Replenishment ProgramForty percent of the potable water distributed for use in the 43 cities of Southern Los Angeles County comes from the Central and West Coast groundwater basins. Over the past century, local water suppliers have drilled wells into the aquifers of these underground basins to reach the high quality groundwater.
Today, with the growth of population, cities and water use, nature's replenishment cannot keep up, and the Water Replenishment District has been charged with the task of spreading or injecting replacement water into the ground to replenish our valuable underground water supply. The spreading grounds are located by the Rio Hondo and San Gabriel Rivers, in the cities of Montebello and Pico Rivera. They are large holding ponds designed for the percolation of surface water into the ground. Local storm runoff, imported water and highly treated recycled water are captured and spread to replenish the Basin. In the West Coast Basin, groundwater is replenished primarily by injection wells. In addition to replenishment, a line of closely spaced injection wells have been constructed to form a barrier of freshwater. Three of these sea water intrusion barriers have been drilled to keep ocean water out of the groundwater basins. The imported water for the barriers originates in Northern California and the Colorado River and is purchased from the Metropolitan Water District of Southern California (MWD). |
For many years, surface water consisting of stormwater runoff and snow melt from the mountains percolated into the ground. Nature replenished the groundwater without man's assistance. The water was captured by the soil and filtered into the aquifers, or natural underground formations of sand and gravel, that collectively formed the two basins.