Editor's note: This story first appeared Sunday as an exclusive for our print readers.

Hoping to encourage customers to generate less trash, the city of Tucson gives customers a break if they downgrade to a smaller trash can.

But hundreds of the 48-gallon barrels are ending up as trash themselves.

In the past 18 months, nearly 900 of them have disappeared, many of them dumped into the landfill along with their castoff cargo, because they slip through the mechanical arms on garbage trucks designed for much larger containers.

Kenneth Bosma is one of about 4,300 Tucsonans who have made a similar decision since July 2010, when the city started making the lower-priced option available.

He's the first to say he wouldn't characterize himself as "a flaming environmentalist," but there are a number of reasons he moved to the smaller barrel.

He wants to be environmentally responsible - he and his wife spend a lot of energy recycling, so they generate just one small bag of trash a week. Also, the larger container doesn't readily fit in his garage. And, at $15 a month, his smaller container is $1.75 cheaper than the standard size.

But in the past year, four of Bosma's barrels have gone missing. At first, he thought a neighbor was playing a prank on him. But then he was home when a city worker came with a replacement and explained the smaller trash cans have been slipping through the grippers on the trash trucks.

Since it's usually too dangerous to fish them out of the trucks, which workers have to do manually, they typically end up the landfill.

Frustrated, Bosma bumped up a size, to a 65-gallon can. "It just defeats our efforts at recycling," he said.

At a base price of $40.56 each, Nancy Petersen, interim director for the city's environmental services department, said that level of loss is not acceptable.

The replacement cost is pushing $36,000. Although city officials say most of the strays have likely gone into the landfill, some have also fallen prey to thieves or storms.

Petersen has a monthly breakdown of the smaller cans that have gone missing. The worst month, September 2010, topped out at 109, followed closely the subsequent month with 97. This year, the numbers have ranged from a low of 19 in June to a high of 62 in August.

Petersen said tests before the start of service seemed to work just fine. But over time, department officials realized the arm technology has some shortcomings. That single piece of equipment has to be able to grasp the gamut from 48-gallon mini-barrels to 300-gallon alley barrels.

The department has modified the grippers, adding coils to help with friction. And it keeps a daily tally showing how many cans have gone missing each day, which helps identify if there's a problem with a certain truck, a certain driver or a certain route.

But that still hasn't gotten the numbers to a comfortable level, she said. Part of the problem is the barrel design, with a wider mouth and a tapering base. Once the driver starts to lose the barrel, whoosh.

After ongoing discussions with the manufacturer, the new solution is to put a longer wheel axle on the base, in the hope that it will catch if it starts to slip. The change will cost only 50 cents more per can, she said.

The department has a few hundred cans still in stock and hopes to modify those, but any new cans will come with the adjusted base.

Petersen said the department is also putting a bar code on the cans, so if they wash away or blow away in a storm the owner can be found more readily.

The department has been back in touch with Bosma, who said he's satisfied that staff is trying to address the problem - but for now, he's sticking with the larger can.

Petersen said she remains convinced the the "right-sized" trash service is an appropriate alternative and said she hopes customers will be patient while the department continues working on resolving the problem.

"There are so many reasons why people might believe that can size is the right one for them. We don't want to lose customer faith in us."

Contact reporter Rhonda Bodfield at rbodfield@azstarnet.com or 573-4243.