Surface-Water Quality of the Skokomish, 

Nooksack, and Green-Duwamish Rivers and 

Thornton Creek, Puget Sound Basin, 

Washington, 1995-98

By S.S. Embrey and L.M. Frans

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 02-4190

Puget Sound Basin

ty Assessment Study Unit

H COLUMBI

ANADA

TED STAT

ett

ue

science for a changing world
Surface-Water Quality of the Skokomish,

Nooksack, and Green-Duwamish Rivers and

Thornton Creek, Puget Sound Basin,

Washington, 1995–98

By S.S. Embrey and L.M. Frans

NATIONAL WATER-QUALITY ASSESSMENT PROGRAM

Tacoma, Washington

2003

Water-Resources Investigations Report 02-4190

U.S. GEOLOGICAL SURVEY
For additional information write to:

Director, Washington Water Science Center

U.S. Geological Survey

1201 Pacific Avenue – Suite 600

Tacoma, Washington 98402

http://wa.water.usgs.gov

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does 

not imply endorsement by the U.S. Government.

Copies of this report can be purchased from:

U.S. Geological Survey

Information Services

Building 810

Box 25286, Federal Center

Denver, CO 80225-0286

U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director
FOREWORD

The U.S. Geological Survey (USGS) is 

committed to serve the Nation with accurate and 

timely scientific information that helps enhance and 

protect the overall quality of life, and facilitates 

effective management of water, biological, energy, 

and mineral resources. Information on the quality of 

the Nation's water resources is of critical interest to 

the USGS because it is so integrally linked to the 

long-term availability of water that is clean and safe 

for drinking and recreation and that is suitable for 

industry, irrigation, and habitat for fish and wildlife. 

Escalating population growth and increasing 

demands for the multiple water uses make water 

availability, now measured in terms of quantity and 

quality, even more critical to the long-term 

sustainability of our communities and ecosystems.

The USGS implemented the National WaterQuality Assessment (NAWQA) Program to support 

national, regional, and local information needs and 

decisions related to water-quality management and 

policy. Shaped by and coordinated with ongoing 

efforts of other Federal, State, and local agencies, the 

NAWQA Program is designed to answer: What is the 

condition of our Nation's streams and ground water? 

How are the conditions changing over time? How do 

natural features and human activities affect the 

quality of streams and ground water, and where are 

those effects most pronounced? By combining 

information on water chemistry, physical 

characteristics, stream habitat, and aquatic life, the 

NAWQA Program aims to provide science-based 

insights for current and emerging water issues. 

NAWQA results can contribute to informed 

decisions that result in practical and effective waterresource management and strategies that protect and 

restore water quality.

Since 1991, the NAWQA Program has 

implemented interdisciplinary assessments in more 

than 50 of the Nation's most important river basins 

and aquifers, referred to as Study Units. Collectively, 

these Study Units account for more than 60 percent 

of the overall water use and population served by 

public water supply, and are representative of the 

Nation's major hydrologic landscapes, priority 

ecological resources, and agricultural, urban, and 

natural sources of contamination. 

Each assessment is guided by a nationally 

consistent study design and methods of sampling and 

analysis. The assessments thereby build local 

knowledge about water-quality issues and trends in a 

particular stream or aquifer while providing an 

understanding of how and why water quality varies 

regionally and nationally. The consistent, multi-scale 

approach helps to determine if certain types of 

water-quality issues are isolated or pervasive, and 

allows direct comparisons of how human activities 

and natural processes affect water quality and 

ecological health in the Nation's diverse geographic 

and environmental settings. Comprehensive 

assessments on pesticides, nutrients, volatile organic 

compounds, trace metals, and aquatic ecology are 

developed at the national scale through comparative 

analysis of the Study-Unit findings. 

The USGS places high value on the 

communication and dissemination of credible, 

timely, and relevant science so that the most recent 

and available knowledge about water resources can 

be applied in management and policy decisions. We 

hope this NAWQA publication will provide you the 

needed insights and information to meet your needs, 

and thereby foster increased awareness and 

involvement in the protection and restoration of our 

Nation's waters. 

The NAWQA Program recognizes that a 

national assessment by a single program cannot 

address all water-resource issues of interest. External 

coordination at all levels is critical for a fully 

integrated understanding of watersheds and for costeffective management, regulation, and conservation 

of our Nation's water resources. The Program, 

therefore, depends extensively on the advice, 

cooperation, and information from other Federal, 

State, interstate, Tribal, and local agencies, nongovernment organizations, industry, academia, and 

other stakeholder groups. The assistance and 

suggestions of all are greatly appreciated.

Robert M. Hirsch

Associate Director for Water
Contents iv

CONTENTS

Abstract ................................................................................................................................................................ 1

Introduction .......................................................................................................................................................... 3

Purpose of Report and Scope of Study ....................................................................................................... 3

Acknowledgments....................................................................................................................................... 4

Description of the Puget Sound Basin Study Unit...................................................................................... 4

Fixed-Site Sampling Network Design ........................................................................................................ 6

Methods of Sample Collection and Analysis....................................................................................................... 9

Water-Sample Collection, Field Procedures, and Sample Preparation....................................................... 9

Field Measurements .................................................................................................................................... 10

Laboratory Analyses ................................................................................................................................... 10

Collection and Analysis of Quality-Control Samples................................................................................. 11

Streamflow Measurements.......................................................................................................................... 13

Loads and Yields......................................................................................................................................... 13

Surface-Water-Quality of the Skokomish, Nooksack, and Green-Duwamish Rivers and Thornton Creek ........ 14

Hydrologic Conditions—Climate and Streamflows ................................................................................... 14

Water Quality—Chemistry, Standards and Criteria, and Loads................................................................. 18

Skokomish River Basin............................................................................................................................... 22

Skokomish River Basin Hydrology ................................................................................................... 22

Skokomish River Basin Water Quality.............................................................................................. 25

Nooksack River Basin................................................................................................................................. 32

Nooksack River Basin Hydrology ..................................................................................................... 32

Nooksack River Basin Water Quality................................................................................................ 36

Nooksack River Basin Organic Chemistry............................................................................... 45

Green-Duwamish River Basin .................................................................................................................... 58

Green-Duwamish River Basin Hydrology......................................................................................... 58

Green-Duwamish River Basin Water Quality ................................................................................... 65

Duwamish River Organic Chemistry........................................................................................ 79

Thornton Creek Basin ................................................................................................................................. 85

Thornton Creek Basin Hydrology...................................................................................................... 85

Thornton Creek Basin Water Quality ................................................................................................ 85

Thornton Creek Organic Chemistry.......................................................................................... 88

Land Use and Water Quality................................................................................................................................ 98

Loads and Yields.................................................................................................................................................. 105

Skokomish River Basin............................................................................................................................... 109

Nooksack River Basin................................................................................................................................. 111

Green-Duwamish River Basin .................................................................................................................... 114

Thornton Creek Basin ................................................................................................................................. 118

Trends in Concentrations of Nitrate and Total Phosphorus ................................................................................. 121

Summary .............................................................................................................................................................. 128

References Cited .................................................................................................................................................. 132
v Contents

Appendix A. National Water-Quality Laboratory Analytical Schedules ............................................................ 140

Table A1......................................................................................................................................................Minimum reporting levels for major ions and trace metals analyzed in 

filtered surface-water samples by inductively coupled plasma, laboratory 

schedule 2701................................................................................................................................. 140

Table A2. Minimum reporting levels for nutrients analyzed in filtered and whole 

surface-water samples, laboratory schedule 2702.................................................................. 140

Table A3. Minimum reporting levels for organic carbon analyzed in surface-water samples, laboratory 

schedule 2075 ........................................................................................................................ 140

Table A4. Minimum reporting levels for pesticides and transformation products 

analyzed in filtered surface-water samples by gas chromatography/mass 

spectrometry, laboratory schedule 2010 ............................................................................... 141

Table A5. Minimum reporting levels for pesticides and transformation products 

analyzed in filtered surface-water samples by high-performance liquid 

chromatography/photodiode-array detection, laboratory schedule 2051 .............................. 142

Table A6. Minimum reporting levels for volatile organic compounds analyzed in whole 

surface-water samples by purge and trap chromatography/mass spectrometry, 

laboratory schedule 2020 ......................................................................................................143

Appendix B.Quality Assurance/Quality Control—Methods, Results, and Discussion .......................................145

Table B1. Concentrations of major ions in field-blank water samples for the 

Puget Sound Basin study unit, Washington ........................................................................... 148

Table B2. Concentrations of nutrients in field-blank water samples for the Puget Sound 

Basin study unit, Washington ............................................................................................... 149

Table B3. Concentrations of dissolved and suspended organic carbon in field-blank water 

samples for the Puget Sound Basin study unit, Washington ................................................. 150

Table B4. Summary of volatile organic compounds detected in source, canister, and 

field blank-water samples for the Puget Sound Basin study unit, Washington .................... 151

Table B5. Concentrations of major ions in replicate environmental water samples for 

the Puget Sound Basin study unit, Washington .................................................................... 152

Table B6. Concentrations of nutrients in replicate environmental water samples for the 

Puget Sound Basin study unit, Washington .......................................................................... 155

Table B7. Concentrations of organic carbon in replicate environmental water samples for 

the Puget Sound Basin study unit, Washington .................................................................... 158

Table B8. Concentrations of pesticide compounds detected in replicate environmental 

water samples for the Puget Sound Basin study unit, Washington ....................................... 160

Figure B1. Graphs showing percentage of recoveries for pesticide compounds in field 

matrix-spiked water samples from the four intensive fixed sites in the Puget 

Sound Basin study unit, Washington ....................................................................................161

Table B9. Summary of percentage of mean recoveries from field-matrix-spike volatile 

organic compound analyses for the Puget Sound Basin study unit, Washington ................. 162

Table B10. Summary of surrogate compound recoveries in filtered water samples for 

pesticide analyses for the Puget Sound Basin study unit, Washington ................................. 162

Table B11. Summary of surrogate compound recoveries in whole water samples for 

volatile organic compound analyses for the Puget Sound Basin study unit, 

Washington ........................................................................................................................... 162
Contents vi

Appendix C. Nutrient Load Estimation............................................................................................................... 163

Table C1. Total nitrogen loads, standard deviations, and regression equations for 

load estimates for surface-water sites in the Puget Sound Basin study 

unit, Washington ................................................................................................................... 166

Table C2. Total phosphorus loads, standard deviations, and regression equations for

load estimates for surface-water sites in the Puget Sound Basin study 

unit, Washington ................................................................................................................... 167

Table C3. Dissolved orthophosphate phosphorus loads, standard deviations, and 

regression equations for load estimates for surface-water sites in the Puget 

Sound Basin study unit, Washington .................................................................................... 168

Table C4. Suspended-sediment loads, standard deviations, and regression equations 

for load estimates for surface-water sites in the Puget Sound Basin study 

unit, Washington ................................................................................................................... 169

Figure C1. Graphs showing predicted and measured daily nutrient loads, and scatterplots 

of nutrient concentrations and streamflows used to calibrate the load-estimate 

regression equations for the Skokomish River (site 1) ......................................................... 170

Figure C2. Graphs showing predicted and measured daily nutrient loads, and scatterplots 

of nutrient concentrations and streamflows used to calibrate the load-estimate 

regression equations for the North Fork Skokomish River (site 2) in the Puget 

Sound Basin study unit, Washington ..................................................................................... 171

Figure C3. Graphs showing predicted and measured daily nutrient loads, and scatterplots 

of nutrient concentrations and streamflows used to calibrate the load-estimate 

regression equations for the lower Nooksack River (site 3) in the Puget Sound 

Basin study unit, Washington ................................................................................................ 172

Figure C4. Graphs showing predicted and measured daily nutrient loads, and scatterplots 

of nutrient concentrations and streamflows used to calibrate the load-estimate 

regression equations for Fishtrap Creek (site 4) in the Puget Sound Basin study 

unit, Washington .................................................................................................................... 173

Figure C5. Graphs showing predicted and measured daily nutrient loads, and scatterplots 

of nutrient concentrations and streamflows used to calibrate the load-estimate 

regression equations for the upper Nooksack River (site 5) in the Puget Sound 

Basin study unit, Washington ................................................................................................ 174

Figure C6. Graphs showing predicted and measured daily nutrient loads, and scatterplots 

of nutrient concentrations and streamflows used to calibrate the load-estimate 

regression equations for the Duwamish River (site 6) in the Puget Sound Basin 

study unit, Washington .......................................................................................................... 175

Figure C7. Graphs showing predicted and measured daily nutrient loads, and scatterplots 

of nutrient concentrations and streamflows used to calibrate the load-estimate 

regression equations for Springbrook Creek (site 7) in the Puget Sound Basin 

study unit, Washington .......................................................................................................... 176

Figure C8. Graphs showing predicted and measured daily nutrient loads, and scatterplots 

of nutrient concentrations and streamflows used to calibrate the load-estimate 

regression equations for Big Soos Creek (site 8) in the Puget Sound Basin study 

unit, Washington .................................................................................................................... 177

Figure C9. Graphs showing predicted and measured daily nutrient loads, and scatterplots 

of nutrient concentrations and streamflows used to calibrate the load-estimate 

regression equations for Newaukum Creek (site 9) in the Puget Sound Basin 

study unit, Washington .......................................................................................................... 178
vii Contents

Figure C10. Graphs showing predicted and measured daily nutrient loads, and scatterplots 

of nutrient concentrations and streamflows used to calibrate the load-estimate 

regression equations for the upper Green River (site 10) in the Puget Sound 

Basin study unit, Washington ................................................................................................ 179

Figure C11. Graphs showing predicted and measured daily nutrient loads, and scatterplots 

of nutrient concentrations and streamflows used to calibrate the load-estimate 

regression equations for Thornton Creek (site 11) in the Puget Sound Basin 

study unit, Washington .......................................................................................................... 180

Figure C12. Graphs showing predicted and measured daily suspended sediment loads, and 

scatterplots of concentrations and streamflows used to calibrate the load-estimate 

regression equations for the Puget Sound Basin study unit, Washington.............................. 181
Figures viii

FIGURES

Figure 1. Map showing location of the Puget Sound Basin study unit, the river basins selected for 

study, and the fixed sampling sites in Washington............................................................................ 5

Figure 2. Boxplots showing distribution of monthly and annual precipitation for the period of 

record at Shelton, Bellingham, and Seattle-Tacoma International Airport, and total 

precipitation during the 1996–98 sample-collection period by month and for each year, 

for the Puget Sound Basin study unit, Washington ........................................................................... 15

Figure 3. Graphs showing departures of monthly precipitation from normal at Bellingham and 

Seattle-Tacoma Airport during the sample-collection period for the Puget Sound Basin 

study unit, Washington ...................................................................................................................... 16

Figure 4. Boxplot showing distribution of annual streamflows for the period of record at fixed sites, 

and annual streamflows for individual water years of the sample-collection period in the 

Puget Sound Basin study unit, Washington....................................................................................... 17

Figure 5. Graph showing percentage of detections of pesticides in water samples from the four 

intensive fixed sites—site 11, Thornton Creek, and site 4, Fishtrap Creek (small streams) 

and site 6, Duwamish River, and site 3, lower Nooksack River (large rivers)—in the Puget 

Sound Basin study unit, Washington................................................................................................. 19

Figure 6. Graphs showing percentage of detections of VOCs at concentrations above the 1999 

laboratory reporting level in samples from four intensive fixed sites—site 11, Thornton 

Creek, and site 4, Fishtrap Creek (small streams) and site 6, Duwamish River, and site 3, 

lower Nooksack River (large rivers)—in the Puget Sound Basin study unit, Washington ............... 20

Figure 7. Graphs showing daily and instantaneous streamflow at the time of sample collection, 

interquartile range of mean daily streamflows for the period of record, and percentage of time 

streamflows are equaled or exceeded at the Skokomish River in the Puget Sound Basin study

unit, Washington................................................................................................................................ 23

Figure 8. Graphs showing daily and instantaneous streamflow at the time of sample collection, 

interquartile range of mean daily streamflows for the period of record, and percentage of time

streamflows are equaled or exceeded at the North Fork Skokomish River (site 2) in the Puget 

Sound Basin study unit, Washington................................................................................................. 24

Figure 9. Graphs and map showing median concentrations of nutrients, suspended sediment, organic 

carbon, and major ions in samples from the Skokomish River (site 1) and the North Fork

Skokomish River (site 2) in the Puget Sound Basin study unit, Washington.................................... 28

Figure 10. Graphs and boxplots showing time series of streamflow and concentrations of total nitrogen,

total phosphorus, dissolved orthophosphate phosphorus, and suspended sediment in samples,

and concentrations by three streamflow periods, for the Skokomish River (site 1) in the

Puget Sound Basin study unit, Washington....................................................................................... 29

Figure 11. Graphs and boxplots showing time series of streamflow and concentrations of total nitrogen, 

total phosphorus, dissolved orthophosphate phosphorus, and suspended sediment in samples,

and concentrations by three streamflow periods, for the North Fork Skokomish River (site 2)

in the Puget Sound Basin study unit, Washington............................................................................. 30

Figure 12. Graphs showing daily and instantaneous streamflow at the time of sample collection, 

interquartile range of mean daily streamflows for the period of record, and percentage of time

streamflows are equaled or exceeded at the lower Nooksack River (site 3) in the Puget 

Sound Basin study unit, Washington................................................................................................. 33

Figure 13. Graphs showing daily and instantaneous streamflow at the time of sample collection, 

and percentage of time streamflows are equaled or exceeded and instantaneous 

streamflow at Fishtrap Creek (site 4) in the Puget Sound Basin study unit, Washington ................. 34
ix Figures

Figure 14. Graphs showing daily and instantaneous streamflow at the time of sample collection, 

interquartile range of mean daily streamflows for the period of record, and percentage of time

streamflows are equaled or exceeded at the upper Nooksack River (site 5) in the Puget 

Sound Basin study unit, Washington................................................................................................. 35

Figure 15. Graphs and maps showing median concentrations of nutrients, suspended sediment, 

organic carbon, and major ions in samples from the lower Nooksack River (site 3), 

Fishtrap Creek (site 4), and the upper Nooksack River (site 5) in the Puget Sound Basin 

study unit, Washington ...................................................................................................................... 41

Figure 16. Graphs and boxplots showing time series of streamflow and concentrations of total

nitrogen, total phosphorus, dissolved orthophosphate phosphorus, and suspended sediment

in samples, and concentrations by three streamflow periods, for the lower Nooksack River

(site 3) in the Puget Sound Basin study unit, Washington................................................................. 42

Figure 17. Graphs and boxplots showing time series of streamflow and concentrations of total 

nitrogen, total phosphorus, dissolved orthophosphate phosphorus, and suspended sediment 

in samples, and concentrations by three streamflow periods, for Fishtrap Creek (site 4) in the 

Puget Sound Basin study unit, Washington....................................................................................... 43

Figure 18. Graphs and boxplots showing time series of streamflow and concentrations of total 

nitrogen, total phosphorus, dissolved orthophosphate phosphorus, and suspended sediment

in samples, and concentrations by three streamflow periods, for the upper Nooksack River

(site 5) in the Puget Sound Basin study unit, Washington................................................................. 44

Figure 19. Graphs showing time series of streamflow and concentrations of selected pesticides 

detected in samples from the lower Nooksack River (site 3) in the Puget Sound Basin study 

unit, Washington................................................................................................................................ 47

Figure 20. Graphs showing time series of streamflow and concentrations of selected volatile 

organic compounds in samples from the lower Nooksack River (site 3) in the Puget Sound

Basin study unit, Washington ............................................................................................................ 49

Figure 21. Graphs showing time series of streamflow and concentrations of selected pesticides

detected in samples from Fishtrap Creek (site 4) in the Puget Sound Basin study unit,

Washington ........................................................................................................................................ 52

Figure 22. Graphs showing time series of streamflow and concentrations of selected volatile

organic compounds detected in samples from Fishtrap Creek (site 4) in the Puget Sound

Basin study unit, Washington ............................................................................................................ 55

Figure 23. Graphs showing daily and instantaneous streamflow at the time of sample collection, 

interquartile range of mean daily streamflows for the period of record, and percentage of 

time streamflows are equaled or exceeded at the Duwamish River (site 6) in the Puget Sound

Basin study unit, Washington ............................................................................................................ 60

Figure 24. Graphs showing daily and instantaneous streamflow at the time of sample collection, 

interquartile range of mean daily streamflows for the period of record, and percentage of 

time streamflows are equaled or exceeded at Springbrook Creek (site 7) in the Puget Sound

Basin study unit, Washington ............................................................................................................ 61

Figure 25. Graphs showing daily and instantaneous streamflow at the time of sample collection, 

interquartile range of mean daily streamflows for the period of record, and percentage of 

time streamflows are equaled or exceeded at Big Soos Creek (site 8) in the Puget Sound 

Basin study unit, Washington ............................................................................................................ 62

Figure 26. Graphs showing daily and instantaneous streamflow at the time of sample collection, 

and the interquartile range of mean daily streamflows for the period of record, and 

percentage of time streamflows are equaled or exceeded at Newaukum Creek (site 9)

in the Puget Sound Basin study unit, Washington............................................................................. 63
Figures x

Figure 27. Graphs showing daily and instantaneous streamflow at the time of sample collection,

and the interquartile range of mean daily streamflows for the period of record, and

percentage of time streamflows are equaled or exceeded at the upper Green River (site 10)

in the Puget Sound Basin study unit, Washington............................................................................. 64

Figure 28. Graphs and map showing median concentrations of nutrients, suspended sediment,

organic carbon, and major ions in samples from the Duwamish River (site 6), Springbrook

Creek (site 7), Big Soos Creek (site 8), Newaukum Creek (site 9), and the upper Green River

(site 10) in the Puget Sound Basin study unit, Washington............................................................... 73

Figure 29. Graphs and boxplots showing time series of streamflow and concentrations of total

nitrogen, total phosphorus, dissolved orthophosphate phosphorus, and suspended sediment

in samples, and concentrations by three streamflow periods, for the Duwamish River (site 6)

in the Puget Sound Basin study unit, Washington............................................................................. 74

Figure 30. Graphs and boxplots showing time series of streamflow and concentrations of total 

nitrogen, total phosphorus, dissolved orthophosphate phosphorus, and suspended sediment

in samples, and concentrations by three streamflow periods, for Springbrook Creek (site 7

in the Puget Sound Basin study unit, Washington............................................................................. 75

Figure 31. Graphs and boxplots showing time series of streamflow and concentrations of total 

nitrogen, total phosphorus, dissolved orthophosphate phosphorus, and suspended sediment

in samples, and concentrations by three streamflow periods, for Big Soos Creek (site 8) in

the Puget Sound Basin study unit, Washington................................................................................. 76

Figure 32. Graphs and boxplots showing time series of streamflow and concentrations of total 

nitrogen, total phosphorus, dissolved orthophosphate phosphorus, and suspended sediment

in samples, and concentrations by three streamflow periods, for Newaukum Creek (site 9)

in the Puget Sound Basin study unit, Washington............................................................................. 77

Figure 33. Graphs and boxplots showing time series of streamflow and concentrations of total 

nitrogen, total phosphorus, dissolved orthophosphate phosphorus, and suspended sediment

in samples, and concentrations by three streamflow periods, for the upper Green River 

(site 10) in the Puget Sound Basin study unit, Washington............................................................... 78

Figure 34. Graphs showing time series of streamflow and concentrations of selected pesticides 

detected in samples from the Duwamish River (site 6) in the Puget Sound Basin study

unit, Washington................................................................................................................................ 82

Figure 35. Graphs showing time series of streamflow and concentrations of selected volatile organic 

compounds in samples from the Duwamish River (site 6) in the Puget Sound Basin study unit,

Washington. ....................................................................................................................................... 84

Figure 36. Graphs showing daily and instantaneous streamflow at the time of sample collection, 

interquartile range of mean daily streamflows for the period of record, and percentage of 

time streamflows are equaled or exceeded at Thornton Creek (site 11) in the Puget Sound 

Basin study unit, Washington ............................................................................................................ 86

Figure 37. Graphs and map showing median concentrations of nutrients, suspended sediment, organic

carbon, and major ions in samples from Thornton Creek (site 11) in the Puget Sound Basin

study unit, Washington ...................................................................................................................... 89

Figure 38. Graphs and boxplots showing time series of streamflow and concentrations of total 

nitrogen, total phosphorus, dissolved orthophosphate phosphorus, and suspended sediment

in samples, and concentrations by three streamflow periods, for Thornton Creek (site 11)

in the Puget Sound Basin study unit, Washington............................................................................. 90

Figure 39. Graphs showing time series of streamflow and concentrations of selected pesticides 

detected in samples from Thornton Creek (site 11) in the Puget Sound Basin study unit,

Washington ........................................................................................................................................ 94
xi Figures

Figure 40. Graphs showing time series of streamflow and concentrations of selected volatile|

organic compounds in samples from Thornton Creek (site 11) in the Puget Sound Basin

study unit, Washington ...................................................................................................................... 96

Figure 41. Graphs showing percentage of detections of pesticides and transformation products in samples

from the four intensive fixed sites—lower Nooksack River (site 3), Fishtrap Creek (site 4),

Duwamish River (site 6), and Thornton Creek (site 11) in the Puget Sound Basin study unit,

Washington ........................................................................................................................................101

Figure 42. Graphs showing percentage of all detections of volatile organic compounds in samples

from the four intensive fixed sites—lower Nooksack River (site 3), Fishtrap Creek (site 4),

Duwamish River (site 6), and Thornton Creek (site 11) in the Puget Sound Basin study unit,

Washington ........................................................................................................................................104

Figure 43. Graphs showing nutrient loads transported in surface water at study sites, and nutrient

yields from the basins by major land-use categories, in the Puget Sound Basin study unit,

Washington ........................................................................................................................................106

Figure 44. Map showing nutrient yields, 1996–98, from study basins in the Puget Sound Basin study unit,

Washington. .......................................................................................................................................107

Figure 45. Graphs showing relation between total phosphorus and suspended-sediment yields, 1996–98,

for the 11 river basins in the Puget Sound Basin study unit, Washington.........................................109

Figure 46. Graphs showing temporal variations in unadjusted and flow-adjusted concentrations of

nitrate and total phosphorus and LOWESS-trend curves for the Skokomish River near

Potlatch, in the Puget Sound Basin study unit, Washington..............................................................122

Figure 47. Graphs showing temporal variations in unadjusted and flow-adjusted concentrations of 

nitrate and total phosphorus and LOWESS-trend curves for the Nooksack River at Brennan, 

in the Puget Sound Basin study unit, Washington.............................................................................123

Figure 48. Graphs showing temporal variations in unadjusted and flow-adjusted concentrations of 

nitrate and total phosphorus and LOWESS-trend curves for the Nooksack River at North 

Cedarville, in the Puget Sound Basin study unit, Washington ..........................................................124

Figure 49. Graphs showing temporal variations in unadjusted and flow-adjusted concentrations of 

nitrate and total phosphorus and LOWESS-trend curves for the Green River at Renton 

Junction, in the Puget Sound Basin study unit, Washington .............................................................125

Figure 50. Graphs showing temporal variations in unadjusted and flow-adjusted concentrations of 

nitrate and total phosphorus and LOWESS-trend curves for Big Soos Creek above Hatchery 

near Auburn, in the Puget Sound Basin study unit, Washington.......................................................126

Figure 51. Graphs showing temporal variations in unadjusted and flow-adjusted concentrations of 

nitrate and total phosphorus and LOWESS-trend curves for Newaukum Creek near Black 

Diamond, in the Puget Sound Basin study unit, Washington............................................................127
Tables xii

TABLES

Table 1. Description of surface-water-quality fixed sampling sites in the Puget Sound Basin

study unit, Washington ...................................................................................................................... 8

Table 2. Summary of standards and criteria for selected water-quality properties, inorganic

constituents, and pesticides, and number of samples that did not meet criteria during

the period 1996–98 in the Puget Sound Basin study unit, Washington............................................. 21

Table 3. Summary of values of field measurements and concentrations of nutrients, major ions,

organic carbon, and suspended sediment in samples from the Skokomish River (site 1) in 

the Puget Sound Basin study unit, Washington................................................................................. 26

Table 4. Summary of values of field measurements and concentrations of nutrients, major ions, 

organic carbon, and suspended sediment in samples from the North Fork Skokomish River 

(site 2) in the Puget Sound Basin study unit, Washington................................................................. 27

Table 5. Correlation between selected water-quality characteristics or concentrations of chemical 

constituents and streamflow for the Skokomish River (site 1) and the North Fork Skokomish 

River (site 2) in the Puget Sound Basin study unit, Washington....................................................... 31

Table 6. Summary of values of field measurements and concentrations of nutrients, major ions, 

organic carbon, and suspended sediment in samples from the lower Nooksack River (site 3) 

in the Puget Sound Basin study unit, Washington............................................................................. 37

Table 7. Summary of values of field measurements and concentrations of nutrients, major ions,

organic carbon, and suspended sediment in samples from Fishtrap Creek (site 4) in the 

Puget Sound Basin study unit, Washington....................................................................................... 38

Table 8. Summary of values of field measurements and concentrations of nutrients, major ions,

organic carbon, and suspended sediment in samples from the upper Nooksack River (site 5) 

in the Puget Sound Basin study unit, Washington............................................................................. 39

Table 9. Correlation between selected water-quality characteristics or chemical constituents and

streamflow for the lower Nooksack River (site 3), Fishtrap Creek (site 4), and the upper 

Nooksack River (site 5) in the Puget Sound Basin study unit, Washington...................................... 45

Table 10. Pesticides in water samples from the lower Nooksack River (site 3) in the Puget Sound

Basin study unit, Washington ............................................................................................................ 46

Table 11. Volatile organic compounds in water samples from the lower Nooksack River (site 3) in the

Puget Sound Basin study unit, Washington....................................................................................... 48

Table 12. Pesticides in water samples from Fishtrap Creek (site 4) in the Puget Sound Basin study

unit, Washington................................................................................................................................ 51

Table 13. Volatile organic compounds in water samples from Fishtrap Creek (site 4) in the Puget

Sound Basin study unit, Washington................................................................................................. 54

Table 14. Summary of values of field measurements and concentrations of nutrients, major ions,

organic carbon, and suspended sediment in samples from Duwamish River (site 6) in the 

Puget Sound Basin study unit, Washington....................................................................................... 68

Table 15. Summary of values of field measurements and concentrations of nutrients, major ions,

organic carbon, and suspended sediment in samples from Springbrook Creek (site 7) in the 

Puget Sound Basin study unit, Washington....................................................................................... 69

Table 16. Summary of values of field measurements and concentrations of nutrients, major ions,

organic carbon, and suspended sediment in samples from Big Soos Creek (site 8) in the 

Puget Sound Basin study unit, Washington....................................................................................... 70
xiii Tables

Table 17. Summary of values of field measurements and concentrations of nutrients, major ions, 

organic carbon, and suspended sediment in samples from Newaukum Creek (site 9) in the 

Puget Sound Basin study unit, Washington....................................................................................... 71

Table 18. Summary of values of field measurements and concentrations of nutrients, major ions, 

organic carbon, and suspended sediment in samples from the upper Green River (site 10)

in the Puget Sound Basin study unit, Washington............................................................................. 72

Table 19. Correlation between selected water-quality characteristics or chemical constituents and 

streamflow for the Duwamish River (site 6), Springbrook Creek (site 7), Big Soos Creek 

(site 8), Newaukum Creek (site 9), and the upper Green River (site 10) in the Puget Sound 

Basin study unit, Washington ............................................................................................................ 79

Table 20. Pesticides in water samples from the Duwamish River (site 6) in the Puget Sound Basin 

study unit, Washington ...................................................................................................................... 81

Table 21. Volatile organic compounds in water samples from the Duwamish River (site 6) in the 

Puget Sound Basin study unit, Washington....................................................................................... 83

Table 22. Summary of values of field measurements and concentrations of nutrients, major ions, 

organic carbon, and suspended sediment in samples from Thornton Creek (site 11) in the 

Puget Sound Basin study unit, Washington....................................................................................... 87

Table 23. Correlation between selected water-quality characteristics or chemical constituents and 

streamflow for Thornton Creek (site 11) in the Puget Sound Basin study unit, Washington ........... 88

Table 24. Pesticides in water samples from Thornton Creek (site 11) in the Puget Sound Basin study 

unit, Washington................................................................................................................................ 91

Table 25. Volatile organic compounds in water samples from Thornton Creek (site 11) in the Puget 

Sound Basin study unit, Washington................................................................................................. 93

Table 26. Ranking of 11 large rivers and small streams by average total nitrogen concentrations 

(the sum of nitrite, nitrate, ammonia, and organic nitrogen) and by average dissolved 

orthophosphate phosphorus concentrations for the Puget Sound Basin study unit, Washington...... 99

Table 27. Pesticides detected in water samples from the study sites, the primary use of these pesticides,

and estimated pounds of active ingredient applied each year in the Puget Sound Basin study 

unit, Washington................................................................................................................................ 102

Table 28. Loads and basin yields during 1996, 1997, and 1998 and their averages for the study

period 1996-98; average loads for the historical period 1980-93; and daily loads, by season, 

for the study period 1996-98 at site 1 and site 2, Skokomish River Basin, in the Puget Sound 

Basin study unit, Washington ............................................................................................................ 110

Table 29. Loads and basin yields during 1996, 1997, and 1998 and their averages for the study 

period 1996-98; average loads for the historical period 1980-93; and daily loads, by season, 

for the study period 1996-98 at site 3, site 4, and site 5, Nooksack River Basin, in the Puget 

Sound Basin study unit, Washington................................................................................................. 112

Table 30. Loads and basin yields during 1996, 1997, and 1998 and their averages for the study 

period 1996-98; average loads for the historical period 1980-93; and daily loads, by season, 

for the study period 1996-98 at site 6, site 7, site 8, site 9, and site 10, Green-Duwamish 

River Basin, in the Puget Sound Basin study unit, Washington........................................................ 116

Table 31. Loads and basin yields during 1996, 1997, and 1998 and their averages for the study 

period 1996-98; average loads for the historical period 1980-93; and daily loads, by 

season, for the study period 1996-98 at site 11, Thornton Creek Basin, in the Puget 

Sound Basin study unit, Washington................................................................................................. 118
Tables xiv

Table 32. Summary of results from seasonal Kendall tests for temporal trends in nitrate 

nitrogen and total phosphorus concentrations at six surface-water sites in the Puget 

Sound Basin study unit, Washington................................................................................................. 121

Table 33. Fecal-indicator bacteria and coliphage in samples collected at selected surface-water 

sites in the Puget Sound Basin study unit, Washington..................................................................... 136

Table 34. Pesticide and volatile organic compounds in storm samples collected on 

October 4, 1996, from Springbrook Creek, site 7, in the Puget Sound Basin study 

unit, Washington................................................................................................................................ 137
Conversion Factors and Vertical Datum xv

CONVERSION FACTORS AND VERTICAL DATUM

CONVERSION FACTORS

Temperature in degrees Celsius (oC) may be converted to degrees Fahrenheit (oF) as follows:

oF=1.8 oC+32.

Temperature in degrees Fahrenheit (oF) may be converted to degrees Celsius (oC) as follows:

oC=(oF–32)/1.8.

Chemical concentrations in water are given in milligrams per liter (mg/L) or micrograms per liter 

(μg/L). Milligrams per liter is a unit expressing the solute per unit volume (liter) of water. One thousand micrograms per liter is equivalent to one milligram per liter. For concentrations less than 7,000 

mg/L, milligrams per liter is equivalent to "parts per million" and micrograms per liter is equivalent to 

"parts per billion." 

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (μS/cm at 25oC).

VERTICAL DATUM

Sea level: In this report "sea level" refers to the National Geodetic Vertical Datum of 1929 (NGVD of 

1929)--a geodetic datum derived from a general adjustment of the first-order level nets of both the 

United States and Canada, formerly called Sea Level Datum of 1929.

Altitude, as used in this report, refers to distance above or below sea level.

Multiply By To obtain

Length

cubic foot per second (ft3/s) 0.02832 cubic meter per second

foot (ft 0.3048 meter

inch (in) 25.4 millimeter

mile (mi) 1.609 kilometer

pound, avoirdupois (lb) 0.4536 kilogram

pound per day (lb/d) 0.4536 kilogram per day

square mile (mi2) 2.590 square kilometer

ton per year (ton/yr) 0.9072 metric ton per year
Abstract 1

Surface-Water Quality of the Skokomish, Nooksack, and 

Green-Duwamish Rivers and Thornton Creek, Puget 

Sound Basin, Washington, 1995-98

S.S. Embrey and L.M. Frans

ABSTRACT

Streamflow and surface-water-quality data were 

collected from November 1995 through April 1998 

(water years 1996–98) from a surface-water network in 

the Puget Sound Basin study unit of the U.S. 

Geological Survey National Water-Quality Assessment 

program. Water samples collected monthly and during 

storm runoff events were analyzed for nutrients, major 

ions, organic carbon, and suspended sediment, and at 

selected sites, samples were analyzed for pesticides and 

volatile organic compounds. Eleven sites were 

established in three major watersheds—two in the 

Skokomish River Basin, three in the Nooksack River 

Basin, five in the Green-Duwamish River Basin, and 

one site in Thornton Creek Basin, a small tributary to 

Lake Washington. The Skokomish River near Potlatch, 

Nooksack River at Brennan, and Duwamish River at 

Tukwila are integrators of mixed land uses with the 

sampling sites locally influenced by forestry practices, 

agriculture, and urbanization, respectively. The 

remaining eight sites are indicators of relatively 

homogeneous land use/land cover in their basins. The 

site on the North Fork Skokomish River is an indicator 

site chosen to measure reference or background 

conditions in the study unit. In the Nooksack River 

Basin, the site on Fishtrap Creek is an indicator of 

agriculture, and the Nooksack River at North 

Cedarville is an indicator site of forestry practices in 

the upper watershed. In the Green-Duwamish River 

Basin, Springbrook Creek is an urban indicator, Big 

Soos Creek is an indicator of a rapidly developing 

suburban basin; Newaukum Creek is an indicator of 

agriculture; and the Green River above Twin Camp 

Creek is an indicator of forestry practices. Thornton 

Creek is an indicator of high-density urban residential 

and commercial development.

Conditions during the first 18 months of 

sampling were dominated by above-normal 

precipitation. For the Seattle-Tacoma area, water year 

1997 was the wettest of the 3 years during the samplecollection period. Nearly 52 inches fell (about 

14 inches above average) and monthly precipitation 

was often 200 percent of normal. The wet years kept 

streamflows generally above normal and contributed to 

high concentrations of pesticides, nutrients, suspended 

sediment, and organic carbon in samples.

On the basis of chemical concentrations, 

dissolved oxygen concentrations, and water 

temperature, the relative quality of water among the 

11 study sites ranged from exceptionally high in the 

North Fork Skokomish and the Green to fair in 

Springbrook and Thornton. Water in the large rivers 

(Skokomish, Nooksack, Green-Duwamish) and in two 

of the small streams in the Puget Sound Lowlands (Big 

Soos and Newaukum) was characterized by dilute 

water chemistry with dissolved solids concentrations 

less than 130 milligrams per liter. Water in three other 

small streams in the Lowlands (Fishtrap, Springbrook, 

and Thornton) had dissolved solids concentrations as 

high as 320 milligrams per liter. Nutrient and pesticide 

concentrations mostly were higher in the small streams 

than in the large rivers. Suspended-sediment 

concentrations, however, were highest in the large 

rivers, with averages ranging from 85 to 

443 milligrams per liter. During storm and flood 

events, suspended-sediment concentrations in samples 

from the Nooksack were as much as 2,800 milligrams 

per liter, and from the Skokomish, 1,500 milligrams per 

liter.
2 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Out of 86 pesticides and 86 volatile organic 

compounds analyzed, a total of 35 pesticides and 11 

volatile organic compounds were detected at 

concentrations above laboratory reporting levels in 

samples collected from the four intensively studied 

sites, the lower Nooksack River, Duwamish River, 

Fishtrap Creek, and Thornton Creek. Herbicides were 

detected more frequently than insecticides. The 

herbicide prometon was detected in 66 percent of all 

124 samples collected, followed by simazine 

(65 percent), atrazine (64 percent), and the insecticide 

diazinon (50 percent). The detected volatile organic 

compounds belonged to one of three general classes—

fuel-related, the trihalomethanes, or solvents.

Water-quality standards and criteria for drinking 

water or for the protection of aquatic life were nearly 

always met, except on occasion by concentrations of 

dissolved oxygen, iron, and manganese in samples 

from Springbrook and Fishtrap, and concentrations of 

diazinon in Thornton and Fishtrap. Concentrations of 

three other insecticides (carbaryl, chlorpyrifos, and 

lindane) also did not meet criteria protecting aquatic 

life in a few samples (from 1 to 5) from Thornton and 

Fishtrap and from the Duwamish River.

Water-quality conditions at the sampling sites 

resulted from natural characteristics of the watersheds 

and from human activities. In the Nooksack and 

Skokomish, natural conditions were probably 

important contributors to the large suspended-sediment 

concentrations observed during high streamflow 

events. However, logging and road building in the 

basins might also have contributed to the suspendedsediment loads. In the forested study basins, the water 

chemistry was more dilute, based on dissolved solids 

and nutrient concentrations. The North Fork 

Skokomish (indicator site of background conditions) 

and the Green (indicator site of forestry and natural 

conditions) were characterized by high-quality water 

with low concentrations of dissolved solids, nutrients, 

and sediment and by standards or criteria that were 

nearly always met. Unlike the high-quality water at the 

background and forestry sites, natural conditions 

appear to have adversely affected the quality of water 

in Springbrook. High concentrations of iron and 

manganese and low dissolved-oxygen concentrations 

were possibly the result of ground-water discharge at 

this site.

Of all the sites, nutrient concentrations were 

highest in the agricultural streams (Fishtrap and 

Newaukum) and next highest in the urban streams, 

indicating that human activities affect the water quality 

of these streams. Of the three large rivers integrating a 

mix of land uses, the lower Nooksack, in an 

agricultural setting, on average had the highest total 

nitrogen and phosphorus concentrations, followed by 

the Duwamish in an urban setting, and the Skokomish 

in a forestry-practices setting.

In both urban and agricultural settings, pesticides 

affected water quality at the four sites sampled for 

organic compounds. However, more types of pesticides 

were found at the agricultural sites than at the urban 

sites. The most pesticides were detected in Fishtrap. 

Many of these were pesticides applied for agricultural 

purposes, but several were pesticides applied in urban 

settings, such as those used in maintaining rights-ofway. In urban Thornton Creek, however, high 

application rates and retail availability of pesticides 

likely resulted in generally higher concentrations, the 

detections of certain pesticides in many samples year 

round, and the number of times insecticide 

concentrations did not meet chronic criteria for the 

protection of freshwater aquatic life.

The two sites located in urban areas also had 

more detections of volatile organic compounds and at a 

higher detection frequency than the two sites in 

agricultural areas. The most compounds were detected 

in Thornton, and in the highest concentrations. 

Conversely, the least number of compounds was 

detected in the lower Nooksack, with only 2 percent 

urban land upstream. Methyl tert-butyl ether, an 

automotive fuel additive, was detected in a few samples 

from Fishtrap. Many solvents, such as trichloroethene 

and tetrachloroethene, were detected only in samples 

from the urban sites on the Duwamish River and 

Thornton Creek. The only volatile organic compound 

with a distinctly agricultural signature was 1,2-

dichloropropane, detected only in Fishtrap Creek 

samples.
Introduction 3

INTRODUCTION

The U.S. Geological Survey (USGS) began the 

National Water-Quality Assessment (NAWQA) 

program in 1991, with hydrologic data collection at 20 

study units throughout the United States. NAWQA 

study units across the nation, using consistent sampling 

and analytical methods, contribute data and 

information on surface- and ground-water quality, bedsediment quality, ecology, biology, and land use to the 

program’s database. These data are being used to 

describe the status and trends in the quality of the 

Nation’s surface- and ground-water resources and to 

identify the major natural and human factors affecting 

water quality (Leahy and others, 1990; 1993). Surfacewater investigations in the study units have several 

objectives, including descriptions of the occurrence and 

spatial distribution of water-quality constituents, 

information on the seasonal variation and frequency of 

occurrence of selected water-quality constituents at key 

locations, and estimation of loads of selected waterquality constituents (Hirsch and others, 1988). During 

the first, high-intensity phase (HIP) of study in each 

study unit, the focus is on the assessment of occurrence 

and distribution (Gilliom and others, 1995).

In 1994, studies began in another 16 study units, 

one of which is the Puget Sound Basin in Washington 

State. Land use and habitat vary greatly in the Puget 

Sound Basin study unit, ranging from remote, forested 

mountain areas to intensively farmed agricultural 

regions or densely populated urban centers. However, 

about 70 percent of Washington State’s population 

lives in the region, making the study unit a 

representative of urban conditions for the NAWQA 

program. Surface-water investigations in the Puget 

Sound Basin study unit began in 1995 with analyses of 

historical data largely collected by State and county 

agencies. This retrospective work included analysis of 

surface-water-quality data collected during 1980-93 

(Embrey and Inkpen, 1998), biological data collected 

through 1995 (Black and Silkey, 1998), and pesticide 

data collected during 1987-95 (Bortleson and Davis, 

1997).

Purpose of Report and Scope of Study

This report presents the results of field 

measurements and laboratory analyses of watercolumn samples collected from the surface-water 

fixed-site sampling network of the Puget Sound Basin 

study unit of NAWQA. Data for the study unit are 

summarized, related to water-quality criteria, 

standards, or guidelines, and discussed in detail for 

each site in the sampling network. Temporal variations 

in hydrology and water quality, relations of stream 

conditions to land use, and transport of selected 

constituents are also discussed.

The scope of work included monthly watersample collections at 11 sites, with additional sampling 

during storm-runoff and high-flow events. Sample 

collection at all 11 sites began in March 1996 and 

continued through April 1998. Some storm-runoff 

samples were collected at selected sites during 

November 1995-February 1996 prior to the HIP. Data 

collection included continuous monitoring of 

streamflow, specific conductance, water temperature, 

and dissolved-oxygen concentration, and water 

samples for measurements of physical properties, 

chemical-constituent concentrations (nutrients, major 

ions, and organic compounds), and suspendedsediment concentrations. The water-quality data for the 

study can be obtained from the NAWQA web site at 

URL http://water.usgs.gov/nawqa/.
4 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Acknowledgments

The authors would like to thank all the Puget 

Sound Basin NAWQA team members and Washington 

District Office personnel for their numerous 

contributions and assistance during the samplecollection, data-management, and report preparation 

phases of the past several years. We would like to 

express great appreciation for Lead Hydrologic 

Technician Kathleen Greene for her work in overseeing 

much of the effort and preparations required for field 

work, including ordering and maintaining supplies and 

equipment, data collection, basic-data records 

management, and her willingness to participate in all 

the pre-dawn storm sampling. The authors also thank 

Joseph Gilbert, a critical member of the field-collection 

teams, for his enthusiasm and diligence in quickly 

learning the techniques required for streamflow data 

collection and water-quality sampling and processing, 

and to Brett Smith of the Spokane office for his role in 

establishing monitoring stations at the beginning of the 

high-intensity phase of data collection, mentoring other 

team members in various aspects of data analysis and 

management, and participating in much of the field 

work during the study. Several others who were 

instrumental in the successful collection of monthly 

sample collections and the oftentimes difficult stormevent samples are noted here— James Ebbert, Gary 

Holloway, Emily Inkpen, Gregory Justin, Moon Kim, 

and Ward Staubitz. In addition to her database 

management tasks for the District Office, Stephanie 

Leisle provided assistance in sampling during storms 

and synoptic studies. We wish also to express our 

gratitude to Frank Voss and Alan Haggland for their 

work in managing the project’s databases and their 

work with geographic information systems in land-use 

analyses, and for Alan’s summaries of quality-control 

data; to David Kresch for analysis of surface-water data 

in the Green-Duwamish River Basin and the 

construction of data sets of daily flows for the 

Duwamish River and Springbrook Creek; and to 

Ginger Renslow, Deanna Walth, and Judith Wayenberg 

for preparation of the manuscript and illustrations for 

publication and for editorial assistance.

Description of the Puget Sound Basin Study Unit

The Puget Sound Basin (PSB) study unit 

encompasses the 13,700-mi2 (square mile) area that 

drains to Puget Sound and adjacent marine waters. The 

area includes all or part of 13 counties in western 

Washington, as well as the Skagit River headwaters and 

part of the Nooksack River Basin in the province of 

British Columbia, Canada (fig. 1). Staubitz and others 

(1997) described in detail the environmental setting 

and the implications of natural and human factors on 

surface- and ground-water resources in the study unit.

The Cascade Range bounds the study unit on the 

east and the Olympic Mountains of the Coastal Range 

bound the study unit on the west. Parts of these two 

mountain ranges and the Puget Sound Lowlands in 

between are included within the study boundaries of 

the PSB. The crest of the Cascade Range averages 

about 7,500 feet in altitude and includes the three 

volcanoes Mount Baker, Glacier Peak, and Mount 

Rainier, with altitudes ranging from 10,541 feet to 

14,410 feet. The crest of the Olympic Mountains 

averages about 3,000 feet. Land-surface altitude of the 

Puget Sound Lowlands is generally less than 600 feet.

The PSB has a Pacific Coast marine climate 

characterized by cool, wet winters and warm, dry 

summers. Average annual air temperatures in the 

Lowlands range from 50 to 60οF (degrees Fahrenheit). 

In winter in the Lowlands, daily temperatures rarely 

fall below freezing; and in summer, daily highs range 

between 70 and 85οF. About 80 percent of the annual 

precipitation falls during the wet season, which begins 

in October and extends through April. In the Lowlands, 

annual precipitation falls mostly as rain, averaging 

about 40 inches per year and ranging from 16 to 

47 inches per year. In the mountains, precipitation 

averages about 90 inches per year and ranges from 60 

to more than 200 inches per year depending on altitude 

and orientation to prevailing storm patterns (Staubitz 

and others, 1997).
Introduction 5

47 ̊

48 ̊

123 ̊ 122 ̊ 121 ̊

49 ̊

1

2

3

4

5

6 7

8

9

10

11

9

EXPLANATION

Study basins

International boundary

County boundary

Study unit boundary

Fixed site and site number

 as listed in table 1

WASHINGTON

WHATCOM

COUNTY

SKAGIT

COUNTY

SNOHOMISH

COUNTY

CLALLAM

COUNTY

JEFFERSON

COUNTY

KITSAP

COUNTY

KING

COUNTY

MASON

COUNTY

THURSTON

COUNTY

LEWIS

COUNTY

PIERCE

COUNTY

SAN JUAN

COUNTY

ISLAND

COUNTY

Bellingham

Everett

Seattle

Olympia

Tacoma

Duckabush River Dose walli ps River

Elwha

River

D ungeness R vi er

Green River at

Renton Junction

Snoqu almie River

Skykomish River

Samish River

Skagit River

Riv

Sti

er

llaguamish River

Suiattle R iver

Deschutes River

Nisqually River

Pu yallup River

White River

Snohomish River

Sauk

Cedar River

BRITISH COLUMBIA

C A N A D A

U N I T E D S T A T E S

Base from U.S. Geological Survey digital data, 1:2,000,000, 1972

Albers Conic Equal-Area Projection

Standard parallels 47 ̊ and 49 ̊, central meridian 122 ̊ Idaho

Oregon

Lake 

Whatcom

Howard A. Hanson

Reservoir

Baker

Lake

Ross

Lake

Lake

Cushman

Lake

Washington

Lake

Sammamish

Lake 

Tapps

Nooksack River

Basin

Skokomish River

Basin

Thornton 

Creek

Basin

Green-Duwamish 

River Basin

Strait of 

Juan de Fuca

Strait of Georgia

Puget So u nd

Hood

Canal

Cushman Powerhouse 

No. 2

Mount Rainier

Glacier Peak

Mount Baker

Cascade

Range

Olympic Mountains

1 10 20 30 40 50 MILES

1 10 20 30 40 50 KILOMETERS

Puget Sound

Basin

CANADA

UNITED

STATES

Figure 1. Location of the Puget Sound Basin study unit, the river basins selected for study, and the fixed sampling sites in Washington.
6 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Fourteen major rivers and numerous minor 

streams drain to Puget Sound and adjacent marine 

waters. The major rivers, with headwaters in the 

mountains, account for more than 91 percent of the 

52,500 ft3/s (cubic feet per second) of mean annual 

surface-water inflow to the study unit’s marine waters 

(Williams, 1981; Staubitz and others, 1997). High 

flows in streams are typical during late October 

through February because of winter rainfall. In the 

major river basins with high-altitude headwaters, flows 

continue to be high through June because of snowmelt. 

Low flows typically occur in all PSB streams during 

August and into September. Flows in some streams are 

also influenced by glaciers or large snow fields in the 

headwaters and by flow regulation at dams and 

reservoirs. In several small basins in the Puget Sound 

Lowlands, Vaccaro and others (1998) indicate that 

more than 70 percent of ground-water recharge 

eventually discharges to streams as baseflow and can 

make up more than 50 percent of the streamflow. In 

large river basins such as the Nooksack River Basin, 

about 80 percent of ground-water recharge eventually 

discharges to the rivers.

About 3.7 million people, or 70 percent of the 

population of Washington State, live in the PSB. Most 

of these people (98 percent) live within 20 miles of the 

Puget Sound shoreline in an urban corridor that 

includes the cities of Seattle, Tacoma, Bellevue, and 

Everett (Staubitz and others, 1997). Between 1970 and 

1990, the population grew by about 37 percent, or 

nearly 1 million people. By 2010, the region is 

expected to gain another 1.1 million people (Staubitz 

and others, 1997).

The three principal types of land use/land cover 

in the PSB study unit are forest, urban, and agriculture. 

Forest land covers about 74 percent, agriculture nearly 

6 percent, and urban development about 9 percent. The 

balance is covered by rangeland, water, tundra, 

glaciers, wetlands, and barren land. In each of the 

major river basins, forests make up more than one-half 

the land cover. Typically, forests cover the basins 

mostly in the uplands and mountains, whereas urban 

and agricultural land uses are concentrated in the 

Lowlands. Most major drainages have some 

agricultural land-use areas, which tend to be restricted 

to the alluvial river valleys.

Fixed-Site Sampling Network Design

NAWQA program study designs vary, depending 

on the basin. Some designs established a fixed-site 

monitoring network within one large river basin 

consisting of the mainstem and its tributary systems. 

The multiple river basins that make up the PSB study 

unit, however, called for a different design to establish 

a network meeting study-unit and national goals. Landuse/land-cover and other ancillary data allowed a 

conceptual stratification of the PSB study unit so that 

rivers draining to Puget Sound are represented by three 

general basin types: (1) rivers draining the Olympic 

Mountains with predominantly forested watersheds, 

(2) rivers draining the Cascade Range-Puget Sound 

Lowlands with forested upper watersheds and 

agricultural or urbanized lower watersheds, and 

(3) small streams draining the Puget Sound Lowlands 

with watersheds that are mostly urban, agricultural, 

forested, or a combination (W.W. Staubitz, U.S. 

Geological Survey, written commun., December 5, 

1995).

Three major basins and their tributaries were 

then selected to represent the three study-unit strata 

types and, therefore, the general range of conditions 

observed within the PSB. The Skokomish River Basin 

represents type 1; the Nooksack and Green-Duwamish 

River Basins represent type 2; and the Lowlands 

tributaries to these rivers represent type 3. The 

Thornton Creek Basin also represents a type 3 basin. 

The three major basins generally represent large-scale 

study unit conditions with mixes of features and 

contain tributaries representing small-scale conditions 

with relatively homogeneous features such as land 

use/land cover. Together, the large-scale basins and 

their tributaries can provide an integrated watershed 

assessment.
Introduction 7

The fixed-site network for the PSB study unit 

consisted of 11 sites where surface-water samples were 

routinely collected. Two sites were established in the 

Skokomish River Basin, three in the Nooksack River 

Basin, five in the Green-Duwamish River Basin, and 

one site in the Thornton Creek Basin (fig. 1). NAWQA 

fixed sites fall into two general types of sites—

integrator or indicator. Integrator sites in the PSB 

represent mixed water-quality conditions in large 

basins consisting of a variety of land-use and human 

and natural influences. Although water quality at the 

integrator sites is influenced by a large part of the 

drainage basin, the site location was generally in a 

setting predominantly influenced locally by forestry 

practices, agriculture, or urbanization. In contrast, 

water quality at indicator sites reflects conditions in 

basins with relatively homogeneous land use. For the 

PSB, 3 of the 11 sites, Skokomish River near Potlatch, 

Nooksack River at Brennan, and Duwamish River at 

Tukwila, are integrator sites located near the mouths of 

their respective basins. The remaining eight sites are 

indicator sites, seven of which are on tributaries within 

the three representative river basins. One site, Thornton 

Creek near Seattle, is on a small tributary stream 

draining into Lake Washington (fig. 1, table 1).

In the Skokomish River Basin, site 1 on the 

Skokomish River near Potlatch is an integrator site with 

influences from forestry practices occurring within the 

South Fork Skokomish River Basin. Site 2 on the North 

Fork Skokomish River (NF Skokomish) is a reference 

indicator site chosen to indicate background conditions 

in the study unit. The basin upstream of this site is 

located within the Olympic National Park and is 

relatively undisturbed.

In the Skokomish River Basin, site 1 on the 

Skokomish River near Potlatch is an integrator site with 

influences from forestry practices occurring within the 

South Fork Skokomish River Basin. Site 2 on the North 

Fork Skokomish River (NF Skokomish) is a reference 

indicator site chosen to indicate background conditions 

in the study unit. The basin upstream of this site is 

located within the Olympic National Park and is 

relatively undisturbed.

In the Nooksack River Basin, site 3 on the 

Nooksack River at Brennan (lower Nooksack) is an 

integrator site influenced by intensive agriculture 

upstream from the sampling site. Site 4, located on 

Fishtrap Creek, represents an intensively farmed (row 

crops, dairy, and poultry) tributary basin with some 

urban influences from part of the basin in Canada and 

the nearby city of Lynden. A second site located on the 

mainstem Nooksack River at North Cedarville (upper 

Nooksack, site 5) is an indicator of forestry practices in 

the upper watershed. This site also functions as an 

integrator site by integrating the water quality of the 

three major forks of the Nooksack River (North, 

Middle, and South Forks) whose drainages consist of 

undisturbed headwaters, logging, some agricultural 

activities, and glacial meltwater conditions.

In the Green-Duwamish River Basin, site 6 on 

the Duwamish River at Tukwila is an integrator site 

with urban influences near the site. Four sites, one on 

each of four tributaries, represents conditions, typical 

of the urban-suburban settings in the PSB. Site 7 on 

Springbrook Creek is an indicator of commercial, light 

industrial, and residential land use; site 8 on Big Soos 

Creek is an indicator of a rapidly developing suburban 

basin; site 9 on Newaukum Creek is an indicator of 

hobby-farm agriculture that includes gardens, horses, 

and llamas, and cattle and dairy agriculture. Site 10 on 

the Green River above Twin Camp Creek (upper 

Green) is an indicator of forestry practices as well as 

conditions in the uppermost parts of basins with 

headwaters in the mountains. Site 11 on Thornton 

Creek is an indicator of long-established, high-density 

residential and commercial development in the north 

Seattle metropolitan area.

The fixed sites are further classified as basic and 

intensive according to the type and degree of 

monitoring. Basic fixed sites characterize the spatial 

and temporal distribution of general water-quality 

conditions and constituent transport in relation to 

hydrologic conditions and contaminant sources 

(Gilliom and others, 1995). Streamflow, specific 

electrical conductance (conductivity), and in some 

cases dissolved-oxygen concentrations, were 

continuously monitored. Water samples were collected 

on a monthly fixed-interval schedule and over a range 

of storm or high-flow events for at least 2 years. Waterquality properties (water temperature, pH, 

conductivity), concentrations of alkalinity and 

bicarbonate, and concentrations of major constituents 

(major ions, nutrients), organic carbon, and suspended 

sediment were analyzed for in these water samples.
8 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Table 1. Description of surface-water-quality fixed sampling sites in the Puget Sound Basin study unit, Washington

[Basic monitoring level included monthly and storm sampling for field parameters, basic inorganic chemistry, and suspended sediment. Intensive monitoring 

level consisted of the basic monitoring sampling frequency and water-quality analyses plus pesticide and volatile organic compound analyses]

River

basin

Site 

No.

Station 

No. Station name

Percentage of land use/land cover 

in basin Monitoring 

level

Site type–land use/land 

cover ordered from 

nearest to most distant 

from the site

Drainage 

area

(square 

miles) Urban Agriculture Forest Other

Skokomish 1 12061500 Skokomish River near 

Potlatch

0.3 1.5 97.5 0.7 Basic Integrator–forestry 

practices, some 

agriculture

1227

Skokomish 2 12056500 North Fork Skokomish River 

below Staircase Rapids 

near Hoodsport

0 0 89.3 10.7 Basic Indicator–Reference 57.2

Nooksack 3 12213140 Nooksack River at Brennan 3 16.4 72.6 8 Intensive Integrator–agriculture, 

forestry practices, 

some urban

790

Nooksack 4 12212100 Fishtrap Creek at Flynn Road 

at Lynden

15.1 72.1 12.8 0 Intensive Indicator–agriculture 

(row crop, dairy), 

some urban

38.1

Nooksack 5 12210700 Nooksack River at North 

Cedarville

.8 1.2 88.2 9.8 Basic Indicator–forestry 

practices, some 

agriculture

589

Green/ 

Duwamish

6 12113390 Duwamish River at Golf 

Course at Tukwila

20.9 6.5 71.1 1.5 Intensive Integrator–urban, mixed 

agriculture, forestry 

practices

461

Green/ 

Duwamish

7 12113375 Springbrook Creek at Tukwila 72.7 19.8 0.5 7 Basic Indicator–urban 

(commercial, light 

industry, residential)

20

Green/ 

Duwamish

8 12112600 Big Soos Creek above 

Hatchery near Auburn

49.9 2.2 45.2 2.6 Basic Indicator–suburban, 

urban

66.7

Green/ 

Duwamish

9 12108500 Newaukum Creek near Black 

Diamond

22.7 36.1 40.6 .6 Basic Indicator–agriculture 

(hobby farms, dairy)

27.4

Green/ 

Duwamish

10 12103380 Green River above Twin 

Camp Creek near Lester

0 0 100 0 Basic Indicator–forestry 

practices

16.5

Thornton 11 12128000 Thornton Creek near Seattle 100 0 0 0 Intensive Indicator–urban (highdensity residential, 

commercial)

12.1

1Includes 99 square miles of the North Fork Skokomish Basin that are noncontributing most of the year.

Intensive fixed sites are a subset of the basic 

fixed sites. In addition to analyses listed above for basic 

fixed sites, data were collected from intensive fixed 

sites to characterize seasonal and short-term temporal 

variability in general water quality as well as the 

occurrence and seasonal patterns in concentrations and 

transport of pesticides and volatile organic compounds 

(VOCs). Pesticides and VOCs were analyzed for in 

water samples from these sites for at least 1 year. 

Continuous monitoring, fixed-interval monthly 

sampling, and storm-event sampling were the same as 

those listed above for basic fixed sites, and some 

additional high-frequency sampling was scheduled 

during selected seasons.
Methods of Sample Collection and Analysis 9

METHODS OF SAMPLE COLLECTION AND 

ANALYSIS

This section presents an overview of standard 

USGS and NAWQA procedures governing sample 

collection, handling, and analysis in the field and in the 

laboratory. Detailed protocols and analytical methods 

can be found in the publications cited in the following 

paragraphs, some of which can be accessed on-line at 

the URLs http://water.usgs.gov/, 

http://wwwnwql.cr.usgs.gov/Public/ref_list.html, and 

http:// wwwnwql.cr.usgs.gov/Public/nwql_memo.html.

Water-Sample Collection, Field Procedures, and 

Sample Preparation

The use of standard USGS sampling equipment, 

cleaning of equipment in preparation for the field, and 

the collection, processing, and handling of water 

samples generally followed the protocols and 

guidelines described in Ward and Harr (1990), Shelton 

(1994; 1997), Sandstrom (1995), and Horowitz and 

others (1994). All samples were processed, preserved, 

and prepared for shipment, and all field determinations 

were completed while at the study site except for the 

processing of filtered sample water for pesticides by 

solid-phase extractions (SPE). The sample water for 

pesticide analyses was extracted at the District’s Field 

Services Unit (FSU) laboratory within 1 or 2 days after 

sample collection, as allowed by the protocols. The 

cone splitter and all bottles used to collect stream 

water, to receive water poured through the cone splitter, 

and to be filled for laboratory analyses were rinsed 

thoroughly with native water prior to collection and 

processing.

For the major constituents and water-quality 

properties, samples were collected from multiple 

verticals spaced in equal-width increments using depthintegrating DH-81 or epoxy-coated D-77 samplers 

(Ward and Harr, 1990). Depth- and width-integrating 

techniques result in a discharge-weighted, composite 

water sample representative of the stream’s chemistry. 

Flood-stage flows sometimes required deviations from 

these protocols, either by using a D-77 equipped with a 

bag sampler or by reducing the number of sampling 

verticals, or both. If pesticides were to be analyzed, 

Teflon collection bottles and nozzle assemblies were 

used; otherwise, polypropylene bottles and nozzles 

were used.

For VOCs and organic carbon, water samples 

were collected at a single vertical in the center flow of 

the stream. Water for VOCs analysis was collected 

directly into 40-mL (milliliter) vials contained in a 

weighted, stainless-steel sampler (Shelton, 1997). 

While completely submerged, the sampler allows the 

vials to be filled by gentle air displacement without 

aeration. After several minutes, the sampler was 

removed from the stream, the vials carefully removed, 

and the sample preserved by acidification with 1:1 

hydrochloric acid/water solution to a pH between 1.7 

and 2.0 standard units. The organic carbon sampler is 

also a weighted sampler, which holds an open bottle 

that fills when lowered beneath the water surface. The 

vials for VOCs and organic carbon samples were then 

shipped with the nutrient samples on ice to the National 

Water Quality Laboratory (NWQL) in Arvada, Colo.

A Teflon cone splitter was used to achieve a final 

composite water sample for field measurements and for 

laboratory analyses of nutrients, major ions, pesticides, 

and suspended sediment (Capel and Larson, 1996). All 

the water collected with the D-77 or DH-81 sampler at 

the verticals was poured through the cone splitter into 

receiving bottles made of Teflon if pesticide analyses 

were involved or made of polypropylene if only 

inorganic analyses were to be done. Sub-samples for 

specific laboratory analyses requiring whole water 

(total phosphorus and total ammonia-plus-organic 

nitrogen concentrations) were obtained by pouring one 

or more of the receiving bottles containing composited 

water back through the cone and capturing the volumes 

from this second split into a specific bottle required by 

the NWQL. The composited water in the remainder of 

the receiving bottles was then used for measurements 

of pH and conductivity on whole water and for 

laboratory analyses requiring filtered water.

After splitting, sample water for analyses of 

selected dissolved nutrients and dissolved major ions 

was filtered through a polypropylene-encapsulated 

filter having a 0.45-μm (micrometer) pore size. For 

dissolved pesticides, water was filtered through a 

142-mm (millimeter)-diameter, 0.7-μm baked, glassfiber filter on an aluminum filter holder (Sandstrom, 

1995). For dissolved and suspended organic carbon, 

water was collected directly into a baked glass bottle 

and filtered under nitrogen pressure through a 47-mmdiameter, 0.45-μm pore size silver filter held in a 

stainless steel filtration device. 
10 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

The filtrate was used for analysis of dissolved organic 

carbon (DOC), and the material retained on the filter 

was used for suspended organic carbon (SOC). Filtered 

water samples for cation analyses were preserved with 

nitric acid. The water for nutrient and organic carbon 

determinations was shipped on ice the same day of 

collection or the following morning for overnight 

delivery to the NWQL. All bottles for major-ion 

analyses, which do not require chilling, were either 

shipped with the chilled samples for convenience or 

held for a later mailing (typically no more than 1 week 

after sampling). The filtered water for pesticides was 

transported to the District’s FSU laboratory on ice and 

refrigerated until extraction onto solid-phase media. 

The SPE cartridges were chilled and shipped the same 

day or within 1-2 days after extraction to the NWQL. 

Bottles for determining suspended-sediment 

concentrations were held at room temperature and out 

of direct light. At the end of each month the samples 

were shipped to the USGS sediment laboratory in 

Vancouver, Wash., for analysis using methods 

described by Guy (1969).

