# Technical Support Document:

**Potential for Excess Local Deposition of U.S. EGU**  **- Attributable**  **Mercury in Areas**  **n ear U.S. EGUs** 2 EPA - 452/R - 11 - 010 November 2011



## Technical Support Document: **Potential for Excess Local Deposition of U.S. EGU**  **- Attributable**  **Mercury in Areas near U.S. EGUs**

U.S. Environmental Protection Agency Office of Air Quality

Planning and Standards Health and Environmental Impacts Division Research Triangle Park, North Carolina3 **DISCLAIMER** This document has been prepared b y staff from the Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency. Any opinions, findings, conclusions, or recommendations are those of the authors and do not necessaril y reflect the views of the EPA. Questions related to this document should be addressed to Dr. Bryan Hubbell , U.S. Environmental Protection Agency , Office of Air Quality Planning and Standards, C504 - 0 2 , Research Triangle Park, North Carolina 2771 1 (email: hubbell.bryan @epa.gov).4

**Executive Summary** Previously , the anal ys is of the potential for excess local mercury deposition surrounding U.S. EGUs was located in Appendix G of the National - Scale Mercury Risk Assessment . In response to public comments, we have moved this information to a separate TSD , re - titled the anal ys is, and provided additional technical details . EPA calculated the average EGU - attributable deposition (based on CMAQ modeling of mercury deposition) in the area 500 km around e ach plant and the average EGU attributable deposition in the area 50 km around each plant . The difference between those two values is the excess local deposition around the plant . This anal ys is shows that there is excess deposition of Hg in the local areas around EGUs, especiall y those with high Hg emissions . Although this is not necessarily indicative of higher risk of adverse effects from consumption of MeHg contaminated fish from water sheds around the U.S. EGUs, it does indicate an increased potential th at Hg from U.S. EGUs will impact local watersheds . **Purpose and Scope of Analysis** P ublished research shows that U.S. coal - fired power plants significantl y contribute to local and regional mercury deposition (Caffrey

et al., 2010; Keeler et al., 2006; White et al., 2009) . As discussed in the preamble to the proposed MATS (U.S. EPA, 2011 b ), for the purposes of the appropriate and necessary finding, EPA determined that information on the potential for excess deposition of mercury in areas surrounding power plants would be useful in informing the finding . The purpose of this analy sis was to evaluate at the national - scale whether there existed excess U.S. EGU - attributable deposition of Hg in locations near EGUs , which would indicate that U.S. EGUs are potentiall y contributing to mercury exposures locally

as well as to the potential exposures that result from the combined deposition from U.S. EGUs at a regional scale . This anal y sis does not address total mercury deposition because global sources of mercury deposition account for a large fraction of total mercury deposition, which would not provide useful information regarding the comparison of local and regional mercury deposition from U.S. EGUs . This analy sis is not intend ed to show “mercury hot spots” based on elevated concentrations of methylmercury in fish tissue but rather of mercury deposition hot spots, defined as excess local U.S. EGU - attributable mercury deposition around power plants relative to regional U.S. EGU - attributable deposition . To reduce the confusion about the term “hotspot”, we have re - titled this analy sis to “Potential for Excess Local U.S. EGU Attributable Deposition of Mercury

in Areas n ear U.S. EGUs” . **Methods** EPA e valuated the potential for “hot spot” deposition near U.S. EGU emission sources on a national scale, based on the CMAQ - modeled Hg deposition for the 2005 and 2016 scenarios (U.S. EPA, 2011 a) . Locations of U.S. EGUs in 2005 and 2016 were mapped based on latitude5

and longitudes extracted from the Integrated Planning Model (IPM), a model of the power sy stem used b y EPA . We calculated 50 km and 500 km buffers around each EGU location using the ArcGI S® geographic information sy stem software (Environmental S ys tems Research Institute, 2010) . We then calculated the spatial averages of the U.S. EGU - attributable deposition (obtained by subtracting estimated mercury deposition with U.S. EGU Hg emissions zeroed out from baseline mercury

deposition from all sources including U.S. EGU Hg emissions) across the grid cells with centers falling inside the 50 km and 500 km buffers. The average deposition within the 500 km buffer represents the likely area in which an EGU contributes to regional deposition . The average deposition within the 50 km buffer is used to characterize local deposition plus regional deposition near the EGU . The spatial surfaces were generated by appl yi ng an averaging kernel to the CMAQ deposition estimates for U.S. EGU - attributable m ercury , which have a 12 km by 12 km gridded spatial resolution . Averaging kernels assign a mean value to each grid cell based on the averages of all neighboring grid cell s within a predefined window as a method to smooth the deposition surface . In this cas e, ker

nel sizes were 50 km and 500 km radiuses . Then 50 km radius average values were subtracted from 500 km radius averages to create the map of excess local deposition . If there were onl y general regional mixing of U.S. EGU mercury and relatively

