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• The annual average impact is difficult to predict accurately <br /> in the absence of measured wind direction statistics for the <br /> site. Assuming that the most frequent wind direction (from <br /> a westerly sector) occurs approximately 15% of the time <br /> during a year, and the mining operation is active five days <br /> per week, the highest annual average at the easterly site <br /> boundary would be on the order of 3 pg/m3. This concen- <br /> tration is 5% of the secondary annual standard. <br /> The concentration estimates given here are, of necessity, <br /> approximate, but they are believed to be conservative. <br /> The estimates are also consistent with experience and field <br /> • monitoring results from other Flatiron operations in the <br /> Boulder area. All results indicate that contributions to <br /> ambient TSP concentrations by mining and related activity <br /> will represent a small fraction of allowable limits . When <br /> a background concentration (approximately 30 ug/m3) is added <br /> to the predicted mining contributions, total concentrations <br /> will remain below National Ambient Air Quality Standards <br /> established to protect public health and welfare. <br /> Discussion <br /> • As indicated in the preceeding sections , gravel mining at <br /> the Deepe Farm site will result in the release of dust and <br /> suspended particulate matter to the atmosphere. These will <br /> C• G-13 <br />