340-245-0200 Risk Estimates (1) When a risk assessment is required under this division, the risk assessment must consider the toxic air contaminants and the Risk-Based Concentrations listed in OAR 340-245-8010 Table 2 to assess excess cancer and noncancer risk. (2) Directions for using the Level 1 Risk Assessment Dispersion Factor Tables. (a) An owner or operator that chooses to perform a Level 1 Risk Assessment under OAR 340-245-0050, must calculate a separate sum of risk for each of the following categories: excess cancer risk, chronic noncancer risk, and acute noncancer risk for the applicable exposure scenarios; (b) When making this calculation, the owner or operator must use the emissions inventory submitted under OAR 340-245-0040(1) for: (A) Excess cancer risk and chronic noncancer risk, the average annual emission rates; and (B) Acute noncancer risk, the maximum daily emission rates. (c) The owner or operator must perform each of the following calculations in paragraphs (A) and (B), except as allowed in paragraph (C): (A) For excess cancer risk and chronic noncancer risk: (i) For each TEU with emissions from a stack, vent, duct, or equivalent opening, use the stack height and distance to the nearest exposure locations to identify the appropriate dispersion factor under OAR 340-245-8010 Table 3A. If the TEU is a volume fugitive source that is not emitted from a stack, vent, duct, or equivalent opening, use the area and height of the building and distance to the nearest exposure locations to identify the appropriate dispersion factor under OAR 340-245-8010 Table 3C; (ii) For each TEU and each toxic air contaminant emitted from the TEU, multiply the annual emission rate by the dispersion factor identified under subparagraph (i) to calculate an air concentration at the nearest exposure location; (iii) For each TEU, divide the air concentration of each toxic air contaminant calculated under subparagraph (ii) by the appropriate RBC of that toxic air contaminant under OAR 340-245-8010 Table 2; (iv) For each TEU, add up the risk from each toxic air contaminant calculated under subparagraph (iii); and (v) For all TEUs, add up all of the risks calculated under subparagraph (iv) to obtain the total excess cancer risk in one million or the total chronic noncancer Hazard Index for the entire source. For chronic noncancer risk, Hazard Indices may be calculated by noncancer target organ or organ systems in consultation with DEQ; (vi) When an existing source emits a mixture of toxic air contaminants assigned noncancer TBACT Risk Action Levels of both a Hazard Index of 3 and a Hazard Index of 5 as identified in OAR 340-245-8010, Table 2, and the combined Hazard Index for all TACs is greater than 3, the owner or operator must calculate a Risk Determination Ratio using the formula in section (5) of this rule. (B) For acute noncancer risk: (i) For each TEU with emissions from a stack, vent, duct, or equivalent opening, use the stack height and distance to the nearest exposure location to identify the appropriate dispersion factor under OAR 340-245-8010 Table 3B. If the TEU is a volume fugitive source that is not emitted from a stack, vent, duct, or equivalent opening, use the area and height of the building and distance to the nearest exposure locations to identify the appropriate dispersion factor under OAR 340-245-8010 Table 3D; (ii) For each TEU and each toxic air contaminant emitted from the TEU, multiply the maximum daily emission rate by the dispersion factor identified under subparagraph (i) to calculate an air concentration at the nearest exposure location; (iii) For each TEU, divide the air concentration of each toxic air contaminant calculated under subparagraph (ii) by the acute RBC for that toxic air contaminant under OAR 340-245-8010 Table 2 (iv) For each TEU, add up the risk from each toxic air contaminant calculated under subparagraph (iii); and (v) For all TEUs, add up all of the risks calculated under subparagraph (iv) to obtain the total acute noncancer Hazard Index for the entire source. Hazard Indices may be calculated by noncancer target organ or organ systems in consultation with DEQ; (vi) When an existing source emits a mixture of toxic air contaminants assigned noncancer TBACT Risk Action Levels of both a Hazard Index of 3 and a Hazard Index of 5 as identified in OAR 340-247-8010, Table 2, and the combined Hazard Index for all TACs is greater than 3, the owner or operator must calculate a Risk Determination Ratio using the formula in section (5) of this rule. (C) Instead of using stack height and distance or area and height of the building and distance to the nearest exposure locations to obtain the appropriate dispersion factor under OAR 340-245-8010 Table 3, the owner or operator may instead use, as a default, the most conservative dispersion factor; (i) For emissions from a stack, vent, duct, or equivalent opening, use the dispersion factor associated with a stack height of five meters and an exposure location distance of 50 meters, which is listed in the upper-left corner of OAR 340-245-8010 Table 3A and 3 B; (ii) For volume fugitive emissions that are not emitted from a stack, vent, duct, or equivalent opening, use the dispersion factor associated with an area of less than or equal to 3,000 