No one ever confused the EPA with logic.
I have 18 years of experience cleaning up hazardous waste sites (hundreds of them), most of them fuel-related releases. I don't disagree that logic and the EPA (or many other environmental enforcement agencies) often don't meet. That being said, all fuels are toxic and carcinogenic, and avgas probably a bit more so than regular auto gas.
First, I use a GATTs jar, and if the sample is clean, it goes back in the tank. If it's only a little bit of water or debris, I'll drain the clean portion back in the tank through the GATTs screen, and discard the rest as haz waste. Then I thoroughly clean the GATTs jar.
When you dump fuel on the ground, it isn't just the lead that's the problem, it's the benzene and a bunch of other components which get into the water. Benzene is the worst, as it often migrates farther from the release point in groundwater than the other contaminants, and, by concentration, is probably the most toxic/carcinogenic of the fuel components.
If you do dump it on the ground (which I don't advocate, unless you want to keep me well employed into my retirement years), the safest thing to do is dump it on hot asphalt, with no cracks. That will cause the fuel to vaporize, and most of the harmful components would degrade quickly in air. The lead would still get into the pavement, and will likely run off during rain events (which is a bad thing). If you dump it on a crack or dirt/grass, much more of the volatile components would find their way into the subsurface and (eventually) groundwater.