[sadface]

One of the projects Terradex, my company, works on is the collection and mapping of various sources of publicly available environmental data. We're based in Palo Alto and actually spent a decent amount of time getting information on various groundwater plumes in Santa Clara County.

We paid extra close attention to this HP plume and a few others like the MEW plume around the Google campus, drawing them in manually from documents, but the vast majority are created based on convex hull calculations from the well information available on geotracker [1]. They are not perfectly accurate but provide a reasonable approximation of plume locations.

We pulled this data together last year during the summer and haven't done much with it since, but if anyone wants to click around and have a look here's a link that will bypass the login requirement: http://cleanupdeck.terradex.com/target/map_icplume/16/37.424.... You just need to click on the "groundwater plumes" layer on the left, and when you click on a blue plume it will bring up an info panel, most of which will have a link to the geotracker page which collates most of the useful information about the plume.

[1]http://geotracker.waterboards.ca.gov/data_download_by_county...