Long-Term AS/SVE for Petroleum Removal in Low-Permeability Piedmont Saprolite

A 3.5-year pilot test of air sparging/soil vapor extraction (AS/SVE) was carried out to determine whether the heterogeneity of the Piedmont saprolite would allow adequate soil vapor velocities and effective vapor-phase extraction rates for petroleum hydrocarbon (PHC) remediation. The objectives were to compare: (1) the effectiveness of pulsed SVE versus pulsed AS/SVE operation; (2) benzene, toluene, ethylbenzene, and xylene (BTEX) versus PHC removal; and (3) biological versus physical removal of PHC. Stack exhaust gas, SVE wells, and soil vapor probes were monitored for total combustible hydrocarbons (TCH), BTEX, O2, CO2, temperature, and flow rate using handheld meters and gas chromatography. The majority of contaminant recovered was removed from the vadose zone via SVE. BTEX and TCH were both effectively removed from the more-permeable and highly contaminated unsaturated-saturated zone interface. Bioremediation accounted for 23% of total removal. Overall, the AS/SVE system physically removed an estimated 18,800 kg of PHC and 5,300 g of BTEX with an average rate of 70 kg d-1 and 0.4 g d-1, respectively, which was consistent with other AS/SVE studies in sandy media.