F. Total Chlorine Emissions Data Below 20 ppmv We corrected all the total chlorine measurements in the data base that were below 20 ppmv to account for potential systemic negative biases in the Method 0050 data in response to comments on the proposed rule. See the discussion in Part Four, Section I. C. 1 below. To account for the bias, we corrected all total chlorine emissions data that were below 20 ppmv to 20 ppmv. We accounted for within test condition emissions variability for the corrected data by imputing a standard deviation that is based on a regression analysis of runto run standard deviation versus emission concentration for all data above 20 ppmv. This approach of using a regression analysis to impute a standard deviation is similar to the approach we used to account for total variability ( i. e., test to test and within test variability) of PM emissions for sources that use fabric filters. II. Emission Limits A. Incinerators The changes in the incinerator standards for existing sources since proposal are:

Standard Proposed Limit Final Limit Dioxin/ Furans ( ng TEQ/ dscm) Sources with dry air pollution control systems or waste heat boilers: 0.28; For others: 0.2 or 0.4 and temperature control at inlet of air pollution control device < 400 ° F For all sources, 0.20 or 0.40 and temperature control < 400 ° F at the air pollution control device inlet Particulate Matter ( gr/ dscf) 0.015 0.013 Semivolatile Metals ( ug/ dscm) 59 230 Low Volatile Metals ( ug/ dscm) 84 92 Total Chlorine ( ppmv) 1.5 32 Alternative to the particulate matter standard: Combined emissions of lead, cadmium and selenium ( ug/ dscm) 59 230 Alternative to the particulate matter standard: Combined emissions of arsenic, berrylium, chrome, antimony, cobalt, manganese, and nickel ( ug/ dscm) 84 92 The changes in the incinerator standards for new sources since proposal are:

Standard Proposed Limit Final Limit Particulate Matter ( gr/ dscf) 0.0007 0.0015 Mercury ( ug/ dscm) 8.0 8.1 Semivolatile Metals ( ug/ dscm) 6.5 10 Low Volatile Metals ( ug/ dscm) 8.9 23 Total Chlorine ( ppmv) 0.18 21 Alternative to the particulate matter standard: Combined emissions of lead, cadmium and selenium ( ug/ dscm) 6.5 10 Alternative to the particulate matter standard: Combined emissions of arsenic, berrylium, chrome, antimony, cobalt, manganese, and nickel ( ug/ dscm) 8.9 23 B. Hazardous Waste Burning Cement Kilns The changes in the standards for existing cement kilns since proposal are:

Standard Proposed Limit Final Limit Mercury ( ug/ dscm) 64 1 Both 3.0 ppmw2 and either 120 ug/ dscm ( stack emissions) or 120 ug/ dscm ( expressed as a hazardous waste MTEC) 3 Particulate matter 0.028 gr/ dscf 0.028 gr/ dscf and 20% opacity4 Semivolatile metals 4.0E 04 lb/ MMBtu5 7.6E 04 lb/ MMBtu5 and 330 ug/ dscm Low volatile metals 1.4E 05 lb/ MMBtu5 2.1E 05 lb/ MMBtu5 and 56 ug/ dscm Total chlorine ( ppmv) 6 110 120 1 The proposed mercury standard was an annual limit. 2 Feed concentration of mercury in hazardous waste as fired. 3 HW MTEC means maximum theoretical emissions concentration of the hazardous waste and MTEC is defined at § 63.1201( a). 4 The opacity standard does not apply to a source equipped with a bag leak detection system under § 63.1206( c)( 8) or a particulate matter detection system under § 63.1206( c)( 9). 5 Standard is expressed as mass of pollutant stack emissions attributable to the hazardous waste per million British thermal unit heat input of the hazardous waste. 6 Combined standard, reported as a chloride ( Cl()) equivalent.

The changes in the standards for new cement kilns since proposal are:

Standard Proposed Limit Final Limit Mercury ( ug/ dscm) 35 1 Both 1.9 ppmw2 and either 120 ug/ dscm ( stack emissions) or 120 ug/ dscm ( expressed as a hazardous waste MTEC) 3 Particulate matter 0.0058 gr/ dscf 0.0023 gr/ dscf and 20% opacity4 Semivolatile metals 6.2E 05 lb/ MMBtu5 6.2E 05 lb/ MMBtu5 and 180 ug/ dscm Low volatile metals 1.4E 05 lb/ MMBtu5 1.5E 05 lb/ MMBtu5 and 54 ug/ dscm Total chlorine ( ppmv) 6 78 86 1 The proposed mercury standard was an annual limit. 2 Feed concentration of mercury in hazardous waste as fired. 3 HW MTEC means maximum theoretical emissions concentration of the hazardous waste and MTEC is defined at § 63.1201( a). 4 The opacity standard does not apply to a source equipped with a bag leak detection system under § 63.1206( c)( 8) or a particulate matter detection system under § 63.1206( c)( 9). 5 Standard is expressed as mass of pollutant stack emissions attributable to the hazardous waste per million British thermal unit heat input of the hazardous waste. 6 Combined standard, reported as a chloride ( Cl()) equivalent.

C. Hazardous Waste Burning Lightweight Aggregate Kilns The changes in the standards for existing lightweight aggregate kilns since proposal are:

Standard Proposed Limit Final Limit Dioxins and furans ( ng TEQ/ dscm) 0.40 0.20 or rapid quench of the flue gas at the exit of the kiln to less than 400 ° F Mercury ( ug/ dscm) 67 1 120 ug/ dscm ( stack emissions) or 120 ug/ dscm ( expressed as a hazardous waste MTEC) 2 Semivolatile metals 3.1E 04 lb/ MMBtu3 and 250 ug/ dscm 3.0E 04 lb/ MMBtu3 and 250 ug/ dscm 1 The proposed mercury standard was an annual limit. 2 HW MTEC means maximum theoretical emissions concentration of the hazardous waste and MTEC is defined at § 63.1201( a). 3 Standard is expressed as mass of pollutant stack emissions attributable to the hazardous waste per million British thermal unit heat input of the hazardous waste.

The changes in the standards for new lightweight aggregate kilns since proposal are:

Standard Proposed Limit Final Limit Dioxins and furans ( ng TEQ/ dscm) 0.40 0.20 or rapid quench of the flue gas at the exit of the kiln to less than 400 ° F Particulate matter 0.0099 gr/ dscf 0.0098 gr/ dscf Mercury ( ug/ dscm) 67 1 120 ug/ dscm ( stack emissions) or 120 ug/ dscm ( expressed as a hazardous waste MTEC) 2 Semivolatile metals 2.4E 05 lb/ MMBtu3 and 43 ug/ dscm 3.7E 05 lb/ MMBtu3 and 43 ug/ dscm 1 The proposed mercury standard was an annual limit. 2 HW MTEC means maximum theoretical emissions concentration of the hazardous waste and MTEC is defined at § 63.1201( a). 3 Standard is expressed as mass of pollutant stack emissions attributable to the hazardous waste per million British thermal unit heat input of the hazardous waste. D. Solid Fuel Boilers The changes in the solid fuel boiler standards for existing sources since proposal are:

Standard Proposed Limit Final Limit Mercury ( ug/ dscm) 10 11 Semivolatile Metals ( ug/ dscm) 170 180 Low Volatile metals ( ug/ dscm) 210 380 Alternative to the particulate matter standard: Combined emissions of lead, cadmium and selenium ( ug/ dscm) 170 180 Alternative to the particulate matter standard: Combined emissions of arsenic, beryllium, chromium, antimony, cobalt, manganese, and nickel ( ug/ dscm) 210 380 The changes in the solid fuel boiler standards for new sources since proposal are:

Standard Proposed Limit Final Limit Mercury ( ug/ dscm) 10 11 Semivolatile Metals ( ug/ dscm) 170 180 Low Volatile metals ( ug/ dscm) 210 380 Alternative to the particulate matter standard: Combined emissions of lead, cadmium and selenium ( ug/ dscm) 170 180 E. Liquid Fuel Boilers We redefined the liquid fuel boiler subcategory into two separate boiler subcategories based on the heating value of the hazardous waste they burn: those that burn waste below 10,000 Btu/ lb, those that burn hazardous waste with a heating value of 10,000 Btu/ lb or greater. See Part Four, Section VI. D. 2 of today's preamble for a complete discussion. The additional changes to the liquid fuel boiler standards for existing sources since proposal are: Final Limit Standard Proposed Limit HW Fuel < 10,000 Btu/ lb HW Fuel > 10,000 Btu/ lb Mercury ( lb/ MM Btu) 3.7E 6 19 ug/ dscm 4.2E 5 Particulate matter ( gr/ dscf) 0.032 0.035 Semivolatile metals ( lb/ MM Btu) 1.1E 5 150 ug/ dscm 8.2E 5 Chromium ( lb/ MM Btu) 1.1E 4 370 ug/ dscm 1.3E 4 Total chlorine ( Lb/ MM Btu) 2.5E 2 31 ppmv 5.1E 2 Alternative to the particulate matter standard: Combined emissions of lead, cadmium and selenium ( lb/ MM Btu) 1.1E 5 150 ug/ dscm 8.2E 5 Alternative to the particulate matter standard: Combined emissions of arsenic, beryllium, chromium, antimony, cobalt, manganese, and nickel ( lb/ MM Btu) 1.1E 4 370 ug/ dscm 1.3E 4 The changes in the liquid fuel boiler standards for new sources since proposal are:

Final Limit Standard Proposed Limit HW Fuel < 10,000 Btu/ lb HW Fuel > 10,000 Btu/ lb Dioxin and Furan, dry APCD ( ng TEQ/ dscm) 0.015 or temp control < 400F for dry APCD 0.40 Mercury ( lb/ MM Btu) 3.8E 7 6.8 ug/ dscm 1.2E 6 Particulate matter ( gr/ dscf) 0.0076 0.0087 Semivolatile metals ( lb/ MM Btu) 4.3E 6 78 ug/ dscm 6.2E 6 Chromium ( lb/ MM Btu) 3.6E 5 12 ug/ dscm 1.4E 5 Total chlorine ( lb/ MM Btu) 7.2E 4 31 ug/ dscm 5.1E 2 Alternative to the particulate matter standard: Combined emissions of lead, cadmium and selenium ( lb/ MM Btu) 4.3E 6 78 ug/ dscm1 6.2E 61 Alternative to the particulate matter standard: Combined emissions of arsenic, beryllium, chromium, antimony, cobalt, manganese, and nickel ( lb/ MM Btu) 3.6E 5 12 ug/ dscm2 1.4E 52 1 New or reconstructed liquid fuel boilers that process residual oil or liquid feedstreams that are neither fossil fuel nor hazardous waste and that operate pursuant to the alternative to the particulate matter standard must comply with the alternative emission concentration standard of 4.7 ug/ dscm, which is applicable to lead, cadmium and selenium emissions attributable to all feedstreams ( hazardous and nonhazardous). 2 New or reconstructed liquid fuel boilers that process residual oil or liquid feedstreams that are neither fossil fuel nor hazardous waste that operate pursuant to the alternative to the particulate matter standard must comply with the alternative emission concentration standard of 12 ug/ dscm, which is applicable to arsenic, beryllium, chrome, antimony, cobalt, manganese, and nickel emissions attributable to all feedstreams ( hazardous and nonhazardous).

