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Integrating environmental tracers and groundwater flow modeling to investigate groundwater sustainability,… Doyle, Jessica 2013

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INTEGRATING ENVIRONMENTAL TRACERS AND GROUNDWATER FLOW MODELING TO INVESTIGATE GROUNDWATER SUSTAINABILITY,  GIBSONS, BC  by Jessica Doyle  B.Sc., The University of Victoria, 2008  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF  MASTER OF SCIENCE in THE FACULTY OF GRADUATE AND POSTDOCTORAL STUDIES (Geological Sciences)  THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver)  August 2013  ? Jessica Doyle, 2013 ii  Abstract  Environmental tracers can provide information on groundwater age, recharge conditions and flow processes. This information is useful for evaluating groundwater sustainability and vulnerability by identifying groundwater provenance and information for water budgets. Gibsons, British Columbia is a growing coastal community relying on groundwater to supply drinking water to two thirds of its 4,300 residents. The Town of Gibsons is proud of its untreated groundwater resource and proactive about keeping it protected and sustainable for future generations.  Samples of noble gases, tritium, and stable isotopes of oxygen and hydrogen were collected from the aquifer. Tracer results improved the site conceptual model by identifying a previously unknown contribution of mountain block recharge (MBR) and by providing recharge elevation estimates using noble gas thermometry.  The updated conceptual model including the mountain block was integrated into a regional three-dimensional numerical groundwater flow model calibrated to both hydraulic heads and to recharge elevation, a non-traditional approach to model calibration. This is the first study to use recharge elevation as a calibration target, which proved to be imperative for constraining bedrock geometry and minimizing model non-uniqueness.  Tracer and modeling results indicate that groundwater in the Gibsons aquifer contains a mixture of approximately 45% MBR and 55% bench recharge. The MBR component is pre-modern (> 50 years) groundwater that recharged at elevation and cold temperatures (~5?C) and has evolved hydrogeochemistry and high concentrations of iii  excess air (EA; >0.005 ccSTP/g) and 4Heterr (>10-9 ccSTP/g). Bench recharge is modern (< 10 years) groundwater recharged at low elevations and warm temperatures (~9?C), and has non-evolved hydrogeochemistry and low concentrations of EA (0.001-0.003 ccSTP/g) and 4Heterr (<10-9 ccSTP/g).  Effects of increased pumping due to population growth and decreased recharge rates caused by climate change were assessed by conducting a sensitivity analysis of groundwater flow. Based on the study results, it is recommended to carry out long-term groundwater monitoring; sustainable groundwater use and community involvement are required to ensure groundwater sustainability.  iv  Preface  This research was done through a collaboration with the University of British Columbia and Waterline Resources. All work in this thesis is original work produced by the Jessica Doyle; however, some figure and research outcomes were used in the following report by Waterline Resources Inc: Waterline Resources Inc. 2013. Aquifer Mapping Study, Town of Gibsons British Columbia. Final Report. 111 pp.    v  Table of Contents Abstract .............................................................................................................................. ii Preface ............................................................................................................................... iv Table of Contents ...............................................................................................................v List of Tables .................................................................................................................... xi List of Figures ................................................................................................................. xiii Acknowledgements ...................................................................................................... xviii Dedication .........................................................................................................................xx Chapter  1: Introduction ...................................................................................................1 Chapter  2: Background, Physical Setting and Conceptual Hydrogeological Model ..5 2.1 Town of Gibsons background ............................................................................. 5 2.1.1 Location .......................................................................................................... 5 2.1.2 Population, water supply and groundwater demand ....................................... 6 2.1.3 Groundwater monitoring network................................................................... 7 2.2 Geographic setting .............................................................................................. 9 2.2.1 Study area........................................................................................................ 9 2.2.2 Land cover and land use ............................................................................... 10 2.2.3 Climate .......................................................................................................... 11 2.2.4 Hydrology ..................................................................................................... 13 2.2.5 Geology ......................................................................................................... 14 2.2.5.1 Local bedrock geology .......................................................................... 14 2.2.5.2 Regional Pleistocene glaciation ............................................................ 15 2.2.5.3 Local unconsolidated and surficial deposits ......................................... 16 vi  2.3 Conceptual hydrogeological model .................................................................. 19 2.3.1 Description of aquifers .................................................................................. 19 2.3.2 Three-dimensional geological model of hydrostratigraphy .......................... 21 2.3.3 Aquifer extent, boundaries and piezometric surface ..................................... 24 2.3.4 Hydraulic properties and average linear groundwater velocity .................... 25 2.3.5 Hydrogeochemistry ....................................................................................... 27 2.3.6 Inter-aquifer and groundwater-surface water interaction ............................. 29 2.3.7 Aquifer recharge and discharge .................................................................... 31 Chapter  3: Environmental Tracers ...............................................................................33 3.1 Introduction ....................................................................................................... 33 3.2 Background of environmental tracers used in this study .................................. 34 3.2.1 Atmospheric noble gases .............................................................................. 34 3.2.2 Tritium .......................................................................................................... 35 3.2.3 Tritium-helium ratios .................................................................................... 36 3.2.1 Stable isotopes of oxygen and hydrogen ...................................................... 37 3.3 Approach ........................................................................................................... 38 3.3.1 Closed equilibrium (CE) model .................................................................... 38 3.3.2 Noble gas thermometry and recharge elevation estimates ............................ 40 3.3.3 Separation of He components to calculate 3H/3He ages ............................... 42 3.4 Field work and analytical methods ................................................................... 43 3.5 Results and discussion ...................................................................................... 46 3.5.1 Tritium and noble gases ................................................................................ 46 3.5.2 Recharge elevations estimated from noble gas signatures ............................ 53 vii  3.5.3 Stable isotopes .............................................................................................. 56 3.6 Environmental tracer summary and implications to the conceptual model ...... 59 3.7 Conclusions ....................................................................................................... 60 Chapter  4: Numerical Groundwater Flow Modeling ..................................................62 4.1 Introduction ....................................................................................................... 62 4.2 Review of conceptual model ............................................................................. 63 4.3 Modeling approach ........................................................................................... 64 4.3.1 Numerical model ........................................................................................... 64 4.3.2 Model calibration .......................................................................................... 66 4.4 Model input ....................................................................................................... 68 4.4.1 Domain .......................................................................................................... 68 4.4.2 Grid design .................................................................................................... 69 4.4.3 Boundary conditions ..................................................................................... 71 4.4.3.1 No flow ................................................................................................. 71 4.4.3.2 Constant head ........................................................................................ 73 4.4.3.3 Recharge ............................................................................................... 73 4.4.3.4 Groundwater extraction ........................................................................ 74 4.4.4 Flow properties ............................................................................................. 75 4.4.5 Initial conditions, solver, and rewetting parameters ..................................... 76 4.4.6 Calibration data ............................................................................................. 77 4.5 Results and discussion ...................................................................................... 79 4.5.1 Recharge ....................................................................................................... 79 4.5.2 Hydraulic conductivity.................................................................................. 81 viii  4.5.3 Model calibration .......................................................................................... 83 4.5.3.1 Calibration to observed head ................................................................ 83 4.5.3.2 Calibration to recharge elevation .......................................................... 86 4.5.4 Model water balance, contribution of MBR and aquifer water budget ........ 88 4.5.5 Sensitivity analysis........................................................................................ 92 4.5.5.1 Water table elevation, recharge elevation and % MBR ........................ 92 4.5.5.2 Bedrock geometry ................................................................................. 99 4.6 Comparison bench model ............................................................................... 102 4.6.1 Bench model results and discussion ........................................................... 103 4.7 Conclusions ..................................................................................................... 106 Chapter  5: Future Groundwater Scenarios ...............................................................109 5.1 Introduction ..................................................................................................... 109 5.2 Expected growth and increase in groundwater demand ................................. 109 5.3 Effects of climate change ................................................................................ 112 5.3.1 Recharge rates ............................................................................................. 113 5.3.2 Sea level rise and salt water intrusion ......................................................... 114 5.4 Approach ......................................................................................................... 116 5.4.1 Future groundwater demand scenarios ....................................................... 116 5.4.2 Climate scenarios ........................................................................................ 118 5.5 Results ............................................................................................................. 119 5.6 Sustainable groundwater management ........................................................... 122 5.6.1 Long-term groundwater monitoring ........................................................... 122 5.6.2 Sustainable groundwater extraction and use ............................................... 123 ix  5.6.3 Community outreach and involvement ....................................................... 123 5.6.4 Additional factors that affect groundwater sustainability ........................... 124 5.7 Conclusions ..................................................................................................... 125 Chapter  6: Conclusions ................................................................................................127 6.1 Environmental tracers to investigate recharge mechanisms and refine conceptual hydrogeological model ............................................................................. 128 6.2 Integration of environmental tracers results into numerical model ................ 130 6.3 Groundwater Scenarios, limitations and future research ................................ 134 References .......................................................................................................................137 Appendices ......................................................................................................................152 Appendix A Calculations ............................................................................................ 152 A.1 Hydraulic gradient ...................................................................................... 152 A.2 Average linear groundwater velocity and residence time ........................... 152 A.3 Water budget calculations ........................................................................... 153 Appendix B Chlorofluorocarbons and sulfur-hexafluoride ........................................ 154 B.1 Background ................................................................................................. 154 B.2 Field and analytical methods ...................................................................... 156 B.3 Results and discussion ................................................................................ 157 B.4 Conclusions ................................................................................................. 160 Appendix C Lab Certificates ...................................................................................... 161 C.1 University of Utah?s dissolved and noble gas analytical results................. 161 C.2 University of Miami CFCs and SF6 analytical results ................................ 162 C.3 University of British Columbia stable isotope analytical results ................ 167 x  Appendix D NGAgeCalculator ................................................................................... 168 Appendix E Sensitivity Analysis Data ........................................................................ 170 E.1 Water table elevation .................................................................................. 170 E.2 Change in % MBR ...................................................................................... 175 E.3 Recharge elevation sensitivity - data for box diagrams .............................. 176 E.4 Overall change in recharge elevation .......................................................... 181  xi  List of Tables Table 1 Town of Gibsons groundwater demand in 2011 (Town of Gibsons, 2012). ......... 6 Table 2 Summary of wells included in the groundwater monitoring network ................... 9 Table 3 Summary of recorded hydraulic property and aquifer testing data for the Gibsons aquifer. .............................................................................................................................. 26 Table 4 Date of purging and sampling, purging method and stabilized parameters for each well. ................................................................................................................................... 44 Table 5 Summary table of noble gas sample collection from pumping and monitoring wells. ................................................................................................................................. 45 Table 6 Summary of analytical results for noble gases, R/Ra, and 3H. ............................ 46 Table 7 a) Modeled recharge parameters and ages with assumed recharge elevation equal to well head elevation. b) Calculated uncertainties. ......................................................... 47 Table 8 Summary of input Hmin/Tmax and Hmax/Tmin pairs as well as estimated recharge elevation and temperature (Tr) ranges. .............................................................................. 56 Table 9 Summary of hydraulic conductivity values used in previous mountain block recharge studies. ................................................................................................................ 66 Table 10 Summary of groundwater extraction rates applied to model ............................. 75 Table 11 Summary of hydraulic conductivity ranges compiled from previous studies. .. 76 Table 12 Convergence Criteria ......................................................................................... 77 Table 13 Water Level Calibration Input Data................................................................... 78 Table 14 Daily water balance in rates (m3/day) calculated in final MODFLOW model. 89 Table 15 Comparison of calibration statistics for base case model and the six altered bedrock models. .............................................................................................................. 102 xii  Table 16. Estimated safe yields (Piteau, 2006) ............................................................... 112 Table 17 Summary of Town Well completion data. ....................................................... 115 Table 18 Future groundwater demand scenarios ............................................................ 117 Table 19. Model Scenario Input Data ............................................................................. 118 Table 20. Future modeling scenario results. Values in black indicates predicted drawdowns that are above the elevation at 70% drawdown or sea level, orange values exceed the elevation at 70% drawdown but remain above the well screen and above mean sea level, and red indicates that the drawdowns are predicted to drop below the top of the well screen elevation or below mean sea level. .............................................................. 120 Table 21 List of potential impacts and further work needed to better understand potential consequences on groundwater sustainability. ................................................................. 125 Table 22 Summary and assessment of groundwater mixing based on all results from all of the wells that were included in the model. ...................................................................... 133 Table 23  CFCs and SF6 measured concentrations, atmospheric mixing ratios and apparent ages. .................................................................................................................. 157  xiii  List of Figures Figure 1 Location of the Town of Gibsons. (Google Earth, 2013;  MapBox, 2013). ......... 5 Figure 2 Town of Gibsons water supply and distribution system, location of Town of Gibsons supply wells (TW1, TW2, TW3 and TW4) and Sunshine Coast Regional District (SCRD) supply wells (Chaster, Soames, and Granthams). ................................................. 6 Figure 3 Groundwaater monitoring network developed by Waterline (2010). .................. 8 Figure 4 Topographic elevation model with study area boundary and major watersheds, and creeks.......................................................................................................................... 10 Figure 5 Climate normal data for the Gower Point climate station averaged over 1971-2000................................................................................................................................... 12 Figure 6 Average snow-water equivalents representing snowpack for n number of years for a) Hollyburn (1100 mASL, 1945-1987) and b) Chapman Creek Headwaters (1022 mASL, 1993-2003). .......................................................................................................... 12 Figure 7 Bedrock geology map (Massey et al., 2005) ...................................................... 15 Figure 8 Local surficial and bedrock geology (McCammon, 1977; Massey et al., 2005).19 Figure 9 Hydrostratigraphic cross section along A-A? trace shown in Figure 8 (Waterline, 2013). ................................................................................................................................ 20 Figure 10 Surficial geology map with cross section A-A? trace as well as boreholes, wells, resistivity profile locations used to create 3D geological model. ........................... 22 Figure 11 3D geological model of each hydrostratigraphic unit within the study area a) bedrock surface, b) Pre-Vashon (Gibsons aquifer), c) Vashon Till (aquitard) and d) Capilano (unconfined aquifer). ......................................................................................... 23 xiv  Figure 12 Pre-Vashon sediments (the Gibsons aquifer), piezometric surface and proposed lateral aquifer boundaries. Groundwater flow direction is indicated by the blue arrows. 25 Figure 13 Location map of groundwater and surface water samples for routine geochemistry. .................................................................................................................... 27 Figure 14 Piper plot of major ion geochemistry of groundwater and surface water samples (Waterline 2013). ................................................................................................ 28 Figure 15 Cross sections through three dimensional geological model of the hydrostratigraphy of the study area showing the relationship between units, and potential groundwater-surface water interations. ............................................................................. 30 Figure 16 Weighted mean of 3H in precipitation from Portland, Oregon. 3H data was compiled and correlated by Manning (personal communication, 2012) based on data from GNIP (2012)...................................................................................................................... 36 Figure 17 Map showing the distribution of apparent 3H/3He age results and the extent and thickness of the Pre-Vashon Sediments, which contain the Gibons aquifer. The piezometric surface and flowlines indicating the general direction of groundwater flow are also included. .............................................................................................................. 50 Figure 18 Schematic cross section of select wells with 3H/3He age and Tr results. ......... 52 Figure 19 Atmospheric lapse as well as 2?C below atmospheric lapse is shown by the grey polygon, and used to estimate recharge elevation ranges for each sample. .............. 55 Figure 20 Stable isotope results on ?D versus ?18O plot relative to global and estimated local meteoric water lines.  Victoria and Saturna Island precipitation points are based on yearly averages.................................................................................................................. 58 xv  Figure 21 Cross section of updated conceptual model that considers mountain block recharge. ............................................................................................................................ 60 Figure 22 Model Domain in a) map view and b) rotated clockwise by 45? in model MODFLOW. ..................................................................................................................... 69 Figure 23 Model Grid in a) map view and b) rotated clockwise by 45? in model grid. ... 70 Figure 24 Cross section through model - column 33 ........................................................ 71 Figure 25 Boundary Conditions ........................................................................................ 72 Figure 26 Histogram of recharge rates calculated by Kerr Wood Leidal (2013) across the Regional District of Nanaimo using a USGS Water Balance Model (McCabe and Markstrom). ...................................................................................................................... 74 Figure 27 Best estimate of recharge elevation ranges. ..................................................... 79 Figure 28 Recharge zones and rates applied to the final calibrated model. ...................... 80 Figure 29 Zones of hydraulic conductivity ....................................................................... 82 Figure 30 Map of modeled and observed piezometric surfaces. ...................................... 84 Figure 31Cross section through model domain (column 78) with 50 m head equipotential contours. ............................................................................................................................ 84 Figure 32 Modeled (calculated) versus observed heads and summary of calibration statistics. ............................................................................................................................ 85 Figure 33 Map of backwards-tracking path lines from final calibrated model. ................ 87 Figure 34 Modeled recharge elevation boxplots overlying noble gas best estimates of recharge elevation ranges. ................................................................................................. 88 Figure 35 Location of zone budgets, calculated total daily recharge and daily recharge calculated for each zone. ................................................................................................... 90 xvi  Figure 36 Cross section through model (column 41) showing the calculated flux of MBR across the Upper ? Mid zone budget interface. ................................................................. 91 Figure 37 Overall model sensitivity plots for a) water table elevation (hydraulic head), b) recharge elevation and c) percent MBR. Error bars on each data point are the standard deviation of the differences between modeled and observed heads or recharge elevation............................................................................................................................................ 95 Figure 38 Sensitivity and variation of recharge elevation with varying values of hydraulic conductivity and recharge rates. Recharge elevations are based on the ten backwards-tracking particles released from each well screen on a well by well basis The shaded grey region signifies the estimated recharge elevation calibration range. ................................ 97 Figure 39 Sensitivity of water table elevation for 6 altered bedrock geometry scenarios. Data points are the mean change in water level and error bars represent the standard deviation from the mean. ................................................................................................ 100 Figure 40 The effects that changes in bedrock geometry have on recharge elevation based on the backwards-tracking particles released along each well?s screen. Bedrock elevations are exported from Visual MODFLOW and regenerated in ArcGIS for the base case scenario as well as six additional scenarios labeled 1 through 6. The black boxes indicate areas where the bedrock surface was altered. ................................................... 101 Figure 41 Calculated versus observed heads and summary of calibration statistics for the no MBR model. ............................................................................................................... 103 Figure 42 Summary of boundary conditions applied to the no MBR model. ................. 104 xvii  Figure 43 Comparison of recharge components in daily total recharge rates and the percent of total recharge for each recharge zone for a) the original model and b) the no MBR model. .................................................................................................................... 105 Figure 44 (Modified from Town of Gibsons Official Community Plan, 2013) ............. 110 Figure 45 Future developments in the Town of Gibsons Official Community Plan (2013).......................................................................................................................................... 111 Figure 46 Atmospheric mixing ratios of CFC-11, CFC-12, CFC-113 and SF6 observed at Niwot Ridge, Colorado (NOAA, 2012) compiled by Bohkle (2004). ............................ 155   xviii  Acknowledgements   I offer sincere gratitude to all of the people who have supported me throughout this research. I owe my greatest thanks to Dr. Tom Gleeson for being an incredible and inspiring supervisor, accompanying me to the field, for all of the discussions (including many evening and weekends), connecting me to colleagues for additional help and enduring patience. I could not have asked for a better supervisor and feel privileged to be his ?first? official graduate student. This research would not have been possible without Dr. Uli Mayer who I owe a huge thank you for agreeing to take me on as a student and for all of the ongoing support, guidance and countless hours of administration. I owe thanks to Dr. Sue Gordon who orchestrated this research project and Waterline Resources Inc. for making it happen. Big thanks to Dr. Andrew Manning for helping me with analyzing and interpreting my environmental tracer data including numerous discussions, ongoing feedback, modeling help and use of his worksheets. Finally, I would like to thank Dr. Roger Beckie, Dr. Diana Allen and Jordan Barclay for opening their doors to me for help and guidance with numerical modeling as well as Dr. Rolf Kipfer for taking his time to discuss my research with him while visiting UBC.   This research was partially funded by a Natural Science and Engineering Research Council (NSERC) Industrial Post-Secondary Scholarship (IPS) and by Waterline Resources Inc., the industry Sponsor. Thanks again to Waterline Resources Inc. for the funding and additional support, including a ?tuition scholarship?, throughout this research. In particular, thank you to Darren David for inviting me to work on my xix  thesis in the Waterline office, treating me like an employee and for all of the discussions, guidance and help over the last year.  Thank you to Dave Newman at the Town of Gibsons for agreeing to partake in this research as well as all of the help during sampling from Norma Brow, Steve Streicker and Mark Hiltz. I would also like to thank Jeff Collins and the Eagle Crest Condo Association, Ted Fiedler, and Julian Burtnick for allowing me to access and sample wells from their private properties.  Huge thanks to Shelley Bayne for guidance, assistance, preparation and organization of field work and to Matt Skinner for teaching me raster math and all of his help with GIS. I owe a very special thank you to Cindy Starzyk for the ongoing discussions, moral support, guidance and mentorship. Thank you to Sharon Blackmore and Holly Peterson for helping and accompanying me in the field as well as discussions and support throughout this research. I am also very grateful for all of the support from the other friends and fellow students in the hydrolab: Laura Lauranzi, Nathan Fretz, Maria Lorca, Natasha Sihota and Trevor Hirsche.   I would especially like to thank all of my friends and family for all of their endless love and support. I owe a big loving thank you to my sister, Emily, for assisting me in the field, accompanying me to the IAH Niagara conference, feeding and housing me during field work, and for all of the ongoing support. Thank you to my Mom and Dad for their love and encouragement. Finally, I would like to thank Clayton for his love, patience, support, field assistance, and all of our adventures that kept me sane while working to achieve my goal. xx  Dedication  To Nana 1  Chapter  1: Introduction  Environmental tracers in groundwater can be used to quantify groundwater age and evaluate aquifer recharge and flow processes (Cook and Bohlke, 2000; Plummer, 2005). Environmental tracer data can also be used to supplement hydraulic data in order to evaluate and improve conceptual hydrogeological models. This can be particularly useful for characterization of groundwater flow in mountain systems because groundwater flow through bedrock is complex and often has little hydraulic data due to the limited number and the expense of drilling wells (Wilson and Guan, 2004; Manning and Solomon, 2005).  