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�L <br /> ATC Associates Inc. <br /> 1117 Lone Palm Avenue, Suite 201 <br /> ("LTC <br /> Modesto, California 95351 <br /> 209-579-2221 <br /> ASSOCIATES i N c . fax: 209-574-2225 <br /> STANDARD OPERATING PROCEDURE <br /> FIELD SOIL VAPOR MONITORING <br /> A representative soil sample will be collected from each sample interval and placed in a ZiplocO plastic <br /> bag. The bag will be sealed and the soil disaggregated. At least ten minutes will be allowed for the soil to <br /> be heated by direct sunlight and for any VOCs in the soil to accumulate in the headspace of the bag, <br /> Volatile gases will then be monitored by inserting the probe of a Photovae 2020 photo ionization detector <br /> (PID). The PID is equipped with a 10.6 eV lamp which is capable of detecting VOCs at concentrations of <br /> 0. 1 parts per million (ppm). The PID will be calibrated on site using 100-ppmV isobutylene-in-air span gas <br /> (equivalent to benzene) prior to drilling operations. PID readings will be recorded in the boring logs. <br />