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1117 Lone Patm Avenue, Suite B
<br /> Modesto, CA 95351
<br /> www.atcassociates.com
<br /> OCYA 209-579-2221
<br /> ASSOCIATES i N c . Fax 209-579-2225
<br /> Environmental,Geotechnical and Materials Engineers
<br /> GROUNDWATER FLOW DIRECTION
<br /> Water levels were measured in monitoring wells MW 1 through MW 10, MW 11 R, and MW12 on
<br /> March 20, 2006. Water levels in the shallow zone (MW 1, MW2, MW3, MW8, MW9, MW 10, and
<br /> MW IR) ranged from 46.23 to 47.94 feet below the tops of the well casing elevations. Water levels
<br /> in the intermediate zone wells (MW4, MW5, MW6, and MW12) ranged from 47.21 to 48.08 feet
<br /> below the tops of the well casing elevations. The water level in the deep zone well, MW7, was 47.76
<br /> 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 March 20, 2006, was calculated to be 0.001 ft/ft or approximately 5 ft/mile.
<br /> 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 samples collected from MW7,
<br /> MW 10, and MW 11 R. BTEX constituents were detected in the groundwater samples collected from
<br /> MW1, MW2, MW3, MW5, MW6, and MW8. The highest concentrations of benzene, 10,000
<br /> • micrograms per liter (pg/L) and 5,000 gg/L, were detected in the groundwater samples collected
<br /> from MW1 and MW8, respectively. TPHg was detected in the groundwater samples collected from
<br /> MW1, MW2, MW3, MW5, MW6, MW8, and MW9. The highest concentrations of TPHg, 130,000
<br /> µg/L and 95,000 gg/L, were detected in the groundwater samples collected from MW1 and MW8,
<br /> respectively. MTBE was detected in the groundwater samples collected from MW2, MW3, MW4,
<br /> and MW9 at concentrations ranging from 0.6 gg/L to 41 gg/L. The highest concentration of MTBE
<br /> was detected in the groundwater sample collected from MW2. 1,2-DCA was detected in the
<br /> groundwater samples collected from MWI through MW6 and MW12 at concentrations ranging from
<br /> 0.6 gg/L to 600 gg/L. The highest concentration of 1,2-DCA was detected in the groundwater sample
<br /> collected from MW L TBA was detected in the groundwater sample collected from MW2 at a
<br /> concentration of 17 gg/L. Analytical results of groundwater samples are summarized in Table 2.
<br /> 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 2006 are shown on Figures 6, 7,
<br /> and 8, respectively. Isoconcentration maps depicting benzene and 1,2-DCA concentrations in the
<br /> groundwater samples collected from the intermediate zone during the first quarter of 2006 are shown
<br /> on Figures 9 and 10, respectively.
<br /> GEOTRACKER DATA UPLOAD
<br /> The depth to water and laboratory data associated with the first quarter 2006 sampling event were
<br /> submitted electronically to the State Water Resources Control Board (SWRCB) Geotracker database
<br /> (confirmation numbers 6028410196 and 2124616444, respectively). Documentation of the data
<br /> submittal is contained in Attachment 3.
<br /> s:lenviromenta1128349Veports12006 IQMR.doc 3 ATC Associates Inc.
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