Response: The EPA agrees with the commenter. 49 IV. D. 9 Comment: One commenter ( 502) stated that EPA can establish the MACT floor based on work practice standards.

Response: The EPA agrees that work practice standards can be established, but is usually only done when it is not possible to set an emission limitation, which is not the case for this rule.

V. EMISSION LIMITATIONS A. Formaldehyde V. A. 1 Comment: Twenty three commenters ( 418, 421, 422, 424, 425, 426, 427, 430, 431, 435, 436, 437, 442, 443, 449, 460, 475, 479, 482, 505, 508, 509, 519) took issue with the data used to set the formaldehyde emission limitation. The commenters noted that the test reports used to set the limit used two different test methods and that the limit was based on only five data points and therefore does not reflect a level of performance that is achievable for all sources. Commenter 443 said that EPA has not provided enough data to know definitively what the standard should be. Commenter 460 stated that EPA must obtain additional information before it can set a floor.

The commenters also had concerns about possible errors in the test reports that are the source of the emissions data used to set the formaldehyde emission limitation. Commenter 437 said that close examination of the five reports uncovers questions regarding the actual test procedures, comparability, data reduction and data reporting that should be revisited before finalizing the formaldehyde concentration limit. All five reports appear to have calculation errors and/ or other data quality issues that significantly affect the reported formaldehyde concentration, the comparability of the results because different test methods were used, and/ or uncertainty associated with the average result. Commenter 449 also reviewed the five tests used to set the standard and found that all of the five tests used do not present valid quantitative results; therefore, data from these tests may not be used to establish a quantitative emission standard for formaldehyde emissions from LPC CTs.

One commenter ( 430) said that CARB 430 may report anomalously low formaldehyde emissions; therefore, the standard may be too stringent and unachievable in practice. Two commenters ( 435, 460) questioned whether the CARB 430 data used to develop the standard followed CARB method requirements. One commenter ( 437) believed that the results from all tests used to determine the MACT floor should be recalculated using CARB 430 procedures so the data can be justifiably compared. The results should also be recalculated using the American Society of Mechanical Engineers measurement uncertainty analysis procedure. The EPA should then use these results for establishing the formaldehyde concentration limit. The commenter estimated that an enforceable formaldehyde concentration limit should be in the range of approximately 100 to 500 ppb. 50 One commenter ( 449) said that a single emission test does not fully reflect the variability that will be seen by the best performing source employing any technology. The EPA should properly assess variability that may be experienced by the best performing sources under the worst foreseeable conditions that are expected to recur. Emission testing conducted by the commenter in conjunction with the Gas Turbine Institute indicates that 43 ppb is not achievable for small industrial and aeroderivative turbines. This is also demonstrated by emission testing that the Wyoming Department of Environmental Quality intends to submit to EPA. The commenter also contended that pooling the emissions data for large General Electric LPC units with emission data for small industrial and aeroderivative turbines fails to recognize the inherent technical differences between these two classes of LPC CTs. The EPA should consider a MACT floor analysis for small units based on emission test data that properly represents the best performing sources within that subcategory. Preliminary analysis for small industrial/ aeroderivative units demonstrates that emissions from 70  500 ppb have been reported.

Several commenters suggested a revised level for the emission limitation. One commenter ( 479) said that EPA must revise the limit upward to at least 63 ppb. Two commenters ( 443, 475) stated that additional formaldehyde data suggests that EPA should consider setting the emission standard to 90 ppbvd given the tremendous variability in the few measurements that are available. One commenter ( 505) submitted a summary table of data for nine tests conducted on LPC CTs; the test results show a variability between high and low loads of 34 percent, also six out of nine tests were above 43 ppb.

One commenter ( 421) said that EPA should consider postponing promulgation until issues related to the data quality are fully resolved.

Response: As stated in the response to comment IV. A. 2, EPA had limited emissions data for stationary combustion turbines at proposal. Due to the limited amount of emissions data EPA had at proposal, EPA requested HAP emissions test data from stationary combustion turbines in the proposed rule. As a result of this request, EPA received new data in the form of several test reports during the comment period and has more than doubled its total data set. Data were received for both diffusion flame and lean premix turbines. New test reports received included many tests conducted using FTIR; at proposal EPA did not have any emissions data conducted using FTIR. Therefore, EPA's data set has been significantly improved, both quantitatively and qualitatively.

As a result of comments received during the comment period, EPA performed an extensive review of tests used at proposal and new tests received during the comment period. A screening analysis of the formaldehyde test data for diffusion flame combustor turbines was conducted. Tests conducted using CARB 430 were evaluated due to the CARB advisory issued April 28, 2000, which stated that formaldehyde data measured by CARB 430 where the NOx emissions were greater than 50 ppm should be flagged as non quantitative. Tests where the NOx emissions were greater than 50 ppm or tests where the NOx levels were unknown were excluded from EPA's analysis. Most of the diffusion flame tests in the Emissions Database were unable to 51 pass the screening. The tests unable to pass the screening were not equipped with add on control for the reduction of HAPs.

The remaining test reports were further analyzed and reviewed to ensure the methods were used correctly in calculating and reporting formaldehyde concentrations and to check that proper QA/ QC procedures were followed. A number of errors were found in the test reports where CARB 430 was used to quantify formaldehyde concentrations. In several instances the CARB 430 reporting protocol was not followed. If the analytical concentration is less than five times the average field blank, then CARB 430 uses five times the field blank as the reported result to correct for interferences or contaminants that can react with the formaldehyde or dinitrophenylhydrazine to yield negative bias. However, many test reports did not report formaldehyde concentrations in this fashion. The formaldehyde concentrations were therefore recalculated where the CARB 430 reporting protocol was not followed correctly. General Electric ( GE) proposed a method for blank correcting in their comments on the proposed NESHAP for stationary combustion turbines. A copy of GE's comments can be obtained from EPA's Edocket Website as Document ID Number OAR 2002 0060 0435. The EPA evaluated formaldehyde emissions estimated using both blank correction procedures ( CARB 430 reporting protocol and proposed GE method), however, EPA chose the CARB 430 protocol because its results are closer to FTIR ( considered the most accurate method) and the correlations to FTIR for both protocols were similar.

No errors were found in test reports which used FTIR to measure formaldehyde concentrations in the stationary combustion turbine exhaust. The reported formaldehyde concentrations were representative of stationary combustion turbines and the measured QA/ QC parameters were within acceptable limits as set in the method.

The EPA agrees that CARB 430 generally understates the formaldehyde concentration in the exhaust gas from stationary combustion turbines. Since EPA Method 0011 is a similar method to CARB 430, it is believed that Method 0011 also understates the emissions of formaldehyde. The EPA feels that FTIR is a more accurate and reliable method. Several test reports were received during the comment period on recent testing on small lean premix combustion turbines which used both CARB 430 and FTIR to measure formaldehyde emissions. An analysis was conducted to correlate formaldehyde concentrations measured by CARB 430 and formaldehyde concentrations measured by FTIR. A linear regression was performed on the CARB 430 and FTIR formaldehyde data from these tests which gave a slope of 1.667 with a correlation coefficient of 0.561. Therefore, EPA concluded that CARB 430 formaldehyde results are on average 1.7 times lower than FTIR formaldehyde results. To account for the differences in the methods, a bias factor of 1.7 was applied to the CARB 430 and Method 0011 formaldehyde emissions data to make these data comparable to FTIR.

As a result of a complete data review including emissions data EPA had at proposal and new emissions data EPA received during the comment period, EPA currently has a very different data set as compared to what it had at proposal. For example, the amount of data for LPC units 52 increased, while the amount of data for DFC units decreased. The new data set includes more emissions data on smaller units as compared to the data set at proposal. As discussed in the responses to comments IV. A. 2 and IV. B. 1, the new data set was used to determine the MACT Floors. For new LPC gas fired units and new LPC oil fired units, a formaldehyde emission limitation of 91 ppb was established for the MACT Floor. It is believed that this emission limitation will be achievable for both small and large size CTs. The EPA considered establishing separate subcategories by size but found that there was little difference among the best performing small and large units. The best performing large LPC unit was controlled by an oxidation catalyst and had formaldehyde emissions of 19 and 91 ppb. The best performing small LPC unit (< 25 MW) had uncontrolled formaldehyde emissions of 68 ppb, which is within the range of emissions for the large LPC unit.

The EPA believes that it has adequately considered the variability in emissions by the best performing source. The EPA has emissions data for two tests for the best performing turbine in the LPC gas fired turbines subcategory; the formaldehyde emissions varied by a factor of 4.8 between the two tests. Since both tests were performed under similar conditions but at different times, they represent the variability of the best performing unit. The MACT floor for this subcategory was set based on the higher formaldehyde measurement, thus the variability of the best performing unit has been accounted for. Similar variability factors were applied for the other subcategories.

V. A. 2 Comment: One commenter ( 488) requested that a mass based emission limit be included as an alternative to the concentration based standard for LPC CTs. Two commenters ( 424, 427) recommended that EPA add a formaldehyde ton per year emission limit alternative.

Response: The EPA does not agree with the commenters. As stated in the preamble, a volume concentration was chosen for the emission limitation because it can be measured directly and is clearly related to the performance of the HAP reduction technology.

V. A. 3 Comment: One commenter ( 443) stated that LPC units that do not meet the formaldehyde standard but are in compliance with the NO x limit should not be required to install additional controls.

Response: The EPA does not agree that units that are not meeting the formaldehyde emission limitation should not be required to install additional controls. Our analysis of the MACT Floor shows that the best performing LPC unit is equipped with add on HAP emission control.

V. A. 4 Comment: Three commenters ( 421, 424, 502) contended that a contradiction exists between the proposed formaldehyde standards of 17,000 ppb for RICE and 43 ppb for CTs. Commenter 421 stated that the CT rule would discourage owners to acquire clean burning turbines, promoting reduced air quality. 53 Response: The EPA is required to regulate stationary combustion turbines and to set MACT according to the provisions set forth in the CAA. The emission standards for other MACT rules do not have any relevance when setting MACT for stationary combustion turbines.

V. A. 5 Comment: One commenter ( 424) requested that the standard value be stated in the same units of measurement of similar formaldehyde combustion source standards, e. g. RICE, for ease of comparison. The commenter asked that any formaldehyde emission level in the final rule be denoted in ppm units rather than ppb.

Response: The EPA believes that it is not necessary to state the emission limitation in the same units of measurement as other combustion source standards. The EPA believes that ppb is the most appropriate unit for this standard; units are not selected on the basis of ease of comparison with other standards.

V. A. 6 Comment: One commenter ( 436) expressed the opinion that the formaldehyde emission limitation could increase the use of diffusion flame turbines and RICE, resulting in substantial increase in emissions.

