Background Study of Arsenic Concentrations at a Rhode Island Site

Abstract

Arsenic concentrations in soils at a property in Newport, Rhode Island, were found to exceed both statewide background levels and remediation criteria. Mean arsenic concentrations of 12.0 mg/kg and 11.7 mg/kg in site and background soils, respectively, are both about four times greater than a background level of 2.7 mg/kg published by the Rhode Island Department of Environmental Management (DEM). A risk-based concentration of 0.4 mg/kg is necessary to meet DEM’s incremental cancer-risk target of 1x10-6. Given the similarity of arsenic concentrations in site and background soils and a lack of evidence of any anthropogenic releases of arsenic, a background study was undertaken to gauge whether concentrations of arsenic at the site are likely due to background conditions. The study was based on measured arsenic concentrations in 20 soil samples from the site and 21 soil samples determined by site investigators to represent background conditions. The mean arsenic concentrations in both site and background soils were found to be statistically similar, but the distributions of on- and off-site data differed, possibly due to land -development patterns. Although the results of the study do not indicate that site arsenic levels differed from background, the regulatory decision required installation of engineered barriers at the site to minimize contact with the soils.