After years of "slow walking" and administrative delays to adhere to the stricter 2010 EPA guidelines for dioxane exposure levels, the Michigan DEQ issued emergency rules 10/27/2016 to tighten Michigan's groundwater dioxane cleanup standard to 7.2 ppb (down from 85 ppb) and its dioxane vapor exposure standard to 29 ppb.
The 7.2 ppb cleanup standard is 2-20 times looser than what many other states use. For 1-in-1,000,000 cancer risk over a 70 year lifetime exposure to dioxane in drinking water, the EPA guidelines say 0.35 ppb is appropriate. For 1-in-100,000 cancer risk over a 70 year lifetime exposure, the EPA guidelines say 3.5 ppb is appropriate. The DEQ uses a 32-year lifetime exposure, so Michigan's standard came in at 7.2 ppb.
The emergency action was taken after Dioxane was discovered in shallow groundwater at Ann Arbor neighborhood park... and after some local governments and legislators called for US EPA intervention to better manage the Gelman site cleanup.
The DEQ still has to convince Pall/Gelman/Danaher to accept the tighter 7.2 ppb cleanup standard for the site and make changes to the Consent Judgement and permit.