MEMORANDUM Date: August 27, 2003 To: Docket ID No. A 2000 56 ( Iron and Steel Foundries)

From: Kevin Cavender, EPA Subject: Determination of the MACT Floor Metal HAP Emission Limits for Iron and Steel Foundries Purpose The purpose of this memorandum is to document the procedures used to determine the MACT floor metal HAP emission limits for iron and steel foundries and to summarize the results.

Conclusion

PM is a reasonable surrogate for metal HAP emissions for melting and pouring emission sources.

The MACT floor PM emission limits for melting furnaces and pouring stations at existing iron and steel foundries are as follows:

S cupolas = 0.006 grains per dry standard cubic feet ( gr/ dscf),

S electric induction furnaces ( EIFs) and scrap preheaters ( SPHs) = 0.005 gr/ dscf,

S electric arc furnaces ( EAFs)] = 0.005 gr/ dscf, and S pouring stations = 0.010 gr/ dscf.

The MACT floor PM emission limits for melting furnaces and pouring operations at a new iron and steel foundry are as follows:

S cupolas = 0.002 gr/ dscf,

S EIFs and scrap preheaters = 0.001 gr/ dscf,

S EAFs = 0.002 gr/ dscf, and S pouring stations and pouring areas = 0.002 gr/ dscf.

An equivalent alternative MACT floor metal HAP emission limit can be calculated from the MACT floor PM emission limits using 8% total metal HAP. 2 General Approach A substantial body of information is available on the types, configurations, and operating conditions of the operational units and air pollution control devices applied across the iron and steel foundry source category. This information was collected through our comprehensive survey of known iron and steel foundries conducted in 1998. From this survey, detailed data are available for 595 iron and steel foundries which provided survey responses ( U. S. EPA, 1998). The detailed survey responses contained information regarding the type of process unit, the air pollution control device used, design information about the control device, and, in some cases, actual performance test data.

Based on the performance test data available for the melting furnaces, baghouses consistently performed much better than wet scrubbers. In terms of both outlet concentrations and mass of emissions per ton of metal melted, the baghouse emission control systems have lower PM emissions than other control systems ( wet scrubber, electrostatic precipitators, or uncontrolled units). For this category of sources, there is very little, if anything, that can be done to meet HAP emission limits aside from installing and operating an effective emission control system. A scrap selection and inspection program can reduce, to some extent, the amount of metal HAP entering a furnace, however, certain metal HAP are necessary constituents in the cast product. The proportion of the metal HAP constituents that can ( and generally are) removed by a scrap selection and inspection programs are a small fraction of the total HAP contained in the scrap material. As such the primary means of reducing HAP emissions from this category of sources is through effective PM emission control systems. As baghouses were used in well over 12 percent of the melting furnaces, we concluded that the wet scrubbers and uncontrolled units were not among the best performing 12 percent of existing sources. Therefore, only data for melting furnaces equipped with baghouses needed to be evaluated in detail in order to identify the level of performance associated with the MACT floor. Once we identified the control systems that were among the top performing 12 percent of units, the performance of these systems were evaluated and ranked individually.

We have interpreted the MACT floor for existing sources ( i. e., the average emission limitation achieved by the best performing twelve percent of existing sources) to be the performance achieved by the median source of the top 12 percent best performing sources, or the 6th percentile unit. We use the 6th percentile unit as the most representative estimate of the average emission limitation achieved by the best performing 12 percent of existing sources because the 6th percentile points to the performance of a specific unit with a combination of actual emissions control measures. The 6th percentile unit is identified by multiplying the total number of units for which we have emissions information by 0.06. The resulting unit that represents the 6th percentile unit is then identified in the ranking of control systems, and the performance of this unit is considered the MACT floor performance limit for existing sources.

For new sources, the MACT floor is the emission control that is achieved in practice by the best controlled similar source. Therefore, the new source MACT floor is simply the performance of the top ranked control system. 3 Information Available to Estimate of Control Device Performance Three types of information were generally available to assess an individual unit's level of performance. These were: actual performance test data; control device outlet concentration design values; and control device percent emission reduction design values. The design values ( either outlet concentrations or percent removal) represent the specifications the control device vendor used in designing the emission control system. Generally, the foundry operator desires to achieve a given emissions limit or emissions reductions. He relays this information to the control device vendor, and the control device vendor designs the control device to meet, at a minimum, the target emissions performance. These design values are often guaranteed performance limits for which the control device vendor may be liable. If the performance of the unit does not meet the design or guaranteed performance requirements, the control device vendor may be responsible to upgrade or replace the control system at their own cost. As such, these design values represent the minimum performance that these units will consistently meet. Therefore, we believe that these values provide a reasonable estimate of a given unit's performance under the most adverse circumstance which can reasonably be expected to recur.

The outlet concentration design values are outlet PM concentration values ( either in gr/ acfm or gr/ dscf) that the baghouse vendor gaurantees the system can meet. As such, the outlet concentration design values directly represent a PM concentration emission limit that the control system could meet on a continuous basis. Actual performance test data, on the other hand, provides a measure of a unit's performance for a specific ( short) period of time, but may not represent the actual range of performance that the unit experiences over the course of typical operating variations ( e. g., variations in production rates or in seasonal temperature, etc.). Therefore, we applied statistical analyses ( which are described in more detail presently) to estimate the actual performance limits ( in terms of outlet PM concentration limits) that the control system can consistently achieve. For units for which both types of emissions information were available, the outlet concentration design value was compared to the statistically derived performance limits based on actual source test data. Both types of information generally lead to the same performance limit, indicating that both types of information are reasonable estimates of actual performance the units.

