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rSecond Quarter 2004 Groundwater Report 8200 N Highway 99, Stockton,CA Page 2 of 6 ' 2004 are summarized in Table 2 The estimated mass removal is summarized in Table 3 Treatment system monitoring logs and laboratory reports are included in Attachments A and B, respectively r 3.0 QUARTERLY SITE WORK r3 1 Groundwater Elevation Measurements ' A Ground Zero technician monitored water levels in all site wells, and collected groundwater samples from monitoring wells MW2 through MW14B and vapor well VWl on June 23, 24 and 25, 2004 ' The depth to groundwater was measured in each well on June 23, 2004 prior to any purging 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 A Zone monitoring wells ranged from 68 21 feet in well MW2 to 74 01 feet in well MW1 Groundwater elevations in the A Zone ranged from 36 13 feet below mean sea ' Ievel (MSL) in well MW2 to 42 93 feet below MSL in well MW 1, which serves as the extraction well for the treatment system Groundwater levels in the A Zone wells, not including pumping well MW1, fell an average of 3 23 feet between March 16, 2004 and June 23, 2004 By comparison, the groundwater elevation in vapor extraction well V W 1 fell by 2 91 feet and the groundwater elevation in the extraction well (MWI) fell by 0 77 feet during the same period ' The groundwater level in B Zone wells MW9B and MW14B measured 68 47 feet btoc and 69 11 feet btoc, respectively Groundwater elevations in both B Zone wells were calculated to be 36 88 feet below MSL Groundwater elevations the B Zone wells fell an average of 3 54 feet between ' March 16, 2004 and June 23, 2004 The groundwater elevation to C Zone well MW13C was measured at 70 94 feet btoc (38 76 feet below MSL), a fall of 4 77 feet between March 16, 2004 and June 23, 2004 ' Groundwater in the A Zone aquifer on June 23, 2004 generally flowed in a northeasterly direction, although a cone of depression is evident around the extraction well The groundwater Igradient across the site was approximately 0 0016 feet per foot Table 4 summarizes groundwater elevations in site monitoring wells Figure 2 presents a potentiometric surface map generated using the June 23, 2004 monitoring data. Attachment C contains field logs ' 3.2 Groundwater Sampling and Analysis P g Y ' An experienced Ground Zero technician purged at least three well casing volumes of water from monitoring wells MW2 through MW14B and vapor well VWl prior to sampling A sample was collected from MW1 on June 14, 2004 as part of the treatment system monitoring (sample designated INF, Table 1) The technician measured the temperature, pH and electrical conductivity of the water during the purging process Samples were collected after the physical r G 1GROUNDZEITULEBURGIRcports\QMR1200412QM2004 doc I