18.6.2 Hazard index Comment: Several commenters ( IV D 73, IV D 75, IV D 122, and IV D 123) stated that HQ for chemical mixes should not be summed to determine the HI unless the primary effects are on the same organ by the same mechanism; otherwise the risk will be overestimated. Commenters IV D 122 and IV D 123 stated that, according to the National Research Council and the Presidential/ Congressional Commission on Risk Assessment and Risk Management, additivity at low doses is more likely to overestimate than to underestimate total risk. ( Complex Mixtures ( NRC 1988), 1997 Presidential/ Congressional Commission on Risk Assessment and Risk Management in Regulatory Decision Making). Response: Our recommended approach for assessing risks from exposure to a mixture of pollutants is to utilize a dose response assessment developed for that mixture. 3 There are few mixtures ( e. g., coke oven emissions), however, for which such assessments are available. When mixture specific dose response assessments are not available, a component by component approach is recommended. The method for component data depends on a judgement of toxicologic similarity among components. The specific term toxicologic similarity represents a general knowledge about the action of a chemical or a mixture and can be expressed in broad terms such as at the target organ level in the body. In our guidance, assumptions about toxicologic similarity are made in order to choose among risk assessment methods. In general, we assume a similar mode of action across mixtures or mixture components and, in some cases, this requirement may be relaxed to require that these chemicals act only on the same target organ. 3 The primary method for component based risk assessment of toxicologically similar chemicals is the HI, which is derived from dose addition. In our guidance, dose addition is interpreted as simple similar action, where the component chemicals act as if they are dilutions or concentrations of each other differing only in relative toxicity. Dose additivity may not hold for all toxic effects. Further, the relative toxic potency between chemicals may differ from different types of toxicity or toxicity by different routes. To reflect these differences, the HI is then usually developed for each exposure route of interest, and for a single specific toxic effect of toxicity to a single target organ. A mixture may then be assessed by several HI, each representing one route and one toxic effect or target organ. 3 While it may be preferable to focus on the addition of HAP HQ that involve the same mechanism or mode of action, that level of information is not generally available. Pending the availability of such data for the HAP components of the mixture being assessed, the method employed is to aggregate HAP HQ by target organ to generate a TOSHI. Affected sources attempting to utilize the health based compliance alternative for HCl will calculate an HI for HCl and Cl 2. Respiratory toxicity is the critical effect for both of these pollutants. Affected sources attempting to utilize the health based compliance alternative for Mn will calculate an HQ because Mn is the only HAP considered for this option.

Comment: Commenter IV D 61 stated that a HI of 1 provides for the statutory mandate of an ample margin of safety. A default HI of 1 is appropriate due to a variety of factors, including the statutory mandate to focus on emissions from title III facilities alone, the extensive 251 layers of conservatism built into both the derivation of the RfC and the pertinent exposure modeling, and the limited exposures to these HAP through other pathways. With regard to threshold HAP, EPA must protect human health with an " ample margin of safety," a term which is not explicitly defined in the CAA. The D. C. Circuit Court of Appeals articulated the purpose of the ample margin of safety determination as obtaining a " reasonable degree of protection" in light of scientific uncertainties and information gaps. NRDC v. EPA, 824 F. 2D 1126, 1152 53 ( D. C. Cir. 1987). The court's interpretation was incorporated verbatim in the 1990 CAAA, and the Supreme Court has consistently held that " when administrative and judicial interpretations have settled the meaning of an existing statutory provision, repetition of the same language in a new statute indicates, as a general matter, the intent to incorporate its administrative and judicial interpretations as well." Bragdon v. Abbott, 524 U. S. 634, 645 ( 1998). The commenter cited several reasons why the existing RfCs and similar inhalation health benchmarks already incorporate sufficient uncertainty factors to fulfill or exceed the ample margin of safety requirements, and believes that because the benchmarks are abundantly protective, an HI of 1 ( or more) should serve as the benchmark for risk based compliance options in the Boiler MACT. Commenters IV D 122 and IV D 123 stated that the Final Report of the Presidential/ Congressional Commission on Risk Assessment and Risk Management supports that HI of 1 provides an ample margin of safety. This Commission was mandated by the 1990 CAA Amendments to provide guidance to the EPA for the implementation of the risk aspects of these Amendments. Specifically, the Commission recommended that EPA should, on the basis of screening assessments of source categories, do further risk assessment and analysis of categories where the noncancer HI exceeds 10.0. The Commission also recommended that, where more detailed risk assessments yield noncancer hazard indices less than 1.0, no further action should be required. Commenter IV D 73 stated that all risk related provisions of § 112 should be guided by the purpose of the ample margin of safety determination  namely, to account for uncertainty in the underlying health value. A HI equal to or greater than 1 should account for uncertainty and provide an ample margin [ of] safety. Commenters IV D 73 and IV D 166 stated that The Report of the Commission on Risk Assessment and Risk Management provides further guidance and supports the commenters' contention that a HI equal to or greater than 1 should provide an ample margin of safety for a threshold HAP. Commenter IV D 49 submitted that a HI of 1 using the RfC ( or similarly derived health benchmark) is the appropriate risk based benchmark for threshold HAP. The commenter noted that EPA's mandate under the CAA's " ample margin of safety" language is to provide a reasonable amount of protection in light of scientific uncertainties and believes that the RfC contains multiple layers of conservatism to account for scientific uncertainty and is amply protective of human health. The commenter stated that source demonstrations should be based on EPA approved modeling techniques, which provide further layers of conservatism. Commenter IV D 78 suggested that HI of 1 be used to determine i[ f] a source should be exempt from MACT. The HI of 1 is defensible because the RfCs used to determine the HI are conservative. The RfCs contain uncertainty factors and assume lifetime exposure to the pollutant, although no person would spend a lifetime at maximum exposure. Commenters IV D 75 stated that an HI of 10 or less should be considered presumptively safe, considering the inherent safety factors in HI. Commenter IV D 75 agreed with other industry commenters that an HQ of one should be considered an acceptable level and sources 252 should not be required to go below that amount to an arbitrary level such as 0.2. Commenter IV D 05 stated that the HI is useful in evaluating site specific impacts, but choosing a generic HI ( some multiple of 1) for application to a wide range of sites is inappropriate. The commenter added that selection of an arbitrary multiple of 1 is not science, does not conform with CAA § 112( d)( 4) and does not protect public health. The commenter added that using background concentrations from NATA and a HI of 1 is inappropriate because NATA information includes warnings that the information is useful for large scale planning purposes and not for local area assessment. Commenter IV D 05 stated that the selection of a 0.2 HI as a rough screening tool seems reasonable, although it is unsupported by any analysis. The commenter added that if a default HI is used, EPA should include a provision that would disallow the use to exclude a facility from MACT, now or in the future, if better background information is available that suggests that the default does not protect public health. The commenter, however, believes that the interpretation that includes the use of such a default to allow exemptions for individual sources is not supported by the CAA, and the expansion of the interpretation to include non threshold pollutants is in direct conflict with § 112( d)( 4) of the CAA. Commenter IV D 14 evaluated the four potential options that EPA proposed to ensure that a risk analysis under § 112( d)( 4) considers the total ambient air concentrations of all the HAP to which the public is exposed. Option 1, which requires that the HI for all pollutants be no greater than 1, does not consider additional sources or background and is unacceptable. Option 3, which uses existing data such as the NATA to determine background and requires that the HI be no greater than 1, is also unacceptable. EPA has clearly stated at public meetings that the NATA is not to be used to make regulatory decisions. The NATA relies on data submitted to EPA voluntarily and has been reported to consistently underestimate measured concentrations. Until EPA requires that HAP inventories be submitted as proposed in the Consolidated Emissions Reporting Rule ( CERR), and the NATA conducts refined modeling around stationary sources, the NATA should not be considered for estimating background concentrations. Option 4, which allows individual facilities to monitoring the HAP backgrounds for use in their own analysis, will require oversight and evaluation by the States to ensure proper site selections and analytical methods and should not be considered. The commenters believe Option 2, which requires that the HI be no greater than 0.2, would be the only viable option at this time using a conservative risk screening analysis. However, the commenters did not endorse using any of the proposed threshold limit applicability methods to exempt process sources from NESHAP requirements. With regard to the HI options, commenter IV D 10 believes the first option ( HI of 1) should be allowed for facilities located in rural areas, while using HI of 0.2 may be appropriate when multiple facilities are present. The commenter submitted that the determination of the base case percentage should be based on a refined typical ( not arbitrary) scenario, and subject to modification for specific cases by showing how they differ from the base case. Commenter IV D 10 would like to see more details on the third and fourth options. Response: Affected sources attempting to utilize the health based compliance alternative for HCl must measure emissions of HCl and Cl 2 and compare the HI to 1.0, as described in Appendix A to subpart DDDDD. Affected sources attempting to utilize the health based compliance alternative for Mn must measure emissions of Mn and compare the HQ to 1.0, as described in Appendix A to subpart DDDDD. We consider that a HI ( or HQ) limit of 1.0 provides an ample margin of safety for protecting public health under CAA § 112( d)( 4) for these health based compliance alternatives. 253 The RfCs that are used to calculate the HI ( or HQ) are developed to protect sensitive subgroups and to account for scientific uncertainties, ensuring that the use of a HI limit of 1.0 provides an ample margin of safety. The TOSHI approach required for HCl and Cl 2 assumes additivity in mixtures of chemicals that target the same organ system. We conclude that a HI ( or HQ) limit of 1.0 is appropriate for the § 112( d)( 4) demonstrations for the boiler and process heater source category that are described in the final rule. In future risk based actions for this and other source categories ( e. g., residual risk rulemakings under CAA § 112( f)), we may identify factors on a case by case basis that would lead us to conclude that HI limits other than 1.0 would be more appropriate for those other actions. The look up tables included in Appendix A to subpart DDDDD of 40 CFR part 63 were developed based on a HI of 1.0 for HCl and Cl 2 and a HQ of 1.0 for Mn. For site specific chronic inhalation risk assessments, affected sources are required to ensure that their HI ( HCl and Cl 2) or HQ ( Mn) are less than or equal to a value of 1.0. Several commenters presumed the use of CAA § 112( c)( 9) for the rule as proposed. However, we are using CAA § 112( d)( 4) and not § 112( c)( 9). We are not considering background emissions in the health based compliance alternatives for HCl and/ or Mn. Rather, as we indicated in the Residual Risk Report to Congress, we intend to assess facility wide emissions of HAP in future residual risk actions under § 112( f)( 2), as appropriate and to the extent it is reasonable and appropriate to do so. See also, 54 Fed. Reg. at 38,059 ( Sept. 14, 1989) ( benzene NESHAP).

