WSP03001

• File Number: 8449.850
• Description: Metro Water Supply Investigation - MWSI
• State: CO
• Basin: South Platte
• Date: 8/1/1995
• Author: Hydrosphere, HRS
• Title: Phase II Conjunctive Use Summary Report - Draft
• Water Supply Pro - Doc Type: Publication

MWSI Project
Phase II Conjunctive Use Summary Report - DRAFT

August 23, 1995

production from each aquifer, Robson (1987) estimated municipal well production from 1979 to
1985 in the Denver Basin aquifers to be approximately 34,000 afi'yr. The current estimate of
municipal well production in Arapahoe and Douglas Counties is 22,000 afJyr.

Since the early 1980's groundwater development has increased in eastern Arapahoe and
Douglas Counties more than other areas ofthe Denver Basin, As a result of the increased
groundwater use in these areas, groundwater levels have declined in these areas more than other
areas of the Denver Basin. Robson (1987) shows measured water level declines in the range of
100 to 200 feet in the Arapahoe aquifer of Arapahoe and Douglas Counties between 1958 and
1978, Over the same time period groundwater levels rose in Denver and southeastern Adams
Counties. Current groundwater level declines in northern Douglas County from 1985 to 1993
averaged 22 feet per year in the Arapahoe aquifer. Declines in the Denver aquifer over the same
location and time period averaged seven feet per year.

Large static water level declines are expected from aquifers under confined aquifer
conditions, such as the Denver, Arapahoe and Laramie-Fox Hills aquifers, Under confined
aquifer conditions the groundwater level is above the top of the aquifer, i,e" the aquifer is full
and under sufficient pressure to rise above the top of the aquifer once a ..4ell is completed into the
aquifer. Groundwater level declines represent a reduction of the aquifer pressure and do not
represent dewatering from aquifer storage, The rate of groundwater level decline will be
reduced when the static water level falls below the top of the aquifer and groundwater is
produced from dewatering of the aquifer sediments,

Wellfield Economics

Two wellfield economic analyses were performed. The analyses determined costs for
groundwater production from the Denver, Arapahoe and Laramie-Fox Hills aquifers, The first
economic analysis was performed to determine the most cost effective area in the Denver Basin
to produce groundwater, A second analysis was then performed to determine the most cost
effective combination of aquifer production from the Denver Basin aquifers. In the first analysis
costs were prepared for two 2,000 afi'yr well fields. One well field was located in the northern
part of the metro area in the vicinity of Denver International Airport, and a second well field was
located in the southern portion of the metro area in western Elbert County near the southeastern
border of Douglas County, Figure C4 shows the general locations of these well fields. The
well fields were located in areas which represent the better hydrogeologic conditions in the
northern and southern portions of the metro area,

In the portion of the Denver Basin north of Township 6 South, the Colorado Division of
Water Resources has divided the Arapahoe aquifer into Upper and Lower Arapahoe aquifers,
The line for Township 6 South is shown on Figure CI. South of Township 6 South the aquifer is
not divided. Therefore, fours wells are required to obtain all the water beneath a parcel from the
Denver, Arapahoe and Laramie-Fox Hills aquifer water north of Township 6 South and three
wells are required south of Townsltip 6 South,

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