ABSTRACT
According to the U.S. Environmental Protection Agency (USEPA 2011), as of March 2011, about 498,295 releases from underground storage tanks (USTs) have been reported nationwide. Cleanups have been initiated at 471,756 of these sites, and 407,680 sites have been cleaned up. The backlog of sites still to be cleaned up is 90,615. The majority of these USTs contained petroleum hydrocarbons, which are a mixture consisting mainly of compounds having low solubilities in water. When added to water, a liquid with low water solubility remains mostly isolated from the water in a separate phase, with a visible boundary between the two liquids.
For this reason, petroleum hydrocarbons and their components are commonly called nonaqueous phase liquids (NAPLs). This chapter and Chapter 8 are an introduction to understanding the environmental behavior of these important pollutants.
