During his 12 years at Englewood Golf Course in Colorado, superintendent David Lee has seen some goofy things pop out of the ground, such as wigs, bowling balls, and car bumpers. But pop-up junk here is something less than surprising: the course sits on a curvaceous mound of trash some 40 feet deep. In some places, all that separates the velvety green from the garbage is a few inches of sod.
Two years ago at a converted landfill called Renaissance Park in Charlotte, North Carolina, a soccer mom went after a stray ball that had fallen into an eroded hole around a light pole. To see in the shadows, she pulled out a pocket lighter. An exploding fireball blew her several feet back from the methane-filled hole. Fortunately, she suffered little more than minor burns and a bad case of the shakes. Signs discouraging open flames and smoking in all five of Charlotte’s landfill parks were quickly posted.
There are far more tangible signs of the waste that lies just inches below the Renaissance landfill cover. On an afternoon after a gentle rain, the ground at the park’s 18-hole golf course crackles like the sound of Rice Krispies. The noise comes from large patches of mud bubbling with gas. It looks like polenta boiling on the stove, observes retired course superintendent Robert Orazi. But it smells like rotten eggs. Last year, Orazi gave up after six years of coaxing the grass and trees to grow on two feet of soil baked dry from the heat of rotting garbage below.
The course is also plagued by uneven settlement that dimples the fairways, tilts putting greens, breaks irrigation pipes, and turns cart paths into rolling whoop-de-doos only a dirt biker would love. Then there’s the Blob, a foot-tall lump of wiggly amber-colored ooze creeping out of the fourth fairway. We tried shoveling it; we tried covering it. It just comes back, says Orazi. Tests show it to be a kind of alga that feeds on the iron-rich liquid that seeps up from below. And pop-up waste? Among the scariest finds, says Orazi, are blood bags and syringes. More typical are the tires and rubber hoses that literally float up through the soil.
The hazards don’t end with belches of garbage and gas. The heat of decaying trash can itself ignite the gases a landfill releases. That may have been the case when a six-foot flame shot from a crack near Renaissance’s sixth green in 1989. Workers quickly doused it. But such landfill fires can spread underground for miles.
Several years ago, in Mountain View, California, an open-air amphitheater built over a landfill erupted in smoke during a Grateful Dead concert. The landfill was equipped with a gas extraction system, but the city had turned over the system’s maintenance to the production company that ran the concert. When the production crew saw the smoke coming out of a crack in the ground, they cranked up the suction. The smoke disappeared, but the suction drew the fire underground and fueled it. Luckily, engineers arrived before anyone was hurt.
Closed structures, of course, are particularly susceptible to landfill gas. Without proper sealing and venting, methane can seep inside a building on or near a landfill and rise to explosive levels. That’s what happened two years ago in a snack bar under construction on a landfill driving range in North Hempstead, New York. One night the water heater kicked on, igniting a fireball that knocked down the walls.
Despite the scare stories, over the past 20 years hundreds of municipalities and landfill operators have fashioned closed landfills into golf courses, parks, ball fields, playgrounds, even ski slopes. There is no national tally--largely because dumps, especially closed dumps, are considered local domain. And there is little regulation. You don’t need an EPA permit to play ball on a landfill, says Allen Geswein, of the Environmental Protection Agency’s office of solid waste. And given the current political climate, I wouldn’t expect any moves in that direction.
Yet the need for more and bigger dumps won’t go away. The United States generates some 209 million tons of municipal waste each year, over four pounds per person per day. Although no one knows exactly how many landfills reach capacity each year, the number is probably well over a hundred, and these monuments to waste cost money to maintain. Since 1993, for example, EPA regulations have required landfill operators to prevent their sites from leaking gas or polluted water for at least 30 years after they’re closed (by then, according to theory, most of the gases from the decomposing garbage will have been released). The associated maintenance costs can reach hundreds of thousands of dollars an acre, which makes conversion to a revenue-generating facility like a golf course attractive-- but problematic.
In 1993 the EPA also set some minimum standards for the design and operation of new landfills. Though aimed at reducing off-site pollution, these rules have the side effect of improving safety and stability on top of landfills as well. They require operators to screen waste for obvious chemical hazards and to refuse medical or toxic waste. Bulk liquids--such as sewage--are acceptable only if they have been solidified with soil or other stabilizers. Operators must also cover each day’s garbage with a six-inch layer of dirt, which reduces the blowing away of trash and odors. The landfill’s final cap, in turn, must consist of at least two feet of compacted soil.
But only last year did the EPA make a move to control some of the gases that bubble to the surface of closed landfills. These gases are produced by the microbial food chain in the anaerobic, or oxygenless, environs of a landfill. Some bacteria, for example, degrade cellulose into sugar. Others eat the sugar, producing the acid that feeds gas-releasing bacteria. The result of their feast is a mix of methane (50 percent), carbon dioxide (40 percent), and nitrogen (9 percent), plus the trace contaminants that produce the foul smell of decay. None of these gases are particularly hazardous when allowed to dissipate in open air, says Martha Smith of the EPA’s office of air quality planning and standards. It’s the remaining 1 percent that includes some scary stuff.
