SANDY — A state-required report documenting the health impacts of an accidental release of fluoride concentrate in Sandy said there were 239 cases of human exposure in which people experienced gastrointestinal symptoms such as vomiting and headaches.

That number is substantially higher than early reports of the Feb. 5 incident, which sent undiluted hydrofluorosilicic acid from a malfunctioning pump into part of the city's drinking water system, affecting 1,500 households, schools and businesses.

The concentrate in its undiluted form is classified as a hazardous, poisonous material that, while it contains fluoride, also contains arsenic, lead, copper, manganese, iron and aluminum. It is a byproduct from phosphate mining operations.

We have taken several steps to ensure that this kind of event can never happen again. – Evelyn Everton, Sandy's deputy mayor

Fluoride was detected at 40 times the federal limit after the release, and two weeks of free blood testing for lead showed one person with elevated levels, according to Salt Lake County health officials.

The release happened as a result of a power surge during a snowstorm.

Evelyn Everton, Sandy's deputy mayor, said the concentrate was stored in a well house, with some of the substance hooked up to a pump injector that had not been in use since 2016.

Everton said city officials believe a contractor may have left the pump on and the surge triggered it to release the concentrate that entered the system. By the next day people started reporting foul-tasting water and physical symptoms.

The city flushed its system and advised impacted residents to do the same. So far, Everton said the city has reimbursed affected households $2,600 for the water use.

At the request of the city, Parsons Behle & Latimer is doing an independent investigation on the city's operational and regulatory response to the event, which prompted the Utah Division of Drinking Water to issue a trio of violations in an administrative order.

That document, on file with the U.S. Environmental Protection Agency, includes violations for exceeding the fluoride level and not meeting public notification requirements. The city can appeal.

In the aftermath of the event, the city's director of public utilities, Tom Ward, was placed on administrative leave. Everton says he remains on leave pending the outcome of the independent investigation.

The city, she added, addressed the issues with the well houses.

"We have taken several steps to ensure that this kind of event can never happen again," she said, including unplugging all fluoride pumps not in use from a power source and closing the valves on discharge lines when the wells are not operational.

The city has 11 fluoride injectors.

In the initial aftermath of the release, city officials thought the area of contamination was confined to 50 homes and did door to door announcements to warn people. However, the area expanded twice as more people continued to report symptoms well after the release.

Utah Poison Control records contained in the state summary show it handled 316 cases possibly linked to the fluoride overfeed, with 163 of those cases followed to a known outcome.

Salt Lake County health records in that same report say 16 households reported symptoms impacting 40 people. The city of Sandy itself reported 11 known cases.

Officials say many of the entities' records could include duplicate cases.

Marie Owens, director of the Utah Division of Drinking Water, said her staff's analysis puts the number at 239 potential human exposure cases.

The city has been reimbursing residents for any medical claims associated with the incident, Everton said.