December 13, 2011(revised April 5, 2012)

Note:

Subject: Data and procedure for handling below detection level data in analyzing various 

pollutant emissions databases for MACT and RTR emissions limits

To: SPPD management and MACT rule writers

From: Peter Westlin, SPPD, MPG

Raymond Merrill, AQAD, MTG

This is a note regarding the handling of below detection level (BDL) data and in developing 

representative detection level (RDL) data in evaluating the floor and setting emissions limits for 

your NSPS, MACT, and RTR rule making projects. At the end of this note is a table which 

includes several updates. The updates include corrected values for metals RDL, an easier to use 

table (e.g., sample volume versus sampling time) and some pollutants not covered in the initial 

table (e.g., HCl and filterable PM).

The RDL determination procedure

The revised procedure for determining an RDL starts with identifying all of the available 

reported pollutant specific method detection levels for the best performing units regardless of 

any subcategory (e.g., existing or new, fuel type, etc.). From that combined pool of data, we 

calculate the arithmetic mean value. By limiting the data set to those tests used to establish the 

floor or emissions limit (i.e., best performers), we believe that the result is representative of the 

best performing testing companies and laboratories using the most sensitive analytical 

procedures. We believe that the outcome should minimize the effect of a test(s) with an 

inordinately high method detection level (e.g., the sample volume was too small, the laboratory 

technique was insufficiently sensitive, or the procedure for determining the minimum value for 

reporting was other than the detection level). We then call the resulting mean of the method 

detection levels as the representative detection level (RDL) as characteristic of accepted source 

emissions measurement performance. 

The second step in the process is to calculate three times the RDL to compare with the calculated 

floor or emissions limit. This step is similar to what we have used before in rulemaking 

applications. We use the multiplication factor of three to approximate reduce the imprecision of 

the analytical method until the imprecision in the field sampling reflects the relative method 

precision as estimated by the ASME study1 that also indicates that such relative imprecision, 

from 10 to 20 percent, remains constant over the range of the methods. For comparing to the 

floor, if three times the RDL were less than the calculated floor or emissions limit (e.g., 

calculated from the UPL), we would conclude that measurement variability was adequately 

addressed. The calculated floor or emissions limit would need no adjustment. If, on the other 

hand, the value equal to three times the RDL were greater than the UPL, we would conclude that 

 1 (ReMAP): PHASE 1, Precision of Manual Stack Emission Measurements; American Society of Mechanical Engineers, Research Committee on 

Industrial and Municipal Waste, February 2001.
the calculated floor or emissions limit does not account entirely for measurement variability. If 

indicated, we substituted the value equal to three times the RDL for the calculated floor or 

emissions limit which results in a concentration where the method would produce measurement 

accuracy on the order of 10 to 20 percent similar to other EPA test methods and the results found 

in the ASME study.

We determined the RDL for each pollutant using data from tests of all the best performers for all 

of the final regulatory subcategories (i.e., pooled test data). We applied the same pollutantspecific RDL and emissions limit adjustment procedure to all subcategories for which we 

established emissions limits. We believe that emissions limits adjusted in this manner better 

ensure measurement variability is adequately addressed relative to compliance determinations 

than did the procedure applied for the proposal that may have been based on data sets smaller 

than seven tests and as few as one test. We also believe that the emissions testing procedures 

and technologies available now and in the future will be adequate to provide the measurement 

certainty sufficient for sources to demonstrate compliance at the levels of the adjusted emissions 

limits when applied in the manner representative of this protocol.

We recommend that rule writers considering emissions limits for these pollutants review 

the existing data sets and compare the RDL values used in earlier analyses with the revised 

RDLs shown in the attached table. We believe that these revised values and the procedures 

described in the table better reflect representative method capabilities and should be used 

in data review for current rule development projects and in setting representative 

emissions limits.

Results of MDL/RDL data analyses

We have collected data used for the boilers rule reconsideration and the proposed utility MACT 

in light of the comments to review the effect of available larger pools of dioxin/furan emissions 

as measured with Method 23 and the Hg emissions as measured with Method 29 of data for these 

sources. The expanded data set represents several hundred emissions tests used in the floor 

calculations (i.e., best performers) for the boilers and utility rules. We presume that data for the 

best performing units also reflect the capabilities of high quality testing companies and 

laboratories. Further, the method detection levels calculated from larger data are more 

representative of the inherent measurement variability both within and between testing 

companies. We have also included data on the RDL values for the individual metals as 

measured with Method 29 based on a similar assessment of data collected during method 

development. The tables attached below express the results in two formats: 

