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i q Former Beacon Station 494 October 8, 1996 Stockton, California Appendix B Closure Report for TPHg, BTEX, total lead, and ethylene dibromide (EDB) The laboratory reported that the highest concentration of TPHg from the UST cavity were less than l mg/Kg The laboratory reported the concentration of TPHg from the piping trenches at below the laboratory detection lunits The highest concentration for total lead detected was reported at 8 2 mg/Kg from the sample collected beneath the product line All analytical results of the soil samples collected and analyzed during the UST removal investigation are summarized on Tables 4 and 5 within Appendix B Also in March 1993, Remediation Testing and Design of Santa Cruz, California conducted a limited soil gas screening and vapor extraction testing at the site The results of the testing activities indicated the presence of hydrocarbons in the soil gas beneath the site and that hydrocarbons could be removed from the subsurface via soil vapor extraction The results of the soil gas screening are compiled on Table 7 within Appendix D AMV calculated the radius-of-influence of vapor-extraction at 29 standard cubic feet per minute (scfm) to be a minimum of 50 feet, with removal rates starting at up to 168 lbs of TPHg per day July 1993 AMV conducted an aquifer pumping test at the site to evaluate aquifer pumping characteristics The test utilized MW-3 as the pumping well with 48 hours of continuous pumping and then intermittently for 12 subsequent days Based on the results of the pumping test, it was decided that long term pumping and drawdown of the groundwater would be effective in controlling plume migration A copy of the Short Term Capture Zone depicted as a result of the pump test as Figure 7 is included within Appendix E It was concluded that longer term, sustained pumping would increase the capture zone This conclusion was supported by groundwater contour maps prepared during later quarterly monitoring activities( Figure 3, Water Table Contour Map of 312195 within Appendix E) 1494 APB 4 HORIZON ENVIRONMENTAL INC