Not many years ago, the ma-jority of the nation's cities and counties owned conveniently-located landfills. Because of the short hauls, few communities needed a transfer station.
Distances between landfills grew, and by the early 1990s, the U.S. En-vironmental Protection Agency re-leased landfill regulations that have caused many smaller landfills to go out of business.
One of the ripples caused by these closures was the rise of small transfer stations. In fact, the majority of U.S. transfer stations are small, ac-cording to a 1994 survey. More than 50 percent of the survey's respondents transfer less than 25 tons per day (tpd) and another 20 percent transfer 25 to 100 tpd.
However, transfer stations are not appropriate for every municipality. To determine if it's appropriate for your community, you must consider economic feasibility, siting, station type, additional design elements, re-cycling and capital costs.
Economics And Siting To determine if a transfer station is economically feasible, compare transfer costs against direct haul costs.
Transfer stations' capital costs include site acquisition and improvements, fixed equipment, buildings, engineering, road tractors and transfer trailers/containers. Operating costs include labor, maintenance, u-tilities, equipment replacements, tires, fuel and insurance.
Capital costs for direct haul in-clude the truck chassis and body; operating expenses include labor, fuel, tires, maintenance and insurance.
Finally, evaluate the transfer station's other advantages such as: * Decreased landfill traffic;
* Decreased refuse collection vehicle maintenance; and
* Increased recycling opportunities.
A transfer station's site is critical to its success. For maximum efficiency, locate the transfer station near the collection area. Also, select a site that is large enough for expansions.
In addition, the facility should be near major haul routes and have access to a dependable water supply (for cleaning and fire protection), electric power and wastewater service. A well, storage tank and pumping system should be included on-site to ensure a constant water sup- ply. To safeguard the expensive transfer trailers as well as the building, a fire protection system would be a sound investment.
Station Type Small and rural transfer stations types include non-compaction and compaction.
Non-compaction stations are de-signed for full-sized transfer trailers or roll-off containers.
At the upper level of the transfer station, collection vehicles back up to steel or concrete hoppers and discharge the waste into an open-top transfer trailer or container. This type of facility is called a "direct dump" transfer station.
If the facility doesn't have hoppers, then users must unload over the edge of a retaining wall, directly into the container. A stationary clamshell or a clamshell attachment on a backhoe/excavator can level and compact the wastes in the trailer.
The direct-dump method requires a minimal amount of equipment and labor to load the trailers. It also can be used in transfer stations which accept wastes directly from the public. However, with this method, trailers must be ready to accept wastes as they are delivered. If unloading space is not available, the vehicles must queue up.
If there's enough space on the up-per floor, wastes can be unloaded during peak periods and pushed into the hopper as trailers become available. However, construction costs for the floor and enclosure may make this method impractical for smaller transfer stations.
This method allows the continuous unloading of wastes, even while changing trailers or containers. Also, unloading vehicles on the floor al-lows recycling and hazardous materials separation before the wastes are loaded into the trailer.
Compaction transfer stations have two levels. Collection vehicles discharge wastes into a hopper or an upper level pit. Next, the wastes are compacted into a transfer trailer or roll-off container attached to the compactor on the lower level.
Many stations use a 10- to 15-foot wide pit to store wastes before compaction. In the pit, a hydraulic push blade moves the waste into the compactor. Although several collection vehicles can dump into the pit at once, waste can't be dumped while the push blade is moving.
At smaller stations, where storage capacity is not always critical, the waste is unloaded directly into the compactor's receiving hopper. How-ever, with this method, only one ve-hicle can unload at a time.
To allow simultaneous unloading, a larger tipping floor can be built on the upper level. This is not typical for the smaller rural transfer stations, which often do not use the extra floor space due to costs (if the storage is located indoors).
The storage pits of newer compaction transfer stations often in-clude moving floors, such as those manufactured by Keith and Hallco, which continuously bring wastes into the compactor chamber allowing collection vehicles to unload without interruption. Moving floors reportedly eliminate the problems that are associated with hydraulic push blades.
Several proprietary transfer systems are on the market. For example, one system allows upper level vehicles to unload wastes into a met-al bin on the lower level. The bin can be rotated to dump the wastes into a trailer or roll-off container on the lower level. This system requires a minimal height differential and re-duces construction costs. The covered bins reportedly prevent moisture from seeping in and reduces the chance of litter blowing away.
