MEMORANDUM

TO: Steam Electric Point Source Category ELG Rulemaking Record

FROM: Jill Lucy, ERG

DATE: September 29, 2015

SUBJECT: Water Quality Module Supporting Documentation (DCN SE04451)

1.0 SUMMARY OF SUPPORTING DOCUMENTATION

ERG supported the U.S. Environmental Protection Agency (EPA) in the development of 

final effluent limitations guidelines and standards (ELGs) for the Steam Electric Power 

Generating Point Source Category (40 CFR Part 423). ERG developed the following resources to 

calculate pollutant concentrations in the water column and sediment of the immediate receiving 

water and evaluate the impacts that receiving water concentrations pose to aquatic life and 

human health under current (i.e., baseline) discharge practices and potential improvements

associated with the regulatory options (Options A, B, C, D, and E).

1

 Immediate Receiving Water (IRW) Model: Water Quality Module.

 IRW Model: Water Quality Module Comparisons Database.

 IRW Model: Water Quality Module Summary Tables Database.

 IRW Model: Water Quality Module Summary Tables Spreadsheet.

The results of these analyses are presented in the Environmental Assessment for the 

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

Source Category (EA Report), Document No. EPA-821-R-15-006 (DCN SE04527). The 

methodology of the IRW model: water quality module is presented in the following 

documentation:

 Water Quality Module: Plant and Receiving Water Characteristics (DCN SE04513) –

This memorandum specifies the methodology used to identify the characteristics of 

the immediate receiving waters evaluated in the water quality module.

 Pollutant Loadings Supporting Documentation (DCN SE04515) – This memorandum 

identifies the supporting documentation used to calculate the pollutant loadings 

evaluated in the water quality module.

 

1 During development of the final rule, EPA decided not to base the final rule on Option F for existing sources due 

primarily to the high cost of that Option, particularly in light of the costs associated with other rulemakings expected 

to impact the steam electric power generating industry (see Section VIII.C.1 of the preamble). As a result, EPA 

chose not to conduct particular analyses for Option F to the same extent that it did for some of the other options 

considered.
Memorandum

September 29, 2015

Page 2

 EA Report, Section 5.1.1 (Water Quality Module) – This section provides an 

overview of the water quality module. 

 EA Report, Appendix C (Water Quality Model Methodology) – This appendix 

presents the model equations, input values, pollutant benchmarks, and methodology 

limitations/assumptions.

ERG completed modeling under two separate industry baseline scopes: 

1. The “With CCR” scope accounts for the Coal Combustion Residuals (CCR) 

rulemaking. See the EA Report for the results of the analyses under this scope: 209 

immediate receiving waters included in the IRW model used for the EA (188 steam 

electric power plants).

2. The “With CCR and CPP” scope accounts for both the CCR rulemaking and the 

Clean Power Plan [Clean Air Act Section 111(d)]. See Appendix I of the EA Report 

for the results of the analyses under this scope: 163 immediate receiving waters 

included in the IRW model used for the EA (143 steam electric power plants).

The results of the IRW model: water quality module are presented in the following

sections of the EA Report:

 Section 6.1 (Water Quality Impacts).

 Section 7.2 (Key Environmental Improvements).

 Section 7.3 (Pollutant-Specific Improvements).

 Section 9 (Conclusions).

 Appendix H (Additional Model Results).

 Appendix I (Analysis for Alternate Scenario with Clean Power Plan).

Table 1 presents a comprehensive listing of the IRW model: water quality module 

supporting documentation for the “With CCR” scope. Table 2 presents a comprehensive listing 

of the IRW model: water quality module supporting documentation for the “With CCR and CPP” 

scope. The tables provide the document control number (DCN), title, and description of each 

record item, and identify whether the record item contains Confidential Business Information 

(CBI).

Table 1. IRW Model: Water Quality Module Record Items – With CCR

DCN Title (Date) Description CBIa

SE04552 Final Steam EA IRW 

Model - Water Quality 

Module - Baseline (CCR)

(050615)

Database used to calculate the total and dissolved receiving 

water concentrations and total sediment concentrations and to 

identify pollutant concentrations that exceed benchmarks for 

aquatic life and human health in the immediate discharge zone 

under baseline conditions. Generates inputs for the wildlife and 

human health module. This version accounts for the CCR 

rulemaking.

Yes
Memorandum

September 29, 2015

Page 3

Table 1. IRW Model: Water Quality Module Record Items – With CCR

DCN Title (Date) Description CBIa

SE04552A1 Final Steam EA IRW 

Model - Water Quality 

Module - Option A 

(CCR) (050615)

Database used to calculate the total and dissolved receiving 

water concentrations and total sediment concentrations and to 

identify pollutant concentrations that exceed benchmarks for 

aquatic life and human health in the immediate discharge zone 

under Option A. Generates inputs for the wildlife and human 

health module. This version accounts for the CCR rulemaking.

Yes

SE04552A2 Final Steam EA IRW 

Model - Water Quality 

Module - Option B

(CCR) (050615)

Database used to calculate the total and dissolved receiving 

water concentrations and total sediment concentrations and to 

identify pollutant concentrations that exceed benchmarks for 

aquatic life and human health in the immediate discharge zone 

under Option B. Generates inputs for the wildlife and human 

health module. This version accounts for the CCR rulemaking.

