Code of Colorado Regulations
1000 - Department of Public Health and Environment
1002 - Water Quality Control Commission (1002 Series)
5 CCR 1002-93 - REGULATION NO. 93 - COLORADO'S SECTION 303(D) LIST OF IMPAIRED WATERS AND MONITORING AND EVALUATION LIST
Section 5 CCR 1002-93.19 - STATEMENT OF BASIS, SPECIFIC STATUTORY AUTHORITY AND PURPOSE; MAY 2021 RULEMAKING; FINAL ACTION JUNE 15, 2021; EFFECTIVE DATE OF AUGUST 14, 2021

1. List Development

2. Incorporation of TMDLs into Table 93.3 of Regulation #93

The commission incorporated category 4 waterbodies (impaired but where a TMDL is not needed) into the main table within Regulation #93, instead of in a separate table at the end of the regulation as they have been in previous versions of this regulation. This organizes all impaired waterbodies and waterbodies under investigation of being impaired into one table. Table 93.3 now includes the following category 4 listings:

3. New Sub Categories 1a (Attaining) and 1b (Attaining with TMDL)

Two new reporting subcategories were created for classifying the attainment status of waterbody segments in order to distinguish between waterbodies in attainment of water quality standards (category 1a) and waterbodies in attainment of water quality standards with approved TMDLs (category 1b). This distinction is important because even after a waterbody is reclassified for a given analyte from 4a (TMDL completed) to 1 (attaining), the TMDL remains in effect. The TMDL remains in place so that the practices that were implemented to improve water quality maintain the restored level of water quality. As more waterbodies with TMDLs are no longer impaired, it is helpful to have a subcategory to quickly locate attaining waterbodies with TMDLs. This will help:

* Potential and existing dischargers understand the locations where waste load allocations may exist.

* Division permit writers find TMDLs on waterbodies in attainment.

* Watershed groups dedicate resources to support continued pollution reduction efforts.

During the Regulation #93 rulemaking hearing, subcategories 1a (attaining) and 1b (attaining with TMDL) are visible within the division's proposal to indicate the proposed action to be taken by the commission to change the attainment status of a waterbody. However, because Regulation #93 reports on waterbodies that are impaired or identified for the M&E List, attaining waterbodies (i.e., subcategories 1a, and 1b) are removed from the final Regulation #93 document. These subcategories will be presented in Colorado's Integrated Water Quality Monitoring and Assessment Report (IR), which is approved by the commission every even numbered year, in an administrative action hearing.

While subcategories 1a and 1b are useful to the state of Colorado as described above, the EPA recognizes them both as category 1. This is similar to other instances in which Colorado developed subcategories such as 3a (no water quality data has been collected), and 3b (waterbody placed on M&E List). In these cases, the EPA recognizes each as simply category 3, insufficient data to determine whether or not the classified uses are being attained.

4. Removal of Adequate Refuge Clause from Regulation #31

In 2016, the commission removed footnote 5(c)(iii) from Regulation #31 which allowed lake and reservoir surface water temperatures to exceed the applicable temperature standards if adequate refuge existed in deeper layers of the water column. Adequate refuge was defined as concurrent attainment of the temperature and dissolved oxygen standard below the surface of the lake or reservoir in deeper layers. The footnote was proposed for removal by the division because an elevation based temperature standard was being considered for adoption by the commission. Although the commission did not adopt the elevation based standard, the footnote allowing for adequate refuge as a part of the lake temperature standard was deleted in error.

Due to the removal of this footnote, data assessed for the 2020 and 2022 Regulation #93 listing cycles were compared to the lakes and reservoir temperature standards without consideration for adequate refuge. This resulted in numerous lakes and reservoirs with exceedances of the temperature standard in the surface layer more than once in 3 years. These lakes and reservoirs would have otherwise been considered attaining temperature standards if the refuge footnote was still in place. For the 2020 303(d) List, the following 7 lakes and reservoirs were added to the 303(d) List as impaired for temperature because adequate refuge was not considered: Lake Avery (COLCWH25_A), Big Creek Reservoir (COUCNP09_B), North Delaney Lake (COUCNP09_C), Lake John (COUCNP09_D), South Delaney Lake (COUCNP09_E), Pearl Lake (COUCYA22_D) and Steamboat Lake (COUCYA22_E). For the 2022 303(d) List, the following 7 new lakes and reservoirs were added to the 303(d) List as impaired for temperature because adequate refuge was not considered: Blue Mesa Reservoir (COGUUG38_C), Grand Lake (COUCUC12_E), McPhee Reservoir (COSJDO04b_B), Lake Nighthorse (COSJAF22_A), Ridgway Reservoir (COGUUN19_A), Vallecito Reservoir (COSJPN03_A) and Willow Creek Reservoir (COUCUC12_D).

For the June 2021 Regulation #31 rulemaking hearing, the commission is considering a proposal by the division to reinstate language that would allow for adequate refuge when assessing temperature for lakes and reservoirs. Reinstatement of the adequate refuge provision is expected to result in attainment of the temperature standards for all of the lakes and reservoirs listed above. In light of this proposed change, the division proposed that the lakes and reservoirs above be included on the 303(d) List with low priority for TMDL development. If the adequate refuge provision is added to the lake temperature standard in June of 2021, the division will prioritize the assessment of the lakes and reservoirs listed above for the 2024 303(d) List, regardless of the division's basin of focus.

5. For the secondary water supply standards of dissolved iron, dissolved manganese and sulfate, the less restrictive of the following two options apply as the numeric standard: existing quality as of January 1, 2000, or the table value criteria in Regulation #31, Tables II and III. For dissolved iron, the table value standard (TVS) is 300 ug/l. For dissolved manganese, the TVS is 50 ug/l. For sulfate, the TVS is 250 mg/l.

The 303(d) Listing Methodology, includes language regarding the determination of existing quality from the year 2000 (EQ 2000). This includes a minimum data requirement and the ability to use data collected after the year 2000 when characterizing existing quality from 2000. The utilization of data collected past the year 2000 is contingent upon there being no new or increased sources of these parameters in the segment being assessed since 2000.

Table 1. summarizes the secondary water supply assessment values used for dissolved iron, manganese, and sulfate for 303(d) or M&E listing actions:

Table 1. Footnotes:

6. Parties to the rulemaking hearing: