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Water Law

Colorado's Four Major Aquifers

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Click the Fluent Water Facts above to learn more about Colorado’s groundwater and the challenges it poses.

Colorado has aquifers, which contain groundwater, throughout the state. Groundwater can be found in many rock formations, and major streams and rivers have accompanying aquifers, although their size and accessibility varies. Below are Colorado’s four major aquifers:

South Platte Aquifer

The South Platte Aquifer follows the South Platte River through northeastern Colorado. This region is heavily populated (70% of Colorado’s population lives there, according to the 2000 Census) and heavily farmed. But the aquifer’s connection to the river means that pumping groundwater affects surface rights.

Type: Alluvial

Depth: 20 feet under Denver, but depths of 200 feet some 160 miles further downstream; average depth is 36 feet

Used for: Mostly irrigation, but some water for local communities

Challenges: Since the late 1960s, drilling of new wells has been restricted, due to the effects on surface rights. Colorado must abide by the terms of the South Platte River Compact, which requires certain amounts of surface water to be sent downstream. Recharge is heavily influenced by return flows, which mostly come from agricultural users. As the water is used and reused for irrigation, it has higher concentrations of dissolved solids and nutrients, which affect water quality. Discharges of municipal wastewater also affect water quality.

San Luis Valley Aquifers

San Luis Valley aquifers are connected to the Rio Grande and its tributaries, so pumping groundwater affects surface water and its rights holders. The Valley faces critical surface and groundwater shortages.

Type: Alluvial

Depth: 100 feet in the northern part of the valley, 40 feet in the southern portion

Used for: Vast majority for irrigation for farms, but some drinking water for local communities

Challenges: Aquifer levels have been steadily dropping. Natural recharge is difficult, as the San Luis Valley receives 7-8 inches of precipitation a year, half of Colorado’s state average. Pumping groundwater affects surface water, and Colorado must meet the terms of the Rio Grande Compact, which requires certain amounts of water to be sent downstream.

Read more about the San Luis Valley's challenges in the Summer 2013 issue of Headwaters magazine.

Denver Basin Aquifer

The Denver Basin aquifer system is a major source of water for South Metro Denver. The system extends from Colorado Springs in the south to Greeley in the north, from the foothills near Golden in the west to the eastern plains near Limon, a surface are of about 6,700 square miles. It includes four aquifers: the Dawson, Denver, Arapahoe, and Laramie-Fox Hills. Each aquifer has different water quality, depths, and water availability.

Type: Sedimentary bedrock

Depth: Shallow wells can reach the Dawson aquifer, the shallowest in the system, but other aquifers are a half-mile below the surface.

Used for: Mostly homes and businesses

Challenges: Extensive development in the South Metro area of Denver has resulted in steady and substantial aquifer declines, especially in the Arapahoe aquifer. Some of the water stored in these deep aquifers may be more than 50 million years old. Studies show that it took tens of thousands of years or more for nature to fill this resource. Since much of this groundwater is considered non-renewable, these rates of decline are not considered sustainable.

Read more about the Denver Basin aquifer, its geology and its challenges, in the Citizen's Guide to Denver Basin Groundwater.

High Plains Aquifer

The High Plains aquifer currently supplies water to about 20% of irrigated farm ground in the United States. It is found in parts of eastern Colorado, but the total aquifer underlies about 174,000 square miles from South Dakota to Texas and New Mexico. In eastern Colorado and eastern New Mexico, this is called the Ogallala formation.

Type: Sedimentary bedrock

Depth: Average of 300 feet below the surface

Used for: Mostly irrigation, with relatively little domestic use

Challenges: Since the 1960s, people have been extracting more water from this aquifer than has been returned. Aquifer recharge comes mostly from local precipitation – but the region receives relatively little precipitation and has high rates of evaporation. New conservation strategies have reduced the amount of water pumped, and withdrawal levels appear to have stabilized.

Water Law Resources

Guide to Colorado Water Law explores the basics of Colorado water law--learn how it has developed and how it is applied today. This, WEco's most popular Citizen's Guide, was authored by Colorado Supreme Court Justice, and WEco Board Vice President, Gregory Hobbs. Take a look or purchase a copy.


Law Supplement Headwaters magazine a special edition of Headwaters that provides an in-depth look at Colorado water law. Browse the magazine to supplement our Citizen's Guide and your knowledge. View it here

Administration Headwaters magazine read how enforcing the law in our water-scarce state can get tricky and meet the men and women who allocate Colorado's most precious resource. Browse the issue here.

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