December 21, 2009

Mr. Kevin Lewis

Air Sciences

Re: Barrick Cortez Hydrogen Cyanide (HCN) Results

Dear Mr. Lewis:

The purpose of this letter is to comment on the val idity of the HCN testing results provided by

Method 320 and CTM-033 from the recent emissions te sting at the Barrick Cortez facility on the exhaust stacks of the two Electrowinning (East and West) stacks, and the Preg/Barren Tank

stack. Method 320 uses a Fourier Transform Infrare d (FTIR) spectrometer to provide on-site,

real-time HCN concentration data. CTM-033 collects HCN in a basic solution for subsequent offsite ion analysis.

As you are aware, the two Electrowinning stacks and the Preg/Barren Tank were tested for HCN in October using FTIR. In November the Electrowinn ing stacks were re-tested for HCN using CTM-033. The results of the November testing were significantly lower than the October results, and the question of which data set is correct is of interest.

Method 320 is known to be susceptible to interferen ce from other gaseous species that absorb infrared light. The degree of interference is a fu nction of the concentrations of interfering species and the absorbance overlap between the interferents and the target analyte. In the current case, known and detected interfering species consisted of water vapor (H 2 O), ammonia (NH 3 ) and carbon dioxide (CO 2 ). The FTIR instrument attempts to correct the tar get analyte concentration for known interfering species. The instrument then determines the influence of the interferents by calculating an SEC (standard error calculation). T his SEC value is statistically determined by the FTIR instrument, and is calculated for each stack m atrix. A conservative rule of thumb with FTIR

data is to use two times the SEC as an estimated un certainty on results. If this approach is used on the Cortez data, the results demonstrate very la rge relative uncertainties on the HCN measurements, and consequently low confidence in th e FTIR results as shown below.

Barrick Cortez FTIR Data

HCN (ppm) CO 2 (ppm) NH 3 (ppm) H 2 O (ppm) (1)

Electrowinning West 4 +/- 3 314 +/- 368 95 +/- 2 24 ,000

Electrowinning East 5 +/- 9 137 +/- 11 144 +/- 3 37 ,000

Preg/Barren Tank 54 +/- 55 103 +/- 9 635 +/- 45 -- (no data)

1 – H 2 O data taken from EPA Method 4 measurements – FTIR data are used for spectral subtraction, but do not provide quantitative result s.

The figures on the following pages provide various FTIR spectra, including stack gas measurements and various standards. The sample spe ctra are provided to show the differences between species with very clear identification (CO 2 , NH 3 and H 2 O) and less conclusive identification (HCN).Stack Matrix EW West (red - bottom) Stacked under C O 2 Standard (pink - top)

Close-up of Stack Matrix (red - top) Overlaid with CO 2 Standard (pink - bottom).

For carbon dioxide, elements of the reference spect rum are easily observed in the stack matrix, including a close-up view of the region used to qua ntify the stack levels.Stack Matrix EW East (red - bottom) Stacked under N H 3 Standard (blue - top)

Close-up of Stack Matrix (red - top) Overlaid with NH 3 Standard (blue - bottom)

Similarly for ammonia, elements of the reference sp ectrum are easily observed in the stack matrix, including a close-up view of the region use d to quantify the stack levels.Stack Matrix (red - bottom) Stacked under H 2 O Standard (pink - top)

Close-up Stack Matrix (red – shorter peaks) and H 2 O Standard (pink – taller peaks)

As with carbon dioxide and ammonia, elements of the water reference spectrum are easily observed in the stack matrix, including a close-up view.Stack Matrix EW West (red - bottom) and HCN Standar d (blue - top)

Close-up of Stack Matrix (red - top) Overlaid with HCN Standard (blue - bottom)Extreme Close-up of Stack Matrix (red – top) Over H CN Standard (green - bottom)

The final three spectra show the FTIR stack data us ed to estimate HCN levels. The zoomed in figure shows the lack of obvious agreement between the stack data and standard. While there are clearly common peaks in the stack data and refe rence standard, there are obvious nearby peaks in the stack spectra indicating some other un identified species with IR absorption in the same region that is used to quantify the HCN. This uncertain agreement is reflected in the high

SEC for the HCN FTIR data.

As with Method 320, and any measurement method, CTM -033 is also subject to potential interferences. The interferences provided in CTM-0 33 consist of acid gases which would reduce the impinger pH, sulfides, oxidizing agents, and bl ank contamination. The absence of acid gases was confirmed by checking the impinger pH after eac h test run. No sulfides or oxidizing species are suspected, and the reagent and train blanks sho wed non-detected cyanide for all samples.

So interferences with the CTM-033 results are not e xpected.

Because of the demonstrated interference issues wit h the Method 320 data, and the apparent lack of similar concerns with the CTM-033 data, it is believed that the FTIR results are subject to substantially higher uncertainty than the CTM-033 d ata. Consequently, the CTM 033 data are believed to be the more representative results, eff ectively invalidating dissimilar FTIR results. Based on this analysis, APT has prepared a final re port for the CTM 033 test data only, which has already been delivered to Barrick Cortez. The summ ary sheets for the Method 320 data are

attached.

Respectfully,

Paul Ottenstein

Technical Director