When bacteria degrade household cleaning products, solvents, paints, and pesticides, they generate vapors that include such nasty carcinogens as benzene, toluene, vinyl chloride, and a half dozen others. Vinyl chloride is a particularly toxic and persistent gas--persistent because it kills the very microbes able to dechlorinate and so detoxify it. The EPA’s new rules require landfill owners to monitor and control these dangerous vapors in the air just above the landfill cover, keeping them within a safety margin of 500 parts per million. Control measures usually include an underground venting system that sucks toxic vapors and other landfill gases aboveground and burns them off.
Unfortunately, EPA regulations apply only to large landfills-- typically those serving more than 100,000 households--that have been opened or modified since 1991. This isn’t to say that smaller and older landfills aren’t of concern, says Smith. The EPA encourages individual states to set higher standards. California, for one, actually does, she adds. Moreover, whether from civic-mindedness or fear of liability, some of the nation’s garbage giants are pioneering new designs for landfills and landfill parks that far exceed government standards.
The 188-acre live Oak Landfill and Recycling Center on Atlanta’s outskirts is a far cry from the haphazard dumps of the past. Roughly the size of several football fields, it is one of the Southeast’s largest landfills--handling some eight tons a minute, 4,500 tons a day. Opened in 1986 by Waste Management--which is the world’s largest waste-disposal company, with some 140 landfills--Live Oak will reach capacity in 2001. After that it may begin a new life as a recreational facility with soccer fields and horseback-riding trails.
Last December trash compactors at the Live Oak site were still spreading refuse on top of two of the three trash heaps that will end up 160 feet high. The first two mounds sit astride a central pit, where the operation’s next phase will begin. Garbage will ultimately fill this pit, then start piling up and out like an inverted mountain against the sides of its sister peaks. The result will be a single flattened pyramid with a playable tabletop some five acres in size.
At the bottom of the still-empty central pit are seven layers of protective barriers for gathering and removing leachate--the polluted liquid from the decaying waste. The uppermost layer is a two-foot blanket of glistening white sand; not ordinary sand but grains manufactured to a specific size. If the grain sizes varied, they would pack together under the weight of the landfill, and smaller grains would fill in the holes between larger ones, preventing the runoff of leachate. Buried within this permeable, carefully milled sand is a horizontal pipe that will carry the leachate to a low-lying area. From there it will be pumped out of the landfill for disposal.
Directly beneath this layer of sand is a thin--.06 inch--sheet of high-density polyethylene (HDPE) plastic. Below the plastic lies a quarter- inch geosynthetic clay liner consisting of two fabric layers filled with a dry granular clay called bentonite. When wetted by, say, a leak in the overlying plastic sheet, the bentonite swells to form a tight, highly impermeable barrier.
The next layer down is the landfill’s drainage system--a thick screen of heavy HDPE perforated pipes. Should any leachate reach this grid, it will drain to a low-lying pit. Leachate filling the pit will lift a float, which sounds an alarm signifying that the primary liner system has been breached. Live Oak operators can then draw the leachate out of the pit by applying suction. An added safeguard is a bottom layer of high-density polyethylene, which in turn lies on top of six inches of compacted clay.
Above these protective barriers, daily operations begin. Unlike the casually heaped dumps of the past, Live Oak conserves space by squeezing every last bit of air out of the garbage, creating a tightly compressed landfill structure. The garbage is sorted and distributed by size and compressibility, then ironed flat by 100,000-pound trash compactors that grind along on broad, cleated rollers. The compacting continues in two-foot layers until some 1,400 to 1,700 pounds of waste have been compressed into every cubic yard of space. Uncompacted, the same cubic yard would hold just 500 pounds.
At day’s end, an eight-to-ten-foot stack of smashed waste is covered with dirt and crushed once more into a cell. Imagining the landfill in cross section, the daily cells form continuous rows called lifts, which in turn become the landfill’s horizontal tissues. Trash compactors grade the landfill’s outer slopes to a 30 to 33 degree angle to maximize the structure’s stability.
The continuous grading and compacting will greatly reduce the settling of garbage after the landfill is closed. More important, the compaction helps ensure that settlement is smooth and even. Though Live Oak Landfill may eventually settle by a dozen or so feet over the next 30 years, the overall shape and surface contours should remain roughly the same.
At five acres, Live Oak’s upper surface is too small to be converted into a golf course, but had that been the plan, bulldozers would have shaped the top layer of refuse into berms, curving fairways, and flattened greens. For the more modest plan of a ball field or equestrian center, the landfill’s upper surface will be graded into a broad, gentle crown with just enough grade, about 5 degrees, to quickly slake off rain.
Before capping the landfill, Live Oak operators will install vertical pipes down through some 140 feet of trash to collect methane-rich gas. Other landfill operators have fashioned even more detailed gas collection systems, including a grid of flexible horizontal perforated pipes that snake through the trash, absorbing gas and feeding it to the vertical gas collection pipes.
