Engineers design modern MSW landfills mindful of two philosophies: maximizing landfill capacity to save on disposal costs and envisioning an end use that's acceptable to the community. If the end use increases landfill and nearby real estate values, so much the better.

By Anne Magnuson

"Obviously, to maximize capacity you must meet requirements for a liner and leachate system," says David Deans, who cited the above philosophies to MSW Management. "You have to maximize the waste you place above the liner and leachate system, so costs go down dramatically with the more tons of waste you put on top." This can result in the final construction of a fairly high pyramid and very steep sideslopes, creating engineering challenges for slope stability, erosion control, and even truck access. A steep landfill mound is not especially conducive to many end uses, says Deans, senior vice president with Post, Buckley, Schuh and Jernigan in Winter Park, FL.

The second philosophy, continues Deans, is to choose your end use in the design stage so as to come up with an appropriate final grade plan. He gives as an example the owners of the Toytown Landfill in Pinellas County, FL, who decided ahead of time to shape the waste in such a way as to accommodate a preplanned 18-hole golf course.

Another concern is aesthetics, says Deans. He recommends that the solid waste authority or department seek large tracts of land for a landfill in order to surround the huge waste piles with visual buffers from adjoining property owners. Otherwise, as occurs while driving south on Florida's Interstate 95, a poor scenic impact ensues as you navigate from landfill to landfill. Notice the Indian River Landfill, the St. Lucie, the Palm Beach County site, and more. "You can see them. Florida is flat."

The control of landfill gas is of utmost importance when designing a recreational facility on a former landfill site. MSW Management learned of an accident caused by exploding methane at a municipal landfill park in Southeast US. A golf course and fields for softball and soccer overlie the closed landfill with portions actively flared at the site's perimeter. The explosion was caused by migration of methane into a cavity beneath a concrete slab under tall lights installed for nighttime soccer practice. When the soccer ball landed in the unexpected hole, the person retrieving the ball lit a lighter to increase visibility. According to MSW's source, the gas exploded like a flash, which blew the individual out of the hole and burned the person's throat and lungs. The injured person is all right now, but it was a bad and scary accident.

The flashing explosion was not the result of inadequate venting or erosion, according to MSW's sources. Instead, they contend it was caused by settlement under the slab that lay under the tall light poles. The slab was located over piles sunk deep into the earth for stability. "After the accident, we figured it out and corrected it. What we found is that you have to make sure you don't have areas where gas can collect in a confined space." This is another reason maintenance is important in conjunction with walking and inspecting the park grounds.

Because of the potential for settlement, erosion, and related concerns regarding landfill gas, Deans argues that a flare is much better for public parks than passive venting. He emphasizes that methane at parks should be either flared or utilized to generate electricity. Further, he recommends evaluating the age of the waste when planning for gas control. The landfill may be allowed to sit for a couple of years before constructing the park since the greatest rate of settlement occurs at the beginning of the landfill's closure life. Deans prefers a cap containing a synthetic liner to prevent the gas from escaping. Careful maintenance, including walking across the entire site to inspect it for cracks and fissures, remains important. For golf courses, Deans suggests that designers use flexible irrigation pipe similar to hose rather than stiff plastic pipe, which might crack as the landfill settles. "It's a little more expensive to install, but you don't have to repair it as much."

As for leachate, Deans notes that to date there is no evidence that the Subtitle D liner and leachate systems are not effective. Yet how happy is Deans with the 30-year federal monitoring requirement for closed MSW landfills? He suggests monitoring for 30 years might become unnecessary. "Of course, you can't prove a negative. If the groundwater is clean, it's clean. The assumption is that if the groundwater comes up dirty, 'Well, dummy, you missed it.'" Deans believes some day engineers will know how to protect drinking-water supplies in such a way that groundwater monitoring will not be needed since engineers now defensively protect groundwater supplies from storage tanks, midnight dumpers, and unexpected MSW landfill contaminants. The present system of monitoring landfills gives enough security, he adds, until something in the future provides a better answer.

Fear of explosion is one reason why so many closed landfills collect all the gas and flare it, treat it to sell as natural gas, or utilize it to generate electricity. A postclosure golf establishment will contain an active venting system to control the methane at the former Holmes Road Landfill in Houston, TX. It has not yet been decided whether to flare it or to install a gas-to-energy facility, says Bill Schlafer, senior project manager for URS Greiner Woodward Clyde in Houston. "I would say it is a 50/50 shot they are going to flare it off."

This 450-ac. site owned by Browning-Ferris Industries (BFI) in Houston was constructed in stages starting in the 1960s. It stopped accepting waste in the late 1970s and began closure monitoring in 1994 in line with Texas regulations. Two golf courses, one an 18-hole link course and the other an 18-hole lakeside facility, will be constructed by a private company that will put up the cash, run the operation, and receive the profits.

