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Evaluation of Potential Impacts <br />From The Proposed Nix Property Sand and Gravel Operation <br />On Shallow Groundwater Levels, Water Wells and Wetlands <br />4.3.2 Evaluation of Potential Impacts from the Proposed Gravel Mine <br />The effects of mining on groundwater levels were evaluated in Sections 4.1 and 4.2. It was <br />assumed that the water surface of an excavated lake on the Nix property would equal the <br />midpoint of the pre-existing groundwater surface across the lake. That is, the lake level would be <br />slightly higher than the existing groundwater surface on the downgradient end of a lake, and <br />slightly lower on the upgradient end. A schematic of this "lake leveling" effect is shown on <br />Figure 3. <br />Sheet 4 shows the groundwater contours in the area (based on the September 14, 2001 <br />measurements), the approximate post-mining pond levels and the estimated maximum changes in <br />groundwater levels along the south boundary of the Nix property. These changes are expected to <br />occur due to the lake-leveling effect previously described. These changes range from ±0.5 to <br />±2.0 feet at the edge of the reclamation ponds immediately north of Weld County Road 28. <br />It is believed that the actual changes in groundwater levels beneath the wetland will be less than <br />shown on Sheet 4 because: (1) the amount of the change will decrease with distance from the <br />ponds (Figure 4), (2) the wetland is upgradient of the ponds, (3) seepage from the pond to the <br />south on the Sage Hill Farm and the pond to the east on the Mayer property will sustain <br />groundwater levels, and (4) diversions and return flows in the laterals to the wetland will <br />maintain groundwater levels. <br />A check on the potential effects from the proposed mine is that there aze two irrigation wells <br />located relatively close to the wetland (Well No.'s 38 and 39 on Sheet 1). These wells aze <br />relatively high capacity, and pumping from them has not affected the wetland. <br />The data collected shows that the wetland currently experiences relatively lazge fluctuations in <br />groundwater levels and hydrologic conditions, and the vegetation in the wetland is relatively <br />tolerant to changes in moisture conditions. Slight changes in groundwater levels, therefore, <br />should not have a significant effect on the wetland. <br />011-074.000 Wright Water Engineers, Inc. Page 13 <br />April 2002 <br />