Advances in Design of LandfillsOver CCB Ponds and LandfillsMike Houlihan, P.E., BCEE, F.ASCEGeosyntec ConsultantsColumbia, Maryland16 January 2013OverviewCurrent State of PracticeProperties of CCBsKey Design IssuesCase HistoriesClosing CommentsCurrent State of the Practice•There is a broad range of operating and regulatorystandards in the USA•New CCB disposal facilities (i.e., those constructedbetween 1994-2004) generally have liner systems•Hundreds of existing CCB disposal facilities have noliner systems•Many of these sites are candidates forvertical/lateral expansions if they can be designedto comply with coming standards and good practiceReference: U.S. Environmental Protection Agency and U.S. Department of the Energy “Coal CombustionWaste Management at Landfills and Surface Impoundments”, 1994-2004, DOE/PI-0004, [2006]....Current State of Practice•Disposal methods have varied historically from wet (inthe South and in parts of the Midwest) to dry, fromengineered disposal facilities to structural fills.•USEPA will soon (?) decide on whether Subtitle C or Dliner requirements will apply•Placement of dry CCBs in engineered monofillcontainment facilities will likely become the requireddisposal method in the future•Relevant containment technologies are well understood,but the unique nature of CCB materials and past disposalpractices requires a new lookat engineering practices forCCB containment system designTypical Coal-Fired Electric Power PlantOverview of CCBsFly ashBottom ashFlue gas desulfurization (FGD) byproducts (i.e., gypsum)Boiler feedwater treatment wastewater solidsWastewater impoundment solidsMetal cleaning wastewater solidsCoal washing operation solidsAlso, water from these operations:Coal pile runoff and wash waterBoiler cleaning wastewatersBoiler blowdown waterCooling tower blowdown waterChange in Paradigmfor Power Companies?7Focus on Fly Ash...SilicateSilt sized (can vary)Round particles - apparently uniformLow unit weight/specific gravityHigh capillary tensionPhysically and chemically – remnants of parent coalIt is difficult to obtain and transport undisturbed samplesfor lab testing- it easily liquefies in transitBUT, excellent drained strengthWhat is Fly Ash?Particle Shape & Mineralogy•Aluminum silicates• Dominantly spherical• Significant internal voids• Void ratio and Gsdifficult to measureParticle size•75% finer than 45μm• Significant silt size fraction• Typically well graded• Varies by coal, facility,combustion process(Geosyntec/GeorgiaTech, 2009)Insitu Properties of Deposited AshNote: Very littlepenetrationresistance withdepth(TVA, 2009)Perhaps analogousto a House of Cards?1Strength of Fly Ash0501001502000 100 200 300 400Effective mean stress, p=(σ1'+σ3')/2 [kPa]

Deviatoric stress, q=( σ 1

- σ 3 )/2 [kPa]e=0.87e=0.80e=0.54e=0.48e=0.42φ=30°φ=35°0501001502002500 100 200 300 400 500Effective mean stress, p=(σ1'+σ3')/2 [kPa]

Deviatoric stress, q=( σ 1

- σ 3 )/2 [kPa]σc=50σc=100σc=300σc=400Series1Series2φ=30°φ=26°Triaxial Shear Strength in Lab•Tests performed on lab remolded specimens• Undrained strength similar to granular soils• Nominal beneficial effect of “density”• Generally dilatative response, even at high stress• Minimal tendency to contract• Strength and response similar to frictionalresponse of sands(Geosyntec/Georgia Tech, 2009)Aging of Ash1Shear wave velocity measurements ofremolded and fresh (i.e., un-hydrated) ashArithmetic Time Log TimeUnanticipated results, as KIF ash isClass F ash with little to no free limeSimilar indications observed in previously hydrated ash and block samples(Georgia Tech, 2009)Fly Ash Characterization ChallengesLimited accurate information available regarding fly ashmaterial propertiesLow CPT tip resistance can be misleading and cause undueconcerns regarding strengthEven Class F ash has been shown to “age” with time whenconfinedKey element is control of water (infiltration