The main objectives of this project are to 1) determine the factors that impact per- and polyfluoroalkyl substance (PFAS) stratification in water columns (surface water and wells), 2) systematically evaluate field materials and procedures (including decontamination) to eliminate bias when collecting water samples, 3) quantify the impact of laboratory sample hold times and storage conditions to eliminate bias in measured PFAS concentrations, and 4) conduct outreach and research translation with state and federal project managers, consultants and contract laboratories.

Technical Approach

The technical approach consists of a three-year course of highly controlled laboratory experiments followed by field experiments. Bench-scale tests will be 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 as well as the potential for sampling procedures to mitigate stratification will be determined. Sampling techniques that mitigate sampling bias will be evaluated at inland (neutral pH and low salinity) and coastal (higher pH and salinity) field sites. Groundwater pumps, tubing, and field sampling materials will be systematically analyzed for PFAS background. Potential bias due to sample storage and hold times will be determined from laboratory tests conducted with groundwater and surface waters by varying sample bottle material and determining the impact of headspace and precipitate formation on PFAS concentrations. Knowledge of industry-standard field practices will be collected and used to inform laboratory and field tests. Key messages and findings will be used to refine guidelines for sampling and storage and communicated through publication, webinars, and short courses.

The three tasks are designed to test the following hypotheses:

  1. PFAS stratification in the water column is a function of water chemistry and the chemical properties of the PFASs present;
  2. Many of the materials that current guidelines prohibit actually do not pose a significant risk of sample contamination, and add unnecessary cost to field sampling efforts, while others not mentioned in guidance (e.g., driller’s materials) may create false positives;
  3. Artifacts that occur during storage due to sample bottle type, subsampling, and storage conditions can be avoided, thus limiting the potential for sample bias.

A surface microlayer sample is collected by repeatedly dipping a glass plate into surface water. PFAS concentrate in the surface microlayer due to their affinity for interfaces. Field studies are ongoing to compare results from different sampling techniques. A field sampler prepares to collect a bulk water sample by skimming along the water surface or submerging the bottle.


The experiments performed for this study will explicitly determine if bias occurs due to stratification under realistic groundwater and surface water conditions. The project will provide data (actual measurements) to support the selection or elimination of field materials and protocols in order to minimize or eliminate PFAS background. Sample storage and handling protocols that eliminate bias also will be identified. Best practices will be assembled into guidance that will be communicated directly to stakeholders. (Anticipated Phase II Project Completion - 2025)


Deeb, R.A., E.L. Hawley, C. Sayler, D. Bogdan, C.E. Schaefer, B. DiGuiseppi, A. Struse, J.A. Field, and T. Schwichtenberg. 2021. Assessing the Potential for Bias in PFAS Concentrations During Groundwater and Surface Water Sampling. SERDP Technology Transfer Producthttps://serdp-estcp-storage.s3.us-gov-west-1.amazonaws.com/s3fs-public/project_documents/ER19-1205_Technical_Report.pdf

Rodowa, A., E. Christie, J. Sedlak, G. Peaslee, D. Bogdan, B. DiGuiseppi, and J. Field. 2020. Field Sampling Materials Unlikely Source of Contamination for Per and Polyfluoroalkyl Substances in Field Samples. Environmental Science and Technology Letters, 7(3):152-163. doi.org/10.1021/acs.estlett.0c00036.

Schaefer, C.E., M.C.S. Lemes, T. Schwichtenberg, and J.A. Field. 2022. Enrichment of Poly- and Perfluoroalkyl Substances (PFAS) in the Surface Microlayer and Foam in Synthetic and Natural Waters. Journal of Hazardous Material, 440:129782. doi.org/10.1016/j.jhazmat.2022.129782.

Schwichtenberg, T., D. Bogdan, C. Carignan, P. Reardon, J. Rewerts, T. Wanzek, and J.A. Field. 2020. PFAS and Dissolved Organic Carbon Enrichment in Naturally Occurring Foams on a Northern U.S. Freshwater Lake. Environmental Science and Technology Letters, 54(22):14455-14464. doi/10.1021/acs.est.0c05697.