CONCORD — A judge has temporarily stopped the state from implementing new regulations on groundwater contamination.

In his ruling, Merrimack County Superior Court Judge Richard B. McNamara wrote that it was likely that the Department of Environmental Services had not conducted an “adequate cost-benefit analysis” when the department decided to regulate chemicals known as PFOS, PFOA, PFHxS and PFNA.

The state’s earlier guideline of 70 parts per trillion standard for perfluorooctanoic acid was reduced to 12 ppt. A level of 38 ppt had been proposed.Communities throughout New Hampshire are grappling to understand how much it will cost to comply with new drinking water quality standards.

On Sept. 30, Plymouth Village Water and Sewer District, Resource Management Inc., Charles G. Hansen and 3M sued the Department of Environmental Services to block the new regulations, which had been scheduled to take effect that day.The strict standards made New Hampshire the first state to require routine testing and treatment for the four chemicals in water systems, landfills and wastewater plants.

The plaintiffs argued that the department did not allow enough notice for public input on the standards, and that they constituted an unfunded mandate.McNamara wrote that the state law prohibiting unfunded mandates likely does not apply to any of the plaintiffs, and that the department provided years of notice that it intended to make rules around PFOS and the other chemicals.

But, McNamara wrote, the Department of Environmental Services likely had not performed a cost-benefit analysis as a 2018 state law required of all new regulations.

The department’s cost-benefit analysis seemed scanty to the plaintiffs, especially when compared with the U.S. Environmental Protection Agency’s standards for preparing cost-benefit analyses.

The higher standards the department wanted to implement would result in much higher costs, the plaintiffs said, between 27 and 35 times higher than the lower standards the department first suggested in January.

DES did not cite any scientific research to justify the higher standards, McNamara wrote.McNamara ruled Tuesday to stop the new regulations from being enacted until the department performs a more robust cost-benefit analysis. The order is to take effect on Dec. 31.

By Josie Albertson-Grove New Hampshire Union Leader