35 Ill. Adm. Code 352.421
Estimation of Projected Effluent Quality
Section 352
Section 352.421 Estimation
of Projected Effluent Quality
a) The first step in determining if a reasonable potential to
exceed the water quality standard exists for any particular pollutant parameter
is the estimation of the maximum expected effluent concentration for that
substance. That estimation will be completed for both acute and chronic
exposure periods and is termed the PEQ. The PEQ shall be derived from
representative facility specific data to reflect a 95 percent confidence level
for the 95th percentile value. These data will be presumed to adhere to a lognormal
distribution pattern unless the actual effluent data demonstrates a different
distribution pattern. If facility specific data in excess of 10 data values is
available, a coefficient of variation that is the ratio of the standard
deviation to the arithmetic average shall be calculated by the Agency. The PEQ
is derived as the upper bound of a 95 percent confidence bracket around the
95th 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
Section 352.410 as appropriate for acute and chronic data sets.
PEQ = (maximum data point)(statistical
multiplier)
Coefficient
of Variation
No. 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
0.8
0.9
1.0
1.1
1.2
1.3
10.1
12.6
15.5
18.7
22.3
26.4
5.4
6.4
7.4
8.5
9.7
10.9
4.0
4.6
5.2
5.8
6.5
7.2
3.3
3.7
4.2
4.6
5.0
5.5
2.9
3.2
3.6
3.9
4.2
4.5
2.6
2.9
3.1
3.4
3.7
3.9
2.4
2.6
2.8
3.1
3.3
3.5
2.3
2.4
2.6
2.8
3.0
3.2
2.1
2.3
2.4
2.6
2.8
2.9
2.0
2.2
2.3
2.4
2.6
2.7
1.9
2.1
2.2
2.3
2.4
2.5
1.9
2.0
2.1
2.2
2.3
2.4
1.8
1.9
2.0
2.1
2.2
2.3
1.7
1.8
1.9
2.0
2.1
2.2
1.7
1.8
1.8
1.9
2.0
2.1
1.6
1.7
1.8
1.9
1.9
2.0
1.6
1.7
1.7
1.8
1.9
1.9
1.6
1.6
1.7
1.7
1.8
1.9
1.5
1.6
1.6
1.7
1.8
1.8
1.5
1.5
1.6
1.6
1.7
1.7
1.3
1.3
1.3
1.3
1.4
1.4
1.1
1.2
1.2
1.2
1.2
1.2
1.1
1.1
1.1
1.1
1.1
1.1
1.0
1.0
1.0
1.0
1.0
1.0
1) If the PEQ is less than or equal to the water quality
standard, there is no reasonable potential and no limit will be established in
the permit.
2) If the PEQ is more than the water quality standard, the Agency
will proceed to consideration of dilution and mixing pursuant to Section
352.422.
b) If facility-specific data of 10 or less data values is
available, an alternative PEQ shall be derived using the table in Section
352.421(a), assuming a coefficient of variation of 0.6, applied to the maximum
value in the data set that has its quality assured consistent with Section
352.410.
1) If the PEQ is less than or equal to the water quality
standard, there is no reasonable potential and no limit will be established in
the permit.
2) If the PEQ exceeds the water quality standard, an alternative
PEQ will be calculated using the maximum value in the data set and a multiplier
of 1.4. If the alternative PEQ also exceeds the PEL, the Agency will proceed to
consider dilution and mixing pursuant to Section 352.422.
3) If the PEQ exceeds the water quality standard but the
alternative PEQ is less than or equal to the standard, the Agency will either
proceed to consider dilution and mixing pursuant to Section 352.422, or will
incorporate a monitoring requirement and reopener clause to reassess the
potential to exceed within a specified time schedule, not to exceed one year.
In determining which of these options to use in any individual application, the
Agency shall consider the operational and economic impacts on the permittee and
the effect, if any, deferral of a final decision would have on an ultimate
compliance schedule if a permit limit were subsequently determined to be
necessary.
c) The Agency shall compare monthly average effluent data values,
when available, with chronic aquatic life, human health and wildlife standards
to evaluate the need for monthly average WQBELs. The Agency shall use daily
effluent data values to determine whether a potential exists to exceed acute
aquatic life water quality standards.
d) The Agency may apply other scientifically defensible
statistical methods for calculating PEQ at the 95
th
percentile value
for use in the reasonable potential analysis as provided for in Procedure 5.b.2
of Appendix F to 40 CFR 132.
e) Regardless of the statistical procedure used, if the PEQ for
the parameter is less than or equal to the water quality standard for that
parameter, the Agency shall deem the discharge not to have a reasonable
potential to exceed, and a water quality based effluent limit (WQBEL) shall not
be required unless otherwise required under Section 352.430.