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Canepa s Car Wash 6230 Pacific Avenue,Stockton,CA Third Quarter Groundwater Monitoring report July 2005 Page 3 of 8 GROUNDWATER ELEVATIONS AND GRADIENT • Groundwater elevation contours estimated for the shallow monitoring wells MW-1 through MW-7 and MW-9 through MW-11 on July 28, 2005 indicated a groundwater gradient generally towards the north/northeast MW-1 is the primary groundwater extraction well for the treatment system, and a cone of depression related to pumping drawdown at that location is generally observed in the groundwater elevation contours However, the system was inadvertently shut down the evening prior to the third quarter monitoring event when a vehicle backed into the enclosure gate, damaged piping on the air ' stripper, and tripped the systems emergency shut-off switch As a result, the groundwater surface had largely recovered to static equilibrium and groundwater elevation contours did not form the localized cone of depression centered on MW-1 as observed during previous quarterly monitoring events An estimated groundwater gradient magnitude of 0 0049 ft/ft towards the north/northeast was calculated using water level data from monitoring wells MW-6 and MW-9 MW-6 and MW-9 are upgradient and down-gradient, with respect to MW-1 The average groundwater elevation measured in the shallow monitoring wells for this event decreased by approximately 0 42 feet since April 13, 2005 The groundwater elevation data for the third quarter sampling event is shown in Table 2, below A hydrograph of historic groundwater elevations is attached as figure 3 (Attachment A) Table 2 Groundwater Elevation Data (July 28, 2005) Well Casing Screen Well Collar Depth to Water Groundwater WELL Interval (feet-bgs) Elevation' (feet) (feet) Elevation �. (feet) MW-1 50-70 1548 3922 -2374 MW-2 50-70 15 29 3870 -2341 MW-3 50-70 15 53 3948 -23 95 MW-4 50-70 15 83 3972 -23 89 MW-5 50-70 1471 3877 -2406 MW-6 45-65 1489 37 82 -2293 MW-7 45-65 1580 3896 -23 16 MW-9 25-45 1484 3891 -2407 ' MW-10 25-45 1472 1 37 86 -23 14 MW-11 25-45 15 12 39 10 -2398 MW-12D 100-110 1499 3829 -2330 Well Collar Elevations are measured from a mark on the top of the well casing and are referenced to GIGS benchmark HS0391 using NAVD 88 datum bgs=below ground surface LABORATORY ANALYTICAL RESULTS Groundwater samples collected from the monitoring wells and SV-4 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 oxygenates/additives 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) • ' CONDOR