A. The limitations set forth herein shall not apply to stacks or dispersion techniques used by the owner or operator prior to December 31, 1970, for which the owner or operator had:
1. Begun, or caused to begin, a continuous program of physical on-site construction of the stack;
2. Entered into building agreements or contractual obligations, which could not be canceled or modified without substantial loss to the owner or operator, to undertake a program of construction of the stack to be completed in a reasonable time; or
3. Coal fired steam electric generating units, subject to the provisions of Section 118 of the Act (Control of Pollution from Federal Facilities) which commenced operation before July 1, 1975, with stacks constructed under a construction contract awarded before February 8, 1974.
B. GEP stack height is calculated as the greater of the following four numbers in subdivisions 1 through 4:
1. 213.25 feet (sixty-five meters).
2. For stacks in existence on January 12, 1979 and for which the owner or operator had obtained all applicable preconstruction permits or approvals required under 40 CFR parts 51 and 52 and Section 17.16.560, Hg = 2.5H.
3. For all other stacks, Hg = H + 1.5L, where:
Hg = Good engineering practice stack height, measured from the ground-level elevation at the base of the stack;
H = Height of nearby structure measured from the ground-level elevation at the base of the stack;
L = Lesser dimension (height or projected width) of nearby structure;
provided that the EPA, state, or local control agency may require the use of a field study or fluid model to verify GEP stack height for the source; or
4. The height demonstrated by a fluid model or a field study approved by the reviewing agency, which ensures that the emissions from a stack do not result in excessive concentrations of any air pollutant as a result of atmospheric downwash, wakes, or eddy effects created by the source itself, nearby structures, or nearby terrain obstacles.
5. For a specific structure or terrain feature, "nearby" shall be:
a. For purposes of applying the formulae in subdivisions 2 and 3 of this subsection, that distance up to five times the lesser of the height or the width dimension of a structure but not greater than 0.8 km (one-half mile);
b. For conducting demonstrations under subdivision 4 of this subsection, means not greater than 0.8 km (one-half mile). An exception is that the portion of a terrain feature may be considered to be nearby which falls within a distance of up to ten times the maximum height (H+) of the feature, not to exceed two miles if such feature achieved a height (H+) 0.8 km from the stack. The height shall be at least forty percent of the GEP stack height determined by the formula provided in subdivision 3, or eighty-five feet (twenty-six meters), whichever is greater, as measured from the ground-level elevation at the base of the stack.
6. "Excessive concentrations" means, for the purpose of determining good engineering practice stack height under subdivision 4 of this subsection:
a. For sources seeking credit for stack height exceeding that established under subdivisions 2 and 3 of this subsection, a maximum ground-level concentration due to emissions from a stack due in whole or in part to downwash, wakes, and eddy effects produced by nearby structures or nearby terrain features which individually is at least forty 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 the requirements for permits or permit revisions under this chapter, 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 forty percent in excess of the maximum concentration experienced in the absence of such downwash, wakes or eddy effects and greater than the applicable maximum allowable increase contained in Section 17.08.150. The allowable emission rate to be used in making demonstrations under subdivision 4 of this subsection shall be prescribed by the new source performance standard which 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 control officer, an alternative emission rate shall be established in consultation with the source owner or operator;
b. For sources seeking credit after October 11, 1983, for increases in existing stack heights up to the heights established under subdivisions 2 and 3 of this subsection, either.
i. A maximum ground-level concentration due in whole or in part to downwash, wakes, or eddy effects as provided in paragraph a of this subdivision, except that emission rate specified by any applicable SIP shall be used, or
ii. The actual presence of a local nuisance caused by the existing stack, as determined by the control officer; and
c. For sources seeking credit after January 12, 1979, for a stack height determined under subdivisions 2 and 3 of this subsection, where the control officer requires the use of a field study or fluid model to verify GEP 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 subdivisions 2 and 3 of this subsection, a maximum ground-level concentration due in whole or in part to downwash, wakes, or eddy effects that is at least forty percent in excess of the maximum concentration experienced in the absence of such downwash, wakes, or eddy effects.
C. The degree of emission limitation required of any source after the respective date given in subsection A of this section for control of any pollutant shall not be affected by so much of any source's stack height that exceeds good engineering practice or by any other dispersion technique.
D. The good engineering practice (GEP) stack height for any source seeking credit because of plume impaction which results in concentrations in violation of national ambient air quality standards or applicable maximum allowable increases under Section 17.08.150 can be adjusted by determining the stack height necessary to predict the same maximum air pollutant concentration on any elevated terrain feature as the maximum concentration associated with the emission limit which results from modeling the source using the GEP stack height as determined herein and assuming the elevated terrain features to be equal in elevation to the GEP stack height. If this adjusted GEP stack height is greater than stack height the source proposes to use, the source's emission limitation and air quality impact shall be determined using the proposed stack height and the actual terrain heights.
E. Before the control officer issues a permit or permit revision under this article to a source based on a good engineering practice stack height that exceeds the height allowed by subsection B of this section, ADEQ shall notify the public of the availability of the demonstration study and provide opportunity for public hearing in accordance with the requirements of Section 17.12.190 and Section 17.13.210.
(Ord. 2017-20 § 2 (part), 2017)
Editor's note— Formerly § 17.12.360.