An intermediate seal separates adjacent landfill cells

An intermediate seal is required if a new storage cell is raised or extended laterally. It is used when the landfill, to be abutted, does not have a sufficient seal to serve as base or an appropriate fill due to differing landfill classifications between the neighbouring cells. Thus, the intermediate seal can serve upper or closure layer of one cell and simultaneously, the base seal for the next.

Intermediate seals are not clearly described in most landfill regulations, so permitting authorities often call for typical base liner requirements. Historically, zoning decisions in municipal solid waste landfills have been issued in which the intermediate sealing should be constructed with the current state of the art barriers, e.g. with an approved geosynthetic clay liner (GCL) serving in place of a traditional mineral seal in combination with an approved geomembrane.

The advantages of this approach are clear: the geosynthetic barrier system is signifi cantly easier to install and takes up less landfill space than a conventional mineral seal (e.g., conventional compacted clay or large­scale ground improvement methods). Furthermore, the flexibility of geosynthetic barriers enables them to adapt to the site­specific conditions and far greater strain acceptance in settlement. Geosynthetics save considerable time and money here, reduce the need for soil and aggregate harvesting and disturbance and greatly reduce transport cost for site materials (as geosynthetics require far fewer truckloads than heavy aggregates). Also, geosynthetic layers, in being substantially thinner, open up revenue-generating airspace for a landfill.

Where the old waste cell does not provide enough stability to support the new cells construction, geogrid reinforcement may be required. This approach may also create a more efficient, space­saving design, such as outlined in national regulations.

Naue solutions: Barrier systems

Carbofol® HDPE geomembranes are used with BAM approval or other national approvals in Class 1-rated landfills (inert waste) as the sole sealing element. In Class II (municipal solid waste; non-hazardous waste) and III landfills (hazardous waste) Carbofol® is used in combination with a mineral/clay layer. This geomembrane meets the stringent chemical and physical requirements that are necessary for a safe, long-life-designed landfill. The surface of Carbofol® is smooth (for slopes up to about 1:9) or homogeneously structured/textured (for steeper slopes). This solution provides a strong barrier against rainwater infiltration and methane migration.

Bentofix® geosynthetic clay liners (GCL) are composite materials made of two layers of geotextile that encapsulate a core of highly swellable powder sodium bentonite. The three layers are needle-punched together very densely and throughly, and the fibers are anchored (“Thermal Lock”) in the bottom geotextile. Needle-punching of the geotextile in manufacturing and a proprietary Thermal Lock process firmly bond the geotextile fibres across the entire surface of the materials. This prevents bentonite erosion and increases the durability of the material. Bentofix® GCLs replace thicker, more complex-to-construct, traditional mineral seals. The geosynthetic approach provides a barrier that is more resistant to desiccation and self-seals against installation damage. The internal shear strength and frictional characteristics of Bentofix® are also sufficient for steeper slopes.