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Correlations between Various Water-Quality Indicators of Recharged Recycled Water in Production Wells in Los Angeles County, California

By Robert Anders and Roy A. Schroeder
U.S. Geological Survey, 5735 Kearny Villa Road, Suite O, San Diego, CA 92123

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Water samples were collected from 23 production wells located within 500 feet (150 meters) of recharge basins in the Montebello Forebay in south-central Los Angeles County that receive local, imported, and reclaimed water; from an upgradient background well; and from effluent from a wastewater-treatment plant (recycled water).  The water samples were analyzed for a broad suite of major and minor inorganic and dissolved organic constituents, nutrients, several isotopes, and selected microbial populations.  These data were used to examine the relations (if any) that exist among various indicators of recycled water in the 23 production wells and the correlations between their concentrations and ground-water traveltimes and well depths.

Significant correlations exist between "excess" chloride (defined as the amount above the natural background level), "excess" boron, and nitrogen concentrations "calculated" (using nitrogen-isotope data) to the time of recharge, although all three methods overestimate recycled-water percentages in the production wells.  There is a high correlation between dissolved organic carbon (DOC) and fluorescence (which results from fluorescent whitening agents), indicating little loss of DOC during recharge and subsequent travel to the production wells.  Ethylenediaminetetraacetic acid and ultraviolet absorbance at 254 nanometers also are indicative of recycled water in the production wells.

In George R. Aiken and Eve L. Kuniansky, editors, 2002, U.S. Geological Survey Artificial Recharge Workshop Proceedings, Sacramento, California, April 2-4, 2002: USGS Open-File Report 02-89

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