Transfer Station Rehab

Robert Carn

Transfer stations across the country are getting an overhaul, and the changes are more than cosmetic. In fact, they are fundamental design changes to accommodate the latest round of solid waste recycling and transportation demands.

The goal of rehabilitating a transfer station is to create a blend of efficient traffic circulation, recovering recyclables and finally, transferring waste.

This theory is being translated into reality at the municipally-owned transfer station in Portland, Ore. Metro South, which began operations in 1981, originally consisted of a 30,000-square-foot structure (150-feet x 200-feet) with a 40-feet wide by 12-feet deep surge pit running the building's full width.

It was designed to receive and transfer 400 to 500 tons per day (tpd) on average, with peak tonnages up to 700 tpd. Currently, Metro South serves both commercial haulers and the general public.

* Commercial packer trucks and dropbox vehicles are weighed on the in-bound scale and enter the building at the south end where they unload the waste into the surge pit. The vehicles leave after going through the truck wash (if necessary) and over the exit scales.

* After being weighed on the inbound scale, the general public proceeds to the station and unloads. Their vehicles then are weighed on exiting the facility, and the appropriate fee is charged. This process adds substantially to the problem of vehicles lining up at the exit scale.

Prior to the late 1980s, the transfer trailers were top-loaded directly from a track-mounted dozer in the surge pit. A tunnel was located at the surge pit's west end for the transfer trailer to maneuver into loading position.

The station has undergone two major modifications. First, in the late 1980s after its local landfill closed, Metro installed compactors to condense its waste, which its transferred to a landfill 150 miles east.

The traffic patterns and unloading operations for commercial trucks and general public vehicles remained the same. However, transfer trailer traffic and loading operations were revised:

* The new compactors were installed at the low end of a ramp at the building's east end. The compactors now are top loaded by the same track-mounted dozers which originally loaded the trailers. The loaded trailers are weighed at the top of the ramp.

* Transfer trailers enter at a new entrance east of the main building, travel down the ramp and then reverse up to the compactors for loading.

* A large area was developed at the east end for trailer parking.

The second major change to Metro South was in 1991 with the addition of a 4,000-square-foot household hazardous waste (HHW) facility. This operation is located in the lower elevation area, where the transfer trailers were formerly loaded.

Proposed Modifications Metro South experienced a couple of major problems last year due to an efficient solid waste collection program, an aggressive statewide recycling goal and a lack of other transfer stations in the greater Portland area:

* Waste volumes exceeded an average of 1,000 tpd with peaks up to 2,000 tpd. The facility was designed for 400 tpd average and 700 tpd peak.

* More than 200 commercial trucks and 300 public vehicles used the facility daily with public vehicles exceeding 600 on the weekend. The facility was designed for a daily average of 80 commercial and 200 public vehicles.

* Significant traffic congestion and queuing problems occurred both before the scales and from the scales to the building. Queuing problems also occurred regularly at the exit scale.

* Due to the pit operations and the limited space in the commercial and public unloading areas, limited capability existed to recover recyclable materials.

* Severe flooding resulted in major damage to the HHW facility in February.

After reviewing the options to improve traffic circulation, reduce vehicle congestion and increase the ability to recover recyclable materials, Metro created a plan, which included:

* Widening the entrance roadway by another lane for a total of three, one exit lane and two in-bound lanes. This allows one for commercial and a second for public vehicles, from the site entrance to the in-bound scales.

* The HHW building would relocate to an area east of the transfer building. This new building will have additional space for storage and room for proper identification. Its location also is high enough to eliminate the chance of flooding.

In its place will be a public drop off area for recyclables. And since both groups will now bypass the in-bound scales, traffic will be reduced.

* When the HHW is relocated, it will be necessary for all vehicles going directly to the HHW facility to stop at the inbound scale.

* When the public unloading area is relocated, all public vehicles will still need to stop at the inbound scales for weighing prior to proceeding to the unload area.

Recycling Modifications Removal of the public from unloading in the main transfer building results in the ability to unload nearly twice as many commercial vehicle loads simultaneously into the surge pit. This reduces the traffic congestion generated by the increased waste volumes.

But, even more importantly, it creates space where "rich" commercial loads, or loads containing a high percentage of recyclable materials, can be unloaded onto the tipping floor and these recyclables removed from the waste stream. Metro can segregate the commercial vehicles onto different sides of the surge pit, depending upon their waste composition.

Another proposed modification was to install a sorting line where "rich" commercial loads can be placed. This sorting line is more efficient than on-floor sorting and will maximize the recyclable materials which can be recovered. The recyclable materials sorted from the line are dropped into the drop boxes located at the old public recyclables unloading area.

Rehabilitation of a transfer station requires a program of data collection, operator involvement, management goals and a plan detailing options and implementation. The final operations must meet the owner's specific re-quirements while being flexible for the future.

Refuse Processed: 700 tons per day (tpd) capacity, 1,400 tons per day average transferred each weekday

Compactors: Amfab TP 500 (100 tons per hour) and Shredding Systems Inc. (100 tons per hour)

Waste Sources And Percentages: 1,100 tpd residential packer trucks, 160 tpd commercial packer and drop box loads and 140 tpd private haulers. There is no construction and demolition debris or curbside collected recyclables at the station.

Service Area: Approximately one-half of greater Portland, Ore., area. 400,000 to 500,000 in population

Local Tipping Fees: $75 per ton. There are no all-purpose landfills in the local area.

Factoid: 60 percent of the traffic is private haulers, representing only 10 percent of the waste volume.