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Why EPA Should Not Establish Numerical Dioxin/Furan Limits in the Industrial Boiler 

MACT and Certain CISWI Dioxin/Furan Limits Should be Adjusted 

(July 15, 2011)

In March 2011, EPA finalized numerical dioxin/furan (D/F) standards for 12 subcategories of 

industrial boilers and process heaters and for 5 CISWI subcategories. Most of the limits are 

lower than any other D/F standards EPA has set in the past for various waste combustion 

source categories (see attachment titled: Comparison of Dioxin Emission Limits in Various U.S. 

Regulations). EPA should set work practice requirements instead of numerical D/F 

standards for industrial boilers and should adjust certain of the CISWI D/F standards to 

account for measurement uncertainty for the reasons outlined below. 

The majority of the data collected in order to set the D/F standards for industrial boilers and 

CISWI energy recovery units are at levels below the capability of the analytical and stack 

test methods to detect emissions of these compounds (all but one of the test runs used to set 

the Boiler MACT limits are marked as “detection level limited”). Much of the test data are 

labeled as being below the method detection limit and the remainder of the data are often 

flagged as being below the level the laboratory feels can be reported with confidence. 

It is not appropriate to treat detection level limited data for purposes of establishing 

regulatory limits in the same manner as detected values because the uncertainty1 associated 

with measurements near or below the method detection limits is too high. The test methods 

were developed over 30 years ago to measure D/F at concentrations then found in some types 

of waste incinerator exhaust (levels orders of magnitude higher than those found in exhaust 

from today’s industrial boilers and CISWI energy recovery units). 

All source emission measurements have random (precision) errors associated with the sample 

collection, sample and equipment handling, sample preparation, and sample analysis. These 

errors define method detection and quantitation limits and uncertainty in a non-arbitrary, 

scientific manner (as discussed further below). When emission levels are much higher than the 

magnitude of these errors, there is a high degree of confidence in the measured value obtained 

from a single or a few test runs. However, as the measured value decreases, the contribution of 

these errors to the measured value increases, thus decreasing the confidence level in the 

accuracy of the measured value from a single or a few runs until the point where the measured 

value cannot be distinguished from the random error (“noise” level). This is the case with 

the boiler D/F data and much of the CISWI D/F data. When this occurs, the measurement 

cannot be distinguished from zero with high confidence. 

The magnitude of D/F measurement errors typically varies with every measurement and is 

affected by the characteristics of the sample, skills of the sampler and analyst, specific 

equipment used, techniques and procedures adopted by individual laboratories and other 

factors even when following the same published test method (in this case, EPA Method 23). 

                                                            1

 Uncertainty here refers to the statistical expression of measurement error, such as defined in ASME 

Performance Test Code 19.1, rather than an inference of something which is unknown. 
2

Although EPA Method 23 procedures minimize measurement errors at the stack emission levels 

and applications for which it was intended, measurement errors are not zero and become 

significant at the extremely low levels in industrial boilers and CISWI energy recovery units. 

In setting the Boiler MACT and CISWI standards, EPA has acknowledged that the emission limit 

should not be set below the capability of the applicable test method. However, EPA did not use 

the widely accepted definition of method detection limit, which is based on the capabilities of 

multiple commercial laboratories to analyze a sample and identify the presence of a chemical 

above the “noise” level. In its place, EPA coined a new term, representative method detection 

limit (RDL) to define a measurement method detection limit which is based on the laboratory 

detection limits reported for the tests with the lowest emissions. This erroneous methodology 

resulted in estimating D/F detection limits that are over 100 times lower than those 

regularly achieved by commercial laboratories. 

The detection limit of an analytical method is commonly defined as the lowest concentration that 

can be distinguished from replicate blanks. The quantitation limit of a method is defined as the 

smallest concentration of the substance which can be measured with an acceptable level of 

uncertainty. Detection limits and quantitation limits are defined in a scientific, non-arbitrary 

manner in various widely-published peer-reviewed consensus guidelines2 and EPA documents. 

Quantitation limits of test methods have great significance when measuring very low 

concentrations of pollutants. In practice, reported values below the method's quantitation 

limit should not be treated as real values. 

The majority of a federal advisory committee on method detection and quantitation limits 

recommended that the quantitation limit of a test method should be based on the 95th percentile 

of what is being achieved by the commercial laboratories3. Using this approach and rounding 

up the quantitation limit to a single digit, as EPA has done for floor setting, would result in a D/F 

TEQ quantitation limit of 0.2 ng/dscm based on analytical procedures alone. However, using 

the results of the ASME ReMAP study4

, which evaluated the precision of Method 23 D/F stack 

testing measurements, a D/F TEQ quantitation limit of 0.27 ng/dscm is derived, which 

addresses the uncertainty of all of the test method components. Thus, if numerical D/F 

standards are set pursuant to Section 129, EPA should not set CISWI D/F TEQ emission 

standards at less than 0.3 ng/dscm. 

