British Columbia Mine Reclamation Symposium

Site specific risk assessments of two former copper concentrate shed sites near Topley, B.C. McKee, P. M.; Morris, N. P.; Nicholson, Ronald V. 2006

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SITE SPECIFIC RISK ASSESSMENTS OF TWO FORMER COPPER CONCENTRATE SHED SITES NEAR TOPLEY, B.C.  P.M. McKee, M.Sc. N.P. Morris, B.Sc. R. V. Nicholson, Ph.D.  EcoMetrix Incorporated 14 Abacus Road Brampton, ON   L6T 5B7  Brian Rosendale  Falconbridge Limited 3 Hawthorne Ave Box 2000 Granisle, BC  V0J 1W0  ABSTRACT  Falconbridge Limited owns two former concentrate transfer sites near Topley, B.C.  The Sites were used for storage and rail shipment of Cu concentrate from the now closed Granisle and Bell mines.  The Sites had other historic uses including road salt storage.  Preliminary and Detailed Site Investigations were completed to evaluate the extent and degree of soil contamination, and site-specific risk assessments (SSRAs) completed to guide the development of Remediation Plans.  At both sites, soils and groundwater contain elevated concentrations of Cu, salt, other metals and organic compounds.  Groundwater modeling demonstrates that Cu is strongly attenuated by formation of poorly- soluble Cu carbonate along flow paths, so that no significant Cu contamination reaches the adjacent Bulkley River or neighbouring properties.  This has been verified by groundwater and river monitoring.  The SSRAs identified no potential human health risk to persons who access the properties or swim and fish in the Bulkley River.  Ecological risks are confined to terrestrial receptors (plants and small wildlife species) assumed to reside within the most contaminated portions of the Sites.  Risks to terrestrial biota are less than those calculated in the SSRAs due to habitat limitations.  For aquatic biota, no significant risks were identified in the river.  The SSRAs concluded that ecological benefit associated with remediation would be minimal, and that risks would remain low provided that the Sites are managed as “Brownfield” industrial sites.  Long-term monitoring is appropriate to ensure that risks remain low.  INTRODUCTION  Falconbridge Limited (Falconbridge) is in the process of remediating the Topley and Richfield Loop Former Concentration-Shed Sites near Topley, British Columbia (Figure 1), according to remediation orders issued under the Contaminated Sites Regulation (CSR) and Waste Management Act (WMA) of British Columbia.  The Topley Site covers about 4.5 hectares with the Bulkley River forming the southern property boundary.  The Richfield Loop Site is about 19 ha in area and is adjacent to an oxbow pond which flows seasonally to the Bulkley River.            The concentrate shed sites were formerly used by Falconbridge and previous owners for transfer of Cu concentrate from the nearby Granisle Mine (Topley) and Bell Mine (Richfield Loop) for rail shipment. The Topley Site was no longer used for concentrate after the early 1980s, while concentrate handling was discontinued at Richfield Loop in the early 1990s.  Prior to use for concentrate handling, both sites were occupied by sawmills.  Until very recently, both sites were also used for storage of road salt.  Site investigations have been completed for the sites under the British Columbia Contaminated Sites Regulations (CSR), including Preliminary Site Investigations (PSI), Detailed Site Investigations (DSI), and draft Remediation Plans.  These studies identified the extent and degree of soil and groundwater contamination at the sites.  These PSI and DSI studies identified the presence of Cu concentrate (Cu sulphide) in soils closest to the concentrate sheds and rail loading areas.  In addition to the PSI and DSI studies, monitoring has included river and oxbow monitoring (benthic invertebrates, bioaccumulation in mussels, sediment toxicity, water quality), monitoring of groundwater quality, and monitoring a seep discharging from the Topley Site into the river.  Various remediation activities have been completed to date including armouring of the river bank to control erosion at the Topley Site, removal of fuel storage tanks and debris, and removal of the concentrate sheds themselves.  