Code of Colorado Regulations
1000 - Department of Public Health and Environment
1002 - Water Quality Control Commission (1002 Series)
5 CCR 1002-36 - REGULATION NO. 36 - CLASSIFICATIONS AND NUMERIC STANDARDS FOR RIO GRANDE BASIN
Section 5 CCR 1002-36.35 - STATEMENT OF BASIS SPECIFIC STATUTORY AUTHORITY AND PURPOSE DECEMBER 9, 2013 RULEMAKING; FINAL ACTION MARCH 11, 2014 EFFECTIVE DATE JUNE 30, 2014

Current through Register Vol. 47, No. 5, March 10, 2024

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

The Commission considered a proposal for feasibility-based site-specific standards for Rio Grande segments 4a (mainstem of Rio Grande River) and 7 (Willow Creek) to replace the existing temporary modifications of "Current Condition" for cadmium, lead and zinc in segment 4a, and the ambient based numeric temporary modifications for cadmium, copper, lead, silver and zinc in segment 7.

The Commission extended the existing Temporary Modifications for Rio Grande segment 4a and Rio Grande segment 7 from 6/30/2015 to 12/31/2016. The Commission also adopted two tiers of site-specific standards for those segments based on the feasibility of reversing historic man-induced sources of metals. The Commission adopted Tier 1 standards which are effective from 1/1/2017 through 12/31/2018. These standards represent predicted improvements in water quality due to the dilution effect of treated effluent from the Bulldog Mine. The Commission also adopted Tier 2 standards, which are effective after 1/1/2019. The Tier 2 standards reflect the further water-quality improvement predicted by a 90% reduction in flow and metal load from the Nelson Tunnel, and a predicted 50% reduction in metal load from the Solomon Mine, in addition to dilution from treated effluent from the Bulldog Mine. The adopted site-specific standards are intended to set water-quality goals for both segments that reflect the lowest ambient concentrations that are feasible to achieve. The Commission expects revisions will be made to the tiered underlying standards as new information become available.

The Commission adopted the proposed extension of the existing Temporary Modifications with the expectation that Rio Grande Silver will propose a sampling plan for the December 2014 Temporary Modification Hearing. The Commission expects the plan to address key areas of uncertainty that need to be better quantified during high flow and low flow conditions such as: