Assessing groundwater recharge mechanisms in the Pampa del Tamarugal Basin of northern Chile's Atacama Desert

Abstract:

The hyper-arid Atacama Desert in northern Chile is one of the driest inhabited places on Earth receiving little to no rain (<5 mm/yr). Within the Tarapacá Region of the Atacama Desert, the Pampa del Tamarugal Aquifer (PTA) is the primary source of water for agriculture, industry, mining, and residential uses. The PTA covers 5,000 km², and is located in the Pampa del Tamarugal Basin, which is situated between the Andes and the Coastal Cordillera, and is filled with ~1700m of Miocene and younger sediments. The source of recharge for the PTA originates as precipitation in the high Andes, which can receive up to 400 mm/yr of precipitation; however, the mechanisms and magnitude of recharge to the PTA are still poorly understood. Here, we present a regional scale, non-isothermal 2-D numerical groundwater model is developed to analyze the time scales and geological controls on fluid flow paths recharging the PTA. Results from this work suggest that (1) both shallow groundwater flow and deep (>1km) hydrothermal fluid circulation are responsible for recharging the PTA; (2) topography and geothermal gradients are the main driving factors for regional groundwater flow; (3) the Altos de Pica member 4, an ignimbrite layer in the sedimentary basin controls both heat and fluid flow in the western part of the basin, this is evident due to the presence of convection cells and meteoric water upwelling and presenting itself as surface water (salars); and (4) it takes meteoric water 100,000 years to travel from the high Andes to reach Pica and 1,000,000 years for salar formation. In addition, this work provides a theoretical basis for the spatial distribution of highly alkaline surface water bodies, known as salars in the western Atacama Desert.