Before conceiving the golf course idea, BFI hired Schlafer's firm to prepare a conceptual plan of potential uses for the Holmes Road site. Four viable possibilities emerged: (1) continual postclosure maintenance, (2) limited waste consolidation involving landfill mining of a small part of the site, (3) maximum waste consolidation to reclaim real estate, and (4) maximum development with commercial/industrial/park development on the northern portion and commercial development on the southern part, an option that included the idea of creating a golf course and a conservation center. Bisecting the overall site between north and south is a fee strip owned by a power company for easement purposes. The landfill acreage has been certified as a brownfield by the City of Houston, making the site eligible for special environmental funding. The area surrounding the landfill property is lightly developed with some industrial businesses, a small low-income subdivision near one corner of the landfill lands, and lots of open space.

Schlafer says locations for a good golf environment must meet two criteria: elevation changes and the presence of water. Because of the way the Holmes Road Landfill developed, this Houston site has both. The property is unusual in that it contains 14 landfill cells with progressively higher mounds from north to south.

The mounds become larger the farther south they were constructed because of the growing appreciation for the real estate value as the site developed. "Just top it off and move it over" was the original idea, but the philosophy changed over the years. Federal and state regulations reflected a growing national interest in saving landfill capacity, thus driving up landfill disposal costs. The highest of the Houston landfill mounds rises 60-80 ft., estimates Schlafer. This is the second highest point in Harris County; the highest being another landfill. Says Schlafer, "This part of Texas is pretty much flat."

Contained in the southern portion are a number of lakes that originally were borrow pits to supply the daily cover and the final cap with onsite soil. Schlafer says the borrow pits have filled with water from the landfill stormwater runoff system. Between the landfill and the housing subdivision is one drainage channel that, like others at the landfill, eventually meanders to offsite bayous. Of the 450 Holmes Road acres, 275 actually received waste and 60 have been turned into lakes.

Because of the configuration of the 14 Holmes Road cells, the original roadways for accepting waste and maintaining the site have been turned into park roads, most constructed on solid ground. A clubhouse, a golf cart barn, and a maintenance facility also will stand on waste-free ground.

Dyer Park, formerly Dyer Boulevard Landfill, features softball, baseball and soccer fields, volleyball and basketball courts, various trails, and a playground.

Another unusual landfill configuration---this one in the equally flat topography of southeast Florida---lent itself to the creation of a recreational facility. Dyer Park, formerly the Dyer Boulevard Landfill, opened in 1997 featuring baseball and softball fields, three soccer fields, two volleyball courts, four basketball courts, a 3.2-mi. competition mountain bike trail, a 3.4-mi. equestrian trail, a model-airplane runway, a 4.12-mi. bike and jogging path, and a children's playground. "Dyer Park is unique because we had a lot of open land between the landfill cells, which allowed us to build structures," says Project Manager Brent Headberg with the Department of Engineering and Public Works at Palm Beach County's Solid Waste Authority (SWA). Several landfill closures and park constructions just consist of bicycle trails and nonstructural-type entities, notes Headberg. "But we have the ability to build baseball diamonds, bathroom facilities, picnic pavilions, and things like that. It is good, solid ground."

The Dyer landfill containing MSW and construction/demolition debris operated in the 1970s and '80s. It closed in 1990 and was capped with PVC liner and soil. An active gas collection system installed in 1990 captures and flares the methane to prevent hazardous gas buildup and odors. As early as 1988, the SWA began foresting the site's perimeter and other open areas with 12,000 indigenous trees and 10,000 grasses to provide a habitat for birds and other wildlife. These scenic green areas give the site an old Florida feel. Now the bicycle path for traditional cycling and the horseback-riding paths stretch along a 6- to 8-ft.-high berm along this forested perimeter. The berm is 10-12 ft. wide, and beyond it one can see interconnecting, runoff-filled lakes that enter the canal system of Palm Beach County. Headberg says all the rainwater from the landfill flows into stormwater ponds that are bled off by a control structure, allowing water to spill over into the lakes when it rises. The park's soccer fields are designed to retain rainwater in the event of a 100-year flood.

A softball game at Dyer Park.

The SWA continues to be responsible for stormwater management, gas control, and leachate disposal, which is pumped off-site to a 1,500-ac. authority complex across the Florida Turnpike from Dyer Park. The leachate is deep-well injected along with the leachate from the authority's active North County Landfill. The leachate is injected several thousand feet into the ground in compliance with Florida regulations.

Injection of leachate into very deep wells is allowed at two Florida landfills---one in Charlotte County and one in Palm Beach County---according to Joseph Haberfeld, professional geologist with the Florida Department of Environmental Protection. "The rationale for deep injection wells is to get rid of unwanted, nonhazardous fluid," he explains. If the leachate is hazardous, it is treated first. The leachate is usually injected into a confined, salt-water aquifer in line with regulated construction standards so that it cannot enter usable groundwater or any aquifer the department is charged to protect. The geological strata above the salt-water aquifer may be 200-2,000 ft. thick. Laterally, the confining geological structure is many, many, many miles wide, covering counties, Haberfeld says.

