GOVERNMENT OF THE NORTHWEST TERRITORIES CLOSING ARGUMENTS FOR

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2 GOVERNMENT OF THE NORTHWEST TERRITORIES CLOSING ARGUMENTS FOR DOMINION DIAMOND EKATI ULC EKATI DIAMOND MINE MISERY UNDERGROUND WATER LICENCE AMENDMENT APPLICATION W2012L Submitted to: Wek ѐezhὶi Land and Water Board # th St, Yellowknife, NT X1A 3S3 April 12,

3 Contents 1.0 Introduction Management Plans Plan Approvals as part of Licence Phase Misery Underground Water Quality Modelling Updates Total Phosphorus Empirical 95% Confidence Intervals Use of an Unvarying Dilution Factor Discharge from the King Pond Settling Facility (KPSF) Security References

4 LIST OF ACRONYMS Aquatic Effects Monitoring Program Canadian Council of Ministers of the Environment Dominion Diamond Ekati ULC Diavik Diamond Mine Inc. Effluent Quality Criteria Environment and Natural Resources Environmental Assessment Government of the Northwest Territories Interim Closure and Reclamation Plan Information Request King Pond Storage Facility Long Lake Containment Facility Metal Mining Effluent Regulations Minewater Management Plan Misery Underground Potentially Acid Generating Processed Kimberlite Surveillance Network Program Total Dissolved Solids Total Suspended Solids Toxicity Modifying Factor United States Environmental Protection Agency Waste Rock Storage Area Waste Rock Operations and Management Plan Wasterwater and Processed Kimberlite Management Plan Water Quality Objectives Wek ѐezhὶi Land and Water Board AEMP CCME Dominion DDMI EQC ENR EA GNWT ICRP IR KPSF LLCF MMER MWMP MUG PAG PK SNP TDS TSS TMF USEPA WRSA WROMP WPKMP WQOs WLWB/Board 3

5 1.0 Introduction The Government of the Northwest Territories (GNWT) is pleased to provide its closing arguments in relation to the Dominion Diamonds Ekati ULC s (Dominion) amendment application for water licence W2012L related to underground mining in the Misery Pit. This submission summarizes the Government of the Northwest Territories (GNWT) concerns regarding the Misery Underground application and provides recommendations for the Wek ѐezhὶi Land and Water Board s (WLWB) consideration. This submission takes into consideration all of the documents provided with the Water Licence application, information provided through Information Requests, Undertakings and discussions at the November 2017 Technical Session and February 2018 Public Hearing, and associated Undertakings. Note GNWT has carried forward the majority of the recommendations and arguments from our Technical Intervention. However, where required, based on additional information and clarification available through Dominion s intervention response and the Public Hearing, the GNWT has modified its recommendations, for the purposes of increasing clarity and accuracy. GNWT appreciates the opportunity to express its concerns and provide recommendations and suggestions to the WLWB on this licence application. 4

6 2.0 Management Plans 2.1 Plan Approvals as part of Licence Phase Within the Water Licence application, Dominion included several management plans and designs and requested the Board review and approve these as part of the amendment application process. GNWT maintains its position provided in its written intervention pertaining to approval of plans with issuance of a licence or licence amendment. Draft plans have been provided by Dominion as part of the licencing process and GNWT is committed to, and supportive of, an expedited review process for these time sensitive plans, following licence issuance. 3.0 Misery Underground Water Quality Modelling Updates 3.1 Total Phosphorus In response to GNWT s Technical Intervention that included recommendations to Dominion from the GNWT s Technical Consultant, Zajdlik and Associates, Dominion attempted to address outstanding concerns on the water quality modeling for MUG and its impacts to the Jay Project. GNWT acknowledged at the Public Hearing that the majority of the questions and recommendations included in the Zajdlik and Associates memo had been resolved by Dominion in their Intervention responses; however, some questions regarding predicted EQC s and phosphorous loadings remained unanswered. As part of Undertakings No. 1 and No. 3, Dominion has provided additional information regarding predicted total phosphorous concentrations within Lac du Sauvage. Upon review of the Undertaking Responses, the GNWT understands that some of the predictions show that total phosphorous within Lac du Sauvage will exceed the benchmark at LDS P1 (i.e., the Discharge location in Lac du Sauvage) and LDS P2 under ice for the Average MUG Project Groundwater Flows and Mean Water Quality. Further, the predicted phosphorus concentrations will exceed the Projected Whole lake Average Total Phosphorus Concentrations in Lac du Sauvage benchmark by even larger amounts under the less conservative scenarios (i.e. higher total phosphorous concentrations). Total phosphorous will also approach the Lac de Sauvage benchmark at LDS P3 (the Narrows) under the average and less conservative modelling scenarios. If the stochastic nature of total phosphorous inputs were to be considered by Dominion, total phosphorous input concentrations that are twice as high could occur. If this was to occur, exceedances of the total phosphorous benchmark within Lac du Sauvage will be even higher than predicted. This uncertainty in total phosphorous loads, potentially resulting in higher chlorophyll a 5

