MEMORANDUM

TO: Steam Electric Rulemaking Record

FROM: Elizabeth Sabol, ERG

TJ Finseth, ERG

DATE: January 29, 2013

SUBJECT: Steam Electric Effluent Guidelines – Methodology for Identifying Surface 

Impoundment Closures Based on Regulatory Options

As part of the compliance cost and pollutant removal estimates, ERG identified combustion 

residual surface impoundments at steam electric plants that will likely remain open, partially 

close, or completely close based on the regulatory options considered as part of the proposed 

rule. For additional details regarding the regulatory options considered as part of the rulemaking, 

see Section 8 of the Technical Development Document for the Proposed Effluent Limitations 

Guidelines and Standards for the Steam Electric Power Generating Point Source Category. EPA 

used the results of the pond closure analysis to estimate costs for best management practices 

(BMP) for surface impoundments as part of the proposed rulemaking. For more information on 

the BMP costs see Section 5.6 of EPA’s Incremental Costs and Pollutant Removals for Proposed 

Effluent Limitation Guidelines and Standards for the Steam Electric Generating Point Source 

Category [DCN SE01957]. Additionally, ERG estimated percent closures for surface 

impoundments determined to partially close based on combustion residual wastewater flow rates 

(in gallons per day (gpd)), capacity (ft3), and impoundment age. EPA used the results of the pond 

closure analysis, flow rate, capacity, and impoundment age to estimate benefits associated with 

avoided impoundment failures. See ERG’s “Methodology for Estimating Impoundment Age, 

Capacity, and Reductions in Capacity Used to Estimate Benefits Associated with Avoided 

Impoundment Failures” memorandum [DCN SE02121] for more information on the percent 

closures methodology for combustion residual impoundments.

1. OVERVIEW

Implementation of the regulatory options evaluated as part of this rulemaking will reduce, and in 

some cases eliminate, FGD wastewater, fly ash transport water, bottom ash transport water, and 

combustion residuals managed in on-site surface impoundments. ERG used data from the 

Questionnaire for the Steam Electric Power Generating Effluent Guidelines (Steam Electric 

Survey) to develop a complete listing of combustion residual impoundments at steam electric 

power plants in the scope of this rule. ERG’s complete listing of combustion residual surface 

impoundments contains 1,097 surface impoundments containing FGD and/or ash combustion 

residual wastewater, solids, or both.

1

The listing also includes a flag for each type of combustion 

 

1 Twenty-seven of these surface impoundments are located at non-coal plants; therefore, there are 1,070 surface 

impoundments located at coal-fired plants that contain FGD and/or ash combustion residual wastewater, solids, or 

both. Additionally, there is one surface impoundment containing FGD and/or ash combustion residual wastewater, 

solids, or both at a petroleum coke-fired plant.
Memorandum

January 29, 2013

Page 2

residual contained within the impoundment (i.e., FGD, fly ash, bottom ash). ERG flagged the 

waste as being contained in the pond if it was identified as a solid waste, process wastewater, or 

both. The Steam Electric Survey did not require plants to differentiate between CCR leachate 

from impoundments versus CCR leachate from landfills. For this reason, ERG was unable to 

evaluate which impoundments contained combustion residual landfill leachate and therefore, 

leachate was not included in the analysis.

ERG used the complete listing of surface impoundments in combination with the regulatory

options considered as part of this rulemaking and those plants incurring costs to comply with the 

proposed rulemaking to determine the effect revisions to the ELGs would have on the population 

of surface impoundments. Table 1-1 presents the five regulatory options evaluated as part of this 

rulemaking and the types of combustion residual surface impoundments each option will affect.

Table 1-1. Regulatory Options and Effects on Surface Impoundment Types

Regulatory 

Option

Combustion Residual 

Waste Stream(s) 

Affected by the 

Regulatory Optiona Treatment

Affects Surface 

Impoundments 

Containing the 

Combustion Residual 

Waste(s):

1 FGD Wastewater Chemical Precipitation FGD

2 FGD Wastewater Chemical Precipitation + Biological Treatment FGD

3 FGD Wastewater Chemical Precipitation + Biological Treatment FGD, Fly Ash 

Fly Ash Transport Water Dry Handling

4 FGD Wastewater Chemical Precipitation + Biological Treatment FGD, Fly Ash, Bottom 

Ash Fly Ash Transport Water Dry Handling

Bottom Ash Transport 

Water

Dry Handling

5 FGD Wastewater Chemical Precipitation + Biological Treatment FGD, Fly Ash, Bottom 

Ash Fly Ash Transport Water Dry Handling

Bottom Ash Transport 

Water

Dry Handling

a

Other combustion residual wastestreams (i.e., combustion residual leachate, gasification wastewater, and flue gas 

mercury control wastewater) are also affected by the proposed effluent guidelines but either the associated surface 

impoundment(s) would be unaffected or those effects are not included in this analysis.

