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Home My WebLink AboutNC0089915_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.