1) The mass of pollutant sample the method can detect quantitatively and is representative of the 

method detection level (RDL) for the set of data collected for the specific rule development; and

2) The lowest concentrations that could be measured quantitatively for a range of sample 

volumes for use in comparing to calculated UPL values and in setting applicable emissions 

limits.
The first table represents a thorough review of D/F emissions data for both the boilers and utility 

data sets. Not too surprisingly, the resulting values are similar but not identical. Our first 

observation is that these calculated representative detection levels are generally greater in 

magnitude than those calculated for the initial reviews and particularly for establishing new 

source limits (i.e., for the single best performing unit). The second observation is that the RDLs 

determined for the utility ICR data set are lower in magnitude than for the boiler data collected 

during an earlier ICR project. We believe that the boiler data set includes some data reported 

incorrectly (e.g., laboratory reporting limits rather than method detection limits) and that the 

utility D/F data set includes fewer of these misreported data. As a result, we believe that the 

RDLs determined from the utility D/F data set are more representative of current expected 

measurement data quality. The application procedures described in the table reflect this 

conclusion.

Also attached to this note is a spreadsheet example of the calculations used to develop these 

values.

As rule writers collect additional data in the future and test methods and techniques improve, 

there will be a need to assess new data for representative method detection capabilities. We will 

prepare new procedures for you and your contractors to use as needed in future rule making 

activities based on these findings. We will build on these procedures to reflect greater reliance 

on the broadest set of measurement data available and provide default values to use when there 

are only a few (e.g., fewer than seven) performance test results available for a source category.

Peter Westlin

Measurement Policy Group

Sectors Policies and Programs Division

Raymond Merrill

Measurement Technology Group

Air Quality Assessment Division

Addressees:

SPPD management

SPPD technical staff

cc:

Conniesue Oldham, MTG, AQAD

Jason Dewees, MTG, AQAD

Kim Garnett, MTG, AQAD

Kristen Benedict, MTG, AQAD

Robin Segall, MTG, AQAD
Summary of pollutant emissions representative method detection level analyses 

and a regulatory emissions limit setting procedure

RDL 

(ng)

3 x 

RDL 

(ng)

3 x RDL Concentrations (ng/dscm)

1 dscm test 2 dscm test 3 dscm test 4 dscm test 6 dscm test 8 dscm test

Ind. Boilers D/F total 

mass

(Method 23)

5.6E-01 1.7E+00 1.7E+00 8.5E-01 5.7E-01 4.3E-01 2.8E-01 2.1E-01

Ind. Boilers TEQ

(Method 23)

8.2E-02 2.5E-01 2.5E-01 1.3E-01 8.3E-02 6.3E-02 4.2E-02 3.1E-02

Utilities D/F total mass

(Method 23) 3.1E-01 9.2E-01 9.2E-01 4.6E-01 3.1E-01 2.3E-01 1.5E-01 1.2E-01

Utilities TEQ

(Method 23) 3.6E-02 1.1E-01 1.1E-01 5.5E-02 3.7E-02 2.8E-02 1.8E-02 1.4E-02

RDL (ug) 3 x RDL 

(ug)

3 x RDL Concentrations (ug/dscm)

1 dscm test 2 dscm test 3 dscm test 4 dscm test

HCl/Cl2 (Method 26A) 6.0E+1 1.8E+2 1.8E+02 9.0E+01 6.0E+01 4.5E+01

PM filterable (Method 5) 2.0E+3 6.0E+3 6.0E+03 3.0E+03 2.0E+03 1.5E+03

Ind. Boiler Hg (Method 29) 8.3E-01 2.5E+00 2.1E+00 1.0E+00 7.1E-01 6.2E-01

120L test 240L test 360L test

HCl/CL2 (Method 26) 1.0E+01 3.0E+01 2.5E+02 1.3E+02 8.3E+01
Summary of pollutant emissions representative method detection level analyses and regulatory emissions limit setting 

procedure for Method 29 Metals using Inductively Coupled Atomic Emission Spectroscopy or Atomic Absorption Analysis

Method 29 Metal

RDL

ICP/AES 

or AA

(ug)

3 X RDL 

ICP/AES or 

AA

(ug)

3 x RDL Concentrations (μg/dscm)

