6. Where should "testing at the...outlet of the last emission control device installed on the selected unit" be conducted?

Outlet testing should be conducted at a suitable location following the applicable control device. This location may be in the stack or in ductwork prior to the stack as long as there is no other control device following the test location.

7. Does EPA have an approved list of stack testing contractors that can perform the speciated mercury analysis?

No. EPA does not have an approved list of stack testing contractors that can perform the speciated mercury analysis. Each company/facility is free to choose it's own test contractor as long as all the criteria for the test program are met.

8. What do I do if I have a sampling location that does not meet Method 1 requirements? What if I have multiple ducts around the control device to be tested?

There are a number of conditions that would cause a sampling location to be unsuitable according to the requirements of Method 1 and, ordinarily, indicate that such a location be rejected or cause increased costs to be incurred. However, because of the nature of the constituent being investigated in this information collection effort (i.e., speciated mercury), the Agency believes that there are approaches available that will allow sampling locations to be used that are consistent with the intent and data quality requirements and that do not cause additional costs to be incurred.

Where the ductwork leading to the control device to be tested does not meet the Method 1 criteria, this should be noted in the proposed draft site-specific test plan. However, since little can reasonably be done to correct the situation, sampling may be performed at the most accessible inlet location without conducting the three-dimensional flow testing that may be needed at several inlet locations to find a suitable location. This is because (a) mercury is primarily in the gaseous phase and is not impacted by uncertainties in the gas flow and the isokinetic sampling rate, and (b) stratification of mercury species is not expected.

In situations where multiple ducts are found and it is believed infeasible to simultaneously sample all of the ducts because of the additional incurred costs, sampling may be conducted in only one duct so long as appropriate process conditions are monitored for all ducts. In this event, the proposed draft site-specific test plan should fully describe the situation. This is because, again, mercury speciation is not expected to be stratified. If this situation occurs at the outlet, however, it is preferred (although not required) that the sampling occur at the stack where there is only one duct.

If the depth of the duct to be sampled is large (e.g., greater than 16 feet) and traversing from opposite sides is not possible or practicable, sample traversing may be done only to a depth of 16 feet. This will alleviate problems incurred with the use of longer probes and, again, results from the fact that the mercury species do not stratify in the ductwork.

In all cases, the specifics (e.g., procedures employed to obtain a representative sample; number of sampling points used) should be detailed in the proposed draft site-specific test plan and, later, in the final emission test report.