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f71 <br /> Supplemental Investigation Report <br /> BP Oil Site No 11193 <br /> C A M B R I A Stockton, California <br /> . October 13, 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 bgs and is located north of the tanks Well MW-1, located south of the <br /> tanks, was properly destroyed during tank replacement activities While conducting the site <br /> monitoring event in October 1999, well MW-2, located north of the tanks, was found to be damaged, <br /> likely a result of tank replacement activities <br /> The maximum concentration of MTBE reported for groundwater samples collected from the <br /> monitoring wells in May 2000 was 75,000 µg/l in well VW-1 As shown on the graph below for well <br /> MW-2, the water table elevation has increased while TPHg concentrations exhibit a decreasing trend <br /> and MTBE concentrations exhibit an increasing trend <br /> Well MW-2 <br /> 35,000 0 <br /> • 30,000 -5 <br /> m <br /> C <br /> 25,000 -10 d <br /> E <br /> m <br /> a <br /> 20,000 -15 a <br /> m <br /> d <br /> 15,000 -20 <br /> 2 <br /> m <br /> 10,000 -25 W <br /> `m <br /> 5,000 <br /> -35 <br /> 12/21/92 12/21/93 12121/94 12/21/95 12/21/96 12/21/97 12/21/98 12/21/99 <br /> Date <br /> TPHg—MTBE --o—Water Ele%ebon - - -Expon (TPHg} Expon (MTBE) <br /> • <br /> 4 <br />