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shales with minor interbeds of sandstone and siltstone. Numerous coal beds are common within the <br />formation and have been mined commercially along the eastern margins of the basin. Minor amounts <br />of water are present within the sandstones, however, they are rarely developed for water supplies. Water <br />quality is generally bad with sulfides and biogenic gas being the major contaminates. <br />The basal portion of the Laramie Formation contains two thick sandstone bed (the A and B <br />sandstones) which are isolated from the rest of the formation and are utilized for water supplies along <br />with the underlying Fox Hills Sandstone. <br />T FOX HILLS AQUIFER -5� WU/ -5 <br />The lower sandstones of the Laramie Formation and the Fox Hills Sandstone comprise what is <br />known as the Laramie -Fox Hills Aquifer. This aquifer underlies approximately 6700 square miles of the <br />Denver Basin and marks the areal extent of the basin for economic ground water development. The <br />Laramie -Fox Hills is between 250 and 350 feet thick with about 150 to 200 feet being fine to medium - <br />grained sandstones. The aquifer typically yield water in quantities sufficient for commercial development, <br />and is extensively utilized in throughout the basin. Well yields generally are in the range of 300 gallons <br />per minute. Both the Laramie -Fox Hills and the Arapahoe Aquifers are generally under artesian pressure <br />at present the present time. <br />The aquifer can sometimes be extended an additional 100 feet in depth into what is commonly <br />known as the Transition Zone of the Pierre Shale. This transition zone contains several siltstone beds <br />which yields small quantities of water. <br />PIERRE SHALE <br />Below the Fox Hills Formation is the Pierre Shale which is composed of approximately 4500 feet <br />of clay shale with only minor sandstone beds. In general there is not sufficient water in any of the sand <br />beds for use in anything besides a single family residence. This formation defines the boundary of <br />commercially developable ground water in the Denver Basin. <br />