F. Hydrochloric Acid Production Furnaces The changes in the hydrochloric acid production furnace standards for existing sources since proposal are:

Standard Proposed Limit Final Limit Dioxin and Furans 0.4 ng TEQ/ dscm Carbon Monoxide/ Total Hydrocarbons and DRE standards as surrogates Total chlorine 14 ppmv or 99.9927% system removal efficiency 150 ppmv or 99.923% system removal efficiency The changes in the hydrochloric acid production furnace standards for new sources since proposal are:

Standard Proposed Limit Final Limit Dioxin and Furans 0.4 ng TEQ/ dscm Carbon Monoxide/ Total Hydrocarbons and DRE standards as surrogates Total chlorine 1.2 ppmv or 99.9994% system removal efficiency 25 ppmv or 99.987% system removal efficiency G. Dioxin/ Furan Testing for Sources Not Subject to a Numerical Standard Today's final rule requires that all sources not subject to a numerical dioxin and furan standard perform a one time test to determine their dioxin and furan emissions. See the discussion in Part Four, Section VII. L. In the proposed rule, this requirement was limited to solid fuel boilers and those liquid fuel boilers with a wet or no air pollution control system. The final rule expands this requirement to include hydrochloric acid production furnaces and those lightweight aggregate kilns that elect to comply with the temperature limit at the kiln exit in lieu of the 0.20 ng TEQ/ dscm dioxin/ furan standard. Those sources are not subject to a numerical dioxin/ furan standard under the final rule for reasons explained in Volume III of the Technical Support Document, Sections 12 and 15. We note that sources not subject to a numerical dioxin/ furan emission standard are subject to the carbon monoxide or hydrocarbon standards and the DRE standard as surrogates.. We are making no changes to the implementation of this requirement. See the proposed rule at 69 FR at 21307 for more information. III. Statistics and Variability A. Using Statistical Imputation to Address Variability of Nondetect Values In the final rule, we use a statistical approach to impute the value of nondetect emissions and feedrate measurements to avoid dampening of the variability of data sets when nondetect measurements are assumed to be present at the detection limit. At proposal, we assumed that nondetects ( i. e., HAP levels in stack emissions below the level of detection of the applicable analytic method) are invariably present at the detection limit. Commenters on the proposed rule stated, however, that assuming nondetects are present at the detection limit dampens emissions variability   a consideration necessary to reasonably ascertain sources' performance over time. This could have significant practical consequence for those data sets ( such as the data base for liquid fuel boilers) dominated by nondetected values. We agree with these commenters, and instead of making the arbitrary assumption that all nondetected values are identical ( which in fact is highly unlikely), we are using a statistical methodology to impute the value of nondetect measurements. The imputation approach assigns a value for each nondetect measurement in a data set within the possible range of values that results in maximizing the 99th percentile upper prediction limit for the data set. For example, the possible range of values for a measurement that is 100% nondetect is between zero and the detection limit. On February 4, 2005 we distributed a direct request for comments on the imputation approach to major stakeholders. We respond to the comments we received in Part Four, Section IV. D of today's notice.

B. Degrees of Freedom when Imputing a Standard Deviation Using the Universal Variability Factor for Particulate Matter Controlled by a Fabric Filter The use of the universal variability factor to impute a standard deviation for particulate emissions from sources controlled with a fabric filter takes advantage of the empirical observation that the standard deviation of particulate emissions from sources is positively correlated to the average particulate emissions of sources. Based on this observation, we use regression analysis to determine the best fitting curve to explain the relationship of average value to standard deviation. In the final rule, we use the actual sample size, rather than an assumed sample size of nine used at proposal, to determine the degrees of freedom for the t statistic to calculate the floor using the standard deviation imputed from the universal variability factor for particulate matter controlled by a fabric filter. At proposal, we used eight degrees of freedom to identify the t statistic to account for within test condition variability ( i. e., run to run variability) for standard deviations imputed from the universal variability factor regression. 28 This is because, on average, about three test conditions with nine individual test runs are associated with each source used to develop the regression curve. A commenter states, however, that this approach can dramatically understate variability when imputing a standard deviation for a source with only three runs because the t statistic is substantially higher for 2 degrees of freedom than 8 degrees of freedom.

28 USEPA, " Draft Technical Support Document for HWC MACT Standards, Volume III: Selection of MACT Standards," March 2004, p. 5 4. We agree with the commenter. Moreover, using the actual number of runs to identify the t statistic rather than assuming nine runs is appropriate given that the true test condition average is less certain for sources with only three runs, and thus there is less certainty in the imputed standard deviation. The higher t statistic associated with a three run data set reflects this uncertainty. In addition, we include emissions data classified as " normal" in the regression analysis for the final rule. At proposal, we used only data classified as CT ( i. e., highest compliance test condition in a test campaign) or IB ( i. e., a compliance test condition that achieved lower emissions than another compliance test condition in the test campaign). We conclude that normal data ( i. e., emissions data that were not used to establish operating limits and thus do not reflect variability in controllable operating parameters) should also be considered in the regression analysis because particulate matter emissions are relatively insensitive to baghouse inlet loading and operating conditions. 29 Including normal emissions in the analysis provides additional data to better quantify these devices' performance variability.

IV. Compliance Assurance for Fabric Filters, Electrostatic Precipitators, and Ionizing Wet Scrubbers The final rule provides additional requirements to clarify how you determine the duration of periods of operation when the alarm set point has been exceeded for a bag leak detection system or a particulate matter detection system: 1. You must keep records of the date, time, and duration of each alarm, the time corrective action was initiated and completed, and a brief description of the cause of the alarm and the corrective action taken. 2. You must record the percent of the operating time during each 6 month period that the alarm sounds. 3. In calculating the operating time percentage, if inspection of the fabric filter, electrostatic precipitator, or ionizing wet scrubber demonstrates that no corrective action is required, no alarm time is counted. 4. If corrective action is required, each alarm shall be counted as a minimum of 1 hour. The final rule also establishes revised procedures for establishing the alarm set point if you elect to use a particulate matter detector system in lieu of site specific operating parameter limits for compliance assurance for sources equipped with electrostatic precipitators and ionizing wet scrubbers. The rule explicitly allows you to maximize controllable operating parameters during the comprehensive performance test to account for variability by, for example, detuning the APCD or spiking ash. To establish the alarm setpoint you may either establish the set point as the average of the test condition run average detector responses during the comprehensive performance test or extrapolate the detector response after approximating the correlation between the detector response and particulate matter emission concentrations. You may extrapolate the detector response up to a response value that corresponds to 50% of the particulate matter emission standard or 125% of the highest particulate matter concentration used to develop the correlation, whichever is greater. To establish an approximate correlation of the detector response to particulate matter emission concentrations you should use as guidance Performance Specification 11 for PM 29 USEPA, " Technical Support Document for HWC MACT Standards, Volume III: Selection of MACT Standards," September 2005, Section 5.3. See also Part Four, Section III. C of this preamble. CEMS ( 40 CFR Part 60, Appendix B), except that you need conduct only 5 runs to establish the initial correlation rather than a minimum of 15 runs required by PS 11. The final rule also notes that an exceedance of a detector response that corresponds to the particulate matter emission standard is not evidence that the standard has been exceeded because the correlation is an approximate correlation used for the purpose of compliance assurance to determine when corrective measures must be taken. The correlation, however, does not meet the requirements of PS 11 for compliance monitoring. In addition, if you elect to use a particulate matter detection system in lieu of sitespecific control device operating parameter limits on the electronic control device, the ash feedrate limit for incinerators and boilers under § 63.1209( m)( 3) is waived. The ash feedrate limit is waived because the particulate matter detection system continuously monitors relative particulate matter emissions and the alarm set point provides reasonable assurance that emissions will not exceed the standard. 30 Finally, you must submit an excessive exceedance notification within 30 days of the date that the alarm set point is exceeded more than 5 percent of the time during any 6 month block period of time, or within 30 days after the end of the 6 month block period, whichever is earlier. The proposed rule would have required you to submit that notification within 5 days of the end of the 6 month block period.

V. Health Based Compliance Alternative for Total Chlorine The final rule includes the following major changes to the proposed health based compliance alternative for total chlorine: ( 1) You must use 1 hour Reference Exposure Levels ( aRELs) rather than 1 hour acute exposure guideline levels ( AEGL 1) as the acute health risk threshold metric when calculating 1 hour HCl equivalent emission rates; ( 2) You must establish a long term average chlorine feedrate limit ( i. e., 12 hour rolling average or an ( up to) annual rolling average) as the annual average HCl equivalent emission rate limit divided by [ 1   system removal efficiency]. You establish the total chlorine system removal efficiency during the comprehensive performance test. The proposed rule would have required you to establish the long term average chlorine feedrate limit as the average of the test run averages of the comprehensive performance test. 31 ( 3) At proposal, we requested comment on whether and how to establish a short term chlorine feedrate limit to ensure that the acute exposure Hazard Index of 1.0 is not exceeded. See 69 FR at 21304. We conclude for the final rule that a 1 hour rolling average feedrate 30 Note that if your incinerator or boiler is equipped with a fabric filter and you elect under § 63.1206( c)( 8)( i) to use a particulate matter detection system in lieu of a bag leak detection system for compliance assurance, the ash feedrate limit is waived. The ash feedrate limit is not waived if you use a bag leak detection system, however, because the alarm level may not ensure compliance with the emission standard when you follow the concepts in the Agency's guidance document on bag leak detection systems to establish the alarm level. 31 Note that, as a practical matter, most sources must establish the chlorine feedrate limit as the average of the test run average feedrate limit during the comprehensive performance test to demonstrate compliance with the semivolatile emission standard. This is because chlorine feedrate is a compliance assurance parameter for the semivolatile metal emission standard. That feedrate limit is based on a 12 hour rolling average. To ensure compliance with the annual average HCl equivalent emission rate limit, however, that feedrate limit cannot exceed the value calculated as the annual average HCl equivalent emission rate limit divided by [ 1   system removal efficiency], where you demonstrate the total chlorine system removal efficiency during the performance test. limit may be needed for some situations ( i. e., if chlorine feedrates can vary substantially during the averaging period for the long term feedrate limit and potentially result in an exceedance of the 1 hour average HCl equivalent emission rate limit). Accordingly, although your eligibility for the health based compliance alternatives is based on annual average HCl equivalent emissions, you must determine considering prescribed criteria whether your 1 hour HCl equivalent emission rate may exceed the national exposure standard ( i. e., Hazard Index not exceeding 1.0 considering the maximum 1 hour average ambient concentration of hydrogen chloride and chlorine at an off site receptor location32) and thus may exceed the 1 hour average HCl equivalent emission rate limit absent an hourly rolling average limit on the feedrate of chlorine. If the acute exposure standard may be exceeded, you must establish an hourly rolling average chlorine feedrate limit as the 1 hour HCl equivalent emission rate limit divided by [ 1   system removal efficiency]. You establish the system removal efficiency during the comprehensive performance test. ( 4) When calculating HCl equivalent emission rates, rather than partitioning total chlorine emissions between chlorine and HCl ( i. e., the Cl2/ HCl volumetric ratio) based on the comprehensive performance test as proposed, you must establish the Cl2/ HCl volumetric ratio used to calculate the annual average HCl equivalent emission rate based on the historical average ratio from all regulatory compliance tests. You must establish the Cl2/ HCl volumetric used to calculate the 1 hour average HCl equivalent emission rate as the highest of the historical ratios from all regulatory compliance tests. The rule allows you to exclude ratios from historical compliance tests where the emission data may not be representative of the current Cl2/ HCl ratio for reasons such as changes to the design or operation of the combustor or biases in measurement methods. The rule also explicitly allows the permitting authority to require periodic emissions testing to obtain a representative average and maximum ratio; ( 5) The look up table analysis has been refined by presenting annual average and 1 hour HCl equivalent emission rate limits as a function of stack height, stack diameter, and distance to property line. In addition, separate look up tables are presented for flat terrain and simple elevated terrain; ( 6) The proposed rule required approval of the eligibility demonstration before you could comply with the alternative health based emission limits for total chlorine. Under the final rule, if your permitting authority has not approved your eligibility demonstration by the compliance date, and has not issued a notice of intent to disapprove your demonstration, you may nonetheless begin complying, on the compliance date, with the annual average HClequivalent emission rate limits you present in your eligibility demonstration. In addition, if your permitting authority issues a notice of intent to disapprove your eligibility demonstration, the authority will identify the basis for that notice and specify how much time you will have to submit additional information or to comply with the MACT total chlorine standards. The permitting authority may extend the compliance date of the total chlorine standards to allow you to make changes to the design or operation of the combustor or related systems as quickly as practicable to enable you to achieve compliance with the MACT total chlorine standards; ( 7) We have revised the approach for determining chlorine emissions if you feed bromine or sulfur during the comprehensive performance test at levels higher than those 32 Under the site specific risk assessment approach to demonstrate eligibility, you must consider locations where people reside and where people congregate for work, school, or recreation. specified in § 63.1215( e)( 3)( ii)( B). Under the final rule, you must use EPA Method 320/ 321 or ASTM D 6735   01, or an equivalent method, to measure hydrogen chloride, and Method 26/ 26A, or an equivalent method, to measure chlorine and hydrogen chloride. You must determine your chlorine emissions to be the higher of: ( 1) the value measured by Method 26/ 26A, or an equivalent method; or ( 2) the value calculated by difference between the combined hydrogen chloride and chlorine levels measured by Method 26/ 26a, or an equivalent method, and the hydrogen chloride measurement from EPA Method 320/ 321 or ASTM D 6735 01, or an equivalent method; and ( 8) The proposed rule would have required you to conduct a new comprehensive performance test if you planned to make changes to the facility that would lower the annual average HCl equivalent emission rate limit. Under the final rule, you would be required to conduct a performance test as a result of a planned change only for a change to the design, operation, or maintenance of the combustor that could affect the system removal efficiency for total chlorine if the change could reduce the system removal efficiency, or if the change would increase the system removal efficiency and you elect to increase the feedrate limits on total chlorine and chloride.

