C

- 1



# XCEM QA APPLIED TO EVALUATION **OF XCEM/M29 MERCURY CONCENTRATION DIFFERENCES**  **MEASURED DURING RELATIVE ACCURACY TESTS** 

**1. INTRODUCTION**  Mercury represents a distinctly

different hazardous element from the others included in this test in that it is more likely to exist in the vapor phase and has been shown to exhibit distinctly different transport properties. These properties appear to have contributed to differences in the mercury concentrations measured by the different methods compared in this test. This app endix discusses the details associated with both the adjustments that were made to the XCEM calibration factors and losses of mercury from particulate deposits after sample collection.

The XCEM mercury

results were, on average, 18% greater than the pred icted concentration, 27% greater than the M29 results, 37% greater than the laboratory XRF measurements of the XCEM deposit spots, and 45% greater than the CVAA measurements on the XCEM deposit spots. Subsequent investigations of these differences strongl y suggest that the XCEM results are the best estimate of the actual mercury concentrations in the stack. It is hy pothesized that the large differences between the XCEM mercury

results and the results from the other methods is due to the loss of mercury fr om the filter deposits after the M29 and XCEM samples were collected and after the XCEM original measurements were made. This hy pothesis is described in more detail in the following subsection. The experimental measurements are described in Subsection C and the results are summarized and discussed in Subsection D. The hy pothesized model is then evaluated relative to the available data in Subsection E. A model has been developed to explain the apparent high XCEM mercury concentrations relative to M29. I n this model, mercury is lost from the particulate fraction of the M29 and XCEM filters after the initial XCEM measurements were made. That is, a substantial fraction of mercury

was associated with the particulate fraction, and the mercury in this particu late was unstable. Since all of the other analy tical methods relied on aged samples, the mercury

concentration results were low due to vaporization of particulate mercury prior to laboratory

anal ys is. As discussed in the following subsection, a substanti al amount of experimental data is available, all of which is supportive of thisC

- 2

hy pothesized model. Most of this experimental data was developed only because of the unique characteristics of the XCEM and the fact that the XCEM elemental measurement is non destructive and the spectra from each of the original measurements were archived.


## 2. **AA**

a. **Experimental**

The initial XCEM measurements were based on the anal ys is of filter deposits, which were a combination of both absorbed vapor phase mercury species and surf

ace deposits of particulate mercury

species. Each deposit was anal yz ed using three different X

- ray excitation conditions, resulting in spectra that were used to determine concentration. All spectra were archived in the XCEM computer. As such, the deposi t was available for further anal ys is and testing, and the original spectra was available for comparison with subsequently

developed spectra. Following the validation testing at TEAD, several tests were conducted b y CES to better understand the mercury

con centration differences between M29 and the XCEM.

 All of the XCEM deposit spots corresponding to all of the M29 runs were reanal yz ed b y CES’s laboratory QuanX XRF analy zer six weeks after the initial validation test. In addition, ten XCEM filter deposit s pots were anal yz ed over a period of two months to evaluate mercury stability . Spectra from these tests were compared to archived spectra from the original validation test.

 The XCEM deposit spots corresponding to M29 Runs 5 and 6 were anal yz ed first by la boratory XRF and then by

cold vapor atomic absorption by an independent laboratory

(Columbia Analy

tical Services).

 The elemental concentrations in the MSE

- TA spiking solutions corresponding to M29 Runs 5 and 6 were anal yt ically determined by

HKM labs in B utte, MT. 

