Abstract

Based on the objectives set out in the project "Drinking water supply in some populations of the departments of Atlántico, Bolívar, Córdoba and Sucre," the product of a Technical Cooperation Agreement between the governments of Colombia and the Netherlands signed in 1985, this report was prepared as a synthesis of the "Hydrogeological Study of the middle and lower Colombian Guajira - Phase 2" conducted by Ingeominas and TNO - DGV of the Netherlands between 1977 and 1978.

The study was carried out in the department of La Guajira, within the area comprised by the foothills of the Serranía de Cocinas to the north and the foothills of the Sierra Nevada de Santa Marta to the south, with the Caribbean Sea as the western boundary and the Venezuelan border as the eastern boundary.

During the project, geological, hydrological, geoelectric, hydrochemical, isotopic, and hydrogeological investigations were carried out i to evaluate groundwater resources given the water needs for all uses in this region of the country.

For reasons beyond the control of Ingeominas and TNO-DGV, it was necessary to suspend the project at the end of 1978, but the information obtained up to that time, complemented with that of the project "Exploration of Aquifers of the Upper and Middle Guajira," allows us to assure that there is an appreciable volume of groundwater available, which has not yet been quantified.

Through the various stages of the project, five hydrogeological units were defined, of which two are considered potentially aquiferous due to their good primary porosity, moderate to high permeability, and are called Quaternary Complex (Q) and Tertiary Detritic Complex (T).

The Quaternary Unit (Q) represents all the Quaternary deposits of continental origin that make up the flat part of the Middle and Lower Guajira, where the presence of a free aquifer of low production was verified with water generally of a sodium chloride type. This water is considered suitable for human consumption towards the southern and central part of the study area. However, it is unsuitable for its high chloride content, from the central part towards the north and near the coast.

The Tertiary Detritic unit (T) comprises sedimentary rocks of marine origin that outcrop mainly to the south of Riohacha, where they behave as recharge zones. In the rest of the area, they are covered by Quaternary deposits. In this unit, a confined aquifer has been developed to produce high flows of sodium chloride water, potable in the regions close to the recharge areas and unsuitable towards the north, where the chloride content exceeds the maximum tolerable by the human organism.

The three remaining hydrogeological units, called Calcareous Unit (K), Mesozoic Detritic Unit (M), and Igneous-Metamorphic Unit (IM), only outcrop in the recharge areas located at the northern and southern ends of the area investigated, lacking importance as aquifers due to their strong compaction. At the southern end, these units are tectonically affected by the Oca fault, which causes secondary porosity due to fracturing along the fault zone and serves as infiltration zones for surface water coming from the Sierra Nevada de Santa Marta, feeding mainly the confined aquifer through underground flows.