PART B OF THE SUPPORTING STATEMENT 

FOR THE INFORMATION COLLECTION REQUEST PACKAGE THAT WILL 

SUPPORT DEVELOPMENT OF STEAM ELECTRIC POWER GENERATING 

EFFLUENT GUIDELINES 

U.S. ENVIRONMENTAL PROTECTION AGENCY 

February 22, 2010
PART B OF THE SUPPORTING STATEMENT 

1. QUESTIONNAIRE OBJECTIVES, KEY VARIABLES, AND OTHER 

PRELIMINARIES 

1(a) Questionnaire Objectives 

The primary objective of this Information Collection Request (ICR) is to gather and 

update information about fossil- and nuclear-fueled steam electric power plants to support 

technical analyses that EPA will use to develop revised effluent guidelines for the steam electric 

power generating industry. More specifically, through this ICR, EPA will administer a 

questionnaire to power plants in order to obtain sufficient information to develop an industry 

profile and to assess the pollutant reductions, costs, and economic achievability of candidate 

pollution control technologies, management practices, and process changes. This information is 

necessary to fulfill requirements established by the Clean Water Act and to inform Agency 

decision making about the appropriate course of regulatory action to address the pollutants 

present in wastewater discharges from steam electric power plants. While EPA has obtained 

certain information through a recently-completed study of the steam electric power generating 

industry and through public sources, it has determined that there are no existing sources for the 

sufficiently-detailed plant- and generator-level data that will be collected through this ICR 

(questionnaire). 

1(b) Key Variables 

EPA will use the information collected from the questionnaire to gain knowledge of 

current steam electric processes, characterize and quantify the pollutants currently discharged by 

the industry, assess technical and economic achievability of available controls, and assess 

potential environmental impacts. The information collected will provide EPA with 

owner/operator-level, plant-level, and/or generating unit-level data on processes, production, and 

costs that complement, and go beyond, data that are available from public sources. EPA is 

investigating the following key variables as they relate to the potential technology options for 

this industrial sector: 

• Proper Characterization and Classification of the Steam Electric Industry; 

• Baseline Estimates of Pollutants Discharged in Steam Electric Process 

Wastewater; 

• BMPs and Pollution Prevention Opportunities that can Reduce Pollutant 

Discharges; 

• Best Available and Best Demonstrated Technologies for Effluent Limitations 

Guidelines and Standards; 

• Potential Environmental Impacts of Steam Electric Process Wastewater; and 

• Costs and Economic Impacts of Candidate Pollutant Control Technologies and 

Practices. 

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Please see Part A, Section 4(b)(i) of this ICR Supporting Statement for detailed 

information on the data to be collected by the questionnaire. 

1(c) Terminology 

Within the sample frame (defined in Section 2(b) below), EPA has classified the fuel 

usage for each plant within the scope of the ICR. This plant fuel classification is based on the 

types of fuels used by each of the generating units operating at the plant. The plant fuel 

classifications are determined in a hierarchical manner as follows: 

First, all coal plants are identified: 

• Coal: one or more units uses coal as its primary or secondary fuel. This includes coal 

units using integrated gasification combined cycle (IGCC); 

Second, all petroleum coke plants are identified: 

• Petroleum Coke: one or more units uses petroleum coke as its primary or secondary 

fuel (and the plant is not already classified as a coal plant); 

Third, plants for which all the units have the same primary fuel type are classified as follows: 

• Gas (all units have gas as the primary fuel type, but do not use combined cycle steam 

turbines); 

• Gas-Combined Cycle (all units have gas as the primary fuel type and use combined 

cycle steam turbines); 

• Oil (all units have oil as the primary fuel type); 

• Nuclear (all units are nuclear); 

Finally, the remaining plants with units having different fuel types are classified as 

combinations as follows: 

• Combination (Gas and Gas-Combined Cycle); 

• Combination (Gas and Oil); 

• Combination (Gas-Combined Cycle and Oil); 

• Combination (Gas and Gas-Combined Cycle and Oil); and 

• Combination (Gas-Combined Cycle and Nuclear and Oil). 

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2. STATISTICAL APPROACH FOR THE SURVEY 

The statistical approach considers the survey’s target population, the available 

information in the sample frame, the sample design, and sources of error. The following sections 

describe each component in detail. 

2(a) Target Population 

The principal task in the development of a sample survey design is establishing a clear, 

concise description of the survey’s target population. The target population consists of the entire 

set of elements on which inferences will be made from the collected survey data. The definition 

should clearly identify every element of the target population so that all non-population elements 

can be excluded. For this survey, EPA has defined the target population to be all fossil- and 

nuclear-fueled steam electric power plants in the U.S. that report as operating under North 

American Industry Classification System (NAICS) code 22. In addition to plant-level 

information, EPA intends to collect information about all units at each plant. EPA will develop 

both plant-level and unit-level estimates from the data. 

