From: "Palazzolo, Michael A." <Michael.Palazzolo@alcoa.com>

To: David Putney/RTP/USEPA/US@EPA

Cc: Rochelle Boyd/RTP/USEPA/US@EPA, <bahner@rti.org>, <green@rti.org>, "Charles D. Johnson" <cdjohnson@aluminum.org>

Date: 04/07/2011 08:02 AM Subject: Surrogate justification

D avid,

Please find attached a justification or rationale for using total fluoride as a surrogate for regulation of metals and POM from prebake potlines. The bottom line is that by regulating total fluoride at the MACT floor level, EPA is already limiti ng metals and POM. This justification is not applicable to POM for Soderberg potlines, but the Soderberg category already has a POM emissions standard.

Please let me know if you have any questions.

Mike

Michael Palazzolo Alcoa, Inc. 201 Is abella Street Pittsburgh, PA 15212

- 5858 Ph: 412

- 553

- 4832Attachment 1. p. 1. of 1

T otal F luoride as a S urrogate for POM and Metals from P re - bake Anode P otline s

For pre

- baked anode potlines, the P rimary Aluminum MACT regulates emissions of total fluoride (TF), requiring:

 M onthly secondary (potroom roof) emission testing for total fluoride ;

 A nnual primary control device emissio ns testing for total fluoride ;

 D aily primary control device visible emission checks ; and

 P rimary control device operation within parametric limits for air flow and ore flow.

Total fluoride consists of approximately 50% particulate fluorides (PF) and 50% gaseous fluoride (HF). These particulate

- and gas

- phase pollutants are controlled using a pot hood
capture system (typically 98% + efficiency) followed by dry alumina injection and a baghouse (dry alumina scrubber)

.

On

- going compliance with the total fl uoride limit, in conjunction with the associated control device monitoring

, ensures that the pot hood capture and dry alumina scrubber systems are operated and maintained at the MACT floor level established by EPA for the various center

work prebake categories.

Metals

- In addition to particulate fluoride ( i.e., fluoride salts), the particulate matter released
from a n aluminum smelting pot also contain s trace amounts of HAP metals . Control of these HAP metals is achieved using the exact same equipment that is used to control the particulate component of total fluoride : the pot hood capture system and dry alumina scrubber baghouse

. So, the MACT floor te chnology for HAP metals is identical to that for total fluoride and control of total fluorides can thus be considered a surrogate for the control of HAP metals.

POM

– POM emissions from an aluminum smelting pot are present as both particulate

- and gas

phas e pollutants. Control of POM emissions is achieved using the exact same equipment that is used to control fluorides: the pot hood capture system and dry alumina scrubber system. Particulate POM are collected by the baghouse and gas

- phase POM are absorbed or condensed on the injected alumina and then collected by the baghouse . A portion of the gas

- phase POM is not removed and passes through the baghouse as does some fraction of gaseous fluoride (HF). So, the MACT floor control technology for POM is ident ical to that for total fluoride and control of total fluorides (PF and GF) and can thus be considered a surrogate for the control of POM
emissions. (Control of POM emissions at the anode bake furnaces is similarly accomplished using a dry alumina scrubber system .)