U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2009–5203

National Water-Quality Assessment Program

Occurrence of Volatile Organic Compounds in 

Selected Urban Streams in the United States, 

1995–2003
Cover. A; Aberjona River at Winchester, Mass.

B; Little Neshaminy Creek near Neshaminy, Penn.

C; Great Egg Harbor River near Sicklerville, N.J.

D; Aberjona River at Winchester, Mass.

E; Arcade Creek near Del Paso Heights, Calif.

B

C

D

E

A
Occurrence of Volatile Organic Compounds 

in Selected Urban Streams in the United 

States, 1995–2003

By David A. Bender, Gregory C. Delzer, Curtis V. Price, and John S. Zogorski

National Water-Quality Assessment Program

Scientific Investigations Report 2009–5203

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2009

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Suggested citation:

Bender, D.A., Delzer, G.C., Price, C.V., and Zogorski, J.S., 2009, Occurrence of volatile organic compounds in selected 

urban streams in the United States, 1995–2003: U.S. Geological Survey Scientific Investigations Report 2009–5203, 

87 pages.
iii

Foreword

The U.S. Geological Survey (USGS) is committed to providing the Nation with credible scientific 

information that helps to enhance and protect the overall quality of life and that facilitates effective 

management of water, biological, energy, and mineral resources (http://www.usgs.gov/). Information on the Nation’s water resources is critical to ensuring long-term availability of water that is safe 

for drinking and recreation and is suitable for industry, irrigation, and fish and wildlife. Population 

growth and increasing demands for water make the availability of that water, now measured in 

terms of quantity and quality, even more essential to the long-term sustainability of our communities 

and ecosystems.

The USGS implemented the National Water-Quality Assessment (NAWQA) Program in 1991 to 

support national, regional, State, and local information needs and decisions related to water-quality 

management and policy (http://water.usgs.gov/nawqa). The NAWQA Program is designed to answer: 

What is the condition of our Nation’s streams and groundwater? How are conditions changing over 

time? How do natural features and human activities affect the quality of streams and groundwater, 

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 and priorities. From 1991–2001, the 

NAWQA Program completed interdisciplinary assessments and established a baseline understanding 

of water-quality conditions in 51 of the Nation’s river basins and aquifers, referred to as Study Units 

(http://water.usgs.gov/nawqa/studyu.html). 

Multiple national and regional assessments are ongoing in the second decade (2001–2012) of 

the NAWQA Program as 42 of the 51 Study Units are reassessed. These assessments extend the 

findings in the Study Units by determining status and trends at sites that have been consistently 

monitored for more than a decade, and filling critical gaps in characterizing the quality of surface 

water and groundwater. For example, increased emphasis has been placed on assessing the quality 

of source water and finished water associated with many of the Nation’s largest community water 

systems. During the second decade, NAWQA is addressing five national priority topics that build 

an understanding of how natural features and human activities affect water quality, and establish 

links between sources of contaminants, the transport of those contaminants through the hydrologic 

system, and the potential effects of contaminants on humans and aquatic ecosystems. Included are 

topics on the fate of agricultural chemicals, effects of urbanization on stream ecosystems, bioaccumulation of mercury in stream ecosystems, effects of nutrient enrichment on aquatic ecosystems, 

and transport of contaminants to public-supply wells. These topical studies are conducted in those 

Study Units most affected by these issues; they comprise a set of multi-Study-Unit designs for 

systematic national assessment. In addition, national syntheses of information on pesticides, volatile 

organic compounds (VOCs), nutrients, selected trace elements, and aquatic ecology are continuing.

The USGS aims to disseminate credible, timely, and relevant science information to address practical 

and effective water-resource management and strategies that protect and restore water quality. We 

hope this NAWQA publication will provide you with insights and information to meet your needs, 

and will foster increased citizen awareness and involvement in the protection and restoration of our 

Nation’s waters.

The USGS recognizes that a national assessment by a single program cannot address all waterresource issues of interest. External coordination at all levels is critical for cost-effective management, regulation, and conservation of our Nation’s water resources. The NAWQA Program, therefore, 

depends on advice and information from other agencies—Federal, State, regional, interstate, Tribal, 

and local—as well as nongovernmental organizations, industry, academia, and other stakeholder 

groups. Your assistance and suggestions are greatly appreciated.

Matthew C. Larsen 

Associate Director for Water
iv

Contents

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

Introduction.....................................................................................................................................................2

Purpose and Scope ..............................................................................................................................2

Previous Investigations........................................................................................................................4

Potential Sources of Volatile Organic Compounds in Urban Streams.........................................6

Acknowledgments................................................................................................................................6

Study Approach..............................................................................................................................................6

Site Selection.........................................................................................................................................6

Field Methods........................................................................................................................................6

Analytical Method.................................................................................................................................7

Selection of Volatile Organic Compound Data.................................................................................7

Quality Assurance/Quality Control.....................................................................................................7

Assessment Level...............................................................................................................................14

Statistical Methods.............................................................................................................................14

Streamflow Record Extension ..........................................................................................................17

Occurrence of Volatile Organic Compounds in Urban Streams ..........................................................17

Overall Occurrence Patterns of Volatile Organic Compounds....................................................17

One or More Volatile Organic Compounds............................................................................17

Volatile Organic Compound Groups........................................................................................18

Individual Volatile Organic Compounds .................................................................................25

Occurrence Patterns of Volatile Organic Compounds by Streamflow Pentile.........................25

One or More Volatile Organic Compounds............................................................................25

Volatile Organic Compound Groups........................................................................................34

Individual Volatile Organic Compounds .................................................................................37

Occurrence Patterns of Volatile Organic Compounds by Season..............................................37

One or More Volatile Organic Compounds............................................................................37

Volatile Organic Compound Groups........................................................................................40

Individual Volatile Organic Compounds .................................................................................42

Comparison of Volatile Organic Compound Concentrations to Benchmarks....................................48

Summary........................................................................................................................................................48

Overall Occurrence Patterns of Volatile Organic Compounds....................................................51

Occurrence Patterns of Volatile Organic Compounds by Streamflow Pentile.........................51

Occurrence Patterns of Volatile Organic Compounds by Season..............................................52

References Cited..........................................................................................................................................53

Glossary.........................................................................................................................................................57

Appendix 1. Figures showing streamflow and statistics for all sites ..............................................60

Appendix 2. Summary of the detection frequency and concentrations by warmer 

 (April through September) and cooler (October through March) 

 months for individual volatile organic compounds at an assessment 

 level of 0.02 microgram per liter, 1995–2003.................................................................80
v

Figures

1. Map showing location of urban stream sites that were sampled for this study, 

U.S. Geological Survey National Water-Quality Assessment Program Study 

Units, and the major river basin in which the site is located ................................................3

2–30. Graphs showing:

2. Number of samples by dilution ratio of the urban stream samples ..........................14

3. Cumulative distribution of total concentrations of volatile organic 

compounds (VOCs) in 869 samples from 37 urban stream sites ................................19

4. Relation between the percentage of 869 urban stream samples and 

the number of volatile organic compounds (VOCs) detected ....................................19

5. Detection frequencies of seven volatile organic compound (VOC) 

groups in urban stream samples.....................................................................................20

6. Distribution of the total number of detections of gasoline hydrocarbons in urban stream samples ..................................................................................20

7. Distribution of the total number of detections of solvents in urban 

stream samples..................................................................................................................21

8. Distribution of the total number of detections of trihalomethanes 

in urban stream samples ..................................................................................................21

9. Distribution of the total number of detections of gasoline oxygenates 

in urban stream samples ..................................................................................................22

10. Distribution of the total number of detections of gasoline oxygenates 

in urban stream samples in low and high methyl tert-butyl ether 

(MTBE)-use areas..............................................................................................................22

11. Relation between detection frequencies, and total concentrations 

for gasoline oxygenates in urban stream samples in low and high 

methyl tert-butyl ether (MTBE)-use areas of the United States ................................23

12. Total volatile organic compound (VOC) concentrations in urban 

stream samples by the seven VOC groups....................................................................24

13. Detection frequencies of the 15 most frequently detected volatile 

organic compounds (VOCs) in urban stream samples ................................................30

14. Concentrations of the 15 most frequently detected volatile organic 

compounds in urban stream samples ............................................................................31

15. Relation between detection frequencies, and concentrations of 

methyl tert-butyl ether (MTBE) in urban stream samples in low and 

high MTBE-use areas of the United States...................................................................32

16. Detection frequencies of one or more volatile organic compounds 

by streamflow pentile in urban stream samples .........................................................33

17. Cumulative distribution of total concentrations of volatile organic 

compound (VOC) concentrations in 869 samples from 37 urban 

stream sites by streamflow pentile.................................................................................33

18. Relation between the percentage of urban stream samples and the 

number of volatile organic compounds (VOCs) detected by 

streamflow pentile.............................................................................................................34

19. Detection frequencies of seven volatile organic compound (VOC) 

groups in urban stream samples by streamflow pentile.............................................35

20. Total volatile organic compound (VOC) concentrations of the seven 

VOC groups in urban stream samples by streamflow pentile....................................36
vi

21. Detection frequencies of the 15 most frequently detected volatile 

organic compounds in urban stream samples by streamflow 

pentile ..................................................................................................................................38

22. Concentrations of the 15 most frequently detected volatile organic 

compounds in urban stream samples by streamflow pentile ....................................39

23. Relation between detection frequencies, and concentrations of 

methyl tert-butyl ether (MTBE) in urban stream samples in low and 

high MTBE-use areas of the United States by streamflow 

pentile ..................................................................................................................................40

24. Cumulative distribution of total volatile organic compound (VOC) 

concentrations in 869 samples from 37 urban stream sites by warmer 

(April through September) and cooler (October through March) 

months .................................................................................................................................41

25. Relation between the percentage of urban stream samples and the 

number of volatile organic compounds (VOCs) detected by warmer 

(April through September) and cooler (October through March) 

months .................................................................................................................................42

26. Detection frequencies of volatile organic compound (VOC) groups 

in urban stream samples in warmer (April through September) and 

cooler (October through March) months.......................................................................43

27. Total volatile organic compound (VOC) concentrations in urban 

stream samples of the seven VOC groups in warmer (April through 

September) and cooler (October through March) months.........................................44

28. Detection frequencies of the 15 most frequently detected volatile 

organic compounds in urban stream samples by warmer (April 

through September) and cooler (October through March) months..........................45

29. Concentrations of the 15 most frequently detected volatile organic 

compounds in urban stream samples by warmer (April through 

September) and cooler (October through March) months.........................................46

30. Relation between detection frequencies, and concentrations of 

methyl tert-butyl ether (MTBE) in urban stream samples in low and 

high MTBE-use areas of the United States by warmer (April 

through September) and cooler (October through March) months..........................47

A1.1.–A1.37 Graphs showing daily streamflow and 20-year pentiles of flow at:

A1.1. Station 01102500, Aberjona River at Winchester, Mass., from 

May 1999 to March 2000...................................................................................................60

A1.2. Station 01209710, Norwalk River at Winnipauk, Conn., from 

November 2001 to September 2002 ................................................................................61

A1.3. Station 01390500, Saddle River at Ridgewood, N.J., from May 1996 

to January 1997 ..................................................................................................................61

A1.4. Station 01403900, Bound Brook at Middlesex, N.J., from April 1996 

to July 2002 .........................................................................................................................62

A1.5. Station 01410784, Great Egg Harbor River near Sicklerville, N.J., 

from April 1996 to March 1998 .........................................................................................62

A1.6. Station 01464907, Little Neshaminy Creek at Valley Road near 

Neshaminy, Pa., from February 1999 to October 2000 .................................................63

A1.7. Station 01467150, Cooper River at Haddonfield, N.J., from December 1998 to October 2000 ..................................................................................................63

A1.8. Station 01571490, Cedar Run at Eberlys Mill, Pa., from January 1994 

to August 1995 ....................................................................................................................64
vii

A1.9. Station 01654000, Accotink Creek near Annandale, Va., from 

October 2001 to September 2002.....................................................................................64

A1.10. Station 02087580, Swift Creek near Apex, N.C., from October 2001 

to July 2003 .........................................................................................................................65

A1.11. Station 02169570, Gills Creek at Columbia, S.C., from February 1996 

to March 1998.....................................................................................................................65

A1.12. Station 02306774, Rocky Creek at State Highway 587 at Citrus Park, 

Fla., from January 2002 to July 2003 ...............................................................................66

A1.13. Station 02335870, Sope Creek near Marietta, Ga., from October 2001 

to September 2002 .............................................................................................................66

A1.14. Station 02419977, Three Mile Branch at North Boulevard at 

Montgomery, Ala., from January 1999 to June 2001....................................................67

A1.15. Station 0242354750, Cahaba Valley Creek at Cross Creek Road at 

Pelham, Ala., from January 1999 to June 2001 .............................................................67

A1.16. Station 03049646, Deer Creek near Dorseyville, Pa., from 

January 1997 to August 1998 ...........................................................................................68

A1.17. Station 03353637, Little Buck Creek near Indianapolis, Ind., from 

March 2001 to September 2002 .......................................................................................68

A1.18. Station 393944084120700, Holes Creek in Huffman Park at 

Kettering, Ohio, from March 1999 to September 2002 .................................................69

A1.19. Station 040869415, Lincoln Creek at 47th Street at Milwaukee, 

Wis., from November 2001 to September 2002 .............................................................69

A1.20. Station 04161820, Clinton River at Sterling Heights, Mich., from 

October 1996 to June 1998 ...............................................................................................70

A1.21. Station 05288705, Shingle Creek at Queen Avenue in Minneapolis, 

Minn., from August 1996 to November 1998..................................................................70

A1.22. Station 05330902, Nine Mile Creek near James Circle at 

Bloomington, Minn., from January 1997 to December 1997 .......................................71

A1.23. Station 05531500, Salt Creek at Western Springs, Ill., from 

March 1999 to March 2000...............................................................................................71

A1.24. Station 06713500, Cherry Creek at Denver, Colo., from October 2001 

to September 2002 .............................................................................................................72

A1.25. Station 07031692, Fletcher Creek at Sycamore View Road at 

Memphis, Tenn., from October 1996 to September 1997.............................................72

A1.26. Station 07379960, Dawson Creek at Bluebonnet Boulevard near 

Baton Rouge, La., from January 1999 to February 2001 ..............................................73

A1.27. Station 08057200, White Rock Creek at Greenville Avenue, Dallas, 

Tex., from October 2001 to September 2002 ..................................................................73

A1.28. Station 08178800, Salado Creek at Loop 13 at San Antonio, Tex., 

from January 1997 to January 1998 ................................................................................74

A1.29. Station 094196783, Las Vegas Wash below Flamingo Wash 

confluence near Las Vegas, Nev., from October 2001 to August 2002 .....................74

A1.30. Station 10168000, Little Cottonwood Creek at Jordan River near 

Salt Lake City, Utah, from March 1999 to April 2000.....................................................75

A1.31. Station 11060400, Warm Creek near San Bernardino, Calif., from 

November 1998 to June 2002 ...........................................................................................75

A1.32. Station 11447360, Arcade Creek near Del Paso Heights, Calif., 

from March 1996 to April 1998 .........................................................................................76
viii

A1.33. Station 12128000, Thornton Creek near Seattle, Wash., from 

March 1996 to May 1998...................................................................................................76

A1.34. Station 12424500, Spokane River at 7 Mile Bridge near Spokane, 

Wash., from February 1999 to October 1999..................................................................77

A1.35. Station 14206950, Fanno Creek at Durham, Oreg., from 

October 2001 to September 2002.....................................................................................77

A1.36. Station 15275100, Chester Creek at Arctic Boulevard at 

Anchorage, Alaska, from January 1999 to September 1999.......................................78

