Application:
LNAPL transmissivity is an accurate metric for understanding LNAPL recovery, is directly proportional to LNAPL recoverability and tracking remediation progress towards residual LNAPL saturation.
LNAPL transmissivity can be used to estimate the rate of recovery for a given drawdown from various technologies.
LNAPL transmissivity is not an intrinsic aquifer property but rather a summary metric based on the aquifer properties, LNAPL physical properties, and the magnitude of LNAPL saturation over a given interval of aquifer.
LNAPL transmissivity will vary over time with changing conditions such as, seasonal fluctuations in water table, changing hydrogeologic conditions and with variability in LNAPL impacts (that is, interval that LNAPL flows over in the formation and LNAPL pore space saturation) within the formation.
Any observed temporal or spatial variability in values derived from consistent data collection and analysis methods of LNAPL transmissivity is not erroneous rather is indicative of the actual variability in subsurface conditions related to the parameters encompassed by LNAPL transmissivity (that is, fluid pore space saturation, soil permeability, fluid density, fluid viscosity, and the interval that LNAPL flows over in the formation).
LNAPL transmissivity is a more accurate metric for evaluating recoverability and mobile LNAPL than gauged LNAPL thickness. Gauged LNAPL thickness does not account for soil permeability, magnitude of LNAPL saturation above residual saturation, or physical fluid properties of LNAPL (that is, density, interfacial tension, and viscosity).
The accurate calculation of LNAPL transmissivity requires certain aspects of the LNAPL Conceptual Site Model (LSCM) to be completely understood and defined in order to calculate LNAPL drawdown correctly. The methodologies for development of the LSCM are provided in Guide E2531. The general conceptual site model aspects applicable to this guide include:
Equilibrium fluid levels (for example, air/LNAPL and LNAPL/water).
Soil profile over which LNAPL is mobile.
LNAPL hydrogeologic scenario (for example, unconfined, confined, perched, macro pores, and so forth).
LNAPL density.
Hydraulic conductivity for each soil type within the well screen interval.
Well screen interval in the vadose and saturated zones.
Incorporation of LNAPL transmissivity can further LSCMs by providing a single comparable metric that quantifies LNAPL recoverability at individual locations across a site.
Each of the methods provided in this document is applicable to LNAPL in confined, unconfined, and perched conditions. Any differences in evaluation are discussed in Section 5.
Purpose8212;The methods used to calculate LNAPL transmissivity have been published over the past 20 years; however little effort has been focused on providing quality assurance for individual tests or refinement of field procedures. In addition to summarizing the existing methods to calculate LNAPL transmissivity, this document will provide guidance on refined field procedures for data collection and minimum requirements for data sets before they are used to calculate LNAPL transmissivity.
Considerations8212;The following section provides a brief review of considerations associated with LNAPL transmissivity testing.
Aquifer Conditions (confined, unconfined, perched)8212;In general, each testing type is applicable to confined, unconfined, and perched conditions; however, consideration should be given to how LNAPL drawdown is ca.........
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