The solvent ( Friendly for the environment) remove the trace of hard crude oil fraction from over the surface of the rock. This cleaning process was around four month later of oil spill.
The solvent go down through the rock, dissolving , removing and cleaning the dry crude oil and leaving it to sand.
The application of the mixture over the hydrocarbons are with the low tide and produce a complex solution with it. This complex, solvent --Hydrocarbons are removed later with the high tide.