5 Colo. Code Regs. § 1002-61.73
The provisions of 25-8-202(1)(d) and (2), 25-8-401, 25-8-501, and 25-8-502, C.R.S., provide the specific statutory authority for the amendments to this regulation adopted by the Water Quality Control Commission (Commission). The Commission has also adopted, in compliance with 24-4-103(4) C.R.S., the following statement of basis and purpose.
BASIS AND PURPOSE
As part of the hearing on Regulation #22, the Site Location and Design Approval for Domestic Wastewater Treatment Works, the Commission made changes to a few terms in section 61.2 , "Definitions". The Commission made changes to the definitions of 'design capacity', 'throughput' and 'treatment capacity' to remove conflicts with definitions in Regulation #22 and to provide better alignment with the federal permitting framework terms.
The Division's proposal changes the term 'design capacity' to 'design flow' in Regulation #61 since the term 'design capacity' in Regulation #22 already aligns to the statute and since Regulation #61 incorporates the term 'design flow' in order to align with the Federal Clean Water Act Regulations, which use that term in describing the threshold for development of pretreatment programs and calculating permit conditions. The Division further proposes to add language to Regulation #61 to clarify that, when an equalization basin, reuse, or reclaimed water exist, the design flow may not accurately represent a facility's effluent discharge flows, and a lower value may be used in calculating permit conditions. When there are multiple outfalls, portions of the design flow or the entire design flow may be designated to specific outfalls in certain circumstances. The added language related to these circumstances does not change the threshold for development of a federal pretreatment program under 40 CFR § 403.8 or the applicability of any federal pretreatment requirements. Following this rulemaking, the Division plans to work with stakeholders to develop guidance that will further address design flow and design capacity issues, particularly circumstances where tiers or multiple design capacities may be appropriate.
The Commission also approved a change to Regulation #61.4(1) (permit application requirements) that, consistent with the approved redefinition of PELs to Water Quality Planning Targets in Regulation 22.2, would allow new permittees to elect to first obtain a permit, and then to obtain site approval. Together, the proposed changes to Regulations #22.2(25) and #61.4(1) would allow permittees in some situations to use an existing or new permit as the Water Quality Planning Target for site approval. These situations would not include instances where site approval or the information contained in a site application is needed first in order to determine whether the imposition of permit conditions can, per Regulation 61.8(1), ensure compliance with the applicable water quality requirements of all affected States or prevent violations of control regulations. The Division anticipates this may be the case for some groundwater permits. Reliance on an existing permit would also not be appropriate for site approval for a facility change that, standing alone, is likely to affect the facility's existing permit limits or the facility's ability to meet those its limits.
The term throughput, within this regulation, specifically relates to domestic wastewater treatment works. The term 'throughput' was modified to remove the phrase "/or" to ensure that both hydraulic and organic loadings were considered since hydraulic residence or flow rate directly impacts the treatment capability of organics through the treatment process. Additionally, a domestic wastewater treatment works must often treat for more than organic constituents. Unit treatment processes targeting non-organic pollutants are also impacted by hydraulic residence or flow rate. In most cases, the organic strength is a representative indicator of the overall strength of the domestic wastewater, including non-organic pollutants.
The Commission deleted the term 'treatment capacity' to more clearly align with Colorado Water Quality Control Act. As previously defined, the term 'treatment capacity' was linked to the Regulation #22 term 'design capacity'. With the potential for 'design capacity' (Regulation #22) to not equal 'treatment capacity' in all cases, the Commission more correctly aligned the term 'treatment capacity' to the term 'throughput' since these two terms function jointly in the evaluation of and triggering actions related to planning and construction of domestic wastewater treatment plant expansions. This change means that the planning and expansion requirements will trigger when throughput and treatment meets specific thresholds relative to the design capacity. The design capacity represents the treatment capability of the domestic wastewater treatment works. The throughput and treatment represent the amount of loading and treatment being utilized based on current loading conditions. "Treatment capacity" was removed in order to align the language of the construction trigger provisions with the language of the WQCA as part of the Commission's goal to harmonize the use of the terms design capacity/design flow across the Commission regulations, the Colorado Water Quality Control Act, and the federal regulations.
The Commission revised or replaced these terms throughout the remainder of Regulation #61.
The Commission modified section 61.14 from "individual sewage disposal systems (ISDS)" to "on-site wastewater treatment systems (OWTS)" to reflect the change resulting from the 2012 modifications to the governing statutes in the Colorado On-site Wastewater Treatment Systems Act, C.R.S., 25-10-101, et seq.
5 CCR 1002-61.73