David Redfield, vice president of marketing integration at the company's Sam's Club division, wasn't initially enthusiastic about the giant discounter's interest in trying to save the planet. "At first we thought this was about saving the whales and the trees," he says. "Then we started looking seriously at what the waste was made of, what it cost us and what we could save, and this thing took on a life of its own."

Mr. Redfield is in charge of the solid-waste-reduction program, and he expects to meet the goal of cutting volume by one quarter in three years ahead of the original deadline. Eventually, the goal is for the stores to dump zero waste into landfills. Currently, they produce in excess of three billion pounds a year.

Mr. Redfield and his team are trying to go beyond recycling programs that bundle waste for sale to recycling centers. Wal-Mart is attempting to turn its waste into a raw-material stream for the suppliers of its merchandise, a process known as closed-looped recycling.