Threats to Hanford's ground water from leaky underground radioactive waste tanks and from the remote chance a tank's dome eventually might collapse have increased the urgency for cleaning out the tanks.

That theme emerged when Department of Energy and Washington Department of Ecology officials met with the Tri-City Herald editorial board earlier this week.

Removing wastes from the tanks quickly is the best way to deal with the threat to ground water, they said.

Hanford has 54 million gallons of radioactive wastes in 149 single- shell underground tanks and 28 newer and safer double-shell tanks.

As they age, the tanks become more likely to leak and, with the oldest single-shell now past 50 years old, eventually susceptible to collapse.

The design life for the oldest tanks was not more than 20 years; for the newer double-shell tanks, 50 years.

A 1993 safety report concluded the oldest tanks could last about 40 more years, if no major changes in operations or stresses occur, Don Wodrich, DOE's senior technical adviser for the tank farms, said in a separate interview.

The possibility of a tank collapsing first was studied in the early 1980s and addressed in the 1993 report.

A tank is essentially a foot-thick concrete shell reinforced with rebar with a quarter-inch steel liner inside. The dome-shaped top is about seven feet underground.

There is a possibility the heavy earth above could push down on a concrete wall so it cracks at the joints with either the dome or floor, which could cause a major break, DOE officials said.

It is a remote possibility, but DOE is keeping an eye on it, said Wodrich and Jackson Kinzer, DOE assistant manager for tank farms.

Suzanne Dahl, the state Ecology department's tank program manager, noted that possibility was mentioned about a year ago in a tank farms environmental study. DOE's calculations appear valid, but the state has not done its own figuring, she said.

The possibility will grow as time passes, Dahl said. She also noted work to clean out the tanks will continue through 2028 under current schedules.

As a precaution, Hanford is watching the ground above. If it sags, DOE would worry. No sagging has been detected, DOE officials said.

As a precaution, DOE restricts using heavy trucks or equipment above older tanks.

Right now, "the real issue is one of leaks," Kinzer said.

Sixty-seven single-shell tanks are suspected leakers. Sixty-three of those have been pumped out to safer double-shell tanks. The remaining four are scheduled to be pumped by September.

Overall, 118 of the 149 single-shell tanks have been pumped out.

The leakage has gained a high profile in recent weeks when DOE confirmed - as many had suspected - that tank wastes had reached the ground water in central Hanford. DOE officials previously suspected tank wastes had reached the ground water but could not confirm it.

About 200 square miles of Hanford ground water has been contaminated for decades by radioactive and hazardous liquids dumped into cribs and trenches. Under about 100 square miles of that land, the ground water contamination exceeds drinking standards.

While tank wastes apparently are a tiny fraction of the volume of contamination, the tank wastes contain an overwhelming amount of the radioactivity in the subterranean wastes.

Since about 99 percent of the highly radioactive tank wastes are still in the tanks, that makes disposing of those wastes a top priority, the state and federal officials said.

The fix-it plan is to convert the wastes into glass. And two corporate teams are scheduled to submit their plans to build glassification plants in January. DOE is to decide in May whether to accept both, one or neither plan.

The glassification plants are scheduled to begin operating in 2002.