In the suit, CLF contends the levels of nitrogen discharged into groundwater by the plant are too high, and that the nitrogen and other nutrients travel underground to nearby Lewis Bay, where the discharge has elevated nutrient levels that feed large algal blooms. The blooms degrade water quality, lower oxygen levels and harm plant and marine animal life.

If the foundation wins the lawsuit, the town’s wastewater plant would then be operated under a more rigorous federal permit under the Clean Water Act.

Christopher Kilian, director of CLF’s Clean Water and Healthy Forests initiative, said the town’s Comprehensive Wastewater Management Plan proposal to upgrade the plant lacks specificity on two key points. It does not specify how the plant will be modernized and it does not identify where two proposed discharge areas will be located or how much they will add to the volume of wastewater treated at the plant and discharged.

The plan should have already identified and permitted the two proposed additional discharge areas, he said, adding that the 30-year rollout of the wastewater plan is too slow.

“You can’t have a plan dragged out for 30 years with no specificity or commitment to real action,” he said. “That’s what we’re looking for, getting past empty promises and loopholes.”

One alleged loophole is the reliance on a state discharge permit that allows higher levels of nutrients on the assumption that nitrogen and other contaminants will be filtered out of the treated water on its trip to coastal water bodies. But Kilian said that is not happening and that groundwater is actually acting more like a pipe than a filter.

That direct connection from wastewater discharge to the ocean via groundwater was recently affirmed in a Supreme Court decision concerning discharge in Maui. It was the basis for two other successful CLF lawsuits in recent years at two resorts in Harwich.

The Wychmere Beach Club and the Wequassett Inn reached settlement agreements with CLF to reduce nitrogen levels flowing into marine water from their treatment plants as a result of the lawsuits

More:Wychmere, Wequassett resorts threat

More:Wequassett resort settles suit over wastewater violation

CLF is asking the court to rule that Barnstable is in violation of the Clean Water Act: This would trigger the requirement of afederal permit,which comes with stricter limits on nutrients and other contaminants.

“Clearly, a connection exists between the input of nutrients into groundwater and the effects on marine water bodies,” Andrew Gottlieb, executive director of the Association to Preserve Cape Cod, said. “But the real question is how to get it effectively remediated.”

He said he is worried that the implementation of the Barnstable wastewater cleanup plan could get tied up in court and delayed due to the CLF suit.

The real intent of the suit may be to prod Cape towns into speeding up the implementation of their own wastewater plans by taking on the county’s largest municipality, he said.

“I think they’re trying to get the attention of every town on Cape Cod, which isn’t a bad thing,” Gottlieb said.

Follow Doug Fraser on Twitter:@dougfrasercct