5 Colo. Code Regs. § 1002-74.10
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.
Background
The Water Quality Control Commission is adopting concurrently a narrative standard for water quality in Segment 1c of Bear Creek, Bear Creek Reservoir. Goals and objectives for improving water quality in Bear Creek Reservoir have been developed by the Bear Creek Basin Management Plan Committee based upon water quality data which has been gathered from 1985-1991.
Bear Creek Reservoir has a very high level of nutrients which causes algal blooms in the growing season, based upon data compiled from the Phase I Clean Lakes Diagnostic/Feasibility Study done in 1988 and 1989. The reservoir can be characterized as eutrophic to hypertrophic.
Algal blooms dominated by species such as the bluegreen alga Aphanizomenon are frequent. During summer stratification the concentration of dissolved oxygen approaches zero throughout the hypolimnion (6-14 meters depth). These low oxygen conditions have eliminated most of the cold water habitat for aquatic life in the months of July, August, and September. Potential for recreation on and in the lake is limited under present conditions.
Due to the short residence time of water in the reservoir and the stratification of the hypolimnion, it is difficult to predict how nutrient loads will affect algae growth in the reservoir. The narrative standard for water quality in the reservoir is designed to set realistic goals for improving the conditions which impair the beneficial uses, primarily to reduce the severity and the frequency of algal blooms. Control of phosphorus in the basin is the primary tool for reducing levels of chlorophyll a in the reservoir.
Local governments, state and federal agencies, and the Denver Regional Council of Governments, who have served on the Bear Creek Basin Management Plan Committee, reached a consensus that control of phosphorus sources without addressing in-lake conditions is unlikely to produce significant improvements in reservoir water quality. The DRCOG Clean Water Plan recommends that hypolimnetic aeration be installed at the reservoir to provide a more consistent oxygen level throughout the reservoir. Studies have indicated that point source phosphorus controls, nonpoint source phosphorus reduction through the use of best management practices, and the operation of hypolimnetic aeration and hypolimnetic withdrawals from the reservoir can, in combination, produce significant water quality improvements and bring the reservoir to a trophic status of mesotrophic to eutrophic, with chlorophyll a concentrations during the growing season substantially reduced from present conditions.
Point Source Phosphorus
The Bear Creek Basin Clean Lakes study concluded that point sources of phosphorus comprise 70 percent of the total phosphorus load to the reservoir during the period of June to September.
There are 14 dischargers in the basin which are subject to the Colorado Discharge Permit System. A study by Arber and Associates of wastewater treatment facilities in the basin showed that biological treatment processes for reducing phosphorus, or simple alum addition to wastewater in a mechanical treatment plant, can achieve a total phosphorus concentration of 1.0 mg/l without major upgrade of treatment facilities and with considerably less operation and maintenance expense than advanced treatment. The basin management plan recommends that point source phosphorus loading in the basin, currently estimated at 21,584 pounds per year, be reduced by 75 percent.
This reduction in phosphorus would allow an annual load from all point sources of 5,395 pounds per year. When dischargers in the basin reach a wastewater treatment level of 1.0 mg/l for effluent phosphorus by 1994, the point source load will be substantially less than the 5,395 pounds allowed by the wasteload allocation in Section 4.6.3 . Population growth in the basin consistent with Denver Regional Council of Governments projections for the year 2000 is provided for while achieving a 75 percent or greater reduction from 1991 levels. It is recognized that some dischargers may reach a point where exceedance of their wasteload allocation could occur at future wastewater flows while achieving the effluent limitation of 1.0 mg/l. Effluent phosphorus concentrations may need to be less than 1.0 mg/l to stay within the wasteload allocation.
The Commission reviewed testimony on the cost and benefits of point source dischargers in the Bear Creek Basin being required to meet a total phosphorus effluent limitation of 0.2 mg/l, similar to point source limits in other basins in Colorado which have adopted phosphorus control regulations, such as Cherry Creek, Chatfield, and Dillon basins. The information presented indicated that an effluent limit of 0.2 mg/l would bring the chlorophyll a concentrations in the reservoir slightly lower than the expected levels if the effluent limit is 1.0 mg/l. It is believed that there would be no perceivable change in the lake to the user if the point source limit was more restrictive but the cost to the dischargers to meet the 0.2 mg/l effluent limit would be much greater. The estimate of capital improvement costs for all dischargers to meet 1.0 mg/l total phosphorus was slightly less than $1,000,000. The estimate for achieving 0.2 mg/l at the design capacity of all facilities could be in excess of $11,000,000. The Commission determined that the adopted effluent limit of 1.0 mg/l will provide a substantial reduction in phosphorus load to the reservoir and is justified as a first step in point source control. The possible need for further controls can be reassessed in subsequent triennial reviews of this regulation.
