For a landfill closure project in Massachusetts, Covanta Energy put an end to constant slope repair with a stable, cost-effective, geosynthetic closure technology.
By Agru America and Watershed Geo – With more than 60 acres of closed landfill space to manage, Steve Melloni, Covanta Energy’s Regional Landfill Manager, has a lot on his plate. Most of his closed waste-to-energy ash landfills are traditional Subtitle D vegetation caps. His site supervisors oversee the monthly maintenance of mowing and the occasional reseeding.
“Most of our maintenance is typically with grass,” said Melloni. “However, when inclement weather strikes much like it has in the last two years, we are on standby to manage any repercussions. That could include costly repairs, such as rebuilding slopes, replacing soil, and re-establishing vegetation.”
In 2014, Melloni and his team began evaluating an alternative closure system called ClosureTurf® for the 12-acre Carver-Marion-Wareham Landfill in Carver, Massachusetts. This particular site overlooks Buzzards Bay, making it heavily exposed to wind, rain, and snow.
The site managers anticipated problems with the slopes, due to the extreme conditions. Slopes would weaken, become unstable, and require rebuilding. It was a process that might need to occur regularly.
The ClosureTurf® system offered a way to eliminate that risk.
“Once we did our research and evaluated other sites, we focused on the long-term aspects of the system,” said Melloni, “and found that ClosureTurf® required very little maintenance, if any, after installation. That was a slam dunk for us.”
The landfill closure system met and exceeded the EPA Subtitle D requirements. And, the three-component closure system did not require any soil coverage.
“We really liked that it provided around 12,000 cubic yards of extra capacity for ash,” said Melloni. “Because the two feet of soil is not required, we were able to use that space to our advantage.”
ALTERNATIVE LANDFILL CLOSURE – GETTING APPROVAL
With the internal decision solidified, the next step proved to be the most challenging. Covanta submitted their application to the regional Massachusetts Department of Environmental Protection (DEP) office. Because this would be the first use of ClosureTurf® in the state, the agency wanted some time to do its homework and fully evaluate each component of the system. With time constraints to complete the project looming, the DEP agreed to allow the system to be used on the 4-acre top deck but required the use of a traditional vegetation system on the side slopes.
The site conditions proved to be somewhat challenging for installation.
“With 30 mph winds, the main concern was getting the Agru Super GripNet® geomembrane to lay down nice and tight in order to avoid wrinkles,” said Melloni. “The crew did an amazing job…. Another thing we experienced on site was when we began installing the engineered synthetic turf, gas began to build-up and we started to see pockets form. We eliminated this by installing a specialized [system-specific] gas vent on every acre. Once the relief values were in place, the turf laid down perfectly. We were able to incorporate this seamlessly with our traditional gas collection system.”
Underneath the geosynthetic cap, gas is generated and rises to the surface where a vacuum created by the differential pressures is vented through the 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.
To date, the site has performed exceptionally well.
“The last two summers have been some of our hottest and we have experienced some torrential down pours,” said Melloni. “The ClosureTurf® system has held up wonderfully with no maintenance to date.”
The Covanta team was so impressed with the CMW project that they specified the system on a separate site in Haverhill, Massachusetts.
AN ADDITIONAL PROJECT
The Haverhill site was a bit different, in that it was overseen by a different agency. A 12-acre installation of ClosureTurf® was approved, which covered the entire area Covanta sought to address.
“Again, we were able to increase ash capacity and consider the cost savings with maintenance,” said Melloni. “We had big diversion berms along the side slopes on this site…. We chose the olive green ClosureTurf® product and my first inclination was that you would see this fake green-colored turf right off the bat. However, the grass and sand infill have blended together so well that you get a very natural-looking, grass-like appearance. I am very pleased with just how real this site looks.”
The back of the berm transitions from 2:1 slopes to 3:1, and while the site operators had some initial concerns that the sand infill could trap and build—and ultimately look out of place—they found that even with considerable precipitation the slopes did not experience any wash overs. The sand held in place.
As with any landfill site, managing water flow effectively can prove to be challenging and very important to the functionality of the design. Created specifically for down chutes, bench drains and perimeter channels, the HydroBinder® cementitious infill provides superior hydraulic performance capable of handling large flows on steep gradients.
“Our action swales on this site turned out to be some of the best we’ve ever done,” said Melloni. “With the water velocity and pressure we get, I was concerned the turf would balloon up and not sit tight on the ground; however, the HydroBinder weighted it down perfectly.”
Because the capping system does not require soil or fertilizing, stormwater runoff is clean of debris. The sand infill provides a natural filter for water running off of the slopes which dramatically improves water quality, making it an effective BMP for Clean Water Act requirements.
Covanta plans to continue using ClosureTurf® in additional landfill closure designs.
“Its hard to imagine a product like this working so well until you see it in action,” said Melloni. “Our sites have performed beautifully and I constantly remind everyone of the cost benefit this has brought to the table.”
Learn more about geosynthetics in landfill closure and other containment applications at Agru America’s website, www.agruamerica.com. See also Watershed Geosynthetics, www.watershedgeo.com.
Ward Hill Neck Landfill
Carver, MA & Haverhill, MA
Civil and Environmental Consultants – Raynham, MA
New England Liner Systems, Inc.
Energy from Waste Ash Monofills
2015 & 2016
4 acres & 12 acres
ClosureTurf product (US Patent Nos. 7,682,105 and 8,585,322; Canadian Patent No. 2,663,170; and other Patents Pending) and registered trademarks are the property of Watershed Geosynthetics, LLC.