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A .! Canepa's Car Wash 248 East Park Street,Stockton,California First Quarter Groundwater Monitoring Report,January 2003 Page 3 of 5 iTable 1 —Groundwater Elevation Data (January 2003) Monitoring Well TOC Elevation Screened Depth to Groundwater Groundwater Interval(b s) Elevation MW-1 1278 45 -65 2617 -1339 MW-2 12 18 45 - 65 2708 -1490 MW-3 13 57 45 - 65 2756 -13 99 MW-4 1266 40- 60 25 80 -13 14 MW-5 1306 40 -60 2731 -1425 MW-6 1353 40 - 60 2751 -1398 MW-7 12 86 40 - 60 2656 -1370 '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 result for the groundwater sample collected from MW-2 by EPA Method 8020 (330 gg/L) was inconsistent with histoncal results The sample was therefore re- analyzed by EPA Method 8260B The results of the EPA Method 8260B analysis indicated that MTBE as not detected at or above the laboratory reported detection limit of 0 5 gg/L in the sample from MW- 2 Histoncal 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 to MW-5 have generally increased as the groundwater elevation has increased(Figure 7, Attachment A) Concentrations of MTBE 1n monitor well MW-6 have ranged from c 0 5 to 21 gg/L over time, with a general trend of increasing concentration since April 2001 (Figure 8, Attachment A) Low concentrations of MTBE have been detected sporadically to groundwater samples collected from monitor wells MW-1, MW-3, MW-4, and MW-7 MTBE has htstoncally 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 to April 1997 for MW-2 i IL 4) CONDOR