Starting next summer, many power plants, hospitals, universities and companies in 36 states will be forced to store low-level radioactive waste on their own property because a South Carolina landfill is closing its doors to them.

The states have known for years that this day would come. But because of political opposition, environmental fears and cost concerns, most of them have done almost nothing to construct new landfills in the meantime.

At issue is the Barnwell County dump site, a 235-acre expanse that opened in 1971 close to the Georgia line. The equivalent of more than 40 tractor-trailers full of radioactive trash from 39 states was buried there each year before South Carolina lawmakers in 2000 ordered the place to scale back because they no longer wanted the state to be the nation's dumping ground.

As of July 1, the landfill will take waste only from South Carolina and the two states with which it formed a partnership, New Jersey and Connecticut.

State and industry officials say the not-in-my-backyard resistance will ironically lead to "temporary" storage sites in backyards across the nation.

"I'm concerned about it, that my hospitals in my neighborhood will have to store this stuff on site," said Rita Houskie, administrator for disposal of the waste in Arkansas, Kansas, Louisiana and Oklahoma. Other states affected by the shutdown include California, New York, Illinois, Florida and Texas.

The danger, some officials say, is that storing the waste in potentially hundreds of locations across the country could allow radiation to escape.

While none of the trash could be used to make a nuclear bomb, some experts fear it could be stolen to make "dirty bombs," which use conventional explosives to scatter radioactive debris.

"As a matter of national security, health and safety, it makes good sense to ultimately dispose of this stuff and not just store it all over the country," said Rick Jacobi, a nuclear engineer and former general manager of the Texas Low-Level Radioactive Waste Disposal Authority.

"There will be hundreds, maybe thousands of them. People won't want to pay others to store the material. They'll find a closet or warehouse or a shed out back and stick it in there and see what happens."

The trash sent to Barnwell includes protective clothing and gloves, tools, cleaning rags, lab equipment, industrial measuring devices and equipment used to treat cancer patients. It does not include spent fuel from nuclear power plants. The waste is stored in steel containers that are put in concrete vaults and then buried in long trenches.

Most waste from hospitals, universities and power plants falls into the lowest-hazard class, which means it decays to nonradioactive levels within 100 years.

The closing of Barnwell will mean roughly 20,000 cubic feet of trash per year, or enough to fill six tractor-trailers, will be turned away.

Only two other landfills now exist nationwide for low-level nuclear waste.

One, in Clive, Utah, takes only the least hazardous trash, such as slightly contaminated clothing. It accepts waste from all states. The other landfill, in Richland, Wash., receives such material along with hotter waste that decays to non-hazardous levels within 500 years. But it accepts shipments from only 11 states, including Idaho, Nevada and Colorado.

Companies have had to store radioactive waste on their property before: The Barnwell site closed in the mid-1990s before reopening. And some companies store material on site now, sometimes waiting to amass enough to make it worthwhile financially to ship the stuff to a landfill.

"We're confident it can be stored safely based on the track record," said Jim Kennedy, senior project manager of the Nuclear Regulatory Commission's low-level waste branch.

If hospitals and power plants are forced to hold on to their waste, it will go into specially designed warehouses. For power plants, that is generally an aboveground bunker with thick concrete walls. The waste must be secured, specially shielded and weathertight.

States had decades in which to build nuclear waste landfills. A 1980 federal law made each state responsible for disposing of non-military low-level waste generated within its borders and encouraged states to work together to develop regional disposal sites.

But those efforts have repeatedly run into resistance. Only one low-level landfill, the one in Utah, has opened in the past 30 years. In 2005, Nebraska was forced to pay $146 million for blocking construction of a landfill for its region.

Some environmentalists say that storing waste on a company site is actually better than shipping it. Power plants, they say, already have places to store highly radioactive spent fuel and have good security. Plus, most medical waste can simply be stored until its radioactivity subsides, after which it can safely be thrown away.

"The reality is there aren't any good choices for radioactive waste right now, so they might as well leave it on site rather than contaminate new sites and transport it across the country, where there could be vehicle accidents," said Michael Mariotte, executive director of Maryland-based Nuclear Information and Resource Services.

Jacobi, the former Texas waste official, said he fears companies storing the waste on their own property will eventually forget about the hot trash, and it could mistakenly be sold as scrap or sent to smelters.

"These things get lost, accidentally recycled or could fall into the hands of the wrong kind of people," he said.

Rich Janati, who heads waste disposal for Pennsylvania, Delaware, Maryland and West Virginia, said radioactive devices, such as gauges used by companies to measure a material's density or moisture, are easily lost and tough to keep track of. Their size makes them "obviously easier for WMD-type activities and terrorist activities if they're not tracked properly," he said.

Inspections of stored waste will be the responsibility of either the NRC or state agencies. The extra workload should not be a problem, Janati said.

Storing the waste on site is just a temporary measure. As for longer-range solutions, the NRC is set to release a report this week on the pros and cons of various ideas. The possible solutions are said to include the creation of a national landfill and the opening of Energy Department dump sites.