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Feature
Article March/April 2001
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Solid waste managers in nonattainment areas should consider how air-quality improvement measures might affect their operations as State Implementation Plans and strategies for emission offsets are put into action across the country. By Risa Fisher Regulatory
Background Texas' Dallas/Fort Worth (DFW) Metroplex is one of the fastest-growing regions of the country. It is known as a modern Sunbelt city with a booming economy based on telecommunications, electronics, retail, and finance. None of these industries is associated with severe air pollution. The metroplex, however, is spread over four urban counties and 14 rapidly developing counties. The benefits of a vibrant economy and high population base bring the penalty of vehicle emissions as people travel long distances to keep the economy fueled. To avoid the severe enforcement consequences of continued noncompliance with the Clean Air Act and to ensure a healthy environment for posterity, leaders from across the region have come together to self-impose a broad spectrum of measures to improve air quality. The solid waste management community was largely absent during the development of these mitigation measures. Consequently, their full impact on solid waste management, and far-reaching secondary consequences, might not have been fully appreciated. Now that commitments have been made to state and federal regulatory agencies, solid waste managers are anxious to understand their responsibilities and options. The following is a discussion of the consequences of the State Implementation Plan (SIP) and potential strategies for emission offsets. Solid waste managers in other nonattainment areas should consider how these or other air-quality improvement measures might affect their operations as similar actions are taken across the country. The DFW Metroplex is a nonattainment area for ozone pursuant to the Clean Air Act. The Texas Natural Resource Conservation Commission (TNRCC), the state's environmental regulatory agency, has adopted new rules revising the SIP to increase air quality to the National Ambient Air Quality Standard attainment level. The DFW SIP is a comprehensive plan designed to reduce nitrogen oxide (NOx) through dozens of measures developed by local task forces. The aggregate of these measures is predicted through air-quality modeling to improve ozone to levels just slightly below attainment levels. If target levels are not attained by 2007, the area is in danger of forfeiting vital federal highway funding. The measures implemented by the DFW SIP affect activities ranging from airport operations to power generation. Two aspects of the SIP will affect solid waste management directly. Although those provisions apply to the four most developed counties in the metroplex (Collin, Dallas, Denton, and Tarrant, with the total population exceeding 4.4 million), the effect of implementation in those four counties will be felt throughout the region. The planning region, represented by the North Central Texas Council of Governments, includes the two counties with the cities of Dallas and Fort Worth and all of the contiguous counties, with a total population of more than 5.1 million. For purposes of this discussion, the four-county implementation area is referred to as the DFW nonattainment area. Along with volatile organic compounds (VOCs), NOx is a precursor to the formation of ozone in the presence of sunlight. Although it is generally accepted that the primary source of ozone precursors in the DFW nonattainment area is VOCs associated with on-road vehicles, the DFW task force that developed the SIP chose not to target VOCs. Therefore, reducing NOx levels in the DFW nonattainment area is a major objective of the SIP. Two provisions of the rules that target NOx have the potential to affect solid waste management systems. They are (1) construction equipment ban for 50-hp-plus diesel engines between 6:00 and 10:00 a.m. June through October and (2) accelerated purchase of cleaner off-highway diesel equipment. The construction ban takes effect in 2005, following the accelerated purchase provisions in 2004. Both allow exemptions for approved Alternative Emission Reduction Plans. Emission Reduction Plans, outlining strategies for achieving emission reductions equivalent to the equipment ban and diesel equipment replacement, are due to TNRCC by May 31, 2002. The executive director is required to approve plans by May 31, 2003, and equivalent reductions must be achieved by June 1, 2005. Plans must also be approved by the United States Environmental Protection Agency (EPA). Diesel fleets at landfills are made up of equipment with engines between 100 and 750 hp. As such, most landfill equipment engines must meet Tier 2 certification standards of at least 10% of the fleet meeting the cleaner standards by the end of 2004, increasing incrementally to 30% by December 2006 and 50% by 2007. The remainder of the fleet must meet more stringent Tier 3 standards by 2007. Operations with new fleets, typically expected to be operational for 10 or more years, could suffer significant financial harm when they have to make unplanned purchases of major equipment between now and 2007. These requirements dictate replacement or retrofit of all off-road diesel equipment by 2007. There is a great deal of concern about whether equipment manufacturers will be up to the task of providing a full range of equipment meeting even Tier 2 standards by the end of 2004, when the first replacements are mandated. Equipment owners will want to phase equipment replacement on schedules that track routine replacement schedules to the greatest extent possible. Inevitably, many pieces will have to be replaced before the end of their useful lives in order to meet percentage replacement goals, even with careful planning. And it is uncertain whether equipment manufacturers will even offer the specific types of Tier 2 and Tier 3 equipment required in the years that solid waste managers plan for equipment replacement. The SIP defines "fleet," for purposes of determining numbers of pieces of equipment, as all off-road diesel equipment under the control of one person, within the size range specified, including pieces under lease for more than one year. A case could be made that a fleet could be all the equipment under the control of a city manager, thus increasing replacement schedule flexibility. As a result of the equipment-use ban, operating and construction equipment will be idle from 6:00 until 10:00 a.m. during warmer months. Affected equipment may include compactors, dozers, loaders, scrapers, water trucks, dump trucks, backhoes, and diesel-powered grinders, shredders, and screens. Operators in the DFW area and in other warm climates prefer early morning operations because of safety concerns regarding heat stress in the hotter late afternoon.