## 3. **AAA**

**a. Results and Discussion**  The mercury

results for the original validation test are summarized in Table C1. There is a clear bias of about 26% between the XCEM results and the M29 results. Normally , the M29 results would be accepted as the b est estimate of stack mercury concentration and it would be assumed that the candidate method (XCEM) was in error. However, because of the total quality

assurance associated with the XCEM and the fact that the XRF anal ys is is non

- destructive, it is possib le to conduct further anal ys es to evaluate the potential cause of this difference. Additionally , the laboratory analy sis results for each component of the M29 sampling trains (i.e. probe, filter, and back half) were determined separatel y, and are availabl e for interpretation.
**Table C.1 Mercury Reported Concentrations During Year 2002 Method 29 Validation Testing.**C

- 3 **PRD M29**  **XC QN**  **CA PRD**  **XC QN**  **CA**

**1** 324 332 367 257 0.98 1.10 0.77 **2** 325 334 381 251 0.97 1.14 0.75 **3** 333 294 365 262 1.13 1.24 0.89 **4** 322 327 368 301 0.98 1.13 0.92 **5** 323 318 379 308 274 1.02 1.19 0.97 0.86 **6** 329 280 378 288 254 1.18 1.35 1.03 0.91 **7** 327 285 392 302 1.15 1.37 1.06 **8** 325 306 406 294 1.06 1.33 0.96 **9** 324 309 405 287 1.05 1.31 0.93 **10** 328 292 395 282 1.13 1.35 0.97 **11** 326 295 397 286 1.11 1.35 0.97 **12** 322 293 389 267 1.10 1.33 0.91 **AVG. 326**  **305 385**  **282 264**  **1.07 1.27**  **0.93 0.88**  **SD 3.3**  **19 14**  **19 13.8**  **0.07 0.10**  **0.09 0.03** 

**μg/DSCM RUN**  **Normalized to M29**

**i. Loss of Mercury From the XCEM Filter** 

**a. Laboratory XRF Measurements (QN)**  Two months after the validation testing, CES’s laboratory QuanX XRF analy zer reanal yz ed the original XCEM deposit samples with good replication for all elements except mercury

(see Table 5 in main body of text). A series of ten spots on the XCEM filter tape were reanal yz ed between on 6/21/02 and 7/11/02. The spots, which represent 10 XCEM runs, showed a consistent mercury loss of about 30% over the three

- week period. Other sources of error such as shifts in geometry or instrument instability

were eliminated as possible sy stematic sources of error by noting that the other elements were replicated within experimental error to a few percent.

**b. XCEM Measurements (XCEM)**  To confirm this loss of mercury , five XCEM deposit spots were re

- anal yz ed by the TEAD XCEM, which was still operating with the same conditions and calibra tion factors as used during the M29 tests about two months earlier. The X

- ray spectra from the original anal ys is of XCEM Run Numbers 939 to 943 (M29 Run Number 4) are compared in Figure C1. This comparison clearly shows that there is good agreement for t he two closest anal yt e peaks for zinc and lead, but a substantial reduction in the peak intensity for the mercury

L

- alpha anal yt e line. A comparison of the XCEM mercury concentrations measured during the M29 testing (5

- 14

- 02) with those measured with the XCEM on 7

- 25

- 02 indicate a 31.4 ± 0.4 μg/m3 reduction in measured concentration. Although this reduction might be associated with possible sy stematic errors such as sample positioning, this possible source of error was eliminated b y comparing other elemen ts such as zinc and lead as well as the ratio of mercury to these elements. TheC

- 4

reduction in mercury

to zinc ratio, for example, was 29.1%, which is in good agreement with the mercury

- measured reduction. Clearly , mercury

was lost from the XCEM deposit af ter the sample was collected and anal yz ed b y the XCEM. As discussed in the following subsection, the available data strongl y suggests that a substantial portion of the M29 mercury was also lost from the M29 PM filter deposits prior to anal ys is.
**Figure C. 1 Comparison of XCEM X** 

**- Ray Spectra Measured During Method 29**  **Testing and Seventy**

**- One Days Later.** 

**ii. Instability of M29 Mercury PM**  **Deposit Highly Likely**  Although there is no direct evidence of the loss of mercury from the M29 samples, there is a mple indirect evidence that a similar loss to that of the XCEM deposit would be expected. This indirect evidence is discussed in the following three subsections.

