Hydrogeological Conceptual Model for the Casiri-Kallapuma Geothermal Zone, Tacna, Perú

The Casiri-Kallapuma geothermal zone is located in southern Peru in the high Andean zone of the Tarata province in the Tacna region. Hydrographically it is found in the Maure river basin and presents a generally semi-rigid climate, with average air temperatures ranging from -5 °C to 24 °C. The hydrogeological characteristics of the medium, such as piezometry, hydraulic parameters and hydrodynamic conditions and the hydrochemical characteristics, affect the feasibility and performance of the geothermal system. The hydrogeological conceptual model for the Casiri - Kallapuma geothermal zone (ZGCK) includes three hydrostratigraphic units, grouped into five aquifers (Capillune Formation, Maure Group, Barroso Group, Pleistocene Volcanics, and Quaternary deposits) with the main and deepest aquifer being the Maure Group, a volcanic aquitard (Sencca Formation), and a volcanic aquifuge (Tacaza Formation). Based on the pumping tests of two wells drilled by the Tacna regional government (Proyecto Especial Tacna) and located in the pampa Pilarpampa, northeast of the Maure river, a water reserve was estimated for the ZGCK, associated with the intercalation of siltstones and sandstones of the Maure Group with transmissivity (T) of 2138 m²/day (very high), hydraulic conductivity (K) of 6.48 m/day and storativity (S) at 2.17 × 10-2. This aquifer is recharged mainly by meteoric water infiltration through the overlying hydrostratigraphic units. The hydraulic conductivity is controlled by normal faults and joints with direction S-N and NE-SW, which influence the transmissibility, the storage of groundwater, and the discharge of cold and thermal waters from the Casiri geothermal system. The Chungara-Pampa Juntopujo zone is where greatest surface discharge of thermal waters occurs at temperatures from ~19 – 86°C.