Appendix 1 

Emissions Inventory Support Memorandum 
Marine Tank Vessel Loading Operations 
1

MEMORANDUM 

TO: Anne Pope, EPA 

FROM: Darcy Wilson, ERG 

DATE: July 23, 2010 

SUBJECT: Emissions Data Used in Residual Risk Modeling for Marine Vessel 

Loading Operations 

The purpose of this memorandum is to provide information on the RTR database used in 

estimating residual risk for the Marine Vessel Loading Operations Maximum Achievable 

Control Technology (MACT) source category. 

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) requires the Environmental Protection Agency (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) requires 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, EPA must develop standards to 

address these remaining risks. As part of this second stage, data were gathered to assess 

the residual risks from the Marine Vessel Loading Operations MACT source category. 

EMISSIONS DATA USED IN RESIDUAL RISK MODELING 

The 2002 National Emissions Inventory (NEI) data served as the starting point for this 

assessment. Using the process MACT code,1 a subset of the NEI was developed that 

contained facility, process, and emissions data for each facility in the Marine Vessel 

Loading Operations source category (MACT code 0603). The 2002 NEI data for Marine 

Vessel Loading Operations were released through an Advanced Notice of Proposed 

Rulemaking (ANPRM) in March of 2007, where NEI revisions for facilities in the 

MACT source category were solicited from State and local agencies, industry 

representatives, and EPA. The revisions that were provided to EPA were incorporated 

into the NEI prior to the initial NATA modeling. 

Risks associated with facilities covered by the Marine Vessel Loading Operations MACT 

standard were modeled in the initial 2005 NATA risk assessment in June of 2009. EPA 

reviewed the results of this analysis, and performed an in-depth review of the NEI data 

 

1

 Assigning data with MACT codes allows EPA to determine reductions attributable to the MACT 

program. The NEI associates MACT codes corresponding to MACT source categories with stationary 

major and area source data. 
2

set for the source category. The NEI was reviewed to identify additional processes with 

Marine Vessel Loading Operation Source Classification Codes (SCCs), and the NEI data 

were compared with data in the EPA’s Toxic Release Inventory (TRI). MACT code and 

emission revisions were made as a result of these analyses. For facilities in the NEI that 

have Marine Vessel Loading Operations but do not have HAP emission estimates (only 

volatile organic compound (VOC) estimates, EPA applied speciation profiles to develop 

surrogate HAP emission estimates. EPA also identified two facilities that are not subject 

to the Marine Vessel Loading Operations NESHAP. 

EPA evaluated the facility-wide risks for Marine Vessel Loading Operations using the 

2005 NEI data and risk assessment results that were released in the 2005 NATA Risk 

Preview with State and local agencies in June of 2010. Revisions were made to the 

emission estimates for one facility. Two facilities were removed from the category—one 

was not subject to the NESHAP, and the other has ceased marine vessel loading 

operations. These revisions were included in the risk analyses, and will be reflected in the 

final NATA risk assessment.