From 1974-1985, Synertek, Inc., leased the area directly uphill from where the Santa Clara Square Apartments currently stand. Synertek manufactured semiconductors, crucial to the production of microchips for computers and other technologies. The manufacturing involved highly toxic chemicals, and several tanks stored underground on site leaked VOCs into the groundwater, contaminating the soil around the area. In 1987, the area was deemed a Superfund site by the Environmental Protection Agency. In spite of this, or the VOCs known to be on site of the SCSA property, the DTSC did not make VOCs a part of their remediation plan for the apartments
This 2006 site report does not show the pollution extending under the apartment site, but who knows.
https://documents.geotracker.waterboards.ca.gov/regulators/d...
Another thing that came to mind: there is a known effect with sound waves - where multiple different sources of sound may not be a problem source themselves (e.g. low level rumbling fans from large buildings) - but then where those sound waves intersect can cause a problem point that impacts biological life; it can be a single source of industrial noise pollution, multiple cases of whole towns getting sick because of it being traced back to the frequencies/vibrations given off by large fans - but what if some noises happen to triangulate to be a problem in your specific unit? It's not impossible.