SITE-SPECIFIC WATER QUALITY OBJECTIVE FOR NITRATE, 2012

Transcription

1 EKATI Diamond Mine Site-Specific Water Quality Objective for Nitrate, 2012 April 2012

2 EKATI DIAMOND MINE SITE-SPECIFIC WATER QUALITY OBJECTIVE FOR NITRATE, 2012 April 2012 Project # Citation: Rescan EKATI Diamond Mine: Site-Specific Water Quality Objective for Nitrate, Prepared for BHP Billiton Canada Inc. by Rescan Environmental Services Ltd.: Yellowknife, Northwest Territories. Prepared for: BHP Billiton Canada Inc. Prepared by: Rescan Environmental Services Ltd. Yellowknife, Northwest Territories

3 EKATI DIAMOND MINE Site-Specific Water Quality Objective for Nitrate, 2012 Executive Summary

4 Executive Summary A site specific water quality objective (SSWQO) was developed for nitrate based on chronic toxicity test data that were available in the literature and from a recent investigation conducted by Nautilus Environmental (2011a and 2011b) on the effect that water hardness has on the toxicity of nitrate. Acceptable toxicity data were available for: one green algal species (Pseudokirchneriella subcapitata); four invertebrates, including two zooplankton (Ceriodaphnia dubia and Daphnia magna), one epibenthic amphipod (Hyalella azteca), and one benthic midge larva (Chironomus dilutus); and four fish, two salmonids (Oncorhynchus mykiss and Salvelinus namaycush), and two non-salmonids (Pimephales promelas and Notropis topeka). These data met the CCME requirements for establishing a Type A water quality guideline using a Species Sensitivity Distribution (SSD). The relationship between water hardness and chronic toxicity has been established for four species, each of which was represented in the SSD. The slope of the relationship between water hardness and toxicity was pooled for these four species to establish a slope that could be used to adjust the toxicity data on the basis of the hardness that the test was conducted under. The approach used for hardness correction followed procedures used by the US EPA for incorporating water hardness into water quality benchmarks for metals requiring such adjustment. The pooled slope was , which was used to adjust the toxicity data to a common hardness. The SSD of the hardness-normalized toxicity data was evaluated using five distributions (Fisher Tippett, normal, logistic, Weibull and Gompertz), and the logistic regression was selected as the most appropriate fit. This distribution resulted in an HC 5, which is the concentration that is considered to be protective of at least 95% of species, of 6.5 mg/l NO 3 -N at a hardness of 60 mg/l. In August 2011 water hardness in lakes downstream of the Long Lake Containment Facility (Leslie, Moose, Nema and Slipper lakes, and two stations in Lac de Gras) ranged between 7.1 mg/l and 139 mg/l (average 60.9 mg/l). After incorporation of the pooled slope, the final equation for the SSWQO was as follows: ( x ln (hardness) 2.032) WQO = e The relationship between water hardness and nitrate toxicity was established across a range of water hardness values of up to approximately 160 mg/l (16.4 mg/l NO 3 -N); values with hardness greater than 160 mg/l were conservatively assumed to have the same nitrate values as determined for that water hardness. Figure 1 shows the proposed SSWQO across a range of hardness values (levelling off after 160 mg/l water hardness), as well as toxicity data that were considered primary or secondary quality, tested at water hardness values ranging from 10 mg/l to 310 mg/l. All of the toxicity test thresholds fall above the proposed SSWQO, indicating that the proposed objective is conservatively protective across the full range of water hardness values. In addition to the ensuring that the requirements for a valid SSWQO derivation were met from the toxicological database as described above, BHP Billiton conducted further site-specific confirmatory tests to increase confidence in the derivation. Tests conducted in water collected from four lakes at EKATI (Slipper, Nema, Moose and Leslie lakes) using an invertebrate (C. dubia) and a fish (P. promelas) demonstrated that the proposed SSWQO was appropriate under the conditions associated with site waters. An additional reduction in toxicity of nitrate was evident in the site waters, over-and-above that established on the basis of hardness, providing an additional level of safety associated with the proposed SSWQO. This additional protection is associated with the balance of major ions present in the site waters. BHP BILLITON CANADA INC. i

5 SITE-SPECIFIC WATER QUALITY OBJECTIVE FOR NITRATE, 2011 Figure 1. Proposed Site Specific Water Quality Objective (SSWQO) for Nitrate as a Function of Water Hardness and Individual Toxicity Test Results for Nitrate ii RESCAN ENVIRONMENTAL SERVICES LTD. (PROJ# /REV C.1) APRIL 2012

6 EKATI DIAMOND MINE Site-Specific Water Quality Objective for Nitrate, 2012 Acknowledgements

7 Acknowledgements This report was produced by James Elphick and Josh Baker (M.Sc.) of Nautilus Environmental, contracted by Rescan Environmental Services Ltd. (Rescan), for BHP Billiton Canada Inc. (BHP Billiton). Review was conducted by Tonia Robb (Ph.D.), Mark Whelly (M.Sc.), and Marc Wen (M.Sc.) of Rescan and by Peter M. Chapman (Ph.D.) of Golder Associates Ltd. BHP BILLITON CANADA INC. iii

