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3 Canepa's Car Wash 248 East Park Street,Stockton,California Second Quarter Groundwater Monitoring Report,April 2003 Page 3 of 5 • Table 1 —Groundwater Elevation Data (April 2003) Monitoring Well TOC Elevation Screened Depth to Groundwater Groundwater Interval(b s) Elevation MW-1 1278 45 - 65 2599 -1321 MW-2 12 18 45 - 65 2683 -1465 MW-3 1357 45 -65 2731 -1374 MW-4 1266 40-60 2564 -1298 MW-5 1306 40-60 2701 -1395 MW-6 13 53 40 -60 2719 -1366 MW-7 1286 40 -60 2633 -1347 '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 methyl tertiary-butyl ether (MTBE) by EPA Method 8020 The MTBE results for the groundwater samples collected from MW-2 and MW-5 by EPA Method 8020 (600 pg/L and 350 µg/L) were inconsistent with historical results The samples were therefore re-analyzed by EPA Method 8260B The results of the EPA Method 8260B analyses indicated that MTBE was not detected at or above the laboratory reported detection limit of 5 0 µg/L in the samples from MW-2 and MW-5 • 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 23 gg/L over time and was at California EPA's maximum contamination level (MCL) of 13 micrograms per liter (µg/L) for April 2003 (Figure 8, Attachment A) This reflects a downtrend from a peak of 21 4g/L in April 2002 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 �ir 11 CONDOR