Yes

SE04552A3 Final Steam EA IRW 

Model - Water Quality 

Module - Option C

(CCR) (050615)

Database used to calculate the total and dissolved receiving 

water concentrations and total sediment concentrations and to 

identify pollutant concentrations that exceed benchmarks for 

aquatic life and human health in the immediate discharge zone 

under Option C. Generates inputs for the wildlife and human 

health module. This version accounts for the CCR rulemaking.

Yes

SE04552A4 Final Steam EA IRW 

Model - Water Quality 

Module - Option D

(CCR) (050615)

Database used to calculate the total and dissolved receiving 

water concentrations and total sediment concentrations and to 

identify pollutant concentrations that exceed benchmarks for 

aquatic life and human health in the immediate discharge zone 

under Option D. Generates inputs for the wildlife and human 

health module. This version accounts for the CCR rulemaking.

Yes

SE04552A5 Final Steam EA IRW 

Model - Water Quality 

Module - Option E (CCR)

(050615)

Database used to calculate the total and dissolved receiving 

water concentrations and total sediment concentrations and to 

identify pollutant concentrations that exceed benchmarks for 

aquatic life and human health in the immediate discharge zone 

under Option E. Generates inputs for the wildlife and human 

health module. This version accounts for the CCR rulemaking.

Yes

SE04553A1 Final Steam EA IRW 

Model - Water Quality 

Module - Comparison 

Database - Option A 

(CCR) (050615)

Database used to compare the water quality module results 

between baseline and Option A. Generates inputs for the Water 

Quality Module Summary Table Generator. This version 

accounts for the CCR rulemaking.

Yes

SE04553A2 Final Steam EA IRW 

Model - Water Quality 

Module - Comparison 

Database - Option B

(CCR) (050615)

Database used to compare the water quality module results 

between baseline and Option B. Generates inputs for the Water 

Quality Module Summary Table Generator. This version 

accounts for the CCR rulemaking.

Yes

SE04553A3 Final Steam EA IRW 

Model - Water Quality 

Module - Comparison 

Database - Option C

(CCR) (050615)

Database used to compare the water quality module results 

between baseline and Option C. Generates inputs for the Water 

Quality Module Summary Table Generator. This version 

accounts for the CCR rulemaking.

Yes
Memorandum

September 29, 2015

Page 4

Table 1. IRW Model: Water Quality Module Record Items – With CCR

DCN Title (Date) Description CBIa

SE04553A4 Final Steam EA IRW 

Model - Water Quality 

Module - Comparison 

Database - Option D

(CCR) (050615)

Database used to compare the water quality module results 

between baseline and Option D. Generates inputs for the Water 

Quality Module Summary Table Generator. This version 

accounts for the CCR rulemaking.

Yes

SE04553A5 Final Steam EA IRW 

Model - Water Quality 

Module - Comparison 

Database - Option E 

(CCR) (050615)

Database used to compare the water quality module results 

between baseline and Option E. Generates inputs for the Water 

Quality Module Summary Table Generator. This version 

accounts for the CCR rulemaking.

Yes

SE04554A1 Final Steam EA IRW 

Model - Water Quality 

Module - Summary Table 

Generator (CCR)

(050615)

Database used to summarize the water quality module results for 

baseline and regulatory options. Generates the Water Quality 

Model Summary Tables spreadsheet. This version accounts for 

the CCR rulemaking.

No

SE04554A2 Final Steam EA IRW 

Model - Water Quality 

Module - Summary 

Tables (CCR) (050615)

Spreadsheet that summarizes the water quality module results 

for baseline and regulatory options. This version accounts for 

the CCR rulemaking.

No

a – Record items containing CBI have been removed from the public record.

Table 2. IRW Model: Water Quality Module Record Items – With CCR and CPP

DCN Title (Date) Description CBIa

SE04568 Final Steam EA IRW 

Model - Water Quality 

Module - Baseline (CPP)

(061515)

Database used to calculate the total and dissolved receiving 

water concentrations and total sediment concentrations and to 

identify pollutant concentrations that exceed benchmarks for 

aquatic life and human health in the immediate discharge zone 

under baseline conditions. Generates inputs for the wildlife and 

human health module. This version accounts for the CCR and 

CPP rulemakings.

Yes

SE04568A1 Final Steam EA IRW 

Model - Water Quality 

Module - Option A (CPP)

(061515)

Database used to calculate the total and dissolved receiving 

water concentrations and total sediment concentrations and to 

identify pollutant concentrations that exceed benchmarks for 

aquatic life and human health in the immediate discharge zone 

under Option A. Generates inputs for the wildlife and human 

health module. This version accounts for the CCR and CPP 

rulemakings.

Yes

SE04568A2 Final Steam EA IRW 

Model - Water Quality 

Module - Option B (CPP)

(061515)

Database used to calculate the total and dissolved receiving

water concentrations and total sediment concentrations and to 

identify pollutant concentrations that exceed benchmarks for 

aquatic life and human health in the immediate discharge zone 

under Option B. Generates inputs for the wildlife and human 

health module. This version accounts for the CCR and CPP 

rulemakings.

