ASARCO GRUPOMEXCO January 25, 2013 Certified Mail No.: 7011 1570 0000 5861 5283 Return Receipt Requested Mr. Thomas Webb U.S. EPA, Region IX Planning Office, Air Division 75 Hawthorne Street (AIR-2) San Francisco, CA 94105 RE: Information Request for Pending BART Determination Dear Mr. Webb: On January 10, 2013, ASARCO LLC (“Asarco”) received

a request for information from the United States Environmental Protection Agency, Region IX (“EPA”) regarding the design, operation and past performance testing of the Hayden Smelter. EPA stated that the requested information wasneeded
to ensurethat its BART determinations

for the Hayden Smelter for 802 and PM 10 are supported
by sound technical analyses. EPA’s request (in italics) and Asarco’s response

tothe requested items (in regular font) is asfollows: Information Needed
to Make

aBART Determination
for SO,: 1. The average daily measurement
for the SO 2 continuous emission monitoring system (CEMS) for the sulfuric acid plant atthe Facility since January

1, 2005 in parts per million (ppm) and the total tons of SO 2 per day recorded by the SO2 CEMS for the sulfuric acid plant since January

1, 2005. Please provide this information

in an electronic format that maybe edited by a spreadsheet programsuch asExcel or comparable software. Please also provide all SO 2 stack test data and relative accuracy testaudits (RATAs) performed for the sulfuric acid plant for the period from January 2005 through December2012. Information responsive

to Item #1 is included onDVD #1, in the BART Determination—SO2 Item #1 folder (GEMs data and 2012 RATAs) and BART Determination—PMIO Item #2 folder (2012 SO 2 stack test data). RATAs for years2005 through 2011 areincluded onDVD #3 and the SO 2 stack testing data for years2005 through 2011 is included onDVD #2. Documentation

of the EPA reference methodology utilized

is included only once (year 2005) and is not replicated for each successive year. 2. The daily production
of sulfuric acid by the sulfuric acid plant since January 2005 in tons. Describe the sourceof the data. Information responsive

toItem #2 is included onDVD #1, in the BART Determination—SO2 Item #2 folder. The data source

is Asarco’s internal Daily Production Report. Asarco considers these data tobe Business Confidential. 100 Hayden Avenue

+P.O.Box

8+ Hayden Arizona 85135 Telephone: 520.356.7811 F’Mr. Thomas Webb, U.S. EPA January25, 2013 Page

2 of 5 3. The daily production
of copper by the coppersmelter since Januaiy 2005 in tons. Describe the sourceof the data. Information responsive

toItem #3 is included onDVD #1, in the BART Determination—SO2 Item #3 folder. The data source
is Asarco’s internal Daily Production Report. Asarco considers these data tobe Business Confidential. 4. The quantity of concentrated
ore processed
by the smelter each calendar month since Januaiy 2005 in tons, along with the average daily percentage

of sulfur of the concentrate. Describe the sourceof the data. Information responsive

toItem #4 is included onDVD #1, in the BART Determination—SO2 Item #4 folder. The data source
is Asarco’s internal Daily Production Report and Feed % Sulfur spreadsheets. Copper concentrates comprise approximately 85% of the material smelted. Incoming concentrates
are sampled and assayed for commercial/settlement purposes. Concentrates
areblended with silica flux (approximately 10%) and byproducts (approximately 5%) in 6500-ton “mixes” that arethe feed material
tothe INCO smelting furnace. The daily sulfur assaysincluded areof the furnace feed and are grab samples for metallurgical spot checks only. Asarco considers these data to be Business Confidential. 5. Monthly material balances
of sulfur (as described

in Specific Provision
Ill. C. I and Attachment

D of Title V Operating Permit 1000042) performed since Januaiy 2005, along with any support documents for each monthly balance. Information responsive

toItem #5 is included onDVD #1, in the BART Determination—SO2 Item #5 folder. Monthly summary pagesareincluded along with monthly sulfur balance worksheets. Asarco considers these data tobe Business Confidential. 6. Copies of all actual SO2 emissions calculations performed since Januaiy

1, 2005 for any copper smelting equipment that wassubmitted

to any regulatoty agency.Include with your response

adetailed description
of all equations relied upon, including the identification

of all data inputs into the equation,

a description
of all emissions factors (EFs) rolled uponand their source,and all other methods
ordata relied uponto perform the calculations; Information responsive

to Item #6 is included onDVD #1, in the BART Determination—SO2 Item #6 folder. The data source
is Asarco’s Air Emission Inventory worksheets. SO 2 emissions from the INCO and converter furnaces primary gasstreams aremeasured
by the Acid Plant tail gasCEM (S2). SO 2 emissions from the INCO furnace ventilation gasstreams aremeasured
by the ventilation gasCEM (SV). SO 2 emissions from the converter secondary gasstreams are measured
by the secondary hood CEM (SH). Flash furnace and converter fugitive SO 2 emissions are quantified using emission factors derived from
a1994/95 fugitive emissions study multiplied
by operating hours. Anode furnace SO 2 emissions are quantified using the fugitive study factors. Anode burner emissions are quantified using AP42 estimations.Mr. Thomas Webb, U.S. EPA January 25, 2013 Page 3of5 7.
A summaryand supporting documentation showing which units atthe Facility comprise the BART-eligible sourceunder the Regional Haze Rule (40 CFR part 51, subpart P) and the BART Guidelines (40 CFR part 51, appendix
Y). Include anyrecords that indicate which units atthe Facility were“in existence”
on August

