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Quarterly Momtonng Report October 1999 Canepa's Car Wash(Pacific Avenue) November 22, 1999 Page -5 ' from 20 98 to 21 98 feet bmsl Since November 1994, the depth to groundwater at the site has ranged from approximately 53 Leet to 32 5 feet bgs The groundwater elevation contour map (Figure 3, ' Appendix A) indicates groundwater mounding in the center of the site in the vicinity of MW-1 and MW- 2 The groundwater mounding effect identified during the October 1999 quarterly groundwater monitoring event is generally consistent with previous monitoring results ' The fourth quarter, 1999, laboratory analytical results are generally consistent with recent historical laboratory analytical results The laboratory analytical results indicate that none of the analytes of interest were detected at or above the laboratory reported detection limits in the groundwater samples collected from MW-5, MW-6, MW-7, and MW-8 BTEX, TPH-G, and MTBE were detected in the groundwater samples collected from MW-1, MW-2, and SV-3 The concentration of MTBE (640 µg/1) reported in the sample collected from MW-1 is significantly lower than the previous concentration reported in July 1999 and represents a return to historical concentrations for this constituent in groundwater samples collected from this well The concentrations of BTEX and TPH-G reported in the sample collected from MW-2 are significantly lower than the previous concentrations reported in July 1999 The concentration of TPH-G (300 mg/1) reported in the sample collected from MW-2 represents a new high for this constituent in groundwater samples collected from this well This result may not be significant however, because EPA Method 602 is highly susceptible to matrix interference for MTBE analysis Benzene (5 9 4g/1) and toluene (1 4 µg/1) were detected in the groundwater sample collected from MW-3 for the first time since June 1995 The concentrations of BTEX, TPH-G, and MTBE detected in the sample collected from SV-3 are significantly lower than the previous concentrations reported for these constituents in July 1997 ' 6.0 RECOMMENDATIONS In the Report — Soil and Groundwater Investigation, dated June 12, 1998, Condor recommended additional soil and groundwater investigation to further characterize the extent of contamination at the site In a faxed document dated July 28, 1998, Mr Ron Rowe of the PHS/EHD requested a work plan describing the recommended additional investigation activities In response to Mr Rowe's request, I Condor submitted a work plan dated November 17, 1998, describing proposed additional investigative activities including the installation of additional monitor wells and soil borings Upon review of the work plan, Mr Rowe requested that the work plan be modified to include deep aquifer characterization with a cone penetrometer Condor has prepared a work plan addendum in a letter dated May 18, 1999, describing the requested deep aquifer characterization and is awaiting PHS/EHD approval The next quarterly monitoring event is scheduled for January 2000 If you need additional information or have any questions, please contact us at(209) 234-0518 Respectfully -,ubmitted, CONDOR EARTH TECHNOLOGIES, INC 01 DONALD F KAESSF Todd C Hafner 'ald F Kresse Senior Geologist LP N�'1;43E] dal fornia Registered �,�� ologist#6430 P 11707 Cnnepa-Pacrfic\Quvterly Momrorn%\19"octoberlQ d�F CAL 13 �� CONDOR