Redline strikeout highlighting changes made during OMB review 230 XIII. What Is the Rationale for Proposing An Alternative Risk Based Standards for Hydrogen Chloride andTotal Chlorine Gas in Lieu of the MACT Standard? Under authority of CAA Section 112( d)( 4), we propose standard procedures to allow you to establish a risk based emission limit for total chlorine in lieu of compliance with the section 112( d)( 2) MACT emission standard. See proposed § 63.1215. The risk based approach would be applicable to all hazardous waste combustors except hydrochloric acid production furnaces. Because we are proposing to use the MACT standard for total chlorine as a surrogate to control metal HAP for the hydrogen chloride production furnace source category, we cannot allow any variance from the standard. For the other hazardous waste combustor source categories, we are proposing the section 112 ( d) ( 4) standard as an alternative to the MACT standard. Sources could choose which of these two standards they would prefer to apply. The alternative risk based emission limit for total chlorine would be based on national exposure standards established by EPA that ensure protection of public health with an ample margin of safety. The standard would consist of a nationally applicable, uniform algorithm that would be used to establish site specific emission limitations based on site specific input from each source choosing to utilizeuse this approach. Thus, these standards would provide a uniform level of risk reduction, consistent with the requirement of section 112( d)( 4) that EPA establish " emission standards", i. e. a requirement established by EPA which limits quantity, rate or concentration of air emissions ( see CAA section 302( k)). We also request comment on an alternative approach to implement section 112( d)( 4) for cement kilns in which we establish a national risk based emission standard for total chlorine that would be applicable to all cement kilns. Under this approach, EPA would issue a single total chlorine emission standard using an emission level that meets our national exposure standards if each cement kiln were to emit at that level. We believe that most hazardous waste combustors are likely to consider establishing riskbased standards for total chlorine because the MACT standards proposed today are more stringent, and in some cases substantially more stringent, than currently applicable standards ( e. g., the total chlorine standard for incinerators is currently 77 ppmv while we propose today a MACT standard of 1.4 ppmv).

A. What Is the Legal Authority to Establish Risk Based Standards? Under the authority of section 112( d)( 4), the Administrator may establish emission standards based on risk, in lieu of the technology based MACT standards, when regulating HAP for which health threshold levels have been established. Under section 112( d)( 4), Congress gave EPA the discretion to consider the health threshold of any HAP and to use that health threshold, with an ample margin of safety, to set emission standards for the source category or subcategory. In the legislative history accompanying this provision, the Senate Report stated, Redline strikeout highlighting changes made during OMB review 1 The Agency also proposed to use Section 112( d)( 4) authority in two other MACT rulemakings the Combustion Turbine MACT ( 68 FR 1888, January 14, 2003), and the Chlorine Production MACT ( 67 FR 44671) but determined that MACT standards for those source categories are not warranted and delisted the source categories from the Section 112( c) list of major sources pursuant to the authority in Section 112( c)( 9).

231 " To avoid expenditures by regulated entities that secure no public health or environmental benefit, the Administrator is given discretionary authority to consider the evidence for a health threshold higher than MACT at the time the standard is under review. The Administrator is not required to take such factors into account; that would jeopardize the standard setting schedule imposed under this section with the kind of lengthy study and debate that has crippled the current program. But where health thresholds are well established, for instance in the case of ammonia, and the pollutant presents no risk of other adverse health effects, the Administrator may use the threshold with an ample margin of safety ( and not considering cost) to set emissions limitations for sources in the category or subcategory." ( S. Rep. No. 228, 101st Cong. 1st Sess. at 171 ( 1989); see also id. at 175 176 ( 1989).)

EPA has previously used section 112( d)( 4) authority in the Industrial Boiler and Process Heater MACT Final Rule signed Feb. 26, 2004, the Pulp and Paper MACT Phase II ( 66 FR 3180, January 12, 2001) and the Lime Manufacturing MACT ( 69 FR 394, January 5, 2004), and has proposed to use it in a different manner in several other MACT rulemakings ( e. g., the Reciprocating Internal Combustion Engine MACT ( 67 FR 77830, December 19, 2002). 1 The approach we propose today is nearly identical to the approach EPA recently adopted for the Industrial Boiler and Process Heater MACT source category, which allows a source to establish a site specific risk based emission limit for threshold HAP using prescribed procedures. This approach differs from the previous MACT rules where EPA simply determined, on a national basis, what level of exposure from each source in the category would be protective of public health with an ample margin of safety, and did not pose significant adverse environmental impacts. This previous approach resulted in a determination that no standard was necessary because no source in the category could exceed such a risk based standard. Today's proposal varies in that the level of protection afforded by the standard is uniform, but the limits for individual sources differ due to site specific factors. As explained later in this section of the preamble, EPA is, however, also considering for cement kilns applying the single national standard approach adopted in earlier rules. B. What Is the Rationale for the National Exposure Standards? We identify as national exposure standards threshold levels that are protective of human health from both chronic and acute exposure. In addition, because EPA has discretion whether or not to promulgate risk based standards pursuant to section 112( d)( 4), we would not allow an alternative standard where emission levels may result in adverse environmental effects that would otherwise be reduced or eliminated. We would not issue the alternative standard even though it Redline strikeout highlighting changes made during OMB review 2 EPA conducted an assessment of the carcinogenicity of chlorine gas and concluded that it is not likely to be a human carcinogen ( see EPA's June 22, 1999 Risk Assessment Issue Paper for Derivation of a Provisional Chronic Inhalation RfC for Chlorine, p. 12). The International Agency for Research on Cancer ( IARC) concluded that hydrochloric acid is not classifiable as to its carcinogenicity to humans ( see IARC Monographs, Vol. 54: Occupational Exposures to Mists and Vapours from Strong Inorganic Acids; and Other Industrial Chemicals ( 1992) p. 189).

3 See EPA's externally peer reviewed " Risk Assessment Issue Paper for Derivation of a Provisional Chronic Inhalation RfC for Chlorine" ( June 22, 1999) that can be found in the docket for today's proposal.

232 may be shown that emissions do not approach or exceed levels requisite to protect public health with an ample margin of safety because we believe the statute requires that we consider effects on terrestrial animals, plants, and aquatic ecosystems in addition to public health in establishing a standard pursuant to section 112( d)( 4). See S. Rep. 228 at 176: " Employing a health threshold or safety level rather than the MACT criteria to set standards shall not result in adverse environmental effects which would otherwise be reduced or eliminated." 1. What Are the Human Health Threshold Levels? a. Chronic Exposure. Hydrogen chloride is corrosive to the eyes, skin, and mucous membranes. Chronic exposure may cause gastritis, bronchitis, dermatitis, and dental discoloration and erosion. Chronic exposure to chlorine gas can cause respiratory effects including eye and throat irritation and airflow obstruction. See discussion in Part One, Section I. E of this preamble. Given that neither hydrogen chloride nor chlorine gas is known to produce a carcinogenic response2, we use reference air concentrations ( RfC) to assess the likelihood of non cancer health effects in humans. The RfC is an estimate of a continuous inhalation exposure to the human population, including sensitive subgroups, that is likely to be without an appreciable risk of deleterious effects over a lifetime. We use an RfC for hydrogen chloride of 20 ug/ m3, as presented in EPA's Integrated Risk Information System ( IRIS). We propose to use an RfC for chlorine gas of 0.2 ug/ m3 based on a provisional assessment prepared by EPA on inhalation hazards from chlorine. 3 This is the same as the value for chlorine used by the State of California's Office of Environmental Health Hazard Assessment, which they refer to as a chronic " Reference Exposure Level" ( REL). 3 Because RfCs can change over time based on new information, the rule would require you to use the current RfC value found at http:// epa. gov/ ttn/ atw/ toxsource/ sumnmary. html. We considered how to account for the fact that chlorine gas photolyzes in the atmosphere in bright sunlight to chlorine ions and then quickly reacts with hydrogen or methane to form hydrogen chloride. The half life of chlorine due to photolysis in bright sunlight is estimated to be Redline strikeout highlighting changes made during OMB review 4 As determined by a modeling analysis done by the Air Pollution Research Center at the University of California at Riverside, as reported in a California Air Resources Board fact sheet, " Toxic Air Contaminant Identification List Summaries  ARB/ SSD/ SES," p. 231, September 1997. See also http:// www. arb. ca. gov/ toxics/ tac/ factshts/ chlorine. pdf.

5 The full definitions of the AEGL values are more nuanced. AEGL 1: The airborne concentration of a substance above which it is predicted that the general population, including susceptible individuals, could experience notable discomfort, irritation, or certain 233 10 minutes. 4 Nonetheless, this is generally sufficient time for the plume to reach nearby groundlevel receptors without significant transformation. In addition, such transformation is possible only a portion of the time. Photolysis does not occur at night and is reduced on overcast or cloudy days. Generally speaking, the rate of photolysis depends on the particular wavelength and intensity of solar radiation reaching the earth's surface which varies greatly depending on the solar angle which changes with the time of day, the season of the year, and the latitude at a given location. While the ideal approach would be explicit modeling of photolysis rates as a function of solar insolation, sky conditions, absorption cross section, quantum yield, and subsequent transformation to hydrogen chloride, to our knowledge no such regulatory air dispersion model currently exists. Because it is reasonable to believe that receptors will be exposed to chlorine gas before appreciable transformation occurs due to the variability and complexity of the transformation and the fact that chlorine gas is considerably more toxic than hydrogen chloride, we conclude that, for the purpose of protection of public health, it is prudent to assume that chlorine gas is not transformed to hydrogen chloride. b. Acute Threshold Levels. Short term exposure to hydrogen chloride may cause eye, nose, and respiratory tract irritation and inflamation and pulmonary edema. Short term exposure to high levels of chlorine gas can result in chest pain, vomiting, toxic pneumonitis, and pulmonary edema. At lower levels, chlorine gas is a potent irritant to the eyes, the upper respiratory tract, and lungs. See Part One, Section I. E To assess effects from acute exposure, we propose towould use the acute exposure guideline level ( AEGL). AEGL toxicity values are estimates of adverse health effects due to a single exposure lasting 8 hours or less. Consensus toxicity values for effects of acute exposures have been developed by several different organizations. EPA, in conjunction with the National Research Council and National Academy of Sciences, is in the process of setting acute exposure guideline levels. A national advisory committee organized by EPA has developed AEGLs for priority chemicals for 10 minute, 30 minute, 1 hour, 4 hour, and 8 hour airborne exposures. They have also determined for each exposure duration the levels of these chemicals that will protect against notable discomfort ( AEGL 1), serious effects ( AEGL 2), and life threatening effects or death ( AEGL 3). 5 To be protective of public health, we propose to use the AEGL 1 Redline strikeout highlighting changes made during OMB review asymptomatic nonsensory effects. However, the effects are not disabling and are transient and reversible upon cessation of exposure. AEGL 2: The airborne concentration of a substance above which it is predicted that the general population, including susceptible individuals, could experience irreversible or other serious, long lasting adverse health effects or an impaired ability to escape. AEGL 3: The airborne concentration of a substance above which it is predicted that the general population, including susceptible individuals, could experience life threatening health effects or death.

6 For hydrogen chloride and chlorine gas ( individually), the AEGL 1 values for 10 minute, 30 minute, 1 hour, and 8 hour exposures are the same. Therefore, when comparing predicted ambient levels of exposure to the AEGL 1 value, we believe it is reasonable to evaluate maximum 1 hour ground level concentrations.

7 See US EPA Glossary of Key Terms for National Air Toxics Assessment, at http:// www. epa. gov/ ttn/ atw/ nata/ gloss1. html.

