LNAPL Transmissivity, Mobility and Recoverability—Utility and Complications

Light non-aqueous phase liquid (LNAPL) mobility, transmissivity (Tn), and recoverability are controlled by a suite of factors, namely release characteristics, the environment in which it resides, its age, physical/chemical properties, and others. LNAPL plumes are dynamic, but typically trend toward field stability after a release stops. Unlike groundwater mobility, finite LNAPL releases represent an ever-diminishing mobile mass due to degradation, residualization, and other factors that will be subsequently examined. For these and other reasons, mobility aspects vary both spatially and temporally. Tn is a useful, but complex, related parameter. It is commonly used to determine the applicability of LNAPL hydraulic recovery. But since it is not constant, a cutoff must be carefully considered, along with its manner of determination. Further, even if a plume is theoretically “recoverable” on a Tn rate basis that has very little relationship to whether that action would be expected to have any net environmental benefit. LNAPL hydraulic recovery is inherently self-limiting and has little net benefit unless a plume is mobile (and contained) or a significant mass recovery percentile is possible, which is rare.