Nationwide studies since the early 2000s indicate that PFAS exist in influent, effluent and residuals (biosolids) of wastewater treatment plants (Bogdan, D. 2021). Some of the most frequently detected PFAS compounds are PFAAs (perfluoroalkyl acids). This makes wastewater treatment plants important in managing and mitigating the environmental spread of PFAAs and a key participant in protecting both human and environmental health.

In Delaware, various wastewater streams (domestic, industrial and municipal) are treated and discharged into surface water bodies (NPDES discharges) as well as onto the ground surface, where it infiltrates the soil and ultimately enters groundwater (on-site wastewater discharges). Additionally, biosolids are land applied at numerous sites across the state, which also has the potential to impact groundwater.

Statewide Studies of PFAS in Wastewater

DNREC’s Water Resource Protection team has started statewide studies of PFAS related to wastewater treatment and utilization.

As these studies are completed, data summaries and other reports will be posted on this page.

PFAS in Biosolids

Biosolids were selected as the initial focus of DNREC’s PFAS investigation.Under a Biosolids Project Design and Sampling Plan (Phase I), samples of biosolids (prior to land application), soils (from a selected land application site) and groundwater (from the monitoring wells installed at the selected site) were collected from December 2022 through the summer of 2024.

The Phase I Data Summary Report of this study was published in March of 2025.

In October of 2024, DNREC initiated a second study examining PFAS in groundwater associated with long-term land application sites (Phase II). Groundwater samples were collected from monitoring wells installed at selected sites from October 2024 through January 2025.

The Phase II Data Summary Report of this study was published in May of 2025. 

To further investigate the potential presence of PFAS in groundwater used for drinking water, DNREC selected groups of domestic wells located downgradient of certain biosolids land application facilities for sampling. As part of this effort, DNREC conducted a Pilot Project to examine domestic wells downgradient of one biosolids land application site, in accordance with the Pilot Project Design and Sampling Plan – Sampling Domestic Wells Located Downgradient of Class B Biosolids Application Sites for PFAS. (Appendix 1: DNREC PFAS Method Analyte List) A Data Summary Report of the Pilot Project study is expected to be published during the first half of 2027.

Continuing DNREC’s efforts to examine PFAS in groundwater associated with long term application sites, domestic wells located downgradient of four additional biosolids application sites have been selected for sampling. Two of the selected locations are now permitted for wastewater disposal. One continues to receive biosolids application on a portion of the site, while the other no longer receives biosolids and is used solely for wastewater disposal. Domestic well sampling is expected to occur in late 2026 or the spring of 2027.

PFAS in Wastewater

During the summer of 2024, field sampling of wastewater influent, effluent and discharge receival media (soil and groundwater) was completed, under a Project Design and Sampling Plan for Wastewater.

A Data Summary Report of this study has been prepared. PFAS compounds were found not only in wastewater influent-effluent, but also in soils where treated wastewater was discharged or sprayed onto and in groundwater from monitoring wells installed at the groundwater discharge facilities.

To address potential presence of PFAS in the groundwater water that is used for drinking water, groups of domestic wells located downgradient of the groundwater discharge facilities were selected, and sampling will be conducted under a Project Design and Sampling Plan for Downgradient Domestic Wells.

To continue the wastewater PFAS study initiated in 2024 (Phase I), a Project Design and Sampling Plan was prepared to collect groundwater samples from the monitoring wells installed at the rest of wastewater facilities that are discharging more than 10,000 gallons per day (Phase II of the wastewater PFAS study).  A total of 37 facilities were identified throughout the State and samples will be collected from 115 monitoring wells.

PFAS in Septic Pump-Outs

Sampling of pump-outs from septic systems was completed in the summer of 2023, under a Project Design and Sampling Plan for septages.

Project Design and Sampling Plans

PFAS in Biosolids: Characterization and Fate

PFAS in Groundwater Associated with Class B Biosolids Land Application Sites

PFAS in Wastewater: Characterization and Fate

PFAS in Septic Pump-Outs: Characterization and Fate

PFAS in Wastewater: Characterization and Fate (Phase II)

Pilot Site Study: James Thompson Fabric Processing Plant

Upon the receipt and evaluation of the laboratory analysis results from the initial of sampling of the PFAS in Wastewater study, James Thompson — a fabric processing plant with an onsite wastewater treatment and disposal facility — was selected as a pilot site for further investigations due to elevated PFAS in samples from the plant.

A Project Design and Sampling Plan was developed. Additional samples of groundwater, surface water, sediment (from wastewater storage pond) and domestic wells downgradient of the facility were collected in the spring of 2024. A Data Summary Report of this pilot study was prepared.

Related Topics:  EPA, GenX, HSCA, PFAS, PFOA, waste and hazardous substances, wastewater, watar, water