### 9/13/2010

To: Docket – ID No. EPA-HQ-OAR-2010-0600

From: Elaine Manning, Sect or Based Assessment Group

Subject: Post Proposal Revisions for Pol ybutadiene Rubber Production Risk and Technology Assessment

The attached minor revisions were made to the Polyutadiene Rubber Production source category risk assessment which was included in the proposal for the Group I Polymers and Resins; Marine Vessel Load ing Operation; Mineral Wool Production; Pharmaceuticals Production; and Printing and Publishing Industry rulemaking issued on October 10, 2008. The updated Table 3.6- 1 Summary of Emissions from the Polybutadiene Rubber Production Source Catego ry and Table 3.6-2 Summary of Source Category Level Risk for Polybutadiene R ubber Production reflecting the minor changes are attached. The most significant change from the October 10, 2008 proposal is the change in the maximum individual risk (MIR ) and hazard index (HI). Since the October 10, 2008 proposal we received some updated em issions information for the polybutadiene rubber production facilities. Based on th is new emissions information, the MIR for cancer has gone up to 30 in a million from the previously proposed MIR of 10 in a million. The HI is now 0.3, up from the value of 0.2 at proposal. The acute results also changed slightly. The attached Appe ndices 1, 6, and 7 provide the supporting information for the changes.

The MACT-allowable emissions of the co mpound (1,3-butadiene) driving the risk from this source category is estimated to be approximately the same as the modeled actual emissions; therefore, th e risks results are equal.

In addition to the risk presented by sour ce category alone as presented in the attached Summary of Source Category Level Risk table, additional analysis was performed to access the “facility-w ide” risk. The results of the residual risk associated with all categories at the know n facilities (facility-wide) ar e presented in the attached Appendix 6: “Detailed Risk Modeling Resu lts”. We used the National Air Toxics Assessment (NATA) database for estimating faci lity-wide risks due to our lack of more recent facility-specific emissions data for so me of the source categories included in the facility-wide analyses. Additionally, b ecause we have not yet begun our thorough
residual risk review for most source categories, we are unable at this time to estimate allowable facility-wide emissions. Thus, our facility-wide analysis is based solely on
actual emissions.

The facility-wide MIR and HI available in Appendix 6 are based on emissions, as identified in the NATA database, from all emi ssions sources at the identified facilities. The facility with the maximum facility-wide ri sks is estimated to have a cancer MIR of 30 in a million and an HI of 0.3 (both MIR and HI located at the same facility). The

### source category contribution to the facility-wid e risk at this facility is over 90% for both
the MIR and the HI.

Table 3.6-1 Summary of Emissions from the Polybutadiene Rubber Production Source Category

Prioritized Inhalation Dose -Response Value Identified by OAQPS

HAP a Emissions (tpy) Number
of
Facilities Reporting

HAP (5
facilities
in data

set) Unit Risk
Estimate for

Cancer? Reference
Concentration for
Noncancer? Health Benchmark
Values for Acute
Noncancer? PBHAP?

Hexane 1,584 4 Υ Υ

Toluene 510 2 Υ Υ
1,3-Butadiene 74 5 Υ Υ Υ
Styrene 68 5 Υ Υ Ethyl Benzene 23 1 Υ

Chlorobenzene 2 1 Υ Υ

Methanol 0.07 1 Υ Υ

Nickel 0.0007 1 Υ Υ Υ

### Table 3.6-2 Summary of Source Category Level Risks for Polybutadiene Rubber Facilities

Result HAP “Drivers” Facilities in Source Category Number of Major Source Facilities Estimated to be in Source Category 5 n/a

Number of Facilities Identified in NEI and
Modeled in Risk Assessment 5 n/a

Cancer Risks Maximum Individual Lifetime Cancer Risk (in 1 million) 30 1 1,3-butadiene

Number of Facilities with Maximum Individual Lifetime Cancer Risk: Greater than or equal to 100 in 1 million 0 n/a Greater than or equal to 10 in 1 million 2 1,3-butadiene Greater than or equal to 1 in 1 million 4 1,3-butadiene

Chronic Noncancer Risks Maximum Reproductive Hazard Index 0.3 1,3-butadiene Number of Facilities with Maximu m Reproductive Hazard Index:

Greater than 1 0 n/a Acute Noncancer Screening Results

Maximum Acute Hazard Quotient 12
0.6
0.2 toluene (REL) toluene (AEGL-1) toluene (ERPG-2)

Number of Facilities With Potential for Acute
Effects 1 toluene (REL)

Acute Noncancer Refined Results Maximum Acute Hazard Quotient 1 toluene

Number of Facilities With Potential for Acute
Effects 0

Population Exposure Number of People Living Within 50 Kilometers
of Facilities Modeled 1,700,000 n/a

Number of People Exposed to Cancer Risk: Greater than or equal to 100 in 1 million 0 n/a Greater than or equal to 10 in 1 million 20 n/a Greater than or equal to 1 in 1 million 24,000 n/a Number of People Exposed to Reproductive Hazard Index : Greater than 1 0 n/a Estimated Cancer Incidence (excess cancer cases per year) 0.003 n/a

Contribution of HAP to Cancer Incidence 1,3-butadiene 98% n/a ethyl benzene 2% n/a

1 The individual source category risk is 20 in a million; however because of the close proximity of 2 facilities in the source category the highest predicted MIR for the source category is 30 in a million.

### Attachments: Appendix 1 Revised Em issions Inventory Support Memorandum Appendix 6 Detailed Risk Modeling Results Appendix 7 Acute Impacts Refined Analysis Figures