Other remedial actions considered have included placement of a layer of crushed limestone and a vegetated soil cover over the areas of greatest contamination by Cu to provide alkalinity to infiltrating water and neutralize acidity generated by the oxidation of concentrate residue in the soil.  Other remedial alternatives considered have been removal of “hotspots” where Cu concentrations are highest, and installation of a limestone-filled trench at the Topley Site to provide for removal of dissolved Cu from the groundwater plume before it reaches the river.  Removal of all soil contaminated at levels above provincial soil quality standards was considered not feasible owing to the very large volumes of contaminated soil present.  Consistent with the B.C. regulations for contaminated sites, soil remediation should be guided based on the intended future use of the properties, and on potential risks to humans and natural biota found at and adjacent to the properties.  Because there will be a need to manage most or all of the contaminated soil on the properties, site-specific risk assessments (SSRAs) were required to evaluate the need for risk management.  The SSRAs for Topley and Richfield Loop included human health risk assessment (HHRA) components and ecological risk assessment (ERA) components, as prescribed by B.C. Ministry of the Environment (MOE) guidance.  APPROACH  Risk Assessment  Risk Assessment identifies and evaluates the connections between chemicals in the environment, the human and ecological receptors which inhabit the local environment and the pathways through which the receptors may be exposed to the contaminants.  The principal elements of an SSRA (including both HHRA and ERA) are:  • Problem Formulation – which develops the blue print for the risk assessment including identification of potential receptors, identification of potential contaminants of concern and identification of the potential exposure pathways, using all relevant site information, • Effects (Toxicity) Assessment – which identifies benchmarks for each receptor and chemical based on toxicological information, • Exposure Assessment – which determines the amount of chemical reaching and entering the receptors, and • Risk Characterization – which compares the degree of exposure to the toxicity benchmarks. Where exposure is greater than the benchmarks, a potential risk is identified.  Groundwater Model  DSI studies identified high concentrations of Cu in groundwater at the Topley Site, at levels up to about 100 mg/L.  Coincident sulphate concentrations were in the order of about 1,000 mg/L.  This groundwater was found to reach seepage entering the river with relatively little attenuation of the sulphate concentrations (less than 10-fold) but with very substantial attenuation of Cu (about 1,000-fold) relative to the most contaminated groundwater at the site.  Copper concentrations in undiluted seep water have typically been 0.1 mg/L or less.  There was a concern that a Cu-rich plume might eventually reach the seep, resulting in Cu contamination in the river and a substantial increase in ecological risk.  A modeling study was completed to evaluate the physical-chemical processes controlling Cu transport in groundwater and to assess the potential for future increases in Cu migration to the river. PROBLEM FORMULATION  General Site Conditions  The PSI and DSI studies identified historic activities at these properties and determined the nature, extent and degree of contamination of soils and groundwater.  Soils and groundwater were contaminated with salt and Cu over significant portions of each property, with the greatest contamination occurring near the concentrate sheds and rail loading areas (Figures 2).  Contamination by petroleum hydrocarbons was also identified at each site, with the contamination greatest near locations where fuel storage tanks were located and near a former diesel generating station at Richfield Loop.  Various other metals were also present at elevated concentrations, generally in association with elevated Cu concentrations.            