The value of space: Effective use of alternative daily cover materials to extend the life of landfills

Soil may not be an ideal landfill daily cover material as it can take up valuable space. Where landfill space is scarce and tipping fees can generate significant income, landfill managers may consider using space-saving alternatives. by Milton F. Knight Landfill operations and environmental agencies throughout developed countries require some form of cover material to be placed over the surface of all new waste that is deposited in the landfill at the end of each day. The general environmental objective of placing a cover daily is to control blowing litter, odours, fires and vectors (birds, insects and animals). Generally, the soil that might be excavated to create the cells where the waste is deposited is sometimes used as the cover material. However, since the soil must be used for other cover purposes such as interim or intermediate cover as well as final capping, often it must be stockpiled and stored. This leads to shortages of soil, and therefore a need for alternative materials. The alternative materials that exist in the UK and elsewhere throughout the world at present include: revenue-generating cover - waste materials approved by regulatory agencies slurry-based products - for example, ConCover or ProGuard materials films - biodegradable plastic films that remain in place after deployment tarps - fire-resistant nylon materials, usually with straps and chains netting - either a burlap or plastic, tightly woven mesh foams - sprayable urea-based foams (originating from fire-fighting foams). ‘Dishing the dirt’ on daily covers In the UK as well as in other EU member countries, soil (or dirt) is the Environment Agency’s prescriptive cover material, but it is worth asking the question whether this makes sense. When a landfill in these countries closes, 20%-30% of the material contained will be soil or dirt that has been used to for either daily cover, the creation of haul roads, or the construction of interior walls. In any country promoting alternative methods of disposal, a greater focus on recycling, and increased life of existing landfills, it is more than merely sensible to consider using ‘alternative daily cover materials’ (ADCM). In fact, their use should be integrated into the national solid waste strategy supported by the landfill industry and government. A case study exemplifies the economic rationale for making this change: Economic rationale: case study For a number of years, a 7000-tonne-per-day municipal landfill in the UK taking in largely household waste used dirt as its primary daily and intermediate cover material. The site manager and the municipality calculated that if they replaced dirt with an alternative daily cover material that took up substantially less space, the landfill would conserve over 106,000 cubic yards (81,042 m3) of space each year, assuming that the specific density of the waste would be 1 metric tonne per m3. The net present value of the increased gate income resulting from the increased capacity over a period of seven more years before final closure was more than £10 million (€1.5 million). The way to attain those savings is through the use of an ADCM that has little or no thickness. Government policy objectives Government policy in the UK and elsewhere would be well advised to emphasize and promote the use of ADCMs not only for extending the life of a landfill, but also for continuing the flow of tax revenue for those extended years. Alternative daily cover material used on a US landfill Click here to enlarge image Continuing with the UK landfill example, the additional tax revenues generated for the previously noted landfill would have been over £1.2 million (€1.8 million) for each remaining year of existence, based on a tax of £15 (€23) per tonne per year. Assuming that a landfill’s life continued for another eight years, the total increased tax revenue would have exceeded £8 million (€12 million). This added tax revenue would have been generated without building a new landfill, and only from utilizing the existing space more efficiently. Fitting as much waste into the landfill as you can The economic rule in deciding what to put into a landfill is to minimize soil and maximize the amount of waste. The operational rule is then to maximize the density of the waste per cubic metre or per cubic yard. If you increase the amount of waste that goes into each cubic metre, you can maximize the financial return for each cubic metre of space constructed. Maximizing density is impacted by several factors: moisture content of the waste (wet waste compacts better) the type of waste (some construction waste does not compact well) weather and local climate operational factors such as the weight of a compactor, the diameter and width of the compacting wheels, and the number of times the compactor goes over the waste how lifts (working-face width, length and depth) are constructed (horizontal lifts generally give you better compaction). Lifts are the dimensional depiction of the new material going into the landfill each day. The lift can be described as a thin, large, flattened rectangular box, or a thicker and smaller top surface area rectangular box. Unfortunately not all of the above factors are within the control of the landfill operator. Three of the factors are in the operators’ control: buying the compacting equipment, choosing the daily cover, and the engineering of the placement, thickness and width of the lifts. What is used as an ADCM and the size of the surface area of the lift have a big impact on the daily cost of cover. Tips on choosing the right ADCM Choosing to use an ADCM is one of the quickest ways to save space and extend the life of a landfill. That said, it is worth bearing in mind the following considerations: For revenue-generating cover that has been approved for use as a daily cover by the regulatory agencies, consider how much of the material you get each day. Are you getting more than you need? What do you do with the extra? Will it cause problems inside the landfill such as redirecting leachate to side hills, or chemically impacting on your leachate? Are you filling up your space with cheap waste for cash flow reasons? Can you mix the material when you want to? Can you use the equipment for only one purpose or multiple purposes? How do your employees like the material, which includes mixing, ease of application, and clean up? Evaluate the cost per square metre. Evaluate the coverage. Effective landfill management To take advantage of using ADCMs, you need to be able to minimize the need to put soil or dirt over the waste for haul roads and tipping areas. Lifts need to be engineered and constructed so the working face you spray today will not need to be covered over with soil the next day. Total surface area of a working face or today’s lift is also a key component to be minimized, which would translate into spraying less product used to cover this area. Figure 1. The creation of horizontal lifts Click here to enlarge image An optimally planned and engineered lift will have a width, length and thickness for the active area (working face) that maximizes the compaction of the waste, and minimizes the