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Beacon Station No 3641 September 9, 2002 <br /> Stockton California Work Plan <br /> " vapor extraction wells VW-7/8, and air sparge well SW-1 Monitoring well MW-5, dual <br /> • <br /> vapor extraction wells VW-516 and VW-718 and air sparge well SW-1 were drilled through <br /> four of the UST cavity conductor casings The eighth soil boring (13-3) was backfilled <br /> In May 1998, Horizon conducted a vapor extraction test (VET), a combined VET and air <br /> sparging test (VET/AST), and an aquifer pumping test The tests were performed to <br /> evaluate remedial alternatives and to develop remediation design criteria <br /> Quarterly groundwater monitoring has been performed at the site since November 1996 <br /> Horizon has been reporting the groundwater monitoring since the first quarter of 1998 <br /> Groundwater monitoring data are summarized in Table 2 Historically, the groundwater <br /> flow direction has varied widely from southwestward around to northward and <br /> southeastward under gradients ranging from 0 001 to 0 02 Flow directions during the past <br /> year have been westward to northwestward and southeastward The depth to water has <br /> ranged from approximately 57 feet bsg in 1996 to 40 feet bsg in 1999 Groundwater <br /> monitoring for the second quarter 2002 indicated a depth to groundwater of approximately <br /> 47 feet, and a northwestward flow direction under a gradient of approximately 0 02, as <br /> shown on Figure 2 <br /> PROPOSED SCOPE OF WORK <br /> The purpose of the proposed work is to complete delineation of the horizontal and vertical <br /> extent of gasoline-range hydrocarbons in soil and groundwater, and to further investigate the <br /> vertical succession of soil types and water-bearing zones (stratigraphy) The investigation is <br /> proposed as two phases 1) an investigation phase to complete delineation of gasoline-range <br /> hydrocarbons in groundwater and supplement stratigraphic data, and 2) well installation <br /> phase to establish points for groundwater monitoring The two phase of work are described <br /> below <br /> • <br /> 641 wp9-02 <br /> Project No 1641 15 3 HORIZON ENVIRONMENTAL INC. <br />