Summary of Comments and Responses on Update of Continuous Instrumental Test Methods Prepared March 2006 Proposed in the Federal Register on October 10, 2003 ( This page included to provide for two sided copying) i TABLE OF CONTENTS Section No. Page 1.0 Summary 1 2.0 List of Commenters 2 3.0 Public Comments and Responses 10 3.1 Rationale for Revisions 10 3.2 Uncertainty of Data 11 3.3 Sampling System Bias, Calibration Drift, and Analyzer Calibration Error 15 3.4 Interference Test 22 3.5 Alternative Dynamic Spike Check 26 3.6 Sampling Traverse Points 29 3.7 Sampling Dilution Systems 36 3.8 Moisture Removal System 37 3.9 Equipment Heating Specifications 41 3.10 Technology Specific Analyzers 42 3.11 Calibration Gases 44 3.12 NO2 Converter Efficiency Test in Method 7E 48 3.13 General Comments 53 3.13.1 Supportive Comments 53 3.13.2 Adverse Comments 54 3.13.3 Other Comments 55 3.14 Specific Comments on Method 3A 61 3.15 Specific Comments on Method 6C 67 3.16 Specific Comments on Method 7E 79 3.17 Specific Comments on Method 10 119 3.18 Specific Comments on Method 20 125 ii ( This page included to provide for two sided copying) 1 1.0 SUMMARY On October 10, 2003, the U. S. Environmental Protection Agency ( EPA) proposed amendments to five instrumental test methods in Appendix A of 40 CFR Part 60. Methods 3A, 6C, 7E, 10, and 20 determine diluent ( oxygen and carbon dioxide), sulfur dioxide, nitrogen oxides, and carbon monoxide emissions from stationary sources. The methods were developed for boilers, electric utility plants, refinery catalytic cracking catalyst regenerators, and gas turbines covered under the New Source Performance Standards ( NSPS) in 40 CFR Part 60. They were later adopted into the Clean Air Markets ( Acid Rain) regulations and State and regional programs. The test methods were not developed at the same time and do not contain consistent equipment and performance requirements. Currently, some methods require more up to date equipment than others and some have more stringent performance requirements than others. These dissimilarities have hampered the current trend of using the methods together in the field. The proposal noted collective changes that would render the methods easier to use by harmonizing their requirements. Obsolete requirements were also updated and flexibility was added by allowing alternatives to various equipment and performance specifications.

On August 27, 1997 ( 62 FR 45369), many of the updates of this action were proposed with a larger action that amended the stationary source testing and monitoring rules in 40 CFR Parts 60, 61, and 63. In that proposal, minor revisions and updates were made and all test methods and performance specifications, and they were revised into the new Environmental Monitoring Management Council ( EMMC) format. Several commenters asserted that the preamble gave inadequate notice of the changes being made to the instrumental methods. They argued that the proposal provided an inadequate basis and purpose statement and that it misled readers into thinking that no substantive changes were being made to the methods. Due to the large number of changes we were making in the regulations at that time, and in light of the Section 307( d) requirements, the commenters requested that we address the instrumental method revisions through a separate proposal and not promulgate them with the rest of the package that was proposed on August 27, 1997.

We understood these concerns and stated our intention in the final rule ( 65 FR 61744) to repropose the revisions to the instrumental methods as a separate rule. The reproposal was published on October 10, 2003. We have considered the comments we received pertinent to these methods in the first proposal and are combining and addressing them in this document with the public comments received on the October 10, 2003 proposal. This comment summary and the Agency= s responses serve as the basis for the revisions made between proposal and promulgation. 2 2.0 LIST OF COMMENTERS First Proposal on August 27, 1997 Item Number in Docket A 97 12 Commenter and Affiliation IV D 03 Kevin L. Kitchen Lehi, Utah IV D 05 Mel S. Schulze Hunton & Williams IV D 06 Phillip Juneau Emission Monitoring, Inc IV D 08 R. T. Shigehara, Vice President Environmental Monitoring, Inc.

IV D 18 Ed S. Surla, Chief Indiana Dept of Environmental Management IV D 19 Raymond A. Walters New Hampshire Dept of Environmental Services IV D 20 R. W. Orchowski Dequesne Light IV D 21 Debra J. Jezouit Baker & Botts L. L. P.

IV D 24 Frances Cameron California EPA IV D 25 Peter Ironwode, Missouri Dept of Natural Resources IV D 26 Ray Walters New Hampshire Air Resources Division IV D 28 Stephen C. Anderson 3 2.0 LIST OF COMMENTERS First Proposal on August 27, 1997 Item Number in Docket A 97 12 Commenter and Affiliation Ct Dept of Environmental Protection IV G 01 Richard L. White, Vice President TU Services IV G 02 Ed S. Surla, Chief Indiana Dept of Environmental Management IV G 04 Billy J. Mullins, President METCO Environmental 4 2.0 LIST OF COMMENTERS ( Cont =

d)

Re proposal on October 10, 2003 Item Number in Docket OAR 2002 0071 Commenter and Affiliation OAR 2002 0071 0002 Tom Gasloli Michigan Dept of Environmental Quality OAR 2002 0071 0003 Tom Gasloli Michigan Dept of Environmental Quality OAR 2002 0071 0004 Mark Patrick TRC Environmental Salt Lake City, UT OAR 2002 0071 0005 Anonymous OAR 2002 0071 0006 Anonymous OAR 2002 0071 0007 Anonymous OAR 2002 0071 0008 Brian Glendening Consumers Energy Company OAR 2002 0071 0009 Reggie Davis, Vice Pres & Gen Mgr Spectrum Systems, Inc.

OAR 2002 0071 0010 Bruce Rising Gas Turbine Association OAR 2002 0071 0011 Kevin L. Kitchen OAR 2002 0071 0012 Bob Finken OAR 2002 0071 0013 Suzanne Blackburn San Diego County Air Pollution Control District OAR 2002 0071 0014 Peter Pakalnis 5 2.0 LIST OF COMMENTERS ( Cont =

d)

Re proposal on October 10, 2003 Item Number in Docket OAR 2002 0071 Commenter and Affiliation LEHDER Environmental Services OAR 2002 0071 0015 Phillip Juneau B3 Systems, Inc.

OAR 2002 0071 0016 Phillip Juneau B3 Systems, Inc.

OAR 2002 0071 0017 Anonymous OAR 2002 0071 0018 Anonymous OAR 2002 0071 0019 Anonymous OAR 2002 0071 0020 Michael A. Klein New Jersey Dept of Environmental Protection OAR 2002 0071 0021 Lee Cecchi Precision Emissions, Inc.

OAR 2002 0071 0022 Scott Evans Clean Air Engineering OAR 2002 0071 0023 Joe Gregoria M& C Products Analysis Technology, Inc.

OAR 2002 0071 0024 Phillip Buillemette Flint Hill Resources OAR 2002 0071 0025 Barbara A. Kwetz Massachusetts Dept of Environmental Protection OAR 2002 0071 0026 Mark W. Bailey Oregon Dept of Environmental Quality 6 2.0 LIST OF COMMENTERS ( Cont =

d)

Re proposal on October 10, 2003 Item Number in Docket OAR 2002 0071 Commenter and Affiliation OAR 2002 0071 0027 Bighorn Environmental OAR 2002 0071 0028 GE Mostardi Platt OAR 2002 0071 0029 John E. Pinkerton National Council for Air & Stream Improvement, Inc.

OAR 2002 0071 0030 Daniel E. Fitzgerald ARI Environmental, Inc.

OAR 2002 0071 0031 John Johnston/ Russell DiRaimo Stork Southwestern Laboratories OAR 2002 0071 0032 Lisa Beal Interstate Natural Gas Association of America OAR 2002 0071 0033 Dominion   Emission Monitoring Support Group OAR 2002 0071 0034 Kenneth R. Loder TRC Environmental Solutions OAR 2002 0071 0035 Michael W. Hartman Air Tech Environmental OAR 2002 0071 0036 Scott Evans Clean Air Engineering OAR 2002 0071 0037 John Smith Texas Comission for Environmental Quality OAR 2002 0071 0038 Lauren Freeman Hunton & Williams for UARG 7 2.0 LIST OF COMMENTERS ( Cont =

d)

Re proposal on October 10, 2003 Item Number in Docket OAR 2002 0071 Commenter and Affiliation OAR 2002 0071 0039 Bill Mayhew Source Test and Consulting Services, Inc.

OAR 2002 0071 0040 Anonymous OAR 2002 0071 0041 Stephen E. Woock Weyerhaeuser Company OAR 2002 0071 0042 David P. Duncan TXU Energy OAR 2002 0071 0043 David Rossman Horizon Engineering OAR 2002 0071 0044 Jack Herbert Oregon Dept of Environmental Quality OAR 2002 0071 0045 David Rossman Horizon Engineering OAR 2002 0071 0046 Kenneth R. Loder TRC Environmental OAR 2002 0071 0047 Jim Steiner TRC Environmental OAR 2002 0071 0048 Calvin Loomis Bison Engineering OAR 2002 0071 0049 Elvin D. Lang, Chief Emissions Measurement Section Alabama Department of Environmental Management 8 2.0 LIST OF COMMENTERS ( Cont =

d)

Re proposal on October 10, 2003 Item Number in Docket OAR 2002 0071 Commenter and Affiliation OAR 2002 0071 0050 Michael W. Stroben EHS Director Duke Energy OAR 2002 0071 0051 Barbara A. Kwetz Massachusetts Dept of Environmental Protection OAR 2002 0071 0052 Barbara A. Kwetz Massachusetts Dept of Environmental Protection OAR 2002 0071 0053 David C. Foerter / Richard A. Hovan Institute of Clean Air Companies OAR 2002 0071 0054 David C. Foerter / Richard A. Hovan Institute of Clean Air Companies OAR 2002 0071 0055 Gregory R. Sims Sr. Project Manager/ Technical Director Weston Solutions OAR 2002 0071 0056 Gregory R. Sims Sr. Project Manager/ Technical Director Weston Solutions OAR 2002 0071 0057 Gregory R. Sims Sr. Project Manager/ Technical Director Weston Solutions OAR 2002 0071 0058 Gregory R. Sims Sr. Project Manager/ Technical Director Weston Solutions OAR 2002 0071 0059 Michael Harley 9 2.0 LIST OF COMMENTERS ( Cont =

d)

Re proposal on October 10, 2003 Item Number in Docket OAR 2002 0071 Commenter and Affiliation Harley Engineering and Technologies ( HEAT)

OAR 2002 0071 0060 Leanne J. Tippett Director State of Missouri Department of Natural Resources OAR 2002 0071 0061 Elvin D. Lang, Chief Emissions Measurement Section Alabama Department of Environmental Management 10 3.0 PUBLIC COMMENTS AND RESPONSES 3.1 Rationale for Revisions 1. Comment: We do not believe the preamble language for the proposal or reproposal adequately reflected the changes being proposed. No supporting documents, technical analysis, discussion, or data to support the proposed methods were included in the electronic docket nor were adequate basis and purpose statements supplied. Section 307( d) of the Clean Air Act ( CAA), which applies to this rule making, requires that the Agency provide a statement of basis and purpose for its proposal. This misled the readers into thinking that the proposal contained no substantive changes to the test methods. One purpose of this provision is to provide adequate notice to potential commenters regarding the content of and rationale underlying the proposal. The EPA should not move forward to final rule making but should withdraw these proposed revisions and develop a complete technical, legal, and policy record to support the proposed revisions, with full public participation. The EPA has not provided the support CAA Section 307 ( d) requires for meaningful opportunity to comment or to support ( with actual data and technical documentation) a final rule. One commenter felt that research to validate the proposed procedures under Method 301 or any other means should have been supplied. ( IV D 05, IV D 20, IV D 21, 0032, 0038, 0039, 0050)

Response: We made an effort to provide an adequate rationale and basis for the proposal since it was a reproposal of what was published in an October 17, 2000 notice that public commenters felt lacked adequate rationale. Our goal was to harmonize, update, and simplify the instrumental test methods. In the proposal, we enumerated the major revisions and explained that most were minor in nature and based on practical, common sense needs that are generally understood by affected parties. That is why the preamble gave a general discussion of the revisions and did not include supporting data and documentation. We believe this provided adequate public notice for the revisions. However, we understand the concern that some of the performance test limits and the use of uncertainty to determine compliance may constitute major changes. In these instances, we were seeking public input on these ideas. We have formulated the final rule so that these points will not result in major changes.