2(b) Sample Frame 

A sample frame is a list or set of procedures for identifying all elements of a target 

population. In addition to listing population elements, sample frames contain such additional 

information as addresses and key characteristics of the population that will be used to draw 

samples. Sample frames are essential to the quality of surveys because sample elements are 

drawn from them. 

Because the target population consists of all fossil- and nuclear-fueled steam electric 

power plants in the U.S. that report as operating under NAICS code 22 and their corresponding 

generating units, EPA has created a sample frame of all such plants and generating units. This 

frame consists of information obtained from databases that are maintained by the Energy 

Information Administration (EIA), a statistical agency of the U.S. Department of Energy (DOE) 

that collects information on existing electric generating plants and associated equipment to 

evaluate the current status and potential trends in the industry. The source of the information 

comes primarily from the 2007 Electric Generator Report (Form EIA-860) and is supplemented 

by information found in Form EIA-923 and a survey conducted by EPA’s Office of Resource 

Conservation and Recovery (ORCR). In addition, EPA identified two facilities that started 

operations after 2007 and has obtained information about them. 

Collectively, the data sources provided key information for each steam electric plant with 

a NAICS code of 22 such as county, state, North American Electric Reliability Council (NERC) 

region, business size (small or non-small), and regulatory status (i.e., regulated by public service 

commission). Also included is the number of each type of generating unit operated at the plant, 

an identifier that specifies the fuel classification of each generating unit for the plant, and an 

identifier for the plant fuel classification that is based on the fuel classifications of the generating 

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units (e.g., coal, gas-combined cycle, nuclear). In addition, the ORCR survey results and the 

EIA-923 data set provide information on the presence of ponds and landfills at the plant along 

with the materials that are stored or disposed in the pond/landfill. The sample frame also includes 

details on each generating unit reported in the EIA-860 data set classified as a steam electric 

generating unit based on the primary NAICS code, such as prime mover and fuel (fossil or 

nuclear), nameplate capacity (in megawatts), unit fuel classification, and the plant where the 

generating unit is housed. EPA considers that it has created a sample frame for this ICR that is 

complete relative to the defined target population. The sample frame contains information on 

1,203 plants containing 2,589 generating units that are within scope of the data collection 

objectives of the questionnaire. 

2(c) Sample Design 

The steam electric questionnaire is comprised of multiple parts. Some parts of the 

questionnaire focus on gathering general information and financial data from each plant selected 

to receive the questionnaire. Other questionnaire parts are structured to collect technical 

information about certain aspects of power plant operations and will be distributed to a subset of 

the plants receiving the questionnaire. For example, Parts B and C collect information about ash 

handling and FGD operations at coal, oil and petroleum coke plants, while Part H collects 

information about operations at nuclear plants. See Part A, Section 2(b)(i) of this Supporting 

Statement for details on the questionnaire parts and the specific types of plants that would 

receive each part. 

Through this ICR, EPA intends to collect information from the industry using a stratified 

cluster-based sample design. The stratification feature of the design is discussed further below. 

Within each stratum, a cluster sample will be collected. A cluster sample is a probability sample 

in which each sampling unit is a collection, or cluster, of elements from the target population. 

Here the sampling unit is a plant which is comprised of a collection of generating units 

(elements). EPA intends to send the questionnaire to a sample (subset) of plants that is generated 

by implementing the sample design. Each selected plant would be required to complete the 

questionnaire for every generating unit at the plant. By requiring only a subset of plants to 

respond to the questionnaire, the survey burden would be greatly reduced. EPA would select 

plants in a manner that would be statistically representative of all plants in the target population. 

The following subsections describe how the sample frame will be stratified, the 

population sizes for each stratum, the sample selection process, and the precision estimates used 

to derive the estimated sample size. 

(i) Stratification 

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The sample design will stratify plants, primarily by their plant fuel classification and 

regulatory status. Stratification involves selecting one or more characteristics of interest and 

dividing the members of the population into strata based on those characteristics. Stratified 

sampling consists of selecting a sample from within each stratum, then combining them to 

constitute the total sample. There are several benefits that result from a stratified sample design, 

including: 
• Ensuring that the sample contains representatives from every stratum;

• Improving the precision of parameter estimates; 

• Allowing important parameters to be estimated at the stratum level; and 

• Allowing certain subpopulations of particular interest to be sampled at a greater 

rate than others. 

