Groundwater Study Assesses Potential for Contamination of Drinking-Water Aquifers in Los Angeles

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Contaminated groundwater found at shallow depths in southern Los Angeles County has the potential to migrate to deeper aquifers, according to a scientific study just published by the U.S. Geological Survey and the Water Replenishment District of Southern California.

LAKEWOOD, Calif. – Contaminated groundwater found at shallow depths in southern Los Angeles County has the potential to migrate to deeper aquifers, according to a scientific study just published by the U.S. Geological Survey and the Water Replenishment District of Southern California. These results confirm previous studies conducted by WRD and the U.S. Environmental Protection Agency.  Over two million residents get approximately 60 percent of their drinking water supply from these deeper aquifers. 

The study focused on aquifers in the 280-square mile Central Groundwater Basin, one of the most heavily used groundwater basins in southern California. The study did not analyze treated tap water delivered to consumers. Groundwater is typically treated by water distributors prior to delivering it to customers to ensure compliance with water quality standards for human health. The regionally coordinated investigation used new and existing data, supplemented with new geologic interpretation techniques. Water chemistry data and groundwater simulation models were used to understand the interconnections and water flow between different aquifer layers. 

“Our investigation concluded that contaminated groundwater found at shallow depths in the northeastern portion of the Central Groundwater Basin could migrate to greater depths where many drinking water supply wells are located,” said Eric Reichard, Director of the USGS California Water Science Center. “Now that we’ve established that the potential for migration is there, the next step is to assess the specific risk this may pose to the main drinking water aquifers.” 

There are multiple sites in the northeast portion of the basin where shallow groundwater contamination is already being investigated and remediated under the oversight of several federal and state regulatory agencies. The results of this new study will allow WRD to anticipate possible future contaminant migration and to plan accordingly to protect uncontaminated areas. Additionally, regulatory agencies can use the study results to inform future monitoring and cleanup actions for contaminated sites located in the Central Groundwater Basin. 

“WRD is responsible for insuring that our precious groundwater aquifers continue to provide clean, safe drinking water now and for future generations.  This study, along with our extensive network of groundwater monitoring wells and our Groundwater Contamination Prevention Program, will allow us to protect local water resources, which is of utmost importance as we strive to become independent from imported water,” said WRD Board President Rob Katherman. 

This study was partially funded by a $250,000 grant from the California Department of Water Resources.  Funding and input from the DWR were critical to the successful completion of this project. The full report about the study, “Characterization of Potential Transport Pathways and Implications for Groundwater Management Near an Anticline in the Central Basin Area, Los Angeles County, California,” is available online.

The Water Replenishment District of Southern California is the regional groundwater management agency that protects and preserves the quantity and quality of groundwater for two of the most utilized urban basins in the state of California. The service area is home to over ten percent of California’s population, residing in 43 cities in southern Los Angeles County. WRD is governed by a publicly elected board of directors which includes Willard H. Murray, Jr., Robert Katherman, Lynn V. Dymally, Sergio Calderon, and Albert Robles.