Section 423.16 - Pretreatment standards for existing sources (PSES)Except as provided in 40 CFR 403.7 and 403.13 , any existing source subject to this subpart which introduces pollutants into a publicly owned treatment works must comply with 40 CFR part 403 and achieve the following pretreatment standards for existing sources (PSES) by July 1, 1984:
(a) There shall be no discharge of polychlorinated biphenol compounds such as those used for transformer fluid.(b) The pollutants discharged in chemical metal cleaning wastes shall not exceed the concentration listed in the following table: | Pollutant or pollutant property | PSES pretreatment standards |
| Maximum for 1 day (mg/l) |
| Copper, total | 1.0 |
(c) [Reserved-Nonchemical Metal Cleaning Wastes].(d)(1) The pollutants discharged in cooling tower blowdown shall not exceed the concentration listed in the following table: | Pollutant or pollutant property | PSES pretreatment standards |
| Maximum for any time (mg/l) |
| The 126 priority pollutants (Appendix A) contained in chemicals added for cooling tower maintenance, except: | (1) |
| Chromium, total | 0.2 |
| Zinc, total | 1.0 |
1 No detectable amount.
(2) At the permitting authority's discretion, instead of the monitoring in 40 CFR 122.11(b) , compliance with the limitations for the 126 priority pollutants in paragraph (d)(1) of this section may be determined by engineering calculations which demonstrate that the regulated pollutants are not detectable in the final discharge by the analytical methods in 40 CFR part 136.(e)FGD wastewater - (1)2020 PSES. Except as provided for in paragraph (e)(2) of this section, for any electric generating unit with a total nameplate generating capacity of more than 50 megawatts, that is not an oil-fired unit, and that the owner has not certified that it will cease coal combustion pursuant to § 423.19(g) , the quantity of pollutants in FGD wastewater shall not exceed the quantity determined by multiplying the flow of FGD wastewater times the concentration listed in table 3 to this paragraph (e)(1). Dischargers must meet the standards in this paragraph (e)(1) by October 13, 2023, except as provided for in paragraph (e)(2) of this section. The standards in this paragraph (e)(1) apply to the discharge of FGD wastewater generated on and after October 13, 2023. Table 3 to Paragraph (e)(1)
| Pollutant or pollutant property | PSES |
| Maximum for any 1 day | Average of daily values for 30 consecutive days shall not exceed |
| Arsenic, total ([MICRO]g/L) | 18 | 8 |
| Mercury, total (ng/L) | 103 | 34 |
| Selenium, total ([MICRO]g/L) | 70 | 29 |
| Nitrate/nitrite as N (mg/L) | 4 | 3 |
(2)2020 PSES subcategories.(i) For FGD wastewater discharges from a low utilization electric generating unit, the quantity of pollutants in FGD wastewater shall not exceed the quantity determined by multiplying the flow of FGD wastewater times the concentration listed in the table 4 to paragraph (e)(2)(ii) of this section. Dischargers must meet the standards in this paragraph (e)(2)(i) by October 13, 2023.(ii) If any low utilization electric generating unit fails to timely recertify that the two year average capacity utilization rating of such an electric generating unit is below 10 percent per year as specified in § 423.19(f) , regardless of the reason, within two years from the date such a recertification was required, the quantity of pollutants in FGD wastewater shall not exceed the quantity determined by multiplying the flow of FGD wastewater times the concentration listed in the table 3 to paragraph (e)(1) of this section. Table 4 to Paragraph (e)(2)(ii)
| Pollutant or pollutant property | PSES |
| Maximum for any 1 day | Average of daily values for 30 consecutive days shall not exceed |
| Arsenic, total ([MICRO]g/L) | 11 | 8 |
| Mercury, total (ng/L) | 788 | 356 |
(3)2024 PSES. Except as provided for in paragraph (e)(4) of this section, for any electric generating unit with a total nameplate generating capacity of more than 50 megawatts and that is not an oil-fired unit, there shall be no discharge of pollutants in FGD wastewater. Dischargers must meet the standards in this paragraph (e)(3) by May 9, 2027, except as provided for in paragraph (e)(4) of this section. The standards in this paragraph (e)(3) apply to the discharge of FGD wastewater generated on and after May 9, 2027.(4)2024 PSES subcategories.(i) For any electric generating unit for which the owner has submitted a certification pursuant to § 423.19(h) , the quantity of pollutants discharged in FGD wastewater shall continue to be subject to standards specified in paragraph (e)(1) or (2) of this section as incorporated into the existing control mechanism. (A) Where such unit has permanently ceased coal combustion by December 31, 2034, there shall be no discharge of pollutants in FGD wastewater after April 30, 2035.(B) Where such unit has failed to permanently cease coal combustion by December 31, 2034, there shall be no discharge of pollutants in FGD wastewater after December 31, 2034.(ii) For FGD wastewater discharged from any coal combustion residual surface impoundment which commences closure pursuant to 40 CFR 257.102(e) after July 8, 2024, the quantity of pollutants in FGD wastewater shall not exceed the quantity determined by multiplying the flow of FGD wastewater times the concentration listed in the table 5 to this paragraph (e)(4)(ii). Table 5 to Paragraph (e)(4)(ii)
| Pollutant or pollutant property | PSES |
| Maximum for any 1 day | Average of daily values for 30 consecutive days shall not exceed |