To select plants that would receive questionnaires, EPA intends to use the following stratification 

variables: 

All Plants: 

• Plant Fuel Classification. EPA’s sample frame identifies the plant fuel 

classification for each plant. EPA intends to stratify by plant fuel classification to 

ensure that the sample design selects plants in each fuel type, because there are 

inherent differences due to the type of fuel used at the plant. For those plants 

classified as “Combination”, the sample frame further delineates them by the 

specific fuels that comprise the combination. The plant fuel classification strata 

are as follows: 

oCoal; 

o Petroleum Coke; 

o Gas; 

o Gas-Combined Cycle; 

o Oil; 

o Nuclear; 

oCombination (Gas and Gas-Combined Cycle); 

oCombination (Gas and Oil); 

oCombination (Gas-Combined Cycle and Oil); 

oCombination (Gas and Gas-Combined Cycle and Oil); and 

oCombination (Gas-Combined Cycle and Nuclear and Oil). 

• Regulatory Status. EPA’s sample frame identifies whether the plant is regulated 

or non-regulated. EPA intends to stratify by regulatory status to ensure that the 

sample design selects both regulated and non-regulated plants, due to inherent 

differences between them. Each stratum defined by plant fuel classification will 

be segregated into two strata (regulated and non-regulated). 

Coal and Petroleum Coke Plants: 

EPA’s sample frame includes additional information about coal plants, which will be 

used to select a subset of coal plants that will receive additional questions (i.e., Parts E, F and G 

of the questionnaire). To minimize burden to small entities, EPA will only collect this additional 

information from plants that are not operated by small entities. EPA intends to collect 

information from plants that have ponds and/or landfills containing coal combustion residues 

(i.e., coal ash or flue gas desulfurization (FGD) wastes). The pond/landfill strata are as follows: 

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• Small entities; 

• Non-small entities: 

o Pond only – FGD: Contains all coal plants identified in the sample frame as 

having a pond with FGD waste as one of its contents, but not a landfill; 

o Pond only – no FGD: Contains all coal plants that have an ash pond that 

does not also receive FGD waste, but has no landfill; 

o Landfill only – FGD: Contains all coal plants that have a landfill with FGD 

waste as one if its contents, but no pond containing coal combustion 

residues (CCR); 

o Landfill only – no FGD: Contains all coal plants that have a landfill that 

contains ash but with no FGD wastes, and did not report operating a CCR 

pond; 

o Ponds and landfill: Contains all plants that have both ponds and landfills 

that contain CCR (either ash or FGD wastes). To minimize the number of 

strata, no distinction in plants here is made by FGD status. EPA believes a 

sufficient number of plants with ponds (both with and without FGD waste) 

and landfills (both with and without FGD waste) will be selected from the 

previous four non-small entity strata so that a further breakdown of those 

plants that have both a pond and a landfill is unnecessary; and 

o No Ponds or landfills: Contains all plants that did not report storing or 

disposing of ash or FGD wastes in a pond or landfill. 

In addition to coal plants, petroleum coke plants that are not identified as small entities 

will also receive Parts E, F, and G of the questionnaire. However, insufficient information was 

available to determine which petroleum coke plants had ponds and/or landfills so they will not be 

stratified by pond/landfill status. 

Accounting for NERC Region: 

EPA is also interested in capturing regional differences in the industry as measured by the 

NERC region of the plant. However, rather than stratify the sample frame explicitly by NERC 

region, EPA will assure geographic diversity in the sample by using a systematic sampling 

approach within each stratum. Stratum members will be sorted by NERC region and every k

th

member of the stratum will be selected systematically, (where k is the ratio of the stratum 

population size to the stratum sample size, rounded to the nearest integer). As a result, the 

representation of each NERC region in the sample should be proportional to the size of the 

population. 

In addition, EPA is interested in capturing information from a representative sample of 

plants in terms of plant capacity (as defined by the nameplate capacity of generating units within 

the plant). EPA considered nameplate capacity as a stratification variable in the design but 

decided not to stratify in this manner as preliminary analysis showed that the systematic 

sampling of plants within each stratum described above will provide a distribution of plants in 

terms of capacity that meets EPA’s objectives. 

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(ii) Population Sizes for Each Stratum 

Table B-1 displays the number of plants within the sample frame, as well as the number 

of generating units within these plants, for each type of plant fuel classification and regulatory 

status. For those plants labeled as “Combination,” a further breakdown was done by the specific 

fuels used in the plant. 

