The U.S. District Court in eastern Louisiana has ordered the U.S. Environmental Protection Agency to determine within six months whether to set new limits on nitrogen and phosphorus pollution that is causing large algae blooms throughout the Mississippi River basin, the Gulf of Mexico and other waters in the U.S.

A decision by the EPA to set numeric limits in states with tributaries that feed into the Mississippi River basin or the Gulf of Mexico that currently do not have such limits in place could have significant implications for engineering and construction firms that work in the wastewater sector. More stringent limits likely would mean more retrofits and upgrades at wastewater treatment plants, says Nathan Gardner-Andrews, general counsel for the National Association of Clean Water Agencies, which represents wastewater utilities. Those retrofits would come at great cost to the treatment plants, he adds. He says most states affecting the Mississippi River basin currently have narrative criteria, which are more flexible than specific numeric limits.

The case stems from a 2008 petition filed by the Mississippi Collaborative, a coalition of environmental groups, asking EPA to establish quantifiable standards and cleanup plans for nitrogen and phosphorus pollution contributing to the algae blooms. However, EPA denied the petition, although it did not say one way or another whether such action was necessary to comply with the Clean Water Act. The environmental groups filed a lawsuit to get EPA to answer directly whether some action was necessary under the CWA. On Sept. 20, the court agreed with the environmental groups. Kelly Foster, Waterkeeper Alliance senior attorney, says, "With this decision, we are hopeful that EPA will finally do what it has long known is necessary to address the Gulf dead zone."

According to a Justice Dept. spokesman, EPA is still reviewing the case.