August 3, 2012 

MEMORANDUM

SUBJECT: Clarification of Cholla and Coronado Emission Rates Used 

FROM: Scott Bohning 

 Air Division, AIR-7 

 EPA Region 9 

TO: Arizona Regional Haze FIP Docket EPA-R09-OAR-2012-0021 

This memorandum documents a conference call between EPA Region 9 and AECOM, a 

consulting firm, concerning emissions data relied upon by EPA in proposing a Federal 

Implementation Plan for Best Available Retrofit Technology (BART) under the Regional Haze 

Rule for several facilities in Arizona. The call occurred at noon PDT on Thursday, July 26, 

2012. Attending from EPA were Scott Bohning and Eugene Chen. AECOM was represented by 

Robert Paine and Seemantini Deshpande. AECOM had e-mailed questions about the source of 

baseline emission rates for Cholla Power Plant and Coronado Generating Station, as used for air 

quality modeling and in certain cost calculations. EPA discussed the data sources relied upon 

and the selection of particular emission rates, and also where clarification of this issues could be 

found in Excel spreadsheets contained in the docket for the proposal. 

AECOM’s e-mail questions, and EPA’s e-mailed responses are contained in an attachment to 

this memorandum. 
RE: questions about baseline emission rates 

Scott Bohning to: Paine, Bob 08/03/2012 01:27 PM

Cc: Eugene Chen, "Deshpande, Seemantini"

Bob -

I meant to get this response to you early in the week, I apologize for not getting this done before now. In 

any case, I think this covers pretty much the same clarifications as our conference call on July 27th, so 

hopefully you got what you needed then. This response has more specifics on locations in some 

spreadsheets in the docket for our Arizona regional haze FIP proposal.

> Coronado... Modeled Baseline Emissions

> 

> For Unit 1,... We found that a higher daily NOx emission rate 

> (35,276 lb/day) occurred on 6/11/2009.

EPA response: All of these CAMD emissions data are contained in the spreadsheet "AZ Max Emission 

Dates.xlsx", available in the docket. Generally EPA avoided data that were within a few months of the 

installation of control equipment, because adjustments of plant operation are needed to accommodate the 

new equipment, and temporarily there can be anomalously high emissions for short periods. There is 

some professional judgment involved in this choice. While EPA agrees that emissions on 6/11/2009 were 

the maximum NOx emissions post-installation, this was during an anomalously high emission period. 

This can be seen from the emissions in the spreadsheet during that first month; emissions vary widely. 

EPA also avoided individual days that appeared to be "spikes" of high emissions, since they may not 

represent typical operations. The chosen day is the 5th highest post-installation, and is near the level of 

other highs seen during the post-installation period. 

> Cholla

> 

> Unit 1 Modeled Baseline Emissions ... We found that higher daily 

> NOx emissions (9,428 lb/day) occurred on 1/30/2010.

> 

> Unit 2 Modeled Baseline Emissions ... We found that higher daily 

> NOx emissions (31,454 lb/day) occurred on 6/14/2008.

> 

> Unit 3 Modeled Baseline Emissions ... We found that higher daily 

> NOx emissions (26,226 lb/day) occurred on 7/2/2009.

EPA response: CAMD data for Cholla are available in the docket; they are sorted from highest to lowest, 

with the top ten indicated in green, and the day selected for modeling shown in red. For all four units, 

EPA chose the highest day post-LNB installation that did not appear to be an anomalously high spike day. 

For unit 1, EPA rejected 1/30/2010 and 10/11/2008 as being isolated spikes, leaving 1/26/2010 as the 

highest emission day ("U113" tab of spreadsheet "AZ_BART_sources_all-Task7-8_2012-06-10.xls").

For unit 2, EPA rejected 6/13/2008 and 9/6/2008 as being isolated spikes, leaving 6/29/2009 as the 

highest emission day ("Cholla_NOx post-control sort" tab of "AZ Max Emission Dates.xlsx")

For unit 3, the LNB installation date was 5/14/2009, according to CAMD; emissions varied erratically for 

some two months after this date, and were excluded by EPA. Also excluded were 2/11/2010 and 

2/12/2010 as being part of an anomalous spike. This left 11/24/2010 as the highest, a value that occurred 

during a period of generally high emissions during November 2010.
> Unit 2 Cost Analysis ... we calculate the average annual NOx emission rate

> from Unit 2 to be 0.2905 lb/MMBtu

> 

> Unit 3 Cost Analysis ... we calculate the average annual NOx emission rate

> from Unit 3 to be 0.2551 lb/MMBtu.

