July 15, 2010 

1 

ESTIMATION OF MACT ALLOWABLE EMISSION LEVELS AND ASSOCIATED RISKS 

AND IMPACTS FOR FOUR GROUP I POLYMERS AND RESINS SOURCE CATEGORIES 

 The purpose of this document is to present analyses related to “MACT allowable” emissions 

levels for four source categories covered by the Group 1 Polymers and Resins NESHAP (Polymers 

and Resins I NESHAP) that are being addressed under EPA’s Risk and Technology Review (RTR) 

program. This program is addressing the statutory requirements in section 112(f) and 112(d)(6) of the 

Clean Air Act for federal air toxics regulations. The regulations are National Emission Standards for 

Hazardous Air Pollutants (NESHAP) contained in 40 CFR part 63. They are commonly referred to as 

Maximum Achievable Control Technology (MACT) standards. The emissions data being used for 

the RTR risk assessments for these categories consists of data representative of “actual” emission 

levels. In addition to the risks associated with these actual emission levels, EPA also considers the 

levels of HAP emissions that sources could emit and still be in compliance with the applicable MACT 

regulation. These emission levels are referred to as “MACT allowable” emissions. The purpose of 

this memorandum is to discuss these MACT allowable emission levels and their impact on the 

baseline risks. 

 The Polymers and Resins I addresses nine source categories, four of which are the subject of 

this memorandum: Epichlorohydrin Elastomers Production, Nitrile Butadiene Rubber Production, 

Polybutadiene Rubber Production, and Styrene Butadiene Rubber and Latex Production. 

 This memorandum is organized as follows. Section 1 presents the estimated maximum risk 

levels based on the actual emission levels for all four source categories, and Section 2 discusses the 

basic approach to estimating the risks from the MACT allowable levels. This is followed by a 

discussion of the estimation of MACT allowable emission level, particularly as it relates to the actual 

emission levels used in the risk assessments. This is followed by a presentation of the estimated risks 

at these MACT allowable levels. 

1.0 Risk Levels Based on Actual Emissions 

 The estimated maximum inhalation risks for these four source categories are summarized in 

Table 1. These risks are based on actual emission levels. 
July 15, 2010 

2 

Table 1. Summary of Estimated Inhalation Risks for the Four Polymers and Resins I Source 

Categories Based On Actual Emissions Levels 

Source Category 

Maximum individual 

cancer risk (in a 

million)1

Maximum chronic 

noncancer TOSHI2

Epichlorohydrin Elastomers Production 10 0.1 

Nitrile Butadiene Rubber Production 2 0.009 

Polybutadiene Rubber Production 30 0.3 

Styrene Butadiene Rubber and Latex Production 10 0.2 

1

 Maximum individual excess lifetime cancer risk. 

2

 Maximum target organ specific hazard index (TOSHI). Target organ system represented by the TOSHI varies across 

source categories. Maximum TOSHI is respiratory for epichlorohydrin elastomers production. Maximum TOSHI for 

nitrile butadiene rubber production, polybutadiene rubber production, and styrene butadiene rubber and latex production is 

based on reproductive effects. 

2.0 Basic Approach to Estimating Risks from MACT Allowable Emission Levels

 Detailed emission point-specific MACT allowable emissions information is not available. 

Therefore, modeling was not conducted to estimate the risks from MACT allowable emission levels. 

 The basic approach to estimate the risks from MACT allowable emission levels was to first 

estimate the relationship between the actual and MACT allowable emission levels, and then to 

estimate the potential risk impacts from the differences between actual and MACT allowable 

emissions. In general, the risk impact was assumed to be proportional to the difference in emission 

levels. For example, if MACT allowable emissions were estimated to be three times as high as actual 

emissions, it was assumed that risks could be as much as three times as high as those estimated from 

the modeling conducted using actual emissions. 

 This assumption regarding the linear relationship between emissions and risks is generally 

reasonable for chronic cancer and noncancer risks. However, using this approach for acute risks 

would likely overestimate the impacts. The acute assessment already has built in numerous 

conservative assumptions. First, the acute assessment assumed a short-term emission rate up to 10 

times that of the average longer term emission rate. Also, the maximum acute risks assume the 

simultaneous occurrence of independent factors that may vary greatly, such as hourly emissions rates, 

meteorology, and human activity patterns. In the assessment using actual emissions, EPA assumed 

that individuals remained for 1 hour at the point of maximum ambient concentration as determined by 

the co-occurrence of peak emissions and worst-case meteorological conditions. These assumptions 

would tend to overestimate actual exposures since it is unlikely that a person would be located at the 

point of maximum exposure during the time of worst-case impact. The addition of another factor to 

account for MACT allowable emissions level further increases the conservativeness of the estimated 

