Wastewater overflows from sewer systems into Maryland's rivers and streams have fallen to their lowest point since 2001, thanks in large part to this year's drought.
A total 24.2 million gallons of untreated sewage had spewed from sanitary sewer systems through September, according to a Capital News Service analysis of Maryland Department of the Environment data. That is 79 percent below the January-to-September average going back to 2001, the year the MDE began providing data on overflows.
The worst year in terms of sewage spills was 2003, when 352.4 million gallons of effluent had burst from sewers by September, largely because of Tropical Storm Isabel. The smallest amount was in another drought year, 2001, which saw 16.1 million gallons.
The CNS analysis focused on sanitary sewer systems, which carry storm water and sewage in separate pipes. It does not include spills from combined sewer systems, an older design that carries sewage and rainwater in the same pipe and easily overflows during heavy rainfall and snowmelt.
The analysis compares each year's January-to-September total because 2007 data is available only through September.
Overflows - sometimes involving millions of gallons of sewage in an incident - pose environmental and health risks, including the release of pollutants and pathogens into waterways. They are also a violation of the federal Clean Water Act.
"There should be no overflows," said Ed Merrifield, director of the Potomac Riverkeeper organization. "The sewage should be going from the toilet or the sink to the sewage treatment plant. It's supposed to be that simple."
Overflows from a sanitary sewer system generally occur when rainwater leaks into sewage pipes that cannot handle the increased flow because of roots, grease and other debris blocking the pipe.
"We get overflow when there's rain. We get too much rainwater in the sewer," said Mark Yoder, the utilities division chief for the Allegany County Department of Public Works.
Spills caused by rain are "relatively clear," Yoder said. "It's mainly rainwater that flows out," not raw sewage.
State and local officials said the drought that hit much of Maryland this year has put less stress on aging sewer pipes, resulting in fewer spilled gallons.
In the meantime, Allegany County and Baltimore City, which together accounted for 60 percent of all sanitary overflow from 2001 to 2006, are under consent decrees to fix their systems.
