Flexible Membrane Liners Research Articles

A Study on the Chemical Resistance of GT Composites

This paper is concerned with the performance of geo-textile (GT) against chemical condition. GT is generally adopted for the upper part of geo-membrane (GM) for waste landfills and thus it is very important to consider the performance of GT against certain chemical environments until landfill is completed. In this study, PVA geo-textile/HDPE geo-membrane was prepared to investigate the waste landfill related properties in terms of long-term performance against chemical conditions imposed. GT composites of PVA GT/HDPE GM, PVA GT and HDPE GM were produced in thermal bonding process. Polyester and polypropylene GT were also manufactured in needle punching process. The experiments have been conducted under a modified version of EPA 9090 test method which is very similar to the method of evaluating chemical resistance of flexible membrane liner by the US Environmental Protection Agency (EPA). In this testing method, samples immersed in chemical of different solutions up to 150 days at 30 day interval were obtained to find tensile strength holding rate and chemical resistance. The analysis in this paper is focused to evaluate the effect of different pH conditions and temperature environments on geo-synthetics weights strength retention. It was concluded from the experiments that tensile strength of GT composites against leachate were reduced by 10 to 20% in both polypropylene and polyester non-woven GT. The reduction was more significant at temperatures of 50 °C than that at 25 °C. The experiments conducted in this study demonstrated that PVA GT is excellent in terms of chemical resistance.

Vadose Zone Characterization and Monitoring Beneath Waste Disposal Pits Using Horizontal Boreholes

Vadose zone characterization and monitoring immediately below landfills using horizontal boreholes is an emerging technology. However, this topic has received little attention in the peer‐reviewed literature. The value of this approach is that activities are conducted below the waste, providing clear and rapid verification of containment. Here we report on two studies that examined the utility of horizontal boreholes for environmental characterization and monitoring under radioactive waste disposal pits. Both studies used core sample analyses to determine the presence of various radionuclides, organic compounds, or metals. At one borehole site, water content and pore‐water chloride concentrations were also used to interpret vadose zone behavior. At another site, we examined the feasibility of using flexible membrane liners in uncased boreholes for periodic monitoring. For this demonstration, these retrievable liners were air‐injected into boreholes on multiple occasions carrying different instrument packages for environmental surveillance. These included a neutron logging device to measure volumetric water at regular intervals, high‐absorbency collectors that wicked available water from borehole walls, or vent tubes that were used to measure air permeability and collect air samples. The flexible and retrievable liner system was an effective way to monitor water content and measure in situ air permeability. The high‐absorbency collectors were efficient at extracting liquid water for contaminant analyses even at volumetric water contents below 10%, and revealed tritium migration below one disposal pit. Both demonstration studies proved that effective characterization and periodic monitoring in horizontal boreholes is both feasible and adaptable to many waste disposal problems and locations.

Numerical modelling of the generation and transport of heat in a bottom ash monofill

Municipal solid waste is incinerated to reduce its volume, toxicity and reactivity. Several studies have shown that the resulting bottom ash has a high exothermic capacity. Temperature measurements in municipal solid waste incineration (MSWI) bottom ash landfills have found temperatures up to 90 °C. Such high temperatures may affect the stability of the landfill’s flexible polymer membrane liner (FML) and may also lead to an accelerated desiccation of the clay barrier. The purpose of this study was to gain detailed knowledge of temperature development under several disposal conditions in relation to the rate of ash disposal, the variation of layer thickness, and the environmental conditions in a modern landfill. Based on this knowledge, a simulation was developed to predict temperature development. Temperature development was simulated using several storage periods prior to the deposition and several modes of emplacement. Both the storage time and the mode of emplacement have a significant influence on the temperature development at the sensitive base of the landfill. Without a preliminary storage of the fresh quenched bottom ash, high temperatures at the bottom of a landfill cannot be avoided.

