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Adequacy Issue#2: Impact to Grassy Valley by Seepage from the Toe of ECOSA <br /> DRMS Adequacy Comment <br /> CC& V has raised some doubt about the potential for the preferential flow path to be circumvented, <br /> which could adversely impact the surface and shallow perched ground water in Grassy Valley. <br /> DRMS is incorrect in this statement. As DRMS correctly notes, in Volume IV, under East Cresson Storage <br /> Area (ECOSA) Evaluation, Section 4.2, CC&V states: <br /> "The potential for impact arises as a result of the fate of the water after it flows out of the base of the <br /> ECOSA. If the water proceeds down through the diatremal volcanic rocks, contacts the abundant <br /> carbonate in the Diatreme and joins the regional ground water system that flows from the Carlton <br /> Tunnel,there will be no net impact, as this is the same fate that it would have had naturally. If however, <br /> the water does not follow the path, but emerges at the toe of the ECOSA and joins the surface water <br /> system in Grassy Valley,then dissolved constituents in it resulting from sulfide oxidation have the <br /> potential to cause impact to surface water and shallow ground water resources in Grassy Valley" <br /> (emphasis added). <br /> However, DRMS does not complete the citation, as CC&V goes on to say: <br /> "The impact assessment therefore addresses the fate of the water from the ECOSA." <br /> That impact assessment is presented in Volume IV, ECOSA Evaluation, Section 4.2. <br /> The impact assessment demonstrates that all water that infiltrates at natural rates into the reclaimed <br /> ECOSA surface will seep vertically from the overburden through the underlying colluvium and bedrock <br /> beneath the facility, and will join the regional groundwater flow system in the volcanic diatremal rock, <br /> which exits via the Carlton Tunnel. In order to be able to perform that impact assessment, a major site <br /> investigation of the ECOSA area was required and performed.This site investigation and evaluation <br /> comprised the following: <br /> 1. Evaluation of baseflow in Grassy Creek. Continuous monitoring of surface water flow in Grassy <br /> Creek was implemented and conducted at three locations.The results show that there is no <br /> baseflow in the location below the ECOSA footprint, demonstrating that there is no lateral flow <br /> of natural infiltration from ECOSA to Grassy Creek'. <br /> 2. Evaluation of piezometric head in the colluvial material in the ECOSA area. This data was <br /> collected from a total of 10 wells within the footprint of ECOSA, and show that in all cases the <br /> water level is always substantially below the ground surface, and in most cases the colluvium is <br /> unsaturated, demonstrating consistent vertical drainage of natural infiltration to the underlying <br /> bedrock'. <br /> 3. Evaluation of the hydraulic conductivity of the surface soil and colluvial material in the ECOSA <br /> area.This data from a total of 26 tested wells, 10 of which are within the footprint of ECOSA, <br /> 1MLE Volume IV, Cresson Project-East Cresson Overburden Storage Area Evaluation ("ECOSA Report"), Plate 5. <br /> 2 ECOSA Report, Plate 12. <br /> Adrian Brown Consultants, Inc. Page 2 of 8 <br />