Part Four: What Are the Responses to Major Comments?

I. Database A. Revisions to the EPA's Hazardous Waste Combustor Data Base Comment: Several commenters identify sources which have ceased operations as a hazardous waste combustor and should be removed from EPA's data base. Response: We agree with commenters that data and information from sources no longer burning hazardous waste should not be included in our hazardous waste combustor data base and should not be used to calculate the MACT standards. We consider any source that has initiated RCRA closure procedures and activities as a source that is no longer burning hazardous waste. This data handling decision is consistent with the approach we used in the 1999 final rule. See 64 FR at 52844. As we stated in that rule, ample emissions data remain to support calculating the MACT standards without using data from sources that no longer burn hazardous waste. As a result, we removed the following former hazardous waste combustors from the data base: the Safety Kleen incinerator in Clarence, New York, the Dow Chemical Company incinerators in Midland, Michigan, and LaPorte, Texas, the two Holcim wet process cement kilns in Holly Hill, South Carolina, the Dow Chemical Company liquid fuel fired boiler in Freeport, Texas, the Union Carbide liquid fuel fired boilers in Hahnville, Louisiana, and Texas City, Texas, and six Dow Chemical Company hydrochloric production furnaces in Freeport, Texas. We are retaining, however, Solite Corporation's lightweight aggregate facility in Cascade, Virginia, in the data base. Even though the facility recently initiated RCRA closure procedures, this data handling decision differs from those listed in the preceding paragraph because Solite Corporation provided this new information in February 2005 while information on the other closures was reported or available to us in 2004. Because we cannot continually adjust our data base and still finalize this rulemaking by the court ordered deadline, we stopped making revisions to the data base in late 2004. Additional facility changes after that date, like Solite Corporation's Cascade facility closure, simply could not be incorporated. Comment: One commenter identifies a source in EPA's data base that should be classified as a boiler instead of a hydrochloric acid production furnace. Response: We agree with the commenter. In today's rule, Dow Chemical Company's boiler F 2820, located in Freeport, Texas, is reclassified in our data base as a boiler. This source is identified as unit number 2020 in our data base.

