Rosemount outlines options to address ‘gross alpha’ exceedance in drinking water; council decision targeted for 2026

The City of Rosemount hosted a public information session on water quality after residents received a mailed notice about elevated “gross alpha” readings. Lee Stafle, Rosemount communications manager, opened the meeting and said the city published the annual water quality report online and will issue quarterly public notices while the violation remains.

Sam Swanson, a compliance engineer with the Minnesota Department of Health’s drinking water protection program, said gross alpha is measured as picoCuries per liter and that the radionuclide running annual average for Rosemount’s sampled wells reached 16 pCi/L — above the federal MCL of 15 pCi/L. “So we issued the violation as is required by the Safe Drinking Water Act and Rosemount issued that first public notice within 30 days,” Swanson said. He told residents the radionuclide rule has been in place since 2004 and that the change was caused by shifting groundwater conditions, not a regulatory change.

Nick Edgar, Rosemount public works director, described the system infrastructure: the city draws from the Jordan aquifer, operates nine wells (eight active), and distributes water through roughly 166 miles of pipe. He said the city has already taken operational steps — sequencing wells so well 8 is last to turn on — and is preparing an engineering and financial matrix of options for council consideration.

Chris Larson of Short Elliott Hendrickson summarized technical options the city is evaluating: temporarily minimizing use of high‑alpha wells (or making them emergency-only), blending water from adjacent wells (for example, piping and controlled mixing between well 8 and well 9, about 2,000 feet apart), or building a centralized treatment plant to remove radionuclides and radium. Larson noted tradeoffs: controlled blending and point‑of‑treatment systems provide predictable results, but a treatment plant would require new trunk mains and likely take multiple construction seasons; it would also treat only the wells tied into that facility unless expanded.

Valerie Nupel of Dakota County’s Groundwater Protection Unit said the county does not regulate municipal sampling or treatment but supports private well owners with testing resources and maintains long‑term groundwater monitoring datasets and an interactive dashboard of private‑well data. Chris Gosnak from the Minnesota Pollution Control Agency urged residents to use MPCA’s online tools to assess contamination history and emphasized that confirming and tracing a contaminant’s source can be a multiyear effort.

Brent (DNR), a water resources planner with the Minnesota Department of Natural Resources, explained appropriation permits and said Rosemount currently operates under an authorization of about 1.183 billion gallons per year and is seeking up to 1.35 billion gallons. He described DNR review priorities — sustainability, monitoring requirements and protections for domestic wells — and said the permit amendment review is underway.

In a panel Q&A, MDH staff said radionuclide testing follows EPA‑specified laboratory methods and is inherently time‑consuming; the agency’s compliance approach relies on a running annual average rather than single samples. The city confirmed well 7 has been placed on emergency backup status and is not used for regular pumping; emergency wells are not routinely sampled for chronic contaminants but are tested annually for acute contaminants like nitrate. On the question of system blending, city and state officials said uncontrolled blending in the distribution system is not an approved controlled remedy, and the city is focusing on point‑of‑source solutions.

Nick Edgar addressed concerns about industrial demand after attendees asked about a planned Meta site. He said a city agreement would allow up to 100,000 gallons at peak use for that site, with typical daily use expected in the 25,000–35,000 gallon range, which the city characterized as small relative to the system’s authorized capacity.

Next steps: city staff will complete a financial analysis of options (capital and operational costs and potential utility rate impacts), finalize a recommended approach and present options to the Rosemount City Council with the goal of a decision in 2026 and potential design or construction beginning in 2027.