Comment: Multiple commenters opposed risk based approaches ( IV D 113, IV D 09, IV D 148, IV D 96, IV D 06, IV D 154, and IV D 118). Commenters IV D 09 and IV D 118 noted that the proposal to include risk based exemptions is critically flawed and opposes adoption of the risk based exemptions into MACT. 191 Commenter IV D 148 stated that the inclusion of case by case risk based exemptions into the first phase of the MACT program will negate the legislative mandate and jeopardize the effectiveness of the national air toxics program to adequately protect public health and the environment and to establish a level playing field. Therefore, the commenter strongly disagrees with inclusion of risk based exemptions in the MACT standard process. The commenter was very concerned that EPA referenced a fundamentally flawed interpretation of § 112( d)( 4) written by an industry ( AF& PA) subject to regulation. Of particular concern was AF& PA's unprecedented proposal to include " de minimis exemptions" and " cost" in the MACT standard process. Commenter IV D 96 stated that in AF& PA's supplemental comments on the Brick and Structural Clay Products ( BSCP) MACT, AF& PA attempted to rebut NRDC's position regarding the risk based approaches. But AF& PA's vague and tortured explanation of how emissions limits for individual facilities would be established actually supports NRDC's position. MACT standards must be set by EPA and must be clear, known, and enforceable. The source specific standard setting process desired by AF& PA would give extensive discretion to private entities and States to establish Federal MACT standards and exemptions, and no precedent for this type of approach was provided by AF& PA or EPA ( and none exists). Commenter IV D 154 is extremely concerned about the policy and technical implications of the risk based exemption proposal. Because of the flaws with the proposal, the commenter is opposed to the adoption of the risk based exemptions to MACT. Commenter IV D 05 stated the belief that the use of risk based concepts to evade MACT applicability is contrary to the intent of the CAA and is based on a flawed interpretation of § 112( d)( 4) of the CAA. The commenter added that the CAA requires a technology based floor level of control and does not provide exclusions for risk or secondary impacts from applying the MACT floor. Commenter IV D 05 stated that from a practical standpoint, the approaches ( to risk based exemptions) in the preamble are not appropriate. Commenter IV D 17 is opposed to risk based exemptions discussed in the preamble and recommends that EPA expeditiously propose and promulgate the rule without such exemptions. Commenter IV D 14 is opposed to the risk based exemptions and called upon EPA to promulgate the remaining technology based MACT standards without the risk based exemptions. Commenter IV D 141 believes that the risk based exemption approaches described in the proposal preamble are not appropriate or workable. The commenter understood that the MACT standards were to be technology based and to have considered the best level of controls on existing boilers. The commenter noted that they operate two small ( 10.5 MMBtu/ hr) firetube natural gas/ propane fired boilers that would be covered by the proposed rule. A brief review by the commenter indicated that there were no controls for HAP on any boilers of the type at the commenter's facility anywhere in the United States. Therefore, Commenter IV D 141 firmly believes that this type of boiler should be fully exempted from the proposed rules. The commenter pointed out that the CAA makes a provision for considering risk once the MACT standards are in place. The commenter believes it would not be appropriate to consider risk until after the MACT standards have been fully promulgated. ( It should be noted that the commenter provided information regarding the insignificant risk associated with boilers of the size and type used at the commenter's facility.) The commenter also noted that the complexity of risk analysis would make its inclusion in the proposed rules very time consuming and extremely difficult to implement. Commenter IV D 96 stated that in separate rulemakings and lawsuits, EPA has adopted legal positions and policies that refute and contradict the very risk based and cost based approaches contained in the proposals. In these other arena, EPA has properly rejected risk 192 assessment to alter the establishment of MACT standards. EPA also has properly rejected cost in determining MACT floors and in denying a basis for avoiding the MACT floor. The commenter attached passages from several EPA briefs: Brief for Respondent Environmental Protection Agency, Sierra Club v. EPA; Brief for Respondent Environmental Protection Agency, Cement Kiln Recycling Coalition v. EPA, No. 99 1457 and consolidated cases, D. C. Cir.) ( Jan. 18, 2001) ( Attachment 1); Brief for Respondent Environmental Protection Agency, National Lime Ass'n v. EPA, 233 F. 3D 625 ( D. C. Cir. 2000) ( July 14, 2000) ( Attachment 3). Commenter IV D 154 stated that the preamble discussion of the risk based approaches is not sufficient to allow for complete public comment and, therefore, it would not be appropriate for EPA to go directly to a final rule ( without reproposal) with any of the approaches outlined in the proposal. The commenter recommended that the risk based exemption proposal be dropped because it is unacceptable. Commenter IV D 10 agreed in principle with EPA's proposed plan to utilize applicability thresholds and risk assessment as an alternative to the proposed MACT limits and applauds EPA's effort to establish an alternative compliance method using risk assessment. However, the commenter felt that the methods being considered as part of the rule are far too complex to warrant detailed comments at this time. Consequently, the commenter requested that EPA draft language for the final Boiler MACT that allows utilization of this option without specifics. The commenter suggested that EPA should then proceed with development of additional rulemaking for review and comment that would provide the specifics and a structured approach for requirements a source would need to satisfy to perform a successful risk assessment. Commenter IV D 135 summarized Administrative Procedure Act issues. The commenter submitted that in many sections, EPA's proposal lacks sufficient detail so as to deprive the public of notice and opportunity to comment. For example, the various delisting and applicability cutoff proposals were so lacking in detail that anything could be a " logical outgrowth" of the proposal. The commenter asserted that section IV. E of the EPA's proposal failed to provide an in depth, reasoned analysis of its action. [ Motor Vehicles Mfrs. Ass'n v. State Farm Mut. Auto Ins. Co., 463 U. S. 29, 43 ( 1983)( requiring an agency to " articulate a satisfactory explanation for its action."] The commenter asserted that EPA must review and re propose insufficiently detailed proposals prior to going to final rulemaking. Commenter IV D 14 stated that the use of sub categorization and source category deletions under § 112( c) have been implemented several times since the MACT program began. The commenters have been unable to comment on the technical merit of the risk analysis employed by the EPA. Until the residual risk analysis procedures have been implemented via the § 112( f) process, risk analysis should not been used in making MACT determinations pursuant to § 112( d)( 4) and, could never be used to establish a MACT floor. Commenter IV D 135 argued that EPA's discussion of the threshold applicability approach lacked the specificity to allow reasoned comment or analysis of the proposal and enumerates several issues related to the proposal that EPA did not discuss or consider. The commenter concluded that EPA's discussion of a threshold applicability approach lacked crucial elements of a valid rulemaking. Response: We are not identifying and deleting a subcategory of sources in this source category pursuant to the authority of CAA § 112( c)( 9). We also are not relying on de minimus authority. Legal issues associated with the health based provisions are addressed in sections 18.2 and 18.4. In addition, de minimis authority is discussed in section 18.3. As discussed above, we are, however, including in the final rule alternative health based emission standards for HCl and Mn based on our authority under CAA § 112( d)( 4). 193 Section 112( d)( 4) authorizes EPA to consider health thresholds, with an ample margin of safety, in establishing emission standards. The analysis necessary to do this can generally be characterized as a risk analysis. Thus, we disagree with the commenter that we must wait for implementation of § 112( f) before utilizing risk analysis.

Comment: Multiple commenters ( IV D 06, IV D 09, IV D 154, IV D 102, IV D 118, and IV D 14) believe that the preambles of individual rule proposals were an inappropriate forum for introducing significant changes in the way that MACT standards are established. Precedentsetting change of the magnitude that EPA has raised should be discussed openly and carefully with all affected parties instead of being buried in the preambles of individual standards. Commenter IV D 05 stated the concern that other parties may miss commenting on the risk based exemptions because they are contained within six separate proposals. The commenter added that to give the issue full consideration, the risk provisions should not be adopted within any of the final rules but should be addressed in one place, such as in revisions to the general provisions of 40 CFR 63 subpart A. Commenter IV D 148 stated that for many years, they have coordinated with OAQPS on development of MACT standards for the national air toxics program, and there has been no indication of any kind regarding inclusion of risk based exemptions in the first phase of the MACT program. The commenter thought it was unprecedented and alarming that EPA is proposing such a radical change at the end of Phase 1 of the MACT standard process. Commenter IV D 148 believes that allowing risk based exemptions requires changes to existing law and that such a debate should take place within the democratic legislative process and not in the MACT standard process. Response: The discussion of health based compliance alternatives was included in individual proposals for several reasons. We recognize that such provisions are only appropriate for certain HAP, and our decision making process required source category specific input from stakeholders. The 10 year MACT standards, which are now being completed, are the last group of MACT standards currently planned for development, and for any risk provisions to be useful, the provisions must be finalized in a timely manner The health based provisions are not available for any other standards that have already been implemented, and any decisions regarding risk must, therefore, be applied on a source category specific basis.

Comment: Commenter IV D 96 stated that the dockets for the MACT proposals that contain the risk approaches make it clear that the White House Office of Management and Budget ( OMB) and industry were the driving forces behind the appearance of these unlawful approaches in EPA's proposals. The commenter cited internal emails between the White House OMB and EPA that reveal OMB officials exerting pressure on EPA to " take ownership" of the deregulatory approaches developed by the AF& PA and Latham and Watkins ( Boilers Docket A 96 47, item IIF 24). The commenter noted that comparison of the BSCP and Plywood and Composite Wood Products ( PCWP) MACT proposal language makes clear that EPA capitulated to OMB pressure to remove references to the risk based exemptions in PCWP preamble section IV. G being " industry's suggested approaches." The commenter cited preamble edits from OMB that the commenter believes reveals an OMB agenda to dictate EPA adoption of industry's risk based approaches, and to signal these plans in the rulemaking proposals, even before public comment has been taken. ( We will evaluate all comments before determining which of the two alternatives will be included in the final rule. See Boilers Docket A 96 47, item II F 24). The commenter also noted that OMB urged support of a dangerous and technically unfounded HI of 10, and that 194 EPA appropriately rejected proposing HI of 10 because EPA had no technical rationale to support this HI option. The commenter condemned the industry driven agenda ( that would allow higher levels of toxic, cancer causing air pollution) that is being promoted by the White House OMB. Commenter IV D 123 stated that accusations by NRDC that EPA has succumbed to industry lobbying and internal pressures are entirely unfounded. Eighty source categories have already been addressed with MACT standards. The remaining source categories are lower priority and include a large number of facilities that pose negligible risk to public health and environment. The EPA purposefully saved those categories for last in accordance with Congress's explicit, risk based priority setting mandate expressed in § 112( e)( 2). EPA has now reached the point where regulation by MACT would result in more environmental harm than good. Response: The commenter is correct in stating that industry representatives and OMB support the inclusion of health based approaches in the final rule as a method of reducing costs. We are required by Executive Order 12866 to submit to OMB for review all proposed and final rulemaking packages that would have an annual effect on the economy of $ 100 million or more. The comments we received from OMB reflect their position that low risk facilities do not warrant regulation. However, the commenter is incorrect in implying that we have not exercised our independent judgement in addressing these issues. Our rationale for adopting the health based approach in the final rule is that such an approach is fully authorized under the CAA.

