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Canepa s Car Wash 6230 Pacific Avenue Stockton,CA Second Quarter Groundwater Monitoring Report,May 2006 Page 4 of 8 Groundwater sample laboratory analytical results for the seven groundwater monitoring wells sampled during the May 2006 event indicate that none of the constituents of concern were detected at or above the laboratory detection limits in MW-4, MW-9, or MW-12D, which is consistent with historic results for those wells Lohtaminant concentrations detected in monitoring well MW-1 have remained at historic - highs since MW-1 was designated the primary pumping well for the on-Site treatment system in October - 2004 (with the exception of concentrations detected in the groundwater samples collected during the December 1994 and June 1995 monitoring events) EDB was detected for the third consecutive time at the Site in MW-1 at a concentration of 5 2 micrograms per liter(pg/L), and 1,2-DCA was detected for the first time in monitoring wells MW-2 and MW-11 at concentrations of 480 pg/L and 7 9 pg/L, respectively The concentrations of benzene and total xylenes (236 µg/l_ and 143 6-µg/L, respectively) in MW-11 were generally elevated compared to historic Ievels for that well Current groundwater sample laboratory analytical results for monitor well MW-3 are generally consistent with historic results and trends(see historic groundwater data, attached) Benzene and MTBE iso-concentration contour maps are included as Figures 4 and 5, respectively Historic laboratory analytical results from groundwater samples collected from monitoring well MW-3 have indicated a trend of increasing MTBE concentrations since April 11, 2001 (see Figure 6, attached) Groundwater sample laboratory analytical results for the current monitoring event are provided in Table 3, below Laboratory certificates of analyses and chain of custody records are included in Attachment F Table 3—Groundwater Sample Laboratory Analytical Results(May 18,200G Constituent Benzene Toluene Ethvl Total MTBE TPH-G Other Gasoline MCLBenzene Xylenes Oxygenates/Additives - 1 µ@JL 150 Ag/L 700 Ag/L 1 750 Ag/L 13 Ag/L- Analytical Analytical Method-+ 8260B 8260B 8260B 8260B 8260B 8015m 8260B Reporting Litnrts-4 0 5µg/L 0 5µg/L 0 5µg/L 1 0 Ag/L 0 5µg/L Q 05 mg/L 0 5--20µg/L Sample I D MW-1 9,070 _4,920 662 _ 2,952__- _6,820 184 _ 5 2(EDB)- MW-2 12,700 716 I,850 3,442 <1 o 28 9 480(1 2-DCA) -- W MW-3— =... �1-OW —=<1 0 X1_0_ _ X2.0. _-2,760�-0 299+_ _31 4(1,2-DCA) - MW-4 <05 <05 <05 <10 <05_- <005 <05-<200 MW-9 <0 5 <0 5 <0 5 <1 0 <0 5 <0 05 <0 5-<20 0 MW-11 236 101 27 1436 149 0 839 7 9(1,2-DCA) 1 MW-12D <0 5 <0 5 <0 5 <l 0 <05 <0 05 <0 5-<20 0 _ SV-4 24,900 13,600 1,280 4,330 101,000 102 <500-<20,000 M Bold analytical data exceed California MGL(Maximum Contaminant Level) Units Analytical, ` mg/L=milligrams per Mer—parts per million(ppm) S T E X=benzene,toluene,ethyl benzene,total xylenes µg/L=micrograms per Mer=parts per billion(ppb) TPH-G=total petroleum hydrocarbons quantified as gasoline Gasoline oxygenates/additives= methyl tertiary-butyl ether(MTBE),ethanol tertiary-butanol(TBA) di-isopropyl ether(RIPE),ethyl tertiary butyl ether(ETRE) tertiary-amyl methvl ether(TAME) 1,2-dichloroethane(I-2-RCA) 1 2-dibromoethane(t 2-ED13) __*The result for this hydrocarbon is elevated due to the presence of single analyte peak(s) in the quantitation range CONDOR