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Canepa s Car Wash 248 East Park Street,Stockton,CallfomEa Second Quarter Groundwater Mon:tonng Report,April 2005 Page 3 of 5 . Table 1 — Groundwater Elevation Data (April 12, 2005) Well Casing Monitoring Well TOC Elevation t Screen Interval Depth to Groundwater Groundwater (feet) Elevation(feet-amsl) (feet-b s) MW-1 1278 45 -65 2635 -1357 MW-2 1218 45 -65 2731 -15 13 MW-3 1357 45 -65 2787 -1430 MW-4 1266 40 -60 2599 -13 33 MW-5 1 1306 40 -60 2759 -1453 MW-6 1353 40 -60 2785 -1432 MW-7 1286 1 40 -60 1 2678 1 -1392 ' TOC Elevation Elevations are measured from a mark on the top of the well casing and are referenced to NGS benchmark HS0391 using NAVD 88 datum bgs=below ground surface amsl=above mean sea level All wells were surveyed on October 5,2001 A4 measurements are to 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 8015B, 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 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-1 at a concentration of 1 0 microgram per liter (gg/L), MW-3 at a concentration of 2 1 µg/L, MW-4 at a concentration of 1 2 µg/L, MW-6 at a concentration of 5 1 }tg/L, and MW-7 at a concentration of 1 5 µg/L No MTBE was detected at or above elevated detection limits of 5 0 µg/L and 50 pg/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 Iaboratory analytical results in July 1997 for MW-2 and in April 1997 for MW-5 1,2-DCA was detected in the groundwater samples collected from monitoring wells MW-4 and MW-5 at concentrations of 0 7 and 140 gg/L, respectively 1,2-DCA was detected in MW-5 at a concentration of 72 pg/L during the previous sampling event in January 2005 The current monitoring event is the first time 1,2-DCA was detected in monitor well MW-4 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 consistent with historic results, groundwater results from • MW-5 showed a modest decline in analyte constituent concentrations comparable to pre-October 2001 levels 1 4M to CONDOR