Numerical investigations on feasibility of surfactant enhanced remediation of polycyclic aromatic hydrocarbons in an unsaturated subsurface system beneath an onshore surface spill site

The adaptability of in situ remediation techniques for low soluble fractions in petroleum products such as polycyclic aromatic hydrocarbon (PAH) is generally constrained due to their limited bio-availability owing to hydrophobicity. In the present study, a numerical model is developed to evaluate the effect of unsaturated hydraulic properties, equilibrium chemical partitioning as well as coupled reactions on the fate and transport of a typical PAH (phenanthrene) originating from a surface spill. Simulation of surfactant enhanced remediation using a non-ionic surfactant (Triton N-101) resulted in significant modifications in unsaturated hydraulic properties. The presence of natural organic matter (adsorption partitioning coefficient of 8.97 × 10-4 L/mg) as well as viable bacterial consortium (specific growth rate > 3.06 × 10-7 /sec) in the soil is found to be favouring the biodegradation in order to limit the reach of phenanthrene up to a depth of 200 cm. The results suggest that selection of surfactant type and dosage affected the extent of solubility enhancement of phenanthrene (from 1.27 to 11.5 mg/L); however, ultimately the typical bio-geochemical features of the subsurface seemed to control the success of remediation.