May 1999

Cleanup project could wrap up Corehole 8 saga

It occurred smack in the middle of ORNL and was once one of the Labís most vexing environmental mysteries. The saga of Corehole 8 began in the mid-1980s when a groundwater test well revealed an underground plume of radioactive contamination from no apparent source.

One of DOEís most prominent budget line items for ORNL in fiscal year 2000 is a project to eliminate the source of contamination—mostly strontium-90—by digging up the culprit, an underground storage tank. Over time, the environmental remediation project that came to be known as Corehole 8 has been an example of how a host of disciplines, including geology, chemistry and engineering, must play together to solve these complex problems.

"Iíve been working with this problem off and on for about 15 years," says Energy Divisionís Dick Ketelle. "This has been a real detective story. Most groundwater problems are."

It wasnít always called Corehole 8. That name, more evocative of a Rat Pack movie, comes from a test well drilled in 1991 as part of the investigation into the underground plume. The yellow posts and pipes of the actual Corehole 8 are prominently situated in the field below ORNLís cafeteria. Ketelle narrates the story.

"In 1985, sample wells were installed around the Lab to see what groundwater contamination was present. One well at First Street, which borders ORNLís west fence, had significant levels of strontium-90. There was nothing to tie it to—no obvious source."

Strontium-90, because it is chemically similar to calcium, seeks bone when ingested. It has a half-life of about 30 years.

"In 1990 and í91, as part of the Main Plant Area Remedial Action project, a series of 10 deeper wells were drilled," Ketelle says. At well number eight, located just downhill from the cafeteria, we saw contamination in the drilling water at 30 feet. At 45 feet the contamination levels increased quite a bit. We stopped at 50 feet because we didnít want to carry contamination down farther or encounter an artesian situation where the contaminated water could be forced up to flow out on the ground.

"That information from Corehole 8 tied in with the isolated First Street well to the west. If you look only at the slope, contamination from Corehole 8 should have gone on south to White Oak Creek, but it was going west."

The answer to that puzzle lay in the rockbed structure underlying the Lab. A layer of limestone, tilting to the southeast, was channeling the water toward First Street instead of to the creek, like a subfloor may channel water far away from a roof leak.

Corehole 8 was a symptom, not a source. The source area includes facilities that date from the Labís earliest days: Building 3019, where radioactive materials are stored and processed; hot cell facilities; the Graphite Reactor and its canal; the North Tank Farm, a series of underground storage tanks; and a number of uderground drain lines.

"We were looking at about half a dozen good source candidates," Ketelle says.

More test wells were drilled in that area, and more contamination was found. Coincidentally, during the operations in the North Tank Farm in the late 1980s, a leak was found at a tank that received low-level waste.

Excavation near that stainless steel tank, which was installed in the 1950s, revealed that the pipe that fed it had broken almost at its inlet. Some of the waste from Building 2026ís labs was flowing around and under the tank, not into it.

"No one knows when the break occurred," Ketelle says. "The limestone bed is right under the tank. We encountered that bed at about the 40 foot depth just to the west at Corehole 8, and the contamination proceeded on toward First Street."

Now that they knew the source, the question remained what to do about it. Some contamination had been detected in storm drains. Those were sleeved to keep it out, but that only caused the waterborne Sr-90 to crop up elsewhere.

"When you block water out of one place, it just finds somewhere else to go," Ketelle says.

This summer a CERCLA removal action will commence to clean up the primary source—Tank W-1a in the North Tank Farm. Tons of contaminated soil from around the tank will be removed, which should stop further contamination from entering the plume.

Removing the contaminated groundwater is trickier. Some contaminated groundwater is already collected and sent to ORNLís Process Waste Treatment Plant at a normal rate of about eight gallons per minute, up to 30 gallons per minute in rainstorms.

The years of work Ketelle and many others at ORNL have invested in Corehole 8 illustrate a characteristic of environmental remediation problems involving groundwater: They arenít always easy to figure out and they are never simple to fix.

In this case familiarity with the complex system of faults and fractures underlying the X-10 site, plus a lot of digging and surveillance, were keys to solving ORNLís Corehole 8 mystery, now entering whatís hoped to be its final chapter.   —B.C.