8 EKATI DIAMOND MINE Site-Specific Water Quality Objective for Nitrate, 2012 Table of Contents

9 EKATI DIAMOND MINE SITE-SPECIFIC WATER QUALITY OBJECTIVE FOR NITRATE, 2011 Table of Contents Executive Summary... i Acknowledgements... iii Table of Contents... v List of Figures... vi List of Tables... vii List of Appendices... vii Abbreviations... ix 1. Introduction Background Nitrate Units Objectives Review of Current and Historical Water Quality Benchmarks Background Existing Generic Water Quality Benchmarks Summary Methods Introduction Site-specific Water Quality Objective Approaches Background Concentration Recalculation Water Effects Ratio Resident Species Approach Selected for the EKATI SSWQO Calculation Compilation of Existing Information Environmental Fate Toxicity Data Evaluation of Relevant Toxicity Data Minimum Requirements for SSD Dataset SSD Data Selection BHP BILLITON CANADA INC. v

10 SITE-SPECIFIC WATER QUALITY OBJECTIVE FOR NITRATE, Derivation of a SSWQO Evaluation of the SSWQO Results Compilation of Existing Information Environmental Fate Chronic Toxicity Data Evaluation of Relevant Toxicity Data Derivation of SSWQO Evaluation of Applicability of the SSWQO to the Site Uncertainty Introduction Relevance of the Toxicological Datasets Inclusion Criteria Minimum Data Criteria Endpoints Used in SSD Suitability of Species Model Fit Standardization of Toxicological Data Tolerance of Organisms Toxicity of Mixtures Summary References... R-1 List of Figures FIGURE PAGE Figure 1. Proposed Site Specific Water Quality Objective (SSWQO) for Nitrate as a Function of Water Hardness and Individual Toxicity Test Results for Nitrate... ii Figure Surface Water Flow through the EKATI AEMP Watersheds Figure Total Nitrate and Hardness Concentrations in Water at AEMP Lake Sites of the Koala Watershed, Figure Total Nitrate and Hardness Concentrations in Water at AEMP Stream Sites of the Koala Watershed, Figure Total Nitrate and Hardness Concentrations in Water at AEMP Lake Sites of the King- Cujo Watershed, Figure Total Nitrate and Hardness Concentrations in Water at AEMP Stream Sites of the King-Cujo Watershed, vi RESCAN ENVIRONMENTAL SERVICES LTD. (PROJ# /REV C.1) APRIL 2012

11 TABLE OF CONTENTS Figure Relationship between Water Hardness and Nitrate Concentration for Leslie, Moose, Nema, and Slipper Lakes at EKATI Figure General Nitrogen Cycle in Aquatic Systems Figure Relationship between Water Hardness and LC 50 Values for Two Species of Fish and Two Invertebrates Figure Relationship between Water Hardness and IC 25 Values from Chronic Toxicity Tests for Two Species of Fish and Two Invertebrates Figure Normalized Slopes of Hardness-Chronic Toxicity Relationships Figure Pooled Normalized Slope of Hardness-Toxicity Relationships for Four Species Figure Long-term Species Sensitivity Distributions for Nitrate Using Five Model Distributions and the Selected Normal Model for Derivation of the SSWQO for Nitrate at EKATI Figure Proposed Site Specific Water Quality Objective for Nitrate as a Function of Water Hardness and Individual Toxicity Test Results for Nitrate List of Tables TABLE PAGE Table Chronic Toxicity Studies Used in the Species Sensitivity Distribution Table Relationship between Water Hardness and Chronic Toxicity of Nitrate Table Summary of Results of Species Sensitivity Distribution Calculations Using Five Models Table Calculated Proposed Site Specific Water Quality Objectives Calculated Across a Range of Hardness Values Appendices are provided on the CD only List of Appendices Appendix A. Nitrate Water Concentrations and Hardness in Lakes and Streams of the EKATI Project Area, 1994 to 2011 Appendix B. Relationship between Water Hardness and Toxicity of Nitrate (Nautilus 2011a and 2011b) Appendix C. Chronic Toxicity Studies on Nitrate Available from the Literature Appendix D. Statistical Analysis of Chronic Species Sensitivity Distribution Using SSD Master Software Appendix E. Toxicity testing in support of a SSWQO for nitrate for EKATI BHP BILLITON CANADA INC. vii

12 Abbreviations EKATI DIAMOND MINE Site-Specific Water Quality Objective for Nitrate, 2012

13 Abbreviations Terminology used in this document is defined where it is first used. AEMP ANZECC/ARMCANZ CCME EC x ETMF HC 5 IC x IPS KPSF LC 50 LLCF LOEC NO 3 -N NAESI NOEC MATC SNP SSD SSWQO SSWQG TMF US EPA WEMP WER WQG WQO Aquatic Effects Monitoring Program Australian and New Zealand Environment Conservation Council and Agriculture and Resource Management Council of Australia and New Zealand Canadian Council of Ministers of the Environment Effective Concentration estimated to cause an effect on x% of exposed organisms Exposure and Toxicity Modifying Factor Hazardous Concentration for 5% of tested species Inhibition Concentration estimated to cause an x% inhibitory effect (e.g., on growth or reproduction) on exposed organisms Ideal Performance Standard King Pond Settling Facility Lethal Concentration to 50% of organisms tested Long Lake Containment Facility Lowest Observed Effects Concentration Nitrate, reported on the basis of nitrogen concentration National Agri-Environmental Standards Initiative No Observed Effects Concentration Maximum Acceptable Toxicant Concentration Surveillance Network Program Species Sensitivity Distribution Site Specific Water Quality Objective Site Specific Water Quality Guideline Toxicity Modifying Factor United States Environmental Protection Agency Wildlife Effects Monitoring Program Water Effects Ratio Water Quality Guideline Water Quality Objective BHP BILLITON CANADA INC. ix

14 1. Introduction EKATI DIAMOND MINE Site-Specific Water Quality Objective for Nitrate, 2012

