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tete- d for total organic vapor, measured in parts per million as benzene (ppm: <br /> t� <br /> volume/volume). Trie insvument way previously calibrated usin0 2100 ppm - <br /> isobutylene standard (in air) and a sensitivity factor of 0.7, which relates the photo- <br /> ionization sensitivity of benzene (10.0 ppm) to the iodization potential of isobutylene <br /> (7A ppm). Results of these tests were used to assist in selection of samples for <br /> laboratory analysis. <br /> Groundwater Sampling <br /> � The groundwater sampling was performed using techniques approved by the Regional <br /> ' Water Quality Control Board. The sampling procedure consists of first measuring the <br /> water level in each well, and checking each well for the presence of floating petroleum <br /> product using an optic probe or a clear Teflon bailer. If no free product is detected, the <br /> wells are purged of a minimum of four casing volumes of water (or until dryness). <br /> During purging, temperature, pH, and electrical conductivity were monitored until <br /> stable in order to ensure that a representative sample was obtained. After the water <br /> levels partially recover, groundwater samples were collected using a Teflon bailer and <br /> placed into appropriate EPA-approved containers. The samples were labeled, log;�d <br /> onto chain-of-custody documents,and transported on ice to the laboratory using,appro- <br /> priate chain-of-custody documentation. <br /> F <br /> Laboratory Analysis <br /> Selected soil and groundwater samples were analyzed in the laboratory for the presence <br /> ' of total petroleum hydrocarbons calculated as gasoline (TPH-gasoline), and benzene, <br /> toluene, ethylberaene, and xylenes (BTEX) compounds. Soil samples were also <br /> analyzed for semi- and non-volatile hydrocarbons calculated as diesel (TPH-diesel). <br /> F V The method of analysis for TPH-gasoline was by modified EPA Methods 8015, 8020, <br /> - and 5030. Final analysis was performed by the purge-and-trap technique with final <br /> { detection by gas chromatography using a flame-ionization detector and a photo- <br /> { ionization detector. The method of analysis for TPH-diesel was by modified EPA <br /> r Method$015. This method involves extracting the samples with solvent and examining <br /> a flame ionization detector. All analyses were <br /> the extract by gas chromatography using <br /> performed by a State-certified laboratory. <br /> i <br /> saptcmber 30,1991 <br /> ter <br /> A-2 <br /> 310010/REPOR7`3 <br /> _yti <br />