Field Measurements

Water temperature, dissolved-oxygen (DO) 

concentration, conductivity, pH, alkalinity, and 

bicarbonate concentration were measured on-site 

following procedures described by Shelton (1994). At 

the center flow vertical, water temperature and DO 

concentration were determined directly in the stream—

temperature with an electronic thermistor and DO with 

a meter and probe. Conductivity and pH were 

measured on unfiltered water composited through the 

cone splitter. Alkalinity, bicarbonate, and carbonate 

concentrations were measured on filtered, composited 

water using incremental titration with a digital titrator 

and sulfuric acid.

Laboratory Analyses

Unless otherwise stated in this report, major-ion 

and nutrient constituents, and pesticide and pesticidetransformation compounds analyzed on filtered water, 

are defined to be dissolved and are referred to simply 

by name. The definition includes iron, manganese, 

phosphorus, orthophosphate phosphorus (hereafter, 

orthophosphate), nitrite nitrogen (hereafter, nitrite), 

nitrite-plus-nitrate nitrogen (hereafter, nitrate), and 

ammonia-plus-organic nitrogen (hereafter, organic 

nitrogen). The nutrients measured in whole water are 

referred to as total phosphorus and total ammonia-plusorganic nitrogen (hereafter, total organic nitrogen). 

VOCs, all analyzed on whole water, are reported as 

total recoverable concentrations and are referred to by 

their name only. Total nitrogen concentration in this 

report is the sum concentration of the different nitrogen 

species detected in a sample—nitrite, nitrate, ammonia, 

and total organic nitrogen.

At the NWQL, samples were analyzed for 

concentrations of nutrients by colorimetry (schedule 

2702). Dissolved and total phosphorus and ammoniaplus-organic nitrogen were analyzed by a microkjeldahl digestion followed by colorimetry as described 

by Patton and Truitt (1992), and dissolved 

orthophosphate, and dissolved ammonia, nitrite, and 

nitrite-plus-nitrate nitrogen by procedures described in 

Fishman (1993). Major ions, iron, and manganese were 

analyzed by ion chromatography and inductively 

coupled plasma (schedule 2701) described by Fishman 

and Friedman (1989) and Fishman (1993). Suspended 

and dissolved organic carbon were analyzed by UVpromoted persulfate oxidation and infrared 

spectrometry (schedule 2075) using the methods of 

Wershaw and others (1987) and Brenton and Arnett 

(1993). Pesticides were determined by two methods: 

high-performance liquid chromatography (HPLC) by 

NWQL schedule 2051 (Werner and others, 1996) and 

gas chromatography-mass spectroscopy (GC/MS) by 

schedule 2010 (Zaugg and others, 1995; Lindley and 

others, 1996). The parameters included in each 

schedule and their associated laboratory minimum 

reporting levels or method detection limits (MRLs or 

MDLs) are given at the end of the report in Appendix 

A, tables A1 to A5.

Most of the samples for VOCs were analyzed 

using purge and trap capillary-column GC/MS by 

NWQL schedule 2020 (Rose and Schroeder, 1995; 

Connor and others, 1998). Prior to April 1996, the 

laboratory method (schedule 2090) analyzed for 59 

compounds with a reporting limit of 0.2 μg/L 

(micrograms per liter) (Rose and Schroeder, 1995). 

Only the first sample at each of the intensive fixed sites 

collected in March 1996 was analyzed using this 

method and no detections were reported. A new 

method was introduced in April 1996 that increased the 

number of analytes to 86 and lowered the reporting 

limits (Connor and others, 1998). 
Methods of Sample Collection and Analysis 11

From April 1996 to April 1997, the new VOC 

analytical method used MRLs that were usually set to 

censor (qualify) data at 0.05 or 0.1 μg/L, but some were 

5 μg/L or higher (Connor and others, 1998). In May 

1997, the laboratory began censoring data at the 

laboratory reporting limit (LRL) (Connor and others, 

1998; Childress and others, 1999). In samples where a 

compound was determined to be present, but at a 

concentration below the LRL or MRL, the 

concentration was quantified and qualified with a 

remark code of E (estimated). An analyte should be 

detected 99 percent of the time if its true concentration 

is equal to or greater than the LRL (Childress and 

others, 1999). Although the discussion in this report 

focuses on compounds that were detected at 

concentrations above the LRL, consideration is also 

given to compounds and concentration values as they 

were reported by the NWQL. A complete list of the 

LRLs for schedule 2020 can be found at the end of the 

report in Appendix A, table A6.

Collection and Analysis of Quality-Control 

Samples

Quality-control samples designed to measure 

bias and variability in the field included several types 

of blank samples, replicate samples, matrix-spiked 

replicate samples, and surrogate-compound spiked 

samples (Mueller and others, 1997). Field blanks 

monitor for possible contamination or bias within the 

sample-collection process and consist of subjecting 

analyte-free water to all aspects of normal sample 

collection, processing, and handling. Source-water 

blanks monitor for potential background 

concentrations of organic carbon or VOCs in the 

analyte-free water used to prepare field blanks and 

consist of pouring the analyte-free water directly into a 

collection bottle submitted to the laboratory for 

analysis. The canister blank monitors for potential 

contamination carry-over from the canister, which 

holds the analyte-free water for preparing the VOC 

field blank, to the VOC sampler. VOC trip blanks are 

used to determine if external VOCs from bottle 

handling and analytical processes, independent of the 

field sample processing scheme, are contaminating the 

samples. Replicate samples measure sampling and 

analytical variability. Split-replicate samples are 

subsamples of a single, larger sample and are used to 

characterize the reproducibility of sample processing 

and the analytical process, and to produce multiple 

samples for spiking purposes. Concurrent-replicate 

samples are multiple samples collected nearly 

simultaneously in time and at the same location. 

Matrix-spiked replicate samples are used to measure 

interference or bias in the analytical results due to 

matrix effects. Field matrix-spiked replicate samples 

provide information about bias, analyte loss during 

shipping, and method performance for the analyses of 

pesticides and VOCs. Surrogate compounds are similar 

in physical and chemical properties to a target analyte, 

but are not normally found in environmental samples. 

Surrogate compounds added to pesticide samples (in 

the field) and to VOC samples (in the laboratory) are 

used to monitor analytical precision and accuracy. The 

results of the quality-control samples collected in the 

field as part of the study are summarized here and 

discussed at the end of the report in Appendix B and 

presented in tables B1 to B11 and in figure B1.

Quality-control samples in the laboratory are 

routinely analyzed as part of the quality-assurance plan 

described by Pritt and Raese (1995). These samples 

include standard reference materials, laboratory 

replicates, laboratory reagent blanks, spikes, and 

surrogates.

Field blanks for inorganic constituents were 

prepared with inorganic grade (IG) water obtained 

from the USGS Ocala (Florida) Field Services Unit 

where this water is quality assured for suitability in the 

testing of equipment and sampling in the field. Field 

blanks for pesticides and VOCs were prepared with 

pesticide grade (PG) water and volatile grade (VG) 

water, respectively, obtained from the NWQL where 

testing of lots showed the waters suitable for use in the 

field. Midway through the study, the NWQL changed 

the preparation method of the VG water. Prior to 

August 1997, the NWQL analyzed each lot of VG 

water by randomly selecting a few containers of the lot 

to check for the presence of VOCs prior to shipment to 

study units. Those lots with detections above the LRL 

were rejected. In August 1997, an additional procedure 

was introduced to remove any low-level VOCs present 

by purging each bottle of VG water with nitrogen gas 

(N2). VOCs found to be present in the VG water by the 

NWQL are listed in Appendix B at the end of the 

report. As discussed in Appendix B, blanks collected 

with the non-N2 purged water had considerably more 

VOC detections than those collected with the N2

purged water.
12 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

All field blanks were prepared at streamside by 

pouring blank water through the bottle-nozzle 

collection assembly and into the bottles used for 

subsequent sample collection. The blank water in the 

collection bottles was then poured through the cone 

splitter and subjected to all the same sample handling, 

processing, and preservation treatments as 

environmental samples. Field blanks for organic carbon 

were prepared by pouring PG or VG water into a baked 

1-liter collection bottle, measuring a 100-mL or 

200-mL aliquot in a glass graduated cylinder, and 

filtering this aliquot through a stainless-steel filtration 

device. The filtrate was analyzed for dissolved organic 

carbon, and material collected on the filter was 

analyzed for suspended organic carbon. Source-water 

blanks for organic carbon were prepared by pouring PG 

or VG water directly into a 125-mL baked glass bottle. 

Source-water blanks for VOCs were prepared by 

pouring the VG water directly into 40-mL vials, 

preserving with the same volume of acid used for 

environmental samples, then sealing and storing on ice 

for shipment. Canister blanks for VOCs were prepared 

by filling the canister with VG water and, grasping the 

vials with clean flask tongs, dipping the vials into the 

VG water. The field blank for VOCs was then prepared 

by submerging the sampler containing 40-mL vials into 

the canister, pouring in sufficient VG water to 

completely submerse the sampler, and allowing the 

sampler to fill the vials through the intake ports. The 

trip blanks were sealed vials of VG water prepared and 

shipped from the NWQL, taken to the field site 

alongside the vials to be used in collection, and then 

shipped back to the laboratory. A complete description 

of the quality-control program for surface-water 

samples can be found in Mueller and others (1997). 

A total of 32 field blanks for major ions 

(table B1), 34 field blanks for nutrients (table B2), 

30 field blanks for organic carbon (table B3), 9 field 

blanks for pesticides, and 16 field blanks for VOCs 

(table B4) were submitted to the NWQL during the 

period December 1995 to February 1998. In the field 

blanks, there were occasional detections of calcium, 

silica, nitrate, total phosphorus, orthophosphate, 

dissolved organic carbon, and a number of VOCs, but 

no detections of pesticides. No adjustments to the 

database were made on the basis of field blanks except 

for a period of time in September-October 1996 when 

values of methylbenzene (toluene) appeared to be 

affected by systematic contamination or positive bias. 

These methylbenzene values were coded with a V 

remark in the USGS database to prevent their inclusion 

in normal data retrievals for analysis and interpretation.

Variability in the chemical data was measured 

with 26 pairs of split replicate samples for major ions, 

29 pairs for nutrients, and 5 pairs for pesticides; and 

with 20 pairs of concurrent replicate samples for 

dissolved organic carbon and 1 pair of concurrent 

replicate samples for VOCs. The amount of variability 

between samples was expressed as the relative percent 

difference in the concentrations. Relative percent 

differences for the major ion samples ranged from 0 to 

58 percent, but median percent differences for each 

constituent were less than or equal to 6.0 percent 

(table B5). Relative differences between replicates of 

nutrient concentrations tended to be larger than for the 

major ions, ranging from 0 to 67 percent with median 

percent differences from 1 to 19 percent (table B6). 

Relative percent differences between replicates of 

organic carbon ranged from 0 to 40 percent with a 

median of 2.5 percent for dissolved, and from 0 to 

100 percent with a median of 0 percent for suspended 

(table B7). For the pesticides, differences between 

replicates ranged from 0 to 40 percent, with median 

differences from 0 to 31 percent (table B8). The pair 

of VOC samples had identical concentrations of 

trichloromethane (chloroform), chloromethane 

(methyl chloride), 1-isopropyl-4-methylbenzene 

(p-isopropyltoluene), and 4-methyl-2-pentanone 

(methyl isobutyl ketone). The pair of methylbenzene 

concentrations differed by 0.01 μg/L. No changes were 

made to any of the inorganic or organic chemical data 

sets on the basis of these replicate data.

In addition, no changes were made to any of the 

data sets on the basis of pesticide and VOC analyte 

recoveries in field-matrix- or surrogate-spiked samples, 

which is consistent with USGS standard practices (Paul 

Capel, Robert Gilliom, and Steven Larson, U.S. 

Geological Survey, written commun., 1996). Percent 

recoveries of the field-matrix-spike compounds were 

within a fairly narrow range (60-140 percent) for the 

schedule 2010 pesticides and the VOCs (Appendix B). 

Average recoveries for laboratory reagent spiked 

samples ranged from about 40 to 120 percent for the 

schedule 2010 pesticides and from 77 to 114 percent 

for the schedule 2020 VOCs. For schedule 2051 

pesticides, however, low recoveries of 7 to 72 percent 

indicated that the reported concentrations of these 

analytes could be low and that a potential for false 

negatives existed.
Methods of Sample Collection and Analysis 13

Additional information and quality-control data 

are available from the Washington District USGS 

office in Tacoma, Washington. Information is also 

available on the World Wide Web at 

http://wwwnwql.cr.usgs.gov/USGS/USGS_tech.html, 

http://water.usgs.gov/owq/quality.html/, and 

http://ca.water.usgs.gov/pnsp/rep/qcsummary.

Streamflow Measurements

Instantaneous streamflow measurements for the 

time of sample collection were made according to 

standard USGS procedures (Rantz and others, 1982) or 

were determined from stage-discharge relations. Stagedischarge relations were mostly used for the 

Skokomish (site 1), NF Skokomish (site 2), and upper 

Green Rivers (site 10), and for Big Soos (site 8) and 

Newaukum Creeks (site 9). Combinations of measured 

streamflow or stage-discharge relations were used for 

Fishtrap (site 4) and Thornton Creeks (site 11). 

Occasionally, flows in Fishtrap Creek were affected by 

backwater when the Nooksack River was high. Daily 

streamflows for Fishtrap during these periods were 

estimated from gaged flows at an upstream site near the 

Canada-United States international boundary. 

Streamflows were measured for the upper Nooksack 

(site 5) or determined from stage-discharge relations 

from the nearby upstream gaging station, Nooksack 

River at Deming. Streamflows for the lower Nooksack 

(site 3) were obtained from stage-discharge relations at 

the upstream site, Nooksack River at Ferndale.

Gages were not established on the Duwamish 

(site 6) because of tidal influences nor on Springbrook 

(site 7) because of frequent backwater conditions. 

Instantaneous streamflows at these sites were measured 

on the day of sample collection and daily streamflows 

were estimated from nearby gages and drainage-area 

relations.

Loads and Yields

The transport (mass discharge) of a constituent past a 

monitoring site in a given amount of time is referred to 

as the load. Constituent loads for this report were 

estimated by the rating-curve method (Cohn and 

others, 1989; Crawford, 1991) using instantaneous 

sample concentration data and daily or unit streamflow 

data. Because some constituent concentrations 

included in this assessment were less than the detection 

limit, parameters of the rating curve were estimated by 

the maximum-likelihood method (Dempster and 

others, 1977; Wolynetz, 1979) or the linear attribution 

method (Chatterjee and McLeash, 1986). The Loadest2 

computer program used to compute loads was selected 

for several reasons: the output includes estimates of 

annual and seasonal average constituent loads; the 

period of interest is user defined and not restricted to 

the calendar or water year; and with Aikaike’s 

information criterion, the user can either specify a 

rating-curve equation or allow the program to choose 

among eight alternative forms of the rating curve for 

the best regression equation describing the data 

(Charles Crawford, U.S. Geological Survey, written 

commun., 1999). The program also provides an 

estimate of the daily load using the Beale ratio 

estimate, a simple estimate that does not include 

seasonal parameters (sine and cosine functions) or 

flow-based stratification (for example, loads calculated 

separately for low and high flows, then summed for a 

total load) (Crawford, 1996). For estimating 

uncertainty in the average loads obtained by the 

maximum-likelihood method, the program uses the 

method described by Likes (1980), which provides a 

minimum-variance unbiased estimate of the variance of 

a sum of lognormal variables, and by Gilroy and others 

(1990), which calculates the exact variance of average 

constituent loads obtained by the rating-curve method 

when the rating-curve parameters and residual-error 

variance are known with certainty. For estimating 

uncertainty with the linear-attribution method, the 

program uses the jackknife method (Efron, 1982), 

which is a robust method for examining sampling 

properties of a statistic with no requirement for 

distributional assumptions (Crawford, 1996). These 

methods and descriptions are detailed by Crawford 

(1996).
14 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

SURFACE-WATER-QUALITY OF THE 

SKOKOMISH, NOOKSACK, AND 

GREEN-DUWAMISH RIVERS AND 

THORNTON CREEK

This section presents the results of 

approximately 2 years of water-sample collection at the 

11 fixed sites located within the Skokomish, Nooksack, 

and Green-Duwamish River Basins and Thornton 

Creek, and summarizes the study unit’s hydrologic and 

water-quality conditions for the study period of water 

years 1996-98.

Sampling conditions during the first 18 months 

of the study were dominated by above-normal 

precipitation. During the last 8 months, conditions 

were drier: precipitation in November and December 

1997 was about 50 percent of normal and early spring 

precipitation (February and April 1998) was also well 

below normal. The overall wet conditions resulted in 

many runoff events and flooding in large rivers and in 

small, lowland streams. These events contributed to 

detections of several kinds of pesticides and VOCs and 

to the presence of high concentrations of pesticides, 

nutrients, suspended sediment, and organic carbon.

Hydrologic Conditions—Climate and Streamflows

Puget Sound Basin weather for water year 1996 

was wet, with temperatures about normal for the year. 

For the greater Seattle-Tacoma area, 50 inches of 

precipitation, about 12 inches above the average for the 

period of record, was recorded at the Seattle-Tacoma 

(SeaTac) International Airport weather station 

(Western Regional Climate Center, 1999) (fig. 2). 

Precipitation during the months of February, April, and 

December 1996 was about 200 percent of normal 

(fig. 3). During the last week of December and the first 

week of January, three major storms brought up to 

2 feet of snow in places, followed by rising 

temperatures and heavy rains during the third storm. 

These three events combined for a total of 6.4 inches of 

precipitation (more than is normal for the entire month 

of December) and caused flooding and mud slides 

throughout the Seattle-Tacoma area.

The northern part of the study unit, represented 

by the weather station at Bellingham, and the western 

part, represented by the station at Shelton, were also 

wet during 1996 (fig. 2). The Bellingham station 

recorded 44 inches of precipitation, which is about 

8 inches above the average for the period of record of 

36 inches; the Shelton station recorded 85 inches, 

20 inches above the average (Western Regional 

Climate Center, 1999).

Water year 1997 was the wettest of the 3 years 

spanning the period of sample collection; temperatures 

were again near normal, except during November when 

record highs were set. A total of 52 inches of 

precipitation, about 14 inches above average, fell over 

the Seattle-Tacoma area. A storm on March 18-20, 

1997, was an event in which the jet stream delivered a 

plume of moisture-laden clouds from the warm, 

southwest Pacific Ocean into the Pacific Northwest, 

resulting in high volumes of rain. These winter storms 

frequently are rain-on-snow events, so coupled with 

heavy rainfall and snowmelt, extreme high flows and 

flooding can occur in PSB rivers. Peak flows for 1997 

were recorded for many PSB rivers during this storm. 

From spring to fall 1997, monthly precipitation ranged 

from 230 percent to about 105 percent of normal 

(fig. 3). At the northern station in Bellingham, total 

precipitation was 48 inches, 13 inches above the 

average, and at Shelton, a total of 100 inches of 

precipitation fell, surpassing the average amount by 

35 inches (Western Regional Climate Center, 1999).

Weather during water year 1998 was relatively 

dry and warm, compared with weather during 1996 and 

1997 and with average conditions at the weather 

stations. Temperatures were above normal except 

during May and June. Record high temperatures were 

set on July 27 and 28, 1998. A total of 32 inches of 

precipitation, 5.8 inches below normal, was recorded at 

SeaTac International Airport. January and May were a 

little wetter than normal by 130 and 120 percent, 

respectively, but April was drier by 43 percent. Belownormal precipitation in June started the summer of 

1998, which became the third driest summer on record 

(Western Regional Climate Center, 1999). Only 

1.4 inches of rain fell during July, August, and 

September, compared to a normal of 3.8 inches. 

Precipitation recorded for the year at Bellingham and 

Shelton, 31 and 57 inches, respectively, was also below 

the averages for these weather stations (Western 

Regional Climate Center, 1999).
Surface-Water Quality of the Skokomish, Nooksack, and Green-Duwamish Rivers and Thornton Creek 15

EXPLANATION

Minimum value

25th percentile

Median

75th percentile

Maximum value

Precipitation, period of record

1996 water year

1997 water year

1998 water year

Precipitation during samplecollection period

Average

20

120

40

60

80

100

20

60

30

40

50

20

60

30

40

50

0

25

5

10

15

20

0

15

5

10

0

15

5

10

Bellingham

Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June July Aug. Sept.

MONTH

Shelton

Seattle-Tacoma Airport

Annual

totals

TOTAL PRECIPITATION, IN INCHES

Figure 2. Distribution of monthly and annual precipitation for the period of record at Shelton, Bellingham, and Seattle-Tacoma 

International Airport, and total precipitation during the 1996–98 sample-collection period by month and for each year, for the Puget Sound 

Basin study unit, Washington.
16 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Snowpack in the mountains was above average 

in water year 1996; average to above average in 1997, 

depending on location; and near or below average in 

1998, except in the Olympic Mountains where 

snowpack was above average (Wiggins and others, 

1997, 1998, 1999). At the Cedar Lake National 

Weather Service station (altitude 1,560 feet) in the 

foothills of the Cascade Range, average total snowfall 

for the July through June period of record (referred to 

here as a winter year) was 71 inches. For winter year 

1995-96, total snowfall was substantially below the 

average, amounting to only 46 inches, but total 

precipitation for the same period was 110 inches, about 

10 inches above normal. During winter year 1996-97, 

however, the snowfall total was 86 inches, of which 

nearly 34 inches fell during December 1996. Snowfall 

during winter year 1997-98 was again well below the 

average with only 21 inches.

Annual streamflows at all the fixed sites having 

long-term gaging records were above average for water 

years 1996 and 1997 (fig. 4), due in part to aboveaverage snowpacks or to above-average precipitation. 

During 1997, the wettest year of the study period, 

annual streamflows in the Nooksack, Duwamish, and 

upper Green Rivers and in Big Soos and Newaukum 

Creeks were near recorded maximum flows for their 

respective periods of record. With a return to drier 

weather in 1998, streamflows were near or below 

average except for the Skokomish and NF Skokomish 

Rivers, in which streamflows remained above normal.

ON D J FM AM J J A S O N D J FM AMJ J A S ON D J FM AM J J A S

1995 1996 1997 1998

300

0

100

200

300

0

100

200

MONTHLY PRECIPITATION, IN PERCENTAGE OF NORMAL

Bellingham

Seattle-Tacoma Airport

Figure 3. Departures of monthly precipitation from normal at Bellingham and Seattle-Tacoma Airport during the 

sample-collection period for the Puget Sound Basin study unit, Washington.
Surface-Water Quality of the Skokomish, Nooksack, and Green-Duwamish Rivers and Thornton Creek 17

Daily flows in the NF Skokomish, Nooksack, 

Duwamish, and upper Green Rivers followed seasonal 

patterns typical of PSB rivers with headwaters in the 

mountains. These patterns include two periods of high 

flows—one in fall and winter with the arrival of the 

rainy season and one during spring snowmelt; and a 

low-flow period in late summer (August-September). 

Daily flows in the small lowland streams followed a 

typical seasonal pattern of one high-flow period during 

fall and winter, followed by flows tapering off in 

magnitude during spring and a low-flow period in late 

summer. 

Daily flows in the Skokomish at site 1 followed a 

season pattern like that of the lowland streams, with 

only one high-flow period during the wet season. This 

is probably due mostly to flow regulation of the NF 

Skokomish, which captures much of the snowmelt in 

reservoirs. In the large rivers, above-average 

snowpacks during the study helped to contribute to 

occasional flooding during rain-on-snow events, such 

as in water years 1996 and 1997, but also helped to 

sustain summertime flows at normal or above-normal 

levels.

EXPLANATION

Annual streamflows for the period of record

1997 water year

1998 water year

Annual streamflows for the 

sample-collection period

Minimum value

25th percentile

Median

75th percentile

Maximum value

Average for the period of record

1996 water year

Skokomish (site 1)

NF Skokomish (site 2)

Lower Nooksack (site 3)

Upper Nooksack (site 5)

Fishtrap (site 4)

Duwamish (site 6)

Springbrook (site 7)

Big Soos (site 8)

Newaukum (site 9)

Upper Green (site 10)

Thornton (site 11)

7

7,000

10

20

30

40

50

70

100

200

300

400

500

700

1,000

2,000

3,000

4,000

5,000

STREAMFLOW, IN CUBIC FEET PER SECOND

Figure 4. Distribution of annual streamflows for the period of record at fixed sites, and annual streamflows for individual water years of 

the sample-collection period in the Puget Sound Basin study unit, Washington.
18 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Water Quality—Chemistry, Standards and 

Criteria, and Loads

Water in the large rivers (Skokomish, Nooksack, 

Green-Duwamish), and in two streams in the Lowlands 

(Big Soos and Newaukum) with large drainage areas 

relative to other lowland streams in the study, was 

characterized by dilute water chemistry with dissolvedsolids concentrations less than 130 mg/L; pH values 

ranging from 6.9 to 8.2 units; and high dissolvedoxygen concentrations with medians ranging from 10.2 

to 12.8 mg/L and minimums not less than 7.6 mg/L. 

Water in the three other streams in the Lowlands 

(Fishtrap, Springbrook, and Thornton) had dissolvedsolids concentrations as high as 320 mg/L; pH values 

ranging from 6.9 to 8.7 units; and dissolved oxygen 

with median concentrations ranging from 5.6 to 

10.4 mg/L and minimum concentrations as low as 

2.3 mg/L (in Springbrook). 

Nutrient concentrations were generally higher in 

the small streams of the Lowlands than in the large 

rivers and were also higher during periods of storm 

runoff. Total nitrogen concentrations (the sum of 

nitrite, nitrate, ammonia, and organic nitrogen 

concentrations) averaged from 1.1 to 3.6 mg/L in the 

small streams of the Lowlands, compared with average 

concentrations of less than 1.0 mg/L in the large rivers. 

Average total nitrogen concentrations in the reference 

and forested rivers were less than 0.1 mg/L. Nutrient 

loads ranged from 6 ton/yr (tons per year) of total 

nitrogen in the Green to 3,200 ton/yr of total nitrogen 

in the lower Nooksack, and from about 2 ton/yr of total 

phosphorus in the Green to 890 ton/yr of total 

phosphorus in the lower Nooksack. Per unit area of 

drainage basin, however, Fishtrap transported the most 

nitrogen on an annual basis, 8.8 ton/mi2 (tons per 

square mile). The largest total phosphorus yield, 

1.2 ton/mi2, was from the upper Nooksack. Inorganic 

nitrogen and total phosphorus loads calculated for this 

study were nearly all higher than loads estimated for 

the period 1980-93 by Embrey and Inkpen (1998) using 

historical data compiled from Washington State 

Department of Ecology’s and King County’s long-term 

monitoring programs. Suspended-sediment 

concentrations were highest in the large rivers, with 

averages ranging from 85 to 443 mg/L. Maximum 

concentrations of more than 3,200 mg/L were 

measured in samples from the upper Nooksack (site 5) 

followed by 1,500 mg/L in a sample from the 

Skokomish (site 1).

During this study, the relative quality of water 

among the 11 sites ranged from exceptionally high in 

the NF Skokomish to fair in Springbrook and Thornton 

Creeks. Descriptors of the relative quality of water used 

in this report were based on concentrations of 

chemicals, dissolved oxygen, and suspended sediment 

and values of specific conductance and water 

temperature.

Out of 86 pesticide compounds analyzed, 

36 compounds (26 herbicides, one herbicide 

transformation product, and nine insecticides) were 

detected in samples from the four sites intensively 

studied during 1996-98. Those pesticides most 

frequently detected were the herbicides prometon, 

simazine, and atrazine and the insecticide diazinon. 

Most of the detections were in samples from the small 

lowland streams Thornton and Fishtrap (fig. 5).
Surface-Water Quality of the Skokomish, Nooksack, and Green-Duwamish Rivers and Thornton Creek 19

Eleven VOCs were detected at concentrations 

above the 1999 LRLs in samples from the four 

intensively studied sites (fig. 6). Each detected 

compound belonged to one of three general classes—

fuel-related compounds, the trihalomethanes, or 

solvents. Compounds detected most often included 

methylbenzene and trichloromethane. As with 

pesticides, more types of VOCs were detected and 

detection frequencies were higher in the small streams 

(Thornton and Fishtrap) than in the large rivers (lower 

Nooksack and Duwamish).

At most sites, existing and applicable standards 

and criteria for surface-water quality and drinkingwater supplies and freshwater-chronic criteria for the 

protection of aquatic life (hereafter referred to as 

aquatic-life criteria) were nearly always met. One 

measurement at the time of sample collection at each of 

four sites did not meet Washington State standards 

(State of Washington, 1992) for dissolved-oxygen 

concentrations, and one sample at Thornton did not 

meet the State standard for pH (table 2). Numerous 

samples exceeded the U.S. Environmental Protection 

Agency (USEPA) 1996 Secondary Maximum 

Contaminant Levels (SMCL) for iron and manganese. 

On many occasions, samples from Springbrook did not 

meet standards and criteria for temperature and for 

dissolved-oxygen, iron, and manganese concentrations. 

Concentrations of nitrate, chloride, fluoride, sulfate, 

and VOCs in all samples from all 11 sites met aquaticlife criteria and USEPA drinking water Maximum 

Contaminant Levels (MCL) and SMCLs. 

Concentrations of four insecticides, however, did not 

meet aquatic-life criteria in a few samples from 

Fishtrap and the Duwamish, and in several samples 

from Thornton.

acetochlor alachlor

atrazine

deethylatrazine

2,4-D

DCPA

dicamba

dichlobenil diuron

EPTC

fluometuron

linuron

metolachlor metribuzin

MCPA

molinate

napropamide

norflurazon

oryzalin

pebulate

prometon

pronamide

simazine

tebuthiuron

terbacil

triclopyr

trifluralin

carbaryl

carbofuran

chlorpyrifos

diazinon

ethoprophos

lindane

malathion

oxamyl

propargite

0

70

10

20

30

40

50

60

DETECTIONS, IN PERCENTAGE OF

TOTAL SAMPLES ANALYZED

Detections for all four sites, 124 samples

Detections in small streams (sites 4 and 11)

Detections in large rivers (sites 3 and 6)

HERBICIDES AND TRANSFORMATION PRODUCTS INSECTICIDES

Figure 5. Percentage of detections of pesticides in water samples from the four intensive fixed sites—site 11, Thornton Creek, and site 4, Fishtrap 

Creek (small streams) and site 6, Duwamish River, and site 3, lower Nooksack River (large rivers)—in the Puget Sound Basin study unit, Washington.
20 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

0 20 40 60 80 100

DETECTIONS, IN PERCENTAGE OF TOTAL SAMPLES ANALYZED

Methylbenzene

Trichloromethane

Ethylbenzene

Dichloromethane

Chlorobenzene

Bromoform

Acetone

4-Methyl-2-pentanone

1,3- plus-1,4-Dimethylbenzene

1,2-Dimethylbenzene

1,2,4-Trimethylbenzene

VOLATILE ORGANIC COMPOUND

no detections

no detections

no detections

no detections

no detections

no detections

no detections

no detections

no detections

Detections in large rivers (sites 3 and 6)

Detections in small streams (sites 4 and 11)

Detections for all four sites, 124 samples

Figure 6. Percentage of detections of VOCs at concentrations above the 1999 laboratory reporting level in samples from four intensive 

fixed sites—site 11, Thornton Creek, and site 4, Fishtrap Creek (small streams) and site 6, Duwamish River, and site 3, lower Nooksack 

River (large rivers)—in the Puget Sound Basin study unit, Washington.
Surface-Water Quality of the Skokomish, Nooksack, and Green-Duwamish Rivers and Thornton Creek 21

Table 2. Summary of standards and criteria for selected water-quality properties, inorganic constituents, and pesticides, and number of samples that did 

not meet criteria during the period 1996–98 in the Puget Sound Basin study unit, Washington

[USEPA drinking-water standards and HAL: U.S. Environmental Protection Agency (1996). USEPA Aquatic Life: U.S. Environmental Protection 

Agency, 1998, CCC (criterion continuous concentration). Because temperature and dissolved oxygen criteria are species dependent and for a warmwatercoldwater matrix, USEPA criteria are not listed. Washington State water-quality standards: State of Washington, 1992. Abbreviations: MCL, maximum 

contaminant level; SMCL, secondary maximum contaminant level; HAL, health advisory level; USEPA, U.S. Environmental Protection Agency; mg/L, 

milligrams per liter; μg/L, micrograms per liter: N, nitrogen; –, no value]

Constituent or property

USEPA drinking 

water standards

HAL

USEPA

Aquatic 

Life

Washington State waterquality standards

Number and 

(percent) of total 

samples not 

meeting criteria

Sites with samples not 

meeting criteria 

(Washington State Class; MCL number of samples) SMCL Class 

AA Class A Class B

Temperature (degrees 

Celsius)

– – – – 116.0 118.0 121.0 6 (1.5) Nooksack at Brennan (A;2), 

Springbrook (A;2), 

Thornton (A;2)

Dissolved oxygen 

(mg/L)

– – – – 29.5 28.0 26.5 29 (7.0) Skokomish (AA;1), 

Nooksack at North 

Cedarville (AA;1), Green 

(AA;1), Springbrook 

(A;25)

pH (units) – 6.5 to 8.5 – 6.5 to 9.0 6.5 to 

8.5

6.5 to 

8.5

6.5 to 

8.5

1 (0.2) Thornton (A;1)

Nitrite (mg/L as N) 1.0 – – – – – – 0 –

Nitrite + Nitrate

(mg/L as N)

10 – – – – – – 0 –

Iron (μg/L) – 300 – 1,000 – – – 48 (11.8) Skokomish (AA;2), Fishtrap 

(A;11), Duwamish (B;7), 

Springbrook (A;25), 

Newaukum (A;1), Green 

(AA;1), Thornton (A;1)

Manganese (μg/L) – 50 – – – – – 100 (24.5) Fishtrap (A;43), Duwamish 

(B;10), Springbrook 

(A;36), Thornton (A;11)

Chloride (mg/L) – 250 – 230 – – – 0 –

Fluoride (mg/L) 4 2 – – – – – 0 –

Sulfate (mg/L) 500 250 – – – – – 0 –

Carbaryl (μg/L) – – 700 30.017 – – – 5 (4.0) Fishtrap (A;3), Thornton 

(A;2)

Chlorpyrifos (μg/L) – – 20 .041 – – – 1 (.8) Thornton (A;1)

Diazinon (μg/L) – – 0.6 4.04 21 (16.9) Fishtrap (A;5), Duwamish 

(B;2), Thornton (A;14)

Lindane (μg/L)1 0.2 – .2 5.01;

6.08

– – – 1 (.8) Thornton (A;1)

1 Not to exceed due to human activities (when natural conditions exceed value shown, no temperature increases will be allowed that will raise 

the receiving water temperature by greater than 0.3 degrees Centigrade). 2 Not to be less than standard shown.

3 Norris and Dost (1992).

4 Menconi and Cox (1994).

5 International Joint Commission Canada and United States (1977). 6 State of Washington (1992)
22 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Skokomish River Basin

The Skokomish River Basin is located entirely 

within the Olympic Mountains physiographic province. 

Population density in the basin is low, in the range of 0-

50 people per square mile (Staubitz and others, 1997). 

Two basic fixed sites were established in the basin 

(fig. 1 and table 1): site 1 on the mainstem Skokomish 

and site 2 on the NF Skokomish. Because nearly all 

flow in the NF Skokomish is diverted away from the 

mainstem through Cushman Powerhouse No. 2 to 

Hood Canal, site 1 is an indicator of the quality of 

water mostly from the SF Skokomish and from the 

lower mainstem Skokomish. Forestry practices 

dominate in the SF Skokomish River Basin and a small 

amount of the drainage area of the lower mainstem is 

used for agriculture. The area drained by site 1 is 

227 mi2, including 99 mi2 in the NF Skokomish River 

Basin that is noncontributing except during dam 

spillage. Site 2 is an indicator of reference or 

background conditions in a forested basin with a 

drainage area of 57.2 mi2.

Skokomish River Basin Hydrology

Annual streamflows during the study period 

exceeded the mean annual streamflow for the period of 

record at both site 1 and site 2 (fig. 4). Precipitation in 

amounts above normal during fall and winter of 1995-

96 and storms with heavy rainfall in November 1995, 

February 1996, and April 1996 contributed to abovenormal streamflows and produced extreme high flows 

on several days. From March through May, daily 

streamflows were variable, ranging from well below 

normal to above normal. Daily streamflows at both 

sites during late spring 1996 were mostly below the 

25th quartile. At site 1, summer and early fall flows 

were within the 25th and 75th interquartile range 

(fig. 7), whereas at site 2, flows remained mostly below 

the 25th quartile (fig.8).

Water year 1997 began with streamflows mostly 

normal during fall and early winter; however, heavy 

rainfall at the end of December caused extreme high 

flows in both rivers. Above-normal precipitation and 

heavy rainfall contributed to high flows again during 

parts of January, February, and March. During spring 

and summer 1997, most all daily flows were near 

normal or above normal, supported in part by an 

average to above-average snowpack that year. The 

water year ended in September with flows well above 

the 75th quartile.

Daily streamflows continued to be above normal 

at the start of water year 1998. At the onset of winter, 

flows were mostly normal, even though precipitation 

was less than the 25th quartile (fig. 2). In January 1998, 

in response to increasing precipitation, streamflows 

rose above the 75th quartile, but by spring, daily flows 

dropped below normal. At site 1, flows remained below 

the 25th quartile through the end of the study period in 

April 1998. At site 2, daily flows were mostly within 

the interquartile range through the end of the study 

period.

Streamflow magnitude at the time of sample 

collection at sites 1 and 2 spanned a wide range, from 

high flows that are exceeded less than 1 percent of the 

time to low flows that are exceeded more than 

90 percent of the time (figs. 7 and 8). Sample 

collections were also evenly distributed over the range 

of flows that can occur at these sites. One sample was 

collected on March 18 at both sites during the regional 

storm that produced a peak flow for 1997 at both sites.

Site 1: Mean annual streamflow for the 

Skokomish for 55 years of record was 1,200 ft3/s, 

which was exceeded by annual streamflows of 1,580, 

1,500, and 1,320 ft3/s for water years 1996-98, 

respectively. In water year 1997, heavy rainfall on 

December 30, 31, and January 1 brought the river to a 

daily mean of 15,000 ft3/s and over flood stage. One 

sample was collected during this storm when the 

highest instantaneous flow at this site for the study 

period was measured (fig. 7). The flow on March 19, 

1997, estimated to be 23,500 ft3/s, approached the 

highest recorded daily flow of 30,000 ft3/s for this site.

Site 2: Mean annual streamflow for the NF 

Skokomish for 74 years of record was 508 ft3/s, which 

was exceeded by annual streamflows of 639, 677, and 

604 ft3/s for water years 1996-98, respectively. In water 

year 1997, the rainstorms at the end of December and 

on New Years Day 1997 produced an annual peak flow 

of 8,140 ft3/s at this site. The March 18–20 rainstorm 

resulted in a daily flow on March 19, 1997, of 

7,300 ft3/s, which is exceeded less than 0.02 percent of 

the time.
Surface-Water Quality of the Skokomish, Nooksack, and Green-Duwamish Rivers and Thornton Creek 23

Streamflow duration, 1944-98

Instantaneous streamflow at sample collection 

 (February 1996-April 1998)

Daily streamflow

Instantaneous streamflow at 

 sample collection, 

 February 1996-April 1998

75th quartile Interquartile range

25th quartile for 1944-98

EXPLANATION

0.01 0.1 1 2 5 10 20 30 40 50 60 70 80 90 95 98 99 99.9

100

100,000

200

300

400

500

700

1,000

2,000

3,000

4,000

5,000

7,000

10,000

20,000

30,000

40,000

50,000

70,000

100

30,000

200

300

400

500

700

1,000

2,000

3,000

4,000

5,000

7,000

10,000

20,000

STREAMFLOW, IN CUBIC FEET PER SECOND STREAMFLOW, IN CUBIC FEET PER SECOND

ONDJFMAMJJASONDJFMAMJJASOND JFMAMJJAS

1995 1996 1997 1998

DAILY AND INSTANTANEOUS STREAMFLOW AND INTERQUARTILE RANGE OF MEAN DAILY STREAMFLOWS

PERCENTAGE OF TIME STREAMFLOWS ARE EQUALED OR EXCEEDED AND INSTANTANEOUS STREAMFLOW

PERCENT

Figure 7. Daily and instantaneous streamflow at the time of sample collection, interquartile range of mean daily streamflows for 

the period of record, and percentage of time streamflows are equaled or exceeded at the Skokomish River in the Puget Sound 

Basin study unit, Washington.
24 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Streamflow duration, 1925-98

Instantaneous streamflow at sample collection,

 (March 1996-April 1998)

EXPLANATION

Daily streamflow

Instantaneous streamflow at 

 sample collection, 

 March 1996-April 1998

75th quartile Interquartile range

25th quartile for 1925-98

30

20,000

40

50

70

100

200

300

400

500

700

1,000

2,000

3,000

4,000

5,000

7,000

10,000

10

20,000

20

30

40

50

70

100

200

300

400

500

700

1,000

2,000

3,000

4,000

5,000

7,000

10,000

0.01 0.1 1 2 5 10 20 30 40 50 60 70 80 90 95 98 99 99.9 99.99

OND J F M A M J J A S O N D J F M A M J J A S O N DJ F M A M J J A S

1995 1996 1997 1998

STREAMFLOW, IN CUBIC FEET PER SECOND STREAMFLOW, IN CUBIC FEET PER SECOND

DAILY AND INSTANTANEOUS STREAMFLOW AND INTERQUARTILE RANGE OF MEAN DAILY STREAMFLOWS

PERCENTAGE OF TIME STREAMFLOWS ARE EQUALED OR EXCEEDED AND INSTANTANEOUS STREAMFLOW

PERCENT

Figure 8. Daily and instantaneous streamflow at the time of sample collection, interquartile range of mean daily streamflows 

for the period of record, and percentage of time streamflows are equaled or exceeded at the North Fork Skokomish River (site 2) in 

the Puget Sound Basin study unit, Washington.
Surface-Water Quality of the Skokomish, Nooksack, and Green-Duwamish Rivers and Thornton Creek 25

Skokomish River Basin Water Quality

A total of 37 water samples from site 1 and 33 

samples from site 2 were analyzed for physical 

properties, field parameters, and concentrations of 

inorganic constituents, organic carbon, and suspended 

sediment. Water in both rivers was chemically dilute, as 

indicated by the conductivity and dissolved-solids 

concentrations. In samples from site 1, conductivity 

ranged from 30 to 80 μS/cm with a median of 

58 μS/cm, and dissolved-solids concentrations ranged 

from 25 to 64 mg/L with a median of 41 mg/L 

(table 3). In samples from site 2, conductivity ranged 

from 34 to 100 μS/cm with a median of 74 μS/cm, and 

dissolved-solids concentrations ranged from 21 to 

67 mg/L with a median of 45 mg/L (table 4). On the 

basis of median concentrations, the dominant cation 

and anion making up the dissolved solids were calcium 

and bicarbonate, respectively (fig. 9). Concentrations 

of nutrients were low, with at least one-half of the 

values for organic nitrogen and phosphorus below 

laboratory MRLs (tables 3 and 4). However, at site 1, 

about 10 percent of the total phosphorus concentrations 

were greater than 0.1 mg/L, USEPA’s (1986a) desired 

goal to prevent nuisance plant growth in streams. With 

only a few exceptions, applicable standards and criteria 

for drinking water, ambient water quality for beneficial 

uses, and the protection of aquatic life were met by the 

water quality at both sites.

In addition to monthly routine samples, 11 of the 

37 samples targeted streamflows during rainstorms or 

snowmelt events. Maximum concentrations of total 

nitrogen, total phosphorus, and suspended sediment 

were typically in samples collected on the rising limb 

or near the peak of the hydrograph during these runoff 

events, such as occurred in March and December 1997 

and in January 1998 (figs. 10 and 11). Concentrations 

of total phosphorus, dissolved and suspended organic 

carbon, iron, and suspended sediment tended to vary 

directly with streamflows, as indicated by Kendall’s tau

(τ), which ranged from 0.3 to 0.7 (table 5). The positive 

correlations are indicative of the tendency for 

particulate matter and constituents adsorbed to the 

particles to enter streams in storm runoff and to be 

resuspended from the stream channel with rising water 

levels and stream energy. Concentrations of dissolved 

solids and major ions, such as bicarbonate, varied 

inversely with streamflows (τ = -0.6 to -0.9), which 

generally indicates dilution effects from rain or 

snowmelt.

Seasonality in water quality is defined by the 

long-term hydrographs for these sites (figs. 7 and 8). In 

the Skokomish River Basin, the high-flow period is 

typically from October through January. The transition 

period, from February through June (at site 1) or 

through July (at site 2), is a time of generally lower 

streamflows than in winter and diminishing flows with 

summer’s approach. The low-flow period is from July 

through September at site 1 and from August through 

September at site 2. The highest concentrations of total 

nitrogen, total phosphorus, and suspended sediment 

tended to occur during the high-flow period (figs. 10

and 11). The one time that an instantaneous dissolvedoxygen concentration did not meet the State’s 

minimum standard was in summer (July 1996).

Site 1: The water in the Skokomish was of 

generally high quality except at times when suspendedsediment concentrations were large. Ten percent of the 

samples had suspended-sediment concentrations 

greater than 600 mg/L with a maximum of 1,470 mg/L 

observed on December 16, 1997. On one occasion, the 

concentration of dissolved oxygen measured at the time 

of sample collection was 9.3 mg/L and did not meet the 

Washington State standard of 9.5 mg/L minimum 

concentration for a Class AA water body (see table 2). 

On two occasions, iron concentrations of as much as 

430 μg/L exceeded the USEPA SMCL of 300 μg/L for 

drinking water. Nitrate, with a median concentration of 

0.09 mg/L, and total organic nitrogen, with a median of 

0.08 mg/L (estimated by log-probability regression, 

Helsel and Cohn, 1988), were the dominant nitrogen 

species (fig. 9). Median concentrations of nutrients, 

suspended sediment, and dissolved and suspended 

organic carbon in samples from site 1 were generally 

greater than those from site 2 (fig. 9).

Site 2: The water in the NF Skokomish was of 

exceptionally high quality. Suspended sediment and 

iron concentrations in samples were low, with iron 

concentrations equal to or less than 25 μg/L and 

90 percent of suspended sediment concentrations less 

than 46 mg/L (table 4). The maximum suspendedsediment concentration observed during the study was 

122 mg/L. As at site 1, nitrate, with a median 

concentration of 0.05 mg/L, and total organic nitrogen, 

with a median of 0.04 mg/L (estimated by logprobability regression), were the dominant nitrogen 

species (fig. 9). In the low-flow period at this site, 

many of the phosphorus and orthophosphate 

concentrations were below laboratory MRLs.
26 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Table 3. Summary of values of field measurements and concentrations of nutrients, major ions, organic carbon, and suspended sediment in samples 

from the Skokomish River (site 1) in the Puget Sound Basin study unit, Washington

[Measurement or concentration - Percentile: Percentiles for data sets with 10 percent or more censored data (values less than the MRL) are estimated 

by log-probability regression (Helsel and Cohn, 1988). Concentrations are dissolved and in milligrams per liter unless otherwise specified. 

Abbreviations: MRL, minimum reporting level; μS/cm, microsiemens per centimeter at 25 degrees Celsius; CaCO3, calcium carbonate; <, less than; 

μg/L, micrograms per liter]

Constituent or property

Measurement or concentration

Minimum

Percentile

MaximumNumber of 

samples

Number of 

samples 

below MRL 

(see tables

A1-A3)

10 25 50

(Median) 75 90

Water temperature (degrees Celsius) 5.4 5.5 6.1 7 10.2 12.6 14.6 37 0

Specific electrical conductance, 

(μS/cm)

30 37 47 58 67 78 80 37 0

pH (units) 7.0 7.2 7.3 7.5 7.6 7.7 7.9 37 0

Dissolved oxygen 9.3 9.9 10.6 11.6 12 12.3 12.5 36 0

Ammonia nitrogen <0.015 <0.015 <0.015 0.013 0.02 0.03 0.04 37 25

Ammonia-plus-organic nitrogen <.1 <.1 <.1 <.1 <.1 <.1 .2 37 36

Ammonia-plus-organic nitrogen, total <.1 <.1 <.1 .08 .14 .24 .45 37 34

Nitrite nitrogen <.01 <.01 <.01 <.01 .01 .01 .02 37 30

Nitrite-plus-nitrate nitrogen <.05 .05 .06 .09 .11 .14 .15 37 5

Phosphorus, total <.01 <.01 <.01 .02 .06 .25 .57 37 15

Phosphorus <.01 <.01 <.01 <.01 <.01 <.01 .14 37 31

Orthophosphate phosphorus <.01 <.01 <.01 .01 .012 .02 .05 37 18

Alkalinity (as CaCO3) 14 16 22 27 30 35 41 37 0

Bicarbonate (as CaCO3) 18 19 27 33 38 43 50 37 0

Calcium 3.5 4.3 5.6 7.2 8.1 8.8 9.5 37 0

Magnesium .81 1.0 1.3 1.7 1.9 2.4 2.5 37 0

Sodium 1.1 1.3 1.5 1.8 2.1 2.2 2.3 37 0

Potassium <.1 <.1 <.1 <.1 .11 .13 .3 37 19

Chloride .6 .88 1.1 1.3 1.4 1.5 1.8 37 0

Sulfate .59 .69 .9 1.2 1.3 1.5 2.5 37 0

Fluoride <.1 <.1 <.1 <.1 <.1 <.1 <.1 37 37

Silica 6.2 7.8 9.4 11 12 14 14 37 0

Iron, in μg/L <3.0 4.1 6.9 12 45.5 81 430 37 5

Manganese, in μg/L <4.0 2.8 2.9 3 5 7 11 37 4

Dissolved solids, residue at 180 

degrees Celsius

25 26 32.5 41 47.5 54 64 37 0

Organic carbon .2 .3 .4 .7 1.1 1.4 2.5 36 0

Organic carbon, suspended <.10 <.10 .1 .2 .9 2.2 6.8 37 7

Sediment, suspended <1 1 2 25.5 261 619 1,470 34 0
Surface-Water Quality of the Skokomish, Nooksack, and Green-Duwamish Rivers and Thornton Creek 27

Table 4. Summary of values of field measurements and concentrations of nutrients, major ions, organic carbon, and suspended sediment in samples 

from the North Fork Skokomish River (site 2) in the Puget Sound Basin study unit, Washington

[Measurement or concentration - Percentile: Percentiles for data sets with 10 percent or more censored data (values less than the MRL) are estimated by 

log-probability regression (Helsel and Cohn, 1988). Concentrations are dissolved and in milligrams per liter unless otherwise specified. Abbreviations: MRL, 

minimum reporting level; μS/cm, microsiemens per centimeter at 25 degrees Celsius; CaCO3, calcium carbonate; <, less than; μg/L, micrograms per liter]

Constituent or property

Measurement or concentration

Minimum

Percentile

MaximumNumber of 

samples

Number of 

samples 

below MRL 

(see tables 

A1-A3)

10 25 50

(Median) 75 90

Water temperature (degrees Celsius) 3.3 3.5 4.2 5 7.8 11.0 12.5 33 0

Specific electrical conductance, (μS/cm) 34 40 60 74 83.5 91 100 33 0

pH (units) 7.2 7.4 7.5 7.7 7.8 7.9 7.9 33 0

Dissolved oxygen 10.2 11.1 11.8 12.8 13.3 13.8 14.9 33 0

Ammonia nitrogen <0.01 <0.015 <0.015 0.014 0.02 0.03 0.04 33 23

Ammonia-plus-organic nitrogen <.1 <.1 <.1 <.1 <.1 <.1 <.1 33 33

Ammonia-plus-organic nitrogen, total <.1 <.1 <.1 .04 .07 .12 .23 33 30

Nitrite nitrogen <.01 <.01 <.01 <.01 <.01 <.01 .01 33 28

Nitrite-plus-nitrate nitrogen <.05 .025 .035 .05 .09 .1 .147 33 17

Phosphorus, total <.01 <.01 <.01 <.01 .01 .05 .08 33 24

Phosphorus <.01 <.01 <.01 <.01 <.01 .009 .015 33 30

Orthophosphate phosphorus <.01 <.01 <.01 <.01 .01 .014 .02 33 24

Alkalinity (as CaCO3) 14 16 24.5 29 33.5 37 40 33 0

Bicarbonate (as CaCO3) 17 19 29.5 36 40.5 45 49 33 0

Calcium 4.9 6.3 9.2 11 13 14 16 33 0

Magnesium .4 .5 .7 .82 1.0 1.1 1.1 33 0

Sodium .7 .9 1.15 1.4 1.6 1.75 1.9 33 0

Potassium <.1 .1 .1 .12 .15 .2 .2 33 3

Chloride .43 .49 .52 .6 .74 .88 .92 33 0

Sulfate 1.8 1.9 3.8 4.6 5.7 6.0 7.4 33 0

Fluoride <.1 <.1 <.1 <.1 <.1 <.1 <.1 33 33

Silica 2.6 3.3 4.1 5.2 5.6 5.8 5.9 33 0

Iron, in μg/L <3.0 <3.0 <3.0 3.5 9.5 17 25 33 21

Manganese, in μg/L <1 <1 <1 <1 <1 1 2 33 29

Dissolved solids, residue at 

180 degrees Celsius

21 27 37.5 45 50 55 67 33 0

Organic carbon .4 .4 .6 .6 1.45 2.2 3.7 33 0

Organic carbon, suspended <.1 <.1 <.1 .1 .2 1.2 1.6 31 12

Sediment, suspended <1 <1 <1 1 6 46 122 33 9
28 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98 Median less than 0.10 mg/L Median less than 0.01 mg/L Median less than 0.10 mg/L

EXPLANATION

Land use/cover

Agriculture

Forest/natural cover/

 other

Urban/built up areas

Basin boundary 

Sample site

Streams

National Forest

 boundary

National Park

 boundary

Lakes

EXPLANATION

NITROGEN

Dissolved nitrite-plus-nitrate

Dissolved ammonia

Dissolved ammonia-plus-organic

Total ammonia-plus-organic

Total phosphorus

Dissolved phosphorus

Dissolved 

 orthophosphate

Suspended sediment

Dissolved organic carbon

Suspended organic carbon

PHOSPHORUS

NITROGEN, IN MILLIGRAMS 

PER LITER (mg/L)

Nitrogen Phosphorus Nitrogen Phosphorus

Skokomish River N.F. Skokomish River

MEDIAN NUTRIENT COMPOSITION

0

0.06

0.08

0.10

0.02

0.04 0.02

0.04

0.05

0 0

10

20

30

SEDIMENT, 

IN MILLIGRAMS PER LITER

PHOSPHORUS, 

IN MILLIGRAMS PER LITER

Skokomish River N.F. Skokomish River

MEDIAN SUSPENDED SEDIMENT

AND CARBON

Suspended

Sediment

Organic

Carbon

Suspended

Sediment

Organic

Carbon

0

0.2

0.4

0.6

0.8

1.0

ORGANIC CARBON, 

IN MILLIGRAMS PER LITER

N.

F. Skokomish River

Olympic National Park

Olympic National Forest

S.F. Skokomish River

Potlatch Hood Canal

Hoodsport

Lower

Cushman Dam

Lake

Kokanee

Cushman Dam

Olympic National Forest

Lake

Cushman

Site 2 - N.F. Skokomish River

Na + K Cl

Ca SO4

Mg HC0 3

-1 0 1

Median milliequivalents

per liter

Site 1 - Skokomish River

Na + K Cl

Ca SO4

Mg HC0 3

-1 0 1

Median milliequivalents

per liter

 123 ̊30' 123 ̊15'

 47 ̊

37'

30"

 47 ̊

22'

30"

 47 ̊

30'

0

0 4 8 KILOMETERS 

4 8 MILES

Median less than 0.10 mg/LMedian less than 0.01 mg/LMedian less than 0.10 mg/L

EXPLANATION

Land use/cover

Agriculture

Forest/natural cover/

 other

Urban/built up areas

Basin boundary 

Sample site

Streams

National Forest

 boundary

National Park

 boundary

Lakes

EXPLANATION

NITROGEN

Dissolved nitrite-plus-nitrate

Dissolved ammonia

Dissolved ammonia-plus-organic

Total ammonia-plus-organic

Total phosphorus

Dissolved phosphorus

Dissolved 

 orthophosphate

Suspended sediment

Dissolved organic carbon

Suspended organic carbon

PHOSPHORUS

NITROGEN, IN MILLIGRAMS 

PER LITER (mg/L)

Nitrogen Phosphorus Nitrogen Phosphorus

Skokomish River N.F. Skokomish River

MEDIAN NUTRIENT COMPOSITION

0

0.06

0.08

0.10

0.02

0.04 0.02

0.04

0.05

0 0

10

20

30

SEDIMENT, 

IN MILLIGRAMS PER LITER

PHOSPHORUS, 

IN MILLIGRAMS PER LITER

Skokomish River N.F. Skokomish River

MEDIAN SUSPENDED SEDIMENT

AND CARBON

Suspended

Sediment

Organic

Carbon

Suspended

Sediment

Organic

Carbon

0

0.2

0.4

0.6

0.8

1.0

ORGANIC CARBON, 

IN MILLIGRAMS PER LITER

N.

F. Skokomish River

Olympic National Park

Olympic National Forest

S.F. Skokomish River

Potlatch Hood Canal

Hoodsport

Lower

Cushman Dam

Lake

Kokanee

Cushman Dam

Olympic National Forest

Lake

Cushman

Site 2 - N.F. Skokomish River

Na + K Cl

Ca SO4

Mg HC0 3

-1 0 1

Median milliequivalents

per liter

Site 1 - Skokomish River

Na + K Cl

Ca SO4

Mg HC0 3

-1 0 1

Median milliequivalents

per liter

 123 ̊30' 123 ̊15'

 47 ̊

37'

30"

 47 ̊

22'

30"

 47 ̊

30'

0

0 4 8 KILOMETERS 

4 8 MILES

Figure 9. Median concentrations of nutrients, suspended sediment, organic carbon, and major ions in samples from the Skokomish River 

(site 1) and the North Fork Skokomish River (site 2) in the Puget Sound Basin study unit, Washington.
Surface-Water Quality of the Skokomish, Nooksack, and Green-Duwamish Rivers and Thornton Creek 29

EXPLANATION

Concentration percentiles

10th percentile

25th percentile

Median

75th percentile

90th percentile

Low-flow

High-flow

Transition

Daily streamflow

Minimum reporting level

FMAMJ J ASOND J FMAMJ J ASOND J FMA

1996 1997 1998

24,000

10,000

20,000

1,700

500

1,000

1,500

FMAMJ J ASOND J FMAMJ J ASOND J FMA

24,000

10,000

20,000

0.06

0.02

FMAMJ J ASOND J FMAMJ J ASOND J FMA

24,000

10,000

20,000

0.6

0.2

0.4

0 0

0 0

0 0

0.04

1,700

0 0

500

1,000

1,500

0.06

0.02

0.04

0.8

0

0.2

0.4

0.6

Dissolved orthophosphate

Total nitrogen

Total phosphorus

Suspended sediment

Dissolved Orthophosphate

CONCENTRATION, IN MILLIGRAMS PER LITER

STREAMFLOW, IN CUBIC FEET PER SECOND

Total Nitrogen and

Total Phosphorus (in blue)

Suspended Sediment

STREAMFLOW PERIODS

 CONCENTRATION, 

IN MILLIGRAMS PER LITER

Oct.-

Jan.

Feb.-

June 

JulySept.Oct.-

Jan.

Feb.-

June 

JulySept.Oct.-

Jan.

Feb.-

June 

JulySept.

Figure 10. Time series of streamflow and concentrations of total nitrogen, total phosphorus, dissolved orthophosphate phosphorus, and suspended 

sediment in samples, and concentrations by three streamflow periods, for the Skokomish River (site 1) in the Puget Sound Basin study unit, Washington.

(Truncated boxplots of concentration percentiles require a minimum of nine observations, otherwise concentrations are plotted as individual points. 

Censored data in the time-series graphs are shown as an open symbol. Boxplots are truncated at the minimum reporting level indicated by solid line.)
30 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

0

0.35

0.2

0.008

0.03

0.01

0.02

0

50

100

150

MAMJ J ASOND J FMAMJ J ASOND J FMA

0

8,000

2,000

4,000

6,000

0

0.35

0.1

0.2

0.3

M

0

8,000

2,000

4,000

6,000

0.008

0.03

0.01

0.02

0

8,000

2,000

4,000

6,000

0

150

50

100

CONCENTRATION, IN MILLIGRAMS PER LITER

STREAMFLOW, IN CUBIC FEET PER SECOND

 CONCENTRATION, 

IN MILLIGRAMS PER LITER

Total nitrogen

AMJ J ASOND J FMAMJ J ASOND J FMA

Dissolved orthophosphate

MAMJ J ASOND J FMAMJ J ASOND J FMA

1996 1997 1998

Total Nitrogen and

Total Phosphorus (in blue)

Dissolved Orthophosphate Suspended Sediment

Suspended sediment

Total phosphorus

STREAMFLOW PERIODS

Oct.-

Jan.

Feb.-

July 

Aug.-

Sept.

Oct.-

Jan.

Feb.-

July 

Aug.-

Sept.

Oct.-

Jan.

Feb.-

July 

Aug.-

Sept.

EXPLANATION

Concentration percentiles

10th percentile

25th percentile

Median

75th percentile

90th percentile

Low-flow

High-flow

Transition

Daily streamflow

Minimum reporting level

Figure 11. Time series of streamflow and concentrations of total nitrogen, total phosphorus, dissolved orthophosphate phosphorus, and suspended sediment in 

samples, and concentrations by three streamflow periods, for the North Fork Skokomish River (site 2) in the Puget Sound Basin study unit, Washington.

(Truncated boxplots of concentration percentiles require a minimum of nine observations, otherwise concentrations are plotted as individual points. Censored 

data in the time-series graphs are shown as an open symbol. Boxplots are truncated at the minimum reporting level indicated by solid line.)
Surface-Water Quality of the Skokomish, Nooksack, and Green-Duwamish Rivers and Thornton Creek 31

Table 5. Correlation between selected water-quality characteristics or concentrations of chemical 

constituents and streamflow for the Skokomish River (site 1) and the North Fork Skokomish River (site 2) in 

the Puget Sound Basin study unit, Washington

Water-quality characteristic or 

chemical constituent

Kendall’s tau correlation coefficient

Skokomish River (Site 1) North Fork Skokomish 

River (Site 2)

Specific electrical conductance -0.87 -0.86

Dissolved solids -.73 -.65

Total nitrogen .15 .03

Dissolved nitrite-plus-nitrate nitrogen .02 -.02

Total ammonia-plus-organic nitrogen .05 .09

Dissolved ammonia-plus-organic nitrogen -.09 -.13

Total phosphorus .54 .27

Dissolved orthophosphate phosphorus .08 .08

Dissolved organic carbon .52 .59

Suspended organic carbon .71 .49

Suspended sediment .74 .52

Bicarbonate -.80 -.87

Iron .41 .48

Manganese .23 .21
32 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Nooksack River Basin

The Nooksack River originates within the 

Cascade Range physiographic province. Below the 

confluence of the three forks, the river drains the Puget 

Sound Lowlands province. Population density in the 

basin is low, with 0–50 people per square mile and 

some population centers of 51–250 people per square 

mile (Staubitz and others, 1997). Three basic fixed sites 

are in the Nooksack River Basin (fig. 1 and table 1): 

site 3 on the lower mainstem Nooksack; site 4 on 

Fishtrap Creek, and site 5 on the upper mainstem 

Nooksack. Site 3 is an integrator of the quality of water 

from the Nooksack River Basin, which consists of 

high-altitude mountains with glacier and snowfields, 

forests, a few small population centers along the lower 

mainstem, and intensive agricultural practices in the 

Lowlands. The river drains an area of 790 mi2 at site 3. 

Site 4 is an indicator of intense agricultural practices 

(dairy, berries, potatoes, corn, poultry); however, 

urban/suburban development in parts of the basin 

(Canada and the nearby city of Lynden) also 

contributes to the water-quality characteristics. Fishtrap 

Creek at site 4 drains an area of 38.1 mi2. Site 5 is an 

indicator of water quality from forest practices and 

from undisturbed high-mountain lands of the upper 

Nooksack River Basin. The Nooksack River at site 5 

drains an area of 589 mi2.

Nooksack River Basin Hydrology

Water year 1996 and 1997 annual streamflows 

were greater than the mean annual streamflow for the 

period of record at site 3 and site 5 (fig. 4). Annual flow 

for 1998 was about equal to the mean annual flow at 

these two sites. No long-term record existed at site 4 

for comparing annual or daily flows observed during 

the study. Flow variability at site 4 as it related to 

climate during the sampling period is illustrated by the 

daily-streamflow hydrograph recorded during this 

study. Precipitation recorded at Bellingham in amounts 

above normal during fall and winter of 1995–96 

contributed to above-normal streamflows. In addition, 

storms with heavy rainfall from November 1995 

through April 1996 produced extreme high flows at 

times (figs. 12, 13, and 14). Daily streamflows in 

March were near normal, but from April through May 

flows ranged from well above normal to below normal. 

In summer and early fall, flows were generally within 

the 25th and 75th interquartile range except for a few 

days in mid-September when locally heavy rainstorms 

brought the flows to above normal. During the dry 

season, above-normal snowpack and glacial meltwater 

helped to sustain flows in the mainstem Nooksack 

River.

In water year 1997, streamflows were mostly 

near the upper quartile of historical flows, with abovenormal precipitation contributing to extreme high flows 

at times from November through March. The regional 

storm of March 18–20, 1997, generated extreme high 

flows at all three sites. Near the end of summer, the wet 

season arrived early, with above-normal rainfall raising 

September flows to above the 75th quartile.

Daily streamflows continued to be above normal 

at the start of water year 1998, with October 

precipitation 140 percent of normal (see fig. 3). During 

winter 1997–98, below-normal precipitation kept 

November, December, and February flows mostly 

within the interquartile range. With more moderate 

rainfall amounts in spring of 1998, daily flows were 

mostly normal until April, the end of the study period. 

Precipitation only 40 percent of normal resulted in low 

flows during April 1998.

Magnitude of streamflows at the time of sample 

collection at sites 3 and 5 spanned a wide range, from 

high flows that are exceeded less than 1 percent of the 

time to low flows that are exceeded more than 

90 percent of the time (figs. 12 and 14). Sample 

collections were relatively evenly distributed over the 

range of flows that can occur at these sites, with some 

clustering of samples between the 50th and 80th 

percentiles at site 5 (fig. 14). Water samples were 

collected at sites 3 and 5 during the November 1995 

storm that generated the highest daily flow observed at 

these two sites during the 3-year study period. Samples 

were also collected at both sites on March 20, 1997, 

during the regional storm that produced a peak flow for 

1997 at each site.