The equipment ban affects both the landfill and the collection and processing fleet. If a landfill were to compress its operations into fewer hours during the day, staffing and equipment needs would increase in order to accommodate higher disposal rates per hour of operation. The work force would have to be bigger to accommodate more vehicles at one time. Alternatively, operating later in the day introduces safety concerns related to afternoon heat and visibility after dark. Keeping the gate open early, without heavy equipment operating, would require significant storage capability, and might introduce odor and vector problems. Finally, site work, cell construction, and capping costs will rise for contracted construction activities if the workday is shortened by four hours or if night construction operations are required. Transfer stations could serve as waste collection points during the morning hours that landfills are not in operation. However, heavy equipment in the station would be affected by the same off-road diesel equipment operation ban as landfill equipment. Few transfer stations are sized to accept this waste flow for four hours without the ability to load material into transfer vehicles. Processing operations, such as composting, brush chipping, and concrete crushing operations, are also dependent on diesel heavy equipment. Therefore, they will be prohibited from operating during the regulated periods. Because it would be necessary to stockpile materials during the restricted operating hours, additional storage area might be required. Gates could open between 6:00 and 10:00 a.m.; however, it would not be possible for diesel landfill equipment to operate during this period. Most landfill operators would have great difficulty accommodating significant quantities of waste over a four-hour period without compacting or covering. In addition to the obvious risks of blowing litter, odor, and vectors from an uncompacted and uncovered face, overall compaction efficiency is lost as loose lifts far exceed the optimum thickness of about 2 ft. prior to compaction. If collection hours are unchanged, but the gate is closed in the early morning, vehicle queuing will soon be a problem related to traffic safety and the expense of idle trucks and drivers. In fact, drivers may be prohibited by contract or regulation from spending more than a given number of hours in a vehicle, further complicating this scenario. Finally, in hot climates such as the DFW region, it will be necessary for drivers to remain in their vehicles during queuing with their engines and air conditioners operating. The actual net effect on air quality in this case would probably be negative, not positive. In light of these issues, it is unlikely that closing processing and disposal facility gates without altering collection hours would be feasible. If the collection fleet cannot access processing and disposal during the early morning hours, collection fleets would have to start operations significantly later. This is a particular concern for commercial collection operations because commercial trucks normally begin their routes around 4:00 a.m. A later collection time would increase the effects of rush-hour traffic on collection and transport efficiencies. Commercial collection vehicles would add to morning rush-hour traffic congestion, while residential trucks might still be on their routes during afternoon rush hour. Collection vehicles in neighborhoods in the afternoon introduce safety concerns during the hot afternoon and possibly after dark. An alternative to delayed collection and processing/disposal would be to compress collection operations into fewer hours, designed so that the first vehicles reach the affected site starting at 10:00 a.m. This would probably necessitate adding collection equipment and redesigning routes. If collection is privatized, renegotiation of collection contracts might be necessary. A nonstandard shift, beginning four hours later, might make staffing more difficult for both collection and disposal. Any operational change, including different operating hours, may require a modification of permit conditions. Private operators of landfills, transfer stations, and processing facilities may activate renegotiation clauses in their contracts. Where collection is privatized, the secondary effects of the equipment-use ban on collection hours and efficiency could entail renegotiating contracts with collection service providers as well. Possible Mitigation Strategies
Several strategies are available for alternate methods of obtaining equivalent emission reductions, as compared to the two provisions described above. Each is based on the premise that NOx emission reductions can be achieved through alternative means. In order to justify a direct tradeoff of tons of emissions reduced through alternative means for emissions reduced as a result of the construction-ban requirements, the alternative reduction would have to be realized between the hours of 6:00 and 10:00 a.m. This is because emissions in the morning have a greater potential for generating ozone through more prolonged exposure to sunlight. If offsets take place during other hours of the day, it may be necessary to apply them only to off-hour emission reductions that might have resulted from equipment replacement with cleaner engines. To apply off-hour reductions to early morning emissions, the alternative net ambient ozone reduction would have to be determined through air-quality modeling - a complex and costly process. To date, it is unclear whether EPA will accept this strategy. One way to reduce landfill equipment emissions and allow increased operating hours is to combine operations with one or more other sites in the nonattainment area. This could be in effect either permanently or only during the months of the construction equipment ban, June through October. Economies of scale could be realized by disposing of waste jointly with that of another city, with significantly less landfill equipment than is currently in operation at the multiple sites. Such a program might be implemented in one of several ways. Joint operations may take place only during the hours of the construction equipment ban, full-time but only during the months of the construction equipment ban, or permanently and alternating between participating landfills. Here again, it is not known whether emission reductions resulting from