NEW ORLEANS (AP) — A major manufacturer of synthetic rubber, Firestone Polymers LLC, has agreed to pay $4 million in fines and an environmental project and make numerous improvements to settle a long list of state and federal air pollution complaints at its plant in southwest Louisiana.

The plant in Sulphur was "Louisiana’s highest emitter of three types of hazardous air pollutants,” violating the Clean Air Act, David Gray, regional administrator of the Environmental Protection Agency, said in a news release Thursday.

The plant illegally emitted thousands of tons of pollutants including nitrogen oxides, carbon monoxide, volatile organic compounds and more than a dozen other substances and chemicals, according to the 127-page federal complaint against the plant near Lake Charles.

Findings of a yearslong federal investigation were made public Thursday in the complaint and the proposed settlement, which is now subject to a 30-day public comment period and final court approval.

The company also was recently accused of polluting nearby waterways. Firestone and eight other companies agreed in April to pay $5.5 million in Superfund cleanup costs for the Calcasieu Estuary, covering more than 19 square miles (49 square kilometers) that include bayous, lakes and a stretch of the Calcasieu River.

Neither consent decree admits any violations or liability.

The new agreement calls for Firestone to pay $3.35 million in fines — nearly $2.1 million to the U.S. government and more than $1.25 million to the Louisiana Department of Environmental Quality. The company also will pay the department $654,125 to improve and replace air monitoring equipment at sites around southwest Louisiana or to buy field monitoring equipment for the department's southwest region as a “beneficial environmental project.”

“Firestone is dedicated to creating a safe working environment for our employees and working toward a sustainable society for the communities we serve,” said a statement sent Friday by Steve Kinkade, a spokesman at Firestone's parent company, Bridgestone Americas Inc., of Nashville, Tennessee.

Although the documents were filed Thursday in U.S. District Court in Lake Charles, the agreement notes that some improvements were made as far back as 2019. That was after Firestone was notified of violations but before the agreement was reached, the news release said.

One piece of equipment to reduce emissions was operating in March 2019, Kinkade said.

The company also reduced concentrations of a solvent and increased inspections and tests of heat exchangers during negotiations, the Justice Department said.

Since 2017, “Firestone Polymers has reduced facility-wide volatile organic compound (VOC) emissions by approximately 98% and hazardous air pollutants by approximately 97%,” Kinkade said.

The Justice Department said Firestone must still meet emissions limits and operating and maintenance requirements, install equipment controls, limit hazardous air pollutants from facility dryers, inspect heat exchangers, install controls and monitors on covered flares, and install flaring instrumentation and monitoring systems.

“Businesses such as Firestone Polymers have a sacred obligation to protect Louisiana’s environment and to use our natural resources wisely,” Acting U.S. Attorney Alexander C. Van Hook said Thursday. “This settlement sends a clear message that those who don’t honor this obligation will be held accountable.”

The earlier consent decree did not say how the nine companies — including two Bridgestone companies related to Firestone Polymers — are to divide the $5.5 million Superfund payment. The federal complaint said the government spent more than $13 million to clean up the area.

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