Investigation of permeability and leaching of hot mix asphalt concrete containing oil-contaminated soils

Oil-contaminated soil (OCS) results from leaking underground storage tanks, oil spills on clean soils, or soils surrounding petroleum refineries and crude oil wells. In Oman, Petroleum Development Oman (PDO) generates more than 50,000 ton/year of oil-contaminated soil. Recycling of OCS can be considered a viable solution to the disposal problem. This paper presents the results of investigating the permeability and leaching of asphalt concrete mixes containing OCS. Two types of soil were obtained from an asset area in northern Oman. Physical and chemical characterizations were performed on the OCS. The two soils were used as a replacement of fine aggregate in the asphalt concrete mix with percentages up to 40%, by total aggregate weight. Mixes were designed using the Marshall mix design method. Optimum asphalt contents were determined and samples were prepared at these asphalt contents and tested for permeability using a flexible-wall permeameter. Environmental assessment was performed by subjecting the mixes to the Toxicity Characteristic Leaching Procedure (TCLP) and analyzing the extract for heavy metals. The permeability was found to decrease with the addition of OCS. A significant decrease resulted when the percentage of OCS was increased to 30%. The leaching tests from the mix indicated that TCLP concentrations of the selected heavy metals were well below the TCLP regulatory limits for all OCS mixes.