NAC445B.064. “Excessive concentration” defined.

“Excessive concentration” means, for the purpose of determining good engineering practice stack height:

     1. For sources seeking credit for stack height exceeding that established under paragraph (b) of subsection 1 of NAC 445B.083, a maximum ground-level concentration due to emissions from a stack due in whole or part to downwash, wakes and eddy effects produced by nearby structures or nearby terrain features which individually is at least 40 percent in excess of the maximum concentration experienced in the absence of such downwash, wakes or eddy effects and which contributes to a total concentration due to emissions from all sources that is greater than an ambient air quality standard. For sources subject to 40 C.F.R. § 52.21, an excessive concentration alternatively means a maximum ground-level concentration due to emissions from a stack due in whole or part to downwash, wakes or eddy effects produced by nearby structures or nearby terrain features which individually is at least 40 percent in excess of the maximum concentration experienced in the absence of such downwash, wakes or eddy effects and greater than a prevention of significant deterioration increment. The allowable emission rate to be used in making demonstrations pursuant to NAC 445B.001 to 445B.3689, inclusive, must be prescribed by the new source performance standard that is applicable to the source category unless the owner or operator demonstrates that this emission rate is infeasible. Where such demonstrations are approved by the Director, an alternative emission rate must be established in consultation with the source owner or operator.

     2. For sources seeking credit after October 11, 1983, for increases in existing stack heights up to the heights established under paragraph (b) of subsection 1 of NAC 445B.083, either:

     (a) A maximum ground-level concentration due in whole or part to downwash, wakes or eddy effects as provided in subsection 1, except that the emission rate specified by any applicable state limit or, in the absence of such a limit, the actual emission rate, must be used; or

     (b) The actual presence of a local nuisance caused by the existing stack, as determined by the Director.

     3. For sources seeking credit after January 12, 1979, for a stack height determined under paragraph (b) of subsection 1 of NAC 445B.083, where the Director requires the use of a field study or fluid model to verify good engineering practice stack height, for sources seeking stack height credit after November 9, 1984, based on the aerodynamic influence of cooling towers, and for sources seeking stack height credit after December 31, 1970, based on the aerodynamic influence of structures not adequately represented by the equations in paragraph (b) of subsection 1 of NAC 445B.083, a maximum ground-level concentration due in whole or part to downwash, wakes or eddy effects that is at least 40 percent in excess of the maximum concentration experienced in the absence of such downwash, wakes or eddy effects.

     (Added to NAC by Environmental Comm’n by R096-05, eff. 10-31-2005)