feet
Denver
Laramie
6000
Aquifer D e s c ri p t i on s
Arapahoe
In the 1980s, when the State Engineer’s Office was asked to
analogy accurately represents the stacked geologic unit/aquifer
classify the aquifers in the Denver Basin in order to regulate
concept, the basin has an asymmetrical bowl shape in cross-
their use, it divided these sedimentary layers into four aqui-
section that is approximately one-half mile thick and 70 miles
fers: the Dawson, Denver, Arapahoe and Laramie-Fox Hills. The
wide. The asymmetry is expressed by low-angle dips of the
5000 4000
Fox Hills
4 Miles
Pierre
aquifer units imperfectly mimic the distribution of the geologic
aquifers along the northern, eastern, and southern margins and
formations of the same names. The four Denver Basin bedrock
high-angle dips along the western margin. For administrative
aquifer layers are stacked like the layers of an onion. The up-
purposes, their boundaries are defined by the Denver Basin
permost aquifer covers the smallest area. Successive under-
Rules promulgated by the State Engineer in 1985. From the top
lying aquifers cover larger and larger areas. While the onion
down they are:
Rock Names
8000
East 4 Miles
West Dawson Butte
Elevation (feet)
Dawson Aquifer
Vertical Exaggeration Approximately 20x
7000
Denver Aquifer
Arapahoe Aquifer
6000 5000 4000
Laramie/Fox Hills Aquifer
Dawson
Denver
Arapahoe
Laramie-Fox Hills
This shallow uppermost aqui-
Underlying the Dawson aqui-
The Arapahoe aquifer includes
The Laramie-Fox Hills aqui-
fer covers an area of approxi-
fer, the Denver aquifer extends
rock units on the west side of
fer underlies the entire 6,700
mately 1,400 square
miles
further north, east, and south
the basin deposited near the
square
in Douglas County, northern
and covers an area of approxi-
mountains by an ancient river
area of the Denver Basin. It is
El Paso County, and western
mately 3,500 square miles. It
fan system. These units possess
made up of both the beach
Arapahoe and Elbert counties.
typically contains fewer sand-
splendid aquifer characteristics.
sandstones of the Fox Hills and
This aquifer is most commonly
stone beds than the Dawson
This aquifer underlies an area
the overlying river sandstone
tapped by shallow domestic
aquifer because the ancient
of approximately 4,700 square
beds in the lower Laramie For-
wells. Water is found in discon-
meandering rivers were less
miles. Deep municipal wells
mation. Coal beds commonly
tinuous lens-shaped sandstone
common, and mudstone beds
along the I-25 corridor are often
occur in the lower part of the
beds deposited by ancient me-
often predominate. Sandstone
drilled in this aquifer and good
Laramie Formation and water
andering rivers. The rocks are
and pebble compositions are
quality wells yield up to 800 gal-
from this aquifer can be high
typically gravel-like and com-
typically volcanic. Wells com-
lons per minute. The aquifer also
in sulfur. Well yields of 350
posed of weathered granite
monly have yields of between
includes rocks deposited farther
gallons per minute are typi-
with typical well yields up to
50-150 gallons per minute. Ap-
east (away from the mountains)
cal. As the deepest of the four
300 gallons per minute. There
proximately 800 high-capacity
but their fine-grained nature re-
aquifers, it is often considered
are approximately 1,900 high-
wells have been completed in
sults in less productive wells, as
to be the aquifer of last resort
capacity wells completed in the
the Denver aquifer with total
found in eastern Elbert County.
for drinking water supplies.
Dawson aquifer that have been
annual permitted withdrawals
The State Engineer’s Office has
The Laramie-Fox Hills aquifer
permitted to withdraw 30,800
of more than 72,600 acre feet.
issued permits for more than
has seen the development of
1,000 high-capacity wells in the
490 high-capacity wells with
Arapahoe aquifer with maxi-
a permitted cumulative maxi-
mum total annual withdrawals
mum withdrawal of 51,600
of more than 168,700 acre feet.
acre feet.
acre feet annually.
Citizen’s Guide to Denver Basin Groundwater
mile
administrative
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