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MEMORANDUM

To: David Putney, U.S. Environmental Protection Agency (EPA), OAQPS

From : David Green and Matt Hakos, RTI International

Date: November 13, 2014

Subject : Development of Emissions Standards to Address Risks for the Primary Aluminum

Production Source Category Pursuant to Section 112( f) of the Clean Air Act

In developing the risk assessment for chronic expos ures, we used the estimated annual average

ambient air concentration of each of the hazardous air pollutants (HAP) emitted by each source for

which we have reliable emissions data in the source category. The air concentrations at each nearby census block centroid were used as a surrogate for the chronic inhalation exposure concentration for a ll the people who reside in that census block.

We then estimated the maximum individual risk (MIR) for each facility as the cancer risk associated with a continuous lifetime (24 hours per day, 7 days per week, and 52 weeks per year for a 70-year period) exposure to the maximum concentrati on at the centroid of an inhabited census block. Individual cancer risks were estimated by multiplyi ng the estimated lifetime exposure to the ambient concentration of each of the HAP (in micrograms per cubic meter) by its unit risk estimate (URE), which is an upper bound estimate of an individual’s probability of contracting cancer over a lifetime of exposure to a concentration of 1 microgram of the p ollutant per cubic meter of air. For residual risk assessments, we generally use URE values from the E PA’s Integrated Risk Information System (IRIS). For carcinogenic pollutants without EPA IRIS values , we look to other reputable sources of cancer dose-response values, often using California EPA (C alEPA) URE values, where available.

More details regarding the risk assessment methods and risk results are available in the Federal Register (FR) Notice and in the document titled Res idual Risk Assessment for the Primary Aluminum Production Source Category in Support of the 2014 S upplemental Proposal (Risk Assessment), which is available in the docket for this action (Docket ID No. EPA-HQ-OAR-2011-0797).

As explained in the supplemental proposal FR Notice and the Risk Assessment, when considering the risks associated with MACT-allowabl e emissions, we estimate that the MIR could be up to 300-in-1 million if the Columbia Falls Alumin um Company facility were to resume its primary aluminum operations with three vertical stud Soderb erg two (VSS2) potlines. This estimated risk results mainly from estimated allowable emissions o f polycyclic organic matter (POM), nickel and arsenic. Based on the model outputs, we estimate th at 59% of this MIR risk is due to POM, 22% is due to arsenic, and 16% is due to nickel. The MIRs for all other facilities in the source category were le ss than 100-in-1 million.

In order to ensure the risks associated with Soderb erg facilities are acceptable, we evaluated the potential to reduce MACT-allowable VSS2 potline emi ssions for the primary HAP driving the cancer risks (i.e., POM, arsenic and nickel) to levels tha t would reduce the cancer risks to 100-in-1 million or less (i.e., the presumptive ceiling of acceptable r isk, based on the Benzene NESHAP, 54 FR 38044, September 14, 1989).2

Regarding POM, the current NESHAP includes an emiss ions limit for POM of 5.7 pounds per ton of aluminum produced (lb/ton) for VSS2 potlines . As noted above, the one facility driving the allowable risks has been idle for 5 years and has n ot operated at capacity since 2000. Also, the VSS2 potline technology is less efficient than the newer , lower emitting prebake technologies. All indicati ons are that this facility will not reopen. However, ba sed on available data from the most recent years th at it was operating, we estimate that if this one VSS2 facility did reopen and if it installed wet roof t op scrubbers that it could achieve a POM emissions lim it of 1.9 lb/ton (0.85 Kg/Mg) of aluminum produced, which would be a significant reduction in allowable POM emissions from this facility. This

limit is 3 times lower than the current limit for P OM from VSS2 potlines. Furthermore, given that there would be variability in emissions during norm al operations, in order for this facility to comply with a limit of 1.9 lb/ton at all times, it would n eed to have average POM emissions considerably lowe r than 1.9 lb/ton. Therefore, under the authority of CAA section 112(f)(2), the EPA is proposing a POM emission limit for VSS2 potlines of 1.9 lb/ton (0.8 5 Kg/Mg) of aluminum. This would reduce the estimated cancer risks due to allowable POM by at l east a factor of 3.

As mentioned above and in the supplemental proposal FR Notice, the one remaining Soderberg plant has been idle for about 5 years and we believ e it is highly unlikely that the facility will reop en, due to its less efficient aluminum production metho d. However, if this facility does resume operations

, we estimate that the capital costs for the roof top wet scrubbers would be about $30 million and that annualized costs would be about $8 million.