square feet, a building height of less than or equal to 20 feet, and an exposure location distance of 50 meters, which is listed in the upper-left corner of OAR 340-245-8010 Table 3C and 3D; and (iii) Using these default dispersion factors will result in protective calculations of risk. If the risks calculated using these default dispersion factors are less than or equal to the applicable Risk Action Levels, the owner or operator may choose to use the risks calculated in this manner to show compliance with the Source Risk Limits. However, if the actual source characteristics such as terrain features, exposure location distances less than 50m, unusual stack or building configurations, or other factors, invalidate the assumptions used to develop the Level 1 Risk Assessment Dispersion Factor Tables, DEQ at its discretion, may disapprove the Level 1 assessment, as described in OAR 340-245-0050 (8)(c). (3) Sum of Risk calculation procedure for Level 2, Level 3 and Level 4 Risk Assessments. (a) An owner or operator that chooses to perform a Level 2, Level 3 or Level 4 Risk Assessment under OAR 340-245-0050, must calculate a separate sum of risk for each of the following risk categories: excess cancer risk, chronic noncancer risk, and acute noncancer risk for the applicable exposure locations; (b) When making this calculation, the owner or operator must use the following modeled ambient concentrations for each toxic air contaminant at all exposure locations: (A) For excess cancer risk and chronic noncancer risk, the annual average concentrations must be used; and (B) For acute noncancer risk, the maximum daily concentrations must be used; (c) The owner or operator must perform the following calculations for each of the risk categories listed in subsection (a) and using the concentrations in subsection (b): (A) For each TEU, divide the modeled concentration of each toxic air contaminant by the appropriate RBC of that toxic air contaminant under OAR 340-245-8010 Table 2 ensuring that the concentration is expressed in micrograms per cubic meter; (B) For each TEU, add up the risk from each toxic air contaminant calculated under paragraph (A); and (C) For all TEUs at each exposure location, add up all of the risks calculated under paragraph (B) to obtain the total excess cancer risk in one million, the total chronic noncancer Hazard Index, or the total acute noncancer Hazard Index for the entire source. For noncancer risk, Hazard Indices may be calculated by noncancer target organ or organ systems in consultation with DEQ. (D) When an existing source emits a mixture of toxic air contaminants assigned noncancer TBACT Risk Action Levels of both a Hazard Index of 3 and a Hazard Index of 5 as identified in OAR 340-247-8010, Table 2, and the combined Hazard Index for all TACs is greater than 3, the owner or operator must calculate a Risk Determination Ratio using the formula in section (5) of this rule. (4) Significant figures and rounding. When a risk is calculated for comparison to a Risk Action Level or Source Risk Limit: (a) The final risk calculation must be rounded off as follows: (A) For comparison to the Aggregate TEU Level, Risk Determination Ratio, and the Source Permit Level, round off to one decimal place; and (B) For comparison to other Risk Action Levels or Source Risk Limits, round off to a whole number; (b) Round up if the last figure to be rounded off is 5 or greater, otherwise round down. (c) Use of rounded numbers in making final risk calculations is not allowed. Only the final risk number may be rounded as described in this section. (5) Calculating a Risk Determination Ratio. The formula for calculating a Risk Determination Ratio is: Combined Noncancer Risk for HI3 chemicals = (Concentration of HI3 chemical #1 / Risk-Based Concentration for chemical #1) + (Concentration of HI3 chemical #2 / Risk-Based Concentration for chemical #2) + continue for all HI3 chemicals emitted Combined Noncancer Risk for HI5 chemicals = (Concentration of HI5 chemical #1 / Risk-Based Concentration for chemical #1) + (Concentration of HI5 chemical #2 / Risk-Based Concentration for chemical #2) + continue for all HI5 chemicals emitted Risk Determination Ratio = (Combined Risk for HI3 chemicals / 3) + (Combined Risk for HI5 chemicals / 5) HI3 = Toxic air contaminants assigned noncancer TBACT Risk Action Level of 3 (OAR 340-247-8010, Table 2 and OAR 340-245-8010, Table 2. HI5 = Toxic air contaminants assigned noncancer TBACT Risk Action Level of 5 (OAR 340-247-8010, Table 2 and OAR 340-245-8010, Table 2. Concentration = monitored or modeled concentrations of toxic air contaminant at exposure location for use in risk assessment. RBC = risk-based concentrations in OAR 340-245-8010 Table 2. Statutory/Other Authority: ORS 468.020, ORS 468.065, 468A.025, 468A.040, 468A.050, 468A.070, 468A.155, Or Laws 2018, ch. 102, § 7, 468A.135 & 468A.337 Statutes/Other Implemented: ORS 468.065, 468A.025, 468A.040, 468A.050, 468A.070, 468A.155, 468A.010, 468A.015, 468A.035, Or Laws 2018, ch. 102, § 7, 468A.337 & 468A.335 History: DEQ 18-2021, amend filed 11/17/2021, effective 11/17/2021 DEQ 11-2020, amend filed 04/29/2020, effective 04/29/2020 DEQ 8-2020, amend filed 04/24/2020, effective 04/24/2020 DEQ 197-2018, adopt filed 11/16/2018, effective 11/16/2018