Transfer Trailer Now Leaving Gate 4A: The Transitioning Transfer Station
Transfer stations are often the only alternative to sending your collection trucks on a long-distance trip to a landfill. But if we recognize that today's transfer station is not just for moving MSW from collection truck to transfer trailer, the opportunities for designing transfer stations into an integrated waste and diversion system are endless - and economical.
The scenario has been repeated across the country: A community's landfill has reached capacity or has become a sociopolitical liability that is better closed. The search for alternative landfill disposal sites commences, and the community identifies a megalandfill that is interested and has the holding capacity to provide the community with disposal space for a decade or more into the future. The only problem is that this landfill is located 50 mi. or more from the community, and it is no longer viable for the collection trucks to haul direct to the landfill.
Another scenario is that the community continues to grow, and the transfer station that was capable of handling 500 tpd a decade ago is trying to shove through 1,000 tpd, and the only place that waste isn't being stored is the station manager's office. Shifts are extended, but it becomes obvious to all that an expansion is necessary.
While the immediate design need for a transfer station is to move MSW quickly through the building, transfer stations can be designed to allow a community to maximize waste diversion opportunities. As with a regional airport hub, with collection trucks acting like commuter aircraft and transfer trailers like jumbo jets, a transfer station can become a gateway in which macroseparation of loads can occur that are then dispatched to other facilities that can perform microseparations into marketable commodities. Through proper site selection and sizing, it becomes feasible for the facility to become a catalyst that maximizes route efficiencies while opening new market opportunities by not constraining the system to construction and demolition (C&D) processing facilities, material recovery facilities (MRFs), and composting facilities that are within driving range of the collection truck.
Where No Transfer Station Now Exists
The most common scenario is the landfill that is slated to reach capacity and the community begins a search for an alternative disposal facility, as was the case in Leon County, FL. The county operates a Class I lined landfill for MSW in addition to a Class III inerts landfill. Facing the need to find an alternative for the MSW landfill, the county began a process to identify a new landfill site or site and construct a transfer station to haul out of the county.
"It actually started almost 10 years ago," recalls Jud Curtis, director of solid waste for Leon County, based in Tallahassee, FL. "The Board of County Commissioners appointed a Citizens Advisory Committee, which was charged with finding a new landfill. It was basically a map-blind process in that you had the regulatory criteria and setbacks from airports, wetlands, issues like that, as well as what the committee's input was. They had various scoring and ranking systems. When they finally were ready to put on a map the sites that the consultant had determined met their criteria, all of the objections came out."
The original process identified an area in the northeast portion of Leon County as the logical location, but it was also an area that was environmentally desirable and was home to sensitive plant and animal species. "When it was all said and done, the board went back to the staff and (asked about) the alternatives to a landfill," says Curtis. "So we went back and we looked at waste-to-energy, MSW composting, and landfill mining of the existing facility."
The other alternative was out-of-county disposal sites. With the assistance of PBS&J, a comprehensive engineering firm with an office in Orlando, FL, the county began a process that ultimately identified four possible sites. "There were potentially four out-of-county landfills," states Curtis. "We put together an RFP (Request for Proposal) that was issued in May 1998. In October of 1998 the Board of County Commissioners awarded a contract to Waste Management to haul and dispose of the county's waste at the Spring Hill Regional Landfill in Jackson County. And the county would be responsible for building and operating the transfer station."
Once an out-of-county landfill was identified, the county then turned to the issue of identifying a location for a transfer station. "In issuing the RFP for hauling and disposal, we asked all potential vendors to bid on the transfer station being located at the current solid waste management facility (landfill)," explains Curtis. "We also gave them the option to bid on hauling and disposal from a transfer station site to be determined but located within a 3-mile radius of the intersection of Capital Circle and I-10 west."
"What that did was gave them basically two locations," describes Dave Deans, vice president of PBS&J. "One on the east side of the city where the existing landfill was located, and one on the west side of the city where a lot more of the population and the new growth are occurring." The site selected was located on the west side of town and resulted in a lower cost for the county due to an 18-mi.-shorter haul distance.
The challenges for siting the transfer station were almost equivalent to those the county faced in siting the landfill. "Don't underestimate the opposition even for a transfer station," observes Curtis. "I think we had been through so much trying to site a landfill that we figured as a group, how hard can a transfer station be after this battle? The transfer station siting turned out to be almost as difficult as the landfill." Adds Dean, "The issues in siting a transfer station are noise and traffic being the top contenders and odor being a sort of a secondary concern. The emotions ran as high in siting the transfer station as they did in deciding not to site a landfill."
