W2012L2-0001 February 8, 2018 Overview

Dominion Diamond Ekati Corporation Potassium Effluent Quality Criterion Water Licence W2012L2-0001 February 8, 2018 Overview • Short-term Potassium EQC • Long-term Potassium EQC – Koala Watershed – King – Cujo and Desperation – Carrie Watersheds • Future Applicability of Potassium SSWQO Short-term Potassium EQC • DDEC has requested to increase the short-term potassium EQC from 82 mg/L to 103 mg/L. • DDEC followed the Type A guideline approach to derive the short term SSWQO for potassium. • DDEC noted that the Species Sensitivity Distribution used to calculate the short term concentration illustrated that, for all species, mean acute values were above the SSWQO. • The GNWT is supportive of the proposed short term SSWQO. Long-term Potassium EQC Koala Watershed • DDEC has requested to amend the long-term potassium EQC to 64 mg/L. • However, water quality predictions suggest that exceedances of the potassium SSWQO are anticipated in the receiving environment over multiple under-ice seasons as a result of solute exclusion. • Potassium concentrations within Moose and Leslie lakes may also exceed SSWQOs. – DDEC notes that these exceedances will be for short periods under ice and expected to have minimal effects on the receiving environment. Long-term Potassium EQC Koala Watershed • GNWT notes the anticipated under ice duration could encompass several months. – During these months aquatic organisms will be exposed to concentrations of potassium above the SSWQO. • GNWT agrees with statements from DDEC and their consultants during the technical sessions that biologically the winter season may be a time of slower metabolic processes. – Note that this is also the time where increased stress can occur known as Winter Stress Syndrome. Long-term Potassium EQC Koala Watershed • The anticipated effects that might occur in downstream areas as a result of an exceedance of the potassium SSWQO include: – Potential adverse effects to sensitive aquatic invertebrates, represented by the amphipod, Hyalella azteca; – Considerable uncertainty around the potential for effects to species represented by the fathead minnow (e.g., lake chub) during the larval stage; and, – Potential for adverse effects to Bivalves, due to a high sensitivity to potassium which should require further examination given the presence of fingernail clams in the area. Long-term Potassium EQC Koala Watershed • It is the GNWT’s position that SSWQOs established for a project once approved by the Board are meant to be maintained in the environment and that EQCs must be appropriately calculated to maintain these concentrations. • This position is supported by: – The Water and Effluent Quality Management Policy (MVLWB, 2011) – The Guidelines for Effluent Mixing Zones (MVLWB/GNWT, 2017) Long-term Potassium EQC Koala Watershed • According to the Water and Effluent Quality Management Policy: “Protection of water quality in the receiving environment is the primary objective. The level of protection will be defined by the water quality standards that have been set site-specifically for the receiving environment in question. Effluent Quality criteria (EQC) will be set for a project to ensure that water quality standards will be met.” (p.48) “EQC are first calculated based on maintaining the concentration of a parameter of potential concern below the SSWQO in the receiving environment.” (p. 53) “EQC are set to ensure that water quality objectives are not exceeded at the edge of a defined mixing zone.” (p. 56). Long-term Potassium EQC Koala Watershed • The GNWT recommends that a 42-day toxicity test be undertaken using H. azteca to evaluate survival, growth, and reproductive endpoints using site water spiked with potassium concentrations at minimum 64 mg/L, 80 mg/L and 100 mg/L to evaluate the response of this sensitive species. • The GNWT recommends that a 30‐day early life stage test be conducted on fathead minnows using site water spiked with potassium concentrations at minimum 64 mg/L, 80 mg/L and 100 mg/L to evaluate hatching success, survival, growth, biomass, and gross morphological alterations. • The GNWT recommends that toxicity testing be conducted on a freshwater bivalve using site water spiked with potassium concentrations at minimum 64 mg/L, 80 mg/L and 100 mg/L. Long-term Potassium EQC King – Cujo and Desperation – Carrie Watersheds • The current Water Licence W2012L2-0001 includes potassium EQC for all areas of effluent discharge including the LLCF, King Pond Containment Facility and Desperation Pond. • The current SSWQO of 64 mg/L was approved by the WLWB in 2016 as “an appropriate water quality objective for potassium downstream of the LLCF”. • GNWT is concerned with applying this SSWQO to watersheds outside of the Koala watershed. Long-term Potassium EQC King – Cujo and Desperation – Carrie Watersheds • The rationale for increasing the EQC for potassium at other discharge locations is related to increasing potassium concentrations in the Koala Watershed. • It is not apparent that an increase is occurring or will occur in any other areas. – The source of Potassium may be localized. • Potassium concentrations in the King-Cujo drainage are currently in the range of 10-20 mg/L. • Per the 2011 MVLWB Policy, evidence of an operational increase is required to support a limit increase. Long-term Potassium EQC King – Cujo and Desperation – Carrie Watersheds • Toxicity tests conducted by Nautilus, and presented in DDEC (2015) suggest the presence of toxicity modifying factors. • Test results suggest a toxicological effect occurred for two aquatic invertebrate species, C. dubia and D. magna, at concentrations substantially higher in site water (collected from Leslie Lake and Cell E of the LLCF) compared to tests conducted with laboratory water. Long-term Potassium EQC King – Cujo and Desperation – Carrie Watersheds • Given that potassium concentrations are not trending towards the higher EQC at the KPSF and Desperation Pond and there are uncertainties associated with the application of the Koala watershed SSQWO for potassium in these areas, GNWT recommends that the potassium EQC of 64 mg/L not be applied for these areas. Should there be an apparent operational need in the future, and technical uncertainties be resolved, the GNWT would support this matter being reconsidered by the Board. Future Applicability of Potassium SSWQO • The GNWT believes that some ameliorating factors exist within site water from Leslie Lake and the LLCF. – There is evidence in the literature that sodium does have an ameliorating effect on potassium (Mount et al. 1997, Mount et al. 2016, Erickson et al. 2017). • The GNWT also notes that geochemical modeling conducted by DDEC shows a decrease in the sodium to potassium ratio over time – Therefore, the level of protection afforded by the current potassium SSWQO over time is uncertain. Future Applicability of Potassium SSWQO • Chronic toxicity testing already occurs for C. dubia at the decant location of the LLCF and should continue to identify any effects from the discharge. • Should ongoing testing indicate increased chronic toxicity, the potassium SSWQO may require re‐evaluation in the future. Thank You.

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