Groundwater use in Colorado dates back to before the turn of the 20th century. Nineteen of Colorado’s 63 counties rely solely on ground water for potable supplies and domestic uses. Groundwater withdrawals by private wells and public water supply systems serve an estimated twenty percent of the state’s population. Agriculture is the largest user of groundwater, primarily for irrigation. However, groundwater is also used to meet nearly all livestock and rural domestic water needs.

Artesian well near Alamosa in the San Luis Valley, Colorado

Groundwater is simply water that occupies the pore spaces or crevices or fractures within soil or rock. Some materials have a greater ability to store and transmit water than others. An aquifer is a groundwater reservoir composed of geologic units that are saturated with water and sufficiently permeable to yield water in a usable quantity to wells and springs. Sand and gravel deposits, sandstone, limestone, and fractured crystalline rocks are examples of geologic units that form aquifers. The USGS identifies seven principal aquifers or aquifer systems in Colorado: South Platte Aquifer, Arkansas Aquifer, High Plains Aquifer, San Luis Valley Aquifer System, Denver Basin Aquifer System, Piceance Creek Basin Aquifer, and the Leadville Limestone Aquifer of west-central Colorado.

Sufficient water for a single household may be relatively easily obtained from wells in the bedrock aquifers, even the crystalline Precambrian rocks of the mountains. However, as households multiply, creating increased demands from many wells, a local aquifer with very limited storage that was sufficient for a few users, may be quickly depleted or polluted. Through wise water-management policies, protective regulations, and conservation activities, we can assure ground water’s availability and suitability for future use.

CGS Groundwater Publications

The CGS published a comprehensive, award-winning Ground Water Atlas of Colorado in 2003, and is in the early stages of producing another, scheduled to be available in 2020.

In 2011 the CGS published three significant reports on groundwater in the Denver Basin. These reports, representing more than a decade of research, provide the most detailed information yet on the distribution of groundwater in the Denver Basin.

The first report OF-11-02 Geology of Upper Cretaceous, Paleocene and Eocene Strata in the Southwestern Denver Basin, Colorado is a compilation of more than 1000 square miles of surface mapping of the aquifers where they are exposed along the mountain front. The mapping was originally carried out at a scale of 1:24,000 and is compiled into a 1:50,000 map consisting of two plates. This compilation also presents a simplified naming classification for the geologic strata of the Denver Basin.

The second report OF-11-01 Notes on the Denver Basin Geologic Maps: Bedrock Geology, Structure, and Isopach Maps of Upper Cretaceous to Paleogene Strata between Greeley and Colorado Springs, Colorado takes what was learned by mapping at the surface and extends it into the subsurface using data from nearly 3,000 wells. This report was a collaborative effort with DMNS, whose personnel also spent more than a decade independently working on the strata in the Denver Basin. The report contains seven maps that illustrate the thickness, depth, and distribution of the various freshwater-bearing strata in the Denver Basin. It also contains a depth map to the Niobrara formation, and a thickness map of the Pierre shale that separates the Niobrara from the freshwater aquifers. Three additional maps of ancient landscapes illustrate why the sandstone aquifers are concentrated near the mountain front. Included is a poster that illustrates the various depositional environments within which the strata were deposited. The poster is also sold separately.

And, finally, the third report OF-11-03 Cross-sections of the Fresh-water-bearing Strata of the Denver Basin contains four north-south and eleven east-west cross-sections of the strata in the Denver Basin. These detailed cross sections integrate surface geologic mapping with subsurface well data to graphically illustrate variability in the types of strata across the entire basin. This report is oriented toward the professional community rather than the general public.

All three publications come in hard copy and include DVDs with detailed PDFs of the plates and GIS shapefiles. These and other groundwater publications may be ordered from the CGS online Bookstore.