Sending up to 3.1 million gallons of radioactive waste to New Mexico for disposal is no solution to Hanford’s leaking underground tanks, according to Hanford Challenge and two other groups focused on environmental issues.

Hanford Challenge of Seattle, the Southwest Research and Information Center of Albuquerque, N.M., and the Natural Resources Defense Council’s nuclear program in Washington, D.C., have sent a joint letter to Energy Secretary Steven Chu.

A Department of Energy (DOE) proposal to send some of Hanford’s tank waste to the Waste Isolation Pilot Plan (WIPP), near Carlsbad, N.M., is costly, unwise and illegal, said the letter.

Instead, DOE should be working to build sound tanks both to get waste out of leaking tanks and also to prepare to eventually feed the waste into the vitrification plant being built to glassify up to 56 million gallons of radioactive waste.

Sending waste from up to 20 of Hanford’s 149 single-shell tanks to WIPP “May provide DOE with an additional method to expedite the overall tank-waste-retrieval effort at Hanford,” DOE said in a statement Wednesday.

It has previously said that before waste could be sent, DOE must persuade the state of New Mexico to modify the WIPP permit to allow certain tank waste to be sent there.

WIPP is the nation’s repository for transuranic waste — which typically is contaminated with plutonium — but does not accept high-level radioactive waste.

DOE also would need to prove to regulators that certain tank waste could be classified as transuranic, rather than high level.

But the groups writing the letter said legal issues are far more complex than modifying the WIPP permit.

The Nuclear Waste Policy Act defines the tank waste as high-level waste and a 2003 ruling in a lawsuit brought by the National Resources Defense Council also found that all waste in Hanford tanks is high-level radioactive waste, the groups said.

The state of Washington has estimated that if a plan to send the waste to New Mexico could be worked out, the soonest any waste could be sent is in two to four years.