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1I7lYU 1p.283p FROM Todd Gamey TO Mncp Alpetl • GII.IYIER GEOPHYSICS, INC. 27203 Amudillo Way, Evergreen, Colorado 130139 02 January 1998 Mitch Albert, Ph.D. President Agile Stone Systems, Inc. 6435 S. Pontiac Court Englewood, CO 80111 Re: Hydrogeology Summary Report Parkdale Project Dear Dr. Albert: III IIIIIIIIIIIIIIII 999 phone 303.67i.83ii far 303.671.8731 This letter report summarizes the hydrogeology of the Pazkdale Project area, Fremont County, Colorado, and is submitted in support of the mine permit application currently before the Colorado Mined Land Reclamation Board. The report is divided into three major sections, which discuss the glacial outwash aquifer, the bedrock aquifers, and conclusions. The hydrogeology of the Par}:dale Project area is best understood and discussed by fvst defining two principal hydrostratigraphiconits, those being the glacial outwash aquifer of Quaternary age and the • bedrock aquifers of Mesozoic age. These aquifers are cut through and hydraulically bounded by the Arkansas River; faulting adds structural boundaries within the bedrock aquifer system. Potentlo- metric heads and water table elevations w7lhin the aquifers are driven by recharge in topographically higher outcrop areas, with discharge at lower elevations through subcrops and to springs. Further information and detailed hydraulic and water balance analyses concerning the glacial outwash aquifer are contained in the Substitute VI'ater Supply Plan submitted to the Division of Water Resouroes in December, 1997. C/utwash Aquifer The glacial outwash aquifer beneath the Project area is a sand and gravel deposit of Quaternary age, as mapped by the USGS and shown in Figure 1-1. This aquifer is bounded ott the north and east by Tallahassee Creek, on the west by Precambrian and Mesozoic rocks, and on the south by the Arkansas River. The total thickness (water saturated plus unsaturated) of the deposit ranges to at least 67 feet, depending on location. Bedrock units of Jurassic and Cretaceous age subcrop beneath the outwash aquifer in the Project area. In stratigraphically ascrnding order these units include the Monson Formation, [he Dakota Group (Purgaloire Formation and Dakota Sandstone), the Colorado Group (Graneros Shale, the Greenhorn Limestone, and fire Carlisle Formation), and the Niobrara Formation. Structurally, the bedrock units were deformed during the Laramide Orogrny into a syncline whose axis trrnds grnerally AI1V-SE and • Hydrogeologv Repor(--Parkdale Project Page 1 of4