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DESIGN REPORT • RI7NOFF POA'DS AND FRESHWATER POND ARCO COAL COMPANY MT. GUNNISON N0. 1 MINE SUMERSET, COLORADO GENERAL This project involves the design and construction of four (4) small dams for the ARCO Coal Company's Mi. Gunnison No. 1 Mine. These dams consist of three (3) storm drainage/sediment control facilities (MB1, MB2 and MB3) and one (1) fresh water storage facility (FW1) as shown on the Drawings accompanying this report. The criteria used in sizing and designing these structures included those of the Colorado Division of Water Resources, the Office of Surface Mining, the Colorado Mined Land Reclamation Board and the Mine Safety and Health Administration. LOCATIO N • The project site is located in Gunnison County, Range 90 W, Township 13 S, ~; Sections 9 and 16, approximately one (1) mile east of Sumerset, Colorado. The drainage basins contributing flow to the ponds are tributary to the North Fork of the Gunnison River and are located in Water Division 4 and Water District 40. The sites are on the north facing slope between the Sylvester Gulch drainage basin and an unnamed basin to the west. No identifiable streams pass through the proposed sites. MB#1 and FLY#1 are located on a natural bench above the valley floor (at an ap- proximate elevation of 6,290 feet). MBn2 and MBn3 are located on the floor of the valley at approximate elevation 6,080 feet. The natural vegetation consists mainly of scrub and range grasses. SOILS INVESTIGATIONS Preliminary soils information was obtained from the Gunnison Soils Conservation Service office. The soils are delineated on the 1 inch = 500 feet contour map provided b}' ARCO and reproduced on Page 10 of the drawing set. A summary of this information is included in Table 1 of this report. The Soils Conservation Service information indicates !• that the soils vary from surface layers of loams to subsurface deposits of clays or cobble. ~/'