Staff Reports
WC Monitor
10/9/2015
Washington River Protection Solutions has begun operating an exhauster to evaporate liquid from Tank T-111, the Hanford Site single-shell tank that is leaking waste into the soil beneath it. “The exhauster is performing as we hoped it would,” said Mark Lindholm, WRPS acting president and project manager, in a statement. “This is an important step in the right direction as we try to minimize liquid inside T-111.” A 30-day test of the exhauster removed 1,000 gallons of liquid and another 1,000 gallons have been removed since Sept. 28. WRPS says 25 to 30 gallons of liquid are being evaporated daily. “By removing the free liquid you are reducing the amount of liquid that could leak from the tank,” said Jeff Lyon of the Washington State Department of Ecology. It also reduces the pressure on the liquid waste, which could slow the rate at which it leaks.
The Department of Energy announced in late 2013 that measurements of waste within Tank T-111 suggested it was leaking. It is the first single-shell tank believed to be leaking since workers completed removing pumpable liquids from all single-shell tanks. A 2014 report for DOE concluded that about 1.8 gallons of waste were leaking from Tank T-111 per day, a decrease from 3.1 gallons per day in June 2013. The tank holds 436,000 gallons of sludge waste and has about 38,000 gallons of liquid throughout the sludge or pooled on top of the waste. The tank was first suspected of leaking in 1974, and most of the pumpable liquid was removed at that time. The tank was suspected of leaking again in 1993, and a jet pump was installed to remove more liquid by 1995.
A portable exhauster was moved last year from the 200 East Area to the T Tank Farm and then parts were fabricated to allow its use on Tank T-111 liquid. “Evaporation using active ventilation costs a small fraction of new pump technologies, requires little labor compared to pumping and requires no double-shell storage space,” Lindholm said. Before the exhauster began operating this summer, the tank had an estimated 2,500 to 4,000 gallons of liquid sitting on top of the sludge. The exhauster is being used to remove that liquid and dry out the liquid in the top few inches of the sludge waste.
If the project proves successful, DOE could use the same approach on more than two dozen other single-shell tanks with liquid on top of other waste. “We think it’s a great project for that,” Lyon said. Exhausters have been used to evaporate liquid from single-shell tanks in the past, but this is the first time WRPS has used the technology to mitigate intrusion of water into tanks, WRPS said. About 130 gallons of water per year are suspected of getting into Tank T-111. Precipitation is suspected of entering through underground concrete pits covered with removable concrete blocks that were used when waste was being added to Tank T-111. The current leak from the tank appears to have begun around 2000 to 2003, assuming there was no major decrease in the intrusion rate at that time. If there was a major decrease, the current tank leak period may have begun earlier, according to the 2014 report for DOE.
