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r <br /> Supplemental Investigation Work Plan <br /> BP Oil Site No. 11193 t <br /> i <br /> C A M B R I A Stockton, California <br /> February 25, 2000 <br /> Groundwater Monitoring: Groundwater monitoring for petroleum hydrocarbons has taken place <br /> since 1992,with the addition of MTBE analysis in 1995. The groundwater monitoring wells screen <br /> from 14-19.5 feet bgs to 32-35 feet bgs. The vapor extraction well, VW-1, screens from <br /> approximately 7 to 17 feet below ground surface (bgs) and is located north of the tanks. Well <br /> MW-1, located south of the tanks,was properly destroyed during tank replacement activities. While <br /> conducting the site monitoring event in October 1999,well MW-2, located north of the tanks, was <br /> found to be damaged, likely a result of tank replacement activities. t <br /> i <br /> The maximum concentration of MTBE reported for groundwater samples collected from the <br /> monitoring wells in October 1999 was 440,000 µg11 in well VW-1. As shown on the graph below <br /> for well MW-2, the water table elevation has increased while TPHg concentrations exhibit a <br /> decreasing trend and MTBE concentrations exhibit an increasing trend. <br /> i <br /> r <br /> Well MW-2 <br /> f <br /> 35,000 - 0 F <br /> 30,000 ' ! <br /> i -5 w <br /> ` a <br /> N <br /> C <br /> 25,000 -- 10 E <br /> 4 y <br /> c 20,O00 <br /> m <br /> y 15,000 - 1 1 1, -20 — <br /> ? ° <br /> o r 1 <br /> U 10,000 _ i I 1 °� -- -25.2 <br /> LU <br /> U7 <br /> r I` cQ <br /> 5,000 -`+ l 1 -30 <br /> -35 <br /> 12/21/92 12/21/93 12/21/94 12/21/95 12/21/96 12/21/97 12/21/98 <br /> Date <br /> a � - <br /> 1{ TPHg MTBE Water Elevation- _Expon. (TPHg) Expon. (MTBE) <br /> 1 F <br /> rtrE <br /> 4 � <br /> 4 <br /> If <br />