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A <br /> Project Descriptions 11 pal AddanBrown <br /> UNDERGROUND GOLD MINE INFLOW, IMPACT, AND CLOSURE <br /> AdrianBrown was retained to perform the groundwater and geochemical evaluation of Echo Bay's <br /> Lamefoot underground gold mine in Washington State to allow expansion from the limited mining <br /> volume which was authorized under the original EIS for the project. This mine was subject to <br /> administration by the U.S.Department of Interior,Bureau of Land Management, as well as the State of <br /> Washington's Department of Environment. The project involves the underground extraction of a high <br /> sulfide gold orebody located in a low permeability limestone and volcaniclastie host rock sequence.The <br /> inflow to the mine was expected to be minimal, but permitting of the mine was complicated by the need <br /> to provide permanent protection of a nearby lake system from mining-related contamination. <br /> AdrianBrown designed and performed a detailed underground evaluation program to establish the <br /> groundwater and geochemical system in which the mine was to be constructed to a level of assurance <br /> sufficient to satisfy the regulators responsible for the issuance of the permit to mine. For the mine <br /> expansion,Echo Bay was required to a"Finding of No Significant Impact",or FONSI. This required a <br /> detailed investigation of the groundwater hydrology and chemistry of the mining area,at both a local and <br /> regional scale. Extensive surface and subsurface drilling was performed to identify the heads and <br /> hydraulic conductivity in the materials in and surrounding the orebody.Inflow to the mine development <br /> drifts was measured for flow and quality,and this inflow(which varied seasonally from 1 gpm to 20 <br /> gpm for the entire development system)was used to estimate gross hydraulic conductivity in the mine <br /> host materials. Using the total dataset a detailed three dimensional groundwater flow model was <br /> constructed for the mine, and the inflow to the developing mine modeled. Following the mining <br /> evaluation,the water level and discharge in the plugged mine was predicted using the same model. <br /> The results of the groundwater flow and refill modeling were input into a customized model of the <br /> geochemistry of the mine pool,both prior to,and after closure,and the quality of water as it moves <br /> through the adjacent rockmass. This model was used to predict the post-closure quality of the water <br /> which would flow out of the mine into the rock adjacent to the mine, and ultimately would enter the <br /> surface water regime, including the adjacent lake. <br /> The results of the analyses were reviewed by nationally recognized technical experts. After detailed <br /> evaluation,the FONSI was issued by the BLM,and the project was able to exploit the majority of the <br /> remaining orebody. <br />