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Any
landfill is an exercise in soil balance, but when you need more
dirt and airspace to survive, you better add a little magic to your
earthmoving efforts. By John Trotti |
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Imagine coming to work one day and finding it’s your job to come up with more space and more dirt–without breaking the bank. That’s what happened to the staff at the Olinda Alpha Landfill (OAL), a Class III Sanitary Landfill located in Orange County, CA, adjacent to the city of Brea. OAL, situated on 562 ac. of county-owned property, is operated by the county’s Integrated Waste Management Department (IWMD). It is the fourth-largest landfill in the state of California with a total annual disposal (1999) of 1.9 million tons. The landfill’s daily maximum permitted disposal capacity is 8,000 tons, and it receives approximately 6,300 tpd of waste. The ultimate site capacity is 123.1 million yd.3
OAL was originally permitted as two waste disposal facilities in adjacent canyons, Olinda and Olinda Alpha, that were divided by a central ridge. Disposal operations started in Olinda Canyon in 1960 and proceeded into Olinda Alpha Canyon in 1981. The portion of the canyon to receive the initial refuse was prepared by clearing and grubbing the native vegetation. Excavation was conducted to obtain the necessary cover material, provide a level deck to conduct unloading operations, and construct the necessary internal roads to access the unloading area. As operations progressed, the canyon was filled generally from front to back, rising in elevation. In 1987, the Orange County Board of Supervisors initiated the North Orange County Landfill and Alternative Technologies Study to identify new sites and/or expand existing landfill sites to provide replacement solid waste disposal capacity in the county. The vertical expansion of OAL was identified as a preferred disposal option. A master plan and various permit documents were subsequently prepared to obtain regulatory approval of the vertical expansion. Approval was granted in 1996 after rigorous environmental review. The master plan defined a phased approach to the expansion that allowed IWMD to maintain operations during the construction stages of the landfill’s expansion. What is unique about OAL is how the vertical expansion of the landfill was accomplished. First, the location of the two landfills side by side lent itself to the strategy of combining the canyons. Second, an innovative engineering design was created, providing an alternative solution that fulfilled the prescriptive requirements of federal Subtitle D regulations. The vertical expansion at OAL combined the two existing waste management units in Olinda Canyon and Olinda Alpha Canyon, respectively, for the purpose of excavating the central ridge separating the two canyons–an operation displacing 7 million yd.3–for a total combined airspace capacity of approximately 123.1 million yd.3 The master planning exercise also identified a shortfall in available soil for cover on-site, determining that it was sufficient only through 2003. Thereafter, if IWMD were to continue in its accustomed mode of operations, it would have to import soil at a cost of $7.50/ton. At this rate, the added cost would amount to $750,000 per year, or in excess of $5 million through 2013. In response to OAL’s soil shortage, site engineering staff devised a more efficient and less costly approach to developing the landfill that revised the projected soil shortfall to the year 2009. Strategies implemented to defer the projected soil shortfall included increased use of alternative daily cover (processed greenwaste), revised fill phases to minimize the number of interim fill slopes requiring large quantities of soil, and use of existing access roads. Even as it became apparent that these strategies would achieve the 2009 target, staff continued to look for ways to extend the landfill’s life still further into the future, and to this end, OAL brought Caterpillar’s Computer Aided Earthmoving System (CAES) onto the site to establish and maintain a uniform deck from which more accurate measurements could be made. In October 2001, a global positioning system (GPS) was installed, and trial operations began using the CAES to provide efficient refuse grading and compaction. The system includes an engineering office base station comprising a surveyed monument, GPS receiver, radio, and computer with CAES software; heavy-equipment machinery consisting of three tractors and one compactor, each equipped with a GPS receiver, radio, and display monitor; and computer hardware and software to assist the design engineer in the preparation of a 3D grading plan for the site. Initial data were converted from existing site-planning AutoCAD files and fed into Caterpillar’s system. The plan is then converted into a CAES file and sent via radio signal into each machine. An onboard monitor shows plan and cross-section views with color-coded existing and proposed grades, and a color-coded plan view allows the operator to see the existing ground as fill, grade, or cut. These displays let the operator visually check the screen for plan conformance without the requirement for other grade controls in the field. The machine data are sent back to the CAES computer via radio and can be downloaded as point files to generate a topographic of the finished fill grade. The project has demonstrated the system’s benefits in achieving precision grade control, a reduction in soil cover requirements, improved compaction, safer operating practices, adherence to regulatory-driven grade requirements, and the preservation of airspace. Dave Lowry, OAL’s general manager, has become a thoroughgoing fan of the CAES system. "We’re able to save seven- to eight-tenths of a foot over the entire working face," he notes. "That’s more than 300 yards of dirt a day." There are many more savings, although they’re not quite so obvious. "A lot of it is in avoided maintenance–low areas and erosion repair. Just the ability to install correct flow lines is a real plus to the operation." Excavation of the central ridge began in 1998 and was completed in October 2000. By agreement between the county and the City of Brea, its closest neighbor, OAL is scheduled to close in 2013; however, at the present fill rate and using best management practices, it is estimated that the active life could be extended to 2017 without additional major construction; 2021 with additional construction. John Trotti is the editor of Grading & Excavation Contractor magazine.
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