combined operations would be allowable as an emission offset during the hours after 10:00 a.m. or between November and May. Ozone modeling would probably be necessary. The conditions defining allowable emission offsets would greatly affect the feasibility of such a scheme. Maximum operating cost reductions would be realized with full-time joint operations, however. It is likely that many disposal operations could absorb most or all of the waste from nearby communities with little or no increase in staffing or equipment. If an operation would need additional equipment or personnel to jointly dispose of waste, that extra equipment or staff could be transferred and the total equipment in operation would still be decreased. The need to "borrow" equipment would strongly favor the scenario of full-time permanent or seasonal joint operations, not just in the mornings. In this event, the option of diverting only a portion of a wastestream to another site to maximize equipment utilization at both facilities should be considered as well. Unless both participating facilities are owned by the same public or private entity, an equitable form of compensation between the participating entities would have to be established through agreement and might include a waste swap or monetary reparation. Another alternate strategy is to contract for disposal all or a portion of Arlington, TX's waste, such as the commercial sector, at a landfill outside the nonattainment area. Unfortunately, the nonattainment area includes Dallas, Tarrant, Collin, and Denton Counties. Therefore, this strategy would probably include a transfer station to be cost-effective, with its associated capital and operating costs. If a transfer station is necessary, it is likely that the entire wastestream would be transported out of the nonattainment area during the enforcement period. The largest difficulty associated with waste export during only the regulated morning hours and the regulated summer months involves the use of city landfill personnel on a part-time or seasonal basis. Compared to reducing equipment usage through joint operations, exporting waste out of the nonattainment counties altogether would result in the accruement of more emission reduction credit. Implementation of a balefill would allow collection vehicles to operate on their current schedules, enabling easier storage and transport of waste for disposal after 10:00 a.m. and enabling greatly reduced diesel equipment requirements. Although baling has its own drawbacks, this might be another alternate method of emission reduction and might also support later start times for disposal operations. Baling might also inhibit methane production, possibly interfering with the terms of the landfill gas recovery contract that is currently in place. Baling operations are typically capital-intensive and represent a very high maintenance commitment. Typically, baling operations have not proven feasible over the long term except in extraordinary situations requiring it, such as under sustained high-wind conditions, or in support of unusual transportation schemes. It might be possible to gain TNRCC approval of trading emission credits with other generators within the same nonattainment area. Those other generators might include city-controlled emission sources or private vehicles with high emission levels, which could be taken out of operation entirely or converted to nondiesel fuels. Rules will be developed by TNRCC addressing emission banking and trading. Examples of an internal tradeoff include further limiting other construction projects in the city, beyond the SIP required limitations, in favor of further landfill operations. In addition to limiting other construction, diesel-burning equipment may be replaced with equipment using other fuels or may be converted. Transit operations, particularly buses, offer opportunities for conversion from diesel to cleaner fuels for emission reduction credit. Operation of wet-cell landfill technology could be another method of emission reduction. Similar to NOx, methane is a significant precursor to ozone generation. Aerobic wet cells reduce emissions of methane as compared to conventional operations that typically have predominantly anaerobic conditions. Anaerobic wet cells, where the waste is covered with plastic rather than soil and gases, are withdrawn from the waste, produce more methane for recovery, and feature induced draft conditions that pull air into the active face rather than letting gases escape through it. Both aerobic and anaerobic cells stabilize much faster than conventional landfill cells. Therefore methane generation is accelerated and fully recovered for the first years and greatly reduced or eliminated much faster thereafter. To date, EPA has not accepted methane reduction as an offsetting ozone reduction strategy. Efforts should be made to gain approval of this strategy based on equivalent ozone reduction. It might be possible to negotiate emission reduction credit with the TNRCC for implementation of an active gas system, particularly one with recovery rather than flaring, such as the system already under contract in Arlington. Opportunities for early implementation might be available. Large-Scale Landfill Biofilters If methane reduction is accepted as an acceptable offset, other strategies exist to reduce methane emissions at landfills. One innovative approach is a layer of biologically active compost over a landfill as a filter for methane emissions before they reach the ambient air. Another approach to emission reductions is to modify collection service levels. For example, cities with twice-weekly collection may switch to once-weekly collection in order to take credit for the resulting net emission reductions. Industry leaders in other Clean Air Act nonattainment areas in the US should participate in the development of their local SIPs from the first opportunity. Only in this way will the effects of SIP provisions be fully appreciated. In addition, it is important to ensure that the broadest possible approach is taken when regulators develop guidelines for evaluating potential emission offsets. In particular, the goal of ambient ozone reduction should be the ultimate standard used when state and federal regulators evaluate alternative emission reduction plans. Risa Fisher is vice president of HDR Engineering in Dallas, TX.
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