Capturing yucky water and cleaning it with nature's tools

Anywhere we harvest runoff from roadways we need to have a way to filter out some of the nasties that motor vehicles leave behind. The main things we don't want getting into our food-growing systems are the petroleum products, like motor oil and hydraulic fluid, and the particles that result from tyre wear, especially the anti-degradants that are mixed in to prevent rubber deterioration and have some really toxic effects on aquatic life.

I'm a fan of biochar bunds or sediment traps placed in the path of the water flow, periodically replaced so that the "used" biochar can be dealt with safely. Unless heavy metals are in the picture, this treatment can be as simple as re-pyrolysis of the used biochar at high enough temperatures to destroy the bad stuff, after which the biochar can go back into the sediment trap or some other beneficial setting.