Losses in Denver Basin Well Efficiency Due to Declining Aquifer Water Levels

Groundwater from municipal Denver Basin aquifer wells is the primary water supply for many communities between Denver and Colorado Springs, Colorado. The Denver Basin aquifers include Cretaceous and Tertiary age interbedded sandstone, siltstone, and shale subdivided into the Dawson, Denver, Arapahoe, and Laramie-Fox Hills sub-aquifers. The Arapahoe aquifer is the most prolific, with municipal well yields ranging from 200 to over 700 gallons per minute and depths ranging from 700 to over 2000 feet.

The Denver Basin aquifers are confined, and pumping exceeds recharge. As a result, groundwater is mined, and reported water level declines range from 10 to over 30 feet per year. Well efficiency is impacted by water level declines and dewatering of well screens during pumping. There has been ample water level decline research, but little analysis regarding changes in well efficiency with pumping water levels below the top well screen. Projections of future well yields with increasingly deep pumping water levels are critical for municipal water supply planning.

A municipal Denver Basin water provider has collected up to seven years of hourly water level measurement and pumping rate data from one Denver aquifer well and five Arapahoe aquifer wells. These data have been evaluated on the basis of specific capacity from more than 4800 individual pumping cycles to assess changes in well efficiency with varying pumping water level depths. No loss in well efficiency was identified with pumping water levels above 75% of the well screens (25% of screens dewatered). Two of the wells exhibited efficiency losses with pumping water levels below 75% of the well screens. These trends are used to project well yield with future water level declines and plan for development of new water supplies.