Officials warn Great Western Reservoir needs major work; staff recommends 7% water‑rate increase and commercial tiers

Broomfield water officials told council on July 21 that Great Western Reservoir is suffering infrastructure degradation that could threaten the reuse water system that supplies parks, HOAs and other customers.

What staff reported Deputy director Mark Laurier described video inspections that show segments of the main outlet pipe beginning to pull apart and internal seals bulging; in the tow‑drain system staff identified mineral accretion that has restricted flow and at least one collapsed pipe partially clogged with rock. Laurier said those symptoms are warning signs that the systems are nearing the end of a serviceable life.

"Pipe segments are pulling apart, and there are these internal seals that we installed in the late nineties and early two thousands to help seal those joints. Those seals are starting to bulge," Laurier said, summarizing the engineering inspection findings.

Great Western is a critical part of the reuse system: staff said the reservoir provides about 70% of overall reuse demand in a typical year, storing winter wastewater‑derived effluent for summer irrigation use. Losing that storage would require substantial alternate supplies or system modifications.

Options and costs Staff presented three conceptual alternatives: • Selective repair: microtunneling to replace sections of outlet pipe and tow‑drain repairs. Lower direct cost but risks leaving older slope‑failure planes in place and could be additive in cost over time. Reservoir would likely be partially usable during some construction. • Full dam replacement: excavate and rebuild the dam to modern standards, replace all infrastructure; staff estimated a direct capital cost of about $48,000,000, with the reservoir offline for roughly two years and a 50+ year expected service life. • Decommissioning: remove the reservoir’s ability to store water (cheapest direct capital outlay), but impose significant indirect costs and require permanent alternative sources (examples under study include use of an owned gravel pit 'Hype Pit' on the South Platte, repurposing Sienna Reservoir, or increased potable‑water supplementation).

Laurier said selective repair costs were trending closer to full replacement as the scope was refined, and that an incremental repair approach could leave unresolved slope stability risks that a full replacement would fix.

Financial and operational implications Staff emphasized that all three alternatives have financial consequences. Full replacement does not include the additional cost of temporary alternative supplies during a two‑year outage; decommissioning would require costly permanent replacements for lost reuse capacity. To manage enterprise funding needs and backlog maintenance, the flow committee and finance staff recommended continuing the previously adopted five‑year rate plan and implementing a 7% water‑rate increase in 2027, a 4% increase in tap fees, and a new 4‑tier commercial rate structure to better align commercial consumption and revenue.

Water quality and conservation Water quality testing of the Big Thompson source showed no PFAS detections in sample results staff reported; the utilities lab renewed its certification July 1. The reuse program is under strain from high summer demand: staff sent letters to reuse customers asking for 20% reductions; parks and other large customers confirmed they would comply.

Next steps Staff will run additional modeling and present a more detailed package to council in September and is targeting a final recommendation in winter that will include costs, funding strategies and a proposed construction schedule if council approves a capital alternative. Councilmembers asked staff to include clearer cost allocations and to outline the operational approaches that would be used if the reservoir were taken offline for repairs.