7 concentrations for downstream users, justifies further monitoring and modeling of actual total phosphorous loads. The increase in chlorophyll a concentrations is particularly relevant since the total phosphorous concentrations for Lac de Gras from Diavik Diamond Mines Incorporated s (DDMI) discharge, which is also considered in the modeling, is uncertain. Using a low or conservative estimate of chlorophyll a (i.e. coefficient of variation of 50%) and predicted chlorophyll a concentration as a result of Dominion s predictions (Dominion, 2018a Undertaking No. 3, Table 3 1), chlorophyll a concentrations will approach the DDMI chlorophyll a AEMP benchmark (4.5 µg/l) under the concurrent discharge scenario. Given these potential scenarios, and in consideration of Dominion s Public Hearing Undertaking responses, the recommendation to consider the stochastic nature of total phosphorous input concentrations as part of a continually improving prediction model remains. Additional modeling studies as GNWT has recommended will provide reviewers an opportunity to compare model predictions for total phosphorous with measured total phosphorous concentrations to confirm the accuracy of predictions and identify whether other management actions are required. Currently, due to the short duration of the MUG project and the projected discharge timing of Misery Pit as part of the Jay Project there will be a significant period between the start of the MUG project and the next scheduled modeling update. This is particularly important as the updated MUG water management plan proposes discharge from KPSF at the beginning of the project. This discharge scenario was not fully considered as part of previous decision (i.e. the Jay Project) on when a modeling update should be completed by Dominion. 3.2 Empirical 95% Confidence Intervals A recommendation was made in GNWT s Technical Intervention to include 95% empirical confidence intervals for predicted analyte concentrations (Appendix A; Section 5.1 of Zajdlik and Associates 2018 memo). The confidence intervals provide an estimate of the precision of the predictions and as such, provide an understanding of how variable the predictions under a specific scenario could be. In Dominion s Technical Intervention response to GNWT, (2018b, Section ) Dominion feels that model input terms have already been reviewed and discussed as part the Jay Project DAR and Water Licence application review processes. The same terms were to have been carried forward into the water quality modelling completed for the MUG Project Water Licence application. While Dominion is correct that previous Jay project model inputs have been reviewed, Dominion has not provided a rationale regarding why 95% empirical confidence intervals for predicted concentrations cannot be provided. The GNWT notes that the recommended confidence intervals are likely not critical for a decision at this time but maintains that they should be included as an improvement for future model outputs. Amended GNWT Recommendation: 6

8 GNWT recommends that Dominion submit a Water Quality Modeling Special Study updating predicted total phosphorus predictions for Lac de Sauvage compared to monitored concentrations. Submittal of the study should be within one year of a full years worth of operational sampling results. Any EQC established within the licence should be revised, if needed, to reflect the results of this study (i.e., analyte concentrations exceeding EQC predictions). 3.3 Use of an Unvarying Dilution Factor Dominion states in the Response to Interventions (2018b, Section 2.2.6) that: The dilution factor of 1.7 was calculated based on an annual average natural runoff volume that reports to Cujo Lake (i.e., 318,000 m 3 /yr) and an annual Discharge volume from the King Pond Settling Facility (KPSF) (i.e., 470,915 m 3 /yr). The authors cite WLWB (2014) as the source of the dilution factor. In that document, the Board recommended to use water flows as opposed to modelled constituents to estimate EQC. The Board decision was to use predicted annual discharge volumes from the KPSF with the average annual natural runoff volume reporting to Cujo Lake. Dominion s argument during the proceeding was that dewatering of Lynx Lake skewed the discharge volume upwards. Consequently, the Board used predicted discharge volumes excluding the dewatering volume. Since that time, volumes being discharged from the KPSF have changed due to the MUG project. A summary of activities and water volumes associated with the KPSF are provided in the tables below. 7

