TRACING A 5000 BARREL SUBSURFACE HYDROCARCARBON PLUME THROUGH A SUBURBAN COMMUNITY

A large hilltop regional tank farm in Northern Virginia recently lost approximately 250,000 gallons of fuel (diesel and gasoline), over a relatively short and recent interval. The fuel moved downhill on the water table (about 5-10 meters below the surface), and then under a surrounding community, which had been constructed approximmately 20 years after construction of the tank farm. Home values, previously not affected by the proximity of the tank farm, fell about 50%, and basement vapors forced several rapid evacuations. US-EPA directed wells were drilled into and in front of the subsurface plume, to determine plume volume, orientation, speed of advancement. and migration direction Vapor phase analyses best delinated the advancing margin of the plume, and revealed an advancement rate of about 100 meters/year. Eventually the plume became almost 1 km in length (and about 50 meters wide), and was halted when a gravel-filled trench was constructed across the path of the plume to collect and stop the downhill movement. Because of the numerous homes over the plume, remediation consisted of fuel removal from the wells, followed by modest efforts at bioremediation.