MEMORANDUM 

From: William Swietlik, USEPA/OW/OST 

Ph: (202) 566-1129, Swietlik.william@epa.gov 

To: Public Docket for the Preliminary 2016 Effluent Guidelines Program Plan 

EPA Docket Number EPA-HQ-OW-2015-0665 (http://www.regulations.gov) 

Date: February 16, 2016 

Re: Summary of Methodology for Handling Non-Detect Data: 304m and Steam Electric 

Power Generating 

As part of its 2015 Annual Review of effluent limitations guidelines and standards 

(ELGs), EPA performed a toxicity ranking analysis (TRA) of all industrial categories, including 

those subject to existing ELGs and those not currently regulated by ELGs, consistent with the 

methodology described in Section 2 of the 2015 Annual Effluent Guidelines Review Report

(2015 Annual Review Report) (U.S. EPA, 2016). For its annual reviews, EPA relies on discharge 

monitoring report (DMR) data reported to the Integrated Compliance Information System for the 

National Pollutant Discharge Elimination System (ICIS-NPDES) and Toxics Release Inventory 

(TRI) data downloaded from the DMR Pollutant Loading Tool1

. While these data sets represent 

the best available existing data EPA has to evaluate pollutants in industrial wastewater discharge, 

the data are derived differently and in many cases, provide limited qualifying information 

regarding reported non-detect values. Recognizing the limitations of the data sets, EPA 

established an approach for handling non-detect data for the purpose of its 304m annual reviews, 

as initially outlined in the 2009 Technical Support Document for the Annual Review of Existing 

Effluent Guidelines and Identification of Potential New Point Source Categories (2009 

Screening Level Analysis or “SLA” Report) (U.S. EPA, 2009). 

This memorandum summarizes EPA’s established methodology for handling non-detect 

data for the purpose of its 304m annual reviews and compares that methodology to the 

methodology EPA used in the Final Rule for the Steam Electric Power Generating Effluent 

Guidelines (80 FR 67838). EPA acknowledges that in certain aspects the 304m methodology for 

handling non-detect data may be different than the methodology employed for ELG rulemakings; 

most recently for the Steam Electric Power Generating ELG, which is appropriate given the data 

and information available and the purposes of the analyses. Furthermore, in the rulemaking 

context, for non-detect data, EPA often has access to qualifying information from the laboratory 

it can use to more accurately characterize non-detect discharges. 

                                                            

1 See http://cfpub.epa.gov/dmr/.
Memorandum 

February 16, 2016 

Page 2 

1.1 Terminology 

For the purpose of this memorandum, EPA references the following terms (as defined for 

the Steam Electric Power Generating rulemaking): 

 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 

ELG support documents as the reporting limit. 

 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. 

 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. 

1.2 Non-Detect Methodology 

1.2.1 304m Non-Detect Methodology for DMR data 

For 304m, EPA uses DMR data (e.g., concentrations, quantities, flows) reported in ICISNPDES to calculate annual pollutant loadings. 

NPDES dischargers report a value and, if appropriate, a qualifier (e.g., =, <, >) for each 

monitoring period (for each pollutant and outfall) to their EPA or state permit program. EPA or 

state permit programs review the DMRs and upload the raw data into ICIS-NPDES. As stated in 

the DMR Pollutant Loading Tool FAQs,2 ICIS-NPDES allows EPA and state permit programs to 

identify pollutant concentrations that are below detection (e.g., commonly the QL, but could also 

be the MDL) by using a “less than” qualifier (<). However, ICIS-NPDES only allows EPA and 

states to identify a single value and qualifier when pollutant monitoring data are below detection, 

eliminating the ability to report all pertinent laboratory information (e.g., MDL, QL, J-value). 

The following is a common data entry procedure used to accommodate the system requirement 

to only report one value and one qualifier for monitoring data that are below detection; however, 

there are no standards or guidance for reporting: 

 “0” (the number zero) in the value field and the “=” qualifier when the pollutant 

concentration is below the MDL. 

                                                            

2

 See http://cfpub.epa.gov/dmr/faq.cfm. 
Memorandum 

February 16, 2016 

Page 3 

 The QL in the value field and the “<” qualifier when the pollutant concentration is below 

the QL. 

The DMR Pollutant Loading Tool employs one of two options in calculating annual 

pollutant loadings that include results identified as below detection (which could be reported as 

the QL or MDL). All other reported values with qualifiers (e.g., =, >) are treated as the specific 

value reported. 

 If all monitoring period concentrations or quantities reported for the calendar year have a 

less than qualifier (<), the total annual load is set to zero. 

 If at least one monitoring period concentration or quantity reported during the year does 

not have a “<” qualifier (i.e., the pollutant is detected at least once), the total calculated 

annual load is estimated using one half of the reported value for qualified concentrations 

or quantities and the reported values for detected results. 

This methodology is consistent with the established 304m annual review methodology as 

described in the 2009 SLA Report (U.S. EPA, 2009). 

Analytical methods used for DMR data are specified in a facility’s NPDES permit. The 

standard conditions of the permit require that, when available, permittees use test procedures 

specified in 40 CFR Part 136. EPA also allows NPDES regulated facilities to use alternate 

analytical wastewater methods.3 However, information about the laboratory analytical methods is 

not collected on DMRs, which means that EPA cannot identify the laboratory analytical methods 

used by NPDES dischargers in the raw data. 

