While removing litter from the Cedar River this summer in Austin, volunteers came across a few spots that looked like motor oil in the water.

Part of the Jay C. Hormel Nature Center’s annual river cleanup, the volunteers found what looked like oil coming up from the river bottom just downstream from the Oakland Avenue East bridge. They told the Cedar River Watershed District, which had helped coordinate the cleanup. District staff contacted the Minnesota Pollution Control Agency, knowing that the oily areas were near the former Austin Gas Manufacturing Company site.

Though the gas plant is long gone, some contaminants from its activities – started more than a century ago – remain in the soil that slopes down to the Cedar River State Water Trail on the southwest side of the Oakland Avenue bridge. Given that these contaminants pose a potential risk to human health and the environment, it’s important to remove or contain them.

Since the cleanup volunteers’ findings, the site’s property owner has done additional testing to define the nature and extent of the contamination in the area, with more cleanup planned now, according to the MPCA. Extensive testing and cleanup dating back to 1991 already had occurred at the nearly 5-acre site that borders Oakland Avenue East and 4th Street Southeast.

“We’re really grateful for these volunteers and others who report areas of concern with our local waterways whether it’s while cleaning up litter or paddling the river,” said Tim Ruzek, CRWD’s outreach coordinator.

As of this winter, trail users along the Cedar River now might notice signs warning of potential contamination from the former gas manufacturing plant. The signs advise people to avoid contact with sediment or water along a short stretch of the Cedar River there, and serve as a temporary precaution until the completion of further cleanup, MPCA says.

Testing of the river in this area found contaminant levels below the threat to drinking water, suggesting that the contaminated sediments are not affecting the river’s water quality, MPCA says. Seasonal and occasional surfacing of contaminants, however, might occur, as evidenced by a localized sheen on the water during testing this year. The MPCA required evaluation with drinking-water standards because they are more stringent than surface-water standards.

From 1905 to 1935, the former plant converted coal into lighting and heating gas, first operating as the Austin Gas Manufacturing Company before being bought in 1924 by the Interstate Power Company, a subsidiary of present-day Alliant Energy. In 1947, Interstate Power sold the site, which became multiple private parcels used by various businesses until the Austin area’s worst-known flooding in 2004 led to those properties being acquired and removed through flood mitigation.

Alliant Energy repurchased the former gas plant site in 2005 and began a voluntary cleanup of the site’s upland portion under a MPCA program. The energy company removed more than 31,000 tons of contaminated soil from the site and heat-treated the soil to destroy pollutants, which included contamination from coal tars, sludges, oils and other chemicals. The thermally treated soils were replaced, covered with fresh topsoil, and planted with grasses and trees for use as a public green space.

Alliant since has sold the site as part of a sale of its electricity and gas distribution business to Minnesota Energy Resources Corp., which continues to work with MPCA on further testing and cleanup, particularly in the site’s lowland area that is green space.

IN BRIEF: Ex-Plant pollution found

Who: Minnesota Pollution Control Agency, Minnesota Energy Resources Corp. and other partnering organizations.

What: Will do additional testing and cleanup at a former gas manufacturing plant site after volunteers removing litter this summer found spots in the Cedar River with an oily sheen.

Where: Near the Oakland Avenue East bridge that crosses the Cedar River State Water Trail.

When: Found in July 2017; warning signs placed recently with additional testing and cleanup to come.

Why: To remove contamination at the site from the gas manufacturing plant’s operations there from 1905 to 1935.