Jan 10, 2013

USGS Study Reports Quality of California Desert Groundwater

Inorganic elements detected at high concentrations in 35% of region's untreated groundwater

California Desert Groundwater Quality U.S. Geologial Survey

Inorganic elements — arsenic, boron, fluoride and five others — were detected at high concentrations in 35% of untreated groundwater used for public water supply in the desert region of Southern California in a recent study by the U.S. Geological Survey (USGS). In contrast, human-made organic chemical constituents and nitrate were found at high concentrations in less than 1% of the desert region’s aquifers.

This study's findings are important, in part, because elsewhere in California, high concentrations of inorganic elements generally are found in 10% to 25% of the aquifer system used for public supply, nitrate in 1% to 8%, and human-made organic chemical constituents in up to 2%. "High" concentrations are defined as above the U.S. Environmental Protection Agency's (EPA) or California Department of Public Health's established maximum contaminant levels (MCLs) or other non-regulatory health-based levels for chemical constituents or elements not having MCLs. USGS did not analyze treated tap water. Water distributors typically treat water supplies prior to delivering them to customers to ensure compliance with water quality standards for human health.

As part of a statewide study assessing groundwater quality, USGS scientists analyzed untreated groundwater from wells in the desert region between 2006 and 2008, looking for as many as 207 chemical constituents. California's desert region includes Antelope Valley, Coachella Valley, Indian Wells Valley, Owens Valley, the Mojave River area and the Colorado River basin.

"Over a 10-year period, the USGS is characterizing groundwater quality in 120 groundwater basins and other areas that supply about 95% of public groundwater supplies," said USGS Director Marcia McNutt. "The new results for the desert region show where, what and how much contamination is in the groundwater, focusing attention on improving water quality where it is needed."

Naturally occurring inorganic elements were found in high concentrations in 22% of Owens Valley, 30% of Antelope Valley, 28% of the Mojave area, 42% of Coachella Valley, 45% of the Colorado River basin and 62% of Indian Wells Valley. In these areas with high concentrations, one or more of the following eight inorganic elements was found at high concentrations: arsenic, boron, fluoride, gross-alpha radioactivity, molybdenum, strontium, vanadium and uranium. These elements are naturally present in rocks and soils, and the water that comes in contact with those materials. High concentrations generally are the result of natural processes, but human activities may have some influence. An additional 28% of the aquifer systems had moderate concentrations, greater than one-half the comparison level, of at least one inorganic constituent.

In contrast, high concentrations of organic constituents (such as solvents, gasoline components and pesticides) and nitrate were found in less than 1% of the desert region's aquifers. Perchlorate was found at high concentrations in 10% of Coachella Valley aquifers and was not found at high concentrations in any of the other areas. High concentrations of organic constituents, nitrate and perchlorate are typically associated with human activity.

"Local water distributors and regional, state and federal agencies, as well as the U.S. EPA, are aware of the presence of arsenic, fluoride, uranium and other inorganic constituents in groundwater in the desert region, and are actively working to manage local groundwater resources and assure that water delivered to consumers meets water quality standards," said Dr. Miranda Fram, chief of the USGS Groundwater Ambient Monitoring and Assessment program.

The full report is available here.