234 values to assess acute exposure: 2.7 mg/ m3 ( 1.8 ppm) for hydrogen chloride, and 1.4 mg/ m3 ( 0.5 ppm) for chlorine gas. 6 Airborne concentrations of a substance above the AEGL 1 could cause notable discomfort, irritation, or certain asymptomatic nonsensory effects in the general population, including susceptible individuals. Please note, however, that airborne concentrations below the AEGL 1 could produce mild odor, taste, or other sensory irritations. Effects above the AEGL 1 ( but below the AEGL 2) are not disabling and are transient and reversible upon cessation of exposure. 2. What Exposures Would You Be Required to Assess? We discuss below the following issues: ( 1) use of the Hazard Index to assess exposure to both hydrogen chloride and chlorine gas; ( 2) exposure to emissions of respiratory irritant HAP other than hydrogen chloride and chlorine gas; ( 3) exposure to emissions of respiratory irritant HAP from collocated sources; ( 4) exposure to ambient background levels of respiratory irritant HAP; and ( 5) whetherour conclusion that acute exposure needs to not be assessed ifto establish emission limits because the Hazard Index for chronic exposure is expected to be higher in all situations. a. Hazard Index. Noncancer risk assessments typically use a metric called the Hazard Quotient ( HQ) to assess risks of exposures to noncarcinogens. The HQ is the ratio of a receptor's potential exposure ( or modeled concentration) to the health reference value or threshold level ( e. g., RfC or AEGL) for an individual pollutant. HQ values less than 1.0 indicate that exposures are below the health reference value or threshold level and, therefore, that such exposures are without appreciable risk of adverse effects in the exposed population. HQ values above 1 do not necessarily imply that adverse effects will occur, but that the likelihood of such effects in a given population increases as HQ values exceed 1.0.7 When the risk of noncancer effects from exposure to more than one pollutant to the same Redline strikeout highlighting changes made during OMB review 235 target organ must be assessed, the effects are generally considered to be additive and the HQ values for each pollutant are summed to form an analogous metric called the Hazard Index ( HI). Assuming additivity, HI values less than 1.0 indicate that exposures to the mixtures are likely to be without appreciable risk of adverse effects in the exposed population. HI values above 1.0 do not necessarily imply that adverse effects from exposure to the mixture will occur, but that the likelihood of such effects in a given population increases as HI values exceed 1.0. For purposes of establishing risk based emission limits for total chlorine, we propose to allow a maximum HI value of not greater than 1.0. b. Exposure to Emissions of Respiratory Irritant HAP other than Hydrogen Chloride and Chlorine Gas . We have identified in the table below 40 HAP that are respiratory irritants, including hydrogen chloride and chlorine gas. See Table XX. Because these HAP affect the same target exposure to these HAP must be considered when determining that the HI is less than or equal to 1.0.

Text Moved Here: 1 Respiratory Irritant HAP 1,2 Epoxybutane Hexachlorocyclopentadiene 1,3 dichloropropene Hexamethylene 1,6 diisocyanate 2,4 Toluene diisocyanate Hydrochloric acid 2 Chloroacetophenone Maleic anhydride Acetaldehyde Methyl bromide Acrolein Methyl isocyanate Acrylic acid Methyl methacrylate Acrylonitrile Methylene diphenyl diisocyanate N hexane Antimony Naphthalene Beryllium Nickel Bis( 2 ethylhexyl) phthalate Nitrobenzene Chlorine Phosgene Chloroprene Phthalic anhydride Redline strikeout highlighting changes made during OMB review 8 Betty Willis, et al, Agency for Toxic Substances and Disease Registry, US Department of Health and Human Services, " Public Health Reviews of Hazardous Waste Thermal 236 Chromium Propylene dichloride Cobalt Propylene oxide Diethanolamine Styrene oxide Epichlorohydrin Titanium tetrachloride Ethylene glycol Toluene Formaldehyde Triethylamine Vinyl acetate End Of Moved Text WIn making this determination, we would consider only those respiratory irritants that are HAP ( as opposed to also considering respiratory irritants that are criteria pollutants) not only because Ssection 112 deals with control of emissions of HAP, but also because ambient levels of criteria pollutants that target the respiratory with hydrogen chloride and chlorine gas ( e. g., SO x, NO x,, PM, ozone) are controlled through the applicable State Implementation Plans demonstrating compliance with the National Ambient Air Quality Standards for these pollutants.

In addition to hydrogen chloride and chlorine gas, several of the respiratory irritant HAP listed in Tthe table XXabove may be emitted by hazardous waste combustors, including the metals antimony trioxide, beryllium, chromium ( VI), cobalt, and nickel, and the organic compounds Bis( 2 ethylhexyl) phthalate, formaldehyde, napthalene, and toluene. 8 We do not Redline strikeout highlighting changes made during OMB review Treatment Technologies: A Guidance Manual for Public Health Assessors," March 2002, Table 4.

237 believe, however, that these respiratory irritant HAP would be emitted by hazardous waste combustors at levels that would result in significant Hazard Quotient values. Beryllium and chromium would be controlled by emission standards for low volatile metals and the remaining metal HAP would be controlled by a particulate matter standard. Emissions of the respiratory irritant organic HAP would be controlled to trace levels by the MACT standards for carbon monoxide or hydrocarbons and destruction and removal efficiency ( DRE). Accordingly, we propose to require you to quantify and assess emissions from the hazardous waste combustor of hydrogen chloride and chlorine gas only; you would not be required to account for these other respiratory irritant HAP because they would not contribute substantially to the Hazard Index.

Table XX c. Exposure to Emissions of Text Was Moved From Here: 1 d. Exposure to Ambient Background Levels of Respiratory Irritant HAP. Background levels of respiratory irritant HAP attributable to emissions from off site sources would not be considered when establishing risk based limits for total chlorine under section 112( d)( 4). Rather, these background levels will be addressed ( as may be necessary) through other CAA programs such as the urban air toxics program. e. Acute Exposure Need Not Be Assessed. We have determined that you need not assess acute exposure to establish an emission limit for total chlorine. You would not be required to model maximum 1 hour average off site ground level concentrations to calculate a Hazard Index ( HI) based on acute exposure for purposes of establishing an emission limit for total chlorine. We conclude that the chronic exposure Hazard Index ( HI) for the hazardous waste combustor( s) would always exceed the acute exposure HI. Thus, the emission limit for total chlorine based on chronic exposure would always be more stringent thatn the limit based on acute exposure. As an Redline strikeout highlighting changes made during OMB review 9 See Trinity Consultants, " Analysis of HCl/| Cl2 Emissions from Cement Kilns for 112( d)( 4) Consideration in the HWC MACT Replacement Standards," September 17, 2003.

10 See USEPA, " Human Health and Ecological Risk Assessment Support to the Development of Technical Standards for Emissions from Combustion Units Burning Hazardous Wastes: Background Document," July 1999.

238 example, the Cement Kiln Recycling Coalition evaluated both chronic and acute exposure to hydrogen chloride and chlorine gas for the 14 cement facilities that burn hazardous waste. 9 In all cases, the chronic HI exceeded the acute HI. In addition, we determined that the Hazard Quotient ( HQ) for chronic exposure was always higher than the HQ for acute exposure for the HAP we evaluated in the risk assessment we used to support the 1999 Final MACT Rule for hazardous waste combustors. 10 Not requiring an acute exposure analysis reduces the burden on both the regulated community and regulatory officials to develop and review an analysis that would be superseded by the chronic exposure analysis when establishing an emission limit for total chlorine. Please note that this discussion relates to evaluating acute exposure in establishing an emission limit for total chlorine. Although we conclude that the chronic exposure Hazard Index would always be higher than the acute exposure Hazard Index, and thus would be the basis for the total chlorine emission rate limit, this relates to acute versus chronic exposure to a constant, maximum average ( e. g., a maximum annual average) emission rate of total chlorine from a hazardous waste combustor. Acute exposure must be considered, however, when establishing operating requirements ( e. g., feedrate limit for total chlorine and chloride) to ensure that shortterm emissions do not result in an acute exposure Hazard Index of 1.0 or greater even though long term ( e. g., annual average) emissions do not exceed the limit. See discussion in Section FG. 1 below. 3. Does the Proposed Approach Ensure an Ample Margin of Safety? Section 112( d)( 4) allows EPA to develop risk based standards for HAP " for which a health threshold has been established", and the resulting standard is to provide an " ample margin of safety." The " ample margin of safety" standard, at least as applied to nonthreshold pollutants, typically connotes a two step process ( based on the standard first announced in the so called Vinyl Chloride decision ( NRDC v. EPA, 824 F. 2d at 1146 ( D. C. Cir. 1987)), whereby EPA " first [ determines] ... a ` safe' or ` acceptable' level of risk considering only health factors, followed by a second step to set a standard that provides an ` ample margin of safety', in which costs, feasibility, and other relevant factors in addition to health may be considered." 54 FR at 38045. It is not clear that Congress intended this analysis to apply to Section 112( d)( 4) standards, since the principal legislative history to the provision indicates that costs are not to be considered in setting standards under Section 112( d)( 4) ( S. Rep. 228 at 173), whereas cost normally is a relevant consideration in the second part of the ample margin of safety process, as described above. Further, if issues of feasibility, cost, and other non health factors are to be taken into account in establishing Section 112( d)( 4) standards, it would be exceedingly difficult, if not practically Redline strikeout highlighting changes made during OMB review 11 Indeed, using the classic two step approach to " ample margin of safety" could result in the same standards we are proposing as MACT for HCl and Cl 2 for all of the affected source categories ( if one assumes that all of the standards would be below protective risk based levels for all sources), since we believe that the proposed technology based standards would be justifiable based on considerations of technical feasibility and cost, and so would provide a reasonable margin of safety beyond the risk based level considered protective.

239 impossible, to do so on a site specific basis, undermining the approach we are proposing here. Nor is it clear that the two step approach is necessarily warranted when considering threshold pollutants, since there is greater certainty regarding levels at which adverse health effects occur. See Vinyl Chloride, 824 F. 2d at 1165 n. 11.11 We specifically request comment on how to ensure that the emission limits calculated using the health threshold values ( e. g., RfCs and AEGL 1 values), and after considering collocated sources of emissions of respiratory irritant HAP from collocated hazardous waste combustors, achieve an ample margin of safety. 4.

5. How Are Effects on Terrestrial Animals Addressed? We believe the RfC values for hydrogen chloride and chlorine gas should be generally protective for chronic effects in most, if not all, fauna. We note that the RfC values are based on animal studies. Although the AEGL 1 values for acute exposure are based on human data, we nonetheless expect that they too would be generally protective of most fauna, absent information to the contrary. 65. How Are Effects on Plants Addressed? EPA has not established ecotoxicity values that are protective of vegetation. Nonetheless, Redline strikeout highlighting changes made during OMB review 12 EPA published the final rule at 69 FR 394, January 5, 2004.

240 for the reasons discussed below we do not believe that ambient concentrations of hydrogen chloride and chlorine gas that meet the human health threshold values discussed above will pose adverse effects on plants. As discussed in the preamble to the Lime Manufacturing NESHAP proposed rule ( 67 FR 78056) 12, chronic exposure to about 600 µ g/ m3 can be expected to result in discernible effects, depending on the plant species. Effects of acute, 20 minute exposures of 6,500 to 27,000 g/ m3 include leaf injury and decrease in chlorophyll levels in various species. The hydrogen chloride RfC of 20 µ g/ m3 is well below the 600 µ g/ m3 effect level, and the AEGL 1 value for hydrogen chloride of 2,700 µ g/ m3 is far below the 6500 µ g/ m3 acute effect level. Therefore, no adverse exposure effects are anticipated. We specifically request additional information on ecotoxicity for both acute and chronic exposure of vegetation to hydrogen chloride and chlorine gas. Redline strikeout highlighting changes made during OMB review 241 Redline strikeout highlighting changes made during OMB review 13 Rather than establishing emission rate limits for hydrogen chloride and chlorine gas, or for total chlorine, for each combustor, you would actually establish an HCl equivalent emission rate limit for each combustor, as discussed below in the text.

