(a) The OEHHA peer-reviewed unit risk factors, oral slope factors, chronic reference exposure levels, reference dose(s) (RfDs), and blood lead values in Table A and B of Appendix I to this Chapter, shall be used for the COPCs that are listed in that Appendix, so long as the Appendix I values remain no less stringent than toxicity criteria available from the source in subdivision (b) below. If Appendix I does not list toxicity criteria for a specific COPC or contains a value that is less stringent, then the toxicity criteria listed under section 69021, subdivision (b) shall be used.

(b) The peer-reviewed unit risk factors, oral slope factors, RfDs, and reference concentrations, in IRIS shall be used where either Appendix I does not specify toxicity criteria for a particular COPC, or the IRIS toxicity criteria value is more stringent than the value listed in Appendix I. If neither Appendix I nor IRIS lists toxicity criteria for a specific COPC, then the toxicity criteria listed under section 69021, subdivision (c) shall be used.

(c) Toxicity criteria from another source, that applies the best available science and is health-based, may be used in human health risk assessments upon approval by the Supervising Toxicologist, of the Department's Human and Ecological Risk Office, or his or her designee, when neither subdivision (a) nor subdivision (b) above specifies toxicity criteria for the particular COPC. Other sources include, but are not limited to: OEHHA toxicity criteria that are not listed in Appendix I (e.g., those toxicity criteria used in U.S. EPA's Regional Screening Levels), U.S. EPA Provisional Peer Reviewed Toxicity Values (PPRTVs), Agency for Toxic Substances and Disease Registry Minimal Risk Levels, PPRTV Appendix Screening Toxicity Values, and U.S. EPA Superfund Health Effects Assessment Summary Table values. However, use of TPH PPRTVs is not required, but may be determined to be appropriate based on site-specific circumstances. Any selected toxicity criteria or value used under this subdivision shall be consistent with Health and Safety Code section 25356.1.5, subdivisions (b) and (c).