and internaldrainage)Each facility will have unique conditions based on materialproperties, construction methodology, operational history,and facility layoutFly Ash Characterization: Implications toClosure and Overfill PracticeFly ash and CCB materials are not typicalgeotechnical construction materials and need to bewell understood to characterize a site correctly anddevelop a good designFly ash properties vary from site to site, and can varywithin a site, as a function of many factors (coalsource, combustion process, air pollution controls,disposal method, disposal site operations, etc.)There is a growing body of knowledge of CCB and flyash properties, although not all of it is publicallyavailable... (EPRI Study should help in this regard)1State of Practice is Advancingfield dataLarge Body of Knowledge from theKingston failure investigationsEPRI StudiesGeotechnical properties of coal ashExpansion over coal ash pondsGroundwater monitoring at CCBdisposal sitesCoal Combustion Ash and ResearchInstitute, UNC CharlotteCenter for Applied Energy Research,University of KentuckyPracticing Engineers (although they arenot always at liberty to share their data)Technology Transfer throughConferences and SeminarKey Design IssuesOverfill Foundation StabilitySettlementSlope StabilitySeismic LiquefactionStatic LiquefactionLeachate Collections SystemsPerformance Assessment of Existing CCR landfillPotential forSettlement ImpactsIndustrial WasteCCB- Dry StackHazardous WasteLand Clearing WasteCCB – Wet StackConstruction/Demo DebrisMunicipal Solid Waste

Greater Less Potential Potential“Area” Settlement “Local” SettlementIndustrial WasteCCB’sHazardous WasteMunicipal Solid WasteLand Clearing WasteConstruction/Demo Debris

Greater Less Potential PotentialPotential forSettlement ImpactsGeneral• Settlement of CCBs in wet ponds is much greater than in dry stacks• Settlement in wet ponds can be in the range of 10% of total thickness of flyash (Class F) pond (based on Geosyntec experience at several sites)• Estimates are sensitive to material properties and can vary widelyPossible Localized Effects• Collapse of a void or poorly compacted CCB• Distortion/damage to liner• LCS grade reversal• Typically evaluated/quantified using analytical methodsPossible Area-Wide Effects• Excessive total settlement and grade reversal• Excessive differential settlement and grade reversal• Evaluated/quantified using conventional analytical methods or numericalmethods (FEM)How Can The Accuracy OfSettlement Estimates Be Improved?1.Specialized Undisturbed Sampling2.InSitu and Lab Testing3.Field Tests: Monitored Preload Fill-Pilot TestMonitored Preload Fill•A MPF provides a method to verify engineering calculations bymeasuring settlements on a pilot scale.•Basically: a large pilot scale test, somewhat expensive so not likelythe first choice of settlement estimate methods•Consists of application of load (soil layers) in increments andmeasurement of:• Settlement/deflection of the surface and subsurface layers• Pore pressures in the subsurface layers•It’s possible that, after a period of MPF performance and publication,the practice and regulators will depend on preload fill demonstrationsless and lessMPF Instrument LayoutData loggerStationSP-1SP-5SP-4SP-6SP-2SP-34” HDPE ProfilerPipePW-6 (40’)PW-7 (70’)PW-1 (40’)PW-2 (70’)PW-3 (30’)PW-4 (60’)PW-5 (90’)SONDEX PipeMPF BoundariesNProfiler “Settlement Measurement”Profiler Settlement Results00.511.522.533.544.50 100 200 300 400 500 600 700 800 900Settlement Profiler Line (southwest to northeast), (ft)

Total Settlement (ft)5/3/20075/14/20075/25/20076/9/20077/10/20078/7/2007Pore Pressure Measurements01000200030004000500060003/19/07 4/8/07 4/28/07 5/18/07 6/7/07 6/27/07 7/17/07 8/6/07 8/26/07Date

