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' Canepa's Car Wash 6230 Pacific Avenue,Stockton,CA Fust Quarter Groundwater Monitoring Report,January 2006 ' Page 3 of 9 . for the treatment system, in conjunction with MW-11 as a secondary extraction well (see Figure 2, Attachment A) The cone of depression around MW-1 on January 27, 2006, indicated a relatively small radius of influence (apparently measurable to a radius of less than 40 feet) because it was measured approximately four days after the pumping was re-initiated following an approximately four-day period of intermittent operation. The small cone of depression, therefore, is partly the result of insufficient time for ' the cone of depression to expand The cone of depression measured on January 27, 2006 was, however, larger than that measured during the previous quarters In addition, the pumping rate, once the pumping was re-initiated, was at an increased rate of approximately 4 29 gallons per minute (down from a maximum rate of approximately 6 gallons per minute) The pumping rate, following the groundwater extraction pump replacement, was increased because of improved pump efficiency An estimated groundwater gradient magnitude of 0 0043 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 MWA, and were outside the radius of influence of the cone of depression formed by groundwater extraction activities in MWA 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 2 21 foot since October 13, 2005 A hydrograph of historic groundwater elevations is included as Figure 3 (Attachment A) It should be noted that the top of the well screens for shallow monitoring wells MW-I through MW-7 were below the water table, consistent with much of the monitoring history at the Site The groundwater elevation data for the first quarter 2006 sampling event is shown in Table 2,below Table 2 —Groundwater Elevation Data (Janua 27,2006) Well Casing Screen Well Collar Depth to Water Groundwater WELL Interval(feet-bgs) Elevation' (feet) (feet) Elevation feet MW-1 50-70 1548 4767 -32 19 MW-2 50-70 1529 3749 -2220 MW-3 50-70 1553 3799 -2246 MW4 50-70 15 83 3828 -2245 I MW-5 50-70 1471 37 19 -2248 MW-6 45-65 1489 3646 -21 57 MW-7 45-65 15 80 3757 -21 77 MW-9 25-45 1484 13731 -2247 MW-10 25-45 1472 3646 -2174 MW-11 25-45 15 12 37 11 -21 99 MW-12D 100-110 1499 3656 -21 57 ' 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 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 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), • to CONDOR