Laserfiche WebLink
v <br /> NORCAL <br /> beophysicol Consultants NORCAL ; <br /> Iir <br /> RECEIVED <br /> BY K/1/C SAC <br /> January 12, 1987 JAN 1511987 <br /> AM PM <br /> 71819110111tI2111213141516 <br /> LKennedy/Jenks/Chilton <br /> 3336 Bradshaw Road, Suite 320 <br /> LSacramento, CA 95827 <br /> Attention: Mr. Dan Graff <br /> Gentlemen: <br /> This letter is to confirm the results of a ground penetrating radar (GPR) ; <br /> survey that we performed, 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 Penetratin:R Radar..(GPR) <br /> GPR is a shallow geophysical survey system that provides a continuous <br /> real-time cross section depicting both vertical and horizontal variation in <br /> the electrical properties of the subsurface, These variations may be caused <br /> by tanks, pipelines, backfill, and other materials. A transmitting and <br /> t receiving antenna is moved over the ground surface as a chart recorder, <br /> Ii. <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 is <br /> most sensitive to buried metal objects such as pipes, rebar, tanks, or <br /> metallic debris. However, it can also detect non-metallic objects such as <br /> fiberglass tanks and pipelines, as well as changes in material types such as <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 the <br /> shallower the penetration. The actual depth of penetration of any antenna <br /> will be greatly affected by the site resistivity and the resistivity <br /> contrasts within the depth of penetration. As the resistivity decreases, so <br /> does the depth of penetration and subsurface definition. Therefore, site <br /> conditions such as saturated clays, or high groundwater levels can severely <br /> limit the performance of the GPR system. <br /> r <br /> 921 Transport Way, Ste. #5 • Petaluma, CA 94952 • Telephone (707)763-1312 t <br /> iii... <br />