Transfer stations seem to be in their heyday as an increasing number of communities turn to long-hauling their solid waste to large, regional landfills.
While this disposal option might look more cost-effective on paper, the distance that collection vehicles must travel could cancel potential savings due to vehicle wear and time lost.
This is where transfer stations come in. Because transfer vehicles require a much larger payload and only a driver, their operational cost per ton is significantly less than that of collection vehicles.
And if the haul distance is far enough, the savings in transportation costs incurred by using a transfer vehicle rather than a collection truck can offset the transfer station's cost even more.
Transfer station design can take many forms and usually is dictated by community needs, site considerations, facility size and economics.
Transfer stations can be as simple as vehicles dumping waste over a retaining wall into trailers or containers. However, open-top, compactor and mini-station facilities represent more sophisticated options.
While the open-top and compactor facilities are on two-levels - an upper level for dumping and a lower level for the transfer vehicles - transfer stations also can be built on one level and bulk-loaded by grapplers or end-loaders.
Transfer stations generally are enclosed within buildings to contain litter, noise and odors, and to provide a more comfortable working environment.
Its architecture depends on cost, aesthetics and location. For example, some facilities are built without doors because they usually are kept open. And in some cases, such as when a site is operating, but the actual building is still under construction, a facility will not be enclosed.
The selection of a facility type and enclosure depends on the site's size, operating mode, configuration, traffic, potential environmental impacts, aesthetics and cost.
Transfer station variations include:
Open-Top. In this most common transfer station, the waste usually is dumped on the floor and pushed through a hopper into an open-top transfer trailer located below the hopper.
Waste also may be dumped directly into the trailer. A pedestal crane, backhoe or similar equipment distributes and levels the trailer's load. The trailer's large size allows it to hold maximum legal loads without compaction.
Advantages of an open-top transfer station are:
* minimal mechanical equipment;
* the ability to handle large waste volumes;
* relatively low operating costs; and
* operational flexibility.
Compactor. Here, waste is dumped into a hopper feeding a stationary compactor, which compacts waste into a specially designed transfer station. Although this facility has higher operating costs due to its mechanical equipment, it has some benefits:
* it can be used in restricted sites; and
* it uses transfer trailers that are smaller than those used for open-top facilities that may better comply with height restrictions.
Mini-Station. The mini-station, or "rural drop-off center," is tailored to rural areas with low waste volume and is provided in lieu of curbside collection. These stations, which usually are not enclosed, also can serve to supplement residential waste collection.
Some mini-stations use small compactors, and the containers, usually roll-offs, are picked up periodically.
Location is Everything Deciding on direct haul vs. transfer haul is more than a matter of initial costs. For example, what is the impact on the existing collection system if a transfer station is added? Even if direct hauling is more economical, the additional hauling time spent by collection vehicles may require adding more routes, vehicles and crews.
Also, if the current system works well and customers are satisfied, there may be resistance to changing the system.
However, a transfer station's benefits to a community include:
* a more convenient waste disposal point, eliminating long distance travel;
* reducing traffic to the distant landfill site;
* a high level of management flexibility, particularly when they are hauling to a regional facility (public or private) and not to their own; and
* allowing a change of disposal sites as locations or fees change, without affecting the rest of the waste management system.
Transfer stations can reduce many operational and financial headaches - when carefully planned. As the following two case studies show, thorough analysis is key to integrating a transfer station into an existing solid waste system.
Slashing Travel Time in Scottsdale The city of Scottsdale, Ariz., experienced unprecedented population growth in the 1980s. However, hand-in-hand with the economic boom came a waste disposal challenge.
To complicate matters, the future availability of the local landfill, which was owned and operated by an outside agency, was uncertain, and thus the city needed an alternative. In particular, Scottsdale desired the flexibility to transport different kinds of waste to a variety of locations.
Once the city determined that a transfer station would meet its needs, it hired Camp Dresser and McKee, Cambridge, Mass., to help design and manage the facility.
The project team located a site next to the Tournament Players Club of Scottsdale, home of the Phoenix Open. Because the area includes exclusive neighborhoods and elite golf courses, the transfer station had to blend in with the surrounding desert landscape and architecture.
