A former industrial site was used for manufacturing and chemical storage over 25 years. During that time, waste and chemical spills from various chemical handling, storage, and transfer activities contaminated the site. Preliminary site characterization data indicate that the contaminants of concern are trichloroethane, benzene, 1,2-dichlorobenzene, and styrene. Soil concentrations of all these contaminants are above 1000 ppm. Previous soil borings had shown that most of the contamination was located 20 to 30 ft below the ground surface. The zone of contamination covers 3 acres. Groundwater occurs at 50 ft below the ground surface, 20 ft above the bedrock surface; it is not contaminated. The soils at the site are sandy clay and fairly homogenous. Based on this information, which remediation method do you recommend for the site? Why?