Table B-1. Numbers of Plants and Generating Units by Plant Fuel Classification and 

Regulatory Status in Sample Frame 

Plant Fuel 

Classification 

Regulatory 

Status 

Number of Plants 

(Sample Frame) 

Number of 

Generating Units at 

these Plantsa 

Regulated 343 966 

Coal Non-Regulated 150 339 

Unknown 2 2 

Regulated 131 318 Gas Non-Regulated 57 142 

Regulated 95 126 Gas-Combined Cycle Non-Regulated 278 379 

Regulated 31 52 Nuclear Non-Regulated 32 48 

Regulated 23 55 Oil Non-Regulated 20 38 

Regulated 0 0 Petroleum Coke Non-Regulated 9 9 

Combination: Gas-CC Regulated 1 5 

and Nuclear and Oil Non-Regulated 0 0 

Combination: Gas-CC Regulated 2 6 

and Oil Non-Regulated 0 0 

Combination: Gas and Regulated 20 69 

Gas-CC Non-Regulated 6 23 

Combination: Gas and Regulated 1 4 

Gas-CC and Oil Non-Regulated 0 0 

Combination: Gas and Regulated 1 4 

Oil Non-Regulated 1 4 

Total 1,203 2,589 

a Plants can have multiple generating units with different fuel types. For example, of the 1307 

(966+339+2) generating units at coal plants, 103 use something other than coal as their primary or 

secondary fuel. 

Table B-1 indicates that 1,203 fossil- and nuclear-fueled steam electric power plants and 

2,589 generating units exist within the sampling frame. There are 495 coal plants that contain a 

total of 1,307 generating units. Coal plants comprise about 41 percent of all plants, and their 

generating units make up half of all generating units at all plants. Of the 495 coal plants, 303 

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(with 886 generating units) contain a pond and/or landfill containing coal combustion residues. 

Table B-2 displays the number of coal plants and corresponding number of generating units by 

each stratum associated with pond and/or landfill status defined in the previous section. Fiftyfive coal plants are classified as being operated by a small business. These plants, in addition to 

the 143 coal plants that did not report storage or disposal of ash or FGD wastes in a pond and/or 

landfill, are not part of the target population for coal plants that will receive Parts E, F, and G of 

the questionnaire. In addition, EPA has excluded two coal plants containing a total of nine 

generating units from the sample frame for Parts E, F, and G of the questionnaire to limit the 

potential burden imposed on these plants recognizing that they may be required to provide 

additional data not covered by this ICR. 

Table B-2. Numbers of Coal Plants (and Corresponding Generating Units) by Stratum 

in Sample Frame 

Business Size Pond/Landfill Number of 

Coal Plants 

Number of Generating 

Units at these Plants 

Small All 55 121 

Pond Only – FGD 39 122 

Pond Only – No FGD 99 313 

Landfill Only – FGD 18 34 

Landfill Only – No FGD 55 142 

Both Pond and Landfill 84 256 

Non-Small 

No Pond or Landfill 143 310 

Total 493a 1298a

a EPA excluded two coal plants (containing nine total generating units) from the sample frame for Parts E, F, 

and G of the questionnaire.

(iii) Sample Selection 

Most parts of the questionnaire focus on gathering information from all coal and 

petroleum coke-fired power plants. Thus, all plants with a fuel classification of “Coal” or 

“Petroleum Coke” will be selected with certainty (i.e., probability of selection equal to one), 

except for Parts E, F, and G. In addition, for strata with ten or fewer plants, EPA assumed that 

the sample would include all plants, while the minimum number of plants sampled would be ten 

within strata containing more than ten plants. As such, all regulated and non-regulated plants 

with a plant fuel classification of “Combination” (except gas and gas-combined cycle) will also 

be selected with certainty. For the remaining non-regulated and regulated plants with plant fuel 

classifications of gas, gas-combined cycle, oil, nuclear, and combination (gas and gas-combined 

cycle), 30 percent of the plants will be randomly selected to receive the questionnaire while 

adhering to the ten plant minimum per stratum. Based on this sampling design, a total of 734 

plants would be selected to receive the questionnaire. EPA assumes a 10 percent non-response 

rate, based upon EPA’s experience in administering similar effluent guidelines questionnaires, 

which would result in a net sample size of 661. Table B-3 shows the number of plants that 

would be selected to receive the questionnaire by the strata formed by plant fuel classification 

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and regulatory status. EPA has determined that the sample size resulting from this design is 

sufficient to meet the objectives of this survey. 

