geochemical and 3D-geometry geophysical survey to assess artificial groundwater recharge potential in the Pacific coast of Baja California, Mexico

A geophysical and geochemical study was carried out in the Maneadero aquifer, Baja California, Mexico, with the aim of identifying potential recharge locations for reclaimed water (RW). This coastal aquifer shows a significant decline in water quality, both as a result of salinization and the pollution by nitrates. Total dissolved solids (TDS) in an extreme case increased from 4 g l⁻¹ in 2000 to 27 g l⁻¹ in 2011. Nitrate as N–NO₃, reaches 46 mg l⁻¹. Based on their geochemistry and location, four water-quality zones are identified: (a) fresh water with TDS ≈ 1 g l⁻¹ in the upper creeks, (b) mixture between seawater and freshwater in the coast-proximal sections, (c) water significantly enriched in nitrate below and adjacent to the town of Maneadero, and (d) brackish water with no signs of current interaction with freshwater. The 3D geophysics identifies the influence of modern recharge areas and also buried flow-paths down to at least 30 m depth. The locations best suitable for aquifer recharge are those with equal or higher TDS concentrations (>2.5 g l⁻¹) than RW, which are located at the brackish water zone and/or at the coastal limits of the mixing zones.