K. Periodic DRE Testing and Limits on Minimum Combustion Chamber Temperature for Cement Kilns Comment: Several commenters oppose the need for cement kilns that burn at locations other than the normal flame zone to demonstrate compliance with the destruction and removal efficiency ( DRE) standard during each comprehensive performance test. These commenters recommend that EPA remove the requirement of § 63.1206( b)( 7)( ii) for cement kilns citing that existing rule provisions ( i. e., the requirements under § 63.1206( b)( 5) pertaining to changes that may adversely affect compliance) are sufficient to require additional DRE testing after changes are made that may adversely affect combustion efficiency. Commenters question EPA's position that cement kilns that burn hazardous waste at locations other than the normal flame zone demonstrate a variability in DRE sufficient to justify the expense of re testing for DRE with each performance test. Commenters point to EPA's data base that includes DRE results from over 30 tests with nearly 250 runs showing consistent DRE results, including sources burning hazardous waste at locations other than the normal flame zone, being achieved by cement kilns. The commenters note several burdens associated with DRE testing that do not result in improved environmental benefit including the purchase of 70 expensive exotic virgin chemicals for performance testing, the risks to workers and contractors associated with the handling of these chemicals, and increasing the length of operation at stressful kiln operating conditions necessary to conduct DRE testing at minimum combustion chamber temperatures. Alternatively, commenters recommend that EPA revise the DRE requirements such that periodic testing is no longer required for cement kilns ( that burn at locations other than the normal flame zone) after they have successfully achieved the DRE standard over multiple testing cycles ( e. g., two or three) under similar testing regimes. That is, the source should only be required to demonstrate compliance with the DRE standard a maximum of two or three times until the source ( that burns at locations other than the normal flame zone) modifies the system in a manner that could affect the ability of it to achieve the DRE standard. Response: We are revising the requirements of § 63.1206( b)( 7)( ii) such that cement kilns that feed hazardous waste at locations other than the normal flame zone need only demonstrate compliance with the DRE standard during three consecutive comprehensive performance tests provided that the source has successfully demonstrated compliance with the DRE standard in each test and that the design, operation, and maintenance features of each of the three tests are similar. These revisions do not affect sources that burn hazardous waste only in the normal flame zone. 71 Prior to today's change, we required sources that feed hazardous waste in locations other than the flame zone to perform periodic DRE testing every 5 years to ensure that the DRE standard continues to be achieved over the life of the unit. See § 63.1206( b)( 7)( ii). We justified this requirement because of concerns that sources that feed hazardous waste at locations other than the flame zone have a greater potential of varying DRE performance due to their hazardous waste firing practices. As we stated in the 1999 rule, we were concerned that the DRE may vary over time due to the design and operation of the hazardous waste firing system, and that those variations may not be identical or limited through operating limits set during a single DRE test ( similar to what we concluded for sources that burn hazardous waste only in the normal flame zone). See 64 FR at 52850. Commenters now question the need for subsequent DRE testing at cement kilns that feed hazardous waste at locations other than the normal flame zone once a cement kiln demonstrates compliance with the MACT DRE standard. The regulatory requirement for the destruction and removal efficiency standard has proved to be an effective method to determine appropriate process controls necessary for the combustion of hazardous waste. We are not convinced that only one DRE test is sufficient to ensure that a cement kiln that burns hazardous waste at locations other than the normal flame zone will continue to meet the DRE standard because temperatures are lower and gas residence times are shorter at the other firing locations. This is especially true given the industry trend to convert to the more thermally efficient preheater/ precalciner kiln manufacturing process. 72 Precalciner kilns use a secondary firing system ( i. e., flash 71 The DRE demonstration for these sources need be made only once during the operational life of a source, either before or during the initial comprehensive performance test, provided that the design, operation, or maintenance features do not change in a manner that could reasonably be expected to affect the ability to meet the DRE standard. See § § 63.1206( b)( 7) and 63.1207( c)( 2)( ii). The source would ensure continued compliance by operating under the operating parameter limits established during this DRE test. 72 For example, Ash Grove Cement in Chanute, KS replaced their two wet process cement kilns with one preheater/ precalciner kiln in 2001. Holcim Inc in Holly Hill, SC has also recently constructed a new 71 furnace) at the base of the preheater tower to calcine the raw material feed outside the rotary kiln. This results in two separate combustion processes that must be controlled   one in the kiln and the other in the flash furnace. The gas temperature necessary for calcining the limestone raw material in the flash furnace is lower than the temperature required making the clinker product. We conclude, therefore, that it is necessary, in spite of the concerns raised by commenters, to retain periodic DRE testing to ensure continued compliance with the DRE standard necessary for the control of nondioxin/ furan organic HAP. We also acknowledge, however, the concerns raised by the commenters. Our DRE data base of operating cement kilns includes results from approximately 25 DRE tests and nearly 200 runs. 73 All data show compliance with the DRE standard. Of these, approximately one quarter of the data are from cement kilns that burned hazardous waste at locations other than the normal flame zone ( e. g., injecting waste at midkiln in a wet process kiln), but we do not have DRE results from every operating cement kiln. Considering available DRE data and the concerns of the commenters, we believe that DRE testing during three consecutive comprehensive performance tests is sufficient to provide needed certainty about DRE performance while reducing the overall costs and toxic chemical handling concerns to the regulated source. Thus, we are revising the requirements of § 63.1206( b)( 7)( ii) such that cement kilns that feed hazardous waste at locations other than the normal flame zone need only demonstrate compliance with the DRE standard during three consecutive comprehensive performance tests provided that the source has successfully demonstrated compliance with the DRE standard in each test and that the design, operation, and maintenance features of each of the three tests are similar. If a facility wishes to operate under new operating parameter limits that could be expected to affect the ability to meet the DRE standard, then the source would need to conduct another DRE test. Once the facility has conducted another three DRE tests under the new operating limits, then subsequent DRE testing would not be required. Accordingly, we are revising the requirements of § 63.1206( b)( 7)( ii). Comment: Several commenters support EPA's proposal to delete the requirement to establish an operating limit on the minimum combustion chamber temperature for dioxin/ furans under § 63.1209( k)( 1) for cement kilns. These commenters point to the high temperatures of approximately 2500 ° F required to make the clinker product. These high temperatures are fixed by the reaction kinetics and thermodynamics occurring in the burning zone and cannot be reduced below minimum values at the whim of the operator and still make a marketable product. In addition to deleting the minimum combustion chamber temperature limit for dioxin/ furans, commenters also recommend, for similar reasons, that EPA delete the minimum combustion chamber temperature requirement under § 63.1209( j)( 1) associated with the destruction and removal efficiency standand. Commenters note that demonstrating the minimum temperature requires operating under stressful operating conditions that can lead to upset conditions and potentially damage the integrity of the manufacturing equipment. Other commenters oppose, however, deletion preheater/ precalciner kiln to replace two wet process cement kilns. Keystone Cement Company in Bath, PA is considering replacing their two wet process cement kilns with a new preheater/ precalciner kiln. See docket item OAR 2004 0022 0384. 73 US EPA, " Final Technical Support Document for HWC MACT Standards, Volume III: Selection of MACT Standards and Technologies," Section 23.4, September 2005. 72 of the minimum combustion chamber temperature limit for cement kilns. These commenters state that all combustion sources, including cement kilns, must meet a minimum combustion chamber temperature limit to control dioxin/ furans and organic HAP emissions given that some cement kilns feed hazardous waste at locations other than the high temperature clinker forming zone of the kiln. Response: We are deleting as proposed the requirement to establish a minimum combustion chamber temperature limit for dioxin/ furan under § 63.1209( k)( 2) for cement kilns. See 69 FR at 21343. However, we retain the requirement for cement kilns to establish and comply with a minimum combustion chamber temperature limit for the destruction and removal efficiency standard under § 63.1209( j)( 1). 74 As discussed in the 1999 rule, nondioxin/ furan organic hazardous air pollutants are controlled by the DRE standard and the carbon monoxide and hydrocarbon standards. See 64 FR at 52848 852. This standard was not reopened in the present rulemaking. We note, however, that the DRE standard determines appropriate process controls necessary for the combustion of hazardous waste. Establishing and monitoring a minimum temperature of the combustion chamber is a principal factor in ensuring combustion efficiency and destruction of toxic organic compounds. As discussed in the previous response, we believe this is especially true given the industry trend to convert to the more thermally efficient preheater/ precalciner kiln manufacturing process, which use two separate combustion processes. We conclude that it is necessary, in spite of the concerns raised by commenters, to retain the minimum combustion chamber temperature limit as related to the DRE standard to ensure that combustion efficiency within the entire kiln system is maintained for the control of nondioxin/ furan organic HAP. However, we acknowledge the difficulties that cement kiln operators face in establishing a minimum combustion chamber temperature limit, including the stressful operating conditions necessary to establish the limit. As we stated at proposal, our data indicate that limiting the gas temperature at the inlet to the particulate matter control device is a critical parameter in controlling dioxin/ furan emissions in cement kilns. See 69 FR at 21344. Therefore, we believe that an operating limit on the minimum combustion chamber temperature is less important to ensure compliance with the dioxin/ furan standard than to ensure compliance with the DRE standard. Thus, we remove the requirement to establish a minimum combustion chamber temperature limit for dioxin/ furan under § 63.1209( k)( 2) for cement kilns. This change does not affect the other operating parameter limits under § 63.1209( k) that must be established for dioxin/ furans, including a limit on the gas temperature at the inlet to the particulate matter control device. Comment: One commenter supports the use of previous minimum combustion zone temperature data, regardless of the test age, in lieu of conducting new, stressful 74 Under the interim standards, cement kilns must establish and continuously monitor limits on minimum gas temperature in the combustion zone for both the dioxin/ furan and DRE standards. As discussed in the preceding paragraph, a source may not need to conduct DRE testing during each comprehensive performance test. If DRE testing is required, then the source will need to establish a minimum combustion zone temperature limit as required under the DRE standard. However, if DRE testing is not required, then ( according to the changes made today) the cement kiln will not be required to establish the minimum combustion chamber temperature limit under the dioxin/ furan standard during a subsequent comprehensive performance test. The minimum combustion chamber temperature operating limit established during previous testing remains in effect, however. 73 DRE testing. That is, if a cement kiln is required to conduct future DRE tests, then the source should not have to re establish a minimum combustion chamber temperature limit during the new test. Rather, the source should have the option to submit minimum combustion chamber temperature results in lieu of re establishing the limit. Response: We reject the commenter's suggestion for reasons discussed above. We believe that it is necessary to retain the link between the minimum combustion chamber temperature limit and the DRE test itself, which will ensure that the combustion efficiency of the entire system will be maintained for the control of nondioxin/ furan organic HAP. Comment: One commenter supports deletion of the minimum combustion chamber temperature requirement for dioxin/ furan under § 63.1209( k)( 2) for lightweight aggregate kilns. Response: We reject the commenter's suggestion. Our data base of dioxin/ furan emissions data shows substantial variability in test results at each source. 75 This may indicate that factors other than limiting kiln exit gas temperatures may be influencing significantly dioxin/ furan formation in lightweight aggregate kilns. As such, we conclude that removing the minimum combustion chamber temperature limit would not be appropriate at this time due to the uncertain nature of dioxin/ furan formation in lightweight aggregate kilns. Thus, we are retaining the requirement to establish a minimum combustion chamber temperature limit for dioxin/ furans under § 63.1209( k)( 2) and § 63.1209( j)( 1) for lightweight aggregate kilns.

