Results show effects of industry and agriculture on groundwater quality
Organic solvents were detected at high concentrations in 18% of the aquifer system used for public supply in the San Fernando and San Gabriel basins in California in a U.S. Geological Survey (USGS) study. However, this groundwater treated before delivery 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% of the groundwater.
As part of a statewide study assessing groundwater quality, USGS scientists analyzed untreated groundwater from wells, not treated tap water, looking for 262 possible constituents. "Over a 10-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," said 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 U.S. EPA [Environmental Protection Agency], 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 (GAMA) 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 generally were clustered in the central and southern San Gabriel Valley and the southern San Fernando Valley. Solvents are used for a number of purposes, including metal plating, machinery degreasing and dry cleaning. Perchlorate, an ingredient in rocket fuel, fireworks, safety flares and fertilizers, also was detected at high concentrations in about 11% of the groundwater in the study area aquifers.
Nutrients such as nitrate and nitrite, used in fertilizers and results from nitrogenous waste, were present at high concentrations in about 9% 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.