Table B-3. Number of Plants in Sample Frame and Number of Plants to be Selected for 

Questionnaire, by Plant Fuel Classification and Regulatory Status 

Plant Fuel 

Classification 

Regulatory 

Status 

Number of Plants 

(Sample Frame) 

Number of Plants 

to Sample 

Regulateda 343 343 

Non-Regulateda Coal 150 150 a

Unknowna 2 2 

Regulated 131 39 Gas Non-Regulated 57 17 

Regulated 95 29 Gas-Combined Cycle Non-Regulated 278 83 

Regulated 31 10 Nuclear Non-Regulated 32 10 

Regulated 23 10 Oil Non-Regulated 20 10 

Regulateda 0 0 Petroleum Cokea

Non-Regulateda 9 9 

Regulateda Combination: Gas-CC 1 1 

and Nuclear and Oila Non-Regulateda 0 0 

Regulateda Combination: Gas-CC 2 2 

and Oila Non-Regulateda 0 0 

Combination: Gas and Regulated 20 10 

Gas-CC Non-Regulateda 6 6 

Regulateda Combination: Gas and 1 1 

Gas-CC and Oila Non-Regulateda 0 0 

Regulateda Combination: Gas and 1 1 

Oil* Non-Regulateda 1 1 

Total 1,203 734 a All plants in stratum are to be selected with certainty (probability equal to one). 

The exact number of generating units selected for the sample will not be known prior to 

the sample draw and must be estimated because the number of generating units varies by plant 

and thus will depend on the specific set of plants selected. Generating units within plants that are 

selected with certainty will automatically be included in the sample. For those plants in a 

stratum that will be sampled at 30 percent, EPA estimated the corresponding number of 

generating units as 30 percent of the total number of generating units in the stratum. Table B-4 

displays the number of generating units for each unit fuel classification. For example, of the 144 

oil units in the sample frame, 51 of them are at plants that will be selected with certainty and an 

additional 93 oil units are at plants that are to be sampled at 30 percent. Thus, the number of oil 

units estimated to be selected for the questionnaire is 51 + 0.30 * 93 = 79. Overall, information 

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from approximately 1,714 generating units would be included in the survey based on 734 plants 

selected for the survey. 

Table B-4. Number of Generating Units in Sample Frame and Approximate Number to 

be Selected for Questionnaire, by Unit Fuel Classification 

Unit Fuel 

Classification 

Number of Units 

(Sample Frame) 

Estimated Number of 

Units to be Selected for 

Survey 

Coala 1,206 1,206 

Gas 557 200 

Gas-CC 567 184 

Nuclear 104 34 

Oil 144 79 

Petroleum Cokea 11 11 

Total 2,589 1,714 a All generating units in these unit fuel classifications are at plants selected with certainty 

(probability equal to one). 

Parts E, F, and G of the questionnaire will be sent to all petroleum coke plants and a 

subset of coal and petroleum coke plants operated by non-small entities that contain either a 

pond and/or a landfill containing coal combustion residues (i.e., coal ash or FGD waste). 

(Insufficient information was available to determine which petroleum coke plants had ponds 

and/or landfills, so all three non-small petroleum coke plants will receive Parts E, F, and G.) For 

those strata of coal plants listed in Table B-2 where information is to be collected, 30 percent of 

the plants will be randomly selected to receive parts E, F, and G of the questionnaire. In 

addition, EPA has identified seven coal plants within these strata that have leachate collection 

systems. EPA has decided to sample these seven plants with certainty to ensure information on 

leachate collection systems is captured in the questionnaire responses. These seven plants will 

be included in the sample selection process so that a total of 30 percent of coal plants will be 

selected. Based on these calculations, a total of 94 coal plants would be selected to receive parts 

E, F, and G of the questionnaire. Table B-5 shows the number of coal plants that would be 

selected to receive parts E, F, and G of the questionnaire by stratum. Assuming a 10% nonresponse rate within each stratum, EPA expects a net sample size of 85 plants. As a result of 

these calculations and assumptions, EPA estimated that having 94 coal plants receive parts E, F, 

and G of the questionnaire would meet its objectives. 

The exact number of generating units selected for the sample will not be known prior to 

the sample draw and must be estimated as the number of generating units varies by plant and 

thus depends on the specific plants selected. Within each stratum, the ratio of generating units to 

plants in the sample frame was multiplied by the number of sampled plants to estimate the 

number of generating units selected for the sample. For example, on average, there are 

122/39=3.13 generating units per coal plant for pond only coal plants with FGD wastes in the 

pond. Thus, the estimated number of generating units in the sample for this stratum would be 

3.13 * 12 sampled plants = 38 generating units. The final two columns of Table B-5 display the 

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number of generating units in the sample frame from coal plants as well as the approximate 

number of generating units from coal plants for parts E, F, and G of the questionnaire. As a 

result of these calculations, approximately 272 generating units from coal plants would be 

represented in parts E, F, and G of the questionnaire. 

