1

Matagorda County emissions 

do not contribute to ozone 

formation in HGB 
2

Declining Emissions and Declining 

Growth Do Not 

Support Nonattainment

• Population Data and Degree of Urbanization: Matagorda County is a

Micropolitan Statistical Area.

• Growth Rates and Patterns: Population in Matagorda County declined by 3%

from 2000 to 2010.

• Traffic and Commuting Patterns: The VMT in Matagorda County declined by

1% from 2002-2008.

• Emissions Data:

– Emission Corrections (2008)

– Emission Corrections (Oil and Gas lb/BBL local data)

– Emission Reductions (2008 - 2010)

• Air Quality Analysis: Matagorda County emissions do not meaningfully

contribute to HGB ozone

– TCEQ Apportionment Analysis

– Area Source VOC Reduction Analysis for Counties Outside of HGB
3

Matagorda County Compared to 47 

Counties Designated BY EPA 

Nationwide

• Matagorda county ranked last with the least VMT of all 47 counties.

• Matagorda County ranked 4th to the bottom in population at 36,702.

• Only 4 counties proposed by EPA, including Matagorda County, are not in a 

Metropolitan Statistical Area (“MSA”). (Matagorda County is a Micropolitan

Statistical Area.) 

• Matagorda does not have sufficient “social or economic ties" to be included

in the 10 county Houston Metropolitan Statistical Area ("Houston Metro").

• EPA inappropriately uses the Consolidated Statistical Area to include

Matagorda County.

– CSA does not require "social or economic ties", only a minimal 15% employment

interchange with another county.

– The use of CSA is particularly arbitrary when basis for the CSA, VMT and

population, for Matagorda County, has declined from 2008 - 2010.
4

Emission Corrections (2008)

• Nonroad NOx

– 7,007 tpy in EPA's Technical Support Document (TSD)

– (2,928) tpy (TCEQ January 11, 2012 Letter to EPA, p. 2)

– 4,079 Revised total NOx

• Nonroad VOC

– 3,153 tpy in TSD

– (664) tpy (TCEQ 1/12/12 EI Discrepancy Table)

– 2,489 Revised Nonroad VOC

• Oil and Gas VOC emissions (Area Sources)

– Oil and Gas Area Sources are 14,662 tpy, 84% of total VOCS in

Matagorda's 2008 Emissions Inventory (EI)

– VOC emissions from condensate tanks, 13,302 tpy, are overestimated

(see next three slides)
5

Emission Corrections 

Oil and Gas Condensate Tank Emissions

Source VOC 

Lbs/BBL

Basis of Estimate 2008 TPY

VOCs

2010 TPY

VOCs

Current TCEQ/TERC Report 33.3 lbs/BBL Statewide default 

emission factor 

from TCEQ study

13,302.03 7,570

Local 

Option 1

TCEQ/TERC –

weighted average 

for production rates 

(See Table 3-3)

16.75 

lbs/BBL

TCEQ statewide 

factor weighted for 

production 

(BBL/day) at well

6,716 3,808 

Local 

Option 2

TCEQ/TERC Study

minus Denton 

County sites with 

200 PSI

12.11 lbs/BBL TCEQ statewide 

factor minus Denton 

County sites with 

200 PSI

4,837 2,753

Local 

Option 3

TCEQ/TERC –

modified for MC-like 

wells (psig less than 

50) (See Table 3-3 

and 3-1)

6.972 

lbs/BBL

TCEQ statewide 

factor modified for 

discharge pressure

2,796 1,585

Local

Option 4

Matagorda County 2.5 lbs/BBL MC Condensate 

sample taken from 

separator before 

discharge to tank 

1,002 568

Regardless of the Local Option chosen, actual VOC emissions are much less than the currently used 33.3 lbs/BBL. 

Therefore, total oil & gas VOC emissions are much less than stated in the EPA Technical Support Document.
6

Oil and Gas Analysis 

by PSI, lb/BBL and County

(Local Option 2)

0

20

40

60

80

100

120

140

160

180

200

TERC

(Denton

Only)

TERC (All

Sites)

TERC

(Without

Denton)

Matagorda

County

(MC)

specific

PSI Avg lb/BBL Avg

*

#

* Avg. PSI based upon 

preliminary estimates 

from operators of 35% of 

2008 condensate BBL

produced in MC.