Groundwater flow at each site was determined to be generally southward towards the Bulkley River at the Topley Site and the CNR railway at Richfield Loop.  Groundwater flows are relatively fast (in the order of metres per day) at both sites.  Despite the rapid flow of groundwater, significantly elevated levels of dissolved Cu do not migrate past property boundaries.  At the Topley Site, approximately 1 – 2 L/s of groundwater from the Site was found to be seeping into the Bulkley River at dissolved Cu concentrations of 0.1 mg/L or less, which was not detectible in the river downstream of the site or near the bank close to the seep location.  The bank of the Bulkley River in the vicinity at the seep was actively eroding, and was remediated by installation of rip-rap to prevent erosion of the river channel towards the contaminated area of the Site. As part of this stabilization, the seep area was excavated, covered with geotextile and a sandy fill, and a standpipe for future sampling installed before the seep and the nearby bank areas were covered with rip- rap.  Accordingly, the former seep now reports to a sand-filter bed and then to the groundwater-river water mixture occupying the interstices of the rip-rap.  Water quality monitoring downstream of the former seep indicates no detectible effect on the background Cu concentration present in the river but a localized effect on specific conductance, caused by chloride and sulphate in the groundwater.  This indicates that Cu loadings from the site to the river are very small.  Contaminants of Concern  Media-specific and chemical-specific site monitoring data sites were reviewed and screened against the relevant B.C. CSR Standards for soil and groundwater.  If maximum measured values for any chemical- medium combination exceeded the relevant standard, then the chemical was deemed a contaminant of concern (COC).  Separate screening was carried out for the human health or ecological assessments and for both soil and groundwater.  Based on this screening process, the ERA and HHRA each had distinct COCs, although many COCs were common to both (Table 1).  Although B.C. soil standards were unavailable for sodium and chloride, these elements were also included as COCs owing to their high concentrations in soil and groundwater and the potential for adverse effects in vegetation and aquatic species.  TABLE 1:   CONTAMINANTS OF CONCERN IN SOIL AND/OR GROUNDWATER, TOPLEY AND RICHFIELD LOOP SITES  Parameter Topley Richfield Loop Benzene √ - Ethylbenzene √ - Xylenes (total) √ - VPH (nC6-nC10) √ √ LEPH √ √ HEPH √ √ 2,3,4,6-Tetrachlorophenol - √ Pentachlorophenol - √ Naphthalene √ - Arsenic √ √ Cadmium √ √ Cobalt √ - Chromium √ √ Copper √ √ Molybdenum √ √ Sodium √ √ Lead √ √ Antimony √ √ Zinc √ √ Boron √ - Chloride √ √ Manganese √ √ Selenium - √  Receptors and Exposure Pathways  Falconbridge intends to manage both the Topley and Richfield Loop sites as “Brownfield” sites, and to retain long-term ownership of the properties to manage risks into the future.  This will limit the potential for human occupation at the Site.  From the standpoint of potential human exposure, the exposure pathways considered include:  • incidental ingestion of soil by a casual trespasser on the Site; • inhalation of dust generated from activities by a trespasser on exposed soils; • consumption of groundwater from a well on the property; • exposure to Bulkley River water affected by COCs entering via contaminated groundwater; and • ingestion of fish obtained from the Bulkley River in the vicinity of the Site. • These receptors and pathways are depicted in Figure 3.         Figure 3:  Human Exposure Pathways.  Swimming and fish consumption pathways are relevant at the Topley Site only. The most sensitive casual trespasser onto the Sites is likely to be a child, who may be exposed via soil ingestion, inhalation, and dermal contact.  For this assessment, it is assumed that the child exposed via soil ingestion and inhalation falls in the 5 to 11-year age class and has an exposure duration of seven years.  The child’s exposure frequency was assumed to be once per week for three hours over six months/year (May to October).  Theoretically, over the long term, one might conservatively assume that a drinking water well is used on these properties.  