**c. Train Location of Mercury Deposits**  The recovery

and anal ys is of the M29 probe, filter, nitr ic acid impingers, sulfuric acid impingers and the h ydrochloric acid rinse were kept separate for both the May 2001 and May 2002 M29 tests. The results are summarized and compared in Table C2. I t is interesting to note that during the 2001 testing, only about 1% of the mercury was deposited on the quartz fiber filter. This is ty pical of most stack measurements of mercury , and as such there is little concern for the stability of the PM deposited on the filter. However, this is not the case for the 2002 m ercury measurements. During these latter tests, 18% of the mercury was deposited on the filter during runs 1 through 5 with no lead in the mercury

- nickel

- zinc spiking solution. After adding lead to the spiking solution, the percent of mercury depositing on the filter increased to 29% for the remaining M29 runs.
**Table C2. Comparison of the Location in M29 Sampling Trains Where the Mercury Was Deposited During the 2001 and 2002 Tests.** 

0 2000 4000 6000 8000 10000 12000 14000**C o** **u n** **t s** 

XCEM 051402 XCEM 072502

**Zinc Mercury** 

**Lead**C

- 5 **YEAR RUNS**  **FILT. PROBE**  **M2B M3A**  **M3B M3C**  **TOTAL** 2001 1-13 1.1 0.1 93 0.4 0.3 5.2 100 2002 1-12 24.7 0.1 71 0.2 0.1 4.1 100 2002 1-5 18.2 0.2 77 0.3 0.1 4.7 100 2002 6-12 29.4 0.1 67 0.2 0.0 3.7 100 2001 1-13 6.0 0.2 414 2.2 1.0 26 450 2002 1-12 166 0.8 484 1.6 0.4 28 681 2002 1-5 129 1.1 551 1.9 0.7 34 718 2002 6-12 191 0.6 437 1.4 0.2 24 654 **Percent on Filter** 

**Mass on Filter (μg)** 

It is interesting to note that during the 2001 M29 tests, the repo rted M29 mercury concentrations were 12% greater than the predicted concentrations; similar to the 18% (12% with corrected solution concentrations) measured this y ear with the XCEM. On the other hand, the 2002 M29 results are 6% less than the predicted co ncentrations rather than 12% greater like last y ear. These results are certainly consistent with the hy

pothesis that M29 mercury results are low because there was a loss of mercury from the M29 quartz fiber filter between the time it was collected on the filter and the time it was anal yz ed. It is also consistent with the fact that man y of the mercury compounds and amalgams of mercury are relativel y unstable and have relatively high vapor pressures. Thus, it should not be surprising that if there is a sub stantial portion of the mercury on the filter as there was during the 2002 tests, there might be a potential for significant loss due to volatilization. I t also needs to be noted that the filters were not stored in a controlled environment from the time they were collected until they

were delivered to the analy tical laboratory

several day s later. During this time, they

may have been exposed to relativel y high ambient temperatures while being transported through the western desert from Tooele, UT to Califo rnia in the back of a closed panel truck.

**d. Correlation with Percent Mercury on M29 Filter**  The percent difference between the M29 mercury results and the XCEM results is significantl y correlated with the percent mercury on the M29 filters as is illustrated in Figure C2. That is, the percent difference between the two methods (percent loss from the M29 filter) is dependent on the fraction of the total mercury measured in the M29 train that is on the filter. This observation is consistent with the proposed hypothesis for the difference between the various methods, that is loss of mercury from the M29 filter.
**Figure C2. Percent Difference Between M29 and the XCEM vs. Percent of Mercury on the M29 Filter** C

- 6 y = 1. 25x - 4 .3 223 R 2 = 0 .8 055

0 10 20 30 40 50

0 10 20 30 40

**Pe rce**  **nt of H**

**g on**  **M 29**  **Fi lte**  **r P** **e r** **c e** **n t** **D i** **f f** **e r** **e n** **c e** **B e** **t w** **e e** **n M** **2 9** **a n** **d X** **C E** **M**

**ii. Precision**  The difference in the mercury concen trations was not likely due to imprecision in either of the two measurements. Mercury was one of two elements spiked by MSE

- TA which were clearly

not present in the background stack emissions. Thus, the variability in the mercury concentration was due pr imaril y to variability in the spiking and stack flow rates. The mercury

precision as measured by the XCEM was 3.8% and 6.1% for M29, which includes the variability in the above two parameters as well as the measurement method variability

.

