Bentofix ‘X’ Coated GCL Caps Off Millar Road Landfill

The Project

The Millar Road Landfill and Recycling Facility is owned and operated by the City of Rockingham in South West WA. As part of the annual cyclic process of opening and closing the city’s municipal sanitary landfill cells, fields 9, 10 and 11 required capping to enclose and secure those respective cells using a Geosynthetic Clay Liner (GCL).

During the tender stage, the City of Rockingham assessed two different styles of GCL from two different suppliers. One included a standard composite needle punched GCL which incorporates bentonite powder sandwiched between two layers of geotextile.

The second option represents the new generation of multicomponent GCLs whereby an additional polyolefin coating is bonded to one side of the GCL. This style of BENTOFIX® is known as the ‘X’ range.

Our Solution

The BENTOFIX® X2 NSP4000 was selected for this project due to a variety of inherent performance advantages. The BENTOFIX® ‘X’ is purpose designed for applications where the liner is required to be placed relatively close to the ground surface such as landfill caps and liquid containment structures.

Near the ground surface, the low confining stresses over the GCL often necessitate an extra level of security over and above the bentonite barrier alone.

Special requirements in these environments include the following:

• Increased resistance to desiccation: once the bentonite is hydrated, the polyolefin coating provides some insurance against rapid bentonite dehydration close to the surface during dry periods (a possible occurrence on landfill caps). Decreased permeability: the ‘X2’ type BENTOFIX® exhibits an ultimate ‘k value’ (hydraulic conductivity) which is significantly lower than uncoated GCLs (10-14 vs 10-11m/s).

• Barrier against ion exchange: where the GCL might come into contact with leachable cations, the clay structure of the GCL may be adversely affected. The applied polymer ‘X’ coating, when faced against the source of the cation contaminants, can help guard against cation exchange.

• Instant gas barrier: bentonite hydration can be a slow process and is dependent on local climates and soil characteristics. Typically, you would expect several days to achieve optimum hydration in wet climates and several months in dry conditions. Landfill capping applications may require an immediate barrier to gas permeation. The ‘X’ coating satisfies this function while the porous bentonite core is hydrating.

• Resistance to root penetration: the ‘X2’ material has been tested and proven to resist root penetration from nearby trees given that the film tends to deflect the immature roots instead of providing pathways for ingress (pores).

The Results

The City of Rockingham has a constant need to minimise risk at a manageable cost in landfill environments. This simple policy drove the final decision to install in excess of 70,000m2 of BENTOFIX® X2 NSP 4000.

All BENTOFIX® GCLs are manufactured to the strictest quality control requirements with roll traceability an integral part of the MQC process. Installation was successfully executed by the contractor, on time and on budget.