One non-functional, inactive well currently exists on each Site.  Although this assumption is not realistic, the ingestion of groundwater as drinking water has been included as an exposure pathway for the hypothetical child receptor.  It was assumed that the quality of water in the wells correspond to the quality of water in nearby monitoring wells at similar depths.  Finally, an adult receptor is assumed to swim in the Bulkley River near the property, and to incidentally ingest some of the water and consume locally caught fish.  Ecological Receptors  Ecological receptors (i.e., species selected for risk calculations in the ERA) were selected based on species known to be present and on site observations.  Receptors were selected to include species of local interest, species thought to be sensitive to the COCs or to have a high potential for exposure, and species which collectively represent a range of feeding habits.  These included both aquatic and terrestrial organisms, as illustrated in Figures 4 and 5.          Figure 4:  Aquatic pathways considered in Topley ERA. At Richfield Loop, the aquatic receptors considered in the ERA were assumed to be exposed to the Oxbow pond adjacent to the Site.  The Oxbow is shallow and apparently fishless, probably owing to winterkill associated with under-ice de-oxygenation.  Accordingly, aquatic receptors considered at Richfield Loop included mallard, bufflehead, salamander and benthic invertebrates.           Figure 5:  Terrestrial pathways considered in Topley and Richfield Loop ERAs. At both Sites, the areas most affected by Cu contained the former concentrate sheds and the surrounding industrial yard, which are characterized by compacted gravelly fill.  These areas are agronomically deficient, and afford little useable habitat for plants or animals.  Effects (Toxicity) Assessment  The Effects Assessment consists of a review of the toxicological properties of the COCs to understand the potential for these COCs to have adverse effects.  Effect Levels, or benchmarks, for each COC represent receptor-specific exposure thresholds beyond which there is a possibility for some measurable adverse effect.  The benchmarks defined for the SSRAs are discussed below for each major receptor group.  For humans, benchmark doses used in the HHRAs were defined for chemical toxic effects, and also for carcinogenic effects for any COCs classed as carcinogens (IARC, 2003).  Toxicity reference values (TRVs) and cancer slope factors were used to estimate risks, and were obtained from the U.S. EPA (e.g., IRIS database), the U.S. Agency for Toxic Substances and Disease Registry (ATSDR, 2003), and Health Canada.  These were compared against COC exposures (doses) to determine human health and cancer risk.  Benchmarks for wildlife exposure were developed for each COC and receptor, using standard ERA guidance (e.g., Suter and Tsao, 1996; Sample et al., 1996; Efroymson et al., 1997a,b).  Where data are available, Effect Concentration (ECx) values were used in preference over No Observable Adverse Effects Levels (NOAELs) or Lowest Observable Adverse Effects Levels (LOAELs), with emphasis on sensitive sub-lethal end-points such as growth or reproduction.  Where ECx values were not available, LOAELs were generally selected as benchmarks.  These benchmarks are in the form of internal dose (i.e., obtained through ingestion of food, water and soil/sediment).  For several receptors, the Effect Levels are in the form of media concentrations rather than internal dose benchmarks.  This applies to biota which are essentially immersed in ambient contaminated media (soil, water, sediment) and subject to continuous exposure.  This includes all true aquatic biota (fish, invertebrates, plants, and amphibians), as well as soil invertebrates and terrestrial plants.  Exposure Assessment  The quantitative determination of degree of COC exposure in both the HHRA and the ERA is dependent on two factors:  1. the concentration of COCs in various media (air, soil, water), and 2. the receptor characteristics that determine to what extent they have contact (direct or indirect) with those media.  