L. One Time Dioxin and Furan Test for Sources Not Subject to a Numerical Limit for Dioxin and Furan Comment. Commenters support the one time dioxin/ furan test for sources not subject to a numerical dioxin and furan standard. Commenters agree that previous testing should be allowed to document the one time test. Response. The final rule requires sources that are not subject to a standard with numerical dioxin and furan levels76 to conduct a one time dioxin and furan test as part of their initial comprehensive performance testing: lightweight aggregate kilns that elect to control the gas temperature at the kiln exit rather than comply with a dioxin/ furan standard of 0.20 ng TEQ/ dscm, solid fuel boilers, liquid fuel boilers with wet or no air pollution control systems, and HCl production furnaces. We will use these data as part of the process of addressing residual risk under CAA section 112( f) and evaluating future MACT standards under section 112( d)( 6). The results may also be used as part of the RCRA omnibus permitting process. Comment. EPA proposed that source not subject to a numerical dioxin and furan limit conduct a dioxin and furan test under worst case conditions. Commenters state that operating under worst case conditions is inconsistent with the CAA Section 112( f)

75 For example, dioxin/ furan emissions from source number 307 range from a low of 0.024 to a high of 57.9 ng TEQ/ dscm. See " Source Category Summary Sheets" available in the docket or USEPA, " Final Technical Support Document for HWC MACT Standards, Volume II: HWC Data Base," September 2005. 76 These sources do, however, need to comply with the carbon monoxide or hydrocarbon standards, as well as the DRE standard as surrogates to comply with today's dioxin and furan emissions control requirements. 74 process, which is to consider actual ( i. e., normal) emissions. Commenters suggest that we require the tests be conducted under normal to above normal conditions. Response. Section 112 ( f) standards evaluate allowable emission levels, although actual emissions levels may also be considered. See 70 FR at 19998 999 ( April 15, 2005). Although we agree with the commenter that, in general, emissions in the range of normal to maximum are considered for section 112( f) determinations, we believe that dioxin/ furan testing to provide information of use in section 112( f) residual risk determinations should be conducted under conditions where controllable operating conditions are maximized to reflect the full range of expected variability of those parameters which can be controlled. This is because dioxin/ furan emissions may relate exponentially with the operating conditions that affect formation. We believe that dioxin/ furan emissions relate exponentially with gas temperature at the inlet to an ESP or fabric filter, 77 and are concerned that emissions may also relate exponentially with the operating parameters ( discussed below) that affect emissions from sources subject to the one time dioxin/ furan emissions test. Emissions testing under operating conditions that are in the range of " normal to above normal" may be exponentially lower than emissions under operating conditions reflecting maximum daily variability of the source. Since testing under normal operating conditions makes no effort to assess operating variability, emissions during such testing would fail to reflect expected daily maximum operating variability and so would not represent time weighted average emissions and would under represent health risk from chronic exposure. Although we acknowledge that sources will not exhibit maximum operating variability each day of operation, we believe that it is important to assess the upper range of emissions that these sources may emit to properly evaluate under section 112( f) whether the MACT standards for dioxin/ furan for these sources ( i. e., absent a numerical emission standard) protect public health with an ample margin of safety. 78 In addition, we note that emissions reflecting daily maximum variability would be most useful for section 112( d)( 6) determinations in the future because they would represent the full range of emissions variability that results from controllable operating conditions. For these reasons, the final rule requires sources to test under feed and operating conditions that are most likely to reflect maximized expected daily variability of dioxin/ furan emissions, as proposed. Such testing is similar to a comprehensive performance test to demonstrate compliance with a numerical dioxin/ furan emission standard where operating limits would be established based on operations during the test. As a practical matter, however, we note that many of the operating parameters discussed below, although controllable to some extent, cannot be quantified and cannot be controlled to replicate the condition in a future test. In addition, some operating parameters we identify may not have as strong a relationship to dioxin/ furan emissions as others. Consequently, the operating conditions are generally described subjectively.

77 See USEPA, " Technical Support Document for HWC MACT Standards, Volume IV: Compliance," July 1999, Chapter 3. 78 Dioxin/ furan are some of the most toxic compounds known due to their bioaccumulation potential and wide range of health effects, including carcinogenesis, at exceedingly low doses. Exposure via indirect pathways is a chief reason that Congress singled out dioxin/ furan for priority MACT control in CAA section 112( c)( 6). See S. Rep. No. 128, 101st Cong. 1st Sess. at 154   155. 75 Based on currently available research, you should consider the following factors to ensure that you conduct the test under operating conditions that seek to fully reflect maximum daily variability of dioxin/ furan emissions: ( 1) dioxin/ furan testing should be conducted at the point in the maintenance cycle for a boiler when the boiler tubes are more fouled and soot laden, and not after maintenance involving soot or ash removal from the tubes; ( 2) dioxin/ furan testing should be performed following ( or during) a period of feeding normal or greater quantities of metals; ( 3) dioxin/ furan testing should be performed while feeding normal or greater quantities of chlorine; ( 4) the flue gas temperature in some portion of the heat recovery section of a boiler should be within the dioxin formation temperature window of 750 to 400 ° F during the testing; ( 5) the testing should not be conducted under optimal combustion conditions ( e. g., combustion chamber temperature should be in the range of normal to the operating limit; hazardous waste feedrate and combustor through put should be in the range of normal to maximum); ( 6) for units equipped with wet air pollution control systems, the testing should be conducted after a high solids loading has developed in the scrubber system ( consistent with normal operating cycles); and ( 7) for solid fuel boilers, the sulfur content of the coal should be equivalent to or lower than normal coal sulfur levels ( within the range of sulfur levels that the source utilizes), and the gas temperature at the inlet to the electrostatic precipitator or fabric filter should be close to the operating limit. In addition, unless sulfur compounds are routinely fed to the boler, dioxin/ furan testing should not be performed after a period of firing high sulfur fuel or injection of sulfur additives. See 69 FR at 21308 for more information. Comment. Commenters state that we should delete the one time testing requirement for dioxin and furans. The Clean Air Act at Section 114( a)( 1)( D) allows EPA to request " any person" to sample emissions. Applying the Section 114 authority to an entire subcategory of sources is overly broad, particularly in the context of having already established appropriate surrogates for dioxin and furan in a MACT rule. Commenters are not aware of EPA taking this approach in previous efforts. ( Section 114 requests have focused on collecting existing information from sources facing future MACT standards). Commenters oppose this approach because it established a precedent they do not favor, and will bring about significant costs and difficulties to provide the data. They suggest that we delete the proposed requirements for a one time dioxin and furan test. Response. We believe that section 114( a)( 1)( D) of the Clean Air Act provides us the authority to require sources to conduct a one time test to generate data which can be used in making later section 112 ( f) determinations for the source category. The results of the testing may also inform the section 112( d)( 6) review and the RCRA omnibus permitting processes. The fact that section 114 specifically indicates that a purpose of gathering information under section 114 is to assist in developing national rules indicates that the provision can have wide sweep extending to all sources in a category. See 69 FR at 21307 308 for a full explanation. We believe a dioxin and furan test costs approximately $ 10,000 when conducted along with other testing. We do not believe this cost is significant, and sources must only perform this test once, not more frequently as would be the case to ensure compliance with a standard. We also allow sources to use prior testing to meet this requirement, and 76 allow sources to use " data in lieu" so they can test one source if they have more than one of the same identical sources. We do not believe that obtaining these data will be difficult, and note that the permitting authority can assist sources in planning their tests.

M. Miscellaneous Compliance Issues Comment: Several commenters state that § 63.1206( c)( 3)( iv) requiring an automatic waste feed cutoff ( AWFCO) if a parameter linked to the AWFCO is exceeded should be revised to reflect § 63.1206( c)( 2)( v)( A)( 1). Section 63.1206( c)( 2)( v)( A)( 1) states that, if the AWFCO is affected by a malfunction such that the malfunction itself prevents immediate and automatic cutoff of the hazardous waste feed, you must cease feeding hazardous waste as quickly as possible. Response: We agree with commenters in principle, but note that the automatic waste feed cutoff system may fail for reasons other than a malfunction. That is, equipment or other failures are malfunctions only if they meet the definition of malfunction at § 63.2. Failures that result from improper maintenance or operation are not malfunctions. Consequently, the final rule revises § 63.1206( c)( 3)( iv) to state that if the AWFCO is affected by a failure such that the failure itself prevents immediate and automatic cutoff of the hazardous waste feed, you must cease feeding hazardous waste as quickly as possible. Revised § 63.1206( c)( 3)( iv) does not refer to malfunctions, however, because the AWFCO system may fail for reasons other than a malfunction. The reference in § 63.1206( c)( 2)( v)( A)( 1) to malfunctions is appropriate because that paragraph addresses requirements during malfunctions. Comment: Several commenters note that the proposed rule did not include a sunset provision for the Interim Standards applicable to incinerators, cement kilns, and lightweight aggregate kilns after the compliance date of the standards we promulgate today ( i. e., the " permanent replacement standards"). Commenters are concerned that, although the Agency intends for the replacement standards to be more stringent than the Interim Standards, that may not be the case in all situations because of the different format used for some of the replacement standards. For example, several of the replacement standards for cement kilns and lightweight aggregate kilns are expressed as hazardous waste thermal emissions. Response: Although we are promulgating the replacement standards in a format that ensures they are not less stringent than the Interim Standards, we agree with commenters that not sunsetting the Interim Standards may lead to confusion as to which standards apply. Consequently, we include a sunset provision in today's rule for the Interim Standards. The Interim Standards will be superseded by the final rule promulgated today on the compliance date. We note, however, that the Interim Standards for total chlorine continue to apply to sources that establish health based limits for total chlorine under § 63.1215. Consequently, we have incorporated the total chlorine Interim Standards in § 63.1215 as they apply as a cap to the health based emission limits. Comment: Several commenters state that the rule should allow extrapolation of ash and chlorine feedrates to establish feedrate limits corresponding to the particulate matter and total chlorine standards. Commenters believe the rationale we use to allow extrapolation of metals feedrates is also applicable to ash and chlorine. 77 Response: The final rule does not allow you to extrapolate ash and chlorine feedrates achieved during the comprehensive performance test to establish feedrate limits comparable to the particulate matter and total chlorine emission standards. We do not allow extrapolation of ash to the particulate matter emission standard because particulate matter ( i. e., soot) may form in the combustor, particularly at times of unstable combustion conditions. Consequently, extrapolating from ash feedrates may underestimate particulate matter emissions and may not ensure compliance with the particulate matter emission standard. We do not allow extrapolation of chlorine feedrates to the total chlorine emission standard because chlorine feedrate is an operating parameter limit to ensure compliance with the semivolatile metal emission standard. Because an increase in chlorine feedrate can increase the volatility of semivolatile metals and we do not know the precise relationship among chlorine feedrate, metal volatility, and metals emissions, extrapolating the chlorine feedrate achieved during the comprehensive performance test to a feedrate comparable to the total chlorine emission standard may not ensure compliance with the semivolatile metal emission standard. If a source complies with the semivolatile metals emission standard under § 63.1207( m)( 2) where the performance test is waived, however, by assuming zero system removal efficiency and limiting the semivolatile feedrate ( expressed as a maximum theoretical emission concentration) to the level of the emission standard, the source may request under § 63.1209( g)( 1) to extrapolate chlorine feedrates during the comprehensive performance test up to the total chlorine emission standard. Comment: Several commenters state that the proposed regulatory language under § § 63.1206( b)( 9)( i) and 63.1206( b)( 10)( i) is inconsistent with the proposed preamble, which states that sources should be allowed to petition for alternative standards provided they submit information showing that HAP contributions to emissions from the raw materials are preventing the source from achieving the emissions standard though the source is using MACT control. 79 The commenters state that the proposed regulatory language, despite the intent signaled in the proposed preamble, inappropriately excludes the provisions of § § 63.1206( b)( 9)( i) and 63.1206( b)( 10)( i) as an alternative option when complying with the replacement emission standards under § § 63.1220 and 63.1221. Response: We agree with the commenters. The proposed regulatory text inadvertently excluded the alternative standard provisions from use by cement and lightweight aggregate kilns under the replacement standards. Accordingly, we are revising the introductory text of § § 63.1206( b)( 9)( i) and 63.1206( b)( 10)( i) by making the alternative standards available under the replacement standards. Comment: One commenter states that the availability of the alternative standard for mercury under § 63.1206( b)( 10)( i) should not be conditioned upon mercury being present only at levels below the detection limit in raw materials, as specified under § 63.1206( b)( 10)( i)( B). The commenter suggests that the approach for mercury should be the same as for other HAP such as semi and low volatile metals under § 63.1206( b)( 10)( i)( A). Response: The commenter misreads the alternative standard provisions under § 63.1206( b)( 10)( i). We note that § 63.1206( b)( 10) includes two separate provisions for cement kilns. The first provision allows sources to petition for an alternative standard 79 For example, see 69 FR at 21268. 78 when a source cannot achieve a standard because of HAP metal or chlorine concentrations in their raw material feedstocks cause an exceedance of a standard despite the source's use of MACT control. See § 63.1206( b)( 10)( i)( A). The term " regulated metals" specified in § 63.1206( b)( 10)( i)( A) includes mercury, semivolatile metals, and low volatile metals. The second provision allows a source to petition for an alternative mercury standard when mercury is not present at detectable levels in the source's raw materials. § 63.1206( b)( 10)( i)( B). These two provisions are indeed separate as discussed in the 1999 rule. See 64 FR at 52962 967. Also note that the conjunction separating paragraphs ( b)( 10)( i)( A) and ( b)( 10)( i)( B) is " or," not " and." Given the potential confusion of the term " regulated metals," we are clarifying the regulatory text by specifying the three metal HAP volatility groups that comprise the term " regulated metals." See revised § 63.1206( b)( 10)( i)( A). Finally, given that the alternative standard provisions are similar for lightweight aggregate kilns, we are also clarifying § § 63.1206( b)( 9)( i)( A) and ( b)( 9)( iv).