Table B-5. Numbers of Coal Plants (and Corresponding Generating Units) by Stratum 

in the Sample Frame as well as to be Selected for Parts E, F, and G of the 

Questionnaire 

Business 

Size Pond/Landfill 

Number 

of Coal 

Plants 

(Sample 

Frame) 

Number of 

Coal Plants 

Selected for 

Parts E, F, and 

G of 

Questionnaire 

Number of 

Generating 

Units at the 

Coal Plants in 

Sample Frame 

Estimated 

Number of 

Generating 

Units in 

Sample 

Small All 55 0 121 0 

Pond Only – FGD 39 12 122 38 

Pond Only – No 

FGD 

99 30 313 95 

Landfill Only – 

FGD 

18 10 34 19 

Landfill Only – 

No FGD 

55 17 142 44 

Both Pond and 

Landfill 

84 25 256 76 

Non-Small 

No Pond or 

Landfill 

143 0 310 0 

Total 493 94 1298 272 

Note that Table B-5 only contains information on coal plants. Also, there are three 

petroleum coke plants operated by non-small entities (each having one generating unit) that will 

be sent parts E, F, and G of the questionnaire. In addition, Part E (but not Parts F and G) will be 

sent to the 230 oil, gas, nuclear, gas-combined cycle, and combination plants identified in the 

final column of Table B-3 that would be selected for the overall questionnaire. 

Table B-6 below provides the summary of the design. 

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Table B-6. Summary of Population, Sample and Subsample Sizes 

Stratum Number of Plants in: 

Population Sample Subsample 

Coal – Small business 55 - 0 

Coal – Pond Only –FGD 39 - 12 

Coal – Pond Only –no FGD 99 - 30 

Coal – Landfill Only – FGD 18 - 10 

Coal – Landfill Only – No FGD 55 - 17 

Coal – Both Pond and Landfill 84 - 25 

Coal – No Pond and Landfill 143 - 0 

Gas 188 56 - 

Gas-Combined Cycle (CC) 373 112 - 

Nuclear 63 20 - 

Oil 43 20 - 

Pet Coke 9 9 - 

Combination: Gas-CC and Nuclear and 

Oil 1 1 - 

Combination: Gas-CC and Oil 2 2 - 

Combination: Gas and Gas-CC 26 16 - 

Combination: Gas and Gas-CC and Oil 1 1 

Combination: Gas and Oil 2 2 

Total 1201 239 94 

 

The population size is the number of plants in the stratum. From the population, we selected a 

sample to receive the questionnaire. The subsample will be required to respond to some 

additional parts of the questionnaires. 

(iv) Precision Estimates for the Given Sample Sizes 

Because a sample of plants will be given the questionnaire rather than all plants within 

the target population, it follows that some degree of uncertainty will be associated with estimates 

made from the data collected from the questionnaires. The precision of these estimates depends 

on both the sample design and the sample size – that is, the number of plants that would be 

selected. One measure of precision is the width of the confidence interval for the estimate. 

Confidence intervals provide a range of values for a particular estimate that would be likely if the 

study were repeated an infinite number of times. Thus, when using 95 percent confidence 

intervals, 95 percent of such intervals would include the true value, if we could take an infinite 

number of samples. The binomial distribution is often used as the basis of sample designs and 

can be used to estimate precision. The binomial distribution applies to situations where there are 

only two outcomes (yes or no) to a dichotomous question such as “Are residues generated by 

cleaning operations?” 

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The presence or absence of the attribute for a particular plant is a dichotomous, or binary, 

variable. The binomial distribution models these data based on the notion of obtaining national 
estimates of the percentage or proportion of plants in the target population (or a subset of the 

target population) that have a particular attribute. The binomial distribution also provides 

estimates of the variance that is used to calculate the confidence intervals. Because a proportion 

of 0.5 (or 50 percent) results in the largest possible variance for the binomial distribution, EPA 

assumed that the probability of one outcome would be 0.5 (e.g., cleaning operation residues are 

generated at 50 percent of the plants). In other words, if the population value is any value other 

than 50 percent, the survey estimate will be more precise – in statistical expectation – than it 

would be if the population value is 50 percent. 

Because EPA is developing a national rule, it is primarily concerned with the precision of 

the overall plant-level and generating unit-level estimates, rather than estimates made within 

strata. Consequently, in estimating the overall sample size, EPA assumed more stringent 

requirements for overall plant-level and generating unit-level estimates than estimates for 

specific plant fuel or unit fuel classifications. Given a sample size of 734 plants described in the 

previous section, EPA would expect to receive completed questionnaires for 661 plants 

(assuming a 10 percent non-response rate). Under these assumptions, the sample would be 

expected, with 95 percent confidence, to yield sufficient data to estimate the value of an 

unknown proportion to within +/- 3.5 percent of its true value for the target population (i.e., 

plants). For example, if 30 percent of the responding plants indicate they generate cleaning 

residues, then there is 95 percent confidence that 30 percent +/- 3.5 percent (i.e. between 26.5 

percent and 33.5 percent) of the entire population of plants generate cleaning residues. 