For humans and ecological receptors, the assumed exposure pathway parameters (amount of water ingested, amount of air inhaled, hours spent at site, etc.) were based on standard approaches and guidance from various agencies including the B.C. Ministry of the Environment, Health Canada and the U.S. EPA.  Ecological receptors were assumed to exhibit a site-occupancy consistent with their home ranges, as indicated by the literature.  All birds and mammals were assumed to be exposed through ingestion of contaminated soil and consumption of contaminated food.  Concentrations of COCs in food were estimated based on published bioaccumulation factors relating to root uptake, and uptake by aquatic biota.  The concentrations of COCs in soil and water used in determining exposure of human and ecological receptors were derived from monitoring data.  The upper 95th percentiles of concentrations of each COC in soil and groundwater investigations were taken as representative.  This is conservative, owing to the fact that the soil and groundwater data in question are based on monitoring that focused on the most contaminated portions of each Site; thus the assumed exposure conditions reflect the highest concentrations found on a limited area and over-state conditions encountered across each Site.  For inorganic COCs in soil, the 95th percentile concentrations were assumed to apply across most of the Sites, because much of each Site contains elevated Cu concentrations.  For organic parameters, only a few square metres of soil are contaminated at either site, and the 95th percentile concentrations were reduced downward to approximate the portion of each property affected.  Exposure of relatively immobile ecological receptors (plants, invertebrates) did not include an area adjustment. To represent surface water, analytical results for samples of seep/standpipe water at the Topley Site were used to conservatively represent water quality in the Bulkley River at the point of groundwater discharge. For near-field conditions, a dilution factor was applied based on the observed dilution measured for chloride, a conservative tracer.  For farfield concentrations, a dilution factor was applied that corresponds to the fraction of the mean annual river flow represented by the estimated flow of the seep.  Risk Characterization  The characterization of risk is completed by comparing the estimate of exposure with the relevant benchmark.  A Risk Quotient (RQ) is calculated by dividing the calculated exposure level by the relevant benchmark for each COC.  In all cases, the threshold for acceptance (no risk) is 1.  An RQ above 1 indicates that a potential risk has been flagged, and that the assumptions used in the calculations should be examined in detail.  After examination, the validity of the elevated RQ is assessed and a conclusion drawn about whether further assessment or risk management is warranted.  For the HHRAs, RQs were calculated for each exposure pathway and COC.  For each COC, an RQ was calculated for each pathway, and the pathway-specific RQs summed for a total RQ. The results of the RQ determinations are presented in Table 2 (toxic risk) and Table 3 (cancer risk).  Of the two age classes, the estimated levels of exposure experienced by the child are substantially larger than those experienced by the adult.  The majority of the risk was found to be associated with ingestion of water from the on-site well.  This exposure pathway was characterized conservatively, and is also not considered realistic (the on-site wells are not functional).  Regardless, this exposure pathway does not give rise to unacceptable risk.  Total RQs for the child and the adult remain below 1 for all COCs, and typically 0.1 or less (Table 4.5).  Cancer risks are less than 1 in 100,000 for the COCs classed as carcinogens (Table 3) and are also considered acceptable.  