The percent emission reduction design values had to be converted to an outlet PM concentration performance limit so that the performance of the control devices could be compared and ranked on a consistent basis. We determined the outlet concentrations associated with each percent emission reduction design value by looking at the available test data for systems that also reported a percent emission reduction design value and by calculating the outlet PM concentration from the anticipated inlet ( uncontrolled) PM concentration for that emission source. By comparing the calculated outlet PM concentrations with the performance limits derived from actual test data, we ensured that the outlet PM concentrations performance limits calculated from the percent emission reduction design values are reasonable estimates of actual performance of the units. 4 For each unit, the ( long term) emission performance limit was calculated based on the available information. For some units, multiple types of information were available to assess the unit's performance. The following hierarchy, in order of preference, was therefore used to assess the performance limits for any given unit.

performance limits based on actual performance test data;

outlet concentration design values ( as directly reported); and

performance limits based on percent emission reduction design values.

Performance limits based on actual test data was given preference because the test data provide credible evidence of actual performance. Outlet concentration design values were given second priority because this design value is in the same concentration units as the desired performance limits. Nonetheless, based on a comparison of the performance limits when multiple types of emissions information were available, we believe that the each of the reported design values provide a reasonable estimate of actual system performance.

Statistical Approach for Estimating Long Term Performance from Test Data The MACT floor performance limit must include a consideration for the unavoidable variability inherent in the process operations and control device performance. The MACT floor must reflect a level of performance that the source upon which the floor is based meets under the most adverse circumstance which can reasonably be expected. Therefore, we must account for unavoidable variability. However, the " achievability" test is not achievability by anyone, but achievability by the MACT floor unit.

Although an emissions source test gives a good indication of the level of control achieved by a unit during the time of the emissions test, we do not believe a single emissions source test, or even a handful of tests, can be used as an estimate of the long term emission limitation achieved for that source due to normal variations in process and control device performance and other factors, such as the inherent imprecision of sampling and analysis, which can not be controlled. Therefore, where emissions source test data were available, we used a statistical method to estimate the emission limitation that a unit could achieve consistently over time.

For each furnace where emissions source test data were available, the emission limitation achieved for that furnace was estimated at the 99th percentile outlet PM concentration using a one sided z statistic test ( i. e., the emission limitation which the furnace is estimated to be able to achieve 99 percent of the time). We evaluated several options to estimate the standard deviation that is needed to perform the z statistic test. Ultimately, we estimated an average relative standard deviation ( RSD) value of 0.4 based on a pooling of all of the available emissions source test data for all metal HAP emissions controlled by baghouses. 5 Detailed Assessment of the MACT Floor Performance Limits The available emissions data are provided in the background information document ( BID) for the proposed rule ( U. S. EPA, 2002). These data were used to analyze the relative standard deviation associated with each individual source test. These data, in combination with other emissions information received in response to the detailed industry survey were used to estimate the performance of the control systems for a given emission source.

Use of PM as a Surrogate for Metal HAP Emissions There are very limited data available to directly characterize the metal HAP emissions from foundries. These data are inadequate to directly develop emission limits for specific metal HAP. We do have, however, a reasonable number of PM emissions source test data for each of the metal HAP emission sources. For the metal HAP emission sources, we believe that PM is a reasonable surrogate for metal HAP because, at the temperatures at which the metal HAP emission control devices operate, the metal HAP are particulate in nature. Therefore, we believe that effective control of PM emissions also provides effective and roughly equivalent control of metal HAP emissions.

We conducted source tests on two cupolas ( one equipped with a baghouse and another equipped with a venturi scrubber) and measured the PM and the metal HAP emissions at the inlet and at the outlet of each control device ( U. S. EPA, 1999a and 1999b). The overall metal HAP removal efficiency measured for these control devices was essentially equivalent to the PM removal efficiency of the device tested. The wet scrubber achieved an overall metal HAP removal efficiency of 94.2 percent while averaging a 95.7 percent PM removal efficiency. The baghouse achieved an overall metal HAP removal efficiency of 99.84 percent while averaging a 99.88 percent PM removal efficiency. Additionally, both of the primary metal HAP constituents in these cupola exhaust streams ( manganese and lead) each exhibited constituent specific emission reductions that were essentially equivalent to the PM removal efficiency of the control device. These data support our hypothesis that PM is a reasonable surrogate for metal HAP emissions and that effective control of PM emissions also provides effective control of metal HAP emissions.

