2012 Excellence in Environmental Engineering and Science™ Competition Winner

E3S Honor Award

2012 Honor Award - Environmental Sustainability

Hickory Ridge Landfill Solar Energy Cover

Entrant: HDR
Person in Charge: Mark Roberts
Location: Conley, Georgia
Media Contact: Mark Roberts, 904-598-8979

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E3S Photos

By using exposed geomembrane solar cap technology, the at-capacity, 48-acre Hickory Ridge Landfill was transformed into the largest solar energy generating facility in Georgia. It is the world’s largest solar energy cap and the first use of the technology as a fully permitted landfill final closure system.

E3S Photos

This new and innovative technology caps the landfill with an enhanced geomembrane anchoring system developed by HDR – essentially taking a durable, high-strength geomembrane material made for outdoor exposure on roofs and securing it to the landfill like a bedsheet through the use of vertical anchor trenches.

E3S Photos

The closure replaces a traditional Subtitle D closure—which drapes a geomembrane liner over the waste and holds it in place with layers of soil and a grass top. This eliminates thousands of tons of greenhouse gases that would be emitted from the mowing and soil replacement activities needed for long-term care of a grass-covered cap, as well as saving the owner more than $1.5 million in maintenance costs over the life of the closure.

E3S Photos

The geomembrane-covered landfill sideslopes provide an ideal, clean and stable surface for thin-film photovoltaic solar panels to be directly adhered. The cover uses 7,000 solar panels to convert sunlight into more than one megawatt of clean, renewable electricity for the owner, Republic Services, and the local community.

E3S Photos

To complete a traditional closure in the middle of Atlanta, contractors would have needed to truck in enough soil to provide two feet of cover over 48 acres, equating to thousands of truck miles and associated emissions, and tens of thousands of tons of imported material. HDR’s design avoided these impacts to the budget and the environment.

E3S Photos

In addition to eliminating the environmental cost of replacing grass and soils, maintaining the integrity of the liner helps ensure the efficient containment of thousands of tons of greenhouse gases generated within the waste mass.


Entrant Profile

HDR was responsible for the permitting and construction design of the alternative closure cap for Hickory Ridge Landfill, which used HDR’s groundbreaking exposed geomembrane solar cap design. The firm was responsible for submitting the permit application package for landfill final closure to the Georgia Department of Natural Resources as a first-of-its- kind, alternative landfill final closure in the state. HDR provided the bid and construction documents, including the construction drawings and specifications for the components of the alternative closure cap construction, earthwork grading, anchor trenches, geomembrane deployment, solar panel layout, wire pathways and inverter locations. The firm also provided construction management and field engineering services during the exposed geomembrane and solar cap deployment.

One of the main reasons this project was possible in 2011 was the further development of the unique geomembrane anchoring system that HDR pioneered on a significantly smaller scale in 2009. HDR’s designers collaborated on applications of exposed geomembrane closures with Dr. J.P. Giroud, who has conducted research on geosynthetics since 1969 and has authored over 350 publications on the subject. HDR refined the design further to incorporate modified suction forces working at different heights of the landfill.

HDR is an employee-owned architecture, engineering and consulting firm with more than 7,800 professionals in 185 locations worldwide. All of them are committed to helping clients manage complex projects and make sound decisions.

Consultants that worked on this project include: American Environmental Group, Geosynthetics Contractor; Cooper Barnett and Page, Earthwork Contractor; Southern Sunpower, Electrical Contractor; Carlisle SynTec, Material Manufacturer.

Project Description

Originality and Innovation

The Hickory Ridge Landfill has the world’s largest solar energy cap—using new and innovative technology to transform a closed landfill into an abundant, reliable, clean energy source. By far the largest landfill solar energy cover in the U.S. and the first application of this technology as a fully-permitted landfill final closure system, the project closed a 48-acre municipal solid waste landfill and installed 7,000 solar panels.

HDR’s innovative next-generation landfill cap design uses a series of anchors to secure the geomembrane directly into the landfill, creating a stable and secure surface for the laminate solar panels and facilitating inspection and repair. The 60-mil, scrim-reinforced thermoplastic polyolefin geomembrane liner is designed for long-term outdoor exposure, with a successful history of UV resistance, seam strength, chemical and puncture resistance and interface friction. HDR chose the material for these properties and its long-term performance warranties – typically 20-30 years.

This cover uses thin-film photovoltaic panels directly adhered to the geomembrane. The ¼-inch-thick panels provide the flexibility to shift when landfill surface waste settles. The lightweight panels have a distributed load of only 3.6 kilograms per meter squared and are easily replaceable. They can generate electricity year round—in high and low light and under high and low temperatures.

Integrated Approach

Clean air, water, and solar energy are now associated with a closed landfill property. The Hickory Ridge Solar Energy Cover creates renewable solar energy by converting sunlight into over one megawatt of electricity. The project allows the closed landfill, a brownfield area, to benefit the community; a strategy with potential to alter the solid waste industry and give life to otherwise unusable land at over 20,000 U.S. landfills.

Unlike traditional closure caps, this anchors directly into the landfill without additional layers of soil and grass on top. The solution eliminates fertilizer use and greenhouse gas emissions associated with long-term turf maintenance. The design also removed the need to truck in soil to cover the cap, reducing thousands of truck miles and tons of imported material. Additionally, the liner’s improved integrity helps ensure efficient containment of greenhouse gases generated within the waste mass.

The cap’s stable sideslopes maintain positive stormwater drainage, preventing water pockets from forming and allowing the surface to dry quickly, eliminating the potential of generating additional leachate from stormwater intrusion into the waste. Instead, clean stormwater is channeled off the liner to produce reusable water for harvesting, without the need for sedimentation and cleaning. Perimeter drainage channels are included to maintain a zero-erosion design.

