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Water Advisory Board — January 2026: Uranium in Chimney Hollow, Water Shortage Planning

ByLedger Updated on Community News, Weather Reading Time: 7 minutes

The January Water Advisory Board meeting covered status updates on water supply, drought outlooks, major capital projects, and policy priorities for the year ahead.

Staff and board members reviewed reservoir levels, recent repairs in the canyon, planned land acquisition around Union Reservoir, legislative guiding principles, and a notable water-quality challenge at Chimney Hollow.

Table of Contents

Where things stand: streamflows, reservoirs, and snowpack

Flows on St. Vrain Creek and the South Platte are well below long-term averages. Measured at the Longmont gauge that morning, St. Vrain flows were about 8.7 cubic feet per second versus a 125-year historic average near 14 cfs. Reservoir storage across the basin is roughly in line with last year but the snowpack is the real concern.

“The snowpack is not great for this time of year. It’s one of the worst years we’ve had in recorded history.”

Highlights:

  • Union Reservoir sat near 60 percent of a 30-year median (about 63 percent full by gauge).
  • Ralph Price Reservoir is closer to 90 percent of median and remains a bright spot.
  • Carter Lake is at about 130 percent of median and should be helpful entering the irrigation season.

The board noted variability and limited reliability in some snowpack reporting sites for the basin; staff are coordinating with NRCS and the district water commissioner to reconcile field measurements with published indices.

Water shortage planning and potential restrictions

With low snowpack and below-average projected flows, staff will evaluate the city’s Water Shortage and Supply Plan this spring. The expected timeline:

  1. Staff presents a detailed report to the board in April.
  2. Within a month or two, the report goes to city council for consideration.

A likely early step is moving to mild (voluntary) restrictions. Any shift to mandatory stages will depend on reservoir projections, inflows to Button Rock, and coordination with state water administrators.

Union Reservoir land acquisition: preserving future options

The city is recommending continued negotiations to purchase a nine-acre parcel north of Union Reservoir (referred to as Parcel W). The acquisition is part of a long-term strategy to preserve land needed for a possible future enlargement of Union Reservoir and to prevent development that would limit enlargement options.

Key details:

  • Parcel size: just over nine acres with one residence and outbuildings.
  • Estimated purchase price: roughly $1.0 to $1.1 million. City funding is programmed for the purchase.
  • Owner requests a typical three-month leaseback option to move after closing.

If enlargement were required and willing sellers could not be negotiated with, condemnation remains a last-resort option. For now, the acquisition is preventive: maintaining flexibility for future storage and pumpback options that make better use of existing water rights.

Wide view of a water advisory board meeting with attendees looking at a screen displaying a reservoir and parcel map

Policy: legislative principles and in‑stream flows

The board approved updated guiding principles for the 2026 legislative session, including a new principle to oppose legislation that would limit municipal funding and financing sources. Board members also discussed adding language to encourage and explore partnerships for in‑stream flows.

Points raised during discussion:

  • In‑stream flows can protect environmental values but may affect municipal water uses since retained water is not available for diversion.
  • Interim in‑stream flow rights have appropriation dates and are junior to existing municipal rights.
  • Staff will continue to monitor filings and bring any particularly significant water‑court or legislative actions to the board’s attention.

Capital projects: repairs, upgrades, and redundancy

Staff presented several infrastructure updates focused on reliability and redundancy rather than growth capacity alone. Highlights included canyon pipeline repairs, a major forebay rehabilitation, and long-term storage/tank planning.

Button Rock — Upper North St. Vrain pipeline

Remote sections of a 30-inch steel pipeline at Button Rock suffered serious damage. Repairs completed and planned included:

  • Large leak repair where a 30-inch section was pancaked by a boulder and washout.
  • Rebuilding access routes and a temporary culvert across city property for emergency maintenance.
  • Replacing eroded cover and installing timber or rock cribbing to stabilize the pipeline bench.

The challenges are logistical — access, steep benches, and remote terrain — which is why the city is working with the county to make emergency access permanent and meet fire standard clearances.

Nelson Flanders forebay — leak repair and relining

The forebay project was a critical unplanned repair. After removing the forebay from service, investigations revealed shallow bedrock on the north edge and limited separation between the liner and bedrock. The remedy included slush grouting and building a thicker clay liner in problem areas.