9 Table 1: Summary of Dominion s Proposed Activities and Water Volumes Associated with the KPSF Year Activity 1 KPSF Inflows 2, 3 (m 3 ) MUG Operations 2020 MUG Operations 2021 MUG Operations 2022 MUG Project Closure and Transition to the Jay Project KPSF Discharge to Cujo Lake 2 (m 3 ) Start of Misery underground construction. 633, ,000 Annual Discharge to the environment from the King Pond Settling Facility to reach elevation 443 m after freshet but before the start of pumping of minewater from Misery underground developments Upgrades to King Pond Settling Facility, which include liner installation at the Saddle Dam (any seepage losses from the upgraded Saddle Dam will report to the Waste Rock Dam Pond) (Golder 2017). losses from the upgraded Saddle Dam will report to the Waste Rock Dam Pond) (Golder 2017). In early September 2018, underground construction is estimated to be advanced below the permafrost base and groundwater inflows to Misery Underground are expected to commence; minewater collected in the underground will be pumped to the King Pond Settling Facility. Management of Misery underground minewater in King Pond Settling Facility. 2,343,000 1,403,700* Completion of mining at the Lynx Pit prior to King Pond Settling Facility reaching capacity (Section 5.0). Management of Misery underground developments minewater in Lynx Pit and transfer of excess minewater. Continued management of Misery underground developments minewater in Lynx Pit and 764, ,000 transfer of excess minewater from King Pond Settling Facility to Lynx Pit. Continued management of Misery underground developments minewater in Lynx Pit. 764, ,000 Completion of mining at Misery underground by end of July , ,000 Decommissioning of the Misery underground developments, by end of August Pumping out of minewater stored in Lynx Pit to the Misery Pit and underground workings, prior to the start of Final Dewatering of the Jay diked area. Final Dewatering of Jay diked area into the top of Misery Pit and to Lynx Pit (Golder 2016). 1 Text regarding activities extracted from Golder (2017b, Section 3.4). 2 DDEC (2017a, Table 1 1) 3 DDEC (2017a refers to Golder (2017b) as the source of these flows. 8

10 * This value may be incorrect. Golder (2017b, Table 2) reports this number as a change in storage in the KPSF. No flow to the environment (flow component D1, Golder 2017b, Table 1) is reported for this time period. This number may reflect a maximum possible drawdown of the KPSF under the assumption that water will meet EQCs. The predicted discharge volumes in Table 1are used to estimate dilution factors below. Table 2: Estimated Dilution Factors for the MUG Project Source Predicted Discharge Volume from KPSF (m 3 /yr) Predicted Dilution Factor 1 Actual Discharge Actual Dilution Factor 1 (m 3 /yr) % Difference= 100% (Observed Expected)/ Observed cannot be cannot be 470, WLWB (2014) 2 estimated estimated WLWB (2014) Predicted 2015 discharge 597, , % WLWB (2014) Predicted 2016 discharge 470, , % WLWB (2014) Predicted 2017 discharge 470, NA WLWB (2014) Predicted 2018 discharge 107, NA Predicted Discharge in 2018 (DDEC 2017a, Table 1 1) 528, NA Predicted Discharge in 2019 (DDEC 2017a, Table 1 1) 1,403, NA Predicted Discharge from 2020 onward (DDEC 2017a, Table 1 1) 384, Total Annual Inflow into Cujo Lake (WLWB, 2014; DDEC, 2018) used is 318,000 (m 3 /yr). 2 DDEC (2015) 3 DDEC (2016) 4 DDEC (2017b) 9