Site 3: Mean annual streamflow for the lower 

Nooksack for 32 years of record at the gage upstream 

(12213100, Nooksack River at Ferndale) was 

3,800 ft3/s, which was exceeded by annual flows of 

4,390 and 5,270 ft3/s during 1996 and 1997, 

respectively. Annual streamflow for water year 1998 

was 3,500 ft3/s. The March 1997 regional storm 

produced a daily mean flow of 33,700 ft3/s, the second 

highest daily flow observed at this site during the study 

period.
Surface-Water Quality of the Skokomish, Nooksack, and Green-Duwamish Rivers and Thornton Creek 33

100,000

800

50,000

1,000

2,000

3,000

4,000

5,000

7,000

10,000

20,000

30,000

40,000

500

700

1,000

2,000

3,000

4,000

5,000

7,000

10,000

20,000

30,000

40,000

50,000

70,000

1995 1996 1997 1998

ONDJFMAMJJASONDJFMAM J J ASONDJFMAMJJAS

0.01 0.1 1 2 5 10 20 30 40 50 60 70 80 90 95 98 99 99.9 99.99

STREAMFLOW, IN CUBIC FEET PER SECOND STREAMFLOW, IN CUBIC FEET PER SECOND

DAILY AND INSTANTANEOUS STREAMFLOW AND INTERQUARTILE RANGE OF MEAN DAILY STREAMFLOWS

PERCENTAGE OF TIME STREAMFLOWS ARE EQUALED OR EXCEEDED AND INSTANTANEOUS STREAMFLOW

PERCENT

Daily streamflow

Instantaneous streamflow at 

 sample collection, 

 November 1995-April 1998

75th quartile Interquartile range

25th quartile for 1967-98

EXPLANATION

Streamflow duration, 1967-98

Instantaneous streamflow at sample collection,

 (November 1995-April 1998)

Figure 12. Daily and instantaneous streamflow at the time of sample collection, interquartile range of mean daily streamflows 

for the period of record, and percentage of time streamflows are equaled or exceeded at the lower Nooksack River (site 3) in the 

Puget Sound Basin study unit, Washington.
34 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

1

1,000

700

2

3

4

5

7

10

20

30

40

50

70

100

200

300

400

500

1

1,000

700

2

3

4

5

7

10

20

30

40

50

70

100

200

300

400

500

STREAMFLOW, IN CUBIC FEET PER SECOND STREAMFLOW, IN CUBIC FEET PER SECOND

0.01 0.1 1 2 5 10 20 30 40 50 60 70 80 90 95 98 99 99.9

PERCENT

O N DJ F M A M J J A S O N D J F M A M J J A S O N DJ F M A M J J A S

1995 1996 1997 1998

Daily streamflow

Instantaneous streamflow at 

 sample collection, 

 March 1996-April 1998

Streamflow duration, 1997-98

Instantaneous streamflow at sample collection,

 (March 1996-April 1998)

DAILY AND INSTANTANEOUS STREAMFLOW

PERCENTAGE OF TIME STREAMFLOWS ARE EQUALED OR EXCEEDED AND INSTANTANEOUS STREAMFLOW

Figure 13. Daily and instantaneous streamflow at the time of sample collection, and percentage of time streamflows are equaled or 

exceeded and instantaneous streamflow at Fishtrap Creek (site 4) in the Puget Sound Basin study unit, Washington.
Surface-Water Quality of the Skokomish, Nooksack, and Green-Duwamish Rivers and Thornton Creek 35

STREAMFLOW, IN CUBIC FEET PER SECOND

STREAMFLOW, IN CUBIC FEET PER SECOND

PERCENT

500

100,000

700

1,000

2,000

3,000

4,000

5,000

7,000

10,000

20,000

30,000

40,000

50,000

70,000

500

50,000

700

1,000

2,000

3,000

4,000

5,000

7,000

10,000

20,000

30,000

40,000

OND JFMAMJJASONDJFMAMJJASONDJFMAMJJAS

1995 1996 1997 1998

0.01 0.1 1 2 5 10 20 30 40 50 60 70 80 90 95 98 99 99.9 99.99

Streamflow duration, 1936-98

Instantaneous streamflow at sample collection,

(November 1995-April 1998)

EXPLANATION

Daily streamflow

Instantaneous streamflow at

sample collection,

November 1995-April 1998

75th quartile Interquartile range

for 1936-98 25th quartile

DAILY AND INSTANTANEOUS STREAMFLOW AND INTERQUARTILE RANGE OF MEAN DAILY STREAMFLOWS

PERCENTAGE OF TIME STREAMFLOWS ARE EQUALED OR EXCEEDED AND INSTANTANEOUS STREAMFLOW

Figure 14. Daily and instantaneous streamflow at the time of sample collection, interquartile range of mean daily streamflows 

for the period of record, and percentage of time streamflows are equaled or exceeded at the upper Nooksack River (site 5) in the 

Puget Sound Basin study unit, Washington.
36 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Site 4: The average streamflow for Fishtrap for 

29 months of record was 78 ft3/s. For the first 4 months 

of the study period with continuous gage record (June–

September 1996), the average flow was 23 ft3/s. 

Annual flows for water years 1997 and 1998 were 109 

and 70 ft3/s, respectively. In water year 1996, late April 

rainstorms generated high flows from April 23–27, 

1996. The storm sample on April 24, 1996, was 

collected when the highest instantaneous flow 

(490 ft3/s) for the study period was measured. The 

March 1997 regional storm produced the highest daily 

flow, 600 ft3/s, observed during the study period.

Site 5: Mean annual streamflow for the upper 

Nooksack for 56 years of record at the gage upstream 

(12210500, Nooksack River at Deming) was 

3,320 ft3/s, which was exceeded by annual streamflows 

of 3,780 and 4,960 ft3/s during 1996 and 1997, 

respectively. Annual flow for water year 1998 was 

3,140 ft3/s. The November 1995 storm resulted in a 

flow of 41,500 ft3/s on November 29, 1995, the highest 

recorded daily mean flow for the period of record at 

this site. The rainstorm of March 1997 produced the 

second highest daily flow, 25,000 ft3/s, observed at this 

site during the study period.

Nooksack River Basin Water Quality

Forty-one water samples from site 3 (table 6), 44 

samples from site 4 (table 7), and 34 samples from site 

5 (table 8) were collected for the analysis of physical 

properties, field parameters, and concentrations of 

inorganic constituents, organic carbon, and suspended 

sediment. Twenty-two samples at site 3 and 32 samples 

at site 4 were collected for pesticide and VOC analyses. 

Water quality at the large river sites, sites 3 and 5, met 

all applicable standards and criteria for drinking water, 

ambient water quality for beneficial uses, and the 

protection of aquatic life. However, in several samples 

from the small stream (site 4), iron and manganese 

concentrations exceeded USEPA drinking-water 

SMCLs, and in a few samples, insecticide 

concentrations exceeded aquatic-life criteria.

High-quality water from the mountain 

headwaters was an important influence on the water 

chemistry of the mainstem Nooksack River and 

contributed to the dilute water chemistry observed in 

samples from sites 3 and 5. At times, however, large 

volumes of runoff led to high flows and to flood 

conditions, in which large amounts of sediment and 

occasionally high concentrations of total phosphorus 

were transported. The chemically dilute water 

chemistry of the Nooksack River was indicated by the 

conductivity and dissolved-solids concentrations. In 

addition, as the river flows from site 5 on the upper 

Nooksack downstream to site 3, these water-quality 

variables changed very little, as indicated by their 

median values. For site 3, the median conductivity was 

89 μS/cm (table 6), and for site 5, the median was 

75 μS/cm (table 8). Median dissolved-solids 

concentrations at site 3 was 58 mg/L and at site 5, 

49 mg/L. On the basis of median concentrations, the 

dominant cation and anion making up the dissolved 

solids in the Nooksack were calcium and bicarbonate, 

respectively, but in Fishtrap Creek the dissolved solids 

were composed primarily of calcium, bicarbonate, and 

sulfate (fig. 15).

Concentrations of nutrients were moderately low 

in the lower Nooksack, with at least 10 percent of the 

organic-nitrogen and phosphorus concentrations below 

laboratory MRLs (table 6); concentrations were low in 

the upper Nooksack, with at least half of the organic 

nitrogen and phosphorus concentrations below MRLs 

(table 8). However, concentrations of total phosphorus 

in 25 percent of the samples were greater than 

0.1 mg/L, USEPA’s (1986a) desired goal to prevent 

nuisance plant growth in streams.

In Fishtrap (site 4), the water chemistry was 

more concentrated and there were more detections of 

pesticides and VOCs than in the Nooksack. The water 

was moderately high in concentrations of inorganic 

compounds as indicated by a median conductivity of 

240 μS/cm and by a median dissolved-solids 

concentration of 151 mg/L (table 7). Water in Fishtrap 

was also richer in nutrients than water in the lower or 

upper Nooksack, with at least 90 percent of the nutrient 

concentrations (except phosphorus and 

orthophosphate) above laboratory MRLs. Twenty-five 

percent of the total phosphorus concentrations were 

greater than 0.1 mg/L. Ground-water discharge and 

agricultural and urban land-use activities are likely 

sources of chemical constituents contributing to the 

more concentrated water chemistry at site 4.
Surface-Water Quality of the Skokomish, Nooksack, and Green-Duwamish RIvers and Thornton Creek 37

Table 6. Summary of values of field measurements and concentrations of nutrients, major ions, organic carbon, and suspended sediment in samples 

from the lower Nooksack River (site 3) in the Puget Sound Basin study unit, Washington

[Measurement or concentration - Percentile: Percentiles for data sets with 10 percent or more censored data (values less than the MRL) are estimated by 

log-probability regression (Helsel and Cohn, 1988). Concentrations are dissolved and in milligrams per liter unless otherwise specified. Abbreviations:

MRL, minimum reporting level; μS/cm, microsiemens per centimeter at 25 degrees Celsius; CaCO3, calcium carbonate; <, less than; μg/L, micrograms per 

liter]

Constituent or property

Measurement or concentration

Minimum

Percentile

MaximumNumber of 

samples

Number of 

samples below 

MRL (see 

tables A1-A3)

10 25 50

(Median) 75 90

Water temperature (degrees Celsius) 0 4.06 5.55 8.3 11.0 15.8 18 41 0

Specific electrical conductance 

(μS/cm)

44 56 73.5 89 116 125 132 41 0

pH (units) 6.9 7.4 7.5 7.6 7.7 7.8 7.9 41 0

Dissolved oxygen 8.8 9.7 10.65 11.15 11.9 12.7 13.8 40 0

Ammonia nitrogen <0.015 <0.015 0.017 0.03 0.045 0.068 0.08 41 12

Ammonia-plus-organic nitrogen <.1 .021 .034 .059 .108 .191 .32 41 34

Ammonia-plus-organic nitrogen, 

total

<.1 .021 .05 .13 .27 .68 2.4 41 22

Nitrite nitrogen <.01 <.01 <.01 .006 .01 .019 .03 41 27

Nitrite-plus-nitrate nitrogen .128 .16 .23 .35 .58 .75 .94 41 0

Phosphorus, total <.01 <.01 .016 .04 .17 .43 7.3 41 4

Phosphorus <.01 <.01 <.01 <.01 .007 .019 .03 41 32

Orthophosphate phosphorus <.01 <.01 <.01 .008 .01 .02 .02 41 22

Alkalinity (as CaCO3) 16 18 24.5 30 38.5 42 44 41 0

Bicarbonate (as CaCO3) 19 22 29.5 36 46.5 51 53 41 0

Calcium 4.7 5.4 7.4 9.5 12 13 14 40 0

Magnesium 1.4 1.9 2.4 3.0 3.8 4.4 4.6 40 0

Sodium .89 1.2 1.9 2.1 3.4 3.7 4.1 40 0

Potassium .2 .5 .5 .7 .9 1.1 1.3 40 0

Chloride .44 .9 1.4 2.0 3.4 3.8 4.0 40 0

Sulfate 2.4 3.1 5.9 8.6 11 12 13 40 0

Fluoride <.1 <.1 <.1 <.1 <.1 <.1 <.1 40 39

Silica 3.8 5.5 6.7 8.1 9.6 10 11 40 0

Iron, in μg/L 6 20 42 66 88 127 190 40 0

Manganese, in μg/L 4 4.8 6.2 11 16 21 26 40 0

Dissolved solids, residue at 

180 degrees Celsius

31 36.5 50 57.5 76 82 98 40 0

Organic carbon .7 .9 1.5 2.2 3.3 4.6 6.8 40 0

Organic carbon, suspended <.2 .2 .3 .55 1.3 3.9 12 40 1

Sediment, suspended 8 15 37 70 301 1,460 2,890 39 0
38 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Table 7. Summary of values of field measurements and concentrations of nutrients, major ions, organic carbon, and suspended sediment in samples 

from Fishtrap Creek (site 4) in the Puget Sound Basin study unit, Washington

[Measurement or concentration - Percentile: Percentiles for data sets with 10 percent or more censored data (values less than the MRL) are estimated by 

log-probability regression (Helsel and Cohn, 1988). Concentrations are dissolved and in milligrams per liter unless otherwise specified. Abbreviations: MRL, 

minimum reporting level; μS/cm, microsiemens per centimeter at 25 degrees Celsius; CaCO3, calcium carbonate; <, less than; μg/L, micrograms per liter]

Constituent or property

Measurement or concentration

Minimum

Percentile

MaximumNumber of 

samples

Number of 

samples 

below MRL 

(see tables A1-

A3)

10 25 50

(Median) 75 90

Water temperature (degrees Celsius) 2 4.5 6.8 10.2 12.95 15.75 17.4 44 0

Specific electrical conductance, (μS/cm) 158 179 211 240 255 264 297 44 0

pH (units) 7.0 7.2 7.4 7.55 7.7 7.7 7.9 44 0

Dissolved oxygen 8.2 9.1 9.7 10.4 11.1 11.8 12.4 44 0

Ammonia nitrogen <0.015 0.02 0.04 0.09 0.22 0.34 1.2 44 1

Ammonia-plus-organic nitrogen <.2 .14 .2 .4 .62 .925 1.8 44 7

Ammonia-plus-organic nitrogen, total <.2 .23 .3 .52 .89 1.4 2.9 44 1

Nitrite nitrogen <.01 .01 .019 .02 .03 .04 0.07 44 2

Nitrite-plus-nitrate nitrogen 1.1 2.0 2.3 2.8 3.3 3.9 4.3 44 0

Phosphorus, total <.01 .01 .02 .06 .12 .22 .43 44 3

Phosphorus <.01 <.01 <.01 .008 .025 .05 .15 44 24

Orthophosphate phosphorus <.01 <.01 <.01 .01 .02 .04 .14 44 18

Alkalinity (as CaCO3) 25 35.5 43 49 57 61 63 44 0

Bicarbonate (as CaCO3) 31 43.5 52 60 69.5 74 77 44 0

Calcium 13 17 20 24 26 27.5 29 44 0

Magnesium 3.3 4.5 5.5 6.6 7.2 7.6 7.7 44 0

Sodium 4.3 5.65 6.9 8.1 8.8 9.2 18 44 0

Potassium 1.8 2.05 2.4 3.0 4.1 4.8 5.5 44 0

Chloride 5.5 7.8 9.5 10 11 12 28 44 0

Sulfate 16 22 27 33 36 37.5 42 44 0

Fluoride <.1 <.1 <.1 <.1 <.1 <.1 <.1 44 44

Silica 8 11 13 15 16 17 18 44 0

Iron, in μg/L 56 100 157 220 319 401 440 44 0

Manganese, in μg/L 49 73 92 128 160 200 232 44 0

Dissolved solids, residue at 

180 degrees Celsius

104 116 136 151 161 174 195 44 0

Organic carbon 1.9 2.25 2.8 3.7 5.0 6.7 11 44 0

Organic carbon, suspended .2 .4 .5 .95 1.7 2.6 3.9 44 0

Sediment, suspended 4 6 11 21 42 135 285 42 0
Surface-Water Quality of the Skokomish, Nooksack, and Green-Duwamish RIvers and Thornton Creek 39

Table 8. Summary of values of field measurements and concentrations of nutrients, major ions, organic carbon, and suspended sediment in samples 

from the upper Nooksack River (site 5) in the Puget Sound Basin study unit, Washington

[Measurement or concentration - Percentile: Percentiles for data sets with 10 percent or more censored data (values less than the MRL) are estimated by 

log-probability regression (Helsel and Cohn, 1988). Concentrations are dissolved and in milligrams per liter unless otherwise specified. Abbreviations: MRL, 

minimum reporting level; μS/cm, microsiemens per centimeter at 25 degrees Celsius; CaCO3, calcium carbonate; <, less than; μg/L, micrograms per liter]

Constituent or property

Measurement or concentration

Minimum

Percentile

MaximumNumber of 

samples

Number of 

samples 

below MRL 

(see tables 

A1-A3)

10 25 50

(Median) 75 90

Water temperature (degrees Celsius) 0.1 3.9 4.9 6.5 11.0 12.4 14.8 35 0

Specific electrical conductance, (μS/cm) 39 50 62 75 92 96 99 35 0

pH (units) 7.1 7.3 7.5 7.6 7.8 7.8 7.9 35 0

Dissolved oxygen 9.4 10.4 10.8 11.8 12.4 12.75 13.7 34 0

Ammonia nitrogen <.015 <0.015 <0.015 0.011 0.02 0.025 0.05 35 24

Ammonia-plus-organic nitrogen <.1 <.1 <.1 <.1 <.1 <.1 .7 35 33

Ammonia-plus-organic nitrogen, total <.1 <.1 <.1 .06 .19 .62 2.3 35 25

Nitrite nitrogen <.01 <.01 <.01 <.01 .006 .01 .026 35 28

Nitrite-plus-nitrate nitrogen .054 .08 .12 .21 .25 .33 .39 35 0

Phosphorus, total <.01 <.01 <.01 .031 .144 .42 1.8 35 12

Phosphorus <.01 <.01 <.01 <.01 .007 .012 .02 35 32

Orthophosphate phosphorus <.01 <.01 <.01 <.01 .007 .011 .017 35 30

Alkalinity (as CaCO3) 15 18 23 29 35 37 42 35 0

Bicarbonate (as CaCO3) 18 21 28 36 42 45 51 35 0

Calcium 4.7 5.5 7.0 8.8 11 11 12 34 0

Magnesium 1.5 1.75 2.0 2.5 3.1 3.4 3.5 34 0

Sodium .9 1.0 1.2 1.4 1.9 2 2 34 0

Potassium .3 .32 .38 .4 .4 .5 .5 34 0

Chloride .4 .5 .7 .9 1.0 1.2 1.4 34 0

Sulfate 2.3 3.1 4.2 6.3 7.5 9.8 12 34 0

Fluoride <.1 <.1 <.1 <.1 <.1 <.1 <.1 34 34

Silica 4.6 5.6 6.6 7.6 8.6 8.95 9.3 34 0

Iron, in μg/L 7.9 11 20 26 44 130 180 34 0

Manganese, in μg/L <4.0 4.4 5.0 6 7.7 13 17 34 1

Dissolved solids, residue at 

180 degrees Celsius

32 38 42 49 59 63 76 34 0

Organic carbon .2 .5 .95 1.4 2.35 3.5 5.4 33 0

Organic carbon, suspended <.1 .1 .2 .3 1.1 2.9 11 32 3

Sediment, suspended 2 8 16 59 530 1,910 3,210 33 0
40 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

In addition to monthly routine samples, about 

25 percent of the samples at each of the three sites were 

collected during stormflow events. Maximum 

concentrations of total nitrogen, total phosphorus, and 

suspended sediment were observed in samples 

collected on the rising limb or near the peak of the 

hydrograph during runoff events, such as occurred in 

November 1995 and January, March, and October 1997 

(figs. 16, 17, and 18). Concentrations of total nitrogen, 

total phosphorus, dissolved and suspended organic 

carbon, iron, and suspended sediment tended to vary 

directly with streamflow, as indicated by Kendall’s τ, 

which ranged from 0.3 to 0.7 (table 9). Concentrations 

of dissolved solids and major ions, such as bicarbonate, 

varied inversely with streamflow (τ = -0.5 to -0.7).

The high-flow period for the Nooksack River 

(figs. 12 and 14) is typically from October to February 

and for Fishtrap Creek from October to March (fig. 13). 

The transition period, from March to July in the 

mainstem, is also a period of high flows due to spring 

snowmelt; but in Fishtrap the transition period is from 

April to July and consists of diminishing flows as 

summer approaches. The low-flow period is August 

and September for the Nooksack and for Fishtrap. At 

all three sites, nutrient and suspended-sediment 

concentrations in samples collected in the high-flow 

period were generally higher than in samples collected 

in the transition and low-flow periods (figs. 16, 17, and 

18).

Site 3: The water in the lower Nooksack was of 

generally good quality except for times when 

suspended-sediment concentrations were large or 

several pesticides and VOCs were present. Ten percent 

of the samples had suspended-sediment concentrations 

of 1,460 mg/L or higher, with a maximum of 

2,890 mg/L observed on October 30, 1997. The sample 

collected on the rising limb of the hydrograph and near 

the peak of the October 30, 1997 storm also contained 

exceptionally high concentrations of total phosphorus 

(7.3 mg/L), total organic nitrogen (2.4 mg/L), and 

dissolved (5.5 mg/L) and suspended organic carbon 

(12.0 mg/L). Field notes on this day indicated 

considerable amounts of large, woody debris consisting 

of trees, logs, and root balls being transported by the 

river. On two occasions, the water temperature 

measured at the time of sample collection was 18.0oC 

(degrees Celsius), equal to the Washington State 

standard for a Class A water body (see table 2). All 

nitrogen species analyzed were present in most 

samples; however, nitrate, with a median concentration 

of 0.35 mg/L, and total organic nitrogen, with a median 

of 0.13 mg/L, were the dominant nitrogen species 

(fig. 15).

Site 4: The water in Fishtrap was of fair quality. 

At times, iron, manganese, and fecal-indicator bacteria 

concentrations were large, and a number of pesticides 

and VOCs were present. In 11 samples, iron 

concentrations exceeded the USEPA SMCL of 

300 μg/L, and in 43 samples, manganese 

concentrations exceeded the SMCL of 50 μg/L (see 

table 2). In 14 samples collected from April 1997–

August 1998, concentrations of Escherichia coli

(E. coli) ranged from 87 to 5,900 col/100 mLs 

(colonies per 100 milliliters) (table 33, at back of 

report). Of these 14 samples, 8 had concentrations 

exceeding 298 col/100 mLs, USEPA’s (1986b) 

recommended single-sample concentration for 

moderate, full-body contact recreation. Suspendedsediment concentrations in samples were low, with 

90 percent of the concentrations less than 135 mg/L. 

Nitrate, with a median concentration of 2.8 mg/L, was 

the dominant nitrogen species (fig. 15).

Site 5: Water in the upper Nooksack was of 

generally high quality except at times when suspendedsediment concentrations were large. Ten percent of the 

samples had suspended-sediment concentrations 

greater than 1,900 mg/L and a maximum observed 

during the study of 3,210 mg/L on October 20, 1997. 

On one occasion, the concentration of dissolved 

oxygen measured at the time of sample collection was 

9.4 mg/L and did not meet the Washington State 

standard of 9.5 mg/L concentration for a Class AA 

water body (see table 2). Nitrate, with a median 

concentration of 0.21 mg/L and total organic nitrogen, 

with a median of 0.06 mg/L (estimated by logprobability regression, Helsel and Cohn, 1988), were 

the dominant nitrogen species (fig. 15). The sample 

collected near the peak of the hydrograph during the 

storm on October 30, 1997, contained the highest 

concentration of total phosphorus (1.8 mg/L), total 

organic nitrogen (2.3 mg/L), and suspended organic 

carbon (11.0 mg/L) observed at this site during the 

study. Considerable amounts of large, woody debris 

were transported by the river during this storm.
Surface-Water Quality of the Skokomish, Nooksack, and Green-Duwamish Rivers and Thornton Creek 41

0

12 24 MILES

12 24 KILOMETERS

0

N.F. Nooksack River sack River

M.F. Nooksack RiverM.F. Nooksack River

S.F. Nooksack River

.F. Nooksack River

Nooksack 

River

0

2

4

0

3

1

2

NITROGEN, 

IN MILLIGRAMS PER LITER (mg/L)

ORGANIC CARBON, 

IN MILLIGRAMS PER LITER

Nitrogen Phosphorus Nitrogen Phosphorus Nitrogen Phosphorus Suspended

Sediment

Organic

Carbon

Suspended

Sediment

Organic

Carbon

Suspended

Sediment

Organic

Carbon

0.08 80

Fishtrap Creek Fishtrap Creek Nooksack River, 

Brennan

Nooksack River, 

Brennan

Nooksack River, 

North Cedarville

Nooksack River, 

North Cedarville

MEDIAN SUSPENDED SEDIMENT

MEDIAN NUTRIENT COMPOSITION AND CARBON

0.02

0.04

0.06

0

20

40

60

SEDIMENT, 

IN MILLIGRAMS PER LITER

PHOSPHORUS, 

0

IN MILLIGRAMS PER LITER

Median less than 0.1 mg/L

122 ̊30' 122 ̊ 121 ̊30'

49 ̊

48 ̊

45'

EXPLANATION

EXPLANATION

Dissolved nitrite-plus-nitrate

Dissolved ammonia

Dissolved ammonia-plus-organic

Total ammonia-plus-organic

Total phosphorus

Dissolved phosphorus

Dissolved 

 orthophosphate

Suspended sediment

Dissolved organic carbon

Suspended organic carbon

Sample site

Land use/cover

Agriculture

Forest/natural cover/

 other

Urban/built up areas Basin boundary 

Streams

NITROGEN PHOSPHORUS

Site 5 - Nooksack River

North Cedarville

Na + K

Ca

Mg

Cl

SO4

HCO 3

Median milliequivalents

per liter

-1 0 1

Site 4 - Fishtrap Creek

Na + K

Ca

Mg

Cl

SO4

HCO 3

-1 0 1

Median milliequivalents

per liter

Site 3 - Nooksack River,

Brennan

Na + K

Ca

Mg

Cl

SO4

HCO 3

Median milliequivalents

per liter

-1 0 1

Figure 15. Median concentrations of nutrients, suspended sediment, organic carbon, and major ions in samples from the lower 

Nooksack River (site 3), Fishtrap Creek (site 4), and the upper Nooksack River (site 5) in the Puget Sound Basin study unit, Washington.
42 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

ND J FMAMJ J ASOND J FMAMJ J ASOND J FMA

0

40,000

20,000

ND J FMAMJ J ASOND J FMAMJ J ASOND J FMA

0

40,000

10,000

20,000

30,000

10,000

30,000

0.008

0.03

0.01

0.02

ND J FMAMJ J ASOND J FMAMJ J ASOND J FMA

1995 1996 1997 1998

0

40,000

10,000

20,000

30,000

0

3,000

1,000

2,000

0

3,000

1,000

2,000

0.008

0.03

0.01

0.02

0

2

1

Dissolved orthophosphate

Total nitrogen

Total phosphorus

Suspended sediment

Dissolved Orthophosphate

CONCENTRATION, IN MILLIGRAMS PER LITER

STREAMFLOW, IN CUBIC FEET PER SECOND

Total Nitrogen and

Total Phosphorus (in blue)

Suspended Sediment

 CONCENTRATION, 

IN MILLIGRAMS PER LITER

0.01

100

0.02

0.05

0.1

0.2

0.5

1

2

5

10

20

50

STREAMFLOW PERIODS

Oct.-

Feb.

Mar.-

July 

Aug.-

Sept.

Oct.-

Feb.

Mar.-

July 

Aug.-

Sept.

Oct.-

Feb.

Mar.-

July 

Aug.-

Sept.

EXPLANATION

Concentration percentiles

10th percentile

25th percentile

Median

75th percentile

90th percentile

Low-flow

High-flow

Transition

Daily streamflow

Minimum reporting level

Figure 16. Time series of streamflow and concentrations of total nitrogen, total phosphorus, dissolved orthophosphate phosphorus, and suspended 

sediment in samples, and concentrations by three streamflow periods, for the lower Nooksack River (site 3) in the Puget Sound Basin study unit, 

Washington.

(Truncated boxplots of concentration percentiles require a minimum of nine observations, otherwise concentrations are plotted as individual points. 

Censored data in the time-series graphs are shown as an open symbol. Boxplots are truncated at the minimum reporting level indicated by solid line.)
Surface-Water Quality of the Skokomish, Nooksack, and Green-Duwamish Rivers and Thornton Creek 43

0

700

200

400

600

1

8

2

4

6

0

700

200

400

600

0

0.5

0.2

0.4

0

700

200

400

600

350

100

200

300

0

Suspended sediment

Total nitrogen

Total phosphorus

Dissolved orthophosphate

CONCENTRATION, IN MILLIGRAMS PER LITER

STREAMFLOW, IN CUBIC FEET PER SECOND

 CONCENTRATION, 

IN MILLIGRAMS PER LITER

MAMJ J ASOND J FMAMJ J ASOND J FMA

MAMJ J ASOND J FMAMJ J ASOND J FMA

MAMJ J ASOND J FMAMJ J ASOND J FMA

1996 1997 1998

Total Nitrogen Suspended Sediment Dissolved Orthophosphate and

Total Phosphorus (in blue, right axis)

1

4

6

8

2

0.01

0.10

0.05

0.15

0

0.4

0.2

0.5

0

200

350

STREAMFLOW PERIODS

Oct.-

Mar.

Apr.-

July 

Aug.-

Sept.

Oct.-

Mar.

Apr.-

July 

Aug.-

Sept.

Oct.-

Mar.

Apr.-

July 

Aug.-

Sept.

EXPLANATION

Concentration percentiles

10th percentile

25th percentile

Median

75th percentile

90th percentile

Low-flow

High-flow

Transition

Daily streamflow

Minimum reporting level

Figure 17. Time series of streamflow and concentrations of total nitrogen, total phosphorus, dissolved orthophosphate phosphorus, and suspended 

sediment in samples, and concentrations by three streamflow periods, for Fishtrap Creek (site 4) in the Puget Sound Basin study unit, Washington.

(Truncated boxplots of concentration percentiles require a minimum of nine observations, otherwise concentrations are plotted as individual points. 

Censored data in the time-series graphs are shown as an open symbol. Boxplots are truncated at the minimum reporting level indicated by solid line.)
44 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

EXPLANATION

Concentration percentiles

10th percentile

25th percentile

Median

75th percentile

90th percentile

Low-flow

High-flow

Transition

Daily streamflow

Minimum reporting level

0

1

2

0.008

0.03

0.01

0.015

0

1,000

2,000

3,000

N D J F M A M J J A S O N D J F M N D J FM A AM J J A SO

N D J F M A M J J A S O N D J F M N D J FM A AM J J A SO

N D J F M A M J J A S O N D J F M N D J FM A AM J J A SO

CONCENTRATION, IN MILLIGRAMS PER LITER

STREAMFLOW, IN CUBIC FEET PER SECOND

 CONCENTRATION, 

IN MILLIGRAMS PER LITER

Total nitrogen

Dissolved orthophosphate

1995 1997 1998 1996

Total Nitrogen and

Total Phosphorus (in blue)

Dissolved Orthophosphate Suspended Sediment

Suspended sediment

Total phosphorus

STREAMFLOW PERIODS

Oct.-

Feb.

Mar.-

July 

Aug.-

Sept.

Oct.-

Feb.

Mar.-

July 

Aug.-

Sept.

Oct.-

Feb.

Mar.-

July 

Aug.-

Sept.

0

40,000

10,000

20,000

30,000

0

3

1

2

0

40,000

10,000

20,000

30,000

0.009

0.020

0.010

0.015

0

40,000

10,000

20,000

30,000

0

3,500

1,000

2,000

3,000

Figure 18. Time series of streamflow and concentrations of total nitrogen, total phosphorus, dissolved orthophosphate phosphorus, and suspended 

sediment in samples, and concentrations by three streamflow periods, for the upper Nooksack River (site 5) in the Puget Sound Basin study unit, 

Washington.

(Truncated boxplots of concentration percentiles require a minimum of nine observations, otherwise concentrations are plotted as individual points. 

Censored data in the time-series graphs are shown as an open symbol. Boxplots are truncated at the minimum reporting level indicated by solid line.)
Surface-Water Quality of the Skokomish, Nooksack, and Green-Duwamish RIvers and Thornton Creek 45

Nooksack River Basin Organic Chemistry

Pesticides detected in water samples from site 3 

and site 4 in the Nooksack River Basin were mostly 

herbicides, of which atrazine and simazine were most 

frequency detected. Of the 86 pesticides analyzed for, 

diazinon, carbaryl, ethoprophos, and malathion were 

among the few insecticides detected. Nearly all of the 

pesticides detected in samples from site 3 on the lower 

Nooksack, which integrates all the water in the basin, 

were also detected in samples from site 4 on Fishtrap 

Creek. However, fewer types of pesticides (only about 

one-half the number) were detected at site 3 than at site 

4. This suggests that, in addition to analyte losses due 

to processes such as transformation or sedimentation, 

pesticides reaching the river from tributaries like 

Fishtrap Creek or from adjacent land areas are diluted 

to concentrations below detection levels by the large 

volume of water in the river. The pesticides found most 

frequently in the Nooksack River Basin were consistent 

with pesticides found most frequently in study units 

across the nation and included atrazine, simazine, 

diazinon, and carbaryl (Larson and others, 1997). Most 

concentrations of the frequently detected pesticides in 

the Nooksack River Basin ranked within or below the 

middle 50-percent range of concentrations in mixed 

land-use river basins studied nationwide in 36 

NAWQA study units during 1991–98 (Ebbert and 

others, 2000).

Site 3: In the lower Nooksack, 16 pesticide 

compounds were found in samples collected from 

March 1996 through July 1997. The most frequently 

detected pesticide, atrazine, was in 15 of 22 samples at 

concentrations as high as 0.042 μg/L (table 10). The 

herbicides simazine and metolachlor were in the next 

most frequently detected pesticides. The insecticides 

diazinon, ethoprophos, and malathion were detected in 

one to two samples and in low concentrations near 

laboratory MRLs. Detections and higher 

concentrations of pesticides tended to coincide with the 

rainy season from October through February (fig. 19).

Table 9. Correlation between selected water-quality characteristics or chemical constituents and streamflow for the lower 

Nooksack River (site 3), Fishtrap Creek (site 4), and the upper Nooksack River (site 5) in the Puget Sound Basin study unit, 

Washington

Water-quality characteristic or 

chemical constituent

Kendall’s tau correlation coefficient

Lower Nooksack River 

(Site 3) Fishtrap Creek (Site 4) Upper Nooksack River (Site 5)

Specific electrical conductance -0.55 -0.49 -0.65

Dissolved solids -.47 -.47 -.53

Total nitrogen .37 .41 -.35

Dissolved nitrite-plus-nitrate nitrogen -.05 .12 .05

Total ammonia-plus-organic nitrogen .47 .70 .38

Dissolved ammonia-plus-organic nitrogen .06 .64 .18

Total phosphorus .67 .59 .58

Dissolved orthophosphate phosphorus .12 .44 <.01

Dissolved organic carbon .57 .58 .45

Suspended organic carbon .59 .49 .53

Suspended sediment .73 .62 .73

Bicarbonate -.57 -.70 -.61

Iron .37 .35 .49

Manganese .08 .21 .19
46 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

For example, metolachlor and deethylatrazine, 

compounds not detected in samples during low-flow 

conditions, were detected in samples during the wet 

season or during storm events. Atrazine and simazine 

varied somewhat directly with streamflows, but the 

relations were weak (Kendall’s τ = 0.4; p-values less 

than 0.05). The three pesticides found in samples from 

site 3 but not from site 4—fluometuron, MCPA, and 

norflurazon—each occurred in only one sample: 

MCPA in a June sample, and fluometuron and 

norflurazon together in a February sample. MCPA is 

used for a variety of agricultural and non-agricultural 

purposes; however, the purpose for which fluometuron 

(commonly used for weed control in cotton) is used in 

the PSB is unknown. Norflurazon is applied to 

blueberries or raspberries (see table 27). No pesticide 

concentration exceeded established drinking-water or 

aquatic-life criteria concentrations.

Table 10. Pesticides in water samples from the lower Nooksack River (site 3) in the Puget Sound Basin study unit, Washington

[Water-quality criteria – Drinking water: U.S. Environmental Protection Agency (1996). Aquatic organisms – Chronic (USGS): U.S. 

Geological Survey (1999a). Based on 22 samples collected March 1996 to July 1997; all concentrations are in micrograms per liter (μg/L); method 

detection limits are from reports by Zaugg and others (1995), Lindley and others (1996), Werner and others (1996), and U.S. Geological Survey 

National Water Quality Laboratory Technical Memorandums 98.03A and 96.06A; MCL, maximum contaminant level; HAL, Health advisory level; 

E, Estimated — a qualitative value that is less than the statistically determined method detection limit of lowest calibration standard; –, no value or 

data]

Pesticide Number of 

detections

Maximum 

concentration 

value

Median 

concentration 

detected

Method 

detection 

limit

Water-quality criteria

Drinking water Aquatic organisms (freshwater)

MCL HAL Acute Chronic Chronic 

(USGS)

Acetochlor 1 0.006 – 0.002 – – – – –

Atrazine 15 .042 0.016 .001 3 3 170 17 1.8

Deethylatrazine 6 E.005 E.004 .002 – – – – –

Diazinon 1 .005 – .002 – 0.6 20.16 20.04 0.08

Diuron 1 E.002 – .02 – 10 – – –

Ethoprophos 1 .019 – .003 – – – – –

Fluometuron 1 .08 – .035 – 90 – – –

Malathion 2 E.005 – .005 – 200 – 3.1 .1

Metolachlor 7 E.004 E.002 .002 – 70 – – 7.8

MCPA 1 E.02 – .17 – 10 – – 2.6

Napropamide 1 .006 – .003 – – – – –

Norflurazon 1 E.17 – .024 – – – – –

Pebulate 1 .085 – .004 – – – – –

Prometon 1 E.01 – .018 – 100 – – –

Simazine 9 .024 E.004 .005 4 4 1100 110 10

Tebuthiuron 1 .087 – .01 – 500 – – 1.6

Terbacil 1 E.092 – .007 – 90 – – –

1Norris and Dost (1992).

2Menconi and Cox (1994).

3U.S. Environmental Protection Agency (1998).
Surface-Water Quality of the Skokomish, Nooksack, and Green-Duwamish Rivers and Thornton Creek 47

E

E

E E E

E

E E E

E

E

E

E

E

E

E

E

E

CONCENTRATION, IN MICROGRAMS PER LITER

STREAMFLOW, IN CUBIC FEET PER SECOND

Atrazine

Deethylatrazine

Simazine

Metolachlor

M A M J J A S O N D J FM A M J J

M A M J J A S O N D J FM A M J J

M A M J J A S O N D J FM A M J J

M A M J J A S O N D J FM A M J J

1996 1997

0

40,000

10,000

20,000

30,000

0.5

0.001

0.002

0.005

0.01

0.02

0.05

0.1

0.2

0

0

40,000

10,000

20,000

30,000

0

0.03

0.01

0.02

40,000

10,000

20,000

30,000

0.0015

0.005

0.002

0.003

0.004

0

40,000

10,000

20,000

30,000

0.001

0.006

0.002

0.004

EXPLANATION

Streamflow

E Concentration estimated

Compound detected

Concentration less than 

 method reporting limit

Figure 19. Time series of streamflow and concentrations of selected pesticides detected in samples from the lower Nooksack River (site 3) in 

the Puget Sound Basin study unit, Washington.
48 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Out of 86 VOCs analyzed for, 15 were detected 

in samples from site 3 (table 11). Carbon disulfide was 

the most frequently detected compound with 15 

detections in 21 samples; however, none of the 

concentrations was above the 1999 LRLs. Only 

methylbenzene was detected at concentrations above 

the LRL. None of the concentrations of VOCs in the 

samples exceeded maximum concentrations specified 

in drinking-water or aquatic-life criteria. 

Methylbenzene concentrations showed some 

correspondence with the season of the year, with the 

highest concentrations observed during late fall and 

early winter (fig. 20), and did not relate to streamflow. 

No patterns with season or magnitude of streamflow 

could be discerned for the other 14 compounds 

detected in samples.

Table 11. Volatile organic compounds in water samples from the lower Nooksack River (site 3) in the Puget Sound Basin study unit, Washington

[Water-quality criteria – Drinking water: U.S. Environmental Protection Agency (1996). Based on 21 samples collected March 1996 to July 1997; all 

concentrations are in micrograms per liter (μg/L); MRL, method reporting level (Connor and others; 1998); LRL, laboratory reporting level; MCL, maximum 

contaminant level; HAL, health advisory level; E, Estimated–a qualifier for an analytical result based on the long-term method detection level, laboratory 

reporting level, and lowest calibration standard (Childress and others, 1999); –, no value or data]

Volatile 

organic compound

Number

of 

detections

Percentage 

of detections above 

1999 LRL and 

(number)

Maximum 

concentration value

Median 

concentration 

detected

MRL

(1999 LRL)

Water-quality criteria

Drinking water

Aquatic 

organisms 

(freshwater)

MCL HAL Chronic

1,2,4-Trimethylbenzene 3 0 E0.01 E0.008 0.056 (0.056) – – –

1,2-Dimethylbenzene (o-Xylene) 3 0 E.01 E.01 .064 (.06) 10,000 10,000 –

1,3-plus-1,4-Dimethylbenzene

(m,p-Xylene)

5 0 E.03 E.01 .064 (.06) 10,000 10,000 –

2-Butanone (Methyl ethyl ketone) 2 0 E.3 – 1.65 (1.6) – – –

1-Isopropyl-4-methylbenzene

 (p-Isopropyltoluene)

4 0 E.007 E.005 .11 (.11) – – –

Acetone 7 0 E2.8 E1.3 4.904 (5) – – –

Benzene 1 0 E.04 – .032 (.1) 5 – 1370

Bromoform 1 0 E.008 – .104 (.1) 100 – –

Carbon disulfide 15 0 E.1 E.01 .08 (.37) – – –

Chloromethane (Methyl chloride) 11 0 E.08 E.04 .254 (.25) – 3 –

Ethenylbenzene (Styrene) 1 0 E.001 – .042 (.042) 100 100 –

Ethylbenzene 3 0 E.01 E.009 .03 (.03) 700 700 190

Methylbenzene (Toluene) 14 79 (11) .34 .09 .038 (.05) 1,000 1,000 12

Naphthalene 1 0 E.008 – .25 (.25) – 20 11.1

Trichloromethane (Chloroform) 3 0 E.007 E.007 .052 (.052) 100 – 11.8

1Environment Canada, 1999
Surface-Water Quality of the Skokomish, Nooksack, and Green-Duwamish Rivers and Thornton Creek 49

MAMJ J ASOND J FMAMJ J

0

0.5

0.1

0.2

0.3

0.4

0

35,000

5,000

10,000

15,000

20,000

25,000

30,000

Methylbenzene (Toluene)

MAMJ J ASOND J FMAMJ J

1996 1997

0.005

1

0.007

0.01

0.02

0.03

0.04

0.05

0.07

0.1

0.2

0.3

0.4

0.5

0.7

CONCENTRATION, IN MICROGRAMS PER LITER

0

35,000

5,000

10,000

15,000

20,000

25,000

30,000

STREAMFLOW, IN CUBIC FEET PER SECOND

Carbon disulfide

Streamflow

Compound detected

Compound detected at an

 estimated concentration

 below the 1999 LRL

Compound not detected

1999 Laboratory Reporting 

 Level (LRL)

EXPLANATION

Figure 20. Time series of streamflow and concentrations of selected volatile organic compounds in samples from the 

lower Nooksack River (site 3) in the Puget Sound Basin study unit, Washington.
50 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Site 4: In Fishtrap, 29 pesticides were found in 

samples collected from March 1996 through 

September 1997. The herbicides atrazine and simazine 

and the transformation product deethylatrazine were 

detected most frequently, each found in 31 of 32 

samples (table 12). Median concentrations of these 

three compounds were 0.056, 0.017, and 0.006 μg/L, 

respectively (table 12). The herbicides prometon and 

tebuthiuron were the next most frequently detected 

pesticides. Of the 29 pesticides detected, 7 were 

insecticides—carbaryl, carbofuran, diazinon, 

ethoprophos, malathion, oxamyl, and propargite. 

Diazinon was detected in 44 percent of the samples in 

concentrations ranging from 0.004 to 0.133 μg/L. Five 

samples had diazinon concentrations exceeding 

0.04 μg/L, a limit recommended by Menconi and Cox 

(1994) for the protection of aquatic life (see table 2). 

Carbaryl was detected in three samples and all three 

had concentrations exceeding 0.017 μg/L, a limit 

recommended by Norris and Dost (1992) for the 

protection of aquatic life.

Most pesticide detections and concentrations in 

samples at site 4 did not correspond to streamflow. 

Atrazine, deethylatrazine, and simazine concentrations 

tended to vary directly with streamflow, but the 

relations were weak (Kendall’s τ ranged from 0.3 to 

0.4; p-values less than 0.01). The timing of applications 

appeared to influence detections and concentrations of 

certain pesticides such as diazinon. Diazinon was often 

detected, sometimes in high concentrations, from 

approximately April through June, corresponding to 

the season when application rates are generally highest. 

Some of the largest concentrations for pesticides such 

as simazine, prometon, and diazinon were in samples 

collected during storm runoff events. Perhaps because 

of different application procedures or treated land 

areas, tebuthiuron and oxamyl were detected in several 

samples collected during May–July 1996, but were not 

in the few samples during May–July 1997 (fig. 21).

Eighteen VOCs were detected at site 4 (table 13). 

Chloromethane was most frequently observed with 22 

detections in 32 samples, but all of these detections 

were below the 1999 LRL. Six compounds—

chlorobenzene, ethylbenzene, dichloromethane, 

methylbenzene, 1,3-plus-1,4-dimethylbenzene (m,pxylene), and 1,2-dimethylbenzene (o-xylene)—were 

detected at concentrations above the LRL. Of these six 

compounds, methylbenzene was detected most 

frequently (85 percent of the 20 samples with 

detections) at concentrations above the LRL. The 

remaining five compounds were detected only once 

each at a concentration above the LRL. None of the 

VOC concentrations was above any of the established 

drinking-water standards or aquatic-life criteria. The 

presence of methylbenzene, methyl tert-butyl ether 

(MTBE), and 1,3-plus-1,4-dimethylbenzene in surface 

water tended to correspond with elevated streamflows 

between October and March (fig. 22). These 

compounds generally were not detected during 

baseflow conditions between June and September 

except for one low-level detection of MTBE. MTBE is 

used year-round in Canada as a fuel-additive to 

gasoline (Duncan Ferguson, B.C. Environment, oral 

commun., 1999), but it is likely that the detections only 

appear during the winter, because the solubility of 

MTBE increases with decreasing temperatures (Lopes 

and Bender, 1998).
Surface-Water Quality of the Skokomish, Nooksack, and Green-Duwamish RIvers and Thornton Creek 51

Table 12. Pesticides in water samples from Fishtrap Creek (site 4) in the Puget Sound Basin study unit, Washington

[Water-quality criteria – Drinking water: U.S. Environmental Protection Agency (1996). Aquatic organisms – Chronic (USGS): U.S. 

Geological Survey (1999a). Based on 32 samples collected March 1996 to September 1997; all concentrations are in micrograms per liter (μg/L); 

bold type indicates value above aquatic life criterion; method detection limits are from reports by Zaugg and others (1995), Lindley and others 

(1996), Werner and others (1996), and U.S. Geological Survey National Water Quality Laboratory Technical Memorandums 98.03A and 96.06A; 

MCL, maximum contaminant level; HAL, Health advisory level; E, Estimated–a qualitative value that is less than the statistically determined 

method detection limit or lowest calibration standard; –, no value or data]

Pesticide Number of 

detections

Maximum 

concentration 

value

Median 

concentration 

detected

Method 

detection 

limit

Water-quality criteria

Drinking water Aquatic organisms (freshwater)

MCL HAL Acute Chronic Chronic 

(USGS)

Acetochlor 4 0.137 0.010 0.002 – – – – –

Alachlor 2 .19 – .002 2 – – – –

Atrazine 31 1.4 .056 .001 3 3 170 17 1.8

Carbaryl 3 E.133 E.074 .003 – 700 10.17 10.017 0.2

Carbofuran 1 E.005 – .003 40 40 1.8

2,4-D 1 .32 – .15 70 70 110 11 4

DCPA 2 E.003 – .002 – – – – –

Deethylatrazine 31 E.014 E.006 .002 – – – – –

Diazinon 14 .113 .013 .002 – 0.6 2.16 2.04 .08

Dicamba 1 E.03 – .035 – 200 1390 139 10

Dichlobenil 2 E.01 – 1.2 – – – – –

Diuron 2 .44 – .02 – 10 – – –

EPTC 6 .026 .005 .002 – – – – –

Ethoprophos 2 .013 – .003 – – – – –

Linuron 3 .32 .12 .002 – – – – 7

Malathion 1 .025 – .005 – 200 – 3.1 .1

Metolachlor 14 .037 .004 .002 – 70 – – 7.8

Metribuzin 2 .025 – .004 – 100 – – 1.0

Molinate 1 .005 – .004 – – – – –

Napropamide 7 .1 .03 .003 – – – – –

Oryzalin 1 .04 – .31 – – – – –

Oxamyl 11 .16 .12 .018 200 200 – – –

Pebulate 2 .08 – .004 – – – – –

Prometon 22 .087 E.006 .018 – 100 – – –

Pronamide 1 E.004 – .003 – 50 – – –

Simazine 31 1.0 .017 .005 4 4 1100 110 10

Tebuthiuron 21 .095 .012 .01 – 500 – – 1.6

Terbacil 2 E.077 – .007 – 90 – – –

Trifluralin 1 .005 – .002 – 5 – – .2

1Norris and Dost (1992).

2Menconi and Cox (1994).

3U.S. Environmental Protection Agency (1998).
52 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

E

E

E

E E

E

E

E E E E E

E E E E

E

E

E

E

E

Simazine

Deethylatrazine

Atrazine

0

200

400

600

0.003

10

0.005

0.01

0.02

0.05

0.1

0.2

0.5

1

2

5

0

200

400

600

0.003

0.2

0.004

0.005

0.007

0.01

0.02

0.03

0.04

0.05

0.07

0.1

0

200

400

600

0.001

0.020

0.005

0.010

0.015

0

200

400

600

3

0.001

0.002

0.005

0.01

0.02

0.05

0.1

0.2

0.5

1

2

Metolachlor

M A MJ J A S ON D J FMA M J J A S

M A MJ J A S ON D J FMA M J J A S

M A MJ J A S ON D J FMA M J J A S

M A MJ J A S ON D J FMA M J J A S

1996 1997

CONCENTRATION, IN MICROGRAMS PER LITER

STREAMFLOW, IN CUBIC FEET PER SECOND

EXPLANATION

Streamflow

E Concentration estimated

Compound detected

Concentration less than 

 method reporting limit

Figure 21. Time series of streamflow and concentrations of selected pesticides detected in samples from Fishtrap Creek (site 4) in the Puget 

Sound Basin study unit, Washington.
Surface-Water Quality of the Skokomish, Nooksack, and Green-Duwamish Rivers and Thornton Creek 53

E

E

E

E

E

E

E

E E

E E

E

0

200

400

600

0.003

0.2

0.004

0.005

0.007

0.01

0.02

0.03

0.04

0.05

0.07

0.1

0

200

400

600

0.0015

0.5

0.002

0.005

0.01

0.02

0.05

0.1

0.2

0

200

400

600

0

0.20

0.05

0.10

0.15

0

200

400

600

0.002

0.2

0.005

0.01

0.02

0.05

0.1

Diazinon

Napropamide

Tebuthiuron

Oxamyl

M A MJ J A S ON D J FMA M J J A S

M A MJ J A S ON D J FMA M J J A S

M A MJ J A S ON D J FMA M J J A S

M A MJ J A S ON D J FMA M J J A S

1996 1997

CONCENTRATION, IN MICROGRAMS PER LITER

STREAMFLOW, IN CUBIC FEET PER SECOND

EXPLANATION

Streamflow

E Concentration estimated

Compound detected

Concentration less than 

 method reporting limit

Figure 21. —Continued.
54 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Table 13. Volatile organic compounds in water samples from Fishtrap Creek (site 4) in the Puget Sound Basin study unit, Washington

[Water-quality criteria – Drinking water: U.S. Environmental Protection Agency (1996). Based on 32 samples collected between March 1996 to September 

1997; all concentrations are in micrograms per liter (μg/L); MRL, method reporting level (Connor and others; 1998); LRL, laboratory reporting level; MCL, 

maximum contaminant level; HAL, health advisory level; E, Estimated–a qualifier for an analytical result based on the long-term method detection level, 

laboratory reporting level, and lowest calibration standard (Childress and others, 1999); –, no value or data.]

Volatile

organic compound

Number of 

detections

Percentage of 

detections 

above 1999 

LRL and 

(number)

Maximum 

concentration value

Median 

concentration 

detected

MRL

(1999 LRL)

Water-quality criteria

Drinking water

Aquatic 

organisms 

(freshwater)

MCL HAL Chronic

1,2,4-Trimethylbenzene 4 0 E0.02 0.0145 0.056 (0.056) – – –

1,2-Dichloropropane 7 0 E.03 E.02 .068 (.068) 5 – –

1,2-Dimethylbenzene

(o-Xylene)

1 100 (1) E.09 – .064 (.06) 10,000 10,000 –

1,3-plus-1,4-Dimethylbenzene 

(m,p-Xylene)

5 20 (1) E.1 E.02 .064 (.06) 10,000 10,000 –

2-Butanone (Methyl ethyl ketone) 7 0 E1.4 E.6 1.65 (1.6) – – –

1-Isopropyl-4-methylbenzene 

(p-Isopropyltoluene)

1 0 E.006 – .11 (.11) – – –

Acetone 8 0 E3.2 1.8 4.904 (5) – – –

Benzene 2 0 E.1 – .032 (.1) 5 – 1370

Carbon disulfide 14 0 E.03 E.015 .08 (.37) – – –

Chlorobenzene 1 100 (1) E.03 – .028 (.028) 100 100 11.3

Chloromethane (Methyl chloride) 22 0 E.1 E.05 .254 (.25) – 3 –

Dichloromethane (Methylene 

chloride)

2 50 (1) E1.6 – .382 (.38) 5 – 198.1

Diethyl ether 1 0 E.09 – .17 (.17) – – –

Ethenylbenzene (Styrene) 1 0 E.01 – .042 (.042) 100 100 –

Ethylbenzene 3 33 (1) E.06 E.003 .03 (.03) 700 700 190

Methylbenzene (Toluene) 20 85 (17) .35 E.01 .038 (.05) 1,000 1,000 12

Methyl tert-butyl ether (MTBE) 6 0 E.09 E.035 .054 (.17) – 20 –

Trichloromethane (Chloroform) 9 0 E.01 E.008 .052 (.052) 100 – 11.8

1Environment Canada (1999).
Surface-Water Quality of the Skokomish, Nooksack, and Green-Duwamish Rivers and Thornton Creek 55

MAMJ J ASOND J FMAMJ J AS

0

0.5

0.1

0.2

0.3

0.4

0

800

200

400

600

Methylbenzene (Toluene)

MAMJ J ASOND J FMAMJ J AS

0

800

200

400

600

STREAMFLOW, IN CUBIC FEET PER SECOND

0

0.20

0.05

0.10

0.15

CONCENTRATION, IN MICROGRAMS PER LITER

Methyl tert-butyl ether (MTBE)

MAMJ J ASOND J FMAMJ J AS

1996 1997

0

800

200

400

600

0

0.12

0.02

0.04

0.06

0.08

0.10

1,3- plus-1,4-Dimethylbenzene (m,p-Xylene)

Streamflow

Compound detected

Compound detected at an

 estimated concentration

 below the 1999 LRL

Compound not detected

1999 Laboratory Reporting 

 Level (LRL)

EXPLANATION

Figure 22. Time series of streamflow and concentrations of selected volatile organic compounds detected in samples from 

Fishtrap Creek (site 4) in the Puget Sound Basin study unit, Washington.
56 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Green-Duwamish River Basin

The Green-Duwamish River originates as the 

Green River within the Cascade Range physiographic 

province and flows about 24 miles through forested 

mountainous terrain into Howard A. Hanson Reservoir, 

which is formed by Howard A. Hanson Dam at river 

mile 64.5 (see fig. 1). Below the dam at about river 

mile 59, the Green River enters the Puget Sound 

Lowlands physiographic province. The remaining 

48 miles of the Green River drains the Puget Sound 

Lowlands and flows through a region of increasingly 

intensive agricultural and urban land use. At river mile 

11, the Green becomes the Duwamish River, which 

flows through some of the more industrialized areas of 

the study unit and then enters Puget Sound. Five basic 

fixed sites were established in the Green-Duwamish 

River Basin (fig. 1 and table 1): Site 6 on the 

Duwamish, site 7 on Springbrook Creek, site 8 on Big 

Soos Creek, site 9 on Newaukum Creek, and site 10 on 

the upper Green River. Site 6 is an integrator of the 

quality of water from the Green-Duwamish River 

Basin, consisting of high-altitude mountains with 

snowfields and forests, regions with a few small 

population centers below the dam, and agricultural, 

commercial/industrial, and residential land uses in the 

Lowlands. The river at site 6 drains an area of 461 mi2. 

Site 7 is an indicator of commercial/industrial and 

residential urban land use within a drainage area of 

20 mi2. Site 8 is an indicator of an urban/suburban 

basin rapidly changing from a more rural and forested 

basin. Big Soos at site 8 drains an area of 66.7 mi2. Site 

9 is an indicator of a largely agricultural basin 

consisting mostly of dairy, cattle, and small horse 

farms, but also with a fair amount of suburban 

development within a drainage area of 27.4 mi2. Site 10 

is an indicator of water quality from forest practices 

and from undisturbed regions of the upper Green River 

Basin. The river at site 10 drains an area of 16.5 mi2.

Green-Duwamish River Basin Hydrology

Annual streamflows for water years 1996 and 

1997 were greater than mean annual flows for the 

periods of record at sites 6, 8, 9, and 10 (see fig. 4). 

Annual flows for 1998 were less than the mean annual 

flows, but were within the interquartile range of flows 

at these four sites. No long-term record existed at 

Springbrook (site 7) for comparing annual or daily 

flows observed during the study. Flow variability in 

Springbrook as it related to climate during the 

sampling period is illustrated by the daily-streamflow 

hydrograph for this study. Precipitation recorded at 

SeaTac International Airport in amounts above normal 

from October 1995 through February 1996 (see fig. 3) 

contributed to above-normal streamflows from 

November 1995 through February 1996. The storms in 

early February 1996 generated the highest daily flows 

observed during the 3-year study period at sites 6–9 

(figs. 23, 24, 25, and 26) and the second highest daily 

flow observed at site 10 (fig. 27). Except for some high 

flows caused by late April–early May storms, daily 

flows from spring through fall were mostly within the 

interquartile range of flows for each site except at site 

10. At site 6, relatively normal flows were due in part 

to flow regulation at Howard A. Hanson Dam. At site 

10, summer daily flows were low, in that most were at 

or below the 25th percentile in magnitude (fig. 27).

In water year 1997, streamflows were mostly 

normal or above normal. At the end of December, a 

storm brought freezing rain and snow to the lower 

elevations. The Seattle-Tacoma area received about 

2 feet of snow. Following the snowfall, warmer 

temperatures and heavy rain from December 30 

through January 1, known locally as the New Year’s 

Day 1997 storm, melted the snow and raised several 

lowland streams to flood levels. Rainfall in amounts up 

to more than twice normal during December 1996 and 

during the regional storm of March 18–20, 1997, 

generated high flows at all five sites. Most daily 

streamflows from late spring into early fall were above 

the 75th quartile because of above-normal rainfall 

amounts.

Daily streamflows continued to be above normal 

at the start of water year 1998. From winter into early 

spring 1998, daily flows were mostly within the 

interquartile range. With precipitation only 40 percent 

of normal for the month of April, daily flows dropped 

below normal and remained below the 25th quartile to 

the end of the study period at the end of April 1998.

Magnitudes of streamflows at the time of sample 

collection at sites 6, 8, 9, and 10 spanned a wide range, 

from high flows that are exceeded less than 1 percent of 

the time to low flows that are exceeded more than 

90 percent of the time (figs. 25, 25, 26, and 27). Sample 

collections were fairly evenly distributed over the range 

of flows that can occur at these sites. Two sets of storm 
Surface-Water Quality of the Skokomish, Nooksack, and Green-Duwamish Rivers and Thornton Creek 57

samples (one near the hydrograph peak and one on the 

falling limb of the hydrograph) were collected at 

sites 6–9 during the New Year’s Day 1997 storm, 

which resulted in the second highest daily flows 

observed at these four sites during the study period. 

Samples were collected at all five sites in the basin 

during the March 1997 regional storm.

Site 6: For the Duwamish River, estimated 

average annual streamflow based on 32 years of record 

at the gage upstream (12113000, Green River near 

Auburn) was 1,480 ft3/s, which was exceeded by the 

annual flows for 1996 and 1997, but not for 1998. 

Estimated annual flows for water years 1996, 1997, and 

1998 were 2,060, 2,090, and 1,220 ft3/s, respectively. 

In water year 1996, samples were collected on 

February 8, 1996, when the highest daily flow observed 

at this site during the study, more than 11,000 ft3/s, 

occurred. In water year 1997, the New Year’s Day 1997 

storm brought the river to a little over 9,000 ft3/s by 

January 2, 1997.

Site 7: For Springbrook, the average streamflow 

estimated using 3 years of record at two upstream 

gages (12113346, Springbrook Creek near Orillia, and 

12113349, Mill Creek near Mouth) was 42 ft3/s. 

Estimated annual flows for water years 1996 and 1997 

were 48 and 45 ft3/s, respectively. The 1998 estimated 

flow was 33 ft3/s. The February 1996 storms brought 

the creek to about 820 ft3/s, the maximum daily flow 

observed during the study. The New Year’s Day 1997 

storm event produced the second highest daily flow, 

530 ft3/s, for the study period.

Site 8: Mean annual streamflow for Big Soos for 

32 years of record was 125 ft3/s, which was exceeded 

by annual flows of 168 and 195 ft3/s for water years 

1996 and 1997, respectively. The 1998 annual flow was 

110 ft3/s. The February 1996 storm brought the creek 

to 3,580 ft3/s, its maximum recorded daily flow for the 

period of record. The daily flow of 1,370 ft3/s during 

the New Year’s Day 1997 storm was a peak discharge 

for 1997.

Site 9: Mean annual streamflow for Newaukum 

for 52 years of record was 60 ft3/s, which was exceeded 

by annual flows of 80.8 and 83.7 ft3/s for water years 

1996 and 1997, respectively. The annual flow for 1998 

was 51.9 ft3/s. The heavy rainstorms in February 1996 

resulted in a flow of 1,670 ft3/s on February 9, which 

was the highest recorded daily flow for the period of 

record at this site. Daily flow during the New Year’s 

Day 1997 storm reached a maximum of 679 ft3/s.

Site 10: Although the period of record for site 10 

is only 6 years, annual and daily flows were compared 

to the mean annual and the interquartile range of flows 

for this study. Based on 6 years of record, the mean 

annual streamflow for the upper Green was 57.8 ft3/s, 

which was exceeded by the annual flows for 1996 and 

1997, but not for 1998. Annual flows for water years 

1996, 1997, and 1998 were 79.0, 81.4, and 50.1 ft3/s, 

respectively. Storms in November and February 

brought the river to more than 1,000 ft3/s, the 

maximum recorded daily flow for the period of record. 

In water year 1997, above-normal precipitation resulted 

in a flow of 465 ft3/s, the second highest daily flow 

observed at this site during the study. One storm 

sample collected early in water year 1998 (on 

October 30, 1997) was during a storm that generated 

a peak discharge for 1997.
58 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Streamflow duration, 1936-98

Instantaneous streamflow at sample collection,

(February 1996-April 1998)

Daily streamflow

Instantaneous streamflow at

sample collection,

February 1996-April 1998

75th quartile Interquartile range

for 1936-98 25th quartile

0.01 0.1 1 2 5 10 20 30 40 50 60 70 80 90 95 98 99 99.9

PERCENT

100

100,000

200

300

400

500

700

1,000

2,000

3,000

4,000

5,000

7,000

10,000

20,000

30,000

40,000

50,000

70,000

STREAMFLOW, IN CUBIC FEET PER SECOND

OND JFMAM J JASONDJFMAM J JASONDJ FMAM J JAS

100

30,000

200

300

400

500

700

1,000

2,000

3,000

4,000

5,000

7,000

10,000

20,000

STREAMFLOW, IN CUBIC FEET PER SECOND

1995 1996 1997 1998

DAILY AND INSTANTANEOUS STREAMFLOW AND INTERQUARTILE RANGE OF MEAN DAILY STREAMFLOWS

PERCENTAGE OF TIME STREAMFLOWS ARE EQUALED OR EXCEEDED AND INSTANTANEOUS STREAMFLOW

Figure 23. Daily and instantaneous streamflow at the time of sample collection, interquartile range of mean daily streamflows for the 

period of record, and percentage of time streamflows are equaled or exceeded at the Duwamish River (site 6) in the Puget Sound Basin 

study unit, Washington.
Surface-Water Quality of the Skokomish, Nooksack, and Green-Duwamish RIvers and Thornton Creek 59

Streamflow duration, 1995-98

Instantaneous streamflow at sample collection,

(December 1995-April 1998)

Daily streamflow

Instantaneous streamflow at

sample collection,

December 1995-April 1998

75th quartile Interquartile range

for 1995-98 25th quartile

0.01 0.1 1 2 5 10 20 30 40 50 60 70 80 90 95 98 99 99.9

1

1,000

2

3

4

5

7

10

20

30

40

50

70

100

200

300

400

500

700

STREAMFLOW, IN CUBIC FEET PER SECOND STREAMFLOW, IN CUBIC FEET PER SECOND

OND JFMAMJJASOND J F MAMJJASON DJFMAMJJAS

1995 1996 1997 1998

1

1,000

2

3

4

5

7

10

20

30

40

50

70

100

200

300

400

500

700

PERCENT

DAILY AND INSTANTANEOUS STREAMFLOW AND INTERQUARTILE RANGE OF MEAN DAILY STREAMFLOWS

PERCENTAGE OF TIME STREAMFLOWS ARE EQUALED OR EXCEEDED AND INSTANTANEOUS STREAMFLOW

Figure 24. Daily and instantaneous streamflow at the time of sample collection, interquartile range of mean daily streamflows for 

the period of record, and percentage of time streamflows are equaled or exceeded at Springbrook Creek (site 7) in the Puget Sound 

Basin study unit, Washington.
60 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

10

20

30

40

50

70

200

100

300

400

500

700

1,000

2,000

3,000

4,000

5,000

STREAMFLOW, IN CUBIC FEET PER SECOND

STREAMFLOW, IN CUBIC FEET PER SECOND

100

200

300

400

500

700

1,000

2,000

3,000

4,000

5,000

10

20

30

40

50

70

0.01 0.1 1 2 5 10 20 30 40 50 60 70 80 90 95 98 99 99.9 99.99

OND JFMAMJJASONDJFMAM J J ASONDJFMAMJJAS

1995 1996 1997 1998

PERCENT

Daily streamflow

Instantaneous streamflow at 

 sample collection, 

 December 1995-April 1998

75th quartile Interquartile range

25th quartile for 1961-98

EXPLANATION

Streamflow duration, 1961-98

Instantaneous streamflow at sample collection,

 (December 1995-April 1998)

DAILY AND INSTANTANEOUS STREAMFLOW AND INTERQUARTILE RANGE OF MEAN DAILY STREAMFLOWS

PERCENTAGE OF TIME STREAMFLOWS ARE EQUALED OR EXCEEDED AND INSTANTANEOUS STREAMFLOW

Figure 25. Daily and instantaneous streamflow at the time of sample collection, interquartile range of mean daily 

streamflows for the period of record, and percentage of time streamflows are equaled or exceeded at Big Soos Creek (site 8) 

in the Puget Sound Basin study unit, Washington.
Surface-Water Quality of the Skokomish, Nooksack, and Green-Duwamish RIvers and Thornton Creek 61

10

20

30

40

50

70

100

200

300

400

500

700

1,000

2,000

STREAMFLOW, IN CUBIC FEET PER SECOND STREAMFLOW, IN CUBIC FEET PER SECOND

5

7

10

20

30

40

50

70

100

200

300

400

500

700

1,000

2,000

0.01 0.1 1 2 5 10 20 30 40 50 60 70 80 90 95 98 99 99.9 99.99

O N DJFMAMJJASONDJFMAMJJASONDJFMA MJJAS

1995 1996 1997 1998

Streamflow duration, 1946-98

Instantaneous streamflow at sample collection,

 (December 1995-April 1998)

Daily streamflow

Instantaneous streamflow at 

 sample collection, 

 December 1995-April 1998

75th quartile Interquartile range

25th quartile for 1946-98

EXPLANATION

DAILY AND INSTANTANEOUS STREAMFLOW AND INTERQUARTILE RANGE OF MEAN DAILY STREAMFLOWS

PERCENTAGE OF TIME STREAMFLOWS ARE EQUALED OR EXCEEDED AND INSTANTANEOUS STREAMFLOW

PERCENT

Figure 26. Daily and instantaneous streamflow at the time of sample collection, and the interquartile range of mean daily 

streamflows for the period of record, and percentage of time streamflows are equaled or exceeded at Newaukum Creek 

(site 9) in the Puget Sound Basin study unit, Washington.
62 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

2

3

1

2,000

4

5

7

10

20

30

40

50

70

100

200

300

400

500

700

1,000

2

3

1

2,000

4

5

7

10

20

30

40

50

70

100

200

300

400

500

700

1,000

STREAMFLOW, IN CUBIC FEET PER SECOND STREAMFLOW, IN CUBIC FEET PER SECOND

0.01 0.1 1 2 5 10 20 30 40 50 60 70 80 90 95 98 99 99.9 99.99

OND JFMAM J J ASONDJ F M A M J J A S O N DJ F M A M J J A S

1995 1996 1997 1998

DAILY AND INSTANTANEOUS STREAMFLOW AND INTERQUARTILE RANGE OF MEAN DAILY STREAMFLOWS

PERCENTAGE OF TIME STREAMFLOWS ARE EQUALED OR EXCEEDED AND INSTANTANEOUS STREAMFLOW

PERCENT

Streamflow duration, 1993-98

Instantaneous streamflow at sample collection,

 (March 1996-April 1998)

Daily streamflow

Instantaneous streamflow at 

 sample collection, 

 March 1996-April 1998

75th quartile Interquartile range

25th quartile for 1993-98

EXPLANATION

Figure 27. Daily and instantaneous streamflow at the time of sample collection, and the interquartile range of mean daily 

streamflows for the period of record, and percentage of time streamflows are equaled or exceeded at the upper Green 

River (site 10) in the Puget Sound Basin study unit, Washington.
Surface-Water Quality of the Skokomish, Nooksack, and Green-Duwamish Rivers and Thornton Creek 63

Green-Duwamish River Basin Water Quality

Forty-two water samples from site 6 (table 14), 

37 samples from site 7 (table 15), 36 samples from site 

8 (table 16) and site 9 (table 17), and 24 samples from 

site 10 (table 18) were collected for the analysis of 

physical properties, field parameters, and 

concentrations of inorganic constituents, organic 

carbon, and suspended sediment. At site 6, 24 samples 

were collected for pesticide and VOC analyses; at site 

7, 2 samples collected during a storm were analyzed for 

pesticides and VOCs. With some exceptions, 

particularly at sites 6 and 7, most applicable standards 

and criteria for drinking water, ambient water quality 

for beneficial uses, and the protection of aquatic life 

were met by the water quality at the sites in this basin. 

