MEMORANDUM

DATE: October 20, 2012

SUBJECT: Effluent Limitations for FGD Wastewater, Gasification Wastewater, and 

Combustion Residual Leachate for the Proposed Effluent Limitations Guidelines 

and Standards for the Steam Electric Rulemaking

FROM: Cuc Schroeder, USEPA

TO: Ronald Jordan, USEPA

Cc: John Rogers, Westat

This report presents the results of the statistical analyses performed on the Flue Gas 

Desulfurization (FGD) and gasification wastewater treatment data and the resulting long-term 

averages, variability factors, and effluent limitations. The treatment technology options for FGD 

wastewater presented in this report are: (i) one-stage chemical precipitation system employing 

both hydroxide and sulfide precipitation and iron coprecipitation (hereafter referred to as 

“chemical precipitation”), (ii) biological (one-stage chemical precipitation employing both 

hydroxide and sulfide precipitation and iron coprecipitation followed by anoxic/anaerobic 

biological treatment , hereafter referred to as “biological”.), and (iii) chemical precipitation 

followed by vapor-compression evaporation system (hereafter referred to as “vaporcompression evaporator”. The treatment technology option for gasification wastewater is 

vapor-compression evaporation system. See the Technical Development Document for the 

Proposed Effluent Limitations Guidelines and Standards for the Steam Electric Power Generating 

Point Source Category (hereafter referred to in this document as Technical Development 

Document) for a detailed description of the FGD and gasification systems and the wastewater 

associated with each waste stream, rationale for selecting plants used in the calculation of the 

effluent limitations for each technology option, and pollutants that are proposed for regulation 

for each technology option. 

The following bullets summarize the plants from which data were used to calculate the 

limits for each technology option for FGD wastewater together with the pollutants that are 

proposed for regulation:

• The effluent limitations for chemical precipitation technology option are based on data 

from Hatfield’s Ferry, Keystone, and Miami Fort. The pollutants proposed to be 

regulated for this technology option are arsenic and mercury.

• The effluent limitations for biological technology option are based by Allen and Belews 

Creek. The pollutants proposed to be regulated for this technology option are arsenic,

mercury, nitrate-nitrite as N, and selenium. While these two plants operate the 

biological treatment system used as the basis for the technology option, neither of 
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these plants include sulfide precipitation in the upstream chemical precipitation system. 

For this reason, EPA is transferring the arsenic and mercury limitations calculated based 

on the chemical precipitation treatment to the biological treatment for FGD wastewater 

(see Section 13 of the Technical Development Document for a detailed discussion of the 

transfer of limitations).

• The effluent limitations for vapor-compression evaporation technology option are based 

on Brindisi. The pollutants proposed to be regulated for this technology option are 

arsenic, mercury, selenium, and total dissolved solids.

The following bullets summarize the plants from which data were used to calculate the 

effluent limitations for gasification wastewater together with the pollutants that are proposed 

for regulation:

• The effluent limitations for vapor-compression evaporation technology option are based 

on Polk and Wabash River. The pollutants proposed to be regulated for this technology 

option are arsenic, mercury, selenium, and total dissolved solids.

In addition to the technology options for FGD and gasification wastewaters discussed in 

the previous paragraphs, EPA is also proposing to establish effluent limitations for combustion 

residuals leachate (hereafter referred to as leachate) at certain facilities based on chemical 

precipitation technology option. The effluent limitations for leachate are based on the transfer

of the effluent limitations calculated for the chemical precipitation technology option for FGD 

wastewater because EPA does not have available data for chemical precipitation treatment of

leachate. This transfer of effluent limitations is appropriate because the pollutants in leachate 

are similar to those in FGD wastewater except at lower concentrations. See Section 13 of the 

Technical Development Document for a detailed discussion of the transfer of limitations.

Section 1 of this report provides an overview of the document. Section 2 provides a brief 

description of the available data used to develop the effluent limitations for each technology 

option. Section 3 describes the data corrections, exclusions, baseline substitutions, and 

aggregation made to the data before calculating the effluent limitations. Section 4 describes the 

data editing procedures used to select datasets for developing the effluent limitations for each 

pollutant at each plant. Section 5 provides the statistical methodology used to calculate the 

effluent limitations together with the long-term average and variability factors. Sections 6, 7, 

and 8 contain a detailed summary of the data together with the effluent limitations for each 

pollutant in each treatment technology option for FGD wastewater. Section 9 contains a 

detailed summary of the data together with the effluent limitations for each pollutant for the 

gasification wastewater treatment technology option. Section 10 presents the overall summary 

of the long-term average, variability factors, and effluent limitations for each pollutant in each 

technology option. Section 11 provides a discussion of the engineering review of the effluent

limitations to verify that the limitations are reasonable based upon the design and expected 

operation of the control technologies.
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In addition to the eleven sections described above, four appendices are attached to the 

report. Appendix 1 contains a list of the data that were corrected due to entry errors and all the 

data that were excluded for various reasons. Appendix 2 contains longitudinal plots (along with 

smoothed curves superimposed over the data) for the plant self-monitoring data that EPA used 

to aid in determining the start-up or initial commissioning period for the treatment system for 

Allen and Belews Creek. Appendix 3 contains a summary of the results of the data editing 

criteria (i.e., long-term average test). Appendix 4 contains a summary of the results of the 

engineering review of the limitations.
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Table of Contents

1. Introduction ............................................................................................................................................ 14

2. Description of Data Used to Calculate Long-Term Averages, Variability Factors, and Effluent Limits... 14

2.1. Overview of the Data ....................................................................................................................... 15

2.2. Analytical Methods.......................................................................................................................... 15

2.3. Combining Data from Multiple Sources within a Plant.................................................................... 16

3. Data Corrections, Exclusions, Baseline Substitutions, and Aggregation................................................. 16

3.1. Data Corrections .............................................................................................................................. 17

3.2. Data Exclusions and Rationale for the Exclusions............................................................................ 17

3.2.1. Excluding mercury samples analyzed using an insufficiently-sensitive analytical method...... 17

3.2.2. Excluding samples collected during the initial commissioning period for the treatment 

system ..................................................................................................................................... 18

3.2.3. Excluding analytical results that were identified as questionable due to quality control 

(QA/QC) issues, abnormal conditions or treatment upset, or were analytical anomalies..... 19

3.3. Baseline Substitutions...................................................................................................................... 21

3.4. Data Aggregation ............................................................................................................................. 23

3.4.1. Aggregation of field duplicates................................................................................................. 23

3.4.2. Aggregation of overlapping samples........................................................................................ 24

4. Data Editing Criteria................................................................................................................................ 24

5. Statistical Methodology .......................................................................................................................... 25

5.1. Definitions and Background............................................................................................................. 25

5.2. Statistical Model Selected for the Data ........................................................................................... 26

5.3. Autocorrelation Analysis.................................................................................................................. 26

5.4. Dataset Requirement....................................................................................................................... 28

5.5. Calculating Effluent Limits for Each Pollutant in Each Technology Option...................................... 28

5.6. Special Case – Effluent Limits Based on Detection Limits................................................................ 29

6. Treatment Technology Option for FGD Wastewater: Chemical Precipitation ....................................... 29

6.1. Chemical Precipitation Treatment for FGD Wastewater: Arsenic ................................................... 31

6.1.1. Longitudinal plots of the data for arsenic (ug/L) ...................................................................... 31

6.1.2. Summary statistics for arsenic (ug/L) ....................................................................................... 31

6.1.3. Plant-specific long-term averages and variability factors, option long-term average and 

variability factors, and effluent limits for arsenic (ug/L)......................................................... 32

6.2. Chemical Precipitation Treatment for FGD Wastewater: Mercury ................................................. 33

6.2.1. Longitudinal plots of the data for mercury (ng/L) .................................................................... 33

6.2.2. Summary statistics for mercury (ng/L) ..................................................................................... 33

6.2.3. Plant-specific Long-term averages and variability factors, option long-term average and 

variability factors, and effluent limits for mercury (ng/L)....................................................... 34

6.3. Chemical Precipitation Treatment for FGD Wastewater: Summary of the Option Long-Term 

Averages, Option Variability Factors, and Effluent Limits............................................................... 34

7. Treatment Technology Option for FGD Wastewater: Biological Treatment .......................................... 35

7.1. Biological Treatment for FGD Wastewater: Arsenic ........................................................................ 36
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7.1.1. Longitudinal plots of the data for arsenic (ug/L) ...................................................................... 36

7.1.2. Summary statistics for arsenic (ug/L) ....................................................................................... 37

7.2. Biological Treatment for FGD Wastewater: Mercury ...................................................................... 38

7.2.1. Longitudinal plots of the data for mercury (ng/L) .................................................................... 38

7.2.2. Summary statistics for mercury (ng/L) ..................................................................................... 39

7.3. Biological Treatment for FGD Wastewater: Nitrate-nitrite as N...................................................... 39

7.3.1. Longitudinal plots of the data for nitrate-nitrite as N (mg/L)................................................... 39

7.3.2. Summary statistics for nitrate-nitrite as N (mg/L).................................................................... 40

7.3.3. Plant-specific long-term averages and variability factors, option long-term averages and 

variability factors, and effluent limits for nitrate-nitrite as N (mg/L) ..................................... 40

7.4. Biological Treatment for FGD Wastewater: Selenium..................................................................... 41

7.4.1. Longitudinal plots of the data for selenium (ug/L)................................................................... 41

7.4.2. Summary statistics for selenium (ug/L) .................................................................................... 42

7.4.3. Plant-specific long-term averages and variability factors, option long-term averages and 

variability factors, and effluent limits for selenium (ug/L)...................................................... 43

7.5. Biological Treatment for FGD Wastewater: Summary of the Option Long-Term Averages, 

Variability Factors, and Effluent Limits............................................................................................ 43

8. Treatment Technology Option for FGD Wastewater: Vapor-Compression Evaporation System........... 44

8.1. Vapor-Compression Evaporation for FGD Wastewater: Arsenic ..................................................... 45

8.1.1. Longitudinal plots of the data for arsenic (ug/L) ...................................................................... 45

8.1.2. Summary statistics for arsenic (ug/L) ....................................................................................... 45

8.1.3. Plant-specific long-term averages and variability factors, option long-term averages and 

variability factors, and effluent limits for arsenic (ug/L)......................................................... 46

8.2. Vapor-Compression Evaporation for FGD Wastewater: Mercury ................................................... 47

8.2.1. Longitudinal plots of the data for mercury (ng/L) .................................................................... 47

8.2.2. Summary statistics for mercury (ng/L) ..................................................................................... 48

8.2.3. Plant-specific long-term averages and variability factors, option long-term averages and 

variability factors, and effluent limits for mercury (ng/L)....................................................... 48

8.3. Vapor-Compression Evaporation for FGD Wastewater: Selenium.................................................. 49

8.3.1. Longitudinal plots of the data for selenium (ug/L)................................................................... 49

8.3.2. Summary statistics for selenium (ug/L) .................................................................................... 49

8.3.3. Plant-specific long-term averages and variability factors, option long-term averages and 

variability factors, and effluent limits for selenium (ug/L)...................................................... 50

8.4. Vapor-Compression Evaporation for FGD Wastewater: Total Dissolved Solids (TDS)..................... 51

8.4.1. Longitudinal plots of the data for TDS (mg/L) .......................................................................... 51

8.4.2. Summary statistics for TDS (mg/L)............................................................................................ 51

8.4.3. Plant-specific long-term averages and variability factors, option long-term averages and 

variability factors, and effluent limits for TDS (mg/L)............................................................. 52

8.5. Vapor-Compression Evaporation for FGD Wastewater: Summary of the Option Long-Term 

Averages, Option Variability Factors, and Effluent Limits............................................................... 52

9. Treatment Technology Option for Gasification Wastewater: Vapor-Compression Evaporation........... 54

9.1. Vapor-Compression Evaporation for Gasification: Arsenic.............................................................. 55

9.1.1. Longitudinal plots of the data for arsenic (ug/L) ...................................................................... 55

9.1.2. Summary statistics for arsenic (ug/L) ....................................................................................... 55

9.1.3. Plant-specific long-term average and variability factors, option long-term average and 

variability factors, and effluent limits for arsenic (ug/L)......................................................... 56
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9.2. Vapor-Compression Evaporation for Gasification: Mercury............................................................ 57

9.2.1. Longitudinal plots of the data for mercury (ng/L) .................................................................... 57

9.2.2. Summary statistics for mercury (ng/L) ..................................................................................... 57

9.2.3. Plant-specific long-term average and variability factors, option long-term average and 

variability factors, and effluent limits for mercury (ng/L)....................................................... 58

9.3. Vapor-Compression Evaporation for Gasification: Selenium .......................................................... 59

9.3.1. Longitudinal plots of the data for selenium (ug/L)................................................................... 59

9.3.2. Summary statistics for selenium (ug/L) .................................................................................... 60

9.3.3. Plant-specific long-term averages and variability factors, option long-term average and 

variability factors, and effluent limits for selenium (ug/L)...................................................... 61

9.4.1. Longitudinal plots of the data for TDS (mg/L) .......................................................................... 61

9.4.2. Summary statistics for TDS (mg/L)............................................................................................ 62

9.4.3. Plant-specific long-term averages and variability factors, option long-term average and 

variability factors, and effluent limits for TDS (mg/L)............................................................. 63

9.5. Vapor-Compression Evaporation for Gasification: Summary of the Option Long-Term Average, 

Option Variability Factors, and Effluent Limits................................................................................ 63

10. Summary of Effluent Limits for Each Treatment Technology Option for FGD, Gasification, and 

Leachate Wastewater........................................................................................................................... 64

11. Engineering Review of the Effluent Limits............................................................................................ 66

11.1. Comparison of the Limits to Effluent Data Used as the Basis for the Limits................................. 66

11.2. Comparison of the Effluent Limits to Influent Data....................................................................... 71

APPENDIX 1: List of All Observations that Were Corrected and Excluded Before Calculating the Limits.. 72

1. Corrections Made to Plant Self-Monitoring Data from Belews Creek................................................ 73

2. List of Data Excluded Due to Samples Analyzed Using an Insufficiently-Sensitive Analytical 

Method............................................................................................................................................ 74

3. List of Data Excluded Due to Samples Being Collected During the Initial Commissioning Period 

for the Treatment System ............................................................................................................... 76

4. List of Data Excluded Due to Analytical Results that Identified as Questionable Due to the 

Quality Control Issues, Abnormal Conditions or Treatment Upset, or Analytical Anomalies......... 76

APPENDIX 2: Plots of Plant Self-monitoring Data with Smoothed Curves to Aid in Determining Initial 

Commissioning Period of Treatment System....................................................................................... 80

APPENDIX 3: Data Editing Criteria Results.................................................................................................. 87

APPENDIX 4: Summary of the Results for the Engineering Review of the Limits....................................... 90

1. Results of the Comparison of the Limits to Effluent Data Used as the Basis for the Limits ............... 91

2. Comparison of the Effluent Limits to Influent Data............................................................................ 94
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List of Tables

Table 1. Summary of the analytical lab methods used for each pollutant................................................. 16

Table 2. Summary of the baseline values used for each pollutant............................................................. 22

Table 3. Aggregation of Field Duplicates. ................................................................................................... 24

Table 4. Summary of Estimated Autocorrelation Values at Allen and Belews Creek................................. 27

Table 5. Numbers of detected and non-detected observations and sample-specific detection limits 

for arsenic (ug/L) by plant and sampling location. ................................................................... 32

Table 6. Summary statistics of arsenic concentration (ug/L) for all detected and non-detected 

samples combined, by plant and sampling location................................................................. 32

Table 7. Plant-specific long-term averages and variability factors, option long-term average and 

variability factors, and limits for arsenic (ug/L) at chemical precipitation effluent. ................ 33

Table 8. Summary statistics of mercury concentration (ng/L) for all detected samples by plant and 

sampling location...................................................................................................................... 34

Table 9. Plant-specific long-term average and variability factors, option long-term average and 

variability factors, and limits for mercury (ng/L) at chemical precipitation effluent. .............. 34

Table 10. Summary of option long-term averages, option variability factors, and effluent limits for 

chemical precipitation FGD wastewater treatment technology. ............................................. 34

Table 11. Numbers of detected and non-detected observations and sample-specific detection limits 

for arsenic (ug/L) by plant and sampling location. ................................................................... 37

Table 12. Summary statistics of arsenic concentration (ug/L) for all detected and non-detected 

samples combined, by plant and sampling location................................................................. 38

Table 13. Summary statistics of mercury concentration (ng/L) for all detected and non-detected 

samples combined by plant and sampling location.................................................................. 39

Table 14. Number of detected, non-detected, and sample-specific detection limits for nitrate-nitrate 

as N (mg/L) by plant and sampling location. ............................................................................ 40

Table 15. Summary statistics of nitrate-nitrite as N concentration (mg/L) for all detected and 

non-detected samples combined by plant and sampling location........................................... 40

Table 16. Lag-1 autocorrelation values, plant-specific long-term averages and variability factors, 

option long-term averages and variability factors, and limits for nitrate-nitrite as N (mg/L) 

at bioreactor effluent................................................................................................................ 41
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Table 17. Number of detected, non-detected, and sample-specific detection limits for selenium 

(ug/L) by plant and sampling location. ..................................................................................... 42

Table 18. Summary statistics of selenium concentration (ug/L) for all detected and non-detected 

samples combined by plant and sampling location.................................................................. 42

Table 19. Lag-1 autocorrelation values, plant-specific long-term averages and variability factors, 

option long-term averages and variability factors, and limits for selenium (ug/L) at 

bioreactor effluent.................................................................................................................... 43

Table 20. Summary of option long-term averages, variability factors, and effluent limits for biological 

FGD wastewater treatment technology. .................................................................................. 44

Table 21. Numbers of detected and non-detected observations and sample-specific detection limits 

for arsenic (ug/L) by sampling location..................................................................................... 46

Table 22. Summary statistics of arsenic concentration (ug/L) for all detected and non-detected 

samples combined by sampling location.................................................................................. 46

Table 23. Plant-specific long-term averages and variability factors, option long-term averages and 

variability factors, and limits for arsenic (ug/L) at brine concentrator distillate and 

crystallizer condensate. ............................................................................................................ 47

Table 24. Summary statistics of mercury concentration (ng/L) for all detected and non-detected 

samples combined by sampling location.................................................................................. 48

Table 25. Plant-specific long-term averages and variability factors, option long-term averages and 

variability factors, and limits for mercury (ng/L) at brine concentrator distillate and 

crystallizer condensate. ............................................................................................................ 48

Table 26. Number of detected, non-detected, and sample-specific detection limits for selenium 

(ug/L) by sampling location....................................................................................................... 49

Table 27. Summary statistics of selenium concentration (ug/L) for all detected and non-detected 

samples combined by sampling location.................................................................................. 50

Table 28. Plant-specific long-term averages and variability factors, option long-term averages and 

variability factors, and limits for selenium (ug/L) at brine concentrator distillate and 

crystallizer condensate. ............................................................................................................ 50

Table 29. Number of detected, non-detected, and sample-specific detection limits for total dissolved 

solid (mg/L) by sampling location. ............................................................................................ 51

Table 30. Summary statistics of total dissolved solids concentration (mg/L) for all detected and nondetected samples combined by sampling location................................................................... 52
Page 9

Table 31. Plant-specific long-term averages and variability factors, option long-term averages and 

variability factors, and limits for TDS (mg/L) at brine concentrator distillate and 

crystallizer condensate. ............................................................................................................ 52

Table 32. Summary of option long-term averages, variability factors, and limits for vaporcompression evaporation technology for FGD wastewater at brine concentrator distillate... 53

Table 33. Summary of option long-term averages, option variability factors, and limits for 

mechanical vapor-compression evaporation technology for FGD wastewater at 

crystallizer condensate. ............................................................................................................ 53

Table 34. Numbers of detected and non-detected observations and sample-specific detection limits 

for arsenic (ug/L) by plant and sampling location. ................................................................... 56

Table 35. Summary statistics of arsenic concentration (ug/L) for all detected and non-detected 

samples combined, by plant and sampling location................................................................. 56

Table 36. Plant-specific long-term average and variability factors, option long-term average and 

variability factors, and limits for arsenic (ug/L) at vapor compression 

evaporator condensate............................................................................................................. 57

Table 37. Numbers of detected and non-detected observations and sample-specific detection limits 

for mercury (ng/L) by plant and sampling location. ................................................................. 58

Table 38. Summary statistics of mercury concentration (ng/L) for all detected and non-detected 

samples combined, by plant and sampling location................................................................. 58

Table 39. Plant-specific long-term average and variability factors, option long-term average and 

variability factors, and limits for mercury (ng/L) at vapor compression evaporator 

condensate................................................................................................................................ 59

Table 40. Numbers of detected and non-detected observations and sample-specific detection limits 

for selenium (ug/L) by plant and sampling location. ................................................................ 60

Table 41. Summary statistics of selenium concentration (ug/L) for all detected and non-detected 

samples combined, by plant and sampling location................................................................. 60

Table 42. Plant-specific long-term averages and variability factors, option long-term average and 

variability factors, and limits for selenium (ug/L) at vapor compression evaporator 

condensate................................................................................................................................ 61

Table 43. Numbers of detected and non-detected observations and sample-specific detection limits 

for TDS (mg/L) by plant and sampling location......................................................................... 62

Table 44. Summary statistics of TDS concentration (mg/L) for all detected and non-detected samples 

combined, by plant and sampling location............................................................................... 62
Page 10

Table 45. Plant-specific long-term averages and variability factors, option long-term average and 

variability factors, and numeric limits for TDS (mg/L) at vapor compression evaporator 

condensate................................................................................................................................ 63

Table 46. Summary of option long-term averages, option variability factors, and limits for vaporcompression evaporation technology for gasification wastewater. ........................................ 63

Table 47. Summary of the option long-term averages and variability factors together with the 

effluent limits for each of the FGD, gasification, and leachate technology option.................. 65

Table 1.1. Summary of the corrected detection indicators for the Belews Creek self-monitoring data, 

arranged by sampling location, pollutant, and sampling date. ................................................ 73

Table 1.2. Summary of the data corrections for the Belews Creek self-monitoring data, arranged by 

sampling location, pollutant, and sampling date...................................................................... 74

Table 1.3. Summary of the mercury data excluded from plant self monitoring data due to using an 

insufficiently-sensitive analytical method. ............................................................................... 75

Table 1.4. Summary of the questionable mercury data excluded due to quality control issues for the 

plant self-monitoring data at Allen and Belews Creek. ............................................................ 77

Table 1.5. Summary of data excluded due to abnormal conditions or treatment upset and analytical 

anomalies.................................................................................................................................. 78

Table 3.1. Summary of the results for data editing procedure performed to select a dataset for 

pollutant at each plant in calculating the limits........................................................................ 89

Table 4.1. Listing of all daily values that are above the daily limits for chemical precipitation 

treatment for FGD wastewater................................................................................................. 91

Table 4.2. For chemical precipitation treatment for FGD wastewater, a listing of all the daily values 

that are above the monthly limits, along with any other daily values collected in the same 

month........................................................................................................................................ 92

Table 4.3. Listing of all daily values that are above the daily limits for the biological treatment 

technology option for FGD wastewater.................................................................................... 92

Table 4.4. For biological treatment for FGD wastewater, a listing of all the daily values that are above 

the monthly limits, along with any other daily values collected in the same month............... 93

Table 4.5. Listing of all daily values that are above the daily limits for vapor-compression evaporation 

treatment for gasification wastewater..................................................................................... 94

Table 4.6. For vapor-compression evaporation treatment for gasification wastewater, a listing of all 

the daily values that are above the monthly limits, along with any other daily values 

collected in the same month. ................................................................................................... 94
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Table 4.7. Summary statistics for the influent (FGD Purge) concentrations for plants from which the 

data were used as the basis for calculating the limits for chemical precipitation treatment 

technology option for FGD wastewater.................................................................................... 95

Table 4.8. Summary statistics for the influent (FGD Purge) concentrations for plants from which the 

data were used as the basis for calculating the limits for biological treatment technology 

option for FGD wastewater....................................................................................................... 95

Table 4.9. Summary statistics for the influent (FGD Purge) concentrations for plants from which the 

data were used as the basis for calculating the limits for vapor-compression evaporation 

treatment technology option for FGD wastewater. ................................................................. 96

Table 4.10. Summary statistics for the influent (vapor compression evaporator influent) 

concentrations from plants for which the data were used as the basis for calculating the 

limits for vapor-compression evaporation treatment technology option for gasification 

wastewater. .............................................................................................................................. 97
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List of Figures

Figure 1. Plot of arsenic (ug/L) data on a logarithmic scale for Hatfield’s Ferry, Keystone, and Miami 

Fort............................................................................................................................................ 31

Figure 2. Plot of mercury (ng/L) data on a logarithmic scale for Hatfield’s Ferry, Keystone, and Miami 

Fort............................................................................................................................................ 33

Figure 3. Plot of arsenic (ug/L) data on a logarithmic scale for Allen and Belews Creek. .......................... 37

Figure 4. Plot of mercury (ng/L) data on a logarithmic scale for Allen and Belews Creek. ........................ 38

Figure 5. Plot of nitrate-nitrite as N (mg/L) data on a logarithmic scale for Allen and Belews Creek 

(for short, the name on the vertical is labeled as nitrite)......................................................... 39

Figure 6. Plot of selenium (ug/L) data on a logarithmic scale for Allen and Belews Creek. ....................... 41

Figure 7. Plot of arsenic (ug/L) data on a logarithmic scale for Brindisi. .................................................... 45

Figure 8. Plot of mercury (ng/L) data on a logarithmic scale for Brindisi. .................................................. 47

Figure 9. Plot of selenium (ug/L) data on a logarithmic scale for Brindisi.................................................. 49

Figure 10. Plot of TDS (mg/L) data on a logarithmic scale for Brindisi. ...................................................... 51

Figure 11. Plot of arsenic (ug/L) data on a logarithmic scale for Polk and Wabash River. ......................... 55

Figure 12. Plot of mercury (ng/L) data on a logarithmic scale for Polk and Wabash River. ....................... 57

Figure 13. Plot of selenium (ug/L) data on a logarithmic scale for Polk and Wabash River....................... 59

Figure 14. Plot of TDS (mg/L) data on a logarithmic scale for Polk and Wabash River. ............................. 61

Figure 2.1. Plot of all self-monitoring data for arsenic (ug/L) for Allen and Belews Creek. ....................... 81

Figure 2.2. Smoothed plot (using LOWESS) of all self-monitoring data for arsenic (ug/L) for Allen and 

Belews Creek............................................................................................................................. 81

Figure 2.3. Plot of self-monitoring data for arsenic (ug/L) for Allen and Belews Creek after exclusions 

described in Sections 3.2.1 and 3.2.3. ...................................................................................... 82

Figure 2.4. Smoothed plot (using LOWESS) of self-monitoring data for arsenic (ug/L) for Allen and 

Belews Creek after exclusions described in Sections 3.2.1 and 3.2.3....................................... 82

Figure 2.5. Plot of all self-monitoring data for mercury (ng/L) for Allen and Belews Creek. ..................... 83

Figure 2.6. Smoothed plot (using LOWESS) of all self-monitoring data for mercury (ng/L) for Allen 

and Belews Creek...................................................................................................................... 83
Page 13

Figure 2.7. Plot of self-monitoring data for mercury (ng/L) for Allen and Belews Creek after 

exclusions described in Sections 3.2.1 and 3.2.3...................................................................... 84

Figure 2.8. Smoothed plot (using LOWESS) of all self-monitoring data for mercury (ng/L) for Allen 

and Belews Creek after exclusions described in Sections 3.2.1 and 3.2.3................................ 84

Figure 2.9. Plot of all self-monitoring data for selenium (ug/L) for Allen and Belews Creek. .................... 85

Figure 2.10. Smoothed plot (using LOWESS) of all self-monitoring data for selenium (ug/L) for Allen 

and Belews Creek...................................................................................................................... 85

Figure 2.11. Plot of self-monitoring data for selenium (ug/L) for Allen and Belews Creek after 

exclusions described in Sections 3.2.1 and 3.2.3...................................................................... 86

Figure 2.12. Smoothed plot (using LOWESS) of self-monitoring data for selenium (ug/L) for Allen and 

Belews Creek after exclusions described in Sections 3.2.1 and 3.2.3....................................... 86
Page 14

1. Introduction

This report presents the results of the statistical analyses performed on the Flue Gas 

Desulfurization (FGD) wastewater and gasification wastewater treatment data and the resulting 

long-term average, variability factors, and effluent limitations for each pollutant in each 

technology option. 

