5 Colo. Code Regs. § 1002-41.15
The provisions of section 25-8-202(1)(a),(b) and (2); 25-8-203; and 25-8-204; C.R.S., provide the specific statutory authority for adoption of the attached regulatory amendments. The Commission also adopted, in compliance with section 24-4-103(4) C.R.S., the following statement of basis and purpose.
STATEWIDE NUMERICAL STANDARDS
In 1989, the Commission adopted certain interim organic pollutant standards, applicable to ground water statewide. Several revisions and additions to those interim standards are now being adopted. In general, the primary purpose of these changes is to provide a more thorough system to assure protection of Colorado's water resources with respect to potential adverse impacts from organic chemicals. One change adopted is to combine previous Tables A and B into a single, consolidated Table A. The Commission believes that this format will be easier to read, and helps to assure elimination of potential inconsistencies between the separate tables.
When the Commission adopted interim organic chemical standards in 1989, the Commission adopted standards based on maximum contaminant levels (MCLs) for all pollutants for which MCLs had been established under the Safe Drinking Water Act. The Commission has now reevaluated this policy and adopted health-based standards for these constituents instead of standards equal to the MCLs, whenever health-based criteria are available. Several considerations have led to this new approach.
The vast majority of the standards adopted in 1989 were already set equal to health-based criteria. MCLs generally are more lenient than health-based criteria, and have been developed taking into account laboratory detection limits and the economic ability of water suppliers to treat for removal of these constituents. The Commission already has attempted to temper the application of stringent health-based standards for non-MCLs organic pollutants by providing for the application of the practical quantitation limit (PQL) concept in determining compliance with the standards. Any dilution present prior to the point of compliance would further temper the application of these standards. Therefore, the Commission has determined that it is a more appropriate policy to base these water quality standards on health-based criteria, rather than MCLs. Revisions have been made to the standards, as now contained in the consolidated Table A.
Standards for a number of additional organic chemicals have been added to the Basic Standards for Organic Chemicals Table in the Basic Standards and Methodologies for Surface Water to help complete Colorado's compliance with section 303(c)(2)(B) of the federal Clean Water Act. The chemicals added are ones listed as priority toxic pollutants, and for which EPA has developed human health or aquatic life criteria under the Clean Water Act. The same additions have been made to the revised Table A in this regulation, for consistency between ground and surface water standards for organic chemicals.
The Commission decided not to include in the consolidated Table standards for total trihalomethanes or for polynuclear aromatic hydrocarbons (PAHs) as a class. The Commission believes that it is more practical to regulate individual chemicals in these groups. Some evidence was submitted indicating that not all PAHs should have the same standard. For now the Commission has adopted these standards based on the available EPA criteria, although if more specific evidence on this issue is brought to the Commission in the future, revisions can be considered.
Several minor clarifications have been adopted for Table A. A footnote has been added to the "standard" column to indicate that these are chronic water quality standards. The "detection levels" column has been relabeled "PQLs", to clarify that the values indicated are practical quantitation limits. In addition, the PQLs for a few parameters were revised to be consistent with the current information from the Colorado Department of Health laboratory.
PARTIES TO THE RULEMAKING HEARING FOR BASIC STANDARDS & METHODOLOGIES FOR SURFACE AND GROUND WATER
5 CCR 1002-41.15