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' June 9, 1999 <br /> California Department of Transportation <br /> Stockton Maintenance Station, Stockton, California Project No 103872-02 <br /> 1 <br />' Benzene and ethylbenzene concentrations in well MW-6 decreased from 12 ppb non-detect <br /> Concentrations of TPH-g in well MW-8 increased from non-detect to 110 ppb and levels of <br />' TPH-d have increased from non-detect to 400 ppb <br /> Concentrations of benzene in well VM-1 decreased from 30 ppb to 24 ppb, ethylbenzene de- <br /> creased from 3 0 ppb to non-detect, and total xylenes decreased from 0 4 ppb non-detect <br /> 1 <br /> Well VW-2 concentrations of benzene increased from 1,100 ppb to 1,500 ppb, toluene increased <br />' from 360 ppb to 460 ppb, ethylbenzene increased from 290 ppb to 750 ppb, and total xylenes <br /> increased from 1,100 ppb to 1,950 ppb MTBE was detected only in well VW-2 at concentra- <br /> tions of 83 ppb and was higher than the December 1998 concentration of 54 ppb <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-dichloroethane, <br />' and 1,2-dichlorobenzene <br /> Analytical data for monitoring wells MW-3, MW-4, MW-5 and MW-10 were not considered or <br />' included in this report due to the elapsed holding period for the water samples delivered to the <br /> lab <br />' 6. RECOMMENDA'T'IONS <br /> Based on the results of the First Quarter 1999 groundwater monitoring analytical results, which <br />' indicated elevated concentration of TPH-g, TPH-d, BTEX, and/or MTBE Ninyo & Moore rec- <br /> ommends 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 />, ,c«kwn <br />