B. Use of Data from Recently Upgraded Sources Comment: Many commenters recommend that EPA remove from the data base ( or not consider for standards setting purposes) emissions data from sources that upgraded their emissions controls to comply with the promulgated emission standards of either the 1999 rule or the 2002 interim standards. Several commenters also state that any emissions data that were obtained or used to demonstrate compliance with the promulgated standards of 1999 or 2002 should not be used for standard setting purposes by the Agency. That is, EPA must evaluate the source category as it existed at the beginning of the rule development process and not after emissions controls are later added to comply with the 1999 or 2002 standards. Several commenters also state that EPA is only partly correct in claiming that the interim standards are not MACT standards because the interim standards were established and considered to be MACT until the Court issued its opinion in July 2001. Until that time, sources proceeded to upgrade their facilities to achieve the standards promulgated in 1999. The rationale for these recommendations is threefold: ( 1) use of the data unfairly ignores the MACT driven reductions already achieved by some sources; ( 2) it is contrary to sound public policy to use data from upgraded facilities to " ratchet down" the MACT floors to a level more stringent because these sources would not have increased their level of performance but for the legal obligation to comply with the standards; and ( 3) EPA's reliance on National Lime Ass'n v. EPA, 233 F. 3d 625, 640 ( D. C. Cir. 2000), for the proposition that the motivation for a source's performance is legally irrelevant in developing MACT floor levels is misplaced because that case involved the initial MACT standard setting process, and not a subsequent rule. One commenter agrees with EPA's proposed position and states that use of data from sources that have upgraded is not only appropriate, but also required by the Clean Air Act. This commenter states that the actual performance of sources that have upgraded their emissions equipment   to meet the 1999 standards or for any reason   is reflected only by the most recently generated emissions data for the source. Thus, the Clean Air Act requires EPA to use the most recently generated data available to it and precludes the Agency from using older, out of date performance data. EPA also received several comments stating that the language of section 112( d)( 3)( A) of the Clean Air Act informs how the Agency should consider emissions data from sources that conducted testing after that 1999 rule was promulgated. One commenter states that the only data which should not be used in calculating the MACT floors are from sources that are subject to lowest achievable emission rates ( LAER). Thus, the commenter states, Congress considered the possibility of significant and recent upgrades, and concluded that EPA should use up to date data to reflect source's performance, but must exclude certain sources from the floor calculation if their upgrades were of a specific degree and were accomplished within a specific period of time. Another commenter states that Congress did not intend to pile technology upon technology as confirmed by section 112( d)( 3)( A) that specifically excludes sources that implemented LAER from consideration when establishing section 112( d) standards. Thus, the commenter states, considering data from sources that have upgraded violates both the language and intent of the Clean Air Act. Another commenter states that, while Congress no doubt contemplated that EPA should use all available emissions information in setting initial MACT standards, neither the statute nor the legislative history suggest that follow up MACT rulemakings require the use of data reflecting compliance efforts with previous MACT standards or interim standards. Response: As proposed, EPA maintains its position on use of post 1999 emissions data. The statute indicates that EPA is to base MACT floors on performance of sources " for which the Administrator has emissions information." Section 112( d)( 3)( A); CKRC, 255 F. 3d at 867. There can be no dispute that post 1999 performance data in EPA's possession fits this description. We also reiterate that the motivation for the control reflected in data available to us is irrelevant. See 69 FR at 21217 218. We further agree with those commenters who pointed out that Congress was explicit when it wanted certain emissions information ( i. e., sources operating pursuant to a LAER standard) excluded from consideration in establishing floors. There is, of course, no such enumerated exception for sources that have upgraded their performance for other reasons. We also do not agree with those commenters arguing ( with respect to the standards for the Phase 1 sources ( incinerators, cement kilns, and lightweight aggregate kilns)) in effect that the present rulemaking involves revision of an existing MACT standard. If this were indeed a revision of a MACT standard under section 112( d)( 6), then EPA would not redetermine floor levels. See 70 FR at 20008 ( April 15, 2005). However, EPA has not to date promulgated valid MACT floors or valid MACT standards for these sources. The 1999 standards do not reflect MACT, as held by the CKRC court. The interim standards likewise do not reflect MACT, but were designed to prevent a regulatory gap and were described as such from their inception. 67 FR at 7693 ( Feb. 13, 2002); see also Joint Motion of all Parties for Stay of Issuance of Mandate in case no. 99 1457 ( October 19, 2001), pp. 11 12 (" The Parties emphasize that the contemplated interim rule is in the nature of a remedy. It would not respond to the Court's mandate regarding the need to demonstrate that EPA's methodology reasonably predicts the performance of the average of the best performing twelve percent of sources ( or best performing source). EPA intends to address those issues in a subsequent rule, which will necessarily require a longer time to develop, propose, and finalize.") EPA consequently believes that it is adopting in this rule the initial section 112( d) MACT standards for hazardous waste burning incinerators, cement kilns, and lightweight aggregate kilns, and that the floor levels for existing sources are based, as provided in section 112( d)( 3), on performance of those sources for which EPA has " emissions information." However, we disagree with the comment that we must make exclusive use of the most recent information from hazardous waste combustion sources. There is no such restriction in section 112( d)( 3). EPA has exhaustively examined all of the data in its possession for all source categories covered by this rule, and determined ( and documented) which data are suitable for evaluating sources' performance. C. Correction of Total Chlorine Data to Address Potential Bias in Stack Measurement Method Comment: Several commenters state that EPA's proposed total chlorine standards of 1.5 ppm for existing incinerators and 0.18 ppm for new incinerators are based on biased data of indeterminate quality and are unachievable. Commenters assert that Method 26A and its RCRA equivalent, SW 846 Method 0050, have a negative bias at concentrations below 20 ppmv when used on stacks controlled with wet scrubbers. Commenters cite two recurring situations when this bias is likely to occur: ( 1) hydrogen chloride dissolving in condensed moisture in the sampling train; and ( 2) hydrogen chloride reacting with alkaline compounds from the scrubber water that are collected on the filter ahead of the impingers. Commenters are particularly concerned about the negative bias associated with stack gas containing substantial water vapor. Commenters note that EPA found in a controlled laboratory study by Steger33 that the bias is between 17 and 29 percent at stack gas moisture content of 7 to 9 percent. This stack gas moisture is much less than the nominal 50% moisture contained in some hazardous waste combustor stacks according to the commenters. Commenters believe this is why EPA's Method 0050, which was used to gather most of the data in the HWC MACT data base, states in Section 1.2 that " this method is not acceptable for demonstrating compliance with HCl emission standards less than 20 ppm." Moreover, commenters state that the procedures in Method 0050 to address the negative bias caused by condensed moisture were not followed for many RCRA compliance tests. The method uses an optional cyclone to collect moisture droplets, and requires a 45 minute purge of the cyclone and sampling train to recover hydrogen chloride from water collected by the cyclone and any condensed moisture in the train. The cyclone is not necessary if the stack gas does not contain water droplets. According to commenters, the cyclone and subsequent purge were often not used in the presence of water droplets because a potential low bias below 20 ppmv was irrelevant when demonstrating compliance with emission standards on the order of 100 ppmv. There was no need for the extra complexity and expense of using a cyclone and train purge given the purpose of the test. Although the data were acceptable for their intended purpose, commenters conclude that the data are not useful for establishing standards below 20 ppmv. For these reasons, commenters suggest that EPA not consider total chlorine measurements below 20 ppmv when establishing the standards. Response: For the reasons discussed below, we corrected all total chlorine measurements in our data base for all source categories that were below 20 ppmv to 20 ppmv to establish the total chlorine floors. Moreover, to address run to run variability given that all runs for several data sets are now corrected to 20 ppmv, we impute a run standard deviation based on a regression analysis of run standard deviation versus total chlorine concentration for sources with total chlorine measurements greater than 20 ppmv. This is the same approach we used to impute variability from sources using fabric filters when determining the particulate matter MACT floors. Effect of Moisture Vapor. Commenters imply that stack gas with high levels of gas phase water vapor will inherently be problematic, particularly at emissions less than 20 ppmv. There is no basis for claiming that water vapor, per se, causes a bias in SW 846 33 Steger, J. L., et al, " Laboratory Evaluation of Method 0050 for Hydrogen Chloride", Proc of 13th Annual Incineration Conference, Houston, TX, May 1994. Method 0050 or its equivalent, Method 26A. Condensed moisture ( i. e., water droplets), however, can cause a bias because it can dissolve hydrogen chloride in the sampling train and prevent it from being captured in the impingers if the sampling train is not properly purged. Water droplets can potentially be present due to entrainment from the wet scrubber, condensation in cooler regions of the stack along the stack walls, and entrainment from condensed moisture dripping down the stack wall across the inlet duct opening. Although Method 0050 addresses the water droplet issue by use of a cyclone and 45 minute purge, the Steger paper ( Ibid.) concludes that a 45 minute purge is not adequate to evaporate all water collected by the cyclone in stacks with a total moisture content ( vapor and condensed moisture) of 7 to 9%. At those moisture levels, Steger documented the negative bias that commenters reference. Steger's recommendation was to increase the heat input to the sample train by increasing the train and filter temperature from 120C ( 248F) to 200C ( 392F). We agree that increasing the probe and filter temperature will provide a better opportunity to evaporate any condensed moisture, but another solution to the problem is to require that the post test purge be run long enough to evaporate all condensed moisture. That is the approach used by Method 26A, which EPA promulgated after Method 0050, and which sources must use to demonstrate compliance with the final standards. Method 26A uses an extended purge time rather than elevating the train temperature to address condensed moisture because that approach can be implemented by the stack tester at the site without using nonstandard equipment. We attempted to quantify the level of condensed moisture in the Steger study and to compare it to the levels of condensed moisture that may be present in hazardous waste combustor stack gas. This would provide an indication if the bias that Steger quantified with a 45 minute purge might also be applicable to some hazardous waste combustors. We conclude that this comparison would be problematic, however, because: ( 1) given the limited information available in the Steger paper, it is difficult to quantify the level of condensed moisture in his gas samples; and ( 2) we cannot estimate the levels of condensed moisture in hazardous waste combustor stack gas because, even though condensed moisture may have been present during a test, method protocol is to report the saturation moisture level only ( i. e., the amount of water vapor present), and not the total moisture content ( i. e., both condensed and vapor phase moisture). We can conclude, however, that, if hazardous waste combustor stack gas were to contain the levels of condensed moisture present in the gas that Steger tested, the 45 minute purge required by Method 0050 would not be sufficient to avoid a negative bias. We also conclude that this is potentially a practical issue and not merely a theoretical concern because, as commenters note, hazardous waste combustors that use wet scrubbers are often saturated with water vapor that will condense if the flue gas cools. Data from Wet Stacks When a Cyclone Was Not Used. Commenters state that Method 0050 procedures for addressing water droplets ( adequate or not, as discussed above) were not followed in many cases because a low bias below 20 ppmv was not relevant to demonstrating compliance with standards on the order of 100 ppmv. We do not know which data sets may be problematic because, as previously stated, the moisture concentration reported was often the saturation ( vapor phase only) moisture level and not the total ( vapor and liquid) moisture in the flue gas. We also have no documentation that a cyclone was used   even in situations where the moisture content was documented to be above the dew point. We therefore conclude that all data below 20 ppmv from sources controlled with a wet scrubber are suspect and should be corrected. Potential Bias Due to Filter Affinity for Hydrogen Chloride. Studies by the American Society of Testing and Materials indicate that the filter used in the Method 0050 train ( and the M26/ 26A trains) may adsorb/ absorb hydrogen chloride and cause a negative bias at low emission levels. ( See ASTM D6735 01, section 11.1.3 and " note 2" of section 14.2.3) This inherent affinity for hydrogen chloride can be satisfied by preconditioning the sampling train for one hour. None of the tests in our database were preconditioned in such a manner. We are normally not concerned about this type of bias because we would expect the bias to apply to all sources equally ( e. g., wet or dry gas) and for all subsequent compliance tests. In other words, we are ordinarily less concerned if a standard is based on biased data, as long as the means by which the standard was developed and the means of compliance would experience identical bias. However, we did correct the wet gas measurements below 20 ppmv to address the potential low bias caused by condensed moisture. This correction would also correct for any potential bias caused by the filter's inherent affinity for hydrogen chloride. This results in a data set that is partially corrected for this issue   sources with wet stacks would be corrected for this potential bias while sources with dry stacks would not be corrected. To address this unacceptable mix of potentially biased and unbiased data ( i. e., dry gas data biased due to affinity of filter for hydrogen chloride and wet gas data corrected for condensed moisture and affinity of filter for hydrogen chloride), we also correct total chlorine measurements from dry gas stacks ( i. e., sources that do not use wet scrubbers). Deposition of Alkaline Particulate on the Filter. Commenters are also concerned that hydrogen chloride may react with alkaline compounds from the scrubber water droplets that are collected on the filter ahead of the impingers. Commenters suggest this potential cause for a low bias at total chlorine levels below 20 ppmv is another reason not to use measurements below 20 ppmv to establish the standards. Although alkaline particulate deposition on the method filter causing a negative bias is a much greater concern for sources that have stack gas containing high levels of alkaline particulate ( e. g., cement kilns, sources equipped with dry scrubbers), we agree with commenters that this may be of concern for all sources equipped with wet scrubbers. Our approach to correct all data below 20 ppmv addresses this concern. Decision Unique to Hazardous Waste Combustors. We note that the rationale for our decision to correct total chlorine data below 20 ppmv to account for the biases discussed above is unique to the hazardous waste combustor MACT rule. Some sources apparently did not follow Method 0050 procedures to minimize the low bias caused by condensed moisture for understandable reasons. Even if sources had followed Method 0050 procedures to minimize the bias ( i. e., cyclone and 45 minute purge) there still may have been a substantial bias because of insufficient purge time, as Steger's work may indicate. We note that the total chlorine stack test method used by sources other than hazardous waste combustors   Method 26A   requires that the cyclone and sampling train be purged until all condensed moisture is evaporated. We believe it is necessary to correct our data below 20 ppmv data because of issues associated exclusively with Method 0050 and how it was used to demonstrate compliance with these sources. Determining Variability for Data at 20 ppmv. Correcting those total chlorine data below 20 ppmv to 20 ppmv brings about a situation identical to the one we confronted with nondetect data. See Part Four, Section V. B. below. The MACT pool of best performing source( s) for some data sets is now comprised of largely the same values. This has the effect of understating the variability associated with these data. To address this concern, we took an approach similar to the one we used to determine variability of PM emissions for sources equipped with a fabric filter. In that case, we performed a linear regression on the data, charting variability against emissions, and used the variability that resulted from the linear regression analysis as the variability for the sources average emissions. In this case, most or all of the incinerator and liquid fuel boiler sources in the MACT pool have average emissions at or near 20 ppmv. We therefore performed a linear regression on the total chlorine data charting average test condition results above 20 ppmv against the variability associated with that test condition. The variability associated with 20 ppmv was the variability we used for incinerator and liquid fuel boiler data sets affected by the 20 ppmv correction. We also considered using the statistical imputation approach we used for nondetect values. See discussion in Section IV. B below. The statistical imputation approach for correcting data below 20 ppmv without dampening variability would involve imputing a value between the reported value and 20 ppmv because the " true" value of the biased data would lie in this interval. This approach would be problematic, however, given that many of the reported values were much lower than 20 ppmv; our statistical imputation approach would tend to overestimate the run to run variability. Consequently, we conclude that a regression analysis approach is more appropriate. A regression analysis is particularly pertinent in this situation because: ( 1) we consider data above 20 ppmv used to develop the regression to be unbiased; and ( 2) all the corrected data averages for which we are imputing a standard deviation from the regression curve are at or near 20 ppmv. Thus, any potential concern about downward extrapolation from the regression would be minimized. We note that, although a regression analysis is appropriate to estimate run to run variability for the corrected total chlorine data, we could not use a linear regression analysis to address variability of nondetect values. To estimate a standard deviation from a regression analysis, we would need to know the test condition average emissions. This would not be feasible, however, because some or all of the run measurements for a test condition are nondetect. In addition, we are concerned that a regression analysis would not accurately estimate the standard deviation at low emission levels because we would have to extrapolate the regression downward to levels where we have few measured data ( i. e., data other than nondetect). Moreover, the statistical imputation approach is more suitable for handling nondetects because the approach calculates the run to run variability by taking into account the percent nondetect for the emissions for each run. 34 A regression approach would be difficult to apply particularly in the case of test conditions containing partial nondetects or a mix of detect and nondetect values. Given these concerns with using a regression analysis to estimate the standard deviation of test conditions with runs that have one or more nondetect ( or partial nondetect) measurements, we conclude that the statistical imputation approach best assures that the calculated floor levels account for run to run emissions variability. Compliance with the Standards. The final standards are based on data that were corrected to address specific issues concerning these data. See the above discussion 34 For multi constituent HAP ( e. g. SVM) the emissions for a run could be comprised of fully detected values for some HAP and detection limits for other HAP that were nondetect. regarding stack gas moisture, filter affinity for hydrogen chloride, and alkaline compound reactions with hydrogen chloride in the sampling train. Sources must demonstrate compliance using a stack test method that also addresses these issues. Sources with wet stacks must use Method 26A and follow those procedures regarding the use of a cyclone and the purging of the system whenever condensed moisture may be present in the sampling system. Finally, all sources   those with either wet or dry gas should precondition the sampling train for one hour prior to beginning the test to satisfy the filter's affinity for hydrogen chloride. The permitting authority will ensure that sources precondition the sample train ( under authority of § 63.1209( g)( 2)) when they review and approve the performance test plan.

