Current through Vol. 42, No. 1, September 16, 2024
(a)
General. OAC
785:45-3-2(c)
prohibits water quality degradation by nutrients which will interfere with the
attainment or maintenance of any existing or designated beneficial use. OAC
785:46-13-3(a)(1)
requires maintenance of any existing or designated beneficial use. This Section
provides a framework which shall be used in assessing threats or impairments to
beneficial uses and waterbodies and watersheds caused by nutrients, and the
consequences of such assessments.
(b)
Determining whether a stream is
nutrient-threatened. The dichotomous process stated in this subsection
shall be used in the determination of whether a stream is nutrient-threatened.
(1) The stream order shall be identified. If
the stream order is 1, 2 or 3, then proceed to paragraph (2). If the stream
order is not 1, 2 or 3, then proceed to paragraph (9).
(2) The stream slope shall be identified. If
the stream slope is greater than or equal to 17 feet per mile, then proceed to
paragraph (3). If the stream slope is less than 17 feet per mile, then proceed
to paragraph (4).
(3) Subject to
the application of the foregoing paragraphs of this subsection, if phosphorus
concentrations in the stream are greater than 0.24 mg/L or if nitrite plus
nitrate concentrations in the stream are greater than 4.95 mg/L, then proceed
to paragraph (5). If such nutrient concentrations are less than the levels
specified in this paragraph, then the stream is not threatened by
nutrients.
(4) Subject to the
application of the foregoing paragraphs of this subsection, if phosphorus
concentrations in the stream are greater than 0.15 mg/L or if nitrite plus
nitrate concentrations in the stream are greater than 2.4 mg/L, then proceed to
paragraph (5). If such nutrient concentrations are less than the levels
specified in this paragraph, then the stream is not threatened by
nutrients.
(5) Subject to the
application of the foregoing paragraphs of this subsection, if the percentage
of canopy shading is greater than or equal to 80%, then the stream is not
threatened by nutrients. If the percentage of canopy shading is less than 80%,
then proceed to paragraph (6).
(6)
Subject to the application of the foregoing paragraphs of this subsection, if
the stream's turbidity is organic, then proceed to paragraph (7). If the
stream's turbidity is inorganic, then proceed to paragraph (8).
(7) Subject to the application of the
foregoing paragraphs of this subsection, if turbidity measured at seasonal base
flow conditions is less than 20 NTU, then the stream is not threatened by
nutrients. If turbidity measured at seasonal base flow conditions is 20 or more
NTU, then the stream is threatened by nutrients.
(8) Subject to the application of the
foregoing paragraphs of this subsection, if turbidity measured at seasonal base
flow conditions is less than 20 NTU, then the stream is threatened by
nutrients. If turbidity measured at seasonal base flow conditions is 20 or more
NTU, then the stream is not threatened by nutrients.
(9) Subject to the application of the
foregoing paragraphs of this subsection, if the stream slope is greater than or
equal to 17 feet per mile, then proceed to paragraph (10). If the stream slope
is less than 17 feet per mile, then proceed to paragraph (11).
(10) Subject to the application of the
foregoing paragraphs of this subsection, if phosphorus concentrations in the
stream are greater than 1.00 mg/L, or if nitrite plus nitrate concentrations in
the stream are greater than 4.65 mg/L, then proceed to paragraph (12). If such
nutrient concentrations are less than the levels specified in this paragraph,
then the stream is not threatened by nutrients.
(11) Subject to the application of the
foregoing paragraphs of this subsection, if phosphorus concentrations in the
stream are greater than 0.36 mg/L, or if nitrite plus nitrate concentrations in
the stream are greater than 5.0 mg/L, then proceed to paragraph (12). If such
nutrient concentrations are less than the levels specified in this paragraph,
then the stream is not threatened by nutrients.
(12) Subject to the application of the
foregoing paragraphs of this subsection, if the stream's inorganic turbidity
measured at seasonal base flow conditions is greater than or equal to 20 NTU,
then the stream is not threatened by nutrients. If the stream's inorganic
turbidity measured at seasonal base flow conditions is less than 20 NTU, then
the stream is threatened.
(c)
Alternative to dichotomous process
for streams.
(1) A wadable stream
shall be deemed threatened by nutrients if the arithmetic mean of benthic
chlorophyll-a data exceeds 100 mg per square meter under seasonal base flow
conditions, or if two or more benthic chlorophyll-a measurements exceed 200 mg
per square meter under seasonal base flow conditions. A non-wadable stream
shall be deemed threatened by nutrients if planktonic chlorophyll-a values in
the water column indicate it has a Trophic State Index of 62 or
greater.
(2) If clear and
convincing evidence indicates a result for a stream different from that
obtained from application of the dichotomous process in (b) of this Section,
then the appropriate state environmental agency may, after completing the
public participation process developed by the Secretary of Environment pursuant
to 27A O.S. 1-2-101, accordingly identify the stream as threatened or not
threatened by nutrients.
(d)
Demonstration that nutrients may be
adversely impacting a beneficial use. If it is demonstrated by the
Trophic State Index or by other relevant data as provided in
785:46-15-1(c)
that nutrient loading in a waterbody may be adversely impacting a beneficial
use designated for that waterbody, then the Board may determine that the
waterbody and its watershed is an NLW, and shall identify the waterbody and
watershed as NLW in Appendix A of OAC 785:45.
(e)
Consequence of identification as
NLW. If a waterbody or its watershed is identified as NLW in Appendix A
of OAC 785:45, then the Board or other appropriate state environmental agency
may cause an impairment study to be performed. Provided, if an impairment study
demonstrates that the uses are not threatened, then the Board shall consider
deleting the NLW identification.
(f)
Consequence of assessment that use
is threatened by nutrients. If it is determined that one or more
beneficial uses designated for a waterbody are threatened by nutrients, then
that waterbody shall be presumed to be nutrient-threatened. If it is determined
or presumed, in accordance with this Section, that a waterbody is
nutrient-threatened, then before the waterbody is determined to be
nutrient-impaired, an impairment study must be completed by the appropriate
state environmental agency.
(g)
Result of impairment study.
(1)
Impaired. If, independent of or in addition to the process set
forth in this Section, an impairment study of a waterbody demonstrates that any
beneficial use designated for a waterbody is impaired by nutrients, then the
appropriate state environmental agency shall initiate the appropriate listing
procedure in accordance with the public participation process developed by the
Secretary of Environment pursuant to 27A O.S. 1-2-101 for each such beneficial
use.
(2)
Not impaired.
If, independent of or in addition to the process set forth in this Section, an
impairment study of a waterbody demonstrates that all beneficial uses
designated for that waterbody are not impaired by nutrients, then the
appropriate state environmental agency shall initiate the appropriate
de-listing procedure in accordance with the public participation process
developed by the Secretary of Environment pursuant to 27A O.S.
1-2-101.
Added at 17 Ok Reg 1775,
eff 7-1-00; Amended at 18 Ok Reg 171, eff 10-25-00 (emergency); Amended at 18
Ok Reg 3379, eff 8-13-01; Amended at 21 Ok Reg 1910, eff 7-1-04; Amended at 22
Ok Reg 1607, eff 7-1-05; Amended at 25 Ok Reg 1455, eff 7-1-08; Amended at 28
Ok Reg 1017, eff 7-1-11
