A numerical study of barometric pumping
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A Numerical Study of Barometric Pumping. Jeff Sondrup AgE 588 Fluid Mechanics of Porous Materials April 11, 2001. Presentation Outline. Introduction Gas Transport & Barometric Pumping Model Description Model Results Conclusions. Subsurface Disposal Area, INEEL.

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A numerical study of barometric pumping

A Numerical Study of Barometric Pumping

Jeff Sondrup

AgE 588

Fluid Mechanics of Porous Materials

April 11, 2001


Presentation outline
Presentation Outline

  • Introduction

  • Gas Transport & Barometric Pumping

  • Model Description

  • Model Results

  • Conclusions



Voc background at the sda
VOC Background at the SDA

  • VOCs first discovered in GW near SDA in 1987

  • Soil gas survey confirmed SDA pits and trenches were a VOC source

  • Inventory search indicated sludges containing VOCs from Rocky Flats buried in SDA (1966-70)

  • Primarily carbon tetrachloride (CCl4) with TCE, PCE, and TCA

  • Vadose zone vapor sampling indicates a large plume

  • GW concentrations ND to slightly above MCL

  • Modeling estimates GW concentrations to peak decades in the future at several times MCL

  • ROD signed in 1994, Soil Vapor Extraction (SVE) preferred alternative

  • Five extraction wells began operating 1996, removed ~75,000 lbs TVOCs, ~48,000 lbs CCl4


Gas transport mechanisms in the vadose zone
Gas Transport Mechanismsin the Vadose Zone

  • Advection (contaminants travel with the bulk movement of air)

    • Natural: water displacement, barometric pressure changes, density

    • Induced: drilling, soil vapor extraction (SVE)

  • Diffusion (random motion of molecules)

  • Sorption (contaminants adhere to the rock/soil)

  • Vapor-Liquid Partitioning (contaminants move into and out of air-water)






Properties of carbon tetrachloride
Properties ofCarbon Tetrachloride



Barometric pressure sine wave approximation
Barometric PressureSine Wave Approximation


Base case simulation no barometric pumping
Base Case Simulation(No Barometric Pumping)


Barometric pumping square wave approximation d t 1 day
Barometric Pumping(Square Wave Approximation Dt=1 day)


Barometric pumping square wave approximation d t 10 day
Barometric Pumping(Square Wave Approximation Dt=10 day)


Barometric pumping sine wave approximation d t 1 day
Barometric Pumping(Sine Wave Approximation Dt=1 day)




Ccl 4 mass remaining in vz
CCl4 Mass Remaining in VZ


Ccl 4 mass accounting barometric pumping square wave d t 1 day
CCl4 Mass Accounting(Barometric Pumping, Square Wave, Dt=1 day)


Conclusions
Conclusions

  • Time step important when simulating BP

  • Square wave approximation is reasonable if pressure patterns predictable and repeatable

  • BP impact small but can be important

  • Impact is site and event specific (depends on contaminant, location, pressure patterns, subsurface)

  • Diffusion is the dominant mechanism

  • BP important for passive soil venting (gas extraction)


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