2. Comment: Implementation of the new requirements will likely increase the cost of established methods. EPA has not demonstrated the necessity of the new requirements to achieve improved emission data or justified the costs associated with the new requirements. ( 0032, 0038)

Response: We believe the changes we have made to add consistency and streamline the methods alone should facilitate the method= s use and reduce costs. We have added flexibility in the choice of analyzer technology where we had only allowed specific types to be used. We believe the overall benefits the revisions bring in enhancing the certainty of data and tester efficiency will justify any additional costs incurred.

3. Comment: The proposed revisions appear to be a collection of many different ideas and concepts, some of which are conflicting, and contain numerous apparent errors, missstatements and/ or inconsistencies as are detailed later. There are so many unresolved issues and 11 deficiencies that it is impossible to determine the impacts that the proposed revisions will have on the regulated industries or the organizations that perform such tests. It is our position that the proposed rule changes, while a step in the right direction, are not sufficiently complete that minimal changes based on comments will allow for final promulgation. With widespread access to the internet, it would seem beneficial to try and come to a broad consensus between industry, testing organizations, and regulators prior to another draft publishing in the Federal Register. ( 0009)

Response: We received a large number of comments in 61 comment letters that addressed most aspects of the methods and made recommendation for improvement. We have made major revisions in the final rule to reflect these recommendations and believe the resulting methods meet the primary objectives to update and harmonize them. Issues of concern on the proposal must be addressed during the public comment period or through the requesting of a public hearing. The closing of the public comment period ends the opportunity for public interchange and further collaboration in designing the final rule beyond this point is legally precluded.

3.2 Uncertainty of Data 4. Comment: The EPA proposes to add Section 1.3 to each of the methods to address the data quality objectives ( DQO) which " define the quality of data you need for the test." The only DQO actually identified in this section, however, is the requirement to evaluate data relative to the applicable emission standard. The remainder of the section allows a " data user" ( which EPA explains is a regulating agency) to exercise discretion regarding whether or not to accept data that has been collected in accordance with the method under some undefined DQO. To provide information related to this undefined DQO, EPA requires that sources calculate the " uncertainty estimate." Significantly, the method contains no performance specification to compare this calculated " uncertainty," but apparently leaves it up to the regulating agency to determine whether data are of sufficient quality to meet the agency's " testing objectives." EPA must identify the acceptable level of uncertainty, and assess the impact of that criterion on the underlying requirements for use of the data. The sole purpose of including QA/ QC procedures in the method is to define the acceptability of the data. Because these are compliance test methods, sources relying on the methods must have certainty that properly obtained results will be sufficient to satisfy their compliance obligations. ( 0008, 0038)

Response: The DQOs for a specific test are defined by the data user since these objectives will vary according to the purpose of the collected data. For example, the quality of data collected to show compliance with an emission standard is more important in the concentration vicinity of the limit than at other concentration levels. Data quality in a market based trading program is most important wherever the emission concentrations may fall. Other data quality needs may differ and the DQOs are set accordingly. Data user discretion becomes a part of the data quality assessment ( DQA) of the test results.

The proposed requirement to calculate the uncertainty of each test run has been dropped. At a future date, EPA may issue a guidance document quantifying the errors associated with the instrumental methods in their present form. A similar exercise was undertaken in 1970 for the original reference methods ( see Shigehara, Todd, and Smith, " Significance of Errors in Stack 12 Sampling Measurements" as sited in the Method 2 bibliography). The objective of such guidance would be to encourage advances in emission testing technology.

5. Comments: It is imperative to preserve the concept that properly quality assured reference method data is the real value. Using uncertainty produces a grey area that will incite many frivolous lawsuits and is ultimately confusing and incorrectly applied in this case. The tester and facility need to have a reasonable assurance that they have met the requirements based on a properly quality assured test. Data Quality Objectives and uncertainty present a number of very serious issues, with a Pandora= s box related to use of continuous emissions monitoring systems ( CEMS) in the Clean Air Markets programs and other compliance programs. There are too many individuals ready to use the perception of uncertainty to continuously challenge any decision made related to compliance. Uncertainty is a statistical concept that is too easy for those without a thorough understanding of statistics to misapply, and these calculations should remain in the ivory tower.

The instrumental methods are " compliance" methods rather than " violation" methods. While the concern may appear to be merely one of " semantics,@ it is both very real and very significant. The instrumental methods included in this notice are the federally defined methods for the determination of compliance with the requirements of various federal NSPS and Clean Air Markets programs as well as federally enforceable State Air Implementation Plans. The requirement and concept of the federal test methods are to provide a means of demonstrating " compliance" with the applicable requirements on the basis of the test method. The addition of an uncertainty calculation opens the door for third parties and regulatory agencies to challenge the validity of compliance demonstrations where the results of a test ( using the federally required method) are below or very close to the standard.

The application of " uncertainty" calculations will subject those who have made a " good faith" demonstration of compliance ( based on one of the instrumental methods in this notice) to the possibility of enforcement. In addition, the inclusion of an " uncertainty" evaluation would increase the cost and duration of enforcement actions, to the detriment of both the parties and the environment. Since CEMS are evaluated against instrumental methods through RATAs and most CEMS use the same technology as the reference methods, measurements with compliance CEMS might be even larger. The application of uncertainty calculations could result in many cases similar to the Louisiana Pacific opacity case and instability in federal Clean Air Market or other emission allowance programs. Please do not include any requirements or references concerning uncertainty in the final instrumental methods. ( 0039, 0059)

Response: See response to Comment 4.

6. Comment: The proposed requirements regarding measurement uncertainty and the use of uncertainty to determine compliance status are inappropriate. In particular, we object to EPA= s recommendations in the methods that permitting authorities may use the uncertainty data to ascertain the compliance status of a source. We note that this approach does not address the fact that existing emission limitations have been developed using emission data derived principally from these same test methods with no consideration of uncertainty. We also note that the proposed revisions failed to provide a definition for uncertainty and the proposed equation for 13 uncertainty ( Equation 7E 5) reflects only two factors, related to bias, rather than the true uncertainty of the measurement. ( 0028) ( 0032)

Response: See response to Comment 4.

7. Comment: It was asserted in the proposal that the use of uncertainty estimates encourages better technology. This assertion is unfounded and appears to be only the opinion of the author. The use of uncertainty estimates may assist in the evaluation of data; however, as applied in this method it only serves to complicate implementation of the method significantly. The entire section on data quality objectives should be removed from the method. Further, this is in direct opposition to the goals of simplifying and reducing costs. ( 0032, 0043)

Response: See response to Comment 4.

8. Comment: ( a) The preamble to the reproposal noted that Amany commenters objected to the proposed bias correction equation and argued it was too complicated. We are proposing to drop the bias correction requirement in favor of calculating the level of uncertainty for a run.@ The proposed bias correction equation used a least square calculation, which did complicate bias corrections without significant benefits. Furthermore, the previously proposed bias correction was based on an incorrect statistical premise. Rather than going back to the original, simple bias correction equation ( which corrected for both bias and drift), EPA has decided to drop altogether any bias correction and has chosen to complicate enforcement by giving the regulating agency the option to determine whether the test results are over or above the emission limit. By adjusting the data for bias, the questions in Section 1.3.1 become moot. ( b) The issue of whether to accept data of lesser quality has nothing to do with the determination of bias. The issue is how much is a small fraction? How will knowing the bias ( which is generally negative) help the agency to decide whether to accept data of less quality, as defined by EPA. The issue exists whether the bias is zero or not. Results with bias correction are of better quality than results without bias correction, and the bias correction should be retained. Will EPA now calibrate the dry gas meter for conventional methods and not apply the correction factor, but instead determine an uncertainty? ( c) It= s interesting to note that EPA has chosen to consider uncertainty for only two measurements ( bias and converter efficiency) and has chosen to ignore the uncertainties incurred in all the rest of the measurements ( calibration gas accuracy, calibration error, gas concentrations, F factor ( including Fo) variations, temperature, pressure, velocity, etc.). Why? ( 0009, 0032)

Response: See response to Comment 4. 14 9. Comment: The uncertainty calculation indicates that the bias tests will tell the user what the uncertainty of the data is. The bias test only tells the user how much bias is being impacted by the sampling system. The uncertainty of the data should be calculated using the 1 minute averages obtained during the test. It involves calculating the variation of the data ( i. e. significant deviations) and plotting a confidence interval. At the end, the user could say he was 95 percent confident that all or some of the data fell below the emission limit. A bias test won= t do this. ( 0035)

Response: See response to Comment 4.

10. Comment: The wording in this section is confusing in a procedural sense, but, more importantly, the section is technically incorrect. It is not clear what EPA= s uncertainty term really means, since it is undefined, and is inappropriately used and should be removed. The current uncertainty term does not consider data system resolution and accuracy, linearity, calibration gas accuracy, ASME or NIST type of analyses, etc., in the analysis. If EPA wants to use uncertainty, it is a complicated enough subject to dedicate an entire method to, as ASME has done, and it should apply to all test methods, not just instrumental test methods. ( 0039)

Response: See response to Comment 4.

11. Comment: The reason for having performance and design specifications is to limit uncertainties. If the uncertainties are too large, then EPA should revise the specifications. ( 0032)

Response: We agree. See the response to Comment 4.

12. Comment: Now that EPA has required the uncertainty to be determined, how will it be used? Will EPA now revise the various subsections of the applicable subparts to legalize its use? The application of uncertainty estimates is unclear, subjective, and unnecessary. We cannot find any criteria for the uncertainty values, and it is not clear how they might be used. ( 0032, 0038)

Response: See the response to Comment 4.

13. Comment: A complete explanation of upper and lower uncertainty, to include the acceptability requirements, is needed. ( 0049)

Response: See response to Comment 4.

14. Comment: It is not obvious how the calculated uncertainty is to be used if the measured concentration does not exceed an emission limit, but the adjusted concentration with uncertainty does. For example, assume a source with an emission limit of 100 ppm nitrogen oxides ( NOx) conducts a 3 run test with results of 95, 98, and 101 ppm. If the bias factor is  0.05, then the uncertainty values would be 99.9, 103.1, and 106.3 ppm, assuming the 2nd term in the equation is zero. The measured values show a 3 run average below 100 ppm, while the 3 run average with uncertainty is greater than 100. It is unclear what conclusion the regulatory agency would make in this case. ( 0029) 15 Response: See the response to Comment 4.

15. Comment: The sampling system bias adjustment in existing Methods 3A, 6C and 7E should be retained and included in the other instrumental test methods. Removal of the bias correction factor from Methods 3A, 6C and 7E and replacement with a statement of uncertainty is a very bad idea and would: ( a) decrease the quality of the measurement results, ( b) complicate and confuse compliance determinations, ( c) significantly detract from determination of bias correction factors and thus the resulting data obtained in market based programs, including the Acid Rain and NOx Budget trading programs. The Method 3A, 6C, and 7E sampling system bias correction factors are specifically that which the name implies. They adjust for the bias demonstrated to occur in the sampling system due to adsorption, absorption, and residual moisture and are based on the differences observed from the injection of calibration standards directly into the analyzer and the same standards injected through the entire sampling and analysis system. The observed deviations are not statistical uncertainty but are definite biases of known direction and magnitude and for which they can and should be corrected. This approach is well understood and widely used. Within the instrumental methods, these corrections are justified because the analyzer calibration error test demonstrates that the system is linear and accurately measures the standards. After the analyzer calibration error specification has been performed, the sampling system bias checks are performed before and after each sample run and used to compensate for the observed bias and drift during the run. This approach is technically correct. This part of the instrumental methods is not broken and does not require fixing. ( 0009, 0016, 0021, 0032, 0034, 0038)

Response: See the response to Comment 4.

3.3 Sampling System Bias, Calibration Drift, and Analyzer Calibration Error 16. Comments: We disagree with eliminating the system bias correction and calibration drift test before and after each run. How about correcting for drift in a worst case way and call the run good if it still meets emissions standards? The analogy is correcting for a bad post test leak check using Method 5. ( 0013, 0021, 0034, 0043)

Response: We agree and have retained the determination of calibration drift and system bias as it existed before.

