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aCa • Appendlkx S DATA ANALYSIS Of the geophysical methods used at this site, only magnetic and GPR data require analysis. Descriptions of the data analysis procedures for these techniques are provided below. TF Computer Processing We up-loaded the TF data we obtained in the survey area to a portable computer and converted them into a format suitable for contouring. The contouring program calculated an evenly spaced array of values (data grid) based on the observed field data. The gridded values were then contoured to produce a TF contour map. TF Contour Map Interpretation Generally speaking, in a region with uniform conditions TF values vary smoothly from one area to another. In contrast, in areas where magnetic variations are strong,the contours are moderately to closely spaced. In many cases, the variations are so strong that the contours are highly contorted and convoluted, with differences of several hundred units. These contorted contours may appear as roughly concentric circles forming "bull's eyes", tightly wound loops and whorls, or elongated parallel lines. If the source of a particular anomaly is an isolated object or a group of . closely spaced objects, the contours may form isolated, somewhat symmetric closures known as "monopoles" (bull's eyes) or paired positive-negative closures known as "dipoles". If the source of a particular anomaly is group of several objects not very closely spaced, then the contours will often form highly irregular, non-symmetric closures. Areas that are typically considered anomalous are those which display large differences in data readings from one locality to the next. Particularly suspicious are areas where there are no obvious nearby above ground sources that could cause the variation. Actual anomaly magnitude and shape are dependent on the relative position and size of the buried objects with respect to the location of the measuring instrument. In general, anomaly magnitude decreases and anomaly width increases as distance (depth) to the source increases. TF monopoles that are centered on a single data point and limited in extent to roughly the data point spacing of the sampling grid are often caused by small, near surface objects. Such objects may consist of well caps, pull boxes, balls of wire, etc. Larger monopoles that extend across an area equal to several data points are typically associated with larger objects. Isolated dipoles are often, but not always, attributed to a single object such as a UST, vault, buried ordnance, etc. A large accumulation of buried objects may appear as a group of closely spaced, contorted anomalies or a single large, less contorted anomaly. Elongated anomalies with parallel contour lines or a linear alignment of circular or elliptical closures is often indicative of a buried pipeline or other elongate object. Those anomalies that are neither monopoles or dipoles often are associated with multiple objects buried near each other, such as those comprising a debris field. • B-1