Compacted Soil Liners Research Articles

A method to assess risk reduction when utilizing geosynthetic clay liners (GCLs) with compacted soil liners

This paper presents an analytical solution developed to estimate probabilities of “failure” or advective flux “exceedance” for the case of a spatially variable geosynthetic clay liner (GCL) situated over a spatially variable compacted soil liner (CSL). The risk of utilizing such a liner system is assessed relative to a regulatory compacted clay-based soil liner. The analytical solution developed is validated over a range of parameters against random field simulation using the Local Average Subdivision method, and the analytical solution is shown to be in good agreement with simulation. The analytical solution is then used to examine the “probability of exceedance” for a spatially variable GCL and CSL combined liner system. It is shown that the use of a GCL can potentially result in a low probability of exceedance when used with a spatially varying, high hydraulic conductivity CSL. The risk of exceedance generally decreases as the hydraulic conductivity of the CSL decreases. An example problem is presented to demonstrate the capabilities of the analytical solution.

Long term hydraulic conductivity of compacted soils permeated with landfill leachate

This study evaluates the relative influence of biological, physical and chemical interactions on the percolation of leachate through compacted soil liners. The long term hydraulic conductivity of compacted silt–bentonite mixtures was measured with distilled water, landfill leachate and a nutrient solution. The soil hydraulic conductivity decreased significantly with time when the permeating liquid contained microorganisms. The decrease of hydraulic conductivity was caused by reduction of the effective porosity due to pore clogging. Pore clogging was analyzed considering physical, chemical and biological processes. The effect of microbes on the hydraulic conductivity of soil liners permeated with leachate prevailed over that produced by physical or chemical interactions. The presence of microbial activity was confirmed by direct observations of the microbial population in the permeating liquid, by microbial exopolysaccharides (EPS) encountered in the soil pores, and from inverse modeling analysis of pore bioclogging. The existence of microbes in the compacting and permeating liquids reduced up to two orders of magnitude the long term hydraulic conductivity. The results were in good agreement with the expected behavior when biofilms develop around soil particles.

A steady-state approach for evaluating the impact of solute transport through composite liners on groundwater quality

New adaptations of analytical equations for predicting the impact of solute transport through composite landfill liners on groundwater quality for steady-state conditions are presented. Analytical equations are developed for evaluating average concentration and mass flow rate in an underlying aquifer resulting from diffusion of volatile organic compounds (VOCs) through intact composite liners and transport of inorganic constituents through defects in composite liners. The equations are applied to evaluate the effectiveness and equivalency of composite liners having either a 0.6 m-thick compacted soil liner or a 6.5 mm-thick geosynthetic clay liner (GCL) overlying an intermediate attenuation layer and an aquifer having horizontal flow. Example analyses for designing composite liners meeting particular performance criteria are also provided. The analytical equations are relatively simple to apply and can be used for preliminary design and analysis, to evaluate experimental results, and to possibly verify more complex numerical models for evaluating the impact of landfills on groundwater quality if consistency of the assumptions of the analytical equations and the more complex numerical models can be specified.

Effects of Fiber Additives on the Desiccation Crack Behavior of the Compacted Akaboku Soil as A Material for Landfill Cover Barrier

In the daily and final landfill cover barrier system, the hydraulic properties of compacted soil liners and the strength of soil can be adversely affected by desiccation cracking, resulting in the loss of effectiveness and integrity of the containment system as a barrier. Recently, there is an interest of using fiber additive to overcome the desiccation cracking problem. In this study, the desiccation crack test was conducted to investigate the effect of fiber additive on suppressing desiccation cracks in compacted Akaboku soils. Polypropylene (C3H6) fiber was used as an additive material for soil sample. The percentages of fiber used were varied as 0.0%, 0.2%, 0.4%, 0.6%, 0.8%, 1.0% and 1.2% (by dry weight of samples). The soil specimens were compacted under the conditions of maximum dry density and optimum water content. The surficial cracking area was measured to determine the crack intensity factor (CIF) of the soil samples. The desiccation crack test results indicated that the percentage of volume change of the compacted soil specimen decreased with addition of fiber. The change in the soil surface area decreased with increasing in the fiber content (FC), and consequently, the volumetric shrinkage strain decreased. The CIF for the soil without fiber (FC = 0.0%) were significantly higher than the soil with fiber additive. The CIF of soil at FC = 0.0% decreased from 2.75% to 0.6% for the soil at FC = 0.2%. It was also found that the maximum crack depth reaches almost 50% of the thickness of the soil without fiber additive. This study suggests the potential application of the fiber additives to soils as an available method to suppress desiccation cracks encountered in landfill cover barriers.