Although the EPA requires only that the gas vented from a landfill be flared, Waste Management is considering another plan for Live Oak. The gas might be drawn off to an on-site power plant and used to generate electricity. In this speculative scenario, the company estimates that for some five to ten years after closure, Live Oak could generate .8 to 2.4 megawatts of power, enough continuous energy to serve perhaps 1,200 to 3,600 homes.
The crowning touch, of course, will be the landfill’s cap, the crucial barrier between its waste and park visitors of the future. At Live Oak, plans call for a composite cover combining natural and synthetic liners. The layer that lies directly above the waste will be an 18-inch layer of compacted clay. Workers will iron the clay with 60,000-pound drum rollers until it’s virtually impermeable to water. Above this layer they will install a synthetic membrane like the plastic that lines the bottom of the landfill. High-density polyethylene is a popular landfill liner because it consists of strings of polyethylene molecules (CH2-CH2) thousands of carbon atoms long. The extreme length and stability of polyethylene’s carbon backbone allows the molecules to pack tightly together like a crystal and so resist the assault of corrosive landfill leachate. However, this extreme density comes at the expense of flexibility. HDPE’s brittleness is not an issue at the bottom of the landfill, where the membrane lies on top of solid ground. But the landfill cover must be able to flex as the garbage beneath it decays and shifts in its bed.
A little chemical manipulation provides the answer: add hexene (C6H12) to the polyethylene. Hexene’s molecular structure prevents it from folding up into the neat, crystalline structure of the polyethylene, thus creating lumpy, disorganized patches in the polyethylene matrix. This extra elbowroom between the tightly packed carbon chains produces a more flexible, less dense polyethylene. By adding pigments and stabilizers to the polyethylene, chemists can ensure that the membrane lasts upwards of 200 years.
To prevent water from pooling onto--and possibly breaking--the landfill cover, Live Oak engineers will install a drainage net just above the surface membrane. Rainwater seeping into this open grid will flow to the landfill’s edge. The drainage net, in turn, will be covered with a synthetic textile, over which will be heaped two feet of soil, seeded with grass. The entire cover system, from compacted clay to top soil, is designed to achieve an impermeability of a ten millionth of a cubic centimeter of water--a leakage rate of less than 147 gallons per acre a year.
When the landfill cover is finished, the top and bottom liners will be sealed together like a gigantic plastic bag. Post-closure maintenance, such as sealing up fractures or repairing leaks, will be costly. Although Waste Management is reluctant to confirm details concerning revenue, the cost of constructing and operating Live Oak-- including buying the land and converting it into a recreation area--will reportedly total some $400,000 an acre. That’s about $75 million, and it sounds staggering until one calculates revenues for the 188-acre landfill. With tipping fees of $32 to $35 a ton, that’s as much as $157,000 a day.
In reality, few landfill parks in this country are as well- financed and state-of-the-art as Live Oak. The typical scenario has been that of a cash-poor local government trying to convert an old, unregulated dump into landfill that can be used as a park. All too often, county engineers simply dump dirt on the landfill, plant some grass, and say here’s your recreation area, says Morton Barlaz, an environmental engineer at North Carolina State University. Without a properly engineered cover and a methane collection system, you’re going to have big problems.
Stories like these strike fear in the hearts of municipal attorneys. The idea of putting people on a landfill makes me shudder, says Ann Moore, an assistant city attorney for Chula Vista, California. As a land-use expert, Moore has followed the landfill conversion trend for many years. It was real fashionable a while back, and now a lot of cities are experiencing big problems, she says. Adds Barlaz, There’s always the risk that local governments won’t have money for the high maintenance these parks demand. When budgets get cut, parks are the first to go.
Others argue that active use may simply be incompatible with the idea of keeping landfills sealed tight within a dry tomb of plastic. Bill Sheehan, director of environmental biology for a landfill engineering company in Lawrenceville, Georgia, warns that even the most durable synthetic covers are likely to be punctured by plant or tree roots. The irrigation needed to keep parks green is another bugaboo. If the added water penetrates the landfill cover, it can overload leachate collection systems. This is a particular problem when irrigation pipes break under the strain of uneven settlement, as they often do.
Still, with dumps filling and open space dwindling, landfill conversions are probably here to stay. And waste disposal companies can point to several thriving examples. Take Mount Trashmore Park in Virginia Beach. Created in 1973 from a 68-foot-high, 650,000-ton garbage heap, the park is now one of the area’s most popular--especially with young children, who flock to the colossal wooden playground at its base. Another success is a 600-acre resort in Industry Hills, California, home of two championship golf courses. Methane from the underlying landfill is used to heat two Olympic-size pools and a hotel laundry in the adjacent Sheraton Conference Center. Then there’s Riverview Highlands, a ski and golf resort built on a 600-acre garbage mound south of Detroit.
Some communities, in fact, have apparently overcome their reluctance and are ready to embrace their trash wholeheartedly. With nearly 6 million tons of refuse already in place, Virginia Beach is now drawing up plans for another landfill-based park to keep Mount Trashmore company--one more than twice as high and 18 times as voluminous as the original. After its makeover, the landfill will be dubbed City View Park, for an obvious reason--from its crest you will be able to see all there is to see. It’s the biggest thing in town.
