colorado department of public health and environment
WATER QUALITY CONTROL COMMISSION
5 CCR 1002-38
regulation no. 38
classifications and numeric standards
for
south platte river basin, laramie river basin
republican river basin, smoky hill river basin
. . . .
38.76	STATEMENT OF BASIS SPECIFIC STATUTORY AUTHORITY AND PURPOSE: APRIL12, 2010 RULEMAKING; FINAL ACTION APRIL 12, 2010; EFFECTIVE DATE JUNE 30, 2010
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 Regulation 31.7(3)(a)(iii), the Commission may grant a temporary modification where there is significant uncertainty regarding the appropriate long-term underlying standard.  The Commission found that significant uncertainty exists as to the selenium standard necessary to protect the aquatic life use.  This uncertainty is expected to be resolved when EPA revises its 304(a) criteria and issues implementation guidance for selenium.  The Commission also found that ambient selenium levels in Marcy Gulch exceed the existing underlying standard and that time is needed to determine whether this is the result of natural or irreversible human-induced conditions.  In view of the uncertainty and its anticipated resolution, the Commission adopted a temporary modification of current conditions (Type iii) with an expiration date of 12/31/15 for segment 16g of the Upper South Platte River.