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FIRST QUARTER 2005 GROUNDWATER FLOW DIRECTION
<br /> ' Water levels were measured in monitoring wells MW1 through MW12 on March 30, 2005. Water
<br /> levels in the shallow zone (MW1, MW2, MW3, MWS, MW9, MW10, and MW11) ranged from
<br /> 49.94 to 51.69 feet below the tops of the well casing elevations. Water levels in the intermediate zone
<br /> ' wells (MW4, MWS, MW6, and MW12) ranged from 49.95 to 51.82 feet below the tops of the well
<br /> casing elevations. The water level in the deep zone well, MW7, was 51.50 feet below the top of the
<br /> well casing elevation. The water level data were used to develop the groundwater elevation contour
<br /> ' maps shown in Figures 4 and 5. Groundwater flow in the shallow zone was variable with eastward
<br /> and northward components flowing toward the center of the site. Groundwater flow in the
<br /> intermediate zone was towards the south. The average hydraulic gradient in the intermediate zone on
<br /> ' March 30, 2005, was calculated to be 0.001 ft/ft or approximately 5 ft/mile. A summary of
<br /> groundwater monitoring data is presented in Table 1.
<br /> ' FIRST QUARTER 2005 ANALYTICAL RESULTS
<br /> MW 1 I was not sampled due to grout infiltration.None of the analytes of interest were detected in the
<br /> ' groundwater sample collected from MW10. BTEX constituents were detected in the groundwater
<br /> samples collected from MW1, MW2, MW3, MW5, MW6, MW7, and MW8. The highest
<br /> concentrations of benzene, 7,000 micrograms per liter (Vg/L) and 6,300 µg/L, were detected in the
<br /> groundwater samples collected from MW1 and MW8, respectively. TPHg was detected in the
<br /> b, groundwater samples collected from MW I, MW2, MW3, MW5, MW6, MW7, MW8, and MW9. The
<br /> highest concentrations of TPHg, 110,000 pg/L and 52,000 µg/L, were detected in the groundwater
<br /> ' samples collected from MW 1 and MW8, respectively. MTBE was detected in the groundwater
<br /> samples collected from MW2, MW3, MW4, MW7, MW9, and MW12 at concentrations ranging from
<br /> 1.0 µg/L to 60 pg/L, respectively. 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 MW 1 through MW9 and MW12 at concentrations ranging from 0.9 µg/L to 890 Pg/L.
<br /> The highest concentration of 1,2-DCA was detected in the groundwater sample collected from MWS.
<br /> TBA was detected in the groundwater samples collected from MW2 and MW3 at concentrations of
<br /> 48 pg/L and 26 pg/L, respectively. EDB was detected in the groundwater sample collected from
<br /> MW7 at a concentration of 0.7 pg/L Analytical results of groundwater samples are summarized in
<br /> ' Table 2. Laboratory data sheets and chain-of-custody documentation are contained in Attachment 2.
<br /> Isoconcentration maps depicting benzene, MTBE, and 1,2-DCA concentrations in the groundwater
<br /> samples collected from the shallow zone during the first quarter of 2005 are shown on Figures 6, 7,
<br /> ' and 8, respectively. lsoconcentration maps depicting benzene, MTBE, and 1,2-DCA concentrations
<br /> in the groundwater samples collected from the intermediate zone during the first quarter of 2005 are
<br /> shown on Figures 9, 10, and 11, respectively.
<br /> ' MONITORING WELL INSTALLATION, DEVELOPMENT, SAMPLING, AND SURVYING
<br /> ACTIVITIES
<br /> On April 7, 2005, an ATC geologist supervised the installation of replacement monitoring well
<br /> MW 11 R to a depth of approximately 65 feet bgs using 2-inch diameter schedule 40 PVC casing. The
<br /> well screen consisted of 20 feet of 0.020-inch factory perforated casing extending from
<br /> s:Ienviromenta11283491reports12005 I&2 QMR.doc 3 ATC Associates Inc.
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