Groundwater Resources for Small Rural and Aboriginal Communities in Chaco Province, Argentina

Geoscientists Without Borders
Water Management Projects

Scarcity of drinking water plagues the Miraflores community of the Chaco Province in northern Argentina.

The economy of this mostly rural community is based on agriculture, cattle raising and brickworks. The main source of freshwater is the surface water which is limited and strongly depends on local rivers stream flows. Freshwater, when affordable, is trucked into the community.

During economically difficult times community members resort to hand dug wells 8-15 meters deep. These shallow wells often have high salt and arsenic concentrations.

The goal is to locate sustainable groundwater resources using electrical prospecting methods

Status In Progress

Statement of Work

The electrical prospecting method is one of the most suitable techniques for searching groundwater resources. It consists in the injection of a known electric current into the ground and the subsequent measure of the electrical potential difference between electrodes strategically placed on the surface. Based on these measurements, electrical resistivity values can be obtained for different depths. Electrical resistivity quantifies the ability of a given material to oppose the flow of an electric current through it. In sedimentary rocks, the electrical resistivity depends on both the mineral composition and the liquid electrolyte content in the pore space. For this reason, determination of this electrical property allows to identify variations in both lithology and salinity of groundwater.

Another useful property for lithological characterization of the subsurface is the electrical chargeability. This property quantifies the ability of a material to store electrical charge. Chargeability can be obtained from induced polarization methods. In the time domain, the induced polarization consists in the measurement of the decaying potential difference between the electrodes once the injected current is turned off. In the frequency domain, it consists in the measurement of the electrical impedance and the phase. Chargeability is more sensitive to surface conduction effects and can be linked to lithological properties (rather than electrolyte contents). The Vertical Electrical Sounding (VES) is a useful method for estimating the vertical distribution of resistivity at a given site. This method is based on the inversion of data measured at the surface of the soil assuming a conceptual model with horizontally homogenous layers. For estimating lateral variations of resistivity a more complex technique is required. The Electrical Resistivity Tomography (ERT) combines vertical and horizontal estimation of resistivity values which are displayed as depth profiles or electrical resistivity images.

Changes observed in resistivity sections can be produced by lithological variations but can also be the result of variations in the groundwater salt concentration. In these cases, the analysis of chargeability can be used to recognize the nature of the observed electrical effects. All these methods described above allow to obtain different characterizations of the electrical resistivity of the subsurface. The correlation between resistivity values and the lithology observed in the monitoring wells will permit the localization of paleochannels, sallow freshwater bodies and deep aquifers.

The analysis of the arsenic content will be performed in situ by a semi-quantitative procedure. This procedure consists in classifying the water quality. More precise determinations of arsenic concentrations will be achieved in laboratory by means of Graphite Furnace Atomic Absorption Spectroscopy (GFAAS). The water for human consumption will be fully analyzed in order to determine not only the presence of other contaminants such as fluor, but also the salinity and bacteriological quality. With regard to the reduction of the arsenic content, an adsorption technique will be employed using accessible iron-rich mineral species. Some members of the work team have extensive experience in designing and applying arsenic and fluor removal techniques. Currently, the team is working on other similar regions affected by this issue, and is having satisfactory results in reducing the contaminant content levels to those established by the World Health Organization (WHO). The removal strategy will be adapted to the local scenario (water quality, access to electricity, shaking conditions in the water-absorbent system, presence of particle materials and use of additives in order to accelerate the sedimentation process, etc).

Principal Investigator

Professor Luis Guarracina, UNLP-CONICET 
GeoHazards International

Team members

The project includes chemists, geologists, geochemists, journalists, logisticians, accountants and engineers from Universidad Nacional de La Plata (UNLP), Buenos Aires Province Scientific Research Council, the National Scientific and Technical Research Council, CEQUINOR, PLAPIMU and INREMI including Professors Agosta, Ainchil, Lia Botto, Cruzado, Rodriguez, Ruiz, Schalamuk, Sofia, Tinto, Tocho, Thomas and others

The SEG Student chapter is involved and includes students – Avellaneda, Castroman, Gelpi, Gomez, Goni, Hurtado, Juarez, Lagos, Perdomo, Solazzi, and others

Miraflores community – Felipe Gomez and team members

 

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