242 C. How Would You Determine if Your Total Chlorine Emission Rate Meets the Eligibility Requirements Defined by the National Exposure Standards? Under the risk based approach to establish an alternative to the MACT standard for your total chlorine emission limit, you would have to demonstrate that emissions of total chlorine from on site hazardous waste combustors result in exposure to the actual most exposed individual residing off site of a Hazard Index of less than or equal to 1.0. ( Put another way, we are proposing to establish this level of risk as the national emission limitation, with the rule further establishing the mechanisms by which this demonstration can be made, such demonstrations yielding a site specific limit for total chlorine.) 13 The rule would also establish two ways by which you could make this demonstration: by a look up table analysis or by a site specific compliance demonstration ( as explained below). The look up table is much simpler to use, but establishes emission rates that are quite conservative because there are few site specific parameters considered and therefore the model's default assumptions are conservative. If you elect not to comply with those conservative emission rates, you may perform a site specific compliance demonstration. The look up table identifies the total chlorine emission limit in terms of a toxicity weighted HCl equivalent emission rate. Under the site specific compliance demonstration alternative, the total chlorine limit would also be expressed as a toxicity weighted HCl equivalent emission rate even though you would model emissions of hydrogen chloride and chlorine gas from each on site hazardous waste combustor. We define the toxicity weighted HCl equivalent emission rate below.. 1. Toxicity Weighted HCl Equivalent Emission Rates Although the MACT emission standards for total chlorine are expressed as a stack gas emission concentration ppmv we must use an emission rate ( e. g., lb/ hr) format for risk based standards. This is because health and environmental risk is related to the mass rate of emissions Redline strikeout highlighting changes made during OMB review 14 HCl production furnaces are not eligible for the risk based total chlorine emission limits because we are proposing that the MACT standard for total chlorine would be used as a surrogate to control metal HAP. Nonetheless, if you operate an HCl production furnace at a facility where you would establish risk based emission limits for total chlorine for other hazardous waste combustors, you would account for total chlorine emissions from the HCl production 243 over time. In addition, we propose to use a toxicity weighted HCl equivalent emission rate ( HClequivalents as the metric for the combined emissions of hydrogen chloride and chlorine gas. The HCl equivalent emission rate considers the RfCs of hydrogen chloride and chlorine gas when calculating the combined emission rate according to this equation:

ER tw =

( ER i x ( RfCHCl/ RfCi)) where: ER tw is the HC1 equivalent emission rate, lb/ hr ER i is the emission rate of HAP i in lbs/ hr RfC i is the reference concentration of HAP i RfC HCl is the reference concentration of HCl Expressing the risk based emission limit as HCl equivalents enables you to use the equation to apportion the emission rate limit between hydrogen chloride and chlorine gas as you choose. Thus, you need to be concerned with ensuring compliance with the HCl equivalent emission rate only, rather than with emission rates for hydrogen chloride and chlorine gas individually. Under the look up table analysis discussed below, you would use the hydrogen chloride and chlorine gas emission rates you choose for each on site hazardous waste combustor to calculate the HCl equivalent emission rate for the combustor. You would sum the HCl equivalent emission rates for your hazardous waste combustors. If you elect to use the site specific compliance demonstration to document eligibility, you would model emission rates of hydrogen chloride and chlorine gas that you choose for each on site hazardous waste combustor to document that the facility Hazard Index is less than or equal to 1.0. You would then use the hydrogen chloride and chlorine gas emission rates you model to establish an HCl equivalent emission rate limit for each combustor. 2. How Would You Conduct a Look Up Table Analysis? You would sum the HCl equivalent rates for all combustors, and compare the sum to the appropriate allowable emission rate in Table XX1 of Subpart EEEproposed § 63.1215. Emission rates are provided as a function of stack height and distance to the nearest property boundary. If you have more than one hazardous waste combustor at your facility, you would use the average value for stack height ( i. e., the averaged stack heights of the different hazardous waste combustors at your facility), and the minimum distance between any hazardous waste combustor stack and the property boundary. 14 Redline strikeout highlighting changes made during OMB review furnace in your risk based eligibility demonstration for the other combustors. If, for example, you use the look up table to demonstrate eligibility, you would include the stack height of the HCl production furnace in the calculation of average stack height for your combustors, and you would consider whether the HCl production furnace stack is the closest hazardous waste combustor stack to the property boundary.

244 If one or both of these values for stack height and distance to nearest property boundary do not match the exact values in the look up table, you would use the next lowest table value. This would ensure that the HCl equivalent emission rate limits are protective. You would not be eligible for the look up table analysis if your facility is located in complex terrain because the plume dispersion models used to calculate the emission rates are not applicable to sources in complex terrain. You would be eligible to comply with the risk based alternative HCl equivalent emission rate limits you calculate for each combustor if the facility HCl equivalent emission rate limit ( i. e., the sum of the HCl equivalent emission rates for all hazardous waste combustors) does not exceed the appropriate value specified in the look up table. Please note, however, that we also propose to cap the HCl equivalent emission rate limits for incinerators, cement kilns, and lightweight aggregate kilns at a level that ensures that the current total chlorine emission standards are not exceeded. See discussion below in Section D. Please note that the emission rates provided in Table XX1 are different from those provided for industrial boilers in the Industrial Boiler and Process Heater MACT rule recently promulgated. This is because the key parameters used by the SCREEN3 atmospheric dispersion model to predict the normalized air concentrations that EPA used to establish HCl equivalent emission rates as a function of stack height and distance to property boundary for industrial boilers stack diameter, stack exit gas velocity, and stack exit gas temperature are substantially different for hazardous waste burning incinerators, cement kilns, and lightweight aggregate kilns. Thus, the maximum HCl equivalent emission rates for hazardous waste combustors would generally be lower than those EPA established for industrial boilers. To ensure that the HCl equivalent emission rate limits in a look up table analysis for hazardous waste combustors would not result in a Hazard Index of more than 1.0, we propose to establish limits based on the maximum annual average normalized air concentrations in US EPA, " A Tiered Modeling Approach for Assessing the Risk Due to Sources of Hazardous Air Pollutants," March 1992, Table 1. Those normalized air concentrations are based on conservative simulations of toxic pollutant sources with Gaussian plume dispersion models. The simulations are conservative regarding factors such as meteorology, building downwash, plume rise, etc. We specifically request comment on whether the HCl equivalent emission rates in Table XX1 are too conservative and thus have limited utility because they apply to all hazardous waste combustors generically. Alternatively, we could establish less conservative emission rates in lookup tables specific to various classes of hazardous waste combustors ( e. g., cement kilns, incinerators) that have similar stack properties that affect predicted emissions. We request comment on whether industry stakeholders would be likely to use the proposed look up table Redline strikeout highlighting changes made during OMB review 15 When calculating Hazard Index values, the final HI value should be rounded to one decimal place given the uncertainties in the analyses. For example, an HI calculated to be 0.94 would be presented as 0.9, while an HI calculated to be 0.96 would be presented as 1.0 ( which would pass the eligibility demonstration). Intermediate calculations should use as many significant figures as appropriate.

245 eligibility demonstration or revised look up tables tailored to specific classes of hazardous waste combustors, in lieu of the site specific compliance eligibility demonstration. 3. How Would You Conduct a Site Specific Compliance Demonstration? If you fail to demonstrate that your facility is able to comply with the alternative riskbased emission limit using the look up table approach, you may choose to perform a site specific compliance demonstration. We are proposing that you may use any scientifically accepted peerreviewed risk assessment methodology for your site specific compliance demonstration. An example of one approach for performing the demonstration for air toxics can be found in the EPA's " Air Toxics Risk Assessment Reference Library, Volume 2, Site Specific Risk Assessment Technical Resource Document,", which may be obtained through the EPA's Air Toxics Website at www. epa. gov/ ttn/ atw. Your facility would be eligible for the alternative risk based total chlorine emission limit if your site specific compliance demonstration shows that the maximum Hazard Index for hydrogen chloride and chlorine gas emissions from all on site hazardous waste combustors at a location where people live ( i. e., the maximum actual most exposed individual) is less than or equal to 1.0, rounded to the nearest tenths decimal place ( 0.1). 15 You would estimate long term inhalation exposures for this individual most exposed to the facility's emissions through the estimation of annual or multi year average ambient concentrations. You would use site specific, qualityassured data wherever possible, and health protective default assumptions wherever site specific data are not available. You would document the data and methods used for the assessment so that it is transparent and can be reproduced by an experienced risk assessor and emissions measurement expert. Your site specific compliance demonstration need not assume any attenuation of exposure concentrations due to the penetration of outdoor pollutants into indoor exposure areas. In addition, we are proposing that the demonstration need not assume any reaction or deposition of hydrogen chloride and chlorine gas from the emission point to the point of exposure. In particular, you would assume that chlorine gas is not photolyzed to hydrogen chloride, as discussed in Section B. 1 above. If your site specific compliance demonstration documents that the maximum Hazard Index from your hazardous waste combustors is less than or equal to 1.0, you would establish a maximum HCl equivalent emission rate limit for each combustor using the hydrogen chloride and chlorine gas emission rates you modeled in the site specific compliance demonstration. Please note, however, that we also propose to cap the HCl equivalent emission rate limits for incinerators, cement kilns, and lightweight aggregate kilns at a level that ensures that the current total chlorine emission standards are not exceeded. See discussion below in Section D. Redline strikeout highlighting changes made during OMB review 246 D. What Is the Rationale for Caps on the Risk Based Emission Limits? The HCl equivalent emission rate limits would be capped for incinerators, cement kilns, and lightweight aggregate kilns at a level that ensures total chlorine emissions do not exceed the interim standards provided by § § 63.1203, 63.1204, and 63.1205. These caps on the risk based emission limits would ensure that emission levels do not increase above the emission levels that sources are currently required to achieve, thus precluding " back sliding." Given the discretionary nature of section 112 ( d) ( 4), and the general purpose of the section 112 ( d) standard setting process to lock in performance of current emission control technology, we think it appropriate to invoke the provision in a manner that does not result in emission increases over current regulatory levels. We considered whether to propose emission caps for boilers at the levels allowed by the RCRA emission standards under § 266.107 but conclude that this would be inappropriate. This is because the RCRA emission standards are also risk based standards but are based on risk criteria that we considered appropriate in 1987 when we proposed those rules. The risk criteria we propose today are substantially different from those used to implement § 266.107. For example, the RfC for hydrogen chloride is higher now while the RfC for chlorine gas is lower. In addition, we considered a Hazard Index of 0.25 acceptable under the RCRA rule, while we propose today a Hazard Index limit of less than or equal to 1.0. Because the risk criteria for the current RCRA rules are substantially different from the risk criteria we propose today for invoking Section 112( d)( 4), we do not believe it is appropriate to use the RCRA standards as a cap for establishing risk based standards under Section 112( d)( 4). Capping risk based emission limits for incinerators, cement kilns, and lightweight aggregate kilns at an HCl equivalent emission rate corresponding to the MACT interim standards would not increase compliance costs ( by definition). Thus, the cap would help ensure that emissions are protective of public health with an ample margin of safety, and that there are no significant adverse environmental impacts. To implement the cap, you would ensure that the hydrogen chloride and chlorine gas emission rates you use to calculate the HCl equivalent emission rate for incinerators, cement kilns, and lightweight aggregate kilns would not result in total chlorine emission concentrations exceeding the standards provided by § § 63.1203, 63.1204, and 63.1205. E. What Would Your Risk Based Eligibility Demonstration Contain? To enable regulatory officials to review and approve the results of your risk based demonstration, you would include the following information, at a minimum: ( 1) identification of each hazardous waste combustor combustion gas emission point ( e. g., generally, the flue gas stack); ( 2) the maximum capacity at which each combustor will operate, and the maximum rated capacity for each combustor, using the metric of stack gas volume emitted per unit of time, as well as any other metric that is appropriate for the combustor ( e. g., million Btu/ hr heat input for boilers; tons of dry raw material feed/ hour for cement kilns); ( 3) stack parameters for each combustor, including, but not limited to stack height, stack area, stack gas temperature, and stack gas exit velocity; ( 4) plot plan showing all stack emission points, nearby residences, and property boundary line; ( 5) identification of any stack gas control devices used to reduce emissions from each combustor; ( 6) identification of the RfC values used to calculate the HCl equivalent Redline strikeout highlighting changes made during OMB review 16 Since the Title V permitting authority is delegated to States in virtually all instances, the permit limit would thus be issued as a matter of State authority ( generally in parallel with a delegation of Section 112 authority pursuant to CAA Section 112( l)), and be reviewable only in State courts.