| Arsenic, total ([MICRO]g/L) | 11 | 8 |
| Mercury, total (ng/L) | 788 | 356 |
(f)Fly ash transport water. Except when the fly ash transport water is used in the FGD scrubber, for any electric generating unit with a total nameplate generating capacity of more than 50 megawatts and that is not an oil-fired unit, there shall be no discharge of pollutants in fly ash transport water. This standard applies to the discharge of fly ash transport water generated on and after November 1, 2018. Whenever fly ash transport water is used in any other plant process or is sent to a treatment system at the plant (except when it is used in the FGD scrubber), the resulting effluent must comply with the discharge standard in this paragraph. When the fly ash transport water is used in the FGD scrubber, the quantity of pollutants in fly ash transport water shall not exceed the quantity determined by multiplying the flow of fly ash transport water times the concentration listed in the table in paragraph (e) of this section.(g)Bottom ash transport water - (1)2020 PSES. Except for those discharges to which paragraph (g)(2) of this section applies, or when the bottom ash transport water is used in the FGD scrubber, for any electric generating unit with a total nameplate generating capacity of more than 50 megawatts, that is not an oil-fired unit, that is not a low utilization electric generating unit, and that the owner has not certified that the electric generating unit will cease coal combustion pursuant to § 423.19(g) , there shall be no discharge of pollutants in bottom ash transport water. The standard in this paragraph (g)(1) applies to the discharge of bottom ash transport water generated on and after October 13, 2023. Except for those discharges to which paragraph (g)(2) of this section applies, whenever bottom ash transport water is used in any other plant process or is sent to a treatment system at the plant (except when it is used in the FGD scrubber), the resulting effluent must comply with the discharge standard in this paragraph (g)(1). When the bottom ash transport water is used in the FGD scrubber, the quantity of pollutants in bottom ash transport water shall not exceed the quantity determined by multiplying the flow of bottom ash transport water times the concentration listed in table 3 to paragraph (e)(1) of this section. (2)2020 PSES subcategories.(i) The discharge of pollutants in bottom ash transport water from a properly installed, operated, and maintained bottom ash system is authorized under the following conditions: (A) To maintain system water balance when precipitation-related inflows are generated from a 10-year storm event of 24-hour or longer duration (e.g., 30-day storm event) and cannot be managed by installed spares, redundancies, maintenance tanks, and other secondary bottom ash system equipment; or(B) To maintain system water balance when regular inflows from wastestreams other than bottom ash transport water exceed the ability of the bottom ash system to accept recycled water and segregating these other wastestreams is feasible; or(C) To maintain system water chemistry where current operations at the facility are unable to currently manage pH, corrosive substances, substances or conditions causing scaling, or fine particulates to below levels which impact system operation or maintenance; or(D) To conduct maintenance not otherwise included in paragraphs (g)(2)(i)(A), (B), or (C) of this section and not exempted from the definition of transport water in § 423.11(p) , and when water volumes cannot be managed by installed spares, redundancies, maintenance tanks, and other secondary bottom ash system equipment.(ii) The total volume that may be discharged to a POTW for the activities in paragraphs (g)(2)(i)(A) through (D) of this section shall be reduced or eliminated to the extent achievable as determined by the control authority. The control authority may also include control measures (including best management practices) that are technologically available and economically achievable in light of best industry practice. In no event shall the total volume of the discharge exceed a 30-day rolling average of ten percent of the primary active wetted bottom ash system volume. The volume of daily discharges used to calculate the 30-day rolling average shall be calculated using measurements from flow monitors.(iii) For bottom ash transport water generated by a low utilization electric generating unit, the quantity of pollutants discharged in bottom ash transport water shall incorporate the elements of a best management practices plan as described in § 423.13(k)(3) .(3)2024 PSES. Except for those discharges to which paragraph (g)(4) of this section applies, for any electric generating unit with a total nameplate generating capacity of more than 50 megawatts, that is not an oil-fired unit, there shall be no discharge of pollutants in bottom ash transport water. The standard in this paragraph (g)(3) applies to the discharge of bottom ash transport water generated on and after May 9, 2027. Except for those discharges to which paragraph (g)(4) of this section applies, whenever bottom ash transport water is used in any other plant process or is sent to a treatment system at the plant, the resulting effluent must comply with the discharge standard in this paragraph (g)(3).(4)2024 PSES subcategories.