Mapping the regional hydrogeological units, flow systems and chemical-thermal groundwater features in a sedimentary basin, Argentina

BLARASIN, MÓNICA; CABRERA, ADRIANA; MALDONADO, LUCIANA; BECHER QUINODOZ, FÁTIMA; MATTEODA, EDEL; GIULIANO ALBO, JESICA; FELIZZIA, JUAN; ECHEVARRIA, KARINA; DEGIOVANNI, SUSANA

Roma

Congreso; 42 nd IAH Congress; 2015

IAH-Sapienza University of Rome

In this paper we show the most important hydrogeological regional characteristics of the South of Córdoba province (Argentina). The maps were made using a Geographical Information System. The work was financed by the government and the products used for hydrological policy management. The main hydrogeological environments are the fissured aquifer in the Comechingones Mountains and the large sedimentary aquifer system in the eastern Pampean plain. The mountains act as a vital water source, mainly due to streams infiltration in the piedmont, which partially feed the groundwater plain system. The sedimentary sequence (Upper Paleogene- Quaternary) has conditioned the hydrostratigraphic ensemble of aquifer, aquitard and aquiclude formations. Groundwater flow direction is WNW-ESE for all the identified aquifer systems.The unconfined aquifer (annual recharge between 8 and 20 per cent of the annual rainfall) is mainly comprised of fluvial and aeolian Quaternary deposits. In river belts and peri-mountain alluvial fans high groundwater volumes are abstracted (up to 500 m3/h). The sediments of confined aquifer systems (CAS) are from continental and marine origin (Upper Paleogene-Lower Pleistocene). CAS are multilayered and lie between depths of 100 and 450 m. Major water stores correspond to CAS comprised of fluvial sediments. Piezometric levels of different CAS layers are generally higher than water table. Artesian wells are common, presenting variable flow rates (up to 250 m3/h). Chemical groundwater composition mainly responds to geologic setting. Groundwater from the unconfined aquifer exhibits an increasing salt content according to the regional flow direction. It shows a geochemical evolution, from calcium and sodium bicarbonate type (recharge areas) to sodium sulfate (intermediate plains) and, finally, to sodium chloride (low areas). Less suitable areas for groundwater abstraction are those where aeolian sediments prevail (high As and F values). CAS have fresh to brackish water that also evolves from bicarbonate to sulfate/chloride type in flow direction. Isotopic results (2H, 18O, 3H, 14C) confirm that: a) the piedmont is the main recharge area; b) the unconfined aquifer holds young water and c) CAS have water ages up to 40,000 BP. Some confined layers have hypo/mesothermal waters (up to 36 ºC) conditioned by the regional geotectonic setting.