5 Colo. Code Regs. § 1002-34.52
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:
Animas River segments 3b and 4a (COSJAF03b and COSJAF04a): temporary modifications of the acute and chronic copper standards (expire 12/31/2022). The Town of Silverton provided an update regarding progress being made in implementing the plan to resolve uncertainty and demonstrating the ongoing justification for the temporary modifications.
There continues to be demonstrated instream nonattainment, predicted compliance issues, and remaining uncertainty regarding the appropriate underlying standards to protect the uses and the extent to which instream and effluent conditions are reversible. The update provided by the Town of Silverton included details regarding the scheduled investigations and actions to resolve the uncertainty pertaining to the reversibility of copper concentrations in their effluent by 12/31/2022. This work includes improvements to the collection systems to reduce inflow and infiltration, as well as improvements to the wastewater treatment facility.
The operative value of the temporary modifications is the narrative "current conditions." In future reviews of these temporary modifications, 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. 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 took no action on the temporary modifications set to expire on or before the effective date of this hearing, allowing the following temporary modifications to expire and be deleted from Appendix 34-1:
La Plata Segment 9 (COSJLP09): acute and chronic ammonia (expires 6/30/2021)
5 CCR 1002-34.52