1 dscm test 2 dscm test 3 dscm test 4 dscm test

Antimony 1.2E+01 3.5E+01 3.5E+01 1.7E+01 1.2E+01 8.6E+00

Arsenic 1.9E+01 5.7E+01 5.7E+01 2.9E+01 1.9E+01 1.4E+01

Barium 8.0E-01 2.4E+00 2.4E+00 1.2E+00 8.0E-01 6.0E-01

Beryllium 1.1E-01 3.3E-01 3.3E-01 1.7E-01 1.1E-01 8.3E-02

Cadmium 1.5E+00 4.5E+00 4.5E+00 2.3E+00 1.5E+00 1.1E+00

Chromium 2.5E+00 7.5E+00 7.5E+00 3.8E+00 2.5E+00 1.9E+00

Cobalt 2.5E+00 7.5E+00 7.5E+00 3.8E+00 2.5E+00 1.9E+00

Copper 2.1E+00 6.3E+00 6.3E+00 3.2E+00 2.1E+00 1.6E+00

Lead 1.5E+01 4.5E+01 4.5E+01 2.3E+01 1.5E+01 1.1E+01

Manganese 7.0E-01 2.1E+00 2.1E+00 1.1E+00 7.0E-01 5.3E-01

Mercury* 5.6E-01 1.7E+00 1.7E+00 8.4E-01 5.6E-01 4.2E-01

Nickel 5.4E+00 1.6E+01 1.6E+01 8.1E+00 5.4E+00 4.1E+00

Phosphorus 2.7E+01 8.1E+01 8.1E+01 4.1E+01 2.7E+01 2.0E+01

Selenium 2.7E+01 8.1E+01 8.1E+01 4.1E+01 2.7E+01 2.0E+01

Silver 2.6E+00 7.8E+00 7.8E+00 3.9E+00 2.6E+00 2.0E+00

Thallium 1.4E+01 4.3E+01 4.3E+01 2.2E+01 1.4E+01 1.1E+01

Zinc 8.0E-01 2.4E+00 2.4E+00 1.2E+00 8.0E-01 6.0E-01

*Mercury analyzed by Cold Vapor AA

RDL = Method derived regulatory detection limit based.

ICP/AES = Inductively Coupled Argon Plasma/Atomic Emission Spectroscopy

AA = Atomic Absorption Spectroscopy

GFAA = Graphite Furnace Atomic Absorption spectroscopy
Summary of pollutant emissions representative method detection level analyses and regulatory emissions limit setting 

procedure for Method 29 Metals using Inductively Coupled Plasma/Mass Spectrometry or Graphite Furnace Atomic 

Absorption Analysis

Method 29 

Metal 

RDL

ICP/MS 

or GFAA

(μg/dscm)

3 X RDL 

ICP/MS 

or GFAA

(μg/dscm)

Concentrations (μg/dscm)