A1.37. Station 16242500, Manoa Stream at Kanewai Field, 

Honolulu, Oahu, Hawaii, from July 1999 to June 2000 .................................................78

Tables

1. Volatile organic compounds included in the U.S. Geological Survey’s 

National Water-Quality Assessment Program.........................................................................8

2. List of urban stream sampling sites by major river basin and Study Unit 

with drainage area, use areas of methyl tert-butyl ether (MTBE), 

percentage urban land use in basin, sampling dates, and streamflow 

discharge statistics by pentile..................................................................................................10

3. Statistical summaries of analytical results for volatile organic compounds 

in source-solution and field-equipment blank samples from 37 urban 

stream sites .................................................................................................................................15

4. Statistical tests used in the report...........................................................................................16

5. Number of samples per month, in cooler and warmer months, and 

in the five streamflow pentiles from 37 urban streams ........................................................18

6. Summary of the detection frequencies and concentrations of volatile 

organic compounds at an assessment level of 0.02 microgram per liter, 

1995–2003, listed in order of decreasing detection frequency ...........................................26

7. Detection frequencies of one or more volatile organic compounds (VOCs) 

at all sites, total number of VOC detections, median number of VOCs 

detected, maximum number of VOCs detected, and median total concentration in urban stream samples by streamflow pentile.......................................................32

8. Detection frequency of one or more volatile organic compounds (VOCs) 

at all sites, total number of VOCs detected, median number of VOCs 

detected, the maximum number of VOCs detected, and median total 

concentration in urban stream samples in warmer and cooler months 

by streamflow pentile.................................................................................................................41

9. Summary by volatile organic compound of the number of samples with 

stream concentration-to-benchmark ratios greater than or equal to 0.1 

and greater than or equal to 1 for drinking-water benchmarks or aquaticlife criteria....................................................................................................................................49
ix

Conversion Factors and Datums

Multiply By To obtain

Area

square mile (mi2) 259.0 hectare (ha)

square mile (mi2) 2.590 square kilometer (km2)

Volume

ounce, fluid (fl. oz) 0.02957 liter (L)

pint (pt) 0.4732 liter (L)

quart (qt) 0.9464 liter (L)

gallon (gal) 3.785 liter (L)

Flow rate

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F=(1.8×°C)+32

Horizontal coordinate information is referenced to North American Datum of 1983 (NAD 83)

Concentrations of chemical constituents in water are given in micrograms per liter (μg/L).

Study Unit Abbreviations, Other Abbreviations, and Symbols

ACAD Acadian-Pontchartrain Drainages

ACFB Apalachicola-Chattahoochee-Flint River Basins

ALBE Albemarle-Pamlico Drainage Basins

ALMN Allegheny-Monongahela River Basins

CAZB Central Arizona Basins

CCPT Central Columbia Plateau

CNBR Central Nebraska Basins

CONN Connecticut, Housatonic, and Thames River Basins

COOK Cook Inlet Basin

DELR Delaware River Basin

DLMV Delmarva Peninsula

EIWA Eastern Iowa Basins

GAFL Georgia-Florida Coastal Plain

GRSL Great Salt Lake Basins

HDSN Hudson River Basin

HPGW High Plains Regional Groundwater Study

KANA Kanawha-New River Basins

LERI Lake Erie-Lake St. Clair Drainages
x

LINJ Long Island-New Jersey Coastal Drainages

LIRB Lower Illinois River Basin

LSUS Lower Susquehanna River Basin

LTEN Lower Tennessee River Basin

MIAM Great and Little Miami River Basins

MISE Mississippi Embayment

MOBL Mobile River Basin

NECB New England Coastal Basins

NROK Northern Rockies Intermontane Basins

NVBR Nevada Basin and Range

OAHU Oahu

OZRK Ozark Plateaus

PUGT Puget Sound Basin

REDN Red River of the North Basin

RIOG Rio Grande Valley

SACR Sacramento River Basin

SANA Santa Ana Basin

SANJ San Joaquin-Tulare Basins

SANT Santee River Basin and Coastal Drainages

SCTX South-Central Texas

SOCA Southern California Basins

SOFL Southern Florida Drainages

SPLT South Platte River Basin

TRIN Trinity River Basin

UCOL Upper Colorado River Basin

UIRB Upper Illinois River Basin

UMIS Upper Mississippi River Basin

USNK Upper Snake River Basin

UTEN Upper Tennessee River Basin

WHMI White, Great and Little Miami River Basins

WILL Willamette Basin

WMIC Western Lake Michigan Drainages

YELL Yellowstone River Basin

α significance level for statistical tests
xi

χ2 chi-squared statistic

μg/L microgram per liter

°C degrees Celsius

< less than

≤ less than or equal to

> greater than

≥ greater than or equal to

BTEX benzene, toluene, ethylbenzene, and xylenes

CAA Clean Air Act

CDF cumulative distribution function

CWA Clean Water Act

CWS community water system

CWSS Community Water Supply Survey

DF degrees of freedom

DIPE diisopropyl ether

DWA Drinking Water Advisory

DWB drinking-water benchmark

ETBE ethyl tert-butyl ether

GC/MS gas chromatography/mass spectrometry

HBSL Health-Based Screening Level

LTQ esti , estimated long-term streamflow for a short-term record site for percentile i

LTQ conci , streamflow for long-term station for each percentile, i, of interest for the 

concurrent period of record

LTQ recordi , streamflow for each corresponding percentile for the entire period of record 

for the long-term station for percentile i

LT–MDL long-term method detection level

MCL Maximum Contaminant Level

MSA metropolitan statistical area

MS4 municipal separate storm sewer system

MTBE methyl tert-butyl ether

NAWQA U.S. Geological Survey National Water-Quality Assessment

NOMS U.S. Environmental Protection Agency National Organics Monitoring Survey

NORS U.S. Environmental Protection Agency National Organics Reconnaissance Survey

NPDES U.S. Environmental Protection Agency National Pollutant Discharge Elimination 

System

NURP U.S. Environmental Protection Agency National Urban Runoff Program
xii

NWQL U.S. Geological Survey National Water Quality Laboratory

ODS Organics Detection System

ORSANCO Ohio River Valley Water Sanitation Commission 

p-value probability value

QA/QC quality assurance/quality control

SDWA Safe Drinking Water Act

STQ conci , streamflow for short-term record site for each percentile, i, of interest for the 

concurrent period of record

TAME tert-amyl methyl ether

THM trihalomethane

TTHMs total trihalomethanes

USEPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey

VOC volatile organic compound

Z Wilcoxon sign-rank and rank-sum test statistics
Occurrence of Volatile Organic Compounds in Selected 

Urban Streams in the United States, 1995–2003

By David A. Bender, Gregory C. Delzer, Curtis V. Price, and John S. Zogorski

Abstract

As part of the U.S. Geological Survey’s (USGS) National 

Water-Quality Assessment (NAWQA) Program, urban 

indicator sites were monitored to (1) characterize the stream 

quality from drainage basins with predominantly residential 

and commercial land use, and (2) determine which selected 

natural and anthropogenic factors affect stream quality. A 

total of 869 water samples were collected from 37 urban 

streams during 1995–2003 and were analyzed for 87 volatile 

organic compounds (VOCs). The occurrence of VOCs in 

urban streams is described in this report for (1) all samples 

as a single dataset, (2) all samples grouped by streamflow 

pentiles, and (3) all samples grouped by warmer (April 

through September) and cooler (October through March) 

months by the detection frequency and (or) concentration of 

(a) any VOC, (b) VOC groups, and (c) individual compounds. 

An assessment level of 0.02 microgram per liter (μg/L) was 

used to compute the detection frequencies and concentrations 

of VOCs. Concentrations of VOCs were compared to (1) U.S. 

Environmental Protection Agency’s (USEPA) drinking-water 

Maximum Contaminant Levels (MCLs) or Drinking Water 

Advisories, (2) Health-Based Screening Levels (HBSLs) 

developed by the USGS in collaboration with the USEPA 

and other agencies, and (3) USEPA and Canadian aquatic-life 

criteria.

One or more VOCs were detected in 97.1 percent of 

869 samples, and one or more VOCs were detected frequently 

(greater than 80 percent) at all sites. The median total VOC 

concentration for all samples was 0.57 μg/L, and total VOC 

concentrations in a single sample ranged from not detected to 

698 μg/L. About 85 percent of the samples contained two or 

more VOCs, and about one-half contained five or more VOCs. 

The gasoline hydrocarbons were the most frequently occurring 

VOC group followed by solvents, trihalomethanes (THMs), 

gasoline oxygenates, organic synthesis compounds, fumigants, and refrigerants. Concentration ranges for most VOC 

groups were distributed over at least two orders of magnitude. 

Fifty-seven of the 87 VOCs analyzed were detected in at 

least one sample at an assessment level of 0.02 μg/L. More 

than one-half of the 30 VOCs not detected in samples were 

organic synthesis compounds. Fifteen compounds had detection frequencies greater than or equal to 10 percent. With the 

exception of toluene and chloroform, the median concentration of each VOC for all samples was less than the assessment 

level. Furthermore, the median concentrations of detections 

for the 15 most frequently occurring VOCs ranged from 0.03 

to 3.9 μg/L, and typically were less than or equal to 0.10 μg/L.

The 869 samples from the 37 sites were stratified into 

five streamflow pentiles (less than 20, 20–less than 40, 

40–less than 60, 60–less than 80, and greater than or equal 

to 80 percent of estimated long-term streamflow statistics) 

for comparison of the occurrence of VOCs. The detection frequency of one or more VOCs by streamflow pentile 

varied only slightly from 96.7 to 97.7 percent. The median 

total VOC concentrations in samples for the five streamflow 

pentiles ranged from 0.39 to 1.0 μg/L. Two or more VOCs 

were present in more than 80 percent of samples in each 

of the five pentiles. The gasoline hydrocarbons, solvents, 

THMs, and gasoline oxygenates occurred frequently (greater 

than 30 percent) in all streamflow pentiles, in contrast to the 

organic synthesis compounds, fumigants, and refrigerants that 

occurred less frequently in urban streams under all streamflow 

conditions. The median total VOC concentrations for gasoline 

hydrocarbons, solvents, gasoline oxygenates, and organic 

synthesis compounds generally increased as streamflow 

increased. In contrast, the median total VOC concentrations 

for THMs and fumigants generally decreased as streamflow 

increased. The median total VOC concentrations for refrigerants showed no pattern as streamflow increased.

Because differences between VOC occurrence and 

streamflow pentiles were small for most comparisons, the 

overall patterns of occurrence for VOCs in urban streams 

were stratified by warmer (April through September) and 

cooler (October through March) months. One or more VOCs 

were detected frequently in both warmer (96 percent of 

410 samples) and cooler months (98 percent of 459 samples). 

However, median concentrations of detections were about 

twice as large in cooler months (0.80 μg/L) than in warmer 

months (0.41 μg/L). The median number of VOCs reported 

in samples in warmer and cooler months was 4 and 5, respectively. In general, the detection frequency of most VOC groups 

was similar or larger in cooler months than in warmer months. 

None of the samples had concentrations greater than 

or equal to an MCL or HBSL. However, six compounds 

(trichloroethene, perchloroethene, cis-1,2-dichloroethene, 
2 Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003

dichloromethane, vinyl chloride, and dibromochloropropane) 

had concentrations less than but within 10 percent of an MCL. 

Three compounds (acetone, 1,1,2,2-tetrachloroethane, and 

acrolien) had concentrations less than but within 10 percent 

of an HBSL. Concentrations of methyl tert-butyl ether in 

59 samples were less than but within 10 percent of the lower 

limit of the USEPA Taste and Odor Drinking Water Advisory 

of 20 μg/L, and concentrations in 5 samples were greater 

than or equal to this lower limit. Toluene and chloroform 

had concentrations greater than the aquatic-life criteria. Five 

additional compounds (trichloroethene, chlorobenzene, naphthalene, acrolien, and 1,2-dichlorobenzene) had concentrations 

less than but within 10 percent of the aquatic-life criteria.

Introduction

The U.S. Geological Survey’s (USGS) National WaterQuality Assessment (NAWQA) Program was implemented 

in 1991. The primary goals of the NAWQA Program are 

to describe the status and trends of the water quality of the 

Nation’s water resources and to identify natural and anthropogenic factors affecting the water quality. The NAWQA 

Program consists of Study Units that include parts of most of 

the Nation’s major river basins (fig. 1) and aquifer systems. 

Most of the NAWQA Program’s efforts to collect waterquality data are focused in the Study Units. Collectively, the 

Study Units include a large percentage of the Nation’s population and water use.

Gilliom and others (1995) described the overall design 

of the NAWQA Program in detail. The NAWQA Program’s 

surface-water design includes monitoring the water quality 

of streams at (1) indicator sites that drain relatively homogenous land-use and physiographic conditions, (2) integrator 

sites that drain mixed land use (usually larger river systems), 

and (3) reference sites that are relatively unaffected by human 

influences. Streams are monitored for streamflow, specific 

conductance, water temperature, and chemical and biological 

constituents (Lopes and Price, 1997). Urban and agricultural 

land uses are the two main land uses being investigated in 

the NAWQA Program. The primary objectives of monitoring 

at the urban indicator sites are to (1) characterize the stream 

quality from drainage basins with predominantly residential 

and commercial land use, and (2) determine which selected 

natural and anthropogenic factors affect stream quality. Lopes 

and Price (1997) provided guidance on the distribution of 

urban indicator sites, site selection criteria, chemical and 

biological sampling, and the basic ancillary data needed to 

identify factors affecting stream quality to foster consistency 

among the Study Units.

Most studies on urban streams in the last few decades 

were completed to characterize the quality of runoff including (1) U.S. Environmental Protection Agency’s (USEPA’s) 

National Urban Runoff Program (NURP), and (2) the National 

Pollutant Discharge Elimination System (NPDES) permitting 

process for cities with populations greater than 100,000 and 

for some smaller cities within urban areas. The NURP and 

NPDES studies sampled only stormwater. In contrast, multiple 

sampling events in the NAWQA Program focused on the 

ambient quality of selected urban streams that have perennial 

flow.

The NAWQA Program began collecting samples for 

analyses of volatile organic compounds (VOCs) at urban indicator (urban stream) sites and selected integrator (large river) 

sites in 1995 (in Study Units that started in 1994) and continued in studies with Study Units that started in 1997 and 2001. 

The urban streams were selected to meet certain criteria to 

assure consistency in chemical data for regional and national 

comparisons, and to address the goals of the ecology component of the NAWQA Program. Samples collected from a total 

of 37 urban indicator sites on urban streams were analyzed for 

87 VOCs (fig. 1).

VOCs are of concern because of their releases to the 

environment resulting from large-scale and widespread use 

in industry, commerce, and everyday products, and because 

of their human toxicity and persistence in the environment 

for some compounds. Federal regulation of VOCs to protect 

public health and welfare began in the 1970s with the passage 

of the Clean Air Act (CAA), Clean Water Act (CWA), Safe 

Drinking Water Act (SDWA), and Resource Conservation and 

Recovery Act (Zogorski and others, 2006).

Purpose and Scope

The purpose of the report is to describe the occurrence 

of 87 VOCs in 37 urban streams in 31 Study Units that were 

sampled in the United States between 1995 and 2003 as part 

of the NAWQA Program. The occurrence of VOCs is characterized nationally by the detection frequency, concentrations, 

spatial distribution, streamflow pentiles, seasonal distribution, 

and the number of compounds in samples. VOC concentrations are compared to drinking-water benchmarks and aquaticlife criteria to describe the significance of VOC occurrence in 

urban streams to human health and aquatic life.

