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RECEIVED AUG 1 7 2001 Drainage Study Division of Minerals and Geelo9Y This drainage study is being developed for the proposed Mamm Creek Gravel Pit in response to the Division of Minerals & Geology's adequacy review comments and to satisfy the requirements for the City of Rifle's Watershed Protection Permit. Balaz & Associates, Inc., BAI, visited the site on February 3, 2001 to locate the storm water and irrigation culverts that cross under lnterstate 70 and to determine what portion of the upgradient drainage basin contributes runoff to the project site. Mr. Jim Snyder, a local rancher and surface owner of a portion of the project site, assisted BAI personnel in locating the storm water and irrigation culverts. The project site is located approximately 1.8 miles east of Rifle, CO in portions of Sections 11, 12, 13 and 14 of Township 6 South and Range 93 West and contains approximately 483 acres. The proposed gravel mining operation is bounded on the north by the Colorado River; on the south by the right of way for Interstate 70; on the east by Mamm Creek and on the west by a ranch at the end of the frontage road. (See Exhibit A -Vicinity Map) The proposed permit area contains 308.36 acres. Roaring Fork Resources, Inc. proposes to mine aggregates from four pits on 122 acres and potentially two future mining areas on 78 acres on the east end of the project area. These pits arc shown on Exhibits DS-1 and DS-2. Drainaee Basin Description The drainage basin includes the project site, the Interstate 70 corridor including the Last Chance Ditch and a bench to the south of the Interstate. The Garfield County Airport is located on this bench. Mamm Creek on the eastern edge of the project site flows water year round. Dry Creek lies toward the western edge of the project site adjacent to three large power lines that cross the site in a north-south direction. The western property line forms the western edge of the drainage basin. The slope of the ground on the project site ranges from 0.5 % to 3.0 % and is generally northerly toward the Colorado River. The airport bench slopes 1.25 % to the northwest toward Dry Creek. The soil types for the project site and the I-70 corridor are shown on Exhibit B and described below. According to the 1985 soil survey of Rifle Area Colorado done by the Soil Conservation Service, the general soils map unit identifies the proposed Mamm Creek Sand & Gravel Pit as being Arvada-Torrifluvents-Heldt. Generally this is deep, well drained to somewhat poorly drained, nearly level to gently sloping soils on benches, terraces, alluvial fans, and flood plains. Arvada soils aze on benches, terraces and fans. They are deep, well drained and alkali affected. The surface layer is loam, the subsoil is strongly alkaline silty clay loam and the substratum is silty clay loam. Tomfluvents are on flood plains and low terraces. They are deep and well drained to somewhat poorly drained. They are sandy loam or loam stratified with sand, gravel or cobbles.