It seems that designing a transfer station should be a simple task. The tipping floor connects to the loading bays. A driveway here and there for moving collection trucks in and transfer trailers out. A scale to weigh incoming and outgoing loads. A building to protect customers, personnel, and equipment from inclement weather. Now you’re ready to receive trash, right?
Partially. While the basics of transfer station design and operations can be summarized fairly quickly, as so many projects can, the details are what often make the difference between a transfer station that moves waste from portal to pit effectively and one where every move interferes with something or someone. Simple issues such as turning radius, ceiling height, floor design, and equipment interfaces need to be considered before issuing the first contract.
By some professional estimates, each year sees 50 or more transfer stations of all sizes being proposed or developed across the country. The vast majority of transfer stations handle 150 tpd or less and serve small communities. Because the production volume is so low in these smaller facilities, configuration concerns are not such a problem. Collection vehicle traffic can range from 10 to 15 trucks per day in these facilities, so interactions between vehicles are usually very controllable, and the amount of waste to be moved is highly manageable.
At the other end of the transfer station spectrum are the behemoths: those 1,000-plus-tpd production giants that serve major metropolitan areas. These facilities experience high volumes of commercial truck traffic at peak times throughout the day. Traffic controls, noise management, and dust and odor suppression become critical issues in these large facilities since they maintain high visibility in the community and every little upset can result in complaints to regulators. Also, with this large volume of waste delivery, storage and processing capacity is also of critical concern. As a facility gets larger, and the hourly throughput volume increases, the criticality of the placement of features increases in order to ensure smooth movement of all materials.
Steps to Building a Transfer Station
The art and science of transfer station design is a major focus of SCS Engineers, a specialty environmental consulting firm. According the Erik Colville, project director with the company’s Bellevue, WA, office, the process of designing a transfer station begins with a standard set of steps that leads the client through the process. “Conceptually, there’s a methodology that you can go through, but it really only exists at the concept level. The specifics of each of these steps varies by project just because each owner, jurisdiction, or locale is unique.”
The process starts with a roundtable meeting with the client and all the stakeholders involved in the project. “That would be the operations and maintenance people, the planners, and the landfill operators–those guys know the wastestream,” Colville points out. “We bring them together and spend at least half a day talking. There really isn’t an agenda other than to get information out on the table. There’s not even a conclusion that’s expected from this session. It’s information-gathering and relationship-building–getting people who have a stake in the process to take a personal interest in it so that they then are advocates rather than becoming some sort of adversary down the road.”
Once the information has been gathered from all the various parties, Colville and his staff prepare a high-level schematic of the design. This process provides the client with some idea of what configuration, shapes, and features can meet their requirements. This document compiles and presents all of the variables and statistics that define what the station will be capable of handling, including the projected number of customers, the tonnage, and the kinds of wastes that will be handled through the facility. According to Colville, this allows the customer to identify features and configurations that they like and don’t like.
All of this information is compiled into a report that forms the foundation for the design portion of the process. “That report essentially stands on its own,” says Colville. “It’s a document that can be shared with all the different stakeholders. They can make their comments to draw that sort of input from the stakeholders so that when we go into the design, we’re not missing major project features.”
Once this information has been reviewed, it’s time to start doing a preliminary design that lays out the transfer station onto the site. It’s during this process that the actual scale and relationship of the features are presented to the client for approval. Once this process is complete, a final design and bid package is prepared. “We would [at this point] be talking with equipment suppliers and evaluating alternative technologies to use in the building for processing, handling, or compaction,” explains Colville. “We’ve allowed the client to grow along with us and with the design as it has progressed so that when we get to the end, the design doesn’t contain surprises.”
While the process can seem straightforward and rote, hidden within the process are the years of experience that can make the difference between an OK result and a good project that satisfies the client’s needs. “As we go through all of those steps, what we are implying and actually attempting to teach each of the clients are the lessons learned over the last 20-some years,” notes Colville, “trying to make sure that the lessons learned are incorporated into the design. All of those kinds of things are not necessarily intuitive, they’re things that are learned from experience.”
