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CRC Environmental Risk Management, Inc. <br /> May 9, 1995 <br /> Page 3 <br /> VMAG Data Computer Processing <br /> We down loaded the VMAG data to a computer and converted it into a format <br /> suitable for computer contouring. The contouring software computed an evenly <br /> spaced array of values (grid) based on the observed field data. These values were <br /> then contoured to produce the Vertical Magnetic Gradient Contour Map, shown on <br /> Plate 2. <br /> Contour Map Interpretation <br /> Generally, magnetic values vary smoothly throughout a given region. Within <br /> culturally active areas, the vertical magnetic gradient tends to be relatively large. In <br /> comparison, the anomalies produced by buried ferrous objects may be considerably <br /> smaller. Areas where the vertical magnetic gradient is steep are defined by closely <br /> spaced contours and are typically considered anomalous. <br /> If the source of a particular anomaly is an isolated object or a group of closely spaced <br /> objects, the contours may form circular or elliptical closures. These may or may not <br /> have paired high and low values indicative of a magnetic dipole. A large <br /> accumulation of buried objects may appear as a group of closely spaced anomalies <br /> or one large anomaly. <br /> Depending on their size and depth, UST's typically produce VMAG anomalies with <br /> magnitudes of several hundred gammas/meter. These anomalies are generally <br /> represented by closely spaced contours that form circular to elliptical closures. The <br /> closures are usually di-polar and cover an area somewhat larger than the UST itself. <br /> However, actual anomaly magnitude and shape are dependent on the relative position <br /> and size of the UST with respect to the location of the data points and surrounding <br /> cultural features. <br /> RESULTS <br /> VMAG Survey <br /> The results of the VMAG survey are presented on the Vertical Magnetic Gradient <br /> Contour Map, Plate 2. The VMAG Contour Map does not exhibit any anomalies with <br /> all of the UST characteristics described above. However, the contours in the <br /> southwest portion of the survey area do indicate VMAG magnitudes in excess of <br />