State environmental regulators are sampling groundwater from monitoring wells in northern New Hanover County after perfluorinated compounds, including GenX, were detected in six of 25 wells that supply the Richardson water treatment plant.
However, the compounds were not detected in finished drinking water.
The plant, operated by the Cape Fear Public Utility Authority, provides drinking water to several communities, including Murrayville, Wrightsboro, and parts of Castle Hayne and Odgen. The source of this public water supply is groundwater tapped from the Castle Hayne and PeeDee aquifers.
While most of the utility’s water treatment plants withdraw from the river, the Richardson plant uses groundwater.
In all, 12 types of PFAS were detected, although not every type was found in every well.
Tests of well water showed levels ranging from 25 ppt to 65 ppt for all PFAS; another well, intended only as an emergency source for the Sweeney plant, contained concentrations of PFAS at 180 ppt. That well is not operating.
No PFAS have been detected in finished drinking water from the Richardson plant during March testing, the utility said. In April, only a trace amount, 0.6 parts per trillion, was detected in one sample, according to the utility.
“We share their concerns, but one data set does not sufficiently help us understand the cause or source of the contamination. DEQ plans to sample areas of concern and expedite testing results,” DEQ Communications Director Megan Thorpe said in a prepared statement.
DEQ said it will conduct its own sampling, but it could take several weeks to receive the results.
The EPA has yet to regulate PFAS or GenX. The state health department has set an unenforceable advisory goal of 140 ppt in drinking water. As part of a consent order, the state Department of Environmental Quality requires Chemours, which had been discharging PFAS into the Cape Fear River for decades, to pay for filter options for owners of private wells where the compounds have been detected above 10 ppt for one, or 70 ppt collectively.
The original source of the widespread PFAS contamination in the Lower Cape Fear River Basin is the Chemours plant, 100 miles upstream. Private drinking water wells around the plant, as well as public drinking water supplies downstream have been polluted from the facility’s discharge.
It’s possible that at least part of the aquifer beneath New Hanover County is now contaminated. In 2017, the utility had pumped water from the Sweeney water treatment plant into an aquifer storage well to keep finished drinking water that could be used during times of high demand. However, the utility suspended the project after it learned that it had unknowingly contaminated the aquifer well because water from the Sweeney plant was contaminated with GenX and other PFAS from Chemours.
The utility found the most recent contamination after sampling the wells to determine how PFAS might move through groundwater near the aquifer storage well. The utility said it is unclear if that well is the source of the other contaminated groundwater wells. Those wells are two to three miles away, and groundwater migrates only about 15 feet a year, at least in the coastal area of New Hanover County.
Speed of groundwater migration can depend on rock and soil types. The Castle Hayne Aquifer is composed of “carbonate rocks,” common in coastal environments, according to the US Geological Survey. The slightly acidic groundwater can carve tunnels in the rock that can be tens of feet wide and even thousands of feet long. Water then moves through these underground networks, although it can’t penetrate undissolved rock.
The Pee Dee Aquifer is made up of fine- to medium-grain sand and black clay.
The finished drinking water from these aquifers is not contaminated, likely because the Richardson plant uses an advanced membrane treatment system, which can remove PFAS, including GenX.
However, the contamination doesn’t end there. The material caught by the membrane filters, known as “concentrate,” is discharged into the Intracoastal Waterway.