Elevated Soil Arsenic Levels at a Former Crude Oil Storage Facility-Assessment, Remediation, and Possible Sources

Abstract

Surface and near-surface soil arsenic levels were measured at a former crude oil storage facility within the greater Los Angeles area of Southern California. Arsenic was present in soil within some portions of the site at concentrations defined as being hazardous by both the State of California and the United States Environmental Protection Agency. The elevated soil total arsenic concentrations ranged from about 30 to 2300 mg/kg and generally occurred in, and adjacent to, the former washing and storage tank locations and along piping runs. In contrast, background concentrations of arsenic in soil at the site ranged from less than the analytical method detection limits (0.5 mg/kg) to approximately 8.0 mg/kg. The elevated soil arsenic concentrations are believed to be the result of the use of arsenical corrosion inhibitors within production wells and possibly the use of arsenical biocides in washing and skimmer tanks. Flow lines from production wells within the oil field to the crude oil storage facility contained crude oil and produced (formation) water. Arsenical corrosion inhibitors placed into the oil wells may have flowed with the crude oil/produced-water streams into the washing and skimmer tanks. Over the course of approximately 55 years of operation, tankage and piping leaks at the facility may have contributed to the elevated soil arsenic concentrations encountered at the site. A site-specific cleanup goal of 22 mg/kg total arsenic was established by the regulatory agency with oversight for the site. Remediation of the arsenic-impacted soil was accomplished by excavation and on site treatment using a chemical fixation process. Confirmatory samples collected after the fixation process was completed verified that the treatment reduced the concentrations of arsenic that could by leached from the soil to nonhazardous levels. The treated soil was subsequently transported offsite to an asphalt recycling facility for incorporation into asphalt paving products.