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artifact, it is possible that the samples in LM 24 and LM 42 may represent <br /> an onsite occurrence of this constituent. Three other purgeable <br /> halocarbons, 1,2-dichloroethane, 1,1,1-trichloroethane, and 1,1,2- <br /> trichloroethane, were above detection in one sample. However, upon <br /> examination of the duplicate or resampling results, each was found to be <br /> below detection, indicating that these results were likely to be laboratory <br /> or sampling artifacts. <br /> 4.3.5.6.2 Purgeable Aromatics (EPA 602) and Total Petroleum <br /> Hydrocarbons (EPA 418.1) . Of the 89 locations sampled for purgeable <br /> aromatics, only two samples collected in 1987 (LM 47 and LM 52) were above <br /> detection limits for benzene, ethylbenzene, and total xylenes. Resampling <br /> results for these locations in 1988 showed all three compounds to be below <br /> detection limits, suggesting that either these compounds are not persistent <br /> in the groundwater at these locations or that the previous results were <br /> sampling or laboratory artifacts. Toluene was detected in a total of 18 <br /> samples between 1987 and 1990, with concentrations for the 1988 samples <br /> ranging from 0.8 to 6.7 ug/1 , and the highest concentration found, 19 ug/1 , <br /> at Wells LM 47 in 1989 and LM 91 in 1990. All values were below the <br /> California DHS drinking water standard of 100 ug/l . Six of the wells are <br /> located in five isolated areas: LM 61 in Contaminant Area 1, LM 82 <br /> slightly downgradient of Contaminant Area 6, LM 58 and LM 60 slightly <br /> downgradient of Contaminant Area 3, and LM 80 and LM 83, separate and far <br /> offsite. The remaining wells with toluene above detection limits are all <br /> located in or downgradient of Contaminant Area 2, with offsite migration <br /> occurring at least as far downgradient as LM 83 (approximately 2700 feet <br /> beyond the facility boundary) . Within the four well clusters, however, the <br /> toluene concentrations are irregularly distributed with depth, suggesting <br /> that the "source" is probably upgradient of Contaminant Area 2. Given the <br /> irregular spatial distribution of the toluene, and the low concentrations <br /> encountered, it is not possible to define a "source," beyond postulating <br /> undocumented spills or leaks at some time in the past. In the soil <br /> samples, toluene was detected only in Boring SB 71, near the northernmost <br /> tip of the Depot, at a concentration of 52 ug/kg just above the detection <br /> limit of 50 ug/kg) . In addition to the purgeable aromatics, TPHs were also <br /> 4-188 <br />