1989 May: Hanford environmental cleanup formally begins with the signing of the Tri-Party Agreement. It set requirements and deadlines for cleanup of massive radioactive and hazardous chemicals left from producing nearly two-thirds of the nations weapons plutonium from World War II through 1988.
1989: Construction contract awarded to build a high-level radioactive waste vitrification plant to begin operating in 1999. Estimated cost was almost $1 billion. Low-activity waste to be grouted.
1990: Department of Energy and its regulators agreed enough information exists for an early start to cleanup of contaminated soil and groundwater along the Columbia River.
1990: Independent panel directing studies into past releases of radioactive materials from Hanford says thousands of Northwest residents may have been exposed to radioactive releases from Hanford from 1944 to 1971.
1991: First amendments to Tri-Party Agreement made over technical, safety and budget issues with planned vitrification plant.
1991: N Reactor, Hanfords last operating plutonium-production reactor, ordered permanently shut down. It had been on standby since 1987.
1991: Wyden Watch List of 52 underground waste storage tanks initiated by Sen. Ron Wyden, D-Ore., over concerns that waste in tanks could explode or catch fire. The list would grow in future years.
1993 July: Hanford Advisory Board established.
1993 August: Hanford worker taped a rock to a rope and dropped it into a waste tank to see if a pipe was plugged.
1993: DOE admits to radiation testing on people during Cold War. Hanford-funded tests included injection of five people with phosphorus 32, irradiation of prison inmate sex organs and exposure of 15 people to tritium.
1995: New plan for vitrification of waste announced — a private company would be sought to treat the waste and would be paid for waste vitrification completed.
1996: Hanford budget reduced to allow DOE to close other nuclear sites early, with expectations that money would be restored as cleanup was completed elsewhere.
1997 March: Waste Receiving and Processing Facility starts operations, becoming first plant in the nation to process solid waste contaminated with plutonium.
1997 May: PUREX deactivated after four years of work. Its the first large-scale deactivation of a nuclear processing facility in the nation.
1997 May: Chemical storage tank explodes at the Plutonium Reclamation Facility at the Plutonium Finishing Plant.
1997 September: HAMMER training center dedicated. It provides hands-on safety training for Hanford workers and first responders.
1997: Ten-year effort to stop dumping liquid, including contaminated liquids into the ground at Hanford, achieves success. Last liquid that was being dumped is diverted to a treatment facility.
1997: DOE confirms that leaked waste from tanks has reached groundwater.
1998 September: C Reactor cocooned, or put in temporary storage.
1998 December: DOE Office of River Protection established to focus only on Hanford waste tanks and treatment of their waste.
1998: 1100 Area in north Richland shifted from DOE to Port of Benton control.
1998: BNFL awarded contract to build a vitrification plant and vitrify waste. Estimated cost is $6.9 billion. Deadlines later are set for start of operation in 2009 and 10 percent of waste treated in 2018.
1999: Draft of Centers for Disease Control study released. Finds no evidence of increased thyroid disease as a result of Hanford releases from 1944 to 1957.
2000 June: Huge range fire burns across 45 percent of Hanford.
2000 July: First shipment of plutonium-contaminated debris leaves Hanford for disposal at the Waste Isolation Pilot Plant in New Mexico.
2000: BNFL says private financing will raise cost of vit plant to $15.2 billion. Its contract is ended.
2000 December: Work starts to move 2,535 tons of irradiated nuclear fuel in the K Basins to dry storage.
2001: DOE issues decision to permanently close the Fast Flux Test Facility, a 400-megawatt research reactor.
2001: The last of 60 tanks removed from the Wyden Watch List.
2001: Energy Employees Occupational Illness Compensation program begun to compensate Hanford and other workers made ill from DOE nuclear work.
2002: Vitrification plant construction begins. Bechtel National, which now has the plant contract, says it will cost $4.4 billion and 10 percent of waste will be treated by 2013.
2003: Government Accountability Project says 67 tank farm workers required medical attention over 20 months for exposure to hazardous fumes.
2003 December: First of 149 single-shell tanks emptied of liquid and solid waste at Hanford.
2004 June: Pumpable liquid removed from all 149 leak-prone single-shell waste tanks.
2004 October: All 2,535 tons of fuel stored underwater in K Basins moved to dry storage at Canister Storage Building.
2004: Workers at the Plutonium Finishing Plant finish stabilizing plutonium that remained there at the close of the Cold War and work transitions to clean up and tear down the plant.
2005: Most construction work stopped at vitrification plant to consider earthquake design standards. Cost estimate of plant construction increases to $9.65 billion.
2006: In-depth study of vitrification plant puts cost at $12.2 billion and start of operations in 2019.
2007 May: All radioactive sludge from the K East Basin transferred to underwater containers in the sturdier K West Basin. K West Basin now holds enough sludge to fill eight dump trucks.
2008 August: Hanford's B Reactor, the worlds first full-scale nuclear reactor declared a National Historic Landmark.
2009 September: All weapons-grade plutonium left at Hanford after the Cold War shipped to Savannah River Site in South Carolina.
2009: DOE agrees not to import radioactive waste to Hanford until the vitrification plant is treating waste already at the site.
2009: Hanford receives $1.96 billion in federal stimulus money to speed shovel-ready cleanup.
2010: Court-enforced consent decree resolves state of Washington lawsuit over missed or at risk Tri-Party Agreement milestones. It extends deadline to empty single-shell tanks from 2018 to 2040. It calls for vitrification plant to start treating waste in 2019 and be fully operating in 2022.
2010 December: Rattlesnake Mountain cleanup completed with Recovery Act money.
2011 September: 200 West Groundwater Treatment Facility, the largest and most sophisticated at Hanford, completed to clean groundwater in central Hanford.
2012 June: Hanford's N Reactor cocooned, bringing total reactors cocooned to six.
2012 September: Cleanup of two-square-miles area near F Reactor completed, including demolishing 112 facilities, digging up 88 waste sites and removing 1.5 million tons of contaminated material. Its the first reactor cleaned up.
2012 October: One of Hanfords 28 double-shell waste tanks, Tank AY-102, confirmed to have a leak between its walls.photo of tank being built
2012: Construction stops at areas of vitrification plant plagued by technical issues. DOE says cost of plant will increase, but it cannot say by how much until technical issues are resolved.
2013: At least one of Hanfords single-shell tanks is leaking waste into the ground. Tanks were thought to be stabilized after pumpable liquid waste was removed.
2013: Eleventh single-shell waste tank emptied.
2014: Plutonium Recycle Test Reactor removed from the 300 Area just north of Richland. About 180 buildings have been torn down in the 300 Area, with only a few still standing.
2014 April: State of Washington triggers dispute resolution on the consent decree after DOE and the state cannot agree on how to amend deadlines to retrieve tank waste and treat it at the vitrification plant.