Pore Water Pressure (psf)PW-6 (40-ft)PW-5 (90-ft)PW-4 (60-ft)PW-1 (40-ft)PW-3 (30-ft)PW-2 (70-ft)PW-7 (70-ft)Key Design IssuesFoundation StabilitySettlementSlope StabilitySeismic LiquefactionStatic LiquefactionLeachate Collections SystemsPerformance Assessment of Existing CCR landfillCauses of Slope Instability•Increased Stress•External Loads – stockpile, equipment*•Increase unit weight*•Remove material by cut/excavation•Undermine by seepage erosion*•Shock – earthquake•Tension crack•Water pressure in crack** Influenced by water(after Sowers, 1979)Causes of Slope Instability•Decreased Strength•Swelling and adsorption of water*•Pore pressure increase*•Structural changes in soil*•Cracking caused by shrink-swell*•Strain and progressive failure•Thawing*•Weathering of soils** Influenced by water(after Sowers, 1979)Key Design IssuesFoundation StabilitySettlementSlope StabilitySeismic LiquefactionStatic LiquefactionLeachate Collections SystemsPerformance Assessment of Existing CCR landfillSeismic LiquefactionLiquefaction of saturated, non-cohesive, uniformly sizedsoils under seismic loading:Seismic LiquefactionThe prevention of seismic liquefaction requires expensive mitigationmethods:Construction of atoe berm(soil embankment) or buttress beyond the edge of thelandfill to maintain confinement of the subgrade;Installation of ashear keyat the edge of the landfill to resist the lateral movementsbelow the edge of the landfill;Performing apreload fillprogram to promote consolidation and reduceliquefaction potential or reduce the effectsof liquefaction, should it occur; andFoundation improvements,such as deep soil mixing and solidification, blastdensification, etc. to eliminate the conditions conducive to liquefaction.Additional study is necessary using laboratory cyclic triaxial and/or directsimple shear testing correlated to the project settingPreliminary laboratory data suggest that the risk of seismically-inducedliquefaction using the traditional analytical methods is over estimatedStatic LiquefactionCaused by relatively rapid loading of the subgrade that causesstrain-induced excess pore pressures that cannot beadequately dissipated, resulting in loss of material strengthand, typically, a bearing-capacity type failureFor proposed developments, can be analyzed during design,and avoided by construction methodsRecent lab testing is finding it difficult to induce staticliquefaction in CCB materialsKey Design IssuesFoundation StabilitySettlementSlope StabilitySeismic LiquefactionStatic LiquefactionLeachate Collections SystemsPerformance Assessment of Existing CCR landfillLeachate Collection SystemsDecreases in functionality caused by:Settlement-induced grade changes in LCS componentsClogging by fine particles and calcificationOverloading of existing leachate collection systems under existinglandfillsAddressed during design through testing and design of excessfiltration capacityThis is a key issue in CCB landfills compared to MSW because ofthe very large working areas that are common at CCB landfillsPonding of surfacewater on working “deck” is a design considerationthat is relatively unique to CCB landfillsOperationalSurfacewater ControlLeachate Collection SystemsTo prevent clogging, landfill LCS layers are typically overlain by a geotextile filterlayer, which must have a relatively small apparent opening size (AOS) to prevent theCCR material from passing through the geotextile.Large overburden pressures caused by the overlying CCR can reduce theeffectiveness of a geotextile filter.To address these design challenges:(i)perform a particle-size analysis of the CCR material to confirm the properties ofthe material that the geotextile must retain;(ii)test the geotextile filter under the expected overburden pressures to assess itsfiltration properties;(iii)provide excess filtration layer surfacearea over/around the collection/drainagegravel as a contingency in case the geotextile filter experiences some clogging;and(iv)provide a method of cleaning out the leachate collection and transmission pipesshould