WSP09428

• File Number: 8449.926
• Description: South Metro Water Supply Study
• State: CO
• Basin: South Platte
• Date: 2/1/2004
• Author: SMWSS Board
• Title: South Metro Water Supply Study
• Water Supply Pro - Doc Type: Publication

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1.3 Non-Trihutarl Ground Water

1.3.) Dem"er Basin - The non-tributary ground water available to the \vater providers in the
South ~tetro Area is from the Denver Basin. The Denver Basin includes four aquifers that
underlie the entire Denver ~tetropolitan Area and large areas north. south and east of Denver.
The Denver Basin generally ranges from the TO\lm of Greeley on the north, to Colorado Springs
on the south. and from the foothills on the west. almost to Limon on the east. The total aerial
extent of the Denver Basin is approximately 6.700 square miles. The extent of the Denver Basin
Fonnation is sho\\TI on Figure 1.2.

A cross-section of the Denver Basin is sho\\TI in Figure 1.3. This figure shov,'s the four aquifers.
or water saturated sandstone layers. that arc bowl-shaped with one aquifer sitting upon the next
separated by low renneability strata. The shallowest aquifer is the Da\vson Fom13tion. The next
deeper aquifer is the Denver Fonnation. The third aquifer is the Arapahoe Fomlation and the
bottom aquifer is the Laramie-Fox Hills Formation. Each ofthesc aquifers consists of sandstone
layers separated by layers of 10\\' pemleability materials.

Douglas County and South-Central Arapahoe County arc underlain by the Denver Uasin aquifers
and this water resource has been used as the primary municipal water source for developing
urban area'i in the Study Area. The aquifers arc deep sedimentary rock formations that are
characterized by very 100v recharge rates and are considered to be a non-renewable watcr
resource. This ground water source has. however. been in relatively plentiful supply and urban
developments have bcen able to use the water to largely meet their water demands.

State and federal studies of the Denver Basin Aquifers havc generally characterized the aquifers'
hydrogeologic nature. This information has been used by regulatory and planning agencies to
describt, water availability and regulations that guidl.' the- management and development of the
ground watl'r resources, Key reports dr.:scribing th~ aquifers include Bedrock AtJ/(~fers in the
Denwr Basin. Colorado - A Qw.Jntitalh'e Water Resources Appraisal- United States Geological
Survey Professional Paper No. 125. 1987 (Reference 1.1) and Dem'cr Basin and Smtih Platte
Ril'Cr Basin Technical SlU(~)' - Senare Bill 96-07-1. Special Waler Committee. October 1997
(Reference 1.2). \lore detailed infomlation can be gathered from those and other reports
referenced in this study.

Approximately 485 square miles of the Denver Basin aquifers underlie Douglas County. The
sedimentary rocks that make up these four major aquifl:rs exhibit highly variable water
producing characteristics across the basin.

1.3.1.1 Da,,,"son Aquifer - The Dawson Aquifer is the upper most aquifer and covers a total of
approximatdy 1.400 square miles. Its greatest thickness is in the south fringes of the Study Area
at over 1200 feet in the vicinity of Monument in EI Paso County. The Dawson is at or near the
land surface throughout the Study Area. The aquifer is primarily a conglomerate of coarse-
grained sandstones \\ith minor amounts of interbedded clay and clay shale. At the base of the
Dawson aquifer and at the interface with the Denver Formation. a shale unit averages 25 to 50
feet.

1.3.1.2 Dcnn'r Aquifer - The Denver aquifer consists of a series of interbedded clay shale.
claystone. siltstone. and sandstone lenses. The aquifer underlies an area of approximatdy 3.500

PJge 1.3