AbstractThousands of leaking underground gasoline tanks have been found throughout California from which a tremendous amount of gasoline has leaked into ground water over the last half century. The most water‐soluble constituent of gasoline is benzene, and it typically contaminates ground water below leaking underground tanks. In a state‐mandated program 7,167 wells serving water‐supply systems throughout California were tested for a broad panel of organic contaminants. Of the wells tested, 812 (11.3%) had detectable concentrations of at least one of the contaminants tested for. Detectable concentrations of benzene were reported for only 10 wells. Similar findings were reported in surveys focused on San Gabriel and San Fernando Basins. While many processes influence the environmental fates of organic contaminants in ground water, the most likely explanation for the nonoccurrence of benzene is that it is destroyed near its source by biodegrad