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Phosphorus and E. coli and their relation to selected constituents during storm runoff conditions in Fanno Creek, Oregon, 1998-99

By Chauncey W. Anderson and Stewart A. Rounds

Water-Resources Investigations Report 02-4232
 

Prepared in cooperation with

CLEAN WATER SERVICES

 

Report cover

 

Contents

Significant Findings
Introduction
    Purpose and Scope
    Description of Study Area
    Acknowledgments
Methods and Quality Assurance
    Discharge and Water Quality
    Quality Assurance Results
Results
    Storms Sampled
    Water Quality
        Discharge
        Solids
        Biochemical Oxygen Demand
        Bacteria
        Phosphorus
        Nitrogen
Summary
References Cited
Appendix A.-- Quality Assurance Program
    Quality Assurance Samples
    Quality Assurance Results
    Table A1. Replicate sample results and
        relative percent differences during storm
        samplings, 1998-99
Appendix B.-- Water quality data from Fanno Creek, Oregon

 

Significant Findings

As part of an ongoing cooperative study between Clean Water Services of Washington County, Oregon, and the U.S. Geological Survey, water-quality data were collected from Fanno Creek, Oregon, during three storms from June 1998 to December 1999. Samples were collected over the discharge hydrograph from three sites during one summer storm, one fall storm, and one winter storm. From these data, the following conclusions were reached for water-quality conditions and processes in Fanno Creek during storm runoff:

  • Discharge was significantly correlated with total solids (TS), total suspended solids (TSS), total volatile suspended solids (TVSS), turbidity, and total phosphorus (TP).
  • Of the different fractions of TS measured, TS was most directly correlated with TSS.
  • Rising limbs of discharge hydrographs had higher concentrations of sediment and TP, possibly indicating that sources were nearby (resuspension of streambed, bank erosion, close upland sources) and that available supplies limited downstream transport.
  • Concentrations of sediment (TS, TSS), TP, and bacteria (E. coli) were greatest and most variable at the most upstream site. Peak bacterial loads were similar at upstream and downstream sites, so additional sources were not evident, or downstream sources were offset by settling or losses of bacteria from upstream.
  • Biochemical oxygen demand during storms was primarily associated with decomposable materials on particulate matter.
  • E. coli concentrations exceeded the State of Oregon single-sample water-quality standard of 406 colonies/100 mL in almost all samples. E. coli concentrations measured during the summer storm were an order of magnitude greater than those measured during the fall or winter storms, primarily due to warmer water and less dilution during the summer storm.
  • E. coli were correlated with suspended sediment (TSS and turbidity), indicating that they were either transported to streams attached to particles bound to resuspended streambed particles, or they had an affinity for particulate material in water.
  • TP concentrations exceeded both the 1998 and 2001 Total Maximum Daily Load (TMDL) criterion concentrations in almost all samples.
  • Soluble Reactive Phosphorus (SRP) in the stream may have originated primarily from ground-water discharge, whereas TP was mostly associated with particulates.


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