Improved Delivery of Remedial Agents Using Surface Foam Spraying with Vertical Holes into Unsaturated Diesel-Contaminated Soil for Total Petroleum Hydrocarbon Removal

Surface foam spraying technologies, employing natural infiltration processes, have recently been suggested to not disturb or mix contaminated soils. However, effective delivery of reactive remedial agents to the bottom area of a contaminated region using only natural infiltration processes can be a challenge. This study aimed to improve the delivery of remedial agents such as oxidants, microorganisms, and nutrients to all depths of 30 cm thick unsaturated diesel-contaminated soil using small vertical soil holes. Three vertical holes, occupying 0.8% of the total soil volume and 3% of the soil surface area, were made inside the 17.3 kg soil column. Persulfate oxidation foam and subsequent bioaugmentation foam spraying were applied for remediation of contaminated soil. Foam spraying with vertical soil holes improved the uniformity of distribution of remedial agents throughout the soil, as evidenced by the uniform pH, higher volumetric soil water content, and a microbial population of >107 CFU/g. Therefore, the total petroleum hydrocarbon (TPH) removal efficiency (88–90%) from bottom soils was enhanced compared to soil columns without holes (72–73%) and the control test (5–9%). The kinetic study revealed that relatively similar TPH biodegradation rates (0.054–0.057 d−1) can be obtained for all soil depths by using this new and simple approach.