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NORCAL <br /> Pacific Environmental Group, Inc <br /> July 10, 1996 <br /> Page 3 <br /> For this investigation, we used a Geophysical Survey Systems, Inc SIR-3 Subsurface <br /> Interface Radar System equipped with a 600 megahertz (MHz) transducer This <br /> transducer is near the center of the available frequency range and is used to provide <br /> high resolution at shallow depths <br /> Electromagnetic Line Location <br /> Electromagnetic line location techniques are used to locate the magnetic field resulting <br /> from an electric current flowing on a line These magnetic fields can arise from <br /> currents already on the line (passive) or currents applied to a line with a transmitter <br /> (active) The most common passive signals are generated by live electric lines and <br /> re-radiated radio signals Active signals can be introduced by connecting the <br /> transmitter to the line at accessible locations or by induction <br /> The detection of underground utilities is determined by the composition and <br /> • construction of the line in question Utilities detectable with standard line location <br /> techniques include any continuously connected metal pipes, cables/wires or utilities <br /> with tracer wires Unless carrying a passive current these utilities must be exposed <br /> at the surface or in accessible utility vaults These generally include water, electric, <br /> natural gas, telephone, and other conduits related to facility operations Utilities that <br /> are not detectable using standard electromagnetic line location techniques include <br /> those made of non-electrically conductive materials such as PVC, fiberglass, vitrified <br /> clay, and pipes with insulated connections <br /> Our instrumentation for this investigation consisted of a Radiodetection RD-400 line <br /> locator and a Fisher TW-6 inductive pipe and cable locator <br /> DATA ACQUISITION <br /> VMG data were collected at 5 foot intervals (stations) along south-north trending <br /> traverses spaced 5 feet apart The limits of the survey are shown on the Location <br /> Map, Plate 1 Following the VMG data acquisition, we downloaded the data to a <br /> portable laptop computer and produced preliminary contour map in the field We <br /> reviewed the maps for locations of VMG anomalies caused by undefined possible <br /> subsurface metallic sources The GPR and EMLL techniques were then systematically <br /> used over each detected anomaly The GPR traverses were obtained along south- <br /> north and/or east-west trending traverses that range in length from 12 to 60 ft The <br /> location of these traverses are shown on Plate 1 <br />