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II <br /> Former Beacon Station No.12 04 February 26,2003 <br /> Stockton California Prelimina Results Re ort and Work Plan Addendum <br /> RESULTS OF ADDITIONAL SUBSURFACE INVESTIGATION <br /> The CPT log (Appendix C) indicates that the soil profile to 130 feet bsg is dominated by silt, <br /> clayey silt and other stiff fine-grained sediments with minor interbedded sands and clay. The <br /> interval from approximately 93 to 100 feet bsg is predominantly characterized by <br /> interbedded gravelly sand and sand. The pore-dissipation test indicated the groundwater <br /> level was approximately 58 feet bsg. <br /> Analytical results of groundwater samples collected via CPT/hydropunch are summarized in <br /> Table 2. Analytical reports and COC doc-iment are contained in Appendix D. <br /> Concentrations of TPHg were reported as 70 micrograms per liter (parts per billion or ppb) <br /> in sample B-5(130'), 750 ppb in sample B-7(100') and 510 ppb in 13-8(100'). <br /> Concentrations of 6.5 ppb benzene and other BTEX compounds ranging from 1.7 to 10 ppb <br /> were reported in sample 13-5(130'). No BTEX compounds were reported in the other <br /> samples and no fuel oxygenates were reported in any sample. Concentrations of DCA were <br /> reported in samples B-7(100') at 15 ppb, in sample B-7(130') at 3.8 ppb and in sample 13- <br /> 8(l 00') at 2.4 ppb. No EDB was reported in any sample. <br /> PROPOSED MONITORING WELL INSTALLATIONS <br /> Results of the CPT investigation indicate that groundwater at a depth of 130 feet bsg in the <br /> monitoring well MW-12 area is impacted with TPHg and BTEX. Results also indicate <br /> groundwater at 100 and 130-feet bsg in soil boring B-7 is impacted with TPHg and DCA, <br /> and groundwater at 100 feet bsg in soil boring B-8 is impacted with TPHg and DCA. <br /> Additional monitoring wells are needed to complete vertical and lateral delineation of <br /> dissolved gasoline groundwater plume. It is proposed to install five additional monitoring <br /> wells (MW-13 through MW-17) at the locations shown on Figure 2. <br /> C:\Projects\1474\14\WPaddnm2-03.doc <br /> Project No. 1474.14 4 HORIZON ENVIRONMENTAL INC. <br />