Temperature development in a modern municipal solid waste incineration (MSWI) bottom ash landfill with regard to sustainable waste management

Municipal solid waste is treated in incineration plants to reduce the volume, the toxicity and the reactivity of the waste. The final product, municipal solid waste incineration (MSWI) bottom ash, was considered as a material with a low reactivity, which can safely be deposited in a MSWI bottom ash landfill, or which can be used, e.g. in road construction after further treatment. However, temperature measurements in MSWI bottom ash landfills showed temperatures up to 90°C, caused by exothermic reactions within the landfill. Such high temperatures may affect the stability of the flexible polymer membrane liner (FML) and may also lead to an accelerated desiccation of the clay barrier. At the beginning of this study it was uncertain whether those reported results would be applicable to modern landfills, because the treatment techniques in MSWI and landfills have changed, bottom and fly ash are stored separately, and the composition of the incinerated waste has changed significantly since the publication of those results. The aim of this study was to gain detailed knowledge of temperature development under standard disposal conditions in relation to the rate of ash disposal, the variation of layer thickness, and the environmental conditions in a modern landfill. Temperatures were measured at nine levels within the body of a landfill for a period of nearly 3 years. Within 7 months of the start of the disposal, a temperature increase of up to 70°C within the vertical centre of the disposal was observed. In the upper and central part of the landfill this initial temperature increase was succeeded by a decrease in temperature. The maximum temperature at the time of writing (May 2000) is about 55°C in the central part of the landfill. The maximum temperature (45.9°C) at the FML was reached 17 months after the start of the deposition. Since then the temperatures decreased at a rate of 0.6°C per month. Temperature variation within each individual layer corresponds to the temperature of the underlying layer and the overall surface-to-volume ratio of the landfill. The temperatures in the uppermost layer are significantly influenced by the ambient temperatures.

A comparison of the convective and diffusive flux of organic contaminants through landfill liner systems

In an effort to protect groundwater, waste disposal regulations now require the use of composite liners consisting of com pacted soil overlain with a flexible plastic membrane liner in both hazardous and municipal solid waste landfills in the USA. When properly installed, composite liners decrease the convective flux of leachate flowing through flaws in the plas tic ; however, even if all flaws could be eliminated, organic chemicals will diffuse through the liner system. Although actual field measurements are not available on the flux of contaminants through landfill liners, field measurements of leachate concentrations at some landfills, leak rates at other landfills and laboratory data on diffusion coefficients, allow estimation of the flux so that convective and diffusive trans port can be calculated. Calculations were made to estimate the flux of five organic chemicals through liners of various designs. For the flexible membrane liner alone, the flux of organic chemicals is dominated by diffusion, and transport by convective flux through flaws is one or two orders of magni tude less. For a 100 cm thick clay liner alone, the flux of organic chemicals is dominated by convective flow since the long path length limits diffusive flux. For a composite liner including a flexible membrane over a 100 cm thick clay liner, the flux of organic chemicals is dominated by convective transport since the diffusion path length through the compos ite liner is much greater than that through the flexible mem brane liner (FML) alone. For a typical composite liner in which the FML contains 30 holes/ha -1, the convective flux of organic chemicals is typically two orders of magnitude greater than the diffusive flux. A liner consisting of an FML, or an FML combined with a thin layer of low permeability soil, will allow a much greater flux of contaminants than a composite liner consisting of an FML and a thick layer of low permeabil ity soil.

Assessment of HDPE geomembrane performance in a municipal waste landfill double liner system after eight years of service

In the late 1970s and early 1980s, environmental regulations were upgraded in a general national movement to effect secure management of our municipal and residual solid wastes. The new regulations required varying combinations of natural and/or synthetic barrier and drainage layers to prevent the unrestricted release of contaminants. The acceptable barrier materials included synthetic flexible membrane liners (FMLs) of various types. One of those most commonly used has been high-density polyethylene (HDPE) geomembrane. HDPE has been selected because of its good chemical resistance characteristics, among others. Background compatibility testing has shown the HDPE geomembrane to be extremely resistant to the leachates that are generated by municipal and residual solid waste landfills. The background testing for design has generally been based on relatively short-term tests that are conducted under extreme conditions to ‘forecast’ service life. Recently, a municipal solid waste landfill double liner system that was constructed in 1988 was exhumed. The HDPE geomembranes of this liner system had been exposed to varying degrees of leachate since 1989. Samples of the HDPE were extracted from the in-place liner system and were laboratory-tested for physical, mechanical and endurance properties. The selected suite of tests duplicated the test protocol conducted in 1988 as part of the liner system construction quality assurance (CQA) program. The results of this testing show that the HDPE properties are still within the range of data generated by the original testing in 1988. No degradation in properties was indicated by this testing program. The HDPE had been exposed to the leachate, methane, and static and dynamic stresses for approximately 8 years. The results of this test program support the design selection of HDPE as the synthetic barrier component of this landfill liner system.

