5 Colo. Code Regs. § 1002-38.68
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 to determine whether the temporary modification should be modified, eliminated or extended.
Language was added to subsection 38.6 to explain the terms "type i" and "type iii" temporary modifications.
In three general cases, the Commission decided to delete temporary modifications, thereby allowing the underlying standards to go into effect:
* Upper So. Platte segment 5b, Geneva Creek, temporary modification for zinc.
* Lower So. Platte segment 2b, temporary modifications for selenium and E coli.
* Upper So. Platte segment 4, temporary modification for copper and zinc.
* Upper So. Platte segment 15, temporary modifications for fecal coliform and E. coli.
* Clear Creek segment 15, temporary modifications for E. coli.
* Big Dry Creek segment 1, temporary modifications for fecal coliform and E. coli.
* Boulder Creek segment 2, temporary modifications for E. coli.
* Boulder Creek segment 7b, temporary modifications for E. coli.
* Boulder Creek segment 10, temporary modifications for E. coli.
* Big Thompson segment 5, temporary modifications for selenium.
* Big Thompson segment 9, temporary modifications for selenium and E coli.
* Big Thompson segment 10, temporary modifications for selenium.
* St. Vrain segment 4b, temporary modifications for copper and lead.
* Cache La Poudre segment 12, temporary modifications for E. coli.
* Lower So. Platte segment 1, temporary modifications for selenium.
* Middle So. Platte segment 1b, temporary modification for ammonia.
* Middle So. Platte segment 5b, temporary modification for ammonia.
* Lower So. Platte segment 1, temporary modification for nitrate.
Temporary modifications provide time for sand and gravel dischargers to work with the Division to determine the most appropriate way to make progress towards resolving non-attainment of underlying selenium standards. The Commission added "type iii", but took no action on the expiration date for the following segments.
* St Vrain segment 6, temporary modification for selenium.
* Big Thompson segment 4b, temporary modification for selenium.
Because parties are working to resolve uncertainty and are on schedule to address these segments at the regularly scheduled basin-wide rulemaking (June 2009), the Commission either added "Type iii" or made the reference consistent, but took no action on the expiration date for the temporary modifications for the following segments:
Upper So Platte segments 16a and 16c: (temporary modifications for selenium). The Selenium Stakeholders presented evidence that they are making progress on their study of selenium sources and appropriate underlying standards and will make a proposal for the 2009 rulemaking hearing.
Big Dry Creek segment 5: (temporary modifications for nitrate, nitrite, benzene, carbon tetrachloride, 1,2-dichloroethanen, 1,1-dichloroethene, tetrachloroethylene, and trichloroethylene). The temporary modification was identified as a "type i" temporary modification. The Department of Energy submitted evidence that progress is continuing and that the temporary modifications are necessary because of the Clean Up agreement.
Boulder Creek, segment 9, Cache La Poudre segments 11 and 12: (temporary modification for copper). The City of Boulder (Boulder Creek) and the City of Fort Collins (Cache La Poudre) submitted evidence that they are making progress on their translator studies.
Clear Creek segments 2, 3a, 3b, 6, 9a, 9b, 11, 13b: (temporary modifications for zinc, lead, copper, manganese, and cadmium - not all segments have all metals). Evidence was submitted that indicated that the Upper Clear Creek Watershed Association is making progress on their study of appropriate underlying standards and will make a proposal for the 2008 rulemaking temporary modification review hearing. The Commission adjusted the expiration date to 7/1/2009.
Big Dry Creek segment 1: The Big Dry Creek Cities presented evidence that the natural or irreversible human-induced ambient water quality levels for selenium in Big Dry Creek Segment 1 at times exceed the relevant table value standard, and an ambient quality based standard, calculated in a manner consistent with Basic Standards requirements, is adequate to protect classified uses. The Commission accepts the Big Dry Creek Cities' evidence as accurate. The Commission expressly finds that the natural or irreversible human-induced ambient water quality levels for selenium in Big Dry Creek Segment 1 exceed the relevant table value standard. Moreover, the proposed ambient quality based standard is adequate to protect classified uses and represents the highest reasonably attainable standard, based on analysis of available data that show elevated instream conditions are attributable to natural or irreversible human induced conditions.
Strong seasonal variation associated with highly managed flow conditions (e.g., releases of irrigation water from Standley Lake) significantly influences selenium concentrations, particularly in the portion of the stream above the wastewater treatment plants. As a result, the Commission adopts seasonal ambient quality based site-specific standards for selenium applicable to Big Dry Creek Segment 1. During the irrigation season (April through October), ambient standards are 7.4 µg/L chronic (dis) and TVS µg/L acute (dis). Ambient-based non-irrigation season (November through March) standards are 15 µg/L chronic (dis) and 19.1 µg/L acute (dis). These calculations are based on the 85% (chronic) and the 95% (acute for the non-irrigation season) of the ambient selenium data collected at three specific instream monitoring locations (bdc1.5, bdc2.0 and bdc4.0) upstream of the three municipal wastewater treatment plant discharges, however, it is the Commission's intent that the existing spatial variability of selenium in Big Dry Creek be maintained. This composite approach was jointly developed by the Cities and the Water Quality Control Division as a reasonable method to establish the ambient based standards and to assess attainment of future stream standards for Segment 1 of Big Dry Creek. The ambient quality based site-specific standards for selenium (acute and chronic) shall apply to the entirety of Big Dry Creek Segment 1. The Commission also removes the temporary modification currently in place for selenium in Big Dry Creek Segment 1.
PARTIES TO THE RULEMAKING
5 CCR 1002-38.68