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Stephanie Fancher, File 9641.12 <br />May 2, 2014 <br />Page 3 <br />and reduce water levels at locations in the alluvium surrounding the proposed pit location. The modeling <br />of the dewatering of the pit indicated that drawdowns as high as approximately 16.98 feet may result from <br />the dewatering of the pit as presented in the attached Figure 1. The impact on the ground water level <br />elevations in the aquifer is more pronounced on the downstream side of the dewatered pit as a result of <br />ground water flow through the alluvial ground water system. The effects of the dewatering of the <br />proposed pit extend downstream approximately 3,400 feet from the pit with drawdowns up to 0.25 feet. <br />The modelled dewatering rate from the pit was approximately 255 gpm which was consistent with the <br />expected dewatering rates based on other nearby pits. <br />Gravel Pit Lining <br />The lining of the proposed Cell 21 gravel pit will cause ground water mounding or an increase in water <br />level on the upstream side of the pit and to cause lowering (shadowing) of the water level on the <br />downstream side of the pit. The modeling of the pit liner indicates that water level increases as high as <br />approximately 2.60 feet on the upstream side of the pit and water level decreases as much as <br />approximately 1.26 feet on the downstream side of the pit may occur as a result of gravel pit lining as <br />presented in the attached Figure 2. The effects of the lining of the pit may extend downstream up to <br />approximately 3,200 feet from the pit with drawdowns up to 0.25 feet. <br />Summary <br />A MODFLOW model was developed and utilized to estimate the potential impact of dewatering <br />and lining the proposed Cell 21 gravel pit at the Loveland Ready Mix Larimer Pits site. <br />Figure 1 and 2 present the modelled changes in water level associated with mining activities <br />related to the proposed Cell 21 gravel pit. <br />Dewatering of the pit may reduce water levels by as much as approximately 16.98 feet in <br />localized areas near the pit location. <br />Lining of the pit may increase water level by as much as approximately 2.60 feet on the upstream <br />side of the pit and reduce water levels by as much as approximately 1.26 feet on the downstream <br />side of the pit in localized areas near the pit. <br />Changes in water level indicated by the modelling were greatest immediately around the pit with <br />changes decreasing with distance from the pit. This trend is consistent with expectations. <br />This effort should provide the necessary information to understand how mining and reclamation <br />activities at the proposed Cell 21 gravel pit may impact localized ground water level elevations.