ATTACHMENT 1: METHODOLOGY

To derive the emissions data, we used the following methodology: We compiled 

emissions data from six of the states most involved in the industry: Colorado, Louisiana, North 

Dakota, Pennsylvania, Texas, and Wyoming. We drew the data from EPA’s two most recent—

2008 and 2011—National Emissions Inventories,1as well as annual emissions data from state 

databases between 2010 and 2012, where available.2 As discussed in the cover letter, we also 

included data from Pennsylvania’s 2011 Unconventional Natural Gas Emissions Inventory 

because the state did not include that data as part of its overall state emissions inventory.3

Next, we narrowed the national and state emissions inventories to emissions of 

representative TRI-listed chemicals, based on their prevalence in data and documents we 

reviewed in drafting the Petition. Emissions inventories that did not provide data for a specific 

chemical are noted in parentheses next to the chemical.

 2,2,4-Trimethylpentane (NEI),

 Benzene,

 Ethylbenzene (NEI),

 Ethylene (CO, ND, PA, NEI),

 Ethylene Glycol (CO, ND, NEI),

 Formaldehyde,

 Hexane,

 Methanol (NEI),

 Toluene, and 

 Xylenes. 

We then filtered for facilities within the oil and gas extraction industry by using Standard 

Industrial Classification (SIC) and North American Industry Classification System (NAICS) 

codes, where indicated.4For facilities whose NAICS or SIC codes were not indicated, 

particularly in Louisiana, we researched each facility using data available in order to determine 

whether it was an industry facility.

We then selected facilities if they emitted more than 10,000 pounds of one of these 

chemicals in at least one year.5From there, we selected facilities for inclusion in Attachment 2 if 

they emitted more than 10,000 lbs in the two most recent years for which data was available.6 In 

most cases, this meant 2010 and 2011 or 2011 and 2012 within a state’s emissions inventories. 

In a few cases, we used data from the two most recent National Emissions Inventories (2008 and 
2

2011), as facilities in certain states reported the release of TRI-listed chemicals only in that data 

source.

We made unit conversions (e.g., short tons to pounds) where necessary. Additionally, we 

calculated the annual emissions when point-level rather than facility-level data was provided; 

that is, we aggregated emissions on the facility level when an inventory did not.

 

1

EPA, 2008 National Emissions Inventory, Version 3: Facility-Level by Pollutant (2013), 

http://www.epa.gov/ttn/chief/net/2008inventory.html (accessed Nov. 2013); EPA, 2011 National 

Emissions Inventory, Version 1: Facility-Level by Pollutant (2013), 

http://www.epa.gov/ttn/chief/net/2011inventory.html (accessed Nov. 2013)

2 Colorado Dep’t of Public Health, Air Pollution Control Div., Emissions Inventory Data 2010-

2012 (on file with EIP); Louisiana Dep’t of Envtl. Quality, Emissions Inventory Data Sets 2010-

2011 (Jan. 2013), 

http://www.deq.louisiana.gov/portal/DIVISIONS/AirPermitsEngineeringandPlanning/Emissions

InventoryHomepage/EmissionsInventoryDataSets.aspx (accessed Nov. 2013); North Dakota 

Dep’t of Health, Air Quality, Emissions Inventory 2010-2012, 

http://www.ndhealth.gov/AQ/EmissionInventory.htm (accessed Nov. 2013); Pennsylvania Dep’t 

of Envtl. Prot., Emissions Inventory: Facility Level 2010-2012 (on file with EIP); Texas 

Comm’n on Envtl. Quality, Emissions Inventory Data 2010-2011 (on file with EIP). For 

additional information on the databases, see Attachment 3.

3

See Pennsylvania Dep’t of Envtl. Prot., 2011 Unconventional Natural Gas Emissions Inventory 

(on file with EIP).

4 As we stated in the Petition, EPA identified the oil and gas extraction industry by SIC Code 13 

when it last considered addition of the industry in 1996. See Addition of Facilities in Certain 

Industry Sectors; Toxic Chemical Release Reporting; Community Right-to- Know, 61 Fed. Reg. 

33,588, 33,592 (June 27, 1996). Since then, the NAICS codes have begun to supplant SIC 

codes, and the industry is also identified by at least seven NAICS codes: 211111 (Crude 

Petroleum and Natural Gas Extraction), 211112 (Natural Gas Liquid Extraction), 213111 

(Drilling Oil and Gas Wells), 213112 (Support Activities for Oil and Gas Operations), 238910 

(Site Preparation Contractors), and 541360 (Geophysical Surveying and Mapping Services). See

NAICS Ass’n, Free NAICS Look Up, http://www.naics.com/search.htm.

5

See Attachment 3.

6

See Attachment 2.