Metro Detroit treatment plants released about 4.5 billion gallons of raw and partially treated sewage into local streams and rivers as a result of last week’s massive rainstorm, according to a preliminary report from the state Department of Environmental Quality.
Of the nearly 9.8 billion gallons of sewage released on Aug. 11, about 46 percent of it was raw sewage, sewage diluted by excess storm water or partially treated sewage, DEQ official Laura Verona said Friday.
“It was a very large event,” but not necessarily one of the region’s biggest, said Phil Argiroff, permit section chief of the DEQ’s Water Resources Division.
In late November 2011, Detroit’s sewer system alone released 9 billion gallons of raw and partially treated sewage, Argiroff said. And November 2011 was a particularly wet month, he said.
The 4.5 billion gallons of sewage would be the equivalent of submerging Detroit’s Belle Isle in about 14 feet of water.
The other 5.3 billion gallons of sewage or 54 percent of what was released on Aug. 11 was treated at local retention facilities and “helped to protect the public’s health,” Argiroff said.
The DEQ isn’t sure when a final report will be ready. But Argiroff noted the department is still waiting to get solid number on released sewage from the George W. Kuhn Retention Basin in Madison Heights, which is a large facility in Oakland County.
And Detroit water officials are re-evaluating some of their discharge numbers, he said.
The preliminary numbers underscore how badly the local infrastructure in Wayne, Oakland and Macomb counties was overwhelmed when 3½ to 6 inches of rain fell across the region in just a few hours on Aug. 11. High volumes of rainfall led to combined sewer and retention basin overflows.
Combined sewer overflows occur in areas where sanitary sewer lines are connected with storm water lines. During heavy rains, the amount of water in the system overwhelms what treatment plants can handle, and untreated sewage can be discharged into local streams and rivers and mix with excess storm water.
This is what happened to nearly 3 billion gallons of sewage from facilities in Detroit, Southgate, Dearborn, Inkster, Dearborn Heights, Redford Township and Port Huron.
Retention basins, designed to hold the excess water during those events, can also overflow.
Thirty-seven communities in the four-county area that includes St. Clair County have combined or partially combined systems, according to the Department of Environmental Quality.
For years, local governments have — to varying levels of success — worked to improve their capacity for handling extreme weather events. Some have separated their lines, while others have constructed new retention basins to prevent sewage from being released
But it’s clear more could be done. On Monday, with Gov. Rick Snyder on hand, Warren Mayor Jim Fouts blamed politics for keeping a new interceptor project from being completed that would have alleviated some of sewer backup the community experienced as a result of the flooding.
“There’s work that already has been done,” Argiroff said, “but there is more work to be done.”
Sewage released via overflows impacts not only local rivers and streams, but Lake Erie and Lake St. Clair as well. Beaches close when E.coli contamination turns up in water samples and advisories go out when fish become contaminated.
Phosphorus contained in the waste has become particularly problematic for Lake Erie. The nutrient, which is also found in fertilizer runoff, helps create the massive algae blooms that have plagued the lake’s western basin for a decade.
So far, thanks to cooler water temperatures this summer, Lake Erie has not seen the spike in algae some had anticipated following the Aug. 11 storm.
“I think it is a function of water temperature, which is mid- to low-70s,” said Sandy Bihn, executive director of the Western Lake Erie Waterkeeper Association, a Toledo-based non-profit dedicated to protecting the lake. “And there is no open lake dumping yet churning things up.”