TRENCH DILEMMA PUZZLES AIR FORCE.

Byline: Jim Skeen Daily News Staff Writer

The big mystery for the Environmental Management Office is what is inside four old, filled-in trenches located in the heart of the main base.

They were part of a chemical weapons storage area in the 1940s, but there are no records indicating what was in the trenches before they were covered.

Each trench is 165 feet long, 15 feet wide and of an unknown depth - topped by at least 3 feet of dirt.

``We have no clue what's in it,'' said Bob Wood, manager of environmental restoration. ``There is no evidence there are chemicals in there, and there's no evidence that there's not.''

If the trenches were located in one of the more remote areas of the base, the Air Force might just fence the area off and leave it alone.

But the trenches are in the equivalent of the base's downtown, just 23.5 feet from a new set of dormitories now under construction.

``The Air Force won't let it sit there,'' said Richard Hector, director of the base Environmental Management Office.

The Air Force became aware of the trenches in September, about the same time contracts were awarded for construction of the new dormitories, officials said.

An archives search determined there was a chemical weapons storage area at the site from 1942 to about 1947 or 1948. At the time, the area was a remote section of Edwards, then named Muroc.

Photographs have been found showing the construction of dormitories in the 1950s next to the trenches - an indication that nothing then considered harmful was buried there, environmental officials said.

Nothing but dirt turned up in four bores drilled at the ends of the trenches. Tests with ground-penetrating radar and electromagnetic equipment revealed nothing, officials said.

``Logic suggests there's nothing there,'' Hector said.

Officials nevertheless consider it unlikely they will choose the option of doing nothing more. Other options are to dig a test pit to see what is in the trenches, entirely dig up the trenches, or use a cleanup method in which high-voltage electricity would turn whatever is in the trenches into glass.

A test pit might miss contaminants, environmental officials said, because there is no indication that whatever is in the trenches is distributed evenly.

Digging up the trenches could be a lengthy, complicated process. A tent would likely be needed over the site, with pressurized air, to keep contaminants from spreading beyond the cleanup area.

The use of electricity would involve sticking probes into the ground to heat whatever is in the trenches to 3,600 degrees. The process has been tested by the U.S. Environmental Protection Agency for purposes such as handling drums of PCB, Wood said.

A contractor will examine the options and supply cost estimates within three months.

The new, $10.8 million dormitories are scheduled to be completed in mid-January. Then the Air Force will decide whether they will be occupied before the trenches are cleaned up.

Wood said he doubts there would be any health hazard, but the Air Force might delay residency in the rooms nearest the trenches until the commotion of cleanup work is past.

Environmental cleanup workers, using ground-penetrating radar and metal detectors, have combed Edwards looking for any remnants of chemical weapons tested or stored in the 1940s and 1950s, Air Force officials said in November.

A nationwide search of military archives identified 11 areas as spots where poisonous gases such as phosgene, cyanogen chloride and hydrogen cyanide might have been used or stored.

The search was spurred by an April 1993 military briefing to Congress and state governors about 68 sites throughout the nation where such weapons were tested, stored or buried.

Maps from the 1940s and 1950s were not accurate enough to pinpoint where chemical weapons might have been stored or used at Edwards, so the ground searches were ordered.

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Photo: (ran in AV and SAC editions only) High-tech environmental searches of a 1940s toxic-gas storage area at Edwards Air Force Base have raised questions about what's in four old trenches.