Effectiveness of compacted soil liner as a gas barrier layer in the landfill final cover system

A compacted soil liner (CSL) has been widely used as a single barrier layer or a part of composite barrier layer in the landfill final cover system to prevent water infiltration into solid wastes for its acceptable hydraulic permeability. This study was conducted to test whether the CSL was also effective in prohibiting landfill gas emissions. For this purpose, three different compaction methods (i.e., reduced, standard, and modified Proctor methods) were used to prepare the soil specimens, with nitrogen as gas, and with water and heptane as liquid permeants. Measured gas permeability ranged from 2.03 x 10(-10) to 4.96 x 10(-9) cm(2), which was a magnitude of two or three orders greater than hydraulic permeability (9.60 x 10(-13) to 1.05 x 10(-11) cm(2)). The difference between gas and hydraulic permeabilities can be explained by gas slippage, which makes gas more permeable, and by soil-water interaction, which impedes water flow and then makes water less permeable. This explanation was also supported by the result that a liquid permeability measured with heptane as a non-polar liquid was similar to the intrinsic gas permeability. The data demonstrate that hydraulic requirement for the CSL is not enough to control the gas emissions from a landfill.

Optimal Design of a Compacted Soil Liner Containing Sorptive Amendments

The design of a compacted soil liner that includes sorptive amendments is presented and evaluated as a combinatorial optimization problem. An objective function based on the materials costs, opportunity costs, and construction costs of the liner was used to evaluate the effect of incorporating four sorptive materials: benzyltriethylammnonium-bentonite, hexadecyltrimethylammonium-bentonite, shale, and granular activated carbon (GAC) into a compacted clay liner in order to mitigate transport of organic solutes through the liner. The results from this study indicate that the inclusion of sorptive amendments as a component in compacted soil liners can effectively retard the transport of organic contaminants through the liner without violating regulatory hydraulic conductivity requirements. In all cases when aqueous transport was considered as a constraint in the objective function formulation, the resulting liner always contained some amount of sorptive amendment. In general, shale and GAC were selected for use in the sorptive liner design for all organic solutes tested. The modeling framework presented in this study is general and could be used to evaluate other types of sorptive materials or additional constraints, and thus represents a flexible new tool for the design of compacted soil liners.

Design of Compacted Lateritic Soil Liners and Covers

Laboratory tests were conducted on three lateritic soil samples to illustrate some pertinent considerations in the design of compacted lateritic soil liners and covers. The three design parameters investigated are hydraulic conductivity, desiccation-induced volumetric shrinkage, and unconfined compressive strength. Test specimens were compacted at various molding water contents using four compactive efforts. The compaction conditions were shown to have some relationship with soil compaction using either the plasticity modulus or the plasticity product (i.e., clay index). For construction quality assurance purposes, the traditional approach was compared with the modern criterion. Deficiencies associated with the traditional approach for soil liners found in literature also apply to lateritic soils. Overall acceptable zones were constructed on the compaction plane to meet design objectives for hydraulic conductivity, volumetric shrinkage strains, and unconfined compressive strength. The line of optimums was identified as a suitable lower bound for overall acceptable zones of lateritic soils. The volumetric shrinkage strain was also identified as the second most important design parameter for lateritic soils. The shapes of the acceptable zones were affected by the fines contents of the soils.

Reliability-based assessment of compacted lateritic soil liners

The first-order reliability method is employed to assess the suitability of lateritic soils as landfill liner materials based on existing models developed from laboratory and field data. The statistical characteristics of lateritic soil properties were first compared with those from which the regression models were developed. Using regression models for hydraulic conductivity, k, and established distributions for the relevant soil parameters, reliability indices are computed considering hydraulic conductivity to have a normal/log-normal distribution. The results indicate that, for the laboratory-based model, reliability index is sensitive to variability in compactive effort and initial degree of saturation. The choice of distribution of initial degree of saturation affects reliability indices significantly and the energy of the British Standard heavy compaction has the highest reliability indices. On the basis of the reliability indices estimated from the field-based model, three variables, namely: compactor weight, initial saturation and plasticity index are identified as significantly affecting the field geometric mean hydraulic conductivity of lateritic soils. However, the hydraulic conductivity of lateritic soils can be better predicted if the compactor weight, as the most significant parameter, can be modelled as Gumbel-type distribution.

