Xcel Energy Comments to the Draft Performance Specification 18 

Xcel Energy would like to the United States Environmental Protection Agency and thank 

the OAQPS staff for allowing us to contribute and comment on the Draft Performance 

Specification 18 specifications and test procedures. Please accept our comments to this 

project.

1. It is based on our experiences of operating an HCl CEMS for 3 years that allow 

me to comment that Dynamic Spiking will not work well as a substitute for Relative 

Accuracy Test Audits (RATA) on extractive systems. On a recent RATA, we 

experienced a leak in the flange that supports the CEMS probe and calibration header that 

went undiscovered until we were performing the annual RATA test. This leak was 

undetectable during daily calibration and would not be uncovered without a stand alone 

RATA sampling train. As I understand the plumbing design of dynamic spiking, it would 

also not detect this type of leak, which would allow an inaccurate CEMS to operate in 

full compliance with PS 18. The flange that had this leak was impossible to examine or 

access without taking the boiler offline and taking the entire CEMS system apart. It is 

not a task that can be part of any routine maintenance schedule. 

2 We have performed many Method 26A tests on our emissions units and have 

found it to be a very durable, well-designed, and accurate sample train that provides 

quality data. We have found it to be a practical tool to evaluate the performance of our 

HCl monitors and have been utilizing it during our annual performance testing. It 

provides us accurate and high quality data that we have compared to our HCL CEMS.

This Draft PS 18 requires duplicate train samplings. This is both problematic and not 

necessary. Many sample locations are not designed for duplicate train testing; they may 

have only one port for testing. The RATA does not need a duplicate train to insure any 

more quality of the RM data; the leak check requirements in the method will insure 

sample integrity and once you have the HCl in solution, it is stable. We employ many of 

the EPA sample trains in our testing regimen; of any train, this one least needs duplicate 

train QA. The paired train will not insure any more quality of the RATA testing regimen. 

If the RM data is of poor quality, the RATA will fail.

3. Since on-site analysis for Method 26A is impractical, the presumption is that we 

would be performing 12 runs for every RATA. Dual trains will not provide any more 

confidence in relative accuracy. It is just an added expense, nearly doubling the cost. A 

disharmonious result of the dual train agreement due to a random event requires that run 

must be excluded. If that event occurred during a single train RATA, I would exclude 

that one from the RATA population as it would disagree with the CEMS. That same

random event has twice the chance of occurring when dual trains are employed. And it is 

not excluding 1 out of 12 runs that is the crux of the matter, but excluding 1 out of the 3 

that I am allowed that makes this a magnified problem. The in-run disagreement will not 

be uncovered until the testing firm is off the stack for a week or two as analysis is 

performed offsite. To summarize, excluding a run due to dual train disagreement is 

equivalent to an inaccurate run and will be one the three runs that will be excluded for the 

RATA. And now there is twice the chance of that happening, for twice the cost.
4. The duration of the sample time extended to 1 hour for Method 26 is not 

necessary. If the laboratory quantitation limit is low enough, the 21-minute RATA runtime is more than adequate. We suggest that PS 18 allows the tester to define the testing 

time that meets their quantitation limits requirements with a minimum of a 21 minute run.

As the analysis is going to be performed off-site, it should be expected the tested facility

will ask for more than the minimum samples to improve the chance for passing the 

RATA. It can be expected that many will require 12 runs for any PS18/Method 26A 

RATA. If the 1 hour runs are required, this will require two days of testing for a RATA 

when it is preferable to see this testing completed in one day. It can and will be as 

accurate if the sample duration is left to best practices and a good knowledge of 

laboratory detection limits. Reaching the quantitation limit or a minimum of 21 minutes 

will suffice for Method 26A. All of these requirements seem to be biased against the 

Method 26A train in favor of other technologies as a reference method. I am unsure why 

this apparent bias exists.

5. P.S. 18 must take into account the possibility of inlet CEMS monitoring. Some 

sources with HCl limits also comply with a 95% control efficiency. If continuous 

monitoring becomes required for units that use control efficiency, PS 18 must have 

flexibility to operate under inlet conditions. For example, the 2 diameter upstream/ 0.5 

diameter downstream may not be practical for inlet sites. Some of the span requirements 

may need to be addressed as the inlet concentrations can range from 50 to 5000ppm, as 

the concentrations can be quite variable at the inlet.

6. I am trying to visualize (From section 8.3.2) “70 percent of the path within the 

inner 50 percent of the stack or duct cross-sectional area.” Could a drawing or diagram 

be included with this?

7. Finally, in section 8.2 it appears there is a word missing between “accessible” and 

“where”

Thank you for allowing Xcel Energy to contribute to this process.

Regards,

John F. Buresh

Senior Environmental Analyst

Xcel Energy