Quality

The finished cover makes as much sense financially as environmentally – benefits recognized by owner, its customers and the public. Completed under the $10 million budget, the project met the completion goal to begin the landfill’s 30-year, post-closure clock in January 2011.

The project exceeded Georgia Environmental Facilities Authority (GEFA) needs, which awarded a $2 million grant. GEFA was particularly satisfied to have construction completed within one year, offering fast results that put the grant funding into action to encourage energy savings and produce renewable energy.

The October 2011 ribbon cutting included a range of public and industry officials, including Georgia Lieutenant Governor Casey Cagle, who praised the project as the future of landfill reuse, saying “I’m confident this will be the standard not only for Georgia, but also the nation.”

Georgia Department of Natural Resources commissioner Mark Williams agreed. “It’s exciting to see the concepts of conservation and effective resource management be put into action by this project,” he said, adding that he hoped the project would serve as an example to “the rest of the nation of what Georgia is doing to be good stewards of our natural resources.”

Contribution to Social or Economic Advancement

The cap’s dual economic-environmental benefits are a win-win situation. The cover generates enough energy to power 224 homes, eliminates environmental impacts of turf maintenance and provides the community a sense of pride.

Installing this type of closure (without solar panels) saves $2.4 million compared to a traditional closure; funds that can be invested in revenue-generating panels. Typical post-closure care costs are avoided, saving over $1.5 million through the closure’s lifetime. The design can incorporate additional panels over time, allowing post-closure maintenance savings to be invested to increase the cap’s energy output. The solar panels provide a new revenue stream, supplying electricity for resale to the local utility and for potential on-site use.

The highly-visible cover has sparked widespread public and industry interest, drawing positive publicity from green energy journals, solid waste publications, the Atlanta Journal-Constitution, and local and national television news agencies. A landfill closure has never before received such positive attention. The publicity focuses on environmental and financial benefits, such as clean energy, reduced emissions, solar renewable energy credits, care cost savings, sale of renewable power and the positive image portrayed by the innovative design. This provides a perfect example of an innovative engineering solution capturing the public’s interest.

Complexity

Implementing innovative technology means establishing new precedents, adding complexity to the environmental approval process. The design itself presented unique challenges related to cover installation and long-term performance without using ballast, pins or point loads.

The project utilizes HDR’s innovative cap design, which had only been used twice before on a significantly smaller scale. This is the only exposed geomembrane solar cap permitted as a landfill final closure cover system. HDR engineered the cap to meet all EPA landfill alternative closure requirements and prepared a permit application for final closure utilizing an alternative landfill closure system.

An innovative but simplified deployment and anchoring technique allowed engineers to design against wind uplift for specific wind events. Input factors included assessment of the maximum recorded local wind velocity, temperature patterns, liner strength and thickness, and sideslope geometry. HDR determined that suction forces due to wind on the landfill’s sideslope change with height and accordingly modified the vertical anchor trench dimensions. Detailed design included a geomembrane panel layout with exact locations and dimensions of every anchor trench, as well as exact locations of each of the 7,000 solar panels.


Click images to enlarge in separate window.

E3S Photos

This landmark design is a milestone in the solid waste industry. It transforms a landfill that has reached its permitted capacity and creates a reuse opportunity for the property that takes advantage of many of the site’s built-in features, such as stormwater runoff controls, site security and access to the electrical grid.

E3S Photos

The exposed geomembrane closure eliminates the potential to generate additional leachate from stormwater intrusion into the waste, instead channeling clean stormwater off the liner into sedimentation basins for on-site reuse or clean off-site discharge.

E3S Photos

The Hickory Ridge Solar Energy Cover generates enough renewable energy to power 224 homes, providing over one megawatt of electricity for resale to the local utility, Georgia Power Co., as well as for potential on-site use. There is also the value of creating solar renewable energy credits and making the project eligible for solar energy incentives and rebates.

E3S Photos

An exposed geomembrane closure saves $2.4 million compared to the installation costs of a traditional 48-acre closure, and can then incorporate any number of solar panels. Detailed design included a geomembrane panel layout with exact locations and dimensions of every anchor trench, as well as exact locations of each of the 7,000 solar panels.

E3S Photos

One of the main reasons this project was possible in 2011 was the further development of the unique geomembrane anchoring system that HDR pioneered on a much smaller scale in 2009. This innovative but simplified technique has become a precedent in exposed geomembrane design, allowing engineers to design against wind uplift for specific wind events.

E3S Photos

HDR’s designers collaborated on applications of exposed geomembrane closures with Dr. J.P. Giroud, who has conducted research on geosynthetics since 1969 and has authored over 350 publications on the subject. HDR refined the design further to incorporate modified suction forces working at different heights of the landfill, and accordingly modified the vertical anchor trench dimensions.

E3S Photos

The exposed geomembrane solar cap design makes inspection and repair of the geomembrane easier and also allows for clean stormwater runoff to be harvested for reuse, without the need for sedimentation and cleaning.

E3S Photos

To handle the increased laminar flow rate off the exposed geomembrane, HDR designed geomembrane-lined perimeter drainage channels similar to large, lined roof gutters to maintain a zero-erosion design.

E3S Photos

The Hickory Ridge Landfill Solar Energy Cover’s distinct shape, bright green color, and south-facing solar array catches the eye of travelers flying in and out of busy Hartsfield-Jackson International Airport, sparking discussion about the unique project’s environmental and economic benefits.


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