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MEMORANDUM

DATE: December 11, 2013

SUBJECT: Emissions Data and Acute Risk Factor Used in Residual Risk Modeling: Acrylic 

and Modacrylic Fibers, Amino/Phenolic Resins, and Polycarbonate Production

FROM: Lesley Stobert, EC/R Incorporated

TO: Nick Parsons, EPA/OAQPS

The purpose of this memorandum is to provide information on the Environmental Protection 

Agency (EPA) Risk and Technology Review (RTR) data used to estimate residual risk for the 

Acrylic and Modacrylic Fibers Production (AMF), Amino/Phenolic Resins Production (APR), 

and Polycarbonate Production (PC) Maximum Achievable Control Technology (MACT) source

categories.

1.0 BACKGROUND

Section 112 of the Clean Air Act (CAA) establishes a two-stage regulatory process to address 

emissions of hazardous air pollutants (HAPs) from stationary sources. In the first stage, section 

112(d) directs the EPA to develop technology-based standards for categories of industrial 

sources. In the second stage, known as the residual risk stage, section 112(f)(2) directs the EPA

to assess the health and environmental risks that remain after sources come into compliance with 

MACT. If additional risk reductions are necessary to protect public health with an ample margin 

of safety or to prevent adverse environmental effects, the EPA must develop standards to address 

these remaining risks.

2.0 DEVELOPMENT OF THE DATA SETS USED IN RESIDUAL RISK MODELING

For the APR and PC source categories, the 2005 National Emissions Inventory (NEI) data served 

as the starting point for this assessment. Due to concerns about possible facility changes that may 

have occurred after 2005 at the one operating major source in the AMF source category, 2008 

NEI data served as the starting point for that source category. Using lists of operating facilities 

known during MACT development in combination with process MACT codes

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in the NEI, lists 

of facilities in the APR, AMF and PC source categories were developed (MACT codes: AMF –

1001, APR – 1347, PC – 1326). These facility lists were used to create a subset of the NEI for 

each source category that contained facility wide emissions data for each facility in each source

category. Facility information was checked against compliance databases and permit information 

to ensure that the facilities were subject to the relevant rules. Specific changes to data within 

each source category are discussed in sections 2.1, 2.2, and 2.3. Additional information gathered 

after the residual risk was modeled are discussed in section 2.4.

 

1 The NEI associates a specific code with emissions and emission points regulated by each MACT standard.
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Upon the request of industry trade groups such as the American Chemistry Council (ACC) and 

the Society of Chemical Manufacturers & Affiliates (SOCMA), the 2005 NEI data was 

voluntarily reviewed by industry for correctness of facility names, Source Classification Codes 

(SCC), MACT codes, emissions, location (latitude and longitude coordinates) and other

modeling parameters contained in the NEI. The proposed revisions were reviewed on a case by

case basis and were accepted where appropriate.

The EPA requested that the one facility in the AMF source category examine the 2008 NEI data, 

identify process MACT codes for each emission point, and, where differences existed, correct or 

update the data. After review of the data, the facility submitted updated information, and the 

updated data formed the basis for the data set used for modeling.

The EPA conducted an extensive review of the location coordinates for all facilities in the 3 

source categories. Locations were plotted and visually reviewed using Google Earth. 

Adjustments were made where emission points were not located in industrialized areas or where 

they did not match the facility address locations. 

Stack and fugitive parameters that did not meet the EPA Quality Assurance (QA) routines and

standards were corrected. Permit data and compliance databases were used to make area/major 

source designations. Finally, a standard QA of the modeling file was conducted. In some cases, 

emissions were assigned to or removed from the AMF, APR or PC source category based on a 

combination of information available in the NEI database, such as the specific chemical emitted, 

the MACT code the emissions were assigned to, the source of the NEI data (some data is from 

state agencies where other data is from the Toxics Release Inventory (TRI)), and the method of 

MACT code assignment in the NEI (data may be assigned by EPA, state agencies, or through 

association with a specific source classification code (SCC)).

Risks associated with facilities covered by the AMF, APR, and PC MACT standards were 

modeled using the resulting files. Specific revisions to each data set are discussed below.

2.1 Development of the AMF data set

The 2008 NEI data had one facility that was documented as having emissions sources subject to 

the AMF MACT standard. In the review of additional information from industry, title V permits, 

EPA compliance databases, and permitting authorities, this list was confirmed.