247 emissions rate; ( 7) calculations used to determine the HCl equivalent emission rate as prescribed above; ( 8) for incinerators, cement kilns, and lightweight aggregate kilns, calculations used to determine that the HCl equivalent emission rate limit for each combustor does not exceed the standards for total chlorine at § § 63.1203, 63.1204, and 63.1205; and ( 9) the HCl equivalent emission rate limit for each hazardous waste combustor that you will certify in the Documentation of Compliance required under § 63.1211( d) that you will not exceed, and the limits on the operating parameters specified under § 63.1209( o) that you will establish in the Documentation of Compliance. If you use the look up table analysis to demonstrate that your facility is eligible for the risk based alternative for the total chlorine emission limit, your eligibility demonstration would also contain, at a minimum, the following: ( 1) calculations used to determine the average stack height of on site hazardous waste combustors; ( 2) identification of the combustor stack with the minimum distance to the property boundary of the facility; ( 3) comparison of the values in the look up table to your maximum HCl equivalent emission rate. If you use a site specific compliance demonstration to demonstrate that your facility is eligible for the risk based alternative for the total chlorine emission limit, your eligibility demonstration would also contain, at a minimum, the following: ( 1) identification of the risk assessment methodology used; ( 2) documentation of the fate and transport model used; and ( 3) documentation of the fate and transport model inputs, including the stack parameters listed above converted to the dimensions required for the model. In addition, you would include all of the following that apply: ( 1) meteorological data; ( 2) building, land use, and terrain data; ( 3) receptor locations and population data; and ( 4) other facility specific parameters input into the model. Your demonstration would also include: ( 1) documentation of the fate and transport model outputs; ( 2) documentation of any exposure assessment and risk characterization calculations; and ( 3) documentation of the predicted Hazard Index for HCl equivalents and comparison to the limit of less than or equal to 1.0. F. When Would You Complete and Submit Your Eligibility Demonstration You would be required to submit your eligibility demonstration to the permitting authority for review and approval. 16 In addition you would submit an electronic copy of the demonstration to REAG@ EPA. GOV ( preferably) or a hard copy to: U. S. EPA, Risk and Exposure Assessment Group, Emission Standards Division ( C404 01), Attn: Group Leader, Research Triangle Park, North Carolina 27711. Requiring prior approval of these eligibility demonstrations is warranted because hazardous waste combustor may feed chlorine at high feedrates which may result in emissions of hydrogen chloride and chlorine gas that approach or exceed the RfCs ( i. e., absent compliance with either the MACT standards or the section 112( d)( 4) risk based standards). Thus, prior Redline strikeout highlighting changes made during OMB review 17 Please note that, if your eligibility demonstration is not approved prior to the compliance date, a request to extend the compliance date to enable you to undertake measures to comply with the MACT standards for total chlorine will not be approved unless you made a good faith effort to submit a complete, accurate, and timely eligibility demonstration and to respond to concerns raised by the permitting authority or U. S. EPA.

248 approval of alternative HCl equivalent emission rate limits is warranted to ensure that emissions are protective with an ample margin of safety. 1. Existing Sources If you operate an existing source, you must be in compliance with the emission standards on the compliance date. Consequently, if you elect to comply with the alternative risk based emission rate limit for total chlorine, you must have completed the eligibility demonstration and received approval from your delegated permitting authority by the compliance date. You would submit documentation supporting your eligibility demonstration not later than 12 months prior to the compliance date. Your permitting officials will notify you of approval or intent to disapprove your eligibility demonstration within 6 months after receipt of the original demonstration, and within 3 months after receipt of any supplemental information that you submit. A notice of intent to disapprove your eligibility demonstration will identify incomplete or inaccurate information or noncompliance with prescribed procedures and specify how much time you will have to submit additional information. If your permitting authority has not approved your eligibility demonstration to comply with a risk based HCl equivalent emission rate( s) by the compliance date, you must comply with the MACT emission standards for total chlorine gas under § § 63.1203A, 63.1204( A), 63.1205A, 63.1216, and 63.1217.17 2. New Sources If you operate a source that is not an existing source and that becomes subject to Subpart EEE, you must comply with the MACT emission standards for total chlorine unless and until your eligibility demonstration has been approved by the permitting authority. If you operate a new or reconstructed source that starts up before the effective date of the emission standards proposed today, or a solid fuel fired boiler or liquid fuel fired boiler that is an area source that increases its emissions or its potential to emit such that it becomes a major source of HAP before the effective date of the emission standards proposed today ( and thus becomes subject to emission standards applicable to major sources, including the standard for total chlorine), you would be required to comply with the emission standards under § § 63.1216 and 63.1217 until your eligibility demonstration is completed, submitted, and approved by your permitting authority. If you operate a new or reconstructed source that starts up after the effective date of the emission standards proposed today, or a solid fuel fired boiler or liquid fuel fired boiler that is an area source that increases its emissions or its potential to emit such that it becomes a major source of HAP after the effective date of the emission standards proposed today ( and thus becomes subject to emission standards applicable to major sources including the standard for total Redline strikeout highlighting changes made during OMB review 249 chlorine), you would be required to comply with the emission standards under § § 63.1216 and 63.1217 until your eligibility demonstration is completed, submitted, and approved by your permitting authority. FG. How Would the Risk Based HCl Equivalent Emission Rate Limit Be Implemented? Upon approval by the permitting authority of your eligibility demonstration, the HClequivalent emission rate limit established in the demonstration for your hazardous waste combustor( s) becomes the applicable emission limit for total chlorine in lieu of the MACT standard for total chlorine. 1. What Are the Testing and Monitoring Requirements? To ensure compliance with the alternative HCl equivalent emission rate limit for your combustor( s), you would conduct performance testing as required for the MACT standards and establish limits on the same operating parameters that apply to sources complying with the MACT standards for total chlorine under § 63.1209( o). You would establish and comply with these operating parameter limits just as you would establish and comply with the limits for the MACT emission standard for total chlorine, with the exception of the chlorine feedrate limit, as discussed below. For example, existing sources would establish these limits in the Documentation of Compliance required under § 63.1211( c) and begin complying with them not later than the compliance date. Existing sources would also revise the operating limits as necessary based on the initial comprehensive performance test and begin complying with the revised operating limits not later than when the Notification of Compliance is postmarked, as required under § § 63.1207( j) and 63.1210( b). The limit on chlorine feedrate required under § 63.1209( o)( 1) would be established differently to ensure compliance with the HCl equivalent emission rate limit rather than the total chlorine emission standard. To ensure that facility wide hazardous waste combustor emissions of HCl equivalents result in exposures equivalent to a Hazard Index of less than or equal to 1.0, the feedrate limit for chlorine would be established as the average of the test run averages and the averaging period for compliance would be one year. A yearly rolling average is appropriate for risk based emission limits rather than the 12 hour rolling average applicable to the MACT standards because the risk based emission limit is based on chronic exposure. As discussed in Section B. 2. e above, although we conclude that the chronic exposure Hazard Index would always be higher and thus be the basis for the total chlorine emission rate limit, we still must be concerned about acute exposure attributable to short term emission rates higher than the maximum average emission rate limit. For example, the annual average limit on chlorine ( i. e., total chlorine and chloride) feedrate would allow a source to feed very high levels of chlorine for short periods of time, potentially resulting in exceedances of the acute exposure Hazard Index based the AEGL 1 values for hydrogen chloride and chlorine gas. We specifically request comment on how a short term limit on chlorine feedrate could be established for each hazardous waste combustor to ensure that the acute exposure Hazard Index is less than or equal to 1.0. One approach would be for you to extrapolate from the chlorine feedrate during the comprehensive performance test to the feedrate projected to achieve emission rates of hydrogen Redline strikeout highlighting changes made during OMB review 18 We also request comment on whether extrapolation of the chlorine feedrate should be allowed to 100% of the Hazard Index limit of 1.0, or whether a more conservative approach of limited extrapolation to a fraction of the Hazard Index ( e. g., 0.8) would be warranted, given the uncertainties inherent in projecting emissions from extrapolated feedrates.

19 We request comment on whether the system removal efficiency a cement kiln demonstrates during a performance test because of the alkalinity of the raw material is reasonably indicative of the system removal efficiency it routinely achieves ( i. e., is the system removal efficiency reasonably reproducible).

20 We would use the normalized maximum 1 hour average concentrations in US EPA, " A Tiered Modeling Approach for Assessing the Risk Due to Sources of Hazardous Air Pollutants," March 1992, Table 2.

250 chloride and chlorine gas that result in an acute exposure Hazard Index of 1.0.18 This feedrate would be a 1 hour average feedrate limit. This approach uses the reasonable assumption that there is a proportional relationship between chlorine feedrate and the emission rate of hydrogen chloride and chlorine gas. To extrapolate feedrates, you would consider the system removal efficiency achieved during the performance test for sources equipped with wet or dry acid gas scrubbers and for cement kilns. 19 Other sources would assume a zero system removal efficiency because any removal efficiency that may be measured would be incidental and not reproducible. The approach discussed above would be applicable if you use the site specific compliance eligibility demonstration. If you use the look up table for your eligibility demonstration, an alternative approach would be needed to establish a short term chlorine feedrate limit. One approach would be to establish a look up table for maximum 1 hour average HCl equivalents based on acute exposure. Acute exposure HCl equivalents would be calculated using the AEGL 1 values for hydrogen chloride and chlorine gas, and the look up table of acute exposure maximum emission rate limits would be based on normalized air concentrations for maximum 1 hour average ground level concentrations. 20 You would extrapolate the chlorine feedrate from the level achieved during the comprehensive performance test to a level that would not exceed the acute exposure HCl equivalent emission rate limit for each combustor provided in the look up table. This feedrate would be a 1 hour average feedrate limit. We specifically request comment on these approaches to establish a short term limit on the feedrate of total chlorine and chloride to ensure that the acute exposure Hazard Index for hydrogen chloride and chlorine gas is less than or equal to 1.0. 2. What Test Methods Would You Use? Although you would comply with the MACT standard for total chlorine using stack Method 26/ 26A, certain sources would not be allowed to use that method to demonstrate Redline strikeout highlighting changes made during OMB review 21 Even though Method 26/ 26A may bias total chlorine emission measurements low for cement kilns for reasons discussed in the text, it is appropriate to allow compliance with the technology based MACT emission standards for total chlorine using that method. Because the MACT standards are developed using data obtained using Method 26/ 26A, allowing that method for compliance will achieve reductions in total chlorine emissions. For the same reason, it would be inappropriate to require compliance with unbiased methods because the average of the best performing sources might not be able to achieve the standard.

22 USEPA, " Draft Technical Support Document for HWC MACT Replacement Standards, Volume III: Selection of MACT Standards and Technologies," March 2004.

