There's a nice blog article from Jim Cahill on the blend wall at http://www.emersonprocessxperts.com/2013/01/addressing-the-renewable-fuel-standard-and-blend-wall/. Here's an excerpt on the RFS program history.
The RFS program was created under the Energy Policy Act (EPAct) of 2005, and established the first renewable fuel volume mandate in the United States. As required under EPAct, the original RFS program (RFS1) required 7.5 billion gallons of renewable- fuel to be blended into gasoline by 2012.Under the Energy Independence and Security Act (EISA) of 2007, the RFS program was expanded in several key ways:
RFS2 lays the foundation for achieving significant reductions of greenhouse gas emissions from the use of renewable fuels, for reducing imported petroleum, and encouraging the development and expansion of our nation’s renewable fuels sector.