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April 8, 2015 

Mr. George Czerniak 

Director, Air and Radiation Division (A-18J) 

EPA Region 5 

77 West Jackson Boulevard, 18th Floor 

Chicago, IL 60604 

Re: Response to the Cooper Environmental Services Post-Closure Date Submittal to 

Docket ID EPA-R05-OAR-2014-0280 on the Viability of the Xact® Multi-metal Continuous 

Emissions Monitoring System Required by EPA on the Veolia’s Sauget, Illinois 

Hazardous Waste Incinerators for the Collection of Metals Data Related to HWC MACT 

Compliance Standards. 

Dear Mr. Czerniak: 

This letter is in response to comments by Cooper Environmental Services (CES) and posted by 

EPA relative to our December 2014 submittal to Docket ID EPA-R05-OAR-2014-0280. Our 

submittal evaluated the viability of using the Xact® Multi-metal continuous emissions monitoring 

system (CEMS) for evaluating Hazardous Waste Combustor (HWC) Maximum Achievable 

Control Technology (MACT) metals emissions compliance of Veolia’s Sauget, Illinois 

hazardous waste incinerators (HWIs). CES’ comments, submitted in February 2015, well after 

the draft Title V Air Permit comment period closing date of December 19, 2014, require us to 

respond at this time. 

CES Point 1: Traverse vs. Single Point Sampling, Isokinetics, and Verification Testing

We and others commented substantially on the particulate matter (PM) transport issues 

associated with accurate continuous metals emissions measurements.1,2 The Xact® CEMS 

obtains samples for analysis via single-point, non-isokinetic sampling. Samples of particle 

bound constituents obtained in such a manner can not be representative of stack gas effluents 

for compliance measurements. CES crudely compensates for the non-isokinetic sampling of 

the Xact® CEMS by operation of their units at super-isokinetic conditions in order to avoid 

consistently collecting data with a low bias and a non-representative sampling reputation. 

TEOMTM PM Emission Stratification Study

In their own defense of the single-point, non-isokinetic PM sampling aspect, CES’ response 

included reference to EPA work that evaluated PM stratification in emissions from a coal-fired 

power plant (CFPP) using the R&P Tapered Element Oscillating Microbalance (TEOMTM) 

monitors. The TEOMTM monitor study was conducted in two parts: 

1. Validation of the TEOMTM monitors accuracy through comparison with manual 

reference methods, and 

2. Evaluation of the precision of side-by-side TEOMTM monitors.3
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First, we specifically note these same types of measurement comparisons be required if a 

proper validation of the Xact® CEMS in terms of accuracy, precision, and bias is to be obtained. 

To our knowledge, no such complete study of the Xact® CEMS has ever been performed. 

In the CFPP study, the relative difference of the paired TEOMTM monitors averaged 7.7% and 

4.5% for co-located and traverse sampling, respectively. CES points to the TEOMTM study as 

evidence that PM emissions stratification is not significant. While this may have been the case 

for a system firing only a single, reasonably uniform fuel under relatively stable stack flow 

conditions, this test in no way substantiates any claim as to the absence of PM stratification in 

all firing cases. Nor, does this testing substantiate the general absence of PM stratification for 

a HWI unit where the wastes treated (fuels) vary and firing conditions are constantly changing. 

Another PM Stratification Study

CES’ response cites another PM stratification study involving traverse and single-point 

sampling. Like the TEOMTM monitor study, no PM stratification was found in that study. 

However, while metals routinely attach to PM, there is no data presented in this other study, or 

the previously cited TEOMTM monitors study, to show metals do so uniformly. In March 2015, 

CES revised and resubmitted the February 2015 submittal to remove the second PM 

stratification study citation. 

TEAD Incinerator Study

The testing of the Xact® CEMS on Tooele Army Depot (TEAD) incinerator in 2001 and 2002 did 

involve an evaluation similar to Part 1 above, the Xact® CEMS versus a paired set of Method 

29 trains. The TEAD test conditions were the correct testing configuration for thorough 

accuracy testing of the Xact® CEMS. Specifically, the sampling was performed on a stack gas 

where the concentrations of the target metal analytes were well above the detection limits of 

both the Xact® CEMS and Method 29 such that accuracy and bias of the CEMS could be 

evaluated. CES has routinely and publicly presented the TEAD data for a select subset of 

metals, but glaringly excludes data for the other metals tested that failed to meet the required 

acceptance criteria. As we note in our December 2014 letter, when the TEAD data for all the 

metals tested are examined, the conclusion can only be the Xact® CEMS design that was 

tested was a substantial failure. To our knowledge, a Part 2 study using paired Xact® CEMS 

units to evaluate the relative precision has never been performed. 

