Waste Containment and Remediation

Reinforced GCL samples from three different projects were partially pre-hydrated on native damp subgrade soils for several weeks, and were then tested for hydraulic conductivity using three real leachates under a variety of effective confining stresses. The samples permeated with MSW leachate were tested under effective stresses of 240, 480, and 720 kPa. The samples permeated with MSW-incinerator ash leachate were tested under effective stresses of 180, 360, and 530 kPa. The samples permeated with pulp & paper waste leachate were tested under effective stresses of 165, 340, and 475 kPa. All of the results showed decreasing hydraulic conductivity with increasing effective stress with the ash leachate being the most sensitive to effective stress, and the pulp & paper leachate being the least sensitive. The hydraulic conductivity of the GCL samples to all of the leachates tended to level off to a common value of about 2 x 10^–12 m/s at effective stresses above 475 kPa.

Laboratory diffusion and permeability tests were performed on GCLs amended with two different types of organobentonites: benzyltriethylammonium-bentonite (BTEA-bentonite) and hexadecyltrimethylammonium-bentonite (HDTMA-bentonite) and compared to results for a GCL constructed with conventional sodium bentonite. Results from the hydraulic conductivity testing indicate the addition of both types of organobentonite results in an increase in hydraulic conductivity. Only a small increase (less than one order of magnitude) in hydraulic conductivity was observed for both types of GCLs amended with up to 20% organobentonite. At higher organobentonite contents, measured hydraulic conductivity for both types of amended GCLs increased by as much as three orders of magnitude. The effective diffusion coefficient measured for both the organobentonite-amended GCLs and the laboratory-constructed sodium bentonite GCLs were similar and ranged from 2.67 x 10^–10 to 4.17 x 10^–10 m²/sec. Considering the strong sorption capacity of organobentonites for organic contaminants, these results suggest that the ability of GCLs to retard the transport of organic contaminants can be improved by substituting 10–20% of the conventional bentonite with an organobentonite.

Since the introduction of geosynthetic clay liners (GCLs) to waste containment facilities, one of the major concerns about their use has been the hydraulic equivalency to a compacted clay liner as required by regulations. Laboratory test results and more recently field observations show that the thickness, or mass per unit area, of hydrated bentonite in a GCL can decrease under normal stress, especially around zones of stress concentration or nonuniform stresses, such as a rock or roughness in the subgrade, a leachate sump, or wrinkles in an overlying geomembrane. This paper describes the effect of bentonite migration on the hydraulic equivalence between a CCL and GCL and the contaminant transport through a thinned GCL. Finally, the paper presents suggestions for protecting hydrated bentonite from stress concentrations and reducing contaminant transport through a GCL.

Because of its low permeability and high swelling characteristics, bentonite is used in various hydraulic barrier systems, including geosynthetic clay liners (GCLs). In order to increase their long-term resistance to contamination, bentonites may be amended during manufacturing through mixing with soluble polymeric compounds. The resulting materials are referred to as polymer-treated, chemically-enhanced, or contaminant-resistant clays, and are arguably resistant to a host of inorganic chemicals. In this study, the advection, diffusion, and sorption characteristics of untreated and polymer-treated bentonite clays are examined. The response of bentonite clays to single and multi-species solutions at various concentrations is evaluated using permeability, diffusion, chemical titration, and index tests. Long-term advection properties are determined from flexible and rigid wall permeability tests, where both chemical and hydraulic equilibrium are established. The results indicate the high dependence of performance on sample homogeneity, pre-hydration conditions, and, to a lesser extent, polymer treatment. The cation exchange capacity and the clay plasticity appear to be more reliable than the swell index as indicators of the hydraulic performance of bentonite permeated with inorganic chemicals.

High temperatures may be encountered at the base of a landfill due to exothermic decomposition occurring in the overlying waste mass or hydration of ash. The corresponding thermal gradients create a risk of outward moisture movement and desiccation of the mineral component of composite lining system. This paper examines the potential effects of this thermally driven moisture movement on the long-term performance of geosynthetic clay liners in landfill basal liner applications. The results of large-scale laboratory experiments conducted in an effort to assess the behaviour of GCLs subjected to thermal gradients in landfill basal liner applications are discussed. In conjunction with this experimental program, a series of numerical models have been used to evaluate the pertinent thermal, hydraulic and mechanical properties of the soil and geosynthetic components of a composite liner system. The combination of insights gained through these programs allows a better understanding of the underlying mechanisms of moisture redistribution and desiccation behaviour. An analysis of the key results obtained through this investigation is presented. The discussion focuses on potential areas of concern with regards to thermally induced desiccation of geosynthetic clay liners. It is recommended that the potential for desiccation be addressed at the design stage of landfill construction, with numerical modeling used to identify potential risks. The avoidance of GCL placement over dry subsoils and the importance of managing heat generation within the landfill are stressed.

This study was conducted to determine long-term thermal regime of landfill liner systems using a field temperature monitoring program and numerical analysis of heat transfer. Temperatures in liner systems that contain geosynthetic clay liners (GCLs) were monitored prior and subsequent to waste placement. Data were collected in three cells at a landfill in Midwestern USA for more than five years. The liner system in one of the cells was left exposed (not covered with waste) for a period exceeding one year subsequent to cell construction. The lowest and highest GCL temperatures were –1°C and 35°C, respectively and the localized temperature gradients ranged from approximately –186°C/m to +134°C/m across the liner system during the exposed period. Seasonal temperature fluctuations were dampened and increasing temperature trends were observed after placement of the first lift of waste over the liner systems. Temperatures in liners reached 30°C under 5-year-old waste with an annual rate of temperature increase of approximately 4°C/a. In general, average temperature gradients decreased, however, high variations in gradients remained subsequent to waste placement. Numerical analysis was used for exposed liner systems to model observed behavior and to predict liner response under varied conditions. Good agreement was observed between measured and predicted temperatures. Temperature distributions in liners were determined for variable thicknesses of sand protective layers in 3 climatic regions. Sand thicknesses of more than 1 m were required to maintain temperatures between 0 and 40°C and thicknesses on the order of 3 m were required to limit seasonal temperature variations to within 10°C in GCLs.

This study investigates the impact of geomembrane texturing on the peak and large-displacement shear strength of the GCL GM interface using a significant commercial database of large-scale direct shear test results. Texturing procedures used by different GM manufacturers were found not to influence GCL-GM interface shear strength. GM texturing, quantified by asperity heights, was found to be highly variable. GM texturing was generally found to improve both the peak and large-displacement shear strength of GCL-GM interfaces. The existence of an optimum asperity height beyond which there is a decrease in large-displacement shear strength was evaluated. The available data indicates that, at least for unhydrated GCL-GM interfaces, an optimum asperity height can be identified.

With increased awareness of the need for long-term, equilibrium flow measurements, the specification and testing community has responded by employing site-specific hydraulic transmissivity tests. In addition, this industry now benefits from a standardized approach to the use of time dependent reduction factors for geosynthetic flow data. Using these reduction factors, relatively short-term flow measurements may be factored with product-specific reduction factors to determine long-term flow performance. This paper focuses on the creep reduction factor associated with the Allowable Flow Equation, and its determination. The technical approaches used to determine compressive creep reduction factors are described and discussed in the context of wider spread use. Creep reduction factor determination is demonstrated on a high-density polyethylene product. Finally, comparisons between reduction factors developed from accelerated and conventional testing are provided.

