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Canepa's Car Wash 248 East Park Street,Stockton,California Fourth Quarter Groundwater Monitoring Report,October 2005 Page 3 of 5 • Table I — Groundwater Elevation Data (October 7,2005) Well Casing Monitoring Well TOC Elevation' Screen Interval Depth to Groundwater Groundwater (feet) Elevation(feet) (feet-b s) MW-1 1278 45 -65 2658 -1380 MW-2 12 18 45 -65 2750 -1532 MW-3 1357 45 - 65 2607 -1250 MW-4 1266 40 -60 2621 -13 55 MW-5 1306 40 - 60 2774 -1468 MW-6 1353 40 -60 2795 -1442 MW-71 1286 40 - 60 2699 -14 13 ' TOC Elevation Elevations am measured from a mark on the top ofthe well casing and are referenced to NGS benchmark HS0391 using NAVD 88 datum bgs=below ground surface All wells were surveyed on October 5,2001 All measurements are in feet LABORATORY ANALYTICAL RESULTS The groundwater samples were analyzed by Argon Laboratories of Ceres, California, for total petroleum hydrocarbons quantified as gasoline (TPH-G) by EPA Method 8015M, and for benzene, toluene, ethyl benzene, and total xylenes (BTEX) and selected gasoline oxygenates/additives by EPA Method 8260B The selected gasoline oxygenates/additives included methyl tertiary-butyl ether (MTBE), tertiary-butanol (TBA), di-isopropyl ether (DIPE), ethyl tertiary-butyl ether (ETBE), tertiary-amyl methyl ether (TAME), 1,2-dichloroethane (1,2-DCA), and 1,2-dibromoethane(EDB) • MTBE was detected in the groundwater samples collected from MW-3 at a concentration of 1 0 microgram per liter (gg/L), MW-4 at a concentration of 0 6 }tg/L, MW-6 at a concentration of 2 2 µg/L, and MW-7 at a concentration of 0 9 �ig/L No MTBE was detected at or above elevated detection limits of 5 0 }tg/L and 100 µg/L in the groundwater samples collected from MW-2 and MW-5,respectively Low concentrations of MTBE have historically been detected sporadically in groundwater samples collected from monitoring wells MW-1, MW-3, MW-4, MW-6, and MW-7 MTBE has historically not been detected at or above raised laboratory reported detection limits in MW-2 and MW-5, with the exception of questionable laboratory analytical results in July 1997 for MW-2 and in April 1997 for MW-5 Laboratory analytical results indicated that 1,2-DCA was detected in the groundwater sample collected from MW-4 at a concentration of 0 6 }tg/L This is the second time 1,2-DCA has been detected in this well The concentration of benzene in monitoring well MW-2 has generally had an inverse relationship with groundwater elevation (Figure 6, Attachment A) In contrast, benzene concentrations in MW-5 have generally increased as the groundwater elevation has increased(Figure 7, Attachment A) Historic groundwater analytical data are presented in Table A, Attachment B Analytical results for the current groundwater monitoring event are generally consistent with historic results, groundwater samples from MW-2 and MW-5 showed a modest decline in analyte constituent concentrations comparable to pre- October 2001 levels n Nuvo� L� CONDOR