From: Rob Bamford <rbamford@ndep.nv.gov> 

 

To: Chuck French/RTP/USEPA/US@EPA 

 

Cc: Mike Elges <melges@ndep.nv.gov> 

 

Date: 10/21/2010 11:29 AM 

 

Subject: ore dryer 

 

Hello Chuck,

Sorry about the confusion on the dry grind paper, you are correct I sent the 

wrong document. The correct document is attached. Also, in regards to a phone 

call with the test group, there is a section of the attached document which I 

think would be relevant to the testing discussion if the testing group could read 

it first. It provides a basis and data examples for our concern regarding Test 

Methods other than M29 and the poor correlation between M29 and other Methods. 

Let me know what you think about sharing with that doc with the test group before 

the discussion and I’ll go chat with Mike and see what is schedule looks like.

Thanks,

-Rob

(See attached file: Review of the Goldstrke Orer Dryers.doc)

|-------------------+-----------------------------|

| (Embedded image |Rob Bamford |

| moved to file: |Supervisor, Nevada Mercury |

| pic00138.jpg) |Control Program |

| Description: |Nevada Division of |

|logo_new01_print_s |Environmental Protection |

| |Bureau of Air Quality |

| |Planning |

| | |

| |Phone: 775-687-9330 |

| |Cell: 775-315-3655 |

| |Fax: 775-687-6396 |

| |E-mail: rbamford@ndep.nv.gov |

|-------------------+-----------------------------|
NDEP-NMCP Review Summary – Barrick Goldstrike

1

Recently, Barrick Goldstrike has submitted a note in response to NDEP’s questions associated with 

ore dryer mercury source test results performed in August 2007. The review was conducted to obtain the 

following primary objectives: 1) to assess representative source test for 2007 annual emission reporting, 

2) to investigate the possibility of contamination during source testing, 3) to analyze the loading of 

mercury to mills over time, and 4) to estimate the effectiveness and appropriateness of the sorbent trap 

method as a reference method proposed by Barrick Goldstrike.

1. Uncertainty Analysis of Source Test Results

The coefficient of variation (COV) is used to measure the consistency of the data across source test 

results. The coefficient of variation (COV) of each test result set is calculated as standard deviation 

divided by mean. It is known that distributions with COV < 1 are considered low-variance, while those 

with COV > 1 are considered high-variance. In other words, a high COV value reflects inconsistency 

among the spiked samples within each test run. The statistical analysis is carried out with source test data 

set available. Average, standard deviation, and coefficient of variation (COV) are calculated for each test 

data set and the results are presented in Table 1. Figure 1 shows the variations of the minimum, average, 

and maximum mercury mass observed during each source test. In fact, the number of samples for each 

data set is insufficient to draw a clear conclusion from statistical analysis. Nevertheless, it seems that the 

October 07 source test data set would provide a relatively better consistency compared to other test data 

set with COV < 1 for Sys 15 and Sys 16, respectively.

Table 1. Comparison of the Consistency of Various Source Test Results

(Note: This result is obtained using source test data sets provided by Barrick Goldstrike)

Date System Total Hg 

Mass (μm)

Average Hg 

Mass (μm) Std Deviation

Coeff. of 

Variance 

(COV)

March 2007

Sys 15 Run #1 5.93

Sys 15 Run #2 4.18 4.57 1.21 0.27

Sys 15 Run #3 3.60

Sys 16 Run #1 158.60

67.75 80.50 1.19 Sys 16 Run #2 39.35

Sys 16 Run #3 5.30

August 2007

Sys 15 Run #1 2292.92

868.00 1234.97 1.42 Sys 15 Run #2 204.24

Sys 15 Run #3 106.85

Sys 16 Run #1 57.49

Sys 16 Run #2 38.91 50.66 10.22 0.20

Sys 16 Run #3 55.59

A Review of 

the Response of Barrick Goldstrike
NDEP-NMCP Review Summary – Barrick Goldstrike

2

Date System Total Hg 

Mass (μm)