Based on estimated sample of 1,714 generating units, the sample (similarly accounting 

for plant non-response) would be expected, with 95 percent confidence, to yield sufficient data to 

estimate the value of an unknown proportion to within +/- 2.5 percent of its true value for the 

target population (i.e., generating units). For example, if 30 percent of the generating units 

generate cleaning residues, then there is 95 percent confidence that 30 percent +/- 2.5 percent 

(i.e. between 27.5 percent and 32.5 percent) of the entire population of generating units generate 

cleaning residues. The precision estimates associated with national plant-level and unit-level 

estimates are calculated based on proportion estimates from Part I of the questionnaire, a part 

sent to all sampled plants. Other questionnaire parts (e.g., Parts B through H) will be sent to only 

a subset of the plant fuel classifications and thus will have a smaller sample size (and, as a result, 

less precision). 

Based on the sample size of 94 coal plants with a pond and/or landfill for parts E, F, and 

G of the survey, EPA would expect to receive completed questionnaires for 85 of these plants 

(assuming a 10 percent non-response rate). Under these assumptions, the sample would be 

expected, with 95 percent confidence, to yield sufficient data to estimate the value of an 

unknown proportion to within +/- 9.2 percent of its true value for the target population (i.e., coal 

plants with ponds/landfills). For example, if 30 percent of the coal plants collect landfill 

leachate, then there is 95 percent confidence that 30 percent +/- 9.2 percent (i.e. between 20.8 

percent and 39.2 percent) of the entire population of coal plants with a pond or landfill collect 

landfill leachate. 

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All of these precision targets will hold when the proportion’s true (unknown) value is 

equal to 0.5, and even greater precision is expected when the true value of the proportion is not 

equal to 0.5. 

2(d) Sources of Error 

In developing the sample design, as described previously, EPA considered the estimated 

precision targets for data collected from the target population. EPA also considered potential 

error that could be associated with estimates calculated from the collected data, due to sources 

associated with sampling, such as response rates, as well as non-sampling sources of error, such 

as processing error. 

(i) Response Rates 

In developing the sample design, EPA considered both unit (questionnaire) and item 

(question) non-response. EPA expects that the response rate would be relatively high for this 

mandatory survey effort, which would be conducted under the authority of Section 308 of the 

Clean Water Act. The cover letters and instructions for the questionnaire would explain the legal 

authority, responsibility to respond, reasons for the questionnaire, and penalty for non-response. 

EPA would use reminder letters and/or telephone calls to remind respondents of the duty to 

respond under Section 308 of the Clean Water Act. If possible, EPA would seek the 

endorsement of the major trade associations, which would be expected to increase the response 

rate from its members. EPA recognizes that some non-response is unavoidable, and in past 

survey efforts, EPA has waived the duty to respond in extreme and rare cases (e.g., natural 

disasters) which also might occur for this survey effort. 

The sample size estimates presented in Section 2(c)(iii) have been adjusted to help ensure 

that the effective sample sizes (i.e., respondents) would be sufficient for precision requirements 

when the non-response rate equals 10 percent. (This assumption of a 10 percent non-response 

rate is based upon a typical effluent guidelines questionnaire.) In addition to increasing the 

initial sample size, EPA would strive to improve the response rate by reminder letters and/or 

telephone calls. Furthermore, after receiving the responses, EPA intends to adjust the 

questionnaire weights for any non-response and to review publicly available information in order 

to determine if non-respondents appear to have different characteristics than respondents. EPA 

would examine these characteristics both for the entire industry and for subgroups in the 

analyses. For any differences, EPA intends to determine the major causes, and to incorporate 

appropriate adjustments for bias. (Bias is the difference between the expected value of an 

estimate and the true value of a parameter or quantity being estimated. If the data collection 

process generates estimates that are consistently (or on average) above or consistently below the 

true value, the data collection process is biased.) 

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To minimize item non-response, EPA’s subject matter experts have worked closely with 

industry to develop questions that would be easy to understand with clearly defined and familiar 

terms, are formatted in a logical sequence, and would request data that are readily available 

within the industry. In this manner, EPA expects to minimize inaccurate or incomplete response 

of the questions that can occur due to misunderstanding or misinterpretation of questions and the 
unintentional skipping of questions by respondents. Additionally, EPA would operate an e-mail 

helpline to assist respondents with the questionnaire. After receipt of the completed 

questionnaires, EPA intends to conduct extensive follow-up with respondents for any item nonresponse. If necessary, EPA would impute responses to key questions in our analyses. 