Tropical residual soil as compacted soil liners

A series of laboratory tests was conducted on a tropical residual soil, which is widespread and readily available over a considerable part of Peninsular Malaysia, to assess whether it could be compacted as hydraulic barriers in waste disposal landfills. Index properties, swelling potential, cation exchange capacity (CEC), compaction characteristics, and hydraulic conductivity of the soil indicate that it is inorganic, very plastic, inactive (activity <0.75), moderately expansive (modified free swell index is about 3.06), and of fair attenuation capacity (for inorganic contaminants). For hydraulic conductivity measurement, the soil was compacted in rigid-wall permeameter moulds at a variety of water contents and compactive efforts and then permeated with de-aired tap water. The results of hydraulic conductivity tests illustrate that hydraulic conductivity lower than 1×10−7 cm/s can be achieved using a broad range of water contents and compactive efforts, including water contents dry of optimum. Its shrinkage and strength properties show that it has minimal potential to shrinkage and has adequate strength to support the overburden pressure imposes by the waste body. These findings suggest that the residual soil can be potentially utilized as compacted soil liner material.

Sedimentary Residual Soil as a Waste Containment Barrier Material

Compacted soil liners are widely used as a waste containment barrier to control or restrict the migration of contaminant/leachate from the landfill into the environment because of their low hydraulic conductivity, attenuation capacity, resistance to damage or puncture, and cost effectiveness. Compacted soil liners are usually composed of natural inorganic clays or clayey soils. If natural clayey soils are not available, kaolinite or commercially available high swelling clay (bentonite) can be mixed with local soils or sand. This study examines the potential of a sedimentary residual soil as a waste containment barrier in landfills. The laboratory experiments conducted were: grain size distribution, Atterberg limits, swelling tests, compaction, volumetric shrinkage strain, unconfined compression, hydraulic conductivity and cation exchange capacity. The experimental results were compared with those recommended by various researchers for evaluation of its suitability. Test results showed that the soil compacted with modified Proctor compaction effort possesses low hydraulic conductivity (≤1 × 10−7 cm/s) and adequate strength. In addition, compacted sedimentary residual soil exhibited little volumetric shrinkage strain of below 4% at this compaction effort. Thus, the sedimentary residual soil could be effectively used for the construction of a waste containment barrier in landfills.

Evaluation of Multidimensional Transport through a Field-Scale Compacted Soil Liner

A field-scale compacted soil liner was constructed at the University of Illinois at Urbana-Champaign by the U.S. Environmental Protection Agency (USEPA) and Illinois State Geological Survey in 1988 to investigate chemical transport rates through low permeability compacted clay liners (CCLs). Four tracers (bromide and three benzoic acid tracers) were each added to one of four large ring infiltrometers (LRIs) while tritium was added to the pond water (excluding the infiltrometers). Results from the long-term transport of Br\U-\N from the localized source zone of LRI are presented in this paper. Core samples were taken radially outward from the center of the Br\U-\N LRI and concentration depth profiles were obtained. Transport properties were evaluated using an axially symmetric transport model. Results indicate that (1) transport was diffusion controlled; (2) transport due to advection was negligible and well within the regulatory limits of \Ik\N\Dsat\N ≤110\U-7\N cm/s; (3) diffusion rates in the horizontal and vertical directions were the same; and (4) small positioning errors due to compression during soil sampling did not affect the best fit advection and diffusion values. The best-fit diffusion coefficient for bromide was equal to the molecular diffusion coefficient multiplied by a tortuosity factor of 0.27, which is within 8% of the tortuosity factor (0.25) found in a related study where tritium transport through the same liner was evaluated. This suggests that the governing mechanisms for the transport of tritium and bromide through the CCL were similar. These results are significant because they address transport through a composite liner from a localized source zone which occurs when defects or punctures in the geomembrane of a composite system are present.

Long-Term Tritium Transport through Field-Scale Compacted Soil Liner

A 13-year study of tritium transport through a field-scale earthen liner was conducted by the Illinois State Geological Survey to determine the long-term performance of compacted soil liners in limiting chemical transport. Two field-sampling procedures (pressure-vacuum lysimeter and core sampling) were used to determine the vertical tritium concentration profiles at different times and locations within the liner. Profiles determined by the two methods were similar and consistent. Analyses of the concentration profiles showed that the tritium concentration was relatively uniformly distributed horizontally at each sampling depth within the liner and thus there was no apparent preferential transport. A simple one-dimensional analytical solution to the advective-dispersive solute transport equation was used to model tritium transport through the liner. Modeling results showed that diffusion was the dominant contaminant transport mechanism. The measured tritium concentration profiles were accurately modeled with an effective diffusion coefficient of 6 × 10\U-4 mm²/s, which is in the middle of the range of values reported in the literature.

