It's the potential for future shortages - and a dispute over how to prevent them - that has some observers alarmed.

The U.S. Department of Energy, which owns the nuclear-weapons site, and the federal Defense Nuclear Facilities Safety Board are at odds over how to stop the site from running low on space for millions of gallons of highly radioactive liquid waste.

''It just seems to me that they don't have a real contingency plan if things really start to go wrong,'' said Don Moniak, an Aiken resident and community organizer for Blue Ridge Environmental Defense League.

The current problem began in January 2000, when officials closed 2H, one of the site's three evaporators. Silica, or fine bits of a glass-like mineral, was building up inside the unit and threatening to clog its pipes.

The evaporators are used to reduce the volume of the liquid waste by evaporating water from it.

A new, larger evaporator, 3H, began operating later that spring, only to be curtailed because of a faulty cooling system. At one point, the evaporator - capable of eliminating as much as 20,000 gallons of waste per day - could run for only 10 days every two months.

All the while, the 2 million gallons of waste then generated annually by the site's Defense Waste Processing Facility was filling the waste tanks, threatening the operation of that plant and others that produce radioactive waste as a byproduct.

The space crunch led to a public flogging by the defense board, which in March criticized the Energy Department for not acting ''with due diligence to address the worsening condition of the SRS Tank Farms.''

The shortage also was a factor in recent leaks of radioactive waste from the site's tank farm.

The search for a new place to store the processing facility's waste led to the oldest waste tanks at the site, long unused because they had only a single carbon-steel hull.

When the tanks were reused, they began leaking waste into secondary containment vessels placed beneath them, and SRS officials were forced to abandon their plan.

''I was looking for a way to gain space until I recovered evaporator performance,'' said Steve Piccolo, the vice president in charge of the high-level waste division for SRS contractor Westinghouse Savannah River Co. ''It turned out not to be the best decision I ever made.''

Now, Mr. Piccolo said, site officials have solutions to the tank-space dilemma. Workers installed a new, stopgap cooling system at the 3H evaporator, and the plant operated for 30 days last month, he said. A permanent fix should be ready within a year, he said.

Site scientists discovered that silica buildup inside the 2H evaporator could be controlled by monitoring concentrations of silica, sodium and alumina in waste fed to the unit, Mr. Piccolo said.

The evaporator could reopen as soon as September, he said.

But as site engineers work to solve short-term problems, long-term issues remain.

The defense board rejected the Energy Department's plan to address its concerns, saying the measure relied on aging systems and assumptions.

Defense board members, Energy Department Undersecretary Bob Card and SRS staffers met Thursday at the site to attempt to resolve the dispute.

''They spent all day specifically looking into this matter,'' defense board Chairman John T. Conway said Friday in a telephone interview from his Washington office. ''This is one of our top priorities.''

Although an agreement hasn't been reached, the two sides are talking, an Energy Department official said.

''The meeting was informative, and there was a lot of information exchanged,'' said Charles Anderson, the department's assistant manager for high-level waste at SRS. ''There was an agreement to continue discussion between the defense board staff and the Energy Department.

''There are a number of other efforts to support our system plan, and that's part of the dialogue that needed to take place.''

But the dispute worries Mr. Moniak, who said the Energy Department should heed the defense board's concerns.

''If two more tanks were to leak, then they would be using emergency space,'' he said.

''It's unfair to put people at SRS in the position of having to work with degraded equipment and a degraded infrastructure in order to prevent something serious from happening,'' he said. ''They should be given the tools they need.''

Reach Brandon Haddock at (706) 823-3409 or bhaddock@augustachronicle.com.