Flexible membrane liners: C. R. Field & S. D. Stone, Civil Engineering — ASCE, 65(4), 1995, pp 60–61

Unless there is a long-range plan for the postclosure use of a landfill--such as turning it into a golf course or a park--final grades are usually designed to be as high and as steep as possible to provide the most usable space for refuse. Engineers designing such landfill closure systems must maximize space and meet federal, state, and local regulations as they ensure that the structure will be stable. In the past, compacted clay was used as a barrier layer in landfill caps. Some engineers concerned about slope stability still prefer to sue clay instead of flexible membrane liners. However, because Subtitle D regulations of the Resource Conservation and Recovery Act require new landfills to have caps that are no more permeable than the bottom liner, only landfills built before promulgation of Subtitle D can be capped with clay. For those landfills, if clay is locally available, a clay cap may be the most economical alternative. Yet a new generation of flexible membrane liners offers engineers new ways to fight instability on landfill slopes.

Estimation of Leakage Rates Through Flexible Membrane Liners

AbstractLeakage rate calculations for both low‐ permeability soil liners and composite liners using flexible membrane liners (FMLs) overlying low‐permeability soil are developed. Latin‐Hypercube simulations with uncertainly assigned to the soil liner hydraulic conductivity value and the spatial frequency of FML holes are used to examine the variability in the liner leakage rates. The low‐permeability soil hydraulic conductivity is the parameter with the greatest effect on landfill liner leakages rates. Composite liners have a significant impact on reducing leakage rates through the landfill liner.

Permachor Method To Predict Diffusivity Coefficients of Organics in Aqueous Solutions in Flexible Membrane Liners

The diffusion of organic contaminants through plastic Flexible Membrane Liners (FMLs) used in landfills and surface impoundments is an important criteria for evaluating synthetic liner performance. An experimental method has been developed and used to measure diffusivities of organic contaminants commonly found in landfill leachate from an aqucous solution through High Density Polyethylene (HDPE). These data were utilized to evaluate the applicability of the Permachor Method developed by Salame (1961) to predict the diffusion of other organics through FMLs. The Permachor equation can be used in combination with the relationship between the partition coefficients of organics in aqueous organic solution and the octanol-water partition coefficients to predict permeability factors which in turn can be used to calculate the diffusion coefficients of a range of organic chemicals in a plastic FML. Once the relationship between permeability and Permachor are determined for a given plastic FML for a few organic chemicals, the method can be used to predict the permeability of many other organic chemicals. The properties of the plastics and the additives used in its formulation including carbon black appear to influence the diffusion rates.

Diffusion coefficients of organics in high density polyethylene (HDPE)

Only limited data are available on the diffusion of volatile organic solvents through flexible membrane liners (FMLs) used for lining impoundments and landfills. To expand this database, a rapid, inexpensive method is needed to measure the diffusion coefficients of volatile organic solvents through FML materials. An absorption method has been developed to determine the diffusion coefficients of volatile organic solvents through FML materials. The method is based on the depletion of an organic compound from an aqueous solution due to absorption by a submerged sample of FML. A numerical solution of Fick's second law of diffusion was used to develop a graph which can be used to determine the diffusion coefficient from the time dependent concentration data. The diffusion coefficients obtained from the absorption tests were validated by comparing them with coefficients determined using a two chamber diffusion cell. The diffusion coefficients determined for toluene and xylene in high density polyethylene (HDPE) were 5.1 × 10 −9 cm 2s −1 and 1.0 × 10 −9 cm 2s −1 by the two methods, respectively. The data indicate that the coefficient of distribution (K d) between the FML and the organic solution, a value which is needed to calculate the diffusion coefficient from the data, can be estimated from the log of the octanol-water partition coefficient (K ow), a commonly measured and reported value for many chemicals.

