On June 25, 1988, the Hanford site was divided into four areas and proposed for inclusion on the National Priorities List. On May 15, 1989, the Washington Department of Ecology, the United States Environmental Protection Agency, and the Department of Energy entered into the Tri-Party Agreement, which provides a legal framework for environmental remediation at Hanford. the agencies are engaged in the world's largest environmental cleanup, with many challenges to be resolved in the face of overlapping technical, political, regulatory, and cultural interests. The cleanup effort is focused on three outcomes: restoring the Columbia River corridor for other uses, converting the central plateau to long-term waste treatment and storage, and preparing for the future. The cleanup effort is managed by the Department of Energy under the oversight of the two regulatory agencies. A citizen-led Hanford Advisory Board provides recommendations from community stakeholders, including local and state governments, regional environmental organizations, business interests, and Native American tribes. Citing the 2014 Hanford Lifecycle Scope Schedule and Cost report, the 2014 estimated cost of the remaining Hanford clean up is $113.6 billion – more than $3 billion per year for the next six years, with a lower cost projection of approximately $2 billion per year until 2046. About 11,000 workers are on site to consolidate, clean up, and mitigate waste, contaminated buildings, and contaminated soil. Originally scheduled to be complete within thirty years, the cleanup was less than half finished by 2008. Of the four areas that were formally listed as Superfund sites on October 4, 1989, only one has been removed from the list following cleanup.