MACT allowable acute risks. Therefore, this analysis does not estimate acute risks for the MACTallowable emissions level. 
July 15, 2010 

3 

3.0 Results of Analysis 

 The Group 1 Polymers and Resins NESHAP addresses emissions from the following types of 

emission sources for all four source categories: (1) storage tanks, (2) front-end process vents, (3) 

back-end process operations, (4) equipment leaks, and (5) wastewater. The process “front-end” 

includes pre-polymerization, reaction, stripping, and material recovery operations. In addition, the 

NESHAP addresses emissions from back-end process operations for the Polybutadiene and Styrene 

Butadiene Rubber and Latex source categories, where the process “back-end” includes all operations 

after stripping (predominately drying and finishing). Table 2 summarizes the formats of the standards 

for these emission points. 

Table 2. Formats of Standards for Group 1 Polymers and Resins I NESHAP 

Emission Source Type Format of Primary Standard 

Storage Tanks Equipment Standards 

Front-End Process Vents Performance Standard (% reduction) 

Back-End Process (only for Polybutadiene 

and Styrene Butadiene Rubber) 

Emission Limit 

(kg emissions/Mg latex or crumb rubber) 

Equipment Leaks Work Practice Standards 

Wastewater Equipment Standards, Performance Standard 

 The ability to estimate MACT allowable emissions for specific emission points, or for specific 

emission point types, is largely dependent on the format of the standards. For equipment standards, 

sources subject to the regulation are required to install specific equipment. Assuming that the 

equipment is maintained properly and is in good working condition (as required), there would not be a 

difference in the actual emissions level and the level allowed by the standard. Similarly, there would 

be no difference between actual and MACT allowable emissions for emission sources subject to work 

practice requirements, provided that facilities are not conducting additional work practices proven to 

reduce emissions beyond those required in the rule. We are not aware of any such situations at 

facilities in these five Group 1 Polymers and Resins source categories. Therefore, for equipment 

leaks and storage vessels, which are subject to equipment and work practice standards, we believe that 

the actual emission levels are a reasonable estimation of the levels allowed by the standard. 

 For wastewater emission sources, the regulation includes an assortment of equipment and 

performance standards. As discussed above, it is reasonable to assume that the actual emissions from 

those sources subject to equipment standards are representative of the MACT allowable emissions. In 

general, it is possible that sources could overcontrol sources subject to a performance standard. This 

would result in the actual emissions being lower than the MACT allowable emissions. However, for 

wastewater sources, we are not aware of any such overcontrol. Therefore, we believe that the actual 

wastewater emission levels are a reasonable estimation of the levels allowed by the standard. 

 For front-end process vents, which are subject to a performance standard, we believe that there 

are situations where sources are utilizing control devices that achieve reductions greater than the 

required 98 percent reduction. However, the continuous monitoring requirements of the rule result in 

situations where reductions greater than 98 percent are required on a continuous basis. Specifically, 

owners and operators are required to conduct performance tests to demonstrate initial compliance. 

During the test, they are required to monitor a specific parameter (e.g., temperature for a thermal 

incinerator). From the data collected during the test, they are required to calculate a parameter level 
July 15, 2010 

4 

(e.g., a minimum temperature) that is indicative of the control device performance achieved during 

the test. Ongoing compliance is then determined based on the continuous monitoring of this 

parameter as compared to the established level (e.g., if the incinerator temperature falls below the 

minimum temperature established during the test it would be an excursion). Therefore, if an 

incinerator was achieving a 99 percent emission reduction during the performance test, the 

temperature level established based on monitoring data collected during the test would be reflective of 

a 99 percent reduction. Thus, the performance level required by the rule would, in effect, be 99 

percent. Because of these requirements, we assume that the actual emission levels are a reasonable 

estimation of MACT allowable emissions for front-end process vents. 

 Since there are no standards applicable to the back-end process emissions from 

Epichlorohydrin, and Nitrile Butadiene Rubber, the MACT allowable and actual emissions are 

equivalent. As shown in Table 2, the format of standards for emissions from back-end process 

operations at plants in the Polybutadiene Rubber Production and Styrene Butadiene Rubber and Latex 

production is an emission limitation based on production. The units of the standard for Polybutadiene 

Rubber Production are kilograms HAP emissions allowed per Megagram of crumb rubber product. 

Crumb rubber is the final product of this process, so MACT allowable emissions can be estimated 

using production data. Since actual production data are confidential business information, an estimate 

of production was determined using published “nameplate” capacities. The result of this calculation 

is that MACT allowable emissions are approximately 10,600 tons/year, which is approximately seven 

times higher than the actual emissions of around 1,600 tons/yr for the plants in the Polybutadiene 

Rubber Production source category. Details of this calculation are provided in Attachment 1. 

 The units of the back-end process operations standard for the Styrene Butadiene Rubber and 

Latex Production source category are kilograms HAP emissions allowed per Megagram of latex. 

