Code of Colorado Regulations
1000 - Department of Public Health and Environment
1002 - Water Quality Control Commission (1002 Series)
5 CCR 1002-71 - REGULATION NO. 71 - DILLON RESERVOIR CONTROL REGULATION
Section 5 CCR 1002-71.10 - STATEMENT OF BASIS, SPECIFIC STATUTORY AUTHORITY AND PURPOSE NOVEMBER, 1995 RULEMAKING

Current through Register Vol. 47, No. 5, March 10, 2024

The provisions of sections 25-8-201(1)(c) 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 24-4-103(4) C.R.S., the following statement of basis and purpose.

BASIS AND PURPOSE

This hearing was requested by the Summit Water Quality Committee. The purpose of the request was to make several changes to the regulation. The first was to update point source phosphorus allocations to reflect point source--nonpoint source tradeoffs that have occurred and to remove point source allocations for minor domestic facilities which have been connected to local sewer systems. These specific changes include adding eleven pounds to the Breckenridge Sanitation District's phosphorus allocation in the regulation as credit for removing the nonpoint source septic system in the LakeView Meadows subdivision. These credits are already reflected in the Breckenridge Sanitation District's CDPES discharge permit. An additional 0.5 pounds of credit is given for the Breckenridge Sanitation District's participation in the removal of the nonpoint source septic system associated with the Breckenridge Ski Areas Peak 8 Restaurant.

Another change in point source phosphorus allocations results from combining the allocations for the Quandry and Skier's Edge Condominiums, since these units are now served by a single wastewater treatment facility and have a single discharge permit. The other changes are the removal of the allocations for septic systems for Breckenridge Ski Areas Peaks 8 and 9, as these areas are now serviced by the Breckenridge Sanitation District's main treatment plant, and removing the allocations for the septic systems serving the Ski Tip Ranch and Snake River Saloon because these areas are now serviced by the Snake River Wastewater Treatment Plant.

The second significant change in this rulemaking was to require that the determination of point source phosphorus allocation credits for nonpoint source controls, as outlined in Section 4.1.5 , will be based on site-specific data on the amount of nonpoint source phosphorus controlled or on use of a water quality modeling approach which approximates the phosphorus poundage which has been reduced. Previously these credits were to be "determined by guidelines or regulations adopted by the Commission". However, the guidelines which have been used address only the procedural aspects of implementing a point-nonpoint source phosphorus trade. No methodology for quantifying credits for nonpoint source controls has been provided. Much of the rationale for adopting the in-lake standard and associated phosphorus allocations was based on information contained in the "Clean Lake Study of Dillon Reservoir in Summit County, Colorado" which includes the Lake Dillon Water Quality model. It is therefore appropriate and consistent to determine credits using the loading equations contained in this model, other appropriate modeling of phosphorus reductions, or site-specific data for the nonpoint source control project which is the basis for the point source credit request.

Since the Clean Lakes Study was completed the model has been updated to reflect information generated by the on-going local water quality monitoring efforts. As a result of re-calibration of the model it is estimated that a total annual phosphorus load in excess of 8,350 pounds, in combination with a water yield from the watershed of 212,000 acre feet, will result in exceeding the water quality standard of 7.4 ug/l total phosphorus, which is a growing season average for the months of July, August, September, and October. Local water quality management efforts are focused on preventing phosphorus loads from exceeding this quantity. Because it is likely that monitoring will continue and that the model will be recalibrated in the future to reflect additional information, local entities requested that the credits be based on the most recent version of the Lake Dillon Water Quality Model or a similar water quality, loading-based model that fulfills the same, basic elements. The revisions adopted assure that this option is available, although not mandated. The Division is required to review and approve any credits, if the request meets the criteria outlined in 4.1.5 (3).

The third significant change made in this regulation revision deals with Section 4.1.6 Control of New Nonpoint Sources. Language is now included which states that the point source phosphorus allocations are based pm the assumption that county and local governments require controls that achieve pound for pound mitigation for all new nonpoint sources of phosphorus. The previous language in this section was unclear as to the intent for nonpoint phosphorus control. Language was added to clarify that if the Division determines that nonpoint source controls do not appear to be adequate to prevent exceedances of the Dillon Reservoir phosphorus standard, then the Commission may reconsider the point source allocations. Any evaluation data gathered by the Division on nonpoint source controls in Summit County will be reported to the county or appropriate local governments. The sentence in the original rule about the Division conducting periodic site inspections if at all possible was deleted as unnecessary, although the Commission intends that the Division will monitor implementation of the rule to the extent that resources permit.

The Commission also chose not to adopt in this hearing two proposals included in the hearing notice. The original proposal would have established a "reserve pool" minor domestic point source allocation for phosphorus. Discussion at the hearing raised issues regarding the appropriate source of phosphorus for a reserve pool allocation, how the reserve pool would be administered, and the disposition of removed allocations. Following further input from the Division and the parties, the Commission has determined that is not necessary or appropriate to establish a reserve pool at this time, particularly considering the difficulties in resolving these issues.

The second proposal that the Commission chose not to adopt would have established a point source to point source transfer mechanism for phosphorus allocations. Following further input from the Division and the parties, the Commission has determined that it is not necessary or appropriate to establish such a transfer mechanism at this time, particularly considering unresolved issues regarding the potential impact of such a transfer mechanism on the total point source phosphorus loadings to the reservoir.

PARTIES TO THE RULEMAKING HEARING