5 Colo. Code Regs. § 1002-33.14
The provisions of 25-8-202(1)(b) and (2), and 25-8-204, C.R.S., provide the specific statutory authority for this amendment.
After hearings held in late 1979, the Commission classified Oak Creek, from the point of discharge of the Oak Creek wastewater treatment plant to the confluence with the Yampa River, as Aquatic Life Class 1 -Cold. At that time, the Commission also adopted an array of numeric standards to protect aquatic life. No ammonia standard was designated for the segment because available evidence indicated that not only was there a limited variety of aquatic life below the Oak Creek drain, but the short distance between the treatment plant and drain in relation to the total segment made it inappropriate to establish an ammonia standard at that time.
In reviewing Colorado's water quality standards, the U.S. Environmental Protection Agency (EPA) noted the lack of an ammonia standard on this segment of Oak Creek and withheld approval of the segment until the Commission either reviewed this segment to determine an appropriate ammonia standard of more fully documented the justification for no standard. The purpose of this hearing is to satisfy EPA's concerns and gain approval of the classifications and standards for the segment.
Fisheries data which was not available at the 1979 hearing indicate that the fishery in Oak Creek is more extensive than originally thought. The data indicates numerous sculpin, dace, and suckers present in the stream. Rainbow trout have been stocked at times in the past by the Colorado Division of Wildlife. The evidence indicates that this stocking is not likely to occur in the future.
In order to protect the resident fish, i.e. sculpin, dace, and suckers, an unionized ammonia standard of .05 mg/l is proposed. This level is based on a site-specific calculation of the 30-day average criterion which should protect the resident species. This calculation is provided in the Site-Specific Criteria Guidelines, U.S. Environmental Protection Agency 1982b. The 30-day criterion was calculated seasonally by a Region VIII EPA computer program using seasonal mean temperature and pH, the reproducing species present in the Creek, and the national acute to chronic ratio of 16. For comparative purposes, the 30-day seasonal criteria calculated for Oak Creek, Segment 7 using combinations of species is given below:
Season | Oak Creek with Rainbow Trout Acute = 16 Chronic | Oak Creek with Salmonids Acute = 16 Chronic | Oak Creek without Rainbow Trout Acute = 16 Chronic | Oak Creek without Rainbow Trout Acute = 25*Chronic |
Nov.-Feb | .020 | .027 | .046 | .028 |
Mar.-Jun. | .034 | .046 | .075 | .048 |
Jul.-Oct. | .034 | .046 | .075 | .048 |
* 25 is acute/chronic for White Sucker which is higher than national value of 16.
It should be noted that the species of suckers present in Oak Creek is the Bluehead for which there is no ammonia toxicity data available and, for that reason, the Division believes that using the national acute-chronic ratio of 16 is probably most appropriate to Oak Creek. However, it is felt that a .05 mg/l unionized ammonia standard should be applied year-round to insure protection of all the reproducing species present in the Creek. This would provide protection to the Bluehead sucker during the critical season (low-flow, temperature, pH) of July-October should the acute-chronic ratio for that species be nearer 25 than 16.
FISCAL IMPACT STATEMENT, OAK CREEK
The beneficiaries of this regulation will be those persons who enjoy the recreation and aesthetic values of Oak Creek and the upper reaches of the Yampa River that these ammonia limits are designed to preserve. While a monetary value has not been estimated for these beneficial uses, past experience has demonstrated them to be quite substantial.
The proposed ammonia limitations are not likely to result in higher costs to the users of the Oak Creek wastewater system, because it is anticipated that good secondary treatment processes should be sufficient to achieve these limits as translated into the Town's permit. Though it is therefore highly unlikely that system users would have to bear the significant costs associated with installing ammonia removal equipment, the Town may have to utilize a higher technology, short of ammonia removal, with the associated initial capital costs. If any, these costs would be manifest as increased user fees, but it is possible that a portion of such expenditures would be offset by a federal construction grant.
5 CCR 1002-33.14