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Feature
Article March/April 2001
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Lancaster County reclaimed approximately 315,500 cubic yards of space in an effort to protect nearby farmland. This article highlights the pros and cons of the reclamation experience. By Gary A. Forster LCSWMA
Reclamation Summary One of Lancaster County, PA's most significant resources is farmland. One of the main goals of the Lancaster County Solid Waste Management Authority (LCSWMA), therefore, is to protect land by minimizing the space needed for landfilling. To achieve this goal, the authority began the construction of a resource recovery facility (RRF) in 1989 to significantly reduce the volume of waste entering its Frey Farm Landfill. It also helped to establish recycling and waste reduction programs in the county. As a result of resource recovery and recycling, less than 12% of the volume of municipal waste generated in Lancaster County ends up at the Frey Farm Landfill for disposal. In February 1991, with the RRF in start-up operations, the authority took another step to preserve landfill space by excavating and incinerating waste buried in the Frey Farm Landfill's first cell, whose 18 ac. were filled to capacity while the RRF was being built. This "landfill mining" project began on a small scale, with only a few hundred tons of waste reclaimed each week. From its experimental start, landfill reclamation evolved into an operation that utilized four authority ash trucks and two open-top transfer trailers to haul more than 1,475 tons of reclaimed waste to the RRF on a weekly basis. By the time the project was completed, approximately 315,500 yd.3 of space were reclaimed. The following report summarizes the LCSWMA reclamation experience for 1992 and 1993, the most productive years of the project. Since the project's inception, the authority and Ogden Martin Systems of Lancaster (OMSL), the RRF's operator, worked together to determine the most efficient and cost-effective manner to excavate and process the waste reclaimed from the Frey Farm Landfill, which varied in age from one to five years. In the first phase of the project, the authority excavated waste and delivered it directly to the RRF without trommeling, where it was mixed with MSW at various ratios and burned. Because of the large amount of cover soil in the reclaimed waste and its moisture content, OMSL, during phase two, began supplementing the waste and MSW with other fuels - primarily propane gas, wood, and tire chips - to increase its energy value. In phase three, the authority purchased a rotary trommel and used it to screen the majority of the cover soil from the reclaimed waste. After eight months, the authority bought a larger trommel with additional screening capability to improve the screening process.
As a result of the work at the Frey Farm Landfill and the RRF, the authority learned that landfill reclamation makes the most economic and operational sense if the waste is trommeled prior to being processed at the RRF. Because of the high percentage of cover soil in the untrommeled waste and its negative effect on combustion characteristics, the amount of such waste processible at the RRF is limited. Removing cover material from the waste produces a cleaner, more efficient fuel. In addition, trommeling the waste produces reusable landfill cover material and maximizes the efficiency of vehicles that haul reclaimed waste to the RRF and transport ash residue to the landfill on the return trip. A summary of the weekly production data, project costs, and assets realized during 1992 and 1993 is provided in Table 1. More than 251,200 tons of waste were excavated during this time, translating to nearly 2,650 tons excavated on a weekly basis. Reclamation activities resulted in the delivery of 1,476 tons of screened waste per week to the RRF for processing. Thus, 56% of the total excavated tons were converted into fuel; 41% of the excavated material was recovered as soil during trommeling operations; and the remaining 3% were noncombustibles that had to be relandfilled. Volumes of excavated material, recovered soil, reclaimed material, and noncombustibles were tracked monthly by field survey methods. Approximately 33% of the project costs were associated with excavation and trommeling operations at the landfill; 31% of the costs were incurred by transporting reclaimed waste to the RRF and hauling ash residue created from the combustion of reclaimed waste back to the landfill; the balance of the project costs was associated with processing fees paid to OMSL and to the RRF and landfill host communities. Revenues obtained from the sale of electricity and recovered ferrous metal offset these operating costs, resulting in net revenues of $3.94 for every ton of reclaimed refuse delivered to the RRF. Additional assets recovered on a weekly basis included cover soil and landfill volume. Therefore, the overall project profit, which includes net revenues and asset additions, amounted to $35,200 per week, or approximately $13.30 for every ton of material excavated. Excavation and Trommeling Data LCSWMA landfill personnel used a Re-Tech 723 trommel with 1-in. square screen openings to process the excavated waste. During the course of the project, LCSWMA landfill personnel made several operational and design improvements to optimize project efficiency. Daily reclamation activities were handled by three equipment operators who excavated the buried refuse, fed the trommel screen, loaded the transport vehicles, and transported screened soil to other locations at the landfill. The landfill mechanic spent 30 minutes each day performing a preoperational inspection and greasing all the fittings on the trommel.