17. Comment: Performance criteria should be left relative to span, rather than modified to be a percent of the emission standard. Using a percent of the emission standard has no technical basis. Performance as a percentage of span is the way instrument manufacturers evaluate their instruments. The current limits are based on what a reasonable well operated measurement system should be capable of. The new approach may also result in performance criteria that cannot be met under certain conditions and would relax the bias specification for sources significantly below the emission standard. We believe the current span specification limits how the tester chooses a span, and this specification ties the span to the emission standard. One commenter suggested making the span no greater than twice the concentration of the emission standard would be more appropriate than the current limit of the span not being more than three times the concentration of the emission standard. The proposed requirement that emissions be 16 between 20 and 100 percent of span should be sufficient to add uniformity to the span selection. Another commenter urged the retaining of the current span based performance criteria and suggested adding safeguards to prevent the selection of an inappropriate instrument range that would relax the performance requirement. ( 0016, 0032)

Response: We believe the current allowable range of span choices is too broad to result in a fair stringency of performance criteria among tester choosing significantly different spans. Defining the span as twice the concentration of the emission standard, as the commenter suggested, appears to be a good idea and would effectively reduce this range. However, in the final rule, we have opted for a different approach that will achieve the desired objective. The term " span" has been replaced with the term " calibration span" which is synonymous with the high calibration gas concentration. Further, the revised rule requires that the calibration span value be selected to ensure that the majority of the emissions fall between 20 and 80 percent of this value. This approach offers several advantages. First, it alleviates concern about the QA status of data points that exceed the high level gas value but are below the current span. Second, if properly chosen, the calibration span should not be exceeded, and the A20 to 80 percent@ guideline will prevent an inordinately high calibration span from being chosen. Fourth, it allows you freedom to set the calibration span equal to the full scale of the analyzer ( if the full scale is the right size for the application) or to quality assure a segment of the range, if the range is over sized.

18. Comments: Many of us use STRATA DAQs, and this proposal renders this software useless because of the change from percent of range to percent of emission standard. The provision for low emitting sources is only good for 3 yrs, which means another software change. This becomes quite expensive. If testers are abusing the analyzer range selection to make the bias test easier to pass, why not have the methods state that the lowest analyzer range consistent with maintaining the measured concentration between 20 percent and 100 percent of that range must be used? Then the bias check can remain as is. ( 0047)

Response: See the response to Comment 17.

19. Comment: The EPA proposes to redefine sampling system bias in terms of the applicable emission limit. What is the definition of emission standard? Is this the same as the emission limit in the site= s operating permit? In any case, using the emission standard as a basis for determining system bias is problematic because the units are frequently not in concentration ( e. g., lbs/ hr, lb/ mmBTU, or lb/ ton stone feed), and there may be multiple limits at a site. This is a can of worms. Testers do not always know the emission standard, analyzers have fixed ranges, new standards may require calibration gases for each source resulting in more added costs and lead time. Conversion tables would require flows which are not always available or needed, and conversion tables would not work well with production based limits. The EPA did not explain why some of the performance specifications are based on the emission standard, while others are based on the span. We do not believe that use of the emission standard is appropriate for any of the criteria. Analyzer performance and accuracy are a function of analyzer span. Use of the emission standard is also problematic in cases where concentrations are corrected to some dilution standard, such as ppm NOx at 15 percent oxygen. ( 0008, 0038, 0043, 0048) 17 Response: See the response to comment 17. The sampling system bias and analyzer calibration drift will continue to be calculated based on the span and not on the emission standard as proposed. The definition of span has been revised to limit tester selection of an inappropriate value.

20. Comment: The alternative sampling system bias specification of " 5 percent of the span if not subject to an emission standard does not provide appropriate criteria for sources subject to emission standards that are also included in a market based trading program. Given the tolerances of gases and the allowable calibration error of the analyzer, it is nearly impossible to meet a bias of 5 percent of an emission standard, and should be based on the upper range of the analyzer. For most sources the span is set at 200 to 250 percent of the standard to capture shortterm peaks, so the proposed change would reduce the allowed error by 40 to 60 percent, and would result in the failure of many tests. When not subject to an emission standard, this is too lenient, and a 1000 ppm span would have an allowable bias of 50 ppm, so it is recommended to use a bias limit of 2 percent of span. ( 0011, 0026, 0029, 0032, 0038)

Response: See the response to Comment 19.

21. Comment: There are problems with using the emission allowable to establish allowable bias. First, not all processes tested are combustion processes, and, second, combustion processes requires one to assume an O2 level, and it does not seem appropriate to determine test run acceptance based on an estimate. Basing drift on the range or span is a better approach. ( 0020)

Response: See the response to Comment 19.

22. Comment: Why change the calibration error and bias calculations to a percentage of the calibration standard? How do the proposed revisions address using a true zero gas for calibration as is most commonly done? Only Method 25A uses this percentage of calibration standard way of calculating the percent errors of calibration, and in so doing, no error can be associated with the zero calibration point. Currently, all 5 methods ( 3A, 6C, 7E, 10 and 20) calculate calibration error as a percent of span of the instrument. Why change this? Calculating everything from the span allows an assessment of the accuracy of the zero gas and does not make meeting the specification harder to accomplish the closer the calibration gas is to zero. The instruments don= t get more accurate the closer the output gets to zero, which is what in effect the proposed revisions would require. To simplify the reference methods, bias should be based on the full scale range of the analyzer. However, the range of the analyzer should be limited so that the majority of the readings are 20 to 80 percent of full scale. ( 0034, 0038)

Response: See the response to Comment 17.

23. Comment: Recently we tested a source with an emission limit of 50 ppm, but had spikes up to 1500 ppm. Basing the bias on percent of the standard would be nearly unachievable. Everything should be based on percent of range, perhaps with the clarification that range be no greater than 200 percent of the standard. Exceptions should include sources with emissions standards less than 15 ppmv, where the minimum required range should be 10 ppmv. For sources 18 that occasionally exceed 200 percent of the emission limit, the range should be considered to be the peak value observed and the upper limit should not exceed the analyzer range or the span gas by more than 10 percent. Calibration gases should be spaced accordingly, and at least one calibration gas should be within 10 percent of the calculated emissions standard, or for sources with emission standards less than 15 ppmv, the calibration standards should be spaced equally ( within 15 percent) over the measurement range. ( 0039)

Response: We understand that accurately testing a complying source with an emission limit of 50 ppm but has spikes up to 1500 ppm is difficult. However, we believe this to be a calibration challenge rather than what should be acceptable bias. The use of a dual range analyzer may be appropriate in such cases. See the response to Comment 17.

24. Comment: Several commenters thought it was inappropriate and unwarranted to base performance criteria on a percentage of the emission standard. The following points were made: a. The definition should instead be the system calibration result divided by the direct calibration result. b. The definition precludes the alternative approach suggested in Section 1.3 for those cases where an emission limit does not exist or should not be used. c. There are concerns about sites without a specific standard for each pollutant, or where there are multiple standards based on different programs. It is not clear what an emission standard is in many cases. For example a gas turbine may mean Part 60, Subpart GG emission standard, the permit limit in ppm at 15 percent oxygen, or the permit limit in lb/ hr. d. The definition should revert to what is current in Method 6C. Bias is a measure of system recovery efficiency and should not be measured in terms of the emission standard. e. To accommodate both dilution and direct systems, the term in the denominator needs to be the concentration of span gas introduced to the system. ( 0013, 0032, 0033, 0038, 0059)

Response: See the response to Comment 17.

25. Comment: Changing the bias calculations from the current procedures is arbitrary and will not increase accuracy. Time and training are needed to implement these changes, which are not better, just different, and eliminating the calibration error correction will reduce accuracy. Since span is currently set at 1.5 to 2.5 times the expected emissions, the proposed rules reduce allowable error by 40 to 60 percent, and combines analyzer error and system bias error. Many monitoring systems will fail to meet this requirement. Analyzer performance is a function of range/ span setting and not a permit limit. We recognize that sometimes unnecessarily high spans are chosen to loosen the specs, but this can be easily corrected by requiring the tester to use a scale such that the majority of readings are between 20 and 80 percent of range. ( 0028, 0038, 0041)

Response: See the response to Comment 17.

26. Comment: We see the definition for span ( Method 7E Section 3.12) has changed. According to the proposed change, the span will be based on the calibration gas instead of the range that the analyzer is set on. So if high level calibration gas is changed so will the span value. Why would the span be based on calibration gas instead of the analyzer range? ( 0008) 19 Response: See the response to Comment 17.

27. Comments: Basing reference method analyzer range on the applicable standard is anticipated to result in forcing the replacement of existing CO analyzers or the addition of new ones with different ranges. This will have a major cost for what otherwise appears to be a minor change in the method procedures. The existing reference methods appear to provide satisfactory and reliable means for obtaining representative measurements. ( 0042)

Response: See the response to comment 17.

28. Comments: Overall, it appears that EPA is complicating the QA/ QC requirements with the use of two separate criteria ( for the analyzer and for the sampling system) and it is not evident how this will improve acceptable measurement system performance. We believe the use of the appropriate certified gas concentration value ( or tag value) as the tolerance criteria for both the analyzer and sampling system bias checks would be a better approach. Then potential emission limits will be incorporated into the tolerance criteria. ( 0029)

Response: We agree that the commenter proposes a viable approach and have revised the performance requirement for both the calibration error and system bias to be relative to the high calibration gas ( calibration span).

29. Comment: At this time we do not perform a bias test as described in Section 8.2.5. We perform the analyzer error and system drift test by introducing calibration gas into the system at the 3 way valve located on the probe. We have had conversations with an EPA representative on this topic who agrees that this method is acceptable. Calibrating through the entire sampling system, eliminating the need for a bias test, should be included as an option in the test method. ( 0008)

Response: The procedure described by the commenter is a variation from the method and requires Administrative approval. The method requires the initial calibration be directly to the analyzer, and a bias test of the entire system must be performed before sampling begins. In this way, the bias of the system can be determined instead of being adjusted out at the calibration. Alternatively, Section 8.2.3 allows the calibration error test gas to be introduced at a point upstream of the analyzer, provided that it is downstream of all sample conditioning equipment.

30. Comment: The proposed requirement to limit calibration error to within 2 percent of the certified gas concentration is unnecessarily restrictive compared to the existing specification of 2 percent of span. The additional restriction is not necessary and does not improve data quality when sampling system bias adjustments are applied to a demonstrated linear system. The EPA has provided no technical basis for such increased restriction and this requirement should be removed. This requirement may also prove impossible to meet if there is any error in the measurement system, because the calibration gases themselves are allowed, and often have, 2 percent error from the tag value. One comment believed that EPA has now specified an accuracy that is 50 times tighter than the analyzer linearity specification, and does not even consider calibration gas error. ( 0012, 0026, 0028, 0029, 0031, 0032, 0038, 0041) 20 Response: We have revised the requirement that calibration error for the low, mid, and high level gases be within 2 percent of their certified tag values in favor of each gas being within 2 percent of calibration span ( high level certified tag value).

31. Comment: According to Section 7.1.3, the low level gas may contain a zero concentration. Since results of division by zero are undefined, calibration error at the zero level cannot be calculated. ( 0012, 0030)

Response: An alternative calibration error of ± 0.5 ppm has been added to grant relief for low measurements and to accommodate the use of zero gas as the low level calibration gas.

32. Comment: Why must the same gases be used to set up the analyzer as for the calibration error test? It appears as if we must perform the calibration error t analyzer calibration error check and bias checks being there to determine how well this was accomplished. The proposed procedure is a waste of time and the current procedure is much preferred. ( 0009, 0013, 0038)

Response: We have dropped the parenthetical note in Section 8.2.3 that notes the calibration gases and the calibration error test gases are the same.

33. Comment: Procedure is acceptable, but for the case of direct calibrations, the resultant concentrations should still be corrected for sampling system bias. Considering the duration of sample runs ( i. e. RATAs at 21 minutes), an option of conducting multiple runs between bias determinations should be included. The risk will be that of the tester and failure would void all runs performed since the last acceptable bias check. For bias corrections, all runs conducted within a set would be corrected with the same pre and post test results. ( 0056)

Response: We believe the commenter makes a good point. We have retained the correction of data for bias as is currently done in the methods.

34. Comment: The analyzer calibration error section is flawed. Allowing two percent of the manufacturer certified concentration for the low, mid and span level calibration gases is too stringent. Assume the low, mid, and span level calibration gases are 10, 50 and 90 ppm. According to the wording, the analyzer must be between 9.8  10.2 ppm, 49.0  51.0 and 88.2  91.8 ppm. In this case, the low level tolerance is 0.2 ppm and the high level tolerance is 1.8 ppm, all for the same range setting. Calibration error must be consistent with the industry standard which is based upon a percentage of the selected range, such as 2 percent of 100 ppm or 2 ppm. It also should be noted that the calibration gases have a tolerance from the certified concentration. Typically, the gas manufacturers guarantee within1 or 2 percent of concentration. This means that, in the above case, the low level calibration gas concentration can potentially be 9.8  10.2 ppm. Since the calibration gas already has a 2 percent tolerance, the analyzer would need to be perfect in its detection.

