Molasses injected into the soil at Hanford last fall is nourishing bacteria and may be a recipe for success in cleaning up the ground water.

It's too soon to call the test of the cleanup technology a success, but it is showing promising initial results.

"We are encouraged," said John Price, environmental restoration project manager for the Washington state Department of Ecology.

The Department of Energy is investigating several ways to clean up chromium that was spilled or dumped near Hanford reactors when they were producing plutonium for the nation's nuclear weapons programs. At three of the reactor areas along the Columbia River, enough chromium pollutes the ground that it's reaching the river.

The largest chromium plume is near the D and DR reactors, where one monitoring well has found toxic chromium at 10,580 parts per billion.

The drinking water standard is 100 parts per billion, but because the chemical is harmful to fish, including spawning salmon, the limit for chromium in river gravel beds is 10 parts per billion.

The Department of Energy and its contractor Fluor Hanford are pumping contaminated water out of the ground there, removing the chromium and then returning the clean water to the ground.

In addition, they've installed an underground chemical barrier -- the in-situ redox manipulation barrier -- to immobilize the chromium and keep it from entering the river in areas where the concentration of chromium in the soil is lower.

The barrier relies on natural iron in the aquifer formation that turns to rust as water contaminated with chromium 6 passes through it. As the iron oxidizes, it gives up electrons that turn the chromium 6 to chromium 3. Chromium 3 is not only nontoxic, but also is less mobile.

After more than eight years, that barrier is showing some weak spots and some chromium 6 is getting through, Price said. Plans are being made to add more iron to the barrier, but in addition researchers at Pacific Northwest National Laboratory are investigating whether adding a rich food supply for microbes could change the ground water chemistry enough to improve the performance of the barrier.

In September, researchers injected a tanker truckload of molasses into the ground, mixing it into a solution that was 95 percent water.

"We were able to inject it the way we wanted to," said Mike Truex, a Pacific Northwest National Laboratory research engineer. The sugar-water mixture spread out from injection wells as researchers had hoped in a 100-foot diameter, a size practical for protecting a long stretch of the river, he said.

Over the next one to two months, bacteria in the ground fed on the sugar, exploding its population.

"The sugars were consumed. What we saw was just like it was in the lab," Truex said. However, the bacteria did not grow enough to clog the flow of water through the ground, which had been one concern of researchers.

As the population of bacteria grew, it consumed more oxygen, turning it into carbon dioxide. And it consumed more nitrates, turning it into nitrogen gas.

That "reduces stress on the barrier," Truex said. "We want all its capacity used for chromium, not eaten up by oxygen and nitrate."

The overfed bacteria also has had a direct affect on the chromium, which was about 150 parts per billion in the area where the molasses was injected. As the large population of bacteria took in the chromium 6, it was converted to chromium 3.

"Our current concentration is down to 20 to 40 parts per billion," Truex said. That's close to a level that will be safe for fish as the ground water is diluted at the river's edge.

But the real test of the technology will be whether results are sustained. Researchers believe that even though the molasses is consumed in a month or two, the large bacteria population should remain for many more months.

They'd like to see results sustained for a year or even two years before another injection of molasses is required.

In late summer they plan a follow up test to see if vegetable oil also would work. Vegetable oil would be more expensive than the molasses sold at about $5,000 a truckload for cattle feed and may not spread out in the ground as easily. But because the oil will take far longer to be dissolved into water and then consumed by bacteria, the results might last two to four years.

"Both are commercial technologies, but we don't know how well they will work here," Truex said.