Traditional geonet geocomposites consist of a geonet core to which is heat laminated a nonwoven needlepunched geotextile on one or both sides. This paper presents engineering properties of new types of geocomposites manufactured using nonwoven heat-bonded and woven geotextiles. Changing the geotextile type is seen to significantly alter the performance characteristics of the geocomposites including filtration properties, transmissivity and flow properties, interface shear strength, ply-adhesion strength and ultraviolet resistance. There are a number of emerging applications of drainage geocomposites, such as bioreactor landfills, pavements, and green roof tops, where these new drainage geocomposites may fulfill the performance requirements better than the traditional nonwoven needlepunched-based drainage composites.

At a municipal solid waste (MSW) landfill located in Michigan, leachate recirculation using a 34 m long by 12 m wide permeable blanket made of geocomposite drainage layer (GDL) was tested. Leachate was injected in the GDL using a perforated HDPE pipe place on the middle and immediately on the top of the GDL running parallel to the width of the blanket. Sixteen moisture content sensors, one piezometer, two thermocouple sensors, and a vertical load sensor were embedded immediately below the GDL blanket to monitor the flow of recirculated leachate. After the blanket was covered with waste, leachate was injected in the blanket at rates ranging from 0.9 to 2.6 m³/hr/m of the blanket width. Data collected from the embedded sensors indicated that the leachate traveled at a rate ranging from 8 to 25 m/hr through the blanket depending upon the rate of injection of the leachate. The rate of leachate flow through the GDL layer was not uniform. However, every moisture content sensor either remained saturated or indicated an increase in the moisture content as a result of leachate recirculation. Hence, we have concluded that the GDL blanket is a feasible alternative for recirculation or injection of leachate in MSW landfills.

There is some question in the industry as to what is an appropriate lamination strength between the geotextile and geonet components of a drainage geocomposite. A recent slippage along this internal interface during soil placement on a 2:1 slope provided evidence that delamination of this interface is a potential issue. Drawing on information gained from this case history plus laboratory test data, this paper suggests a model whereby the lamination strength can be evaluated for slope and placement conditions, and provides guidance for writing geocomposite specifications.

In the late 1990's, the Florida Department of Environmental Protection became concerned that the increased use of geonets in landfill liner systems was not accompanied by appropriate transmissivity testing of these geonets in the designs. Some design professionals were simply using published data on geonet performance rather than determining what was needed based upon site-specific conditions. In addition, since many of Florida's landfills were expanding vertically and leachate recirculation was becoming more common, innovative designs with geonets were being proposed and the potential for improper use of geonets was increasing. Consequently, in 2001 the Department added a rule requirement that geonets used in landfill liner systems be tested with Method ASTM D4716. The maximum design load case requires a minimum test period of 100 hours. This paper summarizes this rule requirement, the basis for it and the concerns the Department has about improper design using geonets and geocomposites.

A field study of asphalt concrete and fluid applied asphalt - geotextile (FAA/GT) was undertaken to evaluate their suitability as a barrier (liner/cover) material in waste containment applications. A test pad consisting of 2–3 mm thick FAA/GT and 10–15 cm thick asphalt cement concrete was designed, constructed using full-scale asphalt paving equipment and its performance monitored. The in situ hydraulic conductivity of the barrier was measured using sealed, double-ring infiltrometers. Core and large block samples were taken from the test pad and analyzed in the laboratory under several conditions including: immediately after compaction, after aging for up to three years and after deformation. The in situ hydraulic conductivity of the barrier was 1 x 10^–9 cm/s to 1 x 10^–10 cm/s. The conductivity range represents the lower limit of quantifiable conductivities with the in situ testing equipment. The laboratory-measured hydraulic conductivity of the specimens sampled immediately after compaction was 1 x 10^–10 cm to 1 x 10^–11 cm/s. The hydraulic conductivities of the same specimens were re-evaluated twice after exposing them to the ambient temperature in the laboratory for a period up to three years. No change in hydraulic conductivity was observed during this period. Beams of aged asphalt concrete were subjected to three point bending to impart distortions in the range from 1/500 to 1/25. Though observable cracks developed in the beam that underwent the maximum distortion of 1/25, there was no appreciable effect on the hydraulic conductivity. The hydraulic conductivity of the asphalt barrier design used in this test pad was uncompromised by aging of 3 years and distortions up to 1/25. Based on the results of the testing performed, asphalt concrete combined with fluid applied asphalt - geotextile proved to be an effective barrier when designed and constructed with low hydraulic conductivity as a goal.

Hydraulic conductivity tests were conducted in the laboratory on compacted sand-bentonite mixtures using calcium chloride solutions at various concentrations and tap water to determine the effects of cation loading on the durability of the mixtures to simulated environmental stresses. Low concentrations of divalent cations are commonly found in groundwater, landfill leachate, and pore water in landfill cover systems that are exposed to wet-dry cycles. The hydraulic conductivity of specimens permeated with 0.05-M and 0.005-M CaCl₂ increased by more than five orders of magnitude when exposed to cyclical wetting and drying and the lower concentration required more cycles to cause the same increase in hydraulic conductivity as with the 0.05-M solution. The hydraulic conductivity of the specimen permeated with tap water did not increase significantly when exposed to cyclical wetting and drying. Index tests were also conducted to measure the swelling potential of the bentonite when hydrated with the various solutions. The swelling potential of the bentonite decreases with increasing concentrations of calcium ions and with additional cycles of wetting and drying.

Although compacted soil liners are designed to minimize advective transport of leachate, a significant quantity of contamination can be transported through liners by diffusion. Due to the inability of landfill liners to impede diffusive transport, enhancement of the sorption capacity of compacted soil liners has been considered as a means to improve liner performance. To mitigate organic contamination, one method of enhancing pollutant sorption is to amend liners with materials such as organobentonites, shale, or activated carbon that are capable of strongly sorbing organic pollutants. In this study, laboratory sorption and permeability testing were performed on hexadecyltrimethylammonium (HDTMA) bentonite, benzyltriethylammonium (BTEA) bentonite, shale, and granular activated carbon in order to evaluate their potential for use as a sorptive amendment in compacted liners. A genetic algorithm optimization model was then developed and used to design a liner containing sorptive amendments that minimized the costs of the system while also minimizing the amount of organic solute transport through the liner. Results from laboratory sorption experiments indicated that granular activated carbon exhibited the highest sorptive capacity for all three solutes tested (benzene, TCE, and 1,2-dichlorobenzene), followed by BTEA-bentonite, HDTMA-bentonite, and shale. Permeability testing results indicate that specimens composed of a mixture of conventional bentonite, sand, and either 3% or 9% amendment by weight had a hydraulic conductivity less than or equal to the regulatory requirement of 1 x 10^–7 cm/s, with the exception of 2.3 x 10^–7 cm/s measured for 3% granular activated carbon. Results from the optimization analysis indicate that the inclusion of sorptive amendments as a component in compacted soil liners can effectively minimize the transport of organic contaminants through the liner without violating regulatory permeability requirements. Shale and activated carbon were predominantly chosen for inclusion over the two organobentonites, a result that can be entirely attributed to the relatively high cost of the organobentonite amendments.

