MEMORANDUM

TO: Steam Electric Rulemaking Record

FROM: Ryan Novak and Deb Bartram, ERG

DATE: 30 September 2015

SUBJECT: Steam Electric Effluent Guidelines Loadings Methodology – Break Out of 

Combined Ash Loadings

1. INTRODUCTION/BACKGROUND

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. 

The U.S. Environmental Protection Agency’s Office of Water, Engineering and Analysis 

Division (EAD) calculated plant-specific loadings for the baseline discharges and key 

technology options considered for control of ash transport water for the effluent limitations 

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

EPA multiplied the plant-specific ash transport water discharge flow rate for each type of ash 

transport water (i.e., fly ash, bottom ash, or combined ash transport water) by the appropriate 

average concentration data set for the type of discharge. Because EPA considered regulatory 

options that would establish different effluent requirements for fly ash and bottom ash, EPA 

analyzed the pollutant loadings and removals for these two wastestreams separately; therefore, 

EPA separated the loadings for combined ash impoundments into fly ash transport water 

loadings and bottom ash transport water loadings. This memorandum describes the methodology 

and data EPA used to estimate the breakout of pollutant loadings associated with combined ash 

impoundments among fly ash transport water and bottom ash transport water.

2. ELECTRIC POWER RESEARCH INSTITUTE WATER CHARACTERIZATION FIELD STUDIES

In 1988, the Electric Power Research Institute (EPRI) initiated the Power Plant Integrated 

Systems-Chemical Emissions Study (PISCES), a multi-media chemical assessment study that 

characterized the distribution of trace substances in air, liquid, and solid wastestreams from 

fossil-fuel-fired electric utility power plants. EPRI provided EPA with the PISCES Water 

Characterization Field Study, Sites A-G reports [EPRI, 1997-2001] that summarize the data 

collected during seven separate sampling episodes to characterize wastewater at coal-fired power 

plants operating impoundments receiving fly ash transport water and/or bottom ash transport 

water. For each of the seven sites sampled, EPA reviewed the reports to determine the 

characteristics of the ash impoundments (e.g., type of wastestreams entering the impoundment, 

pollutant concentrations). The sites were identified as operating the following type of ash 

impoundments:

 Site A – Combined ash impoundment;
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 Site B – Combined ash impoundment;

 Site C – Combined ash impoundment;

 Site D – Combined ash impoundment;

 Site E – Combined ash impoundment;

 Site F – Bottom ash impoundment & combined ash impoundment; and

 Site G – Combined ash impoundment.

Reports for Sites A through D also provided EPA with information regarding the 

respective percentage of pollutant loadings from ash impoundments containing both fly ash and 

bottom ash. These reports include tables presenting loadings to the ash impoundments in kg/day 

associated with each stream entering the impoundment for several metal pollutants.1 Although 

the reports for Site E, Site F, and Site G provide EPA with information on flow contributions to 

the combined ash impoundments, they do not provide the pollutant loadings for each 

wastestream.

EPA reviewed the information regarding the plants to determine whether the data were 

appropriate for use in the analysis. EPA made the following conclusions based on this review:

 Site A was excluded from this analysis of combined ash loadings because the fly 

ash transport water is only transferred to the ash impoundment during occasional 

operation; therefore, the fly ash transport water loadings compared to the bottom 

ash transport water loadings were not representative of the operations at a typical 

plant with both wet fly and bottom ash sluicing.

 Site B was included in the analysis as it consists of both fly and bottom ash 

transport water transferred to the ash impoundment.

 Site C was included in the analysis as it consists of both fly and bottom ash 

transport water transferred to the ash impoundment.

 Site D consists of two separate plants (i.e., Plants A and B). Plant A has wet fly 

ash and bottom ash handling for all six generating units and Plant B has wet 

bottom ash for two generating units, but wet fly ash for only one of the two 

generating units; therefore, only Plant A fly ash and bottom ash loadings data 

were included in the analysis. Plant B loadings data were excluded.

Based on this information, EPA used the loadings from the fly ash and bottom ash transport 

water streams in these EPRI PISCES reports to determine how the calculated combined ash 

loadings for each pollutant should be allocated to the fly ash and bottom ash transport water.

Refer to the “Break Out of Combined Ash Loadings Calculation Workbook” for each of the 

tables that present the ash impoundment influent at Site B, Site C, and Site D [ERG, 2015].

 

1 Table 5-1 and Table 5-2 from PISCES Water Characterization Field Study: Sites A and B Report (DCN SE01818), 

Table 5-1 from PISCES Water Characterization Field Study: Site C Report (DCN SE01819), and Table 5-1 from 

PISCES Water Characterization Field Study: Site D Report (DCN SE01820) provide the pollutant-specific loadings 

for all wastestreams entering the combined ash impoundments at those sites.
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3. CALCULATION OF POLLUTANT-SPECIFIC LOADINGS RATIO

EPA used the fly ash transport water and bottom ash transport water loadings presented 

in the EPRI PISCES reports for the sites described above to calculate a site-specific percent 

loading for fly ash and bottom ash for each pollutant. For each site and available pollutant, EPA 

calculated the percent of the pollutant loading associated with fly ash and bottom ash relative to 

the total ash loading. As demonstrated in Figure 1, for Site C the aluminum fly ash loading is 190 

kg/day and the bottom ash loading is 7.8 kg/day; therefore, EPA calculated a total ash loading of 

197.8 kg/day. EPA determined that 96.06 percent of the total ash aluminum loading is attributed 

to the fly ash and 3.94 percent of the loading is attributed to bottom ash. Although the 

impoundment also received other wastes, EPA used only the contributions from fly ash sluice 

transport water and bottom ash transport water for this calculation. EPA performed this 

calculation for each pollutant available for each of the three sites. Table 1 and Table 2 present the 

percent loading calculated for fly ash and bottom ash, respectively, for each pollutant at each 

site. 