Although we have comparative PM to metal HAP emission reduction data only for cupola emission control system, we have no reason to believe that there is any different relationship between metal HAP amd PM emissions from any other emission point in the foundry. Thus, our data also suggests that PM is a reasonable surrogate for metal HAP emissions for all of the metal HAP emission sources. First, all of the metal HAP emission sources ( cupola, EAF, EIF and pouring operations) are sources of metal fume emissions with similar composition based on a comparison of outlet PM and metal HAP data for these various sources. Second, the percent of metal HAP emissions that is not particulate in nature ( and therefore may not be well correlated to PM emissions) is expected to be the highest in control systems with higher operating temperatures. As cupola control systems generally operate at much higher temperatures than control systems used for EAFs, EIFs, and pouring stations/ areas, the cupola emissions data would 6 be the most likely to exhibit poor metal HAP control for volatile metals ( such as lead) while achieving substantial PM emission control. Since the emissions data suggest that the cupola control systems effectively control these metal HAP emissions ( commensurate with the PM control efficiency suggesting the metal HAP is associated with the PM), it is reasonable to conclude that the metal HAP emissions within the control systems used for all of the metal HAP emission sources are also particulate in nature and that effective control of PM emissions by these systems also provides effective control of metal HAP emissions.

Pooled RSD Value for Metal HAP Emission Sources We evaluated several options to estimate the standard deviation that is needed to perform the z statistic test. We decided not to estimate the standard deviation for each furnace separately based on the available emissions data for just that furnace since most furnaces only have three data points to use in estimating the standard deviation, one data point for each run in a three run emissions source test. Instead, we calculated the relative standard deviation ( RSD) for each source test, which is the standard deviation of the individual source test runs divided by the average of the individual source test runs. This statistic appeared to be relatively consistent across units that had widely different average outlet PM concentrations. There was no pattern suggesting that the best performing units had less variability ( in terms of their RSD values) than other baghouse controlled units.

Table 1 presents the relative standard deviation ( RSD) values calculated for baghouse controlled units for which emission source test data were available. The RSD values were averaged for each type of metal HAP emission source and for the pooled set of all RSD values for all emission sources. An analysis of variance ( ANOVA) was performed on the data and there was no statistically significant difference in the standard deviation estimates for the different metal HAP emission sources. There are three general sources of variability during an emission source test. These are: 1) variability in the process operations, such as melt rate, that might affect the emissions rate from the process; 2) variability in control device performance; and 3) variability/ uncertainty associated with the sampling and analysis method. Since these test data are generated for the same basic type of control system ( fabric filters/ baghouse systems) using the same test methods, the latter two sources of variability are similar for the different emission sources. It appears that either these latter two sources of variability overwhelm the process variability or the process variability for these different sources are roughly equivalent. In any case, the relative standard deviation appears to be consistent for all MACT control systems regardless of the type melting furnace generating the emissions. There is limited data available for pouring stations, which makes the average RSD value for this emission source more uncertain than the RSD values for the melting furnaces. The individual RSD values for the pouring stations fall within the same range as the RSD values for the melting furnaces and the median value is similar to the average and median values for the other emission sources.

After evaluating these data, we decided not to estimate the standard deviation for a specific metal HAP emission source based on just the data available for that source because we have very limited information on some sources ( EAFs and pouring stations) and because the standard deviation estimates for the different emission sources were not statistically different. 7 Additionally, there are many common sources of variability in the emission test results for these different emission sources. We elected, therefore, to use the pooled RSD value for all metal HAP emission sources. Also, when considering the uncertainty associated with the average RSD value, we decided to round the average RSD value to one significant digit. Consequently, an average RSD value of 0.4 was used to calculate the 99th percentile performance limits ( using the zstatistic for all metal HAP emission sources.

Table 1. Summary of Relative Standard Deviations Calculated from Source Test Data for Metal HAP Emission Sources.

Unit Number Relative Standard Deviation ( RSD) Value for Unit Cupola Baghouse EIF Baghouse EAF Baghouse Pouring Baghouse 1 0.43 0.36 0.34 0.37 2 0.18 0.14 0.09 0.29 3 1.56 0.45 0.49 0.18 4 0.37 0.33 0.51 1.13 5 0.74 0.37 0.20 0.52 6 0.60 0.64 1.08 7 0.36 0.58 0.35 8 0.11 0.23 0.06 9 0.32 0.35 0.11 10 0.58 0.45 0.13 11 0.23 0.81 0.17 12 0.34 0.07 0.28 13 0.27 0.00 14 0.01 0.08 15 0.24 0.33 16 0.17 0.58 17 0.21 0.41 Average by Emission Source 0.39 0.36 0.32 0.50 Pooled Average for all Emission Sources 0.38 EIF = electric induction furnace EAF = electric arc furnace 8 By using the pooled RSD value rounded to one significant digit, the RSD value used becomes insensitive to any single test result. Additionally, by pooling the data, there are an adequate number of data points to warrant the use of the z statistic in calculating the performance limits. Without using the pooled data set, the calculated RSD values can be very sensitive to a single test value, especially for small data groups. Furthermore, the statistic used to calculate the confidence interval for these small data groups ( the t statistic) is a function of the number of values within the group. Consequently, without pooling the data, the 99th percentile performance limits ( and subsequently the MACT floor performance limits) could be very sensitive to a single performance test value and the MACT floor determinations would have to be reassessed each time new data become available. Thus, there are both statistical and practical reasons to use the pooled data set in developing the performance limits based on the 99th percentile performance.

The following equation was used to calculate the performance limit from the average PM concentration from a single emissions source test:

Performance Limit = Average PM Concentration × ( 1 + RSD pooled × z statistic).