IX. Site Specific Risk Assessment under RCRA A. What Is the Site Specific Risk Assessment Policy? The Site Specific Risk Assessment ( SSRA) Policy has undergone several revisions since its inception in the 1993 draft Combustion Strategy. Currently, it is the same policy as we expressed in the 1999 final rule preamble. In the 1999 rule, we recommended that for hazardous waste combustors subject to the Phase 1 MACT standards, permitting authorities should evaluate the need for an SSRA on a case by case basis. Further, while SSRAs are not anticipated to be necessary for every facility, they should be conducted where there is some reason to believe that operation in accordance with the MACT standards alone may not be protective of human health and the environment. For hazardous waste combustors not subject to the Phase 1 standards, we continued to recommend that SSRAs be conducted as part of the RCRA permitting process. See 64 FR 52841. Since 1999, we have provided additional clarification of the appropriate use of the SSRA policy and technical guidance in an April 10, 2003 memorandum from OSWER's Assistant Administrator to the EPA Regional Administrators entitled, " Use of the Site Specific Risk Assessment Policy and Guidance for Hazardous Waste Combustion Facilities" ( see Docket # OAR 2004 0022 0083). Most importantly, in this memorandum we reiterated that where a permitting authority concludes that a risk assessment is necessary for a particular combustor, the basis for this decision must be substantiated in each case. The factual and technical basis for any decisions to conduct a risk assessment must be included in the administrative record for the facility per 40 CFR § § 124.7, 124.8, 124.9, and 124.18. In addition, if the facility, or any other party, files comments on a draft permit decision objecting to the permitting authority's conclusions regarding the need for a risk assessment, the permitting authority must respond fully to the comments. Any permit conditions determined to be necessary based either on the SSRA, or because the facility declined to conduct an SSRA, also must be documented and supported in the administrative record. Today, we are codifying additional regulatory language providing authority for SSRAs while maintaining the same basic SSRA policy. It is important to note that all of the requirements of Part 124 referred to above will continue to apply to actions taken in accordance with the additional regulatory language we are codifying. The SSRA 79 regulatory provisions, which establish that the need for an SSRA should be determined on a case by case basis, apply equally to both Phase 1 and Phase 2 sources.

B. Why Might SSRAs Continue To Be Necessary for Sources Complying With Phase 1 Replacement Standards and Phase 2 Standards?

EPA conducted a national evaluation of human health and ecological risk for the MACT standards as proposed in the 1996 NPRM and then revised the evaluation to include more facilities for the 1999 final rulemaking. Based on the results of the final national risk evaluation for hazardous air pollutants ( excluding non dioxin products of incomplete combustion), we concluded that sources complying with the MACT standards generally would not pose an unacceptable risk to human health or the environment. For today's final rule, we did not conduct another national risk assessment as we did for the 1999 rule. Rather, for both the April 20, 2004 NPRM and today's final rule we conducted a comparative risk analysis, comparing the Phase 1 Replacement and Phase 2 Standards to the 1999 promulgated Phase 1 Standards, to determine if there were any significant differences that might influence or impact the potential risk. Similar to the proposal, the comparative analysis conducted for today's final rule focused on several key characteristics: emission rates, stack height, stack gas buoyancy, meteorological conditions ( which include a number of variables), population parameters including density and radial distribution, and correlations among the characteristics themselves. The results of the comparative analysis suggest that the MACT standards for both Phase 1 and Phase 2 sources are generally protective. Therefore, separate national emissions standards under RCRA are unnecessary. See Part Seven: How Does the Final Rule Meet the RCRA Protectiveness Mandate? Although we have concluded that the Phase 1 Replacement and Phase 2 standards are generally protective, as we discussed in the 2004 proposal ( 69 FR 21325), there may be instances where we cannot assure that emissions from each source will be protective of human health and the environment, and therefore an SSRA may be necessary. Furthermore, it should be noted that, just as for the risk assessment for the 1999 rule, the comparative analysis does not account for cumulative emissions at a source or background exposures from other sources. Before discussing factors that may lead permit authorities to consider whether or not to conduct an SSRA, it should be noted that the Agency generally does not expect that facilities that have conducted risk assessments will have to repeat them. As we explained in the 1999 final rule preamble, changes to comply with the MACT standards should not cause an increase in risk for the vast majority of facilities given that the changes will likely be the addition of pollution control equipment or a reduction in the hazardous waste being burned ( see 64 FR 52842). Instances where a facility may need to repeat a risk assessment would be related to changes in conditions that would likely lead to increased risk. For example, if the only changes at a facility relate to the exposed population ( a new housing development is constructed within a few square miles of the source), what was once determined to be protective under a previous risk assessment may now be beyond acceptable levels. Another example would be where a hazardous waste burning cement kiln that previously monitored hydrocarbons in the main stack elects to install a mid kiln sampling port for carbon monoxide or hydrocarbon monitoring to avoid restrictions on hydrocarbon levels in the main stack. Thus, the stack hydrocarbon emissions may increase ( 64 FR 52843, footnote 29). In such situations, we would 80 anticipate that the risk assessment would not have to be entirely redone. It may be as limited as collecting relevant new data for comparison purposes, leading to a decision not to repeat any portion of a risk assessment. Or, it may be more inclusive such that modifications would be made to specific inputs to or aspects of the risk assessment using data from a previous risk assessment, risk burn or comprehensive performance test. In recognition of this, we have added an additional factor to the list of factors at 270.10( l)( 1) to indicate that a previously conducted risk assessment would be relevant in evaluating changes in conditions that may lead to increased risk. The factor reads as follows: " Adequacy of any previously conducted risk assessment, given any subsequent changes in conditions likely to affect risk." The following discussion is intended mainly to address facilities that have not yet conducted an SSRA ( i. e., where it has been determined that one is needed). In the proposal we discussed our conclusion that almost all of the proposed standards for Phase 1 sources were equivalent to or more stringent than the 1999 final standards, with the exception of the mercury standard for new and existing LWAKs and the total chlorine standard for new LWAKs. However, there are additional standards for Phase 1 sources finalized in today's rulemaking that are less stringent than the 1999 final standards. In addition to those discussed in the proposal, the following standards are less stringent than the 1999 final standards: mercury for new cement kilns and semi volatile metals for existing cement kilns; dioxin/ furan for existing and new LWAKs, mercury for existing and new LWAKs, and total chlorine for existing and new LWAKs. Because these standards exceed the levels which were evaluated in the 1999 national risk assessment, especially with respect to mercury and dioxin/ furan standards for which the national risk assessment showed high end risks at or near levels of concern, permit authorities may decide on a case by case basis that an SSRA is appropriate to determine whether the less stringent Replacement standards are protective. In addition, the comparative analysis results suggest concern regarding the dioxin/ furan standard for LWAKs and thus, permit authorities may consider site specific factors in determining whether the standard is sufficiently protective. Specific to Phase 2 sources, we mentioned earlier that we conducted the same comparative risk analysis for Phase 2 sources as we did for Phase 1 sources ( i. e., by comparing the Phase 2 standards to the 1999 final standards for Phase 1 sources). Although several MACT standards for Phase 2 sources are more stringent than the BIF standards under RCRA, there are a few MACT standards that may be cause for concern on a case by case basis, as they are either less stringent than some of the 1999 final standards or the comparative risk analysis suggests concern. They are: the particulate matter standard ( and certain metals such as antimony and thallium), mercury standard, and total chlorine standard for solid fuel fired boilers ( SFBs); the dioxin/ furan standard ( carbon monoxide or total hydrocarbon as surrogate controls, versus a numerical standard) for HCl production furnaces; and the dioxin/ furan standard for liquid fuel fired boilers ( LFBs) with dry APCDs. In addition, dioxin/ furan emissions data for LFBs with wet or no APCDs indicate an observed level ( 1.4 ng TEQ/ dscm) of more than three times the highest dioxin/ furan standard evaluated in the 1999 national risk assessment ( 69 FR 21285). 80 Thus, these standards may warrant site specific risk consideration, especially 80 The comparative analysis did not specifically suggest concern as it has for other source categories, but per the reference to the proposal, we have some concern regarding the protectiveness of the standard. 81 with respect to the dioxin/ furan standards. That is, due to the complexity of the dioxin/ furan formation mechanism and given the toxicity of dioxin/ furans81, an SSRA may be needed based on the specific emission levels of each source not subject to a numerical standard. For additional discussion on the protectiveness of standards, please refer to Part Seven: How Does the Final Rule Meet the RCRA Protectiveness Mandate? There are also site specific factors beyond the standards that can be important to the SSRA decision making process. As discussed in the proposal, examples include a source's proximity to a water body or endangered species habitat, repeated occurrences of contaminant advisories for nearby water bodies, the number of hazardous air pollutant emission sources within a facility and the surrounding community, whether or not the waste feed to the combustor is made up of persistent, bioaccumulative or toxic contaminants, and sensitive receptors with potentially significantly different exposure pathways, such as Native Americans ( 69 FR 21326). Also, there are several uncertainties inherent in the 1999 national risk assessment. 82 Thus, the same uncertainties related to the fate and transport of mercury in the environment and the biological significance of mercury exposures in fish ( i. e., once mercury has been transformed into methylmercury, it can be ingested by the lower trophic level organisms where it can bioaccumulate in fish tissue), as well as the risk posed by non dioxin products of incomplete combustion, remain today and may influence a permitting authority's decision. Last, we are finalizing the option for Phase 2 area sources to comply with specific MACT standards as provided by CAA § 112( c)( 6) specific pollutants authority. These area sources may need to conduct an SSRA for the remaining RCRA standards that they choose to comply with ( i. e., since they do not address the potential risk from indirect exposures to long term deposition of metals onto soils and surface waters). 83 In addition to the examples provided in the previous paragraph, we also expressed that an SSRA may be necessary with respect to the proposed thermal emission standards. With respect to Phase 1 sources, we had noted in the proposal that the thermal emission standards for semi volatile and low volatile metals for cement kilns and LWAKs may be of concern because they directly address emissions attributable to hazardous waste versus a source's total HAP metal emissions. See 69 FR 21326. However, we are requiring sources to comply with both the thermal emission standards and the Interim Standards in today's final rulemaking, since compliance with the thermal emission standards may not always assure compliance with the Interim Standards. As a result, the thermal emission standards for cement kilns and LWAKs no longer pose the uncertainties that they had in the proposal. 84 In regard to Phase 2 sources, the concern at the time of proposal was with respect to the thermal emission standards for liquid fuel fired boilers. However, the comparative analysis for today's final rulemaking for liquid fuel fired boilers, which is 81 There is ongoing uncertainty in cancer and other health effects levels for chlorinated dioxins and furans. 82 Uncertainties stem from a lack of information regarding the behavior of mercury in the environment and a lack of sufficient emissions data and parameter values ( e. g., bioaccumulation values) for nondioxin products of incomplete combustion. See 64 FR 52840 52841. 83 Currently, there are only five area sources that this may apply to; they are interim status units in the process of conducting an SSRA as part of their final permits. 84 An exception would be the semivolatile metal Interim standard for existing cement kilns, which is less stringent than the 1999 final standard. As we noted, permit authorities may consider the need for an SSRA as a result. 82 based on total stack emissions from these sources while assuming compliance with the thermal standards, does not suggest that risks for LFBs are cause for concern ( except as otherwise noted, e. g., dioxins).

