Glass is infinitely recyclable, so it’s easy to imagine that the bottles and jars you put out at the curb every week are headed off to be melted down and remade — baby-food jar into baby-food jar, beer bottle into beer bottle, forever and ever, amen. But not in Denver, or in many other Colorado communities with single-stream recycling, where everything from paper to plastic to glass is thrown into the same bin. Instead of being endlessly recycled, the glass that Denver residents put in their purple bins is reused only once, as a liner for landfills.

Surprised? That’s understandable. The city doesn’t draw attention to the fact — and hasn’t since it became the first place in Colorado to switch to single-stream recycling in 2005, in an effort to get more residents to participate. “Single-stream itself is a very positive thing,” says Eric Heyboer of the Colorado Department of Public Health and Environment. “When you make it really convenient for people to recycle, they will recycle more.”

But convenience on one end creates more work on the other. The stuff that’s collected in the single-stream process must be sorted so that the paper, plastic and aluminum can go their separate ways. While the workers and machines at recycling facilities can separate the junk mail from the yogurt tubs and pop cans, they have a harder time picking out the glass.

That’s because it’s broken. Between your curb and the recycling center, glass is jostled, dumped and smashed numerous times. By the end of the sorting process, it looks like recycling confetti: broken glass mixed with shreds of paper, bottle caps and other tiny detritus.

At Colorado’s biggest recycling facility, which is located in Denver and owned by a private company called Waste Management, that confetti is transported to landfills, where it’s used in place of sand or gravel to line trash pits. The glass acts as a filter for the liquid that seeps out of the decomposing garbage, allowing the liquid to be collected and processed so that it doesn’t contaminate the groundwater. It’s known as a “beneficial reuse,” and the upside is that it saves natural resources from being used instead. The downside is that the glass is only reused once.

Every piece of glass that is recycled in the city’s single-stream ends up as landfill liner Facebook

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So how much glass is that? Waste Management won’t say how many cities or counties in Colorado it contracts with, but company officials report that its Denver facility ends up with 25,200 tons of beneficial-reuse glass each year. In 2014, more than 20 percent of that — or 5,500 tons — came from the city of Denver, where it’s estimated that glass makes up 16 percent of the recycling stream.

In other words, every piece of glass that is recycled in the city’s single-stream ends up as landfill liner.

Those facts recently inspired two companies to try to improve the way that Denver — and the rest of Colorado — recycles its glass. Momentum Recycling, out of Utah, is building a facility that will use high-tech optical sorters to clean the shards of single-stream glass so they can be recycled into new glass instead of being used in landfills. Clear Intentions, based in Denver, has its own facility where it sorts glass that it collects separately from bars and restaurants through its Glass Valet program. That glass is also recycled into new glass.

“I cannot say how excited I am that these two companies have come to Colorado,” says Marjorie Griek, executive director of the Colorado Association for Recycling, a nonprofit organization that promotes recycling. “Glass has been a difficult issue for many years.”

Glass isn’t the only problem. Although Colorado is known for its green image, state recycling statistics tell a different story.

Colorado’s “diversion rate,” which is the amount of waste that’s diverted from landfills through recycling and composting, is just 23 percent, according to the CDPHE. The national rate is 34.5 percent, although experts agree that the way that Colorado calculates its rate differs from the way the federal Environmental Protection Agency figures the national rate.

A better comparison may be the numbers reported in a 2014 Columbia University study that surveyed all fifty states about how much waste they divert from their landfills. Colorado’s answer put the state in the bottom half of the nation.

“We’re pretty bad,” Griek says. “It’s really rather depressing.”

There are several reasons for this dismal showing, experts say. One is geography. Colorado has plenty of vacant land on which to build landfills, which means that those landfills charge lower “tipping fees” to waste haulers to dump their trash than landfills in states where open land is scarce. When it’s cheap to dump trash, municipalities and haulers have less financial incentive to offer recycling programs.

“We’re pretty bad. It’s really rather depressing.” Facebook

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Colorado is also unusual, says the CDPHE’s Heyboer, “because we’re such a big state, with pockets of population centers, and in those population centers you have the Boulders, the Tellurides and the Aspens of the world that are super-gung-ho about recycling and have a green image. And then you have the rest of Colorado, which is a little different.”

For the rest of Colorado, recycling can be expensive. Most recycling facilities are located along the Front Range. It can be challenging for a far-flung trash hauler to collect enough empty pop cans to make it worthwhile to drive to Denver in order to take them to a recycling facility or sell them to an “end market” — the companies that take the used cans and turn them into new ones. “It eats into a lot of their profits,” Heyboer says.