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“MONITORING OPTIONS AND/OR CONSIDERATIONS FOR MERCURY FROM GOLD MINES” 

NDEP RESPONSE 

February 26, 2010 

A. CEMS to Roasters 

NDEP re-asserts that CEMS for roasters would not be feasible at this time, given the current state of 

the CEMS technology and the inability to certify a CEM for the mercury concentration levels 

typical of an ore roaster. Also pertinent is the concern that the data generated by the CEMS could 

not be restricted to use as a tool for evaluating “operations and maintenance.” Any data monitored 

and recorded using CEMS could be deemed “credible evidence” and would be ripe for compliancerelated litigation. 

Of further concern is that the CEM standard would be based on “manufacturer’s specifications.” To 

our knowledge, CEMS technology varies by manufacturer and, as a result, the associated 

maintenance, calibration and operations also varies. This variability would make it difficult to 

evaluate the performance of controls between the roasters. NDEP’s preference would be to suspend 

consideration of mercury CEMS on roasters until a monitor standard and a certification/calibration 

standard have been promulgated. Due to the rapid promulgation of the FMACT, it is unlikely that 

the proposed CEM requirement (for only 4 ore roaster stacks) could drive the technology to meet 

implementation timelines. 

NDEP does find merit in the approach of annually reviewing and re-establishing operational 

parameters during a stack performance test. This approach could help verify operational 

parameters, especially if ore resources or processes vary. 

The NDEP recognizes EPA’s concerns that emission units with the potential to be very large 

mercury emitters may deviate or “spike” between annual stack tests. This concern is alleviated with 

additional test data to increase statistical confidence, comprehensive parametric monitoring, and 

alarms and interlocks. 

B. Carbon adsorbers 

1. NDEP reiterates its previous stance that portable mercury analyzers are currently not an 

appropriate regulatory monitoring or compliance tool. Their usefulness is limited for a number of 

reasons. There is no promulgated standard for the analyzers or the calibration of the analyzers. 

Typically, portable analyzers are intended for ambient air measurements and not an exhaust gas 

stream. Acquiring a time-weighted average from the analyzer’s measurements and the application 

of the data is questionable and re-visits legal concerns regarding “credible evidence.” Proper 

training, operation, maintenance of the portable analyzer and prevention of contamination will also 

be crucial, as the mining facilities, and not professional test companies, would perform the portable 

analyzer measurements. 
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2. NDEP recognizes EPA’s concern that carbon beds may experience “break through” and “spikes” 

between annual stack test events. Of note, it is not clear if all carbon beds would be required to 

have the proposed sorbent trap. Would a threshold PTE establish applicability? It may have limited 

value to manage/regulate traps on units with low PTE that already have multiple parametric 

monitoring requirements. NDEP would recommend that the sorbent trap option not be 

implemented alone, but co-implemented with option #3 of this Section. 

3. This is NDEP’s preferred option and is most similar to the NMCP approach. This approach has 

been vetted by the NDEP and the industry and is currently being implemented. 

4. The NDEP does not feel that this should be a stand-alone option. If implemented, it should be 

co-implemented with item B.3, above. The “trigger” to re-examine the fixed replacement time 

based upon a “change in process” is a bit clumsy and perhaps makes this option unnecessary, given 

the relative simplicity of directly measuring the carbon as established in B.3, above (and in 

conjunction with annual stack testing). 

C. Carbon adsorber temperature 

The NDEP does not take issue with the proposal to measure carbon bed temperature. However, it 

needs to be clarified if the continuous monitoring requires continuous record keeping and what, if 

any, averaging periods might apply. The NDEP also notes that it is more difficult (and costly) to 

retrofit existing units with continuous monitoring. Continuous monitoring also requires more 

Agency resources to review the records--it is not clear to NDEP that this is a meaningful ROI. 

Other options for consideration are alarms and interlocks to replace continuous monitoring. Alarms 

and interlocks are more readily retro-fitted onto existing equipment and can alert, or automatically 

shutdown process that vary from pre-defined operational parameters. Alarms and interlocks are 

useful to ensure continuous performance. 

D. Venturi Scrubber 

Water flow rate and pressure drop are meaningful parameters. EPA may also consider some 

language regarding the quantity and/or maintenance of packing materials/trays. As noted in 

Sections above, interlocks and alarms may be effective to perform “continuous monitoring.” 

E. Monitoring for roasters (scrubbers) 

In the EPA-provided draft notes, unique roaster regulations were proposed for each roaster by 

facility. The NDEP recommends that regulations not be specifically tailored for each facility, but 

rather to write standards that could apply to all roasters, including potential new roasters. The 

NDEP proposes that roaster regulations be generated for two groups of roasters: roasters that use 

titration and roasters that use real time monitoring of ORP and pH. 

The Newmont and Barrick roasters both use titration to manage their mercury scrubbers. Barrick 

measures chloride ion content by titration 1x per day and Newmont does it 4x per day. Newmont 

likely does it 4x per day due to the requirements of the acid plant. 
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Of note, the draft document provided by EPA states that Barrick also monitors additional scrubber 

parameters such as spray header pressure and temperature and states that nothing beyond titration is 

performed for Newmont. A review of Title 5 and Phase-2 permits for Newmont and Barrick reveals 

that both roasters monitor additional operational parameters and several of those parameters are 

common to both roasters. 

It makes sense that any facility which recovers Hg0 from calomel via electrowinning have a 

scheduled bleed event. This would apply at Newmont and Jerritt. Although Barrick does not 

electrowin their calomel, their bleed events are still critical for scrubber performance. Of note, 

Newmont’s and Jerritt’s electrowinning of chlorinated calomel has not been specifically identified 

in a permit or been stack-tested to assess the potential mercury emissions from this process. 

In contrast to the Barrick and Newmont scrubbers, Jerritt performs continuous ORP and pH 

monitoring with multiple monitors to follow the chemical reaction of their mercury scrubber. While 

the continuous ORP and pH are surrogates for titration, the benefit is that the continuous 

measurements will follow any potential material or process deviations closer to “real time” than 

daily or shift titration measurements and allow quicker correction. The ORP and pH monitors are 

attached to alarms and interlocks. The real-time ORP and pH monitoring at Jerritt is required 

pursuant to the current Consent Decree. It would be undesirable to put Jerritt in a situation where 

their real-time monitoring would conflict with the FMACT requirement to perform lab titration. 

For NvMACT, NDEP will also focus on quench/condensers/heat exchangers prior to scrubber trains 

which are critical to conditioning the gas stream. In addition, particulate controls such as entoleters 

(Jerritt) and wet ESPs (Newmont and Barrick) also play a critical role in conditioning the gas 

streams prior to the mercury scrubbers. 

Roasters and their related control technology trains could also benefit from alarms and interlocks on 

crucial components.