This article from Biodiesel Magazine says that while the agency seems to have a handle on gasoline with more than 10 percent ethanol, there’s a bit more gray area when it comes to biodiesel:
While the draft guidance issued by the EPA would apply to USTs delivering gasoline containing more than 10 percent ethanol, no specific percentage threshold has yet been identified by the agency for biodiesel. According to the agency, it is aware that there may be compatibility issues with UST system equipment used to store biodiesel, but does not have any sufficient data on the compatibility of various biodiesel blends with UST system equipment that is currently in use. In other words, much of the research that has been carried out on this type of equipment for ethanol fuel blends has not addressed biodiesel fuel blends. For example, the agency notes that the U.S. DOE is currently testing the compatibility of UST systems with midlevel blends, but to the EPA’s knowledge no equivalent testing is being conducted for biodiesel-blended fuels.
The EPA also states that it acknowledges that no UST equipment has been listed by Underwriter Laboratories for use with biodiesel, but also notes that UL has issued a statement indicating that biodiesel blends of up to 5 percent will not require UL investigation. However, the UL statement cited by EPA also said that fuel blends containing higher percentages of biodiesel may have significant impacts on UST materials and components. For these reasons, the EPA said it will be seeking comments on what percentage of biodiesel in fuel blends should be included in the proposed guidance.
You can read the proposed guidance here.