Diffusion Coefficients of Organics in High Density Polyethylene (HDPE)

Only limited data are available on the diffusion of volatile organic solvents through flexible membrane liners (FMLS) used for lining impoundments and landfills. To expand this database, a rapid, inexpensive method is needed to measure the diffusion coefficients of volatile organic solvents through FML materials. An absorption method has been developed to determine the diffusion coefficients of volatile organic solvents through FML materials. The method is based on the depletion of an organic compound from an aqueous solution due to absorption by a submerged sample of FML. A numerical solution of Fick's second law of diffusion was used to develop a graph which can be used to determine the diffusion coefficient from the time dependent concentration data. The diffusion coefficients obtained from the absorption tests were validated by comparing them with coefficients determined using a two chamber diffusion cell. The diffusion coefficients determined for toluene and xylene in high density polyethylene (HDPE) were 5.1 × 10-9 cm2s-1 and 1.0 x 10-9 cm2s-1 by the two methods, respectively. The data indicate that the coefficient of distribution (Kd) between the FML and the organic solution, a value which is needed to calculate the diffusion coefficient from the data, can be estimated from the log of the octanol-water partition coefficient (Kow), a commonly measured and reported value for many chemicals.

Reclamation of site used for impoundment of wastewater from a pesticide industry ‐ a case study

Abstract Wastewater generated from a pesticide industry containing 15 to 20% HCl was neutralised and stored in three solar evaporation ponds (SEP)lined with Flexible Membrane Liner(FML). Characteristics of the pond water showed the presence of high concentration of dissolved solids which were mainly due to salts such as chloride and sulfate of calcium and sodium. High performance liquid chromatographic (HPLC) analysis of pond water did not indicate the presence of sevin. A variation in the chemical composition of the sediment samples was observed from top to bottom layers. The study revealed that the salts and organics were retained mostly in the upper portion of the pond sediment thus indicating remote possibility of percolation. The possible treatment alternatives/remedial measures to be adopted for cleanup of the ponds are discussed.

Flexible Membrane Liner Testing in Waste Management

Flexible membrane liners (FMLs) have grown, and must continue to grow, in importance across the solid and hazardous waste management industry. Their study has increased in importance as their applications have increased. This paper develops new criteria for testing, as well as discussing the implications. Current test procedures are based upon standard materials tests that do not combine the many stress factors acting on a liner under a landfill. There are no field data against which to calibrate tests that must predict service lives far longer than experience. The anticipated service life of these materials as liners makes it critical to enhance the representation of field conditions in laboratory testing.

Book Reviews: NEW DEVELOPMENTS AND TRENDS IN GROUND WATER PROTECTION WITH FLEXIBLE MEMBRANE LINERS. By Dr Ing. R. Krause, 1989. Published by SLT Lining Technology GmbH, Pollhornweg 17 D-2102, Hamburg 93, Germany, 100 pp. No price. Reviewed by Alan Parker, GIBB Environmental Sciences, Abingdon, U.K

Book Reviews: NEW DEVELOPMENTS AND TRENDS IN GROUND WATER PROTECTION WITH FLEXIBLE MEMBRANE LINERS. By Dr Ing. R. Krause, 1989. Published by SLT Lining Technology GmbH, Pollhornweg 17 D-2102, Hamburg 93, Germany, 100 pp. No price. Reviewed by Alan Parker, GIBB Environmental Sciences, Abingdon, U.K

The effectiveness of composite lining systems in controlling the leakage of leachate from sanitary landfills to groundwater