This report is focused primarily on the summary of the data and the development of 

long-term averages, variability factors, and effluent limitations. Thus, this report does not 

include a description of (i) FGD and gasification systems and the wastewater associated with 

each waste stream, (ii) all available treatment technology options for each waste stream, (iii) 

the rationale for selecting plants used in the calculation of the effluent limitations for each 

technology option, (iv) the rationale for transferring limitations for different technology 

options, or (v) a discussion of the baseline values used for adjusting the data before calculating 

the effluent limitations. For detailed discussion of the items mentioned above, see the 

Technical Development Document.

In this document, for simplicity, the proposed effluent limitations guidelines and 

standards are referred to as “limits”. The terms option long-term averages and option 

variability factors refer to the technology options rather than the regulatory options described 

in Section 8 of the Technical Development Document. The term “detected” refers to analytical 

results measured and reported above the sample-specific quantitation limit (QL); and the term 

“non-detected” refers to values that are below the method detection limit (MDL) and those 

values measured by the laboratory as being between the MDL and the QL in the original data 

(before adjusting for baseline). The long-term averages, variability factors, and effluent limits

were calculated out to five decimal points for accuracy. However, to simplify the presentation 

the values presented in this document have been rounded to three decimal points. All 

exclusions, baseline substitutions, and aggregation of data were made prior to performing the 

statistical analyses presented in Sections 6, 7, 8, and 9. Finally, the Excel Spreadsheet titled

“Sampling Data Used as the Basis for Effluent Limitations for the Steam Electric Rulemaking”

contains the listing of all the available data, the excluded data, the baseline values for each 

pollutant, and the final concentration values that were used in the limit calculations, among 

other relevant data items. This Excel Spreadsheet is in the record as DCN SE02002 (this 

spreadsheet will hereafter be referred to as DCN SE02002).

2. Description of Data Used to Calculate Long-Term Averages, Variability 

Factors, and Effluent Limits

This section provides an overview of the available data at each plant selected as the 

basis for the effluent limits for each technology option, the analytical methods used to analyze 

each of the pollutants, and the rationale for combining sampling data from multiple sources at 

each plant into a single dataset for the plant.
Page 15

2.1. Overview of the Data

In developing the effluent limits for the FGD and gasification wastewater treatment 

technologies, EPA used data from the following eight power plants: Allen, Belews Creek, 

Hatfield’s Ferry, Keystone, Miami Fort, Brindisi, Polk, and Wabash River. The following bullets 

provide a brief overview of the data source available for each plant (see Sections 6, 7, 8, and 9

for a more detailed description of the data at each of the plants):

• At Hatfield’s Ferry, Keystone, and Miami Fort, sampling data were available from two 

sources: (i) EPA sampling episodes (hereafter referred to as “EPA sampling”) and (ii) EPA 

directed sampling through letters issued under authority of CWA section 308 (hereafter 

referred to as “CWA 308 sampling”). The data were collected at two sampling locations: 

FGD purge and chemical precipitation effluent. 

• At Allen and Belews Creek, sampling data were available from three sources: (i) plant 

self monitoring (hereafter referred to as “plant self-monitoring”) data for several years 

of operation provided by Duke Energy, (ii) EPA sampling, and (iii) CWA 308 sampling. 

The data were collected at three sampling locations: FGD purge, bioreactor influent, and 

bioreactor effluent.

• At Brindisi, the sampling data available were from EPA sampling. The data were 

collected at three sampling locations: FGD purge, brine concentrator distillate, and 

crystallizer condensate.

• At Polk and Wabash River, the sampling data available were from CWA 308 sampling. 

For Polk, the data were collected at four sampling locations: neutralized weak acid 

waste stream, vapor compression evaporator influent, vapor compression evaporator 

condensate, and forced circulation evaporator condensate. For Wabash River, the 

sampling data were collected at four sampling locations: sour water treatment influent, 

steam stripper effluent, vapor compression evaporator influent, and vapor compression 

evaporator condensate.

2.2. Analytical Methods

The table below summarizes the analytical methods used to analyze each pollutant. 

Note that the footnote in the table does not apply to the arsenic and selenium self-monitoring 

data at Allen and Belews Creek plants since analytical method 200.8 was used to analyze data 

from all sampling locations.
Page 16

Table 1. Summary of the analytical lab methods used for each pollutant.

Analytical method Pollutant

200.8, 6020 Arsenic 1, Selenium 1

1631E, FGS – 069 Mercury 2

353.2 Nitrate-nitrite as N

2540C Total Dissolved Solids 1: Method 200.8 was used at each of the sampling locations except for FGD purge (this applies to all data except plant selfmonitoring at Allen and Belews Creek). At FGD purge, a combination of methods 200.8 and 6020 was used since the analysis 

procedure was “calculated total” instead of “total”. 

2: Method 1631E was used at each of the sampling locations except for FGD purge. At FGD purge, a combination of methods 

1631E and FGS - 069 was used since the analysis procedure was “calculated total” instead of “total”.

2.3. Combining Data from Multiple Sources within a Plant

Typically, if sampling data from a plant were collected over two or more distinct time 

periods, EPA analyzes the data from each time period separately. In past Effluent Limitations 

Guidelines and Standards, EPA has analyzed data as if each time period represents a different 

plant since these data can represent different operating conditions due to changes in 

management, personnel, and procedures. On the other hand, when EPA obtains the data (such 

as EPA sampling and plant self-monitoring data) from a plant during the same time period, EPA 

usually combines the data from these sources into a single dataset for the plant for the 

statistical analyses.

As described in Section 2.1, data for most of the plants came from multiple sources such 

as EPA sampling, CWA 308, or plant self-monitoring. For three plants (Allen, Belews Creek, and 

Hatfield’s Ferry), the multiple sources of the data were collected during overlapping time 

periods, thus, EPA combined these data into a single dataset for the plant. For two plants 

(Keystone and Miami Fort), the multiple sources of the data were collected during nonoverlapping time periods. However, in these instances the time period between the nonoverlapping data collection periods was relatively small (two months). Furthermore, EPA has no 

information to indicate that the data represent different operating conditions. Thus, EPA also 

combined the multiple sources of data for each of these plants into a single dataset for the 

plant. This approach is consistent with EPA’s traditional approach for other effluent guidelines 

rulemakings. Three plants (Brindisi, Polk, and Wabash River) had data from a single source, and 

for these plants it was not necessary to combine data. For a listing of all the data and their 

sampling sources for each of the plants, see DCN SE02002.

3. Data Corrections, Exclusions, Baseline Substitutions, and Aggregation

This section describes the data corrections, exclusions, baseline substitutions, and 

aggregations made to the data before developing the effluent limits for each pollutant in each 

technology option. It should be noted that even though EPA is not using the arsenic and 

mercury data from Allen and Belews Creek to calculate the limits for biological treatment 

system (for the reason described above and in Section 7), EPA did perform data corrections, 
Page 17

exclusions, baseline substitutions, and aggregation for the arsenic and mercury data at these 

two plants.

3.1. Data Corrections

Several corrections were made to the plant self-monitoring data at Belews Creek due to 

data entry errors. In July 2011, EPA’s Engineering and Analysis Division obtained the plant selfmonitoring data for Allen and Belews Creek from Duke Energy. After an initial review of the 

data, some inconsistencies were found and EPA subsequently asked Duke Energy to address the 

potential errors (an email from Ronald Jordan to Nathan Craig on 07/20/2011 summarized the 

apparent inconsistencies). Duke Energy responded to EPA’s request in an email from Nathan 

Craig to Ronald Jordan (dated 07/21/2011). The data issues that were clarified dealt with data 

entry errors in certain detection indicators (see Table 1.1 in Appendix 1). Further, after 

continued interaction between Ron Jordan and Nathan Craig, other data entry errors were also 

corrected (see Table 1.2 in Appendix 1).

3.2. Data Exclusions and Rationale for the Exclusions

Prior to calculating the effluent limits, EPA thoroughly evaluated the available data 

for each plant. EPA identified certain data that warranted exclusion from the limit 

calculations because: (i) samples were analyzed using an insufficiently-sensitive analytical 

method (i.e., use of EPA Method 245.1 instead of Method 1631E for mercury); (ii) the 

samples were collected during initial commissioning period for the treatment system; or (iii) 

the analytical results were identified as questionable due to quality control issues, 

abnormal conditions or treatment upsets, or were analytical anomalies. Appendix 1 of this 

document provides a listing of each of the data points that were excluded. 

The subsections below provide a detailed discussion of the rationale for each of the 

exclusions mentioned above.

3.2.1. Excluding mercury samples analyzed using an insufficiently-sensitive analytical method

The plant self-monitoring data at Allen and Belews Creek were collected by Duke Energy 

to evaluate and optimize the operation of the treatment systems, but note that they are not 

NPDES compliance monitoring samples. In some cases, Duke Energy analyzed the samples for 

mercury using EPA Method 1631E, while other samples were analyzed for mercury using EPA 

Method 245.1. Method 245.1 was approved by EPA in 1974 and can achieve measurements of 

mercury down to 200 parts per trillion (ppt), although the Method 245.1 data for both plants 

set the detection limit for mercury in the bioreactor samples at 1 part per billion (ppb). EPA 

approved Method 1631E in 2002. This newer method has a detection level of 0.5 ppt, making it 

400 times more sensitive than Method 245.1.

In a memorandum issued by EPA’s Office of Wastewater Management, EPA directed 

permitting authorities to ensure that sufficiently-sensitive analytical methods are used when 
Page 18

deciding whether to set a permit limitation for mercury and for sampling and analysis of 

mercury pursuant to the monitoring requirements within a NPDES permit1. One measure for 

determining whether a method for mercury is “sufficiently sensitive” is that its method 

detection level is low enough relative to the amount of mercury in a plant’s discharge that the 

method detects the level of mercury present in the discharge. Since these self-monitoring 

samples were not collected for the purpose of demonstrating compliance with NPDES permit 

limits, Duke Energy had the discretion to choose whichever analytical method it wished to use. 

However, the detection level for Method 245.1 is not low enough to detect the concentration 

of mercury present in the bioreactor influent and bioreactor effluent samples, making it 

inappropriate for use in calculating permit limits. Similarly, data for samples analyzed with 

Method 245.1 are inappropriate for use in calculating limits for effluent limitations guidelines 

and standards for discharges from power plants. Therefore, all mercury results that were 

analyzed using Method 245.1 for bioreactor influent and bioreactor effluent samples were 

excluded (see Appendix 1 for a listing of these exclusions).

3.2.2. Excluding samples collected during the initial commissioning period for the treatment

system

EPA generally excludes data associated with the initial start-up or commissioning period 

for a new wastewater treatment system because the data tend to exhibit relatively high 

variability not representative of typical operation. During the initial commissioning period, the 

treatment system undergoes a variety of testing to demonstrate that hydraulic flows through 

the system and equipment such as pumps, valves, and other equipment operate as designed. 

During this period, it is common for changes in process operations to occur as the treatment 

system undergoes performance verification testing (sometimes referred to as acceptance 

testing) and the operation is modified to identify approaches to optimize (i.e., minimize) 

operational costs or to make adjustments to improve pollutant reductions. Refinements that 

may take place during the commissioning period include adjustments to chemical feed 

locations and/or feed rates; evaluating different pump cycles, filter backwash cycles, clarifier 

overflow rates, or sludge removal cycles; and changes to the chemicals used. Generally, this 

initial period of operation also serves as a time when the operators gain familiarity with the 

intricacies of the treatment system operation. During this acclimation and optimization period 

the effluent concentration values may exhibit higher variability than would typically be 

observed for a well-operated treatment system, producing occasional extreme values (either 

high or low concentrations). After this initial adjustment period, a well-operated system should 

operate at steady state (or more precisely, a “quasi-steady state”) with relatively low variability 

around a long-term average. 

Since the plant self-monitoring data for Allen and Belews Creek Stations included the 

initial startup and commissioning period for the treatment systems, EPA needed to determine 

the duration of the commissioning period and to exclude these data points before the analyses 

 1 James A. Hanlon, Director, Office of Wastewater Management. “Analytical Methods for Mercury in National 

Pollutant Discharge Elimination System (NPDES) Permits,” August 23, 2007.
Page 19

were performed. The commissioning period for the self-monitoring data at Allen and Belews 

Creek was determined from an engineering perspective based on extensive experience 

evaluating treatment systems at power plants and other industry sectors and knowledge of the 

physical, chemical, and biological treatment processes employed and by looking at the 

longitudinal plots of all the data. In addition to the longitudinal plots of individual data, smooth 

curves (obtained by LOWESS) superimposed on the individual data plots were also examined to 

help determine when the treatment system appeared to stabilize (see Appendix 2). The

smoothing technique used (LOWESS) makes minimal assumptions about the distribution of the 

data and is meant to highlight patterns of the data (see Cleveland (1979, 1981) for more 

details). In examining the longitudinal plots, EPA looked at two types of plots: plots of all the 

available data and plots of data after the exclusions described in Sections 3.2.1 above and 3.2.3

below. The conclusions from both of these approaches were consistent. The initial six months 

of operation was determined to represent a reasonable estimate of the commissioning period 

for the treatment systems. The data associated with the commissioning periods were excluded 

from the data used to calculate the limits. The data excluded from each of the plants due to the 

commissioning period are summarized below:

• For Allen Station, data from March 3, 2009 through August 26, 2009 were excluded.

• For Belews Creek Station, data from February 6, 2008 through July 31, 2008 were 

excluded.

3.2.3. Excluding analytical results that were identified as questionable due to quality control

(QA/QC) issues, abnormal conditions or treatment upset, or were analytical anomalies

The bullets below provide a rationale for the exclusions made to the data prior to 

performing statistical analyses (see Appendix 1 for a listing of all these exclusions) for the 

reasons other than discussed in Sections 3.2.1 and 3.2.2 above. Note that for a majority of the 

dates, the FGD purge value was retained in the dataset since these values were not identified as 

questionable. The purge values that were retained were used to evaluate the treatment 

performance. Thus, in such instances, EPA assumed the FGD purge data accurately reflected the 

pollutant concentrations in the wastewater transferred to the wastewater treatment system 

(i.e., treatment system influent) and that the questionable data were associated with the 

characterization of treatment system performance (i.e., treatment system effluent or 

intermediate sampling point).

• Analytical results that were identified as questionable due to quality control issues: EPA 

excluded all mercury data collected at Allen and Belews Creek that Duke Energy 

identified as questionable due to quality control issues. Duke Energy stated that these 

data are questionable because they suspected that the matrix spike/matrix spike 

duplicate (MS/MSD) were not conducted using the FGD wastewater matrix or the

MS/MSD indicated inadequate recoveries. EPA lacked sufficient laboratory quality 

control data for these results to make an independent assessment of whether these 

mercury results should have been retained and included in the statistical analyses.
Page 20

• Abnormal conditions or treatment upset: EPA excluded all of the data collected at Allen 

on dates 3/8/10, 3/22/10, 4/5/10, 4/26/10, 5/10/10, and 5/25/10 for this reason. When 

reviewing the data, EPA observed periodic occurrences in early 2010 of unusually high 

concentrations of arsenic in the bioreactor effluent relative to effluent from the 

bioreactor influent treatment stage. According to Duke Energy personnel, the treatment 

system suffered an upset condition beginning 3/2/10, that particularly impacted arsenic 

concentrations exiting the bioreactor. The treatment system suffered pipe failures in the 

bioreactor on 3/2/10 and 3/11/10, dislodging a portion of the carbon within the 

bioreactor cells. It took approximately four weeks for repairs to be completed, and 

additional time for the treatment system performance to stabilize. According to Duke 

Energy, elevated arsenic concentrations in the bioreactor effluent during the period 

March through May 2010 are likely attributable to the pipe breakages and related repair 

activities. Despite the claim from Duke Energy that only arsenic concentrations were 

affected, EPA made the decision to exclude all data collected from date of the first pipe 

failure until the end of May. 

• Abnormal conditions or treatment upset: EPA excluded mercury data collected on 

10/5/10 at the chemical precipitation effluent at Hatfield’s Ferry. This exclusion was due 

to an unusually high analytical result inconsistent with proper operation of the 

BAT/NSPS chemical precipitation treatment technology. Specifically, based on 

information in the record, the sampling result indicates that the sample may have been 

contaminated during sample collection or was adversely affected by treatment system 

upset. The decision to exclude the analytical result (978 ng/L) is supported by the plant’s 

NPDES compliance monitoring data for that time period. The maximum daily value 

reported for FGD wastewater treatment system effluent for the month of October 2010 

was 127 ng/L. If the excluded value accurately represented the mercury concentration 

in the plant’s FGD treatment system effluent, due to the hydraulic residence times and 

mixing that occurs in the FGD absorber and the wastewater treatment system, similarly 

high concentrations of mercury should have been reflected in the plant’s NPDES

compliance monitoring samples. Furthermore, the maximum daily values reported by 

the plant for each monthly reporting period for August 2010 through February 2011 

were also substantially lower than the excluded value, ranging from 108 ng/L to 268 

ng/L. The excluded value may be the result of sample contamination occurring during 

sample collection. EPA used “clean sampling” techniques for its field sampling program, 

including requiring plant staff to also use such procedures when collecting the CWA 308 

samples. These clean sampling procedures are intended to minimize the potential for 

contaminating samples, particularly in environments where dust and other 

contaminants are present. For all plants in the field sampling program, except Hatfield’s 

Ferry, the CWA 308 sampling was conducted after EPA had first conducted its on-site 

field sampling program. This approach enabled plant staff to become familiar with the 

specialized sampling collection protocols used for “clean sampling” prior to initiating 

their CWA 308 sampling. However, in the case of Hatfield’s Ferry, the plant initiated the 

CWA 308 sampling prior to the EPA field sampling and unfamiliarity with the clean 

sampling protocols may have allowed the October 2010 sample to become 
Page 21

contaminated. If the excluded result is not associated with sample contamination, then 

it indicates that the plant did not exercise good control of the treatment system during 

startup following a shutdown period. All three generating units had been shutdown for 

at least a week preceding the December 2010 sampling event. Unit 3 then started up on 

October 3, generating electricity at approximately one-third capacity for the unit. Unit 3 

then operated at nearly full load on October 4 and approximately two-thirds load on 

October 5, but then shutdown again on October 6. Based on the information in the 

record, the FGD wastewater treatment system likely was not operating in a stable 

manner during this period.

• Analytical anomalies: EPA excluded questionable duplicate mercury data collected on 

6/9/10 at the bioreactor effluent at Belews Creek. This exclusion was made since the 

duplicate value (6,440 ng/L) was drastically different from the split sample value (247

ng/L), as well as other results for that sample point, and so deemed an analytical 

anomaly. 

• Analytical anomalies: EPA also excluded questionable selenium data collected on 

7/14/10 at the bioreactor effluent at Belews Creek. This exclusion was made since this 

observation (299 ug/L) is much higher than any other observed in the remainder of 

dataset. EPA evaluated the selenium contributions in the FGD purge and bioreactor 

influent (total and dissolved selenium, as well as concentrations of selenate and 

selenite), and the values for total selenium, selenite, and selenate in the bioreactor 

effluent (there are no dissolved selenium results for the bioreactor effluent on that 

date). In addition, EPA evaluated the concentrations for total selenium, dissolved 

selenium, selenite, and selenate at all three sampling locations for the months 

preceding and following the July 14 sampling event. Duke Energy personnel reported no 

indication of abnormal events or activities at the time of sample collection. They were 

unable to explain the result and noted that samples of the ash basin (which receives 

treated FGD wastewater) collected around the same time period did not exhibit a 

similar increase in selenium concentrations. Even taking into account the concentration 

of selenate present in the FGD purge and bioreactor influent samples, the bioreactor 

effluent is substantially higher than would be expected based on the demonstrated 

performance of the bioreactors at both Allen and Belews Creek Stations. Furthermore, 

the Duke Energy self-monitoring data includes sampling results for other days when 

high concentrations of selenate were present in the FGD purge and the bioreactor 

influent, yet the selenium concentrations in the bioreactor effluent were below the 

proposed effluent limit based on the biological treatment technology option. Since no 

plausible explanation validating the extreme observation could be determined, EPA 

excluded the bioreactor effluent selenium observation for July 14, 2010.

3.3. Baseline Substitutions

In general, EPA used detected values or sample-specific detection limits (for nondetected values) in calculating the effluent limits. However, there were some instances where 

EPA substituted a baseline value for a detected value or a sample-specific detection limit. The 
Page 22

baseline value was used in the calculations to account for the possibility that a certain detected 

result may be at a lower concentration than can be reliably achieved by well-operated 

laboratories. This approach is consistent with the way EPA has calculated effluent limits in 

previous effluent guidelines rulemakings. After excluding all the necessary data as described in 

Section 3.2 above, EPA compared each reported result to a baseline value. When a detected 

value or sample-specific detection limit (i.e., sample-specific quantitation limit) was lower than 

the baseline value, EPA used the baseline value instead and classified the value as non-detected 

(even if the actual reported result was a detected value). For example, if the baseline value was 

5 ug/L and the laboratory reported a detected value of 3 ug/L, EPA’s calculations would treat 

the sample result as being non-detected with a sample-specific detection limit of 5 ug/L.

The table below presents the baseline values that were used for each pollutant for this 

rulemaking. It should be noted that in cases when all the concentration values are above the 

baseline value, then the baseline value has no effect on the concentration values and 

subsequent limits. Data for mercury, nitrate-nitrite as N, and total dissolved solids were all

above the baseline values, thus, no baseline substitution was performed. DCN SE02002 

provides a listing of all the data, the indicator of whether a baseline substitution was 

performed, and the value after the baseline substitution was performed.

See Section 13 of Technical Development Document for a detailed discussion of the 

baseline values for each pollutant.

Table 2. Summary of the baseline values used for each pollutant.

Pollutant Baseline Value (unit)

Arsenic 2 ug/L

Mercury 0.5 ng/L

Nitrate-nitrite as N 0.05 mg/L

Selenium 5 ug/L

Total Dissolved Solids 10 mg/L

In addition to calculating the proposed limits for each pollutant for each technology 

option adjusting for the baseline values shown above, EPA calculated what the effluent limits

would be using all valid reported results (i.e., without substituting baseline values and/or 

changing the classification of the result). EPA’s purpose in calculating the effluent limits using 

the data as reported was to allow a comparison between the proposed effluent limits (using 

baseline values listed above) and the limits that would be obtained without the use of baseline 

substitution. These results are presented in the memo titled “Assessment of Effluent 

Limitations and Standards with No Baseline Substitution for the Steam Electric Rulemaking” 

from Ronald Jordan and Cuc Schroeder (dated November 18, 2012) to the Steam Electric 

Rulemaking Record. This memo is in the record as DCN SE02000 (this memo will hereafter be 

referred to as DCN SE02000).
Page 23

3.4. Data Aggregation

EPA used daily values in developing the effluent limits. In cases with two or more 

samples per day, EPA mathematically aggregated these samples to obtain a single value for 

that day (the procedure to aggregate the samples is described in the subsections below). For 

the sampling data used in this rulemaking, there are instances when multiple sample results

are available for a given day. This occurred with field duplicates, overlaps between plant selfmonitoring and EPA sampling, or overlaps between plant self-monitoring and CWA 308 

sampling.

When aggregating the data, EPA took into account whether each value was detected (D) 

or non-detected (ND). Measurements reported as being less than the sample-specific detection 

limit (or baseline values, as appropriate) are designated as non-detected (ND) for the purpose 

of statistical analyses to calculate the effluent limits. In the tables and data listings in this 

document and in the rulemaking record, EPA uses the indicators D and ND denote the 

censoring type for detected and non-detected values, respectively.

The subsections below describe each of the different aggregation procedures. They 

are presented in the order that the aggregation was performed; i.e., field duplicates were 

aggregated first, and then any overlaps between plant self-monitoring and EPA sampling data 

or CWA 308 sampling were aggregated.

3.4.1. Aggregation of field duplicates

During the EPA sampling episodes, EPA collected field duplicate samples as part of the 

quality assurance/quality control activities undertaken to ensure that the quality of the data 

collected is appropriate for their intended use. Field duplicates are two samples collected for 

the same sampling point at approximately the same time. The duplicates are assigned different 

sample numbers, and they are flagged as duplicates for a single sampling point at a plant. 

Because the analytical data from a duplicate pair are intended to characterize the same 

conditions at a given time at a single sampling point, EPA averaged the data to obtain one value 

for each duplicate pair.

In most cases, both duplicates in a pair had the same censoring type, so the censoring 

type of the aggregated value was the same as that of the duplicates. In some instances, one 

duplicate was a detected (D) value but the other duplicate was a non-detected (ND) value. 

When this occurred, EPA determined that the aggregated value should be treated as detected 

(D) because the pollutant is confirmed to be present at a level above the sample-specified 

detection limit in one of the duplicates. DCN SE02002 lists the data before the aggregation as 

well as after the aggregation.

Table 3 below summarizes the procedure for aggregating the sample measurements 

from the field duplicates. 
Page 24

Table 3. Aggregation of Field Duplicates.

If the field 

duplicates are:

Censoring type 

of average is: Value of the aggregate is: Formulas for aggregate values of duplicates

Both detected D Arithmetic average of measured values (D1 + D2)/2

Both non-detected ND Arithmetic average of sample-specific 

detected limits (or baseline) (DL1 + DL2)/2

One detected and 

one non-detected D

Arithmetic average of measured value 

and sample-specific detection limit (or 

baseline)

(D + DL)/2

D: detected.

ND: non-detected.

DL: sample-specific detection limit.

3.4.2. Aggregation of overlapping samples

At the Allen and Belews Creek plants, sampling data were available from EPA sampling, 

CWA 308 sampling, and plant self-monitoring. As explained in Section 2.3 above, there was 

some overlap between the data from these sources. On some days at a given plant, samples 

were available from two sources, specifically, plant self-monitoring and either EPA sampling or 

CWA 308 sampling. When these overlaps occurred, EPA aggregated the measurements from 

the available samples to obtain one value for that day. DCN SE02002 lists the data before the 

aggregation as well as after the aggregations.

The procedure averaged the measurements to obtain a single value for that day. When 

both measurements had the same censoring type, then the censoring type of the aggregate 

was the same as that of the overlapping values. When one or more measurements were 

detected (D), EPA determined that the appropriate censoring type of the aggregate was 

detected because the pollutant is confirmed to be present at a level above the sample-specific 

detection limit in one of the samples. The procedure for obtaining the aggregated value and 

censoring type is similar to the procedure shown in Table 3 above.

4. Data Editing Criteria

After excluding and aggregating the data, EPA applied data editing criteria on a 

pollutant-by-pollutant basis to select the datasets to be used for developing the effluent limits

for each technology option. These criteria are referred to as the long-term average test (or LTA 

test). EPA established the LTA test to ensure that the pollutants for which limits are being 

proposed were present in the influent at sufficient concentrations to evaluate treatment 

effectiveness at the plant. The influent first had to pass a basic requirement that 50% of the 

influent measurements for the pollutants had to be detected at any concentration. If the 

dataset at a plant passed the basic requirement, then the data had to pass one of the following 

two criteria to pass the LTA test:
Page 25

Criterion 1. At least 50% of the influent measurements in a dataset at a plant were 

detected at levels equal to or greater than 10 times the baseline value (shown in 

Section 3.3).

Criterion 2. At least 50% of the influent measurements in a dataset at a plant were 

detected at any concentration and the influent arithmetic average was equal to or 

greater than 10 times the baseline value (shown in Section 3.3).

If the dataset at a plant failed the basic requirement, then EPA automatically set both 

Criteria 1 and 2 to “fail”. If the dataset for a plant failed the basic requirement, or passed the 

basic requirement but failed both criteria, EPA would exclude the plant’s effluent data for that 

pollutant when calculating limits. Through the application of the LTA test, EPA ensures that the 

limits result from treatment of the wastewater and not simply the absence or substantial 

dilution of that pollutant in the waste stream.

After performing the LTA test for all the pollutants at each plant that was selected as the 

basis for the limits for this rulemaking, it was found that all the datasets passed the LTA test 

except for arsenic and mercury data at Wabash River. Thus, data for arsenic and mercury at 

Wabash River were excluded from the calculation of the limits. See Appendix 3 for the results of 

the LTA test for each pollutant at each plant.

