Groundwater Recharge
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A Managed aquifer recharge stores water underground when a suitable supply is available. The water may later support wells or river flow, but it must first pass quality checks because contaminants can also move below the surface. B The cross-section shows recharge through a shallow basin rather than injection through a deep borehole. Engineers examine soil permeability, the depth of groundwater and the direction of underground flow before selecting the site. C At the surface, an infiltration basin holds pretreated water long enough for it to seep downward. Directly below the basin, the unsaturated zone contains both air and water in its pores. The water table marks the upper boundary of ground whose pores are fully saturated. D Below that boundary lies the aquifer, a permeable body of rock or sediment that stores and transmits groundwater. A monitoring well reaches this saturated layer at the side of the basin, allowing samples and water-level readings to be collected over time. E Operators compare water entering the basin with samples from the well. A rising water level may indicate successful recharge, whereas a change in chemistry can reveal that treatment or travel through the soil is altering the water. F The drawing simplifies a three-dimensional groundwater system. Recharge at one basin does not prove that water will remain available locally, because pumping, geological barriers and regional flow can change its eventual destination.