Field test of high molecular weight alcohol flushing for subsurface nonaqueous phase liquid remediation

A pilot scale field test of non-aqueous phase liquid (NAPL) removal using h igh molecular weight alcohols was conducted at Operable Unit 1, Hill Air Fo rce Base, Utah. Petroleum hydrocarbons and spent solvents were disposed of in chemical disposal pits at this site, and these materials are now present in the subsurface in the form of a light nonaqueous phase liquid (LNAPL). This LNAPL is a complex mixture of aromatic and aliphatic hydrocarbons, chl orinated solvents, and other compounds. The field experiment was Performed in a 5 m by 3 m confined test cell, formed by driving interlocking sheet pi le walls through the contaminated zone into an underlying clay. The test in volved the injection and extraction of about four pore volumes (1 pore volu me = 7000 L) of a mixture of 80% tert-butanol and 15% n-hexanol. The contam inants were removed by a combination of NAPL mobilization and enhanced diss olution, and the results of postflood soil coring indicate better than 90% removal of the more soluble contaminants (trichloroethane, toluene, ethylbe nzene, xylenes, trimethylbenzene, naphthalene) and 70-80% removal of less s oluble compounds (decane and undecane). The results of preflood and postflo od NAPL partitioning tracer tests show nearly 80% removal of the total NAPL content from the test cell. The field data suggest that a somewhat higher level of removal could be achieved with a longer alcohol injection.