Transfer Stations
Determining Transfer Station Size and Capacity
The physical size of a planned transfer station is typically determined based on the following factors:
The definition of the service area. Sometimes this is relatively simple, such as “all waste generated by Anytown, USA,” or “all waste collected by Acme Hauling Company.” Other times, the service area is more difficult to define because of varying public and private roles in solid waste management and the changing availability of existing disposal facilities.
The amount of waste generated within the service area, including projected changes such as population growth and recycling programs.
The types of vehicles delivering waste (such as car or pickup truck versus a specially designed waste-hauling truck used by a waste collection company).
The types of materials to be transferred (e.g., compacted versus loose MSW, yard waste, C&D), including seasonal variations.
Daily and hourly arrival patterns of customers delivering waste. Hourly arrivals tend to cluster in the middle of the day, with typical peaks just before and after lunchtime. Peak hourly arrivals tend to dictate a facility’s design more than average daily arrivals.
The availability of transfer trailers, intermodal containers, barges, or railcars, and how fast these can be loaded.
Expected increases in tonnage delivered during the life of the facility. For example, in a region with annual population growth of 3 to 4 percent, a facility anticipating a 20-year operating life would typically be designed for about twice the capacity that it uses in its first year of operation.
The relationship to other existing and proposed solid waste management facilities such as landfills, recycling facilities, and waste-to-energy facilities. The same factors are used to determine the size of the following transfer station features:
Amount of off-street vehicle queuing (waiting) space. At peak times, vehicles must often wait to check in at a facility’s “gatehouse” or “scale house.” It is important that the queue (line) not block public streets or impede vehicular or pedestrian traffic.
Number and size of unloading stalls, and corresponding number of transfer trailer loading positions.
Short-term waste processing and storage areas (for holding waste until it can be reloaded into transfer vehicles).
Present and projected daily, weekly, and annual waste volumes (including seasonal variations) are important in planning facility size to accommodate waste deliveries. The maximum rate at which waste is delivered is a crucial consideration as well. In general, it is best to build a facility to accommodate present and projected maximum volumes and peak flows, with a preplanned footprint for facility expansion. A useful exercise is calculating how much tipping floor space a facility would require to store a full day’s waste in case of extreme emergency. One approach to estimating the required tipping floor space is to begin with a base area of 4,000 square feet and add to it 20 square feet for each ton of waste received in a day (assuming the waste will be temporarily piled 6 feet high on the tipping floor).1 For example, if the facility receives 100 tons of waste per day, a tipping floor space of 6,000 square feet would be required (i.e., 4,000 ft2 + (100 TPD x 20 ft2/ton) = 6,000 ft2) “Chapter 4: Collection and Transfer” in EPA’s Decision
Maker’s Guide to Solid Waste Management also provides a series of formulas for helping determine transfer station capacity.
Number and Sizing of Transfer Stations
Design capacity is determined by the maximum distance from which waste can be economically delivered to the transfer station. The area that can efficiently reach the waste transfer station determines the volume of waste that must be managed, which is the facility’s initial design capacity. Beyond a certain distance, another transfer station might be necessary, or it might become just as cost-effective to direct haul to the disposal facility.
Transfer stations serving rural or tribal areas tend to be small. They are optimally located within a reasonable driving time from the service area’s largest concentration of homes and businesses. For example, a rural transfer station could be located near one of the service area’s larger towns and sized to take waste from all waste generators within about 30 miles. As an example, two 50-ton-per-day transfer stations might each serve six small communities. Alternately, fewer transfer stations could be used, necessitating longer average travel distances. For example, one 100-ton-per-day transfer station could be used to serve the same 12 small communities, but it would be located farther from the outlying communities.
In urban or suburban areas, the same situations exist. A midsize city (population
500,000), for example, might decide that two 800-ton-per-day transfer stations would best serve its community. This same city could alternately decide that a single 1,600-ton-per-day transfer station is its best option, even when the longer driving distances are considered. When deciding which approach is best for a community, issues to consider include the impacts the transfer station(s) will have on the surrounding area, siting complications, and the cost to build and operate the transfer station(s). Each approach offers advantages and disadvantages that must be reconciled with local needs.
The biggest advantage of constructing large transfer stations is the economies of scale that can significantly reduce capital and operational costs. Centralizing waste transfer operations allows communities to reduce equipment, construction, waste handling, and transportation costs. The siting of a single facility may often prove easier than siting multiple facilities. Large facilities are also conducive to barge or rail operations that can further decrease traffic-related impacts on the community. Along related lines, however, a major drawback to building a single large facility is locating a tract of land that adequately meets facility requirements. Large facilities also tend to concentrate impacts to a single area, which can create the perception of inequity, especially when one neighborhood is shouldering the burden for the entire city. A single facility can result in longer travel times, which leads to increased down time for the collection crew and increased wear and tear on collection vehicles. Another consideration is that a single facility cannot divert waste to a backup facility if a need arises. The single facility must have additional equipment in case of equipment failure or other emergencies.
In other situations, multiple smaller sites might better address a community’s waste management needs. Decentralizing waste transfer operations spreads lesser impacts over a wider area, which helps address equity issues. Although it is generally more expensive to build and operate several small transfer stations rather than one large station with the same total capacity, savings from reduced travel times might offset these capital costs and result in lower overall system costs. Multiple facilities also are better able to serve as backups for one another in case of scheduled or emergency shutdowns of facilities. The major disadvantage to building multiple facilities is that the difficulties encountered in siting a single facility can become multiplied.
Future Expansion
Transfer stations are frequently designed to accommodate future expansion. Often, this is accomplished by siting the facility on a larger parcel of land than would otherwise be necessary and preplanning the site and buildings so expansion can occur without negatively affecting other functions on the site or the surrounding community. Although expansion of effective capacity can sometimes be accomplished simply by expanding the hours of operation, this approach is not always effective because the transfer station must accommodate the collection schedules of vehicles delivering waste to the facility. In addition, increased operating hours might not be compatible with the surrounding community.
—www.epa.gov/osw/nonhaz/municipal/pubs/r02002.pdf.
Note
Solid Waste Association of North America. 2001. Transfer Systems Management Training Course. SWANA. Washington, DC.