precipitates form or sediments accumulate that could reduce pipeconveyance capacityLeachate Collection SystemsTo prevent clogging, landfill LCS layers are typically overlain by a geotextile filterlayer, which must have a relatively small apparent opening size (AOS) to prevent theCCR material from passing through the geotextile.Large overburden pressures caused by the overlying CCR can reduce theeffectiveness of a geotextile filter.To address these design challenges:(i)perform a particle-size analysis of the CCR material to confirm the properties ofthe material that the geotextile must retain;(ii)test the geotextile filter under the expected overburden pressures to assess itsfiltration properties;(iii)provide excess filtration layer surfacearea over/around the collection/drainagegravel as a contingency in case the geotextile filter experiences some clogging;and(iv)provide a method of cleaning out the leachate collection and transmission pipesshould precipitates form or sediments accumulate that could reduce pipeconveyance capacityLCS Clogging Potential for CCBs: FGD10oz/yd2NW GEOTEXTILE FILTER8” DIA. SDR-9PERFORATED HDPENO. 2 STONESUBGRADECOMPACTED CLAY LINERSOIL COVERGraded Filter Drainage SystemKey Design IssuesFoundation StabilitySettlementSlope StabilitySeismic LiquefactionStatic LiquefactionLeachate Collections SystemsPerformance Assessment of Existing CCR landfillPerformance Assessment ofExisting FacilityEvaluate During Expansion Design:Liner System of Underlying LandfillData collection – is it available?Consider lack of siting criteria if a very old fillStability of underlying materialsOlder design standardMay not allow vertical expansionLeachate Collection SystemPipe strength - may not allow vertical expansionAccess to cleanouts, leachate removal, etc.Resulting slopes may not result in positive drainageCCB Expansion Project ExamplesTVA Kingston, TN – Peninsula Landfill,2010-2012Cardinal Landfill, OH: Improvement ofPoor Foundation, 2008R. Paul Smith, MD/WV – MSE BermCapacity Enhancement, 2008Case HistoriesCASE HISTORY ONE:Vertical Expansion Over Closed CCB PondCASE HISTORY TWO:Lateral Expansion and Overfill on CCB LandfillCASE HISTORY THREE:Overfill and Lateral Expansion on CCB Landfill and PondCase History #1 – VerticalExpansion Over Closed CCB PondOverview:110-acre Ash Pond Subgrade35 m of Mostly Saturated Fly Ash SubgradeClass I High Hazard Dam DownstreamLateral Groundwater InflowDesign Challenges:Significant site geometry constraintsDesire to construct expansion in small incrementsUtilize the existing footprint as much as practicalCase History #1:Site LayoutCase History #1: Cross SectionDesign Approach1.Design InvestigationUndisturbed and disturbed samplingBorings and cone penetrometer with dissipationtesting2.Liquefaction EvaluationLiquefaction potential was considered in the designFacility designed with a horizontal confining layer to restrain movementsConsolidation water drained using an underdrain layer of bottom ash todissipate pore pressuresDesign Approach3.Hydrostatic Uplift Potential- Lateral Groundwater InflowMitigated using Bottom Ash Underdrain below Liner to Dissipate PorePressuresMitigated using Sand Underdrain on Side Slopes4.Settlement EvaluationMitigated using a Moving Preload to Remove Significant Settlementbefore ConstructionHydrostatic UpliftHydrostatic UpliftCap/Liner Design Cross-SectionGeotechnical Design ConsiderationsHydrostatic UpliftChallenges:high GWT, increased pore pressures, groundwater seepage.Solutions:Side slope drainage blanket of 60-cm thick granular material below isolation layer.Groundwater underdrain of 60-cm thick granular material below isolation layer.Slope StabilityChallenges:Static and seismic slope stability for side slopes over fly ash, side slopes adjacent tothe mine spoil berm, and side slopes adjacent to the high wall.Solutions:Several failure modes, including filling