18.1.2 Effects on MACT program Comment: Commenters IV D 06, IV D 09, IV D 154, IV D 102, IV D 148, IV D 17, IV D 14, and IV D 118 stated that the proposal to include risk based exemptions is contrary to the 1990 CAAA which calls for MACT standards based on technology rather than risk as a first step. Congress incorporated the residual risk program under § 112( f) to follow the MACT standards ( not to replace them). The need for the technology based approach has been recently reinforced by the results of the National Air Toxics Assessment ( NATA), which indicates that exposure to air toxics is very high throughout the country in urban and remote areas. Commenters IV D 154, IV D 09, IV D 102, IV D 118, and IV D 85 added that risk based approaches will be used separately to augment and improve technology based standards that do not adequately provide protection to the public. Commenter IV D 148 believes that § 112( b)( 4) of the CAA and the regulatory precedent established in over 80 MACT standards rejects the inclusion of risk in the first phase of the MACT standards process. Commenter IV D 06 added that § 112( f) of the CAA was developed to address residual risks remaining after implementation of technology based MACT standards and was intended to provide additional protection, not replace technology controls. Commenter IV D 148 added that they have been unable to substantiate the basis for EPA's support of the regulatory relief sought by industry through riskbased exemptions. In fact, the use of risk assessment at this stage of the MACT program is directly opposed to title III of the CAA. Commenter IV D 148 attached an EPA fact sheet and testimony by two individuals that supports this position. Commenter IV D 85 recognized the merits of focusing on the highest risk facilities, but believes the risk based exemption approach would not survive any legal challenges as they appear to be contrary to the intent of the CAAA of 1990. Response: We disagree that inclusion of health based compliance alternatives, in the form of emission standards based on the authority of § 112( d)( 4), in the final rule is contrary to the 195 1990 CAAA. The Boiler MACT is a technology based standard developed using the procedures dictated by § 112 of the CAA. The only difference in the Boiler MACT and other MACT is that we used our discretion under § 112( d)( 4) to base appropriate parts of the Boiler MACT on established health thresholds, with an ample margin of safety. We believe that the Boiler and process heater source category is particularly well suited for a health based compliance alternative, established pursuant to the criteria set forth in § 112( d)( 4). In addition to the fact that there are established health thresholds for HCl and Mn, EPA has determined that some of the facilities in this source category do not emit these pollutants in amounts that pose a significant risk to the surrounding population. Those sources that can demonstrate that the emissions of HClequivalents and Mn meet the threshold emission levels will be in compliance with the MACT. The criteria are based on health protective estimates of risk and the threshold emission levels will provide ample protection of human health and the environment. Inclusion of health based compliance alternatives in the final rule does not alter the MACT program. Rather, it merely represents EPA availing itself, in appropriate circumstances, of the authority Congress granted it in § 112( d)( 4) of the CAA. We recognize that such provisions are only appropriate for certain HAP, and our decision making process required source categoryspecific input from stakeholders. The 10 year MACT standards, which are now being completed, are the last group of MACT standards currently planned for development, and for any risk provisions to be useful, the provisions must be finalized in a timely manner Although NATA may show measurable concentrations of toxic air pollution across the country, these data do not suggest that EPA should not establish health based emission standards pursuant to its authority under § 112( d)( 4) when it determines that it is appropriate to do so. The alternative health based emission standards included in the final rule will ensure that affected sources which choose to comply with those standards do not emit HCl and/ or Mn at levels that are harmful to public health. A discussion of background concentrations is provided in section 18.6.

Comment: Commenters IV D 09, IV D 14, IV D 154, IV D 102, IV D 148, and IV D 118 stated that the risk based exemption proposal removes the " level playing field" that would result from the proper implementation of technology based MACT standards. Establishing a baseline level of control is essential to prevent industry from moving to areas of the country that have the least stringent air toxics programs, which was one of the primary goals of developing a uniform national air toxics program under § 112 of the 1990 CAA amendments. The risk based approaches would jeopardize future reductions of HAP in a uniform and consistent manner across the nation. Commenters IV D 09 and IV D 118 stated that the NATA data show that virtually no area of the country has escaped measurable concentrations of toxic air pollution. The NATA information indicates that exposure to air toxics is high in both densely populated and remote rural areas. Commenter IV D 123 provided the following, in response to NRDC comments regarding the proposals potential removal of a level playing field; ( 1) As a policy matter, NRDC's argument would be that EPA should impose unnecessary and potentially environmentally damaging controls for the sole purpose of equalizing control costs across sources. Such a result is at odds with stated purpose of CAA. ( 2) As factual matter, NRDC's claim that risk based approach would favor facilities located away from population centers is incorrect. As contemplated, the risk based 196 approaches to the NESHAP would be key to the comparison of health benchmarks with potential maximum exposure, regardless of whether actual receptors are present at the exposure location. Presence or absence of human populations would have no effect on whether facilities would qualify. Response: We agree that one of the goals of developing a uniform national air toxics program under § 112 of the 1990 CAAA was to establish a level playing field. We do not believe that providing health based compliance alternatives for sources that can meet them in the final rule will do anything to create an unlevel playing field for sources subject to this rule. The final rule and its criteria for demonstrating eligibility for the health based compliance alternatives apply uniformly to boilers and process heaters across the nation in the large solid fuel fired subcategory. The final rule establishes two baseline levels of emissions reduction for HCl and Mn, one based on a traditional MACT analysis and the other based on EPA's evaluation of the health threat posed by emissions of these two pollutants. All boilers and process heaters in the applicable subcategory must meet one of these baseline levels, and all boilers and process heaters in the applicable subcategory have the same opportunity to demonstrate that they can meet the alternative healthbased emission standards. The criteria for demonstrating eligibility for the alternative healthbased emission standards are not dependent on local air toxics programs. Therefore, concerns regarding facilities moving to areas of the country with less stringent air toxics programs should be alleviated. Although NATA may show measurable concentrations of toxic air pollution across the country, these data do not suggest that EPA should not establish health based emission standards pursuant to its authority under § 112( d)( 4) when it determines that it is appropriate to do so. The alternative health based emission standards included in the final rule will ensure that affected sources which choose to comply with those standards do not emit HCl and/ or Mn at levels that are harmful to public health.

Comment: Commenters IV D 06, IV D 09, IV D 14, IV D 154, IV D 102, IV D 118, and IV D 17 stated that the proposal to allow risk based exemptions would divert back to the time consuming NESHAP development process that existed prior to the CAAA. Under this process, which began with a risk assessment step, only eight NESHAP were promulgated during a 20 year period. If the proposed approaches are inserted into upcoming standards, the commenters fear the MACT program ( which is already far behind schedule) would be further delayed. Commenter IV D 168 supported EPA efforts to determine alternative MACT setting methodologies but strongly recommended that these be pursued separately from this rulemaking. This will provide for timely issuance of final Reciprocating Internal Combustion Engine ( RICE) and Boiler/ Process Heater MACT standards relative to the settlement deadline. Commenters IV D 09 and IV D 118 stated that it is evident that the proposed approach to risk based exemptions would require extensive debate and review in order to launch, which will further delay promulgation of the remaining MACT standards. Commenters IV D 09 and IV D 118 stated that delays could be exacerbated by litigation following legal challenges to the rules, and such delays would trigger the MACT hammer, which would unnecessarily burden the State and local agencies and the industries. The commenters concluded that, obviously, further delay is unacceptable. Commenter IV D 130 did not want to be in a position of implementing the § 112( j) program and urged EPA to not delay the issuance of any MACT standard. 197 Commenters IV D 17 and IV D 118 stated that the proposed approaches will jeopardize expeditious promulgation of remaining MACT standards. The commenters noted that according to a recently proposed EPA rule regarding § 112( j), the regulated community and State and local agencies would have to proceed with Part 2 permit applications, followed by case by case MACT, if EPA misses the newly agreed upon MACT deadlines by as little as two months. This would be time consuming, costly, and burdensome for both regulators and the regulated community. Commenter IV D 148 noted that the Inspector General recently found that EPA is nearly two years behind in fulfilling its statutory responsibilities for implementing Phase 1 MACT standards. This delay potentially harms the public and environment. The inclusion of risk based exemptions in 10 year MACT standards will only further delay this process. Commenter IV D 154 stated that the risk assessment exemption could significantly delay compliance with MACT for sources trying unsuccessfully to opt out using the exemption. Commenter IV D 96 stated that the EPA's proposal would cripple the MACT program which is already in disarray. The risk based approach could delay the HAP emissions reductions required by § 112. EPA's MACT program is already delayed and the incorporation of improper risk assessment into the technology based standard process will only exacerbate the delay. The EPA lacks adequate emissions and exposure data, source characterization data, and health and ecological effects information to conduct this process anyway. The commenter attached portions of a report from EPA's Office of Inspector General that lists describes EPA's challenges related to the air toxics program. The commenter believes that the air toxics program is flawed and is failing to protect public health and the environment, and therefore, it is irresponsible for EPA to pursue a deregulatory agenda that will further weaken the effectiveness of EPA's air toxics program. Commenter IV D 96 noted that EPA acknowledged the complexity and delays associated with the proposed risk based approaches in deciding not to adopt the approaches in the BSCP rulemaking. Response: We disagree that allowing health based compliance alternatives in the final rule will alter the MACT program or affect the schedule for promulgation of the remaining MACT standards, especially this Boiler MACT rule. In fact, it has not caused such a delay for this rule. We do not anticipate any further delays in completing the remaining MACT standards. The setting of alternative health based emission standards in the final rule affects only the boiler and process heater source category, and not any other MACT standards. We believe that the approach taken in the final rule is particularly well suited to HCl and Mn, which are the only pollutants for which health based compliance alternatives are included. For some facilities, the pollutants are currently emitted in amounts that do not expose anyone in the surrounding population to concentrations above the established health threshold. As a result, emissions of HCl and/ or Mn at these facilities do not pose a significant risk to the surrounding population. Only those affected sources that demonstrate that their emissions are below the health based emission standard( s) are eligible for the compliance alternatives. The criteria are based on health protective estimates of risk and will provide ample protection of human health and the environment. Including health based compliance alternatives for the boiler and process heater source category does not mean that we will automatically provide such alternatives for other industries. Rather, as has been the case throughout the MACT rule development process, we will undertake in each individual rule to determine whether it is appropriate to exercise its discretion to use its authority under § 112( d)( 4) in developing applicable emission standards. Furthermore, we have 198 no intentions of re opening previously promulgated NESHAP in light of decisions made specific to the boilers and process heaters source category. The Boilers NESHAP is being promulgated by the February 2004 court ordered deadline. Any delays in implementation of the Boilers NESHAP caused by legal challenges, which could and often do occur for any MACT standard we promulgate without a health based approach, are beyond our control.

