§ 250.606. Development of site-specific standards.
(a) If an unacceptable risk is identified by the assessments described in § 250.602 (relating to risk assessment procedures), a person shall perform one of the following:
(1) A remediation that eliminates all current and probable future exposure pathways.
(2) A remediation utilizing a standard developed under a site-specific risk assessment that is protective of human health and the environment.
(b) A person who chooses to use a standard developed under a site-specific risk assessment shall meet the human health and environmental protection requirements identified in § 250.402 (relating to human health and environmental protection goals).
(c) The development of site-specific standards shall be based on the standard in § 250.605(b)(2) (relating to sources of toxicity information) or the components of risk assessment in § 250.602, the appropriate exposure factors identified in § 250.603 (relating to exposure factors for site-specific standards), the fate and transport modeling requirements of § 250.604 (relating to fate and transport modeling requirements for exposure assessments) and the toxicity values of § 250.605 (relating to sources of toxicity information).
(d) The following factors shall be considered in the development of the risk assessment and in the development of site-specific standards:
(1) Groundwater in aquifers.
(i) Natural environmental conditions that affect the fate and transport of contaminants, such as natural attenuation, shall be determined.
(ii) The person shall identify routes of exposure for aquifer groundwater such as human exposure to groundwater by ingestion, human inhalation of regulated substances from volatilization and migration of these substances into buildings or other areas where humans could be exposed, human ingestion of regulated substances in surface water or other site-specific surface water exposure pathways with respect to groundwater discharges or releases to surface water, human inhalation of regulated substances in air, or other site-specific air exposure pathways with respect to release of regulated substances from groundwater to air.
(2) Nonaquifer groundwater. The persons shall consider current and probable future exposure scenarios, such as human exposure as described in paragraph (1)(ii).
(3) The person shall consider current and probable future exposure scenarios, such as:
(i) Human ingestion of soil when direct contact exposure to the soil may reasonably occur.
(ii) Exposure to groundwater by ingestion with respect to leaching of regulated substances from soils to groundwater.
(iii) Human inhalation of regulated substances from volatilization and migration of these substances into below grade occupied space.
(iv) Human ingestion of regulated substances in surface water or other site-specific surface water exposure pathways with respect to regulated substances migration from soil to surface water.
(v) Human inhalation of regulated substances in air or other site-specific air exposure pathways with respect to the release of regulated substances from soil to air.
(4) If ecological receptors have been identified under § 250.311 (relating to evaluation of ecological receptors) or § 250.402, and are impacted, a remedial activity that eliminates current or future exposure pathways, or a standard, shall be developed to protect the receptors from the direct impacts.
(e) In determining soil and groundwater site-specific standards, the person shall identify the land use of the site with reference to current and currently planned future land use and the effectiveness of institutional or legal controls placed on the future use of the land.
(f) In determining soil and groundwater site-specific standards, the person shall use appropriate statistical techniques, including Monte Carlo simulations as appropriate, to establish statistically valid cleanup standards. The report for a risk assessment to develop site-specific standards shall discuss the degree of uncertainty associated with the risk assessment.
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