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Canepa's Car Wash 248 East Park Street,Stockton,California Fourth Quarter Groundwater Monitoring Report,October 2002 Page 2 of 5 • FIELD OBSERVATIONS All monitor wells were purged using a clean, single-use, polypropylene, disposable bailer Approximately three well casing volumes of water were purged from each well The purged water from each well was placed in 55-gallon drums and left on site pending laboratory analytical results No sheen or separate phase petroleum was noted in field inspection samples from the wells, but a strong petroleum odor was noted in the groundwater inspection samples from wells MW-2 and MW-5 GROUNDWATER ELEVATIONS AND GRADIENT The static water level in each well was measured to the nearest 0 01-foot with a battery-operated, flat tape, water-level meter The groundwater monitoring field forms and groundwater measurement field form are included in Attachment C The groundwater table has been above the top of all well screens since the August 1996 monitoring event The average groundwater elevation measured during the October 2002 monitoring event was approximately 1 60 feet lower than that of the previous quarter The groundwater elevation contours for the current monitoring event indicate a groundwater gradient generally toward the northeast, consistent with previously reported gradient information Table 1 —Groundwater Elevation Data (October 17, 2002) Monitoring Well TOC Elevation Screened Depth to Groundwater Groundwater Interval(bgs) Elevation MW-1 1278 45 -65 2618 -1340 MW-2 1218 45 -65 2710 -1492 MW-3 1357 45 -65 2760 -1403 MW-4 1266 40-60 2582 -13 16 • MW-5 1306 40- 60 2731 -1425 MW-6 13 53 40 - 60 2745 -1392 MW-7 1286 40 -60 2657 -1371 'TOC Elevation Elevations are measured from the top of the well casing and are referenced to NGS benchmark HS0391 using NAVD 88 datum All wells were surveyed on October 5,2001 All measurements are in feet LABORATORY ANALYTICAL RESULTS The groundwater samples were analyzed by Excelchem Environmental Laboratories, Inc for total petroleum hydrocarbons quantified as gasoline (TPH-G) by EPA Method 8015m, for benzene, toluene, ethyl benzene, and total xylenes (BTEX) by EPA Method 8020, and for selected gasoline oxygenates/additives by EPA Method 8260B The gasoline oxygenates/additives include methyl tertiary-butyl ether (MTBE), ethanol, tertiary-butanol, di-isopropyl ether (DIPE), ethyl tertiary-butyl ether (ETBE), and tertiary-amyl methyl ether (TAME) Historical groundwater analytical data are presented in Table A, Attachment B A summary of the laboratory analytical results is presented in Table 2, on the next page Laboratory report sheets indicating analytical methods used,reporting limits,and the results of the analyses are included in Attachment D The concentration of benzene in monitor well MW-2 generally has 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) Concentrations of MTBE in monitor well MW-6 have ranged from <0 5 to 21 �ig/L over time, with an general trend of increasing concentration since April 2001 (Figure 8, Attachment A) Low concentrations of MTBE have been sporadically present in groundwater samples collected from monitor well MW-3 Concentrations of • MTBE slightly above the laboratory detection limit have historically been detected in the monitor wells on the L1� CONDOR