Assessment of the Performance of Engineered Waste Containment Barriers (2007) / Chapter Skim
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5 Containment System Performance
5 Containment System Performance
Pages 65-92
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From page 65... ...
. For New york, "modern" means both the leachate collection system and the primary barrier since 1988, when the state issued new regulations for MSW layers are working.
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From page 66... ...
aSSESSmENT Of ThE pERfORmaNCE Of ENgiNEEREd waSTE CONTaiNmENT baRRiERS BoX 5.1 Types of data available on Waste containment landfills and impoundment system Performance Few data exist on containment system performance. One of the most comprehensive studies on short- and medium-term performance of contain ment systems was conducted by Bonaparte et al.
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From page 67... ...
Leakage through Diffusive flux may constitute a significant portion of total the GM-GCL systems was generally equal to or less than that flux through a liner system, particularly for well-constructed through the GM-CCL systems, and the rates were dramatically composite liners and low hydraulic conductivity (less than about 1 × 10–10 m/s) compacted clay liners.
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From page 68... ...
. Exhumation and undisturbed sampling single- and composite liner systems in Wisconsin for periods have also been used to obtain chemical concentrations in exceeding 20 years indicate that a wide variety of volatile compacted clay liners (Reades et al., 1989; King et al., Reades organic compounds in various concentrations have appeared 1993; Rowe, 2005)
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From page 69... ...
This problem can be mitigated in a number the potential for diffusive flux, including the long-term flux of ways, including placing the leachate collection system of volatile organic compounds, should be considered when under vacuum, placing gas collection trenches in the waste designing a facility. adjacent to the side slope (taking care not to draw too much oxygen into the system)
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From page 70... ...
. In addition, two instances of Temperatures of 30 to 40°C have been observed on base liner damage were caused by landfill fires, two were caused liners after 5 to 10 years, and higher temperatures can develop by installing gas wells, and one was caused by desiccation even earlier when there is moisture augmentation (Koerner cracking when the compacted clay liner was left exposed for and Koerner, 2005)
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From page 71... ...
CONTaiNmENT SySTEm pERfORmaNCE BoX 5.3 case history on the Temperature environment for a geosynthetic composite liner This case history illustrates how temperatures within a liner system vary with time and are influenced by waste placement conditions. Data were col lected from a Michigan landfill with a bottom liner that included (from top to bottom)
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From page 72... ...
With the exception The evidence suggests that properly designed and con- of landfill gas migration problems, the environmental perstructed cover systems at MSW and hazardous waste landfills formance of fully covered sites was superior to that of sites and RCRA and CERCLA sites can effectively isolate waste that were not fully covered. This conclusion is consistent and contaminated soil and groundwater from the environ- with numerous observations that construction of an effecment.
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From page 73... ...
This system ing the effectiveness of capping as a remedy at RCRA or has an essentially flat barrier layer, with a top deck grade CERCLA sites. not greater than 6 percent and side slopes with a maximum The observed and inferred good performance of cover inclination of 6H:1V.
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From page 74... ...
A drop in flow rate from 60 percent underlying barrier layers, and the effectiveness of evapo- of the annual rate of precipitation when the landfill cells transpirative barrier layers at minimizing leakage. were receiving waste to 13 percent and 1 percent of annual Percolation rates for cover systems containing single precipitation after 1 and 10 years of closure, respectively, was compacted soil layers have been measured using pan lysi- reported in a hazardous waste containment facility (Haikola meters in test plots in four climatic regions for durations up et al., 1995)
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From page 75... ...
. However, because the decomposition process 5.1.3 leakage Through Vertical Barriers decays exponentially with time for a homogeneous mass and because different sections of large landfills have varying The primary function of most vertical waste containment decomposition rates, the remaining 20 percent of the degra- barriers is to control the lateral subsurface migration of liqdation capacity may take significantly longer.
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From page 76... ...
. Few problems with vertical waste containment barrier included soil-bentonite (21 sites)
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From page 77... ...
CONTaiNmENT SySTEm pERfORmaNCE BoX 5.6 case history on Vertical Wall Performance This case illustrates how, under the right conditions, a gravel-filled trench can serve as an effective vertical barrier against offsite migration of hazardous and toxic wastes. About 75 million liters of liquid hazardous and toxic industrial wastes were disposed of at the Hardage Site near Oklahoma City, from 1972 to 1980.
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From page 78... ...
This The assumption of perfect contact between the geomemsection describes predictive models of how the individual brane and the subsoil can provide a lower bound to the leakcomponents of the system interact to contain contaminant age through holes in a geomembrane over a compacted clay transport. Both elements are necessary in order to adequately liner or GCL.
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From page 79... ...
. The potential for contaminant migra Thus, the typical observed leakage for composite liners tion increases through a hole in the geomembrane at or near with both compacted clay liners and GCLs can be readily the wrinkle.