C. What Changes Are EPA Finalizing With Respect To the Site Specific Risk Assessment Policy?

In the 1999 final rule preamble, we included a revised site specific risk assessment ( SSRA) policy recommendation to account for promulgation of the new technology based CAA MACT standards for Phase 1 sources. We recommended that permitting authorities evaluate the need for an SSRA on a case by case basis for hazardous waste combustors subject to the Phase 1 MACT standards. For hazardous waste combustors not subject to the Phase 1 standards, we continued to recommend that SSRAs be conducted as part of the RCRA permitting process if necessary to protect human health and the environment. We indicated that the RCRA omnibus provision authorized permit authorities to require applicants to submit SSRA results where an SSRA was determined to be necessary. For the reasons described in the previous subsection, we believe that additional controls may be necessary on a site specific basis to ensure that adequate protection is achieved in accordance with RCRA. Consequently, because SSRAs are likely to continue to be necessary at some facilities ( mainly those that have not previously conducted an SSRA), we concluded that it is more appropriate to include a regulatory provision that explicitly provides for the permit authority to require SSRAs on a case by case basis and add conditions to RCRA permits based on SSRA results. Therefore, instead of relying on RCRA § 3005( c)( 3) and its associated regulations at § 270.10( k) when permitting authorities conduct or require a risk assessment on a site specific basis ( i. e., as applicable to those newly entering the RCRA permit process), we had proposed to codify the authorities provided by sections 3004( a) and ( q) and 3005( b). See proposed regulations at 69 FR 21383 21384, § § 270.10( l) and 270.32( b)( 3). In proposing to codify these authorities, we stated that we were not requiring that SSRAs automatically be conducted for hazardous waste combustion units, but that the decision of whether or not a risk assessment is necessary must be made based upon relevant factors associated with an individual combustion unit and that there are combustion units for which an SSRA will not be necessary. Further, we explained that the proposed language would provide notice to the regulated community that an SSRA may be necessary to support a source's permit, while reminding the permit agency of the need to evaluate whether an SSRA would be necessary on a site specific basis. Despite our efforts to explain that by codifying these provisions, we are only modifying the statutory authority under which we implement the SSRA policy while maintaining the same SSRA policy from a substantive standpoint, commenters generally opposed EPA's proposed codification. The comment most frequently presented was that the proposed regulatory language is not helpful to anyone ( i. e., regulated community, the public or permitting agencies), is redundant with the omnibus authority, and sets an extremely low hurdle for regulators to require SSRAs. We disagree that the new regulatory language is not helpful and that it sets an extremely low hurdle for regulators to require SSRAs. We believe that the new provisions are beneficial in two ways: 1) they provide notice to the regulated community 83 and public that an SSRA may be necessary to support a source's permit; and 2) they remind the permitting agencies of the importance of evaluating whether an SSRA would be necessary on a site specific basis. The new regulatory provision in no way expands or supplements the authority on which EPA had previously relied   i. e., omnibus and § 270.10( k), thus it does not provide any more or less authority to permit authorities ( i. e., lower or raise the hurdle) to require SSRAs. We agree that, because the proposed language provides permitting authorities with no greater authority than the omnibus authority, it is somewhat duplicative of § 270.10( k). However, as noted, EPA believes this provision offers important benefits to both the agency and the regulated community, and as explained further below, EPA has adopted a slightly modified version of the proposal pursuant to RCRA § 3004( a) and § 3005( b). See also discussion in subsection F. Another common view expressed by commenters is that, although extensive risk assessments that have been performed for more than a decade, showing lack of risk to human health and the environment, EPA continues to require SSRAs without a technical evaluation of the historical results. To the contrary, EPA Regional permit writers have found that certain chemicals ( especially dioxin and mercury) 85 pose excess risk in certain circumstances   even under the Interim Standards and consequently find it necessary to assess risk to human health and the environment based on site specific conditions at the facility. In EPA Regions 7 and 10 for example, some facilities have RCRA risk based permit conditions that establish more frequent sampling or limits on feed rate for specified metals to ensure that ecologically sensitive areas are not adversely impacted. Many commenters also state that CAA § 112( f) residual risk process is the appropriate method to assess risk for hazardous waste combustors complying with MACT, not RCRA risk assessments. Specifically, one commenter argued that EPA lacked statutory authority to rely on the omnibus provisions to require SSRA and SSRAbased controls on the grounds that § 112( f) of the Clean Air Act establishes a specific provision to control any residual risk from combustor emissions. We disagree with commenters for two reasons. First, as we explained in the 1999 final rule preamble, the omnibus provision is a RCRA statutory requirement and the CAA does not override RCRA. Promulgation of the MACT standards, therefore, does not duplicate, supersede, or otherwise modify the omnibus provision or its applicability to the sources covered by today's rule. Second, the SSRA under RCRA is usually conducted prior to issuance of the final permit. The CAA residual risk determination is generally made eight years after promulgation of the MACT standards for a source category. Accordingly, a permit authority currently facing a permit decision could not rely on these yet unwritten residual risk standards to resolve its identified concern that the MACT standard may not be sufficiently protective at an individual site. In addition, even though we believe that § 3005( c)( 3) and its associated regulations provide the authority to require and perform SSRAs and to write permit conditions based on SSRA results, we are not relying on these provisions as the authority for § 270.10( l). Rather, we are relying on § § 3004( a) and ( q) and 3005( b). See 69 FR 21327.

85 Dioxin is a common risk driver due to ongoing uncertainty in cancer and other health effects levels for chlorinated dioxins and furans. Mercury is also a common risk driver due to uncertainties implicit in the quantitative mercury analysis. See discussion in Part Seven, Section II. and 64 FR 52997. Thus, it is not uncommon for permit authorities to require risk based RCRA permit limits ( based on risk assessment results) to control emissions of these pollutants. 84 With respect to the costs incurred when conducting an SSRA, several commenters raised the concern that our approximations do not include portions of actual costs ( e. g., data gathering, QA/ QC, and third party consultants, risk assessors, and plant personnel time to coordinate and review SSRA efforts and collect facility data), thus resulting in artificially low costs. Commenters cited additional reasons why they feel that EPA's cost estimates are too low including our assumptions that: ( 1) SSRAs are a one time or infrequent cost; ( 2) most SSRAs fall under " normal" versus " unusual" situations; and ( 3) the cost of conducting a risk burn during a trial burn adds only 20% more to the cost. Regarding the comment that we did not include actual costs for our estimates of overall costs to conduct an SSRA, we agree that some costs were overlooked. We did include the costs related to conducting an SSRA under " normal" and " unusual" conditions, SSRA data collection in conjunction with a regular performance burn, and a full independent risk burn including protocol, sampling, analysis, and report. However, we did not capture facility time associated with data collection and management related to the SSRA. Consequently, we have revised our cost estimate for performing these activities; see chapter 4 of the background document entitled, Assessment of the Potential Costs, Benefits, and Other Impacts of the Hazardous Waste Combustion MACT Replacement Standards   Final Rule, [ INSERT PUBLICATION DATE FOR FINAL RULE]. In response to the broader comment that our cost estimates are too low ( for several reasons mentioned previously), we agree that our estimate of a 20% additional cost to conduct a risk burn with a trial burn may have been conservative and therefore, we have adjusted our previous estimate to include a range of 20% to 40%. The total SSRA cost range has also been updated from $ 141K   $ 370K to $ 157K  $ 815K. 86 With respect to our assumption that the majority of SSRAs are conducted under " normal" conditions ( lending to overall lower cost estimates), we do believe that the majority of future SSRAs will fall under the " normal" conditions. 87 We believe this is appropriate due to: lack of new facilities coming on line for which there is no previous test data; availability of commercial modeling software; and finalization of the " Human Health Risk Assessment Protocol for Hazardous Waste Combustion Facilities" guidance, or " HHRAP" guidance. However, we do recognize that some facilities can be more complex than others in the hazardous waste combustion universe. Therefore, we have identified a portion of facilities that are likely to incur " unusual" costs for a future SSRA and have revised our cost analysis to reflect inclusion of these higher cost facilities. See background document, Assessment of the Potential Costs, Benefits, and Other Impacts of the Hazardous Waste Combustion MACT Replacement Standards   Final Rule, [ INSERT PUBLICATION DATE FOR FINAL RULE]. Also, we maintain our assumption that SSRAs generally represent a one time cost unless a facility significantly changes its operations or if receptors change such that an increase in risk is anticipated as a result. Even so, as explained earlier in subsection B.,

86 The high end of this range applies only to those systems operating under " unusual conditions" ( the available data suggest that there are only five such facilities). 87 Normal conditions assume use of previously collected performance burn data, use of standard commercial modeling software that meet Agency guidance, and limited interactions with State and Federal oversight authorities. Unusual conditions assume the need for site specific modeling, extensive interactions with stakeholders and regulators, an extended time frame, and targeted ecological analyses. 85 we would anticipate that the risk assessment would not have to be entirely redone. It may be as limited as collecting relevant new data for comparison purposes, leading to a decision not to repeat any portion of a risk assessment. Or, it may be more inclusive such that modifications would be made to specific inputs to or aspects of the risk assessment using data from a previous risk assessment, risk burn or comprehensive performance test. With respect to chemical weapons demilitarization facilities, we recognize that due to their specialized waste streams and multiple treatment units, SSRAs, in many cases, are not one time events and as a result, their SSRA costs are relatively high. The high costs can be attributed to the necessity for each chemical weapons demilitarization facility to perform surrogate trial burns and then agent trial burns for each furnace and each agent campaign ( e. g., GB ( Sarin), VX, and HD ( Sulfur Mustard)). For example, a chemical weapons demilitarization facility would conduct GB trial burns on all the furnaces and then complete destruction of the GB stockpile, followed by VX trial burns and VX stockpile and finally, the HD trial burns and the HD stockpile. This effectively extends the input to the risk assessment of the trial burn data over most of the operational life of the facility. Last, several commenters raised the concern that EPA's proposal to codify the authority to require SSRAs on a case by case basis and add conditions to RCRA permits based on SSRA results, violates the due process protections afforded under the current structure, where SSRAs are required and performed pursuant to RCRA § 3005( c)( 3) omnibus authority. Commenters were further concerned that the proposed language in § 270.10( l) would remove existing procedural safeguards by allowing the Agency to require a very expensive SSRA before the draft permit is even issued, thus violating EPA's own procedural standards as well as due process. It appears as though commenters believe that the procedures ( and procedural protections) currently applicable whenever an SSRA is conducted are unique to circumstances in which the permitting authority proceeds under the authority of RCRA § 3005( c)( 3)   the " omnibus" provision. This is incorrect. All of the specific procedural requirements the commenters have raised would be applicable whether the permitting authority proceeded under § 270.10( l), as EPA proposed, or pursuant to RCRA § 3005( c)( 3) and § 270.10( k), as is the current practice. All of the requirements established in Part 124 continue to apply, whether EPA proceeds under § 270.10( l) or under § 270.10( k). As we discussed in the proposal, the basis for the decision to conduct a risk assessment, or to request additional information to evaluate risk or determine whether a risk assessment is necessary, must be included in the administrative record for the facility and made available to the public during the comment period for the draft permit. See 40 C. F. R. § § 124.7 [ statement of basis]; 124.9 [ administrative record for draft permit]; 124.18 [ administrative record for final permit]. If the facility, or any other party, files comments on a draft permit decision objecting to the permitting authority's conclusions regarding the need for a risk assessment, the permitting authority must respond fully to the comments. Any permit conditions determined to be necessary based either on the SSRA, or because the facility declined to conduct an SSRA, also must be documented and supported in the administrative record. The commenters' concern that § 270.10( l) allows the permitting authority to require the SSRA prior to the issuance of a draft permit, and therefore the applicant would have no opportunity to comment or challenge that determination, is equally 86 unfounded. There is effectively no practical or substantive distinction between the circumstance when a permit authority communicates the decision that an SSRA is necessary to issue the permit prior to issuing the draft permit, or as part of the draft permit. In either case, if a facility refuses to provide a risk assessment or data to support a risk assessment requested under this provision, the regulations at part 124 make clear that the appropriate recourse is for the permit authority to deny the permit ( See 40 CFR § § 124.3( d); 124.6( b) and 270.10( c). The basis for the denial would essentially be the same in either case that the information before the agency gives rise to a concern that the MACT may not be sufficiently protective, which the agency is unable to dispel based on the information before it. Consequently, the permit authority cannot determine that the permit meets RCRA's standard for permit issuance. An as noted above, all of the requirements of Part 124 would apply to actions taken in accordance with § 270.10( l). For additional discussion on this issue, please refer to the Response to Comments background document for this final rule. 88 Despite the many reasons offered by commenters opposing our proposal, we continue to believe that our proposed approach is appropriate. As discussed in the proposal ( 69 FR 21327) and in the previous subsection, although the Phase 1 Replacement and Phase 2 standards provide a high level of protection ( i. e., they are generally protective) to human health and the environment, thereby allowing us to nationally defer the RCRA emission requirements to MACT, additional controls may be necessary on an individual source basis to ensure that adequate protection is achieved in accordance with RCRA. Until today, we have relied exclusively upon RCRA § 3005( c)( 3) and its associated regulations at § 270.10( k) when conducting or requiring an SSRA. We continue to believe that § 3005( c)( 3) and its associated regulations provide the authority to require and perform SSRAs and to write permit conditions based on SSRA results. In fact, as the next subsection will explain, EPA will likely continue to include permit conditions based on the omnibus authority in some circumstances when conducting these activities, and state agencies in states with authorized programs will continue to rely on their own authorized equivalent. However, because SSRAs are likely to continue to be necessary at some facilities, we are finalizing the authority to require them on a case by case basis and add conditions to RCRA permits based on SSRA results under the authority of RCRA § § 3004( a) and ( q) and 3005( c). Therefore, we are finalizing § § 270.10( l) and 270.32( b)( 3) with some minor modifications to provide further clarification of the Agency's intent.

