Long-term bioremediation of a subsurface plume in silty soil

In northern Virginia, a loss from a tank farm has produced two plumes, containing about 200,000 gal of diesel fuel, jet-A fuel, and gasoline. Evidence suggests that the longest part of the contamination plume moved to its present length of 2,500 ft in less than 5 years. Since natural biodegradation would require about 2,500 years to reduce the hydrocarbon contamination to the remediation endpoints, other methods have been considered. Excavation of the plumes would take an estimated 5 years. However the tank farm is surrounded by commercial buildings and expensive homes, and many of these buildings would have to be removed to reach the plumes. Enhanced natural bioremediation would require about 200 years at a start-up cost of about $1 million dollars and recurring costs of approximately $500,000/year. Infiltration galleries and enhanced subsurface permeability could reduce the remediation time to as little as 20 years.