The value of the z statistic for a one sided 99 percent confidence level is 2.326. Given the pooled RSD value of 0.4, the performance limit is simply:

Performance Limit = Average PM Concentration × 1.93.

MACT Floor for Cupolas Emissions information was available for 143 cupolas. Based on industry survey data and information regarding new control device, there are 62 cupolas ( 43 percent) controlled by baghouses, 71 ( 50 percent) controlled by venturi scrubbers, 1 ( 1 percent) controlled by an ESP, and 8 ( 6 percent) that are uncontrolled for metal HAP. We also have emissions data for PM from source tests conducted on 36 cupolas: 12 controlled by baghouses; 23 controlled by wet scrubbers; and 1 controlled by an electrostatic precipitator ( ESP).

We compared the available PM emissions data for cupolas using baghouses, wet scrubbers, and the ESP in terms of control efficiency, outlet concentration, and mass emissions per ton of metal melted. Based on all of these indicators of performance, we determined that cupolas with baghouses perform substantially better than cupolas with scrubbers or ESPs in controlling PM emissions. For example, the worst performing baghouse system had an average outlet PM concentration that was half of the value of the best performing wet scrubber. Similarly, on the basis of pounds of PM emitted per ton of metal melted, all of the baghouse controlled units performed as well or better than the best performing wet scrubber. Based on the available emissions data, baghouses are clearly the better performers of the three control technologies used to control PM and HAP metal emissions from cupolas. Consequently, units with venturi scrubbers and ESPs were not included in the detailed ranking of the best performing units because the available emissions source test data clearly demonstrated that the furnaces controlled with these devices were not among the best performing 12 percent of sources. 9 We therefore ranked the available emissions information for units controlled with baghouses. The performance limits for cupola units that only reported percent removal efficiencies for their control systems were assigned as follows:

systems reporting removal efficiencies of 99 % or greater were assigned a performance limit of 0.007 gr/ dscf;

systems reporting removal efficiencies less than 99 % were assigned a performance limit of 0.015 gr/ dscf.

These performance limits were based on both an examination of the available performance data for cupola units that also reported a design percent removal efficiency and on the calculation of performance limits using the reported design percent removal efficiency for the unit's control system and the uncontrolled emission factor for cupolas. By comparing the calculated outlet PM concentrations with the performance limits derived from actual test data, we ensured that the outlet PM concentrations performance limits calculated from the percent emission reduction design values are reasonable estimates of actual unit's performance.

Table 2 presents the ranking of the top performing cupola units. The 6th percentile unit, which characterizes the MACT floor for existing sources, is the 9th ranked cupola ( 143 × 0.06 = 9). The performance limit achieved by this unit is an outlet PM concentration of 0.006 gr/ dscf. The top ranked cupola achieved a performance limit of 0.002 gr/ dscf, which is the MACT floor for new sources.

Table 2. Ranking of Best Performing Cupola Control Systems Cupola Rank Number Performance Limit ( gr/ dscf) Comment 1 0.002 New source MACT Floor; " horizontal" baghouse 2 0.002 " horizontal" baghouse 3 0.003 4 0.004 5 0.004 6 0.004 7 0.006 8 0.006 9 0.006 Existing source MACT Floor 10 0.006 11 0.007 12 0.007 10 The two cupolas that achieved 99th percentile outlet PM concentrations of 0.002 gr/ dscf both employed a novel pulse jet baghouse with horizontally supported bags rather than the traditionally designed vertically hanging bags. According to an operator of one of these novel baghouses ( Cavender, 2002), a lighter weight fabric can be used when the bags are horizontally supported. When bags hang vertically ( as in traditional baghouses), the tops of the bags must be strong enough to hold up the weight of the entire bag ( generally 2 or 3 ft long) and the entire filter cake on that bag. A light weight bag would not be able to support the weight, and would tear. By having the bags supported horizontally, they are able to reduce the weight the bag material supports to only the small amount under the horizontal support ( typical bags are 4 to 6 inches in diameter). The light weight bag is easier to clean and is more permeable, which allows for a more even distribution of the air flow. Heavier weight bags tend to get more material caught in the bag material, and as a result need to be cleaned more frequently and more vigorously. The contact indicated that, " since 80% of emissions are associated with cleaning," by lowering the cleaning frequency, the baghouse emissions are lowered. The light weight bag is also more permeable, so that pressure drop is reduced, and air flow is more evenly distributed. This, along with the low A/ C ratio for these baghouses, allows more of the PM material to be collected on the bag surface, rather than becoming impregnated into the fabric, making it easier to clean the bags.

MACT Floor for Electric Induction Furnaces ( EIFs) and Scrap Preheaters ( SPHs)

There are 1,394 EIFs at iron and steel foundries that provided survey responses to the comprehensive survey of iron and steel foundries. There are also 177 SPHs at iron and steel foundries, and all these SPHs are used specifically with EIF melting operations. Baghouses and cartridge filters ( or fabric filters) are used for controlling melting operations for 388 EIFs ( 28 percent); wet scrubbers are used for 21 EIFs ( 1.5 percent); and cyclones are used for 2 EIFs ( 0.1 percent). Of the 177 SPHs used at iron and steel foundries, 64 are controlled by baghouses, 11 are controlled by cyclones, and 2 are controlled by wet scrubbers. Of the 64 SPHs that are controlled by baghouses, 59 are employed in conjunction with EIFs that are also equipped with baghouses. Of those 59 SPHs, 43 are controlled by the same baghouses as their associated EIF. Because SPHs are used in conjunction with EIFs and because PM emissions from SPHs are typically controlled with the same control device used to control the PM emissions from their associated EIF, we elected to establish a single MACT limit for both EIFs and SPHs.

