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Work Plan for Alluvial Groundwater Characterization, Big Elk Mine AdrianBrown <br />8 3/4-inch monitoring wells <br />8 2-inch monitoring wells <br />4 paired 2-inch and 3/4-inch monitoring wells <br />Each of the major drainages has been targeted for baseline alluvial groundwater chazacterization. Five <br />of the proposed locations are tributary to the Williams Fork, to the south. The remainder aze tributary to <br />the Yampa River to the north. Ten of the monitoring wells will be located near existing surface water <br />monitoring stations. Project-related surface facilities such as the load-out azea vrll be equipped with <br />upgradient and downgradient monitoring wells. Minor modifications of the exact well locations may be <br />made in the field, based on access and hydrologic understanding on site. <br />The paired wells will be individual completions, located approximately 15-25 feet apart. The paced <br />wells will be installed for the purpose of 1) determining water quality comparability between the 2-inch <br />and 3/4-inch completions, and 2) having a neazby observation well for hydraulic property (storage) <br />determination from pump testing. <br />Wells will be installed using alight-weight (12,000 lb., six-wheel) Hurricane drill rig. The drilling and <br />installation of the 2-inch and 3/4-inch wells are described briefly below, and are outlined in detail in the <br />Standard Operating Procedures (attached). <br />Drilling and Completing 2-inch Wells <br />The 2-inch wells will be drilled using an 8-inch OD hollow stem auger. Samples will be collected using <br />a solid-spoon sampler, which will be driven in advance of the augers. At the discretion of the on-site <br />hydrogeologist, samples may be collected continuously, or intermittently (not to exceed ten feet without <br />collecting a sample). The holes will be drilled to the alluvium bedrock contact, which is generally <br />expected to occur at about 40 feet below ground surface. The on-site hydrogeologist will be responsible <br />for identifying the geologic contact between alluvium and bedrock. Samples will be logged according to <br />standazd geologic nomenclature (Wentworth grain size classification). The upper ten feet of samples <br />will be retained for possible AVF soils investigation. <br />The wells will be completed using 2-inch ID, flush-threaded, 10-slot, PVC screen and blank casing. <br />Wells will be screened below the water table, with the top of the screen located not more than 5 feet <br />below the top of the water table and not less than 10 feet below ground surface, where practical. The <br />bottom of the screen located at the bottom of the borehole. The wells are generally expected to contain <br />20-30 feet of screen, and samples will be representative of the entire saturated aquifer thickness. Blank <br />casing will extend from the top of the screen to the surface, and at least ]0 feet of surface seal will be <br />installed. A filter pack of 20-30 Colorado silica sand will installed through the inner tube of the augers, <br />and the augers will be pulled back to expose the screen. In this manner, the filter pack will be placed <br />azound the well screen, to a height of 2-3 feet above the top of the screen. Enviroplug (or comparable <br />brand) bentonite chips will be placed in the annulaz space, from the top of the sand to approximately <br />four feet below ground surface. The bentonite will be hydrated using potable water. <br />The surface completion will consist of a 6-inch diameter steel surface casing, with locking aluminum <br />I cap. This casing will be set 2.5-3 feet into a concrete monument, and will extend 2-2.5 feet above <br />o...:e... ~aavr owro~z a <br />