A Very Long Road for Military Nuclear Waste Slowly, slowly, the Energy Department is moving forward with solidifying the liquid nuclear wastes left over from cold-war weapons production. On Thursday, the department said it had closed two more of the 51 underground tanks at the Savannah River Site in western South Carolina. The high-level waste was mixed with molten glass to keep it chemically locked up for millennia, and the lower-level material was mixed with a kind of cement that is supposed to keep it in place until the radioactivity dies down. The department has 22 tanks at Savannah River that do not meet Environmental Protection Agency standards, mostly because they are single-wall tanks rather than double-wall. It closed two of them in 1997 but has faced numerous technical problems. Now it says it will have four more done by 2014 or 2015, and all of them by 2028. It is starting with the tanks that are closest to the water table because their contents would spread most rapidly if they leaked. The area has a high water table. Yet the "closed" tanks are not actually empty. "More than 99 percent of the waste originally stored in these two tanks has been removed,"" said Thomas P. D'Agostino, undersecretary of energy. Since the tanks held more than a million gallons each, that could leave tens of thousands of gallons in place. One problem is that the tanks have cooling coils and other hardware in place that makes cleaning difficult. But the department says it has developed new methods, including robotic tools, to get the tanks cleaner. Another problem is that the process of emptying the waste includes spraying new materials inside to get the liquids flowing. An environmental group, the Natural Resources Defense Council, sued the department after the last round of tank closures, arguing that the radioactive material left behind could eventually enter soil and groundwater, and that the department was granting itself too much discretion in deciding how clean was clean enough. Congress eventually stepped in to clarify that in South Carolina and Idaho, some waste could be left behind. At similar tanks in New York and Washington State, the question was left open. Congress ordered that the Nuclear Regulatory Commission, which does not ordinarily get involved in military projects, act as a consultant on the question. Geoffrey Fettus, a lawyer with the environmental group, said on Thursday, "We view with some skepticism measuring progress by closing tanks rather than measuring progress by removing nuclear waste and properly disposing of it." Mr. D'Agostino said that the tanks would be filled with grout, and that this would immobilize the remainder. And the plutonium, the longest-lived material, will not migrate in the dirt, he said. The tanks and the waste aren't going anywhere. The grouted material is in giant blocks, called monoliths, nearby, and the material put into glass is destined to go to whatever federal repository is eventually established, following the cancellation of the Yucca Mountain waste repository in Nevada. The amount of plutonium in the waste tanks is uncertain. Savannah River was built to make plutonium, and the material in the tanks is what was left over after the material was produced in reactors and scavenged in chemical plants. But a fair amount ended up in the waste tanks, according to Robert Alvarez, an outside expert who formerly worked for the Department of Energy. "These two tanks provide proof in principle that we now understand what it takes to move forward,"" Mr. D'Agostino said in a conference call with reporters. The department has spent $50 million to empty these two tanks and get the process set up to empty more, which involved out a procedure that was approved by the Nuclear Regulatory Commission. The commission regulates civilian use of nuclear materials but was called in as an independent outside check on the Energy Department. David Moody, the Energy Department's manager at Savannah River, said the department had been working on the tank-emptying process since the 1980s.