2.2 Development of the APR data set

The 2005 NEI data had 22 facilities that were documented as having emissions sources subject to 

the APR MACT. In the review of additional information from industry, title V permits, EPA 

compliance databases, and permitting authorities, three additional facilities were added and 

seven were removed from the list due to facility closures, not being subject to the APR MACT 

standard or not being a major source of HAP. The resulting list included 18 facilities. 

Some emissions were reassigned to the APR source category for 10 facilities based on a 
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combination of information related to the specific chemical emitted, the SCC, the MACT code 

the emissions were assigned to, the source of the NEI data, and the method of MACT code 

assignment in the NEI. As methanol, formaldehyde, phenol, and triethylamine are commonly 

used and can be expected from APR production, principally, emissions of these chemicals were 

scrutinized. Using this combination of information, emissions were also reassigned away from 

the APR source category to the MACT code for the Hazardous Organic NESHAP for one 

facility. These emissions changes resulted in the addition of emissions to the APR source 

category of approximately 8 tpy methanol, 3 tpy phenol, 2 tpy formaldehyde, 2 tpy triethylamine, 

and less than 1 tpy of other chemicals. 

Supplemental emissions information within the source category was received from and accepted 

for NEI11136. Some emissions sources at NEI11136 were reassigned out of the source category

after input from the facility.

2.3 Development of the PC data set

The 2005 NEI data had 4 facilities that were documented as having emissions sources subject to 

the PC MACT. In the review of additional information from industry, title V permits, EPA 

compliance databases, and permitting authorities, this list was confirmed.

Some emissions were reassigned to the PC source category for each facility based on combined 

information related to the specific chemical emitted, the SCC, the MACT code the emissions 

were assigned to, the source of the NEI data, and the method of MACT code assignment in the 

NEI. As methylene chloride and phosgene are commonly used, and emissions of these chemicals 

can be expected from PC production, emissions of these chemicals were scrutinized. In addition, 

emissions of triethylamine and ethyl chloride may be expected from this source category. 

Triethylamine is a catalyst that can be used in the PC production process, and ethyl chloride can 

be a by-product of the polymerization reaction, depending on the solvents and other chemicals 

used in the process. The scrutiny and reassignment of some of these emissions to the PC source 

category resulted in the addition of 74 tpy of ethyl chloride, 40 tpy triethylamine, 6 tpy 

methylene chloride and 0.2 tpy phosgene to the source category. 

2.4 NACAA and State Review

On February 4, 2013, after residual risk modeling had been conducted for these three source 

categories, the EPA asked the National Association of Clean Air Agencies (NACAA) to review 

the emissions data for APR and PC facilities in several states. The state of Texas was also asked 

to review emissions data for the APR and PC facilities in their state. The results of this review 

are discussed in further detail below. A list of all of the facilities subject to this review can be 

found in Appendix A.

The state of North Carolina confirmed that the three APR facilities in that state were still active 

and subject to the APR MACT standards. For one facility (NEI56485), they indicated that 

several emission points previously assigned to the APR source category were subject to a 

different MACT standard. For another facility (NEI46350), they also indicated that two minor 

emission points previously assigned to the APR source category were subject to a different 
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MACT standard.

The state of South Carolina confirmed that the one APR facility in that state was still active and 

subject to the APR MACT standards. The state provided 2005 NEI emissions data for this 

facility to confirm the data used by the EPA.

The state of Texas confirmed that the one APR facility and two PC facilities in that state were 

still active and subject to the APR and PC MACT standards, respectively. There were no 

revisions to the emissions data.

As the revisions provided by these states was either only to confirm that the facilities were still 

active and subject to the applicable MACT standard, or to remove emission points from the 

source category, the EPA made the decision not to remodel the risk for these categories. Should 

the EPA choose to remodel the residual risk for these source categories in the future, the revised 

dataset will reflect the changes described above.