Based on the combustion residual types flagged during the development of the surface 

impoundment listing, ERG flagged surface impoundments as the following:

 FGD Only;

 Fly Ash Only;

 Both FGD and Fly Ash;

 Bottom Ash Only;

 Both FGD and Bottom Ash;

 Both Fly Ash and Bottom Ash; and

 All Wastes (FGD, Fly Ash, and Bottom Ash).
Memorandum

January 29, 2013

Page 3

ERG identified the following outcomes for surface impoundments for this analysis: 

 Not Affected – The implementation of the regulatory option being evaluated will 

not affect the operation of the impoundments.

 Closure – The implementation of the regulatory option being evaluated will 

eliminate all the combustion residual wastes (e.g., FGD wastewater, fly ash, 

and/or bottom ash) currently stored in the surface impoundment; therefore, ERG 

assumes the plant will close the surface impoundment.

 Partial Closure – The implementation of the regulatory option being evaluated 

will eliminate at least one, but not all, of the combustion residual wastes currently 

stored in the surface impoundment; therefore, ERG assumes the plant will stop 

sending the affected combustion residual waste(s) to the surface impoundment, 

but the impoundment will continue receiving the other wastes (i.e., a “partial 

closure”).

ERG also used information from the Steam Electric Survey to identify surface impoundments 

that will not be affected as part of the regulatory options because of assumptions ERG made in 

the compliance cost estimates. The impoundments determined unaffected, regardless of 

combustion residual type and regulatory option, are those impoundments identified as remaining 

functional as part of a complete recycle system, remaining functional as part of the FGD 

wastewater treatment system, or remaining functional for bottom ash complete recycle systems 

at plants incurring bottom ash management costs.

ERG analyzed the impoundment type (e.g., FGD only, All Wastes) to determine the type of 

outcome for each impoundment associated with a regulatory option. Table 1-2 presents the likely 

outcomes associated with each regulatory option, excluding the surface impoundments

determined to be unaffected regardless of combustion residual type and regulatory option,

described above.

Table 1-2. Outcomes for Types of Surface Impoundments Associated with 

Each Regulatory Option

Type of Impoundment

Regulatory Option

1 2 3 4 5

FGD Only Closure Closure Closure Closure Closure

Fly Ash Only Not Affected Not Affected Closure Closure Closure

Both FGD and Fly Ash Partial Closure Partial Closure Closure Closure Closure

Bottom Ash Only Not Affected Not Affected Not Affected Closure Closure

Both FGD and Bottom 

Ash Partial Closure Partial Closure Partial Closure Closure Closure

Both Fly Ash and Bottom 

Ash Not Affected Not Affected Partial Closure Closure Closure

All Wastes Partial Closure Partial Closure Partial Closure Closure Closure

Note: This table does not reflect the outcomes for those surface impoundments determined to be unaffected because

they remain functional as part of a complete recycle system, remain functional as part of the FGD wastewater 

treatment system, or remain functional for bottom ash complete recycle systems at plants incurring bottom ash 

management costs.
Memorandum

January 29, 2013

Page 4

2. IDENTIFICATION OF IMPOUNDMENT CLOSURES AND PARTIAL CLOSURES

To identify impoundments that will be affected by the proposed rulemaking, ERG used the 

complete listing of combustion residual surface impoundments, complete with impoundment 

type flags, and the listing of plants incurring compliance costs for FGD wastewater, fly ash, 

and/or bottom ash. ERG used the following process for identifying surface impoundments as 

closures and partial closures.

First, ERG flagged impoundments for FGD costs, fly ash costs, and/or bottom ash costs based on 

the lists of plants incurring costs for FGD wastewater, fly ash, and/or bottom ash. For each plant 

incurring a cost, a corresponding cost flag was marked for all impoundments at the plant. 

