Mercury Marine dredging Cedar Creek to remove PCBs
CEDARBURG - Like massive shop vacuums on floating platforms, two hydraulic dredgers started sucking contaminated muck off the bottom of Cedar Creek on Monday as part of Mercury Marine's ongoing removal of toxic chemicals from the stream.
Dredger operators are guided by GPS to previously identified sediment layers containing unsafe amounts of industrial chemicals known as PCBs, Mercury Marine project manager Craig Dousharm said.
As the muck is lifted up, pumps on each platform push the load through an orange-colored pipeline suspended in the water to a field at Adlai Horn Park. Pedestrians or motorists passing the park off Columbia Road have seen its gradual transition since last year from recreational fields to a three-acre black mat marking the location of a special water treatment plant and sediment storage yard.
Contractors for Mercury Marine have begun the second and final year of a $24.8 million cleanup of a section of the creek and floodplain that extends from the Ruck Pond dam downstream to the Wire & Nail factory dam. This stretch of the stream includes Columbia Pond, an impoundment behind the Columbia Mills dam; and Wire & Nail Pond, held back by the former factory dam.
The cleanup plan approved by the U.S. Environmental Protection Agency calls for removing 98% of the PCBs from the two impoundments. A total of 55,000 cubic yards of contaminated sediment — weighing in at 80,000 tons — will be dredged out of the creek.
RELATED: Cedar Creek cleanup resumes
PCBs banned since 1976
Manufacture of PCBs was banned in 1976 after numerous studies confirmed the chemicals can cause health problems. PCBs are harmful to the human immune system, can cause developmental impairments in children and are considered probable human carcinogens.
On Monday morning, both dredgers were working in Columbia Pond. One platform was parked south and upstream of an island off the park, and a second platform was parked downstream of the island. Ducks swimming between the island and park shoreline paid no attention to the unusual vessels.
As work progresses, one dredger will be moved downstream to the Wire & Nail Pond, Dousharm said. The orange-colored muck transport pipeline serving that platform will be extended up to a mile downstream of the water treatment plant before cleanup is done in that pond.
Dredging of both ponds will be completed in September, Dousharm said. If the weather cooperates with the company's plan, contractors expect to start restoring the park's recreational fields by the end of the year.
When contaminated muck removed by dredgers reaches the park, it is pumped into large fabric bags — 300 feet long by 65 feet in circumference — atop the mat, said Paul Olander, onsite project manager for La Crosse-based prime contractor J.F. Brennan Co.
Water seeps out of small pores in the heavy fabric and onto the mat, where it flows downhill to a deep channel. The water is pumped into a specially designed treatment plant set up at the park where it goes through a series of filters to remove PCBs and other contaminants.
Testing must confirm there are no detectable levels of PCBs remaining in the water before it can be returned to the creek. On Monday, clean water discharged to the creek formed bubbles on the water's surface just a few feet offshore.
On the mat, one heavy fabric bag will be filled at a time, Olander said. By summer's end, the entire three-acre mat will be covered by bags stacked four deep.
When water stops oozing out of the bags, the fabric will be opened and the sediment will be transferred to trucks for shipment to landfills for disposal, according to Dousharm. The mat is made of multiple layers of heavy plastic sheets and fabric designed to prevent contaminants from leaking into the soil and reaching groundwater.
Polychlorinated biphenyls, or PCBs, were in hydraulic fluids used in equipment inside a former Mercury Marine die-casting factory on St. John Ave. in Cedarburg. Fluids that leaked onto floors were rinsed into drains that emptied into a storm sewer.
The sewer emptied into the creek at Ruck Pond, and the factory became a major source of the chemicals that accumulated in creek bed sediment and the floodplain, according to federal and state environmental officials.
Prior to this two-year effort, Mercury Marine had spent $30 million since the early 1990s on separate cleanups of the Ruck Pond in 1994 and the former Hamilton Pond floodplain in 2001, as well as its former die-casting plant on St. John Ave. The company also cleaned the storm sewer between the factory and Ruck Pond. The factory was demolished in 2005.
Mercury Marine, the Fond du Lac-based manufacturer of marine engines, including outboards, inboards, sterndrives and pod drives, is a division of Brunswick Corp.
Don Behm can be reached at firstname.lastname@example.org and twitter.com/conserve.