D. Mercury Data for Cement Kilns Comment: Several commenters state that EPA's data base of mercury emissions data ( and associated feed concentrations of mercury in the hazardous waste) are unrepresentative and unsuitable for use in determining MACT standards for cement kilns. These comments are supported by an extensive amount of data submitted by the cement manufacturing industry including three years of data documenting day to day levels of mercury in hazardous waste fuels fired to all 14 hazardous waste burning cement kilns. 35 The commenters recommend that EPA use the commenter submitted data as the basis for assessing cement kilns' performance for control of mercury because it is the most complete and representative data available to EPA. Response: We agree that the commenter submitted mercury data are more representative than those we used at proposal. First, these data represent a significantly larger and more comprehensive dataset compared to the one used to support the proposed mercury standard. The commenter submitted data document the day to day levels of mercury in hazardous waste fired to all cement kilns for a three year period covering 1999 to 2001. In total, approximately 20,000 measurements of the concentration of mercury in hazardous waste are included in the dataset. When considered in whole, these data describe the performance ( and variability thereof) of all cement kilns for the three year period because each measurement represents the mercury concentration in the burn tank used to fire the kiln over the course of a day's operation ( or longer period). 36 In comparison, the data used to support the proposed floor level consisted of a much smaller dataset of approximately 50 test conditions representing a snapshot of performance somewhere in the range of normal operations, with each test condition representing a relatively short period of time ( e. g., several hours). 37 As discussed at proposal, we were concerned regarding the 35 See docket item OAR 2004 0022 0049. 36 Mercury is a volatile compound at the typical operating temperatures of the air pollution control devices used by cement kilns ( i. e., baghouses and electrostatic precipitators). Most of the mercury exits the cement kiln system as volatile stack emissions, with a smaller fraction partitioning to the clinker product or cement kiln dust. Thus, in general, there is a proportional relationship between the mercury concentration in the hazardous waste and stack emissions of mercury ( i. e., as the mercury concentration in hazardous waste increases ( assuming mercury concentrations in other inputs such as raw materials and fossil fuels ( coal) and other factors remain constant), emissions of mercury will correspondingly increase). 37 EPA's dataset for mercury for cement kilns is not like the RCRA compliance test emission data for other HAPs where each source designs the compliance test such that the operating limits it establishes account for the variability it expects to encounter during its normal operations ( e. g., semi and low volatile metals). This representativeness of this smaller dataset. See 69 FR at 21251. In addition, the commentersubmitted dataset allows us to better evaluate the only mercury control technique used by existing hazardous waste burning cement kilns   controlling the feed concentration of mercury in the hazardous waste. The commenters have demonstrated convincingly that the mercury dataset used at proposal does not properly show the range of performance and variability in performance these cement kilns actually experience, while the significantly more robust dataset submitted by commenters does illustrate this variability. Thus, we conclude the larger commenter submitted dataset is superior to EPA's smaller testing dataset. We note that our MACT floor analysis of the commenter submitted dataset to determine which sources are the best performers and to identify a mercury standard for cement kilns is discussed in the background document. 38 Additional discussion of issues related to the mercury standard for cement kilns is found in Part Four, Section VI. B of the preamble.

E. Mercury Data for Lightweight Aggregate Kilns Comment: One commenter, an owner and operator of seven of the nine operating lightweight aggregate kilns, states that the mercury dataset used by EPA at proposal is a limited and unrepresentative snapshot of performance of their seven kilns. To support their position that the snapshot emissions data are unrepresentative, the commenter submitted eight months of data documenting levels of mercury in hazardous waste fuels fired to their lightweight aggregate kilns. 39 Response: We agree with the commenter that their mercury data submission is more representative than those used at proposal. As discussed in a notice for public comment sent directly to certain commenters, 40 the commenter submitted dataset documents the day to day levels of mercury in hazardous waste fuels fired to Solite Corporation's Arvonia kilns between October 2003 and June 2004. The dataset consists of over 310 measurements of the concentration in mercury in hazardous waste. Each measurement represents the mercury concentration of the burn tank used to fire the kiln over the course of a day's operation ( or longer period). In comparison, the data used to support the proposed floor level consisted of a smaller dataset of 15 test conditions. The nature of the mercury data submitted by the commenter is the same as we received for the cement kiln category discussed in the preceding section. For similar reasons, we accept the more comprehensive commenter submitted dataset as one that better shows the range of performance and variability in performance for these lightweight aggregate kilns. One notable difference, however, is that the commenter submitted mercury data only for its company ( representing seven of nine lightweight aggregate kilns). Thus, we received no data documenting day to day levels of the concentration of mercury in hazardous waste fuels for the other two lightweight aggregate kilns owned by a different company. For these two lightweight aggregate kilns, we continue to use available data available in our database. 41 is not necessarily true for mercury for cement kilns as shown in our analysis of our mercury dataset at proposal. See 69 FR at 21251. 38 USEPA, " Technical Support Document for HWC MACT Standards, Volume III: Selection of MACT Standards," Sections 7.5.3 and 11.0, September 2005. 39 See docket items OAR 2004 0022 0270 and OAR 2004 0022 0333. 40 See docket item OAR 2004 0022 0370. 41 Unlike that is available for the commenter's kilns, we note that we have compliance test emissions data, which is designed to maximize operating parameters ( e. g., HAP feedrates) that affect emissions, for the Comment: One commenter opposes the use of the commenter submitted mercury data because EPA would be uncritically accepting a limited and select data set from a commenter with a direct interest in the outcome of its use. Instead, the commenter suggests EPA use its section 114 authority to obtain all data that are available, not just the data selected by that commenter. Response: We disagree that we uncritically accepted the commenter submitted mercury data. The reason the commenter submitted data collected between October 2003 and June 2004 is that the facility was, prior to October 2003, in the process of upgrading its on site analysis equipment. One outcome of this laboratory upgrade was its capability to detect mercury in hazardous waste at lower concentrations. Prior to the upgrade, the facility's on site laboratory was capable of detecting mercury in the hazardous waste at a concentration of approximately 2 ppmw, which is a level such that the vast majority of measurements would neither be detected nor useful for identifying best performers and their level of performance. 42 The June 4, 2004 cutoff date represents a practicable date that measurements could still be incorporated into the commenter's public comments to the proposed rule, which were submitted on July 6, 2004. Finally, the commenter provided all waste fuel measurements during this period and states reliably that no measurements made during this period were selectively excluded. 43 We also reject the commenter's suggestion that we use our authority under section 114 of the Clean Air Act to obtain additional hazardous waste mercury concentration data from the facility. There is no obligation for us to gather more performance data, given that the statute indicates that we are to base floor levels on performance of sources " for which the Administrator has emissions information." Section 112( d)( 3)( A); CKRC, 255 F. 3d at 867. In addition, given our concerns about the usefulness of measurements with high detection limits discussed above, the collection of additional data prior to the laboratory upgrade would not be productive. When balanced against the expenditure of significant resources, both in time and level of effort, to collect several more months of data, we conclude that obtaining additional mercury measurements is unnecessary because the available eight months of data   including over 310 individual measurements   represent a significant amount of data that we judge to be adequately reflective of the source's performance and variability in performance.

F. Incinerator Database Comment: Commenters state that many of the top performers ( e. g., 3011, 3015, 3022, 349) dilute emission concentrations in the stack by burning natural gas to initiate reactive waste ( e. g., explosives, inorganic hydrides) or to decontaminate inert material. Commenters do not believe these units should be considered " representative" of the overall incinerator source category and should not be used to establish standards for incinerators combusting primarily organic wastes.

other two kilns. For additional discussion on how these data were analyzed in conjunction with the commentersubmitted data, see the document " Technical Support Document for HWC MACT Standards, Volume III: Selection of MACT Standards," Section 7.5.3 and 12.0, September 2005. 42 A mercury concentration of 2 ppmw in the hazardous waste corresponds to a stack concentration of approximately 200 ug/ dscm, which is well above the interim standard of 120 ug/ dscm for mercury. 43 See also docket items OAR 2004 0022 0233 and OAR 2004 0022 0367. Response: Source 3022 has closed and has been removed from the database. Emission data from source # 3015 ( ICI explosives) has been excluded for purposes of calculating the particulate matter floor because the test report indicates this source was primarily feeding scrap metal, which we conclude to be an atypical waste stream from a particulate matter compliance perspective. 44 The sources identified by the commenter are among the best performing sources in two instances. Source 3011 is the second ranked best performer for the particulate matter standard. This source is among the best performers for particulate matter because it uses a state of the art baghouse that is equipped with Teflon coated bags. There is no evidence to suggest that this source was diluting its particulate matter emissions. We acknowledge that we do not have ash feed data for the test conditions that were used in the particulate matter standard analysis. However, this source had the third and fourth highest metal feed control levels among all the sources used in the MACT analysis for the semivolatile and low volatile metal standards. 45 We therefore conclude that it is appropriate to include this source in the MACT analysis that determines the relevant best performers for particulate matter. Source 349 is the eighth ranked ( out of 11) best performer for the particulate matter standard. We acknowledge that the ash feed level for this source is lower than most incinerators equipped with baghouses. However, particulate matter emissions from sources equipped with baghouses are not significantly affected by the ash inlet loading to the baghouse. 46 This is further supported by the fact that this source is ranked eighth among the best performers. We conclude source 349 is a best performer not because of its relatively low ash feed level, but rather because it is equipped with a well designed and operated baghouse. It is therefore appropriate to include this source in the MACT analysis. Comment: Commenters state that source 341 should not be considered in the MACT analysis because it is a small laboratory waste burner that processes only 900 lbs/ hr of waste. Commenters claim that more than 80 percent of the waste profile is nonhazardous waste. Response: We approached this comment by asking if it would be appropriate to create a separate subcategory for source 341. We conclude it is not necessary to subcategorize hazardous waste incinerators based on the size of combustion units. This is because the ranking factors used to identify the relevant best performing sources are normalized in order to remove the influence that combustion unit size would otherwise have when identifying best performing sources. See part 4 section III. D below. Air pollution control system types ( a ranking factor for particulate matter) are generally sized to match the corresponding volumetric gas flow rate in order to achieve a given control efficiency. The size of the combustor therefore does not influence a source's ability to achieve a given control efficiency. System removal efficiency and hazardous waste feed control MTECs 44 We did not have ash feed data for source 3015. We acknowledge that ash feed control levels do not significantly affect particulate matter emissions from sources equipped with baghouses. However, in this instance, the particulate matter emissions from this source may not be representative because this source may not have been feeding any appreciable levels of ash given that scrap metal feeds generally would not contribute to the ash loading into the baghouse. 45 We note that feed control levels are normalized based on each source's gas flowrate. The feed control levels used to assess performance are therefore appropriate indicators that directly address whether emissions of these pollutants are in fact being diluted by the combustion of natural gas. 46 See USEPA, " Technical Support Document for the HWC MACT Standards, Vol I: Description of Source Categories," September 2005, Section 3.2.2, for further discussion. ( ranking factors used by the SRE/ Feed methodology as described in part 4 section III. B below) are also not influenced by the size of the combustor. 47 Emission limitations are similarly normalized to remove the influence of combustion unit size by expressing the standards as emission concentration limits rather than as mass emission rate limits. See section III. D. This is illustrated in the following example. Assume there are two cement kilns side by side with similar designs, the only difference being one is twice the size of the other, producing twice as much clinker. They both have identical types of air pollution control systems ( the larger source is equipped with a larger control device that is appropriately sized to accommodate the larger volumetric gas flow rates and achieves the same control efficiency as the smaller control device). If we were to assess performance based on HAP mass emission rates ( e. g., pounds per hour), the smaller source would be the better performer because its mass emission rates would be half of the mass emission rate of the larger source, even though they both are achieving the same back end control efficiency. Emission concentrations, on the other hand, are calculated by dividing the HAP mass emission rate ( e. g., pounds per hour) by the volumetric gas flowrate ( e. g., cubic feet per hour). In the above example, both sources would have identical HAP emission concentrations ( the larger source has twice the mass emission rate, but twice the volumetric gas flow rate), accurately reflecting their identical control efficiency. Emission concentrations normalize the size of each source by accounting for volumetric gas flowate, which is directly tied to the amount of raw material each source processes ( and subsequently the amount of product that is produced). This is a reason we point out that normalization eliminates the need to create subcategories based on unit size. See part four section III. D. Further, it would be difficult to determine an appropriate minimum size cutoff in which to base such a subcategorization determination. Such a subcategorization scheme could also yield nonsensical floor results, as was the case when we assessed subcategorizing commercial incinerators and on site incinerators. 48 We have identified source 341 as the best performing source for particulate matter and low volatile metals. It is the single best performing source for these standards because it is equipped with a state of the art baghouse. 49 This source, which simultaneously feeds hazardous and nonhazardous wastes, conducted several emission tests that reflected different modes of operation. The amount of nonhazardous waste that was processed in the combustion unit varied across test conditions. We could not ascertain the exact amount of hazardous waste processed in the test condition that was used in the MACT analysis for low volatile metals because the test report stated the wastes that were processed were a mixture of hazardous and nonhazardous wastes, although we estimate that at least 26% of the waste processed was nonhazardous. 50 We 47 System removal efficiency is a measure of the amount of the pollutant that is removed from the flue combustion gas prior to being emitted and likewise is not influenced by the size of the combustor because backend control systems are sized to achieve a given performance level. Hazardous waste feed control levels are normalized to remove the influence of combustor size by dividing each source's mass feed rate by its volumetric gas flowrate. 48 See USEPA, " Technical Support Document for the HWC MACT Standards, Volume III: Selection of MACT Standards", September 2005, Section 4.3.2 for further discussion. 49 See USEPA, " Final Technical Support Document for the HWC MACT Standards, Volume I: Description of Source Categories", September 2005, Section 3.2.1, for further discussion. 50 See USEPA, " Final Technical Support Document for the HWC MACT Standards, Volume I: Description of Source Categories", September 2005, Section 2.1 for further discussion. note that we are aware of several other incinerators that processed nonhazardous waste at levels greater than 26 percent during their emission tests. We therefore do not believe this to be atypical operation that warrants subcategoriztion. Moreover, the fact that this source was feeding nonhazardous wastes does not result in atypically low hazardous waste low volatile metal feed control levels, as evidenced by the relative feed control ranking for this source of thirteenth among the 26 sources assessed in the MACT analysis. It also has the highest normalized hazardous waste feed control level among the best performing sources, and has the fifth best low volatile metal system removal efficiency among those same 26 sources. We repeat that this source is being identified as the best performing source primarily because it is equipped with a highly efficient baghouse, not because it is feeding low levels of HAP metals attributable to its hazardous waste. Furthermore, this source is not the lowest emitting source in the database. There are two sources with similar, but slightly lower low volatile metal compliance test emissions ( one commercial incinerator and one onsite, non commercial incinerator). This provides further evidence that the emissions from this source appropriately represent emissions of a relevant best performing source. Regarding the particulate matter standard, source 341 does not have atypically low ash feed rates as compared to other sources equipped with baghouses. Out of the nine best performing particulate matter sources for which we have ash feed information, this source ranks fourth ( a ranking of one is indicative of the lowest ash feed rate). Nonetheless, as previously discussed, particulate matter emissions from sources equipped with baghouses are not significantly affected by the ash inlet loading to the baghouse. We note that particulate matter emissions from the second and third best performing source are not significantly different from this source, providing further evidence that this source is representative of the range of emissions exhibited by other well designed and operating incinerators equipped with baghouses. 51 Comment: Commenters state that sources 3018 and 3019 are identified as best performers for mercury emissions for incinerators. After evaluating the trial burn plans for these sources, the commenter believes the data should not be used to calculate the MACT floor because the spiking rate for mercury was extremely low for a compliance test. The ranking for feedrate is therefore unrepresentative. The commenter suggests that these test results should be characterized as ` normal'. Response: We have verified that the emission tests performed for sources 3018 and 3019 reflect the upper range of mercury emissions that are not to be exceeded by these sources, and that their spiked mercury feed rates were back calculated from a risk assessment. We therefore conclude that we properly characterized these emissions as compliance test emissions data because they reflect the emissions resulting from the upper bound of hazardous waste mercury feedrates from these sources. 52 Consequently, these data are properly included with the other data used to calculate floor standards for mercury for incinerators.