In samples from sites 6 and 7, iron and manganese 

concentrations often exceeded USEPA SMCLs for 

drinking water.

High-quality water from headwaters in the 

mountains is the basis of the dilute water chemistry 

observed in samples from the mainstem Green and 

Duwamish Rivers. The chemically dilute nature of the 

water quality was indicated by the conductivity and 

dissolved-solids concentrations. As the river flows 

from site 10 on the upper Green downstream to site 6, 

there was an increasing trend in major-ion and nutrient 

concentrations, as indicated by the medians (fig. 28). In 

samples from site 6, median conductivity and 

dissolved-solids concentration were 87 μS/cm and 

62 mg/L, respectively (table 14), and from site 10, 

median conductivity and dissolved-solids 

concentration were 41 μS/cm and 36 mg/L, 

respectively (table 18). On the basis of median 

concentrations, calcium and bicarbonate were the 

dominant cation and anion, respectively, making up the 

dissolved solids at sites 6 and 10 (fig. 28). Nutrient 

concentrations were moderately low at site 6, with at 

least 10 percent of organic nitrogen and phosphorus 

values below laboratory MRLs. However, 25 percent of 

the total phosphorus concentrations were greater than 

0.1 mg/L, USEPA’s (1986a) desired goal to prevent 

nuisance plant growth in streams (table 14). At site 10, 

most organic-nitrogen concentrations and half of the 

total and dissolved phosphorus concentrations were 

below laboratory MRLs (table 18).

Concentrations of water-chemistry constituents 

were higher at sites 7, 8, and 9 on lowland tributaries to 

the Green-Duwamish than in the mainstem river. The 

constituent concentrations at these sites ranged from 

moderately high at site 7 to moderately low at sites 8 

and 9. At site 7, the median conductivity was 

242 μS/cm and the median dissolved-solids 

concentration was 152 mg/L (table 15). At sites 8 and 

9, median conductivities were less than 150 μS/cm and 

median dissolved-solids concentrations were less than 

110 mg/L (tables 16 and 17). On the basis of median 

concentrations at site 7, the dominant anion was 

bicarbonate; the cations were a mix of sodium, 

calcium, and magnesium in nearly equal proportions 

(fig. 28). At sites 8 and 9, the dominant cation was 

calcium and the dominant anion was bicarbonate.

Nutrient concentrations were moderately high in 

samples from sites 7 and 9, with more than 75 percent 

of the values for organic nitrogen and phosphorus 

above laboratory MRLs. In addition, at least 50 percent 

of the total phosphorus concentrations at both of these 

sites were greater than 0.1 mg/L, USEPA’s (1986a) 

desired goal to prevent nuisance plant growth in 

streams. Nutrient concentrations at site 8 were 

moderately low, with at least 10 percent of organicnitrogen and phosphorus concentrations below 

laboratory MRLs. Ground-water discharge and human 

agricultural and urban land-use activities are the likely 

sources of chemical constituents that contribute to the 

more concentrated water chemistry in the tributaries.

In addition to monthly routine samples, from 17 

to 36 percent of the samples collected at each of the 

five sites were targeted to stormflow events. The 

highest concentrations of nitrogen, phosphorus, and 

suspended sediment tended to occur in samples 

collected on the rising limb or near the peak of the 

hydrograph during runoff events (figs. 29, 30, 31, 32,

and 33). Kendall’s τ, which ranged from 0.4 to 0.6 

(table 19), indicated that concentrations of suspended 

organic carbon and suspended sediment varied directly 

with streamflows at the five sites in this basin. 

Concentrations of dissolved solids and major ions, such 

as bicarbonate, varied inversely with streamflow 

(τ = -0.6 to -0.8), except at site 9 and site 10. Although 

there was a general tendency for dissolved-solids 

concentrations to vary inversely with streamflow at 

these two sites, τ was only -0.1 and -0.2, respectively.
64 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Seasonality in water quality is defined by the 

long-term hydrographs for all the sites except 

Springbrook Creek (site 7). The high-flow period is 

typically from October to February for sites 6 and 10 

and from November to February for sites 8 and 9. The 

transition period, from March to July at sites 6 and 10, 

is also a period of relatively high flows because of 

spring snowmelt or releases of water from Howard A. 

Hanson Dam; but at sites 8 and 9, the transition period 

is from March to June and features diminishing flows 

as summer approaches. The low-flow period is August 

and September for sites 6 and 10 and from July to 

September at sites 8 and 9. Seasonality in Springbrook 

(site 7) was defined to be the same as for the other two 

tributaries, Big Soos and Newaukum (sites 8 and 9). 

Except at sites 7 and 9, the highest nutrient and 

suspended-sediment concentrations typically occurred 

in samples collected during the high-flow period 

(figs. 29, 31, and 33). At sites 7 and 9, some of the 

highest nutrient and suspended-sediment 

concentrations were observed in samples collected 

during the transition period (figs. 30 and 32).

Site 6: The water in the Duwamish was of 

generally good quality except at times when iron and 

manganese concentrations were relatively large and a 

number of pesticides and VOCs were present. Ten 

percent of the samples had iron and manganese 

concentrations greater than 400 and 70 μg/L, which 

exceeded USEPA SMCLs of 300 and 50 μg/L, 

respectively, for drinking water (see table 2). These 

exceedances occurred mostly in late spring or summer 

(July and August, 1996) when streamflows were about 

500 ft3/s or less. All nitrogen species analyzed for were 

present in most samples, however nitrate, with a 

median concentration of 0.41 mg/L, and total organic 

nitrogen, with a median of 0.2 mg/L (estimated by logprobability regression), were the dominant nitrogen 

species (fig. 28).

Site 7: The water in Springbrook was of fair 

quality; concentrations of iron and manganese were 

frequently high and instantaneous dissolved-oxygen 

concentrations low. More than half of the samples, with 

concentrations greater than 500 μg/L, exceeded 

USEPA drinking-water SMCL for iron, and 90 percent 

of the samples, with concentrations greater than 

70 μg/L, exceeded USEPA drinking-water SMCL for 

manganese. In 25 of the 37 samples, the concentration 

of dissolved oxygen measured at the time of sample 

collection did not meet the Washington State standard 

of 8.0 mg/L minimum concentration for a Class A 

water body (see table 2). On two occasions, the water 

temperature at the time of sample collection was 

18.1oC and exceeded the Washington State standard of 

18.0oC maximum temperature for a Class A water 

body. All nitrogen species analyzed for were present 

above laboratory MRLs in nearly all the samples. The 

dominant nitrogen species were total and dissolved 

organic nitrogen with median concentrations of 0.66 

and 0.44 mg/L, respectively, and nitrate with a median 

of 0.43 mg/L (fig. 28).

Contrary to the other four sites in the basin, 

constituent concentrations in Springbrook tended to 

vary inversely with streamflow, indicating dilution 

effects from rain and occasionally from snowmelt. 

Kendall’s τ for the nitrogen species, orthophosphate, 

bicarbonate, iron, manganese, conductivity, and 

dissolved solids ranged from -0.1 to -0.8 (table 19). 

These tendencies, in addition to the relatively high 

nitrogen and phosphorus concentrations during the 

transition and low-flow periods (fig. 30), suggest that 

ground water is an important source of nutrients at this 

site. Other factors suggesting an important groundwater contribution to the quality of water included 

reddish precipitates on undisturbed bottom sediments, 

low dissolved-oxygen concentrations, and the yearround high concentrations of iron and manganese in 

many of the samples. Dissolved-oxygen concentrations 

generally did not meet the State’s standard for a 

Class A water body except during the winter months of 

November, December, and January.

Site 8: The water in Big Soos was of good 

quality. At all times during the study, water 

temperatures, dissolved-oxygen concentrations, and pH 

levels met Washington State standards for a Class A 

water body. However, samples collected from April 

1997–September 1997 showed E. coli to be present in 

the creek. Concentrations of E. coli ranged from 21 to 

750 col/100 mLs (table 33). Of the eight samples 

collected for bacteria analyses, two samples exceeded 

298 col/100 mLs, USEPA’s (1986b) recommended 

single-sample level for moderate, full-body contact 

recreation. Otherwise, all other applicable standards 

and criteria for drinking water, ambient water quality 

for beneficial uses, or the protection of aquatic life 

were met by the water quality at this site. Nitrate, with 

a median concentration of 0.88 mg/L, was the 

dominant nitrogen species (fig. 28). Dissolved and total 

organic nitrogen was present in many of the samples, 

but median concentrations were less than about 

0.2 mg/L.
Surface-Water Quality of the Skokomish, Nooksack, and Green-Duwamish Rivers and Thornton Creek 65

Site 9: Water in Newaukum Creek was of 

moderately good quality in the respect that water 

temperatures, dissolved-oxygen concentrations, and pH 

levels met Washington State standards for a Class A 

water body. However, nutrient concentrations were 

large, with a maximum nitrate concentration of 

3.5 mg/L, ammonia of 1.3 mg/L, and total phosphorus 

of 0.66 mg/L. Nitrate, with a median concentration of 

2.1 mg/L, was the dominant nitrogen species (fig. 28). 

On one occasion, a water sample had an iron 

concentration of 310 μg/L that exceeded USEPA 

SMCL for drinking water. In a sample collected on 

August 4, 1998, concentrations of fecal-coliform 

bacteria exceeded the State’s standard of 

100 col/100 mLs for a Class A water body and 

enterococci bacteria exceeded 89 col/100 mLs, 

USEPA’s (1986b) recommended single-sample level 

for moderate, full-body contact recreation (table 33).

Site 10: Excluding a single sample that was 

collected during a large runoff event in October 1997, 

the water in the upper Green River was of high quality, 

similar to that of the study’s reference site on the NF 

Skokomish R. Organic nitrogen was detected only in 

the October storm sample. Nitrate, detected in only 

38 percent of the samples, had a median concentration 

of 0.04 mg/L (estimated by log-probability regression) 

(fig. 28). In samples collected from April 1997–

October 1997, E. coli were present at low 

concentrations, ranging from less than 1 to 

10 col/100 mLs (table 33). None of the eight samples 

collected for bacteria analyses exceeded USEPA’s 

(1986b) recommended single-sample levels for contact 

recreation. In the October storm sample, the 

suspended-sediment concentration was 243 mg/L and 

was the maximum observed for this site; however, 

90 percent of sample concentrations were less than 

15 mg/L. Also in this storm sample, the iron 

concentration of 520 μg/L was the maximum observed 

at this site and exceeded the USEPA SMCL for 

drinking water. All other applicable standards and 

criteria for drinking water, ambient water quality for 

beneficial uses, and protection of aquatic life were met 

by the water quality at this site.
66 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Table 14. Summary of values of field measurements and concentrations of nutrients, major ions, organic carbon, and suspended sediment in samples 

from Duwamish River (site 6) in the Puget Sound Basin study unit, Washington

[Measurement or concentration - Percentile: Percentiles for data sets with 10 percent or more censored data (values less than the MRL) are estimated by 

log-probability regression (Helsel and Cohn, 1988). Concentrations are dissolved and in milligrams per liter unless otherwise specified. Abbreviations: MRL, 

minimum reporting level; μS/cm, microsiemens per centimeter at 25 degrees Celsius; CaCO3, calcium carbonate; <, less than; μg/L, micrograms per liter]

Constituent or property

Measurement or concentration

Minimum

Percentile

MaximumNumber of 

samples

Number of 

samples 

below MRL 

(see tables 

A1-A3)

10 25 50

(Median) 75 90

Water temperature (degrees Celsius) 4.1 5.75 6.8 9.05 13.5 17.6 19.1 42 0

Specific electrical conductance, 

(μS/cm)

47 49 64 87 102 169 187 42 0

pH (units) 7.0 7.2 7.4 7.4 7.5 7.6 7.7 42 0

Dissolved oxygen 7.6 8.2 9.3 10.25 11.35 11.9 12.4 42 0

Ammonia nitrogen <0.015 <0.015 0.02 0.03 0.05 0.09 0.12 42 11

Ammonia-plus-organic nitrogen <.1 <.1 <.1 .12 .18 .29 .4 42 31

Ammonia-plus-organic nitrogen, 

total

<.1 <.1 .13 .2 .4 .57 1.5 42 15

Nitrite nitrogen <.01 <.01 <.01 .006 .01 .02 .03 42 26

Nitrite-plus-nitrate nitrogen .08 .21 .3 .41 .46 .63 .82 42 0

Phosphorus, total .02 .03 .03 .05 .11 .17 .73 42 0

Phosphorus <.01 <.01 <.01 .02 .03 .05 .07 42 16

Orthophosphate phosphorus <.01 <.1 .011 .02 .03 .05 .06 42 4

Alkalinity (as CaCO3) 14 18 23.5 31 39 55 64 42 0

Bicarbonate (as CaCO3) 17 22 28.5 37.5 47 66 77 42 0

Calcium 4.1 4.7 6.2 7.8 8.95 13 14 41 0

Magnesium 1.2 1.3 1.6 2.3 2.9 4.5 5.1 41 0

Sodium 2.6 2.8 3.4 5.0 6.6 12.8 14 41 0

Potassium .3 .5 .7 .84 1.1 1.3 1.6 41 0

Chloride 1.3 1.6 2.0 3.4 5.7 12.8 15 41 0

Sulfate 1.8 2.7 3.2 3.7 4.6 5.3 6.1 41 0

Fluoride <.1 <.1 <.1 <.1 <.1 <.1 <.1 41 41

Silica 9.3 11 12 14 14 16 18 41 0

Iron, in μg/L 32 50 76 130 195 427 540 41 0

Manganese, in μg/L 6 11 16 28 48 77 110 41 0

Dissolved solids, residue at 

180 degrees Celsius

36 42 4.57 62 72 102 120 41 0

Organic carbon 1.3 1.4 1.6 1.95 2.5 3.5 4.5 42 0

Organic carbon, suspended .2 .3 .4 .6 1.0 2.4 12 42 0

Sediment, suspended 7 9 15 31 109 250 787 41 0
Surface-Water Quality of the Skokomish, Nooksack, and Green-Duwamish Rivers and Thornton Creek 67

Table 15. Summary of values of field measurements and concentrations of nutrients, major ions, organic carbon, and suspended sediment in samples 

from Springbrook Creek (site 7) in the Puget Sound Basin study unit, Washington

[Measurement or concentration - Percentile: Percentiles for data sets with 10 percent or more censored data (values less than the MRL) are estimated by 

log-probability regression (Helsel and Cohn, 1988). Concentrations are dissolved and in milligrams per liter unless otherwise specified. Abbreviations: MRL, 

minimum reporting level; μS/cm, microsiemens per centimeter at 25 degrees Celsius; CaCO3, calcium carbonate; <, less than; μg/L, micrograms per liter]

Constituent or property

Measurement or concentration

Minimum

Percentile

MaximumNumber of 

samples

Number of 

samples 

below MRL 

(see tables 

A1-A3)

10 25 50

(Median) 75 90

Water temperature (degrees Celsius) 1.3 5.2 7.7 10.1 16.3 17.1 18.1 37 0

Specific electrical conductance, 

(μS/cm)

63 86 147.5 242 329 413 551 37 0

pH (units) 6.9 7.0 7.1 7.2 7.3 7.4 7.6 37 0

Dissolved oxygen 2.3 2.5 4.15 5.6 8.85 10.1 12.2 37 0

Ammonia nitrogen <0.02 0.02 0.09 0.2 0.36 0.5 0.68 37 3

Ammonia-plus-organic nitrogen .25 .3 .36 .44 .66 .9 1.0 37 0

Ammonia-plus-organic nitrogen, total .3 .44 .51 .66 .77 .92 1.2 37 0

Nitrite nitrogen <.01 .007 .01 .02 .03 .04 .06 37 9

Nitrite-plus-nitrate nitrogen .21 .3 .32 .43 .52 .67 .75 37 0

Phosphorus, total .078 .09 .11 .17 .21 .25 .38 37 0

Phosphorus <.01 .01 .02 .03 .045 .06 .08 37 3

Orthophosphate phosphorus <.01 .01 .02 .03 .04 .07 .08 37 1

Alkalinity (as CaCO3) 19 29 47 89 132 159 174 37 0

Bicarbonate (as CaCO3) 24 35 57 109 161 194 212 37 0

Calcium 5.4 7.5 11 17 24 27 28 37 0

Magnesium 1.9 2.7 4.25 7.3 12 14 16 37 0

Sodium 3.2 4.3 8.2 17 26 35 58 37 0

Potassium 1.3 1.5 1.9 2.85 3.9 4.4 6.0 37 0

Chloride 3.2 3.8 6.4 14 20 26 54 37 0

Sulfate 3.6 4.5 7.2 9.5 11 12 12 37 0

Fluoride <.1 <.1 .1 .16 .2 .3 .6 37 8

Silica 5.0 6.7 10 18 26 31 33 37 0

Iron, in μg/L 79 204 253 510 1,070 1,600 1,940 37 0

Manganese, in μg/L 47 71 128 230 467 590 964 37 0

Dissolved solids, residue at 

180 degrees Celsius

42 56 90 152 220 249 321 37 0

Organic carbon 2.9 3.4 4.65 5.3 6.1 6.5 6.7 37 0

Organic carbon, suspended .2 .3 .5 .8 2.0 3.5 9.1 37 0

Sediment, suspended 5 8 12 17 55 81 215 35 0
68 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Table 16. Summary of values of field measurements and concentrations of nutrients, major ions, organic carbon, and suspended sediment in samples 

from Big Soos Creek (site 8) in the Puget Sound Basin study unit, Washington

Measurement or concentration - Percentile: Percentiles for data sets with 10 percent or more censored data (values less than the MRL) are estimated by logprobability regression (Helsel and Cohn, 1988). Concentrations are dissolved and in milligrams per liter unless otherwise specified. Abbreviations: [MRL, 

minimum reporting level; μS/cm, microsiemens per centimeter at 25 degrees Celsius; CaCO3, calcium carbonate; <, less than; μg/L, micrograms per liter]

Constituent or property

Measurement or concentration

Minimum

Percentile

MaximumNumber of 

samples

Number of 

samples 

below MRL 

(see tables 

A1-A3)

10 25 50

(Median) 75 90

Water temperature (degrees Celsius) 5.1 6.1 7.1 9.7 12.9 14.9 16.3 37 0

Specific electrical conductance, 

(μS/cm)

87 102 110.5 123 134 141 147 37 0

pH (units) 7.3 7.6 7.7 7.8 7.9 8.1 8.1 37 0

Dissolved oxygen 9.7 9.9 10.4 11.3 12.15 12.6 12.9 36 0

Ammonia nitrogen <0.015 <0.015 <0.015 0.011 0.03 0.06 0.18 36 21

Ammonia-plus-organic nitrogen <.1 .09 .13 .17 .3 .33 .6 36 16

Ammonia-plus-organic nitrogen, total <.2 <.2 <.2 .225 .4 .56 .99 36 11

Nitrite nitrogen <.01 <.01 <.01 .01 .02 .03 .05 36 20

Nitrite-plus-nitrate nitrogen .482 .64 .68 .875 .98 1.1 2.6 36 0

Phosphorus, total <.01 .01 .02 .03 .04 .13 .33 36 4

Phosphorus <.01 <.01 .01 .014 .02 .03 .16 36 17

Orthophosphate phosphorus <.01 .01 .01 .02 .02 .03 .17 36 6

Alkalinity (as CaCO3) 23 31 34 40 47 50 54 35 0

Bicarbonate (as CaCO3) 28 38 41 49 57 61 65 35 0

Calcium 7 8.6 9.5 11 12 13 14 36 0

Magnesium 2.4 3.2 3.4 3.8 4.4 4.8 5 36 0

Sodium 4.1 4.9 5.4 5.8 6.3 6.6 6.9 36 0

Potassium .9 .93 1.1 1.2 1.4 1.6 2.1 36 0

Chloride .81 2.8 3.0 3.4 3.8 4.1 4.9 36 0

Sulfate 4.8 6.6 7.5 8.4 9.3 9.9 13 36 0

Fluoride <.1 <.1 <.1 <.1 <.1 <.1 .1 36 34

Silica 8.3 11 12 14 16 18 19 36 0

Iron, in μg/L 38 47 56 74 95 112 150 36 0

Manganese, in μg/L 4 5.7 8.0 9 12 14 15 36 0

Dissolved solids, residue at 

180 degrees Celsius

58 69 77 84 90 95.5 102 36 0

Organic carbon 1.3 1.6 2.7 3.8 5.1 5.7 7.3 35 0

Organic carbon, suspended <.1 .2 .3 .4 .7 1.3 5.6 34 2

Sediment, suspended <1 1 5 8 31 121 292 35 3
Surface-Water Quality of the Skokomish, Nooksack, and Green-Duwamish Rivers and Thornton Creek 69

Table 17. Summary of values of field measurements and concentrations of nutrients, major ions, organic carbon, and suspended sediment in samples 

from Newaukum Creek (site 9) in the Puget Sound Basin study unit, Washington

[Measurement or concentration - Percentile: Percentiles for data sets with 10 percent or more censored data (values less than the MRL) are estimated by 

log-probability regression (Helsel and Cohn, 1988). Concentrations are dissolved and in milligrams per liter unless otherwise specified. Abbreviations: MRL, 

minimum reporting level; μS/cm, microsiemens per centimeter at 25 degrees Celsius; CaCO3, calcium carbonate; <, less than; μg/L, micrograms per liter]

Constituent or property

Measurement or concentration

Minimum

Percentile

MaximumNumber of 

samples

Number of 

samples 

below MRL 

(see tables 

A1-A3)

10 25 50

(Median) 75 90

Water temperature (degrees Celsius) 5.5 5.8 6.4 8.7 11.95 15.3 17.3 36 0

Specific electrical conductance 

(μS/cm)

97 127.5 136.5 148 155 161 175 36 0

pH (units) 7.6 7.8 7.9 8.0 8.0 8.1 8.2 36 0

Dissolved oxygen 8.7 9.7 10.65 11.35 12.2 12.8 13.1 36 0

Ammonia nitrogen <0.015 <0.015 0.014 0.052 0.19 0.32 1.3 36 9

Ammonia-plus-organic nitrogen <.2 <.2 .2 .4 .9 1.1 2.6 36 9

Ammonia-plus-organic nitrogen, total <.2 <.2 .22 .525 1.0 1.6 2.3 36 6

Nitrite nitrogen <.01 .01 .02 .03 .05 .06 0.07 36 2

Nitrite-plus-nitrate nitrogen 1.0 1.5 1.7 2.1 2.4 2.9 3.5 36 0

Phosphorus, total .02 .04 .06 .16 .34 .46 .66 36 0

Phosphorus <.01 .037 .06 .1 .275 .37 .51 36 2

Orthophosphate phosphorus <.01 .05 .06 .1 .22 .31 .38 36 1

Alkalinity (as CaCO3) 26 35 41 48 53 55 61 35 0

Bicarbonate (as CaCO3) 32 43 50 59 64 67 75 35 0

Calcium 7.7 10 12 13 15 16 17 36 0

Magnesium 2.4 3.3 3.8 4.2 4.6 4.9 5.2 36 0

Sodium 4.3 5.4 5.9 6.2 6.6 7.5 7.8 36 0

Potassium 1.5 1.7 2.3 3.4 5.3 6.4 7.7 36 0

Chloride .9 4.3 4.5 5 6.2 7.1 8.9 36 0

Sulfate 3.8 5.1 5.6 6.0 7.3 8.6 14 36 0

Fluoride <.1 <.1 <.1 <.1 <.1 <.1 .1 36 35

Silica 11 13 16 18 20 20 21 36 0

Iron, in μg/L 15 26 50 97 140 207 330 36 0

Manganese, in μg/L <2 2.0 3.3 5.2 9.0 13 20 36 2

Dissolved solids, residue at 

180 degrees Celsius

70 94 96 107 113 118 125 36 0

Organic carbon 1.2 1.5 2.7 4.2 8.1 9.4 11 35 0

Organic carbon, suspended .2 .3 .4 .7 1.3 1.9 3.9 35 0

Sediment, suspended <1 2 5 9.5 19 62 123 34 1
70 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Table 18. Summary of values of field measurements and concentrations of nutrients, major ions, organic carbon, and suspended sediment in samples 

from the upper Green River (site 10) in the Puget Sound Basin study unit, Washington

[Measurement or concentration - Percentile: Percentiles for data sets with 10 percent or more censored data (values less than the MRL) are estimated by 

log-probability regression (Helsel and Cohn, 1988). Concentrations are dissolved and in milligrams per liter unless otherwise specified. Abbreviations:

MRL, minimum reporting level; μS/cm, microsiemens per centimeter at 25 degrees Celsius; CaCO3, calcium carbonate; <, less than; μg/L, micrograms per 

liter]

Constituent or property

Measurement or concentration

Minimum

Percentile

MaximumNumber of 

samples

Number of 

samples 

below MRL 

(see tables 

A1-A3)

10 25 50

(Median) 75 90

Water temperature (degrees Celsius) 3.2 3.7 4.95 6.5 9.35 12.6 13.1 25 0

Specific electrical conductance 

(μS/cm)

33 33 36 41 48 51 53 25 0

pH (units) 7.3 7.3 7.5 7.6 7.7 7.8 7.8 24 0

Dissolved oxygen 9.4 9.6 10.9 11.95 13.6 14.15 15 24 0

Ammonia nitrogen <0.015 <0.015 <0.015 0.012 0.02 0.05 0.07 24 14

Ammonia-plus-organic nitrogen <.1 <.1 <.1 <.1 <.1 <.1 <.1 24 24

Ammonia-plus-organic nitrogen, 

total

<.1 <.1 <.1 <.1 <.1 <.1 .46 24 23

Nitrite nitrogen <.01 <.01 <.01 <.01 .01 .02 .02 24 19

Nitrite-plus-nitrate nitrogen <.05 .02 .03 .04 .07 .09 .13 24 15

Phosphorus, total <.01 <.01 <.01 <.01 .01 .026 .16 24 18

Phosphorus <.01 <.01 <.01 <.01 <.01 .014 .03 24 21

Orthophosphate phosphorus <.01 .006 .008 .01 .018 .02 .02 24 9

Alkalinity (as CaCO3) 13 14.5 16 18 22 23 24 24 0

Bicarbonate (as CaCO3) 16 18 19.5 22 27 28 29 24 0

Calcium 3.3 3.5 3.7 4.4 5.1 5.7 5.9 24 0

Magnesium .56 .58 .665 .75 .88 .96 1.0 24 0

Sodium 2.2 2.3 2.6 2.9 3.3 3.45 3.7 24 0

Potassium <.1 .1 .1 .125 .2 .225 .49 24 1

Chloride .4 .5 .53 .7 .79 1.1 1.2 24 0

Sulfate .63 .71 .9 1.03 1.27 1.3 1.5 24 0

Fluoride <.1 <.1 <.1 <.1 <.1 <.1 <.1 24 24

Silica 11 12 13 13 13 13 15 24 0

Iron, in μg/L <3 <3 3.0 4.0 9.8 29 520 24 5

Manganese, in μg/L <1 <1 <1 <1 <1 <1 8 24 22

Dissolved solids, residue at 

180 degrees Celsius

23 27 33 36 38 40 43 24 0

Organic carbon .5 .6 .6 .9 1.4 2.5 4.7 23 0

Organic carbon, suspended <.1 <.1 .1 .11 .2 .45 3.1 24 7

Sediment, suspended <1 <1 1 1 2 15 243 22 4
Surface-Water Quality of the Skokomish, Nooksack, and Green-Duwamish RIvers and Thornton Creek 71

0

0

4

4

8 MILES

8 KILOMETERS

Sample site

Land use/cover

Agriculture

Forest/natural cover/

 other

Urban/built up areas

Basin boundary

Streams

Lakes

Dissolved nitrite-plus-nitrate

Dissolved ammonia

Dissolved ammonia-plus-

 organic

Total ammonia-plus-

 organic

Total phosphorus

Dissolved phosphorus

Dissolved orthophosphate

Suspended sediment

Dissolved organic carbon

Suspended organic carbon

NITROGEN

EXPLANATION

EXPLANATION

PHOSPHORUS

47 ̊

15'

47 ̊

30'

122 ̊15' 121 ̊45'

Green Rive r

Howard A. Hanson

Reservoir

Lake Sawyer

Nitrogen

MEDIAN NUTRIENT COMPOSITION

SEDIMENT, 

IN MILLIGRAMS PER LITER

PHOSPHORUS, 

IN MILLIGRAMS PER LITER

ORGANIC CARBON, 

IN MILLIGRAMS PER LITER

MEDIAN SUSPENDED SEDIMENT

AND CARBON

Duwamish River Springbrook

Creek

Big Soos

Creek

Newaukum 

Creek

Green River

Duwamish River Springbrook

Creek

Big Soos

Creek

Newaukum 

Creek

Green River

0

2

4

6

0

0.05

0.10

0.15

0.20

0

10

20

30

40

0

1

2

PhosphorusNitrogen PhosphorusNitrogen PhosphorusNitrogen PhosphorusNitrogen Phosphorus

Suspended

Sediment

Organic

Carbon

Suspended

Sediment

Organic

Carbon

Suspended

Sediment

Organic

Carbon

Suspended

Sediment

Organic

Carbon

Suspended

Sediment

Organic

Carbon

Median less than 0.015 mg/L Median less than 0.10 mg/L Median less than 0.10 mg/L

NITROGEN, 

IN MILLIGRAMS PER LITER (mg/L)

Na + K

Ca

Mg

Cl

SO4

HCO 3

Median milliequivalents

per liter

Site 6 - Duwamish River

-1 0 1

Mg

Na + K

Ca

Cl

SO4

HCO 3

Median milliequivalents

per liter

Site 7 - Springbrook Creek

-2 0 2

Mg

Na + K

Ca

Cl

SO4

HCO 3

Median milliequivalents

per liter

-1 0 1

Site 10 - Green River

Na + K

Ca

Mg

Cl

SO4

HCO 3

Median milliequivalents

per liter

-1 0 1

Site 9 - Newaukum Creek

Na + K

Ca

Mg

Cl

SO4

HCO 3

Median milliequivalents

per liter

-1 0 1

Site 8 - Big Soos Creek

0

0

4

4

8 MILES

8 KILOMETERS

Sample site

Land use/cover

Agriculture

Forest/natural cover/

 other

Urban/built up areas

Basin boundary

Streams

Lakes

Dissolved nitrite-plus-nitrate

Dissolved ammonia

Dissolved ammonia-plus-

 organic

Total ammonia-plus-

 organic

Total phosphorus

Dissolved phosphorus

Dissolved orthophosphate

Suspended sediment

Dissolved organic carbon

Suspended organic carbon

NITROGEN

EXPLANATION

EXPLANATION

PHOSPHORUS

47 ̊

15'

47 ̊

30'

122 ̊15' 121 ̊45'

Green Rive r

Howard A. Hanson

Reservoir

Lake Sawyer

Nitrogen

MEDIAN NUTRIENT COMPOSITION

SEDIMENT, 

IN MILLIGRAMS PER LITER

PHOSPHORUS, 

IN MILLIGRAMS PER LITER

ORGANIC CARBON, 

IN MILLIGRAMS PER LITER

MEDIAN SUSPENDED SEDIMENT

AND CARBON

Duwamish River Springbrook

Creek

Big Soos

Creek

Newaukum 

Creek

Green River

Duwamish River Springbrook

Creek

Big Soos

Creek

Newaukum 

Creek

Green River

0

2

4

6

0

0.05

0.10

0.15

0.20

0

10

20

30

40

0

1

2

PhosphorusNitrogen PhosphorusNitrogen PhosphorusNitrogen PhosphorusNitrogen Phosphorus

Suspended

Sediment

Organic

Carbon

Suspended

Sediment

Organic

Carbon

Suspended

Sediment

Organic

Carbon

Suspended

Sediment

Organic

Carbon

Suspended

Sediment

Organic

Carbon

Median less than 0.015 mg/L Median less than 0.10 mg/L Median less than 0.10 mg/L

NITROGEN, 

IN MILLIGRAMS PER LITER (mg/L)

Na + K

Ca

Mg

Cl

SO4

HCO 3

Median milliequivalents

per liter

Site 6 - Duwamish River

-1 0 1

Mg

Na + K

Ca

Cl

SO4

HCO 3

Median milliequivalents

per liter

Site 7 - Springbrook Creek

-2 0 2

Mg

Na + K

Ca

Cl

SO4

HCO 3

Median milliequivalents

per liter

-1 0 1

Site 10 - Green River

Na + K

Ca

Mg

Cl

SO4

HCO 3

Median milliequivalents

per liter

-1 0 1

Site 9 - Newaukum Creek

Na + K

Ca

Mg

Cl

SO4

HCO 3

Median milliequivalents

per liter

-1 0 1

Site 8 - Big Soos Creek

Figure 28. Median concentrations of nutrients, suspended sediment, organic carbon, and major ions in samples from the Duwamish River 

(site 6), Springbrook Creek (site 7), Big Soos Creek (site 8), Newaukum Creek (site 9), and the upper Green River (site 10) in the Puget Sound 

Basin study unit, Washington.
72 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98 CONCENTRATION, IN MILLIGRAMS PER LITER

Total Nitrogen and

Total Phosphorus (in blue)

Dissolved Orthophosphate Suspended Sediment

0

1

2

0

0.06

0.07

0.04

0.02

0

500

1,000

0

5,000

10,000

13,000

0

5,000

10,000

13,000

0

5,000

10,000

13,000

0

2.5

1

2

0.02

0.01

0.07

0.04

0.06

0

600

800

1,000

200

400

CONCENTRATION, IN MILLIGRAMS PER LITER

STREAMFLOW, IN CUBIC FEET PER SECOND

Total nitrogen

FMAMJ J A SON D J FMAMJ J A SON D J FMA

FMAMJ J A SON D J FMAMJ J A SON D J FMA

FMAMJ J A SON D J FMAMJ J A SON D J FMA

Dissolved orthophosphate

1996 1997 1998

Suspended sediment

Total phosphorus

STREAMFLOW PERIODS

Oct.-

Feb.

Mar.-

July 

Aug.-

Sept.

Oct.-

Feb.

Mar.-

July 

Aug.-

Sept.

Oct.-

Feb.

Mar.-

July 

Aug.-

Sept.

EXPLANATION

Concentration percentiles

10th percentile

25th percentile

Median

75th percentile

90th percentile

Low-flow

High-flow

Transition

Daily streamflow

Minimum reporting level

Figure 29. Time series of streamflow and concentrations of total nitrogen, total phosphorus, dissolved orthophosphate phosphorus, and suspended 

sediment in samples, and concentrations by three streamflow periods, for the Duwamish River (site 6) in the Puget Sound Basin study unit, 

Washington.

(Truncated boxplots of concentration percentiles require a minimum of nine observations, otherwise concentrations are plotted as individual points. 

Censored data in the time-series graphs are shown as an open symbol. Boxplots are truncated at the minimum reporting level indicated by solid line.)
Surface-Water Quality of the Skokomish, Nooksack, and Green-Duwamish RIvers and Thornton Creek 73

0

2

1

0.10

0.05

0

100

200

300

D J F MA M J J AS OND J FMA M J J A SON DJFMA

D J F MA M J J AS OND J FMA M J J A SON DJFMA

D J F MA M J J AS OND J FMA M J J A SON DJFMA

0

800

840

840

840

200

400

600

0

800

200

400

600

0

800

200

400

600

0

2.0

0.5

1.0

1.5

0.01

0.06

0.08

0.10

0.02

0.04

0

200

300

100

CONCENTRATION, IN MILLIGRAMS PER LITER

STREAMFLOW, IN CUBIC FEET PER SECOND

 CONCENTRATION, 

IN MILLIGRAMS PER LITER

Dissolved orthophosphate

1995 1997 1998 1996

Total Nitrogen and

Total Phosphorus (in blue)

Dissolved Orthophosphate Suspended Sediment

Suspended sediment

Total nitrogen

Total phosphorus

STREAMFLOW PERIODS

Oct.-

Feb.

Mar.-

June 

JulySept.Oct.-

Feb.

Mar.-

June 

JulySept.Oct.-

Feb.

Mar.-

June 

JulySept.

0

EXPLANATION

Concentration percentiles

10th percentile

25th percentile

Median

75th percentile

90th percentile

Low-flow

High-flow

Transition

Daily streamflow

Minimum reporting level

Figure 30. Time series of streamflow and concentrations of total nitrogen, total phosphorus, dissolved orthophosphate phosphorus, and 

suspended sediment in samples, and concentrations by three streamflow periods, for Springbrook Creek (site 7) in the Puget Sound Basin study 

unit, Washington.

(Truncated boxplots of concentration percentiles require a minimum of nine observations, otherwise concentrations are plotted as individual points. 

Censored data in the time-series graphs are shown as an open symbol. Boxplots are truncated at the minimum reporting level indicated by solid 

line.)
74 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

0

3

2

0

0.4

0.2

0

100

200

300

0

500

1,000

1,400

0

500

1,000

1,400

0

500

1,000

1,400

0

5

2

4

0

0.3

0.4

0.1

0.2

0

200

300

100

CONCENTRATION, IN MILLIGRAMS PER LITER

STREAMFLOW, IN CUBIC FEET PER SECOND

 CONCENTRATION, 

IN MILLIGRAMS PER LITER

Total nitrogen

1995 1997 1998 1996

Total Nitrogen Suspended Sediment Dissolved Orthophosphate

 and Total Phosphorus (in blue)

Suspended sediment

STREAMFLOW PERIODS

Nov.-

Feb.

Mar.-

June 

JulyOct.Nov.-

Feb.

Mar.-

June 

JulyOct.Nov.-

Feb.

Mar.-

June 

July.-

Oct.

1

Dissolved orthophosphate

Total phosphorus

D J F MA M J J AS OND J FMA M J J A SON DJFMA

D J F MA M J J AS OND J FMA M J J A SON DJFMA

D J F MA M J J AS OND J FMA M J J A SON DJFMA

EXPLANATION

Concentration percentiles

10th percentile

25th percentile

Median

75th percentile

90th percentile

Low-flow

High-flow

Transition

Daily streamflow

Minimum reporting level

Figure 31. Time series of streamflow and concentrations of total nitrogen, total phosphorus, dissolved orthophosphate phosphorus, and 

suspended sediment in samples, and concentrations by three streamflow periods, for Big Soos Creek (site 8) in the Puget Sound Basin study unit, 

Washington.

(Truncated boxplots of concentration percentiles require a minimum of nine observations, otherwise concentrations are plotted as individual 

points. Censored data in the time-series graphs are shown as an open symbol. Boxplots are truncated at the minimum reporting level indicated by 

solid line.)
Surface-Water Quality of the Skokomish, Nooksack, and Green-Duwamish RIvers and Thornton Creek 75

0

2

4

6

0.4

0.6

0.8

0.2

0

50

100

150

D J F MA M J J AS OND J FMA M J J A SON DJFMA

D J F MA M J J AS OND J FMA M J J A SON DJFMA

D J F MA M J J AS OND J FMA M J J A SON DJFMA

0

800

200

400

600

0

800

200

400

600

0

800

200

400

600

0

2

6

7

4

0

0.6

0.8

0.2

0.4

0

100

150

50

CONCENTRATION, IN MILLIGRAMS PER LITER

STREAMFLOW, IN CUBIC FEET PER SECOND

 CONCENTRATION, 

IN MILLIGRAMS PER LITER

1995 1997 1998 1996

Total Nitrogen Suspended Sediment Dissolved Orthophosphate and 

Total Phosphorus (in blue)

Suspended sediment

Total nitrogen

STREAMFLOW PERIODS

Nov.-

Feb.

Mar.-

June 

JulyOct.Nov.-

Feb.

Mar.-

June 

JulyOct.Nov.-

Feb.

Mar.-

June 

JulyOct.

Total phosphorus

Dissolved orthophosphate

0

EXPLANATION

Concentration percentiles

10th percentile

25th percentile

Median

75th percentile

90th percentile

Low-flow

High-flow

Transition

Daily streamflow

Minimum reporting level

Figure 32. Time series of streamflow and concentrations of total nitrogen, total phosphorus, dissolved orthophosphate phosphorus, and 

suspended sediment in samples, and concentrations by three streamflow periods, for Newaukum Creek (site 9) in the Puget Sound Basin study 

unit, Washington.

(Truncated boxplots of concentration percentiles require a minimum of nine observations, otherwise concentrations are plotted as individual 

points. Censored data in the time-series graphs are shown as an open symbol. Boxplots are truncated at the minimum reporting level indicated by 

solid line.)
76 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

EXPLANATION

Concentration percentiles

10th percentile

25th percentile

Median

75th percentile

90th percentile

Low-flow

High-flow

Transition

Daily streamflow

Minimum reporting level

0

0.4

0.6

0.2

0.008

0.07

0.01

0.02

0.03

0.04

0.05

0.1

0

0.2

0.1

0

10

20

200

300

MAMJ J ASOND J FMAMJ J ASOND J FMA

0

0.6

0.2

0.4

M

0

200

400

500

0

200

400

500

0.07

0.2

0.005

0.007

0.01

0.02

0.03

0.04

0.05

0.1

0

400

200

0

500

500

0

20

10

220

250

260

CONCENTRATION, IN MILLIGRAMS PER LITER

STREAMFLOW, IN CUBIC FEET PER SECOND

 CONCENTRATION, 

IN MILLIGRAMS PER LITER

Total nitrogen

AMJ J ASOND J FMAMJ J ASOND J FMA

Dissolved orthophosphate

Total phosphorus

MAMJ J ASOND J FMAMJ J ASOND J FMA

1996 1997 1998

Total Nitrogen Suspended Sediment Dissolved Orthophosphate and

Total Phosphorus (in blue)

Suspended sediment

STREAMFLOW PERIODS

Oct.-

Feb.

Mar.-

June 

JulySept.Oct.-

Feb.

Mar.-

June 

July.-

Sept.

Oct.-

Feb.

Mar.-

June 

JulySept.

Figure 33. Time series of streamflow and concentrations of total nitrogen, total phosphorus, dissolved orthophosphate phosphorus, and suspended 

sediment in samples, and concentrations by three streamflow periods, for the upper Green River (site 10) in the Puget Sound Basin study unit, 

Washington.

(Truncated boxplots of concentration percentiles require a minimum of nine observations, otherwise concentrations are plotted as individual points. 

Censored data in the time-series graphs are shown as an open symbol. Boxplots are truncated at the minimum reporting level indicated by solid line.)
Surface-Water Quality of the Skokomish, Nooksack, and Green-Duwamish Rivers and Thornton Creek 77

Duwamish River Organic Chemistry

 Thirteen pesticides, mostly herbicides, were 

found in Duwamish River (site 6) samples collected 

from March 1996 through May 1997 (table 20). The 

herbicide simazine was detected most frequently, found 

in 18 of 24 samples at concentrations as high as 

0.194 μg/L and with a median of 0.0195 μg/L. The 

herbicide prometon, present in 15 samples, was the 

next most frequently detected pesticide and was closely 

followed in frequency by detections of the herbicides 

atrazine and tebuthiuron, which were present in 14 

samples. These herbicides were also detected in a large 

percentage of samples from study units nationwide 

(Larson and others, 1997), although in the Duwamish, 

tebuthiuron was detected more frequently, occurring in 

about 60 percent of samples compared to the national 

rate of about 10 percent of samples. Diazinon in eight 

samples and propargite in one sample were the only 

insecticides detected. Diazinon concentrations in two 

samples exceeded 0.04 μg/L, a limit recommended for 

the protection of aquatic life by Menconi and Cox 

(1994). No other pesticide concentration exceeded 

water-quality criteria concentrations established for 

drinking water or aquatic life. Most concentrations of 

the frequently detected pesticides at site 6 ranked 

within or below the middle 50 percent range of 

concentrations in mixed land-use river basins studied 

nationwide in 36 NAWQA study units during 1991–98. 

The exceptions were a few samples having simazine, 

tebuthiuron, and diazinon concentrations in the highest 

25 percent range (Ebbert and others, 2000).

Table 19. Correlation between selected water-quality characteristics or chemical constituents and streamflow for the Duwamish River (site 6), 

Springbrook Creek (site 7), Big Soos Creek (site 8), Newaukum Creek (site 9), and the upper Green River (site 10) in the Puget Sound Basin study unit, 

Washington

Water-quality characteristic or 

chemical constituent

Kendall’s tau correlation coefficient

Duwamish River 

(Site 6)

Springbrook Creek 

(Site 7)

Big Soos Creek 

(Site 8)

Newaukum Creek 

(Site 9)

Upper Green River 

(Site 10)

Specific electrical conductance -0.73 -0.77 -0.80 -0.53 -0.64

Dissolved solids -.70 -.77 -.60 -.12 -.21

Total nitrogen .15 -.35 -.40 .47 .16

Dissolved nitrite-plus-nitrate nitrogen .10 -.20 .2 .08 .08

Total ammonia-plus-organic nitrogen .24 -.20 .50 .66 .07

Dissolved ammonia-plus-organic 

nitrogen

.12 -.45 .30 .62 <.01

Total phosphorus .36 .12 .41 .64 .18

Dissolved orthophosphate phosphorus .08 -.27 -.18 .54 -.30

Dissolved organic carbon .34 -.33 .62 .59 .19

Suspended organic carbon .37 .42 .48 .59 .54

Suspended sediment .57 .61 .65 .64 .35

Bicarbonate -.75 -.76 -.78 -.77 -.72

Iron -.51 -.25 .27 .45 .26

Manganese -.60 -.47 -.35 .50 .08
78 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

All but two (2,4-D and metolachlor) of the 

pesticides detected in samples from this basinintegrator site were found in samples from Thornton 

Creek (site 11), the study’s only intensively sampled 

urban-indicator stream, but one that is not a tributary to 

the Green-Duwamish River. Metolachlor was detected, 

however, in samples collected during a storm event 

from Springbrook (site 7), a tributary to the Duwamish 

(table 34 at the end of the report). Although known 

more for its use as an agricultural herbicide in other 

parts of the country, metolachlor has also been 

indicated for use on turf and fencelines, and on golf 

courses in the northeast United States (Jack Barbash, 

U.S. Geological Survey, written commun., December 

1998) (see table 27). In the late 1980’s, it was 

estimated that about 5,300 pounds of metolachlor were 

applied in King County for agricultural and nonagricultural purposes (Tetra Tech, 1988).

Although several pesticides tended to be detected 

more during the rainy season from November to April 

(fig. 34), concentrations did not correlate with 

streamflow (τ less than 0.3; p-values less than 0.05). 

Season, timing of applications, and storm events 

appeared to have the most influence on pesticide 

detection frequencies and concentrations. Highest 

concentrations for most pesticides tended to occur in 

spring samples, particularly in storm-event samples. 

Diazinon concentrations tended to be highest in spring 

samples, corresponding to the season of high 

application rates (fig. 34). The two times when 

diazinon concentrations exceeded a recommended 

level for the protection of aquatic life were in April 

1996 storm-event samples. For atrazine, 

deethylatrazine, prometon, and diuron, the highest 

concentrations were also observed in the April 1996 

storm-event sample.

Of the 86 VOCs that were analyzed for, 26 

different compounds were detected in samples from 

site 6 (table 21). However, only 2 of the 26 compounds 

(methylbenzene and 1,3-plus-1,4-dimethylbenzene) 

were detected at concentrations above the 1999 LRLs. 

Methylbenzene, the most frequently detected 

compound, was in 16 samples, 59 percent of which had 

concentrations above the LRL. Chloromethane was 

detected second-most frequently with 13 detections, 

but with all of them in concentrations below the LRL. 

The compound cis-1,2-dichloroethene was present in 

11 samples, none of which had concentrations above 

the LRL. The general absence of concentrations above 

the LRLs could be due in part to dilution, because of 

the volume of water in this river and because of highquality water released from the upper watershed at 

Howard A. Hanson Dam. None of the VOC 

concentrations exceeded any drinking-water or aquaticlife criteria concentrations. Detections or 

concentrations of methylbenzene and 1,3-plus-1,4-

dimethylbenzene did not appear to relate with 

magnitude of streamflow, and although VOCs were 

found throughout the year at both high streamflow in 

the winter months and during baseflow conditions, the 

detections seemed to occur more frequently with rainy 

wet conditions during winter (fig. 35). Increased 

methylbenzene concentrations occasionally 

corresponded to peaks in streamflow such as during the 

storm in April 1996, but concentrations remained low 

during other storms such as in January 1997. Similarly, 

concentrations of 1,3-plus-1,4-dimethylbenzene were 

generally low throughout the year with occasional 

increases in concentrations such as during September 

1996 and February 1997.
Surface-Water Quality of the Skokomish, Nooksack, and Green-Duwamish Rivers and Thornton Creek 79

Table 20. Pesticides in water samples from the Duwamish River (site 6) in the Puget Sound Basin study unit, Washington

[Water-quality criteria – Drinking water: U.S. Environmental Protection Agency (1996). Aquatic organisms – Chronic (USGS): U.S. 

Geological Survey (1999a). Based on 24 samples collected March 1996 to May 1997; all concentrations are in micrograms per liter (μg/L); bold

type indicates value above aquatic life criterion; method detection limits are from reports by Zaugg and others (1995), Lindley and others (1996), 

Werner and others (1996), and U.S. Geological Survey National Water Quality Laboratory Technical Memorandums 98.03A and 96.06A; MCL, 

maximum contaminant level; HAL, Health advisory level; E, Estimated–a qualitative value that is less than the statistically determined method 

detection limit or lowest calibration standard; –, no value or data]

Pesticide Number of 

detections

Maximum 

concentration 

value

Median 

concentration 

detected

Method 

detection 

limit

Water-quality criteria

Drinking water Aquatic organisms (freshwater)

MCL HAL Acute Chronic Chronic 

(USGS)

Atrazine 14 0.015 0.005 0.001 3 3 170 17 1.8

2,4-D 1 .10 – .15 70 70 110 11 4

Deethylatrazine 5 E.005 E.004 .002 – – – – –

Diazinon 8 .083 .011 .002 – 0.6 20.16 20.04 0.08

Dichlobenil 3 E.03 E.02 E1.2 – – – – –

Diuron 9 E.69 .11 .020 – 10 – – –

Metolachlor 12 .013 .004 .002 – 70 – – 7.8

Prometon 15 .02 E.006 .018 – 100 – – –

Pronamide 2 .008 – .003 – 50 – – –

Propargite 1 .003 – .013 – – – – –

Simazine 18 .194 .0195 .005 4 4 1100 110 10

Tebuthiuron 14 .09 .010 .010 – 500 – – 1.6

Triclopyr 1 .12 – .25 – – 15,600 1560 –

1Norris and Dost (1992).

2Menconi and Cox (1994).
80 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

E E

E E

E

E

E

E

E

E E E E

E

E

E

E

E

E E

E

E

E

MA MJ J A SON DJFMAM J

MA MJ J A SON DJFMAM J

MA MJ J A SON DJFMAM J

MA MJ J A SON DJFMAM J

MA MJ J A SON DJFMAM J

0

11,000

5,000

10,000

0

0.02

0.01

0

12,000

5,000

10,000

0.002

0.5

0.005

0.01

0.02

0.05

0.1

0.2 Simazine

0

12,000

5,000

10,000

0.0015

0.05

0.002

0.003

0.004

0.005

0.007

0.01

0.02

0.03

0.04 Metolachlor

1996 1997

0

12,000

5,000

10,000

0.003

0.1

0.004

0.005

0.007

0.01

0.02

0.03

0.04

0.05

0.07

0

12,000

5,000

10,000

0.5

0.002

0.005

0.01

0.02

0.05

0.1

0.2 Diazinon

Atrazine

CONCENTRATION, IN MICROGRAMS PER LITER

STREAMFLOW, IN CUBIC FEET PER SECOND

Prometon

EXPLANATION

Streamflow

E Concentration estimated

Compound detected

Concentration less than 

 method reporting limit

Figure 34. Time series of streamflow and concentrations of selected pesticides detected in samples from the Duwamish River (site 6) in 

the Puget Sound Basin study unit, Washington.
Surface-Water Quality of the Skokomish, Nooksack, and Green-Duwamish Rivers and Thornton Creek 81

Table 21. Volatile organic compounds in water samples from the Duwamish River (site 6) in the Puget Sound Basin study unit, Washington

[Water-quality criteria – Drinking water: U.S. Environmental Protection Agency (1996). Based on 24 samples collected between March 1996 to May 1997; 

all concentrations are in micrograms per liter (μg/L); MRL, method reporting level (Connor and others, 1998); LRL, laboratory reporting level; MCL, 

maximum contaminant level; HAL, health advisory level; E, Estimated–a qualifier for an analytical result based on the long-term method detection level, 

laboratory reporting level, and lowest calibration standard (Childress and others, 1999); –, no value or data]

Volatile

organic compound

Number of 

detections

Percentage of 

detections above 

1999 LRL and 

(number)

Maximum 

concentration value

Median 

concentration 

detected

MRL

 (1999 LRL)

Water-quality criteria

Drinking water

Aquatic 

organisms 

(freshwater)

MCL HAL Chronic

1,1,1-Trichloroethane 2 0 E0.01 – 0.032 (0.032) 200 200 –

1,2,4-Trimethylbenzene 6 0 E.02 E0.015 .056 (.056) – – –

1,2-Dimethylbenzene 

(o-Xylene)

5 0 E.04 E.009 .064 (.06) 10,000 10,000 –

1,3-plus-1,4-Dimethylbenzene 

(m,p-Xylene)

9 18 (2) E.08 E.01 .064 (.06) 10,000 10,000 –

1,4-Dichlorobenzene 3 0 E.008 E.003 .05 (.05) 75 75 126

2-Butanone (Methyl ethyl 

ketone)

5 0 E.6 E.4 1.65 (1.6) – – –

2-Ethyltoluene (o-Ethyl toluene) 1 0 E.006 – .1 (.1) – – –

1-Isopropyl-4-methylbenzene 

(p-Isopropyltoluene)

5 0 E.006 E.004 .11 (.11) – – –

4-Methyl-2-pentanone (Methyl 

isobutyl ketone)

1 0 E.3 – .374 (.374) – – –

Acetone 9 0 2.5 E1.4 4.904 (5) – – –

Benzene 2 0 E.09 – .032 (.1) 5 – 1370

Bromoform 1 0 E.01 – .104 (.1) 100 – –

Carbon disulfide 8 0 E.06 E.01 .08 (.37) – – –

Chloroethene (Vinyl chloride) 2 0 E.01 – .112 (.11) 2 – –

Chloromethane (Methyl 

chloride)

13 0 E.06 E.03 .254 (.25) – 3 –

Dichloromethane (Methylene 

chloride)

2 0 E.08 – .382 (.38) 5 – 198.1

Ethenylbenzene (Styrene) 2 0 E.01 – .042 (.042) 100 100 –

Ethylbenzene 5 0 E.02 E.007 .03 (.03) 700 700 190

Iodomethane (Methyl iodide) 1 0 E.008 – .076 (.21) – – –

Methylbenzene (Toluene) 16 81 (13) E.3 E.08 .038 (.05) 1,000 1,000 12

Methyl tert-butyl ether (MTBE) 1 0 E.01 – .112 (.17) – 20 –

Naphthalene 1 0 E.03 – .25 (.25) – 20 11.1

Tetrachloroethene 9 0 E.01 E.01 .038 (.1) 5 – 1111

Trichloroethene 9 0 E.01 E.009 .038 (.038) 5 – 121

Trichloromethane (Chloroform) 5 0 E.01 E.007 .052 (.052) 100 – 11.8

cis-1,2-Dichloroethene 11 0 E.03 E.01 .038 (.038) 70 70 –

1Environment Canada, 1999
82 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

MAMJ J ASOND J FMAMJ J

0.5

0.1

0.2

0.3

0.4

CONCENTRATION, IN MICROGRAMS PER LITER

0

12,000

2,000

4,000

6,000

8,000

10,000

STREAMFLOW, IN CUBIC FEET PER SECOND

Methylbenzene (Toluene)

MAMJ J ASOND J FMAMJ J

1996 1997

0.10

0.02

0.04

0.06

0.08

0

12,000

2,000

4,000

6,000

8,000

10,000

1,3- plus-1,4-Dimethylbenzene (m,p-Xylene)

0

0

Streamflow

Compound detected

Compound detected at an

 estimated concentration

 below the 1999 LRL

Compound not detected

1999 Laboratory Reporting 

 Level (LRL)

EXPLANATION

Figure 35. Time series of streamflow and concentrations of selected volatile organic compounds in samples from the Duwamish River (site 6) 

in the Puget Sound Basin study unit, Washington.
Surface-Water Quality of the Skokomish, Nooksack, and Green-Duwamish Rivers and Thornton Creek 83

Thornton Creek Basin

The Thornton Creek Basin is a subbasin of the 

Lake Washington drainage and located entirely within 

the Puget Sound Lowlands physiographic province. 

Population density in the basin is high, on the order of 

600–1,000 people per square mile. Site 11 (fig. 1 and 

table 1) was established near where the creek enters 

Lake Washington. Site 11 is an indicator of a fully 

developed urban basin, largely residential, but with 

large shopping malls and commercial development and 

an interstate freeway bisecting the basin. The creek at 

site 11 drains an area of 12.1 mi2.

Thornton Creek Basin Hydrology

Mean annual streamflow, based on 10 years of 

record at site 11, was 12.9 ft3/s. Average flow for 

7 months of record (March through September) in 1996 

was 7.5 ft3/s. Annual flows for water years 1997 and 

1998 were 12.7 and 10.2 ft3/s, respectively. Through all 

of summer 1996, daily streamflows were below normal 

or near the lower part of the interquartile range 

(fig. 36). Spring rains caused the creek to rise above the 

upper quartile on several days in April and May, and 

rain in early September brought the stream back to 

normal levels for early fall.

Water year 1997 began with normal streamflows 

in October and November. Winter 1997–98 

streamflows were mostly within the interquartile range 

but were punctuated by streamflows rising well above 

the 75th quartile. The snow storm at the end of 

December and warm temperatures accompanied by 

heavy rainfall during the New Year’s Day 1997 storm 

produced a flow of 129 ft3/s, the highest daily flow 

during the study period. Above-normal precipitation 

kept flows within the interquartile range or higher in 

the spring until the end of May. The extreme low flows 

of June 1997 were the result of water diversions for 

wetland construction in the upper part of the basin. At 

the first of July, flows returned to typical levels and 

remained near the upper quartile to the end of the water 

year.

During water year 1998, daily flows were mostly 

within the interquartile range, except at times during 

rainstorm events or when flows dropped below the 25th 

quartile, such as in December when precipitation was 

only about 50 percent of normal (see fig. 3). Most daily 

flows were below the 25th quartile again in April 1998 

at the end of the study period, in response to belownormal precipitation.

Streamflows at the time of sample collection 

were evenly distributed over the range of flows that 

occur at this site. Flow magnitudes ranged from high 

flows that are exceeded less than 0.06 percent of the 

time to low flows that are exceeded more than 

99 percent of the time (fig. 36). The sample collected 

on December 31, 1996, was during the storm that 

generated the peak discharge for 1997 and the highest 

daily flow observed at this site during the study. One 

sample collected in June 1997 was during the time 

when the minimum flows were set for the period of 

record.

Thornton Creek Basin Water Quality

Forty-six water samples from site 11 were 

collected for the analyses of physical properties, field 

parameters, and concentrations of inorganic 

constituents, organic carbon, suspended sediment, and 

pesticides; 47 samples were collected for VOC analysis 

(table 22). The water in Thornton Creek was of fair 

quality. At times, iron and manganese concentrations 

were large and a number of pesticides and VOCs were 

present. In one sample, the iron concentration exceeded 

USEPA drinking-water SMCL of 300 μg/L, and in 11 

samples, manganese concentrations exceeded the 

SMCL of 50 μg/L (see table 2). On two occasions, 

water temperature measured at the time of sample 

collection slightly exceeded the Washington State 

standard of 18.0oC for a Class A water body, and on 

one occasion, the pH value at the time of sample 

collection did not meet the State standards. In samples 

collected from April 1997–August 1998, 

concentrations of the fecal-indicator bacteria, E. coli,

ranged from 98 to 9,600 col/100 mLs (table 33). Of the 

14 samples collected, 9 samples exceeded 

298 col/100 mLs, USEPA’s (1986b) recommended 

single-sample concentration for moderate, full-body 

contact recreation. Of five insecticides detected in 

samples, concentrations of four did not meet aquaticlife criteria in at least one sample. No other applicable 

standards and criteria for drinking water, ambient water 

quality for beneficial uses, and protection of freshwater 

aquatic life were exceeded by constituent 

concentrations at this site.
84 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Streamflow duration, 1946, 1962-68, 1996-98

Instantaneous streamflow at sample collection, 

 (March 1996-April 1998)

Flow was diverted for a 

 time during wetland construction

 in headwaters of basin.

Daily streamflow

Instantaneous streamflow at 

 sample collection, 

 March 1996-April 1998

75th quartile Interquartile range for 1946, 

25th quartile 1962-68, 1996-98

200

1

2

3

4

5

7

10

20

30

40

50

70

100

200

100

0.7

5

10

20

30

40

50

70

STREAMFLOW, IN CUBIC FEET PER SECOND

STREAMFLOW, IN CUBIC FEET PER SECOND

0.01 0.1 1 2 5 10 20 30 40 50 60 70 80 90 95 98 99 99.9 99.99

0.7

ONDJFMAM J J ASONDJFMAMJJASONDJFMAMJJAS

1995 1997 1998

1

2

3

4

7

1996

EXPLANATION

DAILY AND INSTANTANEOUS STREAMFLOW AND INTERQUARTILE RANGE OF MEAN DAILY STREAMFLOWS

PERCENTAGE OF TIME STREAMFLOWS ARE EQUALED OR EXCEEDED AND INSTANTANEOUS STREAMFLOW

PERCENT

Figure 36. Daily and instantaneous streamflow at the time of sample collection, interquartile range of mean daily 

streamflows for the period of record, and percentage of time streamflows are equaled or exceeded at Thornton Creek (site 

11) in the Puget Sound Basin study unit, Washington.
Surface-Water Quality of the Skokomish, Nooksack, and Green-Duwamish Rivers and Thornton Creek 85

Table 22. Summary of values of field measurements and concentrations of nutrients, major ions, organic carbon, and suspended sediment in samples 

from Thornton Creek (site 11) in the Puget Sound Basin study unit, Washington

[Measurement or concentration - Percentile: Percentiles for data sets with 10 percent or more censored data (values less than the MRL) are estimated by 

log-probability regression (Helsel and Cohn, 1988). Concentrations are dissolved and in milligrams per liter unless otherwise specified. Abbreviations:

MRL, minimum reporting level; μS/cm, microsiemens per centimeter at 25 degrees Celsius; CaCO3, calcium carbonate; <, less than; μg/L, micrograms per 

liter]

Constituent or property

Measurement or concentration

Minimum

Percentile

MaximumNumber of 

samples

Number of 

samples 

below MRL 

(see tables 

A1-A3)

10 25 50

(Median) 75 90

Water temperature (degrees Celsius) 3.5 6.2 8.1 11.95 13.7 16.1 18.2 46 0

Specific electrical conductance 

(μS/cm)

55 96 176 224 242.5 251 254 46 0

pH (units) 7.1 7.5 7.8 7.9 8.0 8.1 8.7 46 0

Dissolved oxygen 8 9.1 9.55 10.45 11.6 12.1 13.9 46 0

Ammonia nitrogen <0.015 <0.015 0.02 0.05 0.07 0.18 0.47 46 9

Ammonia-plus-organic nitrogen <.2 <.2 <.2 .2 .3 .43 1.2 46 15

Ammonia-plus-organic nitrogen, 

total

<.2 <.2 <.2 .3 .6 1.18 4.0 46 7

Nitrite nitrogen <.01 <.01 <.01 .014 .02 .04 .04 46 14

Nitrite-plus-nitrate nitrogen .45 .59 1.00 1.26 1.40 1.60 1.7 46 0

Phosphorus, total <.01 .03 .04 .05 .09 .30 1.1 46 1

Phosphorus <.01 .01 .02 .03 .04 .06 .28 46 5

Orthophosphate phosphorus .01 .02 .02 .03 .04 .06 .10 46 0

Alkalinity (as CaCO3) 16 30 58.5 80.5 87 91 96 46 0

Bicarbonate (as CaCO3) 20 37 71.5 95 106 111 117 46 0

Calcium 4.9 8.1 15 18 20 21 22 46 0

Magnesium 1.7 3.5 7.8 11 12 12.8 13 46 0

Sodium 1.7 3.2 6.1 7.85 8.3 8.7 10 46 0

Potassium 1.2 1.4 2.1 2.4 2.6 2.7 3.1 46 0

Chloride 1.3 3.0 5.55 7.05 7.5 8.1 14 46 0

Sulfate 4.0 7.0 14 17 18 19 20 46 0

Fluoride <.1 <.1 <.1 <.1 .1 .1 .11 46 37

Silica 4.1 8.8 18 25 29 31 34 46 0

Iron, in μg/L 51 75 97 131 182 200 3,800 46 0

Manganese, in μg/L 16 23 31 40 50 62 420 46 0

Dissolved solids, residue at 

180 degrees Celsius

39 67 118.5 150.5 162 173 199 46 0

Organic carbon 2.0 2.4 2.85 3.6 4.55 5.7 9.6 45 0

Organic carbon, suspended .2 .2 .3 .45 1.6 6.1 17 46 1

Sediment, suspended <1 4 6 8 43.5 135.5 484 44 1
86 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

The concentrations of inorganic compounds 

were moderately high, as indicated by conductivity, 

with a median of 224 μS/cm, and by dissolved solids, 

with a median of 150 mg/L (table 22). On the basis of 

median concentrations, calcium and magnesium were 

the dominant cations and bicarbonate was the dominant 

anion making up the dissolved solids (fig. 37). Nutrient 

concentrations were also moderately high, with 

75 percent of nitrate concentrations at 1.0 mg/L or 

higher and phosphorus detected above laboratory 

MRLs in 90 percent or more samples (table 22). Nearly 

25 percent of the concentrations of total phosphorus 

were greater than 0.1 mg/L, USEPA’s (1986a) desired 

goal to prevent nuisance plant growth in streams. All 

species of nitrogen analyzed for were present in most 

samples; however, nitrate, with a median concentration 

of 1.26 mg/L was the dominant nitrogen species.

