(a) Proposal of Concentration Limits--For each Constituent of Concern (COC) specified pursuant to § 20395 (or for a solid waste constituent that is addressed by a cleanup and abatement action taken pursuant to SWRCB Resolution No. 92-49), the discharger shall propose one of the following for each medium (under § 20415, including ground water, surface water, and the unsaturated zone) monitored pursuant to § 20415 of this article:

(b) Adoption of Concentration Limits--The RWQCB shall review the proposed concentration limits and statements and shall approve, modify, or disapprove each proposed limit and each proposed statement. Upon final approval by the RWQCB, each concentration limit and each statement shall be specified in WDRs. The RWQCB shall approve more than one concentration limit for different Monitoring Points in the same medium only if:

(c) Establishing a CLGB--For a corrective action program, the RWQCB shall establish a CLGB [under ¶(a)(3)] only if the RWQCB finds that it is technologically or economically infeasible to achieve the background value for that constituent and that the constituent will not pose a substantial present or potential hazard to human health or the environment as long as the CLGB is not exceeded. In making this finding, the RWQCB shall consider the factors specified in ¶(d), the results of the engineering feasibility study submitted pursuant to § 20425(c), data submitted by the discharger pursuant to § 20425(d)(2) to support the proposed CLGB, public testimony on the proposal, and any additional data obtained during the evaluation monitoring program.

(d) Considerations--In establishing a CLGB for a constituent of concern, the RWQCB shall consider the following factors:

(e) CLGB Ceiling--In no event shall a CLGB for a constituent of concern exceed the lowest concentration that the discharger demonstrates and the RWQCB finds is technologically and economically achievable. No provision of this section shall be taken to allow a CLGB for a constituent of concern to exceed the maximum concentration that would be allowed under other applicable statutes or regulations [e.g., Maximum Concentration Limits established under the federal Safe Drinking Water Act (P.L. 93-523, codified as Subchapter XII of the Public Health Service Act at 42 USC 300f, et. seq.; regulations establishing MCL's are located in 40 CFR Part 141, Subpart B), etc.].

(f) Receptor Location--For ground water, in evaluating risk pursuant to ¶(d) to any biological receptor, the risk shall be evaluated as if exposure would occur at the Point of Compliance.

(g) Additivity--Proposals for CLGBs shall include a demonstration that the aggregate of hazardous constituents in the environment will not result in excessive exposure to a sensitive biological receptor. In the absence of scientifically valid data to the contrary, theoretical risks from chemicals associated with the release from the Unit shall be considered additive across all media of exposure, and shall be considered additive for all chemicals having similar toxicological effects or having carcinogenic effects.

(h) Applicability--A CLGB may only be applied during corrective action, or during detection monitoring following corrective action, at Monitoring Points at which “measurably significant” (see § 20164) evidence of the release has been determined.

(i) Decreasing the CLGB--When a detection monitoring program incorporating a CLGB is reinstated after a corrective action program has been terminated, each CLGB shall be re-evaluated during each review of WDRs or at least every five years. If the RWQCB, upon re-evaluation, determines that the concentration of a constituent of concern in ground water, surface water, or the unsaturated zone is lower than its associated concentration limit by a “measurably significant” (see § 20164) amount, the concentration limit for that constituent shall be lowered to reflect current water quality.