Comment: Commenter IV D 73 stated that adoption of the Drinking Water Program's concept of a HI of 0.2 is not supportable. The commenter added that, at a minimum, before EPA could import the drinking water policy into air programs, the agency would need to evaluate the available scientific data   for the HAP of concern in each individual rulemaking   to determine whether the data justify a conclusion that 80 percent of the exposures to those pollutants come from sources outside the source category. Response: Affected sources attempting to comply with the health based alternatives in the final rule will compare their HI ( HCl and Cl 2) and/ or HQ ( Mn) values to 1.0.

Comment: Commenter IV D 154 stated that in the case of RICE and boilers/ process heaters, which emit acrolein, there appears to be no reasonable limit ( that would allow sufficient protection between the contribution of a potentially affected source and the existing background concentrations of non carcinogens) since exposure to acrolein is predicted to be high almost everywhere in the country ( based on NATA). Uniformly applied NESHAP are necessary to move this country toward lower exposures to irritants like acrolein. Response: The EPA performed an assessment of respiratory HAP, CNS HAP, and other acid gas HAP emitted from industrial boilers and process heaters and determined that only HCl, Cl 2, and Mn contribute significantly to risk. Therefore, these are the only HAP relevant for the health based compliance alternatives in the final rule. Measurement of acrolein emissions are not included.

18.6.3 Short term health effects Comment: Commenter IV D 14 stated that the proposal did not [ address] threshold limitation guideline values for short term exposure. Commenter IV D 14 stated that HCl has a 254 short term guideline value established by CalEPA. Commenter IV D 14 stated that HCl is capable of eliciting strong upper respiratory responses and short term evaluation should be part of any health risk assessment undertaken. Response: We agree with the need to consider acute effects. The EPA conducted a screening assessment and determined that acute exposures to HCl, as well as other respiratory and acid gas HAP, emitted from boilers and process heaters are unlikely to adversely affect human health. Therefore, affected sources attempting to comply with the health based option for HCl will not be required to conduct an acute assessment.

