SECTION 165:29-3-76. Tier 1A ORBCA

(a)   Unless otherwise directed by the PSTD, the owner or operator must compile information in order to assess the site using the Risk-Based Corrective Action (RBCA) process described in the ORBCA Guidance Document. (The ORBCA Guidance Document is available on the Commission website and at the offices of the Petroleum Storage Tank Division of the Oklahoma Corporation Commission.) The RBCA process must be implemented with a three (3) tiered approach that must involve an increase in the level of data collection and analysis from one tier to the next. Some conservative default parameters under the Initial Site Characterization Tier 1A process must be replaced with more site-specific parameters under the Tier 2 and Tier 3 process. PSTD will review the results and recommendations at the completion of the Tier 1A analysis and decide if a more site-specific tiered analysis is required by initiating a Tier 2 or Tier 3 process, or whether remedial action should be performed as provided for in this Subchapter.

(b)   PSTD will only accept and review reports, worksheets, checklists, closure reports or other relevant documents which incorporate the RBCA process, or any other acceptable risk analysis, from a Commission Licensed Environmental Consultant.

(c)   The RBCA Tier 1A process is as follows:

(1)   Tier 1A: Non-site-specific risk-based screening method used to determine corrective action goals using limited site-specific data.

(A)   Tier 1A establishes conservative cleanup goals called modified Risk-Based Screening Levels (RBSLs). Only the Fate and Transport Parameters cited in the ORBCA Guidance Document may be replaced by site-specific information obtained through site investigation and assessment. Justification must be provided when changes in any of the default Fate and Transport Parameters are indicated. The default Exposure Factors cannot be modified, nor can degradation rates be used under a Tier 1A evaluation. This evaluation must be performed using the models cited in Appendix C of the ORBCA Guidance Document. The modified RBSLs take into consideration regional characteristics, aesthetic criteria, and other appropriate standards such as Maximum Contaminant Levels (MCLs) for water. Tier 1A modified RBSLs are derived from standard exposure scenarios using current Reasonable Maximum Exposure (RME) toxicological parameters and conservative contaminant migration models. RBSL values are determined by the PSTD using one (1) in one million (1,000,000) as a Target Risk Limit for carcinogens and a Hazard Quotient (HQ) not greater than one (1.0) as a Target Risk Limit for non-carcinogens. One (1) in ten thousand (10,000) is the acceptable Target Risk Limit for carcinogens for future potential receptors.

(B)   The most likely Point of Exposure (POE) for current and potential future beneficial use of fresh groundwater should be determined. The concentration at this Point of Exposure for each Chemical of Concern (COC) must not exceed the Target Risk Limits cited in this Section.

(C)   Unless otherwise directed by PSTD under Tier 1A the owner or operator must drill and install a minimum of four (4) two-inch (2") diameter monitoring wells outside of the UST pit or AST containment or product piping trench excavation zones. These wells must be located as follows:

(i)   One (1) well must be installed in an apparent upgradient location to any known potential source at the site on or as close to the release as possible.

(ii)   One (1) well must be installed in a location most likely to be contaminated.

(iii)   One (1) well must be installed in a location that will allow the determination of an accurate groundwater gradient.

(iv)   One (1) well must be installed in the direction of the nearest probable Point of Exposure either at the nearest property line or fifty feet (50') from the source of contamination, whichever is closer, or at another location as determined by PSTD. This well will be the Point of Compliance (POC) well for the Tier 1A evaluation unless there is a Point of Exposure nearer to the source of contamination, in which case the Point of Exposure will also become the Point of Compliance. The concentration for each Chemical of Concern in the Point of Compliance well should not exceed the Tier 1A standards as calculated using the ORBCA Guidance Document. If a drinking water supply well has been identified within 330 feet of the site, groundwater MtBE must be tested at the Point of Compliance. 0.020 mg/L will be considered the level of concern for MtBE and may require further assessment and corrective action.

(2)   Tier 1A: Risk-Based Screening Level corrective action goals developed using limited site-specific data.

(A)   This evaluation must be performed using the same models as those which are cited in Appendix C of the Guidance Document.

(B)   Only the Fate and Transport Parameters cited in the ORBCA Guidance Document may be replaced by site-specific information obtained through site investigation and assessment. Justification must be provided when changes in any of the Tier 1A default Fate and Transport Parameters are indicated. The Tier 1A default Exposure Factors cannot be modified, nor can degradation rates be used under a Tier 1A evaluation.

(3)   Within forty-five (45) days of release confirmation, or according to a schedule established by PSTD, the owner or operator must submit the information required in the Tier 1A evaluation as a report. This report must be submitted in the online format established by PSTD.

(d)   PSTD may re-evaluate a Tier 1A analysis of a site, for the purpose of closure, on a case-by-case basis.

[Source: Added at 17 Ok Reg 2317, eff 6-26-00; Amended at 18 Ok Reg 1085, eff 5-11-01; Amended at 22 Ok Reg 1785, eff 7-1-05; Amended at 31 Ok Reg 1022, eff 9-12-14; Amended at 32 Ok Reg 811, eff 8-27-15; Amended at 35 Ok Reg 1033, eff 10-1-18; Amended at 37 Ok Reg 1157, eff 10-1-20]