Environmental tracer results can also provide additional, non-traditional or ?unconventional? calibration targets in numerical groundwater models (Newman et al., 2010; Sanford et al., 2011). Unconventional calibration data obtained using environmental tracer results can include age and travel times (Reilly et al., 1994; Goode, 1996), solute distributions (Christensen et al., 1995; Anderman et al., 1996), heat (Bravo et al., 2002; Heilweil et al., 2012) or a combination of these methods (Sanford et al., 2004; Manning and Solomon, 2005). The use of unconventional calibration targets is becoming a common approach to minimizing model non-uniqueness.  Understanding groundwater age, recharge, and flow characteristics is critical for evaluating aquifer sustainability and vulnerability (Sanford 2002; Scanlon et al. 2002; Senthilkumar and Elango 2004; Sophocleous 2005; Gleeson et al. 2010; Sophocleous 2010). Policy and management schemes cannot be implemented without reliable spatially and temporally distributed recharge estimates (Sophocleous, 2005) and a good understanding of water budgets. 2   Groundwater sustainability has been defined by Alley et al. (1999) as ?the development and use of groundwater in a manner that can be maintained for an indefinite time without causing unacceptable environmental, economic or social consequences?. Many aquifers worldwide are stressed or depleted in groundwater due to over extraction and lack of sustainable management (Giordano, 2009; Sophocleous, 2010; Gleeson et al., 2012). In Canada, groundwater resources are becoming threatened by urbanization, climate change, mining and energy production, agriculture and contamination; however, the Council of Canadian Academics (2009) believe that Canada has the potential to become a world leader in sustainable groundwater management practices. They suggest that sustainable management of groundwater resources should include all levels of government and the development of scientific programs and policies: ?The interjurisdictional nature of groundwater necessitates the development of a cooperative approach, uniting municipal, provincial, and federal government agencies in the development of scientific programs and policies that will ensure Canada?s groundwater resources are managed sustainably.? The Gibsons aquifer study is an example of a cooperative approach that uses science to guide sustainable groundwater management.   The Town of Gibsons, British Columbia, is a growing coastal community that utilizes groundwater to supply two thirds of its 4,300 residents with drinking water. The main aquifer, the Gibsons aquifer, is a deep, semi-confined formation of sand and gravel bound by the Coast Mountains in the north and the Ocean to the south. Groundwater from the Gibsons aquifer was internationally recognized and won ?best tasting water in the world? at the 2007 Berkeley Springs International Water Tasting Contest and in 2009 the Town of Gibsons was 3  awarded ?the most liveable community? at the International Awards for Livable Communities.   The Town of Gibsons is expecting and is planning for significant growth over the next few decades.  Since 1986, the Town of Gibsons has recorded almost 70% growth (Town of Gibsons, 2013). Within the current boundaries, the Town?s full build-out capacity is 10,000 people. Delcan (2005) predicts that population could reach 10,000 residents by 2026 given a high growth rate of 4% and groundwater demand could double from approximately 2000 m3/day to 4000 m3/day.   Groundwater from the Gibsons aquifer is an invaluable resource to the Town. The Town of Gibsons is proud of their pristine water supply and is proactive and motivated to keep it clean and sustainable for future generations. Two hypotheses drive this research:   1)  Environmental tracers can delineate groundwater age, recharge and flow processes of the Gibsons aquifer; and  2)  A numerical groundwater model calibrated to hydraulic heads and environmental tracer results can be effectively integrated into a groundwater planning and governance framework to provide an adequate approach for sustainable groundwater management for small to medium municipalities.   These hypotheses will be examined in the content of the subsequent four chapter of this thesis:  4  - The current conceptual hydrogeological model of the Gibsons aquifer is improved and refined in Chapter 2 by compiling all existing geological and hydrogeological data and by building a three-dimensional geological model of the study area; - Environmental tracers of noble gases, tritium and helium (3H/3He), and stable isotopes are examined in Chapter 3 in order to quantify groundwater age, determine recharge locations and processes, and further improve and refine the conceptual hydrogeological model of the Gibsons aquifer; - Chapter 4 integrates the updated conceptual model and tracer results into a regional three-dimensional numerical groundwater flow model calibrated to both hydraulic heads and to recharge elevation, and used to quantify recharge rates and the overall water budget of the Gibsons aquifer; - The long-term effects of increased pumping due to population growth and decreased recharge rates caused by climate change to the Gibsons aquifer are simulated in Chapter 5 to provide insight for the Town of Gibsons to guide sustainable management of their groundwater resource; and  - Chapter 6 provides an overall summary of results, conclusions and implications of this study as well as suggestions for future work that will further this research.   5  Chapter  2: Background, Physical Setting and Conceptual Hydrogeological Model 2.1 Town of Gibsons background 2.1.1 Location   The Town of Gibsons is located in southwestern British Columbia, Canada (Figure 1). The Town is situated on the southern tip of the Sunshine Coast surrounded by Howe Sound, the Georgia Strait and Mt. Elphinstone and is accessible via a 40 minute ferry ride from Vancouver.      Figure 1 Location of the Town of Gibsons. (Google Earth, 2013;  MapBox, 2013). 6  2.1.2 Population, water supply and groundwater demand  The Town of Gibsons supplies untreated groundwater from the Gibsons aquifer to 73% of its current 4,473 residents (Statistics Canada, 2011). All four of the Town supply wells are all located in Lower Gibsons where the aquifer is confined and has flowing artesian conditions. Three (TW1, TW3, and TW4) of the four supply wells are active. Town Well 2 (TW2) is only used as back up when TW3 is down for maintenance. Groundwater supply from the Town wells is distributed to residents in Lower and Middle Gibsons (Figure 2).    Table 1 summarizes current groundwater demand based on the 2011 population and average groundwater extraction recorded by the Town of Gibsons.    Figure 2 Town of Gibsons water supply and distribution system, location of Town of Gibsons supply wells (TW1, TW2, TW3 and TW4) and Sunshine Coast Regional District (SCRD) supply wells (Chaster, Soames, and Granthams).   Table 1 Town of Gibsons groundwater demand in 2011 (Town of Gibsons, 2012). Total population as of 2011 4,437 people Population supplied groundwater from the Gibsons aquifer 3,239 people Average daily groundwater extraction from the Town wells in 2011 1856 m3/day Average water use per person per day 0.573 m3/day  7   The remaining 27% are supplied surface water from the Chapman Creek Watershed by the Sunshine Coast Regional District (SCRD). The SCRD also distributes groundwater from the Chaster, Soames and Granthams supply wells as indicated in Figure 2. However, this groundwater is supplied locally within the SCRD near each well. The SCRD was not able to provide groundwater use data from these wells.   2.1.3 Groundwater monitoring network  Waterline (2010) completed a field verification survey and established a groundwater monitoring network (Figure 3). The network includes the four Town of Gibsons supply wells and seven additional monitoring wells. Two of the monitoring wells are nested piezometers (MW06-1, MW06-2) completed by Piteau (2006), two are deep wells (WL10-01, WL10-02) drilled by Waterline (2010), two are privately-owned supply wells (70651, Strata) and one is an old abandoned deep well (School Board) that was recommissioned by Waterline (2010). Table 2 lists and describes each of the monitoring wells in the network. 8   Figure 3 Groundwaater monitoring network developed by Waterline (2010).     Wells included in the monitoring network are used to collect groundwater samples and to measure and record water levels. Pressure transducers were installed in all of the monitoring wells that do not have pumps installed. The Strata well is the only well with a dedicated pump that has enough room to manually measure water levels. Pumping levels in the Town wells are recorded by the Town of Gibson?s supervisory control and data acquisition (SCADA) system; otherwise, when pumps are turned off, the recorded level is the height of the discharge pipe that diverts the artesian overflow.   9  Table 2 Summary of wells included in the groundwater monitoring network Well Name   Description Easting Northing Ground Elevation (mASL) Well Depth (mBGL) Hydro-Stratigraphic Unit  Water Level Level (mBTOC) School Board Deep monitoring well 460524 5473736 153 139 Pre-Vashon 101.5 MW06-1A Nested piezometer 462812 5472468 99.5 78 Pre-Vashon 74.9 MW06-1B 462812 5472468 99.5 78 Capilano 3.9 MW06-2A Nested piezometer 462130 5472688 121.5 102 Pre-Vashon 97.2 MW06-2B 462130 5472688 121.5 102 Capilano 2.9 Strata  Private pumping well 462486 5472360 110.5  unknown Pre-Vashon 87.6 TW 1 Town of Gibsons Supply Wells 463057 5472034 12.7 42 Pre-Vashon Artesian TW 2 462924 5471757 18 15 Pre-Vashon Artesian TW 3 462943 5471715 18.5 26 Pre-Vashon Artesian TW 4 463143 5472141 13 20 Pre-Vashon Artesian WL10-01  Deep monitoring wells 461597 5473033 139.5 141 Pre-Vashon 106.7 WL10-02  462263 5472238 107.5 123 Pre-Vashon 84.4 70651 Private pumping well 462156 5471290 93 116 Bedrock  NA Abbreviations are: mASL, meters above sea level; mBGL, meters below ground level; mBTOC, meters below top of casing.   2.2 Geographic setting 2.2.1 Study area  The study area is defined by the catchment boundaries of the two major watersheds that encompass the Town of Gibsons (Figure 4). The topographic elevation in the study area ranges from sea level in Lower Gibsons to almost 1200 m at the peak of Mt Elphinstone, part of the Coast Mountain Range. The ground surface is low gradient in Lower Gibsons, increases slope towards Upper Gibsons and forms a gently sloping bench extending to the base of Mount Elphinstone where topographic relief sharply rises to the top of the Mountain. The landscape of the study area has been shaped by erosion and deposition during the Quaternary Period by glacial, glacio-fluvial, fluvial and marine processes that have occurred over the past 2.6 million years (Claque, 1994).   10   Figure 4 Topographic elevation model with study area boundary and major watersheds, and creeks.   2.2.2 Land cover and land use  The study area has a mixture of residential, rural, commercial, industrial, agricultural use and forestry. Commercial, industrial and higher density residential uses are generally concentrated within the Town of Gibsons boundary. An in-depth description of land use and land cover within the Town of Gibsons is described by AECOM (2010). Outside the boundary use is mainly rural, residential and forestry, interspersed with a small portion of Soames Hill 11  agricultural land. According to the Biogeoclimatic Ecosystem Classification system (British Columbia Ministry of Forests, Lands and Natural Resource Operations, 2012) the study area is within the Coastal Western Hemlock zone and the Mountain Hemlock zone near the top of Mt. Elphinstone.     2.2.3 Climate The study area has a temperate coastal climate. Most precipitation falls during winter months as rain (lower elevations) or snow (higher elevations), and summers are generally warm and dry. The Gower Point Environment Canada (34 mASL) climate station has historic climate data recorded from 1971-2000. At this station, average annual airtime temperature is 10.2?C and average annual precipitation is 1369 mm, 97% of which falls as rain (Environment Canada, 2012). Figure 5 summarizes the climate normal data for the Gower Point climate station. Due to orographic effects, precipitation is expected to increase with elevation towards the mountain. No climate stations exist on Mt. Elphinstone; however, Chapman and Reksten (1991) suggest that precipitation reaches up to 2250 mm per year at the top of Mt. Elphinstone.  The British Columbia Ministry of Environment (2012) has historical snow survey data for Chapman Creek (1022 mASL, 1993-2003) located 15 km north of Mt. Elphinstone and Hollyburn (1100 mASL, 1945-1987) located 25 km east. At both locations, snowpack has been measured as snow-water equivalents summarized in box plots in Figure 6. Based on the available data, maximum snow accumulation is recorded in April and spring snowmelt begins in May or June. It is reasonable to assume that snowpack accumulated on Mt. Elphinstone behaves similarly. 12    Figure 5 Climate normal data for the Gower Point climate station averaged over 1971-2000.   Figure 6 Average snow-water equivalents representing snowpack for n number of years for a) Hollyburn (1100 mASL, 1945-1987) and b) Chapman Creek Headwaters (1022 mASL, 1993-2003).  0 5 10 15 20 0 50 100 150 200 250 300 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Temperature (?C) Precipitation (mm) Month Precipitation and Temperature at Gower Point 1971-2000  Lat: 49?39'  Long: -123?54'  El:34 mASL Snowfall (cm) Rainfall (mm) Average Monthly Precipitation (?C) Minimum (?C) Maximum (?C) 13  2.2.4 Hydrology  Four creeks are located within the study area boundary; Chaster Creek, Gibsons Creek, Soames Creek and Charman Creek (Figure 4).  1. Chaster Creek has a 1000 Ha watershed that is fed by several tributaries originating from 350 to 900 mASL. In general, Chaster Creek flows south from Mt. Elphinstone towards the Georgia Strait.  2. Gibsons Creek has a watershed catchment of 320 Ha that originates near the top of Mt. Elphinstone and discharges into Howe Sound. Along Lower Gibsons, three storm culverts drain into Gibsons Creek. 3. The Soames Creek watershed is 180 Ha, located near the eastern boundary of the study area.  The creek originates near the base of Soames Hill and flows into Howe Sound.  4. Charman Creek originates from a discharge pipe in Upper Gibsons and flows along a series of natural stream beds, engineered ponds and culverts that collect run-off and storm discharge from a 160 Ha watershed. Stream flow data for this study is limited. No stream flow data was collected over the duration of this study and historic stream flow data from Environment Canada (2012) only exists for Chaster Creek from May to October 1965 and for Charman Creek from January to May 2001. As a result, stream flow data could not be evaluated against precipitation and groundwater hydrographs in order to assess or model groundwater-surface water interactions.    14  2.2.5 Geology  2.2.5.1 Local bedrock geology  Local bedrock geology consists of early Middle Jurassic Bowen Island Group metasediments and metavolcanics with Late Jurassic and Early Cretaceous intrusions of granodiorite (Figure 7). The Bowen Island group is an assemblage of greenschist facies sedimentary and volcanic rocks that is described by Friedman et al. (1990) as strongly foliated, fine-grained amphibolites intercalated with green chlorite schist with local exposures of pale grey, white and green fine-grained schistose meta-volcanic rock. It is noted that within the study area the assemblage transitions from volcanic-rich in the southeast to sedimentary dominated in the northwest (Friedman et al., 1990). Late Jurassic calc-alkaline/alkaline intrusions of variably foliated biotite-hornblende quartz-diorite and granodiorite underlie most of the Town of Gibsons. To the west of the study boundary is a younger Early Cretaceous intrusion that consists of variably foliated granodiorite (Monger, 1994 and Monger and Journey, 1994). A sharp contact between Bowen Island Group and the Late Jurassic granodiorite runs along the lower reaches of Gibsons Creek and trends northwest along the base of Mt. Elphinstone. The nature of the contact is unknown.   15    Figure 7 Bedrock geology map (Massey et al., 2005)  2.2.5.2 Regional Pleistocene glaciation Most of the landscape and landforms observed in the study area were shaped by glacial and interglacial processes during the Pleistocene. During the latest and largest Fraser Glaciation southwestern BC, montane glaciers formed between 19,000 and 30,000 BP before they advanced, coalesced, and thickened to create the maximum extent of the Cordilleran Ice Sheet at 15,000 BP. At this time, ice surface was above 2300 mASL. After 14,500 BP, the 16  regional climate began to warm causing ice to retreat and disappear over the next 5,000 years (Clague, 1994).  Erosion and deposition occurred during the advance and retreat of glaciers. Glacial erosion is most active during the advancement phase as ice scours, scrapes and plucks away the underlying bedrock creating features such as cirques, ridges, horns, over-deepened valleys and bedrock-nunataks (Clague, 1994). During the advancement phase, glaciers from the southwest Coast Mountains and Vancouver Island flowed towards and coalesced with ice flowing down the Strait of Georgia, producing a large piedmont lobe that extended down to the Puget Lowlands of Washington. The Town of Gibsons was situated at the confluence of this piedmont lobe and another lobe flowing southwest from Howe Sound.  Quaternary sediments up to 300 m thick underlay the lowlands bordering the Strait of Georgia, referred to as the Georgia Lowlands. Throughout this region, sediments were deposited during the advance and retreat of glaciers during the Fraser Glaciation. Loading and unloading of the Cordilleran Ice Sheet also led to isostatic adjustments and, coupled with eustatic changes, caused significant sea level fluctuations. Along the Strait of Georgia, sea level rose up to almost 200 m above today?s sea level, leaving various marine deposits observed across the Sunshine Coast at elevations up to 180 mASL (McCammon, 1975).  2.2.5.3 Local unconsolidated and surficial deposits Within the study area the following deposits have either been mapped on surface (Figure 8) or recorded in drill logs: 1. Pre-Vashon Deposits were deposited ahead of the ice as it advanced along the Georgia Strait and are likely of the same origin as the Quadra Sands (Clague, 1977). The basal deposits are laminated silts and stony clays that record a period of marine 17  submergence. The upper deposits are fluvial, possibly a series of coalescing deltas (Fyles, 1963) that tend to appear below the 100 m contour interval (Clague, 1977). Beneath the Town of Gibsons, Pre-Vashon deposits are flat-lying interbeds of silt, sand and gravel that sit nonconformably on top of bedrock. Exposures of the Pre-Vashon deposits are mapped along the deep incised valley along Langdale Creek and otherwise are only recorded in well logs. The Gibsons aquifer is comprised of the Pre-Vashon sediments.  2. Vashon Drift sediments are glacial deposits from the Fraser Glaciation including till, glacio-fluvial and glacio-lacustrine sediments that are likely the result of alpine glaciation. As ice overrode the area, sediments were deposited either ice-proximally or in direct contact with ice (Hicock and Armstrong, 1985). An erosional unconformity defines the contact with the underlying Pre-Vashon sediments (Fyles, 1963). Thickness of the Vashon Drift is recorded up to 50 meters and comprises hard packed silt, clay, sand, gravel and stones, primarily found below elevations of 1000 m above sea level. In the Sunshine Coast region the Vashon represents the remnants of a thick ground moraine that extends regionally and consists of till (concrete-like mixture of pebbles in a sandy matrix; blue-grey fresh and brown when weathered) with occasional lenses of sand and gravel. In Gibsons, Vashon till deposits are covered by the younger Capilano sediments up to an elevation of about 180 mASL; however, local exposures along incised stream beds and at lower elevations along the coastline have been observed.  3. Capilano sediments are retreat-phase glacio-fluvial, glacio-marine and marine sediments deposited on the seafloor and as raised deltas and intertidal and beach 18  sediments (Armstrong, 1981). Deposits are found at elevations below 180 mASL, (McCammon, 1977) the approximate sea level relative to land prior to isostatic re-adjustment. The basal unit of the Capilano sediments is a marine/glacio-marine clay-rich veneer observed to be a few centimeters up to 9 meters thick and often composed of stony till-like clay, commonly referred to as hardpan. At elevations below about 180 mASL, intertidal and beach sediments overly the marine veneer. The shallow, ?perched? Capilano aquifer is composed of these sediments. Several active and abandoned gravel pits are located at higher elevations along the lower slopes of Mt. Elphinstone. These are glacio-fluvial sands and gravels deposited by fans and deltas along the paleo shoreline prior to isostatic adjustment.  4. Salish sediments are postglacial to recent deposits at current sea level through fluvial, lacustrine, deltaic, shoreline or aeolian geomorphic processes (Fyles, 1963). In Gibsons, Salish sediments are mapped along creek beds and the shoreline.  19   Figure 8 Local surficial and bedrock geology (McCammon, 1977; Massey et al., 2005).    2.3 Conceptual hydrogeological model 2.3.1 Description of aquifers  Cross section A-A? in Figure 9 displays the hydrostratigraphy and the relationship between bedrock and the unconsolidated deposits described above. The cross section trace is included in Figure 10. The Gibsons aquifer resides within the Pre-Vashon sediments that sit on top of and abut onto bedrock. Given the number of bedrock ?knobs? (Gospel Rock, The Bluff, and Soames Hill in Figure 8) formed by glacial erosion, bedrock in the subsurface is expected to be highly undulating. The Pre-Vashon sediments vary in thickness according to 20  bedrock but are thickest beneath mid Upper Gibsons where well logs have recorded deposits up to 100 m thick.    Figure 9 Hydrostratigraphic cross section along A-A? trace shown in Figure 8 (Waterline, 2013).   Both the Vashon Till and the basal marine/glacio-marine Capilano deposits have aquitard properties. As a result, they have been grouped together within the Vashon Till hydrostratigraphic unit and will be discussed as the Vashon till aquitard from herein. The Vashon Till aquitard varies in thickness from a few meters thick in lower Gibsons to greater than 50 m thick towards the base of Mt. Elphinstone. In Lower Gibsons the Vashon till confines the Gibsons aquifer and all of the Town of Gibsons supply wells, located in this area, exhibit flowing artesian conditions.   Beneath the Upper Gibsons ?bench? the Gibsons aquifer becomes partially saturated and the depth to the top of the water table can exceed 100 m below ground. The aquifer 21  remains capped by the Vashon till which is believed to extend regionally as exemplified by the blowing well conditions observed in MW06-1A. MW06-1A is completed at the top of the water table in the Gibsons aquifer. Because the upper portion of the screen is exposed to the unsaturated zone, the well has been observed to suck or blow air depending on barometric pressure. Blowing conditions are observed during the onset of a high-pressure system that causes the formation to compress and force air out of the well. The reverse process takes place during a low pressure system and the well is observed to suck air. This phenomenon has only been observed in partially unsaturated aquifers that have a low permeability confining unit covering the extent of the aquifer (NGWA, 1999). This suggests that the Gibsons aquifer is regionally capped by the Vashon Till aquitard.  The Capilano aquifer is perched on top of the Vashon till within the Capilano intertidal beach sediments along most of Upper Gibsons. The Capilano aquifer is unconfined and depth to the top of the water table ranges from near ground surface to roughly 10 m below ground.   2.3.2 Three-dimensional geological model of hydrostratigraphy  The undulating nature of the bedrock and non-uniform thickness of the unconsolidated deposits are a result of the glacial and interglacial processes that have shaped the landscape of the study area. Geometry of both bedrock and the unconsolidated deposits significantly influence groundwater flow. In order to better understand and visualize the subsurface, delineate the extent of the Pre-Vashon sediments, and assess groundwater flow through the Gibsons aquifer, a three-dimensional geological model was developed using Leapfrog Hydro? (Figure 11).  22   Figure 10 Surficial geology map with cross section A-A? trace as well as boreholes, wells, resistivity profile locations used to create 3D geological model.    Leapfrog Hydro is a geological modeling software package that uses the radial basis function to interpolate three-dimensional geological data (Cowen et al., 2002). In this study, a 3D geological model was developed using geological data available in well logs, geophysical resistivity profiles, and mapped surface geology (Figure 10). In order to represent the hydrostratigraphic units described above, over 30 cross sections similar to section A-A? (Figure 9) were created in order to group well log and geophysical lithology descriptions according to each unit. The geological model was created based on the simplified hydrostratigraphy that was input into Leapfrog.  23   Figure 11 3D geological model of each hydrostratigraphic unit within the study area a) bedrock surface, b) Pre-Vashon (Gibsons aquifer), c) Vashon Till (aquitard) and d) Capilano (unconfined aquifer).    24  2.3.3 Aquifer extent, boundaries and piezometric surface   The extent and thickness of the Pre-Vashon sediments from the geological model as well as the piezometric surface of the Gibsons aquifer is shown in Figure 12. A thick channel of Pre-Vashon sediments extends from the northwest to the southeast through the middle of the study area beneath the southwestern Town of Gibsons boundary. Based on the bedrock surface from the geological model, it appears that Pre-Vashon thickness corresponds to glacially eroded bedrock valleys.  The bulk of the Gibsons aquifer is most likely within a thick Pre-Vashon channel where most of the deep wells completed in the Gibsons aquifer are located.  Pre-Vashon deposits are also slightly thicker near the SCRD supply wells (Chaster, Soames, and Granthams); however, it is uncertain how connected these are to the Gibsons aquifer, especially considering the channelized nature of the Pre-Vashon deposits. The Pre-Vashon sediments are very thin in the geological model between the main channel and the SCRD wells. This could be a result of the limited number of deep wells drilled within these areas; however, resistivity profiles and bedrock outcrops suggest that bedrock surface is higher. Additionally, groundwater hydrographs presented by Waterline (2013) do not show any response from pumping of the SCRD wells.  As a result, the red dashed lines in Figure 12 indicate the proposed lateral aquifer boundaries.  The piezometric surface was contoured using average water levels observed in the monitoring wells and assuming a hydraulic head of 2 m above ground surface in the Town wells. All of the Town wells flow artesian and hydraulic heads have not been measured since the date each well was drilled between, 1966 and 1999. In general, groundwater within the Gibsons aquifer flows northwest to southeast following topography and the geometry of the 25  channel. Based on the piezometric surface, the overall hydraulic gradient is approximately 0.6% (Appendix A.1). Given a relatively low hydraulic gradient but flowing artesian conditions in the Town of Gibsons supply wells, the Pre-Vashon sediments containing the Gibsons aquifer likely have a high hydraulic conductivity.    Figure 12 Pre-Vashon sediments (the Gibsons aquifer), piezometric surface and proposed lateral aquifer boundaries. Groundwater flow direction is indicated by the blue arrows.  2.3.4 Hydraulic properties and average linear groundwater velocity  Hydraulic properties calculated from aquifer testing completed by Waterline (2013) as part of this study and by others (Piteau, 1999; 2000) in previous studies are summarized in 26  Table 3. Based on Darcy?s flow equation, the average linear groundwater velocity was calculated to be approximately 350 m/year using the following equation:       where   is the geometric mean of the measured hydraulic conductivity values (6.0 x 10--4 m/s),   is the average porosity (0.33),  and    is the hydraulic gradient (0.6%;). This calculation suggests that it takes ~10 years for groundwater to flow from the base of Mt. Elphinstone down to the coastline suggesting that groundwater in the Gibsons aquifer should be generally modern (less than 50 years old; Appendix A.2).  Table 3 Summary of recorded hydraulic property and aquifer testing data for the Gibsons aquifer. Well Storage Coefficient ?S? Transmissivity ?T?  (m2/day) Hydraulic Conductivity ? ? (m/s) Porosity ? ? Method Reference TW4 NA 38 1.0E-04 NA Cooper-Jacob Piteau, 2000  3.0E-03 Hazen  1.0E-02  5.0E-03  4.0E-03 TW99-01 4.1E-04 56 1.4E-04 Na Cooper-Jacob Piteau, 2000 5.9E-04 31 7.8E-05 Hantush 4.9E-04 596 1.5E-03 Cooper-Jacob Piteau, 1999 NA  5.4E-04 Hazen  8.3E-04  1.1E-03 TW99-02 NA  2.7E-04 NA Hazen Piteau, 1999  7.2E-05  5.4E-03  8.6E-04  9.5E-04 WL10-01 NA  4.9E-04 NA Hvorslev Waterline, 2013  1.7E-04  4.6E-04 0.26 Hazen  9.6E-05 0.37 WL10-02 NA  1.3E-04  Hvorslev Waterline, 2013  1.2E-04  5.3E-04 0.28 Hazen  3.5E-03 0.42 Notes: TW99 series were drilled and abandoned by Piteau (1999). TW99-01 was located next to and was a pilot hole for TW4 and TW99-01(463150 mE, 5472146 mN) was located in Upper Gibsons (462808 mE, 5472875 mN). The Cooper Jacob (1946) and Hantush (1962) methods are used to determination aquifer transmissivity and storativity parameters using pumping test data, Hvorslev (1951) method for single well slug test analysis, and the Hazen (1892) method for hydraulic conductivity estimates using grain size distribution data.   27  2.3.5 Hydrogeochemistry  Samples of groundwater and surface water were collected by Waterline (2010, 2013) and analyzed for routine chemistry. The map in Figure 13 shows the wells and location of surface water stations where samples were collected from and Figure 14 summarizes the major ion geochemistry results in a Piper plot.   Figure 13 Location map of groundwater and surface water samples for routine geochemistry.   Three groups of major ion geochemistry are distinguished in the Piper plot in Figure 13. Most samples have a similar sodium-calcium-magnesium bicarbonate signature and plot in group 1. This group includes groundwater from the Gibsons aquifer, Capilano aquifer, and 28  surface water from all of the Creeks suggesting that insignificant geochemical evolution has taken place.   Figure 14 Piper plot of major ion geochemistry of groundwater and surface water samples (Waterline 2013).    Group 2 samples are similar to group 1, but have elevated concentrations of chloride. Group 2 includes groundwater samples collected from the MW06-2 nested piezometer completed in both the Gibsons (MW06-2A) and Capilano (MW06-2B) aquifers as well as from a downstream Charman Creek surface water sample (CHAR2). MW06-2 is located on the same property as the Gibsons Aquatic Centre which may explain the elevated chloride concentrations. The elevated concentration in both the MW06-2A and 2B piezometers indicates that water from the Capilano aquifer may be recharging the Gibsons aquifer in that area, or that there is a potential leak in the seal between piezometers. Similarly, the elevated 29  chloride concentration in the downstream Charman Creek sample indicates that groundwater most likely from the Capilano aquifer, or potentially from the Gibsons aquifer, is discharging to the Charman Creek.  Group 3 consists of two samples (WL10-01 and School Board) that have a slightly evolved geochemical signature compared to the rest of the samples. These wells are completed in the Gibsons aquifer but located near the back of the aquifer near the base of Mt. Elphinstone. The slightly evolved geochemical signature suggests that groundwater in these wells may have a different recharge source compared to groundwater samples collected in the other wells, or that it was exposed to different sediments along its flowpath.   2.3.6 Inter-aquifer and groundwater-surface water interaction  In the absence of creek monitoring data, the three dimensional geologic model is useful to examine the potential for groundwater-surface water interaction as well as interaction between the Gibsons and Capilano aquifers. The geologic model can be explored through the generation of cross sections in order to visualize the geometry, thickness and relationships of the subsurface hydrostratigraphic units and location of the piezometric surface. The three-dimensional cross section B-B? in Figure 15 is an example of a ?slice? through the geological model.     30   Figure 15 Cross sections through three dimensional geological model of the hydrostratigraphy of the study area showing the relationship between units, and potential groundwater-surface water interations.   