While the first training session provided a general overview of the spreadsheet tool and its use, this session will focus on specific examples showing how recharge data are used to estimate the transmissivity of LNAPL occurring in both confined and unconfined conditions. Assumptions and other considerations will also be discussed.

ASTM E-2856-11, Standard Guide for Estimation of LNAPL Transmissivity, identifies four primary methods to measure LNAPL transmissivity.  However, one of those four methods, recovery data analysis, has four sub-methods based upon the remediation technology used.  And one of those sub-methods, total fluids recovery data, can be further subdivided based on whether you plan to analyze long-term steady state data or instantaneous ratio test data.  The above chart graphically depicts the four primary methods and the associated sub-methods to create a clear visual picture of the multiple methods available under the ASTM standard.

The spreadsheet can be used to estimate LNAPL transmissivity in unconfined, confined, and perched conditions.  The tool does not automatically estimate transmissivity from recharge data, but requires varying degrees of user consideration with regard to the data and other input parameters.  The API spreadsheet tool and supporting documentation were developed to complement the new guide on LNAPL transmissivity published by ASTM (E2856-11).

Three-dimensional (3D) visualizations can provide powerful analytical capabilities in addition to “pretty pictures”.  3D visualization is particularly useful in conjunction with detailed microstratigraphic investigations (e.g., CPT), vertical Light Non-Aqueous Phase Liquid (LNAPL) impact profiles (e.g., laser induced fluorescence [LIF]), long-term equilibrium well gauging data, well construction data, and detailed topographic surveys.  While many factors control LNAPL distribution and migration potential, perhaps none is more important than microstratigraphy.

The capillary properties of thin stratigraphic horizons may be sufficient to either facilitate or inhibit LNAPL movement through the soil.  A microstratigraphic investigation (e.g., CPT) can identify such layers, and greatly facilitate understanding of the LNAPL conceptual site model (LCSM).  Macro-analysis of the microstratigraphic data can provide a broader understanding of critical stratigraphic geometries (e.g., LNAPL “traps” in high spots on the base of confining layers).  The addition of LNAPL impact profiles (e.g., LIF) can provide an understanding of the distribution and historical migration pathways of LNAPL through the soil profile within the microstratigraphic setting.  Long-term equilibrium gauging data provides a tool to evaluate the hydrogeologic conditions of the LNAPL (e.g., perched, confined, unconfined LNAPL), and data to identify critical surfaces (e.g., minimum historical NAPL/water interface elevation by well, which provides an estimated lower limit of the occurrence of mobile LNAPL).  Well construction and topographic data allow analysis of critical areas such as potential surface seeps.

All of this data can be combined into various types of 3D visualizations that can be rotated and sliced in any direction to better understand the 3D relationships of microstratigraphy, LNAPL distribution, and groundwater elevations.  Critical areas of the 3D blocks may be zoomed in to explore in detail the micro-scale stratigraphic variations critical to understanding LNAPL distribution and migration potential.  A stronger LCSM leads to better remediation design and optimization decisions.

Dr. Muthu’s experience includes sites impacted with petroleum hydrocarbons and chlorinated solvents.  He has conducted NAPL nature and extent studies, NAPL mobility and recoverability field investigations and modeling, risk assessment and vapor intrusion analyses, statistical analysis and interpretation of a wide range of environmental data, guidance document development and training for software, and report preparation consistent with state and federal environmental regulations.

Dr. Muthu received his Bachelor of Science degree in Civil Engineering and his Doctorate in Environmental Engineering from the University of Houston.  His doctoral dissertation is entitled “Residual NAPL Saturations in Unsaturated Soils for Two- and Three-Fluid Phase Systems”, and dealt with analysis and evaluation of residual NAPL saturation in various media subject to various hydraulic head stress levels.  Dr. Muthu is an active member of ASTM International, the American Society of Civil Engineers, the Texas Association of Environmental Professionals, and the Society of Petroleum Engineers.