When I met Jerry San Pietro in 2005, he had been retired for more than a decade and had moved to Cripple Creek, 130 miles southwest of Rocky Flats. Although he now lived well away from the site and from any potential toxic plume that could spread from it, he remained concerned. So each month for two years, he drove three hours each way to attend meetings convened by the DOE to oversee the final stages of the cleanup.

The Rocky Flats cleanup could be considered an unmitigated success. Initial estimates pegged the effort at 70 years and $36 billion, but the company selected to remediate the site, Kaiser-Hill, completed the job in less than 10 years for a fixed sum of about $7 billion, thanks to a combination of imaginative thinking and technological innovation -- shipping the waste in larger, less labor-intensive configurations, for instance, and developing spray-on coatings that solidified to render contaminated parts less dangerous for transport and disposal. But the company also had some help from the DOE and Congress. By designating the site a wildlife refuge, the Energy Department was able to tailor the cleanup to protect a wildlife refuge worker spending 40 hours a week on site from a more than 1-in-500,000 chance of cancer in excess of normal -- rather than, say, a small child in a subdivision who lived and played in the dirt there. This "risk-based end state," as it is called, essentially tinkered with the definition of "clean" to allow Kaiser-Hill to aspire to a much lower standard, at a much lower cost.

Local environmental activists had problems with this on a number of fronts. First, they believed that exposure standards -- based mainly on cancer incidence data from Japanese survivors of the atomic bomb attacks on Hiroshima and Nagasaki -- substantially underestimated the risks from protracted low-level exposure to radiation. They also believed that the regulators in charge of the cleanup disregarded evidence that plutonium is more mobile and dangerous when suspended in dirt and groundwater than previous research had indicated. And they worried that activities such as hiking and biking on the wildlife refuge would stir up particles of plutonium-laden dust. The activists recommended the site be cleaned instead to a near-"background" level that would protect a subsistence farmer living on the land and raising crops there.

Their arguments did carry some weight. In 1996, the Department of Energy and Kaiser-Hill agreed to allow up to 651 picocuries of plutonium to remain in each gram of Rocky Flats soil. After the locals reacted with outrage, they reworked the numbers, and in 2003 signed a final agreement allowing 50 picocuries per gram in the top three feet of soil, 1,000 at a depth of three to six feet, and no limit on how much plutonium is allowed to remain below six feet. That 50 picocurie number, however, is higher than that allowed in cleanups of other, smaller plutonium-contaminated sites handled by the DOE. In addition, many of the important production buildings were built underground, both to obscure them from sight and protect them from nuclear attack. They required a phenomenal amount of underground infrastructure, from waste storage areas to the miles-long tangle of pipes and process lines that carried solutions from room to room and building to building. "We always think of buildings going up," said Alice Brace, a fire inspector at the site. "In this case, the buildings went down."

Infrastructure was not the only thing hidden underground. Besides overseeing work with radioactive materials inside the factory buildings, radiation monitors like Jerry San Pietro also patrolled the grounds around the plant. Over the years, said San Pietro, "we found things" -- radioactive leach fields, buried plutonium hemi-shells, landfills and dirt-covered mounds containing toxic brews of plutonium-contaminated oil, volatile organic compounds and heavy metals. Whenever he found those "things," San Pietro's supervisors would castigate him. "You weren't supposed to be looking. That's not part of your job," they told him.

San Pietro's uncle, who worked at Rocky Flats in the 1950s and '60s, reported seeing a D8 Cat on the perimeter of the plant property scooping a hole so deep he couldn't see the machine below the rim. The uncle later saw workers burying barrels of waste in the hole. He also told San Pietro about a map of underground burials at Rocky Flats. When San Pietro served on the union safety committee, he asked to see the map. After he threatened a Freedom of Information Act request, management allowed him and another union leader to view it in a room without pen or paper. "When I saw the map laid out on that table, I was amazed at how much plutonium, americium, uranium, acetones and solvents were buried out there. There's that many burial sites, and they know what's in them, and they're leaving them there?" he said.

San Pietro's uncle died in the mid-1990s, and San Pietro believes himself to be the last hourly worker alive who had seen the map. After the cleanup commenced, he began asking his colleagues still on the job at Rocky Flats about the sites described on the map. He came to believe that there were no plans to clean many of the spots he found most troubling; some, he suspected, were in the proposed wildlife refuge, not the industrial area where the cleanup took place. He began writing to the DOE, to Colorado's congressional delegation, to the oversight panel and to protest groups, and traveling to cleanup meetings. "Rocky Flats," he told them, "is the largest unlicensed nuclear burial site in the United States."