scenarios analyzed. Strength gains offoundation through preloading. Liner, cover, and interim berm slopes limited to 3H:1V.SettlementChallenges:Limited data on flyash behavior, large settlements, liner strains, effect on LCS slopes.Solutions:Insitu (CPT/SPT), lab (consolidation and shear strength), and monitored preload testfill programs. Steeper slopes for underdrain andLCS pipes to account for settlement.Preload sequence before liner construction.LiquefactionChallenges:Material deposited in an ash pond is known tobe susceptible to seismic liquefaction.Limited data on liquefaction behavior of flyash was available.Solutions:Identified potentially liquefiable zones using grain size and CPT. Used residual shearstrengths using Stark and Olson approach.Increased soil layer thickness overliquefied zone to achieve a calculated FS > 1.Geotechnical MonitoringMonitored Preload:•800 ft X 500 ft, 3H:1V, 35 ft of flyash and mine spoils, 5 ft lifts•Settlement plates•Vertical extensometer (SONDEX pipe)•Horizontal settlement profiler•Vibrating wire pore pressure transducers•Topographic settlement plate surveys00.511.522.533.544.50 100 200 300 400 500 600 700 800 900Settlement Profiler Line (southwest to northeast), (ft)

Total Settlement (ft)5/3/20075/14/20075/25/20076/9/20077/10/20078/7/2007856.3876.3896.3916.3936.3956.3976.3996.3-0.5 0 0.5 1 1.5 2 2.5 3 3.5Total Settlement (ft)

Elevation (ft)020406080100120140 SONDEX Pipe Depth (ft)4/12/074/22/075/3/075/14/075/25/20076/9/20077/10/20078/7/2007Monitoring,Lessons Learned•Fly ash materials, while very looseand saturated, were significantly lesscompressible and more free-draining than previously understood.•Use redundant instrument systems.•Perceived fatal flaws were addressed through collection of relevant site-specificinformation.•Vertical drains were not needed.Lessons learnedfrom the monitoredpreload program:Case History #2 – LateralExpansion and OverfillOverview:90-acre Dry Ash FillOperated periodically as wet settling ponds areexcavated10-15 years of disposal capacity neededAdjacent to downhill, undeveloped areaDesign Situation:Provide expansion capacity but anticipate potentialretirement of plantConstruct expansion in small incrementsCASE HISTORY TWO –Expansion and OverfillEXISTINGLANDFILLPHASE 1LATERALEXPANSIONPHASE 2 RSSVERTICALEXPANSIONCASE HISTORY TWO –Expansion and OverfillCASE HISTORY TWO –Expansion PhasesThree Expansion Phases:1.Lateral, lined expansion2.Vertical, lined expansion using reinforced soil slope (RSS)3.Vertical, unlined expansion over new facility footprintCASE HISTORY TWO- Phase 1Lateral ExpansionCASE HISTORY TWO –Phase 2 – Vertical/RSS ExpansionCase History #3 – VerticalExpansion Over Closed CCB PondOverview:Existing 250-acre CCB landfillA 50,000,000 yd3expansion neededAdjacent to a 300-acre inactive (not closed) ash pondDesign Challenges:Utilize the existing footprint as much as practicalExpand laterally over ash pondSignificant site geometry constraintsSignificant mine voids below edge of footprintCH #3: Design ApproachSite characterization of ash in the pond using boringsand CPTuprobesSpecialized evaluation of existing LCS pipes plus videoinspectionGeometry constraints overcome through CCBexcavation/relocation and increasing vertical expansionMine voids mitigated primarily by excavation/replacementFoundation water pressures managed using underdrainsystem:Underdrain Considerations:Initial ConditionAshNativeSubgradeExistingPond LevelPhreaticSurfaceCCB Pond Dewatering StageAshNativeSubgradeLoweredPond LevelPhreaticSurfaceCover/Liner System ConstructionAshNativeSubgradeLandfill Lineror PondCover SystemLoweredPond LevelInfiltratingGroundwaterThe Situation to Avoid...AshNativeSubgradeLandfillLinerSystemInfiltratingGroundwaterRising WaterLevel in thePondUnderdrain SolutionAshNativeSubgradeLandfillLinerSystemInfiltratingGroundwaterBreakoutsalong thePerimeterContinuedRising WaterLevelsPhreaticSurfaceUnderdrainSystemCase Study 3: Observations1.Need to accurately identify geology/subgrade2.Assess structural integrity of as-built existing LCS3.Understand the long-term groundwater pore pressureconditions in ash/subgrade and be prepared to designunderdrain system for groundwater as “leachate”One More Example:Ash Facility Closure•Alternative closure techniques andalternative (and potentiallyinnovative) beneficial uses of ashponds that are to be closed under theproposed EPA regulations.