[en] Two problems associated with groundwater flow were fully identified by the application of geochemical techniques. The first was related to the Palacio tunnel, where infiltration of 400 litres/min caused caving-in and other problems which held up construction for several months. To anticipate further problems and to plan the requisite engineering work, a study was carried out to locate the origin of the groundwater responsible for these difficulties. Water samples were taken from the four possible sources: a pool, a series of large fissures, superficial fluvioglacial deposits and the Guadalupe sandstone which crops out one kilometre from the cave-in site. After correlation of the results of chemical analyses with geological and hydrological information about the area, the conclusion was reached that the groundwater in question flows from the Guadalupe sandstone through fractures and secondary openings. The second problem studied was that of the immense Quebradablanca landslide caused by infiltration of water into and percolation through alluvial deposits. A drainage system had already been designed to intercept and collect direct infiltration water above the alluvium, thereby preventing the latter from becoming saturated. The present study was carried out to determine whether there was groundwater flow from the rocks adjacent to the alluvium. The results of the geochemical analysis indicate that most of the water does in fact come from the adjacent hard rock rather than from direct infiltration of rain-water above the alluvium. This shows that the drainage system designed is insufficient for preventing saturation of the rock and that a more extensive and costly system would be needed to control the groundwater flow. (author)