Additionally, ERG also flagged impoundments marked as complete recycle, part of the FGD 

wastewater treatment, or bottom ash management.

ERG marked those impoundments flagged as complete recycle and part of the FGD wastewater 

treatment system for all regulatory options as “Not Affected” because ERG assumes these 

impoundments will remain open. ERG assumes that complete recycle impoundments will remain 

open so that the plant can continue operating a complete recycle system, which is in compliance 

with the proposed rulemaking for FGD wastewater, fly ash transport water, and bottom ash 

transport wastewater. Additionally, ERG determined that seven plants would continue to operate 

FGD impoundments as part of their FGD wastewater treatment because it would be more cost 

effective than installing equalization tanks to accommodate the large FGD wastewater flow. 

ERG marked those impoundments flagged as incurring bottom ash management costs and having 

bottom ash combustion residual wastes as “Not Affected” because ERG assumes that these 

plants will continue to operate their bottom ash impoundments to achieve complete recycle. ERG 

identified those plants receiving bottom ash management costs as those plants that recycle a 

majority (more than 90 percent) of their bottom ash transport water for reuse as bottom ash 

transport water or other plant operations that do not lead to discharges. Therefore, ERG expects 

these plants to adjust their recycle operations to achieve complete recycle, rather than install dry

bottom ash handling.

For the remaining impoundments, ERG identified complete closures. Complete closures are 

impoundments that will likely close because all of the combustion residual waste currently 

transferred to the impoundment will likely no longer be transferred to the impoundment. ERG 

identified complete closures for each regulatory option using the following assumptions:

 Regulatory Options 1 and 2:

— The type of impoundment is “FGD Only;” and

— The FGD cost flag for the impoundment is marked “Yes.”

 Regulatory Option 3:

— The type of impoundment is “FGD Only” or “Fly Ash Only” or “Both

FGD and Fly Ash;” and

— The FGD and/or fly ash cost flag for the impoundment is marked “Yes.”
Memorandum

January 29, 2013

Page 5

 Regulatory Options 4 and 5:

— Any Cost Flag (FGD, fly ash, and/or bottom ash) is marked “Yes.”

2

Additionally, ERG identified partial closures for each regulatory option. These closures represent 

ponds that will remain open because at least one type of combustion residual waste will continue 

to be transferred to the impoundment, but additionally, at least one type of combustion residual 

waste will likely no longer be transferred to the impoundment. ERG identified partial closures 

for each regulatory option using the following assumptions:

 Regulatory Options 1 and 2:

— The type of impoundment is “Both FGD and Fly Ash” or “Both FGD and 

Bottom Ash” or “All Wastes;” and

— The FGD cost flag for the impoundment is marked “Yes.”

 Regulatory Option 3:

— The type of impoundment is “Both Fly Ash and Bottom Ash” or “Both 

FGD and Bottom Ash” or “All Wastes;” and

— The FGD and/or fly ash cost flag for the impoundment are marked “Yes.”

OR

— The impoundment is flagged as part of FGD wastewater treatment; and

— The type of impoundment is “Both FGD and Fly Ash;” and

— The fly ash cost flag for the impoundment is marked “Yes.”

OR

— The impoundment is flagged for complete recycle; and

— The type of impoundment is “Both FGD and Fly Ash;” and

— The FGD cost flag for the impoundment is marked “Yes.”

 Regulatory Options 4 and 5:

— The impoundment is flagged as bottom ash management; and 

— The type of impoundment is “Both Fly Ash and Bottom Ash” or “Both 

FGD and Bottom Ash” or “All Wastes;” and

— The FGD and/or fly ash cost flag for the impoundment are marked “Yes.”

OR

— The impoundment is flagged as part of FGD wastewater treatment; and

— The type of impoundment is “Both FGD and Fly Ash” or “Both FGD and 

Bottom Ash” or “All Wastes;” and 

— The fly ash and/or bottom ash cost flag for the impoundment are marked 

“Yes.”

The remaining impoundments not flagged as closures or partial closures were considered to be 

unaffected by the ELG.

The results of the impoundment closure analysis associated with the proposed ELG are presented 

in the file titled “Revised Pond Closure Analysis Including Partial Benefits (DCN SE01772).

 

2

For Regulatory Options 4 and 5, ERG assumes that all combustion residual surface impoundments (except those 

determined to be unaffected regardless of combustion residual type and regulatory option) located at plants that 

incur compliance costs will close.