### 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) fo r the Steam Electric Power Generating Industry. This memorandum describes EPA’s methodology for calculating flue gas desulfurization (FGD) pollutant loadings for steam electric power plan ts that indirectly di scharge FGD wastewater through publicly owned treatm ent works (POTWs).
EPA identified a few plants that reported di scharging 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 pollu tant 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 pr ecipitation system at ba seline 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 Loadin g (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 percenta ge of the pollutant loading that will be removed by a well-operated POTW (see Table 1).

In response to public comments on the propos ed rule, EPA accounted for additional pollutant removals at POTWs which reduce th e post-compliance loadings for plants that indirectly discharge relative to plants that di rectly discharge. EPA a pplied POTW removals toMemorandum September 30, 2015 Page 2

both baseline and post-compliance loadings for plan ts that indirectly di scharge (using Equation 1). This fully accounts for the additional polluta nt 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, 2005Memorandum 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 Difference Load (lb/yr) TWPE Load (lb/yr) TWPE

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.

R EFERENCES

1. Eastern Research Group (ERG). 2005. POTW Percent Removals Used for the TRI Release Databases (August 2005). DCN SE02932.