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i 21 December 2001, AGE-NC Project No. .95-0.106 IPage 3 of 5' 4.2. ' ANALYTICAL RESULTS OF GROUND WATER SAMPLES •,.Petroleumhydrocarbons were detected in the ground water samples collected from monitoring wells ' MW-1 and MW-4; MWA is located slightly cross and down-gradient from the former UST excavation and MW-4 is located further north in the generally down-gradient direction. TPH-g was detected at concentrations of 1.1,000 micrograms per Iiter (µg/1} and 4,760. go, respectively, in ' samples from the two wells. Benzene was detected at 840.µg/l and 63 gg/l-in samples from MW-1 and-MW-4,respectively..Other volatile aromatic compounds were detected at concentrations of 730 µg/l,-and 8.1 gg/1 toluene, 99 µg/1-and 110 µg/l ethylbenzene and'650 µg/I and 68 ggll xylenes in . ' '-samles from MW-1 and MW-4, respectively. , Neither TPH-g nor BTEX compounds were detected in the ground water samples from monitoring r wells MW-2, MW-3, MW-5, MW-6 (upper ), MW-6 (lower) and MW-7. MTBE was not detected 'in any of the ground water samples. Analytical results of ground water samples are summarized on Table 2. The laboratory report(MAI Lab ID 84122 through 84129), QA/QC and chain-of custody 1 are included in Appendix B. ' 5.0. SUMMARY AND CONCLUSIONS ' The following conclusions were drawn from the results of the site investigation: ward on 19 November 2001, and gradients were' The ground water was generally north calculated to range from 0.004 toward' the north-northwest to 0.0'1 -toward the north-.• northeast. • Dissolved petroleum hydrocarbons were detected in ground water samples from monitoring, wells MW-1 and MW-4,'located cross to down-gradient.on-site and down-gradient off-site, respectively, from the former UST excavation. BTEX compounds were detected in the water samples collected from MW-1 and MW-4; the 'concentrations of benzene in both samples exceeded-the` State of California maximum contaminant level(MCL).of.l ug/l for drinking water- The detected concentration of TPH-g.in the sample collected from. MW-1 during the November 2001 monitoring'event. was.,significantly higher •than,samples analyzed since November 1996. Iii addition,the sample collected'frbm MW-1 containedthe highest reported concentration of benzene since monitoring begain in July 1996. • The concentrations'of analytes detected"in the_ground'water samples from MW-4 have incteased significantly since the May 260,1 monitoring event, although they ai•e within the range detected since monitoring began in 1996.- Advanced GeoEnvironmental,Inc.