Statutes, codes, and regulations
Colorado Administrative Code
Department 1000 - Department of Public Health and EnvironmentDivision 1002 - Water Quality Control Commission (1002 Series)
Rule 5 CCR 1002-38 - REGULATION NO. 38 - CLASSIFICATIONS AND NUMERIC STANDARDS SOUTH PLATTE RIVER BASIN LARAMIE RIVER BASIN REPUBLICAN RIVER BASIN SMOKY HILL RIVER BASIN
Section 5 CCR 1002-38.10 - STATEMENT OF BASIS AND PURPOSE

5 Colo. Code Regs. § 1002-38.10

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Current through Register Vol. 47, No. 20, October 25, 2024
Section 5 CCR 1002-38.10 - STATEMENT OF BASIS AND PURPOSE
I.Introduction

Prior to the adoption of the Commission's "Basic Regulations," (5 CCR 1002-8) what is now known as Segment 14 of the South Platte River Basin was classified B1 and B2. In regulations adopted by the Commission on April 6, 1981, Segment 14 was classified as a warm water aquatic life class I stream (see 5 CCR 1002-8). A water quality standard for unionized ammonia of .06 mg/l, with a temporary modification of .1mg/l, was established at that time in conjunction with the aquatic life classification.

On June 15, 1981, the Cities of Littleton and Englewood, Colorado, petitioned pursuant to 25-8-403, C.R.S. 1973 for administrative reconsideration and rehearing on the classification of segment 14 of the South Platte River Basin as class I, warm water aquatic life, and the modification of an ammonia standard in segment 14 of 0.06 mg/l.

On June 29, 1981, the request was denied. The Commission then decided, however, to conduct a new public rulemaking hearing to determine whether to maintain or amend certain use classifications and water quality standards for the segment.

Based on the record of this hearing, the Commission has determined that the existing aquatic life classification and the existing water quality standard for unionized ammonia should be retained.

II.WARM WATER AQUATIC LIFE CLASS I CLASSIFICATION

Notwithstanding some evidence that aquatic habitat limits the numbers and diversity of aquatic organisms in this stream segment, and some evidence that the presence of sensitive species is also limited, the Commission is persuaded by the weight of the evidence that this is a class I aquatic life stream. This conclusion is based on the following findings:

1. The ratio of rough to game fish is representative of east slope warm water plains streams generally, indicating a fair population of sensitive fish species.
2. Despite some siltation and some habitat impairment streambed improvements as well as natural conditions generally provide good or adequate habitat for warm water species.
3. There is evidence that fish spawning takes place in this segment.
4. The diversity of the fishery is adequate to warrant a class I aquatic life classification.
5. Limitations on the presence and condition of aquatic life are related to both water quality factors and to habitat impairment.
6. Given the historical improvements in habitat, water quality, and aquatic life since 1965, a class I classification appropriately reflects the results of significant community efforts to improve the South Platte River.
III.UNIONIZED AMMONIA WATER QUALITY STANDARD - .06 mg/l; TEMPORARY MODIFICATION .1 MG/L

The record reveals conflicting evidence regarding the unionized ammonia water quality standard necessary to protect resident aquatic life. The Commission has determined that the existing standards, i.e., .06 mg/l (Water Quality Standards) and .1 mg/l (Temporary Modification) should be retained for the following reasons:

1. There is substantial evidence of relationships among ammonia toxicity and pH, temperture, and alkalinity. However, the record does not provide the Commission with a satisfactory basis for linking these variables to a specific Water Quality Standard to protect the varieties of species present, except with application of the gill theory.
2. Significant uncertainties with respect to application of the gill theory preclude the Commission from utilizing it at this time.
3. The Commission recognizes that a site specific approach to the establishment of Water Quality Standards for ammonia is the preferred approach. However, no site specific bioassays have been performed, and the details of any other application of site specific factors is a matter currently under review at EPA and within the field of aquatic toxicology.
4. The .06 mg/l unionized ammonia standard is considered by the Water Quality Control Commission at this time to be generally necessary and sufficient to protect the sensitive warm water species found in this segment, as well as in Colorado generally. Furthermore, differences between the South Platte and the Cache la Poudre River, such as flows, temperature, water chemistry, and the presence of different species, indicate that the .1 mg/l unionized ammonia standard applicable for the Poudre and elsewhere is inappropriate here.
5. The .06 mg/l unionized ammonia standard is generally met in the stream at this time, although some excursions above this standard do occur. The .1 mg/l temporary modification is adequate to account for such excursions without penalizing dischargers for their occurrence.
6. The evidence submitted by the Division on the mixing zone study indicates that the .06 mg/l unionized ammonia standard is being met in the study area by the existing Bi-City treatment plant, and will continue to be met in the near term without additional treatment and without taking into account the dilution effect of additional flows, mixing zone considerations, or other similar factors utilized in writing permit effluent limitations.
7. The existing standard and temporary modification will have no effect on capital-intensive requirements for existing discharges at this time. Compliance schedules to reduce ammonia levels will not be required of dischargers until a wasteload allocation is established. Future effects are hypothetical and uncertain. As the Commission considers the temporary modification in the future, and in the conduct of its required trienniel review, such factors can be re-evaluated in the light of more specific facts and in conjunction with advancing scientific information on the establishment of site-specific standards.
IV.ECONOMIC REASONABLENESS

The Commission has considered the economic reasonableness of this action and concludes as follows:

1. Evidence indicates that the .06 mg/l unionized ammonia standard is met now below the discharge point of the existing Bi-City Treatment Plant. The .1 mg/l temporary modification is adequate to account for excursions above the standard without imposing additional treatment requirements on dischargers. the existing 20 mgd Bi-City Plant.
2. Specific cost figures submitted by Littleton and Englewood indicate potential total impacts, not incremental impacts.
3. Because no immediate economic impacts will occur, and because there are administrative remedies to specificaly address economic impacts if they materilize in the future, the decision to retain the existing aquatic life classification and ammonia standards is economically reasonable. Administrative remedies potentially available in the future include those specified by C.R.S. 1973, 25-8-204(3), 503(4), and 202(1)(f).

5 CCR 1002-38.10

38 CR 03, February 10, 2015, effective 6/30/2015
38 CR 17, September 10, 2015, effective 12/31/2015
39 CR 03, February 10, 2016, effective 3/1/2016
39 CR 03, February 10, 2016, effective 6/30/2016
39 CR 23, December 25, 2016, effective 12/30/2016
40 CR 03, February 10, 2017, effective 6/30/2017
40 CR 09, May 10, 2017, effective 6/30/2017
41 CR 01, January 10, 2018, effective 1/31/2018
41 CR 03, February 10, 2018, effective 6/30/2018
42 CR 04, February 25, 2019, effective 6/30/2019
43 CR 03, February 10, 2020, effective 6/30/2020
43 CR 17, September 10, 2020, effective 12/31/2020
44 CR 01, January 10, 2021, effective 2/14/2021
44 CR 05, March 10, 2021, effective 6/30/2021
44 CR 17, September 10, 2021, effective 12/31/2021
45 CR 17, September 10, 2022, effective 9/30/2022
45 CR 21, November 10, 2022, effective 11/30/2022
46 CR 10, May 25, 2023, effective 6/14/2023