Determination of chemical-constituent loads during base-flow and storm-runoff conditions near historical mines in Prospect Gulch, upper Animas River watershed, southwestern Colorado

4 Introduction 6 Problem 6 Purpose and Scope 6 Physical Setting 9 Geology and Mineralogy of Prospect Gulch 11 Relation of Prospect Gulch Water Chemistry to Drainage from Non-Mined Areas and Areas Disturbed by Mining 13 Methods and Sampling Plan 15 Theory of Tracer-Dilution Techniques 15 Field Sampling Methods 15 Selection of Sampling Locations 16 Monitoring of Tracer Concentrations and Timing of Weather Conditions 18 Analytical Accuracy of Tracer-Dilution Discharge Measurements 18 Water-Quality Sampling Techniques and Analytical Methods 20 Results and Discussion 21 Changes in Chemical-Constituent Loads with Distance Downstream during Base-Flow Conditions 21 Specific Conductivity and pH during Field Reconnaissance 21 Chemical-Constituent Loads on September 15, 1998 23 Changes in Chemical-Constituent Loads caused by Storm-Runoff Conditions 25 First Flush 29 Peak Runoff 30 Conclusions 30 References Cited 36