Materials and Techniques to Maintain Slope Integrity and Prevent Erosion at Landfills

Credit: LSC

While skeptics may scoff, ardent followers believe a palm reader can examine your hand and reveal personal characteristics. But a visit to your local landfill (certainly a less mystical venture) is a revealing exercise of another kind that leaves little guesswork about your community.

“On any given day, an observation of offloaded trash says a lot about the local community and our society at large,” observes Tony Eith, head of quality assurance services for Pittsburgh-based Civil and Environmental Consultants, Inc. (CEC).

“Under this lens, we are clearly a throwaway society that no longer finds it cost-effective, expedient, or possibly even desirable to fix or repair most of our possessions. So out and off they go.”

Despite the increasing amount of cast-offs, Eith says that few if any new landfills are being created, which has sparked the growth in novel recycling services to retain more usable product for repurposing. Whatever is left over continues to pile up, but with the guidance and direction of CEC services, existing landfill acreage is made increasingly efficient, turning mountains of trash into environmentally secure, attractive, vegetated slopes. And many of these become useful to the community as recreational areas, once again serving the public whose decomposing recliner frames of yesterday lie beneath the feet of today’s hikers.

“Operating under the premise that innovation and safety are key to any work we do, CEC offers a broad range of services such as civil engineering, environmental engineering, water resources, and waste management to diverse markets; landfills are a big market sector for us,” he says.

CEC provides start-to-finish services for waste management entities “from permitting to construction, and completion of capping the filled cells or creating the optimum environment for new cells on existing properties.

“One of our biggest roles for landfills is in the area of quality assurance (QA) services. This QA expertise is specific toward the building of final caps on completed landfill slopes,” says Eith.

Although each state and county has their own regulations, most permanent landfill slopes are typically a 3:1 configuration. “If you have something steeper, you have to get a permit modification in order to build that, and we can help to facilitate this process.”

In the design process, Eith says you can have steeper slopes initially, and “as the cell becomes full, this will modify and flatten out over time as another cell is built over it and becomes an internal part of the landfill. In other words, you can have steep 1:1 slopes, but only as a temporary measure.”

He describes one process in a permit plan whereby you actually overbuild, and as the built-in air space compresses, what starts out as a steeper slope becomes compressed.

“What you are doing is starting out at 2:1, but in 1–5 years you have settlement and since you built in air spaces, you are actually getting the same tonnage into that space, but after time it becomes a slope of 3:1. As more tons are permitted in this configuration, you create stormwater diversion channels and design the appropriate underdrain network to handle liquid seeps. This includes pumping stations and drains that convey out to storage where it can get hauled to a treatment plant, although increasingly these days, you are required to have the treatment plant onsite.”

Eith says that in past designs, “It used to be that you would use soil geosynthetics to control the slopes, but now you need two other things.

“You need a surface gas collection to take the gases that migrate up to the cap, and then control the collection of the seeps under the cap. The issue here is when gas lifts up the cap, it fills up with liquid and you see the wales on slopes of liquid with gas lifting them up.”

But, he adds, preventing the generation of methane gas from the trash is also a bad idea because “then you end up with another set of significant problems. Ideally, the key is to collect the gas, manage it, and burn it, and generate steam for electricity to either run your operation or sell back to the grid.”

“This process, and mining the landfills for as much recyclable as possible to repurpose these materials, is how all landfills of the future can and should operate,” he says.

Eith adds that the company name, “Civil and Environmental Consultants,” is what they do, and “the engineers here have valuable in-the-trenches experience with landfills and really understand that you have to build it right the first time.

“You can’t build the slopes wrong, and then have a permitting issue to fix; we can get it right at the beginning, and also help correct problems if they occur. We’re enthusiastic about our diverse role in helping these operators achieve all their goals across the board.”

Credit: LSC
EGFM after 3 weeks

Covering Every Angle
More than 25 years ago, the innovators at LSC Environmental Products changed the way landfills “get covered up” each day by pioneering a product that could be spray-applied on a daily basis. Their novel technology launched Posi-Shell Environmental Coatings. Today, LSC offers a full line of spray-applied technology to meet various persistent challenges that solid waste facilities face on a daily basis.

Company president Joel Lanz says the upstate New York company gives landfill and waste management operators a simplified solution to their erosion and environmental protection challenges by providing both the unique products and the equipment to apply them to their properties.

“We sell the spray covering products but we also manufacture the most robust landfill application equipment on the market. Our Posi-Shell is a mineral-based cover that can be spray-applied for short-term solutions such as overnight cover, but with the addition of a hardener, our customers have a solution for the long term such as intermediate cover, rainwater infiltration control, slope protection, and gas collection system enhancement.”

Lanz says the company teaches operators and landfill staff how to mix and apply the products with the option to either purchase or lease the application machinery from LSC, or, “If they own a hydroseeder, all our product goes through standard equipment as well with no problem.”

Lanz describes how their products can literally save the day in erosion management for sites who have a cell that is closing, or whose steep slopes must be covered but seeding efforts fail. He explains why this can occur.

