The atmospheric release of benzene, toluene, ethylbenzene, and xylene from contaminated soils

Abstract

Chemicals may enter the environment in a number of ways accidents, spills during transport, leakage from waste disposal or storage sites, or discharge from industrial facilities. Hydrocarbons usually enter the environment through accidental spills or the leaking of storage tanks and their piping. The number of leaking underground storage tanks (LUST) that are reported to government agencies has dramatically increased in the past several years. It is estimated that of 2.1 million buried fuel tanks, 360,000 sites will be reported leaking by 1997. The Environmental Protection Agency (EPA) estimates that it will take 20 to 30 years and an average of $ 1 00, 000 to $400, 000 per site to remediate all sites. Many techniques have been developed for the remediation of gasoline contaminated soils. Excavation and removal of soils containing hydrocarbons is the most widely used remediation technique because of immediate and total site cleanup. Benzene, toluene, ethylbenzene, and xylene (BTEX) combined are from 10 to 40 percent of unleaded gasoline. During the excavation of LUST and the storage of the contaminated soils, many of the lighter compounds in gasoline (including BTEX) volatilized into the atmosphere. The objectives of this study were to: evaluate the impact of soil type on the volatilization of BTEX from excavated soil-, evaluate the impact of the thickness of the layer of excavated soil on the volatilization of BTEX; and evaluate the impact of a layer of sewage sludge placed over the excavated soil on the volatilization of BTEX from the soil. In the studies, BTEX exhibited a two phase vaporization process. During the first phase (24 to 72 hours) of vaporization, free product is the source of BTEX released into the atmosphere. Sixty to ninety percent of the BTEX applied to the soil was vaporized during the first phase of volatilization. During the second phase of release, the vaporization of BTEX occurred slowly as the smaller fractions of BTEX volatilized from the other phases of the soil system. Ninety to one hundred percent of the BTEX applied was vaporized during the experiments. The rate of volatilization from a Brackett clay soil was approximately IO% less than the rate from a Weswood silt loam soil. The lower amount of BTEX volatilized was attributed to the higher organic carbon content and higher clay content in the Brackett clay soil. There was no significant observed effect on the rate and amount of volatilization from different depths of excavated soil. Increasing the amount of organic matter in a soil, such as adding a layer of sewage sludge, decreased the rate and amount of BTEX volatilization.