Middletown’s Department of Public Works disclosed a fluoride overfeed incident at the Lisonbee water treatment plant that occurred on Nov. 10 and was discovered in mid-December, the department told the Common Council.

"An operator inputted the wrong decimal point on the SCADA system, which caused the fluoride to overdose," Commissioner Twill said. He said the event involved chemical feed over a multi-hour period and that the chief operator did not receive an immediate report from the shift operator.

Twill said the city has conducted required testing and so far has "not detect[ed] any elevated level of fluoride into our distribution system," attributing that finding to routine entry- and distribution-point sampling. He said Albany and Orange County health departments are investigating in parallel with the city’s own review.

City officials described immediate operational changes meant to prevent a repeat. They temporarily stopped fluoride feed pending installation of controls; removed a larger chemical feed pump and installed a smaller pump limited to a modest maximum flow; added more alarming and stricter SCADA login controls that log users out after two minutes; and revised procedures so operators cannot change alarm set points without written direction from the chief operator.

Twill said the measures also include tighter checks on who can change SCADA settings and increased accountability through audit logs. He told the council, "So even if the operator makes a mistake... the chemical feed pump cannot pump much higher number than 12 gallons per day versus 7 gallons per day is what we need." The comment summarized the change to a lower-capacity pump intended to reduce the magnitude of any single human entry error.

City officials said they informed the Department of Health as soon as the issue was identified and have been coordinating calculations to verify the amount of fluoride fed and the timeframe. Twill said some earlier estimates of the quantity and rate are being re-evaluated as the city completes its calculations.

The council heard no evidence in the meeting that elevated fluoride reached customers; testing reported at the meeting found no detectable elevation in the distribution system. Officials framed the incident as a human error compounded by reporting breakdowns and described technical and procedural fixes intended to reduce both the chance of an error and the likelihood that an error would go unreported.

The next steps listed by the department are to complete the internal calculations of quantity and timing, share investigative findings with the Department of Health, and continue additional monitoring while the new controls remain in place.