Figure 15 shows that the incised valleys of both Charman and Gibsons Creek cut through the intertidal beach sediments that contain the Capilano aquifer and into the Vashon Till. Here, it is likely that groundwater from the Capilano aquifer discharges into the creeks. Because the Vashon Till thins in these regions, these areas could be potential windows for recharge to the Gibsons aquifer. The piezometric level of the Gibsons aquifer is below the 31  bottom of the incised creek bed signifying that along this section the aquifer does not discharge into either creek. At lower elevations in Lower Gibsons however, the piezometric level could intersect the bottom of the creek beds and become areas of discharge.  The shallow Capilano aquifer is perched on top of the Vashon Till and is hydraulically disconnected from the Gibsons aquifer. However, it is possible that vertical leakage through the Vashon Till from the Capilano to the Gibsons aquifer takes place as indicated by the downward arrows. Although not observed in the geologic model, it is also possible that gaps in the Vashon Till exist, providing additional recharge windows.   2.3.7 Aquifer recharge and discharge  Aquifer recharge to the Gibsons aquifer is not well constrained. As discussed above, windows for recharge may exist through creeks or gaps in the Vashon till or as vertical leakage through the Vashon till. Piteau (2006) and Waterline (2010) suggest that significant recharge could take place through the Capilano glacio-fluvial deposits located near the base of Mt. Elphinstone. Because very few wells are drilled in this area, it is uncertain how deep the Vashon till aquitard was eroded during the deposition of the glacio-fluvial deposits. If significant erosion took place, these deposits could be potential recharge windows. Another area of potential recharge is along the bedrock slopes of Mt. Elphinstone. Fractures in intrusive rocks have been recorded in well logs within the study area some of which are water-bearing. Unfortunately little data exists in the bedrock along Mt. Elphinstone and it is difficult to assess its potential recharge contribution. Recharge to the Gibsons aquifer will be investigated further by the environmental tracer study. 32  Most of the groundwater within the Gibsons aquifer that is not extracted by wells is assumed to discharge into the ocean. A smaller portion of discharge also occurs through several springs that have been observed along the coastline in Lower Gibsons (Piteau, 2006; Waterline 2010) and as discussed above, some groundwater may discharge into the creeks near the shoreline where incised creek valleys may be at a lower elevation than the piezometric surface. Discharge from the Capilano aquifer has been observed through springs along the steep slope between Upper and Lower Gibsons and potentially occurs into the creeks that cut through the Capilano deposits. Residents in upper Gibsons have observed seasonal waterlogged lawns that could be a result of water levels in the Capilano aquifer rising to ground level during wet, high recharge conditions (AECOM, 2010).     33  Chapter  3: Environmental Tracers 3.1 Introduction Environmental tracers in groundwater can provide valuable insights on past and present flow conditions including groundwater age, groundwater mixing, geochemical and microbial processes, aquifer vulnerability as well as recharge rates, processes and locations (Cook and Bohlke, 2000, Plummer, 2005).  Information obtained through environmental tracers can supplement hydraulic data to evaluate and improve conceptual hydrogeological models and provide additional calibration targets in numerical groundwater models (Newman et al., 2010; Sanford et al., 2011).  Environmental tracers include solute isotopes, isotopes of hydrogen or oxygen in the water molecule, and gas tracers that either dissolve into groundwater at recharge or accumulate in the subsurface from radioactive decay. Each tracer is only applicable for certain timescales of flow, therefore, for a particular study, tracers are selected based on the current understanding of the initial conceptual model. Environmental tracers can also be categorized into two groups: natural tracers and historical tracers. Natural tracers are tracers that are created or transported in the environment by natural processes whereas historical tracers have been introduced to the environment by anthropogenic sources (Scanlon et al., 2002; Healy, 2010). Based on initial groundwater age estimates using Darcy flow calculations, a suite of groundwater samples were collected and analyzed for tracers applicable to relatively young groundwater (less than 50 years old which is also termed ?modern? groundwater). These include: noble gases (Ar, He, Kr, Ne, Xe), tritium (3H), chlorofluorocarbons (CFCs), sulfur-hexafluoride (SF6), and stable isotopes of oxygen (O18) and hydrogen (D). The objectives of 34  this study are to quantify groundwater ages, determine recharge locations and processes, and improve and refine the current conceptual hydrogeological model of the Gibsons aquifer. Apparent groundwater ages will be calculated using 3H/3He ratios, recharge locations will be evaluated based on noble gas concentrations as well as from stable isotope values and groundwater flow processes will be assessed based on results and patterns from all of the tracers analyzed. Due to the thick unsaturated zone above the upper portion of the Gibsons aquifer revealed from the updated conceptual model (Chapter 2), tracers of CFCs and SF6 are not adequate for application to the study area and are discussed in Appendix B.  3.2 Background of environmental tracers used in this study 3.2.1 Atmospheric noble gases Atmospheric noble gases are naturally occurring gases with well-known concentrations that are constant through time on the time scale of interest. During recharge at the water table, noble gases are in solubility equilibrium with pore air in the unsaturated zone. It is assumed that pore-air is equivalent to atmospheric air and the concentration of dissolved noble gases reflect the temperature, pressure and salinity according to Henry?s Law at the time of recharge. Therefore, measured noble gas concentrations in groundwater can be used as a natural tracer to reconstruct climate conditions at recharge (Kipfer et al., 2002). Processes such as excess air, radioactive decay and molecular diffusion can slightly affect noble gas concentrations in groundwater; however, these processes are minimal and can be taken into account when reconstructing recharge parameters (Stute and Schlosser, 2000).   35  3.2.2 Tritium   Tritium (3H) is a historical tracer introduced in large concentrations to the environment by thermonuclear testing in the 1950?s and 1960?s. It is a radioactive isotope of the hydrogen atom with a half-life of 12.32 years and can become part of the water (3H1HO) molecule by oxidation in the atmosphere (Solomon and Cook, 2000). Concentration of 3H in precipitation began to increase in 1952 when thermonuclear testing was initiated and peaked in 1963 when testing was banned. Since then concentrations have decayed through time, and since about 1990, concentrations have dropped to between 4 and 15 TU. Background levels of 3H are produced naturally by cosmic rays colliding with the nitrogen atoms in the atmosphere and by alpha decay of lithium-7 as well as low, localized concentrations of anthropogenic 3H is introduced to the atmosphere by nuclear power plants, nuclear fuel reprocessing plants, luminescent watches, compasses and exit signs (Clark and Fritz, 1997). The use of 3H as an environmental tracer was first recognized by Begemann and Libby (1957).  The concentration of 3H in precipitation varies spatially and has been recorded through time at various locations around the world. Figure 16 shows 3H levels in tritium units (TU) in the precipitation from the closest station with long-term data in Portland, Oregon, (GNIP, 2012 compiled by A. Manning, 2012). One TU unit is equivalent to one molecule of 3H1HO in 1018 molecules of 1H2O (Solomon and Cook, 2000).  3H in groundwater is derived from precipitation and thus the concentration of 3H in groundwater reflects the atmospheric 3H concentration at the time of recharge. Because 3H is radioactive, groundwater that has lost contact with the atmosphere for a prolonged period of time (many decades or longer) exhibits low or non-detectable levels of 3H (Kazemi, et al., 36  2006). Therefore, groundwater containing a measurable amount of 3H indicates that the groundwater is at least partially modern (<60 years). 3H concentrations can also be detected in groundwater that is a mixture of differently aged meteoric water. Analyzing for 3H can help determine the age of water and provide information on groundwater recharge and flow. The method is semi-quantitative and should always be accompanied by additional age-dating methods.   Figure 16 Weighted mean of 3H in precipitation from Portland, Oregon. 3H data was compiled and correlated by Manning (personal communication, 2012) based on data from GNIP (2012).  3.2.3 Tritium-helium ratios   The use of 3H to date groundwater is now limited because background levels of pre and post bomb peak 3H are beginning to be indistinguishable (Kazemi et al., 2006). Groundwater age dating using tritium-helium (3H/3He) ratios introduced by Tolstikhin and Kamensky (1969) is becoming a preferred method as it does not require known input sources of 3H, and noble gas analysis can separate the He components (Kipfer et al., 2002). 3H continuously decays to tritiogenic helium (3He) that volatilizes when exposed to the 0 200 400 600 800 1000 1200 1940 1960 1980 2000 Weighted Mean of 3H in Precipitation (TU) Year 37  atmosphere. However once any amount of tritium is incorporated below the water table 3He can no longer volatilize and becomes trapped in the groundwater. As a result, groundwater can be sampled for both 3H and 3He in order to calculate the length of time it took for the water to travel from the recharge area to the sampling location (Schlosser et al., 1988). As mentioned, groundwater does accumulate additional sources of He in the subsurface including radiogenic 3He and 4He(3Herad, 4Herad), terrigenic 4He (4Heterr) and additional 3He from excess air and need to be taken into account when calculating apparent 3H/3He ages (Solomon and Cook, 2000).   3.2.1 Stable isotopes of oxygen and hydrogen  Oxygen-18 (18O) and Deuterium (D) are naturally occurring stable isotopes of oxygen (16O) and hydrogen (1H). Both isotopes can form a molecule of water without changing its chemical character; however, water molecules containing 18O or D are heavier due to the additional protons. Natural hydrologic processes can cause isotope fractionation between light and heavy water molecules. For example, light water molecules preferentially evaporate from the ocean and therefore meteoric waters are always depleted in 18O and D compared to ocean water. Similarly, water molecules precipitate ?first? creating both altitudinal and continental effects to isotopic fractionation in meteoric waters ? precipitation at higher elevations or in the middle of continents are enriched in 18O and D compared to precipitation that falls at low elevations near coastlines (Gat, 1996). Due to such characteristics, stable isotopes of oxygen and hydrogen in groundwater can be used as natural tracers to help determine recharge sources, mechanisms, paleoclimates, estimate discharge rates, understand 38  groundwater-surface water interactions, and mechanisms of groundwater salinization (Coplen et al., 2000).  3.3 Approach  3.3.1 Closed equilibrium (CE) model The measured concentrations of atmospheric noble gases in groundwater can be used to reconstruct climate conditions during recharge (Stute and Schlosser, 1993). Noble gas solubility is a function of the temperature, pressure and salinity at equilibrium across the air-water interface according to Henry?s Law:              where    is the partial pressure in the gas phase,         is Henry?s coefficient, dependent on temperature and salinity and    is the mole fraction (concentration) of the dissolved gas in the water phase (Aeschbach-Hertig et al., 1999). In groundwater, the air-water interface is the unsaturated-saturated interface where gases in the pore air space are in equilibrium with the top of the water table (Stute and Schlosser, 2000). In addition to solubility equilibrium concentrations of atmospheric noble gases, groundwater can also accumulate radiogenic and terrigenic sourced noble gases (mainly He) as well as excess atmospheric noble gases by a process known as ?excess air? (Aeschbach-Hertig et al., 2000; Kipfer et al., 2002).  Excess air is a phenomenon observed only in groundwater where entrapped air bubbles are dissolved and create an excess of atmospheric noble gases above solubility equilibrium concentrations (Heaton and Vogel, 1981; Aeschbach-Hertig et al., 1999, 2000, 2008). The entrapment of excess air is believed to take place during infiltration and often reflects the magnitude of water table fluctuations at the recharge location (Heaton and Vogel, 39  1981; Aeschbach-Hertig et al., 2000; Kipfer et al., 2002; Ingram et al, 2007). It has also been observed that the excess air component of noble gases is fractionated and the heavier noble gases are more enriched than the light noble gases compared to pure air (Stute et al., 1995; Aeschbach-Hertig et al., 1999; Ballentine and Hall, 1999; Aeschbach-Hertig et al., 2000; Weyhenmeyer et al., 2000; Holocher et al., 2001; Kipfer et al., 2002).  To account for excess air and fractionation, the closed-equilibrium (CE) model introduced by Aeschbach-Hertig et al. (2000) has been used to calculate recharge temperatures from measured noble gas concentrations. The CE model assumes that solubility equilibrium takes place in the quasi-saturated zone between initially air-saturated groundwater and a finite volume of entrapped air under a constant hydrostatic pressure in a closed system. It also assumes that the enrichment of heavier noble gases in excess air takes place during re-equilibration between the air-saturated water and air bubbles when gases are re-partitioned and the more soluble gases, the heavier noble gases, preferentially dissolve into groundwater (Kipfer et al., 2002). The CE model is described by the following equation:                                                 where   is the measured concentration of noble gas  , that includes    , the solubility equilibrium concentration of gas   as a function of  , temperature,  , salinity, and  , pressure (ie. elevation) at recharge, as well as the fractionated excess air component of gas   where    is the initial amount of entrapped air,   is the degree of fractionation and    is the volume fraction of gas   (Aeschbach-Hertig et al., 2000).   Using Manning?s NGAgeCalculator (personal communication, 2012), a chi-square minimization method adapted from Aeschbach-Hertig et al. (1999) and Ballentine and Hall 40  (1999), the measured noble gas concentrations were applied to the CE model in order to solve for unknown recharge parameters. Chi-square (?2) is the misfit between measured and modeled data and, if there is more measured noble gas concentrations than unknown recharge parameters, the magnitude of ?2 represents the probability that the CE model accurately describes the data (Manning and Caine, 2007). The ?2 minimization equation is described below:                     where   is the measured concentration of gas  ,       is the modeled concentration and     is the experimental     errors (Manning and Solomon, 2003). Because accumulated sources of He can cause unacceptable ?2 values, only three recharge parameters (          ) can be solved for using four gas concentrations (Ar, Kr, Ne, Xe). For the initial analysis, the additional unknown recharge parameter,  , was assumed to be the pressure at the elevation of each well head from which the samples were collected.  3.3.2 Noble gas thermometry and recharge elevation estimates Noble gas thermometry has often been used to calculate paleoclimates and recharge temperatures in studies where recharge location and elevations are well constrained (Mazor, 1972; Andrews and Lee, 1979; Beyerle et al., 1998, 1999; Ingram et al., 2007). However, in cases where recharge elevation is unknown, noble gas thermometry can also be used as recharge elevation tracers (Zuber et al., 1995; Aeschbach-Hertig et al. 1999; Manning and Solomon, 2003; Manning, 2011; Heilweil et al., 2012). Because recharge elevations are 41  unknown in this study, an approach similar to Manning (2011) and Heilweil et al. (2012) was taken to estimate recharge elevation using noble gas data.  Noble gas solubility equilibrium concentrations are dependent on both temperature and pressure (elevation), therefore different temperate and elevation pairs can result in the same noble gas concentrations (Aeschbach-Hertig et al. 1999; Ballentine and Hall, 1999; Manning, 2011). Based on the assumption that water table temperature decreases with elevation proportional to the linear atmospheric lapse rate, the maximum (Tmax) and minimum (Tmin) recharge temperatures were calculated using the NGAgeCalculator based on the minimum (Hmin) and maximum (Hmax) recharge elevations for each sample. For each sample, Hmin is the elevation at each well head from which the sample was collected and Hmax for all samples is the elevation at the top of Mt. Elphinstone (1160 mASL).  In mountain recharge systems, the temperature at the water table may not be equivalent to the ambient atmospheric temperature (Manning and Solomon, 2003; Manning, 2011; Heilweil et al. 2012) because of high recharge rates (Forster and Smith, 1988; Heilweil et al. 2012) or snowmelt contributing to recharge (Manning and Solomon, 2003; Manning 2011). Since the study area is in a humid climate and experiences high annual precipitation rates that potentially result in relatively high recharge rates (5-20% of precipitation) and the mountain within the study area, Mt. Elphinstone, accumulates a significant snowpack during the winter months that melts during the late spring and early summer, it was assumed that the water table temperature could be up to 2?C cooler than the ambient average air temperature. A 2?C cooler water table temperature is consistent with findings from Manning and Solomon (2003) in the Wasatch Mountains in Utah.    42  3.3.3 Separation of He components to calculate 3H/3He ages   Several sources of 3He and 4He can be present in groundwater and must be taken into account when calculating apparent 3H/3He ages. Total 3He (       ) includes the following components:                                   where       is the atmospheric solubility equilibrium concentration,      , is the excess air component,         is tritiogenic 3He component, the radioactive decay product of 3H, and         is the terrigenic component produced from subsurface nuclear reactions, mainly by U and Th-series decay (Solomon and Cook, 2000; Kipfer et al., 2002).   Similar to       , components of        include the same sources as       ; however, excludes the tritiogenic component.                              The NGAgeCalculator was used to separate and quantify each 3He and 4He components and calculate apparent 3H/3He ages. The      /       and      /       components are determined as part of the CE Model based on modeled recharge temperatures and excess air parameters as well as measured 3H,       , and R/Ra ratios. Both         and         are sourced from U and Th-series decay and from the deep crust and non-atmospheric fluids. In young groundwater, accumulated terrigenic He components are minimal, but were taken into account by assuming an Rterr (terrigenic 3He/4He ratio) of 2.01 x 10-7, a value typical for igneous and volcanic-derived deposits. Finally,        is the difference between total 3He in the sample and the determined concentrations of all other 3He components. More in-depth descriptions and methodologies of sources and separation of He 43  components are described by Schlosser et al. (1988, 1989), Solomon and Cook, (2000) and Kipfer et al. (2002).  3.4 Field work and analytical methods Groundwater or gas samples were collected from wells in April 2011 for stable isotopes of oxygen-18 (O18), deuterium (D), tritium (H3), noble gases (Ar, Ne, Xe, He, Kr), chlorofluorocarbons (CFCs) and sulfur-hexafluoride (SF6).  All wells were purged until parameters stabilized prior to sampling. Wells with dedicated pumps were purged by pumping and other wells were purged by bailing. Table 1 summarizes the date each well was purged and sampled, the purging method and the stabilized parameter values. Stable isotopes, tritium and noble gases were collected from all wells listed in Table 1.  Tritium samples were collected in duplicate 1L wide-mouth Nalgene bottles. Bottles were rinsed with well water several times before filling to the top with no headspace and minimal bubbles. Lids were tightened and secured with electrical tape. Samples were analyzed at the University of Utah Dissolved and Noble Gas Lab (2012) using the helium ingrowth method (Bayer et al., 1989) where samples were degassed, sealed, then left to allow tritium (3H) in the water to decay to tritiogenic helium (3He). After six to twelve weeks, 3He concentrations were measured on a Mass Analyzers Products ? Model 215-50 Magnetic Sector Mass Spectrometer. Concentrations of 3He directly correlate to the amount of 3H decayed. For every six samples, four standards are analyzed and logged by the lab, maintaining analytical precision of one percent or less.    44  Table 4 Date of purging and sampling, purging method and stabilized parameters for each well.  Samples for noble gases were collected as either water samples in copper tubes (Weiss, 1968; Stute and Schlosser, 2000) or as gas samples using advanced diffusion samplers (Gardner and Solomon, 2009). For wells with dedicated pumps, groundwater samples were collected in 9.5 mm refrigeration grade copper tubes by connecting a hose from the pump to the tube on one side and another hose for discharge on the other side. Once a steady stream of water with no turbulence or air bubbles continuously flowed through the tube, stainless steel clamps were used to seal the discharge end of the tube followed by the inflow end, to ensure the tube was full of groundwater that had no contact with the atmosphere. Advanced diffusion samplers were used to collect gas samples in all of the monitoring wells with no dedicated pumps. The sampler body consists of a silica membrane that allows gases in the groundwater to diffuse across the membrane and into the body. Samplers were attached to 6.4 mm polyethylene tubing and deployed down to mid-screen depth in each well and left for at least one week for gases in the groundwater to equilibrate across the membrane. Prior to collecting the sample, an air pump was attached to the end of the tubing to force air down the tubing from surface. Once the pump was pressurized to 60 Well Date   Purging Method Stabilized Parameters Tmes (?C) pH EC (?s/cm) MW06-1A April 15, 2011 1L plastic bailer 8.8 7.64 125 MW06-2A April 14, 2011 1L plastic bailer 8.4 7.38 246 MW06-2B April 19, 2011 0.5L plastic bailer 10.5 5.90 132 WL10-01 April 16, 2011 6L stainless steel bailer 9.0 8.47 237 WL10-02 April 17, 2011 6L stainless steel bailer 8.5 7.57 142 Town Well 1 April 13, 2011 Pump 9.1 7.63 82 Town Well 2 April 13, 2011 Pump 9.0 7.21 120 Town Well 3 April 13, 2011 Pump 9.2 7.16 118 Town Well 4 April 13, 2011 Pump 8.9 7.6 82 70651 April 22, 2011 Pump 9.8 8.27 194 Strata Well April 19, 2011 Pump 9.3 7.45 139 45  psi, a mechanism in the sampler closed off and sealed the diffused gases that were contained within the stainless steel tip from the environment. Finally, the sampler was removed from the well and the sampler tip was clamped with a stainless steel clamp to ensure the gases were trapped in the tip until analysis. Table 5 is a summary of the noble gas sample collection from each well.   Table 5 Summary table of noble gas sample collection from pumping and monitoring wells. Well Name Elevation (mASL) Screen Top (mbg) Screen Bottom (mbg) Sampling Method Sample Depth (mbg) Depth to Water (mbg) Length of Equilibrium Time in Well MW06-1A 99.5 74.4 77.7 ADS 77 74.8 11 days MW06-2A 121.5 98.9 101.9 ADS 101 97.1 7 days MW06-2B 121.5 11.3 14.3 ADS 14 0.49 7 days WL10-01 139.5 137.2 140.2 ADS 139 111.9 10 days WL10-02 107.5 120.4 123.4 ADS 122 85.1 9 days TW#1 12.7 19.8 22.9 PCCT    TW#2 18 13.1 14.6 PCCT    TW#3 18.5 21 24.5 PCCT    TW#4 13 11.9 15.5 PCCT    70651a 82.6 10 93 PCCT    Stratab 110.5     PCCT      Abbreviations: mASL, meters above sea level; mbg, meters below ground; ADS, advanced diffusion sampler; PCCT, pumped clamped copper tube;  ccSTP/g, cubic centimeters per gram of water at standard temperature and pressure.  a70651 is open in bedrock between 10-93 mbg. bNo well log exisits for Strata Well  Noble gases were analyzed at the University of Utah Dissolved and Noble Gas Lab in 2012, using a Stanford Research SRS - Model RGA 300 quadrupole mass spectrometer (MS) to determine the abundance of Ne, Ar, Kr, Xe and N2 and a Mass Analyzers Products ? Model 215-50 Magnetic Sector Mass Spectrometer to measure 3He and 4He. Gases collected with the Advanced Diffusion Sampler were directly analyzed on the MS; however, gases from the groundwater samples collected in the copper tubes had to be stripped off and collected under vacuum before being transferred to the MS. 3He and 4He results are reported as total 4He and R/Ra ratios ? the measured 3He/4He ratio (R) divided by the atmospheric 46  3He/4He ratio (Ra), approximated by Clarke et al. (1976) to be 1.384 x 10-6. The lab guarantees analytical precision for 4He and R/Ra within one percent, Ne and Ar within two percent and for Kr, Xe, and N2 within five percent based on compiled reports of daily standards run (four standards for every six samples). Lab certificates of all analytical results are available in Appendix C.  3.5 Results and discussion 3.5.1 Tritium and noble gases  Analytical results for the tritium and noble gas analyses are summarized in Table 6. Results for all gases except He are reported as total concentrations. He is reported in the measured concentration of 4He and R/Ra ratios. The reported 3H value is based on the concentration of 3H in each sample determined by the 3He in-growth method described in section 3.3.   Table 6 Summary of analytical results for noble gases, R/Ra, and 3H. Well Name Ar total (ccSTP/g) Ne total (ccSTP/g) Kr total (ccSTP/g) Xe total (ccSTP/g) 4He total  (ccSTP/g) R/Ra 3H (TU) MW06-1A 4.38E-04 2.29E-07 9.43E-08 1.45E-08 5.26E-08 1.07 2.65 MW06-2A 4.45E-04 2.27E-07 9.15E-08 1.45E-08 5.33E-08 1.09 4.86 MW06-2B 4.19E-04 2.46E-07 1.02E-07 1.37E-08 5.69E-08 1.00 3.31 WL10-01 4.88E-04 2.89E-07 1.11E-07 1.57E-08 1.00E-07 0.83 0.05 WL10-02 4.67E-04 2.51E-07 1.03E-07 1.53E-08 6.79E-08 1.36 3.52 TW#1 4.54E-04 2.39E-07 1.08E-07 1.55E-08 5.57E-08 1.59 3.93 TW#2 4.41E-04 2.43E-07 9.88E-08 1.44E-08 5.23E-08 1.41 5.67 TW#3 4.63E-04 2.46E-07 1.09E-07 1.56E-08 5.43E-08 1.34 4.28 TW#4 4.13E-04 2.30E-07 1.02E-07 1.44E-08 5.37E-08 1.31 5.54 70651 4.97E-04 3.15E-07 1.16E-07 1.57E-08 7.79E-08 0.99 1.77 Strata 4.45E-04 2.52E-07 1.08E-07 1.50E-08 5.42E-08 1.24 6.62 47    Using the NGAgeCalculator, analytical results were input into the CE model to solve for           , and separate He components in order to calculate apparent 3H/3He ages (Appendix D). Results are summarized in Table 7a and calculated uncertainties are in Table 7b.   Table 7 a) Modeled recharge parameters and ages with assumed recharge elevation equal to well head elevation. b) Calculated uncertainties. a)   CE Model Sample Name H (mASL) Tr (?C) EA (cc STP/g) Ae (cc STP/g) F ?2 4Heterr (cc STP/g) Initial 3H (TU) 3Hetrit (TU) Apparent Age (years) MW06-1A 99.5 8.6 0.0027 0.0847 0.86 2.03 -3.69E-11 5.1 2.5 11.8 MW06-2A 121.5 9.1 0.0031 0.1143 0.85 6.71 1.40E-10 7.7 2.9 8.3 MW06-2B 121.5 8.7 0.0027 0.0090 0.62 2.23 -1.01E-10 3.7 0.4 2.0 WL10-01 139.5 5.8 0.0061 0.0212 0.56 0.05 3.31E-08 6.8 6.8 85.8 WL10-02 107.5 7.6 0.0045 0.0660 0.78 0.47 1.04E-08 22.5 19.0 33.0 TW1 12.7 6.0 0.0025 0.0272 0.82 0.06 1.25E-09 23.1 19.1 31.4 TW2 18 7.6 0.0024 0.0547 0.87 7.92 -5.50E-10 17.6 11.9 20.1 TW3 18.5 5.9 0.0029 0.0519 0.84 1.35 -2.38E-10 14.7 10.4 21.9 TW4 13 7.9 0.0013 0.0013 0.00 1.02 1.68E-11 15.2 9.7 17.9 70651 82.6 5.7 0.0072 0.0155 0.41 0.54 3.13E-09 3.3 1.5 11.0 Strata 110.5 6.3 0.0028 0.0296 0.81 7.74 -5.06E-10 13.7 7.1 13.0   b) Uncertainties Sample Name Tr (?C) EA (cc STP/g) Ae (cc STP/g) F 4Heterr (cc STP/g) Initial 3H (TU) 3Hetrit (TU) Apparent Age (years) MW06-1A 1.3 0.0005 0.1521 0.15 1.88E-10 0.4 0.3 1.3 MW06-2A 1.3 0.0005 0.1609 0.14 2.04E-10 0.4 0.3 0.9 MW06-2B 2.3 0.0010 0.1319 0.29 1.58E-10 0.4 0.3 1.6 WL10-01 2.9 0.0015 0.1007 0.20 2.18E-09 1.1 1.1 3.3 WL10-02 2.2 0.0011 0.1493 0.17 1.56E-09 1.0 1.0 1.1 TW1 1.8 0.0010 0.1311 0.36 1.49E-09 0.9 0.9 1.0 TW2 0.9 0.0003 0.0260 0.03 1.82E-10 0.5 0.4 0.8 TW3 1.2 0.0006 0.0743 0.12 1.88E-10 0.5 0.4 0.8 TW4 0.7 0.0002 0.0070 0.07 1.93E-10 0.5 0.4 0.8 70651 2.4 0.0014 0.0467 0.20 2.42E-09 1.2 1.2 - Strata 1.0 0.0005 0.0230 0.04 1.75E-10 0.5 0.4 0.7 48   All five noble gases were used in the model except for He which was excluded in samples that had He    values greater than twice one-sigma analytical uncertainty (WL10-01, WL10-02, TW1 and 70651; Appendix A). Higher He ?2 values are most likely attributed to the presence of terrigenic He. Most samples had overall ?2 values of less than 5% except for MW06-2A, TW2 and Strata which have either slight excess in Ne (TW2, Strata) or Kr (MW06-2A; Appendix A). For the following discussion of results it is important to note that all wells are screened in the Gibsons aquifer except for MW06-2B, completed in the Capilano aquifer and 70651, which is open in bedrock.  Calculated recharge temperatures (Tr) reflect modeled solubility equilibrium noble gas concentrations at pressures from well head elevations as listed in Table 7a. Tr values range from 5.7?C to 9.1?C. The coolest Tr values were calculated in samples collected from 70651, WL10-01, TW3, TW1 and the Strata wells. The warmest Tr values were calculated in MW06-1A, MW06-2A and MW06-2B. Groundwater temperatures measured during sampling (Tmes) from wells screened in the Gibsons aquifer range from 8.4?C to 9.3?C, in MW06-2B screened in the Capliano aquifer, 10.5?C was measured, and 9.8?C was obtained from well 70651, which is open in bedrock (Table 4 with Tmes). The average ambient atmospheric temperature (Tatm) recorded at the Gower Point Climate station is 10.2?C (Environment Canada, 2012). By comparing Tr to both Tmes and  Tatm, the following observations are made: 1. Tmes in all wells completed in the Gibsons aquifer are cooler (by about 1?C) than Tatm, suggesting that groundwater in the deep Gibsons aquifer is cooler than the ambient air temperature. This could be a result of a significant component of cold water 49  recharging the aquifer, as indicated by cool Tr values calculated in WL10-01, TW3, TW1 and Strata. Cold Tr values could be a result of recharge at high elevations and/or have snowmelt and winter rains dominating recharge. 2. Tmes in MW06-2B (10.5?C) closely reflects Tatm (10.2?C); however, Tr is slightly cooler (8.6?C). This could suggest the shallow unconfined Capilano aquifer is mainly recharged at lower elevations but may have a small contribution of recharge that occurs at higher elevations or by snowmelt. Because this aquifer is shallow, over time it is likely that the groundwater warms up to roughly Tatm. 3. Tmes (9.8?C) in 70651 is slightly cooler than Tatm (10.2?C) and warmer than Tr (5.7?C). Because the well is open in bedrock from 10-93 m below ground level, groundwater in 70651 is mixed and Tmes reflects both Tatm and Tr.  4. Tr in MW06-1A (8.6?C) and MW06-2A (9.1?C) are similar to Tr in MW06-2B (8.7?C) suggesting that groundwater flowing through these wells may have similar recharge sources. 5. Tr values calculated in WL10-02 (7.6?C), TW2 (7.6?C), TW4 (7.9?C) and Strata (6.3?C) are mid-range.   Apparent 3H/3He ages show an unexpected trend as displayed on the plan view map in Figure 17 ? ages do not increase linearly with flow direction. The oldest apparent 3H/3He age is 86 years old calculated in WL10-01, the well located farthest from the ocean. Significantly younger ages of about 20 to 30 years old are calculated in the Town wells (TW1, TW2, TW3, TW4), located at the discharge end of the aquifer where the aquifer is confined and flow is artesian. As expected, the youngest apparent age of 2 years old is from 50  the MW06-2A well completed in the shallow Capilano aquifer; however, the youngest ages in the Gibsons aquifer are located mid-aquifer in MW06-2A (8 years), MW06-1A (12 years) and the Strata well (11 years). Well 70651 also has a young age, but is an open borehole in bedrock, outside of the Gibsons aquifer. WL10-02 is located mid-aquifer and has an age of 33 years, considerably older than the 11 year old age calculated for the Strata well.    Figure 17 Map showing the distribution of apparent 3H/3He age results and the extent and thickness of the Pre-Vashon Sediments, which contain the Gibons aquifer. The piezometric surface and flowlines indicating the general direction of groundwater flow are also included.    51   Select results are displayed in a schematic cross section (Figure 18) in order to better understand the 3H/3He age and Tr distribution. In cross section, the trend in age and Tr distribution becomes more apparent ? 3H/3He ages increase and Tr values decrease with depth and with proximity to Mt. Elphinstone. The observed distributions suggest that groundwater in the Gibsons aquifer consists of two primary recharge components: 1) modern water (<10 years old) with warm recharge temperatures (~9?C) that recharges at low elevations by leakage through the Vashon Till and 2) pre-modern water (>50 years old) with cold recharge temperatures (~5?C) that recharges and flows through fractures in bedrock along Mt. Elphinstone and into the Gibsons aquifer. Groundwater sampled from wells screened mid-depth within the aquifer, (WL10-02, Strata, TW1, TW2, TW3, TW4) have mid-range Tr and ages and therefore could contain a mixture of the recharge two end-members or have longer residence times with increasing distance from recharge at mid-elevations. The process by which groundwater recharges the Gibsons aquifer via flow through bedrock fractures within Mt. Elphinstone is known as mountain block recharge (MBR) (Manning, 2002; Wilson and Guan, 2004). 