Ohio Administrative Code
Title 3745 - Ohio Environmental Protection Agency
Chapter 3745-2 - Attainment and Protection of Surface Water Quality Standards (WQS)
Section 3745-2-05 - Calculating wasteload allocations
Universal Citation: OH Admin Code 3745-2-05
Current through all regulations passed and filed through September 16, 2024
[Comment: For dates of non-regulatory government publications, publications of recognized organizations and associations, federal rules and federal statutory provisions referenced in this rule, see rule 3745-2-02 of the Administrative Code.]
(A) For discharges of toxic and carcinogenic pollutants to flowing receiving waters, a wasteload allocation (WLA) for a pollutant shall be calculated for each water quality criterion applicable in accordance with rule 3745-2-04 of the Administrative Code using the following mass balance equation:
[WQC(Qeff + Qup) - Qup(WQup)] / Qeff
Where:
WQC = water quality criterion as established in rule 3745-2-04 of the Administrative Code.
Qeff = effluent flow as established in paragraph (A)(4) of this rule.
Qup = per cent of the stream design flow as established in paragraphs (A)(1) and (A) (2) of this rule.
WQup = background water quality as established in paragraph (A)(3) of this rule.
Alternative modeling methods (including, but not limited to, continuous simulation or probabilistic analyses) may be used at the discretion of the director if they are demonstrated to be appropriate and protective of applicable water quality criteria.
(1)
The following stream design flows shall be used to determine WLAs for
discharges to flowing receiving waters, unless otherwise specified in this
rule.
(a) 7Q10 for average aquatic life
criteria (except for ammonia-nitrogen).
(b) 1Q10 for maximum aquatic life criteria
(except for ammonia-nitrogen).
(c)
HMQ for agricultural water supply, human health, and aesthetic
criteria.
(d) 90Q10 for wildlife
criteria.
(e) The per cent of
stream design flow contained in paragraph (A)(2) of this rule shall be used in
all WLAs, except as specifically provided by paragraph (A)(2)(f) of this rule.
The per cent of stream design flow used for conducting WLAs to achieve maximum
and average water quality criteria shall be the same, except as provided in
paragraphs (A)(2)(d) and (A)(2)(e) of this rule.
(f) Stream design flows for streams that are
impacted by reservoirs or other physical alterations which impact stream flow
shall be determined on a case-by-case basis, taking into account relevant
site-specific factors. Stream design flows for such impacted stream segments
shall be established at levels to ensure protection of designated
uses.
(g) Alternative flows may be
used at the director's discretion if the flow is as protective as those listed
in this paragraph.
(2)
The stream/discharge flow ratio (SDR) is the ratio of annual 7Q10 to effluent
design flow.
(a) If the annual 7Q10 is less
than or equal to 1.0 cubic feet per second, or if the SDR is equal to or less
than 10.0, one hundred per cent of the applicable stream design flow shall be
used in the WLA.
(b) If the SDR is
equal to or greater than 252.0, the WLA shall be calculated using twenty-five
per cent of the applicable stream design flow.
(c) If the SDR is greater than 10.0 but less
than 252.0, the WLA shall be calculated using the per cent of the applicable
stream design flow determined by the following equation:
Per cent = 103.1 - 0.31(SDR)
(d) Exceptions for discharges to flowing
streams in the lake Erie basin include all of the
following:
(i) WLAs to maintain average
criteria shall be calculated using twenty-five per cent of the applicable
stream design flow.
(ii)
WLAs to maintain maximum criteria shall be calculated using the SDR to
determine the applicable percentage of the stream design flow, as established
in paragraphs (A)(2)(a) to (A)(2)(c) of this rule.
(iii) No new discharges of bioaccumulative
chemicals of concern (BCCs) shall be allowed a mixing zone after December 30,
2002.
(iv) For
existing discharges of BCCs, mixing zones shall be phased out. No mixing zone
shall be available after November 15, 2010, unless the discharger demonstrates
to the satisfaction of the director, that a mixing zone is necessary for
technical, economic, or water conservation reasons.
(e) Exceptions for discharges to flowing
streams in the Ohio river basin:
(i) No new
discharges of bioaccumulative chemicals of concern (BCCs) shall be allowed a
mixing zone after December 30, 2002.
(ii) For existing discharges of BCCs, mixing
zones shall be phased out. No mixing zone shall be available after November 15,
2010, unless the discharger demonstrates to the satisfaction of the director,
that a mixing zone is necessary for technical, economic, or water conservation
reasons.
(f) Exceptions
for direct discharges to the Ohio river. The following stream design flows and
percentages of stream design flows shall be used for WLAs for direct discharges
to the Ohio river:
(i) WLAs to maintain
average aquatic life criteria shall use ten per cent of the 7Q10.
(ii) WLAs to maintain maximum aquatic life
criteria shall use one per cent of the 7Q10.
(iii) WLAs for human health criteria for
carcinogens, agricultural water supply criteria, and aesthetic criteria shall
use ten per cent of the HMQ.
(iv)
WLAs for human health criteria for non-carcinogens shall use one hundred per
cent of the 7Q10.
(g) A
mixing demonstration may be conducted to justify the use of alternate
percentages of stream design flow, in accordance with rule
3745-1-06 of the Administrative Code.
(3) Background water quality shall
be determined using the following methods.
(a)
If representative ambient data are available, all of
the following apply:
(i) The arithmetic
mean shall be used if the number of observations is less than ten.