18.7 RISK ASSESSMENT FRAMEWORK ISSUES: ESTIMATING RISKS TO ECOLOGICAL RECEPTORS Comment: Commenters IV D 60, IV D 61, IV D 62, IV D 119, IV D 122, and IV D 123 submitted that the RfC for HCl is protective of environmental effects. The commenters noted that in both of EPA's prior risk based determinations not to regulate HCl ( pulp and paper chemical recovery combustion MACT and chlorine production MACT), EPA concluded that a human health based applicability cutoff would also protect other environmental values. The commenters believe EPA has no reason to reach a different conclusion in the Boiler MACT context. Commenters IV D 26, IV D 104, and IV D 150 stated that scientific literature suggests that there are not likely to be any significant and widespread adverse environmental effects to wildlife, aquatic life, and other natural resources attributable to Mn. Commenters IV D 17 and IV D 118 stated that the proposal does not address ecological risk that may result from uncontrolled HAP emissions, especially in those areas with sensitive habitats but few people nearby to be exposed. Commenter IV D 148 stated that EPA provided inadequate discussion of how environmental risks will be evaluated. The commenter added that the CAA requires that EPA consider the environment as well as public health, and at a minimum, a facility would be required to conduct an assessment based on EPA's Guidelines for Ecosystem Assessment ( 1998). The commenter referred EPA to Appendix A of " Generic Assessment for Endpoints for Ecological Risk Assessment" for a detailed discussion on the legal basis from " such statutes as the CAA... that require EPA to consider and protect organism level attributes or various taxa including fish, birds, and plants and more generally, animals, wildlife, aquatic life, and living things." Response: An ecological assessment is normally required under § 112( d)( 4), ( c)( 9), and ( f)( 2) of the CAA regarding the presence or absence of " adverse environmental effects" as that term is defined in CAA § 112( a)( 7). To identify potential multimedia and/ or environmental concerns, the EPA has identified HAP with significant potential to persist in the environment and to bioaccumulate. However, this list does not include HCl, Cl 2, or Mn which are the only HAP relevant for the health based compliance alternatives under the final rule. Additionally, a screening level analysis conducted by the EPA indicates that acute impacts of these HAP from boiler facilities are highly unlikely. For these reasons we do not believe that emissions of HCl, Cl 2 or Mn from boiler facilities will pose a significant risk to the environment, and facilities attempting to comply with the risk based alternatives for these HAP are not required to perform an ecological assessment. 255 18.8 RISK ASSESSMENT FRAMEWORK ISSUES: TIERED APPROACH AND RISK ASSESSMENT GUIDANCE 18.8.1 Tiered approach Comment: Multiple commenters ( IV D 05, IV D 10, IV D 14, IV D 24, IV D 26, IVD 61, IV D 72, IV D 73, IV D 75, IV D 104, IV D 146, IV D 150, IV D 166, and IV D 186) commented on the tiered modeling approach. Several commenters ( IV D 10, IV D 26, IV D 72, IV D 73, IV D 75, IV D 104, IV D 146, IV D 150, IV D 166, and IV D 186) support EPA's proposed tiered modeling approach, which begins with simple " look up tables" and progresses to more refined facility specific risk assessments. Commenter IV D 05 stated that the State of Wisconsin uses a tiered approach that first allows sources to demonstrate compliance if their potential emissions, stack height, and exhaust direction are within the ranges provided in conservative look up tables. The second tier allows affected sources to provide site specific modeling to demonstrate compliance with ambient air standards at the property line. In general, the tiered approach has worked well in Wisconsin. Commenter IV D 75 added that EPA should be flexible in accepting evolving improvements in exposure assessment and risk modeling, and should take into account the inherent strengths and weaknesses of the types of modeling used. Commenters IV D 73 and IV D 166 stated that an initial simplified tier of risk assessment, such as look up table, nomograph, or equivalent, should be embedded in individual rulemakings. The commenters added that a guidance document should address two additional tiers of assessment: a conservative screening approach, and a flexible refined approach. Commenter IV D 73 stated that a risk assessment guidance document should not attempt to address policy and regulatory decisions. Rather, regulatory goals and policies should be put forth within individual notice and rulemakings. Appropriate risk assessment endpoints of concern will also be established within these rulemakings. Commenter IV D 73 stated that rulemakings that use source conducted risk assessment should appropriately focus the initial scope of the assessment on the HAP, sources, and other parameters of concern through applicability criteria specified with the individual rulemakings. Commenter IV D 73 added that refined risk assessments ( 3rd tier) should allow for more accurate estimates of maximum individual risk, and could accomplish this through: ( 1) modeling ambient exposures to an actual human receptor location; ( 2) use of exposure factors or models; ( 3) use of realistic exposure assumptions based on site specific data ( residential tenure, etc.); and, ( 4) use of probabilistic analysis of uncertainty and variability. Commenter IV D 61 believes that a stepped risk based compliance option would be most effective and efficient in achieving the goals of the Boiler MACT. As an initial threshold matter, the commenter believes that sources operating within certain fueling limitations should be exempted from the requirements of the final rule. HAP content in fuel is one of the most significant determinants to HAP emissions, and, as a result, sources that only operate on low HAP fuel would never be expected to exceed any of the MACT limits in the proposed rule. To demonstrate compliance, sources would pick their worst case fuel and demonstrate that uncontrolled emissions from that fuel ( assuming all HAP in the fuel is emitted) do not exceed the limits. The second step, for affected sources that do not qualify based on fuel, a simple screening model, such as EPA's Screen III, could be used to demonstrate that HAP emissions are below the health benchmark. Additional steps could require the use of more sophisticated models. 256 Commenter IV D 24 suggested that EPA should establish automatic subcategory delisting criteria where a facility that meets the criteria can apply for automatic delisting. The commenter further suggested that such criteria would be based on fuel type and usage as well as control efficiency, if any were used. On the other hand, Commenter IV D 14 stated that if EPA decides to pursue an up front risk analysis approach, it should not be a tiered approach. The development of generic risk screening approach under the § 112( d)( 4) framework will need to be conservative, and the use of a ( non tiered) conservative approach would represent the least cost to the regulated community and would be the least time consuming for States reviewing the facility's application. Response: We discussed a tiered analytical approach in the preamble to the proposed rule, beginning with relatively simple look up tables and followed by increasingly more site specific but more resource intensive tiers of analysis, with each tier being more refined and less conservative. In the final rule, we are adopting a somewhat different approach for meeting the requirements of CAA § 112( d)( 4). The basis for this approach stems from the general air toxics assessment approach presented in the Residual Risk Report to Congress, which was developed with full consideration of EPA risk assessment policy, guidance, and methodology. 2 Affected sources can demonstrate eligibility for the health based emission limits by using site specific emissions test data and look up tables that were developed using health protective input parameters. These look up tables are included in Appendix A of subpart DDDDD of 40 CFR part 63. Affected sources that cannot demonstrate eligibility based on the health protective screening assessment ( i. e., look up tables) may use more refined site specific risk assessments as described in Appendix A of subpart DDDDD of 40 CFR part 63 and in other analytical tools such as the " Air Toxics Risk Assessment Reference Library," ( which may be appropriate for specific sources). A more refined analysis requires more effort, but produces results that are less uncertain and less conservative ( i. e., less likely to overestimate risk). 2 For site specific modeling, we will consider assessments that, in conjunction with the criteria specified in Appendix A of subpart DDDDD of 40 CFR part 63, use risk methodology and modeling techniques other than that described in the EPA's " Air Toxics Risk Assessment Reference Library" provided they have undergone scientific peer review pertinent to their use in the submitted assessment. For more information on how site specific modeling can be performed, affected sources are referred to the EPA " Air Toxics Risk Assessment Reference Library," which describes possible approaches for conducting the site specific modeling. No automatic delisting criteria have been included in the final rule, as suggested by one commenter. No specific exemption based on fuel type has been included as part of the healthbased compliance alternatives. All affected sources with boilers and process heaters in the applicable large solid fuel fired subcategory have an opportunity to demonstrate that they can meet the health based compliance alternatives for HCl and Mn. Fuel analysis requirements related to continuous compliance demonstration are addressed elsewhere in this document. The § 112( d)( 4) authority used to provide the health based compliance alternatives for the HCl emission limit and Mn ( TSM) emission limit is discussed in section 18.2.

Comment: Commenters IV D 122 and IV D 123 described EPA's proposed tiered modeling approach and noted that, while most sources would use this modeling approach, they believe facilities should be allowed to use any EPA approved modeling technique to demonstrate that its emissions are below the applicable health benchmark. Commenters IV D 122 and IV D 257 123 believe that Tier I ( screening level analyses or look up tables) will be sufficient to make the low risk finding for HCl. Response: Appendix A of subpart DDDDD of 40 CFR part 63 describes the process by which affected sources can demonstrate that boilers and process heaters meet the health based compliance alternatives. Affected sources may demonstrate that boilers and process heaters in the large solid fuel fired subcategory meet the health based compliance alternatives using either ( 1) the " look up table" analysis described in Appendix A of subpart DDDDD of 40 CFR part 63 or ( 2) site specific modeling ( described in Appendix A of subpart DDDDD of 40 CFR part 63 and other analytical tools, which may be appropriate for a specific source, such as EPA's " Air Toxics Risk Assessment Reference Library"). Affected sources electing to conduct site specific modeling can use any scientifically defensible, transparent, and peer reviewed methodology they choose in conjunction with the criteria specified in Appendix A of subpart DDDDD of 40 CFR part 63. An example of how site specific modeling can be performed is described in the EPA " Air Toxics Risk Assessment Reference Library."

