35 Ill. Adm. Code 355.205
Estimation of Projected Effluent Quality
Section 355
Section 355.205 Estimation
of Projected Effluent Quality
The Projected Effluent Quality
(PEQ) is the estimation of the maximum expected effluent concentration.
Individual PEQs shall be estimated for all summer and winter acute, chronic
and subchronic exposure periods.
a) The PEQ shall be derived from representative facility specific
data to reflect a 95 percent confidence level for the 95
th
percentile value. These data will be presumed to adhere to a lognormal
distribution pattern with a coefficient of variation of 0.6 unless the
facility's effluent data demonstrates a different distribution pattern. If
facility specific data in excess of 10 data values is available, a facility
specific coefficient of variation that is the ratio of the standard deviation
to the arithmetic average may be calculated. The PEQ is derived as the upper
bound of a 95 percent confidence bracket around the 95
th
percentile
value through a multiplier from the following table applied to the maximum
value in the data set that has its quality assured consistent with subsection
(f).
PEQ = (maximum
data point)(statistical multiplier)
Coefficient of Variation
No.
of Samples
0.1
0.2
0.3
0.4
0.5
0.6
0.7
1
1.4
1.9
2.6
3.6
4.7
6.2
8.0
2
1.3
1.6
2.0
2.5
3.1
3.8
4.6
3
1.2
1.5
1.8
2.1
2.5
3.0
3.5
4
1.2
1.4
1.7
1.9
2.2
2.6
2.9
5
1.2
1.4
1.6
1.8
2.1
2.3
2.6
6
1.1
1.3
1.5
1.7
1.9
2.1
2.4
7
1.1
1.3
1.4
1.6
1.8
2.0
2.2
8
1.1
1.3
1.4
1.6
1.7
1.9
2.1
9
1.1
1.2
1.4
1.5
1.7
1.8
2.0
10
1.1
1.2
1.3
1.5
1.6
1.7
1.9
11
1.1
1.2
1.3
1.4
1.6
1.7
1.8
12
1.1
1.2
1.3
1.4
1.5
1.6
1.7
13
1.1
1.2
1.3
1.4
1.5
1.6
1.7
14
1.1
1.2
1.3
1.4
1.4
1.5
1.6
15
1.1
1.2
1.2
1.3
1.4
1.5
1.6
16
1.1
1.1
1.2
1.3
1.4
1.5
1.6
17
1.1
1.1
1.2
1.3
1.4
1.4
1.5
18
1.1
1.1
1.2
1.3
1.3
1.4
1.5
19
1.1
1.1
1.2
1.3
1.3
1.4
1.5
20
1.1
1.1
1.2
1.2
1.3
1.4
1.4
30
1.0
1.1
1.1
1.1
1.2
1.2
1.2
40
1.0
1.0
1.1
1.1
1.1
1.1
1.1
50
1.0
1.0
1.0
1.0
1.0
1.0
1.0
60
or greater
1.0
1.0
1.0
1.0
1.0
1.0
1.0
Coefficient of Variation
No.
of Samples
0.8
0.9
1.0
1.1
1.2
1.3
1
10.1
12.6
15.5
18.7
22.3
26.4
2
5.4
6.4
7.4
8.5
9.7
10.9
3
4.0
4.6
5.2
5.8
6.5
7.2
4
3.3
3.7
4.2
4.6
5.0
5.5
5
2.9
3.2
3.6
3.9
4.2
4.5
6
2.6
2.9
3.1
3.4
3.7
3.9
7
2.4
2.6
2.8
3.1
3.3
3.5
8
2.3
2.4
2.6
2.8
3.0
3.2
9
2.1
2.3
2.4
2.6
2.8
2.9
10
2.0
2.2
2.3
2.4
2.6
2.7
11
1.9
2.1
2.2
2.3
2.4
2.5
12
1.9
2.0
2.1
2.2
2.3
2.4
13
1.8
1.9
2.0
2.1
2.2
2.3
14
1.7
1.8
1.9
2.0
2.1
2.2
15
1.7
1.8
1.8
1.9
2.0
2.1
16
1.6
1.7
1.8
1.9
1.9
2.0
17
1.6
1.7
1.7
1.8
1.9
1.9
18
1.6
1.6
1.7
1.7
1.8
1.9
19
1.5
1.6
1.6
1.7
1.8
1.8
20
1.5
1.5
1.6
1.6
1.7
1.7
30
1.3
1.3
1.3
1.3
1.4
1.4
40
1.1
1.2
1.2
1.2
1.2
1.2
50
1.1
1.1
1.1
1.1
1.1
1.1
60
or greater
1.0
1.0
1.0
1.0
1.0
1.0
1) If the PEQ determined in this Section is less than or equal to
the applicable acute water quality standard, there is no reasonable potential
and no WQBEL will be established in the permit unless otherwise warranted under
Section 355.201(c).
2) If the PEQ as determined in this Section exceeds the
applicable acute water quality standard but does not exceed the PEL determined
through Section 355.209, there is no reasonable potential and no WQBEL will be
established unless otherwise warranted under Section 355.201(c).
b) The Agency shall compare calculated PEQ values derived from
monthly average effluent data, when available, with the applicable chronic
water quality standard to evaluate the need for monthly average WQBEL using the
same method described in subsection (a) of this Section. If a monthly average
WQBEL is included in an NPDES permit, the Agency will also include a daily
maximum WQBEL to enforce the acute water quality standard.
c) The Agency shall compare calculated PEQ values derived from
the highest weekly average total ammonia effluent data, when available, with
the applicable subchronic water quality standards to evaluate the need for a
weekly average WQBEL using the same method described in subsection (a) of this
Section.
d) The Agency may apply other scientifically defensible
statistical methods for calculating PEQ at the 95 percent upper confidence
level for use in the reasonable potential analysis. For new or existing
discharges where no prior operating record is available, PEQ shall be estimated
based on knowledge of the tributary wastewater characteristics and treatment
facility capabilities. For existing sources where the PEQ for the term of the
permit cannot be accurately characterized by historical performance data as
specified in subsection (a) of this Section due to significant changes in
tributary loading, plant operating parameters or other factors affecting
treatment efficiency during the term covered by the permit, a PEQ
representative of the future permit term may be estimated by analysis of the
historical data consistent with subsection (a) with adjustment of the
historical value to reflect the change expected from the anticipated loading or
operating changes.
e) Regardless of the statistical procedure used, if the PEQ for
ammonia nitrogen (as N) is less than or equal to the water quality standard,
the Agency shall deem the discharge not to have a reasonable potential to
exceed and a WQBEL shall not be required unless otherwise required under
Section 355.201.
f) Data Requirements
The derivation of PEQ is based on the effluent quality
demonstrated by self-monitoring data as required by the NPDES permit or
Agency-generated data, such as effluent sampling or facility-related stream
studies. Effluent data used in the derivation of PEQ shall be representative
of the concentration and variability of ammonia nitrogen in the discharge
anticipated for the applicable period of the NPDES permit. Data shall be
collected and analyzed in accordance with USEPA or Agency approved sampling and
analytical methods (40 CFR 136). The following criteria shall be followed in
data selection:
1) the most recent five years of data shall be used unless the
Agency determines that an alternative period better represents the time period
for which effluent quality is being projected. Such alternative time periods
may include, but are not limited to, shorter periods that reflect changed
discharge characteristics resulting from changes in manufacturing activities or
wastewater treatment systems; and
2) data anomalies resulting from collection, analysis or
recording errors or atypical plant operating conditions may be eliminated from
the data.