Conference Agenda

<p>Geomembranes are now part of most designs when dealing with leachates. Good practices suggest performing an electrical leak location survey to ensure imperviousness, or to lower leakage risks to the lower level. Several methods are available for exposed and covered tests, and the relevancy of exposed methods is often questioned: Won’t all leaks be found during the covered survey? Tiny leaks such as defects in extrusion seams may be found during dipole survey with ideal conditions, but can be hard or even impossible to locate precisely. This scenario has been witnessed in an industrial waste treatment pond as well as in a compost pad leachate pond where a leak area was identified. The protection and drainage layer had been removed, but leak was too small to be noticeable to the naked eye and equipment was inappropriate to investigate any further. This led to a waste of time and uncertainty on all parties regarding the physical and financial responsibility of the defect, whereas a common water puddle leak location survey would have located those leaks and they would have been repair long before the installation of the drainage layer.</p>

Geosynthetics sorption sheet is one of the promising materials against geogenic contami-nated soils. It offers a new function: sorption in addition to the traditional geosynthetics functions. Since infiltrated water is drained during contaminants capture, the geosynthetic sorption sheet has both a drainage function for water and a barrier function for toxic chemicals. This work evaluated the performance of the geosynthetics sorption sheet. Batch sorption tests against arsenic (0.1-20 mg/L) were conducted to evaluate sorption performance, while soil tank tests using a tank (110 cm x 80 cm x 12 cm) were conducted to evaluate the effect of the preferential flow. When arsenate concentration 0.1 mg/L was contacted to the sheet, more than 80% of arsenic was sorbed at the contact time of 15 minutes. Arsenate was much sorbed than arsenite. Soil tank tests elucidated that the parti-cle size of the ground surrounding the sheet may affect the seepage water distribution more than the sheet's presence.

<p>A cap is an engineered impermeable barrier designed to cover the top of contaminated waste and prevent precipitation leaching from the waste and into the environment. In landfills, the cap also serves to control gas emissions from the waste. Materials used in a cap must not only survive aggressive installation conditions, but they must also be resilient to the deteriorating effects of long service life and environmental exposure. Bituminous geomembranes (BGMs) have been proposed by various authors as a material well suited to perform the barrier function of a cap in both exposed and unexposed conditions. In Australia, the application of BGMs for capping contaminated waste is growing rapidly. This paper describes three recent successful capping projects designed using a BGM barrier including two mining applications and one landfill application. For each project, the rational for the material choice is explained and the technical challenges of the design and installation are described. The examples presented will give designers greater confidence in the use of a BGM as a cap in new and technically challenging applications.</p>

Geosynthetic clay liners (GCLs) are widely used as a hydraulic barrier due to their low hydraulic conductivity. However, wet and dry cycles by diurnal and seasonal temperature changes and contact with electrolytes induce cracks and compression of the diffuse double layer. This hampers the efficiency of bentonite contained in the GCL. Under this situation, the polymerized ben-tonite (HYPER clay) has demonstrated better performance against cracking compared to untreated clay. One of the possible reasons for the enhanced efficiency might be the improvement in suction/water retention capacity. Thus, the suction characteristics of the HYPER and untreated clay GCLs were investigated. The paper presents the filter paper total suction test's results of GCLs, along drying and wetting paths, in the form of soil water retention curves and its comparison with the results of the water activity method. Distilled water and seawater were used as wetting solutions. The results showed a higher water retention capacity of HYPER clay GCLs compared to untreated clay. In short, the improved performance of HYPER clay GCLs under wet and dry cycles is due to enhanced suction characteristics.