18.2 LEGAL ISSUES: SECTION 112( d)( 4) AUTHORITY 18.2.1 Section 112( d)( 4) Authority to Exempt Sources Comment: Multiple commenters ( IV D 40, IV D 61, IV D 72, IV D 73, IV D 75, IVD 122, IV D 123, IV D 166, IV D 172, IV D 173, IV D 175, IV D 183, and IV D 186) believe that § 112( d)( 4) provides EPA with authority to exclude sources that emit threshold pollutants from regulation. The commenters indicated that § 112( d)( 4) allows for discretion in developing MACT standards for HAP with health thresholds. This is consistent with the plain language of the statute, which states that: " With respect to pollutants for which a health threshold has been established, the Administrator may consider such threshold level, with an ample margin of safety, when establishing emission standards under this subsection." The commenters stated that the use of § 112( d)( 4) authority also is supported by CAA's legislative history, which emphasizes that Congress included § 112( d)( 4) in the CAA to prevent unnecessary regulation of source categories. Multiple commenters ( I D 61, IV D 122, IV D 123, IV D 172, IV D 175, and IV D 186) referenced Sen Rep. 101 228, at 176 ( 1989), reprinted in 1990 U. S. C. C. A. N. 3385, 3560: "[ W] here some sources do emit more than the threshold amount, the Administrator is authorized by section 112( d)( 4) to use the no observable effects level or NOEL ( again with an ample margin of safety) as the emission limitation in lieu of more stringent " best technology" requirements. Following this scenario, only those sources in the category which present a risk to public health ( those emitting in amounts greater than the safety threshold) would be required to install controls, even though the general policy is " maximum achievable technology everywhere." Again, there is a means to avoid regulatory costs which would be without public health benefit. Several commenters ( IV D 73, IV D 166, and IV D 175) cited a Senate report ( S. Rep. No. 228, 101st Congress Sess. 171 ( 1990)) that makes clear the intent of 112( d)( 4) as follows: " to avoid expenditures by regulated entities which serve no public health or environmental benefit, the Administrator is given discretionary authority to consider the evidence for a health threshold higher than MACT at the time the standard is under review .... Employing a health threshold or safety level rather than the MACT criteria to set standards shall not result in adverse environmental effects which would otherwise be reduced or eliminated." Commenter IV D 175 added that under this risk based approach, EPA must select controls which " provide the greatest protection to human health ( unless the incremental health protection is negligible and there are very significant environmental values that would be afforded protection by some other configuration)." Id. at 168 ( commenter emphasis added). Commenter IV D 72 pointed out that Congress does not differentiate between technology based " emission standards" set under § 112( d)( 3) versus " health threshold" based 199 " emission standards" set under § 112( d)( 4). Instead, the statute explicitly treats emission standards promulgated under § § 112( d)( 3) and 112( d)( 4) as equivalent by not distinguishing between those emission standards under the residual risk provisions of § 112( f). The commenter stated that, in short, by using the phrase " standards developed pursuant to subsection ( d)," Congress was indicating that EPA could develop technology based emission standards under § 112( d)( 3) OR health based emission standards under 112( d)( 4). According to the commenter there is no indication under § 112( f) that emission standards must first be technology based and only secondarily health or risk based. Moreover, by specifically referring to provision " in effect before the date of enactment of the CAAA of 1990" and citing the Benzene NESHAP ( promulgated under the pre 1990 § 112), Congress appears to be explicitly approving the risk methodology set forth in the D. C. Circuit's Vinyl Chloride decision and followed by EPA in the Benzene NESHAP. Commenter IV D 72 stated that this explicit approval provides definition of how Congress intended " risk," and by extrapolation, health based standards, is to be addressed under the 1990 CAA. Commenter IV D 75 added that EPA is permitted to establish alternative standards as long as it ensures that ambient concentrations are less than the health thresholds plus a margin of safety and the emissions do not cause adverse environmental effects. Multiple commenters ( IVD 123, IV D 122, IV D 07, IV D 75, and IV D 61) pointed out that EPA has exercised such authority and cited the Pulp and Paper MACT. In addition, in the Pulp and Paper MACT, EPA identified circumstances in which they would decline to exercise 112( d)( 4) authority   where significant or widespread environmental harm would occur as a result of emissions from the category and the estimated health thresholds are subject to substantial scientific uncertainty. The commenters stated that EPA determined that these considerations were not relevant to emissions from the pulp and paper source category, and the commenters believe that the same is true for their source categories and that the same treatment is warranted for many facilities within the source categories. The commenters noted that facilities that cannot meet the risk criteria would remain subject to the MACT requirements. With regard to comments by NRDC that EPA may not grant individual sources exemptions from MACT standards because EPA must promulgate a MACT based emission standard for the entire group of sources, commenter IV D 123 stated the following. Contrary to NRDC's and Earthjustice's comments, the risk based approaches are squarely in line with the plain meaning of § 112( d)( 4). The commenter pointed out that the Senate report cited ( Sen Rep. No. 228, 101st Congress, 1st Sess 175 6 ( 1990)) clearly indicates that Congress contemplated that sources within the same category or subcategory would be subject to varied regulatory requirements, depending on the risk they pose to public health. Nothing in the statutory definition of " emission standard" suggests that the term is limited to a requirement for the installation of control technology. The commenter believed the risk based compliance options would meet this requirement because they would apply to an entire source category or subcategory. The commenter suggested EPA could create a subcategory for low risk sources and tailor an emission standard to this subcategory, or apply to all sources in the category a NESHAP containing multiple compliance options, one or more being risk based. Finally, commenter IV D 23 stated that Earthjustice's comment that EPA's authority under § 112( d)( 4) is limited to pollutants and does not empower EPA to exempt facilities from compliance with emission standards should be rejected for two reasons; 1) § 112( d)( 4) pertains to development of emission standards that apply to facilities, not to pollutants, and 2) § 112( d)( 4) grants authority to develop standards that may be less stringent than the MACT floor, which itself is based on performance of facilities, not 200 pollutants. Therefore, any exemption authority granted by § 112( d)( 4) must apply to facilities. Several commenters ( IV D 07, IV D 10, IV D 61, IV D 101, IV D 117, IV D 123, IVD 146, IV D 172, IV D 179, and IV D 186) believed that a risk based compliance option under § 112( d)( 4) is particularly appropriate for HCl emissions. The commenters supported use of 112( d)( 4) for those units that can demonstrate that they pose a low risk to the public. Commenters IV D 117, IV D 146, IV D 172, and IV D 179 stated that EPA should provide an exemption from HCl controls in cases where it is demonstrated that HCl emissions will not result in air concentrations above the inhalation RfC for HCl. Commenters IV D 186 and IVD 117 noted that public exposure to HCl should be well below the RfC for HCl. Commenter IVD 117 noted that no unit risk estimate for HCl was mentioned in the proposal, and therefore, use of § 112( d)( 4) is justified. Commenter IV D 07 believed that an approach allowing emissions limit exceptions if a de minimus health risk exists is valid and asked that EPA consider allowing it for HCl emissions from wood waste boilers. The commenter noted that EPA's 112( d)( 4) determination in the Pulp and Paper rule was based on an Inhalation RfC for HCl " defined as an estimate ( with an uncertainty spanning perhaps an order of magnitude) of a daily inhalation exposure that, over a lifetime, would not likely result in the occurrence of noncancer health effects in humans." The RfC for HCl is 20 micrograms/ cubic meter. Based on emissions from recovery furnaces up to 1,016 tons/ year, EPA stated that " at the 95% confidence interval, the maximum concentration predicted to which people are estimated to be exposed is 0.3

g/ m3, 60 times less than the inhalation reference concentration." The commenter requested that EPA examine the rationale behind the 1998 decision not to regulate HCl, and supports EPA's applicability cutoff approach which would allow any source which can demonstrate that HCl inhalation RfC is not exceeded be exempted from the proposed rule. Commenter IV D 117 stated that EPA should use its discretion under § 112( d)( 4) to recognize that there is no need to set emission limits for HCl because the risks are well below the RfC. The commenter stated that EPA should adopt an applicability cutoff from HCl controls based on EPA's § 112( d)( 4) authority to exempt individual facilities from HCl controls provided that the facilities can demonstrate that their HCl emissions do not result in concentrations above the RfC. The commenter noted that no unit risk estimate for HCl was mentioned in the proposal, and therefore, use of § 112( d)( 4) is justified. Commenters IV D 62, IV D 119, and IV D 160 submitted that EPA has concluded that HCl is a threshold pollutant with a well defined health threshold and properly has invoked the Agency's § 112( d)( 4) authority in choosing not to regulate HCl emissions in prior NESHAPs. The commenters cited a NESHAP finalized in 2001, in which the Agency exempted from regulation HCl emissions from chemical recovery combustion sources at pulp mills. In this case, EPA noted it " has the discretion under § 112( d)( 4) to develop risk based standards for some categories emitting threshold pollutants, which may be less stringent than the corresponding ` floor' based MACT standard would be." The Agency found that no further control of HCl is necessary because " HCl levels emitted from recovery furnaces are below the threshold value within an ample margin of safety." The commenters added that EPA similarly has proposed not to regulate HCl emissions from the Chlorine Production source category. Commenter IV D 61 stated that EPA invoked § 112( d)( 4) authority in choosing not to impose control requirements on HCl emissions from chemical recovery furnaces at pulp mills ( 40 CFR part 63, subpart MM). See 63 Fed. Reg. 18754, 18765 ( April 15, 1998). Commenters IV D 122 and IV D 123 noted that in the pulp and paper chemical recovery furnaces rule, EPA 201 was able to make a source category determination that every source in the category met the criteria under § 112( d)( 4) for HCl. The commenters believed the large number and variety of sources, coupled with the diverse use of fuels, in the Boiler MACT precludes EPA from taking the source category wide approach that it used in the pulp and paper rule. Commenter IV D 122 agreed with establishing a risk based compliance mechanism for HCl. The commenter believed EPA has legal authority and that such an approach would reduce the economic impact of MACT on the wood products industry and maximize environmental benefits by targeting only the HCl emissions from boilers that present a risk to human health and the environment. Sources taking a risk based exemption for HCl would still have to comply with limits for metals, mercury , and organics. The commenter noted that federally enforceable permit limits could ensure that emissions remain at low risk levels, and that the risk based approaches could be structured in a manner that does not adversely impact State resources. Commenter IV D 180 stated that EPA should exercise its considerable legal authority under the CAA, as detailed in the comments of AF& PA, to develop a regulatory approach to HCl ( from boilers) that both significantly reduces the economic impact of the rule on the forest products industry and maximizes environmental benefits. The commenter suggested that where facilities are able to demonstrate that emissions of HCl are below levels of concern, they would take federally enforcable permit limits to ensure that emissions do not increase. Those facilities, however, would not be required to install unnecessary controls. Commenter IV D 174 stated that the case for exempting boilers and process heaters that fire solid fuels other than coal ( and a number of coal fired units) is at least as strong as the case for exempting pulp and paper industry combustion sources under § 112( d)( 4). The commenter urged EPA to use its § 112( d)( 4) authority to avoid forcing many facilities to install costly, energy ineffecient control equipment that will serve no useful purpose in terms of reducing risks to human health and the environment. Commenters IV D 73 and IV D 166 suggested that EPA develop risk based emission standards, particularly for emissions of HCl. Under § 112( d)( 4), Congress authorized EPA to consider risk based endpoints when setting NESHAP for threshold HAP. HCl is a threshold HAP and one that generally presents little risk to the public or the environment when emitted from boilers and process heaters, as shown by modeling conducted by the commenter. Commenter IV D 49 approved of a risk based compliance approach under CAA § 112( d)( 4) as particularly appropriate for emissions of HCl. The commenter observed that EPA had previously invoked its CAA § 112( d)( 4) authority to address low risk sources of HCl, and felt that the boiler source category was a particularly appropriate candidate for a risk based approach. The commenter noted that the BSCP MACT, as signed by the Administrator, did