Design, Installation, and Operation of a Passive DNAPL Barrier at a Former Wood-Treating Site

摘要

Sites where relatively large volumes of viscous, dense nonaqueous-phase liquids (DNAPLs) have entered the subsurface prove difficult to remediate. DNAPL at such sites could remain mobile for years and removing sufficient DNAPL to reach groundwater MCLs has proven difficult or infeasible at many DNAPL sites. Consequently, remedial programs at such sites often include a DNAPL-barrier and/or collection component to address DNAPL migration from source zones. Historically, DNAPL barriers frequently constituted impermeable structures such as sealed steel sheet-pile walls, plastic curtains, and bentonite-slurry walls. A potentially unwanted consequence of such barriers is alteration of the groundwater flow field near the barrier. Such alteration may also allow DNAPL to migrate around the barrier. Active groundwater pumping from behind such barriers can mitigate undesirable alterations in the groundwater flow field. Such pumping systems can also be designed to collect and remove DNAPL. The primary disadvantage of this approach is that the pumping system must be operated until DNAPL mobility is reduced or eliminated, which could be many years, and extracted groundwater from DNAPL source zones usually requires treatment. These two factors add significant operation and maintenance costs to such a remedy.