Code of Colorado Regulations
1000 - Department of Public Health and Environment
1002 - Water Quality Control Commission (1002 Series)
5 CCR 1002-35 - REGULATION NO. 35 - CLASSIFICATIONS AND NUMERIC STANDARDS FOR GUNNISON AND LOWER DOLORES RIVER BASINS
Section 5 CCR 1002-35.32 - STATEMENT OF BASIS SPECIFIC STATUTORY AUTHORITY AND PURPOSE DECEMBER 2010 RULEMAKING REGARDING TEMPORARY MODIFICATIONS; FINAL ACTION JANUARY 10, 2011; EFFECTIVE DATE JUNE 30, 2011

A. Ammonia: The type i temporary modifications of ammonia standards on 3 segments were reviewed. Tine Commission deleted tine temporary modification on Lower Dolores segment 2 as it is no longer needed. The Commission took no action on San Miguel segment 5. The temporary modification will expire on 12/31/2011. On Lower Gunnison segment 4a, the Commission corrected the numeric value for the ammonia chronic temporary modification from 0.02 mg/L to 0.06 mg/L which had been modified in error in 2009. The temporary modification will expire on 12/31/2011.

B. Metals: Temporary modifications of the metals standards were reviewed. They will expire on 12/31/2012. When originally adopted, time was allotted to allow dischargers time to assess potential changes to their discharge permits. It is anticipated that these will be addressed as part of the basin-wide review in June 2012:

Upper Gunnison segments 8, 12, and 16

North Fork Gunnison segments 3, 5, and 6b

Uncompahgre segments 3a, 4b and 12

Lower Gunnison segments 2, 4a and 7

San Miguel segments 2, 3b, and 5

C. San Miguel River segment 4b: Tri-State Generation and Transmission Association, Inc. (Tri-State) proposed revisions to the Classifications and standards for San Miguel River segment 4b. The Commission found that the existing thermal discharge from Tri-State's Nucia power plant is not causing harm to the aquatic community based on fish and macroinvertebrate data collected in 2008 and 2009. Site-specific temperature standards were adopted to reflect the existing thermal conditions in San Miguel segment 4b. The summer temperature standards apply from March through October and are based on the maximum WAT and DM measured in Segment 4b (below Tri-State's mixing zone, 2,000 ft below the outfall) from April 16, 2008 through Oct 27, 2010. The winter temperature standards apply from November through February and are equivalent to the cold-stream tier-!! winter temperature standards.

If no additional biological data is available in subsequent reviews, the site-specific summer temperature standards may be revised upwards using the following equations:

Summer DM above Tri-State NucIa plant discharge + 0.8°C = revised DM for segment 4b

Summer MWAT above Tri-State NucIa plant discharge + 0.4°C = revised MWAT for segment 4b

The 0.8°C for DM and 0.4°C for MWAT are the measured difference in temperature between the monitoring locations upstream and downstream of Tri-State's plant discharge on the days the maximum DM and MWAT were recorded. The biological data from 2008 and 2009 shows that this amount of warming does not cause harm to the biological community, and is protective of the Aquatic Life use. The temporary modification for temperature was deleted.

The Commission changed the use classification from Aquatic Life Cold 2 to Aquatic Life Warm 1 based on evidence presented by Tri-State of the overwhelming preponderance of warm water fish and macroinvertebrate species in segment 4b and no evidence of cold water fish reproduction. The more intensive sampling in 2008 and 2009 demonstrated that the segment supports a wide variety of warm water fish and macroinvertebrates, which supports the change to class 1 (warm).

PARTIES TO THE RULEMAKING HEARING