3.0 ACUTE RISK

As outlined in Appendix B: Analysis of Data on Short-Term Emission Rates Relative to LongTerm Emission Rates (Palma and Smith, 2009), short-term emission rates can be estimated based 

on annual average rates in order to assess risk associated with acute exposure. For RTR 

rulemakings, unless more detailed information is available, it is generally assumed that the 1-

hour emission rate for each facility exceeds the annual average hourly emission rate by tenfold, 

and that this tenfold emission spike could coincide with worst-case meteorological conditions 

and the presence of a human receptor at the facility boundary. This method was developed as a 

means of screening for potentially significant acute exposures. This factor of ten was applied to 

all average annual hourly emission rates for a source, with one exception, as described below.

A factor of two for acute risk was chosen for emissions from equipment leaks. However, this 

factor was chosen after most of the risk assessment was already complete and was therefore only

applied to several facilities showing the highest risk. The factor of two was chosen because

emissions from equipment leaks are inherently different from other emission sources at chemical 

manufacturing facilities. While we believe that it is possible that worst-case short-term emission 

episodes from sources such as process vents, stacks, or flares may be as high as ten times the

annual average due to events such as upsets or process flow variability, this does not apply to 

equipment leaks. Equipment leaks are not affected acutely by variable flow in a system and thus 

cannot emit in the same way as aforementioned emission sources during a large-scale upset. In 

addition, a large uncertainty factor has already been incorporated into the emission rate estimates 

from equipment leaks.

To calculate emissions from equipment leaks for these source categories, testing for equipment 

leaks is conducted on a regular basis, and when a leak is measured using EPA Method 21, a

predetermined emission factor from EPA’s Protocol for Equipment Leak Emission Estimates

document is applied. When these emission rates for equipment leaks were developed, the EPA 

used data from a number of different studies of bagged samples at petroleum and synthetic

organic chemical manufacturing facilities. In these studies, the EPA measured for leaks using 
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EPA Method 21 and where leaks were found, the concentration was recorded, the leak was 

bagged, and an estimate of the mass emission rate was calculated from the bagged sample. From

the results of these studies, mass emission rates were found to vary up to five orders of 

magnitude for a given EPA Method 21 concentration reading. A correlation was developed based 

on these results, which was inherently biased towards higher emission rates.2

If an event causing a pressure increase occurred in a process stream where a leak was present, we 

would not expect the concentration of HAP in the equipment leak to change because the HAP 

concentration is only a function of the composition of the process stream. The emissions estimate

is based on a concentration measurement using a toxic vapor analyzer (TVA) used as a part of 

EPA Method 21, and has already incorporated variability, as discussed above. Therefore, we do 

not believe that emissions from equipment leaks pose a large acute risk.

Based on this information, we do not believe it is appropriate to add another order of magnitude

of uncertainty to emissions from equipment leaks, and that a factor of two is more appropriate. A 

list of facilities where we used the factor of two instead of ten is provided in Appendix 7 of the 

risk assessment document.

REFERENCES

Palma, Ted and Roy Smith. Appendix B: Analysis of Data on Short-Term Emission Rates 

Relative to Long-Term Emission Rates. Risk and Technology Review (RTR) Risk 

Assessment Methodologies. Prepared for U.S. Environmental Protection Agency. 

Research Triangle Park, NC. Publication No. EPA-452/R-09-006. June 2009.

1995 Protocol for Equipment Leak Emission Estimates. U.S. Environmental Protection Agency. 

Research Triangle Park, NC. Publication No. EPA-453/R-95-017. November 1995.

 

2 More detailed discussion on how these correlations were developed can be found in Appendix

B of the EPA’s Protocol for Equipment Leak Emission Estimates document.
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Appendix A – List of Facilities Subject to NACAA Review

Facility Name NEI ID City State Source Category

EMERALD CAROLINA CHEMICAL, LLC NEINC0595 Charlotte NC Amino and Phenolic Resins Production

GEORGIA-PACIFIC CONWAY OPERATIONS NEI46350 CONWAY NC Amino and Phenolic Resins Production

HEXION SPECIALTY CHEMICALS, INC. NEI56485 FAYETTEVILLE NC Amino and Phenolic Resins Production

NEVAMAR CO LLC NEI7964 HAMPTON SC Amino and Phenolic Resins Production

LUFKIN RESIN PLANT NEI12810 LUFKIN TX Amino and Phenolic Resins Production

BAYTOWN PLANT NEI13287 BAYTOWN TX Polycarbonate Production

DOW CHEMICAL CO FREEPORT FACILITY NEI11295 Freeport TX Polycarbonate Production