Response: The EPA does not agree that the formaldehyde emission limitation would increase the use of DFC CTs and RICE. The commenter did not provide any clarifying information to explain why the use of DFC CTs would be increased. New DFC units are subject to this rule and have emission limitations; the EPA has also proposed a NESHAP for stationary RICE which includes similar requirements to this rule, i. e. formaldehyde limits. Therefore there would be no incentive to use these units instead of LPC units. In addition, limitations for other pollutants, such as NOx, are also a factor.

V. A. 7 Comment: One commenter ( 436) observed that variations in atmospheric methane can result in variation in formaldehyde levels that exceed the proposed level of 43 ppbvd.

Response: The EPA agrees with the commenter that atmospheric levels of formaldehyde could be as high as 43 ppbvd. However, EPA believes that any ambient formaldehyde would be combusted in the turbine and would have little effect on the stack levels of formaldehyde.

V. A. 8 Comment: One commenter ( 417) stated that the 43 ppbvd limit should be changed to 25 ppbvd because EPA did not consider data provided to the CT MACT Work Group on tests performed on CTs using two different emission control technologies that resulted in substantially lower formaldehyde and HAP emissions. According to the commenter, both technologies demonstrated the ability to guarantee formaldehyde emissions of less than 25 ppbvd. Therefore, EPA should consider the HAP advantages provided by these control technologies when determining the formaldehyde limit.

Response: The commenter did not provide any details about whether these technologies are commercially available and if they can be retrofit on existing units. Without any information 54 regarding the feasibility and availability of these control technologies, EPA is unable to address the concern directly. As a result, EPA is not changing the NESHAP in response to this comment.

V. A. 9 Comment: One commenter ( 502) remarked that the formaldehyde limit is not justified considering the relatively small risks associated with the HAPs being emitted by the CT category.

Response: Risk is not a consideration in establishing emission standards under CAA section 112, except in those limited instances where an alternate standard for a threshold pollutant can be established pursuant to CAA section 112( d)( 4).

V. A. 10 Comment: One commenter ( 435) requested that the rule allow the EPA Administrator to enter into agreements with a manufacturer of lean pre mix combustion turbines to certify as compliant with the 43 ppb formaldehyde standard each model or other class of turbine that its testing demonstrates meets the standard. Notice of each proposed agreement could be published in the Federal Register, with an opportunity for public comment prior to finalization of the agreement.

Response: The EPA believes that performance testing and continuous parametric monitoring is a better method to determine continuous compliance than a one time factory test. The EPA therefore does not agree with the commenter.

B. CO V. B. 1 Comment: Twenty seven commenters ( 412, 418, 419, 420, 421, 422, 424, 425, 426, 427, 430, 431, 437, 440, 442, 443, 444, 445, 446, 449, 460, 475, 479, 484, 502, 508, 509) urged EPA to revise the CO emission limitation of 95 percent reduction because it does not represent actual emission reductions achievable by oxidation catalysts since it is based solely on two tests from a catalyst vendor, and it does not account for variability in catalyst performance. The commenters also noted that catalysts may not achieve the same level of CO reduction for multiple years and recommended that the rule provides for potential long term degradation of catalyst performance in practical turbine applications.

Three commenters ( 424, 427, 449) said that it is inappropriate for EPA to rely on emissions data for the SCONO x ( EM x GT) system to establish the emission performance achieved by traditional, passive oxidation catalysts. One commenter ( 430) questioned whether the reductions reported by the catalyst vendor have been achieved in practice by an operating CT owned and operated independent of the vendor. Two commenters ( 430, 449) observed that the SCONO x catalyst operates in temperature range of 300  700

F, consequently a heat exchanger may be required to lower the exhaust gas temperature, at significant additional cost. One commenter ( 449) remarked that the emission testing conducted for the SCONO x system represents inflated performance in terms of CO percent reduction due to the high CO levels at the inlet to the SCONO x system. 55 Eight commenters ( 420, 422, 443, 446, 460, 475, 479, 502) stated that 90 percent reduction of CO is a more appropriate emission limitation. One commenter ( 419) stated that they have catalysts that have been achieving about 90 percent reduction, not 95 percent. One commenter ( 430) noted that they have found it impossible to achieve 95 percent reduction, and that EPA has not shown 95 percent is achievable in practice. One commenter ( 437) recommended that the limit be set at 75 percent reduction. Two commenters ( 442, 449) advised that the reduction should be set at 88 percent. The basis for a limit of 88 percent is review of recent permitted emission limits for turbines with catalysts and confirmed by two recent CARB BACT assessments. Two commenters ( 424, 427) felt that 80 90 percent reduction is more appropriate for new CTs; for existing CTs, insufficient data exists to set a percent reduction level for retrofit applications as the temperature window available for the retrofit catalyst may not be within the optimum temperature range for the catalyst. Two commenters ( 426, 430) noted that in the preamble to the proposed rule, EPA reviewed design data from catalyst vendors and determined that the typical emission reduction for CTs is 90 percent CO reduction, with only a few systems designed to meet greater than 95 percent. One commenter ( 430) stated that the MACT floor should be as required by section 112( d)( 3)( A) of the CAA, the level of control achieved by the average of the best performing 12 percent of existing sources, and therefore would likely be significantly less than 95 percent reduction.

Also, two commenters ( 431, 484) requested that the CO reduction requirement be reduced for retrofit installations of oxidation catalyst on existing LPC turbines.

Response: The EPA believes that 95 percent reduction of CO is achievable through the use of oxidation catalyst control. The percent reduction is a design parameter of the oxidation catalyst control system. The costs for proper design and operation of such a system were included in our analysis. The EPA does not agree with the commenters' statements that 95 percent reduction is not achievable, however, as discussed in the response to comment VI. A. 1, the alternative CO emission limitation has been removed from the final rule due to CO measurement difficulties. Thus, the commenters' concerns are moot.

V. B. 2 Comment: Twenty seven commenters ( 412, 419, 420, 422, 424, 425, 426, 427, 430, 431, 435, 437, 442, 446, 449, 465, 469, 470, 475, 482, 484, 485, 488, 501, 502, 505, 518) requested that a CO outlet concentration limit option be added. Five commenters ( 435, 437, 446, 475, 505) recommended that EPA specify a CO emission limitation of 5 ppm. Two commenters ( 485, 501) recommended a CO limitation of 1 ppm. Two commenters ( 424, 427) suggested that EPA provide that CTs emitting less than 50 ppm CO at full load would comply with the MACT standard. One commenter ( 449) recommended an outlet standard of 6 ppm, based on the BACT recommendation by CARB for turbines rated 3 MW to 50+ MW. One commenter ( 425) stated that EPA could set the standard based on review of recent BACT/ LAER determinations. One commenter ( 426) recommended an outlet standard of 3 ppmvd at 15 percent O 2 for CTs equipped with catalyst and new LPC CTs. A separate rate should be set for CTs not equipped with catalyst ( limit would be greater than 3 ppmvd). A CO limit of 5 10 ppmvd is reasonable for new DFC CTs. One commenter ( 518) said that EPA should review the existing data correlating CO 56 emissions with formaldehyde emissions ( and collect additional data if necessary) to determine the limit. The commenter believed the limit would be in the 2 to 5 ppm range ( New Jersey has recently permitted LPC CTs with oxidation catalysts with allowable CO emissions in the range of 2 to 5 ppmvd at 7 percent O 2).

Commenter 505 noted that a single emission limit for CO would reduce the costs of compliance and negate the need to use inadequate test methods to determine compliance with the formaldehyde limit. Two commenters ( 465, 470) remarked that a single CO concentration limit would lessen the amount of record keeping for affected facilities by not having to collect two CO concentrations and calculate the percent reduction.

Response: The emissions data at the time of proposal showed that CO reduction across an oxidation catalyst was strongly correlated to HAP reduction, while the CO concentration and HAP concentration was not. Thus, it would not have been appropriate to have a CO outlet concentration limit.

V. B. 3 Comment: One commenter ( 424) said that the addition of a catalyst to reduce CO emissions will result in CO being subject to regulation as a HAP.

Response: The concern raised by the commenter is moot because this rule does not have any requirements for CO. However, as discussed in the response to comment VI. A. 1, the alternative CO emission limitation has been removed from the final rule due to CO measurement difficulties. Therefore the EPA does not feel that it is appropriate to establish a CO outlet concentration limit.

V. B. 4 Comment: One commenter ( 472) asserted that EPA's claim that a CO standard will result in some unspecified degree of reduction in some unidentified HAP falls far short of establishing an adequate surrogacy relationship between CO and the other HAPs. Furthermore, one commenter ( 436) stated that no correlation between CO and formaldehyde emissions at subppm levels has been demonstrated. The role of atmospheric CO levels on the development of a CO formaldehyde correlation must be examined. The CO in the exhaust may bear no relationship to the HAPs generated by the turbine if a significant percentage of air used in the CT bypasses the combustion zone. Likewise, commenter 424 said that a correlation between CO and formaldehyde emissions should exist, yet this correlation is hard to establish due to current measurement problems. To provide an acceptable surrogate for formaldehyde measurement, a precise, repeatable correlation must be established.

Similarly, one commenter ( 445) did not agree that there is a relationship between CO reduction and HAP reduction. Instead, the commenter believed a relationship exists between VOC and HAP. EPA's proposal to use CO reduction as a surrogate for HAP reduction will not accurately reflect a like reduction.

Response: As stated in the response to comment VI. A. 1, the alternative CO emission 57 limitation has been removed from the final rule due to CO measurement difficulties. Thus, the commenters' concerns are moot.

C. Duct Burners V. C. 1 Comment: Three commenters ( 422, 431, 484) sought an allowance for site specific emission limits where duct burners are utilized and the formaldehyde limit applies. Three commenters ( 422, 431, 502) recommended that facilities should be allowed to either accept the formaldehyde limit at the stack with the duct burner in operation, or be allowed to petition the EPA for an alternate ( higher) formaldehyde limit for the combined turbine/ duct burner co firing.

Response: The EPA has incorporated the commenters' suggestions that facilities be allowed to accept the formaldehyde limit at the stack with the duct burner in operation. The EPA does not believe it is necessary to specify in the rule that affected sources are allowed to petition EPA for an alternate formaldehyde limit.

V. C. 2 Comment: Two commenters ( 443, 486) observed that in some cases there is no means to separately monitor CO/ HAPs from the turbine and duct burner, because the catalyst may be after the duct burner. Two commenters ( 508, 509) remarked that EPA should address and resolve compliance and monitoring issues for combined cycle units using duct burners.

Response: The EPA acknowledges that in some cases it may not be possible to separately monitor emissions from the turbine and duct burner. The final rule has been revised to allow sources to meet the limit with their duct burner in operation if they choose to do so.

