USGS

Water Resources of Colorado

Determination of Instream Metal LoadsUsing Tracer-Injection and Synoptic-Sampling Techniques in Wightman Fork,Southwestern Colorado, September 1997

by Roderick F. Ortiz and Kenneth E. Bencala

Available from the U.S. Geological Survey, Branch of Information Services, Box 25286, Denver Federal Center, Denver, CO 80225, USGS Water-Resources Investigations Report 00–4154, 26 p., 12 figs.

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Abstract

Spatial determinations of the metal loads in Wightman Fork can be used to identify potential source areas to the stream. In September 1997, a chloride tracer-injection study was done concurrently with synoptic water-quality sampling in Wightman Fork near the Summitville Mine site. Discharge was determined and metal concentrations at 38 sites were used to generate mass-load profiles for dissolved aluminum, copper, iron, manganese, and zinc. The U.S. Environmental Protection Agency had previously identified these metals as contaminants of concern.

Metal loads increased substantially in Wightman Fork near the Summitville Mine. A large increase occurred along a 60-meter reach that is north of the North Waste Dump and generally corresponds to a region of radial faults. Metal loading from this reach was equivalent to 50 percent or more of the dissolved aluminum, copper, iron, manganese, and zinc load upstream from the outfall of the Summitville Water Treatment Facility (SWTF). Overall, sources along the entire reach upstream from the SWTF were equivalent to 15 percent of the iron, 33 percent of the copper and manganese, 58 percent of the zinc, and 66 percent of the aluminum load leaving the mine site. The largest increases in metal loading to Wightman Fork occurred as a result of inflow from Cropsy Creek. Aluminum, iron, manganese, and zinc loads from Cropsy Creek were equivalent to about 40 percent of the specific metal load leaving the mine site. Copper, iron, and manganese loads from Cropsy Creek were nearly as large or larger than the load from sources upstream from the SWTF.


Table of Contents

Abstract

Introduction

Purpose and Scope

Description of Study Area

Acknowledgments

Study Approach

Background Chloride and Streamflow Conditions

Tracer Injection

Synoptic Sampling

Tracer-Injection and Synoptic-Sampling Results

Chloride Flux

Chloride Profiles

Discharge Profiles

Synoptic-Sampling Results

Metal Loads

Primary Study Reach

Secondary Study Reach

Summary

References Cited

Appendix

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