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Canepa's Car Wash 6230 Pacific Avenue Stockton CA Second Quarter Groundwater Monitoring Report,May 2006 � Page 3 of 8 gradient toward MW-1 (cone of depression) Monitoring well MW-1 is currently used as the primary groundwater extraction well for the treatment system, in conjunction with MW-11 as a secondary extraction well (see Figure 2, attached) The cone of depression around MW-1 on May 18, 2006, indicated a radius of influence of approximately 50 feet In addition, the pumping rate during the current quarterly monitoring event was at a relatively increased rate of 4 4 gallons per minute, indicative of improved pump efficiency An estimated groundwater gradient magnitude of 0 0039 ft/ft towards the northeast was measured using water level data from monitoring wells MW-6 and MW-9 (MW-6 and MW-9 are upgradient and down- gradient, respective to MW-1, and outside the radius of influence of the cone of depression formed by groundwater extraction activities in MW-1 during the monitoring event) The average depth to groundwater measured in the shallow monitoring wells for this event, excluding MW-1 and MW-11, decreased (increase in groundwater elevation) by approximately 1 64 feet since January 27, 2006 A hydrograph of historic groundwater elevations is included as Figure 3, attached It should be noted that the tops of the well screens for shallow monitoring wells MW-1 through MW-7 were below the water table, consistent with much of the monitoring history at the Site The groundwater elevation data for the second quarter 2006 sampling event is shown in Table 2,below Table 2—Groundwater Elevation Data (May 18,2006 Well Casing Screen Well Collar Depth to Water Groundwater WELL Interval (feet-bgs) Elevation' (feet) (feet) Elevation feet MW-1 50-70 1548 4398 -2850 i MW-2 50-70 1529 3579 -2050 MW-3 50-70 15 53 3632 -2079 MW-4 50-70 15 83 3658 -2075 MW-5 50-70 1471 3554 -2083 MW-6 45-65 1489 3480 -1991 MW-7 45-65 1580 3588 -2008 MW-9 25-45 1484 3565 -2081 MW-10 25-45 1472 3476 -20 04 MW-11 25-45 15 12 3558 -2046 MW-12D 100-110 1499 3508 -2009 ' Well Collar Elevations are measured from a mark on the top of the well casing and are referenced to NGS benchmark HS0391 using NAVD 88 datum bgs=below ground surface LABORATORY ANALYTICAL RESULTS Groundwater samples collected from the monitoring wells and soil vapor extraction well were analyzed for total petroleum hydrocarbons quantified as gasoline (TPH-G) by EPA Method 8015M and benzene, toluene, ethyl benzene, and total xylenes (BTEX) and selected gasoline oxygendtesiddditives by EPA Method 8260B by Excelchem Environmental Labs of Roseville, California (Excelchem) The selected oxygenates/additives included MTBE, ethanol (EtOH),tertiary-butanol (TBA), di-isopropyl ether(DIPE), ethyl tert-butyl ether (ETBE), tert-amyl methyl ether (TAME), 1,2-dichloroethane (1,2-DCA), and 1,2- dibromoethane (EDB) The current (May 2006) laboratory analytical results for soil vapor extraction well SV-4 indicate a trend of decreased concentrations of BTEX, MTBE, and TPH-G relative to historic laboratory analytical results for that we]1 %t4 CON DOR