The "Autorite des amenegements des valees des Voltas (AVV)" is establishing new rural settlements in the Volta valleys. First, a survey of available water supplies is performed. Economic aquifers in Precambrian terrains are deep (15-50 m) and usually occur in fractured zones accompanying faults. Such zones can be identified on aerial photographs, but their precise location on the ground is virtually impossible by visual means. Because of the small size of the aquifers, a location error of 5 m can make the difference between a productive well and a dry hole.Traditionally, resistivity profiling has been used as the means of locating the fractured zones in the field. Our studies suggest that the task can be performed faster, cheaper and more accurately by VLF and EM methods. Because of the limited choice of transmitting stations receivable in Upper Volta, the VLF method is not sufficiently sensitive to detect conductors with a strike between 45" and 105". The results obtained with a multifrequency, horizontal-loop EM (HLEM) system were satisfactory in all investigated areas. During the 1980 field season, 35 target areas were surveyed. Of the 24 holes drilled so far, 23 are productive.The weathered layer is a source ofdistinctive HLEM anomalies, which are characteristic of the underlying rocks. Therefore, different interpretational procedures had to be developed for granitic and volcano-sedimentary areas. Despite the high background level of in-phase and quadrature components, which varied with thickness and conductivity of the weathered layer, aquifers could be detected at a depth greater than 30 m. Attempts were made to interpret the 932-955.

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