Saint-Gobain Performance Plastics’ plant on Daniel Webster Highway in Merrimack is at the center of groundwater pollution concerns in the region.

MERRIMACK — State officials have set a date next month for a public hearing on a draft permit for the installation and operation of air pollution control equipment at Saint-Gobain Performance Plastics Corporation in Merrimack.

The public hearing will be held Tuesday, Nov. 5, at 6 p.m. in the all-purpose room at James Mastricola Upper Elementary School, 26 Baboosic Lake Road in Merrimack, officials with the state Department of Environmental Services said.

Following the conclusion of the hearing, DES staff are expected to provide an update on the Saint-Gobain site investigation and the response to assessing drinking water impacts relative to the new Per- and Polyfluoroalkyl Substances (PFAS) drinking water standards (MCLs) and Ambient Groundwater Quality Standards (AGQS).

Residents in the impacted communities of Bedford, Litchfield, Londonderry, Manchester and Merrimack are encouraged to attend the public hearing, officials said.

Earlier this month, DES officials required Saint-Gobain to investigate and apply for a permit to install air pollution controls on its local facility, which tests show continues to have small emissions of PFAS compounds, which could be contributing to the existing groundwater issues. Currently, there are areas surrounding the plant that have detected more than 70 parts per trillion of perfluorooctanoic acid in the groundwater.

Saint-Gobain has worked with NHDES over the past two years to perform a series of stack tests to evaluate its emissions.

PFOA contaminants were first discovered in two faucets at Saint-Gobain in 2016.

Two years later, as PFOA contamination spread in groundwater testing, DES reached a consent decree with Saint-Gobain to provide municipal water to properties with contaminated wells in Merrimack, Litchfield and Bedford.

In 2016, a few months after PFOA was discovered at two faucets at Saint-Gobain, the plant made improvements to one of its smokestacks in an effort to decrease the amount of residual contaminants being emitted.

PFOA (perfluorooctanoic acid) and PFNA (perfluorononanoic acid) are among a group of chemicals known as perfluorinated alkylated substances (PFAS), widely used in industries making coatings, paints and other products. They do not break down in the environment.

Earlier this year, Saint-Gobain began piloting a treatment system for its air emissions at the facility, which was also designed to determine whether next-generation compounds were exiting through the plant’s smokestacks.

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