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.

Abstract of presentation to be given by Mike Hawthorne of H₂A (coauthors Andrew Kirkman of AECOM and Mark Adamski of BP America) at the LNAPL Site Management Strategies Session of the 2011 Battelle Bioremediation and Sustainable Environmental Technologies Conference, Reno, Nevada, June 27-30, 2011.

Background. Existing LNAPL distribution literature is heavily biased towards ideal unconfined conditions representing static water-table elevations.  Mobile LNAPL has been documented at multiple sites to be submerged below the water-table as well as existing perched above the water-table.  Given the substantially exaggerated apparent NAPL thicknesses (ANT) that can occur in wells under these conditions, the identification of confined or perched LNAPL at a site is critical to correctly characterize the mobile LNAPL interval thickness and stratigraphic occurrence in the LNAPL Conceptual Site Model (LCSM).  A more accurate LCSM will lead to better metrics for both LNAPL characterization and remediation.  For example, ANT in wells is a poor metric for remediation because the ANT represents LNAPL confining pressure rather than recoverability or thickness of the mobile LNAPL interval.  The presence of confined or perched LNAPL may also have a profound effect on LNAPL remediation technology selection.

Approach. LNAPL flow vertically is inhibited due to non-wetting phase capillary pressure limitations rather than soil permeability limits.  However, LNAPL confining capillary pressures typically coincide with reduced grain size in unconsolidated sediments.  Therefore, an improved understanding of microstratigraphy results in more precise identification of potential confining or perching layers.  Improved characterization tools (e.g., laser induced fluorescence or LIF, baildown testing, soil core analyses) simplify identification of confined or perched mobile LNAPL intervals.  By combining microstratigraphic characterization tools (e.g., soil core analyses) with mobile LNAPL interval identification tools (e.g., baildown testing, diagnostic gauge plots), stratigraphic intervals containing mobile LNAPL may be identified even under confined, perched or interbedded conditions.

Results. This presentation will discuss methods to identify confined and perched LNAPL, and will include a review of site-specific examples of both simple and complex confined and perched LNAPL sites.  The tools discussed include hydrostratigraphs, diagnostic gauge plots, visual soil boring data, CPT and laser induced fluorescence borings, soil core photography and core analyses, and baildown test data.

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.”

Q: Shannon, what strengths do you bring to the H₂A team?
A: My dual-engineering background has proven to be a valuable asset.  Two of our key areas of expertise at H₂A, active site remediation and applied NAPL science, require a knowledge of soil science, multi-phase fluid mechanics, and chemical/physical separation processes.

Q: What do you do when you are not saving the planet?
A: I talk shop with my husband, also an engineer, and spend time with my family.  We have two little boys who keep us hopping with their love of dirt and bugs.

Q: What is the last book that you read?
A: Llama, Llama Red Pajama by Anna Dewdney with my two-year-old.

H₂A recently made note of a new visitor frequenting our off-site system maintenance facility.  A common gray fox has taken up residence and is making itself at home in the tall foliage behind the building.

Here are three things you may not know about foxes – they are omnivores, eating both meats and vegetables; they can climb trees and often den in hollow tree trunks; and although more active under the cover of dark, they are not strictly nocturnal.