51 Source 341 particulate matter emissions, after accounting for variability, equated to 0.0015 gr/ dscf. The second and third ranked particulate matter sources emissions, considering variability, equated to 0.0018 and 0.0023 gr/ dscf, respectively. 52 See February 11, 2005 memo to docket titled " October 20 Conference Call with Squibb Manufacturing regarding Source # 3018 and 3019". Comment: Commenters state the trial burn plan for sources 3018 and 3019 describes these units to be of similar design. Thus the difference in results between these two similar sources is indicative of additional variability above and beyond the run to run variability and should be assessed if the data are deemed usable at all. Response: We conclude both of these sources are in fact unique sources that should be assessed as individual sources for purposes of the MACT analysis. Although these sources are of similar design, we do not believe they are identical, in part because: 1) the facility itself conducted separate emission tests for the two units ( rather than trying to avail itself of the ' data in lieu' option, which could save it the expense of a second compliance test, the obvious inference being that the source or regulatory official regards the two units as different); and 2) discussions with facility representatives indicated these units are similar, but not identical. 53 As a result, it would be inappropriate to assess emissions variability by combining the emissions of these two sources into one test condition given they are not identical units. Comment: Commenters state that emissions data from source 327 should not be used to calculate dioxin/ furan and mercury floors because they claim the carbon injection system did not appear to function properly during the test. Response: We agree with the commenters. We have determined that this source encountered problems with its carbon injection system during the emissions test from which the data were obtained and subsequently used in EPA's proposed MACT analysis. We have also verified that this source did not establish operating parameter limits for the carbon injection system as a result of this test. 54 We therefore have excluded this mercury and dioxin data from the MACT analysis, and have instead used emissions data from an older test condition to represent this source's emissions. Comment: Commenters state that the emissions data from source 3006 were based on a miniburn to determine how close the unit was to achieving the interim MACT standards. The commenter questions whether these data should be used for purposes of calculating MACT standards. Response: The fact that a source conducts a voluntary emissions test ( e. g., a miniburn) to determine how close it is operating to upcoming emission standards does not necessarily lead us to conclude that the emission data are inappropriate for purposes of calculating MACT standards. However, since proposal, we have determined that this source did not measure cadmium emissions during this emissions test. As a result, we conclude the semivolatile metal emissions data from this source should not be used in the MACT standard calculation for semivolatile metals because the data do not represent the source's combined emissions of lead and cadmium.

II. Affected Sources A. Area Source Boilers and Hydrochloric Acid Production Furnaces Comment: Five commenters state that the area sources subject to the proposed rule are negligible contributors to 112( c)( 6) HAP emissions and should not be subject to major 53 Also see February 11, 2005 memo to docket titled " October 20 Conference Call with Squibb Manufacturing regarding Source # 3018 and 3019". 54 See July 15, 2005 memo to docket titled " Telephone Conversation with Utah DEQ Regarding 2001 Clean Harbor Emission Test." source standards for 112( c)( 6) HAP. Commenters note that requiring compliance with MACT for 112( c)( 6) HAP and RCRA for other toxic pollutants is more complicated and burdensome for sources than complying only with RCRA. Although an area source can choose to become regulated as a major source in order to reduce some RCRA requirements, they would become subject to more onerous emissions limits under Subpart EEE and the other MACT requirements. One of these commenters states that subjecting an area source to major source standards under 112( c)( 6) sends a negative message to industry that EPA does not value emissions reduction and/ or chemical substitution, or other methods used by area sources to achieve that status. EPA is no longer providing any incentive for sources to take such difficult yet environmentally beneficial steps to become an area source. Imposing Title V permitting requirements on an entire facility that operates as an area source of hazardous air pollutants ( HAPs) will impose an unfair and undue burden on the facility. Another of these commenters states that section 112( c)( 6) requires in pertinent part that EPA list categories and subcategories of sources assuring that sources accounting for not less than 90% of the aggregate emissions of each pollutant ( specified in 112( c)( 6)) are subject to standards under Section 112( d)( 2) or ( d)( 4). In 1998, EPA published a notice identifying the list of source categories accounting for the section 112( c)( 6) HAP emissions and to be regulated under section 112( d) to meet the 90% requirement. ( 63 FR 17838) At the time, EPA acknowledged that MACT standards for a number of the source categories had not yet been promulgated, and stated that when the regulations for each of those categories are developed, EPA will analyze the data specific to those sources and determine, under Section 112( d), in what manner requirements will be established. EPA also stated that:

" Some area categories may be negligible contributors to the 90% goal, and as such pose unwarranted burdens for subjecting to standards. These trivial source categories will be removed from the listing as they are evaluated since they will not contribute significantly to the 90% goal." ( 63 FR 17841)