D. Other V. D. 1 Comment: One commenter ( 431) recommended that sources be able to choose to meet either a CO percent reduction, CO outlet concentration limit, or a formaldehyde concentration limit.

Thirteen commenters ( 418, 420, 425, 426, 430, 431, 440, 442, 443, 449, 469, 471, 475) requested that CTs with oxidation catalysts be allowed to comply with the formaldehyde emission limit. Commenter 469 noted that uncontrolled CO emissions from a LPC turbine are inherently low, making it difficult to achieve compliance with a 95 percent reduction limit.

Response: As stated in the response to comment VI. A. 1, the alternative CO emission limitation has been removed from the final rule due to CO measurement difficulties. Thus, the comment is moot.

V. D. 2 Comment: Eight commenters ( 418, 420, 424, 425, 427, 430, 442, 449) stated that the rule should only apply emission standards to the load range represented by the emissions data used to determine emission limitations. Commenters 430 and 424 said that the emission standard 58 should apply only at full load. Commenter 420 said the emission standards should only apply within a 60 to 100 percent base load range. Commenter 449 advised that EPA should specify in the final rule that the performance test should be conducted at full load conditions. Full load should be defined as 100 percent ± 10 percent and owner/ operators should be allowed to conduct the performance test at any load condition within that range.

Response: The emission standards are based on data from testing at high loads ( 90 percent and greater). To address the concerns expressed by the commenters about the emission standards being applicable at full load only, the final rule specifies that the performance test must be conducted at high load conditions, defined as 100 percent ± 10 percent.

V. D. 3 Comment: Two commenters ( 442, 449) contended that the emission standards should only apply for ambient temperatures ranging from 0

F to 100

F ( this is the range typically guaranteed by the manufacturer). One commenter ( 427) said that firing temperature was not considered in the rationale for setting the emission limitations.

Response: The EPA does not have any information to indicate that there would be a significant technological problem to operate turbines at ambient temperatures below 0

F and above 100

F and the commenters did not provide any information to support their comment. Information provided by operators of turbines on Alaska's North Slope indicated that they have experienced problems with turbine operation during cold temperatures but the temperatures on the North Slope are well below 0

F for sustained periods ( they provided the supporting temperature data). The information provided by the North Slope turbine operators was based on actual operating experience, not manufacturer guarantees. In the absence of any information to support the request to apply the emission standards only at ambient temperatures between 0

F and 100

F, EPA does not agree with this comment.

V. D. 4 Comment: One commenter ( 412) expressed support for the development and potential use of alternative control technologies to reduce HAP emissions.

Response: The commenter's support is acknowledged by EPA.

V. D. 5 Comment: One commenter ( 443) stated that EPA's suggestion that the CO CEMS requirement could be replaced with a requirement to demonstrate a percent reduction in formaldehyde is unreasonable.

Response: The EPA does not agree that a requirement to demonstrate a percent reduction in formaldehyde is unreasonable, however, the final rule does not contain such a requirement.

V. D. 6 Comment: One commenter ( 505) remarked that in the first paragraph under section II. D of the proposal preamble (" What Are the Emission Limitations and Operating Limitations"), the phrase " new or reconstructed" should be removed from item ( 2). 59 Response: The EPA is in agreement that phrase " new and reconstructed" should not have been in item ( 2). The phrase should also not have been in item ( 1).

V. D. 7 Comment: Three commenters ( 421, 437, 460) argued that EPA's data demonstrate that there is no substantive difference in formaldehyde emissions between DFC and LPC CTs. A no control standard should therefore be issued for both the DFC and LPC combustion system design, i. e. all gas turbines. The commenters cited data from ICCR database  11 non DLN turbines were reported with emission concentrations to be less than 44 ppb. The commenters questioned the accuracy of test methods. Also cited was a GRI/ EPRI report that shows that installation of a DLN combustor configuration on a gas turbine, all other components being equal, does not result in a reduced emission level of formaldehyde and based on questionable measurement accuracy any differences on a ppb level are negligible.

Response: The EPA does not agree with the commenters' contention that there is no substantive difference in formaldehyde emissions between DFC and LPC CTs. Emissions data at the time of proposal showed a difference in HAP emissions between DFC and LPC units; the data received since proposal continues to support this conclusion. An examination of formaldehyde test data for both DFC and LPC CTs shows that uncontrolled formaldehyde emissions for stationary LPC units are significantly lower than those of stationary DFC units. The difference varies, but uncontrolled DFC CTs emit on average about five times more HAP as compared to uncontrolled LPC CTs.

V. D. 8 Comment: One commenter ( 415) said that the standards should be cut by 50 percent.

Response: The commenter did not provide any details or supporting details about why the standards should be cut by 50 percent. Thus, EPA is unable to address the comment directly.

V. D. 9 Comment: One commenter ( 421) believed that there are significant data quality issues with the Emissions Database. The commenter recommended that the National Academy of Sciences or the National Academy of Engineering review the database for data quality.

Response: As stated in the response to comment IV. A. 2, EPA had limited emissions data for stationary combustion turbines at proposal. Due to the limited amount of emissions data EPA had at proposal, EPA requested HAP emissions test data from stationary combustion turbines in the proposed rule. As a result of this request, EPA received new data in the form of several test reports during the comment period and has more than doubled its total data set. Data were received for both diffusion flame and lean premix turbines. New test reports received included many tests conducted using FTIR; at proposal EPA did not have any emissions data conducted using FTIR. Therefore, EPA's data set has been significantly improved, both quantitatively and qualitatively.

As a result of comments received during the comment period, EPA performed an 60 extensive review of tests used at proposal and new tests received during the comment period. A screening analysis of the formaldehyde test data for diffusion flame combustor turbines was conducted. Tests conducted using CARB 430 were evaluated due to the CARB advisory issued April 28, 2000, which stated that formaldehyde data measured by CARB 430 where the NOx emissions were greater than 50 ppm should be flagged as non quantitative. Tests where the NOx emissions were greater than 50 ppm or tests where the NOx levels were unknown were excluded from EPA's analysis. Most of the diffusion flame tests in the Emissions Database were unable to pass the screening. The tests unable to pass the screening were not equipped with add on control for the reduction of HAPs.

The remaining test reports were further analyzed and reviewed to ensure the methods were used correctly in calculating and reporting formaldehyde concentrations and to check that proper QA/ QC procedures were followed. A number of errors were found in the test reports where CARB 430 was used to quantify formaldehyde concentrations. In several instances the CARB 430 reporting protocol was not followed. If the analytical concentration is less than five times the average field blank, then CARB 430 uses five times the field blank as the reported result to correct for interferences or contaminants that can react with the formaldehyde or dinitrophenylhydrazine to yield negative bias. However, many test reports did not report formaldehyde concentrations in this fashion. The formaldehyde concentrations were therefore recalculated where the CARB 430 reporting protocol was not followed correctly. General Electric ( GE) proposed a method for blank correcting in their comments on the proposed NESHAP for stationary combustion turbines. A copy of GE's comments can be obtained from EPA's Edocket Website as Document ID Number OAR 2002 0060 0435. The EPA evaluated formaldehyde emissions estimated using both blank correction procedures ( CARB 430 reporting protocol and proposed GE method), however, EPA chose the CARB 430 protocol because its results are closer to FTIR ( considered the most accurate method).

No errors were found in test reports which used FTIR to measure formaldehyde concentrations in the stationary combustion turbine exhaust. The reported formaldehyde concentrations were representative of stationary combustion turbines and the measured QA/ QC parameters were within acceptable limits as set in the method.

Due to the extensive review of the data and also the acquisition of new data, EPA feels that it has addressed the commenters concerns regarding the data quality issues with the Emissions Database.

V. D. 10 Comment: One commenter ( 425) expressed the view that the rule discourages any control option other than an oxidation catalyst. Requiring a source to petition for approval of operating limitations creates a high degree of uncertainty for a company and shifts the burden of rulemaking from EPA to the regulated source.

Response: The EPA does not agree with the commenter. The proposed rule required sources equipped with oxidation catalyst control to meet a CO emission reduction limitation and 61 other sources were required to meet a formaldehyde emission limitation. In the final rule, the CO emission reduction limitation has been eliminated and sources are not restricted to using oxidation catalyst control to meet the formaldehyde emission limitation. The final rule requires turbines complying with the emission limitation using oxidation catalyst control to monitor catalyst inlet temperature as an operating limitation. Sources that are not using oxidation catalyst control must petition the Administrator for approval of operating limitations ( or approval of no operating limitations). The EPA is not aware of any add on HAP control other than oxidation catalyst systems but would like to allow the use of other controls as they become available. Since there is no information on other types of controls that may be utilized in the future, the EPA is not able to specify appropriate operating limitations at this time. Therefore, the final rule requires sources that are using other controls to petition the Administrator for approval of appropriate operating limitations.

V. D. 11 Comment: One commenter ( 437) said that EPA should make provisions for CTs that are designed as LPC but may operate as DFC because of either ambient temperature or load variations. EPA should require that the CT meet MACT standards for LPC CTs only when in the LPC operating mode. If the turbine shifts from LPC to DFC ( or a hybrid between LPC and DFC), EPA can require operation of all pollution control equipment ( which will be required as a permit condition anyway), but not require the CT meet any emission limitations.

Response: In the final rule, the requirements for LPC units are the same as for DFC units. Therefore, EPA does not feel that it is necessary to make provisions for CTs that are designed as LPC but may operate as DFC, since the requirements for both types of units are not different.

V. D. 12 Comment: One commenter ( 520) remarked that they were pleased that EPA is proposing no emission requirements for new turbines, reconstructed turbines, and existing diffusion flame turbines.

Response: The commenter is correct in stating that existing DFC turbines had no requirements in the proposed rule; this is also the case in the final rule. The EPA believes the commenter misread the requirements in the proposed rule for new and reconstructed turbines, because their statement is not correct, there were emission requirements for new and reconstructed turbines. The final rule also has emission requirements for new and reconstructed turbines.

VI. MONITORING, RECORDKEEPING, REPORTING A. CO CEMS VI. A. 1 Comment: Twenty commenters ( 412, 418, 419, 424, 427, 433, 435, 437, 440, 442, 443, 449, 465, 470, 479, 485, 486, 488, 501, 502) requested that the CO CEMS requirement be removed and periodic testing/ parametric monitoring be adopted. Six commenters 62 ( 412, 427, 449, 465, 470, 479) cited the cost burden of a CEMS, with five of those commenters ( 412, 427, 449, 465, 470) noting that a requirement for CO CEMS imposes an excessive cost burden for smaller turbines. Commenter 449 also noted that CEMS have typically not been required on small turbines and personnel would not be familiar with CEMS operation and maintenance, resulting in increased capital and operating costs. Furthermore, commenter 449 felt that there would not be significant emissions reductions for the use of CEMS compared to the use of inlet temperature monitoring and periodic emission testing; the requirement is inconsistent with previous EPA decisions on monitoring, and there are deficiencies in the test methods and performance protocols. Commenter 419 questioned whether the low measurements can be made accurately and reliably on a continuous basis without jeopardizing the flexibility of facility operations.