TABLE 2:   RISK QUOTIENTS FOR HUMAN (PUBLIC) RECEPTORS AT RICHFIELD LOOP AND TOPLEY SITES  COC Richfield Loop Child Topley Child Topley Adult Benzene - 9.0E-4 - Ethylbenzene - 3.7E-05 - Xylenes (total) - - VPH (nC6-nC10) 6.0E-4 0.019 - LEPH 0.0055 0.061 - HEPH 0.0078 0.28 - Naphthalene - 1.0E-4 - 2,3,4,6-Tetrachlorophenol 1.5E-5 - - Pentachlorophenol 0.015 - - Arsenic 0.39 0.25 0.016 Cadmium 0.27 0.037 0.003 Cobalt - - - Chromium 1.0E-4 2.5E-05 3.9E-07 Copper 0.034 0.048 0.002 Manganese 0.19 - - Molybdenum 0.0072 0.036 0.0002 Sodium - - - Lead 0.069 0.042 9.0E-4 Antimony 0.071 0.010 0.002 Selenium 0.054 - - Zinc - - - Boron - 0.074 2.3E-05 Chloride - - -  TABLE 3:   CANCER RISKS FOR HUMAN (PUBLIC) RECEPTORS, EXPOSED TO CARCINOGENS, RICHFIELD LOOP AND TOPLEY SITES  COC Richfield Loop Child Topley Child Topley Adult Benzene - 6.8E-6 - Arsenic 7.9E-6 5.0E-6 3.2E-7 Cadmium 3.7E-11 8.8E-12 -  For the ERAs, RQs were calculated for each receptor species considered (Table 4).  For mammals and birds, pathway-specific and total RQs were calculated by dividing dose estimates by benchmark doses. For plants, fish, invertebrates, and amphibians, a single RQ was calculated by dividing media concentrations by the relevant media concentration benchmarks.  For all COCs, these risks are substantially overstated because they are based on assumed exposure to upper bound concentrations which occur in the gravelly, compacted fill in the industrial yards adjacent to the former sheds.  These fills are agronomically deficient and unlikely to support significant vegetation growth or associated invertebrate, bird and mammal assemblages.  In the case of hydrocarbons, these risks are significantly overstated because the upper-bound concentrations producing these theoretical risks occur at depth in the soil below the depth important for root development.  For Cu and Mo, RQs exceeded 100 for plants and soil invertebrates at both sites.  While these high RQ values indicate a potential for adverse effects, these risks are identified for areas where the physical aspects of the soil a growing medium (compaction, gravel content, poor drainage) are limiting as noted above.  Also, for Cu, we found that soil is not toxic to plants growing on Bell Mine tailings containing about 2,000 mg/kg, some 40 times greater than the benchmark of 50 mg/kg used to calculate RQ in plants.  Similarly, Mo risk is overstated, based on observations of plant growth on molybdenum-rich Bell Mine tailings, and on the fact that Mo phytotoxicity has not been observed under field conditions (Neuman et al., 1987).  For aquatic biota residing in the Bulkley River adjacent to the Topley Site, no RQs exceeded 1 (Table 4). This is consistent with the results of rainbow trout and Daphnia toxicity testing of undiluted seepage, which consistently showed non-toxic conditions.  For biota at the Richfield Loop Oxbow, the RQs for waterfowl were below 1 (Table 4).  For benthic invertebrates and other aquatic species, RQs for some metals including Cu exceeded 1 owing to sediment (rather than water) concentrations.  However, a benthic community and sediment toxicity evaluation of the Oxbow (BEAK, 1999) determined that sediment impacts were minor.  Oxbow water quality was unimpacted by Cu or other metals, indicating no risk to the Bulkley River downstream.  In summary, the risk assessments identified COCs in soil that may have potential to cause adverse effects, especially to soil invertebrates and plants, although this is principally a theoretical risk owing to important habitat limitations in the most affected areas, effectively preventing exposure.  For small mammals and birds, the risk of adverse effects is lower.  In the aquatic environment, information on standpipe/seep dilution rates in the Bulkley River and on the toxicity of standpipe water shows that there is no risk to aquatic receptors in the Bulkley River. T A B L E  4 : M A G N IT U D E  O F R IS K  Q U O T IE N T  V A L U E S D E T E R M IN E D  F O R  T O PL E Y  (T ) A N D  R IC H FI E L D  L O O P (R L ) E C O L O G IC A L  R E C E PT O R S   R ob in   Ju nc o  V ol e  O w l  Pl an ts  T er re st ri al  In ve rt eb ra te s      A qu at ic  B io ta   T  R L  T  R L  T  R L  T  R L  T  R L  T  R L  M al la rd 1 B uf fle he ad 1 M us kr at 2 M in k2  T  R L  Et hy lb en ze ne  - - - - - - - - √ - √ - - - - - - - V PH  - - - - - - - - √ √ √ √√  - - - - - - LE PH  - - - - - - - - √√  √√  √√  √√  - - - - - - H EP H  √ - - - - - - - √√  √√  √√ √ √√  - - - - - - N ap ht ha le