5. Statistical Methodology

The sections below provide the following: (i) general definitions and background, (ii) 

statistical model selected for the data, (iii) analysis of autocorrelation, (iv) dataset requirement, 

(v) the calculation of the effluent limits, and (vi) description of how the limit was set in a special 

case where most of the observations were non-detects. 

5.1. Definitions and Background

In developing the effluent limits, a statistical procedure is used that involves fitting 

effluent data to a distribution and estimating specified upper percentiles of the fitted 

distribution. The bullets below describe in detail the important quantities that are typically 

estimated based on the effluent data. 

• The long-term average (LTA) is the average concentration that is achieved over a period 

of time. The long-term average is the mean of the underlying statistical distribution of 

the daily effluent values.

• The daily maximum limitation is the highest allowable discharge in any one day. The 

daily maximum limitation is the estimate of the 99th percentile (denoted as P99) of the 

distribution of the daily effluent values.
Page 26

• The daily variability factor is the ratio of the daily maximum limitation to the LTA. This 

ratio represents the relationship between the large values and the average treatment 

performance level that a well-designed and well-operated treatment system should be 

capable of achieving at all times.

• The monthly average limitation is the highest allowable average of discharges calculated 

from the effluent data collected over a calendar month (or period of time specified in 

the permit). The monthly average limitation is the estimate of the 95th percentile 

(denoted as P95) of the distribution of the monthly averages of the daily effluent values. 

• The monthly variability factor is the ratio of the monthly average limitation to the LTA.

5.2. Statistical Model Selected for the Data

In calculating the long-term average, variability factors, and effluent limits, a statistical 

model is assumed for the distribution of the effluent data. For this rulemaking, EPA selected 

the modified delta-lognormal distribution to model pollutant effluent concentration to develop 

the long-term average, variability factors, and limits. A typical effluent dataset from EPA 

sampling, CWA 308 sampling, or from a plant’s self-monitoring consists of a mixture of detected 

and non-detected values. The modified delta-lognormal distribution is appropriate for such 

datasets because it models the data as a mixture of detected measurements that follow a 

lognormal distribution and non-detect measurements that occur with a certain probability. The 

model also allows for the possibility that non-detected measurements occur at multiple 

sample-specific detection limits. Because the data appeared to fit the modified delta-lognormal 

model reasonably well, EPA has determined that this model is appropriate for these data. See 

Appendix B of the Technical Development Document for an overview of the statistical model 

and a description of the procedures EPA used to estimate these parameters.

5.3. Autocorrelation Analysis

Effluent concentrations that are collected over time may be autocorrelated. The data 

are positively autocorrelated when measurements taken at specific time intervals, such as one 

or two days apart, are similar. For example, positive autocorrelation would occur if the effluent 

concentration was relatively high one day and was likely to remain high on the next and 

possibly succeeding days. Because the autocorrelated data affect the true variability of 

treatment performance, EPA typically adjusts the variance estimates for the autocorrelated 

data, when appropriate. 

For this rulemaking, whenever there was sufficient data for a pollutant at a plant to 

evaluate the autocorrelation reliably, EPA estimated the autocorrelation and incorporated it 

into the calculation of the limits. For a plant without enough data to reliably evaluate and 

obtain a reliable estimate of the autocorrelation, EPA set the autocorrelation to zero in the 

calculation of the effluent limits. EPA did so because it is reasonable to set the autocorrelation 

to zero whenever there is not a sufficient amount of data to reliably evaluate the 

autocorrelation and when there is no correlation available that can be transferred from a 
Page 27

similar technology and waste stream. See the memorandum titled “Serial correlations for 

Steam Electric with and without adjustment for baseline values [EP-C-10-023 WA 2-6 (Steam 

Electric)]” from John Rogers to Cuc Schroeder, dated April 15, 2013, for details of the statistical 

methods and procedures used to determine the autocorrelation values, as well as a detailed 

discussion of the minimum number of observations needed to obtain a reliable estimate of the 

autocorrelation. This memo is in the record as DCN SE02001 (this memo will hereafter be 

referred to as DCN SE02001). The following paragraphs describe the instances where EPA was 

able to obtain an estimated autocorrelation and the assumptions made about the 

autocorrelation when there were too few observations to estimate the autocorrelation.

For the biological treatment technology for FGD wastewater (represented by Allen and 

Belews Creek plants), EPA was able to perform a statistical evaluation of the autocorrelation 

and obtain a reliable estimate of the autocorrelation because several years of data were 

available for these plants. For arsenic and mercury, EPA is proposing to transfer the limits from 

the chemical precipitation technology option for FGD for these pollutants (see Section 13 of the 

Technical Development Document for a detailed discussion of the transfer of the limits). The 

Allen and Belews Creek plants do not include sulfide precipitation in the upstream chemical 

precipitation system to achieve the BAT level of control for arsenic and mercury, thus, the 

arsenic and mercury data from these plants were not appropriate for use in estimating 

autocorrelation. However, if EPA was to use these data to estimate autocorrelation for arsenic 

and mercury, it would follow the methodology used to estimate autocorrelation for selenium.

Table 4 below lists the autocorrelation values used in the limits calculation for nitrate-nitrite as 

N and selenium. 

Table 4. Summary of Estimated Autocorrelation Values at Allen and Belews Creek.

Pollutant Correlation value used for limit calculations

Selenium 0.291 Nitrate-nitrite as N 1

1

: There were only eight observations available for nitrate-nitrite as N (only EPA sampling and CWA 308 sampling 

data available) at Allen and Belews Creek, so EPA was not able to evaluate the autocorrelation. However, EPA 

transferred the autocorrelation from selenium since these two chemicals behave similarly in the biological 

treatment system.

For the chemical precipitation treatment option for FGD wastewater (represented by 

Hatfield’s Ferry, Keystone, and Miami Fort plants), for the vapor-compression evaporation 

treatment technology option for FGD wastewater (represented by Brindisi), and for the vaporcompression treatment technology option for gasification wastewater (represented by Polk and 

Wabash River), EPA was unable to perform an evaluation and obtain a reliable estimate of the 

autocorrelation because there were too few observations available at the plants. Thus, for 

these plants, EPA set the autocorrelation to zero in the calculation of the limits. EPA did so 

because there were not sufficient data to reliably evaluate the autocorrelation, nor did EPA 

have a valid correlation estimate available that could be transferred from a similar technology

and waste stream.
Page 28

5.4. Dataset Requirement

The statistical model requires at least two distinct detected values in order to estimate 

the variance of the distribution (i.e., to allow the variability factor to be calculated). Generally, 

EPA has been reluctant to estimate a variability factor from plants with a small number of 

detected observations. The minimum number of observations required to calculate the 

variability factor has been evaluated on a case-by-case basis. For example, for the Organic 

Chemicals, Plastics and Synthetic Fibers (OCPSF) rulemaking, a variability factor was estimated 

for a plant if it had at least 7 daily observations with at least 3 observations above the detection 

limit. In the Iron and Steel rulemaking, a variability factor was estimated for a plant if it had at 

least three observations, at least two of which were above the detection limit. For the steam 

electric rulemaking, a variability factor was estimated for a plant if it had at least three 

observations, at least two of which were above the detection limit.

5.5. Calculating Effluent Limits for Each Pollutant in Each Technology Option

EPA calculated the percentiles that are used as a basis for the limits by multiplying the 

long-term average (the option long-term average discussed below) by the appropriate 

variability factors (the option variability factor discussed below). The paragraphs below 

describe the calculation of the option long-term average, option variability factors, and effluent 

limits. As mentioned in Section 1, the option long-term averages and variability factors in this 

document refer to the long-term average and variability factors for that particular technology 

option, not the regulatory option described in Section 8 of the Technical Development 

Document. 

The option long-term average is calculated for a pollutant using two steps. First, EPA 

calculated the plant-specific long-term average for each pollutant that had enough distinct 

detected values by fitting a statistical model to the daily concentration values. In cases when a 

dataset for a specific pollutant did not have enough distinct detected values, then the statistical 

model was not used to obtain the long-term average. In these cases, the plant-specific longterm average for each pollutant was the arithmetic mean of the available daily concentration 

values. Second, the option long-term average for each pollutant is calculated as the median of 

the plant-specific long-term averages for that pollutant.

The following describes the calculations performed to obtain the option variability 

factors. First, EPA calculated the plant-specific variability factors for each pollutant that had 

enough distinct detected values by fitting a statistical model to the daily concentration values. 

Each plant-specific daily variability factor for each pollutant is the estimated 99th percentile of 

the distribution of the daily concentration values divided by the plant-specific long-term 

average. Each plant-specific monthly variability factor for each pollutant is the estimated 95th

percentile of the distribution of the 4-day average concentration divided by the plant-specific 

long-term average. The calculation of the plant-specific monthly variability factor assumes that 

the monthly averages are based on the pollutant being monitored weekly (approximately four 

times each month). In cases when there were not enough distinct detected values for a specific 
Page 29

pollutant, then the statistical model was not used to obtain the variability factors. In these 

cases, the data for the pollutant at the plant was excluded from the calculation of the option 

variability factors.

Finally, the daily maximum limit for each pollutant for each technology option is the 

product of the option long-term average and option daily variability factors. The monthly 

average limit for each pollutant for each technology option is the product of the option longterm average and option monthly variability factors.

5.6. Special Case – Effluent Limits Based on Detection Limits

Although the percentile estimates described in the section above play an important role 

in determining daily maximum and monthly average effluent limits, they are not a requirement 

under the Clean Water Act and are not always used as the basis for effluent limits. In situations 

where there are too few detected results, the statistical models are not appropriate for use in 

obtaining the effluent limits since reliable estimates could not be calculated from the model. In 

such instances, EPA has instead established the daily effluent limits based on a detection limit. 

Also, the monthly average limit is not established when the daily limit is based on the detection 

limit. The purpose of a monthly average limit is to require dischargers to provide better control, 

on a monthly basis, than required by the daily maximum limit. However, for these pollutants, 

current analytical methods cannot measure below the detection limit specified for the daily 

maximum limit. Thus, even if a permitting or pretreatment authority requires more frequent 

monitoring for these pollutants than once a month, monthly average limits would still be 

expressed as less than detection limits.

6. Treatment Technology Option for FGD Wastewater: Chemical Precipitation

EPA used data from three coal-fired power plants (Hatfield’s Ferry, Keystone, and Miami 

Fort) to develop the long-term averages, variability factors, and effluent limits for the chemical 

precipitation treatment technology option for FGD wastewater. The pollutants for which the 

limits are calculated are arsenic and mercury.

The following provides a detailed summary of all the available data for each plant. The 

available data from each of the plants came from the following two sources: EPA sampling and 

CWA 308 sampling. As explained in Section 2.3, EPA combined these two sources of data at 

each plant into a single dataset for the plant. The data described below include all the available 

data prior to any of the exclusions. 

Hatfield’s Ferry Sampling Data

The sampling data were collected at two sampling locations: FGD Purge and chemical 

precipitation effluent. The bullets below provide a brief summary of the data:
Page 30

• EPA sampling data collected by EPA between 12/06/2010 and 12/10/2010.

• CWA 308 sampling data collected by the plant one day per month for four consecutive 

months. These data were collected on 10/5/2010, 11/10/2010, 1/12/2011, and 

02/09/2011.

Keystone Sampling Data

The sampling data were collected at two sampling locations: FGD Purge and chemical 

precipitation effluent. The bullets below provide a brief summary of the data:

• EPA sampling data collected by EPA between 09/13/2010 and 09/17/2010.

• CWA 308 sampling data collected by the plant one day per month for four consecutive 

months. These data were collected on 10/7/2010, 11/4/2010, 12/9/2010, and 

01/13/2011. 

Miami Fort Sampling Data

The sampling data were collected at two sampling locations: FGD Purge and chemical 

precipitation effluent. The bullets below provide a brief summary of the data for each of the 

data sources:

• EPA sampling data collected by EPA between 07/12/2010 and 07/16/2010.

• CWA 308 sampling data collected by the plant one day per month for four consecutive 

months. These data were collected on 09/28/2010, 11/2/2010, 12/7/2010, and 

01/14/2011. 

EPA attempted to use the available data to estimate the autocorrelation. However, for 

Hatfield’s Ferry, Keystone, and Miami Fort, EPA was not able to perform an evaluation of the 

autocorrelation because there were too few observations available at the plants. Thus, for 

these plants, EPA set the autocorrelation to zero in the development of the limits for the 

reasons described in section 5.3.

The sections below provide the following for each of the pollutants at each of the 

plants: longitudinal plots of the data, summary statistics, and plant-specific long-term average 

and plant-specific variability factors (see Appendix B for an overview of the statistical model 

and the procedures used to estimate the plant-specific long term average and variability 

factors). Also provided in the sections below are the option long-term average, option 

variability factors, and effluent limits for each pollutant. All exclusions, baseline substitutions, 

and aggregation of data were made prior to conducting the analyses presented below.
Page 31

6.1. Chemical Precipitation Treatment for FGD Wastewater: Arsenic

6.1.1. Longitudinal plots of the data for arsenic (ug/L)

Below are the longitudinal plots of the arsenic concentrations (on a logarithmic scale) 

for Hatfield’s Ferry, Keystone, and Miami Fort. In the plots below, the plot on the left shows the 

concentrations for Hatfield’s Ferry, the plot in the middle shows the concentrations for 

Keystone, and plot on the right shows the concentrations for Miami Fort. 

Figure 1. Plot of arsenic (ug/L) data on a logarithmic scale for Hatfield’s Ferry, Keystone, and

Miami Fort.

6.1.2. Summary statistics for arsenic (ug/L)

The table below provides summary statistics for the numbers of detected and nondetected observations together with the sample-specific detection limits by sample location 

and plant. For example, for Hatfield’s Ferry at the FGD Purge sampling location, all 8 

observations were detected; at the chemical precipitation effluent sampling location, of the 8 

observations, 6 observations were detected and 2 were non-detected. Of the 2 non-detects, 

both had a detection limit of 4 ug/L (shown at the top of the column).

5 10 20 50 100 200 500 1000 2000 5000

Hatfields Ferry

 (logarithmic scale)

Date

 Note: Detected = o Non-Detected = *

Arsenic (ug/L)

Oct 10 Nov 10 Dec 10 Jan 11 Feb 11

* *

FGD Purge

Chem Prep. Eff.

5 10 20 50 100 200 500 1000 2000 5000

Keystone

 (logarithmic scale)

Date

 Note: Detected = o Non-Detected = *

Arsenic (ug/L)

Sep 10 Oct 10 Nov 10 Dec 10 Jan 11

*** * * * *

FGD Purge

Chem Prep. Eff.

5 10 20 50 100 200 500 1000 2000 5000

Miami Fort

 (logarithmic scale)

Date

 Note: Detected = o Non-Detected = *

Arsenic (ug/L)

Jul 10 Sep 10 Nov 10 Dec 10 Jan 11

* *

FGD Purge

Chem Prep. Eff.
Page 32

Table 5. Numbers of detected and non-detected observations and sample-specific detection

limits for arsenic (ug/L) by plant and sampling location.

Plant Name Sampling Location

(Total Observations 2

) Indicator (n) 3

Sample Specific Detection Limits for 

Arsenic (ug/L)

Detection Limit = 4

Hatfield’s Ferry 1

FGD Purge (N = 8) D (n=8)

Chemical Prep. Effluent (N = 8) D (n=6)

ND (n=2) 2

Keystone 1

FGD Purge (N = 8) D (n=8)

Chemical Prep. Effluent (N = 8) D (n=1)

ND (n=7) 7

Miami Fort 1

FGD Purge (N = 8) D (n=8)

Chemical Prep. Effluent (N = 8) D (n=6)

ND (n=2) 2 1

: Combination of EPA sampling and CWA 308 sampling. 2

: Detected and non-detected observations combined. 3

: D = detected and ND = non-detected.

The table below provides the summary statistics for all observations (detected and nondetected combined) for each sampling location at each of the plants. 

Table 6. Summary statistics of arsenic concentration (ug/L) for all detected and non-detected

samples combined, by plant and sampling location.

Plant Name Sampling Location Summary Statistics for Arsenic (ug/L)

N 2 Minimum Mean Median Maximum Std

Hatfield’s Ferry 1 FGD Purge 8 300.0 1,796.3 1,575.0 4,610.0 1,471.2

Chemical Prep. Effluent 8 4.0 6.6 5.9 11.0 2.7

Keystone 1 FGD Purge 8 450.0 1,815.0 2,035.0 3,080.0 1,021.6

Chemical Prep. Effluent 8 4.0 4.0 4.0 4.1 0.02

Miami Fort 1 FGD Purge 8 320.0 727.3 682.5 1,310.0 315.9

Chemical Prep. Effluent 8 4.0 4.5 4.4 5.0 0.4 1

: Combination of EPA sampling (4 daily samples) and CWA 308 sampling (4 monthly samples).

2

: Detected and non-detected observations combined.

6.1.3. Plant-specific long-term averages and variability factors, option long-term average and

variability factors, and effluent limits for arsenic (ug/L)

The table below provides the plant-specific LTA, plant-specific variability factors, option 

LTA, option variability factors, and effluent limits for arsenic at the chemical precipitation 

effluent. 
Page 33

Table 7. Plant-specific long-term averages and variability factors, option long-term average and

variability factors, and limits for arsenic (ug/L) at chemical precipitation effluent.

TYPE Plant Name N2 LTA

Daily 

Variability 

Factor

Monthly 

Variability 

Factor

Limits

Daily Monthly

PlantSpecific

Hatfield’s Ferry 1 8 (D = 6, ND = 2) 6.682 2.285 1.373

Keystone 1 8 (D = 1,ND = 7) 4.0063 --4 --4

Miami Fort 1 8 (D = 6,ND = 2) 4.483 1.197 1.072

Option 4.483 1.741 1.223 7.805 5.480 1

: Combination of EPA sampling and CWA 308 sampling. 2

: D = detected and ND = non-detected. 3

: Long-term average is the arithmetic mean since there were too few detected observations (not able to estimate 

the variance of the distribution).

4

: Nearly all observations were non-detected, so the variability factors could not be calculated. 

6.2. Chemical Precipitation Treatment for FGD Wastewater: Mercury

6.2.1. Longitudinal plots of the data for mercury (ng/L)

Below are the longitudinal plots of the mercury concentrations (on a logarithmic scale) 

for Hatfield’s Ferry, Keystone, and Miami Fort.

Figure 2. Plot of mercury (ng/L) data on a logarithmic scale for Hatfield’s Ferry, Keystone, and

Miami Fort.

6.2.2. Summary statistics for mercury (ng/L)

All observations at each of the sampling locations for Hatfield’s Ferry, Keystone, and 

Miami Fort were detected. The table below provides summary statistics for all observations for

each sampling location at each of the plants. 1e+02 1e+03 1e+04 1e+05 1e+06

Hatfields Ferry

 (logarithmic scale)

Date

 Note: Detected = o Non-Detected = *

Mercury (ng/L)

Oct 10 Nov 10 Dec 10 Jan 11 Feb 11

FGD Purge

Chem Prep. Eff.

1e+02 1e+03 1e+04 1e+05 1e+06

Keystone

 (logarithmic scale)

Date

 Note: Detected = o Non-Detected = *

Mercury (ng/L)

Sep 10 Oct 10 Nov 10 Dec 10 Jan 11

FGD Purge

Chem Prep. Eff.

1e+02 1e+03 1e+04 1e+05 1e+06

Miami Fort

 (logarithmic scale)

Date

 Note: Detected = o Non-Detected = *

Mercury (ng/L)

Jul 10 Sep 10 Nov 10 Dec 10 Jan 11

FGD Purge

Chem Prep. Eff.
Page 34

Table 8. Summary statistics of mercury concentration (ng/L) for all detected samples by plant

and sampling location.

Plant Name Sampling Location Summary Statistics for Mercury (ng/L)

N 2 Minimum Mean Median Maximum Std

Hatfield’s Ferry 1 FGD Purge 8 184,000.0 465,125.0 467,000.0 789,000.0 216,886.7

Chemical Prep. Effluent 7 31.8 75.8 38.4 228.0 70.4

Keystone 1 FGD Purge 8 18,800.0 404,225.0 514,000.0 622,000.0 213,272.3

Chemical Prep. Effluent 8 26.4 62.8 52.6 119.0 35.9

Miami Fort 1 FGD Purge 8 44,000.0 235,375.0 227,500.0 384,000.0 116,880.8

Chemical Prep. Effluent 8 101.0 167.6 146.0 295.0 70.7 1

: Combination of EPA sampling and CWA 308 sampling. 2

: Detected and non-detected observations combined (all observations were detected).

6.2.3. Plant-specific Long-term averages and variability factors, option long-term average and

variability factors, and effluent limits for mercury (ng/L)

The table below provides the plant-specific LTA, plant-specific variability factors, option 

LTA, option variability factors, and effluent limits for mercury at chemical precipitation effluent. 

Table 9. Plant-specific long-term average and variability factors, option long-term average and

variability factors, and limits for mercury (ng/L) at chemical precipitation effluent.

Type Plant Name N2 LTA

Daily 

Variability 

Factor

Monthly 

Variability 

Factor

Limits

Daily Monthly

Plantspecific

Hatfield’s Ferry 1 7 (D = 7, ND = 0) 75.404 4.083 1.766

Keystone 1 8 (D = 8, ND = 0) 64.260 3.257 1.584

Miami Fort 1 8 (D = 8, ND = 0) 168.569 2.286 1.361

Option 75.404 3.209 1.570 241.948 118.396 1

: Combination of EPA sampling and CWA 308 sampling. 2

: D = detected and ND = non-detected.

6.3. Chemical Precipitation Treatment for FGD Wastewater: Summary of the Option 

Long-Term Averages, Option Variability Factors, and Effluent Limits

The table below provides a summary of the option long-term averages, option variability 

factors, and effluent limits for arsenic and mercury. 

Table 10. Summary of option long-term averages, option variability factors, and effluent limits

for chemical precipitation FGD wastewater treatment technology.

Pollutant Autocorrelation 

Value

Option 

LTA

Option Daily 

Variability Factor

Option 

Monthly 

Variability 

Factor

Daily 

Limit 1

Monthly 

Average 

Limit 1

Arsenic (ug/L) 0 4.483 1.741 1.223 8 6

Mercury (ng/L) 0 75.404 3.209 1.570 242 119 1

: Effluent limitations greater than 1.0 have been rounded upward to the next highest integer. 
Page 35

7. Treatment Technology Option for FGD Wastewater: Biological Treatment

EPA used data from two coal-fired power plants (Allen and Belews Creek) to develop the

long-term averages, variability factors, and effluent limits based on the chemical precipitation 

followed by biological treatment technology option for FGD wastewater. Summary statistics for 

arsenic, mercury, nitrate-nitrite as N, and selenium are presented for these two plants. The 

data from these two plants were used to calculate the limits for nitrate-nitrite as N and 

selenium. As noted above, while these two plants operate the biological treatment system used 

as the basis for the technology option, neither of these plants includes sulfide precipitation in 

the upstream chemical precipitation system. For this reason, EPA is proposing to transfer the 

arsenic and mercury limits calculated based on the chemical precipitation technology option to 

biological technology option for FGD wastewater (see Section 13 of the Technical Development 

Document for a detailed discussion of the transfer of limits). 

The following provides a detailed summary of all the available data for each plant. The 

available data from each plant came from the following three sources: (i) plant self-monitoring, 

(ii) EPA sampling, and (iii) CWA 308 sampling. As explained in Section 2.3, EPA combined the 

multiple sources of data at each plant into a single dataset for the plant. The data described 

below includes all the available data prior to any of the exclusions. 

Allen Sampling Data

The sampling data were collected at three sampling locations: FGD purge, bioreactor 

influent, and bioreactor effluent. The bullets below provide a brief summary of the data:

• Plant self-monitoring data collected by the plant over a period of several years. The 

original data provided were collected between 03/03/2009 and 05/23/2011.

• EPA sampling data collected by EPA between 08/02/2010 and 08/06/2010.

• CWA 308 sampling data collected by the plant one day per month for four consecutive 

months. These data were collected on 10/5/2010, 11/1/2010, 12/6/2010, and 

01/12/2011.

Belews Creek Sampling Data

The sampling data were collected at three sampling locations: FGD purge, bioreactor 

influent, and bioreactor effluent. The bullets below provide a brief summary of the data:

• Plant self-monitoring data collected by the plant over a period of several years. The 

original data provided were from 02/06/2008 to 05/25/2011.

• EPA sampling data collected by EPA between 06/07/2010 and 06/11/20110.

• CWA 308 sampling data collected by the plant one day per month for four consecutive 

months. These data were collected on 10/6/2010, 11/3/2010, 12/8/2010, and 

01/18/2011.
Page 36

EPA was able to estimate the autocorrelations for use in the calculation of the limits at 

Allen and Belews Creek (at the bioreactor effluent sampling location) because several years of 

data were available for these plants. See DCN SE2001 for the statistical method and results of 

the autocorrelation values for each pollutant. Thus, the estimated autocorrelation values were 

used in developing limits for each pollutant for this technology option. However, an 

autocorrelation value of zero (0) was also used to assess the sensitivity of the limits to the 

correlation values used. The effluent limits calculated using both approaches are presented 

below. The proposed limits for this technology option are based on the calculations that 

incorporated the estimated autocorrelations.

The sections below provide the following for each of the pollutants at each of the 

plants: longitudinal plots of the data and summary statistics. Also provided in the sections 

below are the plant-specific and option long-term averages, plant-specific and option variability 

factors, and effluent limits for nitrate-nitrite as N and selenium. All exclusions, baseline 

substitutions, and aggregation of data were made prior to conducting the analyses described 

below.

7.1. Biological Treatment for FGD Wastewater: Arsenic 

Sections below provide the longitudinal plots and summary statistics for arsenic. EPA did 

not calculate the limits for arsenic using the Allen and Belews Creek because EPA is transferring 

the arsenic limits calculated based on the chemical precipitation technology option to the 

biological technology option for FGD wastewater (see Section 13 of the Technical Development 

Document for a detailed discussion of the transfer of limits). If EPA was to use these data to 

calculate limits for arsenic, it would follow the same methodology used to calculate the limits 

for nitrate-nitrite as N and selenium for this technology option.

7.1.1. Longitudinal plots of the data for arsenic (ug/L)

Below are the longitudinal plots of the arsenic concentrations (on a logarithmic scale) 

for Allen and Belews Creek. In the plot below, the plot on the left shows the concentrations for 

Allen from 09/09/2009 to 05/23/2011, while the plot on the right shows the concentrations for 

Belews Creek from 08/01/2008 to 05/25/2011. Note that the data collected in the first six 

months for each plant was excluded because it represented the initial commissioning period for 

the treatment system.
Page 37

Figure 3. Plot of arsenic (ug/L) data on a logarithmic scale for Allen and Belews Creek.

7.1.2. Summary statistics for arsenic (ug/L) 

The table below provides summary statistics for the numbers of detected and nondetected observations together with the sample-specific detection limits by sample location 

and plant. 

Table 11. Numbers of detected and non-detected observations and sample-specific detection

limits for arsenic (ug/L) by plant and sampling location.

Plant Name Sampling Location

(Total Observations 2

) Indicator (n)3 Sample Specific Detection Limits for Arsenic (ug/L)

2 3 4 4.5 5 7 10 14.5 52

Allen 1

FGD Purge (N = 63) D (n = 63)

Bioreactor Influent (N = 63) D (n = 1)

ND (n = 62) 1 5 16 3 37

Bioreactor Effluent (N = 62) D (n = 27)

ND (n = 35) 5 26 4

Belews Creek 1

FGD Purge (N = 70) D (n = 70)

Bioreactor Influent (N = 71) D (n = 9)

ND (n = 62) 5 1 18 1 36 1

Bioreactor Effluent (N = 71) D (n = 4)

ND (n = 67) 17 1 6 1 12 29 1 1

: Combination of EPA sampling, CWA 308 sampling, and plant self-monitoring. 2

: Detected and non-detected observations combined. 3

: D = detected and ND = non-detected.

The table below provides summary statistics for all observations (detected and nondetected combined) for arsenic concentrations by sampling location and plant. 

