5 Colo. Code Regs. § 1002-73.13
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 Chatfield Basin has been designated as the Chatfield Sub-watershed through the Denver Regional Council of Government's Clean Water Plan. The basin boundary has been modified to a watershed boundary with recognition of drainage from Park County. This control regulation only applies to the Chatfield Sub-watershed portion of the South Platte Watershed.
A modification of the definition of "Chatfield Basin Authority" was considered but not adopted. The proposed definitional change would have described industrial dischargers as "ex-officio members." The purpose of the proposed modification was to describe the status of industrial dischargers such as Lockheed Martin Astronautics, who are assigned a phosphorus wasteload allocation and work closely with the Authority in an advisory capacity, but are not full member signatories to the intergovernmental agreement creating the Authority. A description of the role of these industrial dischargers was deemed unnecessary in this control regulation. The relationship between industrial dischargers and the Authority is already defined by the Chatfield Basin Authority Agreement.
The previous control regulation did not define the water quality conditions which established the reservoir total phosphorus load at 59,000 pounds per year. This 59,000 pound per year total phosphorus load is based on the reservoir's capacity to assimilate total phosphorus from all sources and not exceed the reservoir standard of 0.027 mg/l. The 59,000 pounds per year is related to a one in ten year recurrence low flow condition (Q10) which corresponds to 261,000 ac-ft per year of flow through the reservoir. Therefore, the allowable total phosphorus pounds reaching the reservoir which will not cause an exceedence of the total phosphorus standard is flow dependent.
The point sources of total phosphorus from the Chatfield Sub-watershed are limited to 7,358 pounds per year. The remaining annual total phosphorus load of 51,642 pounds is attributable to a combination of nonpoint and background sources derived from the entire South Platte Watershed. Since limited water quality data exists on the distribution of total phosphorus in the watershed caused by precipitation to the reservoir and base-flow in South Platte River portion of the watershed, a wasteload allocation specific to background sources can not be reasonably estimated from available data. As a result, the control regulation should not separate the total phosphorus allocation between background and nonpoint sources. The Chatfield Basin Authority should evaluate these background and nonpoint source allocations and report to the Commission at the 1998 Triennial Review.
The Authority recommends that wasteload allocation processes be consistent between adopted basin or watershed control regulations. The land disposal and land application wasteload definitions and determinations as adopted in the Cherry Creek Basin Control Regulation have been incorporated into the Chatfield Sub-watershed Control Regulation. This will allow the Authority and the Division to more efficiently administer land disposal or land treatment wasteloads.
A new section has been added to allow point source to point source trading for total phosphorus. A wastewater treatment facility could be authorized to exceed the 1.0 mg/l effluent limit or allocated wasteload for phosphorus, if an alternate permitted facility makes an equivalent reduction in either effluent limit or wasteload allocation. This provision will allow for flexibility among permitted facilities to accommodate unexpected growth and development.
The Chatfield Basin Authority submitted a nonpoint source compliance report to the Water Quality Control Commission in January 1996 which was approved. A summary report defines the nonpoint source management program and ongoing activities of the Authority. The Authority will continue to maintain a nonpoint source management program. Structural best management practices constructed within the watershed will be evaluated by the Authority to determine the total phosphorus removal efficiencies. This efficiency data can be used in assigning nonpoint source credits to point sources as part of a phosphorus trading program.
A change to the annual report from the Authority to the Commission was made. The annual report will be made available to the Commission on or before May 15 of each year which covers the pervious calendar year.
PARTIES TO THE RULEMAKING HEARING
SEPTEMBER, 1996
5 CCR 1002-73.13