The commenter believes the " two or fewer" area source boilers identified by EPA in the present rulemaking are " negligible contributors" to the 90% goal and therefore, should not be required to adopt the same MACT emission limitations and requirements as major sources of the 112( c)( 6) pollutants. The commenter believes EPA's decision to subject area source boilers and hydrochloric acid production furnaces is incorrect, unsupported by the administrative record, and therefore arbitrary and capricious. One commenter states that, if EPA regulates area sources, it should significantly reduce the administrative burden for area sources by: exempting them from Title V provisions for Subpart EEE requirements; exempting them from compliance with the General Provisions of 63 Subpart A; limiting them to a one time comprehensive performance test; or limiting other applicable requirements. Response: We continue to believe that boiler and hydrochloric acid furnace area sources warrant regulation under the major source MACT standards for mercury, dioxin/ furan, carbon monoxide/ hydrocarbons, and destruction and removal efficiency pursuant to section 112( c)( 6). As discussed at proposal ( 69 FR at 21212), section 112( c)( 6) of the CAA requires EPA to list and promulgate section 112( d)( 2) or ( d)( 4) standards ( i. e., standards reflecting MACT) for categories and subcategories of sources emitting seven specific pollutants. Five of those listed pollutants are emitted by boilers and hydrochloric acid production furnaces: mercury, 2,3,7,8 tetrachlorodibenzofuran, 2,3,7,8 tetrachlorodibenzo p dioxin, polycyclic organic matter, and polychlorinated biphenyls. As discussed below, EPA must assure that source categories accounting for not less than 90 percent of the aggregated emissions of each enumerated pollutant are subject to MACT standards ( and of course is not prohibited from requiring more than 90 percent of aggregated emissions to be controlled by MACT standards). Congress singled out the pollutants in section 112( c)( 6) as being of `` specific concern'' not just because of their toxicity but because of their propensity to cause substantial harm to human health and the environment via indirect exposure pathways ( i. e., from the air through other media, such as water, soil, food uptake, etc.). Furthermore, these pollutants have exhibited special potential to bioaccumulate, causing pervasive environmental harm in biota and, ultimately, human health risks. Section 112( c)( 6) of the CAA requires EPA to list categories and subcategories of sources of seven specified pollutants to assure that sources accounting for not less than 90 percent of the aggregate emissions of each such pollutant are subject to standards under CAA section 112( d)( 2) or 112( d)( 4). In 1998, EPA issued the list of source categories pursuant to section 112( c)( 6), and that list is published at 63 Fed. Reg. 17838, 17849, Table 2 ( April 10, 1998). In the 1998 listing, EPA identified the following three subcategories of the HWC source category that emit one or more of the seven section 112( c)( 6) pollutants: ( 1) hazardous waste incinerators ( emit mercury, dioxin, furans, polycyclic organic matter ( POM) and polychlorinated biphenyls ( PCBs)); ( 2) Portland cement manufacture: hazardous waste kilns   ( emit mercury, dioxin, furans, and POM); and ( 3) lightweight aggregate kilns: hazardous waste kilns   ( emit dioxin, furans, and mercury). These three subcategories are all subject to today's rule, which is issued pursuant to CAA section 112( d)( 2). As explained below, the HWC NESHAP effectively controls emissions of the identified section 112( c)( 6) pollutants from the identified subcategories. Accordingly, EPA considers the sources in these three subcategories as being " subject to standards" for purposes of section 112( c)( 6). Specifically, with regard to hazardous waste burning incinerators, cement kilns, and lightweight aggregate kilns, EPA is adopting in this final rule MACT standards for mercury and dioxins/ furans. EPA has already adopted MACT standards for control of POM and PCBs emitted by these sources in the 1999 rule, which standards were not reopened or reconsidered in this rulemaking. These standards are the CO/ HC standards, which in combination with the Destruction Removal Efficiency ( DRE) requirement, assure that these sources operate continuously under good combustion conditions which inhibit formation of POM and PCBs as combustion by products, or destroy these HAP if they are present in the wastes being combusted. 55 See discussion in Part Four, Sections V. A and V. B of this preamble. The HWC NESHAP also applies to hazardous waste burning boilers and hydrochloric acid production furnaces. In particular, for these boilers and furnaces, this rule 55 Courts have repeatedly upheld EPA's authority under CAA section 112( d) to use a surrogate to regulate hazardous pollutants if it is reasonable to do so. See, e. g., National Lime, 233 F. 3d at 637 ( holding that EPA properly used particulate matter as a surrogate for HAP metals). addresses emissions of dioxin/ furan, mercury, POM and PCBs either through specific numeric standards for the identified HAP, or through standards for surrogate pollutants which control emissions of the identified HAP. We estimate that approximately 620 pounds of mercury are emitted annually in aggregate from hazardous waste burning boilers in the United States. 56 Also, we estimate that hazardous waste burning boilers and hydrochloric acid production furnaces emit in aggregate approximately 2.3 and 0.2 grams TEQ per year of dioxin/ furan, respectively. Controlling emissions of these HAP from area sources consequently reduces emissions of these HAP through application of MACT standards. We note that only major source boilers and hydrochloric acid furnaces are subject to the full suite of subpart EEE emission standards. 57 Section 112( c)( 3) of the CAA requires us to subject area sources to the full suite of standards applicable to major sources if we find `` a threat of adverse effects to human health or the environment'' that warrants such action. We cannot make this finding for area source boilers and halogen acid production furnaces. 69 FR at 21212 Consequently, as proposed, area sources in these categories would be subject only to the MACT standards for mercury, dioxin/ furan, and polycyclic organic matter and polychlorinated biphenyls ( through the surrogate standards for carbon monoxide/ hydrocarbons and destruction and removal efficiency) to control the HAP enumerated in section 112( c)( 6). RCRA standards under Part 266, Subpart H for particulate matter, metals other than mercury, and hydrogen chloride and chlorine gas would continue to apply to these area sources unless an area source elects to comply with the major source standards in lieu of the RCRA standards. See § 266.100( b)( 3) and the revisions to § § 270.22 and 270.66. Commenters refer to the " two or fewer" potential area source boilers we identified at proposal as " negligible contributors" and, therefore, conclude that these area sources should not subject to major source standards for emission of these HAPs. Commenters did not quantify the amount of emissions from area sources, and did not even identify how many area sources are at issue. We do not know how many boilers and hydrochloric acid furnaces are area sources. We apparently underestimated the number given that four companies commented on the proposed rule saying that area sources should not be subject to major source standards for mercury, dioxin/ furan, PCBs, and polycyclic organic matter, and one of those companies indicates it operates multiple area sources. Consequently, we continue to believe that area sources in these categories may have the potential to emit more than negligible levels of these HAP. We also note that the major source standards are tailored to minimize the compliance burden for sources that emit low levels of HAP. Commenters raise concerns about applying the major source standards for HAP enumerated in section 112( c)( 6) to liquid fuel boiler area 56 See USEPA `` Technical Support Document for HWC MACT Standards, Volume V: Emission Estimates and Engineering Costs,'' September, 2005, Section 3.

57 We note that as a practical matter, however, the same MACT standards apply to both major and area source HCl production furnaces. This is because major sources are subject to the following standards: CO/ HC, DRE, and total chlorine. Because the CO/ HC and DRE standards are surrogates to control dioxin/ furan, and the total chlorine standard is a surrogate to control metal HAP, area sources are subject to the same standards that address dioxin/ furan, polycyclic organic matter, polychlorinated biphenyls, and mercury. There is an enforcement difference between the requirements, however. For area sources, an exceedance of the total chlorine standard ( or failure to ensure that compliance is maintained) relates to control of mercury only while for a major source, the same failure relates to control of mercury, other metal HAP, and HCl and chlorine. sources. The emission standard compliance burden for liquid fuel boilers that have the potential to emit only low levels of mercury, dioxin/ furan, and polycyclic organic matter is minimal. For example, sources that emit low levels of mercury because their feedstreams have low levels of mercury can elect to comply with the mercury emission standard by documenting that the mercury in feedstreams will not exceed the standard assuming zero removal by emission control equipment. We note that 75% of the liquid fuel boilers in our data base, and the two boilers cited by commenters, do not have emission control devices. The compliance burden for the major source standards for dioxin/ furan and for the surrogates to control other polycyclic organic matter   carbon monoxide/ hydrocarbons and destruction and removal efficiency ( DRE) should also be minimal for area source liquid fuel boilers. The dioxin/ furan standard applicable to the 90% of liquid fuel boilers with wet or no air pollution control equipment is compliance with the carbon monoxide/ hydrocarbon standard and the DRE standard. Liquid fuel boilers already comply with these same standards under RCRA. The surrogate standards to control other polycyclic organic matter are also the carbon monoxide/ hydrocarbon and DRE standards. Finally, we note that the DRE requirement under Subpart EEE is less burdensome than the DRE requirement under RCRA. Under Subpart EEE, a source needs to conduct a one time only DRE test, provided that design and operation does not change in a manner than could adversely affect DRE. Under RCRA, the DRE test must be conducted each time the RCRA permit is renewed. The incremental compliance burden associated with the other Subpart EEE major source requirements, such as the operations and maintenance plan, the startup, shutdown, and malfunction plan, operator training, and the automatic waste feed cutoff system should also be minimal for liquid fuel boilers without an emission control device. In addition, most of the requirements are either identical to or very similar to requirements under RCRA with which these area sources are already complying. 58 B. Boilers Eligible for the RCRA Low Risk Waste Exemption Comment: Several commenters state that EPA should exempt those boilers that qualify as Low Risk Waste Exemption ( LRWE) burners under the RCRA Boiler and Industrial Furnace Rule at § 266.109 from the MACT particulate matter and destruction and removal efficiency ( DRE) standards because EPA has not: ( 1) made a demonstration that the data used to provide the exemption to low risk burners under RCRA is no longer valid; or ( 2) established in the affirmative that regulating these units will provide any benefit to human, health and the environment. Commenters believe that regulating LRWE units under Subpart EEE is unnecessary and inconsistent with RCRA subtitle C and more importantly, appears to be controlling LRWE units for control's sake. Commenters also state that EPA has not properly addressed the requirements of CAA section 112( n)( 7) regarding the inconsistency between the requirements for Low Risk Waste Exempt ( LRWE) units under RCRA and those of Subpart EEE. The purported purpose of 58 RCRA, 40 CFR Part 264 requirements that are similar to MACT requirements include: the general inspection requirements and personnel training requirements of Subpart B; the preparedness and prevention requirements of Subpart C, including design and operation of facility, testing and maintenance of equipment, and access to communications or alarm system; the contingency plan and emergency procedures requirements of Subpart D; and the operating requirements and monitoring and inspection requirements of Subpart O. section 112( n)( 7) is to allow EPA to avoid imposing additional emission limitations on a source category subcategory when such limitations would be unnecessary and duplicative. In addition, commenters state that the costs associated with this MACT are much more than improved feed control or better back end control. This proposed rule also requires substantial dollar investment in improved data acquisition, computer controls and recordkeeping systems, performance testing, training, development of plans, and other regulatory requirements. Response: Boilers and hydrochloric acid production furnaces that currently qualify for the RCRA § 266.109 low risk waste exemption are not exempt from Subpart EEE under the final rule. The Administrator does not have the authority under CAA section 112( d) to exempt sources that comply with RCRA § 266.109. Indeed, there is no necessary connection between the two provisions, since one is technology based and the other is risk based. CAA section 112( d)( 2) requires the Administrator to establish technology based emission standards, standards that require the maximum degree of reduction in emissions that is deemed achievable. Although section 112( d)( 4) gives the Administrator the authority to establish health based emission standards in lieu of the MACT standards for pollutants for which a health threshold has been established, we cannot use that authority to develop health based standards for sources that comply with RCRA § 266.109 because those sources emit HAP for which a health threshold has not been established. The final rule complies fully with CAA section 112( n)( 7) by coordinating applicability of the RCRA and CAA requirements and precluding dual requirements. For example, RCRA requirements that are duplicative of MACT requirements will be removed from the RCRA operating permit when the permitting authority issues a certification of compliance after the source submits a Notification of Compliance. We also note that the MACT standards are tailored to impose minimal burden on sources that have low emissions of HAP. The particulate matter emission standard and associated testing can be waived ( similar to the § 266.109 exemption) for boilers that elect to document that emissions of total metal HAP do not exceed the limits provided by § 63.1206( b)( 14). Hydrochloric acid production furnaces are not subject to a particulate matter emission standard. The compliance burden with the destruction and removal efficiency ( DRE) standard is also minimal given that it is a one time test, provided that the source does not change its design or operation in a manner that would adversely affect DRE. In addition, the compliance burden for sources with low levels of metals in their feedstreams is minimal. Sources can document compliance with the metals emission standards by assuming all metals in the feed are emitted ( i. e., by assuming zero system removal efficiency). Under this procedure, boilers burning relatively clean wastes are not required to conduct a performance test to document compliance with the metals emission standards. Further, we note that the MACT standard to control organic HAP emissions other than dioxin/ furan is the same as the RCRA standard   demonstrating good combustion conditions by complying with a carbon monoxide standard of 100 ppmv. Finally, we note that the ancillary requirements under MACT ( e. g., personnel training; operating and maintenance plan; startup, shutdown, and malfunction plan) should not pose substantially higher costs than similar requirements under RCRA. See response to comment in Section A above. To the extent that compliance costs increase, we have accounted for those costs in our estimates of the cost of the final rule. 59 C. Mobile Incinerators Comment: A mobile incinerator used as a directly fired thermal desorption unit at a Superfund remediation site should not be an affected source under this rule. Response: EPA is not determining or changing the applicability of any hazardous waste burning unit under today's rule. A combustion unit that treats hazardous waste and meets the definition of incinerator at 40 CFR 260.10 is an affected source under this rule. 40 CFR part 63 also defines a source as any building, structure, facility, or installation which emits or may emit any air pollutant. A mobile incinerator at a remediation site meets this definition. Comment: One commenter states that a subcategory with different standards must be created for mobile incinerators, or the standards for incinerators must be calculated using actual emissions data from mobile units. Response: EPA did not have any emissions data from mobile incinerators in the database for the proposed rule. That data base was developed over many years with ample opportunity for public comment. We developed a data base for incinerators to support the 1996 proposed rule ( 61 FR 17358) and noticed that data base for public comment on January 7, 1997 ( 64 FR 52828). We updated that data base in July 2002, and noticed the revised data base for public comment ( 67 FR 44452). We used that revised data base to support the proposed rule. We did not receive comments providing data for mobile incinerators as a result of either public notice. One commenter on the proposed rule provided a summary of emissions data from one test at a mobile incinerator. The commenter suggested that the data support its view that its mobile incinerator is unique and that EPA should consider subcategorizing incinerators according to mobile incinerators versus other incinerators. We analyzed these data and conclude that the final standards are readily achievable by this source. Moreover, as explained elsewhere, EPA's approach to assess the need for subcategorization is to apply a statistical test to determine whether the emissions data are statistically different from the remaining group. Given that owners and operators of mobile incinerators have not provided emissions data prior to proposal, and that the commenter provides summarized data for only one mobile incinerator ( which also indicate that the source can achieve the emission standards in the final rule); we are not compelled to gather additional information, particularly given our time constraints to promulgate the final rule under a court ordered deadline. Comment: In support of subcategorizing mobile incinerators, commenters state that mobile thermal treatment systems are substantially different from hazardous waste incinerators. They are much smaller in size, firing capacity rate, refractory lining, and operating temperatures. Most of them treat contaminated soil so have very high particulate feedrate loading with high ash content, rapid kiln rotation rate, and counter current flow design like cement kilns. This results in high particulate matter emissions. They operate only for a short duration at a site ( usually less than 6 months), and have no flexibility with regard to their waste feed.

