Consultants update Douglas County water plan: population projections, provider survey and Denver Basin groundwater study

Consultants working on the Douglas County 2050 water plan updated the Douglas County Water Commission on June 23, outlining population-projection scenarios, the status of a countywide water-provider survey and early results from a Denver Basin groundwater study that uses a PETRA geophysical-analysis tool.

The presentation matters because county planners will use the combined population and groundwater analyses to recommend water-supply policies, limits on groundwater use in unincorporated areas and monitoring needs that could affect development approvals and well-permitting decisions.

Will Koger, a consultant with Forsgren Associates, told the commission the technical team is compiling population and demand projections through 2050 and will reconcile figures from multiple sources. "There's the State Demographer's Office, which is projecting about 467,000 for Douglas County by 2050, and the county comprehensive plan shows a different series of projections," Koger said. He said Forsgren will "mesh" those sources with water-provider forecasts and present a recommended projection for analysis.

Katie (county staff) said the water-provider survey is roughly halfway complete: 14 of 31 providers have returned surveys, 12 are in process and four providers have not yet been reached. "South Metro Water Supply Authority has helped coordinate survey responses from its members," she said.

Bill Fronczak of LRE Water presented the groundwater analysis approach. The team has digitized and reviewed geophysical logs (about 555 logs to date) and is using a PETRA workflow to map lateral extent, saturated thickness and "net sands" — the permeable sand lenses the team treats as the recoverable portion of the Denver Basin aquifers. "We will compare our PETRA physical-availability estimates with the state's SB 5 legal computations to see where physical and legal water estimates diverge," Fronczak said.

Fronczak described preliminary findings that the Arapahoe aquifer is "the workhorse" in much of the county's Denver Basin exposures, while the Fox Hills unit appears less productive in several mapped areas. He said the team is also preparing water-level trend hydrographs using USGS and DWR data and will recommend additional monitoring sites.

Commissioners and staff pressed for clarity about how the analysis will be used. Harold Snathals (Water Commissioner) asked whether the team could provide interim materials so commission members can learn to use the interactive maps and data. "It'd be very helpful if we might even get some partial information as it comes together so we get used to actually working with the data," Snathals said. Don Langley (Water Commissioner) asked whether the PETRA work will include incorporated jurisdictions; the consultants said the physical analysis will cover the entire county but noted the county intends to be careful about comparing physical-availability results to municipal decrees.

Consultants gave technical thresholds used in the analysis: they flagged a PETRA resistivity threshold near 12 ohm-meters as a heuristic to identify sand packages likely to yield recoverable water, and they said some Fox Hills targets are roughly 2,000 feet deep in the county's far southeast. The team said it will subtract exempt (domestic) wells and pre-1973 protection cylinders from county unincorporated totals to avoid double-counting existing uses.

Staff and commissioners identified near-term policy questions to track as the technical work continues: whether to limit irrigated turf (nonfunctional ornamental grass) served by exempt or other wells in unincorporated Douglas County; whether commercial development should be allowed to rely on aquifer withdrawal where municipal service and tap connections are available; and whether changes to county guidance on tap fees or municipal connection incentives are warranted.

Timeline: consultants said the groundwater technical memorandum is expected in draft next year and the full master water-plan report is on a roughly one-year schedule. The commission asked staff to schedule work sessions and interim briefings as technical products become available.

The presentation included technical context on state legal frameworks. Fronczak referenced SB 5 (Senate Bill 5) as the basis for some state Denver Basin computations and described "deemed consent" treatments and pre-1973 cylinders used in adjudications. The consultants emphasized they will present both physical-availability numbers and state-legal computations for comparison.

Next steps: Forsgren and LRE Water will continue compiling survey returns, finalizing PETRA cross sections and producing water-level trend summaries. Staff will circulate interim materials and coordinate future briefings, including an education session on aquifer storage and recovery (ASR) being offered by Castle Rock staff later in July.

The commission did not take formal action on the consultants' report at the June 23 meeting; commissioners asked staff to track the policy questions and bring them back alongside the technical deliverables.