Assessment of the Performance of Engineered Waste Containment Barriers (2007) / Chapter Skim
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4 Performance of Barrier System Components
4 Performance of Barrier System Components
Pages 37-64
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From page 37... ...
defects arising from induced deformations. Key performance Hydraulic conductivity data on compacted clay lowconcerns for earthen barriers, such as compacted clay liners, permeability soil layers for 85 cases from active landfill cells include the following: (8)
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From page 38... ...
; inadequate hydration (encapsulated GCLs) Granular and geosynthetic Inadequate capacity Clogging due to soil infiltration, biological action, and mineral drainage layers precipitation; geosynthetic drainage layers are also susceptible to soil and geosynthetics penetration and creep of the geonet core Evapotranspirative barriers Defective material; inadequate thickness; inability Inadequate storage capacity for infiltration; inability to sustain to establish vegetation vegetation; cracking and development of other secondary permeability features; erosion, penetration by vegetation or animals Vertical barriers Defective material; "windows" due to caving and Cracking; desiccation of earthen barriers above the water trapped low-quality material; leakage at joints table; chemical incompatibility of earthen and concrete between panels; lack of continuity in grouted barriers; corrosion of metallic barriers and of reinforcement in barriers and extraction well systems concrete barriers; anti-oxidant depletion and stress cracking of polymer barriers; clogging of vertical extraction trenches and wells Asphaltic cement barriers Defective material Cracking due to shrinkage or deformation, degradation of the asphalt binder or supplemental material (e.g., crumb rubber)
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From page 39... ...
1.0E-07 Infiltration Rate or Hydraulic Conductivity (m/s) Infiltration Rate Hydraulic Conductivity 1.0E-08 1.0E-09 1.0E-10 80 0 20 40 60 Time (days)
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From page 40... ...
The devel- Desiccation of compacted clay liners in cover systems has opment of secondary features in a clay barrier as a result of been reported to result from both drying and freezing (Bendesiccation, freeze/thaw damage, or tensile strains can cause son and Khire, 1997; Benson, 1999; Albrecht and Benson, significant increases in hydraulic conductivity. This effect 2002; Albright et al., 2006)
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From page 41... ...
Fortunately, available Most, if not all, of the available data on chemical compat evidence suggests that many, if not most, natural clay soils ibility of compacted clay liners or other earthen barriers are used as compacted clay liners have relatively low plasticity based on the results of laboratory tests, performed either as index values. For example, of the 85 compacted clay liners part of the design process for the waste containment facility
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From page 42... ...
. Con of compacted clay soils by hydrophobic organic liquids has sequently, waste containment barriers that contain significant resulted in significant increases in hydraulic conductivity bentonite contents, such as compacted sand-bentonite and (e.g., Fernandez and Quigley, 1985)
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From page 43... ...
Earthen barrier layers in cover with a minimum of 1.5 m of compacted clay, compared to systems are susceptible to veneer instability, wherein a planar 0.91 m required by RCRA Subtitle D Subsequent to 1996, failure surface develops along one of the interfaces in the both Wisconsin and RCRA have required a composite liner system.
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From page 44... ...
and barriers are also susceptible to a variety of mechanical refined subsequently by other investigators. Measurements performance problems, including erosion and cracking of of flow rates through geomembranes are sparse, although earthen cover systems, disruption of base liner barrier lay monitoring of leak detection systems provides information ers due to foundation instability, and veneer failure of cover on likely leakage levels (Bonaparte et al., 2002)
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From page 45... ...
A cushion should not of geomembrane barriers, immediately after installation, can be used for subgrade puncture protection because it would be obtained using electrical leak detection surveys. These negate the "intimate contact" between the geomembrane and surveys are generally conducted after the leachate collection underlying low-permeability layer required for composite gravel is placed on top of the primary geomembrane and can liner effectiveness.
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From page 46... ...
An HDPE geomembrane used in a contaminated soil containment facility for 7 years exhibited Service Life (years) a Temperature (°C)
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From page 47... ...
. Exposure of the overlying geomembrane 4.3 geosYNTheTic claY liNers to large temperature extremes can result in moisture loss and shrinkage of GCLs on side slopes.
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From page 48... ...
were independent of Chemical degradation of the hydraulic conductivity of GCLs fluid chemistry. is possible when relatively high concentrations of divalent The importance of performing hydraulic conductivity cations such as calcium and magnesium in the natural pore tests long enough to achieve chemical equilibrium between water or soil cause cation exchange with the sodium in the the effluent and influent has been demonstrated for both bentonite.
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From page 49... ...
. Second, the hydraulic con cation, combined with the chemical incompatibility effects ductivity of GCLs to chemical solutions with ionic strengths of cation exchange discussed in the previous section, can greater than about 0.2 to 0.4 M can be higher than the typical cause increases of as much as three to five orders of magregulatory standard value of 1 × 10–9 m/s, and much higher in nitude in hydraulic conductivity.
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From page 50... ...