not include the risk based approach, and urged EPA to fully consider the concept of risk based approaches in the boiler MACT and other MACT rules and to provide such an approach in the final boiler rule. The commenter believed that the risk based approach would provide an optimal means to meet EPA's goals for the MACT program without unintended consequences to the environment, the community, and the source that accompany a default emissions standard. Commenter IV D 49 provided several benefits of a risk based approach. The commenter submitted that a risk based approach would provide a means to address communities desires to avoid the perception of pollution associated with a visible steam plume, ensure that HCl emissions are below established health thresholds, and achieve the goals of the MACT rule in a considerably less costly manner. Commenter IV D 49 provided a case example of how the risk based approach would be 202 appropriate on a site specific basis, and could provide the community, environment, and regulated source a better outcome than would be achieved if the approach were not provided in the final rule. The commenter operates a boiler in Tacoma, Washington that is used to provide process steam by combusting wood by products. Under the proposed regulation, the boiler would be subject to the HCl emissions standard proposed in Table 1 to Subpart DDDDD. To assure compliance with the proposed HCl standard, the commenter might have to install additional costly control equipment that would create a visible steam plume ( re adding a plume to the Tacoma skyline and waterfront that was eliminated over a decade ago with strong community support), and would add 500,000 gallons per day to the mill's water consumption. The commenter related that the boiler began operation in 1991, replacing an older boiler with significantly higher PM emissions. The installation of the boiler and electrostatic precipitator ( ESP) resulted in the biggest single improvement in Tacoma's air quality in over a decade and was fundamental in Tacoma achieving the National Ambient Air Quality Standards ( NAAQS) for PM10. Commenter IV D 143 strongly supported adoption of a risk based compliance mechanism for HCl under EPA's § 112( d)( 4) authority. The commenter noted that facilities that are able to demonstrate their emissions do not present a risk to human health or the environment should not be required to install costly controls as would otherwise be required under the MACT standards. The commenter felt that the final rule should include provisions for facilities to use an approved EPA method such as dispersion modeling to demonstrate that ambient concentrations of HCl are below a risk based emission standard and therefore be exempted from the emission control and monitoring requirements under the MACT standards. Commenter IV D 173 strongly supported the proposed applicability cutoffs for HCl under EPA's 112 ( d)( 4) authority since the available data suggest that a significant proportion of industrial boilers and process heaters do not emit HCl in an amount that would result in exceedance of applicable health benchmarks. The commenter believed that incorporating this option into the final rule would provide significant cost savings by foregoing the requirement for add on controls on boilers and process heaters whose emissions do not result in HCl concentrations the exceed health benchmarks. Commenter IV D 14 disagreed that § 112( d)( 4) can be interpreted to allow exemption of individual pollutants ( i. e., HCl). Commenter IV D 135 contended that alternative scenarios concerning HCl cutoffs constitute impermissible attempts to circumvent the control requirements for HCl. Under another applicability cutoff scenario, the Agency suggested that any threshold HAP eligible for exemption under CAA § 112( d)( 4) that are controlled by control devices different from those controlling non threshold HAP would still be able to use the applicability cutoff. This scenario represented an illegal attempt to circumvent the control requirements for HCl altogether, and ignored the case law holding that standard setting under § 112( d) is not limited to consideration of particular control technologies. [ See Cement Kiln Recycling Coalition v. EPA, 255 F. 3D 855 ( D. C. Cir. 2001)]. Many of the nonthreshold pollutants are metals that would be controlled by particulate matter controls. Other nonthreshold HAPs are organic emissions for which the Agency proposed a " no control" MACT floor. HCl, on the other hand, would need to be controlled by a scrubber. If finalized, this exemption would potentially allow 59 percent of the emissions from this source category to go uncontrolled ( assuming that the Agency could successfully contrive an exposure modeling approach that would result in exposures less than the RfC). The commenter believed that exempting HCl emissions from control is unacceptable, particularly since EPA proposed HCl as a surrogate measure for all the inorganic HAP emitted by this source category. Hence, an 203 exemption that excluded HCl emission points from control requirements would also exclude emissions of all the other inorganic HAP that would likely include hydrogen cyanide and hydrogen fluoride. Multiple commenters ( IV D 05, IV D 14, IV D 96, IV D 113, IV D 135, and IV D 148) stated that the plain meaning of § 112( d)( 4) does not allow EPA to make MACT standard exemptions for individual sources. Commenters IV D 05 and IV D 148 believe that § 112( d)( 4) applies to categories of sources. Commenters IV D 96 and IV D 135 noted that § 112( d)( 4) states that " with respect to pollutants for which a health threshold has been established, the Administrator may consider such threshold level, with ample margin of safety, when establishing emission standards under this subsection." Commenter IV D 96 stated that the plain language of the CAA specifies that EPA cannot refuse to set emission standards for listed sources. The commenter contended that it is unlawful to refuse to set an emission standard for a group of sources that are part of a listed source category. The EPA must establish emission standards that apply to a whole listed source category. Section 112( d)( 4) only gives EPA authority to " consider" an established health threshold in establishing emission standards. The commenter believed that the section does not give EPA the ability to waive standards altogether because the provision is only available " when establishing emission standards under this subsection." The U. S. Court of Appeals for the D. C. Curcuit has squarely held that EPA was not allowed to make a " no control" determination for a pollutant emitted by a listed source category ( National Lime Ass'n v. EPA, 233 F. 3D 625, 633 34 ( D. C. Cir 2000)). Commenter IV D 96 also stated that subsection 112( d) directs the Administrator to establish emission standards " for each category or subcategory" of sources, not for each individual source. In setting a schedule for developing 112( d) regulations, subsection 112( e) makes clear that the deadlines are for the establishment of emission standards " for categories and subcategories of sources," not for individual sources. The commenter continued that while subsection 112( j) authorizes a permitting authority to establish HAP emission limitations specific to a single source, the authorization applies only if the Administrator has not yet promulgated emission standards for the category to which the source belongs. The commenter believed therefore, that the effect of the phrase, " when establishing emission standards under this section," is to limit subsection 112( d)( 4)' s authorization to instances in which the Administrator is establishing an emission standard for an entire category or a subcategory of sources. Commenter IV D 96 added that the only time § 112 mentions individualized standard setting is under the " MACT hammer" provisions in § 112( j). The specific language used by Congress in § 112( j) shows that had Congress wished to create authority to establish individualized exemptions, it would have included similarly precise language in subsection 112( d)( 4). Commenter IV D 96 stated further that § 112( d)( 4) authorizes the Administrator alone to consider health thresholds, and only when she is establishing emission standards for an entire category or subcategory of sources, and therefore, EPA cannot rely on 112( d)( 4) to allow permitting authorities to approve " applicability cutoffs" that are less stringent than MACT. Commenter IV D 135 asserted that the establishment of applicability cutoffs for threshold and nonthreshold pollutants based on § 112( d)( 4) of the CAA is contrary to law. The commenter claimed the CAA does not authorize EPA to finalize any of the three applicability cutoff scenarios described in the proposal preamble as alternatives to a MACT standard from the source category. Commenter IV D 135 claimed that when a source category is listed, the Agency must establish 204 emission standards that apply to the whole category and cites the language of sections 112( c)( 1) and ( d)( 1). The commenter asserted the statutory language clearly mandates that EPA set emissions standards for HAPs from all categories and subcategories, even for those pollutants with established health thresholds. Commenter IV D 135 pointed out that because of the plain statutory language, the U. S. Court of Appeals for the D. C. Circuit has squarely held that EPA was not allowed to make a " no control" determination for a pollutant emitted by a listed category of sources [ National Lime Ass'n v. EPA, 233 F. 3D 625, 633 34 ( D. C. Cir. 2000)]. The commenter asserted that given the weight of legal authority requiring EPA to establish emissions standards for HAPs from all sources, the agency cannot finalize the applicability cut off approach without first providing some legal rationale for its reinterpretation of § 112( d)( 4). Commenter IV D 14 believed that EPA has misinterpreted the provision in 112( d)( 4). Section 112( d)( 4) does not state that EPA can use applicability thresholds " in lieu of" the § 112( d)( 3) MACT floor requirements. The commenter interpreted § 112( d)( 4) to state that health based thresholds can be considered when establishing the degree of the MACT floor requirements, but it should not be used to supplant the requirements established pursuant to § 112( d)( 3). Commenters IV D 96, IV D 113, and IV D 135 stated that the legislative history of § 112( d)( 4) clearly rejects EPA's proposed facility by facility MACT exemptions. The commenters noted that Congress considered and rejected the applicability cutoffs upon which EPA now solicits comment. The House version of the 1990 Amendments allowed States to issue permits that exempted a source from compliance with MACT rules if the source presented sufficient evidence to demonstrate negligible risk. The Senate version of the 1990 Amendments contained no such provision. The commenters pointed out that in conference, Congress considered both the House and Senate versions and rejected the House bill's exemption for specific facilities in favor of the Senate bill's language. Commenter IV D 96 also noted that the conference report on the 1990 CAAA states, "[ i] t is the conferees' intent that EPA not use the permit hammer approach ( case by case) to avoid or delay meeting MACT requirements." Thus, Congress expressed desire for a category based approach to MACT standard setting rather than a time consuming and delay inducing facility byfacility approach. Commenter IV D 96 also pointed out that in describing § 112, Senator Durenberger explained on the floor that managers were unhappy with EPA's practice under § 111 " of establishing cutoffs that result in excluding some sources within a category or subcategory from the emission limitations or control measures otherwise required." Thus, Senator Durenberger clearly recognized that individualized exemptions from a MACT standard could create an uneven playing field for the industry. The commenter believed that reading § 112( d)( 4) as EPA suggests leads to uneven and unfair treatment of very similar sources and contradicts Congress's wish that facilities be regulated on a categorical basis rather than on an individual basis. Commenter IV D 96 further stated that the legislative history for the CAA shows that § 112( d)( 4) cannot be a basis for non applicability. Both Houses of Congress put forward riskbased exemptions from HAP standards but chose not to adopt them. The commenter pointed out that emission standards under § 112 apply to " major sources" which emit in excess of 10 tpy of a given HAP. A prior version of the bill would have allowed EPA to decline to regulate higherpolluting sources if they emitted threshold pollutants. The fact that this provision did not become law indicated to the commenter that the current CAA does not permit EPA to avoid regulating facilities by pointing to evidence of a health threshold. The Senate bill would have allowed EPA 205 to set a size cutoff higher than 10 tpy for categories of sources emitting threshold pollutants ( See S. 1630, 101st Cong., 1st Sess., § 301 ( amending section 112( c)( 5)). A Senate report explaining the provision said " under section 112( c)( 5) the Administrator may set a lower boundary for the category of major sources which is higher than 10 tons per year ( but which provides an ample margin of safety to protect public health). If there are no sources emitting the pollutant in that amount in a particular category, then no regulation under section 112( d) need be promulgated." ( S. Rep. 101 228, 101st Cong., 1st Sess. at 176 ( 1989)) The commenter also noted that during the 1990 CAAA debate, the House bill would have allowed individual facilities to escape MACT if a risk analysis showed that the source posed a negligible hazard. However, this proposal was not in the Senate bill, and the conference rejected the idea for the final legislation. ( See 1 Legislative History at 866 ( Statement from Senator Durenberger) (" The authority for such exemptions was not present in the Senate bill, and the House receded to the Senate on this point. The provision was deleted in conference."). Commenter IV D 135 submitted that Congress did not require EPA to consider the evidence