Average Hg 

Mass (μm) Std Deviation

Coeff. of 

Variance 

(COV)

October 2007

Sys 15 Run #1 11.78

Sys 15 Run #2 9.37 7.62 5.26 0.69

Sys 15 Run #3 1.71

Sys 16 Run #1 6.03

Sys 16 Run #2 5.84 4.86 1.86 0.38

Sys 16 Run #3 2.72

April 2008

Sys 15 Run #1 2.29

17.45 26.35 1.51 Sys 15 Run #2 47.88

Sys 15 Run #3 2.19

Sys 16 Run #1 2.98

Sys 16 Run #2 4.61 3.59 0.89 0.25

Sys 16 Run #3 3.19

Figure 1. Variations of the Minimum, Average and Maximum Hg Mass Observed during Each Source 

Test (Note: This graph is created using source test data sets provided by Barrick Goldstrike)

1

10

100

1000

10000

1 2 3 4 5 6 7 8

Source Test Events

Hg mass (um) in Logarithmic Scale

Minimum

Average

Maximum

Sys 15

March 07 

Sys 16

March 07 

Sys 15

August 07 

Sys 16

August 07 

Sys 15

Oct. 07 

Sys 16

Oct. 07 

Sys 15

April 08 

Sys 16

April 08 
NDEP-NMCP Review Summary – Barrick Goldstrike

3

2. Investigating the Possibility of Contamination during Source Testing

Barrick Goldstrike’s pre-heater systems (System 15 and System 16) were designed to operate 

identically so mercury emission rates should not show a considerable difference between the two systems. 

However, source test results demonstrate a wide distribution ranging from 2.0 (ug/dscm) to 34.2 

(ug/dscm) or 0.0008 (lb/hr) to 0.015 (lb/hr) in average total mercury concentration excluding the

erroneous August 07 test results (see Table 2). In March 2007, Barrick Goldstrike conducted an 

unofficial source test of mercury emitted from pre-heaters for internal use. The test results seem to be 

consistent except Sys 16-Run 1 and Sys 16-Run 2 of Table 3. For this reason, NMCP proposes several 

possible scenarios for a sudden change in mercury emissions during stack source testing. 

Table 2. Summary of Stack Source Test Results

System March 07

ug/dscm (lb/hr)

August 07

ug/dscm (lb/hr)

October 07

ug/dscm (lb/hr)

April 08

ug/dscm (lb/hr)

Sys 15 1.9 (0.001) 341.2 (0.154) 3.5 (0.0017) 10.0 (0.0037)

Sys 16 34.2 (0.015) 25.2 (0.01) 2.5 (0.001) 2.0 (0.0008)

Table 3. Unofficial March 07 Source Test Results

System & Run# Hg Emission

(ug/dscm)

Sys 15 - Run1 2.44

Sys 15 – Run2 1.73

Sys 15 – Run3 1.54

Sys 16 - Run1 82.43

Sys 16 – Run2 17.58

Sys 16 – Run3 2.68

2.1 Baghouse operation & maintenance

The baghouse operational data was investigated to estimate the impact of a substantial increase of 

particle bound mercury levels during source testing. Pressure drop across the baghouse gives an 

indication of the resistance to gas flow (drag) and the effectiveness of the filtration system. In general, 

when the baghouse is operating properly the removal efficiency is usually in excess of 99.9%1

. However, 

abnormal baghouse operations such as sudden failure or deviations outside of manufacture’s 

recommended parameters could cause greatly increased particle-bound mercury levels due to very fine 

particles smaller than approximately 10μm2

.

