HomeMy WebLinkAboutNC0089915_Other Agency Documents_20200918 (2)Old Outfall 002 Total Table 3+ PFAS EPA Calculated Limitations
January 22, 2020
PFAS Compounds. Treatment testing demonstrated that 99% removal of the indicator
compounds PFMOAA and HFPO-DA was achievable using GAC. Treatment testing also
demonstrated that at least 99% removal of the total of other tracked and reported PFAS
compounds in the Table 3+ and EPA Mod 537 MAX analyses was achieved when PFMOAA and
HFPO-DA were also removed by 99%. EPA Mod 537 analytical method is a US EPA approved
analytical method to quantify a specific set of PFAS compounds for drinking water. The Table 3+
compounds were identified as part of the consent order and are proposed to be utilized for old
outfall 002 limitations.
24-hour influent characterization results of Table 3+ and Modified EPA 537 PFAS were presented
in Attachment 1 of the Engineering Report on Wastewater Treatability for Old Outfall 002 which
was submitted with the NPDES permit application. The Table 3+ influent concentration are
included at the end of this appendix.
A Total Table 3+ PFAS concentration of 125.59 µg/L was calculated for the influent by summing
the concentrations of each quantified compound across the Table 3+ results. Compounds
reported as non -detect in the influent sample were below the practical quantification limit
detection; they were considered to have a concentration of zero when calculating the Total Table
3+ PFAS concentration for the influent
Estimated average monthly limit (AML) and maximum daily limit (MDL) concentrations for Total
Table 3+ PFAS were calculated using the guidance presented in the 1991 EPA Technical Support
Document for Water Quality -based Toxic Controls (TSD)as follows:
• The 99% removal requirement for Total Table 3+ PFAS influent load that represents the
Long Term Average (LTA) for a log -normal distribution of treated effluent concentrations.
o LTA (Total Table 3+ PFAS) = (1-0.99)(125.59 µg/L) = 1.2559 µg/L
• Assumed coefficient of Variance (C.V.) = 0.6 (EPA Conservative Estimate EPA 1991 TSD)
• Assumed Number of samplings per month = 2
Table 5-2 in the 1991 EPA Technical Support Document presents (TSD) the calculations for
Maximum Daily Limit (MDL) as follows:
MDL = LTA • ez6-o.s62
The value for the LTA multiplier (ez'-o.s62) are presented in Table 5-2 of the TSD at a C.V. of 0.6
and 991" percentile occurrence probability, the LTA multiplier is 3.11 Therefore, the 99%
confidence interval MDL for Total Table 3+ PFAS was calculated as follows:
• MDL (Total Table 3+ PFAS) = (3.11)•(1.2559 µg/L) = 3.91 µg/L
The Average Monthly Limits (AML) is calculated according to Table 5-2 in the 1991 EPA
Technical Support Document as follows:
1
AML = LTA • eZ6n-o.56n2
The value for the LTA multiplier applicable to the AML (eZ6n-o.56n2) for C.V. of 0.6, n = 2
(samples per month) and951" percentile occurrence probability is 1.80. Therefore, the 95%
confidence interval AML for Total Table 3+ PFAS was calculated as follows:
• AML (Total Table 3+ PFAS) _ (1.80)•(1.2559 µg/L) = 2.26 µg/L
In summary, the following Total Table 3+ PFAS discharge limits are proposed:
Parameter
Average Monthly Limit (AML)
Maximum Daily Limit (MDL)
Total Table 3+ PFAS
2.26 µg/L
3.91 µg/L
NPDES Permit Writer's Manual
https://www.epa.gov/npdes/npdes-permit-writers-manual
5.2.3.5 Statistical Considerations When Establishing Case -by -Case TBELs
The quality of the effluent from a treatment facility will normally vary over time. If, for example,
BODS data for a typical treatment plant were plotted against time, one would observe day-to-
day variations of effluent concentrations. Some of that behavior can be described by
constructing a frequency concentration plot. From the plot, one could observe that for most of
the time, BODS concentrations are near some average value. Any treatment system can be
described using the mean concentration of the parameter of interest (i.e., the long-term
average) and the variance (or coefficient of variation) and by assuming a particular statistical
distribution (usually lognormal).
When developing a case -by -case limitation, permit writers can use an approach consistent with
the statistical approach EPA has used to develop effluent guidelines. Specifically, the maximum
daily limitation could be calculated by multiplying the long-term average achievable by
implementation of the model technology or process change by a daily variability factor
determined from the statistical properties of a lognormal distribution. The average monthly
limitation can be calculated similarly except that the variability factor corresponds to the
distribution of monthly averages instead of daily concentration measurements. The daily
variability factor is a statistical factor defined as the ratio of the estimated 99th percentile of a
distribution of daily values divided by the mean of the distribution. Similarly, the monthly
variability factor is typically defined as the estimated 95th percentile of the distribution of
monthly averages divided by the mean of the distribution of monthly averages.
1991 EPA Technical Support Document for Water Quality -Based Toxics
Control
https://www3.epa.gov/npdes/pubs/owmO264.pd
Coefficient of Variation Appendix E Page E-3 CV
5.5.4 Probability Basis (Page 110)
MDL-0.01 probability basis (99t" percentile level)
AML-0.05 probability basis (95t" percentile level)
24-Hour Influent Table 3+ and HFPO-DA Characterization Results
OOF2 Option B Location (Proposed Dam)
Parameter
Units
Result
Byproduct 1 (PFESA BP 1)
µg/L
0.38
Byproduct 2 (PFESA BP 2)
µg/L
0.31
Byproduct 4 (PFESA BP 4)
µg/L
0.38
Byproduct 5 (PFESA BP 5)
µg/L
0.82
Byproduct 6 (PFESA BP 6)
µg/L
< 0.015
DFSA
µg/L
Note (1)
EVE Acid
µg/L
0.034
Hydro -EVE Acid
µg/L
0.19
McFOSA
µg/L
< 0.035
M-McFOSE-M
µg/L
< 0.11
MMP
µg/L
Note (1)
MTP
µg/L
Note (1)
N EtFOSAM
µg/L
< 0.037
N-EtFOSE-M
µg/L
< 0.060
NVHOS
µg/L
0.78
2,3,3,3-Tetrafluoro-2-(pentafluoroethoxy)propanoic acid (PEPA)
µg/L
1.9
PES
µg/L
< 0.046
PFECA B
µg/L
< 0.060
PFECA G
µg/L
< 0.041
Perfluoro-2-methoxyacetic acid (PFMOAA)
µg/L
85
Perfluoro(3,5-dioxahexanoic) acid (PF02HxA)
µg/L
17
Perfluoro(3,5,7-trioxaoctanoic) acid (PF030A)
µg/L
5.1
Perfluoro(3,5,7,9-tetraoxadecanoic) acid (PF04DA)
µg/L
1.6
Perfluoro(3,5,7,9,11-pentadodecanoic) acid (PF05DA)
µg/L
0.58
Perfluoro-2-methoxypropanoic acid (PMPA)
µg/L
5.4
PPF Acid
µg/L
Note (1)
R-EVE
µg/L
0.12
Perfluoro-2-propoxypropanoic acid (HFPO-DA; "Dimer Acid")
µg/L
6.0
(l) Presence acknowledged.