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California Department of Transportation November 4, 1999 Shop 10 Maintenance Station, Stockton, California Project No 103872-02 In well MW-13, TPH-G decreased in concentration from 500 ug/l to 450 µg11 Benzene de- creased from 471 ug/1 to 85 µg/1, ethylbenzene increased from non detect levels to 37 µg/1, and total xylenes decreased from 9 0 ug/l to non detect In well MW-14, total xylenes increased from non detect to 6 8 µg/l TPH-G increased in well VM-1 from 3,700 ug/1 to 8,820 µg11 and TPH-D increased from non detect levels to 700 µg/1 Concentrations of benzene increased from non detect levels to 3,890 gg/l, toluene has decreased from 86 ug/l to non detect levels, ethylbenzene has increased from 917 ug/l to 1,000 µg/l, and total xylenes have increased from 608 ug/l to 1,220 µg/1 In well VM-2, TPH-G decreased in concentration from 64,000 ug/l to 18,200 µg/1, and concen- trations of TPH-D increased from non detect levels to 900 µg/1 Concentrations of benzene increased from 2,250 µg/1 to 7,920 µg/1, toluene increased from 1,180 µg/l to 3,680 µg/l, ethyl- benzene increased from 245 ug/1 to 773 µg/1, and total xylenes increased from 572 ug/l to 1,720 µg/l According to laboratory analytical data for 8260B, other VOCs that were detected during the current groundwater sampling event are 1,2-dichloroethane, 1,2,4-tnmethylbenzene, 1,3,5- trimethylbenzene, naphthalene, n-butylbenzene, tert-butylbenzene, sec-butylbenzene, p- isopropyltoluene, and isopropylbenzene A trip blank (TB-1) was placed inside the cooler during transport to AL and analyzed using method 8260B None of the constituents for which the analysis were performed were detected in the trip blank sample 6. RECOMMENDATIONS Based on the results of the Third Quarter 1999 groundwater monitoring analytical results, which indicated elevated concentrations of TPH-G, TPH-D and/or BTEX, Ninyo & Moore recom- mends that quarterly groundwater monitoring continue at the site shop 10 doc 5