The EPA has announced that it will issue guidance addressing petroleum vapor intrusion by late 2012.  According to the EPA, petroleum contaminants biodegrade into non-toxic products like carbon dioxide and water through natural microbial activity as they near the surface, thereby reducing the risk of vapor intrusion from petroleum sources.  The final guidance is expected to take into account the biodegradation of petroleum compounds, and to treat petroleum contamination less strictly than other sources of contamination where vapor intrusion is more likely.  In an EPA released information paper dated March, 2012, the EPA stated “by quickly identifying cases where biodegradation is unlikely to result in significant petroleum vapor attenuation, you can use financial resources most effectively to protect public health by addressing the sites where [petroleum vapor intrusion] is more likely.”  Once adopted, the guidance will provide a uniform standard to apply in all USEPA regions.