The same section states that zero gas must be within 0.25 percent of analyzer upper range. If the range is 100 ppm, the analyzer response to zero gas must be less than 0.25 ppm. This is 21 impractical; a reasonable analyzer response to zero gas would be within 2.0 percent of the analyzer upper range limit. ( 0011)

Response: The commenters points are well taken. We have revised the allowable analyzer calibration error to within 2 percent of the calibration span or 0.5 ppm, whichever is less restrictive. References to a zero gas and the corresponding analyzer calibration error criterion have been dropped.

35. Comments: Section 8.2.5 refers to a zero gas. What if the calibration gas is a lowlevel non zero gas? A specification for a non zero gas is needed for a stable response. Since zero times zero is zero and 97 percent of zero is zero, the instrument is doomed if the response ever hits zero. Perhaps, this should be zero level value or a stable response to the zero ( or lowlevel gas.

Response: The mention of Azero@ gas in Section 8.2.5 is in error. It has been corrected to Alow level@ gas.

36. Comment: Where performance specifications are included, we suggest that EPA consider addressing significant figures by expanding these to another decimal place, such as 2.0 percent of span, 5.0 percent of tag value, etc. If this is not done, then technically, these specifications could round up to 0.4 percent higher than what they were originally intended. ( 0038)

Response: The commenter raises a valid point. The performance specifications now contain 2 significant figures.

37. Comment: The EPA has proposed a number of QA requirements that are unreasonable and unnecessary and will result in the failure of many otherwise valid tests. In most cases, the requirements tester must meet are more stringent than those the manufacturer must meet. We believe these issues clearly pose a significant burden on small entities, such as ours, who have invested everything into their businesses in good faith and with good intentions. ( 0039)

Response: The changes we have made in the final rule will mitigate the commenter= s concerns.

38. Comment: Would it be plausible to add an alternative to the sample line test? In extreme conditions, when it is difficult or impossible to run a sample line to a source, can one take a 30 minute sample in a Tedlar bag, then transport it to an analyzer? ( 0048)

Response: We believe the commenter= s suggestion has technical merit. However, it is more appropriate to obtain approval for this alternative under 40 CFR Part 60.8 on a case by case basis to determine if the bag sample meets the sampling time needs of the underlying regulation.

39. Comment: For hot wet systems performing the response time test, is it 0.5 percent of the certified dry gas value or 0.5 percent of the certified dry gas plus water value? If the system measures both gas and diluent simultaneously, shouldn= t the bias specification consider the 22 combination? To consider the bias separately will require moisture determination ( with its inaccuracies) to adjust the measured concentration to dry conditions. In some cases, 0.5 percent of certified value may be unattainable. ( 0012, 0032, 0049)

Response: The system response time criterion has been changed in the final rule. The response time is now defined as the time it takes for the measured gas concentration to increase to a value that is within 95 percent or 0.5 ppm ( whichever is less restrictive) of the certified upscale gas concentration or until the response is 0.5 ppm or 5.0 percent of the upscale gas concentration when the low level gas is used. The system bias test uses dry cylinder gas to test the measurement system. The hot wet sampling system surfaces may be wet during the bias test but there is no way to measure this residual moisture or correct its effect on the test gas. The bias test determines the recovery of test gas under simulated test conditions. Since the normal operation of hot wet systems handles moisture by keeping it in the vapor state during sampling and not on correcting the results, moisture correction during the bias test of such systems in not appropriate. The bias test only evaluates the pollutant measuring component of a system since the calculation is based on the recovery of the test gas, not the test gas corrected for diluent 3.4 Interference Test 40. Comments: The EPA= s rationale for conducting the interference test on an annual basis has not been shown. Please provide data that show an annual interference test is necessary. Today= s generation of analyzers do not have many, if any, interference problems. Furthermore, the manufacturer should perform these tests or they should only be required after major instrument modifications. Annual interference testing puts a major burden on the testing industry, causes many practical problems, and results in unclear issues for implementation. An initial certification along the lines of 40 CFR 53 with a 5 yr phase in is a more sensible alternative. The requirement needs to be modified and reduced in scope. The proposed test has a very high cost to low benefit ratio and would require many gases that would only be used once a year. ( 0008, 0011, 0012, 0013, 0016, 0027, 0029, 0030, 0032, 0033, 0034, 0035, 0038, 0047, 0056)

Response: The commenters have raised valid concerns. The proposed requirement to conduct the interference test on an annual basis has been dropped. The interference check will be a one time test, except for major instrument modifications, as is the current requirement. The tester must have information available for inspection showing that potential interferences encountered during a test do not affect the test results.

41. Comment: With respect to interference checks, the burden of performing annual checks at every type of source and specific instrument would be costly and time consuming. This is of minimal concern after the initial factory certification because these things do not really change and no component is actively eliminating interferences from stack or calibration gas. Many of our sources are working at low emission rates, even at zero. Has EPA looked at the quality of performing interference checks on very low concentrations, and what should we do when the emissions are at or near zero? Our last source tested at 0.3 ppmv sulfur dioxide ( SO2), and this is difficult to get with the Barium Thorin titration. Maybe issuing a reference document of when interferences are of concern would be better. Why even do instrumental testing when 23 you have to do wet chemistry interference tests every year? It should be one time test for the life of the instrument. ( 0028, 0048)

Response: We have dropped the requirement to conduct an annual interference test. However, the interference test must be repeated whenever major component repairs are made. Instruments that measure emissions below 15 ppm on a routine basis must pass a manufacturer's stability test.

42. Comment: The EPA has not provided data ( or technical discussion) to support the Agency's apparent concern that many of the substances listed in Table 7E 3 of Method 7E could cause interferences in the method measurements or that interferences by those substances would differ by source category. The proposed interference check significantly expands the scope of testing and substantially increases the costs of the methods. ( 0038)

Response: The Agency has not evaluated the interference concerns of different analyzers and their use at the various regulated facilities. Therefore, the proposed interference check was an attempt to include all suspected interferent under what was believed to be the best evaluation conditions. From the public comments, it appears the interference test is better served through a general performance requirement that can be individually suited to the analyzer type and testing needs than through the specific requirements of the proposal. We therefore give Table 7E 3 as a list of potential interferents that the tester can use to evaluate the analyzer for future test sites. The tester is required to have documentation available showing that the analytical system used is not affected ( beyond 2.5 percent of analytical span) by potential interferents at the sources tested.

43. Comment: The number of gases now needed for interference checks has been increased significantly ( Table 7E 3 lists 11 gases). Costs will be increased due to the number of gases to complete these checks. Can you provide guidance as to which gases must be introduced into which analyzers? Is not oxygen an interfering gas for some analyzers? If no oxygen is present, how would this affect the readings? ( 0014, 0025, 0032)

Response: The number of gases needed in a particular interference test will vary according to analyzer type. Each listed test gas may not be appropriate for each analyzer type. The tester or manufacturer must evaluate the potential of the listed test gases or other possible interferences to affect the analyzer performance and plan the test accordingly. The tester must have documentation available to show that potential interferences at tested sources do not exceed 2.5 percent of the calibration span.

44. Comment: Some instruments use selective scrubbing to remove interferences. In these cases, the removal efficiency should be verified after each test using the same principle as that of the NO2 to NO converter test. They should be tested using those gases that the scrubber claims to remove. ( 0016)

Response: Instruments that use selective scrubbing to remove interferences should test the scrubber at appropriate intervals and have documentation to verify that it meets the 2.5 percent interference criterion. 24 45. Comment: The method states that the interference test should be performed with and without NOx and ( NO and NO2). The procedure is not clear. Does this imply the checks must be completed with NOx mixtures for all interferent gases? This makes a total of 8 mixtures and 8 single component cylinders. Why is the interference test required with and without NOx present and at a concentration of at least 80 percent of span? ( 0014, 0033, 0036, 0047)

Response: A particular interference check should be tailored to fit the needs of the specific analyzer type and may be designed to evaluate the potential interferents singly, collectively through a manifold, or in blends. For some analyzers, the appropriate pollutant will be NOx, for others, it may be NO or NO2. We have reduced the specifics of the proposed interference test to allow the tester or manufacturer flexibility in choosing what is appropriate for their testing needs. Instead of requiring analyzers be evaluated with specific interferents at specific concentrations both with and without NOx, or single NOx component, the methods now require that documentation be possessed to show that interference from potential interferents at the test location are within 2.5 percent of calibration span.

46. Comment: May a correction factor be used to correct the data if the interference can be quantified? ( 0036)

Response: Interference effects beyond 2.5 percent of calibration span are unacceptable and may not be corrected for.

47. Comment: The proposed interference check with its 11 gases is extensive and would be better left to the analyzer manufacturer, possibly conducted along with the stability test. Manufacturers should be urged to conduct this procedure and provide a copy of the data and a signed certification for the purchaser. Analyzers can be type certified for specific source categories. ( 0014, 0033, 0041)

Response: The interference test may be designed and conducted by the manufacturer.

48. Comment: Not all sources are going to have ammonia, hydrogen chloride, hydrogen, or nitrous oxide present in the effluent. The interference test should only be done for those compounds present in the gas stream to be tested. ( 0047)

Response: Table 7E 3 is a listing of potential interference gases that may be encountered at various test sites. The table is not exhaustive, and the interference test may include other compounds not listed. Most analyzers are affected by only a few of the listed gases. The interference check should be designed to evaluate the potential interferences at facilities subsequently tested.

49. Comment: Since all monitors have multiple ranges, the 80 percent of analyzer range implies a test for every source category and analyzer range. Is this necessary? ( 0047)

Response: The requirement to test at 80 percent of the analyzer range has been dropped. 25 50. Comment: Method 6C contains too many interference tests. The interference test comparing Method 6C to Method 6 is obsolete and should be deleted to meet the stated intention of the rule of removing obsolete specifications, harmonizing similar requirements, and simplifying the procedures to enhance their utility and reduce the costs of testing. ( 0041)

Response: The Method 6C/ Method 6 comparison test is now listed as an alternative interference check procedure and is completely discussed in Section 16. This simplifies the main method text where the interference check against interference gases is discussed.

51. Comment: Add to Section 16 of Method 7E to incorporate an annual primary interference gas recheck. ( 0041)

Response: We have dropped the requirement to repeat the instrument interference test on a yearly basis.

52. Comments: In Method 7E, the interference test per source category criteria is not listed as it is in Method 6C, Section 8.3. Is there a way to include a list of source categories in the document? ( 0014)

Response: We have revised the interference check in Method 6C to conform to that of Method 7E. The Method 6C/ 6 comparison interference check is now given as an allowable alternative to the interference check using interferent gases. The requirement to conduct the interference check at each different source category only applies to the alternative ( Method 6C/ 6 comparison) interference check.

53. Comment: It is not necessary to perform the interference response tests for individual source categories, such as 250 ppm of an interference emitted from a coal fired boiler being more or less identical if it were measured at a hazardous waste incinerator. Interference response could be accurately quantified over a range of different concentrations, rather than source categories. A one time check on each model by the manufacturer should demonstrate that the analyzer technique does not show interference. ( 0038)

Response: See response to previous comment.

54. Comment: In the preamble section to the proposed rule, under the comments received from the first proposal of revisions, the comments on the interference test only apply to Method 6C. That was not clear until I read all the methods. ( 0020)

Response: The commenter is correct. The comments refer to the Method 6C interference test as it was published in the first proposal.

3.5 Alternative Dynamic Spike Check 55. Comment: Our association supports including an alternative dynamic spike procedure for calibration error tests and sampling system bias checks; however, the procedures are overly burdensome, internally inconsistent, and technically unsupported. As proposed, the procedure 26 discourages testers from using it. The procedure should only require the tester to follow a standard written procedure without having to be show certified proficiency with the procedure within the previous year. The analyte spiking method is itself self certifying. The EPA already allows it as one option in validating new test methods in Method 301. Procedures for analyte spiking are in practice and have been used for many years. The procedure should be revised to reflect approaches that have been successfully implemented and accepted by EPA.

In addition, the proposed pre test spike accuracy of ± 5 percent is not achievable in many cases for sources subject to low concentration standards. In all cases, the pre and post test spike criterion should be ± 10 percent. We also think it ill advised to defer to the manufacturer's stability test in place of a pre test spike and to confirm that an array of instrument operating parameters are within manufacturer specifications for certain reporting scenarios. ( 0032)

Response: The commenter made valid points and offered useful suggestions. We have dropped the requirement that testers be certified for their procedure. The procedures have been revised to allow testers to use any documented procedures. The spike recovery accuracy has been changed to ± 10 percent for both pre test and post test spikes. The manufacturer's stability test has been dropped as an alternative to the pre test spike.

