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materials 80 to 90 percent. Control efficiencies depend upon local climatic conditions, source <br /> properties and duration of control effectiveness. Wet suppression has a carryover effect <br /> downstream of the point of application of water or other wetting agents, as long as the surface <br /> moisture content is high enough to cause the fines to adhere to the larger rock particles. <br /> In addition to fugitive dust control techniques, some facilities use add-on control devices to <br /> reduce emissions of PM and PMIO from sand and gravel processing operations. Controls in use <br /> include cyclones,wet scrubbers,venturi scrubbers,and fabric filters. These types of controls are <br /> ` rarely used at construction sand and gravel plants,but are more common at industrial sand and <br /> gravel processing facilities. <br /> ` Air emissions were determined for the operation of the crushed stone processing units. The air <br /> emission calculations accounted for the proposed production levels,the number,types, and size <br /> of equipment, and the type of material processed and emission controls, if any. The emission <br /> factors were determined using the methodology found in Section 11.19 of EPA's AP-42. Table <br /> AQ-1 presents the emission factors for the stone processing operations. A substantial portion of <br /> ` the air emissions from gravel processing consists of heavy particles that may settle out within the <br /> plant area. <br /> ;` Fugitive sources include the transfer of sand and aggregate,truck loading,mixer loading, vehicle <br /> traffic, and wind erosion from aggregate storage piles. The amount of fugitive emissions <br /> generated during the transfer of sand and aggregate depends primarily on the surface moisture <br /> content of these materials. <br /> TABLE AQ-1 <br /> EMISSION FACTORS FOR STONE PROCESSING <br /> ir. Uncontrolled Controlled <br /> Number of Emission Factor Emission Factor <br /> Emission Point Equipment (lbs/ton of material) (lbs/ton of material) <br /> Conveyor Belt 41 0.0014 0.000048 <br /> Feeder/Hopper 4 0.0055 0.0014 <br /> ! Screens 9 0.015 0.00084 <br /> 6. <br /> Crushers 3 0.0024 0.00059 <br /> Washer/Scrubber 5 NA 0.00010 <br /> Truck Loading 3 0.000016 NA <br /> Truck Unloading 3 0.0001 NA <br /> V <br /> NA=Not applicable. <br /> SOURCE:Compilation of Air Pollutant Emission Factors,AP-42,Fifth Edition,Volume I:Stationary Point and Area <br /> Sources,Section 11.19.2 Crushed Stone Processing,January, 1995. <br /> 3 <br /> i <br /> t. <br />