251 compliance with the risk based HCl equivalent emission rate limit. 21 Cement kilns and sources equipped with a dry acid gas scrubber should use EPA Method 320/ 321 or ASTM D 6735 01 to measure hydrogen chloride, and the back half ( caustic impingers) of Method 26/ 26A to measure chlorine gas. Incinerators, boilers, and lightweight aggregate kilns should use EPA Method 320/ 321 or ASTM D 6735 01 to measure hydrogen chloride, and Method 26/ 26A to measure total chlorine, and calculate chlorine gas by difference if: ( 1) the bromine/ chlorine ratio in feedstreams is greater than 5 percent; or ( 2) the sulfur/ chlorine ratio in feedstreams is greater than 50 percent. a. Method 26/ 26A Has a Low Bias for Hydrogen Chloride in Certain Situations. Method 26/ 26A has a low bias for hydrogen chloride for sources that emit particulate matter than can adsorb hydrogen chloride: cement kilns and sources equipped with a dry acid gas scrubber. Particulate matter caught by the Method 26/ 26A filter scrubs hydrogen chloride from the sample gas, and can result in measurements that are biased low by 2 to 30 times. 22 Chlorine gas is not adsorbed so that chlorine gas emissions are not biased by this mechanism. b. Method 26/ 26A Can Have a Low Bias for Chlorine Gas and a High Bias for Hydrogen Chloride, but Has No Bias for Total Chlorine. Method 26/ 26A also has a low bias for chlorine and a high bias for hydrogen chloride when bromine is present at significant levels. Bromine has a strong effect on the bias. Although the various interhalogen reactions are extremely complex and may depend on a variety of system parameters, it appears that each bromine molecule can react with a chlorine molecule in the acidic impingers of Method 26/ 26A where hydrogen chloride is captured, converting the chlorine to chloride ions which are reported as hydrogen chloride. Total chlorine measurements ( i. e., hydrogen chloride and chlorine gas, combined, reported as HCl equivalents), however, are not affected. To minimize this bias, we propose to require sources that have a bromine/ chlorine feedrate exceeding 5 percent to use alternative methods discussed below. Given the strong bias that bromine can have on M26/ 26A measurements, we believe a 5 percent limit on the ratio is within the range of reasonable values that we could select. We specifically request comment on this or other approaches to minimize the bromine bias. Method 26/ 26A also has a low bias for chlorine and a high bias for hydrogen chloride when sulfur is present at substantial levels relative to the levels of chlorine. The capture of chlorine in the acidic impingers that collect hydrogen chloride has been shown to rapidly increase Redline strikeout highlighting changes made during OMB review 252 when the ratio of SO2/ HCl ( both expressed in ppmv) exceeds 0.5. Again, total chlorine measurements are not biased. To minimize this bias, we believe that a 50 percent limit on the ratio of the sulfur/ chlorine feedrate is within the range of reasonable values that we could select. We specifically request comment on this or other approaches to minimize the sulfur dioxide bias. c. Unbiased Methods Are Available. The Agency recently developed three methods for hydrogen chloride in the context of the Portland Cement MACT rule for purposes of area source determinations: Methods 320, 321, and 322. Although M322 ( GFCIR, Gas Filter Correlation Infra Red) is easier to use and less expensive than M320/ M321 ( FTIR, Fourier Transform Infra Red), the Agency did not promulgated M322 in the final Portland Cement MACT rule because of accuracy concerns resulting from emissions sampling of lime manufacturing kilns in the context of developing the Lime Manufacturing MACT rule. The Agency has also adopted an American Society of Testing and Materials ( ASTM) standard for measuring hydrogen chloride emissions: ASTM D 6735 01. This method ( and M321) is allowed for area source determinations under the Lime Manufacturing MACT rule. 69 FR 394 ( Jan. 5, 2004). The method is an impinger method, like M26/ 26A, but with several improvements. For example, the method uses a rejection probe ( i. e., the probe is directed counter to the gas flow), the filter is heated to minimize adsorption of hydrogen chloride on particulate matter that may catch on the filter, glassware must be conditioned, and improved quality assurance/ quality control procedures are prescribed. GH. How Would You Ensure that Your Facility Remains Eligible for the Risk Based Emission Limit? 1. Changes Over Which You Have Control Changes in design, operation, or maintenance of a hazardous waste combustor that may affect the rate of emissions of HCl equivalents from the combustor are subject to the requirements of § 63.1206( b)( 5). If you change the information documented in the demonstration of eligibility for the HClequivalent emission rate limit which is used to establish the HCl equivalent emission rate limit, you would be subject to the following procedures. a. Changes that Would Decrease the Allowable HCl Equivalent Emission Rate Limit. If you plan to make a change that would decrease the allowable HCl equivalent emission rate limit documented in your eligibility demonstration, you would comply with § 63.1206( b)( 5)( i)( A C) regarding notifying the permitting authority of the change, submitting a comprehensive performance test schedule and test plan, comprehensive performance testing, and restriction on burning hazardous waste prior to submitting a revised Notification of Compliance. An example of a change that would decrease the allowable HCl equivalent emission rate limit is location of the property boundary closer to the nearest hazardous waste combustor stack when using the look up table to make the eligibility demonstration. b. Changes that Would Not Decrease the Allowable HCl Equivalent Emission Rate Limit. If you determine that a change would not decrease the allowable HCl equivalent emission rate limit documented in your eligibility demonstration, you would document the change in the operating record upon making such change. If the change would increase your allowable HClequivalent emission rate limit and you elect to establish a higher HCl equivalent limit, you must Redline strikeout highlighting changes made during OMB review 253 submit a revised eligibility demonstration for review and approval. Upon approval of the revised eligibility demonstration, you must comply with § 63.1206( b)( 5)( i)( A)( 2), ( B), and ( C) regarding submitting a comprehensive performance test schedule and test plan, comprehensive performance testing, and restriction on burning hazardous waste prior to submitting a revised Notification of Compliance. 2. Changes Over Which You Do Not Have Control Over time, factors and information over which you do not have control and which you use to make your eligibility demonstration may change. For example, if you use a site specific compliance demonstration, individuals may locate within the area impacted by emissions such that the most exposed individual may be exposed to higher ground level concentrations than previously estimated. This could lower your allowable HCl equivalent emission rate limit. Consequently, you would be required to review the documentation you use in your eligibility demonstration every five years on the anniversary of the comprehensive performance test and submit for review with the test plan either a certification that the information used in your eligibility demonstration has not changed in a manner that would decrease the allowable HClequivalent emission rate limit, or a revised eligibility demonstration for a revised HCl equivalent emission rate limit. H I. Request for Comment on an Alternative Approach: Risk Based National Emission Standards As noted earlier, another approach to implement section 112( d)( 4)   and one EPA has used in past MACT rules   would be to establish national emission standards for each source category to ensure that the emissions from each source within the category are protective of public health with an ample margin of safety ( and do not pose adverse environmental impacts). Under this approach, dispersion modeling of representative worst case sources ( or all sources) within a category would be used to identify an emission level that meets the section 112( d)( 4) criteria for all sources within the category. Thus, the same risk based national emission standard would be established for each source in each source category under this approach, rather than the approach we discuss above of establishing a national exposure standard based on a uniform level of protection that you would use to establish a site specific emission limit. The approach of establishing a risk based national emission standard for a source category has the advantage of being less burdensome to implement both for the regulated community and regulatory authorities . It has the disadvantage, however, of requiring documentation " up front" to support the proposed emission standards. EPA does not have the time, data, or resources to conduct the analyses required to support this approach. The Cement Kiln Recycling Coalition ( CKRC), however, has submitted documentation Redline strikeout highlighting changes made during OMB review 23 Trinity Consultants, " Analysis of HCl/| Cl2 Emissions from Cement Kilns for 112( d)( 4) Consideration in the HWC MACT Replacement Standards," September 17, 2003.

254 supporting a national risk based emission standard for total chlorine for cement kilns. 23 CKRC uses normalized air concentrations from ISC PRIME and ISCST3 to estimate maximum annual average and maximum 1 hour average off site ground level concentrations of hydrogen chloride and chlorine gas for each source. CKRC assumes that each kiln emits total chlorine at 130 ppmv, the current Interim Standard, and that emissions of hydrogen chloride and chlorine gas partition at the same ratio as measured during the most recent compliance test. The analysis indicates that the facility Hazard Index for 1 hour exposures was below 0.2 for the kilns at all facilities, and the facility Hazard Index for long term exposures was below 0.2 for the kilns at 8 of 14 facilities. Emissions from kilns at the remaining 6 facilities can potentially result in facility Hazard Index values up to 0.7. Notwithstanding that CKRC followed the guidance we suggested to identify a section 112( d)( 4) risk based emission standard for a source category, we conclude that establishing a stack gas concentration based total chlorine standard of 130 ppmv may not be protective with an ample margin of safety. Even though the highest Hazard Index for any facility in the category is below the maximum HI of less than 1.0, the Hazard Index value for a facility could increase even though sources do not exceed an emission standard of 130 ppmv. This is because the Hazard Index is affected by the mass emission rate ( e. g., lb/ hr) of hydrogen chloride and chlorine gas individually. Thus the Hazard Index could increase from the values CKRC has calculated even though each source complies with a 130 ppmv total chlorine emission standard given that: ( 1) the RfC for chlorine gas is 100 times lower than the RfC for hydrogen chloride; ( 2) the partitioning of total chlorine between hydrogen chloride and chlorine gas could change so that a greater portion is emitted as chlorine; and ( 3) the mass emission rate of hydrogen chloride and chlorine gas would increase if the stack gas flowrate increases. Because of these concerns, the more appropriate metric for a risk based standard for total chlorine would be the toxicity weighted HCl equivalent emission rate discussed above in Section C. 1. To achieve our dual objective of establishing a protective risk based emission standard expressed as a toxicity weighted HCl equivalent emission rate ( lb/ hr) and ensuring that the standard does not allow total chlorine emission concentrations ( ppmv) higher than the current interim standard of 130 ppmv, we propose that thean HCl equivalent emission rate limit be established as follows: that is achievable by all cement facilities. ( 1) calculate theThis would be an HCl equivalent emission rate for each source assuming stack gas concentrations for total chlorine of 130 ppmv and partitioning betweenwhich on site cement kiln emissions of hydrogen chloride and chlorine gas and maximum stack gas flowrates achieveddo not exceed a Hazard Index of 1.0. To make this determination, facilities would assume that emissions of hydrogen chloride and chlorine gas partition at the same ratio as measured during the most recent compliance test; and ( 2) establish the national emission standard as the lowest toxicity weighted HCl equivalent emission rate for any source in the category. Calculating. Finally, the HCl equivalent emission Redline strikeout highlighting changes made during OMB review 24 See 63 FR at 14196 ( March 24, 1998).

25 For the same reasons, HCl equivalent emission rates that CRRC may use in an eligibility demonstration for the source category would be biased conservatively high.

255 rate for each source assuminglimit would be capped, if necessary, at a stack gas concentration forlimit that ensures that total chlorine of 130 ppmv is appropriate in the first step because CKRC has already apportioned total chlorine between hydrogen chloride and chlorine gas for each source and determined that a facility Hazard Index of less than or equal to 1.0 would not be exceeded at an emission concentration ofs for each kiln do not exceed 130 ppmv for total chlorine. . If this information and supporting documentation is provided to us, we would promulgate a toxicity weighted HCl equivalent emission rate that would be applicable to cement kilns.

. On a related matter, we evaluated whether using hydrogen chloride and chlorine gas emissions data obtained with stack sampling Method 26/ 26A to project hydrogen chloride and chlorine gas emissions in CKRC's analysis compromised the results. Method 26/ 26A is known to underestimate hydrogen chloride emissions from cement kilns. 24 We discuss above in Section F. 2 concerns about Method 26/ 26A and the rationale for proposing to require sources to use methods other than Method 26/ 26A to measure emissions of hydrogen chloride and chlorine gas for compliance with risk based standards. Briefly, Method 26/ 26A results for hydrogen chloride are biased low for cement kilns, although results for chlorine gas are unaffected. Even though CKRC used Method 26A results to apportion the 130 ppmv total chlorine assumed emissions between hydrogen chloride and chlorine gas for each source, the calculated Hazard Index values are not compromised. Given that the hydrogen chloride emission levels are biased low, the chlorine gas/ hydrogen chloride ratio that CKRC used to apportion the 130 ppmv total chlorine emissions between chlorine gas and hydrogen chloride emissions for each source is biased high. Thus, CKRC projected chlorine gas emissions that are biased high and hydrogen chloride emissions that are biased low. These biases result in calculating conservative ( i. e., higher than actual) Hazard Index values because the health threshold values are lower for chlorine gas than for hydrogen chloride. 25 Thus, actual Hazard Index values at an emission level of 130 ppmv total chlorine would be lower than those that CKRC calculated.

XIV. How Did EPA Determine Testing and Monitoring Requirements for the Proposed Rule? Redline strikeout highlighting changes made during OMB review 26 Please note that we also propose to revise the existing schedule for the initial comprehensive performance test for incinerators, cement kilns, and lightweight aggregate kilns. Under the proposed revised schedule, owners and operators of incinerators, cement kilns, and lightweight aggregate kilns would be required to conduct the initial comprehensive performance test to document compliance with the replacement standards proposed today ( § § 63.1203A1219, 63.1204A1220, and 63.1205A1221) within 12 months of the compliance date. See discussion in Part Three, Section I. F.

