The main HQ isn't actually on top of a superfund site, but an ex-dump. We derive a fair amount of methane from the decaying matter underneath shoreline...
The Shoreline Amphitheater (yes, the idiots who ran Mtn. View back then couldn't tell an amphitheater from a theater) was built over the dump.
The first few events revealed the danger when people sitting on the lawn portion actually set the lawn afire with their lighters, due to methane seeping through the soil.