One of the most significant lessons that he sees is the issue of traffic flow on the site. “More often than not, not understanding what the customer who comes into the transfer station needs to do with his vehicle [will lead to] conflicts.” For example, self-haul customers are favoring long wheel-based pickup trucks that, when coupled with a trailer, have turning radii similar to those of semi-trucks. Another problem is the siting of the building itself and the effect that has on dust- and litter-control off-site. “They [the buildings] kind of get plunked down into a site whichever way it makes sense,” he observes. “If you haven’t dealt with where the prevailing wind comes from and the changes in the prevailing wind each day, you frequently end up with a problem.”
Weber County, Utah
Many of the lessons discussed above were applied to the Weber County Transfer Station, located in Ogden, UT. The county purchased the 25-ac. site in 1999 to replace a temporary transfer station that itself replaced the landfill that closed. Construction of the transfer station began in November 1999, with completion a year later. The facility is designed to handle up to 1,200 tpd of solid waste and, in its first full year of operation, handled an average of 600 tpd with a peak loading of up to 800 tpd during the summer. The station now handles about 1,500 customers and provides service to 15 cities, the largest being Ogden, and the unincorporated county.
To minimize the vehicular conflict between small and large vehicles, the 4,000-ft.2 tipping floor is split down the middle, with residential customers handled on one side and commercial on the other. Garbage is compacted using a Caterpillar 826 compactor that precompacts the garbage prior to loading. The compactor is assisted by Cat 950 and 966 loaders to push the loads to the loading tunnel.
Unique to this station is the fact that it was designed to be served by railcars instead of transfer trailers. Empty cars are placed on two inbound storage tracks. The empty railcars are then moved to the loading track, entering from the rear of the building, and moved into place over a scale through the use of a Trackmobile. Above, a Cat 316 excavator straddles the loading chute, tamping up to 42 tons of garbage into each car. Once the car is loaded, it is moved out to one of two outbound tracks for pickup and shipment to the East Carbon Development Corporation’s landfill, located approximately 300 mi. away.
For Karlene Linford, solid waste director for the Weber County Solid Waste Disposal Department, the first step in designing a new transfer was to understand the basics. “I went to the SWANA Transfer Station Design course, then I went to other transfer stations to see what they were doing,” she recalls. “Plus we used the temporary transfer station for two or three years, so we kind of knew some of the things that we needed to incorporate in this facility.”
The roundtable approach to designing the transfer station presented by SCS Engineers worked well for Linford and her staff. “They have a concept that you work with it all the time, everyday,” she states. “They would bring their ideas in and say this is the way we’re going to set it up.” One of the issues that had to be addressed was the traffic flow and type of vehicles. “We did a survey of the amount of cars we had coming in and going out, and we did it over a year’s time. That gave us an idea of how many people we would have on-site at one particular time.” This survey information was then used to develop a traffic flow plan for the site that it could handle.
While siting issues with the surrounding neighbors were of concern during the process, Linford is pleased with the final results. “What I really like about this facility is you don’t know this is a transfer station when you drive by. We have the whole operation inside–the garbage comes into the building, and it’s loaded into a container and covered before it ever leaves.” With the new facility now a year in operation, are there any changes she would make in retrospect? “I’d probably curb the landscaping so the trucks wouldn’t run over the grass, make the doors 20 feet wide, and make the building wider, maybe 250 feet instead of 200 so there is more room for the commercial haulers to back in and out.”
Even old transfer stations can learn new tricks. For example, Waste Management’s transfer station that services the metropolitan Atlanta, GA, area was originally constructed in 1994 as an open-top, tunnel load facility. The facility handled an average of 1,150 tpd on a tipping floor of approximately 12,000 ft.2, with a peak loading of 1,500 tpd. The facility sees approximately 190 trucks per day.