A total of 869 water samples collected from 37 urban 

streams were analyzed for VOCs using a low-level, “information rich” analytical method (Connor and others, 1998) at the 

USGS’s National Water Quality Laboratory (NWQL). The 

occurrence of VOCs is described for (1) all samples as a single 

dataset, (2) all samples grouped by streamflow pentiles, and 

(3) all samples grouped by warmer (April through September) and cooler (October through March) months. The first 

approach provides a general national-scale perspective on 

the occurrence of VOCs. The second approach examines the 

similarities or differences in VOC occurrence on the basis of 

streamflow condition, and the third approach examines the 

similarities or differences on the basis of warmer and cooler 

months.

The occurrence of VOCs is characterized by the detection frequency and (or) concentration of (1) any VOC (that is, 
Figure 1. Location of urban stream sites that were sampled for this study, U.S. Geological Survey National Water-Quality Assessment Program Study Units, and the major river 

basin in which the site is located.

CACI

KANS

GAFL

MISE

RIOG

OZRK

MOBL

TENN

CAZB

SANJ

SCTX

ALBE

CNBR

SPLT

SACR

LERI

ACAD

SANT

LIRB

TRIN

EIWA

ACFB

SOFL

WHMI

GRSL

PODL

UIRB

YELL

UMIS

USNK

NECB

WMIC

UCOL

CONN

WILL

HDSN

CCYK

PUGT

DELR

NVBR

LINJ

CCYK

PODL

SANA

NVBR

OAHU

COOK

SANA

NROK

LSUS

ALMN

Major river basin

NAWQA Program Study Unit1

Urban stream site—Number is  site identification1See Study Unit abbreviations in the 

 "Study Unit Abbreviations, Other  Abbreviations, and Symbols"  section at the front of the report

EXPLANATION

14206950

12424500

12128000

11447360

11060400

08178800

08057200

07379960

07031692

06713500

05531500

04161820

03049646

02419977

02335870

02306774

02169570

10168000

05330902

05288705

02087580

01410784

01403900

01102500

040869415

094196783

0242354750

393944084120700 03353637

01654000 01571490

01467150

01464907

01390500 01209710

16242500

15275100

Missouri

California

Pacific Northwest

Rio Grande, Colorado,

and Great Basin

Lower Mississippi,

Arkansas-White-Red,

and Texas-Gulf

South Atlantic-Gulf

and Tennessee

New England and

Mid-Atlantic

Great Lakes, Ohio, 

Upper Mississippi,

and Souris-Red-Rainy

Missouri

California

Pacific Northwest

Rio Grande, Colorado,

and Great Basin

Lower Mississippi,

Arkansas-White-Red,

and Texas-Gulf

South Atlantic-Gulf

and Tennessee

New England and

Mid-Atlantic

Great Lakes, Ohio, 

Upper Mississippi,

and Souris-Red-Rainy

Hawaii

Alaska

02306774

0 200 400 MILES0 200 400 KILOMETERS

Base modified from U.S. Geological Survey digital data, 1990, 1:2,000,000Albers Equal-Area Conic projectionStandard parallels 29°30′N and 45°30′N, central meridian 96°00′WNorth American Datum of 1983

14206950

12424500

12128000

11447360

11060400

08178800

08057200

07379960

07031692

06713500

05531500

04161820

03049646

02419977

02306774

02169570

10168000

05330902

05288705

02087580

01410784

01403900

01102500

040869415

094196783

0242354750

393944084120700 03353637

01654000 01571490

01467150

01464907

01390500 01209710

16242500

15275100

02335870

Introduction 3
4 Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003

detection of one or more compounds in a sample), (2) VOC 

groups (that is, gasoline hydrocarbons, solvents, trihalomethanes (THMs), gasoline oxygenates, organic synthesis 

compounds, fumigants, and refrigerants), and (3) individual 

VOCs. VOC concentrations are compared to (1) USEPA’s 

drinking-water Maximum Contaminant Levels (MCLs) or 

Drinking Water Advisories (DWAs), (2) Health-Based Screening Levels (HBSLs) developed by the USGS in collaboration 

with the USEPA, the New Jersey Department of Environmental Protection, and the Oregon Health & Science University, 

and (3) aquatic-life criteria.

Previous Investigations

Many water-quality studies for rivers and streams, to 

date, have focused on large drinking-water sources, stormwater quality for permitting purposes (for example, NPDES 

permits), and other contamination issues within a specific 

drainage basin. In addition, some studies in urban rivers and 

streams have been undertaken to identify specific sources of 

water-quality degradation. Summaries of selected studies with 

emphasis on findings for surface waters are included in this 

section.

The USEPA has been active in characterizing VOCs in 

drinking water supplies since the 1970s with the passage of 

the SDWA in 1974. Westrick (1990) described and presented 

some of the results for each of the following surveys: (1) the 

National Organics Reconnaissance Survey (NORS), (2) the 

National Organics Monitoring Survey (NOMS), and (3) the 

Community Water Supply Survey (CWSS).

The NORS sampling was one of the earliest data gathering efforts (January–April 1975) for the SDWA and emphasized THMs and two other VOCs (1,2-dichloroethane and 

carbon tetrachloride). The NORS sampling, in early 1975, 

included 80 water supplies, of which 64 were surface-water 

supplies. Minimum quantifiable concentrations for NORS 

sampling ranged from 0.2 to 0.4 microgram per liter (μg/L) 

for 1,2-dichloroethane and from 1 to 2 μg/L for carbon 

tetrachloride.

The NOMS sampling focused on vulnerable watersupply systems and supplies with selected THM data. The 

NOMS sampling included 113 water systems, of which 92 

were surface-water systems, in three phases. Phase I had 

fairly high minimum quantitation limits, and the analytical 

methodology was not well documented; therefore, the results 

were not discussed by Westrick (1990). Samples from Phase 

II were analyzed for nine VOCs, with minimum reporting 

levels ranging from 0.005 to 0.2 μg/L. The most frequently 

occurring VOCs in surface water sampled during Phase II 

were trichloroethene (22 of 92 samples), carbon tetrachloride 

(10 of 89 samples), 1,4-dichlorobenzene (6 of 92 samples), 

and benzene (5 of 92 samples). Samples from Phase III were 

analyzed for 10 VOCs, with minimum reporting levels ranging 

from 0.005 to 0.4 μg/L. In Phase III, the most frequently 

occurring VOCs in surface water were trichloroethene 

(17 of 88 samples), carbon tetrachloride (11 of 88 samples), 

1,4-dichlorobenzene (27 of 89 samples), and trichlorobenzene 

(10 of 89 samples).

The CWSS sampling began in 1976 to characterize 

the drinking water supplied by community water supply 

systems with respect to contaminants in the National Interim 

Primary Drinking Water Regulations. A secondary objective of the CWSS sampling was to obtain additional data 

on THMs and synthetic VOCs in community water systems 

(CWSs). The CWSS sampling included 436 CWSs, of which 

106 were surface-water systems. Samples for the CWSS 

were analyzed for 14 VOCs with a minimum reporting level 

for all VOCs of 0.5 μg/L. The most frequently detected 

VOCs in the 106 surface-water systems were xylenes (7 of 

100 samples), toluene (3 of 100 samples), carbon tetrachloride 

(3 of 106 samples), perchloroethene (3 of 106 samples), and 

1,1,1-trichloroethane (3 of 106 samples).

In 1978, the Ohio River Valley Water Sanitation Commission (ORSANCO) implemented the Organics Detection 

System (ODS) to monitor VOCs and other contaminants 

from accidents and spills and to identify exceedances of 

drinking-water regulations (Lundgren and Lopes, 1999). The 

NAWQA Program conducted a retrospective analysis of data 

from ORSANCO’s ODS for 1987–96 to assess VOCs in the 

Ohio River and its major tributaries that are used by public 

water suppliers (Lundgren and Lopes, 1999). Briefly, the 

NAWQA analysis included 15 ORSANCO monitoring sites 

and 21 VOCs regulated in drinking water at an assessment 

level of 0.05 μg/L. The five most frequently detected VOCs 

were chloroform (26 percent), benzene (11 percent), toluene 

(6.4 percent), dichloromethane (3.9 percent), and 1,3-dichlorobenzene (3.4 percent). All 21 VOCs were detected in one 

or more samples. Most of the 21 VOCs had similar or larger 

detection frequencies in cooler months (October through 

March) than in warmer months (April through September) with the exceptions of chloroform, dichloromethane, 

1,4-dichlorobenzene, chlorobenzene, and 1,1,1-trichloroethane. Fourteen VOCs had downward trends during 1987–96 in 

monthly mean concentrations and nine VOCs had significant 

downward trends in percentage detection.

Achten, Kolb, and Püttmann (2002) and Achten, Kolb, 

Püttmann, and others (2002) provided an overview of 

methyl tert-butyl ether (MTBE) in rivers and wastewater in 

Germany. The method detection limit for these studies was 

0.01 μg/L. MTBE concentrations in the lower parts of the 

Rhine and Main Rivers ranged from 0.23 to 0.3 μg/L and 

0.08 to 0.21 μg/L, respectively. They also measured MTBE in 

small urban streams with and without large industrial inputs. 

Concentrations were larger in the urban streams with industrial input (0.15 to 0.30 μg/L) than in urban streams without 

industrial inputs (0.025 to 0.10 μg/L). MTBE concentrations 

were slightly greater than the method detection limit in rural 

streams. MTBE concentrations in rivers also were correlated 

with increased measured concentrations of MTBE in precipitation. Wastewater samples from two sewage plants showed 

MTBE concentrations of about 0.10 to 0.30 μg/L. Riverbank 
Introduction 5

water also was sampled from the Lower Rhine and Lower 

Main Rivers with average concentrations of about 0.08 μg/L in 

the Lower Rhine riverbank waters and concentrations ranging 

from 0.052 to 0.25 μg/L in the Lower Main riverbank waters.

The occurrence of 41 VOCs in surface waters and treated 

wastewater in Greece was investigated by Nikolaou and others 

(2002). The method detection limit for compounds in this 

study ranged from 0.01 to 0.25 μg/L. Samples were collected 

from 10 rivers, 7 lakes, 3 gulfs, and 4 wastewater treatment plants from October 1998 to September 1999. Sixteen 

individual VOCs were detected in surface waters: chloroform, 

trichloroethene, perchloroethene, carbon tetrachloride, hexachlorobutadiene, 1,2,4-trichlorobenzene, 1,1,2-trichloroethane, 

toluene, 2-chlorotoluene, 4-chlorotoluene, 1,3,5-trimethylbenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,-dichlorobenzene, naphthalene, and 1,2,3-trichlorobenzene.

Yamamoto and others (1997) monitored 30 sites within 

urban rivers and estuaries of Osaka, Japan, to determine the 

concentrations and distribution of 55 VOCs. The method 

detection limits for VOCs in this study ranged from 0.05 to 

0.98 μg/L. Forty VOCs were detected, and 30 VOCs were 

detected in 5 percent or more of the samples. Solvents were 

the most ubiquitous of the VOCs detected in samples. All the 

rivers and estuaries sampled contained dichloromethane and 

chloroform. Four VOC occurrence patterns were noted by 

Yamamoto and others (1997): (1) the most common VOCs 

showed maximum concentration fluctuations due to irregular 

spills and loadings; (2) one VOC (cis-1,2-dichloroethene) 

showed a stable concentration distribution due to fixed 

loading; (3) some VOCs were specific to an industrial site; 

and (4) some VOCs had uniform concentration profiles and 

entered the rivers from multiple sources. Diurnal variations of 

some VOCs also were noted.

Grady (2003) and Delzer and Ivahnenko (2003) provided 

results from a national survey of MTBE in drinking-water 

sources for a random survey and a focused survey, respectively. The random and focused surveys were designed to 

provide information on the occurrence and distribution of 

MTBE and 65 other VOCs in untreated groundwater and 

surface-water sources of drinking water used by CWSs in 

the United States at a common assessment level of 0.2 μg/L. 

The random survey included 954 drinking-water sources, of 

which 171 rivers, streams, aqueducts, or canals were sampled. 

The focused survey sampled 20 rivers and (or) streams used 

as a source water by CWSs that were known or suspected to 

be contaminated by MTBE. The random and focused studies 

showed that VOCs frequently occur in rivers and streams used 

as source waters. THMs were the most frequently occurring 

VOC group in the random survey in river and (or) stream 

waters followed by MTBE, gasoline hydrocarbons, solvents, 

organic synthesis compounds, and fumigants.

The USEPA NURP program was designed to provide 

information to determine whether urban runoff was causing 

water-quality problems and to provide an information base for 

policy decisions for urban stormwater runoff and control (U.S. 

Environmental Protection Agency, 1982, 1983a, 1983b). For 

the NURP program, 121 urban runoff samples from 28 locations in the United States were analyzed for priority pollutants. 

The most frequently detected VOCs were dichloromethane 

(11 percent), chloroform (9 percent), naphthalene (9 percent), 

trichloroethene (6 percent), 1,1,1-trichloroethane (6 percent), 

and ethylbenzene (6 percent).

The primary objective of the CWA is to restore and 

maintain the chemical, physical, and biological integrity of 

the Nation’s waters (U.S. Environmental Protection Agency, 

2000a). To achieve the objective and goals of the CWA, a 

variety of programs to control the discharge of pollutants to 

receiving waters were established by the USEPA. Section 

402 of the CWA established the NPDES permit program to 

specifically control the discharge of pollutants from pointsource dischargers. The NPDES program covers animal 

feeding operations, combined sewer overflows, industrial and 

commercial facilities, municipalities and wastewater treatment plants, sanitary sewer overflows, and stormwater. The 

NPDES stormwater permit program has two phases. Phase I of 

the stormwater permit program requires NPDES permits from 

two broad categories of stormwater discharges: (1) municipal 

separate storm sewer systems (MS4s) serving populations of 

100,000 or more and (2) discharges associated with industrial 

activity. The Phase II regulations address discharges from 

smaller municipalities with populations of 50,000 or more 

(U.S. Environmental Protection Agency, 1999a). The rule also 

allows municipalities covered in Phase I that are automatically 

designated because they are within a larger urbanized area to 

obtain a waiver from the otherwise applicable requirements 

if the discharges from small municipalities are not causing 

impairment of a receiving water body. Delzer and others 

(1996) provided a summary of the occurrence of select VOCs 

in urban stormwater in the United States during 1991–95 for 

NPDES studies completed by the USGS in 16 cities. The 

10 most frequently detected VOCs at an assessment level of 

0.2 μg/L were toluene, xylenes, chloroform, trimethylbenzenes, perchloroethene, naphthalene, MTBE, dichloromethane, bromodichloromethane, and ethylbenzene. The median 

concentrations for individual VOCs were less than 1 μg/L, 

with the exception of MTBE (1.5 μg/L).

Lopes and Dionne (1998) provided a summary of VOCs 

in highway runoff and urban stormwater. Briefly, VOCs were 

present in highway runoff and urban stormwater with larger 

concentrations from industrial areas and during winter months 

than in nonindustrial areas and during summer months. This 

indicates that urban land surfaces may be the primary nonpoint 

source of most VOCs. Temperature also may be an important 

factor in the occurrence of VOCs in surface waters with more 

VOCs present at lower temperatures than at higher temperatures. Lopes and Dionne (1998) also reported that VOCs were 

present in precipitation and snowmelt.

