GROUNDWATER RESOURCES IN DOUGLAS COUNTY CO, A DEPLETING ASSET

The bedrock aquifers in the Denver Basin are largely made up of rocks that were deposited in the Denver Basin as the Rocky Mountains rose to the west. While vast areas of the basin are underlain by water-bearing rocks, the quality and character of the aquifers vary greatly as you move away from the mountain front and away from the source of clastic materials. The resulting lateral variability has made it challenging both to legally define aquifer layers unambiguously and to quantify the amount of recoverable water present within these aquifers.

The aquifer geometries and porosity/permeability characteristics vary as a function of depositional environments. Strata deposited near the mountain front in fluvial distributary fan systems have high sand/shale ratios and typically exhibit stacked and well-interconnected fluvial sandstone units that can yield over 800 gallons of water per minute to deep municipal water wells. As you move 10-20 km from the mountain front the sandstone bodies become increasingly segregated by impermeable mudstone layers, and reservoir quality diminishes, with wells in same age-strata yielding less than 100 gallons per minute.

A data base of electric logs from over 1400 water wells and oil/gas test wells has been calibrated by comparison to continuous rock cores to develop a high resolution geologic history for the basin. Detailed maps show paleogeographic reconstructions and aquifer thickness variations. These maps are presently being used by municipal planners to more effectively manage and plan for future potable water sources in the basin.

Data published by the Colorado State Engineer indicate that potentiometric surfaces are falling rapidly (at rates of over 1 inch per day) in selected aquifers. The three-dimensional models derived from our studies help us to project the remaining water well life in the area south of Denver. At present rates of fall, many water wells have only decades of remaining useful life. Innovative development practices and groundwater injection are tools that could be used to mitigate the loss of our subsurface water resources.