Leachate, the hazardous liquid that percolated through the refuse layers of a sanitary landfill, if it leaks through the landfill lining system, can become a serious source of groundwater pollution. In the past, leaks have been detected in many landfills lined with flexible membrane liners (FML) whose failure may be attributed to flaws such as imperfect seaming, rips, and tears of the membrane, or from chemical attack that dissolves the membrane. Recent studies have shown that composite lining systems which include either a clayey subbase or a layer of geotextile in addition to the FML, can substantially reduce the leakage of leachate. Therefore in this study, four different lining systems are proposed and evaluated to determine their effectiveness in controlling leachate flow under various degree of flaws (referred to as leakage fraction LF) in the FML. The Hydrologic Evaluation of Landfill Performance (HELP) computer model of the Environmental Protection Agency of USA, currently the most widely accepted model for predicting the performance of leachate collection systems in that country, is used to evaluate the following lining systems: (1) a single FML or liner, (2) a single FML with a clayey composite, (3) a single FML with a geotextile called Claymax, and (4) a double FML. Based on the climatic conditions and the present lining construction cost of Alaska, the study shows that a single FML or liner is the most economical but it is also the least effective in controlling leachate flow. Design (3), a single FML with a geotextile, costs about 50 percent more but it reduces the leakage of leachate by several orders. Design (2) is also effective but the cost incurred in constructing a 3 feet thick clayey subbase is prohibitive and thus to effectively and economically minimize the hazards of potential groundwater contamination by leachate, Design (3) is recommended as the composite lining system for future landfill sites.

Fundamental approach to service life of flexible membrane liner's (FML's)

Predicting the service life of flexible membrane liners (FML's) exposed to chemicals has usually been done by physical or mechanical changes after exposure. The report summarized here presents an alternative approach--that to water for periods up to fifteen months were tested by five different chemicals and transport related measurements. The results indicated that monitoring the transport properties of FML's exposed to particular chemicals over a reasonable exposure time could be considered as one possible method for predicting an FML's lifetime.

Technical note on cold weather installation of HDPE

In order to successfully seam HDPE flexible membrane liners (FMLs) in cold weather (less than 4·5°C (40°F), FML temperature may not be the most important factor. Secondary cold weather effects such as frozen subgrade, bridging, snow and ice removal, and worker discomfort pose a much more significant risk to the integrity of the liner installation.

Reliability-based design of secure landfill flexible membrane liners (FMLs) : Vita, C L Proc 24th symp on engineering geology and soils engineering, Coeur d'Alene, 29 Feb–2 March 1988P345–358. Publ Washington: Washington State University, 1988

Reliability-based design of secure landfill flexible membrane liners (FMLs) : Vita, C L Proc 24th symp on engineering geology and soils engineering, Coeur d'Alene, 29 Feb–2 March 1988P345–358. Publ Washington: Washington State University, 1988

Chemical mass transport measurements to determine flexible membrane liner lifetime : Lord, A E; Koerner, R M; Swan, R H Geotech Test JV11, N2, June 1988, P83–91

Chemical mass transport measurements to determine flexible membrane liner lifetime : Lord, A E; Koerner, R M; Swan, R H Geotech Test JV11, N2, June 1988, P83–91

Assessment of techniques for in Situ repair of flexible membrane liners: Final Report

The feasibility of using either patching or plugging to make in situ repairs of damaged areas in in-service flexible membrane liners (FMLs) was investigated. Applying the basic criteria used in assessing and testing liners and seams in FMLs that are being installed, it appears highly questionable that conditions required for preparation of adequete seams and permanent repairs can be met with FMLs exposed below waste. Exposed liners, however, can be repaired if the proper conditions of cleanliness and dryness are met. Repairing with formed-in-place plugs holds some promise for short-term use; however, the compatibility of the plugging material with the waste liquid should be assessed. Experimental studies relating to preparation of high density polyethylene (HDPE) seams made with a heat gun indicate the importance of surface preparation in acheiving adhesion between the two pieces of liner being seamed. Cleanliness and fresh surfaces are necessary. Compatibility tests of six different potential plugging materials (five epoxies and one cement) in five simulated test media show the importance of the medium on the ability of the material to set and with long-term integrity of the cured materials.