We have credible emissions source test data for 57 EIFs ( and 15 SPHs) controlled by 19 fabric filters ( 17 baghouses and 2 cartridge filter), 2 EIFs controlled by venturi scrubbers, 2 EIFs controlled by cyclones, and 7 uncontrolled EIFs. We ranked these data in terms of outlet PM concentration achieved. Again, the performance of units controlled by a baghouse was significantly better than the performance of units that controlled by other control systems or units that had no emissions control. Given the predominant use of baghouses and the relative performance of the baghouse controlled units compared to other SPH/ EIF units, we only needed to consider units controlled with fabric filters to identifying the top performing units. 11 We calculated the performance limit for each unit using the available performance data and reported control device design values. The performance limits for EIF and SPH/ EIF units that only reported percent removal efficiencies for their control systems were assigned as follows:

systems reporting removal efficiencies greater than 99.95 % were assigned a performance limit of 0.002 gr/ dscf;

systems reporting removal efficiency between 99.5 % and 99.95 % ( inclusive) were assigned a performance limit of 0.005 gr/ dscf;

systems reporting removal efficiencies less than 99.5 % were assigned a performance limit of 0.015 gr/ dscf.

These performance limits were based on both an examination of the available performance data for EIF units that also reported a design percent removal efficiency and on the calculation of performance limits using the reported design percent removal efficiency for the unit's control system and the uncontrolled emission factor for EIFs. By comparing the calculated outlet PM concentrations with the performance limits derived from actual test data, we ensured that the outlet PM concentrations performance limits calculated from the percent emission reduction design values are reasonable estimates of actual unit's performance.

Table 3 presents the ranking of the top performing EIFs. Based on 1,394 EIF and SPH/ EIF emission sources, the 6th percentile would be represented by the 84th best performing unit ( 1,394 × 0.06 = 84). Based on our ranking of the performance limits achieved by the existing EIFs and SPH/ EIFs, we determined that the MACT floor for metal HAP control at existing sources is a PM emission concentration of 0.005 gr/ dscf. The new source MACT floor is represented by the top ranked EIF or SPH/ EIF unit, which is a performance limit of 0.001 gr/ dscf. Again, the control system operated by the best performing source is technologically different than the traditionally operated baghouse control system. In this case, a series of traditional fabric filter control technologies ( a baghouse and a cartridge filter) is used with a high efficiency particulate arresting ( HEPA) filter for the top performing EIF emission source.

[ Note: if SPHs are treated as separate sources, the MACT floor for both new and existing sources would be the same as the combined source. Also, if we considered that there are 1,574 SPH/ EIF sources ( 1,394+ 177), the existing source MACT floor, which would be the 94th topranked source, would still be 0.005 gr/ dscf].

MACT Floor for Electric Arc Furnaces ( EAFs)

Based on the information collected through our comprehensive survey of iron and steel foundries, there are 83 iron and steel foundries ( out of 595 respondents) that reported using a total of 163 melting EAFs. Of these 163 EAFs, baghouses are used to control melting emissions for 160 EAFs ( 98 percent), with only 3 EAFs uncontrolled for melting. 12 Table 3. Ranking of Best Performing EIF and SPH/ EIF Control Systems EIF or SPH/ EIF Rank Number Performance Limit ( gr/ dscf) Comment 1 thru 8 0.001 New source MACT Floor; control system of a baghouse, cartridge filter, and HEPA filter operated in series.

9 thru 27 0.001 28 thru 48 0.002 49 ane 50 0.003 51 thru 67 0.004 68 thru 147 0.005 Existing source MACT Floor Outlet PM concentration data are available for 10 baghouses that are used to control the emissions from 23 EAFs operated by iron and steel foundries. No emissions data were available for uncontrolled units. However, it is reasonable to assume that the controlled units perform better than uncontrolled units. Furthermore, as 98 percent of the units are controlled by a baghouse system, it is reasonable to expect that the 3 uncontrolled EAFs were not among the best performing units.

We calculated the performance limit for each EAF using the available performance data and reported control device design values. The performance limits for EAFs that only reported percent removal efficiencies for their control systems were assigned as follows:

systems reporting removal efficiency of 99.5 % or greater were assigned a performance limit of 0.005 gr/ dscf;

systems reporting removal efficiencies less than 99.5 % were assigned a performance limit of 0.015 gr/ dscf.

These performance limits were based on both an examination of the available performance data for EAF units that also reported a design percent removal efficiency and on the calculation of performance limits using the reported design percent removal efficiency for the unit's control system and the uncontrolled emission factor for EAFs. By comparing the calculated outlet PM concentrations with the performance limits derived from actual test data, we ensured that the outlet PM concentrations performance limits calculated from the percent emission reduction design values are reasonable estimates of actual unit's performance.

