Dominion Diamond Ekati ULC

Transcription

1 Dominion Diamond Ekati ULC Street SW (403) Calgary, Alberta T2P 1T1 (403) fax 15 Violet Camsell-Blondin - Chair Wek èezhìi Land and Water Board #1, th Street Yellowknife, NT X1A 3S3 Dear Ms. Camsell-Blondin: Dominion Diamond Ekati ULC is pleased to submit responses to Information Requests (IRs) resulting from the Technical Session held in Yellowknife, NT on November 28, Please find the IR responses attached. If you have any questions or concerns please contact me at extension 2401 or claudine.lee@ddcorp.ca. Sincerely, Claudine Lee, Head Environment Att. Misery Underground Project Information Request Responses (#1-8) Record #: HSE RCD ENV 852 Document Owner: Environment Department Date: Template # EKA TEM

2 IR#1 Information Request (IR) No.: 1 Source: Technical Session November 28, 2017 (1:50:45 of Day 1 PM Recording) Information Request: Dominion to provide information from Schedule 6, Condition 1(h) of W2012L in the Wastewater and Processed Kimberlite Management Plan (WPKMP). Proponent Response: An anticipated schedule of volumes of Discharge to and from the King Pond Settling Facility with the Misery Underground (MUG) Project is provided in Table 1-1. Following existing practices at the Ekati mine, water within King Pond Settling Facility will be sampled and tested for water quality prior to Discharge. The anticipated volumes presented in Table 1-1 are maximum values that could be Discharged and are based on values presented in Table 2 of the MUG Project Mine Water Management Plan (Golder 2017; Appendix E of the MUG Project Water Licence application), considering the high groundwater inflow case and average climate conditions. The overall volume that can be Discharged from the King Pond Settling Facility will be dependent on the sampled water quality and meeting the established King Pond Settling Facility effluent quality criteria (EQC). Table 1-1 King Pond Settling Facility Schedule of Discharge Volumes Year Inflow to King Pond Settling Facility (total of all volumes that report to the facility) ,300 m 3 528,000 m ,343,000 m 3 1,403,700 m on 764,000 m 3 384,000 m 3 m 3 = cubic metres. Discharge from King Pond Settling Facility to Receiving Environment (Cujo Lake) References: Golder (Golder Associates Ltd.) Misery Underground Project Mine Water Management Plan. Submitted to Dominion Diamond Ekati Corporation. 4 August Available at: %20WL%20Amendment%20-%20Misery%20UG%20-%20Appendix%20E%20- %20Mine%20Water%20Management%20Plan%20-%20Aug%2015_17.pdf 1

3 IR#2 Information Request (IR) No.: 2 Source: Technical Session November 28, 2017 (0:42:00 of Day 1 PM Recording) Information Request: Dominion to provide hydrogeological information that provides the groundwater flux and loading from the bottom of Misery Pit into Lac de Gras and to confirm it is the same for Misery Underground project as it was for the Jay project (one and two times total dissolved solid [TDS] scenarios). Proponent Response: Information relevant to the groundwater flux and loading from Misery Pit to Lac de Gras in the postclosure period is provided in Appendix 8C of the Developer s Assessment Report (DAR) for the Jay Project (DDEC 2014). In the DAR, the post-closure seepage rate from Misery Pit to Lac de Gras was initially set at 54 cubic metres per day (m 3 /d), which was part of the Environmental Assessment Conservative Scenario. The seepage rate was subsequently adjusted to 45 m 3 /d for the Reasonable Estimate Scenario developed during the environmental assessment review for the Jay Project (Golder 2015). The seepage rate of 45 m 3 /d was carried into the water quality modelling completed for the Jay Project Water Licence amendment application (Golder 2016). The groundwater outflow from the Misery Pit with the Misery Underground (MUG) Project is expected to be similar to the relatively small groundwater flux used in the water quality modelling for the Jay Project Water Licence application. Conceptually, Misery Pit with the Misery Underground development could potentially result in increased groundwater seepage from the Misery Pit and underground workings over the open pit alone (i.e., as a result of deeper workings below the pit). However, because the predictions developed for the Misery Pit without the underground workings were conservative (e.g., assumed direct hydraulic connection between the pit lake and Lac de Gras), actual groundwater seepage from the pit to Lac de Gras (with or without the MUG Project) would be expected to be significantly less than what was incorporated into the water quality modelling for the Jay Project Water Licence application. A review of the model as part of this response indicated a lower seepage rate from Misery Pit (40 m 3 /d) was used in the water quality modelling completed for the MUG Project (Golder 2017; Appendix F of the MUG Project Water Licence amendment application) than that used in the Jay Project Water Licence application (45 m 3 /d). The model was subsequently re-run with a seepage rate of 45 m 3 /d. The results indicate that the timeframe for Misery Pit to evolve to a freshwater lake (Figure 2-1) is shorter than presented in Appendix F, and is similar to the timeframe for the Jay Project without MUG Project minewater being stored in Misery Pit. Hydrogeological modelling indicates that in all cases considered, seepage from the Misery Pit towards Lac de Gras in post-closure would occur at relatively low rates in the mid-10s of m 3 /d. Because of that and regardless of the value used, the outcomes are the same: Misery Pit is predicted to become a freshwater lake in the long-term; and 1