52     Figure 18 Schematic cross section of select wells with 3H/3He age and Tr results.    Excess air (EA), the sum of all excess air components for all noble gases included the CE model as well as the calculated amount of 4Heterr agree with the idea of MBR. Manning and Caine (2007) observed that groundwater sampled from bedrock wells had the highest concentrations of EA. In this study, well 70651 is the only bedrock well and has the highest EA concentration (0.0072 cc STP/g). WL10-01, which has the oldest 3H/3He age, is located closest to the base of Mt. Elphintone (the ?mountain block?) and is screened directly above the top of bedrock, also has a high EA concentration (0.0061 cc STP/g). This could suggest that groundwater flowing across WL10-01 recently recharged into the Gibsons aquifer via MBR. Similarly, 4Heterr values are generally higher in samples that have relatively older apparent 3H/3He ages and/or colder Tr values. This is likely a result of more 4Heterr 53  accumulating during groundwater flow through the mountain block that has the potential for greater U and Th-series decay in the granodiorite and metavolcanic bedrock.   Noble gas thermometry and 3H/3He dating have limitations that could affect results. Limitations include: - Groundwater flow through fractured rock has been noted to affect 3H/3He ages due to 3He loss by matrix diffusion (Cook et al., 1996). This could have an implication on the MBR component of groundwater to have apparently younger 3H/3He ages. - Noble gas samples were collected both by the copper tube method and the advanced diffusion sampler method (Table 5). It is possible that different sampling methods could slightly alter results although Gardner and Solomon (2009) suggest this is unlikely.  Although limitations could slightly affect results, the calculated 3H/3He ages, Tr, EA, and 4Heterr values all reveal similar trends. This suggests that these limitations do not change the overall finding from the noble gas and tritium data and given the scope of this study, even semi-quantitative results improve the conceptual hydrogeological model.    3.5.2 Recharge elevations estimated from noble gas signatures  Ranges of plausible recharge elevations  were estimated based on where Hmax/Tmin and Hmin/Tmax end-members, connected by dashed lines for each sample, intersect the atmospheric lapse rate line (upper bound) and the -2?C below atmospheric lapse rate line (lower bound) shown in Figure 19. For all samples Hmax is 1160 mASL, the elevation at the top of Mt. Elphinstone and Hmin is the elevation at each well head. Tmin and Tmax are the Tr values calculated by inputting Hmax and Hmin into the NGAgeCalculator (Manning, personal 54  communication).  Values of Hmin, Hmax, Tmin and Tmax as well as estimated recharge ranges and corresponding estimated Tr ranges are summarized in Table 8.  Estimated elevation and Tr ranges represent the potential range of average recharge elevation and Tr for groundwater sampled at each well. Results indicate that a significant portion of recharge occurs at relatively high elevations on Mt. Elphinstone in addition to a component of recharge that takes place at lower elevations. Due to sampling and lab uncertainties, quantified in Table 7b, it is important to remember that ranges of recharge elevation are approximate and could be larger than shown in Table 8.55   Figure 19 Atmospheric lapse as well as 2?C below atmospheric lapse is shown by the grey polygon, and used to estimate recharge elevation ranges for each sample.MW06-1A MW06-1A MW06-2A MW06-2A MW06-2B MW06-2B WL10-01 WL10-01 WL10-02 WL10-02 TW1 TW1 TW2 TW2 TW3 TW3 TW4 TW4 70651 70651 Strata Strata 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 2 3 4 5 6 7 8 9 10 Elevation (mASL) Temperature (?C) MW06-1A MW06-2A MW06-2B WL10-01 WL10-02 TW1 TW2 TW3 TW4 70651 Strata 56  Table 8 Summary of input Hmin/Tmax and Hmax/Tmin pairs as well as estimated recharge elevation and temperature (Tr) ranges. Well  Hmin (mASL)  Tmax     (?C) Hmax (mASL) Tmin     (?C) Recharge Elevation Range (mASL) Estimated  Tr Range (?C) Min  Max  Max  Min MW06-1A 99.5 8.6 1160 7.4 99.5 - 310 8.6 - 8.4 MW06-2A 121.5 9.1 1160 8.2 121.5 - 220 9.1 - 9.0 MW06-2B 121.5 8.7 1160 5.2 121.5 - 420 8.7 - 7.6 WL10-01 139.5 5.8 1160 2.9 600 - 1140 4.5 - 2.9 WL10-02 107.5 7.6 1160 5 140 - 640 7.5 - 6.4 TW1 12.7 6.0 1160 2.8 650 - 1180 4.3 - 2.7 TW2 18 7.6 1160 4.9 190 - 680 7.2 - 6.0 TW3 18.5 5.9 1160 3 630 - 1140 4.5 - 3.0 TW4 13 7.9 1160 3.6 170 - 900 7.3 - 4.6 70651 82.6 5.7 1160 2.7 670 - 1200 4.1 - 2.6 Strata 110.5 6.3 1160 3.4 490 - 1020 5.3 - 3.8  3.5.3 Stable isotopes  Stable isotope results are summarized on the ?D versus ?18O plot in Figure 20 where differences between measured and international VSMOW reference 18O/16O and D/H ratios are plotted relative to the global meteoric water line (GMWL) and the estimated local meteoric water line. The local meteoric water line was estimated based on average 18O/16O and 2H/1H ratios recorded from the Saturna Island and Victoria Canadian Network for Isotopes in Precipitation monitoring stations (2012). Tabulated lab results are available in Appendix B. Analytical error was within acceptable range for the Whistler standard: <1 per mil for D and < 0.3 per mil for O18.   Stable isotope in samples collected from wells, springs and creeks are plotting into three distinct groups: 1.  Charman Creek samples plot high up and slightly right of the GMWL and very close to the estimated local meteoric water line. Rainwater that falls at low latitudes, low altitudes, or under warm conditions plot relatively high up along the GMWL. This signature could suggest that Charman Creek is mainly fed by 57  rainwater that may have undergone evaporation causing the deuterium enrichment to plot right of the GMWL. 2. Groundwater and spring samples are depleted in 18O and D compared to all surface water samples and plot further down the GMWL. Samples that plot further down the GMWL are typically depleted in D and 18O due to cooler conditions that can be caused by high latitude recharge, or precipitation that falls as snow. These samples also show additional 18O depletion by plotting left of the GMWL and the estimated local meteoric water line. The depletion of 18O can also be attributed by the contribution of snowmelt.  3. Samples collected from Chaster and Gibsons Creek are more depleted in D and 18O than Charman Creek, but enriched in D and 18O compared to the groundwater and springs samples. This relationship could suggest that Chaster and Gibsons creeks contain a mixture of rainwater and groundwater, that precipitation feeding Chaster and Gibsons Creek falls at high elevation or that the creeks are fed to a substantial degree by snowmelt.   58   Figure 20 Stable isotope results on ?D versus ?18O plot relative to global and estimated local meteoric water lines.  Victoria and Saturna Island precipitation points are based on yearly averages.    Based on the observed stable isotope signatures in groundwater from the Gibsons aquifer, a significant portion of recharge is derived from precipitation that fell at cool temperatures, high elevations or may have a component of snowmelt. Stable isotopes also suggest that there may be groundwater-surface water interaction between the aquifer and Gibsons and Chaster Creeks. Because only one stable isotope sampling event was completed, these findings are tentative, especially for the surface water bodies. Nonetheless, they do agree with findings from the tritium and noble gas results. Due to seasonal variation, in order to complete an in-depth stable isotope analysis, frequent -85 -83 -81 -79 -77 -75 -73 -71 -69 -67 -65 -13 -12.5 -12 -11.5 -11 -10.5 -10 -9.5 -9 dD vs VSMOW d18O vs VSMOW Global Meteoric Water Line TW#1 TW#2 TW#3 TW#4 WL10-01 WL10-02 MW06-1A MW06-2A MW06-2B STRATA 70651 FDLW MW06-1A dup Charman Creek Chaster Creek Gibsons Creek Springs Victoria Precipitaion (20 masl) Saturna Island Precipitation (178 masl) Groundwater  Chaster and Gibsons Creek  Charman  Creek Estimated Local Meteoric Water Line Global Meteoric Water Line 59  (monthly) groundwater, surface water and precipitation samples over at least a two-year time frame are required.  3.6 Environmental tracer summary and implications to the conceptual model  Tritium and noble gas results distinguished two end members of recharge that enters the Gibsons aquifer: 1. Mountain block recharge that occurs at high elevations along Mt. Elphinstone, flows through fractures in the bedrock and into the Gibsons aquifer. This end member has cold recharge temperatures (~5?C), pre-modern apparent 3H/3He ages (>50 years), and high concentrations of EA (>0.005 ccSTP/g) and 4Heterr (>10-9 ccSTP/g). 2. Upper Gibsons ?bench? recharge that takes place at lower elevations by vertical percolation through the overlying Vashon till or through gaps or recharge windows along incised creek valleys. This component of recharge has warm recharge temperatures (~9?C), modern apparent 3H/3He ages (<10 years old), and low concentrations of EA (0.001-0.003 ccSTP/g) and 4Heterr (<10-9 ccSTP/g). Although recharge end-members determined by the tritium and noble gas results could not be detected in stable isotope ratios from groundwater samples, the overall depleted 18O signature agrees that a significant component of recharge occurs at high elevations and may have a contribution of snowmelt.   Prior to the environmental tracer study recharge locations and processes were uncertain, and the role of mountain block recharge was not considered to be a significant source of recharge.  Waterline (2010) speculated that the bedrock contact between the Bowen Island Group and the granodiorite could be a fault contact and a potential conduit 60  for flow. However, Piteau (2006) surmised that the Capilano glacio-fluvial deposits near the base of Mt. Elphinstone are more likely the significant recharge area. Results from the environmental tracer study suggest that the contribution of MBR is more significant than previously considered. Figure 21 is a cross section that summarizes the improved conceptual hydrogeological model.   Figure 21 Cross section of updated conceptual model that considers mountain block recharge.  3.7 Conclusions  Environmental tracers of noble gases (Ar, He, Kr, Ne, Xe), tritium (3H), chlorofluorocarbons (CFCs), sulfur-hexafluoride (SF6), and stable isotopes of oxygen 61  (O18) and hydrogen (D) were sampled and analyzed from the Gibsons aquifer to quantify groundwater ages, determine recharge locations and processes, and improve and refine the current conceptual model for the aquifer. Apparent 3H/3He ages show that groundwater in the Gibsons aquifer ranges from 8 to 86 years old. Based on the distribution of age results, noble gas calculated recharge temperatures, estimated recharge elevations, excess air, 4Heterr concentrations, as well as stable isotope ratios of D/H and 18O/16O, groundwater in the Gibsons aquifer, consists of two recharge end-members: 1) modern water (<10 years old) with warm recharge temperatures (~9?C) that recharges at low elevations by leakage through the Vashon Till and 2) pre-modern water (>50 years old) with cold recharge temperatures (~5?C) that recharges and flows through fractures in bedrock along Mt. Elphinstone and into the Gibsons aquifer. Due to the deep depth to the top of water table in the upper portion of the aquifer (>100 m), CFCs and SF6 were inadequate tracers for this study (Appendix B).  The environmental tracer findings have significantly improved the understanding of the hydrogeological conceptual model of the Gibsons aquifer. However, specific recharge rates and the relative contributions of recharge end-members remain uncertain. The updated conceptual model needs to be input into a numerical groundwater model in order to quantify specific rates and recharge contributions.   62  Chapter  4: Numerical Groundwater Flow Modeling 4.1 Introduction Environmental tracer results identified two major components of recharge to the Gibsons aquifer: mountain block recharge (MBR) and ?bench? recharge. MBR is pre-modern water that recharged at high elevations, may have some contribution of snowmelt, and flows through fractures in the mountain block before entering the Gibsons aquifer. Bench recharge takes place at lower elevation where modern water either percolates through Capilano glacio-fluvial deposits, incised creek valleys, or windows in the basal Capilano and Vashon Till aquitard.  Although environmental tracers were fundamental to determining recharge components and processes to better constrain the conceptual hydrogeological model, specific recharge rates and the relative contributions of MBR and bench recharge remain uncertain. In order to quantify the contributions of recharge to the Gibsons aquifer, a three-dimensional numerical groundwater flow model was developed. Numerical groundwater flow models are mathematical representations of natural groundwater flow systems solved by computer programs (ASTM D5447-04, 2010).  Models can be used to synthesize existing hydrogeological data, quantify current groundwater conditions, determine and quantify system dynamics including, recharge, groundwater-surface water interaction, and discharge, predict future groundwater conditions, and identify areas where more data, information or monitoring is needed (Wels, 2012).   The objectives of the numerical modeling are to: 1) integrate the geological model, the updated conceptual model and tracer results into a regional three-dimensional numerical groundwater flow model, 2) calibrate the model to observed water levels as 63  well as recharge elevations estimated from noble gases, 3) estimate recharge rates, the contribution of MBR and the overall water budget of the Gibsons aquifer, and 4) compare model results to a model that assumes no MBR to stress how important the tracer study was to better understanding groundwater flow, recharge and the overall water budget of the Gibsons aquifer.    4.2 Review of conceptual model The geological and initial conceptual hydrogeological model is explained in detail in Chapter 2 and refinements to the conceptual model based on results from the tracer study are summarized in Chapter 3. The Gibsons aquifer is comprised of the Pre-Vashon sediments which are pre-glacial outwash sand and gravels that become silty at the base of the deposit.  Near the coastline, in Lower Gibsons, the aquifer is artesian. Beneath Upper Gibsons and towards the base of Mt. Elphinstone the piezometic level of the Gibsons aquifer is deep, up to ~100 m below ground, and the Pre-Vashon sediments become partially unsaturated between the top of the water table and base of the Capilano and Vashon Till aquitards. The Capilano aquifer is a shallow unconfined aquifer within the Capilano intertidal beach sands that is perched on top of the Capilano marine clay and Vashon Till aquitard. At the base of Mt. Elphinstone are deep, dry, Capilano fluvial deposits that have an uncertain hydraulic connection to the Gibsons aquifer.   Based on the geochemistry and environmental tracer results, samples of groundwater from the Gibsons aquifer collected closest to the base of the mountain have the most evolved geochemical signature, the oldest apparent 3H/3He ages, and the coldest noble gas-calculated recharge temperatures suggesting that the aquifer receives recharge 64  through the mountain block. The ?mountain block? refers to the bedrock that makes up Mt. Elphinstone and it is assumed that water flows through fractures in the bedrock generally following the topographic gradient before discharging into the Gibsons aquifer.  Groundwater is diverted from the Gibsons Aquifer by pumping from three municipal supply wells and one private well and artesian overflow from two of the supply wells. Water that is not diverted from the aquifer eventually discharges as springs along the coastline or directly into the ocean at Gibsons harbour. The interaction between groundwater from the Gibsons aquifer and the minor creeks in the study area is not well understood. Stream flows were not monitored over the duration of this study and as a result could not be included in the numerical model due to lack of calibration data. Similarly, the location and flow rates of most springs are not known and it is difficult to decipher if discharge from springs is from the Gibsons or Capilano aquifer. As a result, springs were not designated in the model, instead, spring discharge is assumed to be included in discharge to the ocean since springs are generally located within 10 m above sea level.  4.3 Modeling approach  4.3.1 Numerical model The numerical groundwater flow model was constructed using the commercial software package Visual MODFLOW 2009.1. Visual MODFLOW uses the finite difference code MODFLOW-2000, developed by the United States Geological Survey to solve the saturated groundwater flow equation. MODFLOW-2000 assumes confined three-dimensional flow with water-table approximations and that the model grid is 65  aligned along the principal directions of hydraulic conductivity (Reilly and Harbaugh, 2004). Given the regional nature of the study area and the available input and calibration data available, MODFLOW was a suitable numerical model code to use. Finite element codes such as FEFLOW, SEEPW or Hydrogeosphere are capable of modeling unsaturated zone processes and therefore are better suited for modeling groundwater-surface water interaction. However as mentioned previously, insufficient field data was collected to model and calibrate groundwater-surface water interactions. Similarly, due to the lack of physical data in the mountain block, such as drilled boreholes, well logs or fracture data, at the regional scale it is more appropriate to model flow through fractured bedrock as a continuum, assuming the model scale is greater than the representative elementary volume, rather than as discrete fracture networks (Manning, 2002; Kahn et al., 2008).   Previous mountain block recharge studies that have modeled hydraulic conductivity as a three-dimensional tensor that decreases with depth (Table 9). Hydraulic conductivity decreases with depth due to a near-surface ?active layer? that is likely to have a higher density of fractures caused by weathering, unloading, exfoliation, as well as the enhancement of fractures as a result of surficial movement (Wilson and Guam, 2004; Manning and Solomon, 2005; Manning and Caine, 2007; Golder Associates, 2010). Manning and Caine (2007) used down-hole temperature profiles to estimate depth of active groundwater circulation at the Handcart Gulch watershed in Colorado. They found that a maximum depth of about 200 m below ground, or 150 m below the water table was the average depth to which groundwater temperatures deviated from the slope of the 66  geothermal gradient. Kahn et al. (2008) continued this study and performed pumping tests at various depths in wells completed in bedrock to quantify hydraulic conductivity and storage parameters. Smerdon et al., (2009); however, took a simpler approach and modeled all bedrock using a single homogeneous hydraulic conductivity.  Table 9 Summary of hydraulic conductivity values used in previous mountain block recharge studies. Study Location Lithology Depth (mbg) Hydraulic Conductivity (m/s) Manning and Solomon, 2005 Salt Lake Valley and the Wasatch Mountains Combination of granitic intrusions, quartzites interbedded with shales, and mixed sedimentary rock. 200 <2x10-6 500 <1.1x10-6 1000 7.5x10-7 to 2.4x10-7 2000+ >1.6x10-7 Kahn et al., 2008* Handcart Gulch, Colorado Gneiss 97-197 4.3x10-9 Porphyry 28-128 6.8x10-9 Gneiss 4.4-5.5 5.0x10-6 5.5-7.7 1.0x10-6 7.7-9.9 5.0x10-7 9.9-12.1 1.0x10-7 12.1-32.9 5.0x10-8 Quartzite 10.7-23.7 5.0x10-6 Smerdon et al., 2009 BX Creek watershed, north Okanagan Basin, BC Granitic gneiss, argillacesous limestone, volcanics and sedimentary rocks. All bedrock 4x10-8  4.3.2 Model calibration The purpose of model calibration is to determine whether the simplified numerical model represents the natural observed groundwater flow system. Traditionally, observed hydraulic heads and measured groundwater fluxes are collected in the field and used as calibration targets in the numerical model. It is ideal to have as many calibration targets as possible and to have both heads and fluxes in order to minimize parameter correlation between recharge and hydraulic conductivity to create a unique solution that 67  represents the natural groundwater system (Poeter and Hill, 1997; Sanford, 2002; Hunt el al., 2005).  The use of non-traditional or ?unconventional? calibration targets is becoming a common approach to minimize model non-uniqueness. Previous studies have used groundwater ages or travel times (Reilly et al., 1994; Goode, 1996), solute distributions (Christensen et al., 1995; Anderman et al., 1996), observed groundwater-surface water interactions (Hunt el al., 2005), heat (Bravo et al., 2002; Heilweil et al., 2012) or a combination of these (Sanford et al., 2004; Manning and Solomon, 2005) in order to constrain parameter estimation. In this study, recharge elevation ranges were used as calibration targets in addition to observed hydraulic head data. As described in Chapter 3, noble gas recharge temperatures were used to estimate recharge elevation based on the assumption that air and water table temperature decreases with elevation. Due to a high degree of uncertainty, apparent 3H-3He ages were not used as calibration targets. In order to calibrate to recharge elevation, the MODPATH/MODPATH-PLOT package in MODFLOW was used to compute and display three-dimensional particle path lines. MODPATH/MODPATH-PLOT is a post-processing package developed by the USGS (Pollock, 1994) that uses semi-analytical particle tracking scheme to compute particle flow paths, cell by cell, until the particle is terminated by a boundary or internal source or sink. MODPATH is the code that calculates particle flow paths and MODPATH-PLOT graphically displays the results. Particles can be specified to track either forwards or backwards.  Calibration to recharge elevation was achieved by placing 10 backwards-tracking particles along the length of well screens for all wells that were sampled and analyzed for 68  noble gases. It is assumed that the termination points of the backwards-tracking particles mark the recharge location of groundwater that flows to each well. Elevations were measured from the surface of the model directly above the point of termination in order to represent ground elevation at recharge.   4.4 Model input 4.4.1 Domain The model domain extends from the top of Mount Elphinstone to the ocean at Gibsons Harbour, in Howe Sound. The upper portion of the model domain boundaries from the base to the top of Mount Elphinstone is defined by the watershed catchment boundaries.  The lower portion of the model domain covers the thickest part of the Pre-Vashon sediments containing the Gibsons aquifer, generally following the proposed lateral boundary shown in Figure 12. As a result, well 70651 was not included in the model. Figure 22a shows the model domain in map view and how it relates to the watershed boundaries, the thickness of the Pre-Vashon deposits and to the direction of groundwater flow according to the piezometric surface.  Figure 22b shows the model domain in Visual MODFLOW oriented 45? to the east in order to align the model with the principal direction of groundwater flow (northwest to southeast).  69   Figure 22 Model Domain in a) map view and b) rotated clockwise by 45? in model MODFLOW.  4.4.2 Grid design The grid consists of 140 rows, 70 columns and 5 layers with uniform 50 m by 50 m grid cells in the x and y direction (Figure 23). Grid layers are specified according to geologic layers defined in the 3D geological model developed in Leapfrog and edited so that layers are continuous, have a minimum thickness of 10 m, and have enough vertical cell overlap to minimize numerical instability. 70   Figure 23 Model Grid in a) map view and b) rotated clockwise by 45? in model grid.  The upper model surface, top of layer 1, is defined by an elevation model created in ArcGIS using 20 m TRIM points (DataBC, 2003) along Mt. Elphinstone, 1 m contour lines (SCRD, 2012) along the bench down to the coastline and bathymetry data (Canadian Hydrometric Services, 2012) to a maximum model surface depth of 20 m below sea level. The bottom of layer 1 is defined by the bottom of the Vashon till up to an elevation of 40 mASL, continues at 40 mASL along the bench until topography is equal to 160 mASL near the base of Mt. Elphinstone. From this point upwards, the bottom of layer 1 remains constant at 120 m below the elevation of the model surface/topography in order to ensure sufficient vertical cell overlap. The bottom of layers 2, 3, 4 and 5 are defined so that a bottom of layer exists at an elevation equal or 71  close to the logged or estimated depth to bedrock in each of the monitoring wells. Figure 24, a cross section through the model grid along column 33, displays the defined layers.   Figure 24 Cross section through model - column 33  4.4.3 Boundary conditions  4.4.3.1 No flow The base of the model, the lateral boundaries, and the surface of the model over the area where the Gibsons aquifer has fully confined conditions, were all specified as a no-flow (zero flux) Neumann boundary. Because bedrock was included in the model, it is assumed that bedrock is inactive or impermeable beneath 50 m below sea level. The lateral boundaries along the upper reaches of the model (along the mountain) and along the east side of the model are defined by the watershed catchment boundaries. It is assumed that the natural grundwater divides are equivalent to the surface water divides and therefore can be specified as no-flow. On the western side, no flow is defined by bedrock highs in the subsurface. The lateral no flow boundary is represented by the green line in Figure 25.    72   Figure 25 Boundary Conditions  In Lower Gibsons where the aquifer is fully saturated and confined, the surface of the model is specified as no flow. In Figure 25, this is represented by the white area that receives 0 mm of recharge per year since it has an upward hydraulic gradient. There are several springs in this area that could suggest that there is some discharge through the confining unit. However, the discharge rates out of the springs, the number and distribution of springs, and the conductance term needed to be applied to the drain 73  package in order to account for the springs in the model are unknown. Therefore, it is assumed that the surface of the model is impermeable, and water that would have exited via springs, is discharged to the ocean instead. This is a reasonable assumption given the regional scale of the model and the proximity of the springs to the ocean. 4.4.3.2 Constant head The Dirchlet constant head boundary condition of 0 mASL was applied to layer 1 along the ocean to represent the average long-term sea level. The constant head boundary is shown as red cells in Figure 25. It was applied to all cells that have a surface elevation of 0 mASL or less.  4.4.3.3 Recharge  The recharge package represents Neumann specified flux boundary conditions where recharge is applied as a constant downward vertical flux to the uppermost active layer of the model. Recharge zones were created based on orographic precipitation patterns, surface geology, aquifer saturation, slope, elevation and proximity to snow accumulation and or snow melt. Recharge rates were initially selected based on previous estimates by Piteau (2006), 150 mm/year, but were modified during model calibration within the range of recharge rates calculated by Kerr Wood Leidal (2013) for the Regional District of Nanamio with very similar geology, climate and groundwater conditions (Figure 26). Both rates and zones were examined during the calibration process.  74   Figure 26 Histogram of recharge rates calculated by Kerr Wood Leidal (2013) across the Regional District of Nanaimo using a USGS Water Balance Model (McCabe and Markstrom).  4.4.3.4 Groundwater extraction The wells package also represents the Neumann specified flux boundary condition and was used to simulate groundwater extraction from the Gibsons Aquifer. Three active Town of Gibsons supply wells account for most of the total groundwater extracted from the aquifer. In order to represent steady state conditions, pumping rates were calculated by averaging three years (2009-2011) of total groundwater extracted recorded from each of the Town Wells.  Town Well 1 and Town Well 4 have installed flow diverters that divert artesian overflow to storm drains while the pumps are off. Overflow from both wells have been monitored from March 2011 to December 2012 and the average flux in included in Table 10. Due to lack of monitoring data prior to 2011, it has been assumed that average yearly overflow for 2009 and 2010 were the same as observed in 2011 and 2012. Therefore, 0 100 200 300 400 500 600 700 Frequency Average Annual Recharge Rates mm/year 75  diverted artesian overflow becomes an additional constant flux out of the Aquifer. To account for this, overflow rates were added to the pumping rates in Town Well 1 and Town Well 4.  Table 10 Summary of groundwater extraction rates applied to model  Extraction Well Name Water Use Flux Out (m3/day) Total Flux Out (m3/day) Town Well 1 Town Supply 174.7 338.0 Artesian Overflow 163.3 Town Well 3 Town Supply 1667.1 1667.1 Town Well 4 Town Supply 164.4 271.1 Artesian Overflow 106.7 Strata Condo Well Assumed Flux to Water Feature 100 100  The Strata Well, also listed in Table 10 is a private well on a strata-controlled condominium complex that operates daily. The groundwater extracted from this well is used to feed a water feature that flows into a series of man-made ponds. The Strata Council would not allow for a flow meter to be installed, nor were they aware of the pumping rates. Therefore an average groundwater extraction rate of 100 m3 per day was assumed and applied to the Strata Condo well.  4.4.4 Flow properties Hydraulic conductivity is the only flow parameter required to run a steady state flow model. The spatial distribution of the hydraulic conductivity zones were initially specified according to geological layers determined in the 3D geo-model (Chapter 2) and values of hydraulic conductivity by historic pump tests, slug tests, grain size analyses or values recorded in the literature. Table 11 summarizes the range of measured and historic 76  values of hydraulic conductivity in the Vashon till aquitard as well as in the Gibsons aquifer (Pre-Vashon sediments) as discussed in Chapter 2. Equivalent porous medium conductivities for bedrock are described in section 4.3.1. Values and distribution of the hydraulic conductivity zones were refined during the calibration process.   Table 11 Summary of hydraulic conductivity ranges compiled from previous studies. Hydrolitholigcal Unit Range of Hydraulic Conductivity Values (m/s) References Vashon till aquitard 7.1x10-9 ? 1.9x10-4 Jones, 1999  Utting, 1974 Gibsons aquifer (Pre-Vashon) 10-2  ? 5.2x10-5 Waterline 2013 Piteau 1999,2000  4.4.5 Initial conditions, solver, and rewetting parameters  All model simulations were run using the MODFLOW 2000 pre-conditioned conjugate gradient (PCG2) solver with convergence criteria summarized in Table 12. Due to the steep topography and the unconfined areas of the aquifer, it was appropriate to set the damping factor in the PCG2 package to 0.5. Model simulations were run in steady state to simulate the average long term pumping conditions and observed water levels in the aquifer. The initial condition of the model was fully saturated to minimize dry cell issues.   The steep topography and unconfined nature of the upper portion of the aquifer also made it necessary to run the model with cell wetting activated. If cell wetting is not activated, cells that go dry during a simulation become inactive and are removed from the model solution. Dry cells were re-activated if the head below the dry cell is 0.1 m above the bottom of the dry cell. Head values in re-activated cells were calculated from heads in 77  the surrounding active cells. All model layers were treated as convertible (confined or unconfined); however, the cells within the bottom 10 m were kept saturated throughout all of the simulations. Rewetting calculations were conducted every iteration required to solve the steady state model.  Table 12 Convergence Criteria Solver PCG Maximum outer iterations 300 Maximum inner iterations 50 Head change criterion 0.1 m Residual criterion 0.1 m3/day Damping factor 0.5 Printout interval 10 Pre-conditioning method Polynomial Relaxation parameter n/a  4.4.6 Calibration data The model was calibrated using average long-term hydraulic head data and recharge elevation ranges estimated using noble gas thermometry. Pressure transducers were placed in all of the monitoring wells in November 2009, except in WL10-01 and WL10-02, which were drilled in April 2010 to monitor water levels. Because the model is steady state, average observed water levels were used for calibration targets. Table 3 summarizes the observed water level calibration data that was input into MODFLOW using the observation wells package.  