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California Department of Transportation August 17, 1999 <br /> Stockton Maintenance Station, Stockton, California Project No 103872-02 <br />' In well VW-1 concentrations of TPH-G increased from non detect levels to 550 ug/I and benzene <br /> decreased from 24 ug/1 to 8 ug/l A duplicate sample (VW-11) was taken at VW-1 and the ana- <br />' Iytical data was within 10% of the primary samples <br /> In Nell VW-2 concentiattons of TPH-G increased from 2 100 ug/I to 5 700 ug/1 since Apel 1999 <br /> and TPH-D decreased from 320 ug/l to non detect levels Benzene decreased from 1,500 ug/l to <br /> I865 ug/1, toluene decreased from 460 ug/l to 57 ug/1, ethylbenzene decreased from 750 ug/l to <br /> non detect levels, and total xylenes decreased fiom 1,950 ug/l to 302 ug/l MTBE concentrations <br />' decreased from 83 ug/I to 76 ug/l <br />' According to laboratory analytical data using EPA method 8260B additional compounds were <br /> detected in samples from various on-site wells These compounds include 1,2-di chloro ethane, n- <br />' butylbenzene, isopropylbenzene, tert-butylbenzene, and 1,3,5-tiimethylbenzene <br /> A trip blank (TB-1) was placed in the cooler during transport of the samples and analyzed using <br /> method 8260B When the trip blank was analyzed by AL a concentration of 10 ug/l of chloro- <br /> form was detected in the sample No other compounds were detected <br />' 6 RECOMMENDATIONS <br /> Based on the results of the Second Quarter 1999 groundwater monitoring analytical results, <br />' which indicated elevated concentration of TPH-G, TPH-D, BTEX, and/or MTBE Ninyo & <br /> Moore recommends that quarterly groundwater monitoring continue at the site <br /> 7. LIMITATIONS <br />' The environmental services described in this report have been conducted in general accordance <br /> with current regulatory guidelines and the standard-of-care exercised by environmental consult- <br /> ants performing similar work in the project area No other warranty, expressed or implied, is <br /> made regarding the professional opinions presented in this report Please note that this portion of <br /> the study did not include an evaluation of geotechnical conditions or potential geologic hazards, <br /> which will be provided by Ninyo & Moore under a separate cover <br />' stocktDn doc <br />