D. How Will the New SSRA Regulatory Provisions Work?

The new regulatory provisions are finalized under both base program authority ( § 3004( a) and § 3005( b)) and HSWA authority ( § 3004( q)). That is, changes made to regulations applicable to boilers are promulgated under HSWA authority, whereas changes made to regulations applicable to incinerators are promulgated under non HSWA authority. Consequently, when it is determined that an SSRA is needed, the applicability of these provisions will vary according to the type of combustion unit ( whether it is regulated under 3004( q), or only 3004( a) and 3005( b)), and the authorization status of the state. Depending on the facts, the new authority would be 88 See final Response to Comment to the HWC MACT Standards, Volume 5, Miscellaneous. 87 applicable, or the omnibus provision would remain the principal authority for requiring SSRAs and imposing risk based conditions where appropriate. See 69 FR 21327. According to the state authorization section of this preamble ( see Part Five, Section IV.), EPA does not consider these provisions to be either more or less stringent than the pre existing federal program, since they simply make explicit an authority that has been and remains available under the omnibus authority and its implementing regulations. Thus, states with authorized equivalents to the federal omnibus authority will not be required to adopt these provisions, so long as they interpret their omnibus authority broadly enough to require risk assessments where necessary. 89 The provisions of § § 270.10( l) and 270.32( b)( 3) adopted in today's rule are substantially similar to the provisions EPA proposed. Section 270.10( l) continues to explicitly provide that a permit authority has the authority to evaluate, on a case by case basis, the need for an SSRA. EPA has also retained its proposed language that explicitly provides that, where an SSRA is determined to be necessary, the permit authority may require a permittee or an applicant to conduct an SSRA, or to provide the regulatory agency with the information necessary to conduct an SSRA on behalf of the permittee/ applicant. The final provision also essentially retains the standard laid out in the proposal: that a permit authority may decide that an SSRA is warranted based on a conclusion that additional controls beyond those required pursuant to 40 CFR parts 63, 264, 265, or 266 may be needed to ensure protection of human health and the environment under RCRA. In § 270.32( b)( 3), EPA has also explicitly codified the authority for permit authorities to require that the applicant provide information, if needed, to make the decision of whether an SSRA should be required. However, EPA has adopted some further clarifications to the final provisions in response to comments. In response to comments that the regulatory language EPA had proposed still fails to provide the regulated community with adequate notice that an SSRA might be required, and what that might entail, EPA has included additional language to address those issues. Specifically, EPA has included a sentence stating that the information required under § 270.10( l) can include the information necessary to evaluate the potential risk to human health and/ or the environment resulting from both direct and indirect exposure pathways. EPA has also added language to remind permit authorities that the determination that the MACT standards may not be sufficiently protective is to be based only on factors relevant to the potential risk from the hazardous waste combustion unit at the site, and has provided a list of factors to guide the permit authority in making that determination. See subsections E. and F. for further discussion. The applicability language of § § 270.19, 270.22, 270.62, and 270.66 also has been amended to allow a permit authority that has determined that an SSRA is necessary to continue to apply the relevant requirements of these sections on a case by case basis and as they relate to the performance of the SSRA after the source has demonstrated compliance with the MACT standards. As previously noted, the requirements at 40 CFR Part 124 continue to apply to actions taken to implement § 270.10( l). Thus, if the permitting authority concludes that a risk assessment or additional information is necessary for a particular combustor, the 89 Authorized states are required to modify their programs only when EPA enacts federal requirements that are more stringent or broader in scope than existing federal requirements. This applies to regulations promulgated under both HSWA and non HSWA authorities. 88 permitting authority must provide the factual and technical basis for its decision in the permit's administrative record and must make it available to the public during the comment period for the draft permit. If the facility or any other party files comments on a draft permit decision objecting to the permitting authority's conclusions regarding the need for an SSRA, the authority must respond fully to the comments. In addition, the SSRA must be included in the administrative record and made available to the public during the comment period. Any additional conditions and limitations determined to be necessary as a result of the SSRA must be documented and supported in the administrative record as well. 90 E. What Were Commenters' Reactions to EPA's Proposed Decision Not to Provide National Criteria for Determining When an SSRA Is or Is Not Necessary?

In the proposal, we stated that we were not proposing national criteria ( e. g., guiding factors) for determining when an SSRA is necessary. Although we had developed a list of qualitative guiding factors for permit authorities to consult when considering the need for an SSRA in the September 1999 final rulemaking ( revised from the April 1996 NPRM), we never intended for them to comprise an exclusive list for several reasons. Mainly, we felt that the complexity of multi pathway risk assessments precluded the conversion of the qualitative guiding factors into more definitive criteria. See 69 FR 21328. Commenters generally agreed that the risk assessment guidance and policy should not be codified. They agreed in principle that it is important to keep the decision to require an SSRA flexible because factors vary from facility to facility. However, several commenters raised the concern that the proposed language of § 270.10 ( l) was too vague. For example, one commenter suggested that any additional guidance clarifying how risk assessments should be performed and that providing standards or goals to be achieved by the operating conditions would be helpful. Another commenter felt that EPA should identify specific factors that the regions and authorized states should consider, and specific criteria that should be met, before requiring an SSRA or additional emission controls or other standards. We agree with commenters that additional guidance would be beneficial and have taken a number of actions in this regard. First, EPA is adopting a more detailed regulatory provision that provides a non exclusive list of guiding factors for permit authorities to use in determining whether the MACT will be sufficiently protective at an individual site, and consequently, whether an SSRA is warranted. Section 270.10( l) now requires that the permit writer's evaluation of whether compliance with the standards of 40 CFR part 63, Subpart EEE alone is protective of human health or the environment be based on factors relevant to the potential risk from a hazardous waste combustion unit, including, as appropriate, any of the specifically enumerated factors. These factors reflect the eight guiding factors that EPA has discussed in several rule preambles. See 61 FR 17372, 64 FR 52842, and 69 FR 21328. However, EPA has also incorporated a few minor revisions to reflect the standards promulgated today, and to reflect the fact that the factors will be codified.

90 Additional clarification on the appropriate use of the SSRA policy and technical guidance is provided in the April 10, 2003 memorandum from Marianne Lamont Horinko entitled " Use of the Site Specific Risk Assessment Policy and Guidance for Hazardous Waste Combustion Facilities." ( See Docket # OAR 2004 0022 0083). 89 EPA has revised the language of the factors so that the language is consistent between the provisions. Consistency of phrasing is generally more important in regulations, which are binding, than in guidance. For example, some of the factors listed in the 1999 preamble used the phrase " presence or absence" while other used the phrase " identities and quantities." EPA has adopted the phrase " identities and quantities," on the grounds that it more precisely expresses the concept intended by both phrases. EPA has also made minor revisions to reduce redundant text, and to shorten the provisions, in the interests of clarity. For example, rather than addressing the proximity of receptors in two factors, EPA addresses this issue in a single factor. However, nothing contained in either of the original factors was deleted as part of this revision. None of the revisions described here substantively change the issues to be considered from those contained in the original eight guiding factors. In addition to these minor technical revisions, EPA has included language to clarify that one potentially relevant factor for consideration is the " identities and quantities of persistent, bioaccumulative or toxic pollutants considering enforceable controls in place to limit those pollutants." This reflects changes made between the proposed and final MACT standards ( e. g., the proposed rule called for beyond the floor dioxin limits for some sources; those were not promulgated in the final rule). Another change is the EPA has deleted the factor that listed " concerns raised by the public." The regulation will allow the decision to be based on any one of the listed factors, and public concern, unaccompanied by an identifiable risk, would not provide an adequate basis for determining that an SSRA was warranted. Finally, as discussed previously in subsection B., EPA has added an additional factor to indicate that a previously conducted risk assessment would be relevant in evaluating changes in conditions that may lead to increased risk. The factor reads as follows: " Adequacy of any previously conducted risk assessment, given any subsequent changes in conditions likely to affect risk." See § 270.10( l)( 1). One commenter raised the concern that the eight guiding factors the Agency specified in its Federal Register notice at 64 FR 52842 ( September 30, 1999) did not adequately focus on the central question of whether there are likely to be emissions that would be uncontrolled under the Subpart EEE final rule. They argued that, as an example, under guiding factor # 5, if the waste containing highly toxic constituents are being addressed by the Subpart EEE standards, the fact that there might be such wastes should not justify an SSRA. The commenter apparently misunderstands that the factors were not intended to function as stand alone criteria for requiring an SSRA   i. e., to use their example, the commenter believes that the mere fact that highly toxic constituents are present in the waste would justify an SSRA without consideration of whether the MACT emission standards were sufficiently protective. This is an incorrect reading of EPA's proposed regulation. Rather, the factors were always intended to function as considerations that might be relevant to the determination of whether the MACT was sufficiently protective. However, the regulatory structure EPA has adopted in the final rule makes perfectly clear that the critical determination is that " compliance with the standards of 40 CFR part 63, Subpart EEE alone may not be protective of human health or the environment." Further, the provision states that this determination is to be based only on factors relevant to the potential risk from the hazardous waste combustion unit, including, as appropriate, the listed factors. EPA believes that these provisions make 90 clear that the determination of whether to require an SSRA is to be based on consideration of the conditions at the facility site, including, for example, an evaluation of all enforceable controls in place to limit emissions. Further discussion of EPA's revised provisions can be found in subsection F. Second, as discussed in more detail below, EPA is issuing a revised risk assessment guidance document that we believe will provide additional insight to help users. While clearly delineating between risk management and risk assessment, the HHRAP explains in great detail a recommended process for performing and reporting on cost effective, scientifically defensible risk assessments. It includes numerous recommended defaults, while at the same time is flexible enough to incorporate sitespecific values. Although the HHRAP provides numerous recommendations, it remains merely guidance and consequently leaves the final decisions up to the permitting authority. We believe that the revised HHRAP guidance will provide further assistance to permit writers, risk assessors and facilities in determining whether or not to conduct an SSRA and what and how much information is required for the SSRA.

