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! • S <br /> URS Operating Services,Inc. ARR for ESI(elimax <br /> START,EPA Reeion VIII Revi$ion: 0 <br /> Contract No.68-W5-0031 Date: 04/1998 <br /> Page 4 of 37 <br /> Samples collected for the SSI were not analyzed for molybdenum and aqueous samples were not <br /> analyzed for dissolved metals. A review of the SSI sampling data revealed that an additional source <br /> of contamination potentially existed in the 2.1-miles to 3.1-miles increment downstream of the CM <br /> NPDES outfall. The above results, combining with the need for sampling for molybdenum and <br /> dissolved metals, indicated the need for further sampling to determine if similar releases are present <br /> during low flow. Additionally, it was determined that additional sampling data were needed to <br /> pinpoint the downstream extent of inorganic contamination in Tenmile Creek and to delineate other <br /> potential sources of inorganic contributions along Tenmile Creek. <br /> The upgradient sediment sample from the 1994 SSI collected from Kokomo Creek was analyzed to <br /> contain DDT as a Tentatively Identified Compound(TIC)at 690 parts per billion(ppb)(URS 1994). <br /> The identification of this highly persistent pesticide has aroused concern as to its potential source. <br /> UOS contacted the U.S. Forest Service regarding pesticide use in the San Isabel National Forest. <br /> The last application of DDT in Colorado by the U.S. Forest Service was in the 1930s near <br /> Monument,Colorado;Granby,Colorado;and on the Rio Grande River in southern Colorado. The <br /> U.S.Forest Service has used a biological agent called `BT"since the 1930s against pests formerly <br /> treated with DDT(U.S.Forest Service 1995). The origin of this detection of DDT is unknown and <br /> there are no discernable sources of DDT in the Kokomo Creek drainage. <br /> 3.3 SITE CHARACTERISTICS <br /> 3.3.1 Geology and Hvdrogeology <br /> Consolidated bedrock units at the CM site consist of Precambrian basement rock(primarily <br /> east of the Mosquito Fault)and Paleozoic sedimentary beds(primarily west of the Mosquito <br /> Fault)(USGS 1974). The Precambrian unit is comprised of gneiss and migmatite,which <br /> is intruded by stocks, dikes, and sills of the Silver Plume Granite. Sedimentary strata <br /> (limestone,shale,and sandstone)belonging to the Minturn and Maroon formations comprise <br /> the Paleozoic units. Many of the sedimentary rocks have undergone metamorphic alteration. <br /> Both the Precambrian and Paleozoic units have been intruded by Tertiary Age stocks,dikes, <br /> and sills of quartz monzonite composition(CMC 1980). <br /> 75-51119.00 <br /> F:\START\CLIMAX\Final.ARR\CLIMAX.TXT.wpd:bas <br />