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<br /> 16
<br /> ' GROUNDWATER FLOW DIRECTION
<br /> Water levels were measured in monitoring wells MWl through MW10, MW11R, and MW12 on
<br /> September 28, 2005. Water levels in the shallow zone (MW1, MW2, MW3, MWS, MW9, MW10,
<br /> and MW11R) ranged from 51.03 to 52.83 feet below the tops of the well casing elevations. Water
<br /> levels in the intermediate zone wells (MW4, MW5, MW6, and MW12) ranged from 52.18 to 53.04
<br /> ' feet below the tops of the well casing elevations. The water level in the deep zone well, MW7, was
<br /> 52.76 feet below the top of the well casing elevation. The water level data were used to develop the
<br /> groundwater elevation contour maps shown in Figures 4 and 5. Groundwater flow in the shallow
<br /> ' zone was variable with eastward and northward components flowing toward the center of the site.
<br /> Groundwater flow in the intermediate zone was towards the south. The average hydraulic gradient in
<br /> the intermediate zone on September 28, 2005, was calculated to be 0.0003 ft/ft or approximately 2
<br /> ft/mile.A summary of groundwater monitoring data is presented in Table 1.
<br /> ANALYTICAL RESULTS
<br /> None of the analytes of interest were detected in the groundwater sample collected from MW10.
<br /> BTEX constituents were detected in the groundwater samples collected from MW 1, MW2, MW3,
<br /> ' MW5, MW6, and MWS. The highest concentrations of benzene, 4,100 micrograms per liter (gg/L)
<br /> and 4,000 gg/L, were detected in the groundwater samples collected from MW1 and MW8,
<br /> respectively. TPHg was detected in the groundwater samples collected from MW1, MW2, MW3,
<br /> MW5, MW6, MW8, and MW9. The highest concentrations of TPHg, 120,000 µg/L and 40,000 µg/L,
<br /> were detected in the groundwater samples collected from MWI and MW8, respectively. MTBE was
<br /> detected in the groundwater samples collected from MW2, MW3, MW7, and MW9 at concentrations
<br /> ranging from 1.3 gg/L to 43 µg/L. The highest concentration of MTBE was detected in the
<br /> groundwater sample collected from MW2. 1,2-DCA was detected in the groundwater samples
<br /> collected from MW2 through MW9, MW 11 R, and MW 12 at concentrations ranging from 1.0 gg/L to
<br /> 600 gg/L. The highest concentration of 1,2-DCA was detected in the groundwater sample collected
<br /> from MW3. TBA was detected in the groundwater samples collected from MW2 and MW3 at
<br /> concentrations of 29 gg/L and 22 gg/L, respectively. Analytical results of groundwater samples are
<br /> ' summarized in Table 2. Laboratory data sheets and chain-of-custody documentation are contained in
<br /> Attachment 2. Isoconcentration maps depicting benzene, MTBE, and 1,2-DCA concentrations in the
<br /> groundwater samples collected from the shallow zone during the third quarter of 2005 are shown on
<br /> Figures 6, 7, and 8, respectively. Isoconcentration maps depicting benzene and 1,2-DCA
<br /> concentrations in the groundwater samples collected from the intermediate zone during the third
<br /> quarter of 2005 are shown on Figures 9 and 10, respectively.
<br /> GEOTRACKER DATA UPLOAD
<br /> The depth to water and laboratory data associated with the third quarter 2005 sampling event were
<br /> submitted electronically to the State Water Resources Control Board (SWRCB) Geotracker database
<br /> (confirmation numbers 4771574258, 7275198042, and 6223704516). Documentation of the data
<br /> submittal is contained in Attachment 3.
<br /> s:lenviromental1283491reports12005 3QMR.doc 3 ATC Associates Inc.
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