Yes
Memorandum

September 29, 2015

Page 5

Table 2. IRW Model: Water Quality Module Record Items – With CCR and CPP

DCN Title (Date) Description CBIa

SE04568A3 Final Steam EA IRW 

Model - Water Quality 

Module - Option C (CPP)

(061515)

Database used to calculate the total and dissolved receiving 

water concentrations and total sediment concentrations and to 

identify pollutant concentrations that exceed benchmarks for 

aquatic life and human health in the immediate discharge zone 

under Option C. Generates inputs for the wildlife and human 

health module. This version accounts for the CCR and CPP 

rulemakings.

Yes

SE04568A4 Final Steam EA IRW 

Model - Water Quality 

Module - Option D (CPP)

(061515)

Database used to calculate the total and dissolved receiving 

water concentrations and total sediment concentrations and to 

identify pollutant concentrations that exceed benchmarks for 

aquatic life and human health in the immediate discharge zone 

under Option D. Generates inputs for the wildlife and human 

health module. This version accounts for the CCR and CPP 

rulemakings.

Yes

SE04568A5 Final Steam EA IRW 

Model - Water Quality 

Module - Option E (CPP)

(061515)

Database used to calculate the total and dissolved receiving 

water concentrations and total sediment concentrations and to 

identify pollutant concentrations that exceed benchmarks for 

aquatic life and human health in the immediate discharge zone 

under Option E. Generates inputs for the wildlife and human 

health module. This version accounts for the CCR and CPP 

rulemakings.

Yes

SE04569A1 Final Steam EA IRW 

Model - Water Quality 

Module - Comparison 

Database - Option A 

(CPP) (061515)

Database used to compare the water quality module results 

between baseline and Option A. Generates inputs for the Water 

Quality Module Summary Table Generator. This version 

accounts for the CCR and CPP rulemakings.

Yes

SE04569A2 Final Steam EA IRW 

Model - Water Quality 

Module - Comparison 

Database - Option B

(CPP) (061515)

Database used to compare the water quality module results 

between baseline and Option B. Generates inputs for the Water 

Quality Module Summary Table Generator. This version 

accounts for the CCR and CPP rulemakings.

Yes

SE04569A3 Final Steam EA IRW 

Model - Water Quality 

Module - Comparison 

Database - Option C 

(CPP) (061515)

Database used to compare the water quality module results 

between baseline and Option C. Generates inputs for the Water 

Quality Module Summary Table Generator. This version 

accounts for the CCR and CPP rulemakings.

Yes

SE04569A4 Final Steam EA IRW 

Model - Water Quality 

Module - Comparison 

Database - Option D

(CPP) (061515)

Database used to compare the water quality module results 

between baseline and Option D. Generates inputs for the Water 

Quality Module Summary Table Generator. This version 

accounts for the CCR and CPP rulemakings.

Yes

SE04569A5 Final Steam EA IRW 

Model - Water Quality 

Module - Comparison 

Database - Option E

(CPP) (061515)

Database used to compare the water quality module results 

between baseline and Option E. Generates inputs for the Water 

Quality Module Summary Table Generator. This version 

accounts for the CCR and CPP rulemakings.

Yes
Memorandum

September 29, 2015

Page 6

Table 2. IRW Model: Water Quality Module Record Items – With CCR and CPP

DCN Title (Date) Description CBIa

SE04570A1 Final Steam EA IRW 

Model - Water Quality 

Module - Summary Table 

Generator (CPP)

(061515)

Database used to summarize the water quality module results for 

baseline and regulatory options. Generates the Water Quality 

Model Summary Tables spreadsheet. This version accounts for 

the CCR and CPP rulemakings.

No

SE04570A2 Final Steam EA IRW

Model - Water Quality 

Module - Summary 

Tables (CPP) (061515)

Spreadsheet that summarizes the water quality module results 

for baseline and regulatory options. This version accounts for 

the CCR and CPP rulemakings.

No

a – Record items containing CBI have been removed from the public record.

2.0 CORRECTIONS TO THE IRW MODEL

As an outcome from the public review and comment process, ERG incorporated the 

following correction to the IRW model: water quality module:

 ERG corrected the water quality module partition coefficients for each of the ten 

modeled pollutants, which are presented in Table C-4 of Appendix C to the EA 

Report. These coefficients were selected from EPA’s Partition Coefficients for 

Metals in Surface Water, Soil, and Waste (Final) (EPA-600-R-05-074) (DCN 

SE01892), which presents the coefficients in logarithmic form (i.e., the values 

presented are the logarithm of the partition coefficient). The water quality module 

incorporated these values without first converting them from logarithmic form to 

linear form. This resulted in an underestimate of the amount of pollutant sorbed to 

suspended sediment and bottom sediment and an overestimate of dissolved pollutant 

concentrations in the water column. ERG corrected this error by converting the 

coefficients to linear form prior to incorporation into the water quality module.