Transforming Landfills Into Resources

A landfill can be like a baby: It is helpless to care for itself; while it’s growing, it eats all day; at night when resting, it must be protected from the elements; and it belches constantly. If you’re lucky, it won’t stir up much fuss. If you’re not lucky, the neighbors can become quite annoyed.

Landfills can grow to tremendous size; Puente Hills landfill (now retired) outside Los Angeles—once the largest landfill in the US—grew in 60 years to a 500-foot-tall mountain of trash on a 1,300-acre site. Sadly, for every landfill, the day also comes when it too must be retired and put to rest permanently. While it may sound a little strange, in its afterlife, a landfill can become an even more complex creature than during its heyday. It continues to belch; it continues to require protection from the elements such as rain, wind, and foraging creatures; and the environment around it must be shielded from effluents leaching out from below. Ultimately, a retired landfill will require ongoing care for up to 100 years or more.

A former landfill can be a nuisance or a treasure. It can reflect a troubled past or help light the way to a brilliant future. The difference between a pleasant productive life and afterlife, and a problem child with an unpleasant legacy can lie on the fabric of the thinnest of films.

Garbage and Resources at River Birch
The goal of landfill operations is to make sure that what goes into a landfill stays in the landfill. However, innovative landfill operators have begun to realize there are two kinds of things in a landfill: garbage and resources. The objective is to control the former and to access, manage, and in some cases, profitably harvest the latter. The challenge is to do so at a reasonable cost with minimal disturbance to neighbors and the surrounding environment. Vic Culpepper sought to achieve such results in harvesting the landfill-generated gas at the River Birch landfill just outside of New Orleans, LA.

Federal regulations for landfills under Subtitle D require that waste in a landfill be covered at the end of each day. Protecting the landfill every evening from precipitation, controlling gases produced by decaying organics, and discouraging foraging by fauna including troublesome birds and vermin are major responsibilities for landfill operators. According to Culpepper, technical director of River Birch landfill, one of the most labor-intensive and costly tasks in landfill management is making sure the garbage gets tucked in safely every evening.

Initially, says Culpepper, daily cover operations at River Birch landfill followed EPA’s guideline of applying 6 inches of soil over the entire working surface of the active face at the close of each operational day.

But there were problems with this approach for River Birch, he says. “It was extremely difficult for us, especially with the type of clay in our area. A lot of times you had to apply more than six inches—more like a foot—to get adequate cover.” Culpepper also tried using a spray-applied cover material, which, he notes, “worked moderately well, but was expensive and difficult to put down to ensure adequate cover.”

River Birch’s operators continued looking at different options to fulfill the mandated daily cover requirement. In the search, says Culpepper, the important criteria for selecting a daily cover system for included cost efficiency and simply “how well it covers.” In addition, he says, it was important to find a technology that would conserve airspace to maximize the volume of permitted space available for trash. He wanted a thin material to avoid sacrificing 6 inches to a foot of airspace just to deploy cover material every evening.

The operators of River Birch landfill had built up a revenue stream harvesting methane gas, generated by decaying garbage, and selling it on the fuel market. Therefore, says Culpepper, the landfill would require a daily cover method that would facilitate the “trash-to-trash contact” needed to support the biological breakdown processes responsible for generating the raw landfill gas resource.

Culpepper opted for EPI Environmental Products’ Enviro Cover System. The system consists of the Enviro Cover—a nonreusable polyethylene film developed to meet requirements for alternative daily covers—along with the Enviro Cover Deployer, a versatile and efficient applicator for placement of the cover. A third element is the method of application, which provides ballast and seal at panel overlaps to create a continuous impermeable barrier between the waste and the surrounding environment.

Culpepper explains that the Enviro Cover System is simple to deploy using the Enviro Cover Deployer, which spools the cellophane-like cover over the treatment area in continuous sheets. As it proceeds over the treatment area, the vehicular-mounted system lays down an anchoring ballast of sand or soil along the overlapped edges of each sheet, significantly reducing the time it takes to complete daily coverage of the landfill’s working surface compared to traditional daily covers.

