Converting landfill gas to usable renewable natural gas fuel for solid waste disposal and district vehicles
Managing the myriad material that flows into international solid waste streams presents an increasingly complex mix of engineering, scientific, and technical challenges. Tetra Tech is meeting these challenges through an aggressive program of innovative landfill design, site monitoring and management, repurposing old waste storage facilities, and responding to unique waste management needs.
Tetra Tech’s responsive and innovative approach to solid waste management services recently earned us a #1 ranking in Solid Waste from Engineering News-Record. Our Solid Waste Initiative has quadrupled revenue from this service line—from $25 million in 2008 to $100 million in 2012. To support our solid waste practice, we have grown to include more than 1,000 planners, engineers, geologists, scientists, construction managers, and field support personnel representing 20 operating units.
Tetra Tech engineers and technicians have designed and constructed highly specialized waste containment systems, installed leachate management and landfill methane recovery systems, capped an existing facility with a photovoltaic-cell-studded cover, built recreational facilities on old landfills, and responded to public emergencies related to subsidence and gas migration that test the limits of technology and human ingenuity. Solid waste management issues engage the full range of Tetra Tech’s professional services, from engineering and science to construction management and regulatory compliance.
Innovative Landfill Design
Landfill design is defined by waste characteristics, site conditions, and environmental and other considerations, such as groundwater protection, leachate and gas production, and post-closure use. Leachate—generated by precipitation and groundwater percolating through solid waste—can impact aquifers and is usually handled through prevention, in the form of impermeable covers and liners, and treatment through collection and internal recirculation or delivery to a treatment facility.
Tetra Tech subsidiary Ardaman and Associates (AAI) designed the liner system that protects groundwater from leachate generated in a new coal ash storage facility for the Orlando Utilities Commission’s (OUC) Stanton Energy Center.
“The landfill cell has six layers in all,” says AAI’s Mohamad Al-hawaree. “The bottom is six inches of compacted clay. Then a 60 mil high-density polyethylene (HDPE) secondary liner with a geocomposite is laid over that, which contains the leachate leak detection system. Above that is the primary liner—also 60 mil HDPE. The leachate collection system lays on top of the primary liner, covered by two feet of clean sand, which allows for drainage. The ash is stored on top of the sand, and the protective cap goes over that.” Leachate collected is recirculated internally.
Al-hawaree says the design and permitting package for the 90-acre Orlando project, which serves the second largest public utility provider in Florida, was completed on an extremely aggressive seven-month schedule.
“The expanded waste facility was needed so the utility commission could maintain full capacity electricity generation for OUC’s flagship power plant east of Orlando,” he notes.
Regulatory approval was obtained in two months, with construction of the first cell completed eleven months later. Tetra Tech’s design, permitting, construction, and project management teams collaborated to meet the schedule without sacrificing safety, working more than 130,000 hours with zero incidents. The full design included a double-lined, three-cell landfill with leachate collection and leak detection systems, plus a 22-acre stormwater pond.
Treatment of Landfill Gas Byproducts
Methane formation in landfills is also a familiar topic in the industry. Decomposing waste produces gases such as methane, carbon dioxide, and other volatile organic compounds. Landfills—especially those handling the nearly 500 million tons of municipal and construction waste generated annually in the United States—rank as the third largest source of man-made methane emissions. About half of the gas produced in municipal solid waste is methane, a potent and combustible greenhouse gas (GHG). Landfill gas systems relieve internal pressure from landfills and prevent gases from migrating laterally and threatening surrounding structures. Recovered gas is either flared or developed as an alternative energy source
In 2010, Tetra Tech was selected as a special consultant to the U.S. Environmental Protection Agency’s Landfill Methane Outreach Program, a voluntary assistance program facilitating the reduction of methane emissions from landfills by encouraging the recovery and beneficial use of landfill gas as an energy resource.
Tetra Tech’s broad, extensive experience in handling landfill gas was enhanced with the 2013 acquisition of American Environmental Group (AEG). The firm has been a key player in developing some of the largest landfill projects in the United States and is the leading construction firm for landfill gas systems. Carl Apicella, one of AEG’s founders, leads a team of more than 500 professionals who handle a wide range of waste management duties, including gas system design and construction for both new and old landfills. AEG’s other services include geosynthetics, operations and maintenance, power management, and landfill design.
“The municipal solid waste sector has been a very steady business for us,” Apicella says. “With municipal waste, gas can be a major factor, and that’s where we can really help.”
