More goes into the construction of a landfill than meets the eye, and at the Northern Tier Solid Waste Authority, a small municipal waste disposal facility in Bradford County, PA. A project to expand the landfill there is employing state-of-the-art technology and materials to meet the stringent demands of today’s environment-conscious waste disposal industry.
As the Northern Tier Solid Waste Authority’s (Authority) original 27-acre landfill nears full-capacity, an additional 19-acre plot has been purchased and is being prepared to accommodate the steady flow of waste that arrives at the facility daily, said Dave Terrill, executive director of the Authority.
Terrill and his crew at the landfill spent most of the spring and summer excavating the first, four-acre plot of the new landfill in preparation for the next phase of work, which includes the laying down of a liner and 18 in. of aggregate material where drainage pipes will be placed. Using a Caterpillar D7-H dozer, a John Deere 850L dozer and a Caterpillar D3 dozer, Terrill kept the excavation work in-house by employing members of his landfill crew to grade the plot.
The square-shaped plot was graded at a slope toward one of its corners to allow drainage of leachate, the residual fluids that drain from garbage, to a pump, which transfers the leachate to an on-site treatment plant.
“Most landfill operations would contract-out that kind of work,” said Terrill, “but it worked well for us to have our employees do the work. We are a very hands-on operation here and this allowed the employees here to feel they had a hand in the construction of the new landfill.”
After the excavating was complete, the crew laid down a 6-in. layer of sub-base made up of a clay-like material screened down. The plot was then ready for the next phase of the work, for which Terrill contracted GSE Liners Inc., of Houston, TX.
“A landfill today is more than just a place to dump your garbage,” said Al Detillo, of GSE Liners Inc., “it is a science.”
Detillo applied that science by laying down the geo-textile liner that blankets the floor of the landfill. The liner, made of non-woven polypropylene, is a vital component in modern landfill construction as it prevents the garbage and its leachate from being absorbed into the earth.
The process of laying down the geo-textile liner consists of covering the sub-base with one layer of liner, then two layers of net-like material, another layer of geo-textile liner and finally a cushioning liner that protects the material from the 18 in. of aggregate that will be placed on top of it, said Detillo.
“This is the most advanced liner design available,” said Terrill. “Not only is it used underneath the garbage, but when the landfill reaches full-capacity we use it to seal it over. It is designed for strength and to meet the Environmental Protection Agency’s standards.”
The liner arrived on-site in rolls that Detillo’s crew then stretched out over the sub-base and then “welded” each layer together using a fusion welder for plastic-like material.
Before the netting is applied over the first layer of liner a leak test is performed on every seam to test to ensure its impermeability to liquid. This was done with a vacuum box, which draws air through air channels along the seams designed to test for leakage.
With the two layers of liner and two layers of netting installed the cushioning layer was applied next. The sections of the cushion are sewn together using hand-held stitching machines using a 401 chain stitch, said Detillo.
“It is a very simple installation process,” said Detillo, “but not anyone can do it – our technicians are trained and it requires skill to sew the cushion together right.”
With the liner installed, Terrill’s crew will place 18 in. of aggregate, screened on site using an Extec Screener, on top of the liner where a network of drainage pipes will be laid.
“We used a sand material at this point in our original landfill.” said Terrill, “but we decided to use an aggregate material this time around because we felt it would have better drainage properties than sand. We have screened all the material down to 3/4 in. pieces or less.”
When the material is laid down on the liner, which Terrill said his crew will begin working on this month, the piping will be interspersed within it and will lead to a pump house at the low end of the landfill. The piping is dotted with small holes, which will allow leachate to be drawn into it. The final preparation of the landfill will be the blanketing of the aggregate material with 3 ft. of shredded tires on which the garbage will be placed. Terrill said the shredded tires act as a further buffer between the garbage and the liner and will be porous enough to coax drainage.
“The shredding was done right here using our own shredder and using tires that have been dumped here,” said Terrill. “So this is a chance to recycle these tires for a good use.”
Kathy Murphy, an environmental engineer on staff at the Authority, said the installation of each component of the $700,000 project is inspected by a quality control engineer following guidelines imposed by state and federal environmental regulations. From the characteristics of the earth used in the sub-base to the welds in the liner and the size of aggregate material used around the piping network, each aspect of the landfill construction is watched closely, she said.
Quality Assurance Engineer Tom Kieffer, the on-site inspector, said his job is to “make sure it is all done right.”
“People are not aware of what goes into the construction of a landfill,” he said. “All the materials used, the techniques employed and every detail of the landfill are watched for quality assurance. This is about protecting the environment and the method they are using here is the safest anyone has come up with yet.”
This story also appears on Aggregate Equipment Guide.
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