From environmental views, use of biological approaches only are be prefered. In soils with highly hydrophobic petroleum contamination such as PAH, these compounds strongly interact with soil matrix and can form separate phases because of low water solubility as result not readily degraded by microorganisms. Previous process in very aged contaminated soils specially in clay textures can be more strong thus bioavailability of hydrophobic compounds limited. For enhance the bioremediation efficiency, Chemical pretreatment of petroleum contaminated soils by Fenton/Fenton-like reactions which made oxidation products more soluble in water can be good options to overcomes the limitations of bioavailability so the time of bioremediation process would be reduced.

All the best

From my personal experience, degradation of PAHs occurs better and faster using, co-substrates with structural and functional affinity such as citral, limonene, eugenol, further lignin, salts of humic and fulvic acids, which polmérical structure resembles the complex structure of the aromatic hydrocarbons. Microorganism such as Penicillium chrysogenum , Aspergillus niger, Mucor and lignolítics fungi degrade PAHs efficiency. To reduce the hydrophobicity of these compounds employed molecular sieves zeolite  as Clipnotitlolita, which hydrate and made available Microorganisms water required, besides interacting with PAHs and immobilized, this is the condition for complex molecules such as PAHs , can be metabolized.

Both chemical preoxidation and addition of surfactants maybe an option in special cases, especially for the components refractory to biodegradation.

Adding the same time is counterproductive because both will eat each other. For labscale experiments we experienced beneficial effect of adding first oxidant than surfactant (case of PAH contaminated fine fraction). For application of surfactants for recalcitrant PAH contamination in our experience one has to avoid preferential biodegradation of surfactants. See http://appliedcolloidssurfactants.blogspot.com/2005/07/open-source-surfactant-combinations.html