Site Savvy

WHEN A COMMUNITY LEARNS that a transfer station will be built next to an airport, it might not welcome its new neighbor. But thanks to savvy planning, Snohomish County, Wash., is proving that the skies can be friendly.

In the late 1990s, the county was facing a waste volume problem. The county's three recycling and transfer stations were working beyond their capacity, processing more than 440,000 tons of waste per year. Customers endured lengthy delays, service restrictions and frequent equipment malfunctions at the facilities.

To reduce the over-loads, the county decided to replace two of the older transfer stations with ones capable of handling at least 1,500 tons per day. One of the new stations was sited adjacent to a large, publicly operated commercial airport, so there were concerns about safety and feasibility that needed to be addressed in the facility design.

The Airport Road Recycling and Transfer Station (ARTS) is wedged in a tight space between a wetland on the north and an airport runway protection zone on the south. The airport operations staff and the Federal Aviation Administration (FAA), in particular, were worried that ARTS would attract birds, which would strike the planes. They also were concerned that the facility would create a reflective glare and that lights would negatively impact air traffic controllers and pilots.

To help prevent a potential bird problem, the design team hired to assist with the project avoided installing permanent open-water detention ponds, which are attractive to waterfowl, but are the normal and least expensive method of providing stormwater detention. Instead, four large underground storage vaults were substituted, so there are no open-water bodies on the site. Two temporary sedimentation/detention ponds were used during the 24-month construction period, but these were netted to keep birds from gathering around the water.

Another source of bird attraction is the garbage. So to reduce the chance of offering birds a free lunch, the facility was fully enclosed. The designers recognized that waste from inside the building could be tracked onto the pavement outside the tipping floor, which also would attract birds. Consequently, the county constructed interior truck washout stations and track-off grating.

As another precaution, the county installed anti bird-perching devices throughout the facility. These included bird deterrent wires along the edges and ridges of all the building roofs, as well as bird spikes on perching ledges, such as the coiling door hoods and the exterior light fixtures.

Building lighting posed an issue for local airport officials and the FAA. Daylighting of buildings can reduce operating costs while boosting staff productivity and satisfaction. However, to prevent light from escaping skyward from roof skylights and distracting pilots at night, the designers instead installed sidewall translucent panels.

Airport officials also were concerned that a glare from the sun from would reflect off the transfer station's low-slope metal roof and interfere with the vision of the air traffic control tower. The transfer station facility designers were confident they could alleviate that problem, but their work was complicated by the fact that the airport's new, taller control tower would not be built until after the transfer station opened. So, a glare study using a graphical model was developed based on a celestial dome concept.

Once the existing and new tower positions were located relative to the exterior surfaces of the transfer station, sightlines refracted off of the building surfaces were projected onto a celestial canopy in the model. Using the annual solar patterns as a guide, project designers noted where the sun's path potentially could coincide with the reflected extent of the building roof.

The graphic depictions showed that the resulting angular difference between the sun glare reflected from the building and from the sky was negligible. This demonstrated to the FAA that only the roof, and not the walls, had reflective potential, as well as proved that the actual sun angle occurs in the same field of view as the transfer station roof. The conclusion reached in the glare study was that actual direct sun glare predominates in the control tower field of view during the period when building reflection is possible. Reflected glare from the building was considered an insignificant contribution.

Nevertheless, to further decrease the potential for roof glare, the county coated roof panels with an ultra-low-gloss finish of 10 percent, versus the normal panel gloss finish of 70 percent.

ARTS, which opened in October 2003, now features an open-plan, columnless, flat-floor tipping floor that is built with two levels to provide separation between the commercial and self-haul customers. The 10-acre facility, designed to process at least 1,500 tons of municipal solid waste per day, includes a large self-haul customer recycling area and a scale facility. Since the station opened, there have been no problems with birds congregating at the facility or interfering with aircraft.

Despite what the community initially thought, ARTS has proved that transfer stations and airports are not necessarily incompatible. In fact, a transfer station can be a good neighbor to an airport when the safety issues are understood and addressed comprehensively during design.
Karl R. Hufnagel
R.W. Beck Inc.