4 IR#2 The small volume of seepage does not result in significant adverse effects to surface water quality in Lac de Gras. Varying the seepage rate in the water quality model only changes the expected timing of when Misery Pit becomes a fully freshwater lake over the long-term (i.e., thousands of years). Figure 2-1 Misery Pit Vertical Slice Spreadsheet Model Results Average MUG; 2xTDS Scenario Post-closure seepage to Lac de Gras is expected to be much lower than modelled due to the conservatism included in the modelling predictions (DAR Appendix 8C, response to DAR-GNWT-IR-11). The conservatism associated with the post-closure Misery Pit seepage projection to Lac de Gras is a result of the following assumptions incorporated into the analysis: The seepage predictions assumed that there is a direct connection between Misery Pit and Lac de Gras via a lineament that could be associated with an enhanced permeability zone (EPZ). In all likelihood, a structural discontinuity associated with this lineament may not extend to Lac de Gras or its permeability may be much lower than assumed. It is well recognized that structural discontinuities like faults can act as barriers to flow as much as they can act as conduits for flow. Without this direct connection, post-closure seepage to Lac de Gras would be much lower than modelled. The transmissivity properties of a hypothetical EPZ between Misery Pit and Lac de Gras was derived by assuming that all inflow to the Misery Pit during mining originated from this EPZ. SWS (2010) reported that this inflow most likely originated from the active layer and not from deeper bedrock. Hence, the assumed transmissive properties are considered conservatively high (i.e., any connection 2

5 IR#2 between the pit and the lake, if it exists, is likely weaker). With lower transmissive properties of the EPZ, if it existed, the post-closure seepage to Lac de Gras would be lower than modelled. Testing at nearby kimberlite pipes, and elsewhere in the Canadian Shield, showed that bedrock permeability generally decreases with depth. However, the post-closure model assumed that the transmissive properties of the hypothetical EPZ remain constant with depth. Lower EPZ transmissivity at depth would lead to a reduction in predicted seepage, in particular near the base of the pit lake. References: DDEC (Dominion Diamond Ekati Corporation) Developer s Assessment Report for the Jay Project. Submitted to the Mackenzie Valley Environmental Impact Review Board. October Yellowknife, NWT, Canada. Available at: Golder Associates Ltd. (Golder) Jay Project. Compendium of Supplemental Water Quality Modelling. Submitted to Dominion Diamond. April 7, Available at: Golder Jay Project Water Licence Water Quality Model Updates. Submitted to Dominion Diamond Ekati Corporation. June Available at: %20Appendix%20B%20-%20Water%20Licence%20Model%20Updates%20-%20Part%201%20- %20Jun%207_16.pdf Golder Ekati Mine Misery Underground Water Quality Model Updates. Submitted to Dominion Diamond Ekati Corporation. August 14, Available at: - Ekati - WL Amendment - Misery UG - Appendix F - Water Quality Predictions Report - Aug 15_17.pdf SWS (Schlumberger Water Services [Canada] Inc.) Misery Resource Development Definition Study Feasibility, Hydrology and Hydrogeology. Submitted to BHP Billiton Diamonds Inc. 3

6 IR#3 Information Request (IR) No.: 3 Source: Technical Session November 28, 2017 (1:22:43 of Day 1 PM Recording) Information Request: Dominion to provide figures representing the water quality in the upper layer of the Misery pit for the duration of operations (two times TDS scenario for each EQC variable). Proponent Response: The mean and 95 th percentile projected water quality conditions in the decant layer of Misery Pit for the period of operational Discharge during the Jay Project, with Misery Underground (MUG) Project, were extracted from the Misery Pit hydrodynamic model for the 2xTDS scenario for each Effluent Quality Criteria (EQC) parameter, and the following groundwater inflow scenarios: Average MUG Project groundwater inflow scenario; and, High MUG Project groundwater inflow scenario. Results for the Average MUG Project groundwater inflow scenario are presented in Figures IR3-1 to IR3-24, and results for the High MUG Project groundwater inflow scenario are presented in Figures IR3-25 to IR

7 IR#3 Figure IR3-1. Simulated Misery Pit Decant Layer Chloride Concentrations Average MUG Groundwater Scenario Mean Figure IR3-2. Simulated Misery Pit Decant Layer Nitrate Concentrations Average MUG Groundwater Scenario Mean Figure IR3-2. Simulated Misery Pit Decant Layer Ammonia Concentrations Average MUG Groundwater Scenario Mean Figure IR3-4. Simulated Misery Pit Decant Layer Total Phosphorus Concentrations Average MUG Groundwater Scenario Mean Figure IR3-5. Simulated Misery Pit Decant Layer Cadmium Concentrations Average MUG Groundwater Scenario Mean Figure IR3-6. Simulated Misery Pit Decant Layer Chromium Concentrations Average MUG Groundwater Scenario Mean 2

8 IR#3 Figure IR3-7. Simulated Misery Pit Decant Layer Cobalt Concentrations Average MUG Groundwater Scenario Mean Figure IR3-8. Simulated Misery Pit Decant Layer Copper Concentrations Average MUG Groundwater Scenario Mean Figure IR3-9. Simulated Misery Pit Decant Layer Iron Concentrations Average MUG Groundwater Scenario Mean Figure IR3-10. Simulated Misery Pit Decant Layer Lead Concentrations Average MUG Groundwater Scenario Mean Figure IR3-11. Simulated Misery Pit Decant Layer Uranium Concentrations Average MUG Groundwater Scenario Mean Figure IR3-12. Simulated Misery Pit Decant Layer Aluminum Concentrations Average MUG Groundwater Scenario Mean 3