2 5 10 20 50 200 500 2000

Allen

 (logarithmic scale)

Date

 Note: Detected = o Non-Detected = *

Arsenic (ug/L)

Sep 09 Dec 09 Jun 10 Sep 10 Jan 11 Apr 11

**

**

** * *** * * *** ** ** *

*

*

* ****** * * * **   ** 

*

***

*

* ***

*

***

*

* * *** ** ** *

FGD Purge

Bioreactor Inf.

Bioreactor Eff.

2 5 10 20 50 200 500 2000

Belews Creek

 (logarithmic scale)

Date

 Detected: o Non-Detected: *

Arsenic (ug/L)

Aug 08 Jan 09 Jun 09 Nov 09 Apr 10 Sep 10 Feb 11

************************ * * * **

** *

*

** ******

*

*

*

*

*

***

*

**

*

**

*

*

*********

************ ****** * * **

** * **********

*

*

*

**

*

***

*

**

*

**

*

*

*********

FGD Purge

Bioreactor Inf.

Bioreactor Eff.
Page 38

Table 12. Summary statistics of arsenic concentration (ug/L) for all detected and non-detected

samples combined, by plant and sampling location.

Plant Name Sampling Location Summary Statistics for Arsenic (ug/L)

N 2 Minimum Mean Median Maximum Std

Allen 1

FGD Purge 63 105.0 233.3 208.0 619.0 112.9

Bioreactor Influent 63 2.0 7.9 10.0 10.0 2.7

Bioreactor Effluent 62 2.0 5.9 5.0 20.1 3.1

Belews Creek 1

FGD Purge 70 92.0 411.4 278.0 2,820.0 377.0

Bioreactor Influent 71 4.0 8.9 10.0 52.0 5.9

Bioreactor Effluent 71 2.0 6.2 5.0 14.5 3.6 1

: Combination of EPA sampling, CWA 308 sampling, and plant self-monitoring. 2

: Detected and non-detected observations combined.

7.2. Biological Treatment for FGD Wastewater: Mercury

Sections below provide the longitudinal plots and summary statistics for mercury. EPA 

did not calculate the limits for mercury using the Allen and Belews Creek because EPA is 

transferring the mercury limits calculated based on the chemical precipitation technology 

option to the biological technology option for FGD wastewater (see Section 13 of the Technical 

Development Document for a detailed discussion of the transfer of limits). If EPA was to use 

these data to calculate limits for arsenic, it would follow the same methodology used to 

calculate the limits for nitrate-nitrite as N and selenium for this technology option.

7.2.1. Longitudinal plots of the data for mercury (ng/L)

Below are the longitudinal plots of the mercury concentrations (on a logarithmic scale) 

for Allen and Belews Creek.

Figure 4. Plot of mercury (ng/L) data on a logarithmic scale for Allen and Belews Creek. 1e+01 1e+03 1e+05

Allen

 (logarithmic scale)

Date

 Note: Detected = o Non-Detected = *

Mercury (ng/L)

Sep 09 Dec 09 Jun 10 Sep 10 Jan 11 Apr 11

FGD Purge

Bioreactor Inf.

Bioreactor Eff.

1e+01 1e+03 1e+05

Belews Creek

 (logarithmic scale)

Date

 Detected: o Non-Detected: *

Mercury (ng/L)

Aug 08 Jan 09 Jun 09 Nov 09 Apr 10 Sep 10 Feb 11

FGD Purge

Bioreactor Inf.

Bioreactor Eff.
Page 39

7.2.2. Summary statistics for mercury (ng/L)

All observations at each of the sampling locations for Allen and Belews Creek were 

detected. The table below provides summary statistics for all observations for mercury 

concentrations by sampling location and plant. 

Table 13. Summary statistics of mercury concentration (ng/L) for all detected and non-detected

samples combined by plant and sampling location.

Plant Name Sampling Location Summary Statistics for Mercury (ng/L)

N 2 Minimum Mean Median Maximum Std

Allen 1

FGD Purge 62 18,500.0 52,219.4 49,950.0 120,000.0 22,934.2

Bioreactor Influent 38 22.7 358.8 242.5 1,320.0 382.2

Bioreactor Effluent 39 1.9 13.0 9.9 54.6 12.2

Belews Creek 

1

FGD Purge 73 1,000.0 194,417.8 185,000.0 697,000.0 120,110.3

Bioreactor Influent 40 6.8 7,647.9 112.5 53,300.0 17,768.8

Bioreactor Effluent 38 2.0 111.6 11.5 746.0 177.6 1

: Combination of EPA sampling, CWA 308 sampling, and plant self-monitoring data. 2

: Detected and non-detected observations combined (all observations were detected).

7.3. Biological Treatment for FGD Wastewater: Nitrate-nitrite as N 

7.3.1. Longitudinal plots of the data for nitrate-nitrite as N (mg/L)

Below are the longitudinal plots of the nitrate-nitrite as N concentrations (on a 

logarithmic scale) for Allen and Belews Creek.

Figure 5. Plot of nitrate-nitrite as N (mg/L) data on a logarithmic scale for Allen and Belews

Creek (for short, the name on the vertical is labeled as nitrite). 0.1 0.2 0.5 1.0 2.0 5.0 10.0 50.0

Allen

 (logarithmic scale)

Date

 Note: Detected = o Non-Detected = *

Nitrite (mg/L)

Aug 10 Oct 10 Nov 10 Dec 10 Jan 11

*** * * * *

FGD Purge

Bioreactor Inf.

Bioreactor Eff.

0.1 0.2 0.5 1.0 2.0 5.0 10.0 50.0

Belews Creek

 (logarithmic scale)

Date

 Detected: o Non-Detected: *

Nitrite (mg/L)

Jun 10 Oct 10 Dec 10 Jan 11

*** *

FGD Purge

Bioreactor Inf.

Bioreactor Eff.
Page 40

7.3.2. Summary statistics for nitrate-nitrite as N (mg/L) 

The table below provides summary statistics for the numbers of detected and nondetected observations together with the sample-specific detection limits by sample location 

and plant.

Table 14. Number of detected, non-detected, and sample-specific detection limits for

nitrate-nitrate as N (mg/L) by plant and sampling location.

Plant Name Sampling Location

(Total Observations 2

) Indicator (n)3

Sample Specific Detection Limit for 

Nitrate-nitrite as N (mg/L)

Detection Limit = 0.1

Allen 1

FGD Purge (N = 8) D (n = 8)

Bioreactor Influent (N = 8) D (n = 8)

Bioreactor Effluent (N = 8) D (n = 1)

ND (n = 7) 7

Belews Creek 1

FGD Purge (N = 8) D (n = 8)

Bioreactor Influent (N = 8) D (n = 8)

Bioreactor Effluent (N = 8) D (n = 3)

ND (n = 5) 5 1

: Combination of EPA sampling and CWA 308 sampling. 2

: Detected and non-detected observations combined. 3

: D = detected and ND = non-detected.

The table below provides summary statistics for all observations (detected and nondetected combined) for nitrate-nitrite as N concentrations by sampling location and plant. 

Table 15. Summary statistics of nitrate-nitrite as N concentration (mg/L) for all detected and

non-detected samples combined by plant and sampling location.

Plant Name Sampling Location Summary Statistics for Nitrate-nitrite as N (mg/L)

N 2 Minimum Mean Median Maximum Std

Allen 1

FGD Purge 8 14.0 32.0 29.5 51.0 15.4

Bioreactor Influent 8 13.0 22.5 21.5 39.0 10.4

Bioreactor Effluent 8 0.1 0.1 0.1 0.13 0.01

Belews Creek 1

FGD Purge 8 14.0 16.6 15.5 21.0 2.7

Bioreactor Influent 8 12.0 17.1 17.5 21.0 3.1

Bioreactor Effluent 8 0.1 0.12 0.1 0.15 0.02 1

: Combination of EPA sampling and CWA 308 sampling. 2

: Detected and non-detected observations combined.

7.3.3. Plant-specific long-term averages and variability factors, option long-term averages and

variability factors, and effluent limits for nitrate-nitrite as N (mg/L)

The table below provides the plant-specific long-term averages, plant-specific variability 

factors, option long-term averages, option variability factors, and effluent limits for nitratenitrite as N at bioreactor effluent. 
Page 41

Table 16. Lag-1 autocorrelation values, plant-specific long-term averages and variability factors,

option long-term averages and variability factors, and limits for nitrate-nitrite as N (mg/L) at 

bioreactor effluent.

TYPE Plant Name N2 Autocorrelation

Value3 LTA

Daily 

Variability 

Factor

Monthly 

Variability 

Factor

Limits

Daily Monthly

PlantSpecific

Allen 1 8 (D=1,ND=7) 0 0.104 4 --5 --5

0.291 0.104 4 --5 --5

Belews 

Creek 1 8 (D=3,ND=5) 0 0.115 1.395 1.144

0.291 0.115 1.499 1.157

Option 

0 0.109 1.395 1.144 0.153 0.125

0.291 0.110 1.499 1.157 0.164 0.127 1

: Combination of EPA sampling and CWA 308 sampling. 2

: D = detected and ND = non-detected. 3

: Correlation ranges from -1 to 1, with a value of 0 indicating that EPA assumed no correlation in the data. 4

: Long-term average is the arithmetic mean since there were too few detected observations (not able to estimate 

the variance of the distribution).

5

: Nearly all observations were non-detected, so the variability factors could not be calculated. 

7.4. Biological Treatment for FGD Wastewater: Selenium

7.4.1. Longitudinal plots of the data for selenium (ug/L)

Below are the longitudinal plots of the selenium concentrations (on a logarithmic scale) 

for Allen and Belews Creek.

Figure 6. Plot of selenium (ug/L) data on a logarithmic scale for Allen and Belews Creek.

5 10 50 500 5000

Allen

 (logarithmic scale)

Date

 Note: Detected = o Non-Detected = *

Selenium (ug/L)

Sep 09 Dec 09 Jun 10 Sep 10 Jan 11 Apr 11

*

** * ****** * * * **   ** *

**

** * ****** ** * *** * **

FGD Purge

Bioreactor Inf.

Bioreactor Eff.

5 10 50 500 5000

Belews Creek

 (logarithmic scale)

Date

 Detected: o Non-Detected: *

Selenium (ug/L)

Aug 08 Jan 09 Jun 09 Nov 09 Apr 10 Sep 10 Feb 11

* ******************** * * * **

* * ** * **** * *** **

*

*

* ******

FGD Purge

Bioreactor Inf.

Bioreactor Eff.
Page 42

7.4.2. Summary statistics for selenium (ug/L)

The table below provides summary statistics for the numbers of detected and nondetected observations together with the sample-specific detection limits by sample location 

and plant.

Table 17. Number of detected, non-detected, and sample-specific detection limits for selenium

(ug/L) by plant and sampling location.

Plant Name Sampling Location 

(Total Observations 2

) Indicator (n) 3

Sample Specific Detection Limits for 

Selenium (ug/L)

5 10 15

Allen 1

FGD Purge (N = 63) D (n = 63)

Bioreactor Influent (N = 63) D (n = 63)

Bioreactor Effluent (N = 63)

D (n = 4)

ND (n = 59) 54 5

Belews Creek 1

FGD Purge (N = 76) D (n = 76)

Bioreactor Influent (N = 75) D (n = 75)

Bioreactor Effluent (N = 77) D (n = 26)

ND (n = 51) 23 27 1 1

: Combination of EPA sampling, CWA 308 sampling, and plant self-monitoring data. 2

: Detected and non-detected observations combined. 3

: D = detected and ND = non-detected.

The table below provides summary statistics for all observations (detected and nondetected combined) for selenium by sampling location and plant.

Table 18. Summary statistics of selenium concentration (ug/L) for all detected and 

non-detected samples combined by plant and sampling location.

Plant Name Sampling Location Summary Statistics for Selenium (ug/L)

N 2 Minimum Mean Median Maximum Std

Allen 1

FGD Purge 63 849.0 1,685.2 1,660.0 3,260.0 452.1

Bioreactor Influent 63 57.7 324.0 113.0 1,140.0 322.6

Bioreactor Effluent 63 5.0 5.6 5.0 11.7 1.6

Belews Creek 1

FGD Purge 76 1,660.0 6,797.3 6,625.0 26,200.0 3,139.0

Bioreactor Influent 75 58.0 337.9 121.0 2,940.0 516.9

Bioreactor Effluent 77 5.0 9.4 10.0 29.4 5.1 1

: Combination of EPA sampling, CWA 308 sampling, and plant self-monitoring data. 2

: Detected and non-detected observations combined.
Page 43

7.4.3. Plant-specific long-term averages and variability factors, option long-term averages and

variability factors, and effluent limits for selenium (ug/L)

The table below provides the plant-specific long-term averages, plant-specific variability 

factors, option long-term averages, option variability factors, and effluent limits for selenium at 

bioreactor effluent. 

Table 19. Lag-1 autocorrelation values, plant-specific long-term averages and variability factors,

option long-term averages and variability factors, and limits for selenium (ug/L) at bioreactor 

effluent.

TYPE Plant 

Name N2

Autocorrel

ation

Value3

LTA

Daily 

Variability 

Factor

Monthly 

Variabilit

y Factor

Limits

Daily Monthly

PlantSpecific

Allen 1 63 (D=4, ND=59) 0 5.581 1.869 1.330

0.291 5.551 1.627 1.192

Belews 

Creek 1 77 (D=26, ND=51) 0 9.444 3.249 1.536

0.291 9.359 2.663 1.450

Option 

0 7.513 2.559 1.433 19.224 10.764

0.291 7.455 2.145 1.321 15.990 9.849 1

: Combination of EPA sampling, CWA 308 sampling, and plant self-monitoring data. 2

: D = detected and ND = non-detected. 3

: Correlation ranges from -1 to 1, with a value of 0 indicating that EPA assumed no correlation in the data.

7.5. Biological Treatment for FGD Wastewater: Summary of the Option Long-Term Averages,

Variability Factors, and Effluent Limits

The table below summarizes the option long-term average, option variability factors, 

and effluent limits for each pollutant for biological treatment technology option for FGD 

wastewater. It should be noted that the option long-term averages and variability factors, and 

effluent limits presented in previous tables also included values assuming zero autocorrelation. 

However, the limits proposed for this rulemaking are based on the autocorrelation obtained 

from the data. The table below presents the results for the option long-term averages, option 

variability factors, and daily maximum and monthly average limits that incorporated the 

autocorrelations. As described above, EPA is proposing to transfer the arsenic and mercury 

limits from the chemical precipitation technology option to biological technology option. Thus, 

the table below presents the arsenic and mercury limits based on the chemical precipitation 

technology option.
Page 44

Table 20. Summary of option long-term averages, variability factors, and effluent limits for

biological FGD wastewater treatment technology.

Pollutant Autocorrelati

on Value

Option 

LTA

Option Daily 

Variability 

Factor

Option 

Monthly 

Variability 

Factor

Daily 

Limit2

Monthl

y Limit2

Arsenic (ug/L) 1 -- 4.483 1.741 1.223 8 6

Mercury (ng/L)1 -- 75.404 3.209 1.570 242 119

Nitrate-nitrite as N (mg/L) 0.291 0.110 1.499 1.157 0.17 0.13

Selenium (ug/L) 0.291 7.455 2.145 1.321 16 10 1

: Long term average, variability factors, and limits were transferred from the chemical precipitation treatment 

technology option for FGD wastewater. 2

: Effluent limitations greater than 1.0 have been rounded upward to the next highest integer. Effluent limitations 

less than 1.0 are rounded up to the next highest hundredths decimal place.

8. Treatment Technology Option for FGD Wastewater: Vapor-Compression 

Evaporation System

EPA used data from Brindisi power plant to calculate the effluent limits for the chemical 

precipitation followed by vapor-compression evaporation treatment technology option for FGD 

wastewater. The pollutants for which the effluent limits are calculated are arsenic, mercury, 

selenium, and total dissolved solids.

The effluent limits were calculated for the following two sampling locations: (i) brine 

concentrator distillate and (ii) crystallizer condensate. The proposing effluent limits for this 

technology option were based on the sampling location that produced the higher effluent 

limits. Setting the effluent limits on the higher concentration stream is necessary in this 

instance to ensure plants operating a well-designed and well-operated evaporator system can 

meet the effluent limits, regardless of whether they sample the effluent streams separately or 

as a combined stream (see Section 13 of the Technical Development Document for a detailed 

discussion).

Brindisi sampling data were collected by EPA between 04/05/2011 and 04/07/2011. 

Data were available at the following sampling locations: FGD Purge, brine concentrator

distillate, and crystallizer condensate.

EPA attempted to use the available data to estimate the autocorrelation. However, for 

Brindisi, EPA was not able to perform an evaluation of the autocorrelation because there were 

too few observations available at the plant. Thus, EPA set the autocorrelation to zero in 

developing the limits for the reasons described in section 5.3.

The sections below provide the following for each of the pollutants: longitudinal plots of 

the data, summary statistics, and plant-specific long-term average and variability factors (see 

Appendix B for an overview of the statistical model and the procedures used to estimate the 
Page 45

plant-specific long term average and variability factors). Since only one plant was used, the 

option long-term average and option variability factors are the same as the plant-specific longterm average and variability factors.

8.1. Vapor-Compression Evaporation for FGD Wastewater: Arsenic

8.1.1. Longitudinal plots of the data for arsenic (ug/L)

Below is the longitudinal plot of the arsenic concentrations (on a logarithmic scale) for 

Brindisi.

Figure 7. Plot of arsenic (ug/L) data on a logarithmic scale for Brindisi.

8.1.2. Summary statistics for arsenic (ug/L)

The table below provides summary statistics for the numbers of detected and nondetected observations together with the sample-specific detection limits for each sample 

location. 

5 10 20 50

Brindisi

 (logarithmic scale)

Date

 Note: Detected = o Non-Detected = *

Arsenic (ug/L)

Apr-05-11 Apr-06-11 Apr-07-11

* * *

FGD Purge

Brine Conc. Dist.

Crystallizer Condensate
Page 46

Table 21. Numbers of detected and non-detected observations and sample-specific detection

limits for arsenic (ug/L) by sampling location.

Plant 

Name

Sampling Location

(Total Observations 1

) Indicator (n) 2

Sample Specific Detection Limits for 

Arsenic (ug/L)

Detection Limit = 4

Brindisi

FGD Purge (N = 2) D (n=2)

Brine Concentrator Distillate (N = 3) ND (n=3) 3

Crystallizer Condensate (N = 3) ND (n=3) 3 1

: Detected and non-detected observations combined. 2

: D = detected and ND = non-detected.

The table below provides summary statistics for all observations (detected and nondetected combined) for each of sampling location.

Table 22. Summary statistics of arsenic concentration (ug/L) for all detected and non-detected

samples combined by sampling location.

Plant Name Sampling Location

Summary Statistics for Arsenic (ug/L)

N 1 Minimu

m

Mean Median Maximum Std

Brindisi

FGD Purge 2 53.0 54.0 54.0 55 1.41

Brine Concentrator Distillate 3 4.0 4.0 4.0 4.0 0

Crystallizer Condensate 3 4.0 4.0 4.0 4.0 0 1

: Detected and non-detected observations combined (all observations are non-detected).

8.1.3. Plant-specific long-term averages and variability factors, option long-term averages and

variability factors, and effluent limits for arsenic (ug/L)

The table below provides the plant-specific long-term averages and variability factors, 

option long-term averages and variability factors, and effluent limits for arsenic at two sampling 

locations: brine concentrator distillate and crystallizer condensate. 

Since all observations were non-detected, the statistical model was not used to obtain 

the long-term average and variability factors (see Sections 5.4, 5.5, and 5.6). The daily limits for 

both sampling locations were set based on the detection limit. The monthly average limits are 

not established when the daily limit is set equal to the detection limit. 
Page 47

Table 23. Plant-specific long-term averages and variability factors, option long-term averages

and variability factors, and limits for arsenic (ug/L) at brine concentrator distillate and

crystallizer condensate.

Type Plant 

Name

Sampling 

Location N 1 LTA

Daily 

Variability 

Factor

Monthly 

Variability 

Factor

Limits

Daily Monthly

Plant –

Specific Brindisi

Brine 

Concentrator 

Distillate

3 

(D=0, ND=3) 4.0 2 --3 --3

Crystallizer 

Condensate

3 

(D=0, ND=3) 4.0 2 --3 --3

Option

Brine 

Concentrator 

Distillate

4.0 2 --3 --3 4 4 --5

Crystallizer 

Condensate 4.0 2 ---3 --3 4 4 --5

1

: D = detected and ND = non-detected. 2

: Long-term average is the arithmetic mean since all observations were non-detected (not able to estimate the 

variance of the distribution).

3

: All observations were non-detected, so the variability factors could not be calculated. 4

: Limit is set equal to the detection limit. 5

: Monthly average limit is not established when the daily limit is equal to detection limit.

8.2. Vapor-Compression Evaporation for FGD Wastewater: Mercury

8.2.1. Longitudinal plots of the data for mercury (ng/L)

Below is the longitudinal plot of the mercury concentrations (on a logarithmic scale) for 

Brindisi.

Figure 8. Plot of mercury (ng/L) data on a logarithmic scale for Brindisi.

5 10 50 500 5000

Brindisi

 (logarithmic scale)

Date

 Note: Detected = o Non-Detected = *

Mercury (ng/L)

Apr-05-11 Apr-06-11 Apr-07-11

FGD Purge

Brine Conc. Dist.

Crystallizer Condensate
Page 48

8.2.2. Summary statistics for mercury (ng/L)

All observations at each of the sampling locations for Brindisi were detected. The table 

below provides summary statistics for all observations for each sampling location.

Table 24. Summary statistics of mercury concentration (ng/L) for all detected and non-detected

samples combined by sampling location.

Plant Name Sampling Location Summary Statistics for Mercury (ng/L)

N 1 Minimum Mean Median Maximum Std

Brindisi

FGD Purge 2 21,100.0 24,000.0 24,000.0 26,900.0 4,101.2

Brine Concentrator Distillate 3 2.9 3.3 3.1 4.0 0.6

Crystallizer Condensate 3 10.9 17.3 20.4 20.7 5.6 1

: Detected and non-detected observations combined (all observations were detected).

8.2.3. Plant-specific long-term averages and variability factors, option long-term averages and

variability factors, and effluent limits for mercury (ng/L)

The table below provides the plant-specific LTAs and plant-specific variability factors,

option LTAs and variability factors, and limits for mercury at two sampling locations: brine 

concentrator distillate and crystallizer condensate.

Table 25. Plant-specific long-term averages and variability factors, option long-term averages

and variability factors, and limits for mercury (ng/L) at brine concentrator distillate and 

crystallizer condensate.

Type Plant 

Name

Sampling 

Location N1 LTA

Daily 

Variability 

Factor

Monthly 

Variability 

Factor

Limits

Daily Monthly

Plant –

Specific Brindisi

Brine 

Concentrator 

Distillate

3

(D=3, ND=0) 3.348 1.453 1.144

Crystallizer 

Condensate

3

(D=3, ND=0) 17.788 2.192 1.338

Option

Brine 

Concentrator 

Distillate

3.348 1.453 1.144 4.865 3.829

Crystallizer 

Condensate 17.788 2.192 1.338 38.989 23.799

1

: D = detected and ND = non-detected.
Page 49

8.3. Vapor-Compression Evaporation for FGD Wastewater: Selenium

8.3.1. Longitudinal plots of the data for selenium (ug/L)

Below is the longitudinal plot of the selenium concentrations (on a logarithmic scale) for 

Brindisi.

Figure 9. Plot of selenium (ug/L) data on a logarithmic scale for Brindisi.

8.3.2. Summary statistics for selenium (ug/L)

The table below provides summary statistics for the numbers of detected and nondetected observations together with the sample-specific detection limits by sample location.

Table 26. Number of detected, non-detected, and sample-specific detection limits for selenium

(ug/L) by sampling location.

Plant 

Name

Sampling Location 

(Total Observations 1

) Indicator (n) 2

Sample-Specific Detection Limits for 

Selenium (ug/L)

Detection Limit = 5

Brindisi

FGD Purge (N = 2) D (n = 2)

Brine Concentrator Distillate (N = 3) ND (n = 3) 3

Crystallizer Condensate (N = 3) ND (n = 3) 3 1

: Detected and non-detected observations combined. 2

: D = detected and ND = non-detected.

The table below provides summary statistics for all observations (detected and nondetected combined) for each sampling location.

5 10 20 50 100 200

Brindisi

 (logarithmic scale)

Date

 Note: Detected = o Non-Detected = *

Selenium (ug/L)

Apr-05-11 Apr-06-11 Apr-07-11

* * *

FGD Purge

Brine Conc. Dist.

Crystallizer Condensate
Page 50

Table 27. Summary statistics of selenium concentration (ug/L) for all detected and 

non-detected samples combined by sampling location.

Plant Name Sampling Location Summary Statistics for Selenium (ug/L)

N 1 Minimum Mean Median Maximum Std

Brindisi

FGD Purge 2 220.0 255.0 255.0 290.0 49.5

Brine Concentrator Distillate 3 5.0 5.0 5.0 5.0 0.0

Crystallizer Condensate 3 5.0 5.0 5.0 5.0 0.0 1

: Detected and non-detected observations combined (all observations were non-detected).

8.3.3. Plant-specific long-term averages and variability factors, option long-term averages and

variability factors, and effluent limits for selenium (ug/L)

The table below provides the option plant-specific LTAs and variability factors, option 

LTAs and variability factors, and effluent limits for selenium at two sampling locations: brine 

concentrator distillate and crystallizer condensate.

All observations were non-detected, so the statistical model was not used to obtain the 

long-term average and variability factors. The daily limits for both sampling locations were set 

based on the detection limit. The monthly average is not set when the daily limit is based on 

the detection limit.

Table 28. Plant-specific long-term averages and variability factors, option long-term averages

and variability factors, and limits for selenium (ug/L) at brine concentrator distillate and 

crystallizer condensate.

Type Plant 

Name

Sampling 

Location N1 LTA

Daily 

Variability 

Factor

Monthly 

Variability 

Factor

Limits

Daily Monthly

Plant –

Specific Brindisi

Brine 

Concentrator 

Distillate

3 

(D=0, ND=3) 5.0 2 --3 --3

Crystallizer 

Condensate

3 

(D=0, ND=3) 5.0 2 --3 --3

Option

Brine 

Concentrator 

Distillate

5.0 2 --3 --3 5 4 --5

Crystallizer 

Condensate 5.0 2 --3 --3 5 4 --5

1

: D = detected and ND = non-detected. 2

: Long-term average is the arithmetic mean since all observations were non-detected (not able to estimate the 

variance of the distribution).

3

: All observations were non-detected, so the variability factors could not be calculated. 4

: Limitation is set equal to the detection limit. 5

: Monthly average limitation is not established when the daily limit is equal to detection limit.
Page 51

8.4. Vapor-Compression Evaporation for FGD Wastewater: Total Dissolved Solids (TDS)

8.4.1. Longitudinal plots of the data for TDS (mg/L)

Below is the longitudinal plot of the TDS concentrations (on a logarithmic scale) for 

Brindisi.

Figure 10. Plot of TDS (mg/L) data on a logarithmic scale for Brindisi.

8.4.2. Summary statistics for TDS (mg/L)

The table below provides summary statistics for the numbers of detected and nondetected observations together with the sample-specific detection limits by sample location.

Table 29. Number of detected, non-detected, and sample-specific detection limits for total

dissolved solid (mg/L) by sampling location.

Plant 

Name

Sampling Location 

(Total Observations 1

) Indicator (n) 2

Sample-Specific Detection Limits for 

TDS (ug/L)

Detection Limit = 10

Brindisi

FGD Purge (N = 2) D (n = 2)

Brine Concentrator Distillate (N = 3) D (n = 2)

ND (n = 1) 1

Crystallizer Condensate (N = 3) D (n = 2)

ND (n = 1) 1 1

: Detected and non-detected observations combined. 2

: D = detected and ND = non-detected.

The table below provides summary statistics for all observations (detected and nondetected combined) for each sampling location. 10 50 500 5000

Brindisi

 (logarithmic scale)

Date

 Note: Detected = o Non-Detected = *

TDS (mg/L)

Apr-05-11 Apr-06-11 Apr-07-11

*

FGD Purge

Brine Conc. Dist.

Crystallizer Condensate
Page 52

Table 30. Summary statistics of total dissolved solids concentration (mg/L) for all detected and

non-detected samples combined by sampling location.

