2022-12-19_GENERAL DOCUMENTS - C1981010

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Generating Station as a result of the combustion of Trapper Mine coal over the next 9.4 years (3.73 kg x 9.4= 35.06 kg). No current data or modeling are available to indicate how much of the mercury that is emitted by either the Craig Station or the Hayden Station is deposited annually within the airshed used in this assessment. However, a recent contaminant modeling effort conducted for the Four Corners Power Plant and Navajo Mine Energy Project(FCPP&NMEP) (EPRI 2014)included detailed modeling of the emissions and deposition of mercury produced at the Four Corners Power Plant. In those models, it was determined that approximately 95 percent of all mercury emitted by the Four Corners Power Plant rises high enough into the atmosphere to be carried by prevailing wind currents and out of the local area analyzed in that effort. Although environmental conditions at the Craig Generating Station may be somewhat different, and our analysis here involves a much smaller amount of coal to be combusted, that modeling effort provides a roughly comparable situation that will assist us with our analysis. Assuming a five percent local mercury deposition rate, 0.187 kg of mercury would be deposited in the local action area each year from the combustion of the proposed Trapper Mine coal at the Craig Generating Station (3.73 kg x 0.05). Over the proposed life of the project(9.4 years), this would equate to 1.76 kg of locally-deposited mercury (0.187 kg x 9.4). An alternative method of estimating the amount of mercury that would be deposited from the proposed project can be derived from an examination of a local mercury deposition monitoring site. A Mercury Deposition Network(MDN)monitoring site is located in Routt County just east of Steamboat Springs on Buffalo Pass. It is at the eastern edge of the airshed analyzed for this project(see map in BA). These monitoring stations measure the levels of mercury that are deposited during precipitation events (i.e. wet deposition). The Buffalo Pass site is the nearest MDN receptor to the action area. The Craig Generating Station is approximately 45 miles west of the Buffalo Pass MDN site. This site has provided data on the wet deposition of mercury to the MDN since 2007. Data from this station in 2013 indicated that there was an annual deposition of 9.757 µg/m2 of mercury at that location (NAPD 2015). Using the results of the emission and deposition modeling conducted at FCPP as a possible scenario, and assuming that the average annual deposition of 9.757 µg/m2 of mercury is equally distributed throughout the Yampa and White River watersheds (a combined total of 34,362 km2); an annual deposition of 335.27 kg of mercury is calculated. The entirety of the Colorado River Fish Action Area is within these two watersheds and is 10,514 km2 (BA, Figure 6). Therefore, assuming an even distribution of mercury deposition,there would be a total of 102.59 kg of mercury deposited annually over the entire Action Area. However, if the results of the FCPP &NMEP model are used,then only five percent of the mercury deposited would be emitted from local sources and the other 95 percent would come from global or other distant sources. If we assume that all local mercury deposition is from the two coal-fired power plants (likely an overestimate), this would indicate that the proportional amount of mercury deposited annually that comes from the two local generating stations is 5.13 kg (5 percent from local sources) across the entire Action Area (102.59 kg x 0.05). The proportion of local mercury attributable to the Craig Generating can be estimated by comparing the ratio of coal that is combusted amongst the two generating stations. According to 46