9 IR#3 Figure IR3-13. Simulated Misery Pit Decant Layer Chloride Concentrations Average MUG Groundwater Scenario 95th Figure IR3-14. Simulated Misery Pit Decant Layer Nitrate Concentrations Average MUG Groundwater Scenario 95th Figure IR3-15. Simulated Misery Pit Decant Layer Total Ammonia Figure IR3-16. Simulated Misery Pit Decant Layer Total Concentrations Average Groundwater MUG Scenario 95th Phosphorus Concentrations Average Groundwater MUG Scenario 95th Figure IR3-17. Simulated Misery Pit Decant Layer Cadmium Concentrations Average MUG Groundwater Scenario 95th Figure IR3-18. Simulated Misery Pit Decant Layer Chromium Concentrations Average MUG Groundwater Scenario 95th 4

10 IR#3 Figure IR3-19. Simulated Misery Pit Decant Layer Cobalt Concentrations Average MUG Groundwater Scenario 95th Figure IR3-20. Simulated Misery Pit Decant Layer Copper Concentrations Average MUG Groundwater Scenario 95th Figure IR3-21. Simulated Misery Pit Decant Layer Iron Concentrations Average MUG Groundwater Scenario 95th Figure IR3-22. Simulated Misery Pit Decant Layer Lead Concentrations Average MUG Groundwater Scenario 95th Figure IR3-23. Simulated Misery Pit Decant Layer Uranium Concentrations Average MUG Groundwater Scenario 95th Figure IR3-24. Simulated Misery Pit Decant Layer Aluminum Concentrations Average MUG Groundwater Scenario 95th 5

11 IR#3 Figure IR3-25. Simulated Misery Pit Decant Layer Chloride Concentrations High MUG Groundwater Scenario Mean Figure IR3-26. Simulated Misery Pit Decant Layer Nitrate Concentrations High MUG Groundwater Scenario Mean Figure IR3-27. Simulated Misery Pit Decant Layer Total Ammonia Figure IR3-28. Simulated Misery Pit Decant Layer Total Concentrations High MUG Groundwater Scenario Mean Phosphorus Concentrations High MUG Groundwater Scenario Mean Figure IR3-29. Simulated Misery Pit Decant Layer Cadmium Concentrations High MUG Groundwater Scenario Mean Figure IR3-30. Simulated Misery Pit Decant Layer Chromium Concentrations High MUG Groundwater Scenario Mean 6

12 IR#3 Figure IR3-31. Simulated Misery Pit Decant Layer Cobalt Concentrations High MUG Groundwater Scenario Mean Figure IR3-32. Simulated Misery Pit Decant Layer Copper Concentrations High MUG Groundwater Scenario Mean Figure IR3-33. Simulated Misery Pit Decant Layer Iron Concentrations High MUG Groundwater Scenario Mean Figure IR3-34. Simulated Misery Pit Decant Layer Lead Concentrations High MUG Groundwater Scenario Mean Figure IR3-35. Simulated Misery Pit Decant Layer Uranium Concentrations High MUG Groundwater Scenario Mean Figure IR3-36. Simulated Misery Pit Decant Layer Aluminum Concentrations High MUG Groundwater Scenario Mean 7

13 IR#3 Figure IR3-37. Simulated Misery Pit Decant Layer Chloride Concentrations High MUG Groundwater Scenario 95th Figure IR3-38. Simulated Misery Pit Decant Layer Nitrate Concentrations High MUG Groundwater Scenario 95th Figure IR3-39. Simulated Misery Pit Decant Layer Total Ammonia Concentrations High MUG Groundwater Scenario 95th Figure IR3-40. Simulated Misery Pit Decant Layer Total Phosphorus Concentrations High MUG Groundwater Scenario 95th Figure IR3-41. Simulated Misery Pit Decant Layer Cadmium Concentrations High MUG Groundwater Scenario 95th Figure IR3-42. Simulated Misery Pit Decant Layer Chromium Concentrations High MUG Groundwater Scenario 95th 8

14 IR#3 Figure IR3-43. Simulated Misery Pit Decant Layer Cobalt Concentrations High MUG Groundwater Scenario 95th Figure IR3-44. Simulated Misery Pit Decant Layer Copper Concentrations High MUG Groundwater Scenario 95th Figure IR3-45. Simulated Misery Pit Decant Layer Iron Concentrations High MUG Groundwater Scenario 95th Figure IR3-46. Simulated Misery Pit Decant Layer Lead Concentrations High MUG Groundwater Scenario 95th Figure IR3-47. Simulated Misery Pit Decant Layer Uranium Concentrations High MUG Groundwater Scenario 95th Figure IR3-48. Simulated Misery Pit Decant Layer Aluminum Concentrations High MUG Groundwater Scenario 95th 9

