o r one-dimensional, unsatura-P e c l e t number i s the dimensionless parameter vd/D*, where v i s the average pore v e l o c i t y , d i s the average p a r t i c l e diameter, and D* i s the c o e f f i c i e n t of molecular d i f f u s i o n . The s o l u t e d i s p e r s i o n B i n c r e a s i n g l y dominated by mechanical d i s p e r s i o n as (D^/D*)/(Peclet no.) approaches u n i t y . (D^ = c o e f f i c i e n t of mechanical d i s p e r s i o n ) . The exact slope depends on the nature porous medium and the f l u i d . ted, t r a n s i e n t s o l u t e t r a n s p o r t described by the advection-d i s p e r s i o n equation: D (21) where D = hydrodynamic d i s p e r s i o n , nr C = s o l u t e c o n c e n t r a t i o n , mg/£ v = i n t e r s t i t i a l v e l o c i t y , m/s 9 = volumetric water content, m3/nr t = time, s z = flow d i r e c t i o n coordinate. The hydrodynamic d i s p e r s i o n i s dominated by mechanical d i s p e r -s i o n f o r f l o w r a t e s t y p i c a l of snow. Colbeck, t h e r e f o r e , s et D = vd where d i s the mean g r a i n s i z e and solved f or the propagation r a t e f o r a given s o l u t e c o n c e n t r a t i o n : The f i r s t term represents the so l u t e advection, which occurs at the i n t e r s t i t i a l v e l o c i t y of the water p a r t i c l e s . The complex second term describes the hydrodynamic d i s p e r s i o n of the i m p u r i t i e s . To avoid elaborate numerical approximations, Colbeck suggests that the solute d i s p e r s i o n i n snow may be neglected. Equation (5) then reduces t o : dz | dt 'c e^9z 9 2C 8 z (22) v dz dt 46. (23) The i n t e r s t i t i a l v e l o c i t y , v, can be determined by Colbeck's g r a v i t y dominated flow theory, (Colbeck, 1972). Equation (6) i n s e c t i o n 2.5.3 reduces t o , S r i , " 3 v <24> z when n e g l e c t i n g the i r r e d u c i b l e water s a t u r a t i o n , S .. Based on wi Colbeck's d e r i v a t i o n , then, the propagation of the impurity f r o n t i s equal to the a c t u a l p a r t i c l e v e l o c i t y , and about one t h i r d of the i n f i l t r a t i n g water wave v e l o c i t y f o r the corresponding f l u x . F i e l d d i s t r i b u t i o n of c h l o r i d e and water i n a s o i l w i t h a high r e s i d u a l water content showed that the advancing front of the i n f i l t r a t i n g water moved 2-2.5 times f a s t e r than the s a l t ( B r e s l e r , 1973, p. 982). Colbeck concludes that more data i s r e q u i r e d to c o r r e l a t e the water f l u x and the t r a c e r movement i n order to t e s t the v a l i d i t y of the advection t r a n s p o r t theory f o r i s o t h e r m a l , deep g l a c i e r snow-f i e l d s . Experimental Observations Concentration and m i g r a t i o n of i m p u r i t i e s i n " a c i d " snow have been i n v e s t i g a t e d over the l a s t 10-15 years. The r e s u l t s of the l a b o r a t o r y and f i e l d experiments i n d i c a t e that 50-90% of the i m p u r i -t i e s are associated with the f i r s t 30% of the meltwater. The " a c i d " 47. snow experiments are elab o r a t e and t h e i r r e s u l t s u s e f u l , s i n c e the p h y s i c a l p r i n c i p l e s , and thus the experimental procedures, are s i m i l a r to those of e f f l u e n t snow d i s p o s a l systems. The few, ex p l o r a t o r y e f f l u e n t snow f i e l d t e s t s undertaken to date i n d i c a t e that a p o l l u t a n t removal e f f i c i e n c y b e t t e r than 90% i s po s s i b l e f o r B0D 5, phosphate and ammonia. The d e s t r u c t i o n of most types of c o l i f o r m b a c t e r i a appears to be instantaneous and v i r t u a l l y complete. This s e c t i o n summarizes the experimental r e s u l t s from the freeze c o n c e n t r a t i o n , a c i d snow, and e f f l u e n t snow d i s p o s a l s t u d i e s a v a i l a b l e . Impurity Concentration by Fr e e z i n g : Recent work on c o n c e n t r a t i o n of wastewaters by f r e e z i n g i s reported by Halde (1980). His research i n v e s t i g a t e d the concentra-t i o n e f f i c i e n c y of i n e r t p a r t i c l e s (CaC0 3 and c l a y ) , organic mole-cules ( g l u c o s e ) , ions (Na + and Ci~), and sewage sludges by upward f r e e z i n g under l a b o r a t o r y c o n d i t i o n s . Freezing without s t i r r i n g , r e s u l t e d i n entrapment of the i m p u r i t i e s i n h o r i z o n t a l l a y e r s w i t h c l e a r i c e i n between. As the a p p l i e d mixing energy increased, higher impurity separation was achieved. Halde a l s o found that a reduced f r e e z i n g r a t e of 10 mm/hr produced s l i g h t l y b e t t e r separation e f f i c i e n c y than the 30 mm/hr used i n most of the t e s t s . The highest separation e f f i c i e n c y was observed f o r the lowest CaC0 3 c o n c e n t r a t i o n (10 kg/m 3), f o r which 100% of the p a r t i c l e s were concentrated i n the top 5 cm of the 25 cm la b o r a t o r y column. The 48. recovery f o r the lowest concentration of the other impurities were: clay 90%, glucose 80% (5 kg/m 3), and NaCl 70% (5 kg/m 3). The separ-a t i o n e f f i c i e n c y decreased 20-30% f o r a tenfold increase i n impurity concentration. Halde (1980) applied the p r i n c i p l e s of freeze concentration to the dewatering of raw primary, activated, and digested sewage sludges. He found that the raw sludge of larger p a r t i c l e s i z e and lower solids concentrations achieved 97% recovery i n the upper 15% of the column. The separation of the activated sludge was almost as successful. The s o l i d s recovery i n the top 5 m of the freeze column improved from 65% to 90%, when the smaller p a r t i c l e s of digested sludge were coagulated with an organic p o l y e l e c t r o l y t e . Halde's findings extend previous research of impurity r e j e c t i o n during freezing of d i l u t e solutions to solutions of high i n e r t , i o n i c and organic impurity concentration. Mixing was required to carry impurities away from the ice-water interface i n order to main-t a i n a stable freezing f r o n t . The vigorous mixing may also p a r t l y explain the very high separation e f f i c i e n c y of i n e r t p a r t i c l e s , as compared to i o n i c and organic solutes. The s l i g h t l y better recovery of glucose than NaCl support the Malo and Baker (1968) findings that organic solutes concentrate better than inorganic solutes. Baker (1967a, 1967b) developed a cascade freezing laboratory technique f o r concentration of v o l a t i l e or reactive organic compounds (which may be altered during standard thermal or solvent concentration procedures). The recovery of trace amounts of organic 49. material was found to be essentially complete for single stage freezing, as long as the c r i t i c a l recovery volume of about 15% was not passed. This compares favourably with the recovery volumes reported by Halde (1980). Baker found that complex mixtures of organic compounds did not reduce the separation efficiency of a particular organic compound, whereas the presence of dissolved inorganic salts did. The negative effect of salts was reduced when the freezing solutions were stirred. Stirring did not affect the separation of organic solutes in d i s t i l l e d water. Core testing of lake ice confirms the laboratory solute concen-tration findings. Adams and Lassenby (1982) examined the vertical distribution of ions in lake ice and proposed that these conducti-vity profiles may describe the limno-climatic events of the winter. They found the conductivity of the bottom black ice to be very low, indicating efficient freeze separation during lake freeze-over. Ice formed by freezing of flooded water was white and showed a marked increase in conductivity towards the ice interface below. Successive floodings produced interfaces with conductivities of 10 times that of the black ice and top layers of white ice. The Arctic research of Nakawo and Frederking (1981) revealed some interesting information related to freeze concentration during overland flow. They were studying the salinity and resulting strength of sea ice built up by flooding, with the purpose of predicting the ice thickness required to support d r i l l rigs. Sea 50. water was discharged r a d i a l l y from two side-by-side bore h o l e s , r e s u l t i n g i n a platform with maximum thickness at the centre and taperi n g towards the n a t u r a l i c e thickness over about 100 m. The s a l t c oncentration of the b u i l t - u p i c e increased from about 2.5% near the pump discharge to about 4.0% at the d i s t a n c e of 60 m. The s a l i n i t y of sea water was about 3.2%. This s a l i n i t y d i s t r i b u t i o n was a r e s u l t of s o l u t e r e d i s t r i b u t i o n by f r e e z i n g of water onto the underlying i c e . The r e l a t i v e l y low separation e f f i c i e n c y measured i n Nakawo and Frederking's experiment may be due to the high s o l u t e concentration of sea water and low flow v e l o c i t i e s on the 0.4% i n c l i n e there r e s u l t i n g i n an unstable f r e e z i n g f r o n t and bulk entrapment of b r i n e . This suggestion i s supported by Halde's (1980) f i n d i n g s of s i g n i f i c a n t l y lower s e p a r a t i o n at higher i n i t i a l s o l u t e concentrations and lower s t i r r i n g r a t e s . A c i d Snow: The e f f e c t s of a c i d p r e c i p i t a t i o n on the water ecosystem have been studied e x t e n s i v e l y i n Norway since 1972. The r e s u l t s of s e v e r a l f i e l d and l a b o r a t o r y experiments conclude that the i o n i c i m p u r i t i e s i n a c i d snowpacks are concentrated 5-6 times i n the f i r s t 10% of the meltwater. This slug of high i m p u r i t y c o n c e n t r a t i o n , and hence low pH, have been found to cause serious damage to the aquatic environment ( i n c l u d i n g high f i s h m o r t a l i t y ) i n the bedrock-c o n t r o l l e d drainage basins t y p i c a l of the Norwegian mountain regions. Although not s t r e s s e d i n the Norwegian r e p o r t s , the melt-freeze c o n c e n t r a t i o n of i m p u r i t i e s may be b e n e f i c i a l to drainage basins of s u i t a b l e s o i l s and ve g e t a t i o n . The i o n i c i m p u r i t i e s may 51. be retained i n the s o i l , u t i l i z e d by the vegetation, or oxidized by chemical or b a c t e r i a l means. Johannessen and Henriksen (1978) studied the release of i o n i c impurities from atmospheric snow samples of d i f f e r e n t concentra-tio n s . F i e l d lysimeter observations showed a s i x - f o l d concentration increase of impurities i n the f i r s t 10% melt f r a c t i o n . The concen-trations observed i n the laboratory were somewhat lower, mainly because the homogenized snow samples were melted continuously by a thermostatic jacket of 2.5-3°C along the f u l l length of the walls. This may have reduced the e f f e c t of the cascade-like melt freeze action described i n section 2.6.3, as snow near the bottom had l i t t l e chance to r e d i s t r i b u t e impurities. Johannessen and Henriksen found the r e s u l t s to be independent of concentration over a t e n - f o l d concentration range. They also concluded that the ion si z e and charge were not important factors i n the segregation process. Dahl et a l . (1980), Seip et a l . (1980) and others c a r r i e d out natural snowmelt i n v e s t i g a t i o n s on seven small catchment basins i n the southern mountain region of Norway (approx. elev. 500 m). The basin areas ranged from 75-1300 m2 and had heather on a 15 cm s o i l cover over about 40% of the basin. The rest of the drainage basins' surface consisted of bedrock outcrop. Dahl et a l . (1980) investigated the movement of radioactive tracers during the spring snowmelt i n three mini-catchment basins. The tracers were sprayed evenly over the snowpack i n the beginning 52. of the melt p e r i o d ( A p r i l , 1978). The runoff volume and t r a c e r c o n c e n t r a t i o n were determined d a i l y . They found that the f i r s t 30% of the melt contained 80% of the ^ C a and 90% of the 3 5 S 0 4 t r a c e r r e l a s e d by the meltwater. Mass balance c a l c u l a t i o n s revealed t h a t 60% of the 3 5 S 0 1 + and 85% of the 4 5 C a were r e t a i n e d i n the s o i l and v e g e t a t i o n . The s o i l was e s s e n t i a l l y unfrozen during the s p r i n g melt p e r i o d . Dahl et a l (1980) a l s o determined the c o n c e n t r a t i o n p r o f i l e s of the t r a c e r s on two occasions and found that the slug a d d i t i o n of t f 5Ca moved w i t h a d i s t i n c t c o n c e n t r a t i o n f r o n t through the snowpack. The p r o f i l e s revealed the high degree of s p a t i a l v a r i a t i o n s of snow de n s i t y and i m p u r i t y c o n c e n t r a t i o n s . Seip et a l . (1980) stud i e d the f r a c t i o n a t i o n and runoff of the most important ions found i n n a t u r a l a c i d snow. They used the same samples as Dahl et a l . f o r t h e i r i n v e s t i g a t i o n . The r e s u l t s i n d i -cate that the e a r l y melt f r a c t i o n s had s i g n i f i c a n t l y higher impurity concentrations. From the diagrams given, one may deduce that the f i r s t 30% melt f r a c t i o n contained roughly 80% of the s u l f a t e and n i t r a t e but only 60% sodium and c h l o r i d e . The mini-catchment snowmelt studies show agreement with other i n v e s t i g a t i o n s , i n that the composition of the meltwater changes considerably as i t passes through the s o i l and v e g e t a t i o n (Overrein et a l . , 1980). Many ions are temporarily or permanently r e t a i n e d i n the s o i l . The e f f e c t of v e g e t a t i o n under winter c o n d i t i o n s appears to be l e s s f o r f i e l d than f o r l a b o r a t o r y experiments. However, d e f i n i t e conclusions could not be drawn, because of l i m i t e d data. Colbeck. (1981) simulated the enrichment of atmospheric p o l l u t -ants i n meltwater runoff by adding NaCl to the surface of sieved snow placed i n 35 cm long columns. The columns were subjected to simulated d i u r n a l melt c o n d i t i o n s i n the l a b o r a t o r y . In s p i t e of using t e n s i o n p l a t e s f o r c o l l e c t i o n of meltwater, Colbeck b e l i e v e d some d i l u t i o n of the f i r s t melt occurred; thus the a c t u a l e l e c t r i c a l c o n d u c t i v i t i e s may have been somewhat higher than those observed. The f i r s t 10% of the melt had an impurity concentration of 5x the average (41 umhos/cm). Colbeck a l s o d i s t r i b u t e d NaCl i n four evenly spaced l a y e r s i n a 17 cm deep snow column. The r e s u l t i n g lower i m p u r i t y c o n c e n t r a t i o n of 2.5x the average f o r the f i r s t 10% melt f r a c t i o n i s l i k e l y due to the shorter distance a v a i l a b l e f o r freeze e x t r a c t i o n of water (only 4 cm f o r the bottom NaCl l a y e r ) . Colbeck concluded that the worst scenario f o r environmental damage, by sudden r e l e a s e of atmospheric p o l l u t a n t s from a snow-cover, would be a period of d i u r n a l melt-freeze weather c o n d i t i o n s followed by a slow melt. He suggests that t h i s combination would remove the l a r g e s t q u a n t i t y of i m p u r i t i e s with minimum meltwater d i l u t i o n . This c o n c l u s i o n i s based on two important assumptions; f i r s t l y , that the drainage basin i s impermeable and secondly that the d i u r n a l weather c o n d i t i o n s are the main cause of i m p u r i t y c o n c e n t r a t i o n and m i g r a t i o n i n a snowpack. E f f l u e n t Snow D i s p o s a l : Treatment and d i s p o s a l of sewage e f f l u e n t through snowmaking were f i r s t i n v e s t i g a t e d at s k i r e s o r t s , as a winter a l t e r n a t i v e to spray i r r i g a t i o n or surface water d i s p o s a l . The f i e l d t e s t s under-54. taken to date are: Big Bromley S k i Area, Vermont and Steamboat Springs, Colorado (Wright-McLaughlin Engineers, 1975)); Blue Mountain Resorts, Collingwood, Ontario (Ontario M i n i s t r y of the Environment, 1982); and Kobes, B.C. near Fort St. John (SIGMA Engineering, 1982). In a l l four s t u d i e s snow was produced from n o n - d i s i n f e c t e d lagoon e f f l u e n t and the snowpack was sampled p e r i o d i c a l l y during the s p r i n g snowmelt. Runoff q u a l i t y was estimated by sampling of ponded meltwater at the s i t e . No groundwater samples were taken. S o i l samples were taken by some i n v e s t i g a t o r s but a n a l y s i s and c o n c l u -sions are l a c k i n g . The grab samples of the four s t u d i e s c l e a r l y show that the e f f l u e n t p o l l u t a n t s are removed from the snow. The estimated t o t a l removal r a t e s , i n c l u d i n g changed during snowmaking, are 70-90% B0D 5, 70-90% (NH 3+NH l t +), 95±% PO^, and 99+% f o r t o t a l c o l i f o r m s . However, the grab sample r e s u l t s are not s u f f i c i e n t f o r drawing conclusions regarding c o n c e n t r a t i o n mechanisms of the i m p u r i t i e s , t h e i r m i g r a t i o n path and the i m p u r i t y mass balance. A l l of the i n v e s t i g a t o r s recommended f u r t h e r and b e t t e r c o n t r o l l e d t e s t s , to determine the processes by which i m p u r i t i e s become concentrated i n snow. In a d d i t i o n to the snowpack and meltwater t e s t s , the Ontario study undertook a comprehensive e v a l u a t i o n of the b a c t e r i a l d e s t r u c -t i o n and chemical parameter removal during the snow production process. They concluded that the f r e e z i n g , rather than the atomizing a c t i o n , was r e s p o n s i b l e f o r the almost complete destruc-t i o n of c o l i f o r m s . 55. Wright-McLaughlin Engineers (1975) and Wright (1976) d i s c u s s the experimental set-up and r e s u l t s from a w i n t e r t e s t program f o r conversion of lagoon e f f l u e n t to snow. Observations of snow type, c o l o u r , odour and chemical c h a r a c t e r i s t i c s were made. Composite snow samples, taken at 10, 20 and 40 f t (3.3, 6.6 and 13.2 m) away from the n o z z l e , were analysed f o r B0D 5, TDS, TSS, N0 3, TP, pH, and f e c a l c o l i f o r m s . The authors d i d not s p e c i f y at what depth the snow was sampled. The e f f l u e n t snow was produced p r i m a r i l y i n February. The snowpack was sampled three times during A p r i l . The runoff q u a l i t y was estimated from ponded meltwater samples taken on May 1. The e f f l u e n t snow was o f f - w h i t e with a s l i g h t odour and had a water equivalence of 25 to 35%. The r e s u l t s I n d i c a t e that the p o l l u t a n t r e duction occurred p r i m a r i l y i n the snowpack and not during the snow production process. The t o t a l p o l l u t a n t removal, as estimated from the ponded meltwater samples were 93% B0D 5, 87% TDS, 98% TP, 60% N0 3-N, and -70% NH3~N. The f e c a l c o l i f o r m count of the ponded meltwater was 45 per 100 ml. The report suggested that the p o l l u t a n t s i n f i l t r a t e d the u n d e r l y i n g g r a v e l l y , sandy s o i l . The s o i l had v i r t u a l l y no v e g e t a t i o n and was l o c a t e d 8 f t . (2.4 m) above the adjacent r i v e r . SIGMA Engineering (1982) ran a s m a l l p i l o t study converting about 600,000 I m p e r i a l g a l l o n s (2,720 m3) of e f f l u e n t from an over-flowing evaporation lagoon i n t o snow. The s i t e was grass covered w i t h a few shrubs and t r e e s . The s i t e had a t h i n organic t o p s o i l cover over c l a y . The ground was frozen at the time of snow produc-56. t i o n and p a r t i a l l y thawed during the spring snowmelt sampling. Due to the fr o s t and the tight underlying s o i l , s i g n i f i c a n t meltwater runoff was observed. SIGMA made the snow i n March and c o l l e c t e d snowpack and runoff samples during the spring snowmelt on A p r i l 28 and May 7. The snow samples were taken from the upper and lower layers of the pack. Runoff samples were c o l l e c t e d upstream and downstream from the ef f l u e n t snow p i l e . It i s possible that the runoff samples were contaminated by pollutants deposited by e a r l i e r lagoon overflow or by runoff from a nearby horse c o r r a l . SIGMA also c o l l e c t e d f i v e s o i l samples during the experiment, the res u l t s of which were inconclusive. The samples showed s i m i l a r snowpack p u r i f i c a t i o n as observed i n the Wright-McLaughlin Engineers' (1975) study. The pollutant concentration near the surface was generally 1/3 to 1/2 of the concentrations near the snowpack base. The f e c a l and t o t a l c o l i f o r m l e v e l s of both layers were below the detection l i m i t of 2 MPN/100 ml. The runoff c o l l e c t e d immediately downstream of the snowpack on May 7 (end of snowmelt period) showed a conductivity and BOD^ reduction of about 80%. The reductions on A p r i l 28 were 50% B0D5 and 65% conductivity. The Ontario Ministry of the Environment (OME) and the Delta Group (Ontario Ministry of the Environment, 1982) investigated pollutant and b a c t e r i a l reduction during snow production and storage. They produced snow from lagoon e f f l u e n t during January and February. The snow was deposited on an old grassy a i r f i e l d , which had 20-25 cm top s o i l and 25-30 cm of s i l t y c l a y over c l a y . The research group conducted over 2800 chemical and 1000 m i c r o b i a l t e s t s of lagoon e f f l u e n t , e f f l u e n t snow, meltwater and a e r o s o l s . The e f f l u e n t snow was sampled immediately a f t e r each snow production run and w i t h time. The snow-pack samples were c o l l e c t e d f i v e times during the winter from the top 10 cm, the middle, and the bottom 10 cm of the pack. Nine samples of meltwater were c o l l e c t e d from pools or depressions l e f t on the s i t e a f t e r the snow had melted. S o i l samples were taken but had not yet been analysed. The research group a l s o c o l l e c t e d a e r o s o l samples f o r determination of the c o n c e n t r a t i o n of airborne microorganisms. The p r e l i m i n a r y r e s u l t s are: A n a l y s i s of the f r e s h l y produced snow showed that b e t t e r than 99% of the t o t a l and f e c a l c o l i f o r m s were destroyed during snow production. The research group concluded that the d e s t r u c t i o n i s due to the f r e e z i n g of water d r o p l e t s to snow, since atomizing of wastewater, without f r e e z i n g , had l i t t l e e f f e c t on the b a c t e r i a l s u r v i v a l . A f u r t h e r r e d u c t i o n of c o l i f o r m s was observed to occur i n the snowpack. The f e c a l c o l i f o r m count was reduced to l e s s than the d e t e c t i o n l i m i t of 10 MPN/100 ml a f t e r only 24 hrs. The research team a l s o s t u d i e d other s t r a i n s of b a c t e r i a , some of which had a higher s u r v i v a l r a t e . Aerosol concentrations of c o l i f o r m s were somewhat higher than those reported adjacent to a e r a t i o n s e c t i o n s of secondary treatment p l a n t s . The authors suggest that the reason may be the higher c o l i f o r m count of the poor q u a l i t y e f f l u e n t used. The snow production process was reported to a l t e r the concen-t r a t i o n of s e v e r a l chemical parameters; however, a c l e a r trend does 58. not seem evident from the r e s u l t s presented i n Table 2 of the r e p o r t . One may speculate, as d i d the authors, that the suspended s o l i d s i n c r e a s e i s c o n s i s t e n t and may be p a r t l y due to the p r e c i p i -t a t i o n of hardness and p o s s i b l y to coagulation of organic m a t e r i a l . Some of the c o n c e n t r a t i o n i s a l s o due to evaporation of water, which may be as high as 20% under low humidity c o n d i t i o n s . The r e d u c t i o n of TKN i s l i k e l y due to v o l a t i l i z a t i o n of f r e e ammonia. The v a r i -a t i o n i n B0D 5 i s so high that sampling and a n a l y s i s problems are suspected. I t i s p o s s i b l e t h a t a c a r e f u l a n a l y s i s of the changes and co-changes of the chemical parameters may provide some b e t t e r conclusions as to the e f f e c t of the snow formation process. R e s u l t s from Wright-McLaughlin i n d i c a t e e s s e n t i a l l y no change f o r a l l para-meters, except ammonia. As f o r the b a c t e r i a l d e s t r u c t i o n i n v e s t i g a -t i o n , the atomizing process had l i t t l e or no e f f e c t on the chemical parameters. A 60 cm deep snow p i l e was sampled a t day 0, 7, 10, 29 and 49. The samples were taken from the top, middle and bottom of the p i l e . The p o l l u t a n t c oncentrations decreased w i t h depth and time. The reductions a f t e r 49 days were 72% B0D 5, 95% PO^, and 87% NH 3. Nine meltwater samples c o l l e c t e d at the end of the snowmelt, from pools or depressions on the s i t e , had concentrations of only 3.2 mg/1 B0D 5, 0.05 mg/1 P0 4 and l e s s than 0.1 mg/1 NH 3. These low concen-t r a t i o n s may be p a r t l y due to d i l u t i o n by p r e c i p i t a t i o n or meltwater from surrounding areas. U n f o r t u n a t e l y , one can only speculate as to where the p o l l u t a n t s ended up. The report suggests that most of the p o l l u t a n t s i n f i l t r a t e d the s o i l . 