Here, the waste was mixed with additional supernatant and sludge, then transferred to the MVSTs when an acceptable solids concentration was reached. By September 2000, approximately 53,000 gallons of sludge and supernatant waste was successfully retrieved from Tank W-9, signaling completion of the majority of the GAAT retrieval efforts. At the start of GAAT retrieval in June 1997, more than 300,000 gallons of supernatant and about 96,000 gallons of sludge waste were stored in the eight gunite tanks. In just over three years, the GAAT Remediation Team cleaned all eight tanks to a level the Tennessee Department of Environment and Conservation deemed acceptable for closure activities to commence. By September 2000, only 7,500 gallons of combined sludge and supernatant remained in the tanks, reducing the curie count from 85,838 curies to just under 4,200 curies.
Curies express the rate at which a radioactive material gives off particles and disintegrates.
One curie is the amount of radioactivity in 1 gram of the isotope radium-226. One curie gives off 37 billion disintegrations per second. A typical home smoke detector contains about 1 millionth of a curie of radioactivity. Completion of GAAT retrieval represents a significant site milestone toward completing the GAAT Remediation Project. In addition to successfully accelerating cleanup efforts at ORNL, results of the GAAT retrieval activities provide valuable lessons learned and information for other DOE tank sites currently evaluating retrieval options and developing plans for their retrieval projects.