15 IR#4 Information Request (IR) No.: 4 Source: Technical Session November 28, 2017 (1:50:45 of Day 1 PM Recording) Information Request: Dominion to provide additional information to support assurance that increased loading limits for phosphorus would not impact the downstream environment or licensees. Proponent Response: During the permitting process for the Jay Project Water Licence amendment application, technical advisors to the Wek èezhìi Land and Board (WLWB) requested a water quality model scenario that evaluated the influence of the Jay Project on downstream users if all developments (i.e., Ekati, Diavik, and the Jay Project) were Discharging at their approved Effluent Quality Criteria (EQC). In the response to Jay Project Information Request (IR) #47, an EQC model scenario was developed where Discharge from the Diavik Mine and Ekati mine was assumed to occur at the maximum average concentration approved EQC, and the proposed maximum average concentration EQC for the Jay Project. In this scenario, it was assumed that Discharge from the Diavik Mine would be extended until the end of the Jay Project. Details of the water quality model setup and results are provided in the response to IR #47 (DDEC 2016). Water quality modelling completed in support of the Misery Underground (MUG) Project Water Licence amendment application (Golder 2017) indicated that phosphorus loadings in the Discharge from Misery Pit to Lac du Sauvage during mining of the Jay Pit would be slightly higher in comparison to water quality modelling completed to support the Jay Project Water Licence application. During the MUG Project Technical Session, Dominion Diamond proposed an updated total phosphorus loading-based EQC, accounting for the additional Discharge period for the Jay Project including the MUG Project. To provide assurance that increased loading limits for phosphorus would not impact the downstream environment or licencees, Dominion Diamond proposes to update total phosphorus projections using the updated EQC model developed for the response to IR #47 for the following scenarios: Average MUG Groundwater; Jay Project 2xTDS scenario; and, High MUG Groundwater; Jay Project 2xTDS scenario. Since total phosphorus is not correlated to total dissolved solids (TDS), the 1xTDS scenario will produce comparable loading estimates to the 2xTDS scenario, and as such, does not require updating. Dominion Diamond will present water quality results at the assessment locations indicated in Figure 4-1, which are consistent with the locations presented in the response to IR #47. Due to the computational run times, the model results will be presented in a memorandum to be submitted to the WLWB on January 8,

16 IR#4 Figure 4-1 Lac de Gras Model Assessment Locations Note: The circle is the location of the Diavik Mine discharge in the Lac de Gras model. Model results will be presented at the locations represented by the circle and the square. N = North; m = metres. 2

17 IR#4 References: Dominion Diamond Ekati Corporation (DDEC) Jay Project Water Licence Application Response to Information Request-47. Submitted to the Wek èezhìi Land and Water Board. November Available at: Jay Project - Response to IRs 39, 47, and 48 - DDEC - Nov 4_16.pdf Golder Associates Ltd. (Golder) Ekati Mine Misery Underground Water Quality Model Updates. Submitted to Dominion Diamond. August 14, Available at: - Ekati - WL Amendment - Misery UG - Appendix F - Water Quality Predictions Report - Aug 15_17.pdf 3

18 IR#5 Information Request (IR) No.: 5 Source: Technical Session November 28, 2017 (2:23:50 of Day 1 PM Recording) Information Request: Dominion to provide a discussion on the necessity for an EQC for chloride, discharging at SNP Station and any mitigation options available that would align with the Mackenzie Valley Land and Water Board (MVLWB) s Water and Effluent Quality Management Policy. If deemed necessary, provide a proposed EQC for chloride with supporting rationale. Dominion to also provide a screening for any other variables potentially requiring an EQC. Proponent Response: 1 EFFLUENT QUALITY CRITERIA FOR CHLORIDE As described in Appendix F (Ekati Mine - Misery Underground Water Licence Model Updates; Golder 2017) of the Misery Underground (MUG) Project Water Licence Amendment Application, Dominion Diamond proposes to develop a sub-level retreat (SLR) to mine the Misery pipe below the open pit (i.e., the Misery Underground). Because the SLR and underground mine workings will be developed below permafrost, the minewater reporting to Misery Pit and Misery underground workings is expected to have elevated salinity concentrations. During the MUG Project, minewater will initially be pumped to the King Pond Settling Facility until Lynx Pit is available. As a result, parameter concentrations associated with the increased salinity are projected to be elevated in the King Pond Settling Facility between 2018 and 2022 (Figure 6, Appendix F of the MUG Project Water Licence amendment application). Dominion Diamond intends to Discharge water from the King Pond Settling Facility as long as it meets established Effluent Quality Criteria (EQC) at the Surveillance Network Program (SNP) station in the Ekati mine Water Licence WL2012L2-0001, but recognizes that the potential for elevated salinity concentrations associated with underground mining operations in Misery Pit may warrant the establishment of an EQC for chloride at station (i.e., King Pond Settling Facility). After the MUG Project, minewater in Lynx Pit and King Pond Settling Facility will be transferred to Misery Pit; therefore, following the MUG Project, only a proportionally small quantity of underground minewater from the Misery underground workings will remain in King Pond Settling Facility. In response to the Information Request (IR), Dominion Diamond has developed an EQC for chloride, as the primary constituent of interest in underground minewater that could be of interest for Discharge from King Pond Settling Facility (i.e., SNP Station ). Dominion Diamond would not object to inclusion of this EQC in the Water Licence at Station Method for Calculating Chloride Effluent Quality Criteria A method for establishing EQC at SNP Station that is consistent with the Wek èezhìi Land and Water Board (WLWB) Policy and that has been employed by the WLWB for this purpose is set out in the WLWB Reasons for Decision (WLWB 2014) for the Lynx amendment to the Ekati mine Water Licence 1-1

