Both the US Environmental Protection Agency (EPA) Federal Regulations as well as the European Council Directive on the Landfill of Waste describe prescriptive cross sections for hazardous and non-hazardous waste landfill base lining systems.
Sealing
The base lining is designed to prevent the escape of contaminants from landfill waste into underlying soils. A properly constructed liner system should also allow for the controlled collection and removal of landfill leachate for subsequent treatment.
In regions where local soils are not suitable for the construction of hydraulic barriers, Bentofix® geosynthetic clay liners (GCLs) can be used to protect the hydrogeological resources by providing an effective barrier against potential risks to the environment. Typical compacted clay liners (CCL) are difficult as well as expensive to build. In many cases, they are subjected to installation conditions that can cause desiccation cracking and create preferential flow paths. Bentofix® GCLs can replace or augment the typical CCL in most designs to minimise the effects of desiccation. Once covered, Bentofix® GCLs quickly hydrate with existing soil moisture to form a low permeable barrier. The quick and easy installation methods used for Bentofix® yield substantial cost and time savings when compared to expensive construction methods typical for CCLs.
When used in combination with Carbofol® HDPE geomembranes, Bentofix® GCLs can achieve the superior hydraulic performance obtained with exceptional intimate contact, and can minimise lateral flow of leachate - in the unlikely event of a puncture. A composite liner system incorporating Carbofol® and Bentofix® as the independent sealing elements is extremely effective when containing both polar as well as non-polar contaminants.
As Bentofix® geosynthetic clay liners are needle-punched over their entire surface area, they are capable of transmitting shear forces on steep slopes as well as within base lining systems. Bentofix® products produced with mechanically bonded nonwovens on both outer surfaces can be used to achieve higher interface friction angles and shear strengths.
Smooth surfaced 2.0 mm thick HDPE Carbofol® geomembranes are well suited for the lining of landfill base seals with slopes up to 9h:1v, and are available in various structured or textured versions for more demanding conditions. Unique surface structures and textures are used to address different slope inclinations and loads. During the manufacturing process, surface textures and structures are added directly to the layer of pliable HDPE Carbofol® geomembrane by a molding or spraying process. This step creates a homogeneous structured geomembrane made from a single material or resin, maximising the product shear strength characteristics.
Protection
High quality protection Secutex® needle-punched polypropylene (PP) nonwovens limit geomembrane damage and deformation during installation as well as during subsequent operational use.
Assuming a well compacted subgrade, a CCL or a Bentofix® GCL, a 2 mm thick HDPE geomembrane and a 30 - 50 cm thick leachate collection layer with 16 mm to 32 mm sized gravel, the following guide can be used to determine the mass per unit area for the Secutex® protection layer:
Height of waste
Mass per unit area of needle-punched Secutex ® nonwovens
15 m
800 g/m
25 m
1,200 g/m
35 m
2,000 g/m
50 m
3,000 g/m
Prior to the utilisation of a nonwoven for puncture protection, puncture tests similar to the cylinder test (DIN EN 13719) are recommended with site-specific materials and the test protocol as specified by the design engineer.
In instances where high chemical concentrations in the leachate are possible, NAUE can supply needle-punched Depotex® nonwovens with chemical resistant HDPE fibres.
Reinforcement
Long-term slope stability can be obtained with Secugrid® geogrids, either alone or in conjunction with other geosynthetic materials. When used with a geomembrane, Secugrid® reinforcement products can support the down slope forces while protecting the Carbofol® geomembrane from potentially harmful stresses.
The low initial elongation and the interlocking nature of the Secugrid® with mineral drainage layers ensures immediate stress transfer and avoids installation deformation. The relatively thick, flat, monolithic elements of the Secugrid® provide structural security with all normal installation loads.
Conclusion:
The repair or remediation of a base liner is technically difficult and expensive. It is for this reason that high quality products, which can ensure long-term performance, need to be selected during the design phase of a project.
With complete geosynthetic solutions from NAUE, your next lining system will have the latest in geosynthetic innovations and the quality you need to ensure long-term performance.
Landfills
