5 Colo. Code Regs. § 1002-33.61
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 scheduled to expire before December 31, 2020 to determine whether the temporary modification should be modified, eliminated, or extended.
For the temporary modifications set to expire after the effective date of this hearing, the commission reviewed progress toward resolving the uncertainty in the underlying standard and/or the extent to which conditions are a result of natural or anthropogenic conditions, and evaluated whether the temporary modifications were still necessary. The commission took no action on the following temporary modifications:
Blue River Segment 14 (COUCBL14): temporary modification of the chronic molybdenum standard (expires 6/30/2020). Climax Molybdenum Company continues to make progress to resolve the uncertainty, and the commission continues to believe that an expiration date of 6/30/2020 provides sufficient time to resolve the uncertainty.
However, the commission and parties identified concerns regarding whether "status quo" of the waterbody and effluent was being preserved, per the requirements of "current condition" temporary modifications at 31.7(3)(d). The commission directed Climax to work with stakeholders as part of this hearing to determine if existing uses are being protected and status quo is being preserved instream and in the discharge.
In this rulemaking hearing, parties disagreed about what period of record and sites should be used to represent the baseline or "status quo" that is to be preserved, and multiple options were presented to the commission. Climax restarted mining operations in May 2012, which resulted in an increase in molybdenum concentrations in Climax's effluent and Tenmile Creek. The "current condition" temporary modification was adopted in June 2014, after mining restarted and affected water quality. Until further analyses are completed, the commission has determined that the "status quo" to be preserved is the post-mining water quality condition represented by data collected from May 2012 to June 2014, when the temporary modification was originally adopted. Water quality data from two sites on Tenmile Creek near Frisco (Climax site "Frisco 3rd Ave" and Denver Water site "Ten Mile Creek above Dillon") and Climax's effluent (Outfall 001a) were evaluated to establish the instream and effluent baseline conditions.
For the May 2012 to June 2014 period of record, the 50th percentile molybdenum concentrations in Tenmile Creek and Climax's effluent were 170 µg/L and 490 µg/L, respectively. These values can be used as an interim baseline to compare to data collected after the temporary modification was adopted in June 2014 using the ambient standards assessment technique in Appendix B of the 303(d) listing methodology. While a long-term (2012 to 2018) trend analysis of Tenmile Creek water quality data identified a statistically significant increasing trend in instream molybdenum concentrations since Climax restarted mining operations in 2012, 50th percentile molybdenum concentrations in Tenmile Creek and Climax's effluent from the 2015 to 2018 period of record are not statistically significantly different from the 2012 to 2014 baseline values. In addition, the ambient standards assessment methodology comparing 2012 to 2014 vs 2015 to 2018 does not indicate that the lower confidence limit of the 50th percentile molybdenum concentration in 2015 to 2018 is higher than the baseline. Based on this information, at this time, the commission finds "status quo" is currently being preserved.
This hearing has highlighted challenges with "current condition" temporary modifications and how to evaluate whether "status quo" is being preserved. The commission has a hearing scheduled for November 2019 to consider a change to the underlying standard and delete the temporary modification for Tenmile Creek. While the commission does not intend that this temporary modification will be reviewed or extended, if it is, the commission directs the division to develop a numeric operative value(s) to replace the existing narrative operative value of "current condition". The purpose of this change will be to establish a baseline condition which must be preserved in Blue River Segment 14 and facilitate future evaluations of status quo preservation. Considerations in the development of the numeric value(s) will include, but are not limited to, temporal and spatial variability in molybdenum concentrations. Climax and interested stakeholders will continue to participate in this process, including continued collection and sharing of data to support evaluations of whether status quo is being preserved and existing uses are being protected.
In addition, the commission expects that Climax will share a written report detailing its investigations for molybdenum including identification of sources/source control, influent control measures, water management alternatives, available blending, potential treatment and treatment optimization options, the expected effluent quantity and quality that could be achieved with each alternative, and an estimated cost for each alternative with all stakeholders by July 1, 2019 and provide an opportunity for input. Climax shall identify any gaps in this information at that time. Further, the commission encourages Climax to share more information and data with the public and interested parties on a routine and ongoing basis.
5 CCR 1002-33.61