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ST CONSTRUCTION OF THE 1 ENHANCED BARRIER SYSTEM IN THE WORLD www aquatan com 27 11 974 5271 aqua aquatan com

INTRODUCTION Geosynthetic materials have been successfully installed as effective barriers in various types of earth and concrete structures over the past 50 years However as technology and research in the geosynthetics field evolved it was found that composite liners have certain limitations and that heat can significantly decrease the service life of geosynthetic components According to the highly respected US Environmental Protection Agency current standards do not adequately address toxic pollutant discharge frequently resulting in toxic chemical seepage from unlined ponds and dry waste landfills into ground and surface waters Although the Agency s concerns refer mainly to pollution caused by coalrelated products the reality is that clean water is the source of life and hence it is critical to a sustainable future The worldwide survey of regulatory standards for waste management and pollution control GRI Report No 34 of 2007 GRI s Second Worldwide Survey of Solid Waste Landfill Liner and Cover Systems indicated that authorities Page 2 of 8 prefer geosynthetic composite liners for pollution control over clay and modified soil liner systems COMPOSITE LINER A composite liner can be defined as a flexible membrane liner in intimate contact with a mineral liner The mineral liner can either be a compacted clay liner CCL or a geosynthetic clay liner GCL THE EBS PROVIDES DESIGNERS WITH A PRACTICAL LOWMAINTENANCE AND COST EFFECTIVE SOLUTION TO ADDRESS THE REQUIREMENTS ENFORCED BY REGULATORS The performance of such composite liners should be evaluated based on total solute transport which considers both advective losses and diffusion of volatile organic compounds VOCs from the waste stream Foose et al 2002 Construction phase influences The climatic conditions that are prevalent during construction can significantly reduce liner performance Sunshine may induce desiccation cracking of the clay component in particular of pre hydrated and uncovered GCLs as well as induce wrinkles in the geomembrane which would lead to increased advective losses Excessive rain on the clay component can lead to displacement of the fine fraction at the interface and resultant pervious zones while wind too can displace the fine fraction which is critical to controlling impermeability Hydration of the GCL component of a composite liner prior to its exposure to leachate is required However this hydration should take place after application of a normal load Vangapaisel et al 2002 This is extremely difficult when the GCL is part of a composite liner and isolated from soil moisture by either the leakage detection system or underlying secondary liner geomembrane Pre hydration by means of spraying water on the GCL immediately prior to covering with a geomembrane induces damages such as squeeze of the bentonite and preferential flow paths through desiccation cracks The failure to pre hydrate a GCL prior to its exposure to

leachate especially if containing hydrocarbons or salts will result in a loss of performance Service life influences The lifetime prediction of a geomembrane has been addressed by numerous authors Sangam Rowe 2002 Koerner Hsuan 2003 Rowe 2005 for exposure to elevated temperature and various fluids These elevated temperatures significantly reduce the service life of the geomembrane may induce desiccation cracking of underlying clay components of composite liners and increase the total solute transport REGULATORS ARE MOVING IN THE DIRECTIONOF REQUIRING DESIGNERS TO ADDRESS THE MITIGATION OF HEAT ON A BARRIER INSTALLATION The relatively small temperature increase in the lower range of 10 C to 35 C on a composite liner increased diffusion by 100 and hydraulic conductivity or advection Page 3 of 8 by 80 Rowe 2005 Similar considerations need to be given to the drainage system performance which is affected by both normal stress resulting in intrusion and elevated temperatureinduced deformations causing a reduction in performance of geosynthetic drainage systems composite liner has a significant impact on thermal conductivity and the leak detection or under drainage system has significant air voids which act as a thermal barrier with the result that heat builds up in the primary liner and accelerates its degradation unless mitigated TEMPERATURE CONSIDERATIONS INNOVATING TO OVERCOME THE CHALLENGES The negative effect of temperature on geosynthetic components is a topic that attracted the attention of numerous researchers over the past decade The seriousness of this limitation has been recognised by leading geomembrane manufacturers who are investing in the development of temperatureresistantgeomembranes Ramsey Wu 2013 Investigation of the thermal conductivity of GCLs showed that thermal conductivity increased with the increase in moisture content Singh Bouazza 2013 This may lead to the GCL acting as an insulator if it is not properly hydrated which will cause elevated temperatures on the primary geomembrane The moisture content of the clay component in the The foregoing shows that there is a need in the geomembrane industry to mitigate the effects of elevated temperature on composite liners postloading hydration of GCLs and the removal of VOCs to expand the performance of the conventional geomembrane installations Principles of the Enhanced Barrier System A concept was developed which involves drawing a fluid under negative pressure through a pervious zone adjacent to the barrier so that the fluid can be used both to cool the primary composite lining and adjacent drainage systems and to introduce moisture to the GCL beneath the overlying geomembrane for its hydration after placement of a normal load and prior

