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Canepa s Car Wash 248 East Park Street,Stockton California Third Quarter Groundwater Monitoring Report,July 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 moderate to 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 It should be noted that the groundwater table has been above the top of all well screens since the August 1996 monitoring event The average groundwater elevation measured dunng the July 2002 monitoring event was approximately 0 63 feet lower than measured 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 The estimated groundwater gradient of 0 0 10 1 ft/ft towards the northeast was calculated using water level data from monitor wells MW-2, M W-4, and M W-6 Table I —Groundwater Elevation Data (July 5, 2002) Monitoring Well TOC Elevation Screened Depth to Groundwater Groundwater Interval (bgs) Elevation MW-1 12 78 45 -65 2457 -11 79 MW-2 12 18 45 -65 2548 -13 30 MW-3 1357 45 - 65 2600 -1243 MW-4 1266 40 -60 2423 -11 57 MW-5 13 06 40 -60 2567 -1261 MW-6 13 53 1 40 - 60 2592 -1239 IL M W-7 1286 1 40 - 60 2493 -1207 '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 Exelchem 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 giaundwater 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 ieporting limits,and the results of the analyses are included in Attachment D The concentration of benzene has generally decreased with time in monitor well MW-2 as the groundwater elevation has increased (Figure 6, Attachment A), the benzene concentration in MW-2 decreased from 49 micrograms per liter (µg/L) in April 2002 to 42 µg/L in July 2002 In contrast, benzene concentrations in well MW-5 have generally increased as the groundwater elevation has increased (Figure 7, Attachment A), the benzene concentration level in MW-5 decreased from 10,000 gg/L in April 2002 to 8,200 gg/L in .July 2002 i i+M' CONDOR