27 For this reason, in the technical support documents for today's proposed rule we also refer extensively to the technical support documents for the Phase I rule.

28 Those boilers that would be subject to a numerical dioxin/ furan standard ( i. e., liquid fuel fired boilers equipped with an electrostatic precipitator or fabric filter) would be required to conduct periodic comprehensive and confirmatory testing. Other boilers would be 256 The CAA requires us to develop regulations that include monitoring and testing requirements. CAA section 114 ( a) ( 3). The purpose of these requirements is to allow us to determine whether an affected source is operating in compliance with the rule. We propose testing and monitoring requirements for solid fuel fired boilers, liquid fuelfired boilers and hydrochloric acid production furnaces that are identical to those applicable to incinerators, cement kilns, and lightweight aggregate kilns under § § 63.1207, 63.1208, and 63.120926 Please note, however, that we discuss below a proposed requirement for boilers that would not be subject to a numerical dioxin/ furan emission standard to conduct a one time test for dioxin/ furan emissions. In addition, in Part Three of today's preamble, we request comment on, or propose revisions to, several compliance requirements. Any amendments to the compliance requirements that we promulgate would be applicable to all hazardous waste combustors. In addition, we discuss below in this section proposed compliance procedures for emission standards that would be based on normal rather than compliance test data and that would be applicable to all hazardous waste combustors subject to such a standard. Finally, we discuss below in this section proposed compliance procedures for emission standards based on hazardous waste thermal emissions that would be applicable to all hazardous waste combustors. The rationale for the testing and monitoring requirements, and implementation of the requirements, is the same as discussed in the rulemakings promulgating those requirements for hazardous waste burning incinerators, cement kilns, and lightweight aggregate kilns, and as discussed in Part Three of today's preamble. See 61 FR 43501 ( August 23, 1996), 62 FR 24212 ( May 2, 1997), 67 FR 6791 ( February 13, 2002), and 67 FR 6967 ( February 14, 2002). For this reason, we only summarize those identical requirements and our rationale for them in today's notice. 27 A. What Is the Rationale for the Proposed Testing Requirements? The proposed rule requires solid fuel fired boilers and liquid fuel fired boilers to perform an initial comprehensive performance test for dioxin/ furan28, mercury, particulate matter, Redline strikeout highlighting changes made during OMB review required to conduct a one time test for dioxin/ furan emissions under the conditions discussed below in the text.

29 Because the dioxin/ furan confirmatory test is conducted under operating conditions that are within the range of normal operations rather than at the upper end of the range of normal operations as during a comprehensive performance test, you would not reestablish operating conditions for dioxin/ furan based on the confirmatory performance test.

257 semivolatile metals, low volatile metals, and total chloride to demonstrate compliance with emission standards. Hydrochloric acid production furnaces would be required to perform an initial comprehensive performance test for dioxin/ furan and total chloride to demonstrate compliance with emission standards. All three source categories are also subject to the destruction and removal efficiency standard. Compliance with the destruction and removal efficiency standard, however, is based on a one time emissions test, and previous destruction and removal efficiency testing under RCRA requirements may be used for that demonstration if design, operation, or maintenance of the source has not changed in a manner that could adversely affect combustion efficiency and, thus, destruction and removal efficiency. Finally, all three source categories would be required to demonstrate compliance with the carbon monoxide/ hydrocarbon emission standard during the comprehensive performance test ( and at all other times). The comprehensive performance test would be conducted every five years to ensure that the performance of the air pollution control device has not deteriorated and that other factors that may affect emissions have not caused an increase in emissions above the standards. The proposed rule also requires confirmatory testing to ensure compliance with the dioxin/ furan emission standards, the test to be conducted mid way between comprehensive performance tests when operating under typical conditions rather than at performance test conditions. More frequent confirmatory testing for dioxin/ furan is needed because dioxin/ furan emissions can be affected by various and interrelated factors, some of which are not fully understood, and because of the particular health hazard posed by emissions of dioxin/ furan. To ensure continuous compliance with the emissions standards, you would be required to establish limits on key operating parameters susceptible to continuous monitoring. The limits would be based on operating values achieved during the comprehensive performance test when the source successfully demonstrates compliance. 29 Because operating limits are calibrated based on operations during the comprehensive performance test, sources generally operate at the upper end of the range of normal operations during these tests. These proposed requirements are discussed below in Section XII. C. B. What Are the Dioxin/ Furan Testing Requirements for Boilers that Would Not Be Subject to a Numerical Dioxin/ Furan Emission Standard? As explained earlier, we are not proposing numerical dioxin/ furan emission standards for solid fuel fired boilers and for those liquid fuel fired boilers that are equipped with wet scrubbers or no particulate control device. Rather, those boilers would be subject to the carbon Redline strikeout highlighting changes made during OMB review 30 Incinerators equipped with waste heat recovery boilers are known to emit high levels of dioxin/ furan, and hydrochloric acid production furnaces with waste heat recovery boilers can also emit high levels of dioxin/ furan. Because the mechanisms that affect formation and control of dioxin/ furan are complex and not fully understood, we are concerned that some of the factors that cause high dioxin/ furan emissions from incinerators and hydrochloric acid production furnaces equipped with waste heat recovery boilers may also affect dioxin/ furan emissions from boilers.

258 monoxide/ hydrocarbon emission standard and the destruction and removal efficiency standard to help minimize dioxin/ furan emissions. See discussion in Part Two, Sections X. A and XI. A. We propose that solid fuel fired boilers and those liquid fuel fired boilers that would not be subject to a numerical dioxin/ furan emission standard conduct a one time dioxin/ furan emission test to quantify the effectiveness of today's proposed surrogate dioxin/ furan emission controls. This test would be performed no later than the initial comprehensive performance test required under the proposed standards. The results of this one time test would be reported with the test results for the first comprehensive performance test. See proposed § 63.1207( b)( 3). 1. What Is the Rationale for Requiring the Test? We are adopting this provision pursuant to our authority in CAA Section 114 ( a)( 1)( D), which allows EPA to require " any person ... who is subject to any requirement of this chapter" ( which includes Section 112) on a one time, periodic or continuous basis, to " sample such emissions ( in accordance with such procedures or methods, at such locations, at such intervals, during such periods and in such manner as the Administrator shall prescribe)". The purpose of such monitoring is " developing or assisting in the development of" standards under various provisions of the Act, including Section 112. In this case, monitoring will assist in making determinations under both Section 112( d)( 6) and Section 112( f), which could lead to development of standards under either or both of these provisions. Section 112( d)( 6) of the Act requires us to " review, and revise as necessary emission standards promulgated under this section no less than every eight years." We believe testing that results from compliance with today's proposed standards will, in nearly all cases, establish an adequate database for us to perform this review. However, we would not have sufficient dioxin/ furan emissions data for those boilers that are subject to the carbon monoxide/ hydrocarbon standard and destruction and removal efficiency standard in lieu of a numerical dioxin/ furan standard. We have data from approximately one third of the boilers that are not subject to a numerical dioxin/ furan standard. Although those data indicate that these sources emit low concentrations of dioxin/ furan despite the absence of any dioxin/ furan control equipment, we are concerned about extrapolating this performance to the entire universe of the subject boilers because our data set may not be statistically random and the potential hazard posed by dioxin/ furan is high. In fact, the design of these sources would seem to have the potential for formation of significant dioxin/ furan concentrations. 30 We think this proposed testing would add a one time cost of approximately $ 10,000 for each source for which dioxin/ furan test data are not already available, and the cost appears reasonable to enable us to meet our Section 112( d)( 6) and Redline strikeout highlighting changes made during OMB review 31 Lee, C. W.; Kilgroe, J. D.; Raghunathan, K. Environ. Eng. Sci. 1998, 15( 1), 71 84.

32 Gullett, B. K.; Touati, A.; Lee, C. W. Environ. Sci. Technol. 2000, 34, 2069 2074.

259 112( f) mandates. Section 112 ( d) ( 6) requires EPA, at specified times, to determine if further technology based emission reductions are warranted. Quantified dioxin/ furan emission information from these sources will assist in this determination. Section 112( f) requires EPA ( among other things) to determine if emissions from all sources subject to Section 112( d) standards must be further reduced in order to assure an ample margin of safety to protect public health. Having actual emission data from these sources obviously will assist in making the required Section 112( f) determinations for these sources. 2. What Are the Operating Requirements for the Test? You must perform the dioxin / furan test under feed and operating conditions that are most likely to maximize dioxin/ furan emissions, similar to a dioxin/ furan comprehensive performance test. Based on currently available research, the following factors should be considered for the testing: ( 1) dioxin/ furan testing should be conducted at the point in the maintenance cycle for the 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 the 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; ( 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; and ( 7) for solid fuel fired boilers, the sulfur content of the coal should be equivalent to or lower than normal coal sulfur levels, 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 unit, dioxin/ furan testing should not be performed after a period of firing high sulfur fuel or injection of sulfur additives. The majority of these recommendations are based on research demonstrating that soot deposits can enhance dioxin/ furan formation in the presence of chlorine and catalytic metal contaminants, with formation continuing even after cessation of those contaminant feeds to the system. 31,32 The boiler tube deposits serve as a sink and source for dioxin/ furan reactants ( catalytic metals and chlorine), and combined soot copper deposits have been shown to cause more dioxin/ furan formation than a deposit of soot or copper alone. From analysis of soot deposits taken from different sections of a firetube boiler, the highest measured dioxin/ furan concentrations were found in those deposits containing the highest concentrations of copper and chloride. Those same deposits were removed from the boiler passages where flue gas temperatures ranged from 600 300 C, which is within the often cited optimal temperature region Redline strikeout highlighting changes made during OMB review 33 Takaoka, M.; Liao, P.; Takeda, N.; Fujiwara, T.; Oshita, K. Chemosphere 2003, 53, 153 161.

34 Please note that we discuss in Section XIII of the preamble above concerns with the accuracy of M26/ 26A for measuring emissions of total chlorine for cement kilns. As we explain there, although M26/ 26A is appropriate for demonstrating compliance with the MACT standards for cement kilns, it is not acceptable for demonstrating compliance with risk based standards developed under authority of Section 112( d)( 4) of the Act.

260 for dioxin/ furan formation. Tube deposits have also been shown to have a negative effect on dioxin emissions when those deposits have been affected by sulfur dioxide, which is why dioxin/ furan testing is not recommended following a period of feeding higher than normal levels of sulfur to the boiler. The recommendation not to test under optimal combustion conditions has been explained previously in the September 1999 Final Rule preamble discussion. See 64 FR at 52937. Good combustion practices minimize dioxin/ furan emissions by: ( 1) destroying trace dioxins/ furans that may be present in feed streams; ( 2) minimizing gas phase formation of dioxins/ furans; and ( 3) minimizing dioxin/ furan precursors that may enhance post combustion formation. For units equipped with wet air pollution control systems, it is also recommended that testing be conducted after a high solids loading has developed in the scrubber system. Research conducted to explore the phenomenon of increased dioxin/ furan flue gas concentrations across some wet scrubber systems has shown differing flue gas outlet dioxin/ furan homologue profiles than flue gas inlet profiles to the scrubber, but similar flue gas outlet homologue profiles to scrubber suspended solids and sludge profiles. 33 This result suggests that some type of memory effect may be associated with suspended solids in a scrubber system which can cause higher dioxin/ furans emissions. You may use data in lieu of testing to document dioxin/ furan emissions for similar on site boilers. In addition, dioxin/ furan emission data from previous testing would be acceptable, provided the test was performed in a manner likely to maximize dioxin/ furan emissions. C. What Are the Proposed Test Methods? The proposed emission standards are method based standards, meaning that the stack test methods used for compliance must be the same as those used to generate the emissions data we used to calculate the standards. Because alternative stack methods may report lower emissions, it is appropriate to require use of the same methods for compliance as sources used to generate the emissions data in our data base. For this reason, you would be required to use the following stack test methods for compliance: ( 1) Method 29 for mercury, semivolatile metals, and low volatile metals; and ( 2) Method 26/ 26A for total chlorine. 34 For dioxin/ furan, the rule would require use of Method 0023A unless you receive approval to use Method 23. We discuss the rationale for allowing sitespecific approvals to use Method 23 in Part Three, Section II. D of today's preamble. In addition, for particulate matter, you would be required to use either Method 5, the method used to generate Redline strikeout highlighting changes made during OMB review 35 Method 0023A, however, is included in " Test Methods for Evaluating Solid Waste, Physical/ Chemical Methods," EPA Publication sw 846 Third Edition ( November 1986), as amended.

