SO2 NAAQS Designation Modeling Analyses for DRR Applicable Sources Compliance Demonstration - Case Study

摘要

The "Data Requirements for Characterizing Air Quality for the Primary SO2 NAAQS" (40 CFR 51.1200, herein referred to as the Data Requirements Rule - DRR) applies to the Piti and Cabras Guam Power Authority (GPA) electrical generating stations and thus requires an air quality review either by dispersion modeling or air quality monitoring. The purpose of the air quality review is to support the U.S. Environmental Protection Agency (EPA) and the Guam EPA (GEPA) in establishing the sulfur dioxide (SO2) National Ambient Air Quality Standard attainment status for the area on the Territory of Guam that may be significantly impacted by SO2 emissions from the applicable sources and other nearby contributors. GPA was advised by GEPA that the preferred path to complying with the DRR was through a dispersion modeling analysis. In compliance with the DRR requirements and prescribed schedule, GPA submitted a timely modeling protocol and initial compliance modeling demonstration by January 13, 2017. Comments received from GEPA and EPA on the initial submission suggested using actual emissions and re-running the modeling analyses based on the revised Guideline on Air Quality Models (Appendix W to 40 CFR 51) and new version of the AERMOD modeling system (version 16216r). Multiple disparate data sets including monthly fuel oil deliveries, episodic fuel oil firing logs, and hourly and daily power generation records were analyzed to compile three-year hourly emission data for each applicable source. It was found that the new version of the AERMOD modeling system led to significant reduction of predicted concentrations in many areas while increasing modeled impacts in other areas of the modeled domain when compared to AERMOD version 15181 predicted concentrations. This paper presents the procedure developed to determine hourly emissions from proxy operational data and the impact of using the latest modeling guidance and model version on the predicted concentrations from the DRR applicable sources and other nearby marine vessel sources of SO2 emissions. Recommendations for potential area compliance designation consideration are also provided.