Transit-Time Design for Diffusion through Composite Liners

Transit-time design methods are presented in this paper for determining the design thickness for composite liners consisting of a geomembrane and a compacted soil liner or geosynthetic clay liner. The design methods are based on a closed-form analytical solution for transient solute diffusion of volatile organic compounds in a composite liner and results from a numerical model. An analytical solution for diffusion in a two-layer soil profile, which is useful for transit-time design of composite liners, is also presented. The analytical solutions are used to develop graphical solution charts that can be used to design composite liners for which the effluent concentration and contaminant flux are less than a specified value. Design examples are included for a composite liner having a compacted soil liner and a composite liner having a geosynthetic clay liner. The method is relatively simple to apply and can be used for preliminary design of composite liners, evaluating experimental results, and verifying more complex numerical models.

SEEPAGE LOSSES FROM ANIMAL WASTE LAGOONS: A SUMMARY OF A FOUR–YEAR INVESTIGATION IN KANSAS

Seepage losses from animal waste lagoons can affect groundwater quality if liquid effluent is not properly contained within the basin. Seepage rates from 20 anaerobic lagoons were measured using water balance methods. Study locations included 14 swine sites, 5 cattle feedlots, and a single dairy. Seepage results and basin geometry were used to estimate the hydraulic conductivity (Ks) of the compacted soil liner at each site. Seepage data and waste chemistry were used to calculate rates of chemical export into the vadose zone. Profiles of ammonium–nitrogen (N) and other chemicals were determined by sampling soils beneath old lagoons. Seepage rates from 20 lagoons averaged 1.1 mm/d and ranged from 0.2 to 2.4 mm/d. Fifteen of the 20 lagoons had seepage rates between 0.5 and 1.5 mm/d. The variation among locations was small despite large differences in soil types and depths to groundwater. On average, the Ks of lagoon liners was 1.8 U 10–7 cm/s. Variation in seepage rates and Ks among sites was lognormally distributed. There was evidence that seepage was moderated by the organic sludge that blankets the bottom of lagoons. Concentrations of nitrogen, phosphorus, and other waste constituents were, on average, 3 to 5 times higher in swine waste lagoons compared to cattle feedlot lagoons. Ammonium–N seepage into the subsoil ranged from 2000 to 5000 kg ha–1 yr–1 at the larger swine sites but averaged 385 kg ha–1 yr–1 at cattle feedlots. Soil cores showed that concentrations of ammonium–N, organic–N, phosphorus, and other cations were highest near the original floor of the lagoon but decreased markedly with depth. In most cases, concentrations of nutrients in the soil returned to background levels about 3 m under the lagoons. Additional research is needed on fate and transport of contaminants that accumulate beneath lagoons and best management practices for lagoon closure.

Selection of Liner Materials and Design of Hazardous Water Facilities in Saudi Arabia

Rapid development in Saudi Arabia has produced a broad spectrum of wastes. In the last two decades, several refineries and petrochemical industries have been established. These industries have produced sludges and other toxic wastes which need proper planning for their handling and disposal. This paper covers design and selection of liner materials for two hazardous waste disposal sites. One of them is located in the Eastern Province of Saudi Arabia, while the second one is located in the Western part. The paper will present complete design details of the natural compacted and geosynthetic soil liners and the leachate collection and removal system for primary liners and leak detection/leachate collection and removal system for secondary liners.

Predicting Leakage through Composite Landfill Liners

Leakage through composite landfill liners having various characteristics was analyzed using existing analytical and numerical models developed for the study. Three-dimensional numerical models were used to analyze leakage through circular defects and two-dimensional numerical models were used to analyze leakage from defective seams. Leakage rates predicted with the numerical models were compared to leakage rates predicted using existing equations and analytical models currently being used. These comparisons show that existing equations and analytical models all have limitations and no universal equation or method is available for predicting leakage rates. To overcome some of the deficiencies in the existing equations and models, new equations were developed based on results from the numerical models. Recommendations are made for using the new equations, existing equations, and analytical models to predict leakage rates in thick composite liners having a geomembrane overlaying a compacted soil liner and thin composite liners having a geomembrane overlaying a geosynthetic clay liner.