19 IR#5 W2012L For chemical constituents of the Discharge 1, the procedure is to apply a dilution factor of 1.7 to the established chronic (or long-term) site-specific water quality objective (SSWQO) to calculate the maximum average concentration EQC (Equation 1). The dilution factor for Cujo Lake considers the annual natural runoff volume that reports to Cujo Lake and the annual Discharge volume from the King Pond Settling Facility. Dominion Diamond has developed a possible maximum average concentration EQC for chloride for station using the same method, where the chronic SSWQO for chloride is the hardnessdependent equation from Elphick et al. (2011) and hardness refers to the hardness concentrations in Cujo Lake in accordance with the current requirement of the Water Licence (Table 5-1). A possible maximum concentration of any grab sample (maximum grab concentration) EQC was calculated by multiplying the maximum average concentration EQC by a factor of two (Equation 2).To make sure that the maximum grab concentration EQC is protective against acute toxicity, the calculated maximum grab concentration EQC was compared to the short-term exposure hardness-dependent SSWQO (Elphick et al. 2016) (Table 5-2). The maximum EQC was set equal to the lesser of the initial calculation or the SSWQO. Maximum Average Concentration EQC = Dilution Factor Water Quality Objective in Cujo Lake [Eq. 1] Table 5-1: Chronic Chloride Hardness-Dependent Site-Specific Water Quality Objective for Cujo Lake Cujo Lake Hardness (mg/l as CaCO 3) <10 64 Site-Specific Water Quality Objective (mg/l) 10 and [ln(Cujo Lake Hardness) 204.1] > Source: Elphick et al. (2011). mg/l = milligrams per litre; < = less than; > = greater than; = less than or equal to; = greater than or equal to; CaCO3 = calcium carbonate. Maximum Grab Concentration EQC = 2 Maximum Average Concentration EQC [Eq. 2] Table 5-2: Acute Chloride Hardness-Dependent Site-Specific Water Quality Objective for Discharge from the King Pond Settling Facility King Pond Settling Facility Hardness (mg/l as CaCO 3) >30 and 300 [0.297 log(kpsf Hardness)+2.23] 10 > Source: ERM (2016). Site-Specific Water Quality Objective (mg/l) mg/l = milligrams per litre; < = less than; > = greater than; = less than or equal to; = greater than or equal to; CaCO3 = calcium carbonate. Three equations are presented for EQC for chloride (Table 5-3). The first equation is the maximum average concentration EQC. The second equation is the maximum average concentration EQC multiplied 1 Except total petroleum hydrocarbons, ph, and potassium. 1-2

20 IR#5 by a factor of two. The third equation is the acute hardness-dependent SSWQO for Discharge from the King Pond Settling Facility. Table 5-4 presents the initial calculated EQC for chloride at a range of hardness concentrations in Cujo Lake and compares the maximum grab concentration EQC to the acute SSWQO. At Cujo Lake hardness concentrations greater than 20 milligrams per litre as calcium carbonate (mg/l as CaCO3), the maximum grab concentration EQC, calculated by taking the maximum average concentration EQC and multiplying the concentration by a factor of two, exceeds the acute hardness-dependent SSWQO for Discharge from KPSF (i.e., the maximum grab concentration EQC shaded in grey exceed the acute SSWQO in Table 5-4). Table 5-3: Effluent Quality Criteria Equations for Chloride Parameter Maximum Average Concentration (a) (mg/l) Maximum Concentration of Any Grab Sample (a) (mg/l) Chloride 1.7 [116.6 ln(cujo Lake Hardness) 204.1] Minimum of: 3.4 [116.6 ln(cujo Lake Hardness) 204.1] (a) Or 10 [0.297 log(kpsf Hardness)+2.23] (b) a) The hardness concentration to be used is the hardness concentration as analyzed from the most recent sample collected during open water at SNP Station (i.e., Cujo Lake). The equation is valid for waters with a hardness between 10 and 160 mg/l as CaCO3. For hardness levels greater than 160 mg/l as CaCO3, the chronic SSWQO calculated at 160 mg/l as CaCO3 applies. b) The hardness concentration to be used is the hardness concentration as analyzed from the most recent sample collected during open water at SNP Station (i.e., King Pond Settling Facility). The equation is valid for waters with a hardness between 30 and 300 mg/l as CaCO3. For hardness levels greater than 300 mg/l as CaCO3, the acute WQO calculated at 300 mg/l as CaCO3 applies. mg/l = milligrams per litre; CaCO3 = calcium carbonate; SNP = Surveillance Network Program; SSWQO = site specific water quality objective. Table 5-4: Initial Calculated Effluent Quality Criteria for Chloride at SNP Station Parameter Chloride Cujo Lake Hardness (mg/l as CaCO 3) Chronic Hardness- Dependent SSWQO (a) (mg/l) Maximum Average Concentration (mg/l) (b) Equation a (Table 5-3) Maximum Concentration of Any Grab Sample (e) (mg/l) King Pond Settling Facility Hardness (c) (mg/l as CaCO 3) Acute Hardness- Dependent SSWQO (d) (mg/l) < < , , , , , ,

