The Michigan Department of Environmental Quality (MDEQ) Air Quality Division (AQD) has proposed to substantially amend the regulations on emissions of toxic air contaminants (TACs) from proposed new or modified sources for which a permit to install is required. The proposed rules would enact a number of reforms recommended in February 1997 by a special committee that was formed to review AQD's air toxics rules. The reforms will provide new exemptions from certain requirements and provide new alternatives for TAC emission sources to comply with the air toxics requirements.
Most of the proposed changes concern the requirements pertaining to health-based screening levels and related dispersion modeling analyses of TAC emissions from proposed new or modified sources. Health-based screening levels are the maximum ambient concentration of a TAC that may legally result from a new or modified source.
One significant proposed change is that sources that will emit less than 10 pounds per month and 0.14 pounds per hour of a noncarcinogenic TAC would be exempt from the health-based screening levels. This exemption would not apply to carcinogens and certain other "high concern" TACs identified in the proposed rules. Also exempt from health-based screening level requirements would be certain emission units subject to regulation under the federal EPA hazardous air pollutant (HAP) regulations and other sources that MDEQ determines, on a case-by-case basis, will not cause or contribute to a violation of Mich. Admin. Code r. 336.1901, which essentially prohibits emissions that constitute a nuisance.
Under the proposed amendments, a proposed new or modified TAC source would be required to use the best available control technology for toxics (T-BACT), even if the source is exempt from health-based screening level requirements, unless: (a) the source is subject to a National Emission Standard for Hazardous Air Pollutants (NESHAP) promulgated under the Clean Air Act (CAA) or a case-by-case maximum achievable control technology (MACT) determination under the CAA; (b) the source's maximum allowable emission rate will be, for a carcinogen, 0.1 pounds per hour or less or, for a noncarcinogenic TAC, 1.0 pounds per hour or less; or (c) the source will only emit TACs that are particulates or VOCs and complies with the best achievable control technology (BACT) or the lowest achievable emission rate (LAER) requirements for particulates and VOCs.
The proposed revisions would also allow ambient concentrations of TACs emitted from a proposed new or modified source to exceed an applicable health-based screening level by a factor of 10 on industrial property and public highways, under certain conditions. Other proposed amendments would substantially revise the methods for conducting dispersion modeling analyses of TAC emissions to demonstrate compliance with the health-based screening levels.
The proposed revisions would also establish several new alternative methods for calculating the allowable emission rate for a TAC from a process that will not result in an exceedance of an applicable screening level. Some of the new alternative methods are intended to estimate the allowable emissions more accurately than the methods currently employed by MDEQ, while others are intended to be easier to use than the current methods.
A public hearing on these proposed rules was held on August 14, 1997, and written comments were accepted until that date. The proposal would modify Mich. Admin. Code r. 336.1230 - .1232 and .1299 and would add new rules Mich. Admin. Code r. 336.1224 to .1229. Copies of the proposed rules can be obtained by contacting the MDEQ at (517) 373-7069.
This article was prepared by S. Lee Johnson, a partner in our Environmental Department, and previously appeared in the October 1997 edition of Michigan Environmental Compliance, a monthly newsletter written by Honigman Miller Schwartz and Cohn on environmental regulatory developments in Michigan and published by M. Lee Smith Publishers. To subscribe, contact the publisher by either phone at 1-800-274-6675; email at custserv@mleesmith.com; the internet at http://www.mleesmith.com; or by mail at M. Lee Smith Publishers LLC, 5201 Virginia Way, P.O. Box 5094, Brentwood, TN 37024-5094.