Hanford's main landfill for low-level radioactive waste has plenty of space left to expand, but already contains 60 percent to 70 percent of the allowable amount of some key radionuclides, according to the Hanford Advisory Board.

It's recommending that the Department of Energy take a new look at those limits, which are based on a performance assessment that's about 15 years old.

The limits were based on a very conservative assessment that didn't take into account protective measures at the Environmental Restoration Disposal Facility, such as a liner at its bottom and a protective cap that will be placed over its top when it is filled and closed, according to DOE.

The landfill is the linchpin for much of Hanford cleanup, accepting most of the contaminated soil that's being dug up near the Columbia River and the debris from contaminated buildings that are being demolished. More than 8 million tons of waste have been disposed of at the landfill and it's currently undergoing an expansion to add its ninth disposal cell.

"It appears likely that ERDF's ultimate capacity may be limited by the inventories of certain key radionuclides ... rather than the volume of wastes disposed, with a consequence that acceptance of wastes containing these radionuclides may be limited," the board wrote in advice at its June meeting.

The board supports the expansion of the landfill as long as it is done in a way that protects human health and the environment long term, the board said.

In the years since the landfill was planned, more has been learned about how water moves through the soil at Hanford and transports radioactive contaminants. That could change estimates of the risk of contaminants in the landfill eventually reaching ground water, the board said.

DOE should consider the new understanding of the way contaminants may be moved through the soil and how fast that happens in a revised performance assessment for the landfill, the board said.

Based on its evaluations, DOE may need to consider additional treatment of wastes disposed of at the landfill to minimize the chance that they contaminate ground water long term, the board said. In some cases, including for technetium, additional treatment technologies may need to be developed, the board said. More ground water monitoring wells and increased leak detection also may be required at the landfill.

The board recommended that DOE create a tracking system for radioactive contaminants that could end up in the landfill and keep a running summary of remaining capacity.