59. F e r t i l i z a t i o n of f o r e s t s i n v o l v e s spraying of urea p e l l e t s from a i r c r a f t . To determine the f a t e of f e r t i l i z e r deposited on snow, two f i e l d experiments were conducted by the P a c i f i c Forest Research Centre, V i c t o r i a (Environment Canada), during the winters of 1981 and 1982. F e r t i l i z e r s and potassium c h l o r i d e were a p p l i e d to 2 m diameter, s i n g l e t r e e p l o t s . Porous ceramic water samplers were i n s t a l l e d at d i f f e r e n t s o i l depths on each p l o t , and a l s o 2-3 m downslope. Unpublished r e s u l t s demonstrate that the i m p u r i t i e s moved q u i c k l y through snow and i n t o the s o i l . The downslope s o i l samples d i d not pick up any of the i m p u r i t i e s ; however, Hetherington suggests that t h i s could be a r e s u l t of inadequate sampling, since c h l o r i d e i s normally q u i t e mobile i n s o i l . L a t e r observations of t r e e growth response i n d i c a t e that the f e r t i l i z e r was r e t a i n e d i n the s o i l and u t i l i z e d by the t r e e s . (Hetherington, 1984, Personal Communication). 2.6. Impurity Removal Hypothesis As e a r l i e r s t a t e d , the mechanisms by which i m p u r i t i e s i n snow become concentrated during the melting process are only p a r t i a l l y understood. This i s e s p e c i a l l y true f o r conversion of e f f l u e n t to snow. One purpose of the extensive l i t e r a t u r e review was to gather and synthesize Ideas and concepts r e l a t i n g to the process of impur-i t y c o n c e n t r a t i o n and removal from an e f f l u e n t snowpack. The r e s u l t i n g i m purity c o n c e n t r a t i o n hypothesis i s presented below. The main i m p u r i t i e s i n snow made from c h l o r i n a t e d secondary sewage e f f l u e n t are s o l u b l e n u t r i e n t s , s o l u b l e organics and some 60. c o l l o i d a l m a t e r i a l . R e c a l l t h a t machine made snow c r y s t a l s are g e n e r a l l y formed by instantaneous f r e e z i n g of super cooled d r o p l e t s by i n t e r n a l or contact n u c l e a t i o n ; thus, although freeze concentra-t i o n of i m p u r i t i e s towards the d r o p l e t centre i s p o s s i b l e i f l a r g e d r o p l e t s are f r o z e n slowly (Appendix C), the very high f r e e z i n g r a t e during snowmaking w i l l l i k e l y prevent any impurity r e d i s t r i b u t i o n during f r e e z i n g . Upon d e p o s i t i o n , snow c r y s t a l s undergo continuous metamorphism. The c r y s t a l growth and rounding reduce the f r e e surface energy of i n d i v i d u a l snow c r y s t a l s towards the thermodynamic e q u i l i b r i u m of l a r g e spheres, under zero net melt c o n d i t i o n s . This g r a i n boundary mig r a t i o n provides an opportunity f o r the snow i m p u r i t i e s to concen-t r a t e a t the surface of the g r a i n s . As the smaller snow g r a i n s melt due to curvature induced thermal g r a d i e n t s , i m p u r i t i e s are released to the porewater. Subsequent r e f r e e z i n g of porewater onto the l a r g e r g r a i n s ( r e q u i r e d to maintain thermodynamic e q u i l i b r i u m ) r e j e c t s the i m p u r i t i e s i n t o the i n t e r s t i t i a l water (see Figure 2 . 1 ) . A s i m i l a r process concentrates i m p u r i t i e s during rounding of i r r e g u l a r grains or g r a i n c l u s t e r s . In t h i s case, water vapour i s transported from convex to concave regions by a curvature induced g r a d i e n t . The dynamic metamorphic process, t h e r e f o r e , e f f e c t i v e l y p u r i -f i e s the i n d i v i d u a l snow grains and concentrates the i m p u r i t i e s a t the g r a i n s u r f a c e s , where they are r e a d i l y a v a i l a b l e f o r t r a n s p o r t by melt or r a i n water. 61. Surface melt or rainwater c a r r i e s the i m p u r i t i e s concentrated a t the surfaces of the snow g r a i n s , as i t p e r c o l a t e s downward. The i m p u r i t i e s w i l l be f u r t h e r concentrated when the water r e f r e e z e s . The freeze c o n c e n t r a t i o n may be v i s u a l i z e d as an e x t r a c t i o n process, whereby water i s drawn from the s o l u t i o n by f r e e z i n g onto snow g r a i n s as the melt s o l u t i o n i n f i l t r a t e s c o l d e r snow l a y e r s (see Figure 2.2). The i n c r e a s i n g l y concentrated s o l u t i o n w i l l move at a decreasing r a t e as the water content approaches the i r r e d u c i b l e l e v e l (5-6% of pore volume). Repeated melt-freeze c y c l e s w i l l produce a high c o n c e n t r a t i o n i n the f i r s t melt-water discharges. The l i t e r a t u r e g e n e r a l l y i n d i c a t e d (Colbeck. and Anderson, 1982), that d i u r n a l melt-freeze c y c l e s and thus a favourable sequence of weather events are e s s e n t i a l f o r achieving s i g n i f i c a n t i m p u r i t y c o n c e n t r a t i o n i n snow. This guided the e a r l y experiments to i n v e s t i g a t e the expected increase i n impurity concentration w i t h i n c r e a s i n g number of simulated d i u r n a l melt-freeze c y c l e s . From the above l i t e r a t u r e review i t i s evident that the complex nature of i m p u r i t y m i g r a t i o n through seasonal snowpacks cannot, as ye t , be q u a n t i t a t i v e l y described by a process-oriented r e l a t i o n s h i p . One must t h e r e f o r e r e s o r t to an e m p i r i c a l r e p r e s e n t a t i o n based on observed r e s u l t s f o r d i f f e r e n t operating c o n d i t i o n s . I t was assumed that the cumulative f r a c t i o n i m p u r i t y removed from the snow could be expressed as a f u n c t i o n of the cumulative melt, i . e . : C(t) = f ( m e l t ( t ) ) (25) freeze melt impurities F i g u r e 2 .1 Grain Purification by Curvature Induced Metamorphism. M E L T C O N C E N T R A T E Figure 2 . 2 Impurity Concentration by Freeze Extraction of Water from Snowmelt. where C(t) = cumulative impurity f r a c t i o n discharged from the snowpack at time, t melt(t) = cumulative meltwater f r a c t i o n . The experimental program was designed to investigate the form of t h i s function and i t s dependency on s i g n i f i c a n t v a r i a b l e s such as the melt rate, the number of melt-freeze cycles, and the snowpack depth and temperature. 3. MATERIALS AND METHODS 3.1 Experimental Program The objective of the research was to in v e s t i g a t e the processes by which impurities i n snow become concentrated, and to determine the r e l a t i o n s h i p between degree of impurity concentration and important variables such as melt conditions, snowpack depth and temperature, and impurity type and i t s i n i t i a l concentration. Five groups of experiments (four i n the laboratory and one i n the f i e l d ) were c a r r i e d out to achieve the research objective. The laboratory program progressed from concept development, design of methods and procedures, evaluation of important parameters, to f i n a l tests on snow made from secondary sewage e f f l u e n t s . The f i e l d experiment was c a r r i e d out to check the r e s u l t s obtained under laboratory conditions with those i n the f i e l d . An outline of the experimental program i s summarized i n Table 3.1. The f i r s t group of experiments included a l l the exploratory t e s t s conducted as part of the formulation of the research program. Freeze concentration concepts, and experimental materials and procedure were evaluated. The r e s u l t s formed the basis f o r the subsequent laboratory test design. A summary of the materials, methods and r e s u l t s are presented i n Appendix B and C. The next group of experiments further refined the experimental methods and investigated the e f f e c t of extreme operating conditions on the degree of impurity concentration i n snow made from a s a l t s o l u t i o n . The degree of concentration was estimated from conducti-v i t y measurements because of the Inherent ease and high reproduci-b i l i t y of t h i s t e s t . There was no p a r t i c u l a r reason f o r using TABLE 3.1. Outline of Experiments. 65. Experimental Type Main Focus Experimental Set of of Experiments Experiments Conditions (1) Number Number of of Experiments Replications Lab 1 (2) Exploratory Explore freeze Dye concentration - snowmaking cone. - melt-freeze cone. KC1 concepts - freezing of solutions Lab 2 Preliminary Refine a) +2.5 to -12°C KC1 experimental b) AM, MF, CM procedures; c) 10-90 cm test extreme d) 500-1500 mg/i range of parameters Lab 3 Baseline Test effect of a) -1"C, MF, CM KC1 depth, amb. c) 45 & 90 cm Brine temp.; imp. d) 200-1000 mg/i cone; melt mode Lab 4 Sewage Test specific a) -1°C, MF, CM Effluent removal for c) 90 cm sewage impuri- d) typical effluent ties under baseline conditions Field Field Compare labor- a) Natural env. cond. Brine atory results c) 200 cm to those d) ~ 300 mg/i(3> obtained under f i e l d conditions (1) a) Ambient temperatures ; b) Melt mode (AM - ambient melt, MF -2-4 2-8 2&4 melt-freeze cycles, CM continuous melting); c) depth of snow; d) average impurity concentration of snow. Methods and results presented in Appendix B and C. Average concentration estimated by mass balance of snow and melt samples. (2) (3) TABLE 3.2 - Laboratory Analysis of Sewage Effluent Samples. Parameter T K N ( 1 ) mh+ + NH3 NO3 + N02 T P ( 1 ) T0C Method Technicon Analyser II Stannous Combust-Chloride ion -Infrared Detection^) 1.0 0.003 0.04 0.1 0.007(4> limit, mg/i Experimental Error( 3>, 2 2 1 4 2 1 5 Reference Technicon Technicon Technicon Technicon Standard Standard N0.321-74A N0.154-71W No.l00-70W No.327-73W Methods Methods (1974) (1973) (1973) (1974) (1980) (1980) (1) Digested with sulfuric acid on a block, digester. (2) As given by the reference. (3) Average experimental error estimated from test replications. (4) For 10 cm Light Path. 66. potassium c h l o r i d e over other types of s a l t . In the t h i r d set of experiments ( b a s e l i n e experiments) a l s o used snow made from potassium c h l o r i d e s o l u t i o n were used f o r the reasons given above. These experiments i n v e s t i g a t e d the e f f e c t of two l e v e l s of melt mode, snow depth, and i n i t i a l i m p u r i t y concentra-t i o n . One parameter at a time was v a r i e d around the e s t a b l i s h e d b a s e l i n e c o n d i t i o n s of 90 cm depth and 1000 mg/1 KC1. The snow temperature were kept at -1° C e l c i u s . The number of r e p l i c a t i o n s ranged from two to e i g h t as shown i n Table 3.1. The c o n c e n t r a t i o n of the d i s s o l v e d secondary sewage e f f l u e n t i m p u r i t i e s ; phosphorus, n i t r o g e n and r e s i d u a l o rganic matter were i n v e s t i g a t e d under b a s e l i n e c o n d i t i o n s and two l e v e l s of melt mode. The f i e l d experiments were conducted to look a t the m i g r a t i o n and c o n c e n t r a t i o n of a s a l t s o l u t i o n added to the surface of a n a t u r a l snowpack. The r e s u l t s were compared to a s i m i l a r experiment conducted In the la b o r a t o r y under b a s e l i n e melting c o n d i t i o n s . 3.2. Experimental Equipment The snowmaking equipment set-up i s shown i n Photos 1 and 2, Appendix E. The equipment co n s i s t e d of one i n t e r n a l mixing, conver-gent snowgun (SMI seeder gun); one constant temperature bath (operated at +1°C); and one c e n t r i g u a l pump (operated at approx. 2 £/min and 700 kPa). The snow was made i n a walk - i n cold chamber of 3m x 3m f l o o r area. The r e f r i g e r a t i o n of the c o l d room was l i m i t e d to a minimum temperature of -12°C. A fan provided a constant c i r c u -l a t i o n of the a i r i n the c o l d chamber. A 12.5 mm diameter a i r l i n e 67. s u p p l i e d compressed a i r from the l a b o r a t o r y compressed a i r system. The a i r pressure at the snowgun was about 600-700 kPa. The a i r discharge r a t e was not measured. The potassium c h l o r i d e s o l u t i o n s were prepared from l a b o r a t o r y grade KC1 and d i s t i l l e d water. C h l o r i n a t e d sewage e f f l u e n t was c o l l e c t e d from an a c t i v a t e d sludge sewage treatment p l a n t (Mamquam STP, Squamish, B.C.), stored overnight at +1°C and converted to snow the f o l l o w i n g day. The machine snow was placed i n 150 mm ID p l e x i g l a s s columns of 100 cm height (Figure 3.1; and P i c t u r e s 5 and 6, Appendix E ) . The snow was melted by heat generated from a general purpose 60 W l i g h t -bulb placed i n a metal r e f l e c t o r . The r e f l e c t o r had a 5 cm s t r i p of i n s u l a t i o n taped to i t s outside rim. The i n s u l a t i o n was r i d i n g on the snow surface and provided a snug f i t to the column w a l l . The c o l d chamber r e f r i g e r a t i o n u n i t was operated with a three hour d e f r o s t c y c l e . The d e f r o s t c y c l e l a s t e d 15 minutes during which the temperature rose 2-3°C. The temperature returned to i t s preset l e v e l w i t h i n 30 minutes of the onset of the d e f r o s t c y c l e . The f i e l d experiment was conducted at Cypress P r o v i n c i a l Park some 30 km north of Vancouver. The s e l e c t e d s i t e was f l a t (2-3% slope) and open, but received some afternoon shade from the nearby f o r e s t . The e l e v a t i o n of the s i t e i s approximately 1200 m. The s i t e c o n f i g u r a t i o n i s shown i n Photo 9 (Appendix E ) . About 5.5 kg of Windsor, non-iodized, coarse household s a l t was d i s s o l v e d i n about 35 I of water. The bri n e s o l u t i o n was a p p l i e d Temperature Control + I°C t o + 5 ° C Sample Bottle- Vent Metal Reflector with 60 W Lightbulb. Controlled by timer Insulation, 5 cm strip Man-ma4e Snow Plexiglass Column 139 mm ID •PVC Nipple 60 mm Plastic Tube Plywood Box Figure 3.1 Laboratory Melt Column 69. w i t h a water can to a 3 m x 3 m p l o t of mature, m e l t i n g , i s o t h e r m a l snowpack. The melting c o n d i t i o n s of the snow r e s u l t e d i n r a p i d d i s t r i b u t i o n of the warm b r i n e (~ 10°C) throughout the depth of the pack. Mass balance c a l c u l a t i o n i n d i c a t e that some brine drained from the m e l t i n g pack (~ 15%). The snowpack and meltwater were sampled weekly over the two months dur a t i o n of the experiment. The snow samples were c o l l e c t e d by p i t excavation and the meltwater from l y s i m e t e r s i n s t a l l e d at the base of the pack (Photo 10, Appendix E ) . Snow temperatures and v i s u a l c h a r a c t e r i s t i c s were recorded a t the time of sampling (see Appendix F f o r d a i l y weather r e c o r d s ) . 3.3. Experimental Procedures The snowgun was operated a t 600-700 kPa w i t h an average water flow of 0.4 to 0.8 l i t r e s per minute. The a i r flow was not measured. The c o l d chamber temperature was -12°C at the s t a r t of the snow production and increased to -5°C a f t e r production of enough snow f o r one melt column (4-5 l i t r e s of s o l u t i o n converted to snow over 5-10 minutes). The water flow was t h r o t t l e d down as the temperature increased i n the attempt to maintain constant, medium-dry snow consistency. The flow of water was adjusted based on v i s u a l o bservations of the snow formed a t the w a l l . This procedure r e s u l t e d i n some u n c o n t r o l l e d d e v i a t i o n s of the consistency of snow produced a t d i f f e r e n t times. The snow consistency a l s o v a r i e d across the c o l d chamber w a l l . Most of the snow formed at the centre of the t r a j e c t o r y and had a higher water equivalence than the snow formed a t the periphery. Four f r e s h snow samples were c o l l e c t e d from the w a l l and melted i n 70. 170 ml wide mouth sample b o t t l e s . Care was taken not to d i s t u r b the snow "rime f e a t h e r s " (see Photo 3, Appendix E ) , thus the obtained values of the water equivalence were r e p r e s e n t a t i v e of the f r e s h snow. The snow was scraped o f f the w a l l , placed i n 20-25 cm l i f t s and the column shaken gently u n t i l no f u r t h e r compaction was v i s u a l l y e vident. The water equivalence of the packed snow was estimated from the t o t a l snowmelt volume. The term snow "wetness" was used as a q u a l i t a t i v e measure of the packing c h a r a c t e r i s t i c s of the snow. I t i s based on the f r e s h and packed water equivalence (w.eq.) and on v i s u a l observations of the snow co n s i s t e n c y . "Dry" snow had a f r e s h snow w.eq. of l e s s than 8%, a packed w.eq. of about 20%, and was l o o s e , f l u f f y and required c o n s i d e r a b l e f o r c e to form snowballs. "Wet" snow had a f r e s h snow w.eq. of greater than 15%, a packed w.eq. of gr e a t e r than 30%, and was wet, cohesive and formed l a r g e b a l l s during scraping and packing of the columns. The "wet" snow produced a lumpy snowpack w i t h numerous a i r p o c k e t s , whereas the "dry" snowpack appeared uniform. Melt-freeze (MF) c o n d i t i o n s were simulated i n the l a b o r a t o r y by a 15 minute melt period followed by a 1 to 3 hour period of r e f r e e z i n g . About 30% of the snow was melted over 3-4 days. Other experiments melted the snow continuously over about 6 hours (continuous melt mode). Two experiments induced melting by i n c r e a s -i n g the c o l d room temperature to between +1.5°C and +2.5°C (ambient melt mode). This r e s u l t e d i n the melt o c c u r r i n g mainly from the column s i d e s . The meltwater from a l l the experiments was c o l l e c t e d a t the base of the column at random i n t e r v a l s , and the cumulative i m p u r i t y removal a s s o c i a t e d w i t h each c o l l e c t e d melt f r a c t i o n estimated. However, to standardize the p r e s e n t a t i o n of the more than 700 data p o i n t s , the i m p u r i t y d i s t r i b u t i o n s were normalized to the .05, .10, .15, .20 and .30 melt f r a c t i o n s . (The c o l l e c t e d melt f r a c t i o n s ranged from 1.4% to 100%.) The normalized i m p u r i t y d i s t r i b u t i o n s were then averaged over the number of r e p l i c a t i o n s performed (2-8). The i m p u r i t y removal f r a c t i o n s are based on the average i m p u r i t y c o n c e n t r a t i o n of the snow and meltwater samples ( C 0 ) . The average c o n c e n t r a t i o n of the f r e s h l y produced snow (C^) was determined from the four grab samples c o l l e c t e d from the c o l d chamber w a l l s . The i m p u r i t y mass balance f o r i n d i v i d u a l columns was estimated as (C -C')/C . o o o The r e s i d u a l snow was removed by thawing of the s i d e s and the base of the p l e x i g l a s s column. The thawing was done by running c o l d tap water over the column u n t i l the r e s i d u a l snow would s l i d e out i n one piece. The snow was brought back i n t o the c o l d room and cut i n t o 5 cm segments using a f r o z e n meat saw ( P i c t u r e 4, Appendix E ) . The top segment was cut to an equivalent thickness of 5 cm a l l o w i n g f o r the melt depression i n the middle of the snow surface. The samples were put i n t o p l a s t i c c ontainers and measured f o r i m p u r i t y c o n c e n t r a t i o n and water equivalence. F i e l d Experiment The snow and meltwater samples were c o l l e c t e d by p i t excava-t i o n . The f i r s t sample p i t was excavated at one corner of the p l o t . Subsequent samples were taken about 3/4 m i n t o the pack from the 72. l a s t sample l o c a t i o n . The p i t s were r e f i l l e d w i t h snow between sample c o l l e c t i o n s . The r e f i l l i n g and the progressive excavation minimized any p o t e n t i a l w a l l e f f e c t and produced samples which were r e p r e s e n t a t i v e of a continuous snowpack. Two meltwater l y s i m e t e r s were^^ i n s t a l l e d on the ground sur-face at the bottom of the pack, about 3/4 m i n t o the pack from the p i t w a l l . The l y s i m e t e r rims were c a r e f u l l y packed with snow and pressed i n t o the o v e r l y i n g snow to ensure proper h y d r a u l i c connec-t i o n from the pack to the l y s i m e t e r s , as water w i l l not d r a i n from a f r e e snow surface u n t i l i t has accumulated to a depth equal to the a i r entry value of the snow. Wankiewicz (1978) reported pressure g r a d i e n t zones at the base of r i p e snowpacks to be 5 cm to 7 cm. He recommended that unenclosed l y s i m e t e r s be designed with r a i s e d rims equal to the height of the pressure g r a d i e n t zone. Samples f o r l a b o r a t o r y determination of c o n d u c t i v i t y were taken every 20 cm, s t a r t i n g at 10 cm above the ground. "Undisturbed" snow samples were excavated from two separate v e r t i c a l s e c t i o n s and care-f u l l y poured i n t o wide mouth p l a s t i c c o n t a i n e r s of 170 ml volume ( P i c t u r e 11, Appendix E ) . The snow temperatures were measured on s i t e . 3.4. Measurements The c o l d room temperature was recorded c o n t i n u o u s l y , and the meltwater box temperature checked p e r i o d i c a l l y , by thermistors with The l y s i m e t e r s were constructed from 100 mm d i a . PVC pipe. They had a rim height of 75 mm and a volume c a p a c i t y of 0.7 l i t r e s . 73. 