According to the EPA Baghouse design manual, a baghouse is normally operated with a pressure

drop across the unit of 4 to 10 in H2O and many units operate at less than 6 in of H2O. It is known that 

performance variations such as pressure drop, gas flow rate, and bag failure in a baghouse system could 

make it difficult to provide predictable particulate levels which directly affect total mercury

concentration. The following is a summary of the pressure drop of Sys 15 and Sys 16 and is given in 

Table 4.
NDEP-NMCP Review Summary – Barrick Goldstrike

4

Overall, the baghouse pressure drops appeared to be in the manufacture’s recommended range (1.5 to 

11.0 in H2O). There were no significant differences in the pressure drops among the four stack source test

results, although there was a slight increase of pressure drop on the October 07 source test. The data 

demonstrates that the increase in pressuredrop had no impact on mercury emissions.

Table 4. Comparison of the Baghouse Pressure Drops and Mercury Emissions

Test Date System

BH Static Classifier

Avg. ∆P (in H2O)

BH Dynamic Classifier

Avg. ∆P (in H2O)

Hg Emission 

(lb/hr)

March 2007 System 15 4.44 4.25 0.001

System 16 4.88 4.25 0.015

August 2007 System 15 4.33 5.05 0.154

System 16 5.29 5.19 0.010

October 2007 System 15 9.11 7.69 0.002

System 16 7.21 6.26 0.001

April 2008 System 15 4.03 4.16 0.004

System 16 4.05 4.06 0.001

2.2 Dust pickup points

It was hypothesized that a large number of dust pickup points located at each air slide may be a 

potential unpredictable and intermittent mercury source. Barrick Goldstrike recently responded to 

NDEP’s question regarding the role of dust pickup points saying that it was designed to maintain a 

negative pressure in the air slides and to control fugitive dust (see Figure 2). Any particulate fugitives 

would be under negative pressure and would be routed to the pick-up point baghouse and not emit 

directly to atmosphere. Thus, dust pickup points do not seem affect a dramatic increase in mercury 

emission.

Figure 2. Schematic Diagram of 

Dust Pickup Points

Dust pickup points
NDEP-NMCP Review Summary – Barrick Goldstrike

5

2.3 Contamination of sample impinger solutions

Figure 3 illustrates the EPA reference method 29 for total mercury analysis. Generally, the first two 

impingers containing hydrogen peroxide (H2O2/HNO3) solution are used to capture only oxidized 

mercury (Hg2+) and the acidified potassium permanganate (KMNO4/H2SO4) impingers are used to capture 

elementary mercury (Hgo

)

3

. 

Figure 3. EPA Ref. Method 29 - Sampling Train 
NDEP-NMCP Review Summary – Barrick Goldstrike

6

Complete mercury level analysis results by each impinger were provided to NDEP-NMCP. Most of 

the mercury source test results seem relatively consistent except for the August 07 source test results.

Oxidized mercury (Hg2+) concentration levels after the HNO3 rinse showed much lower concentration 

levels than the hydrogen peroxide impingers. It seems reasonable to assume that there is almost no 

mercury residue left on the surface of the impingers.

However, considerably high levels of elemental mercury (Hg0

) were found in an aqueous solution of 

the KMNO4 impingers and HCl rinse for March 07 Sys 16 and August 07 Sys 15 stack source tests. It 

could be evidence of possible contamination. According to Serne4

, KMnO4/H2SO4 absorbing agent used 

in the impingers should be prepared onsite so it is fresh each test day. To avoid contamination of the 

absorbing reagent during preparation onsite, a clean sample train preparation and cleanup area must be 

used. 

In addition, Laudal5 from the Federal Energy Technology Center of DOE (Department of Energy)

reported that “It has been found that the greatest source of error in the Ontario Hydro Method (OHM) 

procedure is not in the sampling but in the preparation of the impinger solutions following sampling. The 

preparation steps include 1) tearing down the impinger train, 2) transferring solutions to flasks or bottles, 

and 3) digesting of the solutions”. OHM is a modification of EPA Method 301, and is identical to 

Method 29 except for three additional impingers containing KCl. Hence, a mercury (mostly in elemental

mercury form) leak to the surrounding area could likely be the cause of potential contamination while

conducting sample recovery in the field. As a result, elemental mercury levels may be abnormally high in 

the KMNO4 impingers which capture elemental mercury. 