Table 4 presents the ranking of the top performing EAFs. As there is emissions information on 163 EAF sources, the 6th percentile would be represented by the 10th best performing unit ( 163 × 0.06 = 10). Based on our ranking of the emission limitation achieved by the existing EAFs, we determined that the MACT floor for metal HAP control at existing EAF sources is a PM emission concentration of 0.005 gr/ dscf. The new source MACT floor is 13 represented by the top ranked EAF, which is a performance limit of 0.002 gr/ dscf. Unlike the new source MACT floor control systems for cupola and EIF, there is no apparent technological difference in the control systems used for the highest ranked EAF and the other top ranked EAF control systems ( all are traditionally designed baghouses). It is clear, however, that new EAF units could meet this limit with either traditional baghouse control systems or with the advanced systems that are currently used for some cupolas and EIFs.

Table 4. Ranking of Best Performing EAF Control Systems EAF Rank Number Performance Limit ( gr/ dscf) Comment 1 0.002 New source MACT Floor 2 0.003 3 0.003 4 0.003 5 0.003 6 0.004 7 0.004 8 0.004 9 0.004 10 0.005 Existing source MACT Floor 11 0.005 12 0.005 MACT Floor for Pouring Stations We have information on 1,317 pouring stations from our survey of the industry. Baghouses are used to control 178 ( or 13.5 percent) of these pouring stations and wet scrubbers are used to control 35 ( or 2.7 percent) of the pouring stations. The majority of pouring stations ( 1,104 pouring stations or 83.8 percent) do not control PM ( or metal HAP) emissions.

Outlet PM concentration data are available for 8 baghouses used to control 16 pouring station emissions and 2 wet scrubbers used to control 5 pouring station emissions. Because there was some overlap in the performance of the baghouse and wet scrubber control systems when applied to pouring station emission control, and because of the limited number of controlled units, we included the performance data for both baghouses and wet scrubbers when ranking the performance of pouring stations. We calculated the performance limit for each pouring station using the available performance data and the reported control device design values. The performance limits for pouring stations that only reported percent removal efficiencies for their control systems were assigned as follows: 14

systems reporting removal efficiency of 99.8 % or greater were assigned a performance limit of 0.002 gr/ dscf;

systems reporting removal efficiency of 99.5 % or greater but less than 99.8% were assigned a performance limit of 0.005 gr/ dscf;

systems reporting removal efficiency of 99 % or greater but less than 99.5% were assigned a performance limit of 0.010 gr/ dscf;

systems reporting removal efficiencies less than 99 % were assigned a performance limit of 0.020 gr/ dscf.

These performance limits were based on both an examination of the available performance data for pouring stations that also reported a design percent removal efficiency and on the calculation of performance limits using the reported design percent removal efficiency for the unit's control system and the uncontrolled emission factor for pouring stations. By comparing the calculated outlet PM concentrations with the performance limits derived from actual test data, we ensured that the outlet PM concentrations performance limits calculated from the percent emission reduction design values are reasonable estimates of actual unit's performance.

Table 5 presents the ranking of the top performing pouring stations. The 6th percentile of 1,317 sources is the performance of the 79th best performing unit. Based on our ranking of the emission limitation achieved by these pouring stations, we determined that the MACT floor for metal HAP control at existing sources is a PM emission concentration of 0.010 gr/ dscf. The new source MACT floor is represented by the top ranked pouring station control system, which is a performance limit of 0.002 gr/ dscf.

Table 5. Ranking of Best Performing Pouring Station Control Systems Pouring Station Rank Number Performance Limit ( gr/ dscf) Comment 1 thru 18 0.002 New source MACT Floor; all of these pouring stations use baghouses. 19 and 20 0.003 Baghouses 21 and 22 0.004 Baghouses 23 thru 37 0.005 Baghouse used for 13 pouring stations; wet scrubber used for 2 pouring stations. 38 and 39 0.006 Baghouses 40 thru 43 0.007 Baghouses 40 thru 43 0.008 Baghouse used for 3 pouring stations; wet scrubber used for 1 pouring station. 49 thru 53 0.009 Baghouses 54 thru 146 0.010 Existing source MACT Floor; baghouse used for 78 pouring stations; wet scrubber used for 15 pouring stations. 147 thru 213 0.020 15 MACT Floor for Pouring Areas We have information on 435 pouring areas from the foundry industry survey. Baghouses are used to control 20 ( or 4.6 percent) of these pouring areas and wet scrubbers are used to control 2 ( or 0.5 percent) of the pouring areas. A total of 413 ( or 95 percent) of the 435 pouring areas do not control pouring emissions.

Outlet PM concentration data are available for only one pouring area. Due to the lack of data for pouring areas, we used the same algorithm developed for pouring stations to estimate the performance limits for pouring areas that only reported percent removal efficiencies for their control systems. We believe that this is reasonable because of the similarities in the emissions source and the control systems, when used, for pouring stations and pouring areas. Specifically,

systems reporting removal efficiency of 99.8 % or greater were assigned a performance limit of 0.002 gr/ dscf;

systems reporting removal efficiency of 99.5 % or greater but less than 99.8% were assigned a performance limit of 0.005 gr/ dscf;

systems reporting removal efficiency of 99 % or greater but less than 99.5% were assigned a performance limit of 0.010 gr/ dscf;

systems reporting removal efficiencies less than 99 % were assigned a performance limit of 0.020 gr/ dscf.