F. What Are EPA's Responses to the Cement Kiln Recycling Coalition's Comments on the Proposal and What is EPA's Final Decision on CKRC's Petition?

In the proposal, we provided a lengthy discussion in response to CKRC's petition for rulemaking ( 69 FR 21325   21331). In its petition, CKRC presented two requests with respect to SSRAs: ( 1) that EPA repeal the existing SSRA policy and technical guidance because CKRC believes that the policy and guidance " are regulations issued without appropriate notice and comment rulemaking procedures"; and ( 2) after EPA repeals the policy and guidance, " should EPA believe it can establish the need to require SSRAs in certain situations, CKRC urges EPA undertake an appropriate notice and comment rulemaking process seeking to promulgate regulations establishing such requirements." Additionally, CKRC stated that it does " not believe that these SSRAs are in any event necessary or appropriate" and that they disagree with EPA's use of the RCRA omnibus provision as the authority to conduct SSRAs. Finally, CKRC raised three general concerns: ( 1) whether an SSRA is needed for hazardous waste combustors that will be receiving a RCRA permit when the combustor is in full compliance with the RCRA boiler and industrial furnace regulations and/ or with the MACT regulations; ( 2) how an SSRA should be conducted; and ( 3) what is the threshold level for a " yes" or " no" decision that additional risk based permit conditions are necessary. We believe our tentative decision in the proposal addressed each request and concern presented in their petition. However, in its comments, CKRC has restated many of the same issues with new emphasis. Thus, we believe it is appropriate to address their major comments in the following paragraphs. 9 1. Whether SSRAs are Necessary for Facilities in Full Compliance with BIF or MACT Regulations In its comments, CKRC continues to question the need for any SSRAs at facilities that are in full compliance with the MACT EEE standards. CKRC also states that "[ our]