15 1. Introduction 1.1 BACKGROUND BHP Billiton Canada Inc. (BHP Billiton) operates the EKATI Diamond Mine (EKATI) located approximately 300 km northeast of Yellowknife, Northwest Territories, Canada. The mine site is in the southern Arctic ecoregion. BHP Billiton is committed to minimizing the impacts of EKATI on the aquatic environment, and to sustainable management of the aquatic environment. BHP Billiton developed the Aquatic Effects Monitoring Program (AEMP) to document any changes that occurred following mine construction, operation, and expansion, and to provide early warnings of environmental changes. The AEMP at EKATI is a requirement specified in BHP Billiton s Class A Water Licence (W2009L2-0001). The Water Licence outlines the regulatory requirements for water quality at EKATI. For several water quality variables there are Water Licence discharge criteria that must not be exceeded. A discharge criterion for nitrate is provided only for effluent discharge from Two-Rock Settlement Pond (Surveillance Network Program (SNP) station 0008-Sa3) located in the Horseshoe Watershed at the Sable development, which has not yet been constructed. There is no discharge criterion for nitrate in effluent discharge from the Long Lake Containment Facility (LLCF) (SNP station ) or the King Pond Settling Facility (SNP station ). Along with discharge water quality, water quality downstream of LLCF and KPSF is also monitored. Receiving water quality is compared to generic national guidelines provided by the Canadian Council of Ministers of the Environment (CCME 2007a). These guidelines do not have any legal or regulatory standing, but are used as default receiving environment benchmarks. For some water quality variables, a site specific water quality objective (SSWQO) is appropriate and provides a modified generic guideline value to better represent local conditions and the biological community present at the site. The Water Licence does not specify a guideline for nitrate concentrations for SNP stations and However, BHP Billiton has adopted performance standards established by Environment Canada for the agriculture industry (Guy 2008) for nitrate toxicity as part of their assessment of receiving environment quality. This benchmark is 4.7 mg/l NO 3 -N, and was considered appropriate for use at EKATI since the approach taken in development of the Ideal Performance Standard (IPS) was largely consistent with current methods employed for development of Canadian water quality guidelines (WQGs), including use of a Species Sensitivity Distribution (SSD) for guideline derivation (CCME 2007b). The toxicity data used in the derivation of the IPS were also largely relevant to EKATI, with the exception that one-third of the data used in development of the IPS were for amphibians. Although amphibians are known to occur in the Northwest Territories, the EKATI area is beyond their known distribution which is generally below the tree line (ENR 2006, 2012a and 2012b). In addition, amphibians have not been observed during the wildlife effects monitoring program (WEMP) or other biological surveys at EKATI (B. Milakovic and K. Kuker personal communication). Regardless, the IPS was considered to be a conservative benchmark for monitoring the receiving environment and more relevant than the existing CCME guideline for nitrate. The current AEMP was designed to detect effects in the EKATI receiving environment within two major watersheds (Figure 1.1-1). In the Koala Watershed, the AEMP monitors waters downstream of the LLCF, including the LLCF discharge (SNP station ), Leslie Lake, Leslie-Moose Stream, Moose Lake, Moose- Nero Stream, Nema Lake, Nema Martine Stream, Slipper Lake, Slipper-Lac de Gras Stream, and two lake monitoring sites in Lac de Gras (S2 and S3). Within the King-Cujo Watershed, the AEMP monitors water BHP BILLITON CANADA INC. 1-1

16 SITE-SPECIFIC WATER QUALITY OBJECTIVE FOR NITRATE, 2011 downstream of the KPSF including the KPSF discharge (SNP station ), Cujo Lake, Cujo Outflow Stream, Christine-Lac du Sauvage Stream, and two monitoring sites in Lac du Sauvage (LdS1 and LdS2). Nitrate concentrations in the Koala watershed have been increasing since commissioning of the mine and have periodically exceeded the water quality objective of 4.7 mg/l NO 3 -N in Leslie, Moose and Nema lakes, but not in downstream water bodies (Figure 1.1-2; Appendix A). However similar increases in nitrate have not been observed in streams and lakes of the King-Cujo Watershed (Figure to 1.1-5; Appendix A). Recent investigations have established that water hardness plays an important role in modifying the chronic toxicity of anions such as sulphate and chloride (Elphick et al. 2011a and 2011b). Consequently, an investigation was conducted to establish whether water hardness also alters the toxicity of nitrate; the results of these tests have demonstrated that water hardness does indeed reduce the toxicity of nitrate (Nautilus Environmental 2011a and 2011b; Appendix B). The mechanism responsible for this effect has not been definitively established; however, it is likely that the mechanism relates either to competition between ions at passive ionic uptake sites or to effects that the hardness-related ions (i.e., calcium and/or magnesium) have on membrane permeability. The latter mechanism has its basis in osmoregulation; under low ionic strength conditions, freshwater organisms are limited in their ability to obtain necessary ions from the surrounding media, and may open uptake channels to maximize uptake of essential nutrients, whereas under higher ionic strength conditions, the permeability of the membrane may be reduced, since the organisms have less difficulty acquiring the ions required for homeostasis. Therefore, under low hardness (ionic) conditions, ions including nitrate may have a greater chance of being taken up by organisms than under high hardness conditions when ion channels are more controlled. The results of AEMP monitoring have indicated that water hardness has increased in water bodies downstream of the LLCF and to a lesser extent, the KPSF (Figures to 1.1-5; Appendix A). A strong relationship between water hardness and nitrate concentration is observed in samples collected from Leslie, Moose, Nema, and Slipper lakes (Figure 1.1-6), particularly in cases where nitrate concentrations have approached and exceeded the current IPS water quality objective (i.e., in Leslie and Moose Lakes). Thus, any role that water hardness plays in modifying the toxicity of nitrate is highly relevant to this site. The CCME WQG for nitrate is currently under review and a draft of the revised guideline was issued for public comment in February As part of this effort, published and otherwise available studies investigating the toxicity of nitrate in short- and long-term exposures have been reviewed by CCME and evaluated for data quality. In addition to the recent review conducted by the CCME, toxicological data for nitrate are available from a recent investigation conducted by Nautilus Environmental (2011a and 2011b); these investigations have increased the available dataset on toxicological effects associated with nitrate, as well as demonstrating the role that water hardness plays in modifying the toxicity of nitrate. In addition, a small amount of additional data were available from other investigations published subsequent to the recent review conducted by CCME and were reviewed. The availability of additional chronic toxicity data, as well as the notable effect of water hardness on toxicity of nitrate, strongly supports development of a SSWQO for nitrate that considers water hardness as a Toxicity Modifying Factor (TMF) per CCME (2007b). 1.2 NITRATE UNITS The convention for reporting nitrate concentrations differs between jurisdictions and individual investigations, with some reporting concentrations of nitrate as NO 3 and others as nitrogen (i.e., as NO 3 -N). The difference between these values corresponds to the proportionate difference between the molar mass of NO 3 ( g/mol) and N ( g/mol). Values reported in the present document are reported as NO 3 -N, and data have been corrected, where necessary, using these molar masses (i.e., values reported as NO 3 have been divided by and reported here as NO 3 -N). 1-2 RESCAN ENVIRONMENTAL SERVICES LTD. (PROJ# /REV C.1) APRIL 2012

