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Canepa s Car Wash 248 East Park Street Stockton,Calitomia First Quarter Groundwater Monitoring Report,January 2004 Page 3 of 5 • Table 1 —Groundwater Elevation Data (January 2004 Monitoring Well TOC Elevation' Well Casing Depth to Groundwater Groundwater Screen Interval (feet) Elevation(feet-amsl) {feet-bgs} MW-1 1278 45 - 65 27 18 -1440 MW-2 1218 45 - 65 28 10 -1592 MW-3 13 57 45 - 65 2868 -15 11 MW-4 1266 40 - 60 2679 -14 13 M 1306 40 -60 28 33 -1527 MW-6 13 53 40 -60 28 53 -1500 MW-7 1286 40 - 60 2756 -1470 '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 ams]=above mean sea level 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 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 8 8 µg/L, MW-2 at a concentration of 55 pg/L, MW-3 at a concentration of 5 0 µg/L, and MW-6 at a concentration of 5 7 µg/L MTBE was not detected at or above an elevated detection limit of 1000 µg/L in the groundwater sample collected from MW-5 Because the result for the MW-2 sample was inconsistent with historical results and the detection limit for the MW-5 sample was elevated, the samples were re-analyzed 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 and MW-5 at or above the laboratory reported detection limits of 0 5 pg/L and 10 0 pg/L, respectively 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) Concentrations of MTBE in monitor well MW-6 have ranged from < 0 5 to 23 µg/L historically and MTBE was not detected at or above the laboratory reported detection limit of 5 0 lig/L during the July and November 2003 monitoring events, MTBE was detected at a concentration of 5 7 µg/L during the current monitoring event 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 Q� CONDOR