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with aluminum foil secured under a ring-type threaded lid. The jar is warmed for approximately 20 minutes, then the foil is pierced and the head-space within the jar is tested for total organic vapor, measured in parts per million as benzene (ppm: V volume/volume). The instrument was previously calibrated using a 100 ppm isobutylene standard (in air) and a sensitivity factor of 0.7, which relates the photo- ionization sensitivity of benzene (10.0 ppm) to the ionization potential of isobutylene (7.0 ppm). Results of these tests were used to assist in selection of samples for laboratory analysis. Groundwater Sampling The groundwater sampling was performed using techniques approved by the Regional Water Quality Control Board (RWQCB). The sampling procedure consists of first measuring the water level in each well, and checking each well for the presence of floating petroleum product using an optic probe or a clear Teflon bailer. If no free product is detected, the wells are purged of a minimum of four casing volumes of water (or until dryness). During purging, temperature, pH, and electrical conductivity were monitored until stable in order to ensure that a representative sample was obtained. After the water levels partially recover, groundwater samples were collected using a Teflon bailer and placed into appropriate EPA-approved containers. The samples were labeled, logged onto chain-of-custody documents, and transported on ice to the laboratory using appropriate chain-of-custody documentation. Laboratory Analysis Selected soil and groundwater samples were analyzed in the laboratory for the presence of total petroleum hydrocarbons calculated as gasoline (TPH-gasoline), and benzene, toluene, ethylbenzene, and xylenes (BTEX) compounds. Soil samples were also analyzed for semi- and non-volatile hydrocarbons calculated as diesel (TPH-diesel). The method of analysis for TPH-gasoline was by modified EPA Methods 8015, 8020, and 5030. Final analysis was performed by the purge-and-trap technique with final detection by gas chromatography using a flame-ionization detector and a photo- ionization detector. The method of analysis for TPH-diesel was by modified EPA Method 8015. This method involves extracting the samples with solvent and examining the extract by gas chromatography using a flame ionization detector. All analyses were performed by a state-certified laboratory. 3100103/REPORT3 A - 2 June 11, 1992 r