18.8.2 Risk assessment guidance Comment: Commenter IV D 148 stated that EPA's proposal for risk based exemptions effectively misinterprets not only the CAA but also the guidelines and science policies established by EPA to ensure adequate protection of public health and the environment. EPA proposes a disorganized and cursory approach to implement risk based exemptions, which falls far below the quality of risk analysis typically required by EPA across other EPA programs. The proposal does not adhere to EPA's established guidelines for characterizing human health and ecological risks. The proposal does not incorporate risk assessment guidelines for conducting multi pathway risk assessments. The proposal does not reference EPA guidelines for cumulative risk assessment that specifically require consideration of non inhalation pathways. The goals of EPA's March 1995 Risk Characterization Policy of transparency, clarity, consistency, and reasonableness in EPA risk assessments apply to risk assessment practices across the EPA. The inconsistencies between EPA's proposal to provide risk based exemptions in the MACT standard process and risk assessment guidelines undermine many regulatory programs throughout the EPA. ( The commenter listed numerous programs). Commenter IV D 148 also stated that the critical deficiency in the [ risk based] scheme reflects a fundamental misunderstanding of the use of public health and ecological risk assessments in the regulatory process. The commenter added that the hallmark of the federal risk assessment guidelines is a series of policy memos that require EPA programs to conduct risk assessments consistently across all federal environmental programs. The approaches outlined by AF& PA's white papers neglect to include risk characterization, which provides needed and appropriate information to decision makers. The approaches also do not incorporate the critical recommendation of the Commission of Risk Assessment and Risk Management to establish a framework for stakeholder based risk management decision making. These omissions in the proposals will prevent regulatory agencies from demonstrating to the public that public health and the environment are adequately protected. However, commenter IV D 123 stated that the proposal is consistent with EPA risk assessment guidelines and policies and they believe that NESCAUM's technical objections are without merit. Specifically the commenter stated that: ( 1) The proposal is not inconsistent with EPA's risk assessment guidelines and policies; and ( 2) The contemplated risk based applicability 258 criteria are not in conflict with the classification of carcinogens and non carcinogens. Response: We discussed a tiered analytical approach in the preamble to the proposed rule, beginning with relatively simple look up tables and followed by increasingly more site specific but more resource intensive tiers of analysis, with each tier being more refined. In the final rule, we are adopting a somewhat different approach for meeting the requirements of CAA § 112( d)( 4). The basis for this approach stems from the general air toxics assessment approach presented in the Residual Risk Report to Congress, which was developed with full consideration of EPA risk assessment policy, guidance, and methodology. 2 Affected sources can comply with a health based alternative for Mn and/ or HCl. EPA has identified those HAP with greatest potential to cause multimedia or environmental impacts. However, this list does not include HCl, Cl 2, or Mn which are the only HAP relevant for the health based compliance alternatives under the final rule. Therefore, affected sources attempting to comply with the health based alternative in the final rule are not required to perform a multipathway analysis. Additionally, a screening level analysis conducted by the EPA indicates that acute impacts of these HAP from boiler facilities are highly unlikely. For these reasons we do not believe that emissions of HCl, Cl 2 or Mn from boiler and process heater facilities will pose a significant risk to the environment, and affected sources attempting to comply with the risk based alternatives are not required to perform an ecological assessment. Because Mn, HCl and Cl 2 are threshold non carcinogenic pollutants, affected sources will only be required to assess non carcinogenic endpoints in their modeling.

Comment: Commenter IV D 184 stated that EPA should incorporate peer reviewed and validated scientific methods and use high quality data to assess risk. It is critical that any riskbased air toxics regulation be based on up to date science, including the use of accurate and current emissions data, health effects information, modeling techniques, and risk assessment methodologies. Response: Appendix A of subpart DDDDD of 40 CFR part 63 describes the process by which affected sources can demonstrate that boilers and process heaters meet the health based compliance alternatives. Affected sources can demonstrate eligibility for the health based emission limits by using site specific emissions test data and look up tables that were developed using health protective input parameters. These look up tables are included in Appendix A of subpart DDDDD of 40 CFR part 63. Affected sources that cannot demonstrate eligibility based on the health protective screening assessment ( i. e., look up tables) may use more refined sitespecific risk assessments as described in Appendix A of subpart DDDDD of 40 CFR part 63 and in other analytical tools such as the " Air Toxics Risk Assessment Reference Library," ( which may be appropriate for specific sources). Affected sources will be required to conduct emission testing for HCl, Cl 2, and Mn from the boiler and process heater source category.

Comment: Commenters IV D 73 and IV D 166 stated that any risk based approaches should be consistent with the policies in development for the residual risk rules. Commenters IVD 166 and IV D 73 stated that EPA should specify many of the procedures for facility specific risk assessments in guidelines rather than in the rules, because procedures set in rules could be seen as precedent setting and could impact the residual risk program. For example, the commenters believe that EPA should specify the threshold levels by which a source would be excluded from a rule, as well as any Tier 1 look up tables, in each individual rule. In contrast, the specifics for how sources should carry out Tier 2 and Tier 3 risk assessments should be left 259 flexible in guidelines now under development by EPA for the residual risk program. Commenters IV D 09, IV D 118, and IV D 154 stated that the tools needed to identify sources eligible for the risk based exemption would be the same tools necessary for a § 112( f) residual risk assessment. It is the commenters' understanding that these tools are not yet ready for general use. Commenter IV D 148 stated that the cancer risk guidelines are currently undergoing public review. Commenter IV D 14 has serious reservations with EPA's apparent attempt to conduct an ad hoc risk analysis for specific source categories by seeking comments on the specific elements to be included in the risk analysis and do not believe these rulemakings are an adequate forum to develop this risk analysis process. The commenters believe that any risk analysis conducted by the EPA must adhere to the risk assessment principles outlined in the Residual Risk Report to Congress. Response: We agree that the tools needed to identify sources eligible for health based compliance alternatives are the same tools necessary for a § 112( f) residual risk assessment; as stated in the Residual Risk Report to Congress, we intend to rely on the general methodology and process illustrated by the framework presented in that report in our risk assessment activities throughout the air toxics program. Appendix A of subpart DDDDD of 40 CFR part 63 describes the process by which affected sources can demonstrate that boilers and process heaters meet the health based compliance alternatives. Affected sources may demonstrate that boilers and process heaters in the large solid fuel fired subcategory meet the health based compliance alternative using either ( 1) the " look up table" analysis described in Appendix A of subpart DDDDD of 40 CFR part 63 or ( 2) site specific modeling ( described in Appendix A of subpart DDDDD of 40 CFR part 63 and other analytical tools, which may be appropriate for a specific source, such as EPA's " Air Toxics Risk Assessment Reference Library"). Affected sources electing to conduct sitespecific modeling can use any scientifically defensible, transparent, and peer reviewed methodology they choose in conjunction with the criteria specified in Appendix A of subpart DDDDD of 40 CFR part 63. An example of how site specific modeling can be performed is described in the EPA " Air Toxics Risk Assessment Reference Library." The " Air Toxics Risk Assessment Guidance Library" is the same document that could be used, where appropriate, for facility specific residual risk assessments required under CAA § 112( f). This document has been peer reviewed and was developed according to the principles, tools and methods outlined in the Residual Risk Report to Congress. However, it may not be appropriate for all sources, and for that reason, sources and EPA may consider alternative analytical tools. The comment that the new cancer guidelines are still under review is correct but as stated in the November 29, 2001 Federal Register notice ( 66 FR 59593), these 1999 draft guidelines are to be considered the interim guidance. 5 18.8.3 Model regulatory text Comment: Commenter IV D 123 provided model regulatory text that could be used to incorporate an HCl risk based compliance option into the final rule ( see Attachment D to IV D 123). The commenter believes that their suggested regulatory text will allow for implementation of a risk based compliance option that minimizes administrative burdens on States and industry, ensures protection of human health and the environment, provides for continuous compliance, is 260 transparent to regulators, industry and the interested public, and is readily enforceable. Response: We acknowledge receipt of the model regulatory text submitted by the commenter. However, we have developed our own regulatory text in the final rule ( Appendix A of subpart DDDDD of 40 CFR part 63) to specify how affected sources must demonstrate that they meet the health based compliance alternatives for HCl and Mn.

