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mills, hammer mills,or jet mills. The ground material then is classified by wet screening,dry — screening,or air classification. At some plants,after initial crushing and screening,a portion of the sand may be diverted to construction sand use. After initial crushing and screening,industrial sand and gravel are washed to remove unwanted dust and debris and are then screened and classified again. The sand(now containing 25 to 30 _ percent moisture)or gravel then goes to an attrition scrubbing system that removes surface stains from the material by rubbing in an agitated, high-density pulp. The scrubbed sand or gravel is diluted with water to 25 to 30 percent solids and is pumped to a set of cyclones for further — desliming. If the deslimed sand or gravel contains mica, feldspar,and iron bearing minerals, it enters a froth flotation process to which sodium silicate and sulfuric acid are added. The mixture then enters a series of spiral classifiers where the impurities are floated in froth and diverted to waste. The purified sand,which has a moisture content of 15 to 25 percent, is conveyed to drainage bins where the moisture content is reduced to about 6 percent. The material is then dried — in rotary or fluidized bed dryers to a moisture content of less than 0.5 percent.The dryers generally are fired with natural gas or oil, although other fuels such as propane or diesel also may be used. After drying,the material is cooled and then undergoes final screening and classification — prior to being stored and packaged for shipment. Emissions from the production of sand and gravel consist primarily of particulate matter(PM) and particulate matter less than 10 micrometers (PM10) in aerodynamic diameter,which are emitted by many operations at sand and gravel processing plants,such as conveying, screening, — crushing,and storing operations. Generally,these materials are wet or moist when handled, and process emissions are often negligible. A substantial portion of these emissions may consist of heavy particles that settle out within the plant area. Emissions from dryers include PM and PM 10,as well as typical combustion products including CO and NOx. In addition,dryers may be sources of volatile organic compounds(VOC)or sulfur oxides (SOx)emissions, depending on the type of fuel used to fire the dryer. With the exception of drying,emissions from sand and gravel operations primarily are in the form of fugitive dust, — and control techniques applicable to fugitive dust sources are appropriate. Some successful control techniques used for haul roads are dust suppressant application,paving,route modifications, and soil stabilization; for conveyors,covering and wet suppression; for storage — piles,wet suppression,windbreaks,enclosure, and soil stabilizers; for conveyor and batch transfer points,wet suppression and various methods to reduce freefall distances (e. g.,telescopic chutes, stone ladders,and hinged boom stacker conveyors); and for screening and other size classification, covering and wet suppression. Wet suppression techniques include application of water, chemicals and/or foam,usually at crusher or conveyor feed and/or discharge points. Such spray systems at transfer points and on material handling operations have been estimated to reduce emissions 70 to 95 percent. Spray — systems can also reduce loading and wind erosion emissions from storage piles of various