The state environmental agency reports "promising" results from a pilot project to remediate contamination around the Christina River.
The so-called “A Street Ditch” is a channel off the Christina River in south Wilmington. It’s contaminated with PCBs, which are industrial chemicals that are toxic to animals, and considered by the EPA probable human carcinogens.
The state Department of Natural Resources and Environmental Control (DNREC) is trying to clean up the ditch. In 2019, DNREC and its partners piloted a combination of carbon pellets to absorb the PCBs along with concentrated microorganisms to break them down.
DNREC hydrologist John Cargill, who’s leading the A Street cleanup, says this seems to be working.
“Our initial results after five months looked very good,” Cargill said. “The results after one year leveled out a little bit. But we’re still seeing decreases across the board in the bioavailable portion of the contaminant in the sediment porewater, which is where the exposure occurs to the bottom of the food chain.”
“So very, very promising,” he added.
Monitoring in July 2020, one year from the start of remediation, showed a reduction in concentrations of dissolved PCBs in the sediment porewater—the water trapped between grains of sediment at the bottom of the channel–across the entire project area, according to DNREC. But the agency says results from two of the nine samples collected, one from surface water and one from sediment, showed “localized increases in PCB concentrations,” which officials are investigating. DNREC plans to sample the site again in July.
Cargill says the ultimate goal of DNREC’s multiple watershed restoration projects is “clean fish and clean water,” as soon as possible.
“The metric that we’re using as an end point really is fish tissue,” Cargill said. “The risk assessments that we do to determine how many fish should or shouldn't be eaten in a waterway are all based upon these concentrations within the fish tissue and the potential health effects that they could have.”
PCBs are the largest contributor to fish consumption advisories the state issues, according to DNREC.
Cargill says the technique could eventually be used in other contaminated sites in Delaware, but the focus is on cleaning up sources of the contamination first.