18.9 PROGRAM ISSUES: STATE RESOURCES Comment: Commenters IV D 09, IV D 14, IV D 17, IV D 85, IV D 102, IV D 118, IV D 130, and IV D 154 contended that the proposal will place a very intensive resource demand on State and local agencies to review source's risk assessments. State/ local agencies may not have expertise in risk assessment methodology or the resources needed to verify information ( e. g., emissions data and stack parameters) submitted with each risk assessment. Commenter IV D 130 stated that they do not have the resources to conduct extensive risk analyses and requested assistance from EPA in any way needed if this option is to work. Commenter IV D 14 stated that if EPA intends to have the affected industries conduct the analysis, then EPA must consider the cost incurred by States which may lack the necessary expertise to evaluate and review these analyses. The current proposal is silent on these implementation and cost issues. Commenters, IV D 17, IV D 102, and IV D 154 stated that because the procedures for preparing these risk assessments on a large scale basis and for assessing the potential adverse effects of the pollutants emitted ( e. g., taking into account existing background and looking for a threshold level for carcinogens) are untried and will require extensive debate and review to launch, even more time and resources will be needed. Commenter IV D 154 expressed concern about exempting a facility based on limited emission data if EPA established a subcategory listing low risk sources. Commenter IV D 148 pointed out that the proposal only considers cost for the regulated source category, and not for regulatory agencies. The EPA did not consider the costs and resources associated with: ( 1) the public process required in reviewing/ approving the proposed approaches and, if approved, making substantial changes to existing regulations; ( 2) the development of methods and guidance for human health and ecological risk assessments of affected sources; ( 3) the review by already budgetarily constrained State agencies of the assessments and assurance of adequate public participation in the process; and ( 4) the collection/ verification of source specific data needed for conducting risk assessments. Commenter IV D 148 added that the proposals do not address the critical need for qualified assessors to evaluate the scientific and technical basis for exempting facilities from regulation on a case by case basis, and estimated that if 1 additional full time employee ( FTE) were required per State to review risk based exemptions, the costs would be an additional $ 7.5 million annually. Commenter IV D 05 stated that they are concerned about the potential cost and workload that risk provisions would place on permitting authorities. The commenter added that the permitting authorities would need to either perform or verify the risk analyses, and that diverting State and local resources to focus on presumably insignificant sources would detract from efforts associated with significant sources. The commenter pointed out some of the specific items that would add burden to the State and local agencies, including data verification for background concentrations and ongoing assurance that low risk facilities remain low risk. Because EPA understands the difficulty with risk assessments, commenter IV D 06 found it perplexing that EPA believes such analyses at the State and local levels would be an efficient way to protect public health. 261 By contrast, other commenters ( IV D 123 and IV D 180) believe that a risk based program can be structured and implemented in a manner that does not adversely impact limited State resources. Commenter IV D 148 believes that EPA should work closely with States and industry to implement the risk based approach in a non burdensome manner. Commenter IV D 123 stated that the risk based approaches, like other MACT standards, would simply be incorporated into each State's existing title V program. Because the title V framework already exists, the addition of a risk based MACT standard would not require States to overhaul existing permitting programs. Commenter IV D 123 added that the risk based approach would not increase the number of sources regulated by each State. The commenter believes that the final MACT rule itself should set forth the applicability criteria  including the threshold levels of exposure  that sources must meet to qualify for a risk based determination. Each source would have the burden of demonstrating that its exposures are below this limit, and therefore the States would not be required to develop their own risk assessment guidance or to conduct source specific risk assessments. Commenter IV D 123 stated that the risk assessment guidance to be issued by EPA within the next several months will streamline the risk based approach and further reduce any burden on the States. Commenters IV D 123 and IV D 180 supported having States charge reasonable increased fees ( as a component of annual operating permit fees or other fees) to cover any significant additional workload demands associated with reviewing moredetailed Tier 2/ 3 modeling. Response: The health based compliance alternatives for HCl and Mn which we have adopted in the Boiler NESHAP do not rely solely on site specific risk assessments and, therefore, should not impose significant resource burdens on States. Further, the required compliance demonstration methodology is structured in such a way as to avoid the need for States to have significant expertise in risk assessment methodology. We have considered the commenters' concerns in developing the criteria defining eligibility for these compliance alternatives, and we believe that the approach that is included in the final rule provides clear, flexible requirements and enforceable compliance parameters. The final rule provides two ways that an affected facility may demonstrate eligibility for complying with the alternative health based emission standard. First, look up tables, which are included as Tables 2 ( HCl) and 3 ( Mn) in Appendix A of subpart DDDDD, allow affected facilities to determine, using a limited number of site specific input parameters, whether emissions from their affected sources might cause a HI ( or HQ) limit to be exceeded. If an affected facility cannot demonstrate eligibility using a look up table, a modeling approach can be followed. Appendix A to the final rule presents the criteria for performing this modeling. Regarding commenters' concerns with looking for a threshold level for carcinogens, the compliance alternatives only apply to HCl and Mn, which are not carcinogens. Also, regarding the concern expressed by one commenter about exempting a facility based on limited emission data if EPA established a subcategory listing low risk sources, we have not used § 112( c)( 9) authority to establish a low risk subcategory for the boilers and process heaters source category. With respect to guidance for performing site specific modeling, all of the procedures for performing such modeling are available in peer reviewed scientific literature, and therefore, no additional guidance needs to be developed. Only a portion of the major facilities in the large solid fuel fired boilers and process heaters subcategory will submit eligibility demonstrations for the compliance alternatives. Of this portion of major sources, we believe that most will be able to demonstrate eligibility based on simple analyses ( e. g., using the look up tables provided in Appendix A). However, it is likely that 262 some affected facilities will require more detailed modeling. The criteria for demonstrating eligibility for the compliance alternatives are clearly spelled out in the final rule. Because these requirements are clearly spelled out and because any standards or requirements created under § 112 are considered applicable requirements under part 70, compliance alternatives would be incorporated into title V programs, and States would not have to overhaul existing permitting programs. Finally, with respect to the burden associated with ongoing assurance that affected facilities which opt to do so continue to comply with the health based compliance alternatives, the burden to States will be minimal. Rather than developing detailed recordkeeping and reporting requirements for facilities that initially qualify for the health based compliance alternatives, we are requiring periodic review of the compliance demonstration and certification that the affected source still qualifies for the alternatives every five years to ensure continuing compliance. Additionally, before changing key parameters that may impact an affected source's ability to continue to meet one or both of the health based compliance alternatives, the affected source is required to evaluate its ability to continue to comply with the health based compliance alternative( s) and submit documentation to the permitting authority supporting continued eligibility for the compliance alternative. Finally, in accordance with the provisions of title V of the Clean Air Act and part 70 of 40 CFR ( collectively " title V"), the owner or operator of any affected source opting to comply with the health based compliance alternatives will be required to certify compliance with those standards on an annual basis. We believe that the promulgation of specific health based compliance alternatives and a uniform methodology for demonstrating compliance with those alternatives alleviates any concern regarding the public process required in reviewing/ approving the proposed approaches and making substantial changes to existing regulations. It also addresses concerns regarding the costs and resources associated with assuring adequate public participation in the process of reviewing site specific risk analyses. To ensure that affected sources which choose to comply with the health based compliance alternatives continue to comply with those options after the initial compliance demonstration, specified assessment parameters ( e. g., HCl equivalent and/ or manganese emission rate, boiler heat output, etc.) must be included in their title V permit as enforceable requirements. Draft permits and permit applications must be made available from the State or local agency responsible for issuing the permit, or in the case where EPA is issuing the permit, from the EPA regional office. Members of the public may request that the state or local agency include them on their public notice mailing list, thus providing the public the opportunity to review the appropriateness of these requirements. Every proposed title V permit has a 30 day public comment period and a 45 day EPA review period. If EPA does not object to the permit, any member of the public may petition EPA to object to the permit within 60 days of the end of the EPA review period.

