ADDRESSING URBANIZATION IMPACT THROUGH MANAGED AQUIFER RECHARGE IN SOUTHERN LOS ANGELES COUNTY

Rapid and expanding urbanization of southern Los Angeles County in the first half of the 20^th century resulted in extreme overdraft of the Central and West Coast Groundwater Basins, yielding to swiftly falling groundwater levels, seawater intrusion, and loss of local supplies. Solutions were implemented to fix this problem including introduction of imported water from northern California and the Colorado River, reduction in pumping through adjudications, construction of seawater barrier injection wells and surface spreading recharge facilities, and the creation of the Water Replenishment District of Southern California (WRD) to perform managed aquifer recharge (MAR).

The WRD service area covers 420 square miles, includes 43 cities, and a population of nearly 4 million residents. Since 1959, MAR activities have returned nearly 10 million acre feet (3.2 trillion gallons) of water to the basins’ aquifers, helping to eliminate overdraft, preventing continued seawater intrusion, and restoring the usability of the groundwater basins. Stormwater, imported water and recycled water are used for MAR, in addition to an “In-Lieu” program that pays groundwater producers to temporarily shut down their wells. MAR activities are funded by a Replenishment Assessment levied on groundwater producers that is currently set by WRD at $283 per acre foot of groundwater pumped.

Current and future challenges to meet the groundwater needs of the WRD service area includes reduction of natural recharge through climate change impacts, reduction in imported water availability due to drought and environmental issues, and groundwater quality impacts. To meet these challenges, many agencies are developing programs to be more self-reliant on their available groundwater and recharge supplies. For example, WRD has developed a program called Water Independence Now, or “WIN”, with the purpose of becoming independent from imported water for its MAR needs. To do this, more recycled water and stormwater will be needed to replace the imported water. Six projects are part of the WIN program and will replace 34,000 acre feet of imported water used for MAR with recycled water or stormwater. All projects scheduled to be completed by 2020 at a cost of approximately $200 million.