April 10, Ms. Violet Camsell-Blondin Chair Wek èezhìi Land and Water Board #1, th Street Yellowknife, NT, CA, X1A 2P6

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1 April 10, 2015 Ms. Violet Camsell-Blondin Chair Wek èezhìi Land and Water Board #1, th Street Yellowknife, NT, CA, X1A 2P6 Dear Ms. Camsell-Blondin, Re: Lynx Lake Dewatering Plan As per Part E, Item 1 of Water License W2012L2-001 (Conditions Applying to Dewatering and Drawdown) Dominion Diamond Ekati Corporation (DDEC) is submitting this Dewatering Plan for Lynx Lake prior to the commencement of dewatering. DDEC is developing the Lynx Pit located approximately 3 km southwest of the exiting Misery Pit and Camp location. The project will use the existing infrastructure at the Misery Pit and Camp and kimberlite will be processed in the Process Plant located at the Main Ekati Camp. The Lynx Land Use Permit was granted by the Wek èezhìi Land and Water Board (WLWB) on April 30, 2014 and Water Licence W2012L2-001 was amended on June 30, 2014 to include Lynx Pit Development. In advance of the development of Lynx Pit, Lynx Lake will be fished out and dewatered. The Lynx Lake Offsetting and Fish-out Plan was submitted to Fisheries and Oceans on March 13, During the evaluation and planning of the lake dewatering, DDEC evaluated pipeline and pump sizes, pumping locations, flow rates, and possible erosion and mitigation measures. DDEC reviewed the potential surface water quality effects, hydrology effects, the characteristics of Lynx Lake and Lynx Creek and based the Dewatering Plan below on this information.

2 Figure 1. Lynx Lake Bathymetry In fulfillment of the requirements listed in Schedule 4, Item 2 of W2012L for a Dewatering Plan, please see details of the plan to dewater Lynx Lake below: a) Volume of water produced by Dewatering: The total volume of Lynx Lake is estimated at 483,000 m3 with a maximum depth of 27 m based on bathymetric data collected in 2013 (Figure 1). The estimated volume of water to be pumped to Lac de Gras in Stage 1 is 260,000 m3 and the estimated volume of water to be pumped to King Pond in Stage 2 is 223,000 m3. b) A schedule for Dewatering or Drawdown and maximum pump rates: The schedule plans to remove the water from the Lynx Lake after 2015 spring freshet and after Phase 1 of the Lynx Lake Fish-out has been completed. The pumping is expected to begin near the beginning of July and will be in two stages. Stage 1 will continue until the threshold for Total Suspended Solids (TSS) in the pumped water is reached (see item k

3 below). This is anticipated to be approximately the upper 5 m of the lake. During Stage 1 pumping, water will be pumped to Lac de Gras as per the Lynx Project approval. Stage 2 will be the pumping of the lower portion of Lynx Lake to King Pond. Stage I: Will occur during the Phase II Fish-out. Pumping will proceed until the TSS threshold is reached as per item k (anticipated to be approximately 2 weeks). The planned is to use one Godwin HL 250 pump at a rate of 745 m 3 /hr pumping continuously. The estimated start of Stage 1 will be the beginning to middle of July. Stage 2: Will occur after the completion of Stage 1 and the pumping has been switched to King Pond. See item k for information on determining the switch to pumping to King Pond. The pump rate for Stage 2 is planned at 330 m 3 /hr using one Godwin HL150 pump. Stage 2 pumping will proceed until the lake is dewatered (anticipated to be approximately 31 days with the above pump and pumping rate). The dewatering of Lynx Lake is expected to be completed by the middle of September c) Pumping methods including locations of intake and outflow structures: An access road, as part of the Lynx Pit ring road, will be constructed around Lynx Lake to access the Lynx Outflow Channel located on the east side of the lake (Figure 2). The pump intake location for Stage 1 intake is planned to be located close to this location, and relatively deep (approx. 5.0 m water depth) as identified by the bathymetry. The pump location will be moved as the water is drawdown to take advantage of deeper water locations. Water will be pumped through a HDPE 12 pipeline into a boulder-rich area of the Outflow Channel to minimize the potential for erosion (Photo 1). For Stage 2, the pump intake location will be on the north and west side of Lynx Lake where the permanent Lynx Pit dewatering line will be located. A HDPE 12 pipeline will be used to pump the water to King Pond. The outflow into King Pond will be located where current minewater from Desperation Pond and the Waste Rock Dam area is put in to King Pond. Pumps will have appropriate fish screens installed as per the Department of Fisheries and Oceans Freshwater Intake End-of-Pipe Fish Screen Guidelines, All pumps will have secondary containment and be inspected daily by the Operations team and during refuelling.

