Eco-lining for landfill site

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Mt Cooee landfill has received a new geosynthetic liner in a project that aims to make the site more environmentally friendly.

Project overseer Dave Hannan said it was one of the final stages in an effort to prevent landfill leachate from reaching the Clutha River.

Irrigation ditches were dug at the base of the landfill face before the fibre was laid, and last week’s work was the final step.

“This is the last part of a major project,” Mr Hannan, a former Wasteco environmental manager, said.

“It will stop leachate getting into the Clutha River.

“The landfill is essentially finished now.”

The new material is a geosynthetic clay liner, called elcoseal, and produced by Geofabrics in Australia.

It is a needle-punched reinforced composite, combining two durable geotextile outer layers with a core of sodium bentonite clay that expands to create a hydraulic barrier.

Mr Hannan said the material far surpassed what they would routinely use at landfills.

“It’s only about [2.5cm] thick . . . but it’s equivalent to a one metre layer of clay.”

He said some of the further benefits were that, unlike traditional clay layers, it could not be eroded by wind, and it would not crack in the sun.

“It’s also a third of the cost,” he said.

Geofabrics sales engineer Mike van den Arend agreed.

“Once you factor in the cost of trucking in all of the clay, it can become very expensive, very quickly.”

Mr van den Arend said the geosynthetic fibre not only eased financial costs but also environmental costs from truck fumes.

Use of the product remains rare in Otago and Southland, where high density polyethylene (HDPE) liners are more commonly used for landfills and irrigation ponds.

But Mr Hannan said there were difficulties with that kind of liner.

“You often have to get a specialist to weld an HDPE liner .. It has to be double seam welded.”

The elcoseal came in large rolls that were held aloft by a digger, then dragged down the hill in sheets and flattened down on to the landfill face, and pasted together with more bentonite clay.

There was one drawback with the elcoseal rolls though, he said.

Anyone laying down the sheets needed to wear a face mask for protection against bentonite, which was not very nice if it expanded in your lungs.

The last touch would be a layer of topsoil, to be planted out with toitoi and flaxes.