TCE was used in cleaning circuit boards. Fairchild, anyone?

The TCE plumes on both sides of 101 are well mapped and understood, as are the directions of their movements. The plume under Orion Park is not from the semiconductor manufacturers that used to operate on the other side of 101.

Is this a new plume? The existing plume map(s) that I have seen didn't show anything in the Orion Park area.

The plume was on the base itself. Actually running right under Hangar 1. (Another reason not to save that white elephant).

Let us keep incidents like this in mind when we plan new development. Thorough environmental impact studies are important. You can probably break ground on a new project quicker if you don't do one. But cleaning up after the fact is almost always more expensive and contentious than not polluting in the first place.

Fairchild, Intel and Raytheon had semiconductor manufacturing operations (not actually using TCE for circuit board cleaning, but similar) in the area of Middlefield-Ellis-Whisman (MEW) that was under EPA Superfund supervision in the 1980s. Extensive long-term remediation projects began then - soil excavation and aeration, walls deep underground around sites with extraction systems, and so forth. The good news is that the companies took responsibility and that the TCE had not reached any drinking water supply wells. The MEW "merged plume" was known to head under 101 towards Moffett, where there was evidence of an underground concentration of TCE from washing off airplanes and so forth. Because the subsurface hydrogeology in the MEW area is very jumbled, and there were multiple sources there and at Moffett, it was not possible to depict the clear flow of materials in distinct streams. Nevertheless, as Old Ben notes, there were reasonable maps of where the stuff from any one source was heading. It was widely speculated that some day the amount of stuff under and likely around Moffett would get more attention, which seems to be the case as various land repurposing projects come along.