Ten train cars worth of formaldehyde averaged over the entire atmosphere would be nothing to worry about, I agree. Let's say that two train cars worth sank int

Ten train cars worth of formaldehyde averaged over the entire atmosphere would be nothing to worry about, I agree. Let's say that two train cars worth sank into the ground before breaking down. Now there's two train cars worth of formaldehyde in the groundwater in a localized area. It's not obvious to me that this is a safe situation. There are plenty of plausible scenarios that could be reality, that would be a very unsafe situation for local residents. Thus is should be treated as though it is that worst-case bad scenario unless shown otherwise, rather than wand-waving "oh it's probably fine". These are people's lives that are at stake.