•Forecast how the most recentlyproposed regulations would affectinnovation and future technology.•Prepared a Report on AshImpoundment that client can use intheir near-term assessment ofoptions.Case History (Facility Closure):Saltville Soda Ash Disposal Ponds• Two ponds at an industrial facility owned by Olin with Ammonia soda ashwaste required closure. Pond dikes were located next to Holston River, inVirginia.• Pond 5: 1925 to 1971, 76 acres, 100 fthigh dikes, 35 to 70 feet deep sodaash, also received mercury contaminated wastewater, liquids collected andtreated on site prior to discharge.• Pond 6: 1964 to 1972, 45 acres, 20 – 30 ft high dikes, less mercurycontaminated water, liquids were decanted and discharged to the river.Case History (Facility Closure):Saltville Soda Ash Disposal PondsGeosyntec provided:• Geotechnical characterization of soda ashand test fill program• Evaluation of capping alternatives andlikely long-term performance• Detailed design of cover systems forPond 5 and 6• On-call support during constructionDikes constructed usingprocess waste mixed withslaked limeSaltville: Geotechnical Monitoring•10 ft high test fill•Total Settlements•Areal settlement since 1981 exceeds8 feet in some areas•Test fills - 0.5 to 1.0 feet duringconstruction•2 to 3 feet in first 9 months•Differential Settlements•Differential settlements are believedto be generally proportional to totalsettlements, but test fill resultsindicate that there is a non-uniquerelationshipSaltville: ResultsMeasured settlementswithin basin are lessthan 6 inches, 10 to 15years after closureand are in closeagreement withpredicted resultsbased on landformgrading design“LandformGrading”Analogous DesignsAvtex Fibers NPL Superfund Site, Virginia (ET cover,lightweight fill, reinforced cap, consolidation)Wood River Impoundment, IllinoisFinal Closure Design and CQAOnondaga Lake Containment Facility over WasteImpoundments and Subaqueous Lake CappingOther Overfills over Coal Ash Ponds:1. Allen Steam Generating Station, BelmontNC, Duke Energy (operating by 2010)2. Rush Island and Meramec Stations, St.Louis MO, Ameren (proposed)3. Also: Others in Illinois, Indiana, etc.Upper surfacesolidified beforeclosureLiquefactionevaluation of softlake sediments andproposed capImpoundmentslocated within100-yr flood plainClosing Comments•Landfills can be, and have been, developed over CCB ponds and fills.•At the current state of the practice, site-specific field and laboratory data on CCBproperties is strongly recommended.•Pore pressure buildup is a key design consideration, and can likely be managed overthe typical timeframe for development of a CCB overfill.•CCB disposal facilities can be designed to mitigate the effects of seismic and/or staticliquefaction.•Develop a plan to manage groundwater and saturated CCRs below the landfill toavoid buildup of pore pressures that could lead to foundation instability.•For overfills, conduct a thorough evaluation of the existing landfill leachate collectionsystem and liner stability to verify that the LCS will can function under the increasedpressures resulting from the overfill CCR materials.Acknowledgements1.Contributing Clients:American Electric PowerAllegheny Energy Supply/First EnergyTennessee Valley Authority2.Co-workers/contributors:John Seymour, Paul Sabatini, William Steier, RodolfoSancio, John Esser, Sarah Fick, Scott SheridanTHANK YOU!