5 Colo. Code Regs. § 1002-38.67
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 city of Boulder ("Boulder") originally proposed a Biotic Ligand Model (BLM)-based copper Water Effect Ratio (WER) for Segment 9 of Boulder Creek from the city of Boulder wastewater treatment plant (WWTP) point of discharge to the confluence with Coal Creek. After discussions with the Division and EPA regarding use of the Biotic Ligand Model in Colorado, Boulder revised its proposal by requesting a type iii temporary modification for copper based on uncertainty pursuant to Rule 31.7 . The Commission adopted Boulder's revised proposal.
The temporary modification recognizes the uncertainty created by the evolving guidance regarding use of a WER, BLM, or other appropriate copper standard to protect the aquatic life use in Colorado, as well uncertainty about whether protective levels can feasibly be attained in the effluent of the Boulder WWTP. An additional source of uncertainty is whether or not a translator study will provide adequate relief for the WWTP.
The temporary modification has been set to expire on December 31, 2009. During the term of the temporary modification Boulder will investigate whether a copper translator (from a dissolved criterion to a potentially dissolved or total recoverable permit limit) will address its needs. In addition, the Commission anticipates that there will be an expanded dialogue between EPA, the Division and interested parties regarding the appropriate methods for setting site-specific copper stream standards.
With a 2009 expiration date, Boulders' progress will be reported to the Commission at the December 2007 and December 2008 annual Temporary Modification Review hearings and the need for a temporary modification expiration date beyond December 31, 2009 will be reviewed at that time. If a translator is inadequate, the Commission recognizes that more time may be needed to develop a site-specific standards proposal.
The temporary modification is set at "current condition." It is the intention of the Commission that when implementing this temporary modification in a CDPS permit, and interpreting the term current condition, the Division will assess the current effluent quality, recognizing that it changes over time due to variability in treatment plant removal efficiency and influent loading from industrial, commercial, and residential sources. One necessary element of an approach to maintain the current condition would be a requirement that the total loading from commercial and industrial contributors be maintained at that level as of the date of adoption of the temporary modification and that neither the concentration nor the frequency of high concentration shall increase over historic levels and frequency.
PARTIES TO THE RULEMAKING HEARING
5 CCR 1002-38.67