9 CKRC provided numerous comments organized by subtitles. Rather than relying on this format in the preamble, we have organized the comments and responses according to the concerns initially raised in the petition, and consistent with the discussion presented in the proposal. 91 Petition challenged EPA to explain why, if there is any need for SSRAs at all under RCRA, there is a rational basis for why it has limited the entire SSRA program to hazardous waste combustors." They argue that, " The point is that if the " omnibus" words in RCRA mean what EPA says they mean for hazardous waste combustors, why do they not mean the same thing for all of the other TSD facilities that also pose the same kind of " what if" hypotheticals that EPA throws out in its preamble?" As discussed above in subsection B., and in greater detail below, EPA believes that risk assessments will continue to be necessary at some facilities. For example, based on the inconclusive results from the national risk assessment conducted for the 1999 final rule and the comparative risk analysis conducted for today's rule, EPA is not able to conclude that all MACT standards will be sufficiently protective for every facility ( e. g., non dioxin PICs not previously modeled, no numerical dioxin/ furan emission standard for solid fuel fired boilers, liquid fuel fired boilers with wet or no APCDs, and hydrochloric acid production furnaces, etc.). EPA also provided examples of site specific factors that might lead risk assessors to decide that the MACT standards may not be sufficiently protective, and therefore an SSRA may be necessary ( e. g., if a source's emissions are comprised of persistent bioaccumulative or toxic contaminants). EPA also discussed this issue at length in both the 2004 proposal, and the 1999 rule preamble. See 69 FR 21326 and 64 FR 52842. Given these uncertainties, the SSRA provides significant support for the Agency's 1006( b) determination supporting the elimination of separate RCRA emission standards for MACT EEE facilities. We disagree that our discussion of standards ( and site specific factors) that may warrant a risk evaluation at certain types of facilities are mere " what if" hypotheticals. The examples that we discussed in both the earlier preambles and above were based on the 1999 national risk assessment and a comparative risk analysis, which concluded that either there was not enough information to make a definitive protectiveness determination or that uncertainty in cancer and other health effects levels of dioxin and furans, for instance, make it difficult to draw conclusions about potential risks. Furthermore, the discussions with respect to the protectiveness of certain standards ( i. e., some are less stringent today than the 1999 standards) in subsection B., present a reasonable basis for permitting authorities to consider whether or not risk should be evaluated. In support of our position that the examples we have provided in the 1999 final rule preamble, the 2004 proposed rule preamble, and this final rule, are more than " what if" hypotheticals, we have placed copies of completed risk assessments where riskbased limits were found to be necessary in the docket for today's final rule ( see OAR 2004 0022). The CKRC fails to acknowledge that there are many aspects of hazardous waste combustors and the combustion process itself, which make this category of TSD facilities different from others, and which factor heavily into our SSRA policy. Consider that many combustion facilities feed a wide array of waste streams comprised of many hazardous constituents. The combustion of these constituents results in complex chemical processes ( which are difficult to predict) occurring throughout the combustion unit. The end product is stack emissions comprised of a variety of compounds different from those that enter the process, and thus are difficult to predict because they can vary greatly based on the many variables of the individual combustion unit, making them difficult to address ( i. e., there are no specific emissions standards to limit certain 92 compounds such as products of incomplete combustion). For example, in attempting to maximize the destruction of organic compounds, products of incomplete combustion are often generated as a consequence. Further, due to stack dispersion, hazardous waste combustors have the potential to affect several square miles. Other types of TSD facilities' operations typically do not encompass such complex processes or have the potential to adversely affect receptors for several square miles. It should be noted that hazardous waste combustors are not the only type of TSD subjected to site specific evaluations of risk. We take a site specific approach to regulating miscellaneous units under Part 264, subpart X. Because it is not possible to develop performance standards and emission limits for each type of treatment unit that may fall under this broad category, we rely on general environmental performance standards to meet our mandate under § § 3004 ( a) and ( q) that standards governing the operation of hazardous waste facilities be protective of human health and the environment. For example, § 264.601( c) requires " Prevention of any release that may have adverse effects on human health or the environment due to migration of waste constituents in the air, considering: ( 6) the potential for health risks caused by human exposure to waste constituents; and " For all intents and purposes, subparts X units are subject to SSRAs as well. In addition, the question of whether an SSRA continues to be necessary is partly a function of the fact that EPA is seeking to rely on CAA MACT standards in order to eliminate RCRA emissions standards for these facilities. As noted above, because the MACT is technology based, and because of uncertainties in our national risk assessments, permit writers' ability to conduct an SSRA in individual cases provides important support for our deferral. RCRA § § 3004( a) and ( q) mandate that standards governing the operation of hazardous waste combustion facilities be protective of human health and the environment. To meet this mandate, we originally developed national combustion standards under RCRA, taking into account the potential risk posed by direct inhalation of the emissions from these sources. With advancements in risk assessment science since promulgation of the original national standards ( i. e., 1981 for incinerators and 1991 for boilers and industrial furnaces), it became apparent that the risk posed by indirect exposure ( e. g., ingestion of contaminants in the food chain) to long term deposition of metals, dioxins/ furans and other organic compounds onto soils and surface waters should be assessed in addition to the risk posed by direct inhalation exposure to these contaminants. We also recognized that the national assessments performed in support of the original hazardous waste combustor standards did not take into account unique and site specific considerations which might influence the risk posed by a particular source. Therefore, until EPA was able to revise its regulations, to ensure the RCRA mandate was met on a facility specific level for all hazardous waste combustors, we strongly recommended that site specific risk assessments ( SSRAs), including evaluations of risk resulting from both direct and indirect exposure pathways, be conducted as part of the RCRA permitting process. In those situations where the results of an SSRA showed that a facility's operations could pose an unacceptable risk ( even after compliance with the RCRA national regulatory standards), additional risk based, site specific permit conditions could be imposed pursuant to RCRA's omnibus authority, § 3005( c)( 3). 93 Rather than establish separate emission standards under RCRA, EPA decided to coordinate its revisions to the RCRA emissions standards for hazardous waste combustors with the adoption of the MACT standards pursuant to § 112( d) of the CAA. See 64 FR 52832. In the rulemaking establishing the MACT standards for incinerators, cement kilns and lightweight aggregate kilns ( Phase 1 sources), relying on RCRA § 1006( b), EPA determined that in most cases, the MACT standards would be sufficiently protective that separate RCRA emission standards and operating conditions would not need to be included in the facility's RCRA permit. However, for a variety of reasons, EPA lacked sufficient factual basis to conclude that a complete deferral of RCRA requirements could be supported for all facilities. Section 1006( b) conditions EPA's authority to reduce or eliminate RCRA requirements on the Agency's ability to demonstrate that the integration meets RCRA's protectiveness mandate ( 42 U. S. C. 6005( b) ( 1)). See Chemical Waste Management v. EPA, 976 F. 2d 2, 23, 25 ( D. C. Cir. 1992). To support its RCRA § 1006( b) determination, EPA conducted a national evaluation of both direct and indirect human health and ecological risks to determine if the MACT standards would satisfy the RCRA mandate to protect human health and the environment. That evaluation, however, did not quantitatively assess the proposed standards with respect to mercury and nondioxin products of incomplete combustion. This was due to a lack of adequate information regarding the behavior of mercury in the environment and a lack of sufficient emissions data and parameter values ( e. g., bioaccumulation values) for nondioxin products of incomplete combustion. Since it was not possible to suitably evaluate the proposed standards for the potential risk posed by mercury and nondioxin products of incomplete combustion, in order to support our 1006( b) determination, we continued to recommend that SSRAs be conducted for some facilities as part of the permitting process until we could conduct a further assessment once final MACT standards were promulgated and implemented. Specifically, we recommended that for hazardous waste combustors subject to the Phase 1 MACT standards hazardous waste burning incinerators, cement kilns and light weight aggregate kilns permitting authorities should evaluate the need for an SSRA on a case by case basis. We further stated that while SSRAs are not anticipated to be necessary for every facility, they should be conducted where there is some reason to believe that operation in accordance with the MACT standards alone may not be protective of human health and the environment. For hazardous waste combustors not subject to the Phase 1 standards, we continued to recommend that SSRAs be conducted as part of the RCRA permitting process. See 64 FR 52841. As discussed in subsection B., EPA believes that SSRAs may continue to be necessary for some Phase 1 facilities. For the Phase 2 sources, our comparative risk analysis generally indicates that, although the MACT standards for Phase 2 sources are appreciably more stringent than the current RCRA BIF standards, an SSRA may be necessary to confirm that a facility will operate in a way that is protective of human health and the environment. Thus, for both Phase 1 and Phase 2 sources, we continue to believe that SSRAs may be necessary for some facilities. 91 We generally believe the MACT standards will 91 As discussed in section B., we expect that facilities that have previously conducted an SSRA will not need to conduct another in consideration of today's final standards. Only those facilities newly subject to the RCRA permitting requirements, or existing sources where changes in conditions could lead to increased risk, may need to conduct or modify an existing SSRA. 94 be protective; in most cases they are substantially more protective than the existing RCRA part 264, 265, and 266 requirements. However, because HWCs manage hazardous waste and process it by burning and emitting the by products into the air, a multitude of potential exposure pathways exist. These exposure pathways can also vary substantially based on site specific factors associated with an individual combustion unit and the surrounding site. Such factors make it difficult for the Agency to conclude that a single, national risk assessment provides adequate factual support for its determination that the technology based MACT standards will be sufficiently protective. This is further complicated by the fact that, for certain parameters, the Agency lacked sufficient information to quantitatively assess the risk, but is relying on a combination of quantitative and qualitative assessments of the MACT standards' protectiveness. Nonetheless, EPA does not believe that the uncertainty is so great that it would preclude a deferral under 1006( b) for the affected categories of facilities; nor does EPA believe that these uncertainties necessarily support requiring a risk assessment for all such facilities. Conditions at the facility might confirm that the MACT standards are sufficiently protective, without the need for a facility wide risk assessment. For example, if the results of the MACT testing demonstrated that the facility's dioxin emissions fall below the levels estimated in the database EPA used for its comparative risk assessment, the uncertainties in EPA's comparative risk assessment would not, by itself, support a decision to require an SSRA. Such decisions require an evaluation of the conditions at the site, and EPA believes it important to retain the flexibility for permit authorities to take these conditions into account. Accordingly, EPA believes that the regulatory structure adopted in today's rule strikes the appropriate balance between these competing factors. In response to EPA's statement in the proposal that non HAP emissions, which were beyond the direct scope of MACT, may pose risk which could necessitate an SSRA ( 69 FR 21326), CKRC pointed out that the same could be said for other types of TSDs, such as landfills, land treatment systems, etcetera, and EPA has not addressed this point in its preamble. As previously noted, combustion units are distinct from other types of TSDs due to the wide array of waste streams being fed to the unit, the complex chemical processes throughout the combustion unit, stack emissions comprised of a wide variety of compounds that are difficult to address, and the potential to impact receptors for several square miles due to stack dispersion. A further distinction is that EPA is seeking to rely on the MACT standards to eliminate national RCRA stack emissions standards under § 1006( b). Unless EPA can affirmatively demonstrate that RCRA's protectiveness standards are met, the Agency cannot eliminate RCRA requirements. A number of uncertainties remain concerning the protectiveness of the MACT standards based on the uncertainties remaining in the supporting national risk assessment and comparative analysis, and the variability of site specific factors from one facility to another. Permitting authorities' ability to resolve these uncertainties through the use of the SSRA, where appropriate, provides important support for the Agency's 1006( b) finding. Furthermore, as we have noted, under omnibus, to the extent permitting authorities believe there are problems with other types of TSDs, they can impose requirements and request additional information, including an SSRA in accordance with § 270.10( k). Also as previously noted, Part 264, subpart X specifically incorporates site specific consideration of risk into its regulatory framework. 95 Next, CKRC comments that EPA has a non discretionary duty under CAA § 112( f) to address and take care of any " residual risk" from MACT facilities in the future in any event. We discussed why we do not believe that the residual risk process should or can take the place of an SSRA under RCRA in subsection C. of this SSRA preamble, as well as in the 1999 rule preamble ( 64 FR 52843). In short, because the residual risk standards have not yet been established, permit writers cannot rely on this process in reaching current permitting decisions or in acting on currently pending permit applications. 2. Codification of EPA's Technical Guidance. In response to our explanation in the proposal that risk assessment guidelines should be flexible and reflect current science, CKRC gave three comments: ( 1) not a word of the current SSRA guidelines has been changed in 3 years; ( 2) it is easy to write regulations that have provisions that might be applied differently in different situations, and at least many basic, fundamental points can go in regulations, while some details can be in guidance   EPA writes regulations accompanied by " fill in the small details" guidance all the time; and 3) EPA seems to have no real problems with regulatory fixes anyway. In addition, CKRC provides several comments related to the previous three throughout their comment document, which are addressed below. None of these comments address the specific issue EPA raised, which is that, while it certainly is possible to codify our risk assessment guidance, for a variety of reasons, we disagree that it would be appropriate to issue these technical recommendations as a regulation. As we previously explained, risk assessment   especially multi pathway, indirect exposure assessment   is a highly technical and evolving field. Any regulatory approach EPA might codify in this area is likely to become outdated, or at least artificially constraining, shortly after promulgation in ways that EPA cannot anticipate now. In support of this, we noted specific examples of problems we experienced in implementing the BIF regulations. See 69 FR 21330. Further, we explained that at the time of codification, BIF risk assessments were not intended to address indirect routes of exposure, thus making the parameters easier to implement. Today, however, risk assessments are more complex due to the necessary inclusion of multi pathway and indirect exposure routes. Given the complexity of multipathway and indirect exposure assessments and the fact that risk science is continuously evolving, it would be difficult and again, overly constraining, to codify risk parameters today. We note as well, in this regard, that several commenters agreed that codification of EPA's risk assessment guidance would be too constraining for both the agency and the regulated community. We also believe that a guidance approach is consistent with the fact that permit authorities must make site specific decisions whether to do risk assessments at all. We think that it makes little sense to allow this kind of flexibility regarding whether to do a risk assessment and for what purposes, while prescribing how one must be conducted if one is required. In fact, permitting authorities, in some cases, have developed their own guidance methodologies responsive to the specific needs associated with their facilities. For example, North Carolina, Texas, and New York have each developed their own risk assessment methodologies. Further, facilities that choose to conduct SSRAs themselves can choose alternative approaches in applying methodologies as well. We think this flexibility employed in the field supports our judgment that risk assessment 96 methodologies should not be codified. CKRC's comments failed to address any of these issues. Turning to the remainder of CKRC's specific points   CKRC's assertion that the technical guidance has not been amended in the past three years is inaccurate. A revised HHRAP guidance, that has been amended to take into account the technical recommendations from both the public comments and peer review, is published in conjunction with this rule. In addition, as noted above, in some cases, permitting authorities have developed their own methodologies responsive to the specific needs associated with their facilities. With respect to CKRC's third point, the regulatory corrections made to the MACT rules were necessary either to fix an error or omission or to resolve potential legal issues. To codify technical tools and chemical information pertinent to the risk process simply is not prudent, as this information is continually changing and would almost always be out of date. Granted, when this information is presented in guidance, it can just as easily become outdated, however, facilities and risk assessors are free to use the most up to date air modeling tools and toxicity values available ( i. e., they would not be bound to regulations requiring the use of obsolete tools and information). We continue to believe that publishing our technical recommendations as regulation would remove much of the flexibility that is important in evaluating risk on a site specific basis. CKRC discounts EPA's statement that codification of risk assessment is the exception arguing that " Neither TSCA or CERCLA, however, specifically commands EPA to define the type of information necessary for a permit application through the rulemaking process as RCRA does. Moreover, the TSCA and CERCLA examples EPA cites are not analogous to the situation where a permit applicant can be denied a permit   or at least strung through months or years of tortuous and costly submissions, revision, and resubmission  to obtain a permit." Even if TSCA and CERCLA were not considered to be analogous, that does not change EPA's fundamental rationale that codification of highly technical risk assessment guidance is not appropriate. EPA does not believe that RCRA § 3005( b) requires EPA to codify an exhaustive list of every possible piece of information that might be required in a permit. To some extent, that is the reason for having a permit process   to allow site specific conditions to be taken into account. Nevertheless, EPA has revised part 270, pursuant to RCRA § 3004( a) and § 3005( b) to specifically provide that a risk assessment may be necessary, where there is reason to believe that the MACT standards may not be sufficiently protective. This was done wholly to address the petitioner's concern that the current regulations do not adequately provide notice that an SSRA might be necessary as part of a permit application. This provision, while it does not provide as much detail as the petitioner wishes, clearly " defines the type of information necessary for a permit application." CKRC complains that the Agency did not address in its proposed response the petitioner's discussion of the " strong case law compelling the conclusion that ` guidance' documents EPA has issued for conducting SSRAs must