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r <br /> <br />Haul roads were simulated using the volume source option in ISC. The spacing between <br />volume sources alone the road was approximately 100 - l~0 meters. The initial sigma y and <br />sigma z values were selected based on the source spacing following guidance in the [SC model <br />users manual. <br />Wind erosion sources such as coal storage piles and associated vehicle activities un these <br />piles were simulated as area sources. Where the area source was irregularly shaped. multiple <br />azea sources were employed to obtain the best fit [o the actual emissions. <br />J.3 RECEPTOR INPUTS <br />Model receptors were arransed in rectangular srids surrounding the propem boundary of <br />MCC's West Elk ~[ine. Figure 4-1 displays the West Elk ~~Iine ambient air boundary along with <br />the ISC model receptor grid. Receptors were placed at 100-meter intervals along the ambient air <br />boundary and at ?~0-meter intervals out to approximately X00 meters from the boundary. The <br />boundary receptors and 3d0-meter grid receptors were applied only along the northern bounden'. <br />because the majority of West Elk emission sources are in close proximity to this boundary. <br />Otherwise. a X00-meter resolution receptor grid was employed. Limiting the geographic eaten[ <br />of the fine receptor grid was done to provide for reasonable model execution times. One the <br />maximum impact location was identified a "hot-spot" receptor grid with ~0-to-100 meter spacing <br />was added around maximum impact receptors. The "hot spot' modeling will be included in [he <br />updated modeling study with the complete year of meteorological data. <br />The ambient air boundary represents a combination of fenced propeay plus physical <br />barriers from steep terrain. All of [he area excluded from ambient air lies within propem owned <br />and controlled by MCC. A physical barrier (fence) exists along the northern property boundary <br />where public encroachment to MCC's propem (along Colorado Hiehway I33 and the North <br />Fork of the Gunnison River) is most likely (and where the maximum~P:~i-10 model predictions <br />occur). [n addition. ivfCC plans [o locate additional fencing along hydrological drainages and <br />other spots of potential public access. [n steep topoeraphy, fencing is impractical and also <br />interferes with wildlife migration. However. in these areas. the topoeraphy itself presents a <br />sufficient physical barrier to public access. <br />In addition to the receptor grid described above. receptors were placed at the location of <br />two other nearby mining operations (Oxbow dining and Bowie Resources j. Nu other air <br />pollution sources exist in the vicinity of [he West Elk dine. The [SCST~ results at [hose <br />receptors were compared to APCD si~ni~icant impuct lore/s to determine the need for a modeling <br />study of cumulative impacts. [t (CC's impacts were found to be below the signiJicmv import <br />levels. a cumulative Pal-l0 modeline study is unnecessary under Colorado's mudding <br />guidelines. Fur PSI-l0. the significant impact levels are LO micrograms per cubic meter [annual <br />mean) and ..0 micrograms per cubic meter (maximum'_•1-hour average[. <br />Terrain elevations Cot receptors were de;ermined Crom ~S Geoloeical Sur:ev i~SGS <br />digital terrain data for the area. Terrain heights for receptors were interpolated using the nearest <br />USGS digital terrain points. <br />~-- <br />