Comment: Commenter IV D 14 stated that if EPA intends to have the affected industries conduct the analysis, then EPA must consider the additional cost incurred by smaller sources to do the analysis. Commenter IV D 24 pointed out that since delisting based on risk will require collection and submission of data and air quality modeling, small sources, which are likely to have small risk, will probably not be able to afford the cost of requesting delisting unless EPA establishes automatic subcategory delisting criteria. Response: As mentioned previously, there are two ways that an affected source in the 263 large solid fuel fired boilers and process heaters subcategory may demonstrate eligibility for the health based compliance alternatives of the final rule: ( 1) look up tables, and ( 2) a site specific modeling approach. The look up tables include Table 2 of Appendix A to the final rule to determine if an affected source is eligible for the alternative compliance option for the HCl emission limit and Table 3 of Appendix A to determine if an affected source is eligible for excluding Mn from the TSM emission limit. The look up tables allow an affected source to determine, using a limited number of site specific input parameters ( i. e., stack parameters, distance to fence line, and emission rates), whether they are eligible for one of the health based compliance alternatives. Attempting to demonstrate eligibility for one of the health based compliance alternatives is completely voluntary. An affected source that is not eligible for one of the health based compliance alternatives based on look up tables is not required to pursue a modeling approach ( which can be increasingly complex and expensive as it becomes more refined). Each affected source must weigh the costs of making an eligibility demonstration with the costs of MACT compliance. We believe that, in general, the costs associated with demonstrating eligibility for the health based compliance alternatives will be lower than the costs associated with complying with MACT for many affected sources, including smaller facilities and other facilities that have not already otherwise installed pollution controls. Successfully demonstrating eligibility for the health based compliance alternative( s) will result in cost savings for smaller affected sources because these facilities will not have to expend the costs, i. e., the costs of installing or upgrading, operating, and maintaining the add on emission controls needed to comply with the MACT emission limits . The cost and economic analyses developed as part of the MACT rulemaking were based on the costs to install, maintain, and operate controls and to comply with the MACT requirements. The costs associated with voluntarily conducting risk analyses were not estimated. Therefore, our estimates of costs associated with the final rule are conservative, because the control costs that would be incurred to comply with the HCl emission limit are significantly higher than the costs of conducting the risk analyses that in some cases would be required to qualify for the health based compliance alternative for the HCl emission limit. Similarly, the control costs of complying with the MACT PM or TSM emission limits are higher than the costs of conducting the risk analyses that for some affected facilities would be required to demonstrate eligibility to comply with the health based alternative excluding Mn from the TSM emission limit.