Many commenters recommended alternatives to the CO CEMS requirement. One commenter ( 475) suggested the option of monitoring compliance with a one time performance test for CO. One commenter ( 443) said that an option could be reliance on a federal CO permit limit combined with periodic CO stack testing. If the permitted CO limit is relatively high, compliance with the formaldehyde limit at that level could first be determined using an initial formaldehyde test. If the CO limits/ concentration are low, initial formaldehyde testing should not be necessary. The commenter recommended that EPA establish a default minimum compliance demonstration at 5 ppm. One commenter ( 433) recommended that EPA evaluate periodic stack tests, conducted on the same schedule as relative accuracy test audit ( RATA) testing as an alternative to CEMS. At a minimum, this approach should be pursued for units with oxidation catalyst systems that would qualify as peaking units under the Acid Rain Program and are not otherwise required to conduct emissions monitoring for CO or other pollutants.

One commenter ( 419) said that a more workable solution would be to measure downstream CO, but only if a CEMS is already required for NO x. A catalyst efficiency test could be performed periodically to confirm continued reduction efficiency ( should include option to perform this check with portable analyzer). One commenter ( 440) said that if EPA includes an option to monitor CO emissions using CPMS rather than CO CEMS, a requirement to replace a catalyst bed when the pressure drop increases by more than 2 inches of water from the drop measured during the initial performance test may not be appropriate. Particular vendors are better able to specify the conditions under which catalyst replacement is warranted.

Response: In the preamble for the proposed rule, EPA solicited comments on the performance capabilities of a state of the art carbon monoxide ( CO) continuous emission monitoring system ( CEMS) and its ability to measure the low concentrations of CO in the exhaust of a stationary combustion turbine following an oxidation catalyst control device. In general commenters did not support CO CEMS, stating that existing CO CEMS technology and EPA performance criteria are not adequate to reliably and accurately measure trace levels of CO. Due to the CO measurement difficulties, EPA has decided to remove the CO emission reduction limitation from the rule. Therefore, while EPA recognizes the concerns expressed by the commenters, measurement of CO using a CO CEMS or any other means will not be required, and 63 the comments are moot.

VI. A. 2 Comment: One commenter ( 518) favored the option of CO CEMS to measure CO emissions at the exhaust from a stationary CT or following an oxidation catalyst emission control device ( i. e. CO outlet concentration limit monitored with CEMS).

Response: As stated in the response to comment VI. A. 1, EPA does not feel that an outlet concentration limit is appropriate. Due to the CO measurement difficulties, EPA has decided to remove the CO emission reduction limitation from the rule. Therefore, the comment is moot.

VI. A. 3 Comment: Two commenters ( 444, 475) requested that EPA provide justification for the 4 hour averaging period or use an averaging period that is justified. Four commenters ( 422, 431, 437, 502) said that the averaging time for CO emissions should be extended to 24 hours to be consistent with the Boiler/ Process Heater MACT.

Response: As discussed in the response to comment VI. A. 1, the emission limitation for CO reduction has been removed in the final rule, thus this comment is moot. However, the EPA does not agree that the 4 hour averaging period is not justified. Gas fired units have less variability in the feed stream than other sources such as coal fired boilers; therefore a shorter averaging time is appropriate for those units.

VI. A. 4 Comment: One commenter ( 488) recommended that the final rule contain provisions for using one set of CEMS that would sequentially monitor both the inlet and outlet.

Response: The EPA is amenable to using one CEMS to sequentially monitor both the inlet and outlet, however, as discussed in the response to comment VI. A. 1, EPA has decided to remove the CO emission reduction limitation from the rule due to the CO measurement difficulties. Therefore, the comment is moot.

VI. A. 5 Comment: Three commenters ( 465, 470, 471) stated that it is doubtful that representative samples can be easily and reliably obtained prior to the CO catalyst. Commenter 471 said that EPA should provide additional support and/ or guidance regarding the most appropriate method for accurately measuring upstream CO emissions.

Response: The EPA recognizes the commenters' concern that there could be difficulties in measuring prior to the CO catalyst. However, as discussed in the response to comment VI. A. 1, EPA has decided to remove the CO emission reduction limitation from the rule due to the CO measurement difficulties. Therefore, the comment is moot.

VI. A. 6 Comment: Three commenters ( 422, 431, 502) felt that there is no justification for O 2 and CO 2 CEM at both inlet and outlet of catalyst; use of the outlet O 2 or CO 2 concentration is more than adequate to correct the CO concentration at both the inlet and outlet. 64 Response: The EPA agrees that use of the outlet O 2 or CO 2 concentration is more than adequate to correct the CO concentration at both the inlet and outlet. However, as discussed in the response to comment VI. A. 1, EPA has decided to remove the CO emission reduction limitation from the rule due to the CO measurement difficulties. Therefore, the comment is moot.

B. Performance Testing VI. B. 1 Comment: Three commenters ( 443, 447/ 448, 460) requested that EPA clarify that performance testing is only required at full load. One commenter ( 443) said that the rule should allow sources the option to conduct tests at other loads as necessary to avoid interfering with sources' operating flexibility. One commenter ( 460) recommended that compliance testing requirements in the rule account for the possibility that in some CT applications, full load may not be achievable during a scheduled compliance test.

One commenter ( 420) suggested that performance testing should be conducted within a 60 to 100 percent base load operating range, taking into account operating conditions used to establish applicable vendor guarantees for oxidation catalyst efficiency as well as design criteria used to develop permitted outlet CO or formaldehyde emissions limitations.

Response: As stated in the response to comment V. D. 2, the emissions standards are based on emissions data from testing conducted at high loads ( 90 percent and greater). The EPA has addressed the commenters' concerns by clarifying in the final rule that the performance testing should be conducted at high load conditions, defined as 100 percent ± 10 percent.

VI. B. 2 Comment: One commenter ( 465) remarked that subsequent performance testing ( suggest no more frequent than annually) is needed for units meeting the formaldehyde limit. There should also be some methodology for the demonstration of continuous compliance.

Response: The EPA agrees with the commenter that subsequent performance testing is needed for units meeting the formaldehyde limit. As a result of this comment, the final rule includes a requirement for annual performance testing for formaldehyde for these units. The EPA also agrees that there should be some methodology for the demonstration of continuous compliance and has designated requirements for continuous compliance in the final rule. For sources equipped with oxidation catalyst control, continuous compliance will be demonstrated by continuously monitoring the inlet temperature to the catalyst and maintaining the inlet temperature within the range suggested by the catalyst manufacturer. Sources that are not equipped with oxidation catalyst control must petition the Administrator for approval of operating limitations or approval of no operating limitations.

VI. B. 3 Comment: One commenter ( 504) stated that the LPC subcategory should not have an initial compliance demonstration for the emission limit. No demonstration is needed if the unit has an initial compliance demonstration for its respective NO x limit. 65 Response: An initial compliance demonstration that includes both formaldehyde and NOx would be necessary to establish that the formaldehyde emission limit is being achieved at the same time the NOx limit is being achieved. However, as discussed in the response to comment VI. B. 2, the final rule does not allow continuous compliance to be demonstrated by meeting low NOx emission levels required by a federally enforceable permit, so this comment is moot.

VI. B. 4 Comment: One commenter ( 502) said that EPA should allow facilities to use existing test data to demonstrate compliance with the emission limitation if the test was conducted using the same methods specified in the rule and no process changes have been made since the test, or it can be demonstrated that the results of the performance test reliably demonstrate compliance despite process changes. The commenter recommended that EPA revise the proposed 40 CFR § 63.6110 by adding the following paragraph:

" An owner or operator is not required to conduct a performance test to determine outlet formaldehyde concentration on units for which a performance test was previously conducted for determining compliance with a regulation promulgated by the EPA and the test was conducted using the same methods specified in this subpart and either no process or equipment changes have been made since the test, or the owner or operator can demonstrate that the results of the performance test, with or without adjustments, reliably demonstrate compliance despite process or equipment changes."

Response: Since there are no emission limitation requirements for existing sources in the final rule, EPA expects that few facilities will have existing test data to demonstrate compliance with. Facilities that came online after the proposal would be the only sources that may have conducted emissions testing prior to the stack testing requirements of the final rule and EPA will allow facilities to use existing test data to demonstrate initial compliance with the emission limitation if the data is of good quality and is no older than two years. The facility must petition the Administrator for approval, and demonstrate that the tests were conducted using the same test methods specified in the subpart, the test method procedures were correctly followed, no process or equipment changes have been made since the test, and the data is of good quality and is less than two years old. Existing test data can only be used to demonstrate initial compliance; after the initial compliance demonstration, facilities must then begin to follow the annual compliance test schedule.

VI. B. 5 Comment: One commenter ( 502) requested that EPA allow a facility with identical CTs to conduct performance tests on only one of the units to demonstrate compliance with the emission limits for all of the identical units.

Response: The EPA does not agree that it is appropriate to allow a facility with identical CTs to conduct performance tests on only one of the units to demonstrate compliance with the emission limits for all of the identical units. It is our experience that emissions from identical units can vary significantly. 66 VI. B. 6 Comment: One commenter ( 437) recommended that the initial performance test period for demonstration of CO reductions be increased from 4 to 24 hours or longer to obtain results representative of the normal duty cycle.

Response: The EPA does not agree with this comment; it is believed that 4 hours is sufficient time to conduct the initial performance test.

VI. B. 7 Comment: One commenter ( 483) advised EPA to consider an exemption from further MACT performance testing for oxidation catalyst equipped lean premix turbine combined cycle units.

Response: The EPA does not agree that there should be an exemption from further MACT performance testing for lean premix turbine combined cycle units equipped with oxidation catalyst control. Subsequent performance testing is necessary to demonstrate that the emission limitations continue to be met.

VI. B. 8 Comment: One commenter ( 443) did not support EPA's suggestion that if it required compliance with the formaldehyde limit and not a percent reduction of formaldehyde it might require " more frequent emission testing" ( alternative to CO CEMS).

Response: The commenter did not identify the frequency of testing that they do not support. Thus, EPA is not able to respond to this comment.

C. Other VI. C. 1 Comment: One commenter ( 486) requested that the rule clarify that LPC CTs with oxidation catalysts will not be required to use CEMS. The rule should also clarify if CO CEMS for DFC units is an alternative or if it is always required. The commenter noted that all the utility size CTs constructed in Massachusetts over the last several years are LPC units and incorporate CO catalysts.