Facilities subject to this standard utilize an emulsion process, where the reaction occurs in a waterbased solution forming a latex. Following the formation of this latex, steam is injected into the latex 

which results in the coagulation of solid rubber crumb, which is the final product. It should be noted 

that there are nine major source facilities in the data set for the Styrene Butadiene Rubber and Latex 

Production source category. However, only three of these facilities produce rubber. At the six other 

facilities, the final product is styrene butadiene latex. Therefore, they do not produce a solid product 

and do not have back-end processes. While an estimate of the amount of final crumb product can be 

obtained from “nameplate” capacities, an additional assumption regarding the relative weight of the 

crumb in the latex is required. The result of this calculation is that MACT allowable emissions are 

approximately 1,100 tons/yr, which is around five times higher than the actual emissions of 

approximately 240 tons/yr from the styrene butadiene rubber production facilities in the source 

category that are subject to this emission limitation. Details of this calculation are also provided in 

Attachment 1. 

 Table 3 summarizes the ratios of MACT allowable to actual emissions for the five Group 1 

Polymers and Resins source categories. As discussed above and summarized in Table 3, the only 

emission point type where the MACT allowable emissions levels are different from the actual 

emissions levels are the back-end process emissions from the Polybutadiene Rubber and Styrene 

Butadiene Rubber and Latex source categories. Table 4 shows the overall back-end emission levels 

for these two source categories. Overall for the emissions from all sources from the category, the 

MACT allowable emissions from the Polybutadiene Rubber source category are seven times as high 

as the actual emissions. This ratio is four for the Styrene Butadiene Rubber and Latex source 

category. 
July 15, 2010 

5 

Table 3. Summary of MACT Allowable to Actual Emission Ratios for Four of the 

Group 1 Polymers and Resins Source Categories 

Ratio of MACT Allowable Emissions to Actual Emissions 

Source Category Storage 

Vessels 

Front-End 

Process 

Vents 

Back-End 

Process 

Operations 

Equipment 

Leaks Wastewater 

Epichlorohydrin 1:1 1:1 1:1 1:1 1:1

Nitrile Butadiene 

Rubber 1:1 1:1 1:1 1:1 1:1

Polybutadiene 

Rubber 1:1 1:1 7:1 1:1 1:1

Styrene Butadiene 

Rubber and Latex 1:1 1:1 5:1 1:1 1:1

Table 4. Summary of MACT Allowable to Actual Emission Emissions for 

Polybutadiene Rubber and Styrene Butadiene Rubber and Latex 

HAP Emissions (tons/yr) Emission Source Type Actual MACT Allowable 

Polybutadiene Rubber 

Back-end process vent 1,594 10,593 

Styrene Butadiene Rubber and Latex 

Back-end process vent 237 1,140 

 The risk assessment conducted for these categories in 2010 did not explicitly estimate risks 

from individual emission sources types. However, it did identify the sources that contribute at least 

90 percent of the maximum risk. Using this information on the risk driver emission sources, 

estimates were made of the upper bound impact the higher MACT-allowable back-end emissions 

levels could have on the maximum risks. Following is an example of this methodology. 

 The maximum cancer risk from a hypothetical polybutadiene rubber production facility was 

8.2 in 1 million,a

 which would be reported at 8 in 1 million. Assume HAP emissions from a front-end 

process vent contributed 85 percent of this risk and HAP emissions from a storage tank contributed 

10 percent. Therefore, the sources contributing 95 percent of this maximum cancer risk, or 7.8 in 1 

million, were known. Since the ratio of MACT-allowable to actual emissions for these source types 

was 1:1, this would represent the MACT-allowable risk from these sources. While the contribution 

from back-end process emissions was not explicitly reported, the upper bound contribution of the 

back end process emissions would be 5 percent of this maximum cancer risk based on actual 

emissions, or 0.4 in 1 million. A factor was applied to account for the fact that some HAP emitted 

from the back-end process operations are not carcinogens (i.e., do not have a unit risk estimate) and 

would not contribute to the estimated cancer risks. The mass percentage of carcinogens to 

noncarcinogens was applied to the upper bound risk contribution to estimate the potential contribution 

to the maximum cancer risk based on actual emissions. Assuming that the only 30 percent of the 

 

a Note: Risks are only reported to one significant figure. However, this calculation was conducted with raw risk numbers 

before this rounding. 
July 15, 2010 

6 

back-end emissions, by mass, were of carcinogenic HAP, the potential risk from the back end would 

be 0.12 in 1 million. Applying the 7:1 factor would indicate that the MACT-allowable cancer risk 

from back-end process emissions is 0.8 in 1 million. Adding this risk to the 8.2 in 1 million MACTallowable risk from the front-end vents and storage tanks, the upper bound maximum cancer risk at 

the MACT-allowable level would be 9 in 1 million. 