1.2.2 304m Non-Detect Methodology for TRI data 

For TRI data, the facilities report estimated annual loadings associated with releases to 

surface waters and POTWs. These annual loadings can be based on engineering estimates or 

specific monitoring data. Unlike DMR, EPA does not calculate annual loadings for TRI data 

based on concentration, quantity, or flow data for a reporting period, as these data are not 

available in the raw TRI dataset. 

If a facility uses monitoring data to estimate annual loadings for TRI, TRI guidance 

suggests facilities use one half the detection limit to estimate annual loadings associated with 

non-detect results, except for certain pollutants. For example, current TRI guidance for dioxin 

suggests using a value of zero for non-detect results instead of one half the detection limit, if that 

is how the method being used treats non-detects (e.g., EPA Method 1613). Because the facilities 

report the estimated releases directly to TRI, the details about the underlying estimation method 

and monitoring data are unknown (e.g., analytical method, QL, MDL). EPA notes that the use of 

one half the detection limit is not applied consistently to TRI data (as it is up to the facility 

                                                            

3 See http://www.epa.gov/cwa-methods/alternate-test-procedures.
Memorandum 

February 16, 2016 

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reporting the releases to determine how to report and how to apply the TRI guidance), unlike 

EPA’s methodology for calculating pollutant loadings from DMR data described above. 

In general, for the annual 304m screening-level review process, EPA uses the loads 

reported to TRI as is and does not make any adjustments to them. However, EPA may contact 

facilities to confirm TRI discharges for data that appear to be outliers. During these contacts, 

EPA may ask to review any monitoring data used to estimate releases or ask if all sampling 

results associated with the pollutant in question were below detection. For only these outlier 

facilities, if EPA identifies that all monitoring data for a specific pollutant are non-detect, the 

load is zeroed, consistent with the methodology applied to the DMR data. EPA notes that this 

methodology is only applied to the small percentage of facilities that are contacted during the 

outlier review and have monitoring data. 

1.2.3 Steam Electric Rulemaking Power Generating Non-Detect Methodology 

For the Steam Electric Power Generating rulemaking (for all wastestreams), EPA’s 

estimates of baseline pollutant loadings and pollutant removals were derived using one half of 

the sample-specific QL (i.e., the reporting limit) for all qualified results (U-Qualified or JQualified), as illustrated in Figure 1 (U.S. EPA, 2015). 

Figure 1. Steam Electric Methodology for Estimating Baseline Pollutant Loadings and 

Removals 

 

EPA was able to determine the QL for all qualified results in the FGD data set that EPA 

used in pollutant loadings/removal calculations because the QL was available in the EPA 

sampling and industry-submitted data. In some instances, for fly ash and bottom ash transport 

water, there were insufficient data available to determine the respective sample-specific QL. In 

these instances the data point was reported as a “less than” result along with a value, but EPA did 

not know whether the reported value was the sample-specific MDL or QL. For the purpose of 

estimating pollutant loadings and removals, EPA assumed the reported value was the QL and 

used one-half that value in the calculations. For both FGD and ash, EPA only calculated 

wastestream-specific pollutant loadings for pollutants with at least one detection in the 

concentration dataset. EPA did not use data where all the data points in the data set were reported 

as qualified. EPA also completed a data quality review to determine if the data were acceptable 

for use in the pollutant loadings calculations. This review included a specific review of 

acceptable analytical methods (U.S. EPA, 2015). 

QL

(4.0)

0 MDL

(1.2)

1⁄2 QL

(2.0)

U-Qualified Result J-Qualified Result
Memorandum 

February 16, 2016 

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1.3 Data Limitations and Considerations 

 The DMR data in ICIS-NDPES do not include the analytical method; therefore, EPA 

cannot confirm the reported value for below detection results (e.g., MDL, QL), unlike the 

data reviewed and used in the Steam Electric Power Generating rulemaking. 

 For DMRs, facilities or EPA and state data entry personnel may enter zero for results 

below the MDL, and in those instances, zero is used in the load estimations. Facilities 

may also report averaged data on DMRs, which are also not flagged in the raw ICISNPDES data. 

 EPA only contacts a small number of outlier facilities to confirm discharges when 

reviewing loads for TRI. This is the only instance where EPA may zero a load based on 

non-detect monitoring data in TRI (as it is not available in the raw data and can only be 

collected during follow up). During these follow up calls, EPA may consider requesting 

the analytical method for the monitoring results to compare to the list of methods at 40 

CFR Part 136 to confirm that they are sufficiently stringent and that zeroing the loads is 

appropriate. 

 Because the 304m annual review is a screening-level review with a specific analytical 

purpose and objective, the current methodology is appropriate so that the rankings aren’t 

biased by pollutants that are all non-detect (i.e., dioxin). 

1.4 References 

1. U.S. EPA. 2009. Technical Support Document for the Annual Review of Existing 

Effluent Guidelines and Identification of Potential New Point Source Categories. EPA821-R-09-007. Washington, D.C. (October). EPA-HQ-OW-2008-0517-0515. 

2. U.S. EPA. 2015. Incremental Costs and Pollutant Removals for the Final Effluent 

Limitations Guidelines and Standards for the Steam Electric Power Generating Point 

Source Category. Washington, D.C. (September). EPA-HQ-OW-2009-0819-6472. 

3. U.S. EPA. 2016. 2015 Annual Effluent Guidelines Review Report. Washington, D.C. 

(June). EPA-821-R-16-002. EPA-HQ-OW-2015-0665. DCN 08209.