Response: As discussed in the response to comment VI. A. 1, CO CEMS are not required in the final rule. Thus, the clarifications requested by the commenter are not necessary.

VI. C. 2 Comment: Eight commenters ( 433, 443, 447/ 448, 471, 475, 483, 486, 505) recommended that CTs equipped with oxidation catalysts be given the option to meet the formaldehyde emission limitation. Commenter 471 said that requiring CO CEMS for units with oxidation catalysts places an unfair additional burden on those facilities that are among the best controlled and have the lowest emissions. Commenter 483 contended that LPC, combined cycle units with selective catalytic reduction ( SCR) and oxidation catalyst systems should be recognized as cleaner, and the final rule should be amended to not conflict with new source review ( NSR) permit monitoring requirements. The commenter recommended that EPA not require additional monitoring before the control units. If unit's initial test is below the 43 ppbvd limit, continuous 67 compliance could be assured through continuing to meet the permitted CO or NO x limit after the catalyst unit. Commenter 486 had a similar comment for LPC units equipped with oxidation catalysts.

Commenter 475 recommended that EPA provide the option to demonstrate compliance with the formaldehyde emission limit based on a one time performance test conducted at the inlet to the oxidation catalyst. Commenter 443 proposed that EPA allow units installing catalysts to make a demonstration of compliance with the formaldehyde limit through periodic formaldehyde tests performed at the stack ( annual testing should be more than sufficient). Commenter 433 stated that testing for formaldehyde emissions should be required even when an oxidation catalyst system is present, especially for larger CTs ( greater than 10 or 50 MW).

Response: These commenters all were concerned that CTs equipped with oxidation catalyst control were restricted to meeting the CO reduction limitation and installing CO CEMS. The commenters felt that these turbines should be given the option to meet the formaldehyde limitation. As discussed in the response to comment VI. A. 1, the CO reduction emission limitation and CO CEMS requirement has been dropped from the final rule and turbines equipped with oxidation catalyst control can meet a formaldehyde emission limitation. Thus the concerns expressed by the commenters have been adequately addressed.

VI. C. 3 Comment: Four commenters ( 420, 443, 444, 475) endorsed EPA's proposal to allow LPC CTs to rely upon low NO x levels to demonstrate continuous compliance following initial testing. Commenter 444 requested that it be extended to all types of turbines that have low NO x levels permitted by an enforcement agency. Two of the commenters ( 443, 475) recommended that EPA establish a minimum NO x emission limitation of 15 ppm. There would be no requirements for additional emission testing or monitoring to demonstrate MACT compliance if a given LPC CT is operating at or below 15 ppm NO x concentration in the exhaust gas stream.

Response: The EPA acknowledges the support expressed by the commenters. However, as discussed in the response to comment VI. B. 2, comments received during the comment period led us to establish requirements for annual stack testing and continuous parametric monitoring in the final rule. The option to rely upon low NOx levels is not in the final rule.

VI. C. 4 Comment: Two commenters ( 465, 470) stated that CO is likely a more reliable indicator of HAP emissions than NO x since NO x formation is inversely related to the emission of CO and HAPs. A protocol needs to be developed on how to correlate the formaldehyde emission rate with the surrogate emission rate. One commenter ( 470) said that EPA should use CO emissions as a surrogate for formaldehyde for LPC units. Likewise, two commenters ( 420, 430) recommended that EPA allow testing and monitoring of a surrogate for formaldehyde, such as VOCs or CO.

Response: As discussed in the response to comment VI. A. 1, there are difficulties in measuring CO at the outlet of combustion turbines equipped with oxidation catalyst control. 68 Therefore, using a surrogate CO emission rate is not a viable option. The commenter did not provide any supporting data to indicate a surrogate relationship between VOC and HAP, thus, EPA is unable to address their comment.

VI. C. 5 Comment: One commenter ( 429) expressed the view that a combination of periodic Method 320 measurements and frequent or continuous surrogate measurements would give a high level of confidence to the actual performance and HAP emissions at a low cost. Initial emission measurements and periodic ( every 3 5 years) should be conducted and can provide a calibration of the CO surrogate to the actual aldehyde level to facilitate monitoring in the interim periods between Method 320 tests. Another option is FTIR CEMS, however, the commenter believes CT emissions can be adequately monitored by periodic Method 320 testing with Method 320 calibrated CO surrogate measurements in between formal emission tests.

Response: As discussed in the response to comment VI. A. 1, the option to use CO as a surrogate has been removed from the final rule, therefore, some of the comments expressed are moot. The EPA agrees with the commenter that periodic Method 320 measurements are appropriate for formaldehyde and that method is allowed in the final rule.

VI. C. 6 Comment: Two commenters ( 435, 502) requested that the proposed rule provide that emissions from CTs are to be determined on a net basis, subtracting ambient formaldehyde. One commenter ( 424) suggested that sources should balance measurement of trace emissions ( aldehydes, HC, CO) by also measuring ambient or background levels. Similarly, one commenter ( 423) recommended that EPA provide an option to allow simultaneous testing of exhaust gases and incoming air. Those who fail the stack test due to high ambient formaldehyde in the bypass air could normalize the emission test by testing intake air as well. An additional standard could be based on the difference in measured formaldehyde between exhaust and intake air. A differential formaldehyde option would need to be placed in several locations in the final rule, including Tables 1, 3, and 4. Suggested language is given in the comment. Commenter 423 cited a study of ambient air in St. Louis that showed formaldehyde levels that would exceed the proposed 43 ppb emission limit as rationale.

Response: The EPA does not believe that ambient formaldehyde will have a significant effect on stack levels of formaldehyde, due to the extremely high combustion temperatures of CTs, which results in the formaldehyde being destroyed in the combustion air.

VI. C. 7 Comment: One commenter ( 420) requested that in addition to proposed requirements for CEMS for CO and performance testing, EPA should include alternatives for monitoring utilizing protocols developed based on EPA's final CAM rule.

Response: As discussed in the response to comment VI. A. 1, the final rule does not have a requirement for CO CEMS and CO performance testing due to public comments indicating that the CO stack testing methods and CO CEMS could not measure the low CO levels that are achieved particularly by LPC units with oxidation catalyst controls. Therefore, the comment is 69 moot.

VI. C. 8 Comment: One commenter ( 443) said that EPA should not require petitions for additional operating parameters.

Response: The EPA does not agree with the commenter. The petitions for additional operating parameters are intended for HAP control systems that have not been demonstrated yet. The response to comment V. D. 10 provides detailed rationale supporting the requirement to petition for additional operating parameters.

VI. C. 9 Comment: One commenter ( 502) recommended that the wording of § 63.6120( f) should be changed to ensure that some new, arbitrary formaldehyde limit would not be imposed. For example, the following words could be added to ( f): " to assure that the formaldehyde emission limit of 43 ppb will be met."

One commenter ( 417) suggested that the wording of § 63.6120( f) should be modified from ". . . additional operating limitations to be established during the initial performance test and continuously monitored thereafter" to " operating limits to demonstrate compliance with the formaldehyde emission concentration limitation during the initial performance test and continuously monitored thereafter."

Response: The EPA is amenable to clarifying the wording of § 63.6120( f) to make it clear that the operating limits are for the formaldehyde limit in the rule. The EPA has incorporated these suggestions in the final rule by adding clarifying language to § 63.6120( f).

VI. C. 10 Comment: One commenter ( 417) said that the wording of § 63.6120( f) should be revised from " . . . your stationary combustion turbine is not diffusion flame or lean premix, you must petition the Administrator . . ." to read " . . . the stationary combustion model is not diffusion flame or lean premix, the manufacturer must petition the Administrator . . . ." The rationale for the change is that this only needs to be done once for each model.

Response: The EPA does not agree with the commenter that this should only be done once for each model. The option to petition the Administrator should be utilized on a site specific basis, not for an entire model line of a turbine.

VI. C. 11 Comment: One commenter ( 417) recommended that the wording of § 63.6120( g)( 3) be revised to read " The limits proposed for the model turbine with a discussion of how these limits were developed and why the applicant feels they will assure compliance with the limitations. If data is not available to determine the limitations at the time the petition is submitted, the petition must include a discussion of how you will establish the upper and/ or lower values for the parameters which will be establish the limits on these parameters in the operating limitations:" 70 Response: The EPA does not agree that this change is necessary. The EPA feels that the language in the section is adequate as written.

VI. C. 12 Comment: One commenter ( 417) recommended that in § 63.6120( h)( 7), EPA should change ". . . infeasible or unreasonable. . . " to ". . . infeasible, unreasonable or unnecessary. . . "

Response: The EPA has accepted the commenter's recommendation and made this change to § 63.6120( h)( 7).

VI. C. 13 Comment: One commenter ( 417) requested that EPA change the title of Table 6 to read " Other than Diffusion flame or Lean Pre mix" and also change the table to reflect that if the Administrator concurs that § 63.6120( h) applies, no monitoring is required.

Response: As a result of new information received since proposal, the requirements in Table 6 no longer apply only for turbines that are not DFC or LPC. Thus, the comment is moot.

VI. C. 14 Comment: One commenter ( 502) contended that the requirement that deviations must be accounted for in addition to exceedances is overly burdensome ( § 63.6150( d)( 4)). Reporting should only require identification of start, stop, and malfunction periods.

Response: The requirements in § 63.6150( d)( 4) were for CTs using CEMS to comply with an emission limitation. The requirement to use CEMS has been removed in the final rule, thus this comment is moot.

VI. C. 15 Comment: One commenter ( 437) asked that EPA clarify in § 63.6150( a) that only those units subject to an emission limitation must comply with the reporting requirements.

Response: The EPA agrees with the commenter that the rule should clarify which units must comply with reporting requirements. This has been clarified in the final rule.

VII. TEST METHODS A. Formaldehyde 1. CARB 430 VII. A. 1.1 Comment: Four commenters ( 412, 421, 436, 449) urged EPA to re review all emission tests using CARB 430. Commenter 412 noted that CARB had issued an advisory about the use of CARB 430. Commenter 449 stated that any historical data from DFC units using this method should be considered suspect, including data from the CT Emissions Database and AP 42 71 emission factors. Unless proven otherwise, the DFC CT test data should be designated " nonquantitative based on the Method 430 advisory from CARB. Commenter 436 said that a study of the accuracy and precision of CARB 430 at low ppb levels is needed to determine the significance of the test data on which the standard is based.

Response: The EPA reviewed the CARB advisory issued on April 28, 2000 and additional background material in the GRI Topical Report entitled " Investigation of Interferences with Aqueous 2,4 DNPH Based Methods for Measurement of Aldehydes in Natural Gas Combustion Exhaust" submitted by Commenter 449. As a result of comments received during the comment period, EPA performed an extensive review of tests used at proposal and new tests received during the comment period. A screening analysis of the formaldehyde test data for diffusion flame combustor turbines was conducted. Tests conducted using CARB 430 were evaluated due to the CARB advisory, which stated that formaldehyde data measured by CARB 430 where the NOx emissions were greater than 50 ppm should be flagged as non quantitative. Tests where the NOx emissions were greater than 50 ppm or tests where the NOx levels were unknown were excluded from EPA's analysis.

