After 5+ years of delay, the DEQ has settled on a tightening of Michigan's 1,4-dioxane cleanup standard from 85 ppb to 7.2 ppb to come near to the 2010 EPA guidelines for dioxane. It would have been 3.5 ppb under the EPA guidelines for dioxane at a 1-in-100,000 cancer risk over a 70 years lifetime exposure, but the DEQ kept in place its weaker 32-year exposure standard... perhaps under the faulty assumption "What contamination could possibly last longer than 32 years?"
States that use the 1-in-1,000,000 cancer risk over a 70-years lifetime exposure (like Michigan used to have until 1995) use the EPA 0.35 ppb guideline for dioxane.
The 7.2 ppb standard will not be effective immediately. It still has to go through approval steps at the DEQ, LARA and the state legislature.
When in place, the tighter standard should help protect area water supplies from further damage.
Links: DEQ statement Mlive article