A constant drip, drip, drip has added about 3,300 gallons of water over 18 years to one of Hanford's underground tanks holding radioactive waste.
Last year, an assessment of routine measurements in Hanford's 149 single-shell waste tanks found that the level of waste might be slowly rising in 52 of the tanks.
Seven months later, the Department of Energy has answers about what might be going on in three of them.
Engineers inserted video cameras through risers that allow access from the ground into the enclosed underground tanks to inspect them and see if they could find potential sources of water intrusion, including from rainfall and snow melt.
In two of the tanks, BY-101 and BY-111, they found no evidence that water was getting into the tanks.
But the video of Tank BY-102, with a capacity of 750,000 gallons, shows a slow drip from a concrete pit drain. Underground concrete pits covered with removable concrete blocks were used when waste was being moved into or among tanks when Hanford was still producing plutonium for the nation's nuclear weapons program.
If any waste spilled during operations, it would flow into a floor drain in the pit and then go into a tank.
The video shows water collecting in the bottom of a small crater in the surface of the Tank BY-102 waste at about the same level that liquid is sitting within the tank among the pores of the waste. Contractor Washington River Protection Solutions estimates that the water drip has increased the level of "interstitial water" beneath the waste's surface in the huge tank by about six inches.
The tank has previously been pumped to retrieve as much liquid as possible, but has about 40,000 gallons of liquid throughout the waste that could not be readily pumped out. The drip is adding possibly 100 to 200 gallons of water a year.
"Compared to the scale of retrieval, most people would consider it pretty small potatoes," said Dennis Washenfelder, tank and pipeline integrity engineering manager for Washington River Protection Solutions.
The DOE contractor does not believe the additional water has a significant impact now on waste storage conditions in the tank.
Liquid waste was pumped from all the single-shell tanks, in part, to reduce the threat of the tanks leaking. An estimated 1 million gallons of waste has leaked from the tanks into the soil beneath them in the past.
Tank BY-102 is not a tank that is suspected of having leaked. However, the Washington State Department of Ecology, the regulator of the tanks, is concerned about what impacts the additional water may have on corrosion of the tank.
Now most of the liquid appears to be collecting in the center of the tank rather than near metal.
Washington River Protection Solutions still is in the early stages of solving the mystery of why a study of measurements showed waste in 52 tanks apparently increasing.
This year, video inspections of eight or nine more tanks are planned and that information will help officials better understand if there is a water-intrusion problem that needs to be addressed, Washenfelder said.
Tanks picked for inspection are those most likely to have water intrusion. For some tanks, an average increase of a couple thousands of an inch a year had been detected from measurements, with some of the readings taken four times a year for decades.
But in 21 tanks, measurements indicated larger increases of up to an average of about three-quarters of an inch a year.
For Tank BY-102, the state is working with DOE and its contractor to rewrite its monitoring process.
"We expect them to identify why the pit is leaking into the tank and if it is fixable," said Jeff Lyon, the Washington State Department of Ecology manager for tank waste storage.
Research also is being done on tank chemistry, and changes to the monitoring process for tanks and the response to changes in the liquid level also may be considered.
The level of liquid waste in the tanks can be difficult to measure because the top surface of the waste in many tanks is rough and uneven. A plummet is lowered on a wire into the tank until it hits waste and it could be hitting different places on the surface of the waste when it is lowered.
In addition, the waste contaminates the plummet, sometimes getting trapped on its end. A small amount of water is flushed down the wire to remove it. The water could be pooling in a pocket beneath the plummet, which could change the measurement but would not mean an increase in the level of waste across the tank.
That the video inspection found water intrusion in only one of three tanks shows that "we are taking a very conservative approach in identifying potential anomalies when it comes to shifts in liquid waste levels inside the tanks," Washenfelder said.
-- Annette Cary: 582-1533; email@example.com; Twitter: @HanfordNews