The Top of the Heap

Cheryl L. Dunson

When asked to correct a common misnomer about his home state of Alaska, Joel Grunwaldt, solid waste director for the city of Anchorage, responds, "We don't live in igloos."

The 28-year veteran of the Anchorage Regional Landfill (ARL) also is quick to point out that managing a solid waste facility in one of the coldest states in the Union opens opportunities to collect data on and study a subject solid waste industry professionals know little about: cold climate landfill management.

The innovative practices and technologies used to combat the demands of Alaska's harsh, frigid climate tipped the scale for the Solid Waste Association of North America's (SWANA) judges when they bestowed this year's Landfill Excellence Gold Award on ARL.

Serving a population of 250,000 people who generate almost 1,000 tons of solid waste per day, ARL was one of the first landfills in the country to exceed Subtitle D regulations at a time when Subtitle D didn't exist.

ARL also was designed to meet the geological challenges of being located in one of the highest seismic regions in North America.

ARL houses an on-site weather station for data collection relating to meteorology and landfill operations. A sophisticated system of temperature probes and heaters are used regularly to measure the temperature and composition of methane gas as well as to pre-treat leachate.

The station tracks a variety of meteorological factors such as air temperature, wind direction and speed, barometric pressure and precipitation levels. Recording data every hour, the weather station's computer bank is downloaded every three months to correlate landfill activity to weather conditions.

The soft-spoken Grunwaldt, who has served as director of solid waste services since 1975, says the reason for ARL's sophisticated technology and cutting-edge approach is as simple as just "wanting to do the right thing."

For example, when the municipality needed to expand its landfill, it was faced with two problems: The earthquakes the region experiences every year and no available land adjacent to the site.

The municipality's solution was found next door at an army base. In exchange for free disposal of its waste, the base gave the landfill 300 acres of land.

After the swap, the municipality made several design and construction modifications to the site's 1987 permit to protect it from seismic activity.

"Our slopes were modified to a more gradual grade, and cell shapes were changed to better depict the 1993 Subtitle D requirements," Grunwaldt says.

"A buttress berm also was constructed to enhance the stability of existing cells Nos. 1, 2 and 3, and new cells Nos. 4 and 5 were combined to provide a more stable fill sequence," he adds.

To compliment design changes, ongoing waste mass analyses are performed as part of operational duties to ensure that the waste doesn't move during certain ground acceleration forces.

Due to the limited availability of local clay sources, ARL was the first Alaskan landfill to construct a geocomposite liner (GCL). "We convinced the state regulators that a GCL design was a better system," Grunwaldt says.

Unlike compacted clay liners, GCLs aren't susceptible to increased risk of permeability from freeze/thaw cycles. In addition, GCL's quick installation helps to reduce the risk of weather-related problems, especially those attributed to cold temperatures.

Anchorage averages six months of extremely cold weather, which keeps the waste mass relatively cold. A system of thermistors (temperature sensing devices) are inserted into the cells at 10-foot intervals at various depths to gather internal data on landfill temperature, gas generation and concentration rates.

"There has not been a lot of research on landfills that operate in cold climates," Grunwaldt says. "Our data indicates things are certainly different [at cold landfills] than what we find in existing literature."

For example, after 11 years of operation, ARL only has started to detect minor amounts of methane gas. This is because despite its frigid conditions, Anchorage's average precipitation rate is 16 inches. The cold waste mass, combined with minimal rainfall, deters methane gas production.

The city currently is upgrading ARL's leachate collection and pre-treatment system by adding heaters to the leachate lagoons. Without this heat, the lagoons' underwater aeration systems sometimes create "small volcanoes" of frozen leachate, Grunwaldt explains.

The benefits of Anchorage's commitment to data collection at its landfill will reach far beyond the city limits. "We installed the weather station and the thermistors to generate a database that will help others in the future," Grunwaldt says.

Building a Better Mouse Trap When visitors to the Delaware Solid Waste Authority's (DSWA) Southern Solid Waste Management Center (SSWMC) in Dover see the giant flumes cascading down the landfill slopes, funneling thousands of gallons of stormwater to huge retention ponds, they often compare it to a water theme park.

But SWANA's Landfill Excellence Silver Award recipient is not just the product of a creative passion shared by DSWA Executive Director N.C. Vasuki and his staff; it's also an experiment in the making that could shape the future of landfill closure regulations.

Exhausted and capped, two cells of DSWA's 540-acre solid waste facility have been joined and appear smooth and glistening following a rain shower.

Noticeably void of vegetation and spanning 45 acres, the test cells were initiated to investigate whether closure could be accomplished economically while providing easier access to entombed waste in the event that landfill mining becomes feasible.

"We'd seen exposed [liner] applications for lagoons, so why not [use it] for a landfill?" asks Ann Germain, DSWA's supervising engineer.

"Unreinforced caps have performed well over the past eight years at two one-acre test cells at our Central facility," she explains. "With Mr. Vasuki's imagination and desire to explore new technologies in the hope of saving money, we decided to try it on a larger scale at the Southern landfill."

DSWA's inability to excavate cover soil on-site due to an extremely high groundwater table prompted the authority to consider the exposed cap option.

Because groundwater is "practically at ground level," the facility's borrow pits immediately became wetlands upon excavation, Germain says.

To combat this, DSWA imports borrow material from about 10 miles off-site. "But when you consider covering 45 acres with two feet of soil and vegetative cover, the costs add up," she says.

When the second cell reached capacity in 1997, DSWA approached the Delaware Department of Natural Resources and Environmental Control with the idea of combining the first two cells and performing a "long-term intermediate closure project," Germain says.

