"INTRODUCTION Contamination of ground water by hydrocarbons is a problem of concern to the petroleum industry. Various facilities such as service stations@ distribution centers@ and refineries have had releases of petroleum products (e.g.@ gasoline and diesel) to the subsurface. With growing awareness of the problem and the potential impact to drinking. Water supplies from ground water@ concern about hydrocarbon contamination of these aquifers has intensified. Osgood (1974)@ has documented some of the short term effects and the UST (Underground Storage Tanks) program by US EPA has been initiated in response to these growing concerns. Because of the large demand by society for petroleum products@ it is essentially inevitable@ considering the large volume stored and transported@ that some hydrocarbons will be released to the environment. The location@ definition and subsequent cleanup of these releases are in the interest of all parties. Once a release has occurred and the scope of the problem defined@ mitigation steps are initiated. Groundwater pumping for containment and recovery of the free hydrocarbon is most often used to remove the major portion of the contaminant from the environment. Bulk removal techniques alone are effective but cannot make the groundwater"" pure@ since trace contaminant levels can continue to make the water unpalatable. For example@ the threshold of odor is 0.1-0.5 mg/1 for petroleum (Kirkor 1951); 0.0005 mg for gasoline (Meldolder et al. 1953) and diesel oil (Holluta 1961); and 0.2-0.5 mg/1 for fuel oil (Holluta 1961). These levels are well below toxicity levels and therefore the goal is often to lower the contaminant level so the water is restored to a palatable@ odor-free condition. The purpose of this project was to examine the behavior of colloidal gas aprons (CGA's) injected into an unconfined ground water aquifer@ and the ability to direct them laterally along the water table interface The goal was to see if CGA's@ perhaps including nutrients and microorganisms in the formulation@ could be injected to enhance biodegradation in the hydrocarbon contaminated saturated zone and water table interface. More specificity@ the objectives of Phase I of this study was to demonstrate: (1) the efficiency of delivering colloidal gas aprons to desired locations within an unconfined groundwater aquifer@ and (2) the ability of CGA's to be generated and pumped in a pilot test size facility. The objective of Phase II of this project was to demonstrate the efficiency of delivering CGA's to the water table within an unconfined groundwater aquifer. and to move CGA's laterally (1) along a clean water table interface and (2) along a hydrocarbon (kerosine) contaminated water table interface."