|
;a 1117 Lone Palm Avenue, Suite B
<br /> Modesto, CA 95351
<br /> www.atcassociates.com
<br /> 209-579-2221
<br /> .�. Fax 209-579-2225
<br /> ASSOCIATES I N C .
<br /> Environmental,Geotechnical and Materials Engineers
<br /> GROUNDWATER FLOW DIRECTION
<br /> Water levels were measured in monitoring wells MW 1 through MW 10, M W 11 R, and MW 12 on
<br /> December 29, 2005. Water levels in the shallow zone (MW1, MW2, MW3, MWS, MW9, MW10,
<br /> and MW IR) ranged from 48.83 to 50.59 feet below the tops of the well casing elevations. Water
<br /> levels in the intermediate zone wells (MW4, MW5, MW6, and MW12) ranged from 49.85 to 50.72
<br /> feet below the tops of the well casing elevations. The water level in the deep zone well, MW7,.was
<br /> 50.37 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 December 29, 2005, was calculated to be 0.001 ft/ft or approximately 5
<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 samples collected from MW 10 and
<br /> MW11R. BTEX constituents were detected in the groundwater samples collected from MW1, MW2,
<br /> MW3, MW5, MW6, MW7, and MW8. The highest concentrations of benzene, 4,800 micrograms per
<br /> liter (gg/L) and 5,300 gg/L, were detected in the groundwater samples collected from MW1 and
<br /> + MW8, respectively. TPHg was detected in the groundwater samples collected from MW 1, MW2,
<br /> MW3, MWS, MW6, MWS, and MW9. The highest concentrations of TPHg, 87,000 ptg/L and 60,000
<br /> gg/L, were detected in the groundwater samples collected from MW 1 and MW8, respectively.
<br /> MTBE was detected in the groundwater samples collected from MW2, MW3, MW7, MW8, and
<br /> MW9 at concentrations ranging from 1.5 pg/L to 43 µg/L. The highest concentration of MTBE was
<br /> detected in the groundwater sample collected from MWS. 1,2-DCA was detected in the groundwater
<br /> samples collected from MW 1 through MW9 and MW 12 at concentrations ranging from 0.8 pg/L to
<br /> 640 gg/L. The highest concentration of 1,2-DCA was detected in the groundwater sample collected
<br /> from MW8. TBA was detected in the groundwater sample collected from MW2 at a concentration of
<br /> 41 gg/L. Analytical results of groundwater samples are summarized in Table 2. Laboratory data
<br /> sheets and chain-of-custody documentation are contained in Attachment 2. Isoconcentration maps
<br /> depicting benzene, MTBE, and 1,2-DCA concentrations in the groundwater samples collected from
<br /> the shallow zone during the fourth quarter of 2005 are shown on Figures 6, 7, and 8, respectively.
<br /> Isoconcentration maps depicting benzene and 1,2-DCA concentrations in the groundwater samples
<br /> collected from the intermediate zone during the fourth quarter of 2005 are shown on Figures 9 and
<br /> 10, respectively.
<br /> GEOTRACKER DATA UPLOAD
<br /> The depth to water and laboratory data associated with the fourth quarter 2005 sampling event were
<br /> submitted electronically to the State Water Resources Control Board (SWRCB) Geotracker database
<br /> (confirmation numbers 4562.010049 and 2060316920, respectively). Documentation of the data
<br /> . submittal is contained in Attachment 3.
<br /> s;\enviromental1283491reports12005 4QMR.doc 3 ATC Associates Inc.
<br />
|