The hydraulic conductivity of clay significantly increases when permeated with high concentrations of inorganic solutions due to changes in clay chemistry and fabric. Chemical amendment of clays using soluble polymeric compounds creates a clay-polymer fabric that can be engineered to provide an attractive alternative for containment systems. The amended material can be made to resist different classes of chemical contaminants and span a broad range of engineering properties. In the present study, polymer treated clays are prepared by sorbing polymers to the surface of commercial sodium bentonite. Three classes of polymers: cationic, anionic and nonionic, are used in the study. All the polymers are water-soluble polyacrylamides in granular form. Basic engineering properties of the polymer-treated clay are investigated through a series of liquid limit and swell index tests. Mixing procedures are discussed, and compared to industrial processes used to synthesize contaminant resistant clays. Permeability tests are performed to evaluate the performance when permeated with highly concentrated salt solutions. The void ratio, initial wetting conditions, and polymer type are found to have a significant effect on the hydraulic conductivity.

Despite the global focus on waste reduction, re-use and recycling, the use of engineered landfills with either single or composite lining systems is, and will continue to be a major waste disposal method. The use of composite lining systems in landfills to effectively minimize the discharge of contaminants to groundwater is not common in most tropical, developing countries. In addition, there is also a lack of data on the performance of tropical clayey soils as liners. Adopting liner technology developed in temperate regions for application in the tropics may not be practical and cost-effective, as there are significant differences in geological, environmental and material properties in the two regions. In order to develop or reliably adopt a practical and cost-effective liner technology for tropical environments, geoenvironmental assessment of tropical soils during their interactions with the intended leachate must be undertaken. A study was undertaken to determine the suitability of two clayey soils from Ghana (West Africa) as engineered landfill liner materials. The hydraulic conductivity, before and after permeation with municipal solid waste (MSW) landfill leachate, was evaluated in a constant-flow fixed wall permeameter. The impact of the permeant on the hydraulic conductivity, mineralogy, chemical composition and some geotechnical properties of the clayey soils are presented. The results of the study suggest that the tropical soils may be used effectively as liners to minimize the discharge of contaminants into groundwater.

This study presents an assessment of the use of a typical Japanese marine clay, Ariake clay, as a soil barrier and its application in a new proposed soil barrier system. Two types of heavy metals, Cd²⁺ and Pb²⁺, are selected as key contaminants for laboratory diffusion testing. Using a commercially available contaminant transport software, the diffusion coefficients and partition coefficients were back-calculated from the results of the diffusion test. The diffusion coefficients are found to be consistent with previously published values. The lab test data were applied for evaluating the performance of a new barrier system in which the Ariake clay is utilized. Numerical analyses of contaminant transport through the barrier are performed to characterize the temporal variation in concentrations and mass flux of Cd²⁺ and Pb²⁺ in the aquifer underlying the landfill. The results show that within the long-term post-closure period, the concentrations of Cd²⁺ and Pb²⁺ were much lower than those regulated by the Japanese government, indicating that the new barrier system is effective. By parametric analysis, some factors controlling the performance of the proposed soil barrier system are discussed. Design parameters are recommended for practice.

The equations that describe the macroscopic transport of a solution containing a binary electrolyte through a semi-permeable membrane are derived following the approach of the Thermodynamics of Irreversible Processes. This approach for the description of the macroscopic transport of the solution doesn't provide any physical interpretation of the phenomena involved. As a result, a macroscopic transport model able to provide a physical interpretation of the phenomenological parameters is proposed. Such a model is able to explain the dependency, observed in laboratory experiments, of the chemico-osmotic efficiency coefficient, ω, on the solute concentration, C_s, and to explain the dependency of the other experimental parameters on ω.

Biokinetics in engineered soils is a subject of relatively recent interest. In this paper, results are presented from experimental studies to address the bioclogging mechanisms. The primary focus of this study is to assess the relative importance of biomass growth vs. biogas generated in the soil pores. Experiments were conducted using Pseudomonas aeruginosa as the bacterial culture and compacted mixtures of kaolinite and Ottawa sand as porous media. Results indicated about one order-of-magnitude reduction of permeabilities when the bacteria were introduced through a nutrient solution in the influent chamber. Compacted specimens prepared using a bacterial inoculum and permeated with nutrient solution alone showed that growth kinetics prevented the specimens from ever reaching the saturated hydraulic conductivities with respect to distilled deionized water. Bacterial counts in the influent and in the effluent revealed that the kinetic processes were similar in soil media and in the pure nutrient solution medium. Reductions in permeabilities were attributed to the biogas generated during bacteria permeation. Pore-size distributions of bioclogged specimens showed lager pores, which was also consistent with visual observations of specimen cracking and gas bubble accumulation at the surface of the specimens, particularly in the case of specimens prepared with bacteria inoculum.

The purpose of this project was to complete a six year natural weathering study on a series of geosynthetics an concurrently complete a 20,000 hour accelerated weathering study. An energy equivalency method was used to establish a rough relationship of approximately 1000 hours of accelerated weathering being equal to one year of natural exposure. This relationship was seen to be consistent with the results of the natural and accelerated studies, as well as to other examples of such relationships in the literature. The 20,000 hour accelerated exposure allowed us to compare the performance of highly UV resistant materials such as 1.5 mm HDPE stabilized with carbon black, and thinner polyolefin geoemembranes stabilized with pigment and additional UV stabilizers. The results of our study suggest that a thinner (0.75 mm) geomembrane can perform equivalently to a 1.5 mm HDPE geomembrane when sufficient UV stabilizing additives are utilized.

Plasticizers are used to make PVC flexible so it can be used as a geomembrane for containment purposes. Plasticizers can migrate from PVC geomembranes over time because of contact with air, liquid, and an absorbent solid material. Plasticizer migration can reduce the flexibility of PVC geomembranes. This paper discusses the three mechanisms of plasticizer migration and the factors influencing these mechanisms, such as plasticizer molecular weight and linearity of plasticizers. The paper recommends that a minimum average plasticizer molecular weight of 400 be used to ensure long-term plasticizer retention in the field. The weighted-average method for calculating the average molecular weight is recommended when two or more plasticizers are incorporated into the PVC geomembrane.

Geomembranes used in separation liners between old and new waste in vertical expansions of landfills may be subject to strain caused by differential settlement. Therefore, it is important to define a maximum allowable strain (MAS) that any given geomembrane can tolerate without compromising its required service life. In a number of instances some very low values have been proposed; as low as 0.25% to 1.0% for high density polyethylene (HDPE). Such low numbers are likely based on German regulations for HDPE landfill liners that require a maximum allowable global strain of 3% and a limiting local strain due, for example, to protruding drainage stones, of 0.25%. The low allowable strain values adopted by the German regulators have been based on products and practices utilized in the 1980s and do not reflect current conditions, nor do they address geomembranes other than HDPE. This paper presents the background and reasoning for updating the MAS values for geomembranes.

