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R f � a total organic vapor,measured in parts per million as benzene(ppm: 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 tl-ese tests were used to assist in selection of samples for Iaboratory analysis. Groundwater Sampling The groundwater sampling was performed using techniques approved by the Regional Water Quality Control Board. 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 pYobe 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 appro- priate chain-of-custody documentation.. } Laboratory Analysis Selected soil and groundwater samples were analyzed in the laboratory for the presence of low-boiling hydrocarbons (calculated as gasoline), and benzene, toluene, ethylben- zene, and xylenes (BTEX) compounds. Selected soil samples were also analyzed for high-boiling hydrocarbons such as diesel,kerosene and waste oil. The method of analy- sis for low-boiling hydrocarbons (calculated as gasoline and BTEX compounds) is 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 high- boiling hydrocarbons (calculated as kerosene, diesel, and waste oil)is by modified EPA Method 8015. This rnethod involves extracting the samples with solvent and examining the extract by gas chromatography using a flame ionization detector. Analysis for volatile organic hydrocarbons was performed by EPA Methods 624 and 8240 for groundwater samples,and by EPA Methods 601 and 8010 for soil samples.The samples were prepared by the purge and trap method prior to introduction into the gas chromatograph, and final detection was by mass spectrometry. Quality control method -- --- ------ —blanks_for...soil-and groundwater,which_were_produced.within_the._-laboratory,_shoved._____.__-___.____._____.____________.___ occasional detectable concentrations of methylene chloride and acetone. These blanks do not represent soil or groundwater sampled at the site, and therefore do not reflect 310010/REPORT A-2 February 13,1991