From green bin to black gold at Sonoma Compost. 

Halfway through a tour of Sonoma Compost, on a hill above the green rolling valleys of Petaluma, I stick my hand into a freshly turned pile of decaying organic material. It’s steaming hot. So hot, you could stick a turkey into the middle and it would be slow-cooked by the following day, says Sonoma Compost general manager Pam Davis. 

I’ve come to Sonoma County’s full-scale industrial composting facility to discover what happens to the vegetable scraps, eggshells, and pasta that I collect in a bowl on my kitchen sink. Where do they go after being unceremoniously dumped in my stinky green bin? Davis, who has worked for years in waste management, is a gregarious and knowledgeable tour guide. Sonoma Compost’s goal, she says, is to build healthy soil. But it’s quite the process to get from green bin to black gold.

Since I live in Santa Rosa, my bin is picked up weekly by a collection truck owned by the Ratto Group. The truck then delivers the mix of materials to Sonoma Compost, up the hill from the Central Disposal Site on Mecham Road. On a recent warm April morning, I see truck after truckdump their goods. Sure, there is a fair amount of yard debris, leaves, and food scraps, but there are just as many items that aren’t compostable: a water cooler, old sheets, pants, a plastic water gun, fast food wrappers, Styrofoam, red tinsel, bags full of trash, water bottles, beer bottles, and lots of potting soil bags. 

You wouldn't believe what comes through here. ~ Pam Davis

Watching the waste pile up, I feel an existential crisis coming on, the kind that can only happen when you find yourself staring into the tailpipe of consumption. Davis says it takes five full-time workers to clean and sort the material.

“You wouldn’t believe what comes through here,” she says. “This isn’t half as bad as I’ve seen it. Sometimes we get loads that are more than half trash.” Once, someone even dumped a dead pet snake.

Why are people abusing their green bins like this? Some people just don’t care (Davis calls it “deliberate defiance”), but mostly, she says, it’s a lack of education, a basic misunderstanding of how the waste stream works.

In Sonoma County, about 35 percent of residential garbage is food waste, totaling nearly 800 tons a week. Without Sonoma Compost, hundreds of tons of yard and food waste would end up in the landfill. Owned by Alan Siegle and Will Bakx, the company launched in 1993 as an expansion of Bennett Valley Farm Compost. After the California Integrated Waste Management Act passed in 1989, counties were mandated to divert 50 percent of all solid waste from landfills through reduction, recycling, and composting. Under a contract with the Sonoma County Waste Management Agency, the facility processes about 300 tons of material a day or 100,000 tons a year.


Michael Woolsey Photography

Gardeners and landscapers can also self-haul yard waste and building materials here. Recycled (non-pressure-treated) wood is used to make path mulch. Sonoma Compost also partners with local businesses on waste disposal. During my visit, a semi rolled in with piles of feathers from a local poultry processer. The feathers are mixed into 60 percent of the compost, giving it a high-nitrogen content.

The system works like this: After being delivered by commercial collection trucks or self-haul, the materials are sorted and screened for non-organic contents. What can’t be composted is tossed into a bin, destined for the landfill. Everything else is put into what Davis calls “the grinder.” The resulting tiny bits are formed into 10-foot-tall windrows, hundreds of feet long. A hulking windrow turner, a machine straight out of Star Wars, rolls through the piles, turning them five times over the course of a few weeks. In the meantime, microbial activity does its magic.

The material is screened again to remove contaminants and anything missed during the first screen. By this point, the waste is transformed into organic compost, available in Biodynamic, low-and high-nitrogen formulations. It’s then loaded onto a tractor and carried back up to the retail space where it can be purchased by the public. The compost is also delivered by cubic yard to landscapers, grape growers, and farmers.   

I watch the lumbering, oil-guzzling machines grind, spit out, and churn the compost, clouds of dust and steam rising up, and feel conflicted. Industrial-scale composting is deeply dependent on fossil fuels. The question is, does that make the whole process a contradiction in terms?

Ideally, composting would be done at home, Davis says. 

“The Sonoma Compost perspective revolves around highest and best end-use,” she explains. “Our feeling is, don’t create the waste in the first place. Plant appropriately for your landscape so you don’t have a lot to prune. If you do create the waste, then try to use it onsite.”

Facing new legal challenges, Sonoma Compost may soon stop supporting Sonoma County’s needs. But with a global crisis of depleted topsoil, building healthy soil is the right thing to do.

“The more healthy the soil your food is grown in, the more healthy your food will be,” Davis says. “If we can help foster more healthy soil in everybody’s backyard, then that would be fabulous.”

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