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: FW : Modeling of Background SO Modeling of Background SO Modeling of Background SO 2 Sources for the Sources for the Sources for the McElmo Creek Gas Plant Flare Scott Bohning Scott Bohning to: thormel 03/24/2011 10:08 AM Bcc: Andrew Chew Archive: This message is being viewed in an archive .

Tom -
Thanks, that's good news. My preference would be for a stand-alone document, and for a report, but I guess a letter would be OK and would presumably cover much the same material , including e.g. model settings, list of sources and their emissions and locations , summary of terrain & meteorology, summary of high concentrations and their locations. And yes, I think it would be best if we got the digital files of model inputs and outputs.
Thanks for your quick work on this!

- Scott B.

-- =+=+=+=+=+=+=+=+=+=+=+=+=+=+= "Scott Bohning" <bohning.scott@epa.gov> U.S. EPA Region 9, AIR-7 415/947-4127 fax-3579

"Tom Hormel" 03/23/2011 05:14:18 PM Scott,

From: "Tom Hormel" <thormel@mcvehil-monnett.com> To: Scott Bohning/R9/USEPA/US@EPA Cc: <pflynn@rnrc.net> Date: 03/23/2011 05:14 PM Subject: FW: Modeling of Background SO2 Sources for the McElmo Creek Gas Plant Flare

Scott,

We completed AERMOD 1-hour SO2 modeling of emission s from the McElmo Creek Gas Plant flare with available SO2 emissions and source parameter data p rovided by the Colorado Air Pollution Control Division and the Utah Department of Air Quality. T he question we have is on the format of report summarizing air modeling approach, emissions and mo deled air impacts that you would like to see. Do you want an report addendum that would be inserted as an appendix to the 2008 submittal or a stand-alone document in letter or report format? I assume that you would also want digital files of t he model input and output, including the meteorologica l data used for the modeling.

I look forward to your response.

Thomas Hormel McVehil-Monnett Associates, Inc. Vice President & Sr. Project Manager 44 Inverness Drive East, Bldg C. Englewood, CO 80112 303.790.1332 mcvehil

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Sent: Tuesday , March 15, 2011 5:42 PM To: thormel@mcvehil-monnett.com Subject: Re: Modeling of Background SO2 Sources for the McElmo Creek Gas Plant Flare

Tom -

I apologize for being hard to get a hold of these past two days... thank you for writing this summary.

It really sounds like there just are not that many SO2 sources around there! Although I doubt it will affect the outcome, I would still prefer at least a few sources to be thrown in just in case , and also to forestall any possible challenge on the inclusiveness. My suggestion would be to include the sources within 20 km, and if those are all quite small and there is a somewhat larger one within , say 30 km, the include that one as well.

- Scott B.

-- =+=+=+=+=+=+=+=+=+=+=+=+=+=+= "Scott Bohning" <bohning.scott@epa.gov> U.S. EPA Region 9, AIR-7 415/947-4127 fax-3579

From: "Tom Hormel" <thormel@mcvehil-monnett.com>

To: Scott Bohning/R9/USEPA/US@EPA

Cc: <pflynn@rnrc.net>

Date: 03/15/2011 03:59 PM Subject: Modeling of Background SO2 Sources for the McElmo Creek Gas Plant Flare

Scott,

This e-mail presents an update to acquiring and mod eling background SO 2 emissions data with the McElmo Creek Gas Plant flare for comparison to the 1-hour SO 2 standard. I contacted the following agencies to acquire background SO 2 emissions data:

1. Utah Department of Air Quality (UDAQ) 2. Colorado Air Pollution Control Division (CAPCD) 3. Southern Ute Indian Tribe Air Quality Pr ogram 4. Ute Mountain Indian Tribe

I also called the Navajo Nation air quality program phone number and left a message. The followingresponses were received from these agencies:

1. The UDAQ e-mailed background SO 2 data from a facility located south of Blanding wit h a total of 0.7 tons per year (tpy) average for the last two ye ars and apparently is the only facility within 50 k m. of the McElmo Creek Gas Plant, approximately 40 km. away.

2. The CAPCD e-mailed background SO 2 data from various facilities with total emissions of approximately 34 tpy, located approximately 15 to 5 0 km. from the McElmo Creek Gas Plant.

3. Responses received from the Tribal agenc ies indicated that publicly available information o n background SO 2 emission source data from facilities on Tribal Lan d are not available

I also did an Internet search for recent NEPA studi es performed in the Four Corners Area and found tha t the only available study was the Desert Rock Energy Project Draft EIS. SO 2 emission source data in this document are from large power plant sources only, l ocated at least 100 km. from the McElmo Creek Gas Plant. Therefore, it is not appropriate to include these data in cumulative 1-hour SO2 modeling for t he flare.

We also performed an inquiry on EPA’s AirExplorer w ebsite for monitored 1-hour SO 2 data and found that the closest monitoring site with available data is in Farmington, New Mexico, located approximately 80 km. from the gas plant. Maximum monitored 1-hour SO2 c oncentrations range from 42 to 79 μg/m 3 for 2008, 2009 and 2010. Monitored 99 percentile 1-hour SO 2 concentrations for 2008, 2009 and 2010 range from 29 to 66 μg/m 3 . The 2008 – 2010 average of the 99 percentile val ues will be used to add to modeled 1-hour SO 2 concentrations.

Given the limitations on available background SO 2 data, we propose to model the flare for 1-hour SO 2 with the background SO2 data provided by the UDAQ and th e CAPCD and add the monitored average 99 percentile 1-hour concentration to compare to the 1 -hour SO 2 standard of 196 μg/m 3 . However, we would also like you to consider whether background SO 2 emission sources from the UDAQ and CAPCD should be modeled at all in this case because of the recen t EPA guidance memo, dated March 1, 2011, which applies to modeling of 1-hour NO 2 and SO 2 . On Page 16 of this memo, EPA suggests “that the emphasis on determining which nearby sources to include in t he modeling analysis should focus on the area withi n about 10 kilometers of the project location in most cases.” The basis of this statement is that model ed 1-hour NO 2 and SO 2 impacts decrease significantly more with distance than when the longer-term averaging periods are modeled. Thus, we think it is appropriate to not model the state agency background data because the closest emission source is located at least 15 kilometers from the McElmo Creek Gas Plant.

Please review this e-mail to confirm our proposed a pproach for cumulative 1-hour SO2 modeling of the McElmo Creek Gas Plant flare.

Thanks,

Thomas Hormel McVehil-Monnett Associates, Inc. Vice President & Sr. Project Manager 44 Inverness Drive East, Bldg C. Englewood, CO 80112303.790.1332

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