RENSSELAER – City public works and water employees went door to door Wednesday and Thursday to notify residents that the city’s drinking water exceeded the state and federal contamination levels for trihalomethanes.

The maximum level for trihalomethanes is 80 parts per billion. The contaminant tested at 85.435 ppb in a running annual average at one test location and 81.275 PPB at a second location.

Trihaolmethanes are a group of chemicals that include cholorform, bromoform, bromodichloromethane and chlorodibromomethane. They can form in water treated with chlorine, which reacts with acids from decomposing vegetation such as leaves or plants. Long-term exposure to the chemicals may cause cancer and other health maladies.

The city of Rensselaer's contamination level, which is based on the average through the year, was caused by Troy performing maintenance work earlier this year on its pipeline from the Tomhannock Reservoir, said Rich Elder, Rensselaer County’s environmental health director.

Rensselaer and the Saratoga County town of Halfmoon were affected by the maintenance work at the time when their quarterly tests for trihalomethanes occurred, Elder said. When those figures were averaged with succeeding quarterly test, the levels exceeded 80 ppb.

Troy sells water to Rensselaer, Halfmoon and other communities. Some residents in North Greenbush and East Greenbush also received the notices since they are tied into the Rensselaer water supply.

Mayor Daniel Dwyer said the city is alerting residents by going door to door as a cautionary measure. He said the city wanted to ensure that tenants were notified instead of the notices just being mailed to landlords. He said the city is well aware of public concerns about drinking water contamination, especially as a result of PFOA issues in Hoosick Falls.

Elder said the county is working with Troy and the state to improve treatment options to avoid future trihalomethane contamination.