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INTRODUCTION <br />' Lafarge West, Inc. (Lafarge) is currently in the process of permitting a new sand and gravel <br />mine located southeast of the City of Longmont. The Duckworth Pit will be located in the <br />North 'h of Section 16, Township 2 North, Range 68 West in Weld County The site lies <br />' between Boulder Creek and Idaho Creek Idaho Creek serves as a tamer ditch for several <br />irrigation ditches in the area including the Smith & Emmons Ditch which currently rims <br />through the site. The ditch will be relocated as part of the mining operation. Figure-1 <br />shows a general vicinity map of the site and the surrounding area. <br />The Duckworth Pit will be operated as a commercial sand and gravel mine and will be <br />' operated in conjunction with Lafarge's Cottonwood Pit located to the southwest of the <br />Duckworth Pit. The operation will expose sand and gravel deposits located within the South <br />Platte River alluvium for extraction. In the general vicinity of the Duckworth Pit, <br />' groundwater hydraulically connected to the South Platte River is encountered at depths <br />ranging from two feet to ten feet from the surface. <br />' To enable dry-mining at the site, the site will be dewatered by constructing trenches on the <br />up-gradient side of the pit. Water collected in the dewatering trenches will be discharged <br />into either the Smith & Emmons Ditch or Idaho Creek where it will be conveyed to the St. <br />' Vrain River or discharged into an existing lake located immediately to the north of the site. <br />Mining at the site is expected to last approximately two years after which reclamanon of the <br />site will leave two unlined lakes. <br />Within one-half mile of the Duckworth Pit there are two small capacity domestic wells and <br />one high capacity imgation well. The high capacity imgation well is located to the northeast <br />of the site. The two domestic wells are located to the nonh and south of the site, <br />respectively The approximate location of these three wells is shown in Figure-1. Also in <br />the vicinity of the Duckworth Pit are several unlined lakes that are the result of previous <br />gravel mining in the area. These lakes are a part of several small residential developments in <br />the area. Due to the proposed dewatering operation at the Duckworth Pit, these wells and <br />lakes may be adversely affected through disruption or changes to the groundwater flow and <br />water IeveLs in the area. <br />The purpose of this groundwater study is to evaluate the potential groundwater impacts due <br />to the proposed dewatering operation associated with reining at the Duckworth Pit. The <br />three-dimensional numerical groundwater model, MODFLOW, developed by the United <br />States Geological Survey (LJSGS), was used to simulate groundwater flow in the area and the <br />effects of the mining operation at the Duckworth Pit on the surrounding groundwater flow. <br />Lafarge West, Inc. -1- Applegate Group, Inc. <br />Duckworth Pi[ Groundwater Study March, 2004 <br />