Source test results of Sys 16 Run #1 and Run #2 illustrated in Table 3 could be a good example of 

contamination, showing unexpectedly high mercury levels compared to other results. Mercury emissions 

from Sys 15 and Sys 16 would be expected to be in the range of 1 to 3 (ug/dscm) because source testing 

was conducted under nearly the same operational conditions (ore mercury content, throughput, 

temperature, velocity, flow rate, baghouse pressure drop, and so on). However, some observed values 

showed extremely high levels of mercury during the continuous source testing events. Therefore, Sys 16 

Run #1 and Run #2 shown in Table 2 imply a strong evidence of contamination.

3. Effect of the Mercury Loading:

The effect of the mercury loading on mercury emissions was investigated using the data set available. 

Figure 4 depicts the variation in the daily feed level of mercury for Sys 15 from May ‘07 to May ‘08. A 

polynomial curve fitting is used to best fit a series of data points to a line and is shown by a red line in 

Figure 4 below. The average feed levels of mercury on August 3 and October 2 were found to be 

approximately 25.2 (ppm) and 8.2 (ppm), respectively. The mercury feed level on August 3 was increased 

about 28.6% higher than the daily average mercury feed level of approximately 18 (ppm). On the 

contrary, the mercury feed level on October 22 was decreased by 54.4% lower than the average mercury 

feed level. The October stack source test results showed a relatively lower emission of mercury with a 

given lower mercury content in ore (see Table 5). 

In conclusion, it would be difficult to conclude that the relatively high levels of mercury feed (7ppm 

higher than daily average) on August 3 could make unexpectedly high contributions of mercury emissions 

when compared with the October test results. 
NDEP-NMCP Review Summary – Barrick Goldstrike

7

Figure 4. Variations in the Daily Feed Level of Mercury for Sys 15 (May ’07 - May ‘08)

0

10

20

30

40

50

60

1 51 101 151 201 251 301 351 401 451 501 551 601 651

Test Event

Hg Loading (ppm)

Sys 15

Poly. (Sys 15)

Average Hg loading level = 18.1 (ppm) Polynomial curve fitting

August 3, '07 

(25.2 ppm)

Oct. 22, '07 

(8.2 ppm)

May 11 - July August - October Nov. - Dec. Jan. - March April - May

April 4, '08 

(13.6 ppm)

Year 2007 Year 2008

Mercury Emissions Observed

Log Hg 

Emissions 

(μg/dscm)

0.5

0.0

1.5

1.0

2.5

2.0
NDEP-NMCP Review Summary – Barrick Goldstrike

8

Table 5. Comparison of the Average Feed Levels and Emissions of Mercury

Date Average Feed Level of 

Mercury (ppm)

Mercury Emissions

ug/dscm (lb/hr)

August 3, 2007 (Sys 15) 25.2 341.2 (0.154)

October 22, 2007 (Sys 15) 8.2 3.5 (0.0017)

April 4, 2008 (Sys 15) 13.6 10.0 (0.0037)

According to Barrick Goldstrike’s memo on September 18, 2008, total mercury contents in ore were

measured by Barrick Goldstrike and third party analytical laboratory using 2 different analytical methods, 

ICP (inductively coupled plasma) and CVAA (cold vapor atomic absorption), for the same ore samples. 

The results showed remarkable differences between the ICP and CVAA methods. In general, the ICP 

method allows simultaneous or rapid sequential determination of mercury in a short period of time6

. The 

CVAA method is extremely sensitive to interference from volatile organics, chlorine, and sulfur 

compounds6

. Knight et. al7 conducted a comparative study and found that the ICP-MS measurements 

appeared to be 57% of the CVAA values for the real hair samples. The authors confirmed that there were 

significant losses of mercury that occur when using ICP-MS. Clearly, further investigations might be

necessary to assess this issue, and particular attention should be paid to quantitative analysis of mercury 

content in ores.

