GREENSBORO — The city water system is moving ahead with plans that should leave it well prepared for whatever emerges from the federal government’s newly announced effort to investigate the industrial chemical PFOS and its sister chemicals in drinking water, utility officials say.

The city Department of Water Resources is starting a lengthy process to upgrade the Mitchell Water Treatment Plant with equipment that can safely remove PFOS, its sister chemical PFOA and similar compounds, said Mike Borchers, assistant director of the city Department of Water Resources.

“It’s the premiere treatment technology for PFOS and PFOA,” Borchers said of the “granular activated carbon” system the city is planning for the Mitchell Water Treatment Plant at an estimated cost of about $20.8 million.

The GAC system is the centerpiece of a package of upgrades at Mitchell that are expected to carry a total price tag of about $31 million. Borchers said that the figures are estimates.

Excessive exposure to the family of chemicals that includes PFOS is linked to problems with thyroid function, cholesterol levels, immune response and developmental progress in children. Evidence is less definitive for certain types of cancer.

The U.S. Environmental Protection Agency announced last week that it is starting a review process that could take several years and might lead to a firm cap on the amount of PFOS and its relatives allowed in drinking water.

Greensboro officials discovered several years ago that water from the Mitchell plant had fluctuating levels of PFOS in particular, which at times exceeded health limits currently recommended by the federal government.

The EPA has a health advisory level of 70 parts per trillion for PFOS, PFOA or the two combined in drinking water. But it is a guideline that’s not mandatory.

The guideline is based on a lifetime risk assessment for someone drinking water at that level of contamination every day.

The two chemicals were used for decades in products ranging from fire-fighting foams and stain-resistant carpeting for PFOS, to PFOA’s role in the manufacturing process that created such non-stick surfaces as Teflon.

Domestic manufacturers phased them out in recent years, but they can still be found in some imported goods and in products made before the phaseout.

GAC treatment is so effective against PFOS and related compounds that Borchers said he is confident whatever new limits the EPA might eventually set, the Mitchell plant’s planned filtering technology would be up to the task.

Borchers estimated that it would take roughly a year for the local project to be designed by an engineering consultant and win approval from the state Department of Environmental Quality. It likely would take another 18 months to two years to complete construction, he said.

If all goes well, the system could be in working order sometime in 2022, according to Borcher’s estimate.

In the interim, Greensboro has installed rented equipment that the Mitchell plant can use when needed to screen out enough PFOS and PFOA to bring combined levels down below the current federal advisory.

The plant’s leased equipment performs acceptably when needed, but the planned GAC system is the “Cadillac” of treatment methods for removing PFOS and similar compounds, Borchers said.

Last month, the City Council approved a $2.8 million deal to buy 2.5 acres next to the Mitchell plant for the upgrades. The purchase includes several apartment buildings and other property with frontage on Battleground Avenue, Seminole Drive and Whilden Place.

Borchers said 35 tenants of the apartments will have until the end of September to find new places to live. He said the city will work with them and provide some form of “relocation assistance,” but details remain to be worked out.

In addition to the new GAC building envisioned on land now occupied by apartments, the city is planning to improve sedimentation basins, revise the plant’s backwash and sludge collection systems, and build a new structure for electrical components and backup power.

City officials believe that PFOS has accumulated for decades in the industrial area that includes Piedmont Triad International Airport, where a main tributary to the Lake Brandt reservoir rises — Horse Pen Creek.

They think the accumulation stems largely from firefighters’ heavy use of foams that contain PFOS to squelch fuel-based fires and for training exercises, both at the airport and in the area around it.

Located near the intersection of Battleground Avenue and Benjamin Parkway, the Mitchell plant draws its water supply through a pipeline from Lake Brandt about 9 miles away.

City water officials first found intermittent, high levels of PFOS and lesser amounts of PFOA in drinking water from the Mitchell plant about four years ago. That was after EPA required all larger-scale water systems in the nation to test for them and several other “emerging contaminants.”

City officials began weekly tests in Lake Brandt and at the Mitchell plant last year after they detected a spike well above the PFOS/PFOA health advisory in late July. Readings since then have stayed well below the EPA advisory.

Borchers said there seems to be a relationship between dry spells and spikes in PFOS/PFOA. The city has hired a consultant to study the problem and develop a “predictive model” to help staff at the water plant accurately forecast when spikes are about to occur, he said.

That would allow them to use their filtering equipment at the plant more effectively, he said.

“We don’t want to be reactive. We want to be proactive,” Borchers said.

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Contact Taft Wireback at 336-373-7100 and follow @TaftWirebackNR on Twitter.

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