Source, distribution, and management of perchlorate in water from wells in the upper Santa Ana River basin, California

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Perchlorate (ClO4-), a commercially produced oxidizer used in solid propellants, has contaminated public-supply wells in parts of the upper Santa Ana River basin. Both industrial and agricultural sources of perchlorate are present within the basin. 

Map showing San Bernardino Valley Municipal Area

 San Bernardino Valley Municipal Area

(Public domain.)

Although shallow aquifers are more susceptible to contamination, vertical migration of perchlorate through discontinuities in fine-grained layers that separate aquifers, or as a result of flow through well bores, has contaminated deeper aquifers. This has contributed to the extent of contamination and complicated management options available to local water purveyors.

The purpose of this study is to assess the source, vertical distribution, and fate of perchlorate in water from wells in the upper Santa Ana River basin. Data collected as part of this study will be used to evaluate management options to reduce perchlorate concentrations in water from wells.

The study approach includes collection of samples from the surface discharge from 20-25 selected production and monitoring wells. Samples from these wells will be analyzed for a range of chemical and isotopic constituents including the stable isotopes of oxygen and chloride within the perchlorate molecule, and nitrogen and oxygen within the nitrate molecule. These data will be used to determine the source (industrial versus agricultural) of the perchlorate, and to determine if degradation of perchlorate has occurred. Coupled well-bore flow and depth-dependent water quality data also will be collected from 4 selected wells. Depth-dependent water-quality samples will be analyzed for perchlorate and other selected constituents to determine the vertical distribution of perchlorate within aquifers and to characterize potential sources. Well-bore flow and depth-dependent water-quality data will be interpreted at the well-bore scale using numerical ground-water flow models to determine how perchlorate is moving through aquifers to wells. Well-bore flow models also will be used to determine if well-modification can be used to reduce perchlorate concentrations from wells allowing them to remain in service without the need for additional treatment to remove perchlorate.