EPA further analyzed and reviewed the remaining test reports to ensure the methods were used correctly in calculating and reporting formaldehyde concentrations and to check that proper QA/ QC procedures were followed. A number of errors were found in the test reports where CARB 430 was used to quantify formaldehyde concentrations. In several instances the CARB 430 reporting protocol was not followed. If the concentration is less than five times the field blank, CARB 430 uses five times the field blank as the reported result to correct for interferences or contaminants that can react with the formaldehyde or dinitrophenylhydrazine to yield negative bias. However, many test reports did not report formaldehyde concentrations in this fashion. EPA therefore recalculated the formaldehyde concentrations where the CARB 430 reporting protocol was not followed correctly.

VII. A. 1.2 Comment: Nine commenters ( 424, 430, 435, 436, 442, 449, 460, 479, 502) expressed concerns regarding the accuracy and precision at levels commensurate with the proposed standard. Two of the commenters ( 424, 479) noted that CARB 430 is susceptible to interferences. One commenter ( 436) said that sample loss and measurement uncertainties can contribute to large measurement variability. One commenter ( 449) asserted that CARB 430 should not be included as an appropriate method for DFC CTs.

One commenter ( 429) contended that CARB 430 is an indirect measurement method and is inferior to Method 320. CARB 430 cannot give realistic results due to the following: formaldehyde results tend to be negatively biased with high scatter, especially at low concentrations; there are other problems with high field and analyte blanks; the tester must know the NO 2 concentration prior to testing, introducing another uncertainty into the measurement; the method can give false acetaldehyde detections; data cited showing inconsistencies with CARB 430; and the high level of variations and biases observed may lead to future compliance problems or public lawsuits over falsely detected species or negative catalyst performance. 72 Two commenters ( 485, 501) observed that the minimum detection limits are higher than the MACT Floor. Standard procedures for handling blank corrections and non detects should be added to the promulgated test methods. The method should be validated for combustion sources and revised to provide for longer sampling runs necessary to achieve the detection levels needed to reliably and routinely measure ppb level formaldehyde. Longer sample runs are problematic.

Two commenters ( 435, 437) recommended modifications to CARB 430 and guidelines to enhance the measurement reliability for CARB 430. Commenter 435 stated that with the modifications, CARB 430 can achieve a detection level less than 43 ppb. Similarly, commenter 437 said that the use of CARB 430 is conditionally supported, but additional guidance and deviations from the method as currently published should be provided. Field validation of the method performance for CT applications according to EPA Method 301 is recommended. That commenter also recommended that EPA should require use of paired sampling trains for every test run. If the precision of any one test run with paired sampling trains is poor due to apparent random contamination, it should be explicitly permitted to disregard the suspect sample results.

One commenter ( 435) recommended that the CARB 430 reporting protocol be revised to reflect the actual emissions from the CT. The rule should indicate that when using CARB 430 to demonstrate compliance with the proposed standard, the reporting criteria should not be as indicated in CARB 430 but should be the stack measurement minus the average field blank measurement. Conversely, one commenter ( 437) recommended that EPA should retain the CARB 430 reporting limit procedures, or a valid statistical measure of uncertainty such as the 95 percent upper confidence bound, to reflect data quality. Since the method was developed for much higher in stack formaldehyde concentrations, and hence much higher blank contamination levels, EPA should develop an alternative calculation procedure to account for increased likelihood of very low level blank contamination.

Response: The EPA agrees with the nine commenters' concerns regarding the accuracy of CARB 430 levels commensurate with the proposed standard. EPA agrees with the commenters who noted that CARB 430 is susceptible to interferences or who said that sample loss and measurement uncertainties contribute to large measurement variability. EPA agrees with Commenter 429 that the method is an indirect measurement method, however, EPA disagrees that CARB 430 cannot give realistic results; in some cases EPA believes that CARB 430 can provide realistic data. However, EPA also agrees that Method 320 would be the better compliance method. Therefore EPA has specified either Method 320 or ASTM D6348 03 as the compliance procedure. As discussed in the response to comment VII. A. 5.1, ASTM D6348 03 is an acceptable alternative to Method 320.

VII. A. 1.3 Comment: One commenter ( 443) remarked that EPA does not explain how it calculated the 2 3 ppb detection limit cited in the preamble for CARB 430; EPA should explain the procedure used to calculate the detection limit and to review the calculation results. The commenter also said that EPA's method for determining the detection limit of CARB 430 significantly overstates the practical source measurement capabilities of this method. 73 Response: The EPA used reported responses from low level standards or blanks to calculate standard deviation of the responses and then multiplied that by three to estimate a detection limit potentially attainable.

VII. A. 1.4 Comment: One commenter ( 443) expressed the view that ambient formaldehyde may affect CARB 430 test results. The commenter requested that EPA conduct ambient tests and develop ways to correct for ambient contributions/ contamination in the results. The EPA should design its standard and compliance methods to ensure that sources' compliance status is not susceptible to fluctuations in ambient formaldehyde concentrations.

Response: The EPA agrees that ambient formaldehyde may affect CARB 430 results; Method 320 and ASTM D6348 03 results will be less affected. However, since Method 320 and ASTM D6348 03 are the only test methods allowed in the final rule to demonstrate compliance, this comment is moot.

2. FTIR/ EPA Method 320 VII. A. 2.1 Comment: Nine commenters ( 420, 424, 435, 436, 443, 449, 460, 479, 502) expressed concerns regarding the accuracy, precision, and reliability at levels commensurate with the proposed standard. Three commenters ( 435, 460, 502) said that the method is not acceptable for demonstrating compliance without extensive modifications. One commenter ( 502) noted that there is little, if any, FTIR data at low ppb levels. One commenter ( 443) stated that the method's lenient performance specifications allow significant measurement error in reportable results. One commenter ( 420) noted that FTIR testing is only offered by a limited number of providers, requires special expertise and significant capital investment, and is still a relatively immature field of endeavor. One commenter ( 424) said that many stakeholders are not supportive of FTIR because of the attendant costs, sensitivity and interference problems, and need for considerable operator expertise.

Two commenters ( 443, 479) noted that the method is susceptible to interferences from water vapor, NO 2, and hydrocarbons. Likewise, one commenter ( 436) said the method is susceptible to interferences from water vapor and carbon dioxide, and the method cannot be the preferred measurement technique without a field demonstration of the feasibility of measuring formaldehyde at low ppb in LPC exhaust.

One commenter ( 479) said that an instrument with a pathlength of 200 meters ( m) would be needed ( possible but would have to be set up at an off site facility). Samples would have to be transported for sampling very quickly. Contamination of samples during transport is also a concern. One commenter ( 443) contended that there are not enough testing companies with instruments of sufficient path length to measure at that low levels. The commenter estimated that path lengths higher than 100 to 125 m will be needed. The commenter is aware of only two FTIRs equipped with a 100 125 m path length cell and neither have been tested and validated in the field for compliance testing purposes. The commenter said that EPA has not provided any 74 data to assess what effect the extended path length required for low level formaldehyde measurement will have on instrument precision, accuracy, signal strength, or potential interferences.

One commenter ( 443) stated that the method's minimum detection limit is too high to provide any confidence in measurements at the 43 ppb level. The FTIRs currently being used to some degree in the field with modified procedures have formaldehyde detection limits of approximately 50 60 ppb. One commenter ( 449) expressed support for the use of extractive FTIR but had reservations about EPA's statement that the method is capable of achieving below 43 ppb. The commenter believed that this level of detection is not achievable in practice and that EPA should consider that the test method must be achievable in practice by professionals with a level of expertise, and a required capital investment, commensurate with the current standards in the emission source test community.

Two commenters ( 485, 501) stated that FTIR can achieve the detection limits necessary to quantify sub ppm formaldehyde emissions, but at high costs and only with pre concentrating measures to remove water vapor and/ or CO 2, specialized equipment ( long path length) and extremely rigorous quantitative analysis. The FTIR test method must be revised to incorporate approved methods and procedures for selecting path length, pre concentrating emissions or otherwise reducing routinely achievable detection levels.

One commenter ( 437) expressed conditional support for the use of FTIR but said that additional field studies are needed to demonstrate minimum detection limits and practical quantitation limits. Field validation of the method performance for CT applications according to EPA Method 301 is recommended.

Response: The FTIR technology is rapidly improving and this trend will continue. As a result, EPA received a divergence of opinions reflecting this rapidly changing trend. Method 320 is a self validated performance based method that will allow the use of this improved technology and not suppress it. Current state of the art methodology can identify and measure formaldehyde concentrations well below the current emission limitation with a path length of 10 meters or less. Some of the older technology may require 100 or even 200 meter path length. The method has a pretest preparation and evaluation procedure to determine the optimum sampling system configuration for measuring formaldehyde customized to the technology the tester is using. Detection levels in FTIRs are limited either by noise or by interference from other gases. Measurement of formaldehyde has very little interference so one can get close to the noise limited detection with state of the art technology. EPA agrees with Commenter 443 that some of the performance criteria may be more lenient than needed by current state of the art technology, but it is sufficient. The cost to conduct a test is not the primary concern of EPA, however, as indicated by Commenter 429, the cost appears to be decreasing, as would be expected in the free market system. Water vapor ( and other) interferences are taken into consideration in the pretest planning. 75 VII. A. 2.2 Comment: One commenter ( 429) expressed the view that Method 320 is the most accurate, precise, and cost effective method for formaldehyde measurements. It does not have the physical or chemical limitations of the other formaldehyde methods. The commenter said that in 1998, FTIR detection limits of 10 ppbv were obtained with a 80 meter pathlength cell. With subsequent advances in instrumentation hardware and software, 8 ppbv with a 10 meter pathlength cell is now achievable and demonstrated in the field. Recent field data shows further improvement of the detection limit to 6 ppb. An eventual reduction of detection limit to near the 3 ppbv theoretical limit obtainable with current instrumentation at 10 meters pathlength is foreseen. It is possible to achieve this over a 1 hour measurement period.

According to the commenter, the current cost of Method 320 measurements is extremely competitive to that of other methods. Data were cited that shows that for two turbines, the cost for testing is virtually identical to that for other methods. At three turbines and more, the Method 320 per turbine cost drops below that of the other methods. The cost for one turbine test on site is $ 11,765.

