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<br /> VATC
<br /> 1117 Lone Palm Avenue, Suite Modesto, GA 953511www.atcassociates.com
<br /> 209-579-2221
<br /> ASS O C I ATE S I N C . Fax 209-579-2225
<br /> Environmental, Geotechnical and Materials Engineers
<br /> from approximately 56 to 64 feet bgs and was underlain by silt to approximately 67 feet bgs .
<br /> Clay was encountered from approximately 67 to 72 feet bgs and was underlain by silty sand to
<br /> approximately 75 feet bgs. Clay was encountered from approximately 75 to 76.5 feet bgs and was
<br /> underlain by silty sand to approximately 79.5 feet bgs. Clayey sand was encountered from
<br /> approximately 79. 5 to 81 feet bgs and was underlain by clay to approximately 86 feet bgs. Clayey
<br /> sand was encountered from approximately 86 to 87 feet bgs and was underlain by clay to the
<br /> terminal depth of the boring at 92 feet bgs.
<br /> Soil boring logs with detailed descriptions of soil types are contained in Appendix A. Figure 4
<br /> -i shows the line of cross-section, and a generalized, cross-sectional interpretation of subsurface
<br /> conditions is shown on Figure 5.
<br /> 3.2 Hydrogeolo"
<br /> Water levels were measured in monitoring wells MWl through MW10, MW11R, MW12
<br /> through MW16, MW18, and MW19 on March 6, 2008. Water levels in the shallow zone (MWI ,
<br /> MW2, MW3 , MW8, MW9, MW10, MW11R, MW13 , MW14, and MW16) ranged from 42.42 to
<br /> 44. 19 feet below the tops of the well casing elevations. Water levels in the intermediate zone
<br /> wells (MW4, MW5, MW6, MW12, MW18, and MW19) ranged from 42.78 to 44 .35 feet below
<br /> Ll the tops of well casing elevations. Water levels in the deepest wells, MW7 and MW15 , were
<br /> 44. 05 and 43 .55 feet below the tops of the respective well casing elevations. The water level
<br /> data were used to develop groundwater elevation contour maps (Figures 6 and 7). Groundwater
<br /> - flow in the shallow zone was variable, trending in an easterly direction with a calculated
<br /> hydraulic gradient of 0 .0005 ft/ft or approximately 2.6 ft/mile. Groundwater flow in the
<br /> intermediate zone was towards the south, southeast beneath the subject site, becoming more
<br /> - easterly off-site southeast of the subject site. A summary of groundwater monitoring data is
<br /> presented in Table 2.
<br /> —� 4.0 ANALYTICAL RESULTS
<br /> None of the analytes of interest were detected in the groundwater sample collected from MWl6 .
<br /> BTEX constituents were detected in the groundwater samples collected from MWI , MW3,
<br /> MW5, MW6, and MW8 . The highest concentrations of benzene, 3,200 micrograms per liter
<br /> l (lig/L) and 3, 100 µg/L were detected in the groundwater samples collected from MW6 and
<br /> MW8, respectively. GRO were detected in the groundwater samples collected from MWI ,
<br /> MW29 MW3, MW5, MW6, MW8, and MW9. The highest concentrations of GRO, 110,000 µg/L
<br /> and 32,000 pg/L, were detected in the groundwater samples collected from MWI and MW8,
<br /> respectively. MTBE was detected in the groundwater samples collected from MW2, MW3 ,
<br /> MW8, and MW9 at concentrations ranging from 2.2 gg/L to 44 µg/L. The highest concentration
<br /> of MTBE was detected in the groundwater sample collected from MW8 . 1,2-DCA was detected
<br /> in the groundwater samples collected from MW2, MW3 , MW4, MW5, MW6, MW8, MW9,
<br /> MW12, MW18, and MW19 at concentrations ranging from 0.76 µg/L to 490 µg/L. The highest
<br /> S:\Enviromental\28349\rcports\inv rpt 2008.doc 6 ATC Associates Inc.
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