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In the landfill business, success relies on the same old issue: airspace management—which in turn still comes down to the basic process of increasing compaction and decreasing soil use. By Neal Bolton Why—with so much industry agreement on the merits of compaction and soil minimization—do we still see such a wide range of perfaormance among landfills? Very often this is a management issue, with the operation reflecting the manager’s ability to understand and apply basic principles. In essence, there are three possible reasons for this:
The first two reasons imply no fault to the manager and can be easily corrected. The third is the result of more serious, underlying issues and may require serious corrective measures. Our discussion here will deal with reasons 1 and 2.
Identifying the Problem However, regardless of fault, the manager is still responsible. If your car’s speedometer was off by a factor of 10%, you could be speeding dangerously—though quite innocently—down the highway. Of course the fact you were oblivious to the problem will be pointless when a state trooper tags you with a radar gun. You might be asking, “How in the world could a landfill manager be unaware of poor compaction or excessive soil use?” It could be as simple as a poorly calibrated speedometer. The permit application, upon which the landfill’s permit is based, likely describes in detail the process of spreading and compacting trash. Without a doubt, the design engineer made some assumptions in regard to the landfill’s expected compaction rate. The engineer said it and the state approved it. It must be right. You have just passed speedometer checkpoint 1. In most states, landfill regulations are consistent in their requirement that waste be properly spread and compacted. If the inspection reports do not identify a problem with compaction, then it must be OK, huh? You have passed speedometer checkpoint 2. Many landfills provide some form of operator training. As a result, most operators are aware of the importance of compacting trash. So if the landfill has a compactor and the operators run the thing every day, then obviously the requirement for compaction is being met. All systems are go with speedometer checkpoint 3. Periodically, a surveying firm produces a topographic map of the landfill. One of the deliverables of this task is an analysis of the overall compaction density. If the surveyor isn’t careful to consider settlement of underlying waste, quantify inbound tonnage, factor in diverted material, identify the location of temporary stockpiles, account for the volume of soil imported for use as cover, and delineate the true limits of the current active fill area, the volume calculations could contain significant errors. But hey, if the number sounds reasonable, well…you’ve passed speedometer checkpoint 4. At many landfills, checkpoints 1 through 4 may appear satisfactory. In this manner a landfill can operate for years without ever knowing that its speedometer is out of whack. But you can bet that sooner or later somebody is going to pull out a radar gun and pull the trigger on the problem. It may appear when the 20-year lined area fills up in 12 years. Or it might be when excessive settlement causes the surface-drainage or gas-collection system to fail. At some point, that faulty “compaction” speedometer will be exposed. In a similar way, a manager can be fooled into thinking the cover-soil ratio is acceptable. As with compaction, placement of 6 inches of cover soil is described in the permit documents, included in the inspection reports, and recognized by all as integral to a sound operation. It’s likely the entire crew understands the goal of placing 6 inches of soil as daily cover. And the confidence and capabilities of a skilled operator can be impressive—especially when perched atop a 45-ton tractor! Thus, if the landfill’s top operators say they are using 6 inches of cover soil, then by golly they’re using 6 inches! Finally, if the periodic volume calculations don’t include a careful evaluation of excavated soil reconciled with load counts, everyone can be led to believe that all is well. One of the most common deceptions occurs when poor waste compaction is combined with excessive use of soil. The resulting overall airspace consumption rate can masquerade as good compaction and minimal soil use. Don’t bet your landfill’s life on a speedometer that hasn’t been properly calibrated. Savvy landfill managers recognize that good intentions are not enough to ensure excellence, nor will ignorance remove responsibility under the scrutiny of that radar gun. By now some landfill managers may be sweating. “OK,” one may admit, “maybe I could improve my operation, but how?” Good question. Here’s the answer: benchmark and verify. Dealing With the Problem Similarly, during a physical exam a doctor will check basic indicators, such as pulse, blood pressure, core temperature, and breath rate. These, too, are basic benchmarks, but when properly measured and understood they reveal volumes about an individual’s health. In the same way, operational benchmarks can reveal much about a landfill’s performance. Let’s take a look at some foundational benchmarks. Compaction Benchmarks In order to accurately measure waste density, all other material must be factored out. The list of other material often includes soil, rubble, landfill gas (LFG) pipes, gravel, and anything else that is not waste and takes up volume in the landfill. Similarly, the inbound-waste-tonnage figures must also be accurate. Common errors result from using a conversion factor to convert inbound loads from volume to weight, or by improperly accounting for recycled materials that are excluded from the wastestream. Alternative daily cover (ADC) made from processed greenwaste or woodwaste must also be accounted for. Sometimes this material is counted as waste and its weight and volume are included