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�. I I Wilmom <br /> t. <br /> tested for total organic vapor, measured in parts per million as benzene (ppm: <br /> volume/volume). The instrument was previously calibrated using a 100 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 ionization potential of isobutylene <br /> (7.0 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 i <br /> t' 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 clear Teflon bailer. If no free product is detected,the <br /> irewells are purged o a minimum of four casing volumes of water (or until dryness).. <br /> During purging, temperature, pH, and electrical conductivity were monitored until <br /> 6 stable in order to ensure that a representative sample was obtained. After the water <br /> levels partially recover, groundwater ,awples were collected using a Teflon bailer and <br /> placed into appropriate EPA-approved containers. The stiaiples were labeled, logged <br /> onto chain-of-custody documents,and transported on ice to the laboratory using appro- <br /> �. priate chain-of-custody documentation. 3 <br /> Laboratory Analysis <br /> i <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, ethy.lbenzene, and xylenes (BTEX) compounds. Scil samples were also <br /> analyzed for semi- and non-volatile hydrocarbons calculated as diesel (TPH-diesel}. ; <br /> t The method of analysis for TPH-gasoline was by modified EPA Methods 8015, 8020, <br /> i_ 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 /> Method 8015. This method involves extracting the samples with solvent and examining . <br /> the extract by gas chromatography using a flame ionization detector. All analyses were <br /> performed by a State-certified laboratory. <br /> 6- <br /> 6- <br /> -2 <br /> r+ <br /> 1 <br /> 6' September 30,1991 <br /> 310010/REPORT"_' A-2 p <br />