In the face of uncertainty and expense hampering the development of new landfills, today's landfill operators are investigating and implementing a family of measures to conserve airspace and thereby extend landfill life.

By Charles D. Bader

This is an uncertain period for the development of new landfills. Compounding what has become a lengthy, expensive, and uncertain process of siting, permitting, and constructing new landfills are governmental delays in approving regulations and legislation that could significantly impact the design and economic viability of new landfills. For one thing, the update of Subtitle D regulations had still not been issued at the time of this writing. As pointed out by Bob Gardner, senior vice president of SCS Engineers's solid waste operations in Tampa, FL, "It has been 12 years since Subtitle D rules were last updated, and technology has subsequently been developed in ways that weren't envisioned in 1991. These developments have pushed the envelope of possible landfill design as a number of states have shown. The update is long overdue; it should be remembered that after the new federal rules are issued, the states have to modify their rules to conform, and this process could take as much as a year to complete."

At the same time, needed government support for landfill gas recovery still lingers in Congress. Jean Bogner, president of Landfills + Inc. of Wheaton, IL, asserts that government support will be critical to the full development of the landfill gas recovery industry, which has such important implications for new landfills, particularly anaerobic bioreactor landfills. Holly Smithson, SWANA's director of government affairs, estimates that 1.76 cents per kWh is the minimum support needed to make gas recovery sufficiently viable to attract investors.

"Both houses of Congress are addressing this issue," she says. "The House has extended Section 29 covering nonconventional fuels in general and has added Section 45, which just covers electric generating projects. The Senate has yet to complete its energy package. However, the prospects of getting landfill gas qualified under Section 45 of the final bill are fairly good given the administration mantra, 'Increase domestic energy production.' Everyone seems sold on the technology."

In the meantime, though, the gas recovery industry languishes at the same size it has been for the last 15 years. The only real trend that Mike Michels, division vice president with EMCON/OWT Inc., sees is utilities' interest in using landfill gas projects as an offset to their greenhouse gas emission costs. "Because methane is 21 times more potent than greenhouse gases, some utilities now think that it would be cheaper to have a gas collection and flare system in a small closed landfill than to upgrade their smokestack cleaning devices," Michels says. "Every bit of methane that is destroyed in this way can be used by the utility." And perhaps in some situations, it might be feasible to capture rather than flare the gas and use microturbines to provide power for a local business.

Emphasis on Conserving Airspace

With all this delay and uncertainty, the landfill industry has been shifting its emphasis to conserving airspace at existing landfills in order to extend landfill life and increase the amount of waste they can accept prior to closure. The payoff from saving landfill airspace can be enormous. David Lowry, landfill manager of the Olinda-Alpha Landfill in Brea, CA, says his 7,000-tpd landfill is conserving 106,000 yd.³/yr. This additional capacity, if used to accept more waste per day, would yield a net present value of increased gate income of more than $10 million before its projected closure date of December 2013. And huge savings is possible with smaller landfills too. Tony Knight of New Waste Concepts Inc. in Erie, MI, has calculated that for a landfill with an average working face of just 4,000 ft.², the daily soil cover of 11-in. depth totals 38,519 yd.³/yr. That loss of airspace with nonrevenue-producing soil has an annual cost of lost revenue of $397,800 and will cut the remaining life of the landfill by 44%.

Clearly, with the difficulty in siting, permitting, and constructing landfills today, more and more landfill operators are recognizing that conservation of airspace can be a big payoff strategy. And they are going about conserving airspace in four principal ways:

1. Accelerated decomposition through bioreactive processes
2. Greater compaction of both waste and cover
3. New approaches to filling
4. Using alternative daily covers (ADCs) instead of just soil

Bioreactor Landfills

SWANA has defined a bioreactor landfill as "any permitted Subtitle D landfill or landfill cell where liquid or air is injected in a controlled fashion into the waste mass in order to accelerate or enhance biostabilization of the waste." Although there have been a number of research and pilot projects, full-scale bioreactor landfills have yet to be out into operation. Both to utilize leachate and reduce the amount of liquid that would be needed, most of the anaerobic bioreactor pilot projects rely on leachate recirculation. Under current Subtitle D regulations, leachate recirculation is not permitted if a liner other than the prescribed (and overdesigned) Subtitle D liner is used. However, this has not stopped the research and design on leachate recirculation. Several states and EPA itself (under its Excel program) have granted waivers permitting the use of alternative liners to permit the research to go forward. And the eagerly awaited update of Subtitle D is expected to approve less expensive alternative liners.