Many of the NAWQA Study Units that collected VOC 

samples at urban indicator sites provided summaries: Cook 

Inlet Basin (COOK; Glass and others, 2004); Delaware River 

Basin (DELR; Fischer and others, 2004); Great Salt Lake 

Basins (GRSL; Thiros, 2000; Waddell and others, 2004); 
6 Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003

Long Island-New Jersey Coastal Drainages (LINJ; O’Brien 

and others, 1997; Terracciano and O’Brien, 1997; Reiser 

and O’Brien, 1998; Ayers and others, 2000); Great and Little 

Miami River Basins (MIAM; Rowe and others, 2004); New 

England Coastal Basins (NECB; Campo and others, 2003; 

Robinson and others, 2004); Northern Rockies Intermontane 

Basins (NROK; Clark and others, 2004); Oahu (OAHU; 

Anthony and others, 2004); Santa Ana River Basin (SANA; 

Belitz and others, 2004); South-Central Texas (SCTX; Ging 

and others, 1997; Ging, 1999; Bush and others, 2000); Upper 

Illinois River Basin (UIRB; Fitzpatrick and Colman, 1992; 

Groschen and others, 2001); and Upper Mississippi River 

Basin (UMIS; Andrews and others, 1995; Stark and others, 

2001).

Potential Sources of Volatile Organic 

Compounds in Urban Streams

Urban environments provide many potential sources of 

VOCs to surface waters. Some VOCs found in urban streams 

and rivers may be associated with their use in gasoline and 

other petroleum products, or as industrial solvents, carriers, 

and solvents in pesticides and paints (U.S. Environmental 

Protection Agency, 1999b). Other VOCs may be associated with their use as metal degreasers, industrial solvents, 

dry-cleaning agents, paint and ink formulations, synthetic 

polymers, and plastic wrap, and are usually associated with 

groundwater (U.S. Environmental Protection Agency, 1999b, 

2000b). Some VOCs also may be formed in chlorinated drinking water by the reaction of free chlorine with organic matter 

(Ivahnenko and Zogorski, 2006). Some VOCs reported in 

urban streams have the potential to originate from the atmosphere (Pankow and others, 1997; Lopes and Bender, 1998; 

Lopes and others, 2000; Bender and others, 2000; Scott J. 

Kenner, U.S. Geological Survey, oral commun., 2006) and 

runoff from parking lots (Lopes and others, 2000). Many 

organic compounds may be scavenged from the atmosphere 

by precipitation (Kawamura and Kaplan, 1983; Ligocki and 

others, 1985; Knap and others, 1988; Dewulf and Langenove, 

1999; Lopes and others, 2000). Surface waters are vulnerable to many contaminants from one or more sources in the 

upstream watershed (for example, point-source discharges and 

stormwater) but also have a potential to reduce the occurrence and concentrations of contaminants through dilution and 

outgassing to the atmosphere.

Acknowledgments

The authors would like to thank USGS field personal for 

the long hours spent collecting and processing the samples. 

Scott J. Kenner, Thomas J. Lopes, and David C. Reutter are 

acknowledged for providing reviews that improved the report.

Study Approach

This section provides an overview of the approach for 

this study. Site selection, field methods, analytical method, 

selection of the VOC data for analyses, quality assurance/

quality control, assessment level, statistical methods, and the 

extension of the streamflow record are described.

Site Selection

As noted previously, urban indicator sites were selected 

to meet certain criteria and assure consistency in data for 

regional and national comparisons. The urban indicator sites 

were selected in residential and commercial land uses and 

ideally were integrated with other NAWQA study components for a more comprehensive understanding of hydrologic, 

chemical, and biological processes in urban environments 

(Lopes and Price, 1997). Ideal settings were drainage areas 

of 19.3 square miles (50 square kilometers) or larger, with 

perennial streamflow and well-defined drainage boundaries. Ideally, the sampling reaches were to have riparian and 

channel conditions representative of the urban setting and 

have channels suitable for ecological studies. The drainage 

for the urban indicator sites could contain urban stormwater 

but not have point sources or large industrial and agricultural 

land uses because these sources can mask the water-quality 

signature of the residential/commercial land use (Lopes and 

Price, 1997). The population density of the drainage basin was 

to be representative of the residential/commercial areas in the 

metropolitan statistical area (MSA), and the age of the urban 

development should be known.

Field Methods

Water samples and associated field quality-assurance/

quality-control (QA/QC) samples were collected following guidelines described in Shelton (1997) and in the USGS 

National Field Manual (U.S. Geological Survey, variously 

dated). Briefly, VOC stream samples were collected with the 

VOC hand sampler at the centroid of the stream or by hand 

dipping sample vials if the VOC sampler could not be fully 

submerged in the stream. All VOC samples were preserved 

with 1:1 hydrochloric acid to a pH of 2, chilled to 4 degrees 

Celsius (°C), and shipped to the NWQL for analysis. Field 

quality-control samples included source-solution and field 

blanks, replicate samples, and field matrix spikes following 

guidelines described in Shelton (1997) and Mueller and others 

(1997).
Study Approach 7

Analytical Method

The VOC samples from the urban streams were 

analyzed at the NWQL using the low-level analytical method 

described in Connor and others (1998). The method analyzes 

for 87 VOCs (table 1) by purge and trap gas chromatography/mass spectrometry (GC/MS) and tentatively identifies unknowns within the sample. Because m- and p-xylene 

co-elute in the method, the reported concentration is counted 

as one compound in the analyses and results for individual 

VOCs. The use of GC/MS provides enhanced qualitative 

compound identification before the determination of the 

compound’s concentration. The reporting by NWQL of 

low-level concentrations is supported, in part, by the use of 

laboratory QA/QC samples including, for example, bracketing 

blanks. The method also uses a long-term method detection 

level (LT–MDL) that accounts for the long-term variance of 

multiple instruments, multiple operators, and multiple calibrations for individual compounds over several months in a year 

(Connor and others, 1998; Childress and others, 1999). The 

LT–MDL varies for each compound and also can vary with 

time. The method reports concentrations below the lowest 

calibration standard as estimated using an “E” remark code 

(Childress and others, 1999).

Selection of Volatile Organic Compound Data

The results of the VOC analyses for the urban stream 

samples were retrieved from the USGS NAWQA data warehouse (http://water.usgs.gov/nawqa/data) on March 4, 2004. 

The selection criteria required that a site be classified as an 

urban indicator site, have samples collected over a minimum 

of 6 months, and have a minimum of six samples spread 

over the sampling period. These selection criteria resulted in 

903 samples from 37 urban indicator sites. The 37 sites are 

listed and described in table 2. Information given for each 

site includes the major river basin and Study Unit in which 

the site is located, station name and identification number, 

drainage area, MTBE-use area, percentage of urban land use 

in the watershed, sampling period, and estimated streamflow 

pentiles. MTBE-use areas are classified as low or high, with 

high MTBE use in areas of the United States where MTBE 

was present in gasoline at higher levels (greater than or equal 

to 3 percent by volume in gasoline) during the sampling period 

(Moran and others, 2004). The Spokane River (site 12424500), 

with a large drainage area, is included because it was classified 

as an urban indicator site and because of the rapid urbanization 

in the lower part of the basin (at and upstream from the urban 

indicator site).

Some samples for VOC analysis are diluted at the NWQL 

because of known or suspected large concentrations or sample 

foaming. When samples are diluted, the reporting levels for 

the analyses are raised in the same ratio as the sample dilution (for example, a twofold dilution raises the reporting 

levels by a factor of 2). A review of the dilution ratios for the 

903 samples resulted in 869 samples that were not diluted 

or diluted only twofold (that is, 50–50 dilution; fig. 2). The 

remaining 34 analyses were removed from further consideration in this report because dilution ratios greater than 2 

raise the laboratory reporting levels larger than most reported 

concentrations for urban streams. Removal of the 34 samples 

diluted three or more times does not affect the individual VOC 

occurrence and concentration summaries, with the exception 

of methyl butyl ketone, which would have had more frequent 

occurrence and larger concentrations if the 34 samples had 

been retained in the dataset.

Quality Assurance/Quality Control

The VOC dataset and field QA/QC samples from the 

37 sites were reviewed for systematic contamination before 

attempting to interpret the environmental data. Characterization of systematic contamination in surface-water samples 

was based on data from associated source-solution and 

field-equipment blanks. Systematic contamination is defined 

as one-directional and typically similar in magnitude. Three 

guidelines were used to determine systematic contamination: 

(1) direct evidence of contamination, (2) the contamination 

is sufficiently understood to allow some interpretation of the 

environmental data (generally, this requires that the contamination can be shown to be systematic and that the source and 

magnitude can be identified), and (3) the concentration of 

the contamination is substantial relative to the environmental 

concentration.

Source-solution blanks are blanks used to describe the 

quality of the source of water used for field-equipment blanks 

and the degree to which the composition of the blank solution 

could have changed from the time of laboratory certification 

to the time of use (U.S. Geological Survey, variously dated). 

Field-equipment blanks are used to determine the concentrations of target analytes that could be present in environmental 

samples attributable to field procedures for equipment cleaning and sample handling (U.S. Geological Survey, variously 

dated). Table 3 provides a summary of VOC detections for 

source-solution and field-equipment blank samples collected 

as part of the urban stream sampling. Because VOCs were 

detected in source-solution blanks and the subsequent fieldequipment blanks, a study was completed to evaluate carryover contamination of VOCs (Taglioli and others, 2000). The 

carryover study showed that, even when source-solution water 

containing VOCs was used to collect field-equipment blanks, 

VOCs did not carryover to subsequently collected surfacewater samples. This was likely due to extensive rinsing with 

native water prior to sample collection. Concentrations of 

VOCs detected in field-equipment blanks generally were less 

than or equal to 0.02 μg/L.

None of the 869 urban stream samples showed systematic contamination and, therefore, no additional samples were 

removed before analyses and interpretations. The urban stream 

VOC dataset was not reviewed for random contamination.
Table 1. Volatile organic compounds included in the U.S. Geological Survey’s National Water-Quality Assessment Program.—

Continued

[USGS, U.S. Geological Survey; VOC, volatile organic compound; --, not applicable]

Compound name Chemical Abstract 

Service number1

USGS 

parameter 

code

VOC group Alternate name or 

abbreviation

Bromomethane 74–83–9 34413 Fumigant --

Dibromochloropropane 96–12–8 82625 Fumigant DBCP; 1,2-Dibromo-3-chloropropane.

1,4-Dichlorobenzene 106–46–7 34571 Fumigant --

1,2-Dichloropropane 78–87–5 34541 Fumigant --

cis-1,3-Dichloropropene 10061–01–5 34704 Fumigant --

trans-1,3-Dichloropropene 10061–02–6 34699 Fumigant --

Ethylene dibromide 106–93–4 77651 Fumigant EDB; 1,2-Dibromoethane.

1,2,3-Trichloropropane 96–18–4 77443 Fumigant --

Benzene 71–43–2 34030 Gasoline hydrocarbon --

n-Butylbenzene 104–51–8 77342 Gasoline hydrocarbon --

sec-Butylbenzene 135–98–8 77350 Gasoline hydrocarbon --

tert-Butylbenzene 98–06–6 77353 Gasoline hydrocarbon --

Ethylbenzene 100–41–4 34371 Gasoline hydrocarbon --

2-Ethyltoluene 611–14–3 77220 Gasoline hydrocarbon 1-Ethyl-2-methylbenzene.

Isopropylbenzene 98–82–8 77223 Gasoline hydrocarbon --

4-Isopropyltoluene 99–87–6 77356 Gasoline hydrocarbon --

Naphthalene 91–20–3 34696 Gasoline hydrocarbon --

Styrene 100–42–5 77128 Gasoline hydrocarbon Ethenylbenzene.

Toluene 108–88–3 34010 Gasoline hydrocarbon Methylbenzene.

1,2,3-Trimethylbenzene 526–73–8 77221 Gasoline hydrocarbon --

1,2,4-Trimethylbenzene 95–63–6 77222 Gasoline hydrocarbon --

1,3,5-Trimethylbenzene 108–67–8 77226 Gasoline hydrocarbon --

1,2,3,4-Tetramethylbenzene 488–23–3 49999 Gasoline hydrocarbon --

1,2,3,5-Tetramethylbenzene 527–53–7 50000 Gasoline hydrocarbon --

o-Xylene 95–47–6 77135 Gasoline hydrocarbon 1,2-Dimethylbenzene.

m- and p-Xylene m:108–38–3 

p:106–42–3

85795 Gasoline hydrocarbon 1,3- and 1,4-Dimethylbenzene.

tert-Amyl methyl ether 994–05–8 50005 Gasoline oxygenate TAME.

Diisopropyl ether 108–20–3 81577 Gasoline oxygenate DIPE.

Ethyl tert-butyl ether 637–92–3 50004 Gasoline oxygenate ETBE.

Methyl tert-butyl ether 1634–04–4 78032 Gasoline oxygenate MTBE; 2-Methoxy-2-methyl propane.

Acrolien 107–02–8 34210 Organic synthesis compound 2-Propenal.

Acrylonitrile 107–13–1 34215 Organic synthesis compound 2-Propenenitrile.

Bromochloromethane 74–97–5 77297 Organic synthesis compound --

Carbon disulfide 75–15–0 77041 Organic synthesis compound --

3-Chloro-1-propene 107–05–1 78109 Organic synthesis compound --

trans-1,4-Dichloro-2-butene 110–57–6 73547 Organic synthesis compound --

1,1-Dichloroethene 75–35–4 34501 Organic synthesis compound --

1,3-Dichloropropane 142–28–9 77173 Organic synthesis compound --

2,2-Dichloropropane 594–20–7 77170 Organic synthesis compound --

1,1-Dichloropropene 563–58–6 77168 Organic synthesis compound --

Ethyl methacrylate 97–63–2 73570 Organic synthesis compound --

Hexachlorobutadiene 87–68–3 39702 Organic synthesis compound --

Iodomethane 74–88–4 77424 Organic synthesis compound Methyl iodide.

Methyl acrylate 96–33–3 49991 Organic synthesis compound --

Methyl acrylonitrile 126–98–7 81593 Organic synthesis compound --

8 Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003
Table 1. Volatile organic compounds included in the U.S. Geological Survey’s National Water-Quality Assessment Program.—

Continued

[USGS, U.S. Geological Survey; VOC, volatile organic compound; --, not applicable]

Compound name Chemical Abstract 

Service number1

USGS 

parameter 

code

VOC group Alternate name or 

abbreviation

Methyl methacrylate 80–62–6 81597 Organic synthesis compound --

1,2,3-Trichlorobenzene 87–61–6 77613 Organic synthesis compound --

Vinyl acetate 108–05–4 77057 Organic synthesis compound --

Vinyl bromide 593–60–2 50002 Organic synthesis compound Bromoethene.

Vinyl chloride 75–01–4 39175 Organic synthesis compound Chloroethene.

Dichlorodifluoromethane 75–71–8 34668 Refrigerant CFC–12.

Trichlorofluoromethane 75–69–4 34488 Refrigerant CFC–11.

Trichlorotrifluoroethane 76–13–1 77652 Refrigerant CFC–113; 1,1,2-Trichloro-1,2,2-trifluoroethane.

Acetone 67–64–1 81552 Solvent 2-Propanone.

Bromobenzene 108–86–1 81555 Solvent --

Carbon tetrachloride 56–23–5 32102 Solvent Tetrachloromethane.

Chlorobenzene 108–90–7 34301 Solvent --

Chloroethane 75–00–3 34311 Solvent --

Chloromethane 74–87–3 34418 Solvent Methyl chloride.

2-Chlorotoluene 95–49–8 77275 Solvent --

4-Chlorotoluene 106–43–4 77277 Solvent --

1,2-Dichlorobenzene 95–50–1 34536 Solvent --

1,3-Dichlorobenzene 541–73–1 34566 Solvent --

1,1-Dichloroethane 75–34–3 34496 Solvent --

1,2-Dichloroethane 107–06–2 32103 Solvent --

cis-1,2-Dichloroethene 156–59–2 77093 Solvent --

trans-1,2-Dichloroethene 156–60–5 34546 Solvent --

Diethyl ether 60–29–7 81576 Solvent --

Dibromomethane 74–95–3 30217 Solvent Methylene bromide.

