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w <br /> Laboratory Procedures <br /> All of the samples collected during the field phase of the <br /> survey were analyzed according to EPA Method 602 on a gas chromato- <br /> graph equipped with a flame ionization detector (GC/FID) , but using <br /> direct injection instead of purge and trap. Analytes selected for <br /> standardization were: <br /> methyl tertiary butyl ether (MTBE) <br /> benzene <br /> toluene <br /> ethylbenzene <br /> meta- and para- xylene <br /> ortho-xylene <br /> These compounds were chosen because of their utility in evaluating <br /> the presence of petroleum products such as fuels, lubricating oils, <br /> ar_d non-halogenated solvents. <br /> -�. FID Total Volatiles values were generated by summing the areas <br /> of all integrated chromatogram peaks and calculating using the in- <br /> strument response factor for toluene. Injection peaks, which also <br /> t �y contain the light hydrocarbon methane, were excluded to avoid the <br /> skewing of Total Volatiles values due to injection disturbances <br /> and biogenic methane. <br /> The analytical equipment was calibrated using an instrument- <br /> response curve and injection of known concentrations of the above <br /> f standards. Retention times of the standards were used to identify <br /> the peaksin the chromatograms of the field samples, and their <br /> response factors were used to calculate the analyte concentrations. . <br /> -- The tabulated results of the laboratory analysis of the soil gas <br /> samples are reported in micrograms per liter (uVI) in Tablf 1. <br /> Map sample points with no data shown indicate .that the analyte <br /> concentrations in the samples were below the detection limit. <br /> ,t <br />