Crews are drilling deep into southeast Washington's Priest Rapids Dam on the Columbia River to find out the extent of damage after leaks were recently discovered.
So far, crews have drilled about 80 core samples in the dam's spillway structure, and they plan to drill more than 200 altogether over the next couple months.
Two of the holes are leaking three to four gallons of water per minute, according to Grant Public Utility District officials.
That leak has been traced to a lift joint, which is a seam between two pours of concrete located near the bottom of the dam.
To lessen the pressure until they know more, operators have lowered the pool behind the dam about three feet below what would be normal for this time of year. That might become tricky when spring melt comes. But dam operators said the structure is still safe.
The exploratory drilling costs about $30,000 a day.
Behind the dam lies Priest Rapids Lake, which is about 80 feet deep and stretches 18 miles up the Columbia River. Priest Rapids is the last dam upriver from the Hanford nuclear cleanup site.