Groundwater is the primary source of water for people living in rural areas, especially during seasons when surface water is contaminated or unavailable. In Colombia, people use groundwater as drinking water without additional treatment. In addition, there is no infrastructure for wastewater collection and sewage treatment in the region of the Middle Magdalena Valley. The current study aims to evaluate the quality of groundwater in this region to determine any potential health hazards associated with its consumption. To reach the objective, three (3) physicochemical and microbiological sampling campaigns were carried out during different hydrological periods. A total of 428 groundwater samples were analyzed for over 28 parameters. The results were compared with the water quality standards proposed by the US EPA and Colombian regulations for human consumption. The analysis revealed the presence of total and fecal coliforms in 89% and 58% of the analyzed samples, respectively, identifying them as the main contaminants in groundwater. Furthermore, the pH levels did not meet the standards set by the US EPA in 33.8% of the cases and by Colombian regulations in 31.02%. Additionally, 32.8%, 17.6%, 14.3%, and 10.9% of the samples failed to meet the established thresholds for apparent color, magnesium, iron, and nitrates, respectively, under both standards. Moreover, only the analyses of selenium, mercury, and zinc complied with the quality standards under both regulatory frameworks. Based on the Colombian Drinking-Water Quality Risk Index (CDWQRI-IRCA), the risk associated with water quality meant for human consumption was assessed. The results showed that over 84% of the samples analyzed posed a high risk to human health, 4.6% posed a medium risk, 5.5% posed a low risk, and only 5.7% posed no risk at all. Additionally, official mortality statistics for children under four years old were reviewed, which revealed two deaths in 2019 due to Acute Diarrheal Disease (ADD) caused by consumption of contaminated water. Therefore, it is crucial to implement water treatment systems, establish aqueducts in rural areas, and conduct rigorous and systematic monitoring of drinking water to ensure it is safe for human consumption. It is also important to track morbidity and mortality rates associated with water consumption.

This study presents a methodology for estimating hydraulic conductivity (K) from well geophysical logs, with the aim of improving the parameterization of hydrogeological models in data-scarce regions. The lack of data poses a challenge for aquifer characterization, especially in contexts requiring integrated groundwater management. In such contexts, indirect methods can support estimation of key hydraulic parameters. The proposed methodology was applied to wells which penetrate Neogene–Quaternary hydrogeological units of the sedimentary aquifer system in the Middle Magdalena Valley, Colombia. Effective porosity was estimated from sonic and gamma ray logs, while temperature profiles were derived from the regional geothermal gradient and calibrated with field measurements. Hydraulic conductivity was estimated using an approach based on the Csókás method and validated through comparison with 131 pumping tests and alignment with the parameterization of a previously calibrated regional groundwater flow model. Pumping tests yielded geometric mean K values of 1.56 m/day in floodplain deposits (QFal), 1.36 m/day in U4, and 0.96 m/day in U3. K values from well logs ranged from 1.65 to 2.95 m/day, within the same order of magnitude. These findings support the proposed methodology as a viable alternative for the parameterization of numerical hydrogeological models in data-scarce environments.

The characterization of the inherent heterogeneity of aquifer systems on a regional scale represents one of the main challenges in the study of groundwater, especially when there are uncertainties associated with the scarcity of hydrogeological information (Maliva, 2016).Based on the implementation of a numerical hydrogeological model in a regional scale, the objective of this study was to characterize the most recent geological formations which have the greatest hydrogeological potential in the Middle Magdalena Valley (VMM) in Colombia. The VMM is bounded by the Eastern Cordillera of the Colombian Andes and the Bucaramanga-Santa Marta fault to the east and the San Lucas Mountain range and the Central Cordillera to the west. This is considered one of the main hydrogeological basins in the country, in which a high potential of hydrocarbon production from the exploitation of unconventional deposits has also been identified (Sarmiento et al., 2015; Londoño, 2019).  For these reasons, the groundwater management, based on the characterization of this hydro system, has a national interest.In this study the characterization of the heterogeneity was approached from the estimation of hydraulic parameters by solving the inverse problem by means of a hydrogeological model on a regional scale (Carrera et al., 2005; Zhou et al., 2014). For this, 153 pumping tests were carried out and interpreted, allowing to parameterize the model in seven iso-conductivity zones. Also 12,383 discrete static level data were measured and collected in 19 years -time window and they were used in the calibration process. Furthermore, three field campaigns for measuring in-situ parameters (electrical conductivity, pH, dissolved oxygen, and temperature) were performed they served to enhance the conceptual model.Based on this, variations in hydraulic conductivities were identified on a regional scale for each iso-conductivity zone, fluctuating by four (4) orders of magnitude. The main flow direction was in the south-north, parallel to the Andes cordillera and therefore to the Magdalena River, and with some minor local flows perpendicular to them, producing important outflows from the system in permanent lentic water bodies in the north. The results of the research are encouraging, but at a regional scale they still do not allow to have a high resolution of the heterogeneity of the hydro system models for decision making, so it is suggested to implement stochastic models at a regional scale and to construct multi-purpose groundwater monitoring networks in this basin.AcknowledgmentsThe researcher thanks the MEGIA Research Project, Contingent Recovery Contract FP44842-157-2018 funded by Minciencias and the National Hydrocarbons Agency.