1 dscm test 2 dscm test 3 dscm test 4 dscm test 5 dscm test

Antimony 1.1E+00 3.3E+00 3.3E+00 1.7E+00 1.1E+00 8.3E-01 6.6E-01

Arsenic 4.0E-01 1.2E+00 1.2E+00 6.0E-01 4.0E-01 3.0E-01 2.4E-01

Barium** 8.0E-01 2.4E+00 2.4E+00 1.2E+00 8.0E-01 6.0E-01 4.8E-01

Beryllium 8.0E-02 2.4E-01 2.4E-01 1.2E-01 8.0E-02 6.0E-02 4.8E-02

Cadmium 3.0E-02 9.0E-02 9.0E-02 4.5E-02 3.0E-02 2.3E-02 1.8E-02

Chromium 3.0E-01 9.0E-01 9.0E-01 4.5E-01 3.0E-01 2.3E-01 1.8E-01

Cobalt 3.0E-01 9.0E-01 9.0E-01 4.5E-01 3.0E-01 2.3E-01 1.8E-01

Copper** 2.1E+00 6.3E+00 6.3E+00 3.2E+00 2.1E+00 1.6E+00 1.3E+00

Lead 3.0E-01 9.0E-01 9.0E-01 4.5E-01 3.0E-01 2.3E-01 1.8E-01

Manganese 3.0E-01 9.0E-01 9.0E-01 4.5E-01 3.0E-01 2.3E-01 1.8E-01

Mercury* 5.6E-01 1.7E+00 1.7E+00 8.4E-01 5.6E-01 4.2E-01 3.4E-01

Nickel** 5.4E+00 1.6E+01 1.6E+01 8.1E+00 5.4E+00 4.1E+00 3.2E+00

Phosphorus** 2.7E+01 8.1E+01 8.1E+01 4.1E+01 2.7E+01 2.0E+01 1.6E+01

Selenium 8.0E-01 2.4E+00 2.4E+00 1.2E+00 8.0E-01 6.0E-01 4.8E-01

Silver** 2.6E+00 7.8E+00 7.8E+00 3.9E+00 2.6E+00 2.0E+00 1.6E+00

Thallium 3.0E-01 9.0E-01 9.0E-01 4.5E-01 3.0E-01 2.3E-01 1.8E-01

Zinc 8.0E-01 2.4E+00 2.4E+00 1.2E+00 8.0E-01 6.0E-01 4.8E-01

*Mercury analyzed by Cold Vapor AA

** Common metals analyzed by Inductively Coupled Plasma/AES or Flame Atomic Absorption Spectroscopy

RDL = Method derived regulatory detection limit based on 1.25 dscm collected in 1 hour.

ICP/MS = Inductively Coupled Argon Plasma/Mass Spectrometry
GFAA = Graphite Furnace Atomic Absorption spectroscopy

Except for assessing boiler and CISWI data, we recommend that you select D/F data calculated from the utilities’ data set rather than 

for the industrial boilers in conducting the following analyses.

1. Calculate the UPL for your respective data set in units of pollutant mass as sampled by the test method (e.g., total ng of D/F, 

total TEQ of D/F, ug of Hg). 

2. Compare the 3xRDL mass value (shown in bold) to the calculated UPL. If 3xRDL mass < UPL mass, use the UPL value for 

rulemaking. If 3xRDL > UPL, use the 3xRDL value for rulemaking. For source categories other than boilers, use the 3xRDL 

D/F values shown above for Utilities.

3. Alternatively, you may calculate the UPL for your data set in units of pollutant concentration (ng/dscm for D/F, ug/dscm for 

Hg). If so, repeat steps 1 and 2 selecting the concentration associated with the sample volume appropriate for your ICR or 

regulatory decision. You may also determine to convert the values in the table to other emissions formats (e.g., lb/MMBtu or 

lb/MWh) for these comparisons.
Example spreadsheet:

(ng/dscm @ 7 percent O2) ng ng

mass (average 

of all congener 

data in set)

TEQ (average of 

all TEQ per 

congener in set) lab mass TEQ

Total OCDD 2.19E-02 6.24E-06 8.77E-02 2.50E-05

Total 

OCDF 6.72E-03 1.89E-06 2.69E-02 7.55E-06

1,2,3,4,6,7,8 HpCDD 2.95E-03 2.70E-05 1.18E-02 1.08E-04

1,2,3,4,6,7,8 HpCDF 6.10E-03 6.02E-05 2.44E-02 2.41E-04

1,2,3,4,7,8 HxCDD 1.16E-03 1.06E-04 4.63E-03 4.25E-04

1,2,3,4,7,8 HxCDF 8.24E-03 8.10E-04 3.30E-02 3.24E-03

1,2,3,4,7,8,9 HpCDF 3.08E-03 3.00E-05 1.23E-02 1.20E-04

1,2,3,6,7,8 HxCDD 1.33E-03 1.23E-04 5.32E-03 4.93E-04

1,2,3,6,7,8 HxCDF 9.64E-04 8.83E-05 3.86E-03 3.53E-04

1,2,3,7,8 PeCDD 4.40E-03 4.33E-03 1.76E-02 1.73E-02

1,2,3,7,8 PeCDF 1.82E-03 5.26E-05 7.29E-03 2.10E-04

1,2,3,7,8,9 HxCDD 3.37E-03 3.26E-04 1.35E-02 1.30E-03

1,2,3,7,8,9 HxCDF 7.81E-04 6.93E-05 3.12E-03 2.77E-04

2,3,4,6,7,8 HxCDF 2.35E-03 2.27E-04 9.40E-03 9.09E-04

2,3,4,7,8 PeCDF 1.61E-03 4.61E-04 6.43E-03 1.85E-03

2,3,7,8-TCDD 3.38E-03 3.34E-03 1.35E-02 1.34E-02

2,3,7,8-TCDF 2.24E-03 2.18E-04 8.98E-03 8.73E-04

max DL 2.19E-02 4.33E-03 8.77E-02 1.73E-02

min DL 7.81E-04 1.89E-06 3.12E-03 7.55E-06

mean DL 4.26E-03 6.05E-04 1.70E-02 2.42E-03

sum 7.24E-02 1.03E-02 2.90E-01 4.11E-02

RDL = EDL x 2 1.45E-01 2.06E-02 5.80E-01 8.22E-02

RDL x 3 > floor? 4.35E-01 6.17E-02 1.74E+00 2.47E-01