DWR_2882592

• Title: GROUND WATER LEVELS IN THE DENVER BASIN BEDROCK AQUIFERS
• Year: 2006
• Document Type - Publications and Reports: Ground Water Levels Report

. hydrogeologic units known as the Upper and Lower Dawson aquifers. This separation is based
on the presence of an approximately 50-foot thick shale layer that hydraulically isalates the
Upper and Lower Dawson aquifer units. The Dawson aquifer is separated from the underlying
Denver aquifer by a clay shale sequence ranging from 25 to 50 feet thick.
DENVER AQUIFER
The Denver aquifer consists of a series of interb�edded clay shale, clay, claystone,
siltstone and sandstone lenses. Carbonaceous material and coal beds are common within the
hydrogeologic unit. The aquifer underlies an area of approximately 3,540 miles and varies in
thickness from a feather edge up to 1,000 feet. Distinctive characteristics of the aquifer are the
fine-grained nature of the material composing the aquifer and sandstone lenses of limited areal
extent.
Although the aquifer is utilized extensively for domestic water supplies, relati�ely low
well yields (generally 20 to 5� gallons per minute (gpm}) limit its use primarily to indi�idual
residential wells; however, a number of municipal wells have been developed with yields up to
10� gpm. The higher yield wells are not indicative of the aquifer's potential in most areas.
The Denver aquifer is separated from the underlying Arapahve aquifer by an extensive
clay shale uni# approximately 50 feet thick. The clay shale interval serves as a hydraulic barrier
between the aquifers.
ARAPAHUE AQUIFER
The Arapahoe aquifer is composed of interbedded conglomerates, sandstones, siltstones,
and clay shales. The aquifer underlies an area of almost 4,700 square miles and is generally
about 400 feet thick. The northern portion of the hyd�rogeologic unit can be subdivided into an
upper and lower aquifer that is separated by a shale sequence ranging from 50 to 100 feet thick.
High capacity wells (304+ gpm} are common in the Arapahoe and the aquifer is used
extensively to supply municipal water systems. Water quality is generally good in the aquifer as
e�idenced by its use by Deep Rock Water to obtain water for bottling.
LARAMTE F4RMATIUN
The major part of the Laramie Formation forms the aquitard or hydraulic bamier that
separates the Arapahoe aquifer from the underlying Laramie-Fox Hi11s aquifer. The formati�n
consists of approximately 40� feet of clay shales with rninor interbeds of sandstone and siltstone.
Coal beds are common within the formation and ha�e been mined commercially along the
eastern margin of the basin. Minor amounts of water are present within the sandstones, but are
rarely developed for water supplies. Water in the sandstone units is of generally poor quaiity due
to the presence of sulfides and biogenic gas.
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