All of Colorado’s groundwater is presumed to be tributary, and therefore allocated and administered under the prior appropriation system, unless it can be proven that the groundwater is non-tributary (insignificantly hydrologically connected) to a surface stream. If proven to be non-tributary, the groundwater is governed by a modified form of the prior appropriation system (WEC, 2015; Houpt, 2014). The State Engineer still administers non-tributary and Denver Basin groundwater under its well permit and rulemaking authority, but the Colorado Groundwater Commission and local groundwater management districts administer groundwater in the Designated Basins. The following briefly describes the allocation and administration authority over the different types of groundwater (for a more detailed discussion of the different types of groundwater, see the “Groundwater Resources” section):
Groundwater that is hydrologically connected to a surface stream and which has the ability to influence the amount or direction of flow of water in that stream. Tributary groundwater is allocated and administered according to the prior appropriation system, as described above. As with any groundwater well in the state, a well permit is required from the State Engineer.
Non-tributary groundwater, located outside of any designated groundwater basin, is groundwater where the withdrawal will not, within 100 years, deplete the flow of a natural stream at an annual rate greater than one-tenth of one percent of the annual rate of withdrawal. This type of groundwater is allocated according to overlying land ownership based on an assumed 100-year aquifer life, as opposed to the priority system. The Office of the State Engineer oversees permitting and administration. While a well permit is mandatory to pump non-tributary groundwater, a water court decree is optional.
Not non-tributary groundwater is water withdrawn from specified Denver Basin aquifers that do influence stream flows in a meaningful way, but are nevertheless allocated differently than tributary waters because of their unique hydrologic characteristics and importance to the economy. Withdrawals of this type of groundwater within the Denver Basin aquifers requires at least four percent of the water pumped to be returned to the surface streams, and in some cases, actual replacement of depletions. As with non-tributary groundwater, not non-tributary groundwater is allocated according to overlying land ownership based on an assumed 100-year aquifer life; however, not non-tributary groundwater requires both a well permit and a water court-decreed augmentation plan.
Designated groundwater is a type of non-tributary groundwater located in one of the “Designated” Basins (areas in the eastern plains with very little surface water) determined by the Colorado Ground Water Commission. The 1965 Ground Water Management Act created a modified prior appropriation system for designated groundwater where the Colorado Ground Water Commission is responsible for issuing well permits, while the Commission, State Engineer and local Ground Water Management Districts administer them. There are currently eight of these designated basins on the eastern plains and 13 Ground Water Management Districts within the designated basins.
Geothermal water is groundwater that is heated by the earth’s energy, and by harnessing the physical properties of steam and heat, geothermal water can be used to generate energy. All subsurface geothermal fluids are considered part of Colorado’s groundwater resources and are subject to the Colorado Geothermal Resources Act. As with all other types of groundwater use in the state, a permit from the State Engineer is required for use of this type of groundwater. Geothermal resources are administered and managed according to the “Geothermal Well Rules” by the Colorado Division of Water Resources.
It is important to note a major caveat in terms of Colorado’s groundwater allocation and administration: exempt wells. Exempt wells are small-capacity wells (typically 15 gallons per minute) for domestic, stock-watering and low-intensity commercial uses in locations where other supplies are not available (Jones & Cech, 2009). They are allowed in tributary, nontributary, not nontributary and designated groundwater aquifers, but are exempt from the rules of allocation and administration of those other types of groundwater. Two statutes govern exempt wells: C.R.S. 37-92-602 for exempt wells outside of designated basins, and C.R.S. 37-90-105 for exempt wells inside designated basins. The State Engineer is responsible for processing exempt well applications and issuing the well permits.