sure how long its double-shell tanks can safely store waste. That waste was originally scheduled to be removed by 2018. By 2008 the revised deadline was 2040. By 2008 of radioactive waste was traveling through the groundwater toward the Columbia River. This waste was expected to reach the river in twelve to fifty years if cleanup does not proceed on schedule. Under the Tri-Party Agreement, lower-level hazardous wastes are buried in huge lined pits that will be sealed and monitored with sophisticated instruments for many years. Disposal of plutonium and other high-level wastes is a more difficult problem that continues to be a subject of intense debate. As an example, plutonium239 has a half-life of 24,100 years, and a decay of ten half-lives is required before a sample is considered to cease its radioactivity. In 2000 the DOE awarded a $4.3billion contract to Bechtel, a San Francisco-based construction and engineering firm, to build a vitrification plant to combine the dangerous wastes with glass to render them stable. Construction began in 2002. The plant was originally scheduled to be operational by 2011, with vitrification completed by 2028. According to a 2012 study by the Government Accountability Office, there were a number of serious unresolved technical and managerial problems. In 2013 the estimated costs were $13.4billion with commencement of operations estimated to be in 2022 and about three decades of operation. A potential radioactive leak was reported in 2013; the cleanup was estimated to have cost $40billion, with $115billion more required. Another leak was reported in April 2021. In May 2007 state and federal officials began closed-door negotiations about the possibility of extending legal cleanup deadlines for waste vitrification in exchange for shifting the focus of the cleanup to urgent priorities, such as groundwater remediation. Those talks stalled in October 2007. In early 2008 a $600million cut to the Hanford cleanup budget was proposed. Washington state officials expressed concern about the budget cuts, as well as missed deadlines and recent safety lapses at the site, and threatened to file a lawsuit alleging that the DOE was in violation of environmental laws. They appeared to step back from that threat in April 2008 after another meeting of federal and state officials resulted in progress toward a tentative agreement. Some of the radioactive waste at Hanford was supposed to be stored in the planned Yucca Mountain nuclear waste repository, but after that project was