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Occurrence and Distribution of Pesticide Compounds in Surface Water of the Santa Ana Basin, California, 1998–2001

By Robert Kent, Kenneth Belitz, Andrea J. Altmann, Michael T. Wright,and Gregory O. Mendez

U.S. GEOLOGICAL SURVEY

Scientific Investigations Report 2005-5203

Sacramento, California 2005

National Water-Quality Assessment Program


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Abstract

     A study of the occurrence and distribution of pesticide compounds in surface water of the highly urbanized Santa Ana Basin, California, was done as part of the U.S. Geological Survey’s National Water-Quality Assessment Program (NAWQA). One-hundred and forty-eight samples were collected from 23 sites, and analyzed for pesticide compounds during the study period from November 1998 to September 2001. Sixty-six different pesticide compounds were detected at varying frequencies and concentrations, and one or more pesticides were detected in 92 percent of the samples. All pesticide concentrations were below maximum levels permitted in drinking water. However, two compounds—diazinon and diuron—exceeded nonenforceable drinking water health-advisory levels in at least one stream sample, and five compounds exceeded guidelines to protect aquatic life—carbaryl, chlorpyrifos, diazinon, lindane, and malathion. Twenty-two pesticide compounds were detected in at least 25 percent of the samples collected from any one fixed site. These are identified as “major” pesticide compounds and are emphasized in this report.

     The degree to which pesticides were used in the basin, as well as their physical-chemical properties, are important explanatory factors in stream pesticide occurrence, and most pesticides probably enter streams with urban runoff. Stormflow substantially increases urban runoff, and storm effects on stream pesticide concentrations sometimes persist for several days or weeks after the storm. Water sources other than urban runoff also deliver pesticide compounds to surface water in the basin. For example, atrazine may enter streams in gaining reaches where ground water carries high loads as a result of historical use in the basin. Also, the data suggest that lindane, and perhaps bromacil, are present in treated wastewater, the predominant source of water to streams in the Santa Ana Basin.

CONTENTS

Abstract
Introduction
     Study Unit Description
     Purpose and Scope
     Study Design
          Fixed Sites
          Additional Studies
               Urban Land-Use Gradient (ULUG) Study
               Pesticides in Reservoirs
Methods and Data Analysis
     Sample Collection and Processing
     Analytical Methods
     Statistical Methods
     Method of Evaluating Physical-Chemical Properties of Pesticides
     Quality-Control Samples
Results
     Pesticide Compounds Detected in the Santa Ana Basin
          Major Pesticides
     Factors Contributing to the Occurrence of Selected Pesticides
          Pesticide Use
          Pesticide Chemical Properties
          Historical Atrazine Use
          Stream Site Location and Water Source
          Stormflow
     Stream Pesticide Concentrations Compared to Drinking-Water Standards and Aquatic Life Guidelines
     Pesticide Concentrations in the Santa Ana Basin Compared with Concentrations Nationwide
     In-Stream Changes in Pesticide Concentrations
     Pesticides in a Water-Supply Reservoir
     Quality-Control Results
          Blanks
          Replicate Samples
          Spikes
     Implications of Extended Holding Times for Lab Code 9060 Samples
Summary and Conclusions
References Cited
Appendixes


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Water Resources of California
U.S. Department of the Interior, U.S. Geological Survey
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