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From page 80... ...
Moreover, diffusive and advective flow modeling polyethylene geomembrane over a 3-m-thick compacted of cementitious vertical barriers is further complicated by clay liner was investigated after 14 years of use as a leachate the difficulty of separating the material/physical coefficients lagoon liner (Rowe, 2005; Lake and Rowe, 2005b)
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From page 81... ...
with respect to evaluating the TABLE 5.4 Models for Predicting Percolation Performance of Waste Containment Covers Model Process Solved Parameters Comments FEHM 1D, 2D, 3D, transient FEM/ Multiphase, multicomponent heat, mass, gas, Limited pre- and postprocessor with 3D grid FVM air, including double porosity flow; can solve generator available from independent sources; contaminant flow as advection/ dispersion or USA only particle tracking HELP 1D, quasi 2D, analytical Water balance Climate and soil database included HyDRUS-2D 2D, transient and steady state Pressure, with vapor flow, temperature, and Pre- and postprocessor included; CAD mesh FDM chemical transport generation add on LEACHM 1D, quasi 2D, transient and Pressure, temperature flow, and chemical Originally an agricultural model; quick run-times; steady state FDM transport free online RAECOM 1D steady state radon-gas Radon-gas concentration and flux through a Can automatically optimize layer thickness diffusion multilayer system SoilCover 1D, transient FEM Pressure, temperature, vapor pressure, oxygen Pre- and postprocessor included; code flux unavailable; freeware TOUGH 2 1D, 2D, 3D transient and Pressure, temperature, vapor, gas in porous or Limited pre- and postprocessor available from steady state IFDM fractured media independent suppliers; code available; users can customize UNSAT-H 1D, transient FDM Pressure with vapor; temperature (optional) Pre- and postprocessor available but excluded; code available VADOSE/W 2D, transient and steady state Pressure, temperature, vapor pressure, oxygen Enhanced pre- and postprocessor, climate FEM or radon diffusion.
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From page 82... ...
balance of ET covers; vegetative response to changes in SWS should be simulated internally in water balance analyses rather than prescribed in the input data NOTES: ET = evapotranspiration; PET = potential ET; SRO = surface runoff; SWCC = soil water characteristic curve; SWS = soil water storage.
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From page 83... ...
Advective transport of gas is expected to control gas movement through The integrity and performance of landfill liner, cover, porous materials (e.g., leachate collection layers) , and diffu- and vertical barrier systems can be affected by both global sive transport is expected to be the dominant mechanism for and local slope stability.
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From page 84... ...
Ironically, the composite geomembrane lowconducted to determine a factor of safety against various permeability soil barrier system developed to minimize admodes of global slope stability failure. Barrier layers may vective transport of contaminants from the landfill provided be particularly susceptible to global stability failure as they a plane of weakness along which the failure surface develcreate a planar surface along which the shear strength may oped.
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From page 85... ...
. Field performance of the test plots was in substantial in their covers in Cincinnati, Ohio, in 1994 (Daniel et al., agreement with the stability analyses based on the labora1998)
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From page 86... ...
phisticated analyses may be required to predict these effects, Significant uncertainties, however, remain about the long- simple engineering measures can often be used to mitigate term performance of containment system elements (e.g., the local instability risk (e.g., use of a "slip sheet" above a side long-term durability of reinforced GCLs, the long-term per- slope liner to mitigate downdrag on the liner due to waste formance of leachate collection and removal layers and cover settlement)
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From page 87... ...
fills and other facilities where large deformations adjacent A new generation of reinforced GCLs with thermalto or across the barrier system are anticipated. locked fibers has shown significantly higher postpeak shear strengths in laboratory tests than previous GCLs, with failure occurring at the geotextile-geomembrane interface over a Impact of GCL Strength on Stability wide range of overburden pressure, even when the GCL is The internal shear strength of GCLs is of particular con- hydrated under low overburden pressures prior to testing cern for local and global stability of landfills because of the (Kavazanjian et al., 2006b)
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From page 88... ...
However, when accounting for the effects of oxygen limitation, a service lifetime approach 5.2.7 modeling concrete Barrier Performance ing 100 years for the reinforcing fibers has been estimated for buried applications (Salman et al., 1998)
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From page 89... ...
port of leachate and gas and diffusive transport of chemical compounds through the liner. Advective-diffusive-dispersive 5.3.2 multidimensional contaminant Transport models transport models are required to predict contaminant transport across vertical barriers.
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From page 90... ...
MULTIMED can consider models are required to solve the ADRE in more than one parameter uncertainty, both steady state and transient flow, dimension. However, several simplified models for multidi and up to 11 different chemical species simultaneously.
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From page 91... ...
construction. An additional attenuation layer may be required • Predicting the performance of concrete barriers: The to control diffusive transport in liner systems involving a ability of computer models to predict long-term performance GCL or thin compacted clay liner.
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