Lecture 18Leachate and gas production in landfillsMass balance for MSW landfillCollection systemsFactors that influence leachate generationLeachate generation at MSW landfillEstimating leachate generation in active landfillPrecipitationPore squeeze liquidEvaporationMoisture adsorption by wasteLeachate generation at active MSW landfillLeachate collection systemInstalling leachate collection pipeInstalling drainage layerLeachate drainage layerPrimary leachate collection system (PCLS)Geonet drainage layerGeonet installationLeachate collection systemDrainage pipePipe installation at landfillPipe installationDrain designDrain design configurationsMound model for drainage spacingSizing of leachate collection pipesPipe capacity design chartLeachate collection pipe designLeachate collection via riser pipes above single linerLeachate sump designLeachate sump designLeachate collection – double linerLeachate collection pumpLeachate sump riser pipeFilter layer designFilter layer designFilter layer designFilter layer designGeotextile cloggingSecondary leachate collection system (SLCS)Secondary leachate collection system (SLCS)Prefabricated drainsLandfill BiogeochemistryLandfill BiogeochemistryLandfill Gas ProductionProblems with landfill gasLandfill gas compositionLandfill gasesLandfill gas productionHydrocarbons in landfill gasGas generation ratesLandfill gas collectionCollection systemsPassive gas ventingActive gas collectionDesign considerations for gas collectionFlare for gas disposal at Crapo Hill LandfillLecture 18Leachate and gas production in landfillsMass balance for MSW landfillWaste in → Leachate + gas + transformed mass + waste remainingPrecipitation and ground-water inflow → leachate + moisture in wasteCollection systemsLeachatecollectionGascollection Compacted soil liner Secondary FMLDrainage/protection layer with secondary leachate collection system Solid waste Drainage/protection layer with primary leachate collection system Primary FMLGeotextile Gas Vent Layer Geotextile Barrier Protection Top Soil Cover Vegetative Cover Drainage Layer FMLFactors that influence leachate generationPrecipitationGround-water intrusionMoisture content of wasteParticularly if sludge or liquids are disposedDaily cover during filling periodFinal cover designLeachate generation at MSW landfillAdapted from: Qian, X., R. M. Koerner, and D. H. Gray. Geotechnical Aspects of Landfill Design and Construction. Upper Saddle River, New Jersey: Prentice Hall, 2002.0Jul-88 Jan-89 Jan-90Jul-895001000150020002500300035004000Jul-90 Jan-91 Jul-91 Jul-92Jan-92 Jan-93 Jan-94Jul-93DateLCRS Flow Rate (1phd)Active Filling Cover Installed Cell ClosedLCRS = Leachate Collection and Removal Systemlphd = Liters per hectare per day 1 lphd = 3.65 mm/yr.1000 mm/yr = 27,400 lphdAverage annual precipitation: 1000 mm/yr (39.4 in/year). Closure included placement of a geomembrane cover.Estimating leachate generation in active landfillLA= P + S – E – WA LA= leachate from active area P = precipitationS = pore squeeze liquid from wasteE = evaporationWA = waste moisture adsorption(all in units of L3/T)PrecipitationSee image at the Web site of the National Atmospheric Deposition Program,http://nadp.sws.uiuc.edu/isopleths/maps2002/ppt.gifAccessed May 13, 2004.Pore squeeze liquidNegligible for most wastesCan be significant for wastewater sludges –measured in laboratory testsEvaporationSource: Hanson, R.L., 1991, Evapotranspiration and Droughts, in Paulson, R.W., Chase, E.B., Roberts, R.S., and Moody, D.W., Compilers, National Water Summary 1988-89--Hydrologic Events and Floods and Droughts: U.S. Geological Survey Water-Supply Paper 2375, p. 99-104. http://geochange.er.usgs.gov/sw/changes/natural/et/Moisture adsorption by wasteTypical initial moisture content of waste1.5 in/ft 12 cm/mField capacity of waste 4 in/ft 33 cm/mAvailable moisture adsorption capacity of waste2.5 in/ft 21 cm/mSource: Bagchi, A., 1994. Design, Construction, and Monitoring of Sanitary Landfill, Second Edition. John Wiley & Sons, New York.Leachate generation at active MSW landfill0Feb-97Mar-97Apr-97May-97Jun-97Jul-97Aug-97Sep-97Oct-97Nov-97Dec-97Jan-98Feb-98Mar-98Apr-98May-98Jun-98Jul-98Aug-98Sep-98Oct-98Nov-98Dec-98Jan-99Feb-99Mar-99Apr-99May-99Jun-99Jul-99Aug-9920406080100120140160180200Leachate Generation Rate and Precipitation (mm)Precipitation and Leachate Generation Rate at a Municipal Solid Waste Landfill in Active ConditionPrecipitationDateLeachate Generation RateAdapted from: Qian, X., R. M. Koerner, and D. H. Gray. Geotechnical Aspects of Landfill Design and Construction. Upper Saddle River, New Jersey: Prentice Hall, 2002.Leachate collection systemLeak Detection SystemPrimary Liner SystemPrimary LeachateCollection PipePrimary LeachateCollection SystemSecondary LeachateCollection PipeSecondary Liner SystemSloped Cell SubgradeExample of Leachate Collection System with Sloped SubgradeAdapted from: Qian, X., R. M. Koerner, and D. H. Gray. Geotechnical Aspects of Landfill Design and Construction. Upper Saddle River, New Jersey: Prentice Hall, 2002.Installing leachate collection pipeSee image at the Web site of Biometallurgical Pty Ltd. www.users.bigpond.com/BioMet/photos/photos1.htm. Accessed May 13, 2004.Installing drainage layerSee image at the Web site of Biometallurgical Pty Ltd. www.users.bigpond.com/BioMet/photos/photos1.htm. Accessed May 13, 2004.Leachate drainage layerDrainage layers are considered as small aquifers: flow characteristics defined in terms of transmissivity (or thickness and hydraulic conductivity), length, and widthUse Darcy’s Law to predict flow per unit widthDarcy’s Law may not apply to some geonets, etc., because flow may be turbulentGeonet manufacturers quote the transmissivity of geonetshowever since there is not a good alternative calculation procedurePrimary leachate collection system (PCLS)EPA minimum technology guidance regulations in 1985Requirements:Granular soil drainage material30 cm thickK ≥ 0.01 cm/sec (T > 3 x 10-5m2/sec = 0.02 ft2/min)(equivalent to sand and gravel)Slope > 2%Include perforated pipeInclude layer of filter soilMust cover bottom and side walls of landfill (side walls can be difficult to construct and maintain)Source: U.S. EPA, 1989. Seminar Publication: Requirements for Hazardous Waste Landfill Design, Construction, and Closure. Report Number EPA/625/4-89/022. Center for Environmental Research Information, U.S. Environmental Protection Agency, Cincinnati, Ohio. August 1989.