4. Estimating the Effectiveness and Appropriateness of the Sorbent Trap Method 

Barrick Goldstrike stated that EPA Method 29 (H2O2 and KMnO4 impingers) and OHM (H2O2,

KMnO4 and KCl impingers) are very similar methods in theory and should produce very similar results if 

total mercury is only considered. However, according to the D.O.E. EERC (Energy & Environmental 

Research Center) final report5

, OHM appears to be much higher than EPA Method 29 in total mercury

concentration. The main reason was primarily due to additional three impingers containing potassium 

chloride solutions (KCl) which exhibited high mercury spikes compared to H2O2 and KMnO4 impinger 

solutions as shown in Table 6. The OHM test results from mining sites in Nevada also showed similar 

trends like the D.O.E. EERC test results. Therefore, it seems obvious that OHM is considerably higher 

than EPA Method 29 in total mercury concentration. 

Originally, Ontario Hydro Method (OHM) and EPA Method 29 were the only acceptable reference 

methods for mercury measurement. In August 2007, EPA released a direct and final rule that allowed two 

other reference methods such as EPA Method 30A (instrumental reference method) and 30B (sorbent trap 

method). EPA Method 30B (sorbent trap) was developed to analyze vapor phase mercury levels (e.g., Hgo

and Hg2+

)

8

. Method 30B does not consider quantifying particle-bound mercury. Method 30B is known to 

be very sensitive to high temperature and pressure. Furthermore, sampling using the Method 30B

procedures is strongly affected by the high particulate loading. The sorbent trap tests conducted by Nunn 

showed that the high temperature of the off-gas stream resulted in desorption of the spiked mercury 

samples, and prevention of adsorption of the native mercury vapors in the gas stream9

. 

Table 6. Direct Comparison of Performance of Three Mercury Absorbing Impingers5

Sample ID KCl (g/m3) H2O2 (g/m3) KMnO4 (g/m3) Total Hg (g/m3)

ZM-D1-OH-1 17.36 0.07 7.80 25.24

ZM-D1-OH-2 9.47 0.07 4.30 13.85

ZM-D1-OH-3 17.41 0.01 7.14 24.57
NDEP-NMCP Review Summary – Barrick Goldstrike

9

ZM-D1-OH-4 4.92 0.04 4.47 9.44

ZM-D2-OH-1 4.21 0.06 2.17 6.45

ZM-D2-OH-2 10.12 0.45 5.96 16.54

ZM-D2-OH-3 5.45 0.36 3.37 9.19

ZM-D2-OH-4 11.27 0.56 5.78 17.62

On the other hand, Barrick Goldstrike compared the relationship among three source test methods 

(Method 29B, OHM, and Sorbent Trap) using August 07 source test results and proposed that the sorbent 

trap method would provide consistent results (see Table 7). In fact, the sorbent trap method does not 

require the complex sample recovery procedures which could cause a possible source of error. However, 

it would not be appropriate to conclude with only one data set. Hence, further test results are required to 

support Barrick’s statement. 

Table 7. Comparison of Three Source Test Methods Used (August 2007)

System M29 OHM Sorbent #1 Sorbent #2 Sorbent #3

Sys 15 (ug/dscm) 341 3953 0.68 1.05 0.91

Sys 16 (ug/dscm) 25 1598 0.61 1.13 0.32

5. Conclusions & Recommendations

Conclusions

The following conclusions are obtained based upon the analysis of source test results provided by

Barrick Goldstrike.

1. Statistical analysis is performed to compare the consistency among source test data sets. The 

October 07 source test data set shows a better consistency with low COV values for both Sys 15 and 

Sys 16.

2. Baghouse pressure drops and several dust pickup points do not seem to have the effect of a sudden 

increase in mercury concentration during source testing.

3. Unexpectedly high levels of total mercury would seem to have happened by contamination while 

preparing impinger solutions and performing sample recovery including acid-rinsing the impinger 

surfaces. Therefore, further investigation of future source test data are more likely required to 

understand and clarify the impact of contamination. 

