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2-1 • 2.0 APPROACH I Ertec personnel used an ABEM Terremeter Low frequency A.C. resis- tivity unit to perform the survey. Both profiling and sounding techni- ques were used. There is a great deal of electrical interference at the mine site. Buried gas Lines, power lines, several iron fences, and grounded equipment and structures had a noticeable but not detrimental effect on portions of the resistivity survey. Welding vas also taking place on the dragline during much of the survey. A Wenner electrode array (Figure 1) was used for all resistivity profiling. The technique uses the same spacing between the current electrodes and the potential electrodes. It is easy to use and the measured potential differences are large and therefore more definitive for interpretation. Linea 1 and 2 were initially profiled using 50-foot electrode spacing and 50-Foot at at ion spacing. Line 2 was surveyed again at 100-foot electrode spacing and 100-foot station spacing. Linea three • through seven were all profiled using 100-foot electrode spacing and 100-foot at at ion spacing. The data was first plotted on a semi-log ,_ graph, apparent resistivity versus station number, and then analyzed qualitatively for areas of high apparent resist iv itiea which would indicate poorer conducting layers such as sands and gravels. The data was then plotted at a scale of L" ~ 600 feet on an overlay of the Keeneburg Mine site map and a contour map of apparent resistiv h ies was prepared. This data was analyzed qualitatively for paleo-channel locations. A paleo-channel location map (Plate 1) was prepared using [he 40 ohm-foot contour as the arbitrary extent of Ennis Draw. Vertical electric soundings were performed at 49 locations to determine the vertical variation of apparent earth reaistivities and stratigraphy. A Wenner array was set up about the et at ion perpendicular to the profile line. The electrode spacing was increased logarithmically and apparent reaistivities were calculated at each spacing. The data was then plotted on three-cycle log-log graph paper, apparent resistivity as • the ordinate and electrode spacing as the abscises.