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HARLAN & ASSOCIATES, INC. <br /> Mr. Walter Avramenko <br /> Colorado Department of Public Health & Environment <br /> June 3, 1996 <br /> Page 2 <br /> prior to their implementation. <br /> Response: Based on discussions with the Division of Minerals and Geology during the <br /> May 13, 1996, field reconnaissance, the Work Plan has been amended to include <br /> sampling of the discharge directly from the haulage tunnels and from the Old Refuse Pile <br /> and Rock Tunnel Waste Pile in addition to the Sutey Pile. These changes in the <br /> proposed field sampling and analysis program have been incorported in Table 1 of the <br /> Work Plan (copy attached). <br /> 3. Comment: Three ground-water samples will be collected from alongside Coal Creek to <br /> the northeast of the maintenance shop. On Figure I it appears as though these three <br /> sampling points are located to the north of Coal Creek, opposite the facility. All samples <br /> should be collected from locations along the south side of the creek. All existing seeps <br /> should be sampled, particularly if ground water emerges from separate and distinct <br /> areas. In the event that driven or drilled wells are used to sample ground water, these <br /> sampling locations should be positioned such that they are located close to and <br /> downgradient of the maintenance shop (east to northeast). <br /> Response: The ground-water samples to be collected along the embankment north and <br /> northeast of the maintenance shop will be collected from locations on the south side of <br /> Coal Creek and where possible from locations above the site perimeter ditch which <br /> parallels the stream. <br /> 4. Comment: Every effort must be made to ensure that the single monitoring well GS-1 is <br /> truly located downgradient of the Sutey Pile. Although three monitoring wells are <br /> typically used to define the direction of ground-water,flow and characterized water <br /> quality in the vicinity of an area of concern, a single well that is positioned correctly may <br /> be adequate for reconnaissance purposes. However, considering the large size of the <br /> Sutey Pile and the reasons for sampling ground water beneath it (possible releases from <br /> buried wastes in a limited area), the Division recommends that several ground-water <br /> samples be collected from directly downgradient of the pile using driven wells. Unlike <br /> the single well approach proposed, the increased coverage and,analytical data generated <br /> using multiple drive wells may be sufficient to conclusively demonstrate that the pile has <br /> no impact on ground-water quality. <br /> Response: The Sutey Pile is located within the lower reach of a natural drainage basin. <br /> Surface runoff in this drainage basin above the Sutey Pile has been diverted to the west <br /> around the pile and into an adjacent drainage to the west. Based on the surface <br /> topography prior to placement of the Sutey Pile and also on field evidence, monitoring <br /> well GS-1 is located in the valley bottom which extends to the north beneath the pile. <br /> As such, the well is suitably located to assess water quality immediately downgradient <br />