Soil properties for the Contiguous United States at a 250-meter resolution, based on 30-meter resolution data from the Polaris database

Per- and polyfluoroalkyl substances (PFAS) chemicals are known to strongly sorb onto soils when being transported downward through the vadose zone. The degree to which this sorption occurs depends on the length of the specific PFAS molecular chain and the properties of the soil. The properties with greatest influence on the soils PFAS sorption potential are percent silt and clay, and organic matter content (Fabregat-Palau and others, 2021), which have small size fractions that provide more sorption sites. In addition to sorption, the estimated long-term mean-annual vertical transport velocity of any chemical in a soil zone can be calculated given the recharge rate and volumetric water content. The latter can be calculated given the recharge rate, percent clay, and saturated hydraulic conductivity (Clapp and Hornberger, 1978). Also, the retardation factor can be calculated if the bulk density and water content are known. Given these requirements, raster data of these soil properties, in addition to several others, were downloaded from the Polaris Soils database made available in 2019, and used in preliminary analyses to assess the vulnerability of shallow groundwater to perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) contamination at a national scale. The POLARIS data that were chosen in this study were percent silt, percent clay, percent sand, percent organic matter, saturated water content, saturated hydraulic conductivity, and bulk density. Rasters of these soil properties for each of the six depth layers included in the database were created for the contiguous United States (see compressed files percentclay.7z, percentsilt.7z, percentsand.7z, bulkdensity_bd.7z, saturatedhydraulicconductivity_ksat.7z, soilwatercontent_theta_s.7z, and soilorganicmatter_om.7z in Child Item section). The resulting rasters were used in analyses to create rasters of PFOS and PFOA sorption distribution coefficients (Kd values) as well as a classified soil raster based on the classic ternary diagram of the U.S. Department of Agriculture (Davis and Bennett, 1927). A 250-m resolution was chosen to be coincident with the 1-kilometer resolution grid of the USGS national hydrogeologic framework (Brassington and Younger, 2010). The POLARIS data are well represented at this, and even finer, resolutions (Chaney and others 2016). Future analyses to be conducted include combining these files with other existing rasters of mean-annual recharge and depth to the water table (Zell and Sanford, 2020) to develop a raster representing the vulnerability of shallow groundwater to PFOA and PFOS contamination for the contiguous United States.

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  "010:12"
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  "geospatial"
]