4 Figure 2. Lynx Lake Stage 1 Discharge Location to Lynx Outflow d) The design of any erosion prevention structures in the areas where water or Waste is Discharged: For the Stage 1 dewatering to Lac de Gras, the Lynx Lake Outflow will be used (Figure 2). Lynx Lake Outflow is approximately 650 m long, is a low-entrenched, boulder dominated channel, where a significant portion of the flow is expected to travel through the void spaces within these boulder areas. The flows through the channel should disperse the energy of the water being discharged from Lynx Lake. The use of the natural outflow reduces the risk of impact to the area. For these reasons, Lynx Lake Outflow has been selected as the best dewatering location (Photo 1 and Photo 2). If monitoring in the Lynx outflow channel identifies erosion requiring mitigation (see item e below), potential end of pipe structures to reduce velocities, disperse flow, and mitigate erosion may include building an end of pipe riprap pad or the adjustment of boulders to allow for appropriate flow. Additional measures may include the adjusting the flow rate to decrease potential erosion. Alternately, flow could be switched to King Pond to avoid erosion in the channel. These will be determined based on the monitoring and inspection program. For the Stage 2 dewatering to King Pond, no erosion protection structures are required. The discharge location to King Pond is where current discharge from other mine structures (Desperation Pond/Waste Rock Storage Area) is located.

5 Photo 1: Lynx Outflow from Lynx Lake facing northeast

6 Photo 2: Lynx Outflow from Lynx Lake to Lac de Gras facing northwest e) The description of procedures for inspecting any erosion along the affected watercourse; During the Stage 1 dewatering of Lynx Lake, operations personnel will perform daily inspections of the discharge area of the Lynx Outflow Channel, along the 650 m channel, at Lac de Gras, and monitor for any significant or unexpected erosional issues. No erosion is anticipated as the water will be discharged into a boulder-rich area and follow the current Outflow for Lynx Lake. Once the Stage 1 dewatering is completed, water from Lynx Lake will be pumped via permanent pipeline along the Lynx Access Road and Winter Road Access to King Pond (Figure 3). Operations personnel will perform daily inspections of the intake area and permanent pipeline to King Pond.