21 IR#5 Parameter Cujo Lake Hardness (mg/l as CaCO 3) Chronic Hardness- Dependent SSWQO (a) (mg/l) Maximum Average Concentration (mg/l) (b) Equation a (Table 5-3) Maximum Concentration of Any Grab Sample (e) (mg/l) King Pond Settling Facility Hardness (c) (mg/l as CaCO 3) Acute Hardness- Dependent SSWQO (d) (mg/l) , , , > , a) The chronic hardness-dependent SSWQOs were calculated using the equation in Table 5-1 and hardness concentrations from Cujo Lake. b) The maximum average concentration EQC were calculated using the equation in Table 5-3 and the chronic hardness-dependent SSWQOs. c) Hardness concentrations in the King Pond Settling Facility were set equal to the hardness concentration in Cujo Lake times 1.7 (i.e., dilution factor). d) The acute hardness-dependent WQOs were calculated using the equation in Table 5-2 and hardness concentrations from the King Pond Settling Facility. e) The maximum grab concentration EQC were calculated using the equation in Table 5-3. Chloride concentrations shaded in grey are greater than the acute hardness-dependent SSWQO. mg/l = milligrams per litre; CaCO3 = calcium carbonate; EQC = effluent quality criteria; SNP = Surveillance Network Program; SSWQO = site-specific water quality objective. 1.2 Possible Chloride Effluent Quality Criteria To protect against acute toxicity at the point of Discharge, the maximum grab concentration EQC were set equal to the acute SSWQO (Table 5-5). Table 5-5 presents possible EQC for chloride at SNP Station Table 5-5: Possible Effluent Quality Criteria for Chloride at SNP Station Parameter Chloride Cujo Lake Hardness (mg/l as CaCO 3) Maximum Average Concentration (mg/l) Maximum Concentration of Any Grab Sample (a) (mg/l) < > a) The chloride concentrations shaded in grey were set equal to the acute hardness-dependent SSWQO. mg/l = milligrams per litre; CaCO3 = calcium carbonate. 1-4

22 IR#5 2 SCREENING FOR OTHER PARAMETERS OF INTEREST AT SNP STATION Screening Method The following steps were performed to screen for other possible parameters of interest potentially requiring EQC for Discharge from the King Pond Settling Facility to Cujo Lake during the MUG Project (i.e., 2019 to 2022): 1. Water quality parameters to undergo screening were identified as those that have WQOs in Cujo Lake, but do not have EQC stipulated in Ekati mine Water Licence W2012L (Table 5-6). 2. Maximum average concentration EQC were calculated for remaining parameters of interest using the same approach described in Section 1 for chloride. Table 5-6: Screening Parameters Potentially Requiring Effluent Quality Criteria Screening Parameters Total aluminum Total iron Total selenium Total antimony Total lead Total silver Total barium Total manganese Total strontium Total boron Total mercury Total uranium Total cadmium Total molybdenum Total vanadium Total chromium Total nickel Total zinc 3. These maximum average concentration EQC were then compared to MUG Project underground water quality projections during the ice-covered and open-water seasons and King Pond Settling Facility water quality projections during the open-water season (i.e., July, August, and September) when Discharge from the King Pond Settling Facility to Cujo Lake typically occurs. The modelling completed to develop water quality projections for the King Pond Settling Facility was described in Appendix F (Ekati Mine - Misery Underground Water Licence Model Updates; Golder 2017) of the MUG Project Water Licence Amendment Application. If both the underground water quality projections and the King Pond Settling Facility water quality projections for a parameter were greater than the maximum average concentration EQC, then that parameter was screened in as a potential parameter requiring EQC. 2.2 Screening Results Additional parameters that may require EQC in Water Licence W2012L at SNP station during the MUG Project are: Total aluminum Total cadmium Total chromium Total iron Total uranium 2-5

23 IR#5 Dominion Diamond has developed possible maximum average concentration and maximum grab concentration EQC for the additional parameters using the same methods described in Section 1.1. For cadmium, the chronic hardness-dependent SSWQO equation was used for the possible EQC (Table 5-7). Tables 5-8 and 5-9 present possible EQC for total cadmium and total aluminum, chromium, iron, and uranium. Table 5-7: Chronic Cadmium Hardness-Dependent Site-Specific Water Quality Objective for Cujo Lake Cujo Lake Hardness (mg/l as CaCO 3) Site-Specific Water Quality Objective (mg/l) < and 280 (10 [0.83 log(cujo Lake Hardness) 2.46] )/1000 > Source: CCME (2014). mg/l = milligrams per litre; < = less than; > = greater than; = less than or equal to; = greater than or equal to; CaCO 3 = calcium carbonate. Table 5-8: Effluent Quality Criteria for Cadmium at SNP Station Parameter Cujo Lake Hardness (mg/l as CaCO 3) Chronic Hardness- Dependent SSWQO (a) (mg/l) Maximum Average Concentration (mg/l) (b) Equation a (Table 3) Maximum Concentration of Any Grab Sample (c) (mg/l) < Cadmium > a) The SSWQOs were calculated using the hardness-dependent equation from CCME (2014) and hardness concentrations from Cujo Lake. 2-6

