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

and about 8,200 acre-feet per year percolated from the Denver aquifer to the Arapahoe aquifer
(Reference 1.1).

Since about 1980, the sum of natural discharge and well pumping has exceeded the rate of
recharge of the aquifers. Because the rate of extraction is greater than the rate of recharge, the
Denver Basin aquifers are considered to be non-renewable water resources.

1.3.5 Ground Water Ownership - Colorado water law for non-tributary ground water (Senate
Bill 5) ties water ownership to the ownership of the land below which the aquifer lies. Hence,
non-tributary ground water ownership is generally with the private landowner. The water
providers acquire the non-tributary ground water rights by requiring dedication of such rights to
the water provider for service. Therefore, the non-tributary water rights available to the water
provider are generally those water rights associated with the property within their boundaries.
These water rights are generally not sufficient to meet the high demands of urban development
and hence, the water provider must supplement these water rights through other sources. Other
sources generally include limited surface water, reuse of its consumable non-tributary ground
water and surface water, and if practical, through the importation of additional ground water
supplies.

1.3.6 Production Rates - The primary issue that affects the development of ground water
supplies is the limited ability to produce waters from each of these aquifers. In general, these
aquifers consist of very dense sandstones, which are relatively slow draining, and the production
levels in gallons per minute are somewhat limited. The best producing aquifer is the Arapahoe
aquifer where supplies are developed generally at rates from 300 up to 1500 gallons per minute.
These high production rates, combined with the good water quality of the Arapahoe aquifer,
make it the most desirable ground water supply by far. The production rates of wells in the
Dawson and Denver Formations are generally in a range from between 50 and 200 gallons per
minute and in the Laramie-Fox Hills Formation are between 100 and 300 gallons per minute.
These production rates are representative of the South Metro Area, but even here will vary
widely, with production rates higher or lower than these ranges at some locations.

Municipal water delivery systems are generally designed for a maximum day demand, with peak
hour demands met through storage. To date, these South Metro water providers, with the
exception of Centennial Water, have met their peak day demand by developing enough wells to
produce at this peak rate. Therefore, a water provider will typically have three to four times the
number of weIIs necessary to meet average demands just to meet the summer peaking. Hence,
these water providers tend to have numerous weIIs with many operating only a few months a
year.

The other option available to water providers to meet summer peaking is through the use of
surface reservoirs. However, because of the cost of surface reservoirs and the extensive
treatment required once water is stored in an open reservoir, development of additional wells for
peaking has been the economic alternative.

The South Metro Area currently produces approximately 22,000 acre feet of water supply each
year from the Denver Basin Aquifers. Approximately 75% of the supplies produced today are

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