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• The Geometrics G-858 cesium vapor magnetometer is typically used to obtain vertical magnetic ' gradient data. This instrument features a built-in memory that stores the vertical magnetic gradient and survey grid information. The information can be down loaded to a computer for further processing. ' Data Analysis ' Computer Processing ' The EM and VMG data are downloaded to a personal computer and converted it into a format for contouring. The contouring program (SURFER Version 8.0 by Golden Software) calculates an evenly spaced array of values(grid)based on the observed field data. Finally, these gridded values are contoured to produce EM(TC and IPC)and VMG contour maps. The contour intervals for each map are typically selected based upon the specific intensities, as well as for clarity of presentation. The contour maps are then analyzed to determine potential locations that may represent buried landfill material. Contour Map Interpretation The TC,IPC, and VMG contour maps show the respective variations in the electromagnetic terrain conductivity,electromagnetic in-phase component,and vertical magnetic gradient values within the ' survey area. Each contour map is characterized by a series of contour lines that represent specific values. Areas that lack contour lines,or where the contours are spaced far apart,indicate a minimal change or variation in the respective values. This is indicative of relatively uniform conditions. Areas where contours are closely spaced indicate variations that are not uniform and probably caused by local sources. ' In areas where there are significant quantities of above or below ground metal objects,the measured values are relatively large. These areas are characterized by numerous closely spaced contours. If ' the source of the anomaly is linear(e.g. underground utilities,railroad spurs, culvert, etc.),then the contours tend to parallel the object, and are closely spaced in close proximity to the object. If the below ground source is localized (e.g. buried drum, isolated metal debris, etc.), then the contours tend to form circular or elliptical closures that enclose the object. The larger the object and the closer it is to the geophysical instrument,the more contours there are in a given area. Variations that cannot be attributed to known above and/or below ground objects (metal well casings, reinforced ' concrete surface drain,above ground 55 gallon drums,utilities,etc.)are caused by unknown buried objects and are considered anomalous. ' Buried landfill material is often characterized by circular to elliptical contour closures. These closures can vary from large circular closures that cover broad areas,to clusters of small closures that ' A-2