In this paper, the theory of gas diffusion through porous media is briefly summarized and then experimental and analytical methods are presented to estimate the effective oxygen diffusion coefficient (D_e) based on a finite mass equation. Laboratory oxygen diffusion tests were performed on potentially acid generating (PAG) tailings at various water contents to determine D_e. These tailings originated from the Premier Gold Project (PGP) located near Stewart, British Columbia, Canada (~ 56°05^'N, 130°00^'W). Analytical results from these tests were in excellent agreement with estimates obtained with well-known software (Pollute V6) and a method based on the soil parameters of volumetric air and water contents and tortuosity. D_e for the PGP tailings was approximately 5.3 x 10^–8 m²/s at the soil saturation of 80% and 1.9 x 10^–6 m²/s at the soil saturation of 4 to 23%. Oxygen concentrations in two PGP field test plots are also presented. One test plot contained 0.75 m potentially acid generating (PAG) tailings overlain by 0.5 m coarse sand and gravel and 0.1 m top soil (Control Plot) and the other contained the layers (from bottom to top) of 0.75 m PAG tailings, 0.1 m fine sand, a Geosynthetic Clay Liner (GCL), 0.1 m fine sand, 0.3 m coarse sand and gravel, and 0.1 m top soil. The placement of the GCL significantly lowered the oxygen concentrations in the tailings below the GCL. Most oxygen concentrations below the GCL were lower than 1.0 % Vol whereas Control Plot oxygen concentrations ranged from 0.3 to 20% Vol. The estimated oxygen flux was 26.3 kg/m²/year for the Control Plot and 0.187 kg/m²/year for the GCL Plot.

A design procedure is proposed to select landfill cover materials. The specific case of inclined covers that limit infiltration due to the capillary barrier effect is investigated. A well known model for the calculation of the diversion capacity is employed. Material selection is mainly based on hydraulic conductivity functions (k-functions). The capillary break layer (CBL; bottom layer) of an ideal inclined capillary barrier should include a material within which capillarity forces are as weak as possible for the infiltration rate considered, whereas the moisture retaining layer (MRL; top layer) must be capable to develop the strongest capillarity forces possible, for the same infiltration rate. In addition, the MRL must be as permeable as possible, so that water is efficiently drained downslope and out of the cover. Application of the proposed procedure shows that a combination of coarse materials (such as sand over gravel) diverts water over greater lengths than barriers employing fine-grained materials as MRL.

Capillary barrier systems constructed using non-cohesive soil as the fine-grained layer have been studied extensively. However, capillary barrier systems constructed using a cohesive soil have not been fully studied. In this study, a capillary barrier model consisting of residual soil as the fine-grained layer and gravelly sand as the coarse-grained layer was constructed in an infiltration box apparatus. To study its performance as a water barrier for slope stabilization purpose, the capillary barrier model was subjected to several infiltration and evaporation processes. Tensiometers for the measurement of pore-water pressures, time domain reflectometry (TDR) for the measurement of volumetric water content and weighing balances for the measurement of water balance, were used in the experiment. Simulated rainfall and evaporative flux were applied to the capillary barrier model using a rainfall simulator and evaporation simulators, respectively. From the experimental results, it was found that the recovery of water storage of the capillary barrier model constructed using residual soil was very slow during the evaporation process under laboratory ambient conditions. Previous study showed that recovery of water storage is an important design variable for capillary barrier system that functions under high precipitation rates. In this study, additional evaporative flux using fan was applied to the capillary barrier model in order to simulate evaporation process in the field. It should be noted that the measured potential evaporation in the capillary barrier model due to the application of the fan was less than the potential evaporation in Singapore. The experimental results showed that capillary barrier effect existed in the capillary barrier model constructed using residual soil as the fine-grained layer. The recovery of water storage of the capillary barrier model can be accelerated using additional evaporation simulator so that the capillary barrier system can effectively function under high precipitation rates.

This paper presents the results of a study on the utilization of monolithic covers of local soils for municipal solid waste (MSW) fills in the State of São Paulo, Brazil, by means of simulations with a numerical code using unsaturated soil parameters and local climate data. Two sites were studied - Campinas and Ilha Solteira - located in regions with high demand for MSW disposal sites. A lateritic clay and a lateritic clayey sand were selected due to their availability in the regions. Water retention curves for compacted specimens of the two soils were obtained by the filter paper method and fitted to the van Genuchten model, as required by the employed code, Visual Hydrus. The influence of compaction water content on cover performance was investigated by determining water retention curves at four compaction water contents for the lateritic clay and two compaction water contents for the lateritic clayey sand. Real precipitation and evaporation data for one year were used. Simulated monocover thickness were 1 m and 4 m. Results showed that, for both sites, 1-m-thick covers meet the requirement of maximum annual percolation rate of 30 mm/year, when the soil is compacted at the optimum or wet of optimum water content. There is, therefore, the possibility of using monocovers with performance comparable to prescriptive compacted soil covers for the studied conditions.

Regulatory approval of evapotranspirative covers is usually based on numerical modeling of cover percolation during the design process, followed by post-closure moisture monitoring to verify adequacy of cover performance and validity of the numerical model. However, there are no well-established guidelines on how moisture monitoring data can be used to calibrate/validate the numerical model and verify adequate cover performance. This paper evaluates data from a Southern California landfill instrumented with TDR moisture probes to develop such guidelines. The TDR readings were found to be a good indicator of moisture trends and fluctuations within the cover. However, in fine-grained soils, TDR probes tend to overestimate the moisture content and location-specific nonlinear calibration functions are required to achieve reasonable accuracy of moisture measurements. The numerical unsaturated flow model UNSAT-H was able to reasonably predict the measured moisture response of the cover, provided near-surface cover degradation was incorporated into the model. Guidelines are provided for calibration of TDR readings in fine-grained soils and the use of near surface cover degradation as a calibration parameter for the unsaturated flow model. The calibrated model is validated by comparisons with observed moisture fluctuations within the cover.

Water balance data from a test section simulating a monolithic alternative cover were compared to predictions made with two numerical models: UNSAT-H and Vadose/W. On-site data were used as model input to the greatest extent practical. More accurate predictions were obtained with Vadose/W than UNSAT-H. Surface runoff was overpredicted appreciably by UNSAT-H, which affected all subsurface hydraulic processes. In contrast, Vadose/W accurately predicted surface runoff, evapotranspiration, and the temporal variations in soil water storage. However, neither model predicted percolation accurately. Both models also failed to capture a key change in the transpiration pattern during the last winter-summer period of the study. Differences in the method used to simulate precipitation intensity appear partly responsible for the difference in accuracy by which the two models predict surface runoff. Simulations were conducted with the lower boundary condition as a unit gradient or a seepage face to evaluate how this boundary condition affects predictions of the water balance. Essentially the same predictions were obtained regardless of the lower boundary that was used.

This paper provides an overview of a geomembrane based gas storage bladder which was designed and built successfully at the Luggage Point WWTP in Brisbane. It discusses several design and construction issues including the need by designers for wide strip tensile and seam tests on reinforced geomembranes.

Geosynthetic bunker liners have been used in North American golf course new construction and remediation projects for approximately five years although the requisite geotechnical engineering and geosynthetics knowledge has been in use for decades in more traditional civil engineering applications (e.g. road construction, shoreline protection, etc.). There would likely be more widespread use of and specification of geosynthetic bunker liners if there existed a greater fundamental understanding of the science behind their performance. In this context, a `bunker liner' is actually a relatively thick and highly permeable product specifically intended to entrain and stabilize bunker sand (with the primary economic benefit of reduced labor costs associated with sand washouts caused by rainfall or irrigation watering). These products are substantially different from the more traditional, thinner, needlepunched non-woven geotextile products. Traditional geotextiles have been used in the past but with mixed to poor results. Today's commercially available bunker liner products all vary somewhat in their appearance and design but have all demonstrated an ability to function successfully for their intended purpose at one level or another (i.e. sand stabilization, subgrade separation, filtration and drainage), at least on a short-term basis. Although the immediate success of these products is generally recognized, there has been little technical development toward the understanding of their functionality or how to accomplish bunker design with the use of these products and in various different situations. In the effort to give structure to the geotechnical aspects of bunker liner design, this article proposes a design methodology for bunker liners as it relates to their long-term drainage and filtration performance.

