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Canepa's Car Wash 248 East Park Street,Stockton,California Fourth Quarter Groundwater Monrtonng Report,October 2004 Page 3 of 5 . Table I —Groundwater Elevation Data (October 2004) Monrtonng Well TOC Elevation Well Casing Depth to Groundwater Groundwater Screen Interval (feet) Elevation(feet-amsl) (feet-bgs) MW-1 1278 45 -65 2832 -1554 MW-2 12 18 45 -65 2930 -17 12 MW-3 13 57 45 -65 2990 -1633 MW4 1266 40 -60 2793 -1527 MW-5 13 06 40 -60 2958 -1652 MW-6 13 53 40 -60 2978 -1625 MW-7 1 1286 1 40 -60 1 2876 -1590 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 ams1=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 Argon Laboratories of Ceres, California, for total petroleum hydrocarbons quantified as gasoline (TPH-G) by EPA Method 801513, and for MTBE, benzene, toluene, ethyl benzene, and total xylenes (BTEX) by EPA Method 8260B MTBE has historically been analyzed by EPA Method 8020 with confirmation analyses conducted by EPA Method 826013, however, due to numerous inconsistencies in analytical results, it was decided that EPA Method 8260B would be used as the primary analytical method for future analyses for MTBE and BTEX MTBE was detected in the groundwater sample collected from MW-1 at a concentration of 0 8 micrograms per liter(lig/L), MW-3 at a concentration of 2 2 [tg/L, MW-4 at a concentration of 1 1 jig/L, MW-6 at a concentration of 5 1 pg/L, and MW-7 at a concentration of 1 0 pg/L MTBE was not detected at or above elevated detection limits of 10 0 µg/L and 40 0 µg/L in the groundwater samples collected from MW-2 and MW-5,respectively Low concentrations of MTBE have been detected sporadically in groundwater samples collected from monitoring wells MW-1, MW-3, MW-4, MW-6, 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 questionable laboratory analytical results in July 1997 for MW-2 and in April 1997 for MW-5 The concentration of benzene in monitoring 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) Historic groundwater analytical data are presented in Table A, Attachment B Analytical results for the current groundwater monitoring event are consistent with histone results, groundwater results from MW- 5 showed a modest decline in analyte constituent concentrations comparable to pre-October 2001 levels A summary of the laboratory analytical results for the current monitoring event is presented in Table 2, on the following page Laboratory report sheets indicating analytical methods used, reporting limits, and the results of the analyses are included in Attachment D 1 �� CONDOR