Voracious bacteria help clean up pollution at Hanford

Scientists use vinegar to stimulate the microbes to break down carbon tetracholride contaminating the ground.

By James Long of the Oregonian staff Wednesday, July 19, 1995

Vinegar-swigging microbes have destroyed about 10 percent of a dangerous chemical polluting an area of ground water near the Hanford Nuclear ReservationÍs plutonium finishing plant, giving scientists hope that their unorthodox cleanup experiment is working.

'Things are cooking right along,' said Daniel B. Anderson of Battelle Pacific Northwest Laboratory, the Department of Energy's main research arm at Hanford.

Battelle began the experiment about a month ago, looking for a cheap way to get rid of hundreds of tons of carbon tetrachloride that were dumped into the ground from 1952 to 1973, along with millions of gallons of waste water. Carbon tet was used as a solvent in the manufacture of plutonium for nuclear warheads.

Scientists began putting vinegar into the ground water a month ago to see whether they could trick soil bacteria into attacking the chemical.

According to Anderson, the microbes seem to have reduced the carbon tet concentration in the test area from about 2,000 parts per billion to 1,800 in the past two weeks.

"We're hoping we'll drop it significatnly, maybe down to 500," he said.

Carbon tetrachloride isn't radioactive but is suspected of causing cancer. The maximum allowable concentration in drinking water is 5 parts per billion. Anderson does not expect to get the water that clean- partly becasue the vinegar experiment affects only part of the contaminated seven-square mile plum.

"So there's always more carbon tet flowing into the system from all around it," Anderson said.

However, he thinks the experiment is giving every indication that a full-scale bug program would work.

Scientists first got the idea of adding vinegar to the plume a couple of years ago, after extensive studies of the soil and water around the plutonium plant revealed that two-thirds of the carbon tetrachloride dumped there seemed to be missing.

Then they looke at other pollutants that had been dumped with the carbon tet and found things such as lard oil, which had been used in maching plutonium, and other chemicals such as nitrates.

Further study showed that the plant had accidentally created a bioremediation experiment in which the lard and other organic materials thrown out with the carbon tetrachloride had stimulated soil bacteria to start cleaning things up.

Vinegar seems to speed the process even more. A final report is expected in December.

The experiment also will show how much objectionable chloroform the bacteria produce along with the carbon dioxide and salt- byproducts of disntegrated carbon tetrachloride.

"A little chloroform may still be OK if it's under the drinking water standards," Anderson said. "If not, there's another group of organisms we can stimulate to take care of the chloroform. They like butane."