The group has coupled their landfill gas collection system capabilities with power management services to create an integrated mix that includes well field data monitoring, collection system piping installation, modifications and repairs, and power generation. Facilities typically include combined heat and power, turbines, and alternative fuel internal combustion engines. Our factory-trained and certified personnel can service a wide range of engines and manage various power generation operation and maintenance contracts. The team also provides site monitoring and management.
In Canada, Tetra Tech provides specialized biogas collection, combustion, and energy production services. We are also a leading player in addressing greenhouse gas reduction, both in Quebec and internationally. Our Canadian solid waste team, led by Stephen Davidson, has been active in the province’s climate change and green technology plans, which include four biogas drawdown/combustion projects, construction of a three-megawatt biogas power plant, and studies of gas potential at sites.
In cooperation with Transforce, we developed a new electricity cogeneration plant in Sainte-Cecile-de-Milton, Quebec, which produces enough power to supply 450 homes. The facility uses thermal energy from the engine to heat wastewater at the site, accelerating biogas production. Burning the methane—rather than venting it to the atmosphere—reduces greenhouse gases by more than 30,000 tons annually.
Topping off the list of innovative landfill services is the first solar energy generating landfill cap in the United States, which AEG installed a few years ago near San Antonio, Texas. The company recently completed a similar project near Atlanta, Georgia. The landfill is covered with a thermoplastic olefin (TPO) geomembrane. The modified TPO is designed for long-term exposure and service life, which a solar energy project requires.
The group’s work on the 5.6-acre system involved installing the TPO membrane and solar energy array, which included bonding 35 flexible solar pods to the geomembrane panels. Each pod consists of two rows of 15 thin-film photovoltaic panels—1,050 panels in all. After on-site fabrication was determined to be the best option, certified technicians welded nearly seven miles of seams for this first-of-its-kind project—with no seam failures during quality control testing.
Repurposing Old Waste Storage Facilities
Although waste material might not get much respect—it is, after all, waste—it enjoys a fairly comfortable, pampered, long-term retirement. Old landfills often see significant upgrades in their status after closure, and Tetra Tech has developed broad expertise as a leading waste facility makeover artist. Two recent projects highlight how Tetra Tech’s integrated engineering and science capabilities can create new life for old landfills.
In California’s high-tech Silicon Valley, the Mountain View Athletic Field sits within a historic regional park near Google’s global headquarters. Christine Arbogast of our California-based waste management practice worked with the city of Mountain View to design a recreational park featuring soccer, lacrosse, and softball fields—while protecting the subterranean Western Burrowing Owl, subject of a petition for threatened/endangered status in California.
Arbogast, Peter Skopek, and their team provided geotechnical engineering, planning, design, and permitting support services for the development of the new park on the old landfill. Successful execution of the work required balancing several interrelated factors, including protecting the integrity of the existing landfill cover, continuing measures to control migration of landfill gas, accommodating the landfill settlement, protecting the owl’s habitat, and developing a first-class athletic park for the community.
“The site is adjacent to San Francisco Bay, in a former tidal wetlands area,” says Paul Mitchell, the group’s marketing director. “Since landfill surfaces are prone to differential settlement, special care was taken during the design of structures and foundation systems to be built over existing waste fill areas.”
Arbogast adds that the team used an iterative process, aided by significant public and stakeholder input, to define and analyze conceptual alternatives for proposed project features. The layout was also reviewed to ensure compatibility with the city of Mountain View’s traffic circulation, safety, and sustainability plans. The final design includes a lighted synthetic turf soccer/lacrosse field and softball diamond with fences, passive and active open space, minimal hardscape, benches and tables, parking with a drop-off area, and open space areas dedicated to owl foraging habitat. The design phase of the project was recently completed, with construction under way during 2013.
In Kentucky, Tetra Tech is also improving recreational experiences on a retired landfill. Herb Lemaster and his teammates were selected by the state division of waste management to assist in designing a cleanup plan for an abandoned Fayette County household waste landfill. The facility sits on the Raven Run Nature Sanctuary, a popular hiking, birdwatching, and natural area on the banks of the Kentucky River, south of Lexington.
The former Jacks Creek Pike Landfill operated during the 1960s and early 1970s. In 1971, it was covered with soil, closed, and abandoned after a waste fire. The site was placed on a priority cleanup list in 2002 because of potential threats to human health and the environment, mostly related to high-volume leachate generation caused by natural springs in the area that flowed through the waste mass.
To address the leachate problems without disturbing large areas of the sanctuary, Lemaster and his group worked with state agency personnel to develop a plan for implementing a nondisruptive phytoremediation approach. The technology uses trees and other plants to passively clean up soils and remove pollutants from the environment, reducing the quantity of and improving the quality of leachate while maintaining the sanctuary’s natural landscape.