1°C d i v i s i o n s . The temperature p r o f i l e of the f i e l d snowpack was measured by a mercury reference thermometer with 0.1°C d i v i s i o n s . The c o n d u c t i v i t y of the meltwater and snow samples were measured using Radiometer Type CDM3G S p e c i f i c C o n d u c t i v i t y Meter. The measurements were taken at room temperature (21-23°C) and adjusted to 25°C according to Standard Methods (1980). Orthophosphate (PO^) was determined w i t h i n 12 hours, using the stannuous c h l o r i d e manual c o l o r i m e t r i c method described i n Standard Methods (1980). The r e s t of the meltwater was preserved by s u l p h u r i c a c i d a d d i t i o n (pH < 2 ) , s t o r e d at +4°C and te s t e d w i t h i n two weeks of sampling. T o t a l K j e l d a h l N itrogen (TKN), ammonia n i t r o g e n (NH^ + NH 3), n i t r a t e plus n i t r i t e (N0 3 + N0 2 ) , and T o t a l Phosphorus (TP) were analyzed on the Technicon Autoanalyzer I I , according to the manufacturer's methods, No. 321-74A (1974), No. 154-71W (1973), No. 100-70W (1973), and No. 327-73W (1974). TKN and TP samples were digested with s u l f u r i c a c i d on a block d i g e s t e r . The T o t a l Organic Carbon (TOC) content of the samples was determined by the Combustion-Infrared Method, using a Beckman Model 915 T o t a l Carbon Analyser according to the manufacturer's i n s t r u c -t i o n s and Standard Methods (1980). A l l t e s t s were performed on f i l t e r e d samples. The samples were f i l t e r e d through Whatman F i l t e r Paper No. 4. Table 3.2 l i s t s the t e s t methods, t h e i r d e t e c t i o n l i m i t s , estimated experimental e r r o r , and reference. 3.5. Sources of E r r o r Experimental e r r o r s were a s s o c i a t e d w i t h equipment, sampling and measurements. The equipment-induced e r r o r s of t h i s experiment are b e l i e v e d to have been s m a l l . The sources i n c l u d e the heat source, the cold chamber, and the t e s t column. To avoid systematic and cumulative e r r o r s the four experimental columns were packed w i t h snow and located i n the c o l d chamber i n random order. The r e f l e c t o r heat sources were l i k e w i s e a l l o c a t e d at random. E r r o r s associated with the snowmelt sampling are bel i e v e d to be n e g l i g i b l e f o r the improved procedure of the sewage e f f l u e n t and b a s e l i n e experiments, when the meltwater was c o l l e c t e d d i r e c t l y i n t o the sample b o t t l e s . During the p r e l i m i n a r y experiment, the melt-water was c o l l e c t e d i n Erlenmeyer f l a s k s and t r a n s f e r r e d to the sample b o t t l e s . These r e s u l t s were c o r r e c t e d f o r the estimated amount of sample remaining i n the f l a s k a f t e r t r a n s f e r . The r e s i d u a l volumes were determined by adding a known volume of water to a dry f l a s k and measuring the decant. The r e s i d u a l melt volumes were thereby estimated to be 1.0 ± .5 ml. N e g l i g i b l e contamination occurred during thawing and removing of the r e s i d u a l snow from the melt columns, s i n c e any water generating by melting along the side w a l l was held by tension w i t h i n the snow (snow columns were f r o z e n overnight p r i o r to sampling). The snow volumes were correct e d f o r the estimated 5 ml w.eq. snow l o s s during s l i c i n g of each segment. The measurement of the segment t h i c k n e s s , and i t s depth from the surface, were w i t h i n ± 0.5 cm and ± 1 cm r e s p e c t i v e l y . S t r i p p i n g of ammonia occurred during s l i c i n g , m e l t i n g and 75. f i l t e r i n g of the r e s i d u a l snow samples. Of the 15-20% t o t a l ammonia s t r i p p e d from the snowpack, most may have occurred during the sampling and t e s t i n g procedures. E r r o r s i n c l u d e d e v i a t i o n s caused by sample p r e s e r v a t i o n , and pr e p a r a t i o n , and instrumental s e n s i t i v i t y . The reported d e t e c t i o n l i m i t s of the t e s t s performed are l i s t e d i n Table 3.2. I t i s d i f f i c u l t to q u a n t i f y the i n d i v i d u a l sources of e x p e r i -mental e r r o r s o u t l i n e d above. However, mass balance estimates and comparison of t e s t r e p l i c a t i o n s provide an i n d i c a t i o n of the expected experimental r e p r o d u c i b i l i t y . The impurity mass balance estimates i n c l u d e a l l the experimental m a t e r i a l s , methods and measurements. The average mass balance f o r the potassium c h l o r i d e b a s e l i n e experiments were 2.0% ± 3.0%, which i s w e l l w i t h i n accept-able l i m i t s . Another method that can be used to estimate the p r e c i s i o n of the experiments i s to perform t e s t r e p l i c a t i o n s . P a i r s of columns packed w i t h the same snow were used i n the sewage e f f l u e n t e x p e r i -ments. The i n i t i a l impurity concentrations of each column were estimated through mass balance of the meltwater and snow p r o f i l e samples. The observed d e v i a t i o n of the i n i t i a l impurity concentra-t i o n f o r each column p a i r was averaged over the three experimental r e p l i c a t i o n s . The r e s u l t s are presented i n Table 3.2. The estimated experimental e r r o r ranged from 1% f o r ammonia and phosphate to 4% f o r n i t r i t e and n i t r a t e . These estimates represent the average e r r o r f o r the meltwater and snow p r o f i l e samples, and does not includ e the sampling and measurement e r r o r s of the f r e s h l y produced snow. 76. 4. RESULTS AND DISCUSSION This chapter discusses the experimental r e s u l t s , and t h e i r implications i n the l i g h t of the impurity removal hypothesis postu-l a t e d e a r l i e r . It also presents data on impurity p r o f i l e s i n the re s i d u a l snow and suggests ways of using these p r o f i l e s for predic-t i o n of expected impurity removal. P r a c t i c a l a p p l i c a t i o n of the findings to f u l l - s c a l e operations are also presented. 4.1. Pre-Experiment Tests Dye and potassium c h l o r i d e solutions were allowed to freeze i n a laboratory cold room, with the cold room set at various tempera-tures to c o n t r o l the rate of f r e e z i n g . These tests confirmed that a l l but a small f r a c t i o n of the impurities were excluded from the ic e f o r low freezing rates (Photo 7, Appendix E and Table B . l , Appendix B). However, with a high rate of freezing, the ice front grew unevenly and pockets of concentrated s o l u t i o n became trapped behind the advancing ice front and were incorporated i n the i c e . Other tests were performed i n which a potassium c h l o r i d e solu-t i o n was f i l t e r e d through gravel, sand, and crushed ice at various flowrates and freezing temperatures. These te s t s showed that impurities are concentrated by extraction of water from the so l u t i o n by f r e e z i n g onto the porous media. The impurity concentration was greater for greater s p e c i f i c surface area of the porous medium, lower medium temperature and lower flowrates. The tests also showed snow to be a more e f f e c t i v e water extraction media than sands and gravels. Tests were also c a r r i e d out to study the d i s t r i b u t i o n of 77. i m p u r i t i e s during the f r e e z i n g of d r o p l e t s (Appendix C). The purpose of the t e s t s was to check whether any impurity segregation i s p o s s i b l e during the formation of machine-snow. The t e s t s i n v o l v e d f r e e z i n g dye d r o p l e t s at temperatures as low as -35°C and v i s u a l i n s p e c t i o n of the dye d i s t r i b u t i o n i n the f r o z e n d r o p l e t . The t e s t s showed that i m p u r i t i e s are concentrated towards the centre of the g r a i n when f r o z e n r e l a t i v e l y slowly (~ 20 mm/min). However, the f r e e z i n g r a t e of machine-snow i s an order of magnitude g r e a t e r . At t h i s r a t e , the f r e e z i n g f r o n t i n s t a b i l i t y i s b e l i e v e d to be g r e a t e r , thus r e s u l t i n g i n a uniform d i s t r i b u t i o n of micro " b r i n e pockets" throughout the i n d i v i d u a l snow g r a i n s . 4.2. Impurity Removal During M e l t i n g P r e l i m i n a r y Experiments The p r e l i m i n a r y experiments were undertaken to explore the c o n c e n t r a t i o n of KC1 snow under three melt modes: (1) m e l t - f r e e z e c y c l e s ; (2) continuous melt; and (3) ambient melt. The i n i t i a l snow concentrations ranged from approximately 500-1500 mg/Jl KC1 and the c o l d chamber temperature v a r i e d from + 2.5°C (ambient melt) to -12°C ( m e l t - f r e e z e ) . Table 4.1 summarizes the experimental c o n d i t i o n s and r e s u l t s . R e s u l t s f o r each t e s t r e p l i c a t i o n are presented i n Table A.4, Appendix A. In the f i r s t experiment KC1 snow of 1000 mg/£ c o n c e n t r a t i o n was melted at -10°C under simulated melt-freeze (MF) c y c l e s . Very l i t t l e 'surface m e l t i n g took place at t h i s temperature and the experiment was ended a f t e r 49 melt-freeze c y c l e s . The experiment 78. TABLE 4.1. Potassium Chloride Removals Observed During the Preliminary Experiment Experiment Re pi. Ho. M e l t ^ Mode Impurity^ 2) Cone, mg/i Cold Chamber temp. °C Snow Depth, cm (3) Averagev ' Meltrate ml/MF cycle Impurity Removals for Given Melt Fractions, -051 .101 .151 .20I Z .30 P 1 ( 4 ) 4 MF 1000 -1,-2.-12 90 - - - - - -P2 3 MF 1000 -2 90 16.9 59 90 94 95 -P3 4 MF 1000 -1 90 32.7 49 76 87 93 97 P4 1 MF 500 -1 90 60.3 48 72 76 92 98 1 1500 48 75 82 93 96 P5 4 MF 1000 -0.5 90 69.5 48 78 91 95 97 P6 4 CM 1000 -1 90 430<5> 52 77 85 89 93 P7 4 AM 1000 +2.5 20 11.5 28 50 66 77 90 P8 4 AM 1000 +1.5 10 3.9 21 38 53 66 84 (1) Melt-freeze cycles (MF), Continuous Melt (CM), Ambient Melt (AM). (2) Approximate KC1 concentration mg/£. The actual concentration as determined by conductivity measurements are given in Table A.3, Appendix A. (3) The meltrate decreased with time and metamorphisms of the snow as shown for CM melt conditions in Figure 4.17. The values given represent the average excluding the f i r s t and last melt fractions. (4) These columns.were sampled before melt discharges to determine the impurity front migration. (5) This meltrate has the units of mi/hr. TABLE 4.2. Potassium Chloride Removals for the Baseline Experiments^. Experiment Repl. Melt Impurity Snow Snow Impurity Removals for Number No. Mode Cone. Depth Wetness Given Melt Fractions, % (B«Baseline) mg/i cm .05 j .10 j .15 | .20 j .30 BI 8 MF 1000 90 Med. 53 81 90 94 97 B2 8 CM 1000 90 Med. 55 79 87 90 94 B3 4 CM 1000 45 Med. 41 67 81 87 93 B A ( 2 ) 2 Med. 51 76 85 89 93 1 CM 1000 90 Dry 56 86 95 96 97 1 Wet 44 68 77 83 88 B5 3 CM 200 90 Med. 48 72 83 88 91 B6<3> 2 MF Brine-<4> 90 Med. 53 76 85 89 93 1 on-snow Wet 39 66 72 79 84 (1) Cold chamber temperature was -1 ± 0.5°C. (2) The results from the two medium wetness columns are also included in experiment B2 (3) This experiment simulated forest fertillzation-on-snow rather than sewage disposal A brine of coarse household salt was irrigated on the surface of snow column with a background conductivity of only 5-6 iiS/cm. (4) The equivalent uniform salt concentration was approximately 400 mg/t NaCi. 79. d i d not produce any melt discharge but i m p u r i t y movement was evident from the snow p r o f i l e samples ( S e c t i o n 4.3). The c o l d room tempera-tures during the r e s t of the t e s t s ranged from -0.5°C to -2°C. Temperatures of -0.5°C and -1°C produced s i m i l a r KC1 c o n c e n t r a t i o n , whereas the i m p u r i t y concentrations a s s o c i a t e d w i t h the e a r l y melt f r a c t i o n s were considerably higher f o r a snow temperature of -2°C (Table 4.1). The e f f e c t of i n i t i a l i m p u rity s t r e n g t h was t e s t e d next. The i n i t i a l KC1 concentrations of the snow were 500, 1000, and 1500 mg/Jl. The e f f e c t s of these impurity s t r e n g t h l e v e l s on the potassium removal were not d e t e c t a b l e . I t had been expected that the degree of impurity c o n c e n t r a t i o n could be d i r e c t l y r e l a t e d to the number of MF c y c l e s and hence the weather c o n d i t i o n s before s p r i n g melt. Sudden and continuous melt c o n d i t i o n s were expected to produce very l i t t l e i m p u r i t y concentra-t i o n . To t e s t t h i s hypothesis, snow columns were melted over 4-6 hours. The r e s u l t s were s u r p r i s i n g . The continuous melt (CM) con-d i t i o n s produced impurity removals s i m i l a r to those observed under simulated melt-freeze c y c l e s ( F i g . 4.1). This l e d to the r e v i s e d melt-freeze hypothesis described i n S e c t i o n 4.6. The p r a c t i c a l i m p l i c a t i o n of t h i s f i n d i n g i s s i g n i f i c a n t . I f c o r r e c t , i t means that the weather c o n d i t i o n s are not important f o r a c h i e v i n g a h i g h degree of i m p u r i t y removal from e f f l u e n t snowpacks and that m i l d winter c o n d i t i o n s may not be d e t r i m e n t a l to the o v e r a l l performance of a f u l l - s c a l e e f f l u e n t d i s p o s a l o p e r a t i o n . Because of the Import-ance of t h i s f i n d i n g , the b a s e l i n e and the sewage e f f l u e n t e x p e r i -ments performed were a l l t e s t e d under both CM and MF c o n d i t i o n s . 1.0 0.8 "5 § 0.6 e or ~ 0.4 v_ a 1 1 1 — 4 — - — ' < — : ^ L E G E N D O M F , - 0 . 5 « C , - I « C . - If 5 0 0 . 1000. 1500 mg L -A M F , - 2 * C . I 0 0 0 m g / L _ • C M , - l ' C , l O O 0 m g / L ' I I I 0 0.05 0.10 0.15 0.20 0.25 0-30 Cumulative Melt Fractions Figure 4.1 Potassium Chloride Removals for Various Solute Strengths, Snow Temperatures, and Melt Modes. I.Oi 1 1 1 1 r 0 0.05 0.10 0.15 0.20 0.25 0.30 Cumulative Melt Fractions Figure 4.2 Removal of Potassium Chloride from Shallow Snowpacks Under Ambient Melt Conditions. 81. The l a s t set of experiments involved melting of potassium chloride snow at above zero room temperature. This was done for two reasons. F i r s t l y , the r e s u l t s could be compared to impurity concen-tratio n s i n snow as reported i n the acid p r e c i p i t a t i o n l i t e r a t u r e (Johannessen and Henriksen, 1978). Secondly, i t was believed that degree of impurity removals obtained would r e f l e c t the i n i t i a l d i s t r i b u t i o n of impurities i n i n d i v i d u a l snow grains. The r e s u l t s were inconclusive and i t was concluded that the ambient melt tests cannot be used to determine the impurity d i s t r i b u t i o n during snow-making. Potassium Chloride Baseline Experiments Baseline experiments were c a r r i e d out to study the e f f e c t s of two values of snow depths, i n i t i a l impurity concentration and melt mode on the meltwater impurity d i s t r i b u t i o n . One parameter was varied at a time around the baseline conditions of cold chamber temperature -1°C, impurity concentration 1000 mg/Jl KC1, snow depth 90 cm and continuous melting. One experiment was also conducted at three l e v e l s of snow wetness. Table 4.2 shows the experimental parameters and the average r e s u l t s . Results for each test r e p l i c a -t i o n column are presented i n Table A3, Appendix A. The f i r s t experiment ( B l , Table 4.2) was undertaken to deter-mine the impurity removals under the baseline conditions of MF cycles, 1000 mg/£ KC1 impurity strength, 90 cm snow depth, and -1°C snow temperature. In the second experiment (B2) the snow columns were melted continuously but under otherwise simlar conditions to experiment B l . The r e s u l t s confirmed the f i n d i n g of the preliminary 82. experiments, namely that the number of atmospheric melt-freeze cycles has l i t t l e e f f e c t on the o v e r a l l potassium chloride removals. Figure 4.3 shows that the removals were i d e n t i c a l at the early melt f r a c t i o n s . Simulated melt-freeze cycles produced about 4% better removals of KC1 f o r the 0.20 melt f r a c t i o n (8 r e p l i c a t i o n s ) . Experiment B3 was car r i e d out to study the e f f e c t of snow depth. The snow was packed to a depth of 45 cm i n 4 columns ( r e p l i c a t i o n s ) and the snow melted continuously. The r e s u l t s are shown i n Figure 4.4. The removal of KC1 was considerably l e s s f o r the f i r s t melt frac t i o n s as compared to the 90 cm depth. However, the removals were e s s e n t i a l l y the same f o r l a t e r melt f r a c t i o n s of .2 and .3. The implications of these findings are further discussed i n the summary (Section 4.6). B r i e f l y , these observed di f f e r e n c e s i n impurity removals are a d i r e c t r e s u l t of the length of the snow column. The longer the column, the longer the path of the surface meltwater. This longer path w i l l r e s u l t i n an increase i n the number of successive, i n t e r n a l melt-freeze c y c l e s . Since only 45 cm of snow was used i n each column, enough snow was a v a i l a b l e from one snow production run to pack two columns. This gave the opportunity to i s o l a t e the deviations caused by v a r i -ations i n snow consistency (Table 4.5). The e f f e c t of the i n i t i a l impurity strength on the degree of melt-freeze concentration was studied i n experiment B5. Snow was produced with an i n i t i a l concentration of 200 mg/£ KC1, only 1/5 of the baseline concentration. As shown i n Figure 4.4, the e f f e c t of the reduction i n impurity strength was small. The impurity removal f r a c t i o n associated with the 0.2 melt f r a c t i o n was only 2% l e s s than 8 3 . Figure 4.3 Effects of Melt Mode and Impurity Application on the Removal of Salt for Baseline Conditions (-1°C, 90cm depth). Figure 4.4 Effects of Snow Depth and Solute Strength on Potassium Chloride Removal Under Continuous Melt Conditions at -1°C. 84. that observed f o r the b a s e l i n e c o n d i t i o n s of a 1000 mg/£. V a r i a t i o n of sewage e f f l u e n t concentrations were l e s s than that of the potassium c h l o r i d e as t e s t e d i n experiment B5. This l e d to the t e n t a t i v e c o n c l u s i o n that v a r i a t i o n i n sewage e f f l u e n t strength w i l l not s i g n i f i c a n t l y a f f e c t the degree of i m p u r i t y removal. A more d e t a i l e d s c r u t i n y of t h i s c o n c l u s i o n i s presented i n the f o l l o w i n g S e c t i o n (Sewage E f f l u e n t Experiments). The l a s t experiment (B6) was undertaken to i n v e s t i g a t e the m i g r a t i o n and co n c e n t r a t i o n of i m p u r i t i e s added to the surface of a pure snowpack. I t s main purpose was to l i n k the f i e l d r e s u l t s to those obtained i n the l a b o r a t o r y . The r e s u l t s , however, can a l s o be compared to the removals observed f o r uniformly contaminated snow-packs. The comparison of f i e l d and l a b o r a t o r y r e s u l t s are discussed i n S e c t i o n 4.5. The e f f e c t of the i n i t i a l impurity d i s t r i b u t i o n on the degree of i m p u r i t y removals i s shown i n Fi g u r e 4.3. As shown i n t h i s f i g u r e , both the uniform and the surface d i s t r i b u t i o n of impur-i t y produced e s s e n t i a l l y the same degree of i m p u r i t y c o n c e n t r a t i o n . The mean and standard d e v i a t i o n of a l l the CM and MF e x p e r i -ments are shown i n Figure 4.5. The sm a l l standard d e v i a t i o n r e f l e c t s the f i n d i n g that melt mode, impurity strength and d i s t r i b u -t i o n , snow depth, and snow temperature had l i t t l e e f f e c t on the o v e r a l l removal r a t e s . Sewage E f f l u e n t Experiments The f i n a l set of experiments was c a r r i e d out to i n v e s t i g a t e the removal of sewage e f f l u e n t i m p u r i t i e s under b a s e l i n e c o n d i t i o n s of -1°C and 90 cm depth. The removals f o r both the continuous melt and 85. 1 .u 1 1 1 - 4 — 4 >» 0.8 - T j S ^ — "k. 3 Q. E 1—( 0.6 — to > LEGEND o 0.4 O Boi«lin«+Pr»iminbr> 3 Experiments E 3 0.2 X Ont Standard o - / Deviation 0 Z , 1 1 0 0.05 0.10 0.15 0.20 0.25 0.30 Cumulative Melt Fraction Figure 4.5 - Mean Removal of Potassium Chloride for Various Solute Strengths, Snow Depths, Temperatures and Melt Modes. 0 0.05 0.10 0.15 0 . 2 0 0 .25 0.30 Cumulative Melt Fractions Figure 4.6 Effect of Snow Wetness on Potassium Chloride Removal Under Continuous Melt Conditions. 86. the melt-freeze c o n d i t i o n s were t e s t e d again f o r sewage e f f l u e n t because of i t s important i m p l i c a t i o n f o r f u l l - s c a l e operations, as discussed. The e f f e c t s of temperature and snow depth were assumed to be s i m i l a r f o r KC1 and sewage e f f l u e n t . C h l o r i n a t e d e f f l u e n t from an a c t i v a t e d sludge treatment p l a n t was used. The e f f l u e n t used f o r the CM and MF experiment was c o l l e c t e d at d i f f e r e n t times and had somewhat d i f f e r e n t i m p u r i t y concentrations as shown i n Table 4.3. Phosphorus was found, unexpectedly, to be concentrated to a l e s s e r degree than n i t r o g e n ^ T h i s seems to c o n t r a d i c t Johannessen and Henriksen's (1978) f i n d i n g that i o n s i z e and charge had l i t t l e e f f e c t on the degree of impurity r e d i s t r i b u t i o n during melting of snow. However, orthophosphate i s known to be s t r o n g l y adsorbed to p a r t i c l e s u r f a c e s . I t i s l i k e l y , t h e r e f o r e , that some of the ortho-phosphate was r e t a i n e d i n the snowpack by organic p a r t i c l e s of the sewage e f f l u e n t . This co n c l u s i o n i s supported by the very low orthophosphate c o n c e n t r a t i o n of the melt run o f f (about 2% of the e f f l u e n t concentration) from the t e s t s i t e s i n Steamboat Springs, Colorado (Wright-McLaughlin Engineers, 1975) and Blue Mountain, Ontario (Ontario M i n i s t r y of the Environment, 1982). Most p a r t i c l e s would have been r e t a i n e d at the ground surface and would not have been present i n the c o l l e c t e d run o f f samples. 