County consultant: Denver Basin aquifers broadly reliable now but warrant periodic review

El Paso County commissioners heard a technical review of the Denver Basin aquifers on Oct. 21 and were told the basin remains a usable but nonrenewable water resource that requires ongoing monitoring.

Consultant Bruce Lytle, now with Moore Engineering, told the Board of County Commissioners that long-term water-level records and geophysical logs show most monitoring and nonexempt production wells in El Paso County have water levels at or above the top of the named Denver Basin aquifers — Dawson, Denver, Arapahoe and Laramie/Fox Hills — although some local wells show partial dewatering and regional declines in pressure in parts of the Arapahoe.

"The Denver Basin really is not part of the hydrologic cycle," Lytle said, summarizing the geology and why recharge is minimal; the aquifer water was deposited millions of years ago and behaves like "a big bathtub" of largely nonrecharging supply. He added the state allocation method counts only saturated thickness and does not credit pressure held in confined sands.

Why it matters: the Denver Basin supplies municipal, district and irrigation wells across northern and eastern El Paso County. Lytle told commissioners the county’s local 300-year allocation approach provides an added layer of conservatism beyond the state’s 100-year allocation, and he recommended continuing the county’s monitoring approach rather than making immediate code or policy changes.

Key findings and caveats

- Data sources: Lytle’s team compiled long-term hydrographs (water-level records) supplied by several local water providers and compared them to geophysical logs filed with the state. The review used cross sections across the county to show how aquifer thickness and depth vary by location.

- Overall status: Most sampled wells — particularly in the Denver and Arapahoe aquifers — remain at or above the top of the formation in El Paso County. Where water levels have declined, Lytle said they generally remain within the confined portion of the aquifer and often show recovery after pumping stops.

- Local variability: The county-sized portion of the Denver Basin is geologically complex and interbedded (sandstone/shale). Yields and responses can change over short distances; a property half a mile away can produce very differently from a neighbor because of depositional differences and the presence or absence of productive sandstone layers.

- Aquifer-specific notes: The Dawson is the shallowest and covers a smaller area; it shows some localized dewatering but is widely used by residential (exempt) wells, so municipal providers typically limit use of the Dawson. The Denver and Arapahoe are the "workhorse" aquifers; Lytle showed some regional declines in the Arapahoe but said it remains a viable source overall. The Laramie/Fox Hills is deep, less developed, sometimes has water-quality issues (salinity, methane, hydrogen sulfide) but in places can be productive and is typically costly to develop.

- Data gaps and limits: Lytle noted that pumping records were not generally provided, so hydrograph interpretation sometimes required inference (pumping vs. static levels). A small number of wells had anomalous records (replacement-well records, gaps) that merit further investigation.

Policy and next steps

- No immediate code change recommended: Based on the dataset presented, Lytle told the commissioners he would not recommend immediate changes to county policy or code governing Denver Basin wells, but he urged continued monitoring and periodic reassessments.

- Posting and transparency: Megan Harrington, El Paso County planning director, said, "After the work session today, we will post the slides and the evaluation on the county website, on the county planning website, along with the video direct to the work session for the public."

- Legal followup: The county attorney’s office agreed to research the county’s statutory authority and limits related to local actions affecting groundwater and potential well-interference protections. Senior Assistant County Attorney Lori Sego said the county’s subdivision review process already requires water-resource reporting from central water providers that typically lists wells and water-right ownership.

Direct quotations are limited to speakers on the record during the presentation and Q&A. Lytle emphasized the nonrenewable nature of the Denver Basin resource and explained that state allocation rules historically assume a 100-year minimum useful life; he also warned that a recently adopted state approach that counts total allowable withdrawal as a volume can force shutdowns once that volume is reached even if pressure remains in parts of an aquifer.

What commissioners asked and decided

- Commissioners pressed Lytle on how water-level declines should be interpreted, whether residential wells are at risk from deeper municipal wells, and how replacement wells are reported. Lytle said vertical movement between the major named aquifers is limited by shale layers, so wells completed in different aquifers generally do not interfere vertically.

- Direction given: staff will publish the consultant slides and the evaluation on the county website; the county attorney’s office will research legal parameters for local authority and report back to the board. No formal vote or regulatory change was recorded at the meeting.

Ending

County planning staff and the presenter said they will make the slides and evaluation public; Lytle left contact information for follow-up technical questions. Commissioners indicated support for continued monitoring and for having county attorneys investigate the legal questions raised during the session.