Abstract: Approximately 50 percent of the potable, industrial, and agricultural water supply in Venezuela comes from ground water, mined through some 40,000 wells scattered around the country. The majority of the productive aquifers consist of quaternary deposits in mountain valleys and coastal lowlands, all of which are situated in areas with limited or low precipitation. Intensive exploitation of several of these aquifers for the last 30 years has resulted in overdraft conditions and ground water contamination, causing serious socio‐economic consequences in various regions of Venezuela. This paper reviews the quality and quantity aspects of overdrafted aquifers in Venezuela, which can he classified into three major categories: (1) aquifers in the coastal lowlands in the stales of Falcon and Zulia of northern Venezuela: (2) the intermontane Carora and Quibor Valley Aquifers: and (3) aquifers in the Lake Valencia Watershed. If current trends of aquifer overexploitation continue, further water deficits and irreversible environmental damage are predicted.

Structural processes occurring upon electrochemical cycling in P2-Nax[LiyNizMn1-y-z]O2 (x, y, z ≤ 1) cathode materials are investigated using 23Na and 7Li solid-state nuclear magnetic resonance (ssNMR). The interpretation of the complex paramagnetic NMR data obtained for various electrochemically-cycled NaxNi1/3Mn2/3O2 and NaxLi0.12Ni0.22Mn0.66O2 samples is assisted by state-of-the-art hybrid Hartree-Fock/density functional theory calculations. Two Na crystallographic environments are present in P2-Nax[LiyNizMn1-y-z]O2 compounds, yet a single 23Na NMR signal is observed with a shift in-between those computed for edge- and face-centered prismatic sites, indicating that Na-ion motion between sites in the P2 layers results in an average signal. This is the first time that experimental and theoretical evidence are provided for fast Na-ion motion (on the timescale of the NMR experiments) in the interlayer space in P2-type NaxTMO2 materials. A full assignment of the 7Li NMR data confirms that Li substitution delays the P2 to O2 phase transformation taking place in NaxNi1/3Mn2/3O2 over the range 1/3 ≥ xNa ≥ 0. 23Na ssNMR data demonstrate that NaxNi1/3Mn2/3O2 samples charged to ≥3.7 V are extremely moisture sensitive once they are removed from the cell, water molecules being readily intercalated within the P2 layers leading to an additional Na signal between 400 and 250 ppm. By contrast, the lithiated material NaxLi0.12Ni0.22Mn0.66O2 shows no sign of hydration until it is charged to ≥4.4 V. Since both TMO2 layer glides and water intercalation become increasingly favorable as more vacancies are present in the Na layers, the higher stability of the Li-doped P2 phase at high voltage can be accounted for by its higher Na content at all stages of cycling.