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0 NE 0 P H Y S I C A L • <br /> NORCAL CNC SULTANTS <br /> NORCAL <br /> ' January 25, 1999 <br /> Ms. Hollis Phillips <br /> URS Greiner <br /> ' 100 California Street, Suite 500 <br /> San Francisco, CA 94111-4529 <br /> Dear Ms. Phillips: <br /> ' This report presents the findings of the geophysical investigation performed by NORCAL <br /> Geophysical Consultants, Inc. on a vacant lot located near the intersection of Arch Road and <br /> Highway 99 in Stockton, California. The field survey was conducted on January 15, 1999 <br /> by NORCAL Geophysicist Donald J. Kirker and Geophysical Technician Lee Hurvitz. Logistical <br /> support was provided by Hollis Phillips of URS Greiner. <br /> SITE DESCRIPTION AND PURPOSE <br /> The area of investigation, as specified by URS Greiner, is a 35,000 square foot vacant lot. <br /> It is bound by a barbed wire fence and Highway 99 to the east, a frontage road to the west, <br /> and a barbed wire fence to the north and south. The survey area is asphalt/gravel covered <br /> and generally free of above ground cultural objects and debris. A large overhead metal <br /> structure (billboard) is located in the south portion of the survey area. <br /> Information, provided by URS Greiner, indicates that this site was formerly occupied by a <br /> service station. However, records are incomplete as to the removal of the underground <br /> ' storage tanks (UST's) used at this station. Therefore, the purpose of the geophysical <br /> investigation is to obtain subsurface information that will aid in determining if UST's exist at <br /> this site. <br /> ' METHODOLOGY AND INSTRUMENTATION <br /> ' Since the north half of the survey area is generally open and free from above ground features, <br /> and the south half comprises a large overhead metal structure, we have divided the site into <br /> two separate survey areas. We refer to them as the North Area and the South Area, as <br /> ' shown on Plate 1 . <br /> North Area <br /> For the geophysical survey in the North Area, we used the vertical magnetic gradient (VMG), <br /> ground penetrating radar (GPR), and electromagnetic line locating (EMLL) methods. The VMG <br /> method was used to determine the presence of buried ferrous metal that may indicate the <br /> presence of a UST. The GPR and EMLL methods were used to aid in further characterizing <br /> the source of any detected VMG anomalies. <br /> 1350 INDUSTRIAL AVENUE SUITE A • PETALUMA, CA 94952 <br /> TELEPHONE (707) 763-1312 • FAX (707) 762-5587 <br />