Study Finds High Nitrate & Perchlorate Levels in California Groundwater

Statewide study surveyed groundwater for more than 300 contaminants

Nitrate was detected at high concentrations in one-quarter of the aquifer system used for the Inland Empire public water supply. Additionally, high concentrations of perchlorate were found in 11% of the aquifer system, and in moderate concentrations in 53%. This aquifer system includes the Upper Santa Ana Valley, San Jacinto and Elsinore groundwater basins in California. High nitrate and perchlorate concentrations were not found in the Elsinore groundwater basin.

As part of a statewide study assessing groundwater quality, U.S. Geological Survey (USGS) scientists analyzed untreated groundwater from wells, not treated tap water, looking for more than 300 possible constituents. Groundwater is typically treated by water purveyors prior to delivering it to customers to ensure compliance with water quality standards.

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

Nitrate and perchlorate in the Upper Santa Ana Watershed enter groundwater mostly through human-related activities. Sources of nitrate include agriculture, effluent from wastewater treatment plants and septic systems. Perchlorate sources include rocket fuel, fireworks, safety flares and fertilizers. Elevated concentrations of both nitrate and perchlorate in drinking water have been associated with adverse health effects and are monitored by the California Department of Public Health.

"Local water purveyors [and] regional agencies, as well as the U.S. EPA [Enviromental Protection Agency], are aware of the presence of nitrates and perchlorates in groundwater in the Inland Empire and are actively working to manage local groundwater resources," said Dr. Kenneth Belitz, chief of the USGS Groundwater Ambient Monitoring and Assessment program.

Of the 49 inorganic compounds analyzed, nitrate was the compound most commonly detected in the aquifer system at concentrations above health standards for drinking water. Groundwater was analyzed for perchlorate because its occurrence in drinking water supplies in California is an emerging concern for water managers. Among the organic compounds analyzed, solvents used for a number of purposes, including manufacturing and cleaning, were detected at high concentrations in about 3% of the aquifer system, and in moderate concentrations in about 9%.

"Results from this study indicate that human activities in industry and agriculture are the primary factors affecting local groundwater quality throughout the Inland Empire aquifer system," said Robert Kent, a USGS hydrologist and lead author of the report prepared in collaboration with the California State Water Resources Control Board.

U.S. Geological Survery

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