A temporary car park is frequently required by car and truck manufacturers for up to 20,000 new vehicles prior to shipping to distributors. Vehicles should remain clean and undamaged. Rather than pave large areas, and for economy, manufacturers have typically leased large fields. To preclude having to clean vehicles and to tow them when stuck in mud it was thought that a geocomposite product could be used to provide a clean temporary traffic/parking surface. A few installations have been made using a conventional geotextile/geonet/geotextile composite. Nonwoven geotextiles were made with UV resistant flame retardant polypropylene (PP) fibers. Joints were made by thermally welding the overlapping geotextiles.

Most geosynthetics play a passive role, e.g. barriers stop the passage of liquids: reinforcement provides tensile resistance, but only after an initial strain has occurred; and drains provide a passage for water but do not cause the water to flow. New applications for geosynthetics can be identified if the geosynthetic can provide an active role, initiating chemical or physical change to the matrix in which it is installed as well as providing the established functions. Smart geosynthetics are ideal candidates to initiate electro-kinetic processes. It has already been established that conductive geosynthetics, acting as electrodes can be used to effect the movement of contaminants through soil to the electrodes and then adsorb them. Using electrophoresis it is possible to dewater industrial wastes, which are currently untreatable and can only be disposed of in vast tailings lagoons. Conductive geosynthetics can be used to reduce the volume of industrial wastes by electro-osmosis thus significantly lowering the cost of disposal; the use of conductive reinforcement can permit the use of fine wet materials as fill for reinforced structures. Initial studies have shown that the use of electrically conductive band drains could prevent liquefaction of susceptible soils during earthquakes. Other applications can be seen in different fields such as sport and horticulture. The use of conductive geosynthetics can resolve some of the problems inherent in many large stadia, such as the detrimental effect of shade on growing surfaces. An electrically conductive geosynthetic laid as a continuous porous membrane at root level provides oxygen directly to the root system as well as offering a method to control drainage, aeration, and ball bounce. A working model of this technology was exhibited in the Science Museum in London during the 2002 football world cup. Designing with smart geosynthetics involves consideration of soil properties not usually considered in design. The paper identifies these and illustrates their relevance. A number of new applications for smart geosynthetics are identified.

The purpose of this study is to evaluate whether the bottom clay layer at coastal landfill sites will maintain the required barrier function even if piles are installed through the clay layer to ensure the bearing capacity of structures constructed over the landfill sites. The transmissivity of the interface between the clay and the steel was measured with a newly-developed rigid-wall permeameter, which has earth pressure transducers on the top and the bottom caps of the cell so as to determine the side-wall friction. Processed Fukakusa clay (LL = 41.9%, PL = 21.4%) was pre-consolidated at 90 or 180 kPa and was trimmed to have a diameter 2 mm smaller than the 80 mm diameter of the permeameter cell to intentionally create a space between the clay and the side-wall. Vertical pressure levels ranging from 11.25 to 360 kPa were applied, and a hydraulic gradient across the specimen was applied for each vertical pressure. As the vertical stress increased, the friction grew larger between the clay and the steel, and the interface transmissivity decreased. The measured transmissivity was very low, when the clay was under a normal state of consolidation or the OCR (over-consolidation ratio) was smaller than 1.5, and ranged from 0 to 2 x 10^–7 cm²/s. Two different indices of equivalent hydraulic conductivity were proposed, namely, one that considers the total amount of leakage and a second that considers the seepage velocity. Although the work presented in this paper represents the preliminary investigation and the simplicity of the test program limits the application, it is considered that the installation of piles through the bottom clay layer at coastal landfill sites may be environmentally acceptable under the certain conditions in which the clay is deformable enough against the overburden pressure to close the gap between the clay and the pile.

Existing remediation techniques of petroleum contamination often take many years to achieve regulatory levels and require high operating costs with complicated logistics. The possibility exists that increased remediation efficiency of petroleum — contaminated soils can be accomplished at temperatures less than 80 °C, while not significantly increasing cost or complicating remediation operation. To this end, a batch testing program was developed to assess the viability of increased temperatures on the desorption efficiency of benzene on a fine-grained sand, kaolinite, and a natural soil (silty sand). Samples first underwent sorption testing at 20°C, before being subjected to desorption testing at 20, 40, 60, and 80°C respectively. Testing results support the hypothesis that increased temperatures lead to higher desorption efficiency. Results indicated 40°C as the optimum temperature to achieve a balance of increased efficiency with minimal cost increase. The sorption and desorption kinetics are discussed in view of soil type, organic content, and contamination level.

This paper presents the results from a study on nonreactive solute transport in fine-grained soils under consolidation. The objective is to study the influence of consolidation on the migration of solute in saturated clays during the consolidation process. Bromide (Br^–) and chloride (Cl^–) were used as the tracers. Bromide was present only in the upper half of the 70 mm height specimen for the consolidation test, while chloride was homogeneous through the whole specimen because it was present in the kaolin powder used to prepare the soil sample. The consolidation tests were conducted under constant stress of 25 kPa with single drainage on the top boundary. Solution samples were collected for chemical analysis from the surrounding solution during the test and from the pore fluid of the specimen after it was sliced into four quarters and centrifuged. Analysis of the results shows that the effect of consolidation-induced advection on hydrodynamic dispersion is not significant. An equation was derived to estimate the advection velocity based on Terzaghi's one-dimensional consolidation theory. It was found that consolidation-induced advection velocity is very high (theoretically infinity) in the beginning of consolidation at the drainage surface, and decreases to zero when the consolidation is nearly concluded or near the non-flow boundary. Analysis of the Peclet numbers suggests that the consolidation-induced advection is the dominant transport mechanism only in a very short period of time after the start of the consolidation and in a very small region near the drainage surface. The temporal and spatial range that advection dominates is dependent on the consolidation stress, drainage length, porosity, hydraulic conductivity and molecular diffusion coefficient. Therefore the influence of consolidation on the nonreactive solute transport may not be significant except for providing an additional transport mechanism in addition to diffusion during the consolidation process.

A model for predicting air-flow patterns generated during the remediation technology of insitu air-sparging (IAS) is presented. The model assumes that the groundwater is initially hydrostatic and that the pressure of air in the plume generated by IAS is spatially, but not temporally, constant. The air pressure in the propagating plume is calculated using the ideal gas law, while the pore pressure in the groundwater adjacent to the plume is calculated using the Young-Laplace equation. Groundwater flow induced by excess pore water pressure is described by Darcy's law, and the expansion or contraction of the air plume boundaries is determined by the magnitude and direction of this flow. The model uses parameters, such as soil porosity and intrinsic permeability that can be determined from standard measurements at field sites. By dividing the model domain into cells of small, finite size, macroscopic the heterogeneity of soil properties can be accounted for. The paper describes the model, discusses the assumptions made in its development, compares the model predictions with experimental results from laboratory tests, and summarizes plans for its further refinement.

