Hanford recently began extracting an abnormally high concentration of toxic carbon tetrachloride vapors from a 200 West Area burial trench.

The extraction - sucking out vapors with a vacuum pump - began Nov. 11, and Fluor Hanford hopes to have the carbon tetrachloride concentrations down to benign levels by mid-December.

This filled-in trench is one of several near Hanford's Plutonium Finishing Plant that hold many thousands of barrels and containers of highly radioactive transuranic wastes.

These trenches have narrow vertical pipes inserted from the ground's surface to the trenches' bottoms to collect air samples to see if any toxic or radioactive vapors are leaking.

In the summer of 2002, samples from one trench showed carbon tetrachloride fumes grossly exceeding federal safety standards.

Carbon tetrachloride vapors are heavier than air and are expected to settle among the bottom layer of stacked barrels inside the trench.

The Department of Energy and Fluor want to start unearthing and removing barrels of transuranic wastes from the trench the middle of next month to be checked, processed and eventually shipped to a permanent storage site near Carlsbad, N.M.

Fluor installed a vapor extraction pump at the trench's east end, where the densest carbon tetrachloride is, said Dick Wilde, director of Fluor's ground water protection program. Extraction of the transuranic waste barrels will begin at the west end, where the toxic fumes don't exist or are at benign levels.

The extraction equipment is pumping out about 100 cubic feet of air a minute. When pumping began, the concentration of extracted carbon tetrachloride was about 70 parts per 1 million parts of air.

The concentration of the carbon tetrachloride vapors currently pumped out is about 30 parts per million, Wilde said.

Fluor is trying to dilute the carbon tetrachloride's density to 5 parts per million, which is the level allowed for breathing without special equipment.

Even when the concentration is diluted to breathing levels, workers still will be allowed to wear breathing equipment when working in this trench and its neighboring sites, Wilde said.