MEMORANDUM 

TO: Steam Electric Rulemaking Record 

FROM: Dan-Tam Nguyen 

DATE: September 30, 2015 

SUBJECT: Methodology for Applying POTW Removals to FGD Pollutant Loadings 

Calculations 

 ERG is providing technical support to the U.S. Environmental Protection Agency’s 

Office of Water, Engineering and Analysis Division (EAD) for development of effluent 

limitations guidelines and standards (ELGs) for the Steam Electric Power Generating Industry. 

This memorandum describes EPA’s methodology for calculating flue gas desulfurization (FGD) 

pollutant loadings for steam electric power plants that indirectly discharge FGD wastewater 

through publicly owned treatment works (POTWs). 

EPA identified a few plants that reported discharging FGD wastewater to a POTW rather 

than discharging directly to surface water. See the FGD CPP Loads Database for more 

information on these plants (DCN SE05887). To account for pollutant reductions achieved by 

POTWs, EPA adjusted baseline and option pollutant loadings for these plants by applying 

percent removals expected from well-operated POTWs, as illustrated in Equation 1. EPA 

identified one plant that operated a chemical precipitation system at baseline and also applied 

POTW removals for this plant the chemical precipitation technology option loadings. Table 1 

provides the percent removals expected from well-operated POTWs [ERG, 2005]. 

 Indirect Pollutant Loading (lb/yr) = Pollutant Loading × (1- POTW Removal) (1) 

Where: 

Indirect Pollutant Loading 

Pollutant Loading 

= 

= 

The pollutant-specific loadings (baseline or option) that 

are indirectly discharged to surface water via a POTW, 

in pounds/year, 

The pollutant-specific loadings (baseline or option) that 

are transferred from the steam electric power plant to 

the POTW, in pounds/year, and 

POTW Removal = The estimated percentage of the pollutant loading that 

will be removed by a well-operated POTW (see Table 

1). 

In response to public comments on the proposed rule, EPA accounted for additional 

pollutant removals at POTWs which reduce the post-compliance loadings for plants that 

indirectly discharge relative to plants that directly discharge. EPA applied POTW removals to 
Memorandum 

September 30, 2015 

Page 2 

both baseline and post-compliance loadings for plants that indirectly discharge (using Equation 

1). This fully accounts for the additional pollutant removals that would occur at the POTW 

following implementation of these technology options. Table 2 compares the loadings estimates 

for the calculated baseline and technology options between the proposed rule and the final rule. 

The technology option loadings estimates decrease by less than 0.2 percent. 

Table 1. POTW Removals 

Analyte POTW Removal Percentage 

Aluminum 91.0% 

Ammonia 39.0% 

Antimony 66.8% 

Arsenic 65.8% 

Barium 55.2% 

Beryllium 61.2% 

Biochemical Oxygen Demand NA 

Boron NA 

Cadmium 90.1% 

Calcium NA 

Chemical Oxygen Demand NA 

Chloride NA 

Chromium 80.3% 

Chromium (VI) NA 

Cobalt 10.2% 

Copper 84.2% 

Cyanide, Total NA 

Iron NA 

Lead 77.5% 

Magnesium NA 

Manganese 40.6% 

Mercury 90.2% 

Molybdenum NA 

Nickel 51.4% 

Nitrate Nitrite as N 90.0%

Nitrogen, Kjeldahl NA

Phosphorus, Total NA

Selenium 34.3%

Silver 88.3%

Sodium NA

Sulfate NA

Thallium 53.8%

Tin NA

Titanium NA

Total Dissolved Solids NA

Total Suspended Solids NA

Vanadium 8.3%

Zinc 79.1%

Source: ERG, 2005 
Memorandum 

September 30, 2015 

Page 3 

Table 2. Revised Estimates Accounting for POTW Removals in FGD Pollutant Loadings 

Option 

Proposed Rule Estimate Final Rule Estimate % TWPE 

Load (lb/yr) TWPE Load (lb/yr) TWPE Difference 

Baseline Loadings 5,306,937,801 2,010,628 

 

5,306,937,801 2,010,628 0.00%

Chemical Precipitation 4,413,522,312 1,073,810 

 

4,413,411,807 1,072,287 -0.14%

Biological Treatment 4,402,966,151 925,882 

 

4,402,955,528 925,056 -0.09%

Note: The FGD pollutant loadings presented in this table do not reflect population changes due to implementation of 

the Coal Combustion Residuals (CCR) Rule or the Clean Power Plant (CPP) Rule. Pollutant loadings include 

loadings for FGD wastewater pollutants of concern (POCs) only. 

REFERENCES

1. Eastern Research Group (ERG). 2005. POTW Percent Removals Used for the TRI 

Release Databases (August 2005). DCN SE02932.