to the risk of its exposure to leachate previously published Gundle et al 2013 The fluid gas liquid or twophase mixture passing through the pervious zone also maintains the leak detection system at a low to zero concentration of VOCs thus preventing their further diffusion into the adjacent environment The negative pressure is essential to ensure no introduction of oxygen to the waste body through a discontinuity of the base geomembrane which could induce spontaneous combustion depending on the composition of the contained waste The negative pressure results in a net outward flow towards the leakage detection system sump Figure 1 describes the working principle of the system in a solid waste site specifically where all three functions of the enhanced barrier system EBS are utilised It is important to note that one or any combination of the three functions of the EBS can be utilised depending on project requirements Benefit of the EBS The regulatory standards are becoming increasingly stricter Regulators are moving in the direction of requiring designers to address the mitigation effects of heat on a barrier installation to ensure that Figure 1 EBS working principle in a solid waste facility This concept was verified by a range of laboratory experiments as well as by an infield application The results of these experiments were Page 4 of 8 the required design service life is achieved Furthermore should VOCs be present in the containment facility the designer has to address these and provide a solution to prevent VOCs from contaminating the subsoil The EBS provides designers with a practical low maintenance and costeffective solution to address the requirements enforced by regulators Even more important it extends the barrier s service life extracts VOCs and overcomes construction challenges regarding hydrating and maintaining the optimal hydration of the clay component ultimately to protect the environment PROJECT DESCRIPTION Design The first EBS application in the world was specified by the consulting engineering firm Royal HaskoningDHV to be installed at a hazardous waste sludge lagoon The total solute transport analysis showed that significant VOC concentrations in the waste stream would diffuse through the contaminant containment barrier system The site foundations and operational constraints favoured an all geosynthetic solution in which both the primary and secondary barrier would be a composite geomembrane plus geosynthetic clay liner

separated by a leak detection system which would also be a geosynthetic product Due to the nature of the liquid waste to be contained it was evident that the GCL needed to be pre hydrated i e hydrated prior to exposure to waste containing hydrocarbons Similarly the diffusion of VOCs from the liquid waste containment had to be prevented from migrating to the groundwater regime and hence either a significant sorption layer would be required or VOCs had to be removed from the leak detection system The facility is 13 hectares in footprint and 10 metres deep The waste facility design was able to conform to the conventional doublecomposite liner with an intermediate leak detection layer complying with the hazardous waste lagoon containment barrier standard Class A Landfill in accordance with NEMWA Regulation 636 published in August 2013 This barrier design addressed seepage but required the EBS to mitigate the risk of diffusion of VOCs and hydration of the primary GCL Figure 2 is a diagrammatic explanation of the barrier system and Page 5 of 8 the working principle of the EBS sheets to ensure a practical design The most important design aspect to ensure successful operation of the system is that of even airflow throughout the facility Each facility is unique and the site specific parameters as well as the composition of the barrier system components have to be taken into account at the start of a design Consideration was given to the pre hydration means of the GCLs in the primary and secondary composite liners the rate and direction of the advancing wetting front and the direction of potential pollutant migration This led to the selection of different GCLs for the enclosed primary barrier and for the secondary barrier applications To ensure even airflow through the facility as well Figure 2 Barrier system and working principle of EBS as to optimise the size and power consumption of the mechanical extraction fan the facility is divided into compartments The width of the compartments is calculated based on the pressure drop over the corresponding flow section to ensure evenly distributed flow as well as taking into account the width of the geomembrane The vacuum induction system with inlets and outlets was designed to make use of readily available fittings and vacuum pumps The system is designed to induce condensation at the fluid inlet to assist with the rapid hydration of the primary barrier GCL

