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' Beacon Station No 641 December 8, 1997 <br /> Stockton__Qahfbrnia Additional SUbsurface Investigation ReppU <br /> storage tanks (USTs) located in the western portion of the property The locations of these <br /> facilities and other pertinent site features are depicted on the Site Plan (Figure 2) <br /> On June 11, 1996, Horizon personnel were onsite to perform soil sampling subsequent to <br /> removal and prior to replacement of the USTs Four, single-walled, steel USTs and <br />' associated product lines were removed at that time Each UST had a 10,000-gallon capacity <br /> and was used for the storage of regular, plus, and premium grades of unleaded gasoline All <br />' four USTs had been contained in a common cavity as shown on Figure 2 <br /> In June 1996 three new (two 10,000-gallon and one 12,000-gallon capacity), double-walled, <br /> fiberglass-clad, steel USTs were installed in the overexcavated cavity During the <br />' replacement of the USTs, ten 18-inch diameter conductor casings were installed in the <br />' overexcavated UST cavity These conductor casings were installed to facilitate future <br /> assessment drilling through the overexcavated UST cavity The conductor casing lengths <br /> were between 10 and 18 feet below surface grade (bsg) [mak Closure Letter.,Report, <br /> Horizon, August 2, 1996) <br /> FIELD WORK <br />' The field work was performed in two phases The first phase of field work was conducted <br /> prior to the station remodeling in the area that would be beneath the proposed western <br /> dispenser island and canopy The second phase of field work was conducted after evaluation <br /> of the first phase data and a revision to the workplan The work was accomplished as <br />' outlined in Horizon's Work Plans No 1641-12, dated June 24, 1996, and the letter workplan <br /> revision 1641-12r, dated August 15, 1997 These workplans were submitted to and <br /> approved by the SJC PHS/EHD in July 1996 and September 1997, respectively <br /> Horizon obtained boring/well drilling permits from SJC PHS/EHD prior to beginning each <br /> phase of the work (Appendix A) Prior to beginning the second phase of work, Horizon <br /> obtained an off-site access agreement to drill west of the site Underground Services Alert <br /> 1641-13t <br /> rP 2 HORIZON ENVIRONMENTAL INC <br />