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Groundwater Moniiodng and Mitigation Plan for <br />Heit Aggregate Resource Operation-Weld County <br />Aquatic and Wetland Nursery and Coyle Properties <br />(Figure 2). Nursery plants are reportedly irrigated by sub-irrigation from shallow groundwater <br />and by several wells owned by AWC. Concern was expressed by AWC regarding possible <br />impacts on their operation from lowered groundwater levels due to the pit. The Coyles own land <br />southwest of the proposed pit (Figure 2) and reportedly rely on natural sub-irrigation of a pasture <br />by shallow groundwater. They expressed concern with their pasture drying up due to lowered <br />groundwater levels caused by the Heit Pit. <br />Potential impacts on groundwater were assessed in the Mazch 2003 WWE report using the U.S <br />Geologic Survey's (USGS) MODFLOW-2000 computer model. Model boundary conditions and <br />parameters were obtained from USGS reports with data from the late ] 900s. It was assumed that <br />a slurry wall would be constructed that meets state standazds for an impermeable wall. The <br />modeling predicted a slight rise of the groundwater table on the upgradieni side of the proposed <br />pit and a slight lowering on the downgradient side. Approximately 2 feet of drawdown was <br />predicted immediately north of the wall, with 0.5 feet of drawdown approximately 1200 feet to <br />the north, and southeast of the pit. <br />Concern was expressed during the meeting on July 1, 2003 by AWC and Ms. Coyle that more <br />current information was not available for use for the modeling in the March 2003 study. <br />Accordingly, obtaining groundwater measurements for updating the modeling and to assess <br />potential impacts was proposed by the applicant. <br />3.0 PROPOSED MONITORING PLAN <br />Monitoring would be conducted for three purposes: 1) establish pre-mining groundwater levels, <br />2) monitor groundwater levels during operation of the proposed pit to assess whether it was <br />affecting groundwater levels, and 3) provide current groundwater level data that could be used to <br />update the modeling, if necessary. <br />It is recommended that groundwater be measured in several existing wells owned by AWC and <br />the Coyles and in a series of piezometers constructed at key locations. Figure 3 shows the <br />' 021-110.030 Wright Water Engineers, Inc. Page 2 <br />July 2003 <br />