1. The n i t r o g e n and phosphorus of the sewage e f f l u e n t and the r e s u l t i n g snowmelt were mainly i n the form of ammonium (~98%) and orthophosphate (~93%) r e s p e c t i v e l y . TABLE 4.3. Impurity Removals Observed during Melting of Secondary Sewage Effluent Snow under Baseline C o n d i t i o n s ^ . Impurity Melt<2> I n i t i a l ( 3 ) Impurity Removals for given Mode Cone. Meltwater Fractions, Z C o .05 .10 .15 .20 .30 Conductivity CM 318 39 61 75 82 88 uS/cm MF 298 58 74 80 83 88 TKN, CM 16.4 38 62 76 83 90 mg/1 MF 10.8 58 74 80 83 87 NH,, CM 15.9 40 63 76 83 90 mg/l as N MF 10.8 57 73 80 83 87 N03 + N0 2. CM 0.31 35 55 66 72 77 mg/l as N MF 0.60 52 74 80 82 86 TP, CM 1.04 27 48 62 73 84 mg/l MF 2.04 26 43 52 57 65 CM 0.94 27 48 63 74 85 mg/l as P MF 1.95 26 43 51 57 65 T0C< 4\ CM 16.8 29 46 56 63 71 mg/l MF 17.5 43 56 61 64 71 TOC CM 34 54 67 76 85 MF 54 71 76 80 89 (1) Baseline Conditions: snow column depth - 90 cm; cold chamber tempera-ture • -1°C; snow wetness " medium (2) Continuous Melt (CM) - 4 r e p l i c a t i o n s Melt-Freeze (MF) - 2 r e p l i c a t i o n s (3) Average concentrations as measured from fresh snow samples. (4) Based on meltwater and snowpack. measurements. (5) Corrected for mass conservation ( i . e . mass balance - 0). TABLE 4.4. Restricted Exponential Regression of Impurity Removals^ With Respect to the Cumulative Meltwater Fraction. Type M e l t " ) Number of of k<3) ^ ( 4 ) Impurity Mode Replications T K N ( 5 ) CM 24 8.1 0.92 MF 12 8.5 0.66 CM+MF 18 8.3 0.73 T P ( 6 ) CM 24 6.4 0.93 MF 12 4.0 0.77 CM+MF 18 5.6 0.82 CM 24 6.9 0.86 MF 12 8.4 0.16 CM+MF 18 7.4 0.69 CM 102 10.3 0.74 MF 48 13.1 0.91 CM+MF 150 11.2 0.79 1 The form of the exponential decay equation i s : y - 1 -kx - e . where: y » impurity removal f r a c t i o n ; x - meltwater f r a c t i o n ; k - c o e f f i c i e n t (2) MF - Melt-Freeze cycles; CM - Continous Melt. (3) k - (Jx i yp/Jx2 (4) Approximate correlation c o e f f i c i e n t , I 2 . (5) The ammonia and conductivity have approximately the same f i t as TKN (98Z of TKN i s ammonia). (6) Approximately same f i t for orthophosphate (92Z of TP i s PO~). (7) Exponential curve f i t for the corrected values (see Table 4.3). (8) Baseline experiments only. 88. The removal of e f f l u e n t i m p u r i t i e s from snow under continuous melt and simulated melt-freeze c y c l e s are compared i n Figures 4.7 through 4.14. Ammonium and t o t a l organic carbon concentrations are almost i d e n t i c a l at 0.2 melt f r a c t i o n f o r the two melt c o n d i t i o n s . However, the e f f e c t of the melt c o n d i t i o n s on the im p u r i t y removals as s o c i a t e d with the e a r l i e r f r a c t i o n s d i f f e r from those of the potassium c h l o r i d e experiments. The c o n c e n t r a t i o n of potassium c h l o r i d e was v i r t u a l l y the same f o r both melt c o n d i t i o n s ( F i g u r e 4.3), whereas the co n c e n t r a t i o n of ammonium and organic carbon were considerably higher f o r MF than CM at the .05 and .10 melt f r a c t i o n . The orthosphosphate on the other hand had s i m i l a r removals f o r CM and MF at the f i r s t melt f r a c t i o n s but the CM co n d i t i o n s produced s i g n i f i c a n t l y higher degree of removal a t the .2 and .3 meltwater f r a c t i o n . Why the ammonium and orthophosphate show d i f f e r e n t freeze c o n c e n t r a t i o n behaviour cannot be deduced from t h i s research. The d i f f e r e n c e i n freeze c o n c e n t r a t i o n behaviour may be l i n k e d to the nature of the i m p u r i t y , such as orthophosphate's a f f i n i t y to p a r t i c l e s u r f a c e s . The n i t r i t e + n i t r a t e i m p u r i t y was not inc l u d e d i n the above d i s c u s s i o n because i t s low i n i t i a l c o n c e n t r a t i o n may have r e s u l t e d i n g r e a t e r measurement e r r o r s and hence lower p r e c i s i o n . This impurity f o l l o w s the concentration p a t t e r n of ammonium, with CM c o n d i t i o n s producing somewhat lower i m p u r i t y concentrations at the f i r s t melt f r a c t i o n s but approaching those of the MF experiments f o r the l a t e r 0.2 cumulative melt discharge. The removals of t o t a l organic carbon (TOC) present i n the e f f l u e n t are shown i n Figure 4.14. Mass balance estimates showed a 10-35% increase i n TOC during 8 9 . 1.0 0 . 8 > o E 0 . 6 ce •= 0.4 O L E 0 . 2 I I I I I , X ——~~" L E G E N D 0 C O N D . T K N . N H j _ // / A T P . P O 4 _ r i i i • NO 3 + N 0 2 • 0 0 . 0 5 0 . 1 0 0 . 1 5 0 . 2 0 0 . 2 5 C u m u l a t i v e M e l t F r a c t i o n s 0 . 3 0 Figure 4 .7 R e m o v a l of S e w a g e E f f l u e n t I m p u r i t i e s U n d e r Continuous M e l t C o n d i t i o n s . Figure 4 . 8 R e m o v a l of Total O r g a n i c C a r b o n U n d e r C o n t i n u o u s M e l t C o n d i t i o n s . 90. Figure 4.9 Sewage Effluent Impurities Removal Under Melt- Freeze Conditions. Figure 4.10 Total Organic Carbon Removal Under Melt-Freeze Conditions. 1.0 l i l I 1 0.8 > o E 0.6 -a> or LEGEND 0.4 -mp O Continuous Melt — 0.2 A Melt-Freeze — 0 K i l l 0 0.05 0.10 0.15 0 . 2 0 0 . 2 5 0 . 3 0 Cumulative Melt Fractions Figure 4.11 Conductivity and Total Kjeldahl Nitrogen Removals Under Melt -Freeze and Continuous Melt Conditions. Figure 4.12 Total Phosphorus Removal Under Me l t - F reeze and Continuous Melt Conditions. 92. 1.0 0 . 8 "o > o E 0 . 6 CU CC >. •c 0 . 4 Q. E 0 . 2 0 1 1 1 1 1 • ~ —i - ^ ' A — ' — -L E G E N D — _ / / 0 C o n t i n u o u s M e l t — / / M e l t - F r e e i t 1 0 0 . 0 5 0 . 1 0 0 . 1 5 0 . 2 0 0 . 2 5 0 . 3 0 C u m u l a t i v e M e l t F r a c t i o n s Figure 4.13 Nitrate R e m o v a l U n d e r M e l t - F r e e z e and Continuous M e l t C o n d i t i o n s . Figure 4 . 1 4 Total O r g a n i c R e m o v a l U n d e r M e l t - F r e e z e and C o n t i n u o u s M e l t C o n d i t i o n s . 93. m e l t i n g . The most l i k e l y source of organic contamination i s the sample b o t t l e s . Tests using d i s t i l l e d water i n d i c a t e d that the maximum c o n t r i b u t i o n of organics from the new sample b o t t l e s was 1-2 mg/£. The r e s i d u a l snow had an average TOC conc e n t r a t i o n of about 10 mg/£. I t s volume c o n s i s t e d of about 70% of the t o t a l snow column. The maximum c o n t r i b u t i o n of organics from the sample b o t t l e s , t h e r e f o r e , i s only 7-14% of the t o t a l TOC mass. Another 5% er r o r may be due to the TOC a n a l y s i s , as shown i n Table 3.2. Since the reason f o r the increase i n TOC could not be explained s a t i s f a c -t o r i l y , both the measured and corrected values were presented. The cor r e c t e d values were co r r e c t e d to s a t i s f y the mass balance of TOC i n each melt column. N a t u r a l melting of snow f o l l o w s a d i u r n a l p a t t e r n during most of the w i n t e r . The d a i l y s o l a r r a d i a t i o n input generates surface melt that refreezes i n s i d e the pack. Spring c o n d i t i o n s or midwinter thaws may increase the temperature of the whole snowpack to 0°C at which point no meltwater would r e f r e e z e . In l i g h t of the mixed m e l t i n g regime o c c u r r i n g n a t u r a l l y , i t was decided to use the aver-age CM and MF e f f l u e n t impurity removals as an i n d i c a t i o n of f u l l -s c a l e performance u n t i l f i e l d r e s u l t s are a v a i l a b l e (Figure 4.15). I t i s concluded then, that a 90 cm deep e f f l u e n t pack with an average temperature of -1°C w i l l concentrate about 65% of the phos-phorus, 70-75% of the organic carbon and 87% of the ni t r o g e n i n the f i r s t 20% of the meltwater discharge, even f o r s i t e s which may experience m i l d periods during the winter. 1.0 0.8 e 0.6 OJ 0.2 0 1 1 I 1 1 1 L E G E N D - // / o COND,TKN, N H j _ T P , P 0 4 • T O C 1 c o r r e c t e d 1/ 1 1 1 0 0.05 0.10 0.15 0.20 0.25 0.30 Cumulotive Melt Fractions Figure 4.15 Average Removals of Sewage Effluent Impurities for Continuous Melt and Melt-Freeze Conditions . Impurity Concentrations, Cs/Co Figure 4.16 Impurity Migration Through Snow as Observed During the Preliminary Experiments. Impurity Removal Function The i m p u r i t y removal from snow during m e l t i n g can be expressed as a f u n c t i o n of the cumulative meltwater discharge. The shape of the i m p u r i t y removal p l o t s shown previously,suggest that the impurity removal decays e x p o n e n t i a l l y with the cumulative meltwater discharge. Many b i o l o g i c a l and p h y s i c a l processes, i n c l u d i n g the standard Biochemical Oxygen Demand (BOD 5) t e s t i s described by a f i r s t - o r d e r e x p onential decay f u n c t i o n which i m p l i e s t h a t the r a t e of change i n a c o n s t i t u e n t i s p r o p o r t i o n a l to the amount present. The f u n c t i o n i s of the form: , -kx y = 1 - e where i n t h i s case: y = cumulative f r a c t i o n of impurity removed x = cummulative meltwater f r a c t i o n k = decay c o e f f i c i e n t The decay c o e f f i c i e n t k may be determined by l i n e a r r e g r e s s i o n on the transformed f u n c t i o n : -Hn (1-y) = kx y' = kx which i s the equation of a s t r a i g h t l i n e through the o r i g i n and with the slope k. Using the l e a s t square method f o r r e s t r i c t e d l i n e a r r e g r e s s i o n ( r e g r e s s i o n through o r i g i n ) g i v e s : k = (Zx^ p/ZxJ The c o r r e l a t i o n c o e f f i c i e n t , r z , i s i n l o g a r i t h m i c u n i t s and cannot be transformed by ta k i n g the a n t i l o g a r i t h m . However, we can use I 2 as an approximation of the goodness of f i t of the exponential func-t i o n . The approximate c o r r e l a t i o n c o e f f i c i e n t I 2 , i s estimated from the non-transformed exponential equation wit h the independent v a r i a b l e s , y, expressed i n i t s o r i g i n a l u n i t s . i 2 = [Hy± - y ) 2 - 2 ( y ± - y i ) 2 ] / J : ( y i - y ) 2 where y = mean i m p u r i t y removal f r a c t i o n The values of the decay c o e f f i c i e n t , k, and the c o r r e l a t i o n c o e f f i -c i e n t , I 2 , f o r the d i f f e r e n t experiments are given i n Table 4.4. One should use caution when comparing c o r r e l a t i o n c o e f f i c i e n t s f o r d i f f e r e n t experiments. The c o e f f i c i e n t i s a f f e c t e d by the sample s i z e ( e s p e c i a l l y f o r n<30) and range. Larger sample s i z e reduces the r 2 or I 2 whereas a grea t e r range inc r e a s e s the values. The sample s i z e used ranged from 12 to 150, and the goodness of f i t of the e x p o n e n t i a l equation was acceptable f o r most c o n d i t i o n s . Improved f i t may have been achieved i f the impurity removals had been sampled across the whole range of meltwater f r a c t i o n s . As i t were, the normalized f r a c t i o n s of 0.05, 0.10, 0.15, 0.20, and 0.30 were used which r e s u l t e d i n a biased r e g r e s s i o n f o r the e a r l y melt f r a c t i o n s . The impurity removal data f i t the exponential decay model f a i r l y w e l l f o r some c o n d i t i o n s , whereas the f i t f o r others were u n s a t i s f a c t o r y . The removal of sewage e f f l u e n t i m p u r i t i e s had an I 2 v a l u e s ranging from 0.86 to 0.92 (n - 24) f o r continuous m e l t i n g c o n d i t i o n s . The model underestimates the impurity removal of the e a r l y melt f r a c t i o n s f o r melt-freeze c o n d i t i o n s . The opposite i s true f o r potassium c h l o r i d e . In t h i s case, the MF removals f i t t e d the model w e l l ( I 2 = 0.91, n = 48), whereas CM c o n d i t i o n s r e s u l t e d i n model overestimation at the e a r l y melt f r a c t i o n . The combined r e s u l t s f o r CM and MF c o n d i t i o n s produced c o r r e l a t i o n c o e f f i c i e n t s ranging from 0.69 to 0.82. Snow Consistency The production of snow was l i m i t e d by the s m a l l s i z e of the co l d chamber. The amount of snow made during each run was normally only enough to pack one t e s t column. The c o l d room temperature rose from -12°C to -5°C during one run. The air/w a t e r r a t i o had to be in c r e a s e d as the temperature rose to keep the snow r e l a t i v e l y dry. The adjustments were made from v i s u a l observation of the snow c o n s i s t e n c y . This s u b j e c t i v e o p e r a t i o n a l procedure caused u n c o n t r o l l e d v a r i a t i o n i n the snow moisture content. I t was a l s o observed that packing of the snow Into columns v a r i e d c o n s i d e r a b l y with the wetness of the snow. Experiment B4 (Table 4.2) was done to t e s t the e f f e c t of snow wetness (or packing c h a r a c t e r i s t i c s ) on the impurity removal e f f i c i e n c i e s . Snow of d i f f e r e n t "wetness" was packed i n four t e s t columns. Two columns contained snow of medium wet snow, one w i t h dry snow and one w i t h wet snow. The wet snow formed lumps during handling and packed unevenly i n the column, whereas the dry snow packed evenly. The medium wet snow r e s u l t e d i n a reasonably even snowpack. As the r e s u l t s of Table 4.2 and Figure 4.6 show, the snow "wetness", and t h e r e f o r e packing c h a r a c t e r i s t i c s , had a considerable e f f e c t on the impurity removal performance. The KC1 removal from the dry snow reached 95%, w i t h the 0.15 melt discharge, whereas l e s s than 80% was removed from the wet snow. When r e a l i z i n g the c o n s i d e r a b l e e f f e c t extreme snow c o n s i s t e n -c i e s and r e s u l t i n g packing c h a r a c t e r i s t i c s had on the KC1 removals, i t was decided to determine the e f f e c t of s m a l l v a r i a t i o n s i n the consistency of the medium wet snow on removal e f f i c i e n c i e s . The e x p l o r a t o r y nature of the experiments d i d not lend i t s e l f to formal a n a l y s i s of variance or separation of the snow consistency e f f e c t . However, r e s u l t s were a v a i l a b l e from t e s t runs where two and four columns were packed with i d e n t i c a l snow. These columns contained snow of the same consistency. Any d e v i a t i o n i n observed i m p u r i t y removal, t h e r e f o r e , was only due to m e l t i n g and sampling procedures and not due to v a r i a t i o n s of the snowmaking process. By comparing (2) the mean d e v i a t i o n of these t e s t runs to the mean d e v i a t i o n of Snow wetness i s a q u a l i t a t i v e c h a r a c t e r i s t i c based on the f r e s h and packed snow water equivalent and on v i s u a l observations of the snow consistency and handling c h a r a c t e r i s t i c s o u t l i n e d i n S e c t i o n 3.3. Too few data p o i n t s (2 to 8) were a v a i l a b l e to use the more common measure of the v a r i a t i o n about the mean, the Standard D e v i a t i o n . The d e f i n i t i o n of the Mean D e v i a t i o n i s given i n Table 4.5, note ( 1 ) . 99. the r e g u l a r runs (where snow of d i f f e r e n t snow consistency was used i n each column) one can q u a n t i f y the e f f e c t of u n c o n t r o l l e d snow consistency v a r i a t i o n s . This approximate a n a l y s i s , shown i n Table A.5, suggests that about 1/2 to 2/3 of the t o t a l observed i m p u r i t y removal d e v i a t i o n was due to v a r i a t i o n s i n snow consistency, the r e s t being a t t r i b u t e d to v a r i a t i o n s i n snow melting and sampling procedures. The observed i m p u r i t y removal d e v i a t i o n s , due to v a r i a t i o n s i n the snow consistency, i s r e a l l y a r e s u l t of the subsequent snow packing. "Wet" snow produced lumpy snowpacks which may have induced melt channel formation. This i s thought to be a c h a r a c t e r i s t i c of the l a b o r a t o r y c o n d i t i o n s , however. Snow produced under f i e l d c o n d i t i o n s forms a snowpack d i r e c t l y and hence the e f f e c t of moisture on the packing c h a r a c t e r i s t i c s i s expected to be s m a l l . 4.3 R e s i d u a l Snow C h a r a c t e r i s t i c s Impurity P r o f i l e s As snow melted from the s u r f a c e , i m p u r i t i e s were released and concentrated towards a f r o n t which moves through the snowpack and i n t o the ground (or i n t o sample b o t t l e s ) . For a l l but four t e s t columns, the snow was sampled a f t e r most of the i m p u r i t i e s had been removed and hence revealed only the t a i l end of the i m p u r i t y pro-f i l e . The four columns, f o r which the potassium c h l o r i d e p r o f i l e s are p l o t t e d i n Figure 4.16 (page 94), were a l l part of the f i r s t p r e l i m i n a r y experiment (Table 4.1). They contained 90 cm of 1000 mg/Jt KC1 snow and were melted under MF c o n d i t i o n s and ambient temperatures of -1, -2, and -12°C. The i m p u r i t y c o n c e n t r a t i o n of a 100. TABLE 4.5. Mean Deviations*- ' of Observed Potassium Choride Removals. Parameter Experience No. of Replications Melt Fractions 0.1 0.2 Average Mean Deviation for columns of idential snov/2),Z S.B3.P7 2,2,4 2.2 0.7 Average Mean Deviation between test replications^3), % B1.B2.B5 8,8,3 4.2 2.2 Mean Deviation due to variations in snow consistency,Z 48 68 (1) Mean Deviation - i I |X±-X|-(2) Enough snow was made for these tests to f i l l two columns rather than only one as for all the other experiments. The average mean devia-tion for the 5 experiments is shown in the table. (3) The replications of each experiment used snow produced at different times. These values represent the total mean deviation due to uncontrolled factors. TABLE 4.6. Observed Changes in Impurity Concentrations During Laboratory Production of Sewage Effluent Snow^ 1). E X P E R I M E N T TKN N H 3 + N H £ ( 2 ) NO3+NO2 ( 3 ) T P P0| S1.S2 S3.S4 S5.S6 +1.3 -1.3 -1.1 -5.2 +2.9 -2.7 -11.6 -7.7 +20 +10.6 +3.8 +2.0 +9.8 +2.7 +2.0 Average Adjusted*-*-* Average +1 -2.2 -4.0 -7.5 +0.4 -4.6 +5.5 0 +4.8 0 (1) The change in impurity concentration is given in percent with respect to the effluent feed. (2) Temperature +1°C; pH - 6.9. (3) Low measurement accuracy of the (NO^ +NO^ ) may explain these large variations. (4) The evaporation for the KC1 baseline experiments was 4.8 ± 0.7 (n-21). The adjusted mean change in concentration excludes evaporation effects. 101. 5 cm snow segment increased to more than 4 times the i n i t i a l snow concent r a t i o n , as the impurity f r o n t migrated towards the base of the snowpack (snow segment i m p u r i t y c o n c e n t r a t i o n i n c l u d e s the snow matrix and i s thus considerably lower than that of the pore s o l u t i o n as explained below). The KC1 p r o f i l e s were c a l c u l a t e d based on the c o n c e n t r a t i o n of KC1 averaged over the bulk volume of each segment. In order to estimate the c o n c e n t r a t i o n of the i m p u r i t y f r o n t , one would need to know the water content of each segment. This water content was not measured but can be estimated from Wankiewicz (1979). The melt f l u x of 6x10" 6 m/s observed during the continuous melt experiments represents a water content, 9 , of about 10% and 25% according to snow c h a r a c t e r i s t i c curves obtained by Wankiewicz f o r w i n t e r and summer snowpacks, r e s p e c t i v e l y . For a water content of 10-25% the degree of c o n c e n t r a t i o n of solute i n the e a r l y melt i s : (1/0.25 to 1/0.1) x 4 = 16 to 40. This compares w e l l to the impurity concentration of the f i r s t meltwater samples (C = 15-20 times C ). o The f i n d i n g s that i m p u r i t i e s are removed from the snow and migrates through the snowpack as a d i s t i n c t wave has a l s o been observed by others. Dahl et a l . (1980) i n v e s t i g a t e d the movement of t r a c e r s through n a t u r a l snowpacks. They found that a slug a d d i t i o n of **5Ca t r a c e r moved as a d i s t i n c t f r o n t through the pack. As the melting progresses, i m p u r i t i e s are removed and the snow becomes purer as shown i n Figure 4.16. The i m p u r i t y c o n c e n t r a t i o n at the surface i s l i k e l y a f u n c t i o n of the impurity mass remaining 102. i n the pack at the time of sampling. By determining t h i s r e l a t i o n -ship one would only have to sample the surface snow, rather than the f u l l snowpack, to estimate the amount of i m p u r i t y remaining. A method of r e l a t i n g a "normalized" impurity removal f r a c t i o n to the depth a t which i t was sampled i s proposed. The " n o r m a l i z a t i o n " i n v o l v e d two steps. F i r s t the i n f l u e n c e of i n i t i a l c o n c e n t r a t i o n was removed by presenting the r e s i d u a l snow i m p u r i t y concentrations ( C ) as a r a t i o of the i n i t i a l c o n c e n t r a t i o n ( C ). In the second s o step r e s u l t s from experiments terminated at d i f f e r e n t times i n the melting process (and thus d i f f e r e n t r e s i d u a l i m p u r i t y c o n c e n t r a t i o n p r o f i l e s ) were correct e d to a s i m i l a r point of comparison, by d i v i d -i n g the i m p u r i t y c o n c e n t r a t i o n f r a c t i o n s (C g/C Q) by the f r a c t i o n of impurity remaining i n the snow (R). The "normalized" r e s i d u a l snow con c e n t r a t i o n s were then p l o t t e d a g a i n s t depth of sampling (Figure 4.17). The f o l l o w i n g example i l l u s t r a t e s the use of t h i s model: Example: Removal of TKN from an E f f l u e n t Snowpack C q = i n i t i a l c o n c e n t r a t i o n of snow •> 15 mg/Z TKN C G = r e s i d u a l i m p u r i t y c o n c e n t r a t i o n at s p e c i f i e d depth 1 mg/Z TKN at 10 cm R = f r a c t i o n of i m p u r i t y remaining i n the snow which give s C / C = 1/15. From Figure 4.17 we get ( C / C )/R ~ 1.5 • Brine MF —1 I ; I ' 2.5 7.6 12.5 Snow Depth, cm Figure 4.17 Impurity Concentrations in Top 15 cm of Residual Snow Based on Conductivity Measurements. (1= One Standard Deviation). 104. which gives us an estimate of the f r a c t i o n of impurity remaining i n the snow of: R = !f^£= %2|L= 0 . 0 4 5 ~ X.J 1.5 * This means that about 95% of the TKN has been removed from the snow by the meltwater. V i s u a l Observations The snow was packed i n p l e x i g l a s columns, thus providing an opportunity to observe the percolation pattern during melt. The melt pattern was also revealed during sampling of the r e s i d u a l snow. The snow was placed i n the columns and then allowed to reach the ambient room temperature (usually overnight). The snow s e t t l e d 1 0 - 3 0 cm, due to metamorphism during the temperature e q u i l i b r a t i o n period. As the melt progressed, the snow s e t t l e d further to about 4 0 - 5 0 cm, before the f i r s t melt drained from the column. A c a p i l l -ary f r i n g e of about 5 cm was evident at the base of the column. Melt-freeze conditions produced melt channels, as evidenced by the presence of f i n g e r l i k e i c i c l e s . T y p i c a l diameters of these i c i c l e s were 2-5 cm. The i c i c l e s covered about 5 0 % of the t o t a l area, the r e s t consisted of coarse grained, spring snow. Similar channels were also evident i n the f i e l d experiment described i n Section 4 . 5 . The amount of i c e increased with the number of MF cycles, and with lower ambient temperatures. In f a c t , for tempera-tures of -2°C and lower, the columns became plugged with i c e a f t e r 105. only 10-20% of the snow had melted. Continuous-melt c o n d i t i o n s produced homogeneous coarse, grained snow with d e n s i t i e s ranging from 40-55%, t y p i c a l of s p r i n g or f i r n snow. Hy d r a u l i c C h a r a c t e r i s t i c s Continuous m e l t i n g c o n d i t i o n s changed f r e s h , c o l d , low d e n s i t y snow to wet, mature, isothermal snow over 4-6 hrs. The i n i t i a l melt discharge r a t e of about 1000 ml/hr dropped q u i c k l y to about 50U ml/hr and then slowly tapered o f f towards a pseudo-steady s t a t e of about 300 ml/hr (q = 6 x l O ~ 6 m/s) (Figu r e 4.18). The i n i t i a l high melt f l u x i s a r e s u l t of re l e a s e of water held by c a p i l l a r y t e n s i o n , as r a p i d g r a i n coarsening i s induced by the presence of water. The subsequent gradual decrease of the basal discharge i s a r e s u l t of snow compaction. Colbeck's g r a v i t y flow theory (Colbeck, 1974) i s r e s t r i c t e d to mature, isothermal snowpacks and does not apply to i n i t i a l l y dry or f r e s h l y wetted snowpacks, as observed i n these experiments. In a d d i t i o n , precise surface f l u x measurements are required f o r estima-t i o n of the wave speed through the pack, i n order to determine the i n t r i n s i c p e r m e a b i l i t y of the snow under t r a n s i e n t flow c o n d i t i o n s . The observed f l u x of 6 x l 0 ~ 6 m/s i s about an order of magnitude greater than snow melt f l u x e s o c c u r r i n g n a t u r a l l y , but s t i l l w e l l w i t h i n the unsaturated flow regime. The p e r m e a b i l i t y at t h i s f l u x was estimated to be about l x l O - 1 2 m2 using Darcy's Law f o r g r a v i t y dominated flow (Equation ( 9 ) ) . This i s about 2-3 orders of magni-tude lower than the saturated p e r m e a b i l i t i e s reported by Colbeck and Anderson (1982) and Wankiewicz (1979). The snow c h a r a c t e r i s t i c s 106. curves obtained by Wankiewicz suggest a r e l a t i v e p e r m e a b i l i t y , k(8)/k , of the snow of 1 0 - 3 f o r the observed f l u x of 6*10 - 6 m/s. S c l t T his compares w e l l to the 1 0 - 2 to 1 0 - 3 r e l a t i v e p e r m e a b i l i t y estimated above. 