Modelo Hidrogeoquímico e Isotópico de Acuíferos Confinados. Córdoba. Argentina

CABRERA, A.; DAPEÑA, C.; BLARASIN, M.; PANARELLO, H.O.; MATTEODA, E.

Quito, Ecuador

Congreso; IX Congreso Latinoamericano de Hidrología Subterránea; 2008

ALHSUD

The objective of this work is to present a preliminary hydrogeochemical and isotopic model of confined deep aquifers in the studied area, resources of greatest interest due to the bad quality of the unconfined aquifer. Conventional methodologies were used and hydrochemical maps, Schoeller diagrams, box plots and dendrograms (Q mode) were obtained. The isotopic analysis (18O and 2H) were very significant in the assessment of these deep aquifers since the few sedimentological and hydraulic data of the deepest layers made difficult a hydrogeologic classification. The deepest sediments (120 m to 350 m), fluvial materials with wide ranging texture, were assigned to Upper Tertiary units. Three deep multilayered aquifer systems were defined taking into account depths and groundwater quality: a semiconfined system (SAS), a confined system with low confinement grade (SCA) and a confined system with high confinement grade (SCB). Although all of them contain fresh waters (CE < 2,800 μS/cm), hypothermal and mesothermal (29ºC-36ºC) and sodium sulphate geochemical type, the SAS (120 m-200 m) and SCA (225-290 m) levels displayed the most saline waters (CE >1,800 μS/cm) and the greatest concentrations of As and F- and similar isotopic content to thephreatic system (§18O = -5.0 a -4.6 y §2H = -32 a -28 ), being able to suppose a feasible hydraulic connection between these aquifers. The isotopic composition of local and western allochthonous streams and the characteristics of deepest confined levels (SCB, 225-340 m), with always artesian wells, better groundwater quality (CE < 1800 μS/cm) and different isotopic composition (§18O -6,6 and §2H -43 ) allow us to assume recharge sectors located outside this area, in the western perimountain region.