By unanimous vote, the Sauk County Board of Supervisors passed a resolution last night urging the U.S. Army to clean up residual mercury contamination in Lake Wisconsin at Gruber’s Grove Bay. Despite a $6-million dredging project several years ago, more than 50,000 cubic yards of contaminated sediments remain throughout the bay.
In 2003, the Army Corps of Engineers conducted a dredging project that was supposed to remove all sediments with mercury concentrations above 0.36 mg/kg in accordance with a permit issued by the WDNR. The dredging moved more than 85,000 cubic yards of bay sediments to a landfill inside Badger.
Follow-up testing conducted earlier this year verified that residual mercury levels are nearly as high as before; the highest detected level was 15.8 mg/kg. The highest contaminant concentrations were found at the shoreline, adjacent to nearby homes and farmland.
Elevated levels may extend beyond the bay and into Lake Wisconsin, according to Dr. Jerry Eykholt, an independent consultant working with Badger’s Restoration Advisory Board. “All three core locations in Gruber’s Grove Bay nearest Lake Wisconsin had mercury concentrations exceeding 1 mg/kg,” Eykholt said. “Therefore some of the impacted sediments may be beyond Gruber’s Grove Bay.”
During Badger’s active production years, industrial and sanitary wastewater was discharged directly into Gruber’s Grove Bay. In addition to mercury, the bay contains toxic levels of lead, copper, and zinc.