Section 4.6.3 provides for equivalent phosphorus reduction for small wastewater dischargers with 20,000 gallons per day design capacity or less. This equivalent reduction must be arranged through an agreement between the small discharger and the entity providing the equivalent reduction. The Jefferson County Mountain Water Quality Association, which consists of the City of Lakewood, Jefferson County, Evergreen Metropolitan District, West Jefferson County Sanitation District, Genesee Water and Sanitation District, Kittredge Sanitation and Water District, Willowbrook Water and Sanitation District, the Town of Morrison, Forest Hills Metropolitan District, Conifer Sanitation Association, and Jefferson County R-1 School District, shall be provided the opportunity to review and comment on all equivalent reduction agreements prior to approval of such agreements by the division. The division shall incorporate equivalent phosphorus reduction provisions in the discharge permit of both parties to the agreement.
The allowable point source phosphorus load established in Section 4.6.3 provides for a reserve pool of phosphorus which can be utilized by a new wastewater treatment facility (domestic or industrial) in the future or by an existing facility that may need to expand their capacity. Anyone who uses phosphorus from the reserve pool must design for and achieve a total phosphorus effluent concentration of 1.0 mg/l and use no more than 100 pounds of phosphorus as an annual allocation or whatever portion of the 100 pounds that remains unallocated at the time the new or expanded facility is proposed.
Nonpoint Source Phosphorus
Nonpoint sources of phosphorus to Bear Creek Reservoir are estimated to be 50 percent or more of the annual load to the reservoir. The Clean Lakes study estimates the orthophosphorus from nonpoint sources at 20,995 lbs. per year. Existing legal authority of county, state, and federal agencies to issue erosion control and grading permits or to require best management practices will be used to control nonpoint sources of phosphorus in the basin. Jefferson County has enacted a grading permit system and erosion control program, Section 11 of Jefferson County Zoning Resolution No. CC91-762, "Grading Permit and Erosion and Sediment Control", effective January 1, 1992, which applies to many activities in the county. The Commission will review the performance of county and local entities in the basin in implementing erosion and sediment controls through triennial review of this regulation. Where an entity in the Bear Creek Basin is issued a permit under authority of Environmental Protection Agency Regulations 40 CFR 122, 123, and 124, "National Pollutant Discharge Elimination System Permit Application Regulations for Stormwater Discharges", as amended, such permits will define stormwater management requirements which may include measures to control phosphorus from point sources of stormwater. Management of urban runoff and control of sediments is expected to reduce the nonpoint source loading of phosphorus to the reservoir.
The Bear Creek Basin Clean Lakes study indicates there is a substantial nonpoint source loading of nutrients in the basin in areas where there are only very small wastewater point sources or no point source discharges. The study estimated that there are about 6,500 individual sewage disposal systems (ISDS) in the basin with an estimated 1.6 million gallons per day of sewage flow in the individual systems. The use of ISDS for wastewater disposal in the basin is predicted to increase by 30 percent from 1989 -2010. The Clean Lakes study used selected literature information to predict ISDS nonpoint loadings for planning purposes. The Commission believes that specific measurement of ISDS loading and septic system treatment performance needs to be done in order to quantify ISDS impact on the nonpoint source phosphorus loading in the basin. Jefferson County, municipalities, and districts in the basin are encouraged to jointly design and conduct an ISDS study to get better information on ISDS nutrient loading so that the Commission can evaluate the impacts at the first triennial review of this regulation and recommend control strategies, which may include additional criteria in Jefferson and Clear Creek County regulations for approval of new ISDS or upgrade of existing ISDS. The protocol for any ISDS study should be approved by the division and public participation in the scope and protocol of the study is encouraged.
Water Quality Monitoring
Section 4.6.5 on the monitoring of phosphorus is required so that the phosphorus control measures in the basin and in-lake management practices can be evaluated as to effectiveness in improving the water quality of Bear Creek Reservoir. This requires that the major inflow streams to the reservoir, Turkey Creek and Bear Creek, be monitored for nutrient loadings and other appropriate parameters, as well as in-lake water quality monitoring which measures the physical, chemical and biological status of the reservoir. The monitoring procedures shown in Appendix A provide for water quality assessment of the basin and a quality assurance/quality control plan for the monitoring program. The basin monitoring program may be changed periodically with review and approval by the division.
The Commission requires that an annual report be submitted which summarizes information on water quality in the Bear Creek Basin. This provision provides for oversight of the monitoring program as well as documentation of the implementation of phosphorus controls required by this regulation. The annual report will help the Commission determine if the classified beneficial uses of the reservoir are being attained.
5 CCR 1002-74.10