A typical bin costs approximately $30,000 (not including installation, retaining wall and site improvements). Additional fencing, enclosures and other methods which re-duce blowing litter will considerably increase costs.
When selecting containers or trailers, consider the volume of waste and the type of transfer station. For example, containers (roll-off bins) are ideal for small transfer stations where the small volume of incoming waste does not justify transfer trailers and large tractors. Roll-off containers can be ordered with an open-top for non-compaction transfer sta- tions or enclosed for compaction stations.
On the other hand, larger transfer stations usually require transfer trailers, which typically can hold 15 to 25 tons. At non-compaction stations, open-top trailers contain ap-proximately 65 to 110 cubic yards and include a variety of unloading systems.
Compaction systems use enclosed trailers, which are backed up to the compactor's discharge opening and locked in place. These trailers are u-sually smaller than open-top units since they hold compacted waste. Transfer trailers which range between 65 to 85 cubic yards cost an estimated $40,000 to $50,000 each.
Design Considerations Most small transfer stations select a pre-engineered metal building with metal siding since it is cost-effective. Architecturally finished concrete blocks can be combined with the metal exterior to brighten the ap-pearance of the transfer stations. In addition, trees and shrubs may soften the rough appearance.
Enclosing the hoppers or compactors inside the building will re-duce odors, rodents, dust, noise and blowing litter. Odor control systems can be connected to the ventilation system and, in dry climates, where dust is a major problem, automatic or manual water spray systems can moisten waste as it's unloaded into the hoppers or compactors.
To control loud noises, the roadways should be designed so that ref-use collection and transfer vehicles don't have to climb steep slopes.
Scales and computerized systems, which compute charges and record the amount and types of incoming wastes, have become a necessity at small transfer stations. A basic electronic load cell scale (installed) costs an estimated $35,000 to $55,000.
A small scale house should be provided if the facility is open to private haulers or if the public is charged a fee. Several manufacturers can provide prefabricated booths and basic computer systems. A computer system with equipment and software will cost approximately $7,500.
Large transfer stations need to provide fuel storage and dispensing facilities for fuel-driven transfer tractors, backhoe/excavators and wheel loaders. However, safety and environmental requirements have made these facilities costly for small transfer stations.
Safety should be a primary consideration in the design and operation of a transfer station. Install drop-off boxes outside the building for small loads or separate unloading slots to keep the public's vehicles away from commercial and municipal collection vehicles. Equip the public-accessible push pits or hoppers with guard rails. Removable railings can be provided for unloading space which is used by large collection vehicles. Fence in the site perimeter and al-ways lock the gates when the facility is not in use.
Recycling Methods Several low-cost recycling methods are available for small and rural communities. For example, one simple method provides several bins or roll-off containers for recyclable ma-terials. However, it is very important to position the bins or containers in an area that is easily accessible and away from large refuse collection ve-hicles. When the bins or containers are full, they can be transported to a processing center. Many rural communities often work with nonprofit groups to process recyclables.
Small, portable picking systems can be used in communities with curbside collection programs. To justify this system, the community should generate sufficient amounts of commingled recyclables which re-quire separation before shipment or processing.
To inspect the incoming materials, they must be unloaded onto the floor before being pushed into a compactor or open-top trailer. If, for ex-ample, a load contains a lot of corrugated cardboard, the operator can retrieve the material before it's loaded in the trailer.
Stations should use double-walled tanks to collect motor oil for recycling. Waste oil processors contract with communities to collect the oil from the transfer stations.
Household hazardous wastes collection also should be considered in the facility's design. In states which require household hazardous waste collection, the transfer station is an ideal location. If a rural community lacks the technical and economic re-sources to process or analyze the hazardous wastes, it may want to limit this operation to collection and employ a hazardous waste contractor to remove and dispose the material.
Specially designed storage trailers can store small amounts of household hazardous wastes. These units typically include provisions for fire protection, secondary liquid containment, explosion-proof construction, ventilation systems, corrosion-resistant coatings and grating.
Transfer station construction and operation costs vary from area to ar-ea. The capital costs of small transfer stations range from $100,000 for uncovered, non-compaction, roll-off facilities to approximately $600,000 to $700,000 for enclosed, non-compaction, single hopper transfer stations which include on-the-floor storage space.
Other construction costs include site work, utilities, building foundation and superstructure, compaction equipment and the scales and scale booth. Special architectural finishes and difficult site conditions can considerably increase costs.
Do not be fooled by the size of a small transfer station: small tonnages do not necessarily mean small construction and operational costs.