5 Colo. Code Regs. § 1002-73.17
Sections 25-8-202 and 25-8-205, C.R.S., provide the specific statutory authority for adoption of the revisions to this regulation. The Commission also adopted, in compliance with Section 24-4-103(4), C.R.S., the following statement of basis and purpose.
BASIS AND PURPOSE
The Commission adopted a new total phosphorus allowable load in Section 73.3 of this regulation. Although the allowable load was revised, the total phosphorus allocations were not revised. Therefore, the Commission included a list of tasks to be completed to support development of revised allocations of the new allowable load in the Control Regulation. It was the Commission's intent that until the allocations are revised, the existing nonpoint and point source allocations remain applicable.
Based on information presented by the Division during the July 2007 triennial review hearing, the Commission scheduled a rule-making hearing to consider revisions to the control regulation and to related water quality standards in Regulation #38. Specifically, the Commission heard evidence that the phosphorus standard in Chatfield Reservoir had been exceeded in 5 of the last 6 years, while the chlorophyll goal was not exceeded. The Commission agreed that the linkages between in-lake chlorophyll and total phosphorus concentrations and between total phosphorus concentrations and total phosphorus load to the reservoir are critical to the basis of the Control Regulation and TMAL and that these linkages should be reviewed.
The Commission directed the Division to conduct a limited scope Technical Review of the Control Regulation TMAL and the underlying standard. The scope of the technical review was limited to the in-lake total phosphorus standard, chlorophyll goal, and the allowable load to attain these. The scope of the technical review did not include an examination of the allocation of the total phosphorus load. As part of this Technical Review, the Division provided reports and made monthly presentations to the Chatfield Watershed Authority Technical Review Committee from September 2007 through May 2008. The reports and presentations provided the basis for the proposal the Commission heard in this rule-making hearing.
Based on the results of the Technical Review, the Commission adopted revised site-specific standards for total phosphorus and chlorophyll for Chatfield Reservoir in relevant sections of Regulation #38. These standards are total phosphorus of 0.030 mg/L and chlorophyll a of 10 µg/l measured through the collection of samples that are representative of the mixed layer during summer months (July, August, September) and with a maximum allowable exceedance frequency of once in five years. As a result of these changes to the site-specific standards, the Commission adopted a new allowable load of total phosphorus of 19,600 lbs/y under a median inflow of 100,860 AF/y in this Control Regulation. The new allowable load better reflects the linkage between watershed total phosphorus load and the in-lake total phosphorus concentration.
The Commission directed the Division and the Authority to develop new nonpoint source and point source allocations related to the new allowable load for submittal during the next control regulation triennial review. The Commission acknowledged that progress toward development of the allocations will be contingent on the availability of suitable funding to support completion of the tasks identified in Section 73.3 . The Commission also recognized that control regulation definitions and language may need to be revised to support future updates to the TMAL.
5 CCR 1002-73.17