5 Colo. Code Regs. § 1002-73.11
The provisions of sections 25 8 202(1)(c), (h) and (2); and 25 8 205; C.R.S., provide the specific statutory authority for adoption of 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 Colorado Water Quality Control Commission adopted a water quality standard for phosphorus for the Chatfield Reservoir on August 14, 1984 of 0.027 mg/l total phosphorus measured throughout the water column in Chatfield Reservoir for the months of July, August and September. The standard was based upon water quality data and hydrologic conditions of 1982.
Total phosphorus loading to the Chatfield Reservoir varies with the water yield in the basin. 1982 water quality data and hydrologic conditions were used to determine the phosphorus standard. However, the phosphorus allocations to different sources, as shown in Section 4.7.3 of this regulation, is based on further modeling of phosphorus loadings estimated for both present and future conditions. The estimated loadings are shown in Table 4 of the Chatfield Basin Study and are adopted as part of the 208 Water Quality Management Plan covering the Chatfield Basin. The total allowable pounds of phosphorus estimated in the Chatfield study is 36,400 pounds per year. This total poundage is not expected to cause the 0.027 mg/l numeric standard to be exceeded, although it may be exceeded at higher water yields. The 0.027 mg/l total phosphorus standard was adopted by the Commission with the intent of maintaining the chlorophyll a level in the reservoir at no more than 0.017 mg/l during the growing season. Although a majority of the phosphorus loading to the Chatfield Reservoir comes from background sources from the South Platte River, the control of point and nonpoint sources of phosphorus to the reservoir is essential to maintaining the water quality and the classified uses of the reservoir. Point source effluent limits have been identified which will meet the numeric standard for total phosphorus in the reservoir, based on projections of point source phosphorus loading in the basin and the modeling of different concentrations of phosphorus as an effluent limit. The 0.2 mg/l 30 day average concentration for point source phosphorus can be achieved by mechanical wastewater treatment or land application of effluent, in most cases. This level of treatment can be provided at a reasonable cost.
The Chatfield Basin Water Quality Study of 1988 indicated that if the expected flows of wastewater in the basin were treated to a level of 0.2 mg/l total phosphorus, then nonpoint sources of phosphorus would not have to be reduced until after the year 2000 and the water quality standard of 0.027 mg/l would be maintained.
Section 4.7.4 of the regulation requires that an ammonia wasteload allocation be developed for the Plum Creek Basin. The adopted ammonia standards for segments 8, 9, 10a, 10b, and 11b of the South Platte Basin, which are in the Plum Creek drainage, are 0.02 mg/l unionized or 0.06 mg/l. The Plum Creek drainage is shown in the 1988 305(b) report of the Water Quality Control Division as "threatened" for ammonia. The Plum Creek segments, except for 11 and 11a, are classified for water supply uses. Nitrates from wastewater discharges could impact that use. The original scope of work for the Chatfield Basin Study, which was started in 1985, included a wasteload allocation plan for ammonia as one of the tasks. The wasteload plan was not finished at the time of the control regulation adoption.
The Chatfield Basin Water Quality Task Force has not identified controls or practices for nonpoint sources of phosphorus. However, the estimate of nonpoint sources of phosphorus in the Basin is 9,600 pounds per year. This is a significant source and can be attributed mainly to stormwater runoff in the watershed. Best management practices can be used to reduce phosphorus in stormwater. A goal of 50% removal has been set for nonpoint phosphorus reduction. The nonpoint source control plan required by Section 4.7.5 shall determine if 50% removal basin wide is achievable and weigh the relative costs and benefits. Hence, the regulation requires that a basin wide control plan be developed for nonpoint sources and submitted by January 1, 1992. The basin wide control plan may examine the potential for trading point and nonpoint source phosphorus as a component of the overall plan. This will allow about three years for further studies and development of institutional arrangements for nonpoint source controls.
Section 4.7.6 provides for an annual report on the Chatfield Basin to be submitted to the Commission for the purpose of updating information about water quality in the Basin and to track progress in implementing this regulation and meeting the adopted water quality standards for the Plum Creek Basin and the Chatfield Reservoir.
The Perry Park Water and Sanitation District requested that the compliance date for meeting the point source discharge limit for total phosphorus in section 4.7.4 be changed to January 1, 1993, only for their district. The Division intends to provide advance of allowance funding for planning and design of wastewater facility improvements and intends to provide assistance from the State Revolving Fund so that Perry Park can upgrade their treatment facility to meet the 0.2 mg/l phosphorus limit. Such assistance would be available in 1990 providing that Perry Park can qualify financially for the loan. If loan funds are not available to Perry Park, or problems are encountered in completing the project by January 1, 1991, the Division shall give an extension to the compliance date if Perry Park requests a variance from the control regulation and the variance criteria in section 25 8 205(6) of the Water Quality Control Act is met.
The provisions in section 4.7.4 , 4.7.5 , and 4.7.6 of the regulation are expected to be carried out by a basin wide group of municipal, county, private, and other entities which are currently in the process of formulating an intergovernmental agreement. When this organization is formed, it is expected that such basin group will be designated as management agency for the Chatfield Basin.
5 CCR 1002-73.11