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injury to surrounding wells, the operator of the site will take all necessary actions to remedy the <br />injuries. <br />Potential Impacts to Surrounding HydroloQic Balance from Operation <br />As discussed elsewhere in this Amendment, the western portion of the site is already being <br />mined pursuant to the existing permit. The site is mined intermittently, and temporarily <br />dewatered to facilitate such mining. Pursuant to this amendment and to the existing permit, the <br />western cell of the site will be immediately lined and used as a storage reservoir. The eastern <br />two cells will be mined and lined at a later date. <br />Mining and reclamation activities at the Hokestra Pit will impact groundwater flow in the <br />surrounding alluvial aquifer, but can be accomplished without causing adverse impacts to <br />surrounding structures or injury to vested water rights. Groundwater in the aquifer is tributary to <br />the St. Vrain River and provides a yeaz-round source of inflow to the River, which varies <br />monthly as a function of upland irrigation and runoff from precipitation. As a result of both the <br />dewatering operations and the lining of the site, the natural groundwater flow in the azea will be <br />modified. <br />The reach of the St. Vrain River that may be impacted by the operation is about a half mile long. <br />The St. Vrain River in this azea is generally characterized as a gaining river due primarily to <br />runoff and return flows from irrigation. During the mining phase of operations, prior to lining of <br />the respective portions of the site, groundwater from the acfive portion of the site will be <br />discharged directly to the St. Vrain River. Thus, the St. Vrain River will experience no net- <br />change in inflow to the river during mining. <br />During periods of active mining and dewatering to the St. Vrain River, the elevation of the <br />groundwater table in the immediate vicinity of the actively mined cell may decrease. However, <br />just as the mining and dewatering operations aze intermittent and temporary, so too will be the <br />impacts to the groundwater flow in the azea during mining. Further, this is not a significant <br />departure from previous operations at the site which have seen no adverse impacts to <br />surrounding wells or other structures in the azea. To the extent that the dewatering operations <br />may impact existing structures, the groundwater monitoring and mitigation plan discussed below <br />will be protective of those structures. <br />After the western portion of the site is lined, there is the potential for mounding of groundwater <br />up-gradient of the site, and shadowing (a reduction in groundwater levels) down-gradient of the <br />site. Groundwater flow in the area is generally from a south to north direction. Characteristic of <br />the alluvial aquifer in this azea, and based on previous USGS studies, the hydraulic gradient is <br />generally negligible in the immediate vicinity of the site; i.e., the azea is chazacterized by slow <br />movement of groundwater. Due to this fact, the likelihood of any mounding and/or shadowing <br />effects from the lining of the site is small, or, to the extent it does occur, should be minimal. <br />However, to the extent that mounding and/or shadowing does occur, mounding can be expected <br />to the south of the site, and shadowing to the east. To the extent this occurs, the groundwater <br />monitoring and mitigation plan discussed below will be protective of existing structures. <br />Weld County Hokesba Pit <br />DMG 112 PermitAmendrnent <br />Page 11 <br />