Wild Horse Reservoir Project Alternatives

As part of the National Environmental Policy Act (NEPA) process for the Wild Horse Reservoir Project, the Bureau of Land Management (BLM) identified a set of project alternatives for in-depth analysis for the Environmental Impact Statement (EIS). These alternatives will be evaluated for their ability to meet Aurora Water’s Goal and Objective while minimizing potential environmental, social, and economic impacts. In the NEPA process, BLM plans to analyze:

Wild Horse Reservoir (known as the Proposed Action)
Wild Horse South Reservoir Alternative
Small Wild Horse Reservoir + Denver Basin Aquifer Storage and Recovery (ASR) Alternative
Spinney Mountain Reservoir Enlargement Alternative
No Action Alternative—Denver Basin ASR (if the Proposed Action is not approved)

UPDATE: After evaluating these alternative locations, Aurora Water determined that the Wild Horse South Reservoir alternative has several potential advantages and is shifting the proposed project site from the original Wild Horse Reservoir site to the Wild Horse South Reservoir site for the required environmental reviews and permit applications. Aurora Water is working with federal, state, and local government agencies on environmental reviews and permit application processes. More information will be shared at our upcoming project update presentations on February 25 at 7 pm and February 27 at noon. Learn more about these events. If you have any questions, please email us at wildhorsereservoir@auroragov.org.

See map of alternatives and descriptions below.

Map of the proposed alternatives for the Wild Horse Reservoir Project. Click for larger image.

Map of Denver Basin Aquifer Storage and Recovery (ASR). Click for larger image.

Wild Horse Reservoir (Proposed Action)

Aurora Water is proposing to build the Wild Horse Reservoir in Park County, Colorado, approximately six miles west of Spinney Mountain Reservoir near Hartsel. The reservoir—which would cover a surface area of approximately 1,700 acres and store 95,000 acre-feet of water—would be off channel, meaning no dams would block existing rivers or streams. Water would be supplied into the reservoir through a new inlet pipeline connected to the existing Otero pipeline. A new outlet pipeline would transport water from Wild Horse Reservoir to Spinney Mountain Reservoir as needed.

Importantly, water stored in the proposed reservoir would be supplied from Aurora Water’s existing Colorado and Arkansas River water rights so no new water rights or decrees would be required.

Wild Horse South Reservoir Alternative

The Wild Horse South Reservoir Alternative would consist of a reservoir storing 95,000 acre-feet of water in Park County, Colorado, approximately 10 miles south of Hartsel and approximately 10 miles southwest of Spinney Mountain Reservoir. The reservoir would be off channel, meaning no dams would block existing rivers or streams. Water would be transported to the reservoir through a new inlet pipeline connected to the existing Otero pipeline. A new outlet pipeline would transport water from the reservoir to Spinney Mountain Reservoir as needed. The reservoir would require one dam. Similar to the proposed action, no new water rights or decrees would be pursued for this alternative.

Small Wild Horse Reservoir + Denver Basin Aquifer Storage & Recovery Alternative

The Small Wild Horse Reservoir + Denver Basin Aquifer Storage and Recovery (ASR) Alternative would consist of:

A reservoir storing 45,000 acre-feet of water located in Park County, Colorado, about six miles west of Spinney Mountain Reservoir near Hartsel.
A system of deep underground wells and pipelines located within the city of Aurora, Colorado, in Arapahoe County.

The smaller reservoir would be off channel, meaning no dams would block existing rivers or streams. Water would be transported to the reservoir through a new inlet pipeline connected to the existing Otero pipeline. A new outlet pipeline would transport water from the reservoir to Spinney Mountain Reservoir as needed. Similar to the proposed action, no new water rights or decrees would be pursued for this alternative.

The ASR system would include 21 ASR well sites and a network of pipelines for storage in the Denver Basin Aquifer. The ASR wells would be deep aquifer wells that would allow water to be injected and withdrawn from the aquifer. A new pump station at Griswold Water Purification Facility (WPF) would pump the treated water through a bidirectional pipeline network to the ASR wells to inject for storage. The ASR wells would withdraw stored water as needed and then pump the water to a desalination facility for treatment and back to Griswold WPF for treatment and distribution.

Spinney Mountain Reservoir Enlargement Alternative

The existing Spinney Mountain Reservoir is located in Park County below the confluence of the Middle Fork and South Fork of the South Platte River, approximately three miles upstream from Eleven Mile Canyon Reservoir. The Spinney Mountain Reservoir Enlargement Alternative consists of increasing the storage capacity of the existing on-channel (South Platte River) reservoir by an additional 130,000 acre-feet to a total of 184,000 acre-feet. The Spinney Mountain Reservoir Enlargement Alternative would require the existing dam to either be raised by 22 feet or replaced with a new dam constructed downstream of the existing dam. A new saddle dam on the northern end of the reservoir would also be required to complete the enlargement. Similar to the proposed action, no new water rights or decrees would be pursued for this alternative.

No Action Alternative—Denver Basin Aquifer Storage and Recovery (ASR)

The No Action Alternative consists of an ASR system located within the City of Aurora, Colorado, in Arapahoe County. The ASR system would include 21 ASR well sites and a network of pipelines for storage in the Denver Basin Aquifer. The ASR wells would be deep aquifer wells that allow water to be injected and withdrawn from the aquifer. A new pump station at Griswold Water Purification Facility (WPF) would pump the treated water through a bidirectional pipeline network to the ASR wells to inject for storage. The ASR wells would withdraw stored water as needed and then pump the water to a desalination facility for treatment and back to Griswold WPF for treatment and distribution.

Surveys for NEPA Process

With landowner permission, natural resource and cultural surveys were conducted on the proposed project site and alternatives in 2025. The information gathered from these surveys will be used for the evaluations that are part of the environmental review.