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Refined Dispersion Modeling This section presents the methodology used for the refined dispersion modeling analysis. This section addresses all of the fundamental components of an air dispersion modeling analysis vincluding: • Model selection and options; .. • Receptor spacing and location; • Meteorological data; and • Source release characteristics. The dispersion modeling analysis estimated ambient DPM concentrations as a result of incremental project emission increases and then determined differential cancer risk. The dispersion modeling included onsite equipment. MODEL SELECTION AND OPTIONS The AERMOD dispersion model (Version 9935 1) was used for the modeling analysis. AERMOD is the U.S. EPA preferred dispersion model for general industrial purposes. The AERMOD model is the appropriate model for this analysis based on the coverage of simple, i intermediate, and complex terrain. It also predicts both short-term and long-term(annual) average concentrations. The model was executed using the regulatory default options(stack-tip downwash, buoyancy-induced dispersion, final plume rise),default wind speed profile categories, L default potential temperature gradients, and no pollutant decay. Building wake effects were also addressed. The model is based on the Industrial Source Complex-3 (ISC3) model and PRIME downwash algorithm. Special features of AERMOD include its ability to treat the vertical inhomogeneity of the planetary boundary layer, special treatment of surface releases, irregularly-shaped area sources, a three plume model for the convective boundary layer,limitation of vertical mixing in the stable boundary layer,and fixing the reflecting surface at the stack base. A treatment of dispersion in the presence of intermediate and complex terrain is used that improves on that currently in use in y ISCST3 and other models. ` The selection of the appropriate dispersion coefficients used in the modeling depends on the land use within three kilometers (km)of the Port of Stockton. The land use typing was based on the classification method defined by Auer(1978);using pertinent United States Geological Survey �0 (USGS) 1:24,000 scale(7.5 minute)topographic maps of the area. If the Auer land use types of heavy industrial, light-to-moderate industrial,commercial, and compact residential account for L50% or more of the total area,the Guideline on Air Quality Models recommends using urban dispersion coefficients; otherwise, the appropriate rural coefficients were used. Based on 1- observation of the area surrounding the Vernalis, rural dispersion coefficients were applied in the `. analysis. L