4.4. Impurity Changes During Snow Pro d u c t i o n and M e l t i n g The feed s o l u t i o n (2 r e p l i c a t i o n s ) and the f r e s h snow (4 r e p l i c a t i o n s ) were sampled immediately a f t e r the snow was made. The r e s u l t s of the potassium c h l o r i d e b a s e l i n e experiments suggest that about 5% of the water evaporated during snowmaking i n the c o l d chamber (Table A.3, Appendix A). The evaporation r a t e increased from zero to about 10%, as the air/water r a t i o was Increased from th a t of wet snow to dry snow. The evaporation i n the c o l d chamber was l i m i t e d by r a p i d water vapour s a t u r a t i o n of the ambient a i r . F i e l d operations w i l l operate at a lower a i r / w a t e r r a t i o , but w i l l have much greater evaporation p o t e n t i a l under favourable c o n d i t i o n s . The e f f l u e n t i m p u r i t y measurements were c o r r e c t e d f o r c o n c e n t r a t i o n due to evaporation (~ 5%). The r e s u l t s i n d i c a t e that phosphorus remained unchanged, whereas n i t r o g e n decreased by 7.5% during the snowmaking process (Table 4.6). The r e d u c t i o n of n i t r o g e n was p r i m a r i l y due to s t r i p p i n g . The a i r flow during snow-making i s s u f f i c i e n t f o r e f f i c i e n t s t r i p p i n g of ammonia; however, the s o l u b i l i t y of NH3 i s very high at the low temperature of +1°C. More i m p o r t a n t l y , though, i s the i o n i c d i s t r i b u t i o n with pH. At the e f f l u e n t pH of 7, the c o n c e n t r a t i o n of NH 3 i s very low and most of ammonia i s i n the form of NHV. 107. Changes i n i m p u r i t y c o n c e n t r a t i o n during the snow melting process and during the sample c o l l e c t i o n and measurements procedures were determined from mass balance estimates (see Table 4.7 and A.3). The potassium c h l o r i d e showed a mass gain of about 2% which i s w e l l w i t h i n the expected experimental e r r o r . The same i s t r u e f o r the observed 2% to 5% l o s s of phosphorus. The ammonia s t r i p p i n g of about 17% may have occurred p a r t l y during the m e l t i n g and p a r t l y during the sampling procedures. The l a b o r a t o r y experiments l a s t e d only 3-4 days f o r MF and about 6 h r s . f o r CM c o n d i t i o n s . The short d u r a t i o n of the e x p e r i -ments r e s t r i c t e d any b i o l o g i c a l a c t i v i t i e s . A f i e l d t e s t program should t r y to e s t a b l i s h changes o c c u r r i n g w i t h i n an e f f l u e n t snow-pack, i n a d d i t i o n to the important i m p u r i t y c o n c e n t r a t i o n process. I t should a l s o determine the extent of ammonia s t r i p p i n g by the snowgun f o r d i f f e r e n t operating c o n d i t i o n s . 4.5. F i e l d Experiment The f i e l d experiment conducted at Cypress P r o v i n c i a l Park, West Vancouver, B r i t i s h Columbia, was c a r r i e d out to i n v e s t i g a t e the i m p u r i t y removal from snow under n a t u r a l m e l t i n g c o n d i t i o n s . A household s a l t s o l u t i o n was added to the surface of the n a t u r a l snowpack. A brine-on-snow experiment (exp. B6, Table 4.2) was a l s o conducted i n the l a b o r a t o r y f o r the purpose of comparing the f i e l d and l a b o r a t o r y c o n d i t i o n s . The f i e l d experiment was exposed to f a r more u n c e r t a i n t i e s than the l a b o r a t o r y : (1) The brine a p p l i c a t i o n may have been non-uniform: (2) Snowmelt drainage occurred p a r t l y through melt channels and some TABLE 4.7. Impurity Mass Balances Estimated From Melt and Residual Snow Measurements' ) Exp. Repl. TKN (NH3+NHJ) NOyHNO^2) TP P0| 1 -17.6 -18.3 -2.6 -3.2 -6.3 2 -18.7 -19.0 0 -4.0 -5.4 CM 3 -18.7 -16.5 -4.2 +3.6 -3.9 4 -17.1 -16.5 -4.2 +1.2 -2.6 1 -12.9 -17.6 +20 -5.4 -7.7 MF 2 -11.1 -16.7 +10 -3.4 -7.7 Average -16.0 -17.4 — -1.9 -5.6 (1) Presented as percent change from the i n i t i a l impurity con-centration of the snow. (2) Poor accuracy of ( N O 3 + N O 2 ) measurements at the low concen-tration observed l i k e l y caused the large variations shown. TABLE 4.8. Impurity Removals from a Natural Snowpack Irrigated with Brine*- 1). Parameters 0 7 14 Time 21 of Sampling, days 28 1 35 j 42 j 49 59 66 Density of i r r i g a t e d ^ ) snowpack, % 40 43.9 41.3 44.2 44.4 44.5 47.0 48.5 47.6 47.9 Water equiv. of total snowpack*-2), mm/m^  800 835 940 1070 1100 1130 1160 1180 1230 1250 Estimated Salt application*- ', uS/cm 560 405 645 600 335 565 600 315 348 420 Cumulative S a l t ^ ) fractions, % 0 0 0 8.3 20.1 25.7 35.8 85.7 94.8 98.6 Cumulative Melt^ 5) fractions, % 0 0 0 1.4 2.3 7.7 9.9 19.9 38.6 62.0 (1) Average densities for the original depth of 200 cm. (2) Water equivalence of the whole snowpack, including precipitation, during the 2 month duration of the experiment (mean conductivity ~ 25 uS/cm). (3) Salt addition as estimated from mass balance calculation of snow profile and meltwater conductivity measurements for each vertical sample section. (4) Amount of salt discharged with the melt presented as a fraction of the total salt added to the snow. (5) As fractions of the whole snowpack. 109. may have bypassed the melt c o l l e c t o r s (3) P r e c i p i t a t i o n during the experiment d i l u t e d the average s a l t concentration of the snowpack. However, an attempt was made to account f o r these uncertainties and to normalize the re s u l t s for better comparision with the laboratory r e s u l t s . The methods and reasoning of the adjustments are described below. About 450 mm water equivalent of atmospheric p r e c i p i t a t i o n f e l l during the experiment, most of i t as snow (see Appendix F for d a i l y weather records). The average conductivity of the p r e c i p i t a t i o n (~25 uS/cm) was much lower than the average conductivity of the snowplot (~700 uS/cm). The water equivalence of the added p r e c i p i -t a t i o n was equal to about 50% of the water i n the o r i g i n a l snowpack. V i s u a l observations indi c a t e that most of t h i s p r e c i p i t a t i o n drained through melt channels and thus did not s i g n i f i c a n t l y d i l u t e the impurity concentrations of the o r i g i n a l pack. Besides, any d i l u t i o n during the f i r s t melt discharge would have been small because of the small melt volumes involved. The snow samples and meltwater d i s -charge were c o l l e c t e d from the o r i g i n a l snowpack where melt channels were evident. The meltwater c a l c u l a t i o n s f o r each sampling day were based on a hypothetical snow column with a t o t a l water equivalence equal to that of the o r i g i n a l pack plus p r e c i p i t a t i o n , and with an i n i t i a l impurity mass equal to the sum of the snow and meltwater measure-ments. A p a r t i c u l a r s a l t removal, then, r e f e r s to the cumulative removal of s a l t as a f r a c t i o n of the estimated i n i t i a l impurity mass for that day. For example, the 20.1% removal estimated f o r Day 28 refers to the "apparent" i n i t i a l s a l t addition of 335 pS/cm as 110. estimated from conductivity measurements (Table 4.8). The meltwater volumes were estimated based on melt c o l l e c t e d by lysimeters. The melt Is presented as a f r a c t i o n of the water equivalence of the whole snowpack including p r e c i p i t a t i o n . Impurity Removal by Meltwater The mature snowpack was sampled with depth before the s t a r t of the experiments. The low conductivity of the snowpack (~3.4 uS/cm) c l e a r l y demonstrated that low concentrations of impurities are removed under natural melting conditions. The average conductivity of f r e s h snow was determined (by sampling throughout the experi-mental period) to be about 25 uS/cm. This suggests that about 80-85% of the a c i d i c impurities had been removed from the natural snow-pack under f i e l d conditions. The estimated removal of the added s a l t with the f i r s t 20% melt was also about 85%. Figure 4.19 shows the observed s a l t removals for brine-on-snow experiments conducted i n the laboratory and i n the f i e l d . The lower experimental control and hence greater uncertainty of the f i e l d experiment i s evident from the greater spread of the data points. In spite of the lower experimental control, the f i e l d r e s u l t s compare w e l l with those of the laboratory, i n d i c a t i n g that the concentration and migration of impurities behave s i m i l a r l y under natural melt conditions as under the melt conditions used i n the laboratory. (Daily temperatures recorded at a nearby weather s t a t i o n are presented i n Appendix F.) 111. 0 0.1 0.2 0.3 . 0.4 0.5 0.6 Cumulative Melt Water Fraction Figure 419 -Impurity Removals from Brine Irrigated Snowpacks. Figure 4.20 Impurity Profiles During Reid Experiment 112. Impurity P r o f i l e s The impurity p r o f i l e s of the snowpack were determined by p i t excavation and sampling of the snow every 20 cm with depth. Two r e p l i c a t i o n samples were taken at each depth. The r e p l i c a t e s showed considerable v a r i a t i o n s (up to 50%) as a r e s u l t of the i r r e g u l a r structure and drainage of natural snowpacks. Figure 4 . 2 0 shows that the impurities are concentrated and move as a f r o n t . However, the natural weather conditions cause some i r r e g u l a r i t i e s not observed i n the laboratory. The impurity front of Day 7 had reached a depth of about 6 0 cm and a bulk concentration of 2 . 2 C Q"^ (which i s equal to a pore s o l u t i o n concentration of about 10 to 15 times C 0 as described i n Section 4 . 3 ) . As a r e s u l t of c o l d weather, the snowpack temperature dropped below the fre e z i n g point of the impurity front solution and froze i t i n place. Later surface melts may have drained through melt channels and thus by-passed the impurity front. This i s indicated by the slow d i s s i p a -t i o n of the f r o n t and lowering of the conductivity immediately below the front. Freeze concentration i n the lower part of the pack allowed a second smaller impurity front to form. The above discussion i s speculative and based on l i m i t e d sampling of the snowpack. One should keep i n mind that each p r o f i l e was measured at a d i f f e r e n t l o c a t i o n and that the structure and drainage of the pack varied. In s p i t e of the d i f f e r e n c e s mentioned C = i n i t i a l s a l t a d d i t i o n as estimated from mass balance c a l c u -o l a t i o n s of each time of sampling. 113. and i n l i g h t of the l e s s e r experimental c o n t r o l of the f i e l d t e s t , i t appears that the concentration and mi g r a t i o n of i m p u r i t i e s i n snow behave s i m i l a r l y under f i e l d and l a b o r a t o r y c o n d i t i o n s . B e t t e r c o n t r o l l e d f i e l d experiments using snow made from sewage e f f l u e n t should be c a r r i e d out to v e r i f y t h i s c o n c l u s i o n . V i s u a l Observations The snow p r o f i l e and meltwater samples were obtained by p i t excavation. Some i n t e r e s t i n g v i s u a l observations of the exposed snowpack are presented here. The snow was coarse grained and wet on the day of the s a l t a p p l i c a t i o n . Two i c e lenses were present at about 50 cm and 90 cm above the ground. The lenses had p a r t l y degraded by Day 35. The surface of the o r i g i n a l pack and a l s o the snow base metamorphosed to coarse, loose "sugar" snow w i t h time. A s o l i d , 5 cm t h i c k i c e l a y e r formed at the base as the melting progressed. The most i n t e r e s t i n g observed change was the formation of " i c i c l e - l i k e " i c e v e i n s . The veins were f i r s t observed a f t e r about 3 weeks. They had a diameter of approximately 5 cm and were spaced about 20-30 cm apart. The bases of the veins were lo c a t e d at the new/old snow boundary. The formation of such v e i n s (or f i n g e r s ) i s explained by Wankiewicz (1979). For fine-over-coarse snow, two drainage condi-t i o n s are p o s s i b l e . For low flows, and hence low snow moisture content, the unsaturated p e r m e a b i l i t y of the coarse snow may be l e s s than t h a t of the f i n e r snow and the drainage w i l l be impeded. As the water content i n c r e a s e s , the coarse l a y e r p e r m e a b i l i t y w i l l 114. exceed that of the f i n e r snow and causing water to d r a i n i n d i s t i n c t f i n g e r s . This drainage phenomenon i s well known i n s o i l physics. For a d e t a i l e d d e s c r i p t i o n r e f e r to H i l l e l (1980). In t h i s f i e l d experiment, new snow which f e l l during the experiment formed a f i n e grained layer on top of the coarse grained o r i g i n a l snowpack. Surface melt drained through the fine snow and developed drainage channels (or fingers) as the melt i n f i l t r a t e d the coarse snow (accelerating horizon). Much of the melt may have reached the bottom of the pack through these channels and therefore did not contribute to impurity d i l u t i o n . The drainage of surface melt through these drainage channels was supported by the low conductivity of this water from melted i c e vein samples. The conductivity ranged from 25 uS/cm to 50 uS/cm, which i s only s l i g h t l y higher than that of freshly f a l l e n snow. Because of t h e i r low conductivity, the i c e veins were the f i r s t to melt as the snowpack warmed up towards the end of the experiment. On Day 59, about 35% of the snow had melted and the snow was again uniformly coarse grained. 4.6. Summary The experimental r e s u l t s c l e a r l y showed that impurities incor-porated into snow c r y s t a l s are removed during the melting process of the snow. The e f f e c t of the melt regime on the degree of removal was s u r p r i s i n g l y small. In f a c t , for a l l p r a c t i c a l purposes the impurity removal with the f i r s t 20% of the melt may be considered to be independent of the melt conditions, and of the i n i t i a l impurity 115. c o n c e n t r a t i o n of the snow. For example, a f i v e - f o l d i n c r e a s e i n the i n i t i a l impurity concentration r e s u l t e d i n only a 2% improvement i n the removal e f f i c i e n c y . Reducing the depth from 90 cm to 45 cm reduced the impurity removal by about 5%. A red u c t i o n i n snow temperature from -1°C to -2°C had a s i m i l a r l y s m a l l e f f e c t . Impurity f r a c t i o n s i n the e a r l y melt were only s l i g h t l y lower i n the continuous melt experiments than i n those exposed to a number of surface melt-freeze c y c l e s . Since the i m p u r i t i e s were i n i t i a l l y w e l l d i s t r i b u t e d throughout the snowpack, the s u r p r i s i n g l y high impurity concentration i n the meltwater produced under CM c o n d i t i o n s can only be explained by the f a c t t h a t m e l t i n g and f r e e z i n g took place as the melt s o l u t i o n made i t s way through the snowpack. This l e d to a r e v i s i o n of the o r i g i n a l hypothesis p o s t u l a t e d i n Secti o n 2.6. I t appears that the degree of impurity removal i n snow i s e s s e n t i a l l y independent of the number of surface melt-freeze c y c l e s . I t i s b e l i e v e d that the impurity c o n c e n t r a t i o n i s caused by g r a i n coarsening and successive i n t e r n a l melt-freeze c y c l e s . As the melt s o l u t i o n ( c o n t a i n i n g i m p u r i t i e s released by the g r a i n coarsening p r o c e s s ) , p e r c o l a t e s i n t o the lower, c o l d e r snow, the water f r a c t i o n freezes l e a v i n g a more concentrated s o l u t i o n i n the pore spaces. Thus, although the snow surface may melt co n t i n u o u s l y , the melt f r o n t goes through a number of i n t e r n a l melt-freeze c y c l e s during which the i m p u r i t i e s become h i g h l y concentrated i n the pore water and are discharged with the e a r l y melt f r a c t i o n s . The above hypothesis i s a l s o supported by the observation that impurity removal increased somewhat with i n c r e a s i n g snow depth and decreasing snow temperature. Both of these c o n d i t i o n s allow a 116. greater number of successive i n t e r n a l melt-freeze c y c l e s . Sewage eff l u e n t impurities were not concentrated to the same extent as the potassium c h l o r i d e . The average percentage of e f f l u -ent impurities i n the f i r s t 20% of the melt ranged form 65% for orthophosphate to 86% for ammonia, whereas the removal of potassium chloride was about 92%. The lesser removal of orthophosphate with the melt may have resulted from retention of orthophosphate by adsorption onto e f f l u e n t p a r t i c l e s i n the snow. The nitrogen removal associated with the meltwater (86%), i s presented as a f r a c t i o n of the average impurity concentration of snow (estimated by mass balance of meltwater and residual snow samples). This average concentration does not include ammonia l o s t by s t r i p p i n g (~25%). The t o t a l nitrogen removal, including ammonia st r i p p i n g would then equal about 89% (= ^ ' ^ " j * ^ * ^ ) . The r e s u l t s showed that the impurity f r a c t i o n can, for a l l p r a c t i c a l purposes, be expressed as a function of the cumulative melt f r a c t i o n . A simple, f i r s t - o r d e r exponential decay function adequately describes the impurity removal f o r most conditions: y = 1.0 - e where y = x cumulative f r a c t i o n of dissolved material, cumulative f r a c t i o n of meltwater 117. k = decay c o e f f i c i e n t The decay c o e f f i c i e n t has a mean value of 11.5 f o r potassium c h l o r i d e and a range from 5.5 ( f o r phosphorus) to 8.5 ( f o r nitrogen) f o r the n u t r i e n t s i n the sewage e f f l u e n t s . The above equation can be used i n conjunction with a snowmelt model, such as that discussed i n the next chapter, to make pre-l i m i n a r y estimates of the runoff q u a l i t y from an e f f l u e n t d i s p o s a l snowpack. These estimates could be used f o r a s s e s s i n g the f e a s i -b i l i t y of t h i s d i s p o s a l method f o r any p a r t i c u l a r s i t e . An i n t e r e s t i n g consequence of the f i n d i n g that the i m p u r i t y removal from snow i s almost independent of the temperature regime during m e l t i n g , i s that t h i s d i s p o s a l method need not be l i m i t e d to c o l d c l i m a t e s , but could be f e a s i b l e anywhere that the winter temperatures get low enough to allow conversion of e f f l u e n t to snow i n the f i r s t place. Once the snow i s made, whether i t melts immediately or through a number of d i u r n a l melt-freeze c y c l e s , melting should r e s u l t i n a high degree of impurity removal with the e a r l y meltwater f r a c t i o n s . 118. 5. MODEL FOR PREDICTION OF RUNOFF RATES AND QUALITY D i s p o s a l of sewage e f f l u e n t through conversion to snow does not e l i m i n a t e the i m p u r i t i e s . I t simply provides a method of separating the i m p u r i t i e s from the bulk of the snowpack. The i m p u r i t i e s are concentrated i n the e a r l y melt which a l s o comes o f f most s l o w l y . Design of a d i s p o s a l system should allow the e a r l y melt water to i n f i l t r a t e the s o i l and allow the bulk of the l a t e r d i l u t e meltwater to run o f f . This requires e s t i m a t i o n of rate and c o n c e n t r a t i o n of the melt discharge and p a r t i t i o n of the melt i n t o s o i l i n f i l t r a t i o n and surface run o f f . A simple computer model f o r e s t i m a t i o n of these parameters i s proposed i n t h i s chapter. Program documenta-t i o n , examples of use, and the APL computer code are presented i n Appendix D. The modified temperature-index model developed by Quick & Pipes (1976) and described i n S e c t i o n 2.3, was chosen f o r t h i s computer program. The p a r t i t i o n i n g of the snowmelt i n t o overland flow and i n f i l t r a t i o n depends on the i n f i l t r a b i l i t y of the s o i l ( n e g l e c t i n g any impeding e f f e c t s of the s o i l surface and v e g e t a t i o n ) . The i n f i l t r a t i o n r a t e i s a f u n c t i o n of the s o i l water.content. I t i s g r e a t e s t f o r dry s o i l and decreases to the saturated h y d r a u l i c con-d u c t i v i t y ( K g ) as the s o i l water content i n c r e a s e s to s a t u r a t i o n ( H i l l e l , 1980). E s t i m a t i o n of the a c t u a l i n f i l t r a t i o n r a t e s r e q u i r e s I n - s i t u measurement of the s o i l water content which i s d i f f i c u l t to o b t a i n during the m e l t i n g p e r i o d . The saturated h y d r a u l i c c o n d u c t i v i t y was used t h e r e f o r e , as an approximation of the i n f i l t r a t i o n r a t e . This approximation r e s u l t s i n an underestimate of i n f i l t r a t i o n r a t e s and hence a conservative estimate of the runoff r a t e s . I t i s assumed that e a r l y snow produc-t i o n w i l l prevent ground f r o s t and that the s o i l / v e g e t a t i o n surface does not impede the meltwater i n f i l t r a t i o n . The removal of impuri-t i e s w i t h the meltwater can be expressed as a simple exponential decay f u n c t i o n of the cumulative melt discharge, as given i n the -kx previous s e c t i o n (y = 1.0-e ). The program described h e r e i n i s proposed as an a i d to the designer's c a l c u l a t i o n s . D e t a i l e d i n s t r u c t i o n s and s e v e r a l examples of c a l c u l a t i o n s are presented i n Appendix D. The program r e q u i r e s as input d a i l y temperatures and an estimate of the s o i l ' s saturated h y d r a u l i c c o n d u c t i v i t y . The user can run a s e n s i t i v i t y a n a l y s i s on the snowpack depth to determine the ranges of depths required to achieve a s p e c i f i e d removal of phosphorus or n i t r o g e n , w h i l e at the same time meeting s p e c i f i e d runoff q u a l i t y g u i d e l i n e s . The c i t y of Vernon, B r i t i s h Columbia, was used f o r the example c a l c u l a t i o n s . Vernon t r e a t s i t domestic sewage by the t r i c k l i n g f i l t e r process and disposes of the e f f l u e n t by spray i r r i g a t i o n . However, the spray i r r i g a t i o n system has not been able to accommo-date a l l of the e f f l u e n t during the l a s t few years, r e s u l t i n g i n c o n t r o v e r s i a l d i r e c t discharge of the e f f l u e n t to the Okanagan Lake system. The examples used demonstrate that snowmaking of the e f f l u -ent w i l l provide f o r low cost winter d i s p o s a l . A conservative s a t u r a t e d h y d r a u l i c c o n d u c t i v i t y of 10~ 6 m/s and a snowpack depth of 5 m produced no runoff (max. melt r a t e ~ 5 x l 0 ~ 7 m/s), as estimated by the computer program, and thus a l l the phosphorus and n i t r o g e n i n f i l t r a t e d the s o i l . For the h y p o t h e t i c a l case of a t i g h t s o i l 120. w i t h a satura t e d h y d r a u l i c c o n d u c t i v i t y of 10~ 7 m/s about 64% of the snowpack would run o f f . The removal of phosphorus was estimated to be about 68%. Reducing the snow depth to 2.5 m reduced the runoff to 47%, removed 80% of the phosphorus, and reduced the average phosphorus con c e n t r a t i o n of the r u n o f f . The e f f e c t s of weather can l i k e w i s e be estimated. 121. 