18.10 PROGRAM ISSUES: TITLE V AS IMPLEMENTATION MECHANISM Comment: Commenter IV D 148 stated that risk based exemptions are such an implausible interpretation of the CAA that states do not even have the authority to grant them under their title V permit programs. Therefore, the commenter is not aware of any approach to ensure that emissions remain below specified levels. MACT standard applicability is the gatekeeper for being subject to a title V operating permit. Once a source is exempt from a MACT standard, it would be exempt from the monitoring, reporting and recordkeeping requirements needed to demonstrate compliance. Similarly, commenter IV D 135 noted that EPA requested comment on how to implement applicability cutoffs without specifying what methods are being considered. For example, EPA did not discuss or consider the fact that States currently do not have authority to provide for riskbased exemptions for sources subject to MACT standards through the title V permit program. 264 Commenter IV D 96 stated that implementing the § 112( d)( 4) exemption interpretation through title V would be unlawful and unworkable. Congress knew how to authorize States to establish case by case emission standards using a post rulemaking title V permit as an implementing mechanism because it did so in 112( j). Congress did not do so in [ section] 112( d)( 4), and EPA lacks authority to delegate [ section] 112( d)( 4) powers to States. EPA may not implement any 112( d)( 4) applicability cutoff through any post rulemaking mechanism such as a title V permit. With the exception of carefully delineated compliance monitoring, reporting, and certification provisions in the statute, title V permits may not create applicable requirements or exemptions from applicable requirements. Even if this approach was legal, passing familiarity with the title V program, the resource challenges faced by States, and the widespread delays in issuing title V permits makes it clear that this approach is unworkable. Commenter IV D 96 noted that State permit engineers and officials that prepare and issue title V permits generally are not experts in risk assessment or air dispersion modeling. States and the public would be confronted with more self serving facility arguments and data than could be adequately scrutinized, which could cause important health and risk determinations to be rubber stamped, or cause the permit process to grind to a halt. Most State title V permit programs are already behind the statute's permit issuance deadlines, and implementation of EPA's risk based approach would exacerbate this unlawful situation further. Several commenters supported implementing the risk based approaches in the Industrial/ Commercial/ Institutional Boilers and Process Heaters rule through the States' existing title V programs. Commenter IV D 75 suggested that States which qualify and choose to do so should be delegated the authority to implement risk based alternatives. The commenter added this would allow States to coordinate between the MACT alternatives and State air toxics requirements. Commenter IV D 123 stated that implementation of the § 112( d)( 4) risk based approach through title V would be lawful and workable. According to the commenter, no facility specific post rulemaking mechanisms, nor expansion of the scope of title V permit process, would be necessary, just the incorporation of the NESHAP's risk based compliance option, which would contain the criteria for showing what the source would have to meet to qualify for the risk based approach. The commenter believed that the objections from other commenters to the risk based criteria were invalid, arguing that their objections were in tension with the conclusions of a CAAAC Workgroup on State/ Local/ Tribal air toxics issues and that their comments provided no basis for concluding that States lack the legal authority to implement risk based approach. Commenter IV D 05 stated that title V permits seem to be the obvious implementation tool, and that title V permits could provide enforceable limitations, appropriate recordkeeping requirements, and periodic review upon renewal. The commenter added that since the rule would apply only to major sources, title V permits already are required and would not be an added burden; title V could also be used to implement applicability cutoffs, but that the workload involved with the options requiring modeling, ambient monitoring, or other means to establish background concentrations would be a hindrance to any implementation mechanism. In addition, the commenter stated that with respect to potential risk based provisions, monitoring is more useful for demonstrating non compliance than compliance because the regulation would apply to potential emissions under any weather conditions, whereas monitoring reflects current weather and emission conditions. Response: With regard to title V permits creating applicable requirements or exemptions from applicable requirements, the requirements for qualifying for the health based compliance 265 alternatives are clearly spelled out in Appendix A to Subpart DDDDD, and any standards or requirements created under § 112 are considered applicable requirements under part 70. Unless an affected source meets these conditions, it will remain subject to the HCl and Mn regulatory requirements in the final rule. Therefore, the parameters used to demonstrate eligibility for the health based compliance alternatives would be incorporated into title V permits as federally enforceable permit terms and States would not have to overhaul existing permitting programs. We note that our rules implementing title V of the CAA specifically provide for situations such as this. For example, in its provisions governing what types of permit revisions may proceed through the abbreviated " minor permit modification" process, our rules state that such procedures may not be used " to establish or change a permit term or condition for which there is no corresponding underlying applicable requirement and that the source has assumed to avoid an applicable requirement to which the source would otherwise be subject." 40 C. F. R. 70.7( e)( 2)( i)( A)( 4); 71.7( e)( 1)( i)( A)( 4). We believe that permit terms reflecting an affected source's eligibility clearly represent such terms, and are therefore allowed under title V. Also, such terms would be required to be added or revised through the more formal " significant modification" procedures of 40 C. F. R. 70.7( e)( 4) and 71.7( e)( 3). Affected sources will initially demonstrate that they qualify for a health based compliance alternative using either the look up tables provided in Appendix A to the final rule or site specific modeling following the methodology and criteria in Appendix A to the final rule. They will keep records of the information used in developing the eligibility demonstration. Affected sources will not be required to perform detailed risk analyses for public review, although the public will have an opportunity to comment on draft permit terms and conditions that reflect eligibility demonstrations, and to judicially challenge final EPA approvals of eligibility demonstrations under CAA § 307( b)( 1). We acknowledge the resource challenges faced by States, however, we believe that most affected sources qualifying for the low risk provisions will be able to do so through use of the look up tables. The only facility data needed to use the look up tables are stack parameters, HClequivalent or Mn emission rates, and fence line distances. Other than the HCl equivalent emission rates, these data are routinely included in title V permit applications and none of the data should require review by experts in risk assessment or air dispersion modeling. For affected sources that do site specific modeling, all of the procedures for performing such modeling are available in peer reviewed scientific literature. As far as the title V permit programs being behind the statute's permit issuance deadlines, the incorporation of the NESHAP requirements is a necessary step that will require some resources, and inclusion of the health based compliance alternatives should be a straightforward part of the process and should not cause significant delay.

18.11 PROGRAM ISSUES: EFFECTS ON OTHER SOURCE CATEGORIES Comment: Commenter IV D 175 noted that in the MACT Proposal, EPA proposes three separate approaches to focus on sources that pose the greatest adverse health and environmental impacts: ( 1) an applicability cutoff for threshold pollutants; ( 2) subcategorization and delisting; and ( 3) the use of a concentration based applicability threshold. The commenter believes each of these approaches may be appropriate in different contexts, and encourages EPA to continue to consider these approaches in forthcoming MACT promulgations. Response: The inclusion of health based compliance alternatives in the final rule affects 266 only the boiler and process heater source category and not other source categories.

Comment: Commenter IV D 72 stated that delisting low risk subcategories is consistent with the CAA and good public policy. The commenter pointed out that the Taconite Iron Ore Processing source category presents an ideal scenario for technologically defined low risk subcategory delisting. For example, it would be appropriate to divide the source category into two source categories: one for the thermal operations and one for the material handling operations. Based on preliminary evaluations, emissions from the material handling operations present such a low ambient impact that they easily meet criteria set forth in § 112( c)( 9). Commenter IV D 72 stated for purpose of the Taconite Iron Ore Processing source categories, maintaining the MACT floors as established ( with some minor corrections) would be appropriate. Response: The inclusion of health based compliance alternatives in the final rule affects only the boiler and process heater source category and not other source categories.

18.12 OTHER ISSUES 18.12.1 Commenters referencing other commenters Comment: Commenter IV D 148 endorsed the comments submitted by STAPPA/ ALAPCO. Response: We acknowledge the commenter's support of the comments submitted by the STAPPA/ ALAPCO. Our responses to the specific comments submitted by the STAPPA/ ALAPCO are provided elsewhere in this document.

Comment: Commenters IV D 166 and IV D 179 supported the comments provided by the American Chemistry Council ( IV D 73) and the CIBO ( IV D 119). Commenter IV D 107 submitted comments identical to those of CIBO ( IV D 119). Response: We acknowledge the commenters' support of the comments submitted by the American Chemistry Council and CIBO. Our responses to the specific comments submitted by the American Chemistry Council and CIBO are provided elsewhere in this document.

Comment: Commenter IV D 45 strongly endorsed comments submitted by the AF& PA ( IV D 123). Response: We acknowledge the commenter's support of the comments submitted by AF& PA. Our responses to the specific comments submitted by AF& PA are provided elsewhere in this document.

Comment: Commenter IV D 101 incorporated the comments of the Rubber Manufacturers Association ( IV D 146) by reference. Response: We acknowledge the commenter's support of the comments submitted by the Rubber Manufacturers Association. Our responses to the specific comments submitted by the Rubber Manufacturers Association are provided elsewhere in this document.

18.12.2 Attachments to certain comments Comment: Commenter IV D 123 attached ( see Attachment B of IV D 123) for 267 consideration their " Response to Specific Objections to the Risk Based Approaches Raised Previously in the Context of EPA's Proposed National Emission Standards for Hazardous Air Pollutants for Brick and Structural Clay Products Manufacturing and National Emission Standards for Hazardous Air Pollutants for Clay Ceramics Manufacturing." Commenter IV D 122 cited AF& PA's responses to objections raised by NESCAUM, NRDC, and Earthjustice. Response: The comments included in the attachment to comment IV D 23 have been summarized elsewhere in this document, and our responses to these comments are provided elsewhere. We acknowledge the support of commenter IV D 122 for the comments submitted by AF& PA. We acknowledge comments regarding comments submitted by others. However, we have responded to those specific comments submitted by others rather than agreeing or disagreeing with one commenter's assessment of another's comments.

