In order to get regional material credit for steel can an average percentage be used of all the mills that sourced scrap within 500 miles of the project site? For the Extraction Distance can the most extreme (greatest) distance be listed? Or does each mill have to be listed individually?
I would post this question to the LEED NC forum, since there are many more users there. I haven't ever tried the approach you suggest but if you don't know where the scrap was sourced then you may have to assume the worst.