340-122-0244 Cleanup Rules for Leaking Petroleum UST Systems: Risk-Based Concentrations This rule describes the requirements for developing risk-based concentrations for use in establishing remediation levels in corrective action plans under OAR 340-122-0250. (1) A conceptual model must be developed for the site describing how exposure to contaminants is reasonably likely to occur. (a) The conceptual site model must be based on, at a minimum: (A) The magnitude and areal and vertical extent of soil and groundwater contamination; (B) The concentration of applicable contaminants of concern in each contaminated medium; (C) The likelihood for exposure to occur, given the concentration, location, and mobility of the contaminants in conjunction with factors such as local climate, geology, and hydrogeology; and (D) Information on current and reasonably likely future land and water uses in the area of potential impact. (b) Subject to site-specific conditions, the following exposure pathways must be considered in the conceptual site model: (A) Direct contact with contaminated soils resulting in exposure due to a combination of dermal contact, soil ingestion, vapor inhalation, and particulate inhalation; (B) Leaching from soils to underlying groundwater with subsequent groundwater ingestion; (C) Volatilization from soils to outdoor air and subsequent inhalation; (D) Volatilization from soils to indoor air and subsequent inhalation; (E) Ingestion or other exposure to contaminated groundwater; (F) Volatilization from groundwater to outdoor air and subsequent inhalation; and (G) Volatilization from groundwater to indoor air and subsequent inhalation. (c) Subject to site-specific conditions, the following exposure scenarios must be considered in the conceptual site model: (A) Exposure to adults and children as typified by single-family residential living conditions; (B) Exposure to adults as typified by industrial or commercial working conditions; and (C) Exposure to adults whose occupation requires increased direct contact with soil as typified by a trench worker. (d) Depending on conditions found at the site, the Department may require the evaluation of additional exposure pathways and scenarios. (2) Risk-based concentrations must be developed for contaminants of concern identified during the site characterization or other site investigation activities, including total petroleum hydrocarbons (TPH) when appropriate, for exposure pathways and scenarios identified in the conceptual site model. (a) The Department shall develop and maintain, in accordance with OAR 340-122-0252, a table of generic risk-based concentrations that may be used for this purpose; or (b) A responsible person may calculate site-specific risk-based concentrations by employing contaminant fate, transport, and exposure models. (A) Sources of models and default exposure parameters include: (i) Applicable Department of Environmental Quality generic remedy guidance documents developed pursuant to OAR 340-122-0252; (ii) ASTM Standard Guide for Risk-Based Corrective Action Applied at Petroleum Release Sites (ASTM E 1739-95); and (iii) US EPA Risk Assessment Guidance for Superfund. (B) The Department may approve the use of other models if they are deemed appropriate for the proposed task. (C) A responsible person may propose, subject to the Department’s approval, the use of site-specific exposure parameters in place of default exposure parameters. (3) Risk-based concentrations for protection of the environment must be developed if contamination poses a potential risk exceeding the acceptable risk levels for ecological receptors. Unless the Department determines that screening is required for threatened and endangered species, screening for potential ecological impact is not required if: (a) Contaminated soils are only present at a depth greater than 3 feet below ground surface, or, if present at a shallower depth, such soils cover an area no greater than 0.125 acre; (b) Surface water has not been affected by the release; (c) Contaminated groundwater does not and is not reasonably likely to discharge to surface waters or otherwise reach the surface in a manner that might result in contact with ecological receptors; and (d) Contaminated groundwater does not and is not reasonably likely to come into contact with aquatic sediments. [Publications: Publications referenced are available from the agency.] Statutory/Other Authority: ORS 465.400 & 466.746 Statutes/Other Implemented: ORS 465.200 - 465.455 & 466.706 - 466.835 History: DEQ 23-1998, f. & cert. ef. 11-2-98