WRRCTR No.159 Decontamination of Chromium-Contaminated Soil in Hawai'i

Abstract

Approximately 1 841 m3 (65,000 ft^3) of chromium-contaminated soil, classified as hazardous waste (>5 mg/l chromium extract concentration as measured by the EP toxicity test) was found near the new pipe shop at the Pearl Harbor Naval Shipyard on Oahu, Hawaii. Unless treated to a safe level, the contaminated soil required disposal in a Class 1 landfill, the closest being in the continental United States. Based on simple laboratory and pilot plant procedures, the project proved that chromium could be effectively leached from the soil to a safe level by using a nearly 1:4 weighted soil to water ratio; reducing the pH to 2.5; adding sodium metabisulfite to chemically reduce chromium from Cr+6 to Cr+3 ; and then raising the pH to 8.5 to precipitate the chromium from solution. A full-scale operation, following the technology that was developed, successfully treated the soil to a safe level and subsequent testing of the treated soil at the disposal (landfill) site confirmed the effectiveness of the treatment operation.