in the overall waste-density calculation. In other cases, it may be excluded. Either way, be sure to correctly handle the weights and volumes used to calculate waste density. When evaluated correctly, topographic maps can provide an accurate benchmark of waste density. On the downside, it may be a year or more before the results are available. And unfortunately, if compaction is poor or soil use excessive, lots of landfill airspace can be wasted in a year. A short-term compaction test is another compaction benchmark and can be used to provide much faster results. Performing a compaction test is as simple as surveying an area, placing waste in that area for a short period of time, resurveying to determine the volume filled. Of course the inbound tonnage must be recorded accurately. Getting a regulatory variance from placing cover soil during the test will eliminate the need to count loads of soil or factor out the volume it consumed. For tests that last longer than a few days, consider using some type of ADC that consumes little or no airspace. This type of density test can be very accurate, but keep in mind that it represents only a snapshot. In order to confirm that test results represent “typical” operations, it’s a good idea to track compactor hours during the test. This information, provided as a production rate (tons per compactor hour), ties directly to the results of the compaction test and can be monitored throughout the year. When conducting a compaction/density test, try to run it at the compactor’s average (annual) production rate. To calculate the compactor’s average production rate, simply divide last year’s tonnage by the number of compactor hours logged during the same time period. For example, if the landfill received 143,300 tons of waste last year, and the compactor worked 1,660 hours during that time period, its average production rate was 86 tons per hour. Target this production rate during your test. If you conduct a density test as described above and determine your compactor yields a density of 1,360 pounds per cubic yard at a production rate of 86 tons per hour, you have defined a solid, site-specific By maintaining this production rate (86 tons/hour) throughout the year, you can expect to achieve a waste density of 1,360 pounds per cubic yard. Please note: This is only an example, and every landfill should perform its own site-specific density test. The density achieved by a compactor will vary from site to site because of differences in the wastestream, operator technique, precipitation, and a host of other factors. But the compactor at a given landfill will generally produce consistent results if used at a constant production rate. The simplest and most meaningful compaction benchmark is tons per hour. Fortunately, it is also quite easy to track. As a crosscheck, you should calculate the landfill’s density on an annual basis as explained earlier using topographic maps. Some landfills also conduct periodic field surveys to check waste density. By carefully tracking waste density and comparing the results to historical benchmarks, you can track compactor performance. Soil Benchmarks And although the increasing use of ADC has helped mitigate this problem to some extent, it still remains the major issue at most landfills. Let me explain. Simply buying an ADC product and expecting it to save soil is like buying gym shoes and expecting they’ll get you into shape. To achieve either of those goals, a significant amount of planning and work is also necessary. Again, a common obstacle is a landfill manager simply not knowing there is a problem with excessive soil use. As discussed earlier, the landfill industry assumes daily cover to be 6 inches. This is only in theory. In practice it is much higher, and a simple 5-minute exercise can highlight such a problem. Measure that portion of the day’s cell that will receive daily cover soil. One quick way is to stand at the corner of the cell and use a laser range-finder to measure the width and length of the cell. Let’s say it is 4,000 square feet (30 feet by 50 feet). Simply count the number of loads of soil used to cover that area. Again, let’s assume it takes 12 loads with a scraper having an 18-cubic-yard payload. Multiply the number of loads (12) times the average payload (18 cubic yards) times 27. The result—5,832—is the number of cubic feet of soil used for cover. Finally, divide the volume of soil (5,832 cubic feet) by the surface area (4,000 square feet). The resulting answer (1.458 feet) is the average depth of cover soil placed. Multiplying by 12 converts it to inches. Thus the final result is 17.5 inches. Here’s the formula for this example: (loads x payload x 27) ÷ (length x width) x 12 = average depth of cover soil (in inches) Despite our industry’s target of 6 inches of daily cover, research conducted by our company indicates an average depth of 16 inches. So far we’ve limited our discussion to measuring how the landfill is currently performing. This is vital information. However, it doesn’t provide a means for improving performance—or even knowing if there is room to improve. It just tracks what’s happening. Here are some tips for getting the most out of your compaction and daily cover operation. Compaction Tips For example, different types of waste may require varying levels of compaction effort. Experienced machine operators know this and adjust accordingly. But one of the more subtle tricks is to manage moisture of various loads. If you crumpled a piece of paper into the smallest possible volume, you would see a significant level of compaction. But if you were to first wet the paper, it would compact even more. This occurs on a large scale at every landfill. Savvy operators will intentionally mix wet loads (e.g., packer trucks from restaurants or hotels) with paper-rich loads (office/commercial) to distribute that moisture to the paper…and ultimately achieve better density. Along that same line, another