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.
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
1. Paint Brush Hills Metropolitan District2. Tri-State Generation and Transmission Association4. Mountain Water and Sanitation District5. City of Grand Junction6. Colorado Division of Wildlife8. U. S. Environmental Protection Agency9. City of Colorado Springs and Colorado Springs Utilities38 CR 01, January 10, 2015, effective 6/30/201538 CR 03, February 10, 2015, effective 6/30/201539 CR 03, February 10, 2016, effective 3/1/201639 CR 03, February 10, 2016, effective 6/30/201639 CR 23, December 25, 2016, effective 12/30/201640 CR 03, February 10, 2017, effective 6/30/201740 CR 17, September 10, 2017, effective 12/31/201742 CR 04, February 25, 2019, effective 6/30/201943 CR 03, February 10, 2020, effective 6/30/202044 CR 05, March 10, 2021, effective 6/30/202144 CR 17, September 10, 2021, effective 12/31/202145 CR 17, September 10, 2022, effective 9/30/202246 CR 10, May 25, 2023, effective 6/14/2023