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: .. ., . , L. 01 July 2002 AGE-NC Project No. 95-0106_ IPage 3 of 4 3.2. ANALYTICAL•RESULTS OF GROUND WATER SAMPLES Petroleum hydrocarbons we're detected in the ground water samples collected from monitoring wells MW-1 and MW-4; MW-1 is located slightly cross and down-gradient from the former UST I • excavation and MW-4 is loc_ ated further north in the generally down gradient direction.TPH-g was detected at concentrations of 3,000 micrograms per liter (pg/l) and 1,600 µg/f, respectively,,iri samples from the two wells. Benzene was detected,at 960 µg/1 and 31 µg/l in samples from MW-1 I and MW-4 respectively. Other concentrations of volatile aromatic compounds detected in samples . , MW-1 and MW-4 include 170 gg/l and 6.2 µg/1 toluene, 32 µg/l and 30 µg/l ethylbenzene and 220 µg/l and 16 µ.g/1 xylenes, respectively. Neither TPH-g nor BTEX compounds were detected in the,groundwater samples from monitoring wells MW-2, MW-3, MW-5, MW-6 (upper), MW-6 (lower),and'MW-7. MTBE was not detected ground water samples. Anal ical'results of ground water samples are summarized on in any of the grou p yt gr p - . Table 2. The laboratory report(MAt Lab ID 0205429-001A through 0205429-008A), QA/QC and chain-of-custody are included.in Appendix C. • , 4.0. SUMMARY AND CONCLUSIONS The following-conclusions were-drawn from the results of the site investigation: • The ground water-was generally northward on 29 May 2002, and gradients were calculated to range from 0.006 toward the north-northwest to 0.005 toward the northeast. Dissolved-petroleum hydrocarbons were detected in ground water samples from monitoring well MW-4, located down-gradient off-site from the former UST excavation, and,MW-1 located just north of the former UST area. • BTEX compouri_ds were detected in the water samples collected from MW-4 and MW-1. The. ' concentrations of benzene in'the samples, exceeded the -State of California maximum contaminant.level (MCL) of 1 µg11 for drinking water. Analytical data from monitoring wells MW-2 and MW-7 limits the horizontal extent of dissolved hydrocarbons south and east of the site, respectively.-Analytical data from wells MW,3 -and MW-6 limits the extent'of dissolved hydrocarbons northeastward of the site. Analytical data-from monitoring well MW'5 limits the extent of dissolved.hydrocarbons ' north-westward of the site. The extent of dissolved hydrocarbons to the west is not completely defined at this time. ' Continued detection of TPH=g and BTEX in groundwater samples collected from the off-site . well MW4 indicates that the plume of impacted ground water has-migrated off-site towards . ' - Advanced GeoEnvironmental,Inc.