Douglas County hears groundwater analysis showing lower physically recoverable water than legal allocations

Douglas County Water Commission members heard an update Aug. 25 on the county'wide water plan that emphasized technical mapping and a comparison between legal water allocations and what consultants consider physically recoverable groundwater.

Forest Grown Associates project manager Will Koger and Bill Fronczak of LRE Water described a multi-part analysis including a water-provider survey, a geophysical ("Petra") analysis of well logs, and an SB 5 (statutory) grid-based inventory of subsurface water. "We're now working on drafts of the water supply and demand analysis and the land use policy analysis phases 1 and 2, looking to complete those by the end of the year," Koger said.

The consultants told commissioners why the work matters: county land-use decisions hinge on both legally adjudicated water and what can actually be pumped from the ground. "What we're trying to do here is get the county the information that in the unincorporated areas ... how much water really is in these various aquifers?" Fronczak said.

Fronczak summarized the technical approach. He said the team synthesized State Engineer Office (SEO) records to classify domestic (exempt) and non-domestic wells, used Petra and geophysical logs to place wells in the correct aquifer (for example, Upper Dawson, Lower Dawson, Denver, Arapahoe, Fox Hills), and produced a 2-by-2-mile SB 5 grid to estimate volumetric storage across aquifers. He described comparing the state's saturated-thickness estimates to the consultants' net-sands analysis derived from logs and noted the team will subtract municipal/provider wells and pre-existing (pre-1913) diversions from the unincorporated-area total.

The team reported preliminary counts and data points discussed by commissioners: the survey of water providers had 25 completed responses including 12 members of the South Metro Water Supply Authority, three outstanding responses and two very small providers the team could not reach. Fronczak said there are roughly 9,500 wells in the Denver Basin portion of the county and "close to 6,000 wells" in the shallow Dawson aquifer combined (Upper and Lower Dawson where applicable). He said about 500 well logs were used in the Petra analysis to characterize net sands and aquifer tops and bottoms.

Consultants flagged a recurring finding: actual, physically recoverable water can be meaningfully less than adjudicated (decreed) amounts. "Based upon a single well analysis with actual construction from today, you know, we're seeing that there's less physical water available than actual legal water," Fronczak said. He and commissioners discussed that economic and technical limits ' drilling cost, pumping depth, energy cost ' affect recoverability and that municipalities, not individual homeowners, are more likely to afford very deep wells.

The consultants showed sample cross sections and a heat map (net-saturated sands) for the Denver Basin and described the Arapahoe aquifer as "a pretty good aquifer" though deeper and costlier to access. They explained their 12-ohm-meter cutoff in resistivity logs as a practical threshold below which sands are unlikely to produce viable flow for extraction.

Commissioners pressed implementation questions. Harold Smethals asked whether municipal provider service areas would be excluded from the unincorporated-area availability calculations; Fronczak said service areas and extraterritorial service areas reported by providers would be treated as provided water and removed from the unincorporated tally. Trisha Bernhard asked how saturated-thickness estimates from the state would be reconciled with Petra-derived net-sand estimates; Fronczak said the team will compare both datasets and has seen both positive and negative discrepancies in prior work.

Other topical items shown in the interactive map demonstration included click-to-view SEO pump and well-construction records, color-coded maps by aquifer and by whether wells are multiply completed, and monitoring point overlays for observed water-level trends. Commissioners asked whether the map would show water-quality indicators such as radium; Fronczak replied that municipal water-provider data will be incorporated where available but that rural domestic samples are inconsistent.

No ordinance or regulatory action was taken at the meeting. Commissioners and consultants agreed the next deliverables are draft water-supply and land-use policy analyses, with the team aiming to complete drafts by the end of the year for public engagement and incorporation into a final water plan.

Ending: The commission did not vote on substantive policy at the Aug. 25 session; the consultants said they will return with written draft analyses and interactive mapping tools that county staff and commissioners can use to assess land-use proposals and provider needs.