Coal-Fired Power Plant Study 

Later studies of an “improved” version of the Xact® CEMS design were performed by CES on 

two CFPPs.4

 One study involved dynamically enriching a slipstream of CFPP stack gas with 

multiple metals using the Quantitative Aerosol Generator (QAG). This study compared the 

variance between the Xact® CEMS reported concentrations and the “known” concentration of 

the generated aerosol. The stated purpose of this study was to evaluate “any potential 

interferences from the coal-fired effluent”. The second study involved the Xact® CEMS versus 

paired Method 30B sampling for mercury. The sampling point for this study was performed 

between the electrostatic precipitator (ESP) and wet scrubber. Neither study involved direct 

sampling of the stack gas in the stack versus Method 29 or Method 30B as required by 

Performance Specification 10 (PS-10). 
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Eli Lilly Validation Study

In the Eli Lilly (Lilly) testing of the Xact® CEMS, Method 29 comparisons were replaced with 

QAG reference aerosol comparisons.5

 Similar to the CFPP study, the QAG was used to enrich 

a slipstream of stack gas that was then sampled non-isokinetically. We comment in our 

December 2014 letter and again later in this letter about the representativeness of the QAGsimulated emissions as related to particulate behavior. As would be expected under such 

controlled conditions, consistent results were obtained. However, at no time was there any 

testing performed with direct comparisons of the Xact® CEMS to Method 29 sampling of actual 

incinerator emissions. 

ETV Ambient Air Monitor Study

The EPA, via the Environmental Technology Verification (ETV) Program, evaluated the Xact® 

625. CES has posted the summary of this particular study on its website 

(http://cooperenvironmental.com/wp-content/uploads/2014/08/Xact625_ETVReportsummary.pdf) and included the summary as an attachment the December 2014 submittal to 

Docket ID EPA-R05-OAR-2014-0280. The full report can be found at EPA’s website 

(http://nepis.epa.gov/Adobe/PDF/P100FK6B.pdf). The mission of the ETV is to facilitate the 

deployment of innovative or improved environmental technologies through performance 

verification and dissemination of information thereby accelerating the acceptance and use of 

improved and cost-effective technologies.6

 This particular study was performed by Battelle. 

The reason CES does not include the full ETV study is evident when the full report is 

examined. 

The ETV study evaluated the ability of the Xact® 625 as an ambient air monitor to provide 

quantitative measurements of metals in particulate matter with an aerodynamic diameter less 

than 10 micrometers (PM10). The ETV study compared the Xact® 625 results to concurrent 

ambient air monitoring being performed at sites in East Liverpool and Marietta, Ohio. The 

existing monitor, a Partisol Plus 2025 Sequential Ambient Particulate Sampler, was operated in 

accordance with EPA Method IO-3.1 and served as the reference method. A total of 23 metals 

were reported hourly by the Xact® 625 over a period of approximately 80 days. Daily averages 

of the Xact® 625 metals readings that exceeded the daily quantitation limits (“QLs”) of the 

analyzer were compared to corresponding results determined for 19 of the 23 target metals by 

analysis of the filters from the Partisol Plus 2025 monitor performed via inductively coupled 

plasma/mass spectrometry (ICP/MS). 

The poor performance and lack of verification of the Xact® 625 is commented upon throughout 

the document. Of the 19 metals examined by both methodologies, the Xact® 625 results for 

12 metals were almost always below the respective QLs of the Xact® 625, and consequently 

no comparisons could be made to the reference results. For this reason, the Xact® 625 could 

not be evaluated for 12 of 19 metals. Additionally, the ETV study notes that the Xact® reported 

a nearly constant and unrealistic ambient concentration of molybdenum (Mo) due to an 

incorrect energy window for that metal in the X-ray fluorescence (XRF) analysis. The ETV 

study acknowledged that, for purposes of the experiment, the Xact technology was not 

accurate for measurement of molybdenum (Mo). Of the 23 ambient air metals determined by 

the Xact® 625, only six (6) were left to be possibly verified: calcium (Ca), manganese (Mn), 

selenium (Se), zinc (Zn), copper (Cu), and lead (Pb). The ETV study noted that: 
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“the daily average Xact® 625 results were highly correlated and in close 

quantitative agreement with ICP/MS analysis results for most of the six metals, 

and ... the Xact® 625 achieved data completeness of over 95%.”. 

