KENNEWICK — U.S. Sen. Ron Wyden, D-Ore., is asking when the Department of Energy knew underground tanks were leaking radioactive waste at Hanford and whether the issue immediately was reported.

He asked the Government Accountability Office to investigate those and other issues Tuesday in his new role as chairman of the Senate Energy and Natural Resources Committee.

Also Tuesday, the Washington State Senate Energy, Environment and Telecommunications Committee said it would hold a hearing at 8 a.m. Thursday to learn more about Hanford's leaking tanks.

DOE announced Feb. 15 that the level of waste in one of Hanford's single-shell tanks, T-111, was dropping by up to 300 gallons a year. It was the first suspected leak since as much liquid as possible was pumped from the enclosed tanks in 2004.

Then last week, Washington Gov. Jay Inslee said he had learned after meeting with Energy Secretary Steven Chu that five more tanks are leaking.

Wyden is asking the GAO to look into how the recent tank problems were identified and whether changes need to be made in the monitoring program for single-shell tanks.

Inslee said data had been collected on waste levels, but not properly analyzed to discover the problem in the huge tanks.

The rate of seepage from all six tanks combined is estimated to be less than 3 gallons a day, according to DOE. Together the tanks have a capacity of more than 1.5 million gallons of waste.

Wyden wants to know if maintenance programs at the tanks are adequate to prevent water intrusion and also leaks from the tanks. If not, he wants to know what other action should be taken.

A closer look at waste levels in the tanks was prompted by a study that suggested that the level of waste in some tanks was increasing, possibly because rain water or snowmelt was getting into the tanks.

He also asked the GAO whether DOE methods to report tank problems to regulators and the public could be improved.

The state Senate hearing Thursday is planned to help the Legislature better understand what it can do to address the problem.

"Given the gravity of the situation and the enormity of the issues involved, it is exceedingly important that we continue the discussion with the state Department of Ecology to ascertain the most effective and efficient method of cleanup," Sen. Sharon Brown, R-Kennewick, said in a statement. The state is a regulator of DOE's work at the Hanford tanks.

DOE said it has not observed any discernible change in the contamination levels in monitoring wells near the underground tanks, but is continuing to watch them closely.

The ground already is contaminated after about 1 million gallons of waste leaked from the tanks over decades before 2004. Some of the waste has reached the groundwater, but movement toward the Columbia River five miles away is slow.