5 Colo. Code Regs. § 1002-72.27
The provisions of 25-8-202(1)(c), and (2) and 25-8-205, C.R.S. provide the specific statutory authority for adoption of these regulatory amendments. The Commission also adopted, in compliance with 24-4-103(4) C.R.S., the following statement of basis and purpose.
At the same time that these changes were adopted in Regulation #72, the Commission adopted consistent changes in Regulation #38, Classifications for Numeric Standards, for South Platte River Basin, Laramie River Basin, Republic River Basin, Smoky Hill River Basin (5 CCR 1002-38).
BASIS AND PURPOSE
As a result of the data and analyses brought forward as part of the March 2009 Rulemaking Hearing, the Commission revised the Reservoir Control Regulation, adopting with relatively minor changes revisions proposed by the Cherry Creek Basin Water Quality Authority. The Commission rejected revisions proposed by the Parker Water and Sanitation District. This statement provides an analysis of the basis and purpose for changes to each of the major sections of the control regulation. The major substantive revisions include removal of all TMAL related components from the regulation, establishment of a concentration-based watershed management approach for phosphorus control, establishment of a discharge effluent limit of 0.20 mg/l for drinking water treatment facilities in the Basin, and establishment of a three-tiered stormwater system for development and redevelopment.
Background and Overview
Based on the 2000-2001 rulemaking hearings, the Commission established and maintained a phased phosphorus TMAL of 14,270 pounds for the Cherry Creek Reservoir, with allocations of the TMAL divided among nonpoint point sources, background sources, wastewater facility sources, industrial process wastewater sources, and individual sewage disposal systems.
Under the 2001 revisions, the Commission directed the Cherry Creek Basin Water Quality Authority (Authority) to proceed expeditiously in implementing both technology and information based controls necessary to meet the new water quality standards and protect the designated uses. The Commission further noted that additional investigations would be necessary to support the calculation of a new TMAL, understanding that additional point source and nonpoint source control efforts would be necessary in the future. To this end, the Authority and its member agencies completed fourteen special studies, collected monitoring data, constructed and maintained Pollutant Reduction Facilities (PRFs), improved water quality facilities in Cherry Creek State Park and surrounding sub-watersheds, and worked closely with interested parties in the watershed to control phosphorus in the Cherry Creek Basin (Basin).
At the same rulemaking hearing, the Commission also retained a Total Maximum Annual Load (TMAL) of 14,270 pounds of total phosphorus to the Reservoir provided in Regulation #72, with a consideration that this be a "phased TMAL" while the Authority completed the requested studies. An inlake phosphorus goal of 40 ug/L (July through September seasonal average) would result in the attainment of the chlorophyll a standard.
The Authority has provided data to the Commission and Water Quality Control Division (Division) from studies conducted since 2000 indicating that the concentration of phosphorus in Reservoir inflows has a more direct correlation to chlorophyll a levels in the Reservoir than does the phosphorus load. As a result, by controlling total phosphorus through a management strategy approach at the inflow to the Reservoir, it is expected that water quality will continue to improve in the Reservoir.
Definitions
The following changes or additions were made to terms of general applicability. The definitions "Concentration," and "Concentration Based Control of Phosphorus," "Enhanced BMP," "Flow Weighted Concentration," and "Pollutant Reduction Facility" were included to explain the use of those terms in Section 72.3 concerning the Authority's approach to control phosphorus in the watershed and ultimately in Cherry Creek Reservoir. The definitions of "Phosphorus Bank," "Reserve Pool," "Trading Ratio," "Trading Program," and "Wasteload Allocation" were stricken from the regulation, since a concentration-based approach to phosphorus control is not based on mass of phosphorus removed. Additionally, definitions and terminology have been modified to consistently reflect the move from a load-based to a concentration-based approach to phosphorus control.
Removal of TMAL Requirements
The Commission recognizes that the appropriate designated projects conducted to support Phase I of the TMAL program have been completed and therefore struck those requirements from the regulation. Additionally, based on comments received from EPA and the Division, the Commission struck all Total Maximum Annual Load (TMAL) language from Regulation #72 (Control Regulation). As necessary, the Commission will direct the Division and the Authority to work with EPA in developing a separate TMAL document for the Reservoir.
Concentration-based Management Strategy for Phosphorus Control in the Basin
The Commission revised this section to recognize the Authority's ongoing phosphorus control measures in the Cherry Creek watershed. Watershed and reservoir modeling results have shown that, although population growth and surface flows have increased in the Basin, the total phosphorus concentration in the inflow to the Reservoir has remained relatively constant. These results provide a basis for the Commission to conclude that point and nonpoint source controls for total phosphorus (point source treatment facilities, PRFs, 208 agency processes, and permitted MS4 activities) are successfully reducing total phosphorus concentrations in stormwater and surface water flows to the Reservoir.
This Section also includes additional language to clarify that concentration-based source control projects address both nonpoint source projects and regulated stormwater projects. This Section further deletes TMAL related language. Finally, definitions and terminology have been modified to consistently reflect the move from a load-based to a concentration-based approach to phosphorus control.
Point Source Effluent Limit Modifications
Based on the evidence provided during this hearing process, the Commission has revised this section to be consistent with the current Reclaimed Water Control Regulation, Regulation #84. It has also concluded that it was appropriate to set a phosphorus concentration limit for any effluent discharged in connection with drinking water treatment equal to that of the source water. Therefore, this section was revised to include a phosphorus concentration limit of 0.20 mg/l for any effluent discharged in connection with drinking water treatment.
