just going to chime in here since I am also at an environmental consulting firm, but specialize in air sampling / exposure to airborne contaminants. you can sample specifically for vinyl chloride (NIOSH 1007), rather than total volatile organic compounds (TVOCs), using charcoal tube media. Cost is about $75USD/sample. You can also use a passive badge, which is about as easy as air sampling can get, to also sample specifically for vinyl chloride. An open characterization VOC sample can easily get up to $500/sample. It would likely be preferable to compare the air sample results to ACGIH TLV's as a starting point, since OSHA PEL's tend to be slow to be revised (in this, it looks like the values are actually the same either way, at 1 ppm). But - ACGIH TLV, OSHA PEL, NIOSH REL, others etc are intended for 8-hour exposure periods with 16hr recovery periods, for 40 hr work weeks. Measurements of a contaminant within a home is a different scenario since there could potentially be someone within the home 24 hours, so the exposure limit criteria would likely come down quite a bit, potentially to 0.1 ppm.

If i'm not mistaken EPA 6820D intends to quantify VOCs in solid waste media. That may not be the best route in this instance.

The other consideration to deal with is that concentrations of vinyl chloride (and others) are likely to subside quickly over time due to its volatility. So you'd have to think ahead - if you get 'high' results the first time you sample, and then 'low' results if you sampled again a week later, was that a significant risk to your health? There'd be other contaminants to worry about - carbon monoxide, hydrochloric acid, phosgene (to manage perceptions from the public & media), respirable particulate (PM2.5), potentially metals like iron oxide / manganese / maybe aluminum from the rail cars themselves etc.