GSE GundSeal Geosynthetic Clay Liners (GCLs)

Q: What are GSE GundSeal GCLs?

A:  GSE GundSeal GCLs are a bentonite clay/polyethylene geomembrane composite liner for one step deployment as a replacement for all or part of a compacted clay liner (CCL). The product combines a low permeability 15 mil to 80 mil (0.4 mm to 2.0 mm) polyethylene geomembrane with .75 lb/sq ft (3.7 kg/sq m) loading of high grade sodium bentonite using a non-toxic non polluting adhesive. Together, they act as a low permeability self sealing liner.

Q: How is GSE GundSeal GCLs different from other GCLs?

A: By definition, a geosynthetic clay liner is defined as a factory manufactured geosynthetic hydraulic barrier consisting of clay supported by geosynthetic carriers, such as geomembranes or geotextiles. GundSeal, referred to as a geomembrane supported GCL attaches the bentonite directly to a geomembrane using a non-toxic adhesive. Other GCLs, referred to as fabric encased GCLs, encapsulate the bentonite between geotextiles.

Q: What applications are suitable for GSE GundSeal GCLs?

A:  GSE GundSeal GCLs can be used for most waste containment applications suitable for a bentonite based material as a replacement for all or part of a compacted clay liner (CCL). This includes landfill liners and caps, secondary containment, impoundments and lagoons. GSE GundSeal GCLs should not be used for exposed applications given that the bentonite requires a confining pressure to perform effectively.

Q: How are GSE GundSeal GCLs rolls packaged and handled?

A:  GSE GundSeal GCLs rolls are typically 17.5 ft (5.3 m) wide and approximately 150 ft to 200 ft (45 m to 60 m) long, dependent upon the geomembrane backing thickness, and approximately 4200 lb. (1900 kg). The material is rolled on continuous cardboard cores and protected with an outer wrap of HDPE geomembrane and finally stretch wrapped with visquine. The rolls are handled with loading straps supplied with each roll

Q: How is the material installed?

A:  GSE GundSeal GCLs is simply unrolled in place similar to installing rolls of carpet. The rolls are typically deployed with the bentonite side up, liner side down, with a separate overlying geomembrane as a replacement for all or part of a CCL. Alternately, the material can be deployed with the bentonite facing down, geomembrane side up, as a one product composite (geomembrane/clay) liner

Q: What is difference between sodium bentonite and calcium bentonite?

A:  Bentonite is a montmorillonite clay formed from altered volcanic ash originally deposited in prehistoric marine environments. Sodium bentonite was formed in a salt water marine environment and calcium bentonite formed in a fresh water environment. Bentonite is unique in that it has the ability to absorb water and expand up to 15 times its original weight for sodium bentonite and approximately 3 times its original weight for calcium bentonite. With this absorption of water and expansion, the result is a marked decrease in clay hydraulic conductivity well below that of typical clays.

Q: Is GSE GundSeal GCLs technically equivalent to a typical compacted clay liner (CCL)?

A:  Yes. GSE GundSeal GCLs has the hydraulic equivalence to a standard compacted clay liners which range in thickness from 1 ft to 5 ft (0.3 m to 1.5 m) of low permeability soil. Given the low hydraulic conductivity of GSE GundSeal GCLs (less than 4 x 10-14 m/sec) compared to a typical CCL (1 x 10-9 m/sec), flow through the GSE GundSeal GCL is more than 100,000 times less than a typical compacted clay.

Q: What is the difference in hydraulic conductivity between GSE GundSeal GCLs and fabric encased GCLs?

A:  The permeability of typical fabric encased GCLs is that of the bentonite layer, approximately 5 x 10-11 m/sec. Given that the construction of GSE GundSeal GCL includes a geomembrane carrier geosynthetic, this decreases the product permeability to less than 4 x 10-14 m/sec. Therefore, the GSE GundSeal GCL is more than 1,000 times less permeable than the fabric encased GCLs.

Q: How are GSE GundSeal GCLs seams made?

A:  The typical seams between installed panels are made by simply overlapping the material. The lengthwise seams are typically overlapped a minimum 6 inches (150 mm) and the widthwise seams are overlapped 1 ft (300 mm).

Q: What kind of geomembranes can GSE GundSeal GCLs be made with?

A:  GSE GundSeal GCL is typically manufactured with a HDPE geomembrane ranging in thickness from 15 mil (0.4 mm) up to 80 mil (2.5 mm). The geomembrane can be either smooth surfaced or textured surface depending upon project slopes and stability requirements.

Q: Can GSE GundSeal GCLs be used to replace a composite liner (geomembrane/compacted clay layer)?

A:  Yes. The bentonite clay component of GSE GundSeal GCLs can be used to replace all or part of a CCL and the geomembrane backing of GSE GundSeal GCLs can be substituted for the required geomembrane.

Q: Can GSE GundSeal GCL panels be welded together like typical geomembranes?

A:  Yes. For applications that require the geomembrane backing of GSE GundSeal GCLs to be welded, such as when it is used as a composite liner, the GundSeal geomembrane backings can be welded together at seams. The material is manufactured with protective edge tape which keeps bentonite from being attached to the length wise edges. This tape is removed after installation and just prior to welding which creates a clean edge for fusion or extrusion welding. To replace the bentonite at the seam area, a GSE GundSeal GCL seam strip is positioned under the seam which ensures continuous bentonite under the welded geomembrane seam.

Q. Can GSE GundSeal GCLs be used for sloping applications?

A:  Yes. For project slopes requiring increased friction resistance and shear strength, GundSeal is manufactured with a textured geomembrane. The textured geomembrane increases friction resistance with the bentonite coating of GSE GundSeal GCL. Additionally, when GSE GundSeal GCL l is deployed bentonite side up with a separate overlying geomembrane, this design effectively encases the bentonite coating between two geomembranes which gives the greatest guarantee of long term stability.

Q. Is GSE GundSeal GCLs compatible with all leachates and waste streams?

A:  No. The compatibility of the bentonite coating of GSE GundSeal GCL with the leachate or waste stream must be evaluated for each application. Sodium bentonite is compatible with many chemicals and compounds. However, the swelling and permeability of sodium bentonite is negatively affected in the presence of liquids containing concentrated salts (such as brines), concentrated organic solutions (such as hydrocarbons), divalent cation concentrations (such as Ca++ and Mg++), and strong acids (pH <5) or bases (pH>11).

Q. Can GSE GundSeal GCLs be used in applications with liquids that present problems for bentonite compatibility?

A:  Project specific. If the bentonite is pre-hydrated with typical water prior to exposure to the harsh liquids, the bentonite may do well and perform long term. However, this must be evaluated on a project specific basis which makes it an ideal clay for projects requiring lakes.

Q. How are GSE GundSeal GCLs affected by wet-dry cycles or freeze-thaw cycles as may be experienced by seasonal changes in temperature and groundwater elevation?

A:  Unaffected. Extensive research has demonstrated that high purity sodium bentonite, as is used in the GSE GundSeal GCL, combined with the protective geomembrane backing, that GSE GundSeal GCL is unaffected by wet-dry and freeze thaw cycles.

Q. Is GSE GundSeal GCLs available with different types of bentonite or bentonite loading?

A:  Yes. GSE GundSeal GCL is available with a contaminant resistant bentonite for applications which require a bentonite with a compatibility with harsher liquids or leachates. The bentonite content of GSE GundSeal GCLs can also be increased up to a loading of about 1.5 lb/sq ft (7.4 kg/sq m).