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No culprit identified in Greensboro 1,4-Dioxane spills from 2021; investigation continues

This graph shows levels of 1,4-Dioxane during the June and November spills, represented by the spikes. The original limit in the Special Order of Consent is shown in orange; the amended order limit is shown in red. There is no drinking water standard for 1,4-Dioxane, but the EPA has set a health advisory goal of 35 ppb. That represents a 1-in-10,000 elevated cancer risk.

Four months after the most recent 1,4-Dioxane spill that contaminated Pittsboro’s drinking water, the City of Greensboro has not pinpointed a source of the hazardous chemical that entered its sewer system. However, city officials are focusing on the Patton trunk line, a part of the city’s sewer system that sends wastewater to the TZ Osborne treatment plant.

The spills occurred in June and November 2021, and resulted in high levels of the compound, a likely carcinogen, to enter the Haw River, which is Pittsboro’s water supply. Although unregulated in drinking water, the EPA has set a health advisory goal of 35 parts per billion for 1,4-Dioxane. Surface water goals are even stricter, at 0.35 ppb. In Pittsboro,  levels of the compound exceeded those goals during both events, including in water flowing from private taps.

Traditional water and wastewater treatment systems can’t remove 1,4-Dioxane.

Sampling of wastewater from the Patton trunk line, located in south Greensboro, showed concentrations of 1,4-Dioxane at 369 parts per billion during the November spill. (There was not a sampler in place on that trunk line when the June spill occurred.) Considering that line transports 10 million gallons of wastewater per day — and the level of 1,4-Dioxane was that high even after dilution — a significant amount of the chemical must have entered the system, said Jenny Graznak, assistant regional supervisor at the NC Department of Environmental Quality’s Winston-Salem office.

Graznak updated the Environmental Management Commission today on the investigation.

The City of Greensboro lists 29 Significant Industrial Users that discharge into the sewer system. Of those, six discharge into the Patton trunk line. And of those industrial users, five — Vertellus, Elastic Fabrics, Lanxess, Precision Fabrics and Shamrock Environmental — had results higher than 15 ppb. GSO Platers, the sixth user, did not. However, based on the five users’ sampling results and the amount of their wastewater discharges, Greensboro officials have ruled them out as the source of either the June or November spills.

The Airport trunk line, which has five Significant Industrial Users, also feeds the Patton trunk line, Graznak said.

Since the June spill, the City has installed continuous surveillance samplers at four trunk lines, including Patton and Airport.

The spills violated a Special Order of Consent between the City and DEQ. (Greensboro was fined $5,000 for the violation; it’s been paid.) That order stemmed from a previous incident, in mid-2019, in which extremely high levels of 1,4-Dioxane entered the city’s wastewater treatment plant and then proceeded downstream and contaminated Pittsboro’s drinking water. In that instance, Shamrock Environmental was the source, city officials said at the time. Since then, Shamrock has instituted more diligent sampling protocols and pre-treatment systems, Greznak said. DEQ officials visited the Shamrock facility last year.

Fayetteville Public Works Commission, which is also downstream from Greensboro, and the Haw River Assembly sued over the Special Order of Consent, arguing it was too lenient. As part of a settlement agreement, the number of sampling locations increased from 26  to 57.

In addition, Significant Industrial Users whose wastewater sampling — conducted by the City — shows levels of 1,4-Dioxane above 100 ppb must complete a source investigation, evaluation and survey for their facility. These facilities meet that criteria: Chemol and Evonik, which discharge into the Arlington trunk line; Ecolab, which sends its wastewater into the Airport trunk line; and Vertellus, which is on the Patton trunk line.

On May 1, the level of 1,4-Dioxane that triggers a source investigation becomes more stringent — 31.5 ppb. And in May 2023, the level decreases further to 23 ppb.

Assistant DEQ Secretary Sushma Masemore told the EMC that the state is continuing to investigate. “We’re trying to get a better understanding of possible sources,” Masemore said, including examining closed industrial sites where groundwater wells have high levels of 1,4-Dioxane.

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