6. CONCLUSIONS AND RECOMMENDATIONS Snowmaking provides t e r t i a r y treatment and disposal of d i s i n -fected sewage e f f l u e n t . The method i s based on the p r i n c i p l e that dissolved material present i n snow becomes concentrated i n the early melt through metamorphic and melt-freeze processes, thus leaving the remaining snow r e l a t i v e l y pure. The s o i l i n f i l t r a b i l i t y of the s i t e only needs to be s u f f i c i e n t f o r i n f i l t r a t i o n of the low rate early snowmelt discharge, to achieve removal of most of the nutrients and r e s i d u a l organic matter. Snow metamorphisism releases Impurities from snow c r y s t a l s to the i n t e r s t i t i a l water as large c r y s t a l s grow at the expense of smaller ones under curvature induced temperature gradients. As surface meltwater c a r r i e s the impurities downwards, the s o l u t i o n becomes concentrated by freezing of water onto the lower colder snow c r y s t a l s . If the snowpack Is cold enough even the concentrated pore water s o l u t i o n w i l l freeze, but i t w i l l be the l a s t to freeze and the f i r s t to melt i n each cy c l e . Thus, over a number of melt-freeze c y c l e s , the s o l u t i o n becomes incr e a s i n g l y concentrated as i t pene-trates into the pack and eventually becomes the f i r s t melt to be discharged. This concentration and transportation process i s too complex for rigorous a n a l y s i s . Analysis of solute transport i n snow i s r e s t r i c t e d to mature, melting snowpacks i n which no refreezing takes place and which behaves approximately l i k e a conventional porous medium. Therefore, a simple empirical formulation was developed for pred i c t i o n of the degree of impurity removal from snow. The degree to which impurities became concentrated i n the early melt f r a c t i o n was found to be v i r t u a l l y independent of the 122. melt c o n d i t i o n s and the i n i t i a l c o n c e n t r a t i o n of the s o l u t i o n . As a r e s u l t , the r e l a t i o n s h i p between the impurity removal and the cumu-l a t i v e melt f r a c t i o n can, f o r a l l p r a c t i c a l purposes, be modelled by an exponential decay process c h a r a c t e r i z e d by a s i n g l e "decay" para--kx meter: y = 1.0 - e (where y = f r a c t i o n of i m p u r i t y removed; x = cumulative melt f r a c t i o n ; k = decay c o e f f i c i e n t ) . Procedures f o r assessment and design of e f f l u e n t snow d i s p o s a l systems were developed based on t h i s equation. The cumulative melt f r a c t i o n was computed using a snowmelt model developed by Quick and Pipes (1976). The p a r t i t i o n of the melt i n t o i n f i l t r a t i o n and run o f f was • estimated from the saturated h y d r a u l i c c o n d u c t i v i t y of the s o i l . Other conclusions drawn from the research observations i n c l u d e : 1. The impurity f r a c t i o n s removed from e f f l u e n t snow with the f i r s t 0.2 f r a c t i o n of the melt were 0.65 f o r phosphorus and 0.86 f o r n i t r o g e n . Snow made from potassium c h l o r i d e s o l u t i o n s experienced a 92% removal w i t h the 0.2 melt f r a c t i o n . The lower degree of conc e n t r a t i o n observed f o r phosphorus i s l i k e l y a r e s u l t of i t s high a f f i n i t y f o r p a r t i c l e s present i n the snow. Most of these p a r t i c l e s would remain on the s i t e and thus the e f f e c t i v e phosphorus removal, as estimated from the run o f f q u a l i t y , would be s i g n i f i c a n t l y higher than the 65% i n d i c a t e d by the melt discharge. 2. Test performed using snow made from potassium c h l o r i d e s o l u -t i o n s i n d i c a t e d that the degree of impurity concentration i s v i r t u a l l y independent of: melt mode, snow depth, snow temperature, and i n i t i a l c o n centration the s o l u t i o n s . Only s l i g h t improvement i n 123. the degree of i m p u r i t y c o n c e n t r a t i o n was observed f o r deeper snow columns, lower snow temperatures and higher i n i t i a l c o n centration of the potassium c h l o r i d e s o l u t i o n s . Continuous m e l t i n g snow columns produced impurity removal only s l i g h t l y lower than those melted under simulated melt-freeze regime. These observations suggest that the concentration of i m p u r i t i e s i s a r e s u l t of successive i n t e r n a l melt-freeze c y c l e s r a t h e r than d i u r n a l c y c l e s o c c u r r i n g at the surface of the snowpack. 3. The l a b o r a t o r y snow conversion process d i d not a f f e c t the phosphorus and potassium c h l o r i d e concentrations apart from an approximately f i v e percent c o n c e n t r a t i o n by evaporation. The process s t r i p p e d , on the average, eight percent of the ammonia present i n the e f f l u e n t . A f u r t h e r 15 to 20% r e d u c t i o n of ammonia occurred during melting and sampling of the snow. The t o t a l n i t r o -gen removal was about 90%, i n c l u d i n g the amount of ammonia s t r i p p e d . 4. The f i e l d t e s t showed that impurity removal from snow under n a t u r a l m e l t i n g c o n d i t i o n s i s s i m i l a r to those observed i n the l a b o r a t o r y . I t a l s o i n d i c a t e d that the i n i t i a l impurity d i s t r i b u -t i o n throughout the snowpack had l i t t l e e f f e c t on the r a t e of impurity removal (surface a p p l i c a t i o n vs. snowmaking). 5. Samples taken at d i f f e r e n t depths c l e a r l y showed that i m p u r i -t i e s moved as a d i s t i n c t f r o n t through the snowpack. The maximum degree of concentration of the impurity f r o n t was estimated to be 15 to 40 times the i n i t i a l i m p u r i t y c o n c e n t r a t i o n of the snow. This compares w e l l to the 15 to 20 t4mes degree of co n c e n t r a t i o n observed i n the f i r s t melt discharge. 6. The snow columns melted continuously achieved a pseudo steady s t a t e melt discharge of 6 x l 0 ~ 6 m/s. This melt rate i s approximately 1-2 orders of magnitude gre a t e r than the r a t e s o c c u r r i n g n a t u r a l l y . The perm e a b i l i t y of the snow at t h i s f l u x was 1 0 " 1 2 m2 which i s 2-3 orders of magnitude lower than t h a t of saturated snow. The r e s u l t s from t h i s research program suggest that snowmaking could provide a p r a c t i c a l d i s p o s a l a l t e r n a t i v e f o r d i s i n f e c t e d secondary e f f l u e n t s f o r communities faced w i t h e f f l u e n t d i s p o s a l r e s t r i c t i o n s i n the winter. The r e s u l t s i n d i c a t e that the degree of i m p u r i t y concentration i n snow i s v i r t u a l l y independent of the melting c o n d i -t i o n s . This i m p l i e s that the e f f l u e n t snow d i s p o s a l method need not be r e s t r i c t e d to c o l d c l i m a t e s , but could be f e a s i b l e at any s i t e where the winter temperatures get low enough to produce snow. Once the e f f l u e n t has been converted to snow, a high degree of removal of n u t r i e n t s and r e s i d u a l organics i s expected whether the snow melts immediately or through a number of d i u r n a l melt-freeze c y c l e s . I t i s a l s o conceivable that snowmaking can be extended to d i s p o s a l of primary e f f l u e n t s . This would r e q u i r e f u r t h e r l a b o r a t o r y work on c o l i f o r m d e s t r u c t i o n and on the e f f e c t s of increased presence of c o l l o i d a l and suspended matter. Such work should f o l l o w a success-f u l f i e l d demonstration of secondary e f f l u e n t d i s p o s a l through snow-making. Recommended f u r t h e r research i n c l u d e a f i e l d program to t e s t 125. the f i n d i n g s of t h i s research under n a t u r a l c o n d i t i o n s . In p a r t i c u -l a r , the f i e l d program should address the p o s s i b l e a d d i t i o n a l phos-phorus removal due to ads o r p t i o n onto p a r t i c l e s u r f a c e s ; optimum snowmaking c o n d i t i o n s f o r ammonia s t r i p p i n g ; and n u t r i e n t i n f i l t r a -t i o n and uptake by the s o i l / v e g e t a t i o n system. Further research should a l s o be d i r e c t e d at development of a rigorous process d e s c r i p t i o n of s o l u t e t r a n s p o r t i n " c o l d " snow. REFERENCES 126. Adams, W.P. and Lasenby, D.C, 1982. "Lake Ice Growth and Co n d u c t i v i t y " . Proceedings Western Snow Conference. Anderson, E.A., 1973. "National Weather Service River Forecast System - Snow Accumulation and A v i a t i o n Model". NOAA Tech. Memo. NWS HYDRO-17, U.S. Dept. Commer., Washington, D.C. Baker, R.A., 1967a. "Trace Organic Contaminant Concentration by Free z i n g - I : Low Inorganic Aqueous S o l u t i o n s " . Water Research 1, 61-77. Baker, R.A., 1967b. "Trace Organic Contaminant Concentration by Free z i n g - I I : Inorganic Aqueous S o l u t i o n s " . Water Research 1, 97-113. Bear, J . , 1972. "Dynamics of F l u i d s i n Porous Media". American E l s e v i e r , New York. B r e s l e r , E., 1973. "Simultaneous Transport of Solutes and Water Under Transient Unsaturated Flow C o n d i t i o n s " . Water Resour. Res. 9 , 975-986. Chen, J . and Kevorkian, V., 1968. "Mass Production of 300-Micron Water Dro p l e t s by Air-Water Two-Phase Nozzles". Ind. Eng. Chem. Process Des. Develop. 7, 586-590. Chen, J . and Kervorkian, V., 1971. "Heat and Mass Transfer i n Making A r t i f i c i a l Snow". Ind. Eng. Chem. Process Des. Develop. 10, 75-78. Colbeck, S.C, 1972. "A Theory of Water P e r c o l a t i o n i n Snow". J . G l a c i o l . 11, 369-385. Colbeck, S.C, 1974a. "The C a p i l l a r y E f f e c t s on Water P e r c o l a t i o n i n Homogeneous Snow". J . G l a c i o l . 13, 85-97. Colbeck, S.C, 1974b. "Water Flow Through Snow Overlying an Impermeable Boundary". Water Resour. Res. 10, 119-123. Colbeck, S.C, 1975. "A Theory f o r Water Flow Through a Layered Snowpack". Water Resour. Res. 11, 261-266. Colbeck, S.C, 1976. "The P h y s i c a l Aspects of Water Flow Through Snow" i n Advances i n Hydroscience, ed. Ven Te Chow, Academic P r e s s , New York, 11, 165-200. Colbeck, S.C, 1977. "Tracer Movement Through Snow". IAHS-AISH Publ. 118, 255-262. Colbeck, S.C, 1979. "Grain C l u s t e r s i n Wet Snow". J . C o l l o i d I n t e r f a c e S c i . 77, 371-384. 127. Colbeck, S.C. 1981. "A Simulation of the Enrichment of Atmospheric P o l l u t a n t s i n Snow Cover Runoff". Water Resour. Res. 17, 1383-1388. Colbeck, S.C. and Anderson, E.A. 1982. "The Pe r m e a b i l i t y of a M e l t i n g Snow Cover". Water Resour. Res. 18, 904-908. Colbeck, S.C. and Davidson, G., 1973. "Water P e r c o l a t i o n Through Homogeneous Snow". In the Role of Snow and Ice i n Hydrology: Proc. Banff Symposia, Sept. 1972. UNESCO-WHO-IAHS, 242-257. Corte, A.E., 1982. " V e r t i c a l M i g r a t i o n of P a r t i c l e s i n Front of a Moving Freezing Plane". J . of Geophysical Res., 67, No. e, 1085-1090. Dahl, J.B., Ovenild, C , Seip, H.M. and T o l l a n , 0., 1979. "Omsetting av Kalsium og s u l f a t i smeltevann og i regnvann pa sma f e l t e r undersokt ved h j e l p av r a d i o a k t i v e t r a c e r e " . SNSF-project IR 49/79, Norwegian Forest Research I n s t i t u t e , 65 p. de Quervain, M.R., 1973. "Snow S t r u c t u r e , Heat and Mass F l u x Through Snow", i n The Role of Snow and Ice i n Hydrology: Proc. Banff Symposia, Sept. 1972, UNESCO-WHO-IAHS, 203-226. Doronin, Yu.P. and K h e i s i n , D.E., 1977. "Sea Ice", Amerind P u b l . Co., New D e l h i . Drost-Hansen, W., 1967. "The Water-ice I n t e r f a c e as Seen from the L i q u i d Side". J . C o l l o i d I n t e r f a c e S c i . 25, 131-160. Freeze, R.A. and Cherry, J.A., 1979. "Groundwater". P r e n t i c e -H a l l . G i l p i n , R.R., 1979. "A Model of the ' L i q u i d - l i k e * Layer between Ice and a Substrate w i t h A p p l i c a t i o n s to Wire Regulation and P a r t i c l e M i g r a t i o n " . J . C o l l o i d I n t e r f a c e S c i . 68, 235-251. G i l p i n , R.R., 1980. " T h e o r e t i c a l Studies of P a r t i c l e Engulfment". J . C o l l o i d I n t e r f a c e S c i . 74, 45-63. Glen, J.W., Homer, D.R. and Paren, J.G., 1977. "Water at Grai n Boundaries: I t s Role i n the P u r i f i c a t i o n of Temperate G l a c i e r Ice". IAHS-AISH, Publ. 118, 263-271. Gross, G.W., 1968. "Some E f f e c t s of Trace Inorganics on the Ice-Water System". Adv. Chem. Ser. 73, 27-97. Halde, R., 1980. "Concentration of Impur i t i e s by Progressive F r e e z i n g " . Water Research 14, 576-580. 128. Hetherington, E., 1982. P a c i f i c F orest Research Centre, Environment Canada, V i c t o r i a , B.C., Personal Communication. H i l l e l , D., 1980. "Fundamentals of S o i l P h y s i c s " . Academic Press, New York. Hobbs, P.V., 1974. "Ice P h y s i c s " . Clarendon Press, Oxford. Johannessen, M. and Henriksen, A., 1978. "Chemistry of Snow Meltwater: Changes i n Concentration During M e l t i n g " . Water Re sour. Res. 14, 615-619. LaChapelle, E., 1973. " F i e l d Guide to Snow C r y s t a l s " . Univ. of Wash. Press. Langhan, E.J., 1981. "Physics and P r o p e r t i e s of Snowcover", i n Handbook of Snow, ed. Gray, D.M. and Male, D.H., Pergamon Press, 275-337. Male, D.H. and Granger, R.J., 1979. "Energy and Mass Fluxes at the Snow Surface i n a P r a i r i e Environment", i n Proc. Modeling Snow Cover Runoff, eds. Colbeck, S.C. and Ray, M., U.S. Army Cold Reg. Res. Eng. Lab., Hanover, N.H., 101-124. Male, D.H. and Gray, D.M., 1981. "Snow Cover A b l a t i o n and Runoff", i n Handbook of Snow, ed. Gray, D.M. and Male, D.H., Pergamon Press, 360-436. Malo, B.A. and Baker, R.A., 1968. " C a t i o n i c Concentration by Fr e e z i n g " . Adv. i n Chem. Ser. 73, 149-163. Metcalf and Eddy, Inc., 1979. "Wastewater Engineering: Treatment D i s p o s a l and Reuse", second ed., McGraw-Hill, Inc. Nakawo, M. and Frederking, R., 1981. "The S a l i n i t y of A r t i f i c a l B u i l t - u p Ice Made by Successive F l o o d i n g of Sea I c e " . IAHR, I n t . Symp. on Ice, 516-525. 0'Byrne, J.M. and Haynes, D., 1973. "Use of a Snow Gun f o r Production of a Model Snow M a t e r i a l " . Proc. 30th Eastern Snow Conference, 15-19. Ontario M i n i s t r y of Environment, 1982. "Storage and Renovation of Sewage E f f l u e n t by Conversion to Snow". Interim Report, T e c h n i c a l Support Sect i o n , 77 p. Overrein, L.N., Seip, H.M. and T o l l a n , A., 1980. "Acid P r e c i p i t a t i o n - E f f e c t s on For e s t and F i s h " . F i n a l Report SNSF-project, FR 1980. P e r l a , R.I. and M a r t i n e l l i , M., 1976. "Avalanche Handbook". U.S. Dep. A g r i c , A g r i c . Handbook 489, 238 p. 129. P i t t e r , R.L. and Pruppacher, H.R., 1973. "A Wind Tunnel I n v e s t i g a -t i o n of Freezing of Small Water Drops F a l l i n g at Terminal V e l o c i t y i n A i r " . Quart. J.R. Met. Soc. 99, 540-550. Quick, M. and Pipes, A., 1976. "A Combined Snowmelt and R a i n f a l l Runoff Model". Can. J . C i v . Eng., 3,3 449-460. Raymond, C.F. and Tusima, K., 1979. "Grain Coarsening of Water Saturated Snow". J . G l a c i o l o g y 22, 83-105. Romkens, M.J.M. and M i l l e r , R.D., 1973. "M i g r a t i o n of M i n e r a l P a r t i c l e s i n Ice with a Temperature Gradient". J . C o l l o i d I n t e r f a c e S c i . 42, 103-111. Schemenauer, R.S., Berry, M.0. and Maxwell, J.B., 1981. "Snowfall Formation", i n Handbook of Snow, ed. Gray, D.M. an Male D.H., Pergamon Press, 129-152. Seip, H.M., Abrahamsen, G., Christophersen, N., Gj e s s i n g , E.T., Stuanes, A.O., 1980. "Snow and Meltwater Chemistry i n M i n i -catchments". SNSF-project IR 53/80, Norwegian Forest Research I n s t i t u t e , Aas, Norway, 51 p. Shimizu, H., 1970. " A i r P e r m e a b i l i t y of Deposited Snow". Low Temperature S c i . Ser. A 22, 1-32. SIGMA Engineering L t d . , 1982. "Kobes Compressor S t a t i o n -Snowmaking E f f l u e n t D i s p o s a l Study", Report to Westcoast Transmission Company L t d . , Vancouver, B.C. Sommerfeld, R.A. and LaChapelle, E., 1970. "The C l a s s i f i c a t i o n of Snow Metamorphism". J . G l a c i o l . 9 , 3-17. Standard Methods, 1980. "Standard Methods - For the Examination of Water and Wastewater", publ. APHA-AWWA-WPCF, Washington, D.C, USA. Technicon Autoanalyser I I , 1973a. " N i t r a t e and N i t r i t e i n Water and Wastewater", Ind. Method No. 100-70W, Technicon Ind. Systems, Tarrytown, N.Y., USA. Technicon Autoanalyser I I , 1974a. "Phosphorus/BD Acid Digest", Ind. Methods No. 327-73W, Technicon Ind. Systems, Tarrytown, N.Y., USA. Technicon Autoanalyser I I , 1974b. "Ammonical Nitrogen/BD A c i d D i g e s t " , Ind. Methods No. 321-74A, Technicon Ind. Systems, Tarrytown, N.Y., USA. Technicon Autoanalyser I I , 1973b. "Ammonia i n Water and Seawater", Ind. Methods No. 154-71W, Technicon Ind. Systems, Tarrytown, N.Y., USA. 130. T e r w i l l i n g e r , J.P. and D i z i o , S.F., 1970. " S a l t R e j e c t i o n Phenomena i n the Freezing of S a l i n e S o l u t i o n s " . Chem. Eng. S c i . 25, 1331-1349. U.S. Army Corps of Engineers, 1956. "Snow Hydrology, Summary Report of the Snow I n v e s t i g a t i o n s " . U.S. Army Corps Eng., North P a c i f i c Div., P o r t l a n d , Oregon. Wankiewicz, A., 1978. "Water Pressures i n Ripe Snowpacks". Water Resour. Res. 1 4 , 593-600. Wankiewicz, A., 1979. "A Review of Water Movement i n Snow", i n Proc. Modeling Snow Cover Reg. Res. Eng. Lab., Hanover, N.H., USA, 222-252. Wright, K.R., 1976. "Sewage E f f l u e n t Burned to Snow: Provides Storage, Removes P o l l u t a n t s " . J . C i v i l Eng. ASCE, 88-89. Wright-McLaughlin Engineers, 1975. "Storage and Renovation of Sewage E f f l u e n t i n A r t i f i c i a l l y Created Snowpack". Report to Upper Yampa Water Conservancy D i s t r i c t , Steamboat Springs, Colorado, USA. 131 APPENDIX A - ADDITIONAL RESULTS LIST OF TABLES A . l . Continuous Melt Results of Secondary Sewage E f f l u e n t Snow Experiments A.2. Melt-Freeze Results of Sewage E f f l u e n t Snow D i s p o s a l Experiments A.3. Potassium Chloride B a s e l i n e Experimental R e s u l t s A.4. P r e l i m i n a r y Experimental R e s u l t s A.5. Impurity P r o f i l e s f o r KC1 Snow Exposed to Simulated Melt-Freeze Conditions A.6. Sewage Impurity D i s t r i b u t i o n i n the Top 15 cm of Residual Snow Produced by Continuous Melt Conditions A.7. Sewage Impurity D i s t r i b u t i o n i n the Top 15 cm of Residual Snow Produced by Melt-Freeze Conditions A.8. P o t a s s i um Chloride D i s t r i b u t i o n i n the Top 15 cm of Residu a l Snow Produced by Melt-Freeze Conditions A.9. Potassium Chloride D i s t r i b u t i o n i n the Top 15 cm of Residual Snow Produced by Continuous Melt Conditions A.10. Impurity P r o f i l e s of a N a t u r a l Snowpack I r r i g a t e d With Brine A.11. Mean and Standard D e v i a t i o n of Observed Potassium C h l o r i d e Removals A.12. Snowpack Temperature P r o f i l e s Observed During the F i e l d Experiment Id* TABLE A . l . Continuous Melt Results of Sewage Effluent Snow Disposal Experiments. Repl. Type I n l t l a l ( 1 ) Haas Total Water Equlv. of Impurity Removals for of Concentrations Balance Melt snow, X Cumulative Melt Fractions. Impurity uS/cm Volume, Z C 1 C 0 ] 0 X X Packed 1 Residual .05 .10 .15 .20 j .25 .30 COND. 318 329 + 3.5 1 34 57 70 _| 1— 79 84 86 TKN 15.6 12.9 -17.6 32 57 71 80 84 87 NH,+NHU+ 15.3 12.5 -18.3 35 59 73 81 85 89 SI NO,+NO, 0.38 0.39 - 2.6 42.5 20.8 41.4 32 52 64 71 75 78 TP 1.25 1.21 - 3.2 22 41 55 66 73 79 P Oi» 1.12 1.05 - 6.3 22 40 54 66 74 80 TOC 18.5 21.1 +14.1 22 41 50 57 62 65 T0C1(2) 0 24 45 58 66 71 75 COND. 337 + 6.0 42 62 73 80 84 86 TKN 12.7 -18.7 43 63 75 83 85 89 NH,+NHLI+ 12.4 -19.0 42 64 74 81 85 88 S2 NO:+NO. 0.38 0 43.1 21.6 42.5 41 59 69 74 77 80 TP 1.20 - 4.0 25 44 56 67 75 80 P 0* 1.06 - 5.4 23 43 58 69 76 80 TOC 20.6 +11.4 32 47 57 64 69 72 TOC1 0 35 50 65 74 79 82 COND. 318 348 + 9.4 36 58 76 84 87 90 TKN 17.1 13.9 -18.7 36 60 77 84 87 90 NH,+NH + 16.4 13.7 -16.5 38 61 77 84 88 92 S3 NO,+NO, 0.24 0.23 - 4.2 39.5 20.2 45.7 31 51 63 69 72 75 TP 0.83 0.86 + 3.6 30 52 69 80 86 88 P O l i 0.76 0.73 - 3.9 31 54 71 81 87 90 TOC 15.0 18.7 +24.7 30 47 57 65 69 73 TOC1 0 36 57 72 80 86 90 COND. 343 + 7.9 42 68 79 85 88 90 TKN 14.2 -17.1 42 67 79 86 88 90 SA NH,+NHU 13.7 -16.5 43 68 79 86 89 92 NO,+N0, 0.23 - 4.2 41.0 20.0 44.2 35 56 66 71 73 75 TP 0.84 + 1.2 30 54 69 79 84 87 P O i 0.74 - 2.6 31 56 70 80 85 89 TOC 18.7 +24.7 33 50 60 65 69 73 TOC1 0 40 62 74 83 88 91 (1) CQ - as estimated from fresh snow samples; C - as estimated from meltwater and residual snow samples. Same snow packed In column 1 and 2, 3 and 4. (2) TOC1 values have" been corrected to a mass balance of OX. TABLE A.2. Melt-Freeze Results of Sewage Effluent Snow Disposal Experiments. Repl. Type I n l t i a l ( 1 ) Mass Total Water Equiv. of Impurity Removals for of Concentrations Balance Melt snow, X Cumulative Melt Fractions, Impurity uS/cm Volume X C'o | co X X Packed j Residual .05 .15 1 '2° 1 .25 .30 COND. 298 324 + 8.7 61 75 81 84 87 89 TKN 10.8 9.4 -12.9 60 74 80 84 87 89 NH,+NHU+ 10.8 8.9 -17.6 60 74 80 84 87 89 S5 NO^ +NO, 0.60 0.50 +20.0 33.8 19.6 53.0 59 73 79 82 84 86 TP 2.04 1.93 - 5.4 26 43 53 59 65 68 P C \ 1.95 1.80 - 7.7 27 44 53 60 65 68 TOC 17.5 20.7 +18.3 44 55 60 64 67 71 TOC1 52 65 70 74 79 82 COND. 353 +18.5 54 73 79 81 84 86 TKN 9.6 -11.1 55 74 80 84 86 88 NH,+N0u+ 9.0 ^16.7 53 72 79 82 84 86 S6 N0,+N0, 0.55 +10.0 30.0 20.3 55.7 45 74 80 82 84 85 TP 1.97 - 3.4 26 42 50 55 59 62 PO„ 1.80 - 7.7 25 41 49 54 58 61 TOC 23.6 +34.9 41 57 61 64 67 70 TOC1 0 56 76 81 86 91 95 (1) Cg - as estimated from fresh snow samples; C - as estimated from meltwater and residual snow samples. same snow packed In column 1 and 2, 3 and 4. (2) TOC1 values have been corrected to a mass balance of OX. TABLE A.3. P o t a s s i u m C h l o r i d e B a s e l i n e E x p e r i m e n t a l R e s u l t s Exp. Re p i . No. I n l t l Concen uSi C o a l W . r a t i o n s cm C o M a a s ( 2 ) B a l a n c e tlontsr Z Water F r e s h E q u l v . of X Packed j Snow, R e s i d u a l T o t a l M e l t V o l . Z I m p u r i t y C u m u l a t i v e .05 I .10 1 Removals f o r Melt F r a c t i o n s , .15 1 .20 I .25 .30 1 1973 1944 -1.5 4.5 7.6 23.7 57.7 32.4 49 80 92 96 97 98 2 1981 1908 -3.7 4.3 12.8 28.3 51.7 20.8 57 86 92 95 96 97* B l 3 2023 1869 -7.6 4.7 9.6 30.9 49.1 22.4 53 76 86 91 93 94* MF 4 2023 1940 -4.1 4.6 9.1 23.9 53.2 20.9 51 81 91 94 96 96* 1000 5 2195 2268 +3.3 4.6 10.7 27.2 55.7 24.9 54 77 87 92 96 96* 90 6 2027 2045 +0.9 6.7 10.6 27.8 57.0 20.2 52 78 90 94 96 96* 7 2082 2037 -2.2 4.3 11.0 30.0 57.3 13.1 56 85 92* 95* 97 97* 8 1996 2128 -6.2 6.3 10.7 27.8 64.2 12.7 48 83 93* 96* 98 98* 1 1940 1940 0 4.9 9.8 25.7 55.7 55.3 50 72 79 86 89 91 2 2028 1982 -2.3 4.4 10.1 23.0 55.7 44.4 64 86 90 92 95 96 B2 3 2096 2135 +1.9 5.2 12.3 30.4 46.0 42.9 53 72 80 85 88 88 CM 4 2103 2036 -3.3 5.4 - 24.8 44.3 38.3 55 84 90 93 95 96 1000 5 1965 1902 -3.2 4.6 13.8 29.1 43.8 46.4 55 80 87 90 93 94 90 6 . 