"An anaerobic bioreactor accelerates the decomposition and stabilization of waste," explains Abdul Mulla Saleh of Camp Dresser & McKee in Tampa, FL. "At a minimum, leachate or water is injected into the bioreactor to stimulate the natural biodegradation process. Bioreactors often need other liquids, such as stormwater, wastewater, and wastewater treatment plant sludge, to supplement leachate in order to enhance the microbiological process by purposeful control of the moisture content. This differs from a landfill that simply recirculates leachate for liquids management. Landfills that simply recirculate leachate may not necessarily operate as optimized bioreactors.

"Moisture content is the single most important factor that promotes the accelerated decomposition. The bioreactor technology relies on maintaining optimal moisture content near field capacity - ranging between 35% and 65% based on site-specific conditions - and adds liquids when it is necessary to maintain that percentage. The moisture content, combined with the biological reaction of naturally occurring microbes, decomposes the waste. The microbes can be either aerobic or anaerobic. A side effect of the bioreactor is that it produces landfill gas, such as methane, in an anaerobic unit at an earlier stage in the landfill's life and at a much higher rate of generation than traditional landfills.

"Decomposition and biological stabilization of the waste in a bioreactor landfill can occur in a much shorter time frame than occurs in a traditional 'dry tomb' landfill, providing a potential decrease in long-term environmental risks and landfill operating and postclosure costs. Potential advantages of bioreactors include a 15% to 30% gain in landfill space due to a decrease in density of the waste mass."

This gain in airspace from landfill-waste biodegradation and settlement in a bioreactor landfill was demonstrated in a 9,000-ton cell in Yolo County, CA, under the direction of Ramin Yazdani, assistant director of the Yolo Division of Integrated Waste Management and the driving force behind the county's multiyear development program. "Figure 1 graphs the results of [the pilot project's] operation," Yazdani says. "Based on these data, which we collected over [a period of] almost four years, the time it takes a bioreactor landfill to stabilize (five to 10 years) might be 30 years less than current landfill expectations."

Bryan Stirrat, president of Bryan A. Stirrat & Associates of Diamond Bar, CA, favors a very different approach to the design and operation of a bioreactor landfill. "The typical anaerobic bioreactor landfill design calls for injection wells or pipes that drop water into the waste," he points out. "Initially that works well as the liquid takes about a month or so to percolate to the bottom of the waste. Thereafter, though, the liquid has found its path and may well flow to the bottom in a matter of minutes. Therefore you have to keep changing your injection system or move your pipes. You use a lot of water that way, and potable water is a precious commodity in arid areas, such as the Southwest.

"I believe you must wet the waste each day as you place it in the cell. Using a water truck and a sprayer gets the water into the waste economically, and it increases your ability to compact each day's waste. Even more important, MSW can absorb a large amount of liquid - up to 50% of its weight, in fact. Compacting will squeeze some of this water out, but most of it will be retained. It will take a long time for leachate to build up because the waste will absorb so much water and retain that water while it contributes to the bioreaction of the waste."

Greater Compaction

Waste compaction has taken on a new dimension with the introduction of much larger, more powerful, and more precise landfill compactors. For example, Caterpillar's 836G landfill compactor is a huge machine, weighing close to 60 tons and powered by a 525-hp engine. Lowry has two of these behemoths at the Olinda-Alpha Landfill. "We push up the trash with D10 dozers," he explains, "and the compactors compact the trash in place at an average compaction of 133 pounds per square yard. This gives a flat compacted area for the greenwaste we use for daily cover. The dozers fluff the process screen to make sure the face is completely covered by greenwaste, and then the compactors go back over it to compact the greenwaste in too."

Lowry has his compactors - indeed all his landfill vehicles - equipped with the Caterpillar/Trimble global positioning system (GPS) based Computer-Aided Earthmoving System (CAES). Using positioning data from the GPS, the differential CAES provides extremely accurate real-time monitoring that enables precision control, monitoring, and recording of grades/slopes and compaction passes. According to Caterpillar's Dennis Greene, the display in the compactor's cab provides a precise comparison of the current surface (measured by GPS as the machine traverses the terrain) versus the desired (design) surface along the compactor's axis - both in front and in back of the compactor. "Several design profiles can be displayed simultaneously; for example, 'top of trash' and 'top of soil.' The profiles are color-coded for clarity and can include additional below-grade surfaces, such as liner location.

