Superfund Sites with Dense Non-Aqueous Phase Liquids (DNAPLs) may require additional groundwater treatment under a recent guidance document issued by the U.S. Environmental Protection Agency (EPA) on September 19, 2011. The OSWER directive, Clarification of OSWER’s 1995 Technical Impracticability Waiver Policy, #5355.5-32, instructs Regions to discard the 1995 guidance document that had advised Regions to provide Technology Impracticability (TI) waivers to sites where a DNAPL was contributing to groundwater contamination. According to the newest guidance “much progress” has been made in treatment of DNAPLs so Regions should not automatically grant a TI waiver without making additional evaluation of in-situ treatment options. In addition, the guidance “reminds” the Regions that even where a TI waiver is granted, EPA’s expectations are to prevent further migration of the contaminated groundwater plume, and that the remedy to be implemented must still be protective of human health and the environment.
A DNAPL is derived from a liquid that is denser than water. A significant spill of these liquids, including chlorinated solvents (such as trichloroethylene, tetrachloroethene, and 1,1,1-trichloroethane) tends to sink through the groundwater and pool when it reaches an impermeable layer of clay or bedrock. The recent guidance can be expected to make it more difficult to justify a remedy that allows a DNAPL to remain in place untreated.