2010 1924 -4.4 5.3 13.2 24.7 45.7 36.2 60 85 91 93 95 96 7 | same as exp. 4, r e p l i c a t i o n s no. 1 and 2 B3 CM 1000 45 1 2 3 4 2044 2040 2072 2061 1972 2012 +1.4 +0.8 -3.3 -1.4 4.6 5.2 9.3 9.9 26.6 26.4 25.8 26.6 45.8 45.0 43.7 45.2 38.7 39.2 39.6 39.5 42 41 41 40 65 69 67 66 81 82 80 81 88 8H 86 87 91 91 90 91 93 93 92 93 B4 CM 1000 90 1 2 3 4 2024 1951 1993 1947 1889 1957 1923 1975 -6.7 +0.3 -3.5 +1.4 5.0 4.0 7.4 0.2 11.6 12.8 7.4 22.3 25.3 24.8 19.1 31.8 42.6 39.3 47.7 40.2 38.3 40.0 33.4 32.5 52 50 56 44 79 73 86 68 87 83 95 77 90 87 96 83 92 90 97 86 93 92 97 88 B5 CM 200 90 1 2 3 415 437 443 444 468 457 +6.5 +6.7 +3.1 4.3 4.8 4.5 10.9 8.5 10.9 23.5 20.8 21.9 40.8 44.6 42.2 38.4 37.9 40.1 45 55 43 68 79 70 81 88 81 85 91 87 88 93 89 89 94 91 B6 MF B r i n e 90 1 2 822 765 6.1 5.3 - - 10.0 10.1 21.6 21.7 46.6 51.7 28.1 26.1 44 61 70 81 81 89 86 92 89 94 91 95 * M i s s i n g v a l u e s r e p l a c e d by w e i g h t e d a v e r a g e s . (1) CQ • measured c o n d u c t i v i t y of f r e s h l y made snow. C Q • e s t i m a t e d c o n d u c t i v i t y from m e l t w a t e r and r e s i d u a l snow samples. ( 2 ) Mean - -2.0 ± 3.0Z ( n - 2 2 ) . B5 was not I n c l u d e d due t o e x p e c t e d c o n t a m i n a t i o n . (3) Mean - 4.8 ± 0.71 ( n - 2 1 ) . B4.3 and B4.4 were not i n c l u d e d . ( 4 ) Mean - 10.7 ± 1.5Z ( n - 2 2 ) . B4.3 and B4.4 were n o t i n c l u d e d . TABLE A.4. P r e l i m i n a r y E x p e r i m e n t a l R e s u l t s ( l ) Exp. R e p l . I n i t i a l ^ 1 ) M a s s ^ E v a p p r a - Water E q u i v . of Snow, T o t a l I m p u r i t y Removals f o r Mo. C o n c e n t r a t i o n s B a l a n c e t W 3 7 Z M e l t C u m u l a t i v e M e l t F r a c t i o n s , uS cm V o l . Z c o C o X F r e s h Packed R e s i d u a l Z .05 .10 | .15 .20 .30 P I 1 1890 _ 16.2 12.6 20.4 _ 49MF - _ _ _ MF 1000 2 2014 1704 -15.4 9.5 13.4 22.9 49.1 14MF - - - - --12,-1,-1 3 2126 2144 + 0.8 11.7 14.0 20.9 39.6 70MF - - - - --2,90 4 2431 2096 -13.8 30.6 - 30.8 56.6 58MF - - - - -P2 1 2357 1778 -25.6 23.9 25.7 91.5 10.1 61 92 MF 1000 2 2414 2645 + 9.5 20.8 25.0 87.3 21.8 47 87 94 95 96* -2, 90 3 2096 1892 - 9.7 11.9 28.1 65.6 9.3 69 90 P3 1 1987 2042 + 2.8 4.5 33.8 64.0 17.9 51 77 88 93 MF•1000 2 1990 1916 - 3.7 4.6 10 26.5 70.8 22.7 47 71 85 92 97* - 1 , 90 3 2000 1934 - 3.3 4.5 21.5 65.4 24.0 47 77 89 95 4 2018 1962 - 2.8 5.4 19.2 61.0 20.6 50 77 87 93 P4 1 3185 3139 - 1.4 - 10.7 28.6 48.7 37.3 48 72 76 92 98 MF 500/1500 2 1047 956 - 8.7 12.7 23.7 48.7 27.9 48* 75 82 93 96 - 1 , 90 P5 1 1995 2106 + 5.6 3.7 11 27.4 47.5 22.8 46 78 92 96 98* MF 1000 2 2129 2057 - 3.4 4.1 8 25.9 47.1 23.3 48 77 90 93 96* -0.5, 90 3 2183 2044 - 6.4 5.9 8 27.0 55.2 27.3 51 78 92 95 98 4 2141 2126 - 0.7 5.4 8 30.4 55.3 15.2 48 78 91 94* 97* P6 1 1936 2075 + 7.2 3.9 9.5 23.7 57.6 59.5 54 80 87 91 95 CM 1000 2 1961 2157 +10.0 3.8 - 23.8 49.3 60.8 50 77 85 89 93 - 1 , 90 3 2040 2011 - 1.4 3.4 10.7 25.5 48.3 53.7 55 80 88 92 95 4 2023 2026 + 0.1 4.0 8.9 26.4 41.5 49.3 49 72 80 85 90 P7 1 1944 + 1.9 28.9 30 52 67 78 90 AM 1000 2 1907 1944 + 1.9 3.6 11.3 33.6 - 100 27 48 65 76 90 +2.5, 20 3 1926 + 1.0 32.3 30 52 67 76 90 4 1972 + 3.4 29.3 25 46 64 78 91 P8 1 1983 + 1.1 23.0 20 36 50 63 83 AM 1000 2 1962 1984 - 4.0 4.3 8.3 21.0 - 100 20 36 50 62 . 81 +1.5, 10 3 2012 + 2.5 22.0 22 40 57 71 87 4 2027 + 3.3 21.0 22 38 53 67 85 * M i s s i n g v a l u e s have been r e p l a c e d by wei g h t e d a v e r a g e s • (1) CQ - measured c o n d u c t i v i t y o f f r e s h l y made snow. C _ • e s t i m a t e d c o n d u c t i v i t y from m e l t w a t e r and r e s i d u a l snow samples. (2) Mean - +0.2 ± 4.4X ( n - 2 2 ) . Not I n c l u d i n g PI and P2-(3) Mean - 4.4 ± 0.7X ( n - 1 4 ) . (4) Mean - 10-3 ± 2.0Z ( n - 1 4 ) . TABLE A.5. Impurity Profiles for KC1 Snow Exposed to Simulated Melt-Freeze Conditions Snow Experiment PI Experiment^) Depth, cm Repl. 1 Repl. 2 Repl. 3 Repl. 4 P3,P4,P5,P6 MF 1000 MF 1000 MF 1000 MF 1000 MF 1000 -12, 90 -1, 90 -1, 90 -2, 90 (n - 15) 2.5 0.24 0.07 0.11 0.05 0.025 7.5 0.68 0.12 0.32 0.06 12.5 1.1 0.17 0.45 0.08 17.5 1.5 0.20 0.79 0.16 22.5 0.28 1.26 0.17 27.5 0.40 1.88 0.41 32.5 1.14 2.16 0.48 0.100(2> 37.5 1.93 1.30 1.37 42.5 1.15 3.10 47.5 1.09 3.83 (1) Average slope of impurity profiles for snow columns after melt. (2) Depth - 30 cm. (3) PI - Preliminary Experiment #1. TABLE A.6. Sewage Impurity Distribution In the Top 15 cm of Residual Snow Produced by Continuous Melt Conditions'^'. Type Replication Residual Normalized Impurity Fractions, of No. Impurity eye R ) with depth Impurity In Snow C R > Z 2.5 J 7.5 j 12.5 COND 1 8.9 1.44 1.78 1.64 2 7.9 1.67 1.49 1.45 3 7.2 1.35 1.85 1.74 4 6.7 1.87 1.62 1.81 TKN 1 8.4 1.16 1.85 1.85 2 7.5 1.47 1.58 1.68 3 7.2 1.20 1.70 1.70 4 6.8 1.76 1.66 1.56 NH3 1 7.1 1.45 1.72 1.50 +NV 2 6.8 1.51 1.43 1.48 3 6.1 1.32 1.53 1.68 4 5.7 1.55 1.49 1.64 TP 1 14.0 1.59 1.91 1.98 2 12.5 1.33 1.87 1.67 3 8.7 1.78 1.92 1.64 4 9.2 2.15 1.90 1.77 P0~ 3 1 12.6 1.13 1.74 1.81 2 11.2 1.18 1.60 1.68 3 6.5 1.90 2.32 2.11 4 7.5 1.80 1.80 1.62 Mean 1.53 1.74 1.70 Std. Dev. 0.28 0.21 0.16 (1) The residual snow remaining i n the column after sufficient melt had been collected were cut in 5 cm segments and their volume and impurity concentrations measured TABLE A.7. Sewage Impurity Distribution i n the Top IS cm of Residual Snow Produced by Melt-Freeze Conditions^'. Type Replication Residual Normalized Impurity Fr« ctions. of No. Impurity cs/c R, with depth Impurity In Snow C R . * 2.5 | 7.5 | 12.5 COND 1 9.6 0.79 1.05 1.60 2 14.2 0.66 0.96 1.49 TKN 1 9.8 0.98 1.19 1.63 2 12.3 1.10 1.27 1.44 NH3 1 9.8 0.90 1.08 1.90 2 13.6 0.73 0.92 1.87 TP 1 29.8 0.63 1.20 2.03 2 38.0 0.67 1.18 1.91 P0„ 1 30.1 0.59 1.18 2.10 2 39.2 0.60 1.22 1.50 Mean Std. Dev. 0.77 1.13 1.75 0.17 0.12 0.24 (1) The residual snow remaining i n the column after s u f f i c i e n t melt had been collected were cut In 5 cm segments and their volume and impurity concentrations measured. TABLE A.8. Potassiua Chloride Distribution In the Top 15 cm of Residual Snow Produced by Melt-Freeze Conditions^'. Experiment Replication Residual Normalized Impurity Fractions, (3) No. Impurity cs/c depth in Snow CR. * 2.5 | 7.5 | 12.5 Bl 1 1.4 0.93 0.94 1.41 -1, 90 2 4.6 0.26 0.34 0.58 1000 3 7.9 0.29 0.43 0.51 4 5.3 0.30 0.44 0.64 5 4.5 0.31 0.63 0.94 6 6.2 0.19 0.37 0.63 7 9.2 0.27 0.44 0.74 8 10.6 0.24 0.46 0.71 P2 1 7.3 0.51 0.60 0.72 -2, 90 2 5.8 0.91 0.95 0.99 1000 3 11.5 0.28 0.42 0.98 P3 1 6.5 0.16 0.27 0.48 -1, 90 2 4.7 0.27 0.60 0.92 1000 3 3.7 0.48 0.85 1.27 4 6.3 0.31 0.58 0.95 P4 1 1.0 0.82 0.99 1.40 -1, 90 2 4.8 0.57 1.18 1.74 500/1500 P5 1 2.9 0.34 0.36 0.70 -0.5, 90 2 5.0 0.20 0.46 0.69 1000 3 2.3 0.36 0.60 1.17 4 8.5 0.33 0.59 0.60 Mean 0.40 0.60 0.89 Std. Dev. 0.23 0.25 0.34 (1) The residual snow remaining i n the column after sufficient melt had been colleted were cut In 5 cm segments and their volume and impurity concentrations measured. (3) Bl - Baseline Experiment #1. P2 - Preliminary Experiment #2. TABLE A.9. Potassium Chloride Distribution In the Top 15 cm of Residual Snow Produced by Continuous Melt Conditions' Experiment (3) Replication No. Residual Impurity in Snow C R . * Impurity^) c ^ S P c ; c - " 1 3 & depth Normalized Impurity Fractions, C S /C R , with depth 2.5 1 7.5 j 12.5 B2 3 5.3 4.4 0.88 1.26 1.71 - 1 , 90 4 3.0 4.0 0.83 1.67 1.96 1000 5 3.0 2.5 0.93 1.49 1.81 6 3.2 1.8 0.96 1.14 1.86 7 3.7 3.5 0.78 1.16 1.87 8 4.0 3.0 0.91 1.40 1.70 B3 1 4.3 0.4 1.57 1.62 - 1 , 45 2 4.6 0.8 1.59 1.67 1000 3 4.9 3.1 1.10 1.93 2.00* 4 4.5 1.3 1.50 1.64 B4 1 1.8 0.4 1.31 1.39 1.55 - 1 , 90 2 8.4 5.3 0.61 1.37 1.23 1000 B5 1 8.1 4.1 1.37 1.41 1.26 - 1 , 90 2 4.7 - 1 . 7 2.12 1.62 1.75 200 3 6.7 3.7 1.27 1.69 1.83 P6 1 1.3 0 2.59 2.59 3.2* - 1 , 90 2 1.6 2.7 2.03 2.81 3.0* 1000 3 1.4 0 2.12 2.01 2.12 4 5.2 4.8 1.20 1.78 2.13 Mean 1.35 1.67 1.95 Std. Dev. 0.54 0.43 0.43 (1) The re sidual snow rei saining in the column after s uff lc ient melt had been collected were cut In 5 cm segments and their volume and impurity concentrations measured. (3) Bl « Baseline Experiment #1. P2 - Preliminary Experiment 02. * Missing values have been replaced by weighted averages. TABLE A.10. Impurity Profi les of a Natural Snowpack Irrigated with Brine Depth o f ( 2 ) Irrigated Snowpack, cm 3 Day 7 Apr i l 10 17 Day 14 Day 21 24 Day 28 1 Day 35 May 8 Day 42 15 Day 49 25 Day 59 June 1 Day 66 505 805 750 420 705 750 395 440 525 10 0.16 0.05 0.12 0.10 0.06 0.05 0.013 0.013 0.015 30 0.65 0.89 0.61 0.34 0.20 0.32 0.015 0.015 0.021 50 1.49 1.20 1.17 0.69 0.53 0.63 0.015 0.027 0.027 70 1.33 1.43 0.96 0.91 0.66 0.79 0.016 0.038 0.031 90 0.98 0.98 0.70 0.70 0.6L2 0.56 0.026 0.109 0.049 110 1.14 1.33 0.81 0.79 1.90 0.60 0.054 0.137 130 0.42 0.73 0.79 0.71 0.71 0.46 0.076 0.114 150 1.02 1.15 1.03 0.98 1.06 0.80 0.25 0.075 170 1.03 0.99 1.35 1.06 1.27 0.56 0.70 (1) The impurity concentrations are reported as fractions of the adjusted average i n i t i a l brine concentration (Cc/CQ). (2) The depth i s that of the i rr igated snowpack and does not Include later snowfalls. (3) In i t ia l salt concentration of the or iginal snowpack. It i s equal to the "estimated salt applications' l is ted in Table 4.8 divided by the water equivalence of the original pack (0.8 m 3/o 2). The average actual brine application was about 700 (pS/cm)/Z. TABLE A.11. Mean and Standard Deviation of Observed Potassium Chloride Removals Experiment Parameter Impurity removal for cumulative meltwater fractions .05 .10 .15 .20 .30 Preliminary and Baseline experiments^ ' Mean Standard Deviation 50.8 6.1 77.5 6.6 86.9 5.2 91.4 3.7 94.8 2.8 ( 1 ) A l l but B6, P7 and P8 are Included (n - 42) TABLE A.12. Snowpack Temperature Profi les Observed during the Field Experiment (1) Total Depth Measured From Bottom cmv ' Depth of Apri l 17 Apr i l 24 May 1 May 8 May 15 Irrigated Snowpack, Day 21 Day 28 Day 35 Day 42 Day 49 Apr i l 3 Apr i l 10 Day 7 Day 14 Surface +5 +4 +2 +(3) 240 0 230 0 0 0 210 0 0 0 0 190 0 0 -0.10 0 0 170 10 0 0 -0 .10 -0 .05 0 150 30 -0.20 0 -0 .15 -0.10 -0.05 130 50 -0.25 - 0 . 1 -0.25 -0.10 -0.05 110 70 -0.30 -0 .15 -0.30 -0.20 -0.05 90 90 -0.40 -0.20 -0 .40 -0.30 - 0 . 1 70 110 -0.40 -0.25 -0 .45 -0 .30 - 0 . 1 50 130 -0.45 -0.25 -0 .45 -0.30 - 0 . 1 30 150 -0.45 -0 .20 -0 .45 -0.35 - 0 . 1 10 170 -0.45 -0.25 -0.25 -0.30 - 0 . 1 Bottom 180 -0.20 _ - - _ loose^*) loose frozen loose frozen loose (1) The snowpack was isothermal (0*C) throughout on March 27 (Day 0), May 25 (Day 59) and June 1 (Day 66). The snow temperatures were not measured on Apr i l 3 and 10. A l l temperatures were measured in the afternoon. (2) Total snow depth including snow fa l len after the brine application. (3) Surface temperature was well above freezing but was not measured. (4) Snow temperatures were not measured. However, "loose" texture indicate temperatures of 0*C or higher whereas "frozen" texture indicate temperatures below freezing. APPENDIX B - PRE-EXPERIMENT TESTS The o b j e c t i v e of these t e s t s was to explore the p r i n c i p l e s of freeze c o n c e n t r a t i o n f o r treatment and d i s p o s a l of wastewater. Of the s e v e r a l concepts tested were: snowmaking; lagoon f r e e z i n g ; and overland f r e e z e . These p r e l i m i n a r y experiments provided g u i d e l i n e s f o r the formal research programs. Freeze Concentration by Porous Media Im p u r i t i e s are concentrated when water f r e e z e s . In the case of meltwater p e r c o l a t i n g through a sub-zero porous media, pure water i s extracted from the melt s o l u t i o n by f r e e z i n g onto the media. This p a r t i c u l a r experiment looked at the c o n c e n t r a t i o n of a potassium c h l o r i d e s o l u t i o n (1000 mg/£ KC1) by g r a v i t y f i l t r a t i o n through g r a v e l , sand and snow columns. Some conclusions are: 1. I m p u r i t i e s are c o n c e n t r a t i o n by pure water freeze e x t r a c t i o n . 2. Concentration e f f e c t s increase w i t h i n c r e a s i n g surface are of the porous medium. 3. Snow i s more e f f e c t i v e i n c o n c e n t r a t i n g i m p u r i t i e s than i n e r t m a t e r i a l s . 4. Concentration e f f e c t s decrease w i t h i n c r e a s i n g f l o w r a t e . Freeze Concentration of S o l u t i o n s Freezing of " d i r t y " water produces clean i c e and a very d i r t y concentrate. These experiments were conducted to get a v i s u a l p i c t u r e of the e f f e c t s of freeze concentration (using Dye) and to get a f e e l f o r the freeze c o n c e n t r a t i o n k i n e t i c s f o r potassium c h l o r i d e (100 mg/£ KC1). Beakers of dye s o l u t i o n s were subjected to a d i f f e r e n t heat l o s s r a t e s . Some beakers were exposed to heat l o s s through the sides and top, and others from the surface only ( s i m u l a t i n g f r e e z i n g of. lagoons). Some observations are: 1. Freezing from the surface and sides produced a concentrated "bulb" i n the lower centre of the beaker. 2. Heat l o s s through the surface only produced c l e a r i c e and a concentrated s o l u t i o n as shown i n P i c t u r e 7, Appendix E. 3. At f r e e z i n g rates greater than 5 mm/hr, some dye entrapment was evident, as w e l l as a much higher d e n s i t y of a i r bubbles i n the i c e . 4. A i r bubbles f r o z e i n the i c e on s t r i n g s perpendicular to the f r e e z i n g f r o n t advance. Freeze concentration k i n e t i c s of 100 mg/Jl KC1 s o l u t i o n were i n v e s t i g a t e d using i n s u l a t e d columns placed i n a c o l d chamber of a i r temperatures ranging from -0.5°C to -2.5°C. The r e s u l t s i n d i c a t e that e x c l u s i o n of KC1 from the i c e i s r a t e dependent. Low f r e e z i n g r a t e s of l e s s than 1 mm/hr. produce i c e containing only a few percent KC1. Freezing rates of about 5mm/hr r e s u l t e d i n up to 20% s a l t i n c o r p o r a t i o n . Ice c r y s t a l only allows 0.01% KC1 i n t o i t s l a t t i c e ( T e r w i l l i n g e r and D i z i o , 1970). Thus the s a l t i n c o r p o r a t i o n observed was due to bulk entrapment. When the d i f f u s i o n r a t e s away from the f r e e z i n g f r o n t i s l e s s than the f r e e z i n g rate advance, b r i n e i s accumulated i n a s l u s h zone at f r o n t . The f r e e z i n g f r o n t i s then unstable and extends " f i n g e r s " of i c e i n t o the l i q u i d and o f t e n f r e e z i n g around b r i n e pockets. This was a l s o v i s u a l l y evident by a 1-2 cm gray slush zone at the f r e e z i n g f r o n t , with some large i c e d e n d r i t e s extending s e v e r a l cm i n t o the l i q u i d phase. I t i s obvious then that to improve the s a l t concentration by f r e e z i n g , one must minimize the bulk entrapment. To do so, one must remove the impurity r i c h l a y e r from the advancing f r e e z i n g f r o n t , e i t h e r by mixing or by reducing the f r e e z i n g r a t e s to l e s s than the d i f f u s i o n r a t e . Concentration of I m p u r i t i e s i n Snow Imp u r i t i e s i n snow are concentrated towards the snow-soil i n t e r f a c e by melt-freeze a c t i o n . This set of experiments formed the basis f o r the development of the l a b o r a t o r y equipment and procedures used f o r the formal research program. In these experiments, i c e - r i n k scrapings were used as " a r t i f i c i a l " snow. The "snow" was placed to a depth of 1 m i n a 250 mm diameter p l e x i g l a s s column. A 150 watt, i n s u l a t e d r e f l e c t o r l i g h t was placed above the snow and turned on f o r 15 minutes every 3 hrs. The ambient a i r temperature was about -2°C, u n t i l c o l d chamber tr o u b l e melted the snow prematurely. The i c e r i n k "snow" had a very low impurity c o n c e n t r a t i o n . In f a c t , i t was no higher than Vancouver tap water. The c o n c e n t r a t i o n of the f i r s t meltwater were 5-6 times the concentration of the i c e r i n k "snow", which i s s i m i l a r to the r e s u l t s reported by Johannessen and Henriksen (1978) and Colbeck (1980) f o r ac i d snow experiments. P r a c t i c a l A p p l i c a t i o n s Three s p e c i f i c a p p l i c a t i o n s for freeze concentration of wastewater were considered by these p r e l i m i n a r y experiments, namely: shallow lagoons, overland f r e e z e , and sno-disposal. The shallow lagoons concept where pure i c e i s harvested from the s u r f a c e , and the concentrate withdrawn from the bottom, seems promising f o r A r c t i c c o n d i t i o n s . The concentrate may be f u r t h e r t r e a t e d i n a h i g h - r a t e , aerobic lagoon i n the summer. . The overland freeze provides higher heat losses than the lagoons, as w e l l as p r o v i d i n g mixing at the s o l i d - l i q u i d i n t e r f a c e . The concentrate obtained can be stored for summer b i o l o g i c a l treatment. This treatment seems a l s o best s u i t e d f o r very c o l d c o n d i t i o n s . The sno-disposal system, though, i s a l s o f e a s i b l e i n areas of moderate winter c l i m a t e s . I t can be combined with summer spray i r r i g a t i o n f o r small communities. I t i s p a r t i c u l a r l y s u i t e d f o r sewage d i s p o s a l at s k i - r e s o r t s , where conventional e f f l u e n t d i s p o s a l may be severely r e s t r i c t e d d u r ing the w i n t e r . TABLE B - l . FREEZE COLUMN RESULTS Ice Produced (mm) Freezing Rates, (mm/hr) Ice Conductivity (umhos/cm) Corrected Cone. C g , mg/l KC1 Ice Volume, (A) Bulk Cone. C b , mg/Z D i s t r i b u t i o n Coef f ic ient "o - V C b ( 5 ) 70 0.74 270 136( 2) 0 . 1 4 2 ( L ) 1000 0.136 115 5.22 488 252 0.233 1073 0.235 91 1.70 508 263 0.184 1205 0.218 74 1.61 560 291 0.150 1342 0.217 60 1.22 (3) - 0.122 1483 -72 0.78 305 155 0.146 1775<4> 0.087 (1) Total column volume = 1.824 l\ Cross -sect ional area = 2026.8 mm2. (2) Conductivity readings of ice corrected to KC1 concentrations, mg/A. (3) Lost sample. (4) Calculated bulk l i q u i d concentrations (Measured • 1500 mg/£). (5) However Terwi l l iger et a l . (1970) reports k Q of less than 1 0 - l + for NaCl and suggests that any sa l t which enters the ice! phase does so by bulk entrapment. TABLE B.2. MELT-FREEZE RESULTS Melt-Freeze Meltwater Conductivity Concentration Cumulative Cycles (mi) (uS/m) C/Co Melt Sal t % % 31 430 69 4.95 1.4 8.0 3 9 ( D 970 71 5.48 3.2 26.7 47 3275 19.6 1.55 10.9 44.1 5 A ( 2 ) 6625 14.8 1.25 22.1 70.7 62( 3 ) 17200 4.0 0.38 57.3 89.3 (1) Cold room shutdown from 119.5 hrs to 122.25 hrs . Maximum temp . -+ 10°C. (2) Cold room gradually warmed up over preceeding 12 hrs from -2°C to 0°C due to malfunctions. (3) Average ambient room temperature over l a s t 24 hrs was + 1°C. Total meltwater volume generated was about 11 l i t r e s . (4) I n i t i a l snow conduct iv i ty , C Q , was 12.3 umhos/cm. (5) Snow density - 0.46. (6) Total snow volume - 67 l i t r e s . Total l i qu id volume » 67 x 0.46 - 30 l i t r e s . APPENDIX C - FREEZING OF WATER DROPLETS The impurity d i s t r i b u t i o n of i n d i v i d u a l , f r e s h l y made machine snow g r a i n s may be important to the subsequent c o n c e n t r a t i o n by g r a i n coarsening and melt-freeze a c t i o n . Machine snow i s b a s i c a l l y f r o z e n water d r o p l e t s of somewhat d i s t o r t e d s p h e r i c a l shape. The short time i n t e r v a l f o r f r e e z i n g prevents the growth of d e n d r i t i c c r y s t a l s . The short formation time i s a l s o l i k e l y to preclude c o n c e n t r a t i o n of i m p u r i t i e s towards the snow g r a i n centre. Uniform i m p u r i t y d i s t r i b u t i o n probably r e s u l t s i n formation of micro "brine pockets" throughout the g r a i n , since only trace amounts can be d i r e c t l y i ncorporated i n t o the c r y s t a l l a t t i c e . The f r e e z i n g of dye d r o p l e t s was undertaken to get a q u a l i t a -t i v e understanding of p o s s i b l e i m p u r i t y c o n c e n t r a t i o n during f r e e z -ing under various c o n d i t i o n s . More s p e c i f i c a l l y , the experiments were done to t e s t the hypotheses: 1) Impurity c o n c e n t r a t i o n toward g r a i n centre occurs during slow f r e e z i n g of d r o p l e t s . 2) No concentration occurs at high f r e e z i n g r a t e s (such as experienced by machine snow). 3) High f r e e z i n g rates produce uniformly d i s t r i b u t e d micro "brine pockets". Methods Dye d r o p l e t s were frozen i n kerosene of -1°C, -5 to -10°C, and about -35°C temperatures. The temperature of -35°C was achieved by packing the kerosene f i l l e d tubes i n d r y - i c e . Rhodamine dye sample of "low", "medium" and "high" c o n c e n t r a t i o n were used. The drop s i z e s were approximately 4 mm i n diameter. The frozen d r o p l e t s were observed under a microscope i n a c o l d chamber at temperatures of -5°C to -10°C. Res u l t s Some i n t e r e s t i n g v i s u a l observations were made. Most d r o p l e t s f r o z e i n t o d i s t o r t e d s p h e r i c a l shapes w i t h bulges and sometimes sp i k e s . A l l d r o p l e t s submerged i n kerosene of -35°C froze q u i c k l y (5 to 10 sec) and l o u d l y cracked i n t o p e r f e c t halves. This i s i n t e r e s t i n g indeed since i t i m p l i e s that d i s s o l v e d a i r (which may a l s o be considered an i m p u r i t y ) was concentrated towards the centre, producing s u f f i c i e n t pressure build-up to crack the frozen d r o p l e t . Microscopic observations revealed dye concentration towards the d r o p l e t centre f o r a l l cases except f o r "high" dye s o l u t i o n f r o z e n at -35°C. The amount of dye incorporated i n t o the i c e seemed to i n c r e a s e w i t h i n c r e a s i n g f r e e z i n g r a t e and i n c r e a s i n g dye c o n c e n t r a t i o n . The microscopic observations a l s o revealed i n t e r e s t i n g bubble p a t t e r n s , that r e f l e c t the i m p u r i t y c o n c e n t r a t i o n process during f r e e z i n g . An advancing f r e e z i n g f r o n t pushes the i m p u r i t i e s ( i n c l u d i n g d i s s o l v e d a i r ) ahead. However, f r e e z i n g f r o n t i n s t a b i l i t y causes pockets of i m p u r i t i e s ( a i r bubbles) to be fr o z e n i n t o the i c e . The higher the f r e e z i n g r a t e , the greater the f r o n t i n s t a b i l i t y w i l l be and the more and l a r g e r bubbles w i l l be trapped. A schematic of a t y p i c a l d r o p l e t h a l f , frozen at -35°C (Freezing r a t e ~ 20 mm/min) i s shown i n Figure C l . The s t r i n g of bubbles are aligned perpendicular to the f r e e z i n g f r o n t , t r a c i n g i t s advance. The dye d i s t r i b u t i o n shows a s i m i l a r c o n c e n t r a t i o n p a t t e r n , the outer 1/3 being almost c l e a r i c e w i t h some bare l y v i s i b l e specs of dye. The middle 1/3 had some patches of dye as w e l l as more dye specs. The centre was uniformly coloured and had a very dark core of about 1/10 the droplet diameter. Conclusion Hypotheses (1) and (3) were confirmed by these experiments. The question s t i l l remains whether machine snow w i l l produce an I n i t i a l impurity concentration f o r i n d i v i d u a l g r a i n s . However, the machine snow t y p i c a l l y freezes an order of magnitude f a s t e r than the highest f r e e z i n g rate t e s t e d . I t i s th e r e f o r e u n l i k e l y that any conce n t r a t i o n towards the g r a i n centre w i l l occur. I f i t does, i t w i l l r e s u l t i n a delay In the subsequent g r a i n coarsening and melt-freeze c o n c e n t r a t i o n of i m p u r i t i e s . APPENDIX D - DESIGN MODEL DOCUMENTATION AND COMPUTER CODE Program Documentation This program estimates the impurity removal e f f i c i e n c i e s and run o f f c h a r a c t e r i s t i c s of an e f f l u e n t snow d i s p o s a l system. The program i s i n t e r a c t i v e and prompts the user f o r a l l necessary input The e f f e c t of s e n s i t i v e parameters such as snow depth and s o i l i n f i l t e r a b i l i t y can be q u i c k l y checked without having to repeat the data i n p u t sequence. This s e c t i o n describes the program s t r u c t u r e and then b r i e f l y e x p l a i n s the tasks of each i n d i v i d u a l f u n c t i o n . A flowchart of the p r e d i c t i o n model i s shown i n Figure D l . Figure D.2 d e p i c t s the h i e r a r c h y of the a c t u a l APL f u n c t i o n s . To s t a r t the program, the user types i n the a b b r e v i a t i o n of the impurity he/she wants to i n v e s t i g a t e . The program then prompts the user f o r i n p u t s . The user has a choice between monthly or d a i l y estimations and can run s e n s i t i v i t y a n a l y s i s on c r i t i c a l parameters by s k i p p i n g the weather input sequence. The program p r i n t s the runoff volume and impurity c o n c e n t r a t i o n . A d d i t i o n a l r e s u l t s