BOARD00363

• Board Meeting Date: 5/24/2004
• Description: Artificial Recharge of Ground Water in Colorado - A Statewide Assessment
• Board Meetings - Doc Type: Memo

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Artificial Recharge of Ground Water in Colorado
A Statewide Assessment

While a withdrawal rate less than 500,000 ac-ft per year may represent a depletion ofthe
resource of less than one half of one percent per year, the resource is considered non-renewable.
Pressures to increase exploitation of the aquifer are mounting. The portion of the Denver
metropolitan region covering western Arapahoe County and northeastern Douglas County relies
most heavily on the Denver Basin aquifers. Water levels in the Arapahoe aquifer in this area
have been declining up to 30 feet per year. At this rate of decline, water levels could drop to the
top of the currently confined Arapahoe aquifer in ten years, or less. Furthermore, declining
water levels result in greater pumping costs and decreasing well yields that ultimately result in
higher costs to produce the water.

With the prospect of skyrocketing costs and rapidly increasing demand on this non-renewable
resource, several districts in the Denver Metropolitan region have either completed pilot studies
or have initiated ASR projects since the mid-1980s. Concurrently, the DWR has implemented a
set ofmles and regulations governing how ASR can be managed in the Denver Basin. These
important regulations allow banking of water in place as well as banking ofrecharged water
imported from other sources.

ASR pilot studies were first undertaken by Parker Water and Sanitation District (Parker WSD)
and Willows Water District (Willows WD) in the mid-1980s (WSWC, 1998). Willows WD
(CWW-1 in Figure VI-3) participated in the US Bureau of Reclamation High Plains States
Groundwater Demonstration Program with the Denver Basin Aquifer Recharge Demonstration
Project between 1990 and 1997 (Lytle, 2003b). Results of these pilot studies indicated that ASR
was a viable technology in the basin. Parker WSD (CPW -I in Figure VI-3) currently does not
have a source of recharge water; however, ASR implementation is in the long-term plan for thc
district (Lytle, 2003a) once a surface-water supply is secured.

Full scale ASR implementation in the Denver Basin was first undertaken by Centennial Water
and Sanitation District (Centennial WSD) in 1992 (Hemenway and Grundemann, 2002). The
Centennial WSD supplies the vast Highlands Ranch community in Douglas County (CNT-1 in
Figure VI-2) with water and operates a well field completed in the Denver, Arapahoe, and
Laramie-Fox Hills aquifers. In addition, the district has tributary surface-water rights on the
South Platte River system. Tributary water is drawn directly from the South Platte River and
through alluvial wells. During periods of surplus tributary water, treated water from the South
Platte system is injected in a series of ASR wells. ASR wells are equipped with down-hole
control valves that allow both extraction and injection through the pump column.

Castle Pines Metropolitan District (Castle Pines MD), which supplies water to the Castle Pines
community in Douglas County (CPA-2 in Figure VI-2), began operating an ASR well in the
Arapahoe aquifer in 1998 (Jehn, 2003). The source water is obtained from the district's not-non-
tributary Denver aquifer wells and is treated prior to injection in the ASR well. The district also
plans to install a tributary well field in the Plum Creek alluvium once an augmentation decree
has been obtained that will provide additional source water.

Total recharge volumes for ASR in the Denver Basin for the period 1992 through 2002 are listed
in Table VI-2. Annual recharge volumes range between 220 and 1,410 ac-ft. The total volume
ofrecharge for the period is just under 8,000 ac-ft.

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