Figure 1. Example Calculation of Percent Aluminum Loadings Associated with 

Fly Ash and Bottom Ash at PISCES Site C

Note: The table presented is an abbreviated version of Table 5-1 from PISCES Water Characterization Field Study: 

Site C Report (DCN SE01819).

1 – Samples of plant waste and coal pile runoff were shaken to resuspend solids, rather than allowed to settle like 

ash sluice wastes.

2 – Coal pile runoff is annualized over a year from 5 years of rainfall data.

EPA then calculated an overall average percent loading for fly ash transport water and 

bottom ash transport water for each pollutant using the site-specific percentages, as shown in 

Table 1 and Table 2. Because EPA did not have data available to calculate an average percent 

loading for fly ash and bottom for all pollutants in the combined ash impoundment dataset, EPA 

calculated the average percent loading for fly ash and bottom ash based on the pollutants 

available, 85.9 and 14.1 percent, respectively, and used this value for the allocate the loading for 

all other pollutants. Therefore, EPA assumed fly ash transport water and bottom ash transport 

water account for 85.9 and 14.1 percent, respectively, of all combined ash loadings (not flow) for 

those pollutants for which an analyte-specific value could not be calculated using the EPRI data. 
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These average percent loadings for fly ash and bottom ash are presented in Table 3 for each 

pollutant available. Refer to the “Break Out of Combined Ash Loadings Calculation Workbook” 

for the data used in these calculations [ERG, 2015]. EPA applied the percentages in Table 3 to 

allocate the loadings from combined ash impoundment effluent to fly ash transport water and 

bottom ash transport water.

4. REFERENCES

1. Electric Power Research Institute (EPRI). 1997 - 2001. PISCES Water Characterization 

Field Study, Sites A-G. Palo Alto, CA. DCNs SE01818-01823

2. ERG. 2015. Eastern Research Group, Inc. Break Out of Combined Ash Loadings 

Calculation Workbook. (30 September). DCN SE05586A1.
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Table 1. Calculation of Fly Ash Average Percent of Loading for All Three PISCES Plants

Al Sb As Be Ca Cu Fe Hg Ni Se Zn TSS

Fly Ash Site B 92.95% 89.29% 99.08% 96.00% 97.52% 85.96% 71.43% 96.15% 99.54% 81.89%

Fly Ash Site C 96.06% 93.33% 98.36% 83.33% 95.74% 98.04% 90.91% 79.22%

Fly Ash Site D (Plant A) 88.43% 95.59% 77.68% 42.86% 59.83% 41.18% 99.42% 89.74% 92.64%

Fly Ash Average 92.48% 89.29% 96.00% 96.00% 77.68% 79.58% 76.37% 71.43% 77.69% 99.00% 90.33% 84.58%

Note: EPA calculated the average percent loading for fly ash and bottom ash based on the pollutants available, 85.9 and 14.1 percent, respectively, and assumed this value 

for the percent breakout for the other pollutants for which loads were calculated for combined ash impoundments.

Table 2. Calculation of Bottom Ash Average Percent of Loading for All Three PISCES Plants

Al Sb As Be Ca Cu Fe Hg Ni Se Zn TSS

Bottom Ash Site B 7.05% 10.71% 0.92% 4.00% 2.48% 14.04% 28.57% 3.85% 0.46% 18.11%

Bottom Ash Site C 3.94% 6.67% 1.64% 16.67% 4.26% 1.96% 9.09% 20.78%

Bottom Ash Site D (Plant A) 11.57% 4.41% 22.32% 57.14% 40.17% 58.82% 0.58% 10.26% 7.36%

Bottom Ash Average 7.52% 10.71% 4.00% 4.00% 22.32% 20.42% 23.63% 28.57% 22.31% 1.00% 9.67% 15.42%

Note: EPA calculated the average percent loading for fly ash and bottom ash based on the pollutants available, 85.9 and 14.1 percent, respectively, and assumed this value 

for the percent breakout for the other pollutants for which loads were calculated for combined ash impoundments.
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Table 3. Percent Loadings for Fly Ash and Bottom Ash in Combined Ash Impoundments

Analyte Percent Loading Fly Ash (%) Percent Loading Bottom Ash (%)

Aluminum 92.5 7.5

Antimony 89.3 10.7

Arsenic 96.0 4.0

Beryllium 96.0 4.0

Calcium 77.7 22.3

Copper 79.6 20.4

Iron 76.4 23.6

Mercury 71.4 28.6

Nickel 77.7 22.3

Selenium 99.0 1.0

Zinc 90.3 9.7

TSS 84.6 15.4

Overall Average 85.9 14.1

Note: The values in this table have been rounded to the tenth decimal place.