PLAQUEMINE - The Dow Chemical Co. is now on the hook to clean up a groundwater supply in the Plaquemine area after a state judge found that the company has contaminated the aquifer through its negligence.

At issue is the Upper Plaquemine Aquifer, a groundwater supply that has tested positive for the vinyl chloride carcinogen several times dating back to 1997, court records show.

In the class-action lawsuit filed on the behalf of several thousand landowners between Bayou Plaquemine and Dow’s Plaquemine facility, attorneys including Rob Marionneaux argued that Dow contaminated the area’s ground water through a series of chemical spills and leaks dating back 20 years.

“It’s one of the worst environmental disasters in Louisiana’s history,” Marionneaux said Friday.

At the conclusion of the 25 days of testimony in 18th Judicial District Court, state ad hoc Judge Jerome M. Winsberg ruled that Dow is responsible for cleaning up the “threat to public health.”

Dow has denied being the source of the contamination since it first became public in 2001.

On Friday, Dow spokeswoman Stacey Chiasson responded further in a statement saying the company “strongly disagrees” with the allegations.

“Dow will evaluate the court’s ruling further and will continue to vigorously defend the case,” Chiasson said.

Near the end of the two-page ruling issued late last month, the judge writes that the most feasible way to deal with the contamination is through a process called Monitored Natural Attenuation, or MNA.

MNA is a process where naturally occurring bacteria breaks down the vinyl chloride eventually mitigating the contaminant’s threat to public safety, court records show.

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While still denying culpability in the contamination, Chiasson said Dow is committed to being a good neighbor, and has worked with both state and federal agencies since 2004 in implementing the MNA process in the Plaquemine area.

Dow also has voluntarily installed 19 test wells in the area and has worked with the state to monitor vinyl chloride levels in the groundwater on a quarterly basis, she said.

“We’ve told this community from the beginning that we would be part of the solution no matter the source of contamination,” added Sharon Cole, Dow’s Louisiana operations site director.

“We understand that because of our technical expertise and long history of engagement, our community expects us to be part of the solution,” Cole said.

Cole further said that tests have shown that vinyl chloride levels have decreased and the area of contamination hasn’t expanded.

But Marionneaux disputed that claim Friday, saying other tests taken as recently as last year have shown the contamination is expanding south toward wells owned by the city of Plaquemine.

When the two sides meet in front of the judge next month to discuss how to proceed with the cleanup, Marionneaux said he plans to argue for a more aggressive monitoring approach suggested by the state.

Marionneaux said additional monitoring wells need to be installed and water samples should be tested on a monthly, and not quarterly, basis.

All parties involved need to focus on the long term, he said, because it could be several years before the contamination’s health effects are understood.