24 IR#5 b) The maximum average concentration EQC were calculated were calculated by multiplying the SSWQO by a dilution factor of 1.7. c) The maximum grab concentration EQC were calculated by multiplying the maximum average concentration EQC by a factor of two. mg/l = milligrams per litre; CaCO 3 = calcium carbonate; CCME = Canadian Council of Ministers of the Environment; EQC = effluent quality criteria; SNP = Surveillance Network Program; SSWQO = site-specific water quality objective. Table 5-9: Effluent Quality Criteria for Aluminum, Chromium, Iron, and Uranium at SNP Station Parameter SSWQO (mg/l) (a) Maximum Average Concentration (mg/l) (b) Equation a (Table 3) Maximum Concentration of Any Grab Sample (c) (mg/l) Aluminum Chromium Iron Uranium a) The chronic SSWQOs for aluminium was from CCREM (1987), chromium was from CCME (1999), iron was from CCREM (1987), and uranium was from CCME (2011). b) The maximum average concentration EQC were calculated by multiplying the SSWQO by a dilution factor of 1.7. c) The maximum grab concentration EQC were calculated by multiplying the maximum average concentration EQC by a factor of two. mg/l = milligrams per litre; CCME = Canadian Council of Ministers of the Environment; EQC = effluent quality criteria; SNP = Surveillance Network Program; SSWQO = site-specific water quality objective. 3 WATER AND EFFLUENT QUALITY MANAGEMENT POLICY The WLWB also requested Dominion Diamond provide mitigation options available that would align with the Mackenzie Valley Land and Water Board (MVLWB) Water and Effluent Quality Management Policy. The Water and Effluent Quality Management Policy (MVLWB 2011; the Policy) lists two objectives for regulating waste in the Northwest Territories: 1. water quality in the receiving environment will allow for current and future water uses; and 2. the amount of waste to be deposited in the receiving environment will be minimized. EQC developed for King Pond Settling Facility, as per WLWB (2014) and that presented above, were derived such that the first objective of the Policy was met. The EQC were calculated using appropriate water quality benchmarks for the protection of aquatic life, and where applicable, incorporated influences by site-specific conditions (i.e., hardness) in Cujo Lake. Specific monitoring through the SNP and Aquatic Effects Monitoring Program (AEMP), and the application of the Aquatic Response Framework under the AEMP, will make sure that the receiving environment is protected, so that current and future use of the water can be maintained. The second objective of the Policy will be met through the environmental and waste plans in place for the MUG Project. On a broader level, the Ekati mine has well-developed waste management plans based on 19 years of operating experience, which directly incorporate the MUG Project or provide an effective basis for the MUG-specific plans. Waste management practices for the MUG Project are described in the Project Description (Appendix A of the MUG Project Water Licence Amendment application) and the Mine Water Management Plan (Appendix E of the application). 3-7

25 IR#5 During mining of the MUG Project, only water stored in King Pond Settling Facility that meets EQC will be Discharged. Mitigation that would be applied for the MUG Project if monitoring data indicate EQC cannot be met is storing all non-compliant water in existing facilities (i.e., Lynx Pit) and not Discharging (response to ECCC-10); water balance modelling indicates that there is sufficient capacity to store all non-compliant water. 4 SUMMARY Dominion Diamond acknowledges the discussion of underground minewater in Discharge from King Pond Settling Facility at the Technical Session and the ensuing IR. In response to that discussion and the IR, Dominion Diamond would not object to the addition of the EQC for chloride calculated herein for SNP Station in Ekati mine Water Licence W2012L (Table 5-5). Additional parameters that may require EQC in Water Licence W2012L at SNP during MUG Project are total aluminum, cadmium, chromium, iron, and uranium. The EQC that would be developed for these parameters would follow the same approach used for chloride and would meet the objectives for regulating waste in the MVLWB Policy as outlined in Section 2.2. References: CCME Canadian Water Quality Guidelines for the Protection of Aquatic Life: Chromium - Hexavalent chromium and trivalent chromium. In: Canadian Environmental Quality Guidelines, Canadian Council of Ministers of the Environment, Winnipeg, MB, Canada. CCME Canadian Water Quality Guidelines for the Protection of Aquatic Life: Uranium. In: Canadian Environmental Quality Guidelines, Canadian Council of Ministers of the Environment, Winnipeg, MB, Canada. CCME Canadian Water Quality Guidelines for the Protection of Aquatic Life: Cadmium. In: Canadian Environmental Quality Guidelines, Canadian Council of Ministers of the Environment, Winnipeg, MB, Canada. CCREM (Canadian Council of Resource and Environment Ministers) Canadian Water Quality Guidelines. Prepared by the Task Force on Water Quality Guidelines of the Canadian Council of Resource and Environment Ministers. Dominion Diamond Ekati Corporation (DDEC) Effluent Quality Criteria Report for the Jay Project, Submitted to the Wek'èezhı ı Land and Water Board as part of the Type A Water Licence Application for W2012L for inclusion of the Jay Project. October Available at: %20Appendix%20J%20-%20Jay%20Project%20EQC%20Report%20-%20Jun%207_16.pdf Elphick JRF, Bergh KD, Bailey HC Chronic toxicity of chloride to freshwater species: Effects of hardness and implications for water quality guidelines. Environ Toxicol Chem 30: ERM Consultants Canada Ltd. (ERM) Ekati Diamond Mine: Short-term Site-specific Water Quality Objective for Chloride. Prepared for Dominion Diamond Ekati Corporation by ERM Consultants Canada Ltd. Yellowknife, NWT, Canada. 4-8