17 Job No February ± Inset B Upper Exeter Lake y Fa e Inset C Lac du Sauvage LDS 1 Bearclaw LDS 2 Christine Inset A CELL B Inset C 1:850, Upper Panda CELL A 20 Grizzly Cujo Diavik EKATI CAMP LL CE [ Kilometres Koala Watershed r ltu Vu y Ba gis no. EKA C KPSF Panda Diversion Channel LLCF C trip LD CEL EL L Little Inset A Airs Kodiak E Lac de Gras Mo Leslie OLD CAMP o se 1:70,000 Counts R d oa to Nero y er is M Nema 1:80,000 Flow Direction Inset B Monitored Lake Nanuq Reference Lake Watershed Boundary :80,000 Lac de G ras 3 Kilometres S :80, Projection: UTM12, NAD83 Note: IKONOS Image from 2006 (Overview map), IKONOS Image from July 2006 (Inset C) S FIGURE Surface Water Flow through the EKATI AEMP Watersheds Sli pp er BHPB Claim Block Boundary

18 PROJECT # ILLUSTRATION # a32690f February 20, Nitrate Nitrate (as mg/l NO 3 -N) (LLCF) Leslie Moose Nema Slipper S2 S3 April July August September 0 Detection Limit Current WQO Year 300 Hardness Hardness (as mg/l CaCO³) (LLCF) Leslie Moose Nema Slipper S2 S3 April July August September 0 Detection Limit Year Note: The current WQO for Nitrate is 4.7 mg/l NO3-N and is based on the Ideal Performance Standard developed by Guy (2008). Total Nitrate and Hardness Concentrations in Water at AEMP Lake Sites of the Koala Watershed, Figure 1.1-2

19 PROJECT # ILLUSTRATION # a32692f February 20, Nitrate Nitrate (as mg/l NO 3 -N) Leslie Moose Moose Nero Nema Martine Slipper Lac de Gras June July August September 0 Detection Limit Current WQO Year 300 Hardness Hardness (as mg/l CaCO³) Leslie Moose Moose Nero Nema Martine Slipper Lac de Gras June July August September 0 Detection Limit Year Note: The current WQO for Nitrate is 4.7 mg/l NO3-N and is based on the Ideal Performance Standard developed by Guy (2008). Total Nitrate and Hardness Concentrations in Water at AEMP Stream Sites of the Koala Watershed, Figure 1.1-3

20 PROJECT # ILLUSTRATION # a32691f February 20, Nitrate Nitrate (as mg/l NO 3 -N) (KPSF) Cujo LdS2 LdS1 April July August September 0 Detection Limit Current WQO Year 300 Hardness Hardness (as mg/l CaCO³) (KPSF) Cujo LdS2 LdS1 April July August September 0 Detection Limit Year Note: The current WQO for Nitrate is 4.7 mg/l NO3-N and is based on the Ideal Performance Standard developed by Guy (2008). Total Nitrate and Hardness Concentrations in Water at AEMP Lake Sites of the King-Cujo Watershed, Figure 1.1-4

21 PROJECT # ILLUSTRATION # a32695f February 20, Nitrate Cujo Outflow Christine Lac du Sauvage Nitrate (as mg/l NO 3 -N) June July August September 0 Detection Limit Current WQO Year Hardness 300 Hardness (as mg/l CaCO³) Cujo Outflow Christine Lac du Sauvage June July August September Detection Limit Year Note: The current WQO for Nitrate is 4.7 mg/l NO3-N and is based on the Ideal Performance Standard developed by Guy (2008). Total Nitrate and Hardness Concentrations in Water at AEMP Sream Sites of the King-Cujo Watershed, igure 1.1-5