7 f) A description of, and mitigation measures for, any predicted hydrological or water quality impacts to downstream water bodies: There are no predicted hydrological or water quality impacts to the downstream water body (Lac de Gras) based on the use of the Lynx Lake Outflow, the small volume of water to be pumped to Lac de Gras and the similarity of water quality between Lynx Lake and Lake de Gras. There are no predicted hydrological or water quality impacts to King Pond as this is designated as a minewater settling pond as receives mine water from other locations (Desperation Pond/Waste Rock Dam). g) The schedule and locations for water quality monitoring necessary to evaluate any effects to the Receiving Environment cause by Lynx Lake Dewatering: For the Stage 1 pumping program (anticipated to be approximately 2 weeks), water quality samples will be collected for complete chemical analysis at the start of pumping, weekly during pumping, and at the end of pumping. Total suspended solids will be analysed daily during pumping. These data will enable an evaluation of potential effects to the receiving environment. These data will be reported to the WLWB in the Dewatering Report. The environmental impact assessment conducted by the WLWB concluded that adverse effects are not anticipated. Water quality is measured in King Pond as part of the discharge requirements under the Ekati Water Licence and as part of the Surveillance Network Program. Monitoring of water quality in the receiving environment downstream of King Pond (Cujo Lake) is measured as part of the Aquatic Effects Program. The results of these programs are reported to the Water Board monthly (SNP) and annually (AEMP/Water Licence Annual Report). Therefore, no additional monitoring is required in King Pond. h) The frequency, location, and procedures for monitoring flow rates in the Discharge stream and where appropriate, in the receiving water body: Flow rates and total volumetric flows will be monitored daily by way of a flow meter. The flow meters will be located along the discharge pipeline from Lynx Lake to Lynx Lake Outflow, downstream of the pump. Flow rates from Stage 2 of the dewatering will be monitored by flow meter located on the permanent pipeline. i) The design of the pipeline and related facilities; A 12 HDPE DR9 pipeline with be used for both Stage 1 and Stage 2 dewatering. The pipeline in Stage 1 will be a temporary line to accommodate the initial pumping of Lynx Lake to Lac de Gras. The pipeline in Stage 2 will utilize the permanent line following the Lynx Access Road and the Winter Access Road to King Pond for the Lynx pit dewatering (Figure 3).

8 Figure 3: Permanent Lynx Pit dewatering pipeline along Lynx Access Road and Winter Access Road j) The procedures and rates for Dewatering to minimize erosion of the downstream water bodies, adjacent shorelines and, in winter, damage to spawning habitat from the development of icings, overflows, or glaciation. Operations personnel will perform daily inspections of the discharge area at the end of the discharge pipe and along the natural Lynx Lake outflow channel to Lac de Gras and monitor for any significant or unexpected erosional issues. For Stage 1, the Lynx Outflow is being utilized to eliminate potential erosion to Lac de Gras downstream and its shorelines. For

9 Stage 2, the water will be pumped to King Pond which is internal to the water management facilities and not a risk to the receiving environment. The pump speed can be adjusted to increase or decrease the volume of water pumped as operationally required. Dewatering is planned for the open-water season such that there is no risk of glaciation, icings or overflows. k) A description of how the Licensee will link the results of monitoring to those corrective actions necessary to prevent or minimize any Dewatering-related effects to the Receiving Environment. The description shall include, but not be limited to: i. Definitions, with rationale, of Action Levels applicable to monitoring identified under Schedule 4, Item 2g) and h). At a minimum, Action Levels should be set that: 1. define a level of Discharge quality or receiving water quality that indicates that water from Lynx Lake should cease to be discharged to Lac de Gras and be redirected to the King Pond Settling Facility; and, 2. Define a level of Discharge quality or receiving water quality that indicates that additional monitoring (i.e., through the SNP or AEMP) should be undertaken. As described in the above Dewatering Plan, only the volume of water from Stage 1 will be pumped to the receiving environment. The threshold to end Stage 1 pumping is Total Suspended Solids as identified through the WLWB Project approval. As the Ekati Water Licence W2012L2-001 amended to include Lynx Lake includes an Effluent Water Quality Criteria for TSS, this will be used as the action threshold. When daily monitoring for TSS reaches the EQC grab sample limit of 25 mg/l, Stage 1 pumping will be stopped. Analysis for TSS is conducted at the Ekati Mine Environment laboratory such that the actual concentrations will be know within several hours of sample collection. No water quality action levels are required for the Stage 2 pumping to King Pond. King Pond is part of the internal minewater management facilities and, as such, provides protection to the receiving environment. The water level in King Pond will be monitored daily during pumping from Lynx Lake to ensure that the established freeboard level is not exceeded. If the safe freeboard level is reached, pumping from Lynx Lake will stop.

10 DDEC trusts that you find this plan to be clear, informative and in fulfilment of the requirements of Schedule 4, Part 1 of W2012L Please contact the undersigned at claudine.lee@ekati.ddcorp.ca or should you have any questions. Yours sincerely, Dominion Diamond Ekati Corporation Claudine Lee, M.Sc., P.Geol. Superintendent Environment