5 Colo. Code Regs. § 1002-37.28
The provisions of C.R S. 25-8-202 (1)(a), (b) and (2); 25-8-203; 25-8-204; and 25-8-402; provide the specific statutory authority for adoption of these regulatory amendments. The Commission also adopted in compliance with 24-4-103(4) C.R.S. the following statement of basis and purpose.
BASIS AND PURPOSE
Pursuant to the requirements in the Basic Standards (at 31.7(3)), the Commission reviewed the status of temporary modifications to determine whether the temporary modification should be modified, eliminated or extended.
The type i temporary modifications of ammonia standards on four segments were reviewed. The Commission deleted the temporary modifications on Lower Yampa segment 2 and Lower Colorado segment 2a, as they are no longer needed. The Commission took no action on Lower Colorado segments 2b and 13b.
The Commission took no action on the temporary modification of the temperature standard for Lower Colorado segment 13b or the selenium temporary modification for Lower Colorado 13d.
Tri-State Generation and Transmission Association, Inc. proposed revisions to segment 4e of the Lower Colorado. Based on a Use Attainability Analysis for Dry Creek and an Unnamed Tributary near Rifle, Colorado and other information on the record, the Commission concluded that existing Segment 4e should be split into two segments at the Last Chance Ditch crossing.
* Segment 4e includes the mainstem of Dry Creek, all tributaries and wetlands from the source to immediately above the Last Chance Ditch crossing. This segment was found to be ephemeral and effluent dependent and was, therefore, designated Use Protected. The UAA showed that segment 4e does not support fish and supports limited macroinvertebrates as a result of limited flow. In response to Tri-State's proposal that the agriculture standards are protective of the limited aquatic community in this segment the Commission retained Aquatic Life Cold 2, Recreation N, and Agriculture use classifications. However, the Commission recognized there is uncertainty regarding the protectiveness of the agriculture metal standards in Tri-State's proposal. Therefore, the Commission kept the aquatic life standards and extended the temporary modifications for copper and iron to provide time to resolve this uncertainty. The existing temporary modification for temperature was deleted.
* New segment 4f includes the mainstem of Dry Creek and all tributaries and wetlands from a point immediately above the Last Chance Ditch crossing to the confluence with the Colorado River. This short segment of Dry Creek receives flow at times from the Last Chance Ditch and supports a broad assemblage offish and macroinvertebrates, including cold-water species. Therefore, the segment was designated reviewable, with Aquatic Life Cold 1, Recreation N, and Agriculture use classifications, and assigned the cold stream tier II temperature standard.
PARTIES TO THE RULEMAKING HEARING
5 CCR 1002-37.28