of a health threshold in setting standards under § 112. The legislative history states the following: The Administrator is not required to take the evidence of a health threshold into account; that would jeopardize the standard setting schedule imposed under this section with the kind of lengthy study and debate that has crippled the current program. But where health thresholds are well established,... and the pollutant presents no risk of other adverse health effects, including cancer, for which no threshold can be established, the Administrator may use the threshold with an ample margin of safety ( and not considering cost) to set emissions limitations for sources in the category or subcategory. [ S. Rep. 101 228 at 171]. Commenter IV D 96 also noted AF& PA's argument in its supplemental comments on the BSCP rulemaking ( see Docket A 99 30, Item IV G 5) that risk based exemptions are lawful because the CAA directs EPA to consider health risk in establishing the order of source categories to regulate and to perform residual risk evaluations. The commenter stated that Congress knew how to authorize risk based decisionmaking when that is what it wanted to do ( e. g., establishing order of source categories for regulation and, consideration of residual risk). The commenter concluded that had Congress wanted to authorize or direct EPA to exempt facilities from the MACT requirement on the basis of case by case risk assessments, it would have done so. Commenter IV D 96 added that EPA has itself insisted in briefs filed in federal courts that the CAA does not permit EPA to temper MACT requirements on the basis of risk assessments. For instance, EPA has declared that " risk reduction is not a factor to be considered in developing standards under section 112( d)," and that "[ t] he legislative history confirms that risk assessments cannot be used to lessen the stringency of MACT standards." [ EPA Brief as Respondent in Cement Kiln Recycling Coalition v. Browner, D. C. Circuit Case No. 99 1457, January 18, 2001, at 99 ( Attachment 1 to IV D 96). EPA Brief as Respondent in Copper MACT Case, March 6, 2003, at 36 36 ( Attachment 2 to IV D 96).] Commenter IV D 96 disagreed with AF& PA's argument that legislative history supports individual exemptions from MACT standards. The commenter repeated the Senate Report passage quoted in AF& PA's white paper: " The Administrator is authorized by Section 112( d)( 4) to use the no observable effects level ( NOEL) ( again with an ample margin of safety) as the emission limitation in lieu of more stringent best technology requirements. Following this 206 scenario, only those sources in the category which present a risk to public health ( those emitting in amounts greater than the safety threshold) would be required to install controls, even though the general policy is " maximum achievable technology" everywhere." Commenter IV D 96 stated that this passage does nothing more than grant EPA the authority to set a category wide emission standard more or less stringent than MACT based on health risk. The statement also clarifies that facilities able to meet an emission standard ( whether MACT or threshold based) without installing controls need not install controls. Commenter IV D 96 stated that each of the three scenarios proposed by EPA ( exempt low risk facilities emitting only threshold pollutants; allow 112( d)( 4) for threshold and non threshold pollutants; and exempt emission points at a facility that emit only threshold pollutants) are unlawful. The third scenario is unlawful because there is no statutory provision within the CAA that could be read to authorize emission point by point exemption. Response: We believe that we have properly exercised the authority granted to us pursuant to § 112( d)( 4) of the CAA in establishing health based emission standards for HCl and Mn which are applicable to the large solid fuel fired subcategories. We believe that § 112( d)( 4) authorizes us to by pass the mandate in § 112( d)( 3) in appropriate circumstances. Those circumstances are present in the large solid fuel fired Boiler subcategories. Section 112( d)( 4) provides us with authority, at our discretion, to develop health based emission standards for HAP's " for which a health threshold has been established", provided that the standard reflects the health threshold " with an ample margin of safety." ( The full text of the § 112( d)( 4): "[ w] ith respect to pollutants for which a health threshold has been established, the Administrator may consider such threshold level, within an ample margin of safety, when establishing emission standards under this subsection.") We presumptively apply § 112( d)( 4) only to HAP's that are not carcinogens because Congress clearly intended that carcinogens be considered nonthreshold pollutants. ( Staff of the Senate Committee on Environment and Public Works, A Legislative History of the Clean Air Act Amendments of 1990, Vol. 1 at 876, statement of Senator Durenberger during Senate Debate of October 27, 1990: " With respect to the pollutants for which a safe threshold can be set, the authority to set a standard less stringent than maximum achievable control technology is contained in subsection ( d)( 4). With respect to carcinogens and other non threshold pollutants, no such authority exists in subsection ( d) or in any other provision of the Act.") The legislative history further indicates that if we invoke this provision, we must assure that any emission standard results in ambient concentrations less than the health threshold, with an ample margin of safety, and that the standards must also be sufficient to protect against adverse environmental effects ( S. Rep. No. 228, 101st Cong. at 171). ( Section 112( a)( 7) of the CAA defines the term " adverse environmental effect" as " any significant and widespread adverse effect, which may reasonably be anticipated, to wildlife, aquatic life, or other natural resources, including adverse impacts on populations of endangered or threatened species or significant degradation of environmental quality over broad areas.) Costs are not to be considered in establishing a standard pursuant to § 112( d)( 4) ( Ibid.). Both the plain language of § 112( d)( 4) and the legislative history cited above indicate that we have the discretion under § 112( d)( 4) to develop health based standards for some source categories emitting threshold pollutants, and that those standards may be less stringent than the corresponding " floor" based MACT standard would be. We do not believe that our use of such standards is limited to situations where every affected source in the category or subcategory can comply with them. As is the case with technology based standards, a particular affected source's 207 ability to comply with a health based standard will depend on it's individual circumstances, as will what it must do to achieve compliance. In developing health based emission standards under § 112( d)( 4), we seek to assure that those standards ensure that the concentration of the particular HAP to which an individual exposed at the upper end of the exposure distribution is exposed does not exceed the health threshold. The upper end of the exposure distribution is calculated using the " high end exposure estimate," defined as " a plausible estimate of individual exposure for those persons at the upper end of the exposure distribution, conceptually above the 90th percentile, but not higher than the individual in the population who has the highest exposure" ( EPA Exposure Assessment Guidelines, 57 FR 22888, May 29, 1992). We believe that assuring protection to persons at the upper end of the exposure distribution is consistent with the " ample margin of safety" requirement in § 112( d)( 4). Regarding the comment that an exemption that excluded HCl emission points from control requirements would also exclude emissions of all other inorganic HAP that would likely include hydrogen cyanide and hydrogen fluoride, affected facilities attempting to utilize the health based alternative compliance option for HCl will be required to evaluate emissions of HAP in addition to HCl. We conducted an assessment of boiler emissions and determined that, of the acid gas HAP controlled by scrubbing technology, Cl 2 is responsible for the great majority of risk and HCl is responsible for the next largest portion of the total risk. The contributions of other HAP, including hydrogen fluoride, to the total risk were negligible. Therefore, affected facilities attempting to utilize the health based alternative compliance option for HCl, either by conducting a look up table analysis or by conducting a site specific risk assessment, must include emission rates of Cl 2 and HCl from their boilers. We do not expect hydrogen cyanide emissions from boilers covered under the final rule. We emphasize that use of § 112( d)( 4) authority is wholly discretionary. As the legislative history described above indicates, cases may arise in which other considerations dictate that the Agency should not invoke this authority to establish less stringent standards, despite the existence of a health effects threshold that is not jeopardized. For instance, we do not anticipate that we would set less stringent standards where the estimated health threshold for a contaminant is subject to large uncertainty. Thus, in considering appropriate uses of our discretionary authority under § 112( d)( 4), we consider other factors in addition to health thresholds, including uncertainty and potential " adverse environmental effects," as that phrase is defined in § 112( a)( 7). We agree that § 112( d)( 4) is appropriate for establishing emission standards for HCl and Mn applicable to the large solid fuel fired Boiler subcategories, and therefore we have established such standards as health based compliance alternatives for affected sources in those subcategories. Affected sources in the large solid fuel fired Boiler subcategories which believe that they can demonstrate compliance with one or both of the health based emission standards may choose to comply with those standards in lieu of the otherwise applicable MACT based standard.

18.2.2 Health based approaches as emission standards Comment: Commenters IV D 61, IV D 122, and IV D 123 stated that the risk based approaches can be implemented as an " emission standard" within the statutory definition of the term. The commenters stated that the risk based approaches being considered by EPA can, and should, be implemented as compliance options, rather than outright exemptions from MACT standard applicability. This approach fits with the statutory definition of " emission standard" and 208 " emission limitation" as used in § 112. Nothing in the definition equates " emission standard" with the requirement to install control technology. If the risk based approach is implemented as a compliance option, then the " emission standard" set by EPA would be the emission rate that corresponds with the concentration of HAP at the property line that is below the health benchmark for threshold HAPs, and below the one in a million risk level for non threshold carcinogens. Commenters IV D 61, IV D 122, and IV D 123 stated that EPA's implementation of the risk based approach as a compliance option clearly would meet the statutory definitions of " emission limitation" and " emission standard" ( defined identically by CAA § 302( k)) by placing federally enforceable limitations on facility HAP emissions. That this cap would be based on correlations with risk based property line concentrations does nothing to detract from this conclusion. Commenters IV D 122 and IV D 123 added that the risk based approaches are not an attempt to " refuse to set an emission standard." The commenters asserted that an emission standard is not a requirement to install control technology  but rather a term defined in the CAA as a limitation on the quantity, rate, or concentration of emissions of air pollutants. EPA's implementation of risk based approaches as compliance options would meet the statutory definition of emission limitations. The commenters stated that NRDC acknowledges that facilities able to meet an emission standard ( whether MACT based or threshold based) without installing controls should not install controls. Commenter IV D 75 stated that risk based alternatives are not exemptions but will function as indirect emission limits that must be maintained by the facilities to assure that the criteria are met, and, thus, such alternatives for low risk facilities are supportable by EPA's authority under § 112( d)( 4) and 112( c)( 9) of the CAA and EPA's inherent de minimis authority. Commenter IV D 96 disagreed that risk based approaches can function as emission standards. The commenter pointed out that AF& PA asserts for the first time in its supplemental comments on the BSCP rule ( see Docket A 99 30, Item IV G 5) that the risk based approaches it advocates are " compliance options, rather than outright exemptions from the MACT standard." This creative packaging fails to hide the unlawful shape of AF& PA's suggested approaches. Section 112( d)( 2) mandates MACT emission standards for each HAP source category and subcategory. Neither AF& PA nor EPA has offered any evidence that could support the notion that a source whose emissions are below a " risk based emission standard" is achieving MACT for the source's category. Subsection 112( d)( 4) permits EPA to consider an established health threshold for a particular HAP when setting an emission standard for that HAP in a particular source category. But nothing in either subsections 112( d)( 2) or ( d)( 4) even implies the authority to promulgate, for a single HAP, different emission standards for different facilities within the same source subcategory. Response: As is explained in the previous response in this section, we believe that we have properly exercised the authority granted to us pursuant to § 112( d)( 4) of the CAA in establishing health based emission standards for HCl and Mn which are applicable to the large solid fuel fired subcategories. We believe that § 112( d)( 4) authorizes us to by pass the mandate in § 112( d)( 3) in appropriate circumstances. Those circumstances are present in the large solid fuelfired Boiler subcategories.