In addition to monthly routine samples, 13 of the 

46 samples were collected during rainstorms or 

snowmelt events. Total organic-nitrogen and 

phosphorus, organic-carbon, and suspended-sediment 

concentrations varied directly with streamflows, with 

Kendall’s τ correlation coefficients ranging from 0.5 to 

0.6 (table 23). The highest nutrient and suspendedsediment concentrations tended to correspond with 

relatively small runoff events in spring rather than with 

the large flows (fig. 38). Concentrations of nutrients in 

filtered water (nitrate and orthophosphate) showed a 

weak tendency to vary inversely with streamflow 

(τ = -0.4 and -0.2, respectively). Dissolved-solids, 

bicarbonate, and conductivity all varied inversely with 

streamflows (τ = -0.7 to -0.8). These negative relations 

generally indicate dilution of the stream’s water 

chemistry by runoff from rain or occasionally 

snowmelt.

On the basis of the long-term hydrograph for 

site 11 (see fig. 36), the highest streamflows occur 

during high-flow periods from October through 

February, followed by a transition period of gradually 

diminishing flows from March through June. The lowflow period is from July through September when the 

stream is at or near baseflow levels. The highest 

suspended-sediment concentrations were in samples 

collected during the high-flow and transition periods. 

On the other hand, medians and interquartile ranges of 

concentrations indicated nutrient concentrations to be 

similar across the three periods. The weak but negative 

correlations of dissolved nutrient concentrations with 

flow, and generally stable concentrations of the 

nutrients over the year, suggest a relatively constant 

source of the dissolved species of nitrogen and 

phosphorus to the creek, such as from shallow ground 

water.

Thornton Creek Organic Chemistry

A total of 20 pesticides and transformation 

compounds were detected in samples collected from 

March 1996 through April 1998 (table 24). Most of the 

compounds detected were herbicides. The herbicide 

prometon was detected most frequently, in 45 of 46 

samples at concentrations as high as 0.201 μg/L and 

with a median of 0.025 μg/L. Simazine and dichlobenil 

were the next most frequently detected, in 23 and 21 

samples, respectively.

Of the 20 pesticide compounds detected, 5 were 

insecticides—carbaryl, chlorpyrifos, diazinon, lindane, 

and malathion. These insecticides are used for pest 

control on turf, lawns, ornamentals, berries, and 

structures (see table 27), and all but lindane are readily 

available to the public through retail sales (Dale Davis, 

Washington Department of Ecology, written commun., 

February 1998; Voss and others, 1999). 

Table 23. Correlation between selected water-quality characteristics or 

chemical constituents and streamflow for Thornton Creek (site 11) in the 

Puget Sound Basin study unit, Washington

Water-quality characteristic or chemical 

constituent

Kendall’s tau 

correlation 

coefficient

Thornton Creek 

(Site 11)

Specific electrical conductance -0.73

Dissolved solids -.68

Total nitrogen .23

Dissolved nitrite-plus-nitrate nitrogen -.35

Total ammonia-plus-organic nitrogen .51

Dissolved ammonia-plus-organic nitrogen .41

Total phosphorus .46

Dissolved orthophosphate phosphorus -.17

Dissolved organic carbon .48

Suspended organic carbon .62

Suspended sediment .60

Bicarbonate -.81

Iron -.15

Manganese .07
Surface-Water Quality of the Skokomish, Nooksack, and Green-Duwamish Rivers and Thornton Creek 87

0

0.8 1.6 MILES

0.8 1.6 KILOMETERS

0

Site 11 - Thornton Creek

Na + K

Ca

Mg

Cl

SO4

HCO 3

Median milliequivalents

per liter

-2 0 2

0

2

4

0

1.5

0.5

1.0

ORGANIC CARBON, 

IN MILLIGRAMS PER LITER

Nitrogen Phosphorus Suspended 

Sediment

Organic

Carbon

8

10

MEDIAN SUSPENDED SEDIMENT

MEDIAN NUTRIENT COMPOSITION AND CARBON

0.02

0.04

0.06

0

2

4

6

SEDIMENT, 

IN MILLIGRAMS PER LITER

PHOSPHORUS, 

0

IN MILLIGRAMS PER LITER

1

3

Lake 

Washington

Northgate

Mall

Jackson Park

Golf Course

NE 145th Street

NF Thornton

Creek

SFThornto n

Creek Lake City

Way NE

I

5

I

5

122 ̊21' 122 ̊19' 122 ̊17'

47 ̊

45'

47 ̊

42'

30"

NITROGEN, 

IN MILLIGRAMS PER LITER (mg/L)

EXPLANATION

EXPLANATION

Total phosphorus

Dissolved phosphorus

Dissolved 

 orthophosphate

Dissolved nitrite-plus-nitrate

Dissolved ammonia

Dissolved ammonia-plus-organic

Total ammonia-plus-organic

Suspended sediment

Dissolved organic carbon

Suspended organic carbon

Sample site

Land use/cover

Forest/natural cover/

 other

Lakes

Urban/built up areas Basin boundary 

Streams

NITROGEN PHOSPHORUS

Figure 37. Median concentrations of nutrients, suspended sediment, organic carbon, and major ions in samples from Thornton Creek 

(site 11) in the Puget Sound Basin study unit, Washington.
88 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Dissolved orthophosphate

Total nitrogen

Total phosphorus

Suspended sediment

Dissolved Orthophosphate Suspended Sediment

MAMJ J ASOND J FMAMJ J ASOND J FMA

0

150

50

100

0.2

0.1

MAMJ J ASOND J FMAMJ J ASOND J FMA

1996 1997 1998

0

150

50

100

1

5,000

10

100

1,000

0

5

2

4

0

1.2

0.5

1.0

0.2

0.1

1

500

2

5

10

20

50

100

200

MAMJ J ASOND J FMAMJ J ASOND J FMA

0

0

150

50

100

0

1.5

0.5

1.0

6

2

4

MAMJ J ASOND J FMAMJ J ASOND J FMA

0

150

50

100

0

0

STREAMFLOW PERIODS

STREAMFLOW, IN CUBIC FEET PER SECOND

CONCENTRATION, IN MILLIGRAMS PER LITER

 CONCENTRATION, 

IN MILLIGRAMS PER LITER

Total Nitrogen and

Total Phosphorus (in blue)

Oct.-

Feb.

Mar.-

June 

JulySept.Oct.-

Feb.

Mar.-

June 

JulySept.Oct.-

Feb.

Mar.-

June 

JulySept.

EXPLANATION

Concentration percentiles

10th percentile

25th percentile

Median

75th percentile

90th percentile

Low-flow

High-flow

Transition

Daily streamflow

Minimum reporting level

Figure 38. Time series of streamflow and concentrations of total nitrogen, total phosphorus, dissolved orthophosphate phosphorus, and suspended sediment in 

samples, and concentrations by three streamflow periods, for Thornton Creek (site 11) in the Puget Sound Basin study unit, Washington.

(Truncated boxplots of concentration percentiles require a minimum of nine observations, otherwise concentrations are plotted as individual points. Censored 

data in the time-series graphs are shown as an open symbol. Boxplots are truncated at the minimum reporting level indicated by solid line.)
Surface-Water Quality of the Skokomish, Nooksack, and Green-Duwamish Rivers and Thornton Creek 89

The most frequently detected insecticide, diazinon, was 

detected in 39 samples (85 percent of the samples 

collected) at concentrations ranging from 0.003 to 

0.501 μg/L. Diazinon concentrations in fifteen of these 

samples exceeded 0.04 μg/L, a limit recommended for 

the protection of aquatic life by Menconi and Cox 

(1994) (see table 2). In the 1980’s, approximately 

83,000 pounds of diazinon were applied within the 

study unit, about half (39,600 pounds) within King 

County (Tetra Tech, 1988). Diazinon also is the 

insecticide purchased at the highest rate by the public 

through retail outlets in King County (Voss and others, 

1999). Two samples had concentrations of carbaryl that 

exceeded 0.017 μg/L, a limit recommended for the 

protection of aquatic life by Norris and Dost (1992). 

Lastly, one sample contained chlorpyrifos at a 

concentration of 0.074 μg/L, which exceeded the 

USEPA (1998) aquatic-life criterion of 0.041 μg/L, and 

one sample contained lindane at a concentration of 

0.02 μg/L, which exceeded the International Joint 

Commission Canada and United States (1977) aquaticlife guideline of 0.01 μg/L. Insecticides purchased by 

the public for use on lawns and gardens affected the 

water quality and contributed to the frequency of 

detections and concentrations above criteria (Voss and 

others, 1999).

Table 24. Pesticides in water samples from Thornton Creek (site 11) in the Puget Sound Basin study unit, Washington

[Water-quality criteria – Drinking water: U.S. Environmental Protection Agency (1996). Aquatic organisms – Chronic (USGS): U.S. 

Geological Survey (1999a). Based on 46 samples collected March 1996 to April 1998; all concentrations are in micrograms per liter (μg/L); bold

type indicates value above aquatic life criterion; method detection limits are from reports by Zaugg and others (1995), Lindley and others (1996), 

Werner and others (1996), and U.S. Geological Survey National Water Quality Laboratory Technical Memorandums 98.03A and 96.06A; MCL, 

maximum contaminant level; HAL, Health advisory level; E, Estimated–a qualitative value that is less than the statistically determined method 

detection limit or lowest calibration standard; –, no value or data]

Pesticide Number of 

detections

Maximum 

concentration 

value

Median 

concentration 

detected

Method 

detection 

limit

Water-quality criteria

Drinking water Aquatic organisms (freshwater)

MCL HAL Acute Chronic Chronic 

(USGS)

Atrazine 19 0.006 E0.003 0.001 3 3 170 17 1.8

Carbaryl 4 E.044 E.014 .003 – 700 10.17 10.017 0.2

Chlorpyrifos 3 .074 .015 .004 – 20 2.083 2.041 .041

DCPA 1 .002 – .002 – – – – –

Deethylatrazine 2 E.002 – .002 – – – – –

Diazinon 39 .501 .026 .002 – 0.6 3.16 3.04 .08

Dichlobenil 21 E1.2 E.04 1.2 – – – – –

Diuron 4 .45 .135 .02 – 10 – – –

EPTC 1 .005 – .002 – – – – –

Lindane 1 .02 – .004 .2 .2 2.95 4.08 .01

Malathion 10 .042 .0185 .005 – 200 – 2.1 .1

MCPA 2 .07 – .17 – 10 – – 2.6

Napropamide 2 .054 – .003 – – – – –

Oryzalin 1 .43 – .31 – – – – –

Prometon 45 .201 .025 .018 – 100 – – –

Pronamide 1 .008 – .003 – 50 – – –

Simazine 23 .37 .007 .005 4 4 1100 110 10

Tebuthiuron 1 .025 – .01 – 500 – – 1.6

Triclopyr 1 .82 – .25 – – 15,600 1560 –

Trifluralin 2 .007 – .002 – 5 – – .2

1 Norris and Dost (1992).

2U.S. Environmental Protection Agency (1998).

3Menconi and Cox (1994).

4State of Washington (1992).
90 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

The most frequently observed pesticides at 

site 11, prometon, simazine, and diazinon, were also 

the pesticides detected most frequently at urbanindicator sites sampled in NAWQA study units 

nationwide during 1992-95 (Larson and others, 1997). 

Most of the concentrations of these frequently detected 

pesticides at site 11 ranked within the middle50 percent or within the lowest-25-percent range of 

concentrations in urban streams studied nationwide in 

36 NAWQA study units during 1991–98. Several 

concentrations, particularly of diazinon, were in the 

highest-25-percent range of concentrations (Ebbert and 

others, 2000).

Except for diazinon and prometon, pesticide 

concentrations were not related to magnitude of 

streamflows. For prometon and diazinon, 

concentrations were positively correlated with flow, but 

the relations were weak (Kendall’s τ was 0.4 and 0.5, 

respectively; p-values less than 0.001). Season and 

timing of applications appeared to have the greatest 

influence on pesticide concentrations and detection 

frequencies. Some of the largest concentrations were in 

samples collected in spring or early summer from 

about March through May, particularly if during a rain 

event. Dichlobenil, rarely detected in winter, was found 

in most all spring and summer samples (fig. 39). 

Diazinon concentrations peaked in the spring and again 

in the fall when applications in urban areas are 

common. The high concentrations of diazinon at the 

end of May 1997 and in April 1996 during storms 

exceeded both the acute (0.16 μg/L) and chronic 

(0.04 μg/L) criteria concentrations recommended by 

Menconi and Cox (1994) for the protection of aquatic 

organisms. Both diazinon and prometon, present in so 

many samples, were detected in relatively high 

concentrations in baseflow samples as well. The source 

of relatively high concentrations of diazinon and 

prometon in some of the baseflow samples was 

probably precipitation that washed these pesticides into 

the stream. For example, detections of high 

concentrations of diazinon and malathion on August 5, 

1996, came after 0.74 inch of rain fell on August 2, and 

it was raining again on the day of collection. In that 

sample, the maximum concentration of malathion 

(0.042 μg/L) and one of the higher values of diazinon 

(0.13 μg/L) were observed.

Of the four intensive fixed sites, the Thornton 

Creek samples contained the most VOCs: 32

compounds (table 25). Ten compounds (acetone, 

bromoform, trichloromethane, ethylbenzene, 

dichloromethane, 4-methyl-2-pentanone, 

methylbenzene, 1,2,4-trimethylbenzene, 1,3-plus-1,4-

dimethylbenzene, and 1,2-dimethylbenzene) were 

detected at concentrations above the 1999 LRLs the 

greatest number of times (see fig. 6). In 80 percent of 

the samples with VOC detections, concentrations of 

methylbenzene exceeded the LRL the greatest number 

of times. Although detections of several VOCs were 

numerous, no VOC concentration exceeded any 

established drinking-water or aquatic-life criteria.

A comparison of detections of compounds in 

concentrations above LRLs with streamflows at the 

time of sampling indicated that several compounds 

typically were found during wet winter months 

(fig. 40). The compounds 1,3-plus-1,4-

dimethylbenzene, 1,2,4-trimethylbenzene, and 4-

methyl-2-pentanone were detected mostly between 

September and May when streamflows were at their 

highest. Conversely, methylbenzene, acetone, and 

trichloromethane were detected during both the 

summer and winter months. Trichloromethane is a byproduct of the chlorination process for drinking-water 

supplies and its presence in streamwater might indicate 

mixing of chlorinated water supplies with the stream. 

Some of the highest trichloromethane concentrations 

were in samples collected during summer baseflow 

conditions, indicating that a shallow source, such as 

shallow ground water or sewer lines, might be 

contributing trichloromethane to the stream. 

Additionally, trichloromethane concentrations might be 

higher during the summer because of the increased 

outdoor use of chlorinated public water supplies.
Surface-Water Quality of the Skokomish, Nooksack, and Green-Duwamish Rivers and Thornton Creek 91

Table 25. Volatile organic compounds in water samples from Thornton Creek (site 11) in the Puget Sound Basin study unit, Washington

[Water-quality criteria – Drinking water: U.S. Environmental Protection Agency (1996). Based on 47 samples collected between March 1996 to May 1998; 

all concentrations are in micrograms per liter (μg/L); MRL, method reporting level (Connor and others, 1998); LRL, laboratory reporting level; MCL, 

maximum contaminant level; HAL, health advisory level; E, Estimated–a qualifier for an analytical result based on the long-term method detection level, 

laboratory reporting level, and lowest calibration standard (Childress and others, 1999); –, no value or data]

Volatile

organic compound

Number of 

detections

Percentage 

of detections 

above 1999 

LRL and 

(number)

Maximum 

concentration 

value

Median 

concentration 

detected

MRL

(1999 LRL)

Water-quality criteria

Drinking water

Aquatic 

organisms 

(freshwater)

MCL HAL Chronic

1,2,3,4-Tetramethylbenzene 

(Prehnitene)

4 0 E0.04 E0.02 0.23 (0.23) – – –

1,2,3,5-Tetramethylbenzene (Isodurene) 2 0 E.05 – .24 (.24) – – –

1,2,3-Trimethylbenzene 5 0 E.03 E.02 .124 (.12) – – –

1,2,4-Trimethylbenzene 12 33 (4) .12 E.035 .056 (.056) – – –

1,2-Dimethylbenzene (o-Xylene) 6 50 (3) .1 E.06 .064 (.06) 10,000 10,000 –

1,3-plus-1,4-Dimethylbenzene 

(m,p-Xylene)

17 29 (5) .2 E.04 .064 (.06) 10,000 10,000 –

1,3,5-Trimethylbenzene 3 0 E.02 E.01 .044 (.044) – – –

1,4-Dichlorobenzene 5 0 E.01 E.007 .05 (.05) 75 75 126

(1-Methylethyl)benzene 

(Isopropylbenzene)

1 0 E.006 – .032 (.032) – – –

2-Butanone (Methyl ethyl ketone) 8 0 1.17 E.8 1.65 (1.6) – – –

2-Ethyltoluene (o-Ethyl toluene) 5 0 E.03 E.01 .1 (.1) – – –

1-Isopropyl-4-methylbenzene 

(p-Isopropyltoluene)

20 0 E.044 E.01 .11 (.11) – – –

4-Methyl-2-pentanone (Methyl isobutyl 

ketone)

13 54 (7) E1.0 E.4 .374 (.374) – – –

Acetone 20 35 (7) 12.5 2.7 4.904 (5) – – –

Benzene 16 0 E.1 E.035 .032 (.1) 5 – 1370

Bromoform 2 50 (1) .17 – .104 (.1) 100 – –

Carbon disulfide 14 0 .105 E.015 .08 (.37) – – –

Chlorobenzene 1 0 E.002 – .028 (.028) 100 100 11.3

Chloroethane 2 0 E.09 – .12 (.12) – – –

Chloromethane (Methyl chloride) 15 0 .135 E.04 .254 (.25) – 3 –

Dichloromethane (Methylene chloride) 5 60 (3) 1.36 .45 .382 (.38) 5 – 198.1

Diethyl ether 2 0 E.06 – .17 (.17) – – –

Ethenylbenzene (Styrene) 7 0 E.01 E.009 .042 (.042) 100 100 –

Ethylbenzene 8 38 (3) E.05 E.015 .03 (.03) 700 700

Iodomethane (Methyl iodide) 1 0 E.009 – .076 (.21) – – –

Methylbenzene (Toluene) 40 80 (32) .526 E.1 .038 (.05) 1,000 1,000 12

Naphthalene 10 0 .16 E.075 .25 (.25) – 20 11.1

Tetrachloroethene 22 0 E.03 E.01 .038 (.1) 5 – 1111

Tetrahydrofuran 1 0 E.3 – 1.148 (9.0) – – –

Trichloromethane (Chloroform) 43 28 (12) .16 E.04 .052 (.052) 100 – 11.8

n-Butylbenzene 3 0 E.01 E.01 .186 (.19) – – –

n-Propylbenzene 4 0 E.02 E.009 .042 (.042) – – –

1 Environment Canada (1999).
92 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

E

E

E

E E

E

E

E

E

E E E E E

E

E E E E

E E

E E

E E

E E E E E E E

E

E

Streamflow

E

Concentration less than

 method reporting limit

EXPLANATION

Compound detected

Concentration estimated

0

150

50

100

0

0.010

0.002

0.004

0.006

0.008

0

150

50

100

0.002

0.4

0.005

0.01

0.02

0.05

0.1

0.2 Simazine

1996 1997 1998

0

150

50

100

0

0.25

0.1

0.2

Prometon

0

150

50

100

0.0002

10

0.001

0.01

0.1

1

Dichlobenil

Atrazine

CONCENTRATION, IN MICROGRAMS PER LITER

STREAMFLOW, IN CUBIC FEET PER SECOND

M A M J J AS O N D J FM A M J J A SO N D J FM A

M A M J J AS O N D J FM A M J J A SO N D J FM A

M A M J J AS O N D J FM A M J J A SO N D J FM A

M A M J J AS O N D J FM A M J J A SO N D J FM A

Figure 39. Time series of streamflow and concentrations of selected pesticides detected in samples from Thornton Creek (site 11) in the 

Puget Sound Basin study unit, Washington.
Surface-Water Quality of the Skokomish, Nooksack, and Green-Duwamish Rivers and Thornton Creek 93

EXPLANATION

Streamflow

E

Concentration less than

 method reporting limit

Compound detected

Concentration estimated

Chlorpyrifos

Malathion

Diazinon

Carbaryl

0

150

50

100

0.002

0.1

0.003

0.004

0.005

0.007

0.01

0.02

0.03

0.04

0.05

0.07

0

150

50

100

0

0.05

0.02

0.04

0

150

50

100

0.001

1

0.002

0.005

0.01

0.02

0.05

0.1

0.2

0.5

M AM J J A S OND J FM AMJ J A SO N D J FM A

M AM J J A S OND J FM AMJ J A SO N D J FM A

M AM J J A S OND J FM AMJ J A SO N D J FM A

M AM J J A S OND J FM AMJ J A SO N D J FM A

1996 1997 1998

0

150

50

100

0.002

0.1

0.003

0.004

0.005

0.007

0.01

0.02

0.03

0.04

0.05

0.07

CONCENTRATION, IN MICROGRAMS PER LITER

STREAMFLOW, IN CUBIC FEET PER SECOND

E E

<0.01

<0.01

E

E

E

Figure 39. —Continued.
94 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

MAMJ J ASOND J FMAMJ J ASOND J FMAM

0

1.0

0.2

0.4

0.6

0.8

CONCENTRATION, IN MICROGRAMS PER LITER

0

150

50

100

STREAMFLOW, IN CUBIC FEET PER SECOND

Methylbenzene (Toluene)

MAMJ J ASOND J FMAMJ J ASOND J FMAM

0

150

50

100

0

0.20

0.05

0.10

0.15

Benzene

MAMJ J ASOND J FMAMJ J ASOND J FMAM

0

150

50

100

0

0.3

0.1

0.2

1,3- plus-1,4-Dimethylbenzene (m,p-Xylene)

MAMJ J ASOND J FMAMJ J ASOND J FMAM

1996 1997 1998

0

150

50

100

0

0.15

0.05

0.10

1,2,4-Trimethylbenzene

Streamflow

Compound detected

Compound detected at an

 estimated concentration

 below the 1999 LRL

Compound not detected

1999 Laboratory Reporting 

 Level (LRL)

EXPLANATION

Figure 40. Time series of streamflow and concentrations of selected volatile organic compounds in samples from Thornton Creek 

(site 11) in the Puget Sound Basin study unit, Washington.
Surface-Water Quality of the Skokomish, Nooksack, and Green-Duwamish Rivers and Thornton Creek 95

MAMJ J ASOND J FMAMJ J ASOND J FMAM

0

20

5

10

15

CONCENTRATION, IN MICROGRAMS PER LITER

0

150

50

100

STREAMFLOW, IN CUBIC FEET PER SECOND

Acetone

MAMJ J ASOND J FMAMJ J ASOND J FMAM

0

150

50

100

0

0.20

0.05

0.10

0.15

Trichloromethane (Chloroform)

MAMJ J ASOND J FMAMJ J ASOND J FMAM

0

150

50

100

0.005

5

0.01

0.02

0.05

0.1

0.2

0.5

1

2 Carbon disulfide

MAMJ J ASOND J FMAMJ J ASOND J FMAM

1996 1997 1998

0

150

50

100

0

1.5

0.5

1.0

4-Methyl-2-pentanone (Methyl isobutyl ketone)

Streamflow

Compound detected

Compound detected at an

 estimated concentration

 below the 1999 LRL

Compound not detected

1999 Laboratory Reporting 

 Level (LRL)

EXPLANATION

Figure 40. —Continued.
96 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

LAND USE AND WATER QUALITY

Water-quality conditions at the fixed sites reflect 

natural characteristics of the watersheds and those 

resulting from human activities. In the Nooksack and 

Skokomish Rivers, natural features such as steep 

gradients, high-energy stream channels, and unstable 

alluvial streambeds of the mountainous upper 

watersheds are important factors affecting suspendedsediment concentrations, which can be large during 

high streamflow events. In summer, water in the 

Nooksack becomes turbid with a finely ground rock 

material called glacial flour. It is possible that extensive 

logging and road building in the Nooksack and 

Skokomish watersheds are also contributing to the 

suspended-sediment loads, but the extent of this 

contribution is unknown. In the forested study basins, 

dissolved solids and nutrient concentrations were low. 

At the reference site on the NF Skokomish and the 

forestry-practices indicator site on the upper Green, 

natural conditions were reflected in water that was of 

high quality with low concentrations of dissolved 

solids, nutrients, and sediment, and standards and 

criteria that were nearly always met. The other 

forestry-practices sites (with more than 80 percent 

forest in their basins), the upper Nooksack and 

Skokomish, had water of similarly good quality, with 

some differences that were likely due to natural 

conditions. For example, some of the large phosphorus 

concentrations were in samples from the upper 

Nooksack, indicating that geologic material might be a 

natural source of phosphorus in this watershed. In 

general, nutrient concentrations were lowest among the 

forested sites. In a ranking of the 11 study sites by 

average nitrogen and orthophosphate concentrations, 

the reference and the forestry-practices sites ranked 

near the bottom of the list (table 26).

Unlike the reference and forestry sites with high 

quality of water, natural conditions might be adversely 

affecting the quality of water in the urban indicator 

stream Springbrook, where the sampling reach appears 

to be in a ground-water discharge zone. The high 

concentrations of iron and manganese, low dissolvedoxygen concentrations, and perhaps some of the 

generally high concentrations of phosphorus observed 

during the study might be attributed to the quality of 

ground water discharging to this reach. These 

conditions resulted in iron and manganese 

concentrations exceeding USEPA SMCLs in most of 

the samples, and in low concentrations of dissolved 

oxygen.

Human activities have pronounced effects on 

water quality at sites in both agricultural and urban 

basins. Small streams and large rivers in urban and 

agricultural settings had, on average, higher nitrogen 

concentration, and small streams had higher 

orthophosphate concentrations, than the reference 

stream, NF Skokomish (table 26). Total nitrogen 

concentrations were highest in the small, agricultural 

streams (Fishtrap and Newaukum), with averages of 

about 3 mg/L. Total nitrogen concentrations in the 

small, urban streams were about half the average 

concentrations of the agricultural streams (table 26). 

Among the large rivers integrating a mix of land uses, 

the lower Nooksack in an agricultural setting, and the 

Duwamish in an urban setting, had the highest 

concentrations of total nitrogen. Average total nitrogen 

in these two rivers exceeded that of the large rivers in 

forested settings, such as the Skokomish, which had an 

average total nitrogen concentration of only 0.13 mg/L. 

On the basis of average orthophosphate concentrations, 

small urban streams ranked near the top of the list, but 

the average (0.04 mg/L) was considerably lower than 

the 0.14 mg/L average concentration for the small 

agricultural stream, Newaukum Creek.
Land Use and Water Quality 97

Table 26. Ranking of 11 large rivers and small streams by average total nitrogen concentrations (the sum of nitrite, nitrate, ammonia, and 

organic nitrogen) and by average dissolved orthophosphate phosphorus concentrations for the Puget Sound Basin study unit, Washington

[Average total phosphorus concentration: Bold concentrations exceed U.S. Environmental Protection Agency’s (1986a) goal to prevent nuisance 

plant growth in streams. Basin size: Basin size in square miles is shown in table 1. mg/L, milligrams per liter]

Total nitrogen

Large river or small stream

 (site No.)

Average total 

nitrogen 

concentration, 

in mg/L

Average total 

phosphorus 

concentration, 

in mg/L

Average dissolved 

orthophosphate 

phosphorus 

concentration,

in mg/L

Basin size Land use

Fishtrap (site 4) 3.54 0.086 0.018 small agriculture

Newaukum (site 9) 2.82 .21 .142 small agriculture

Thornton (site 11) 1.73 .129 .035 small urban

Big Soos (site 8) 1.2 .052 .022 small urban

Springbrook (site 7) 1.1 .165 .035 small urban

Nooksack at Brennan (site 3) 0.66 .294 .009 large mixed; agriculture setting

Duwamish (site 6) .65 .088 .024 large mixed; urban setting

Nooksack at North Cedarville (site 5) .39 .148 .005 large mixed; forestry setting

Skokomish (site 1) .13 .075 .01 large mixed; forestry setting

North Fork Skokomish (site 2) .07 .012 .007 small reference/undeveloped

Green (site 10) .07 .012 .012 small forestry

Dissolved orthophosphate phosphorus

Large river or small stream

 (site No.)

Average total 

nitrogen 

concentration, 

in mg/L

Average total 

phosphorus 

concentration, 

in mg/L

Average dissolved 

orthophosphate 

phosphorus 

concentration,

in mg/L

Basin size Land use

Newaukum (site 9) 2.82 0.21 0.142 small agriculture

Thornton (site 11) 1.73 .129 .035 small urban

Springbrook (site 7) 1.1 .165 .035 small urban

Duwamish (site 6) 0.65 .088 .024 large mixed; urban setting

Big Soos (site 8) 1.2 .052 .022 small urban

Fishtrap (site 4) 3.54 .086 .018 small agriculture

Green (site 10) .07 .012 .012 small forestry

Skokomish (site 1) .13 .075 .01 large mixed; forestry setting

Nooksack at Brennan (site 3) .66 .294 .009 large mixed; agriculture setting

North Fork Skokomish (site 2) .07 .012 .007 small reference/undeveloped

Nooksack at North Cedarville (site 5) .39 .148 .005 large mixed; forestry setting
98 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Pesticides from human activities affected water 

quality at all four intensively studied sites in both urban 

and agricultural settings. More types of pesticides were 

found at the agricultural sites than at the urban sites 

(fig. 41). Of the four sites, the most pesticides were 

detected in Fishtrap and more types of pesticides were 

detected in the lower Nooksack than in the Duwamish. 

The diversity of pesticides found at the agricultural 

sites probably reflected the detection of pesticides for 

urban and domestic use and those used in maintaining 

rights-of-way in addition to pesticides applied for 

agricultural purposes. Prometon and tebuthiuron, 

considered as mostly urban-use herbicides, were quite 

prevalent in samples from Fishtrap Creek. Both 

compounds are widely used along roads, railroads, 

fencelines, and industrial areas for general brush 

control and on lawns, and both are available to the 

general public in retail stores (Dale Davis, Washington 

State Department of Ecology, written commun., 

February 1998; Voss and others, 1999). The more 

urbanized areas in the upper part of the basin, the 

nearby city of Lynden, and the relatively high density 

of roads, ditches, and levees could all be potential 

sources of these herbicides to the creek. Some 

insecticides in samples from Fishtrap, such as carbaryl, 

might come from urban or agricultural uses, or both. 

Carbaryl, diazinon, and malathion are available in retail 

stores and used in urban settings and, along with the 

insecticides carbofuran, ethoprophos, oxamyl, and 

propargite, are listed for agricultural applications to 

beans, strawberries, raspberries, potatoes, and alfalfa 

(Gianessi and Puffer, 1991 and 1992) (table 27).

Although more types of pesticides were detected 

in samples from agricultural sites than from urban sites, 

pesticides were applied in larger quantities in the urban 

areas. Approximately 783,000 pounds of herbicides 

(92,500 pounds for agricultural purposes) and 

367,000 pounds of insecticides (40,000 pounds for 

agriculture) were applied annually to the PSB study 

unit (Tetra Tech, 1988; U.S. Geological Survey, 1999c) 

(table 27). About 18 percent of the total herbicide 

applications were within King County, where Thornton 

Creek and the Duwamish River are located, and 

9 percent were within Whatcom County, where 

Fishtrap Creek and the Nooksack River are located. 

Detections of insecticides, however, were more 

frequent and were generally higher in concentration in 

urban streams than in agricultural streams, probably 

because of the quantity of insecticide used in urban 

areas. Thirty-one percent of the total insecticide 

applications (agricultural and non-agricultural) were 

within King County and only about 3 percent of the 

agricultural and non-agricultural applications of 

insecticides were within Whatcom County. High 

concentrations of insecticides (which often did not 

meet aquatic-life criteria) in the urban streams also 

probably reflected these high percentages of pesticide 

applications and the availability of insecticides in urban 

areas.

More VOCs were detected and at a higher 

detection frequency at the two sites located in urban 

areas than at the two sites in agricultural areas (fig. 42). 

For example, 31 compounds were detected in samples 

from Thornton (100-percent urbanized basin) and 27 

compounds were detected in samples from the 

Duwamish. Conversely, the least number of VOCs (16) 

were detected at the lower Nooksack, with only 2 

percent urban land upstream. Many of the VOCs found 

at all four sites are fuel related, such as the benzene, 

methylbenzene, 1,3-plus-1,4-dimethylbenzene, and 

1,2-dimethylbenzene compounds. The fuel-related 

compounds originating from vehicle emissions and 

perhaps some spills or leaks could enter the streams by 

direct runoff from streets and highways and from 

precipitation containing small amounts of dissolved 

VOCs. MTBE, an automotive fuel additive used in 

Canada, was found at concentrations below the 1999 

LRL in a few samples from Fishtrap, which has about 

two-thirds of its drainage area in Canada. MTBE is 

generally not used in Washington and was detected in 

only one other sample taken at the Duwamish River.

Another group of compounds detected at all sites 

were trihalomethanes (THM). Trichloromethane was 

found at all four sites and bromoform was found at all 

but Fishtrap Creek. THMs can be formed as byproducts from the chlorination of drinking water and 

trichloromethane is also used as an industrial solvent 

(Minear and Amy, 1995). The most THM detections 

and the highest concentrations were in urbanized 

Thornton, where their presence is likely due to 

chlorinated public water supplies and possibly to 

industrial releases into the atmosphere from the greater 

metropolitan area.
Land Use and Water Quality 99

acetochlor alachlor atrazine deethylatrazine2,4-DDCPA

dicamba

dichlobenil diuron EPTC fluometuron linuron

metolachlor metribuzin MCPA

molinate

napropamide norflurazon oryzalin pebulate prometon pronamide simazine

tebuthiuron terbacil triclopyr trifluralin

carbaryl

carbofuran chlorpyrifos diazinon

lindane

malathion oxamyl

propargite

0

100

20

40

60

80

DETECTIONS, IN PERCENT OF SAMPLES ANALYZED

Fishtrap Creek,

 agricultural land use

Thornton Creek,

 urban land use

HERBICIDES AND TRANSFORMATION PRODUCTS INSECTICIDES

acetochlor alachlor atrazine deethylatrazine2,4-DDCPA

dicamba

dichlobenil diuronEPTC fluometuron linuron

metolachlor metribuzin MCPA

molinate

napropamide norflurazon oryzalin pebulate prometon pronamide simazine

tebuthiuron terbacil triclopyr trifluralin

carbaryl

carbofuran chlorpyrifos diazinon

ethoprophos

ethoprophos

lindane

malathion oxamyl

propargite

0

100

20

40

60

80

Lower Nooksack River,

 mixed land use in an agricultural setting

Duwamish River,

 mixed land use in an urban setting

HERBICIDES AND TRANSFORMATION PRODUCTS INSECTICIDES

Figure 41. Percentage of detections of pesticides and transformation products in samples from the four intensive fixed sites—lower 

Nooksack River (site 3), Fishtrap Creek (site 4), Duwamish River (site 6), and Thornton Creek (site 11) in the Puget Sound Basin study unit, 

Washington.
100 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Table 27. Pesticides detected in water samples from the study sites, the primary use of these pesticides, and estimated pounds of active ingredient 

applied each year in the Puget Sound Basin study unit, Washington—Continued

Pesticide Primary use

Estimated applied active ingredient, in thousands of pounds 

per year

In study unit for 

agricultural 

purposes

In study unit In King 

County

In Whatcom 

County

HERBICIDES 92.5 783 141 71.5

Acetochlor Corn – – – –

Alachlor Corn 5.4 9.4 0.8 2.6

Atrazine Corn, forestry, rights-of-way, Christmas trees1 6.0 44.4 18.3 3.6

2,4-D Agriculture, forestry, urban, wheat, barley, oats, corn, hay, 

rights-of-way, turf, lawns; available in retail stores

17.4 311 25.2 11.6

Dicamba Forestry, urban, wheat, corn, seed crops, oats, rights-of-way, 

fencelines, turf, lawns; available in retail stores

0.9 55.4 19.2 3.6

DCPA Lawns, turf, ornamentals, seed crops .2 0.02 .02 –

Dichlobenil Urban, industrial sites, rights-of-way, golf-courses, under 

asphalt, raspberries; available in retail stores

.2 7.1 3.5 .3

Diuron Railways, rights-of-way, ornamentals, ornamental bulbs, seed 

crops, wheat, oats, raspberries

1.2 37.1 5.4 .3

EPTC Potatoes, beans, corn, alfalfa, urban residential; available in 

retail stores

28.4 – – –

Fluometuron Corn (Unknown in the study unit) – – – –

Linuron Corn, potatoes, carrots, roadsides, fencelines .4 – – –

Metolachlor Corn, potatoes, green beans, green peas, turf, fencelines, golf 

courses (New Jersey)

5.8 5.3 .3 1.8

Metribuzin Potatoes, alfalfa, grass seed, wheat, green peas, turf grasses 4.5 .3 – .09

MCPA Wheat, barley, grass seed, green peas, turf, lawns, urban 

residential; available in retail stores.

2.3 – – –

Molinate Unknown in study unit; golf courses (Japan); rice elsewhere – – – –

Napropamide Strawberries, raspberries, ornamental bulbs, turf, lawns 3.8 .5 .2 .05

Norflurozon Blueberries and raspberries1, nut trees 1.4 – – –

Oryzalin Urban, ornamental bulbs, lawns, golf courses, blueberries and 

raspberries1; available in retail stores

2.4 5.4 3.3 .2

Pebulate Unknown in the study unit – – – –

Prometon Road, railway, fenceline rights-of-way, lawns; industrial sites; 

urban residential; available in retail stores

– 109 28.3 32.6

Pronamide Alfalfa, seed crops, raspberries, turf, woody ornamentals, golf 

courses, forestry

1.8 5.8 .4 .2

Simazine Raspberries, strawberries, seed crops, turf, golf courses, lawns, 

aquatic control, brush control

2.7 97.3 19.7 2.6

Tebuthiuron Pasture, brush control, under asphalt1; rights-of-way, industrial 

sites, lawns

– 33.0 8.3 10.3

Table 27. Pesticides detected in water samples from the study sites, the primary use of these pesticides, and estimated pounds of active ingredient 

applied each year in the Puget Sound Basin study unit, Washington

[Pesticide: 2,4-D, (2,4-dichlorophenoxy) acetic acid; DCPA, dimethyltetrachloroterephthalate; EPTC, S-ethyl dipropylthiocarbamate; MCPA, (4-chloro-2-

methylphenoxy) acetic acid; HCH, hexachlorocyclohexane. Primary use: Uses compiled from Tetra Tech (1988); Gianessi and Puffer (1991 and 1992); 

Staubitz and others (1997); Voss and others (1999); Jack Barbash (U.S. Geological Survey, written commun., December 1998); Dale Davis (Washington State 

Department of Ecology, written commun., February 1998). Estimated applied active ingredient in study unit for agricultural purposes: U.S. Geological 

Survey (1999c); http://water.wr.usgs.gov/pnsp/anstrat/index.html#hdr1 accessed on February 24, 2000. Estimated applied active ingredient in study unit, 

and in King and Whatcom Counties: Tetra Tech (1988). –, no value]
Land Use and Water Quality 101

HERBICIDES – Continued

Terbacil Alfalfa, grass seed, strawberries, raspberries .5 1.9 – –

Triclopyr Forestry brush control, rights-of-way, urban residential, lawns; 

available in retail stores

– 54.6 7.8 .7

Trifluralin Potatoes, carrots, green beans, green peas, lawns, golf courses, 

urban residential; available in retail stores.

7.2 5.5 .4 1.0

INSECTICIDES 40 367 112 11.6

Carbaryl Beans, strawberries, raspberries, lawns, turf, ornamentals, urban 

residential; available in retail stores

3.2 37.3 14.2 3.1

Carbofuran Alfalfa, potatoes, strawberries 3.1 1.7 .4 .1

Chlorpyrifos Corn, alfalfa, strawberries, structural pest control, lawns, golf 

courses; urban residential; available in retail stores

6.1 39.4 18.5 1.6

Diazinon Berries, potatoes, row crops, household insects, lawns, urban 

residential; available in retail stores

5.8 83.1 39.6 3.5

Ethoprophos Potatoes, turf, golf courses 8.0 – – –

Lindane (gamma-HCH) Urban insecticide for Puget Sound (Tetra Tech, 1988) – 2.6 1.3 .1

Malathion Alfalfa, fruits, ornamentals, strawberries, blueberries, 

raspberries; available in retail stores

6.2 203 38.0 3.2

Oxamyl Raspberries in Canada, potatoes in Washington State (Inkpen 

and others, 2000) Potatoes in Gianessi and Puffer (1990)

2.3 – – –

Propargite Christmas trees, conifers, ornamentals, potatoes, alfalfa, 

strawberries

5.3 – – –

1 Reported for use in the Willamette Basin study by Anderson and others (1996).

Table 27. Pesticides detected in water samples from the study sites, the primary use of these pesticides, and estimated pounds of active ingredient 

applied each year in the Puget Sound Basin study unit, Washington—Continued

Pesticide Primary use

Estimated applied active ingredient, in thousands of pounds 

per year

In study unit for 

agricultural 

purposes

In study unit In King 

County

In Whatcom 

County

Many solvents were found in surface-water 

samples, particularly those samples taken from the 

Duwamish and Thornton. Carbon disulfide, 

chloromethane, and 4-methyl-2-pentanone were the 

most commonly detected solvents and were found at all 

four sites. However, many solvents were only found at 

the more urbanized sites. For example, the chlorinated 

solvents trichloroethene (TCE) and tetrachloroethene 

(PCE) were detected only in Duwamish and Thornton 

samples.

The only VOC that was distinctly for agricultural 

use was 1,2-dichloropropane, detected only in Fishtrap 

Creek (fig. 42). Historically, 1,2-dichloropropane was 

used as a soil fumigant and its use has been banned; 

however, at the time of this study, it was still contained 

in minute amounts in formulations of 1,3-

dichloropropene (Zebarth and others, 1998). Although 

1,3-dichloropropene has not been sold in Canada since 

1993 (Zebarth and others, 1998), it was still applied in 

the Washington State part of Fishtrap Creek Basin 

(Cindy Moore, Washington State Department of 

Agriculture, written commun., 1998) and might be a 

source of the 1,2-dichloropropane.
102 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

1,1,1-Trichloroethane

1,2,3,4-Tetramethylbenzene

1,2,3,5-Tetramethylbenzene

1,2,3-Trimethylbenzene

1,2,4-Trimethylbenzene

1,2-Dichloropropane

1,2-Dimethylbenzene

1,3- and 1,4-Dimethylbenzene

1,3,5-Trimethylbenzene

1,4-Dichlorobenzene

(1-Methylethyl)benzene

2-Butanone

2-Ethyltoluene

1-Isopropyl-4-methylbenzene

4-Methyl-2-pentanone

Acetone

Benzene

Bromoform

Carbon disulfide

Chlorobenzene

Chloroethane

Chloroethene

Chloromethane

Dichloromethane

Diethyl ether

Ethenylbenzene

Ethylbenzene

Iodomethane

Methylbenzene

Methyl tert-butyl ether

Naphthalene

Tetrachloroethene

Tetrahydrofuran

Trichloroethene

Trichloromethane

cis-1,2-Dichloroethene

n-Butylbenzene

n-Propylbenzene

0

100

20

40

60

80

DETECTIONS, IN PERCENT OF SAMPLES ANALYZED

1,1,1-Trichloroethane

1,2,3,4-Tetramethylbenzene

1,2,3,5-Tetramethylbenzene

1,2,3-Trimethylbenzene

1,2,4-Trimethylbenzene

1,2-Dichloropropane

1,2-Dimethylbenzene

1,3- plus-1,4-Dimethylbenzene

1,3,5-Trimethylbenzene

1,4-Dichlorobenzene

(1-Methylethyl)benzene

2-Butanone

2-Ethyltoluene

1-Isopropyl-4-methylbenzene

4-Methyl-2-pentanone

Acetone

Benzene

Bromoform

Carbon disulfide

Chlorobenzene

Chloroethane

Chloroethene

Chloromethane

Dichloromethane

Diethyl ether

Ethenylbenzene

Ethylbenzene

Iodomethane

Methylbenzene

Methyl tert-butyl ether

Naphthalene

Tetrachloroethene

Tetrahydrofuran

Trichloroethene

Trichloromethane

cis-1,2-Dichloroethene

n-Butylbenzene

n-Propylbenzene

0

100

20

40

60

80

Fishtrap Creek,

 agricultural land use

Thornton Creek,

 urban land use

Lower Nooksack River,

 mixed land use in an agricultural setting

Duwamish River,

 mixed land use in an urban setting

VOLATILE ORGANIC COMPOUND

Figure 42. Percentage of all detections of volatile organic compounds in samples from the four intensive fixed sites—lower Nooksack River 

(site 3), Fishtrap Creek (site 4), Duwamish River (site 6), and Thornton Creek (site 11) in the Puget Sound Basin study unit, Washington.
Loads and Yields 103

LOADS AND YIELDS

An estimate of loads is useful for assessing the 

quantity of constituents transported by rivers to 

receiving bodies of water, such as Puget Sound and 

Lake Washington, and for comparing yields of these 

constituents for river basins with different 

characteristics and land-use activities. In this study, the 

maximum likelihood estimation method (MLE) was 

selected for estimating loads of total nitrogen (using 

the sum of nitrite, nitrate, ammonia, and organicnitrogen concentrations), phosphorus (using 

concentrations determined on unfiltered water), and 

orthophosphate (using concentrations determined on 

filtered water) at all 11 sites. This selection was based 

on several factors described in Appendix C, which 

details the load estimates and provides graphs of 

predicted and measured daily loads, graphs of nutrient 

and suspended-sediment concentrations plotted as a 

function of streamflow, and tables of the regression 

equations, annual average loads and their standard 

deviations.

 In general, the standard deviations for totalnitrogen load estimates were smaller than those for the 

phosphorus-load estimates, possibly because there 

were fewer censored values in the nitrogen data sets 

than in the phosphorus data sets (Appendix tables C1-

C3). Nitrogen, in at least the nitrite-plus-nitrate form, 

was nearly always detected at concentrations above the 

MRL, whereas phosphorus and orthophosphate were 

typically detected at low concentrations and a high 

percentage were censored at the MRL. With 36 to 

42 percent of their data sets censored, the standard 

deviations for total nitrogen loads at the NF Skokomish 

and upper Green Rivers were about 9 and 2 tons per 

year, or 18 and 40 percent of their annual total nitrogen 

loads, respectively (Appendix table C1). Predicted 

daily and annual loads of total nitrogen from the 

regression equations agreed reasonably well with 

measured loads at most sites.

With 41 to 73 percent of their data sets censored, 

the estimates of annual phosphorus loads in the 

Skokomish and NF Skokomish had standard deviations 

of 40 and 73 percent, respectively (Appendix table C2). 

The annual orthophosphate load in the NF Skokomish 

had a standard deviation of 9 percent (Appendix 

table C3). At most sites the predicted annual loads of 

phosphorus and orthophosphate appeared reasonable 

when compared to measured loads, even though daily 

loads could be quite different. During parts of the wet 

season of water year 1997, the equations tended to 

overpredict daily loads of phosphorus or 

orthophosphate at some sites.

Suspended-sediment loads were estimated by the 

MLE method at 7 of the 11 sites. At the other four sites, 

the linear attribution estimation (LAE) method was 

selected because the rate of censoring was low (less 

than 20 percent of the observations) and test statistics 

indicated a non-normal distribution of the residuals 

from the concentration-flow regression. Sites with the 

largest standard deviations for annual suspendedsediment loads included the upper Green, with a 

standard deviation of more than 100 percent, Big Soos 

with 56 percent, the Skokomish with 48 percent, and 

the NF Skokomish with 46 percent (Appendix 

table C4). Although predicted daily loads of suspended 

sediment could be quite different from measured, the 

predicted annual loads appeared reasonable when 

compared with measured annual loads. The exceptions 

were the above four sites, for which large standard 

deviations and percent differences between measured 

and predicted loads indicate that results for these sites 

should be viewed with caution.

Loads are directly related to streamflow, and 

therefore are largest during periods of high streamflow 

and are generally largest from those watersheds with 

big drainage areas. Nutrient loads transported during 

the runoff and high streamflow periods of the rainy fall 

and winter seasons greatly exceeded summertime 

loads. For total nitrogen and phosphorus, average daily 

loads in winter were typically 2 to 3 orders of 

magnitude greater than average daily loads in summer. 

Nutrient loads estimated for the 11 sites ranged from 

6.0 to 3,200 ton/yr of total nitrogen and from about 2 to 

890 ton/yr of phosphorus, with the smaller values 

corresponding to the upper Green River (drainage area 

of 16.5 mi2) and the larger values corresponding to the 

lower Nooksack (drainage area of 790 mi2) (fig. 43).

Yields in this study are constituent loads per unit 

of drainage area and allow comparisons to be made 

among sites with different basin characteristics. Annual 

average nutrient yields ranged from 0.4 to 8.8 ton/mi2

(tons per square mile) of total nitrogen in the upper 

Green and Fishtrap, respectively, and from about 

0.1 ton/mi2 of phosphorus in Thornton and the upper 

Green, to 1.2 ton/mi2 of phosphorus in the upper 

Nooksack. Of the three major study basins, nutrient 

yields were largest from the Nooksack River Basin and 

smallest from the Skokomish River Basin (fig. 44).
104 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Skokomish River

Upper Nooksack River

Lower Nooksack River

Duwamish River

Upper Green River

NF Skokomish River

Fishtrap Creek

Newaukum Creek

Big Soos Creek

Springbrook Creek

Thornton Creek

0

3,500

500

1,000

1,500

2,000

2,500

3,000

NUTRIENT LOADS, IN TONS PER YEAR

0

3,000,000

500,000

1,000,000

1,500,000

2,000,000

2,500,000

SUSPENDED SEDIMENT LOAD, 

IN TONS PER YEAR

0

10

2

4

6

8

NUTRIENT YIELDS, 

IN TONS PER YEAR PER SQUARE MILE

0

5,000

1,000

2,000

3,000

4,000

SUSPENDED SEDIMENT YIELD, 

IN TONS PER YEAR PER SQUARE MILE

LARGE RIVERS SMALL STREAMS

Skokomish River

Upper Nooksack River

Lower Nooksack River

Duwamish River

Upper Green River

NF Skokomish River

Fishtrap Creek

Newaukum Creek

Big Soos Creek

Springbrook Creek

Thornton Creek

Mixed

(forestry)

Mixed

(agriculture)

Mixed

(urban)

Forestry,

Reference

Agriculture Urban

EXPLANATION

Total nitrogen

Total phosphorus

Dissolved orthophosphate

Suspended sediment

Figure 43. Nutrient loads transported in surface water at study sites, and nutrient yields from the basins by major land-use 

categories, in the Puget Sound Basin study unit, Washington.
Loads and Yields 105

10 20 30 40 50 MILES

0 10 20 30 40 50 KILOMETERS

0

EXPLANATION

Study basins

International boundary

County boundary

Study unit boundary

Fixed site and site number

 as listed in table 1

Yields:

 Total nitrogen (black arrows) and 

 total phosphorus (white arrows);

 width of arrow tail is proportional to

 yield -- (1 millimeter = 0.5 ton per

 square mile).

11

1

2

4

5

10

9

7

6

8

11

3

Bellingham

Everett

Seattle

Tacoma

Olympia

Green-Duwamish 

River Basin

Thornton Creek

Basin

Skokomish River

 Basin

Base from U.S. Geological Survey digital data, 1:2000000, 1972

Albers Conic Equal Area Projection

Standard parallels 47 ̊ and 49 ̊, central meridian 122 ̊

Nooksack River

 Basin

BRITISH COLUMBIA

CANADA

UNITED STATES

WHATCOM 

COUNTY

SKAGIT 

COUNTY

ISLAND

COUNTY

SAN JUAN

COUNTY

CLALLAM

COUNTY

JEFFERSON

COUNTY

KITSAP

COUNTY

SNOHOMISH

COUNTY

KING

 COUNTY

PIERCE

COUNTY

MASON

COUNTY

THURSTON 

COUNTY

LEWIS COUNTY

P uyallup

River Nisqually

River

Deschutes River

Olympic Mountains

Cascade Range

Strait of Georgia

Baker 

Lake

Lake

Washington

Lake

Cushman

Ross

Lake

Strait of Juan de Fuca

Hood Canal

Puget Sound

Sauk

Suiattle River

Sa m ish River

Skagit River

Stillaguamish River

River

Dungeness River

Elwha

River

47 ̊

48 ̊

123 ̊ 122 ̊ 121 ̊

49 ̊

Figure 44. Nutrient yields, 1996–98, from study basins in the Puget Sound Basin study unit, Washington.
106 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

This is consistent with previous work in the PSB, 

which showed nutrient yields to be highest from basins 

dominated by agricultural land-use practices and 

related to source-loading rates from animal manures, 

fertilizers, and precipitation (Embrey and Inkpen, 

1998). The Nooksack River Basin was estimated to 

receive 9.1 tons of nitrogen and 1.3 tons of phosphorus 

per square mile of drainage basin, which were among 

the highest source-loading rates estimated for the major 

PSB watersheds (Embrey and Inkpen, 1998). The 

Skokomish River Basin had one of the lowest rates, 

receiving 0.4 ton of nitrogen and 0.2 ton of phosphorus 

per square mile of drainage basin. From Fishtrap and 

Newaukum Creeks, the two streams indicative of water 

quality from agricultural basins, total nitrogen yields 

were the highest of all 11 streams (fig. 43).

The annual average nutrient yields from the 

urban and suburban basins, ranging from 1.6 ton/mi2 of 

total nitrogen from Thornton Creek to 3.0 ton/mi2 of 

total nitrogen from Big Soos Creek, were also well 

above those from the reference and forestry basins 

(figs. 43 and 44). Nutrient source loading to the GreenDuwamish River Basin, which includes Big Soos, was 

estimated at 4.5 ton/mi2 of nitrogen and 0.69 ton/mi2 of 

phosphorus (Embrey and Inkpen, 1998). Precipitation 

was an important part of this source loading, 

contributing 1.1 ton/mi2 of nitrogen and 0.12 ton/mi2

of phosphorus. However, because the data were 

unavailable, a potentially important nutrient 

contribution was not included in total source-loading 

estimates for urban watersheds—the loading from 

residential and commercial fertilizer applications, as 

well as unknown amounts from miscellaneous waste 

such as leaking sewers, pets and wildlife, or failing 

septic systems.

In contrast to nitrogen, phosphorus yields were 

more variable among the land-use categories. For 

example, the yield of phosphorus from the Skokomish, 

with very little agricultural land use in the basin, was at 

least twice that of Fishtrap Creek, with largely 

agricultural land use. And even though both Fishtrap 

and Newaukum are in agricultural basins, Fishtrap 

yielded more total nitrogen (about 1 ton/mi2 more) but 

less phosphorus (about one-third less). Natural sources 

of phosphorus, in association with suspended sediment, 

might account for some of the variation observed in 

total phosphorus yields. Phosphorus yields tended to 

correspond to suspended-sediment yields at most of the 

sites (fig. 45).

Compared with loads estimated by Embrey and 

Inkpen (1998) using historical data collected mostly by 

State and county agencies, inorganic-nitrogen and 

phosphorus loads were generally higher during this 

1996–98 study. A combination of factors probably 

contributed to these differences, including sampling 

methods (discharge-weighted sample collection used in 

this study) and the inclusion of several storm and floodevent samples collected during this study, which 

contributed high nutrient concentrations to the data 

sets. In particular, above-normal streamflows during 

1996 and 1997 would have resulted in higher load 

calculations for this study.
Loads and Yields 107

Skokomish River Basin

During the study, the Skokomish transported 

about 210 ton/yr of total nitrogen, 170 ton/yr of 

phosphorus, and 16 ton/yr of orthophosphate to Hood 

Canal. The load of suspended sediment amounted to 

about 570,000 ton/yr (table 28). Except for 

orthophosphate, the highest loads of the study period 

were transported during 1996 and 1997, and the lowest 

in 1998. About 71 percent of the total nitrogen load, or 

150 ton/yr, was composed of inorganic nitrogen—

nitrate, nitrite, and ammonia. The inorganic nitrogen 

load of this study was essentially the same as the 

170 ton/yr estimated for the historical period of 1980–

93 (Embrey and Inkpen, 1998). The phosphorus load, 

however, was more than 2.5 times the 60 ton/yr 

estimated for the historical period because of abovenormal streamflows during the study and higher 

phosphorus concentrations. Twenty-five percent of 

phosphorus concentrations observed during this study 

were greater than 0.06 mg/L, whereas less than 

10 percent of the historical data exceeded 0.06 mg/L. 

Nutrient loads transported during fall and winter 

greatly exceeded summertime loads. In winter, the 

Skokomish transported an average of about 

2,600 lb/day (pounds per day) of total nitrogen, 

2,100 lb/day of phosphorus, and 7,000,000 lb/day of 

suspended sediment. With lower flows in summer, the 

average loads dropped to about 170 lb/day of total 

nitrogen, 15 lb/day of phosphorus, and 10,000 lb/day of 

suspended sediment.

The NF Skokomish transported 49 ton/yr of total 

nitrogen, 15 ton/yr of phosphorus, and 4.5 ton/yr of 

orthophosphate to Lake Cushman during the study. The 

load of suspended sediment amounted to 14,000 ton/yr 

(table 28). About 90 percent of the total nitrogen load, 

or 44 ton/yr, was composed of inorganic nitrogen. 

During winter, in response to increased streamflows, 

the NF Skokomish transported an average of 420 lb/d 

of total nitrogen, 150 lb/d of phosphorus, and 

140,000 lb/d of sediment. In summer, the average loads 

were reduced to about 120 lb/d of total nitrogen, 

10 lb/d of phosphorus, and 2,700 lb/d of suspended 

sediment.

50 50,000 100 1,000 10,000

SUSPENDED SEDIMENT YIELD, IN POUNDS PER DAY

0.5

20

0.7

1

2

3

4

5

7

10

TOTAL PHOSPHORUS YIELD, 

IN POUNDS PER DAY

Skokomish R (1)

Lower

Nooksack R (3)

Duwamish R (6)

Big Soos Cr (8)

Upper

Green R (10)

Newaukum Cr (9)

Springbrook Cr (7)

Fishtrap Cr (4) Thornton Cr (11) NF Skokomish R (2)

Upper

Nooksack R

(5)

Figure 45. Relation between total phosphorus and suspended-sediment yields, 

1996–98, for the 11 river basins in the Puget Sound Basin study unit, Washington
108 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Table 28. Loads and basin yields during 1996, 1997, and 1998 and their averages for the study period 1996-98; average loads for the historical period 

1980-93; and daily loads, by season, for the study period 1996-98 at site 1 and site 2, Skokomish River Basin, in the Puget Sound Basin study unit, 

Washington

[–, not calculated; ton/mi2, tons per square mile]

Site name 

(site No.)

Total nitrogen loads and yields Inorganic nitrogen load 

(tons per year)

Total nitrogen load, by season

(pounds per day)

Yearly load (tons) Yearly yield (ton/mi2) Annual 

average 

load for 

1996-98 

(tons)

Annual 

average 

yield for 

1996-98 

(ton/mi2)

For study 

period 

1996-98 

(Percentage 

of total 

nitrogen load)

For 

historical 

period 

1980-93

Winter Spring Summer Fall

1996 1997 1998 1996 1997 1998

Skokomish 

River (1)

260 200 170 1.1 0.88 0.75 210 0.91 150 (71) 170 2,600 660 170 1,200

North Fork 

Skokomish 

River (2)

50 52 46 .87 .91 .80 49 .86 44 (90) – 420 290 120 250

Site name

(site No.)

Phosphorus loads and yields Phosphorus loads, by season

(pounds per day)

Yearly load (tons) Yearly yield (ton/mi2) Annual 

average 

load for 

1996-98 

(tons)

Annual 

average 

yield for 

1996-98 

(ton/mi2)

Annual average 

load for the 

historical period 

1980-93 (tons)

Winter Spring Summer Fall

1996 1997 1998 1996 1997 1998

Skokomish 

River (1)

220 170 100 0.97 0.75 0.44 170 0.73 60 2,100 760 15 760

North Fork 

Skokomish 

River (2)

16 22 8 .28 .38 .14 15 .26 – 150 100 10 73

Site name 

(site No.)

Orthophosphate phosphorus loads and yields Orthophosphate phosphorus loads,

by season (pounds per day)

Yearly load (tons) Yearly yield (ton/mi2) Annual 

average 

load for 

1996-98 

(tons)

Annual 

average 

yield for 

1996-98 

(ton/mi2)

Annual 

average 

load for the 

historical 

period 1980-

93 (tons)

Winter Spring Summer Fall

1996 1997 1998 1996 1997 1998

Skokomish 

River (1)

14 16 17 0.06 0.07 0.07 16 0.07 13 190 62 22 79

North Fork 

Skokomish 

River (2)

2 4 7 .03 .07 .12 4.5 .08 – 37 21 13 28
Loads and Yields 109

Table 28. Loads and basin yields during 1996, 1997, and 1998 and their averages for the study period 1996-98; average loads for the historical period 

1980-93; and daily loads, by season, for the study period 1996-98 at site 1 and site 2, Skokomish River Basin, in the Puget Sound Basin study unit, 

Washington—Continued

Site name 

(site No.)

Suspended-sediment loads and yields Suspended-sediment loads, by season,

(pounds per day)

Yearly load (tons) Yearly yield (ton/mi2)

Annual 

average 

load for 

1996-98 

(tons)

Annual 

average 

yield for 

1996-98 

(ton/mi2)

Annual 

average 

load for 

the 

historical 

period 

1980-93 

(tons)

Winter Spring Summer Fall

1996 1997 1998 1996 1997 1998

Skokomish 

River (1)

790,000 660,000 260,000 3,500 2,900 1,100 570,000 2,500 – 7,000,000 3,200,000 10,000 2,400,000

North Fork 

Skokomish 

River (2)

17,000 18,000 6,700 300 310 120 14,000 240 – 140,000 68,000 2,700 96,000

Annual total nitrogen and orthophosphate yields 

were similar for both sites in the Skokomish River 

Basin (fig. 44). At both sites, the total nitrogen yields 

were 0.9 ton/mi2 per year; at site 1 and site 2, the 

orthophosphate yields were 0.07 and 0.08 ton/mi2 per 

year, respectively. The phosphorus yield from the basin 

at site 1 (0.73 ton/mi2 per year), however, was more 

than double the yield (0.26 ton/mi2 per year) from the 

NF Skokomish River Basin at site 2. Source-loadings 

to the Skokomish River Basin from agricultural 

activities and precipitation were estimated to be about 

0.4 ton/mi2 total nitrogen and 0.2 ton/mi2 phosphorus 

(Embrey and Inkpen, 1998). Because the NF 

Skokomish is the study’s reference basin, the loads at 

site 2 represent background levels of riverine nutrient 

transport and nutrient loadings to PSB watersheds from 

natural sources, such as rock weathering, biological 

fixation, and precipitation. Yields of similar magnitude 

as site 2 indicated that much of the total nitrogen and 

orthophosphate transported from the Skokomish River 

Basin at site 1 is from natural sources. However, the 

considerably larger phosphorus and suspendedsediment yields at site 1 than at site 2 indicated that 

forestry practices, roads, and other human activities in 

the lower Skokomish River Basin and in the SF 

Skokomish River Basin added to the phosphorus and 

suspended-sediment loads observed at site 1.

Nooksack River Basin

During the 1996–98 study, the lower Nooksack 

River transported 3,200 ton/yr of total nitrogen, 

890 ton/yr of phosphorus, and 43 ton/yr of 

orthophosphate to Bellingham Bay. The load of 

suspended sediment was about 1,800,000 ton/yr (table 

29). The highest loads were transported during 1996 

and 1997, and the lowest in 1998. About 62 percent of 

the total nitrogen load, or 2,000 ton/yr, was composed 

of inorganic nitrogen—nitrate, nitrite, and ammonia. 

This inorganic nitrogen load was not much different 

from the 1,700 T/yr for the historical period of 1980–

93 (this value is revised from the value published by 

Embrey and Inkpen, 1998). However, as a result of 

above-normal streamflows in 1996 and 1997 and 

higher concentrations, the phosphorus load was about 

four times larger than the 260 ton/yr estimated for the 

historical period. Twenty-five percent of phosphorus 

concentrations observed during this study were greater 

than 0.17 mg/L, whereas less than 10 percent of the 

historical data exceeded 0.17 mg/L. Nutrient loads 

transported during fall and winter greatly exceeded 

summertime loads. In winter, the lower Nooksack 

transported an average of 35,000 lb/d of total nitrogen, 

7,600 lb/d of phosphorus, and 13,000,000 lb/d of 

suspended sediment. In response to lower flows in 

summer, the average loads dropped to 4,800 lb/d of 

total nitrogen, 1,600 lb/d of phosphorus, and 

4,500,000 lb/d of suspended sediment.
110 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Table 29. Loads and basin yields during 1996, 1997, and 1998 and their averages for the study period 1996-98; average loads for the historical period 

1980-93; and daily loads, by season, for the study period 1996-98 at site 3, site 4, and site 5, Nooksack River Basin, in the Puget Sound Basin study unit, 

Washington

[–, not calculated; ton/mi2, tons per square mile]

Site name 

(site No.)

Total nitrogen loads and yields Inorganic nitrogen load 

(tons per year)

Total nitrogen load, by season

(pounds per day)

Yearly load (tons) Yearly yield (ton/mi2) Annual 

average 

load for 

1996-98 

(tons)

Annual 

average 

yield for 

1996-98 

(ton/mi2)

For study 

period 

1996-98 

(Percentage 

of total 

nitrogen load)

For 

historical 

period 

1980-93

Winter Spring Summer Fall

1996 1997 1998 1996 1997 1998

Nooksack 

River (3)

3,500 3,700 2,300 4.4 4.7 2.9 3,200 4.0 2,000 (62) 11,700 35,000 12,000 4,800 18,000

Fishtrap 

Creek (4)

– 420 250 – 11 6.6 330 8.8 280 (85) – 3,600 2,100 570 1,100

Nooksack 

River (5)

1,700 1,900 1,100 2.9 3.2 1.9 1,600 2.7 830 (52) 750 14,000 5,100 3,000 12,000

Site name

(site No.)

Phosphorus loads and yields Phosphorus loads, by season

(pounds per day)

Yearly load (tons) Yearly yield (ton/mi2) Annual 

average 

load for 

1996-98 

(tons)

Annual 

average 

yield for 

1996-98 

(ton/mi2)

Annual average 

load for the 

historical period 

1980-93 (tons)

Winter Spring Summer Fall

1996 1997 1998 1996 1997 1998

Nooksack 

River (3)

1,200 1,100 400 1.5 1.4 0.51 890 1.1 260 7,600 2,400 1,600 8,100

Fishtrap 

Creek (4)

– 15 6 – 0.39 .16 11 0.28 – 130 60 10 34

Nooksack 

River (5)

740 1,100 340 1.3 1.9 .58 720 1.2 160 5,600 3,400 1,800 5,000

Site name 

(site No.)

Orthophosphate phosphorus loads and yields Orthophosphate phosphorus loads,

by season (pounds per day)

Yearly load (tons) Yearly yield (ton/mi2) Annual 

average 

load for 

1996-98 

(tons)

Annual 

average yield 

for 1996-98 

(ton/mi2)

Annual 

average 

load for the 

historical 

period 1980-

93 (tons)

Winter Spring Summer Fall

1996 1997 1998 1996 1997 1998

Nooksack 

River (3)

44 53 34 0.06 0.07 0.04 43 0.06 44 320 230 170 230

Fishtrap Creek 

(4)

– 3 1 – .08 .03 2.0 .05 – 24 11 2 7

Nooksack 

River (5)

– – – – – – 6-40 .01-.07 21 – – – –
Loads and Yields 111

Table 29. Loads and basin yields during 1996, 1997, and 1998 and their averages for the study period 1996-98; average loads for the historical period 

1980-93; and daily loads, by season, for the study period 1996-98 at site 3, site 4, and site 5, Nooksack River Basin, in the Puget Sound Basin study unit, 

Washington—Continued

Site name 

(site No.)

