Climate change will stress sewer systems
By Jeff Kart
Bay City Times
Published April 6, 2007
Climate change is expected to drive more harmful sewage into the Great Lakes unless officials build extra capacity into wastewater treatment systems, a federal study says.
But Michigan communities in the Saginaw Bay area and elsewhere aren't accounting for climate change when they go about constructing and upgrading wastewater plants that are expected to last far into the future.
State Department of Environmental Quality leaders will be examining a draft ''screening assessment'' released for comment last month by the U.S. Environmental Protection Agency.
But for now, state standards for wastewater treatment systems are based on past precipitation events, said DEQ engineer Thomas Knueve in Lansing.
The EPA study says standards also should represent predictions of future conditions, including more intense rain events forecasted for the Great Lakes region in coming decades.
Systems that don't account for a changing climate won't perform as expected, because the proportion of rainfall during storms is expected to increase, resulting in more stormwater runoff, EPA officials say.
At the same time, increased air temperatures, evaporation and other factors are expected to mean that wastewater discharged will be less diluted and more harmful to ecosystems.
Knueve said the study makes sense, and could affect state design standards in the future.
But more data is needed.
''It's hard to change the standards, saying you're going to change it based on future theory,'' he said. ''Until it happens, you can't really say 'I'm going to change my standard.'''
Sewer projects under way, almost completed or planned for construction soon in the area include upgrades in Tuscola County's Denmark Township; Gladwin County's Billings Township; Sebewaing, Bad Axe and Harbor Beach in Huron County; Oakley in Saginaw County; and Sandusky, Croswell, Marlette and Snover in Sanilac County, said Thomas McDowell, a DEQ engineer in Bay City.
None of those projects are being built to deal with climate change, state officials say.
During intense rain events, the capacity of combined sewer systems, like those in Bay City, Essexville and Saginaw, can be exceeded, resulting in the discharge of tens of millions of gallons of partially treated wastewater. On Thursday night, the Saginaw Wastewater Treatment Plant reported an overflow of almost 83 million gallons of partially treated sewage into the Saginaw River.
Knueve said the federal report will have more meaning when it's finalized. For now, it's a draft, developed by the EPA's National Center for Environmental Assessment.
Based on that draft, Knueve figures sewer systems would have to be designed with 10-40 percent extra capacity to account for future climate change.
''If you're designing for a 4-inch storm over a 24-hour period, in actuality you should be designing for a 4.5-inch storm in the future,'' based on the EPA study, Knueve said.
Combined systems in Michigan are designed to handle 1.43 inches of rain in an hour, which has a 10 percent chance of occurring every year.
Separated sewer systems, like the Bay County Wastewater Treatment Plant, which serves local townships, are designed to handle 3.56 inches of rain in a day, which has a 4 percent chance of occurring every year.
McDowell said design standards are driven in part to balance public health risks with costs.
''You could design for a 100-year storm, but you know how big those basins and how expense that would be?'' he said.
More information on the assessment is available online at www.epa.gov/ncea.
- Jeff Kart covers the environment and politics for The Times. He can be reached at 894-9639 or by e-mail at firstname.lastname@example.org.