LECTURE 11SVE & AIR SPARGING DESIGN, PERMEABLE REACTIVE BARRIERSSoil Vapor ExtractionSVE DesignSVE DesignApparent permeabilityGas pressureUnits for gas calculationsUnits for gas calculationsSVE design processSVE Applicability NomographDetermine applicability of SVESVE Applicability NomographDetermine applicability of SVE“Practical method” for SVE designEstimate vapor concentration in soilEstimate removal rate and removal timeRefine estimate of vapor flow rateRefine estimate of vapor flow rateRevise removal rate and removal timeSVE for mixturesAir permeability testingType curves for permeability testsType curves for permeability testsType curves for permeability testsType curves for permeability testsJacob Type CurveInterpreting Jacob Type CurveType curve with leakageLeakage effects in aquifer responseDetermine radius of influenceDetermine radius of influenceDesign of SVE systemsDesign consideration for SVESVE designVariations on SVEAir spargingDesign considerations for air spargingPilot tests for air spargingDesign considerations for air spargingDesign considerations for air spargingVariations on air spargingPermeable reactive barrierZero-valence iron wallZero-valence iron wallZero-valence iron wallZero-valence iron wallOther materials for treatment walls for chlorinated solventsDesign of treatment wallsColumn TestAnalysis of column-test resultsDesign of treatment wallsDesign curves for PRBPRB Effectiveness Over TimeTreatment wall design alternativesFunnel and Gate SystemPermeable Reactive Barrier InstallationBio-Polymer Installation of PRBAlternative PRB treatment mediaLos Alamos National LaboratoryMulti-media PRB at Los Alamos, NMDownstream view of multi-media PRBSide view of multi-media PRBPRB installation cost = $0.9 millionPermeable reactive barriersSoil FlushingSoil FlushingLECTURE 11SVE & AIR SPARGING DESIGN, PERMEABLE REACTIVE BARRIERSSoil Vapor ExtractionSee image at the Web site of Wayne Perry, Inc., Soil Vapor Extraction Systems, http://www.wpinc.com/remedy/remedy30.html Accessed May 11, 2004.Source: Wayne Perry, Inc., undated. Soil Vapor Extraction Systems. Wayne Perry, Inc., Buena Park, CA. http://www.wpinc.com/remedy/remedy30.html. Accessed November 17, 2002.SVE DesignVapor transport in the subsurfaceqa= airflow per unit area [L/T] (specific discharge)ka= apparent permeability of soil [L2]µa= air viscosity [M/L/T] = 1.8 x 10-4g/cm-s = 0.018 cP∇Pa= pressure gradient [(M/L/T2)/L] = [M/L2/T2]ρa= density of air [M/L3] ≅ 0.0012 g/cm3g = gravitational acceleration [L/T2]aaaaPkq ∇µ=SVE DesignVapor transport equation is simply Darcy’s Law:KiAAgPgkAPkAqQaaaaaaaaaa=⎟⎟⎠⎞⎜⎜⎝⎛ρ∇µρ=∇µ==()222322232LLLTLLTLLMTLMLTMTLLML⎟⎠⎞⎜⎝⎛⎟⎠⎞⎜⎝⎛=⎟⎟⎟⎟⎠⎞⎜⎜⎜⎜⎝⎛⎟⎠⎞⎜⎝⎛⎟⎠⎞⎜⎝⎛⎟⎠⎞⎜⎝⎛⎟⎠⎞⎜⎝⎛⎟⎠⎞⎜⎝⎛⎟⎠⎞⎜⎝⎛=Units:Apparent permeabilityApparent permeability of soil is closely related to intrinsic permeability but somewhat greaterPorosity is decreased by moisture in soilGas slippage (non-zero velocity at solid surfaces) increases transportIntrinsic permeability approximates apparent permeability in absence of site-specific dataGas pressureAbsolute pressure is measured relative to an absolute pressure of zeroAtmospheric pressure = 14.7 psia = 1 atmospherepsi = pounds (force) per square inchAbsolute pressure cannot be negativeGauge pressure is measured relative to atmospheric pressureDefine atmospheric pressure as zero = 0 psigGauge pressure can be negativePgauge= Pabs– 14.7 (in psi units)Units for gas calculationsVolumetric air flowEquipment is based on standard conditions—need to convert to actual conditions for designCFM = cubic feet per minuteSCFM = standard cubic feet per minuteACFM = actual cubic feet per minutetemp standard 460temp actual460pressure actualatm 1SCFM ACFM++××=Units for gas calculationsConcentrationConcentration is measured and reported in ppmv(parts per million by volume)Convert to mass per volume with:ppmv273)(T0.08211000MWatm in Pmg/L+×××=SVE design processTest applicabilityEstimate vapor concentrationEstimate removal rate and timeRough estimateEstimate removal rate and timeEstimate vapor flow rateRefined estimateField permeabilitytestingDesignDesignSVE Applicability NomographVapor Pressure (mm Hg)Success Very LikelyHigh (Gravel, Coarse Sand)WeeksMonthsMonthsYearsYearsWeeksMedium (Fine Sand) Low (Clay)Match PointSuccess Less LikelySuccess SomewhatLikelyButanePentaneBenzeneTolueneXylenePhenolAldicarbNaphthalene10410310210110-110-210-310-41SVE Likelihood of Success Time Since ReleaseSoil Air PermeabilityWeeksMonthsYearsAdapted from: Suthersan, S. S. Remediation Engineering: Design Concepts. Boca Raton, Florida: Lewis Publishers, 1997.Determine applicability of SVEApplicability of SVE depends on contaminants and porous mediumUse design nomograph:Select appropriate soil permeabilityWithin that soil permeability, enter on right at “time since release”Move horizontally to “soil air permeability”Draw straight line to “contaminant/vapor pressure”Where line crosses “SVE likelihood of success” gives first estimate of successSVE Applicability NomographVapor Pressure (mm Hg)Success Very LikelyHigh (Gravel, Coarse Sand)WeeksMonthsMonthsYearsYearsWeeksMedium (Fine Sand) Low (Clay)Match PointSuccess Less LikelySuccess SomewhatLikelyButanePentaneBenzeneTolueneXylenePhenolAldicarbNaphthalene10410310210110-110-210-310-41SVE Likelihood of Success Time Since ReleaseSoil Air PermeabilityWeeksMonthsYearsAdapted from: Suthersan, S. S. Remediation Engineering: Design Concepts. Boca Raton, Florida: Lewis Publishers, 1997.Determine applicability of SVEOther considerations not in nomograph:SVE is less effective in moist soilSVE is less effective in high organic content soil“Practical method” for SVE designNext step after determining SVE is applicableReference (widely cited):P.C. Johnson, C.C. Stanley, M.W. Kemblowski, D.L. Byers, and J.D. Colthart, 1990. A Practical Approach to the Design, Operation, and Monitoring of In Situ Soil-Venting Systems. Ground Water Monitoring Review, Vol. 10, No. 2, Pp. 159-178. Spring 1990.Estimate vapor concentration in soilCest= estimated vapor concentration [mg/L]xi= mole fraction of component i in NAPL (e.g., benzene in gasoline [dimensionless]Piv= pure component vapor pressure at temperature T [atm]Mw,i= molecular weight of component i [mg/mole]R = gas constant [L-atm/mole/ºK]T =