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1.0 Introduction <br />A groundwater flow model was developed for the Parsons Mine (site) and adjacent off- <br />site areas near Windsor, Colorado (Figure 1). The model was designed to evaluate the <br />generalized groundwater flow regime in the unconfined alluvium and weathered bedrock <br />aquifer and to assess potential effects of proposed dewatering and post-mining <br />reclamation of the Parsons Mine on nearby shallow groundwater wells. The model was <br />used to evaluate potential groundwater impacts by estimating the extent and magnitude of <br />drawdown resulting from dewatering various parts of the site. <br />The model was designed and simulations were conducted using the Visual MODFLOW <br />program, version 4.1.0.145, developed by Waterloo Hydrologic Software, Inc. Visual <br />MODFLOW is a graphical interface with pre- and post-processors for the MODFLOW <br />groundwater flow model (McDonald & Harbaugh, 1988), which can be used to simulate <br />groundwater flow in two or three dimensions. <br />For this application, sufficient data do not exist to support development of a detailed and <br />fully calibrated groundwater flow model. Therefore, average and representative <br />groundwater conditions, hydrogeologic parameters, climatic conditions, and stratigraphy <br />were estimated to perform simulations that are expected to represent the relative effect of <br />the mine dewatering operation. Several sensitivity analyses were performed to evaluate <br />the relative effect of certain parameter estimation variances. <br />EnviroGroup Limited