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1.r •s <br /> B-2.2 Qualitative Field Screening <br /> An organic vapor detector, such as a Photovac TIP, using a photo-ionization detector (PID) or a <br /> Foxboro flame-ionization detector (FID), is used to provide a qualitative screening of each soil <br /> sample collected from the borings. The organic vapor detector measures ionizable compounds in <br /> the air in parts per million by volume (ppmv). Field calibration is performed using a calibrated <br /> span gas such as 100 ppm isobutylene. Ambient air is used to set the instrument to zero. The <br /> soil contained in the cone of the sampler or in a brass tube is exposed and screened with the <br /> organic vapor detector. The vapor reading is noted as the field screening result. <br />