<p>The impact of environmental influences, such as drying and dissolved salt, on the permeability of geosynthetic clay liners (GCLs) is of major relevance for geotechnical engineering and in technical practice. These issues currently become more and more important as long drying periods occur more frequently due to global warming, which requires a re-evaluation of many engineered structures. However, the cracking during drying and self-healing during subsequent rewetting / rehydration is extremely complex and, in many cases, not yet fully understood.</p>

<p>The current study addresses the hydration and desiccation of GCLs with bentonite in different conditions (powder and granules bentonite) and potentially permanent damage due to desiccation-induced cracking, which has already been proven in a previous study (Lieske et al., 2020). The focus is set on the identification of the soil mechanical mechanisms relevant for the cracking process, time dependence of the drying process and permanent loss of the sealing capability.</p>

<p>For this purpose, an extensive multi-scale laboratory program was carried out and analytical approaches from classical unsaturated soil mechanics were adopted for interpretation. A medium scale system test in an equipped column (TDRs and Tensiometer) was conducted in order to study the time-dependent hydration behavior<strong>,</strong> when hydrated from the subsoil. The GCLs hydrated in this test were subsequentially dried using the vapor equilibrium technique and the evolution of potential cracks was investigated by means of x-ray imaging. In parallel, desiccation was studied systematically in a broad range of suctions (0.01 – 84 MPa) using axis translation and vapor equilibrium technique. Based on small-scale tests (water retention behavior, specific surface area, cation exchange capacity, compression behavior) on the pure bentonite fillings, the state of the GCL is determined<strong>,</strong> where permanent damage is to be expected.</p>

<p>Lieske, W., et al. (2020). Suction and crack propagation in GCLs subjected to CaCl2-solutions. <em>GeotextilesAndGeomembranes</em>, <em>48</em>(6), 973-982.</p>

<p>Construction and testing sequences at large facilities can require multiple hectares of geomembrane to remain exposed for some time between installation and placement of cover materials. Winds create uplift pressure that can lift an unballasted geomembrane, creating risks ranging from moving the membrane out of place to complete destruction of an installed geomembrane. </p>

<p>The sloped ridge/valley topography used for drainage and stability in landfill cells often resembles an airfoil shape that creates uplift pressure that enhances risk of uplifting an exposed geomembrane to damage </p>

<p>Previous efforts have defined the mechanics of wind uplift for exposed geomembranes in smaller pond configurations where geomembranes can remain exposed during their service life. However testing and cover aggregate availability often prevent covering a geomembrane during construction, leaving it at risk of being uplifted, displaced, damaged, or even destroyed in sudden high winds.</p>

<p>This paper re-examines wind uplift mechanics for exposed geomembranes and proposes a potential risk/time-weighted procedure for different topographies to minimize the risk of geomembrane damage and loss due to sudden and extreme wind events that occur during construction. </p>

<p>At Kendall Bay in Sydney/Australia, the New South Wales Environment Protection Authority (NSW-EPA) issued a sediment remediation declaration for a significantly contaminated area adjacent to a former gasworks facility. Today, the disused industrial site has become a modern residential neighborhood. Therefore, not only the area on land was redeveloped, but also the sediments in the bay.</p>

<p>It was determined that remediation was required where the sediments contain total polyaromatic hydrocarbon (PAH) concentrations greater than 25 mg/kg on average and Total Recoverable Hydrocarbon (TRH) of more than 4000 mg/kg on average. To remediate the highly contaminated sediments a subaqueous cap with an active geocomposite was built. The horizontally installed active geocomposite adsorbs the organic pollutants that enter the surface water with the groundwater discharge. Percolation of the pollutants is thus prevented over several decades. In addition, the odor of the organic contaminants is bound by the use of only small quantities of activated carbon of approx. 3,400 g/m². The geocomposite was attached to the shoreline and was unrolled of a barge assisted by divers. A steel frame was used to sink the material, ensuring controlled ballasting for mechanical protection.</p>

<p>The full-scale remediation works was successfully completed between Sept 2019 and October 2020.</p>

<p>Sediment capping provides several advantages when compared to dredging or other typical solutions. It is less energy intensive and does not require dewatering and disposal of the contaminated soil. It reduces exposure and related risks, minimizing impacts to living organism in the water body. In Kendall Bay, it was demonstrated that the installation process can be done quickly and can be used in almost any situation, including various aquatic environments such as rivers, harbors, lakes, wetlands, etc. The conference paper and presentation will cover the key aspects of designing and constructing a sediment cap with active geocomposites.</p>