4. The effect of the mercury loading on mercury emissions was investigated and found that the 

relatively high levels of mercury feed on August 3 could not be a main reason for extremely high 

levels of mercury emissions. 

5. Each mercury emission test method has distinct advantages and disadvantages depending on the 

test objectives. Impinger methods require much attention to many factors including: acid rinse of the 

impinger surfaces (or sample recovery), moisture content, particle size, flue gas temperature, 

flowrate, isokinetic sampling, etc. The sorbent trap method is relatively simple to prepare in the field 

and potentially lead to less contamination while conducting source sampling6

. However, it should be 
NDEP-NMCP Review Summary – Barrick Goldstrike

10

noted that the sorbent trap method is only designed to measure total vapor phase mercury levels under 

low particulate conditions. In addition, the high temperature of the off-gas stream could result in 

desorption of the spiked mercury samples, and prevention of adsorption of the native mercury vapors 

in the gas stream. Thus, the sorbent trap method would seem not to be appropriate.

6. It would be unfound to conclude that Sys 16 (south pre-heater) showed produce substantially more 

mercury emissions than Sys 15 (north pre-heater) due to somewhat different operational conditions

such as ore mercury content, throughput, and baghouse performance. 

7. In closing, the March 07 test data submitted from Barrick Goldstrike was unofficial and the August 

07 test showed a strong evidence of contamination. Moreover, the April 08 test was outside of the 

reporting year. Therefore, NDEP-NVMC concludes that the October 07 test data is the most 

appropriate for the 2007 annual emission reporting of ore mill dryers (Sys 15 & 16).

Recommendations

1. Field blanks are recommended as part of the QA/QC activities associated with stack sample 

collection. If the field blanks show contamination above background or surrounding levels, steps must 

be taken to reduce the contamination to below background levels5

. For this reason, field blank sample

results would be very important in interpreting and understanding source test results. Therefore, it 

would be helpful if Barrick Goldstrike could provide the results for blank samples to ensure that there 

is no possible contamination around the sampling location.

2. It would be recommended that Method 29 stack source testing should be made by at least two or 

three trained operators for effective stack sampling and source recovery. Ideally, the operator should 

be a licensed or certified technician to minimize contamination errors. It is questionable if one 

operator, alone, could conduct a proper Method 29 test. 

References

1. U.S. Environmental Pollution Agency, “Operation and maintenance manual for fabric filters”, 1984.

2. Sigma-Aldrich, Whatman quantitative filter papers, Ashless and Grad 40.

3. U.S. Environmental Pollution Agency, “Method 29 – Determination of metal emissions from stationary 

sources”, http://www.epa.gov/ttn/emc/promgate/m-29.pdf.

4. J. Serne, “An overview and comparison of available mercury emission test methods for boilers”, SES 

(Source Evaluation Society) Conference, 2006.

5. D. Laudal, “Field validation of the Ontario Hydro mercury speciation sampling method at site E-29”, 

U.S. DOE Federal Energy Technology Center, July 1999. 

6. U.S. Environmental Pollution Agency, “Test methods for evaluating solid waste, physical/chemical 

methods”, http://www.epa.gov/waste/hazard/testmethods/sw846/pdfs/chap3.pdf, 2007.

7. R. Knight, S.J. Haswell, S.W. Stephen, and J. Batty, “Determination of mercury in hair by coupled 

CVAA-ICP-MS”, J. of Analytical Atomic Spectrometry, Vol. 14, pp.127-129, 1999. 
NDEP-NMCP Review Summary – Barrick Goldstrike

11

8. U.S. Environmental Pollution Agency, “Method 30B – Determination of total vapor phase mercury 

emission from coal-fired combustion sources using carbon sorbent traps”, August 2007. 

9. A. Nunn, “Mercury methods evaluation test program results”, The Air Compliance Group, August 

2007.