This is part of CapRadio’s new series “Great Question!” where our we answer listeners' most pressing inquiries. Learn more at capradio.org/greatquestion.

It can be easy to forget about yard waste after you’ve put it in the curbside bin — unless you’re one of the people tasked with hauling, sorting, filtering and grinding it.

Ellen Chapman doesn’t work in waste-processing. She’s a “semi-retired” teacher who runs the theatre program at a local middle school in the city of Sacramento. But as an avid gardener, she doesn’t take green “waste” for granted.

Chapman tends a thriving kitchen garden in her Land Park home’s backyard, and she keeps up her own small compost for leaves, plant trimmings, cut grass and kitchen scraps. She has a lemon and a pomegranate tree, and blackberry bushes grow along her fence. When the berries are ripe, “you see squirrels running around back here with blue paws,” Chapman said.

But when it comes time to prune her fruit trees and woodier bushes, the branches and larger trimmings are too big for her small compost to break down. So, like many city residents, Chapman stuffs that plant material in her dark green yard waste bin for curbside pick-up.

That weekly ritual got her wondering: Where does this green waste go, and what ultimately becomes of it?

Question asker Ellen Chapman and reporter Julia Mitric talk about green waste in Chapman's yard.Andrew Nixon / Capital Public Radio

As an electric-hybrid car owner, her nightmare scenario involved all of it being dumped into a landfill. In that case, the plant material would break down and release methane, a potent greenhouse gas, instead of being recycled for a sustainable use like compost or mulch.

CapRadio’s quest for an answer to Chapman’s question led to an 80,000-square-foot facility in Sacramento known as the Elder Creek Transfer Station. It’s run by Republic Services, a national waste management company contracted by the city of Sacramento to handle residential yard waste.

But the journey to the station begins in front of people’s homes, when the city’s light blue trucks pick up yard waste bins and offload the contents at the transfer station.

Click here to see an overview of the journey that green waste takes once it leaves residents' yards.

Those 96 gallon plastic bins are known in the business as “toters,” according to Bill Thomson, an operations manager at the Elder Creek station, where recycling, garbage and green waste from several local municipalities are sorted and processed.

The processing site is an extremely loud environment with a distinct smell. Trucks travelling in reverse constantly beep their way around the lot as they enter, drop their contents, and go off on their next route. Trailer trucks move in and out all day, from 6 a.m. to 5 p.m., or longer during the peak season, November through January, when the city is collecting leaves outside of homes. Several types of heavy machinery scoop and grind yard waste on the backside of the station.

The semi-enclosed area of the station, where the contents of recycling bins land, smells like produce that has gone bad, what with remnants of food and liquids are stuck to plastic bags, containers and bottles.

While Thomson was walking through the station during a recent tour of the facility, an incredibly loud noise exploded about 25 feet away. Without flinching, he said it could be a basketball getting crushed, or a large, air-filled plastic bag. Thomson doesn’t wear ear plugs or listen to the radio while he’s at work since he has to pay attention for unusual sounds. If he hears a distinct noise, such as grinding, he knows the equipment has encountered a problem.

The process Thomson oversees has several stages. First, blue city trucks dump green waste onto concrete in an outdoor area behind the station.

Next, a team of up to five workers, suited up in protective equipment, manually sort through the pile looking for contaminants, which is anything that’s not plant matter or soil.

In order to comply with California regulations, Republic must ensure the processed yard waste that leaves the station has no more than .05 percent contamination from non-green waste materials, Thomson said.

Plastics are far and away the most common contaminant, he says. But he’s seen many random objects end up in the residential green waste collection. The worst? An actual engine block.

Thomson says they also get a lot of concrete or rocks. Some dirt is OK. And a wood fence post can safely go in the yard waste toter.

Once workers remove the larger, visible pieces of non-organic waste, a front loader scoops up the material and puts into “the grinder”: a giant, diesel-fueled machine that does just as its name suggests. The yard waste material passes through several screens on its way into the grinder, which Thomson says filter out smaller pieces of concrete, bits of steel and stones so they don’t damage the machine.

The processed material from the grinder is then heaped into a pile, scooted down a shaft and dropped directly into the bed of a trailer truck. Once filled to capacity, the trailer leaves the station for one of two locations.

Up to 90 percent of the ground-up green waste heads to Silva Ranch in San Martin, south of San Jose. The ranch layers the material on top of the soil to reduce the need for irrigation. And the remaining 10 to 20 percent of it travels to a Republic Services “multi re-use facility” in Manteca.

After the green waste is mixed with other materials, it goes back to the Elder Creek Transfer Station in Sacramento. There’s a pile of it that’s available to residential customers for free. (Thomson says residents will be asked to show identification to demonstrate that they live in one of the municipalities served by Republic.) Republic also packages some of the filtered green waste for commercial sale.

Thomson says it’s always “interesting” when people ask him about the trash business.

“I don’t think people realize how much is involved once it leaves their curb or comes out from under their sink,” he said. “They think it just magically disappears. That’s not the case at all. ”

For her part, Chapman was reassured to find out that Sacramento’s residential green waste from bins and leaf collection is diverted away from landfill.

But, ultimately, it’s the choices residents make, whenever they lift the lids of their bins, that will determine how “green” the outcome will be.