Effects of Development On Groundwater Availability in the Denver Basin Aquifer System, Colorado

The Denver Basin aquifer system is a critical water resource for municipal, industrial, and domestic uses along the semi-arid Front Range urban corridor of Colorado.  Population of the metropolitan areas overlying the Denver Basin aquifers has approximately doubled from 1.3 million in 1970 to about 2.7 million in 2005 and is expected to double again in the next 50 years.  Development has been especially extensive on the western margin of the basin between Denver and Colorado Springs, and Denver Basin confined aquifers provide much of the municipal water supply in this area.  Denver Basin groundwater is administratively recognized as nonrenewable, and permitted pumping rates are based on the concept of a 100-year aquifer life.  The U.S. Geological Survey Denver Basin Groundwater-Availability Study assessed effects of development on groundwater resources by developing a transient three-dimensional groundwater flow model for the basin, which is a useful tool for analysis of past and future groundwater management.  Study results indicate land-use changes in the Denver Basin have increased water use on the landscape, and increased pumping from the confined bedrock aquifers has accelerated the removal of water from storage.  Storage-loss from the confined aquifers is expected to continue increasing as drawdowns increase and aquifers convert to unconfined conditions.  Spatially, 50 percent of the 2003 bedrock-storage depletion was from the metropolitan area between Denver and Colorado Springs.  The effects of storage depletion include lowered regional potentiometric surfaces, altered groundwater-flow directions, increased downward movement of water through confining layers, and reduced discharge from bedrock to alluvial aquifers compared to predevelopment conditions.  Conjunctive-use projects, conservation, water reuse, and importation of renewable water likely can extend the practical useable life of the Denver Basin aquifers.  Recurring monitoring and modeling of groundwater availability are especially important to document the effects of continued pumping and guide future water-management decisions.