In writing the law, Congress included a safety valve and told the EPA to set the mandate to meet "the projected volume available" in the event of a shortfall.

WSJ: Review & Outlook: Zero Dark Ethanol

In order to stop flood waters overwhelming central London and to save the massive expense of building fresh flood walls and defences, some land could be set aside to act as a safety valve, catching flood waters and storing them until the danger has passed.

BBC: London's drowning

Nothing's set in stone, of course, and Valve's still very much in the exploratory phase of its Steambox push.

ENGADGET