Construction The earthworks construction commenced in mid 2013 and the liner installation in November 2013 The project was successfully completed in November 2015 Earthworks preparation General geomembranelined earth dam construction principles were applied which included engineered sloping walls and floors with a regular slope towards the lowest point of the dam with subsoil drains standard compaction requirements and surface finishes EBS installation Standard geomembrane installation practice was followed giving attention to specific design principles and thermal expansion and contraction wrinkles Figure 3 Lining and pipe installation in progress critical importance to ensure proper performance of the system and the effective separation between compartments Particular care was taken to ensure that the installation fully met the design requirements Quality control Being the first large scale installation of this innovative technology in the world extensive quality control and diligent construction supervision were imperative to ensuring the successful outcome of the project Strict quality control was enforced by auditing both the geomembrane manufacturer s facility in Germany and the pipe manufacturer s facility in Anchor trenches were adapted to accommodate the fluid extraction system Timeous backfilling of trenches was important to prevent any localised tension in the geomembrane due to thermal expansion and contraction Pipe connections to the geomembranes as well as the installation of other piping components were of Page 6 of 8 Figure 4 Electric Leak Detection ELD in progress

Table 1 Cause of holes vs size of holes Noske and Touze Foltz 2000 South Africa to ensure that materials were supplied according to specification Apart from this third party quality control testing was conducted on the various materials to ensure conformity to the project specifications From a construction risk management perspective the EBS part of the project consisted of five major processes Earthworks preparation for geosynthetics Earthworks preparation for piping Geosynthetics installation Piping installation Capping operation As with any liner installation it was shown that risks of defects to barrier systems resulted from stones 71 2 and heavy equipment 15 6 Table 1 refers As a result of this Aquatan performed postconstruction quality control Page 7 of 8 by conducting an electric leak detection ELD survey on the completed facility utilising the dipole method Despite the fact that there were spotters present during the process of capping the liner four defects were picked up by the ELD process All four defects were repaired see Figure 5 Had it not been for the ELD procedure the performance of the barrier and the EBS would have been compromised containment barrier systems CONCLUSION As a result of effective collaboration between all project stakeholders innovative engineering quality workmanship and stringent construction supervision the world first enhanced barrier system EBS an innovative technology in the geosynthetics industry was successfully installed on this 13 ha hazardous waste sludge lagoon Figure 5 One of the four defects identified by the ELD After construction the facility was filled with hazardous waste sludge and the leak detection system monitored for performance This confirmed the exceptional value of the EBS in improving the postconstruction performance of contaminant Figure 6 Airflow measurement and calibration at one of the air intakes The EBS is successfully performing its function of hydrating and keeping the

GCL in a hydrated state to effectively mitigate the risk of diffused VOCs negatively impacting the groundwater regime Figure 6 shows the airflow measurement at one of the air intakes located along the perimeter of the facility REFERENCES Foose G J Benson C H Edil T B 2002 Comparison of solute transport in three composite liners Journal of Geotechnical and GeoEnvironmental Engineering Volume 128 p 391 403 Gundle C J Meyer P J Meyer W Sch ffner M 2013 Technological response for mitigating environmental impacts to achieve long term pollution prevention GhIGS GeoAfrica 2013 Conference Koerner R M Hsuan Y G 2003 Lifetime prediction of polymeric geomembranes used in new dam construction and rehabilitation Proceedings Assoc of State Dam Safety Officials Conference Lake Harmony Pennsylvania ISBN 0 13 726175 6 Nosko V Touze Foltz N 2000 Geomembrane liner failure Modelling of its influence on contaminant transfer Proceedings of the Second European Page 8 of 8 Geosynthetic Conference P tron Editore Bologna p 557 560 Ramsey B Wu Y 2013 Advances in Geomembranes Thermal properties and elevated usage temperatures GhIGS GeoAfrica 2013 Conference Rowe R K 2005 Long term performance of containment barrier systems Geotechnique 55 9 p 631 678 Sangam H P Rowe K 2002 Effects of exposure conditions on the depletion of antioxidants from high density polyethylene geomembranes Canadian Geotechnical Journal Volume 39 p 1221 1230 Singh R M Bouazza A 2013 Thermal Conductivity of Geosynthetics Geotextiles and Geomembranes 39 p 1 8 Vangpaisal T Bouazza A Kodikara J 2002 Gas permeability of a needlepunched geosynthetic clay liner subjected to wetting and drying Geosynthetics 7th ICG Delmas Gourc Girard eds p 841 844