> 

> Unit 4 Cost Analysis ... we calculate the average annual NOx emission rate

> from Unit 4 to be 0.262 lb/MMBtu.

EPA response: Baseline emission factors in NOx lb/MMBtu were taken directly from CAMD reports of 

annual emissions, rather than from averaging daily CAMD data. Because EPA focussed on the period 

when LNB was fully in place at Cholla, 2011 values were used. For Cholla units 2, 3, and 4, the CAMD 

annual values are 0.295, 0.254, and 0.260 lb/MMBtu NOx, respectively.

Let Eugene or me know if you need anything else.

- Scott Bohning

-- 

=+=+=+=+=+=+=+=+=+=+=+=+=+=+=

"Scott Bohning" <bohning.scott@epa.gov>

U.S. EPA Region 9, AIR-7

415/947-4127 fax-3579

From: "Paine, Bob" <bob.paine@aecom.com>

To: Eugene Chen/R9/USEPA/US@EPA, Scott Bohning/R9/USEPA/US@EPA

Cc: "Deshpande, Seemantini" <Seemantini.Deshpande@aecom.com>

Date: 07/26/2012 11:19 AM

Subject: RE: questions about baseline emission rates

Eugene and Scott, here are the questions that we want to cover in our call today.

Coronado

Modeled Baseline Emissions

For Unit 1, EPA used a baseline period from May 16, 2009 – Dec 31, 2010 since the unit was 

retrofitted with low NOx burners (LNBs) that became operational on May 16, 2009. For 

baseline modeling, EPA used maximum daily NOx emissions (33,208) from Unit 1 that 

occurred on 11/3/2010. We found that a higher daily NOx emission rate (35,276 lb/day) 

occurred on 6/11/2009. 

By the way, we agree with EPA’s baseline emissions for Coronado Unit 2, based upon the 

maximum baseline heat input of 106,706.7 MMBtu/day to occur on 9/5/2008.

Cholla

Unit 1 Modeled Baseline Emissions

For Unit 1, EPA used a baseline period from Jan 1, 2008 – Dec 31, 2010. For baseline 

modeling, EPA used maximum daily NOx emissions (8,392 lb/day) from Unit 1 that occurred on 

2/7/2008. We found that higher daily NOx emissions (9,428 lb/day) occurred on 1/30/2010. 
Unit 2 Modeled Baseline Emissions

Unit 2 was retrofitted with LNBs in early 2008. Therefore, EPA used a baseline period from 

2/29/2008 - 12/31/2010, to include the period when the LNBs were operational. For Unit 2’s 

baseline emissions for modeling, EPA used the maximum daily NOx emissions (27,636 lb/day) 

that occurred on 6/29/2009. We found that higher daily NOx emissions (31,454 lb/day) 

occurred on 6/14/2008.

Unit 3 Modeled Baseline Emissions

Unit 3 was retrofitted with LNBs in mid 2009. Therefore, EPA used a baseline period from 

5/14/2009 - 12/31/2010, to include the period when the LNBs were operational. For Unit 3’s 

baseline emissions for modeling, EPA used the maximum daily NOx emissions (23,156 lb/day) 

that occurred on 11/24/2010. We found that higher daily NOx emissions (26,226 lb/day) 

occurred on 7/2/2009.

Unit 4 Modeled Baseline Emissions

Unit 4 was retrofitted with LNBs in early 2008. Therefore, EPA used a baseline period from 

4/1/2008 - 12/31/2010, to include the period when the LNBs were operational. For Unit 4’s 

baseline emissions for modeling, EPA used the maximum daily NOx emissions (28,842 lb/day) 

that occurred on 11/28/2010, which we agree with. 

Unit 2 Cost Analysis

For the cost analysis, EPA used a baseline emission rate of 0.295 lb/MMBtu which, according 

to EPA, is based on the 2011 average emission rate of Unit 2. However, we calculate the

average annual NOx emission rate from Unit 2 to be 0.2905 lb/MMBtu. Maybe the method of 

averaging is different and we need to understand it.

Unit 3 Cost Analysis

For the cost analysis, EPA used a baseline emission rate of 0.254 lb/MMBtu which, according 

to EPA, is based on the 2011 average emission rate of Unit 3. However, we calculate the

average annual NOx emission rate from Unit 3 to be 0.2551 lb/MMBtu.

Unit 4 Cost Analysis

For the cost analysis, EPA used a baseline emission rate of 0.260 lb/MMBtu which, according 

to EPA, is based on the 2011 average emission rate of Unit 4. However, we calculate the

average annual NOx emission rate from Unit 4 to be 0.262 lb/MMBtu.

Bob