ABSTRACT
Cases of groundwater contamination by leaking underground storage tanks (USTs) have been increasing throughout the United States since early 1970s. 1 , 2 , 3 The most common cases are the contamination caused by leaking gasoline USTs. It is estimated that in the United States the total number of leaking gasoline USTs could be about 100,000 at the present time, and this figure may increase to about 350,000 by 1995. 4 Groundwater contamination by benzene, toluene and xylenes (BTXs) is coincident with the leaking USTs since gasoline contains approximately 3% benzene, 9 to 11% toluene, or 10 to 12% xylenes as antiknock additives.
