YOUNGSTOWN — The city Department of Public Works reported a sudden spike of mercury in wastewater coming from the city’s treatment plant in April.
The plant exceeded its mercury effluent limit of 12 ng/l that month, prompting Paul Joseph, assistant plant superintendent, to submit a letter Friday to the Ohio EPA’s Twinsburg offices.
Two different samples had mercury measured at an average 13.69 ng/l, according to the letter. Samples that measure at least 75 percent of the effluent limit must be reported to the EPA, according to the plant’s permit, issued in July 2018.
“Although exceedances of mercury discharges above 12 nanograms per liter are not classified as violations, the permit does require these exceedances to be reported,” said EPA spokesman Anthony Chenault. “Sources of mercury can include residential (e.g. thermometers and electrical devices) and industrial facilities. Mercury is measured in parts per trillion, and any minor amount can trigger a notice of elevated levels.”
Chuck Shasho, city public works superintendent, said mercury was also found coming into the plant, meaning it originated somewhere in the wastewater collection system.
It’s the first time the plant has exceeded the mercury limit since its permit was issued, according to the letter.
The plant has been approved to discharge into the Mahoning River as well as Mill Creek and several other water bodies in the area, according to its permit.
Shasho said the EPA is not holding the city accountable for the mercury discharge just yet — and he called this an “isolated incident” — but the current effluent limit in place previews enforceable limits taking effect in the near future, meaning the city may have to trace its origin by moving upstream, testing manholes.
“If we start seeing it again or more often … at that point, we’ll start intensive sampling,” Shasho said. “We will have to start looking for a source in the collection system.”