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Dewatering Evaluation Report Varra Grovel Operation Greeley, Colorado Page 2 Background Information The Varra gravel quarry occupies a portion of the northeast corner of Section Nine and the central portion of the north-half of Section 10, Township 5 North, Range 67 west of the 6~' Principal Meridian. The surrounding land use consists of agricultural, rural residential, commercial and open-cut gravel quarry operations. The permitted mine area occupies an estimated 230 acres with 73 acres of the operation dewatered and excavated to bedrock. Hydrogeologic data for this analysis were obtained from local well owners, the State Engineer's data bases, current mining operation data and water resource evaluation reports documenting the local and regional hydrogeology. The water table at the site is located in unconsolidated alluvial deposits associated with the Cache la Poudre River. Soil conditions generally consist of varying thicknesses of top soil underlain by sand and gravel deposits, which in turn are underlain by Pierre Shale. Over the entire area the average saturated thickness of the sand and gravel deposits (prior to mining) is estimated at 26 feet. The natural hydraulic gradient as documented by past water resource investigation reports is on the order of 0.002 feet per foot, with the depth to water varying between 6 and 15 feet below ground surface. Continuous water well yields in the area can exceed 1,500 gallons per minute (Hillier and Schneider, 1979). The natural groundwater flow direction is to the east -northeast. Seasonal water table fluctuations of between one and three feet are common for this area; however, fluctuations of greater than ten feet have been documented during drought conditions (Schneider, 1983). The primary source of recharge to the unconsolidated aquifer is precipitation and irrigation returns (Schneider, 1983). The mine is dewatered by allowing groundwater to flow from the side walls of the excavation into ditches excavated into the shale bedrock at the toe of the excavation walls. The ditches are sloped so water drains to the north toward the Cache la Poudre River. The water is then pumped from the excavation into the river. A settling pond is located west of the dewatering operation. The regional site location is depicted on Figure 1. Site conditions are depicted on Figure 2.