18.2.3 Section 112( d)( 4) Authority for Carcinogens and Non Carcinogens 209 Comment: Many commenters ( IV D 72, IV D 75, IV D 108, IV D 172, and IV D 175) supported the use of § 112( d)( 4) applicability cutoffs for both threshold and non threshold pollutants. Comenter IV D 172 stated that nothing in § 112( d)( 4) limits it to non carcinogens, and EPA should consider 112( d)( 4) whenever it sets emission standards for HAP regardless of health endpoint. Commenter IV D 172 added that advances in risk assessment science indicate that some carcinogens may be threshold pollutants. Commenters IV D 72, IV D 75, IV D 108, and IV D 172 believe that a health threshold of one in one million cancer risk is appropriate for non threshold pollutants. Commenter IV D 108 added that a HI would need to be calculated to include all pollutants emitted by a boiler or process heater for that unit to be added to the subcategory that would be delisted. Commenter IV D 03 agreed with Hunton & Willams ( on behalf of the UARG, IV D 186) that the EPA failed to utilize its authority to establish a health threshold for setting MACT standards for carcinogens and non carcinogens. Commenter IV D 10 stated that EPA should use the latest science with regard to thresholds for compounds that EPA has traditionally viewed as non threshold. Commenter IV D 75 stated that the language in 112( d)( 4) does not limit EPA's ability to set emission standards to only threshold pollutants but states that "[ w] ith respect to pollutants for which a health threshold has been established, the Administrator may consider such threshold..." Rather, EPA may issue standards for any pollutant for which a threshold may be established. For non threshold carcinogens, EPA could use 112( d)( 4) authority and could establish a " threshold" risk of one in one million. Such a de facto threshold is supported by the use of one in one million as the presumptive acceptable risk for both the delisting process in § 112( c)( 9) and in the residual risk program under § 112( f). The commenter added that the D. C. Circuit court noted in NRDC v. EPA ( the vinyl chloride decision) that safe does not always mean risk free and that a risk of cancer between one in ten thousand and one in one million can be an acceptable risk. Congress specifically incorporated the vinyl chloride decision into the 1990 CAAA. Commenters IV D 122 and IV D 123 stated that § 112 ( d)( 4) may be properly applied to carcinogenic HAPs that EPA determines have a threshold of safe exposure. The CAA places no limitation on EPA's authority. For some pollutants a MACT emissions limitation may be far more stringent than is necessary to protect public health, whereas, EPA may set an emission limitation under § 112( d)( 4) where it is possible to establish a level of exposure that is safe. EPA has welldeveloped methodologies and extensive experience in setting " safe" levels of exposure. Congress recognized that not all HAP should be regulated at the stringency of the MACT floor which is consistent with the intent to avoid expenditures which secure no public health or environmental benefit. Section 112( d)( 4) authority exists with respect to pollutants for which a health threshold has been established and therefore can be applied to carcinogens as well as noncarinogens. Although, legislative history generally distinguishes between threshold pollutants and carcinogens, EPA should not view those as overriding the clear statutory language. Agency policy and science has evolved over the last 12 years to allow for a carcinogen to have threshold of action. Nothing in statue exists to preclude EPA's regulatory programs from keeping pace with the state of the art in scientific understanding. Commenters IV D 122 and IV D 123 also stated that application of § 112( d)( 4) authority to threshold carcinogens would not conflict with other provisions of the CAA. Sections 112 ( c)( 9)( B)( i) and 112( f)( 2)( A) specify cancer risk of one in a million as the level below which sources need not be regulated with further controls. In the context of implementing risk based 210 approaches in the MACT program, the commenters submitted that EPA can and should use a de minimis, one in a million risk level as the health benchmark. Commenters IV D 122 and IV D 123 believed EPA can use a risk based approach for non threshold pollutants, including metals. Commenter IV D 123 included additional discussion in their Attachment A. Several commenters ( IV D 05, IV D 96, IV D 113, IV D 135, IV D 148, and IV D 154) stated that § 112( d)( 4) does not apply for source categories that emit carcinogens. Several commenters ( IV D 96, IV D 113, IV D 135, and IV D 154) stated that legislative history makes it clear the § 112( d)( 4) is only to be used when a there is a wellestablished health threshold. Commenter IV D 113 cited legislative history that makes it clear that Congress did not intend EPA to establish and carcinogens as " threshold" pollutants under § 112( d)( 4). Commenter IV D 154 stated that the concept of cancer exposure below a threshold is untried, and Congress clearly intended that carcinogens be considered non threshold pollutants. Commenter IV D 96 stated that, even if permissible, deregulation under § 112( d)( 4) is rarely available and noted that EPA may only use the authority for pollutants with a wellestablished health threshold. The commenter pointed out that § 112( d)( 4) only allows EPA to substitute a health threshold for a MACT standard when the threshold " has been established." The term " has been" means that the accepted threshold is already in existence. The commenter stated that Congress did not intend for EPA to use this provision to spend time to determine if a threshold exists. The term " established" shows Congress's intent that EPA have a high degree of scientific certainty before using its § 112( d)( 4) authority. Legislative history supports this interpretation ( See S. Rep. 101 228 at 171). According to the commenter, Congress also specified that EPA must have direct evidence of no effects ( i. e., use of NOEL) before invoking § 112( d)( 4). The EPA must be sure that there are no effects from exposure at the level chosen for the emission standard. Commenter IV D 96 stated further that EPA may not use the authority for carcinogens and other non threshold pollutants. The § 112( d)( 4) provision is unavailable for non threshold pollutants. All carcinogens must be treated as non threshold pollutants. The commenter submitted that it is clear throughout the history of the CAAA that Congress legislated with an understanding that carcinogens do not have a safe threshold. In recognition of Congressional intent, EPA traditionally has interpreted § § 112( d)( 4) to exclude consideration of carcinogens. The commenter quoted the proposed pulp and paper NESHAP ( 63 FR 18754,18765, proposed April 15, 1998): EPA has not applied § 112( d)( 4) to carcinogens because Congress clearly intended them to be non threshold pollutants. Commenter IV D 135 asserted that the establishment of applicability cutoffs for threshold and nonthreshold pollutants, as EPA proposed, is technically unsound and contrary to good public policy. Congress has clearly stated that carcinogens are not threshold pollutants. The commenter added that regardless of whether EPA believes that there have been advances in risk assessment science that might allow the agency to better evaluate dose response relationships, an attempt to do so here would be EPA impermissibly subverting the judgement of Congress. Commenter IVD 135 also asserted that, even assuming, arguendo, that EPA had the authority to establish cutoffs for threshold pollutants, this authority could not apply to nonthreshold pollutants. The commenter claimed it is clear that Congress legislated an understanding that there is no safe threshold for carcinogens [ see for example S. Rep 101 228 at 175] and provides supporting language from Senator Durenberger. The commenter concluded that attempting to determine a threshold for carcinogens would contravene Congressional intent. [ 68 Fed. Reg. at 1689/ 1]. 211 Commenter IV D 96 stated that allowing carcinogens to escape regulation under § 112( d)( 4) would conflict with other portions of the CAA. The commenter believed EPA's interpretation would give it authority to ignore source that emits a threshold carcinogen ( if such a thing exists) and pose greater than one in a million risk. The commenter submitted that this conflicts with the plain language of the more specific delisting provision § 112( c)( 9)( B)( i), which only allows a category that emits a carcinogen to be delisted if risk can be shown to be less than one in a million for any source in the category. It also conflicts with the residual risk assessment provision in 112( f)( 2)( A) which requires EPA to promulgate residual risk standards if the cancer risk remains above one in a million after MACT is applied. Response: We agree that unless scientific evidence indicates otherwise, carcinogens should be treated as non threshold pollutants. As is explained in response 18.2.1, § 112( d)( 4) provides us with authority, at our discretion, to develop health based standards for HAP's " for which a health threshold has been established," provided that the standard reflects the health threshold " with an ample margin of safety." Consequently, the boiler rule includes health based alternative compliance options only for the threshold pollutants HCl and Mn.

18.2.4 Carcinogens as Threshold Pollutants Comment: Commenter IV D 72 believes, as supported by draft EPA guidelines for carcinogen risk assessment, that some carcinogens are threshold pollutants, and EPA should recognize the inherent " legal threshold" for carcinogens that Congress put into the CAA, i. e., " lifetime excess cancer risks to the individual most exposed to emissions from a source in the category or subcategory to less than one in one million." The commenter noted that EPA's assertions that Congress may have intended the concept of a " threshold" compound to automatically mean " non carcinogen," is effectively destroyed by the clear and literal language of subsection 112( f)( 2)( A), i. e., that the provisions for carcinogens under § 112( f) are not limited to technology based NESHAP standards promulgated under § 112( d)( 3), but instead merely address " standards promulgated pursuant to subsection ( d)." Had Congress intended § 112( d)( 4) to apply only to non carcinogens, then it would not have included the provisions of § 112( d)( 4) when addressing constraints on emissions of carcinogens under § 112( f)( 2)( A). Commenter IV D 72 stated that there is no mystery as to what constitutes an acceptable level of risk, a question which EPA seems to ponder in the recently proposed rulemakings. Congress answered the question when it cited the Benzene NESHAP, stating in § 112( f)( 2): "( A)... If standards promulgated pursuant to subsection ( d) and applicable to a category or subcategory of sources emitting a pollutant ( or pollutants) classified as a known, probable, or possible human carcinogen do not reduce lifetime excess cancer risks to the individual most exposed to emissions from a source in the category or subcategory to less than one in one million, the Administrator shall promulgate [ residual risk] standards under this subsection for such source category. ( B) Nothing in subparagraph ( A) or in any other provision of this section shall be construed as affecting, or applying to the Administrator's interpretation of this section, as in effect before the date of enactment of the Clean Air Act Amendments of 1990 and set forth in the Federal Register of September 14, 1989 ( 54 Federal Register 38044)." Subsection 112( f)( 2)( B) explicitly defers to the holding in the pre eminent Vinyl Chloride case and thus sets the standards for evaluating acceptable health limits for HAP. Response: As explained in response to comment 18.2.1, we presumptively apply § 112( d)( 4) only to HAP's that are not carcinogens because in the absence of scientific evidence 212 to the contrary it has been our policy to consider carcinogens as nonthreshold pollutants. The legislative history indicates that if we invoke this provision, we must assure that any emission standard results in ambient concentrations less than the health threshold, with an ample margin of safety, and that the standards must also be sufficient to protect against adverse environmental effects ( S. Rep. No. 228, 101st Cong. at 171). ( Section 112( a)( 7) of the CAA defines the term " adverse environmental effect" as " any significant and widespread adverse effect, which may reasonably be anticipated, to wildlife, aquatic life, or other natural resources, including adverse impacts on populations of endangered or threatened species or significant degradation of environmental quality over broad areas.) Costs are not to be considered in establishing a standard pursuant to § 112( d)( 4) ( Ibid.).

