U prof studies pollutants in runoff

Professor Bruce Wilson took runoff samples of a Bloomington marsh.

Alex Robinson

Retention Pond C in Bloomington, Minn. has, on occasion, overflowed with polluted water. Bioproducts and biosystems engineering professor Bruce Wilson is determined to help find out why.

The four-acre pond serves as a buffer between Long Meadow Lake and urban developments such as the Minneapolis-St. Paul International Airport, The Mall of America and the city of Bloomington. Or at least it’s supposed to.

The concept Bloomington officials had in mind for Pond C was to hold storm water runoff and filter out pollutants until the water was clean enough to flow harmlessly into Long Meadow Lake.

Home to many waterfowl and migratory bird species, the lake is a large spring-fed marshland and is part of the Minnesota Valley Wildlife Refuge.

Pond C does its job mostly, but large rain storms sometimes overflow it with runoff from impervious surfaces, like parking lots and roads. The polluted runoff then spills into Long Meadow Lake.

Wilson studied the watershed systems in 2005 and 2006 to find target areas that could be altered to reduce runoff.

He took runoff samples and measured the amounts of pollutants, such as magnesium, chloride and phosphorous. The pollutants most commonly come from car exhaust and lawn fertilizer, Wilson said.

If introduced to a wetland, the pollutants could kill small invertebrates, which are the main source of food for many types of waterfowl.

Last week Wilson wrapped up his study, but said the results didn’t describe the gravity of the situation.

“Water sheds are very complicated systems,” he said.

When Wilson was conducting his research, there were not many rainstorms that curved results, he said.

Wilson said if he had taken samples during a rainier time period, like the past few months, the amount of pollutants found would likely be much higher.

More extensive samples and more data would need to be gathered to better describe the situation, Wilson said.

University scientist Bradley Hansen, who worked with Wilson on the research project, said for all pollutants to be swept away from an area there has to be 1.5 to 2 inches of rain.

“We did get a lot of good data, but we didn’t get the big storm events,” Hansen said.

The city of Bloomington is planning to expand the size of Pond C so it can hold more storm water. Hypothetically, less water would then spill into the marsh.

Dave Warburton, a contaminants biologist from the U.S. Fish and Wildlife Service, said that while he’s glad the city is expanding the pond, pollutants from runoff should not be overlooked.

“The city wants to improve Pond C and we fully support that,” Warburton said. “We also want to make sure that that is not the only thing done to minimize storm water runoff.”

Todd Schmidt assisted Wilson with research in 2006 before graduating from the University last summer.

Schmidt said it’s important for the University to work with local cities and national agencies to help solve complex problems.

The project was more than just another experience to put on the résumé, Schmidt said.

“It wasn’t just a way to get my degree,” he said. “It was personally satisfying for me.”