5 Colo. Code Regs. § 1002-72.20
The provisions of sections 25?8?202(1)(c), (h) and (2); 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 sections 24?4?103(4) C.R.S., the following statement of basis and purpose.
BASIS AND PURPOSE:
The regulations were amended regarding land application of treated wastewater.
[Section 4.2.2] First, consistent with Section 6.15.0, et seq., 5 CCR 1002-2, these regulations now distinguish between the two types of land application: land disposal and land treatment.
[Section 4.2.3] The regulations reflect that wasteloads for all sources represent total permissible loads to the Reservoir, according to the 1984 modeling. The phosphorus standard was adapted for Cherry Creek Reservoir so the modeling has considered loads to the Reservoir not the Basin, as the limiting factor. Phosphorus which may be contributed to the Basin is either removed or controlled in the Basin and, therefore, would not affect the Reservoir wasteloads. The regulation was clarified to accurately reflect that the wasteloads are for the Reservoir.
[Section 4.2.4] The modification to the table in section 4.2.4.1 is made to harmonize the control regulation with a consolidation of the wastewater service areas of the Arapahoe Water and Sanitation District and the Cottonwood Water and Sanitation District which has been incorporated in the approved Clean Water Plan for the basin.
[Section 4.2.4] This regulation was modified to set forth the formulas that are used for calculating phosphorus concentrations and for calculating wasteloads from point source dischargers. The calculations clarify how the monthly volume of total effluent will be measured and how analytical results of effluent samples will be incorporated into the formulas.
[Section 4.2.4] For dischargers utilizing land treatment, the land application is an important step in their final treatment process, reducing the concentration of pollutants in the effluent and providing uptake for nutrients. Therefore, for dischargers utilizing land treatment, the quantity and quality of the effluent is determined from the effluent percolate that reaches lysimeters placed in the land application area.
Generally, for land application sites the treated effluent is land applied at agronomic rates. When effluent is applied at agronomic rates no water reaches the lysimeters, so the return flow and phosphorus concentrations are zero. Although the fields or land application areas are uniformly irrigated with effluent, on occasions some of the lysimeters will be dry and others have return flow. A percentage of those lysimeters recording flow, even though other lysimeters in the same field were dry and reported no phosphorus concentrations, have had effluent concentrations exceeding 0.2 mg/l. Thirty-day average phosphorus concentrations exceeding 0.2 mg/l have been reported in violation of phosphorus limits.
[Section 4.2.4] For land disposal, the discharger does not account for any reductions in volume or nutrient uptake resulting from the land application. Therefore, dischargers using land disposal will measure the effluent quantity and quality at the wastewater treatment plant, after treatment, but before land application.
[Section 4.2.5] The regulation has been amended to allow a 30-day flow-weighted average phosphorus concentration for dischargers using land treatment of 1.0 mg/l total phosphorus. The regulations maintain the phosphorus concentration limit for direct dischargers and dischargers using land disposal at .2mg/l as a 30-day average, and .5 mg/l as a daily maximum concentration. The 1.0 mg/l total phosphorus limit is consistent with the phosphorus concentrations allowed in the Bear Creek and Chatfield Basin Control Regulations, two other phosphorus limited reservoirs in the state. It is understood that in order to reach permitted hydraulic capacities it may be necessary for dischargers to maintain average phosphorus concentration levels less than 1.0 mg/l.
[Section 4.2.5] Estimated return flows from new land treatment sites must be calculated for the purpose of issuing site approvals and discharge permits. For the purpose of determining the phosphorus concentrations and wasteloads from new land treatment sites, when the discharger has an augmentation plan approved by Water Division One, District Court, State of Colorado, the augmentation plan will be used to calculate anticipated return flows. When a discharger for new land treatment sites does not have an approved augmentation plan that sets forth the means for calculating the return flows, the applicant will generally use the Soil Conservation Service Technical Manual Release No. 21, "Irrigation Water Requirements" (Rev. Sept.1970) and the Cottonwood curve for return flows to determine the estimated return flows. Upon actual land treatment of wastewater effluent, the return flows or effluent volume shall be the amount measured in the lysimeters and calculated by the formula.
[Section 4.2.6] The wasteload analysis and allocation for nonpoint sources includes stormwater, even that stormwater which is now subject to an NPDES permit. The nonpoint source load has been and remains 10,290 pounds of phosphorus annually. This load was determined assuming approximately 20,580 pounds of nonpoint phosphorus contributed to the Basin and that 50% of that phosphorus load would be removed or controlled through best management practices and water quality facilities. The regulation acknowledges that the load to the Reservoir is 10,290 pounds, however, it is still anticipated that loads to Cherry Creek Basin will be greater than 10,290 pounds but will be reduced or controlled by such means as are appropriate to reduce and maintain the total nonpoint source load to the Reservoir at 10,290 pounds per year or less.
[Section 4.2.6] The control regulation previously allowed a nonpoint source credit program, which is now further detailed. Phosphorus credits from nonpoint source projects may be granted to allocations to the reserve pool or the point source dischargers sponsoring the project provided that the projects demonstrate removal of nonpoint source phosphorus. The project sponsors will need to conduct appropriate water quality monitoring to demonstrate the quantity of phosphorus removed. Upon application by a project sponsor for nonpoint source phosphorus credits, the Authority will review the proposal and make recommendations to the Division regarding the grant of phosphorus credits. Phosphorus credits approved by the Division will be incorporated and reflected in the 208 Plan. At the next rulemaking hearing or triennial review of the regulation amendments to the regulation will be proposed to incorporate the credits.
PARTIES TO THE RULEMAKING HEARING
5 CCR 1002-72.20