Leaky sewer pipes cause growing problem

By Kate Golden
Wisconsin Center for Investigative Journalism

A Milwaukee scientist who has found sewage migrating from old pipes through soil and into the storm-water lines that drain to lakes or streams says the problem is likely to elsewhere.

“In any urban area, this is going to be an issue,” said Sandra McLellan, professor and senior scientist at the University of Wisconsin-Milwaukee’s School of Freshwater Sciences.

From 2008 to 2012, McLellan and colleagues from her laboratory analyzed more than 1,300 water samples from storm-water outfalls in six Milwaukee-area watersheds, looking for a bacterium that indicates the presence of human sewage. They found the marker in every watershed.

In the Menomonee River watershed alone, more than half of the outfalls were chronically contaminated with sewage.

The findings indicate that “stormwater inputs continue to create a public health risk at these rivers and their tributaries, and by extension, to Lake Michigan and local beaches,” according to a draft of their report, which was paid for in part by the Milwaukee Metropolitan Sewerage District and the Wisconsin Department of Natural Resources.

The amount of sewage may be substantial. Early work in the most contaminated areas of the Menomonee River found that storm water from nearly half of the investigated outfalls was composed of at least one-quarter sewage.

McLellan said she has seen outfall samples that resembled pure sewage.

Combined sewer and storm-water pipe systems long have been known to contaminate water bodies. But McLellan said she has focused on parts of Milwaukee where the pipes are separate, as they are in Madison.

Sandra McLellan, professor and senior scientist at the University of Wisconsin-Milwaukee’s School of Freshwater Sciences, samples water in June off the school’s dock wall in the inner harbor of Milwaukee. She has found evidence of sewage migrating from old pipes through soil and into storm-water lines. (Photo courtesy of Sandra McLellan)

She said inland lakes such as Madison’s may be more sensitive to the contamination than Lake Michigan, which more easily can dilute pollution.

The U.S. Environmental Protection Agency has acknowledged it could be a problem nationwide.

But the idea is new that the pathway from sewer pipes to storm drains might be a significant source of contamination even in areas with separate systems.

Whether it is happening in Madison is unknown, said Trina McMahon, a University of Wisconsin-Madison professor of civil engineering who studies the area’s Yahara lakes. Three years ago, when she was on a multiagency committee considering how to improve the Yahara lakes’ beaches, she said, she was not concerned about the cross-contamination.

“I was a skeptic about the (human) bacteria or pathogens being in the storm water,” she said. “But the work coming out of UW-Milwaukee has really changed my mind on that.”

Many pipes in Wisconsin and across much of the nation are crumbling. Of Madison’s 800 miles of publicly owned sewer pipes, the oldest are from the early 1900s and are made of clay.

Army Lt. Col. Chris Gellasch, while a graduate student at UW-Madison a decade ago, found human viruses in Madison’s groundwater, indicating that the sewer pipes were leaking. His project traced those viruses to deep groundwater aquifers from which drinking water is drawn.

He did, however, also find that major rainfalls correlated with a surge of effluent levels in sewer pipes to “suggest a connection between the two sewer systems,” he said.

Madison City Engineer Greg Fries said he knows how leaky the pipes are. In fact, water infiltrating them is a significant problem, which is why Madison is spending $1.3 million this year on an ongoing project to line the old sewer pipes with epoxy. It renders them about as good as new and costs far less than replacing them, Fries said. That project will continue for at least five years and will cover only the city-owned lines.

Fries agreed there is potential for a problem but is not convinced it is widespread in Madison. Sanitary sewer pipes are typically laid 10 feet deep, while storm-water pipes are around 4 feet.

The exception, he said, might be in areas such as the Isthmus, where the storm-water and sewer lines are in shallow groundwater.

McMahon, the UW-Madison professor, said more research could help determine which pipes are most in need of replacement or fixing.

“It would make sense,” she said, “to put some resources into trying to figure out just how big of a problem it is.”