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Mr Jeff Wong ' • Page 3 of 5 contamination east of the former tankpit The investigation included the installation and sampling of ' three shallow monitoring wells (MW 10, MW 11, MW 12), one B Zone well (MW 14B), one C Zone well (MW13C), and one vapor extraction test well (VW1) In addition, a soil vapor extraction pilot test was ' conducted to evaluate the feasibility of using vapor extraction to reduce the mass of gasoline contamination in the subsurface ' The results of the investigation were detailed in a technical summary report dated May 20, 2004, which was submitted to EHD and RWQCB A site plan is presented on Figure 2 ' 5.0 QUARTERLY SITE WORK ' A Ground Zero technician monitored water levels in all site wells, and collected groundwater samples from monitoring wells MW2 through MW 14B between December 10 and 12, 2003 A sample was collected from well MW 1 (INF, Table 2) on December 15, 2003 as part of the treatment system ' monitoring and sampling program 5.1 Groundwater Elevation Measurements tThe depth to groundwater was measured in each well using a Solinst electronic water level probe Groundwater elevations were calculated by subtracting the measured depth to water from the respective well head elevation The measured depth to groundwater below the tops of the well casings (btoc) in ' the shallow A Zone monitoring wells on December 10, 2003 ranged from 65 99 feet in well MW2 to 67 37 feet in well MW 11 The depth to groundwater in well MW 1 was measured at 68 53 feet btoc on December 12, 2003 Groundwater elevations in the shallow aquifer beneath the site ranged from 33 91 ' feet below mean sea level (MSL) in well MW2 to 37 45 feet below MSL in well MW 1 Groundwater levels in shallow monitoring wells MW2 through MW8 rose an average of 130 feet between September ' 10, 2003 and December 10, 2003 The groundwater level in B Zone wells MW913 and MW14B measured 65 90 feet btoc and 66 64 feet ' btoc, respectively The groundwater level in C Zone well MW 13C measured 67 16 feet btoc Groundwater in the A Zone aquifer on December 10, 2003 generally flowed in a northeasterly direction, ' although a cone of depression is evident around well MW 1, which serves as the extraction well The groundwater gradient across the site was approximately 0 0018 feet per foot (ft/ft) Table 4 summarizes groundwater elevations in site monitoring wells Figure 3 presents a potentiometric surface map ' generated using the December 10, 2003 monitoring data 5 2 Groundwater Sampling and Analysis ' An experienced Ground Zero field technician purged at least three casing volumes of water from monitoring wells MW2 through MW 14B prior to sampling the wells The technician measured the temperature, pH and electrical conductivity of the water during the purging process Samples were collected after the physical parameters stabilized and water levels in the wells recovered to at least 80% of their respective pre-purged levels The samples were temporarily stored in an ice chest refrigerated to a temperature of approximately 4°C and delivered under chain of custody protocol to Argon ' Laboratories (ELAP #2359) for analysis Purged groundwater was contained in appropriately labeled DOT-approved 55-gallon drums in accordance with 49 CFR part 172 and 40 CFR part 262 Copies of ' G IGROUNDZEITULEBURGIReports\QMR000314QM2003 doc