"For compactors, the CAES display plan view shows compaction passes, precisely indicating where the appropriate number of passes have been completed. If desired, a 'truck-lift' feature can also be superimposed on the plan view. This composite view indicates areas of a new lift that have been spread with thickness such that full-depth compaction will not be achieved. Both the compactor and the dozer systems also include an 'inclined plane' feature, which allows an operator to create a slope between two points for grade matching or a plane through a single point with whatever compound slopes are desired."

"This system has made a 100% difference in our compaction," Lowry says. "We get airspace savings not just because of the force of the compaction per yard of waste. We also get it from the system's ability to carry an absolutely correct grade in both the trash and the final processed greenwaste that goes on top. Because the CAES is capable of carrying multiple entries in its unit, you can set that unit to carry any grade you want. Once the trash is in place according to the precise data given, the operator simply switches the display screen to determine the cover thickness that has to go down. Therefore we don't lose any airspace because of excess dirt or excess greenwaste.

"When we cover the trash at night, the greenwaste ADC goes on the active slope. The top deck still requires dirt. If we didn't have a correct bottom grade, we would either have to add or delete dirt when we finish out at night. In most cases, it would be to add. In reality, operators in this situation add as much as 18 inches of dirt on top. Dirt in is dirt gone, and it is taking up airspace only because the bottom grade wasn't put in correctly. Since using the CAES, we're getting correct grades. We have verified this by digging cross-sectional trenches in the waste to see where the dirt line is, and we have found that the dirt thickness is a consistent 7 to 8 inches deep over the entire deck."

Actually this precision filling and compacting did more than save airspace at Olinda-Alpha. Several years ago, Lowry calculated that his soil reserve would be depleted by 2010, some three and a half years before the scheduled closing of the landfill in December 2013. Based on then-current usage rates, this projected a cost of $15.5 million to import the needed soil. Today Olinda-Alpha's usage of soil has been reduced by such an extent that now-current soil reserves are projected to be adequate through 2013 without importing any additional soil.

New Approaches to Filling

A similar approach was advanced in the May/June 2002 issue of MSW Management by Thomas M. Yanoschak of Camp Dresser & McKee's Raleigh, NC, office. In an article titled "Pile It Higher and Deeper: Increasing Landfill Capacity Using Mechanically Stabilized Earth Walls," he postulates a 1,000- x 1,000-ft. landfill with 3:1 slopes and a height of 143 ft. In the normal configuration, this landfill, which has a 55-ft.-wide perimeter berm, was calculated to have a maximum capacity of 2.4 million yd.³ By building a mechanically stabilized earth wall with a 1:3 outer slope and extending it an additional 30 ft. above the existing perimeter berm (even though that would require a wedge of structural fill within the limits of the waste), he calculated that the net capacity of this 1,000- x 1,000-ft. landfill would be increased by 45% to 3.4 million yd.³

Using ADC Materials

"If you spent all that money in siting and building a landfill, why would you want to fill it up by adding 6 or more inches of dirt for daily cover 312 times each year?" rhetorically asks Chris Campman, manager of solid waste at Gannett Fleming in Valley Forge, PA. "There are various different materials on the market that will do just as good a daily-cover job as soil but won't take up nearly as much space in a landfill. Particularly at sites that are dirt-poor, these ADC materials are competitive in cost to soil, and they use up significantly less landfill airspace. I'm referring to foam, slurry, and tarp covers."

Foam

According to Sales Manager Rebekah Gormish of Rusmar Inc. in West Chester, PA, long-duration foam forms a mechanical barrier that is independent of the waste. "Our AC-600 foams," she says, "are water-based, nonhardening foams that can be applied during excavation and for overnight or weekend coverage to prevent emissions. The foam is made by mixing chemicals and waters automatically at the site and then injecting compressed air to apply it using a pneumatic foam unit. The foam is applied via a hose line to form a 3- to 6-inch blanket with the consistency of shaving cream. It occupies no airspace when it is covered with waste the next day."

Rusmar supplies the product, the storage/dilution system, and the application equipment on a turnkey basis. The application equipment is available either as a trailer-mounted unit or as a self-propelled unit integrated with a Caterpillar vehicle. The units use a unique foam manifold system that distributes the foam onto the waste in a bidirectional manner. When attached to the trailing edge of a vehicle, the manifold directs the foam downward in two distinct streams that overlap slightly, leaving a uniform covering in a 12-ft. swath. Only one worker is needed for the application.