Suspended-sediment loads and yields Suspended-sediment loads, by season,

(pounds per day)

Yearly load (tons) Yearly yield (ton/mi2)

Annual 

average 

load for 

1996-98 

(tons)

Annual 

average 

yield for 

1996-98 

(ton/mi2

)

Annual 

average 

load for 

the 

historical 

period 

1980-93 

(tons)

Winter Spring Summer Fall

1996 1997 1998 1996 1997 1998

Nooksack 

River (3)

2,400,000 2,300,000 690,000 3,000 2,900 870 1,800,000 2,300 – 13,000,000 6,300,000 4,500,000 15,000,000

Fishtrap 

Creek (4)

– 6,900 2,600 – 180 68 4,700 120 – 58,000 27,000 4,300 15,000

Nooksack 

River (5)

2,300,000 3,700,000 800,000 3,900 6,300 1,400 2,300,000 3,900 – 12,000,000 14,000,000 8,600,000 15,000,000

1This value was published as 1,400 in Embrey and Inkpen (1998); since revised to 1,700.

The tributary Fishtrap Creek transported 

330 ton/yr of total nitrogen, 11 ton/yr of phosphorus, 

and 2.0 ton/yr of orthophosphate to the lower 

Nooksack. The load of suspended sediment was about 

4,700 ton/yr (table 29). Constituent loads transported in 

1997 were about twice as large as loads transported in 

1998. About 85 percent of the total nitrogen load, or 

280 ton/yr, was composed of inorganic nitrogen. In 

winter, Fishtrap transported an average of 3,600 lb/d of 

total nitrogen, 130 lb/d of phosphorus, and 58,000 lb/d 

of sediment. In summer, the average loads dropped to 

570 lb/d of total nitrogen, 10 lb/d of phosphorus, and 

4,300 lb/d of suspended sediment.

The upper Nooksack River transported 

1,600 ton/yr of total nitrogen, 720 ton/yr of 

phosphorus, and 2,300,000 ton/yr of suspended 

sediment at the sampling site at North Cedarville 

(table 29). An estimate using the Beale ratio 

(Crawford, 1996) indicated that orthophosphate loads 

ranged from 6 to 40 ton/yr. The river at North 

Cedarville transported the highest loads of nutrients 

and suspended sediment for the 3-year study in 1997. 

Fifty-two percent of the total nitrogen load, or 

830 ton/yr, was composed of inorganic nitrogen; thus, 

at 48 percent, organic nitrogen was an important 

component of the total nitrogen load. As in the lower 

Nooksack, the inorganic nitrogen load of this study was 

only slightly larger than the load of 750 ton/yr and the 

phosphorus load was about four times larger than the 

load of 160 ton/yr estimated for the historical period of 

1980–93 (Embrey and Inkpen, 1998). Fifty percent of 

phosphorus concentrations observed during this study 

were greater than 0.03 mg/L, whereas only 25 percent 

of the historical data exceeded 0.03 mg/L. In response 

to higher streamflows and concentrations, the upper 

Nooksack transported in winter an average of 

14,000 lb/d of total nitrogen and 5,600 lb/d of 

phosphorus, which were much higher than loads 

transported during summer low flows. Suspended 

sediment transported during winter averaged 

12,000,000 lb/d, but dropped to 8,600,000 lb/d in 

summer.

In terms of unit area, the annual total nitrogen 

yield from the Nooksack River Basin at site 3 was 

4 ton/mi2 (fig. 44). This increase of 1.3 ton/mi2 over the 

total nitrogen yield from the upper Nooksack River 

Basin at site 5 is indicative of the more intensive 

agricultural land-use activities in the lower Nooksack 

River Basin. Fishtrap Creek at site 4 yielded 

8.8 ton/mi2 of total nitrogen to the lower Nooksack. 

Nitrogen-source loadings each year to the Nooksack 

watershed from animal manures, agricultural 

fertilizers, and precipitation was estimated to be about 

9 ton/mi2, with more than half the loading from animal 

manures (Embrey and Inkpen, 1998). 
112 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

The annual phosphorus yield of 1.1 ton/mi2 and the 

orthophosphate yield of 0.06 ton/mi2 from the lower 

basin at site 3 were essentially the same as the yields 

from the upper basin at site 5 (fig. 44), indicating that 

the main sources of phosphorus to the Nooksack River 

are in the upper basin. Yields of only 0.28 ton/mi2 of 

phosphorus and 0.05 ton/mi2 of orthophosphate from 

Fishtrap Creek at site 4 indicated that the lowland 

tributary basins yield relatively small amounts of 

phosphorus to the lower Nooksack River.

In addition to phosphorus, the upper basin is also 

the main source of suspended sediment in the lower 

Nooksack. At site 5, the upper Nooksack yielded 

3,900 ton/mi2 of suspended sediment, a large portion of 

which is lost by settling or by dilution within the reach 

downstream from site 5 to site 3. At site 3, the 

suspended-sediment yield was 2,300 ton/mi2. Although 

some agriculture exists in the upper Nooksack 

watershed, land use is mostly a combination of 

undeveloped terrain, forestry practices, and road 

building, and the latter two are reported to be important 

sources of suspended sediment (U.S. Forest Service, 

1995) in the river. Other sources of nutrients and 

suspended sediment to the Nooksack River Basin 

include natural sources such as rock weathering, 

biological fixation, and precipitation.

Green-Duwamish River Basin

During the 1996–98 study, the Duwamish River 

transported an average of 1,300 ton/yr of total nitrogen, 

190 ton/yr of phosphorus, and 44 ton/yr of 

orthophosphate to Puget Sound. About 270,000 ton/yr 

of suspended sediment were transported to the Sound. 

The river transported the highest loads during 1996 and 

1997 and the lowest in 1998 (table 30). Sixty-six 

percent of the total nitrogen load, or 860 ton/yr, was 

composed of inorganic nitrogen—nitrate, nitrite, and 

ammonia, which was about 60 percent larger than the 

520 ton/yr estimated by Embrey and Inkpen (1998) for 

the historical period 1980–93. The phosphorus load of 

this study was about twice the estimate for the 1980–93 

historical period. Above-normal streamflows and 

higher concentrations account for the higher nutrient 

loads estimated for this 1996–98 study. Concentrations 

of ammonia and of nitrite-plus-nitrate nitrogen 

observed in this study were generally higher than the 

historical data, and 25 percent of phosphorus 

concentrations observed during this study were greater 

than 0.1 mg/L, whereas less than 10 percent of the 

historical data exceeded 0.08 mg/L. In response to 

higher streamflows, loads transported during fall and 

winter greatly exceeded summertime loads. In winter, 

the Duwamish transported an average of 15,000 lb/d of 

total nitrogen, 2,300 lb/d of phosphorus, and 

710,000 lb/d of suspended sediment. With low flows 

and low concentrations in summer, the average loads 

dropped to about 1,700 lb/d of total nitrogen, 200 lb/d 

of phosphorus, and 22,000 lb/d of suspended sediment.

Springbrook transported an average of 44 ton/yr 

of total nitrogen, 6.9 ton/yr of phosphorus, and 

1.3 ton/yr of orthophosphate to the Duwamish. The 

load of suspended sediment was 1,800 ton/yr 

(table 30). About 57 percent of the total nitrogen load, 

or 25 ton/yr, was composed of inorganic nitrogen, so, at 

43 percent, organic nitrogen was an important 

component of the total nitrogen load. For this study, the 

inorganic nitrogen load was a little lower (by about 

20 percent) and the phosphorus load a little higher (by 

about 15 percent) than the loads estimated for the 

historical period of 1980–93 (Embrey and Inkpen, 

1998). Contrary to the pattern seen in concentration 

data from the 10 other sites in this study, nutrient 

concentrations in samples from Springbrook during 

this study were generally lower than the historical data. 

Nutrient and suspended-sediment loads transported 

during fall and winter greatly exceeded summertime 

loads. In winter, the creek transported an average of 

470 lb/d of total nitrogen, 71 lb/d of phosphorus, and 

4,400 lb/d of suspended sediment. In response to low 

flows during summer, the average loads were reduced 

to 75 lb/d of total nitrogen, 11 lb/d of phosphorus, and 

220 lb/d of suspended sediment.

Big Soos transported 200 ton/yr of total nitrogen, 

9.5 ton/yr of phosphorus, 2.9 ton/yr of orthophosphate, 

and 13,000 ton/yr to the Green River (table 30). 

Seventy-five percent of the nitrogen load, or 150 ton/yr, 

was composed of inorganic nitrogen. The inorganic 

nitrogen load of this study was about 30 percent greater 

than an estimate of 110 ton/yr for the historical period 

of 1980–93 (Embrey and Inkpen, 1998), and the 

phosphorus load was about 60 percent greater than the 

load for the historical period. Above-normal 

streamflows during 1996 and 1997 resulted in the 

higher calculations of loads for this 1996–98 study. 

With higher streamflows in winter, Big Soos 

transported 2,700 lb/d of total nitrogen, 140 lb/d of 

phosphorus, and 270,000 lb/d of suspended sediment. 
Loads and Yields 113

Summertime loads fell to 210 lb/d of total nitrogen, 

7 lb/d of phosphorus, and 1,700 lb/d of suspended 

sediment.

Newaukum transported 210 ton/yr of total 

nitrogen, 27 ton/yr of phosphorus, and 14 ton/yr of 

orthophosphate to the Green River. The load of 

suspended sediment amounted to 2,200 ton/yr. The 

loads were all considerably higher in 1996 and 1997 

than in 1998 (table 30). Inorganic nitrogen made up 

76 percent (160 ton/yr) of the total nitrogen load. The 

inorganic nitrogen load of this study was about 

30 percent larger than the estimate of 120 ton/yr for the 

historical period of 1980–93 (Embrey and Inkpen, 

1998), and the phosphorus load was a little more than 

twice the load of 12 ton/yr for the historical period. 

Concentrations of ammonia and of nitrite-plus-nitrate 

nitrogen observed during this study were generally 

similar to the historical data. Fifty percent of 

phosphorus concentrations in this study were equal to 

or greater than 0.16 mg/L, whereas, only about 

25 percent of the historical data exceeded 0.16 mg/L. 

The high concentrations and above-normal 

streamflows resulted in the higher estimates of loads 

for the 1996–98 period than for the 1980–93 period. In 

winter, Newaukum transported an average of 2,300 lb/d 

of total nitrogen, 420 lb/d of phosphorus, and 

36,000 lb/d of suspended sediment. With low flow in 

summer, average loads were reduced to 410 lb/d of 

total nitrogen, 18 lb/d of phosphorus, and 1,000 lb/d of 

suspended sediment.

 Loads in the headwaters of the GreenDuwamish River Basin at site 10 were about 6 ton/yr of 

total nitrogen, 0.7 ton/yr of orthophosphate, and 

510 ton/yr of suspended sediment (table 30). Using the 

Beale ratio estimate, the load of phosphorus ranged 

from 2 to 2.6 ton/yr. Inorganic nitrogen made up 

85 percent (5.1 ton/yr) of the total nitrogen load. 

During winter, the upper Green transported about 

38 lb/d of total nitrogen, 4.6 lb/d of orthophosphate, 

and 3,500 lb/d of suspended sediment. Summertime 

loads were only 13 lb/d of total nitrogen, 2.1 lb/d of 

orthophosphate, and 420 lb/d of suspended sediment.

The Green-Duwamish River Basin yielded, per 

year, an average of 2.8 ton/mi2 of total nitrogen, 

0.4 ton/mi2 of phosphorus, and 0.1 ton/mi2 of 

orthophosphate (fig. 44) to Puget Sound and 

represented combined nutrient-source loadings to the 

watershed from human land-use activities and natural 

processes. Total nitrogen loading each year to the basin 

from animal manures, agricultural fertilizers, and 

precipitation was about 4.5 ton/mi2 and phosphorus 

loading was 0.65 ton/mi2 (Embrey and Inkpen, 1998). 

Upstream from site 6 on the Duwamish River, the 

mainstem received nearly 13 ton/mi2 of total nitrogen, 

1.5 ton/mi2 of phosphorus, and 0.6 ton/mi2 of 

orthophosphate from the three tributary basins included 

in this study, Springbrook, Big Soos, and Newaukum. 

The yields at site 6 indicated dilution of tributary inputs 

of nutrients, probably by the volumes of high-quality 

water coming from the upper basin. Annual nutrient 

yields from Springbrook Creek Basin were 2.2 ton/mi2

of total nitrogen, 0.3 ton/mi2 of phosphorus, and 

0.06 ton/mi2 of orthophosphate. Springbrook is 

primarily an urban basin (72.7 percent of the basin 

area) with some agriculture (19.8 percent of the basin 

area), so much of the nutrient-loading sources would be 

from commercial and residential fertilizer applications, 

some from agricultural activities, and some from 

natural sources. Big Soos at site 8 yielded 3.0 ton/mi2

of total nitrogen, 0.1 ton/mi2 of phosphorus, and 

0.04 ton/mi2 of orthophosphate to the Green River. 

About 50 percent of the Big Soos Creek Basin is urbansuburban, with much of the upper basin in residential 

and commercial development; 45 percent of the basin 

is forested and about 2 percent of the basin is 

agricultural consisting mostly of small farms. Nutrientloading sources would be largely from commercial and 

residential fertilizer applications, precipitation, and 

other natural sources. Annual nutrient yields from 

Newaukum at site 9 was 7.6 ton/mi2 of total nitrogen, 

1.0 ton/mi2 of phosphorus, and 0.5 ton/mi2 of 

orthophosphate. Newaukum is primarily an agricultural 

basin, partly dairy and beef cattle and partly hobby 

farms with horses or other animals. Nutrient-loading 

sources would be mostly animal manures, agricultural 

fertilizers, and precipitation. The upper Green at site 10 

yielded only 0.4 ton/mi2 of total nitrogen, 

approximately 0.1 ton/mi2 of phosphorus, and 

0.04 ton/mi2 of orthophosphate. Land use in the upper 

Green is a mix of forestry practices and undeveloped, 

forested terrain. Thus, nutrient source loadings to the 

upper basin would derive from human activities 

associated with timber harvest, roads, and recreation, 

and natural sources such as rock weathering, biological 

fixation, and precipitation. 
114 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Table 30. Loads and basin yields during 1996, 1997, and 1998 and their averages for the study period 1996-98; average loads for the historical period 

1980-93; and daily loads, by season, for the study period 1996-98 at site 6, site 7, site 8, site 9, and site 10, Green-Duwamish River Basin, in the Puget 

Sound Basin study unit, Washington

[–, not calculated; ton/mi2, tons per square mile]

Site name 

(site No.)

Total nitrogen loads and yields Inorganic nitrogen load 

(tons per year)

Total nitrogen load, by season

(pounds per day)

Yearly load (tons) Yearly yield (ton/mi2) Annual 

average 

load for 

1996-98 

(tons)

Annual 

average 

yield for 

1996-98 

(ton/mi2)

For study 

period 

1996-98 

(Percentage 

of total 

nitrogen load)

For 

historical 

period 

1980-93

Winter Spring Summer Fall

1996 1997 1998 1996 1997 1998

Duwamish 

River (6)

1,500 1,400 840 3.2 3.0 1.8 1,300 2.8 860. (66) 520 15,000 6,900 1,700 4,400

Springbrook 

Creek (7)

52 47 33 2.6 2.4 1.6 44 2.2 25. (57) 31 470 230 75 200

Big Soos 

Creek (8)

240 240 120 3.6 3.6 1.8 200 3.0 150. (75) 110 2,700 1,100 210 520

Newaukum 

Creek (9)

230 250 150 8.4 9.1 5.5 210 7.6 160. (76) 120 2,300 1,200 410 680

Green River 

(10)

7.0 7.1 4.0 0.42 0.43 0.24 6.0 0.37 5.1 (85) – 38 54 13 27

Site name (site 

No.)

Phosphorus loads and yields Phosphorus loads, by season

(pounds per day)

Yearly load (tons) Yearly yield (ton/mi2) Annual 

average 

load for 

1996-98 

(tons)

Annual 

average 

yield for 

1996-98 

(ton/mi2

)

Annual average 

load for the 

historical period 

1980-93 (tons)

Winter Spring Summer Fall

1996 1997 1998 1996 1997 1998

Duwamish 

River (6)

290 200 75 0.63 0.43 0.16 190 0.4 89 2,300 880 200 720

Springbrook 

Creek (7)

7.6 7.4 5.6 .38 .37 .28 6.9 .34 5.9 71 37 11 32

Big Soos Creek 

(8)

12 12 4.6 .18 .18 .07 9.5 .14 6.2 140 50 7.0 16

Newaukum 

Creek (9)

42 29 10 1.5 1.1 .36 27 .98 12 420 90 18 63

Green River 

(10)

– – – – – – 2-2.6 .12-.16 – – – – –
Loads and Yields 115

Table 30. Loads and basin yields during 1996, 1997, and 1998 and their averages for the study period 1996-98; average loads for the historical period 

1980-93; and daily loads, by season, for the study period 1996-98 at site 6, site 7, site 8, site 9, and site 10, Green-Duwamish River Basin, in the Puget 

Sound Basin study unit, Washington—Continued

Site name 

(site No.)

Orthophosphate phosphorus loads and yields Orthophosphate phosphorus loads,

by season (pounds per day)

Yearly load (tons) Yearly yield (ton/mi2) Annual 

average 

load for 

1996-98 

(tons)

Annual 

average 

yield for 

1996-98 

(ton/mi2

)

Annual 

average 

load for the 

historical 

period 1980-

93 (tons)

Winter Spring Summer Fall

1996 1997 1998 1996 1997 1998

Duwamish 

River (6)

55 51 28 0.12 0.11 0.06 44 0.1 46 450 250 87 190

Springbrook 

Creek (7)

1.5 1.4 1.0 .08 .07 .05 1.3 .06 – 12 9.0 3.0 5.0

Big Soos 

Creek (8)

3.0 3.4 2.4 .04 .05 .04 2.9 .04 2.2 33 14 5.0 12

Newaukum 

Creek (9)

19 16 7.2 .69 .58 .26 14 .51 7 190 61 16 39

Green River 

(10)

0.8 0.8 0.6 .05 .05 .04 0.7 .04 – 4.6 6.0 2.1 3.1

Site name 

(site No.)

Suspended-sediment loads and yields Suspended-sediment loads, by season, (pounds 

per day)

Yearly load (tons) Yearly yield (ton/mi2)

Annual 

average 

load for 

1996-98 

(tons)

Annual 

average 

yield for 

1996-98 

(ton/mi2)

Annual 

average 

load for the 

historical 

period 

1980-93 

(tons)

Winter Spring Summer Fall

1996 1997 1998 1996 1997 1998

Duwamish 

River (6)

500,000 240,000 59,000 1,100 520 130 270,000 580 – 3,900,000 970,000 120,000 970,000

Springbrook 

Creek (7)

2,400 1,900 1,000 120 95 50 1,800 88 – 24,000 7,000 1,200 6,900

Big Soos 

Creek (8)

23,000 14,000 2,400 340 210 36 13,000 200 – 250,000 35,000 1,700 9,300

Newaukum 

Creek (9)

3,600 2,300 810 95 84 30 2,200 81 – 36,000 9,000 1,000 3,200

Green River 

(10)

900 480 150 55 29 9 510 31 – 3,500 3,600 420 3,700
116 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Thornton Creek Basin

During the period 1997–98, the urban stream 

Thornton Creek transported 20 ton/yr of total nitrogen, 

1.5 ton/yr of phosphorus, 0.4 ton/yr of orthophosphate, 

and 530 ton/yr of suspended sediment to Lake 

Washington (table 31). Seventy percent of the total 

nitrogen load, or 14 ton/yr, was composed of inorganic 

nitrogen; at 30 percent, organic nitrogen was an 

important component of the total nitrogen load. The 

inorganic nitrogen load of 14 ton/yr for this study was 

essentially the same as the estimate of 15 ton/yr for the 

historical period of 1980–93 (Embrey and Inkpen, 

1998); the phosphorus load for the historical period 

was estimated at 1 ton/yr, which was a little less than 

the estimate for the 1997–98 study period. Ammonia 

and phosphorus concentrations in about 10 percent of 

the samples collected during this study were higher 

than concentrations in the historical data; nitrite-plusnitrate concentrations, however, were similar to the 

historical data. The higher load estimates in this study 

might in part result from using different methods to 

calculate loads; but the above-normal streamflows 

during this study would result in higher loads than 

those for the historical period of 1980–93. In winter, 

Thornton transported an average of 160 lb/d of total 

nitrogen, 12 lb/d of phosphorus, and 6,700 lb/d of 

suspended sediment. In summer, with lower 

streamflows, average loads dropped to 52 lb/d of total 

nitrogen, 3 lb/d of phosphorus, and 360 lb/d of 

suspended sediment.

The annual total nitrogen yield from Thornton 

Creek Basin was 1.6 ton/mi2 (fig. 43 and 44), the 

annual phosphorus yield was 0.1 ton/mi2, and the 

orthophosphate yield was 0.03 ton/mi2. Thornton is a 

fully developed urban basin, thus nutrient loading 

sources would mostly come from commercial and 

residential fertilizer applications, precipitation, and 

natural sources.

Table 31. Loads and basin yields during 1996, 1997, and 1998 and their averages for the study period 1996-98; average loads for the historical period 

1980-93; and daily loads, by season, for the study period 1996-98 at site 11, Thornton Creek Basin, in the Puget Sound Basin study unit, Washington

Site name 

(site No.)

Total nitrogen loads and yields Inorganic nitrogen load 

(tons per year)

Total nitrogen load, by season

(pounds per day)

Yearly load (tons) Yearly yield (ton/mi2) Annual 

average 

load for 

1996-98 

(tons)

Annual 

average 

yield for 

1996-98 

(ton/mi2)

For study 

period 

1996-98 

(Percentage 

of total 

nitrogen load)

For 

historical 

period 

1980-93

Winter Spring Summer Fall

1996 1997 1998 1996 1997 1998

Thornton 

Creek (11)

– 22 17 – 1.8 1.4 20 1.6 14 (70) 15 160 130 53 85

Site name (site 

No.)

Phosphorus loads and yields Phosphorus loads, by season

(pounds per day)

Yearly load (tons) Yearly yield (ton/mi2) Annual 

average 

load for 

1996-98 

(tons)

Annual 

average 

yield for 

1996-98 

(ton/mi2)

Annual average 

load for the 

historical period 

1980-93 (tons)

Winter Spring Summer Fall

1996 1997 1998 1996 1997 1998

Thornton 

Creek (11)

– 1.9 1.0 – 0.16 0.08 1.5 0.12 1 12 11 3.0 6.0
Loads and Yields 117

Table 31. Loads and basin yields during 1996, 1997, and 1998 and their averages for the study period 1996-98; average loads for the historical period 

1980-93; and daily loads, by season, for the study period 1996-98 at site 11, Thornton Creek Basin, in the Puget Sound Basin study unit, Washington—

Continued

Site name 

(site No.)

Orthophosphate phosphorus loads and yields Orthophosphate phosphorus loads,

by season (pounds per day)

Yearly load (tons) Yearly yield (ton/mi2)

Annual 

average 

load for 

1996-98 

(tons)

Annual 

average 

yield for 

1996-98 

(ton/mi2)

Annual 

average 

load for 

the 

historical 

period 

1980-93 

(tons)

Winter Spring Summer Fall

1996 1997 1998 1996 1997 1998

Thornton 

Creek (11)

– 0.4 0.3 – 0.03 0.02 0.4 0.03 0.6 2.5 2.1 1.5 2.3

Site name 

(site No.)

Suspended-sediment loads and yields Suspended-sediment loads, by season, (pounds 

per day)

Yearly load (tons) Yearly yield (ton/mi2)

Annual 

average 

load for 

1996-98 

(tons)

Annual 

average 

yield for 

1996-98 

(ton/mi2)

Annual 

average 

load for 

the 

historical 

period 

1980-93 

(tons)

Winter Spring Summer Fall

1996 1997 1998 1996 1997 1998

Thornton 

Creek 

(11)

– 680 380 – 56 31 530 44 – 5,500 3,200 800 2,200
118 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

TRENDS IN CONCENTRATIONS OF 

NITRATE AND TOTAL PHOSPHORUS

The seasonal Kendall test (Crawford and others, 

1983) was applied to data collected by Washington 

State Department of Ecology and King County to 

determine the trend in nitrate and total phosphorus 

concentrations over time at six sites in the PSB. Five of 

these sites were sampled during this study and one, 

Green River at Renton Junction, is 2 river miles 

upstream from site 6 of this study, the Duwamish River. 

The new site was included because it was the only 

station on the Green with an extensive period of record. 

For four sites, the seasonal Kendall test was performed 

on nitrate and total phosphorus concentrations for 

water years 1980–97. For the Skokomish River, the test 

was performed for water years 1984–97; for the Green 

River at Renton Junction, it was performed on nitrate 

concentrations for water years 1980–97 and on total 

phosphorus concentrations for calendar year 1981 

through water year 1997. The analytical method for 

total phosphorus changed at the beginning of 1981 

(Robert Brenner, City of Seattle Metropolitan Services, 

written commun., 1999), so total phosphorus data 

collected at sites in the Green River Basin prior to 1981 

were not included in the trend tests. Streamflow data 

were obtained at on-site or nearby gages. For the Green 

River at Renton Junction, Nooksack River at North 

Cedarville, and the Nooksack River at Brennan, 

streamflow data were from gaging stations located at 

Green River at Auburn, Nooksack River at Deming, 

and Nooksack River at Ferndale, respectively.

The seasonal Kendall test is a nonparametric test 

that compares the relative ranks of the data rather than 

the actual concentration values. Because monthly data 

were available, the seasons were defined to be the 

12 months; therefore, only January data are compared 

with January data, and so forth for the rest of the 

months. If more than one sample was collected during 

a month, the median value was used. All possible pairs 

of monthly data are compared in the test. If a value 

later in time is higher, then a plus is recorded; if a value 

later in time is lower, then a minus is recorded. If an 

upward trend is present, there will be many more 

pluses than minuses. If no trend is present, then the 

numbers of pluses and minuses are about equal. 

Because the seasonal Kendall test uses ranks instead of 

concentration values, it easily handles censored values 

(below method reporting levels), which were set to half 

of the lowest censored concentration (Crawford and 

others, 1983).

The seasonal Kendall test was performed on both 

unadjusted and flow-adjusted concentrations. The 

locally weighted scatterplot smoothing (LOWESS) 

technique (Cleveland, 1979) was used to help remove 

changes in concentrations caused by streamflow. The 

LOWESS procedure fits a curve to scatterplots of 

constituent concentrations and streamflows measured 

at the time of sampling. To compute flow-adjusted 

concentration, the residual between the observed value 

and the value predicted by the fitted curve is added to 

the mean constituent concentration. Negative numbers 

sometime result because the flow-adjusted 

concentrations are the sum of the regression residual 

and the mean concentration.

A trend was considered to be statistically 

significant if the p-value from the seasonal Kendall test 

was less than or equal to 0.10. The p-values were 

adjusted for serial correlation (Hirsch and Slack, 1984); 

however, keeping the number of seasons relatively 

small, such as the selection of 12 seasons, helps to 

reduce problems caused by serial correlation (Crawford 

and others, 1983). Scatterplots for both unadjusted and 

flow-adjusted concentrations for nitrate and total 

phosphorus are shown in figures 46 through 51 for all 

data from 1970 to 1998. The LOWESS curves are 

shown to help identify trends in the concentrations.

Overall, nitrate and total phosphorus 

concentrations were mostly stable (table 32). No 

downward trends were detected. Significant upward 

trends in nitrate concentrations were detected at three 

of the six sites. Total phosphorus concentrations 

showed an upward trend only at Newaukum. However, 

these trend results should be used with caution. 

According to Hopkins (1993), false or misleading 

trends can appear especially if concentrations are near 

the method detection limits.

The Skokomish had a significant upward trend in 

nitrate concentration for both unadjusted and flowadjusted data between 1984 and 1997; however, the 

concentrations appear to have leveled off since the mid1990’s (fig. 46). The trend test indicates, as measured 

by the slope, that the flow-adjusted nitrate 

concentrations increased by 0.0036 mg/L per year. 
Trends in Concentrations of Nitrate and Total Phosphorus 119

A significant upward trend in nitrate concentrations 

was also found by Hopkins (1993), who analyzed data 

from 1979 to 1991. Hopkins also found a significant 

upward trend in total phosphorus concentrations, but 

no trends in either flow-adjusted or unadjusted total 

phosphorus concentrations were found in this study, 

which might indicate that total phosphorus 

concentrations have leveled off since the early 1980’s.

In the Nooksack River Basin, there were no 

trends in unadjusted or flow-adjusted concentrations of 

nitrate or total phosphorus at either of the two sites. 

Nitrate concentrations at the lower Nooksack River 

appear to have increased slightly from the early 1970’s 

until about 1987, but have since leveled off (fig. 47). 

Total phosphorus concentrations at both Nooksack 

River sites, as well as the nitrate concentrations at the 

upper Nooksack River have remained fairly level since 

the 1970’s (fig. 47 and 48). Hopkins (1993) also did not 

find any trends in either nitrate or total phosphorus 

concentrations at the lower Nooksack River between 

1979 and 1991.

In the Green River Basin, there were no trends in 

nitrate or total phosphorus concentrations for either 

flow-adjusted or unadjusted data for the Green River at 

Renton Junction (fig. 49). The steep downward change 

in total phosphorus concentrations during the 1970’s 

(data that were not used in the trend analysis) at the 

Green River at Renton Junction is believed to result 

from using a different analytical method (Robert 

Brenner, City of Seattle Metropolitan Services, oral 

commun., 1999). There were, however, significant 

upward trends in both flow-adjusted and unadjusted 

nitrate concentrations for Big Soos (fig. 50) and 

Newaukum (fig. 51) Creeks. As indicated by the trend 

test slope (rate of change, table 32), flow-adjusted 

nitrate concentrations for Big Soos showed an increase 

of 0.01 mg/L per year, and for Newaukum, a slightly 

larger increase of 0.014 mg/L per year. Additionally, 

both unadjusted and flow-adjusted total phosphorus 

concentrations in Newaukum showed a significant 

upward trend, whereas Big Soos had no significant 

trends. The increase in flow-adjusted total phosphorus 

concentrations at Newaukum was about 0.002 mg/L 

per year. Although nitrate and total phosphorus 

concentrations for Big Soos and Newaukum had 

upward trends between 1980 and 1997, it appears that 

the trends might be reversing with decreasing 

concentrations beginning in the mid-1990’s.

Table 32. Summary of results from seasonal Kendall tests for temporal trends in nitrate nitrogen and total phosphorus concentrations at six surface-water sites in 

the Puget Sound Basin study unit, Washington

[UP, statistically significant upward trend; NT, no trend; p-value from the Seasonal Kendall test; trend is considered significant if p-value is less than or equal to 0.1; 

Nitrate, nitrite plus nitrate nitrogen; mg/L, milligrams per liter; <, less than; –, no value; Ecology, Washington State Department of Ecology]

Site name Period of 

analysis

Trends

Source of 

data 

(agency)

Unadjusted for streamflow Adjusted for streamflow

Nitrate

(p-value)

Rate of 

change 

(mg/L per 

year)

Total 

phosphorus

(p-value)

Rate of 

change 

(mg/L per 

year)

Nitrate

(p-value)

Rate of 

change 

(mg/L per 

year)

Total phosphorus

(p-value)

Rate of 

change 

(mg/L per 

year)

Skokomish River near 

Potlatch

1984-97 UP

(<0.01)

0.0033 NT

(0.21)

– UP

(<0.01)

0.0036 NT

(0.21)

– Ecology

Nooksack River at 

Brennan

1980-97 NT

(.46)

– NT

(.43)

– NT

(.11)

– NT

(.21)

– Ecology

Nooksack River at 

North Cedarville

1980-97 NT

(.14)

– NT

(.63)

– NT

(.18)

– NT

(.35)

– Ecology

Green River at Renton 

Junction

1980-971 NT

(.34)

– NT

(.87)

– NT

(.29)

– NT

(.47)

– King 

County

Big Soos Creek near 

Auburn

1980-97 UP

(.01)

.0127 NT

(.36)

– UP

(.03)

.01 NT

(.50)

– King 

County

Newaukum Creek near 

Black Diamond

1980-97 UP

(.05)

.0124 UP

(.01)

0.0018 UP

(.04)

.0142 UP

(<.01)

0.0017 King 

County

1 Seasonal Kendall test performed for calendar year 1981 through water year 1997 for total phosphorus.

TRENDS IN CONCENTRATIONS OF NITRATE AND TOTAL PHOSPHORUS
120 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

1970

0.8

0

0.2

0.4

0.6

NITRATE AS NITROGEN,

IN MILLIGRAMS PER LITER

1970

0.20

-0.05

0

0.05

0.10

0.15

TOTAL PHOSPHORUS,

IN MILLIGRAMS PER LITER

NITRATE AS NITROGEN, 

FLOW-ADJUSTED CONCENTRATION, 

IN MILLIGRAMS PER LITER

1970

0.8

0

0.2

0.4

0.6

TOTAL PHOSPHORUS,

 FLOW-ADJUSTED CONCENTRATION, 

IN MILLIGRAMS PER LITER

1970

0.20

-0.05

0

0.05

0.10

0.15

1980 1990 2000 1980 1990 2000

1980 1990 2000 1980 1990 2000

Slope = 0.0033

 p = less than 0.01

Slope = -0.0005

 p = 0.21

Slope = -0.0006

 p = 0.20

Slope = 0.0036

 p = less than 0.01

Unadjusted data Flow adjusted data

Figure 46. Temporal variations in unadjusted and flow-adjusted concentrations of nitrate and total phosphorus and LOWESS-trend curves for the 

Skokomish River near Potlatch, in the Puget Sound Basin study unit, Washington.
Trends in Concentrations of Nitrate and Total Phosphorus 121

1970

NITRATE AS NITROGEN,

IN MILLIGRAMS PER LITER

1970

TOTAL PHOSPHORUS,

IN MILLIGRAMS PER LITER

NITRATE AS NITROGEN, 

FLOW-ADJUSTED CONCENTRATION, 

IN MILLIGRAMS PER LITER

1970

TOTAL PHOSPHORUS,

 FLOW-ADJUSTED CONCENTRATION, 

IN MILLIGRAMS PER LITER

1980 1990 2000 1970 2000

2000

1980 1990

1980 1990 1980 1990 2000

Unadjusted data Flow adjusted data

-0.2

0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0.4

-0.1

0

0.1

0.2

0.3

-0.2

0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0.4

-0.1

0

0.1

0.2

0.3

Slope = 0.0004

 p = 0.46

Slope = 0.0025

 p = 0.11

Slope = 0

 p = 0.43

Slope = 0.0005

 p = 0.21

Figure 47. Temporal variations in unadjusted and flow-adjusted concentrations of nitrate and total phosphorus and LOWESS-trend curves for the 

Nooksack River at Brennan, in the Puget Sound Basin study unit, Washington.
122 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

0

2.0

0.5

1.0

1.5

0.4

-0.1

0

0.1

0.2

0.3

2.0

0

0.5

1.0

1.5

0.4

-0.1

0

0.1

0.2

0.3

Slope = -0.002

 p = 0.14

Slope = -0.002

 p = 0.18

Slope = 0

 p = 0.63

Slope = 0.0004

 p = 0.35

1970 1980 1990 2000 1970 1980 1990 2000

1970 1980 1990 2000 1970 1980 1990 2000

NITRATE AS NITROGEN,

IN MILLIGRAMS PER LITER

TOTAL PHOSPHORUS,

IN MILLIGRAMS PER LITER

NITRATE AS NITROGEN, 

FLOW-ADJUSTED CONCENTRATION, 

IN MILLIGRAMS PER LITER

TOTAL PHOSPHORUS,

 FLOW-ADJUSTED CONCENTRATION, 

IN MILLIGRAMS PER LITER

Unadjusted data Flow adjusted data

Figure 48. Temporal variations in unadjusted and flow-adjusted concentrations of nitrate and total phosphorus and LOWESS-trend curves for the 

Nooksack River at North Cedarville, in the Puget Sound Basin study unit, Washington.
Trends in Concentrations of Nitrate and Total Phosphorus 123

Slope = -0.002

 p = 0.34

Slope = -0.002

 p = 0.29

Slope = 0

 p = 0.87

Slope = -0.0002

 p = 0.47

2.0

0

0.5

1.0

1.5

2.0

0

0.5

1.0

1.5

0.25

0

0.05

0.10

0.15

0.20

0.25

0

0.05

0.10

0.15

0.20 Method

change Method

change

1970 1980 1990 2000 1970 1980 1990 2000

1970 1980 1990 2000 1970 1980 1990 2000

NITRATE AS NITROGEN,

IN MILLIGRAMS PER LITER

TOTAL PHOSPHORUS,

IN MILLIGRAMS PER LITER

NITRATE AS NITROGEN, 

FLOW-ADJUSTED CONCENTRATION, 

IN MILLIGRAMS PER LITER

TOTAL PHOSPHORUS,

 FLOW-ADJUSTED CONCENTRATION, 

IN MILLIGRAMS PER LITER

Unadjusted data Flow adjusted data

Figure 49. Temporal variations in unadjusted and flow-adjusted concentrations of nitrate and total phosphorus and LOWESS-trend curves for the 

Green River at Renton Junction, in the Puget Sound Basin study unit, Washington.
124 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98 NITRATE AS NITROGEN, IN MILLIGRAMS PER LITER TOTAL PHOSPHORUS, IN MILLIGRAMS PER LITER

NITRATE AS NITROGEN, 

FLOW-ADJUSTED CONCENTRATION, 

IN MILLIGRAMS PER LITER

TOTAL PHOSPHORUS,

 FLOW-ADJUSTED CONCENTRATION, 

IN MILLIGRAMS PER LITER

Unadjusted data Flow adjusted data

1970 1980 1990 2000 1970 1980 1990 2000

1970 1980 1990 2000 1970 1980 1990 2000

2.0

0.5

1.0

1.5

0.15

0.05

0.10

Slope = 0.012

 p = 0.01

Slope = 0.01

 p = 0.03

Slope = 0.0002

 p = 0.36

Slope = 0.0001

 p = 0.50

2.0

0.5

1.0

1.5

0.15

0.05

0.10

0

0

0

0

Figure 50. Temporal variations in unadjusted and flow-adjusted concentrations of nitrate and total phosphorus and LOWESS-trend curves for Big 

Soos Creek above Hatchery near Auburn, in the Puget Sound Basin study unit, Washington.
Trends in Concentrations of Nitrate and Total Phosphorus 125

-0.05

0.05

0.10

0.15

0.20

0.25

0.30

0.35

-0.05

0

0.05

0.10

0.15

0.20

0.25

0.30

0.35

1970 1980 1990 2000 1970 1980 1990 2000

1970 1980 1990 2000 1970 1980 1990 2000

NITRATE AS NITROGEN,

IN MILLIGRAMS PER LITER

TOTAL PHOSPHORUS,

IN MILLIGRAMS PER LITER

NITRATE AS NITROGEN, 

FLOW-ADJUSTED CONCENTRATION, 

IN MILLIGRAMS PER LITER

TOTAL PHOSPHORUS,

 FLOW-ADJUSTED CONCENTRATION, 

IN MILLIGRAMS PER LITER

Unadjusted data Flow adjusted data

Slope = 0.012

 p = 0.05

Slope = 0.002

 p = 0.015

Slope = 0.002

 p = less than 0.01

Slope = 0.014

 p = 0.04

0

5

1

2

3

4

0

0

5

1

2

3

4

Figure 51. Temporal variations in unadjusted and flow-adjusted concentrations of nitrate and total phosphorus and LOWESS-trend curves for 

Newaukum Creek near Black Diamond, in the Puget Sound Basin study unit, Washington.
126 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

SUMMARY

The Puget Sound Basin study unit team collected 

streamflow and water-quality data from November 

1995 through April 1998 (water years 1996–98) from a 

fixed-site surface-water network consisting of 11 sites 

in western Washington. Water samples for analyses of 

nutrients, major ions, organic carbon, and suspended 

sediment and measurements of physical properties 

were collected monthly, with additional sampling 

during storm-runoff and high-flow events. The fixedsite network was established in three major river 

basins—the Skokomish River Basin with two sites, the 

Nooksack River Basin with three sites, and the GreenDuwamish River Basin with five sites—and in one 

small urban basin, the Thornton Creek Basin with one 

site.

 Three of the 11 sites—Skokomish River near 

Potlatch, Nooksack River at Brennan (lower 

Nooksack), and Duwamish River at Tukwila—are 

integrators of mixed land uses. The sites are located 

near the mouths of their respective basins and are 

locally influenced by forestry practices, agriculture, 

and urbanization, respectively. The remaining eight 

sites are indicators of relatively homogeneous land useland cover in their basins. Seven of the indicator sites 

are on tributaries within the three major river basins 

and one is on Thornton Creek, a small stream draining 

into Lake Washington. The site on the North Fork (NF) 

Skokomish is an indicator site representing reference or 

background conditions in the study unit. In the 

Nooksack River Basin, the site on Fishtrap Creek is an 

indicator site representing an intensively farmed 

tributary basin with some urban influences from part of 

the basin in Canada and the city of Lynden, and the site 

on the Nooksack River at North Cedarville (upper 

Nooksack) is an indicator site of forest practices in the 

upper basin. In the Green-Duwamish River Basin, four 

sites, one on each of four tributaries, are indicators of 

conditions typical of urban-suburban settings in the 

study unit: Springbrook Creek, of commercial and light 

industrial land use; Big Soos Creek, of an urbanizing 

basin; Newaukum Creek, of agriculture that includes 

cattle, horse, and hobby farms; and the upper Green 

River, of forest practices as well as the conditions in 

basins with headwaters in the mountains. Thornton is 

an indicator of long-established, high-density 

residential and commercial development.

Sampling conditions during the first 18 months 

of the study were wet and dominated by above-normal 

precipitation. Water year 1997 was the wettest of the 

3 years in the study period. Nearly 52 inches of 

precipitation fell (about 14 inches above average); 

monthly precipitation was often 200 percent of normal. 

The wet years caused many runoff events and flooding, 

keeping streamflows generally above median values 

and contributing to high concentrations of nutrients, 

suspended sediment, and organic carbon, and to 

detectable concentrations of several volatile organic 

compounds (VOCs) and pesticides.

Water in the Skokomish at site 1 was of generally 

high quality, although suspended-sediment 

concentrations were occasionally high, with a 

maximum of 1,470 mg/L (milligrams per liter). In 2 of 

the 37 samples collected, iron concentrations of as 

much as 430 μg/L (micrograms per liter) exceeded the 

U.S. Environmental Protection Agency (USEPA) 

secondary maximum contaminant level (SMCL) of 

300 μg/L for drinking water. Skokomish water was 

chemically dilute, with a median dissolved-solids 

concentration of 41 mg/L. Nutrient concentrations 

were also low, with at least half of the organic nitrogen, 

nitrite, and dissolved-phosphorus concentrations below 

laboratory minimum reporting levels (MRLs), and a 

median nitrate concentration of 0.09 mg/L.

The water at site 2 on the NF Skokomish was of 

exceptionally high quality. Unlike site 1, suspendedsediment and iron concentrations in samples were low. 

Out of 33 samples, the maximum suspended-sediment 

concentration observed was 122 mg/L and iron 

concentrations were equal to or less than 25 μg/L. The 

water was chemically dilute, with a median dissolvedsolids concentration of 45 mg/L. Concentrations of 

nutrients were also low, with at least half of the total 

and dissolved organic nitrogen, nitrite, total and 

dissolved phosphorus, and orthophosphate 

concentrations below laboratory MRLs and a median 

nitrate concentration of 0.05 mg/L.

The water in the lower Nooksack River (site 3) 

was of generally good quality except for a few 

occasions when suspended-sediment concentrations 

were relatively large and a number of pesticides and 

VOCs were detected. Ten percent of the 41 samples 

had suspended-sediment concentrations greater than 

1,500 mg/L and the maximum was 2,890 mg/L. The 

water was chemically dilute, with a median dissolvedsolids concentration of 57.5 mg/L. 
Summary 127

Concentrations of nutrients were moderate, with about 

10 percent of the ammonia, nitrite, total and dissolved 

phosphorus, and orthophosphate concentrations below 

laboratory MRLs and a median nitrate concentration of 

0.35 mg/L.

Fishtrap Creek (site 4), where 44 samples were 

collected, had water of fair quality except when iron 

and manganese concentrations were large and a 

number of pesticides and VOCs were detected. In 8 of 

14 samples collected from April 1997–August 1998, 

concentrations of Escherichia coli exceeded 298 

col/100mLs (colonies per 100 milliliters), USEPA’s 

recommended single-sample level for moderate, fullbody contact recreation. Occasionally, concentrations 

of iron and manganese did not meet USEPA SMCLs 

for drinking water. Dissolved solids, with a median 

concentration of 151 mg/L, were moderately high. All 

forms of nitrogen analyzed were present in nearly all 

samples, and nitrate, with a median concentration of 

2.8 mg/L, was the dominant nitrogen species.

Thirty-five water samples from the upper 

Nooksack River at site 5 indicated the water was of 

generally high quality except for occasionally high 

suspended-sediment concentrations. Ten percent of the 

samples had suspended-sediment concentrations 

greater than 1,900 mg/L and the maximum observed 

was 3,210 mg/L. The water was chemically dilute, as 

indicated by dissolved solids with a median 

concentration of 49 mg/L. Concentrations of nutrients 

were also low, with at least half of the organic nitrogen, 

nitrite, dissolved phosphorus, and orthophosphate 

concentrations below laboratory MRLs. The median 

nitrate concentration was 0.21 mg/L.

Forty-two water samples were collected from the 

Duwamish River at site 6. Occasionally, iron and 

manganese concentrations were large and a number of 

pesticides and VOCs were detected. Ten percent of the 

samples had iron and manganese concentrations greater 

than 400 and 70 μg/L, respectively, exceeding USEPA 

SMCLs for drinking water. The water was chemically 

dilute, with a median dissolved-solids concentration of 

62 mg/L. Concentrations of nutrients were moderately 

low, with at least 10 percent of the concentrations of 

reduced forms of nitrogen and of dissolved phosphorus 

and orthophosphate below laboratory MRLs. Nitrate, 

with a median concentration of 0.41 mg/L, and total

organic nitrogen with a median of 0.20 mg/L, were the 

most prevalent nitrogen species.

Thirty-seven water samples were collected from 

Springbrook Creek (site 7); two of these samples, 

collected during storm runoff in October 1996, were 

analyzed for pesticides and VOCs. The water in 

Springbrook was of fair quality. In 25 of the 37 

samples, dissolved-oxygen concentration measured at 

the time of collection did not meet the Washington 

State standard of 8.0 mg/L for a Class A water body. 

The water was moderately high in dissolved solids, 

with a median concentration of 152 mg/L, and major 

ions. Concentrations of nutrients were moderately 

high, with more than 90 percent of the ammonia, 

dissolved phosphorus, and orthophosphate 

concentrations above laboratory MRLs and a median 

nitrate concentration of 0.43 mg/L.

A total of 36 samples indicated the water in Big 

Soos Creek at site 8 to be of good quality. 

Concentrations of Escherichia coli were sometimes 

large, ranging from 21 to 750 col/100mLs. Of eight 

samples collected, two had concentrations that 

exceeded 298 col/100mLs, USEPA’s recommended 

single-sample level for moderate, full-body contact 

recreation. The water was moderately low in dissolved 

solids, with a median concentration of 84 mg/L. 

Concentrations of nutrients were also moderately low, 

with most ammonia, nitrite, total organic nitrogen, and 

dissolved phosphorus concentrations below laboratory 

MRLs and a median nitrate concentration of 

0.875 mg/L.

On the basis of 36 samples, the water in 

Newaukum Creek at site 9 was of moderately good 

quality with respect to water temperatures, dissolvedoxygen concentrations, and pH levels that were within 

Washington State standards for a Class A water body. 

In a sample collected on August 4, 1998, 

concentrations of fecal-coliform bacteria exceeded the 

State’s standard of 100 col/100mLs for a Class A water 

body and enterococci bacteria exceeded 

89 col/100mLs, USEPA’s recommended single-sample 

level for moderate, full-body contact recreation. The 

water was moderately low in dissolved solids, with a 

median concentration of 107 mg/L. The creek, 

however, was rich in nutrients relative to other sites in 

this study. Nitrate concentrations were second-highest 

after Fishtrap and total phosphorus concentrations were 

second-highest after Springbrook. Seventy-five percent 

of ammonia and organic nitrogen concentrations and 

90 percent of phosphorus and orthophosphate 

concentrations were above the laboratory MRLs.
128 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

The water in the upper Green River at site 10 was 

of high quality, similar to that of the study’s reference 

site on the NF Skokomish. The water was chemically 

dilute, as indicated by a median dissolved-solids 

concentration of 36 mg/L. Concentrations of nutrients 

were also low; nitrate was detected in only 38 percent 

of the samples, with a median concentration of 

0.04 mg/L. In a single sample collected during a runoff 

event in October 1997, the suspended-sediment 

concentration was 243 mg/L, the maximum observed 

for this site; however, 90 percent of the 24 samples 

collected had suspended-sediment concentrations less 

than 15 mg/L. Also in this October sample, the 

maximum observed iron concentration of 520 μg/L 

exceeded the USEPA SMCL for drinking water.

Water in Thornton Creek (site 11) was of fair 

quality. Out of 46 samples, iron and manganese 

concentrations were occasionally large and a number of 

pesticides and VOCs were detected. Concentrations of 

Escherichia coli in 9 of 14 samples exceeded 

298 col/100mLs, USEPA’s recommended singlesample level for moderate, full-body contact recreation. 

The water had moderately high concentrations of 

dissolved solids, with a median concentration of 

150 mg/L, and was moderately rich in nutrients relative 

to the other sites in this study. All the forms of 

phosphorus analyzed were detected above MRLs in at 

least 89 percent of the samples. All forms of nitrogen 

analyzed were also detected in most of the samples; 

however, nitrate, with a median concentration of 

1.26 mg/L was the dominant nitrogen species.

Several pesticides, most of them herbicides, and 

VOCs, mostly fuel-related, solvent-related, or 

halogenated, were detected in water samples collected 

from the lower Nooksack River, Fishtrap Creek, the 

Duwamish River, and Thornton Creek. Pesticide and 

VOC concentrations tended to be higher and detections 

more frequent during the wet season from about 

November through March. Maximum pesticide 

concentrations often were in storm-runoff samples, 

which usually coincided with the spring season when 

many compounds are typically applied. But 

concentrations could also be high in runoff samples 

during summer and early fall. Except as noted below, 

no pesticide or VOC concentrations exceeded existing 

or applicable water-quality standards or criteria 

concentrations.

In the lower Nooksack River, 16 pesticides were 

detected. Atrazine was detected most often, in 15 of 22 

samples, in concentrations up to 0.42 μg/L and with a 

median of 0.016 μg/L. Fifteen VOCs were detected in 

samples; however, only methylbenzene was detected at 

concentrations above the 1999 laboratory reporting 

level (LRL). 

In Fishtrap, 29 pesticides were detected, nearly 

twice the number detected downstream in the lower 

Nooksack. The herbicides atrazine, simazine, and the 

transformation product deethylatrazine were detected 

in 31 of 32 samples. Seven insecticides—carbaryl, 

carbofuran, diazinon, ethoprophos, malathion, oxamyl, 

and propargite—were also detected. Diazinon 

concentrations in five samples, and carbaryl 

concentrations in three samples, did not meet 

recommended aquatic-life criteria. Eighteen VOCs 

were detected. Chloromethane was most frequently 

detected, in 22 of 32 samples, but all detections were 

below the 1999 LRL. Of six compounds 

(chlorobenzene, ethylbenzene, dichloromethane, 

methylbenzene, 1,3-plus-1,4-dimethylbenzene, and 

1,2-dimethylbenzene) detected at concentrations above 

the 1999 LRLs, methylbenzene was detected most 

frequently (53 percent of samples).

Thirteen pesticides were found in 24 samples 

from the Duwamish River. Simazine, prometon, 

atrazine, and tebuthiuron were the most frequently 

detected pesticides. Diazinon was the only insecticide 

detected and was found in eight samples in 

concentrations as high as 0.083 μg/L. Diazinon 

concentrations in two samples exceeded 0.04 μg/L, a 

level recommended for the protection of aquatic life. 

Twenty-six VOCs were detected; however, only two 

(methylbenzene and 1,3-plus-1,4-dimethylbenzene) 

were detected at concentrations above the 1999 LRLs.

In Thornton Creek, 21 pesticides were detected, 

and again, most of these were herbicides. Prometon 

was detected most frequently, in nearly 100 percent of 

the 46 samples. Of the herbicides, simazine and 

dichlobenil were the next most frequently detected, 

found in 23 and 21 samples, respectively. Five 

insecticides—carbaryl, chlorpyrifos, diazinon, lindane, 

and malathion, were also detected. Diazinon was 

detected in 85 percent of the samples, 15 of which had 

concentrations exceeding 0.04 μg/L, a limit 

recommended for the protection of aquatic life. 

Diazinon was also the insecticide purchased at the 

highest rate by the public through retail outlets in King 

County. Two sample concentrations of carbaryl, one of 

chlorpyrifos, and one of lindane also exceeded limits 

recommended for the protection of aquatic life. 
Summary 129

In urban streams such as Thornton Creek, insecticides 

typically used on residential lawns and gardens have 

increased the frequency of detections and 

concentrations that do not meet criteria. In samples 

from Thornton, 32 VOCs were detected, the most of all 

four sites sampled for VOCs. Ten compounds (acetone, 

bromoform, trichloromethane, ethylbenzene, 

dichloromethane, 4-methyl-2-pentanone, 

methylbenzene, 1,2-dimethylbenzene, 1,3-plus-1,4-

dimethylbenzene, and 1,2,4-trimethylbenzene) were 

detected at concentrations above the 1999 LRLs. More 

than 70 percent of methylbenzene detections were in 

concentrations above the LRL, the most of any site.

Water-quality conditions at the study sites 

resulted from both natural characteristics of the 

watersheds and human activities. In the Nooksack and 

Skokomish Rivers, natural conditions probably 

contributed, in part, to the large suspended-sediment 

concentrations observed during high streamflow 

events. However, logging and road building in the 

basins might also have contributed to the suspendedsediment loads. In the forested study basins, dissolved 

solids and nutrient concentrations were low. At the 

reference site on the NF Skokomish and the forestry 

practices indicator site on the upper Green, natural 

conditions were reflected in high-quality water with 

low concentrations of dissolved solids, nutrients, and 

suspended sediment, and standards or criteria that were 

nearly always met. Unlike the high-quality water at the 

reference and forestry sites, natural conditions appear 

to have adversely affected the quality of water in 

Springbrook Creek. High concentrations of iron and 

manganese and low dissolved-oxygen concentrations 

were possibly the result of ground-water discharge to 

this tributary.

Of all the sites, nutrient concentrations were 

highest in the agricultural streams (Fishtrap and 

Newaukum Creeks) and next highest in the urban 

streams (Springbrook, Big Soos, and Thornton 

Creeks), largely because of human activities. Of the 

three large rivers integrating a mix of land uses, the 

lower Nooksack (in an agricultural setting) had on 

average, the highest total nitrogen and phosphorus 

concentrations, followed by the Duwamish (in an urban 

setting) and the Skokomish (in a forestry practices 

setting). An earlier study showed that fertilizer 

applications to lands within the study unit 

corresponded to nitrogen concentrations and yields 

from the major river basins. Nutrient loads transported 

in the surface water at the 11 sites during this study 

ranged from 6.0 to 3,200 tons per year of total nitrogen 

in the upper Green and the lower Nooksack, 

respectively, and from about 2 to 890 tons per year of 

total phosphorus in the upper Green and the lower 

Nooksack, respectively.

Of the three major river basins of this study, 

nutrient yields were largest from the Nooksack River 

Basin and smallest from the Skokomish River Basin. 

The Nooksack River Basin was estimated to have one 

of the highest source loading rates among the major 

Puget Sound Basin watersheds, receiving 9.1 tons of 

nitrogen and 1.3 tons of phosphorus per square mile of 

drainage, whereas the Skokomish River Basin had one 

of the lowest rates, receiving 0.4 ton of nitrogen and 

0.2 ton of phosphorus per square mile of drainage. 

From Fishtrap and Newaukum Creeks, total nitrogen 

yields of 8.8 and 7.7 tons per square mile, respectively, 

were the highest of the 11 sites. Yields from the urban 

and suburban basins also were well above those from 

the reference and forestry basins. From Big Soos 

Creek, the total nitrogen yield of 3.0 tons per square 

mile was the highest of the urban streams.

Pesticides affected water quality at the four sites 

where they were measured, whether the site was in an 

urban or agricultural setting. More types of pesticides 

were detected in samples from the agricultural sites 

than from the urban sites. The most pesticides were 

detected in Fishtrap Creek. Many pesticides were those 

applied for agricultural purposes, but several were 

pesticides typically applied in urban settings, such as 

those used in maintaining rights-of-way. Although 

more types of pesticides were detected in samples from 

agricultural streams, pesticides were applied in larger 

quantities in the urban areas. In the 1980’s, about 

18 percent of the total herbicide and 31 percent of the 

total insecticide applications in the study unit were to 

King County, where Thornton Creek and the 

Duwamish River are located. About 9 percent of the 

herbicide and 3 percent of the agricultural and nonagricultural applications of insecticides were to 

Whatcom County, where Fishtrap Creek and the 

Nooksack River are located. 
130 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

The generally higher concentrations, the detections of 

certain pesticides in samples year round, and the 

number of times insecticide concentrations did not 

meet aquatic-life criteria in Thornton were at least 

partly because of these high application rates and 

availability of pesticides in urban areas.

More VOCs were detected, and at a higher 

detection frequency, at the two sites in urban areas than 

at the two sites in agricultural areas. The most 

compounds were detected, and in the highest 

concentrations, at Thornton. Conversely, the least 

number of compounds were detected in lower 

Nooksack, with only 2 percent urban land upstream. 

Many VOCs detected in samples from all four sites 

were fuel related. MTBE, an automotive fuel additive 

used in Canada, was detected in a few samples from 

Fishtrap. Many solvents were also detected, 

particularly in samples from the Duwamish and 

Thornton. Carbon disulfide, chloromethane, and 4-

methyl-2-pentanone were the most commonly detected 

solvents. Other solvents, such as trichloroethene (TCE) 

and tetrachloroethene (PCE), were detected only in 

samples from the urban sites. The only VOC with a 

distinctly agricultural signature was 1,2-

dichloropropane, detected only in Fishtrap Creek 

samples. 1,2-dichloropropane was historically used as a 

soil fumigant and, at the time of this study, was present 

in trace amounts in formulations of 1,3-

dichloropropene, which was still applied in the 

Washington State part of Fishtrap Creek Basin.

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———1999b, URL: 

http://wwwsd.cr.usgs.gov/nawqa/vocns/, accessed April 

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———1999c, URL: 

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hydrocarbon impurities present in soil fumigant 

formulations: Water Quality Resources Journal of 

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134 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Table 33. Fecal-indicator bacteria and coliphage in samples collected at selected surface-water sites in the Puget Sound Basin study unit, Washington

[Abbreviations: col/100ml, colonies per 100 milliliters; pfu/100ml; plaque-forming units per 100 milliliters; <, less than; K, estimate based on non-ideal 

count; –, no data]

Date Total coliform, 

col/100mL

Fecal coliform, 

col/100mL

Escherichia coli, 

col/100mL

Enterococcus, 

col/100mL

Clostridium 

perfringens, 

col/100mL

Somatic 

coliphage, 

pfu/100mL

Male-specific 

coliphage, 

pfu/100mL

Thornton Creek near Seattle, 12128000, site 1

19970407 720 – K250 – – – –

19970505 1,600 – 170 – – – –

19970520 26,000 – K9,600 – – – –

19970527 70,000 – 1,900 – – – –

19970612 21,000 – 620 – – – –

19970707 4,000 – 580 – 120 10 16

19970804 13,000 – 460 – <3 12 57

19970908 6,800 – 580 – K28 – –

19971208 8,000 – 320 – – – –

19980112 1,500 – 98 – – – –

19980209 1,600 – 240 – – – –

19980309 13,000 – 520 – – – –

19980406 1,100 – K30 – – – –

19980803 – 870 810 650 – 150 <1

Fishtrap Creek at Flynn Road at Lynden, 12212100, site 3

19970408 5,500 – 280 – – – –

19970506 33,000 – 4,000 – – – –

19970529 77,000 – 5,900 – – – –

19970610 7,000 – 230 – 22 0 6

19970709 190,000 – 5,200 – 77 7 4

19970806 6,700 – 3,200 – <3 31 31

19970910 6,000 – 1,200 – 9 – –

19971210 7,100 – 87 – – – –

19980114 4,500 – 140 – – – –

19980123 36,000 – 2,800 – – – –

19980211 2,600 – 220 – – – –

19980311 2,500 – 410 – – – –

19980408 1,800 – 140 – – – –

19980803 – 1,000 650 330 – 43 <1

Big Soos Creek above Hatchery near Auburn, 12112600, site 8

19970415 160 – 30 – – – –

19970422 790 – 70 – – – –

19970515 2,400 – 21 – – – –

19970617 760 – 160 – K5 76 8

19970715 2,000 – K60 – K4 8 37

19970812 2,000 – 140 – K5 – –

19970826 6,500 – 750 – – – –

19970916 2,000 – 360 – – – –

Newaukum Creek near Black Diamond, 12108500, site 9

19980804 – 210 190 150 – 58 2

Green River above Twin Camp Creek near Lester, 12103380, site 10

19970424 <1 – <1 – – – –

19970521 24 – <1 – – – –

19970616 – – – – K1 <1 7

19970624 77 – K10 – <3 43 17

19970714 66 – <1 – <1 3 21

19970811 160 – K1 – – – –

19970915 180 – <1 – – – –

19971004 K2 – K5 – – – –
Tables 33 and 34 135

Table 34. Pesticide and volatile organic compounds in storm samples collected on October 4, 1996, from Springbrook Creek, site 7, in the Puget Sound 

Basin study unit, Washington

[Values are in micrograms per liter unless otherwise noted. Number in parentheses below parameter or compound name is the U.S. Geological Survey’s 

National Water Information System code. ft3/s, cubic feet per second; E, estimated; –, no data] 

Time

Discharge, 

instantaneous 

(ft3/s)

(00061)

2,6-Diethylaniline, dissolved

(82660)

Acetochlor, 

dissolved

(49260)

Alachlor, 

dissolved

(46342)

alpha-HCH, 

dissolved

(34253)

Atrazine, 

dissolved

(39632)

Azinphosmethyl, 

dissolved

(82686)

Benfluralin, 

dissolved

(82673)

1530 76 <0.003 <0.002 <0.002 <0.002 <0.001 <0.001 <0.002

2010 89 <.003 <.002 <.002 <.002 <.001 <.001 <.002

Time

Butylate, 

dissolved

(04028)

Carbaryl, 

dissolved

(82680)

Carbofuran, 

dissolved

(82674)

Chlorpyrifos, 

dissolved

(38933)

Cyanazine, 

dissolved

(04041)

p,p'-DDE, 

dissolved

(34653)

DCPA, 

dissolved

(82682)

Deethylatrazine, 

dissolved

(04040)

Diazinon, 

dissolved

(39572)

1530 <0.002 <0.003 <0.003 <0.004 <0.004 <0.006 <0.002 <0.002 0.032

2010 <.002 <.003 <.003 <.004 <.004 <.006 <.002 <.002 .037

Time

Dieldrin, 

dissolved

(39381)

Disulfoton, 

dissolved

(82677)

EPTC, 

dissolved

(82668)

Ethalfluralin, 

dissolved

(82663)

Ethoprophos, 

dissolved

(82672)

Fonofos, 

dissolved

(04095)

Lindane 

(gammaHCH), 

dissolved

(39341)

Linuron, 

dissolved

(82666)

Malathion, 

dissolved

(39532)

1530 <0.001 <0.017 <0.002 <0.004 <0.003 <0.003 <0.004 <0.002 <0.005

2010 <.001 <.017 <.002 <.004 <.003 <.003 <.004 <.002 <.005

Time

Metolachlor, 

dissolved

(39415)

Metribuzin, 

dissolved

(82630)

Molinate, 

dissolved

(82671)

Napropamide, 

dissolved

(82684)

Parathion, 

dissolved

(39542)

Parathionmethyl, 

dissolved

(82667)

Pebulate, 

dissolved

(82669)

Pendimethalin, 

dissolved

(82683)

cis-Permethrin, 

dissolved

(82687)

1530 0.023 <0.004 <0.004 <0.003 <0.004 <0.006 <0.004 <0.004 <0.005

2010 .017 <.004 <.004 <.003 <.004 <.006 <.004 <.004 <.005

Time

Phorate, 

dissolved

(82664)

Prometon, 

dissolved

(04037)

Propachlor, 

dissolved

(04024)

Propanil, 

dissolved

(82679)

Propargite, 

dissolved

(82685)

Propyzamide, 

dissolved

(82676)

Simazine, 

dissolved

(04035)

Tebuthiuron, 

dissolved

(82670)

Terbacil, 

dissolved

(82665)

1530 <0.002 E0.015 <0.007 <0.004 <0.013 <0.003 <0.005 <0.01 <0.007

2010 <.002 .019 <.007 <.004 <.013 <.003 <.005 <.01 <.007

Time

Terbufos, 

dissolved

(82675)

Thiobencarb, 

dissolved

(82681)

Triallate, 

dissolved

(82678)

Trifluralin, 

dissolved

(82661)

Silvex, 

dissolved

(39762)

2,4,5-T, 

dissolved

(39742)

2,4-D, 

dissolved

(39732)

2,4-DB, 

dissolved

(38746)

3-Hydroxycarbofuran, 

dissolved

(49308)

1530 <0.013 <0.002 <0.001 <0.002 <0.02 <0.04 1.2 <0.24 <0.01

2010 <.013 <.002 <.001 <.002 <.02 <.04 <0.15 <.24 <.01

Time

4,6-Dinitro-2-

methylphenol, 

dissolved

(49299)

Acifluorfen, 

dissolved

(49315)

Aldicarb, 

dissolved

(49312)

Aldicarb 

sulfone, 

dissolved

(49313)

Aldicarb 

sulfoxide, 

dissolved

(49314)

Bentazon, 

dissolved

(38711)

Bromacil, 

dissolved

(04029)

Bromoxynil, 

dissolved

(49311)

Carbaryl, 

dissolved

(49310)

1530 <0.42 <0.04 <0.55 <0.10 <0.02 <0.01 <0.04 <0.04 <0.01

2010 <.42 <.04 <.55 <.10 <.02 <.01 <.04 <.04 <.01
136 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Table 34. Pesticide and volatile organic compounds in storm samples collected on October 4, 1996, from Springbrook Creek, site 7, Puget Sound Basin 

study unit, Washington—Continued

Time

Carbofuran, 

dissolved

(49309)

Chloramben, 

dissolved

(49307)

Chlorothalonil, 

dissolved

(49306)

Clopyralid, 

dissolved

(49305)

Dacthal 

monoacid, 

dissolved

(49304)

Dicamba, 

dissolved

(38442)

Dichlobenil, 

dissolved

(49303)

Dichlorprop, 

dissolved

(49302)

Dinoseb, 

dissolved

(49301)

1530 <0.11 <0.42 <0.48 <0.23 <0.02 <0.04 <1.2 <0.03 <0.04

2010 <.11 <.42 <.48 <.23 <.02 <.04 <1.2 <.03 <.04

Time

Diuron, 

dissolved

(49300)

Fenuron, 

dissolved

(49297)

Fluometuron, 

dissolved

(38811)

Linuron, 

dissolved

(38478)

MCPA, 

dissolved

(38482)

MCPB, 

dissolved

(38487)

Methiocarb, 

dissolved

(38501)

Methomyl, 

dissolved

(49296)

Neburon, 

dissolved

(49294)

1530 0.56 <0.01 <0.04 <0.02 <0.17 <0.14 <0.03 <0.02 <0.01

2010 E2.4 <.01 <.04 <.02 <.17 <.14 <.03 <.02 <.01

Time

Norflurazon, 

dissolved

(49293)

Oryzalin, 

dissolved

(49292)

Oxamyl, 

dissolved

(38866)

Picloram, 

dissolved

(49291)

Propham, 

dissolved

(49236)

Propoxur, 

dissolved

(38538)

Triclopyr, 

dissolved

(49235)

Bromodichloromethane, total

(32101)

Tetrachloromethane, total

(32102)

1530 <0.02 <0.31 <0.02 <0.05 <0.04 <0.04 1.3 <0.2 <0.1

2010 <.02 <.31 <.02 <.05 <.04 <.04 <0.25 <.2 <.1

Time

1,2-Dichloroethane, total

(32103)

Tribromomethane, total

(32104)

Dibromochloromethane, 

total

(32105)

Trichloromethane, 

total

(32106)

Methylbenzene, total

(34010)

Benzene, 

total

(34030)

Acrolein, total

(34210)

2-Propenenitrile, total

(34215)

Chlorobenzene, total

(34301)

1530 <0.1 <0.4 <0.2 E0.01 <0.1 <0.1 <4 <4 <0.1

2010 <.1 E.03 <.2 E.01 <.1 <.1 <4 <4 <.1

Time

Chloroethane, total

(34311)

Ethylbenzene, 

total

(34371)

1,1,1,2,2,2-

Hexachloroethane, total

(34396)

Bromomethane, total

(34413)

Chloromethane, 

total

(34418)

Dichloromethane, total

(34423)

Tetrachloroethene, 

total

(34475)

Trichlorofluoromethane, 

total

(34488)

1,1-Dichloroethane, total

(34496)

1530 E0.1 <0.1 <0.1 <0.2 <0.4 <0.2 <0.1 <0.2 <0.1

2010 E.1 E.01 <.1 <.2 <.4 <.2 – <.2 <.1

Time

1,1-

Dichloroethene, total

(34501)

1,1,1-Trichloroethane, total

(34506)

1,1,2-Trichloroethane, total

(34511)

1,2-Dichlorobenzene, 

total

(34536)

1,2-Dichloropropane, total

(34541)

trans-1,2-

Dichloroethene, 

total

(34546)

1,2,4-

Trichlorobenzene, 

total

(34551)

1,3-

Dichlorobenzene, 

total

(34566)

1,4-Dichlorobenzene, total

(34571)

1530 <0.2 <0.1 <0.2 <0.1 <0.1 <0.1 <0.4 <0.1 <0.1

2010 <.2 <.1 <.2 <.1 <.1 <.1 <.4 <.1 <.1

Time

Dichlorodifluoromethane, 

total

(34668)

Naphthalene, 

total

(34696)

trans-1,3-

Dichloro-propene, 

total

(34699)

cis-1,3-

Dichloropropene, total

(34704)

Chloroethene, total

(39175)

Trichloroethene, 

total

(39180)

Hexachlorobutadiene, 

total

(39702)

Bromoethene, 

total

(50002)

Ethyl tert-butyl 

ether, total

(50004)

1530 <0.4 <0.4 <0.2 <0.2 <0.2 <0.1 <0.4 <0.2 <0.2

2010 <.4 <.4 <.2 <.2 <.2 <.1 <.4 <.2 <.2
Tables 33 and 34 137

Table 34. Pesticide and volatile organic compounds in storm samples collected on October 4, 1996, from Springbrook Creek, site 7, Puget Sound Basin 

study unit, Washington—Continued

Time

tert-Amyl methyl 

ether, total

(50005)

cis-1,2-Dichloroethene, total

(77093)

Ethenylbenzene, total

(77128)

1,2-Dimethylbenzene, total

(77135)

1,2,4-

Trimethylbenzene, 

total

(77222)

(1-Methylethyl)-

benzene, 

total

(77223)

n-Propylbenzene, 

total

(77224)

n-Butylbenzene, total

(77342)

1,2,3-Trichloropropane, total

(77443)

1530 <0.2 E0.01 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.4

2010 <.2 E.01 <.1 <.1 <.1 <.1 <.1 <.1 <.4

Time

1,2,3-Trichlorobenzene, total

(77613)

1,2-Dibromoethane, total

(77651)

1,1,2-

Trichloro1,2,2-trifluoroethane, total

(77652)

Methyl tertbutyl ether, 

total

(78032)

Diisopropyl 

ether, total

(81577)

1,2-

Dibromo-3-

chloropropane, 

total

(82625)

1,3 & 1,4-

Dimethylbenzene, 

total

(85795)

Dibromomethane, 

total

(30217)

1,1,2,2-

Tetrachloroethane, total

(34516)

1530 <0.4 <0.2 <0.1 <0.2 <0.2 <1 <0.1 <0.2 <0.2

2010 <.4 <.2 <.1 <.2 <.2 <1 <.1 <.2 <.2

Time

Methyl acrylate, 

total

(49991)

1,2,3,4-

Tetramethylbenzene, total

(49999)

1,2,3,5-

Tetramethylbenzene, total

(50000)

trans-1,4-

Dichloro-2-

butene, total

(73547)

Ethyl methacrylate, total

(73570)

Carbon 

disulfide, 

total

(77041)

2-Hexanone, 

total

(77103)

1,1-

Dichloropropene, 

total

(77168)

2,2-Dichloropropane, total

(77170)

1530 <4 <0.1 <0.1 <10 <2 <0.1 <10 <0.1 <0.1

2010 <4 <.1 <.1 <10 <2 E.01 <10 <.1 <.1

Time

1,3-Dichloropropane, total

(77173)

2-Ethyltoluene, 

total

(77220)

1,2,3-

Trimethylbenzene, total

(77221)

1,3,5-

Trimethylbenzene, total

(77226)

1-Chloro-2-

methylbenzene, total

(77275)

1-Chloro-4-

methylbenzene, 

total

(77277)

Bromochloromethane, 

total

(77297)

(1-Methylpropyl)-

benzene, 

total

(77350)

(1,1-Dimethylethyl)-benzene, 

total

(77353)

1530 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.2 <0.1 <0.1

2010 <.1 <.1 <.1 <.1 <.1 <.1 <.2 <.1 <.1

Time

1-Isopropyl-4-

methyl-benzene, 

total

(77356)

Iodomethane, total

(77424)

1,1,1,2-Tetrachloroethane, total

(77562)

3-Chloro-1-

propene, total

(78109)

4-Methyl-2-

pentanone, total

(78133)

Acetone, 

total

(81552)

Bromobenzene, 

total

(81555)

Diethyl 

ether, total

(81576)

Methyl 

acrylnitrile, total

(81593)

1530 <0.1 <0.1 <0.1 <0.2 <10 E7 <0.1 <0.2 <4

2010 <.1 <.1 <.1 <.2 <10 E7 <.1 <.2 <4

Time 2-Butanone, total

(81595)

Methyl 

methacrylate, total

(81597)

Tetrahydrofuran, total

(81607)

1530 E2 <2 <10

2010 <10 <2 <10
138 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Table A1. Minimum reporting levels for major ions and trace metals 

analyzed in filtered surface-water samples by inductively coupled plasma, 

laboratory schedule 2701

[USGS NWIS code: U.S. Geological Survey National Water Information 

System No.; CAS No.: Chemical Abstracts Service No.; MRL, minimum 

reporting level; mg/L, milligrams per liter; μg/L, micrograms per liter; °C, 

degrees Celsius; –, no value]

Compound USGS NWIS 

code CAS No.

