A state review of a potential frac sand mine reclamation project in Chippewa County has found high concentrations of arsenic and other heavy metals at the site and left the Wisconsin Department of Natural Resources with “reasonable concern” groundwater contamination may have occurred.

On Nov. 11, the DNR responded to a request from Chippewa County for a “technical review” of a plan to clean up ponds at a frac sand mining and processing facility owned by Superior Silica Sands in the town of Auburn. Known as process water ponds, the basins allow muds that are washed from grains of frac sand to settle from water that is reused in the process.

A letter from DNR nonmetallic mining coordinator Roberta Walls to Chippewa County Director of Conservation Dan Masterpole said mud samples from the ponds exceeded state safety levels for arsenic, a naturally occurring metal listed as a carcinogen by the Environmental Protection Agency. Officials with Chippewa County didn’t immediately respond to requests for comment.

Dave Rozeboom, DNR northern region remediation and redevelopment program manager, said administrative code sets an arsenic “residual contact level” of three parts per million while a pair of samples taken from holding ponds at the mine had RCLs of 17.7 ppm and 21.6 ppm.

“So, these are certainly above our industrial direct contact standards,” Rozeboom said.

But because arsenic is a naturally occurring compound, Rozeboom said, the samples taken from Superior Silica Sands’ ponds have to be evaluated against background levels, which will require more testing.

In 2013, the DNR published a map showing background arsenic levels from 664 statewide soil samples. None of those taken in the vicinity of the Chippewa County mine showed arsenic levels higher than 8.3 ppm.

Even if mud from the ponds has arsenic concentrations higher than those found offsite, Rozeboom said it wouldn’t require immediate cleanup so long as the mine was still operating under a valid permit. He said that’s because the material is underwater and the DNR assumes workers wouldn’t be working in a process water pond.

“But if that facility closes and the permit is no longer applicable, part of the reclamation plan must require management of that material,” said Rozeboom.

He said a common way companies have managed soil contaminated with excess arsenic is by capping it with soil or other material.

On July 5, Chippewa County suspended Superior Silica Sands’ mining permit after failed attempts to secure an additional $1.6 million in mine reclamation bonds from the company. The county has extended the permit suspension by 30-day increments since then.

Mining companies are required to post reclamation bonds prior to mining and are used by local governments to pay for cleanup if companies go out of business and mines are abandoned. On July 15, Superior Silica Sands’ parent company Emerge Energy Services filed for bankruptcy. The company hasn’t responded to multiple requests for comment since the filing.

If Chippewa County revokes the mining permit for Superior Silica Sands, they’ll be required to use whatever existing reclamation bonds are available to clean up the site.

‘Reasonable concern’

The DNR’s Nov. 11 letter to Chippewa County noted the agency also had “reasonable concern that contamination to groundwater can or may have occurred as a result of operations.” The claim is based on samples of water taken from the Superior Silica Sands’ ponds also containing “elevated levels of aluminum, arsenic, chromium, lead, and manganese” that indicate the site is potentially in violation of state groundwater standards.

The letter describes potential “mounding” beneath the ponds. Rozeboom said that means monitoring wells installed by the company have detected “higher than natural elevation” of the groundwater table near the ponds indicating water is seeping from the ponds into the aquifer.

“If you have a stormwater pond that is above the elevation of groundwater and that pond is not properly lined to prevent drainage, it can be acting as a recharge point to the groundwater, which may be observed as a high spot in the groundwater elevation,” said Rozeboom.

Roberta Walls, who wrote the DNR letter to Chippewa County, told WPR that more data needs to be gathered to see whether the concentrations of metals found in the pond water are also making it into the groundwater, potentially with additional monitoring requirements.

“The best way to approach that would be to first determine what the pathways are from the pond into the groundwater,” Walls said. “We’d have to evaluate what potential there is for movement of those levels in the ponds to make it to groundwater.”