Excavation techniques evolved from the bulk excavation phase to a "strip-mining" technique. This latter approach involved cutting a 50-ft.-wide x 150-ft.-long swath to a specific depth. Once this waste was trommeled, operations moved laterally to the next section, where the process was repeated. Excavation was done in this manner so that operations could be kept downgradient of the existing cut to aid in stormwater control. Temporary berms were also placed around the upper edge of the stripped areas to enhance runoff. The strip-mining method also prevented the accumulation of methane in an excavated pit. Throughout 1992 and 1993, a varying combination of two to four open-top trailers (transfer trailers with tops removed and replaced with a tarp) and three to five ash dump trucks (25-yd. tri-axles) were used to deliver reclaimed waste to the RRF. The trailers hauled 72% of the refuse, while the ash trucks and occasionally a 40-yd. rolloff transported the remainder. Downtime did not sidetrack daily operations. During the project period, unscheduled downtime averaged approximately 45 minutes per operating day. Trommel design improvements made it possible to operate with one maintenance period per year. Scheduled downtime for 1992 and 1993 averaged five to 10 hours per month, or roughly 30 minutes per operating day. The three byproducts of trommeling excavated waste are reclaimed refuse ("overs"), recovered soil ("unders"), and noncombustible, oversized material ("nonprocessibles"). Roughly 67% of the overs contained combustible materials such as paper, cloth, wood, cardboard, household refuse, plastics, roofing, and insulation. Nearly 30% of the overs consisted of noncombustible material such as soil and rocks. The remaining 3% contained recyclable aluminum, bimetallic, and steel cans. The age of the trommeled waste from Cell 1 ranged from 15 to 48 months. Landfill operators noticed a minor amount of decomposition in the refuse. The soil and moisture content of this material also varied significantly, drying out in the winter and late spring. Weather conditions, however, did not negatively compromise reclamation operations, nor did they contribute to a decrease in the higher heating value (HHV) of the waste. LCSWMA performed several physical characterization studies on the unders. The percentage of soil and rocks in this material ranged from 80% to 93%. The other main constituents, comprising roughly 9% of the samples, were paper, glass, plastic, and linoleum. Additionally, the unders were texturally classified as a sandy loam, with a Unified Classification of "SM." These characteristics qualified the unders to be used as daily cover per the requirements of Pennsylvania's Municipal Waste Management Regulations. Results of chemical characterization studies done on the unders and on virgin daily cover soil showed these materials to be very similar. The unders showed significantly higher concentrations of calcium, magnesium, potassium, and sodium than did the cover soil, indicating that leaching has had an effect on the unders chemistry. Few semivolatiles or volatiles were detected in the unders. Of those found, none exceeded regulatory limits. Herbicides (i.e., 2,4-D) were detected in one of the samples; polychlorinated biphenyls, asbestos, and pesticides were not detected in any of the samples. LCSWMA experimented with several different odor control products. Among the products tested were granular and liquid odor suppressants (masking agents) and odor neutralizers that work on the ion-exchange principle to neutralize offensive odor ions. Through experimentation, the authority found that an odor suppressant called Monsanto CX was the most effective product in combating odors. The suppressant was sprayed directly onto the loaded trucks. The product was typically used from early spring to late fall at a rate of roughly 2.4 gal. per operating day. Ambient Air Monitoring at the Reclamation Site
LCSWMA monitored the ambient air at the reclamation site on a quarterly basis beginning in 1992. Both personal and area samples were collected. Trace concentrations of aldehydes, anions, and a few volatile organic compounds (VOCs) were detected in both the personal and area samples. Concentrations detected, however, generally ranged from 5 to 100 micrograms per cubic meter (ug/m3), well below the regulatory limits for these compounds (typically 125,000-435,000 ug/m3). The airborne VOCs most commonly found were xylene, toluene, and methylene chloride. Xylene and toluene were also detected in the unders, indicating that these compounds were volatilizing from the excavated waste and trommeled soil, although not to any great degree. The parameters that were detected as close to Occupational Safety & Health Administration (OSHA) Permissible Exposure Level (PEL) action levels (concentrations that are 50% of the OSHA PEL) for the area and personal samples were silica quartz, total particulate, and respirable dust. The location having the highest concentrations of these parameters was downwind of the trommel, as expected. The majority of the data, however, indicated that particulate and dust concentrations were well below OSHA PEL action levels. The general consensus among RRF operations personnel was that processing-reclaimed material measurably impacted pit management practices, boiler wear and tear, air-pollution control equipment, and residue-handling equipment. As a result of the material's relatively low heat content, maintaining efficient combustion when processing reclaimed waste required that it be mixed thoroughly with the other elements of the wastestream in the waste storage pit. Operators enhanced the HHV of the reclaimed stream by mixing it with tire chips and shredded wood; the entire fuel mixture was then fed to the boilers at a ratio of approximately four parts MSW to one part reclaimed waste. Processing reclaimed waste led to increased wear and tear on the refuse cranes since the material was denser than normal MSW and had to be mixed more thoroughly than the other wastestreams. Approximately 30% additional crane work was required when the units processed landfill waste. The abrasiveness of the reclaimed material (as a result of its soil content) caused increased wear on the feed chute hoppers and the feed tables. These areas were replated after three years of service, compared to a normal replacement of every five years. Also, the high particulate content of the mined wastestream led to premature plugging of the economizers and additional wear and tear on the