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Executive Summary <br />This report presents the results of an evaluation of groundwater conditions at and adjacent to the <br />Stegner Farm gravel mine east of LaPorte, Colorado operated by Aggregate Industries-WCR, Inc <br />(Aggregate Industries). This evaluation addresses the complaints of azea residents, Mr. Darwin <br />Roe and Dr. Bill Martin, that groundwater levels beneath their property have been significantly <br />' lowered since a slurry wall was installed around the Stegner property, and further addresses the <br />requirements of a State Division of Minerals and Geology (DMG) inspection that the evaluation <br />be used specifically: <br />• "To delineate the areal extent of the depression resulting from the presence of the slurry <br />wall, and thus help to establish an approximate boundary of the down gradient <br />depression; and <br />• To define the groundwater surface in the azea north and west of the slurry wall, indicating <br />the extent of the mounding effect imposed by the slurry wall." <br />The results of the evaluation presented in this report indicate that: <br />• Groundwater level increases ("mounding") have occurred along the north and west sides <br />of the slurry wall since it was installed. The highest groundwater levels typically occur at <br />well S-2 which is situated at the approximate center of the northern portion of the slurry <br />wall. The highest groundwater levels that occurred at the upgradient wells (S-1, S-2, S-3, <br />S-4, S-7, and S-8) during 2001 (Table 1) indicate that none of the wells have sustained a <br />groundwater level of two (2) feet or less below the natural ground surface for a period of <br />three weeks, which would require installation of a french drain as set forth in the mining <br />permit. <br />• Groundwater level decreases have occurred in the area of the Roe and Martin properties <br />resulting in a "groundwater depression" downgradient of the slurry wall. The estimated <br />groundwater level decreases are approximately 1.8 feet beneath the Roe property and <br />approximately 1.4 feet beneath the Martin property in December 2001 compared to pre- <br />slurry wall groundwater levels in December 1999. The cause of these groundwater level <br />declines is the combined effect of the local drought conditions, the slurry wall, cessation <br />of irrigation at the Stegner Farm, and local groundwater withdrawal near the Roe and <br />Martin properties. However, even considering all these effects together, the observed <br />groundwater level decrease is less than the 2-foot groundwater level decrease below <br />seasonal low water level incorporated in the Stegner Farm mining permit. <br />