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Canepa's Car Wash 6230 Pacific Avenue,Stockton,CA Fourth Quarter Groundwater Monitoring Report,October 2005 Page 3 of 9 extraction well for the treatment system in conjunction with MW-11 as a secondary extraction well • (Figure 2, Attachment A) The cone of depression around MW-1 and MW-11 on October 13, 2005, indicated a relatively small radius of influence (apparently measurable to a radius of less than 25 feet) because it was measured approximately three days after the pumping was re-initiated following a down period of approximately three days The small cone of depression, therefore, is partly the result of I insufficient time for the cone of depression to expand The cone of depression measured on October 13, 2005 was larger than that measured during the previous quarters In addition, the pumping rate, once the pumping was re-initiated, was at a reduced rate of approximately 3 97 gallons per minute (down from a maximum rate of approximately 6 gallons per minute) The pumping rate, following the repair, was reduced because of pump inlet fouling Subsequent efforts have been made to reduce the fouling and return the system to optunal performance An estimated groundwater gradient magnitude of 0 0044 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 were 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, increased (decrease in groundwater elevation) by approximately 0 32 foot since July 28, 2005 A I hydrograph of historic groundwater elevations is attached as Figure 3 (Attachment A) It should be noted that the top 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 fourth quarter sampling event is shown in Table 2,below Table 2—Groundwater Elevation Data (October 13, 2005) Well Casing Screen Well Collar Depth to Water Groundwater 17 WELL Interval (feet-bgs) Elevation' (feet) (feet) Elevation feet MW-1 50-70 1548 4559 -30 11 MW-2 50-70 1529 3931 -2402 MW-3 50-70 15 53 3987 -2434 MW-4 50-70 15 83 4011 -2428 MW-5 50-70 1471 39 10 -2439 MW-6 45-65 1489 3828 -2339 ' MW-7 45-65 15 80 3941 -2361 MW-9 25-45 1484 3924 -2440 MW-10 25-45 1472 1 3826 -2354 MW-11 25-45 15 12 4238 -2726 MW-12D 100-110 1499 38 53 -2354 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 SVE wells 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), ' ;� CONDOR