Diavik Diamond Mines’ Water Licence W2015L2-0001 Amendment Proceeding
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WORKING WITH THE PEOPLE FOR THE ENVIRONMENT November 23, 2020 By Email Joe Mackenzie Ryan Fequet Chair Executive Director Wek’èezhìi Land and Water Board Wek’èezhìi Land and Water Board 1 - 4905 48 St. 1 - 4905 48 St. Yellowknife, NT X1A 3S3 Yellowknife, NT X1A 3S3 Re: EMAB Intervention for PKMW Water Licence Amendment Application Dear Joe and Ryan, The Environmental Monitoring Advisory Board (EMAB) wishes to thank the WLWB for the opportunity to participate in the proceeding to review the above-captioned water licence amendment application. We respectfully submit EMAB’s intervention for the proceeding. We also include five attachments that are cited in the intervention. All other citations in the intervention are hyperlinked in the Citations section. If you require further information, please contact John McCullum at the EMAB office. Sincerely, Charlie Catholique EMAB Chair CC: EMAB Board and Alternates (by email) Parties to the Environmental Agreement (by email) Environmental Monitoring Advisory Board PO BOX 2577 YELLOWKNIFE, NT X1A 2P9 Ph (867) 766 – 3682 E-mail: [email protected] Environmental Monitoring Advisory Board Intervention to the Wek’èezhìi Land and Water Board on Diavik Diamond Mines’ Water Licence W2015L2-0001 Amendment Proceeding Deposition of Processed Kimberlite into Mine Workings November 23, 2020 EMAB intervention on Diavik Diamond Mines’ Water Licence W2015L2-0001 Amendment Proceeding: Deposition of Processed Kimberlite into Mine Workings EMAB intervention – PKMW Water Licence Proceeding Note to Readers: all documents cited in this intervention are either included in the attachments to the intervention or hyperlinked in the Citations section Contents 1. Water quality thresholds and definition of significance ....................................................................... 3 2. Reliability of predictions ....................................................................................................................... 5 3. Fresh water cap filling design................................................................................................................ 8 4. Benchmarks for unanticipated mixing .................................................................................................. 8 5. Decision to reconnect pit lake to Lac de Gras ....................................................................................... 9 6. Effects on fish/habitat ......................................................................................................................... 10 7. Effects on wildlife ................................................................................................................................ 13 8. Monitoring (pre and post dike breach) ............................................................................................... 14 9. Contingency plans ............................................................................................................................... 18 10. Revised closure objectives .............................................................................................................. 19 11. Cumulative effects on water quality ............................................................................................... 21 12. Feasibility of moving PKC slimes ..................................................................................................... 22 13. WLWB Workplan for Water Licence Amendment Application ....................................................... 23 List of Acronyms ...................................................................................................................................... 25 Citations .................................................................................................................................................. 27 List of Attachments ..................................................................................................................................... 