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MEMORANDUM 

TO: Steam Electric Rulemaking Record 

FROM: Dan-Tam Nguyen 

DATE: July 28, 2015 

SUBJECT: Evaluation of Alternatives for Handling Qualified Analytical Data in the 

Steam Electric Pollutant Loadings 

 

1 Introduction 

For the Steam Electric Rulemaking, EPA collected analytical data from various data sources, 

including EPA’s field sampling and CWA 308 monitoring programs, EPA’s detailed survey for 

the industry, public comments, industry reports, and plant-monitoring data. Depending on the 

source, analytical data can be qualified based on how the concentration compares to samplespecific detection or quantitation limits determined by either the analytical method or the 

instrumentation used to test the wastewater sample. EPA defines the following terms: 

 Method Detection Limit (MDL): The minimum concentration of a substance that can be 

measured and reported with 99 percent confidence that the analyte concentration is 

greater than zero. 

 Quantitation Limit (QL): The minimum concentration of a substance that can be 

reported with a specified degree of confidence that the analyte concentration is less than 

that minimum concentration and greater than the MDL. The QL can be no lower than the 

concentration of the lowest initial calibration standard. The QL is often referred to in 

Effluent Limitation Guidelines and Standards (ELG) support documents as the reporting 

limit. 

Analytical laboratories generally qualify sample results when the measured analyte 

concentrations are below the MDL and/or below the QL (hereafter, termed as “qualified 

results”). As defined below, the analyte concentrations can be qualified as a U-qualified result or 

a J-qualified result, generally designated with a “U” or “J” qualifier, respectively. 

 U-Qualified Result or Non-Detect: The observation below the MDL, often reported as 

“U” by the analytical laboratory. EPA generally refers to this value as a non-detect. 
   

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 J-Qualified Result: Observations reported with an estimated value and associated “J” 

flag by the analytical laboratory, indicating a definitive observation of the analyte in the 

sample that is measured above the MDL but below the lowest initial calibration point. 

Analytical data1 from EPA’s sampling and monitoring programs included information on both 

qualified- and J-qualified results and their related MDLs and QLs; however, data from other 

sources contained varying levels of this information. This memorandum summarizes EPA’s 

methodology and three alternative approaches for handling the varying levels of MDL and QL 

information for qualified results in pollutant loadings and removals estimates. To evaluate the 

differences, EPA calculated pollutant loadings and removals using the three alternative 

approaches and compared the results to the pollutant loadings EPA calculated for the final rule. 

2 EPA Methodology for Handling Qualified Results for the Final Rule 

For all wastestreams, EPA’s estimates of baseline pollutant loadings and pollutant removals for 

the final rule use one half the sample-specific QL (or reporting limit) for all qualified results 

(example shown in Figure 1). 

Figure 1. Example Using EPA Approach for Handling Qualified Results (in bold)

This approach allows EPA to use a consistent methodology for all wastestreams and for all data 

sources using the QL, which was largely available for the analytical data EPA collected. 

Additionally, using “1⁄2 QL” results in a greater probability of some results being above the value 

used in the loadings and some being below the value used in the loadings. The QL is known for 

all qualified results in the FGD data set that EPA used in pollutant loadings/removal calculations. 

However, for fly ash and bottom ash transport water, there are qualified results where there are 

insufficient data available to determine the respective sample-specific QL. In these instances the 

observation is reported as a “less than” result along with a value, but EPA does not know 

                                                            

1 EPA used all data that met its data quality criteria in the calculation of pollutant loadings for the final rule; see the 

Technical Development Document for the Final Effluent Limitations Guidelines and Standards for the Steam 

Electric Power Generating Point Source Category (EPA 821-R-15-007) for more details on these data quality 

criteria.

QL

(4.0)

0 MDL

(1.2)

1⁄2 QL

(2.0)

J-Qualified Result U-Qualified Result
   

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whether the reported value is the sample-specific MDL or QL. For the purpose of estimating 

pollutant loadings and removals, EPA assumed the reported value is the QL and used one-half 

that value in the calculations. 

Although a J-value is the laboratory’s best estimate of the analyte concentration for a J-qualified 

result, EPA chose not to use the estimated J-value associated with J-qualified values because it is 

a measurement made below the lowest point on the initial calibration curve (i.e., QL), and thus, a 

J-value has greater uncertainty than the MDL and QL associated with its result. 

3 Alternative Approaches Considered for Handling Qualified Results 

EPA considered three alternative approaches for handling the qualified results that were included 

in baseline loadings and pollutant removals calculations: 

1. Include U-qualified results at a concentration equal to one half the MDL and Jqualified results at a concentration equal to the midpoint between the MDL and 

QL. 

2. Include U-qualified results at a concentration equal to one half the MDL and Jqualified results at a concentration equal to the reported J-values. 

3. Include U- and J-qualified results at a concentration equal to the QL. 

Each of these alternative approaches is described in detail below. 

Alternative Approach 1 

This alternative approach sets U-qualified results at a concentration equal to one half the MDL 

and J-qualified results at a concentration equal to the midpoint between the MDL and QL (i.e., 1⁄2 

(MDL+QL)), as illustrated in Figure 2. 