The commenter also said that Method 320 requires a few changes to optimize its usage for turbine measurements. They are as follows: Method 320 should be a performance based method; " tweaking" Method 320 will not have any effect on detection limits; Method 320 should be classified as a " stand alone" method in a MACT rule instead of promulgating other inferior methods as alternates; Method 320 should not require revealing of spectral analysis details, reference spectra or sample spectra.

One commenter ( 437) recommended that in addition to the formaldehyde spike procedure and recovery criteria already contained in EPA Method 320, the absence of significant sampling system bias be demonstrated by injecting ultra high purity nitrogen calibration gas at a flow rate exceeding total sampling flow rate at two locations in the sampling system. One location is directly at the inlet of the FTIR sampling cell, and the other is at the back of the sampling probe as close to the probe as practical but upstream of any sample conditioning ( e. g., heated filters). The total absolute difference in measured formaldehyde concentrations at these two locations ( defined as sampling system bias) should be less than 10 percent of the formaldehyde concentration limit, otherwise corrective action to the sampling system must be implemented.

Response: The EPA appreciates the suggestions for improving Method 320 and will consider these as well as any others during periodic reviews. However, the improvement suggestions do not appear to be in the critical path of the standard setting process.

3. EPA SW 846 Method 0011 VII. A. 3.1 Comment: One commenter ( 437) did not support the use of EPA Method 0011 for turbines because: there is no need for isokinetic sampling in CT stacks; compared to CARB 430, the field procedure is more complex, the potential for chronic field contamination is much greater, the QA/ QC procedures are vastly inferior, and the data reporting procedures 76 especially with respect to blanks are more vague; and the method does not have sufficient sensitivity for demonstrating compliance with the proposed formaldehyde limit. One commenter ( 449) remarked that the method should be excluded from the list of acceptable test methods because it uses a similar analytical approach to CARB 430, has not been validated for application to CTs, and has QA requirements considered less than CARB 430. Commenter 443 also noted that this method is similar to CARB 430 and thus will present similar measurement issues.

Six commenters ( 435, 437, 460, 485, 501, 502) noted that the method states that detection limit may be as low as 90 ppb; therefore method does not have demonstrated capability for 43 ppb limit. One commenter ( 429) said that the method is inferior to EPA Method 320.

Two commenters ( 485, 501) recommended that the method should be validated for combustion sources and revised to provide for longer sampling runs necessary to achieve the detection levels needed to reliably and routinely measure ppb level formaldehyde. Longer sample runs are problematic. Standard procedures for handling blank corrections and non detects should be added to the promulgated test methods. More stringent QA/ QC measures are needed.

Response: The EPA agrees with the commenters that the method has many shortcomings and limited application opportunities for use in measuring formaldehyde emissions from combustion turbines. Accordingly, EPA is not including EPA Method 0011 in the final rule. Both EPA Method 0011 and CARB 430 can be requested on a case by case basis as part of EPA's alternative method review process.

4. EPA Method 323 VII. A. 4.1 Comment: Nine commenters ( 435, 437, 442, 443, 449, 460, 485, 501, 502) said that EPA Method 323 should not be used for measuring very low concentrations of formaldehyde. The minimum detection levels of the method are not suitable for the emission standard. One commenter ( 443) noted that the method could not be modified to measure such low concentrations without significantly affecting its accuracy and precision and calling into question the entire validity of the method. Two commenters ( 435, 502) also noted that the method has not been validated or demonstrated for use on CTs with low ppb range formaldehyde emissions. One commenter ( 420) also noted that the method is difficult and costly.

One commenter ( 429) stated that Method 323 is inferior to Method 320. In the commenter's opinion, total water soluble aldehyde methods such as Method 323 are not useful, especially when attempting to calculate total aldehyde emissions. Formaldehyde cannot be differentiated from acetaldehyde, etc. which prevents accurate calculation of total mass of HAPs emitted from the source measured. The commenter has also observed formaldehyde positive biases as high as 300 percent with Method 323 in natural gas fired combustion sources as compared to Method 320. The high level of variations and biases observed may lead to future compliance problems or public lawsuits over falsely detected species or negative catalyst performance. 77 Response: The EPA agrees with the commenters that EPA Method 323 should not be used for measuring low concentrations of formaldehyde from combustion turbines and has therefore not included it in the final rule.

VII. A. 4.2 Comment: One commenter ( 440) requested that EPA include an option to add a cooling coil to the formaldehyde test apparatus. The concern is that CT exhaust will melt the Teflon tubing on the proposed apparatus.

Response: The EPA agrees with the commenter that melting Teflon is a concern.

VII. A. 4.3 Comment: One commenter ( 515) recommended that the proposed Method 323 be clarified to indicate the sampling time required per run.

Response: The EPA agrees that minimum sampling time should have been specified. However, in the final rule EPA is not allowing Method 323 for demonstrating compliance.

5. Other VII. A. 5.1 Comment: Four commenters ( 420, 437, 442, 449) requested that the final rule allow ASTM Method D6348 as equivalent to Method 320.

Response: The ASTM made a few changes to ASTM D6348 98. These were successfully balloted. The EPA accepts the new version as an alternative to Method 320, 40 CFR part 63, appendix A for formaldehyde measurement provided in ASTM D6348 03, Annex A5 ( Analyte Spiking Technique), the percent R must be greater than or equal to 70 and less than or equal to 130.

VII. A. 5.2 Comment: One commenter ( 449) said that EPA Method 316 may be a viable formaldehyde test method for CTs. The final rule should include provisions to use other approved methods, and to incorporate new methods for formaldehyde measurement as they are developed.

Response: The EPA agrees that EPA Method 316 may be an acceptable alternative in limited cases, provided it is modified to prevent a potential negative SO 2 interference as described in the literature. However, additional study and validation would be needed. If there is interest, EPA would be willing to work with interested users to develop an acceptable validation plan.

VII. A. 5.3 Comment: One commenter ( 385) informed EPA that three ASTM standards have been updated: E 337 84 ( 1996) is now E 337 02; D 3154 91 is now D 3154 00; and D 5835 95 is now D 5835 95 ( 2001).

Response: The EPA appreciates the comment; however, these particular ASTM standards are not referenced in the preamble to the final rule, therefore, it was not necessary to update the 78 standards..

VII. A. 5.4 Comment: Nine commenters ( 418, 421, 435, 443, 444, 449, 481, 502, 519) remarked that there is a lack of repeatable and reliable formaldehyde test methodology that is capable of detection at low levels. Commenter 443 observed that assuming a realistic detection limit of 50 ppb for several of the methods, EPA would need to set the standard at 250 ppb or higher ( 5 x DL) to ensure that measurement issues would not lead to a significant number of failures. Commenter 443 also suggested that EPA should give additional consideration to its determination of the MDLs for the proposed methods when it establishes the final formaldehyde emission limit. Furthermore, given the uncertainty in the methods, EPA must provide sources the opportunity to perform additional tests before a required " performance test" would be deemed failed. Also, EPA must ensure in the final rule that no source could be required to use one of the methods to conduct performance testing.

Commenter 421 questioned the validity of EPA Method 0011, CARB 430, and EPA Method 320 or FTIR for measuring extremely low levels of formaldehyde emissions. Commenter 444 said that EPA should reevaluate the data on which the proposed standard is based and whether or not a formaldehyde level that may be set in the final rule can be reliably measured.

Response: The EPA agrees with the commenters that EPA Method 0011 and CARB 430 may not be valid for measuring extremely low levels of formaldehyde emissions. Therefore some of the comments are moot. The EPA does not agree that EPA Method 320 should not be used. Several EPA Method 320/ FTIR experts were consulted and they indicated that detection limits as low as 10 ppb were possible. The EPA agrees that the data on which the proposed standard should be reevaluated. An extensive review of the data was conducted. This review is discussed in great detail in the response to comment V. A. 1.

VII. A. 5.5 Comment: Two commenters ( 435, 460) said that there are several ambient methods available for measurement of formaldehyde, but the matrix of turbine combustion gases makes these methods unsuitable for consideration as valid procedures to document compliance with CT emissions limits.

Response: The EPA acknowledges the comment.

VII. A. 5.6 Comment: One commenter ( 424) recommended that a joint industrygovernment task force for the measurement of aldehydes from gas turbine exhaust be formed.

Response: The EPA would be willing to participate in the task force.

VII. A. 5.7 Comment: One commenter ( 424) contended that CEMS requirements cannot be supported by the current formaldehyde monitoring technology. Formaldehyde testing should be performed on a periodic ( annual) basis or replaced by surrogate CO measurement practices. 79 Response: The rule does not have a CEMS requirement for monitoring formaldehyde.

VII. A. 5.8 Comment: One commenter ( 463) submitted a test report that compared FTIR and CARB 430. The testing was conducted on a Siemens Westinghouse 501F gas fired CT with LPC, SCR, and CO catalyst. Formaldehyde was measured using CARB 430 and FTIR. The CARB 430 results did not compare well with the FTIR results. The formaldehyde emissions using CARB 430 averaged 9 ppb in the turbine exhaust and 5 ppb at the stack. The FTIR results were 47 ppb at the turbine exhaust and 42 ppb at the stack.

Response: The EPA thanks the commenter for submitting the information. The EPA agrees that CARB 430 understates the formaldehyde concentration in the exhaust gas from stationary CTs.

B. CO 1. CEMS VII. B. 1.1 Comment: Twenty three commenters ( 421, 422, 424, 426, 427, 430, 435, 436, 437, 442, 443, 444, 447/ 448, 449, 460, 479, 482, 485, 486, 501, 502, 508, 509) said that CO CEMS cannot reliably measure trace level CO concentrations and 95 percent CO reduction. Commenter 449 remarked that EPA provides no information to show that CEMS are available to accurately measure low CO concentrations, and the use of CO CEMS for low CO levels is well beyond the scope of current 40 CFR 60 CEMS standards. Revisions will be needed to the standards. Also, vendor claims for CO CEMS and CO instrumental analyzers, unless accompanied by emissions test data obtained under known and controlled conditions applicable to the subject source type, should not be considered adequate proof of availability and performance.

Two commenters ( 485, 501) observed that in cases where CO is very low, specifications for calibration drift and relative accuracy set out in PS 4A may be unattainable; for a trace level CO analyzer, alternatives to PS 4A may be necessary. One commenter ( 505) recommended that PS 4 and 4A should be revised to reflect the measurement of CO in the range of 0 10 ppm and 0 1 ppm and also should be harmonized with 40 CFR Part 75 CEMS requirements. Methods for determining the relative accuracy of the CEMS should be developed with the low CO ppm measurement in mind.

Response: The EPA agrees that existing CO CEMS technology and EPA performance criteria are not adequate to reliably and accurately measure trace levels of CO. The ASTM is currently trying to address this issue and EPA is participating.

