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Figure 10 shows the proposed typical extraction well design. The well <br /> would be drilled by the hollow stem auger method with ll 7/8-inch outside <br /> diameter auger flights to a total depth of approximately 30 et <br /> Cibelow <br /> ground surface. The well would be constructed using `; n <br /> nside <br /> diameter, Schedule 40, polyvinyl chloride (EVC) well casing and well <br /> screen with a nominal slot size of 0.02 inches. The well would be <br /> - screened between approximately 12 and 30 feet below ground surface. <br /> Lonestar Industries Number 3 sand would be used as the filter medium for <br /> the well screen. A 2-foot layer of bentonite pellets would separate the <br /> filter sand from the neat cement surface sanitary seal. <br /> Groundwater Treatment <br /> Extracted groundwater can be treated on-site by air stripping or by carbon <br /> absorption. Based on an approximated 5-year duration of broundwater <br /> cleanup with an extraction rate of 8 gpm, air stripping has been selected <br /> as the treatment method for this remedial action plan. <br /> Air stripping is a process used to remove chemical contaminants from water <br /> by blowing air through the water and thus separating VOCs from the liquid. <br /> Advantages of air stripping treatment include effectiveness, low cost, <br /> dependability, and operational simplicity. This technology removes over <br /> 99 percent of VOCs from water. VOCs are commonly removed to nondetectable <br /> levels, producing treated water of quality exceeding state drinking water <br /> es <br /> standards. The air stripping material9logy over hichvthe forcing <br /> contaminated upward <br /> water <br /> " through a column of packing d <br /> moves downward by gravity. The VOCs are volatilized and carried with the <br /> airstream into the atmosphere. <br /> The proposed groundwater treatment system consists of one counter current <br /> air stripping tower. Air would be blown through the tower by a pressure <br /> type blower system. Based on a projected flow rate of 8 goniapm l d an <br /> influent chemical concentration of 340 parts per billion (ppb) <br /> a 1-foot diameter by 25-foot high carbon steel air stripper colu npwould <br /> polypropylene be required. The column would be filled with la feet of of ro lene <br /> packing material. approved for potable water service. The cower would be <br /> designed to treat a maximum of 20 gpm of contaminated groundwater. <br /> Maximum vapor phase chemical emissions from rhe air stripping tower are <br /> estimated at approximately 0.33 pounds per day (lbs/d} <br /> ef on <br /> the projected flow rate of 8 gpm and an influent chemical concenBased t ation <br /> of 340 ppb total VOCs (total VOCs detected at MW-6). <br /> emission estimate, the air stripping system would not likely require vapor <br /> phase control, as indicated by the SJCAPCD, since total emissions are well <br /> below 5 lbs/day. <br /> 20 <br />