can be r e t r i e v e d by ty p i n g the name of the wanted v a r i a b l e . TP = T o t a l phosphorus and orthophosphate TKN = T o t a l K j e l d a h l Nitrogen and ammonia n i t r o g e n TOC = T o t a l Organic Carbon The user types i n the f u n c t i o n name of the p o l l u t a n t he wants to i n v e s t i g a t e . The f u n c t i o n prompts the user f o r the e f f l u e n t c o n c e n t r a t i o n of the chosen p o l l u t a n t and assigns the l a b o r a t o r y determined value f o r exponential decay c o e f f i c i e n t , k, before c a l l i n g on the main program d r i v e r , SNODISP. SNODISP prompts the user f o r the saturated h y d r a u l i c c o n d u c t i v i t y of the s o i l , asks the user to s p e c i f y whether d a i l y or monthly observations are des i r e d and c a l l s on the coresponding snowmelt subroutine, MONMELT or DAYMELT. Once the melt has been c a l c u l a t e d , the user i s asked to input the depth and water equivalence of the e f f l u e n t snowpack. SNODISP then c a l l s on fun c t i o n s to c a l c u l a t e the time i t takes f o r the pack to melt (MELTTIME); the im p u r i t y removal (MFCON); and the runoff volume and impurity concentration (RUNOFF). The f i n a l f u n c t i o n , OUTPUT, p r i n t s the r e s u l t s i n a t a b l e and produces two p l o t s . INPUT/MINPUT c a l l s on YESNO, which asks the user whether he/sh wants to use the weather data already stored i n "inpar" and s k i p to the snowmelt c a l c u l a t i o n f u n c t i o n s . I f new weather input i s r e q u i r e d , MATIN i s c a l l e d . This f u n c t i o n s e t s up the data i n a matrix c a l l e d " i n p a r " , one l i n e at a time. The INPUT/MINPUT f u n c t i o n then c o r r e c t s the temperatures f o r e l e v a t i o n d i f f e r e n c e between the weather s t a t i o n and the d i s p o s a l s i t e before c a l l i n g on DPRINTOUT/PRINTOUT, which p r i n t s the c o r r e c t e d weather in f o r m a t i o n . The subroutines DAYMELT/MONMELT estimates the daily/monthly snowmelt. Both c a l l on RAINSNO, which convert the p r e c i p i t a t i o n to snow, i f the mean temperature i s below f r e e z i n g . DAYMELT then c a l l s COLDCONTENT, which estimate the c o l d content budget of the snowpack based on the mean d a i l y temperatures. TEMPINDEX/MTEMPINDEX c a l c u -l a t e s the temperature index as according to Quick & Pipes (1976). MELTVOLUME c a l c u l a t e s the daily/monthly cumulative melt volumes and store s the informat i o n i n a matrix c a l l e d "outpar". Melt c o n t r i b u t i o n by evaporation/condensation i s i n s i g n i f i c a n t compared to the energy induced melt and thus has not been included i n the proposed model. An EVAP f u n c t i o n can e a s i l y be added to the program l a t e r i f d e s i r e d . The estimated melt discharges do not account f o r any r e t e n t i o n of water i n the pack. Water r e t e n t i o n i n snow i s complex and not e a s i l y modelled. Fresh snow has smaller grains and higher c a p i l l a r y t e n s i o n , thus r e s u l t i n g i n s i g n i f i c a n t r e t e n t i o n of meltwater. Rapid g r a i n coarsening, i n the presence of water, reduces the c a p i l l a r y t e n s i o n and r e l e a s e s the r e t a i n e d water q u i c k l y . About 5-7% of the water remains a f t e r drainage. This i s the i r r e d u c i b l e water content. The meltwater r e t e n t i o n w i l l r e s u l t i n the f i r s t melt discharge being l a t e r and the flow much grea t e r than p r e d i c t e d by the proposed program. The meltwater r e t e n t i o n w i l l be included once the melt-water discharge p a t t e r n from a f i e l d snowpack has been observed ( s i m i l a r to the CM observations shown i n Figure 4.18). k name K s a t i n f i l t Sno Sno(l) Sno(2) Snoeq S o l a r inpar e l e v e l e v ( l ) e l ev(2) dpout=pout T max T m i n T xmax T xmin Rain exponential decay c o e f f i c i e n t impurity name impurity c o n c e n t r a t i o n of sewage e f f l u e n t , mg/£ saturated h y d r a u l i c c o n d u c t i v i t y , m/s s o i l i n f i l t r a t i o n c a p a c i t y , mm/m^-day snowpack depth and water equivalence, 2 element vector snowpack depth, mm snowpack water equivalence, % t o t a l water equivalence of machine snow + p r e c i p i t a t i o n seasonal c o r r e c t i o n f a c t o r f o r s o l a r r a d i a t i o n matrix c o n t a i n i n g c o r r e c t e d weather data input e l e v a t i o n of weather s t a t i o n and d i s p o s a l s i t e , 2 element vector weather s t a t i o n e l e v a t i o n , m d i s p o s a l s i t e e l e v a t i o n , m matrix c o n t a i n i n g weather c o r r e c t e d data maximum d a i l y (monthly) temperature, °C minimum d a i l y (monthly) temperature, °C extreme maximum monthly temperature, °C extreme minimum monthly temperature, °C r a i n f a l l , mm T r a i n Sno T f a c t o r M i f f T mean Tindex Tnindex outpar outpar(;1) outpar(;2) outpar(;3) outpar(;4) outpar(;5) meltsum runoff d m e l t ' p o l l estimated temperature of r a i n f a l l , °C s n o w f a l l , mm water = temperature spread c o r r e c t i o n f a c t o r f o r monthly observations = T — T °C max min» = mean d a i l y (monthly) temperature, C = d a i l y (monthly) temperature index, °C = negative temperature index, °C = estimated parameters, 5 column m a t r i x = time of weather records, days (months) = p o t e n t i a l d a i l y (monthly) snowmelt generation, mm = d a i l y (monthly) r u n o f f , mm = max. cumulative s o i l i n f i l t r a t i o n c a p a c i t y , mm = p o t e n t i a l cumulative snowmelt, mm = cumulative melt f r a c t i o n s = f i n a l r e s u l t s , 6 column m a t r i x = daily/monthly melt increase = daily/monthly i m p u r i t y removal = t o t a l r u n o f f volume, f r a c t i o n of t o t a l snowpack = average i m p u r i t y c o n c e n t r a t i o n of r u n o f f , mg/I Examples N u t r i e n t removals and runoff c h a r a c t e r i s t i c s f o r a p o t e n t i a l s n o - d i s p o s a l s i t e a t Vernon, B r i t i s h Columbia, are presented i n t h i s s e c t i o n , to demonstrate the use of the proposed design model. Vernon t r e a t s i t domestic sewage by a t r i c k l i n g f i l t e r , pumps the e f f l u e n t to a storage lagoon and disposes of i t by spray i r r i g a -t i o n during the summer season. The system served about 25,000 people i n 1981 t r e a t i n g l l x l O 3 m3/d of sewage. The land a v a i l a b l e for i r r i g a t i o n has not been s u f f i c i e n t to dipose of a l l the e f f l u e n t i n recent years. As a temporary measure Vernon has discharged surplus e f f l u e n t to Vernon Creek, while searching f o r e f f l u e n t d i s p o s a l a l t e r n a t i v e s . Winter d i s p o s a l of e f f l u e n t , through snow-making, may provide an e f f e c t i v e and economical s o l u t i o n . The e x i s t i n g spray i r r i g a t i o n system may be modified f o r w i n t e r d i s p o s a l through snowmaking. The purpose of the examples presented i n t h i s s e c t i o n are mainly to i l l u s t r a t e the use of the proposed model the examples and may there f o r e not r e f l e c t the a c t u a l s i t e c o n d i t i o n s . The c a l c u l a -t i o n s are based on records from the Vernon Weather S t a t i o n 1128551 from January through A p r i l , 1982. The saturated h y d r a u l i c c o n d u c t i v i t y of the s i t e has been c o n s e r v a t i v e l y estimated to be i n the order of 1 0 - 6 m/S. A poten-t i a l s i t e near the storage lagoon (Rose's Pond Property) i s reported to have w e l l drained f i l l d e p o s i t s , w i t h s u r f i c i a l t e x t u r e s ranging from loam to g r a v e l l y sandy loam. The slopes are g e n e r a l l y l e s s than 10%. E f f l u e n t concentrations of 8 mg/£ TP and 30 mg/£ TKN (sample c o l l e c t e d January 8, 1981) were used f o r the examples shown. The estimated removal e f f i c i e n c i e s are independent of the i m p u r i t y c o n c e n t r a t i o n s . Impurity c o n c e n t r a t i o n of the runoff can be adjusted by T P a c t u a l ^ a n d T K Nactual^° f o r n u t r i e n t concentrations d i f f e r e n t from those used i n these examples. I t i s assumed that the e f f l u e n t would be converted to snow during the e a r l y winter and placed i n a pack of 5 m depth and 30% water equivalence. Snowmelt c a l c u l a t i o n s were performed from January through A p r i l . No runoff occurred f o r a saturated c o n d u c t i v i t y of 1 0 - 5 m/S and thus a l l the phosphorus and n i t r o g e n i n f i l t r a t e d the s o i l . To demonstrate the performance of the sno-disposal system f o r s i t e s w i t h t i g h t e r s o i l c o n d i t i o n s , subsequent runs used an i n f i l t r a t i o n c a p a c i t y of 1 0 - 7 m/S. This r e s u l t e d i n about 64% r u n o f f , as shown i n the outpout t a b l e s and p l o t s . The corresponding n u t r i e n t removals were estimated to be 68% P and 76%N. The average impurity concentrations of the runoff were 3.95 mg/£ TP and 11.2 mg/£ TKN. A reduced snowpack depth of 2.5 m improved the phosphorus removals from 68% to 81%. The shallower snowpack was estimated to melt 2-1/2 weeks sooner, producing 47% runoff compared to 64% f o r the 5 m pack. The c o n c l u s i o n i s that a shallower pack w i l l produce l e s s runoff and hence b e t t e r impurity removals f o r a s o i l i n f i l t r a b i l i t y of 1 0 - 7 m/S and the given weather p a t t e r n . The above estimates were based on d a i l y weather observations. A quick " f i r s t " estimate of a p o t e n t i a l sno-disposal s i t e may be obtained from monthly observations. For the example given, the monthly model estimates n u t r i e n t s removals of 60% P, which i s some-what l e s s than that predicted by the d a i l y model. ••» « o ill il' •C 3 5 5 s 5 a l s 5 s s H 5 5 2 5 5 5 5 2 5 = s 5 " a s s 5 S 5 s 5 S 5 ^ 2 s £ s 3 s 5 s a s s s s s s s s s = t s s m g 5 ^ ^ 5 H ' .< s „ „ - 5 ? J O O O O O O O O O O O O O O w o o *- - J O O O O O O O O O O O O O O O O O h ; 5: r1 Iff sO O O O O O O O O O O O O O O O O O O O O O O O O O O O O - J J * ^ • TP I ' E l t t M t H Total Phospnorua k-« nee** * PHOSPHORUS • 'Specify e f f l u e n t concentration in mg/1' Cp*» SNOOISP tl] [2] 13] to 1 5 ] I S ) S •TKN<*>* " TKN [1] S-Eatti-atos Total Nitrogen 1 2 ] k-9 [3] name-'NITROGEN' [4] 'Specify e f f l u e n t concantratton m mg/1• [5] Cp-« I E ] SNODISP •TOC<»>' • TOC [1] S-Estlstatee Total Organic CarDon 12] W ! [3] name-'TOTAL ORGANIC CARBON [4) 'Specify i f M u i n t concantrat ion In mg/1 ' [5 ] CP-» [6] SNODISP •CQNO<#>' • COND I 1 ] %*Conduct Iv 1 ty [2] k-14 [3] name-'CONDUCTIVITY' [4] 'Specify e f f l u e n t c o n d u c t i v i t y [5 ] Cp*» 16) SNOOISP •MINPUT<#>" " MINPUT [ 1 ] 'Do you want to input new t a n p t r i t u r i records?' Ob* YESNO »>(bb»NE 1 1X0 'Input temperatur, r a m . and snow information on* I 1 na at a t<ma ( 2 13] ta] 151 16J 1 7 I 18] 19] 1 '01 I ' l ] I U l 1 O ) 1 14] I - 5 ] I 16) I'?] 1 'BI I 19] 120] [2'1 1221 'Month Txmax Tmax Tmtn Tmoan Rain T r a i n Sno Txmi tnpar-MATIN g n1 .1 , 1npar n l - n l t 1 ] o u t p a r • ( n i . 5 tt .0 outparf; t ]*t m 'Temperature c o r r e c t i o n Inpar[;2]-inpar[ ; 2 ] • inpart : J ) . i n p a r ( ; 3 J' inpar t ; 4 j • I npar [ ; 4 )• inpar[:5]"inpar[,5 J• inpart;7 J•lnpar[,7 j-Inpar[ .9 ] • 1npar[ ; 9 ] • PP.INT0UT Enter a l a v a t i o n of weather (elev[1]-elev [ 2I>/ 1 0 0 St and Disposal 7"delev T"da'av 7"de'ev 7-aalav 7"delev 7*da lav •yESN0<»>" • A"V E SNO:V N:S:D;T [t] »• THIS FUNCTION RETURNS A VALUE POP (») Of 1 FOR Y1YE5I AND 0 FOR NINO) 1 2 ] »• THESE VALUES CAN BE USED IN BRANCHING IN MAIN PROGRAM 1 3 ] D-'YNyn' [4 ] A-0 (51 L t : ' y(TES) OR NCN0 1' [6) YN-«# (7] 5-1.YN 1»] »>(5»NE1)XL1 1 9 ] T*eXYNSEPO t'O] »>(T»EQ0 )XL1 [11] A-(YN$E0'Y')|(YN»E0'y') w i tn t me ty. kset (m/sac)' •SN0OISP<»>" • SNODISP [I] *.*Estimates runoff from disposal s i t [2 ] 'Enter saturated hydraulic conaucti [3 ] K s a f a 14] 'Specify d a i l y or monthly oDservations ID or M)' 15) bp*DAYM0N [6] S><bb«NE1>XL1 [7) DAYMELT [8 ] OL2 [9] Lt.MONMELT [10] L2 'Give depth (mm) and density (X) of man-made snow [ I I ] sno-. 112 i snoea'lsno[ 1]"sno [ 2]/1O0)*(*%inpar[ ;7]) [ 1 3 1 MELTTI ME [ 1 4 ) MF CON [15] RUNOF F [16] V r - ( * % r u n o f f [ : 6 ] ) / l i o a o [ 17 j C r * ( * X ( r u n o f f ! ; f ] - r u n o f f 1 : 5] ))/*Xrunoff1 :6] [18 1 OUTPUT "DAY M0N< » >' " A-DAYMON [1 ] S- THIS FUNCTION RETURNS A VALUE FOR (A! OF 1 FOR O(DAY) AND 0 FOR MIM01 [2] B-'DMam' [31 LI:' OIDAY ) 0« MI MONTH) ' [4] DM-«# [5] S-t.DM 16] »>< S*NC1)XL1 [ 7 ] T"»XDM»EPB I S ] «>(TSE00)XL1 [9] A"(DM»£0'0 1| (DMtEO d' ) "M0NMELT<#>" • MONMELT [1 ] $*Calculates monthly cuiaulatlve enot .melt based on montnly max [2] Solar* 0.36 0.64 1 1 36 1.52 1.64 1 .52 1 .36 1 0.64 0.36 0.26 13] Tnlndex -o 14) MINPUT 15] 1*1 16] n l - t . I n o e r 17) n l - n i ( 1 ] [8] outpar»( n1.5)1.0 [9] outpar [ ; 1 )•» . ni [101 L2.»>(ItGTn!)XL1 ["] RAINSNO [<2] MTEMP1N0EX C 73 J ME LTV0LUME [14] 1-1*1 I'M *>L2 [ 16) L1.outpar [;2]"outpar[:2)'30 1<7] outpar[.4 J-outpar[.4)"30 [18] outparf;3J-outpar[^3J"30 I 19] outpar[;5]-outpar[.5]*30 MNPUT<#> • **• Local time estimate exceeded at APLC0I8M*29B30 in se c t i o n APLCOIBM [ U 12] [3] [4) [ 5 ! [61 17) (8) [9] 1 10] HH 1121 [ 13) [ 14] t 15) ('61 I 17) f 18] 1 191 [20] • INPUT 'Do you want to input new tempereture records?' btJ-YESNO <>(betNEi)XO 'Input temperetur, r a i n , and snow information one 1ne at a t i 'Mon Oay TMax Tmean Rain T r i i Sno' 1npar-MATIN 8 n1-t.1npar nl-n1(1] outpar-(nl.5)*.0 outpar[.1]•».ni Temperature c o r r e c t i o n elev.* lnpar[;3]-inpar[ ;3 )«0 T l e i e v [ i ] - e Inpar [ ; 4 ] • inpar [ l)«0 T ' l t H v j 1 ) -a inparj;5J-inoar[;5 ) » 0 7 " ( e i e v [ t ) - e inpar[.71-tnpar( .7 J-o 7-I a lev[ I 1-e DPRINTOUT Enter e l e v a t i o n of weather St and Disposal Site ev[2 ]1/100 'ev(21 ) / t o o lev[2 1)/100 iav(2]1/ t o o •PRINT0UT<#>" • PRINTOUT S-Prlnts out Input data. pout-outpar( ;1).inpar HI 12] [3] 14] [ 5 ] 16] [7] [ 8 ] 'WEATHER STATION-'.(5 0 JFMelev[1)).' I ) . ' mas' SNODISPOSAL SITE- .15 0 SFMala 8 1 7 1 B 1 8 1 8 1 7 1 7 1 $FMpout DPRINT0UTx»»" • DPRINTOUT J ' P r i n t s out d a i l y input data d p o u t - o u t p a r [ ; t ) . i n p a r [ ') [ 2 ] [3 J 14] 'WEATHER STATION-'.(5 0 SFMe!*v[l]), SNODISPOSAL SITE" .(5 0 JFM.i.v [5 ] [ 6 ! [ 7 ] ( 8 ) 19) ' Time : Mon 4 0 6 0 7 0 Tmax S 1 7 Tmean Ra 1 SFMdpout "RAINSN0<*>" " R A I N S N O l i ) I'Converts r a i n to snow based on e l e v a t i o n aajustement [ 2 ] J>(Inpar[1;7 ]»GE0 1X0 [3 1 i n p a r [ . . 8 ] • i n p a r ( i . 6 ) [4] t n p a r t i : 6 ] - 0 "TEMPIN0EX<x>" • TEMP1NDEX [t] S"Calculates temperature index based on d a i l y max and mm temp [ 2 ] Td I f - I npar [ i ; 3 I - ( Tm i n • t npar [ . ; 4 ) ) 13) T Index- Inpar[i:3]*(lTmln+Tdif / 2 ) / ( 1 8*Td'f ' 2))"Tmin "MTEMPINOEX..." • MTEMPtNOEX [ i ] ("Calculates temparature inde* oaaed on montnly max mi 12] S-temperatures I 3) Tdlf•Inpar[ I ; 3 ) - ( Tm.n.1npar[ i : 4 ) ) [4) Tindex-Inpar[ t ; 3]*( ( T m 1 n * T d i f / 2 ) / ( 18 + T d i f / 2 1 t'Tmln [ 5 ] T Index-T Index" Tf actor • ( inpar 1 i ; 2 ) - 1 npar [ l , 9 ) l.'PO B""? • xma* and xmi •COLDCDNTENT<«>" " COLDCONTENT I t ] S" Cold content storage duogel (exponential decay function x - 0 7) [2) «>((Tmean-inpar(i.5))SLEO )XL3 13] Tmnpex-O. 7"Tnindex [4) ».0 [5 ] L3 Tnlndex-(0 7"Tnindex)•Tmean i t and s p l l t a tt between Inf tIt r a t ton "ME LTVOLUME <»> • • MELTVOLUME [1] t * C a l c u l a t e s d a i l y cumulative en 12) $-end runoff. 13] »>(TlnoeK*GEO)XL1 14 ] Tnlnoetx-Tntndex-I tnp. p[ I ;S]-inp»r[ I : 7) 1/160 t5) Outpar[1;Sl-»Xoutper(;J) [6] (>0 [7) L 1 :Outpar[ 1 ;2J-(2-Solar[Inparf t;1]J.Tindex )»0 013 * 1npar[ I;6]"1npar[i 7) I B ] outpar[i;S]..Xoutpar(.3] 1 9 ) *>loutpar{i.2JSLEinfilt*Kaat"B6400"1000)X0 t10] OUtpar|1:3]-Outpar| I ; 2 ] - Inf I 11 t i l ! o u t p a r [ t , a l - ' X o u t p a r j ; 3 ) »ElTTmf<»>-• MLTTIHE S-DatarnMrtaa t i n * r i g u i r M for snow pac* Ml (31 [3] l«) [5] 16] J-0 i t : » > ( ] * a e n i » x o »><outpar[j ;5]sGTsnoaq)%0 «>L1 M F C O N < * > ' • HFCON l - C a l c u l a t a s M«lt f r a c t i o n s ana d t t i r n l n n corresponding p o l l u t i o n l - f r a c t ' o n s A l i o astimatea runoff concentrations •>altsu»»-JsTAoutpar[ ;5] ( ' 1 12! 13! [ 4 ] [5] [6] 17) [SI runoff•(].611.0 runof f [ ,2]-mal tsum/snoaa runoff I:1)•« ) r u n o f f [ ; 3] -!-•(-k"runoff[;2 J) runoffE ;6 ] •JtTAoutear[ ; 3 ] removal ana runoff c o i c t n T r a t i o n a : 2 ] 1 -runof f 1 1.3] "HUWr <»> • ' RUNOFF [ i ] l - C a l c u i a t e s 12] "2 [3] l>(runoff[1:2]1I00)M1 [4 ] ru n o f f I 1 ; 4 ] • (O n a 1 t - 1 - o u t o a r ( i ; 3 ] / o u t o a r [ i 15] runoff[ 1 ; 5 ]"runoff I'.4]-Co/runoff[1:2) [6] l t . l > ( HOT) )S0 [7] »>(runoff[1.2)»EO0>H2 [B j Oa*lt•1-outoar ( t ;3 ) / outoar[ 1 :2 ] [9 ] runof f [ 1 : 4 ] • (dme1t-doolI-runof f[I;3]-runof f [ 1 - 1;3J)-runoff I 1 -[10] t>(dpolUE00IX12 [ 1 1 ] runoff[ 1 ;5]-Opol1-Cp/runoff t 1 .2]-runoff[1-1:2] [ 12] L2 1 -1-1 [13] »>UI :4] •0UTPUT<f>-" OUTPUT [ i ] S-Organizaa output tapia and pl o t s [3 ] [ 4 ] [5] (61 I 7 } 'POLLUTANT- '.JFMname. •RUNOFF CHARACTERISTICS SNOWPACK OEPTM-• vo1 una r r a c t l o n -15 0 JFManoeq).'mn water' (5 3 IFMVr).' Avg Cone 1 9 ) [ 1 0 ] [ " ] H 2 1 (13) t'4) [15] [16] I"] [IS! [19] [20] (21 ) [25] 123] 124] [25] [26] 127] 128) [29] Cumu1stivi Me ' t w i t c F r a c t i o n Cumulativ Pol 1utant Frac t'on PoI.utant Rtnovil by so'1 Meltwater Concent r a t i o n mg/ 1 Runof f Volum« mm/m2 4 0 10 3 12 3 13 3 15 2 12 1 tFHrunoff O U t p l O T " 0 2 fDRoutper O U t p l O t [ ; 1 ] " O U t p a r [ ; t J 35 TO PLOT outpiot 'CUMULATIVE MELT (•) A NO RUNOFF VOLUMES (0) . m*/r*2A U« 1 0 1 1 C 0 ruop 1 ot "UTtruno* ? 35 70 PLOT runplot 'TOTAL POLLUTANT DISCHARGE (0) ANO REMOVAL BV SOIL £•) VERSUS TIME' & •M*TIN<*>' " y MAT IN n;x;y:a;*x;nr [ i ] %* T n i i allow* a matrix to be entered on* row at a t t n f [2] %* n it th* number of columns Entering B w i l l d i s p l a y and drop the [3] t* tast row. To f i n i s h , 0 must be •nt t r a a . [A] X«Sf [5] y ( l.nlS.tEX* [6] L I : * - * * (7] •••1234567890..PBaO [8] »><(OtEP(xtEPa)))%L3 [9] t>(('a$EP--)ICQ»EPx) )%Qu> t [10J *>( ( 'b »EPx ) | < 'B « P x , )r.L2 [11] M->{ 1 . n i l . t E X i c I 12] y y . [ 1 ] xx tn] »>LI (id] L2 nr>(S.y)[1] [ I S ] 'ThU l i n t 1* •' . (S<-My[nr; ] ) [16] 'Enter replacement itne _ or B (to go back one more* _ or Q (to quttt' [17) y-( 1 OJIDRy [18] «>L~ [19] 13:'Un*»Dected character entered Numbers, b. B. q or 0 expected ' [20] 'Please try again (To e x i t enter Ol' [21] «>Li {23 3 Quit Picture 2. Snowgun during production. P i c t u r e 4. S l i c i n g o f r e s i d u a l snow i n t o 5 cm segments. Picture 7. Freeze concentration of a dye and a s a l t s o l u t i o n for insulated beakers exposed to heat loss through the surface only. Picture 8. The f i r s t four meltwater samples c o l l e c t e d during the sewage ef f l u e n t experiment. The b o t t l e on the r i g h t contains the ef f l u e n t feed from which the snow was made. Picture 9. Brine-on-snow f i e l d experiment plot (3 m x 3 m) showing sample excavation p i t . Pi c t u r e 1 0 . C o l l e c t i o n of snowpack samples ( 2 0 cm i n t e r v a l s ) . The sample b o t t l e and thermometer shown i s located at the surface of the o r i g i n a l brine i r r i g a t e d snowpack. Note the texture d i f f e r e n c e of the f i n e "new" snow ov e r l y i n g the coarse, granular " i c e c l u s t e r " snow. APPENDIX F - DAILY WEATHER RECORDS H o i l i b u r n Ridge weather s t a t i o n i s l o c a t e d about 3 km south east of the f i e l d s i t e at 951m e l e v a t i o n . D a i l y temperatures and p r e c p i t a t i o n r e c o r d s f o r March, A p r i l , and May of 19B4, are summarized below. MONTHLY RECORD RESUME MENSUEl •JA* 198A ntti 1103510 t r o u ' t u t a » I » M IAI 4 9 - 2 2 N IOC 1 2 V 1 2 w •c / c-o A(I 9 5 1 m OAKY OJMATf DATA/DONNfES OlMAnOUtS OUOTOttttNE S M . f l A t U f l 'C MAI w. 1 1 s A 1 .0 -1 0 0.0 1 2.0 -2 0 0.0 J 2.5 -5 5 -0.5 9.0 - 5 5 2.( '0.0 -2 0 A.O 11.5 l 5 6.5 '0.0 0 5 5.5 15.b 0 5 7.0 0 Q 0 5.0 1 5 5.5 { 4 T 2 4 5.0 2 0 5.5 4 f.« J 4 ? i .5 - 1 0 0.5 4.0 A 0 ' .0 -1 0 0.0 I'I S ; ' ? 2.5 -1 0 o.a •4 7 7 6 2.0 -1 0 0.5 • '0 i '0 4 2.5 -0 5 1.0 • ' 4 . 4 1 6 4 4.0 -0 5 ' .» a t o a t 0." VC4f 1 8 . 0 1 8 . 0 1 8 . 5 1 5 . 2 1 4 . 0 1 1 . 5 1 2 . 7 1 1 . 0 1 4 . 7 H . 5 1 7 . 7 1 8 . 0 1 7 . 2 1 7 . 5 1 7 . 0 1 6 . 2 . I t O . M A t t O N * OAK * I.II cm 1 6.0 6.0 i» 2 9 . 0 2 9 . 0 10 * 7 . 0 1.0 A8.0 I 1 2 6 . 0 2.0 2 8 . 0 ?3 8.A 8.A Jl t I 14 55.n 3 5 . 0 n 4.0 A.O 8.0 H V 8.0 2.0 1 0 . 0 ' f M . f f A l U t l 1.0 2.5 8.0 7.5 2 . 0 2.5 A . 5 2 . 5 n 2.5 3.5 3.0 7.0 1 0 . 0 1 0 . 0 - 1 . 5 - 1 . 5 0 . 5 0 . 5 - 1.0 0.0 - 0 . 5 - 2 . 0 - 2 . 5 - 3 . 0 - 2 . 5 - 1 . 5 -A.O - 3 . 0 - 2 . 0 - 0 . 3 0 .5 2 . 8 A.O 0.5 1.3 2 . 0 0 . 3 n - 1 . 3 0.5 0 . 8 1.5 3.5 A.O 1 8 . 3 1 7 . 5 15.2 1A.0 1 7 . 5 16.7 1 6 . 0 17.7 m 1 9 . 3 17.5 1 7 . 2 16.5 1A.5 1A.0 . MONTHIY SUMMARY SOMMAIRE MENSUEl »tl ' t ' 4 • 160.8 E 145 47.0 ! 9A.2 I 6A 55.0 : 255.0 E 98 48.0 i 4 . 9 1.5 - 1 . 2 1.8 1 .9 1.7 15.5 -5.0 MONTHLY RKORD RESUME MENSUa 1 9 8 4 AV« 1 1 0 3 5 1 0 HOUituHK » I » M BC / C-0 IAI I O C 1 2 3 - 1 2 w »ii 9 5 1 „ 001 , fi5 DAAY OlMATI DATA/OONNfeS CUMATK3UB 0 » T C 8 M « S MfClOiTATtONtl) 10.0 T 3.6 2.0 2.0 1 H.O J.A 3.2 35.2 35.0 17.0 10.8 2.0 2.0 2.0 I 1A.0 3.4 3.2 35.2 35.0 1 7 . 0 10 . 8 1 0 . 0 1 3.6 2.0 TfMMIATUt! *C 5.5 5.0 1.0 5.0 1.5 4 . 0 0.5 2.5 0.0 1.0 0.5 1.5 1 0 . 0 1 4 . 0 7.5 5.0 - 2 . 5 - 2 . 0 - 1 . 0 - 3 . 5 - 1 . 5 - 5 . 0 - 2 . 5 - 2 . 0 - 2 . 0 - 2 . 5 - 2 . 5 - 1 . 5 - 2 . 0 - 0 . 5 2 . 5 - 1 . 0 1.5 1.5 0.0 0.8 0.0 - 0 . 5 - 1 . 0 0 . 3 - 1 . 0 -0.8 - 1 . 0 0 . 0 4 . 0 6 .8 5.0 2 . 0 1 6 . 5 1 6 . 5 1 8 . 0 1 7 . 2 1 8 . 0 18.5 1 9 . 0 1 7 . 7 1 9 . 0 18.8 1 9 . 0 1 8 . 0 1 4 . 0 1 1 . 2 1 3 . 0 1 6 . 0 MICt'llAtlONIll TIMMIATull "C VN CM t 01 UM MAJ Mt* MM 91 • I 4.6 4 . 6 5.0 - 2 . 5 1 . 3 1 6 . 7 3.0 3.0 3.0 - 0 . 5 2 . 3 1 5 . 7 1.2 1.2 4 . 5 - 0 . 5 2 . 0 1 6 . 0 1 1 . 6 1 1 . 6 7.0 - 2 . 0 2 . 5 1 5 . 5 1 0 . 8 8 . 8 1 9 . 6 4 . 0 - 1 . 0 1.5 1 6 . 5 3.0 3.0 0.5 - 2 . 0 - 0 . 8 1 8 . 8 1.3 - 3 . 0 - 0 . 8 1 8 . 8 S.O - 7 . 0 - 2 . 0 2 0 . 0 6.0 - 6 . 5 - 0 . 3 1 8 . 5 1 0 . 5 - 2 . 5 4 . 0 1 4 . 0 1 1 . 0 0 . 0 5.5 1 2 . 5 8.5 - 1 . 5 3 . 5 1 4 . 5 1 0 . 0 1 0 . 0 5 . 3 - 1 . 0 2 . 3 1 5 . 7 2 3 . 0 1 1 . 8 3 6 . 8 1.5 - 1 . 0 0 . 3 1 7 . 7 . MONTHIY SUMMARY SOMMAKE MCNSUEl MONTHLY KKXXD RfSUMlMENSUa M l 198A M l 1 1 0 3 5 1 0 LAI 4 9 ' ttXlYOUO* l l t l f 22 M tONO 1231 Ml 00>.Jl? • IICI'ltAtlONIll TIMMiAtUtt *C tc. tar DATt WM • 38. •a < 38.0 •rt 3.0 43.0 3.3 - « . S 1.3 14.3 I 1 1 4 . 3 -1.0 1.1 14.2 1 6.0 - 2 . 3 14.2 4 2.0 2.0 4 . 0 -1.0 1.3 14.3 1 t 1 4 . 0 -2.3 0.1 12.1 A 1.3 -2.0 3.3 H .2 1 S.O 8.0 12.0 -1.0 5.3 12.3 1J.3 • 1.0 1 1.0 7.0 2.0 4.3 • 11.5 11.3 3.0 -1.3 0.1 i r . i » 11.0 t 11.0 3.0 -1.0 2.0 14.* II 3.4 3.4 4.0 0.0 3.0 13.9 1» 13.3 13.3 7.0 - 0 . 3 3.3 34.2 •1 30.4 50.4 3.0 2.0 3.3 14.3 14 2.4 t 2.* 3.0 0.0 2.3 11.3 II 1.0 1.0 2.3 •1.0 2 .0 13.2 M 3.6 3.6 3.3 - 1 . 3 i .O 14.0 QA*YgjA«Art r M i A i P a o ^ •MCtrllAtlOMII) trf i m » — m M M 41.8 41.1 12.1 12.1 T T 4.0 0.4 4.4 14.0 1.0 12.0 1.4 1.4 1.4 T 2.4 14.4 1 14.4 1 T . MONTHLY SUMMARY -SOMMAJM MCNSUCl r i f C i r i u n O N s 10TA4 Oi H l . M'«<iH 30.A 3.0 50.A 2 3 1 . 0 I 1 9 3 8 . 4 ( 77 2 5 9 . 1 { 1 0 4 n MW I A I U M -'Sr."," l n a M t •MU 4.9 - 3 . 4 17.0 mm - 0 . 4 -2.2 -2.5 3.3 - 3 . 0 m M « M ' M O l A > 0 . oi&OATVBtc n u n • >r c IOAM iOIAakl , ' •mot • M 433 4 118 

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0062722/manifest

Comment

Related Items