One way to look at light non-aqueous phase liquid (LNAPL) drivers for remediation is to break them down into: (1) physical science issues and (2) human science issues. Physical science drivers include saturation and composition risks. Saturation risks are primarily related to migration of LNAPL, if the LNAPL mass present is great enough for migration to occur. Composition risks are the classic human health and ecological risk-based evaluation pathways that typically address exposure to dissolved-phase or vapor-phase hydrocarbon chemicals of concern (COCs). The primary drivers governing evaluation of remediation need and design of selected remedies should be the physical science drivers, which govern both risk and technical feasibility.
Human science drivers include regulatory requirements, legal issues, business issues, and perception concerns. The primary regulatory requirement of concern is the requirement to “recover to the maximum extent practicable (MEP)”, which has historically resulted in LNAPL remediation goals ranging from no measurable LNAPL to some arbitrary thickness of LNAPL in wells. These MEP requirements are not grounded in multi-phase fluid science and are often unattainable with current remediation technologies. Similarly, the perception that the mere presence of LNAPL requires remediation does not recognize that the LNAPL may pose no risk (if saturations are too low for migration and compositionally the LNAPL contains COCs at concentrations below risk-based thresholds).
Frequently these human science drivers are important, but they may primarily serve as secondary drivers that modify or adjust the selected approach rather than controlling the technology selection or design. For example, attempting to design to an arbitrary MEP (e.g., 1/8 inch measured LNAPL in wells) may result in endless operation of costly remediation systems that achieve little to no improvement in human health or environmental protection. By focusing on the physical science drivers that govern risk and technical feasibility, LNAPL remedies can be designed to efficiently achieve meaningful and lasting protection of human health and the environment.
Some states have already begun to implement this approach (e.g., Texas, Minnesota). For other agencies with arbitrary LNAPL thickness goals, reasonable remedy selection and endpoint metrics may be attainable by demonstrating the “Technical Impracticability” of the arbitrary thickness standard through pilot testing and modeling or analysis of operational remediation data for your site.
Remember – “Have a Plan, Don’t Pump Because You Can.”