5 Colo. Code Regs. § 1002-73.12
The provisions of sections 25-8-202(1)(c) and (2); and 25-8-205; C.R.S. provide the specific statutory authority for adoption of the attached 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 regulation for control of phosphorus in the Chatfield Basin in June, 1989. The regulation was based on phosphorus controls to meet the in-lake phosphorus standard of .027 mg/l in the growing season and to not exceed .017 mg/l chlorophyll a which is the goal for maintaining the beneficial uses of the reservoir. The standards and goals were based on water quality and hydrologic data gathered in 1982. Monitoring data gathered from 1983 - 1991 indicate that the annual phosphorus loading to Chatfield Reservoir is significantly higher than the 36,400 lbs. per year that was estimated in 1984 to be the assimilative capacity of the reservoir, and that the higher total phosphorus loads have not caused the reservoir to exceed the chlorophyll a goal of .017 mg/l. Further modeling of the reservoir indicates that the assimilative capacity of the reservoir for a one in ten year flow regime is 59,000 lbs. per year. When the control regulation was adopted in 1989, the wastewater effluent limitation for phosphorus was 0.2 mg/l. Significant costs have been incurred by the dischargers in the basin to upgrade treatment as well as provide on-going operation and maintenance of advanced treatment facilities. Several dischargers in the basin have not been able to obtain financing for advanced treatment facilities to meet the 0.2 mg/l limit. The Commission adopted the recommendation of the Chatfield Basin Authority and the Division that the effluent limit for total phosphorus be changed to 1.0 mg/l as a 30-day average concentration but with an annual poundage allocation for each discharger that cannot be exceeded. This will increase the allowable phosphorus poundage from point sources to 7,358 lbs. per year. The basis of the annual poundage allocations to the dischargers shown in section 4.7.3 is the projected wastewater flow in the year 2000 at an effluent concentration of 0.6 mg/l. Although the effluent limit for phosphorus is 1.0 mg/l, some or all dischargers may be required to meet a concentration less than 1.0 mg/l in order to stay within their wasteload allocation if population growth rates increase. It is assumed that advanced wastewater treatment must be provided to achieve a concentration lower than 0.6 mg/l. It is assumed that each discharger can stay within the annual poundage allocation by achieving an effluent concentration between 0.6 to 1.0 mg/l. The change to a maximum allowable concentration of 1.0 mg/l will save the dischargers significant dollars in capital and operational costs through the year 2000 while keeping algae growth in the reservoir within target levels.
Section 4.7.4 has been deleted due in part to much slower population growth in the Plum Creek portion of the Chatfield Basin than what was anticipated. Ammonia data has been collected on Plum Creek since the regulation was adopted which indicates that ammonia concentrations in-stream are low and within the unionized ammonia standard of 0.06 mg/l. Discharge permit limits for total ammonia which are written for design capacity flows at low flow conditions are sufficient to protect the stream without requiring a Plum Creek wasteload allocation for ammonia.
The Commission adopted language which allows for phosphorus credits and trading between point source dischargers and allows point source credits if nonpoint source reductions are demonstrated. This provides for flexibility in point source and nonpoint source phosphorus management while maintaining phosphorus loads within the basin targets and wasteload allocations provided for in this regulation. The Division has administrative authority, after review by the Chatfield Basin Authority, to require documentation of phosphorus reduction and appropriate agreements among parties in the basin to insure that phosphorus credits are justified and that trading arrangements are within the scope of this control regulation.
The Chatfield Basin Authority has spent considerable time within the last year looking at the South Platte watershed, which is the main source of water and phosphorus load to the reservoir, in an effort to assess the potential for nutrient loading reductions. The Authority wishes to investigate whether other dischargers in the upper South Platte basin, such as Woodland Park, Bailey, Fairplay, Florissant, and Alma could reduce phosphorus loading in the future and whether they should be subject to the provisions of this control regulation. This issue is expected to be addressed at the next triennial review of the control regulation.
The Commission added a new section on monitoring to address concerns by the Division of Wildlife and the Division of Parks and Outdoor Recreation that the monitoring program conducted by the Chatfield Basin Authority in recent years may not be sufficient to detect nuisance algae blooms or the conditions that may cause nuisance blooms to occur. The Commission determined that the Water Quality Control Division should take the primary role in determining what the appropriate monitoring parameters and frequencies are, in consultation with other interested parties, so that monitoring data over time will better reflect what is causing water quality problems and may be impacting the beneficial uses of the reservoir. The intent is that the Authority will continue to develop an annual monitoring program which the Division shall have the responsibility to review and recommend changes if needed so that the water quality data will be adequate to assess conditions in the reservoir. Other interested parties shall be provided an opportunity annually to have input on the monitoring plan so that appropriate resources can be directed to address water quality impacts.
A study of phosphorus loadings to Chatfield Reservoir and an assessment of nonpoint source phosphorus in the basin was prepared for the Chatfield Basin Authority by Woodward Clyde Consultants in 1992. The study recommends that structural and non-structural best management practices to control nonpoint source phosphorus be used. A schedule to develop specific projects for phosphorus control is included which recommends that engineering be done in 1993 and 1994 with implementation in 1995. Nonpoint source phosphorus loads are not easily identified and additional time is needed to develop control projects. The Chatfield Basin LEMNA nonpoint source demonstration project will be installed in 1993 and evaluated for phosphorus removal through 1994. Jefferson County has adopted an erosion control and grading regulation effective January, 1992 and Douglas County adopted a drainage criteria and erosion control regulation in October, 1992. These regulations are expected to reduce nonpoint phosphorus loadings to the reservoir. The provisions of these local requirements will be made part of the discharge permit conditions of any stormwater permits which are issued by the Division for construction projects in the basin, industrial activities, and for any municipalities that may be covered by municipal stormwater permits in the future. If progress in implementing best management practices to control nonpoint phosphorus is not evident in future years and if county and/or municipal governments in the Chatfield Basin are not enforcing ordinances or regulations to control such sources, then the Commission will consider imposing further restrictions on point source dischargers through reduced wasteload allocations and/or more restrictive effluent limits. Specific plans for monitoring of nonpoint source phosphorus loads in the basin must be periodically submitted to and approved by the Division and progress in controlling nonpoint sources will be reviewed at each triennial review of this control regulation.
PARTIES TO THE RULEMAKING HEARING
JANUARY 4, 1993
5 CCR 1002-73.12