MRL

(mg/L, unless 

otherwise noted)

Calcium 00915 7440-70-2 0.02

Magnesium 00925 7439-95-4 .004

Sodium 00930 7440-23-5 .06

Potassium 00935 7440-09-7 .1

Iron, in μg/L 01046 7439-89-6 10

Manganese, in μg/L 01056 7439-96-5 3

Chloride 00940 16887-00-6 .1

Sulfate 00945 14808-79-8 .1

Fluoride 00950 16984-48-8 .1

Silica 00955 7631-86-9 .05

Residue on evaporation 

at 180 °C

70300 – 10

Table A2. Minimum reporting levels for nutrients analyzed in filtered and 

whole surface-water samples, laboratory schedule 2702

[USGS NWIS code: U.S. Geological Survey National Water Information 

System No.; CAS No.: Chemical Abstracts Service No.; MRL, minimum 

reporting level; LRL, laboratory reporting level; mg/L, milligrams per liter; 

N, nitrogen; P, phosphorus; –, no value]

Compound

USGS 

NWIS 

code

CAS No. MRL/LRL 

(mg/L)

Nitrogen, ammonia, dissolved, as N 00608 7664-41-7 10.015, 20.02

Nitrogen, nitrite, dissolved, as N 00613 14797-65-0 .01

Nitrogen, ammonia + organic, 

dissolved, as N

00623 17778-88-0 1.2,2.1

Nitrogen, ammonia + organic, total, 

as N

00625 17778-88-0 1.2, 2.1

Nitrogen, nitrite + nitrate, dissolved, 

as N

00631 – .05

Phosphorus, total, as P 00665 7723-14-0 .01

Phosphorus, dissolved, as P 00666 7723-14-0 .01

Phosphorus, dissolved, 

orthophosphate, as P

00671 14265-44-2 .01

1Prior to November 1997.

2After November 1997.

Table A3. Minimum reporting levels for organic carbon analyzed in 

surface-water samples, laboratory schedule 2075

[USGS NWIS code: U.S. Geological Survey National Water Information 

System No.; CAS No.: Chemical Abstracts Service No.; MRL, minimum 

reporting level; LRL, laboratory reporting level; mg/L, milligrams per liter; 

–, no value]

Compound USGS NWIS 

code CAS No. MRL/LRL

(mg/L)

Organic carbon, suspended 00689 -- 10.1, 20.2

Organic carbon, dissolved 00681 -- .1

1Prior to November 1997.

2After November 1997.

APPENDIX A. NATIONAL WATER-QUALITY LABORATORY ANALYTICAL SCHEDULES
Appendix A. National Water-Quality Laboratory Analytical Schedules 139

Table A4. Minimum reporting levels for pesticides and transformation products analyzed in filtered surface-water 

samples by gas chromatography/mass spectrometry, laboratory schedule 2010

[USGS NWIS code: U.S. Geological Survey National Water Information System No.; CAS No.: Chemical Abstracts 

Service No.; MRL, minimum reporting level; μg/L, micrograms per liter; DDE, dichlorodiphenyldichloroethylene; DCPA, 

dimethyltetrachloroterephthalate; EPTC, S-ethyl dipropylthiocarbamate; HCH, hexachlorocyclohexane; –, no value]

Pesticide or degradation 

product Type USGS NWIScode CAS No. MRL(μg/L)

2,6-Diethylaniline Transformation product 82660 579-66-8 0.003

Acetochlor Herbicide 49260 34256-82-1 .002

Alachlor Herbicide 46342 15972-60-8 .002

Atrazine Herbicide 39632 1912-24-9 .001

Azinphos-methyl Insecticide 82686 86-50-0 .001

Benfluralin Herbicide 82673 1861-40-1 .002

Butylate Herbicide 04028 2008-41-5 .002

Carbaryl Insecticide 82680 63-25-2 .003

Carbofuran Insecticide 82674 1563-66-2 .003

Chlorpyrifos Insecticide 38933 2921-88-2 .004

Cyanazine Herbicide 04041 21725-46-2 .004

p,p’-DDE Transformation product 34653 72-55-9 .006

DCPA Herbicide 82682 1861-32-1 .002

Deethylatrazine Transformation product 04040 6190-65-4 .002

Diazinon Insecticide 39572 333-41-5 .002

Dieldrin Insecticide 39381 60-57-1 .001

Disulfoton Insecticide 82677 298-04-4 .017

EPTC Herbicide 82668 759-94-4 .002

Ethalfluralin Herbicide 82663 55283-68-6 .004

Ethoprophos Insecticide 82672 13194-48-4 .003

Fonofos Insecticide 04095 944-22-9 .003

alpha-HCH Insecticide1 34253 319-84-6 .002

Lindane (gamma-HCH) Insecticide 39341 58-89-9 .004

Linuron Herbicide 82666 330-55-2 .002

Malathion Insecticide 39532 121-75-5 .005

Metolachlor Herbicide 39415 51218-45-2 .002

Metribuzin Herbicide 82630 21087-64-9 .004

Molinate Herbicide 82671 2212-67-1 .004

Napropamide Herbicide 82684 15299-99-7 .003

Parathion Insecticide 39542 56-38-2 .004

Parathion-methyl Insecticide 82667 298-00-0 .006

Pebulate Herbicide 82669 1114-71-2 .004

Pendimethalin Herbicide 82683 40487-42-1 .004

cis-Permethrin Insecticide 82687 54774-45-7 .005

Phorate Insecticide 82664 298-02-2 .002

Prometon Herbicide 04037 1610-18-0 .018

Propachlor Herbicide 04024 1918-16-7 .007

Propanil Herbicide 82679 709-98-8 .004

Propargite Insecticide 82685 2312-35-8 .013

Propyzamide Herbicide 82676 23950-58-5 .003

Simazine Herbicide 04035 122-34-9 .005

Tebuthiuron Herbicide 82670 34014-18-1 .010

Terbacil Herbicide 82665 5902-51-2 .007

Terbufos Insecticide 82675 13071-79-9 .013

Thiobencarb Herbicide 82681 28249-77-6 .002

Triallate Herbicide 82678 2303-17-5 .001

Trifluralin Herbicide 82661 1582-09-8 .002

Surrogate recoveries MRL (percent)

Diazinon-d10 (surrogate) 91063 100155-47-3 0.1

alpha-HCH-d6 (surrogate) 91065 – .1

1Pesticide can be a component of the technical mixture of lindane as well as a transformation product of lindane 

(Larson and others, 1997).
140 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Table A5. Minimum reporting levels for pesticides and transformation products analyzed in filtered surface-water 

samples by high-performance liquid chromatography/photodiode-array detection, laboratory schedule 2051

[USGS NWIS code: U.S. Geological Survey National Water Information System No. CAS No.; Chemical Abstracts 

Service No.; MRL, minimum reporting level; μg/L, micrograms per liter; 2,4-5-T, (2,4-5-trichlorophenoxy) acetic acid; 

2,4-D, (2,4-dichlorophenoxy) acetic acid; 2,4-DB, 4-(2,4-dichlorophenoxy) butyric acid; MCPA, (4-chloro2-methylphenoxy) acetic acid; MCPB, 4-(4-chloro-o-tolyloxy)butyric acid; BDMC, 4-bromo-3,5-dimethyl phenyl-nmethylcarbamate; –, no value]

Pesticide or degradation 

product Type USGS NWIS code CAS No. MRL(μg/L)

2,4,5-T Herbicide 39742 93-76-5 0.035

2,4-D Herbicide 39732 94-75-7 .15

2,4-DB Herbicide 38746 94-82-6 .24

2-(2,4,5-Trichlorophenoxy) Herbicide 39762 93-72-1 .021

propionic acid

3-Hydroxycarbofuran Transformation product 49308 16655-82-6 .014

4,6-Dinitro-2-methylphenol Herbicide 49299 534-52-1 .42

Acifluorfen Herbicide 49315 50594-66-6 .035

Aldicarb Insecticide 49312 116-06-3 .55

Aldicarb sulfone Transformation product 49313 1646-88-4 .10

Aldicarb sulfoxide Transformation product 49314 1646-87-3 .021

Bentazon Herbicide 38711 25057-89-0 .014

Bromacil Herbicide 04029 314-40-9 .035

Bromoxynil Herbicide 49311 1689-84-5 .035

Carbaryl Insecticide 49310 63-25-2 .008

Carbofuran Insecticide 49309 1563-66-2 .12

Chloramben Herbicide 49307 133-90-4 .42

Chlorothalonil Insecticide 49306 1897-45-6 .48

Clopyralid Herbicide 49305 1702-17-6 .23

Dacthal monoacid Degradation product 49304 887-54-7 .017

Dicamba Herbicide 38442 1918-00-9 .035

Dichlobenil Herbicide 49303 1194-65-6 1.2

Dichlorprop Herbicide 49302 120-36-5 .032

Dinoseb Herbicide 49301 88-85-7 .035

Diuron Herbicide 49300 330-54-1 .020

Fenuron Herbicide 49297 101-42-8 .013

Fluometuron Herbicide 38811 2164-17-2 .035

Linuron Herbicide 38478 330-55-2 .018

MCPA Herbicide 38482 94-74-6 .17

MCPB Herbicide 38487 94-81-5 .14

Methiocarb Insecticide 38501 2032-65-7 .026

Methomyl Insecticide 49296 16752-77-5 .017

Neburon Herbicide 49294 555-37-3 .015

Norflurazon Herbicide 49293 27314-13-2 .024

Oryzalin Herbicide 49292 19044-88-3 .31

Oxamyl Insecticide 38866 23135-22-0 .018

Picloram Herbicide 49291 1918-02-1 .05

Propham Herbicide 49236 122-42-9 .035

Propoxur Insecticide 38538 114-26-1 .035

Triclopyr Herbicide 49235 55335-06-3 .25

Surrogate recoveries MRL (percent)

BDMC (surrogate) 99835 – .1
Appendix A. National Water-Quality Laboratory Analytical Schedules 141

Table A6. Minimum reporting levels for volatile organic compounds analyzed in whole surface-water samples by purge and trap chromatography/mass 

spectrometry, laboratory schedule 2020—Continued

Compound (Common name)

USGS 

NWIS 

code

CAS 

No.

LRL

(μg/L) Compound

USGS 

NWIS

code

CAS 

No.

LRL

(μg/L)

1,1,1,2-Tetrachloroethane 77562 630-20-6 0.044 Benzene 34030 71-43-2 0.1

1,1,1-Trichloroethane 34506 71-55-6 .032 Bromobenzene 81555 108-86-1 .036

1,1,2,2-Tetrachloroethane 34516 79-34-5 .13 Bromochloromethane 77297 74-97-5 .044

1,1,2-Trichloroethane 34511 79-00-5 .064 Bromodichloromethane 32101 75-27-4 .048

1,1,2-Trichloro-1,2,2-

trifluoroethane (Freon 113)

77652 76-13-1 .032 Bromoethene 50002 593-60-2 .1

1,1-Dichloroethane 34496 75-34-3 .066 Tribromomethane (Bromoform) 32104 75-25-2 .1

1,1-Dichloroethene 34501 75-35-4 .044 Bromomethane (Methyl bromide) 34413 74-83-9 .15

1,1-Dichloropropene 77168 563-58-6 .026 n-Butylbenzene 77342 104-51-8 .19

1,2,3,4-Tetramethylbenzene 

(Prehnitene)

49999 488-23-3 .23 Carbon disulfide 77041 75-15-0 .37

1,2,3,5-Tetramethylbenzene 

(Isodurene)

50000 527-53-7 .2 Chlorobenzene 34301 108-90-7 .028

1,2,3-Trichlorobenzene 77613 87-61-6 .27 Chloroethane 34311 75-00-3 .12

1,2,3-Trichloropropane 77443 96-18-4 .16 Trichloromethane (Chloroform) 32106 67-66-3 .052

1,2,3-Trimethylbenzene 77221 526-73-8 .12 Chloromethane (Methyl chloride) 34418 74-87-3 .25

1,2,4-Trichlorobenzene 34551 120-82-1 .19 Dibromochloromethane 32105 124-48-1 .18

1,2,4-Trimethylbenzene 77222 95-63-6 .056 Dibromomethane 30217 74-95-3 .05

1,2-Dibromo-3-chloropropane 82625 96-12-8 .21 Dichlorodifluoromethane 34668 75-71-8 .14

1,2-Dibromoethane 77651 106-93-4 .036 Dichloromethane (Methylene chloride) 34423 75-09-2 .38

1,2-Dichlorobenzene 34536 95-50-1 .048 Diethyl ether (Ethyl ether) 81576 60-29-7 .17

1,2-Dichloroethane 32103 107-06-2 .13 Diisopropyl ether 81577 108-20-3 .098

1,2-Dichloropropane 34541 78-87-5 .068 Ethyl methacrylate 73570 97-63-2 .28

1,3,5-Trimethylbenzene 77226 108-67-8 .044 Ethyl tert-butyl ether 50004 637-92-3 .054

1,3-Dichlorobenzene 34566 541-73-1 .054 Ethylbenzene 34371 100-41-4 .03

1,3-Dichloropropane 77173 142-28-9 .12 Hexachlorobutadiene 39702 87-68-3 .14

1,4-Dichlorobenzene 34571 106-46-7 .05 1,1,1,2,2,2-Hexachloroethane 

(Hexachloroethane)

34396 67-72-1 .36

2,2-Dichloropropane 77170 594-20-7 .078 (1-Methylethyl)benzene 

(Isopropylbenzene)

77223 98-82-8 .032

2-Butanone (Methyl ethyl 

ketone)

81595 78-93-3 1.6 Methyl acrylate 49991 96-33-3 1.4

1-Chloro-2-methylbenzene 

(o-Chlorotoluene)

77275 95-49-8 .042 Methyl acrylonitrile 81593 126-98-7 .57

2-Hexanone 77103 591-78-6 .7 Iodomethane (Methyl iodide) 77424 74-88-4 .21

3-Chloro-1-propene 78109 107-05-1 .2 Methyl methacrylate 81597 80-62-6 .35

1-Chloro-4-methylbenzene 

(p-Chlorotoluene)

77277 106-43-4 .056 Naphthalene 34696 91-20-3 .25

1-Isopropyl-4-methylbenzene 

(p-Isopropyltoluene)

77356 99-87-6 .11 Ethenylbenzene (Styrene) 77128 100-42-5 .042

4-Methyl-2-pentanone (Methyl 

isobutyl ketone)

78133 108-10-1 0.37 Tetrachloroethene 34475 127-18-4 0.1

Acetone 81552 67-64-1 5 Tetrachloromethane 32102 56-23-5 .088

2-Propenenitrile (Acrylonitrile) 34215 107-13-1 1.2 Tetrahydrofuran 81607 109-99-9 9.0

Table A6. Minimum reporting levels for volatile organic compounds analyzed in whole surface-water samples by purge and trap chromatography/mass 

spectrometry, laboratory schedule 2020

[USGS NWIS code, U.S. Geological Survey National Water Information System No.; CAS No., Chemical Abstracts Service No.; LRL, 1999 laboratory 

reporting level; MRL, laboratory minimum reporting level; μg/L, micrograms per liter; –, no value]
142 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Methylbenzene (Toluene) 34010 108-88-3 0.05 Methyl tert-butyl ether (MTBE) 78032 1634-04-4 0.17

Trichloroethene 39180 79-01-6 .038 (1,1-Dimethylethyl)benzene 77353 98-06-6 .1

Trichlorofluoromethane 34488 75-69-4 .09 tert-Amyl methyl ether 50005 994-05-8 .11

Chloroethene (Vinyl chloride) 39175 75-01-4 .11 trans-1,2-Dichloroethene 34546 156-60-5 .032

cis-1,2-Dichloroethene 77093 156-59-2 .038 trans-1,3-Dichloropropene 34699 10061-02-6 .13

cis-1,3-Dichloropropene 34704 10061-01-5 .09 trans-1,4-Dichloro-2-butene 73547 110-57-6 .7

1,3-plus-1,4-Dimethylbenzene 

(m,p-Xylene)

85795 -- .06

n-Propylbenzene 77224 103-65-1 .042 Surrogate recoveries MRL

2-Ethyltoluene (o-Ethyltoluene) 77220 611-14-3 .1 1,2-Dichloroethane-d4 (surrogate) 99832 17060-07-0 .1

1,2-Dimethylbenzene 

(o-Xylene)

77135 95-47-6 .06 1,4-Bromofluorobenzene (surrogate) 99834 460-00-4 .1

(1-Methylpropyl)benzene 77350 135-98-8 .048 Toluene-d8 (surrogate) 99833 2037-26-5 .1

Table A6. Minimum reporting levels for volatile organic compounds analyzed in whole surface-water samples by purge and trap chromatography/mass 

spectrometry, laboratory schedule 2020—Continued

Compound (Common name)

USGS 

NWIS 

code

CAS 

No.

LRL

(μg/L) Compound

USGS 

NWIS

code

CAS 

No.

LRL

(μg/L)
Appendix B. Quality Assurance/Quality Control—Methods, Results, and Discussion 143

APPENDIX B. QUALITY 

ASSURANCE/QUALITY CONTROL—

METHODS, RESULTS, AND DISCUSSION

Between December 1995 and February 1998, 32 

blank-water samples, prepared with inorganic-grade 

water, were submitted for major ion analyses. A total of 

six compounds, mostly all cations, were detected in 

these samples (table B1). Silica was the most 

frequently detected compound, found in 12 of the 32 

blank-water samples; the presence of silica was likely 

an artifact of the glass ampoules for the acid 

preservative. Concentrations of all the detected 

compounds were low and, except for compounds in 

two blank-water samples, well below the minimum 

concentrations detected in streamwater from the site 

where the blank was prepared. One blank prepared at 

the lower Nooksack (site 3) had a chloride 

concentration of 0.17 mg/L (milligrams per liter) and a 

minimum environmental sample concentration of 

0.44 mg/L, and one blank at the upper Green (site 10) 

had an iron concentration of 3.7 μg/L (micrograms per 

liter) and an environmental sample concentration 

reported at less than 3 μg/L on the day of preparation. 

Thus, field or laboratory contamination of samples for 

major ions analyses was generally not of concern and 

no adjustments were made to the database.

Five compounds were detected in 34 blank-water 

samples prepared for nutrient analyses between 

December 1995 and February 1998 (table B2). There 

were no detections of organic nitrogen (total or 

dissolved) or of dissolved phosphorus. In these blanks, 

nitrate was detected most frequently, in 11 of the 34 

blank-water samples; orthophosphate phosphorus was 

detected next most frequently, in 5 of the 34 samples. 

For nitrate, concentrations in the blanks were 

considerably lower, generally from four times to an 

order of magnitude lower, than in the environmental 

samples at the site where the blanks were prepared. At 

the North Fork Skokomish (site 2) and the upper 

Nooksack (site 5), where water was naturally low in 

nutrients, the concentration of orthophosphate in one 

blank sample per site was equal to or larger than the 

environmental concentration on the day of collection. 

This was true also for concentrations of nitrite, nitrate, 

and ammonia in one blank sample prepared at the 

upper Green. These few occurrences indicated that 

systematic bias was not a problem. Because all sample 

collection and processing equipment was rinsed with 

native water before samples were collected and split 

into subsamples, it is believed that the data sets for 

these sites are of satisfactory quality. Therefore, no 

values were deleted from the database, but for 

reference, the value of the environmental sample on the 

day of blank preparation is listed in parentheses 

alongside the value of the blank in table B2.

Between December 1995 and February 1998, 30 

blank-water samples were prepared for organic carbon 

analyses. Dissolved organic carbon was detected in 27 

of these samples and suspended organic carbon in 15 

(table B3). Some of the carbon in the blanks was from 

the source water; in half of the source-water samples, 

levels of dissolved organic carbon ranged from 0.1 to 

0.7 mg/L. This level of carbon indicates some positive 

bias in a few samples from the Skokomish (site 1), 

North Fork Skokomish (site 2), Nooksack (sites 3 and 

5), and upper Green (site 10), with environmental 

concentrations below the 10th percentile. These levels 

were unimportant for the range of concentrations found 

in samples from the other seven sites. The database was 

not adjusted or corrected for organic carbon found in 

the blank samples.

Sixteen blank-water samples for volatile organic 

compounds (VOCs) were prepared with non-nitrogengas-purged volatile-grade (VG) water and submitted 

between April 1996 and February 1997. A total of 18 

compounds was detected in these blanks (table B4). 

One of the 18, bromodichloromethane, was not 

detected in any environmental samples so is not of 

concern. Of the remaining 17 compounds, 8 

(trichloromethane, acetone, tetrahydrofuran, 

chlorobenzene, 2-butanone, ethenylbenzene (styrene), 

ethylbenzene, and benzene) were most likely present in 

the VG water.
144 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Five compounds (1,3-plus-1,4-dimethylbenzene, 

4-methyl-2-pentanone, acetone, chloromethane, and 

methylbenzene) were detected in nitrogen-gas-purged 

blanks but were not detected in the N2-purged VG 

water. The concentrations of these compounds (except 

for methylbenzene) were below the LRLs and are 

estimated. A compound detected in a blank sample was 

also detected in an environmental sample only four 

times: once each for carbon disulfide, chloromethane, 

1,3-plus-1,4-dimethylbenzene, and 1,2-

dichloropropane. However, the concentrations in the 

environmental samples were equal to or greater than 

the highest concentration found in the corresponding 

blanks, indicating that the detection in the 

environmental sample was not caused by carryover of 

any contamination from the blank water. This indicates 

that the VOCs either were in the VG water or were 

introduced in an isolated event, and not the result of 

systematic contamination caused by the sampling 

equipment or procedures. 

In the six blanks that were collected with the N2-

purged VG water in December 1997 and May 1998, 

methylbenzene was detected four times, 1,3-plus-1,4-

dimethylbenzene three times, and acetone, benzene, 

chloromethane, and 4-methyl-2-pentanone once each 

(table B4). Of these compounds, the detection of 

benzene can be explained as its presence in the VG 

source water. The remaining compounds fell below the 

LRLs and the estimated concentrations were generally 

at or below the lower range of environmental 

detections. The general absence of VOCs in the N2-

purged blanks indicates that the sampling equipment 

and procedures most likely did not introduce any 

systematic contamination into the environmental 

samples.

Methylbenzene was detected in 69 percent of 

non-N2-purged blanks and in 66 percent of the N2 -

purged blanks, making it the most frequently detected 

compound in the blank samples. In most of the 

detections, methylbenzene concentrations were 

estimated to be below the LRLs. However, 

methylbenzene had the highest concentration of any 

compound detected in the blanks and was occasionally 

detected at concentrations above the LRL. Because the 

highest methylbenzene concentrations (greater than 

0.5 μg/L) were detected in both the blank and 

environmental samples, were clustered between 

September and October 1996, and were found at all 

four intensive fixed sites, the cause was believed to be 

contamination. Therefore, the eight environmental 

methylbenzene detections during that time period that 

exceeded a concentration of 0.5 μg/L were censored 

from the data set and are not included in any statistical 

or graphical presentation of data. Those detections have 

been censored with a V-code in the NWIS database, 

indicating that the concentrations are believed to be due 

to contamination.

Variability in sampling and analytical methods 

was measured with 26 pairs of split replicate samples 

for major ions, 29 pairs for nutrients, and 5 pairs for 

pesticides; and with 20 pairs of concurrent replicate 

samples for dissolved organic carbon and one pair of 

concurrent replicate samples for VOCs. The variability 

in each pair of samples was expressed as the relative 

percent difference in the concentrations. For all classes 

of compounds, occasionally one member of the pair 

would be reported as less than the MRL or LRL and the 

other member would be reported at a detectable 

concentration typically equal to the MRL or LRL, and 

percent differences for these pairs were not calculated. 

Most of the cations and anions concentrations had 

relative percent differences less than 10 percent 

(table B5) and the median differences for all the major 

ions were 6 percent or less. Variability between results 

was lowest for sulfate, which ranged from 0 to 

5.4 percent, and highest for iron, which ranged from 0 

to 58 percent. Variability tended to be larger for the 

nutrient analyses than for the major ions, ranging from 

0 to 67 percent (table B6). The greatest percent 

differences typically occurred for pairs of samples with 

low concentrations near the analytical reporting limits, 

indicating that the inherent variability in these lowconcentration data needs to be considered in 

subsequent applications, such as load calculations and 

other analyses. Relative percent differences between 

pairs of organic carbon ranged from 0 to 40 percent for 

dissolved, and from 0 to 100 percent for suspended 

(table B7). As with nutrients, large percent differences 

were generally between replicate pairs with low 

concentrations. For the pesticides, differences ranged 

from 0 to 40 percent (table B8). The replicate VOC 

samples had detections of trichloromethane, 

methylbenzene, chloromethane, 1-isopropyl-4-

methylbenzene, and 4-methyl-2-pentanone. The 

concentrations for the replicates were identical for each 

of the detected compounds with the exception of 

methylbenzene, which had a difference of 0.01 μg/L 

between the replicates. No changes were made to any 

of the inorganic or organic chemical data sets based on 

these replicate data.
Appendix B. Quality Assurance/Quality Control—Methods, Results, and Discussion 145

For five pairs of field-matrix spiked water 

samples, recoveries for pesticide compounds ranged 

from about 10 to more than 300 percent, with generally 

lower recoveries for laboratory schedule 2051 

compounds than for schedule 2010 compounds 

(fig. B1). For the majority of schedule 2010 analytes, 

recoveries were good and fairly precise ranging from 

about 60 to 140 percent. Those compounds with 

recoveries greatly different from this range included 

atrazine, azinphos-methyl, carbaryl, carbofuran, 

deethylatrazine, disulfoton, ethalfluralin, linuron, 

methyl-parathion, terbacil, and cis-permethrin. Low 

percent recoveries for some compounds, such as 

carbaryl, carbofuran, terbacil, and permethrin, 

indicated possible matrix interference for some 

samples collected at Thornton Creek. Conversely, high 

percent recoveries for compounds such as atrazine, 

azinphos-methyl, carbaryl, and carbofuran indicated 

possible positive bias for some samples collected at 

Thornton Creek, Fishtrap Creek, and the lower 

Nooksack River. For most schedule 2051 analytes, 

recoveries ranged from 20 to 50 percent (fig. B1). 

Generally low recoveries and precision for schedule 

2051 have previously been reported (Wagner and 

Roberts, 1998; Anderson and others, 1996). For 

samples collected during this study, recoveries were 

particularly low for acifluorfen, aldicarb, aldicarb 

sulfone, chlorothalonil, clopyralid, and dichlobenil. Of 

these, only dichlobenil was detected in samples from 

the sites. Because of low recoveries and the large range 

in recoveries for the schedule 2051 analytes, there is 

potential in environmental water samples for falsenegative analytical results (Wagner and Roberts, 1998) 

and for the magnitude of a pesticide’s concentration to 

be unknown (Anderson and others, 1996).

For eight pairs of field-matrix spiked samples for 

VOCs, recoveries and precision for VOCs in fieldspiked samples were good, ranging from mean 

recoveries of 71 to 101 percent and standard deviations 

from 3 to 26 percent (table B9). Compounds with the 

lowest mean recovery included bromoform and 

chloroethene (71 percent), and 1,4-dichlorobenzene 

(76 percent). Of these, both bromoform and 1,4-

dichlorobenzene were detected in environmental water 

samples, but only bromoform was detected above the 

LRL. On the basis of the pesticide- and VOC-analyte 

recoveries determined on field-matrix spiked replicate 

samples, no changes or adjustments were made to the 

data sets.

All pesticide samples were spiked in the field 

with mixtures of surrogate analytes to monitor the 

precision and accuracy of analytical procedures. Mean 

recoveries for diazinon-d10 and alpha-HCH-d6 in 

samples from the four stations ranged from 99 to 

108 percent (table B10). Mean recoveries of 

terbuthylazine tended to be a little higher than 

diazinon-d10 and alpha-HCH-d6 recoveries, ranging 

from 110 to 120 percent, and mean recoveries for 

BDMC for laboratory schedule 2051 tended to be a 

little lower, ranging from 88 to 92 percent. Surrogates 

for VOC analyses are not added in the field, but are 

added in the laboratory. Recoveries of the VOC 

surrogate analytes were also good, with mean recovery 

of 92 percent for 1,-2-dichloroethane-d4, 106 percent 

for toluene-d8, and 113 percent for 1,4-

bromofluorobenzene (table B11).
146 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Table B1. Concentrations of major ions in field-blank water samples for the Puget Sound Basin study unit, Washington

[USGS NWIS, U.S. Geological Survey National Water Information System; <, less than; μg, micrograms per liter]

Station No. Site 

No.

Sample 

date

Compound (USGS NWIS code), in milligrams per liter and dissolved unless otherwise noted

Calcium 

(00915)

Silica 

(00955)

Iron 

(01046)

(μg/L)

Chloride 

(00940)

Magnesium 

(00925)

Fluoride 

(00950)

Sodium 

(00930)

Manganese 

(01056)

(μg/L)

Potassium 

(00935)

Sulfate 

(00945)

12061500 1 08-14-97 <0.02 <0.01 <3 <0.1 <0.01 <0.1 <0.2 <1 <0.1 <0.1

12061500 1 09-17-97 <.02 <.01 <3 <.1 <.01 <.1 <.2 <1 <.1 <.1

12056500 2 05-28-96 .58 .01 <3 <.1 <.01 <.1 <.2 <1 <.1 <.1

12056500 2 09 17-97 <.02 <.01 <3 <.1 <.01 <.1 <.2 <1 <.1 <.1

12056500 2 11-13-97 <.02 <.01 <3 <.1 <.01 <.1 <.2 <1 <.1 <.1

12213140 3 01-08-97 <.02 .04 <3 <.1 <.01 <.1 <.2 <1 <.1 <.1

12213140 3 06-09-97 <.02 <.01 <3 .17 <.01 <.1 <.2 <1 <.1 <.1

12212100 4 04-24-96 .67 .01 6 <.1 <.01 <.1 <.2 <1 <.1 <.1

12212100 4 10-09-96 <.02 .01 <3 <.1 <.01 <.1 <.2 <1 <.1 <.1

12212100 4 06-10-97 .02 <.01 <3 .16 <.01 <.1 <.2 <1 .1 <.1

12210700 5 12-02-95 <.02 .12 <3 .3 <.01 <.1 <.2 <1 <.1 <.1

12210700 5 04-08-97 <.02 <.01 <3 <.1 <.01 <.1 <.2 <1 <.1 <.1

12210700 5 05-06-97 <.02 .03 <3 <.1 <.01 <.1 <.2 <1 <.1 <.1

12210700 5 02-10-98 <.02 <.1 <1 <.1 <.004 <.1 <.1 <4 <.1 <.1

12113390 6 01-03-97 <.02 <.01 <3 <.1 <.01 <.1 <.2 <1 <.1 <.1

12113390 6 06-18-97 .02 <.01 <3 <.1 <.01 <.1 <.2 <1 <.1 <.1

12113390 6 11-14-97 <.02 .02 <3 <.1 <.01 <.1 <.2 <1 <.1 <.1

12113375 7 12-12-95 <.02 .07 3 .1 <.01 <.1 <.2 <1 <.1 <.1

12113375 7 06-18-97 <.02 <.01 <3 <.1 <.01 <.1 <.2 <1 <.1 <.1

12113375 7 11-14-97 <.02 .02 <3 <.1 <.01 <.1 <.2 <1 <.1 <.1

12112600 8 07-15-97 .02 <.01 <3 <.1 .02 <.1 <.2 <1 <.1 <.1

12112600 8 09 16-97 <.02 <.01 <3 <.1 <.01 <.1 <.2 <1 <.1 <.1

12112600 8 11-12-97 <.02 <.01 <3 <.1 <.01 <.1 <.2 <1 <.1 <.1

12108500 9 05-15-97 <.02 .01 <3 <.1 <.01 <.1 <.2 <1 <.1 <.1

12108500 9 12-15-97 <.02 <.1 <1 <.1 <.004 <.1 <.1 <4 <.1 <.1

12103380 10 05-21-97 <.02 <.01 <3 <.1 <.01 <.1 <.2 <1 <.1 <.1

12103380 10 08-11-97 <.02 .02 <3 <.1 <.01 <.1 <.2 <1 <.1 <.1

12103380 10 09 15-97 <.02 <.01 3.7 <.1 <.01 <.1 <.2 <1 <.1 <.1

12103380 10 11-06-97 <.02 <.01 <3 <.1 <.01 <.1 <.2 <1 <.1 <.1

12128000 11 10-08-96 <.02 .01 <3 <.1 <.01 <.1 <.2 <1 <.1 <.1

12128000 11 06-12-97 <.02 <.01 <3 <.1 <.01 <.1 <.2 <1 <.1 <.1

12128000 11 02-09-98 <.02 <.1 <1 <.1 <.004 <.1 <.1 <4 <.1 <.1
Appendix B. Quality Assurance/Quality Control—Methods, Results, and Discussion 147

Table B2. Concentrations of nutrients in field-blank water samples for the Puget Sound Basin study unit, Washington

[Values in parentheses are for environmental samples collected from the same site on the same date. USGS NWIS, U.S. Geological Survey National Water 

Information System; N, nitrogen; <, less than; –, missing value]

Station 

No.

Site 

No

Sample

date

Compound (USGS NWIS code), in milligrams per liter

Phosphorus, 

total 

(00665)

Dissolved 

phosphorus 

(00666)

Dissolved 

orthophosphate 

phosphorus 

(00671)

Dissolved 

nitrite, as N 

(00613)

Dissolved 

nitrite-plusnitrate, as N 

(00631)

Dissolved 

ammonia, 

as N 

(00608)

Ammoniaplusorganic, as 

N, total 

(00625)

Dissolved 

ammoniaplusorganic, as 

N (00623)

12061500 1 08-14-97 <0.01 <0.01 <0.01 <0.01 <0.05 <0.015 <0.2 <0.2

12061500 1 09-17-97 <.01 <.01 <.01 <.01 <.05 <.015 <.2 <.2

12056500 2 05-28-96 <.01 <.01 <.01 <.01 <.05 <.015 <.2 <.2

12056500 2 09-17-97 <.01 <.01 <.01 <.01 <.05 <.015 <.2 <.2

12056500 2 11-13-97 <.01 <.01 .02 (.02) <.01 <.05 <.02 <.1 <.1

12213140 3 06-09-97 <.01 <.01 <.01 <.01 <.05 <.015 <.2 <.2

12212100 4 04-24-96 <.01 <.01 <.01 <.01 <.05 <.015 <.2 <.2

12212100 4 10-09-96 <.01 <.01 <.01 <.01 <.05 <.015 <.2 <.2

12212100 4 06-10-97 <.01 <.01 <.01 <.01 <.05 <.015 <.2 <.2

12212100 4 07-08-97 <.01 <.01 .01 (.03) <.01 <.05 <.015 <.2 <.2

12210700 5 12-02-95 <.01 <.01 <.01 <.01 <.05 <.015 <.2 <.2

12210700 5 04-08-97 <.01 <.01 <.01 <.01 <.05 <.015 <.2 <.2

12210700 5 05-06-97 <.01 <.01 <.01 <.01 <.05 <.015 <.2 <.2

12210700 5 02-10-98 <.01 <.01 .02 (.01) <.01 .06 (.22) <.02 <.1 <.1

12113390 6 01-03-97 <.01 <.01 <.01 <.01 .05 (.45) <.015 <.2 <.2

12113390 6 06-18-97 <.01 <.01 <.01 <.01 .06 (.22) <.015 <.2 <.2

12113390 6 11-14-97 <.01 <.01 <.01 <.01 <.05 <.02 <.1 <.1

12113375 7 12-12-95 <.01 <.01 <.01 <.01 <.05 <.015 <.2 <.2

12113375 7 06-18-97 <.01 <.01 <.01 <.01 .06 (.31) <.015 <.2 <.2

12113375 7 11-14-97 <.01 <.01 <.01 <.01 <.05 <.02 <.1 <.1

12112600 8 07-15-97 <.01 <.01 <.01 <.01 .06 (.48) <.015 <.2 <.2

12112600 8 09-16-97 <.01 <.01 <.01 <.01 <.05 <.015 <.2 <.2

12112600 8 11-12-97 <.01 <.01 .01 (.03) .02 (.03) .07 (.84) -- <.1 <.1

12108500 9 05-15-97 <.01 <.01 <.01 <.01 <.05 <.015 <.2 <.2

12108500 9 12-15-97 .02 (.07) <.01 <.01 .03 (.03) .06 (2.32) <.02 <.1 <.1

12103380 10 05-21-97 <.01 <.01 <.01 <.01 <.05 <.015 <.2 <.2

12103380 10 08-11-97 <.01 <.01 <.01 <.01 .07 (.05) .03 (.02) <.2 <.2

12103380 10 09-15-97 <.01 <.01 <.01 <.01 <.05 <.015 <.2 <.2

12103380 10 11-06-97 <.01 <.01 <.01 .01 (.01) .07 (.07) .06 (.061) <.1 <.1

12128000 11 04-11-96 <.01 <.01 <.01 <.01 <.05 <.015 <.2 <.2

12128000 11 10-08-96 .01 (.04) <.01 <.01 <.01 <.05 <.015 <.2 <.2

12128000 11 06-12-97 <.01 <.01 <.01 <.01 .09 (.98) <.015 <.2 <.2

12128000 11 07-07-97 <.01 <.01 <.01 <.01 <.05 <.015 <.2 <.2

12128000 11 02-09-98 <.01 <.01 .02 (.04) <.01 .06 (1.37) <.02 <.1 <.1
148 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Table B3. Concentrations of dissolved and suspended organic carbon in field-blank water samples for the Puget Sound Basin study unit, Washington

[Values are in milligrams per liter. USGS NWIS, U.S. Geological Survey National Water Information System; <, less than; na, not analyzed] ]

Station No. Site 

No. Sample date Blank type (99102)

Compound

(USGS NWIS code)

Station No. Site

No.

Sample 

date

Blank type 

(99102)

Compound

(USGS NWIS code)

Carbon, 

dissolved 

(00681)

Carbon, 

suspended 

(00689)

Carbon, 

dissolved 

(00681)

Carbon, 

suspended 

(00689)

12061500 1 04-11-97 source water <0.1 na 12056500 2 02-12-98 field 0.2 <.2

12061500 1 05-08-97 source water <.1 na 12213140 3 08-07-96 field .3 <.1

12056500 2 08-14-97 source water <.1 na 12213140 3 08-07-96 field .3 <.1

12056500 2 02-12-98 source water <.1 na 12213140 3 08-07-96 field .3 <.1

12213140 3 08-07-96 source water .2 na 12213140 3 02-14-97 field .9 .1

12213140 3 08-07-96 source water .2 na 12212100 4 04-24-96 field .6 .2

12213140 3 08-07-96 source water <.1 na 12212100 4 07-09-96 field .3 .1

12213140 3 02-14-97 source water .7 0.2 12212100 4 01-07-97 field .3 .3

12212100 4 01-07-97 source water <.1 na 12212100 4 12-10-97 field .2 <.2

12212100 4 12-10-97 source water <.1 na 12210700 5 12-02-95 field .3 .1

12210700 5 06-09-97 source water <.1 na 12210700 5 06-09-97 field <.1 .1

12210700 5 11-04-97 source water .3 na 12210700 5 11-04-97 field .2 <.2

12113390 6 02-06-97 source water .1 na 12113390 6 09-12-96 field .4 <.1

12113390 6 03-17-97 source water .1 na 12113390 6 02-06-97 field <.1 <.1

12113390 6 02-17-98 source water <.1 na 12113390 6 03-17-97 field .2 .1

12113375 7 03-17-97 source water <.1 na 12113390 6 02-17-98 field .1 <.2

12112600 8 04-15-97 source water .2 na 12113375 7 12-12-95 field .6 .3

12108500 9 04-15-97 source water .1 na 12113375 7 03-17-97 field 0.7 0.6

12103380 10 06-16-97 source water <.1 na 12112600 8 04-15-97 field .2 .1

12128000 11 01-14-97 source water .1 na 12112600 8 02-19-98 field .1 <.2

12128000 11 01-12-98 source water .1 na 12108500 9 04-15-97 field .9 .1

12061500 1 04-11-97 field .8 <.1 12103380 10 06-16-97 field <.1 .1

12061500 1 05-08-97 field .2 <.1 12128000 11 06-07-96 field .4 .2

12061500 1 11-13-97 field .7 <.2 12128000 11 01-14-97 field .3 .1

12056500 2 05-28-96 field .1 .1 12128000 11 01-12-98 field .2 <.2

12056500 2 08-14-97 field .2 na
Appendix B. Quality Assurance/Quality Control—Methods, Results, and Discussion 149

Table B4. Summary of volatile organic compounds detected in source, canister, and field blank-water samples for the Puget Sound Basin study unit, 

Washington

[NWQL, National water quality laboratory; N2, nitrogen gas; VGW, volatile grade water; E, estimated; ND, not detected; μg/L, micrograms per liter]

Compound

NWQL lot 

analysis of nonN2-purged VGW

Field blanks collected with nonN2-purged VGW

NWQL lot 

analysis of 

N2-purged VGW

Field blanks collected with 

N2-purged VGW

Environmental 

samples

Detected 

concentrations 

(μg/L)

Percentage of 

detections 

(number of 

detects)

Range of 

detected 

concentrations

Detected 

concentrations 

(μg/L)

Percentage of 

detections 

(number of 

detects)

Range of detected 

concentrations

Range of detected 

concentrations

1,2,4-Trimethylbenzene ND 18.8 (3) E0.007-E0.02 ND ND ND E0.005-0.12

1,2-Dichloropropane ND 31.3 (5) E.01-E.02 ND ND ND E.01-E.03

1,2-Dimethylbenzene ND 12.5 (2) E.01-E.02 ND ND ND E.007-.1

1,3-plus-1,4-

Dimethylbenzene 

ND 37.5 (6) E.01-E.04 ND 50 (3) E0.0061-

E0.0083

E.008-.2

1,4-Dichlorobenzene ND 37.5 (6) E.009-E.01 ND ND ND E.002-E.01

2-Butanone 0.52, 1.1 37.5 (6) E.3-E.4 E0.01, ND ND ND E.1-E1.4

1-Isopropyl-4-

methylbenzene

ND 12.5 (2) E.005 ND ND ND E.003-E.044

4-Methyl-2-pentanone ND ND ND ND 16.6 (1) E.28 E.1-E1.0

Acetone 1.4, 3.5 56.3 (9) 1.0-2.4 ND 16.6 (1) E.99 E1.0-12.5

Benzene .02, .016 6.3 (1) E.04 ND, E.01 16.6 (1) E.012 E.0091-E.1

Bromodichloromethane ND 25 (4) E.01 ND ND ND ND

Carbon disulfide ND 18.8 (3) E.003-E.01 ND ND ND E.007-.105

Chlorobenzene ND, E.03 37.5 (6) E.004-E.01 ND ND ND E.002-E.03

Chloromethane ND 12.5 (2) E.04 ND 16.6 (1) E.0036 E.0085-.135

Ethenylbenzene ND, E.015 31.3 (5) E.003-E.006 ND ND ND E.001-E.01

Ethylbenzene ND, .037 25 (4) E.006-E.01 ND ND ND E.002-E.06

Methylbenzene ND, .031 68.8 (11) E.08-1.6 ND 66 (4) E.019-E.034 E.03-2.2

Tetrahydrofuran ND, 2.4 50 (8) E.2-E.5 ND ND ND E.3

Trichloromethane .04, E.039 87.5 (14) E.03-E.09 ND ND ND E.005-.16
150 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Table B5. Concentrations of major ions in replicate environmental water samples, Puget Sound Basin, Washington—Continued

Station 

No.

Sample 

date

Site 

No.

Replicate 

type

Compound (USGS NWIS code)

Calcium 

(00915)

Silica 

(00955)

Iron 

(01046)

Chloride 

(00940)

Magnesium 

(00925)

Fluoride 

(00950)

Sodium 

(00930)

Manganese 

(01056)

Potassium 

(00935)

Sulfate 

(00945)

12061500 01-07-98 1 30 6.39 10.864 <10 1.473 1.479 <0.1 1.852 <4 0.1 0.95

30 6.439 11.65 <10 1.531 1.536 <.1 1.86 <4 <.1 .98

Relative percentage of difference 0.8 7 nc 3.9 3.8 nc <1 nc nc 3.1

12056500 09-17-97 2 30 7.087 3.606 11.3 0.485 0.538 <.1 0.927 <1 .13 2.357

30 6.692 3.624 9.791 .436 .52 <.1 1.12 <1 .13 2.36

Relative percentage of difference 5.7 <1 14 11 3.4 nc 19 nc 0 <1

12056500 01-07-98 2 30 12.364 5.527 <10 .917 .952 <.1 1.548 <4 .18 5.091

30 12.465 5.592 <10 .921 .96 <.1 1.554 <4 .12 4.953

Relative percentage of difference <1 1.2 nc <1 <1 nc <1 nc 40 2.7

12213140 02-14-97 3 30 12 9.6 87 4 4 <.1 4.1 21 1.3 12

30 13 10 89 4.1 4.1 <.1 4.3 22 1.3 12

Relative percentage of difference 8 4.1 2.3 2.5 2.5 nc 4.8 4.7 0 0

12213140 11-04-97 3 30 7.798 6.818 64.193 1.707 2.336 <.1 1.892 5.715 .73 5.716

30 7.857 6.852 57.389 1.776 2.338 <.1 1.909 5.503 .74 5.74

Relative percentage of difference <1 <1 11 4 <1 nc <1 3.8 1.4 <1

12212100 07-09-96 4 30 29 18 390 11 7.7 <.1 9.3 92 2.3 37

30 28 17 360 11 7.6 <.1 9.1 91 2.3 37

Relative percentage of difference 3.5 5.7 8 0 1.3 nc 2.2 1.1 0 0

12212100 04-08-97 4 30 25.212 13.92 148.17 10.711 7.017 <.1 8.237 159.44 2.91 35.056

30 25.108 13.804 118.93 10.728 6.971 <.1 8.212 159.44 2.97 34.971

Relative percentage of difference <1 <1 22 <1 <1 nc <1 0 2 <1

12212100 02-11-98 4 30 24.53 16.734 165.39 9.631 6.562 <.1 8.333 161.68 2.8 30.692

30 23.953 16.1 165.06 10.095 6.822 <.1 8.201 166.16 2.82 30.769

Relative percentage of difference 2.4 3.9 <1 4.7 3.9 nc 1.6 2.7 <1 <1

12210700 03-11-97 5 30 10 8.3 21 1.1 3.1 <.1 1.7 6 .4 6.6

30 11 8.8 25 1.1 3.3 <.1 1.9 6 .4 6.6

Relative percentage of difference 9.5 5.8 17 0 6.2 nc 11 0 0 0

Table B5. Concentrations of major ions in replicate environmental water samples for the Puget Sound Basin study unit, Washington

[Replicate types: 10-concurrent, 20-sequential, 30-split, 40-split-concurrent; compound detection values are in milligrams per liter except for iron and 

manganese, which are in micrograms per liter; USGS NWIS, U.S. Geological Survey National Water Information System; <, less than; --, not analyzed; nc, 

not calculated; relative percentage of difference = R1 – R2 × 100, where R1 = sample 1 result and R2 = sample 2 result] 

R1 + R2

2 --------------------    

-------------------------
Appendix B. Quality Assurance/Quality Control—Methods, Results, and Discussion 151

12210700 12-09-97 5 30 11.369 8.877 25.325 1.141 3.326 <.1 1.966 7.353 .5 7.697

30 11.288 8.842 22.727 1.095 3.337 <.1 1.919 6.488 .4 7.704

Relative percentage of difference <1 <1 11 4.1 <1 nc 2.4 12 22 <1

12113390 02-06-97 6 30 7.4 14 86 2.8 2.1 <0.1 4.4 28 0.8 4.2

30 7.3 14 90 3 2.1 <.1 4.3 27 .8 4.2

Relative percentage of difference 1.4 0 4.5 6.9 0 nc 2.3 3.6 0 0

12113390 12-17-97 6 30 6.161 10.797 102.52 2.355 1.833 <.1 3.721 16.174 1.37 3.254

30 6.188 10.878 108.34 2.326 1.85 <.1 3.739 16.416 1.37 3.247

Relative percentage of difference <1 <1 5.5 1.2 <1 nc <1 1.5 0 <1

12113375 12-12-95 7 20 11 13 650 5.9 4.2 <.1 7.9 83 2.4 8.7

20 11 13 650 6.1 4.1 .1 8.1 82 2.3 8.6

Relative percentage of difference 0 0 0 3.3 2.4 nc 2.5 1.2 4.3 1.2

12113375 07-15-96 7 10 27 33 700 24 15 .3 33 320 4.1 12

10 27 33 590 23 15 .3 33 320 4.3 12

Relative percentage of difference 0 0 17 4.3 0 0 0 0 4.8 0

12113375 11-20-96 7 30 12 9.9 390 11 4.3 .1 9.1 71 1.9 11

30 12 9.9 420 11 4.3 .1 9.1 71 1.9 11

Relative percentage of difference 0 0 7.4 0 0 0 0 0 0 0

12113375 01-06-98 7 30 8.967 7.662 234.23 4.407 3.037 <.1 4.87 70.732 1.69 5.603

30 8.995 7.796 245.26 4.335 3.037 <.1 4.898 70.038 1.64 5.463

Relative percentage of difference <1 1.7 4.6 1.6 0 nc <1 1 3 2.5

12112600 12-12-95 8 20 9.5 13 93 3.9 3.3 .1 6.3 4 1.5 8.5

20 9.4 13 93 3.8 3.3 .1 6.3 4 1.6 8.3

Relative percentage of difference 1.1 0 0 2.6 0 0 0 0 6.5 2.4

12112600 10-16-96 8 30 13 18 95 4.4 5 <.1 5.5 14 1.6 13

30 14 19 100 4.4 5.3 <.1 5.9 14 1.7 13

Relative percentage of difference 7.4 5.4 5.1 0 5.8 nc 7 0 6.1 0

12112600 01-06-98 8 30 8.907 11.075 96.029 3.636 3.182 <.1 5.349 7.859 1.46 6.519

30 9.347 11.61 100.57 3.676 3.34 <.1 5.629 8.09 1.65 6.531

Relative percentage of difference 4.8 4.7 4.6 1.1 4.8 nc 5.1 2.9 12 <1

12108500 12-13-95 9 20 12 18 140 7.3 3.9 .1 7.3 6 5.5 6.9

20 12 18 130 7.2 4 .1 7.7 5 5.5 6.9

Relative percentage of difference 0 0 7.4 1.4 2.5 0 5.3 18 0 0

Table B5. Concentrations of major ions in replicate environmental water samples, Puget Sound Basin, Washington—Continued

Station 

No.

Sample 

date

Site 

No.

Replicate 

type

Compound (USGS NWIS code)

Calcium 

(00915)

Silica 

(00955)

Iron 

(01046)

Chloride 

(00940)

Magnesium 

(00925)

Fluoride 

(00950)

Sodium 

(00930)

Manganese 

(01056)

Potassium 

(00935)

Sulfate 

(00945)
152 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

12108500 08-12-96 9 30 15 19 15 5.2 4.8 <.1 6.4 3 1.8 6.4

30 15 18 16 5 4.7 <.1 6.3 3 1.8 6.5

Relative percentage of difference 0 5.4 6.5 3.9 2.1 nc 1.6 0 0 1.6

12108500 07-15-97 9 30 13.833 19.719 167.34 4.423 4.231 <0.1 6.013 5.413 3.39 5.213

30 14.329 20.362 175.36 4.65 4.381 <.1 6.209 5.413 3.6 5.15

Relative percentage of difference 3.5 3.2 4.7 5 3.5 nc 3.2 0 6 1.2

12108500 02-19-98 9 30 13.696 18.996 102.24 4.909 4.42 <.1 6.2 <4 2.8 6.666

30 13.785 19.107 104 4.877 4.443 <.1 6.2 <4 2.8 6.635

Relative percentage of difference <1 <1 1.7 <1 <1 nc 0 nc 0 <1

12128000 06-07-96 11 30 20 29 200 7.8 12 .1 8.2 40 2.4 18

30 18 26 110 7.3 11 .1 7.6 34 2.2 19

Relative percentage of difference 10 11 58 6.6 8.7 0 7.6 16 8.7 5.4

12128000 04-07-97 11 19.337 25.74 154.96 7.159 11.463 <.1 8.375 35.42 2.34 19.03

30 19.724 25.975 157.34 7.231 11.484 <.1 8.331 35.832 2.28 18.914

Relative percentage of difference 2 <1 1.5 1 <1 nc <1 1.2 2.6 <1

12128000 03-09-98 11 40 15.814 18.954 131.04 5.016 8.605 <.1 6.253 45.965 1.86 13.893

40 15.795 18.996 141.32 5.265 8.597 <.1 6.263 46.506 1.83 13.319

Relative percentage of difference <1 <1 7.5 4.8 <1 nc <1 1.2 1.6 4.2

Summary:

Minimum percentage of difference 0 0 0 0 0 0 0 0 0 0

Maximum percentage of difference 10 11 58 11 8.7 0 19 18 40 5.4

Median percentage of difference 0.8 0.85 6 2.6 1.1 0 1.6 1.2 1.6 0.25

Table B5. Concentrations of major ions in replicate environmental water samples, Puget Sound Basin, Washington—Continued

Station 

No.

Sample 

date

Site 

No.

Replicate 

type

Compound (USGS NWIS code)

Calcium 

(00915)

Silica 

(00955)

Iron 

(01046)

Chloride 

(00940)

Magnesium 

(00925)

Fluoride 

(00950)

Sodium 

(00930)

Manganese 

(01056)

Potassium 

(00935)

Sulfate 

(00945)
Appendix B. Quality Assurance/Quality Control—Methods, Results, and Discussion 153

Table B6. Concentrations of nutrients in replicate environmental water samples, Puget Sound Basin, Washington—Continued

Station 

No.

Sample 

date Site No. Replicate type

Compound (USGS NWIS code)

Phosphorus, 

total 

(00665)

Phosphorus 

(00666)

Orthophosphate 

phosphorus

(00671)

Nitrite, as 

N (00613)

Nitriteplusnitrate, as 

N (00631)

Ammonia, 

as N (00608)

Ammoniaplusorganic, as 

N, total 

(00625)

Ammoniaplusorganic, as 

N (00623)

12061500 01-07-98 1 30 0.019 0.014 0.012 <0.01 0.087 <0.02 <0.1 <0.1

30 .024 .014 .011 <.01 .09 <.02 <.1 <.1

Relative percentage of difference 23 0 8.7 nc 3.4 nc nc nc

12056500 09-17-97 2 30 <.01 <.01 <.01 <.01 .06 <.015 <.2 <.2

30 .016 <.01 <.01 <.01 .061 <.015 <.2 <.2

Relative percentage of difference nc nc nc nc 1.7 nc nc nc

12056500 01-07-98 2 30 <.01 <.01 .02 <.01 <.05 <.02 <.1 <.1

30 .026 .02 .011 <.01 <.05 <.02 <.1 <.1

Relative percentage of difference nc nc 58 nc nc nc nc nc

12213140 02-20-96 3 30 .09 <.01 .01 .01 .52 .05 <.2 <.2

30 .05 <.01 .02 .01 .51 .06 <.2 <.2

Relative percentage of difference 57 nc 67 0 1.9 18 nc nc

12213140 02-14-97 3 30 .06 <.01 <.01 .01 .93 .06 <.2 <.2

30 .07 <.01 <.01 .02 .94 .07 .2 <.2

Relative percentage of difference 15 nc nc 67 1.1 15 nc nc

12213140 11-04-97 3 30 .151 .021 .011 <.01 .257 <.02 .237 <.1

30 .162 .014 .023 <.01 .283 <.02 .236 .102

Relative percentage of difference 7 40 7.6 nc 9.6 nc .4 nc

12212100 07-09-96 4 30 <.01 <.01 .01 .02 2.5 .04 .2 .2

30 <.01 <.01 .02 .02 1.5 .03 <.2 <.2

Relative percentage of difference nc nc 67 0 50 29 nc nc

12212100 04-08-97 4 30 .01 <.01 <.01 .02 3.9 .09 .3 .2

30 .02 <.01 <.01 .02 3.9 .08 .3 <.2

Relative percentage of difference 67 nc nc 0 0 12 0 nc

12212100 02-11-98 4 30 .06 <.01 .017 .02 3.555 .084 .466 .334

30 .063 <.01 .013 .019 3.547 .08 .41 .272

Relative percentage of difference 4.9 nc 27 5.1 <1 4.9 13 2.5

12210700 02-20-96 5 30 .05 <.01 <.01 <.01 .21 <.015 <.2 <.2

30 .04 <.01 <.01 <.01 .21 <.015 <.2 <.2

Relative percentage of difference 22 nc nc nc 0 nc nc nc

Table B6. Concentrations of nutrients in replicate environmental water samples for the Puget Sound Basin study unit, Washington

[Replicate types: 10-concurrent, 20-sequential, 30-split, 40-split-concurrent; compound values are in milligrams per liter and dissolved unless otherwise 

noted; USGS NWIS, U.S. Geological Survey National Water Information System; <, less than; --, not analyzed; nc, not calculated; relative percentage of 

difference = R1 – R2 × 100, where R1 = sample 1 result and R2 = sample 2 result]

R1 + R2

2 --------------------    

-------------------------
154 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

12210700 01-08-97 5 30 <0.01 <0.01 <0.01 0.02 0.33 0.03 <0.2 <0.2

30 <.01 <.01 <.01 .01 <.05 .05 <.2 <.2

Relative percentage of difference nc nc nc 67 nc 50 nc nc

12210700 03-11-97 5 30 <.01 <.01 <.01 <.01 .23 <.015 <.2 <.2

30 <.01 <.01 <.01 <.01 .23 <.015 <.2 <.2

Relative percentage of difference nc nc nc nc 0 nc nc nc

12210700 12-09-97 5 30 .01 <.01 <.01 <.01 .209 <.02 <.1 <.1

30 <.01 <.01 <.01 <.01 .219 <.02 <.1 <.1

Relative percentage of difference nc nc nc nc 4.7 nc nc nc

12113390 02-06-97 6 30 .05 <.01 .01 .03 .53 .05 .4 <.2

30 .08 .01 .01 .02 .5 .05 .2 <.2

Relative percentage of difference 46 nc 0 40 5.8 0 67 nc

12113390 12-17-97 6 30 .155 .038 .054 <.01 .661 .049 .626 .273

30 .188 .043 .053 <.01 .663 .05 .684 .252

Relative percentage of difference 19 12 1.9 nc <1 2 8.9 8

12113375 12-12-95 7 20 .1 .05 .04 <.01 .7 .06 .5 .4

20 .1 .05 .05 <.01 .7 .07 .5 .4

Relative percentage of difference 0 0 22 nc 0 15 0 0

12113375 07-15-96 7 10 .129 .024 .05 .056 .633 .236 .539 .437

10 .131 .022 .042 .055 .629 .236 .57 .552

Relative percentage of difference 1.5 8.7 17 1.8 <1 0 5.6 23

12113375 01-06-98 7 30 .101 .02 .026 <.01 .453 <.02 .446 .284

30 .102 .017 .023 <.01 .457 .026 .468 .272

Relative percentage of difference 1 16 12 nc <1 nc 4.8 4.3

12112600 12-12-95 8 20 .03 <.01 .02 <.01 1.4 <.015 .3 .2

20 .03 <.01 .01 <.01 1.4 <.015 .3 .3

Relative percentage of difference 0 nc 67 nc 0 nc 0 40

12112600 10-16-96 8 30 .04 .04 .03 .02 .68 .06 .4 .3

30 .08 .06 .03 .01 .69 .06 .3 .2

Relative percentage of difference 67 40 0 67 1.5 0 29 40

12112600 01-06-98 8 30 .037 .021 .02 <.01 .981 <.02 .401 .225

30 .028 .012 .022 <.01 .956 <.02 .362 .273

Relative percentage of difference 28 54 9.5 nc 2.6 nc 1.2 19

Table B6. Concentrations of nutrients in replicate environmental water samples, Puget Sound Basin, Washington—Continued

Station 

No.

Sample 

date Site No. Replicate 

type

Compound (USGS NWIS code)

Phosphorus, 

total 

(00665)

Phosphorus 

(00666)

Orthophosphate 

phosphorus

(00671)

Nitrite, as 

N (00613)

Nitriteplusnitrate, as 

N (00631)

Ammonia, 

as N (00608)

Ammoniaplusorganic, as 

N, total 

(00625)

Ammoniaplusorganic, as 

N (00623)
Appendix B. Quality Assurance/Quality Control—Methods, Results, and Discussion 155

12108500 12-13-95 9 20 0.35 0.36 0.27 0.04 2.9 0.21 0.8 1

20 .34 .33 .26 .04 2.9 .2 .8 .9

Relative percentage of difference 2.9 8.7 3.8 0 0 4.9 0 1.5

12108500 08-12-96 9 30 .02 .06 .06 .01 1.6 .03 <.2 <.2

30 .04 .05 .06 .01 1.7 .03 <.2 <.2

Relative percentage of difference 67 18 0 0 6.1 0 nc nc

12108500 07-15-97 9 30 .234 .168 .16 .061 1.735 .026 .538 .475

30 .26 .166 .164 .06 1.751 .023 .519 .239

Relative percentage of difference 1.5 1.2 2.5 1.7 <1 12 3.6 66

12108500 02-19-98 9 30 .131 .089 .08 .011 2.773 .031 .421 .282

30 .127 .091 .08 .011 2.767 .037 .434 .277

Relative percentage of difference 3.1 2.2 0 0 <1 18 3 1.8

12128000 06-07-96 11 30 .04 .04 .02 .02 1.2 <.015 .3 <.2

30 .06 .05 .03 .01 1.3 <.015 .3 <.2

Relative percentage of difference 40 22 40 67 8 nc 0 nc

12128000 04-07-97 11 30 .03 .01 .02 <.01 1.3 <.015 <.2 <.2

30 .04 <.01 .02 <.01 1.3 <.015 <.2 <.2

Relative percentage of difference 29 nc 0 nc 0 nc nc nc

12128000 03-09-98 11 40 .049 .021 .024 <.01 1.134 .03 .475 .247

40 .04 .017 .024 <.01 1.133 .028 .293 .196

Relative percentage of difference 2.2 21 0 nc <1 6.9 47 23

12128000 03-09-98 11 40 .042 .015 .024 <.01 1.113 .028 .307 .189

40 .041 .02 .026 <.01 1.126 .031 .29 .191

Relative percentage of difference 2.4 29 8 nc 1.2 1.2 5.7 1.1

Summary:

Minimum percentage of difference 0 0 0 0 0 0 0 0

Maximum percentage of difference 67 54 7.6 67 50 50 67 66

Median percentage of difference 19 16 9.1 1.75 0.9 10 4.8 19

Table B6. Concentrations of nutrients in replicate environmental water samples, Puget Sound Basin, Washington—Continued

Station 

No.

