Medium flow vapour extraction was used to enhance biodegradation of adsorbed phase petroleum hydrocarbon contamination beneath operational underground fuel storage tanks.

Recovery wells were installed to each side of tank farm, screened below the invert of the tanks, spaced in sympathy with soil porosity.
Initial extracted vapour concentrations of TVOC were in excess of 5000ppm and were scrubbed through granular activated carbon vessels prior to discharge to atmosphere. Off-gasses were monitored over a 20 week period and were seen to decay to less than 100ppm.

Biodegradation signature gasses such as methane and carbon dioxide were monitored throughout the works and used to evaluate the degradation conditions.

Flow rates were adjusted to maintain optimum conditions prior to approval and decommissioning. The station remained open throughout.