Scottsdale's growing population and the project's $2 million budget mandated a flexible and cost-effective design.
Designed to control noise and odor, the new single-hopper, or open-top, transfer station can handle 500 tons per day (tpd), with the expansion capability to handle 1,000 tpd.
The building can expand without interior columns because it was designed to span length (150 feet) rather than width (80 feet). All electrical and plumbing were designed to allow permit capacity to double. In addition, twin tunnels were built.
Tipping takes place inside to control outside odor and noise. Because the building length in front of the hopper is 125 feet, various sized collection vehicles can empty their waste easily.
Design flexibility lets different trailer lengths into the hopper, and a height clearance of 23 feet allows collection vehicles to operate with their beds up.
Inside, high-pressure odor control sprays (120 gallons per hour, 1.5 horsepower, 1,000-pounds per square inch pumps) with atomizing fog nozzles are located above the hopper and main tipping areas to stifle odors. The spray ensures better dispersion and minimizes water on the tipping floor.
The Scottsdale facility, which opened in July 1996, has reduced travel time to the landfill from the city's northern areas, increasing the collection vehicles' productivity by 30 percent.
"The new transfer station allows us the flexibility that is needed in the changing solid waste field," says Pete Chavez, Scottsdale's solid waste management director. "The facility accepts recyclables that can be transported anywhere in the greater Phoenix area."
Blending into Santa Fe As Santa Fe, N.M.'s existing landfill neared closure, the city and county of Santa Fe selected a new, more remote landfill site.
The municipality's objectives were to minimize traffic on the access roadways to the new landfill and to continue the old landfill's high level of service.
The answer: Build a transfer station adjacent to the closed landfill.
"To provide for the area's future growth, we considered our waste needs for the next 20 years," explains Cindy Padilla-Cessarich, Santa Fe's solid waste management director.
Operational since May 1997, the Santa Fe transfer station can handle up to 500 tpd.
The 44,000-square-foot facility features separate drop-off areas for pick-up trucks, automobiles and collection trucks. This setup eliminates traffic and increases safety. Two hoppers handle peak waste disposal.
To build the site, the city had to move and replant 400 pinon trees, some of which were more than a century old. The displaced soil was used to close the existing landfill, which saved more than $1 million in cover soil cost.
Since residents were concerned that the facility was close to their neighborhoods, engineers designed it in a Santa-Fe architectural style.
An administration building located at the site looks like the transfer station architecturally and houses showers, bathrooms, computer capabilities and a large conference room.
The scalehouse includes two scales and a computer system and will be integrated with the administration building and city accounting department.
With a little hometown homework, the Santa Fe transfer station is serving as an aesthetically pleasing and efficient solution to the area's waste disposal challenge.
* Scales: Cardinal Scale Manufacturing, full electronic hipless motor truck scales.
* Stationary electric transfer "Grappler" crane from Northshore Manufacturing.
* Dust control misting system by NuTech Environmental Corp.
* Odor control system by NuTech Environmental Corp.
* Average amount of refuse accepted daily: 250 tons/day.
* Capacity: 400 tons/day. Maximum day - 550 tons/day.
* Waste sources: city vehicles only.
* Employees: three-man staff at transfer station, not including the truck drivers.
* Service area: North Scottsdale, Ariz.
Transfer Station: Freightliner tractors; Steco aluminum trailers; Weighmaster software (Information Systems Inc.)
Amount of refuse: Average tonnage is 280-300 tons/day. Peak is 410 tons/ day. The transfer station is open six days a week from 7 a.m. to 5 p.m.
Waste sources: * Private/self-haul (pick-up trucks etc.).
* City of Santa Fe/residential and commercial.
* Commercial (all private commercial haulers).
Employees: 1 superintendent, 3 supervisors, 6 drivers, 2 operators, 5 compliance technicians, 3 account technicians.
Service area: County of Santa Fe, - 110,000 people.
Local tipping fees:
* landfill: $25/ton.
* transfer station: $60/ton.