“When a new cell is opened, the excavation is well below grade and soil is then taken out and put on other slopes. However, this is soil that has been underground for a long time and hasn’t seen the light of day in years.” Being in the dark for decades renders that soil devoid of organic content and lacks the soil nutrients needed for a successful revegetation during final hydroseeding.

“What we do after soil testing is we bring in either our engineered Hydraulic Biotic Soil Amendment (HBSA) called Organix or our Fusion, which is an HBSA combined with our Earth Guard Fiber Matrix, making this a superb topsoil replacement product.

“The Organix amendment will help to promote germination, stabilize the soil, and kickstart seeds toward a very healthy vegetation that is sustainable. With Fusion, you get the erosion control feature through the EarthGuard, plus the soil amendments of Organix necessary for establishing plant growth.”

In many cases, however, Lanz says that vegetation is simply not an option and that’s where Posi-Shell coating is a perfect choice. He cites the US East Coast as one region that receives a lot of rain, and “it’s hard to keep grass on slopes when it’s constantly raining, but there’s also plenty of scenarios where you just can’t grow grass, or it’s not worth it to grow because it isn’t going to be turned into anything else for community use, or the landfill is in a remote area and aesthetics are not critical.”

He says this is where the constituents in the hard armor stucco of Posi-Shell plus hardener can deliver great performance.

In fact, Lanz asserts that Posi-Shell can be sprayed onto the ­steepest of faces.

“Even if you have vertically-baled garbage, you can spray it with the Posi-Shell and it sticks perfectly, even to a straight-sided surface like this. And it covers completely on literally any surface you can think of. Hydroseeding material just can’t do that, but Posi-Shell can,” asserts Lanz.

Keeping aquifers free of contaminants is essential, and rigorous industrial permits in California and elsewhere require that landfills monitor for heavy metals and pollutants to prevent stormwater contamination; penalties are stiff for violations. However, Lanz says operators in California use their EarthGuard product with its fiber-based high-absorbing pellets and are efficiently keeping the stormwater clean.

“Once you spray it on the soils, it offers a protective feature in its ability to decant the rainwater, cleaning it by catching the pollutants. Most of the pollutant constituents are caught in the sediment, and by keeping that stable and in place, we are keeping heavy metals, ash, and other contaminants both from migrating into the air and entering the stormwater.”

Green on Several Counts
For operators grappling with all the variables in choosing a final cover—a lack of soil, or quality soil, a challenging schedule, slope erosion, long-term mowing/maintenance, and regulatory compliance—finding one source that tackles these issues while also offering the best combination of price, efficiency, and performance is a daunting challenge. One solution, however, has positioned itself to rise to the task on all counts, and then some. ClosureTurf is the only closure solution available that provides a predictable benchmark of low-cost construction and reliable performance wherever it is installed.

The ClosureTurf system, which is a final closure system, is owned and patented by Watershed Geo and is comprised of three distinct layers, one of which is the structured geomembrane manufactured by AGRU America. This geomembrane forms an impermeable barrier which is then covered by a natural-looking engineered synthetic turf and a specialized infill that is placed within the turf blades. The membrane foundation seals the slopes, the engineered turf acts as the protective erosion layer protecting the membrane cover, and the added infill can be trafficked and offers additional weather protection. Ultimately, each layer plays a specific role in containment. Two of ClosureTurf’s system components, the geomembrane infiltration layer and engineered turf erosion layer, far exceed the requirements listed within Subtitle D and the CCR Rules.

Green, sustainable, economical, and high-performing were the attributes that Steve Melloni, landfill manager of Massachusetts Covanta Energy, sought for his 60-acre closed landfill. He says that while grass is the typical choice for slopes for the 12-acre Carver-Marion-Wareham Landfill in Carver, MA, that landfill location overlooks Buzzards Bay and is subjected to constant weather conditions such as severe wind, rain, and snow.

Anticipating that the slopes in Carver would weaken and become unstable, requiring the operator to replace soil and revegetate, Melloni and his team looked toward an alternative. They found that the ClosureTurf system offered Covanta a perfect solution to eliminate both the risks of degradation from weather and the costs and labor required to rebuild weakened, unstable slopes.

“Once we did our research and evaluated other sites, we focused on the long-term aspects of the system and found that ClosureTurf required very little maintenance, if any, after installation. That was a slam dunk for us,” says Melloni.

But the decision to choose ClosureTurf on the 12-acre site was just the starting place to navigate through regulatory requirements, weather, and Carver’s site conditions.

Covanta’s project start date was pushed back as the Massachusetts Department of Environmental Protection (DEP) needed time to evaluate the merits of what was that State’s first-ever application for ClosureTurf, before granting application approval. While DEP allowed use of the system on the 4-acre top deck, the agency initially required that traditional vegetation is used on the side slopes for the first project.