Groundwater is one of the main sources of water supply in tropical developing countries; however, its integrated management is often constrained by limited hydrogeological information and increasing anthropogenic pressures on aquifer systems. This study presents the numerical modeling of groundwater flow in the Neogene–Quaternary aquifer system of the Middle Magdalena Valley (Colombia), focusing on the rural area of Puerto Wilches, which is characterized by strong surface–groundwater interactions, particularly with the Yarirí wetland and the Magdalena River. A three-dimensional model was implemented and calibrated in FEFLOW v.8.1 under steady-state and transient conditions, integrating both primary and secondary data. The dataset included piezometric levels measured with water level meters and automatic loggers, hydrometeorological records, 21 physicochemical and microbiological parameters analyzed in 45 samples collected during three field campaigns under contrasting hydrological conditions, 79 pumping tests, detailed lithological columns from drilled wells, and complementary geological and geophysical models. The results indicate a predominant east–west groundwater flow from the Eastern Cordillera toward the Magdalena River, with seasonal recharge and discharge patterns controlled by the bimodal rainfall regime. Microbiological contamination (total coliforms in 69% of groundwater samples) and nitrate concentrations above 10 mg/L in 21% of wells were detected, mainly due to agricultural fertilizers and domestic wastewater infiltration. Particle tracking revealed predominantly horizontal flow paths, with transit times of up to 800 years in intermediate units of the Real Group and around 60 years in shallow Quaternary deposits, highlighting the differential vulnerability of the system to contamination. These findings provide scientific foundations for strengthening integrated groundwater management in tropical regions under agroindustrial and hydrocarbon pressures and emphasize the need to consolidate monitoring networks, promote sustainable agricultural practices, and establish preventive measures to protect groundwater quality.

Water quality is one of the major causes affecting human health, especially in vulnerable populations in developing countries. In Colombia, groundwater is often consumed by rural populations as drinking water without any treatment. Therefore, a groundwater quality assessment in the Middle Magdalena Valley in Colombia (MMV) was conducted to determine potential health hazards associated with its consumption. The study area covers approximately 8500 km2 and is bounded by the piedmont of the San Lucas Mountain range and the Central and Eastern Mountain Ranges of the Andes.In this study, 458 water samples were analyzed. They were collected during three (3) field campaigns conducted between February 2020 and March 2021, encompassing contrasting hydrologic periods. Based on laboratory results, the potential health hazards associated with groundwater consumption were assessed using the Colombian Water Quality Risk Index (CDQRI-IRCA).CDQRI-IRCA values in the MMV ranged from 0 to 80, with a mean of 51 and a standard deviation of 21. Furthermore, more than 84% of the analyzed samples were classified as high risk for human consumption. This outcome is associated with the presence of fecal and total coliforms in 58% and 89% of the analyzed samples, respectively. These parameters hold the highest specific weights in the CDQRI-IRCA calculation.The presence of fecal and total coliforms in groundwater in the MMV is associated with deficiencies in sanitation coverage, particularly in rural areas where water supply wells are often located near septic tanks, handmade pit latrines without proper hygienic protection, or in areas with backyard livestock farming. AcknowledgmentsThe researcher thanks the MEGIA Research Project, Contingent Recovery Contract FP44842-157-2018 funded by Minciencias and the National Hydrocarbons Agency

Sustainable management of hydrogeological systems that supply water and exhibit high hydrologic complexity can be studied through pragmatic numerical modeling supported by field-constrained conceptualization. This study develops a local-scale three-dimensional groundwater flow numerical model using FEFLOW for the Barranca Lebrija settlement in Aguachica town, where the Lebrija River, the Musanda floodplain lake, and groundwater system converge. The numerical model incorporates: (i) the three-dimensional distribution of geological units and lithology; (ii) water level observations from the Musanda floodplain lake; (iii) stage records from the Lebrija River; (iv) boundary conditions and flux estimates inherited from a previous regional groundwater model; and (v) hydraulic heads from two monitoring wells and five community wells. Steady-state and transient conditions were calibrated, and a sensitivity analysis was performed to identify the parameters that most strongly control surface water–groundwater exchange. The simulations reproduce seasonal groundwater level trends and demonstrate the exchange pathways among the river, floodplain lake, and groundwater system. Results indicate dual behavior: during wet periods, flooding of the Musanda floodplain lake driven by high river levels seeps into the underlying aquifer, whereas in dry periods the floodplain lake reverses its role and becomes a principal discharge boundary. This local-scale, boundary-driven approach provides a computationally tractable framework to quantify SW–GW exchange in data-scarce tropical floodplains and supports monitoring design and water-supply management.