be subjected to notice andcomment rulemaking." EPA has chosen not to respond to CKRC's legal interpretation because we believe that it is clear that the guidance documents do not impose mandatory requirements, and therefore need not be issued by notice and comment rulemaking. Nevertheless, EPA notes that in the proposal, the Agency explained that we were in the 97 process of reviewing the guidance documents, and, to the extent we found language that could be construed as limiting discretion, we committed to revise the documents to make clear that they are non binding. See 69 FR 21329. We specifically noted that CKRC indicated in its petition that, in its view, the documents contain language that could be construed as mandatory. While EPA does not necessarily agree, and believes that, in context, it is clear that the recommendations in the documents are discretionary, EPA nonetheless reviewed the documents to ensure that they are carefully drafted. Consequently, under the standards articulated in Appalachian Power Co. v. EPA, 208 F. 3d 1015 ( D. C. Cir. 2000) and subsequent case law, the final HHRAP guidance is truly guidance and does not require notice and comment rulemaking. The HHRAP explains in great detail an acceptable process for performing and reporting on cost effective, scientifically defensible risk assessments. It includes numerous recommended defaults, while at the same time provides the risk assessor or facility full opportunity to incorporate site specific values in place of the defaults. The HHRAP offers numerous recommendations, but requires nothing. EPA has placed a copy of the final guidance document in the docket for today's action ( see OAR 2004 0022). CKRC believes that EPA's technical guidance imposes information requirements upon the RCRA permit applicant that are not contained in any regulations and in fact exceed by orders of magnitude any information requirements contained in the part 270 regulations. We disagree that anything contained in HHRAP is " required" in any way. Moreover, to the extent any individual facility believes the information requested is inappropriate or unnecessary, they can challenge that as part of the permitting process. Lastly, CKRC argues that " The procedures EPA has been using to issue and revise the SSRA guidance do not by any measure comply with the full panoply of procedures and protections offered by the APA process. Most critically, when EPA merely solicits comments on draft guidance documents, it has no duty to respond to comments and provide a rational basis and justification in defense of its choices in the face of comments. EPA is essentially running its entire SSRA program on the basis of " draft" guidance versions for which EPA has never to this day prepared any response to comments." As previously noted, EPA believes the final HHRAP is merely guidance and therefore, EPA is not required to proceed through notice and comment rulemaking pursuant to § 553 of the APA. However, because we want the HHRAP guidance to be useful and clear, we have solicited public review and comment. As a result, it has been improved over the years by including revisions to the guidance based upon feedback from users of the guidance and from experience in the field. A response to comments document has been prepared and released along with the final HHRAP and final MACT rules, even though the Agency was not required to do so. More to the point, because it is only guidance, sources will have the opportunity to raise questions or comments on anything in the guidance as part of the permitting process and the permitting authority will be required to respond to those comments as part of the permitting process. See 40 CFR part 124. Sources will also have the right to challenge the responses or use of the guidance as part of the permitting process. 3. Codification of Criteria for Determining that Additional Risk Based Permit Conditions or an SSRA Is Necessary CKRC argues that EPA's proposed regulatory changes should not be considered as a partial grant because EPA has not codified specific criteria in the proposed 98 regulations for permit authorities to use to decide whether to require an SSRA; to set the risk levels that are deemed protective; or to otherwise provide any further definition as to what it means to protect human health and the environment. In its petition, CKRC requested that after we repeal the policy and guidance ( per the first request), " should EPA believe it can establish the need to require SSRAs in certain situations, CKRC urges EPA to undertake an appropriate notice and comment rulemaking process seeking to promulgate regulations establishing such requirements." As discussed at length in both the proposal ( 69 FR 21325 21327) and the preceding paragraphs, we believe that we have established certain circumstances where the MACT standards may not be protective and that an SSRA may be warranted, based on relevant site specific factors associated with an individual combustion unit. Consequently, we are finalizing regulations that explicitly authorize permitting authorities to conduct or require an SSRA on a site specific basis. This, in our view, grants the second of CKRC's requests. Our response directly addresses a number of CKRC's concerns: ( 1) through a notice and comment rulemaking process, EPA has established circumstances in which an SSRA may be necessary; and ( 2) EPA's regulations will now explicitly acknowledge that an SSRA might be necessary as part of the permitting process, thereby addressing the petitioner's concern that EPA's past approach of relying on RCRA's omnibus authority to implement this policy violates the requirements of RCRA § 3005( b). And as discussed further below, EPA has codified criteria for permit authorities to use to determine whether to require an SSRA. While it does not provide exactly what CKRC requested, the regulated community has had a full opportunity to comment on the need for an SSRA both as part of the 1999 rulemaking and, again, as part of this rulemaking to adopt the provisions of § 270.10( l), which contain an explicit reference to the potential need for an SSRA as part of the permitting process pursuant to RCRA § 3004( a) and § 3005( b). As previously explained, § 270.10( k) does not explicitly mention the potential for an SSRA to be required. Although the rule does not identify a priori that an SSRA will be required in an individual circumstance, but defers that determination to the permitting process, the final rule reflects EPA's findings that an SSRA is not anticipated to be necessary in every circumstance   only where site specific conditions give the permit authority reason to believe that additional controls beyond those required pursuant to 40 CFR parts 63, 264, 265, or 266 may be necessary to protect human health and the environment. CKRC argues that EPA's decision not to codify national criteria renders the regulation impermissibly vague, and therefore, " in their view totally deficient as a legal matter." The petitioner argues that the rule is essentially " a bootstrap attempt to avoid rulemaking requirements by establishing " rules" that give no more guidance or direction than general terms in the statute and in no way channel the decision maker's discretion or put the public on notice of anything." According to CKRC, this unbridled discretion is manifest in three ways: ( 1) no criteria explain how a permit writer is to decide whether to require an SSRA; need merely to conclude " reason to believe"; ( 2) there are absolutely no limits on what type of information or assessments the permit writer may demand and the proposed reg. does not even hint at what type of information or assessments might be demanded; and ( 3) there is not a word of guidance or specification as to what it means to " ensure protection of human health and the environment." The petitioner argues that as a 99 consequence, the proposed § 270.10( l) would be struck down as a " standardless regulation." EPA disagrees that the provisions at § 270.10( l) are impermissibly vague, or otherwise inconsistent with the cases the petitioner cites. In the cited cases the courts found that the regulated entity bore the entire burden of determining how to comply with the challenged regulation in the complete absence of a government generated standard or guidance. See Maryland v. EPA, 530 F. 2d 215, 220 ( 4th Cir. 1975); South Terminal Corp v. EPA, 504 F. 2d 646, 670 ( 1st Cir. 1974). This is entirely distinct from the regulations codified at § 270.10( l). In § 270.10( l) EPA identified the standard for when a risk assessment may be necessary: where the regulatory authority identifies factors or conditions at the facility that indicate that the MACT standards may not be sufficiently protective, and defers the articulation of the more precise requirement to the permitting process, where the onus falls on the permitting authority to identify the basis for its determination. Until the permitting authority provides this further guidance, the regulated entity incurs no obligation. The mere fact that specific factors or facility conditions that form the basis for the determination that an SSRA is warranted will be subsequently identified through the permitting process does not invalidate the regulation. See Ethyl Corp v. EPA, 306 F. 3d 1144, 1149 1150 ( D. C. Cir. 2002). The regulation also identifies the categories of information that might be required for MACT EEE facilities: the information must be necessary to determine whether additional controls are needed to ensure protection of human health and the environment; it can include the information necessary to evaluate the potential risk from both direct and indirect exposure pathways; or it can include the information necessary to determine whether such an assessment is necessary. Here as well, EPA's reliance on the permitting process to provide further specification of the required information is not improper. Moreover, as discussed above in subsection C., in response to commenters' concerns, EPA has revised § 270.10( l) to provide more detail, both with respect to the basis for the determination that an SSRA is necessary, and with respect to the type of information the permit authority might need. EPA has added language to remind permit authorities that the determination that the MACT standards may not be sufficiently protective is to be based only on factors relevant to the potential risk from the hazardous waste combustion unit at the site. EPA has also added language to § 270.10( l) to identify guiding factors for permitting authorities to consult in determining whether the MACT will be sufficiently protective at an individual site. Although the list of guiding factors is not all inclusive, they offer a structure for risk managers ( as well as the regulated community) to use to frame the evaluation of whether a combustor's potential risk may or may not be acceptable. Finally, we note that, unlike the circumstances in the cited cases, § 270.10 is promulgated in the context of an existing permitting regime. The regulatory standards at 40 CFR part 124 provide further structure for both the regulated community and the permit authority. For similar reasons, EPA disagrees that the cited cases compel the Agency to establish risk levels that are deemed protective, or to otherwise provide any further definition as to what it means to protect human health and the environment. We discussed at length throughout the proposal the reasons we believe it would not be appropriate to codify either an exclusive set of national criteria for determining that an 100 SSRA ( or additional risk based permit conditions) would be necessary, or a uniform risk level. The decision to require an SSRA is inherently site specific, thus permitting authorities need to have the flexibility to evaluate a range of factors that can vary from facility to facility. See 69 FR 21328 21331. CKRC has neither presented new factual or policy reasons that would cause the Agency to reconsider the tentative decisions presented in the proposal, nor specifically addressed the issues underlying EPA's decision. Instead, the petitioner has merely reiterated the concerns presented in its petition and its general disagreement with EPA's decision. EPA also disagrees that its new regulatory structure grants permit writers unbridled discretion for many of the same reasons that EPA does not believe that § 270.10( l) is impermissibly vague. As EPA has previously explained, the requirements at Part 124 continue to apply to actions taken to implement § 270.10( l). Moreover, the language of § 270.10( l) makes clear that the onus initially falls on the permitting authority to identify the basis for its conclusion that the MACT standards may not be sufficiently protective. As both part 124 et. seq., and EPA's preamble discussions make clear, facilities will continue to have the opportunity to comment on and challenge the determination. See § § 124.10, 124.11, and 124.19. The regulatory structure adopted in § 270.10( l) mirrors the structure Congress established in sections 3004 and 3005; although 3004 directs EPA to establish national standards, section 3005 recognizes that those standards will be applied on a case by case basis through the permitting process, to allow site specific conditions to be taken into account, and to supplement those standards as necessary. EPA has also provided recommendations through guidance on how an SSRA can be conducted. Although the recommendations are not binding, they provide risk managers ( as well as the facility) with a starting point from which to determine whether a combustor's potential risk may or may not be acceptable. CKRC argues that it appears that rather than following the statutory authorities and requirements to review and amend regulations every 3 years as necessary ( RCRA § 2002( b)), EPA decided to take the easy way out and impose, through non rulemaking " guidance", massive, costly, and confusing requirements leaving unbridled discretion to its permit writers. We disagree that the Agency has attempted to avoid rulemaking in this context. EPA has conducted several rulemakings to amend our regulations. The first was in 1999, when we adopted revised emission standards under the authority of both § 112( d) of the CAA and RCRA to more rigorously control toxic emissions from burning hazardous waste in incinerators, cement kilns, and lightweight aggregate kilns. See 64 FR 52828. At the time, we noted that " today's rule fulfills our 1993 and 1994 public commitments to upgrade emission standards for hazardous waste combustors." We have continued to revise our regulations consistent with and based on the facts before the Agency, taking into account the arguments presented in CKRC's petition. As explained above, we believe that the facts do not support granting all of CKRC's requests. Rather we believe that the MACT standards will generally be protective, and that permit authorities should reach the decision to require an SSRA based on a variety of factors and concerns specific to their sites. In addition, as previously addressed, we believe that our risk assessment guidance should remain as guidance. Several other commenters agree that the guidance should not be codified. 101 The petitioner argues that the regulation EPA has proposed to adopt is so vague, that it is essentially not a regulation, and that consequently, even if finalized, it would not be sufficient to comply with the requirement in RCRA § 3005( b) to specify in regulations, the information necessary to obtain a permit. They compare the level of detail in § 270.10( l) to the lengthy regulations ( codified in 40 C. F. R. part 270) specifying in great detail the information required when one is submitting a RCRA permit application, arguing that " these regulations cover 75 pages of fine print in Code of Federal Regulations," to demonstrate that this regulation would be insufficient under RCRA § 3005( b). In further support of this argument, CKRC cites Ethyl Corporation v. EPA, 306 F. 3d 1144 ( D. C. Cir. 2002). EPA disagrees that its regulations are in any way inconsistent with the decision in Ethyl Corp. At issue in that case was a regulation issued pursuant to section 206( d) of the CAA. Section 206( d) provides that EPA " shall, by regulation, establish methods and procedures for making tests under this section." 42 U. S. C. § 7525( d). The court found that " with CAP 2000, [ the challenged regulation] the EPA does not claim to have itself articulated even a vague durability test. Rather CAP 2000 requires that ` the manufacturer shall propose a durability program' for EPA approval. 40 C. F. R. § 86.182301( a). It thus falls on the forbidden side of the line." Ethyl Corp., 306 F. 3d at 323 324. The Court distinguished the challenged regulation from the situation in which an agency issues a " vague" regulation, and relies on subsequent proceedings to flesh out the specific details. And as the court explained, where " Congress had not specified the level of specificity expected of the agency, we held that the agency was entitled to broad deference in picking the suitable level." 306 F. 3d at 323 ( citing American Trucking Associations v. DOT, 166 F. 3d 374 ( D. C. Cir. 1999) and New Mexico v. EPA, 114 F. 3d 290 ( D. C. Cir. 1997). In § 270.10( l) EPA has articulated the standard for when a risk assessment may be necessary: where the regulatory authority has identified factors or conditions at the facility that indicate that the MACT standards may not be sufficiently protective. EPA has also adopted a list of factors on which permit writers are to rely in reaching this determination. EPA has also identified the categories of information that might be required for MACT EEE facilities: the information must be necessary to determine whether additional controls are needed to ensure protection of human health and the environment; it can include the information necessary to evaluate the potential risk from both direct and indirect exposure pathways; or it can include the information necessary to determine whether such an assessment is necessary. While it does not provide as much detail as the petitioner wishes, this provision unquestionably " defines the type of information necessary for a permit application." Thus, the issue turns on the level of specificity that RCRA § 3005( b) requires, and EPA does not believe that RCRA § 3005( b) requires EPA to publish a list of every possible piece of information that might be required in a permit. Section 3005( b) merely establishes a broad directive that " each application for a permit under this section shall contain such information as may be required under regulations promulgated by the Administrator," and that it shall include the information contained in subsections ( 1) and ( 2), leaving to EPA's discretion to determine the level of specificity at which to promulgate regulations. To some extent, this reflects the reason for having a permit process   to allow site specific conditions to be taken into account. The regulatory 102 structure adopted in § 270.10 mirrors the structure Congress established in RCRA § 3004 and § 3005. Despite the petitioner's comparison to the length of part 270, the length of these provisions are not indicative of any determination of the precise level of detail that § 3005( b) requires, but reflects the fact that EPA has adopted requirements specific to individual types of units. Moreover, notwithstanding the petitioner's characterization, the language at § 270.10( l) is comparable to many other provisions in 40 CFR part 270. See, for example: § § 270.14( b)( 8); 270.16( h)( 1)( 2); 270.22( a)( 6)( i)( C); 270.22( c). Lastly, CKRC argues that the proposed regulation is particularly problematic, because it extends beyond " information" that may already exist. CKRC says that it is one thing to demand that a party go out and gather existing information, but another thing to demand that an applicant conduct " assessments." Moreover, nothing in the regulations prohibits a permit authority from demanding revised assessments, and even more revised assessments. We agree that permit authorities have the authority to require facilities to provide additional information beyond that which already exists. However, based on feedback from EPA Regional permit writers, SSRAs generally represent a one time cost. We do not expect that facilities that have conducted risk assessments will have to repeat them. As discussed in the 1999 final rule preamble, changes to comply with the MACT standards should not cause an increase in risk for the vast majority of facilities given that the changes, in all probability, will be the addition of pollution control equipment or a reduction in the hazardous waste being burned ( see 64 FR 52842). Instances where a facility may need to repeat a risk assessment would be related to changes in conditions that would likely lead to increased risk. 92 In such situations, we would anticipate that the risk assessment would not have to be entirely redone. It may be as limited as collecting relevant new data for comparison purposes, leading to a decision not to repeat any portion of a risk assessment. Or, it may be more inclusive such that modifications would be made to specific inputs to or aspects of the risk assessment using data from a previous risk assessment, risk burn or comprehensive performance test. As discussed in subsection B., we have added a new regulatory provision to indicate a previously conducted risk assessment would be relevant in evaluating changes in conditions that may lead to increased risk. The factor reads as follows: " Adequacy of any previously conducted risk assessment, given any subsequent changes in conditions likely to affect risk." 4. EPA's Cost Estimates for SSRAs CKRC raised several objections to our cost estimates for conducting an SSRA, and provided higher cost estimates ($ 200K to $ 1M, with upper bound of $ 1.3M). We suggested in the proposal, that the higher cost figures provided by CKRC were likely incurred prior to the 1998 release of the Human Health Risk Assessment Protocol ( HHRAP) guidance document. We believe our lower cost estimates can be attributed to the fact that we based them on the conduct of future SSRAs that will benefit from substantially better guidance and commercially available software.