Conceptual models of aquifer systems can be refined and complemented with geophysical data, and they can assist in understanding hydrogeological properties such as groundwater storage capacity. This research attempts to use geoelectrical methods, Electrical Resistivity Tomography and Induced Polarization parameters, for mapping the subsurface in alluvial fans and to demonstrate its applicability; the Punata alluvial fan was used as a case study. The resistivity measurements proved to be a good tool for mapping the subsurface in the fan, especially when used in combination with Induced Polarization parameters (i.e., Normalized Chargeability). The Punata alluvial fan characterization indicated that the top part of the subsurface is composed of boulders in a matrix of finer particles and that the grain size decreases with depth; the electrical resistivity of these deposits ranged from 200 to 1000 Ωm, while the values of normalized chargeability were lower than 0.05 mS/m. The bottom of the aquifer system consisted of a layer with high clay content, and the resistivity ranged from 10 to 100 Ωm, while the normalized chargeability is higher than 0.07 mS/m. With the integration of these results and lithological information, a refined conceptual model is proposed; this model gives a more detailed description of the local aquifer system. It can be concluded that geoelectrical methods are useful for mapping aquifer systems in alluvial fans.

The porous aquifers in the area called Challapampa are the most important groundwater reservoirs that supply drinking water to Oruro city in the highlands of Bolivia. They consist of unconsolidated fluvial–lacustrine deposits, resting on a complex sedimentary bedrock and covered by a thin surficial clay layer. The settings of these geological units and the structures governing the flow patterns have barely been investigated, despite this reservoir having been utilized during the last 50 years. This study applied transient electromagnetic (TEM) soundings and electrical resistivity tomography (ERT) in the middle part of the alluvial fan of River Paria to investigate the thickness of the porous aquifer and detect the relief of the bedrock. Likewise, some results expressed as resistivity models indicate the possible existence of geological structures below the unconsolidated sediments. The average depth of investigation reached in this study is between 200 and 250 m below the surface, for both the applied methods. The geological structures inferred have similar directions as the major faults in the vicinity, from southeast to northwest, which in turn are assumed as part of fractured aquifers underlying the porous aquifers. The geo-electrical techniques were successfully tested in the study area and the resistivity models from TEM complement very well those obtained from ERT. Therefore, extended investigations using the same techniques would help to develop a more complete description of the hydrogeological settings of the aquifer system.

Aridity and seasonality of precipitation are characteristics of the highland region in Bolivia. Groundwater becomes an important and safe source of water when surficial bodies are intermittent and affected by natural and anthropogenic contamination. Decades of exploitation of the Challapampa aquifer, combined with lack of information required to understand the groundwater circulation, represent a challenge for reservoir management. This study analyzes isotopic compositions of deuterium and oxygen-18 in different stages in the hydrologic cycle to assess flow patterns in the aquifer, especially in the alluvial fan of River Paria, where records are more extensive in space and time. Interpretations are based on existing and new data. Some implications, such as the age of water, the evaporation effect in groundwater and some thermal intrusions are supported by stable isotopes, tritium, radiocarbon, and electrical conductivity records. New results confirm that modern precipitation over the mountains surrounding the study area is the most important origin of water for shallow aquifers until exploited depths, 100 m below surface. The origin of water in deeper depths, 400 m, seems related to infiltration at higher altitudes and longer residence times.

The analysis of stable isotopes assisted in identifying that groundwater in the Punata alluvial fan is mainly recharged by heavy flash floods, and the recharge from rainfall is of less importance. In addition, the hydrochemical analysis identified the Pucara River as the main source of recharge. Other streams in the north and northwest of the fan do not seem to contribute to the recharge. The hydrochemistry also shows that there is an increase of the Na⁺ and Cl⁻ concentrations in the middle and distal part of the fan. The salinization of groundwater is most likely a result of the mixing of fresh water with residual saline pore water in the lacustrine deposits and/or ion exchange within these layers. Geophysical surveys assisted in describing the aquifer system layering, and indicated a fine-grained bottom layer where ion exchange might occur. This study demonstrates that the integration of several methods (e.g., hydrochemistry, hydrogeophysics, and stable isotopes) is valuable for clarifying ambiguities during the interpretation process and for characterizing hydrogeological processes in alluvial fans in general.

Although groundwater serves as the predominant source of drinking water across many rural regions and certain urban areas of Rwanda, little is known about this resource. Anthropogenic impacts, such as faecal contamination, as well as geogenic water quality problems, including elevated arsenic, fluoride, iron, and manganese, are among the issues of concern for groundwater quality in Rwanda. Long-term groundwater monitoring can provide data on the evolution of groundwater quantity and quality. It helps to identify trends related to over-abstraction, reduced recharge, and pollution, which supporting resource management decisions. This review assesses the current state of groundwater monitoring in Rwanda by identifying the strengths and weaknesses of existing monitoring efforts, knowledge gaps, and opportunities for improved groundwater monitoring and management. The findings indicate that groundwater quality assessments are only conducted for specific purposes without considering broader issues and that groundwater monitoring in Rwanda is, in many respects, insufficient. Based on these findings, the following recommendations are made: (1) expand the existing groundwater monitoring network to encompass all groundwater types, geological settings, and anthropogenic pressures in Rwanda; (2) install rainfall gauging stations at or near the groundwater monitoring stations to enhance the interpretation of groundwater monitoring data; (3) conduct groundwater sampling campaigns at least twice a year, that include major ion analyses; and (4) to regularly analyze and disseminate the monitoring results.