5 Colo. Code Regs. § 1002-35.49
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, 2022 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 justified.
The commission took no action on the following temporary modifications:
Upper Gunnison Segment 12 (C0GUUG12): seasonal temporary modifications of the acute and chronic cadmium standards, acute and chronic copper standards, and chronic zinc standard (expire 12/31/2022). Mt. Emmons Mining Company (MEMC) provided an update regarding progress being made in implementing the plan to resolve uncertainty and demonstrating the ongoing justification for the temporary modifications.
With the exception of chronic copper, there continues to be demonstrated instream nonattainment and compliance issues, and MEMC continues to make progress on resolving the uncertainty underlying the temporary modifications and determining the extent to which the existing quality is the result of natural or irreversible human-induced conditions. Effluent data provided by MEMC demonstrated there is no longer a compliance issue for chronic copper, so the commission deleted the temporary modification for chronic copper. The update provided by MEMC included details regarding its investigations and activities, which have included source identification, site and source characterization, source reclamation, water and material management, and evaluation of treatment strategies.
The operative values of the cadmium and zinc temporary modifications are numeric, but the operative value of the acute copper temporary modification is the narrative "current condition." In future reviews of the copper temporary modification, the commission will use the following values to compare to the most recent five years of representative data (collected from April, May, and June) to determine if effluent and waterbody quality is maintained and ensure that the existing uses are protected. These values are for use by the commission in future reviews of the temporary modification and are not intended to direct implementation of "current condition" temporary modifications in permits:
Upper Gunnison Segment 21 (C0GUUG21): temporary modification of the chronic uranium standard (expires 12/31/2022). Homestake Mining Company provided an update regarding progress being made in implementing the plan to resolve uncertainty and demonstrating the ongoing justification for the temporary modification.
There continues to be demonstrated instream nonattainment and compliance issues, and Homestake continues to make progress on resolving the uncertainty underlying the temporary modification and determining the lowest practical level of uranium that can be achieved. The update provided by Homestake included details regarding its investigations and activities, which have included evaluations of source load reduction, passive treatment options, and water infiltration management, as well as water quality sampling instream and in downstream domestic wells.
The operative value of the temporary modification is the narrative "current condition." In future reviews of this temporary modification, the commission will use the following values to compare to the most recent five years of representative data to determine if effluent and waterbody quality is maintained and ensure that the existing uses are protected. While the underlying uranium standard is based on the total recoverable fraction, more instream data is available for the dissolved fraction, so dissolved data will be used to characterize status quo and for future reviews. These values are for use by the commission in future reviews of the temporary modification and are not intended to direct implementation of "current condition" temporary modifications in permits:
The commission deleted the temporary modifications on the following segments:
Lower Gunnison Segment 2 (COGULG02): temporary modification of the chronic selenium standard (expires 12/31/2022). The commission deleted this temporary modification because instream selenium data show that the underlying chronic selenium standard is being attained.
5 CCR 1002-35.49