56. Comment: The EPA has not provided sufficient explanation of the procedure for us to understand why they believe the procedure is helpful, or even how the procedure would actually be performed. No data obtained using this procedure has been provided. Because EPA= s description and supporting information for the procedure is so inadequate, we do not even have enough information to comment on the proposal, let alone determine whether our members would benefit from finding someone who did meet EPA= s requirements. Dynamic spiking procedures are not commonly performed and thus most testers will not be able to meet the proposed requirements of having demonstrated ability to follow a written procedure within the last calendar year. Until we see a written procedure and data, we strenuously object to including the dynamic spike procedure, even as an option. It is an unknown and undemonstrated procedure that has no place in a reference method. ( 0038)

Response: The dynamic spiking procedure is not a requirement, but is offered as an alternative to the traditional procedures for validating results for testers who have the desire and proficiency. This procedure will not be allowed under Part 75 applications, except where Administrative approval is granted. Dynamic spiking may not be commonly performed, but the technique is widely recognized as a superior means of evaluating methodology in the field. For a number of years, analyte spiking has been an accepted procedure in Method 301 of Part 63 for validating new methods. The proposed spiking procedure in Method 7E was purposely written in general terms to make it performance based and allow for tester flexibility in choice of procedure ( as in Method 301). We have included an example of an acceptable procedure as guidance for testers. We believe the testing community is better served in this way without any loss of testing quality.

57. Comment: The dynamic spike test is referred to by several names in the methods, most commonly the Alternative Dynamic Spiking Procedure or the Alternative Dynamic Spike 27 Check ( ADSC). We assume that all these names are the same check, and recommend giving the procedure a single name that is used consistently. ( 0025)

Response: Both terms are synonymous. We used the term Alternative Dynamic Spike Procedure.

58. Comment: Dynamic spiking is a good idea if implemented properly. It is not, however, a reliable method for calibration, and is not a good substitute for cal error and bias tests. The 10 percent limit on spike recovery could easily mask significant bias and/ or non linearity and greatly increase the allowed uncertainty of the method. The spiking option alone would not be appropriate for CEMS RATAs because of the level of uncertainty it introduces. EPA should not remove the bias test requirement when dynamic spiking is used. ( 0016)

Response: The concept of dynamic spiking is not new; another name for it is the method of standard additions. As such, if properly implemented, it can be a reliable method of calibration. We do not allow the ADSC as an alternative to the analyzer calibration error test. We believe the ADSC is a better indicator of bias and interferences than the sampling system bias check and the interference test normally required. The ADSC determines the pollutant in its native environment ( in the stack), and as such, better simulates a method's capabilities.

59. Comment: The new dynamic spike and interference tests are especially confusing. We are especially concerned about the lack of a timetable for phasing in the new methods. ( 0025, 0033) ( 0043)

Response: The public will be given a 90 day period after publication of the final rule to implement the revisions to the methods. We have dropped the proposed requirement to redo the interference check on a yearly basis. The interference check may now be performed by the instrument manufacturer. We have removed the proposed language that the alternative dynamic spiking procedure be performed by a person certified within the past year for the particular procedure used. This should add significant clarity to the procedures.

60. Comments: Two commenters thought the application of dynamic spiking to diluent methods ( Method 3A) was inappropriate. One of the commenters thought that if dynamic spiking is used in Method 3A, there should be separate procedures primarily because it deals with diluent gases as opposed to primary pollutants. ( 0032, 0035)

Response: We agree that the dynamic spiking procedure will be rarely used for diluent methods, and have removed all references to the ADSC from Method 3A.

61. Comment: For the spike procedure to work as it is, the process emissions must be 100 percent constant. The requirements are too stringent for processes with temporal variability. We recommend removing this procedure or increasing the allowable to 15 percent. ( 0041)

Response: The dynamic spike procedure may not be appropriate at sources where emission variations over time. The tester should consider this before opting to use this alternative 28 procedure. We have increased the pre test spike recovery allowable from 5 percent to 10 percent. We do not believe the raising of this level to 15 percent is justified.

62. Comment: 40 CFR 136, Appendix B   Definition and Procedure for the Determination of the Method Detection Limit   Revision 1, states " The method detection limit ( MDL) is defined as the minimum concentration of a substance that can be measured and reported with 99 percent confidence that the analyte concentration is greater than zero and is determined from analysis of a sample in a given matrix containing the analyte." This definition could be extended to determining the precision and accuracy at or near the analyte concentration. For the purposes of this evaluation, the definition could be adapted from " method detection limit" to " method quantitation limit" ( MQL). As with MDL, MQL could be defined as follows: " The MQL is defined as the minimum difference in concentration of a substance that can be measured and reported with 99 percent confidence and is determined from analysis of a sample in a given matrix containing the analyte." ( 0012)

Response: The proposed requirement to calculate data uncertainty has been dropped.

63. Comment: Equation 7E 5 is confused about bias and uncertainty. If bias can be determined, it is no longer an uncertainty. Uncertainty indicates a range of random error around a mean value. If there is an uncertainty associated with bias, it is in the precision of the measurement. Note that the accuracy of the cylinder gas has an uncertainty, but since the measurement of bias is a difference between direct and system calibrations using the same gas cylinder, any bias in the gas cylinder value cancels out. Artificially inflating the uncertainty by combining bias and uncertainty together is a poor solution. We recommend using the bias correction based on Equation 7E 3 in Method 7E. Equations 7E 5 and 6 are actually forms of a bias correction procedure, not an expression of uncertainty. If you substitute Equation 7E 3 into Equation 7E 5, take out the conversion efficiency term and rearrange the equation, it becomes the same as the current Method 6C bias/ drift correction equation. ( 0011, 0022, 0029, 0032, 0039)

Response: The proposed requirement to calculate data uncertainty has been dropped and Equations 7E 5 and 7E 6 have been dropped.

64. Comment: Dynamic spiking should be required as an additional QA check when the circumstances require it. We know that at low NOx concentrations, there can be 2 problems that can be evaluated by dynamic spiking. ( 1) Bias due to scrubbing of NO2 can be checked by spiking NO2; and ( 2) ammonia can cause NO2 converter to lose efficiency or the ammonia may be converted to NO. ( 0016)

Response: We have not evaluated the full capabilities of the dynamic spike check enough to make it a requirement in special circumstances.

3.6 Sampling Traverse Points 65. Comment: The EPA proposes to add a requirement to conduct sampling traverses using Method 1 traverse points unless a stratification test is conducted. This requirement will slow testing greatly and increase costs. Performance Specification 2 ( PS 2) recognizes certain 29 instances where stratification may be a potential problem. Sections <IP_ADDRESS> and <IP_ADDRESS> of PS 2 provide reasonable guidance for selecting points for a 3 point traverse. The EPA should use the sampling guidance in PS 2.

For combustion turbines with NOx controls ( steam, water, or ammonia injection), significant stratification can occur if the injection nozzles flow rates are not balanced. In this case, if the results from the 3 traverse points do not agree within 5 percent of the mean, a full traverse should be conducted using Method 1 points. ( 0016)

Response: We agree with the commenter and have adopted the language of PS 2 to describe the selection of traverse points. Unless stratification is suspected, a 3 point traverse test is conducted. Where stratification is suspected, the stratification test must be conducted using 9 or 12 traverse points according to Table 1 2 of Method 1. The option to use single point sampling is allowed when a stratification test shows that fewer samples are sufficient. The noted case of combustion turbines with NOx controls may be the exception to this procedure. In all cases, we have noted that the tester is responsible for collecting representative data.

66. Comment: If stratification is less than 5 percent of the mean, then sampling at a single point should be allowed. If stratification is less than 10 percent, three points at 16.7, 50, and 83.3 percent of the measurement line should be allowed. ( 0011)

Response: These options are allowed in the final methods.

67. Comment: Can there be an option for 1 point or 3 point testing if the source meets 8/ 2 or 2/ 0.5 criteria from flow disturbances or can something similar to PS 2 be used? ( 0031, 0034)

Response: See response to Comment 65.

68. Comment: The proposed requirements to use Method 1 for sample selection are unnecessary for measurement of gaseous exhaust species and should be eliminated from the proposed revisions. Flow disturbances, extreme turbulence, induced draft fans, etc. all create mixing and thus homogeneous gas streams and are very good places to obtain representative gas concentration measurements. ( 0032)

Response: See response to Comment 65.

69. Comments: For the stratification test, Part 75 has specified a method in Appendix A <IP_ADDRESS>. Since the objective is to harmonize the methods, it would be easier to have one method for consistency. ( 0019, 0038)

Response: See response to Comment 65. We have revised the proposed stratification requirement to make it similar to the requirements in Appendix A of Part 75. 30 70. Comments: What is the justification for multiple point Method 1 sampling for gases at all sources, when in the past it was required only at sources with the potential for stratification, such as scrubbers, combined gas streams, etc.? Traversing will require an extra person to do it, and will add about $ 600/ day to the testing costs. With Relative accuracy test audits ( RATA) requiring 3 points and the other instrumental methods calling for Method 1 traverses, RATAs and compliance tests can no longer be done concurrently, unless the stratification check allow only 3 points, which will also add big dollars. We suggest either going with a 3 point multi sample probe or specify when stratification may be observed in a stream. ( 0028, 0029, 0035, 0043, 0048)

Response: See response to Comment 65.

71. Comment: The general sampling point requirements in Section 8.1.2 are confusing and incoherent. ( 0008)

Response: Portions of Section 8.1.2 have been rewritten to add clarity.

72. Comments: A stratification test procedure has been added to Section 8.1.3 and EPA should not attempted to briefly summarize something this complex in a one half paragraph writeup in PS 2 of Appendix B. The appropriate number of sampling points will vary significantly depending on the test location and source conditions. In many cases temporal changes will need to be considered and may require one of several testing techniques. During the period required to perform a stratification test ( typically one hour or more), stack gas pollutant concentrations can easily vary by more than 10 percent, especially downstream of an SO2 scrubber. Most importantly, if stratification were detected, defaulting to a 3 point, across the diameter traverse would frequently not insure the collection of a representative sample. The EPA should eliminate this discussion and make the source owner and test crew responsible for collecting representative data, as is currently the case. ( 0038)

Response: We realize that a brief discussion of determining representative testing may not address all test situations; however, we believe the approach given in the final rule can adequately document the lack of stratification at most sources. We agree that the source owner and test crew are ultimately responsible for collecting representative data.

73. Comment: I agree that stratification may introduce significant errors when a singlepoint strategy is employed; however, the point selection and/ or stratification procedures should be made less cumbersome. Traversing as described in Sections 8.1.1 and 8.1.2 will add significant costs to most test programs. The stratification procedure described in 8.1.3 adds less cost ( though still significant), and allows single point sampling after completing a thorough stratification determination on a source. Once this is conducted on a source, however, I would propose an abbreviated 3 pt stratification check to verify the absence of stratification for subsequent tests. Another alternative which should be included is the " short line" point selection and probe ( 3 points at 0.4, 1.2, and 2.0 meters distance from the stack wall as described in PS 2) in cases where multi point sampling is required. Note that 16.7, 50, and 83.3 percent are often impractical on large diameter stacks. 31 Another problem is that many sources will have greater variability with time rather than with sample point location. In these cases, the short line 3 point sample probe should be sufficient. ( 0009, 0041, 0028, 0029, 0056)

Response: See response to Comment 65. The " short line" point selection of PS 2 has been included as an option except after wet scrubbers or in streams where different pollutant concentrations are combined.

74. Comment: Please clarify which Method 1 traverse points are determined, flow or particulate? ( 0004, 0009, 0028, 0030, 0038, 0039, 0043, 0059)

Response: For the stratification test, nine traverse points are used for rectangular stacks; 12 points are used for circular stacks. Method 1 only applies in the context of locating the test points, not the criteria for distances from flow disturbances.

75. Comment: The requirement to traverse at up to 16 points is an onerous requirement and is contrary to the purpose of simplifying the methods and reducing testing costs. Testing at the three points noted in PS 2 is a better solution. The requirement to sample in accordance with Method 1 is unnecessary when sampling downstream of an induced draft ( ID) fan. The ID fan mixes the gas stream to eliminate stratification and pressurizes the gas to eliminate the possibility of in leakage. Single point sampling should be allowed for all locations downstream of an ID fan. ( 0027, 0029, 0041)

Response: See response to Comment 65.

76. Comment: The sampling point locations should be deleted from the test method because of numerous conflicts with other regulations and lack of legitimate technical criteria for the prescribed sample points. This section begins with a statement, Unless otherwise specified in an applicable regulation or by the administrator, use the traverse points listed in and located according to Method 1. The first part of this sentence requires that the tester be an expert in air pollution regulations. Some Part 60 Subparts, such as Subpart D, specify the sampling location and sample point ( one meter from the stack or duct wall) while other subparts do not. Certain performance specifications in Part 60 and in Part 75 specify sample point traverses and/ or locations for the conduct of relative accuracy tests, while others do not. There are no cases that require sampling 12 or more points to determine representative gas concentrations. EPA has provided no evidence to support this proposition which is potentially very costly and difficult. Many facilities do not have the necessary sample platforms and access and sample ports necessary to conduct the traverses that EPA has specified.