22 PROJECT # ILLUSTRATION # a32713f July 27, 2011 Nitrate (mg/l NO 3 -N) Leslie (R² = ) Moose (R² = 0.96) Nema (R² = ) Slipper (R² = ) Water Hardness (mg/l CaCO 3 ) Figure Relationship between Water Hardness and Nitrate Concentration for Leslie, Moose, Nema and Slipper Lakes at EKATI Figure 1.1-6

23 SITE-SPECIFIC WATER QUALITY OBJECTIVE FOR NITRATE, OBJECTIVES The recent review of nitrate toxicity conducted by CCME, the additional toxicological data for this anion available from Nautilus Environmental (2011a and 2011b; Appendix B) and others, as well as the role that water hardness has been shown to play in modifying the toxicity of nitrate, provide the basis for developing a SSWQO for nitrate at EKATI. Consequently, the objective of this report is the development of a proposed SSWQO for nitrate for the receiving environment at EKATI. The focus of this SSWQO is on toxicity relating to long-term exposure to nitrate, for application in receiving environment long-term monitoring. Because hardness also modifies toxicity in short-term tests, it may be appropriate in the future to establish a hardness-linked SSWQO for short-term exposure. To achieve the above main objective, the following components of deriving a SSWQO for nitrate were completed: o a brief discussion of existing long-term guidelines relative to their applicability to EKATI (Section 2); o a description of the methodology used in deriving the SSWQO (Section 3); o a summarized discussion of the fate and behaviour, chronic toxicity studies, and calculation of the SSWQOs (Section 4); and o a discussion of uncertainties related to each step of the process (Section 5). Development of the SSWQOs followed established Canadian procedures for site-specific benchmark calculations and updated methods for their development (CCME 2003, 2007b), and incorporated methods from US EPA (1985) for inclusion of water hardness as a toxicity modifying factor RESCAN ENVIRONMENTAL SERVICES LTD. (PROJ# /REV C.1) APRIL 2012

24 EKATI DIAMOND MINE Site-Specific Water Quality Objective for Nitrate, Review of Current and Historical Water Quality Benchmarks

25 2. Review of Current and Historical Water Quality Benchmarks 2.1 BACKGROUND In Canada, WQGs are used largely as benchmarks for receiving environments, and do not have legal standing for compliance monitoring. The terms guideline, criterion, trigger value and objective are used by different jurisdictions to generally refer to levels for specific chemicals that are considered safe (i.e., pose minimal risk) in the environment. In Canada, these benchmarks are not equivalent to end-of-pipe discharge limits or standards that are specified in discharge permits; they refer to water quality in receiving water bodies. Historically, Canadian WQGs have been derived using a safety factor approach, as described in CCME (1991). This method involves application of a safety factor (often ten-fold) to the toxicological effect level for the most sensitive species in order to calculate the WQG. This approach generally provides a highly conservative estimate of a concentration of the chemical of interest that would be expected to be safe across a broad spectrum of conditions associated with Canadian environments, as well as accounting for the possibility that species exist that are more sensitive than those that have been tested. However, this approach relies entirely on the results of a single study on a single species and, therefore, is subject to anomalous test results. In addition, in cases where data are only available for a small number of species, it also might not provide adequate protection for all taxa. Environment Canada has updated procedures for establishing WQGs to include the use of a Species Sensitivity Distribution (SSD) where sufficient data exist (CCME 2007b). This approach involves assembling a cumulative distribution of toxicity endpoints for all species for which data are available and extrapolating the guideline based on the goal of protection of at least 95% of species. A sigmoidal distribution is fit to the data using a number of models, and the model that best fits the cumulative distribution (particularly in the lower tail of the distribution where the data for sensitive species occur) is used to determine the concentration that is expected to be protective of 95% of tested species. This concentration is termed the HC 5 (hazard concentration to 5% of the tested species), and is established as the WQG. Despite the apparent acceptance of effects on 5% of species, this approach is considered to be consistent with the guiding principal of protecting all forms of aquatic life because the distribution is comprised of threshold concentrations that are not expected to affect organisms (CCME 2007b). In addition, a protection clause may be invoked to lower the guideline from the HC 5 in the event that a threshold for a protected or otherwise critical species falls below the calculated WQG value. WQGs can be calculated using the SSD approach with data from short-term (typically lethal concentration to 50% of tested species [LC 50 ] values from acute toxicity tests) or long-term exposures (threshold values from long-term tests), in order to calculate short-term or long-term guidelines, respectively. The advantage of using an SSD approach (which is termed a Type A guideline), over application of a safety factor (Type B guideline) is that it uses all of the available data to calculate a benchmark, rather than relying on a single data point. As a result, the SSD approach is less subject to individual anomalies within the dataset. Generic WQGs, whether calculated based on application of a safety factor or use of an SSD, are meant for application across a broad range of water quality conditions and biological community structures. However, site-specific conditions can alter the risk associated with a particular contaminant, as a result of interaction of the substance with water quality characteristics or differences in the BHP BILLITON CANADA INC. 2-1

