This project is being conducted in two phases. Phase I of this project focused on 1) determining the factors that impact per- and polyfluoroalkyl substance (PFAS) stratification in water columns (surface water and wells), 2) systematically evaluating field materials and procedures (including decontamination) to eliminate bias when collecting water samples, 3) quantifying the impact of laboratory sample hold times and storage conditions to eliminate bias in measured PFAS concentrations, and 4) conducting outreach and research translation with state and federal project managers, consultants and contract laboratories.

The principal objective of Phase II of this project is to evaluate whether dedicated sampling equipment left in monitoring wells long-term could create false PFAS detections in the analytical results. A secondary objective is to compare low flow sampling to a three-well volume purge method in both unconsolidated aquifer and fractured bedrock wells. The associated hypothesis to be tested is that sampling method and aquifer type does not have a significant impact on analytical results for PFAS.

Phase I consisted of laboratory experiments followed by field experiments. First, bench-scale tests were performed to determine the extent to which stratification occurs in monitoring wells and surface water. The impact of PFAS concentration and water geochemistry (pH, salinity, organic matter, and colloids) on stratification and the potential for sampling procedures to mitigate stratification were determined. Sampling techniques that mitigate sampling bias were evaluated in the field, and sampling equipment was systematically analyzed for PFAS background. Key messages and findings were used to refine guidelines for sampling and storage, communicated through publications, webinars, and short courses. The technical approach of Phase II will consist of (1) a survey to gather information on the prevalence, use, and most common types of dedicated equipment in long-term monitoring programs, (2) collection of groundwater samples from dedicated equipment and non-dedicated equipment using two methods (low flow and three-well volume purge) from both bedrock and unconsolidated aquifer wells to quantify the impact of PFAS leaching from dedicated sampling equipment, and (3) a sampling equipment leaching test to evaluate long-term leaching of PFAS from pumps used in dedicated equipment.

Phase I Results

Phase I results showed that PFAS enrichment in the surface microlayer of surface waters does not have substantial effects on measured PFAS bulk water concentrations, except when foam is present. A literature review and laboratory studies evaluating field sampling materials indicated that while PFAS may be present on some materials, few pathways exist to bias PFAS concentrations in water samples. Results indicated that existing guidance documents err on the side of caution and may add unnecessary cost and time to field sampling efforts by restricting materials and practices that do not pose a significant risk of biasing PFAS concentrations. Laboratory-specified hold times and sample storage temperatures reported in the literature were found to be scientifically founded to adequately prevent bias due to PFAS sorption to sampling containers or partial degradation. Key findings and recommendations to improve current PFAS sampling guidance documents were summarized in multiple peer-reviewed publications, technical reports, and webinars.

The project will provide measurements to support the selection of field materials and protocols to minimize PFAS background and prevent bias. The outcomes of Phase II are intended to inform site managers whether their long-term monitoring program applications of dedicated equipment are appropriate and to evaluate contamination risk from the use of equipment between sampling events. The cost and sustainability impact to replace dedicated equipment, or to use rental equipment instead, could be substantial. Comparison of low flow to purge methods is also important to have confidence that the analytical results are representative of aquifer conditions. This would potentially avoid resampling in the future if a bias were later discovered. The results will allow the site managers to have confidence in the continued use of low flow sampling methods. Best practices will be assembled into guidance that will be communicated directly to stakeholders. (Anticipated Phase II Completion - 2026)

Rodowa, A.E., E. Christie, J. Sedlak, G.F. Peaslee, D. Bogdan, B. DiGuiseppi, and J.A. Field. 2020. Field Sampling Materials Unlikely Source of Contamination for Perfluoroalkyl and Polyfluoroalkyl Substances in Field Samples. Environ. Sci. Technol. Lett. 7(3):156-163  https://doi.org/10.1021/acs.estlett.0c00036