<p>For many decades, per- and polyfluoroalkyl substances (PFAS) were used in firefighting foams at airports and military sites. Today, large amounts of soil and consequently groundwater are contaminated with PFAS. Upon reuse of sites, there must be a definite plan on how the con-taminated excavated soil will be addressed. Typically, present waste disposal regulations re-quire the soil to be landfilled. However, transport and disposal of enormous amounts of soil make projects expensive and unecological. For storage or reuse of contaminated soil in the vi-cinity of the excavation innovative contaminant filters are developed. The target is to treat the soil passively, i.e., without labor, energy, or fresh water. Natural precipitation is used to dis-solve PFAS from the soil body and transport downwards through the structure. A permeable contaminant filter is placed at the bottom of the stockpile area. This geocomposite consists of a highly effective amendment sandwiched between two layers of geotextiles. The selective agent extracts PFAS from leachate. To develop a long-life contaminant filter, four perfor-mance factors must be considered: affinity, kinetics, capacity, and irreversibility. Affinity de-scribes the tendency of the sorbent to uptake particular pollutants. Regarding PFAS, it is es-sential that long- and short-chain PFAS are included. The kinetics of the amendment deter-mines whether it is possible to reduce contaminant concentrations below the specified permis-sible threshold while the seepage percolates through the filter at a natural flow rate. The ca-pacity must be greater than the product of the leachate concentration, the total amount of seepage over a defined period, and an appropriate safety factor. Irreversibility precludes subse-quent desorption and thus enables long-term safety of the impoundment. Additionally, there are interdependencies between these factors. The determination of the performance factors and their influence on the design concept are presented and discussed in this paper.</p>

In this study, triaxial permeability and free swell tests were performed on a geosynthetic clay liner (GCL) that had Ca bentonite and was enhanced with the biopolymer, sodium carboxymethyl cellulose (Na CMC) with a concentration of 0.25, 0.5, 1, 2, 5 and 10% by dry mass respectively. The GCL specimens were permeated with a simulated acidic leachate at a temperature of 20, 40, 60 and 80°C. Test results indicated that the temperature increase leaded to an increase in both the permeability and the swell index. As the temperature was increased from 20 to 80°C, the permeability increased by up to 1.5 orders of magnitude. Furthermore, 2% Na CMC was found to be the optimum concentration in the bentonite component of the GCL. 2% Na CMC addition caused the permeability to decrease from 9.81×10-7 to 2.24×10-8 m/s and the swell index to increase from 8.5 to 13.5 ml/2g at 80°C.

<p>Sub-slab Depressurization (SSD) aims to reduce building occupants’ exposure to toxic gases from the soil. These gases can be either generated from contaminated soils (like Volatile Organic Compounds or Landfill Gas) or naturally present in the soil (like Radon). The SSD system is composed from the bottom to the top of a separator geotextile, a drainage layer, and a vapor barrier. One or more gas pits are located according to the gas concentration in the area and to the geometry of the building. Because most of the SSD systems are constructed in high-density population areas (e.g., new construction in old industrial zones), the truck traffic and the noise resulting from the excavation works, and the transportation of granular material is a nuisance for residents. It also damages the local road network that is not designed to handle heavy vehicles traffic. This paper presents the sizing and the use of multi-linear drainage geocomposite as part of the SSD system providing separation and gas collection functions. The geocomposite is composed of non-woven geotextile layers incorporating perforated mini-pipes regularly spaced and running the roll length. It is connected to a collector pipe and to the gas pit. It collects the soil gas and reduces the head losses thanks to the high-density network of perforated mini-pipes into the product and the specific fittings used to connect the product to the main collector pipe. The sizing of the geocomposite is done using laboratory tests and software that characterize the flow capacity and the head losses of the system. Multi-linear drainage geocomposites have been found efficient for both passive and active SSD systems.</p>