“Where it used to take three-and-a-half hours to cover the area with clay and about three hours to cover with the spray-applied cover, it takes about an hour with the Enviro Cover System—with only one person and one machine,” he notes.

In contrast, he says, using a clay cover, “you’d have to have dump trucks and bulldozers and all the people to drive them.”

Culpepper describes the streamlined workflow: toward the end of the workday, as crews begin laying down the Enviro Cover, they leave a small portion of the landfill open for late-arriving loads. “Then, once you’re closed, go ahead and close that area out as well.”

Considering the random constituents of trash, Culpepper says that sharp-edged objects might occasionally punch through the thin-ply Enviro Cover, but that, nonetheless, no surface preparation is needed before applying the cover.

Occasional punctures, he says, are “not an issue. Overall, the amount of complete coverage you get and the shedding of rain from your garbage minimizing your leachate intrusion is still greater, we think, than most other technologies.”

Along with ease of application, Culpepper says the advantages to using an alternative daily cover, such as Enviro Cover, includes its more predictable material cost control and reduced labor costs compared to soil covers. It also enables quick and dirty trash-to-trash contact when the next day’s load comes in.

“All we have to do is drive on top of it the next day and shred it under the truck tires, so we get garbage-to-garbage contact” with trash arriving on subsequent days, says Culpepper.

Culpepper says the smooth learning curve for the crews operating the Enviro Cover System makes the solution very accessible. “You can get a good operator performing this with a week or less of training.”

Deploying innovative operational controls, including “a good gas collection system to pull the gas out of the landfill, good intermediate cover” for dormant sections of the landfill, and the Enviro Cover as an alternative daily cover for the active faces, has helped control odors and maintain River Birch’s standing as a good neighbor, says Culpepper. “I don’t know why more landfills don’t use it,” he adds.

Shining the Light on a Retired Landfill
It is not often that people talk about the convenience of living close to a landfill, but one of the prime functions of any municipality is sanitation, and having some sort of waste disposal facility within convenient reach of homes, businesses, and institutions is part of what makes life in urban districts viable. The Hartford, CT, landfill wasn’t just convenient to neighboring homes and businesses—it was actually within the city of Hartford.

The landfill began accepting trash as far back as 1940. Initially, trash delivered to the site was burned in the open. Incinerators were later constructed, but residents complained about the soot and ash, prompting an end to incineration and implementation of an urban landfill that, by the turn of the century, had approached its full capacity. With expansion of the site under consideration, the neighboring communities voiced their objections, and in 2008, the landfill received its final delivery. Changing times have brought new technologies since then, and today, the former Hartford landfill has worked its way into a secure future delivering clean energy, with a major helping hand from erosion control technology.

Of the 96-acre Hartford landfill site, 66 acres were capped in the traditional manner. According to Chris Eichelberger, vice president of technical marketing for Agru America, this traditional Subtitle D landfill capping method uses a 40-mil geomembrane with a geosynthetic drainage layer.

“Typically, two to three feet of soil is placed above that, with vegetation such as grass planted on top of that,” says Eichelberger.

It sounds simple, but he notes, “If you are the owner of a landfill and don’t have the volume of soil onsite to build up the erosion protective layer, there can be a big logistic and financial challenge of finding that soil and trucking it in.”

In addition, he says, owners face the challenge of not only constructing the slopes from the imported soil, but also planting them with sufficient vegetation to prevent erosion and financially addressing the challenge of ongoing maintenance to those plantings—a responsibility that could trail off into the next century. Such maintenance issues can include providing irrigation, applying fertilizers, and mowing, which can itself be a daunting task on landfill slopes often engineered to a 3:1 ratio.

