I contacted the Bldr to repair the failed silt fence and to add additional measures.

Land Development inspector updated the case (above comment).

Where does it say in the code that rain fall over 2" in 24 hours makes a silt fence failure acceptable Kay?

The erosion and sediment control ordinance 14-38 and the E&SC act of 1975 as amended does not say its acceptable, it says that erosion control measures are designed to withstand up to a 2"/24 hr event after it exceeds that measures may fail. As long as the permittee had the measures installed correctly and maintained them per approved plans then enforcement is defensible. The failed measures must be corrected and designer contacted to see if additional measures are needed. Any silt which gets off site must be cleaned up. This does not keep land owners affected by the resulting siltation from filing civil cases.
I hope that answers your question
Kay

The silt fence has been repaired, the site will continue to be monitored.