LNAPL Transmissivity: Lobbying the Regulators

Petroleum regulations vary significantly depending on the state where the remediation is being conducted. Most regulatory programs allow regulators to dictate progress towards remedial endpoints. In the beginning of a petroleum remediation project, the remedial goal is often to remove as much light non-aqueous phase liquid (LNAPL) from the subsurface as possible. As the thickness of LNAPL in a monitoring well gets smaller and smaller, the recovery endpoint acceptable to the regulator often becomes arbitrary and at times unachievable.

Traditionally, LNAPL thickness in monitoring wells has been used as the primary metric for determining LNAPL recovery endpoints during petroleum remediation projects. However, leaders in the petroleum industry, including the Interstate Technology & Regulatory Council (ITRC), the American Petroleum Institute (API), ASTM International (ASTM), and many regulatory agencies are starting to recognize that LNAPL transmissivity is a better metric than the conventionally used metric of observable LNAPL thickness present in monitoring wells.

  • The observable LNAPL thickness is of limited value in the evaluation of LNAPL mobility or recoverability; and can potentially result in the misinterpretation of site conditions. This is because gauged LNAPL thickness does not account for in situ parameters, such as; soil permeability, magnitude of LNAPL saturation above residual saturation, or physical fluid properties of LNAPL (e.g., density, interfacial tension, viscosity).
  • LNAPL transmissivity is a more comprehensive metric that is dependent on soil type, LNAPL type, LNAPL saturation, and thickness of mobile LNAPL and therefore a better predictor of LNAPL recoverability at a site.
  • According to the ITRC, sites in state regulatory programs in many states including California, Kentucky, and Florida have been closed or denied further action because the usage of LNAPL transmissivity as a metric demonstrated that there was a lack of LNAPL recoverability (irrespective of in-well LNAPL thickness).

Roux Associates has performed investigation, remedial design and construction management services for numerous petroleum clean-up projects throughout the United States. We have extensive experience evaluating the mobility and recoverability of LNAPL at both large and small petroleum remediation sites. Roux has experience using various methods of transmissivity estimation including baildown testing, analysis of hydraulic recovery system data, single well dye tracer analysis, and use of numerical models.

Roux Associates has managed some of the largest LNPAL recovery projects in the country. This has led to decades of experience in not only LNAPL remediation, but also the proven ability to establish reasonable endpoint goals has helped reduce our client’s long term liability and financial exposure. We have been able to successfully educate regulators as to the applicability of LNAPL transmissivity as a feasible metric and shortened the time period required to close sites.

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