Agru America’s Closure Turf can provide an alternative to these obligations. Eichelberger says the technology was developed by a group of civil engineers with a background in solid waste management to address some of the tough issues in landfill closure and post-closure activities.

The technology utilizes Agru America’s geomembrane product with an engineered synthetic turf from Watershed Geosynthetics on top to form the patented system called Closure Turf. The company now has 30 million square feet of Closure Turf installed at more than 25 project sites. Eichelberger says landfill facilities that employ Closure Turf can expect a 90% reduction in post-closure care and maintenance needs.

Making Lemonade From Lemon Peels
In 2008, after close to 70 years of receiving trash from 70 municipalities in Connecticut, Hartford landfill shut its gates to dumping operations for good. David Bodendorf—senior environmental engineer for the Materials Innovation and Recycling Authority (MIRA), the agency that took responsibility for the closed landfill—says installation of the final landfill cap over the entire 96 acres of the working face and slopes was planned and organized around a phased timetable.

“It was a matter of logistics,” he says. “The north and west faces were closer to neighbors, so we wanted to cap them first.”

The south side of the site, fronting the Connecticut River and inaccessible to the public, had a lesser impact on neighboring communities and was scheduled for capping in the later stages of closure. By 2013, with the north and west faces capped and three-quarters of the working surface permanently closed in the traditional manner, what remained was a 35-acre lemon on the south side of the landfill. Bodendorf says MIRA got a brilliant idea: What could be better for a lemon than sunshine? As an alternative to the customary fate of retired landfills as fallow land, the final 35-acre capping and closure installation would embrace the power of the sun and come into a new life as a solar photovoltaic (PV) energy-generation facility.

Noting advances in solar technology and the availability of government incentives for clean energy initiatives, says Bodendorf, “We saw the possibility of doing something other than the traditional capping and closure.”

In 2013, MIRA began accepting bids for an alternative landfill capping technology appropriate for housing a 6-acre, 1-MW solar generation facility. “We wanted to look at more than one technology so prices would come in as competitively as possible,” says Bodendorf.

MIRA “was aware of at least two capping technologies” that could render the site suitable for use as a solar power plant. As they had anticipated, two firms responded, offering differing solutions.

One bidder envisioned a thermoplastic olefin (TPO) exposed membrane deployed over the final 35-acre parcel of the landfill. The proposal specified anchor trenches to hold the membrane in place on the face and slopes. The design envisioned chemically welding a thin-film PV solar material on top of this capping installation as the solar collector.

The competing proposal hinged on the application of the Closure Turf system, a permeable synthetic turf carpet placed over Agru America’s Super Gripnet geomembrane to serve as a platform for an array of ballasted trestle-mounted solar panels.

The Closure Turf synthetic turf protects the underlying geomembrane from ultraviolet (UV) and puncture degradation and allows stormwater to infiltrate through the woven geotextile to either a swale, or drainage downchute, or sub-drain piping. A half-inch nominal thickness of sand spread over and between the tufts of synthetic turf strands adds holding power through the force of gravity while protecting the synthetic turf carpet from UV degradation and puncture damage from above.

Comparing the two technologies, says Bodendorf, he imagined a worst-case scenario in which a final cover material might be degraded. “What if the turf carpet was degraded by the sun and starts blowing away in 10 years—what do we do?”

He could see some potential shortcomings in using a TPO exposed membrane as a final landfill cap. “It’s a smooth-faced product.”

Lacking the textured facing of Agru America’s Super Gripnet to provide the friction to hold a layer of soil on its top, the TPO would not have frictional characteristics to allow the application of a remedial soil cover on a side slope to fix things, feared Bodendorf. “If you did see it start to degrade, and you said, ‘Oh, my god, we’ve got to cover this up with something,’ you couldn’t just throw soil on top of it and walk away,” he says.