Plant Name Sampling Location

Summary Statistics for Total Dissolved Solids (mg/L)

N 1 Minimum Mean Median

Maximu

m Std

Brindisi

FGD Purge 2 13,000.0 14,000.0 14,000.0 15,000.0 1,414.2

Brine Concentrator Distillate 3 10.0 11.0 10.0 13.0 1.7

Crystallizer Condensate 3 10.0 14.0 10.0 22.0 6.9 1

: Detected and non-detected observations combined.

8.4.3. Plant-specific long-term averages and variability factors, option long-term averages and

variability factors, and effluent limits for TDS (mg/L)

The table below provides the plant-specific LTAs and variability factors, option LTAs and 

variability factors, and effluent limits for TDS at two sampling locations: brine concentrator 

distillate and crystallizer condensate.

Table 31. Plant-specific long-term averages and variability factors, option long-term averages

and variability factors, and limits for TDS (mg/L) at brine concentrator distillate and crystallizer 

condensate.

Type Plant 

Name

Sampling 

Location N1 LTA

Daily 

Variability 

Factor

Monthly 

Variability 

Factor

Limits

Daily Monthly

Plant –

Specific Brindisi

Brine 

Concentrator 

Distillate

3

(D=2, ND=1) 11.066 1.541 1.150

Crystallizer 

Condensate

3

(D=2, ND=1) 14.884 3.341 1.572

Option

Brine 

Concentrator 

Distillate

11.066 1.541 1.150 17.054 12.722

Crystallizer 

Condensate 14.884 3.341 1.572 49.734 23.393

1

: D = detected and ND = non-detected.

8.5. Vapor-Compression Evaporation for FGD Wastewater: Summary of the Option Long-Term

Averages, Option Variability Factors, and Effluent Limits 

The tables below summarize the option long-term average, option variability factors, 

and limits for each of the pollutants for the chemical precipitation followed by vapor 

compression evaporation system for FGD wastewater. Table 32 provides the results for brine 

concentrator distillate sampling location while Table 33 provides the results at crystallizer 

condensate sampling location. Since only one plant was used, the option LTA and option 

variability factors are the same as the plant-specific LTA and variability factors. Note that the 
Page 53

effluent limits for regulation for this technology option are based on the crystallizer 

condensate. See Section 13 of the Technical Development Document for a discussion of EPA’s 

reasons for basing the effluent limits for this technology option on the crystallizer condensate

rather than the effluent limits calculated at brine concentrator distillate.

Table 32. Summary of option long-term averages, variability factors, and limits for vaporcompression evaporation technology for FGD wastewater at brine concentrator distillate.

Pollutant Autocorrelation 

value

Option 

LTA

Option 

Daily 

Variability 

Factor

Option 

Monthly 

Variability 

Factor

Daily 

Limit 3

Monthly 

Limit 3

Arsenic (ug/L) 0 4.0 1 ---2 ---2 4 4 --5

Mercury (ng/L) 0 3.348 1.453 1.144 5 4

Selenium (ug/L) 0 5.0 1 ---2 ---2 5 4 --5

TDS (mg/L) 0 11.066 1.541 1.150 18 13 1

: Long-term average is the arithmetic mean since all observations were non-detected (not able to estimate the 

variance of the distribution).

2

: All observations were non-detected, so variability factors could not be calculated. 3

: Effluent limitations greater than 1.0 have been rounded upward to the next highest integer. 4

: Limitation is set equal to the detection limit. 5

: Monthly average limitation is not established when the daily limit is based on the detection limit.

Table 33. Summary of option long-term averages, option variability factors, and limits for 

mechanical vapor-compression evaporation technology for FGD wastewater at crystallizer 

condensate.

Pollutant Autocorrel

ation value Option LTA

Option Daily 

Variability 

Factor

Option Monthly 

Variability 

Factor

Daily 

Limit 3

Monthly 

Limit 3

Arsenic (ug/L) 0 4.0 1 ---2 ---2 4 4 --5

Mercury (ng/L) 0 17.788 2.192 1.338 39 24

Selenium (ug/L) 0 5.0 1 ---2 ---2 5 4 --5

TDS (mg/L) 0 14.884 3.341 1.572 50 24 1

: Long-term average is the arithmetic mean since there were too few detected observations (not able to estimate 

the variance of the distribution).

2

: All observations were non-detected, so the variability factors could not be calculated. 3

: Effluent limitations greater than 1.0 have been rounded upward to the next highest integer. 4

: Limitation is set equal to the detection limit.

5

: Monthly average limitation is not established when the daily limit is based on the detection limit.
Page 54

9. Treatment Technology Option for Gasification Wastewater: VaporCompression Evaporation

EPA used data from two power plants (Polk and Wabash River) to develop the effluent 

limits for the vapor-compression evaporation treatment technology for gasification 

wastewater. The four pollutants for which the limits are calculated are arsenic, mercury, 

selenium, and total dissolved solids. Arsenic and mercury data at Wabash River failed the data 

editing criteria, thus, EPA excluded the arsenic and mercury data from this plant in developing 

the limits for gasification wastewater treatment technology. Even though the Wabash River 

data for arsenic and mercury were not used to develop the limits, summary statistics and plots 

for these two pollutants at this plant are also presented in this section.

For this technology option, EPA considered limits at two sampling locations: (i) forced 

circulation evaporator condensate and (ii) vapor compression evaporator condensate. EPA is 

proposing to set the limits based on vapor compression evaporator condensate data since EPA 

determined that the data collected at forced circulation evaporator condensate did not 

demonstrate typical removal rates for pollutants generally well-treated by evaporation and 

therefore were not adequate to form the basis of the limits. Based on its review of the 

treatment system, EPA believes that the evaporator (or at a minimum the forced circulation 

evaporation stage) was operating abnormally and allowing carryover of pollutants to the 

condensate effluent stream. For this reason, EPA based the limits for this technology option on 

the limits calculated from the vapor compression evaporator condensate data (see Section 13 of 

the Technical Development Document). If EPA was to calculate limits using the data at the 

forced circulation evaporator condensate, it would follow the same methodology used to 

calculate the limits for vapor compression evaporator condensate data.

The following provides a detailed summary of the available data for calculating the 

numeric limits at each plant.

Polk Sampling Data

Polk sampling data were collected by the plant on the following dates: 10/18/2011, 

10/19/2011, 10/26/2011, and 10/27/2011. Data were available at the following sampling 

locations: neutralized weak acid, vapor compression evaporator influent, forced circulation 

evaporator condensate, and vapor compression evaporator condensate.

Wabash River Sampling Data

Wabash River sampling data were collected by the plant between 02/21/2011 to 

02/24/2011. Data were available at the following sampling locations: sour water treatment 

influent, steam stripper effluent, vapor compression evaporator influent (RCC evaporator 

influent), and vapor compression evaporator condensate (RCC evaporator condensate).
Page 55

EPA attempted to use the available data to estimate the autocorrelation. However, for 

both of these plants, EPA was not able to perform an evaluation of the autocorrelation because 

there were too few observations available at each plant. Thus, EPA set that the autocorrelation 

value is zero in the calculation of the limits as described in Section 5.3.

The sections below provide the following for each of the pollutants: longitudinal plots of 

the data, summary statistics, and plant-specific long-term average and variability factors (see 

Appendix B for an overview of the statistical model and the procedures used to estimate the 

plant-specific long term average and variability factors). Also provided in the sections below are 

the option long-term average, option variability factors, and effluent limits for each pollutant.

9.1. Vapor-Compression Evaporation for Gasification: Arsenic

9.1.1. Longitudinal plots of the data for arsenic (ug/L)

Below are the longitudinal plots of the arsenic concentrations (on a logarithmic scale) 

for Polk and Wabash River.

Figure 11. Plot of arsenic (ug/L) data on a logarithmic scale for Polk and Wabash River.

9.1.2. Summary statistics for arsenic (ug/L)

The table below provides summary statistics for the numbers of detected and nondetected observations together with the sample-specific detection limits by sample location 

and plant.

5 10 20 50 100 200

Polk

 (logarithmic scale)

Date

 Note: Detected = o Non-Detected = *

Arsenic (ug/L)

Oct-18-11 Oct-19-11 Oct-26-11 Oct-27-11

* * * *

Vapor Comp. Evap. Cond.

Vapor Comp. Evap. Inf.

Forced Circ. Evap. Cond.

Neut. Weak Acid Waste Stream

5 10 20 50 100 200

Wabash River

 (logarithmic scale)

Date

 Detected: o Non-Detected: *

Arsenic (ug/L)

Feb-21-11 Feb-22-11 Feb-23-11 Feb-24-1

*** *** ** **

Vapor Comp. Evap. Inf.

Vapor Comp. Evap. Cond.

Sour Water Trt. Inf.

Steam Stripper Eff.
Page 56

Table 34. Numbers of detected and non-detected observations and sample-specific detection

limits for arsenic (ug/L) by plant and sampling location.

Plant Name Sampling Location

(Total Observations 1

) Indicator (n) 2

Sample Specific Detection Limits for 

Arsenic (ug/L)

4 4.1 4.2

Polk

Neu. Weak Acid Waste Stream (N = 4) D (n = 4)

Vapor Compr. Evap. Influent (N = 4) D (n = 4)

Vapor Compr. Evap. Condensate (N = 4) ND (n = 4) 4

Forced Cir. Evap. Condensate (N = 4) D (n = 4)

Wabash 

River

Sour Water Trt Influent (N = 4) ND (n = 4) 4

Steam Stripper Effluent (N = 4) ND (n = 4) 2 2

Vapor Compr. Evap. Influent (N = 4)

D (n = 2)

ND (n = 2) 2

Vapor Compr. Evap. Condensate (N = 4) ND (n = 4) 4 1

: Detected and non-detected observations combined. 2

: D = detected and ND = non-detected.

The table below provides summary statistics for all observations (detected and nondetected combined) for each sampling location at each of the plants.

Table 35. Summary statistics of arsenic concentration (ug/L) for all detected and non-detected 

samples combined, by plant and sampling location.

Plant Name Sampling Location Summary Statistics for Arsenic (ug/L)

N 1 Minimum Mean Median Maximum Std

Polk

Neu. Weak Acid Waste Stream 4 140.0 160.0 165.0 170.0 14.1

Vapor Compr. Evap. Influent 4 220.0 280.0 280.0 340.0 49.7

Vapor Compr. Evap. 

Condensate 4 4.0 4.0 4.0 4.0 0.0

Forced Cir. Evap. Condensate 4 29.0 33.0 33.5 36.0 2.9

Wabash River

Sour Water Trt Influent 4 4.1 4.1 4.1 4.1 0.0

Steam Stripper Effluent 4 4.1 4.2 4.2 4.2 0.1

Vapor Compr. Evap. Influent 4 4.0 4.5 4.5 5.0 0.6

Vapor Compr. Evap. 

Condensate 4 4.0 4.0 4.0 4.0 0.0 1

: Detected and non-detected observations combined.

9.1.3. Plant-specific long-term average and variability factors, option long-term average and

variability factors, and effluent limits for arsenic (ug/L)

The table below provides the plant-specific LTA, plant-specific variability factors, option 

LTA and variability factors, and numeric limits for arsenic at vapor compression evaporator 

condensate (using Polk data only). As described above, the arsenic data for Wabash River failed
Page 57

the data editing criteria, so, EPA excluded the arsenic dataset from Wabash River in developing 

the limits for this technology option.

Table 36. Plant-specific long-term average and variability factors, option long-term average and 

variability factors, and limits for arsenic (ug/L) at vapor compression evaporator condensate.

TYPE Plant 

Name

Sampling Location

N1 LTA

Daily 

Variability 

Factor

Monthly 

Variability 

Factor

Limits

Daily Monthly

PlantSpecific Polk Vapor Compr

Evap. Condensate

4 

(D=0,ND=4) 4.00 2 --3 --3

Option Vapor Compr. 

Evap. Condensate

4.00 2 --3 --3 4 4 --5

1

: D = detected and ND = non-detected. 2

: Long-term average is the arithmetic mean since all observations were non-detected (not able to estimate the 

variance of the distribution).

3

: All observations were non-detected, so the variability factors could not be calculated. 4

: Limitation is set equal to the detection limit.

5

: Monthly average limitation is not established when the daily limit is equal to the detection limit.

9.2. Vapor-Compression Evaporation for Gasification: Mercury

9.2.1. Longitudinal plots of the data for mercury (ng/L)

Below are the longitudinal plots of the mercury concentrations (on a logarithmic scale) 

for Polk and Wabash River.

Figure 12. Plot of mercury (ng/L) data on a logarithmic scale for Polk and Wabash River.

9.2.2. Summary statistics for mercury (ng/L)

1 10 100 1000 10000

Polk

 (logarithmic scale)

Date

 Note: Detected = o Non-Detected = *

Mercury (ng/L)

Oct-18-11 Oct-19-11 Oct-26-11 Oct-27-11

Vapor Comp. Evap. Cond.

Vapor Comp. Evap. Inf.

Forced Circ. Evap. Cond.

Neut. Weak Acid Waste Stream

1 10 100 1000 10000

Wabash River

 (logarithmic scale)

Date

 Detected: o Non-Detected: *

Mercury (ng/L)

Feb-21-11 Feb-22-11 Feb-23-11 Feb-24-1

* *

* * * *

*

*

* *

Vapor Comp. Evap. Inf.

Vapor Comp. Evap. Cond.

Sour Water Trt. Inf.

Steam Stripper Eff.
Page 58

The table below provides summary statistics for the numbers of detected and nondetected observations together with the sample-specific detection limits by sample location 

and plant.

Table 37. Numbers of detected and non-detected observations and sample-specific detection

limits for mercury (ng/L) by plant and sampling location.

Plant Name Sampling Location

(Total Observations 1

) Indicator (n) 2

Sample Specific Detection Limits for 

Mercury (ng/L)

0.5 4.95 9.9

Polk

Neu. Weak Acid Waste Stream (N = 4) D (n = 4)

Vapor Compr. Evap. Influent (N = 4) D (n = 4)

Vapor Compr. Evap. Condensate (N = 4) D (n = 4)

Forced Cir. Evap. Condensate (N = 4) D (n = 4)

Wabash 

River

Sour Water Trt Influent (N = 4)

D (n = 3)

ND (n = 1) 1

Steam Stripper Effluent (N = 4)

D (n = 2)

ND (n = 2) 2

Vapor Compr. Evap. Influent (N = 4) ND (n = 4) 1 3

Vapor Compr. Evap. Condensate (N = 4) ND (n = 4) 4 1

: Detected and non-detected observations combined. 2

: D = detected and ND = non-detected.

The table below provides summary statistics for all observations (detected and nondetected combined) for each sampling location at each of the plants.

Table 38. Summary statistics of mercury concentration (ng/L) for all detected and non-detected 

samples combined, by plant and sampling location.

Plant Name Sampling Location Summary Statistics for Mercury (ng/L)

N 1 Minimum Mean Median Maximum Std

Polk

Neu. Weak Acid Waste Stream 4 2,030.0 4,392.5 2,270.0 11,000.0 4,408.9

Vapor Compr. Evap. Influent 4 17.0 70.4 85.9 92.7 36.1

Vapor Compr. Evap. 

Condensate 4 0.8 1.1 1.1 1.3 0.2

Forced Cir. Evap. Condensate 4 5.0 6.1 5.7 8.0 1.3

Wabash River

Sour Water Trt Influent 4 9.9 1,872.3 29.6 7,420.0 3,698.5

Steam Stripper Effluent 4 9.9 22.6 17.2 46.3 17.2

Vapor Compr. Evap. Influent 4 5.0 8.7 9.9 9.9 2.5

Vapor Compr. Evap. 

Condensate 4 0.5 0.5 0.5 0.5 0.0 1

: Detected and non-detected observations combined.

9.2.3. Plant-specific long-term average and variability factors, option long-term average and

variability factors, and effluent limits for mercury (ng/L)
Page 59

The table below provides the plant-specific LTA, plant-specific variability factors, option 

LTA and variability factors, and effluent limits for mercury at vapor compression evaporator 

condensate (using Polk data only). Because the mercury data at Wabash River failed the data 

editing criteria, EPA excluded the data in developing the limits for this technology option. Thus, 

the mercury limits are based on Polk data only.

Table 39. Plant-specific long-term average and variability factors, option long-term average and 

variability factors, and limits for mercury (ng/L) at vapor compression evaporator condensate.

1

: D = detected and ND = non-detected.

9.3. Vapor-Compression Evaporation for Gasification: Selenium

9.3.1. Longitudinal plots of the data for selenium (ug/L)

Below are the longitudinal plots of the selenium concentrations (on a logarithmic scale) 

for Polk and Wabash River.

Figure 13. Plot of selenium (ug/L) data on a logarithmic scale for Polk and Wabash River.

5 10 50 500 5000

Polk

 (logarithmic scale)

Date

 Note: Detected = o Non-Detected = *

Selenium (ug/L)

Oct-18-11 Oct-19-11 Oct-26-11 Oct-27-11

Vapor Comp. Evap. Cond.

Vapor Comp. Evap. Inf.

Forced Circ. Evap. Cond.

Neut. Weak Acid Waste Stream

5 10 50 500 5000

Wabash River

 (logarithmic scale)

Date

 Detected: o Non-Detected: *

Selenium (ug/L)

Feb-21-11 Feb-22-11 Feb-23-11 Feb-24-1

* * *

Vapor Comp. Evap. Inf.

Vapor Comp. Evap. Cond.

Sour Water Trt. Inf.

Steam Stripper Eff.

TYPE Plant 

Name

Sampling Location

N1 LTA

Daily 

Variability 

Factor

Monthly 

Variability 

Factor

Limits

Daily Monthly

PlantSpecific Polk Vapor Compr 

Evap. Condensate

4 

(D=4,ND=0) 1.075 1.632 1.194

Option Vapor Compr. 

Evap. Condensate 1.075 1.632 1.194 1.754 1.284
Page 60

9.3.2. Summary statistics for selenium (ug/L) 

The table below provides summary statistics for the numbers of detected and nondetected observations together with the sample-specific detection limits by sample location 

and plant.

Table 40. Numbers of detected and non-detected observations and sample-specific detection

limits for selenium (ug/L) by plant and sampling location.

Plant Name Sampling Location

(Total Observations 1

) Indicator 2

Sample-Specific Detection Limits 

for Selenium (ug/L)

Detection Limit = 5

Polk

Neu. Weak Acid Waste Stream (N = 4) D (n = 4)

Vapor Compr. Evap. Influent (N = 4) D (n = 4)

Vapor Compr. Evap. Condensate (N = 4) D (n = 4)

Forced Cir. Evap. Condensate (N = 4) D (n = 4)

Wabash 

River

Sour Water Trt Influent (N = 4) D (n = 4)

Steam Stripper Effluent (N = 4) D (n = 4)

Vapor Compr. Evap. Influent (N = 4) D (n = 4)

Vapor Compr. Evap. Condensate (N = 4)

D (n = 1)

ND (n = 3) 3 1

: Detected and non-detected observations combined. 2

: D = detected and ND = non-detected.

The table below provides summary statistics for all observations for each sampling 

location at each of the plants.

Table 41. Summary statistics of selenium concentration (ug/L) for all detected and 

non-detected samples combined, by plant and sampling location.

Plant Name Sampling Location Summary Statistics for Selenium (ug/L)

N 1 Minimum Mean Median Maximum Std

Polk

Neu. Weak Acid Waste Stream 4 6,000.0 7,550.0 7,350.0 9,500.0 1,515.5

Vapor Compr. Evap. Influent 4 720.0 1,277.5 1,295.0 1,800.0 551.5

Vapor Compr. Evap. 

Condensate 4 140.0 277.5 250.0 470.0 149.7

Forced Cir. Evap. Condensate 4 2,500.0 2,675.0 2,650.0 2,900.0 170.8

Wabash River

Sour Water Trt Influent 4 420.0 480.0 485.0 530.0 46.9

Steam Stripper Effluent 4 49.0 152.3 165.0 230.0 75.5

Vapor Compr. Evap. Influent 4 800.0 920.0 890.0 1,100.0 128.3

Vapor Compr. Evap. 

Condensate 4 5.0 5.1 5.0 5.5 0.3 1

: Detected and non-detected observations combined (all were detected).
Page 61

9.3.3. Plant-specific long-term averages and variability factors, option long-term average and

variability factors, and effluent limits for selenium (ug/L)

The table below provides the plant-specific LTA, plant-specific variability factors, option 

LTA and variability factors, and numeric limits for selenium at vapor compression evaporator 

condensate (using both Polk and Wabash River data).

Table 42. Plant-specific long-term averages and variability factors, option long-term average

and variability factors, and limits for selenium (ug/L) at vapor compression evaporator

condensate.

TYPE Plant 

Name

Sampling Location

N2 LTA

Daily 

Variability 

Factor

Monthly 

Variability 

Factor

Limits

Daily Monthly

PlantSpecific

Polk Vapor Compr Evap. 

Condensate

4

(D=4,ND=0) 288.430 3.083 1.545

Wabash 

River

Vapor Compr Evap. 

Condensate

4

(D=1,ND=3) 5.130 --3 --3

Option Vapor Compr. 

Evap. Condensate1 146.780 3.083 1.545 452.560 226.810

1

: Polk and Wabash River combined. 2

: D = detected and ND = non-detected 3

:Nearly all observations were non-detected, so the variability factors could not be calculated. 

9.4. Vapor-Compression Evaporation for Gasification: Total Dissolved Solids (TDS)

9.4.1. Longitudinal plots of the data for TDS (mg/L)

Below are the longitudinal plots of the TDS concentrations (on a logarithmic scale) for 

Polk and Wabash River.

Figure 14. Plot of TDS (mg/L) data on a logarithmic scale for Polk and Wabash River. 10 50 500 5000

Polk

 (logarithmic scale)

Date

 Note: Detected = o Non-Detected = *

TDS (mg/L)

Oct-18-11 Oct-19-11 Oct-26-11 Oct-27-11

Vapor Comp. Evap. Cond.

Vapor Comp. Evap. Inf.

Forced Circ. Evap. Cond.

Neut. Weak Acid Waste Stream

10 50 500 5000

Wabash River

 (logarithmic scale)

Date

 Detected: o Non-Detected: *

TDS (mg/L)

Feb-21-11 Feb-22-11 Feb-23-11 Feb-24-1

* *

* *

Vapor Comp. Evap. Inf.

Vapor Comp. Evap. Cond.

Sour Water Trt. Inf.

Steam Stripper Eff.
Page 62

9.4.2. Summary statistics for TDS (mg/L)

The table below provides summary statistics for the numbers of detected and nondetected observations together with the sample-specific detection limits by sample location 

and plant.

Table 43. Numbers of detected and non-detected observations and sample-specific detection

limits for TDS (mg/L) by plant and sampling location.

Plant Name Sampling Location

(Total Observations 1

) Indicator (n) 2

Sample-Specific Detection Limits for 

TDS (mg/L)

10 200

Polk

Neu. Weak Acid Waste Stream (N = 4) D (n = 4)

Vapor Compr. Evap. Influent (N = 4) D (n = 4)

Vapor Compr. Evap. Condensate (N = 4) D (n = 4)

Forced Cir. Evap. Condensate (N = 4) D (n = 4)

Wabash 

River

Sour Water Trt Influent (N = 4)

D (n = 2)

ND (n = 2) 2

Steam Stripper Effluent (N = 4) D (n = 4)

Vapor Compr. Evap. Influent (N = 4) D (n = 4)

Vapor Compr. Evap. Condensate (N = 4)

D (n = 2)

ND (n = 2) 2 1

: Detected and non-detected observations combined. 2

: D =detected and ND = non-detected.

The table below provides summary statistics for all observations (detected and nondetected combined) for each sampling location at each of the plants.

Table 44. Summary statistics of TDS concentration (mg/L) for all detected and non-detected 

samples combined, by plant and sampling location.

Plant 

Name Sampling Location Summary Statistics for TDS (mg/L)

N 1 Minimum Mean Median Maximum Std

Polk

Neu. Weak Acid Waste Stream 4 26,000.0 27,250.0 26,000.0 31,000.0 2,500.0

Vapor Compr. Evap. Influent 4 4,500.0 4,575.0 4,600.0 4,600.0 50.0

Vapor Compr. Evap. Condensate 4 11.0 16.3 15.5 23.0 5.7

Forced Cir. Evap. Condensate 4 48.0 106.5 114.0 150.0 44.5

Wabash 

River

Sour Water Trt Influent 4 200.0 245.0 210.0 360.0 77.2

Steam Stripper Effluent 4 2,000.0 2,800.0 2,400.0 4,400.0 1,095.4

Vapor Compr. Evap. Influent 4 3,600.0 4,225.0 4,400.0 4,500.0 419.3

Vapor Compr. Evap. Condensate 4 10.0 13.5 11.0 22.0 5.7 1

: Detected and non-detected observations combined
Page 63

9.4.3. Plant-specific long-term averages and variability factors, option long-term average and

variability factors, and effluent limits for TDS (mg/L)

The table below provides the plant-specific LTA, plant-specific variability factors, option 

LTA and variability factors, and numeric limits for TDS at vapor compression evaporator 

condensate (using both Polk and Wabash River data).

Table 45. Plant-specific long-term averages and variability factors, option long-term average

and variability factors, and numeric limits for TDS (mg/L) at vapor compression evaporator 

condensate.

TYPE Plant 

Name Sampling Location N2 LTA

Daily 

Variability 

Factor

Monthly 

Variability 

Factor

Limits

Daily Monthly

PlantSpecific

Polk Vapor Compr Evap. 

Condensate

4 

(D=4,ND=0) 16.512 2.149 1.327

Wabash 

River

Vapor Compr. Evap. 

Condensate

4 

(D=2,ND=2) 13.906 2.818 1.450

Option Vapor Compr. Evap. 

Condensate 1 15.209 2.483 1.389 37.767 21.122

1

: Polk and Wabash River combined. 2

: D = detected and ND = non-detected

9.5. Vapor-Compression Evaporation for Gasification: Summary of the Option Long-Term

Average, Option Variability Factors, and Effluent Limits

The table below summarizes the option long-term averages, option variability factors, 

and effluent limits for vapor compression-evaporation technology option. Note that EPA is 

proposing that the daily and monthly average limitations for mercury for gasification 

wastewater be rounded to two decimal places instead of rounding to the next highest integer in 

order to avoid having the same value for the daily and monthly average limitation.

Table 46. Summary of option long-term averages, option variability factors, and limits for vaporcompression evaporation technology for gasification wastewater.

Pollutant Autocorrelati

on Value

Option 

LTA

Option Daily 

Variability 

Factor

Option Monthly 

Variability 

Factor

Daily 

Limit 3

Monthly 

Limit 3

Arsenic (ug/L) 0 4.0 1 -- 2 -- 2 4 4 --5

Mercury (ng/L) 0 1.075 1.632 1.194 1.76 1.29

Selenium (ug/L) 0 146.780 3.083 1.545 453 227

TDS (mg/L) 0 15.209 2.483 1.389 38 22 1

: Long-term average is the arithmetic mean since all observations were non-detected (not able to estimate the 

variance of the distribution).

2

: All observations were non-detected, so the variability factors could not be calculated. 3

: : Effluent limitations greater than 1.0 have been rounded upward to the next highest integer, except for limits 

for mercury, which were rounded to the next highest hundredths decimal place.

4

: Limit is set equal to the detection limit.

5

: Monthly average limits are not established when the daily maximum limitation is based on the detection limit.
Page 64

10. Summary of Effluent Limits for Each Treatment Technology Option for FGD,

Gasification, and Leachate Wastewater

Sections 6, 7, 8, and 9 above present detailed summary statistics of the data together 

with the long-term averages, variability factors, and effluent limits for each treatment 

technology option for FGD and gasification wastewaters. This section provides an overall 

summary of the option long-term averages, option variability factors, and limits for each 

technology option presented in Sections 6, 7, 8, and 9 above. In addition, this section also 

summarizes the regulation for leachate.

The bullets below provide some important items that are discussed both in previous 

sections and again in this section.