ne  √ - - - - - - - √√  - √√  - - - - - - - Te tra ch lo ro ph en ol  - - - - - - - - - √ - √ - - - - - - Pe nt ac hl or op he no l - √√ √ - √ - √ - - - √√ √ - √√ √ - - - - - - A s - - - √ √ √√  - - √ √ - √ - - - - - √√  C d - - - - - - - - - - - - - - - - - √ C o - - - - - - - - - - - - - - - - - - C r - - - - - - - - - - - - - - - - - √ C u √ √√  √√  √√ √ √√  √√ √ - - √√ √ √√ √ √√ √ √√ √ - - - - - √√  M o √ √ √√  √ √√ √ √√  - - √√ √ √√ √ √√ √ √√ √ - - - - - - N a - - - - - - - - √√  √√  - - - - - - - - Pb  - - - - - - - - - - - - - - - - - √ Sb  - √ - √ - - - - √ √ √ √ - - - - - - Se  - √ - √ - √ - - - √√  - √√  - - - - - - Zn  - √ √ √ - - - - √ √√  √ √√  - - - - - - B  - - - - - - - - √ - - - - - - - - - C l - - - - - - - - √ √ - - - - - - - -  - R is k qu ot ie nt  < 1 (n o ris k) . √ - R is k qu ot ie nt  o f 1 -1 0.  √√  - R is k qu ot ie nt  1 0. 1- 10 0.  √√ √ - R is k qu ot ie nt  > 10 0.  1  M al la rd  a nd  b uf fle he ad  in  R ic hf ie ld  L oo p O xb ow . 2  M us kr at  a nd  m in k at  B ul kl ey  R iv er , T op le y si te .  Groundwater Model  Concern has been expressed that groundwater enriched with high Cu concentrations could eventually migrate to the Bulkley River, resulting in unacceptable impact.  The DSI study and subsequent groundwater monitoring have shown that groundwater flows rapidly from the Topley Site towards the Bulkley River, with little dilution of conservative parameters such as sulphate and chloride, but remains very depleted in Cu relative to groundwater concentrations beneath the most contaminated soils.  A study was carried out to evaluate and model the geochemical processes that control Cu transport in groundwater and to determine whether concentrations that might produce adverse impacts in the river are prevented by these geochemical mechanisms (Stantec 2003).  Using information on stream discharge and the estimated groundwater discharge from the Site to the river, Stantec determined that a Cu concentration in groundwater in the order of 5 mg/L would not result in river concentrations near the seep that exceed the B.C. maximum concentration criterion for aquatic life protection.  Using the PHREEQC geochemical model (Parkhurst and Appelo, 1999) and data on water quality in Topley Site groundwater, it was determined that once released from the mineral sulphide form (chalcopyrite) through oxidization, Cu reacts with alkalinity in groundwater and soil to form malachite (Cu carbonate).  Modeling demonstrated that malachite controls Cu concentrations in groundwater at about 0.3 mg/L.  Other mechanisms including dilution combine to maintain concentrations below 0.1 mg/L in seepage from the site.  Data on Site soils indicate that there is ample carbonate present to effectively attenuate the inventory of Cu present.  Accordingly, it was concluded that a high concentration Cu plume is unlikely to migrate to the river from the zone of greatest contamination. As a contingency, Falconbridge is monitoring the plume regularly and could install a limestone-filled trench across the plume to attenuate Cu in the event that concentrations begin to rise significantly.  Implications of Potential Remedial Actions  The oxidation of Cu sulphide concentrate has been occurring for decades and experience tells us that the rates of reaction and release of Cu are now likely to be declining.  With time, the most exposed sulphide mineral becomes oxidized and either is partially depleted or the surfaces become coated with iron oxides, thereby reducing subsequent rates of reaction and Cu release.  There may at present be more Cu sulphide in the soils that is “protected” from reaction with oxygen either because it occurs below other concentrate material that has oxidized or because it occurs in lenses that retain moisture that reduces access to oxygen.  Removal of Cu “hot spots” has been contemplated for the Topley Site in particular, based on a concern about future risks to the river.  Conceptually, removal of Cu-rich hot-spots would lead to reduced risks of groundwater contamination over the long term.  However, excavation may introduce new risks as a result of soil disturbance, by exposing fresh “unreacted” minerals to oxidation and may also result in the redistribution of any road salt that may remain un-dissolved on Site.  