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| PUBLICATIONS—Scientific Investigations Reports |
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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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.
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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