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County ‘swaps’ litter and debris for clean soil

It’s a dirty business keeping county roads clean, but the King County Road Services Division has a successful program that not only cleans the streets but also recycles the waste collected into useable soil.

A trommel extracts solid waste from reusable soil.

“We collect somewhere in the neighborhood of about 15,000 cubic yards a year,” said Doug Navetski, a senior ecologist with the Roads Division. “We want to do something with it in a responsible manner, so we run it through our SWAP program.”

The Division’s maintenance unit collects the debris through street sweeping and cleaning out storm drains. In 2006, the sweepers collected 4,128 tons of debris and another 5,762 tons was sucked out of the drains.

In order to turn the waste into soil, all litter and contaminants must be removed. For this task, the county uses big machinery along with some microscopic allies.

First the litter needs to come out. The swap program picks up about 22,000 pounds of litter a year from county roads. A big machine called a trommel runs the debris through a revolving screen that separates the dirt from the garbage.

Next, the soil is moved into covered bays where it's stockpiled and allowed to sit for several months. The dirt can contain small amounts of oil or other material. So to tackle that problem, the job is handed over to a smaller set of workers – bacteria and microorganisms that eat the contaminants leaving behind clean soil.

Soil comes off the conveyor belt to later be decontaminated.

Before the SWAP program was launched, the county spent between $550,000 and $730,000 a year to dispose of waste solids from its roads. SWAP has cut that number by about half. And, even through it has a 97 percent efficiency rate, the county hopes to reduce that amount by the year 2030.

“Since 2003, the SWAP program has processed 30,000 cubic yards of materials that used to be sent to landfills,” said Debbie Arima, Roads Maintenance Manager. “This program saves the county money, it provides us with high-quality materials to use in other projects, and delivers multiple environmental benefits.”

Updated:  June 12, 2007

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