Regarding emissions of nickel and arsenic, as expla ined in the Revised Draft Development of the RTR Emissions Dataset for the Primary Aluminum Production Source Category, which is available in the docket for this action, we estimate that the Columbia Falls Aluminum Company facility (again, presuming the highly unlikely scenario wherein this facility resumes primary aluminum reduction operations) would emit about 4,420 pounds of nickel per year and 672 pounds of arsenic per year, assuming operation of 3 potlines at full capacity. We estimate that wet roof scrubbers would achieve a 50 percent reduction in secondary potline emissions of these metals. See CFAC BART Analysis in the docket (Docket No. EPA-HQ-OAR-2011-0797). Therefore , with the wet scrubbers installed and operating, we estimate annual average emissions wou ld be about 2,210 pounds of nickel per year and 336 pounds of arsenic per year. The subject Columbi a Falls Aluminum Company facility is the only facility in the U.S. that utilizes the VSS2 potline technology. Therefore, to estimate emissions of ni ckel and arsenic from this facility and to account for v ariability in emissions during normal operation, we analyzed data on emissions of nickel and arsenic fr om the Alcoa-Massena East facility. We chose to

use emissions data from the Alcoa-Massena East faci lity because it is the only primary aluminum reduction facility in the U.S. (other than the Colu mbia Falls Aluminum Company facility) that utilizes Soderberg potline technology. Specifically, the Alc oa-Massena East facility utilizes horizontal stud Soderberg (HSS) potline technology. Our analysis of the nickel and arsenic emissions data from the Alcoa-Massena East facility results in our estimate of nickel and arsenic emissions of no more than 0.14 lb/ton and 0.012 lb/ton, respectively, from th e Columbia Falls Aluminum Company facility.

To ensure the primary HAP metals (i.e., arsenic and nickel), that are driving some of the allowable cancer risks (along with the POM), are li mited to acceptable levels of emissions, we are proposing facility-wide total potline emissions lim its for arsenic and nickel that reflect a 50 percen t reduction in the estimated potline emissions of tho se metals, along with a consideration of the3

variability in emissions. The EPA is proposing thes e limits pursuant to section 112(f)(2) in order to ensure risks will be acceptable from the Soderberg potline subcategory.

As mentioned above, our analysis of nickel emission s from the Columbia Falls Aluminum Company facility indicates that, after accounting f or normal variability, nickel emissions from this facility are no more than 0.14 lb/ton of aluminum p roduced. Therefore, after installation of wet roof scrubbers, we estimate nickel emissions of no more than 0.07 lb/ton of aluminum produced from this facility. Similarly, we estimate that the installat ion of wet roof scrubbers would reduce arsenic emissions from this facility from no more than 0.01 2 lb/ton of aluminum produced to 0.006 lb/ton of aluminum produced. Therefore, pursuant to section 1 12(f)(2), the EPA is proposing emissions limits of 0.07 lb/ton of aluminum produced for nickel and 0.0 06 lb/ton of aluminum produced for arsenic for the Columbia Falls Aluminum Company facility.

Given that these reductions of metals would be achi eved using the same controls used for POM, there would be no additional cost of control, and there would be risk reductions associated with reduced HAP metal emissions. Assuming the wet scrub bers would achieve a 50 percent reduction in HAP metal emissions, and assuming the facility woul d run 3 potlines, which is the most potlines it operated since the year 2000, we estimate that the roof top wet scrubbers would limit emissions of nickel and arsenic from potlines to about 2,210 pou nds per year of nickel and 336 pounds per year of arsenic, on a facility-wide basis.

Regarding post-control risks, we estimate that with a POM emission limit of 1.9 lbs/ton of aluminum produced for the VSS2 potline subcategory (that is 3 times lower than the current POM emission limit for that potline subcategory) and wi th nickel and arsenic emission limits that reflect a 50 percent reduction in potential emissions of those m etals, that the post control risks would be approximately 100-in-1 million or less, if the plan t did reopen.

Compliance with these emission standards would be d etermined by conducting annual emissions tests including tests of production based nickel and arsenic emissions, and continuous compliance would be demonstrated by facilities cond ucting various types of parametric monitoring, as described in the supplemental proposal FR Notice. T hese nickel and arsenic emission limits, would also apply to all new Soderberg potlines at any fac ility. We estimate that these nickel and arsenic emission limits, in conjunction with the proposed P OM emission limits will decrease the MIR for the Columbia Falls Aluminum Company facility to approxi mately 100-in-1 million or less.