# Based upon site 

specific sampling and 

modeling of one of the 

largest 2010 condensate 

producing leases in MC. Texas Environmental Research Consortium (TERC) Report on VOC

Emissions from Oil and Condensate Storage Tanks found at 

http://files.harc.edu/Projects/AirQuality/Projects/H051C/H051CFinalReport.pdf
7

Oil and Gas Analysis 

by PSI, lb/BBL and County

TERC

(Denton Only)

TERC 

(All Sites)

TERC 

(Without Denton)

Matagorda County

Specific

PSI Avg 200 119.1 45.7 45.4 *

VOC lb/BBL

Avg

56.58 33.3 12.11 2.5 #

* Avg. PSI based upon preliminary estimates from operators of 35% 2008 

condensate BBL produced in Matagorda County.

# Based upon site specific sampling and modeling of one of the largest 

2010 condensate producing leases in Matagorda County. 
8

Emission Reductions 

2008 - 2010

• NOx Reductions to 2010

– (180.86) tpy NOx emission reductions 2008 to 2010 from point sources

– VMT Reduction by 1%

• VOC Reductions to 2010

– TCEQ estimates 8,758 tpy VOCs from oil and gas operations

• (5,904) tpy VOC emission reductions from 2008 to 2010 from oil and gas

area sources (TCEQ Emission Inventory)

• Emissions in 2008 were a result of one-time oil & gas activity in the County.

Not expected to return to that level of activity.

– Local VOC lb/BBL data should be used (previous slides)

– VMT Reduction by 1%
9

VOC Emissions Are not Primary 

Driver of Ozone Formation in HGB

EPA has approved the current SIP strategy based 

primarily on NOx reductions with targeted HRVOC 

controls:

These [Texas SIP] revisions result from more recent information on ozone

formation in the Houston/Galveston area indicating that a combination of

controls on oxides of Nitrogen (NOx) and highly reactive volatile organic

compounds (HRVOCs) should be more effective in reducing ozone than the

measures in the previously approved plan which relied almost exclusively on

control of NOx.

EPA's proposed approval of TCEQ's HRVOC SIP rule, 70 FedReg 58119

(October 5, 2005)

* Oil & Gas VOC emissions comprise 84% of the County’s total VOCs and typically do not include 

HRVOC components therefore, they are not expected to contribute to ozone formation in HGB.
10

HGB Attainment Demonstration SIP Revision for 

the 1997 Eight-Hour Ozone Standard 

(Project No. 2009-017-SIP-NR)

Adoption Date: 03/10/2010
11

Reduction of 273 tpd VOCs (99,645 tpy VOCs) from 

several counties within 200 km of HGB, including 

Matagorda County, resulted in no change to the 

Wallisville Monitor 2018 future case.

HGB Attainment Demonstration SIP Revision for the 1997 Eight-Hour 

Ozone Standard (Project No. 2009-017-SIP-NR) Adoption Date:

03/10/2010
12

Eliminating All VOC and NOx Emissions 

From Matagorda County Will Not 

Meaningfully Contribute to Ozone 

Reduction

TCEQ Technical Analysis Support Documentation by the TCEQ 

Regarding U.S. EPA Responses to State and Tribal 2008 Ozone 

Designation Recommendations

All Matagorda County Emissions Contribute Less 

than 0.20 ppb in 2018 APCA Modeling
13

In case-by-case analysis, Matagorda County Wind Trajectory 

Data Does Not Outweigh Declining Growth, Declining 

Emissions and more Detailed Modeling Data

Declining emissions and population and VMT growth is well documented.

No meaningful contribution to HGB ozone levels: 2005 – 2010 data

– Wind data shows only 0.43% - 1.9%, at most, of the wind impacting an elevated

monitor potentially originated in Matagorda County. (TCEQ January 11, 2012 Letter,

p. 16.)

– Within this small percentage of time, the greatest impact expected from all combined

mobile, non-road, point and area sources Matagorda County emissions, as modeled

by TCEQ, is an average of .18 ppb for 2005 and 2006. (TCEQ January 11, 2012 Letter

as corrected in discussions between EPA and TCEQ.)

No meaningful contribution to ozone formation or reduction: 2018 Data

– 2018 TCEQ sensitivity analysis demonstrated that 273 tpd (99,645 tpy) VOC reduction

had no ozone reduction impact on the Wallisville monitor.

– 2018 TCEQ APCA results for all MC emissions indicates, that if all combined mobile,

non-road, point and area sources were eliminated, the greatest reduction impact

would be 0.20 ppb at the Wallisville monitor.