• EPA is proposing to transfer the effluent limits for arsenic and mercury calculated from 

the chemical precipitation technology option for the FGD to the biological technology 

option for FGD (see Section 13 of the TDD for the rationale for this transfer of limits). •

• For chemical precipitation followed by vapor-compression evaporation treatment 

technology option for FGD wastewater, the effluent limits were based on the data from 

crystallizer condensate sampling location. As explained in Section 8 above, EPA 

calculated limits for this technology option at two separate sampling locations: (i) brine 

concentrator distillate and (ii) crystallizer condensate. The limits selected for the 

rulemaking were based on the stream (i.e., crystallizer condensate) with the higher 

pollutant concentrations. •

• For leachate effluent limits based on chemical precipitation technology option, EPA is 

transferring the effluent limits from the chemical precipitation technology option for 

FGD wastewater because EPA does not have available effluent data for chemical 

precipitation treatment of combustion residual leachate. 

• In most cases, the limits greater than 1.0 were rounded upward to the next highest 

integer, while limits less than 1.0 were rounded up to the next highest hundredths 

decimal place. For mercury for gasification wastewater, after performing the rounding, 

the daily and monthly average limits for mercury for gasification wastewater were the 

same (i.e., both were 2 since the pre-rounded daily and monthly average limitations 

were 1.754 and 1.284, respectively). Thus, in order to avoid having the same value for 

the daily and monthly average limit, EPA is proposing that the daily and monthly 

average limitations for mercury for gasification wastewater be rounded to two decimal 

places.

The table below provides the proposed option long-term average, option variability 

factors, and limitations for each of the FGD, gasification, and leachate technology options. 
Page 65

Table 47. Summary of the option long-term averages and variability factors together with the

effluent limits for each of the FGD, gasification, and leachate technology option. 

Treatment 

Technology 

Option 

Pollutant

Autocorre

lation

Value

Option LTA

Daily 

Variability 

Factor

Monthly

Variability 

Factor

Daily

Limitati

on 4

Monthl

y 

Limitati

on 4

Chemical 

Precipitation For 

FGD 

Arsenic (ug/L) 0 4.483 1.741 1.223 8 6

Mercury (ng/L) 0 75.404 3.209 1.570 242 119

Chemical 

Precipitation 

and Biological 

Treatment For 

FGD 

Arsenic (ug/L) 1 - 4.483 1.741 1.223 8 6

Mercury (ng/L) 1 - 75.404 3.209 1.570 242 119

Nitrate-nitrite 

(mg/L) 0.291 0.110 1.499 1.157 0.17 0.13

Selenium (ug/L) 0.291 7.455 2.145 1.321 16 10

Chemical 

Precipitation 

and 

Evaporation for 

FGD 

Arsenic (ug/L) 0 4.0 2 ---3 ---3 45 -- 6

Mercury (ng/L) 0 17.788 2.192 1.338 39 24

Selenium (ug/L) 0 5.0 2 ---3 ---3 55 -- 6

TDS (mg/L) 0 14.884 3.341 1.572 50 24

VaporCompression 

Evaporation for 

Gasification 

Arsenic (ug/L) 0 4.0 2 -- 3 -- 3 45 -- 6

Mercury (ng/L) 0 1.075 1.632 1.194 1.76 1.29

Selenium (ug/L) 0 146.780 3.083 1.545 453 227

TDS (mg/L) 0 15.209 2.483 1.389 38 22

Chemical 

Precipitation for 

Leachate 

Arsenic (ug/L) 1 -- 4.483 1.741 1.223 8 6

Mercury (ng/L) 1 -- 75.404 3.209 1.570 242 119 1

: Option LTA, option variability factors, and effluent limits were transferred from chemical precipitation 

technology option for FGD wastewater. 2

: Long-term average is the arithmetic mean since all observations were non-detected. 3

: All observations were non-detected, so variability factors could not be calculated. 4

: Effluent limits less than 1.0 are rounded up to the next highest hundredths decimal place.

Effluent limits greater than 1.0 have been rounded upward to the next highest integer, except for effluent limits 

for mercury based on the vapor-compression evaporation treatment technology option for gasification wastewater 

which have been rounded up to the next highest hundredths decimal place. 

5

: Limit is set equal to the detection limit. 6

: Monthly average limits are not established when the daily maximum limitation is based on the detection limit.
Page 66

11. Engineering Review of the Effluent Limits

EPA has performed an engineering review to verify that the effluent limits are 

reasonable based upon the design and expected operation of the control technologies. As part 

of this review, two types of comparisons were performed. First, a comparison was made 

between the effluent limits and the effluent data used to develop the limits. This type of 

comparison helps to evaluate how reasonable the limits are from an engineering perspective. 

Second, a comparison was made between the limits and the influent data. This comparison 

helps evaluate whether the proposed limits are set at a level that ensures that treatment of the 

wastewater would be necessary to meet the limits and that the influent concentrations were 

generally well-controlled by the treatment system.

Section 11.1 presents the results of the comparisons between the limits and all effluent 

data that were used to calculate the limits for each technology option. Section 11.2 presents 

the results of the comparisons between the effluent limits and the influent data values for each 

technology option. See Appendix 4 for a listing of all daily effluent values that are above the 

daily and monthly average limits (along with any other daily values collected in the same 

month).

11.1. Comparison of the Limits to Effluent Data Used as the Basis for the Limits

As part of its data evaluations, EPA compared the value of the effluent limits to the 

effluent values used to calculate the limits. This type of comparison helps to evaluate how 

reasonable the limits are from an engineering perspective. Since EPA is proposing both daily 

and monthly average limits, EPA has performed two comparisons for each pollutant in each 

technology option. EPA first compared the proposed daily limits to the daily effluent values. 

Second, EPA compared the proposed monthly average limits to all the effluent daily values, and 

identified those months where at least one value within a month exceeded the proposed 

monthly average limits. 

After thoroughly evaluating the results of the comparison between the limits and the 

effluent values used to calculate the limits for each treatment technology option for FGD and 

gasification wastewaters, EPA determined that the statistical distributional assumptions used to 

develop the limits are appropriate for the data, and thus the proposed limits for each 

technology option are reasonable. (This conclusion is also true for the leachate limits based on 

the chemical precipitation technology since the leachate limits were transferred from the FGD 

wastewater technology option.) If a plant properly designs and operates its wastewater 

treatment system to achieve the option long-term average for the model technology (rather 

than targeting performance at the effluent limits themselves), it will be able to comply with the 

limits. The sections below discuss the results of the comparisons for each of the technology 

options. 
Page 67

Chemical Precipitation Treatment Technology Option for FGD Wastewater

For the chemical precipitation treatment technology option for FGD wastewater, EPA is 

proposing limits for arsenic and mercury. The limits were calculated using data from three 

plants: Hatfield’s Ferry, Keystone, and Miami Fort.

For both arsenic and mercury, there are some daily effluent concentration values that 

are above both the daily and monthly average limits. After thoroughly examining the data, EPA 

determined that the concentration values that are above both the daily and monthly limits for 

arsenic came from the plant with relatively higher effluent concentration values (i.e., with a 

higher long-term average than the other two plants). EPA observed that the same was true for 

the mercury concentration values that are above both the daily and monthly limits. Since the 

limits are developed using the data from all three plants, it is reasonable to expect that the 

plant with relatively higher concentrations is more likely to have values above the daily and 

monthly limits. As EPA explains below in this section, it is reasonable for this situation to arise in 

the datasets used to calculate the limits and there are specific steps plants can take that enable 

them to improve treatment system performance so that effluent concentrations would be in 

compliance with the proposed limits at all times.

EPA also identified an instance where two (of four) daily values in a month are higher 

than the monthly limit, and the resulting monthly average is equal to the monthly average limit. 

Instances such as this (i.e., where one or more individual results are higher than the monthly 

limitation, but the average of all results in a month are equal to or below the monthly 

limitation) are normal and consistent with the way effluent limits are calculated and 

implemented in NPDES permits. This is illustrated, in fact, by the selenium data for the 

biological treatment technology option, as described in the next section. EPA also identified 

some cases where only one sample was taken during a month and the resulting concentration 

value for that lone sample is above the monthly limit. In such cases, additional monitoring of 

the effluent (e.g., at weekly intervals) would likely result in a monthly average that would fall 

below the monthly average limit.

In addition, EPA identified one month where two (out of four) daily concentration values 

from the month are above the monthly average limit, and the resulting monthly average for all 

four values is above the monthly limit. Based on its engineering judgment developed over years 

of evaluating wastewater treatment processes for power plants and other industrial sectors, 

EPA determined that the combination of additional monitoring, closer operator attention, and 

optimizing treatment system performance to target the effluent concentrations at the 

technology option long-term average will result in lower effluent concentrations that would be 

in compliance with the proposed effluent limits.

EPA noted that while these plants were selected as representing the “best available” 

technology, it does not mean that the plants have the systems fully optimized, especially since 

most of the plants do not have specific limits on the FGD wastewater for the pollutants of 

concern or because their existing limits are well above what the system is achieving. 
Page 68

Specifically, none of these three plants have specific limits for arsenic. Also, only Keystone and 

Hatfield’s Ferry have NPDES permit limits on mercury; however, their current permit limits are 

more than 30 times higher than the proposed BAT effluent limits. For this reason, these plants 

currently do not need to closely monitor the treatment system to confirm performance below 

their permit limit. If these plants were required to meet the proposed limits, EPA believes that 

these plants would be capable of meeting the limits without significant expense. For example, 

EPA’s review of chemical precipitation systems for this industry noted that plants could benefit 

from using an in-house mercury analyzer to monitor the performance of the system on a daily 

basis. Mercury analyzers have been effectively used at a power plant to alert operators when 

mercury concentrations begin trending upward so that they may take steps to adjust treatment 

system performance and remain in compliance with their NPDES permit limits. Furthermore, 

some plants that rely solely on hydroxide precipitation could add sulfide precipitation to 

improve removals of arsenic and mercury. Organosulfide addition, particularly using long-chain 

organosulfide polymers, has been demonstrated to be particularly effective at improving 

mercury removals in chemical precipitation treatment systems. Finally, EPA has also evaluated 

the results of testing at a power plant that, although its FGD wastewater treatment system had 

been in operation for more than a year and was operating at a steady state condition, the plant 

significantly improved the pollutant removal performance merely by altering the dosage rates 

for the wastewater treatment chemical additives. As a result, EPA identified various approaches 

plants can use to improve their performance and achieve the limits. EPA notes that its 

compliance cost estimates for the proposed rule include costs for mercury analyzers, sulfide 

precipitation, and proper dosing of treatment system chemical additives.

Based on the results of the comparisons described above, EPA determined that the 

statistical distributional assumptions are appropriate for the effluent data and that the 

proposed limits are reasonable.

Chemical Precipitation Followed by Biological Treatment Technology Option for FGD 

Wastewater

For the biological treatment technology option for FGD wastewater, EPA is proposing 

limits for arsenic, mercury, nitrate-nitrite as N, and selenium. For arsenic and mercury, EPA 

transferred the limits from the chemical precipitation treatment system for FGD wastewater 

(see Section 13 of the Technical Development Document). Because the limits for arsenic and 

mercury were transferred and since this technology option includes chemical precipitation as a 

first step, the comparison described above for the chemical precipitation technology option is 

relevant for arsenic and mercury. Because of this, EPA expects that the plants employing this 

technology option would be able to comply with the proposed arsenic and mercury limits. 

Furthermore, EPA’s data demonstrate that the biological treatment stage provides pollutant 

reductions for arsenic and mercury (and other pollutants of concern with similar removal 

mechanisms) in addition to the pollutant removals that occur in the chemical precipitation 

stage of the biological treatment technology option (see, e.g., Sections 7.1 and 7.2). Thus, 

plants employing and optimally operating all components of the biological treatment 

technology option (including adding organosulfide to achieve sulfide precipitation) should 
Page 69

achieve pollutant removals for arsenic and mercury (and other pollutants with similar removal 

mechanisms) that are equal to or even greater than the removals based on chemical 

precipitation technology.

For nitrate-nitrite as N at Allen, all daily effluent values are below both the daily and 

monthly limits. For nitrate-nitrite as N at Belews Creek, all daily effluent values are below the 

daily limit. However, there are two nitrate-nitrite as N daily effluent values in different months 

that are above the monthly limit. In each case only one sample was collected during the month. 

As explained above for the chemical precipitation technology option and demonstrated in the 

following paragraph, additional effluent monitoring (e.g., at weekly intervals) would likely result 

in a monthly average that would fall below the monthly limit.

For selenium at Allen, all daily effluent concentration values are below the daily limit. 

Only one daily effluent value (out of two collected in the same month) for Allen is above the 

monthly limit. However, after averaging these two observations, the average for the month is 

below the monthly limit. All other daily concentration values for Allen, spanning the period 

from September 2009 through May 2011, are below the average monthly limit. 

For selenium at Belews Creek, there are some daily effluent observations that are above 

both the daily and monthly limits. After thoroughly examining the data, EPA determined that 

the effluent concentration values at Belews Creek are relatively higher (i.e., with a higher longterm average) than the effluent concentration values at Allen. As discussed above, since the 

limits are developed using the data from both plants, it is reasonable to expect that the plant 

with relatively higher concentrations is more likely to have values above the daily and monthly 

limits. Furthermore, as EPA explained above, there are steps plants can take to achieve better 

treatment system performance to ensure compliance with the effluent limits. EPA indentified 

instances in which some daily effluent values at Belews Creek are above the average monthly 

limit. However, these are the only values that were collected within each of those months. As 

described above, additional effluent monitoring (e.g., at weekly intervals) would likely result in 

a monthly average that would fall below the monthly limit. EPA also identified four instances 

where some (or all) daily values from a month are above the monthly limit, but the daily values 

for other samples collected within the month are below the monthly limit. In these instances, 

the average for all samples collected within the month is above the monthly limit. Three of 

these four instances occur in the first three months of operation (August–October 2008) 

following the end of the initial commissioning period for the treatment system. The Belews 

Creek FGD wastewater treatment system was the first FGD bioreactor system operated by Duke 

Energy, and one of the first two systems to begin operating in the U.S. After evaluating all 

selenium data for the biological treatment technology option (nearly three years of data for 

Belews Creek and nearly two years for Allen, excluding the initial commissioning periods), EPA 

concluded that the selenium results for August-October 2008 reflect less than optimum 

performance of the treatment system due either to the inexperience of operators with this type 

of treatment system, or to continued variability associated with the initial commissioning of the 
Page 70

treatment system, or a combination thereof2. Based on the results of this comparison for the 

biological treatment technology option using the data from Allen and Belews Creek, EPA 

determined that the statistical distributional assumptions are appropriate for the effluent data 

and that the proposed limits are reasonable.

Chemical Precipitation Followed By Vapor-Compression Evaporator Treatment Technology 

Option for FGD Wastewater

For the vapor-compression evaporation treatment technology option for FGD 

wastewater, EPA developed limits for arsenic, mercury, selenium and TDS. The limits were 

calculated using data from Brindisi plant. All daily concentration values are below the daily and 

monthly limits. After thoroughly reviewing the data, EPA determined that the statistical 

distributional assumptions are appropriate for the effluent data and that the proposed limits

are reasonable.

Vapor-Compression Evaporator Treatment Technology Option for Gasification Wastewater

For the vapor-compression evaporation treatment technology option for gasification 

wastewater, EPA is proposing limits for arsenic, mercury, selenium and TDS. The limits were 

calculated using data from both the Polk and Wabash River plants, except for the arsenic and 

mercury limits, which were based only on data from Polk (since data from Wabash River failed 

the LTA test).

For arsenic and mercury, daily concentration values are below both the daily and 

monthly limits. For total dissolved solids, there is one (out of four collected in the same month) 

daily effluent concentration value at Polk above the monthly limit. However, after averaging 

these four observations, the average for the month is below the monthly limit.

For selenium at Polk, there is one daily effluent concentration value above the daily 

limit. Also, there are two (out of four collected in the same month) daily effluent values above 

the monthly average limit. After averaging these four observations, the average for the month 

is above the monthly limit. After thoroughly examining the data, EPA determined that the 

effluent concentration values for selenium at Polk are relatively higher (i.e., with a higher longterm average) than the effluent concentration values at Wabash River. As discussed above, 

since the limits are developed using the data from both plants, it is reasonable to expect that 

the plant with relatively higher concentrations is more likely to have values above the daily and 

 2 Note that although the Belews Creek selenium data (and other pollutant as well) from August-October 2008 may 

be influenced by the initial commissioning period for the treatment system, EPA used these data when calculating 

the proposed effluent limitations for the biological treatment technology option for FGD wastewater. EPA has used 

the August-October 2008 data because although EPA believes that, as a general rule, the initial commissioning 

period duration will be on the order of 3-4 months, and certainly no more than 6 months except in unique 

circumstances; EPA has not confirmed that the initial commissioning for Belews Creek was of such exceptional

duration. Without the information to confirm the commissioning period was still in progress, EPA concluded that 

the sampling data should be used when calculating effluent limits.
Page 71

monthly limits. Additionally, as discussed above in section 13.8.1, the data for the Polk 

treatment system indicates that the evaporator (or at a minimum the forced circulation 

evaporation stage) was operating abnormally and allowing carryover of pollutants to the 

condensate effluent stream. Based upon its review of the data, EPA concluded if the plant 

designs and operates its treatment system to achieve the option long-term average for the 

model technology, then the plant will be able to comply with the proposed limit. Further, EPA 

notes that Polk reuses all treatment gasification wastewater (i.e., condensate) in the 

gasification process and does not discharge any gasification wastewater. As such, the plant’s 

treatment objective is to ensure the wastewater is of sufficient quality for reuse in the process 

rather than to comply with a NPDES permit limit. Thus, EPA concluded that the statistical 

distributional assumption is appropriate for the effluent data and that the proposed limits are 

reasonable.

11.2. Comparison of the Effluent Limits to Influent Data

In addition to comparing the proposed limits to the data used to develop the limits, EPA 

also compared the value of the proposed daily limits to the observed influent concentration 

values. This comparison helps evaluate whether the proposed limits are set at a level that 

ensures that treatment of the wastewater would be necessary to meet the limits and that the 

influent concentrations were generally well-controlled by the treatment system. In doing so, 

EPA confirms that treatment to remove the regulated pollutants will take place. See Appendix 4 

for a detailed listing of the summary statistics for the influent data for each pollutant in each 

treatment technology option. 

For all treatment technology options for both FGD and gasification wastewater, the 

minimum, average, and maximum influent concentration values were much higher than the 

long-term average and proposed limits. Thus, EPA determined that facilities would need to 

treat the wastewater to ensure compliance with the proposed limits and that the proposed rule 

would result in removing the regulated pollutants and other pollutants of concern. 

Furthermore, in evaluating influent concentrations, EPA found that influent concentrations 

were generally well-controlled by the treatment plant for all plants with the model technology. 

In general, the treatment systems adequately treated even the extreme influent values, and the 

high effluent values did not appear to be the result of high influent discharges.
Page 72

APPENDIX 1: List of All Observations that Were Corrected and Excluded Before 

Calculating the Limits

This appendix contains a listing of all the corrections made to the data at Belews Creek 

and a listing of all observations that were excluded as described in Sections 3.1 and 3.2 of the 

document. It should be noted that the excluded data presented in this appendix are similar to

those presented in DCN SE02002. However, the excluded data are presented in this appendix 

by reasons for exclusion rather than by plant within each technology option as presented in the 

DCN SE02002 mentioned above. Further, even though EPA is not using the arsenic and mercury 

data from Allen and Belews Creek to calculate the limits for biological treatment system (for the 

reason described above and in Section 7), EPA did perform data corrections and exclusions for 

the arsenic and mercury data at these two plants.

There are four sections in this appendix. Section 1 provides a summary of all the 

corrections made to the plant self-monitoring data at Belews Creek due to data entry errors 

made by Duke Energy in the original data submittal to EPA. Section 2 contains a summary of 

data that warranted exclusion because the samples were analyzed using an insufficientlysensitive analytical method (i.e., use of EPA Method 245.1 instead of Method 1631E for 

mercury). Section 3 contains a summary of all data that were excluded because the samples 

were collected during the initial commissioning period for the treatment system. Section 4 

contains a summary of data that were excluded because of: (i) analytical results that were 

identified as questionable due to quality control issues, (ii) abnormal conditions or treatment 

upsets, and (iii) analytical anomalies.
Page 73

1. Corrections Made to Plant Self-Monitoring Data from Belews Creek

As described in Section 3.1, after thoroughly reviewing the plant self-monitoring data 

provided by Duke Energy, EPA found some inconsistencies in the data from Belews Creek. EPA 

detailed the inconsistencies found in the data and requested Duke Energy to address the 

potential errors. Duke Energy confirmed that the inconsistencies were due to data entry errors. 

The following tables provide the corrections that EPA made to the plant self-monitoring data 

for arsenic, mercury, and selenium, based on the information from Duke Energy. 

The table below lists the corrections made to the detection indicator for data at Belews 

Creek prior to calculating proposed effluent limits. The data are arranged by sampling location, 

pollutant, and sampling date.

Table 1.1. Summary of the corrected detection indicators for the Belews Creek self-monitoring

data, arranged by sampling location, pollutant, and sampling date.

Sampling Location Pollutant Date Original Indicator 1 Corrected Indicator 1

Bio 1 In

(Bioreactor Influent) Mercury 2/6/2008 D ND

2/9/2008 D ND

Bio 2 Eff

(Bioreactor Effluent)

Arsenic

2/7/2008 ND D

2/8/2008 ND D

2/10/2008 ND D

2/12/2008 ND D

2/13/2008 ND D

2/14/2008 ND D

2/15/2008 ND D

2/16/2008 ND D

2/17/2008 ND D

2/21/2008 ND D

Mercury

2/6/2008 D ND

9/29/2008 ND D

8/11/2010 ND D

9/8/2010 ND D

10/7/2010 ND D

Selenium 3/3/2008 ND D 1

: D = detected and ND = non-detected

The table below lists the corrections made to concentration values for data from Belews 

Creek prior to performing the statistical analyses, based on information provided by Duke 

Energy. 
Page 74

Table 1.2. Summary of the data corrections for the Belews Creek self-monitoring data, arranged 

by sampling location, pollutant, and sampling date.

Sampling Location Pollutant

(unit) Date Original Concentration 

Value (Indicator)1

Corrected Concentration 

Value (Indicator) 1

Bio 1 In

(Bioreactor Influent) Mercury (ng/L)

6/9/2010 59.3 (D) 59,300 (D)

7/14/2010 49.9 (D) 49,900 (D)

8/11/2010 47.7 (D) 47,700 (D)

Bio 2 Eff

(Bioreactor Effluent) Mercury (ng/L) 5/12/2010 1000 (ND) 136 (D)

5/26/2010 136 (D) -

2

1

: D = detected; ND = non-detected 2

: No data available for this date.

2. List of Data Excluded Due to Samples Analyzed Using an Insufficiently-Sensitive Analytical

Method

As described in Section 3.2.1, in some cases, Duke Energy analyzed the samples for 

mercury using EPA Method 1631E, while other samples were analyzed for mercury using EPA 

Method 245.1. The quantitation level for Method 245.1 is not low enough to detect the 

concentration of mercury present in the bioreactor influent and effluent samples, and

therefore, all mercury results that were analyzed using Method 245.1 for bioreactor influent 

and effluent samples were excluded. The table below provides a list of all the excluded data.

It is important to note that there were more data analyzed by Method 245.1 that are 

not listed in the table below since those data points were already excluded because they were

identified as being collected during either the initial commissioning period or a period of 

treatment upset (see Sections 3 and 4 below), which are presented separately.
Page 75

Table 1.3. Summary of the mercury data excluded from plant self monitoring data due to using

an insufficiently-sensitive analytical method.

Plant Name Data Source Date Sampling Location Included 

in Limits

Indicator 1

Concentratio

n (ng/L)

Allen Plant Self-Monitoring 6/29/2010 Bio Treatment Effluent No ND 1,000

Allen Plant Self-Monitoring 8/23/2010 Bio Treatment Effluent No ND 1,000

Allen Plant Self-Monitoring 10/5/2010 Bio Treatment Effluent No ND 1,000

Allen Plant Self-Monitoring 10/6/2010 Bio Treatment Effluent No ND 1,000

Allen Plant Self-Monitoring 10/7/2010 Bio Treatment Effluent No ND 1,000

Allen Plant Self-Monitoring 10/9/2010 Bio Treatment Effluent No ND 1,000

Allen Plant Self-Monitoring 10/10/2010 Bio Treatment Effluent No ND 1,000

Allen Plant Self-Monitoring 10/12/2010 Bio Treatment Effluent No ND 1,000

Allen Plant Self-Monitoring 10/13/2010 Bio Treatment Effluent No ND 1,000

Allen Plant Self-Monitoring 12/1/2010 Bio Treatment Effluent No ND 1,000

Allen Plant Self-Monitoring 12/4/2010 Bio Treatment Effluent No ND 1,000

Allen Plant Self-Monitoring 12/7/2010 Bio Treatment Effluent No ND 1,000

Allen Plant Self-Monitoring 1/12/2011 Bio Treatment Effluent No ND 1,000

Allen Plant Self-Monitoring 1/24/2011 Bio Treatment Effluent No ND 1,000

Allen Plant Self-Monitoring 4/27/2011 Bio Treatment Effluent No ND 1,000

Belews Creek Plant Self-Monitoring 1/27/2010 Bio Treatment Effluent No ND 1,000

Belews Creek Plant Self-Monitoring 2/24/2010 Bio Treatment Effluent No ND 1,000

Belews Creek Plant Self-Monitoring 3/24/2010 Bio Treatment Effluent No ND 1,000

Belews Creek Plant Self-Monitoring 4/7/2010 Bio Treatment Effluent No ND 1,000

Belews Creek Plant Self-Monitoring 6/23/2010 Bio Treatment Effluent No ND 1,000

Belews Creek Plant Self-Monitoring 7/14/2010 Bio Treatment Effluent No ND 1,000

Belews Creek Plant Self-Monitoring 7/28/2010 Bio Treatment Effluent No ND 1,000

Belews Creek Plant Self-Monitoring 8/25/2010 Bio Treatment Effluent No ND 1,000

Belews Creek Plant Self-Monitoring 9/22/2010 Bio Treatment Effluent No ND 1,000

Belews Creek Plant Self-Monitoring 10/27/2010 Bio Treatment Effluent No ND 1,000

Belews Creek Plant Self-Monitoring 11/4/2010 Bio Treatment Effluent No ND 1,000

Belews Creek Plant Self-Monitoring 11/23/2010 Bio Treatment Effluent No ND 1,000

Belews Creek Plant Self-Monitoring 12/8/2010 Bio Treatment Effluent No ND 1,000

Belews Creek Plant Self-Monitoring 1/17/2011 Bio Treatment Effluent No ND 1,000

Belews Creek Plant Self-Monitoring 1/26/2011 Bio Treatment Effluent No ND 1,000

Belews Creek Plant Self-Monitoring 2/16/2011 Bio Treatment Effluent No ND 1,000

Belews Creek Plant Self-Monitoring 3/23/2011 Bio Treatment Effluent No ND 1,000

Belews Creek Plant Self-Monitoring 4/27/2011 Bio Treatment Effluent No ND 1,000

Belews Creek Plant Self-Monitoring 5/25/2011 Bio Treatment Effluent No ND 1,000 1

: D = detected; ND = non-detected
Page 76

3. List of Data Excluded Due to Samples Being Collected During the Initial Commissioning

Period for the Treatment System

As described in Section 3.2.2, EPA generally excludes all data collected during the initial 

commissioning period for the treatment system. Since the plant self-monitoring data for Allen 

and Belews Creek included data collected during initial commissioning period, EPA excluded all 

these data in calculating the limits. The commissioning period for the treatment system at each 

plant was determined as the initial six month period of operation, as follows:

• For plant self-monitoring data from Allen, all data from March 03, 2009 through August 

26, 2009 were excluded.

• For plant self-monitoring data from Belews Creek, all data from February 06, 2008 

through July 31, 2008 were excluded.

4. List of Data Excluded Due to Analytical Results that Identified as Questionable Due to the

Quality Control Issues, Abnormal Conditions or Treatment Upset, or Analytical Anomalies

As described in Section 3.2.3, EPA excluded analytical results that were identified as 

questionable due to quality control issues, abnormal conditions or treatment upset, or 

analytical anomalies. The table below provides a listing of all the data points that were excluded 

for these reasons.

