Sudbury health officials keep Atkinson Pool closed after high combined-chlorine readings; UV, HVAC and draining considered

Sudbury health officials said the Atkinson natatorium (lap pool) will remain closed while town staff investigate persistently elevated combined-chlorine levels, known as chloramines, that can harm indoor-air quality and irritate swimmers.

Vivian, Sudbury health director, told the Board of Health that an inspection during swim practice found the lap pool’s combined-chlorine reading at 0.6 parts per million on Jan. 8, above the state pool code standard of 0 to 0.2 parts per million. The town closed the natatorium that day and applied multiple “shock” treatments to the lap pool; those treatments reduced levels in the short term but did not bring the lap pool into sustained compliance, Vivian said.

The closure matters because chloramines — formed when free chlorine reacts with nitrogen-containing contaminants like sweat or urine — accumulate in indoor pools, worsen air quality near the deck and can cause eye, skin and respiratory irritation. Vivian said chloramines are denser than air and can linger near pool decks, “which is why when facilities put in those large commercial industrial fans on the pool deck, it really helped move the air.” She added that the dive well tested within standards after rebalancing but the lap pool remained elevated.

The town is pursuing several tracks simultaneously. Parks and Recreation and facilities staff are seeking competitive bids for secondary disinfection systems (UV or ozone), which can reduce chloramines, and an HVAC engineer has inspected the natatorium and is scheduled to return to determine whether the air-handling system needs rebalancing. Vivian said the natatorium’s current design locates supply and return on the same interior wall — a layout that can limit airflow across the space — and that an upcoming August renovation will install a new pool pack and permanent stratification fans but will not change the wall location of the supply/return lines.

Dennis Mononey, Sudbury Park and Recreation Department, said the town ordered a UV unit that is expected in roughly three to four weeks and that the pool operator is weighing whether to perform one more shock or to drain and refill the lap pool before UV installation. Mononey provided a size estimate for the lap pool — about 68,000 gallons — and noted the pool water level has fallen several inches because of an apparent ongoing leak.

Board members discussed reopening thresholds. The state code requires combined chlorine at or below 0.2 ppm for reopening; several board members, including Linda Huah Clayton, pressed for a more conservative target of 0 ppm to provide “wiggle room” before allowing heavy bather loads such as swim-team practices. The board did not take a formal vote on a reopening threshold; members recommended continuing concurrent work on UV, HVAC, additional testing and staffing with certified pool operators.

Committee members and staff emphasized monitoring and enforcement steps if the pool reopens. Vivian said Parks and Recreation has improved daily logs and purchased a more accurate test kit since the closure; board members said daily testing should continue and recommended ensuring a certified pool operator is present during peak-use shifts. Vivian also noted the operator must enforce pre-entry rinsing (showers) to reduce nitrogen-containing contaminants that form chloramines.

Board members discussed potential operational and environmental impacts from draining the pool, including frozen ground conditions in winter and downstream water handling; staff said any drawdown would be staged and dechlorinated before discharge.

The board directed staff to continue investigations, get HVAC rebalancing data from the engineer, obtain UV system specifications from the bidder, and return with updates. No formal reopening date was set; staff said any reopening would require verification testing by the health department to confirm compliance with the state pool code before issuing a permit to open.

Ending — Next steps and monitoring

Town staff said they will: (1) complete the HVAC engineer’s follow-up inspection and rebalancing; (2) finalize UV bid specifications and installation scheduling; (3) continue daily chemistry logs with the upgraded test kit; (4) evaluate whether to shock again or drain/refill ahead of UV installation; and (5) return to the Board with the HVAC report and lab results before the committee reconsiders reopening. Board members asked that staff consider reopening first to low bather-load public hours (daytime general public) as a phased approach only if verified levels remain in compliance.