26 SITE-SPECIFIC WATER QUALITY OBJECTIVE FOR NITRATE, 2011 composition of biological communities compared with that available within the dataset used to calculate the generic guideline. Consequently, guidance for derivation of site-specific WQGs (SSWQGs) in Canada has been published by CCME (2003). 2.2 EXISTING GENERIC WATER QUALITY BENCHMARKS The current CCME WQG for nitrate is 13 mg/l as NO 3 (CCME 2003), which corresponds to 2.9 mg/l NO 3 -N. This value was calculated on the basis of application of a ten-fold safety factor to the Lowest Observed Effect Concentration (LOEC) from a test using the Pacific tree frog, Pseudacris regilla. This guideline was not considered appropriate for EKATI since amphibians have not been documented as occuring in receiving environments surrounding the EKATI mine. In addition, procedures for development of WQGs have been updated to consider the distribution of species sensitivities, rather than focussing on individual data points (CCME 2007b). Site-specific toxicity testing was conducted for EKATI in 2003 to evaluate the sensitivity of early life stages of lake trout (Salvelinus namaycush) and lake whitefish (Coregonus clupeaformis), both of which are resident species of fish in the lakes surrounding EKATI. The purpose of this testing was to establish whether species of fish that occur in sub-arctic lakes might be different in their sensitivity to nitrate than the amphibian species on which the CCME WQG was based. The tests were conducted using sodium nitrate spiked into dechlorinated municipal tapwater. The results of these tests indicated that both species were sensitive to nitrate, although the results from the test using lake whitefish were complicated by poor survival of the control fish. The results of these tests have been published in the peer reviewed literature (McGurk et al. 2006), and provide the most sensitive published test endpoint for nitrate for any species. The authors concluded that these species of fish were as sensitive as the amphibian species on which the CCME guideline was based. Consequently, the CCME (2003) WQG for nitrate was initially adopted as a WQO for nitrate at EKATI. In 2008, Environment Canada calculated an Ideal Performance Standard (IPS) for nitrate under the National Agri-Environmental Standards Initiative (NAESI) program (Guy 2008). IPS values were developed as non-regulatory guidelines for water quality in agricultural areas. The guideline value was calculated as the 5 th percentile from a SSD, incorporating a total of 12 species, including four invertebrates (Ceriodaphnia dubia, Daphnia magna, Hyalella azteca and Macrobrachium rosenbergii), four fish (Oncorhynchus mykiss, Oncorhynchus tshawytscha, Pimephales promelas and Salvelinus namaycush) and four amphibians (Pseudacris regilla, Rana aurora, Rana pipiens and Xenopus laevis) (Guy 2008). The derivation approach was analogous to revised guidance for deriving CCME type A WQGs (CCME 2007b). The IPS was established as 20.9 mg/l NO 3, which corresponds to 4.7 mg/l NO 3 -N. Although this value was calculated for application to agricultural areas, there was nothing in the derivation process that was specific to agricultural sources and, consequently, this value was proposed and implemented as a WQO at EKATI in CCME is in the process of revising the Canadian WQG for nitrate using an SSD approach; the draft CCME WQG was released for public comment in February The process used to develop the draft CCME WQG was largely consistent with that utilized in development of the IPS for nitrate, and followed the SSD approach. In general, the dataset employed by CCME in deriving the draft WQG was consistent with that used in development of the IPS for nitrate. The exceptions were that CCME added a species, the Topeka shiner (Notropis topeka), and endpoints for three of the 12 species used in deriving the IPS were different than CCME endpoints because of identification of additional studies or recalculation of the endpoints. The draft CCME WQG is not considered appropriate for application at EKATI since this guideline has not yet been finalized following the public comment period, and it includes species not relevant to the EKATI aquatic community. 2-2 RESCAN ENVIRONMENTAL SERVICES LTD. (PROJ# /REV C.1) APRIL 2012

27 REVIEW OF CURRENT AND HISTORICAL WATER QUALITY BENCHMARKS WQGs for nitrate have been published in other jurisdictions. For example, the British Columbia WQG is 3 mg/l NO 3 -N, based on application of a ten-fold safety factor to data for Pseudacris regilla (BCMoE 2009), similar to the existing CCME guideline discussed above. WQGs for nitrate in Australia and New Zealand were established in 2000 (ANZECC/ARMCANZ 2000) and corrected for an error in 2002; the corrected guideline was established as 7.2 mg/l NO 3 -N (Hickey 2002), based on application of an acute to chronic ratio to a short-term guideline designed to protect 95% of species. Neither the US EPA nor the European Union has established WQGs for nitrate. 2.3 SUMMARY The current Canadian WQG for nitrate relies heavily on data for amphibians. Although amphibians are known to occur in the Northwest Territories, the EKATI area is beyond their known distribution which is generally below the tree line (ENR 2006, 2012a and 2012b). In addition, amphibians have not been observed during WEMP or other biological surveys at EKATI (B. Milakovic and K. Kuker personal communication). Furthermore, subsequent to publication of the Canadian WQG (CCME 2003) and the IPS (Guy 2008), additional data have become available on the toxicity of nitrate and its interaction with water hardness (Nautilus Environmental 2011a and 2011b). Consequently, it is appropriate to reconsider the water quality objective that is currently being employed at EKATI and to develop a revised objective which includes all available and appropriate information. BHP BILLITON CANADA INC. 2-3

28 3. Methods EKATI DIAMOND MINE Site-Specific Water Quality Objective for Nitrate, 2012

