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Pettenati M.,Bureau de Recherches Geologiques et Minieres | Perrin J.,Bureau de Recherches Geologiques et Minieres | Perrin J.,Indo French Center for Ground Water Research | Pauwels H.,Bureau de Recherches Geologiques et Minieres | Ahmed S.,NGRI
Applied Geochemistry | Year: 2013

Overexploitation of crystalline aquifers in a semi-arid climate leads to a degradation of water quality, with the main processes responsible for the observed salt loads probably being irrigation return flow (IRF) and a high evaporation rate. The present study has focused on modelling the F- accumulation caused by IRF below rice paddy fields in the small endorheic Maheshwaram watershed (Andhra Pradesh, Southern India). The transient simulation was performed with a 1D reactive transport PHREEQC column and took into account IRF evaporation, kinetically controlled mineral dissolution/precipitation, ion adsorption on Fe hydroxides, and mixing with fresh groundwater. The results revealed the role of cationic exchange capacity (CEC) in Ca/Na exchange and calcite precipitation, both favouring a decrease of the Ca2+ activity that prevents fluorite precipitation. Iron hydroxide precipitation offers a not inconsiderable adsorption capacity for F- immobilization. The principal sources of F- are fluorapatite dissolution and, to a lesser extent, allanite and biotite dissolution. Anthropogenic sources of F-, such as fertilizers, are probably very limited. After simulating an entire dry-season irrigation cycle (120days), the results are in good agreement with the observed overall increase of Cl- in the Maheshwaram groundwater. The model enables one to decipher the processes responsible for water-resource degradation through progressive salinization. It shows that F- enrichment of the groundwater is likely to continue in the future if groundwater overexploitation is not controlled. © 2012 Elsevier Ltd. Source

Pauwels H.,Bureau de Recherches Geologiques et Minieres | Negrel P.,Bureau de Recherches Geologiques et Minieres | Dewandel B.,Indo French Center for Ground Water Research | Dewandel B.,Bureau de Recherches Geologiques et Minieres | And 5 more authors.
Journal of Hydrology | Year: 2015

Hydrochemical borehole-loggings with a submersible Idronaut Ocean Seven 302 multiparameter probe equipped of F- and NO3-ion-selective electrodes in combination with EC, pH and dissolved oxygen, were applied for characterizing fluoride (F) contamination in a crystalline (hard-rock) aquifer of a small Indian agricultural watershed where groundwater is intensively abstracted for rice irrigation. A high accuracy of F concentrations determined in-situ-shown by comparing with laboratory analyses-was obtained through using conductivity logs for ionic strength consideration. Large variations in chemical composition and particularly of F-concentration were observed inside boreholes, though restricted to the weathered/fractured layer down to 30-35m depth. This conforms to the hydrogeological model of a crystalline aquifer where most groundwater flow occurs in the shallow part of the fractured zone. The general trend of increasing F content with depth results from F accumulation through water-rock interaction, but the shape of the F profile depends on the connectivity of the fracture network close to the borehole. The concentrations seen within the water-table fluctuation zone locally suggest F input from fertilizers in groundwater, in addition to the earlier-demonstrated role of evaporation from irrigation return flow. It is also likely that, locally, the deepening of boreholes has contributed to increasing the population's vulnerability by tapping F-enriched groundwater at depth. © 2015 Elsevier B.V. Source

Negrel P.,Bureau de Recherches Geologiques et Minieres | Pauwels H.,Bureau de Recherches Geologiques et Minieres | Dewandel B.,Bureau de Recherches Geologiques et Minieres | Dewandel B.,Indo French Center for Ground Water Research | And 5 more authors.
Journal of Hydrology | Year: 2011

Groundwater degradation through abstraction, contamination, etc., shows a world-wide increase and has been of growing concern for the past decades. In this light, the stable isotopes of the water molecule (δ18O and δ2H) from a hard-rock aquifer in the Maheshwaram watershed (Andhra Pradesh, India) were studied. This small watershed (53km2) underlain by granite, is endorheic and representative of agricultural land-use in India, with more than 700 bore wells in use. In such a watershed, the effect of overpumping can be severe and the environmental effects of water abstraction and contamination are of vital importance. A detailed and dynamic understanding of groundwater sources and flow paths in this watershed thus is a major issue for both researchers and water managers, especially with regards to water quality as well as the delimitation of resources and long-term sustainability.To this end, the input from monsoon-precipitation was monitored over two cycles, as well as measuring spatial and temporal variations in δ18O and δ2H in the groundwater and in precipitation. Individual recharge from the two monsoon periods was identified, leading to identification of periods during which evaporation affects groundwater quality through a higher concentration of salts and stable isotopes in the return flow. Such evaporation is further affected by land-use, rice paddies having the strongest evapotranspiration. © 2010 Elsevier B.V. Source

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