PFAS Exposure Assessment, Drinking Water Risk Evaluation, and Public Water System Allocation Modeling
Project Overview
RoseyFields conducted a comprehensive technical evaluation of per- and polyfluoroalkyl substances (PFAS) exposure, regulatory compliance, and public water system risk assessment in support of environmental litigation involving PFAS-contaminated drinking water. The project combined environmental chemistry, drinking water regulations, exposure assessment, engineering cost modeling, and environmental forensic analysis to evaluate the occurrence of PFAS in public water systems and the methodologies used to prioritize remediation and allocate treatment costs.
The investigation focused on interpreting emerging federal and state PFAS regulations, evaluating contaminant concentrations relative to proposed drinking water standards, and assessing the technical framework used to estimate remediation costs for impacted public water systems. In addition to reviewing environmental sampling data and regulatory guidance, RoseyFields evaluated the allocation methodology developed for the nationwide 3M Public Water System Settlement, including the scoring algorithms used to estimate treatment needs, remediation costs, and equitable settlement distributions among qualifying water systems.
A principal objective of the investigation was to understand how measured PFAS concentrations, water source characteristics, system capacity, and regulatory exceedances influence environmental risk and anticipated treatment costs. The project also examined how clinical guidance regarding PFAS blood concentrations relates to environmental exposure pathways and public health recommendations, providing a comprehensive evaluation of contaminant occurrence from environmental source through potential human exposure.
By integrating regulatory guidance, environmental engineering, hydrogeology, analytical chemistry, contaminant fate and transport, and exposure science, RoseyFields developed a technically defensible framework for evaluating PFAS contamination in public drinking water systems and the associated environmental and public health implications.
Chemicals of Concern
The investigation evaluated multiple per- and polyfluoroalkyl substances identified by the U.S. Environmental Protection Agency as contaminants of regulatory concern in drinking water. Particular emphasis was placed on perfluorooctanoic acid (PFOA), perfluorooctane sulfonate (PFOS), perfluorohexane sulfonate (PFHxS), perfluorononanoic acid (PFNA), perfluorobutane sulfonate (PFBS), hexafluoropropylene oxide dimer acid (GenX chemicals), perfluorodecanoic acid (PFDA), perfluoroundecanoic acid (PFUnDA), and additional PFAS compounds included within EPA monitoring programs and proposed drinking water regulations.
Because PFAS compounds are highly persistent, resistant to degradation, and capable of long-term migration through groundwater and surface water systems, the investigation evaluated both individual analyte concentrations and cumulative PFAS occurrence. Particular attention was given to compounds subject to proposed federal Maximum Contaminant Levels (MCLs), Hazard Index calculations, and state-specific drinking water standards.
Methods
RoseyFields conducted a multidisciplinary evaluation of PFAS occurrence using environmental sampling data, regulatory guidance, engineering cost models, and public health literature. The investigation reviewed the technical methodology used to classify public water systems, identify impacted water sources, verify analytical results, and prioritize treatment based on contaminant occurrence and system characteristics. Qualifying sampling results were evaluated using validated analytical methods consistent with EPA drinking water monitoring requirements, while environmental data were reviewed for completeness, quality assurance, and regulatory applicability.
The project included a detailed review of the PFAS scoring methodology developed to estimate treatment needs for impacted water systems. Under this framework, individual water sources are assigned PFAS Scores based upon measured concentrations of PFOA, PFOS, and other detected PFAS analytes. These contaminant scores are integrated with verified groundwater well production rates or surface water treatment plant flow rates to estimate both capital treatment costs and long-term operation and maintenance costs associated with PFAS removal technologies.
RoseyFields also evaluated engineering assumptions used to estimate treatment costs, including flow-dependent capital expenditures, operational maintenance requirements, treatment media replacement, contaminant concentration effects, and system-specific adjustments reflecting regulatory exceedances, litigation status, and other technical considerations. The investigation reviewed the mathematical relationships used to estimate treatment costs based on EPA drinking water treatment cost models and evaluated how these engineering assumptions influence overall remediation planning.
