PROJECT DATE: June, 1975 to September, 1976
BACKGROUND: A gasoline spill from a storage tank was found when gasoline fumes were noticed in basements adjacent to the gasoline station. An undetermined amount of gasoline was lost to the shallow, unconfined sandy aquifer of high porosity and permeability. An extensive clay bed lay beneath the aquifer. Establishment of a physical recovery program resulted in the removal of 7,000 gallons, but the gasoline recovery decreased dramatically after two months to the point where only a few gallons were being recovered daily. The state agency in charge of the cleanup directed the operation to continue recovery operations until no trace of liquid gasoline remained on the ground water surface in order that the Millville well field be protected.
ACTION TAKEN: A biostimulation program was begun. Nutrients including ammonium sulfate, disodium phosphate, monosodium phosphate, sodium carbonate, calcium chloride- dihydrate, magnesium sulfate-monohydrate, manganese sulfate-monohydrate and ferrous sulfate-heptahydrate were added to the wells continuously or in batches. Air was introduced into the wells by a carborundum diffuser with an output of 10 SCFM. Producing wells were used to control ground water flow.
EFFECTIVENESS: The biostimulation program was not completely successful; residual gasoline was found at the last sampling period, but no free hydrocarbon was observed in any of the wells after the biostimulation program ended.The gasoline concentrations in cores taken from the aquifer did not seem to change substantially during the biostimulation program. Gasoline was found in the produced water which indicated that pockets of gasoline remained in the aquifer. One well which did not receive nutrients and air was still contaminated with gasoline. After the area near this well was treated, no free gasoline was found in any of the wells, and operations ceased with state approval. Microbial growth and utilization of nutrients and dissolved oxygen backed up the conclusion that enhanced microbial degradation was responsible for the removal of the gasoline.