Currently, no monitoring wells exist in Lower Gibsons where all of the Town supply wells are located. As a result, the pumping level in Town Well 4 was included as an observation point in order to have at least one calibration target in this region. The pumping level in Town Well 4 was the only suitable pumping level to use because it is 78  the most recently drilled supply well and the most efficient well. TW1 and TW3 are much older supply wells and have been observed to be inefficient (Waterline, 2013).  Table 13 Water Level Calibration Input Data Well Easting Northing Ground Elevation (mASL) Mid-Screen Elevation (mASL) Average  Water Level (mASL) School Board 460684 5473611 153 31 34.6 WL10-01 461597 5473033 139.5 0.8 28.5 MW06-2A 462130 5472688 121.5 22.6 24.6 MW06-1A 462812 5472468 99.5 25.1 24.8 WL10-02 462263 5472238 107.5 -14.9 22.7 Strata 462486 5472360 110.5 21 22 Town Well 4 463143 5472141 13 3.8 12.5   As described in section 1.3.2 recharge elevation ranges were also used in model calibration. Figure 27 is a graphical summary of the best estimates of recharge elevation ranges using noble gas thermometry. It is important to note that calibration to recharge elevation is a qualitative process ? the goal is to ensure that overall, backward tracking particles released from each well screen generally track to the estimated recharge elevations.   79   Figure 27 Best estimate of recharge elevation ranges.  4.5 Results and discussion 4.5.1 Recharge  In the calibrated base case model, three zones of recharge were delineated based on mapped surface geology (Chapter 2) and elevation. Recharge results are summarized in (Figure 28).   0 200 400 600 800 1000 1200 Elevation (mASL) 80   Figure 28 Recharge zones and rates applied to the final calibrated model.  Recharge was applied to the bench at a rate of 115 mm per year along the area where the Gibsons aquifer is not fully saturated and the Capilano marine sediments are mapped on surface. Here, recharge is likely to be sourced from the perched Capilano aquifer which recharges the deeper Gibsons aquifer via leakage, fractures or gaps in the Vashon Till/Basal Capilano aquitard. A recharge rate of 130 mm per year was applied to 81  the area with exposures of Vashon Till and Capilano glacio-fluvial deposits near the base of Mt. Elphinstone, and a rate of 145 mm per year was applied along the slopes of Mt. Elphinstone where bedrock or bedrock with a till veneer is mapped on surface. The increase in recharge rates with elevation may be attributed to increased precipitation due to orographic effects, the contribution to recharge by snowmelt, or by the ground condition or slope. All three final recharge rates fall within the three highest frequency ranges of recharge rates in the histogram in Figure 26.  4.5.2 Hydraulic conductivity The base case model includes four zones of hydraulic conductivity representing the average conductivity of each hydrostratigraphic unit (Chapter 2).  Figure 29 summarizes the values and zones of hydraulic conductivity assigned to the 5 model layers. Because the perched Capilano aquifer was not included in the model, the conductivity of layer one along the bench portion of the model (the Green zone in Figure 29), was assumed to equal the average conductivity of the basal Capilano/Vashon Till aquitard ? leakage through the aquitard is what recharges the Gibsons aquifer along the bench. The teal zone in Figure 29 represents the upper portion of the bedrock that is likely fractured as well as some of the fine silts observed at the base of the Pre-Vashon deposits. It has been assumed that each unit behaves as a homogeneous, isotropic porous medium. All values fall within the range of values specified in Table 9 and Table 11.  82   Figure 29 Zones of hydraulic conductivity     83  4.5.3 Model calibration Model calibration was a manual, iterative process whereby values and distribution of hydraulic conductivity and recharge were adjusted until calibration to both observed water levels and recharge elevations were achieved. Values of hydraulic conductivity representing each hydrolithological unit were varied within the measured, historical or compiled literature value ranges. The spatial distribution of each conductivity zone was only modified in areas where no well logs, geophysics or mapped geology could constrain the subsurface geology. Bedrock was the least constrained zone of hydraulic conductivity. Recharge rates were varied within the range of typical recharge rates determined from previous studies of similar climates and recharge conditions (Chapter 2). 4.5.3.1 Calibration to observed head  Figure 30 is a map showing both the modeled and observed piezometric surface from the final calibrated model, the ?base? model and figure X is a cross section with hydraulic head equipotential contours through the model domain, including the mountain.  Figure 32 is a plot of the modeled (calculated) versus observed heads with a summary of the calibration statistics. All modeled heads fall within the acceptable error range considered for this study of ? 2 m from observed heads. The calibration statistics show that an adequate calibration was achieved with a correlation coefficient of 0.993 and a normalized residual mean square of 3.6%.  84   Figure 30 Map of modeled and observed piezometric surfaces.   Figure 31Cross section through model domain (column 78) with 50 m head equipotential contours. 85    Figure 32 Modeled (calculated) versus observed heads and summary of calibration statistics.  The Strata well has the largest difference between modeled and observed heads with a modeled head 1.3 m below the observed head which is not surprising since there is no well log, completion or pumping data available for this well. The increased error could be a result of assuming an incorrect mid well screen elevation or too high of an average daily pumping rate.    86  4.5.3.2 Calibration to recharge elevation Successful calibration to recharge elevation was achieved when path lines from backwards tracking particles generally tracked to each of the estimated recharge ranges. The process was somewhat qualitative, but significantly helped to constrain model parameters. Ten backwards-tracking particles were released along the length of each well screen from wells that were sampled for noble gases.  Figure 33 is a map that shows the backwards-tracking path lines from the final calibrated results. The elevations where each of the ten backwards-tracking particles tracked to were used to construct recharge elevation box plots. For each well, elevation box plots were compared to the best estimates of recharge elevation as shown in Figure 34.    87   Figure 33 Map of backwards-tracking path lines from final calibrated model. 88   Figure 34 Modeled recharge elevation boxplots overlying noble gas best estimates of recharge elevation ranges.  4.5.4 Model water balance, contribution of MBR and aquifer water budget The overall water balance of the model is computed in MODFLOW and summarized in Table 14. In a steady state model, total aquifer recharge should balance total aquifer discharge, as steady state represents equilibrium in the groundwater system. The percent discrepancy between total water in and total water out of the model is a result of numerical residual error.      89  Table 14 Daily water balance in rates (m3/day) calculated in final MODFLOW model. Daily Rates (m3/day) IN Total Recharge 5010.6 OUT Wells 2376.2 Constant Head 2749.9 Total Out 5126.1 IN - OUT -115.5 PERCENT DISCREPANCY -2.28 %  Zone budgets were assigned in MODFLOW in order to calculate the contribution of MBR and the overall water budget of the Gibsons aquifer. Zones were assigned according to the three zones of recharge which also generally coincide with elevation and surface geology. The ?Bench? zone is located where the Capilano marine sediments are on surface, the ?Mid? zone across the Vashon Till and Capilano glacio-fluvial deposits and the ?Upper? zone over the Mountain where bedrock or bedrock with a thin till veneer is mapped.  Based on the annual recharge rates specified in Figure 25, total daily recharge was calculated for each zone and for the entire model in cubic meters per day. A plan view map of the zone budgets and total daily recharge is shown in Figure 35. Each zone was applied to all layers in the model.  90   Figure 35 Location of zone budgets, calculated total daily recharge and daily recharge calculated for each zone.   MBR has been identified as the flux of water that flows from the Upper Zone into the Mid Zone. Figure 36 is a cross section of the modeled zone budgets and the calculated flux of MBR across Upper Zone ? Mid Zone boundary. Based on the calculated total daily recharge rate and the daily flux of MBR, 46% of recharge to the Gibsons aquifer is via MBR.  91   Figure 36 Cross section through model (column 41) showing the calculated flux of MBR across the Upper ? Mid zone budget interface.   The steady state overall water budget of the Gibsons aquifer can be described as;                                                                    where recharge includes precipitation that infiltrates through the Vashon Till and Capilano glacio-fluvial deposits within the Mid zone (    ), leakage from the Capilano aquifer through the basal Capilano and Vashon Till aquitard along the Bench zone (      ), and the flux of MBR through the Upper zone ? Mid zone interface (    ). Discharge includes water diverted via the private Strata condo well and the three municipal supply wells (TW1, TW3, TW4;       ), artesian overflow from TW1 and TW4 (      ), discharge to springs (        ) and discharge to the ocean (      ). Due to lack of spring observation data, the model assumes that discharge to the ocean includes the volume of water that discharges to springs. Because water that is not diverted by wells or by artesian overflow eventually discharges into the ocean         is dependent on how much water is recharged versus 92  how much water is extracted by wells. To assess the overall water budget of the Gibsons aquifer and determine how much groundwater is available for use, the water budget equation is re-written as follows:                                           where the          term indicates that it includes discharge from springs. Based on this calculation, about 2700 m3/day of water naturally discharges from the aquifer into the ocean or springs (Appendix A.3). Some of this water has the potential to be captured from additional pumping via existing or new wells if groundwater demand increases in the future.  This is addressed in Chapter 5.  4.5.5 Sensitivity analysis A sensitivity analysis was performed in order to assess how uncertainties in the input values affect the model outputs. Two approaches to the sensitivity analysis were taken: 1) Values of hydraulic conductivity and recharge were adjusted by ? 50 percent, in order to assess the impact on modeled heads (water table elevation), recharge elevation and the percent of mountain block recharge (% MBR), and 2) zones of conductivity representing bedrock were adjusted in order to assess the effect that bedrock geometry has on hydraulic heads and recharge elevation since the bedrock geometry is poorly constrained. Details of the sensitivity data and results are provided in Appendix E. 4.5.5.1 Water table elevation, recharge elevation and % MBR In Figure 37, each zone of conductivity and recharge were independently adjusted by ? 50 percent in order to assess its influence on modeled heads, recharge elevation and percent mountain block recharge. All analyses were initially run with rewetting activated; 93  however, some of the models did not converge with adjusted parameters with this setting. As a result, the base case model was run with both rewetting on and off and all sensitivity scenarios were compared to both cases. Turning the rewetting on and off has negligible effects on the overall sensitivity results displayed in Figure 37  Figure 37a summarizes sensitivity of the overall change in water level elevation, calculated by averaging the mean difference between modeled and observed hydraulic heads from each observation well. The graph shows that overall water table elevation is most sensitive to conductivity of the Pre-Vashon zone and moderately sensitive to the conductivity of the Vashon Till zone. The model is also sensitive to recharge rates in all zones, but is most sensitive to recharge in the upper mountain recharge zone. Water table elevation is relatively insensitive to conductivity in upper bedrock (fractured bedrock) and lower bedrock. Figure 37b summarizes sensitivity of the overall change in recharge elevation by averaging the mean change in recharge elevation for particles released from all of the wells. Error bars represent the standard deviation from the mean recharge elevation. It is evident that recharge elevation varies widely for each sensitivity scenario. Recharge elevation is most sensitive to conductivity of the Pre-Vashon zone, the Vashon Till zone and to recharge rates in the upper mountain. Similar to sensitivity results from water table elevation, recharge elevation is least sensitive to hydraulic conductivity of the upper and lower bedrock zones.  Figure 37c shows the sensitivity of mountain block recharge (MBR) to each of the adjusted conductivity and recharge zone. Percent MBR was calculated using the ratio of vertical recharge to the Gibsons aquifer to the flux of MBR entering the aquifer. A 94  detailed description on the MBR flux calculation is described in the water budget section (section 1.5.3).  Change in percent MBR is sensitive to variations in recharge rates in all recharge zones; however, greatest change is observed in the Upper Mountain and Bench recharge zones. Adjustments to hydraulic conductivity in all zones have little to no impact on the percent of mountain block recharge.  Sensitivities indicate that recharge rates have the largest degree of influence on all model outputs and hydraulic conductivity values in the Pre-Vashon and Vashon zones have a large influence on water table and recharge elevations.  Parameters that have a large influence on model outputs are likely to be approximated correctly during the calibration process (Johnson, 2010). However, if no observation data exists for the very sensitive parameter, further work or more field data should be collected in order to constrain the modeled parameter. This is the case of the Vashon Till conductivity zone which has no local measurements of hydraulic conductivity and very little data available in literature. The Pre-Vashon, on the other hand, has abundant observation and test data to verify the modeled conductivity value is within the range of observed conductivity. Recharge rates have never been explicitly measured locally; however, modeled rates are within ranges described in section 4.4.3.3. Conductivity values in the mid and upper mountain zones have little to no influence on model outputs and therefore did not have a large impact on model calibration. Insensitive parameters could impact future predictions if the final model calibration did not use correct values. Further studies or fieldwork should be conducted in order to constrain the parameter input range.   95   Figure 37 Overall model sensitivity plots for a) water table elevation (hydraulic head), b) recharge elevation and c) percent MBR. Error bars on each data point are the standard deviation of the differences between modeled and observed heads or recharge elevation.  a) b c 96  For the purpose of this study, no additional data could be collected in order to constrain the conductivity values of the upper and lower bedrock units. Instead, a more detailed analysis was conducted for the sensitivity of recharge elevation ? the data set that provided calibration targets in the bedrock within the Mountain. Box plots in Figure 38 show the effect that changes in conductivity and recharge rates have on the distribution of recharge elevation on a well by well basis, based on the ten backwards-tracking particles released from each well screen. Scenarios that could be run with cell rewetting on (RW On) were also run with cell rewetting off (RW Off) to compare the effect that rewetting has on the particle?s recharge elevation. Recharge elevation was plotted for rewetting turned off only for scenarios that could not converge with rewetting turned on. Turning the rewetting on and off showed some discrepancy in recharge elevation results displayed in Figure 38. As expected based on results shown in Figure 37b, recharge elevation is most sensitive to hydraulic conductivity of the Pre-Vashon and Vashon Till zones and to the recharge rates in the upper mountain. Recharge elevations in Town Well 2, Town Well 4, MW06-1A and MW06-2A are relatively insensitive to any change of parameter value. These wells all have the shallowest well screens, the lowest recharge elevation and based on environmental tracer results, the least amount of MBR water. As a result, flow paths are relatively short and are not as affected by changes in upstream parameters. Some sensitivity to bench recharge and to conductivity of the Pre-Vashon zone is observed in MW06-2A, and to bench recharge in Town Well 4.  97  Figure 38 Sensitivity and variation of recharge elevation with varying values of hydraulic conductivity and recharge rates. Recharge elevations are based on the ten backwards-tracking particles released from each well screen on a well by well basis The shaded grey region signifies the estimated recharge elevation calibration range. 98  Town Well 1, Town Well 4 and the Strata well show the greatest variance in recharge elevation. These wells are pumped regularly and environmental tracer results suggest that water from these wells is a mixture of MBR and bench recharged water. As a result particle recharge elevations have a wide variance representing a mixture of flow paths to each well. Recharge elevation in these wells are most sensitive to conductivity of the Pre-Vashon and Vashon Till zones as well as to recharge in all zones.    Modeled recharge elevations in WL10-01 and WL10-02 are relatively sensitive to all parameters. For both plots most of the box plots remain within the estimated recharge elevation ranges and generally have little variance in recharge elevation. WL10-01 is located closest to the base of Mt. Elphinstone, has a very deep well screen and tracer data suggests that most water flowing through the well screen is from MBR. Parameters that affect particle recharge elevation most significantly are; increase in hydraulic conductivity of the Vashon Till zone, decrease in conductivity of the lower bedrock zone and decrease in recharge rate to the upper mountain. These effects agree with tracer results in that higher conductivity of the Vashon Till zone would induce more infiltration at lower elevations, therefore lower recharge elevation. Similarly a decrease in the conductivity of the lower bedrock unit would result in less infiltration into bedrock in the mountain and therefore a decrease in high mountain recharge. Finally, if recharge rates in the mountain are 50 percent lower, fewer flow paths would recharge at high elevation generating lower elevation recharged flow paths causing greater variance in recharge elevation.  WL10-02 is located about half-way between the base of Mt. Elphinstone and the coastline. The well screen is also about mid-depth between the top of the water table and 99  the base of the aquifer. Tracer results suggest that water flowing through WL10-02 could either be water recharged at mid elevation, or a mixture of MBR and bench recharged water. All box plots have a small range in recharge elevation suggesting that particles to WL10-02 recharge at mid-elevation. Backwards-tracking particles however, are quite sensitive to hydraulic conductivity of the Pre-Vashon and Vashon Till zones and to recharge rates in the mid and upper mountain zones. In some cases, an increase or decrease in these rates cause particle recharge elevations to plot outside of the estimated recharge elevation range. This confirms that these parameters were approximated correctly during the calibration process.  4.5.5.2 Bedrock geometry An additional sensitivity analyses was conducted in order to assess the effect that bedrock geometry has on hydraulic heads and recharge elevation. Six models were generated where specific areas within the upper and/or lower bedrock conductivity zones were changed to zones of Pre-Vashon or Vashon Till in order to simulate changes in bedrock geometry. Modifications were performed in areas where no or limited bedrock data exists, such as borehole, well logs, geophysical profiles or bedrock outcrops. The effect that changes in bedrock geometry have on recharge elevation is summarized in Figure 40. Plots show that backwards-tracking particle recharge elevations are very sensitive to bedrock geometry and that sensitivity varies with the location of bedrock altered.   Sensitivity of bedrock geometry to hydraulic heads (water table elevation) was also assessed and is summarized in Figure 39. The plot shows that the water table 100  elevation is relatively insensitive to each altered bedrock scenario. Calibration statistics for modeled versus observed heads for each scenario were also investigated to see if any discrepancies could be detected. Table 4 summarizes the calibration statistics for the base case model and all of the 6 scenarios with altered bedrock geometries.   Calibration statistics in Table 15 show that only two out of the six scenarios had a maximum residual of greater than 2 m difference than the observed head. All but one scenario had correlation coefficients greater than 0.99 and all scenarios had acceptable normalized residual mean squares. Without the additional recharge elevation calibration targets to constrain bedrock geometry, at least four of the six altered bedrock scenarios could have been selected as the final model. This finding confirms the importance of having recharge elevation as an additional calibration target is for minimizing model non-uniqueness.    Figure 39 Sensitivity of water table elevation for 6 altered bedrock geometry scenarios. Data points are the mean change in water level and error bars represent the standard deviation from the mean. -10 -5 0 5 10 Change in Water Table Elevation (mASL) 1 2 3 4 5 6 Bedrock Scenario 101  Figure 40 The effects that changes in bedrock geometry have on recharge elevation based on the backwards-tracking particles released along each well?s screen. Bedrock elevations are exported from Visual MODFLOW and regenerated in ArcGIS for the base case scenario as well as six additional scenarios labeled 1 through 6. The black boxes indicate areas where the bedrock surface was altered. 102  Table 15 Comparison of calibration statistics for base case model and the six altered bedrock models. Statistic Base Case 1 2 3 4 5 6 Maximum Residual (m) -1.295 -2.061 1.691 -2.092 -1.528 -1.803 -1.43 Minimum Residual (m) 0.019 0.255 0.535 0.003 0.117 -0.25 0.023 Residual Mean (m) 0.294 -0.359 0.759 -0.156 -0.482 -0.157 0.174 Absolute Residual Mean (m) 0.664 0.784 0.986 0.795 0.792 0.722 0.607 Standard Error of Estimate (m) 0.304 0.368 0.297 0.402 0.37 0.346 0.306 Root Mean Square (RMS) (m) 0.801 0.97 1.051 0.998 0.958 0.862 0.77 Normalized RMS (%) 3.625 4.39 4.756 4.514 4.335 3.902 3.486 Correlation Coefficient 0.993 0.99 0.994 0.987 0.993 0.991 0.994  4.6 Comparison bench model Prior to the environmental tracer component of this study, recharge locations and processes were uncertain and the contribution of MBR was considered negligible. Some consideration was put into the potential for groundwater flow through the potential fault contact running NW-SE across the study area (Figure 7), however, the thick deposits of the Vashon Till and the Capilano glacio-fluvial sediments at the base of Mt. Elphinstone were usually considered to be the primary recharge area (Piteau, 2006; Waterline, 2010)  To demonstrate the significance of the environmental tracer results, an additional numerical groundwater model was constructed based on a conceptual model that excludes the mountain block and assumes no MBR. To do this, the original MODFLOW model was regenerated excluding the Mountain Block ? the area of the Mountain specified by the Upper zone in Figure 35 and Figure 36.  Recharge rates were the only parameter adjusted in the bench model.  No adjustments were made to the values or distribution of hydraulic conductivity zones including the geometry of the underlying bedrock. Boundary conditions also remained the same, but the lateral boundary where the mountain block was cut off became a no flow boundary.  103   4.6.1 Bench model results and discussion Given no insight on noble gas estimated recharge elevation ranges, the bench model was calibrated to observed hydraulic heads only. The calibration plot of modeled versus observed heads, including the calibration statistics is shown in Figure 41. Boundary conditions and the final recharge rates determined through model calibration are summarized in Figure 42.    Figure 41 Calculated versus observed heads and summary of calibration statistics for the no MBR model.   Calibration results indicate that the recharge rate along the bench (the blue zone) remained unchanged in order to successfully calibrate the model; however, the recharge rate along the area near the base of Mt. Elphinstone (the teal zone in Figure 42), dramatically increased compared to the original model. To compare recharge results from 104  the original model and the no MBR model, Figure 43 summarizes the differences in daily recharge rates and the percent of overall recharge to each recharge zone.    Figure 42 Summary of boundary conditions applied to the no MBR model.     105   Figure 43 Comparison of recharge components in daily total recharge rates and the percent of total recharge for each recharge zone for a) the original model and b) the no MBR model.   Results indicate that in both models, the component of recharge through the bench is about the same, 35 ? 36%, however in the no MBR model, 69% of recharge occurs as infiltration through the Vashon Till and Capilano glacio-fluvial deposits at the base of Mt. Elphinstone. In comparison, in the original model, only 19% of recharge occurs in this zone and 45.7% takes place at higher elevation along Mt. Elphinstone. In the absence 106  of the environmental tracer study, it is likely that the same recharge assumptions would have been made as in previous studies (Piteau, 2006; Waterline, 2010) and overlooked the contribution of MBR. Insights from environmental tracers; however, significantly improved the understating of recharge to the Gibsons aquifer which has substantial implications for the water budget, aquifer vulnerability and source water protection.   4.7 Conclusions A three-dimensional numerical groundwater model has been developed based on the conceptual model updated by results from the environmental tracer study and calibrated to both observed water levels and noble gas estimated recharge elevations in order to determine recharge rates, the contribution of MBR and the overall water budget of the Gibsons aquifer. The model was also compared to a bench model that represented previous conceptual models that did not consider MBR or recharge through the mountain block. Modeling results indicate that: - Calibration to recharge elevations estimated using noble gas data was essential to constraining recharge rates and zones in the numerical model. - Modeling results and noble gas data indicate that approximately 45% of recharge to the Gibsons aquifer is contributed by MBR - If MBR was not considered, the Vashon Till and Capilano glacio-fluvial deposits near the base of Mt. Elphinstone would be the primary recharge area, contributing 65% of total recharge to the Gibsons aquifer. Based on the simulation results, the Gibsons aquifer receives approximately 5000m3 of recharge per day: ~2000 m3/day is recharged along Mt. Elphinstone and enter 107  the aquifer via MBR, ~1000 m3/day infiltrates through the Vashon Till and Capilano glacio-fluvial deposits near the base of Mt. Elphinstone, and ~2000 m3/day by leakage, fractures or windows in the basal Capilano and Vashon Till aquitard along the bench. Of this, ~2000 m3/day is extracted by wells and ~300 m3/day is diverted by artesian overflow leaving ~2700 m3/day of groundwater that discharges to the ocean and to springs. If, in the absence of the environmental tracer data no MBR was considered as previously believed, ~3000 m3/day recharged through the Vashon Till and Capilano glacio-fluvial deposits near the base of Mt. Elphinstone. Therefore, insights from the environmental tracer study were imperative for improving the understating of the conceptual model and recharge to the Gibsons aquifer which has significant implications for the overall water budget, aquifer vulnerability and source water protection.  An extensive sensitivity analysis was performed to assess the impact that modeled parameter values have on water levels, recharge elevation and the percent of MBR. Recharge rates have the largest degree of influence on all model outputs and hydraulic conductivity values in the Pre-Vashon and Vashon zones have a large influence on water table and recharge elevations, despite only modest variations from the base case values. Similarly, the modeled hydraulic conductivity of the Pre-Vashon zone falls within the range of the numerous conductivity values measured in previous studies, therefore its significant influence on model output increases the confidence of the value assigned. The hydraulic conductivity value assigned to the Vashon Till zone is within range of values recorded in literature; however, because the range is wide and no local field tests or measurements have been conducted, further work or field studies should be considered in order to better constrain the conductivity of the Vashon Till. 108   Model results suggest that ~45% of recharge to the Gibsons aquifer come from the mountain block. As a result, further work to constrain bedrock conductivity should be done. Because recharge elevation is the only calibration data available along the Mountain, where most of the bedrock is located, two additional sensitivity analyses were conducted in the absence of additional hydrogeological data; 1) a detailed analysis of sensitivity and variance of recharge elevation on a well by well basis, and 2) sensitivity of bedrock geometry to water levels and recharge elevation. The analysis of sensitivity and variance of recharge elevation helped to evaluate and compare more detailed flow patterns such as flow path length, pumping effects and groundwater mixing.   Wells with minimal mixing and low recharge elevations were less sensitive to parameter value changes than wells with minimal mixing but higher recharge elevations. Active pumping wells were moderately sensitive, but show greatest variance of recharge elevation due to groundwater mixing. Results from the sensitivity to bedrock geometry analysis show that bedrock geometry significantly influences recharge elevation but minimally affects the water table elevation. These results solidify that the use of noble gas estimated recharge elevations provide an additional and sensitive calibration target for minimizing model non-uniqueness.    109  Chapter  5: Future Groundwater Scenarios 5.1 Introduction  Numerical groundwater flow models are often constructed in order to simulate future groundwater conditions. Based on the available data and observations, a calibrated numerical model represents the current groundwater flow system and can be used as a baseline to evaluate an aquifer?s response to changing use, hydrologic or climate conditions. Therefore, numerical groundwater models can be valuable predictive tools for management of groundwater resources (Wang and Anderson, 1982).   In the previous chapter a calibrated numerical groundwater model was built in order to better understand the present day groundwater flow system and overall water budget of the Gibsons aquifer. The objective of this chapter is to simulate the long-term effects of increased pumping due to population growth and decreased recharge rates caused by climate change on the Gibsons aquifer in order to provide insight for the Town of Gibsons to guide sustainable management of their groundwater resource.  5.2 Expected growth and increase in groundwater demand The population of the Town of Gibsons has steadily increased over the last century. Since 1986, the Town of Gibsons has recorded almost 70% growth. Figure 44 displays population trends observed since 1981 and projected trends based on low (1%), medium (2.5%) and high (4%) per year growth rates (Delcan, 2005). Within the current boundaries, the Town?s full build-out capacity is an estimated 10,000 people. Given the high, 4% growth rate, the Town of Gibsons could reach full build-out as early as 2026.   110   Figure 44 (Modified from Town of Gibsons Official Community Plan, 2013)   Even though current growth appears to be following the low, 1% trend, the Town of Gibsons is planning for significant growth over the next few decades. The Official Community Plan (Town of Gibsons, 2013) outlines several developments planned within the Town including the Upper Gibsons Neighbourhood Plan, Gospel Rock, and the Harbour Plan Area (Figure 45). These developments are designed to accommodate up to about 3,000 additional people to the Town over a 25 to 50 year timeframe.    4,535 4766 5009 5,657 6,400 7,242 7,034 8,559 10,743 2,601 2,675 3,140 3,732 3,906 4,182 4,473  0 2000 4000 6000 8000 10000 12000 1981 1986 1991 1996 2001 2006 2011 2016 2021 2026 Low Growth (1%) Medium Growth (2.5%) High Growth (4%) Measured Population by Canadian Census 111   Figure 45 Future developments in the Town of Gibsons Official Community Plan (2013).   