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California Department of Transportation April 24, 2000 Stockton Maintenance Station, Stockton, California Project No 400296-01 In well MW-6, TPH-G concentrations increased from non detect levels to 380 pg/l In well MW-7, TPH-G concentrations increased from non detect levels to 120 µg/l In well MW-9, TPH-G concentrations increased from non detect levels to 160 µg/1 In well VW-1 concentrations of TPH-G increased from 600 µg/l to 840 pg/l In well VW-2 concentrations of TPH-G increased from 7,800 11g/1 to 9,100 µg11 and TPH-D de- creased from 500 to 200 pg/l Benzene decreased from 873 pg/l to 94 µg/l, toluene decreased from 164 pg/l to 17 µg11, ethylbenzene decreased from 439 to 45 µg/1, and total xylenes de- creased from 1,180 to 122 pg/1 MTBE concentrations increased from non-detect levels to 7 3 µg/1 According to laboratory analytical data using EPA method 8260B additional compounds were detected in samples from various on-site wells These compounds include 1,2,4- • trimethylbenzene, 1,3,5-tnmethylbenzene, and 1,2-dichloroethane 6. RECOMMENDATIONS Based on the results of the First Quarter 2000 groundwater monitoring analytical results, which indicated elevated concentration of TPH-G, TPH-D, BTEX and MTBE, Ninyo & Moore recom- mends that quarterly groundwater monitoring continue at the site 7. LIMITATIONS The environmental services described in this report have been conducted in general accordance with current regulatory guidelines and the standard-of-care exercised by environmental consult- ants performing similar work in the project area No other warranty, expressed or implied, is made regarding the professional opinions presented in this report Please note this study did not include an evaluation of geotechnical conditions or potential geologic hazards • s:a n L 5 /y�nya&*norP.