"Rusmar does not have a 'typical' pricing structure," Gormish says. "Each landfill quote is conceived individually, based on projected usage, equipment needs, distance, and specific site conditions. However, each site ends up paying between 4 cents and 6 cents per square foot - all inclusive (equipment and foam concentrate, including freight, service, and maintenance) - with no capital investment required. We cannot include landfill labor in the cost analysis, but our customers tell us that our system is the least costly in that respect. We also believe that our system provides the highest degree of operator safety, odor control, reliability, bad-weather convenience, and finished appearance in the industry. Everyone agrees that these factors are part of the real cost, but each landfill values them differently."

Slurry

A similar approach has been developed by New Waste Concepts Inc. (NWCI) of Erie, MI. Its Proguard SB product for daily cover is a blend of polymers and recycled fibers that create a slurry when mixed with water or leachate. According to NWCI CEO Tony Knight, "Our slurry is biodegradable and, when sprayed over the working face of a landfill, forms a uniform one-eighth- to quarter-inch-thick encapsulating layer between the waste and the environment that will last for seven to 10 days. Thus, it provides a near-zero-volume cover that exceeds the requirements of daily soil without impacting the airspace."

Because of the viscosity of the slurry, hydroseeding sprayers cannot be used to apply it. Instead, operators buy or lease the ConCover All Purpose Sprayer (CAPS) that NWCI developed for this purpose. Thus, although the cost of the Proguard SB works out to be 1.8 cents/ft.², application costs and other factors must be included to determine the true cost of applied slurry.

"We did a detailed cost analysis of the application of Proguard SB on a landfill with a working face that averages 4,000 square feet," Knight says. "We included all relevant factors, including product cost, freight [600-mile delivery assumed], the amortized cost of the CAPS capital investment, maintenance, fuel, and application labor. These totaled $31,082 per year. The one variable cost that we segregated was [that] of water to be used as a blending agent. If an adequate water supply was readily available, we calculated that the total applied cost of the slurry was 2.5 cents per square foot. However, if that water has to be trucked in from any distance, the total cost of the slurry could rise significantly.

"We think that landfill operators in this situation should substitute leachate for at least some of the water needed to blend the slurry. Not only would this decrease their leachate disposal costs, but it would bring the total applied cost of our slurry down to 2.2 cents per square foot."

This resulted in an annual savings of $12,910 of fully loaded operational costs of applying the slurry instead of 11 in. of soil cover (assuming no soil had to be purchased, just stockpiled and applied). That savings was dwarfed by the net airspace savings, which Knight calculated to be $365,000 a year. Moreover, this saving of airspace would increase the life of this maturing 50,000-tpy landfill from a projected 2.82 years to five years.

Tarpaulins

Tarps are widely used for daily cover, primarily because they can be removed each morning and replaced at the end of the day. Hence, they do not reduce the airspace whatsoever. According to Marlon Yarborough, marketing manager of Airspace Saver Daily Cover (ASDC) of Prairie View, LA, a tarp made of 20-mil Fabrene can easily last two years or more.

"Fabrene is a high-density woven polyethylene-coated fabric manufactured by Fabrene, Inc. that is heat welded together to the desired width," Yarborough says. "A series of high-tensile-strength [6,000-pound] polyester web straps are then sewn on top of the heat welds, as well as around the perimeter of the ASDC, for added strength. Steel D-rings are then sewn on to the ends of the straps approximately 2 feet from the edge.

"There are several ways landfill operators pull a tarp on and off a working face each day. A standard 48-foot by 50-foot tarp weighs only about 200 pounds, so two men, each at the corner of a leading edge of the tarp, can walk it on or off the working face in about 10 minutes. Larger landfills tend to use available onsite vehicles instead of manual means. They simply attach the D-rings to these vehicles and maneuver the cover on or off the working face. When moving the cover, it is best to raise the leading edge as high as possible. In fact, some facilities use a spreader-bar system attached to an excavator bucket to completely lift the cover into place. Reducing the amount of drag as much as possible will allow the ASDC to last longer."

