5 Colo. Code Regs. § 1002-38.82
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 the following statement of basis and purpose pursuant to C.R.S 24-4-103(4).
BASIS AND PURPOSE
The Commission adopted a temporary modification for arsenic set at "current condition" for Boulder Creek Segment 9, pursuant to Regulation 31.7(3)(a)(i)&(ii)(A), (B), and (C). This temporary modification is set to expire on 6/30/2017.
Monitoring data indicate that ambient concentrations of arsenic in Segment 9 exceed "water + fish" table value standards and there is significant uncertainty as to the source and cause (i.e., naturally occurring or irreversible human-induced) of elevated arsenic concentrations in the stream. There is also uncertainty regarding the water quality standard necessary to protect current and future uses. Finally, there is uncertainty regarding the timing of implementing attainable source controls or treatment. The City of Boulder, which is authorized to discharge into Segment 9 under a CDPS permit, demonstrated that it has a predicted water quality effluent limit compliance problem.
The temporary modification is set at "current condition." The Commission intends 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 natural sources in the raw drinking water sources, industrial, commercial, and residential sources. Maintaining the current condition will include maintaining total loading from commercial and industrial contributors at the levels existing on the date of adoption of the temporary modification.
The Commission found that there was substantial uncertainty about the arsenic standard necessary to protect the uses, and the extent to which existing arsenic concentrations are the result of natural or irreversible human-induced conditions. Therefore, this temporary modification falls within both type A and B under Regulation #31, section 31.7 . The Commission adopted this temporary modification to allow time for the City of Boulder to continue a comprehensive monitoring program to identify the sources of arsenic in the City of Boulder raw drinking water sources and Segment 9, and to determine the extent these sources represent naturally occurring or irreversible human-induced conditions. The adopted temporary modification also will allow time to evaluate a recalculated arsenic standard for possible future adoption as a site-specific standard for Segment 9.
PARTIES TO THE RULEMAKING HEARING
5 CCR 1002-38.82