(ii) The median shall be used if the number
of observations is greater than or equal to ten.
(iii) Values reported as less than the
reported analytical detection level shall be replaced with one-half of the
applied detection level in the calculation of the mean or median. If the
analytical detection level for a pollutant is not reported and is not
available, the analytical detection level for the most sensitive analytical
method approved under 40 C.F.R. 136, or other analytical method detection level
deemed acceptable by the director, shall be used.
(b) If all representative ambient data are
below detection, both of the following apply:
(i) Zero shall be used as the background
water quality if default mixing assumptions are being applied and if the
pollutant is not reasonably suspected of causing or contributing to the
impairment or threatening of the designated use in the receiving water.
Background water quality may be determined as part of any study designed to
increase the default mixing levels established in paragraph (A)(2) of this
rule.
(ii)
One-half of the reported analytical detection level for the pollutant or
one-half of the lowest water quality criteria, whichever is lower, shall be
used as the background water quality if the pollutant is reasonably suspected
of causing or contributing to the impairment or threatening of the designated
use in the receiving water. Studies such as those listed in paragraph
(A)(3)(b)(ii)(a) or (A)(3)(b)(ii)(b) of this rule may be substituted for the
values of background water quality in this paragraph if Ohio EPA determines
that the study is scientifically defensible.
(a) The pollutant shall be quantified through
additional monitoring of background water quality with more sensitive
analytical methods.
(b) The
pollutant shall be quantified by another method, such as caged fish or native
fish data.
(c) If no representative ambient data are
available, data considered by the director to be representative of the natural
background conditions for that receiving water shall be used. Such data shall
be evaluated in accordance with paragraphs (A)(3)(a) and (A)(3)(b) of this
rule.
(d) If no representative
ambient data are available and there is no other representative information
available, background water quality shall be determined using the procedures in
paragraph
(A)(3)(b) of this rule. Any
study designed to increase the effluent mixing levels established in paragraph
(A)(2) of this rule shall include determination of background water
quality.
(e)
At the director's discretion, alternate statistical
techniques to determine background water quality may be used if the techniques
are demonstrated to be appropriate.
(4) Effluent design flow. The effluent design
flow used in the WLAs shall be any of the
following:
(a) The average design flow
for publicly owned treatment works (POTW), unless the director reasonably
believes that the actual effluent flow will differ significantly from the
design flow during the life of the permit. In such a case, the effluent flow
shall represent a reasonable estimate of the projected flow for the POTW during
the applicable permit period.
(b) A
reasonable measure of average wastewater flow for dischargers other than
publicly owned treatment works. This flow shall represent a reasonable measure
of actual production, projected to occur during the next NPDES permit
period.
(c) The
projected average design flow for proposed sources.
(d) If no effluent flow is available, the WLA
will be calculated using not more than twenty-five per cent of the stream
design flow.
(5) WLA
results shall not exceed the inside mixing zone maximum (IMZM) unless a mixing
demonstration is completed in accordance with rule 3745-1-06 of
the Administrative Code that justifies an alternate value.
(6) If the background water quality exceeds
an applicable average criterion, the WLA for that criterion shall equal the
applicable average criterion.
(7)
If the background water quality exceeds the maximum criterion, the WLA for that
criterion shall equal the maximum criterion.
(8) Multiple discharges. When it is necessary
to consider multiple discharges in a WLA, the loading capacity may be
distributed among discharges using a method considered appropriate by the
director, based on site-specific considerations.
(9) When determining a WLA for multiple
discharges, the stream/discharge flow ratio shall be calculated as the total
flow at the end of the modeled segment under 7Q10 design conditions minus all
effluent flow, divided by the total effluent flow to the segment. This SDR
shall then be used to calculate the applicable percentage of stream design
flow, using the equation listed in paragraph (A)(2) of this rule. The same
percentage of stream design flow shall be used for each discharge in the
segment.
(B) WLAs for direct discharges to lakes.
(1) WLAs to
maintain average criteria for direct discharges to non-flowing receiving waters
shall be determined using the following equation:
11(WQC) - 10(BACK)
Where:
WQC = water quality criterion as established in rule 3745-2-04 of the Administrative Code.
BACK = background water quality as established in paragraph (A)(3) of this rule.
(2)
Exceptions for bioaccumulative chemicals of concern (BCCs).
(a) No new discharges of BCCs shall be
allowed a mixing zone after December 30, 2002.
(b) For existing discharges of BCCs, mixing
zones shall be phased out. No mixing zone shall be available after November 15,
2010, unless the discharger demonstrates to the satisfaction of the director,
that a mixing zone is necessary for technical, economic, or water conservation
reasons.
(3) WLAs for
the maximum criteria shall be set equal to the IMZM. WLA results shall not
exceed the IMZM unless a mixing demonstration is completed in accordance with
rule 3745-1-06 of the Administrative Code that justifies an
alternate value.
(4) If the
background water quality exceeds an applicable average criterion, the WLA for
that criterion shall equal the applicable average criterion.
(5) A mixing demonstration may be conducted
in accordance with rule 3745-1-06 of the Administrative Code to justify a
different quantity of receiving water in the WLA for average criteria or limits
that exceed the IMZM.
(6) At the
director's discretion, alternate modeling methods may be used if they are
demonstrated to be appropriate and protective of water quality
criteria.
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