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HARLAN & ASSOCIATES, INC. <br /> Mr. Kevin Riordan <br /> District Ranger <br /> U.S. Forest Service <br /> October 23, 1996 <br /> Page 2 <br /> The Federal Maximum Contaminant Level (MCL) for public drinking water supplies is <br /> 0.5 µg/l. The state of Colorado's basic ground-water standard for PCBs is 0.005 µg/l. <br /> Sample Locations <br /> As part of the Coal Basin Mine environmental site assessment, samples were collected <br /> for laboratory analysis from the maintenance yard area, from the tunnel discharge at the portal, <br /> and downgradient from each of the existing waste piles. The waste piles include: (1) the rock <br /> tunnel waste pile, which was sampled downgradient from the construction landfill (RT-1) and <br /> at Outfall 016; (2) the old refuse pile, which was sampled at Seep #4 and at Outfall 001 A; and <br /> (3) the Sutey Pile, which was sampled at the outfall from the Sutey Pile Underdrain (SV-1) and <br /> at monitoring well GS-1. <br /> The sampling locations for the maintenance yard area are shown on Figure 1 and those <br /> for each of the three waste piles and the portal of the haulage tunnels are shown on Figure 2. <br /> Additional Monitoring Wells <br /> In its letter of June 3, 1996, the Division of Minerals and Geology suggested that <br /> additional ground-water monitoring wells be installed near the "Morrison Knudsen Shop". The <br /> Morrison Knudsen Shop is also referred to as the Maintenance Shop and Truck Shop, and is now <br /> labeled on Figure 1. <br /> The issue of ground-water quality beneath the Morrison Knudsen shop was addressed <br /> during the site environmental site assessment by ;ampling a series of natural seeps (Seeps #1, <br /> #2, and #3) at the base of the escarpment along the northern edge of the alluvial fan on which <br /> the shop and maintenance yard are located. The samples from these locations were analyzed for <br /> volatile organics, RCRA metals, PCBs, and general inorganics. Since the water quality in these <br /> seeps is believed to be representative of that beneath the maintenance yard and shop area and <br /> since no evidence was found to suggest adverse water quality impacts from the maintenance yard <br /> area, the installation of additional monitoring wells was not judged to be necessary as part of <br /> this Environmental Site Assessment. <br />