 Table 5 shows the facility-specific comparison of maximum risks based on both actual and 

MACT-allowable emission levels for the Polybutadiene and Styrene Butadiene Rubber and Latex 

source categories. As can be seen from Table 5, the maximum risks for both categories are the same 

at both the actual and MACT-allowable emission levels. Appendix B provides details of these 

estimates. 

Table 5. Facility-Specific Maximum Risks Based on MACT Allowable and Actual Emission 

Levels for Polybutadiene Rubber and Styrene Butadiene Rubber and Latex 

Maximum individual cancer risk 

(in a million) 

Maximum chronic noncancer 

TOSHI 

Facility ID 

Actual 

Emissions 

MACTAllowable 

Emissions 

Actual 

Emissions 

MACTAllowable 

Emissions 

Polybutadiene Rubber Production 

NEI32876 3 3 0.05 0.05 

NEI33012 0.5 0.5 0.01 0.01 

NEI7039 10 10 0.2 0.2 

NEI7446 20 20 0.3 0.3 

NEI8307 9 9 0.2 0.2 

Styrene Butadiene Rubber and Latex Production 

NEI13230 7 7 0.1 0.1 

NEI33015 3 3 0.1 0.1 

NEI8360 10 10 0.2 0.2 

Note: The source category maximum risk from the polybutadiene source category is 30 due to the close proximately of 

facilities 

 Following are the conclusions from this analysis: 

• The only emission point where there is an appreciable difference in emissions at the actual 

level and the MACT allowable level is back-end process operations for the Polybutadiene 

Rubber and Styrene Butadiene Rubber and Latex source categories. 

• The maximum risks based on actual emission levels from the Polybutadiene Rubber and 

Styrene Butadiene Rubber and Latex source categories are based on emissions from sources 

other than the back-end process operations.

• The overall conclusion is that the maximum risks for the four Polymers and Resins 

source categories are the same for both the actual emissions level and the MACT 

allowable emissions level. 
July 15, 2010 

1 

ATTACHMENT A. ESTIMATION OF GROUP 1 POLYMERS AND RESINS BACK-END PROCESS MACT ALLOWABLE EMISSIONS Table A-1. Estimation of MACT Allowable Back-End Emissions for Polybutadiene Rubber 

Facility 

“NamePlate” 

Capacity1

(Mg/yr) 

Actual 

Production 

Capacity2

(Mg/yr) 

MACT 

Allowable 

HAP 

Emissions3

(kg/yr) 

MACT 

Allowable 

HAP 

Emissions 

(tons/yr) 

Actual HAP 

Emissions 

(tons/yr) 

AMERICAN SYNTHETIC RUBBER 180,000 162,000 1,620,000 1,782 362 LANXESS 180,000 162,000 1,620,000 1,782 93 FIRESTONE POLYMERS/ORANGE TX 145,000 130,500 1,305,000 1,436 70 FIRESTONE POLYMERS/LAKE CHARLES LA 180,000 162,000 1,620,000 1,782 685 GOODYEAR 385,000 346,500 3,465,000 3,812 384 

Totals 10,593 1,594 

1 Worldwide Rubber Statistics 2007. International Institute of Synthetic Rubber Producers, Inc. 2 Adjusted to 90% of Nameplate Capacity to account for down times for maintenance shutdowns, product changeouts, etc. 

3 Calculated using the emission standard of 10 kg total organic HAP allowed per Mg of crumb rubber produced. 

Table A-2. Estimation of MACT Allowable Back-End Emissions for Styrene Butadiene Rubber 

Facility 

“NamePlate” 

Capacity1

(Mg/yr) 

Actual 

Production 

Capacity2

(Mg/yr) 

MACT 

Allowable 

HAP 

Emissions3

(kg/yr) 

MACT 

Allowable 

HAP 

Emissions 

(tons/yr) 

Actual HAP 

Emissions

(tons/yr) 

GOODYEAR HOUSTON CHEM PLT 300,000 270,000 432,000 475 153 DSM COPOLYMER/BR PLANT 150,000 135,000 216,000 238 9 ISP ELASTOMER 270,000 243,000 388,800 428 75 

Totals 1,140 237 

1 Worldwide Rubber Statistics 2007. International Institute of Synthetic Rubber Producers, Inc. 2 Adjusted to 90% of Nameplate Capacity to account for down times for maintenance shutdowns, product changeouts, etc. 3 Calculated using the emission standard of 0.4 kg total organic HAP allowed per Mg of latex produced and assuming that the crumb rubber m

latex by weight. ( ) ( ) Mg oduction Actual oductionCapacity Mg yr kg HAP AllowableHAPEmissions kg yr Pr 0.4 25% Pr ( / ) ( / ) = *