Current through Register Vol. 47, No. 17, September 10, 2024
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).