VII. B. 1.2 Comment: One commenter ( 486) suggested that EPA allow data validation to be performed in accordance with 40 CFR § 75.10( d) provisions as an alternative to the two quadrant methodology specified in § 63.6125( a)( 3). The commenter noted that Subparts Da and Db of 40 CFR part 60 allow use of 40 CFR part 75 data validation procedures as an alternative to 80 application of part 60 procedures.

Response: The use of current 40 CFR Part 75 data validation would not be suitable for this Part 63 application. However, CO CEMS are not being required so the suggestion is moot.

VII. B. 1.3 Comment: One commenter ( 419) requested that the 40 CFR part 60 Appendix B, Specification 2 requirements regarding measurement range should be waived, and perhaps even the RATA requirements.

Response: Carbon monoxide CEMS are not being required so the suggestion is moot.

VII. B. 1.4 Comment: One commenter ( 484) recommended that EPA revise the CO CEMS requirement to extend the averaging time and utilize O 2 or CO 2 measurements at only the outlet of the oxidation catalyst.

Response: Based on this comment and other similar comments received during the public comment period, EPA has decided that the CO CEMS systems are not accurate enough to measure the outlet CO concentrations of lean premix combustor turbines with oxidation catalyst systems, which are expected to comprise most of the affected sources. Therefore EPA has decided to not use CO CEMS units for monitoring or compliance and a reply to the comments are moot. However, EPA believes that the 4 hour rolling average is appropriate for combustion turbines burning natural gas and number 2 distillate oil since the fuel composition does not vary significantly. Regarding the comment on measurement of O 2/ CO 2 only at the outlet rather than at the inlet and outlet presumably for indexing purposes, that comment is also moot now but since the O 2/ CO 2 concentration will change only slightly going across the catalyst, one measurement at the outlet could have been used to index both the inlet and outlet concentrations.

VII. B. 1.5 Comment: One commenter ( 443) remarked that the absence of any specific proposals for revision of PS 4A, Method 10, and Procedure 1 of Appendix F, or any data upon which to develop suggestions for revision, make it impossible to comment on necessary revisions. EPA must promulgate some alternative that does not require use of CO CEMS.

Response: Based on this comment and other similar comments received during the public comment period, EPA has decided that the CO CEMS systems are not accurate enough to measure the outlet CO concentrations of lean premix combustor turbines with oxidation catalyst systems, which are expected to comprise most of the affected sources. Therefore EPA has decided to not use CO CEMS units for monitoring or compliance. Consequently, the comment regarding the use of PS 4A, Method 10, and Procedure 1 of Appendix 1 as they were to be used to support the CO CEMS are moot. However, EPA still plans to revise PS 4, Method 10, and Procedure I of Appendix A to improve their accuracy.

VII. B. 1.6 Comment: One commenter ( 485) requested that EPA eliminate the annual RATA requirement for CO CEMS for the Alaska North Slope. 81 Response: Stationary turbines located north of the Arctic Circle ( and therefore the Alaska North Slope) are not being required to install and operate CO CEMS in the final rule, so the suggestion is moot.

VII. B. 1.7 Comment: One commenter ( 419) suggested that the CO range should be set to accurately indicate CO breakthrough rather than continuous measurement.

Response: The EPA understands the commenters position, i. e., to intermittently measure CO levels and take action only when the CO levels are high, indicating CO catalyst breakthrough, indicating that the catalyst system should be replaced. The EPA's preferred position is to use continuous pollutant emissions monitoring whenever the continuous monitoring system is proven to accurately measure the pollutant concentrations and the costs are reasonable. A continuous monitoring system more clearly indicates continuing compliance with the emission limitation, will instantaneously indicate if a process malfunction or control device malfunction is occurring, will result in a quicker response to malfunctions thereby reducing emissions during malfunction, and will clearly indicate when a pollutant breakthrough is occurring. Based on information received during public comments, EPA has decided not to use the CO CEMS and CO stack testing methods since the levels of CO expected to be emitted by CTs would be too low to be accurately measured. Therefore the final rule does not have a CO emission limitation and this comment is now moot.

VII. B. 1.8 Comment: One commenter ( 430) recommended that for units complying with the MACT standard using an oxidation catalyst, the initial performance evaluation for removal efficiency of CO should take into account the operating conditions used by the catalyst vendor to determine design removal efficiency.

Response: The commenter did not indicate how the operating conditions used by the catalyst vendor to determine design removal efficiency was to be obtained and used. Also the commenter did not indicate the relevance of this information to the compliance determination of the oxidation catalyst system. The EPA called the commenter to clarify the commenter's intent. The commenter intended that the EPA required removal efficiency should be consistent with the vendor's design and take into account operating load. An oxidation catalyst system is normally designed by the vendor based on information provided by the owner/ operator, including load and other operating parameters and the removal efficiency. Therefore the owner/ operator should already have knowledge of the load, design removal efficiency, and other parameters. Some commenters indicated that EPA should explicitly state in the regulation that testing at any load is allowed to avoid any confusion. The emission limitations established in the final rule were based on test results measured when the turbines were being operated at high loads ( between 90 and 110 percent). Therefore EPA has indicated in the final rule that performance testing should be conducted at high load; alternatively, sources may choose to conduct testing at lower loads but failure to demonstrate compliance at less than high load is considered a deviation from the emission limitation. 82 VII. B. 1.9. Comment: One commenter ( 419) noted that operating an upstream and downstream CEMS is complicated, even if you timeshare. The commenter questioned whether a dual range analyzer would be needed.

Response: Carbon monoxide CEMS are not being required so the suggestion is moot.

VII. B. 1.10 Comment: One commenter ( 443) stated that measurement of CO directly at the outlet of any CT ( whether simple or combined cycle) would be difficult because of the unrepresentative nature of the CT outlet sampling location. One commenter ( 430) said that for the inlet of an oxidation catalyst, sampling is physically and technologically difficult.

Two commenters ( 465, 470) expressed the view that existing monitoring methodology and technology should be able to accurately measure the CO emissions after control technology.

Response: The EPA agrees with the commenters. However, CO CEMS are not being required so the comments are moot.

2. EPA Method 10 VII. B. 2.1 Comment: Two commenters ( 485, 501) observed that in cases where the uncontrolled exhaust CO is already very low, it will be difficult to show compliance with the 95 percent reduction standard based on Method 10 measurements Response: The EPA agrees with the commenters. However, CO CEMS are not being required so the comments are moot.

VIII. COST/ IMPACTS VII. 1 Comment: Four commenters ( 421, 479, 481, 482) said that EPA has substantially underestimated the cost of the proposed standard. Commenter 482 observed that several of the estimates used to calculate the impacts are not accurate. The following estimates are too low: only 20 percent of turbines will be located at major sources; only 5 percent of new turbines will have to install oxidation catalyst control; and only 10 existing lean premix turbines will have to install oxidation catalysts. Also, the assumption that turbines operate 8760 hours per year, used to calculate the emission reduction, is unrealistic. More realistic figures are 20 percent for simple cycle and 60 percent for combined cycle. Commenter 481 said that a more realistic figure for simple cycle is 30 percent. Commenter 479 said that actual 2002 capacity factors for their LPC turbines averaged about 4 percent. The capacity factors for their DFC turbines were even much lower. Approximately 80 percent of all gas fired CTs currently in operation in the U. S. are operated at annual capacity factors of 10 percent or less. Approximately 65 percent of the CTs are operated at capacity factors of less than 6 percent per year. 83 Response: The EPA acknowledges that the costs of the proposed CT MACT standard could be higher than estimated. For example, the commenter took issue with the percentage of new LPC turbines that may have to put on controls to achieve the emission limitation. The information that was available to us at proposal was that only a small fraction of turbines (~ 5 percent) would find it necessary to install add on controls. In actual practice possibly more owners/ operators would choose to put on controls to assure that the emission limit would be met with a higher margin of safety. Since proposal, new information was obtained which indicates that some LPC turbines have oxidation catalyst systems installed, which establishes the MACT floor for new LPC turbines in the final rule to be the level of performance for a LPC turbine with an oxidation catalyst control system installed. Therefore for purposes of costing, all new turbines, both DFC turbines and LPC turbines, are assumed to have to install oxidation catalyst controls. Therefore the costs of complying with the final standards are not underestimated.

The EPA also agrees that 8,760 hours per year of operation is unrealistic to estimate HAP emissions and agrees with the commenters that stated that 20 percent average capacity factor for simple cycle turbines and 60 percent average capacity factor for combined cycle turbines are more realistic for estimating HAP emissions. The emission reductions are now based on those assumptions. Capacity factors of less than 4 percent to 6 percent were not felt to be representative of all combustion turbines.

The EPA believes that the estimate that only 20 percent of turbines will be located at major sources is the most accurate estimate that could be made based on the information the EPA has.

VII. 2 Comment: Two commenters ( 424, 427) stated that EPA has significantly underestimated the impact on existing LPC turbines. Most existing LPC turbines will require a CO catalyst and CO CEMS because the proposed formaldehyde level is not representative. Commenter 427 estimated that over 120 of their existing fleet of LPC CTs will be affected. Both commenters recommended that existing LPC CTs receive the same treatment as existing DFC, e. g. no control.

Response: As a result of comments, the MACT Floor for existing gas fired and oil fired LPC units was reevaluated and found to be no emission reduction. The final rule therefore does not require existing LPC units to meet an emission limitation, and these units will not be impacted by the rule. Thus, the concerns expressed by the commenters are moot.

VII. 3 Comment: Two commenters ( 424, 427) expressed the view that most new LPC turbines will require a CO catalyst and CO CEMS ( because the proposed formaldehyde level is not representative). The proposed rule will result in very minor reduction of HAP with significant expense.

Response: As discussed in the response to comment IV. B. 1, EPA requested and received new emissions data for LPC units which led to further subcategorization by fuel and a revised 84 formaldehyde emission limitation for gas fired and oil fired LPC turbines. The rule no longer requires units equipped with a CO catalyst to install a CO CEMS. Thus, this concern is moot. The EPA does not agree with the comment that the proposed formaldehyde level is not representative. It is believed that the data set is adequately representative and that the formaldehyde limit has been set correctly according to the requirements in the CAA.

VII. 4 Comment: One commenter ( 446) questioned whether EPA has factored the disposal or regeneration of the spent catalyst into their Environmental, Energy, and Economic Impacts evaluation.

Response: The disposal or regeneration of the spent catalyst has not been factored into the Impacts evaluation. According to catalyst vendors, the catalyst can be washed and restored for ten years or more of continuous operation. Spent catalysts can be returned to the vendor for recycling or disposal. The owner/ operator can receive credits toward a new catalyst for the return of the old one, in the form of cash, metal, or metal account.

IX. RISK Note: All of the comments pertaining to risk are summarized below. There is a single response given at the end of this section for all of the risk comments.