INTRODUCTION Some areas of the underground environment within a few tens of meters of the surface are contaminated with gasoline, particularly in urban centers. Gasoline may leak from underground storage tanks, associated piping, and from distribu tion pipelines. The most prevalent sources are automotive service stations. Under ground releases may sustain liquid gasoline migration for considerable distances through permeable pathways above or along the water table. Gasoline can reside for decades underground; in some cases, long after the source has been aban doned, removed, or converted to other uses. Liquid gasoline is highly volatile, and its vapors are toxic and combustible. A small amount of gasoline introduced into an underground excavation can quickly generate a hazardous atmosphere.