PHREEQC modeling demonstrates that the solubility of malachite increases in the presence of elevated chloride concentration.  Given that risks to the river are low under present conditions and that geochemical controls are expected to maintain this low-risk condition over the long term, it is unnecessary and may be imprudent to disturb the site to remove hotspots.  Furthermore, it also appears unnecessary to place a crushed limestone/soil layer on the surface to minimize Cu mobility at either site, given that natural conditions are adequate to limit mobility.  CONCLUSIONS  The SSRAs for the Topley and Richfield Loop Sites identified no adverse human health risks to persons who may regularly trespass on the properties or swim in the Bulkley River and eat fish from the river.  There is a possibility of some level of localized risk to ecological receptors, especially plants and soil invertebrates.  These risks are limited because the most contaminated soils consist of compacted gravelly fill, which would prevent the development of significant vegetation growth regardless of metal concentration.  For aquatic biota, there is no expectation of any significant adverse effects.  No area of significant or even measurable biological effect is predicted in the Bulkley River adjacent to the Topley Site or downgradient of the Richfield Loop Site.  Aquatic risks appear to be fully mitigated by geochemical mechanisms present in soils and groundwater at these sites.  Risks associated with COCs in soils at Topley appear too limited to warrant soil remediation if the Sites remains under Falconbridge’s ownership and management.  However, groundwater conditions should continue to be monitored at both sites so that if conditions change significantly, contrary to model predictions, then mitigation measures can be implemented to prevent significant impact.  REFERENCES  ATSDR  2003.   Minimum Risk Levels (MRLs). Department of Health and Human Services, US Public Health Service, Agency for Toxic Substances and Disease Registry. Atlanta, GA.  Beak International Incorporated.  1999.  Sampling of Metals and Aquatic Life in the Bulkley River Adjacent to the Former Topley Concentrate Shed Site.  Beak International Incorporated.  2000.  Reclamation Study at the Bell Mine, Granisle, British Columbia. Report Prepared for Noranda Inc.  Ref. 21581.1.  Efroymson, R. A., M. E. Will, and G. W. Suter II. 1997a. Toxicological Benchmarks for Contaminants of Potential Concern for Effects on Soil and Litter Invertebrates and Heterotrophic Process: 1997 Revision. Oak Ridge, TN. ES/ER/TM-126/R2.  Efroymson, R. A., M. E. Will, G. W. Suter II, and A.C. Wooten. 1997b. Toxicological Benchmarks for Screening Contaminants of Potential Concern for Effects on Terrestrial Plants: 1997 Revision. Oak Ridge National Laboratory, Oak Ridge, TN. ES/ER/TM-85/R3. International Agency for Research on Cancer (IARC).  2003.  Carcinogen Classification Database.  Neuman, E.R., J.L. Schrack and L.P. Gough.  1987.  Copper and molybdenum, pp. 215-232. In: Reclaiming Mine Soils and Overburden in the Western United States.  Soil Conservation Society of America, Ankney, Iowa.  Parkhurst, D.L. and C.A.J. Appelo. 1999. User’s Guide to PHREEQC (Version 2) - A Computer Program For Speciation, Batch-Reaction, One-Dimensional Transport, and Inverse Geochemical Calculations. U.S. Geological Survey Water-Resources Investigations Report 99-4259, 310 p.  Sample, B.E., D.M. Opresko and G.W. Suter.  1996.  Toxicological Benchmarks for Wildlife:  1996 Revision.  Risk Assessment Program, Health Sciences Research Division.  Oak Ridge, Tennessee. ES/ER/TM-86/R3.  Stantec Consulting Ltd.  2003.  Assessment of Copper Behaviour and Environmental Implications at the Topley Former Concentrate Shed Site, Topley, B.C.  Ref. 631 22543.1  Suter, G.W. and C.L. Tsao.  1996.  Toxicological Benchmarks for Screening Potential Contaminants of Concern for Effects on Aquatic Biota:  1996 Revision.  Risk Assessment Program, Health Sciences Research Division.  Oak Ridge, Tennessee.


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