While workers were fighting 30 mph winds, Melloni explains that “Our main concern was getting the AGRU Super Gripnet ­geomembrane to lay down nice and tight to avoid wrinkles and maximize performance.” Super Gripnet is a revolutionary geomembrane that combines a geosynthetic drainage layer within the ­structured containment layer. The product delivers the containment and drainage typically achieved with the use of two separate products (e.g., geomembrane & geonet or geocomposite) while also providing unmatched slope stability performance within the ClosureTurf profile.

He says the crew did an amazing job to ensure the membrane was installed correctly. For this project, gas is generated and rises to the surface underneath the ClosureTurf which is then collected and vented. “This gas rises where a vacuum is created by the differential pressures and is then vented through a surficial gas collection foot.

“This proved to be an efficient method of gas collection while reducing the amount of condensate that needed to be managed,” says Melloni, adding that despite the last two summers “being some of the hottest on record along with torrential downpours, the ClosureTurf has helped us wonderfully with no maintenance to date.”

The success of the Carver project led to its approval (this time by a different agency) for the entire 12 acres of Covanta’s Haverhill site, located in the northeast region of the state. Melloni explains that Haverhill had “big diversion berms along the side slopes where the back of the berm transitions from 2:1 to 3:1, and I was concerned the turf’s sand infill would trap and build up, and ultimately look out of place.”

But ClosureTurf defied the odds and “Even with all of the rain, we’ve had no wash-overs and the sand has stayed in place very well.”

Meeting Unique Needs of Legacy Landfills
In 1926, residents in Santa Cruz, CA, welcomed a new landfill “just north of town where Lombardi Creek has carved a deep canyon through the coastal hills,” reported the local newspaper.

“The City can now stop operating the unpopular trash incinerator . . . and at the end of the day, the dump operators will set the garbage on fire and let brisk ocean winds carry the thick clouds of black smoke up and out of sight.”

Thankfully, how times have changed, but Craig Pearson, Superintendent of Resource Recovery for the City of Santa Cruz, explains challenges of managing this legacy 126-acre landfill operation.

“Back then when this operation was started almost a century ago, there was no master plan, and of course today it’s very different in regulations and day-to-day operations. To stay at the cutting edge of management, we have been using the guidance of engineering company Blue Ridge Services to help us extend the life of this legacy landfill. However, what we like about them is that their expertise is more than just engineering but also operational planning.”

Blue Ridge spokesperson Troy Kechely says, “When we started working with Santa Cruz, we saw that they were in a canyon and running out of space and money. So we had to figure out how to delay putting in a liner and see if the state would approve a steeper grade. Regulations on existing waste limits and new liner put a boundary that the waste can’t go outside of. That, and a height restriction means that one of the only ways to gain space is to steepen the slope.”

While the news article extolled that “The canyon will hold tons of garbage for years to come,” no one was thinking about 2017 nor could ever have predicted how “garbage collection” would become a sophisticated waste management profession.

Pearson adds that when he arrived they only had about 6 to 7 more years of fill on the 91-year-old legacy landfill. Therefore, Blue Ridge was key to the long-term planning, surveying, and excavation strategies for new cells.

“Our cells are adjacent to our landfill but in excavation we’re looking at 250,000 cubic yards of dirt that need to be removed, so we have Blue Ridge come in about once a year to take a look and give us both the engineering assistance and also the operational help since we like to keep about 3 to 4 years ahead of things.

“For example, one of our big problems is when we take out all that dirt, instead of having to pay to have it hauled away and then brought back which is not very efficient, they helped us make it work as the 18-inch intermediate cover on our outside slopes.”

And Kechely says, “We specialize in going in and optimizing operations so that they make labor and economic sense.

“You try to identify the shortest distance where we can put that dirt in the short term and put stockpiles on existing waste. I think what we are really about is helping landfills be as efficient as they can be operationally.”

He says they do that through a variety of onsite training; for example, they go into the site and observe what they are doing for a week, following up with a detailed report.

“My specialty is fill sequence and soil management,” explains Kechely. “So I might look at where they put a wet weather tipping pad because when it’s raining, the normal access road to the site could be a mess. But if you install a gravel pad, then no matter how bad it’s raining you can still dump and keep operating right in that cell. You are building the pad out of garbage with a gravel surface.”

Kechely says that a typical fill sequence is 1–2 years in length and you can have four, five, and even six sequences, “so you can see where you are building up to, with a forecast that by this or that date here’s where you need to be, and be out of there by winter.”

He says in soil management, their role is to create fill strategy asking, “How can we do this in an efficient manner to minimize the effort of crew and costs, and take advantage of airspace to achieve our goals?”

Every new landfill cell is first excavated below grade and an approved liner system is installed. “Imagine that hole as a bathtub, for example, “ he says. “You fill it up with dirt in a series of lateral lifts with each subsequent lift connecting to the other. Eventually, the total space is filled up the intended final grade slope, and all the airspace in the bathtub is used up.”

By designing the slope, he says, “You have to minimize air space by compacting each load and pushing it down, and even temporary dirt cover takes up precious airspace. You want to retain as much airspace for garbage as possible. Think of it this way: if you tossed in crumpled paper into that bathtub you’d get a big mound but a lot of airspace. We want to avoid that.” MSW_bug_web


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