Element Concentrations and Grain Size of Sediment from the Similkameen River above Enloe Dam (Enloe Reservoir) near Oroville, Okanogan County, Washington, 2019

Scientific Investigations Report 2022-5073
Prepared in cooperation with Grant County Public Utility District
By: , and 



In 2019, the U.S. Geological Survey conducted a reconnaissance survey of concentrations of 41 trace elements present in bed sediment in the reservoir on the Similkameen River upstream from Enloe Dam, near Oroville, Washington. The Similkameen River drains a watershed containing highly mineralized geologic deposits with current (2019) and historical mining activity. Results of this survey indicated that surface and subsurface sediment are substantially enriched in element concentrations of silver (Ag), arsenic (As), gold (Au), bismuth (Bi), cadmium (Cd), copper (Cu), manganese (Mn), antimony (Sb), selenium (Se), tin (Sn), and tellurium (Te) relative to average concentrations found in upper continental-crustal material. Conversely, concentrations of mercury (Hg) and lead (Pb) in sediment above Enloe Dam (Enloe Reservoir) were generally less than average concentrations in upper continental-crustal material (Hg = 0.05 milligrams per kilogram [mg/kg]; Pb =17 mg/kg). Concentrations of most trace elements were higher in the less than 63-micrometer fraction (silt) and tended to be higher in subsurface than in surface sediment. The concentrations of trace elements were compared to consensus-based aquatic toxicity reference concentrations, Washington State Department of Ecology sediment management standards, and average concentrations of upper continental-crustal material. Arsenic concentrations were consistently elevated above these criteria among samples and often exceeded sediment management standards and aquatic toxicity reference values (both threshold effects and probable effects concentrations). High concentrations of As were measured in sediment with proportionally more material in the less than 63-micrometer size fraction; this result may be related to the presence of ore-processing waste material that has entered the aquatic system from approximately 125 years of mining operations in the basin. Elevated concentrations of chromium and copper that exceed the same criteria as arsenic (As) were measured less consistently and predominantly in the fine-grain size fraction.

Suggested Citation

Cox, S.E., Curran, C.A., Spanjer, A.R., Opatz, C.C., Takesue, R.K., and Bell, J.L., 2022, Element concentrations and grain size of sediment from the Similkameen River above Enloe Dam (Enloe Reservoir) near Oroville, Washington, 2019: U.S. Geological Survey Scientific Investigations Report 2022–5073, 47 p., https://doi.org/10.3133/sir20225073.

ISSN: 2328-0328 (online)

Study Area

Table of Contents

  • Acknowledgments
  • Abstract
  • Introduction
  • Study Methods
  • Sediment Characterization, Element Concentrations, and Isotope Analysis
  • Effects of Milling and Mining on Trace-Element Concentrations
  • Summary
  • References Cited
Publication type Report
Publication Subtype USGS Numbered Series
Title Element concentrations and grain size of sediment from the Similkameen River above Enloe Dam (Enloe Reservoir) near Oroville, Washington, 2019
Series title Scientific Investigations Report
Series number 2022-5073
DOI 10.3133/sir20225073
Year Published 2022
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Pacific Coastal and Marine Science Center, Washington Water Science Center
Description Report: x, 47 p.; Data Release
Country United States
State Washington
Other Geospatial Enloe Dam, Enloe Reservoir
Online Only (Y/N) Y
Google Analytic Metrics Metrics page
Additional publication details