In parallel, the investigation examined current clinical guidance regarding PFAS exposure and biomonitoring. Public health recommendations relating serum PFAS concentrations to recommended medical screening and exposure reduction strategies were evaluated to better understand how environmental contamination may translate into human health considerations. These evaluations were integrated with drinking water exposure pathways, environmental monitoring data, and contaminant occurrence to develop a comprehensive source-to-exposure conceptual model.
Results
The investigation demonstrated that meaningful evaluation of PFAS contamination requires substantially more than comparing measured concentrations with individual regulatory thresholds. Treatment priorities and anticipated remediation costs are strongly influenced by contaminant concentrations, water source production capacity, treatment system size, groundwater or surface water characteristics, regulatory exceedances, and long-term operational considerations. The reviewed allocation methodology integrates each of these factors into a comprehensive engineering-based framework designed to estimate relative treatment needs among impacted public water systems.
The evaluation found that PFAS Scores are determined using the highest measured concentrations of PFOA, PFOS, and other detected PFAS analytes, recognizing that contaminant mixtures often require more complex evaluation than single-compound exceedances alone. These contaminant scores are then combined with adjusted water system flow rates to estimate treatment system size and associated capital expenditures before incorporating projected operation and maintenance costs driven by contaminant concentrations and treatment media replacement frequency.
The investigation also demonstrated that regulatory status significantly influences remediation prioritization. Public water systems exceeding proposed federal Maximum Contaminant Levels or more stringent state drinking water standards receive substantial adjustments within the allocation methodology, recognizing the increased urgency and anticipated costs associated with regulatory compliance. Additional technical considerations, including prior litigation and public water provider classifications, further modify estimated remediation needs through standardized adjustment factors intended to promote equitable allocation among similarly situated systems.
Review of current PFAS exposure guidance further illustrated that human biomonitoring data provide an additional line of evidence when evaluating environmental exposure. Current clinical recommendations encourage progressively greater medical evaluation and exposure reduction measures as serum PFAS concentrations increase, highlighting the importance of identifying and mitigating environmental PFAS sources before chronic exposure results in elevated body burdens. The integration of environmental monitoring, engineering analysis, and public health guidance provides a more complete understanding of PFAS risk than any individual dataset alone.
Conclusions
This investigation demonstrates that evaluation of PFAS contamination in public drinking water systems requires the integration of environmental chemistry, analytical data, engineering design, hydrogeology, regulatory science, exposure assessment, and public health guidance. Modern PFAS investigations extend well beyond identification of contaminant detections and instead require quantitative evaluation of contaminant occurrence, treatment system design, long-term operational costs, regulatory compliance, and human exposure pathways.
The project further demonstrates the value of applying structured environmental forensic methodologies to complex PFAS investigations. By integrating contaminant concentrations, water source production characteristics, engineering cost models, regulatory exceedances, and clinical exposure guidance, RoseyFields developed a comprehensive framework for evaluating environmental contamination and remediation priorities across diverse public water systems.
This investigation was conducted under the direction of Dr. Paul Rosenfeld, an environmental scientist and environmental forensic expert with extensive experience in PFAS contamination, drinking water investigations, groundwater contamination, environmental chemistry, regulatory compliance, and contaminant fate and transport. Through RoseyFields LLC, Dr. Rosenfeld provides technical support for PFAS investigations, drinking water exposure assessments, groundwater evaluations, engineering cost analyses, regulatory review, environmental forensic investigations, and expert witness services involving public water systems and emerging contaminants.
References
National Academies of Sciences, Engineering, and Medicine. Guidance on PFAS Exposure, Testing, and Clinical Follow-Up.
Public Water System Settlement Agreement, Exhibit Q. Allocation Procedures. 3M PFAS Public Water System Settlement.
U.S. Environmental Protection Agency. Proposed National Primary Drinking Water Regulation for Per- and Polyfluoroalkyl Substances (PFAS).
U.S. Environmental Protection Agency. Work Breakdown Structure-Based Cost Model for Granular Activated Carbon Drinking Water Treatment (2023).
U.S. Environmental Protection Agency. Fifth Unregulated Contaminant Monitoring Rule (UCMR 5).