Much of the study work involved addressing these concerns in a systematic approach, through various engineering studies. "We've got a number of constituents (for these studies)," states Dean. "The first one, of course, would be who is running the program. The administration and the governing board are probably your second group of constituents. You have to have the facts and figures to back up the positions that you are taking, and then of course the third is the public. They have to have the confidence that you've done your homework and you've looked into all of the details—not just the technology aspects of things but also the public-interest aspects. That really came back on the county when they established this Citizen's Advisory Committee. That was the level at which you got community values injected into the system. A consultant isn't going to set community values; it's the folks in the community, and then (the values) become the boundary conditions of the constraints within which we go and do our work."
The result of this process is the construction of a 23,000-ft.2, 1,200-tpd facility that is slated to open in March 2003. "The transfer station is about 80% complete," Curtis reported in December 2002. "It's a little unique in that we are using two Marathon S2000 compactors. In an emergency we also have the ability to top load trailers over a 5-foot half wall and then deposit into the trailers that would be at the same height as the push wall. We have that in case of an emergency power failure or the compactor is out of service."
Changing the Pieces When the System Changes
|The Sidewinder operates from the ground in 20 sec. for a faster and safer process at the transfer station. |
Changing waste-system needs created opportunities for Snohomish County, WA, to restructure its waste collection system according to its needs. Faced with a landfill closure in 1990, the county began a restructuring process that includes a transition to waste-by-rail and expansion of the existing system to meet the growth within the county, which is a northern suburb of Seattle.
The county's current system consists of three recycling and transfer stations located in Arlington, Mountlake Terrace, and Everett; five rural drop-box locations in Oso, Sultan, Gold Bar, Granite Falls, and Dubuque Road; the now-closed Cathcart Landfill site; and a temporary recycling and transfer station (TRTS) adjacent to the Cathcart Landfill that provides an alternative transfer site when the other three stations are down for maintenance or repair. Both the Mountlake Terrace (Southwest Recycling and Transfer Station, SWRTS) and Everett (Everett Recycling and Transfer Station, ERTS) stations handle approximately 700-800 tpd, while the Arlington (North County Recycling and Transfer Station, NCRTS) station handles 300-400 tpd. The total system handled approximately 438,000 tons in 2001.
|Airport Recycling & Transfer Station construction progress |
According to Mark Westenskow, project manager for the Solid Waste Management Division of Snohomish County Public Works, the county faced the closure of the Cathcart Landfill in the early 1990s. It initially began a two-prong replacement approach that involved siting a new landfill in the county and contracting to export the waste by rail to an out-of-county landfill. "The county retrofitted the NCRTS and SWRTS with preload AMFAB and SSI compactors to load waste into intermodal containers and developed a system to load waste in the containers at the ERTS," he states. "Since waste export by rail was an untried process and the destination landfill was still not constructed, the county developed a backup landfill for emergency purposes adjacent to the Cathcart Landfill site. Waste export has worked so well that the county never opened the backup landfill but maintains it in reserve."
The ERTS site was actually on a leased property, and the county embarked on a siting process to replace this facility. "Two factors limited expansion of the ERTS site," points out Westenskow. The station was located on an existing landfill that raised significant concerns regarding groundwater contamination and soil stability, as well as a strong desire by the City of Everett to use the property for other purposes. "The county continued to operate at the old site with a rolling, short-term lease, and efforts to site a replacement for the ERTS facility commenced again in 2000."
The county eventually identified a strategy that included reconstructing the existing SWRTS facility to allow for more improved handling capacity and siting and constructing a replacement facility for the Everett station. "Long customer lines, frequent breakdowns, and an analysis of growing tonnages versus compactor capacity made expansion an obvious necessity," recalls Westenskow. As part of the strategy, the ERTS station was retrofitted with a preload compactor, a move that had a short-term payback of only two years, due to improved efficiency and increased bale weights. This strategy provided some relief while construction of the new Airport Recycling Transfer Station (ARTS) was accomplished.
"You'll see that there is actually a lot of other work going on at the other stations," comments Karl Hufnagel of R.W. Beck, the county's on-call solid waste consultant. R.W. Beck's involvement with the county stretches over a 15-year period. "The design of the replacement for the SWRTS, we call it a remodel because it is being replaced at its current location but it's a total rebuild where the old station goes away completely. The site is actually expanded, and a brand-new station from the ground up goes in. That design process actually preceded the ARTS."
The county is involved in a three-phase approach to redesigning the waste transfer system that involved first constructing the TRTS at the Cathcart site while construction proceeds on the ARTS site, scheduled to open in June 2003. The temporary station then allowed the county to shut down the Everett station for its upgrade. "The four-month shutdown of ERTS gave the TRTS a trial run in preparation to handle waste from WSRTS during its upcoming 18-month shutdown," explains Westenskow. "This facility has also been used during other, shorter periods when either ERTS or SWRTS has been closed for repairs." Reconstruction work on SWRTS is scheduled to commence in May 2003.