Seepage Losses and Nitrogen Export from Swine‐Waste Lagoons: A Water Balance Study

AbstractSeepage losses from animal‐waste lagoons could affect ground water quality. Water balance methods were used to study seepage and N export from three swine‐waste lagoons in southwestern Kansas. Lagoons ranged in size from 0.8 to 2.2 ha and had an average waste depth of 5.6 m. Compacted soil liners were 0.30 to 0.46 m thick and built with native soil or, in one case, a soil‐bentonite mixture. Seepage was calculated from measurements of evaporation and changes in depth when the addition or removal of waste was precluded or quantified. Seepage rates were 1.1, 1.1, and 0.8 mm d−1 from the three lagoons, with the lowest rate occurring at the site with a 0.46‐m liner augmented with bentonite. The in situ coefficient of permeability of the soil liners ranged from 7.8 × 10−8 and 1.5 × 10−7 cm s−1. In two lagoons built with silt loam liners (no bentonite), permeabilities on a whole‐lagoon basis were about five times less than those measured from soil cores collected before the addition of waste. Results imply that permeability was reduced by organic sludge on the bottom of the lagoons. The average ammonium‐N concentration in the lagoons was 665 mg L−1, accounting for almost all of the soluble N. Calculations indicate that the ammonium‐N export rates were between 2187 and 2726 kg ha−1 yr−1, but more information is needed regarding the fate of N deposited in the soil beneath lagoons.

Suitability of Hydrologic Evaluation of Landfill Performance (HELP) model of the US Environmental Protection Agency for the simulation of the water balance of landfill cover systems

Cover systems are widely used to safeguard landfills and contaminated sites. The evaluation of the water balance is crucial for the design of landfill covers. The Hydrologic Evaluation of Landfill Performance (HELP) model of the US Environmental Protection Agency was developed for this purpose. This paper discusses some limitations of version 2 of this model and some operational difficulties for the use of this model in Germany, which has been developed for the United States. The model results are tested against field data of the water balance, measured on test fields on the Georgswerder landfill in Hamburg. Theoretically, HELP considers gravitational forces as driving forces of water flow only. Therefore capillary barriers cannot be simulated. Furthermore, the formation of and the flow through macropores are not considered, a main critical process that the diminishes the effectiveness of compacted soil liners. In the output comparison, the matching of measured and simulated data is quite good for lateral drainage, but failed for surface runoff and liner leakage through compacted soil liners. A further validation study is planned for HELP version 3 using a broader range of test field data.

Modeling Impact of Small Kansas Landfills on Underlying Aquifers

Small landfills are exempt from compliance with Resource Conservation and Recovery Act Subtitle D standards for liner and leachate collection. We investigate the ramifications of this exemption under western Kansas semi-arid environments and explore the conditions under which naturally occurring geologic settings provide sufficient protection against ground-water contamination. The methodology we employed was to run water budget simulations using the Hydrologic Evaluation of Landfill Performance (HELP) model, and fate and transport simulations using the Multimedia Exposure Assessment Model (MULTIMED) for several western Kansas small landfill scenarios in combination with extensive sensitivity analyses. We demonstrate that requiring landfill cover, leachate collection system (LCS), and compacted soil liner will reduce leachate production by 56%, whereas requiring only a cover without LCS and liner will reduce leachate by half as much. The most vulnerable small landfills are shown to be the ones with no vegetative cover underlain by both a relatively thin vadose zone and aquifer, and which overlie an aquifer characterized by cool temperatures and low hydraulic gradients. The aquifer-related physical and chemical parameters proved to be more important than vadose zone and biodegradation parameters in controlling leachate concentrations at the point of compliance.

Contaminant transport through a soil liner underlain by an unsaturated stone collection layer

Chloride and sodium migration in an unsaturated stone collection system underlying a compacted soil liner was examined for three different flow rates ranging between 2.5 and 0.017 m/a. Relatively high and uniform concentrations were observed in the unsaturated stone layer. The groundwater velocity played a significant role in contaminant transport through unsaturated stone even at a flow of 0.017 m/a. Experimental observations were accurately predicted using one-dimensional advective–diffusive–dispersive theory. Transport parameters were reduced by modelling the test data. Key words: soil liner, unsaturated flow, diffusion, landfill, collection system.