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Santa Clara River Valley Area Groundwater Quality Assessment Released

Released: 9/26/2011

This USGS report can be found online.

A summary fact sheet of this report can also be found online.

Santa Clara River Valley Groundwater in aquifers beneath Ojai, Ventura, Port Hueneme, Newhall, Camarillo, and Simi Valley that supply untreated drinking water was found to contain high concentrations of several natural and man-made compounds. More specifically, nitrate, radioactive constituents, naturally occurring arsenic, boron, and vanadium, total dissolved solids (an indicator of salinity), sulfate, iron, and manganese were all found to be present at levels above study thresholds.

The assessment also determined what proportions of the studied aquifers contain concentrations of compounds above study thresholds. High concentrations of nitrate are present in 15% of the deep aquifers supplying public wells, radioactive isotopes in 14%, total dissolved solids in 22%, and iron and manganese in about 44%. No high concentrations of organic constituents were found. There were moderate concentrations of radioactive constituents in another 11% of the aquifers and organic constituents in about 2% of the aquifers.

The sampled waters are in deep parts of the aquifer system tapped by public supply wells, and waters are treated to created safe levels for consumption before the water is delivered to consumers. Shallow parts of the aquifer tapped by private wells can have a completely different quality of water and were not analyzed as part of this study.

The thresholds used to identify high concentrations are Federal and California regulatory benchmarks and aesthetic benchmarks related to the taste, color, and other non-health related factors.

The assessment used data from 53 wells and a review of over 230,000 water quality records in a California Department of Public Health database.

The study was conducted by the USGS California Water Science Center and USGS National Water-Quality Assessment Program as part of the California State Water Resources Control Board (SWRCB) Groundwater Ambient Monitoring and Assessment (GAMA) Program.

The main goals of the GAMA Program are to improve groundwater monitoring in California, and to increase the availability of groundwater-quality data to the public. The data collected is used for three types of water-quality assessments: (1) Status—assessment of the current quality of the groundwater resource; (2) Understanding—identification of the natural and human factors affecting groundwater quality; and (3) Trends—detection of changes in groundwater quality.

A report "Status and understanding of groundwater quality in the Santa Clara River Valley, 2007: California GAMA Priority Basin Project" is available online.

Links and contacts within this release are valid at the time of publication.


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