Multiple Modeling Approach for the Aquatic Effects Assessment of a Proposed Northern Diamond Mine Development

Multiple Modeling Approach for the Aquatic Effects Assessment of a Proposed Northern Diamond Mine Development J. A. Vandenberg 0 1 2 M. Herrell 0 1 2 J. W. Faithful 0 1 2 A. M. Snow 0 1 2 J. Lacrampe 0 1 2 C. Bieber 0 1 2 S. Dayyani 0 1 2 V. Chisholm 0 1 2 0 De Beers Canada Inc , 300-5102 50th Ave, Yellowknife, NT X1A 3S8 , Canada 1 Golder Associates Ltd , 102 - 2535 3rd Ave SE, Calgary, AB T2A 7W5 , Canada 2 & J. A. Vandenberg Eight water models were used to assess potential aquatic environmental effects of the proposed Gahcho Kue´ diamond mine on groundwater and surface water flow and quality in the Northwest Territories, Canada. This sequence of models was required to cover different spatial and temporal domains, as well as specific physico-chemical processes that could not be simulated by a single model. Where their domains overlapped, the models were interlinked. Feedback mechanisms amongst models were addressed through iterative simulations of linked models. The models were used to test and refine mitigation plans, and in the development of aquatic component monitoring programs. Key findings generated by each model are presented here as testable hypotheses that can be evaluated after the mine is operational. This paper therefore offers a record of assumptions and predictions that can be used as a basis for post-validation. Sub-arctic; QUAL-W2; GEMSS - GoldSim CORMIX MODFLOW CENorthwest territories Introduction Many complex processes, interactions, and potential effects must be evaluated in predicting the impact of large mining projects on the aquatic environment. This is particularly true in Arctic Canada, where the region is dominated by aquatic features, such that a more accurate term for this landscape might be ‘‘waterscape’’ (Fig. 1). Potential aquatic effects include changes to levels, flow, and chemistry of both surface- and ground-water systems, which can manifest themselves as effects on aquatic and terrestrial biota. All potentially significant adverse environmental effects must be considered as individual components with specific assessment endpoints, within a holistic framework that accounts for interactions amongst each component. Aquatic modelling was undertaken for the De Beers Gahcho Kue´ environmental impact statement (EIS). This project presented a unique set of challenges from a modelling perspective owing to: (1) the dynamic nature of the mine plan and water management plan; (2) the dominance of aquatic features in the region; (3) the different water characteristics between the groundwater and surface waters that will be mixed during operations; and (4) the sensitivity of the pristine waters that will be affected by mining operations. These challenges required an unusually large number of models to interact together, with each model operating within a sub-domain of the overall spatial–temporal domain of the project. While the EIS findings withstood a thorough review by stakeholders and regulators, the true test of accuracy of predictions can only be conducted once operational data have been generated. Several authors have highlighted the need to publish EIS findings in the peer-reviewed literature and to revisit those findings in a post-audit. For example, Dube´ et al. (2013) point to a failure to conduct post-audits as a general shortcoming in the EIS process; regulators and local stakeholders have requested additional monitoring and follow up studies to enhance transparency (DFO 2012; LKDFN 2012; YKDFN 2012) ; Castendyk et al. (2009) noted the paucity of publicly available predictions of pit lake hydrodynamics and chemistry; and Kuipers et al. (2006) highlighted the need to conduct post-audits on EIS predictions. With these considerations in mind, we present herein the key findings from the aquatic assessment. The key findings are re-stated as testable hypotheses that can be verified after the mine has entered construction and early operational phases. Verifying key findings through postaudit monitoring will confirm the accuracy of assumptions and predictions as well as the adequacy of the mitigation. Project Description The proposed project is a diamond mine located at Kennady Lake, approximately 280 km northeast of Yellowknife, Northwest Territories, Canada (Figs. 2, 3). The diamond-bearing kimberlite deposits contain an indicated resource of about 30 million tonnes (t), which are hosted in three vertical pipes named 5034, Hearne, and Tuzo. The kimberlite pipes are predominantly located beneath Kennady Lake and extend from near the bottom of the lake down to more than 300 m below the lake. Diamondiferous kimberlite will be extracted by open-pit-mining methods. The project mine plan was designed with the objectives of minimizing discharges to the environment and limiting the extent of surface disturbance. These objectives will be achieved by isolating and dewatering Kennady Lake, sequenced mining of three open pits, and using the isolated lake for most of the (...truncated)