By Shereen Siewert

The Wisconsin Department of Natural Resources continues to investigate Wausau’s sewer collection system along the Thomas Street corridor after a second round of testing revealed even higher levels of a toxic carcinogen than previously discovered.

The latest test results, taken March 26, involved “grab” samples at sewer mains in eight locations. Five of eight samples tested positive for Pentachlorophenol, or Penta, according to a report by Badger Labs. The samples were taken in the neighborhood where residents have repeatedly expressed concerns over potential toxicity of the soil and groundwater.

“The second round of testing confirmed that our sanitary pipe is taking in groundwater with Penta in it,” said Public Works Director Eric Lindman, who added that the infiltration is targeted at areas below the groundwater table.

An investigation first launched after Wausau Water Works on Jan. 8 conducted similar samples at sewer mains to have a better understanding of the Penta levels coming in to the city’s wastewater plant. In both cases, the grab samples were obtained by lowering a container mounted on a pole into the wastewater stream and scooping up a sample of wastewater, according to city documents. The initial report, dated Jan. 21, showed the presence of Penta, in four of six manholes in the area. Those samples, which ranged from 6 to 22.4 parts per billion, were submitted to the DNR for further review.

The results from the second round of testing range from 19.3 to 29.3 parts per billion, according to the Badger Labs report.

Manhole testing performed in March 2019 and associated Penta levels. Source: City of Wausau documents

The discovery in January prompted the DNR to direct TRC, the consultants for Wauleco, to prepare a scope of service for further investigation of the collection system downstream of the Wauleco discharge point, which lies along the Thomas Street corridor and is part of a brownfield cleanup site.

From 1996 to 1997, past Penta spikes in the wastewater system prompted city officials to resolve contamination by installing join seals in “wet zones” at a number of specific sewer joints. It is unclear whether the current contamination in neighborhood manholes stems from a similar problem.

Lindman said city officials have had conversations with the DNR about the issue as well as Wauleco representatives, who are proposing a report that would “potentially come up with solutions.”

“I do not have a timeline at this point other than we are expecting Wauleco to come up with a formal report and narrative documenting the testing results,” Lindman said.