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Second Quarter,2002 Quarterly Groundwater Monitoring Report Canepa's Car Wash,Park Street Stockton,CA Page 2 • FIELD OBSERVATIONS All monitor wells were purged using a clean, single-use, polypropylene, disposable baler 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 Feld inspection samples from the wells, but a slight to strong petroleum odor was noted in the groundwater inspection samples from wells MW-2, MW-3, and MW-5, and a slight sheen formed on the purge water from monitor well MW-2 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 during the April 2002 monitoring event was approximately 0 19 feet higher than measured the previous quarter The groundwater elevation contours for this monitoring event Indicate a groundwater gradient generally toward the northeast, consistent with previously reported gradient information Table 1 —Groundwater Elevation Data(April 9,2002) Monitoring Well TOC Elevation Screened Depth to Groundwater Groundwater Interval (bgs) Elevation MW-1 1278 45 - 65 2402 -11 24 MW-2 12 18 45 - 65 24 85 -1267 MW-3 13 57 45 - 65 25 33 -11 76 MW-4 1266 40 - 60 23 68 _ -11 02 MW-5 13 06 40 - 60 2493 -11 87 MW-6 13 53 40 - 60 2522 -11 69 MW-7 1286 40 - 60 2435 -11 49 fOC Clevation 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 'Ihe 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 has generally decreased with time in monitor well MW-2 as the groundwater elevation has increased (Figure 6, Attachment A) Benzene concentrations in well MW-5 have generally Increased as the groundwater elevation has increased (Figure 7, Attachment A) It is . important to note that all wells are drowned, with approximately 20 to 15 feet of water above the top of the well screens Ncio� 4 M CONDOR