[deftnerd]

I find it interesting that there were spikes of readings at certain times of day and night. Coupled with the information that the apartments have a VoC barrier, my intuition is that there is a timer somewhere that turns on a fan to clear out the VoC capture space created by the barrier and exhaust the contaminated air to the outside.

If the VoC that's bothering her is heavier than air, it could be being blown upwards from the ground level and then settling back over the building and falling back down and finding its way back into her apartment somehow, like through the range hood, dryer exhaust, plumbing stacks, open windows, or just cracks due to poor craftsmanship.

If she was still at the site, I would recommend looking for what appears to be an exhaust vent of some kind that might be tied to the VOC barrier system and putting a sensor there and seeing if the readings correlate to the timeline of unusual readings in her home

[ericbarrett]

I had a condo in San Francisco. The building was on an old gas station site. The site remediation included a vapor barrier placed below the foundation, and a vent pipe from the soil to 10 feet (I don't remember the exact height, but it was prescripted in the permit) over the roof. Said soil vent had a fan that ran nightly exactly as you suggest, again prescripted by the permit to continue for at least 10 years. So I find this quite plausible. Perhaps her apartment was next to a similar vent pipe which had a leak.

[jeffbee]

Gas stations are this big elephant that nobody speaks of. Essentially every gas station site has polluted soil that makes the site either uninhabitable or uneconomical to remediate.