36 Except that some parameters are limited based on the recommendations/ specifications of the manufacturer of the control device.

37 If you elect to comply with the carbon monoxide standard rather than the hydrocarbon standard, you would be required to document that hydrocarbon emissions during the comprehensive performance test meet the standard.

261 the data in our data base or Method 5i. We allow use of Method 5i because it is more precise than Method 5 at lower particulate matter loadings. These test methods are codified in 40 CFR Part 60, Appendix A. 35 D. What Is the Rationale for the Proposed Continuous Monitoring Requirements? The most direct means of ensuring compliance with emissions limits is the use of continuous emission monitoring systems ( CEMS). We consider other options when CEMS are not available or when we consider the impacts of including such requirements unreasonable. When monitoring options other than CEMS are considered, it is often necessary for us to balance more reasonable costs against the quality or accuracy of the emissions monitoring data. Although monitoring operating parameters cannot provide a direct measurement of emissions, it is often a suitable substitute for CEMS. The information provided can be used to ensure that air pollution control equipment is operating properly. Because most parameter requirements are calibrated during comprehensive performance testing, 36 they provide a reasonable surrogate for direct monitoring of emissions. This information reasonably assures the public that the reductions envisioned by the proposed rule are being achieved. 1. What CEMS Requirements Did EPA Consider? To comply with the carbon monoxide or hydrocarbon emission limits, you would be required to use a carbon monoxide or hydrocarbon CEMS as well as an oxygen CEMS to correct the carbon monoxide or hydrocarbon values to 7% oxygen. See § 63.1209( a). Because boilers and hydrochloric acid production furnaces are currently required to use these CEMS to comply with existing RCRA emission standards for carbon monoxide or hydrocarbons, there would be a minimal incremental compliance cost. 37 We also evaluated the cost of applying hydrogen chloride CEMS to boilers and hydrochloric acid production furnaces. We estimate the capital costs for hydrogen chloride CEMS to be $ 88,000 per unit and annualized costs to be $ 33,000 per unit. We determined these costs would be unreasonably high considering: ( 1) the CEMS detects hydrogen chloride but not chlorine gas, so that compliance with the total chlorine emission standard could not be monitored; ( 2) the effectiveness of operating parameter limits to ensure compliance with the emission standard for total chlorine; and ( 3) the relatively low level of hazard posed by emissions of total chlorine. Redline strikeout highlighting changes made during OMB review 262 Finally, we conclude that toxic metals are not directly measurablethe use of CEMS to document compliance with CEMS, and that CEMS for particulate matter or metal HAP emission standards haves not been demonstrated on hazardous waste combustors in the United States for the purpose of determining compliance. 2. What Operating Parameter Limits Would Be Required? To ensure continuous compliance with the proposed emission limits, you would be required to establish limits on key operating parameters and continuously monitor the parameters including: feedrate of metals, chlorine, and, for some source categories, ash; key combustor operating parameters; and key operating parameters of the control device. See § 63.1209( j o). You would also be required to document monitoring by recordkeeping and reporting. We selected the following requirements based on reasonable cost, ease of execution, and usefulness of the resulting data to both owners and operators and EPA for ensuring continuous compliance with the emission limits. To ensure continuous compliance with the dioxin/ furan emission limit, you would be required to establish: ( 1) a limit on maximum gas temperature at the inlet to a dry particulate matter control device; ( 2) a limit on minimum combustion chamber temperature; ( 3) a limit on maximum flue gas flowrate or production rate; ( 4) a limit on maximum waste feedrate; ( 5) if your combustor is equipped with an activated carbon injection system: limits on the particulate matter control device, as discussed below; a limit on minimum carbon injection rate; a limit on minimum carrier fluid flowrate or pressure drop; and you must specify and use the brand ( i. e., manufacturer) and type of carbon used during the comprehensive performance test, unless you document key parameters that affect adsorption and establish limits on those parameters based on the carbon used in the comprehensive performance test; ( 6) if your combustor is equipped with a carbon bed: you must monitor the bed life to ensure that it has not reached the end of its useful life to minimize dioxin/ furan ( and mercury) emissions at least to the levels required by the emission standards; you must replace the bed or bed segment before it has reached the end of its useful life; you must specify and use the brand ( i. e., manufacturer) and type of carbon used during the comprehensive performance test, unless you document key parameters that affect adsorption and establish limits on those parameters based on the carbon used in the comprehensive performance test; and you must establish a limit on maximum gas temperature either at the bed inlet or outlet; ( 7) if your combustor is equipped with a catalytic oxidizer: limits on minimum and maximum gas temperature at the inlet to the catalyst; you must replace the oxidizer when it has reached the maximum service time specified by the manufacturer; and when replacing the catalyst, the new catalyst must be equivalent to or better than the one used during the previous comprehensive performance test as measured by catalytic metal loading for each metal, space time, and substrate construction; ( 8) if you feed a dioxin/ furan inhibitor into the combustion system: a limit on minimum inhibitor feedrate; and you must specify and use the brand ( i. e., manufacturer) and type of inhibitor used during the comprehensive performance test, unless you document key parameters that affect the effectiveness of the inhibitor and establish limits on those parameters based on the inhibitor used in the comprehensive performance test. See § 63.1209( k). To ensure continuous compliance with the mercury emission limit, owners and operators of boilers would be required to establish: ( 1) a limit on the total feedrate of mercury in all Redline strikeout highlighting changes made during OMB review 38 This is because the mercury emission standard for liquid fuel fired boilers is a hazardous waste thermal emission concentration. Liquid fuel fired boilers would also be required to monitor the heating value of hazardous waste feeds to ensure compliance with the hazardous waste thermal emission concentration.

39 The mercury feedrate limit would be based on levels fed during the comprehensive performance test unless the regulatory authority approves a request for you to extrapolate to a higher allowable feedrate ( and emission rate) limit.

263 feedstreams for solid fuel fired boilers, and a limit on mercury in hazardous waste feedstreams per million Btu of hazardous waste fired for liquid fuel fired boilers; 38,39 ( 2) if your boiler is equipped with a wet scrubber, limits prescribed for control of total chlorine with a wet scrubber, except for a limit on minimum pH of the scrubber water; ( 3) if your boiler is equipped with an activated carbon injection system, limits on the particulate matter control device as discussed below, and limits on the activated carbon injection system as discussed above for dioxin/ furan; and ( 4) if your boiler is equipped with an activated carbon bed, limits on the carbon bed as discussed above for dioxin/ furan. You may comply with mercury feedrate limits only, however, if you elect to assume that all mercury in the feed is emitted. For solid fuel fired boilers, you would assume that all mercury in all feedstreams is emitted under this alternative approach. You would also establish a limit on minimum flue gas flowrate to ensure compliance with the mercury emission standard. For liquid fuel fired boilers where the mercury emission standard is expressed as hazardous waste thermal emissions, you would assume that all mercury in all hazardous waste feedstreams is emitted. Under this alternative compliance approach, you would also establish a limit on minimum flue gas flowrate to ensure compliance with the mercury emission standardYou would have to comply with a hazardous waste thermal feed concentration that would be expressed as the mass of mercury in the hazardous waste per million Btu heat input contributed by the hazardous waste. Also, please note that these compliance requirements would not apply to hydrochloric acid production furnaces, , because ( as explained earlier) we propose to use the total chlorine standard as a surrogate for the mercury, particulate matter, semivolatile metal, and low volatile metal standards for these sources. See § 63.1209( l). To ensure continuous compliance with the particulate matter emission limit, you would be required to establish: ( 1) limits on the control device operating parameters; ( 2) a limit on maximum flue gas flowrate or production rate; and a limit on maximum ash feedrate. If your boiler is equipped with a wet scrubber, you would establish limits on: ( 1) for high energy scrubbers only, minimum pressure drop across the scrubber and either minimum liquid to gas ratio or minimum scrubber water flowrate and maximum flue gas flowrate; and ( 2) for all scrubbers, the solids content of the scrubber liquid or a minimum blowdown rate. If your boiler is equipped with an electrostatic precipitator, ionizing wet scrubber, or fabric filter, please note that we discuss in Part Three, Section II. I. below proposed compliance parameters for these control devices. Briefly, if your boiler is equipped with a fabric filter, you must comply with bag leak detection Redline strikeout highlighting changes made during OMB review 40 This is because the semivolatile metal and low volatile metal emission standards for liquid fuel fired boilers are hazardous waste thermal emission concentrations. You would also be required to monitor the heating value of hazardous waste feedstreams to ensure compliance with the hazardous waste thermal emission concentration.

41 The semivolatile and low volatile metal feedrate limits would be based on levels fed during the comprehensive performance test unless the regulatory authority approves a request for you to extrapolate to higher allowable feedrate ( and emission rate) limits. Please note that the semivolatile and low volatile metal feed limits for liquid fuel fired boilers are hazardous waste thermal concentration limits ( pounds of metal per million Btu), not mass feedrate limits, given that the emission standards are expressed as hazardous waste thermal emissions.

264 system requirements. If your boiler is equipped with an electrostatic precipitator or ionizing wet scrubber, you must either: ( 1) install and operate a particulate matter loading detector as a process monitor to indicate when you must take corrective measures; or ( 2) establish limits on key operating parameters, on a site specific basis, that are representative and reliable indicators that the control device is operating within the same range of conditions as during the comprehensive performance test, and link those operating limits to the automatic waste feed cutoff system. Please note that the particulate matter compliance requirements would not apply to hydrochloric acid production furnaces, as discussed above. See § 63.1209( m). To ensure continuous compliance with the semivolatile and low volatile metal emission limits, you would be required to establish: ( 1) a limit on the maximum inlet temperature to the primary dry particulate matter control device; ( 2) a limit on maximum feedrate of semivolatile and low volatile metals from all feedstreams for solid fuel fired boilers, and a limit on semivolatile metals and low volatile metals in hazardous waste feedstreams per million Btu of hazardous waste fired for liquid fuel fired boilers; 40,41; ( 3) limits ( or process monitors) on the particulate matter control device as discussed above; ( 4) a limit on maximum feedrate of total chlorine or chloride in all feedstreams; and ( 5) a limit on maximum flue gas flowrate or production rate. You may comply with semivolatile and low volatile metal feedrate limits only, however, if you elect to assume that all semivolatile and low volatile metals in the feed is emitted. For solid fuel fired boilers, you would assume that all semivolatile and low volatile metals in all feedstreams are emitted under this alternative approach. You would also establish a limit on minimum flue gas flowrate to ensure compliance with the semi and low volatile metals emission standard. For liquid fuel fired boilers where the semivolatile and low volatile metals emission standards are expressed as hazardous waste thermal emissions, you would assume that all semivolatile and low volatile metals in all hazardous waste feedstreams are emitted. Under this alternative compliance approach, you would also establish a limit on minimum flue gas flowrate to ensure compliance with the semivolatile and low volatile metal emission standardsYou would have to comply with a hazardous waste thermal feed concentration that would be expressed as the mass of semivolatile ( or low volatile) metals in the hazardous waste per million Btu heat input contributed by the hazardous waste. Also, please note that the semivolatile metal and low volatile metal compliance Redline strikeout highlighting changes made during OMB review 42 This is because the total chlorine emission standard for liquid fuel fired boilers is a hazardous waste thermal emission concentration. You would also be required to monitor the heating value of hazardous waste feedstreams to ensure compliance with the hazardous waste thermal emission standard.