29 3. Methods 3.1 INTRODUCTION CCME WQGs are developed in a manner that is expected to be protective at all sites across Canada and accommodating the wide range of conditions that might be observed. Consequently, they typically employ a relatively high degree of conservatism to account for variables that might modify the risk of adverse effects in the environment. Site specific water quality objectives are derived in a manner that takes into consideration the unique characteristics of an individual site, such as biological community structure or physico-chemical characteristics of the environment that alter the potential for toxicity. In rare cases, a site-specific objective may be established at a value that is lower than the generic guideline to protect a critical and sensitive resource; however, typically, a site-specific objective is higher than the generic guideline, since incorporation of site-specific information reduces the need for conservatism that is inherent in the broad applicability of generic benchmarks. Derivation of the SSWQO for nitrate followed the most recent guidance from CCME (2003, 2007b). The main steps for the derivation of a long-term nitrate SSWQO were as follows: 1. Data compilation of existing information including environmental fate, toxicological data, and modifying factors. 2. Identification of relevant toxicological data. 3. Selection of the approach to be used in deriving SSWQOs based on available data. 4. Calculation of objectives and discussion of results and uncertainties. 3.2 SITE-SPECIFIC WATER QUALITY OBJECTIVE APPROACHES The CCME (2003) identified four approaches that can be taken to determine SSWQOs for individual substances: 1) the Background Concentration Approach; 2) the Recalculation Approach; 3) the Water Effects Ratio (WER) Approach; and, 4) the Resident Species Approach Background Concentration The Background Concentration Approach involves establishing a SSWQO on the basis of the range of background conditions of the variable of interest. This approach is typically implemented in cases where there are naturally-elevated concentrations of the variable of interest. This is not the case at EKATI Recalculation Using the Recalculation Approach, the existing generic benchmark is recalculated after limiting the dataset to available toxicological data for species that are considered relevant to the site (i.e., resident species or suitable surrogates representing taxa for which toxicological data are not available). Species that are not relevant (e.g., in this case, tropical species and amphibians) are excluded from the dataset in order to create an SSD which provides an appropriate representation of the biological community found at a specific site Water Effects Ratio Using the Water Effects Ratio (WER) Approach, site and laboratory waters are used in parallel toxicity tests in which the substance of interest is introduced to the water to measure the effect that site water has on the toxicity to one or more species. A difference in sensitivity of test organisms between the test BHP BILLITON CANADA INC. 3-1

30 SITE-SPECIFIC WATER QUALITY OBJECTIVE FOR NITRATE, 2011 waters provides an indication that the site water modifies the toxicity of the substance of interest. This provides justification to alter the water quality benchmark to account for that difference, because WQGs or similar benchmarks are typically derived from toxicity tests conducted in standardized laboratory water. Environmental and toxicity modifying factors (ETMFs) are characteristics in site water that can alter the behaviour, uptake, or toxicity of a substance to organisms Resident Species Using the Resident Species Approach, species that occur in the environment are tested to evaluate whether they are different in sensitivity from those that have been used to derive the existing benchmark. In the case of nitrate, data have already been collected for resident fish species (McGurk et al. 2006), and much of the available dataset for effects of nitrate on aquatic organisms is considered to be relevant to the site Approach Selected for the EKATI SSWQO Calculation The Recalculation Approach was employed for development of the SSWQG for nitrate at EKATI. This approach was considered appropriate because key species that were used to develop existing Canadian WQGs for nitrate, in particular amphibians, are not relevant to the site. Twelve species were incorporated into development of the IPS for nitrate, and one additional species (i.e., 13 in total) was identified in the draft CCME WQG for nitrate. Four of the species used in each of these derivations were amphibians, and are not considered relevant to the site. In addition, the giant river prawn was included in the previous WQG derivations, but is not considered relevant to the site (see Section 4.2 for rationale). Additional data were identified for inclusion in the SSWQO, including for species already represented in the dataset, as well as for two additional species (an invertebrate and a green alga). Sub-Arctic lakes, such as those located within the EKATI watersheds, tend to be oligotrophic and, consequently, generally low in nitrate. Thus, the Background Concentration Approach was not useful. Water Effect Ratio tests were also not employed here, since water quality conditions (other than hardness) were not expected to result in significant change in the sensitivity of organisms to nitrate. Additional tests using resident species were not considered necessary to supplement the recalculation approach. 3.3 COMPILATION OF EXISTING INFORMATION Environmental Fate As part of the initial step in developing the SSWQOs, data on the physical and chemical interactions of nitrate in aquatic systems were compiled and reviewed Toxicity Data The available literature on chronic toxicity of nitrate have recently been comprehensively reviewed by Environment Canada and/or CCME as part of development of the IPS (Guy 2008) and in the draft Canadian water quality guideline for nitrate. The chronic toxicity data that were considered appropriate for inclusion in those documents were reviewed here and considered for inclusion in the SSWQO for nitrate at EKATI. In addition, a literature search was conducted to identify recently published studies on chronic toxicity of nitrate that might not have been captured in the literature review conducted by CCME. The focus of this search was on literature published since Toxicity data were also available from Nautilus Environmental (2011a and 2011b; Appendix B). 3-2 RESCAN ENVIRONMENTAL SERVICES LTD. (PROJ# /REV C.1) APRIL 2012

