Oregon Administrative Rules › Chapter 340 - DEPARTMENT OF ENVIRONMENTAL QUALITY › Division 245 - CLEANER AIR OREGON › Section 340-245-0200 - Risk Estimates

Current through Register Vol. 63, No. 7, July 1, 2024
(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 3B;
(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).