Editor's perspective—LNAPL transmissivity: Mobility is the new state‐of‐the‐art cleanup metric

Historically, the ability to achieve a cleanup standard at sites with petroleum product floating on the groundwater table, referred to as light nonaqueous-phase liquid (LNAPL), has been judged on the amount of remaining LNAPL observed in wells, an approach that seemed perfectly rational at the time it was first developed. Generally, in the past, the entity responsible for the cleanup would hire a consultant and contractor who would use best engineering practices to remove as much petroleum product as possible and then measure the remaining product thickness in wells to compare to an applicable standard, generally a “no measurable product” objective. At many sites, the law of diminishing returns applied and, although the majority of the LNAPL initially present in wells was removed, a thin yet measurable LNAPL layer remained. Cleanup was not achieved, and the remediation team, including the responsible party, was locked in a quagmire over how to best finish the cleanup. Often, the decision would be just to take minimal action by using a long-term passive remediation approach, such as absorbent socks and monitoring. This approach rarely results in a cleanup that meets regulatory acceptance within a reasonable time period. This overall approach, while intuitively practical—you have contamination and need to remove it to achieve a cleanup—neglects an understanding of two important concepts: