El Paso County review finds Denver Basin aquifers broadly pressurized and usable; consultant urges periodic monitoring

El Paso County commissioners on Oct. 21 received a technical evaluation of the Denver Basin aquifers covering the northern and eastern parts of the county and were told the basin remains largely "confined" — meaning wells often still show pressure above the top of the aquifer — even where localized declines exist.

The study, prepared for El Paso County by consultant Bruce Lytle of Moore Engineering and introduced at a Board of County Commissioners work session by Megan Harrington, the county planning director, synthesizes long-term water-level hydrographs and cross sections from water providers and monitoring wells to assess the reliability and limits of Denver Basin groundwater within county boundaries.

Why it matters: county planners, water utilities and developers rely on Denver Basin groundwater for municipal and commercial supplies in parts of unincorporated El Paso County. The basin is a nonrenewable, geologic resource deposited millions of years ago; how the county and local providers manage pumping, development approvals and well siting affects local water availability, potential well interference and long-range planning.

Bruce Lytle, a water-resources consultant who led the analysis, told commissioners the Denver Basin consists of four principal aquifers — Dawson, Denver, Arapahoe and Laramie–Fox Hills — and that his team used cross sections and multi-decade hydrographs provided by local water suppliers and monitoring programs to evaluate conditions. "With all that preamble," Lytle said, "I don't see the Denver Basin aquifers as being immediately at risk." He added, "I would not recommend that you really do any policy or code changes on the Denver Basin. I think you're adequately protecting that supply as best you can being a nonrenewable resource."

Key findings

- Distribution of resources: El Paso County covers about 17% of the Denver Basin. The basin is commonly described as a series of "stacked bowls" in which Dawson is the shallowest and smallest and the Laramie–Fox Hills is the deepest and most extensive.

- Hydrograph signals and interpretation: Lytle said many long-term monitoring wells show water levels at or above the top of the mapped aquifer, which indicates the statutorily defined saturated thickness used for the state allocation formula has not been consumed at those locations. In other wells, water levels dip during use and recover afterward; Lytle attributed those patterns primarily to pumping cycles rather than to basin-wide loss of pressure in most places.

- By aquifer: - Dawson: tends to be the shallowest and is commonly used by residential (exempt) wells. Lytle said many Dawson wells are at or near the top of the aquifer and recommended limiting large municipal or commercial production from Dawson where residential wells depend on it. - Denver: more aerially extensive; some wells show gradual declines but most monitoring points Lytle reviewed remain at or above the top of the formation. - Arapahoe: described as the "workhorse" aquifer. Lytle reported regional declines consistent with substantial use but said most monitored sites remain pressurized (above the top of the aquifer) despite that drawdown. - Laramie–Fox Hills: deep and less developed in much of the county; Lytle said it remains under pressure in many places but can present water-quality issues (salinity, methane, hydrogen sulfide) and higher drilling costs.

- Data and limits: the evaluation relied on hydrographs supplied by providers through the Pikes Peak Regional Water Authority and other entities; response from providers was helpful but not comprehensive. Lytle noted the team did not receive complete pumping records for all wells, so some interpretation of water-level changes required assumptions about when wells were pumping.

Policy and regulatory context

Lytle explained the state allocation approach historically used for Denver Basin wells: a "hundred-year" volumetric allocation is calculated from saturated thickness, and El Paso County applies a local practice of spreading that amount over 300 years for local planning (the county's "300-year rule"). He cautioned commissioners about a state-level policy called the "total allowable withdrawal," which he said counts pumped volume against the hundred-year allotment and can result in a source being shut off once the total allowable volume is reached, even if local water levels appear usable. "The state has come back with what they call a total allowable withdrawal...In my opinion, this is really a bad decision," Lytle said.

Technical and practical takeaways

- Geophysical logs and well completion reports: nonexempt (larger municipal/commercial/irrigation) wells must file geophysical logs and completion reports with the state; those logs underpin the state saturated-thickness maps and help refine local estimates when shared.

- Well costs and yields: Lytle said deep wells can cost roughly $600–$700 per foot and typical production wells in the deeper units may be 1,500–1,800 feet or more; equipping deep wells therefore can run into the low millions of dollars. He noted widely variable yields even on the same parcel (he gave an example of multiple wells on the same 1,300-acre tract producing very different flows).

- Hydrogeologic complexity: the basin is highly interbedded (sand/shale) at small spatial scales, meaning well response and productivity can vary substantially over hundreds of feet. Confined aquifer pressure, not counted in the allocation formula, can provide additional usable water beyond the assumed saturated-thickness allocation.

Board direction and next steps

- Public posting: Harrington said the county will post the slides, the evaluation report and the work-session video to the county planning website after the session.

- Legal follow-up: County staff and the county attorney agreed to research whether county authority and water-court processes provide additional tools for limiting well interference or otherwise protecting existing residential wells when new, higher-capacity municipal wells are proposed.

- Monitoring recommendation: Lytle recommended periodic re-evaluation rather than immediate code or policy changes; he suggested a review interval on the order of multiple years (he recommended no more frequently than every five years for a countywide look) to track trends and inform future policy decisions.

What was not decided

The board did not take formal action or adopt new policy at the session. Commissioners asked for follow-up information and legal analysis; the county attorney offered to research statutory limits and return findings to the board.

Source material and availability

Harrington said the county will publish the consultant slides and the evaluation on the county planning website. Those documents contain the technical cross sections, the list of wells used and the hydrographs summarized at the work session.

Asked whether the findings meant immediate concern for residents on private wells, Lytle said the data do not indicate a basin-wide crisis: "If the water levels are at the top of the aquifer, the full allocation is there." He reiterated that the Denver Basin is a nonrenewable resource and needs continued monitoring and prudent local water planning.

— Megan Harrington, planning director, introduced the item and said staff will post the materials.

— Bruce Lytle, consultant (Moore Engineering), presented the analysis and told commissioners the county's 300-year allocation approach provides extra conservatism but urged continued monitoring.

The county will post the full report and presentation slides on the planning website for public review.