The plan called for consolidating the existing waste into a smaller footprint, installing a passive leachate collection system, replacing the old soil cap, and installing selected trees and other plants. Approximately 26,000 cubic yards of municipal waste and construction/demolition debris were consolidated and moved 100 yards upstream, reducing the landfill footprint by almost 25 percent.
Moving the waste enabled the engineers to isolate and divert a spring-fed stream, decreasing leachate generation by more than 10,000 gallons per day. A passive gravity system directed the remaining leachate through a rock-filled bioswale, allowing natural overland flow and facilitating additional treatment. Last year the project team completed the final phase of the project—the installation of a phytoremediation cap, composed of nearly 30,000 cubic yards of fill and topsoil planted with thousands of sycamores, poplars, and other native tree species.
Special Situations and Unique Needs
For every elderly landfill retiring as a ballpark or nature sanctuary, there are at least two or three others that go rogue. Carl Apicella’s AEG gas busters group is always ready when the call comes in.
“We do a lot of work in this area—modifying gas collection and removal systems, dealing with odors—our clients know we can help them with these types of problems,” Apicella says. “In some cases, there can be public relations issues, with odors and such. We’ve got a lot of experience in this area, and lots of technical and engineering expertise. We can help them get things under control.”
“In some of these more difficult situations, we’re helping to fix things and get our clients back into regulatory compliance,” he says. “A lot of the time we’re working in the waste mass, in a high-pollutant situation, with nasty gas environments, and dangerous situations. We know this arena—we know how to work safe, how to meet the regulatory challenges. Our clients know it, too—they trust us, and they call us back when they have problems.”
Tetra Tech’s experience in solid waste management has been complemented by work with the U.S. Environmental Protection Agency Office of Solid Waste and Emergency Response, which has awarded the company multi-year, multi-million dollar contracts to provide scientific, engineering, and management consulting services to support Superfund, solid waste, emergency management, underground storage tanks, and brownfields programs. Tetra Tech has provided expertise in assessment, hazardous waste cleanup, and emergency response.
Finally, Tetra Tech is also providing assistance to the Texas Brine Company, LLC to address issues related to a land subsidence occurring in Assumption Parish, Louisiana. While not exactly a solid waste effort, the project is addressing several landfill-like engineering and technical challenges. Scientists believe the subsidence occurred after the collapse of an underground salt cavern, which extracted brine and piped it to nearby petrochemical facilities. Tetra Tech’s primary tasks are to install a series of observation and vent wells to mitigate methane gas that has been released into the Mississippi River alluvial aquifer. This extremely challenging project harnesses the expertise of multiple Tetra Tech offices.
Moving Toward Zero Waste
While steady demand for conventional solid waste management services continues, the industry is changing.
“The big thing now is implementing zero-waste management principles and zero-waste generation goals” Mitchell notes. “We’re seeing a broadening scope, including carbon credit programs related to surface emissions of methane gas.”
Tetra Tech is entering the fray, mostly by helping existing clients better assess and manage their waste. “We’re doing a lot of strategic planning with municipalities in this new paradigm,” Mitchell says. “They want to know how they can get themselves organized to plan for the long haul—even 30 years out. Waste minimization, reuse, recycling—everything is being considered.”
Tetra Tech’s zero-waste and sustainability services include planning, environmental management systems, design and construction, education and consultation, management services, and product stewardship.
“The world is changing rapidly—what was only a few years ago looked at as garbage, is now being looked at in a very different way,” says Bert Monesmith of Tetra Tech’s Canadian solid waste practice. “With the costs of energy rising and the tighter regulations regarding pollutant discharges, our clients are shifting the way they look at their waste.”
“A lot of energy goes into making these materials and products—and into disposing of them,” Monesmith says. “By recycling and reusing these materials and products we are creating a more sustainable loop by reducing the overall extraction of our natural resources and the corollary, toxic and GHG emissions.”
With expertise in comprehensive waste planning, Tetra Tech helped establish the city of Vancouver’s waste reduction and diversion plan for municipal facilities, including developing waste reduction targets by facility type and identifying facilities suitable for zero-waste programs. Tetra Tech has provided similar planning guidance for the University of British Columbia and the Canada Mortgage and Housing Corporation.
With sound experience in all areas of waste management, Tetra Tech is well-positioned to meet our clients’ evolving needs. As waste is created, recycled, disposed of, used for energy, and transformed into usable spaces, Tetra Tech is helping to create sustainable solutions for solid waste management.