High Concentrations of Arsenic Found in Some Kern County & Southeast San Joaquin Valley Groundwater
Arsenic was detected at high concentrations in about 20 percent of the aquifer system used for public supply in the Southeast San Joaquin and Kern County basins. Groundwater is used as drinking water and water purveyors typically treat groundwater before delivering it to customers to ensure compliance with water quality standards.
High concentrations of arsenic in the Southeast San Joaquin and Kern County study areas were consistent with findings in other study areas in the eastern San Joaquin Valley, which ranged from 9 to 20 percent.
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. Tap water may be disinfected, filtered, or mixed in order to improve groundwater quality before it is delivered to consumers.
"Results from this study indicate that naturally existing conditions in the aquifers, as well as human activities resulting from urban and agricultural development, affect local groundwater quality in the Southeast San Joaquin Valley and Kern County groundwater subbasins," said Carmen Burton, a hydrologist and author of the USGS report prepared in collaboration with the California State Water Resources Control Board.
Of the 49 inorganic compounds analyzed, arsenic, a trace element, had the highest and most frequently detected concentrations in the aquifer system, above health standards for drinking water. The trace elements, boron and vanadium also occurred in high concentrations. Trace elements are inorganic chemicals with natural sources, and in the two southern San Joaquin Valley study units, these elements can result from the interaction of groundwater and naturally occurring minerals.
"Statewide, naturally occurring trace elements are the most common constituents found above health based thresholds", said Dr. Kenneth Belitz, chief of the USGS Groundwater Ambient Monitoring and Assessment program.
Nitrate, an inorganic compound that can be found both naturally and from human sources, was detected at high concentrations in about 6 percent of the groundwater in the study-area aquifers. Total dissolved solids, inorganic compounds resulting from natural and human sources, were present at high concentrations in 14 percent of the primary aquifers in Kern County, the largest proportion in the Eastern San Joaquin Valley.
The State Water Resources Control Board, which funded the Groundwater Ambient Monitoring & Assessment Program study, collaborated 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.
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