Important changes to Michigan’s Part 201 cleanup criteria became effective September 28, 2012. Among other revisions, inhalation pathway criteria for both soil and groundwater were made more stringent for several constituents or have been developed for some hazardous substances where previously insufficient data was available to develop criteria.

For example, the TCE criteria have decreased substantially, including the concentration in groundwater criterion for volatilization to indoor air, which decreased from 15,000 ppb to 2,200 ppb for residential closures and from 97,000 ppb to 4,900 ppb for nonresidential closures. These changes potentially could affect cleanups at many sites throughout Michigan (particularly vapor intrusion sites), and potentially result in reopeners at sites where the investigation or even the remedy had been completed. These more stringent values will be more difficult (and probably more costly) to achieve.

Revisions also were made to the lead and manganese Final Chronic Value formulas used to determine hardness-dependent GSI values. Industry comments suggest, however, that the modeling used may overestimate the impact on aquatic life. In addition, groundwater-surface water interface (GSI) criteria also were made more stringent for several constituents. Finally, the Michigan Department of Environmental Quality (MDEQ) added a new hazardous substance, phenytoin, to the Part 201 list of hazardous substances. Phenytoin is a pharmaceutical used in certain drugs, e.g., certain types of seizure medications. Thus, pharmacies and other companies that handle drug disposal for their customers will need to ensure that proper care is used in disposing of such medication. MDEQ’s press release for this action is available here or you can contact the authors for additional information.