The only recurring cost of the system is the tarp itself since it is reused day after day until it finally wears out. Yarborough says that 48 x 50 ft. costs about $1,200, should last two years (312 days for six-day-per-week operations), and can be manually pulled on in 10 minutes and off in the same amount of time by two people  (a total of 0.67 man-hour a day). Assuming a loaded labor rate of $22 per hour, the annual cost and the cost per square foot per day of using a tarp that size (2,400 ft.²) can be calculated as follows:

• Cost of Tarp per Year: $1,200 for 2 years = $600
• Cost of Labor per Year: 312 days x 0.67 x $22 = $4,599
• Total Cost per Year: $5,199
• Cost per Square Foot per Day = $5,199/2,400 ft.² for 312 days = $0.0069

Tarpomatic

One of Yarborough's customers is also probably one of his most formidable competitors. ASDC is the exclusive supplier of tarps to the Canton, OH, firm of Tarpomatic Inc. for its Automatic Tarping Machine (ATM). The ATM, which earned the 1997 Innovation of the Year award from Case Western Reserve, is a self-contained unit with spools that enables various types of earthmoving equipment to hydraulically roll out and roll up tarps of various sizes.

According to Tarpomatic, each ATM is custom-fitted to be lifted and transported by the blade of a dozer and offers quick and easy hookup. The product uses a hydraulic drive motor and engaging system to wind and unwind the spool with variable-speed control. Spools can be disconnected and reconnected to utilize one ATM with multiple spools. Controls are mounted in the cab of the dozer or compactor to give the operator control of the engine, height and tilt of the spool, and forward/reverse rolling. This allows for even tracking when winding and unwinding tarps on uneven terrain. The product is designed for 40-ft.-wide panels of various lengths. The spool is capable of holding three 40- x 100-ft. weighted tarps.

That is the configuration used at the Prima Deshecha Landfill in Orange County, CA. According to Public Information Officer Linda Hagthorp, the landfill keeps nine spools in stock, each carrying a 40- x 300-ft. roll of tarp. "Our Cat D94 dozer operator starts at the top of a slope and rolls out a tarp until it covers that day's working face," she says. "If the face is less than 300 feet long, the operator simply drops the spool at the end of the slope. To remove the tarp, the operator picks up the spool and winds up the tarp. Covering a 100-foot by 240-foot working face can be completed in 15 to 20 minutes; removing the tarp from that slope takes about 30 minutes. Our crews at both the Prima Deshecha and Frank R. Bowerman Landfills use the Tarpomatic every day, and they love it!"

Tarpomatic's ATM seems ideal for large landfills, and it appears to be quite cost-effective too, particularly because only one dozer and operator are required to spend less than an hour a day to cover and uncover the working face. According to a CD-ROM that the company distributes, an ATM with a 40-ft.-wide spool is priced at $57,237, which, amortized over five years, costs a landfill operator $31.36 a day (or $0.0042/ft.²) to provide cover for a 7,500-ft.² working face. The cost of three weighted tarps to cover that face is given as $11,076, and since it is assumed they will last three years, the cost per day would be just $10.12 (or $0.0013/ft.²). That's a total of just a $0.005/ft.²The dozer and its operator presumably are working at the landfill anyway, but Tarpomatic estimates that they would have to devote minutes a day covering and uncovering a 7,500-ft.² face. That adds another $0.0033/ft.², bringing the grand total to just $0.0085/ft.², and nobody has to walk on the waste pulling a tarp.

Costs of less than a penny per square foot would seem to be the lowest a landfill operator could expect to pay for ADC, but Lowry does even better. He pays nothing for it.

"California's Orange County has an oversupply of greenwaste," he explains. "And like all California counties, it can get a diversion credit for keeping greenwaste out of its landfills - except as daily cover. Therefore the MRF [material recovery facility] suppliers get paid for collecting and grinding up the greenwaste, and we can get it delivered to us here at Olinda-Alpha Landfill and pay nothing for it. And every ton we take both eases the county's greenwaste disposal problem and creates a diversion credit toward recycling goals.

"It's a true diversion, too, because greenwaste biodegrades over time. We have dug into our landfills and found that the 12 inches of greenwaste we had used for cover four years ago had been biodegraded down to less than 2 inches. So we can positively say that using greenwaste in this way does not significantly detract from our airspace."

As the Olinda-Alpha Landfill experience has clearly shown, conserving landfill airspace can and should be accomplished by a program of several different measures, including accelerated decomposition, greater compaction, new approaches (some of them automated) to filling and grading, and ADC to replace as much soil cover as possible. Given the lengthy, expensive, and politically difficult nature of permitting and constructing new landfills today, it should come as no surprise that more and more landfill owners and operators are investigating and implementing measures to conserve airspace and thereby materially extend the life of their landfills.

Author Charles D. Bader is with Dateline II Communications in Los Angeles, CA.

MSW - September/October 2003