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A spreading ground is a water conservation facility that retains surface water long enough for it to percolate into the soil. spreading grounds must be located where underlying soils are permeable and connected to a target aquifer. Locating them above silt or clay would prevent the surface water from reaching formations that store water.
When natural percolation of precipitation is insufficient to replenish groundwater withdrawn for human use, artificial recharge helps prevent aquifer depletion, subsidence and saltwater intrusion. Spreading grounds are one of several available technologies, and are useful to harness storm water runoff in populated areas with low annual precipitation. For example, Los Angeles County, California has 27 such facilities, and four more operated in conjunction with the department, many of which date to the 1930s.