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Environ Sci Technol

Title:		Probability of detecting perchlorate under natural conditions in deep groundwater in California and the southwestern United States
Author(s):		Fram MS; Belitz K;
Address:		"U.S. Geological Survey, Sacramento, CA 95819-6129, USA. mfram@usgs.gov"
Journal Title:		Environ Sci Technol
Year:		2011
Volume:		20110119
Issue:		4
Page Number:		1271 - 1277
DOI:		10.1021/es103103p
ISSN/ISBN:		1520-5851 (Electronic) 0013-936X (Linking)
Abstract:		"We use data from 1626 groundwater samples collected in California, primarily from public drinking water supply wells, to investigate the distribution of perchlorate in deep groundwater under natural conditions. The wells were sampled for the California Groundwater Ambient Monitoring and Assessment Priority Basin Project. We develop a logistic regression model for predicting probabilities of detecting perchlorate at concentrations greater than multiple threshold concentrations as a function of climate (represented by an aridity index) and potential anthropogenic contributions of perchlorate (quantified as an anthropogenic score, AS). AS is a composite categorical variable including terms for nitrate, pesticides, and volatile organic compounds. Incorporating water-quality parameters in AS permits identification of perturbation of natural occurrence patterns by flushing of natural perchlorate salts from unsaturated zones by irrigation recharge as well as addition of perchlorate from industrial and agricultural sources. The data and model results indicate low concentrations (0.1-0.5 mug/L) of perchlorate occur under natural conditions in groundwater across a wide range of climates, beyond the arid to semiarid climates in which they mostly have been previously reported. The probability of detecting perchlorate at concentrations greater than 0.1 mug/L under natural conditions ranges from 50-70% in semiarid to arid regions of California and the Southwestern United States to 5-15% in the wettest regions sampled (the Northern California coast). The probability of concentrations above 1 mug/L under natural conditions is low (generally <3%)"
Keywords:		"California Environmental Monitoring/methods Groundwater/*chemistry Models, Statistical Nitrates Perchlorates/*analysis Probability Southwestern United States Water Pollutants, Chemical Water Supply/standards;"
Notes:		"MedlineFram, Miranda S Belitz, Kenneth eng Research Support, Non-U.S. Gov't 2011/01/21 Environ Sci Technol. 2011 Feb 15; 45(4):1271-7. doi: 10.1021/es103103p. Epub 2011 Jan 19"