Current groundwater demand is approximately 1856 m3/day based on the total volume of groundwater extracted by Town supply wells in 2011 (Chapter 2). If the total Town of Gibsons population eventually reaches full build out (10,000 people), groundwater demand could increase to 4183 m3/day assuming 73% of the population (7,300 people) is supplied groundwater and the average water use per person per day remains at approximately 0.573 m3/day. Given the calculated safe yields of the three active Town of Gibsons supply wells listed in Table 16, the maximum population that could be supplied groundwater without drilling any new wells is approximately 6,200 112  people. As a result, at least one new supply well would be required in order to meet the groundwater demand under full build out.   Table 16. Estimated safe yields (Piteau, 2006) Well Safe Yield (m3/day) Town Well 1 1,097 Town Well 3 1,313 Town Well 4 1,149 Total  3,359  5.3 Effects of climate change Direct observations of recent climate change documented in the most recent assessment report by the Intergovernmental Panel on Climate Change (IPCC, 2007) include: warming atmospheric temperatures, increasing atmospheric water vapor content, changing precipitation and evaporation patters, modified wind and ocean circulation patterns, increases in intensity and frequency of storm events, decrease in snow accumulation, reduction in sea ice and glacier cover, warmer ocean temperatures and sea level rise. All of these impacts can have an effect on global water resources (Milly et al., 2005; Vorosmarty, 2000) and in particular, groundwater (Kundzewicz and D?ll, 2009).  Numerous studies show that climate change can affect recharge rates (Eckhardt and Ulbrich, 2003; D?ll and Fl?rke, 2005; Holman, 2006; Scibek and Allen; 2006; Jyrkama and Sykes, 2007; D?ll, 2009; Allen et al., 2010; Neukum and Azzam, 2012) and accelerate the risk of salt-water intrusion into coastal aquifers due to sea level rise (FitzGerald et al., 2005; Masterson and Garabedian, 2007; Werner and Simmons, 2009; Lo?iciga et al., 2012).  113  At the local scale, Pike et al. (2010) performed a literature review on recent climate change and possible future climate scenarios for British Columbia. Research suggests that the study area, within the Southwest Coast region of BC, could experience increased temperatures of approximately 1.5?C and annual precipitation to increase by 6 mm by 2050 as a result of climate change. Precipitation however, is expected to vary seasonally and, in summer months, precipitation could decrease by up to 13%. Snow accumulation in the Coast Mountains is projected to decrease with increasing air temperatures, melt earlier and more rapidly in the spring.  5.3.1 Recharge rates It is difficult to predict the effect that climate change will have on recharge rates due to all of the potential variables that play a role in recharge and are affected by climate: precipitation, vegetation, run-off, stream flow, soil, and land use (Feddema and Freire, 2001; Loukas et al., 2002; Yusoff, et al., 2002; Holman, 2006; Scibek et al., 2008; Neukum and Azzam, 2012). On the global scale, D?ll (2009) suggests that climate change could impact long-term average groundwater recharge rates by ?10%. However, Allen et al. (2010) found that in the Sumas Aquifer located in the Fraser Valley, within the same region as the study area, recharge rates could increase up to 23.2% or decrease down to -1.5%, depending on the global climate model used.  One of the observed impacts of increasing atmospheric temperature is the decline of snowfall, accumulation, and the timing and release of spring melt on the Coast Mountains (Pike et al., 2010). Both the noble gas calculated recharge temperatures and the enrichment of the oxygen and deuterium heavy isotope fraction suggests that a large 114  component of recharge to the Gibsons Aquifer is contributed by snowmelt. Therefore, the decline in recharge along Mt. Elphinstone due to snowmelt may have considerable impacts to the Gibsons aquifer. The effect of snow accumulation and snowmelt, along with additional local-scale effects of climate change were not considered in previous recharge estimates and should be taken into consideration for future groundwater scenarios of the Gibsons aquifer.  5.3.2 Sea level rise and salt water intrusion Global melting of snow and ice due to rising atmospheric and ocean temperatures may result in sea level rise that can increase the potential for salt water intrusion into coastal aquifers (FitzGerald et al., 2005; IPCC, 2007). Mean sea level rise predictions along the coastline of the study area range from 0.20 to 0.33 m and extreme sea level rise predictions estimate between 0.89 to1.03 m (Government of Canada, 2008). Additionally, extreme sea level events, related to intense storms, can cause sea levels to reach one meter higher than predicted high tide levels and local coastal seafloor morphology can control wave run-up effects that can create even higher sea levels at a particular location.  Given the coastal nature of the Gibsons aquifer, and the proximity of the Town supply wells to the coastline, salt water intrusion could be a concern to the Gibsons aquifer, especially considering the effects of sea level rise due to climate change. Unfortunately, the location of the fresh water-salt water interface at the point where the Gibsons aquifer discharges to the ocean is unknown. Because the aquifer experiences significant artesian pressure near the coastline, some natural protection exists against salt-115  water intrusion due to the hydraulic gradients. This is only the case as long as increased groundwater extraction from the Gibsons aquifer does not induce salt-water intrusion.  Sea level rise and salt-water intrusion is difficult to assess due to the density differences between salt water and groundwater.  In order to properly assess the potential for salt-water intrusion into the Gibsons aquifer, the current location of the fresh water-salt water interface along with a density dependent numerical groundwater model are required. Ferguson and Gleeson (2012) suggest that coastal aquifers may be more vulnerable to increased groundwater extraction than to predicted sea level rise. Their research emphasizes the fact that time and money spent on long term monitoring and management of groundwater extraction is far more beneficial than efforts to understand and adapt to sea level rise.  In the Gibsons aquifer, there is a much higher risk of inducing salt water intrusion by groundwater extraction than by sea level rise because increased drawdown due to by pumping far exceeds predicted sea level rise caused by climate change. In addition the Town supply wells have increased risk due to the fact that all of the active supply wells (TW1, TW3. TW4) are screened below sea level as indicated in Table 17.  Table 17 Summary of Town Well completion data. Well Ground Elevation (mASL) Top of Screen Elevation (mASL) Bottom of Screen Elevation (mASL) Well Depth (mBG) TW 1 12.7 -7.1 -10.2 42 TW 2 18 4.9 3.4 15 TW 3 18.5 -2.5 -5.8 26 TW 4 13 1.1 -2.5 20   116  5.4 Approach  5.4.1 Future groundwater demand scenarios Future groundwater demand scenarios were selected based on the medium and high 2026 population projections as well as the maximum population that the current supply wells could safely yield. The base case model, described in Chapter 4, is used as the current, base case scenario. Average water use per person per day used in the base case scenario is higher than in all other scenarios because numerous household leaks were fixed in 2011 and average water use decreased from 0.619 m3/day to 0.573 m3/day. As a result, all future groundwater use scenarios assume the up to date 2011 water use data in order to estimate future groundwater demand. All future groundwater scenarios are described in Table 2.  Total groundwater supply is distributed between the active Town of Gibsons supply wells as shown in Table 19. As discussed, average extraction rates from supply wells in the base case scenario are derived from recorded data from 2009 to 2011. Average pumping rates in Scenario 1 are equally distributed between the three active wells and pumping rates in Scenario 2 are the safe yields calculated for each well. Scenario 3 requires an additional supply well and has been subdivided into two scenarios: 3a and 3b. Scenario 3a assumes equally distributed average pumping rates between the four supply wells and Scenario 3b uses varied pumping rates. The rationale for the varied rates will be discussed in section 5.5.    117   Table 18 Future groundwater demand scenarios Name Total population Population on groundwater (73%) Average groundwater use per person (m3/day) Total Groundwater Supply (m3/day) Description Base Case 4,437 3,239 0.671 2006.2 Based on current population and average groundwater use recorded from 2009-2011. Scenario 1 7,000 5,110 0.573 2928 Predicted total population based on medium (2.5%) growth rate. Scenario 2 8,508 6,211 0.573 3559 Calculated population based on existing wells operating at estimated safe yields.  Scenario 3 10,000 7,300 0.573 4182.9 Predicted total population based on high (4%) growth rate.    In addition to the groundwater extracted for groundwater supply, groundwater extracted by the privately owned Strata well as well as the artesian overflow from Town Wells 1 and 4 are also included in total groundwater output from the Gibsons aquifer. Because water from the Strata well is only used to supply a water feature, it has been assumed that the well continues to pump at 100 m3/day.  This is the same rate used in the calibrated base case model. The rates of artesian overflow are also assumed to be the same as average rates recorded from 2009 to 2011 and used in the base case model. This is a conservative approach because increased pumping from the aquifer would likely result in lower rates of artesian overflow.       118  Table 19. Model Scenario Input Data    Base Case Scenario 1 Scenario 2 Scenario 3a Scenario 3b Town of Gibsons Water Supply TW1 (m3/day)  176.2 976 1097 1045.7 1097 TW3 (m3/day)  1667.1 976 1313 1045.7 1313.0 TW4 (m3/day)  164.4 976 1149 1045.7 272.9 Added Well       1045.7 1500.0 Total (m3/day) 2006.2 2928 3559 4182.9 4182.9 Additional Groundwater Extraction TW1 Overflow (m3/day) 163.3 163.3 163.3 163.3 163.3 TW4 Overflow (m3/day) 106.7 106.7 106.7 106.7 106.7 STRATA Condo (m3/day) 100 100 100 100 100 Grand Total OUT (m3/day) 2376.2 3298 3929 4552.9 4552.9  5.4.2 Climate scenarios  The study area within southwestern British Columbia is anticipated to experience climate change over the next century; however, as discussed in section 5.3.1, it is difficult to predict exactly how changes in climate and precipitation will affect recharge to the Gibsons aquifer. Because increased recharge rates results in higher water levels, only decreased recharge rates are applied to the future modeling scenarios in order to assess worst-case scenarios. Because the model is not density dependent, the effects of sea level rise were not included in the future groundwater scenarios. However, because salt-water intrusion is a concern for the Gibsons aquifer, it is also unacceptable to exceed drawdown below sea level.  Climate scenarios are broken into two categories: overall recharge and mountain recharge. Decrease in overall recharge is applied across the entire model in increments of -5%, -10% and -15% of base case recharge values. This approach is meant to simulate general overall changes in precipitation, run-off, or land use that would result in negative 119  recharge rates across the entire study area. In the mountain recharge scenarios, intervals of -10%, -30% and -50% of base case recharge values are applied to only the mountain recharge zone. This approach is taken in order to assess the effect that decreased snowmelt contribution could have on water levels in the Gibsons aquifer.   5.5 Results   Future modeling scenario results are summarized in Table 20. Model results are shown in elevation of drawdown in meters above sea level (mASL). According to British Columbia Ministry of Environment regulations, it is best practice to prevent drawing water levels down past 70% of the available drawdown and it is unacceptable to drawdown below the top of screen elevation. Results are compared to the elevation at the top of each well?s screen as well as the elevation at 70% of the available drawdown or 0 mASL if the elevation at 70% drawdown is below sea level. It is important to note that the non-pumping heads in all of the Town Wells are unknown and have been assumed 2 meters above ground level.     120  Table 20. Future modeling scenario results. Values in black indicates predicted drawdowns that are above the elevation at 70% drawdown or sea level, orange values exceed the elevation at 70% drawdown but remain above the well screen and above mean sea level, and red indicates that the drawdowns are predicted to drop below the top of the well screen elevation or below mean sea level. Scenario Well Name Top of Screen Elevation (mASL) Elevation at 70% drawdown* or Sea Level (mASL) No Climate Change Drawdown Elevation (mASL) Overall Recharge Mountain Recharge 5% Decrease  10% Decrease  15% Decrease  10% Decrease  30% Decrease  50% Decrease  Drawdown Elevation (mASL) Drawdown Elevation (mASL) Drawdown Elevation (mASL) Drawdown Elevation (mASL) Drawdown Elevation (mASL) Drawdown Elevation (mASL) Base Case TW1 -7.1 0 12.70 11.55 10.38 9.79 11.51 10.07 8.71 TW3 -2.5 2.4 11.91 10.75 9.57 8.98 10.72 9.25 7.86 TW4 1.1 3.3 13.14 11.98 10.80 10.19 11.93 10.49 9.11 Scenario 1 TW1 -7.1 0 7.50 6.86 6.67 5.27 6.91 5.42 2.98 TW3 -2.5 2.4 8.66 8.01 7.86 6.40 8.05 6.55 4.07 TW4 1.1 3.3 7.47 6.80 6.55 5.15 6.87 5.32 2.78 Scenario 2 TW1 -7.1 0 5.33 4.14 3.09 1.72 4.89 2.52 -0.31 TW3 -2.5 2.4 6.37 5.59 4.09 2.67 5.94 3.52 0.57 TW4 1.1 3.3 5.20 3.99 2.88 1.44 4.72 2.27 -0.62 Scenario 3a TW1 -7.1 0 2.42 1.95 0.01 -1.69 1.12 -0.77 -3.52 TW3 -2.5 2.4 3.58 3.10 1.09 -0.48 2.23 0.30 -2.59 TW4 1.1 3.3 2.48 1.97 0.01 -1.97 1.14 -0.80 -3.59 New Well -5 0 3.71 2.56 0.64 -0.91 1.74 -0.11 -2.85 Scenario 3b TW1 -7.1 0 2.38 1.82 0.76 -1.09 1.99 -0.88 -3.21 TW3 -2.5 2.4 2.70 2.13 1.02 -0.79 2.31 -0.71 -3.24 TW4 1.1 3.3 3.37 2.79 1.73 -0.28 2.96 0.13 -2.09 New Well -5 0 2.24 1.69 0.63 -1.13 1.86 -1.01 -3.38 * Assume non-pumping head 2 is m above ground level at well location.          121   Drawdown elevations that are predicted to be above the elevation at 70% drawdown and above mean sea level are acceptable groundwater conditions. Predicted drawdown elevations that exceed the elevation at 70% drawdown but remain above the well screen and above mean sea level indicates a warning signal and the Town would be required to reduce pumping. Drawdown elevations that are predicted to drop below the top of the well screen elevation or below mean sea level represent unacceptable predicted groundwater conditions. The following statements summarize the predictive modeling results: - If recharge rates remain the same, under no climate change, modeled drawdown elevations are above 70% available drawdown elevations and above sea level under all scenarios except for Scenario 3a. In Scenario 3a, the drawdown elevation in TW4 is below the 70% available drawdown elevation. Because TW4 has the highest top of screen elevation, pumping rates were varied amongst the supply wells and specifically the rate in TW4 was significantly decreased in Scenario 3b (Table 19). As a result, all predicted drawdown elevations in Scenario 3b have acceptable values.  - Scenario 1 has acceptable drawdown elevations under all climate scenarios except when mountain recharge is decreased by 50%. Under these conditions, the drawdown elevation in TW4 exceeds 70% available drawdown.  - Scenario 2 has acceptable predicted drawdown elevations under both 5% decrease in overall recharge and 10% decreases in mountain recharge. Again, the drawdown elevation in TW4 dips below 70% available drawdown under 10% and 15% decrease in overall recharge as well as 30% decrease in mountain recharge. 122  Under the 50% decrease in mountain recharge scenario, all predicted drawdown elevations are either below sea level or 70% available drawdown. - Under any climate change scenarios, Scenarios 3a and 3b either exceed 70% available drawdown elevation, sea level, or the elevation at top of the well screen.    Future modeling scenario results are useful to help predict the aquifer?s response to increased pumping as well as decreased recharge rates due to climate change. Results are general and are only intended to provide insight for the Town to better guide sustainable groundwater management. In order to ensure groundwater sustainability the Town of Gibsons must conduct long-term groundwater monitoring to accurately measure the aquifer?s response to varying climatic and pumping conditions, warrant sustainable groundwater use by managing current and future groundwater extraction, and increase public awareness and involvement on groundwater sustainability and aquifer protection initiatives.   5.6 Sustainable groundwater management  5.6.1 Long-term groundwater monitoring  The monitoring well network set up by Waterline (2010) enables the Town to monitor long-term groundwater levels as well as groundwater quality. As a part of this study, Waterline (2013) also developed a groundwater monitoring program. The program outlines monitoring frequency, water level threshold values and water quality indicator parameters as a guide for the Town of Gibsons.    123  5.6.2 Sustainable groundwater extraction and use  Sustainable groundwater use and the management of current and future groundwater extraction are critical for aquifer management. The Town of Gibsons has already taken initial measures in order to sustain groundwater use. In 2008, the Town began to install residential water meters that, as of 2011, charge water use on a user pay system (Town of Gibsons, 2010). It is anticipated that by the end of 2013 all businesses and homes will be equipped with water meters. With the onset of water metering in 2011 and the detection of numerous household leaks, average groundwater use per person per day significantly decreased. It is expected that groundwater use will decrease further once all commercial water use is metered. The Town is also trying to educate the public on water conservation and aquifer protection tips.   Additional measures can be taken by the Town to reduce groundwater use. Approximately 275 m3/day of artesian overflow from TW1 and TW4 is being diverted to the storm sewer. If the Town captured and used this overflow, an additional 480 residents could be serviced based on current average water use estimates. Additionally, the Town?s groundwater distribution system is aging and contains numerous leaks. A long-term goal for the Town of Gibsons should be to update the distribution system.  5.6.3 Community outreach and involvement   Community awareness and involvement is an essential aspect to groundwater sustainability. As part of the community outreach component of the Aquifer Mapping Study, Gordon Groundwater (2013) developed a Gibsons aquifer interpretive tour called 124  ?Sustain, Promote, and Protect the Gibsons Aquifer?. The interpretive tour was piloted during Drinking Water Week 2013 and received positive feedback from the community.   The Town of Gibsons also tries to promote groundwater awareness and involvement on groundwater sustainability by welcoming the public to presentations of updates on the Aquifer Mapping Study and by regular posts in the local newspapers. The Town of Gibsons also actively promotes their initiative and proactive approach to initiating the Gibsons Aquifer Study by attending and presenting at conferences and entering international contests, such as International Awards for Liveable Communities (Livcom, 2009).   5.6.4 Additional factors that affect groundwater sustainability Groundwater sustainability has been defined by Alley et al. (1999) as ?the development and use of groundwater in a manner that can be maintained for an indefinite time without causing unacceptable environmental, economic or social consequences?. Additional factors that could have environmental, economic or social consequences on groundwater sustainability include: groundwater-surface water interaction, salt water intrusion and sea level rise, groundwater vulnerability to contamination, land development and change in land cover and land use, geotechnical risks, and transboundary issues with neighbouring communities. In order to ensure groundwater sustainability, further work is required in order to better understand the potential consequences of these impacts, as listed in Table 21.   125  Table 21 List of potential impacts and further work needed to better understand potential consequences on groundwater sustainability. Impact Further Work Potential Consequence Groundwater-surface water interaction Better understanding of groundwater-surface water interaction as well as groundwater discharge to the ocean Ecosystems may rely on groundwater discharge to creeks and ocean Salt water intrusion and sea level rise Installation of monitoring wells required to locate fresh-water salt water interface and monitor groundwater for salt water intrusion and potential effects of sea level rise Groundwater contamination Groundwater vulnerability to contamination Source water protection and inventory of potential contaminants. Contamination of groundwater, health effects, groundwater treatment Land development and change in land cover and land use Assessment of current land cover and land use as well as future development plans, permeable surfaces, and vegetation Recharge and potential contamination affects Geotechnical risks Geotechnical assessment prior to any development Lower Gibsons where the aquifer is flowing artesian and the aquitard could be breached Aquifer blow-out, significant loss of groundwater and groundwater storage Transboundary issues The Gibsons aquifer is beneath both the Town of Gibsons and the SCRD - partnership required in development of successful bylaws and policies that affect groundwater sustainability  Unaccounted groundwater extraction, groundwater contamination  5.7 Conclusions The long-term effects of increased pumping due to population growth and decreased recharge rates by climate change on the Gibsons aquifer were assessed by conducting numerous future groundwater simulations. Results indicate that if recharge rates remain constant (no climate change), the Gibsons aquifer may have the potential to support groundwater demand required by the full build out population of 10,000 people. 126  However, given a 5% decrease in overall recharge or a 10% decrease in mountain recharge, the aquifer begins to reach unacceptable predicted drawdown elevations.  Because the science of predictive modeling involves a high degree of speculation and uncertainty, future groundwater scenario results are very general and are only meant to provide the Town of Gibsons a framework to guide sustainable management of their groundwater resource. It is not guaranteed that the aquifer can sustainably support full built out. Long-term groundwater monitoring, sustainable groundwater use and management of groundwater extraction, as well as community involvement on groundwater sustainability and aquifer protection initiatives are all requirements of sustainable groundwater management. Finally, additional factors include: groundwater-surface water interaction, salt water intrusion and sea level rise, groundwater vulnerability to contamination, land development and change in land cover and land use, geotechnical risks, and transboundary issues. These factors could have environmental, economic or social consequences that need to be addressed in order to ensure groundwater sustainability.    127  Chapter  6: Conclusions  Understanding of the groundwater flow system, recharge processes and reliable estimates of the water budget are required to implement groundwater policy and management schemes to ensure groundwater sustainability (Gleeson et al., 2010; Sanford, 2002; Senthilkumar and Elango, 2004; Sophocleous, 2005; Sophocleous 2010). The Town of Gibsons, British Columbia, is a growing coastal community that supplies untreated groundwater from the underlying semi-confined sand and gravel aquifer to two thirds of its 4,300 residents. Population growth projections predict that full built-out of 10,000 residents could be reached as early as 2027. The Town of Gibsons is proud of their pristine water supply and is proactive and motivated to keep it clean and sustainable for future generations.   In this thesis, environmental tracers were used to delineate groundwater age, recharge and flow processes in the Gibsons aquifer and demonstrated that a numerical groundwater model calibrated to hydraulic heads and environmental tracer results can be effectively integrated into a groundwater planning and governance framework to provide an adequate approach for sustainable groundwater management for the Town of Gibsons and for other small to medium municipalities. Based on an improved and refined conceptual hydrogeological model of the aquifer (Chapter 2), environmental tracers of noble gases, tritium and helium (3H/3He), and stable isotopes were selected to quantify groundwater age, determine recharge locations and processes, and further refine the conceptual hydrogeological model of the Gibsons aquifer (Chapter 3). The updated conceptual model and tracer results were integrated into a regional three-dimensional numerical groundwater flow model, calibrated to both hydraulic heads and recharge 128  elevation, and used to quantify recharge rates and the overall water budget of the Gibsons aquifer (Chapter 4). The long-term effects of increased pumping due to population growth and decreased recharge rates caused by climate change were simulated in order to provide insight for the Town of Gibsons to guide sustainable management of their groundwater resource (Chapter 5).  Newman et al. (2010) promote the use of environmental tracers as insightful and cost-effective tools to investigate groundwater resources and highlight the need for additional research of using and interpreting environmental tracers in heterogeneous aquifers to test and develop hydrogeological models. This thesis exemplifies the use of environmental tracers to identify and characterize recharge mechanisms to the Gibsons aquifer and demonstrates an approach to integrate results into a regional-scale numerical groundwater flow model to evaluate water budgets and simulate long-term effects of increased pumping and climate change and to provide guidance for sustainable groundwater management. An approach similar to this can be a used by other small to medium groundwater dependent municipalities in order to investigate groundwater resources and ensure groundwater sustainability.  6.1 Environmental tracers to investigate recharge mechanisms and refine conceptual hydrogeological model The initial conceptual hydrogeological model of the Gibsons aquifer developed by Waterline (2010) was improved and refined in Chapter 2 by compiling all geological and hydrogeological information including geology, water levels and hydrogeochemistry and by creating a three-dimensional geological model based on existing well log and borehole 129  information, geophysics, and mapped surface geology. The 3D geological model was useful to assess potential inter-aquifer and groundwater-surface water interactions; however, due to the nature of the aquifer it was difficult to predict specific recharge rates, locations and processes. In Chapter 3, Environmental tracers of noble gases, tritium and helium (3H/3He), and stable isotopes were used to quantify groundwater age, determine recharge locations and processes, which helped to better understand the groundwater flow system.  Tritium and noble gas results distinguished two end members of recharge that enters the Gibsons aquifer: 1) mountain block recharge (MBR) that occurs at high elevations along the flanks of Mt. Elphinstone, flows through fractures in the bedrock, and into the Gibsons aquifer. This end member has cold recharge temperatures (~5?C), pre-modern apparent 3H/3He ages (>50 years), and high concentrations of EA (>0.005 ccSTP/g) and 4Heterr (>10-9 ccSTP/g) and 2). The second end-member is comprised of Gibsons ?bench? recharge that takes place at lower elevations, by vertical percolating through the overlying Vashon till or through gaps or recharge windows along incised creek valleys. This component of recharge has warm recharge temperatures (~9?C), modern apparent 3H/3He ages (<10 years old), and low concentrations of EA (0.001-0.003 ccSTP/g) and 4Heterr (<10-9 ccSTP/g). The depleted stable isotope signature in all groundwater samples agrees that a significant component of recharge occurs at high elevations and may have a contribution of snowmelt.  Due to the complexities of mountain-block hydrologic systems and lack of subsurface data available in mountain blocks, MBR is poorly understood (Manning, 2011). This environmental tracer study; however, revealed the contribution of MBR to 130  the Gibsons aquifer by clear, distinguishable tracer results that significantly improved the understanding of the conceptual hydrogeological model.   6.2 Integration of environmental tracers results into numerical model Environmental tracer results can provide additional, non-traditional or ?unconventional? calibration targets in numerical groundwater models (Newman et al., 2010; Sanford et al., 2011). Unconventional calibration data obtained using environmental tracer results including age and travel times (Reilly et al., 1994; Goode, 1996), solute distributions (Christensen et al., 1995; Anderman et al., 1996), heat (Bravo et al., 2002; Heilweil et al., 2012) are becoming a common approach to minimizing model non-uniqueness; however, no studies have ever used recharge elevations as calibration targets. In this thesis, noble gas estimated recharge elevation ranges were used as calibration targets in the numerical model. Recharge elevations were estimated based on an approach similar to Manning (2011) and Heilweil et al. (2012) where noble gas calculated recharge temperatures were also used as recharge elevation tracers (Zuber et al., 1995; Aeschbach-Hertig et al. 1999; Manning and Solomon, 2003; Manning, 2011; Heilweil et al., 2012). A three-dimensional numerical groundwater model was developed in Chapter 4 based on the conceptual model updated in Chapter 3 and calibrated to both observed water levels and noble gas estimated recharge elevations in order to quantify recharge rates, the contribution of MBR and the overall water budget of the Gibsons aquifer. The model was also compared to a ?no MBR? model that did not consider recharge through the mountain block.  131  Numerical modeling revealed that calibration to recharge elevations was essential to constraining recharge rates and zones in the numerical model and minimizing model non-uniqueness. Based on the overall water budget of the Gibsons aquifer, approximately 45% of recharge to the Gibsons aquifer is contributed by MBR, and ~55% by bench recharge (of that, ~20% through the Vashon Till and Capilano glacio-fluvial deposits near the base of Mt. Elphinstone, and ~35% by leakage or recharge windows through the Vashon till aquitard). If, in the absence of the environmental tracer study, MBR was not considered, the Vashon Till and Capilano glacio-fluvial deposits near the base of Mt. Elphinstone would have been interpreted as the primary recharge area, contributing approximately ~55% of total recharge to the Gibsons aquifer as previously believed by Piteau (2006) and Waterline (2010). Therefore, insights from the environmental tracer study were imperative for improving the understating of the conceptual model and recharge to the Gibsons aquifer which has significant implications for the overall water budget, aquifer vulnerability and source water protection. A rigorous sensitivity analysis was conducted to assess the impact of modeled parameter values on water levels, recharge elevation and the percent of MBR. Results from the sensitivity to bedrock geometry analysis show that bedrock geometry significantly influences simulated recharge elevation but minimally affects the water table elevation. Without the additional recharge elevation calibration targets to constrain bedrock geometry, at least four of the six altered bedrock scenarios could have been selected as the final model. This solidifies the notion that noble gas estimated recharge elevations can be used effectively as additional calibration targets for minimizing model non-uniqueness. 132  Both the calibration to recharge elevation and the analysis of sensitivity and variance of recharge elevation helped to evaluate and compare more detailed flow patterns such as groundwater mixing. Active pumping wells (TW1, TW3, and Strata) showed the greatest amount of variance, the highest degree of sensitivity and therefore the greatest amount of groundwater mixing. Monitoring wells were generally less sensitive, had lower variance in recharge elevation and therefore less mixing. These modeling results and observations are consistent with hydrogeochemistry results (Chapter 2) and tritium and noble gas results (Chapter 3) in that groundwater in the Gibsons aquifer contains a mixture of MBR (~45%) and bench (55%) recharged water (Table 22). The MBR end member is pre-modern (apparent age > 50 years), has high recharge elevation, cold recharge temperature (~5?C), evolved geochemistry (group 3), and high concentrations of EA (>0.005 ccSTP/g) and 4Heterr (>10-9 ccSTP/g). The bench end member is modern (apparent age < 10 years), has low recharge elevations, warm recharge has warm recharge temperature (~9?C), non-evolved geochemistry (group 1) and low concentrations of EA (0.001-0.003 ccSTP/g) and 4Heterr (<10-9 ccSTP/g). 133  Table 22 Summary and assessment of groundwater mixing based on all results from all of the wells that were included in the model.   