Small Landfill Finds Big Solution

Mark Cadwallader and Don Hildebrandt

Like other communities, Canada's Prince Edward Island wanted to limit its dependence on landfills. Taking its first step toward this in 1991, the county began a pilot processing program that sorted residential and commercial waste into three categories: compostables, recyclables and the remaining waste.

Three years later, the county broadened the program to include the entire community, an event that triggered the construction of the East Prince Waste Management Facility that would process waste and sell compost.

Today, the "remaining waste" is landfilled - only after the recyclables and compost are removed. This aggressive waste separation program has created the intended results: an East Prince Waste Management Facility Landfill that only disposes of approximately 40 tons per day.

Although this site is a testament to the success of the East Prince Waste Management Program (the first of its kind in Canada), its size has led to a small operational hitch.

While not a problem at larger sites, the traditional ratio of six inches daily cover soil to waste is high at smaller sites because a landfill's capacity includes vertical airspace. Six inches of height at a small site is a much larger proportion of the available volume (airspace) than that same six inches of height would be over a larger landfill.

Simply put, the East Prince Landfill was filling up quickly using six inches of daily cover soil. "We were filling up a million dollar landfill cell with basically borrow material," says Heather Chowan, site manager.

The soil itself was posing yet another significant problem: There were leachate side-slope break-outs caused by the low permeability of the silty/clay-like daily cover borrow soil intercepting the leachate's downward flow.

The situation worsened with freezing conditions and traffic, which was compacting the already low-permeability frozen cover soil and improving the hydraulic barrier, but making the situation worse.

Systems to collect surface runoff and leachate originally were designed separately. However, leachate wasn't seeping down to proper collection layers. It was getting into the surface runoff system by breaking out at the sides along the hydraulic barrier planes of the daily cover.

Consequently, the county decided to merge the side-slope seeps with the leachate collection system's sand layers by digging a long slurry trench down to the collection system. This intercepted and directed the laterally seeping leachate flow to the landfill.

Although this problem had been solved, the county believed the problem could have been avoided with the proper daily cover material. Chowan and engineer Jerry Stewart considered a variety of alternative daily covers (ADCs).

"We not only wanted to save airspace, but we also wanted something that wouldn't cause these problems with leachate side-slope break-outs," Chowan says.

East Prince Landfill eventually chose an ADC system in 1996 from EPI Environmental Products Inc., Conroe, Texas, including Enviro Cover, a degradable/disposable polyethylene that doesn't form a low-permeability plane for the lateral movement of leachate, and the Landfill Rover deployment unit.

But cold weather even created an obstacle for the new system. "Our ballast soil for the Rover hopper would freeze and get stuck, hard like a rock," Chowan says.

The solution? Replacing the soil with crushed recycled glass. The county also built a platform to allow the landfill compactor to pick up the machine.

Thus, all the small landfill's problems were overcome. The new ADC conserves airspace, extends the landfill's life and stops lateral leachate seeps from breaking out.