29 2 EMAB intervention on Diavik Diamond Mines’ Water Licence W2015L2-0001 Amendment Proceeding: Deposition of Processed Kimberlite into Mine Workings 1. Water quality thresholds and definition of significance Issue: Water quality in the pit lake may not meet AEMP Benchmarks, taking into account runoff entering from East Island. Diavik has proposed Revised Ecological Thresholds in the proposal that are 20% higher than AEMP benchmarks. Background: It appears that for the purposes of this water licence amendment, Diavik has not modified its proposal to use the approach to water quality benchmarks that it put forward in the amendment application and in ICRP 4.0 (Diavik, April 2017) ie. using the significance definitions from the Comprehensive Study Report (Canada, 1999). Following from this definition, Diavik proposed that a one-kilometer mixing zone be established around East Island, and that the water quality benchmarks that would be required to be met at this distance would be the current AEMP benchmarks plus 20% (see Diavik Summary Impact Statement, p 44-45, Table 4-3, Revised Ecological Thresholds for Water Quality, Rio Tinto (May 2019b)). This approach is inconsistent with Measure 1 of the Environmental Assessment Report (MVEIRB, January 2020), which requires that Diavik will meet water quality objectives at closure: • Water quality objective 1 of Measure 1 requires: water in at least the top 40 meters of the pit lake that is safe for people, aquatic life and wildlife o This objective means that water quality in the pit lake must meet AEMP Benchmarks at a minimum in order to be protective of aquatic life; Diavik’s proposed Revised Ecological Thresholds are not adequate. Diavik’s proposed water quality benchmarks are also inconsistent with the direction given by the WLWB in its Reasons for Decision on ICRP 4.0 (WLWB, December 2018), and with the approach Diavik has proposed in ICRP 4.1 (Diavik, December 2019). • On p. 42 of the WLWB Reasons for Decision on ICRP 4.0 the WLWB gave the following direction: “Based on the above discussion, DDMI still has some work to do in order to develop closure criteria for SW2 that will be acceptable to all parties. To accomplish this, the Board has determined that the following steps are necessary: 1. If DDMI wishes the Board to consider the use of a regulated mixing zone for setting closure criteria, it should more clearly outline the information as required by the Mixing Zone Guidelines (see Section 6.0 of the Mixing Zone Guidelines). 2. A better understanding of the following is needed to help demonstrate whether a regulated mixing zone will be required: a. The expected dilution in Lac de Gras at the various potential discharge points; and b. Water quality predictions for water in all potential discharge streams and in Lac de Gras. 3. Consideration and discussion of options to address potentially problematic parameters (e.g., different mixing zones and passive treatment).” These steps are reflected in the following revisions the WLWB required to be included in Version 4.1 of the interim CRP (WLWB Reasons for Decision on ICRP 4.0): “Revision # 31: For closure objective SW2: 3 EMAB intervention on Diavik Diamond Mines’ Water Licence W2015L2-0001 Amendment Proceeding: Deposition of Processed Kimberlite into Mine Workings a) Refine and compile predictions for water quality in all streams entering Lac de Gras in consideration of the different sources (e.g., WRSA and PKC Facility) and possible dilution prior to entry into the lake; b) Follow the steps required by the Mixing Zone Guidelines (see Section 6.0) and provide evidence to demonstrate the smallest practicable mixing zone; c) Outline a plume delineation study plan and/or provide substantive information to refine the dilution factor; d) Revise closure criteria for SW2 based on the results of (a) through (c); e) Provide evidence to support the achievability of proposed closure criteria; and f) Include a consideration and discussion of alternative options to address potentially problematic parameters (e.g., different mixing zones, passive treatment, and changes to the proposed closure design).” • In general, it is EMAB’s view that the principles behind the WLWB’s direction should also be followed in relation to mixing of water from the pit lakes with Lac de Gras in order to meet the requirements of Measure 1. Diavik should revise its proposed amendment to address the relevant direction from the WLWB with respect to water quality benchmarks and mixing zones. • Diavik has done a great deal of work in ICRP 4.1 to identify discharges, dilution factors and mixing zones from East Island. This same approach should be applied to discharges from the pit lakes. • EMAB notes Table 4-3 in the SIS: Revised Ecological Thresholds for Water Quality – these are above AEMP benchmarks so not protective of aquatic life. Diavik should commit to meeting benchmarks for protection of aquatic life. • Diavik should clarify whether water entering Lac de Gras from the pit lake is expected to meet AEMP Benchmarks, and whether runoff entering the pit lake from East Island is expected to meet AEMP Benchmarks. • EMAB expects that plankton will live throughout the water column, so Diavik will have to meet aquatic health standards to the depth that any form of aquatic life, including plankton, populate. Recommendations: 1.1 EMAB recommends that Diavik propose mixing zones for runoff entering the pit lake, and for water entering Lac de Gras from the pit lake, if these waters are predicted to be above AEMP Benchmarks.