5 Colo. Code Regs. § 1002-72.18
The provisions of 25-8-202(1)(c) and 25-8-205, C.R.S., provide the specific statutory authority for adoption of the attached regulatory amendments. The commission also adopted, in compliance with 24-4-103(4), C.R.S., the following statement of basis and purpose.
The Cherry Creek Reservoir Control Regulation imposes wasteload allocations for total phosphorus and also specifies effluent limitations for phosphorus. The wasteload allocations provide poundage limitations for major domestic dischargers, as well as for other types of point and nonpoint source discharges. (See sections 4.2.3 and 4.2.4)
The effluent limitations contained in sections 4.2.5 have been revised to require that point source discharges of phosphorus, for a 30-day average, shall not exceed 0.2 mg per liter throughout the year. This change was based on the following factors. Some major domestic dischargers in the Cherry Creek Basin, particularly those utilizing rapid infiltration for treatment and disposal of effluents, have encountered difficulties in meeting the 0.1 mg/l (October-March) and 0.05 mg/l (April-September) limitations previously contained in the regulation. In order to meet those limitations, the dischargers would have been required to construct new wastewater treatment facilities at considerable expense to their residents. When the Cherry Creek Basin Water Quality Management Master Plan was approved, it was assumed that these rapid infiltration systems, operating in their current configuration, would be able to achieve the 0.1/0.05 mg/l effluent limitations. Also, wastewater treatment facilities utilizing other systems, including land application, have encountered difficulties from time to time in achieving the effluent limitations. The master plan provided the basis for adoption of the effluent limitations previously contained in the regulation. Although the dischargers have rehabilitated their systems to improve the quality of their discharges, they have not been able to meet the 0.1/0.05 mg/l effluent limitations.
It should be noted that the wasteload allocations contained in the regulation have not been revised. The wasteload allocations dictate the maximum quantity (pounds) of phosphorus which may be discharged each year by each domestic wastewater discharger. In order to meet their wasteload allocations while discharging at a concentration of 0.2 mg/l phosphorus, hydraulic capacities for some or all of these facilities may be reduced in their discharge permit. All hydraulic capacities in future site approvals shall be determined using the annual phosphorus allocation and an effluent phosphorus concentration of 0.2 mg.l.
Where the applicant for a discharge permit or a site approval can demonstrate, to the Division's satisfaction, that the treatment process is capable of producing an effluent phosphorus concentration of less than 0.2 mg/l, on an annual or seasonal basis, the hydraulic capacity will be established on the basis of the demonstrated phosphorus concentration(s) and the annual allocation. Such demonstration must include, at a minimum, design or operating data which establishes that the process can attain the requested effluent quality over the full range of expected operating conditions during the period in question.
Because the total poundage of phosphorus discharge will continue to be regulated at the same level, the water quality of the reservoir is expected to be protected at the same level under the revisions to the regulation. Moreover, the revisions will allow the Cherry Creek Basin Authority to utilize its collective resources in a manner more beneficial to the water quality of the reservoir. If the revisions had not been made, costly new wastewater treatment plant improvements would have been necessary. The poundage allocation can be met in the short-term by allowing a less restrictive effluent limit and using more of the existing design capacity. Site approvals may require phosphorus concentrations of less than 0.2 mg/l if necessary to meet the wasteload allocation at the design capacity of the treatment facility. No new site approvals shall be granted which would allow construction of treatment facilities which would not meet their wasteload allocation. Under the revisions, however, the Authority will be able to focus on addressing nonpoint source control of phosphorus.
5 CCR 1002-72.18