Hexachloroethane 67–72–1 34396 Solvent 1,1,1,2,2,2-Hexachloroethane.

Methyl butyl ketone 591–78–6 77103 Solvent 2-Hexanone.

Dichloromethane 75–09–2 34423 Solvent Methylene chloride. 

Methyl ethyl ketone 78–93–3 81595 Solvent 2-Butanone.

Methyl isobutyl ketone 108–10–1 78133 Solvent 4-Methyl-2-pentanone.

Perchloroethene 127–18–4 34475 Solvent PCE; Tetrachloroethene.

n-Propylbenzene 103–65–1 77224 Solvent --

1,1,1,2-Tetrachloroethane 630–20–6 77562 Solvent --

1,1,2,2-Tetrachloroethane 79–34–5 34516 Solvent --

Tetrahydrofuran 109–99–9 81607 Solvent --

1,2,4-Trichlorobenzene 120–82–1 34551 Solvent --

1,1,1-Trichloroethane 71–55–6 34506 Solvent --

1,1,2-Trichloroethane 79–00–5 34511 Solvent --

Trichloroethene 79–01–6 39180 Solvent TCE.

Bromoform 75–25–2 32104 Trihalomethane (THM) Tribromomethane.

Bromodichloromethane 75–27–4 32101 Trihalomethane (THM) --

Chloroform 67–66–3 32106 Trihalomethane (THM) Trichloromethane.

Dibromochloromethane 124–48–1 32105 Trihalomethane (THM) --

1

This report contains Chemical Abstract Service numbers (CASRN)®, which is a Registered Trademark of the American Chemical Society. A CASRN is a 

numeric identifier that can contain up to nine digits, divided by dashes into three parts. For example, 67–66–3 is the CASRN for chloroform. The online database 

provides a source for the latest registry number information: http://www.cas.org/. Chemical Abstracts Services recommends the verification of the CASRNs 

through CAS Client ServicesSM.

Study Approach 9
Table 2. List of urban stream sampling sites by major river basin and Study Unit with drainage area, use areas of methyl tert-butyl ether (MTBE), percentage urban land use in 

basin, sampling dates, and streamflow discharge statistics by pentile.—Continued[<, less than; ≤, less than or equal to; ≥, greater than or equal to; --, no data]

Study 

Unit 

abbreviation

(see 

fig. 1)

Station name

Station 

identification 

number

Drainage 

area 

(square 

miles)

MTBEuse 

area

Percentage 

urban 

land use 

in basin

Sample dates

(month/day/year)

Discharge range in each of the streamflow pentiles 

(cubic feet per second1

)

Begin End

≤20 

percent

1

20–<40 

percent

2

40–<60 

percent

3

60–<80 

percent

4

≥80 

percent

5

New England and Mid-Atlantic Major River Basin2

NECB Aberjona River at 

Winchester, Mass.

01102500 27.4 High 79.3 05/14/1999 03/28/2000 <7.7 7.7–<16 16–<27 27–≤47 ≥47

CONN Norwalk River at 

Winnipauk, Conn.

01209710 33 High 50.2 11/30/2001 09/24/2002 <9.6 9.6–<23 23–<44 44–<82 ≥82

LINJ Saddle River at 

Ridgewood, N.J.

01390500 21.6 High 90.0 05/01/1996 01/28/1997 <9.0 9.0–<16 16–<24 24–<41 ≥41

LINJ Bound Brook at 

Middlesex, N.J.

01403900 48.4 High 75.0 04/23/1996 07/09/2002 <16 16–<29 29–<47 47–<82 ≥82

LINJ Great Egg Harbor River 

near Sicklerville, N.J.

01410784 15.1 High 35.8 04/01/1996 03/17/1998 <5.2 5.2–<9.4 9.4–<14 14–<21 ≥21

DELR Little Neshaminy Creek 

at Valley Road near Neshaminy, Pa.

01464907 26.8 High 37.3 02/11/1999 10/12/2000 <5.9 5.9–<12 12–<24 24–<58 ≥58

DELR Cooper River at 

Haddonfield, N.J.

01467150 17 High 69.4 12/03/1998 10/02/2000 <11 11–<15 15–<22 22–<32 ≥32

LSUS Cedar Run at 

Eberlys Mill, Pa.

01571490 12.6 High 59.0 01/10/1994 08/09/1995 <6.7 6.7–<9.5 9.5–<14 14–<20 ≥20

PODL Accotink Creek near 

Annandale, Va.

01654000 23.9 High 85.2 10/23/2001 09/10/2002 <3.7 3.7–<7.8 7.8–<13 13–<27 ≥27

South Atlantic-Gulf and Tennessee Major River Basin2

ALBE Swift Creek near Apex, 

N.C.

02087580 21 Low 33.2 10/12/2001 07/14/2003 <1.0 1.0–<3.9 3.9–<10 10–<21 ≥21

SANT Gills Creek at Columbia, 

S.C.

02169570 59.6 Low 48.9 02/22/1996 03/24/1998 <21 21–<35 35–<57 57–<99 ≥99

GAFL Rocky Creek at State 

Highway 587 at Citrus Park, Fla.

02306774 17.5 Low 40.8 01/31/2002 07/16/2003 <0.3 0.3–<1.2 1.2–<4.2 4.2–<14 ≥14

ACFB Sope Creek near 

Marietta, Ga.

02335870 29.2 Low 60.7 10/11/2001 09/06/2002 <13 13–<20 20–<28 28–<47 ≥47

10 Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003
Table 2. List of urban stream sampling sites by major river basin and Study Unit with drainage area, use areas of methyl tert-butyl ether (MTBE), percentage urban land use in 

basin, sampling dates, and streamflow discharge statistics by pentile.—Continued[<, less than; ≤, less than or equal to; ≥, greater than or equal to; --, no data]

Study 

Unit 

abbreviation

(see 

fig. 1)

Station name

Station 

identification 

number

Drainage 

area 

(square 

miles)

MTBEuse 

area

Percentage 

urban 

land use 

in basin

Sample dates

(month/day/year)

Discharge range in each of the streamflow pentiles 

(cubic feet per second1)

Begin End

≤20 

percent

1

20–<40 

percent

2

40–<60 

percent

3

60–<80 

percent

4

≥80 

percent

5

South Atlantic-Gulf and Tennessee Major River Basin2—Continued

MOBL Three Mile Branch at 

North Boulevard at Montgomery, Ala.

02419977 8.79 Low 82.5 01/12/1999 06/07/2001 <3.6 3.6–<5.1 5.1–<7.6 7.6–<16 ≥16

MOBL Cahaba Valley Creek at 

Cross Creek Road at Pelham, Ala.

0242354750 25.6 Low 11.8 01/06/1999 06/28/2001 <8.2 8.2–<13 13–<26 26–<50 ≥50

Great Lakes, Ohio, Upper Mississippi, and Souris-Red-Rainy Major River Basin2

ALMN Deer Creek near 

Dorseyville, Pa.

03049646 27 Low 14.5 01/27/1997 08/26/1998 <7.6 7.6–<16 16–<18 18–<31 ≥31

WHMI Little Buck Creek near 

Indianapolis, Ind.

03353637 17 Low 54.9 03/14/2001 09/25/2002 <1.3 1.3–<6.9 6.9–<12 12–<23 ≥23

WHMI Holes Creek in Huffman 

Park at Kettering, Ohio

393944084120700 19 Low 65.4 03/09/1999 09/11/2002 <2.4 2.4–<6.5 6.5–<14 14–<28 ≥28

WMIC Lincoln Creek at 

47th Street at Milwaukee, Wis.

040869415 9.56 Low 90.8 11/14/2001 09/10/2002 <1.2 1.2–<2.0 2–<3 3–<6.6 ≥6.6

LERI Clinton River at Sterling 

Heights, Mich.

04161820 309 Low 29.0 10/31/1996 06/03/1998 <122 122–<180 180–<250 250–<360 ≥360

UMIS Shingle Creek at 

Queen Avenue in Minneapolis, Minn.

05288705 28.2 Low 70.4 08/05/1996 11/10/1998 <2.3 2.3–<4.5 4.5–<9.8 9.8–<27 ≥27

UMIS Nine Mile Creek near 

James Circle at Bloomington, Minn.

05330902 44.6 Low 79.6 01/21/1997 12/22/1997 <0.9 0.9–<2.7 2.7–<8.8 8.8–<28 ≥28

UIRB Salt Creek at Western 

Springs, Ill.

05531500 115 Low 81.5 03/02/1999 03/08/2000 <66 66–<89 89–<128 128–<223 ≥223

Study Approach 11
Table 2. List of urban stream sampling sites by major river basin and Study Unit with drainage area, use areas of methyl tert-butyl ether (MTBE), percentage urban land use in 

basin, sampling dates, and streamflow discharge statistics by pentile.—Continued[<, less than; ≤, less than or equal to; ≥, greater than or equal to; --, no data]

Study 

Unit 

abbreviation

(see 

fig. 1)

Station name

Station 

identification 

number

Drainage 

area 

(square 

miles)

MTBEuse 

area

Percentage 

urban 

land use 

in basin

Sample dates

(month/day/year)

Discharge range in each of the streamflow pentiles 

(cubic feet per second1

)

Begin End

≤20 

percent

1

20–<40 

percent

2

40–<60 

percent

3

60–<80 

percent

4

≥80 

percent

5

Missouri Major River Basin2

SPLT Cherry Creek at Denver, 

Colo.

06713500 409 Low 11.5 10/10/2001 09/05/2002 <12 12–<18 18–<25 25–<41 ≥41

Lower Mississippi, Arkanasas-White-Red, and Texas-Gulf Major River Basin2

MISE Fletcher Creek at 

Sycamore View Road at Memphis, Tenn.

07031692 30.5 Low 54.3 10/01/1996 09/24/1997 <0.8 0.8–<2.8 2.8–<6.5 6.5–<26 ≥26

ACAD Dawson Creek at 

Bluebonnet Boulevard near Baton Rouge, La.

07379960 15.1 Low 90.2 01/14/1999 02/09/2001 <1.8 1.8–<6.4 6.4–<19 19–<94 ≥94

TRIN White Rock Creek at 

Greenville Avenue, Dallas, Tex.

08057200 66.4 High 61.2 10/10/2001 09/11/2002 <13 13–<25 25–<43 43–<84 ≥84

SCTX Salado Creek at Loop 13 

at San Antonio, Tex.

08178800 189 Low 41.3 01/23/1997 01/31/1998 <9.3 9.3–<15 15–<22 22–<37 ≥37

Rio Grande, Colorado, and Great Basin Major River Basin2

NVBR Las Vegas Wash below 

Flamingo Wash confluence near Las Vegas, Nev.

094196783 1,352 Low 9.9 10/11/2001 08/20/2002 <4.7 4.7–<6.7 6.7–<9.4 9.4–<11 ≥11

GRSL Little Cottonwood Creek 

at Jordan River near Salt Lake City, Utah

10168000 46 Low 26.8 03/23/1999 04/20/2000 <0.9 0.9–<3.9 3.9–<9.3 9.3–<21 ≥21

California Major River Basin2

SANA Warm Creek near 

San Bernardino, Calif.

11060400 11 High 84.6 11/16/1998 06/13/2002 <0.6 0.6–<2.3 2.3–<6.9 6.9–<20 ≥20

SACR Arcade Creek near Del 

Paso Heights, Calif.

11447360 31.4 High 95.4 03/05/1996 04/23/1998 <0.9 0.9–<1.8 1.8–<2.8 2.8–<5.3 ≥5.3

12 Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003
Table 2. List of urban stream sampling sites by major river basin and Study Unit with drainage area, use areas of methyl tert-butyl ether (MTBE), percentage urban land use in 

basin, sampling dates, and streamflow discharge statistics by pentile.—Continued[<, less than; ≤, less than or equal to; ≥, greater than or equal to; --, no data]

Study 

Unit 

abbreviation

(see 

fig. 1)

Station name

Station 

identification 

number

Drainage 

area 

(square 

miles)

MTBEuse 

area

Percentage 

urban 

land use 

in basin

Sample dates

(month/day/year)

Discharge range in each of the streamflow pentiles 

(cubic feet per second1)

Begin End

≤20 

percent

1

20–<40 

percent

2

40–<60 

percent

3

60–<80 

percent

4

≥80 

percent

5

Pacific Northwest Major River Basin2

PUGT Thornton Creek near 

Seattle, Wash.

12128000 12.1 Low 94.4 03/07/1996 05/14/1998 <5.6 5.6–<7.8 7.8–<10 10–<16 ≥16

NROK Spokane River at 7 Mile 

Bridge near Spokane, Wash.

12424500 5,020 Low 3.2 02/09/1999 10/21/1999 <1,980 1,980–

<2,660

2,660–

<5,360

5,360–

<11,860

≥11,860

WILL Fanno Creek at Durham, 

Oreg.

14206950 31.5 Low 75.7 03/01/1993 09/24/2002 <3.0 3.0–<10 10–<32 32–<55 ≥55

Alaska Basins2

COOK Chester Creek at Arctic 

Boulevard at Anchorage, Alaska

15275100 27.4 Low -- 01/19/1999 09/08/1999 <12 12–<16 16–<20 20–<26 ≥26

Hawaii Basins2

OAHU Manoa Stream at 

Kanewai Field, Honolulu, Oahu, Hawaii

16242500 5.05 Low -- 07/22/1999 06/20/2000 <4.3 4.3–<5.9 5.9–<7.9 7.9–<14 ≥14

1Discharge range in each of the streamflow pentiles based on the most recent 20-year discharge record from the last sampling date (see “Streamflow Record Extension” section).2Seaber and others (1987).

Study Approach 13
Figure 2. Number of samples by dilution ratio of the urban stream samples, 1995–2003.

314

27

5 2

555

555 Number of samples

0

100

200

300

400

500

600

1 2 4 5 10

SAMPLE DILUTION RATIO

NUMBER OF SA

MPLES

869 896 901 903

Cumulative number

 of samples

14 Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003

Assessment Level

An assessment level of 0.02 μg/L was used to compute 

the detection frequencies and concentration summaries of 

VOCs, in part, because of the varying LT–MDLs for each 

compound included in the low-level VOC method. The use 

of an assessment level allows a scientifically based, direct 

comparison between groups of VOCs and between individual 

VOCs. However, detection frequencies computed at this 

assessment level are considered to underestimate the true 

detection in urban streams because of the potential loss of 

information by the censoring of qualified, reported concentrations less than 0.02 μg/L. The statistical summary for 

concentrations is based on all the samples with concentrations censored at the assessment level of 0.02 μg/L. Most of 

the samples had VOC concentrations that were less than the 

assessment level (that is, less than (<) 0.02 μg/L). Median 

concentrations of detections in the report are for the subset of 

samples that had concentrations equal to or greater than the 

assessment level. Total VOC concentrations were calculated as 

the sum of all quantified concentrations (at an assessment level 

of 0.02 μg/L or greater) for all VOCs analyzed in a sample. 

Moran and others (2006) provide a more detailed discussion of 

applying an assessment level to water-quality datasets.