Envisioning this same worst-case outcome, Bodendorf believed the Closure Turf solution would fare much better if the top layer were somehow to degrade. “We’d be left with the Super Gripnet polyethylene that is chemically the same as what we’ve already got on the site. In the worst case, we’ll just put a bunch of dirt over the site, then we’d have a cap that’s a normal membrane cap.”

Sweeping Erosion Away
To achieve installation, after the initial grading to meet subgrade, sand was placed as a cushion layer also serving as a gas vent layer on top of the subgrade. Installers pulled the Super Gripnet out at a rate of about an acre and a half per day “when the weather cooperated,” says Bodendorf. Immediately over the Super Gripnet, they deployed the synthetic turf product. As soon as practical after that, they placed the sand infill by broadcast spreading, booming, and high-speed conveyor to spread the sand up the slopes.

“It’s amazing how easily the Closure Turf can be slid over the membrane, but once it is in place with the sand infill down, it doesn’t slide any further down the hill. When you’re walking on it, it doesn’t feel like it’s sliding down the hill; you can even drive on it,” says Bodendorf.

At the edges, the geomembrane was welded to the adjacent previously installed membrane, to interface with the existing linear low-density polyethylene product called MicroSpike that had been installed on other sections of the landfill. Clean stone filling in the grade between the depth of soil on the old cap and the synthetic turf anchors ties in the new Closure Turf installation to the existing sections of capping.

Although Bodendorf says it took “some effort with broadcast spreaders and high-speed conveyors to cast the sand onto the steeper slopes” and some manpower using brooms to get the sand between the tufts of synthetic grass, the installation went off without a hitch, sidestepping the problems that can arise using traditional capping techniques. “We used traditional caps on 66 acres, and ultimately, it worked out fine, but in each of the preceding phases, we did have times when it rained pretty heavily before the grass started growing, and the contractor lost a lot of soil. When they lose soil, they are losing time and money; the relationship gets strained because they are not as profitable as they would have been if the weather had cooperated. With Closure Turf you take that risk away, or at least minimize it.”

With soil requirements for a traditional cap ranging 18–24 inches, “you might require 100,000 cubic yards of soil cover,” says Bodendorf. “But the half-inch-thick layer of sand over the 35 acres translates into a couple of thousand cubic yards of material, so it’s only 2% of the material that would have to be employed with a traditional cap.”

He adds, “With Closure Turf, once you’ve got your membrane layer installed, the risk of erosion is really eliminated compared to the traditional cap.”

Although he concedes he didn’t run a cost comparison between the Closure Turf system and a traditional cap, Bodendorf notes, “With a traditional cap, so much of the cost of the project is wrapped up in the procurement and placement of the soil. In some cases, there may not be a nearby low-cost source of soil.”

With the alternative membrane cap there is less budgetary uncertainty. “You know about how much the membrane will cost; you know what it will take to install it—how much manpower and about how long it will take,” he says. “It’s probably pretty easy to price for a contractor, but soil can be a lot harder to price.”

With the capping installation complete, MIRA installed the solar panels, and the former Hartford landfill now sells enough power to the grid to electrify 1,000 homes. MIRA is also in the process of establishing a connection to provide power for a Hartford Public Works facility. Bodendorf says the solar array sitting on top of the cap “certainly doesn’t hurt” the cap’s functionality, adding that, because the turf surrounding the panels is synthetic.

“We don’t have to worry about overgrown vegetation ever shading the panels.”

He says the Closure Turf blends aesthetically with the rest of the restored site, consisting of meadows with “diverse populations of birds, deer, and nesting bald eagles nearby.”

In addition to winning a Solid Waste Association of North America (SWANA) Excellence award, the project has gotten great response from the community, and MIRA has led more than a dozen delegations onsite tours.

Bodendorf notes, “People have known the area in the past as a source of odors and nuisance birds, but now they are impressed when they ride to the top of the slope and see the skyline and the turf and the solar installation. We’re convinced we made the right decision.”