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' eala ccal Techaus lac Page 7 G g g Valentine(Castle Motors) Report—Additional Site Characterization Project No 723 2 January 21,2004 ' Figure 2 indicates the locations of geological cross sections presented in Figures 3A and 4A The continuous sampling of MW-7 revealed that the subsurface has a diverse lithology ' The site exhibits little correlation between boreholes and this situation is exacerbated by the fact that different geologists logged the boreholes For this reason the cross sections have sand units combined (sands, clayey sands, silty sands) and silt/clay units combined (clays, silts, sandy clays) This serves to identify the preferential pathways for contaminant ' migration through units of greater hydraulic conductivity Figure 3A illustrates the geology trending from northwest of to southeast side of the site The diagram indicates that more sands are present in the off-site location of MW-7 with on- site soils containing a greater portion of clays and silts The residual contamination bound in the on-site fine grained soil units continues to source the groundwater plume GTI's interpretation of the geology does not identify any sands units as Iaterally continuous The ' silt/clay units do appear to be laterally continuous, however Figure 4A illustrates the geology trending from southwest of to east of the site In this interpretation., both silt/clay and sand units appear to be laterally continuous across the site As with the location of MW-7,more sands are present in the oft-site locations of MW-8 and MW-9 The sand unit at 60 — 75 feet bgs in the vicinity of well MW-201 could be a ' preferential pathway for off-site migration 4.2 Chemical Distribution The results of the soil sample analytical data are included in Table 1, Appendix A The laboratory data sheets are included in Appendix B ' Chemical Distribution in the Soil ❑ Soil samples from borings MW-7 at 30, 41 and 92 feet bgs, and samples from MW-9 at 30, 40 and 75 feet bgs did not contain contaminant concentrations above the laboratory limits ' ❑ The soil sample from boring MW-8 at 30 feet bgs contained 2010 mg/kg TPH-G and BTEX constituents ranging <600— 19,300 ug/kg ❑ The soil sample from boring MW-8 at 40 feet bgs did not contain contaminant concentrations above the laboratory limits ❑ The soil sample from boring MW-8 at 75 feet bgs contained <1 mg/kg TPH-G and BTEX constituents ranging 4 5 —69 3 ug/kg ' ❑ Figure 3B & 4B are the above cross sections with the distribution of gasoline concentrations (TPH-G) in soil included Chemical Distribution in the Ground Water The 4" quarter 2003 groundwater monitoring event was completed on November 26, 2003, before the new wells were developed The next monitoring event is scheduled for the first quarter of 2004 and the results of the new CMTrm wells sampling will be presented in a ' forthcoming quarterly monitoring report 4.3 Contaminant Mass Estimate Calculations ' In order to calculate the TPH-G mass in soil, GTI divided the subsurface into two zones - shallow (0 - 25 feet bgs) and deep (25 - 60 feet bgs) The vertical extent is illustrated in cross section Figure 313, and the lateral extent of these zones is illustrated in Figures 5A &