Diversionary Tactics

Unlike most transfer stations, a new facility near Seattle will be able to sort, process and recover recyclables.

The fact that King County, Wash., is set to build a new transfer station is, in and of itself, not big news. But this isn't your typical transfer station.

This month, the county's Department of Natural Resources and Parks' Solid Waste Division (SWD), which manages approximately 1 million tons of municipal solid waste (MSW) each year through its eight-station transfer system, will begin construction on a 2,500 ton-per-day transfer station in Tukwila, Wash, about 10 miles south of downtown Seattle. The Bow Lake Recycling and Transfer Station, which will feature a flat-floor tipping and receiving area, will replace an existing maceration pit-type transfer station at the same location.

What will set this 70,000-square-foot transfer station apart from its sister stations in King County — and from most transfer facilities around the country — is that the tipping and receiving floor includes a recovered material sorting, holding, baling and loadout area. This 10,000-square-foot processing area will be located at the opposite end of the station from the where MSW will be loaded onto transfer trailers.

The new transfer station, which is slated to begin operations in 2011 also will include separate tipping areas for self-haul residential and commercial customers; an organics and green waste receiving, processing and top-load transfer area; two 120-ton-per-hour preload waste compactors; and a number of features designed to minimize the environmental impact of the facility. These features include:

  • a tire wash for exiting commercial customers to eliminate tracking of waste onto nearby roads;

  • a truck washing station;

  • a dust extraction and collection system;

  • a dust and odor misting system;

  • a vehicle exhaust monitoring system;

  • solar power generation;

  • rainwater collection for use in the non-potable water system;

  • variable fluorescent lighting system for the operations areas combined with extensive natural daylighting; and

  • heat recovery and reduced energy consumption mechanical systems.

Partly because of these features, the new transfer station is slated to receive gold certification from the U.S. Green Building Council's Leadership in Energy and Environmental Design (LEED) program.

The current Bow Lake station serves a large industrial, commercial and warehouse area in addition to a large residential population. Many of the commercial waste loads are rich in recoverable materials, and SWD estimates that nearly 7 percent of the 300,000 tons of waste processed each year at the station could be diverted from landfills.

The materials targeted for recovery include clean wood, cardboard, film plastics, carpet and textiles, and scrap metals. Most of these materials arrive in mixed commercial loads and will require some sorting.

Loads rich with recyclables will be directed to the sorting end of the tipping and receiving floor, well away from the MSW tipping area. SWD expects to use a rubber-tired or rubber-tracked material handler and one or more skid steers to sort this material. Hand sorting will not be used. Occasionally, one of the two large front-end loaders operating in the MSW area will be used in the processing area. But generally, the processing and sorting operation will be kept completely separate from the MSW operations to minimize the contamination of recovered materials. The processing area is in no way intended to be a dirty materials recovery facility.

Once the recyclable material has been sorted, it will be pushed to bunkers where it will be held prior to baling, or — in the case of the carpet, wood and heavy gauge scrap metal — loaded into roll-off boxes. During the baling operation, cardboard, film plastics, textiles and possibly light-gauge scrap metal will be pushed from the holding bunkers onto an in-floor conveyor that will deliver the material to a heavy duty two-ram baler.

Baled materials will be stored in separate holding areas or directly loaded into trailers or containers at one of two loading dock stalls. Material collected in roll-off boxes will leave through the main exit door of the receiving floor. None of SWD's eight stations currently include this sorting and diversion capability, so there will likely be some operational experimentation involved when the new station comes on line.

The primary motivation to incorporate diversion capability in the new transfer station is not the monetary value of the diverted materials — which is good, given today's low prices for most of these materials. Rather, the motivation stems from the desire to minimize disposal costs and the county's objective to increase its diversion and recycling rate, which is currently about 46 percent.

The Bow Lake station operates 24 hours a day and handles about one-third of the total material managed in the King County system. SWD owns and operates the landfill where the county's MSW is currently disposed. Once the new Bow Lake facility opens, SWD will consider exporting the waste from the station to an out-of-county landfill or to other types of disposal sites with the objective of extending the life of its landfill. Therefore, any diversion of materials from disposal will be of considerable value to the county. In order to encourage generators to deliver pure or uncontaminated loads of recyclables to the Bow Lake transfer station, SWD might consider a reduced tipping fee for these loads.

There appears to be growing interest around the country in transfer stations capable of recovering recyclables that, for various reasons, cannot practically be diverted at the generation source. In most instances, retrofitting existing transfer stations that were not sized or configured for this type of recovery operation is not practical, but inclusion of this capability may be worth considering when a new station is planned. The preliminary estimate of the capital cost of the Bow Lake station is around $54 million. The estimated cost of the recyclable processing area is around $2.2 million, including nearly $400,000 in mobile equipment costs.

Karl Hufnagel is a principal and senior project manager in R. W. Beck, Inc.'s Seattle, Wash., office and has been leading solid waste siting, planning, design and construction projects since 1989. He is managing the Bow Lake project design and can be contacted at 206-695-4509 or khufnagel@rwbeck.com for more information about the project.