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i Quarterly Monitoring Report April 2000 i Canepa s Car Wash(Park.Street) Page 5 . in samples collected front tilts well None of the analytes of concern were detected in the groundwater i Sample collected tion, immonitoi well MW-4 TPH-G and all BTEX constituents were detected in the (ri-oundwatei samples collected fiom MW-2 and MW-5 Low concentiations of TPI -G were detected rn the bioundivatei samples collected from MW-I and MW-7 Low concentrations of toluene and TPH-G i were detected in the 4groundwater sample collected fiom MW-3 A low concentration of MTBE was detected In the (-Tioundwater sample collected trom MW-6 i The second quarter 2000, labolatoiy analytical results indicate that the area of groundwater contamination most Impacted by petroleum hydiocarbons is In the northern portion of the site in the vicinity of monitoi wells MW-2 and MW-5 Concentrations of benzene, toluene, and total xylenes have decreased over time I monitor well MW-2, but have increased in monitor well MW-5 (Figures 7-9, Appendix A) Concentrations of MTBE in itmonitor well MW-6 have decreased slightly ovei time (Figure 10) In general, (-oncentiations of analytes have decieased as the groundwater elevation has increased, i except in MW-5, which has seen an increase in contamination It is important to note that since all of the nmonitoiin- wells are drowned, we aie probably not sampling the most shallow water with the highest concentiation of contamination Since Nve are not sampling these high concentrations, the actual i concentrations of the plumes have not been measured and are not known According to Figures 4 and 5, the plumes probably extend beyond the site, therefore the current monitoring wells can not measure the extent of the contaminant plumes i6.0 RECOMMENDATIONS Condor recommends that additional investigation be conducted to further characterize the extent of �. contamination at the site, including the installation and sampling of additional monitor wells rhe existing monitor wells at the site are scieened well below the current groundwater table and do not provide sufficient infoi matron pertaining to the vadose zone/groundwater interface These wells should be replaced with well screens that intercept the groundwater table A work plait describing the recommended installation of tour additional monitor wells (MW-8 through MW-I 1) was prepared and submitted to the PHS/EHD in November 1998 The work plan is currently pending approval by the PHS/EHD Condoi Ieconmmends the following • That the woi k plan submitted to the PHS/EHD be approved • The installation of new monitor wells that are properly screened across the water table IIf You need additional infoiniation of have any questions, please contact us at(209) 234-0518 � p GEO(�G�� I Respectfully submitted, ��, CONDOR EARTH TECHNOLOGIES, INC pp pp,V1D K• � 2 o� Lee H Moise David K Wood �q1Z OF ivp��F Staff Geologist California Registered Geologist 96532 11PDC'V'1:OIG(TS12Pib( nrep��l'iii.5c)uaYeilyivlonitrnin,Reportsl2UUf1Apn11Q1�9R?p{Ydrn I itJ CONDOR