Furthermore, the basis for using Method 1 for gas sampling measurements does not exist and is contrary to basic technical judgment. Method 1 has a procedure for selecting traverse points for particulate matter and for velocity measurements. There is no procedure within Method 1 to select sampling points for gas concentration measurements. The criteria for selecting particulate and velocity sample points and locations are entirely inappropriate for selecting gas sampling locations. While flow disturbances, ID fans, and extreme turbulence are detrimental to velocity measurements and isokinetic sampling for particulate matter, they are actually 32 advantageous for creating a homogeneous concentration, and thus ideal sampling locations, for gas measurements. Further, what if the source geometry does not meet Method 1 criteria? Method 1 is cumbersome on tall, large sources and pointless on small sources with respect to gases. Can EPA generate a guidance document on when to be concerned with stratified streams? Many sampling locations used strictly for instrumental testing do not meet Method 1 criteria, so the rule should be clear that Method 1 only applies in the context of locating the test points, not the criteria for distances from flow disturbances. This will avoid over interpretation of the rules and avoid litigation issues which will surely arise. What is the course of action when Method 1 criteria for upstream/ downstream distance are not met? Note that many facilities are not required to test for velocity or particulate, meaning that the Method 1 criteria have not been an issue under the current instrumental methods. ( 0032, 0038, 0039, 0043, 0048)

Response: See the responses to Comments 65 and 73.

77. Comment: The section on sample point selection is misleading. It says to use the points specified in Method 1 or conduct a stratification check, then it says if we are doing a RATA to use the procedures in the applicable performance specification ( which means 3 points). This is a serious problem, since there are many installations with SCRs that are completely stratified, and 3 points will not provide a representative sample. Section 8.1.3 goes on to describe how many points to use with a stratified stack, which is fine, but the last sentence in 8.1.1 seems to contradict these criteria. ( 0047)

Response: The last sentence notes that the revisions being made do not supersede the current sampling requirements in the CEMS performance specifications. In the performance specifications, the tester is given the minimum requirement of sampling at three points. These or additional points must be selected to assure the acquisition of representative samples over the stack or duct cross section.

78. Comment: It is not as easy as you imply to alleviate Method 1 points by performing a stratification test. Because most gaseous emissions are not stable but have continuous concentration drift, the best stratification test is performed by using two independent sample systems. One system is placed at a set sample point and the second is traversed at Method 1 points. The stationary point is then directly compared to the traversed point. This procedure can take a full day to complete on very large sources. I suggest either go with a three point multisample probe or specify when stratification may be observed within a stream. ( 0048)

Response: We agree that the stratification test described using two independent sampling systems is a good way to determine if emissions are stratified, and this procedure may be used.

79. Comment: The stratification procedure includes no provisions for accounting for temporal variations in the effluent concentration during the stratification test. Hence, sources that cannot operate at a constant effluent concentration cannot be demonstrated to be non stratified. The procedure should be modified to allow use of a dual probe approach and switching between the traverse and stationary sampling probes along with appropriate calculations that separate the spatial and temporal variations. Such procedures have been widely used for over 25 years. For the described test, the operation of the source must be constant ( within 3 percent by definition), 33 precluding its use at any source with temporal variability. Thus, the procedure is not universal and many sources will have to perform multi point sampling. We recommend requiring up to 3 sample points or increasing the allowable variation to 30 percent. The idea of reducing sample points where it can be demonstrated that no stratification exists has a great deal of merit. However, since flow conditions can vary somewhat during a test, it does not seem reasonable to reduce the traverse points below the 3 required in PS 2. ( 0032, 0027, 0041, 0059)

Response: See response to Comments 65 and 78.

80. Comments: Is there a method for confirming that a multi hole probe is properly designed to sample from each hole at the same flow rate? If the method is going to include using such probes, and have criteria for sampling rates, then a procedure sanctioned by EPA to meet the " 10 percent specification is essential. A rake probe ( probe with 3 holes) is described for multipoint traverse. How is 10 percent of the mean flow rate determined? Presently this type of probe is not acceptable for CAMD use, mainly because there is a belief they do not work. This type of probe should not be allowed. Unless such a procedure is used, this will merely create controversy and reduce the data quality EPA is concerned about. There is no reason to prohibit use of a multi point probe that included independently controlled sample extraction lines that simultaneously draw gas at the same rate, but please specifically prohibit the so called rake probe. ( 0003, 0018, 0025, 0032, 0059)

Response: The Agency cannot evaluate all potential technologies nor prescribe procedures for verifying them. We added flexibility to the test methods by allowing options at the tester's discretion and ability to meet stated performance criteria. In this way, we can be less prescriptive while maintaining an acceptable level of performance.

81. Comment: We submit the following comments on Section 8.1.3: ( 1) Setting stratification limits implies allowable deviations ( and hence uncertainty) from the true average. What will EPA do with this uncertainty? ( 2) According to this section, there are two options: ( a) when each point is < 5.0 percent of mean and ( b) when each point is < 10.0 percent of the mean. In the former, a point nearest the mean is used. Although highly unlikely, it is possible that half are exactly + 5 percent and the other half are exactly  5 percent. Therefore, the maximum possible bias is " 5.0 percent. It is more likely that the point nearest the mean is 1 percent or 2 percent, or 3 percent off, in which case, respective biases would be introduced. In the latter option, the possible bias is even worse. The average of the three traverse points could very well be ± 10.0 percent off, in which case a bias of ± 10 percent is introduced. ( c) These biases can be limited by placing an appropriate specification, e. g., " 1.0 percent or even " 0.5 percent ( some examples from stratification tests can be investigated to determine an appropriate figure). Thus, the specification would say a single point that most closely matches or is within " 1.0 percent ( or some other number) of the mean. If a single point does not meet the specification, a combination of points may be used. The same holds true for the latter option. The average of the three points should be within, e. g., " 1.0 percent ( or some other number) of the mean. There should be higher limits ( e. g., 10, 15, or 20 percent) and an absolute limit ( e. g., 0.5 ppm), whichever is less stringent, for low level concentrations. Five percent of a source operating at 1.8 ppm is 0.09 ppm; thus a source ranging from 1.7 to 1.9 ppm with a deviation of 0.10 ppm from the mean would exceed the limits ( stratified). ( 0032) 34 Response: We have not conducted a thorough study of the uncertainty of the allowable deviations for the stratification test. In this rulemaking, we are attempted to add provisions to promote representative sampling that have been lacking in the past. The criteria we added have been in common use in numerous other testing requirements.

82. Comment: The stratification test should not be determined with a NOx concentration corrected for dilution, which would mask the results. Rather, the degree of stratification should be determined based on the absolute, uncorrected concentration. Dilution corrections are in conflict with Part 75 stratification tests. Also there is no standard against which the data are to be corrected. ( 0002, 0010, 0011, 0029, 0039)

Response: We have dropped the requirement that the stratification test be made with diluent corrected pollutant concentrations.

83. Comment: Section 8.1.3 of Method 7E requires that NOx concentrations be corrected for diluent. The detailed procedure is wrong since it will only be comparing NOx variations during the stratification test. For example, if you have one point that has a higher oxygen content, you would adjust the NOx concentration to compare to the other points, thus if there is stratification it would be masked by correction of all NOx concentrations to the same diluent concentration. A higher oxygen or lower carbon dioxide content indicates infiltration of ambient air or unmixed flue gases. Isn= t that stratification? If the diluent concentration for all points is less than or equal to " 5 percent of the mean concentration, then a single point may be sampled. If the range of the individual traverse point diluent concentrations is equal to or less than " 10 percent of the mean, then sample three points at 16.7, 50.0 and 83.3 percent of stack diameter. ( 0011)

Response: See response to Comment 82.

84. Comment: The section refers to determining the point and mean NOx concentrations corrected for diluent, which may not be applicable in all cases. We propose determining the point and mean NOx concentrations in units consistent with the purpose of the test, such as testing an emission limit. ( 0044)

Response: See response to Comment 82.

85. Comment: The wording appears to limit this test to NOx only. If the test is meant to apply to other pollutants, consider changing NOx to pollutant. ( 0025)

Response: Since the stratification test is detailed in Method 7E, the narrative addresses the pollutant as NOx. We have noted that the pollutant of interest is determined in the stratification test.

86. Comment: Once a stratification test has been passed at a source, there should be no requirement to perform this test every year, assuming no major changes have been made to the unit. ( 0028) 35 Response: The requirement to test using Method 1 sampling points in all cases has been dropped. See response to Comment 57. A stratification test should be performed if stratification is suspected at the test location or a 3 point sample shows the concentration at any point deviating from the mean by more than 10 percent. The test must be conducted to assure that representative sampling is performed.

87. Comment: The stratification requirements in Section 8.1.3 do not contain sufficient detail for application to actual testing. For example, for multi load testing ( e. g., NSPS Subpart GG), at what operating load should the stratification test be performed? We believe that only one load level should be checked for stratification. If the load level is an issue, EPA should address that. The EPA should also make clear that if the " 5 or " l0 percent criteria under the stratification test are not met, Section 8.1.1 of the proposed Method 7E should be used to determine the number of sampling points. However, for stacks with low concentrations ( e. g., 2.5 ppm NOx permit limits), some type of alternative stratification criteria should be allowed ( e. g., all points within " 0.5 ppm of the overall average). Meeting a 5 percent ( i. e., 0.13 ppm) or 10 percent ( i. e., 0.25 ppm) criterion is unnecessarily restrictive.

In the event that prior, historical data shows no stratification, and no changes to the stack design or process operations/ controls have occurred since the last stack test, language should be included to allow the stratification test to be waived. Our past experience with numerous reference method stack tests has shown gas concentration stratification is almost never encountered.

The EPA should also consider exempting small stacks ( e. g., < 24 inches) from the stratification testing requirement, since such a test is not likely to be necessary or useful in those cases. ( 0038)

Response: See the response to Comment 65. The special testing conditions for turbines are best addressed under Subpart GG and are beyond the scope of the revisions we are making. An alternative stratification criterion of within 5.0 ppm or 0.5 percent diluent of the average has been added. For measurements used to comply with low concentration limits, single point sampling is allowed if the results of a 3 point stratification test are within 0.5 ppm, and 3 point sampling is allowed if all points are within 1.0 ppm. We believe 3 point sampling is useful for small stacks and is not overly burdensome. This is also a good test to initially show whether likedesign sources experience individual leaks or other phenomena which affect emission stratification.

88. Comment: In Method 20, the diluent was traversed without the pollutant, which took care of temporal changes. In the proposal you now request pollutant and diluent, which means that two samples should be taken and compared. Otherwise most CO, SO2, and NOx samples will have to have the maximum points ( i. e. affects costs). ( 0035)

Response: See response to Comments 65 and 82. 36 89. Comment: Since these methods are used for RATAs, the new method will affect cost/ time, and each test could be as long as 96 min, not 21 as currently stated. ( 0035)

Response: For RATA determinations, the sampling points and sampling times in the applicable performance specifications govern.

90. Comment: In Section 8.1.1, does this mean that when we conduct RATA= s and there is stratification that we traverse over as many as 49 points ( square stack with 7 ports)? This would mean that at a measurement system response time of 1.5 minutes, that each point would be measured for 3 minutes, multiplied by 49 points equals 2 hours, 30 minutes per run. Assuming 10 runs for a normal RATA makes for an awfully long test. We recommend that you return to the 3 point test. ( 0004)

Response: When conducting RATA's, the sampling requirements of the applicable performance specification govern.

