New data is shedding light on the possible source of PFAS chemical contamination at the Coakley Landfill Superfund site on the Seacoast.
The data comes from a contractor for the Coakley Landfill Group, the towns and businesses responsible for pollution at the landfill.
They voluntarily analyzed water from Berry's Brook, which runs out from the landfill and was found last year to contain high levels of PFAS chemicals.
Those are man-made substances that are slow to biodegrade and have been linked to cancer and other diseases.
In a letter sent to federal and state officials Tuesday, the Landfill Group’s contractor says they found the contamination in the brook came from stormwater runoff, not water seeping from within the landfill.
One way to know – the runoff doesn’t contain some contaminants, like 1,4 dioxane, that are known to be inside the landfill.
Officials say it means the PFAS contamination near Coakley may not be coming from waste inside the landfill at all – but instead, from rain that falls on top of the landfill's waterproof cap, and picks up PFAS as it runs into Berry's Brook.
The contractor’s letter also suggests the cap itself could be the source of that PFAS. The cap is partly made of plastics, manufactured in a time when PFAS was common in products that resist things like water.
Officials say they'll need to do a lot more testing on surface water and the cap’s materials, as well as research on how those materials were made, to be sure of the source of the contamination.
An Environmental Protection Agency spokesman says the agency is “happy to see that the Coakley Landfill Group is working on investigating the potential source of PFAS discharge to surface water from the landfill.”
The spokesman says the EPA is reviewing the contractor’s letter and will respond to the Landfill Group about the next steps it’s suggesting.
Read the Landfill Group contractor's letter to EPA and state officials below: