Thursday, Aug. 21, 2008

Vegetable oil in recipe for Hanford cleanup

By Annette Cary, Herald staff writer

Researchers at Hanford are turning to kitchen cupboards for inspiration in cleaning up contaminated ground water at the nuclear reservation.

Wednesday they injected 1,500 gallons of vegetable oil mixed with 55,000 gallons of water into ground water contaminated with toxic chromium that's moving toward the Columbia River.

That followed a similar test last year with 5,500 gallons of molasses.

"It's very elegant and very simple," said Mike Thompson, a Department of Energy hydrogeologist.

The goal is to overfeed the bacteria already in the ground water. As they eat the extra oil or molasses, their population blooms. When the food is gone, they start eating each other.

The sustained feeding reduces the limited amount of available oxygen in the water and then begins converting toxic chromium into a form that is less toxic. It also is less mobile, tending to stick to the soil rather than dissolving in the ground water and moving toward the river.

Pacific Northwest National Laboratory knows the system works in principle. The early results from last summer's molasses injection are promising and bioremediation has worked at other contaminated sites in the nation.

But now DOE, laboratory researchers and Fluor Hanford want to compare results using molasses and using soybean oil. Molasses, which is sold in bulk as cattle feed, is cheaper at about $5,000 for a tanker truckload. But the carbohydrate also is quickly consumed.

The vegetable oil, which cost $20,000, should last longer because its organic compounds are more concentrated and cling to sand underneath the ground to be released slowly into the ground water.

Researchers are expecting the results from vegetable oil to last up to five years, compared to the two-year improvement expected from molasses.

Because oil doesn't mix well with water, researchers have purchased emulsified oil. It has been reduced to drops 50 times smaller than the diameter of a human hair, said Mike Truex, a Pacific Northwest National Laboratory scientist.

The area near D Reactor where the molasses and vegetable oil tests are being conducted is among the most contaminated with chromium on the Hanford site. During the years that Hanford was producing plutonium for the nation's nuclear weapons program, sodium dichromate was mixed with water used to cool Hanford reactors to help prevent corrosion of aluminum.

Chromium contamination has been measured at one place in the D Reactor area at 45 times the drinking water standard, said Dib Goswami, lead program hydrologist for the Washington State Department of Ecology, a Hanford regulator.

While that ground water is not used for drinking water, the contamination does pose an immediate risk to fish.

"This is right next to the active salmon redds," said John Price, environmental restoration project manager for the Department of Ecology. Although harm to salmon has not been observed, chromium has been measured in gravel at the edge of the river above levels considered safe for aquatic life.

Because chromium is so toxic to young fish, standards for aquatic life are 10 parts per billion rather than the 100 parts per billion limit for drinking water.

Ecology has enough confidence in the project to recommend that bioremediation be put on a more aggressive schedule.

"This technology is relatively inexpensive so even if there are a few wrinkles in its application, there is not much monetary risk in scaling it up," Price said.

Already several methods are being used to decrease chromium from reaching the river near D Reactor.

"There is no silver bullet," Price said. "We need a combination of technologies."

Contaminated water is being pumped out of the ground, cleaned and reinjected. But overfeeding bacteria shows promise to produce results more quickly and with less expense.

An underground chemical barrier also was installed nearly a decade ago along the river. It uses iron to manipulate chromium. As the iron oxidizes, it gives up electrons that turn the chromium 6 to chromium 3.

That barrier is showing its age, but the rich food supply for microbes could change the ground water chemistry enough to improve the performance of the barrier along with a recent reinjection of iron.

In addition, DOE continues to look for the primary source of the contamination that continues to allow chromium to seep into ground water. It has narrowed its search to a two-acre area where tanker rail cars unloaded sodium dichromate.