Recharge Elevation Ranges (mASL)Active supply well Monitoring well Active supplu well Active pump well Active supply well Inactive supply Monitoring well Monitoring well Monitoring well6 5.8 5.9 6.3 7.9 7.6 7.6 8.6 9.131 86 22 13 18 20 33 12 80.0025 0.0061 0.0029 0.0028 0.0013 0.0024 0.0045 0.0027 0.00311.25E-09 3.31E-08 -2.38E-10 -5.06E-10 1.68E-11 -5.50E-10 1.04E-08 -3.69E-11 1.40E-101 (not evolved) 3 (evolved) 1 (not evolved) 1 (not evolved) 1 (not evolved) 1 (not evolved) 1 (not evolved) 1 (not evolved) 1 (not evolved)Very sensitive and high variranceModerate sensitivity and low varianceHigh sensitivity and high varianceHigh sensitivity and high varianceLow sensitivity, low varianceLow sensitivity, low varianceHigh sensitvity, low varianceLow sensitivity, low varianceLow sensitivity, low varianceMixture of MBR and bench rechargeMostly MBRMixture of MBR and bench rechargeMixture of MBR and bench rechargeMixture, but mostly bench rechargeMixture, but mostly bench rechargeMixture, or mid-mountain rechargeBench recharge Bench rechargeWell TypeResults SummaryRecharge Temp (?C) Apparent Age (years)Excess Air (EA)Geochemistry GroupSensitvity and  Recharge Elevation Variance4Hterr (ccSTP/g)0 200 400 600 800 1000 1200 Town Well 1 WL10-01 Town Well 3 Strata Town Well 4  Town Well 2 WL10-02 MW06-1A MW06-2A 134  6.3 Groundwater Scenarios, limitations and future research  The long-term effects of increased pumping due to population growth and decreased recharge rates by climate change on the Gibsons aquifer were assessed in Chapter 5 by conducting numerous simulations for future groundwater scenarios. Results indicate that under no climate change, the Gibsons aquifer may have the potential to support groundwater demand required by the full build out population of 10,000 people. However, given a 5% decrease in overall recharge or a 10% decrease in mountain recharge, the aquifer could reach unacceptable predicted drawdown elevations. It is important to remember that predictive modeling is an uncertain science and due to study limitations it is not guaranteed that the aquifer can sustainably support full build out.   Future groundwater scenario results are general and can only be used to help guide sustainable groundwater management. Long-term groundwater monitoring, sustainable groundwater use, management of groundwater extraction, and community involvement initiatives are required to ensure groundwater sustainability. Furthermore, limitations throughout this research as well as additional factors that could have environmental, economic or social consequences need to be addressed. Limitations in this research include: - Tritium and noble gas results are limited by the assumed ratio of terrigenic 3He/4He (Rterr = 2.01 x 10-7) as well as the potential 3He losses due to matrix diffusion in bedrock (Cook et al., 1996). - Although numerical modeling was effective using the finite difference MODFLOW-2000 code given the amount of calibration data available, a finite element code would be more appropriate to handle steep hydraulic and topographic gradients. If more 135  calibration data were available, such as stream flow data and soil properties, a modeling code with unsaturated zone capabilities would be a more reliable. - The Gibsons aquifer is a coastal aquifer that hydraulically connected to the ocean. In order to accurately represent the groundwater system, the location of the fresh water-salt water interface and use a density-dependent numerical groundwater model is required. This is particularly important for the evaluating the potential for salt-water intrusion and effects of sea level rise.  Additional factors that could have environmental, economic or social consequences to groundwater sustainability require further work. These factors include: groundwater-surface water interaction, salt-water intrusion and sea level rise, groundwater vulnerability, land development and change in land cover and land use, geotechnical risks, and transboundary issues. In particular, to further advance this research, a detailed examination of groundwater-surface water interaction is required to 1) determine base flow and ecological impacts of base flow, 2) assess the potential for recharge windows along creeks, 3) understand the connection between creeks and the bedrock aquifer in the mountain block and 4) provide calibration data for numerical modeling. These requirements are imperative for better understanding more specific recharge locations and rates, further assessing MBR characteristics, and eventually developing a fully integrated surface-water groundwater model that can more accurately represent the entire flow system. To date, a fully integrated groundwater-surface water model of a mountain block groundwater system has not been done. Wilson and Guan (2004) stated that more MBR studies are needed to improve data observation and synthesis capabilities and demonstrate predictive modeling. This thesis 136  demonstrates an approach of using noble gas derived recharge elevations as numerical model calibration targets in the mountain block where no physical calibration data exists in order to minimize model non-uniqueness so that predicted groundwater scenarios are as reliable as the data allows. 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Yusoff, I., Hiscock, K.M., Conway, D., 2002. Simulation of the impacts of climate change on groundwater resources in eastern England. In: Hiscock, K.M., Rivett, M.O., Davidson, R.M., (eds) Sustainable groundwater development. Geological Society, London, Special Publication 193: 325-344.  Zuber, A., Weise, S.M., Osenbruck, K., Grabczak, J. and Ciezkowski, W., 1995. Age and recharge area of thermal waters in Ladek Spa (Sudeten, Poland) deduced from environmental isotope and noble gas data. J. Hydrol., 167: 327-349. 152  Appendices Appendix A  Calculations A.1 Hydraulic gradient The equation for hydraulic gradient    is:        where    is the change in hydraulic head across the distance,  . The hydraulic head and distance were measured from the extent and piezometric surface map in Figure 12 (from the back of the aquifer to the coastline, approximately 3000 m).                          A.2 Average linear groundwater velocity and residence time Darcy?s flow equation:       where   is the geometric mean of the measured hydraulic conductivity values,   is the average porosity,  and    is the hydraulic gradient.                                                            Therefore,                    153                                                            A.3 Water budget calculations The overall steady state overall water budget of the Gibsons aquifer is described as;                                                                    where recharge includes precipitation that infiltrates through the Vashon Till and Capilano glacio-fluvial deposits within the Mid zone (    ), leakage from the Capilano aquifer through the basal Capilano and Vashon Till aquitard along the Bench zone (       ), and the flux of MBR through the Upper zone ? Mid zone interface (    ). Discharge includes water diverted via the private Strata condo well and the three municipal supply wells, Town Wells 1, 3 and 4 (      ), artesian overflow from Town Wells 1 and 4 (      ), discharge to springs (        ) and discharge to the ocean (      ).  To assess the overall water budget of the Gibsons aquifer and determine how much groundwater is available for use, the water budget equation is re-written as follows:                                           where         includes discharge from springs.  Therefore,                                                                      154  Appendix B  Chlorofluorocarbons and sulfur-hexafluoride B.1 Background  Chlorofluorocarbons (CFCs) are volatile, synthetic, stable halogenated alkanes first introduced into the atmosphere in the 1930?s when they began to be produced commercially for use in refrigeration (Plummer and Busenberg, 2006). CFCs have been recognized as historic tracers for groundwater studies since the 1970?s (Thompson et al., 1974; Randall and Shultz; 1976; Schultz et al., 1976; Thompson, 1976;Hayes and Thompson, 1977; Randall et al., 1977; Thompson and Hayes, 1979; Thompson et al., 1979). Three compounds of CFCs can be measured in groundwater CFC-12 (dichlorodifluorinemethane, CF2Cl2) initially produced in 1931, CFC-11 (trichlorofluoromethane, CFCl3) produced since 1936 and CFC-113 (trichlorotrifluoroethane, C2F3Cl3) first produced commercially in 1944. CFC-12 and CFC-11 were largely used as coolants in refrigerants and air conditioners but also used in propellants for aerosol cans, solvents, and blowing agents in foams, insulation and packing materials (Plummer and Busenberg, 2000). CFC-113 was used in the electronic industry for the manufacturing of semiconductor chips, vapor degreasing and cold immersion cleaning of microelectronic components and in surface cleaning solvents (Jackson et al., 1992).   In the 1980?s CFCs were recognized as contributors to ozone depletion and during the Montreal Protocol on Substances that Deplete the Ozone in 1987, 37 countries agreed to limit the production of CFCs. Since then almost all international CFC production has ceased and atmospheric concentrations peaked in 1995. Measured concentrations (atmospheric mixing ratios) of all three CFCs in the atmosphere are shown in Figure 16. It is evident that since the mid 1990?s CFCs concentration have stabilized or declined.  155   Sulfur-hexafluoride (SF6) is an odorless, colourless, nontoxic, stable, greenhouse gas recognized as an environmental and historical tracer in 1997 (Busenberg and Plummer). Atmospheric concentrations of SF6 have steadily increased since 1970 (Figure 16) due to industrial production of SF6 beginning 1953 for use in high voltage insulators and for the production of magnesium metal. Natural production of SF6 does exist in very deep igneous and volcanic fluids, but has minimal effects on shallow groundwater concentrations (Busenberg and Plummer, 2000).    Figure 46 Atmospheric mixing ratios of CFC-11, CFC-12, CFC-113 and SF6 observed at Niwot Ridge, Colorado (NOAA, 2012) compiled by Bohkle (2004).   CFCs and SF6 are mostly used in groundwater studies to determine the apparent age of young groundwater. Because atmospheric levels are well documented and CFCs and SF6 are generally stable, the measured concentrations of the gases in groundwater reflect 0 1 2 3 4 5 6 7 8 9 10 0 200 400 600 800 1000 1200 1940 1950 1960 1970 1980 1990 2000 2010 2020 Atnosheric Mixing Ratio of SF6  (pptv) Atmospheric Mixing Ratios of CFC-11, CFC-12, CFC-113 (pptv) Year CFC-11 CFC-12 CFC-113 SF6 156  atmospheric levels at the time of recharge. As a result, the measured concentration of CFCs and SF6 can be compared to atmospheric levels in order to determine the year or apparent groundwater age since recharge. Similar to noble gases, the dissolved concentrations in groundwater are a function of temperature, pressure, salinity, and excess air at the time of recharge according to Henry?s Law. Therefore, recharge parameters determined through noble gas analysis can be applied to CFCs and SF6 apparent age calculations.   B.2 Field and analytical methods Due to the high volatility of CFCs and SF6, groundwater samples for CFCs and SF6 were only collected from wells with dedicated pumps to ensure samples had no contact with the atmosphere (section 3.4). Samples were collected in 500 mL clear Boston Round glass bottles and aluminum-lines caps using the CFC Bottle Sampling Method (USGS, 2013). Bottles were rinsed with groundwater, placed standing up inside a clean bucket with the hose positioned inside and at the bottom of the bottle, and filled so that at least two liters of water overflows out of the glass bottle and into the bucket. Underwater, caps were tapped to remove all bubbles and screwed onto the bottles. Bottles were inspected to ensure no bubbles were present before caps were secured with electrical tape. Analyses were performed at the University of Miami?s Tritium Laboratory (2010) using a custom-built purge-and-trap gas chromatograph with electron capture detection. Gases were purged from water samples with inert gas, held at -15?C in a volume-focusing trap, then heated to release CFCs and SF6 into the gas chromatograph where compounds were separated and analyzed by the electron capture detector.  157  B.3 Results and discussion In order to calculate apparent groundwater ages from measured CFCs and SF6 concentrations, best estimates of recharge temperatures and elevations are required to determine atmospheric mixing ratios at the time of recharge. Best estimates of recharge temperature and elevations (Figure 19) as well as excess air values calculated in section 3.5.1 were input into the USGS? spreadsheet program (Busenberg and Plummer 2005, 2009) to calculate atmospheric mixing ratios and apparent groundwater age. Analytical CFCs and SF6 results, estimated recharge elevation and temperatures as well as excess air are summarized in Table 23a and calculated atmospheric mixing ratio and apparent CFCs and SF6 ages in Table 23b.  Table 23  CFCs and SF6 measured concentrations, atmospheric mixing ratios and apparent ages. a) Tr (?C)  EA (cc STP/g) Recharge Elevation (mASL) Measured concentrations Sample SF6 (fmol/Kg) CFC-11 (pmol/Kg) CFC-12 (pmol/Kg) CFC-113 (pmol/Kg) TW#1 2.7 0.0025 1190 0.000 0.951 0.161 0.022 TW#1 - DUP 2.7 0.0025 1190 0.000 0.847 0.190 0.020 TW#2 6.0 0.0024 680 0.000 1.318 7.433 0.017 TW#3 3.0 0.0029 1200 0.259 2.039 110.4 0.049 TW#4 4.6 0.0013 900 0.113 1.406 0.434 0.021 70651 2.6 0.0072 1220 0.420 0.103 0.541 0.021 Strata 3.8 0.0028 1030 0.000 0.979 0.149 0.003        b)        Calculated mixing ratios (pptv)    Apparent Ages (years) Sample CFC-11 CFC-12 CFC-113  SF6  CFC-11 CFC-12 CFC-113 TW#1 33.976 22.966 2.469  59.3 45.1 54.5 47.5 TW#1 - DUP 31.843 27.984 2.293  59.3 45.3 53.6 48.1 TW#2 54.181 1191.1 2.194  59.3 42.0 Contam. 48.5 TW#3 73.247 15774 5.391  38.8 40.0 Contam. 42.0 TW#4 54.305 66.441 2.537  42.1 42.0 46.6 47.6 70651 3.604 74.591 2.196  36.1 56.6 45.8 48.6 Strata 36.483 21.985 0.308   59.3 44.5 55.0 58.3 158  Results show that CFC-11, CFC-12, CFC-113 and SF6 ages range from about 40 to 50 years old for all samples and that age variation on a well to well basis is comparable to age variation for a single well calculated by each tracer. As a result, it is difficult to interpret groundwater flow patterns or recharge characteristics from the CFCs and SF6 data alone.  Additionally, the CFCs and SF6 apparent ages are all generally older than the apparent 3H/3He ages (Table 7a) calculated for the same wells. These results could be caused by a number of reasons including the possibility that the CFCs and SF6 samples were degassed, or by limitations in either of the tracer methods.  Degassed samples would result in apparently older ages as atmospheric concentrations of CFCs and SF6 have increased with time. Because all ages in all wells are very similar, there is a good possibility that all samples were degassed prior to analysis. Age discrepancies could be attributed to the thickness of the unsaturated zone above the upper portion of the aquifer. In comparison to the 3H/3He method where the ?clock? starts as soon as produced 3He is trapped beneath the water table, given any amount of initial 3H, the CFCs and SF6 method assumes that pore-air directly above the water table has CFCs and SF6 concentrations equivalent to that of the atmosphere at the time of recharge. Cook and Solomon (1995) show that unsaturated zones thicker than 10 m in coarse grained soils can cause a ?lag time? and result in older apparent groundwater ages. In order for pore air to be equivalent to atmospheric, it is required that gases flow advectively through the unsaturated zone. At greater depth however diffusive transport dominates and soil air is no longer equivalent to atmospheric air (Farrell et al., 1966; Kimball and Lemon, 1972).  159  In areas along Upper Gibsons, the depth to top of the Gibsons aquifer water table can exceed 100 m. Therefore it is unrealistic to assume that pore air directly above the water table is equivalent to atmospheric air at the time of recharge. The combined limitations make it difficult to draw any meaningful conclusions from the CFCs and SF6 data, and make it impractical to use lumped parameter mixing models to asses groundwater mixing and mean apparent ages (Zuber and Maloszewski, 1996).  Additional limitations that could further affect apparent CFCs and SF6 ages include microbial degradation of CFCs in anaerobic environments (Khalil and Rasmussen, 1989; Semprini et al., 1992; Lovley and Woodward, 1992), CFC sorption (Ciccioli et al., 1980; Brown, 1980; Jackson et al., 1992), matrix diffusion (Cook and Simmons, 2000), hydrodynamic dispersion (Weissmann et al., 2002) terrigenic sources of SF6 (Busenberg and Plummer, 2000, Koh et al., 2006, 2007), and contamination of both CFCs and SF6 (Kjeldsen and Christophersen, 2001; Kjeldsen and Jensen, 2001; Cook et al., 2006). In the Gibsons aquifer, it appears that two wells, TW2 and TW3, are contaminated in CFC-12. The atmospheric levels of CFC-12 in TW2 (~1,200 pptv) and TW3 (~16,000 pptv) are considerably higher than background concentrations (22-75 pptv) observed in the rest of the wells. The source of CFC-12 contamination is unknown.  All three CFC concentrations can be affected by sewage effluent and the Town of Gibsons sewer treatment plant is located within 200 m upstream from both wells and could be a potential source of contamination. However, Morris et al. (2005) found that concentrations of CFC-12 in a moderately sized aquifer were more than ten times atmospheric levels due to 1/10th of the available CFC-12 contamination from a single domestic refrigerator. There could be a number of potential 160  sources of the CFC-12 contamination and further work is required in order to further assess the sources.   B.4 Conclusions CFCs and SF6 results were inconclusive due the potential that samples degassed and by limitations in the method exacerbated by thick unsaturated zones. Because the depth to the top of the Gibsons aquifer can exceed depths of 100 m along Upper Gibsons, it is inappropriate to assume that pore air directly above the water table is equivalent to atmospheric air at the time of recharge, especially with a perched aquifer on top. CFCs and SF6 results, however, revealed that Town Well 2 and 3 are contaminated in CFC-12. This could indicate possible refrigerant or septic contamination that could be an early warning signal for potential contamination to the Town of Gibsons groundwater supply.  161  Appendix C  Lab Certificates C.1 University of Utah?s dissolved and noble gas analytical results  Sample I.D. N2 total (ccSTP/g) Ar total (ccSTP/g) Ne total (ccSTP/g) Kr total (ccSTP/g) Xe total (ccSTP/g) He4 (ccSTP/g) R/Ra Tritium (TU) Tritium (error +/-) MW06-1A 1.66E-02 4.38E-04 2.29E-07 9.43E-08 1.45E-08 5.26E-08 1.07 2.65 0.16 MW06-2A 1.71E-02 4.45E-04 2.27E-07 9.15E-08 1.45E-08 5.33E-08 1.09 4.86 0.28 MW06-2B 1.61E-02 4.19E-04 2.46E-07 1.02E-07 1.37E-08 5.69E-08 1.00 3.31 0.13 WL10-01 2.01E-02 4.88E-04 2.89E-07 1.11E-07 1.57E-08 1.00E-07 0.83 0.05 0.05 WL10-02 1.82E-02 4.67E-04 2.51E-07 1.03E-07 1.53E-08 6.79E-08 1.36 3.52 0.21 TW1  4.54E-04 2.39E-07 1.08E-07 1.55E-08 5.57E-08 1.59 3.93 0.23 TW2  4.41E-04 2.43E-07 9.88E-08 1.44E-08 5.23E-08 1.41 5.67 0.34 TW3  4.63E-04 2.46E-07 1.09E-07 1.56E-08 5.43E-08 1.34 4.28 0.25 TW4  4.13E-04 2.30E-07 1.02E-07 1.44E-08 5.37E-08 1.31 5.54 0.32 Chaster  4.97E-04 3.15E-07 1.16E-07 1.57E-08 7.79E-08 0.99 1.77 0.07 STRATA   4.45E-04 2.52E-07 1.08E-07 1.50E-08 5.42E-08 1.24 6.62 0.24          Sample I.D. Age - using Ne only (yrs) Ne Age (error +/-) Age - using EA (yrs) EA Age (error +/-) Rterr - assumed Tot Dis Gas (atm) Lab O2 (mg/l) ?Ne (%) MW06-1A 6.1 2.0 10.1 1.0 2.01E-07 1.00 6.0 13.7 MW06-2A 7.5 0.8 9.1 0.8 2.01E-07 1.01 5.8 10.8 MW06-2B -9.9 4.3 -2.1 1.3 2.01E-07 1.07 6.2 22.1 WL10-01 >60 * >60 * 2.01E-07 1.07 0.0 40.2 WL10-02 31.4 1.0 33.0 1.3 2.01E-07 0.97 0.0 24.3 TW1 31.3 1.3 31.8 1.2 2.01E-07   14.30 TW2 17.9 1.91 18.8 1.5 2.01E-07   19.04 TW3 20.3 1.89 21.4 1.5 2.01E-07   17.72 TW4 18.3 1.28 18.3 1.2 2.01E-07   11.83 Chaster 1.7 9.6 11.8 7.1 2.01E-07   52.04 STRATA 10.0 2.1 10.0 2.0 2.01E-07     21.79         Sample I.D. Notes           MW06-1A Kr appears low, good fit (remaining gases), contains O2   MW06-2A Kr appears low, good fit (remaining gases), contains O2   MW06-2B Looks atmospheric, appears modern, contains O2   WL10-01 Good fit, excess He4, sample age sensitive to Rterr   WL10-02 Good fit, excess He4, sample age sensitive to Rterr   TW1         TW2         TW3         TW4         Chaster Sample might contain a mixture of old and new water   STRATA Sample might be slightly stripped in He but looks OK   162  C.2 University of Miami CFCs and SF6 analytical results             August 29, 2013      TRITIUM LABORATORY    Data Release #CFC11-10     University of British Columbia  CFC-097           ________________________  Dr. James D. Happell Associate Research Professor     Distribution:  Jessica Doyle 163   University of British Columbia  6339 Stores Road  Vancouver, BC V6T 1Z4 Data Release CFC11-10,  Job # CFC0097     University of British Columbia     6339 Stores Road      Vancouver, BC V6T 1Z4      Atten: Jessica Doyle      604-741-4218       jessy_doyle@hotmail.com                             Rec. Rec. Client ID Bottle Lab ID# Samp. Arrive Anal. Elev. Temp.       Date Date Date (m) oC           TW#2 1 0097.01 4/13/2011 5/2/2011 5/3/2011 350 10.20 TW#2 2 0097.01D 4/13/2011 5/2/2011 5/3/2011 350 10.20 TW#2 3 0097.D2 4/13/2011 5/2/2011 5/3/2011 350 10.20 Blank 1 0097.02 4/13/2011 5/2/2011 5/3/2011 350 10.20 Blank 2 0097.02D 4/13/2011 5/2/2011 5/3/2011 350 10.20 Blank 3 0097.02D2 4/13/2011 5/2/2011 5/3/2011 350 10.20 TW#4 1 0097.03 4/13/2011 5/2/2011 5/3/2011 350 10.20 TW#4 2 0097.03D 4/13/2011 5/2/2011 5/3/2011 350 10.20 TW#4 3 0097.03D2 4/13/2011 5/2/2011 5/3/2011 350 10.20 TW#1 1 0097.04 4/13/2011 5/2/2011 5/3/2011 350 10.20 TW#1 2 0097.04D 4/13/2011 5/2/2011 5/3/2011 350 10.20 TW#1 3 0097.04D2 4/13/2011 5/2/2011 5/3/2011 350 10.20 TW#3 1 0097.50 4/13/2011 5/2/2011 5/3/2011 350 10.20 TW#3 2 0097.5D 4/13/2011 5/2/2011 5/3/2011 350 10.20 TW#3 3 0097.05D2 4/13/2011 5/2/2011 5/3/2011 350 10.20 Chaster 1 0097.06 4/22/2011 5/2/2011 5/3/2011 350 10.20 Chaster 2 0097.06D 4/22/2011 5/2/2011 5/3/2011 350 10.20 Strata 1 0097.07 4/19/2011 5/2/2011 5/3/2011 350 10.20 Strata 2 0097.07D 4/19/2011 5/2/2011 5/3/2011 350 10.20 Strata 3 0097.07D2 4/19/2011 5/2/2011 5/3/2011 350 10.20                   D in column three indicates duplicate sample,      there is no charge for this analysis.                                                164  Data Release CFC11-10,  Job # CFC0097     University of British Columbia      6339 Stores Road       Vancouver, BC V6T 1Z4       Atten: Jessica Doyle       604-741-4218        jessy_doyle@hotmail.com        Water Concentration             Corrected for Stripping Efficiency     Client ID SF6 error CFC12 error CFC11 error CFC113 error   fmol/kg   pmol/Kg   pmol/Kg   pmol/Kg               TW#2 0.000 0.050 7.367 0.147 1.283 0.026 0.014 0.010 TW#2 0.000 0.050 7.490 0.150 1.338 0.027 0.019 0.010 TW#2 0.000 0.050 7.441 0.149 1.332 0.027 0.018 0.010 Blank 0.000 0.050 0.305 0.006 0.892 0.018 0.020 0.010 Blank 0.000 0.050 0.143 0.003 0.834 0.017 0.021 0.010 Blank 0.000 0.050 0.122 0.002 0.816 0.016 0.018 0.010 TW#4 0.128 0.050 0.420 0.008 1.347 0.027 0.025 0.010 TW#4 0.089 0.050 0.467 0.009 1.469 0.029 0.024 0.010 TW#4 0.122 0.050 0.416 0.008 1.401 0.028 0.014 0.010 TW#1 0.000 0.050 0.157 0.003 0.826 0.017 0.023 0.010 TW#1 0.000 0.050 0.150 0.003 0.865 0.017 0.021 0.010 TW#1 0.000 0.050 0.175 0.004 1.162 0.023 0.023 0.010 TW#3 0.179 0.050 117.858 2.357 2.053 0.041 0.052 0.010 TW#3 0.526 0.050 114.533 2.291 2.080 0.042 0.049 0.010 TW#3 0.071 0.050 98.941 1.979 1.983 0.040 0.045 0.001 Chaster 0.662 0.050 0.541 0.011 0.097 0.002 0.020 0.000 Chaster 0.177 0.050 0.540 0.011 0.108 0.002 0.021 0.000 Strata 0.000 0.050 0.163 0.003 0.983 0.020 0.002 0.000 Strata 0.000 0.050 0.142 0.003 0.991 0.020 0.002 0.000 Strata 0.000 0.050 0.143 0.003 0.964 0.019 0.004 0.000                    Detection limit for SF6 is 0.05 fmol/Kg     Detection limit for CFC-12 & CFC-113 is 0.010 pmol/Kg   Detection limit for CFC-11 is 0.005 pmol/Kg                                          165  Data Release CFC11-10,  Job # CFC0097     University of British Columbia      6339 Stores Road        Vancouver, BC V6T 1Z4       Atten: Jessica Doyle       604-741-4218        jessy_doyle@hotmail.com        Equivalent Atmospheric Concentration                  Client ID SF6 error CFC12 error CFC11 error CFC113 error   pmol/mol   pmol/mol   pmol/mol   pmol/mol              TW#2 0.00 0.00 1432.5 28.6 64.8 1.3 2.4 0.0 TW#2 0.00 0.00 1456.5 29.1 67.6 1.4 3.1 0.1 TW#2 0.00 0.00 1446.9 28.9 67.3 1.3 3.0 0.1 Blank 0.00 0.00 59.3 1.2 45.1 0.9 3.3 0.1 Blank 0.00 0.00 27.8 0.6 42.2 0.8 3.5 0.1 Blank 0.00 0.00 23.7 0.5 41.2 0.8 2.9 0.1 TW#4 0.34 0.01 81.7 1.6 68.1 1.4 4.0 0.1 TW#4 0.24 0.00 90.9 1.8 74.2 1.5 4.0 0.1 TW#4 0.33 0.01 80.9 1.6 70.8 1.4 2.4 0.0 TW#1 0.00 0.00 30.4 0.6 41.8 0.8 3.8 0.1 TW#1 0.00 0.00 29.2 0.6 43.7 0.9 3.5 0.1 TW#1 0.00 0.00 34.1 0.7 58.7 1.2 3.8 0.1 TW#3 0.48 0.01 22918.8 458.4 103.7 2.1 8.5 0.2 TW#3 1.41 0.03 22272.2 445.4 105.1 2.1 8.0 0.2 TW#3 0.19 0.00 19240.1 384.8 100.2 2.0 7.4 0.1 Chaster 1.77 0.04 105.1 2.1 4.9 0.1 3.2 0.1 Chaster 0.47 0.01 105.1 2.1 5.5 0.1 3.5 0.1 Strata 0.00 0.00 31.7 0.6 49.7 1.0 0.4 0.0 Strata 0.00 0.00 27.6 0.6 50.1 1.0 0.3 0.0 Strata 0.00 0.00 27.8 0.6 48.7 1.0 0.6 0.0                    current and max. value for SF6 is ~ 7.2 pmol/mol    current value for CFC-12 is ~ 535 pmol/mol     max. value for CFC-12 was ~ 547 pmol/mol in 2003    current value for CFC-11 is ~ 242 pmol/mol     max. value for CFC-11 was ~ 268 pmol/mol in 1994    current value for CFC-113 is ~ 76 pmol/mol     max. value for CFC-113 was ~ 85 pmol/mol in 1994     166  Data Release CFC11-10,  Job # CFC0097     University of British Columbia      6339 Stores Road       Vancouver, BC V6T 1Z4      Atten: Jessica Doyle       604-741-4218        jessy_doyle@hotmail.com        Recharge Age               In years before sampling date      Client ID SF6 error CFC12 error CFC11 error CFC113 error   years   years   years   years              TW#2 >41 2 Supersaturated 41 2 43 2 TW#2 >41 2 Supersaturated 40 2 42 2 TW#2 >41 2 Supersaturated 40 2 42 2 Blank >41 2 47 2 43 2 42 2 Blank >41 2 53 2 43 2 42 2 Blank >41 2 54 2 44 2 43 2 TW#4 38 2 45 2 40 2 41 2 TW#4 41 2 44 2 40 2 41 2 TW#4 38 2 45 2 40 2 43 2 TW#1 >41 2 52 2 44 2 41 2 TW#1 >41 2 52 2 43 2 42 2 TW#1 >41 2 51 2 41 2 41 2 TW#3 35 2 Supersaturated 37 2 37 2 TW#3 27 2 Supersaturated 37 2 38 2 TW#3 43 2 Supersaturated 37 2 38 2 Chaster 25 2 43 2 55 2 42 2 Chaster 35 2 43 2 55 2 42 2 Strata >41 2 52 2 42 2 48 2 Strata >41 2 53 2 42 2 49 2 Strata >41 2 53 2 43 2 48 2                    Supersaturated indicates that there are additional     non-atmospheric sources of the CFC or SF6 making a valid    age determination impossible.                                           167  C.3 University of British Columbia stable isotope analytical results Number Name dD std dD d 18O std d 18O 1 WL10-02 -80.8 0.34 -11.6 0.15 2 TW#3 -80.0 0.35 -11.5 0.44 Standard Whistler -117.9 0.05 -16.2 0.12 3 OC-SP-03 -51.7 0.74 -7.5 0.30 4 CHASTER -79.4 0.40 -11.8 0.14 5 SP-01 -81.2 0.43 -12.0 0.15 6 MW06-1A dup -80.6 0.50 -12.2 0.05 7 TW#4 -82.1 0.58 -11.7 0.10 8 SP-04 -83.9 0.54 -11.7 0.12 9 SRATA -81.6 0.46 -11.8 0.12 Standard Whistler -118.4 0.41 -16.4 0.12 10 OC-SP-02 -64.1 0.27 -9.5 0.04 11 SP-05 -79.5 0.50 -11.4 0.10 12 FIELD BLK (TW#1) -81.5 0.19 -12.0 0.23 13 SP-02 -80.9 0.49 -11.9 0.14 14 OC-SP-05 -33.6 0.46 -4.8 0.08 15 TW#2 -80.8 0.52 -11.9 0.11 16 FDLW -77.3 0.49 -11.5 0.30 Standard Whistler -117.9 0.57 -16.2 0.09 17 MW06-2A -80.2 0.56 -11.7 0.28 18 SP-03 -77.5 0.31 -10.2 0.08 19 TW#1 -80.9 0.35 -11.3 0.13 20 WL10-01 -81.5 0.65 -11.5 0.17 21 OC-SP-04 -36.8 0.48 -5.9 0.21 22 MW06-2B -81.8 0.44 -11.8 0.09 Standard Whistler -118.4 0.45 -16.4 0.40 23 KELLY-1 -83.6 0.61 -12.0 0.12 24 SP-02 dup -80.0 0.00 -11.8 0.00 25 MW06-1A -81.1 0.58 -12.8 0.10 Uncertainties      19 TW#1 -80.9 0.35 -11.3 0.13 12 FIELD BLK (TW#1) -81.5 0.19 -12.0 0.23   0.7 0.2 0.7 -0.1       25 MW06-1A -81.1 0.58 -12.8 0.10 6 MW06-1A dup -80.6 0.50 -12.2 0.05   -0.5 0.1 -0.6 0.0       13 SP-02 -80.9 0.49 -11.9 0.14 24 SP-02 dup -80.0 0.00 -11.8 0.00   -0.9 0.5 -0.1 0.1         -118  -16.1  Standard Whistler -117.9 0.05 -16.2 0.12   -0.1   0.1    Whistler -118.4 0.41 -16.4 0.12   0.4   0.3    Whistler -117.9 0.57 -16.2 0.09   -0.1   0.1    Whistler -118.4 0.45 -16.4 0.40 168  Appendix D  NGAgeCalculator The NGAgeCalculator was provided by Dr. Andrew Manning at the USGS. (personal communication, 2012) Input Information Recharge Parameters Sample Salinity Recharge Recharge EA Ae F EA Delta Ne N2/Ar Name (per mil) Elevation T (?C) Model (ccSTP/g)  (ccSTP/g) (%       (masl)        Solubility)   MW06-1A 0.00 99.5 8.6 CE 0.0847 0.86 0.0027 13.7% 37.92 MW06-2A 0.00 121.5 9.1 CE 0.1143 0.85 0.0031 15.4% 38.37 MW06-2B 0.00 121.5 8.7 CE 0.0090 0.62 0.0027 20.6% 38.39 WL10-01 0.00 139.5 5.8 CE 0.0212 0.56 0.0061 39.7% 41.19 WL10-02 0.00 107.5 7.6 CE 0.0660 0.78 0.0045 23.4% 39.02 TW1 0.00 12.7 6.0 CE 0.0272 0.82 0.0025 14.1%   TW2 0.00 18 7.6 CE 0.0547 0.87 0.0024 12.4%   TW3 0.00 18.5 5.9 CE 0.0519 0.84 0.0029 14.8%   TW4 0.00 13 7.9 CE 0.0013 0.00 0.0013 11.7%   Chaster 0.00 82.6 5.7 CE 0.0155 0.41 0.0072 51.2%   STRATA 0.00 110.5 6.3 CE 0.0296 0.81 0.0028 16.1%    Recharge Model Fit  Chi^2 Ceiling He Ne Ar  Chi^2 P = 0.10 P = 0.05 Chi^2* Misfit** (%) Incld? Chi^2* Misfit** (%) Incld? Chi^2* Misfit** (%) Incld? 2.03 6.25 7.82 0.00 -0.1% YES 0.00 0.0% YES 0.35 1.2% YES 6.71 6.25 7.82 0.07 0.3% YES 1.07 -2.0% YES 1.21 2.2% YES 2.23 6.25 7.82 0.03 -0.2% YES 0.43 1.3% YES 0.02 -0.3% YES 0.05 4.60 5.99 1090 49.3% NO 0.00 0.0% YES 0.00 0.0% YES 0.47 4.60 5.99 233 18.0% NO 0.00 -0.1% YES 0.05 0.4% YES 0.06 2.71 3.84 5.07 2.3% NO 0.00 0.0% YES 0.00 -0.1% YES 7.92 4.60 5.99 1.11 -1.0% YES 5.94 5.1% YES 0.02 0.3% YES 1.35 4.60 5.99 0.19 -0.4% YES 1.06 2.1% YES 0.01 -0.2% YES 1.02 4.60 5.99 0.00 0.0% YES 0.00 0.1% YES 0.29 -1.1% YES 0.54 2.71 3.84 16.13 4.2% NO 0.00 0.0% YES 0.02 -0.3% YES 7.74 4.60 5.99 0.87 -0.9% YES 6.00 5.2% YES 0.45 -1.3% YES  Recharge Model Fit (continued) Kr Xe N2 Chi^2* Misfit** (%) Included? Chi^2* Misfit** (%) Included? Chi^2* Misfit** (%) Included? 1.63 -6.0% YES 0.04 1.0% YES 0.00 0.0% YES 4.04 -9.1% YES 0.10 1.6% YES 0.22 2.4% YES 0.95 5.1% YES 0.10 -1.6% YES 0.71 -4.0% YES 0.03 0.9% YES 0.01 -0.4% YES 0.01 -0.5% YES 0.38 -3.0% YES 0.03 0.9% YES 0.00 0.1% YES 0.05 1.1% YES 0.01 -0.5% YES   NO 0.61 -3.8% YES 0.24 -2.4% YES   NO 0.01 0.4% YES 0.08 -1.4% YES   NO 0.67 4.3% YES 0.05 1.1% YES   NO 0.43 3.4% YES 0.09 -1.5% YES   NO 0.32 2.9% YES 0.10 -1.5% YES     NO 169  Age and Helium He Heterr Delta Heterr Rterr R/Ra 3Hetrit 3H Apparent Initial         Age 3H (ccSTP/g) (ccSTP/g) (% solubility)     (TU) (TU) (yr) (TU) 5.26E-08 -3.69E-11 -0.1% 2.0E-07 1.074 2.49 2.65 11.8 5.14 5.33E-08 1.40E-10 0.3% 2.0E-07 1.085 2.87 4.86 8.3 7.74 5.69E-08 -1.01E-10 -0.2% 2.0E-07 1.003 0.39 3.31 2.0 3.70 1.00E-07 3.31E-08 71.2% 2.0E-07 0.831 6.77 0.05 85.8 6.82 6.79E-08 1.04E-08 22.4% 2.0E-07 1.364 19.02 3.52 33.0 22.54 5.57E-08 1.25E-09 2.7% 2.0E-07 1.588 19.13 3.93 31.4 23.06 5.23E-08 -5.50E-10 -1.2% 2.0E-07 1.409 11.91 5.67 20.1 17.58 5.43E-08 -2.38E-10 -0.5% 2.0E-07 1.337 10.37 4.28 21.9 14.66 5.37E-08 1.68E-11 0.0% 2.0E-07 1.315 9.67 5.54 17.9 15.21 7.79E-08 3.13E-09 6.7% 2.0E-07 0.991 1.52 1.77 11.0 3.28 5.42E-08 -5.06E-10 -1.1% 2.0E-07 1.237 7.13 6.62 13.0 13.75  Uncertainties Recharge T (?C) Ae (ccST/g) F EA (ccSTP/g) Delta Ne (% Solubility) Heterr (ccSTP/g) Delta Heterr (% Solubility) 3Hetrit (TU) 3H (TU) Apparent Age (yr) Initial 3H (TU) 1.28 0.1521 0.15 0.0005 1.6% 1.88E-10 0.4% 0.34 0.13 1.3 0.4 1.27 0.1609 0.14 0.0005 1.6% 2.04E-10 0.4% 0.34 0.24 0.9 0.4 2.27 0.1319 0.29 0.0010 2.9% 1.58E-10 0.3% 0.33 0.17 1.6 0.4 2.85 0.1007 0.20 0.0015 4.8% 2.18E-09 4.9% 1.09 0.00 3.3 1.1 2.19 0.1493 0.17 0.0011 3.9% 1.56E-09 3.3% 0.96 0.18 1.1 1.0 1.78 0.1311 0.36 0.0010 3.2% 1.49E-09 3.1% 0.92 0.20 1.0 0.9 0.89 0.0260 0.03 0.0003 1.3% 1.82E-10 0.4% 0.44 0.28 0.8 0.5 1.21 0.0743 0.12 0.0006 1.7% 1.88E-10 0.4% 0.42 0.21 0.8 0.5 0.74 0.0070 0.07 0.0002 1.1% 1.93E-10 0.4% 0.44 0.28 0.8 0.5 2.36 0.0467 0.20 0.0014 4.6% 2.42E-09 5.2% 1.23 0.09 #NUM! 1.2 0.98 0.0230 0.04 0.0005 1.4% 1.75E-10 0.4% 0.39 0.33 0.7 0.5 170  Appendix E  Sensitivity Analysis Data E.1 Water table elevation   Re-wetting turned on when possible. Results are compared to heads in base case model with rewetting turned on.   