E2600-10 VES guidance recommends using a critical distance of 30 feet and 100 feet for petroleum and chlorinated vapor migrations, respectively, from the edge of groundwater or soil plumes. Does anyone know where and how these numbers were established?
I think I found the 100 foot reference in a USEPA/OSWER 2002 document called "Draft Guidance for Evaluating Vapor Intrusion to Indoor Air Pathway from Groundwater and Soils." This document says the the 100-foot vapor migration distance, irrespective of petroleum versus chlorinated plumes, is a conservative distance based on empirical data from Coloroda sites where vapor intrusion pathways have been evaluated. I'm guessing chlorinated plumes were the driving factor for establishing that 100-foot distance, but the document doesn't appear to elaborate.
My next question is if there is a published report for the Colorado study referenced in the 2002 USEPA document?
I have no idea where the 30 foot distance came from for petroleum plumes, any ideas?
And does anyone use local vapor migration studies instead of the E2600 guidance?