**iii. Mercury to N**  **ickel Ratio**

Nickel was another element that clearl y was not present in the background, and it was in the same spiking solution as the mercury . Thus, the ratio of mercury should not vary significantl y since the concentrations for these two elements was ke pt constant for these latest tests. The XCEM measured mercury to nickel ratio was 1.37 ± 0.015 (1.1% relative) and close to both the M29 ratio, 1.41 ± 0.116 (8.3 % relative), and the predicted concentration ratio based on the measured solution concentrati on ratio of 1.33. I t is interesting to note that the XCEM precision is significantly better than the M29 ratio precision, both of which should be relativel y independent of factors other than the individual method.

**iv. Low Columbia Analytical Services Resul**  **ts** The XCEM deposit samples submitted to Columbia Anal yt ical Services for CVAA anal ys is were extracted 41 day s after they were analy zed by

CES. Based on an assumed linear loss rate, the expected mercury concentrations at the time of extraction would be
a bout 10% lower than measured b y the CES XRF anal yz er. The observed difference was 14%.C

- 7



## 4. **OTHER POSSIBLE EXPLANATIONS**

**OTHER FACTORS THAT COULD CONTRIBUTE TO DIFFERENCES IN XCEM AND M29 MERCURY MEASUREMENTS** 

1. XCEM MEASUREMENTS
a. Sy stematic Errors i. Impacting All Elements 1. Volume
a. Meter: Could contribute either a positive or negative artifact. Three NI ST traceable meter/regulator compared well during test. Estimated uncertaint y is 3% of the reported flow rate. b. Volume Adjustment: The calculated volume was adjus ted by

a factor of 1.025 (increased by 2.5%) to compensate for incomplete dry ing of the air, which was determined in CES’s laboratory prior to shipping the XCEM. The uncertainty in this adjustment factor is estimated an ±0.020. Because of the actual cond itions during the testing at the Army incinerator, it is thought that this adjustment is possibly

too large for the actual incinerator conditions. Thus, it is possible that the recorded concentrations reported by the XCEM were high by 1 to 2% due to this adjustment factor.
c. Leak: This source of error would contribute a negative artifact to the XCEM results. The XCEM results were greater than the M29 results. As such, this source of error could not explain the observed difference. In addition, the pressur e drop across the filter is monitored during the testing and recorded in the sy stem. No alarms were noted and none were indicated upon review of the data. This source of possible error is expected to contribute well less than 1% to the uncertainty in the flow measurement.

2. Thin Film to Spot Calibration Factor
a. 3. Deposit Positioning (XYZ)
a. Direction of tape flow (X): The accuracy of tape movement in this direction is ±0.025 mm. TheC

- 8 XRF beam intensit y is insensitive to deposit spot position in this dir ection to ± 1mm. The uncertainty in concentration due to positioning error in this direction is expected to be substantially less than 1%. This error would bias the results low because it would tend to place the deposit at a non

- optimal position. b. Perpend icular to tape flow direction and in the same plain (Y): The large axis of the X

- ray beam is aligned in this direction. As such, the XCEM is less sensitive to deposit positioning in this direction. The alignment of the sampling plunger and the anal ys is b eam spot are accurate to ±0.050 mm. The XRF beam intensit y is insensitive to deposit spot position in the Y direction to ±1.5 mm. Misalignment of the tape has no impact on the intensity as long as the spot is on the tape. Thus, error in the alignment of the deposit and anal ys is position in this direction is expected to be insignificant; i.e., substantially less than 1%. This error would bias the results low because it would tend to place the deposit at a non