Permeable, reactive electrochemical redox barriers can be engineered for in situ remediation of groundwater by enhancing oxidation conditions at a permeable anode and/or reducing conditions at a permeable cathode. However, it is necessary to assess the potential for transformation of target contaminants by electrochemical redox. This paper evaluates the effect of current density and presence of chloride ions in groundwater on electrochemical degradation of benzene in solution. Electrochemical reactors, composed of an anode and a cathode separated by a Nafion® membrane, were used to evaluate the effect of three current densities (1, 9 and 18 mA/L) on the transformation of 40 mg/L benzene solution. Transformation is demonstrated at different rates depending on the current density. Under the lowest current density (1.8 mA/L), 56% of benzene was transformed in the first 48 hours and more than 96% was transformed after 216 hours. A much faster rate is noted under 9 mA/L, where 87% of benzene was transformed after 48 hours. The higher current density (18.2 mA/L) produced results similar to the 9 mA/L. The results show that most of the benzene transformation occurred in the first four hours, where both the 9 and 18.2 mA/L densities resulted in benzene concentration less than 2 mg/L after 72 hours. Transformation of by products, including chlorobenzene compounds, continued to occur and final concentrations levels of less than 3 mg/L were reached after 300 hours. The effect of electrolysis on anolyte pH and redox potential was evaluated. Under 9 mA/L, the redox potential increased significantly at the anolyte in the first 8 hours to about 900 mV. After that, the redox potential continued to increase, but at a lower rate until it reached 1380 mV at the end of processing. Similar behavior is noted for the anolyte pH, which decreased significantly in the first 8 hours to less than 2.5 and continued to decrease until it reached pH value of 1.86 at the end of testing.

This paper presents the results of a case history involving the use of the zero valent iron and clay (ZVI-Clay) technology for remediation of chlorinated solvents at a DuPont plant located in Martinsville, Virginia. The ZVI-Clay technology is an in-situ approach to chlorinated solvent remediation that involves addition, via soil mixing, of a stabilizing agent (i.e., kaolin clay) and zero valent iron directly into the source zone. The result is two-fold: decreased mobility of contaminants and degradation of chlorinated solvents via reaction with the zero valent iron. Application of the ZVI-Clay technology to a site in Martinsville, Virginia, contaminated primarily with carbon tetrachloride has resulted in greater than 99% degradation of all chlorinated compounds, including by-products. In addition to describing this case history, current and future research efforts aimed at further developing the technology are described briefly.

The discovery of perchlorate in soil and groundwater at a former road flare manufacturing facility in Santa Clara Valley, California has prompted an extensive program of soil and groundwater characterization, coupled with development, design and implementation of remediation activities on a highly accelerated schedule. Perchlorate concentrations in on-site groundwater have ranged up to a maximum of 550 μg/L in 2003. Perchlorate in on-site soil is predominantly limited to the former process area of the facility with a maximum concentration of 14 mg/kg. A combined soil and groundwater treatment system was initially designed for the site in September 2003, but was later revised to uncouple soil and groundwater treatment. The groundwater extraction and ion-exchange treatment system design was approved in October 2003 and the system was operational by the end of December 2003. The flow rate is anticipated to range seasonally from 75 to 200 gp, to maintain capture in a hydrogeologic environment that sees a seasonal watertable fluctuation of more than 20 feet. To address stakeholder and agency comments regarding the soil component of the combined system, a feasibility study (FS) was performed to address perchlorate remaining in vadose zone soils. The thickness of the vadose zone varies seasonally in response to watertable fluctuations, ranging between 16 to 36 feet. Approximately 40,000 yd³ of vadose zone soil is estimated to contain perchlorate above the site-specific soil screening level of 50 μg/kg generated following USEPA guidance. Based on detailed analyses of overall protection, effectiveness, implementability, community acceptance and cost, the agency and responsible parties agreed to a soil remedy that includes: (i) focused excavation and ex-situ biotreatment of soils containing perchlorate above 7.8 mg/kg (~ 800 yd³ of soil), and (ii) in-situ bioremediation of soils containing perchlorate below 7.8 mg/kg. The soil remedy leverages the infrastructure of the on-site groundwater containment system to facilitate in-situ remediation of the on-site soils. In-situ remediation will consist of amending a portion of the treated (i.e., perchlorate-free) effluent from the groundwater treatment system with a carbon-based electron donor, and applying the amended water to the ground surface above the targeted soil treatment area. As the electron donor infiltrates through the vadose zone soils, it will promote biodegradation of perchlorate. Laboratory biotreatability studies conducted coincident with development of the FS indicated that the addition of various electron donors (e.g., acetate, ethanol, oleate) promoted rapid biodegradation of perchlorate in the soils from concentrations of 1,000 ∞g/kg to less than 4 ∞g/kg within 13 days. The bacteria, which are naturally present in the soil, degrade the perchlorate to harmless chloride and oxygen. The in-situ remediation approach follows from work by Cox et al. (1999) and Borch et al. (2001) demonstrating treatment of perchlorate in vadose zone soils through ex situ composting and surface application and infiltration of electron donors, respectively. The groundwater extraction/treatment system, in addition to providing the treated infiltration water, ensures containment of perchlorate and its degradation products that are washed from the unsaturated soils. It is estimated that two years of continuous in-situ soil bioremediation may be sufficient to achieve the desired soil remediation objectives.

This paper addresses field testing and numerical modeling that investigated use of the Well Injection Depth Extraction (WIDE) technology for saturating a subsurface profile. Although not detailed in this paper, the purpose of delivering liquid to the unsaturated subsurface zone was to extract radioactive contaminants (primarily cesium) at the U.S. Department of Energy Columbus Closure Site's West Jefferson North (WJN) facility (JN-1 Abandoned Filter Bed). The objective of the field testing was to investigate injection flow rate distribution through the piping header and manifold assembly to the soil, investigate the rise in subsurface water table corresponding to pulse and gradual injection modes, and establish water table mounding with time. Results show that a pulse injection caused a localized rise in the subsurface water elevation with subsequent decline over 2–3 hours. A gradual injection leads to a more uniform rise in piezometric head albeit at a smaller magnitude. In one specific test, 4,164 liters of injected water resulted in a mound that extended approximately 10 m down gradient of the test pad area and 5 m up gradient. The maximum mounding front occurred approximately 2 to 3 hrs after completion of the injection cycle. Approximately 0.3 to 0.6 m of rise in subsurface water elevation was recorded with the gradual injection model. In this case, the impacted zone was contained within the area of injection (4.5 m x 4.5 m). Pulse injection from pumped delivery was determined to be more effective than gradual injection in rising and maintaining subsurface water elevations to levels necessary for saturation of soil containing the maximum cesium contamination. Modeling results using Seep/W Version 5 from Geo-Slope International compared well with field measurements.

Two advantages of slug tests for measuring the hydraulic conductivity of soil-bentonite in a cutoff wall are that the soil-bentonite is tested in-place in the cutoff wall and that a larger amount of soil-bentonite is tested than in typical laboratory tests. This paper describes equipment and procedures for performing slug tests using a push-in piezometer tip. Chart solutions are provided for reducing the data considering proximity of the trench walls and the influence of bentonite filter cakes. The procedures described here for performing slug tests using a push-in piezometer tip produce measurements of soil-bentonite hydraulic conductivity that are in very good agreement with the results of other reliable test methods. By performing falling head tests and evaluating the data over a limited range of head drops, it is not necessary to complicate data reduction by taking backfill compressibility into account; however, the excess heads applied in falling head tests must be small to avoid hydraulic fracture because the effective stresses in the backfill are small.

