5 Colo. Code Regs. § 1002-41.28
The provisions of sections 25-8-202(1)(b); 25-8-204; 25-8-402, C.R.S., provide the specific statutory authority for adoption. The Commission also adopted, in compliance with section 24-4-103(4) C.R.S., the following statement of basis and purpose.
BASIS AND PURPOSE:
The Commission adopted revised and new organic chemical standards in section 41.5 . In an effort to keep ground water and surface water organic chemical standards consistent, the changes to section 41.5 were considered during the same hearing that addressed changes to the statewide surface water organic chemical standards in Regulation No. 31 (Basic Standards and Methodologies for Surface Water).
In adopting these new and revised organic chemical standards, the Commission continued to rely on its past policy decisions and precedence documented in Commission Policy 96-2. Additionally, as per Departmental policy, the Commission has relied on the United States Environmental Protection Agency's (EPA) Integrated Risk Information System (IRIS) as its first tier source of toxicological data. Review of the IRIS data that had been updated since the last revisions to 41.5 indicated that the water quality standard for tetrachloroethylene (TCE), needed to be revised. EPA expressed concerns regarding the proposed hybrid standard approach for TCE. In light of the impact that a decision on the hybrid standard for TCE may have on other hybrid standards adopted by the WQCC, and because the human health risk of maintaining the current standard of 5 mg/L is not an order of magnitude above the risk for a standard of .76 mg/L, the Commission decided to not modify the TCE standard at this hearing. The Commission expects the broader issue of hybrid standards will be discussed with EPA and the stakeholders, and that the issue may be revisited at a future hearing. The IRIS review also identified new compounds in the IRIS data that the Commission elected to adopt as water quality standards, these were: biphenyl, methanol, and tetrahydrofuran.
The Commission amended Footnote 6 to Table A in section 41.5(C)(3) to clarify the standards implementation intent of the Commission when a human health based standard is a higher numeric value than the maximum contaminant level in a range between the human health based standard and the maximum contaminant level.
The Commission deleted implementation language for organic chemicals that was deemed no longer necessary.
The Commission added to the footnote an explanation of its intent with how an implementing agency can establish a protection level when there is site-specific information that demonstrates that there is no current or reasonably anticipated future uses of groundwater.
The Commission heard testimony that it is no longer necessary for the Division to approve the Practical Quantification Limitations (PQLs) used by the groundwater standards implementing agencies. The groundwater implementing agencies have their own PQLs or PQL equivalents established under their own authorities. Therefore, section 41.5 was amended to remove the requirement of the WQCD approving PQL's for the groundwater standards implementing agency.
PARTIES TO THE RULEMAKING
5 CCR 1002-41.28