SAN DIEGO —Organic solvents were detected at high concentrations in 18 percent of the aquifer system used for public supply in the San Fernando and San Gabriel basins. However, groundwater is not directly used as drinking water; water purveyors may treat groundwater before delivering it to customers to ensure compliance with water quality standards.
By comparison, in most of the California areas previously studied, organic solvents were often detected in groundwater, but not at high concentrations; statewide, high concentrations of organic solvents were found in less than 2 percent of the groundwater.
As part of a statewide study assessing groundwater quality, U.S. Geological Survey scientists analyzed untreated groundwater from wells, not treated tap water, looking for 262 possible constituents. "Over a ten-year period, the USGS, with our partners in the state of California, is characterizing groundwater quality in 120 basins that provide about 95% of public groundwater supplies," explained USGS Director Marcia McNutt. "The new results for the San Fernando and San Gabriel basins show where, what, and how much contamination is in the groundwater, focusing attention on improving water quality where it is needed."
“Local water purveyors, regional agencies, as well as the US EPA, are aware of the presence of solvents in groundwater in the San Fernando and San Gabriel valleys, and actively manage the quality of water delivered to consumers”, said Dr. Kenneth Belitz, chief of the USGS Groundwater Ambient Monitoring and Assessment program.
Of the 212 organic compounds analyzed, 66 were detected in the aquifer system. Six solvents were detected at high concentrations, above health standards for drinking water. High solvent concentrations were generally clustered in the central and southern San Gabriel Valley, and the southern San Fernando Valley. Solvents are used for a number of purposes include metal plating, machinery degreasing, and dry cleaning. Perchlorate, an ingredient in rocket fuel, fireworks, safety flares, and fertilizers, was also detected at high concentrations in about 11 percent of the groundwater in the study-area aquifers. Nutrients, such as nitrate and nitrite, are used in fertilizers, and result from nitrogenous waste, were present at high concentrations in about 9 percent of the groundwater in the aquifers.
“Results from this study indicate that human activities such as industry and agriculture are the primary factors affecting local groundwater quality throughout the San Fernando and San Gabriel groundwater basins,” said Dr. Justin Kulongoski, a hydrologist and author of the USGS report prepared in collaboration with the California State Water Resources Control Board.
The State Water Resources Control Board’s Groundwater Ambient Monitoring & Assessment Program, which funded the study, is a collaboration with the USGS to monitor and assess water quality in 120 groundwater basins across California over a ten-year period. The main goals of GAMA are to improve comprehensive statewide groundwater monitoring and to increase the availability of groundwater-quality information to the public.
The full report, Status of Groundwater Quality in the San Fernando–San Gabriel Study Unit, 2005: California GAMA Priority Basin Project, and the accompanying non-technical Fact Sheet, Groundwater Quality in the San Fernando-San Gabriel Groundwater Basins, California, are online.
Links and contacts within this release are valid at the time of publication.