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002240 Durango Pumoing Plant - Stage I reaches a maximum observed thickness of about 15 feet in test pit TPDPP- 105. c. Alluvium (Qal). - Samples of alluvium obtained during drilling consisted primarily of sandy lean clay. The minus 3-inch portion of the material averages approximately 65 percent fmes with medium plasticity and 35 percent fine sand. The alluvium sometimes contains a trace of cobbles. The alluvium was observed in drill hole DH-l 06 to be 23 feet thick, however, most of this material has since been removed from the site by UMTRA-site cleanup activities. The remaining alluvium at the site occurs along the western edge of the site and reaches a maximum observed thickness of about 15 feet in test pit TPDPP- I 02, d. Glacial Outwash Terrace (Qt). - Terrace deposits underlie the alluvium in the western portion ofthe site. The terrace was deposited by glacial outwash approximately 3 miles downstream of the terminal moraine during late Pleistocene glaciation, The deposit was differentiated from the alluvium during drilling by an increase in the percentage of gravel, cobbles, and boulders. The minus 3-inch portion consists of approximately 60 percent gravel, 25 percent sand, and 15 percent fines with medium plasticity. The oversize (plus 3-inch) portion ofthe terrace deposits ranges from 15 to 25 percent of the total sample. Gravel, cobbles, and boulders in the deposit are predominantly subrounded. The maximum sized boulder encountered in drilling was about 1,5 feet although some boulders up to 6 feet in nominal size were observed in test pits and during UMTRA site cleanup. The terrace deposits exceed a maximum observed thickness of 15 feet in test pit TPDPP- I 07 10cated along the western edge of the site. The bottom of the terrace was not encountered in this test pit. Most ofthe terrace deposits, particularly in the eastern portion of the site, were removed during UMTRA cleanup. e. Quaternary/Recent River Alluvium (Qsf). - The river alluvium exists as stream fill within the Animas River charmel and as isolated deposits along the river banks (see Drawing No. 69-529-5). The river alluvium was encountered in drill hole DH-I13 where it was intennixed with man-made fill, It occurs as scattered gravel, cobble, and boulders on top of bedrock in the river charmel near the plant intake and as an isolated band of predominantly cobbles and boulders on top of and adjacent to bedrock on the south bank of the Animas River. The material on the river bank generally contains less than 10 percent fines and fine sand which was locally derived by erosion of thin bedded siltstone from the adjacent Point Lookout Sandstone. The river alluvium ranges from 0 to about 5 feet in thickness. f. Quaternary undifferentiated (Qu). - A substantial portion of subsurface exploration was conducted before the DOE removed material from the raffinate pond area. The surficial deposits were hence disturbed during site remediation and clear contacts are now rarely found. Quaternary undifferentiated (Qu), shown on Drawing No. 69-529-15, represents any Geology 00320 - 8