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Mining Plan Exhibit D <br />Site Description <br />The site lies on the north bank of the Colorado River east of the town of Rifle. The site is <br />adjacent to operating and previously operated gravel pits. Gravel mining began to the west of <br />the site in the 1960's. Three large operating gravel mines surround the site. The MMM <br />Chambers Pit is located directly to the west of this site. The Chambers operation produced the <br />existing pit lake located on Yvonne Chambers Property. An expansion to the Chambers Pit <br />was recently approved by the DMG and is being reviewed by the County and City of Rifle, <br />which includes areas along the south side of the river. LaFazge's Mamm Creek Pit lies directly <br />to the south of this pit and the Grant Brothers pit lies to the east. The permit area consists of <br />35.51 acres between the railroad and the river. All of the mined areas lie outside the 100-year <br />floodplain of the river, and most azeas have been used for either irrigated fields or stockyazds. <br />Site Geology <br />The site contains Pleistocene age gravels with a bedrock of Wasatch Formation shale and <br />sandstone. The gravel depth is expected to be 15-25 feet. The gravel has very little fines and <br />is very permeable. In the irrigated fields, up to 5 feet of overburden is expected with the <br />overburden sharply rising to 15 feet in the northern stockyazds. The topsoil is expected to be 3 <br />inches to over 1 foot in thickness. Average topsoil and overburden depths can be seen in the <br />Mining Area Volumes table. The water table level is expected to be around 5330'-5334' in <br />elevation. <br />Pre-Mining Work <br />Pre-mining activities will consist of sediment pond construction, topsoil and overburden <br />stripping, and isolation berm construction. The berm will be a minimum 3 feet tall with 3H:1 V <br />slopes and will be constructed with topsoil of Phase 1. Future mining azeas will be prepazed in <br />a similaz fashion. <br />Construction will begin on the water augmentation pond during the pre-mining phase with a <br />majority of the construction taking place during the initial mining phases. Because the gravity <br />drainage will not be useable until the completion of mining, the augmentation pond will be <br />pumped to meet the augmentation needs. <br />Stormwater and Sediment Control <br />Berms and existing irrigation return ditches will isolate the site from the surrounding area. <br />Therefore, all run-off will drain to the pits or lakes. The pit or lake will contain the 100-Year <br />24-Hour Event. The stormwater volume was determined using the calculations below as <br />described in the "Procedures for Determining Peak Flows in Colorado", which includes and <br />supplements Technical Release No. 55 "Urban Hydrology for Small Watersheds." The <br />following calculations are for Mining Area 1. Similar calculations show that all mining areas <br />11/7/2005 Page D-1 <br />