Statistical Methods

 Non-parametric statistics were used in the analyses 

presented in this report because the data were not assumed 

to be normally distributed. Information on the statistical tests 

can be found in Helsel and Hirsch (1992) and Ott and Longnecker (2001). All statistical tests used a significance value 

(α) of 0.05 for all two-sided test statistics. All statistical tests 

used within this report provide the probability (p-value) for 

the comparisons of the test. The p-value is a measure of the 

confidence that what is observed in the sample is true for the 

population. This significance value was used as the acceptance 

level for the subsequent test statistics (that is, accept null 

hypothesis if p-value is less than α). A Wilcoxon rank-sum test 

was used to compare two independent groups of continuous 

data. A Wilcoxon sign-rank test was used to compare paired 

data. The alternative hypothesis states that observations from 

one group tend to produce larger (or smaller) values compared 

to the other group (Helsel and Hirsch, 1992). The Wilcoxon 

rank-sum and sign-rank tests report a standardized normal 

score (Z value) and the probability (p-value). An example of 

this is the comparison between total VOC concentrations in 

warmer and cooler months. If the alternative hypothesis is 

rejected, then the total concentrations are larger (or smaller) 
Table 3. Statistical summaries of analytical results for volatile organic compounds in source-solution and field-equipment blank samples from 37 urban stream sites at no 

assessment level, 1995–2003.[E, estimated concentration less than the long-term method detection level; --, not applicable]

Compound

Source-solution blank Field-equipment blank

Number 

of 

samples

Number 

of 

detections

Statistical summary of reported 

concentrations (micrograms per liter) Number of 

samples

Number 

of 

detections

Statistical summary of reported 

concentrations (micrograms per liter)

Minimum 

concentration 

Median 

concentration 

Maximum 

concentration 

Minimum 

concentration 

Median 

concentration 

Maximum 

concentration 

Toluene 32 15 E0.006 E0.024 2.3 104 39 E0.007 E0.023 3.6Chloroform 32 2 .019 -- .040 104 27 E.006 .050 .50m- and p-Xylene 32 8 E.006 E.025 .079 103 17 E.007 .030 .10Ethylbenzene 32 4 E.009 E.014 .038 104 16 E.003 E.010 .040Acetone 32 5 E.95 2.7 3.7 103 15 E.60 2.4 7.2Styrene 32 6 E.003 E.015 .027 104 15 E.003 E.010 .14o-Xylene 32 2 .022 -- .047 103 10 E.010 .019 .038Dichloromethane 32 1 -- -- .054 104 9 E.007 .40 4.71,2-Dichloropropane 32 1 -- -- E.020 104 8 E.009 E.010 .020Tetrahydrofuran 32 1 -- -- E.50 103 8 E.30 E.50 8.1Chloromethane 32 0 -- -- -- 104 7 E.004 E.010 E.0401,4-Dichlorobenzene 32 2 E.003 -- .030 104 7 E.006 E.010 .083Methyl ethyl ketone 32 1 -- -- E.60 103 7 E.20 E.40 1.6Chlorobenzene 32 1 -- -- E.010 104 6 E.004 E.010 .020Carbon disulfide 32 0 -- -- -- 103 6 E.003 E.010 .0201,2,4-Trimethylbenzene 32 2 E.013 -- .043 104 6 E.007 E.018 E.024Benzene 32 1 -- -- .026 104 5 E.008 .016 .034Bromodichloromethane 32 0 -- -- -- 104 4 E.010 E.010 E.0101,1,1-Trichloroethane 32 0 -- -- -- 104 4 E.001 E.015 .0344-Isopropyltoluene 32 0 -- -- -- 104 2 E.005 -- E.008Methyl tert-butyl ether 32 0 -- -- -- 104 2 E.030 -- E.051Perchloroethene 32 1 -- -- E.004 104 2 E.003 -- .013Trichlorofluoromethane 32 1 -- -- 2.5 104 2 .13 -- .171Dichlorodifluoromethane 32 0 -- -- -- 104 1 -- -- E.041Ethyl tert-butyl ether 32 0 -- -- -- 103 1 -- -- .044Isopropylbenzene 32 0 -- -- -- 104 1 -- -- .003Methyl isobutyl ketone 32 0 -- -- -- 103 1 -- -- E.040Naphthalene 32 0 -- -- -- 104 1 -- -- E.020n-Propylbenzene 32 1 -- -- E.012 104 1 -- -- E.003Trichloroethene 32 1 -- -- E.005 104 1 -- -- E.0081,1,2-Trichloro-1,2,2-fluoroethane 32 0 -- -- -- 104 1 -- -- E.007Vinyl chloride 32 0 -- -- -- 104 1 -- -- .050

Study Approach 15
Table 4. Statistical tests used in the report.

[VOC, volatile organic compound; MTBE, methyl tert-butyl ether; NE, not equal, <, less than; >, greater than; Prob, probability or p-value]

Statistical test Test statistic Hypothesis Examples as used in this report

Contingency tables Chi-square (χ2) Null hypothesis: 

H0: The variables are independent

Alternate hypothesis: 

H1: The variables are not independent

Determine the independence of the number of 

detections and number of samples between 

VOC groups, flow pentiles, seasons, low and 

high MTBE-use areas. 

Kolmogorov-Smirnov 

goodness-of-fit test

ks Null hypothesis: 

H0: The data are from the same continuous 

distribution

Alternate hypothesis: 

H1: The data are not from the same distributions

Determine if the concentrations of VOC 

groups, flow pentiles, and seasons of the year 

are from the same distributions.

Kruskal Wallis Chi-square (χ2) Null hypothesis: 

H0: All of the groups of data being compared 

have identical distributions

Alternate hypothesis: 

H1: At least one group differs in its distribution

Determine if the number of VOCs present in 

samples are statistically different.

Wicoxon sign-rank Z Null hypothesis:

H0: Prob[x > y] = 0.5

Alternative hypothesis:

H1: Prob[x > y] NE 0.5

H2: Prob[x > y] > 0.5

H3: Prob[x > y] < 0.5

Determine if the number of samples in warmer 

and cooler months are statistically different.

Wilcoxon rank-sum Z Null hypothesis: 

H0: xi and yi are from same distribution

H0: Prob[xi > yi] = 0.5

Alternate hypothesis:

H1: xi is from a distribution that generally is 

lower than that of yi

H1: Prob[xi > yi] < 0.5

Determine if concentrations are statistically 

different between low and high MTBE-use 

areas, and seasons.

16 Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003

in one season than the other. Alternatively, a one-sided null 

hypothesis was used to determine if warmer months had 

significantly larger concentrations than cooler months using 

α = 0.025 (one-sided test statistics). Contingency tables were 

used to measure the association between categorical variables 

(for example, detection frequency between VOC groups) 

using the chi-square (χ2) statistic to test the null hypothesis. 

The null hypothesis is that the two variables are independent 

(Helsel and Hirsch, 1992). The Kruskal-Wallis rank-sum test 

was performed on the number of VOCs present in samples 

to determine if the number of VOCs present in samples were 

statistically different. The null hypothesis tests that the groups 

of data have identical distributions. The Kolmogorov-Smirnov 

goodness-of-fit test was performed on the total concentrations 

to determine if they were from independent distributions. The 

null hypothesis tests that the two variables are from the same 

continuous distribution. These statistical tests are described in 

table 4.
Occurrence of Volatile Organic Compounds in Urban Streams 17

Streamflow Record Extension

The water quality of urban streams can be affected by 

streamflow. Many of the NAWQA Program’s urban streams 

are small and flashy with short-term (1–2 years) streamflow 

records that limited the ability to compare the water-quality 

results on the basis of streamflow on a national or regional 

scale. A simple and robust methodology was used to estimate 

long-term streamflow percentiles at sites with short-term 

streamflow records. Two methodologies were tested for this 

purpose: (1) Matalas and Jacobs (1964) (also cited in U.S. 

Interagency Advisory Committee on Water Data, 1982) and 

(2) a simple flow-ratio method suggested by Kenneth L. Wahl 

(U.S. Geological Survey, oral commun., 2002), which is an 

adaptation of the normal-ratio method described by Gupta 

(2001), hereafter referred to as the flow-ratio method. The 

flow-ratio method was chosen on the basis of simplicity of 

use, no transformation of data was required, there was no 

serial correlation of data, and an assessment that the flow-ratio 

method provided a reasonable estimate of long-term streamflow characteristics for short-term sites.

An annual cumulative distribution function (CDF) of 

streamflow for each sampling site was calculated on the basis 

of about 20 years of streamflow information for each site. If a 

site had at least 20 years of record, then the annual CDF was 

calculated for the most recent 20-year record (17 of the sites). 

If the site had a short-term streamflow record (1–2 years; 20 

of the sites), then a nearby, hydrologically similar long-term 

gaging station (with at least 17 years of streamflow data) was 

used to estimate streamflow for the sampling site. The longterm streamflow data for the sampling site was then estimated 

on the basis of the ratios of streamflow between the short-term 

site and the long-term gaging station by using the following 

equation (Andrew J. Long, U.S. Geological Survey, written 

commun., April 2007):

LT

ST

LT Q est LT Q conc

Q conc

Q record i

i

i

i ,

,

,

= , , (1)

where LTQ esti , is the estimated long-term streamflow for the 

short term site; STQ conci , and LTQ conci , are the streamflow rates 

for each percentile of interest for the concurrent period of 

record for the short-term site and long-term station, respectively; LTQ recordi , is the streamflow rate for each corresponding percentile for the entire period of record for the long-term 

station; and i indicates the percentile of interest. For example, 

i = 10, 20, ..., 100 for every tenth percentile.

To provide valid sample statistics with a sufficient 

number of samples in each streamflow category, the water 

samples analyzed for VOCs were distributed into five annual 

streamflow pentiles (less than 20, 20 to less than 40, 40 to 

less than 60, 60 to less than 80, and greater than or equal 

to 80 percent of estimated long-term streamflow statistics). 

Table 2 contains a summary of the five pentiles of streamflow 

for each sampling site. VOC occurrence interpretations for 

the five streamflow pentiles are contained in the subsequent 

section “Patterns of VOC Occurrence by Streamflow Pentile.” 

Figures showing the streamflow and annual percentiles of 

streamflow for each site are provided in Appendix 1.

The numbers of samples from the 37 sites per month, in 

warmer and cooler months, and by the five streamflow pentiles 

are shown in table 5. The statistical difference (Wilcoxon signrank two-tailed test statistic (Z) = -2.3496, p-value = 0.0188) 

in the total number of samples is significant between the 

warmer and cooler months, and more samples were collected 

in cooler months (Wilcoxon sign-rank single-tailed test statistic (Z) = -2.3496, p-value = 0.0094).

Occurrence of Volatile Organic 

Compounds in Urban Streams

This section describes the occurrence of VOCs in 

urban streams on the basis of analyses of 869 samples from 

37 urban indicator sites. The occurrence of one or more VOCs, 

VOC groups, and individual VOCs at all sites is presented. 

Detection frequencies and a summary of concentrations are 

presented. Also, for the occurrence of one or more VOCs, a 

summary of the number of VOCs per sample is presented. 

Similarly, occurrence by streamflow pentile and by warmer 

(April through September) and cooler (October through 

March) months also is presented for one or more VOCs, VOC 

groups, and individual VOCs. Comparisons of concentrations 

to the previously noted benchmarks describe the significance 

of VOCs in urban streams to human health and aquatic life.

Overall Occurrence Patterns of Volatile Organic 

Compounds

This section describes the overall patterns of VOC occurrence in urban streams. All samples were included in computations as a group without consideration of streamflow condition 

during sampling or season of the year. The occurrence of one 

or more VOCs, VOC groups, and individual VOCs at all sites 

is presented.

One or More Volatile Organic Compounds

One or more VOCs were detected in 97.1 percent of 

869 samples, and one or more VOCs were detected frequently 

at all sites. Detection frequencies for one or more VOCs 

ranged from 85.7 percent for Fletcher Creek at Memphis, 

Tenn., to 100 percent at 27 of the urban indicator sites.

The median total VOC concentration for all samples was 

0.57 μg/L (fig. 3). The total VOC concentrations ranged from 

not detected to 698 μg/L. About 57 percent of the total VOC 

concentrations were less than or equal to 1 μg/L, and about 

93 percent of concentrations were less than 10 μg/L. The 
Table 5. Number of samples per month, in cooler and warmer months, and in the five streamflow pentiles from 37 urban streams, 

1995–2003.

Streamflow 

pentile

Number of samples Number 

of 

samples 

in cooler 

months

Number 

of 

samples 

in warmer 

months

Total 

number 

of 

samples

Cooler months Warmer months Cooler months

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

Low flow 1 6 7 6 4 4 15 19 11 18 11 14 9 53 71 124

2 21 18 11 6 10 18 9 22 10 18 18 16 102 75 177

3 15 20 13 15 19 8 9 8 6 9 17 14 88 65 153

4 14 26 18 14 22 10 3 7 1 6 15 4 83 57 140

High flow 5 25 25 32 58 23 12 20 17 12 10 16 25 133 142 275

Total number 

of samples

81 96 80 97 78 63 60 65 47 54 80 68 459 410 869

18 Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003

largest total VOC concentrations were dominated by the presence of acetone. The larger total concentrations (>10 μg/L) are 

spatially distributed across the Nation, except for Alaska and 

Hawaii, and occurred at about one-half of the sampling sites 

(17 urban streams). Total VOC concentrations were greater 

than 10 μg/L in about one-half of the samples from two sites, 

Bound Brook at Middlesex, N.J., and Shingle Creek at Queen 

Avenue in Minneapolis, Minn.

The number of VOCs detected per sample ranged from 0 

to 27, with about 84.5 percent of the samples containing two 

or more VOCs (fig. 4). No VOCs were found in 2.9 percent 

of samples and only one VOC was present in 12.6 percent 

of samples. Forty-nine percent of the samples had 5 or more 

VOCs present, and 25 percent of the samples had 8 or more 

VOCs present. The samples with 27 VOCs (1 sample) and 

20 VOCs (2 samples) were collected from Bound Brook at 

Middlesex, N.J. Samples with less than 18 VOCs included 

various samples from all the urban stream sites.

Volatile Organic Compound Groups

The seven VOC groups had statistically different probabilities of occurrence (contingency table χ2

 = 2,531.269, 

degrees of freedom (DF) = 6, p-value = 0) in urban stream 

samples. One or more of the gasoline hydrocarbons occurred 

most frequently and were reported in about 79 percent of 

all samples (fig. 5). Solvents, THMs, and gasoline oxygenates also were detected frequently and were found in about 

71, 55, and 40 percent of samples, respectively. In contrast, 

the organic synthesis compounds, fumigants, and refrigerant compounds were detected in 14, 5.5, and 4.5 percent of 

samples, respectively.

The occurrence of gasoline hydrocarbons was dominated 

by the presence of benzene, toluene, ethylbenzene, and o-, m-, 

and p-xylene (BTEX compounds), which comprised about 78 

percent of the detections of gasoline hydrocarbons (fig. 6). The 

occurrence of solvents was dominated by perchloroethene, 

trichloroethene, cis-1,2-dichloroethene, and acetone, which 

collectively comprised about 64 percent of the solvent 

detections (fig. 7). Also, 22 of the 30 solvent compounds 

analyzed in samples were detected in at least one sample. The 

occurrence of THMs was dominated by chloroform, which 

comprised about 80 percent of the THM detections (fig. 8).