Basic dissatisfaction with the way the transfer station operated led Waste Management to retrofit the station in 1998, according to David Stuart, district manager. “We decided to do [the retrofit] for a couple of reasons,” he says. “One is that we realized to mitigate some problems that we had. With the open-top design, all the trash does not go into the top of the truck, so you get a lot of spillage with that. The way our facility is designed, you are able to see the tunnel, so anytime we spilled trash, our neighbors who are right across the street could see the trash on the ground below the loading area. We had to constantly have somebody down there picking that up. You can’t clean it out until the truck pulls out of the way, which means the truck has to drive over all the trash, creating tire problems and damage to the body.
“The other thing was the operation of running the transfer station is very abrasive to your floor and the area where you’re loading. If you are using an open-top loading for a transfer truck, the way you make sure that you maximize your loads is you use some way to compress the trash into the top of the trailer. We used a backhoe that sat right on the transfer station floor and, as the load was pushed into the top of the truck, with his bucket he would press down on the truck to try to get a 20-ton payload. This creates other problems–like the sidewalls of the trailer would get ripped, torn, and buckled.”
The combined concerns of equipment damage, floor maintenance, wind-blown litter, and leachate management led the company to retrofit two 80-tph compactors into the pit. “The decision to clean that up came, and we decided that an investment in these compactors would solve most–if not all–of those problems,” Stuart recalls. “Basically, we took the two holes, and with a little welding and other basic ingenuity, we installed the compactors. We drop the trash into a hopper that feeds the compactor, which compacts trash into the back of a trailer.”
The solution improved productivity in the facility as well as eliminated the problems. The installation of the new compactors also required the company to replace its entire fleet of top-loading transfer trailers because of incompatibility. “We had to sell off our entire fleet of trailers and buy a fleet of 20 trailers that would attach to this compactor,” explains Stuart. “They have to lock into the compactor for it to work, so it was a huge equipment change. But the other benefit was that it eliminated tarping. There’s no tarping involved, and it increased turn time because as soon as the trailer is loaded it’s ready to go. It takes less time to get a 20-ton load on a trailer with these compactors than it does for open-top loading. We probably picked up 10 to 15 minutes per trailer per load by installing these compactors and eliminating tarping.”
According to Stuart, the lessons learned are still continuing as a result of new regulations not considered when the station was built. “Surface-water controls are something I can’t emphasize enough,” he remarks. In 1994, National Pollution Discharge Elimination System requirements weren’t even in place, which require pollutant controls on water discharges resulting from storms, cleaning, and management activities. “We’ve redesigned our entire surface-water management system so that we don’t release anything that’s come in contact with trash to receiving channels around the facility. We handle the water completely different where we manage the entire watershed.”
Another lesson learned is to plan for expansion of the operation. Scale maintenance has become an issue, observes Stuart. “We have one scale at our facility. When you get over 600 tons per day, you really need to start planning for your second scale. When you hit 1,000 tons per day, it probably is time to install it. Our facility is not laid out, and it was never considered for the second scale. If you are planning on building a large transfer station, you should really figure out where it’s going to go–make sure you can put it in and plan on it.”
Finally, Stuart also suggests that as you’re designing the transfer station, consider how major periodic maintenance activities can be done without disrupting the flow of traffic or the movement of waste through the facility. “We’ve resurfaced the floors twice since 1994. Our facility never shut down while we did the process. We were running a 1,100-ton-per-day transfer station on half a floor because we did half of the floor, let it cure for a month, and then did the other half. For about two months, we ran on 50% capacity. We chose to do that in the coldest time of the year because that’s our slowest time, with the least impact on our customers, but it’s the worst time to pour concrete. We had to go with that kind of a nightmare because consideration was never given to how to maintain the facility.”
While the components of a transfer station are simple, consideration for how all the pieces fit together is an important part of the process. Spending time on the front end of the process, with knowledgeable assistance, can help identify exactly what the current needs are for the facility, the limitations of the site and the waste flow, and how to optimize everything for smooth operations. Equally important is gazing into the crystal ball and making an educated guess on what growth might occur in the facility and to at least consider planning additional capability into the system at the time of construction. Finally, with the lessons learned, plan for routine rehabilitation so that when a major rehabilitation is performed, the operation doesn’t fall into the pit.