"The U.S. Environmental Protection Agency (EPA) through its Risk Reduction Engineering Laboratory's Release Control Branch has undertaken research and development efforts to address the problem of leaking underground storage tanks (USTs). Under this effort, EPA is currently evaluating soil washing technology for cleaning soil contaminated by the release of petroleum products leaking from underground storage tanks. The soil washing program evaluated the effectiveness of soil washing technology to remove petroleum products (unleaded gasoline, diesel/home heating fuel, and waste crankcase oil) from an EPA-developed synthetic soil matrix (SSM) and from actual site soils. Operating parameters such as contact time, wash water volume, rinse water vowash waterhwater temperature, and effectiveness of additives were investigated. Further work was conducted to determine what effect, if any, additives have whwash waterto washwater. The additives investigated were CitriKleen (a biodegradable degreasing agent) and an organic surfactant. Actual soils from UST sites in Ohio and New Jersey were washed using the optimum parameters derived for the SSM. The results of the optimization tests using SSM indicated that greater than 90% of petroleum products could be removed from the SSM. In experiments using actual site soils and the same washing conditions, contaminant removal was lower than it was for the SSM experiments. Although the SSM experiments achieved high removals, only 55% of the washed soil mass wawash watered and a washwater containing over 20% swash watersproduced. The washwaters from the actual site soils experiments had less suspended solids, but it also removed fewer contaminants from the SSM."