Section R18-2-1708. Risk Management Analyses

A.      Applicability.

1.        An applicant seeking to demonstrate that HAPRACT or AZMACT is not necessary to prevent adverse effects to human health or the environment by conducting an RMA shall first apply for a permit or significant permit revision that complies with Article 3 of this Chapter.

2.        An applicant seeking to demonstrate that HAPRACT or AZMACT is not necessary to prevent adverse effects to human health or the environment shall conduct a risk management analysis (RMA) according to this Section.

3.        The RMA for a new source shall apply to:

a.         The source’s annual total potential to emit state HAPs for evaluation of chronic exposure; or

b.        The source’s hourly total potential to emit state HAPs for evaluation of acute exposure.

4.        The RMA for a modified source shall apply to:

a.         The source’s annual total potential to emit state HAPs, after the modification, for evaluation of chronic exposure; or

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b.        The source’s hourly total potential to emit state HAPs, after the modification, for evaluation of acute exposure.

5.        An applicant shall conduct an RMA for each state HAP emitted by the source in greater than de minimis amounts.

B.       The applicant may use any of the following methods for con- ducting an RMA:

1.        Tier 1: Equation.

a.         For emissions of a HAP included in a listed group of hazardous compounds, other than those HAPs iden- tified in Table 3 as selected compounds, the appli- cant shall determine a health-based ambient air concentration, under subsection (C)(3).

b.        The applicant shall determine the potential maxi- mum hourly exposure resulting from emissions of the HAP by applying the following equation:

MHE = PPH * 17.68, where:

i.         MHE = maximum hourly exposure in milli- grams per cubic meter, and

ii.        PPH = hourly potential to emit the HAP in pounds per hour.

c.         The applicant shall determine the potential maxi- mum annual exposure resulting from emissions of the HAP by applying the following equation:

MAE = PPY * 1/MOH * 1.41, where:

i.         MAE = maximum annual exposure in milli- grams per cubic meter,

ii.        PPY = annual potential to emit the HAP in pounds per year, and

iii.      MOH = maximum operating hours for the source, taking into account any enforceable operational limitations.

d.        The Director shall not require compliance with HAPRACT for the HAP, under R18-2-1706, or AZMACT, under R18-2-1707, if both of the follow- ing are true:

i.         The maximum hourly concentration deter- mined under subsection (B)(1)(b) is less than the AAAC determined under subsection (C)(3); and

ii.        The maximum annual concentration deter- mined under subsection (B)(1)(c) is less than the CAAC determined under subsection (C)(3).

e.         If either the maximum hourly concentration deter- mined under subsection (B)(1)(b), or the maximum annual concentration determined under subsection (B)(1)(c) is greater than or equal to the relevant AAC:

i.         The Director shall require compliance with HAPRACT under R18-2-1706 or AZMACT under R18-2-1707; or

ii.        The applicant may use the Tier 2, Tier 3 or Tier 4 method for conducting an RMA under sub- section (B)(2).

2.        Tier 2: SCREEN Model. The applicant shall use the SCREEN Model, performed in a manner consistent with the Guideline specified in R18-2-406(A)(6)(a). The applicant shall compare the maximum concentration that is predicted in the ambient air with the relevant ambient air concentration determined under subsection (C).

a.         If the predicted maximum concentration is less than the relevant ambient air concentration, the Director shall not require compliance with HAPRACT under R18-2-1706, or AZMACT under R18-2-1707.

b.        If the predicted maximum concentration is greater than or equal to the relevant ambient air concentra- tion:

i.         The Director shall require compliance with HAPRACT under R18-2-1706, or AZMACT under R18-2-1707; or

ii.        The applicant may use the Tier 3 or Tier 4 method for determining maximum public expo- sure to state HAPs, under subsection (B)(3).

3.        Tier 3: Modified SCREEN Model. The applicant shall use the SCREEN Model, performed in a manner consis- tent with the Guideline specified in R18-2-406(A)(6)(a).

a.         For evaluation of acute exposure, the applicant shall assume exposure in the ambient air.

b.        For evaluation of chronic exposure:

i.         The applicant may use exposure assumptions consistent with institutional or engineering con- trols that are permanent and enforceable out- side the permit.

ii.        The applicant shall notify the Director of these controls. If the Director does not approve of the proposed controls, or if the controls are not per- manent and enforceable outside of the permit, the applicant shall not use the method specified in subsection (B)(3)(b) to determine maximum public exposure to the state HAP.

c.         If the predicted maximum concentration is less than the relevant ambient air concentration, the Director shall not require compliance with HAPRACT under R18-2-1706, or AZMACT under R18-2-1707.

d.        If the predicted maximum concentration is greater than or equal to the relevant ambient air concentra- tion:

i.         The Director shall require compliance with HAPRACT under R18-2-1706, or AZMACT under R18-2-1707; or

ii.        The applicant may use the Tier 4 method for determining maximum public exposure to state HAPs, under subsection (B)(4).

4.        Tier 4: Modified SREEN or refined air quality model. The applicant shall employ either the SCREEN or a refined air quality model, performed in a manner consis- tent with the Guideline specified in R18-2-406(A)(6)(a).

a.         For evaluation of acute exposure, the applicant shall assume exposure in the ambient air.

b.        For evaluation of chronic exposure:

i.         The applicant may use exposure assumptions consistent with institutional or engineering con- trols that are permanent and enforceable out- side the permit.

ii.        The applicant shall notify the Director of these controls. If the Director does not approve of the proposed controls, or if the controls are not per- manent and enforceable outside of the permit, the applicant shall assume chronic exposure in the ambient air.

c.         The applicant may include in the Tier 4 RMA docu- mentation of the following factors:

i.         The estimated actual exposure to the HAP of persons living in the airshed of the source;

ii.        Available epidemiological or other health stud- ies;

iii.      Risks presented by background concentrations of hazardous air pollutants;

iv.       Uncertainties in risk assessment methodology or other health assessment techniques;

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v.        Health or environmental consequences from efforts to reduce the risk; or

vi.       The technological and commercial availability of control methods beyond those otherwise required for the source and the cost of such methods.

d.        The applicant shall submit a written protocol for conducting an RMA, consistent with the require- ments of this Section, to the Director for the Direc- tor’s approval. If the Director does not approve the written protocol, the applicant may:

i.         Submit a revised protocol to the Director;

ii.        Propose HAPRACT under R18-2-1706, or AZMACT under R18-2-1707; or

iii.      Refuse to submit a revised protocol, in which case the Director shall deny the application.

e.         If the predicted maximum concentration is less than the relevant ambient air concentration, or if war- ranted under the factors listed in subsection (B)(4)(c), the Director shall not require compliance with HAPRACT under R18-2-1706, or AZMACT under R18-2-1707.

f.         Except as provided in subsection (B)(4)(e), if the predicted maximum concentration is greater than or equal to the relevant ambient air concentration, the Director shall require compliance with HAPRACT under R18-2-1706, or AZMACT under R18-2-1707.

C.      Health-based Ambient Air Concentrations of State HAPs.

1.        For state HAPs for which the Director has already deter- mined an AAC, the applicant shall use the acute and chronic values listed in Table 3.