26 IR#5 MVLWB (Mackenzie Valley Land and Board) Water and Effluent Quality Management Policy. Yellowknife, NWT, Canada. Wek èezhìi Land and Water Board (WLWB) Reasons for Decision Report Lynx Amendment of W2012L Ekati Diamond Mine. Wek èezhìi Land and Water Board, Yellowknife, NT. April 14,

27 IR#6 and IR#7 Information Request (IR) No.: 6 Source: Technical Session November 28, 2017 (3:23:30 of Day 1 PM Recording) Information Request: Dominion to identify: 1) Costs for removing salvageable mobile equipment, vehicles and other equipment, and cleaning non- salvageable equipment and materials for the Misery Underground project, prior to flooding underground workings and misery open pit; and 2) Whether these costs have been incorporated in the RECLAIM estimate previously, and if so where. Proponent Response: As was indicated in the response to IEMA Recommendation #16 all equipment that is to be left underground will be reclaimed as described in the Interim Closure and Reclamation Plan. This will include draining all fuels, lubricants and removal of hazardous materials including waste batteries. No specific additional costs for these activities were incorporated into the RECLAIM estimate given the overall small scale of the Misery Underground (MUG) project relative to the Ekati site as a whole. In light of the discussions with stakeholders at the technical session, Dominion Diamond has completed a review of underground infrastructure and mobile equipment that would need to be remediated in the unlikely scenario that the MUG project was abandoned. Dominion Diamond notes that underground mining will be completed by reputable contractors who will provide their own mobile equipment, and hence, it is unlikely that they would leave valuable equipment behind. Even if all equipment were abandoned and required drainage and removal of hazardous materials, Dominion Diamond has estimated that underground remediation activities would be minimal, estimated to be approximately one week in duration. Based on a preliminary review of equipment required, Dominion Diamond has estimated that remediation of MUG infrastructure and mobile equipment would result in an additional 5,000 kilograms of waste batteries and 10,000 liters of waste oils that would require collection, shipment, and disposal offsite. Dominion Diamond has provided a revised RECLAIM estimate with this change, labelled as MUG Ref #3. This change represents a minor increase of $ 8,427 to the RECLAIM estimate, with a revised RECLAIM Grand Total of $1,118,781 for the MUG Project. References: BHP Billiton Canada Inc Ekati Diamond Mine Interim Closure and Reclamation Plan. Submitted to the Wek èezhìi Land and Water Board. Yellowknife, NT. August 31,

28 IR#6 and IR#7 Information Request (IR) No.: 7 Source: Technical Session November 28, 2017 (3:24:30 of Day 1 PM Recording) Information Request: Dominion to provide the RECLAIM estimate for land and water separately. Proponent Response: Taking the updated RECLIAM estimate provided in Information Request No.6 Dominion Diamond has provided the following suggested split for MUG RELCAIM land and water costs. RECLAIM Item Land Cost Water Cost Lowering Misery Pit $326,336 Portal - bulkhead and cover entrance $362,904 Cap fresh air raise - concrete cap $158,358 Hazardous Waste Removal $6,433 Subtotal Split: $527,695 $326,336 Subtotal Combined: $854,031 Project Management (5%) 26,385 16,317 Engineering (5%) 26,385 16,317 Health and Safety Plans/Monitoring QA/QC (0.5%) $2,638 1,632 Bonding Insurance (0.5%) $2,638 1,632 Contingency (20%) $105,539 65,267 RECLAIM Grand Total Split $691,281 $427,500 RECLAIM Grand Total Combined $1,118,781 2

29 IR#8 Information Request (IR) No.: 8 Source: Technical Session November 28, 2017 (3:27:30 of Day 1 PM Recording) Information Request: Dominion to identify the key aspects of the conceptual closure plan for the Misery Underground project that Dominion believes require more certainty to move forward with the design and construction of the Misery Underground project. Proponent Response: There are no aspects of the conceptual closure plan for the Misery Underground (MUG) Project that require more certainty to move forward with the design and construction of the MUG Project. Specifically: MUG Project surface equipment and facilities: Closure measures are well-established; there are no unique risks that require specific measures. MUG Project underground workings: Closure measures are well-established and have been demonstrated effective through closure of the Panda underground workings; there are no unique risks that require special measures. King Pond: Closure measures are not changed from those described in the Ekati Mine Interim Closure and Reclamation Plan (ICRP) and the King Pond Fisheries Act Authorization (SC00028); no new risks are introduced through the MUG Project. Lynx Pit: Closure measures are not changed from those described in the Ekati Mine ICRP (as updated through Lynx and Jay Project approvals); no new risks are introduced through the MUG Project. Misery Pit: Closure measures are not changed from those described in the Ekati Mine ICRP (as updated through Jay Project approvals); no new risks are introduced through the MUG Project. Reclamation research topics related to Misery Pit that were identified for the Jay Project are already in place and are not a necessary prerequisite for design and construction of the MUG Project. Water quality modelling predictions for the MUG Project (as provided to the Wek èezhìi Land and Water Board) also confirm acceptable long-term closure water quality for Misery Pit lake in the absence of the Jay Project. It is essential that the conceptual closure plan for the MUG project obtains approval, so that Dominion, with confidence, can incorporate the necessary information into the Ekati mine IRCP for the upcoming July 2018 submission. References: BHP Billiton Canada Inc Ekati Diamond Mine Interim Closure and Reclamation Plan. Submitted to the Wek èezhìi Land and Water Board. Yellowknife, NT. August 31,