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30' <br /> August 1999 <br /> AGE-NC Project No 97-0312 <br /> Page 7 of 8 ' <br /> z Y , <br />' on Tables 6 and 7 The laboratory report and chain-of-custody identified the samples as MW-2 <br /> t through MW-6 rather than UST-2 through UST-6 <br /> 4 0. DISCUSSION AND CONCLUSIONS t <br />' Based upon data collected from the site, AGE concludes the following <br /> • Primarily silty clay and clayey silt were encountered from surface grade to 80 fe--t bsg Silty <br />' sand was encountered from 80 feet to 100 feet bsg _> <br /> • The highest concentrations of hydrocarbons in soil were detected in borings B 14 and B 15 <br /> Iabove 25 feet bsg Low concentrations of hydrocarbons were detected in the four borings <br /> advanced to depths as great as 40 feet bsg <br /> I • Ground water elevation decreased at the site between the March and June 1999 monitoring <br /> events Ground water was approximately 13 to 14 feet above the screened interval in UST-2, <br /> ry UST-3 and UST-4, five feet above the screened interval in UST-5 and 10 feet above the <br /> screened interval in UST-6 <br /> • Concentrations of hydrocarbons incieased in each monitoring well at the site between the <br />' March and June 1999 sampling events despite water levels being over the screens in all <br /> wells <br /> h <br />' The highest concentrations of petroleum hydrocarbons in ground water were detected in the <br /> „ grab water sample collected from boring B l 7 <br /> • Ground water was measured at a depth of approximately 50 feet bsg during the June 1999 <br /> I ' s monitoring event Ho«ever, ground xN ater was not encountered during drilling=until depths <br /> r of 60 to 80 feet bsg Ground water beneath the'site appears to be confined or piesent in thin <br />' sand lenses above 80 feet bsg r <br /> • 1,2-DCA was detected in,UST-5 at a concentration of 1,100 ppb,=exceeding the State of <br /> California drinking eater maximum contaminant level (MCL) of 0 5 ppb <br />' 50 RECOMMENDATIONS <br /> Based upon data obtained from the site, AGE recommends the following - <br /> • Soil boiulgs advanced during Tune 1999 constituted the first phase of the 5,te'Assessinent <br /> Work Plan, dated 20 December 1999 A brief letter stating anticipated total depths of the <br /> Advanced GeoEns it onmcntal Inc <br /> I - <br /> I <br /> e <br /> } A l <br /> 1 r <br />