11 The tables above show that the proposed dilution factor of 1.7 is not conservative; dilution could be as low as 1.23 in Although Dominion notes that in a wet year additional dilution will occur, the converse is also true; in a dry year less dilution will occur. The tables also show that there is a considerable difference between the discharge volumes predicted in the context of the Lynx Project and measured discharge volumes. The discrepancies suggest that when environmental protection is predicated upon a priori model predictions, a degree of conservatism should be used. In order to ensure that the downstream receiving environment is adequately protected by the application of dilution factors, a dilution factor of less than 1.7 should be used. The GNWT notes that Dominion has predicted analyte concentrations in the KPSF and estimated case by case EQCs (DDEC 2014, Table 1). However, the GNWT is of the opinion if such an approach is used, the variability in predicted concentrations should be acknowledged by the using the upper 95 th confidence limit of the predicted concentration in the dilution factor estimate. Further, some thought would have to be given to the treatment of non conservative analytes, such as, total phosphorus and nitrogen species. Amended Recommendations: GNWT recommends that Dominion should not rely on an unvarying dilution factor for conversion of a site specific water quality objective to a maximum average concentration when it is not known what the actual discharge from the KPSF will be. A lower dilution factor than 1.7 should be used. Dominion should modify the cadmium EQC calculation to include a temporally relevant dilution factor. As part of the Water Quality Modeling Special Study, updated predictions should be assessed to see whether predicted concentrations are falling within expected ranges. 4.0 Discharge from the King Pond Settling Facility (KPSF) GNWT s understands that there should be sufficient storage within the KPSF to hold MUG water until such time as the Lynx pit becomes available for storing water. Water from the KPSF could then be transferred to the Lynx Pit, avoiding the need to discharge MUG water to the Cujo Lake. MUG water will be highly saline, and this strategy would avoid discharging saline water into a freshwater watershed. GNWT s position on this subject remains the same as stated in our intervention. In accordance with the MVLWB Water and Effluent Quality Management Policy, the objective of minimizing the amount of waste to be disposed to the receiving environment, could be achieved by reducing or eliminating any mine water from being discharged from the KPSF and is therefore a preferred strategy. However, also

12 in accordance with the MVLWB Policy, if the Board determines that discharge from the KPSF during the MUG project is authorized under this amendment, EQC s for any discharge from the KPSF would be required to ensure that Water Quality Objectives (WQOs) in the receiving environment are maintained. 5.0 Security GNWT identified several security related issues in our intervention, but many of these were addressed by Dominion prior to the Public Hearing. One item that outstanding was whether there is an allowance for removing hazardous material from the underground prior to disposal. For example, Dominion has included an allowance within the estimate of $0.39/L for disposal of waste oil. It is not clear to ENR that this rate is sufficient to also include collection of this material from the underground. In response to IR#6, Dominion indicated that the time required to remove hazardous materials from underground equipment would be on the order of one week. Dominion s security estimate include a unit rate of $7,399/day for cleaning and stripping buildings of hazardous materials, and a similar rate could be used for cleaning/stripping the underground. Therefore, 7 days at $7,399/day would represent a cost of $51,793 for the MUG project. Note, the GNWT understands that such costs have not been accounted for the Panda or Koala underground. It is the GNWT s opinion that such costs should be included. as well. Amended Recommendation: The GNWT recommends that the security estimate for the MUG Project also include a cost to remove and or strip contaminants from the Underground. Further, that such costs should also be included for the Panda and Koala Underground components. 6.0 References DDEC (Dominion Diamond Ekati Corporation) Dominion s Lynx Project, Public Hearing Undertakings, February 14 th, DDEC (Dominion Diamond Ekati Corporation) Ekati Diamond Mine Environmental Agreement and Water Licence Annual Report DDEC (Dominion Diamond Ekati Corporation) Ekati Diamond Mine Environmental Agreement and Water Licence Annual Report 2016.

13 DDEC (Dominion Diamond Ekati Corporation). 2017a. Misery Underground Project Information Request Responses (#1 8), December 15 th, DDEC (Dominion Diamond Ekati Corporation). 2017b. Ekati Diamond Mine Environmental Agreement and Water Licence Annual Report Dominion (Dominion Diamond Ekati ULC). 2018a. RE: W2012L2 0001, W2017D0004: Misery Underground Project Proceedings Submission of Undertakings and Exhibit 1, February 22 nd, Dominion (Dominion Diamond Ekati ULC). 2018b. Re: W2012L Ekati Mine Water Licence Amendment and W2017D0004 Land Use Permit Applications for the Misery Underground Project Response to Interventions, January 30 th, Golder Associates (Golder). 2017a. Ekati Mine Misery Underground Water Quality Model Updates. Submitted to Dominion Diamond Ekati Corporation, Aug 14 th, Golder Associates (Golder). 2017b. Dominion Diamond Ekati Corporation Northwest Territories Canada Misery Underground Project Mine Water Management Plan, Aug 14 th, Golder Associates (Golder) Technical Memorandum Misery Underground Project Supplemental Modelling of Total Phosphorus in Lac de Gras. WLWB (Weḱèezhìi Land and Water Board) W2012L2 0001, Reasons for Decision Development and Mining of the Ekati Lynx Pit.