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0 R C A L <br /> Geophysical Consultants h`ORCAL <br /> r ' <br /> R ~ E L D <br /> 3Y KII/C SAC <br /> January 12, 1987 j Io�i <br /> AM Fid <br /> 718191101iI12111213141516 <br /> Kennedy/Jenks/Chi l ton <br /> 3336 Bradshaw Road, Suite 320 <br /> Sacramento, CA 95827 <br /> Attention: Mr. Iran Graff <br /> Gentlemen: <br /> This letter is to confirm the results of a ground penetrating radar (GPR) <br /> survey that we perf ormad at the Handyman Warehouse Facility in Tracy, <br /> California on December 23, 1986. The field work was conducted by Kenneth <br /> Blom, NORCAL Principal Geophysicist, -with assistance from Dan Graff, <br /> Kennedy/Jenks/Chilton. The purpose of the survey was to locate two <br /> underground fuel tanks and the associated utilities as a basis for <br /> suggesting test boring locations. <br /> Ground Penetrating P.adar (GPR) <br /> GPR is a shallow geophysical survey system that provides a continuous <br /> real-tune cross section- depicting both vertical and horizontal variation in <br /> the electrical properties of the subsurface. These variations may be cause, <br /> by tanks, pipelines, backfill, and other materials. A transmitting and <br /> receiving antenna is moved over the ground surface as a chart recorder, <br /> attached to the antenna by an electrical cable, prints the cross-section of <br /> the shallow subsurface over which the antenna has passed. Typically, GPR i <br /> most sensitive to buried retal objects such as pipes, rebar, tanks, or <br /> metallic debris. Rowe ver, it can also detect non-metallic objects such as <br /> fiberglass tanks and pipelines, as well as changes in mrterial types such a <br /> the boundary between native material and the backfill. in a pipeline trench <br /> or tank excavation. <br /> The resolution and - penetration depth of the radar system depends on the <br /> operating frequency of the antenna and the electrical resistivity of the <br /> ground. The higher the antenna frequency, the better the resolution but th <br /> shallower the nenetrat ion. The actual depth of penetration of any antenna <br /> will be greatly affected by the site resistivity and the resistivity <br /> cc,r_trasts within the depth of penetration. As the resistivity decreases, s <br /> does the depth of penetration and subsurface definition. Therefore, site <br /> conditions such as saturated clays, or high grcuzdwater Ie: els can severely <br /> Iicit the parfor=:ance of the CPR system. <br />