265 requirements would not apply to hydrochloric acid production furnaces, as discussed above. See § 63.1209( n). To ensure continuous compliance with the total chlorine emission limit, you would be required to establish: ( 1) a limit on maximum feedrate of total chlorine and chloride from all feedstreams for solid fuel fired boilers, and a limit on total chlorine and chloride in hazardous waste feedstreams per million Btu of hazardous waste fired for liquid fuel fired boilers; 42 ( 2) a limit on maximum flue gas flowrate or production rate; ( 3) if your combustor is equipped with a high or low energy wet scrubber: a limit on minimum pH of the scrubber water; a limit on either the minimum liquid to gas ratio or the minimum scrubber water flowrate and maximum flue gas flowrate; ( 4) if your combustor is equipped with a high energy wet scrubber, a limit on minimum pressure drop across the scrubber; ( 5) if your combustor is equipped with a low energy wet scrubber: a limit on minimum pressure drop across the scrubber; and a limit on minimum liquid feed pressure to the scrubber; and ( 6) if your combustor is equipped with a dry scrubber: a limit on minimum sorbent feedrate; a limit on minimum carrier fluid flowrate or nozzle pressure drop; and you must specify and use the brand ( i. e., manufacturer) and type of sorbent used during the comprehensive performance test, unless you document key parameters that affect the effectiveness of the sorbent and establish limits on those parameters based on the sorbent used in the comprehensive performance test. If your combustor is equipped with an ionizing wet scrubber, please note that we discuss in Part Three, Section II. I. below proposed compliance parameters for this control device. Briefly, if your combustor is equipped with an ionizing wet scrubber, you must either: ( 1) install and operate a particulate matter loading detector as a process monitor to indicate when you must take corrective measures; or ( 2) establish limits on key operating parameters, on a site specific basis, that are representative and reliable indicators that the control device is operating within the same range of conditions as during the comprehensive performance test, and link those operating limits to the automatic waste feed cutoff system. You may comply with a total chlorine and chloride feedrate limit only, however, if you elect to assume that all chlorine in the feed is emitted. For solid fuel fired boilers, you would assume that all chlorine in all feedstreams is emitted under this alternative approach. You would also establish a limit on minimum flue gas flowrate to ensure compliance with the total chlorine standard. For liquid fuel fired boilers where the total chlorine emission standard is expressed as hazardous waste thermal emissions, you would assume that all chlorine in all hazardous waste feedstreams is emitted. Under this alternative compliance approach, you would also establish a limit on minimum flue gas flowrate to ensure compliance with the total chlorine standardYou would have to comply with a hazardous waste thermal feed concentration that would be expressed as the mass of chlorine in the hazardous waste per million Btu heat input contributed by the hazardous waste. See § 63.1209( o). Redline strikeout highlighting changes made during OMB review 43 Please note, however, that we request comment on the appropriateness of these combustion system leak requirements in Part Three of today's preamble.

266 To ensure continuous compliance with the destruction and removal efficiency standard, you would be required to: ( 1) establish a limit on minimum combustion chamber temperature; ( 2) establish a limit on maximum flue gas flowrate or production rate; ( 3) establish a limit on maximum hazardous waste feedrate; and ( 4) specify operating parameters and limits to ensure that good operation of each hazardous waste firing system is maintained. See § 63.1209( j). E. What Are the Averaging Periods for the Operating Parameter Limits, and How Are Performance Test Data Averaged to Calculate the Limits? Except as discussed in Section XIV. F below, we propose that owners and operators of solid fuel fired boilers, liquid fuel fired boilers, and hydrochloric acid production furnaces establish averaging periods for the operating parameter limits and calculate the limits from comprehensive performance test data under the same approaches required currently for incinerators, cement kilns, and lightweight aggregate kilns. A detailed discussion of how those approaches work, and the rationale for them, are provided at 64 FR at 52919 22 ( September 30, 1999). That discussion is summarized below. We propose the following averaging periods: ( 1) no averaging period ( i. e., instantaneous monitoring) for maximum combustion chamber pressure to control combustion system leaks43; ( 2) 12 hour rolling averages for maximum feedrate of mercury, semivolatile metals, low volatile metals, total chlorine and chloride, and ash; and ( 3) one hour rolling averages for all other operating parameters. We propose a 12 hour rolling average for metal, total chlorine and chloride, and ash feedrate limits to correspond to the potential duration of three runs of a comprehensive performance test, considering that feedrate and emissions, are, for the most part, linearly related. We propose an hourly rolling average limit for all parameters that are based on operating data from the comprehensive performance test, except combustion chamber pressure and metal, chlorine, and ash feedrate limits. Hourly rolling averages are appropriate for these parameters rather than averaging periods based on the duration of the performance test because we are concerned that there may be a nonlinear relationship between operating parameter levels and emission levels of HAP or HAP surrogates. We propose two approaches to calculate limits for operating parameters: ( 1) calculate the limit as the average of the maximum ( or minimum, as specified) rolling averages for each run of the test; or ( 2) calculate the limit as the average of the test run averages for each run of the test. Hourly rolling averages for two parameters combustion gas flowrate or production rate and hazardous waste feedrate   would be based on the average of the maximum hourly rolling averages for each run. Hourly rolling average and 12 hour rolling average limits for all other parameters, however, would be based on the average level occurring during the comprehensive performance test. We conclude that this more conservative approach is appropriate for these parameters because they can have a greater effect on emissions, and because it is consistent with how manual Redline strikeout highlighting changes made during OMB review 44 Manual method emission test results for each run represent average emissions over the entire run.

45 These are maximum emissionsCompliance test emissions represent the upper range of emissions from a source because operating parameter limits for the HAP or HAP surrogate are established based on this compliance test.

267 emissions results are determined. 44 We also conclude that limits based on the average level occurring during the comprehensive performance are readily achievable. This is because sources generally conduct performance testing at the extreme upper end of the range of normal operations to provide the operating flexibility needed after establishing operating parameter limits. Because sources can readily control ( during the performance test and thereafter) the parameters for which limits are established, the operating limits based on the average of the performance test runs should be readily achievable under routine operations. F. How Would Sources Comply with Emissions Standards Based on Normal Emissions? Several proposed emission standards would be based on emissions that are within the normal range of operations for the source rather than on compliance test emissions that represent the extreme upper end of the range of normal emissions: 45 mercury standards for cement kilns, lightweight aggregate kilns, and liquid fuel fired boilers, and semivolatile metal emissions for liquid fuel fired boilers. To ensure compliance with emission standards based on normal emissions data, you would document during the comprehensive performance test a system removal efficiency for the metals and back calculate from the emission standard a maximum metal feedrate limit that must not be exceeded on an annual rolling average. If your source is not equipped with an emission control system ( such as activated carbon to control mercury) for the metals in question, however, you must assume zero system removal efficiency. This is because a source that is not equipped with an emission control system may be able to document a positive system removal efficiency, but it is not likely to be reproducible. It is likely to be an artifact of the calculation of emissions and feeds rather than a removal efficiency that is reliable and reproducible. To ensure that you can calculate a valid, reproducible system removal efficiency for sources equipped with a control system that effectively controls the metal in question, you may need to spike metals in the feed during the comprehensive performance test at levels that may result in emissions that are higher than the standard. This would be acceptable because compliance with an emission standard derived from normal emissions data is based on compliance with an annual average feedrate limit calculated as prescribed here, rather than compliance with the emission standard during the comprehensive performance test. We propose a one year averaging period for the metal feedrate limit because the emission standard represents normal, average emissions. Although the averaging period could be substantially shorter or longer, a one year averaging period is within the range of reasonable averaging periods and would be readily achievable for a standard based on normal emissions. The annual rolling average metal feedrate would be updated each hour based on the average of the 60 Redline strikeout highlighting changes made during OMB review 46 If the hazardous waste thermal emission standard is derived from normal rather than compliance test emissions data, however, the hazardous waste thermal feed concentration would be calculated as discussed above in Section F of the preamble.

268 previous 1 minute averages. We propose to retain the hourly rolling average requirement for the other operating parameter limits, however, for the reasons discussed above ( i. e., to be conservative given the nonlinear relationship between the operating parameter and emissions, and because the limits would be readily achievable). G. How Would Sources Comply with Emission Standards Expressed as Hazardous Waste Thermal Emissions? Several proposed emission standards would be expressed as hazardous waste thermal emissions: mass of pollutant emissions attributable to the hazardous waste feed per million Btu of hazardous waste fed to the combustor. To demonstrate compliance with a hazardous waste thermal emissions based standard during a comprehensive performance test, you would calculate the hazardous waste thermal emissions by apportioning mass emissions of mercury, semivolatile metals, low volatile metals, or total chlorine according to the ratio of the mass feedrate of mercury, semivolatile metals, low volatile metals, or total chlorine and chloride from hazardous waste feedstreams to the feedrate for all feedstreams and dividing by the heat input rate ( i. e., million Btu/ hr) attributable to the hazardous waste. To ensure continuous compliance with the hazardous waste thermal emissions based standard, you would calculate an operating limit based on the hazardous waste thermal feed concentration during the performance test. 46 The hazardous waste thermal feed concentration limit would be calculated as the mass feedrate ( lb/ hr) of mercury, semivolatile metals, low volatile metals, or total chlorine and chloride from hazardous waste feedstreams divided by the heat input rate ( million Btu/ hr) from hazardous waste feedstreams. For compliance, you would continuously monitor the feedrate of hazardous waste on a 12 hour rolling average updated each minute or, for standards based on normal emissions, on a annual rolling average updated each hour. You must know the concentration of mercury, semivolatile metals, low volatile metals, or total chlorine and chloride in the hazardous waste at all times, and the heating value of the hazardous waste at all times. Using this information, you would calculate and record the hazardous waste thermal feed concentration on a 12 hour rolling average, or for standards based on normal emissions, on a annual rolling average updated each hour. Redline strikeout highlighting changes made during OMB review 269 Redline strikeout highlighting changes made during OMB review 270 What Are the Other Proposed Compliance Requirements? We propose other compliance requirements for solid fuel fired boilers, liquid fuel fired boilers, and hydrochloric acid production furnaces that are the same as those currently in place at § 63.1206 for incinerators, cement kilns, and lightweight aggregate kilns. The rationale for the requirements is the same as discussed in previous rulemakings for incinerators, cement kilns, and lightweight aggregate kilns, and compliance procedures would be the same as currently required for those sources. The other compliance requirements include provisions for: startup, shutdown, and malfunction plans; operation and maintenance plans including a requirement for bag leak detector systems for fabric filters; automatic hazardous waste feed cutoff systems, including a requirement for exceedance reporting; combustion system leak requirements; changes in design, operation, or maintenance that could adversely affect compliance with emission standards; operator training and certification requirements; and requirements for sources that elect to comply with the carbon monoxide standard to document one time that hydrocarbons also meet the hydrocarbon standard; and provisions allowing a one time demonstration of compliance with the destruction and removal efficiency standard. Please note that we propose revisions to, or request comment on, some of these compliance requirements in Part Three of the preamble. Any revisions to these requirements that we might make in the final rule would be applicable to all hazardous waste combustors.

XV. How Did EPA Determine Compliance Times for this Proposed Rule? Section 112 of the CAA specifies the dates by which affected sources must comply with the emission standards. New or reconstructed units must be in compliance with the proposed rule immediately upon startup or [ DATE THE FINAL RULE IS PUBLISHED IN THE FEDERAL REGISTER], whichever is later. A new or reconstructed unit for purposes of complying with this proposed rule is one that begins construction after [ DATE THE PROPOSED RULE IS Redline strikeout highlighting changes made during OMB review 47 Please note that a new or reconstructed unit for purposes of complying with the Interim Standards applicable to incinerators, cement kilns, and lightweight aggregate kilns is a unit that began operation after September 30, 1999.

271 PUBLISHED IN THE FEDERAL REGISTER]. 47 Existing sources are allowed up to three years to comply with the final rule. See proposed § 63.1206( a)( 1)( ii) and ( a)( 2). This is the maximum period allowed by the CAA. We believe that three years for compliance is necessary to allow adequate time to design, install, and test control systems that will be retrofitted onto existing units.