(ii) Processing Errors 

Processing errors can occur when questionnaire responses are coded, edited, and entered into the 

database. The design and implementation of the questionnaire database would employ a number 

of quality assurance techniques to reduce the frequency of such errors. These techniques would 

include the following: 

• Electronic questionnaires will directly transfer responses into a survey database 

• Computerized comparison of selected responses to detect inconsistencies and 

illogical responses; 

• Computerized analyses to screen for out-of-range and inconsistent numerical 

values; and 

• Computerized analyses to detect missing numerical data and missing units. 

3. PRETESTS AND PILOT TESTS 

EPA does not intend to pre-test the questionnaire. For more than 30 years, EPA’s 

Engineering and Analysis Division has conducted surveys of numerous industrial sectors to 

collect information to support regulation development activities in the effluent guidelines 

program. While EPA develops different questionnaires for each industry, there are common 

elements for all industries. The questionnaires collect the same basic data such as information 

about processes, treatment, and financial status. Thus, when EPA develops a questionnaire for a 

particular industry, it generally tailors the questions for specific terms and processes used by that 

industry. In past years, EPA has relied predominantly on active participation by trade groups in 

reviewing the questionnaires. In EPA’s experience, such collaboration generally tends to better 

reflect the industry at large than pre-tests. For this reason, EPA considers additional review 

through the pre-test process to be unnecessary for this industry. 

4. COLLECTION METHODS AND FOLLOW-UP 

Please See Part A, Section 5(b) of this ICR for this information. 

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5. DATA PREPARATION AND ANALYSIS 

5(a) Data Preparation 

Upon receipt of completed questionnaires, EPA and its contractors would review the 

questionnaires for completeness and CBI claims. All questionnaires will also be reviewed for 

consistency and reasonableness and follow-up calls will be conducted as needed to clarify 

inconsistencies found in the responses. Reviewed questionnaire files will then be uploaded into 

the questionnaire database. Once the data are uploaded into the database, numerous electronic 

QA activities would be performed and the results would be provided to engineering and 

economic staff for further resolution and documentation. This database would then be used to 

perform data analyses. 

5(b) Analysis 

In support of making decisions that will affect rulemaking, EPA will use the responses 

from this questionnaire to help answer the following questions: 

• What pollutants are currently discharged by power plants and what 

technologies/practices are being used to treat power plants wastestreams? 

• Are process changes, BMPs, treatment technologies, or recycle/reuse processes 

feasible options to reduce pollutant discharges from steam electric power plants? 

• Is subcategorization of the steam electric power generating industry appropriate, 

and if so, what is the correct subcategorization? 

• What are the available technologies for reducing pollutant discharges associated 

with waste streams of concern, such as FGD scrubber purge, ash handling, 

process equipment cleaning wastes, and other wastewaters? 

• What pollutant reductions and other benefits would be realized by implementing 

candidate regulatory options? 

• What are the costs for operators to implement technologies, process changes, and 

best management practices to reduce pollutant discharges? How do these costs 

impact the economics of the steam electric industry? 

The objectives of the information collection would be achieved by the statisticallydesigned sample survey because the resulting inferences and analyses would be as statistically 

unbiased and as precise as is practicable. EPA intends to apply sample weights derived from the 

statistical sample design and adjust for non-response to the data during statistical analysis. 

Weighting the data would allow inferences to be made about all eligible plants and generating 

units, including those that did not respond to the questionnaires. Another advantage is that 

weighted estimates would have smaller variances than unweighted estimates. EPA also intends 

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to evaluate whether estimates could be improved by post-stratifying the detailed questionnaire 

data using the data collected from the survey. EPA would use accepted statistical methods for 

survey statistics, such as those described in Sampling Techniques (Cochran, 1977) and Survey 

Sampling (Kish, 1965). 

See Part A, Section 2(b) of this Information Collection Request for a detailed discussion 

of the technical and economic analyses. 

EPA intends to use the following contractors to assist in conducting this survey: 

Sample Frame Preparation and Analysis: 

Eastern Research Group 

14555 Avion Parkway 

Suite 200 

Chantilly, VA 20151 

Questionnaire Development and Analysis Support (Financial/Economic Data)

Abt Associates Inc. 

55 Wheeler Street 

Cambridge, MA 02138 

Statistical Design and Analysis: 

Battelle 

505 King Avenue 

Columbus, OH 43201 

6. REFERENCES 

Cochran, W.G. (1977). Sampling Techniques. New York: Wiley. 

Kish, L. (1965). Survey Sampling. New York: Wiley.