3.7 Sampling Dilution Systems 91. Comment: There appears to be a grave oversight in the proposed methods for the case of dilution systems, which have been approved by the Emission Measurement Center as alternative method ALT 007 ( Use of Dilution Probes with Instrumental Methods). The new rules should be clearly modified to allow dilution systems or have language implying dry extractive systems removed as not to limit technology choices in the future. Incorporating dilution systems into Method 7E would be one way to do this, and would advance the concept of a technologyneutral method ( and then drop ALT 007). One of the biggest issues with dilution systems is requiring calibration standards that have very defined molecular weights to match the expected effluent, so the dilution rate doesn= t change when the system is operating. Dilution systems typically use a system calibration instead of a direct calibration, and should incorporate a discussion of calibration drift using a procedure similar to bias determination. Although it no longer appears on the EMC website, Guidance Document GD 18 ( 06 18 92) indicated that dilution sampling systems were acceptable for use with EPA Methods 6C, 7E, 20, and 10. The document discussed the virtues and special requirements of dilution extractive sampling and it should seem reasonable to reword the new methods to allow this. If dilution probes are allowed, the difference between molecular weights of the cal gas and sample gas must also be addressed, since this affects the dilution ratio as explained in AAn Operator= s Guide to Eliminating Bias in CEM Systems,@ EPA/ 430/ R 94 016, November 1994, pp 3 5 to 3 9. ( 009, 0016, 0022, 0033, 0034, 0038, 0056)

Response: The methods have been modified to clearly note that dilution systems are acceptable. We have included discussions of calibration gas needs relative to the sample gas molecular weight, calibration drift test variations, and other instructions pertinent to dilution systems that were a part of EMC Guidance Document GD 18. We have also included procedures and specifications pertaining to dilution type systems that are consistent with Chapter 21 of the APart 75 Emissions Monitoring Policy <EMAIL_ADDRESS>37 92. Comment: Please clarify the difference in procedures for direct extractive and dilution extractive systems. The current draft is focused on direct extractive. ( 0059)

Response: See the response to Comment 91.

93. Comment: The test methods should include provisions for additional methods/ analytical approaches that are acceptable in the appropriate test method, including the use of dilution based sampling systems and extractive FTIR measurement systems. ( 0032)

Response: One of the purposes of the rulemaking was to allow for the use of acceptable alternative procedures in the methods. For example, Methods 6C and 7E were reworded to allow analyzers beyond those traditionally required. Discussions have been added to the methods to address the special requirements of dilution based sampling systems.

94. Comment: The method does not address the use of a Standard Gas Dilution system to generate low level calibration gases from high level gases. ( 0013)

Response: A gas dilution system meeting the requirements of Method 205 of Appendix M to 40 CFR 51 may be used to generate low concentration calibration gases except under Part 75 applications, where Administrator approval is required.

3.8 Moisture Removal Systems 95. Comment: The phrase thermo electric type condenser is incorrect and should be thermo electric cooled condenser. Referring to specific types of moisture removal systems and operating temperatures is not technology neutral and should be removed from the rule or clarified as required technology. Passing a bias test should be the real criteria. " Moisture removal system" should be changed to " sample conditioning system." We recommend the dew point temperature at the outlet of the drier must be 60 º F ( 15 ° C) as measured or corrected to and continuously monitored. The language used is a direct quote from the ICAC document and insinuates favoritism towards chillers sold by ICAC members. ( 0009, 0013, 0022, 0023, 0032, 0039, 0054)

Response: The reference to Athermo electric@ type condensers has been dropped to make the item technology neutral. AConditioning equipment@ was used instead of Amoisture removal system.@ This equipment must keep the sample gas above the dew point temperature by either dilution, by heating it prior to analysis ( for a cool, dry measurement system), or through the analysis ( for a hot wet system).

96. Comment: The sampling system bias check must include the same water ( 1 percent absolute) concentration found in the sample. This should be rephrased found in the analyzed sample. Whenever specifications are given, you need a procedure for verifying that the moisture content is indeed within " 1.0 percent absolute. Does this mean that a dilution probe must analyze hot/ wet cal gas ( impossible w/ o compromising the Protocol analysis) or is EPA referring to the moisture concentration as seen by the analyzer? The testing firm will never know what the water content is in advance of the test. ( 0016, 0032, 0038) 38 Response: The proposed requirement that the calibration gas used in the sampling system bias check be within 1 percent absolute of that found in the sample gas has been dropped.

97. Comment: The statement concerning not having to measure moisture content for wet basis pollutant/ diluent analyzers is false. One must measure moisture content in order to demonstrate that the system meets the 1.0 percent absolute moisture specification, even though the specification is meaningless and unnecessary in the first place. We interpret for dilution systems at 100 to 1, we have made moisture 1 percent at most, thereby allowing us to calibrate from cylinders containing no moisture. How does a wet system bias check get the same moisture as a scrubber exhaust? ( 0009, 0011, 0028, 0032, 0035)

Response: See response to Comment 96.

98. Comment: Section 6.1.4 of Method 7E requires some moisture generating system with the calibration gases and will add to the cost and complexity of the tests. ( 0032) Anything out there to just dial up 25 percent moisture, mixed, of course, with the correct ppm of NOx? Get real. We are not aware of any cal gases with stack concentrations of water, because it is thermodynamically impossible to make. This requirement appears to be impossible to meet as a practical matter. ( 0038, 0043)

Response: Analyzers that have water as a potential interference must document that water does not interfere with the analysis, through the testing of wet gases or by other means. Analyzers that are not affected by moisture are not required to make that evaluation.

99. Comment: As written, this section will require heated sample lines with all dilution systems which should not be the case. Thousands of tests have been made with dilution ratios of 100: 1 or higher that do not use heated lines. The only requirement is to maintain the dew point of the diluted sample below that provided by a condenser or dryer. ( 0009, 0059)

Response: See response to Comment 105.

100. Comment: As written, the section precludes the use of permeation dryers, which are currently acceptable to EPA. One commenter mentions Nafion dryers in particular, and presents a lengthy discussion of dryer technologies. Wording should be changed to include condensers, dilution and permeation dryers, with suitable wording to indicate water is removed or reduced, not condensed. Comment discusses several chiller/ dryer designs and a University of California study evaluation of them, and recommends technology neutral language. The Aor similar device@ is a direct quote from ICAC document, so still seems self interested. Further, I would avoid using a permeation dryer in any other context than as a polishing moisture removal system after another condenser. Thermo electric condensers are not the predominant type used, but Teflon coiled condensers in an ice bath with peristaltic pumps for moisture removal, are. ( 0009, 0011, 0023, 0038, 0039, 0054)

Response: See response to Comment 105. 39 101. Comment: There are additional costs to monitor temperatures at the outlet of the drier. Is this necessary since the gas conditioning system is effectively eliminating all moisture prior to the gas outlet? What accuracy does this lend to the method? Is monitoring and recording temperatures what is intended? Regulators in Idaho will want proof. Is there a way of monitoring the dew point in the exit gas stream without adding moisture to the gas stream ( wet bulb temp) or an expensive dew point probe? Even thermocouples will require calibrations. Do we need a data logger, or can the probe pusher record the values? If the regulation says Amust be@, our regulators want proof. This is definitely not simplifying our work. We need details on how this monitoring is to be done, and note that much of the present testing equipment is not capable of measuring these temperatures, and it is not really necessary. ( 0028, 0038, 0043)

Response: Different techniques may be used to prevent condensation. Assurance that the sample is maintained above its dew point may be shown by monitoring the appropriate temperatures or parameters. The tester must verify that the system used does not result in sample loss due to condensation.

102. Comment: Countercurrent heat exchanger designs are difficult to measure exit gas temperature and it is unclear how to use them for this application. ( 0012)

Response: See the response to Comment 101. Where technology does not allow gas temperature to be measured, alternative means may be used to demonstrate that the sample is maintained above its dew point.

103. Comment: Is a 41 ° F dew point possible with any condenser? A 60 ° F dew point is, but a 41 ° F dew point is 20 percent relative humidity at 60 ° F. Why is that necessary when the interference check is mandated? ( 0035)

Response: We are not specifying minimum condenser or dryer outlet temperatures because of the different techniques used to prevent condensation. The tester must verify that the system used does not result in sample loss due to condensation.

104. Comment: The most popular moisture removal system is a chiller type system that cools the sample gas and removes the condensed moisture. Below is a list of and description of moisture removal systems. I have personally used a Nafion Dryer and prefer it to a condenser.

A Nafion Dryer does not condense the water vapor. The water vapor is removed as a gas ( vapor), thus it greatly reduces the potential for removing water soluble compounds like NO2 and SO2. A Nafion Dryer has no need to monitor the drier outlet gas dew point. Condensers function by cooling the gas stream until water ( and other liquids) coalesce, then collecting the condensate and draining it away. Condensers are simple to operate and to understand. Unfortunately, they are very non specific; not only do they remove whatever gases condense at lower temperatures, but also at least a portion of whatever gases dissolve in the condensate. Condenser systems are designed to minimize the contact of the gas stream with the condensate to limit this deficiency, but water soluble gases are always lost to varying degrees, depending upon the solubility of the gas in question. Large amounts of gases such as sulfur dioxide are lost by condensers, and 40 condensers are entirely inappropriate to dry gas streams containing hydrogen chloride or chlorine ( unless its removal is desired).

Desiccant dryers function by binding water to an absorbent. The absorbent may be a solid ( such as silica gel) or a liquid ( such as sulfuric acid) that binds water to its chemical structure as water of hydration. Desiccants are very simple to understand and to operate. Unfortunately, like condensers, they are very non specific, and remove many compounds other than water. Unlike condensers, water cannot be removed from desiccants by simply draining it away. While in operation, desiccants become progressively more loaded with water, and must periodically be regenerated by replacement of the desiccant or by driving off the water. Continuous operation desiccant dryers use either a drastic change in surrounding pressure ( pressure swing heatless desiccant dryers) or a drastic change in surrounding temperature ( temperature swing desiccant dryers) to remove water from one chamber of desiccant while a second chamber is used, and the chambers alternate operation and regeneration.

Permeation dryers function on a principle of selection on the basis of molecular size. Permeation dryers are a microporous material. When forced under pressure across the surface of the microporous material, large molecules tend to remain in the gas stream while small molecules tend to move through the microporous material and be removed. Permeation dryers are very simple to operate, but are primarily suitable as air dryers. Nitrogen and oxygen are larger molecules than water, so air can be dried by this method. Permeation dryers are too non specific to dry complex gas sample streams. Nafion dryers function on a principle of selection on the basis of affinity for the sulfonic acid group. Although water passage through Nafion is described as permeation, Nafion dryers do not operate on the same principles as permeation dryers. Nafion is not a microporous material and does not separate compounds on the basis of their molecular size. For example, Nafion dryers can remove water from a hydrogen stream, even though the hydrogen molecule is much smaller than water. Pressure is not required to drive the process; the driving force for the reaction is the partial pressure of water vapor. Unlike the competing methods, Nafion dryers are highly selective in the compounds they remove. The water moves through the membrane wall and evaporates into the surrounding air or gas in a process called perevaporation. This process is driven by the humidity gradient between the inside and the outside of the tubing. ( 0011)

Response: The commenter presented an interesting and descriptive summary of the major moisture removal systems. See response to Comment 103.

3.9 Equipment Heating Specifications 105. Comments: Throughout the proposed rules, there are numerous references to heating, and it is likely that regulators will conclude that the probe, umbilical, or other equipment be electrically heated. The language should state that the sample be maintained at a temperature above the dew point of the sample gas. In many cases, especially with respect to dilution systems, the necessary heat is provided by the process itself. The language in the rules should be changed to provide a technology neutral approach, and show that the desired temperature may be reached from the process itself. With a dilution system, heating various components to 95 C to prevent condensation is not necessary, and dilution systems should be exempt from these sample 41 conditioning requirements. Why increase the temperature from 250 to 285 F when any moisture will be steam above 212 F? A system at 250 F should meet all conditions. ( 0009, 0010, 0038, 0048)

Response: The language in the methods was revised to make them technology neutral. The requirement was made to maintain the sample gas above the dew point of the stack gas ( including all gas components, e. g. acid gas constituents) so that no loss of sample results. This may be done by heating, diluting, drying, desiccating, or a combination thereof, or by other means. It was noted that heat may be provided by the process itself if heating is the means of preventing sample loss.

106. Comment: Temperatures should match the 248 degrees Fahrenheit temperature required in Methods 4 and 5. ( 0042)

Response: The temperature required to prevent condensation in Methods 4 and 5 is sufficient for testing in most normal gas streams. However, the dew point of the gas streams will increase as higher boiling constituents increase in concentration. At sources high in SO2/ SO3 emissions, the dew point is likely to be higher than 248 EF. Our new approach allows the tester flexibility in preventing condensation, whether by a source specific heating temperature, an appropriate dilution factor, or other means.

107. Comment: Why are temperature requirements being raised to 284 EF, or 77 EF above the dew point? The dew point requirement adds confusion and one more determination that needs to be made to sample properly. There are equipment problems above 135 C, and industry standard of 120 C should be enough to prevent condensation. There are temperature conflicts between sections of the method and the QA/ QC table. ( 0026, .0028, 0031, 0039)

Response: See response to Comment 105.

108. Comment: Needs a clearer and broader definition of dew point. It is important to define total dew point and not be limited to water dew point. ICAC recommends a more complete approach that states to maintain the sample 25 C above the highest dew point in the sample to include acid effects ( H2SO4, H2S, HCl, etc.). ( 0054)

Response: See response to Comment 105.