The occurrence of the gasoline oxygenate group was 

dominated by MTBE, which comprised about 87 percent 

of the gasoline oxygenate detections, followed by tert-amyl 

methyl ether (TAME), which comprised about 11 percent 

of the gasoline oxygenate detections (fig. 9). Also, gasoline 

oxygenates had a much higher detection frequency in high 

MTBE-use areas than in low MTBE-use areas of the United 

States with about 70 percent of the detections in the high 

MTBE-use areas (figs. 10 and 11A). MTBE was the most 

frequently detected gasoline oxygenate in both low and 

high MTBE-use areas. TAME had a larger percentage of the 

detections (15 percent) in high MTBE-use areas than in low 

MTBE-use areas (1 percent; fig. 10), similar to results of the 

national survey of MTBE in drinking-water sources for the 

focused survey (Carter and others, 2006). The only detection 

of ethyl tert-butyl ether (ETBE) was in a high MTBE-use area 

(Cooper River at Haddonfield, N.J). Furthermore, the other 

gasoline oxygenate, diisopropyl ether (DIPE), had several 

detections in a low MTBE-use area (Cahaba Valley Creek at 

Cross Creek Road at Pelham, Ala.). The detection frequencies 

for gasoline oxygenates were about 18 percent and 86 percent 

in low and high MTBE-use areas, respectively (fig. 11A), and 

were statistically different (contingency table χ2 = 366.8698, 

DF = 1, p-value = 0) between the low and high MTBE-use 

areas of the United States.

The concentration distributions between VOC groups 

were all statistically different (Kolmogorov-Smirnov (KS) 

p-values < 0.05) except between the fumigants and refrigerants (KS p-value = 0.9999). The median total concentrations 

of samples with detections were as follows: gasoline hydrocarbons, 0.08 μg/L; solvents, 0.87 μg/L; THMs, 0.04 μg/L; 
Figure 3. Cumulative distribution of total concentrations of volatile organic compounds (VOCs) in 869 samples 

from 37 urban stream sites at an assessment level of 0.02 microgram per liter, 1995–2003.

Figure 4. Relation between the percentage of 869 urban stream samples and the number of volatile 

organic compounds (VOCs) detected at an assessment level of 0.02 microgram per liter, 1995–2003.

0.01

0.1

1

10

100

1,000

0 20 40 60 80 100

CUMULATIVE PERCENTAGE OF SAMPLES

TOTAL VOC CONCENTRATION, IN MICROGRAMS PER LITER

Median = 0.57 microgram per liter

0

25

50

75

100

NUMBER OF VOCs IN URBAN STREAM SAMPLES

PERCENTAGE OF URBAN STREAM SAMPLES WITH EQUAL OR GREATER 

NUMBER OF DETECTED VOCs

1 3 5 7 9 11 13 15 17 19 21 23 25 27

97.1 percent

Occurrence of Volatile Organic Compounds in Urban Streams 19
Figure 5. Detection frequencies of seven volatile organic compound (VOC) groups in urban stream samples at an assessment 

level of 0.02 microgram per liter, 1995–2003.

Figure 6. Distribution of the total number of 

detections of gasoline hydrocarbons in urban stream 

samples at an assessment level of 0.02 microgram 

per liter, 1995–2003. Of the 18 gasoline hydrocarbons 

analyzed for in urban stream samples, 17 were 

detected in at least one sample. Benzene, toluene, 

ethylbenzene, and the xylenes constitute the BTEX 

compounds (1,589 detections).

0 10 20 30 40 50 60 70 80 90 100

Gasoline hydrocarbons

Solvents

Trihalomethanes (THMs)

Gasoline oxygenates

Organic synthesis compounds

Fumigants

Refrigerants

VOC GROUP

DETECTION FREQUENCY, IN PERCENT

684/869

39/869

48/869

117/869

348/869

481/869

618/869

Number of detections/

number samples

o-Xylene

(6 percent)

m- and p -Xylenes

(15 percent)

Ethylbenzene

(4 percent)

Toluene

(41 percent)

Benzene

(12 percent)

10 other gasoline

hydrocarbons

(11 percent) 

4-Isopropyltoluene

(5 percent)

1,2,4-

Trimethylbenzene

(7 percent)

20 Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003
Figure 8. Distribution of the total number 

of detections of trihalomethanes in urban 

stream samples at an assessment level of 

0.02 microgram per liter, 1995–2003. Of the 

four trihalomethanes analyzed for in urban 

stream samples, each were detected in at 

least one sample (596 detections).

Figure 7. Distribution of the total number of detections of solvents in urban stream samples at an 

assessment level of 0.02 microgram per liter, 1995–2003. Of the 30 solvents analyzed for in urban 

stream samples, 22 were detected in at least one sample (1,824 detections).

Dichloromethane

(5 percent)

1,1,1-Trichloroethane

(5 percent)

Perchloroethene

(17 percent)

Trichloroethene

(17 percent)

cis-1,2-Dichloroethene

Acetone (16 percent)

(14 percent)

Chloromethane

(7 percent)

Methyl isobutyl ketone

(4 percent) 

14 other solvents

(15 percent)

Bromoform

(2 percent)

Dibromochloromethane

(5 percent)

Bromodichloromethane

(13 percent)

Chloroform

(80 percent)

Occurrence of Volatile Organic Compounds in Urban Streams 21
Figure 10. Distribution of the total number of detections of gasoline oxygenates in urban stream samples in low and high methyl tertbutyl ether (MTBE)-use areas at an assessment level of 0.02 microgram per liter, 1995–2003. The size of the pie represents the proportion 

of detections in the low (113 detections) and high (289 detections) MTBE-use areas.

Figure 9. Distribution of the total number of detections of gasoline 

oxygenates in urban stream samples at an assessment level of 0.02 

microgram per liter, 1995–2003. Of the four gasoline oxygenates 

analyzed for in urban stream samples, each were detected in at 

least one sample (401 detections).

Diisopropyl ether and

ethyl tert-butyl ether

(2 pecent) 

tert-Amyl methyl ether

(11 percent)

Methyl tert-butyl ether

(87 percent)

tert-Amyl methyl ether

(1 percent)

Diisopropyl ether and

ethyl tert-butyl ether

(7 pecent) 

Methyl tert-butyl ether

(92 percent)

Low MTBE-Use Areas High MTBE-Use Areas

Methyl tert-butyl ether

(84 percent)

Diisopropyl ether and

ethyl tert-butyl ether

(1 percent) 

tert-Amyl methyl ether

(15 percent) 

22 Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003
Figure 11. Relation between (A) detection frequencies, and (B) total concentrations for gasoline oxygenates in urban 

stream samples in low and high methyl tert-butyl ether (MTBE)-use areas of the United States at an assessment level of 

0.02 microgram per liter, 1995–2003.

0.28

0.33

0.09

<0.02

0.01 0.1 1 10 100

TOTAL GASOLINE OXYGENATE CONCENTRATION, IN MICROGRAMS PER LITER

High MTBE-use areas

Low MTBE-use areas

244/284

104/585

B

0 10 20 30 40 50 60 70 80 90 100

High MTBE-use areas

Low MTBE-use areas

DETECTION FREQUENCY OF GASOLINE OXYGENATES, IN PERCENT

104/585

244/284

A

Number of detections/

number of samples

Number of detections/

number of samples

Assessment level

Median concentration of all samples

Total concentration for a single sample

Median of concentrations greater than or 

 equal to the assessment level

EXPLANATION

Occurrence of Volatile Organic Compounds in Urban Streams 23

gasoline oxygenates, 0.24 μg/L; organic synthesis compounds, 

0.03 μg/L; fumigants, 0.03 μg/L; and refrigerants, 0.05 μg/L 

(fig. 12). Furthermore, the concentration ranges for most 

groups were distributed over at least two orders of magnitude, with solvent concentrations distributed over more than 

four orders of magnitude. As noted previously, the large total 

concentrations of solvents were affected by large concentrations of acetone in some samples.

The total concentrations of the gasoline oxygenates were 

statistically different between the high and low MTBE-use 

areas of the United States (fig. 11B) with statistically larger 

total gasoline oxygenate concentrations in high MTBE-use 

areas (Wilcoxon rank-sum Z = 9.8648, one-sided p-value = 0). 

The median total gasoline oxygenate concentrations were 

0.09 μg/L and 0.33 μg/L in low and high MTBE-use areas, 

respectively. Furthermore, total gasoline oxygenate concentrations had a much larger concentration range in high 

MTBE-use areas.
0.02

0.18

0.06

0.05

0.03

0.03

0.24

0.04

0.87

0.08

<0.02

<0.02

<0.02

<0.02

0.01 0.1 1 10 100 1,000

TOTAL VOC CONCENTRATION, IN MICROGRAMS PER LITER

VOC GROUP

Gasoline hydrocarbons

Solvents

Trihalomethanes (THMs)

Gasoline oxygenates

Organic synthesis compounds

Fumigants

Refrigerants

684/869

39/869

48/869

117/869

348/869

481/869

618/869

Number of detections/

number of samples

Assessment level

EXPLANATION

Median concentration of all samples

Median of concentrations greater than or equal to 

 the assessment level

Maximum Contaminant Level for trihalomethanes 

 (U.S. Environmental Protection Agency, 2006)

Total concentration for a single sample

Figure 12. Total volatile organic compound (VOC) concentrations in urban stream samples by the seven VOC 

groups at an assessment level of 0.02 microgram per liter, 1995–2003.

24 Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003
Occurrence of Volatile Organic Compounds in Urban Streams 25

Individual Volatile Organic Compounds

Of the 87 VOCs analyzed for in water samples, 

57 compounds were detected at least once in urban streams at 

concentrations greater than or equal to the assessment level of 

0.02 μg/L (table 6). In contrast, 30 VOCs (16 organic synthesis 

compounds, 8 solvents, 5 fumigants, and 1 gasoline hydrocarbon) were not detected at concentrations greater than or equal 

to this assessment level at any of the sites.

Fifteen of the 57 detected VOCs had detection frequencies greater than or equal to 10 percent, and toluene and 

chloroform had detection frequencies greater than 50 percent. 

The 15 most frequently detected compounds (table 6; fig. 13) 

included 5 gasoline hydrocarbons, 1 trihalomethane, 1 gasoline oxygenate, and 8 solvents. No refrigerants, fumigants, or 

organic synthesis compounds were detected in 10 percent or 

more of the samples.

The concentrations of the 15 most frequently detected 

VOCs are shown in figure 14. Collectively, the concentrations 

for these VOCs ranged over almost five orders of magnitude. 

Concentrations ranged over at least 2 orders of magnitude for 

most of the 15 VOCs.

Considering all samples, including those with nondetections (censored values), median concentrations of 

toluene (0.04 μg/L) and chloroform (0.02 μg/L), the two most 

frequently detected compounds, were equal to or greater than 

the assessment level of 0.02 μg/L. The remaining compounds 

had median concentrations less than the assessment level of 

0.02 μg/L when all samples were considered (table 6); these 

censored median concentrations are shown as 0.02 μg/L on 

figure 14). Medians of concentrations greater than or equal 

to the assessment level (referred to as median concentrations 

of the detections) for the 15 most frequently detected VOCs 

ranged from 0.03 μg/L for four compounds to 3.9 μg/L for 

acetone. Most median concentrations of detections were less 

than or equal to 0.10 μg/L, with the exceptions of those for 

MTBE (0.24 μg/L), acetone (3.9 μg/L), and methyl isobutyl 

ketone (0.2 μg/L).

The detection frequencies (contingency table 

χ2 = 366.8698, DF = 1, p-value = 0) and total concentrations 

of MTBE were statistically different between the low and 

high MTBE-use areas of the United States (Wilcoxon ranksum Z = 21.1983, one-sided p-value = 0), with more frequent 

detections and larger MTBE concentrations in high MTBEuse areas than in low MTBE-use areas (fig. 15). MTBE was 

detected in 18 percent of samples from low MTBE-use areas 

and in 86 percent of samples from high MTBE-use areas. The 

median MTBE concentrations were 0.09 μg/L and 0.33 μg/L 

in low and high MTBE-use areas, respectively. Also, the 

MTBE concentrations in high MTBE-use areas had a larger 

range of concentrations than in low MTBE-use areas.

Occurrence Patterns of Volatile Organic 

Compounds by Streamflow Pentile

Many studies have shown that water quality in streams 

varies with streamflow condition (for example, low flow 

compared to high flow; Whitfield and Schreier, 1981; Sanders 

and others, 1983). This section describes the overall patterns 

of occurrence for VOCs in urban streams stratified into the 

five streamflow pentiles. The 869 samples from the 37 sites 

were stratified into five streamflow pentiles (less than 20, 20 to 

less than 40, 40 to less than 60, 60 to less than 80, and greater 

than or equal to 80 percent of estimated long-term streamflow 

statistics) for comparison of the occurrence of VOCs. All of 

the samples for 37 sites were considered as a group. Occurrence for one or more VOCs, VOC groups, and individual 

VOCs at all sites is presented.

One or More Volatile Organic Compounds

The detection frequency of one or more VOCs by 

streamflow pentile is summarized in table 7 and figure 

16. The detection frequencies of one or more VOCs were 

not significantly different (contingency table χ2 = 0.5722, 

DF = 4, p-value = 0.9661) and did not vary markedly among 

the pentiles of streamflow (fig. 16). Detection frequencies 

ranged from 96.7 percent in the fifth pentile (highest flows) to 

97.7 percent in the second pentile (fig. 16).

The median total VOC concentrations in samples for 

each of the streamflow pentiles were 0.39, 1.0, 0.49, 0.45, and 

0.81 μg/L for the first, second, third, fourth, and fifth pentiles, 

respectively (table 7). The total VOC concentrations were 

statistically different (Kruskal-Wallis χ2 = 17.6145, DF = 4, 

p-value = 0.0015) between the streamflow pentiles. The 

distribution of the concentrations in each streamflow pentile 

is shown in figure 17. The second streamflow pentile (20 to 

less than 40 percent of streamflow) had the largest total VOC 

concentrations for about 48 percent of the samples, and the 

fifth pentile (highest streamflow) had the largest total VOC 

concentrations for about 52 percent of the samples. The largest 

total VOC concentration (698 μg/L) was from the second 

streamflow pentile.

