ASTM E2856-12

4.1.1 LNAPL transmissivity is an accurate metric for understanding LNAPL recovery, is directly proportional to LNAPL recoverability and tracking remediation progress towards residual LNAPL saturation.

4.1.2 LNAPL transmissivity can be used to estimate the rate of recovery for a given drawdown from various technologies.

4.1.3 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.

4.1.4 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.

4.1.5 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).

4.1.6 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).

4.1.7 The accurate calculation of LNAPL transmissivity requires certain aspects of the LNAPL Conceptual Site Model (LCSM) to be completely understood and defined in order to calculate LNAPL drawdown correctly. The methodologies for development of the LCSM are provided in Guide E2531. The general conceptual site model aspects applicable to this guide include:

4.1.8 Incorporation of LNAPL transmissivity can further LCSMs by providing a single comparable metric that quantifies LNAPL recoverability at individual locations across a site.

4.1.9 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 4.2 Purpose—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.

4.3 Precision and Bias—At this time this document aims to provide methodologies for data collection and analysis to yield an accuracy of LNAPL transmissivity values within a factor of two (compared with the unknown actual value). This modest accuracy is reasonable based on the overall industry experience in implementing these procedures and the lack of comparison studies. The objectives initiated through development of this document are to provide improved guidance for more consistent data collection and analysis methodology, which in turn will provide a larger and more accurate data set on which to base future methodology revisions and improvements.

1.2.1 Section 2 presents documents referenced.

1.2.2 Section 3 presents terminology used.

1.2.3 Section 4 presents significance and use.

1.2.4 Section 5 presents general information on four methods for data collection related to LNAPL transmissivity calculation. This section compares and contrasts the methods in a way that will allow a user of this guide to assess which method most closely aligns with the site conditions and available data collection opportunities.

1.2.5 Sections 6 and 7 presents the test methods for each of the four data collection options. After reviewing Section 1.2.6 Section 8 presents data evaluation methods. After reviewing Section 1.3 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.

1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

1.5 This document is applicable to wells exhibiting LNAPL consistently (that is, LNAPL transmissivity values above zero). This methodology does not substantiate zero LNAPL transmissivity; rather the lack of detection of LNAPL within the well combined with proper well development and purging procedures are required to confirm zero LNAPL transmissivity.

1.6 This document cannot replace education or experience and should be used in conjunction with professional competence in the hydrogeology field and expertise in the behavior of LNAPL in the subsurface.

1.7 This document cannot be assumed to be a substitute for or replace any laws or regulations whether federal, state, tribal or local.