We calculated the performance limit for each pouring area with a control system. As with pouring stations, data for both baghouse and wet scrubber controlled pouring areas were included in the ranking. Table 6 presents the ranking of the top performing pouring areas. The 6th percentile of 413 sources is the performance of the 25th best performing unit. As only 22 pouring areas have control systems, the pouring area that reflects the MACT floor does not control emissions. Therefore, the MACT floor for pouring areas at existing sources is no reduction in metal HAP ( or PM) emissions. The new source MACT floor is represented by the top ranked pouring area control system, which is a performance limit of 0.002 gr/ dscf.

Table 6. Ranking of Best Performing Pouring Area Control Systems Pouring Area Rank Number Performance Limit ( gr/ dscf) Comment 1 and 2 0.002 New source MACT Floor; both of these pouring areas use baghouses. 3 0.005 Wet scrubber 4 0.007 Baghouse 5 thru 13 0.010 Baghouses 14 thru 22 0.020 Baghouse used for 8 pouring areas; wet scrubber used for 1 pouring area. 23 thru 413 No emission reduction Existing source MACT Floor; No controls used for these pouring areas. 16 Determination of Alternative MACT Floor Performance Limits Although we believe that PM is a good surrogate for metal HAP emission sources at iron and steel foundries, there are certain circumstances in which high PM emissions may not necessarily translate into high metal HAP emissions. For example, a foundry may use dry scrubbing techniques to control sulfur dioxide ( SO 2) emissions that can result in an increase in PM emissions without a corresponding increase in metal HAP emissions. The PM emission limits for the iron and steel foundries may have the unintended consequence of discouraging dry scrubbing techniques for reducing SO 2 emissions, which may be particularly important for cupola melting furnaces. As we would like to encourage these emission reduction measures, we sought to develop a total metal HAP emission alternative to the PM emission limits.

As stated previously, we have insufficient direct metal HAP emissions data to identify and characterize the top performing 12 percent of sources with respect to metal HAP emissions. Therefore, we cannot directly establish MACT floor performance limits for specific metal HAP or for total metal HAP. However, we do have some information on the metal HAP emissions from various metal HAP sources at iron and steel foundries. Although some of these data are for units that do not meet the MACT floor PM emission limits, the metal HAP to PM emission ratio for units controlled with baghouses that meet the MACT floor PM emission limits are not statistically different than the metal HAP to PM emission ratio for units controlled with wet scrubbers that do not meet the MACT floor PM emission limits. Additionally, for two units for which metal HAP emission reduction data are available ( one unit controlled with a baghouse and one controlled with a wet scrubber), the metal HAP emission reduction efficiency was equivalent to the PM emission reduction efficiency. As such, the relative fraction of metal HAP emitted as a percent of PM emissions does not appear to be a function of the emission control system. By normalizing the HAP emission data by the PM emissions, a larger pool of data is available to assess the expected metal HAP emissions performance and unavoidable variability of units that meet the MACT floor PM emissions limit. That is, by normalizing the HAP emission data by the PM emissions and aggregating these data for the various emission sources at iron and steel foundries, we can develop a reasonable estimate of the magnitude and variability of the HAP content of the PM emitted from these sources. We can then develop a total metal HAP emission limit that is equivalent to the PM MACT floor emission limit by applying this information to the specific system that established the PM MACT floor emissions limit.

The basis of this alternative emission limit is still the PM MACT floor determination as described in the previous section. Therefore, we consider this total metal HAP emission limit to be an alternative that demonstrates compliance with the level of control reflected by the PM emission limit, but that translates the PM limit into a total metal HAP format to allow for demonstration of compliance by sources that have artificially high PM emissions. This metal HAP limit is not a separate and distinct MACT floor requirement.

The available data regarding the metal HAP emissions as a percent of PM are summarized in Table 7. Separate statistical distributions were generated for lead and manganese content, the two HAP that were generally present at the highest concentrations, and a third distribution was 17 generated for the sum of all other metal HAP. [ Note: the " other" metal HAP category generally included data for cadmium, chromium, nickel and mercury. The " other" metal HAP category may underestimate the total concentration of other metal HAP because several of the tests appeared to measure only select metal HAP and did not attempt to measure or report all the metal HAP that would be measured using EPA Method 29.] These three components of the total metal HAP concentration were assumed to be independent distributions, each normally distributed around its average. The minimum concentration for each component was used as the lower limit of the distribution for that component, ensuring no negative concentrations were projected. Five thousand independent random values were generated for each HAP component ( given the minimum concentration limits), and the total metal HAP content was calculated as the sum of the lead, manganese and other metal HAP for a given randomization. This procedure generated 5,000 random estimates of the total metal HAP content as a percent of the PM emissions.

