Seattle and King County, Wash., will invest in multiyear sewage and combined stormwater collection upgrades, including piping and treatment, under agreements that were reached on April 16 with the U.S. Environmental Protection Agency and the Washington State Dept. of Ecology.

The agreements will substantially reduce the amount of sewage and contaminated stormwater entering Puget Sound and pave the way for greater use of green infrastructure projects.

Under its agreement, Seattle will develop and implement a long-term control plan—at an estimated cost of $500 million—to address its combined sewer overflows. According to King County, the improvements and upgrades associated with its long-term CSO plan are expected to cost $711 million in 2010 dollars.

The consent decrees were both structured to allow for an integrated planning approach, which gives the city and county the ability to prioritize projects based on the anticipated water-quality benefit.

"These are the first consent decrees to date that provide this type of flexibility," says Andrew Lee, capital portfolio manager with Seattle Public Utilities. "We can propose to do stormwater projects up front and delay implementation of CSO projects to a later date," he notes.

Rob Grandinetti, EPA compliance officer, says the integrated framework—an approach advocated by the Conference of Mayors and some water groups—allows the city and county the opportunity to address their biggest pollution sources first. "Green infrastructure will play a significant part toward improving water quality and controlling overflows," he says. "We expect to have almost 99% of CSOs eliminated by 2030."

Seattle currently is evaluating projects and will decide within the next year which projects will move forward.

King County has identified nine projects to control CSOs. Submission of plans for the first county project is scheduled for delivery by December 2014, with bidding to be completed by December 2016.