Tracking Down and Addressing Sources of PFAS in Influent Flows Through Strategic Collection System Monitoring and Targeted Outreach

Background
Poly- and Perfluoroalkyl Substances (PFAS) have been commonly used in many industrial applications, fire-fighting materials, and consumer products since the 1950s. These compounds have been associated with various negative human health effects. While manufacture of the most common types of PFAS, such as perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA), has been phased out in the United States, in many cases other types have been substituted into products that sometimes have similar or worse toxicity [1]. Many types of PFAS exist in current domestic and industrial use, and many of the legacy PFAS types are still environmentally ubiquitous. The United States Environmental Protection Agency (EPA) released its strategic roadmap in October 2021 for addressing PFAS in the environment. Part of that strategy is expected to involve additional monitoring and source control for wastewater utilities. Many wastewater utilities are concerned that future regulations may threaten some resource recovery efforts such as beneficial reuse and land application of biosolids. Some states, such as Michigan, have already proactively issued limits to biosolids applications based on PFAS concentrations. Some wastewater utilities around the country have begun to sample their influent, effluent, and biosolids for PFAS. In general, this has provided useful data on the PFAS types in wastewater and their concentrations. However, results have been site-specific with both the types and concentrations of PFAS detected highly dependent on the sewershed properties. However, few wastewater utilities have done monitoring for PFAS in the sanitary collection system to determine the sources of different types of PFAS in the sewershed. While the EPA has provided guidance on the industrial types likely to have high PFAS in their discharges, in most cases the actual discharge concentrations are site-specific even from similar industry types. PFAS are also commonly found in domestic and commercial wastewater due to their widespread use in consumer products. Understanding the types and sources of PFAS present in their sewershed can help wastewater utilities better understand the threat posed by PFAS and help provide the tools to proactively mitigate the sources.
Objectives
Clean Water Services' (CWS's) objective was to determine the threat posed by PFAS and develop strategies to mitigate the threat proactively. This was done through strategic monitoring for PFAS at the treatment plants and within the collection system accompanied by targeted sampling and general outreach to industries, and the commercial, and domestic sectors, followed by development of PFAS minimization plans.
Methods
Between 2019 and 2022, samples were collected from the influent, effluent, and biosolids of CWS's treatment plants, from the soils where biosolids were applied, from specific industries, and from many sanitary sewer manholes. The concentration of 36 types of PFAS were quantified in each sample. Samples were collected approximately quarterly, though not all locations were sampled in each sample event as selected manhole locations in each sample event were determined based on the results from the previous samples to 'chase' high concentrations of specific PFAS 'upstream' to the source. Industries were initially selected for sampling based on EPA guidance. Additional industrial samples were focused on those industries that were identified as sources of PFAS in the initial industrial sampling and through the sanitary manhole sampling. CWS reached out to each industry prior to initial sampling to explain the reasons for sampling, and followed up with initial results. Additional samples were collected and additional outreach was conducted to industries identified as sources of high PFAS concentrations through ongoing industry sampling and strategic sanitary manhole sampling. CWS worked with the Pacific Northwest Pollution Prevention Resource Center (PPRC) to create outreach materials for commercial and domestic sources and to develop a PFAS minimization plan for CWS. CWS continued to work collaboratively with industries identified as sources high sources of PFAS as the concentrations decreased. Ordinances and policies were updated to be able to better regulate PFAS through source control. A dashboard was also created to provide easier access to PFAS data in the sewershed to stakeholders. Because CWS expects to continue monitoring PFAS and other contaminants of emerging concern into the future, in 2022 CWS began efforts to create a trace organics laboratory in order to analyze PFAS samples in-house.
Status
As of the writing of this abstract in Dec 2021, CWS is currently contracting with the PPRC for developing the outreach materials and PFAS minimization plan. While PFAS monitoring and outreach efforts have been ongoing since 2019 and are expected to continue well into the future, much has already been learned about the types of PFAS present, their removal in wastewater treatment, and their sources in the sewershed. Monitoring and targeted outreach has already succeeded in mitigating the two largest individual sources of high PFAS in the influent.
Findings
The concentration of PFAS in CWS influent was relatively low compared to nationwide data, although concentrations of individual PFAS were sometimes high, especially PFOA at the Durham treatment facility (Figure 1). Sampling in the sanitary sewer determined that a single industry was responsible for the elevated PFOA concentrations, and outreach to the industry coupled with additional monitoring resulted in the mitigation of the high PFOA concentrations in the influent. The most commonly detected forms of PFAS present were the 4-, 5-, and 6- carbon chain forms. These were nearly ubiquitous in liquid samples, but concentrations tended to be higher in manholes in industrial areas and at treatment plants where industries make up a large fraction of the wastewater flows, such as Rock Creek (Figure 1). CWS collaborated with largest industrial source to remove PFAS from their supply chain, and concentrations in the sanitary sewer downstream have subsequently decreased. Industries identified as having high concentrations of PFAS in their outfalls were mostly open to discussions with source control personnel, though many are concerned about future regulation. As found across the US, treatment processes were not effective at removing PFAS from influent. The shorter carbon chain compounds tended to be found in the effluent at similar concentrations as the influent, and the longer chain compounds tended to be found in the biosolids (Figure 2). However, concentrations in the soils where biosolids were applied were mostly below detection limits.
Significance
This study demonstrates that monitoring and outreach can be effective at reducing PFAS in wastewater. The results of this study provide a useful case study and template for other utilities seeking to understand the threat posed by PFAS and be able to locate and mitigate the sources without additional regulations or an adversarial relationship with industries.