Site-Specific Risk Evaluation

01. General Requirements. The general requirements for human health risk evaluations must include, at a minimum: (7-1-25) IDAHO ADMINISTRATIVE CODE IDAPA 58.01.24 Department of Environmental Quality Rules for Petroleum Release Corrective Action Section 300 Page 12 a. A conceptual site model that describes contaminant sources; release mechanisms; the magnitude, spatial extent, and temporal trends of petroleum contamination in all affected media; transport routes; current and reasonably likely future land use and human receptors; and relevant exposure scenarios. (7-1-25) b. Toxicity information derived from appropriate sources including, but not limited to, those listed in Subsection 300.01.e. (7-1-25) c. Data quality objectives and sampling approaches based on the conceptual site model that support the risk evaluation and risk management process. (3-31-22) d. Estimated exposure point concentrations for a reasonable maximum exposure based on a conservative estimate of the mean of concentrations of chemicals that would be contacted by an exposed receptor. (3-31-22) e. Exposure analysis including identification of contaminants of concern, potentially exposed populations, pathways and routes of exposure, exposure point concentrations and their derivation, and a quantitative estimate of reasonable maximum exposure for both current and reasonably likely future land and water use scenarios. The EPA RSL and VISL calculators are appropriate sources of reasonable maximum exposure factor information. Alternative sources must be reasonably justified. (7-1-25) f. Risk characterization presenting the quantitative human health risks and a qualitative and quantitative assessment of uncertainty for each portion of the risk evaluation. (3-31-22) g. Risk evaluations may include the use of transport and fate models, subject to Department approval of the model and the data to be used for the parameters specified in the model. (3-31-22) 02. Specific Requirements. Human health risk evaluations must, at a minimum: (7-1-25) a. Utilize an acceptable target risk level as defined in Section 010; (3-31-22) b. Utilize an acceptable target hazard index as defined in Section 010; (3-31-22) c. Utilize an acceptable target hazard quotient as defined in Section 010; (3-31-22) d. Evaluate the potential for exposure from: (3-31-22) i. Groundwater ingestion; (7-1-25) ii. Direct contact with contaminated soils resulting from soil ingestion, dermal contact, and inhalation of particulates and vapors; (3-31-22) iii. Indoor inhalation of volatile chemicals via volatilization of chemicals from soil, groundwater, or free phase product; (7-1-25) iv. Ingestion, inhalation, or dermal exposure to groundwater and/or surface water that has been impacted by contaminants that have leached from the soils; and (7-1-25) v. Other complete or potentially complete routes of exposure; (3-31-22) e. Evaluate the potential for exposure to: (3-31-22) i. Adult and child residential receptors; (3-31-22) ii. Adult construction and utility workers; (3-31-22) iii. Aquatic life; (3-31-22) IDAHO ADMINISTRATIVE CODE IDAPA 58.01.24 Department of Environmental Quality Rules for Petroleum Release Corrective Action Section 400 Page 13 iv. Recreational receptors; and (3-31-22) v. Other relevant potentially exposed receptors; (3-31-22) f. Evaluate the potential for use of impacted groundwater for ingestion based on: (7-1-25) i. The current and historical use of the groundwater for drinking water or irrigation; (7-1-25) ii. The location and approved use of existing groundwater wells in a one half (½) mile radius from the contaminated site at the release point; (7-1-25) iii. The degree of hydraulic connectivity between the impacted groundwater and other groundwater bearing zones or surface water; and (7-1-25) iv. The location of delineated source water protection areas for public drinking water systems. (3-31-22) 301. -- 399. (RESERVED)