Recycled materials were used as often as possible throughout Dyer Park for park benches, picnic tables, and trash receptacles. Playground equipment is composed of recycled plastics, and roadways and some paths are paved with glassphalt. The mountain bike trail consists of sand and crushed rock. "The rougher the road, the better they like it," says Headberg. The roadways and traditional bike trail are located in flat areas without fill, so settlement is not a problem. Some settlement has occurred at the glassphalt model-airplane runway. "It does have a few dips in it, but this has not bothered the model-plane flyers."

A mountain bike competition at Dyer Park, host to a wide variety of recreational activiites.

The SWA complex across the turnpike contains the active landfill, a burn plant that processes solid waste with its ash deposited in the nearby active fill, SWA administrative buildings, and an SWA truck and truck maintenance facility. At present, methane is flared both at Dyer Park and the new landfill. Headberg says piping the methane from Dyer Park beneath the turnpike to a proposed gas-to-energy plant is now under consideration.

The well-known Shoreline at Mountain View, a 750-ac. recreational and wildlife area on San Francisco Bay, CA, is of unusual interest because it represents the best sort of preplanning to turn an undesirable property into a showcase. What started out as a location containing a hog farm, auto-wrecking establishments, and a sanitary sewage treatment plant and its sludge-drying beds is now highly valued real estate.

The decision was made in the 1970s, with the help of an environmental grant, to preserve open space on the bay and construct a regional MSW landfill to serve San Francisco, Sunnyvale, Los Altos, and several other cities, says Senior Civil Engineer Mark Rogge with the Mountain View Department of Public Works. "Yes, absolutely, we designed the landfill for its end use." A master plan was prepared around 1980 to point out the future location of a sailing lake, a golf course, roadways, levees, wetlands, and specific structures. The 461-ac. landfill was laid out as a series of waste-filled cells and a series of engineered landfilled cells; the latter where buildings would be erected. Perimeter levees would surround the structures and site with roadways to be constructed on top of the levees.

Project Manager Tim Raibley, vice president of Brown, Vence & Associates in Roseville, CA, enumerates the amenities at Shoreline: a 10,000-ft., nationally acclaimed, open-air amphitheater; an 18-hole golf course; a 50-ac., salt-water sailing lake and boathouse; four freshwater ponds; two tidal estuaries; a wildlife habitat for the endangered burrowing owl, brown pelican, California least tern, California clapper rail, and others; a clubhouse restaurant near the golf course; a fine-dining restaurant; the oldest house in Mountain View moved to the park to serve as a museum; and biking and jogging trails.

Located on the site are 226 ac. of wetlands, including two streams already present on the site and the lake and ponds used to irrigate the golf course; 100 ac. of engineered fill for building pads and levees; and 87 ac. later set aside for commercial development when the city realized real estate values were rising. The public took to the land well and nearby development increased. Rogge says, "We actually separated out the 87 acres originally planned for landfill as the property became valuable. We started getting high-class businesses in the area. The time for the landfill had ended."

Now the city leases land to Silicone Graphics Inc. for their corporate headquarters. And some of the land is leased for the Shoreline Amphitheater. The landfill gas-to-energy plant, which operated for 15 years, was shut down to accommodate a large nearby company that did not want the gas system located adjacent to its property. "They were going to give us a lot more lease revenues than we would achieve from continuing the electrical generation plant."

Early on, some of the landfill gas was cleaned up with molecular sieves and injected into the local utility's natural gas. This process, also ongoing for about 15 years, has been discontinued as well. Now the methane is flared at a station in the middle of the Mountain View park. "It burns very clean, and you can't really notice it behind a nice decorative masonry block wall," Rogge adds.

Settlement has not been a problem under structures at Shoreline because of the engineered fill beneath them, but it has been an issue under some parking lots that extend over the landfill. "These lots needed to be graded very often right after the landfill closed," says Rogge. "Now it's been several years and grading is not nearly so often. Eventually it will stabilize. It gets better and better every year."

The 50-ac. lake fed from San Francisco Bay was originally the borrow pit for clay used in the bottom liner, the levees, and the final cap. The depth of the soil cap varies from place to place. The minimum was 3 ft. at first, but it was later increased to 5 additional ft.---under parking lots, for example. Cap depth is greater where trees grow. Rogge says drought-resistant trees with shallow roots, many of them Australian varieties, were selected. He adds, "When you go out into the park, it is difficult to tell which part is landfill and which part is not, unless you know.

"I think one of the things that made Shoreline a success was getting rid of the idea, 'Well, it's pretty good for a landfill.' We adopted the policy that the site needs to be as excellent as if it were the best country club in the country." Rogge believes landfill park designers need to think big and think high quality. "Don't ever stand behind the excuse that it's pretty good for a landfill. Think always of the end use."

The goal of Shoreline, says Rogge, was to cover landfill costs and provide benefit to the community. Costs included construction, all the environmental concerns, capping the landfill, and postclosure monitoring. "The goal was for the community to receive an enduring benefit," he adds. "And I think we have achieved our overall goal of the landfill paying for all its expenses. It has covered all its costs."

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