- optimal position.
c. Height of tape above tube and detector (Z): Differences between the tape deposit and calibration standards position in the Z direction can contribute sy stematic error to all of the elements. It is not subject to error in the X and Y directions because the standards are larger than the anal ys is spot. The XCEM has been designed to position the tape deposit in the middle of the XRF anal ys is plain. In this position, the beam is relative insensitive to position in the Z direction at the ±0.1 mm range. The error due to differences in p osition of the tape deposits and the standards has been empirically determined to be less than 0.5% at the 95% confidence level. In this case, the results could be biased either high or low. d. Shape of deposit: Misalignment of the XCEM plunger and the suppo rting button can cause deviations from a circular deposit. In general, the XRF intensity

is insensitive to deposit geometry so long as the spot is smaller than the beam diameter. However, because there are small variations in sensitivity

within the beam area, error can be introduced due to variations in deposit geometry . I t has been empiricall y determined that there is lessC

- 9 than a 3% difference in sensitivity for a deposit the size of the XCEM deposit, 6 mm diameter, and a 3 mm diameter spot (one fourth the area). From observation of the small deviations of spot geometry for actual deposits during these tests, it is estimated that this source would contribute no more than about 1% uncertainty to the reported XCEM results. These deviations, however, woul d be such that it would bias the XCEM results high. ii. Impacting One or More Elements 1. Transport
a. Hg b. PM
c. Hg/Ni 2. Calibration Errors
a. Uncertaint y in Standard Concentration i. Stated Concentrations ii. Sensitivity

Curves b. 3. Spectral Anal ys is
a. Energy

calibration 4. Analy te L ine In terferences
**a. Zn and Pb on Hg**  b. Ba on Cr
c. Pb on As 5. Background/Blank Interferences
a. Cr 6. aa 7. b. Random Errors i. Impacting All elements 1. Tape positioning 

### 2. **Tape Efficiency** ii. Impacting One of More Elements 1. Contamination 2. Counting Statistics 3. Signal to Noise
c. Quality

Assurance and Control Measures During Tests i. XCEM Stability : The stability of the XRF component of the XCEM was monitored with each analy sis, using Pd peak intensity from a Pd rod permanently positioned in the X

- ray

beam. This intensity varied from 95% to 105% of the m ean during the M29 tests compared. Counting statistics was responsible for most of this variability , and no drift trends were apparent. ii. Daily Zero and Span Checks: The XCEM has the capability for automated zero and span checks. These were not conduct ed duringC

- 10 this series of tests. Instead, measurements of NIST and Arm y standards were made at the beginning and end of each day of testing. iii. NI ST and Arm y Standard Measurements 1. NI ST standards (SRM 1832 and 1833) were anal yzed daily during the tests. The y were usuall y run before and after each day s runs. Recovery for Ti, V, Mn, Fe, Cu, Zn, and Pb were 100±2% of the NI ST value. Thin film NIST standards for Cr, Ni, As, Cd, Sn, Sb, Ba and Hg are not available. Hg was calibrated using its relationship to P b and other L

- line standards, and its stability was checked using a HgAg standard, which gave replicate analysis results to within ±3%. 2. The other non

- NI ST standard elements were checked with Army secondary

standards calibrated at CES laboratories. Repeat ed measurements with these standards yi elded recoveries of 100±3%. iv. Energy

Calibration: The XRF anal yz er component of the XCEM was calibrated each morning to minimize impacts of small drifts in peak position. Errors associated with peak drift would be exhi bited in standard replication, which was t ypically less than ±3%. d. Summary

of Potential XCEM Errors
e. Aa f. 2. METHOD 29 MEASUREMENTS
a. M29 Train Replication b. Velocity
c. Loss d. Contamination
e. Laboratory

Anal ys is f. Recovery

Efficiency 3. AAA



## 5. **CONCLUSION**
The weight of evid ence clearl y indicates that the XCEM mercury deposit was unstable as well as the M29 PM deposit on the quartz fiber filter. This instability was most likely

the cause of the difference between the mercury measured b y these two methods and the other method s. I t is highly likel y that if these losses had not occurred, the XCEM would have passed the PS10 relative accuracy tests.C

- 11

It is recommended that in future M29 testing, the filters be immediately sealed and cooled to at least 0°C, stored at below freezin g temperatures and digested as soon as possible after sampling.