This statement appears initially to be a positive finding for the Xact® 625, however, the part 

concerning data completeness simply acknowledges that the Xact® 625 generated data 95% 

of the time over the analysis period. The definitive portion of the statement is “...close 

quantitative agreement with ICP/MS analysis results for most of the six metals.” The study 

goes on to clarify that out of the six (6) metals that could be evaluated, the Xact® 625 could 

only provide unbiased results for four (4) metals: calcium (Ca), manganese (Mn), selenium 

(Se), and zinc (Zn). The test results for copper (Cu) and lead (Pb) exhibited substantial 

problems of bias. 

The HWC MACT rule regulates the emissions of six (6) metals from HWIs: arsenic (As), 

beryllium (Be), cadmium (Cd), chromium (Cr), lead (Pb), and mercury (Hg). Of the ETV study 

short list of metals, lead (Pb) is the only metal of HWC MACT interest, and the results for lead 

(Pb) were substantially biased The lead (Pb) results for 52 data points exhibited a high bias 

that ranged from 8.7 to 339% and averaged nearly 75%. The study does note that part of the 

lead (Pb) bias is due to the blank level of 1 ng/m3

 on the Xact® 625 sample media (tape). 

The ETV study notes the following relative to the quality control (calibration) checks of the 

Xact® 625: 

The results of the automated daily internal QC checks performed by the Xact 

625 were reviewed approximately weekly, each time data were downloaded 

from the instrument. Those results showed stability in Xact 625 operations 

throughout the entire period of operation at both the East Liverpool and Marietta 

sites. Over that entire period the relative standard deviation (RSD) of the Pd 

[palladium] internal standard readings determined in every Xact 625 XRF 

analysis was 2.04%. The instrument’s average flow error was -0.69% (± 

0.004%), where the value in parentheses is the standard deviation (SD) of the 

daily flow check results. The average accuracy relative to upscale rod check 

standards analyzed daily was 100.21% (±0.004%) for Cr, 100.55% (±0.013%) 

for Cd, and 99.79% (±0.007%) for Pb, where accuracy of 100% represents 

perfect agreement with the upscale rod check standard. 

The Xact® technology, when checked against its own standards, appears to perform superbly. 

However, the ETV study lead (Pb) results demonstrate the Xact® technology has significant 

bias issues when compared to the reference method. 

A careful reading of the ETV study, like the earlier TEAD study, shows that the Xact technology 

could not be adequately verified for 19 of the 23 metals that the Xact was designed to target. 

The ETV study includes the following disclaimer: 

“EPA and Battelle make no expressed or implied warranties as to the 

performance of the technology and do not certify that a technology will always 

operate as verified.” 
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CES Point 1 Summary

Metals emissions compliance measurement has two parts: 1) sampling, and 2) analysis. The 

CFPP and Lilly studies address only one-half of the emissions compliance process, specifically 

the analysis portion. The CFPP and Lilly studies do not include comparisons of the Xact®

CEMS to analysis results where the sampling was performed isokinetically. The TEAD and 

ETV studies expose the bias of the sampling portion of Xact® CEMS. The data from TEAD and 

ETV studies show the results are varying and generally biased high. The high bias is due to 

the super isokinetic sampling aspect of the Xact® CEMS purposefully performed so as to avoid 

a low bias reputation. Unless the samples for analysis are obtained isokinetically, the Xact®

CEMS results can never be valid for demonstrating metals emissions compliance. 

CES’ response is a broad diversion from the fact that the Xact® CEMS has never undergone a 

rigorous validation testing process involving a direct comparison with Method 29 under the 

same sampling conditions. For the study to be technically defensible, sampling must be of a 

stack gas where the concentrations of the target metal analytes are well above the detection 

limits of both the Xact® CEMS and Method 29 , and the sampling is performed isokinetically. 

Only then can accuracy, precision, and bias be appropriately assessed. Until such testing is 

performed, the Xact® CEMS can not be accepted or used for any emissions compliance 

purposes. The EPA has failed to require complete validation of this technology by CES before 

requiring Veolia to deploy the Xact® CEMS on the Sauget HWIs. 

CES Points 2 & 3: Particle Size and Saltation during Sample Acquisition

Particles of various sizes exist in a stack gas stream. Cross-sectional velocities within the 

stack may not be uniform, and may vary. As such, particle quantities and sizes may or may not 

be evenly distributed within the stack. Particles in any moving fluid (gas or liquid) making 

transitional changes in direction within a conduit (duct, stack, line, or pipe) will not be evenly 

distributed, and will to some degree make impact with the conduit surfaces, regardless of 

particle size. The degree to which such impaction and possible deposition (saltation) occurs is 

a function of particle size and quality (e.g., adherence properties). Similarly, settling of 

particles occurs in horizontal runs due to gravitational impacts and other factors. 

