Standards for cleanup after a "dirty bomb (search)" terrorist attack would permit long-term radiation levels that pose cancer risks many times greater than those acceptable at Superfund sites, nuclear waste dumps and commercial reactors, according to a draft of a government proposal.

The Homeland Security Department (search) is expected to issue the proposed guidelines, which have been developed over the last two years, within a few weeks, probably before the end of the year. They would become final after a 60-day comment period.

The draft acknowledges that the consequences from a dirty bomb, a device that spreads radioactive material using conventional explosives, "may range from a very small, localized area ... to conceivably many square miles."

And it says that if there is widespread contamination from a dirty bomb or an "improvised nuclear device" — where there actually would be a crude nuclear detonation — areas may have to be put off limits permanently.

In such cases "existing land uses may not be practicable," the document says.

As a result, the interagency task force developing the guidelines decided against issuing specific numerical radiation levels to guide long-term cleanup goals, although an earlier draft written last year contained specific allowable radiation levels proposed by different agencies.

The latest version says cleanup efforts should be guided by radiation benchmarks established by various advisory groups, such as the International Commission on Radiation Protection (search) (ICRP) and the Health Physics Society, as well as federal agencies.

"They basically punted," said Daniel Hirsch, head of an anti-nuclear advocacy group, Committee to Bridge the Gap.

Hirsch said the ICRP benchmark would allow long-term levels of radiation from 100 millirems to as much as 10,000 millirems, a level equivalent to as many as 50,000 chest X-rays over a 30-year period.

The benchmark levels from the Health Physics Society would allow an area to continue to emit 100 millirems to 500 millirems per year, the equivalent of as many as 2,500 chest X-rays over 30 years.

A 500 millirems-per-year radiation exposure is estimated to produce about 1 additional cancer for every 80 people exposed, according to government cancer-risk calculations, said Diane D'Arrigo of the Nuclear Information and Resource Service, a nuclear industry watchdog group.

By comparison, the Environmental Protection Agency (search) requires cleanup standards at Superfund toxic waste to assure an additional cancer risk no greater than 1 in 10,000 people exposed, said D'Arrigo. The government plans to limit the maximum radiation exposure to the public at the proposed Yucca Mountain nuclear waste site to no more than 15 millirems per year.

A typical chest X-ray exposes a person to 6 millirems. Normal background radiation is about 300 millirems per year.

The draft says the guidelines are "not intended to define `safe' or `unsafe' levels of exposure or contamination" but represent "the approximate levels at which the associated protective actions are justified."

The contents of the so-called "interim final" draft document were first reported by an independent newsletter, Inside EPA. Copies of the draft, as well as an earlier version dated July 18, 2003, were obtained and provided Thursday by the Nuclear Information and Resource Service.

Don Jacks, a spokesman for the Federal Emergency Management Agency, said he could not comment on the contents of the draft. He said the document could still change as it goes through the final approval process at FEMA, the White House Office of Management and Budget and the Homeland Security Department and after the planned public comment period.

"Trying to interpret (the guidelines) now is way ahead of the curve," said Jacks.