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LNAPL Transmissivity (Tn) Remediation Design, Progress and Endpoints

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Presentation on theme: "LNAPL Transmissivity (Tn) Remediation Design, Progress and Endpoints"— Presentation transcript:

1 LNAPL Transmissivity (Tn) Remediation Design, Progress and Endpoints
Broad Brush – information dense slides, but we’ll cover much material quickly – handouts provide detail for reference H2A Environmental, Ltd. J. Michael Hawthorne, P.G. September 2010

2 Outline LNAPL multi-phase fluid mechanics review LNAPL metrics review
Introduction LNAPL multi-phase fluid mechanics review LNAPL metrics review LNAPL transmissivity (Tn) principles Applicability Summary Outline

3 Non-Wetting Fluid (Air or LNAPL) Filling Large Pore Spaces
LNAPL at the Pore Scale Multi-Phase Fluid Mechanics Sediment Grains Wetting Fluid (Water) LNAPL co-exists with water in aquifer pores LNAPL only partially fills the aquifer pore space The degree of LNAPL saturation depends upon lithology and fluid properties We now understand that LNAPL co-exists with water in the pore network within the aquifer. It does not float on the water table. The degree of LNAPL saturation depends on the history, lithology, capillary parameters, and fluid properties of the site and the volume of LNAPL released. LNAPL only partially fills the aquifer pore space, and saturation decreases with depth until water fills all the pores. The variation with depth of LNAPL saturation in the subsurface can be predicted when the properties of the subsurface media and fluid are known, and the apparent LNAPL thickness in the well is measured. This is accomplished by using the theories of Farr and McWhorter, and Lenhard and Parker. If sufficient measurements are taken across an LNAPL plume, the total volume of free LNAPL, its migration potential, and the recoverable volume also can be predicted. Spreadsheets (API Publication 4729) to perform these calculations have been made available by Randy Charbeneau for the API. RTDF 2006 Non-Wetting Fluid (Air or LNAPL) Filling Large Pore Spaces

4 Ideal vs. Observed LNAPL Saturations
Saturation curve height = thickness of mobile LNAPL interval Multi-Phase Fluid Mechanics RTDF 2006

5 T vs. Tn / Tn vs. Sn Multi-Phase Fluid Mechanics
Transmissivity (T) for water Unit cross-section, gradient, time Aquifer thickness Single fluid (krw drops out) LNAPL Transmissivity (Tn) Mobile LNAPL interval thickness Multi-fluid (krn matters) “How Much, How Fast” Multi-Phase Fluid Mechanics

6 Ideal LNAPL Metric Collective property incorporates:
Aquifer properties (e.g., permeability) Aquifer type (sand vs. clay) LNAPL properties (e.g., viscosity) LNAPL type (condensate vs. crude oil) Fundamental or characteristic property Repeatable Saturation / mass driven Easy and cheap to measure LNAPL Metrics

7 Non-Ideal Metrics - Thickness
Same mass exhibits different thicknesses in different soil types Inconsistent under varying hydrostatic conditions LNAPL Metrics Modified after Kirkman (2009) Modified after RTDF (2006)

8 Non-Ideal Metrics – Recovery Data
Benefits Direct measure of remediation performance Provides predictive data for decline curve analysis LNAPL Metrics Problems Strongly affected by system operational settings Varies by technology – not directly comparable Can’t be used to predict performance prior to startup

9 Tn – An Improved Metric LNAPL Metrics Tn Advantages
Direct numeric measure of hydraulic recoverability Varies directly with LNAPL saturation / mass Normalizes all sites to a single measurement standard Multiple Methods Measurable prior to, during and after remediation

10 LNAPL Transmissivity (Tn)
Analog to aquifer transmissivity Provides basis for mobility / recoverability analyses Four measurement methods Baildown / skimming tests Recovery data analysis skimming Vacuum enhanced skimming Total fluids pumping Multi-phase extraction Physical properties / modeling Tracer tests Hydraulic recovery only Dissolved and vapor phase risk issues are separate Transmissivity (Tn) Principles

11 Applicability – Uses for Tn
Alternative to laboratory Sn Model calibration parameter Technical impracticability threshold Remediation design parameter Operational progress metric Recovery end point Applicability

12 Applicability - TI Demonstration
Technical Impracticability (TI) requires either: Recovery system data “Can I please turn it off now?” Direct recoverability threshold metric Data from a pilot test and modeling study “Can I please not turn it on?” Robust calibration parameter for TI modeling Applicability

13 Applicability – Remediation Design
Remediation design parameter Compare different technologies (calibrated model) Technology-specific production curves Predicted rate and total volume decline curve analyses Sustainability Design parameters Equipment sizing Waste management / recycling volumes Design cost-benefit analysis Projected operational lifetime Capital vs. mobile infrastructure Applicability

14 Applicability – Operational Progress
Operational Progress Metric Recovery data decline curve analysis (progress towards endpoint) Non-recovery wells to monitor plume progress to endpoint Applicability

15 Tn Endpoint Analysis Hydraulic recovery end point (0.3 to 0.8 ft2/day)
Applicability (Kirkman 2010)

16 Tn Endpoint Analysis Applicability

17 Summary Summary Tn is an improved metric for hydraulic recoverability
Four calculation methods: Baildown / manual skimming testing Recovery data analysis Physical properties analysis Tracer testing Tn use as a metric Indirectly as a robust model calibration parameter Directly as a recoverability threshold ( ft^2/day) Remediation and Tn TI threshold Design parameter End point for hydraulic recovery Summary


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