7, 1977 and which units were“in operation” before August

7, 1962 asdefined under the Regional Haze Rule and the BART Guidelines. Information responsive

to Item #7 is included onDVD #1, in the BART Determination—SO2 Item #7 folder. 8. Provide the following

in formation about the sulfuric acid plant: a.the volume (liters) of catalyst
in each catalyst bed; b. The diameter
of the converter; c.the type of catalyst (including trade-name)

in each catalyst bed; d. the maximum volumetric capacity (liters) of catalyst; a.the amount and type of catalyst replaced during each turn around since 2005; and f.
if ASARCO

is using cesium promoted catalyst, provide the date the facility began using cesium catalyst Information responsive

toItem #8 is included onDVD #1, in the BART Determination—SO2 Item #8 folder. 9. Provide all vendor quotes for cesium promoted catalyst installation that the facility has received. Include anyemission estimates provided by the vendors. Information responsive

to Item #9 is included onDVD #1, in the BART Determination—SO2 Item #9 folder. 10. Provide the following information about process gas capture and treatment: a.Indicate the maximum capacity of the acid plant to accept processoff gases, including both airflow and inlet SO 2 concentration; b. Provide

adetailed description
of what happens
to captured excess gasflow that would othe,wise be vented tothe acid plant when that total gasflow exceeds the capacity of the acid plant; c.Provide

adetailed analysis of the capture efficiency
of gasesemitted from all coppersmelter process equipment; ci. Provide

aschematic diagram showing which equipment

atthe Facility are captured and controlled
orcontrollable
by the acid plant; e.Provide the following

in formation about SO 2 emissions from the Pierce-Smith Converters Secondary System: i. Any and all data, in native format, onmeasurements

orcalculations

of SO 2 concentration

in ppmof gas exiting the Secondary System onan hourly basis (or as frequent asmeasurements

orcalculations are/have been taken/performed) since January

1, 2005;Mr. Thomas Webb, U.S. EPA January 25, 2013 Page
4 of 5

ii. The total daily emissions
of SO 2 in tons from the Secondaiy System since January

1, 2005; iii. The total daily amount of lime in tons injected into the Secondaiy System; iv. An estimation,
ona daily basis, of the control efficiency
of the injected lime for SO v.For in formation provided under
8. c.i and 8. c. iv, a description
of the underlying measurement and/or data used and anycalculations performed. f. For the emergency bypass ventthat is partof the acid plant line, please respond tothe following requests: i. Describe the location of the bypass
in regard to any particulate matter (PM) controls (i.e. is it before orafter each PM control); IL Describe what happens
to process off-gases vented through the bypass (L e.are they emitted directly
tothe atmosphere

or controlled); iii. Describe how the gasflow exiting the bypass
is measured; iv. In achart format, since January

1, 2005, specify the total amount of gas vented through the bypass ona daily basis. Describe the sourceof the data. g.Provide

adetailed description
of SOrladen gasflow emitted from all copper smelter process equipment

atthe Facility (e.g. maximum and typical flow ratesin actual cubic feet perminute (acfm), temperature, and SO2 concentration

in ppm), and whether

it is currently vented
tothe acid plant, to other controls
in place, or to the atmosphere uncontrolled. Information responsive

to Item #10 is included onDVD #1, in the BART Determination—SO2 Item #10 folder. In formation Needed
toMake

aBART Determination
for PM: 1.
A description
of existing PM control for all coppersmelter process equipment

atthe Facility. Information responsive

toItem #1 is included onDVD #1, in the BART Determination—PM10 Item #1 folder. 2. The averagePM and PM 10 emissions from any coppersmelter process equipment

atthe Facility since January 2005 calculated

in tons percalendar month and the assumptions and emission factors relied uponto perform the calculations. Please provide all PM and PM 10 stack tests performed
on anyof this equipment. Information responsive

toItem #2 (including PM stack testdata for year 2012)
is included on DVD #1, in the BART Determination—PMIOItem
#2 folder. PM stack test data for years 2005 through 2011 areincluded onDVD #2.Mr. Thomas Webb, U.S. EPA January25, 2013 Page

5 of 5 3.
A description
of opacity monitors and other equipment and practices used to directly or indirectly measurePM orPM 10 emissions from this equipment. Information responsive

toItem #3 is included onDVD #1, in the BART Determination—PM1O Item #3 folder. 4.
A summary
of all Method

9 opacity measurements taken at any part of smelter since January 2005, including

a description
of the location of the Method

9 reading, the results of the reading, and the nameand affiliation of the individual who took the reading. Information responsive

toItem #4 is included onDVD #1, in the BART Determination—PM1O Item #4 folder. Pursuant
to40 CFR.

§ 2.203, Asarco asserts that the information provided

in response

to Questions

2—5 (DVD
1, BART Determination—S02 Item #2 through Item #5) constitute confidential business information

asdefined
in 40 CFR

§ 2.201 (e), because release of this information could harm Asarco’s competitive position
orrelease Asarco’s business proprietary information concerning

its operating costs and efficiencies. Please contact meat (520) 356-3284
or igarrity(asarco.com

if youhave any questions regarding this response. JG/rcg Enclosures —3 DVDs Sincerely, Manager Technical RenvirolAlRlHayOpslSmelterlOtherCorres/EPABARTRFI1

.10.1 3/AsarcoResponsel.25.13