Originally the SWRTS was to be constructed first, but due to permitting issues, its schedule fell behind. But as part of the design process for the SWRTS, the county held a design "charette" that was attended by county engineering and operational staff, as well as private waste haulers, to discuss design options. "The ARTS project built off a lot of the learning that went on at the SWRTS and its incubation period," comments Hufnagel.
In addition, the county toured more than 20 other transfer stations to examine various design concepts and to talk to operators about what worked and what didn't. "The county's current three stations are a pretty old-fashioned design," remarks Hufnagel. "No one is building stations like that anymore. The new stations that the county is building are flat-floor stations. They tend not to have a waste pit in the middle or a push pit. They generally have flat floors where the waste is pushed and dropped through compactor chutes in the floor and falls to a lower level. This idea of a flat floor is still relatively new."
The county learned some lessons in the design process. "The big thing that we've (made key) is providing flexibility for the operators," remarks Westenskow. "Don't try to box them in to do one thing a certain way because they will find a better way to do it. With our ARTS we've tried to build in enough flexibility for the operators to be able to do things a variety of different ways, depending on the circumstances that face them. That's one of the reasons why we went with the flat floor. The push-pit design basically puts the garbage in the pit and has the rams push it toward the compactor. (There is) not a lot of flexibility and not a lot they can do when they get hit with a big slug of trucks all at once. With the flat floor it gives them that flexibility as to where and how they can transfer the waste. That's really been one of the things that we wanted to make key with the ARTS—to provide flexibility so that we're not locking ourselves in now for the next 20 years. The stations can evolve with the waste to be handled in the future."
Future Flexibility Offers Gateways
Evolving with the changing patterns of waste generation, coupled with waste diversion mandates, might make future transfer stations a gateway to more efficient recycling programs. One of the biggest challenges facing collection operations is maximizing recycling diversion while minimizing costs and efficiency losses. In the traditional collection scenario, there are four components that are segregated and handled separately. These usually include commingled recyclables, mixed fibers, glass, plastics, and metal containers; organics, including greenwaste and foodwastes; C&D wastes; and residual trash and garbage. Each material stream usually has its own separate destination with varying routing efficiencies. For example, while the MRF and transfer station might be within the community, often the C&D and organic fractions have a long trip out of town to a facility.
If properly sized and designed, a transfer station can serve in the same capacity in which a hub airport terminal serves an airline. Collection trucks arrive at the facility with semi-segregated loads, such as a commercial front-load route primarily servicing restaurants or offices. Instead of having to maintain strict route segregation resulting in two or three trucks servicing one customer, collection managers can strike a balance by using one truck to pick up all restaurants within an area, with some route balancing. Then when that truck arrives, its load is segregated into a pile with other trucks handling similar organic materials. When a sufficient load is built, the load then is deposited into a transfer trailer and moved out to the composting facility. Instead of tying up three trucks and six crewmembers, the same volume is handled through a single driver with a transfer trailer.
Sizing of the transfer station to capture these kinds of scenarios depends on the end results, says John Wood, director of waste management services for CH2M Hill. "It's going to depend on how much flexibility you want," he states. "If you double the chore, then you could separate piece by piece. If you added 10 or 20%, then you have the ability to say, 'OK, we've got a couple of loads of C&D coming in. Let's put them off to the side and at the end of the day we'll build a separate truckload and send it just to the C&D fill.' So I think you really need to be looking at a 20%, 25% increase to begin to give some flexibility to stockpile and segregate material."
Critical to this concept is access to a range of disposal options. "Part of it is going to depend on what your disposal facilities are," states Wood. "In those situations, then you would pick trucks. We have a truck that comes in and we know he only collects from restaurants; well, we want that foodwaste to go to the compost facility. You know he is collecting office buildings; he's going to have a lot of office paper in there. We want that material to go over here so it can go to the MRF. So if you have the back-end processing and disposal, you could run a transfer station by the incoming wastestreams."
Many transfer stations that are co-located with recycling facilities already provide some macroseparation of loads, based on what the floor manager sees coming out of the back of the truck. In those cases, a load of cardboard layered between other materials might be scooped out by a bucket loader and dumped onto the feed line for the MRF. But such an arrangement now requires facilities to be co-located. Using transfer stations as gateways might allow even larger processing facilities to be built at locations that are remote from the general populations while maximizing both diversion and collection efficiencies.
While it's unlikely that transfer stations of the future will include runways and baggage handling, the concept of a control tower that communicates with incoming collection trucks to determine load characteristics prior to arrival, while coordinating the movement of trucks and equipment on the floor in order to segregate and move materials efficiently, is not. With the movement to single-stream processing on the collection side, such tr
Author's Bio: Lynn Merrill is director of public services for the City of San Bernardino, CA.