Arapahoe County proposes lower groundwater allowances for future development
County modeling found physically producible groundwater averages about 60% of the amount allowed under state allocation rules. The proposed factors remain unadopted.
Arapahoe County staff are proposing aquifer-specific factors that could reduce how much future development is supported by Denver Basin groundwater. County modeling found that physically producible water in the study area averaged about 60% of the amount allowed under the state’s allocation formula.
The 2024 county water-supply study compares modeled water that can be produced using current well-construction methods with the state’s legal allocation calculations. It puts modeled availability at 60% of the state-rule amount for the Denver aquifer, 42% for the Upper Arapahoe, 27% for the Lower Arapahoe and 71% for the Laramie-Fox Hills. The study says the modeling accounts for regional drawdown and well-to-well interference that the legal formula does not fully reflect.
The draft Water Supply Element would apply those percentages as factors during development review. Staff says the approach is intended to better reflect what the aquifers can sustainably produce. A county presentation illustrated the potential effect with a hypothetical allocation that would support 100 homes under the state calculation and about 59 using a weighted-average factor; it was not an assessment of a specific project.
Commissioners reviewed the draft at an informational study session Sept. 21 and took no final action. The county presentation schedules a Planning Commission hearing for Oct. 20 and a Board of County Commissioners hearing for Nov. 24. If adopted, the element would guide future water-supply review, but the factors would need to be incorporated into development regulations before becoming enforceable standards.