CES’ comments include a schematic of the Xact® 640 CEMS sample transport and setup. The 

Xact® CEMS utilizes a single-point probe in the stack. The indicated sampling rate is 100-600 

liters per minute (lpm). The heated transfer line (maintained at 190o

C) from the stack probe 

includes turns and horizontal runs. From the heated transfer line/stilling chamber, the Xact®

CEMS sample acquisition system extracts a small slipstream (~1 lpm) which is drawn across 

the Xact® CEMS filter media. A sample that is not obtained isokinetically and travels via such 

an extended and circuitous pathway can not be representative of the particle distribution within 

the stack. In fact, the sample acquisition is doubly non-isokinetic; the single point sampling in 

the stack is non-isokinetic and the sub-sample taken from the transfer line/stilling chamber is 

also non-isokinetic. Therefore, the sample obtained for analysis can not be comparable to that 

obtained isokinetically using the manual methods, and where any probe deposited metals are 

also recovered for analysis via reagent rinses. 

Any compensating measures (sampling rate adjustments, etc.) in the Xact® CEMS sample 

acquisition operation will not result in consistently accurate and precise measurements of 
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metals emissions. Any sample collections that are conducted under non-isokinetic conditions 

can not be representative, and therefore can not be accurate. 

CES Point 4: QAG Operation and Representative Sampling

CES appears to have completely missed the point of our comments related to 

representativeness of QAG generated emissions. The point is that the chemical and physical 

properties of the surrogate aerosol emissions generated by the QAG in no way correlate to the 

actual chemical and physical properties of actual emissions encountered in source emissions. 

The metal nitrate aerosols have very different chemical and physical properties than the hard 

fired metal oxides encountered in actual stack gas emissions. Therefore, the surrogate 

aerosols will behave in a considerably different way than a real stack gas matrix and should not 

be considered as an acceptable choice for this application. If a QAG is to be considered an 

acceptable accuracy evaluator system to prove that the Xact CEMS works (which given the 

dynamic conditions in stack emissions, it is seriously questionable), then at a minimum, the 

evaluators should require the use of the same chemical oxide forms as will be encountered in 

actual stack gas to be used for the standardization. The metal nitrate mists are not 

representative and should not be used for this reason. 

A particular point of objection is the use of the QAG for the performance of what CES denotes 

as a Relative Accuracy Test Audit (RATA). CES’ “RATA” methodology for the Xact® CEMS 

redefines the term. As we previously stated in our December 2014 letter, the Xact® CEMS 

“RATA” protocol which entails dynamically spiking a series of reference aerosol concentrations 

using the QAG and comparing the Xact® CEMS responses to the documented concentrations, 

is akin to a calibration error (CE) test. A RATA, as historically understood and performed under 

the EPA air regulations, requires using a reference method (RM), in this case another CEMS, 

operated concurrently. The CES claim about passing numerous “RATA” tests is not accurate 

pursuant to EPA’s typical definition of “RATA”. 

CES Point 6: Xact® CEMS Sampling Cycle and Analysis Times and Duration

We acknowledge the error with regard to the sampling cycle and analysis times and durations 

in our description of the current the Xact® CEMS design. However, the point remains that 

pauses or stops in the Xact® CEMS sampling operation is likely to cause particulate settling in 

the quiescent environment portion of the instrument transport system, no matter how small the 

portion or how short the duration. Sampling interruptions logically imply that particulate 

sampling bias is likely. 

CES Point 7: Vapor Phase Mercury Sampling and Analysis

With regard to our comments relative to impacts of carbon in the stack gas on the performance 

of the Xact® CEMS in measuring mercury emissions from CFPPs, we offer the following 

citation from an EPA update on controlling mercury emissions from CFPPs: 

Mercury may be present in the flue gas in several forms. The specific chemical 

form – known as the speciation – has a strong impact on the capture of mercury 

by boiler air pollution control (APC) equipment.* Mercury may be present in the 

flue gas as elemental mercury vapor (Hg0

), as a vapor of an oxidized mercury 

species (Hg2+), and as particulate-bound mercury (Hgp). 
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Heterogeneous (gas-solid, surface catalyzed) mercury oxidation is more complex 

and depends upon the availability of surfaces having electrophylic groups that 

attract the electron-rich Hg0

 atom. The heterogeneous reactions occur mostly on 

fly ash surfaces or boiler surfaces, especially if the fly ash contains high amounts 

of unburned carbon. A proposed heterogeneous oxidation mechanism indicates 

the chlorination of carbon by HCl is a first step toward heterogeneous oxidation of 

Hg0

 to HgCl2, and adsorption of the mercury onto the carbon. The mercury that is 

adsorbed onto solid surfaces, such as fly ash or unburned carbon, is the 

particulate-bound mercury, Hgp, which can be captured by downstream PM 

control devices. Hence, fly ash characteristics – especially carbon - as well as 

coal chlorine content play an important role in mercury speciation and capture. 