In light of the slight phosphorus concentration variability observed in the Cherry Creek alluvium, the Commission has revised this section to authorize the Division, at the request of permittees, to allow up to a 90-day averaging period for this limit in individual CDPS permits. This provides flexibility to those dischargers that wish to request a longer averaging period and is consistent with the approach used to translate other water quality standards into effluent limits.
In this section 72.4 , the Commission revised this section to recognize that wasteload allocations are not an appropriate approach to phosphorus control in the Cherry Creek watershed for the control of chlorophyll a in the Reservoir. Language in this section, and throughout Regulation #72, has been changed to clarify the Authority's approach to phosphorus control and to remove TMAL related language. References to the phased TMAL, the Trading Program, and mass-based control of phosphorus have been stricken and replaced with the Authority's approach to phosphorus control, to be consistent with revised Section 72.3 . Additionally, definitions and terminology have been modified to consistently reflect the move from a load-based approach to a management strategy approach to phosphorus control.
Because section 72.5 now implements a concentration-based phosphorus control management strategy in the Cherry Creek watershed, the Commission finds that the current trading program is no longer applicable as written. Accordingly, the Commission has stricken the language in this section, but leaves the section as a placeholder for future consideration.
Stormwater Permit Requirements
The Commission's 2001 revisions to the stormwater permitting requirements in section 72.7.2 required installation and operation of Best Management Practices (BMPs) that provide water quality capture volume (WQCV) for "all areas of land disturbance." The Commission acknowledges that over the past eight years, the practical outcome of this revision required that detention ponds, normally designed to reduce developed runoff peak flows to pre-developed levels, also include additional volume and outlet controls that would capture and detain normal runoff for up to 40 hours to reduce sediment and nutrient load discharges from the detention ponds.
Several new definitions were included to correspond with the recent revisions to Regulation #61 (5 CCR 1002-61). These definitions are intended to clarify the distinction in the application of PRFs and BMPs for various categories of sources. References to load were replaced with concentration. Titles have been added to several subsections in the regulation for references to other subsections for clarification. In some cases, the Commission finds that modifications and subsection reformatting efforts were warranted to provide further clarification. These efforts do not result in any substantive change to the subsections.
The remaining substantive revisions to the stormwater permit requirements revolve around the post-construction development and redevelopment requirements outlined in Regulation #61 (5 CCR 1002-61) and stream preservation area considerations. For post-construction development and redevelopment, the Commission adopts a three-tiered approach to stormwater management BMPs to coincide with the requirements found in Regulation #61 (5 CCR 1002-61), while specifically addressing concerns within the Basin. In this vein, the Commission also replaces the previous reference to permanent BMPs found in section 72.7.2 with post-construction BMPs and replaces the reference to construction BMPs with erosion and sediment controls. The Commission also excluded certain limited activities identified as insignificant contributors to water quality degradation from regulation under this section.
With regard to stream preservation areas, the Authority finds that the 100-year floodplain is a reasonable and more easily administrable substitution for alluvium, since a floodplain is more precisely defined. Accordingly, the Commission incorporated language to clarify the Cherry Creek alluvium as being defined by the identified 100-year floodplain of Cherry Creek.
Over the last eight years, the Authority and permittees determined that there were certain types of land disturbances that would not result in water quality degradation and that greater flexibility in BMP selection or requirements was needed to preserve the integrity of the stream preservation area. Thus, the Commission identified specific activities where a land disturbance in a stream preservation area would not be detrimental to water quality, such as construction of a BMP in accordance with this regulation.
Nutrient Controls and Monitoring, Reporting, and Commission Review
Because this Control Regulation is no longer the source of TMAL requirements, references to the Trading Program and mass-based control of phosphorus have been stricken. Finally, definitions and terminology have been modified to consistently reflect the removal of TMAL requirements and the implementation of a concentration-based management strategy for phosphorus control.
The Commission finds it necessary for the Authority to continue to monitor and maintain all nonpoint source runoff PRFs for total phosphorus concentration controls, as well as identify opportunities to control phosphorus in the watershed to reduce total phosphorus concentrations in the Reservoir inflow. Individual monitoring of BMPs need not occur because PRF monitoring upstream and downstream of the project effectively measure the accumulative benefits of BMP implementation in the upstream watershed.
Rejection of Proposal from Parker Water and Sanitation District
Parker Water and Sanitation District proposed to modify Regulation #72 by doubling the effluent phosphorus limits that apply to three categories of wastewater discharge - direct dischargers, land application with return flow factor, and land application with lysimeters. Parker asserted that the change would result in no "meaningful increase in the total phosphorus concentration in the Cherry Creek inflows" and "no significant difference in Reservoir chlorophyll levels." Based on evidence submitted in this rulemaking, the Commission has decided not to adopt the Parker proposal.
The Commission decided not to adopt the proposal because the revised water quality standards depend on the conclusion that all feasible measures have been employed to control release of phosphorus from the watershed. Since the effluent phosphorus limits in the CCBWQA proposal are the same limits that have been in place for almost a decade, it is clear that dischargers have been able to meet those limits. Thus the existing limits are clearly feasible. Relaxing treatment requirements would be inconsistent with the basis for revising the standards, which is the conclusion that strict adherence to current water quality protection efforts will result in improved water quality in the long term.
PARTIES TO THE RULEMAKING
5 CCR 1002-72.27