It has been well established that the confining stresses at which the soil-bentonite is tested at in the laboratory significantly affects the measured hydraulic conductivity. However, the stress state within the soil-bentonite cutoff wall (SBCW) is usually unknown; although it is generally agreed upon that it is less than the geo-static effective stress, defined as (γ' ⋅ z). With a highly compressible material like soil-bentonite, an overestimation of the confining stresses during laboratory testing would lead to an underestimated determination of the field hydraulic conductivity, thereby establishing a non-conservative cutoff wall permeability. A total of 57 piezocone penetration and pore pressure dissipation tests were conducted in a SBCW as part of a post-construction Quality Assurance (QA) testing program. The piezocone tests were used to provide an estimate of the in-situ effective stress of the SBCW, while the pore pressure dissipation tests were used to provide estimates of the in situ hydraulic conductivity. Results of the testing program showed that utilizing a pre-consolidation pressure correlation from the piezocone penetration pore pressure can provide reasonable estimates of the in-situ effective stress when compared to Arching and Lateral Squeezing theories. These results can aid in the laboratory evaluation of the hydraulic conductivity. Pore pressure dissipation results provided in-situ hydraulic conductivity results that compared favorably to laboratory flexible wall permeability tests.

The strength and compressibility of two soil-bentonite backfill mixtures were characterized through a laboratory program that included 1-D consolidation tests and triaxial compression tests. The triaxial compression tests were performed on normally consolidated and overconsolidated specimens, and they included isotropically consolidated undrained and drained test conditions. Procedures for preparing and testing soft soil-bentonite mixtures are discussed, including procedures for forming specimens and appropriate use of area and membrane corrections. The test results are presented in this paper, and they are compared with other published values, where available. The results include values of coefficient of consolidation as a function of effective stress, compression and recompression ratios, pore pressure response during undrained loading, the ratio of undrained shear strength to consolidation pressure, effective stress friction angle, and at-rest lateral earth pressure coefficient. Index property values for the soil-bentonite mixtures are provided so that the results presented here can be compared with those for other soil-bentonite mixtures. Findings for soil-bentonite mixtures include the following: (1) the values of compression ratio are smaller than for most natural clays, (2) excess pore water pressure generation during undrained compression is much greater than for most natural clays, (3) the ratio of undrained shear strength to consolidation pressure is much lower than for most natural clays, (4) the effective stress friction angle often falls in the range of 31 to 33 degrees, and (5) the measured value of at-rest lateral earth pressure coefficient was 0.57.

Soil-bentonite (SB) slurry trench cutoff walls have been used for over 30 years as subsurface vertical barriers to control ground water flow and contaminant transport. Despite the millions of square feet of cutoff wall that have been constructed, little is known about the time-dependent behavior of the backfill and, in particular, the change in shear strength with aging. From experience, practitioners know that the backfill, which is initially placed as a semi-fluid material, gains strength with time. What has not been known is whether this time-related strength gain is due entirely to consolidation of the backfill or some other mechanism. This paper presents the results of laboratory and field testing of a SB slurry trench cutoff wall. Laboratory studies included consolidation and slump testing. Field studies included testing a constructed wall using vane shear, earth pressure cells, and settlement plates. The results of these tests demonstrate an increase in shear strength within a few days of backfill placement. This initial increase in shear strength is attributed to consolidation of the low-permeability backfill. The shear strength continues to increase with time, behavior that the authors attribute to two factors. The first is secondary consolidation or creep. The second is broadly termed "aging" and is attributed in part to the thixotropic nature of the bentonite used in the backfill mixture. Recommendations for the design shear strength for SB backfill are also included.

A vertical leachate recirculation system was evaluated for its potential to recirculate leachate into landfilled waste. Leachate was recirculated through eleven vertical wells installed at three different depths. The results of recirculation tests performed over a 6-month duration are presented in this paper. The results indicated that specific capacity of vertical wells decreased with well depth. The specific capacity per unit screen length of the vertical wells ranged from 1.2 x 10^–6 to 1.2 x 10^–5 m³/s-m². The mean specific capacity of lines installed at three different depths were significantly (p<0.025) different from each other and were in the following order: shallow well (depth ~6 to 8 m) > middle well (depth~12 to 16 m) > deep well (depth~18 m). A potential reason for lower specific capacity for deep wells is the lower hydraulic conductivity of the waste in deeper sections due to higher overburden pressure. While the data presented in this paper are based on preliminary injection tests and may not represent steady-state condition, the results provide important insight into the hydrodynamic behavior of bioreactors.

A field research program is being performed by CReeD, the research department of Veolia Environnement group in order to assess the performance of a bioreactor landfill and determine an optimal bioreactor working face. The project compares two independent full scale landfill cells on the same site with the same quality of waste: the first one is managed as a bioreactor cell with leachate recirculation and the second one as a control cell without recirculation. The bioreactor cell is characterized by a watertight and gastight top cover (HDPE geomembrane) to minimize odors/gas emissions, to provide better biogas quality (no air intrusion), and to permit improved control of the hydraulic mass balance (no rainwater entrance). The injection system is composed of 18 vertical wells including 8 telescopic wells. These were designed and located in order to have the best moisture distribution in the waste mass. Geophysical instrumentation was installed in this cell to evaluate injection performance (range of injection wells, moisture distribution fields). For each cell, the biogas is collected using vertical wells. However, the number of wells was increased and an horizontal subsurface network was added in the bioreactor cell in order to collect the overproduction of biogas due to the acceleration of the waste biodegradation. Gas and leachate in the two cells are collected separately. An analysis and a control of the following physical, chemical and mechanical parameters for each cell is therefore possible during the period of waste stabilisation: (1) the quality and the quantity of leachate produced; plus the quantity and the quality of the injected leachate in the bioreactor cell; (2) the quality and the quantity of biogas produced; (3) the estimation of Biological Methane Potential (BMP tests) and moisture of waste samples versus time; and (4) the waste settlement. Injection into the bioreactor cell started in September, 2003. No clear trend relative to the leachate recirculation can be identified because we have only six months of data. However, first results highlight the influence of the watertight and gastight topcover: in the biogas coming from the bioreactor, there is no or few oxygen. We also identified the necessity to modify the way of working on the bioreactor cell in order to emphasise the leachate recirculation effects on the waste degradation. Improvements are presented.

Horizontal landfill conduits are often the primary means for liquid and gas exchange within the bioreactor landfill waste mass. However, operational problems have historically plagued these components. Differential settlement, crushing, and waterlogging have been so common that engineers often treated horizontal conduits as sacrificial infrastructure. Many years of development and experience at projects initially in New York State, and now in many other states, have shown that structurally reinforced conduits have the survivability necessary for long-term use. The remaining design challenge has been development of multi-function access and cleaning terminals to support long-term operations. This paper will describe and give an installation case history of a new, integrated, landfill conduit terminal system that provides easy access for control of all normal functions such as gas extraction or leachate injection, and gives access for high-pressure jet cleaning and excess liquid removal. Air can also be forced into the system if desired. This system is a technological breakthrough, which will provide a new level of control and improved maintenance for permanent horizontal landfill conduits.

