the ground since about 2010. In 2012 the DOE also discovered a leak from a double-shell tank caused by construction flaws and corrosion in the tank's bottom, and that twelve other double-shell tanks had similar construction flaws. Since then, the DOE began monitoring single-shell tanks monthly and double-shell tanks every three years. The DOE also changed the methods by which they monitored the tanks. In March 2014 the DOE announced further delays in the construction of the Waste Treatment Plant, which will affect the schedule for removing waste from the tanks. Intermittent discoveries of undocumented contamination have slowed the pace and raised the cost of cleanup. The cleanup effort was managed by the DOE 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 cleanup is $113.6billionmore than $3billion per year for the next six years, with a lower cost projection of approximately $2billion per year until 2046. About eleven thousand workers were 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. While major releases of radioactive material ended with the reactor shutdown in the 1970s and many of the most dangerous wastes are contained, there were continued concerns about contaminated groundwater headed toward the Columbia River and about workers' health and safety. Cleanup activities The most significant challenge is stabilizing the of high-level radioactive waste stored in the 177 underground tanks. By 1998 about a third of these tanks had leaked waste into the soil and groundwater. By 2008 most of the liquid waste had been transferred to more secure double-shelled tanks; however, of liquid waste, together with of salt cake and sludge, remains in the single-shelled tanks. DOE lacks information about the extent to which the 27 double-shell tanks may be susceptible to corrosion. Without determining the extent to which the factors that contributed to the leak in AY102 were similar to the other 27 double-shell tanks, DOE could not be