GROUNDWATER MINING OF BEDROCK AQUIFERS IN THE DENVER BASIN

The Denver Basin bedrock aquifer system is an important source of water for municipal and agricultural uses in the Denver and Colorado Springs metropolitan areas. The Denver area is one of the fastest growing areas in the United States with a population of 1.2 million in 1960 that has increased to over 2.4 million by 2000. This rapid population growth population has produced a corresponding increase in demand for potable water. Historically, the Denver area relied on surface water, however, in the past 10 years new housing and recreation developments have begun to rely on groundwater from the bedrock aquifers since surface water is essentially fully appropriated and in short supply.

The Denver basin bedrock aquifer system consists of Tertiary and Cretaceous age sedimentary rocks known as the Dawson, Denver, Arapahoe and Laramie-Fox Hills Aquifers. The number of bedrock wells has increased from 12,000 in 1985 to 33,700 in 2001 and the withdrawal of groundwater has caused water level declines of 250 feet. Water level declines for the past 10 years have ranged from 10 to 40 feet per year. The groundwater supplies were once thought to last 100 years but estimates now are 10 to 15 years for areas on the west side of the basin.

Extensive development of the aquifer system has occurred in the last 25 years especially near the center of the basin in Douglas and El Paso Counties where rapid urban growth continues and surface water is lacking. Groundwater is being mined from the aquifer system because the discharge by wells exceeds the rate of recharge. Concern mounts that increased groundwater withdrawal is causing rapid water level declines, increased cost to withdraw groundwater, and reduced groundwater storage. Since the long-term sustainability of the groundwater resource is doubt, water managers believe that the life of the Denver Basin aquifers can be extended with artificial recharge, water reuse, restrictions on lawn watering, well permit restrictions and conservation measures.