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04/27/2017 DEQ Extends Emergency Rules to Establish Safer Dioxane Standards



After dragging its feet for more than 6 years to adhere to stricter dioxane guidelines issued in 2010 by the EPA, the DEQ issued an emergency rule on October 27, 2016, tightening dioxane groundwater cleanup standard from 85 ppb to 7.2 ppb... and setting a dioxane vapor intrusion standard of 29 ppb for water in close contact with basements.

Unable to get both the 7.2 ppb groundwater standard and the 29 ppb vapor intrusion standard permanently approved, the DEQ had to issue a second emergency rule on April 27, 2017, just before the first one expired. However, the second one left off the 29 ppb vapor intrusion standard while keeping the 7.2 ppb groundwater standard. The DEQ is reevaluating the vapor intrusion standard and proposing that it be 1900 ppb instead since dioxane does volatilize to air as readily as some other chemicals. A value for exposure via dioxane in water vapor from wet basements also needs to be evaluated since that kind of exposure has never been studied.

The DEQ is hoping that it can make the 7.2 ppb groundwater standard permanent by October 27, 2017. If not, the standard may revert to 85 ppb!


An interesting aside... Pall's 2016 1st Quarterly Report Deep Plume Map (above) shows a small portion of a 7.2 ppb plume boundary. But that 7.2 boundary disappears on their 2016 3rd Quarterly Report Deep Plume Map... only to reappear on the 2017 1st Quarterly Report Deep Plume Map (but without being labeled). It's almost as though Pall created maps with 7.2 plume boundaries, but tried to remove them before sharing the maps with the DEQ.

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