Other flue gas species – especially SO3 and H2O – have also been shown to 

affect mercury speciation, tending to suppress Hg0

 oxidation to Hg2+. This is due 

to competition for active sites on the surface of carbon or other flue gas solids. In 

general, bituminous coals tend to have higher chlorine contents and also tend to 

produce higher levels of unburned carbon (UBC) in the fly ash. As a result, the 

flue gas from the burning of bituminous coals tends to contain higher amounts of 

Hg2+ species while that of subbituminous and lignite coals tends to contain more 

Hg0

 vapor. 

*Note: In general it is thought that Hg0

 will not be removed by pollution control 

equipment without first converting it to another form of mercury – either Hg2+ or 

Hgp. However, there is also the possibility for interaction between a charged 

surface and the elemental mercury vapor. These interactions may be in the form 

of electrostatic, van de Waals, and polarization energies (elemental mercury 

vapor is polarizable).7

 

The principles associated with mercury capture and emissions control from CFPPs equally 

apply to the Xact® CEMS filter media. Relying on EPA’s work cited above, we conclude our 

comments are accurate relative to the better performance of the Xact® CEMS in measuring 

mercury emissions from CFPPs being partially attributable to the absorption of mercury on 

unburned carbon and subsequent PM capture. 

Conclusion

The Xact® CEMS fails to match the results obtained with EPA reference methods when direct 

comparisons are made and these data are understood. The Xact® CEMS does not obtain 

samples isokinetically and can not be accurate. The high bias of the Xact® CEMS-determined 

metals emissions resulting from super isokinetic operation falsely overstates metals emissions. 

The Xact® CEMS measured metals emissions data are not usable or reliable for continuous 

metals emissions compliance demonstration for a HWI. 
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Please contact us to discuss the specifics of our comments or any questions you may have. 

Regards, 

William C. Anderson, PhD 

Senior Analytical Project Manager 

TestAmerica, Inc. 

Chris E. McBride, PE 

Consultant/Principal 

Focus Environmental, Inc. 
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1 Baxter, Robert, 2014. Evaluation of the Xact Multi-Metal CEMS. December 11, 2014. 

2

 Fuchs, Michael. 2014. Comments by Michael Fuchs on behalf of Veolia ES Technical Solutions. L.L.C. 

on the Draft Title V Permit and the Statement of Basis Dated October 2014

3

 Real Time Measurement Of Particulate At Low Concentration From The Emission Of Stationary Source 

In The Steel And Power Industries Using a TEOM

TM 

based Emissions Monitor, Edward C. Burgher, 

Rupprecht & Patashnick Co; Gilles Gonnet, Ecomesure, B.P. 13. 

4 Review of Monitoring Experience with Xact®

 Multi-Metal Continuous Emissions Monitor, Paper #29; 

Krag Petterson, Cooper Environmental Services, LLC, Beaverton OR; 33rd International Conference on 

Thermal Treatment Technologies & Hazardous Waste Combustors, October 13-15, 2014, Baltimore, 

MD. 

5

 Validation of Three New Methods for Determination of Metal Emissions Using a Modified 

Environmental Protection Agency Method 301, ISSN 1047-3289 Journal of the Air & Waste 

Management. Association, 56:1733–1742 (2006); Catherine A. Yanca, Douglas C. Barth, Krag A. 

Petterson, Michael P. Nakanishi, and John A. Cooper, Cooper Environmental Services, LLC, Portland, 

OR; Bruce E. Johnsen, SAIF Co., Portland, OR; Richard H. Lambert, Engineering Tech Center, Eli Lilly 

and Co., Indianapolis, IN; Daniel G. Bivins, U.S. Environmental Protection Agency, Research Triangle 

Park, NC 

6

 Environmental Technology Verification Report, Cooper Environmental Services LLC Xact 625 

Particulate Metals Monitor, Prepared by Battelle Under a cooperative agreement with U.S. 

Environmental Protection Agency, EPA/600/R-12/680, September 2012 7

 Control of Mercury Emissions from Coal Fired Electric Utility Boilers: An Update Air Pollution 

Prevention and Control Division National Risk Management Research Laboratory Office of Research 

and Development, U.S. Environmental Protection Agency, Research Triangle Park, NC. February 18, 

2005.