Note that additional data from Belews Creek that were identified as questionable due to 

quality control issues are not listed here since those data were collected during the initial 

commissioning period and were already excluded for that reason (see Section 3 of this 

appendix).
Page 77

Table 1.4. Summary of the questionable mercury data excluded due to quality control issues for

the plant self-monitoring data at Allen and Belews Creek.

Plant Name Data Source Date Sampling Location Included 

in Limits Indicator1 Concentration (ng/L)

Allen Plant Self-Monitoring 12/29/2009 Bio Treatment Influent No D 710

Allen Plant Self-Monitoring 12/29/2009 Bio Treatment Effluent No D 11

Allen Plant Self-Monitoring 1/11/2010 Bio Treatment Influent No D 92

Allen Plant Self-Monitoring 1/11/2010 Bio Treatment Effluent No D 14.2

Belews Creek Plant Self-Monitoring 8/4/2008 Bio Treatment Influent No D 4.9

Belews Creek Plant Self-Monitoring 8/4/2008 Bio Treatment Effluent No D 2.4

Belews Creek Plant Self-Monitoring 8/11/2008 Bio Treatment Influent No D 4.8

Belews Creek Plant Self-Monitoring 8/11/2008 Bio Treatment Effluent No D 2.7

Belews Creek Plant Self-Monitoring 8/18/2008 Bio Treatment Influent No D 24

Belews Creek Plant Self-Monitoring 8/18/2008 Bio Treatment Effluent No D 5.3

Belews Creek Plant Self-Monitoring 8/25/2008 Bio Treatment Influent No D 27

Belews Creek Plant Self-Monitoring 8/25/2008 Bio Treatment Effluent No D 6.4

Belews Creek Plant Self-Monitoring 9/2/2008 Bio Treatment Influent No D 3.1

Belews Creek Plant Self-Monitoring 9/2/2008 Bio Treatment Effluent No D 2.1

Belews Creek Plant Self-Monitoring 9/8/2008 Bio Treatment Influent No D 2.7

Belews Creek Plant Self-Monitoring 9/8/2008 Bio Treatment Effluent No D 4.1

Belews Creek Plant Self-Monitoring 9/15/2008 Bio Treatment Influent No D 12

Belews Creek Plant Self-Monitoring 9/15/2008 Bio Treatment Effluent No ND 1

Belews Creek Plant Self-Monitoring 9/22/2008 Bio Treatment Influent No D 8.1

Belews Creek Plant Self-Monitoring 9/22/2008 Bio Treatment Effluent No ND 1

Belews Creek Plant Self-Monitoring 9/29/2008 Bio Treatment Influent No D 3.4

Belews Creek Plant Self-Monitoring 9/29/2008 Bio Treatment Effluent No D 3.7

Belews Creek Plant Self-Monitoring 12/3/2008 FGD Purge No D 16,000

Belews Creek Plant Self-Monitoring 12/3/2008 Bio Treatment Influent No D 19 2

Belews Creek Plant Self-Monitoring 12/3/2008 Bio Treatment Effluent No D 3.6

Belews Creek Plant Self-Monitoring 12/10/2008 FGD Purge No D 44,000

Belews Creek Plant Self-Monitoring 12/10/2008 Bio Treatment Influent No D 15 2

Belews Creek Plant Self-Monitoring 12/10/2008 Bio Treatment Effluent No D 2 2

Belews Creek Plant Self-Monitoring 12/17/2008 Bio Treatment Influent No D 7.6 2

Belews Creek Plant Self-Monitoring 12/17/2008 Bio Treatment Effluent No D 2.9 2

Belews Creek Plant Self-Monitoring 12/22/2008 Bio Treatment Influent No D 20 2

Belews Creek Plant Self-Monitoring 12/22/2008 Bio Treatment Effluent No D 1.4 2

Belews Creek Plant Self-Monitoring 12/29/2008 Bio Treatment Influent No D 12 2

Belews Creek Plant Self-Monitoring 12/29/2008 Bio Treatment Effluent No D 2.4 2

Belews Creek Plant Self-Monitoring 1/7/2009 Bio Treatment Influent No D 5 2

Belews Creek Plant Self-Monitoring 1/7/2009 Bio Treatment Effluent No D 2.8 2

Belews Creek Plant Self-Monitoring 1/14/2009 Bio Treatment Influent No D 15 2

Belews Creek Plant Self-Monitoring 1/14/2009 Bio Treatment Effluent No D 2.3 2

Belews Creek Plant Self-Monitoring 1/22/2009 Bio Treatment Influent No D 4.7 2

Belews Creek Plant Self-Monitoring 1/22/2009 Bio Treatment Effluent No D 3.9 2

Belews Creek Plant Self-Monitoring 1/28/2009 Bio Treatment Influent No D 12 2

Belews Creek Plant Self-Monitoring 1/28/2009 Bio Treatment Effluent No D 2.6 1

: D = detected; ND = Non-detected 2

: For these dates, sampling data were analyzed by two laboratories: BrooksRand and Prism. In general, EPA would average the data 

from two available sources into a single value to use in calculating of limits. However, since the data analyzed by the Prism laboratory 

(listed in the table) were identified by Duke Energy as questionable due to quality control issues, EPA has excluded these data and 

used only the sampling data from BrooksRand. Thus, for the given dates, EPA used the data analyzed by BrooksRand to develop the 
Page 78

limits. Note that EPA lacked sufficient laboratory quality control data for these results to make an independent assessment of whether 

these mercury results should have been retained and included in the statistical analyses.

The table below provides a list of all the excluded data due to abnormal conditions or 

system upset and analytical anomalies. Note that the table includes some data that could also 

be excluded due to an insufficiently-sensitive analytical method.

Table 1.5. Summary of data excluded due to abnormal conditions or treatment upset and

analytical anomalies.

Plant 

Name Data Source Date Sampling Location Pollutant

(unit)

Include

d in 

Limits

Exclusion 

Commen

t

Indi

cato

r

1

Concent

ration

Allen Plant Self-Monitoring 3/8/2010 FGD Purge Arsenic (ug/L) No

System 

upset 

due to 

pipe 

breakage. 

Exclude 

all data

D 553

Allen Plant Self-Monitoring 3/8/2010 Bio Treatment Influent Arsenic (ug/L) No ND 5

Allen Plant Self-Monitoring 3/8/2010 Bio Treatment Effluent Arsenic (ug/L) No D 7

Allen Plant Self-Monitoring 3/22/2010 FGD Purge Arsenic (ug/L) No D 452

Allen Plant Self-Monitoring 3/22/2010 Bio Treatment Influent Arsenic (ug/L) No ND 5

Allen Plant Self-Monitoring 3/22/2010 Bio Treatment Effluent Arsenic (ug/L) No D 22.5

Allen Plant Self-Monitoring 4/5/2010 FGD Purge Arsenic (ug/L) No D 309

Allen Plant Self-Monitoring 4/5/2010 Bio Treatment Influent Arsenic (ug/L) No ND 5

Allen Plant Self-Monitoring 4/5/2010 Bio Treatment Effluent Arsenic (ug/L) No D 9

Allen Plant Self-Monitoring 4/26/2010 FGD Purge Arsenic (ug/L) No D 206

Allen Plant Self-Monitoring 4/26/2010 Bio Treatment Influent Arsenic (ug/L) No ND 5

Allen Plant Self-Monitoring 4/26/2010 Bio Treatment Effluent Arsenic (ug/L) No D 6.3

Allen Plant Self-Monitoring 5/10/2010 FGD Purge Arsenic (ug/L) No D 615

Allen Plant Self-Monitoring 5/10/2010 Bio Treatment Influent Arsenic (ug/L) No ND 5

Allen Plant Self-Monitoring 5/10/2010 Bio Treatment Effluent Arsenic (ug/L) No D 63.1

Allen Plant Self-Monitoring 5/25/2010 FGD Purge Arsenic (ug/L) No D 535

Allen Plant Self-Monitoring 5/25/2010 Bio Treatment Influent Arsenic (ug/L) No ND 5

Allen Plant Self-Monitoring 5/25/2010 Bio Treatment Effluent Arsenic (ug/L) No D 63.9

Allen Plant Self-Monitoring 3/8/2010 FGD Purge Mercury (ng/L) No D 65200

Allen Plant Self-Monitoring 3/8/2010 Bio Treatment Influent Mercury (ng/L) No D 50.5

Allen Plant Self-Monitoring 3/8/2010 Bio Treatment Effluent Mercury (ng/L) No D 5.98

Allen Plant Self-Monitoring 3/22/2010 FGD Purge Mercury (ng/L) No D 51400

Allen Plant Self-Monitoring 4/5/2010 FGD Purge Mercury (ng/L) No D 59700

Allen Plant Self-Monitoring 4/5/2010 Bio Treatment Influent Mercury (ng/L) No D 812

Allen Plant Self-Monitoring 4/5/2010 Bio Treatment Effluent Mercury (ng/L) No D 22.4

Allen Plant Self-Monitoring 4/26/2010 FGD Purge Mercury (ng/L) No D 40300

Allen Plant Self-Monitoring 4/26/2010 Bio Treatment Effluent Mercury (ng/L) No ND 1000

Allen Plant Self-Monitoring 5/10/2010 FGD Purge Mercury (ng/L) No D 41100

Allen Plant Self-Monitoring 5/10/2010 Bio Treatment Influent Mercury (ng/L) No D 113

Allen Plant Self-Monitoring 5/10/2010 Bio Treatment Effluent Mercury (ng/L) No D 5.76

Allen Plant Self-Monitoring 5/25/2010 FGD Purge Mercury (ng/L) No D 65600

Allen Plant Self-Monitoring 5/25/2010 Bio Treatment Effluent Mercury (ng/L) No ND 1000

Allen Plant Self-Monitoring 3/8/2010 FGD Purge Selenium (ug/L) No D 1860

Allen Plant Self-Monitoring 3/8/2010 Bio Treatment Influent Selenium (ug/L) No D 100

Allen Plant Self-Monitoring 3/8/2010 Bio Treatment Effluent Selenium (ug/L) No D 4.7

Allen Plant Self-Monitoring 3/22/2010 FGD Purge Selenium (ug/L) No D 1800

Allen Plant Self-Monitoring 3/22/2010 Bio Treatment Influent Selenium (ug/L) No D 75.8

Allen Plant Self-Monitoring 3/22/2010 Bio Treatment Effluent Selenium (ug/L) No D 3.1
Page 79

Plant 

Name Data Source Date Sampling Location Pollutant

(unit)

Include

d in 

Limits

Exclusion 

Commen

t

Indi

cato

r

1

Concent

ration

Allen Plant Self-Monitoring 4/5/2010 FGD Purge Selenium (ug/L) No D 1450

Allen Plant Self-Monitoring 4/5/2010 Bio Treatment Influent Selenium (ug/L) No D 75.3

Allen Plant Self-Monitoring 4/5/2010 Bio Treatment Effluent Selenium (ug/L) No D 2.7

Allen Plant Self-Monitoring 4/26/2010 FGD Purge Selenium (ug/L) No D 1690

Allen Plant Self-Monitoring 4/26/2010 Bio Treatment Influent Selenium (ug/L) No D 353

Allen Plant Self-Monitoring 4/26/2010 Bio Treatment Effluent Selenium (ug/L) No D 3.2

Allen Plant Self-Monitoring 5/10/2010 FGD Purge Selenium (ug/L) No D 1400

Allen Plant Self-Monitoring 5/10/2010 Bio Treatment Influent Selenium (ug/L) No D 86.9

Allen Plant Self-Monitoring 5/10/2010 Bio Treatment Effluent Selenium (ug/L) No D 2.6

Allen Plant Self-Monitoring 5/25/2010 FGD Purge Selenium (ug/L) No D 5350

Allen Plant Self-Monitoring 5/25/2010 Bio Treatment Influent Selenium (ug/L) No D 96.2

Allen Plant Self-Monitoring 5/25/2010 Bio Treatment Effluent Selenium (ug/L) No D 3.5

Hatfield’

s Ferry CWA 308 Sampling 10/5/2010 Chem Prep. Effluent Mercury (ng/L) No

Abnormal 

condition 

or 

treatmen

t upset

D 978

Belews 

Creek EPA Sampling 6/9/2010 Bio Treatment Effluent 

Dup Mercury (ng/L) No Analytical 

anomalie

s

D 6440

Belews 

Creek Plant Self-Monitoring 7/14/2010 Bio Treatment Effluent Selenium (ug/L) No D 299

1

: D = detected; ND = non-detected.
Page 80

APPENDIX 2: Plots of Plant Self-monitoring Data with Smoothed Curves to Aid in

Determining Initial Commissioning Period of Treatment System

As explained in Section 3.2.2, EPA excluded some data collected during the initial 

commissioning period of the treatment system from the plant self-monitoring data from Allen 

and Belews Creek. The initial commissioning period was determined from an engineering 

perspective based on extensive experience evaluating treatment systems at power plants and 

other industry sectors and knowledge of the physical, chemical, and biological treatment 

processes employed and by looking at the longitudinal plots of all the data. In addition to the 

longitudinal plots of the data, smooth curves obtained by LOWESS (Cleveland, 1979 and 1981)

superimposed on the individual data plots were also examined to help determine when the 

treatment system appeared to stabilize. In examining the longitudinal plots, EPA looked at two 

types of plots: plots of all the available plant self-monitoring data and plots of data after the 

exclusions for plant self-monitoring data described in Sections 3.2.1 and 3.2.3. The conclusions

from both of these approaches were consistent. The initial six months of operation was 

determined to represent a reasonable estimate of the commissioning period for the treatment 

systems. 

This appendix contains the longitudinal plots for arsenic, mercury, and selenium that 

engineers used as aids in determining the commissioning period for Allen and Belews Creek. 

Four plots are given for each pollutant in this appendix. The first plot shows all the available

data points for the plant self-monitoring (before all the exclusions for plant self-monitoring data 

described in Sections 3.2.1 and 3.2.3) for Allen and Belews Creek. The second plot is based on 

all available data (as in the first plot) with smooth curves (obtained by LOWESS) superimposed 

on the individual data. The third plot is a plot of the data after all necessary exclusions for plant 

self-monitoring (as described in Sections 3.2.1 and 3.2.3). The fourth plot is the plot of the data 

after all necessary exclusions (as in the third plot) with smooth curves (obtained by LOWESS)

superimposed on the individual data points. 

For each plot, the plot on the left shows concentrations for Allen from March 3, 2009 to 

May 23, 2011. The plot on the right shows concentrations for Belews Creek from February 6, 

2008 to May 25, 2011. Within each plot, the plots on the upper row shows the concentrations 

collected at all three sampling locations, while the plots on the bottom row show the 

concentrations only at the bioreactor influent and bioreactor effluent. The red line on the plot 

represents the end of the commissioning period.
Page 81

Figure 2.1. Plot of all self-monitoring data for arsenic (ug/L) for Allen and Belews Creek.

Figure 2.2. Smoothed plot (using LOWESS) of all self-monitoring data for arsenic (ug/L) for Allen 

and Belews Creek.

0 1000 2000

Allen

Date (Vertical line at 8/26/09, end of commissio 

 Detected: o Non-Detected: *

Arsenic (ug/L)

Mar 09 Jun 09 Sep 09 Dec 09 Mar 10 Jun 10 Oct 10 Jan 11 Apr 11

********************************************************** * * ****** * ** * * * * * * ** ** * ******* * ******** ** * ***** * * ** *

FGD Purge

Bioreactor Inf.

Bioreactor Eff.

0 50 150 250

Allen

Date (Vertical line at 8/26/09, end of commissio 

 Detected: o Non-Detected: *

Arsenic (ug/L)

Mar 09 Jun 09 Sep 09 Dec 09 Mar 10 Jun 10 Oct 10 Jan 11 Apr 11

*********************************************************** *** * * ***** * * ****** * ** * * * * * * ** ** * *********** * *************   **  **********   ** ** **

Bioreactor Inf.

Bioreactor Eff.

0 1000 2000

Belews Creek

Date (Vertical line at 7/31/08, end of commissio 

 Detected: o Non-Detected: *

Arsenic (ug/L)

Feb 08 Jun 08 Nov 08 Apr 09 Sep 09 Feb 10 Jul 10 Nov 10 Apr 11

****************** ******** ********** ****** * * * * * * * ************ ** ******** * ************* ** *************************** * * * * * * * * * ** ********   ** *** ******   ** *

FGD Purge

Bioreactor Inf.

Bioreactor Eff.

0 50 150 250

Belews Creek

Date (Vertical line at 7/31/08, end of commissio 

 Detected: o Non-Detected: *

Arsenic (ug/L)

Feb 08 Jun 08 Nov 08 Apr 09 Sep 09 Feb 10 Jul 10 Nov 10 Apr 11

****************** ******** ********** ****** * * * * * * * ************ ** ********

*

************* ** *************************** * * * * * ***** **** * * * * ** ********   ** *** *

***** ****

Bioreactor Inf.

Bioreator Eff.

0 1000 2000

Allen

Date

Arsenic (ug/L)

Mar 09 Jun 09 Sep 09 Dec 09 Mar 10 Jun 10 Oct 10 Jan 11 Apr 11

FGD Purge

Bioreactor Inf.

Bioreactor Eff.

0 50 150 250

Allen

Date

Arsenic (ug/L)

Mar 09 Jun 09 Sep 09 Dec 09 Mar 10 Jun 10 Oct 10 Jan 11 Apr 11

Bioreactor Inf.

Bioreactor Eff.

0 1000 2000

Belews Creek

Date

Arsenic (ug/L)

Feb 08 Jun 08 Nov 08 Apr 09 Sep 09 Feb 10 Jul 10 Nov 10 Apr 11

FGD Purge

Bioreactor Inf.

Bioreactor Eff.

0 50 150 250

Belews Creek

Date

Arsenic (ug/L)

Feb 08 Jun 08 Nov 08 Apr 09 Sep 09 Feb 10 Jul 10 Nov 10 Apr 11

Bioreactor Inf.

Bioreactor Eff.
Page 82

Figure 2.3. Plot of self-monitoring data for arsenic (ug/L) for Allen and Belews Creek after

exclusions described in Sections 3.2.1 and 3.2.3.

Figure 2.4. Smoothed plot (using LOWESS) of self-monitoring data for arsenic (ug/L) for Allen

and Belews Creek after exclusions described in Sections 3.2.1 and 3.2.3.

0 1000 2000

Allen

Date (Vertical line at 8/26/09, end of commissio 

 Detected: o Non-Detected: *

Arsenic (ug/L)

Mar 09 Jun 09 Sep 09 Dec 09 Jun 10 Sep 10 Jan 11 Apr 11

********************************************************** * * ****** * * * ** ** * ******* * ******** ** * ***** * * ** *

FGD Purge

Bioreactor Inf.

Bioreactor Eff.

0 50 150 250

Allen

Date (Vertical line at 8/26/09, end of commissio 

 Detected: o Non-Detected: *

Arsenic (ug/L)

Mar 09 Jun 09 Sep 09 Dec 09 Jun 10 Sep 10 Jan 11 Apr 11

*********************************************************** *** * * ***** * * ****** * * * ** ** * *********** * *************   **  **********   ** ** **

Bioreactor Inf.

Bioreactor Eff.

0 1000 2000

Belews Creek

Date (Vertical line at 7/31/08, end of commissio 

 Detected: o Non-Detected: *

Arsenic (ug/L)

Feb 08 Jun 08 Nov 08 Apr 09 Sep 09 Feb 10 Jul 10 Nov 10 Apr 11

****************** ******** ********** ****** * * * * * * * ************ ** ******** * ************* ** *************************** * * * * * * * * * ** ********   ** *** ******   ** *

FGD Purge

Bioreactor Inf.

Bioreactor Eff.

0 50 150 250

Belews Creek

Date (Vertical line at 7/31/08, end of commissio 

 Detected: o Non-Detected: *

Arsenic (ug/L)

Feb 08 Jun 08 Nov 08 Apr 09 Sep 09 Feb 10 Jul 10 Nov 10 Apr 11

****************** ******** ********** ****** * * * * * * * ************ ** ********

*

************* ** *************************** * * * * * ***** **** * * * * ** ********   ** *** *

***** ****

Bioreactor Inf.

Bioreator Eff.

0 1000 2000

Allen

Date

Arsenic (ug/L)

Mar 09 Jun 09 Sep 09 Dec 09 Jun 10 Sep 10 Jan 11 Apr 11

FGD Purge

Bioreactor Inf.

Bioreactor Eff.

0 50 150 250

Allen

Date

Arsenic (ug/L)

Mar 09 Jun 09 Sep 09 Dec 09 Jun 10 Sep 10 Jan 11 Apr 11

Bioreactor Inf.

Bioreactor Eff.

0 1000 2000

Belews Creek

Date

Arsenic (ug/L)

Feb 08 Jun 08 Nov 08 Apr 09 Sep 09 Feb 10 Jul 10 Nov 10 Apr 11

FGD Purge

Bioreactor Inf.

Bioreactor Eff.

0 50 150 250

Belews Creek

Date

Arsenic (ug/L)

Feb 08 Jun 08 Nov 08 Apr 09 Sep 09 Feb 10 Jul 10 Nov 10 Apr 11

Bioreactor Inf.

Bioreactor Eff.
Page 83

Figure 2.5. Plot of all self-monitoring data for mercury (ng/L) for Allen and Belews Creek.

Figure 2.6. Smoothed plot (using LOWESS) of all self-monitoring data for mercury (ng/L) for

Allen and Belews Creek. 0e+00 3e+05 6e+05

Allen

Date (Vertical line at 8/26/09, end of commissio 

 Detected: o Non-Detected: *

Mercury (ng/L)

Mar 09 Jun 09 Sep 09 Dec 09 Mar 10 Jun 10 Oct 10 Jan 11 Apr 11

******************************************************* * * * * ***** *** ** *

FGD Purge

Bioreactor Inf.

Bioreactor Eff.

0 20000 50000

Allen

Date (Vertical line at 8/26/09, end of commissio 

 Detected: o Non-Detected: *

Mercury (ng/L)

Mar 09 Jun 09 Sep 09 Dec 09 Apr 10 Jul 10 Oct 10 Jan 11 Apr 11

**************************************************** * * * * ***** *** ** *

Bioreactor Inf.

Bioreactor Eff.

0e+00 3e+05 6e+05

Belews Creek

Date (Vertical line at 7/31/08, end of commissio 

 Detected: o Non-Detected: *

Mercury (ng/L)

Feb 08 Jun 08 Nov 08 Apr 09 Sep 09 Feb 10 Jul 10 Nov 10 Apr 11

********************************************* ** * * ** * ** * * **** *** * * *

FGD Purge

Bioreactor Inf.

Bioreactor Eff.

0 20000 50000

Belews Creek

Date (Vertical line at 7/31/08, end of commissio 

 Detected: o Non-Detected: *

Mercury (ng/L)

Feb 08 Jun 08 Dec 08 Jun 09 Nov 09 Mar 10 Aug 10 Jan 11

*********************************************** ** * * ** * ** * * **** *** * * *

Bioreactor Inf.

Bioreator Eff.

0e+00 3e+05 6e+05

Allen

Date

Mercury (ng/L)

Mar 09 Jun 09 Sep 09 Dec 09 Mar 10 Jun 10 Oct 10 Jan 11 Apr 11

FGD Purge

Bioreactor Inf.

Bioreactor Eff.

0 20000 50000

Allen

Date

Mercury (ng/L)

Mar 09 Jun 09 Sep 09 Dec 09 Apr 10 Jul 10 Oct 10 Jan 11 Apr 11

Bioreactor Inf.

Bioreactor Eff.

0e+00 3e+05 6e+05

Belews Creek

Date

Mercury (ng/L)

Feb 08 Jun 08 Nov 08 Apr 09 Sep 09 Feb 10 Jul 10 Nov 10 Apr 11

FGD Purge

Bioreactor Inf.

Bioreactor Eff.

0 20000 50000

Belews Creek

Date

Mercury (ng/L)

Feb 08 Jun 08 Dec 08 Jun 09 Nov 09 Mar 10 Aug 10 Jan 11

Bioreactor Inf.

Bioreactor Eff.
Page 84

Figure 2.7. Plot of self-monitoring data for mercury (ng/L) for Allen and Belews Creek after

exclusions described in Sections 3.2.1 and 3.2.3.

Figure 2.8. Smoothed plot (using LOWESS) of all self-monitoring data for mercury (ng/L) for

Allen and Belews Creek after exclusions described in Sections 3.2.1 and 3.2.3. 0e+00 3e+05 6e+05

Allen

Date (Vertical line at 8/26/09, end of commissio 

 Detected: o Non-Detected: *

Mercury (ng/L)

Mar 09 Jun 09 Sep 09 Dec 09 Jun 10 Sep 10 Jan 11 Apr 11

******************************************************* * * ***** *** ** *

FGD Purge

Bioreactor Inf.

Bioreactor Eff.

0 20000 50000

Allen

Date (Vertical line at 8/26/09, end of commissio 

 Detected: o Non-Detected: *

Mercury (ng/L)

Mar 09 Jun 09 Sep 09 Dec 09 Jun 10 Sep 10 Jan 11 Apr 11

**************************************************** * * ***** *** ** *

Bioreactor Inf.

Bioreactor Eff.

0e+00 3e+05 6e+05

Belews Creek

Date (Vertical line at 7/31/08, end of commissio 

 Detected: o Non-Detected: *

Mercury (ng/L)

Feb 08 Jun 08 Nov 08 Apr 09 Sep 09 Feb 10 Jul 10 Nov 10 Apr 11

********************************************* * * ** * ** * * **** *** * * *

FGD Purge

Bioreactor Inf.

Bioreactor Eff.

0 20000 50000

Belews Creek

Date (Vertical line at 7/31/08, end of commissio 

 Detected: o Non-Detected: *

Mercury (ng/L)

Feb 08 Jun 08 Dec 08 Jun 09 Nov 09 Mar 10 Aug 10 Jan 11

*********************************************** * * ** * ** * * **** *** * * *

Bioreactor Inf.

Bioreator Eff.

0e+00 3e+05 6e+05

Allen

Date

Mercury (ng/L)

Mar 09 Jun 09 Sep 09 Dec 09 Jun 10 Sep 10 Jan 11 Apr 11

FGD Purge

Bioreactor Inf.

Bioreactor Eff.

0 20000 50000

Allen

Date

Mercury (ng/L)

Mar 09 Jun 09 Sep 09 Dec 09 Jun 10 Sep 10 Jan 11 Apr 11

Bioreactor Inf.

Bioreactor Eff.

0e+00 3e+05 6e+05

Belews Creek

Date

Mercury (ng/L)

Feb 08 Jun 08 Nov 08 Apr 09 Sep 09 Feb 10 Jul 10 Nov 10 Apr 11

FGD Purge

Bioreactor Inf.

Bioreactor Eff.

0 20000 50000

Belews Creek

Date

Mercury (ng/L)

Feb 08 Jun 08 Dec 08 Jun 09 Nov 09 Mar 10 Aug 10 Jan 11

Bioreactor Inf.

Bioreactor Eff.
Page 85

Figure 2.9. Plot of all self-monitoring data for selenium (ug/L) for Allen and Belews Creek.

Figure 2.10. Smoothed plot (using LOWESS) of all self-monitoring data for selenium (ug/L) for 

Allen and Belews Creek.

0 10000 20000

Allen

Date (Vertical line at 8/26/09, end of commissio 

 Detected: o Non-Detected: *

Selenium (ug/L)

Mar 09 Jun 09 Sep 09 Dec 09 Mar 10 Jun 10 Oct 10 Jan 11 Apr 11

***************************************************** *** * * * ****** ****** ** * ***** * **

FGD Purge

Bioreactor Inf.

Bioreactor Eff.

0 1000 2000 3000

Allen

Date (Vertical line at 8/26/09, end of commissio 

 Detected: o Non-Detected: *

Selenium (ug/L)

Mar 09 Jun 09 Sep 09 Dec 09 Mar 10 Jun 10 Oct 10 Jan 11 Apr 11

***************************************************** *** * * * ****** ****** ** * ***** * **

Bioreactor Inf.

Bioreactor Eff.

0 10000 20000

Belews Creek

Date (Vertical line at 7/31/08, end of commissio 

 Detected: o Non-Detected: *

Selenium (ug/L)

Feb 08 Jun 08 Nov 08 Apr 09 Sep 09 Feb 10 Jul 10 Nov 10 Apr 11

************************************* *** ******************** * * * * * * * * ** ** *** ***

FGD Purge

Bioreactor Inf.