 Figure 2. Example Using Alternative Approach 1 for Handling Qualified Results (in bold) 

Alternative Approach 1 requires knowledge of both the QL and the MDL and can only be used 

in instances when both values are provided in the data. EPA field sampling and CWA 308 data 

QL

(4.0)

0 MDL

(1.2) Midpoint between 

QL and MDL

(2.6)

U-Qualified Result J-Qualified Result

1⁄2 MDL

(0.6)
   

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and a limited amount of industry data include both values. For purposes of this analysis, for all 

remaining industry data where the MDL is unknown for qualified results, EPA set the qualified 

results equal to 1⁄2 QL. Where there are insufficient data available to determine the respective 

sample-specific QL, EPA used the approach described in Section 2. 

Alternative Approach 2 

This alternative approach sets U-qualified results at a concentration equal to 1⁄2 the MDL and Jqualified results at a concentration equal to the reported J-values, as illustrated in Figure 3. 

 

Figure 3. Example Using Alternative Approach 2 for Handling Qualified Results (in bold) 

Similar to Alternative 1, this alternative requires knowledge of both the QL and the MDL and 

can only be used when these two values are provided in the data. For all non-detects where the 

MDL is unknown and for J-qualified results without reported J-values, EPA set the concentration 

equal to 1⁄2 QL. Where there are insufficient data available to determine the respective samplespecific QL, EPA used the approach described in Section 2. 

Alternative Approach 3 

This alternative approach sets all U- and J-qualified results equal to the QL, as shown in Figure 

4. For data where the QL is not available, EPA set the qualified results equal to the MDL. 

Although Alternative Approach 3 would allow for use of a consistent methodology for all 

wastestreams and across all data sources like in the methodology EPA used for the final rule, 

using the QL for all qualified results overestimates the baseline and option loadings because all 

qualified results are actually measured with a specified degree of confidence below the QL. 

QL

(4.0)

0 MDL

(1.2) Reported J-value 

U-Qualified Result J-Qualified Result

1⁄2 MDL

(0.6)
   

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Figure 4. Example Using Alternative Approach 3 for Handling Qualified Results (in bold) 

4 Comparison of EPA’s Approach to Alternative Approaches on Pollutant Loadings and 

Removals 

EPA performed pollutant loadings and removals calculations for each wastestream and 

technology option using each of the three alternative approaches for handling qualified results. 

EPA compared the resulting pollutant loadings and removals against those used for the final 

ELG. 

QL

(4.0)

0 MDL

(1.2)

J-Qualified Result U-Qualified Result
   

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Table 1 presents a summary of the difference in pollutant loadings and removals for FGD 

wastewater and 

Table 2 presents a summary for fly ash and bottom ash transport water. 

Based on the results of this comparison, EPA determined that using any of the alternative 

approaches for FGD wastewater resulted in small variations in pollutant loadings and removals 

from EPA’s approach. Alternative Approaches 1 and 2 also resulted in small variations from 

EPA’s approach for fly ash and bottom ash transport water, although Alternative Approach 3 

showed a larger increase in TWPE pollutant loadings and removals. As discussed earlier in this 

memo, EPA does not favor this approach because all qualified results are actually measured with 

a specified degree of confidence below the QL; therefore, using the full QL in this alternative 

approach for all qualified results tends to overestimate the estimated baseline and option 

loadings. 
   

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Table 1. Comparison of EPA and Three Alternative Pollutant Loadings and Removals for 

FGD Wastewater 

Alternative 

Approach Technology Option 

% Change in Pollutant 

Loadings 

Relative to Final ELG 

% Change in Pollutant 

Removals Relative to 

Final ELG 

lbs TWPE lbs TWPE 

1 

Baseline -0.00015 -0.085 NA NA 

Chemical Precipitation -0.00010 -0.31 -0.00039 0.18 

Biological Treatment -0.00010 -0.35 -0.00040 0.15 

2 

Baseline -0.00032 -0.090 NA NA 

Chemical Precipitation -0.00036 -0.30 -0.00008 0.16 

Biological Treatment -0.00036 -0.34 -0.00012 0.13 

3 

Baseline 0.0020 0.47 NA NA 

Chemical Precipitation 0.0037 0.82 -0.0069 -0.036 

Biological Treatment 0.0037 0.98 -0.0069 -0.012 

Table 2. Comparison of EPA and Three Alternative Pollutant Loadings and Removals for 

Fly Ash and Bottom Ash Transport Water 

Alternative 

Approach Technology Option 

% Change in Pollutant 

Loadings 

Relative to Final ELG 

% Change in Pollutant 

Removals Relative to 

Final ELGa

lbs TWPE lbs TWPE

1 Fly Ash Transport Water Baseline 0.00 0.00 0.00 0.00 

Bottom Ash Transport Water Baseline 0.00000027 0.21 0.00000027 0.21 

2 Fly Ash Transport Water Baseline 0.00 0.00 0.00 0.00 

Bottom Ash Transport Water Baseline -0.0000032 -0.053 -0.0000032 -0.053 

3 Fly Ash Transport Water Baseline 0.078 15 0.078 15 

Bottom Ash Transport Water Baseline 0.15 37 0.15 37 

a - The change in the removals for fly ash and bottom ash transport water are approximately equal to the change in 

the baseline loadings because it is a zero discharge option. However, there are some plants that will continue to 

discharge fly ash and bottom ash transport water after implementation of the rule because they are generating 

units with a capacity of 50 MW or less, or oil-fired generating units, that are not facing any more stringent 

requirements than already exist under the previously established best practicable control technology currently 

available (BPT) regulations.