Table 7. Metal HAP Emissions Data as a Percent of PM Emissions Test/ Facility Docket Item Furnace Type % Pb % Mn % other metal HAP American Brass and Iron II I 27 Cupola  BH 1.99% 1.73% 0.12% Pacific Steel II I 20 EAF 8.64% 0.69% Charlotte Pipe Cupola BH 0.26% 1.08% 0.07% U. S. Pipe  NJ II I 49 Cupola BH 2.04% 0.77% U. S. Pipe  NJ II I 24 Cupola BH 2.35% Euvrard& Jackson II I 30 Cupola 0.12% 6.20% 0.06% Northern Steel II D 114 EAF 0.22% 0.07% Atchison Casting II D 100 Cupola Gray Iron 0.36% 0.85% Atchison Casting II D 100 Cupola Nodular 0.19% 0.49% Great Lakes II D 50 Cupola 0.21% 1.76% 0.01% GM SMCO II A 32 Cupola WS 1.10% 7.28% 0.14% Waupaca Tell City II A 30 Cupola BH 1.03% 0.59% 1.88% Griffin Pipe  NJ II D 60 Cupola 3.98% 0.22% Briggs & Stratton II D 80 Cupola 1991 1.28% 0.03% Briggs & Stratton II D 80 Cupola 1994 0.06% 2.08% 0.05% Griffin Wheel AL 11 EAF 0.11% 2.68% 1.21% CMI MI 13 Cupola WS 0.29% 2.18% Auburn IN 12 Cupola WS 1.62% 3.33% 0.98% Auburn IN 12 Preheater cyclone 0.70% 1.35% 0.71% Auburn IN 12 EIF 0.25% 0.74% Blanchester OH 11 Cupola WS 2.20% CERP Mexico II I 63 Pouring 0.42% 2.01% 2.08% Average 1.01% 2.70% 0.58% Std Deviation 1.08% 2.49% 0.64% Minimum 0.060% 0.225% 0.006% 18 For each of the emissions source with an existing source PM emissions limit ( i. e., for cupolas, EAFs, EIFs and scrap preheaters, and pouring stations), the average PM emissions concentration for the source that was identified as the 6th percentile unit ( i. e., the source that set the MACT floor performance limit) was used as the average PM emissions concentration. The average RSD value of 0.4 was used to calculate the relative standard deviation associated with the average PM emissions concentration for each source. Five thousand independent random PM concentration values were generated for each PM emissions source. The 5,000 PM emissions concentrations for each emissions source were randomly paired with the 5,000 estimates of total metal HAP content ( as a percent of the PM emissions) to project the distribution of metal HAP emissions concentrations for each emissions source. The 99th percentile total metal HAP concentration was then selected from the projected distributions. Using this approach, we account for the co variability in the metal HAP concentrations and in the PM emissions. We believe that this approach provides an emissions limit that is equivalent to the MACT floor PM emissions limit because the metal HAP emission limits were based on the average performance of the 6th percentile emissions source ( as a measure of the average performance of the top 12 percent of sources). The 99th percentile metal HAP concentrations determined from these distributions are equivalent to 7.5 percent of the 99th percentile PM emissions limit ( i. e., the MACT floor PM emissions limit) for each of the emission sources. As the " other" metal HAP content may be slightly biased low and because of the relative accuracy of the assessment ( generally one significant figure), it is appropriate to round the metal HAP to PM ratio to one significant digit or 8 percent. Therefore, a total metal HAP emissions limit that is equivalent to the PM MACT floor emissions limit can be calculated as 8 percent of the PM emissions limit ( i. e., 0.08 times the PM emissions limit). As the identification of the unit that represents the MACT floor is based on the PM emissions performance, we do not believe that the metal HAP emission limits, as derived here, represent a separate MACT floor that must be met at all sources, but rather an alternative emissions limit that is expected to be equivalent to the MACT floor PM emissions limit that is offered to provide regulatory flexibility.

References Cavender K., 2002. Personal communication with Tom McManamy, as recorded in " Grede baghouse information" e mail from K. Cavender, EPA/ OAQPS/ ESD/ Metals Group to A. Vervaert, EPA/ OAQPS/ ESD/ Metals Group and J. Coburn, RTI. April 25, 2002.

U. S. Environmental Protection Agency, 1998. Compilation of Information from Questionnaire Forms Submitted by Iron and Steel Foundries to the U. S. EPA Office of Air Quality Planning and Standards. Office of Air Quality Planning and Standards, Research Triangle Park, NC.

U. S. Environmental Protection Agency, 1999a. Iron and Steel Foundries Manual Emissions Testing of Cupola Baghouse at Waupaca Foundry in Tell City, Indiana. Office of Air Quality Planning and Standards, Research Triangle Park, NC. EPA 454/ R 99 017A and EPA 454/ R 99 017B. June. 19 U. S. Environmental Protection Agency, 1999b. Iron and Steel Foundries Manual Emissions Testing of Cupola Wet Scrubber at General Motors Corp., Saginaw, Michigan. Office of Air Quality Planning and Standards, Research Triangle Park, NC. EPA 454/ R 99 025A and EPA 454/ R 99 025B. July.

U. S. Environmental Protection Agency, 2002. National Emission Standards for Hazardous Air Pollutants ( NESHAP) for Iron and Steel Foundries  Background Information for Proposed Standards. Air Quality Planning and Standards, Research Triangle Park, NC. EPA 453/ R 02 013. December.