In EPA’s recently proposed Utility MACT, no dioxin/furan standards are proposed for coal and 

oil-fired EGUs because the majority of the data are below method detection and/or reporting 

limits (“non-detect,” or ND). The levels of D/F reported by industrial boilers are very low, 

similar to utility boilers. EPA states in the Utility MACT preamble, “Overall, the available test 

                                                            2

 For example, Keith, L.H. et al., Principles of Environmental Analysis, Anal. Chem. 1983, 55, 2210-

2218. 

3

 Report of the federal advisory committee on detection and quantitation approaches and uses in 

Clean Water Act Programs submitted to the Environmental Protection Agency (EPA). December 

2007. 

4

 Lanier, W.S. and Hendrix, C.D. Final Report -- Reference Method Accuracy and Precision (ReMAP): 

Phase 1 Precision of Manual Stack Emission Measurements, ASME International, Washington, D.C. 

(2001). 
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methods are technically challenged, to the point of providing results that are questionable for all 

of the organic HAP.5

” 

The Utility MACT preamble indicates that EPA believes D/F formation is inhibited by the lack 

of precursors such as available chlorine or by a high sulfur-to-chlorine ratio6. The same 

principles apply for some industrial boilers and process heaters. For example, coal and residual 

oil-fired boilers will have high sulfur to chlorine ratios and some types of biomass boilers will 

have low available chlorine. Many industrial boiler designs and fuels typically exhibit other 

conditions inhibiting D/F formation, such as low unburned carbon and catalyzing elements in the 

fuels, high combustion temperatures, and short gas residence times at critical lower 

temperatures. 

One-time stack test data from only 1 or 2 units are being used to set D/F limits for each 

subcategory. Even if the D/F test methods were not being stretched beyond their limits, this 

approach does not provide emissions data representative of the normal range of operations and 

fuel compositions, ambient environmental conditions, geographic locations and other factors 

that may influence air pollutant emissions. The performance of the top 12 percent of all 

CISWI units cannot be determined using only a few data points. 

As demonstrated by the measurement issues noted, quantifying the actual, extremely low or 

non-existent dioxin emission levels for the Boiler MACT floor units is technologically 

impracticable (as well as economically impracticable, given that the technological 

problems cannot be overcome by investing reasonable resources into the problem), and 

thus, it is not feasible to prescribe or enforce an emission standard for D/F emissions for 

these units. Clean Air Act Section 112(h)(1) supports establishing a work practice standard for 

D/F in the Boiler MACT, as was done in the recently proposed Electric Generating Unit (“Utility”) 

MACT rule7. The required tune-ups and other emissions reductions in the Industrial Boiler 

MACT will result in improved combustion and minimize conditions conducive to D/F formation 

without establishing a numerical emission standard. 

Several sets of comments have been submitted that provide more detail on these points: 

o AF&PA Comments at EPA-HQ-OAR-2002-0058-3213 and reconsideration petition (see in 

particular Appendix A) at EPA-HQ-OAR-2002-0058-3293

o CIBO Comments at EPA-HQ-OAR-2002-0058-2702 

o ACC Comments at EPA-HQ-OAR-2002-0058-2792 

o API/NPRA Comments at EPA-HQ-OAR-2002-0058-2935 

o CRWI Comments at EPA-HQ-OAR-2002-0058-2824 

o NCASI Comments at EPA-HQ-OAR-2002-0058-2804 and additional detail in a paper to 

be submitted to EPA on July 15, 2011 

o ENVIRON Comments at EPA-HQ-OAR-2002-0058-2809 

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 76 FR 25040

6

 76 FR 25023 

7

 76 FR 24976
4

0.001

0.01

0.1

1

10

100

1000

Municipal Waste Incinerators Class II Unit

Other SW Incinerators

Municipal Waste Incinerators Class I Existing Units

Hosp/Med/Inf Waste Incinerators Small Older Units

Municipal Waste Incinerators New Units

Sewage Sludge Incinerators Existing Units

Hosp/Med/Inf Waste Incinerators Small Existing Unit

Hosp/Med/Inf Waste Incinerators Medium

Hosp/Med/Inf Waste Incinerators Large

Haz Waste Combustor MACT Existing Sources w/o dry...

CISWI ERU Existing Liq/Gas

Boiler MACT Biomass Suspension Burners

Portland Cement Kiln MACT

Haz Waste Combustor MACT

2011 CISWI Existing Incinerators

Haz Waste Combustor MACT New Sources

Boiler MACT Gas 2

CISWI ERU Existing Bio/Coal

Hosp/Med/Inf Waste Incinerators Large New

Proposed PVC MACT Process Vents

Boiler MACT Biomass FB

Hosp/Med/Inf Waste Incinerators Small New

Boiler MACT Biomass Stoker

Boiler MACT Existing Coal pulverized

Boiler MACT Existing Coal stoker

Boiler MACT New Biomass Fuel Cell

Dioxin Limit, ng/dscm @ 7% O2

Comparison of Dioxin Emission Limits in Various U.S. Regula

Category 200TEQBackyard barrel burninHMIWI MWI Coal Utility Boilers 

Metal Smelting/Refinin

2011 Boiler MACT data Cement kilns Residential wood/oil co

0.3 ng/dscm D/F TEQ quantitation limit