way to increase compaction is to rework the underlying waste before placement of the initial layer of trash in a new cell. Many landfills strip all available cover soil prior to constructing each day’s cell. This provides the obvious benefit of reusing soil. But this process also exposes, to some degree, the underlying waste—waste that in many cases has been in place and covered for weeks or months. Because of the heat and moisture often associated with decomposition, the moisture content of the paper and wood fibers may be higher and more evenly distributed. It’s in an ideal condition to be recompacted. By spending a few minutes running the compactor over this older waste, the operator may gain a significant amount of immediate compaction/consolidation. Initial steps for understanding the factors that affect compaction include identification and segregation of trash by type, using the appropriate size and type of machine. One should also follow standard procedures for the following:
Daily Cover Tips
These are some of the more common ways to minimize soil use, but there is another, perhaps more effective, way. My father told me a story about this guy who went to the doctor. While talking to the doctor, the guy touched his shoulder, winced, and said, “See, Doc, it hurts when I do that.” The doctor, a very practical fellow, told the man, “Then don’t do that.” Probably not a very helpful recommendation, but certainly it would be effective in eliminating the pain. If you want to reduce the amount of cover soil used at your landfill, why not simply stop using soil—at least to the extent possible? Follow the lead of other landfills and begin using ADC. There are many types of ADC, including tarps, film, spray-on materials, and a wide variety of waste-derived materials such as ground-up woodwaste or greenwaste. Lots of types, but they all provide the common benefit of reducing soil use and saving airspace. Regardless of which type you use, the important thing is that you do use ADC. A user of the Tarp Deployment System (TDS) manufactured by Mercer Motor Works affirms the importance of using ADC. Another prefers the Tarpomatic system. As it is with many landfill managers, the decision to use ADC—in these cases, tarps—was based on a desire to save airspace and decrease operating costs. One of the key factors, especially for landfills contemplating or just beginning to use ADC, is regulator buy-in. It’s vital that the folks who regulate your landfill understand why you want to use ADC, and how it may affect the operation. Here is a key point: Even though placement of 6 inches of daily cover is a prescriptive requirement, it is actually based on a performance standard. In other words, 6 inches of daily cover is intended to provide certain benefits:
Under close scrutiny, there is no form of ADC that provides the exact same performance that soil does. In fact, different soil types can also provide various levels of performance. The point is, different types of ADC may work better than others at a given landfill. Ease of use and cost savings are two important factors to consider when choosing ADC for your landfill. From an economic standpoint, there is little question that ADC saves money by saving airspace. In many cases, ADC makes economic sense by simply avoiding the cost of hauling and placing the soil. A final factor in the success of any ADC program is team buy-in. When we get right down to it, neither you nor I will be placing ADC. Rather it is the crew, working as a team, who will be doing it. And it’s the crew who will make or break the ADC program at your landfill. Brian Van Straten, operations manager at the Buena Vista Landfill in Watsonville, CA, offers a great example of this. After trying various types of ADC materials, he settled on Posi-Shell, a spray-on ADC. Van Straten notes, “By using ADC, our cover ratio has improved from a low of approximately 3:1 to as high as 8:1.” The Buena Vista Landfill also constructs horizontal daily cells that are stacked one on another to create an overall weekly cell. “We don’t count machine passes,” Van Straten explains, “we run our compactor all day.” By working the compactor on a flat cell and constantly trimming and compacting throughout the day, the landfill is achieving a waste density of 1,380 pounds per cubic yard. This is a great example of the benefits to be gained by compacting properly and using ADC. Of course it also speaks highly of the crew’s ability to improve efficiency through the use of innovative techniques and materials. At the Sarpy County Landfill in Springfield, NE, Landfill Manager Duwaine Brigman also touts the benefits of ADC. Like Buena Vista, Sarpy County made the decision to use Posi-Shell to save airspace and cut costs. Yet shortly after acquiring the Posi-Shell system, it received a surprise affirmation. “While excavating a portion of the landfill, we found soil, a lot more than we expected,” Brigman says. “In some cases, we found veins of soil up to 18 inches thick.” He goes on to explain, “Since using the Posi-Shell ADC system, we have had a tremendous reduction in soil use.” The benefits of using ADC are easy to understand, but for those with a creative mind, they can include more than cutting costs and saving soil. At the Sarpy County Landfill, the crew adds approximately 200 gallons of latex paint, extracted from its household hazardous waste facility, into every batch of ADC it runs through its Posi-Shell sprayer. Talk about diversion creativity! Improvements in compaction equipment and technique, along with innovations in the types and uses of ADC, promise great benefits for the landfill industry. But as the landfill crews at Buena Vista and Sarpy County already know, positive change requires teamwork and a willingness to try something new. Neal Bolton is a consultant specializing in landfill operations and management. MSW - November/December 2007
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