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Dustin Czapla Page 2 of 7 <br />Loesch Pit, M-1981-068, Garfield County, CO. Oct. 4, 2010 <br />Technical Revision - Pit wall liner <br />flows from irrigation upgradient from the site adds to the possibility of groundwater seepage <br />into the pit. Groundwater seepage from the adjacent Colorado River is generally negligible, <br />from an operational perspective, simply due to topography and the general strike of the <br />bedrock to the northwest beneath the gravel deposits. The surface topography of the <br />Colorado River valley between Silt and Mamm Creek north of 1-70 and south of the river <br />drains generally northwest towards the river at approximately a 0.5% gradient. Bedrock in this <br />area is fairly shallow, typically from 10 to 30 feet beneath the ground surface, and follows the <br />same general slope or dip as the surface topography. <br />GROUNDWATER MANAGEMENT <br />A drainage ditch (Figure 2) exists along the east and north sides of the site. It is my <br />understanding that this drainage ditch was excavated by the Federal Government, likely the <br />Soil Conservation Service in the 1940's. It is typically 8' to 10' deep and flows water year <br />around. Excavation of this type of drainage ditch was common in the 1940's - 1970's to <br />control ground water caused by irrigation practices. The USGS topographic map for Silt, CO <br />indicates that the drainage ditch was constructed post 1962 and pre-1982 2. Regardless, <br />aerial photographs from the USGS from 1990 to 1993 show that the ditch was in place prior to <br />mining at the site. <br />The importance of the ditch is how it controls groundwater levels, both currently during <br />operations, and in the future after reclamation. The surface of the water in the ditch can <br />become a boundary condition, i.e., an elevation to which groundwater downgradient of the <br />ditch cannot be exceeded. In the post-reclamation era of the pit, the depth of the ditch at 8' to <br />10' below the ground surface effectively controls groundwater levels in the pit at water levels at <br />least 8' to 10' beneath the top of the pit walls on the east and north sides of the pit. Ina similar <br />fashion, the ditch prevents water from the pit backing up onto property east of the pit. <br />2 USGS, Topographic Map for Silt, CO quadrangle, 1962, revisions 1982, Map # 39107-E6-TF-024 <br />WATZR RFSOURCE CONSULTANTS, LLC