Arsenic is often present in soils naturally or from historical anthropogenic activities. Arsenic is commonly a constituent of potential concern at environmental remediation sites, even where there is no reason to suspect a release. Site risks are frequently driven by arsenic, and risk-based screening levels below background are not uncommon. However, determining whether arsenic concentrations are consistent with background typically requires an extensive background data set. The ability to gain access to representative background locations owned by third parties is problematic at best in any characterization study. Consequently, many sites undergo characterization and potentially remediation for arsenic concentrations in soil that may in reality be representative of background (natural or anthropogenic). This study examines a large soil arsenic background data set to provide insight on typical concentrations of arsenic that are naturally occurring or represent anthropogenic background.

Between 1995 and 2001, over 1,600 background soil samples were collected from 189 sites in Kentucky, Maryland, New York, Ohio, Pennsylvania, Virginia, and West Virginia. Samples were collected using strict Quality Assurance/Quality Control procedures under a United States Environmental Protection Agency (USEPA) Superfund Administrative Order on Consent (AOC) and were analyzed by USEPA-approved laboratories. All data were verified and 10% underwent detailed data validation. Arsenic concentrations in samples retained for statistical analysis ranged from 1.1 mg/kg to 89 mg/kg. Data are evaluated by state and by geology and are compared to USEPA and state risk-based screening levels (RBSLs). Some standard background threshold values (BTVs) are derived for each state and distinct geology. The BTVs are greater than RBSLs. This extensive, regional data set should be considered by all stakeholders involved in relevant risk-based decisions related to arsenic in soils. The consideration of this data set and the BTVs may aid in the appropriate identification of arsenic in soils below typical background concentrations. In turn, the use of BTVs may aid in identifying where risks are truly elevated relative to background, and thus where remediation may or may not be appropriate.