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s NORCAL Pacific Environmental Group, Inc. July 10, 1996 Page 4 -- DATA ANALYSIS Computer Processing The down loaded VMG data were converted into a format for contouring. The contouring program calculated an evenly spaced array of values (gridded) based on the observed field data. These gridded values were contoured to produce the VMG Contour Map. Contour Map Interpretation Generally, VMG values vary smoothly throughout a given region that does not have magnetic sources. Areas where variations are strong can be due to nearby above or below ground sources and are defined by closely spaced contours. Where there are no above ground sources, those variations are, typically considered anomalous. If the source of a particular anomaly is an :isolaed object or a group of closely spaced objects, the contours may form circular or elliptical closures. A large accumulation of buried objects may appear as a group of closely spaced anomalies or one large anomaly. ' Actual anomaly magnitude and shape are dependent on the relative position and size of the buried objects with respect to the location of the data points. In general, anomaly magnitude will decrease and anomaly width will increase as distance (depth) to the source increases. Anomalies may or may not have paired high and low values creating what are known as magnetic dipoles. GPR Data Analysis We examined the GPR records for hyperbolic reflection patterns characteristic of UST's and underground utilities. We also reviewed the records for changes in reflection character that could indicate variations in fill material associated with an excavation. RESULTS The results of the geophysical investigation are presented on the Location Map, and the Vertical Magnetic Gradient Contour Map, Plates 1 and 2, respectively. The location map (Plate 1 ) shows the limits of the survey area, the cultural features in close proximity to the survey area, and the GPR traverses. The VMG Contour Map