Laserfiche WebLink
hydrogeologic units known as the Upper and Lower Dawson aquifers. This separation is based <br />on the presence of an approximately 50 -foot thick shale layer that hydraulically isolates the <br />Upper and Lower Dawson aquifer units. The Dawson aquifer is separated from the underlying <br />Denver aquifer by a clay shale sequence ranging from 25 to 50 feet thick. <br />DENVER AQUIFER <br />The Denver aquifer consists of a series of interbedded clay shale, clay, claystone, <br />siltstone and sandstone lenses. Carbonaceous material and coal beds are common within the <br />hydrogeologic unit. The aquifer underlies an area of approximately 3,500 miles and varies in <br />thickness from a feather edge up to 1,000 feet. Distinctive characteristics of the aquifer are the <br />fine-grained nature of the material composing the aquifer and sandstone lenses of limited areal <br />extent. <br />Although the aquifer is utilized extensively for domestic water supplies, relatively low <br />well yields (generally 20 to 50 gallons per minute (gpm)) limit its use primarily to individual <br />residential wells; however, a number of municipal wells have been developed with yields up to <br />100 gpm. The higher yield wells are not indicative of the aquifer's potential in most areas. <br />The Denver aquifer is separated from the underlying Arapahoe aquifer by an extensive <br />clay shale unit approximately 50 feet thick. The clay shale interval serves as a hydraulic barrier <br />between the aquifers. <br />ARAPAHOE AQUIFER <br />The Arapahoe aquifer is composed of interbedded conglomerates, sandstones, siltstones, <br />and clay shales. The aquifer underlies an area of almost 4,700 square miles and is generally <br />about 400 feet thick. The northern portion of the hydrogeologic unit can be subdivided into an <br />upper and lower aquifer that is separated by a shale sequence ranging from 50 to 100 feet thick. <br />High capacity wells (300+ gpm) are common in the Arapahoe and the aquifer is used <br />extensively to supply municipal water systems. Water quality is generally good in the aquifer as <br />evidenced by its use by Deep Rock Water to obtain water for bottling. <br />LARAMIE FORMATION <br />The major part of the Laramie Formation forms the aquitard or hydraulic barrier that <br />separates the Arapahoe aquifer from the underlying Laramie -Fox Hills aquifer. The formation <br />consists of approximately 400 feet of clay shales with minor interbeds of sandstone and siltstone. <br />Coal beds are common within the formation and have been mined commercially along the <br />eastern margin of the basin. Minor amounts of water are present within the sandstones, but are <br />rarely developed for water supplies. Water in the sandstone units is of generally poor quality due <br />to the presence of sulfides and biogenic gas. <br />2 <br />