(i) For any electric generating unit for which the owner has submitted a certification pursuant to § 423.19(h) , the quantity of pollutants discharged in bottom ash transport water shall continue to be subject to standards specified in paragraph (g)(1) or (2) as incorporated into the existing control mechanism.(A) Where such unit has permanently ceased coal combustion by December 31, 2034, there shall be no discharge of pollutants in bottom ash transport water after April 30, 2035.(B) Where such unit has failed to permanently cease coal combustion by December 31, 2034, there shall be no discharge of pollutants in bottom ash transport water after December 31, 2034.(ii) For bottom ash transport water discharged from any coal combustion residual surface impoundment which commences closure pursuant to 40 CFR 257.102(e) after July 8, 2024, the quantity of pollutants in bottom ash transport water shall not exceed the quantity determined by multiplying the flow of bottom ash transport water times the concentration listed in table 6 to this paragraph (g)(4)(ii). Table 6 to Paragraph (g)(4)(ii)
| Pollutant or pollutant property | PSES |
| Maximum for any 1 day | Average of daily values for 30 consecutive days shall not exceed |
| Arsenic, total ([MICRO]g/L) | 11 | 8 |
| Mercury, total (ng/L) | 788 | 356 |
(h)Flue gas mercury control wastewater. For any electric generating unit with a total nameplate generating capacity of more than 50 megawatts and that is not an oil-fired unit, there shall be no discharge of pollutants in flue gas mercury control wastewater. This standard applies to the discharge of flue gas mercury control wastewater generated on and after November 1, 2018. Whenever flue gas mercury control wastewater is used in any other plant process or is sent to a treatment system at the plant, the resulting effluent must comply with the discharge standard in this paragraph.(i)Gasification wastewater. For any electric generating unit with a total nameplate generating capacity of more than 50 megawatts and that is not an oil-fired unit, the quantity of pollutants in gasification wastewater shall not exceed the quantity determined by multiplying the flow of gasification wastewater times the concentration listed in the table following this paragraph (i). Dischargers must meet the standards in this paragraph by November 1, 2018. These standards apply to the discharge of gasification wastewater generated on and after November 1, 2018. | Pollutant or pollutant property | PSES |
Maximum for
any 1 day | Average of daily
values for 30
consecutive days
shall not exceed |
| Arsenic, total ([MICRO]g/L) | 4 | |
| Mercury, total (ng/L) | 1.8 | 1.3 |
| Selenium, total ([MICRO]g/L) | 453 | 227 |
| Total dissolved solids (mg/L) | 38 | 22 |
(j)Combustion residual leachate - (1)2024 PSES.(i) Except for those discharges to which paragraph (j)(2) or (j)(1)(ii) of this section applies, there shall be no discharge of pollutants in combustion residual leachate. The standard in this paragraph (j)(1)(i) applies to the discharge of combustion residual leachate generated on and after May 9, 2027. Except for those discharges to which paragraph (j)(2) of this section applies, whenever combustion residual leachate is used in any other plant process or is sent to a treatment system at the plant, the resulting effluent must comply with the discharge standard in this paragraph (j)(1)(i).(ii) After the retirement of all units at a facility, the quantity of pollutants in CRL shall not exceed the quantity determined by multiplying the flow of CRL permeate times the concentrations listed in the table 7 to § 423.13(g)(3)(i) or the flow of CRL distillate times the concentrations listed in the table in § 423.15(b)(13) . (2)2024 PSES subcategories.(i) Except as described in paragraph (j)(2)(i)(A) of this section, the EPA is declining to establish PSES for electric generating units for which the owner has submitted a certification pursuant to § 423.19(h) and is reserving such standards to be established by the control authority on a case-by-case. (A) Where such unit has permanently ceased coal combustion by December 31, 2034, the quantity of pollutants in combustion residual leachate shall not exceed the quantity determined by multiplying the flow of combustion residual leachate times the concentration listed in the table 7 to this paragraph (j)(2)(i)(A) no later than April 30, 2035. Table 7 to paragraph (j)(2)(i)(A)
| Pollutant or pollutant property | PSES |
| Maximum for any 1 day | Average of daily values for 30 consecutive days shall not exceed |
| Arsenic, total ([MICRO]g/L) | 11 | 8 |
| Mercury, total (ng/L) | 788 | 356 |
(B) Where such unit has failed to permanently cease coal combustion by December 31, 2034, there shall be no discharge of pollutants in FGD wastewater after December 31, 2034.(ii) For combustion residual leachate discharged from any coal combustion residual surface impoundment which commences closure pursuant to 40 CFR 257.102(e) after July 8, 2024, the quantity of pollutants in combustion residual leachate shall not exceed the quantity determined by multiplying the flow of combustion residual leachate times the concentration listed in table 8 to this paragraph (j)(2)(ii). Table 8 to Paragraph (j)(2)(ii)
| Pollutant or pollutant property | PSES |
| Maximum for any 1 day | Average of daily values for 30 consecutive days shall not exceed |
| Arsenic, total ([MICRO]g/L) | 11 | 8 |
| Mercury, total (ng/L) | 788 | 356 |
47 FR 52304, Nov. 19, 1982, as amended at 80 FR 67901 , Nov. 3, 2015; 82 FR 43500 , Sept. 18, 2017; 85 FR 64720 , Oct. 13, 2020 82 FR 43500 , 9/18/2017; 85 FR 64720 , 12/14/2020; 89 FR 40299 , 7/8/2024