area that must be covered. Where thickness is minimal, compaction may increase, but the total width and length will result in a large surface area that requires either more soil or a larger amount of the ADCM to meet regulatory requirements. Although there is some debate about whether flat lifts or sloped lifts get better compaction, one statistic favours the flat lift. A flat lift is favoured because a compactor can increase the number of wheel revolutions in an eight-hour period by going 3 miles (5 km) per hour as opposed to 1.5 miles (2.3 km) per hour. Doubling the speed doubles the tooth penetrations. However, flat lifts yield to placing soil over yesterday’s waste for haul roads and tipping areas. Figure 1 shows how horizontal lifts are created with an alternative daily cover placed over the waste at the end of a day of landfilling. Figure 2. Comparison of saved space between horizontal lift profile and landfill not having to use soil over old waste for haul roads Click here to enlarge image In flat lifts, the waste is brought in on a haul road that is created on the surface of the waste deposited the previous day. The dotted rectangle in Figure 1 reflects the soil and stone that would be deposited the next day over the waste which had already been covered with an ADCM. A UK landfill using a flat lift profile and ADCM Click here to enlarge image The ADCM in Figure 1 is represented by the bold black line above the waste. The only value the ADCM provides is to save some time at the end of every day, but the next day, soil has to be brought in to place over the ADCM, so that trucks laden with waste can move their loads close to the tipping area. The photograph of a UK landfill above shows an actual landfill using a flat lift profile, placing the haul road on top, which negates the space-saving aspect of using an ADCM. The haul road and tipping area can be removed before the next lift is placed to minimize soil usage. The real benefit of using an ADCM is dispensing with the need to put soil between the lifts. Figure 2 shows the space saved for two horizontal lifts placed in the landfill if you can eliminate the soil haul road, or at least eliminate or minimize the soil left in the landfill from the creation of a haul road for each lift. The solution requires the following: create lifts so that the amount of soil that is used each day for the tipping area (area where the waste trucks back up and dump their waste) is minimized make the surface area where you apply your ADCM is an area where you will not drive over with your waste trucks. Figure 3. Pushing the waste uphill - creating the longest section for covering with an ADCM Click here to enlarge image Establishing lifts on a 1 to 4 grade, and pushing the waste uphill (see Figure 3) creates a working-face lift where the largest surface area is not going to be transited by trucks hauling waste. It also makes sure that it is ADCM rather then soil that is going to be the cover later between each lift. Pushing the waste uphill is not mandatory. You can set up the process by pushing the waste downhill while you are compacting. The haul road and the tipping area move only marginally each day. Figure 3 shows the portion of the tipping area and haul road that is removed before the next day’s waste is added. The daily cover ADCM layers between each lift are shown in Figure 3. Because we are not transiting over this waste with our waste trucks, there is little soil or dirt needed to create haul roads. Along the top of lift (the area noted for interim alternative cover or soil), is an area that could be coated with an ADCM that has a longer life span. At some point, when the series of sloped lifts shown in Figure 3 are completed, you would begin to construct the next series of lifts. You will at this point need to create a haul road and tipping area that will cross the waste surface to the point where you will begin to construct your next series of sloped lifts. But again, it is important to remove the soil as you move back across the surface of the old series of waste lifts. What is the cost of the ADCM? In nearly all cases, the value of the space saved is 20-30 times greater than the cost of purchasing the ADCM. This is inclusive of the labour cost to apply the ADCM. There should be no reason a landfill manager today doesn’t look at or consider using an approved ADCM. Although there is a time when the phrase ‘if it ain’t broke, don’t fix it’ may make sense, if you have not at least explored using an ADCM, you are throwing away good money. The future: real values of space Globally, the focus is on landfill diversion. Recycling targets tell us that we want to achieve waste recycling at levels in excess of 50%, maybe someday at levels of 80%-90%. Alternate waste technologies and new goals of recycling foretell a reduction in demand for landfill space. The truth, however, is that the world is still going through cycles of population growth and movement. A Chinese landfill using a flat lift profile testing an alternative cover material, NWC’s ProGuard IIB Click here to enlarge image In the UK the actual amount of waste is growing at just under double-digit levels, yet the country is focused on both developing and using alternate waste technologies, and increasing the focus on recycling efforts. Tipping fees over the past 10 years have increased, in part due to taxes levied on the waste, but also in part due to the laws of supply and demand, specifically fewer landfills and growing waste. With additions to the UK’s population coming from the European continent and other parts of the world, it is unlikely that we will see a reduction in demand for landfills as holders of household waste. This picture is true in China, with the exception that the population movement is from the rural areas to the urban areas. Imagine the pressures that would be exerted on the infrastructure when over 400 million people will move to the urban areas in the next five years. Although different in scale, managing and building strategies for the handling of household waste are equally as important to EU member countries. Thus to understand the real value of a cubic metre of waste, we cannot look to the fees that are charged per metric tonne as the waste transits over the scales at the landfill. We need to look to look at what the fees will be in 10-20 years, driven by the following factors: a declining stockpile of available storage space for waste an increased flow of waste, caused by a mobile (foreign) population moving to where employment, better living standards, higher levels of economic freedoms exist increased costs of construction and for materials used in the creation of the space available. These increased costs include increases in the operating costs for the equipment used everyday. And one should not forget price fluctuations in diesel oil, steel and lubricants. It should come as no surprise that more and more of the landfill companies and controlling political subdivisions in the UK, other EU member countries, or China are investigating and implementing measures to conserve space and thereby materially extend the life of their landfills. Milton F. Knight is CEO of New Waste Concepts and Director of NWC-UK Ltd. e-mail: mfknight@nwci.com