My couple cents to the picture (as seen).
I'm a chemist, mainly with cosmochemistry (meteorites) and geochemistry, but I have some experience with atmospheric and environmental chem as well (did post-doc at Atmospheric Chemistry Lab at UMD).
What the
beach photos (Emre Kelly) and
meteo-radar picture tell me:
1. the brown-colored smoke is nitrogen tetroxide, N2O4.
2. It was NOT a *single-event incident*, rather there were several N2O4 releases (from different vessels presumably);
3. It was a massive N2O4 release.
From the radar picture (from "how FAR did the cloud go before dissipating") I would guess *many tons* of N2O4.
However, it is very likely that meteorological radars improved significantly since my times (late 90s). So given improved contrast and sensitivity, I'd put a lower estimate - **
several hundreds of kilos to first tons of N2O4 total**
4. Finally, it looked like an "oxidizer-rich explosion".
Although this is just a feeling

Obviously, the video clip is made by phone FROM a computer monitor, therefore color balance may be significantly OFF.
For environmental impact:
I'd expect no significant consequences, all N2O4 and MMH will be gone on the scale of hours/days, BUT
there will be mandatory extensive analyses (water, air) to confirm this.
Which are quite expensive, hopefully covered by insurance.