Bioreactor Eff.

0 1000 2000 3000

Belews Creek

Date (Vertical line at 7/31/08, end of commissio 

 Detected: o Non-Detected: *

Selenium (ug/L)

Feb 08 Jun 08 Nov 08 Apr 09 Sep 09 Feb 10 Jul 10 Nov 10 Apr 11

************************************* *** ******************** * * * * * * * * ** ** *** ***

Bioreactor Inf.

Bioreator Eff.

0 10000 20000

Allen

Date

Selenium (ug/L)

Mar 09 Jun 09 Sep 09 Dec 09 Mar 10 Jun 10 Oct 10 Jan 11 Apr 11

FGD Purge

Bioreactor Inf.

Bioreactor Eff.

0 1000 2000 3000

Allen

Date

Selenium (ug/L)

Mar 09 Jun 09 Sep 09 Dec 09 Mar 10 Jun 10 Oct 10 Jan 11 Apr 11

Bioreactor Inf.

Bioreactor Eff.

0 10000 20000

Belews Creek

Date

Selenium (ug/L)

Feb 08 Jun 08 Nov 08 Apr 09 Sep 09 Feb 10 Jul 10 Nov 10 Apr 11

FGD Purge

Bioreactor Inf.

Bioreactor Eff.

0 1000 2000 3000

Belews Creek

Date

Selenium (ug/L)

Feb 08 Jun 08 Nov 08 Apr 09 Sep 09 Feb 10 Jul 10 Nov 10 Apr 11

Bioreactor Inf.

Bioreactor Eff.
Page 86

Figure 2.11. Plot of self-monitoring data for selenium (ug/L) for Allen and Belews Creek after

exclusions described in Sections 3.2.1 and 3.2.3.

Figure 2.12. Smoothed plot (using LOWESS) of self-monitoring data for selenium (ug/L) for Allen

and Belews Creek after exclusions described in Sections 3.2.1 and 3.2.3.

References

Cleveland, W. S. (1979) Robust locally weighted regression and smoothing scatterplots. J. Amer. Statist. 

Assoc. 74, 829–836.

Cleveland, W. S. (1981) LOWESS: A program for smoothing scatterplots by robust locally weighted 

regression. The American Statistician, 35, 54.

0 10000 20000

Allen

Date (Vertical line at 8/26/09, end of commissio 

 Detected: o Non-Detected: *

Selenium (ug/L)

Mar 09 Jun 09 Sep 09 Dec 09 Jun 10 Sep 10 Jan 11 Apr 11

***************************************************** *** * * * ****** ****** ** * ***** * **

FGD Purge

Bioreactor Inf.

Bioreactor Eff.

0 1000 2000 3000

Allen

Date (Vertical line at 8/26/09, end of commissio 

 Detected: o Non-Detected: *

Selenium (ug/L)

Mar 09 Jun 09 Sep 09 Dec 09 Jun 10 Sep 10 Jan 11 Apr 11

***************************************************** *** * * * ****** ****** ** * ***** * **

Bioreactor Inf.

Bioreactor Eff.

0 10000 20000

Belews Creek

Date (Vertical line at 7/31/08, end of commissio 

 Detected: o Non-Detected: *

Selenium (ug/L)

Feb 08 Jun 08 Nov 08 Apr 09 Sep 09 Feb 10 Jul 10 Nov 10 Apr 11

************************************* *** ******************** * * * * * * * * ** ** *** ***

FGD Purge

Bioreactor Inf.

Bioreactor Eff.

0 1000 2000 3000

Belews Creek

Date (Vertical line at 7/31/08, end of commissio 

 Detected: o Non-Detected: *

Selenium (ug/L)

Feb 08 Jun 08 Nov 08 Apr 09 Sep 09 Feb 10 Jul 10 Nov 10 Apr 11

************************************* *** ******************** * * * * * * * * ** ** *** ***

Bioreactor Inf.

Bioreator Eff.

0 10000 20000

Allen

Date

Selenium (ug/L)

Mar 09 Jun 09 Sep 09 Dec 09 Jun 10 Sep 10 Jan 11 Apr 11

FGD Purge

Bioreactor Inf.

Bioreactor Eff.

0 1000 2000 3000

Allen

Date

Selenium (ug/L)

Mar 09 Jun 09 Sep 09 Dec 09 Jun 10 Sep 10 Jan 11 Apr 11

Bioreactor Inf.

Bioreactor Eff.

0 10000 20000

Belews Creek

Date

Selenium (ug/L)

Feb 08 Jun 08 Nov 08 Apr 09 Sep 09 Feb 10 Jul 10 Nov 10 Apr 11

FGD Purge

Bioreactor Inf.

Bioreactor Eff.

0 1000 2000 3000

Belews Creek

Date

Selenium (ug/L)

Feb 08 Jun 08 Nov 08 Apr 09 Sep 09 Feb 10 Jul 10 Nov 10 Apr 11

Bioreactor Inf.

Bioreactor Eff.
Page 87

APPENDIX 3: Data Editing Criteria Results

This appendix contains a summary of the results of the data editing criteria on a 

pollutant-by-pollutant basis to select a dataset at each plant to be used for calculating the 

effluent limits for each technology option (described in Section 4 of the document). These 

criteria are referred to as the long-term average test (or LTA test). EPA established the LTA test 

to ensure that the pollutants for which limits are being proposed were present in the influent at 

sufficient concentrations to evaluate treatment effectiveness at the plant. The data editing 

procedure is specified as follows: first, the influent had to pass a basic requirement that 50% of 

the influent measurements for the pollutant have to be detected at any concentration. If the 

dataset for a pollutant at a plant passed the basic requirement, it then had to pass one of the 

following two criteria to pass the LTA test:

Criterion 1. At least 50% of the influent measurements in a dataset at a plant are

detected at levels equal to or greater than 10 times the baseline value (shown in 

Section 3.3).

Criterion 2. At least 50% of the influent measurements in a dataset at a plant are 

detected at any concentration and the influent arithmetic average equal to or greater 

than 10 times the baseline value (shown in Section 3.3).

If the dataset at a plant failed the basic requirement, then EPA automatically set both 

Criteria 1 and 2 to “fail”. If the dataset for a plant failed the basic requirement, or passed the

basic requirement but failed both criteria, EPA would exclude the plant’s effluent data for that 

pollutant when calculating the limits. Through the application of the LTA test, EPA ensures that 

the limits result from treatment of the wastewater and not simply the absence or substantial 

dilution of that pollutant in the waste stream.
Page 88

The table below shows how each pollutant at each plant fared with respect to the basic 

requirement and the two criteria of the LTA test. The bullets below provide a brief description 

for the important columns in the table:

• Column “N” presents the total number of influent observations (detected and nondetected combined)

• Column “Percent Detected for Influent (%)” shows the percent of influent observations 

that are detected.

• Column “Basic Requirement” contains an indicator of whether the dataset passed (or 

failed) the basic requirement in the data editing criteria.

• Column “Baseline Value” shows the baseline value for each pollutant.

• Column “% Influent values ≥10*baseline value” contains the percent of influent 

observations that are at least 10 times the baseline values.

• Column “Criterion 1” contains an indicator of whether the dataset passed (or failed) 

criterion 1 of the LTA test.

• Column “Mean Influent” shows the mean of the influent concentrations.

• Column “Criterion 2” contains an indicator of whether the dataset passed (or failed) 

criterion 2 of the LTA test.

The influent sampling location at each plant is given in the bullets below:

• FGD Purge: Allen, Belews Creek, Hatfield’s Ferry, Keystone, Miami Fort, and Brindisi.

• Vapor Compression Evaporator Influent: Polk and Wabash River.

As shown in the table, the data for each pollutant at each of the plants all passed the 

LTA test, except for arsenic and mercury at Wabash River. Since the data for these pollutants 

failed the LTA test, EPA excluded the Wabash River data for these pollutants in developing the 

limits for gasification wastewater.
Page 89

Table 3.1. Summary of the results for data editing procedure performed to select a dataset for

pollutant at each plant in calculating the limits.

Plant 

Name

Pollutant

(unit) N 1

Percent 

Detected for 

Influent (%)

Basic 

Requirem

ent2

Baseli

ne 

Value

% Influent 

values ≥ 

10*baseline 

(%)

Criteri

on 1

Mean 

Influent

Criterio

n 2

Allen Arsenic (ug/L) 63 100 Passed 2 100 Passed 233.3 Passed

Allen Mercury (ng/L) 62 100 Passed 0.5 100 Passed 52,219.4 Passed

Allen Nitrate Nitrite as N 

(mg/L) 8 100 Passed 0.05 100 Passed 32.0 Passed

Allen Selenium (ug/L) 63 100 Passed 5 100 Passed 1,685.2 Passed

Belews 

Creek Arsenic (ug/L) 70 100 Passed 2 100 Passed 411.4 Passed

Belews 

Creek Mercury (ng/L) 73 100 Passed 0.5 100 Passed 194,417.8 Passed

Belews 

Creek

Nitrate Nitrite as N 

(mg/L) 8 100 Passed 0.05 100 Passed 16.6 Passed

Belews 

Creek Selenium (ug/L) 76 100 Passed 5 100 Passed 6,797.3 Passed

Hatfield’s 

Ferry Arsenic (ug/L) 8 100 Passed 2 100 Passed 1,796.3 Passed

Hatfield’s 

Ferry Mercury (ng/L) 8 100 Passed 0.5 100 Passed 465,125.0 Passed

Keystone Arsenic (ug/L) 8 100 Passed 2 100 Passed 1,815.0 Passed

Keystone Mercury (ng/L) 8 100 Passed 0.5 100 Passed 404,225.0 Passed

Miami Fort Arsenic (ug/L) 8 100 Passed 2 100 Passed 727.3 Passed

Miami Fort Mercury (ng/L) 8 100 Passed 0.5 100 Passed 235,375.0 Passed

Brindisi Arsenic (ug/L) 2 100 Passed 2 100 Passed 54.0 Passed

Brindisi Mercury (ng/L) 2 100 Passed 0.5 100 Passed 240,00.0 Passed

Brindisi Selenium (ug/L) 2 100 Passed 5 100 Passed 255.0 Passed

Brindisi TDS (mg/L) 2 100 Passed 10 100 Passed 14,000.0 Passed

Polk Arsenic (ug/L) 4 100 Passed 2 100 Passed 280.0 Passed

Polk Mercury (ng/L) 4 100 Passed 0.5 100 Passed 70.4 Passed

Polk Selenium (ug/L) 4 100 Passed 5 100 Passed 1,277.5 Passed

Polk TDS (mg/L) 4 100 Passed 10 100 Passed 4,575.0 Passed

Wabash 

River Arsenic (ug/L) 4 50 Passed 2 0 Failed 4.5 Failed

Wabash 

River Mercury (ng/L) 4 0 Failed 0.5 75 Failed 8.7 Failed

Wabash 

River Selenium (ug/L) 4 100 Passed 5 100 Passed 920.0 Passed

Wabash 

River TDS (mg/L) 4 100 Passed 10 100 Passed 4,225.0 Passed

1

: Total number of observations (detected and non-detected combined). 2

: if a dataset fails the basic requirement, EPA automatically set both Criteria 1 and 2 to Failed.
Page 90

APPENDIX 4: Summary of the Results for the Engineering Review of the Limits

As described in Section 11, to evaluate whether the proposed limits are reasonable, EPA 

performed an engineering review to verify that the limits are reasonable based upon the design 

and expected operation of the control technologies. EPA performed two types of comparisons 

for this evaluation. First, EPA compared the limits to the effluent data used to develop the 

limits. Second, EPA compared the limits to the influent data. This appendix contains a listing of 

the daily effluent concentration values that are above the maximum daily and monthly average 

limits for each pollutant in each technology option. In addition, the list of effluent daily values 

collected in the same month as any daily value that exceeded the monthly limitation are also 

given in this appendix. 

There are two sections in this appendix. Section 1 contains the results of the 

comparisons between the limits and effluent data used to develop the limits for each 

technology option. Section 2 contains the results of the comparisons between the limits and 

influent data for each technology option.
Page 91

1. Results of the Comparison of the Limits to Effluent Data Used as the Basis for the Limits

Tables below provide the listing of the daily effluent values that are above the daily 

limits. In addition, a list of the daily values that are above the average monthly limits (and all 

other values in the same month in which any daily value is above the monthly limit) is also 

provided for each treatment technology option for FGD and gasification wastewaters.

Chemical Precipitation Treatment Technology Option for FGD Wastewater

The table below provides a list of all the daily data that are above the maximum daily 

limits for each pollutant.

Table 4.1. Listing of all daily values that are above the daily limits for chemical precipitation

treatment for FGD wastewater.

Plant Name Data Source Pollutant

(unit) Date Daily Limit 1

Concentr

ation

Indica

tor 2

Above 

daily limit

Hatfield’s Ferry CWA 308 Sampling Arsenic (ug/L) 1/12/2011 8 11 D Yes

Hatfield’s Ferry CWA 308 Sampling Arsenic (ug/L) 2/9/2011 8 10 D Yes

Miami Fort CWA 308 Sampling Mercury (ng/L) 9/28/2010 242 256 D Yes

Miami Fort CWA 308 Sampling Mercury (ng/L) 11/2/2010 242 295 D Yes 1

: Daily limit set for each pollutant.

2

: D = detected and ND = non-detected

The table below provides a list of all the daily values that are above the monthly limits

for each pollutant. Also included in the table are all other daily values collected in the same 

month as any daily value that exceeded the monthly limitation. For example, for arsenic at 

Hatfield’s Ferry, there are two daily observations in December, 2010 that are above the daily 

limits and two other daily observations collected the same month that are not above the daily 

limits.
Page 92

Table 4.2. For chemical precipitation treatment for FGD wastewater, a listing of all the daily 

values that are above the monthly limits, along with any other daily values collected in the 

same month.

Plant Name Data Source Pollutant

(unit) Date Monthly Limit1

Concentr

ation

Indic

ator2

Above 

monthly

limit

Above 

daily

limit

Hatfield’s Ferry EPA Sampling Arsenic (ug/L) 12/7/2010 6 5.4 D No No

Hatfield’s Ferry EPA Sampling Arsenic (ug/L) 12/8/2010 6 4.6 D No No

Hatfield’s Ferry EPA Sampling Arsenic (ug/L) 12/9/2010 6 6.4 D Yes No

Hatfield’s Ferry EPA Sampling Arsenic (ug/L) 12/10/2010 6 7.6 D Yes No

Hatfield’s Ferry CWA 308 Sampling Arsenic (ug/L) 1/12/2011 6 11 D Yes Yes

Hatfield’s Ferry CWA 308 Sampling Arsenic (ug/L) 2/9/2011 6 10 D Yes Yes

Hatfield’s Ferry CWA 308 Sampling Mercury (ng/L) 11/10/2010 119 228 D Yes No

Miami Fort EPA Sampling Mercury (ng/L) 7/13/2010 119 101 D No No

Miami Fort EPA Sampling Mercury (ng/L) 7/14/2010 119 104.9 D No No

Miami Fort EPA Sampling Mercury (ng/L) 7/15/2010 119 148 D Yes No

Miami Fort EPA Sampling Mercury (ng/L) 7/16/2010 119 165 D Yes No

Miami Fort CWA 308 Sampling Mercury (ng/L) 9/28/2010 119 256 D Yes Yes

Miami Fort CWA 308 Sampling Mercury (ng/L) 11/2/2010 119 295 D Yes Yes

Miami Fort CWA 308 Sampling Mercury (ng/L) 12/7/2010 119 144 D Yes No

Miami Fort CWA 308 Sampling Mercury (ng/L) 1/14/2011 119 127 D Yes No 1

: Monthly limit set for each pollutant.

2

: D = detected and ND = non-detected.

Chemical Precipitation Followed by Biological Treatment Technology Option for FGD 

Wastewater

The table below provides a list of all daily observations at Allen or Belews Creek that are 

above the daily limits for each pollutant (see discussion in Section 11 of the document for a 

detailed discussion of the comparison).

Table 4.3. Listing of all daily values that are above the daily limits for the biological treatment

technology option for FGD wastewater.

Plant Name Data Source Pollutant

(unit) Date Daily Limit 1

Concentra

tion

Indicat

or 2

Above daily

limit

Belews Creek Plant Self-Monitoring Selenium (ug/L) 8/18/2008 16 18.9 D Yes

Belews Creek Plant Self-Monitoring Selenium (ug/L) 8/25/2008 16 19.6 D Yes

Belews Creek Plant Self-Monitoring Selenium (ug/L) 9/8/2008 16 21.3 D Yes

Belews Creek Plant Self-Monitoring Selenium (ug/L) 9/15/2008 16 22.4 D Yes

Belews Creek Plant Self-Monitoring Selenium (ug/L) 9/29/2008 16 17.9 D Yes

Belews Creek EPA Sampling Selenium (ug/L) 6/9/2010 16 16.6 D Yes

Belews Creek EPA Sampling Selenium (ug/L) 6/11/2010 16 25 D Yes

Belews Creek CWA 308 Sampling Selenium (ug/L) 12/8/2010 16 29.35 D Yes

1

: Daily limit set for each pollutant.

2

: D = detected and ND = non-detected.
Page 93

The table below provides a list of all the daily values that are above the monthly limits

for each pollutant, along with other daily values collected in the same month.

Table 4.4. For biological treatment for FGD wastewater, a listing of all the daily values that are 

above the monthly limits, along with any other daily values collected in the same month.

Plant Name Data Source Pollutant

(unit) Date Monthl

y Limit1

Concen

tration

Indica

tor2

Above 

monthl

y limit

Above 

daily 

limit

Allen Plant Self-Monitoring Selenium (ug/L) 5/9/2011 10 5 ND No No

Allen Plant Self-Monitoring Selenium (ug/L) 5/23/2011 10 11.7 D Yes No

Belews Creek CWA 308 Sampling Nitrate-nitrite as 

N (mg/L) 11/3/2010 0.13 0.15 D Yes No

Belews Creek CWA 308 Sampling Nitrate-nitrite as 

N (mg/L) 1/17/2011 0.13 0.14 D Yes No

Belews Creek Plant Self-Monitoring Selenium (ug/L) 8/4/2008 10 10 ND No No

Belews Creek Plant Self-Monitoring Selenium (ug/L) 8/11/2008 10 15 D Yes No

Belews Creek Plant Self-Monitoring Selenium (ug/L) 8/18/2008 10 18.9 D Yes Yes

Belews Creek Plant Self-Monitoring Selenium (ug/L) 8/25/2008 10 19.6 D Yes Yes

Belews Creek Plant Self-Monitoring Selenium (ug/L) 9/2/2008 10 12.5 D Yes No

Belews Creek Plant Self-Monitoring Selenium (ug/L) 9/8/2008 10 21.3 D Yes Yes

Belews Creek Plant Self-Monitoring Selenium (ug/L) 9/15/2008 10 22.4 D Yes Yes

Belews Creek Plant Self-Monitoring Selenium (ug/L) 9/22/2008 10 10.1 D Yes No

Belews Creek Plant Self-Monitoring Selenium (ug/L) 9/29/2008 10 17.9 D Yes Yes

Belews Creek Plant Self-Monitoring Selenium (ug/L) 10/6/2008 10 15.6 D Yes No

Belews Creek Plant Self-Monitoring Selenium (ug/L) 10/12/2008 10 10 ND No No

Belews Creek Plant Self-Monitoring Selenium (ug/L) 10/20/2008 10 10.7 D Yes No

Belews Creek Plant Self-Monitoring Selenium (ug/L) 10/26/2008 10 10 ND No No

Belews Creek EPA Sampling Selenium (ug/L) 6/8/2010 10 7.3 D No No

Belews Creek EPA Sampling Selenium (ug/L) 6/9/2010 10 16.6 D Yes Yes

Belews Creek EPA Sampling Selenium (ug/L) 6/10/2010 10 5.1 D No No

Belews Creek EPA Sampling Selenium (ug/L) 6/11/2010 10 25 D Yes Yes

Belews Creek Plant Self-Monitoring Selenium (ug/L) 6/23/2010 10 5 ND No No

Belews Creek Plant Self-Monitoring Selenium (ug/L) 7/28/2010 10 12 D Yes No

Belews Creek CWA 308 Sampling Selenium (ug/L) 12/8/2010 10 29.35 D Yes Yes

1

: Monthly limit for each pollutant.

2

: D = detected and ND = non-detected.

Chemical Precipitation Followed By Vapor-Compression Evaporation Treatment Technology 

Option for FGD Wastewater

All concentration values at both brine concentrator distillate and crystallizer condensate 

are below the daily and monthly limits.
Page 94

Vapor-Compression Evaporation Treatment Technology Option for Gasification Wastewater

The table below provides a list of all the daily data that are above the maximum daily 

limits for each pollutant.

Table 4.5. Listing of all daily values that are above the daily limits for vapor-compression 

evaporation treatment for gasification wastewater.

Plant Name Data Source Pollutant

(unit) Date Daily Limit 1 Concentration

Indicat

or 2

Above 

daily limit

Polk EPA Sampling Selenium (ug/L) 10/26/2011 453 470 D Yes 1

: Daily limit set for each pollutant.

2

: D = detected and ND = non-detected.

The table below provides a list of all the daily values that are above the monthly limits

for each pollutant, along with other daily values collected in the same month. 

Table 4.6. For vapor-compression evaporation treatment for gasification wastewater, a listing 

of all the daily values that are above the monthly limits, along with any other daily values 

collected in the same month.

Plant 

Name Data Source Pollutant

(unit) Date Monthly 

Limit 1

Concentr

ation

Indicato

r 2

Above 

Monthl

y limit

Above 

daily 

limit

Polk EPA Sampling Selenium (ug/L) 10/18/2011 227 180 D No No

Polk EPA Sampling Selenium (ug/L) 10/19/2011 227 140 D No No

Polk EPA Sampling Selenium (ug/L) 10/26/2011 227 470 D Yes Yes

Polk EPA Sampling Selenium (ug/L) 10/27/2011 227 320 D Yes No

Polk EPA Sampling TDS (mg/L) 10/18/2011 22 23 D Yes No

Polk EPA Sampling TDS (mg/L) 10/19/2011 22 12 D No No

Polk EPA Sampling TDS (mg/L) 10/26/2011 22 11 D No No

Polk EPA Sampling TDS (mg/L) 10/27/2011 22 19 D No No 1

: Daily limit set for each pollutant.

2

: D = detected and ND = non-detected.

2. Comparison of the Effluent Limits to Influent Data

In addition to comparing the proposed limits to the effluent data used to develop the 

limits, EPA also compared the proposed limits to the influent data. Sections below provide the 

influent summary statistics for all plants from which the data were used as the basis for 

calculating the limits.
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Chemical Precipitation Treatment Technology Option for FGD Wastewater

Table below provides the summary statistics for influent (FGD Purge) for arsenic and 

mercury at Hatfield’s Ferry, Keystone, and Miami Fort. Also provided in the table are the 

proposed daily maximum limits for each pollutant.

Table 4.7. Summary statistics for the influent (FGD Purge) concentrations for plants from which

the data were used as the basis for calculating the limits for chemical precipitation treatment 

technology option for FGD wastewater.

Pollutant

(proposed daily limits)

Plant Name

Summary Statistics for influent by Pollutant and Plant Name 

N Minimum Median Mean Maximum

Arsenic

(Daily Limit = 8 ug/L)

Hatfield’s Ferry 8 300.0 1,575.0 1,796.3 4,610.0

Keystone 8 450.0 2,035.0 1,815.0 3,080.0

Miami Fort 8 320.0 682.5 727.3 1,310.0

Mercury 

(Daily Limit = 242 ng/L)

Hatfield’s Ferry 8 184,000.0 467,000.0 465,125.0 789,000.0

Keystone 8 18,800.0 514,000.0 404,225.0 622,000.0

Miami Fort 8 44,000.0 227,500.0 235,375.0 384,000.0

Chemical Precipitation Followed By Biological Treatment Technology Option for FGD 

Wastewater

The table below presents the influent (FGD Purge) summary statistics for all plants from

which the data were used as the basis for calculating the limits. Also provided in the table are 

the proposed daily limits for each pollutant. It should be noted that even though EPA 

transferred the limits for arsenic and mercury from chemical precipitation to the biological 

treatment technology option for FGD wastewater, the comparison between the influent values 

for Allen and Belews Creek and the limits for the chemical precipitation technology option are 

still provided below.

Table 4.8. Summary statistics for the influent (FGD Purge) concentrations for plants from which

the data were used as the basis for calculating the limits for biological treatment technology 

option for FGD wastewater.

Pollutant

(proposed daily limits) Plant Name Summary Statistics for influent by Pollutant and Plant Name

N Minimum Median Mean Maximum

Arsenic1

(Daily Limit = 8 ug/L )

Allen 63 105.0 208.0 233.3 619.0

Belews Creek 70 92.0 278.0 411.4 2,820.0

Mercury1

(Daily Limit = 242 ng/L)

Allen 62 18,500.0 49,950.0 52,219.4 120,000.0

Belews Creek 73 1,000.0 185,000.0 194,417.8 697,000.0

Nitrate-nitrite as N

(Daily Limit = 0.17 mg/L)

Allen 8 14.0 29.5 32.0 51.0

Belews Creek 8 14.0 15.5 16.6 21.0

Selenium

(Daily Limit = 16 ug/L)

Allen 63 849.0 1,660.0 1,685.2 3,260.0

Belews Creek 76 1,660.0 6,625.0 6,797.3 26,200.0 1

: The limits were transferred from chemical precipitation for FGD wastewater.
Page 96

Chemical Precipitation Followed By Vapor-Compression Evaporation Treatment Technology 

Option for FGD Wastewater

The table below presents the influent (FGD Purge) summary statistics for all plants from

which the data were used as the basis for calculating the limits. Also provided in the table are 

the proposed daily limits for each pollutant.

Table 4.9. Summary statistics for the influent (FGD Purge) concentrations for plants from which 

the data were used as the basis for calculating the limits for vapor-compression evaporation 

treatment technology option for FGD wastewater.

Pollutant

(proposed daily limits)

Plant Name Summary Statistics for influent by Pollutant and Plant Name

N Minimum Median Mean Maximum

Arsenic

(Daily Limit = 4 ug/L, based on the 

detection limit)

Brindisi 2 53.0 54.0 54.0 55.0

Mercury

(Daily Limit = 39 ng/L ) Brindisi 2 21,100.0 24,000.0 24,000.0 26,900.0

Selenium

(Daily Limit = 5 ug/L, based on the 

detection limit)

Brindisi 2 220.0 255.0 255.0 290.0

Total Dissolved Solids

(Daily Limit = 50 mg/L) Brindisi 2 13,000.0 14,000.0 14,000.0 15,000.0

Vapor-Compression Evaporation Treatment Technology Option for Gasification Wastewater

The table below presents the influent summary statistics for all pollutants at Polk and 

Wabash River. Also provided in the table is the proposed daily limit for each pollutant. As 

mentioned above, the data for arsenic and mercury at Wabash River failed the data editing 

criteria, thus the data for these two pollutants at Wabash River were excluded from developing 

the limits for this technology option. However, for completeness, the summary statistics for 

arsenic and mercury are provided in the table below.
Page 97

Table 4.10. Summary statistics for the influent (vapor compression evaporator influent) 

concentrations from plants for which the data were used as the basis for calculating the limits

for vapor-compression evaporation treatment technology option for gasification wastewater.

Pollutant

(proposed daily limits) Plant Name Summary Statistics for influent by Pollutant and Plant Name

N Minimum Median Mean Maximum

Arsenic

(Daily Limit = 4 ug/L, based on 

detection limit)

Polk 4 220.0 280.0 280.0 340.0

Wabash River 4 4.0 4.5 4.5 5.0

Mercury

(Daily Limit = 1.76 ng/L)

Polk 4 17.0 85.9 70.4 92.7

Wabash River 4 5.0 9.9 8.7 9.9

Selenium

(Daily Limit = 453 ug/L)

Polk 4 720.0 1,295.0 1,277.5 1,800.0

Wabash River 4 800.0 890.0 920.0 1,100.0

Total Dissolved Solids

(Daily Limit = 38 mg/L )

Polk 4 4,500.0 4,600.0 4,575.0 4,600.0

Wabash River 4 3,600.0 4,400.0 4,225.0 4,500.0