109. Comment: States 140 C or 25 C above the dew point, whichever is higher. It should say whichever is lower since there is no concentration of moisture that will condense above 284 F unless under extreme pressure. ( 0035, 0039)

Response: The language has been changed to allow the tester to choose which procedure or technology is used to prevent condensation. We only require the sampling system maintain the sample gas above the dew point of the stack gas so that no loss of sample results. This may be done by heating, diluting, drying, desiccating, or a combination thereof, or by other means. 42 110. Comment: This section rules out unheated in stack filters if the stack temp is not > 25 C above the dew point and makes our direct probe to condenser conditioner obsolete... you are prescribing the system rather than making it performance based. To make three systems to meet your specifications will cost approximately $ 24,600 plus operating costs. ( 0043)

Response: See response to Comment 109.

111. Comment: The Method 7E measurement system requirement that equipment to be heated to 140 C or 25 C above the dew point is excessive, and many sources will have dew points much lower than 140 C. The requirement should mirror other methods with an acceptable operating range ( i. e. Method 5 at 120 + 14 C), with an increased requirement ( 14 25 C) above the dew point where appropriate. The current proposal will render many systems with selflimiting heaters unusable and will significantly increase test costs. Change the wording to heated to at least 100 C or 25 C above the concentration dew point of the sample, whichever is lower, or back to EPA= s original wording. ( 0039, 0056)

Response: See response to Comment 105.

112. Comment: The section suggests that probe and flow material must be externally heated, but in some cases with stack exhausts > 284 F this will not be necessary. ( 0038)

Response: See response to comment 105.

113. Comment: A heated sample line is not required for in situ dilution probes and is therefore not an essential component. If the exhaust gases are very hot, it may even be necessary to cool the probe. The language should state that the conditions should be maintained at a temperature above the dew point of the sample gas which must include all of the gas components, such as acid in lieu of water only. All of the new methods contain similar language related to the minimum operating temperature, which one commenter shows calculations to be 284 F, which is in excess of 250 F, a more realistic value. ( 0009, 0010, 0011, 0022, 0029)

Response: See response to Comment 105.

3.10 Technology Specific Analyzers 114. Comment: The performance criteria contained in the proposed method are not sufficient to justify the last sentence in this section: AAnalyzers operating on other principles may also be used provided the performance criteria are met.@ For example, analyzers using electrochemical cells provide completely unreliable results when not operated in diffusion limiting conditions even though such analyzers could meet the criteria of the proposed method while operating outside of diffusion limited conditions. The method would need to include special procedures such as those included in ASTM D 6522 00. However, these procedures would be completely inappropriate for chemiluminescent analyzers. No one set of performance specifications is appropriate for all analytical techniques. ( 0032). 43 Industry has been generating data for many years with reference method instrumentation, so just deleting terms such as chemiluminescence or NDUV without a clearly defined means of determining analytical uncertainties in new technologies is a recipe for disaster in the courts. Dropping the chemiluminescence requirement and allowing electrochemical cell analyzers to be used for NOx testing raises concerns about data quality, since these analyzers are more prone to ambient influences, stability problems, and operator error. We recommend that this concern be assessed prior to relaxing the NOx detection principle of 7E. ( 0023, 0037)

Response: It may be difficult to prescribe a set of performance specifications that appropriately evaluate all analytical techniques 100 percent of the time. However, we believe the interference, calibration error, and bias tests provide an adequate assessment of performance the majority of the time. We are making the methods as flexible and performance based as possible and are not requiring specific tests that check specific analyzer peculiarities. The electrochemical analyzer has been shown to be capable of producing reliable results in an ETV verification study.

115. Comment: References to specific technologies should be removed. ( 0009, 0054)

Response: References to specific technologies have been removed.

116. Comment: The Agency is commended on the approach taken in recognizing the uncertainty in all monitoring. In particular, we agree with the language in Section 1.3 of Method 7E which states that data of lesser quality may be accepted if the data user deems that the testing objectives are met. We also agree with moving to a more technology neutral, performance based approach, specifically by opening up Method 7E to non chemiluminescent analyzers. ( 0022)

Response: Although EPA appreciates these supportive comments, the Agency notes that the Adata quality assessment@ section, including the requirement to calculate and report the uncertainty of the test data, was not retained in the final rule.

117. Comment: ICAC recommends substantially improving the proposal by ( 1) adding an analogous performance based test method for CO emissions measurement; and ( 2) removing any references to specific types of instruments or sampling components or systems from the body of the proposal ( i. e. make it technology neutral). ( 0053)

Response: We agree and made these changes in the final rule.

118. Comment: The EPA should require any new technology to pass a Method 301 validation procedure or equivalent prior to its acceptance for reference testing. The Method 301 process could be used to identify potential interference for a particular technology, and the testing to quantify it could be part of a guidance document. Without a clear cut means of determining the analytical uncertainty between a new performance based technology and the previous reference method, the quality and defensibility of the data will suffer greatly. ( 0023)

Response: We do not think a Method 301 validation is needed for the new technologies we are allowing in the instrumental test methods. We believe the prescribed performance tests will ensure that analytical uncertainty is minimized. 44 119. Comment: In Section 6.2, the use of specific technologies should be removed from this section and are more appropriate in the preamble, if at all. The goal of the proposed rules is to move to performance based test methods and including references to specific instruments, sampling components, and systems would undermine that goal. ( 0009)

Response: In the proposed rule, we attempted to incorporate performance based criteria as our knowledge of various technologies allowed. Since we had not fully studied the potential technologies and the ability of the Method 6C performance tests to adequately evaluate the analytical uncertainties of these technologies, we believed it was appropriate to mention the technology options that have been successfully used for the SO2 analyzer. However, the final rule does allow the use of Aother@ technology options, provided the performance specifications can be met.

120. Comment: The rule should maintain a technology neutral posture and should not refer to a specific technology. ( 0054)

Response: See the response to Comment 119.

3.11 Calibration Gases 121. Comment: The selection of span gases should be tied to the emission limit or equivalent limit and not to the measured concentrations. ( 0031)

Response: We have defined the calibration span gas in terms of the measured concentrations to maximize the measurement accuracy in the range of measurements.

122. Comment: This section does not list the allowed gas combinations, like those shown in 3A and 6C. Note that NO in air is not recommended since it would oxidize to NO2. ( 0038)

Response: Method 7E now notes that the calibration gas must be NO in nitrogen.

123. Comments: Pages 58840 and 58841, end of 2nd paragraph, says that the cal gases now required in Methods 3A, 6C, and 7E are being proposed for Method 10, which implies the use of 3 gases ( zero, mid and span). Item 4 of the proposed changes, however, says three cal gases would be required for each test method ( Method 10 now requires four gases). In Section 7.1 of Method 7E ( 7.1.1, 7.1.2, and 7.1.3; and also 8.2.5?) it states a span, mid, and low are used. To me this implies 4 gases in total ( zero, low, mid and span). Please clarify, and if four gases are used, recognize the increased cost effect of requiring this. Also define what constitutes a zero gas. ( 0004, 0014, 0020, 0027)

Response: Methods 3A, 6C, 7E, 10, and 20 require three calibration gases: low ( which may include zero), mid, and high. The cited instances of ambiguity in the methods have been corrected. 45 124. Comment: Only five gas blending options are listed for calibration gases. Especially given the rigorous interference checks outlined elsewhere, this is hard to justify. This use of O2 in N2 in calibration gases is not allowed in Method 3A but this is the primary and most commonly used calibration gas for O2 analyzers. Blending CO2 or O2 with other gases shown not to interfere should be allowed, especially CO, NOx/ CO2 in N2, O2/ CO2 in N2, etc., and the wording should be changed to allow flexibility. A number of common and viable options have been excluded. Comment lists 4 specific mixtures based on compounds just mentioned. Does CO or NOx blending affect the feasibility of the interference check? In addition, we typically use CO, NO, and CO2 in N2 mixtures. In addition, we use propane in some blends without interference. Scott Specialty Gases, Air Products, Praxair, Matheson, and Messer catalogs for commercially available offer additional protocol blends other than those mentioned above ( 0004, 0009, 0011, 0013, 0028, 0030, 0035, 0038, 0039, 0043, 0048, 0059)

Response: Blended calibration gases are allowed in the final rule provided they meet the requirements of the Traceability Protocol and the additional gas components are shown not to interfere with the analysis.

125. Comments: Section 7.1 of 6C should allow additional blended gases, including mixtures with NO ( provided no oxygen is present), CO, methane, propane, etc., provided that the gases meet Protocol standards. This also applies to 3A, 7E, 10, and 20. I recommend removing this section altogether in all the methods. Many other comments recommended additional gas blends, and are also summarized in comments for each of the individual methods. ( 0039, 0059)

Response: See the response to Comment 124.

126. Comments: The proposed mid level cal gas range of 20 to 70 percent is an improvement over the existing 40 to 60 percent. It allows more leeway and freedom to use a representative cal standard for those emissions that are between 20 to 40 percent and 60 to 70 percent of the analyzer span. ( 0038)

Response: After further consideration, we have decided to retain the A40 to 60 percent of calibration span@ requirement for the mid level gas. The Agency believes that this ensures a better evaluation of the analyzer= s linear response. If the mid gas line were lowered to 20 percent of calibration span, it would be possible to do the analyzer calibration error test with low, mid and high level gases of 19, 21 and 80 percent of calibration span ( since the low level gas concentration can be up to 20 percent of span).

127. Comment: Method 3A should explicitly allow the use of ambient air as 1) a high range calibration gas for O2 analyzers and 2) as a zero gas for non dilution based systems with CO2 analyzers where appropriate for the measurement range of the system. ( 0032)

Response: Ambient air is generally unacceptable for use as a calibration gas in Method 3A. Prepurified air may be acceptable in some cases. However, without prior permission, only gases of traceabiliy protocol quality are allowed for calibration gases. 46 128. Comment: It is not clear whether the cylinder gases used for Method 3A calibrations are to be prepared according to EPA protocol. A lot of controversy and delay can be avoided if the gases used during a compliance demonstration are EPA protocol gases with a current certificate at the time of the test. ( 0059)

Response: See the response to Comment 127.

129. Comment: Why not allow the ability to mix CO and/ or NOx into these blends. Does it affect the feasibility of the interference check? ( 0004)

Response: See the response to Comment 124.

130. Comment: Only five gas blending options are listed for calibration gases. Especially given the rigorous interference checks outlined elsewhere, this is hard to justify. Blending SO2 with other gases shown not to interfere should be allowed. CO could be one component of a gas mixture, a mixture of SO2/ NOx/ CO2 in N2, etc., should be allowed, and the method should be rewritten to allow this flexibility. A number of common and viable options have been excluded. In addition, we use propane blends without interference. See Scott Specialty Gases, Air Products, Praxair, Matheson, and Messer catalogs for commercially available protocol blends other than those mentioned above. ( 0009, 0011, 0027, 0035, 0038, 0039, 0048, 0059)

Response: See the response to Comment 124.

131. Comment: It is not clear whether it is acceptable to prepare calibration gas mixtures from high concentration EPA Protocol gases in accordance to Method 205. If so, will this be acceptable to both EPA= s OAR and CAMD? The method does not address the use of a Standard Gas Dilution system to generate low level cal gases from high level gases. ( 0013, 0059)

Response: Method 205 may be used to dilute calibration gases of traceability protocol quality. Method 205 may only be used under part 75 of this chapter with Administrator approval.

132. Comment: Zero gas is not defined; only low, mid, and span gases are listed. Zero gas is required in the analyzer calibration error test and should be defined. ( 0035)

Response: The final rule requires three gas concentrations for the analyzer calibration error test, i. e., low, mid and high. The rule makes clear that the tester may use a zero gas as the low level calibration gas.

133. Comment: The sentence AThe calibration gas certification ( or recertification) must be complete and the test must be completed before the expiration date @

needs some editing. The first sentence says, AMust be certified according to the Protocol.@ Must be certified requires completion. Is the word test referring to the emission test? Perhaps the first sentence should be Your calibration gas must be certified ( or recertified) in accordance . . . The second sentence should read The calibration gas shall not be used after its expiration date. The statement, The goal is to bracket the sample concentrations and have at least one calibration gas below and one above the measurements should be deleted or clearly rewritten as a suggestion so as to not be 47 mistaken for a requirement that would be misinterpreted where emissions are highly variable ( containing spikes) and or where a calibration gas closely approximates the effluent concentration but does not necessarily fall above or below the exact concentration ( 0032, 0038).

Response: The suggested calibration gas certification language has been added. The goal of bracketing the sample concentrations with calibration gas has been listed as a recommendation whenever possible.