By Dr. Ian Pepper, The University of Arizona
- To evaluate the incidence and mobility of PFAS analytes in soils that have received land-applied biosolids for multiple years.
- To measure PFAS concentrations in groundwater co-located with land application sites to create paired data sets of soil and water PFAS concentrations.
- To evaluate land application sites nationally across the U.S. with differing soils, depths to groundwater and climates, including irrigated and non-irrigated sites.
- To utilize the collected field data to validate a screening level transport model that predicts the potential of PFAS leaching to groundwater.
A total of 25 to 30 sites across the U.S. are anticipated. Figure 1 shows the current states where a site has been identified. At each site, personnel work pro-bono to sample soils within 3 plots:
- Control plot – no biosolids
- Low biosolids rate land application plot
- High biosolids rate land application plot
At each plot, soil samples are obtained via a soil core at 1’, 3’ and 6’ depths. Three cores are taken from each plot, resulting in a total of 27 soil samples (3 plots x 3 cores x 3 depths). Whenever possible, corresponding groundwater samples are also obtained. During all sampling events, the same standardized procedures are used, with appropriate protocols utilized to prevent PFAS contamination during sampling. All samples are shipped to the University of Arizona Water and Energy Sustainable Technology (WEST) Center where they are processed and subsequently analysed for PFAS analytes at the Arizona Laboratory for Emerging Contaminants (ALEC).
PROGRESS TO DATE
A total of 22 sites have been identified to date. Sampling began in the fall of 2022, and has continued through the 2022/2023 winter and spring 2023. Table 1 shows that a total of 10 sites so far have been sampled and several are scheduled for sampling. One site is located in Eastern Washington (Figure 2), and is headed up by Deirdre Griffin LaHue, a Washington State University faculty member.
Needless to say, this is not a simple project and the weather has not always cooperated. Weather related delays included a hurricane in Florida, and intense rainfall in Northern Texas. In addition, one California site also had weather issues. It is also worth noting that sampling began in the southern-most U.S. States and has moved north as seasons progressed from winter to spring. PFAS analysis is now underway for biosolids amended soils from several sites, and early data has shown PFAS analyte soil concentrations to be in the low ppb range for most samples.
Following all sites being sampled and PFAS analyses completed, data will be analyzed, and soil from select sites will be chosen for extensive soil analysis and characterization prior to the initiation of modeling the data. Priority of sites chosen for soil analysis will be given to sites with paired soil and water data sets, and/or interesting PFAS soil concentrations.
The project is successfully underway and on track to allow for the accomplishment of the study objectives. It is expected that all sites will be sampled by the end of 2023 and modeling will be concluded by the end of 2024.