59 USEPA `` Technical Support Document for HWC MACT Standards, Volume V: Emission Estimates and Engineering Costs,'' September, 2005. Response: We recognize that there is variability between various sources' with regard to size, capacity, operating temperatures etc., and so we applied a statistical test to assess the need of subcategorization, as has been discussed above. The emissions data provided by the commenter also indicate the source can achieve the final standards. The soil entrained in desorber off gases of mobile incinerators has a relatively large particle size, and is very easy to capture with conventional particulate control systems ( such as a fabric filter) used by the incinerators. Comment: Since mobile incinerators are relocated from site to site, the new source standard should not apply based on the erection date of the mobile unit. Response: We are not changing the applicability of a new or reconstructed source designation in this rulemaking. The relocation issue is addressed in the definition of " construction" in 40 CFR Section 63.2, which states: " Construction does not include the removal of all equipment comprising an affected source from an existing location and the reinstallation of such equipment at a new location . . . ." ( emphasis added). Therefore, the relocation of an existing Subpart EEE affected source, such as a mobile incinerator, would not result in that mobile incinerator becoming a " new" source. Keep in mind also that the relocation exemption only applies to affected sources. If a mobile incinerator is relocated from an R& D facility ( where the unit is not an affected source per Table 1 to Section 63.1200) to a location where the mobile incinerator would become an affected source, the relocation exemption within the definition of " construction" would not apply and the mobile incinerator would be a " new" source. Also, with regard to leased sources, the owner/ operator of the facility is responsible for all affected sources operating at his/ her facility regardless of whether the sources are owned or leased. The owner or operator should obtain from the leasing company all relevant information pertaining to the affected source in order to be able to demonstrate that the affected source is operating in compliance with the appropriate standards.

III. Floor Approaches In this section we discuss comments addressing methodologies used in this rule for determining MACT floors. We address comments relating both to general, overarching issues and to the specific methodologies used in the rule. Our most important point is that the methodologies EPA selected reasonably estimate the performance of the best performing sources by best accounting for these sources' total variability.

A. Variability 1. Authority to Consider Emissions Variability Comment: Many commenters concur with our approach to account for emissions variability while several commenters believe that our approach does not adequately account for emissions variability. See discussions on separate topics below. One commenter, however, states that use of variability factors ( however derived) is inherently unlawful and arbitrary and capricious. The commenter notes that, because floors for existing sources must reflect the " average" emission level achieved by the relevant best performing sources, they cannot reflect any worse levels of performance from the best performers. Indeed, the argument is that the Clean Air Act already accounts for variability by requiring EPA to base existing source floors on the average emission level achieved by the best performing sources. The commenter continues by stating that EPA has added variability factors both to each individual source's performance and to the collective performance of the alleged best performers, in each case purporting to find an emission level that the individual or group would meet ninety nine times out of 100 future emission tests. Thus, EPA ignores sources' measured performance in favor of the theoretical worst performance that might ever be expected from them. By looking to the best performers' worst performance rather than their average performance, EPA would set weaker floors than the Clean Air Act allows. In addition, the commenter notes that EPA's approach to account for emissions variability is arbitrary and capricious because EPA never explains why it chose the 99th percentile for its variability adjustments rather than some other percentile. Finally, the commenter notes that EPA appears to indicate that its variability analysis would either be applied to variation between sources or would affect EPA's statistical analysis of the variation between sources. The commenter states that any attempt by EPA to add a variability factor to adjust for intersource variability is unlawful and arbitrary and capricious. Response: Our response explains our approach to estimating best performing sources' variability and addresses the following issues: ( 1) considering the variability in each source's performance is necessary to identify the best performing sources and their level of performance ( 2) EPA reasonably considered variability in ranking sources to identify the best performers and in considering the range of best performing sources' performance over time to identify an emission level that the average of those sources can achieve; ( 3) considering variability at the 99th percentile level is reasonable; ( 4) considering intersource variability by pooling run to run variability is appropriate; and ( 5) compliance test conditions do not fully reflect all of best performing sources' performance variability. a. Variability Must Be Considered. Variability in each source's performance must be considered at the outset in identifying the best performing sources. This is simply another way of saying that best performers are those that perform best over time ( i. e. day in, dayout a reasonable approach. This approach not only reasonably reflects the statutory language, but also furthers the ultimate objective of section 112 which is to reduce risk from exposure to HAP. Since most of the risk from exposure to emissions from this source category is associated with chronic exposure to HAP ( see Part 1 section VI above), assessing a source's performance over time by accounting for variability is reasonable and appropriate. For similar reasons, variability must be considered in ascertaining these sources' level of performance. Floors for existing sources must reflect " the average emission limitation achieved by the best performing 12 percent" of sources, and for new sources, must reflect " the emission control that is achieved in practice by the best controlled source." Section 112 ( d) ( 3). EPA construes these requirements as meaning achievable over time, since sources are required to achieve the standards at all times. This interpretation has strong support in the case law. See Sierra Club v. EPA, 167 F. 3d 658, 665 ( D. C. Cir. 1999), stating that " EPA would be justified in setting the floors at a level that is a reasonable estimate of the performance of the ` best controlled similar unit' under the worst reasonably foreseeable circumstances. It is reasonable to suppose that if an emissions standard is as stringent as ` the emissions control that is achieved in practice' by a particular unit, then that particular unit will not violate the standard. This only results if ` achieved in practice' is interpreted to mean ` achieved under the worst foreseeable circumstances'; see also National Lime Ass'n v. EPA, 627 F. 2d 416, 431 n. 46 ( D. C. Cir. 1980) ( where a statute requires that a standard be ` achievable,' it must be achievable under " the most adverse circumstances which can reasonably be expected to recur"); The court has further indicated that EPA is to account for variability in assessing sources' performance for purposes of establishing floors, and stated that this assessment may require EPA to make reasonable estimates of performance of best performing sources. CKRC, 255 F. 3d at 865 66; Mossville Environmental Action Now v. EPA, 370 F. 3d 1232, 1242 ( D. C. Cir. 2004)( maximum daily variability must be accounted for when establishing MACT floors). 60 Indeed, EPA's error in CKRC was not in estimating best performing sources' variability, but in using an unreasonable means of doing so. CKRC, 255 F. 3d at 866; Mossville, 370 F. 3d at 1241. Since the emission standards in today's rule must be met at all times, the standards need to account for performance variability that could occur on any single day of these sources' operation ( assuming proper design and operation). See Mossville, 370 F. 3d at 1242 ( upholding MACT floor because it was established at a level that took into account sources' long term performance, not just performance on individual days). Moreover, since EPA's database consists of single data points ( because there are no continuous emission monitors for HAPs in stack emissions), EPA must of necessity estimate long term performance, including daily maximum performance, from this limited set of short term data. b. EPA Reasonably Considered Variability in Ranking Sources to Identify the Best Performers and in Considering the Range of Best Performing Sources' Performance Over Time to Identify an Emission Level that the Average of Those Sources Can Achieve. ( 1) Selecting Best Performing Sources. Each of the floor methodologies used in the rule considers various factors in ranking which sources are the best performing. For each methodology, we therefore consider the quantifiable variability of the ranking factors in determining which are the best performing sources. 69 FR at 21230 31. Specifically, we assess run to run variability ( normally the only type of variability which we can quantify) of the factors used under each methodology to rank best performers. Where SRE/ Feed is the ranking methodology, we thus assess run to run variability of hazardous waste HAP feedrate and of system removal efficiency. Where ranking is based on sources' emissions ( the straight emissions methodology), we assess the run to run variability of emission levels. Where we use the air pollution control device methodology for ranking, we assess the run torun variability of emissions of the lowest emitting sources ( as we do for straight emissions) using the best air pollution control devices. For hydrochloric acid production furnaces, we assess the run to run variability of total chlorine system removal efficiency. Id. 61 To account for run to run variability in these ranking factors, we rank sources by the 99th percentile upper prediction limit ( UPL99). The UPL99 is an estimate of the value that the source would achieve in 99 of 100 future tests if it could replicate the operating conditions of the compliance test. Id. at 21231.

60 See also Chemical Manufacturers Ass'n v. EPA, 870 F. 2d 177, 228 ( 5th Cir. 1989) (" The same plant using the same treatment method to remove the same toxic does not always achieve the same result. Tests conducted one day may show a different concentration of the same toxic than are shown by the same test the next day. This variability may be due to the inherent inaccuracy of analytical testing, i. e. ` analytical variability,' or to routine fluctuations in a plant's treatment performance.") 61 These ranking methodologies are discussed later in this section of the preamble, and in USEPA, " Technical Support Document for HWC MACT Standards, Volume III: Selection of MACT Standards," September 2005, Section 7. ( 2). Assessing the Best Performers' Level of Performance Over Time. Once we identify the best performing sources, we need to consider their emissions variability to establish a floor level that the average of the best performing sources can achieve day in, day out. There are two components of emissions variability that must be considered: run torun variability and test to test variability. Run to run emissions variability encompasses variability in individual runs comprising the compliance tests, and includes uncertainties in correlation of monitoring parameters and emissions, and imprecision of stack test methods and laboratory analyses. See 69 FR at 21232.62 Test to test emissions variability is the variability that exists between multiple compliance tests conducted at different times and includes the variability in control device collection efficiency caused by testing at different points in the maintenance cycle of the emission control device63, and the variability caused by other uncontrollable factors such as using a different stack testing crew or different analytical laboratory, and by different weather conditions ( e. g., ambient moisture and temperature) that may affect measurements. We are able to quantify run to run variability. We do so by applying a 99th percentile modified upper prediction limit to the averaged emissions of the best performing sources. Id. at 21233 and Technical Support Document Volume III section 7.2. The modified upper prediction limit accounts for run to run variability of the best performers by pooling their run variance ( i. e., within test condition variability). 64 See Chemical Manufacturer's Ass'n v EPA, 870 F. 2d 177, 228 ( 5th Cir. 1989) ( upholding use of a variability factor derived, as here, by pooling the performance variability of the best performing plants). Using this approach, we ensure that the average of the best performing sources will be able to achieve the floor in 99 of 100 future performance tests, assuming these best performing sources could replicate their performance when attempting to operate under identical conditions to those used for the compliance test establishing the source as best performing. As just noted, we call this value the modified UPL 99. The only instance in which we are able to quantify test to test variability ( as noted above, the other significant component of total operating variability) is for fabric filters ( baghouses) when used to control emissions of particulate matter. The modified UPL 99 in these instances reflects not only run to run variability, but test to test variability as well. That total variability is expressed by the Universal Variability Factor which is derived from analyzing long term variability in particulate matter emissions for best performing sources across all of the source categories sources that are equipped with fabric filters. 69 FR at 21233. See also the discussion below in Section III. A. 2.