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and the two offsite cluster wells MW6A and MW7A The current groundwater gradient <br /> shows a flow direction to the northwest at a gradient of 0 0012 ft/linear R (MWS to <br /> MW6A) <br /> B ZONE <br /> Monitor wells MW2, MW3, MW4, MW5 penetrate both the A and B zones Figure 4B <br /> show the gradient determination for the B Zone The B zone gradient and flow direction <br /> is similar to that as shown in the A zone <br /> RESULTS OF CERTIFIED ANALYSIS OF GROUNDWATER SAMPLES <br /> MONITOR WELLS <br /> Monitor wells MW2, MW3, MW4, and MW5 penetrated both the A and B zones <br /> Contaminants found in these wells would mix with the groundwater of both zones <br /> Figure 5A represents the hydrocarbon groundwater plume in the A zone and shows an <br /> elongated plume extending west of MW2 out to "Geoprobe" hole P9 were degradation <br /> has left only minor TPHg(470 ug/L), Toluene (0 65 ug/L) and tert-Butanol (11 ug/L), the <br /> degradation byproduct of MTBE Highest concentrations of TPHg are associated with <br /> well MW6A at 15000 ug/L The area that was over-excavated contained temporary <br /> piezometers PZ1A and PZ2A and contained the highest concentration of hydrocarbons <br /> with 140,000 ug/L and 62,000 ug/L TPHg respectively on January 31, 2003 <br /> Figure 5B represents the hydrocarbon groundwater plume in the B zone and shows a <br /> similar elongated plume extending west from MW2 out to "Geoprobe" hole P9 where <br /> degradation has left only minor amounts of Toluene (0 81 ug/L), Xylenes (0 83 ug/L) <br /> and MTBE (1 6 ug/L) Again the highest concentrations are associated with monitor well <br /> MW6B, 640 ug/L The area that was over-excavated contained temporary piezometers <br /> PZ1B and PZ213 with 40,000 ug/L and 16,000 ug(L TPHg respectively on January 31, <br /> 2003 <br /> Figure 6 illustrates the subsurface lithology and the extent of the A and B zones <br /> groundwater plumes within the A and B zones Also shown in cross section is the extent <br /> of the over-excavation and residual soil contamination February 28, 2003 <br /> RECOMMENDATIONS <br /> 1) Submit a workplan to install a 4 inch diameter monitor/recovery well within the <br /> excavated area Install a northern extent cluster monitoring well (A and B zones), <br /> north of former well location MWl and install a down gradient cluster morutoring <br /> • well (A and B zones)to document the lateral extent west of probe Bole P9, see Figure <br /> 3 <br /> 6 QM 3`d 2003 <br />