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May 06, 2010 3:24 am

Crews installing liner at Cody landfill

Written by Tribune Staff

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Crews with Colorado Lining International work to install a white-colored geosynthetic clay liner, a Wyoming-manufactured product called Bentomat, in the Park County Regional Landfill outside Cody last week. It is the third of five layers used to line the cell. The pit pictured here is expected to hold all of Park County's household waste over the next eight to 10 years. Some 500,000 yards of dirt were displaced to dig the hole. Tribune photo by CJ Baker

A new phase of the Park County Regional Landfill in Cody is being constructed to prevent any contaminants from reaching groundwater — and there are plenty of redundancies in place to make sure it works.

In the newly-dug cell for municipal solid waste — your run-of-the-mill household garbage — a total of five protective layers are being laid to trap and collect any and all liquid runoff from the waste — stuff known as leachate.

Then, when the leachate is pumped from the pit to a collection pond, it will travel in pipes inside pipes — one 3-inch line inside a 6-inch line. And when it arrives at the leachate collection ponds — which have three liners — there is a backup pond in place.

“It's pretty elaborate for a landfill,” said Howard Tuss, project superintendent for MK Weeden Construction, while giving a tour of the site last week. The Lewistown, Mont.-based company is running the $2.8 million project to dig and line the new cells.

From mid-January through March, crews under Weeden supervision moved about 750,000 yards of dirt. At the height of activity, three haul trucks, an excavator and four scrapers were put to work, Tuss said.

The need to line the cell for municipal solid waste is due to new state regulations designed to protect groundwater from leachate.

“Leachate is basically what comes out of a septic tank, if you think about it, just not as far along,” said Park County Landfill Manager Tim Waddell.

At the outset, Waddell expects little leachate in the new Cody pit, with a small amount produced from rainfall. But some is likely as the garbage begins to decay, he said.

The eight-acre cell, part of the first phase of a three-phase plan, is expected to last about eight years, said Brian Edwards, project engineer with Holm, Blough and Co. It's projected to hold around 160,000 tons of waste.

Later this summer, this site outside Cody will begin housing Meeteetse's household waste, and starting in 2012, the plan is for it to hold Powell's as well. Both Powell and Meeteetse's sites are scheduled to close due to the too-high cost of lining cells at those locations.

At the base of the pit in Cody, the prepared subgrade — basically smoothed out soil — represents the first layer of liner, said Edwards.

On top of that, is a black double-sided geocomposite that serves as an under-drain for any rising groundwater that seeps up from below. The layer, around a quarter of inch thick, contains a plastic net surrounded by two fabric blankets, Edwards said.

Next up is a white-colored geosynthetic clay liner — which is essentially bentonite between woven layers of fabric — serves as a kind of back-up liner, Edwards said. The product, called Bentomat, is manufactured in Lovell by Cetco.

Above that comes the primary layer of liner — high density polyethylene. This black plastic layer looks a lot like a garbage bag, Edwards said, but it's about 10 times thicker. Also, rather than being smooth, this layer is textured to prevent it from slipping on top of the other layers, he said.

The fifth and uppermost layer is a single-sided geocomposite. This layer has a blanket-like fabric on a plastic net to drain off the leachate, Edwards said.

Finally, of top of all the layers will come two feet of dirt — about 35,000 yards worth, said Tuss.

Two drains run up and down the pit — east to west — while one at the bottom runs south to north, collecting any leachate gathered.

The pit slopes at a 2-percent grade towards the northeast corner, where a pump house will be installed to suck out the leachate.

The liquid then will be pumped to leachate collections ponds, where the liquids will evaporate, leaving behind a kind of salty residue. There are two equally-sized leachate ponds, one providing redundancy in case one side develops a leak or needs to be cleaned out, Waddell said.

The elaborate lining of the pit for municipal solid waste contrasts sharply with the smaller one to the west that has been dug for construction and demolition materials — dry garbage.

There's no requirement that the so-called C&D pits be lined.

“It's just a hole in the ground,” said Waddell.

Last week, it contained nothing other than some standing rainwater and the occasional flock of bathing sea gulls.

After the Powell landfill closes to municipal solid waste in 2012, the county hopes to continue operating a construction and demolition cell there.

Weeden's work on the new Cody cells is scheduled to wrap by July 1, though that's weather dependent.

“I think it's going to be a pretty elaborate landfill, compared to what you have now, anyway,” said Tuss.