This article presents results for the research conducted by the University of New Orleans in which three pilot-plant scale lysimeters were used in a comparative evaluation of the effect of recirculating treated and untreated leachate on waste stabilization rates. Three lysimeters were filled with waste prepared with identical composition. One was operated as a facultative landfill bioreactor (FLB) with external leachate pre-treatment prior to recirculation; the second was operated as anaerobic landfill bioreactor (ALB) with straight raw leachate recirculation; and the third one was the control unit and operated as a conventional (dry) landfill. A leachate treatment plant composed of an electrocoagulation/settling unit and two fluidized bed reactors (FBRs) in series was used in conjunction with the FLB lysimeter. In this article the results presented by de Abreu (2003) regarding organic matter stabilization, nitrogen management, stabilization phases, gas composition, leachate production, and waste compressibility in the three lysimeters are analyzed, showing that the Facultative Landfill Bioreactor is a promising technology for waste treatment and disposal.

The degradation of Municipal Solid Waste (MSW) over time, and associated settlement, is of special importance when estimating air space, designing interim and final closure covers of landfills, as well as planning vertical expansion of existing facilities. Most settlement models applied to solid waste were developed for inorganic soils or peat. Furthermore, these models were not developed considering the leachate recirculation effect on settlement. In case of bioreactor landfills, waste settlement will include creep as well as biological components due to the accelerated degradability of waste particles as leachate is recycled. The objective of this paper is to present a settlement prediction model, which accounts for changes in material characteristics as a function of the waste degradation rate. As biodegradation takes place, the organic solid mass is converted to gas and the void ratio increases with a subsequent increase in waste settlement. In general, published settlement models do not capture these phenomena. The model developed herein is based on the results of an experimental program. Settlement components including creep and biodegradation effects are identified as a function of the state of decomposition. Twenty four one-dimensional oedometer tests (63.5 mm cell) were performed on shredded refuse in laboratory-scale reactors for measurement of compression indices representing primary (C_c), creep (C_αi) and biological (C_βi) on samples ranging from fresh to well-decomposed refuse. Particles of length equal to no more than half the diameter of the test cell were included. The time factors, t_i, t₂, t₃ and t₄ for the compressibility were determined from the gas production curve and existing field settlement data, and utilized for model development. The proposed model was verified using the settlement model parameters obtained from laboratory test and comparing predicted settlement with observed field settlement from several landfills.

Settlement prediction is one of the main concerns in design and maintenance of a bioreactor landfill. Accurate prediction is essential for design of piping systems used for the delivery of re-circulated leachate and collection of gases. Though the major component of settlement is due to the decomposition of municipal solid waste over several years, considerable amount of settlement takes place during the initial construction stage too, which is usually unnoticeable as it happens during construction. A comprehensive model for settlement analysis of a bioreactor landfill should be able to demonstrate not only the settlements due to biodegradation but also the settlements that occur due to mechanical compression during initial construction stage. Often an overall compressibility index is defined similar to that of clays, to explain compressibility of waste, but not much attention has been paid to the settlement behavior during the initial stage or during construction. This manuscript describes a procedure to compute settlements due to mechanical reasons in a bioreactor landfill by separating that from the biodegradation. Then a new conceptual framework was proposed to numerically predict the settlements using time dependent waste properties and landfill geometry.

Settlement in municipal solid waste (MSW) is an important factor affecting landfill management, whether the landfill is operated as a conventional or bioreactor landfill. Mechanical settlement results from compression and consolidation caused by the weight of the waste. Biological settlement occurs following deterioration and subsequent volume loss due to corrosion, oxidation, combustion and decay. Bioreactor landfill technology aims to optimize biological settlement through controlled leachate recirculation. Settlement measurements can allow managers to better estimate waste degradation rates, locate "hot" and "cold" spots, and increase bioreactor efficiency by directing leachate to low-settlement zones. This paper reviews past and current efforts to monitor MSW landfill settlements and presents a new method for monitoring settlement in landfills. Time domain reflectometry (TDR) is a technique utilized to locate and quantify physical changes along a transmission line, such as a coaxial cable, by tracking voltage reflections. While the TDR technique does not work well when cables are pulled in direct tension, it has been shown that prescribing loops along a cable significantly enhances the sensitivity of TDR measurements in tension. When cables are stretched such that the loop radius progressively decreases, voltage reflection amplitude increases as the loop kinks at its apex. The proposed method was evaluated experimentally in a settlement tank filled with a simulated daily cover composed of a moist paper-sand mixture. The tank is a steel frame structure with tempered glass sheets as sidewalls for visual observation of waste settlement along the boundaries. A galvanized steel plate centered at the base of the tank can be lowered to create a subsidence zone. A series of experiments were performed using single-loop and multi-looped cables embedded in the waste and monitored as the plate is lowered. The results show that loops located within the subsidence zone compress as the waste settles, and that the magnitude of voltage reflection increases as the waste continues to settle. Thus the method has the potential to detect and monitor local settlement in MSW landfills.

Bioreactor landfills are more and more gaining in popularity, because of their interest in waste management. Bioreactors use enhanced microbiological processes to stabilize organic waste within 10 to 15 years of implementation, instead of 30 to 50 years for classical sanitary landfills. Modeling reactive transport phenomena within bioreactor landfills is a crucial issue to improve the efficiency of those engineered landfills. The goal is to control gas and liquid flows and to optimise the valorisation of refuses as well as to decrease the stabilisation time by controlling microbiological activity. This work aims to develop a three dimensional multiphase, multi-component model, which would help landfill operators to manage their site. Our first work consisted in the development of a conceptual mechanistic model which correctly describes the different phenomena that occur during the waste biodegradation. We adopted a relatively complex microscopic model involving four phases, including a biofilm, and nine constituents. The biofilm phase is considered as a continuum where the biological reactions take place. The associated macroscopic equations are discussed using results from a volume averaging method. Micro-scale equations at the "pore" level are averaged over a representative elementary volume, to obtain the macro-scale equations based on the microstructure of the wastes. The final model couples mass balance equations with momentum and energy equations. The solid wastes are separated into four categories according to their biodegradability. Production and consumption terms are included in the model for each reactant with different kinetics according to aerobic or anaerobic conditions. They involved simplified Monod kinetics taking into account the biomass activity and the availability of substrates. Kinetic coefficients also include temperature dependence and terms taking into account oxygen availability and moisture content. On this basis, a two dimensional finite volume code is developed.

Accelerated stabilization of municipal solid waste (MSW) through the recirculation of leachate and/or addition of water and air has been investigated intensely over the past several years. In general there are many benefits to this approach of enhancing the rate of waste biodegradation including increased settlement and valuable air space, reduced leachate toxicity and treatment costs, and lessened post-closure concerns. Aerobic operation maximizes these benefits while also raising other concerns. In particular, the addition of oxygen into a heterogeneous matrix wherein pockets of methane may exist could exacerbate combustion potential. Moreover, addition of water and/or leachate increases the unit weight and may reduce effective stresses. As such, it is vital that the appropriate amount of air and moisture be distributed throughout the waste without an excessive use of wells or trenches that pose financial or logistical obstacles. Soil vapor extraction studies have shown that simultaneous injection and extraction can move fluid through porous media with greater efficiency than one or the other individually. This paper describes aspects of the largest reported (approx. 10 m³) laboratory-scale bioreactor designed to simulate the aerobic decomposition of MSW under controlled air injection and vapor extraction. One of the objectives of this laboratory effort is to investigate and model the flow of water, leachate and air as related to system performance. Data generated from this work are intended to provide a basis for model verification as well as insight into field application.