Threshold limited kinetics of aromatic hydrocarbons in shallow soil systems

Remediation of petroleum-contaminated soils by biological decomposition is rapidly becoming a preferred methodology at numerous sites, particularly gas stations. Experience has shown that excavating the affected soils and landfarming in 4-inch to 8-inch lifts, above grade is the most effective method as critical design parameters can be accurately controlled. A common misconception with this practice, however, is that the rate of mineralization of hydrocarbons is directly proportional to their concentration over a wide range of concentrations. It is often assumed that microorganisms are able to metabolize and presumably are able to grow on all low concentrations of organic compounds. It was the objective of this study to assess the degradation kinetics of four landfarming plots which exhibited varying initial concentrations but similar soil types. It is important to understand the kinetic limitations of microbial systems. Cleanup criteria typically being set by state and federal regulators for benzene under the Resource Conservation and Recovery Act (RCRA) and the Comprehensive Environmental Compensation and Liability Act (CERCLA) range from 100 ppm to less than 1 ppm in soils. It was found that benzene concentrations below 100 ppm, cell growth patterns and benzene losses suffered significant threshold kinetic restraints