baghouses. OMSL was paid a fee that averaged $3.03/ton of reclaimed material processed to cover these additional costs. The soil content of the reclaimed stream led to higher ash-generation rates at the facility than at comparable facilities that process only MSW, which caused additional wear on the residue handling system. Ash-generation rates were roughly 5-7% higher than when processing strictly MSW. Energy Values of the Wastestreams The average HHV of the total fuel mixture for the project period was 5,059 Btus/lb. This average value was derived from monthly determinations of the wastestreams' HHV by using Ogden's steam correlation method. One eight-hour boiler calorimetry test was conducted on a unit fired with 100% reclaimed waste. The HHV of the reclaimed material was found to be 3,084 Btus/lb. LCSWMA also estimated the HHV of its reclaimed stream on a monthly basis. Assumptions were made regarding the HHV of the various wastestreams. Each wastestream's assumed HHV was then multiplied by the monthly wastestream tonnage (in percent) for each material. The resulting value was then set equal to the HHV of the fuel mixture as determined using the steam correlation method and the equation solved for the HHV of the reclaimed waste. The average HHV of the mined waste using this calculation method was 3,149 Btus/lb. Emissions at the Lancaster RRF are monitored on a continuous basis through the use of the facility's Continuous Emissions Monitoring System. Emissions statements are filed with Pennsylvania's Department of Environmental Protection on a quarterly basis for emissions of carbon monoxide, hydrogen chloride, nitrogen oxide, and sulfur dioxide. None of the parameters' quarterly average emissions exceeded permitted levels during the processing of reclaimed waste. Operators noticed over time, however, that combusting reclaimed waste tended to cause an increase in hydrogen-chloride emissions. The chemical characterizations done on the unders revealed it to have high concentrations of sodium, potassium, magnesium, and calcium. Thus, the unders are contributing to, but are not the sole cause of, elevated hydrogen-chloride emissions at the facility. Comparison With a Related Landfill Reclamation Project From mid-November to mid-December 1993, LCSWMA participated in a joint project with the York County Solid Waste Authority (YCSWA) to excavate and burn a small portion of YCSWA's landfill that contained 15- to 20-year-old trash. It was hoped that some conclusions could be drawn regarding the effect waste age had on the energy value, air emissions, and ash quality at the RRF. Physical characterization studies showed that the York County wastestream contained similar percentages of combustible, noncombustible, and recyclable materials. The higher degree of decomposition in the York County stream was evidenced by a greater amount of fine granular material. Also, the soil content of the York County mined waste was 24% higher than Lancaster's reclaimed stream as a result of greater amounts of cover soil used during original landfilling. Despite its degraded state and soil content, however, the older wastestream was still considered to be trommelable and combustible. Chemical characterization analyses of the unders showed the LCSWMA reclaimed stream to have higher total metals concentrations of arsenic, barium, cadmium, lead, and mercury. The lower concentrations in the older York County waste might have indicated that these metals were leached out of the older waste. Ash-residue generation rates when burning the York County reclaimed material were roughly 5.3% higher than the typical LCSWMA percentages as a result of the higher soil content of the York mined stream. In general, the testing undertaken established that the chemistry of the ash generated from the combustion of 15- to 20-year-old refuse did not differ markedly from residue resulting from the combustion of waste mixed with one- to five-year-old reclaimed material. The HHV range for the York County reclaimed stream was 1,069-2,249 Btus/lb., considerably lower than the LCSWMA stream. Several factors contributed to the low value. There was an unusually high amount of rainfall during the project period, and a quarrying type of excavation was used, which resulted in a very dirty, wet end product. LCSWMA feels that, with a few minor improvements, the HHV of the older wastestream could have been improved to a level close to that achieved with the LCSWMA waste. None of the RRF air emissions experienced during the time of the York County project exceeded the facility's air permit. Operators noticed that the older wastestream also produced relatively high hydrogen-chloride emissions, similar to levels experienced when processing the Lancaster stream. The air monitoring tests performed at Cell 1 of the Frey Farm Landfill were also done at the York County reclamation site. A greater quantity of VOCs was detected at the Cell 1 site than at York County, possibly because of the age of the refuse, since gas generation rates decline exponentially after a landfill is closed. It was found, however, that compounds such as methylene chloride, ethylbenzene, Freon-11, xylene, styrene, and toluene were present at both sites. The conclusion regarding reclamation site emissions is that excavating and trommeling waste buried for one to 20 years produces ambient concentrations of hazardous air pollutants that are several orders of magnitude below the OSHA-permissible exposure levels. The obvious benefit from reclamation operations is that the space created helps extend the life of the landfill. Reclamation can also be used to remediate problem sites, such as those that are unlined or whose liners are in need of repair. Additionally, the LCSWMA experience shows that a significant quantity of soil can be recovered and used as daily cover. Reclaimed material can be successfully processed at a modern-day RRF, as long as it is mixed well with other wastestreams. The relatively low HHV reclaimed stream can be offset by the co-combustion of higher HHV supplementary fuels. The additional tonnage provided by the mined waste can be used to maximize boiler efficiency, power production, and electric revenues. Recommendations for Reclamation Operations LCSWMA has the following recommendations related to reclamation operations at a landfill and resource recovery facility:
Gary A. Forster, P.E., is the resource recovery contract manager for the Lancaster County (PA) Solid Waste Management Authority.
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