Sample 

date Site No. Replicate 

type

Compound (USGS NWIS code)

Phosphorus, 

total 

(00665)

Phosphorus 

(00666)

Orthophosphate 

phosphorus

(00671)

Nitrite, as 

N (00613)

Nitriteplusnitrate, as 

N (00631)

Ammonia, 

as N (00608)

Ammoniaplusorganic, as 

N, total 

(00625)

Ammoniaplusorganic, as 

N (00623)
156 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Table B7. Concentrations of organic carbon in replicate environmental water samples, Puget Sound Basin, Washington—Continued

Station No. Sample date Site No. Replicate type

Compound (USGS NWIS code)

Carbon, dissolved 

(00681)

Carbon, suspended 

(00689)

12056500 04-11-97 2 concurrent 0.6 nc

.4 0.1

Relative percentage of difference 40 nc

12056500 09-17-97 2 split 2.1 .3

2.2 .3

Relative percentage of difference 4.7 0

12213140 05-07-97 3 concurrent 2.5 .7

2.4 .5

Relative percentage of difference 4.1 33

12213140 11-04-97 3 split 3.3 1.3

3.6 1.3

Relative percentage of difference 8.7 0

12212100 07-09-96 4 split 2.2 .4

2.2 .4

Relative percentage of difference 0 0

12212100 04-08-97 4 split 2.6 .5

2.6 .5

Relative percentage of difference 0 0

12212100 05-06-97 4 concurrent 6 1.7

5.5 1.9

Relative percentage of difference 8.7 11

12212100 02-11-98 4 split 3.1 1.5

3.1 1.4

Relative percentage of difference 0 6.9

12210700 01-08-97 5 split 2.3 .4

2.3 .5

Relative percentage of difference 0 22

12210700 12-09-97 5 split 1.1 .2

1 .2

Relative percentage of difference 9.5 0

12113390 09-12-96 6 concurrent 1.4 .5

1.4 .5

1.4 .6

Relative percentage of difference R1 & R2 0 0

Relative percentage of difference R1 or R2 & R3 0 18

12113390 05-16-97 6 concurrent 1.3 .5

1.2 .5

Relative percentage of difference 8 0

Table B7. Concentrations of organic carbon in replicate environmental water samples for the Puget Sound Basin study unit, Washington

[Compound detection values are in milligrams per liter. USGS NWIS, U.S. Geological Survey National Water Information System; <, less than;

--, not analyzed; nc, not calculated; relative percentage of difference = × 100, where R1 = sample 1 result and R2 = sample 2 

result]

R1 – R2

R1 + R2

2 --------------------    

-------------------------
Appendix B. Quality Assurance/Quality Control—Methods, Results, and Discussion 157

12113390 12-17-97 6 split 3.3 2.6

3.3 2.1

Relative percentage of difference 0 21

12113375 07-15-96 7 concurrent 4.9 0.7

5.3 .6

Relative percentage of difference 7.8 15

12113375 01-03-97 7 concurrent 4 .4

4.1 .4

Relative percentage of difference 2.5 0

12113375 01-06-98 7 split 4.3 1.4

4.4 1.2

Relative percentage of difference 2.3 15

12112600 10-16-96 8 split 4.2 .3

4.2 .1

Relative percentage of difference 0 100

12112600 01-06-98 8 split 5.1 1.2

5 1.3

Relative percentage of difference 2 8

12108500 08-12-96 9 split 1.2 .3

1.3 .2

Relative percentage of difference 8 40

12108500 11-15-96 9 concurrent 9.6 .6

9.7 .6

Relative percentage of difference 1 0

12108500 02-19-98 9 split 3.9 1

3.8 1

Relative percentage of difference 2.6 0

12103380 07-14-97 10 concurrent 0.7 .2

.7 .2

Relative percentage of difference 0 0

12128000 06-07-96 11 split 2.5 .4

2.4 .4

Relative percentage of difference 4.1 0

12128000 04-07-97 11 split 2.8 .3

2.9 .3

Relative percentage of difference 3.5 0

Summary:

Minimum percentage of difference 0 0

Maximum percentage of difference 40 100

Median percentage of difference 2.5 0

Table B7. Concentrations of organic carbon in replicate environmental water samples, Puget Sound Basin, Washington—Continued

Station No. Sample date Site No. Replicate type

Compound (USGS NWIS code)

Carbon, dissolved 

(00681)

Carbon, suspended 

(00689)
158 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Table B8. Concentrations of pesticide compounds detected in replicate environmental water samples for the Puget Sound Basin study unit, 

Washington

[Compound detection values are in micrograms per liter. USGS NWIS, U.S. Geological Survey National Water Information System; <, less than; E, estimated; nc, not calculated; relative percentage of difference = ¥ 100, where R1 = sample 1 result and R2 = sample 2 result]

Station No. Sample

date Site No. Replicate type

Compound (USGS NWIS code)

Atrazine 

(39632)

Deethylatrazine 

(04040)

Diazinon 

(39572)

EPTC 

(82668)

Metolachlor 

(39415)

Prometon 

(04037)

Simazine 

(04035)

Tebuthiuron 

(82670)

Dichlobenil 

(49303)

12212100 04-08-97 4 split 0.032 E0.006 <0.002 <0.002 0.004 E0.004 0.008 0.019 <1.2

.031 E.006 E.002 <.002 E.004 E.004 .008 .019 <1.2

Relative percentage of difference 3.2 0 nc nc 0 0 0 0 nc

12212100 06-10-97 4 split .0171 E.00305 E.0035 E.00146 E.0024 E.005 .0111 <.01 <1.2

.0218 E.00278 E.00234 E.00195 <.002 E.0055 .0132 .0122 <1.2

Relative percent age of difference 24 9.3 40 29 nc 9.5 17 nc nc

12128000 04-07-97 11 split E.002 E.002 E.003 <.002 <.002 0.019 E.003 <.01 <1.2

E.002 E.002 E.002 <.002 <.002 E.018 E.003 <.01 <1.2

Relative percentage of difference 0 0 40 nc nc 5.4 0 nc nc

12128000 03-09-98 11 splitconcurrent<.001 <.002 .0309 <.002 <.002 .02 .011 <.01 E0.1

<.001 <.002 .0245 <.002 <.002 .0194 .011 <.01 E.08

Relative percentage of difference nc nc 23 nc nc 3 0 nc 22

12128000 03-09-98 11 splitconcurrent<.001 <.002 .026 <.002 <.002 .0181 .0103 <.01 E.08

<.001 <.002 .0241 <.002 <.002 E.0179 .0101 <.01 E.12

Relative percentage of difference nc nc 7.6 nc nc 1.1 2 nc 40

Summary:

Minimum percentage of difference 0 0 7.6 29 0 0 0 0 22

Maximum percentage of difference 24 9.3 40 29 0 9.5 17 0 40

Median percentage of difference 3.2 0 31 29 0 3 0 0 31

R1 – R2

R1 + R2

2 --------------------    

-------------------------
Appendix B. Quality Assurance/Quality Control—Methods, Results, and Discussion 159

2,6-Diethylaniline

Acetochlor

Alachlor

Atrazine

Azinphos-methyl

Benfluralin

Butylate

Carbaryl

Carbofuran

Chlorpyrifos

Cyanazine

DCPA

Deethylatrazine

Diazinon

Dieldrin

Disulfoton

Ethalfluralin

Ethoprophos

Fonofos

Lindane

Linuron

Malathion

Metolachlor

Metribuzin

Molinate

Napropamide

Parathion

Methyl-parathion

Pebulate

Pendimethalin

Phorate

Prometon

Propachlor

Propanil

Propargite

Pronamide

Simazine

Tebuthiuron

Terbacil

Terbofos

Thiobencarb

Triallate

Trifluralin

alpha-BHC

-Permethrin cis

-DDE p,p’

PESTICIDE LABORATORY SCHEDULE 2010 ANALYTE

0

400300200100

ANALYTE RECOVERY, IN PERCENT

EPTC

PESTICIDE LABORATORY SCHEDULE 2051 ANALYTE

2,4,5-T

2,4-D

2,4-DB

Silvex

3-Hydroxycarbofuran

DNOC

Acifluorfen

Aldicarb

Aldicarb sulfone

Aldicarb sulfoxin

Bentazon

Bromacil

Bromoxynil

Carbaryl

Carbofuran

Chlorothalonil

Clopyralid

Dacthal monoacid

Dicamba

Dichlobenil

Dichlorprop

Dinoseb

Diuron

Fenuron

Fluometuron

Linuron

MCPA

MCPB

Methiocarb

Methomyl

Neburon

Norflurazon

Oryzalin

Oxamyl

Picloram

Propham

Propoxur

Triclopyr

806040

0

20

EXPLANATION

Lower Nooksack River Replicates, 8/7/96Fishtrap Creek Replicates, 7/9/96Duwamish River Replicates, 9/12/96Thornton Creek Replicates, 6/18/96Thornton Creek Replicates, 4/6/98

Figure B1. Percentage of recoveries for pesticide compounds in field matrix-spiked water samples from the four intensive fixed sites in the Puget Sound Basin study unit, Washington.
160 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Table B9. Summary of percentage of mean recoveries from fieldmatrix-spike volatile organic compound analyses for the Puget Sound Basin 

study unit, Washington

Volatile organic compound Mean 

(percent)

Standard 

deviation 

(percent)

Number of 

samples

1,1,1-Trichloroethane 98 3 8

1,1-Dichloroethene 92 8 8

1,2-Dichloroethane 101 10 8

1,4-Dichlorobenzene 76 11 8

Bromodichloromethane 89 5 8

Bromoform 71 6 8

Chloroethene 71 26 8

Dibromochloromethane 82 5 8

Ethylbenzene 89 3 8

Methyl tert-butyl ether 86 3 8

Tetrachloroethene 88 10 8

Tetrachloromethane 99 6 8

Trichloroethene 90 7 8

Table B10. Summary of surrogate compound recoveries in filtered water 

samples for pesticide analyses for the Puget Sound Basin study unit, 

Washington

[Values are percentages. USGS NWIS, U.S. Geological Survey National 

Water Information System; nc, not calculated]

Station 

No.

(Site No.)

Number 

of 

samples

Compound (USGS NWIS code)

BDMC 

(99835)

Diazinon

-d10 

(91063)

Terbuthylazine 

(91064)

AlphaHCH-d6 

(91065)

12213140 

(3)

22 Mean

Standard 

deviation

89

12

104

12

112

13

99

13

12212100 

(4)

32 Mean

Standard 

deviation

91

11

105

12

110

14

101

13

12113390 

(6)

24 Mean

Standard 

deviation

88

7.2

108

24

120

26

107

24

12128000 

(11)

46 Mean

Standard 

deviation

95

14

108

9.8

112

13

107

13

12113375 

(7)

2 Mean

Standard 

deviation

nc

nc

nc

nc

nc

nc

nc

nc

All 

stations

126 Mean

Standard 

deviation

92

14

106

14

113

16

104

16

Table B11. Summary of surrogate compound recoveries in whole water 

samples for volatile organic compound analyses for the Puget Sound Basin 

study unit, Washington

[Values are percentages. USGS NWIS, U.S. Geological Survey National 

Water Information System; nc, not calculated]

Station 

No

(Site No.)

Number 

of 

samples

Compound (USGS NWIS code)

1,2-

dichloroethane-d4 

(99832)

Toluene-d8 

(99833)

1,4-bromofluorobenzene 

(99834)

12213140 

(3)

22 Mean

Standard 

deviation

89

12

104

12

112

13

12212100 

(4)

32 Mean

Standard 

deviation

91

11

105

12

110

14

12113390 

(6)

24 Mean

Standard 

deviation

88

7.2

108

24

120

26

12128000 

(11)

46 Mean

Standard 

deviation

95

14

108

9.8

112

13

12113375 

(7)

2 Mean

Standard 

deviation

nc

nc

nc

nc

nc

nc

All 

stations

126 Mean

Standard 

deviation

92

14

106

14

113

16
Appendix C. Nutrient Load Estimation 161

APPENDIX C. NUTRIENT LOAD 

ESTIMATION

The regression equations generated by the 

Loadest2 computer program and indicated to best fit 

the calibration data are listed for each of the 11 sites in 

table C1 for total nitrogen loads, table C2 for total 

phosphorus loads, table C3 for dissolved 

orthophosphate phosphorus (orthophosphate) loads, 

and table C4 for suspended-sediment loads. Except for 

the NF Skokomish, Newaukum, and the upper Green, 

all regression equations to estimate total nitrogen loads 

contained the sine and cosine functions to account for 

the seasonality in the data sets, which indicated that 

variation in the concentration data was great enough 

that it could not be explained by streamflow alone. 

Only two of the equations to estimate phosphorus loads 

included the seasonality terms and these were for the 

lower Nooksack and Thornton. This indicated that, for 

most of the sites, most of the variation in phosphorus 

concentrations was explained by streamflow. For 

orthophosphate, seasonality terms were in the 

equations for 5 of 10 sites; the terms were not in 

equations for the lower Nooksack, Fishtrap, 

Duwamish, Newaukum, and upper Green. For 

suspended sediment, the seasonality terms were 

included in four equations—for the NF Skokomish, 

upper and lower Nooksack, and Newaukum. Many of 

the regression equations also included terms such as the 

log-normal streamflow-squared term [ln(Q)2] to help 

fit the equation to the calibration data.

All nutrient load estimates were calibrated with 

the daily streamflow value on the day of sample 

collection except for one—the phosphorus load in the 

upper Nooksack. Although some investigators prefer 

daily streamflow for estimating daily loads, the use of 

instantaneous streamflow is also acceptable (Charles 

Crawford, USGS, written commun., 1999). In the case 

of the upper Nooksack, instantaneous streamflows at 

the time of sample collection were used in the 

calibration file because these values lowered the 

standard deviation of the annual average load of 

phosphorus from 66 to 46 percent, the average percent 

difference between measured and predicted daily loads 

from 333 to 309 percent, and the difference between 

measured and predicted annual load from 81 to 

-15 percent (table C2). Instantaneous streamflows 

rather than the daily streamflows at the time of sample 

collection were also used in the calibration files for 

suspended-sediment load estimations at the upper 

Nooksack, Springbrook, and Thornton because 

standard deviations (SDs) and percent differences were 

improved (table C4).

In general, SDs for annual average nitrogen-load 

estimates were smaller than for phosphorus and 

orthophosphate load estimates. Sites having data sets 

with low concentrations and many observations 

censored at the MRL typically had large SDs. For 

example, the nitrogen data set for the upper Green 

River was 42 percent censored and the standard 

deviation was 40 percent of the load estimate 

(table C1). Excluding the upper Green, SDs of the 

annual average nitrogen loads ranged from 3 to 

18 percent. For phosphorus, SDs ranged from about 9 

to 73 percent including those of sites with greatly 

censored data sets (Skokomish and NF Skokomish) 

(table C2). The overall censoring rate for nitrogen is 

lower than for the phosphorus species partly because of 

the construction of the calibration data sets; 

specifically, if one of the nutrient parameters (00625 

and 00631) used to calculate total nitrogen (parameter 

00600) was missing (censored at the MRL), the total 

nitrogen was estimated to be equal to the sum of the 

remaining forms of nitrogen detected in the sample. 

Thus, for example, for an analysis with organic 

nitrogen-plus-ammonia (parameter 00625) censored at 

the MRL, but with a value reported for nitrite-plusnitrate (parameter 00631), a value of total nitrogen 

equal to the nitrite-plus-nitrate concentration was used 

in the calibration data set for load estimation. If 

ammonia was also present, the sum of the ammonia 

and nitrite-plus-nitrate nitrogen concentrations was 

used. For some sites, such as the NF Skokomish, the 

substitution estimate for the total nitrogen parameter 

was a large part of the data set; at other sites, such as 

Springbrook and Thornton Creeks, all the nitrogen 

forms necessary for calculating total nitrogen by the 

algorithms of the USGS database were present for 

many of the samples. If no nitrogen forms were present 

to substitute, then total nitrogen was set to less than 

0.05 mg/L, which is the reporting level for the typically 

dominant form of nitrogen in surface water, nitriteplus-nitrate nitrogen.
162 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

For all nutrient load estimates, the maximum 

likelihood estimation (MLE) method was selected over 

the linear attribution estimation (LAE) method because 

the data sets contained little or no censored data and the 

MLE and the LAE produced essentially the same 

results. For suspended-sediment loads, however, the 

degree of censoring affected the choice of load 

estimation method. Loads computed with the LAE 

method use a bias-transformation correction factor that 

is computed from the residuals of the rating curve 

regression. When a value is censored, the residual is 

unknown. When a large percentage of the data are 

censored, the transformation factor will be biased, 

resulting in a biased estimate of the mean load, whereas 

the MLE method does not have this limitation (Charles 

Crawford, USGS, written commun., 1999). Thus, the 

MLE was favored for the load estimates when more 

than 20 percent of a data set was censored. Predictions 

of the concentration percentiles using the MLE also 

compared better with the concentration percentiles of 

the actual data than those using the LAE.

For suspended-sediment load estimates, the 

MLE method was selected for 6 of the 11 sites and the 

LAE method for the remaining 5 sites (table C4). The 

highest rate of censoring (27 percent) was for the NF 

Skokomish data set. Except for the upper Green, SDs 

for average annual sediment loads ranged from 

17 percent to 56 percent. The SD for the upper Green 

was greater than 100 percent, indicating the results 

should be viewed with caution and suggesting that 

further data collection is needed to better define the 

relation of suspended sediment and steamflow at this 

site. If censoring rates were not a factor, and if the 

normality test statistic and the p-value indicated that 

the regression residuals followed a non-normal 

distribution, the LAE method was selected (Charles 

Crawford, USGS, written commun., 1999). Thus, for 

the upper Nooksack, Duwamish, Springbrook, 

Newaukum, and Thornton, the suspended-sediment 

load was estimated with the LAE method.

Figures C1 through C11 show, for each of the 11 

fixed sites, predicted daily loads and measured loads of 

total nitrogen, phosphorus, and orthophosphate over 

time. Figure C12 shows the same type of information 

for suspended sediment. These figures include 

scatterplots of the calibration data used by the loadestimation program showing concentration as a 

function of daily or instantaneous streamflow. Percent 

differences between measured and predicted daily 

loads of total nitrogen were large for some sites, 

ranging from an average of 1.6 percent at Fishtrap to 

125 percent at the NF Skokomish (table C1). However, 

percent differences between predicted and measured 

loads on an annual basis were much smaller, ranging 

from -26 to less than 1 percent, indicating that, on 

average, the estimated annual loads were reasonable.

Predicted annual loads of phosphorus and 

orthophosphate also agreed reasonably well with 

measured loads for about half the sites. At Skokomish, 

Fishtrap, upper Nooksack, Big Soos, and Thornton, the 

equations tended to overpredict daily loads of 

phosphorus or orthophosphate during parts of water 

year 1997. As with nitrogen loads, the predicted and 

measured daily loads varied greatly, with average 

differences ranging from 14 to 309 percent for 

phosphorus and from -9 to 130 percent for 

orthophosphate. Except for the NF Skokomish 

phosphorus loads, though, the predicted annual loads 

agreed reasonably well with measured annual loads, 

with differences ranging from -23 to 21 percent for 

phosphorus and from -22 to 31 percent for 

orthophosphate (see tables C2 and C3). For the NF 

Skokomish, there was a 74 percent difference between 

the measured and predicted annual phosphorus load, 

which was probably due to low concentrations and a 

highly censored (73 percent) data set.
Appendix C. Nutrient Load Estimation 163

Predicted annual loads of suspended sediment 

agreed reasonably well with measured loads for most 

sites. For the Skokomish, NF Skokomish, Duwamish, 

and Big Soos, the equations tended to overpredict the 

suspended-sediment loads. As with the nutrients, 

average percent differences between measured and 

predicted daily suspended-sediment loads were 

sometimes large, ranging from 11 percent at 

Springbrook to 284 percent at the Skokomish. Percent 

differences between predicted measured annual 

loads were smaller for all sites, ranging from -48 to 

88 percent (table C4). The load estimates for the 

Skokomish, NF Skokomish, Duwamish, Big Soos, 

upper Green, and Thornton should be viewed with 

caution because of the large standard deviations, the 

extreme variability between measured and predicted 

daily loads, and the large percent difference between 

measured and predicted annual loads.

For Fishtrap and Thornton Creeks, the daily 

streamflow data sets were not complete for water year 

1996. Streamgages installed at these sites did not begin 

recording daily flows until late May 1996 and 

March 1996, respectively. Thus all annual loads 

estimated for these two sites are based on the 2 years of 

complete streamflow record, 1997 and 1998, available 

during the study.
164 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Table C1. Total nitrogen loads, standard deviations, and regression equations for load estimates for surface-water sites in the Puget Sound Basin study 

unit, Washington

[Annual load: Annual load, from the regression equation for the simulation period (10/01/95 - 09/30/98); calculated as annual load, in tons = annual average 

load, in pounds per day, times 365 days, divided by 2000. Average percentage of difference between measured and predicted daily loads: Measured daily 

loads, in pounds, are calculated by multiplying the constituent concentration and instantaneous or daily streamflow measured on the day of sample collection. 

Predicted daily loads, in pounds, are the regression-equation results for the days of sample collection. Measured and predicted loads: Measured load, in tons 

per year, is estimated by multiplying the simple average of the measured daily loads by 365 days. Predicted load, in tons per year, is estimated by multiplying 

the simple average of daily loads predicted for the days of sample collection by 365 days. Percentage of difference = [(predicted - measured)/measured] * 100; 

ln, natural logarithm; Q, streamflow in cubic feet per second; sin, sine; cos, cosine; dectime, time in fractional years; --, no value; MLE, maximum likelihood 

estimate; dload, daily load, in pounds]

Site name 

(Site No.)

Annual 

load 

(tons)

Annual load 

standard 

deviation, in 

tons, and (as 

percentage)

Average percentage of 

difference between 

measured and 

predicted daily loads 

(pounds)

Measured and 

predicted 

loads, in tons 

per year, and 

(percentage of 

difference)

Regression equation

Censored 

data 

(percent)

Skokomish River (1) 210 29. (14) 49 640; 570

(-10)

MLE: ln(dload) = 6.3877 + 1.0366ln(Q) 

+ 0.14968ln(Q)2 - 

0.21928sin(dectime) + 

0.35471cos(dectime)

8

North Fork Skokomish 

River (2)

49 8.9 (18) 125 89; 91

(0.2)

MLE: ln(dload)=5.143 + 1.0776ln(Q) 36

Lower Nooksack River (3) 3,200 220. (6.9) 14 5,850; 5,900

(0.8)

MLE: ln(dload)=9.2020 + 1.2585ln(Q) 

+ 0.10488sin(dectime) 

+ 0.68187cos(dectime)

0

Fishtrap Creek (4) 1330 110. (3.0) 1.6 480; 450

(-6.4)

MLE: ln(dload)=7.6999 + 1.0939ln(Q) 

- 0.06444ln(Q)2 + 

0.15458sin(dectime) + 

0.11826cos(dectime) 

- 0.09019dectime

0

Upper Nooksack River (5) 1,600 200. (12.5) 32 3,400; 2,900

(-16)

MLE: ln(dload)=8.2301 + 1.4532ln(Q)

- 0.18879sin(dectime) 

+ 0.52754cos(dectime)

0

Duwamish River (6) 1,300 150. (12) 34 2,100; 2,000

(-5.0)

MLE: ln(dload)=8.3513 + 0.8101ln(Q) 

+ 0.16238ln(Q)2

+ 0.29708sin(dectime) 

+0.46756cos(dectime)

0

Springbrook Creek (7) 44 1.3 (3.0) 1.7 70; 71

(1.3)

MLE: ln(dload)=5.5426 + 0.87089ln(Q) 

+ 0.055932sin(dectime) 

+ 0.090628cos(dectime) 

- 0.065345dectime

0

Big Soos Creek (8) 200 12. (6.0) 5.2 310; 300

(-2.3)

MLE: ln(dload)=7.1444 + 0.095208ln(Q) 

+ 0.086982sin(dectime) 

+ 0.41256cos(dectime) 

- 0.14288dectime

0

Newaukum Creek (9) 210 11. (5.2) 6.2 308; 310

(0.6)

MLE: ln(dload)=7.106 + 1.1741ln(Q) 

- 0.093713ln(Q)2

0

Upper Green River (10) 6.0 2.4 (40) 105 8.0; 6.0

(-26)

MLE: ln(dload)=2.5669 + 1.1906ln(Q) 42

Thornton Creek (11) 120 10.9 (4.5) 7.5 24.8; 25.1

(1.5)

MLE: ln(dload)=4.3827 + 1.0855ln(Q) 

+ 0.12241sin(dectime) 

- 0.032546cos(dectime)

0

1 Calculated from load estimates for the complete water years 1997 and 1998 only.
Appendix C. Nutrient Load Estimation 165

Table C2. Total phosphorus loads, standard deviations, and regression equations for load estimates for surface-water sites in the Puget Sound Basin 

study unit, Washington

[Annual load: Annual load, from the regression equation for the simulation period (10/01/95 - 09/30/98); calculated as annual load, in tons = annual average 

load, in pounds per day, times 365 days, divided by 2000. Average percentage of difference between measured and predicted daily loads: Measured daily 

loads, in pounds, are calculated by multiplying the constituent concentration and instantaneous or daily streamflow measured on the day of sample collection. 

Predicted daily loads, in pounds, are the regression-equation results for the days of sample collection. Measured and predicted loads: Measured load, in tons 

per year, is estimated by multiplying the simple average of the measured daily loads by 365 days. Predicted load, in tons per year, is estimated by multiplying 

the simple average of daily loads predicted for the days of sample collection by 365 days. Percentage of difference = [(predicted - measured)/measured] * 

100; ln, natural logarithm; Q, streamflow in cubic feet per second; sin, sine; cos, cosine; dectime, time in fractional years; –, no value; MLE, maximum 

likelihood estimate; dload, daily load, in pounds]

Site name 

(Site No.)

Annual 

load 

(tons)

Annual load 

standard 

deviation, in 

tons, and (as 

percentage)

Average percentage 

of difference 

between measured 

and predicted daily 

loads 

(pounds)

Measured and 

predicted 

loads, in tons 

per year, and 

(percentage of 

difference)

Regression equation

Censored 

data 

(percent)

Skokomish River (1) 170 68. (40) 270 630; 710

(12)

MLE: ln(dload) = 4.7457 + 2.1801ln(Q) 41

North Fork Skokomish 

River (2)

15 11. (73) 55 34; 59

(74)

MLE: ln(dload)=2.1177 + 1.4814(Q) 

+ 0.48016ln(Q)2

73

Lower Nooksack River (3) 890 200. (22) 54 3,700; 2,900

(-22)

MLE: ln(dload)=6.8581 + 3.1232ln(Q) 

- 0.36967ln(Q)2 - 0.44919sin(dectime) 

+ 0.052735cos(dectime)

10

Fishtrap Creek (4) 111 12.0 (18) 62 18; 17

(-6.0)

MLE: ln(dload)=3.3276 + 2.0133ln(Q) 

+ 0.17042ln(Q)2

7

Upper Nooksack River (5) 720 330. (46) 309 2,200; 1,900

(-15)

2MLE: ln(dload)=5.799 + 3.6862ln(Q) 

- 0.54765ln(Q)2

34

Duwamish River (6) 190 31. (16) 41 430; 380

(-12)

MLE: ln(dload)=6.1382 + 1.4551ln(Q) 

+ 0.24499ln(Q)2

0

Springbrook Creek (7) 6.9 0.6 (8.7) 14 12; 11

(-4.3)

MLE: ln(dload)=3.5589 + 1.0474ln(Q) 

- 0.085863ln(Q)2

0

Big Soos Creek (8) 9.5 2.0 (21) 81 22; 17

(-23)

MLE: ln(dload)=3.4184 + 1.5624ln(Q) 11

Newaukum Creek (9) 27 6.0 (22) 58 31; 38

(21)

MLE: ln(dload)=4.1531 + 1.8088ln(Q) 0

Upper Green River (10) 32-2.6 – – 2.2; –

(–)

– 75

Thornton Creek (11) 11.5 10.4 (27) 100 2.7; 3.0

(14)

MLE: ln(dload)=1.1371 + 1.8727ln(Q) 

+ 0.00155sin(dectime)

- 0.41633cos(dectime)

02

1Calculated from load estimates for the complete water years 1997 and 1998 only.

2Regression equation calibrated with instantaneous streamflow (parameter 00061) in place of daily streamflow (parameter 00060).

3Beale ratio estimate (Crawford, 1996). 
166 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

Table C3. Dissolved orthophosphate phosphorus loads, standard deviations, and regression equations for load estimates for surface-water sites in the 

Puget Sound Basin study unit, Washington

[Annual load: Annual load, from the regression equation for the simulation period (10/01/95 - 09/30/98); calculated as annual load, in tons = annual average 

load, in pounds per day, times 365 days, divided by 2000. Average percentage of difference between measured and predicted daily loads: Measured daily 

loads, in pounds, are calculated by multiplying the constituent concentration and instantaneous or daily streamflow measured on the day of sample collection. 

Predicted daily loads, in pounds, are the regression-equation results for the days of sample collection. Measured and predicted loads: Measured load, in tons 

per year, is estimated by multiplying the simple average of the measured daily loads by 365 days. Predicted load, in tons per year, is estimated by multiplying 

the simple average of daily loads predicted for the days of sample collection by 365 days. Percentage of difference = [(predicted - measured)/measured] * 

100; ln, natural logarithm; Q, streamflow in cubic feet per second; sin, sine; cos, cosine; dectime, time in fractional years; --, no value; MLE, maximum 

likelihood estimate; dload, daily load, in pounds]

Site name 

(Site No.)

Annual 

load (tons)

Annual load 

standard 

deviation, in 

tons, and (as 

percentage)

Average 

percentage of 

difference between 

measured and 

predicted daily 

loads

(pounds)

Measured and 

predicted loads, 

in tons per year, 

and (percentage 

of difference)

Regression equation

Censored 

data 

(percent)

Skokomish River (1) 16 1.8 (11) 37 45; 44

(-2.1)

MLE: ln(dload) =3.5323 + 0.76949ln(Q) 

+ 0.24054ln(Q)2 - 0.045632sin(dectime) 

+ 0.47958cos(dectime) + 0.26367dectime

49

North Fork Skokomish 

River (2)

4.5 0.4 (8.9) 24 8.5; 8.9

(4.9)

MLE: ln(dload)=2.1867 + 0.87207ln(Q) 

- 0.29034sin(dectime) 

+ 0.24506cos(dectime) 

+ 0.63633dectime

73

Lower Nooksack River (3) 43 3.3 (7.7) -9.3 76; 70

(-8.8)

MLE: ln(dload)=5.2051 + 1.0989ln(Q) 56

Fishtrap Creek (4) 12.0 10.4 (20) 5.0 4.0; 3.2

(-22)

MLE: ln(dload)=1.8405 + 1.7693ln(Q) 

+ 0.24331ln(Q)2

41

Upper Nooksack River (5) 26-40 – – 28;–

(–)

– 86

Duwamish River (6) 44 5.1 (12) 51 67; 70

(4.5)

MLE: ln(dload)=5.1664 + 1.05ln(Q) 

+ 0.11638ln(Q)2

10

Springbrook Creek (7) 1.3 0.2 (15) 28 1.96; 2.0

(3.5)

MLE: ln(dload)=1.8423 + 0.93975ln(Q) 

+ 0.26336sin(dectime) 

- 0.23241cos(dectime)

2.7

Big Soos Creek (8) 2.9 0.4 (14) 44 3.1; 4.0

(31)

MLE: ln(dload)=2.6321 + 0.66256ln(Q)

- 0.15966sin(dectime) 

+ 0.31885cos(dectime)

17

Newaukum Creek (9) 14 2.9 (21) 130 20; 21

(4.5)

MLE: ln(dload)=3.823 + 1.5027ln(Q) 2.8

Upper Green River (10) 0.7 0.08 (11) 44 0.66; 0.73

(11)

MLE: ln(dload=1.1239 + 0.828613ln(Q) 38

Thornton Creek (11) 10.38 10.03 (7.9) 20 0.45; 0.44

(-2.6)

MLE: ln(dload)=0.49122 + 0.99741ln(Q) 

- 0.22626sin(dectime) 

- 0.22208cos(dectime)

0

1Calculated from load estimates for the complete water years 1997 and 1998 only.

2Beale ratio estimate (Crawford, 1996).
Appendix C. Nutrient Load Estimation 167

Table C4. Suspended-sediment loads, standard deviations, and regression equations for load estimates for surface-water sites in the Puget Sound Basin 

study unit, Washington

[Annual load: Annual load, from the regression equation for the simulation period (10/01/95 - 09/30/98); calculated as annual load, in tons = annual average 

load, in pounds per day, times 365 days, divided by 2000. Average percentage of difference between measured and predicted daily loads: Measured daily 

loads, in pounds, are calculated by multiplying the constituent concentration and instantaneous or daily streamflow measured on the day of sample collection. 

Predicted daily loads, in pounds, are the regression-equation results for the days of sample collection. Measured and predicted loads: Measured load, in tons 

per year, is estimated by multiplying the simple average of the measured daily loads by 365 days. Predicted load, in tons per year, is estimated by multiplying 

the simple average of daily loads predicted for the days of sample collection by 365 days. Percentage of difference = [(predicted - measured)/measured] * 100; 

ln, natural logarithm; Q, streamflow in cubic feet per second; sin, sine; cos, cosine; dectime, time in fractional years; --, no value; MLE, maximum likelihood 

estimate; LAE, linear attribution estimate; dload, daily load, in pounds]

Site name 

(Site No.)

Annual load 

(tons)

Annual load 

standard 

deviation, in 

tons, and (as 

percentage)

Average 

percentage of 

difference 

between 

measured and 

predicted daily 

loads 

(pounds)

Measured and 

predicted loads, 

in tons per year, 

and (percentage 

of difference)

Regression equation Censored data 

(percent)

Skokomish River (1) 570,000 270,000 (48) 284 1,500,000; 

2,700,000

(85)

MLE: ln(dload) = 11.723 + 2.8062ln(Q) 9

North Fork Skokomish 

River (2)

14,000 6,400 (46) 80 37,000; 49,000

(31)

MLE: ln(dload)=8.3856 + 2.2075ln(Q) 

+ 0.39712ln(Q)2 

- 0.57326sin(dectime) 

- 0.076696cos(dectime)

27

Lower Nooksack River (3) 1,800,000 310,000 (17) 37 6,400,000: 

7,000,000

(9.4)

MLE: ln(dload)=14.266 + 3.2984ln(Q) 

- 0.30232ln(Q)2

- 0.36187sin(dectime) 

- 0.25892cos(dectime)

0

Fishtrap Creek (4) 14,700 1800 (17) 46 8,900; 7,600

(-14)

MLE: ln(dload)=9.4784 + 2.0258ln(Q) 

+ 0.17579ln(Q)2

0

Upper Nooksack River (5) 2,300,000 420,000 (19) 93 7,000,000; 

5,900,000

(-16)

2LAE: ln(dload)=13.745 + 4.0916ln(Q) 

- 0.53322ln(Q)2

+ 0.092885sin(dectime)

- 0.45368cos(dectime)

0

Duwamish River (6) 270,000 60,000 (22) 82 520,000; 

680,000

(30)

LAE: ln(dload)=12.6 + 1.8916ln(Q) 

+ 0.33201ln(Q)2

0

Springbrook Creek (7) 1,800 350 (19) 11 4,800; 4,300

(-9.9)

2LAE: ln(dload)=8.6289 + 1.6051ln(Q) 0

Big Soos Creek (8) 13,000 7,300 (56) 171 12,000; 23,000

(88)

MLE: ln(dload)=9.272 + 2.4213ln(Q) 9

Newaukum Creek (9) 2,200 570 (26) 79 3,400; 3,100

(-6.7)

LAE: ln(dload)=8.2517 + 1.7659ln(Q) 

+ 0.51568sin(dectime) 

+ 0.169cos(dectime)

3

Upper Green River (10) 3510 6,200 (>100) 63 270; 220

(-19)

MLE: ln(dload)=6.1389 + 1.4796ln(Q) 19

Thornton Creek (11) 1530 1170 (32) 220 2,200; 1,200

(-48)

2LAE: ln(dload)=6.5066 + 1.8007ln(Q) 2

1Calculated from load estimates for the complete water years 1997 and 1998 only. 2Regression equation calibrated with instantaneous streamflow (parameter 00061) in place of daily streamflow (parameter 00060). 3Load estimate based on data set excluding a large concentration outlier measured in October 1997.
168 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

10

100,000

20

50

100

200

500

1,000

2,000

5,000

10,000

20,000

50,000

100,000

10

20

50

100

200

500

1,000

2,000

5,000

10,000

20,000

50,000

10

10,000

20

50

100

200

500

1,000

2,000

5,000

O N D J FMAMJ J ASON D J FMAMJ J ASON D J FMAMJ J AS

1995 1996 1997 1998

0.01

0.02

0.05

0.1

0.2

0.5

0.005

0.01

0.02

0.05

0.1

0.2

0.5

0.005

0.1

0.007

0.01

0.02

0.03

0.04

0.05

0.07

100 100,000 1,000 10,000

100 100,000 1,000 10,000

100 100,000 1,000 10,000

O N D J FMAMJ J ASON D J FMAMJ J ASON D J FMAMJ J AS

O N D J FMAMJ J ASON D J FMAMJ J ASON D J FMAMJ J AS

1

2

5

1

1

DAILY DISCHARGE,

IN CUBIC FEET PER SECOND

DAILY DISCHARGE,

IN CUBIC FEET PER SECOND

DAILY DISCHARGE,

IN CUBIC FEET PER SECOND

TOTAL NITROGEN LOAD, 

IN POUNDS PER DAY

TOTAL PHOSPHORUS LOAD, 

IN POUNDS PER DAY

DISSOLVED ORTHOPHOSPHATE LOAD,

IN POUNDS PER DAY

TOTAL NITROGEN CONCENTRATION,

IN MILLIGRAMS PER LITER

TOTAL PHOSPHORUS CONCENTRATION,

IN MILLIGRAMS PER LITER

DISSOLVED ORTHOPHOSPHATE CONCENTRATION, 

IN MILLIGRAMS PER LITER

EXPLANATION

Daily loads, predicted using

 regression equation (tables C1-C3)

Daily load, measured

Concentration, measured

Figure C1. Predicted and measured daily nutrient loads, and scatterplots of nutrient concentrations and streamflows used to calibrate the load-estimate 

regression equations for the Skokomish River (site 1).
Appendix C. Nutrient Load Estimation 169

TOTAL NITROGEN CONCENTRATION,

IN MILLIGRAMS PER LITER

TOTAL PHOSPHORUS CONCENTRATION,

IN MILLIGRAMS PER LITER

DISSOLVED ORTHOPHOSPHATE CONCENTRATION,

 IN MILLIGRAMS PER LITER

TOTAL NITROGEN LOAD, 

IN POUNDS PER DAY

TOTAL PHOSPHORUS LOAD, 

IN POUNDS PER DAY

DISSOLVED ORTHOPHOSPHATE LOAD,

IN POUNDS PER DAY

DAILY DISCHARGE,

IN CUBIC FEET PER SECOND

DAILY DISCHARGE,

IN CUBIC FEET PER SECOND

DAILY DISCHARGE,

IN CUBIC FEET PER SECOND

10

10,000

20

30

40

50

70

100

200

300

400

500

700

1,000

2,000

3,000

4,000

5,000

7,000

1

20,000

2

5

10

20

50

100

200

500

1,000

2,000

5,000

10,000

1

1,000

2

5

10

20

50

100

200

500

O N D J FMAMJ J ASON D J FMAMJ J ASON D J FMAMJ J AS

1995 1996 1997 1998

0.01

0.02

0.05

0.1

0.2

0.5

0.005

0.1

0.007

0.01

0.02

0.03

0.04

0.05

0.07

0.005

0.1

0.007

0.01

0.02

0.03

0.04

0.05

0.07

10 10,000 100 1,000

10 10,000 100 1,000

10 10,000 100 1,000

O N D J FMAMJ J ASON D J FMAMJ J ASON D J FMAMJ J AS

O N D J FMAMJ J ASON D J FMAMJ J ASON D J FMAMJ J AS

1

EXPLANATION

Daily loads, predicted using

 regression equation (tables C1-C3)

Daily load, measured

Concentration, measured

Figure C2. Predicted and measured daily nutrient loads, and scatterplots of nutrient concentrations and streamflows used to calibrate the load-estimate 

regression equations for the North Fork Skokomish River (site 2) in the Puget Sound Basin study unit, Washington.
170 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98 TOTAL NITROGEN LOAD, IN POUNDS PER DAY TOTAL PHOSPHORUS LOAD, IN POUNDS PER DAY DISSOLVED ORTHOPHOSPHATE LOAD, IN POUNDS PER DAY

1,000

500,000

2,000

3,000

4,000

5,000

7,000

10,000

20,000

30,000

40,000

50,000

70,000

100,000

200,000

300,000

400,000

1

1,000,000

2

5

10

20

50

100

200

500

1,000

2,000

5,000

10,000

20,000

50,000

100,000

200,000

500,000

10

10,000

20

50

100

200

500

1,000

2,000

5,000

O N D J FMAMJ J ASON D J FMAMJ J ASON D J FMAMJ J AS

1995 1996 1997 1998

1,000 100,000 10,000

1,000

0.1

10

0.2

0.5

1

2

5

1,000

0.005

10

0.01

0.02

0.05

0.1

0.2

0.5

1

2

5

0.005

0.1

0.007

0.01

0.02

0.03

0.04

0.05

0.07

10,000 100,000

10,000 100,000

O N D J FMAMJ J ASON D J FMAMJ J ASON D J FMAMJ J AS

TOTAL NITROGEN CONCENTRATION,

IN MILLIGRAMS PER LITER

TOTAL PHOSPHORUS CONCENTRATION,

IN MILLIGRAMS PER LITER

DISSOLVED ORTHOPHOSPHATE CONCENTRATION,

 IN MILLIGRAMS PER LITER

DAILY DISCHARGE,

IN CUBIC FEET PER SECOND

DAILY DISCHARGE,

IN CUBIC FEET PER SECOND

DAILY DISCHARGE,

IN CUBIC FEET PER SECOND

O N D J FMAMJ J ASON D J FMAMJ J ASON D J FMAMJ J AS

EXPLANATION

Daily loads, predicted using

 regression equation (tables C1-C3)

Daily load, measured

Concentration, measured

Figure C3. Predicted and measured daily nutrient loads, and scatterplots of nutrient concentrations and streamflows used to calibrate the load-estimate 

regression equations for the lower Nooksack River (site 3) in the Puget Sound Basin study unit, Washington.
Appendix C. Nutrient Load Estimation 171

TOTAL NITROGEN CONCENTRATION,

IN MILLIGRAMS PER LITER

TOTAL PHOSPHORUS CONCENTRATION,

IN MILLIGRAMS PER LITER

DISSOLVED ORTHOPHOSPHATE CONCENTRATION,

 IN MILLIGRAMS PER LITER

TOTAL NITROGEN LOAD, 

IN POUNDS PER DAY

TOTAL PHOSPHORUS LOAD, 

IN POUNDS PER DAY

DISSOLVED ORTHOPHOSPHATE LOAD,

IN POUNDS PER DAY

DAILY DISCHARGE,

IN CUBIC FEET PER SECOND

DAILY DISCHARGE,

IN CUBIC FEET PER SECOND

DAILY DISCHARGE,

IN CUBIC FEET PER SECOND

5

50,000

10

20

50

100

200

500

1,000

2,000

5,000

10,000

20,000

0.01

10,000

0.02

0.05

0.1

0.2

0.5

1

2

5

10

20

50

100

200

500

1,000

2,000

5,000

0.1

1,000

0.2

0.5

1

2

5

10

20

50

100

200

500

MAM J J A SON D J FMAMJ J ASON D J FMAMJ J AS

1996 1997 1998

10

1

10

2

3

4

5

7

10

0.005

1

0.01

0.02

0.05

0.1

0.2

0.5

10

0.005

1

0.01

0.02

0.05

0.1

0.2

0.5

100 1,000

100 1,000

100 1,000

MAM J J A SON D J FMAMJ J ASON D J FMAMJ J AS

MAM J J A SON D J FMAMJ J ASON D J FMAMJ J AS

EXPLANATION

Daily loads, predicted using

 regression equation (tables C1-C3)

Daily load, measured

Concentration, measured

Figure C4. Predicted and measured daily nutrient loads, and scatterplots of nutrient concentrations and streamflows used to calibrate the load-estimate 

regression equations for Fishtrap Creek (site 4) in the Puget Sound Basin study unit, Washington.
172 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

100

1,000,000

200

500

1,000

2,000

5,000

10,000

20,000

50,000

100,000

200,000

500,000

1

500,000

2

5

10

20

50

100

200

500

1,000

2,000

5,000

10,000

20,000

50,000

100,000

200,000

10

1,000

20

30

40

50

70

100

200

300

400

500

700

O N D J FMAMJ J ASON D J FMAMJ J ASON D J FMAMJ J A S

O N D J FMAMJ J ASON D J FMAMJ J ASON D J FMAMJ J AS

O N D J FMAMJ J ASON D J FMAMJ J ASON D J FMAMJ J AS

1995 1996 1997 1998

1,000

0.05

10

0.1

0.2

0.5

1

2

5

1,000

0.005

10

0.01

0.02

0.05

0.1

0.2

0.5

1

2

5

1,000

0.005

0.1

0.007

0.01

0.02

0.03

0.04

0.05

0.07

10,000 100,000

10,000 100,000

10,000 100,000

TOTAL NITROGEN CONCENTRATION,

IN MILLIGRAMS PER LITER

TOTAL PHOSPHORUS CONCENTRATION,

IN MILLIGRAMS PER LITER

DISSOLVED ORTHOPHOSPHATE CONCENTRATION,

 IN MILLIGRAMS PER LITER

TOTAL NITROGEN LOAD, 

IN POUNDS PER DAY

TOTAL PHOSPHORUS LOAD, 

IN POUNDS PER DAY

DISSOLVED ORTHOPHOSPHATE LOAD,

IN POUNDS PER DAY

DAILY DISCHARGE,

IN CUBIC FEET PER SECOND

INSTANTANEOUS DISCHARGE,

IN CUBIC FEET PER SECOND

DAILY DISCHARGE,

IN CUBIC FEET PER SECOND

EXPLANATION

Daily loads, predicted using

 regression equation (tables C1-C3)

Daily load, measured

Concentration, measured

Figure C5. Predicted and measured daily nutrient loads, and scatterplots of nutrient concentrations and streamflows used to calibrate the load-estimate 

regression equations for the upper Nooksack River (site 5) in the Puget Sound Basin study unit, Washington. 

(Daily loads for dissolved orthophosphate phosphorus could not be calculated by the regression method because more than 80 percent of the data were 

censored at the minimum reporting level).
Appendix C. Nutrient Load Estimation 173

200

500,000

500

1,000

2,000

5,000

10,000

20,000

50,000

100,000

200,000

10

100,000

20

50

100

200

500

1,000

2,000

5,000

10,000

20,000

50,000

20

5,000

30

40

50

70

100

200

300

400

500

700

1,000

2,000

3,000

4,000

100

0.05

10

0.1

0.2

0.5

1

2

5

100

0.01

1

0.02

0.05

0.1

0.2

0.5

100

0.005

0.1

0.007

0.01

0.02

0.03

0.04

0.05

0.07

1,000 10,000 100,000

1,000 10,000 100,000

1,000 10,000 100,000

O N D J FMAMJ J ASON D J FMAMJ J ASON D J FMAMJ J AS

O N D J FMAMJ J ASON D J FMAMJ J ASON D J FMAMJ J AS

O N D J FMAMJ J ASON D J FMAMJ J ASON D J FMAMJ J AS

1995 1996 1997 1998

TOTAL NITROGEN CONCENTRATION,

IN MILLIGRAMS PER LITER

TOTAL PHOSPHORUS CONCENTRATION,

IN MILLIGRAMS PER LITER

DISSOLVED ORTHOPHOSPHATE CONCENTRATION,

 IN MILLIGRAMS PER LITER

TOTAL NITROGEN LOAD, 

IN POUNDS PER DAY

TOTAL PHOSPHORUS LOAD, 

IN POUNDS PER DAY

DISSOLVED ORTHOPHOSPHATE LOAD,

IN POUNDS PER DAY

DAILY DISCHARGE,

IN CUBIC FEET PER SECOND

DAILY DISCHARGE,

IN CUBIC FEET PER SECOND

DAILY DISCHARGE,

IN CUBIC FEET PER SECOND

EXPLANATION

Daily loads, predicted using

 regression equation (tables C1-C3)

Daily load, measured

Concentration, measured

Figure C6. Predicted and measured daily nutrient loads, and scatterplots of nutrient concentrations and streamflows used to calibrate the load-estimate 

regression equations for the Duwamish River (site 6) in the Puget Sound Basin study unit, Washington.
174 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

10

10,000

20

30

40

50

70

100

200

300

400

500

700

1,000

2,000

3,000

4,000

5,000

7,000

1

1,000

2

3

4

5

7

10

20

30

40

50

70

100

200

300

400

500

700

0.1

200

0.2

0.5

1

2

5

10

20

50

100

O N D J FMAMJ J ASON D J FMAMJ J ASON D J FMAMJ J AS

1995 1996 1997 1998

1 1,000 10 100

0.005

1 1,000 10 100

0.05

1 1,000 10 100

0.5

2

0.6

0.7

0.8

0.9

1

1.5

1

0.07

0.1

0.2

0.3

0.4

0.5

0.7

0.2

0.007

0.01

0.02

0.03

0.04

0.05

0.07

0.1

O N D J FMAMJ J ASON D J FMAMJ J ASON D J FMAMJ J AS

O N D J FMAMJ J ASON D J FMAMJ J ASON D J FMAMJ J AS

TOTAL NITROGEN CONCENTRATION,

IN MILLIGRAMS PER LITER

TOTAL PHOSPHORUS CONCENTRATION,

IN MILLIGRAMS PER LITER

DISSOLVED ORTHOPHOSPHATE CONCENTRATION,

 IN MILLIGRAMS PER LITER

TOTAL NITROGEN LOAD, 

IN POUNDS PER DAY

TOTAL PHOSPHORUS LOAD, 

IN POUNDS PER DAY

DISSOLVED ORTHOPHOSPHATE LOAD,

IN POUNDS PER DAY

DAILY DISCHARGE,

IN CUBIC FEET PER SECOND

DAILY DISCHARGE,

IN CUBIC FEET PER SECOND

DAILY DISCHARGE,

IN CUBIC FEET PER SECOND

EXPLANATION

Daily loads, predicted using

 regression equation (tables C1-C3)

Daily load, measured

Concentration, measured

Figure C7. Predicted and measured daily nutrient loads, and scatterplots of nutrient concentrations and streamflows used to calibrate the load-estimate 

regression equations for Springbrook Creek (site 7) in the Puget Sound Basin study unit, Washington.
Appendix C. Nutrient Load Estimation 175

TOTAL NITROGEN CONCENTRATION,

IN MILLIGRAMS PER LITER

TOTAL PHOSPHORUS CONCENTRATION,

IN MILLIGRAMS PER LITER

DISSOLVED ORTHOPHOSPHATE CONCENTRATION,

 IN MILLIGRAMS PER LITER

TOTAL NITROGEN LOAD, 

IN POUNDS PER DAY

TOTAL PHOSPHORUS LOAD, 

IN POUNDS PER DAY

DISSOLVED ORTHOPHOSPHATE LOAD,

IN POUNDS PER DAY

DAILY DISCHARGE,

IN CUBIC FEET PER SECOND

DAILY DISCHARGE,

IN CUBIC FEET PER SECOND

DAILY DISCHARGE,

IN CUBIC FEET PER SECOND

50

50,000

70

100

200

300

400

500

700

1,000

2,000

3,000

4,000

5,000

7,000

10,000

20,000

30,000

40,000

1

10,000

2

5

10

20

50

100

200

500

1,000

2,000

5,000

O N D J FMAMJ J ASON D J FMAMJ J ASON D J FMAMJ J AS

1995 1996 1997 1998

500

2

3

4

5

7

10

20

30

40

50

70

100

200

300

400

0.2

5

0.3

0.4

0.5

0.7

1

2

3

4

0.005

1

0.01

0.02

0.05

0.1

0.2

0.5

0.005

0.1

0.007

0.01

0.02

0.03

0.04

0.05

0.07

10 10,000 100 1,000

10 10,000 100 1,000

10 10,000 100 1,000

O N D J FMAMJ J ASON D J FMAMJ J ASON D J FMAMJ J AS

O N D J FMAMJ J ASON D J FMAMJ J ASON D J FMAMJ J AS

1

EXPLANATION

Daily loads, predicted using

 regression equation (tables C1-C3)

Daily load, measured

Concentration, measured

Figure C8. Predicted and measured daily nutrient loads, and scatterplots of nutrient concentrations and streamflows used to calibrate the load-estimate 

regression equations for Big Soos Creek (site 8) in the Puget Sound Basin study unit, Washington.
176 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

50

50,000

70

100

200

300

400

500

700

1,000

2,000

3,000

4,000

5,000

7,000

10,000

20,000

30,000

40,000

1

50,000

2

5

10

20

50

100

200

500

1,000

2,000

5,000

10,000

20,000

1

10,000

2

5

10

20

50

100

200

500

1,000

2,000

5,000

TOTAL NITROGEN LOAD, 

IN POUNDS PER DAY

TOTAL PHOSPHORUS LOAD, 

IN POUNDS PER DAY

DISSOLVED ORTHOPHOSPHATE LOAD,

IN POUNDS PER DAY

TOTAL NITROGEN CONCENTRATION,

IN MILLIGRAMS PER LITER

TOTAL PHOSPHORUS CONCENTRATION,

IN MILLIGRAMS PER LITER

DISSOLVED ORTHOPHOSPHATE CONCENTRATION,

 IN MILLIGRAMS PER LITER

1

10

2

3

4

5

7

0.01

2

0.02

0.05

0.1

0.2

0.5

1

0.005

1

0.01

0.02

0.05

0.1

0.2

0.5

DAILY DISCHARGE,

IN CUBIC FEET PER SECOND

DAILY DISCHARGE,

IN CUBIC FEET PER SECOND

DAILY DISCHARGE,

IN CUBIC FEET PER SECOND

10 1,000 100

10 1,000 100

10 1,000 100

O N D J FMAMJ J ASON D J FMAMJ J ASON D J FMAMJ J AS

O N D J FMAMJ J ASON D J FMAMJ J ASON D J FMAMJ J AS

O N D J FMAMJ J ASON D J FMAMJ J ASON D J FMAMJ J AS

1995 1996 1997 1998

EXPLANATION

Daily loads, predicted using

 regression equation (tables C1-C3)

Daily load, measured

Concentration, measured

Figure C9. Predicted and measured daily nutrient loads, and scatterplots of nutrient concentrations and streamflows used to calibrate the loadestimate regression equations for Newaukum Creek (site 9) in the Puget Sound Basin study unit, Washington.
Appendix C. Nutrient Load Estimation 177

0.5

2,000

1

2

5

10

20

50

100

200

500

1,000

0.1

1,000

0.2

0.5

1

2

5

10

20

50

100

200

500

0.1

100

0.2

0.5

1

2

5

10

20

50

O N D J FMAMJ J ASON D J FMAMJ J ASON D J FMAMJ J AS

O N D J FMAMJ J ASON D J FMAMJ J ASON D J FMAMJ J AS

O N D J FMAMJ J ASON D J FMAMJ J ASON D J FMAMJ J AS

1995 1996 1997 1998

0.01

1

0.02

0.05

0.1

0.2

0.5

0.005

1

0.01

0.02

0.05

0.1

0.2

0.5

0.005

0.1

0.007

0.01

0.02

0.03

0.04

0.05

0.07

1 1,000 10 100

1 1,000 10 100

1 1,000 10 100

TOTAL NITROGEN CONCENTRATION,

IN MILLIGRAMS PER LITER

TOTAL PHOSPHORUS CONCENTRATION,

IN MILLIGRAMS PER LITER

DISSOLVED ORTHOPHOSPHATE CONCENTRATION,

 IN MILLIGRAMS PER LITER

TOTAL NITROGEN LOAD, 

IN POUNDS PER DAY

TOTAL PHOSPHORUS LOAD, 

IN POUNDS PER DAY

DISSOLVED ORTHOPHOSPHATE LOAD,

IN POUNDS PER DAY

DAILY DISCHARGE,

IN CUBIC FEET PER SECOND

DAILY DISCHARGE,

IN CUBIC FEET PER SECOND

DAILY DISCHARGE,

IN CUBIC FEET PER SECOND

EXPLANATION

Daily loads, predicted using

 regression equation (tables C1-C3)

Daily load, measured

Concentration, measured

Figure C10. Predicted and measured daily nutrient loads, and scatterplots of nutrient concentrations and streamflows used to calibrate the loadestimate regression equations for the upper Green River (site 10) in the Puget Sound Basin study unit, Washington.

(Daily loads for total phosphorus could not be calculated by the regression method because 75 percent of the data were censored at the minimum 

reporting level).
178 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

TOTAL NITROGEN CONCENTRATION,

IN MILLIGRAMS PER LITER

TOTAL PHOSPHORUS CONCENTRATION,

IN MILLIGRAMS PER LITER

DISSOLVED ORTHOPHOSPHATE CONCENTRATION,

 IN MILLIGRAMS PER LITER

TOTAL NITROGEN LOAD, 

IN POUNDS PER DAY

TOTAL PHOSPHORUS LOAD, 

IN POUNDS PER DAY

DISSOLVED ORTHOPHOSPHATE LOAD,

IN POUNDS PER DAY

DAILY DISCHARGE,

IN CUBIC FEET PER SECOND

DAILY DISCHARGE,

IN CUBIC FEET PER SECOND

DAILY DISCHARGE,

IN CUBIC FEET PER SECOND

5

2,000

7

10

20

30

40

50

70

100

200

300

400

500

700

1,000

0.1

30

0.2

0.3

0.4

0.5

0.7

1

2

3

4

5

7

10

20

0.05

500

0.1

0.2

0.5

1

2

5

10

20

50

100

200

0.5

0.7

10

1

2

3

4

5

7

0.5

0.005

0.2

0.007

0.01

0.02

0.03

0.04

0.05

0.07

0.1

0.5

0.005

5

0.01

0.02

0.05

0.1

0.2

0.5

1

2

1 10 100200

1 10 100200

1 10 100200

MAM J J A S ON D J FMAMJ J ASON D J FMAMJ J AS

1996 1997 1998

MAM J J A S ON D J FMAMJ J ASON D J FMAMJ J AS

MAM J J A S ON D J FMAMJ J ASON D J FMAMJ J AS

EXPLANATION

Daily loads, predicted using

 regression equation (tables C1-C3)

Daily load, measured

Concentration, measured

Figure C11. Predicted and measured daily nutrient loads, and scatterplots of nutrient concentrations and streamflows used to calibrate the loadestimate regression equations for Thornton Creek (site 11) in the Puget Sound Basin study unit, Washington.
Appendix C. Nutrient Load Estimation 179

SUSPENDED SEDIMENT CONCENTRATIONS,

IN MILLIGRAMS PER LITER

SUSPENDED SEDIMENT CONCENTRATIONS,

IN MILLIGRAMS PER LITER

SUSPENDED SEDIMENT CONCENTRATIONS,

IN MILLIGRAMS PER LITER

SUSPENDED SEDIMENT LOAD, 

IN POUNDS PER DAY

SUSPENDED SEDIMENT LOAD, 

IN POUNDS PER DAY

SUSPENDED SEDIMENT LOAD, 

IN POUNDS PER DAY

DAILY DISCHARGE,

IN CUBIC FEET PER SECOND

DAILY DISCHARGE,

IN CUBIC FEET PER SECOND

DAILY DISCHARGE,

IN CUBIC FEET PER SECOND

100

1,000,000,000

200

500

1,000

2,000

5,000

10,000

20,000

50,000

100,000

200,000

500,000

1,000,000

2,000,000

5,000,000

10,000,000

20,000,000

50,000,000

100,000,000

200,000,000

500,000,000

10,000

1,000,000,000

20,000

50,000

100,000

200,000

500,000

1,000,000

2,000,000

5,000,000

10,000,000

20,000,000

50,000,000

100,000,000

200,000,000

500,000,000

100

10,000,000

200

500

1,000

2,000

5,000

10,000

20,000

50,000

100,000

200,000

500,000

1,000,000

2,000,000

5,000,000

100

0.5

10,000

1

10

100

1,000

1,000

1

10,000

2

5

10

20

50

100

200

500

1,000

2,000

5,000

10

0.5

1,000

1

2

5

10

20

50

100

200

500

1,000 10,000 100,000

10,000 100,000

1,000 10,000

O N D J FMAMJ J ASON D J FMAMJ J ASON D J FMAMJ J AS

O N D J FMAMJ J ASON D J FMAMJ J ASON D J FMAMJ J AS

1995 1996 1997 1998

O N D J FMAMJ J ASON D J FMAMJ J ASON D J FMAMJ J AS

Skokomish

(site 1)

NF Skokomish

(site 2)

Lower Nooksack

(site 3)

EXPLANATION

Daily loads, predicted using

 regression equation (table C4)

Daily load, measured

Concentration, measured

Figure C12. Predicted and measured daily suspended sediment loads, and scatterplots of concentrations and streamflows used to calibrate the

load-estimate regression equations for the Puget Sound Basin study unit, Washington.
180 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

10

1,000,000

20

50

100

200

500

1,000

2,000

5,000

10,000

20,000

50,000

100,000

200,000

500,000

10,000

100,000,000

20,000

50,000

100,000

200,000

500,000

1,000,000

2,000,000

5,000,000

10,000,000

20,000,000

50,000,000

1,000

1,000,000,000

2,000

5,000

10,000

20,000

50,000

100,000

200,000

500,000

1,000,000

2,000,000

5,000,000

10,000,000

20,000,000

50,000,000

100,000,000

200,000,000

500,000,000

1995 1996 1997 1998

OND J FMAMJ J ASOND J FMAMJ J ASOND J FMAMJ J AS

O N D J FMAMJ J ASON D J FMAMJ J ASON D J FMAMJ J AS

O N D J FMAMJ J ASON D J FMAMJ J ASON D J FMAMJ J AS

10

1

1,000

2

5

10

20

50

100

200

500

100

1

1,000

2

5

10

20

50

100

200

500

1,000

0.5

10,000

1

10

100

1,000

100 1,000

10,000 100,000

1,000 10,000 100,000

DAILY DISCHARGE,

IN CUBIC FEET PER SECOND

INSTANTANEOUS DISCHARGE,

IN CUBIC FEET PER SECOND

DAILY DISCHARGE,

IN CUBIC FEET PER SECOND

SUSPENDED SEDIMENT CONCENTRATIONS,

IN MILLIGRAMS PER LITER

SUSPENDED SEDIMENT CONCENTRATIONS,

IN MILLIGRAMS PER LITER

SUSPENDED SEDIMENT CONCENTRATIONS,

IN MILLIGRAMS PER LITER

SUSPENDED SEDIMENT LOAD, 

IN POUNDS PER DAY

SUSPENDED SEDIMENT LOAD, 

IN POUNDS PER DAY

SUSPENDED SEDIMENT LOAD, 

IN POUNDS PER DAY

upper Nooksack

(site 5)

Duwamish

(site 6)

Fishtrap

(site 4)

EXPLANATION

Daily loads, predicted using

 regression equation (table C4)

Daily load, measured

Concentration, measured

Figure C12..—Continued.
Appendix C. Nutrient Load Estimation 181

INSTANTANEOUS DISCHARGE,

IN CUBIC FEET PER SECOND

DAILY DISCHARGE,

IN CUBIC FEET PER SECOND

DAILY DISCHARGE,

IN CUBIC FEET PER SECOND

100

1,000,000

200

500

1,000

2,000

5,000

10,000

20,000

50,000

100,000

200,000

500,000

10

100,000,000

20

50

100

200

500

1,000

2,000

5,000

10,000

20,000

50,000

100,000

200,000

500,000

1,000,000

2,000,000

5,000,000

10,000,000

20,000,000

50,000,000

10

2,000,000

20

50

100

200

500

1,000

2,000

5,000

10,000

20,000

50,000

100,000

200,000

500,000

1,000,000

1 1,000 10 100

1

500

2

5

10

20

50

100

200

10 5,000 100 1,000

0.5

1,000

1

2

5

10

20

50

100

200

500

10 1,000 100

1

200

2

5

10

20

50

100

O N D J FMAMJ J ASON D J FMAMJ J ASON D J FMAMJ J AS

O N D J FMAMJ J ASON D J FMAMJ J ASON D J FMAMJ J AS

O N D J FMAMJ J ASON D J FMAMJ J ASON D J FMAMJ J AS

1995 1996 1997 1998

Springbrook

(site 7)

Big Soos

(site 8)

Newaukum

(site 9)

EXPLANATION

Daily loads, predicted using

 regression equation (table C4)

Daily load, measured

Concentration, measured

SUSPENDED SEDIMENT CONCENTRATIONS,

IN MILLIGRAMS PER LITER

SUSPENDED SEDIMENT CONCENTRATIONS,

IN MILLIGRAMS PER LITER

SUSPENDED SEDIMENT CONCENTRATIONS,

IN MILLIGRAMS PER LITER

SUSPENDED SEDIMENT LOAD, 

IN POUNDS PER DAY

SUSPENDED SEDIMENT LOAD, 

IN POUNDS PER DAY

SUSPENDED SEDIMENT LOAD, 

IN POUNDS PER DAY

Figure C12. —Continued.
182 Surface-Water Quality, Puget Sound Basin, Washington, 1995–98

10

1,000,000

20

50

100

200

500

1,000

2,000

5,000

10,000

20,000

50,000

100,000

200,000

500,000

10

500,000

20

50

100

200

500

1,000

2,000

5,000

10,000

20,000

50,000

100,000

200,000

0.5

1,000

1

2

5

10

20

50

100

200

500

0.5

1,000

1

2

5

10

20

50

100

200

500

1 1,000 10 100

0.5 200 1 10 100

O N D J FMAMJ J ASON D J FMAMJ J ASON D J FMAMJ J AS

O N D J FMAMJ J ASON D J FMAMJ J ASON D J FMAMJ J AS

1995 1996 1997 1998

DAILY DISCHARGE,

IN CUBIC FEET PER SECOND

INSTANTANEOUS DISCHARGE,

IN CUBIC FEET PER SECOND

SUSPENDED SEDIMENT CONCENTRATIONS,

SUSPENDED SEDIMENT LOAD, 

IN MILLIGRAMS PER LITER

IN POUNDS PER DAY

Upper Green

(site 10)

Thornton

(site 11)

EXPLANATION

Daily loads, predicted using

 regression equation (table C4)

Daily load, measured

Concentration, measured

Figure C12..—Continued.
Embrey, S.S. and Frans, L.M. SURFACE-WATER QUALITY OF THE SKOKOMISH, NOOKSACK, AND GREEN-DUWAMISH RIVERS AND THORNTON CREEK, PUGET SOUND BASIN, WASHINGTON, 1995-98 USGS-WRIR 02-4190

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