Facts:

  • Forebay provides roughly 30 million gallons of raw-water storage — about one day of peak summer demand.
  • The repair was a competitively bid, roughly $2 million project and is intended to stop seepage long term.
  • Staff expected to begin filling the forebay again as soon as dam office substantial completion is confirmed.

Montgomery tank replacement (near Highway 66)

The existing steel tank built in the 1960s is corroding and nearing the end of useful life. The new design moves the tank slightly northeast, increases usable capacity from about four to 6.4 million gallons, and adds a redundant pipeline connection to improve operational flexibility.

Design decisions responded to county and community input: the new tank will sit mostly below grade with a low-profile roof to minimize visual impacts and respect the historic Montgomery Farm setting. Construction is estimated at about three years out once permits and contracting proceed.

Chimney Hollow update: the uranium challenge

Chimney Hollow dam construction reached substantial completion in late 2025, but an unexpected water-quality issue emerged during a 2023 emergency discharge.

Tests revealed elevated uranium concentrations that are traceable to the granitic rock quarried for the dam embankment.

Important context:

  • The uranium content in the quarried rock is relatively low — roughly a thousand times less than typical low-grade ore — but some of that uranium exists in a soluble form that can affect reservoir water quality.
  • Northern Water and partners have identified mitigation options that span operational choices and potential treatment approaches.
  • No project water deliveries from Chimney Hollow will occur until a mitigation plan assures compliance with public-health standards.

Staff offered to invite Northern Water to present directly to the board in the coming months to explain mitigation strategies, system operations, and implications for supplemental water supplies such as Colorado-Big-Thompson deliveries.

Water rights diligence, rates, and funding

Running and defending municipal water rights is ongoing work. Staff file diligence cases in water court periodically to preserve conditional rights until they can be made absolute. In 2025 the city completed diligence filings on several rights; 2026 will focus on the Fairgrounds Reservoir diligence.

On rates: Council adopted a multi-year rate plan that included roughly a 9.8 percent adjustment beginning January 1. That three-year rate strategy funds existing bond obligations (including the city’s share of major projects) and supports maintenance and replacement of aging infrastructure. Work on a water master plan will feed the next rate discussion planned for 2027.

Conservation rebates moved in-house

Indoor water-efficiency rebates previously administered through Efficiency Works were brought in-house. Staff will operate the rebate program while collaborating with Northern Water and neighboring utilities on a regional rebate portal. Rebate payments will be applied as bill credits rather than mailed checks during the transition year.

What this means for customers and stakeholders

The city’s near-term focus is resilience: protecting supply during low inflows, stabilizing critical infrastructure, and ensuring water quality before bringing new storage online. Some key takeaways:

  • Conservation remains valuable; voluntary restrictions are likely before mandatory stages are considered.
  • Planned infrastructure work prioritizes redundancy and reliability over new capacity in the immediate term.
  • Major projects like Chimney Hollow and reservoir enlargements will continue to be managed with safety, regulation, and cost recovery in mind.

FAQ

Will Longmont implement watering restrictions this spring?

Staff will evaluate the Water Shortage and Supply Plan in April and present recommendations to the board and council. At minimum, mild voluntary restrictions are likely given current snowpack and flow projections. Mandatory stages would follow only if future projections and reservoir behavior warrant them.

Is Chimney Hollow safe to use now?

The dam construction is complete, but the reservoir is not being filled for project water because of uranium concentrations found in some quarried rock. Northern Water and partner agencies are developing mitigation and treatment options. No water deliveries will occur until mitigation ensures compliance with health standards.

Why is the city buying land near Union Reservoir?

Acquiring parcels at the reservoir boundary preserves future options for an eventual reservoir enlargement and pumpback infrastructure. Purchases are preventive: they prevent subdivision or development that would impede future water-storage projects.

How will recent rate increases be used?

The multi-year rate plan supports bond payments, major capital projects, increased maintenance, and replacement of aging distribution infrastructure. A water master plan will refine priorities and help determine future rate needs before the next formal rate review in 2027.

How do I apply for a water-efficiency rebate?

Rebates are currently processed internally. Applications will be reviewed by city staff and bill credits will replace mailed checks during the transition. Staff are working with Northern Water and neighboring cities on a regional rebate portal to simplify future participation.

Closing notes

This period emphasizes stewardship: managing limited supplies, repairing and modernizing critical infrastructure, and coordinating regionally on policy and operations. Expect continued updates through spring as the board and staff track snowpack, reservoir fills, project completion milestones, and any legislation that could affect municipal water funding or in‑stream flow policy.

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