5 Colo. Code Regs. § 1002-38.42
The provisions of 25-8-202(1)(b), 25-8-204, and 25-8-402, C.R.S. provide specific statutory authority for adoption of this regulatory amendment. The Commission also adopted in compliance with 24-4-103(4), C.R.S. the following statement of basis and purpose.
The Cities of Westminster and Thornton submitted a rulemaking proposal to the Water Quality Control Commission in August, 1988 that included a numeric standard for total phosphorus in Standley Lake, Segment 2 of Big Dry Creek, South Platte Basin. The Commission did not adopt the proposed standards but requested that the parties jointly agree on a scope of work and funding mechanism to develop any necessary additional data to determine appropriate permanent water quality standards to protect Standley Lake as a water supply. Parties to the 1989 hearing, which included Westminster, Thornton, Northglenn, Arvada, Golden, and Jefferson County, commissioned a study by the U.S. Geological Survey to develop additional data on Standley Lake in 1989 and 1990. In September, 1993, the Cities of Westminster, Thornton, and Northglenn (the Standley Lake Cities) submitted a rulemaking proposal to the Commission for a narrative water quality standard for phosphorus and total inorganic nitrogen, and a control regulation for point and nonpoint sources of nutrients in the Standley Lake Drainage, consisting of the Upper Clear Creek Basin; that portion of the Lower Clear Creek Basin tributary to Standley Lake and to the three canals (Farmers High Line Canal, Church Ditch, and Croke Canal) supplying Standley Lake; and Standley Lake itself (the Standley Lake Drainage).
In December, 1993, the Clear Creek Watershed Management Agreement (Agreement) was developed and signed by local governmental and private entities that would be affected by the proposed standards and control regulation. The Agreement provided for submission by the parties of an alternative rulemaking proposal for a narrative standard for Standley Lake. The entities that are party to the Agreement include the Upper Clear Creek Basin Association, the City of Golden, the City of Arvada, Jefferson County, the Jefferson Center Metropolitan District, the City of Westminster, the City of Thornton, the City of Northglenn, the City of Idaho Springs, Clear Creek County, Gilpin County, the Blackhawk-Central City Sanitation District, the City of Blackhawk, Central City, the Town of Georgetown, the Town of Empire, the Town of Silverplume, the Central Clear Creek Sanitation District, the Alice/St. Mary's Metropolitan District, Clear Creek Skiing Corporation, Henderson Mine, the Church Ditch Company, the Farmers High Line Canal and Reservoir Company, and the Farmers Reservoir and Irrigation Company.
The Commission adopted the alternative proposal for a narrative standard, which provides that the trophic status of Standley Lake be maintained as mesotrophic. The purpose of this narrative standard is to protect the classified beneficial uses of Standley Lake by maintaining the existing trophic condition. Trophic state or condition is a descriptive classification based on lake nutrient status and the level of biological productivity. Lakes with few available nutrients and a low level of biological productivity are termed oligotrophic; those with high nutrient levels and high productivity are termed eutrophic. Lakes that are in between oligotrophic and eutrophic are termed mesotrophic.
Data collected over the last nine years for chlorophyll a for Standley Lake indicate that the Lake has been mesotrophic over that period. The trophic status of Standley Lake is based on the average magnitude of trophic state indicators measured during the period from March 1 through November 30. The various entities involved in this proceeding have different theories as to the mechanisms determining the water quality in Standley Lake. The Standley Lake Cities believe that there is a risk of algal growth that would impact water supply uses of the Lake in its current state. In any event, the trophic status of the Lake should be maintained at mesotrophic to minimize the risk of use impairment.
The Commission has adopted numeric phosphorus standards for three other Colorado lakes to maintain existing trophic condition. The narrative standard approach is used here as an alternative that provides flexibility in establishing nutrient control and reduction strategies in the Standley Lake Drainage. This flexibility is needed due to uncertainty in identifying significant nutrient contributors to the Lake, in predicting the specific in-lake nutrient concentrations required to maintain the mesotrophic condition, and in predicting Lake response to algae growth from nutrient reduction.
The Commission found that requirements in the Agreement to conduct water quality monitoring of the Standley Lake Drainage, as well as implementation of best management practices and controls on a voluntary basis, provide a reasonable approach to reducing nutrient loading in the Standley Lake Drainage and maintaining the mesotrophic condition of the Lake. The Commission's intent is that the maintenance of a mesotrophic status be monitored in a cooperative effort by entities in the Standley Lake Drainage and that no new or more stringent effluent limitations or nutrient wasteload allocations be included in wastewater discharge permits for point sources in the Clear Creek Basin.
It is the intent of the Commission and the parties to this hearing that the results of additional testing and monitoring, and of implementation of certain best management practices and controls on a voluntary basis will be summarized and reported to the Commission annually until the next triennial review of this narrative standard in 1997. The first such annual report shall be made available to the Commission in April of 1995. If at the Triennial Review in 1997 it appears that the narrative standard is not being met, and that substantial progress in reducing nutrient loads to the Lake is not being made, additional measures may be required in future rulemaking proceedings. Such additional measures could include numeric standards and/or effluent limitations for phosphorus and/or nitrogen in the Upper Clear Creek Basin, and additional best management controls in Standley Lake.
PARTY STATUS LIST February 8, 1994
5 CCR 1002-38.42