Data were collected in the American River basin from February to October 1979 for use in assessing the water quality in the basin. The basin covers 2,163 square miles of the western slope of the central Sierra Nevada. Basin headwaters are located primarily between Donner Summit and Carson Pass. Water-quality data were collected at 14 stream sites and at 3 sites on Folsom Lake and include selected measurements and analyses for physical, chemical, and biological properties and constituents. Water samples analyzed for dissolved constituents were filtered through a 0.45-ym membrane filter. Nutrient samples were preserved by chilling 0°C to 4°C. Trace-element samples were placed in acid-rinsed polyethylene bottles and acidified with nitric acid to a pH less than 2. Chemical determinations were made at the U.S. Geological Survey Central Laboratory in Arvada, Colo. Onsite measurements of pH and specific conductance were made by using portable meters. Temperature was measured with a handheld thermometer. Dissolved-oxygen concentration was determined by the azide modification of the Winkler method, and alkalinity by electrometric titration method. These methods are described by Skougstad and others (1979). Water discharge was determined by direct measurement, using the methods described by Buchanan and Somers (1969), or from records from nearby gaging sites. Lake samples were taken at selected depths or composited for selected depth intervals with a 4-liter Van Dorn-type sampler. Vertical-profile measurements of temperature, dissolved oxygen, specific conductance, and pH were made with a Martek Mark VI Water Quality Analyzer during each visit to the lake site. Water transparency was measured by a Secchi disk (Reid, 1961, p. 100). In addition, light penetration was measured with a Montedoro-Whitney Model LMT-8B submarine photometer. Light transmission was measured with a Martek Model XMS IN SITU Transmissometer, with a *4-m path-length sensor.

Introduction Background Objectives and scope Acknowledgments Description of study area Catchment area selection and description I nstrumentation : Equipment used Operation of equipment Data collection 11 Rainfall and runoff quantity data 11 Rainfall and runoff quality data Rainfall quality samples Runoff quality samples Runoff data collection for special studies ERA 129 priority pollutants study ERA NURP special metals study Atmospheric dry-deposition samples Street-surface particulate samples Dry-weather runoff quality samples Project laboratory procedures 21 Runoff samples 21 Rainfall samples Atmospheric dry-deposition samples Analytical methods Quality assurance EPA 129 priority pollutants study EPA NURP special metals study Data storage References cited ILLUSTRATIONS Page Figure 1. Index map of California showing Fresno study area 2. Photograph of multiple-use stormwater retention basin with inundated baseball diamond 3. Map showing location of catchment areas, and rainfall and runoff monitoring sites Contents 111

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