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Tuesday, September 30, 2014 |  Madison, WI: 44.0° F  Overcast
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Stormwater runoff challenge looms
Regulators mandate major reductions over the next few years
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A soon-to-be-installed catch basin.
A soon-to-be-installed catch basin.
Credit:Mary Langenfeld

Greg Fries feels like he's gotten stuck cleaning up somebody else's mess. Much of the work he's doing to improve stormwater quality in Madison owes to infrastructure put in place decades ago with little consideration to water quality.

"We're figuring out how to fix a problem from the 1800s, when we were dumping sewage in the lakes," says Fries, a principal engineer with the city's engineering division who works extensively with stormwater issues. "The topic of stormwater treatment didn't come until the early 1970s. Up until then, the only thing we worried about stormwater was getting it off the property as quickly as possible."

Under regulations by the Environmental Protection Agency and the Department of Natural Resources, cities must reduce their stormwater pollution by 20% of total volume by Oct. 1, 2008, and 40% by 2013.

"Everything washed off from agricultural and urban surfaces [is] going straight into our waterways, and we would like to reverse that trend by any means that is effective," says Roger Bannerman, a DNR water resources management specialist. "[Treating] stormwater is definitely going to improve the situation. There are so many sources of pollutants, if we keep controlling them the lakes have to get better."

Driven by these deadlines, the city of Madison has enacted as many controlling measures as possible. Already, it has surpassed the 2008 threshold, but additional measures will be needed to meet the standards for 2013.

One main strategy employed by the city is the use of standard catch basins and commercial units that swirl water out while allowing sediments to settle to the bottom. According to Fries, roughly 30% of the total stormwater output currently flows through these devices.

The city of Madison has installed more than half a dozen of the larger devices in the last few years and has plans to add more. But while the devices certainly make for cleaner stormwater, the per-unit price ranges from $25,000 to $100,000, not including installation costs that usually total about $10,000. Because of changing technology, it is difficult to say how many more must be installed by 2013.

Moreover, the devices compete for the underground space taken up by water main, sanitary sewers, gas and electric, transmission lines, and downtown steam tunnels that run from power plants to the university and government buildings.

"Storm sewers are not the only devices underground," Fries says. "[Catch basins] are typically eight feet in diameter, and the smaller, narrower downtown streets are 28 feet curb to curb.... Trying to fit an eight-foot structure in the ground can be really difficult."

What most people consider pollution in lakes - cigarette butts, aluminum cans and other assorted debris - is not even regulated by the DNR. The regulatory standards refer to sediment that is less than 1/100th of an inch in diameter.

These particles, known as total suspended solids, are so small that it is difficult to remove them from urban stormwater discharges. Water flows quickly after rainstorms, and the abundance of concrete does not allow sediments to settle out before washing into lakes.

In Madison, an estimated 7.9 million pounds of total suspended solids are generated each year, of which 5.6 million pounds end up in the water supply. That means the city is now effectively removing about 30% of the total.

Pollution sources include construction-site erosion, runoff from streets and parking lots, and discharge from industrial and sewage treatment plants. Washed along with these urban pollutants is runoff from agricultural areas and suburban neighborhoods. These often contain fertilizers that promote the excessive algae growth in lakes that Madison has been battling for decades.

Like other cities, Madison is adopting an integrated approach. Some practices seek to control pollutants in water; some help reduce the volume of water that runs off; and some slow the rate at which stormwater flows back into waterways after large storms.

One of the most effective strategies is installing rain gardens, which can be done by ordinary citizens. Rain gardens use certain kinds of plantings to increase the amount of rainwater that gets absorbed into the ground. This keeps runoff and attendant pollutants from entering the stormwater system.

"Prevention is the way to go, in my opinion," says Bannerman. "But if we can't use prevention, we have to put all these devices in place."

Besides catch basins, the city has since the 1970s used retention ponds and detention basins on new developments. They serve as a type of dry bathtub that fills up during a storm event, to decrease flooding. The technology was improved in the '80s, when retention-based permanent ponds became more efficient at settling out smaller particles.

Fries says about 70% of all stormwater in Madison receives some level of treatment. But current technology can only remove a fraction of total suspended solids. That will make it difficult for the city to meet the mandatory reduction thresholds.

"Statewide, there are lots of cities with core downtown areas that will have a problem meeting 40% reduction [by 2013]," says Fries. "It is a problem for any areas built before the 1940s."

Fries suspects meeting the 2013 goal will require "a new program of some type; to be honest we are not sure what this program would be. It's unclear how many municipalities will be able to meet that goal statewide."

Originally, the city of Madison hoped it could achieve much of the required reductions by stepping up its regimen of street sweeping. But a study released this March conducted by the city, DNR and U.S. Geological Survey proved otherwise.

According to Fries, the study found that only 1% to 6% of total suspended solids were being removed with this method, far less than the hoped-for 10% to 15%. This leaves the city of Madison with an additional burden to reach the 40% requirement.

"From a municipality standpoint," says Fries, "street sweeping is expensive, and we don't get significant credit for it from the DNR; but we still have to do it." Now the city realizes it must add other approaches and explore new technologies. And it must do so at possibly considerable expense, with only five budget cycles to go before 2013.

"It's going to be a long process to get them all implemented," says R.J. Waschbusch of the U.S. Geological Survey, who has conducted numerous studies in Madison. "At this point there is no magic bullet. At this point you can only build on things and chip away at it."

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