If, in addition, the effective diffusion coefficients (2001) showed that the saturated hydraulic conductivity for a given chemical species are similar between the GCL of a needle-punch-reinforced sodium GCL buried under a and a compacted clay liner (not unexpected since the GCL moderate thickness (0.66 m)
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From page 51... ...
ample, the rate of leakage through a 1-m-thick compacted clay liner with a hydraulic conductivity of 1 × 10-9 m/s Field evidence of leachate collection system performance commonly exhibits deposits of both biofilm and inorganic would increase by about 300 percent if the head on the liner mineral precipitate on the surface of granular materials. increases from 0.3 to 3 m (i.e., assuming a 1-m-thick clay These deposits reduce the drainable porosity and hydraulic liner with zero head at the base)
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From page 52... ...
Clogging by fine particles There is some evidence to suggest that monofilament woand/or roots has reduced the drainage capacity of a cover ven geotextiles selected in accordance with Giroud's (1996) drainage layer and led to slope failure due to increased pore recommendations are likely to experience less clogging water pressures in several cases (e.g., Koerner and Soong, and reduction in hydraulic conductivity with time than the 1998; Bonaparte et al., 2002; Richardson and Pavlik, 2004)
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From page 53... ...
pERfORmaNCE Of baRRiER SySTEm COmpONENTS BoX 4.4 case history on clogging in a leachate collection system This case history illustrates that leachate collection systems can clog, giving rise to both a significant leachate mound and a rapid increase in temperature on the liner. The Keele Valley Landfill, described in Box 4.3, is divided into four quadrants (Rowe, 2005)
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From page 54... ...
. However, field measurements of performance of drainage Use of carbonate gravel in the drainage layer has been sug- layers in leachate collection or cover systems are much less gested as unsuitable because it could dissolve and contribute common than for barrier layers.
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From page 55... ...
Longer-term concerns for PCC walls include cracking caused by several possible mechanisms and corrosion of reinforcement. 4.6 VerTical Barriers Driven sheet pile walls can be an attractive alternative for Vertical waste containment barriers (cutoff walls)
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From page 56... ...
In situ hydraulic conductivity tests can be the hydraulic conductivity of soil-bentonite backfill in pilotconducted within the wall following construction. In situ scale cutoff walls showed that laboratory tests performed on tests include slug tests, piezocone soundings with pore pres- remolded and thin-walled tube samples, respectively, yielded BoX 4.5 case histories on Performance assessments for evapotranspirative Barriers These case histories illustrate the field performance of evapotranspirative barriers.
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From page 57... ...
. Although the initial The possible effects of chemical incompatibility, de- hydraulic conductivity of a cement-bentonite-slag mixture may be >10–9 m/s upon initial emplacement, laboratory testscribed above for earthen barriers and geosynthetic clay liners, may also apply to soil-bentonite cutoff walls.
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From page 58... ...
Cracks that develop Construction quality assurance procedures for cement as a result of placement conditions (e.g., plastic shrinkage, bentonite walls are similar to those for soil-bentonite settlement) can be minimized by using good construction vertical barriers.
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From page 59... ...
mixture, use of nonmetallic reinforcement, and more rigorous CQA procedures may limit cracking in concrete slabs Concerns about medium- and long-term performance of used as barriers for waste containment, some cracking ap- sheet pile vertical barriers include deterioration of the joint pears to be inevitable with current technology and must be sealing material due to chemical incompatibility, material accommodated in the design of the barrier. degradation, sustained hydraulic gradients, the impact of Construction quality assurance of PCC barriers generally ground displacement and vibrations on the integrity of joint consists of strength testing of cylinders created at the time seals, corrosion of steel sheet piles, and stress cracking of the concrete mix is poured.
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From page 60... ...
This system Geomembranes have been used as vertical barriers either provides both an effective waste containment barrier and alone or in conjunction with other relatively low permeability source reduction. A fluid collection and removal system at materials, such as in composite cutoff walls (see Chapter 2)
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From page 61... ...
Cracks also affect the rate panel barriers and lack of continuity in grouted barriers can of diffusive transport through the barrier, even if they are not have a similar effect on vertical barrier effectiveness. through-going, as they allow fluids containing the diffusing Despite the existence of several laboratory and field methions to penetrate the barrier through advective flow, shorten- ods to measure the hydraulic conductivity of soil-bentonite ing the diffusion pathway and increasing the rate at which and cement-bentonite walls, none are free of complicating the adsorptive capacity of the barrier is expended.
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From page 62... ...
However, large-scale field per- to date have focused on the components used in cover and meability tests like the sealed-ring infiltrometer, which are liner systems. Available quantitative information documentused to detect the effects of cracking and nonhomogeneities ing the field performance of earthen barriers, particularly on the hydraulic conductivity of earthen barriers (see Box compacted clay liners, is based largely on the results of in 4.1)
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From page 63... ...
only as the underlying component of a composite liner with Short-term concerns with geosynthetic clay liners include an overlying geomembrane and sufficient overburden to the possibility of defective materials and separation of overmaintain intimate contact between the geomembrane and the lapped GCL panels. Chemical incompatibility (increases in compacted clay liner.
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From page 64... ...
cracking mechanisms as PCC. Nonmetallic reinforcement Short-term performance concerns for vertical barriers (e.g., synthetic fibers, geogrids, geotextiles)
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