LECTURE 8SOURCE CONTROL AND MANAGEMENT OF MIGRATIONClasses of Site RemediationCover systems (“caps”)Landfill Cover LayersCap layers: VegetationCap layers: soil layerCap layers: Protection layerCap layers: Filter layerCap layers: Drainage layerCap layers: Low K layerCap layers: Gas vent layerWhy a composite liner?Why a composite liner?What’s wrong with this picture?Flow through clay linerFlow through clay linerFlow through hole in FMLFlow through FMLFlow through composite linerReferences for liner leakage formulas:Flow through composite linerFlow through linersObservations on composite linersCapping as remedial actionGeomembrane and GeosynthenticLiner InstallationVertical cut-off wallsSlurry wallsSlurry Wall ConstructionExtended Backhoe for Slurry WallsClamshell Bucket for Deep WallsClamshell BucketHydromill for Deepest Slurry WallsSlurry wall constructionTypical vertical section for slurry wallAlternative vertical section for “hanging” slurry wall for LNAPLSAlternative horizontal plansSoil mechanics of slurry wallsPermeability of slurry wallsMaterials for slurry wallsMaterials for slurry wallsSlurry wall performanceEPA review of slurry wall successPotential sources of failure (leaks)Interlocking Sheet PilesSheet Pile InstallationSheet Pile GroutingGrout curtainsGrouting methodsGrouting patternsGrout materialsSolidification/stabilization (S/S)S/S is second most common source-control technology at Superfund sitesWastes treated by S/SS/S agentsPozzolansInorganic agentsSoliditech Ex-situ S/S ProcessEx-Situ Stabilization in Pug MillEx-Situ Stabilization in Pug MillIn-situ methodsShallow Soil MixingLarge Diameter Auger for Soil MixingSoil Mixing Machine for Deep Soil MixingDeep Soil MixerIn-situ vitrificationIn-situ vitrification processChemical containmentLECTURE 8SOURCE CONTROL AND MANAGEMENT OF MIGRATIONClasses of Site RemediationSource controlTechnologies to contain or treat sources of contamination (wastes or contaminated soil)Management of migrationTechnologies to control the movement of contaminants away from sources (usually in ground water)Cover systems (“caps”)Prevent physical contact and exposure to wasteSufficient cap may be enough thickness of soil to prevent humans or animals from digging into wasteReduce (or almost eliminate) precipitation infiltrationReduces/prevents transport of contaminants to ground water by infiltrating waterLandfill Cover LayersSource: Federal Remediation and Technologies Roundtable, February 12, 2003. 4.30 Landfill Cap (Soil Containment Remediation Technology). Federal Remediation and Technologies Roundtable, February 12, 2003. 4.30 Landfill Cap (Soil Containment Remediation Technology). http://www.frtr.gov/matrix2/section4/4_30.html. Accessed February 26, 2003.Cap layers: VegetationPurposes:Erosion controlInfiltration reduction by evapotranspirationCharacteristics:Shallow rooted plantsLow nutrient needsDrought and heat resistantSource: Federal Remediation and Technologies Roundtable, February 12, 2003. 4.30 Landfill Cap (Soil Containment Remediation Technology).Cap layers: soil layerPurposes:Support vegetationProtect underlying layersTypically 60-cm thickCrushed stone or cobbles may substitute in arid environmentsSource: Federal Remediation and Technologies Roundtable, February 12, 2003. 4.30 Landfill Cap (Soil Containment Remediation Technology).Cap layers: Protection layerAlso called “biotic barrier”90-cm layer of cobbles to stop burrowing animals and deep rootsNot always includedSource: Federal Remediation and Technologies Roundtable, February 12, 2003. 4.30 Landfill Cap (Soil Containment Remediation Technology).Cap layers: Filter layerPrevents clogging of drainage layer by fines from soil layerMay be geosynthetic filter fabric or 30-cm sandSource: Federal Remediation and Technologies Roundtable, February 12, 2003. 4.30 Landfill Cap (Soil Containment Remediation Technology).Cap layers: Drainage layerMinimizes contact between infiltrated water and low K layers belowPrevents ponding of water on geomembrane linerDrains by gravity to toe drains At least 30 cm of sand with K = 10-2cm/sec or equivalent geosyntheticSource: Federal Remediation and Technologies Roundtable, February 12, 2003. 4.30 Landfill Cap (Soil Containment Remediation Technology).Cap layers: Low K layer“Composite liner”: both geomembrane and low-K soil (clay)Low K prevents infiltration of water into waste: hydraulic barrierGeomembrane: at least 0.5 mm (20-mil ) thickCompacted clay: at least 60 cm with K ≤ 10-7cm/sSource: Federal Remediation and Technologies Roundtable, February 12, 2003. 4.30 Landfill Cap (Soil Containment Remediation Technology).Cap layers: Gas vent layerNeeded if waste will generate methane (explosive) or toxic gasSimilar to drainage layer: 30 cm of sand or equivalent geosyntheticConnected to horizontal venting pipes (minimal number to maintain cap integrity)Source: Federal Remediation and Technologies Roundtable, February 12, 2003. 4.30 Landfill Cap (Soil Containment Remediation Technology).Why a composite liner?Geomembrane (or FML – flexible membrane liner)Impervious for practical purposes except at holes, tears, imperfectly sealed seamsWith good construction QA/QC (quality assurance/ quality control), FML has one hole per acre (one hole per 0.4 hectare)Why a composite liner?Compacted clay linerProvides hydraulic and diffusional barrier at holes or breaksFMLClayComposite liner provides far more effective barrier than either FML or clay aloneWhat’s wrong with this picture?FMLClayDrainage layer between FML and clay removes the advantage of composite liner !!!Drainage layerPonded waterClayFlow through clay linerIf clay is saturated and water is ponded to depth h:hydraulic gradient, i, through clay is:Kiq or,KiAQ1DDhi==>+=hDSource for this and next several slides on flow through liners: U.S. EPA, 1991. Design and Construction of RCRA/CERCLA Final Covers. Report Number EPA/625/4-91/025. U.S. Environmental Protection Agency, Cincinnati, Ohio. May 1991.Unsaturated soilFlow through clay linerLiner qualityK(cm/s)Rate of flow (gal/ac/day)Rate of flow(L/ha/day)Poor 1 x 10-61,200 11,000Good 1 x 10-7120 1,100Excellent 1 x 10-812 110Flow through 90-cm clay liner due to 30-cm headFlow through hole in FMLOrifice equation:()area holea6.0t coefficien orifice Cgh2aCQB5.0B=≈==Ponded waterhArea aFlow through FMLLiner qualityHoles per acreRate of flow (gal/ac/day)Rate of flow(L/ha/day)Poor 30 @ 0.1 cm210,000 93,000Poor 1 @ 1