5 Colo. Code Regs. § 1002-38.44
The provisions of 25-8-202(1) (b) and (2); 25-8-204; and 25-8-402 CHRIS provide the specific statutory authority for adoption of these regulatory amendments. The Commission also adopted in compliance with 24-4-103(4), CHRIS, the following statement of basis and purpose.
BASIS AND PURPOSE:
The dissolved oxygen standards applicable to segment 15 prior to this hearing were:
5.0 mg/L May 1 to July 31 for Early Life Stage (ELS); and
4.5 mg/L August 1 to April 30 for Older Life State (OLS).
These values were initially adopted in 1986 with the 5.0 mg/L ELS period ending on July 15. Although not adopted as such by the Commission, the EPA approved these values as instantaneous minima. EPA further declined to approve the application period of the 4.5 mg/L standard during the period July 16 through July 31. Subsequently, another hearing was held in 1987 and the period of application for the ELS was changed to July 31 to satisfy EPA. In the 1991 South Plate River basin hearing, the Commission "continued" the then applicable dissolved oxygen standards and stated its intention that these standards be applied as minimum 1-day means in conformance with the Division's established modeling procedures. At that time, the Commission, the Division and Metro agreed that Metro would do additional studies to form the basis for acute and chronic site-specific standards for Segment 15. These studies were undertaken by Metro with input and participation by the Division, EPA and the DOW. Based on the results of these studies, Metro proposed the dissolved oxygen standards included in the hearing notice for this hearing.
Prior to the hearing, EPA stated that a number of the proposed revisions did not satisfy its evaluation criteria and EPA did not have sufficient basis to approve certain portions of the proposal. On the other hand, EPA stated that enough information was presented to justify the acceptance of the following standards for Segment 15:
EPA recommended that the Commission not take action on the standards until:
As a result, the October 1994 Commission hearing was continued to February 1995 so that the parties could develop a Memorandum of Understanding which addressed the outstanding concerns. Such a Memorandum of Understanding has been signed by the Division, the Division of Wildlife, EPA and Metro and is a part of the record in this proceeding. The Commission is adopting the final underlying DO standards, the interim underlying standards and the temporary modifications recommended in the Memorandum of Understanding.
The final underlying standards consist of those DO standards for which sufficient information was presented in the record by Metro for approval by EPA and adoption by the Commission.
The interim underlying standards for the ELS 1-Day Minimum and OLS 7-Day Mean of Minimums are based on the EPA national criteria for dissolved oxygen. It is anticipated that Metro will propose modifying these standards as a result of the further studies to be completed.
The temporary modifications for the 1-Day Minimums (ELS and OLS) and the 7-Day Mean of Minimums consist of the currently existing ambient conditions as monitored in 1993 and 1994 by the Division and Metro. These temporary modifications are effective until December 31, 1997.
It is anticipated that a hearing will be scheduled before the Commission in the spring of 1997 to consider modifications to the interim underlying DO standards. Metro may also request that revised temporary modifications be adopted to provide the time needed for construction of any improvements required to meet the 1997 standards.
PARTIES TO THE RULEMAKING HEARING
5 CCR 1002-38.44