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<br />( <br /> <br />0022~9 <br /> <br />Durango Pumoing Plant. Stage I <br /> <br />~ <br /> <br />B. Surficial materials within this area include man-made fill from UMTRA-site cleanup <br />activities, Quaternary alluvium, Quaternary glacial outwash terrace deposits, and <br />Quaternary/recent river alluvium. Most of the surficial deposits have been excavated <br />from the area with the exception of the western edge of the area where they are present in <br />thicknesses of up to 20 feet. Bedrock to be excavated consists of the Cretaceous Point <br />Lookout Sandstone. The surficial and bedrock units are shown on geologic sections F-F <br />through G-G. <br /> <br />I. Surficial deposits: <br /> <br />a. Man-made fill includes approximately 0.5 to one foot of clayey topsoil <br />which blankets the site and localized fill consisting of clayey gravel which <br />currently reaches a maximum thickness of about 10 feet. Portions of the <br />gravelly fill were used as an equipment staging area by the UMTRA-site <br />contractor. Fill encountered in drill hole DH-I13 was placed prior to <br />UMTRA-site cleanup for access to the contractor's pump at the river. The <br />upper 3 feet of fill encountered was placed for drill pad construction. <br /> <br />b. Quaternary glacial alluvium was encountered in drill holes DH-107 and- <br />108 and has since been excavated from tl1ese areas during UMTRA <br />cleanup. It was encountered in test pit TPDPP-l 02 between elevations <br />6501 and 6486 feet. The alluvium consists of sandy lean clay having <br />about 65 percent fines with low to medium plasticity and about 35 percent <br />predominantly fine sand. The alluvium occurs west of geologic section A- <br />A'and is shown on geologic sections C-C' and D-D' <br /> <br />c. Quaternary outwash terrace deposits were encountered in drill holes DH- <br />112 and -113, -119, -120, and -122 ranging in depth from 0.2 to a <br />maximum observed depth of 15.7 feet below ground surface at DH -122. <br />These deposits consist of clayey gravel with cobbles and boulders and <br />exceed a total depth of 16.0 feet in test pit TPDPP-102. Most of the <br />outwash material north and east of drill hole DH-122 has been removed by <br />UMTRA cleanup. <br /> <br />2. Bedrock: <br /> <br />a. Bedrock to be excavated for the pumping plant and inlet channel consists <br />of interbedded siltstone and sandstone of the Point Lookout Sandstone and <br />was encountered in drill holes DH-107, -108, -Ill through -113, and -119 <br />through -122. The bedrock surface within the planned excavation area <br />rises from elevation 6438 where it is exposed in the Animas River <br />channel, to elevation 6465.3 in drill hole DH-llllocated approximately <br />300 feet south ofthe river along section A-A. The top of rock reaches a <br />maximum elevation of approximately 6475 near the western limit of the <br />switchyard area. The rock surface is irregular and slopes gently toward <br />the east to a minimum elevation of approximately 6460 on the eastern <br />edge. It is shown diagranunatically on the geologic sections and is <br />contoured on the Bedrock Contour Map (see Drawing. No. 69-529-9). <br /> <br />b. Lithologies encountered during drilling consist of siltstone with <br />interbedded sandstone and minor shale. Drill holes DH -107, -Ill through <br /> <br />Geology <br />00320 - 17 <br />