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„ Canepa s Car Wash 248 East Park Street Stockton,California Second Quarter Groundwater Monitoring Report,May 2004 Page 3 of 5 iTable 1 —Groundwater Elevation Data(May 2004 Monitoring Well TOC Elevation Well Casing Depth to Groundwater Groundwater Screen Interval (feet) Elevation(feet-amsl) (feet-bgs) MW-1 12 78 45 - 65 2664 -13 86 MW-2 12 18 45 - 65 2749 -15 31 MW-3 1357 45 - 65 2806 -1449 MW-4 1266 40 - 60 2628 -1362 MW-5 1306 40 - 60 2770 -1464 MW-6 13 53 40 - 60 2794 -1441 MW-7 1286 40 - 60 2699 -14 13 '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 All measurements are to feet LABORATORY ANALYTICAL RESULTS The groundwater samples were analyzed by Excelchem Environmental Laboratones, 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 methyl tertiary-butyl ether (MTBE)by EPA Method 8020 The EPA Method 8020 analyses indicated that MTBE was detected in the groundwater sample collected from MW-1 at a concentration of 41 µg/L, MW-2 at a concentration of 16,000 [ig/L, MW-3 at a concentration of 140 µg/L, and MW-5 at a concentration of 7,000 pg/L MTBE was not detected at or above a detection limit of 5 0 pg/L in the groundwater samples collected from MW-4, MW-6, and MW-7 Because the results for the MW-1, MW-2, MW-3, and MW-5 samples were inconsistent with historical results, the samples were reanalyzed for MTBE by EPA Method 8260B The results of the EPA Method 8260B analyses indicated that MTBE was not detected in the samples from MW-2, MW-3, and MW-5 at or above the laboratory reported detection limits of 5 0, 5 0, and 50 µg/L, respectively MTBE was detected at a concentration of 1 1 �tg/L in the groundwater sample collected from MW-1 Historical groundwater analytical data are presented in Table A, Attachment B A summary of the laboratory analytical results for the current monitoring event 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 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) Low concentrations of MTBE have been detected sporadically in groundwater samples collected from monitor wells MW-1, MW-3, MW-4, and MW-7 MTBE has historically not been detected at or above laboratory reported detection limits in MW-2 and MW-5, with the exception of a questionable laboratory analytical result in April 1997 for MW-2 i S �� CONDOR