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:~ <br />(! A I--i <br />~I <br />CTL/THOMPSON, INC. <br />CONSULTING GEOTEC HIVIC AL AND MF.TERI~=.LS ENGINEERS <br />July 23, 1982 <br />Colorado Yampa Coal Company <br />P.0. Box 772129 <br />Steamboat Springs, Colorado 80477 <br />Attention: Mr. Michael J. Kondeiis <br />Subject: Construction Observation <br />Portions of Excess Spoil <br />Area 2A, Eckman Park <br />Job No. 8242 <br />Gentlemen: <br />At your request, a representative of our office was present during <br />backfilling of a portion of the keyed buttress fill at the subject spoil <br />disposal area. The purpose of our inspection was to observe that tfle <br />buttress excavation was bottomed in appropriate materials and to take field <br />density tests on the backfill materials. This letter summarizes the <br />construction and our observations. <br />Our firm prepared a geotechnical investigation (Job No. 56646) in <br />September, 1979 which provided reco«rnendations for the construction of the <br />overall spoil area. Construction of much of the disposal site was begun in <br />March of 1980. Due to the projected mining sequence, it was decided ttlat <br />the entire disposal area would not be immediately required. Initial <br />construction included foundation preparation and construction of the keyed <br />buttress trench for all but about the northeastern one-quarter of the <br />disposal area. Observations we made during initial construction are <br />summarized in a letter dated August 7, 1980 (Job No. 6210). <br />The work we recently observed included the extension of tfle buttress trench <br />below the northeastern portion of the disposal site. The trench was about <br />350 to 400 feet in length and appeared to connect to the previously <br />constructed buttress at tfle southwest. The bottom of the trench was about <br />40 feet in width and extended 5+ feet into hard bedrock. Photographs 1 and <br />2 in Appendix A show the overall excavation. Photographs 3 and 4 show the <br />bedrock exposed in side~,valls near the bottom of the trenc'n. At the oeepest <br />point, the trench was about 26 feet belo:r surrounding grades. <br />The buttress trench was backfilled using rlayay sandstone developed from <br />mining operations. The construction procedure included transporting the <br />sandstone from the borro~.v area and depositing the materials in the <br />excavation using self-loading scrapers. 'dhen about 6 inches of material <br />1971 WEST '2TH avE~~UE DENVER. COLORADO H0.0.: ,?C 3~ n_'S 077: <br />