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23 February 1998 <br /> AGE-NC Project No 95-0130 <br /> Page 4 of 5 <br /> detected for the first time in water samples collected from wells MW-2 VW-1 C, VW-2A <br /> and VW-3A <br /> • Concentrations of benzene detected in samples collected from wells MW-I through M W-3, <br />' MW-5 VW-IC V W-2A and VW-3A ,N ere above the State of California Maximum <br /> Contaminant Level (MCL) for drinking water of 1 0 ppb The approximate distribution of <br /> dissolved benzene in NNelIs with appropriate screen intervals (MW-5, VW-1, VW-2 and VW- <br /> 3) is depicted in Figure 4 Well screen interN als are listed in Table 1 <br /> • Concentrations of toluene vN ere abo-N e the MCL of 150 ppb in wells VW-1 C, VW-2A and <br />' VW-3A concentiations of ethylbenzene NN ere aboNe its MCL of 700 ppb in wells VW-1 C <br /> VW-2A and V W-3A concentrations of xylenes were above the MCL of 1,750 ppb in wells <br /> VW-1C VW-2A and VW-3A <br />' • Utilizing EPA methods 8020 and 8260 concentrations of MTBE were detected above the <br /> laboratory reporting limits in samples from Aells MW-1 MW-3 VW-1C VW-2A and VW- <br /> 3A <br /> • Utilizing EPA method 8260 concentrations of DIPE TAME, and ETRE were not detected <br /> above the laboratory repoi ting limits in any samples <br /> • The elex ated concenti ations of pets oleum hvdrocai bons detected in samples collected from <br /> wells VW-IC VW-2a and VW-3A indicates that these «ells are within the dissolved <br />' petroleum hydrocaibon core area of the plume <br /> A plot of depth to ground eater and TPH-g concentrations over time (Appendi\ E) suggests <br /> a positive correlation at MW-5 bemeen increasing ground water depths and increasing TPH- <br /> g concerntiations <br /> 50 RECOMMENDATIONS <br />' Based on the results of this and prey sous monitoring e\ents and on AGE s familiarity \\itlz the site, <br /> AGE recommends <br />' • Installation of the rennediation system should commence upon regulatory approval of the <br /> Remedial Action Roi k Plan, dated 03 July 1997, submitted to the PHS-EHD for an in-situ <br />' soil vapor emiaction/air spaiging system Aithin the petroleum hydrocarbon ` core area ' <br /> • Utilization of wells \ W-I C VW-2A and VW-')A for characterization of ground water <br /> conditions in the ` core area <br />' • Continued quarterly ground eater monitoring The next quarterly monitoring and sampling r <br /> is scheduled for March 1998 <br /> 4rhaucu!Ckuf tntruunuut tl,1ite <br />