Comment: Commenter IV D 148 included multiple attachments, including the following: Attachment 1 Congressional Record, E2383, November 11, 1999 Attachment 2 EPA Science Policy Council, Policy on Evaluating Health Risks to Children Attachment 3 EPA Science Policy Council, Memorandum on EPA Risk Characterization Program, March 21, 1995 Attachment 4 EPA Science Policy Council, Elements to Consider When Drafting EPA Risk Characterizations, March 1995 Attachment 5 EPA Science Policy Council, Policy for Risk Characterization, February 1995 Attachment 6 EPA Science Policy Council, Policy for Risk Characterization, March 1995 Attachment 7 EPA Science Policy Council, Memorandum on New EPA Policy on Evaluating Health Risks to Children, October 20, 1995 Attachment 8   Fact Sheet, Report to Congress on Residual Risk Attachment 9   Statement of John D. Graham, Ph. D., Director, Center for Risk Analysis, Harvard School of Public Health, October 14, 1999 Attachment 10   Statement of Lee P. Hughes, Vice President, Corporate Environmental Control, Bayer Corporation, on behalf of the American Chemistry Council, before the Senate Environment and Public Works Committee on Clean Air Act Residual Risk, October 3, 2000. Response: We acknowledge submittal of the attachments referenced by commenter IV D 148.

18.12.3 Miscellaneous Comment: Commenter IV D 96 noted that a September 30, 2002 email from Amy Vasu, EPA, to Jim Eddinger and Sims Roy, EPA, mentions 20 e mails to Bryon Allen, OMB, and 2 e mails to Alex Cristofaro, EPA, from Ms. Vasu. EPA Docket A 96 47 ( boilers docket), Document II F 24. The commenter believes the docket is incomplete because they were unable to identify that number of e mails from Ms. Vasu to Mr. Allen in the referenced dockets and because they were unable to locate any e mails between OMB and Mr. Christofaro in the docket for A 96 47. The commenter urged EPA to ensure that all required documents are included in the administrative dockets for all of the relevant proposals. The public's right to comment has already been jeopardized by the failure to include all relevant and required documents in these dockets. Response: We disagree that the public's right to comment has been compromised. We 268 requested public comments on the proposed Boiler NESHAP, and not on correspondence between EPA and OMB that occurred prior to proposal of the NESHAP. In terms of Document No. II F 24 of the docket for the Industrial Boiler NESHAP, it contains all the relevant ( to the Industrial Boiler MACT rulemaking) e mails. The cover e mail was referring to the entire OMB correspondence for both Boiler and RICE rulemakings. The emails relevant to the RICE rulemaking were not included in the item entered into the Industrial Boiler docket.

Comment: Commenter IV D 148 expressed concern with the April 30, 2002 memorandum, " Method for Approximate (" Top Down") Estimate of Aggregate Cancer Risk Associated With Two Maximum Achievable Control Technology ( MACT) Source Categories: RICE and Industrial/ Commercial/ Institutional Boilers." The commenter stated that the analysis had no scientific, technical, or policy basis and apparently had not been peer reviewed. The commenter objected to the document and suggests that EPA remove it from the docket, and delete all references to it. Response: The document that the commenter refers to was used in the development of the proposal for the Boilers MACT, and therefore, it remains in the project docket. The document explains the approach we used prior to proposal to estimate cancer risk associated with the boiler and process heater source category. Peer review is not required for documentation placed in NESHAP dockets, as the public has an opportunity to comment on the proposed rulemaking and the supporting information and analyses, just as the commenter has done. We acknowledge the commenter's objection to the document.

Comment: Commenter IV D 113 argued that EPA must regulate all units that combust any solid waste under § 129 rather than § 112. Because § 129 does not permit EPA to establish risk based exemptions, it would be unlawful for EPA to do so for boilers and process heaters that combust any solid waste. Response: The health based compliance alternatives apply to large solid fuel fired boilers and process heaters regulated under the final rule developed pursuant to § 112 ( and not § 129). The health based compliance alternatives do not apply for solid waste combustors regulated under § 129.

Comment: Commenter IV D 118 stated that the proposed risk based approach would not be necessary if EPA were to include a minimum boiler/ process heater size cutoff. This size cutoff could be established using standard EPA refined air pollution modeling procedures in conjunction with the most stringent federal or State ambient air limits for HAP to model the air impacts associated with uncontrolled HAP emissions from the " model" boiler/ process heater. A similar process was used by the Industrial Combustion Coordinated Rulemaking Federal Advisory Committee Act ( ICCR FACA) process when selecting the HAP of interest for boilers/ process heaters. The size based applicability limits should be adequate for addressing both the size of the HAP source and the cost effectiveness of the requirements. Response: As discussed elsewhere in this document, we are not including a lower size cutoff.

Comment: Commenter IV D 135 was furthermore concerned that EPA's HCl concept, if finalized, would allow sources whose HCl emissions would be excluded from the § 112( d) standards, to claim to be area sources. The commmenter observed that HCl is probably the 269 1. U. S. Environmental Protection Agency. 1994. Methods for Derivation of Inhalation Reference Concentrations and Application of Inhalation Dosimetry. Office of Research and Development. EPA/ 600/ 8 90/ 066F.

2. U. S. Environmental Protection Agency. 1999. Residual Risk Report to Congress. Office of Air Quality Planning and Standards, Research Triangle Park, NC 27711. March 1999. EPA 453/ R 99 001; available at http:// www. epa. aov/ ttn/ oarpa/ t3/ meta/ m8690. html.

3. U. S. Environmental Protection Agency. 2000. Supplementary Guidance for Conducting Health Risk Assessment of Chemical Mixtures. Office of Research and Development. EPA/ 630/ R 00/ 002.

4. U. S. Environmental Protection Agency. 1986. Guidance for Conducting Health Risk Assessment of Chemical Mixtures. Risk Assessment Forum, Washington, DC. EPA/ 630/ R 98/ 002; available at http:// cfpub. epa. gov/ ncea/ raf/ recordisplay. cfm? deid= 20533.

5. U. S. EPA. 1999. Guidelines for Carcinogen Risk Assessment. NCEA F 0644. Risk Assessment Forum, Washington, DC. pollutant emitted in quantities greater than 10 tons and would result initially in the source being classified a major source under § 112( a)( 1). A subsequent claim by a facility that is an area source ( because its HCl emissions are exempted) would exclude the facility from all MACT standard requirements. The commenter asserted that this potential outcome is clearly contrary to the intent of the CAA. Response: Major sources of HAP are those stationary sources or groups of stationary sources that are located within a contiguous area under common control that emit or have the potential to emit, considering controls, 9.07 Mg/ yr ( 10 tpy) or more of any one HAP or 22.68 Mg/ yr ( 25 tpy) or more of any combination of HAP. Area sources are those stationary sources or groups of stationary sources that are not major sources. ( See CAA § § 112( a)( 1) and 112( a)( 2), and 40 CFR § 63.2). Major/ area source determinations are based on the total HAP emissions from the facility, regardless of the emission limits that the source is required to meet. This is true regardless of whether the emission limits required for the source are MACT emission limits or a health based alternative. Thus, just because a source may meet health based compliance alternative for HCl does not mean that the HCl emissions from the facility will not be considered in the sources major/ area source determination. If sources emit more than 10 tpy of HCl, then they would be considered a major source, regardless of whether they meet the healthbased compliance alternative for HCl or the MACT emission limit for HCl.

References