31 METHODS 3.4 EVALUATION OF RELEVANT TOXICITY DATA The data available in the compiled toxicity studies were reviewed and classified as either primary, secondary or unacceptable, consistent with the CCME (2007b) criteria for review of toxicological data for consideration in WQG development. Studies were classified as primary if they, at a minimum, met the following criteria: use of measured concentrations; control response reported and acceptable; concentration-response shown or evident from the reported endpoints; ETMF information provided (at least hardness data); study design and replication reported; and, proper statistics used. Studies that provided a minimum of ETMF information (hardness) and control response were classified as secondary data. Studies in which control performance did not meet acceptable limits or where insufficient supporting information was provided were considered unacceptable. Data that were considered either primary or secondary were included in the SSD, except in cases where other primary or secondary data were available for a different, more sensitive endpoint for that species. In some cases, studies that provided useful information but did not meet the criteria for primary or secondary data quality were used as supporting information but were not used directly in the calculation of the SSWQO. All other studies were excluded from further consideration. The test duration was evaluated for each study included in the derivation of the long-term SSWQO as outlined in CCME (2007b). Toxicity tests that were suitable for use in derivation of a long-term SSWQO were defined as those that met the following criteria (CCME 2007b): o o o fish - test durations of 21 days, or 7 days if involving the egg or larval stages, based preferentially on non-lethal endpoints of growth, egg/larval development, or reproduction; invertebrates - non-lethal endpoints (growth, reproduction) from test durations of 96 hours for shorter lived invertebrates or of 7 days for longer lived invertebrates, and lethal endpoints from tests of 21 days for longer lived invertebrates (lethal endpoints for < 21 day tests for shorter lived species were considered on a case-by-case basis); and, plants/algae - growth test durations exceeding 24 hours. Studies were screened for relevance in the context of species present at the site. A species was classified as resident if it belonged to the same genus as a species present at EKATI. Toxicity data for species that are present at EKATI were preferred; however, only a limited number of standardized toxicity tests exist for aquatic species. Therefore, in the absence of data for resident species, surrogate species that were taxonomically related to resident taxa (for example, were within the same taxonomic family) or occurred in other sub-arctic lakes were included to provide a robust and relevant dataset Minimum Requirements for SSD Dataset In order to calculate a chronic SSD, the following are the minimum dataset requirements (CCME 2007b): o o o fish - require at least three studies on freshwater fish species, including one salmonid and one non-salmonid; invertebrates - require at least three studies on freshwater invertebrate species, at least one of which is a planktonic crustacean species; and, plants/algae - at least one plant or algal species is required. In the case where plants or algae are among the most sensitive taxa, a chemical is classed as phytotoxic and thereby requires two studies for an acute SSD, or three studies for a chronic SSD. BHP BILLITON CANADA INC. 3-3

32 SITE-SPECIFIC WATER QUALITY OBJECTIVE FOR NITRATE, SSD Data Selection Following screening of studies for validity for use in the SSD dataset for nitrate, the complete dataset was examined. Only the most sensitive endpoint from each species was included (e.g., reproduction or growth, not both), resulting in only one data point per species in the SSD. In some cases, similar endpoints were available from more than one test with identical conditions for an individual species. In cases where the tests were considered sufficiently similar, the geometric mean of the values reported in the various studies was calculated and used in the SSD. However, in cases where one data point was considered more sensitive because of a methodological difference, such as use of a different lifestage, a longer test duration, or a more appropriate statistical evaluation of the data, the more sensitive test result was utilized, and the less sensitive data were excluded. For chronic toxicity tests, a variety of toxicological endpoints may be available, including those based on point estimates (e.g., IC x or EC x values, which refer to the concentration of chemical that is expected to inhibit or effect x% of the population) and those based on hypothesis tests (e.g., the No Observed Effect Concentration [NOEC], Lowest Observed Effect Concentration [LOEC] and Maximum Acceptable Toxicant Concentration [MATC]). The NOEC is the highest tested concentration that shows no significant difference relative to the control, the LOEC is the lowest tested concentration that is significantly adversely affected relative to the control, and the MATC is the geometric mean of the NOEC and LOEC. In general, point estimates derived from regression analysis are the most appropriate endpoint for use in WQG development. CCME (2007b) guidance lists the order of preference for chronic endpoints as follows: No-Effects Threshold EC x /IC x > EC 10 /IC 10 > EC /IC > MATC > NOEC > LOEC > EC /IC > Nonlethal EC 50 /IC 50 As shown, regression-based point estimates, such as the EC 10 or EC 25, are generally considered to be more appropriate than hypothesis tests, such as the NOEC, LOEC, and MATC values, since results from hypothesis tests can be significantly affected by aspects of study design, such as replication and spacing between test concentrations (CCME 2007b). However, care needs to be taken in interpretation of EC 10 and IC 10 results, since toxicity tests rarely have the statistical power to detect this level of adverse effect with a reasonable degree of confidence. Consequently, where sufficient data were available, the shape of the dose-response and the variability in the dataset were considered carefully to establish the most appropriate endpoint for inclusion in the SSD. 3.5 DERIVATION OF A SSWQO In the case of nitrate, the Recalculation Approach provided the most appropriate tool for establishing a site-specific objective at EKATI. In addition, there is significant evidence that water hardness plays an important role as a toxicity modifying factor for nitrate (Nautilus Environmental 2011a and 2011b), and hardness is strongly correlated with nitrate concentrations in the receiving environment surrounding EKATI. Thus, in addition to recalculation, an approach following that utilized by the US EPA (1985) in deriving hardness-linked benchmarks for metals (such as zinc, cadium and copper) was employed here in order to incorporate water hardness as a TMF for nitrate. Hardness has not previously been incorporated into WQGs for nitrate since previous investigations have not evaluated the role of this water quality variable on toxicity of nitrate; however, the evidence of this interaction is compelling. In order to incorporate hardness as a modifying factor, the slopes of the relationships between chronic toxicity and water hardness for four species for which these data were available (three invertebrates, Ceriodaphnia dubia, Hyalella azteca and Chironomus tentans, as well as one fish, Pimephales promelas), were evaluated and compared. The dataset for each species was normalized using the geometric mean of the toxicity endpoints (in this case, IC 25 values) and the geometric mean of the 3-4 RESCAN ENVIRONMENTAL SERVICES LTD. (PROJ# /REV C.1) APRIL 2012