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Beacon Station No 1641 July 10 2003 Stockton California Preltmmary Results Report and Work Plan Addendum J In September 1997, Horizon drilled eight soil borings Seven borings were completed as • groundwater monitoring wells MW-2 through MW-5, dual vapor extraction well VW-5/6, vapor extraction wells VW-7/8, and air sparge well SW-1 Monitoring well MW-5, dual vapor extraction wells VW-5/6 and VW-7/8 and air sparge well SW-1 were drilled through four of the UST cavity conductor casings The eighth soil boring (13-3) was backfilled In May 1998, Horizon conducted a vapor extraction test (VET), a combined VET and air sparging test (VET/AST), and an aquifer-pumping test The tests were performed to evaluate remedial alternatives and to develop remediation design criteria ; Quarterly groundwater monitoring has been performed at the site since November 1996 Horizon has been reporting the groundwater monitoring since the first quarter of 1998 Groundwater monitoring data are summarized in Table 1 Historically, the groundwater flow direction has varied widely from southwestward around to northward and southeastward under gradients ranging from 0 001 to 0 02 Flow directions during the past • year have been westward to northwestward and southeastward The depth to water has ranged from approximately 57 feet bsg in 1996 to 40 feet bsg in 1999 Groundwater monitoring for the first quarter 2003 indicated a depth to groundwater of approximately 46 feet, and a southeastward flow direction under a gradient of approximately 0 002, as shown on Figure 2 ADDITIONAL SUBSURFACE INVESTIGATION The preliminary phase of the additional subsurface investigation consisted of collection of soil and groundwater samples from the saturated zone at various locations and depths Groundwater analytical results were used to evaluate proposed location and well construction specifications for additional site monitoring wells The preliminary investigation phase was performed with a cone-penetrometer test (CPT) rig . capable of generating a soil profile log and collecting discrete-depth groundwater samples W Padd nm7-03 Project No 1641 16 HORIZON ENVIRONMENTAL INC