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Making it easy in Louisiana

A GEOMEMBRANE and geosynthetic clay liner composite has been used as an economic alternative on a Louisiana landfill extension.

The 1200ha River Birch municipal solid waste landfill is in the lower reaches of the Mississippi River flood plain, about 30km southwest of New Orleans in Jefferson Parish, Louisiana, USA.

Groundwater level is typically at ground surface and local soils and hydraulic conditions consist of saturated organic-rich Holocene clays with a net upward groundwater gradient that can create difficult working conditions and present particular challenges for landfill cell construction and maintenance.

For example, a drainage system is needed to minimise groundwater surcharge under the lining system and to prevent the geosynthetic clay liner (GCL) prehydrating.

At River Birch a GCL with an underlying 1mm HDPE geomembrane vapour barrier was incorporated into the design of the bottom lining system of the 112,000m 2cell expansion as an approved replacement for 600mm of the required 900mm compacted clay liner.

The lining system, designed by Mader-Miers Engineering (Lafayette, LA), effectively encapsulates the GCL between two welded geomembranes, resisting hydration of the bentonite from both below and above and thus minimising potential pre-hydration from groundwater.

The leachate collection system above and groundwater under-drain system below the geomembrane-GCL-geomembrane liner included synthetic drainage geocomposites.

In evaluating economic alternatives related to the liner materials and speed of installation, Mader-Miers Engineers chose the GSE GundSeal geomembrane supported GCL as a cost-effective replacement for the separate 1mm geomembrane and GCL components of the design.

This product combines 4. 9kg/m 2sodium bentonite adhered to the specified geomembrane with a non-toxic adhesive, therefore acting as a one product composite liner system.

Given the intimate contact and effective seal formed between the bentonite coating and the overlying/underlying geomembranes, seams between the GundSeal GCL panels are simply overlapped a minimum 150mm, eliminating the need for welding had the separate 1mm geomembrane been used.

To gain regulatory approval for this concept, MaderMiers Engineering's Paul Miers approached the Louisiana Department of Environmental Quality (LADEQ) with technical consulting support from Dr David Daniel of the University of Illinois.

Effective seam performance was demonstrated based on field and laboratory testing and the 1mm HDPE GundSeal overlapped seam concept was evaluated and subsequently approved by LADEQ's engineering manager Bijan Sharafkhani.

Houston-based GSE Installation Services, with the construction quality assurance services of RCMS (Prairieville, LA), began work on the 112,000m 2three-layer lining system in May. The installation was completed within a month, almost two months ahead of schedule and under budget.

Larry Munger, GSE Installation project manager, attributed the efficient installation to a stable and well prepared subgrade, good weather during installation, an estimated 50% decrease in installation time because there was no need for welding, and using 10. 2m wide geomembrane rolls instead of the standard 6. 8m wide rolls.

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