Document V32rovK6EEwMwdJ05Xqdrx8eg

AR226-2635 23 AR226-2635 AIR QUALITY DISPERSION MODELING ANALYSIS OF C8 EMISSIONS DuPont Fayetteville, North Carolina Facility Prepared by: Charles J. Zarzecki DuPont Engineering Technology (DuET) Environmental Section Wilmington, DE 19898 April 1,2003 1. Introduction The DuPont Fayetteville plant conducted air dispersion modeling of ammonium perfluorooctanoate (C8) emissions from its facility. The following sections describe the dispersion modeling methodology and the results of the analysis. All air quality impact analyses have been conducted in accordance with approved dispersion modeling techniques detailed in the U. S. EPA's "Guideline on Air Quality Models", which is codified as Appendix W to 40 CFR Part 51. 2. Emissions Inventory The following is the stack information that was assembled in order to conduct the air quality modeling: Location: 697638 meters E, 3857918 meters N Stack height: 85 ft Stack exit temperature: 70 deg F Flow rate: 11,500ACFM Stack diameter: 1.58ft C8 emission rate: 0.00224 g/s 3. Meteorological Data The nearest location that takes hourly meteorological observations is Pope Air Force Base in Fayetteville, NC. Meteorological observations at the airport are considered representative of the site and of conditions affecting transport and dispersion of stack emissions. Therefore, five years of hourly surface observations from the observation station at Pope Air Force Base were used in the refined air quality dispersion analysis. Hourly meteorological data for the period 1995-1999 was used in this study. Concurrent twice-daily upper air data from the upper air observation station located in Greensboro, NC was used along with Pope surface temperatures to obtain hourly mixing depths. 4. Model Selection The area surrounding the Fayetteville plant is primarily non-urban. The U. S. EPA procedures classify land use within 3 kilometers of the site by the Auer method. Review of U. S. Geological Survey (USGS) maps, aerial photographs, and site visits clearly indicated that the area is well over 50% non-urban. The terrain immediately surrounding the plant can be considered as gently rolling, with terrain elevations remaining below stack top. With this in mind, we used the Industrial Source Complex Short Term Model (ISCST3) as the primary model to estimate long-term pollutant concentrations. ISCST3 is a steady-state Gaussian model recommended by the U.S. EPA, and is included in the "Guidelines on Air Quality Models" for modeling of pollutant emissions from industrial-type sources subject to significant building downwash. Refined ISCST3 modeling was conducted using five years C:\fayetteville\c801.doc 2 of sequential hourly meteorology from the observation facility located at Pope Air Force Base as described above. 5. Receptor Selection A receptor grid with 100-meter spacing extending out to a minimum distance of 2 km from the plant property line was used. Receptors were also placed on the property line at 25 meter intervals. No receptors were placed inside the plant property line. The receptor grid can be seen in Figure 1. The model was run with the elevated terrain height option. Terrain elevations were imported from digital elevation map (DEM) files provided by the USGS. A Cartesian receptor grid of this type is considerably more dense 1han recommended by the U.S. EPA in the Guidelines on Air Quality Models (U.S. EPA, 1998) for modeling a facility of this type. 6. Modeling Procedures The most recent version ofISCST3 (version 00101) was used in the air quality dispersion modeling of all receptors. All model options were set to the U.S. EPA regulatory default version of ISCST3. The model was run in the rural mode since the land area in the immediate vicinity of the Fayetteville plant is more than 50% rural. Any effects of aerodynamic downwash caused by structures adjacent to the modeled stacks were included in the ISCST3 modeling analysis. Air quality dispersion modeling was conducted on an hour-by-hour basis using the five years of meteorological data described above. The C8 modeling results were summarized for the annual averaging period. 7. Results The dispersion modeling results are presented in Table 1. As can be seen in the table, the maximum predicted annual average C8 concentration is 0.00141 ug/m3. This concentration occurs at the Fayetteville plant property line. The results are presented graphically in Figure 2. C:\fayetteville\c801 .doc 3 Year 1995 1996 1997 1998 1999 Table 1 Maximum Predicted C8 Concentrations Maximum Annual Prediction 0.00115 ug/m3 0.00140 ug/m3 0.00141 ug/m3 0.00120 ug/m3 0.00126 ug/m3 Location 696207E, 3856312N 698376E, 3858634N 698386E, 385861 IN 698376E, 3858634N 698386E, 385861 IN C:\fayetteville\c801 .doc Figure 1 Receptor Grid C:\fayetteville\c801.doc Figure 2 Fayetteville C8 - Annual Average 1997 Met Data 386100CH 386000CH 3859000- 3858000- E 38570003856000^ 3855000H 3854000-^ 3853000-^ 694000 695000 696000 697000 698000 meters 699000 700000 701000 Contour Interval 0.0001 iig/m3 C:\fayetteville\c801.doc