Base Case  Vashon Till (2e-6 m/s) Pre-Vashon (2.2e-4 m/s) Well Observed Water Level (mASL) Base-Case Modeled Water Level rewetting on (mASL) Increase 50% to 3e-6 m/s* Absolute difference compared to base case water levels (m) Decrease 50% to 1e-6 m/s Absolute difference compared to base case water levels (m) Increase 50% to 3.3e-4 m/s* Absolute difference compared to base case water levels (m) Decrease 50% to 1.1e-4 m/s Absolute difference compared to base case water levels (m) School Board 28.50 35.22 34.80 -0.41 40.15 4.93 30.70 -4.51 50.15 14.93 MW06-1A 24.20 25.11 25.21 0.10 29.51 4.40 25.01 -0.10 30.63 5.52 MW06-2A 25.20 26.29 25.02 -1.27 32.05 5.76 22.05 -4.24 38.74 12.45 WL10-01 22.70 28.57 27.38 -1.19 34.11 5.54 23.81 -4.76 42.23 13.66 WL10-02 28.50 22.72 21.31 -1.41 28.91 6.19 19.29 -3.43 33.42 10.70 TW1  -  12.70 10.44 -2.27 20.56 7.86 11.32 -1.38 18.32 5.62 TW3  -  11.91 9.71 -2.21 19.68 7.77 10.85 -1.06 16.62 4.71 TW4  -  13.14 10.87 -2.27 20.98 7.84 11.62 -1.53 19.01 5.86 Strata 22.00 20.71 19.58 -1.12 27.23 6.53 dry  30.36 9.65 Mean Difference     -1.34  6.31  -2.63  9.23 Standard deviation     0.83  1.29  1.81  3.70 * Model did not converge with re-wetting turned on - results from model with rewetting turned off    171       Base Case   Upper Bedrock (5e-7 m/s) Lower Bedrock (5e-8 m/s) Well Observed Water Level (mASL) Base-Case Modeled Water Level rewetting on (mASL) Increase 50% to 7.5e-7 m/s* Absolute difference compared to base case water levels (m) Decrease 50% to 2.5e-7 m/s* Absolute difference compared to base case water levels (m) Increase 50% to 7.5e-8 m/s Absolute difference compared to base case water levels (m) Decrease 50% to 2.5e-8 m/s* Absolute difference compared to base case water levels (m) School Board 28.50 35.22 35.21 -0.004 36.52 1.30 35.60 0.38 35.85 0.63 MW06-1A 24.20 25.11 23.79 -1.32 28.06 2.95 24.17 -0.94 26.55 1.44 MW06-2A 25.20 26.29 26.36 0.07 26.77 0.48 26.61 0.32 26.65 0.36 WL10-01 22.70 28.57 28.68 0.11 29.06 0.49 28.91 0.34 28.96 0.38 WL10-02 28.50 22.72 22.76 0.04 23.16 0.44 23.03 0.31 23.06 0.34 TW1 - 12.70 12.64 -0.07 13.02 0.32 12.95 0.25 12.96 0.26 TW3 - 11.91 11.88 -0.03 12.27 0.36 12.19 0.28 12.20 0.29 TW4 - 13.14 13.04 -0.11 13.43 0.28 13.36 0.21 13.38 0.23 Strata 22.00 20.71 20.55 -0.16 21.62 0.92 20.99 0.29 21.08 0.37 Mean Difference   -0.16  0.84  0.16  0.48 Standard deviation   0.44  0.86  0.42  0.38 * Model did not converge with re-wetting turned on - results from model with rewetting turned off        Base Case  Bench Recharge (115 mm/year) Mid-Mountain Recharge (130 mm/year) Well Observed Water Level (mASL) Base-Case Modeled Water Level rewetting on (mASL) Increase 50% to 172.5 mm/year Absolute difference compared to base case water levels (m) Decrease 50% to 57.5 mm/year* Absolute difference compared to base case water levels (m) Increase 50% to 195 mm/year Absolute difference compared to base case water levels (m) Decrease 50% to 65 mm/year Absolute difference compared to base case water levels (m) School Board 28.50 35.22 39.18 3.96 32.69 -2.53 38.09 2.87 33.41 -1.81 MW06-1A 24.20 25.11 29.76 4.65 22.23 -2.88 26.39 1.28 24.57 -0.54 MW06-2A 25.20 26.29 30.66 4.37 22.79 -3.50 28.87 2.58 24.55 -1.74 WL10-01 22.70 28.57 32.95 4.38 25.07 -3.50 31.26 2.69 26.11 -2.46 WL10-02 28.50 22.72 27.04 4.32 19.32 -3.40 25.19 2.47 21.08 -1.64 TW1  -  12.70 16.97 4.27 9.13 -3.57 15.03 2.33 11.13 -1.57 TW3  -  11.91 16.19 4.28 8.34 -3.57 14.28 2.37 10.32 -1.59 TW4  -  13.14 17.46 4.32 9.48 -3.66 15.47 2.33 11.57 -1.57 Strata 22.00 20.71 25.33 4.62 dry  23.20 2.49 18.86 -1.85 Mean Difference     4.35  -3.33  2.38  -1.64 Standard deviation     0.20  0.40  0.45  0.50   .   Base Case  Upper-Mountain Recharge (145 mm/year) 172  Well Observed Water Level (mASL) Base-Case Modeled Water Level rewetting on (mASL) Increase 50% to 217.5 mm/year* Absolute difference compared to base case water levels (m) Decrease 50% to 72.5 mm/year* Absolute difference compared to base case water levels (m) School Board 28.50 35.22 42.65 7.43 29.49 -5.73 MW06-1A 24.20 25.11 29.01 3.90 25.73 0.62 MW06-2A 25.20 26.29 33.05 6.76 21.77 -4.52 WL10-01 22.70 28.57 35.59 7.02 23.72 -4.85 WL10-02 28.50 22.72 29.22 6.50 18.53 -4.19 TW1 - 12.70 18.76 6.06 8.71 -3.99 TW3 - 11.91 18.06 6.15 7.86 -4.05 TW4 - 13.14 19.18 6.04 9.11 -4.03 Strata 22.00 20.71 27.21 6.50 dry  Mean Difference   6.26  -3.84 Standard deviation   1.00  1.90    Re-wetting turned off. Results are compared to heads in base case model with rewetting turned off.    Base Case Vashon Till (2e-6 m/s) Pre-Vashon (2.2e-4 m/s) Well Observed Water Level (mASL) Base-Case Modeled Water Level rewetting off (mASL) Increase 50% to 3e-6 m/s* Absolute difference compared to base case water levels (m) Decrease 50% to 1e-6 m/s Absolute difference compared to base case water levels (m) Increase 50% to 3.3e-4 m/s* Absolute difference compared to base case water levels (m) Decrease 50% to 1.1e-4 m/s Absolute difference compared to base case water levels (m) School Board 28.50 35.59 34.80 -0.79 40.15 4.56 30.70 -4.89 50.15 14.56 MW06-1A 24.20 25.05 25.21 0.16 28.72 3.66 25.01 -0.04 30.51 5.46 MW06-2A 25.20 26.42 25.02 -1.39 31.13 4.71 22.05 -4.37 38.55 12.14 WL10-01 22.70 28.72 27.38 -1.34 33.21 4.49 23.81 -4.91 42.04 13.32 WL10-02 28.50 22.84 21.31 -1.53 27.98 5.15 19.29 -3.55 33.26 10.43 TW1 - 12.75 10.44 -2.32 19.62 6.87 11.32 -1.43 18.22 5.47 TW3 - 11.98 9.71 -2.28 18.75 6.77 10.85 -1.13 16.53 4.54 TW4 - 13.18 10.87 -2.30 20.01 6.84 11.62 -1.56 18.89 5.71 Strata 22.00 20.82 19.58 -1.23 26.28 5.47 dry  30.21 9.39 Mean Difference    -2.73  9.00  -1.45  5.39 Standard deviation    1.91  1.18  0.81  1.18 * Model did not converge with re-wetting turned on - results from model with rewetting turned off 173    Base Case   Upper Bedrock (5e-7 m/s)  Lower Bedrock (5e-8 m/s) Well Observed Water Level (mASL) Base-Case Modeled Water Level rewetting off (mASL) Increase 50% to 7.5e-7 m/s* Absolute difference compared to base case water levels (m) Decrease 50% to 2.5e-7 m/s* Absolute difference compared to base case water levels (m) Increase 50% to 7.5e-8 m/s Absolute difference compared to base case water levels (m) Decrease 50% to 2.5e-8 m/s* Absolute difference compared to base case water levels (m) School Board 28.50 35.59 35.21 -0.38 36.52 0.93 35.60 0.01 35.85 0.26 MW06-1A 24.20 25.05 23.79 -1.26 28.06 3.01 24.25 -0.80 26.55 1.50 MW06-2A 25.20 26.42 26.36 -0.06 26.77 0.35 26.86 0.44 26.65 0.23 WL10-01 22.70 28.72 28.68 -0.03 29.06 0.34 29.17 0.45 28.96 0.24 WL10-02 28.50 22.84 22.76 -0.07 23.16 0.32 23.24 0.41 23.06 0.22 TW1 - 12.75 12.64 -0.12 13.02 0.27 13.11 0.36 12.96 0.21 TW3 - 11.98 11.88 -0.10 12.27 0.29 12.36 0.37 12.20 0.22 TW4 - 13.18 13.04 -0.14 13.43 0.25 13.52 0.34 13.38 0.20 Strata 22.00 20.82 20.55 -0.27 21.62 0.81 21.20 0.39 21.08 0.26 Mean Difference     -0.27  0.73  0.22  0.37 Standard deviation     0.39  0.89  0.40  0.42    Base Case  Bench Recharge (115 mm/year) Mid-Mountain Recharge (130 mm/year) Well Observed Water Level (mASL) Base-Case Modeled Water Level rewetting off (mASL) Increase 50% to 172.5 mm/year Absolute difference compared to base case water levels (m) Decrease 50% to 57.5 mm/year* Absolute difference compared to base case water levels (m) Increase 50% to 195 mm/year Absolute difference compared to base case water levels (m) Decrease 50% to 65 mm/year Absolute difference compared to base case water levels (m) School Board 28.50 35.59 39.18 3.59 32.69 -2.90 38.09 2.50 33.41 -2.18 MW06-1A 24.20 25.05 29.70 4.65 22.23 -2.82 26.13 1.08 25.20 0.14 MW06-2A 25.20 26.42 30.73 4.31 22.79 -3.63 28.55 2.13 23.96 -2.45 WL10-01 22.70 28.72 33.04 4.32 25.07 -3.65 30.95 2.24 26.15 -2.57 WL10-02 28.50 22.84 27.09 4.25 19.32 -3.52 24.87 2.03 20.54 -2.30 TW1 - 12.75 16.96 4.20 9.13 -3.62 14.70 1.94 10.49 -2.27 TW3 - 11.98 16.20 4.22 8.34 -3.64 13.96 1.98 9.67 -2.31 TW4 - 13.18 17.43 4.25 9.48 -3.70 15.11 1.94 10.92 -2.26 Strata 22.00 20.82 25.37 4.55 dry  22.87 2.06 dry  Mean Difference     4.26  -3.43  1.99  -2.02 Standard deviation     0.30  0.36  0.38  0.89 174     Altered Parameter Rewetting On Rewetting Off Average Change in Water Level Standard Deviation Average Change in Water Level Standard Deviation Increase Vashon -1.34 0.83 -1.45 0.81 Decrease Vashon 6.31 1.29 5.39 1.18 Increase Pre-Vashon -2.63 1.81 -2.73 1.91 Decrease Pre-Vashon 9.23 3.70 9.00 3.61 Increase Transition Zone -0.16 0.44 -0.27 0.39 Decrease Transition Zone 0.84 0.86 0.73 0.89 Increase Bedrock 0.16 0.42 0.22 0.40 Decrease Bedrock 0.48 0.38 0.37 0.42 Increase Bench Recarge 4.35 0.20 4.26 0.30 Decrease Bench Recharge -3.33 0.40 -3.43 0.36 Increase Mid-Mountain Recharge 2.38 0.45 1.99 0.38 Decrease Mid-Mountain Recharge -1.64 0.40 -2.02 0.89 Increase Upper-Mountain Recharge 6.26 1.00 6.15 0.90 Decrease Upper-Mountain Recharge -3.84 1.90 -3.95 1.99   Base Case  Upper-Mountain Recharge (145 mm/year) Well Observed Water Level (mASL) Base-Case Modeled Water Level rewetting off (mASL) Increase 50% to 217.5 mm/year* Absolute difference compared to base case water levels (m) Decrease 50% to 72.5 mm/year* Absolute difference compared to base case water levels (m) School Board 28.50 35.59 42.65 7.06 29.49 -6.10 MW06-1A 24.20 25.05 29.01 3.96 25.73 0.68 MW06-2A 25.20 26.42 33.05 6.63 21.77 -4.65 WL10-01 22.70 28.72 35.59 6.87 23.72 -5.00 WL10-02 28.50 22.84 29.22 6.38 18.53 -4.31 TW1 - 12.75 18.76 6.01 8.71 -4.04 TW3 - 11.98 18.06 6.08 7.86 -4.12 TW4 - 13.18 19.18 6.00 9.11 -4.07 Strata 22.00 20.82 27.21 6.39 dry  Mean Difference     6.15  -3.95 Standard deviation     0.90  1.99 175  E.2 Change in % MBR Parameter Increase or Decrease of Value Tested (50%) MBR Flux (m3/day) Total recharge % MBR Base Case MBR Flux (rewetting on) 2290.5 5010.6 45.7% Base Case MBR Flux (rewetting off) 2291.9 5010.6 45.7% Vashon Increase to 3e-6 m/s 2253.1 5010.6 45.0% Decrease to 1e-6 m/3 RW-on 2293.9 5010.6 45.8% Decrease to 1e-6 m/3 RW-off 2291.7 5010.6 45.7% Pre-Vashon  Increase to 3.3e-4 m/s 2290.8 5010.6 45.7% Decrease to 1.1e-4 m/s RW-on 2284.7 5010.6 45.6% Decrease to 1.1e-4 m/s RW-off 2293.6 5010.6 45.8% Upper Bedrock Increase to 7.5e-7 m/s 2290.6 5010.6 45.7% Decrease to 2.5e-7 m/s 2289 5010.6 45.7% Lower Bedrock Increase to 7.5e-8 m/s RW-on 2286.1 5010.6 45.6% Increase to 7.5e-8 m/s RW-off 2292.6 5010.6 45.8% Decrease to 2.5e-8 m/s 2288.9 5010.6 45.7% Bench Recharge Increase to 172.5 mm/year RW-on 2288.2 5893.9 38.8% Increase to 172.5 mm/year RW-off 2292.9 5893.9 38.9% Decrease 57.5 mm/year 2293.2 4127.2 55.6% Mid-Mtn Recharge Increase to 195 mm/year RW-on 2296.1 5487.4 41.8% Increase to 195 mm/year RW-off 2302.8 5487.4 42.0% Decrease to 65 mm/year RW-on 2286.6 4533.8 50.4% Decrease to 65 mm/year RW-off 2283.6 4533.8 50.4% Upper-mtn Recharge Increase to 217.5 mm/day 3429.4 6155.7 55.7% Decrease to 72.5 mm/year 1164.4 3865.5 30.1%  Change in % MBR Altered Parameter RW on RW off Increase Vashon 0.01% -0.02% Decrease Vashon -0.12% 0.03% Increase Pre-Vashon -0.75% -0.77% Decrease Pre-Vashon 0.07% 0.00% Increase Upper Bedrock 0.00% -0.03% Decrease Upper Bedrock -0.03% -0.06% Increase Lower Bedrock -0.09% 0.01% Decrease Lower Bedrock -0.03% -0.06% Increase Bench Recarge -6.89% -6.84% Decrease Bench Recharge 9.85% 9.82% Increase Mid-Mountain Recharge -3.87% -3.78% Decrease Mid-Mountain Recharge 4.72% 4.63% Increase Upper-Mountain Recharge 10.00% 9.97% Decrease Upper-Mountain Recharge 15.59% 15.62%  176  E.3 Recharge elevation sensitivity - data for box diagrams TW1 ? Recharge Elevations (mASL) Particle Base Case Vashon Pre-Vashon  Upper Bedrock Lower Bedrock Bench Recharge Mid-Mtn Recharge Upper-mtn Recharge RW On RW Off Increase RW-off Decrease RW-on Decrease RW-off Increase RW-off Decrease RW-on Decrease RW-off Increase RW-off Decrease RW-off Increase RW-on Increase RW-off Decrease RW-off Increase RW-on Increase RW-0ff Decrease RW-off Increase RW-on Increase RW-0ff Decrease RW-on Decrease RW-off Increase RW-0ff Decrease RW-off 1 1022 637 612 252 260 237 342 390 614 637 647 655 572 218 165 522 762 644 747 857 833 158 2 940 592 597 230 244 217 329 367 601 452 604 590 522 192 161 449 762 623 726 745 820 152 3 647 514 574 222 215 205 310 310 544 319 566 560 435 177 157 385 572 574 715 704 774 149 4 614 533 574 216 204 192 268 268 502 319 504 524 407 176 154 366 413 435 680 647 739 149 5 572 497 552 210 199 176 260 230 417 319 452 485 379 171 152 354 199 379 452 485 658 143 6 551 349 560 204 183 171 244 244 367 305 355 394 252 171 150 324 175 292 331 199 516 143 7 411 192 537 175 174 166 236 252 316 237 223 204 164 157 148 324 170 244 205 159 440 140 8 192 151 523 169 230 161 222 222 148 184 165 153 148 148 147 284 160 421 151 176 397 137 9 155 146 481 164 158 154 215 210 145 160 157 145 145 147 146 252 160 210 146 159 381 137 10 144 140 260 154 164 154 204 204 144 150 154 146 143 147 146 223 155 230 144 616 352 137 Average 525 375 527 200 203 183 263 270 380 308 383 386 317 170 153 348 353 405 430 475 591 145 q1 247 161 527 171 176 162 226 224 190 197 180 166 152 150 147 294 163 256 165 182 408 138 min 144 140 260 154 158 154 204 204 144 150 154 145 143 147 146 223 155 210 144 159 352 137 median 562 423 556 207 202 174 252 248 392 312 404 440 316 171 151 339 187 400 392 551 587 143 max 1022 637 612 252 260 237 342 390 614 637 647 655 572 218 165 522 762 644 747 857 833 158 q3 639 528 574 221 226 202 300 300 534 319 551 551 428 177 156 380 532 539 706 690 765 149  TW2 ? Recharge Elevations (mASL) Particle Base Case Vashon Pre-Vashon  Upper Bedrock Lower Bedrock Bench Recharge Mid-Mtn Recharge Upper-mtn Recharge RW On RW Off Increase RW-off Decrease RW-on Decrease RW-off Increase RW-off Decrease RW-on Decrease RW-off Increase RW-off Decrease RW-off Increase RW-on Increase RW-off Decrease RW-off Increase RW-on Increase RW-0ff Decrease RW-off Increase RW-on Increase RW-0ff Decrease RW-on Decrease RW-off Increase RW-0ff Decrease RW-off 1 117 118 117 116 116 118 116 116 118 118 118 118 118 110 110 135 118 117 117 117 118 117 2 116 116 117 114 114 97 115 114 117 116 116 116 117 108 108 132 115 115 114 117 117 117 3 114 114 113 110 110 97 112 112 114 114 114 114 114 104 104 132 112 112 111 113 114 114 4 110 109 109 108 108 117 108 108 109 110 110 110 110 100 100 121 110 110 108 109 110 113 5 105 105 105 104 104 116 106 108 105 106 105 105 105 98 98 119 106 106 105 105 108 109 6 100 100 103 100 100 113 104 100 100 100 100 100 100 94 94 117 100 100 100 98 104 105 7 94 96 98 94 94 108 99 98 94 94 96 96 96 89 89 111 98 98 96 96 98 98 8 89 92 92 89 89 103 92 92 89 89 94 94 94 97 97 98 92 92 89 97 90 96 9 102 103 85 103 103 98 97 89 103 103 103 97 97 103 103 98 97 97 103 103 97 103 10 97 107 103 97 97 92 97 89 97 97 97 97 97 97 97 103 97 97 97 97 98 97 Average 104 106 104 104 104 106 105 103 105 105 105 105 105 100 100 117 105 104 104 105 105 107 q1 100 100 98 100 100 98 99 98 100 100 100 97 97 97 97 111 98 98 100 98 98 103 min 89 92 85 89 89 97 92 89 89 89 94 94 94 89 89 98 92 92 89 96 90 96 median 105 105 105 104 104 108 106 108 105 106 105 105 105 100 100 119 106 106 105 105 108 109 max 117 118 117 116 116 118 116 116 118 118 118 118 118 110 110 135 118 117 117 117 118 117 q3 114 114 113 110 110 116 112 112 114 114 114 114 114 104 104 132 112 112 111 113 114 114 177  TW3 ? Recharge Elevations (mASL) Particle Base Case Vashon Pre-Vashon  Upper Bedrock Lower Bedrock Bench Recharge Mid-Mtn Recharge Upper-mtn Recharge RW On RW Off Increase RW-off Decrease RW-on Decrease RW-off Increase RW-off Decrease RW-on Decrease RW-off Increase RW-off Decrease RW-off Increase RW-on Increase RW-off Decrease RW-off Increase RW-on Increase RW-0ff Decrease RW-off Increase RW-on Increase RW-0ff Decrease RW-on Decrease RW-off Increase RW-0ff Decrease RW-off 1 913 907 639 867 1028 161 452 341 951 927 913 927 939 867 959 649 954 959 595 156 989 171 2 699 791 595 714 989 148 361 341 879 922 649 840 894 754 907 378 954 965 325 135 965 147 3 471 744 303 587 959 138 290 315 767 744 498 644 585 758 867 326 813 867 134 136 741 134 4 348 361 135 563 892 136 315 280 355 498 471 633 510 685 828 233 578 854 134 134 697 134 5 315 348 133 523 852 134 268 290 291 473 361 450 473 555 823 217 544 819 135 133 675 135 6 303 341 135 498 668 135 239 251 173 282 291 403 521 605 685 197 517 567 132 131 642 132 7 168 246 131 507 587 135 229 251 314 225 384 292 213 288 639 151 517 409 131 124 642 123 8 138 185 126 473 511 134 189 189 150 213 181 225 171 225 369 135 397 384 124 120 593 117 9 150 135 126 268 511 133 147 150 137 165 148 225 135 226 273 134 290 354 123 127 473 113 10 134 135 123 361 440 126 174 155 135 138 135 141 521 169 169 123 256 268 118 118 375 139 Average 364 419 245 536 744 138 266 256 415 459 403 478 496 513 652 254 582 645 195 131 679 135 q1 168 246 131 498 587 134 229 251 173 225 291 292 213 288 639 151 517 409 131 127 642 123 min 138 135 126 268 511 133 147 150 137 165 148 225 135 225 273 134 290 354 123 120 473 113 median 315 348 135 523 852 135 268 280 314 473 384 450 510 605 823 217 544 819 134 133 675 134 max 913 907 639 867 1028 161 452 341 951 927 913 927 939 867 959 649 954 965 595 156 989 171 q3 471 744 303 587 959 138 315 315 767 744 498 644 585 754 867 326 813 867 135 135 741 135  TW4 ? Recharge Elevations (mASL) Particle Base Case Vashon Pre-Vashon  Upper Bedrock Lower Bedrock Bench Recharge Mid-Mtn Recharge Upper-mtn Recharge RW On RW Off Increase RW-off Decrease RW-on Decrease RW-off Increase RW-off Decrease RW-on Decrease RW-off Increase RW-off Decrease RW-off Increase RW-on Increase RW-off Decrease RW-off Increase RW-on Increase RW-0ff Decrease RW-off Increase RW-on Increase RW-0ff Decrease RW-on Decrease RW-off Increase RW-0ff Decrease RW-off 1 271 257 241 169 171 219 167 167 276 243 241 231 241 148 146 418 194 188 309 276 157 179 2 225 219 214 158 165 205 162 162 232 214 215 210 214 146 143 401 175 175 241 214 154 171 3 205 205 199 151 161 175 157 157 210 194 199 178 199 143 141 232 169 169 199 182 148 163 4 188 188 182 144 154 188 151 151 169 179 182 163 182 141 137 276 163 154 175 169 146 158 5 166 175 171 137 148 167 148 148 161 172 171 154 163 134 137 214 154 148 165 163 140 151 6 161 165 163 134 144 154 143 143 151 163 163 148 158 131 131 175 148 143 161 158 138 148 7 151 158 158 163 141 161 138 138 144 154 158 143 148 129 125 188 144 137 134 148 132 144 8 146 151 148 127 134 137 135 135 137 148 148 134 144 122 122 200 137 131 141 144 129 137 9 137 144 143 120 127 143 129 129 178 143 143 194 137 115 110 214 131 161 151 137 132 134 10 175 137 137 148 120 148 122 122 194 134 137 169 171 103 103 166 182 163 137 134 140 134 Average 183 180 176 145 147 170 145 145 185 174 176 172 176 131 130 248 160 157 181 173 142 152 q1 151 158 158 134 141 154 138 138 151 154 158 148 148 129 125 200 144 143 151 148 132 144 min 137 144 143 120 127 137 129 129 137 143 143 134 137 115 110 175 131 131 134 137 129 134 median 166 175 171 144 148 167 148 148 169 172 171 163 163 134 137 214 154 154 165 163 140 151 max 271 257 241 169 171 219 167 167 276 243 241 231 241 148 146 418 194 188 309 276 157 179 q3 205 205 199 158 161 188 157 157 210 194 199 194 199 143 141 276 169 169 199 182 148 163 178  Strata ? Recharge Elevations (mASL) Particle Base Case Vashon Pre-Vashon  Upper Bedrock Lower Bedrock Bench Recharge Mid-Mtn Recharge Upper-mtn Recharge RW On RW Off Increase RW-off Decrease RW-on Decrease RW-off Increase RW-off Decrease RW-on Decrease RW-off Increase RW-off Decrease RW-off Increase RW-on Increase RW-off Decrease RW-off Increase RW-on Increase RW-0ff Decrease RW-off Increase RW-on Increase RW-0ff Decrease RW-on Decrease RW-off Increase RW-0ff Decrease RW-off 1 800 725 637 904 811  922 844 723 688 745 695 723 863 767   893 680 560   844   2 784 641 637 848 671  893 768 592 641 725 671 686 803 695   784 614 530   735   3 725 628 604 734 652  848 747 516 608 598 566 680 687 661   784 576 218   715   4 671 590 448 723 644  833 688 452 608 427 544 641 680 653   695 653 120   704   5 438 576 122 687 615  771 680 238 440 413 381 610 341 560   537 407 120   680   6 237 407 118 687 592  575 644 305 381 252 355 578 330 407   504 407 118   662   7 159 224 118 635 572  759 635 271 237 133 271 425 671 288   438 407 117   647   8 122 117 117 628 560  725 606 122 119 120 119 237 185 237   427 342 118   631   9 118 127 117 560 470  695 606 117 118 117 117 118 141 201   319 329 117   637   10 117 117 116 534 504   348 603 118 118 117 117 117 117 117   118 117 116   533   Average 417 415 303 694 609 dry 737 682 345 396 365 384 482 482 459 dry 550 453 213 dry 679 dry q1 159 224 118 635 572  725 635 238 237 133 271 425 330 288   438 407 118   647   min 118 117 117 560 470  575 606 117 118 117 117 118 141 201   319 329 117   631   median 438 576 122 687 615  771 680 305 440 413 381 610 671 560   537 407 120   680   max 800 725 637 904 811  922 844 723 688 745 695 723 863 767   893 680 560   844   q3 725 628 604 734 652   848 747 516 608 598 566 680 687 661   784 614 218   715    WL10-01 ? Recharge Elevations (mASL) Particle Base Case Vashon Pre-Vashon  Upper Bedrock Lower Bedrock Bench Recharge Mid-Mtn Recharge Upper-mtn Recharge RW On RW Off Increase RW-off Decrease RW-on Decrease RW-off Increase RW-off Decrease RW-on Decrease RW-off Increase RW-off Decrease RW-off Increase RW-on Increase RW-off Decrease RW-off Increase RW-on Increase RW-0ff Decrease RW-off Increase RW-on Increase RW-0ff Decrease RW-on Decrease RW-off Increase RW-0ff Decrease RW-off 1 1047 961 486 1008 751 961 737 840 753 1016 975 753 657 724 901 793 725 915 874 745 944 1002 2 1047 676 486 979 742 901 725 825 745 1016 975 715 657 716 868 779 716 816 796 733 901 990 3 1033 669 486 950 742 866 716 809 724 1016 975 733 569 716 811 767 716 751 769 715 901 975 4 1022 659 486 950 742 866 716 781 724 1016 901 710 553 707 815 753 707 751 772 707 901 648 5 826 639 471 874 742 867 709 759 724 975 794 684 521 699 816 745 699 751 759 707 901 592 6 796 630 471 858 742 852 700 725 724 840 779 676 490 699 816 736 690 753 747 700 901 494 7 783 621 467 715 729 837 691 709 733 840 765 668 456 690 799 725 690 753 736 691 903 443 8 769 609 467 673 729 823 684 692 715 677 767 669 413 690 804 716 684 753 723 691 886 360 9 759 599 467 665 729 807 684 684 715 668 745 659 392 684 804 700 684 753 716 691 886 342 10 756 582 467 659 742 852 676 737 724 659 753 648 391 684 804 765 707 753 707 684 870 327 Average 883.8 665 475 833 739 863 704 756 728 872 843 692 510 701 824 748 702 775 760 706 899 617 q1 783 621 467 715 729 837 691 709 724 840 767 669 456 690 804 725 690 751 736 691 901 443 min 759 599 467 665 729 807 684 684 715 668 745 659 392 684 799 700 684 751 716 691 886 342 median 826 639 471 874 742 866 709 759 724 975 794 684 521 699 815 745 699 753 759 707 901 592 max 1047 961 486 1008 751 961 737 840 753 1016 975 753 657 724 901 793 725 915 874 745 944 1002 q3 1033 669 486 950 742 867 716 809 733 1016 975 715 569 716 816 767 716 753 772 715 901 975  179  WL10-02 ? Recharge Elevations (mASL) Particle Base Case Vashon Pre-Vashon  Upper Bedrock Lower Bedrock Bench Recharge Mid-Mtn Recharge Upper-mtn Recharge RW On RW Off Increase RW-off Decrease RW-on Decrease RW-off Increase RW-off Decrease RW-on Decrease RW-off Increase RW-off Decrease RW-off Increase RW-on Increase RW-off Decrease RW-off Increase RW-on Increase RW-0ff Decrease RW-off Increase RW-on Increase RW-0ff Decrease RW-on Decrease RW-off Increase RW-0ff Decrease RW-off 1 361 209 500 937 725 699 799 779 249 473 298 216 201 261 242 554 261 483 674 682 688 993 2 326 201 494 922 699 699 801 767 238 473 298 205 194 255 236 554 255 438 662 674 690 967 3 298 201 491 850 674 690 801 767 234 455 285 194 194 255 236 544 255 318 648 668 682 967 4 171 194 477 754 692 680 785 767 218 440 277 178 184 238 232 544 242 293 633 657 732 940 5 158 184 454 741 664 680 785 767 213 440 267 175 175 221 232 529 229 285 619 652 721 911 6 158 175 429 741 657 671 785 767 225 440 267 175 175 205 224 512 221 267 610 644 721 914 7 149 175 356 730 657 671 785 767 190 412 255 175 175 188 208 500 205 261 587 644 711 856 8 144 170 242 732 657 661 785 767 175 394 249 175 175 170 188 496 197 255 565 644 675 807 9 131 170 218 732 657 653 772 767 167 394 238 170 170 166 173 483 188 232 529 644 675 682 10 126 170 229 781 657 658 772 742 201 375 225 170 170 164 166 447 178 308 512 629 675 602 Average 202 185 389 792 674 676 787 766 211 430 266 183 181 212 214 516 223 314 604 654 697 864 q1 149 175 356 732 657 671 785 767 190 412 255 175 175 188 208 500 205 261 587 644 682 856 min 131 170 218 730 657 653 772 767 167 394 238 170 170 166 173 483 188 232 529 644 675 682 median 158 184 454 741 664 680 785 767 218 440 267 175 175 221 232 529 229 285 619 652 690 914 max 361 209 500 937 725 699 801 779 249 473 298 216 201 261 242 554 261 483 674 682 732 993 q3 298 201 491 850 692 690 799 767 234 455 285 194 194 255 236 544 255 318 648 668 721 967  MW06-1A ? Recharge Elevations (mASL) Particle Base Case Vashon Pre-Vashon  Upper Bedrock Lower Bedrock Bench Recharge Mid-Mtn Recharge Upper-mtn Recharge RW On RW Off Increase RW-off Decrease RW-on Decrease RW-off Increase RW-off Decrease RW-on Decrease RW-off Increase RW-off Decrease RW-off Increase RW-on Increase RW-off Decrease RW-off Increase RW-on Increase RW-0ff Decrease RW-off Increase RW-on Increase RW-0ff Decrease RW-on Decrease RW-off Increase RW-0ff Decrease RW-off 1 99 99 99 103 103 99 99 107 103 99 99 99 103 103 103 99 103 103 99 99 103 99 2 99 99 99 103 103 99 99 99 103 99 99 99 103 103 103 99 103 103 99 99 103 99 3 99 99 99 103 103 99 99 99 99 99 99 99 103 103 103 99 103 99 99 99 103 99 4 99 99 99 103 103 99 99 99 99 99 99 99 103 99 103 99 103 99 99 99 103 99 5 99 99 99 103 99 99 99 99 99 99 99 99 103 99 99 99 99 99 99 99 103 99 6 99 99 99 99 99 99 99 99 99 99 99 99 103 99 99 99 99 99 99 99 103 99 7 99 99 99 99 99 99 99 99 99 99 99 99 103 99 99 99 99 99 99 99 99 99 8 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 9 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 10 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 Average 99 99 99 101 101 99 99 100 100 99 99 99 102 100 101 99 101 100 99 99 101 99 q1 99 99 99 99 99 99 99 99 99 99 99 99 103 99 99 99 99 99 99 99 99 99 min 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 median 99 99 99 103 99 99 99 99 99 99 99 99 103 99 99 99 99 99 99 99 103 99 max 99 99 99 103 103 99 99 107 103 99 99 99 103 103 103 99 103 103 99 99 103 99 q3 99 99 99 103 103 99 99 99 99 99 99 99 103 103 103 99 103 99 99 99 103 99  180  MW06-2A ? Recharge Elevations (mASL) Particle Base Case Vashon Pre-Vashon  Upper Bedrock Lower Bedrock Bench Recharge Mid-Mtn Recharge Upper-mtn Recharge RW On RW Off Increase RW-off Decrease RW-on Decrease RW-off Increase RW-off Decrease RW-on Decrease RW-off Increase RW-off Decrease RW-off Increase RW-on Increase RW-off Decrease RW-off Increase RW-on Increase RW-0ff Decrease RW-off Increase RW-on Increase RW-0ff Decrease RW-on Decrease RW-off Increase RW-0ff Decrease RW-off 1 154 153 150 192 175 140 268 268 148 199 154 155 153 154 153 217 192 176 148 149 252 135 2 154 152 148 192 175 140 260 260 148 199 154 154 152 154 153 212 184 170 148 149 244 135 3 152 152 149 184 170 140 252 252 152 192 153 153 152 153 152 205 184 170 148 149 237 135 4 152 151 148 184 169 140 260 252 148 192 152 153 152 152 152 205 184 165 148 149 237 135 5 152 150 148 175 165 140 244 244 149 184 152 152 150 152 151 199 165 165 148 148 231 135 6 150 150 147 175 164 140 244 237 151 184 151 151 148 151 150 199 170 161 147 148 223 135 7 150 150 147 170 160 140 237 237 151 171 152 151 148 150 150 192 165 160 147 148 217 135 8 148 148 147 169 158 140 237 230 152 170 150 150 150 150 149 192 161 160 147 148 216 135 9 141 148 147 165 155 140 230 230 151 166 148 149 149 149 149 184 160 155 147 147 210 135 10 142 147 147 164 160 140 223 223 152 176 151 149 151 149 149 184 160 155 147 147 204 135 Average 150 150 148 177 165 140 246 243 150 183 152 152 151 151 151 199 173 164 148 148 227 135 q1 150 150 147 170 160 140 237 237 148 171 151 151 149 150 150 192 165 160 147 148 217 135 min 141 148 147 165 155 140 230 230 148 166 148 149 148 149 149 184 160 155 147 147 210 135 median 152 150 148 175 165 140 244 244 151 184 152 152 150 152 151 199 170 165 148 148 231 135 max 154 153 150 192 175 140 268 268 152 199 154 155 153 154 153 217 192 176 148 149 252 135 q3 152 152 148 184 170 140 260 252 151 192 153 153 152 153 152 205 184 170 148 149 237 135 181  E.4 Overall change in recharge elevation Rewetting On Base Case  Vashon   Pre-Vashon Upper Bedrock Average Recharge Elevation RW-On (mASL) Increase Decrease Increase Decrease Increase Decrease Well Ave Recharge Elevation (mASL) Difference from base  case (RW-on) m Ave Recharge Elevation (mASL) Difference from base  case (RW-on) m Ave Recharge Elevation (mASL) Difference from base  case (RW-on) m Ave Recharge Elevation (mASL) Difference from base  case (RW-on) m Ave Recharge Elevation (mASL) Difference from base  case (RW-on) m Ave Recharge Elevation (mASL) Difference from base  case (RW-on) m MW06-1A 99 99 0 101 2 99 0 99 0 99.8 0.8 99 0 MW06-2A 149.5 147.8 -1.7 177 27.5 140 -9.5 245 95.5 150.2 0.7 183.3 33.8 WL10-01 883.8 475.4 -408.4 833.1 -50.7 863.2 -20.6 703.8 -180 728.1 -155.7 872.3 -11.5 WL10-02 202.2 389 186.8 792 589.8 676.2 474 787 584.8 211 8.8 429.6 227.4 TW1 524.8 527 2.2 199.6 -325.2 183.3 -341.5 263 -261.8 379.8 -145 308.2 -216.6 TW2 104.4 104.2 -0.2 103.5 -0.9 105.9 1.5 104.6 0.2 104.6 0.2 104.7 0.3 TW3 363.9 244.6 -119.3 536.1 172.2 138 -225.9 266.4 -97.5 415.2 51.3 458.7 94.8 TW4 182.5 175.6 -6.9 145.1 -37.4 169.7 -12.8 145.2 -37.3 185.2 2.7 174.4 -8.1 Strata 417.1 303.4 -113.7 694 276.9 dry   736.9 319.8 345.4 -71.7 395.8 -21.3  Rewetting On Base Case Lower Bedrock Bench Recharge Average Recharge Elevation RW-On (mASL) Increase Decrease Increase Decrease Well Ave Recharge Elevation (mASL) Difference from base  case (RW-on) m Ave Recharge Elevation (mASL) Difference from base  case (RW-on) m Ave Recharge Elevation (mASL) Difference from base  case (RW-on) m Ave Recharge Elevation (mASL) Difference from base  case (RW-on) m MW06-1A 99 99 0 101.8 2.8 100.2 1.2 99 0 MW06-2A 149.5 151.7 2.2 150.5 1 151.4 1.9 198.9 49.4 WL10-01 883.8 842.9 -40.9 509.9 -373.9 700.9 -182.9 747.9 -135.9 WL10-02 202.2 265.9 63.7 181.3 -20.9 212.3 10.1 516.3 314.1 TW1 524.8 382.7 -142.1 316.7 -208.1 170.4 -354.4 348.3 -176.5 TW2 104.4 105.3 0.9 104.8 0.4 100 -4.4 116.6 12.2 TW3 363.9 403.1 39.2 496.2 132.3 513.2 149.3 254.3 -109.6 TW4 182.5 175.7 -6.8 175.7 -6.8 131.2 -51.3 248.4 65.9 Strata 417.1 364.7 64.4 481.5 64.4 481.8 64.7 dry    Rewetting On Base Case Mid-Mountain Recharge Upper-Mountain Recharge Average Recharge Elevation RW-On (mASL) Increase Decrease Increase Decrease Well Ave Recharge Elevation (mASL) Difference from base  case (RW-on) m Ave Recharge Elevation (mASL) Difference from base  case (RW-on) m Ave Recharge Elevation (mASL) Difference from base  case (RW-on) m Ave Recharge Elevation (mASL) Difference from base  case (RW-on) m MW06-1A 99 100.6 1.6 99 0 101.4 2.4 99 0 MW06-2A 149.5 172.5 23 147.5 -2 227.1 77 135 -15.1 WL10-01 883.8 701.8 -182 759.9 -123.9 899.4 234.9 617.3 -47.2 WL10-02 202.2 223.1 20.9 603.9 401.7 697 512.1 863.9 679 TW1 524.8 352.8 -172 429.7 -95.1 591 215.9 144.5 -230.6 TW2 104.4 104.5 0.1 104 -0.4 105.4 -0.6 106.9 0.9 TW3 363.9 582 218.1 195.1 -168.8 679.2 259.9 134.5 -284.8 TW4 182.5 159.7 -22.8 181.3 -1.2 141.6 -38.3 151.9 -28 Strata 417.1 549.9 132.8 213.4 -203.7 678.8 263.6 dry  182  Rewetting Off Base Case Green Vashon  Pre-Vashon Upper Bedrock Average Recharge Elevation RW-Off (mASL) Increase Decrease Increase Decrease Increase Decrease Well Ave Recharge Elevation (mASL) Difference from base  case (RW-off) m Ave Recharge Elevation (mASL) Difference from base  case (RW-off) m Ave Recharge Elevation (mASL) Difference from base  case (RW-off) m Ave Recharge Elevation (mASL) Difference from base  case (RW-off) m Ave Recharge Elevation (mASL) Difference from base  case (RW-off) m Ave Recharge Elevation (mASL) Difference from base  case (RW-off) m MW06-1A 99 99 0 100.6 1.6 99 0 99.8 0.8 99.8 0.8 99 0 MW06-2A 150.1 147.8 -2.3 165.1 15 140 -10.1 243.3 93.2 150.2 0.1 183.3 33.2 WL10-01 664.5 475.4 -189.1 739 74.5 863.2 198.7 756.1 91.6 728.1 63.6 872.3 207.8 WL10-02 184.9 389 204.1 673.9 489 676.2 491.3 765.7 580.8 211 26.1 429.6 244.7 TW1 375.1 527 151.9 203.1 -172 183.3 -191.8 269.7 -105.4 379.8 4.7 308.2 -66.9 TW2 106 104.2 -1.8 103.5 -2.5 105.9 -0.1 102.6 -3.4 104.6 -1.4 104.7 -1.3 TW3 419.3 244.6 -174.7 743.7 324.4 138 -281.3 256.3 -163 415.2 -4.1 458.7 39.4 TW4 179.9 175.6 -4.3 146.5 -33.4 169.7 -10.2 145.2 -34.7 185.2 5.3 174.4 -5.5 Strata 415.2 303.4 -111.8 609.1 193.9 dry   682.1 266.9 345.4 -69.8 395.8 -19.4  Rewetting Off Base Case Lower Bedrock Bench Recharge Average Recharge Elevation RW-Off (mASL) Increase Decrease Increase Decrease Well Ave Recharge Elevation (mASL) Difference from base  case (RW-off) m Ave Recharge Elevation (mASL) Difference from base  case (RW-off) m Ave Recharge Elevation Difference from base  case (RW-off) m Ave Recharge Elevation (mASL) Difference from base  case (RW-off) m MW06-1A 99 99 0 101.8 2.8 100.6 1.6 99 0 MW06-2A 150.1 151.7 1.6 150.5 0.4 150.8 0.7 198.9 48.8 WL10-01 664.5 691.5 27 509.9 -154.6 823.8 159.3 747.9 83.4 WL10-02 184.9 183.3 -1.6 181.3 -3.6 213.7 28.8 516.3 331.4 TW1 375.1 385.6 10.5 316.7 -58.4 152.6 -222.5 348.3 -26.8 TW2 106 104.7 -1.3 104.8 -1.2 100 -6 116.6 10.6 TW3 419.3 478 39.4 496.2 76.9 651.9 232.6 254.3 -165 TW4 179.9 172.4 -5.5 175.7 -4.2 129.5 -50.4 248.4 68.5 Strata 415.2 383.6 -19.4 481.5 66.3 458.6 43.4 dry    Rewetting Off Base Case Mid-Mountain Recharge Upper-Mountain Recharge Average Recharge Elevation RW-Off (mASL) Increase Decrease Increase Decrease Well Ave Recharge Elevation (mASL) Difference from base  case (RW-off) m Ave Recharge Elevation (mASL) Difference from base  case (RW-off) m Ave Recharge Elevation (mASL) Difference from base  case (RW-off) m Ave Recharge Elevation (mASL) Difference from base  case (RW-off) m MW06-1A 99 99.8 0.8 99 0 101.4 2.4 99 0 MW06-2A 150.1 163.7 13.6 148.2 -1.9 227.1 77 135 -15.1 WL10-01 664.5 774.9 110.4 706.4 41.9 899.4 234.9 617.3 -47.2 WL10-02 184.9 314 129.1 603.9 419 697 512.9 863.9 679 TW1 375.1 405.2 30.1 474.7 99.6 591 215.9 144.5 -230.6 TW2 106 104.4 -1.6 105.2 -0.8 105.4 -0.6 106.9 0.9 TW3 419.3 644.6 225.3 131.4 -287.9 679.2 259.9 134.5 -284.8 TW4 179.9 156.9 -23 172.5 -7.4 141.6 -38.3 151.9 -28 Strata 415.2 453.2 38 dry  678.8 263.6 dry   183    Rewetting On Rewetting Off Altered Parameter Average Change in Recharge Elevation Standard Deviation Average Change in Recharge Elevation Standard Deviation Increase Vashon -51.2 160.2 -14.2 133.1 Decrease Vashon 72.7 254.2 98.9 203.2 Increase Pre-Vashon -16.9 236.3 24.6 236.7 Decrease Pre-Vashon 47.1 261.1 80.8 225.2 Increase Upper Bedrock -34.2 73.0 2.8 34.6 Decrease Upper Bedrock 11.0 116.4 48.0 106.0 Increase Lower Bedrock -15.1 59.4 6.2 25.0 Decrease Lower Bedrock -45.4 152.8 -8.4 68.0 Increase Bench Recarge -40.6 147.2 20.8 127.7 Decrease Bench Recharge 2.5 154.5 43.9 139.7 Increase Mid-Mountain Recharge 2.2 127.2 58.1 80.9 Decrease Mid-Mountain Recharge -21.5 177.3 32.8 193.3 Increase Upper-Mountain Recharge 132.6 182.6 169.7 176.6 Decrease Upper-Mountain Recharge -32.1 316.0 9.3 292.3  

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