even d eposition across broad regions, then we would expect that the average U.S. EGU attributable deposition within 50 km of an EGU would be about the same as the average U.S. EGU attributable deposition within 500 km of the EGU . The difference between the avera ges of the 50 km and 500 km buffers is thus a measure of excess local deposition . **Results** This analy sis shows that there is excess deposition of Hg in the local areas around EGUs, especiall y those with high Hg emissions . Although this is not necessarily i ndicative of higher risk of adverse effects from consumption of MeHg contaminated fish from water sheds around the U.S. EGUs, it indicate s an increased potential that Hg from U.S. EGUs will impact local watersheds around the EGU sources, and not just impact regional deposition. Figure 1 shows a map of the excess local deposition based on the 2005 CMAQ modeling . Figure 2 shows excess local deposition based on the 2016 Base Case . As shown in Figure 1, there is heterogeneity in the amount of excess local deposition around plants . S ome plants , especiall y those with high mercury emissions, have local deposition that is less than the regional average deposition, suggesting that most of the mercury from those plants is transported regionally , or that other EGU s in the vicinity of those plants dominate the deposition of mercury near the plants.6

Summary statistics for the excess local deposition are provided in Table 1 . Table 1 shows both the mean excess deposition around all U.S. EGUs and the mean excess deposition around just the top 10 percent of Hg emitting U.S. EGUs . Table 1 also shows the excess Hg deposition as a percent of the average regional deposition to provide context for the magnitude of the local excess deposition . In2005, for all U.S. EGU, the exc ess was approximately 1.2 times the average deposition, while local deposition was approximately 3.5 times the regional average for the top 10 percent of Hg emitting U.S. EGU s . By 2016, the absolute levels of excess deposition decrease , but the local exces s still remains approximately 3 times the regional average for the highest 10 percent of Hg emitting U.S. EGUs. This analy sis shows that there is excess deposition of Hg in the local areas around EGUs, especiall y those with high Hg emissions . Although this is not necessarily indicative of higher risk of adverse effects from consumption of MeHg contaminated fish from waterbodies around the U.S. EGUs, it does indicate an increased chance that Hg from U.S. EGUs will impact local waterbodies around the EGU sources, and not just impact regional deposition.7 **Figure 1 .**  **Excess Local Deposition in 2005** 8 **Figure 2 .**  **Excess Local Deposition in 2016 (Base Case)** 9

**Table 1 .**  **Excess local deposition of H**  **g based on CMAQ**  **modeled Hg**  **deposition**

**Category of Results 50km**  **- Radius**  **- Average Excess Local Deposition values**  **(μg/m 2**  **) Mean Across EGUs (percent of regional average** 

**deposition) 2005 Scenario**  **2016 Scenario All U.S. EGU sites with Hg emissions >0** 

**(672 sites)** 1.65 (119%) 0.36 (93%) **Top ten percent U.S. EGU in Hg**

**emissions (67 sites)**  4.89 (352%) 1.18 (302%)

**References** Caffrey , J.M., Landing, W.M., Nolek, S.D., Gosnell, K.J., Bagui, S.S., Bagui, S.C., 2010. “ Atmospheric deposition of mercury and major ions to the Pensacola (Florida) watershed: spatial, seasonal, and inter - annual variability . ” Atmospheric Chemistry and Physics 10, 5425 - 5434. Keeler, G.J., L andis, M.S., Norris, G.A., Christianson, E.M., Dvonch, J.T., 2006. “ Sources of mercury wet deposition in Eastern Ohio, USA. ” Environmental Science &Technology 4 0, 5874 - 5881. White, E.M., Keeler, G.J., L andis, M.S., 2009. “ Spatial Variability of Mercury

Wet Deposition in Eastern Ohio: Summertime Meteorological Case Study Anal ys is of Local Source In fluences. ” Environmental Science &Technology 43, 4946 - 4953. Environmental Sy stems Research Institute (ESRI), 2010. ArcGIS Desktop 10 Service Pack 2 with ArcInfo Licence [Software ]. Environmental Systems Research Institute, Inc. Redlands, CA. 92373. USA. URL : http://www.esri.com U.S. Environmental Protection Agency (U.S. EPA). 2011a. Air Quality Modeling Technical Support Document: EGU Mercury Analysis . EPA - 454/R - 11 - 00 8 . U.S. Environmental Protection Agency (U.S. EPA). 2011b. National Emission Standards for Hazardous Air Pollutants from Coal- and Oil- fired Electric Utility Steam Generating Units and Standards of Performance for Fossil-Fuel-Fired Electric Utility, IndustrialComm ercial-Institutional, and Small Industrial- Commercial-Institutional Steam Generating Units . Federal Register.United States

Environmental Protection Agency Office of Air Quality Planning and Standards Health and Environmental Impacts Division Research Tri angle Park, NC Publication No. EPA - 452/R - 11 - 010 November 2011