With the blessings of state regulators, DSWA personnel prepared to address several design and operating demands to make the cap a functional reality.

The occurrence of methane gas and its effect on the cap, coupled with torrential stormwater flows and other seasonal elements, tested DSWA engineers' creative juices. "As organics decompose, they emit gas that has a higher volume than waste and liquid," Germain says.

"Unlike conventional closure caps where clay, soil and vegetative cover are layered on top of synthetic liner, just a geomembrane without any weight causes the liner to bubble up - in some cases as much as eight to 10 feet," she says. "We had to think of something that could take care of it."

Engineers proposed an elaborate methane gas collection system that incorporated 40 to 50 extraction trenches that were placed strategically underneath the geomembrane along the cells' sideslope at 80-foot intervals.

In each trench, a perforated pipe was covered with drainage stone and a textile material. As methane rises to the cell's surface, a vacuum applied to the pipes collects the gas and feeds it to a central flare.

"The gas collection system helped to solve two problems," Germain says. "It kept the liner both from bubbling and from taking flight in high winds."

Permitted to withstand 80 miles per hour winds, the cap has weathered gusts up to 95 miles per hour. The gas extraction system forces the liner to adhere to the waste cell.

Another design consideration was the absence of grass to slow stormwater from barreling down the cap when it rains.

Sometimes compared to whitewater rapids, the torrential water streams are directed to two corners of the cell by berms, which run along the cell's side slopes.

Equipped with downshoots that resemble water slides, the berms direct water into a box culvert underneath the landfill's internal road and into one of three ponds.

"We've probably got the water flow to justify a water park, but the rip rap at the end of the downshoots would make for a painful ride," Germain jokes.

Exposed to the elements, the cap was designed to endure the sun's ultraviolet rays as well as the affects of expansion and contraction during temperature changes.

Because it's easier to work with gravity instead of against it, Germain says an exposed liner has a tendency to expand downhill, which results in excessive bunching at the cell's toe.

To eliminate downflow creep, DSWA selected a reinforced polypropylene liner, which is stronger than high-density polyethylene and is less susceptible to the negative effects of expansion and contraction.

The $5 million closure project took approximately one year to complete, and Germain admits the verdict is still out on the cap's cost-effectiveness due to a redesign of the watershoots that occurred in the middle of the project.

"It's difficult to say if we saved money because this was the first time we've ever done a project like this, and we paid to have the watershoots built twice," she says. "But based on what we know now, we think it would be cheaper to do again."

However, Germain is eager to see how the cap withstands the East Coast's brutal winter. "Leachate rates have gone down, but we've had a dry summer," she says. "Now, we're looking forward to the torrential downpours and snows."

Good Landfills, Good Neighbors Thirty-five miles north of Dallas, the city of Denton, Texas, has created a self-sufficient integrated solid waste management program, which includes a 330-ton per day landfill that earned SWANA's Landfill Excellence Bronze Award.

Despite hydrogeological constraints and minimal waste volumes, Denton began planning for the future in the early '80s.

Today, it is preparing to move into its first Subtitle D cell in a 155-acre facility that eventually will provide its constituents with more than 35 years of airspace.

Charles Watkins, director of Denton's solid waste department, makes no bones about the city's success, attributing it to creative engineering and design, a deliberate public education program and a dedicated landfill staff.

"As part of the city's utility department, [Denton's solid waste department] wanted to become a leader in the landfill industry as well as in solid waste management in general," Watkins says.

Despite a high groundwater table, the new landfill incorporates a sophisticated groundwater protection program, which includes soil-bentonite slurry cut-off walls to direct the water around the landfill's northern and western perimeters.

A single-pass dewatering method resembling a french drain extends 25 feet below the landfill's liner to channel a rising water table to a sump where water is pumped out as it becomes necessary.

To aid future construction, the slurry walls were marked with magnetic devices at various intervals to apprise construction crews of the wall's location.

"We made several concessions during permitting to promote a neighbor-friendly facility," Watkins says.

Although the landfill has been in existence since 1985, a great deal of growth and development in the vicinity has changed the community's rural character, prompting city leaders to exceed the minimum zoning and regulatory requirements.

"We went into the permitting process just like any other property developer," Watkins says.

"There were two ways to approach it: We could do just enough to meet the minimum zoning requirements or we could be a good neighbor and apply for a specific-use permit," he explains.

The city opted for the latter approach and now, an extensive landscaping and tree screening program shields the landfill from its growing number of neighbors.

During the permitting process, the city also agreed to other concessions, such as traffic routing, litter collection on roads leading to the landfill and a facility height restriction.

"We lowered the facility's final elevation by 15 feet and sacrificed several million cubic yards of airspace, but it was worth it to gain the public's good will," Watkins says.

To safeguard the facility's economic future, the city chose to become the exclusive owner of the community's collection program. "In the early 1990s, we were an open city, and our service was marginal," Watkins says.

"We looked at selling our commercial system," he continues. "Even though we received an attractive offer from a major hauler, the bidding generated so much public interest and support for a city-owned system that our city council decided not to sell and instead chose to remain the exclusive provider of solid waste services."

With the city gaining complete control of the community's commercial and residential collection, the landfill is assured of waste volumes and its enterprise fund remains healthy.

"The city of Denton recognized the need to take responsibility for its own waste," Watkins says. "So why not have a facility we can be proud of? That desire has been instilled in our landfill manager and his staff. They're committed, educated and proud of their operations."