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REGULATING LNAPL MOBILITY

REVIEW. LNAPL CHARACTERIZATION FRAMEWORK. . . Cmax. Cres. Should We Try to Recover to the Maximum Extent Practicable?. . Cpeak. . . Csat. Cmax. Cres. Cpeak. Csat. . MOBILITY RISK. . UNIT RECOVERY COST (O

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REGULATING LNAPL MOBILITY

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    1. REGULATING LNAPL MOBILITY Stephen S. Boynton, P.E., LSP Subsurface Environmental Solutions, LLC

    2. REVIEW

    3. LNAPL CHARACTERIZATION FRAMEWORK

    4. Should We Try to Recover to the Maximum Extent Practicable?

    5. WHAT DO WE AGREE UPON? Current public welfare UCL (1/2”) is not working well and is prohibiting closure of some LNAPL sites Product thickness measurements in monitoring wells are not a good indicator of LNAPL risk

    6. SUMMARY OF PROPOSED APPROACH Eliminate the current “thickness based” public welfare UCL of ˝” LNAPL in the formation Achieve NSR for current conditions Use “Mobility Criterion” as a way to address “potential” future risk to public welfare Provide LSP flexibility for evaluating potential mobility Make sure proposed mobility standard constitutes a “bright line”

    7. POTENTIAL CURRENT RISKS Vapor Intrusion Utility worker/construction worker Dermal Contact Dissolved phase impacts to water supply wells Discharge to surface water (dissolved and/or LNAPL) Continuing Source Explosion

    8. THE PLUME STABILITY CONUNDRUM

    9. PLUME STABILITY vs. POTENTIAL MOBILITY/RECOVERABILITY

    10. HOW LONG DOES IT TAKE TO REACH PLUME STABILITY?

    11. CONCLUSIONS MOST LNAPL PLUMES ARE STABLE THIS IS A VERY GOOD THING! RECOVERABLE LNAPL WILL EXIST WITHIN THE STABLE PLUME FUTURE “SUDDEN MOBILIZATION” OF LNAPL IS HIGHLY UNLIKELY

    12. ALTERNATIVE LNAPL MOBILITY EVALUATION TECHNIQUES Weight of Evidence LNAPL saturations/concentrations below Cres at all locations within LNAPL plume LNAPL < PLM (Practical Limit of Mobility) LNAPL Inherent Mobility (baildown tests) < PLIM

    13. LNAPL MOBILITY

    14. WEIGHT OF EVIDENCE LNAPL Release Volume and Plume Extent Soil Permeability Environmental Setting Age of Release LNAPL Viscosity Comparison to Published Values Product Thickness Measurements

    15. COMPARISON to Cres

    16. PLM APPROACH

    17. MOBILITY DEFINED

    18. RELATIVE OIL PERMEABILITY

    19. THE “PLM” CONCEPT Site mobility must be below the “Practical Limit of Mobility” or “PLM” Mo < PLM ki * kro .

    20. RECOMMENDED PLM Tech Practices Committee recommends a PLM that is the equivalent of a water saturated soil with a hydraulic conductivity of 10-4 cm/sec. To calculate the mobility equivalent we assume water with a viscosity of 1.0 cP and a density of 1 g/cc, and soil with a hydraulic conductivity of 10-4 cm/sec. Need to convert soil hydraulic conductivity to intrinsic permeability

    21. PLM CALCULATION PLM = ki * kro and ki = (khm)/(?g) m Now assume: kro = 1.0 (i.e. fully saturated soil with a single pore fluid) So expression for PLM reduces to: PLM = kh/(?g) Now just plug in values for kh, ? and g

    23. PLM IMPLEMENTATION

    25. COSTS Viscosity & Density (3 Temps) $265 Residual Saturation (centrifugal) $325 Relative Permeability Tests $1200

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