18.2.5 Section 112( d)( 4) Authority for Emission Points That Emit Both Threshold and Non Threshold Pollutants Comment: Commenters IV D 73 and IV D 166 believe that EPA could implement a § 112( d)( 4) emissions limitation under both the first and third scenarios discussed in the preamble ( scenario 1: exempt low risk facilities emitting only threshold pollutants, scenario 3: exempt emission points at facilities that emit only threshold pollutants). However, the commenters believe that the use of a § 112( d)( 4) emissions limit as described under the third scenario in the preamble would provide the maximum benefit of the § 112( d)( 4) provision. Under this scenario, facilities that emit both threshold and nonthreshold pollutants could achieve exemption from MACT controls for threshold HAP emission points based on their ability to meet the associated health threshold for those HAP. Another possible use of the § 112( d)( 4) emissions limitation that EPA discussed would apply to both threshold and nonthreshold pollutants. Commenter IV D 40 believes the threshold approach to establishing emission standards would be ideal for facilities that only emit threshold HAPs, but that it could also be applied to facilities that can accurately monitor and differentiate the emissions of threshold and nonthreshold HAPs, which would allow a facility to estimate the impact of exposure to threshold and non threshold HAPs separately. Response: As is explained in response 18.2.1, we have chosen to use the authority of § 112( d)( 4) to provide an alternative to the HCl regulatory requirements of the final rule for affected facilities in the large solid fuel fired boilers and process heaters subcategory that demonstrate their subpart DDDDD unit HCl and Cl 2 emissions result in a maximum HI of 1.0 outside the facility area. Different controls are needed to reduce acid gas emissions than are used to reduce PM ( HAP metal) emissions from boilers and process heaters. The acid gases emitted from boilers, i. e., HCl, Cl 2, and HF, are threshold pollutants. Similarly, an affected facility in the large solid fuel fired boilers and process heaters subcategory that demonstrates that their subpart DDDDD unit Mn emissions result in a maximum hazard quotient ( HQ) of 1.0 outside the facility area has the option of complying with the emission standard for TSM minus Mn. As is the case with the acid gases, Mn is a threshold pollutant.

18.3 LEGAL ISSUES: DE MINIMIS AUTHORITY Comment: Numerous commenters ( IV D 61, IV D 72, IV D 73, IV D 75, IV D 123, IV D 166, and IV D 175) stated that EPA has inherent authority to promulgate risk based 213 exemptions and cited several caselaw examples of appellate courts upholding EPA's application of its de minimis authority. Commenter IV D 61 stated that a risk based compliance option for both threshold and non threshold HAPs is well within EPA's authority under the CAA and the de minimis doctrine articulated by appellate courts. The commenter stated that appellate caselaw makes clear that EPA may lawfully exempt de minimis sources of risk from MACT level controls because the legislative mandate of CAA § 112 is not " extraordinarily rigid" and the exemption is consistent with the CAA's health protective purpose. CAA § § 112( c)( 9) and 112( f)( 2) clearly indicate that Congress considered a cancer risk below one in a million to be de minimis and therefore insufficient to justify regulation under CAA § 112. Under this approach, EPA would specify an emission standard as a de minimis level of cancer risk, and sources would have the option to comply with the NESHAP by demonstrating that their emissions result in exposures below this risk level. Commenters IV D 61 and IV D 123 argued that EPA's de minimis authority properly is evaluated vis à vis the statutory design. Appellate caselaw establishes EPA's authority to exempt de minimis sources as long as the legislative mandate is not " extraordinarily rigid" and the exemption is consistent with the legislative purpose  in this case, the " health protective purpose of the statute." Commenters IV D 72 and IV D 61 cited Alabama Power Co. v. Costle, 636 F. 2D 323 ( D. C. Cir. 1979) where the court explained that categorical exemptions from the requirements of a statute may be permissible: [ A] s an exercise of agency power, inherent in most statutory schemes, to overlook circumstances that in context may fairly be considered de minimis. It is commonplace, of course, that the law does not concern itself with trifling matters, and this principle has often found application in the administrative context. Courts should be reluctant to apply the literal terms of a statute to mandate pointless expenditure of effort. 636 F. 2D at 360. The commenters also cited the more recent D. C. Circuit decision that: As long as the Congress has not been extraordinarily rigid in drafting the statute, however, there is likely a basis for an implication of de minimis authority to provide an exemption when the burdens of regulation yield a gain of trivial or no value. Environmental Def. Fund v. EPA, 82 F. 3D 451, 466 ( D. C. Cir. 1996) Commenter IV D 61 stated that EPA's frequent exercise of its de minimis authority has withstood judicial challenge. The Agency's application of this authority, as well as its treatment by reviewing courts, uniformly has turned on the degree of risk at issue, not on the mass of emissions to be regulated. The commenter stated that appellate courts consistently have upheld EPA's application of its de minimis authority in a line of cases that, according to the D. C. Circuit, have established " virtually a presumption in its favor." Public Citizen v. Young, 831 F. 2D at 1113. These decisions include the following:  EDF v. EPA, 82 F. 3D 451, 466, 469 ( D. C. Cir. 1996) { This case deals with EPA's transportation conformity regulations promulgated under CAA § 176}  Public Citizen, 831 F. 2D at 1112  Ohio v. EPA, 997 F. 2D 1520 ( D. C. Cir. 1993) { This case deals with de minimis exemptions from CERCLA requirements on the basis of no appreciable health risk}  Alabama Power Co., 636 F. 2D at 360  Ober v. Whitman, 243 F. 3D 1190 ( 9th Cir. 2001) { This case deals with exemption of de minimis sources of PM 10 under a Federal 214 Implementation Plan [ FIP]}  Industrial Union Dept., AFL CIO v. American Petroleum Inst., 448 U. S. 607, 663 64 ( 1980). See IV D 123 Attachment A for quotes from these court decisions. Commenters IV D 61 and IV D 123 stated that the D. C. Circuit has invalidated EPA's de minimis authority only where it was applied under statutory designs that are " extraordinarily rigid." In Public Citizen, the D. C. Circuit refused to allow a de minimis exception to the " Delaney Clause" in the Pure Food and Drug Act, which provided that a color additive will be deemed unsafe if it is found to induce cancer in man or animal. 831 F. 2D at 1108. In distinguishing its own precedent, the D. C. Circuit later noted that "[ t] he Public Citizen court relied heavily on the almost inescapable terms of the Delaney Clause and the substantial legislative history supporting an absolutist application of the language." Ohio, 997 F. 2D at 1534 ( emphasis added, quotations omitted). As discussed below, CAA § 112 contains no such absolutist language so as to preclude EPA's application of its de minimis authority. Commenters IV D 61 and IV D 123 stated that the statutory design and legislative purpose expressed in CAA § 112 fully justify emission standards based on de minimis levels of cancer risk. The roots of de minimis authority exist in the language of CAA § 112, and CAA § 112 itself provides clear indication of congressional intent as to what constitutes a de minimis cancer risk for purposes of MACT. Congress expressly included de minimis provisions in the title III program. Despite its initial emphasis on MACT based control technology, the overall structure of CAA § 112 is overwhelmingly risk based. This emphasis on risk renders de minimis considerations especially appropriate. Unlike, e. g., the Delaney Clause, CAA § 112' s mandates are not absolute. For example, CAA § 112( c)( 9)( B)( i) authorizes source category delisting if the category ( or subcategory) creates less than a 10 6 cancer risk; CAA § 112( c)( 9)( B)( ii) allows delisting if non carcinogenic HAP emissions do not exceed levels adequate to protect public health with an ample margin of safety. Congress included de minimis principles in § 112( g)( 1). In addition, Congress included other provisions in CAA § 112 that demonstrate that the statutory design is not " extraordinarily rigid." See, e. g., CAA § § 112( a)( 2) and ( c)( 3); 112( a)( 7); 112( c)( 7); 112( f)( 2)( C); 112( d)( 5) and ( f)( 5); and 112( i)( 5)( E). Commenter IV D 61 stated that CAA § 112 provides clear indication of Congressional intent as to the degree of risk that properly is to be considered de minimis. A cancer risk of one in a million is the touchstone for further review under the " residual" risk provision of CAA § 112( f). ( The residual risk provisions thus call for additional controls if and only if the remaining risk from affected sources exceeds one in a million, but do not call for a reduction of risk to the maximum exposed individual [ MEI] below this level. Rather, the provisions generally call for reduction of MEI risk to a level no higher than 1 in 10,000, although in some cases, risks greater than 1 in 10,000 may be allowable.) Similarly, a one in a million cancer risk is the threshold below which EPA is authorized under CAA § 112( c)( 9)( B) to remove entire source categories from the purview of MACT regulation. Where Congress has authorized the wholesale removal of entire source categories on the basis of a cancer risk below one in a million, EPA is certainly warranted in exercising its de minimis authority to provide a significantly more limited emission standard premised on the same level of risk. Commenters IV D 61 and IV D 123 contended that use of the phrase " de minimis" in CAA § 112( g)( 1) does not limit EPA's exercise of its de minimis authority in the MACT context. Although the phrase " de minimis" is only used in CAA § 112( g)( 1), there is no legal or policy 215 basis for assuming that Congress intended to preclude EPA's exercise of its de minimis authority in every other regulatory context affecting HAPs. Federal agencies, including EPA, are presumed to have de minimis authority regardless of whether such authority is expressly granted by statute. Appellate caselaw recognizes that federal agencies have an inherent authority to exempt de minimis sources of risk from even highly prescriptive statutory requirements, so long as the legislative mandate is not " extraordinarily rigid" ( EDF, 82 F. 3D at 466) and the exemption is consistent with the legislative purpose ( here, the health protective purpose of the CAA). The commenters argued that CAA § 112 is not " extraordinarily rigid" and that Congress had ample opportunity to make § 112 " extraordinarily rigid" when it developed the 1990 CAAA. The commenters stated that EPA's exercise of its de minimis authority under CAA § 112 is consistent with traditional canons of statutory interpretation. The argument that the isolated use of the term " de minimis" in CAA § 112( g)( 1) somehow precludes the exercise of EPA's de minimis authority in setting the MACT floor does not withstand scrutiny under principles of statutory interpretation for three reasons: ( 1) the use of a term in one statutory provision is, at most, a weak indicator of congressional intent to foreclose the term's application in other statutory provisions ( See, e. g., Mourning v. Family Publications Serv., Inc., 411 U. S. 356 ( 1973) and also United States v. Vonn, 535 U. S. 55 ( 2002) summarized on pp. 58 59 of IV D 61); ( 2) the preclusive effect of the isolated use of a term is even more attenuated where, as here, the provision in which the term appears has little in common with the provision in which its absence would be interpreted ( see City of Columbus v. Ours Garage & Wrecker Serv., 536 U. S. 424 ( 2002)); and ( 3) any purported preclusive effect is weakened further in the context of agency rulemaking, such as the process of MACT standard setting. Commenter IV D 123 attached a white paper in the context of the boiler MACT ( see attachment A of IV D 123). Arguments presented in the white paper that are not discussed elsewhere in this document are summarized below for the white paper submitted with IV D 123. Commenter IV D 123 stated that the Congressional intent expressed in the CAA § 112( d)( 3)( A) MACT floor language did not preclude consideration