MEMORANDUM 

TO: Steam Electric Rulemaking Record 

FROM: TJ Finseth, ERG 

DATE: 19 April 2013 

SUBJECT: Evaluation of Generating Capacity Thresholds for FGD Wastewater and 

Bottom Ash Transport Water 

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. EPA, with 

the support of ERG, evaluated wastewater flow rates and pollutant concentration data from 

survey responses, site visits, sampling episodes, trade associations, individual power plants, 

states, and previous rulemakings to estimate pollutant discharge loadings associated with the 

discharge of FGD wastewater, fly ash transport water, bottom ash transport water, and 

combustion residual landfill leachate. In addition, EPA estimated the corresponding pollutant 

removals associated with installing and operating the proposed candidate BAT technology 

options for each of these wastestreams. 

As described in Section 8.1.3.1 of the Technical Development Document for the Proposed 

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

Source Category (TDD), EPA is proposing to establish BAT limits equal to BPT for existing oilfired units. Additionally, as described in Section 8.1.3.2 of the TDD, EPA is also proposing to 

establish BAT effluent limits equal to BPT for existing generating units with a total nameplate 

generating capacity of 50 MW or less. EPA is proposing to establish these BAT limits for all 

eight of the regulatory options described in Section 8 of the TDD; however, for regulatory 

Options 3b and 4a, EPA is proposing to use a different capacity threshold for certain 

wastestreams. 

For Regulatory Option 3b, EPA is proposing to establish numeric effluent limits for mercury, 

arsenic, selenium, and nitrate-nitrite in discharges of FGD wastewater from steam electric 

facilities with a total plant-level wet-scrubbed capacity of 2,000 MW or greater.1

 As part of the 

analysis, EPA also evaluated other plant-level wet-scrubbed capacity thresholds. Table 1 

presents the number of plants that would incur costs and the total pollutant removals (both 

pounds and TWPE) that would be achieved at other plant-level wet-scrubbed capacity thresholds 

for FGD wastewater for Option 3b. 

 

1

 Total plant-level wet-scrubbed capacity is calculated by summing the nameplate capacity for all of the units that 

are serviced by wet FGD systems. 
Memorandum 

April 19, 2013 

Page 2 

Table 1. FGD Wastewater Plant-Level Wet-Scrubbed Capacity Threshold Evaluationa

Plant-Level WetScrubbed Capacity 

Threshold (MW) 

Number of Plants 

Incurring Costs 

Pollutant Removals Achieved by Regulationb 

Pounds Removed

(lbs/yr) 

TWPE Removed 

(TWPE/yr) 

Nonea 116 1,160,000,000 2,620,000

500 94 1,120,000,000 2,470,000

1,000 61 944,000,000 1,770,000

1,500 37 668,000,000 1,200,000

2,000 17 446,000,000 908,000

Note: Removals are rounded to three significant figures. 

a – All threshold evaluations for FGD wastewater include establishing BAT effluent limits equal to BPT for existing 

generating units with a total nameplate generating capacity of 50 MW or less. 

b – Excludes loadings for BOD, COD, TSS, and TDS. 

For Regulatory Option 4a, EPA is proposing to establish “zero discharge” effluent limits for all 

pollutants in bottom ash transport water, with the exception of all generating units with a 

nameplate generating capacity of 400 MW or less. As part of the analysis, EPA also evaluated 

other unit-level capacity thresholds. Table 2 presents the number of plants that would incur costs 

and the total pollutant removals (both pounds and TWPE) that would be achieved at other unitlevel thresholds for bottom ash transport water for Option 4a.2

Table 2. Bottom Ash Transport Water Unit-Level Capacity Threshold Evaluation

Unit-Level Capacity 

Threshold (MW) 

Number of Plants 

Incurring Costs 

Pollutant Removals Achieved by Regulationa 

Pounds Removed

(lbs/yr) 

TWPE Removed 

(TWPE/yr) 

50 240 1,700,000,000 2,710,000

100 220 1,590,000,000 2,540,000

200 172 1,280,000,000 2,050,000

300 138 1,100,000,000 1,750,000

400 115 991,000,000 1,570,000

500 100 918,000,000 1,430,000

600 67 739,000,000 1,150,000

Note: Removals are rounded to three significant figures. 

a – Excludes loadings for BOD, COD, TSS, and TDS. 

 

2

 EPA estimated the bottom ash transport water pollutant removals associated with Option 4a by developing 

adjustment factors that were applied to the pollutant removals associated with bottom ash transport water based on 

the 50 MW unit-level capacity threshold. For more details on how EPA estimated the bottom ash transport water 

pollutant removals, see the memorandum entitled, “Memorandum to the Rulemaking Record: Methodologies for 

Estimating Costs and Pollutant Removals for Steam Electric ELG Regulatory Option 4a” (DCN SE03834). The 

same methodology was used to estimate the pollutant removals for the other bottom ash transport water unit-level 

capacity thresholds presented in Table 2.