In an Aug. 5 consent decree signed with regulators and environmentalists, the Metropolitan St. Louis Sewer District has agreed to set a schedule for $4.7 billion of upgrades to its sewers and treatment plants over the next 23 years.

Under the pact, the Metropolitan St. Louis Sewer District (MSD) will be required to install a variety of pollution controls, including construction of three large storage tunnels from about two miles to nine miles in length, and expansion of capacity at two treatment plants. The settlement was signed with the U.S. Environmental Protection Agency, the state of Missouri and the Missouri Coalition of the Environment Foundation. It is the result of a mediation process that began in 2008, says an MSD spokesman.

MSD says it already spent $2.3 billion over the past two decades to eliminate more than 300 sewer overflows. These controls, plus new ones under the consent decree, will reduce by nearly 13 billion gallons per year the volume of sewer overflows into waterways, officials say.

By the end of 2012, MSD has agreed to remove 50 of nearly 200 overflow discharge points. In 2013, it will submit a sanitary-sewer master plan, including system modeling and analysis. The district also agreed to cut 85% of its overflow outfalls by 2023 and the rest by 2033.

The consent decree also stipulates that MSD spend $230 milion to alleviate flooding to reduce stresses on the system during rain events and sewage flow into the Mississippi River. Further, it will invest at least $100 million in large-scale green infrastructure programs and $30 million on sewer-pipe replacement in minority communities in St. Louis. The district will pay a $1.2-million civil penalty, too. The spokesman did not say when project bidding would start.

The settlement resolves litigation brought by the federal government in 2007 alleging that, on at least 7,000 occasions between 2001 and 2005, failures in MSD's sewer system resulted in overflows of raw sewage into homes, yards, public parks, streets and playgrounds. The settlement is the latest in a series EPA efforts to reduce flows of raw sewage and contaminated stormwater. “This agreement will bring jobs and long-term economic investments while significantly improving the environment,” says EPA regional administrator Karl Brooks.

In a statement, MSD said, “There has never been any question about the need for continued work to upgrade and modernize the nation's fourth-largest sewer system. The true question is how quickly this work is completed, which is the driver behind continued increases in monthly sewer bills.” The settlement is subject to a 30-day public-comment period and court approval.