of non HAP environmental impacts. The CAA's structure, appellate case law, and Agency practice suggest that EPA should take a broad view of the terms " best performing" and " emission limitations" considering the non HAP disbenefits of controls. This interpretation is supported because: ( a) EPA and the D. C. Circuit have previously interpreted the phrase " best performing" as encompassing non HAP environmental impacts ( see 66 FR 3180, 3187 ( January 12, 2001), NESHAP for Chemical Recovery Combustion Sources at Kraft, Soda, Sulfite, and Stand Alone Semichemical Pulp Mills); ( b) the CAA calls for excluding from the MACT floor calculation sources that have complied with recent emission standards ( lowest achievable emission rate [ LAER] standards) directed toward criteria pollutants rather than HAPs; and ( c) the MACT floor language in not limited to an evaluation of HAP emissions, but rather contains the more general term " emissions limitation" whereas surrounding language refers specifically to HAP emissions. The commenter argued that when Congress uses different terms in the same section of a statute that Congress intends different meanings ( see e. g., American Petroleum Instit. v. EPA, 198 F3d 275 ( D. C. Cir. 2000)). The commenter believes these three points support their conclusion that § 112 is not " extraordinarily rigid." The commenter also contended that EPA has de minimis authority under § 112 that is consistent with the health protective purpose of the statute, as expressed by the provisions health 216 based regulatory thresholds. CAA § 112 differentiates between threshold HAPs ( for which a health benchmark can be established) and non threshold HAPs. Providing de minimis exemptions below the regulatory thresholds contained in the CAA for both types of HAPs is justified under D. C. Circuit precedent because it " squares with the health protective purpose of the statute." ( Ohio, 997 F2d at 1535). Commenter IV D 123 stated that irrespective of § 112( d)( 4), EPA has ample de minimis authority to implement risk based approaches for non threshold carcinogens. The commenter argued that NRDC's characterization of the nature and extent of EPAs de minimis authority is contradicted by the unanimous weight of appellate caselaw. Appellate caselaw establishes that EPA has inherent authority to make determinations affecting de minimis sources of risk even under highly prescriptive statutory requirements, so long as the legislative mandate is not " extraordinarily rigid" and the exemption is consistent with legislative intent. Sections 112( c)( 9) and ( f)( 2) are properly construed not as sources of de minimis authority, but as indications of the level of cancer risk Congress considered to be de minimis. NRDC's claim that EPA has rejected its de minimis authority in the context of § 112 is contradicted by the relevant rulemaking record and by EPA's general practice. The instance cited by NRDC, where EPA declined to exercise its de minimis authority was a substantially different scenario. In the cited rulemaking, EPA declined to apply the de minimis doctrine to change the MACT floor determination, noting that the doctrine may not be invoked to alter the MACT floor on the basis of a cost benefit analysis. The de minimis doctrine in this case is not being advanced as a basis for EPA to alter its MACT floor determination. Nor is it being advanced on the basis of a cost benefit analysis, but rather on the basis of the acknowledged minimal risks that the rules would regulate. The legislative history cited by NRDC does to limit EPA's de minimis authority under § 112. Sen. Durenberger's statements are best viewed as one legislator's opinion as to what a piece of legislation should mean, rather than a definitive explanation of Congressional intent. The supreme court has held that " the remarks of a single legislator, even the sponsor, are not controlling in analyzing legislative history." Sen Durenberger's statement was a discussion of the express authority granted by the residual risk provisions of § 112( f), not of EPA's implicit de minimis authority, and as a result, should have no bearing on EPA's de minimis authority, even if given weight. Commenter IV D 61 cited EPA's brief in National Lime Association v. EPA, 233 F. 3D 625 ( D. C. Cir. 2000) and noted that the D. C. Circuit held that EPA reasonably declined to provide a de minimis exemption on the basis of cost for the Portland Cement NESHAP, but the court did not limit EPA's de minimis authority under CAA § 112 in any other way. Commenter IV D 72 stated that EPA has wrongfully attempted to deny its de minimis authority based on the National Lime Association v. EPA court case. 233 F. 3D 625 ( D. C. Cir. 2000) In that case, the court found, in part, that the CAA does not provide for exemptions from emission standards based upon either cost concerns or a source emitting a de minimis quantity of HAP when a MACT floor exists for the source category. The court did not address the issue of EPA's authority to provide for exemptions based upon either de minimis emissions or de minimis effect upon human health and the environment. The commenter stated that they are not arguing for cost based exemptions; rather they believe that EPA can structure the MACT rules in such a way that de minimis levels of emissions or de minimis levels of risks to public health are not subject to the technology based standards developed under § 112( d)( 3). Commenter IV D 72 stated that case law ( National Lime) prohibits EPA from exempting a source category based on a de minimis quantity if MACT floor exists, but does not prohibit EPA from exempting based on a de minimis effect, even if there is a floor. 217 Commenter IV D 72 further indicated that unless a statute is " extraordinarily rigid," relevant case law ( Alabama Power) allows using de minimis concepts in regulatory programs when the statute would otherwise yield a " gain of trivial or no value" or if the statute would require " absurd or futile results" in terms of risk to human health and the environment. The commenter agreed with AF& PA white papers, which show that de minimis applicability exemptions based on risk and the risk based delisting of sources are prime examples of EPA's authority to consider de minimis and to determine whether a NESHAP results in a " gain of trivial or no value" or leads to " absurd or futile results." Commenter IV D 72 stated that the statute provides both implicit and explicit de minimis authority, and added that this position is supported by the statute itself in that sections 112( c)( 9)( B), 112( d)( 4), and 112( f)( 2)( A) all discuss the objectives of the § 112( d) standards in terms of the effect of the pollutants on human health and the environment. None of these provisions require that HAP be regulated simply for the sake of regulation, but, rather, provide guidance as to what constitutes " acceptable" emissions based on the health impact of those emissions. The commenter stated that § 112( d)( 4) provides that MACT standards set under § 112( d)( 3) need not be any more stringent than necessary to protect public health with an ample margin of safety. Hence, there is no requirement to control HAP simply for the purpose of controlling HAP. Commenter IV D 72 stated that the case law supports EPA's de minimis authority. The Vinyl Chloride case outlined EPA's authority for determining what constitutes a de minimis or " safe" level of exposure to a HAP, particularly with respect to carcinogens. Among the courts findings were: the Administrator must make an initial determination of what is " safe;" and, the Administrator's decision does not require a finding that " safe" means " risk free" or a finding that the determination is free from uncertainty. Furthermore, in § 112, Congress provides clear guidance to EPA regarding what it considers an " ample margin of safety" for compounds that may be carcinogens. Specifically, a " safe" level is that which poses a risk of excess cancer to the most exposed individual to less than one in one million. The EPA is empowered to promulgate a de minimis exemption from a NESHAP based upon the Administrator's determination of an acceptable level of exposure to a HAP that protects human health and the environment with an ample margin of safety. Commenter IV D 72 agreed with AF& PA that EPA makes de minimis applicability determinations ( e. g., HON for equipment leaks, and a recently issued direct final rule to exempt " Noncommercial incineration of dead animals, the onsite incineration of resident animals..." 67 FR 55129, August 28, 2002). EPA issued a direct final rule to exempt " non commercial incineration of dead animals, the on site incineration of resident animals for which no consideration is received or commercial profit is realized, as authorized in section 269.020.6, RSMo 2000." The MDNR submitted information that emissions from these sources is minimal and that the exemption should not have an adverse impact on ambient air quality. No existing incinerators in this source category are subject to the operating permit program, due to their de minimis size. This is clearly an exemption based on de minimis authority. Commenter IV D 72 stated the case that EPA should allow no exemptions when all of the emission reductions benefit health and the environment; should allow for exemptions when the all of the effects are de minimis; and should do a combination of the two for cases where some of the reductions yield benefits, but part of the reductions do not. EPA should regulate only those sources that would provide benefit. Commenter IV D 75 stated that § 112 also provides EPA with the authority to exclude 218 sources through its de minimis authority. The commenter stated that relevant case law ( see EDF v. EPA, 82F. 3D 451, 466 ( D. C. Cir. 1996)) gives EPA the authority to incorporate de mimimis concepts into regulatory programs as long as the governing statute is not " extraordinarily rigid." Section 112 has several references to risk, distinguishing among sources, and alternative approaches to § 112( d)( 3) MACT standards. Section 112 cannot be viewed as " extraordinarily rigid." The commenter also believes it is appropriate based on the decision by the D. C. Circuit in Alabama Power v. Costle, 636 F. 2nd 323 ( D. C. Cir 1979), for EPA to establish exemptions from what " in context may fairly be considered de minimis." 636 F2. nd, 323, 360. Commenters IV D 73 and IV D 166 believe that EPA could accomplish the same outcome as a § 112( d)( 4) emissions limitation if it applied an emissions limitation on nonthreshold pollutants using its inherent de minimis authority instead of a limit based on § 112( d)( 4). Commenter IV D 175 asserted that EPA has the authority to promulgate risk based standards for non threshold pollutants. The commenter stated that the courts have long recognized that EPA has the inherent authority to promulgate de minimis exemptions under most circumstances, even where the statute does not expressly authorize such an exemption and cites the following examples: In Envt'l Defense Fund v. EPA, 82 F. 3D 451, 466 ( D. C. Cir. 1996), the court held that "[ a] s long as the Congress has not been ` extraordinarily rigid' in drafting the statute... ` there is likely a basis for an implication of de minimis authority to provide [ an] exemption when the burdens of regulation yield a gain of trivial or no value.' " Id. at 466( citations omitted)( commenter emphasis added). The court found " nothing in the [ CAA] to preclude the EPA's identification of categories of [ exempt activities] that would produce either no or a trivial level of emissions[.]" Id. at 466 7. According to the commenter, although the EDF ruling was in the context of the Clean Air Act transportation conformity regulations, the court's reasoning applies equally to any other Clean Air Act program, including the MACT program.

In another case, the court held that categorical exemptions from a statutory requirement constitute " an exercise of agency power, inherent in most statutory schemes, to overlook circumstances that in context may fairly be considered de minimis." Alabama Power Co. v. Costle, 636 F. 2D 323, 360 ( D. C. Cir. 1979). The commenter noted that the court reasoned that the ability to create a deminimis exemption " is not an ability to depart from the statute, but rather a tool to be used in implementing the legislative design." Id.

Similarly, in Ober v. Whitman, 243 F. 3D 1190 ( 9th Cir. 2001), the Ninth Circuit upheld EPA's exemption of de minimis sources of PM 10 from control requirements under a federal implementation plan.