Tier 1 Evaluation

Tier 1 Evaluation A. Tier 1 Evaluation Target Risk Level The TRGs presented in the Tier 1 TRG table, Appendix A, are based on either: (1) a 1x10-6 target risk level for each carcinogenic chemical, (2) a hazard index not to exceed 1 for each systemic toxicant, or (3) constituent TRG concentrations established through federal/state programs (i.e., Safe Drinking Water Act). The values presented in the Tier 1 TRG table will be modified periodically based on EPA updates of toxicity values obtained from the sources presented in Rule 2.2.5(B)(3)(b) of this Subchapter 2. B. Tier 1 Evaluation Procedures (1) The basic methodology for a Tier 1 Evaluation shall be the comparison of the highest concentration of each contaminant in each media to the TRGs provided in the Tier 1 TRG table. Results of the comparison will be used to determine if the site specific data are: (a) at or below the unrestricted risk value; (b) above the unrestricted risk value, but at or below the restricted risk value; or (c) above the restricted risk value. (2) Sites that do not require an ecological evaluation beyond the Site Ecological Checklist and that exhibit chemical concentrations that are at or below the unrestricted TRGs do not require further evaluation or action. Such sites are not eligible for the Brownfields Program since remediation is not necessary as required in Section 49-5-5(b) of Mississippi Code Annotated, as amended. (3) Sites with chemical concentrations in soils that are greater than the unrestricted TRGs but below the restricted TRGs may: (a) clean-up and/or remove the affected media to a value at or below the unrestricted TRG values resulting in an unrestricted land-use site; (b) implement appropriate institutional controls (i.e., land use restriction and agreed order with MDEQ) resulting in a restricted land use site; or (c) perform a Tier 2 Evaluation. (4) Sites with chemical concentrations in soils that exceed the restricted TRGs may: (a) clean-up and/or remove the affected media to a value at or below the unrestricted TRG values resulting in an unrestricted land use site; (b) clean-up and/or remove the affected media to a value at or below the restricted TRG values but above the unrestricted TRG values resulting in a restricted land use site and implement appropriate institutional controls (i.e., land use restriction and agreed order with MDEQ); or (c) perform a Tier 2 Evaluation. (5) Sites with chemical concentrations in groundwater that are greater than the unrestricted TRGs may: (a) clean-up the affected media to a value at or below the unrestricted TRG values resulting in an unrestricted land-use site; (b) implement appropriate institutional controls (i.e., land use restriction and agreed order with MDEQ) resulting in a restricted land use site; or (c) perform a Tier 2 Evaluation. (6) MDEQ may consider utilizing the Method Detection Limit (MDL) in place of the Target Remediation Goal (TRG) on a case by case basis. (7) In areas of a site where chemical concentrations of petroleum hydrocarbon indicator compounds (e.g., BTEX, PAHs, MTBE) are not quantifiable to the Tier 1 TRGs (e.g., dilution and/or matrix interference) may: (a) use the Tier 1 TRGs for TPH-GRO/DRO for performing a Tier 1 Evaluation; or (b) perform a Tier 2 TPH Fractioning Evaluation.