The numbers of VOCs detected in samples were statistically different among the streamflow pentiles (Kruskal-Wallis 

χ2 = 12.4974, DF = 4, p-value = 0.014). The total number of 

VOC detections and median number of VOCs reported per 

sample were highest in the fifth pentile (1,657 VOC detections 

and 6 VOCs per sample; table 7). The lowest total number of 

VOC detections and median number of VOCs were in the first 

pentile (554 VOC detections and 3 VOCs per sample). The 

first and fourth pentiles had a maximum of 16 VOCs present 
Table 6. Summary of the detection frequencies and concentrations of volatile organic compounds at an assessment level of 0.02 microgram per liter, 1995–2003, listed in order 

of decreasing detection frequency.—Continued[VOC, volatile organic compound; <, less than; ND, not detected; E, estimated]

Compound name VOC group Number of sites Number of samples

Number of 

samples 

with 

detections

Detection 

frequency 

(percent)

Statistical summary for concentrations including non-detections 

(micrograms per liter)

Minimum 25th percentile Median 75th percentile Maximum

Toluene Gasoline hydrocarbon 37 867 648 75 <0.04 <0.04 0.04 0.09 11Chloroform Trihalomethane (THM) 37 869 480 55 <.02 <.02 .02 .04 1.9Methyl tert-butyl ether Gasoline oxygenate 37 869 348 40 <.11 <.11 <.11 .15 44Trichloroethene Solvent 37 869 299 34 <.04 <.04 <.04 .05 1.5Perchloroethene Solvent 37 869 297 34 <.03 <.03 <.03 .04 1.1cis-1,2-Dichloroethene Solvent 37 869 294 34 <.02 <.02 <.02 .04 7.6Acetone Solvent 36 856 261 30 <4.9 <4.9 <4.9 1.7 698m- and 

p-Xylene Gasoline hydrocarbon 36 856 239 28 <.06 <.06 <.06 E.02 .69

Benzene Gasoline hydrocarbon 37 869 194 22 <.02 <.02 <.02 <.02 .21Chloromethane Solvent 37 868 128 15 <.17 <.17 <.17 <.17 .301,2,4-Trimethylbenzene Gasoline hydrocarbon 37 869 108 12 <.06 <.06 <.06 <.06 .99o-Xylene Gasoline hydrocarbon 36 856 97 11 <.04 <.04 <.04 <.04 .36Dichloromethane Solvent 37 869 95 11 <.06 <.06 <.06 <.06 1.41,1,1-Trichloroethane Solvent 37 869 94 11 <.03 <.03 <.03 <.03 1.3Methyl isobutyl ketone Solvent 36 856 82 10 <.37 <.37 <.37 <.37 1.5Carbon disulfide Organic synthesis 

compound

36 856 81 9.5 <.04 <.04 <.04 <.04 .20

Methyl ethyl ketone Solvent 36 855 78 9.1 <1.6 <1.6 <1.6 <1.6 5.7Bromodichloromethane Trihalomethane (THM) 37 869 77 8.9 <.03 <.03 <.03 <.03 .884-Isopropyltoluene Gasoline hydrocarbon 37 869 74 8.5 <.07 <.07 <.07 <.07 2.11,1-Dichloroethane Solvent 37 869 66 7.6 <.03 <.03 <.03 <.03 .16Ethylbenzene Gasoline hydrocarbon 37 869 60 6.9 <.03 <.03 <.03 <.03 .13Chlorobenzene Solvent 37 869 46 5.3 <.03 <.03 <.03 <.03 .371,4-Dichlorobenzene Fumigant 37 868 45 5.2 <.03 <.03 <.03 <.03 .26tert-Amyl methyl ether Gasoline oxygenate 36 856 44 5.1 <.08 <.08 <.08 <.08 .17Naphthalene Gasoline hydrocarbon 37 869 38 4.4 <.25 <.25 <.25 <.25 .301,1-Dichloroethene Organic synthesis 

compound

37 869 31 3.6 <.02 <.02 <.02 <.02 .06

26 Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003
Table 6. Summary of the detection frequencies and concentrations of volatile organic compounds at an assessment level of 0.02 microgram per liter, 1995–2003, listed in order 

of decreasing detection frequency.—Continued[VOC, volatile organic compound; <, less than; ND, not detected; E, estimated]

Compound name VOC group Number of sites Number of samples

Number of 

samples 

with 

detections

Detection 

frequency 

(percent)

Statistical summary for concentrations including non-detections 

(micrograms per liter)

Minimum 25th percentile Median 75th percentile Maximum

Dibromochloromethane Trihalomethane (THM) 37 868 29 3.3 <0.1 <0.1 <0.1 <0.1 0.501,2,3-Trimethylbenzene Gasoline hydrocarbon 36 856 28 3.3 <.06 <.06 <.06 <.06 .22Styrene Gasoline hydrocarbon 37 869 27 3.1 <.04 <.04 <.04 <.04 .10Trichlorotrifluoroethane Refrigerant 37 869 27 3.1 <.03 <.03 <.03 <.03 .151,3,5-Trimethylbenzene Gasoline hydrocarbon 37 869 24 2.8 <.04 <.04 <.04 <.04 .252-Ethyltoluene Gasoline hydrocarbon 36 856 22 2.6 <.06 <.06 <.06 <.06 .18Tetrahydrofuran Solvent 36 856 22 2.6 <1.2 <1.2 <1.2 <1.2 3.31,2,3,5-Tetramethylbenzene Gasoline hydrocarbon 36 856 14 1.6 <.14 <.14 <.14 <.14 .14Chloroethane Solvent 37 869 14 1.6 <.12 <.12 <.12 <.12 .10Dichlorodifluoromethane Refrigerant 37 869 11 1.3 <.1 <.1 <.1 <.1 .58Tetrachloromethane Solvent 37 869 11 1.3 <.06 <.06 <.06 <.06 .04Diisopropyl ether Gasoline oxygenate 35 763 9 1.2 <.1 <.1 <.1 <.1 .05Bromoform Trihalomethane (THM) 37 869 10 1.2 <.06 <.06 <.06 <.06 .54n-Propylbenzene Solvent 37 869 10 1.2 <.04 <.04 <.04 <.04 .08Diethyl ether Solvent 36 856 9 1.1 <.08 <.08 <.08 <.08 .431,2,3,4-Tetramethylbenzene Gasoline hydrocarbon 36 856 9 1.1 <.14 <.14 <.14 <.14 .35Vinyl chloride Organic synthesis 

compound

37 869 9 1.0 <.06 <.06 <.06 <.06 .94

Acrolien Organic synthesis 

compound

13 308 3 .97 <1.5 <1.5 <1.5 <1.5 3.4

trans-1,2-Dichloroethene Solvent 37 869 6 .69 <.03 <.03 <.03 <.03 3.5n-Butylbenzene Gasoline hydrocarbon 37 869 5 .58 <.12 <.12 <.12 <.12 E.042-Chlorotoluene Solvent 37 869 4 .46 <.03 <.03 <.03 <.03 .071,2-Dichloropropane Fumigant 37 869 2 .23 <.03 <.03 <.03 <.03 .031,1,2,2-Tetrachloroethane Solvent 37 869 2 .23 <.09 <.09 <.09 <.09 .08Trichlorofluoromethane Refrigerant 37 869 2 .23 <.03 <.03 <.03 <.03 .08Ethyl tert-butyl ether Gasoline oxygenate 36 856 1 .12 <.05 <.05 <.05 <.05 .02

Occurrence of Volatile Organic Compounds in Urban Streams 27
Table 6. Summary of the detection frequencies and concentrations of volatile organic compounds at an assessment level of 0.02 microgram per liter, 1995–2003, listed in order 

of decreasing detection frequency.—Continued[VOC, volatile organic compound; <, less than; ND, not detected; E, estimated]

Compound name VOC group Number of sites Number of samples

Number of 

samples 

with 

detections

Detection 

frequency 

(percent)

Statistical summary for concentrations including non-detections 

(micrograms per liter)

Minimum 25th percentile Median 75th percentile Maximum

sec-Butylbenzene Gasoline hydrocarbon 37 869 1 0.12 <0.03 <0.03 <0.03 <0.03 0.02Dibromochloropropane Fumigant 37 869 1 .12 <.21 <.21 <.21 <.21 .091,2-Dichlorobenzene Solvent 37 869 1 .12 <.05 <.05 <.05 <.05 .181,3-Dichlorobenzene Solvent 37 869 1 .12 <.03 <.03 <.03 <.03 .021,2-Dichloroethane Solvent 37 869 1 .12 <.13 <.13 <.13 <.13 E.03Isopropylbenzene Gasoline hydrocarbon 37 869 1 .12 <.03 <.03 <.03 <.03 .03Acrylonitrile Organic synthesis 

compound

36 858 0 ND <1.2 <1.2 <1.2 <1.2 <1.2

Bromobenzene Solvent 37 869 0 ND <.03 <.03 <.03 <.03 <.03Bromochloromethane Organic synthesis 

compound

37 869 0 ND <.04 <.04 <.04 <.04 <.04

Bromomethane Fumigant 37 869 0 ND <.15 <.15 <.15 <.15 <.15tert-Butylbenzene Gasoline hydrocarbon 37 869 0 ND <.05 <.05 <.05 <.05 <.053-Chloro-1-propene Organic synthesis 

compound

36 856 0 ND <.07 <.07 <.07 <.07 <.07

4-Chlorotoluene Solvent 37 869 0 ND <.05 <.05 <.05 <.05 <.05Dibromomethane Solvent 37 869 0 ND <.05 <.05 <.05 <.05 <.05trans-1,4-Dichloro-2-

butene

Organic synthesis 

compound

36 856 0 ND <.7 <.7 <.7 <.7 <.7

1,3-Dichloropropane Organic synthesis 

compound

37 869 0 ND <.06 <.06 <.06 <.06 <.06

2,2-Dichloropropane Organic synthesis 

compound

37 869 0 ND <.05 <.05 <.05 <.05 <.05

1,1-Dichloropropene Organic synthesis 

compound

37 869 0 ND <.03 <.03 <.03 <.03 <.03

cis-1,3-Dichloropropene Fumigant 37 869 0 ND <.05 <.05 <.05 <.05 <.05trans-1,3-Dichloropropene Fumigant 37 869 0 ND <.09 <.09 <.09 <.09 <.09Ethylene dibromide Fumigant 37 869 0 ND <.04 <.04 <.04 <.04 <.04Ethyl methacrylate Organic synthesis 

compound

36 856 0 ND <.18 <.18 <.18 <.18 <.18

28 Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003
Table 6. Summary of the detection frequencies and concentrations of volatile organic compounds at an assessment level of 0.02 microgram per liter, 1995–2003, listed in order 

of decreasing detection frequency.—Continued[VOC, volatile organic compound; <, less than; ND, not detected; E, estimated]

Compound name VOC group Number of sites Number of samples

Number of 

samples 

with 

detections

Detection 

frequency 

(percent)

Statistical summary for concentrations including non-detections 

(micrograms per liter)

Minimum 25th percentile Median 75th percentile Maximum

Hexachlorobutadiene Organic synthesis 

compound

37 869 0 ND <0.14 <0.14 <0.14 <0.14 <0.14

Hexachloroethane Solvent 36 857 0 ND <.14 <.14 <.14 <.14 <.14Iodomethane Organic synthesis 

compound

36 856 0 ND <.08 <.08 <.08 <.08 <.08

Methyl acrylate Organic synthesis 

compound

36 856 0 ND <.6 <.6 <.6 <.6 <.6

Methyl acrylonitrile Organic synthesis 

compound

36 856 0 ND <.6 <.6 <.6 <.6 <.6

Methyl butyl ketone Solvent 36 856 0 ND <.7 <.7 <.7 <.7 <.7Methyl methacrylate Organic synthesis 

compound

36 856 0 ND <.35 <.35 <.35 <.35 <.35

1,1,1,2-Tetrachloroethane Solvent 37 869 0 ND <.03 <.03 <.03 <.03 <.031,2,3-Trichlorobenzene Organic synthesis 

compound

37 869 0 ND <.27 <.27 <.27 <.27 <.27

1,2,4-Trichlorobenzene Solvent 37 869 0 ND <.07 <.07 <.07 <.07 <.071,1,2-Trichloroethane Solvent 37 869 0 ND <.06 <.06 <.06 <.06 <.061,2,3-Trichloropropane Fumigant 37 869 0 ND <.07 <.07 <.07 <.07 <.07Vinyl acetate Organic synthesis 

compound

12 201 0 ND <5. <5. <5. <5. <5.

Vinyl bromide Organic synthesis 

compound

36 856 0 ND <.1 <.1 <.1 <.1 <.1

Occurrence of Volatile Organic Compounds in Urban Streams 29
Figure 13. Detection frequencies of the 15 most frequently detected volatile organic compounds (VOCs) in urban stream samples at an 

assessment level of 0.02 microgram per liter, 1995–2003.

0 10 20 30 40 50 60 70 80 90 100

DETECTION FREQUENCY, IN PERCENT

Number of detections/

number samples

Toluene

Chloroform

Methyl tert-butyl ether

Trichloroethene

Perchloroethene

cis-1,2-Dichloroethene

Acetone

m- and p-Xylene

Benzene

Chloromethane

1,2,4-Trimethylbenzene

o-Xylene

Dichloromethane

1,1,1-Trichloroethane

Methyl isobutyl ketone

648/867

82/856

94/869

95/869

97/856

108/869

128/868

194/869

239/856

261/856

294/869

297/869

299/869

348/869

480/869

Solvent

Gasoline oxygenate

Trihalomethane

Gasoline hydrocarbon

VOC group

30 Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003

in samples, the second and third pentiles had a maximum of 

18 VOCs present, and the fifth pentile had a maximum of 

27 VOCs present.

Two or more VOCs were detected in more than 

80 percent of samples in each of the five pentiles. The fifth 

pentile had the highest detection frequency (86.6 percent) of 

two or more VOCs, followed by the second, first, and fourth 

streamflow pentiles. The third streamflow pentile (40 to less 

than 60 percent of streamflow) had the smallest detection 

frequency (82 percent) of two or more VOCs (fig. 18).
Figure 14. Concentrations of the 15 most frequently detected volatile organic compounds in urban stream samples, 

1995–2003.

0.001 0.01 0.1 1 10 100 1,000 10,000

CONCENTRATION, IN MICROGRAMS PER LITER

Assessment level

Median concentration of all samples

Median of concentrations greater 

 than or equal to the assessment 

 level (median concentrations of

 the detections) 

Concentration less than the 

 assessment level

Concentration greater than or 

 equal to the assessment level

Median long-term method 

 detection level

Maximum Contaminant Level 

 (U.S. Environmental Protection 

 Agency, 2006)

Drinking Water Advisory 

 (U.S. Environmental Protection 

 Agency, 1997)

Health-Based Screening Level 

 (Toccalino and others, 2006)

Aquatic-life criteria (Canadian 

 Council of Resource and 

 Environment Ministers, 1991) 

Toluene

1,2,4-Trimethylbenzene

o-Xylene

Dichloromethane

1,1,1-Trichloroethane

Methyl isobutyl ketone

cis-1,2-Dichloroethene

Acetone

m- and p-Xylene

Benzene

Chloromethane

Chloroform

Methyl tert-butyl ether

Trichloroethene

Perchloroethene

EXPLANATION

Occurrence of Volatile Organic Compounds in Urban Streams 31
Figure 15. Relation between (A) detection frequencies, and (B) concentrations of methyl tert-butyl ether (MTBE) in 

urban stream samples in low and high MTBE-use areas of the United States at an assessment level of 0.02 microgram per 

liter, 1995–2003.

0.001 0.01 0.1 1 10 100 1,000

MTBE CONCENTRATION, IN MICROGRAMS PER LITER

High MTBE-use areas

Low MTBE-use areas

244/284

104/585

B

0 10 20 30 40 50 60 70 80 90 100

High MTBE-use areas

Low MTBE-use areas

DETECTION FREQUENCY OF MTBE, IN PERCENT

104/585

244/284

A

Number of detections/

number of samples

Number of detections/

number of samples

Assessment level

MTBE concentration for a single sample

Median of MTBE concentrations greater 

 than or equal to the assessment level

Table 7. Detection frequencies of one or more volatile organic compounds (VOCs) at all sites, total number of VOC detections, median 

number of VOCs detected, maximum number of VOCs detected, and median total concentration in urban stream samples by streamflow 

pentile at an assessment level of 0.02 microgram per liter, 1995–2003.

Streamflow 

pentile

Number of 

samples

Number of 

samples with 

detected VOCs

Detection 

frequency 

(percent)

Total 

number of 

VOCs detected 

in all samples

Median 

number of 

VOCs detected 

in samples

Maximum 

number of 

VOCs detected 

in samples

Median total 

concentration 

(micrograms 

per liter)

Low flow 1 124 121 97.6 554 3 16 0.39

2 177 173 97.7 921 4 18 1.0

3 153 148 96.7 750 4 18 .49

4 140 136 97.1 738 4 16 .45

High flow 5 275 266 96.7 1,657 6 27 .81

32 Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003
Figure 16. Detection frequencies of one or more volatile organic compounds by streamflow pentile in urban 

stream samples at an assessment level of 0.02 microgram per liter, 1995–2003. 

Figure 17. Cumulative distribution of total concentrations of volatile organic compound (VOC) 

concentrations in 869 samples from 37 urban stream sites by streamflow pentile at an assessment level of 

0.02 microgram per liter, 1995–2003.

90 92 94 96 98 100

STREAMFLOW PENTILE

DETECTION FREQUENCY, IN PERCENT

Low flow 1

4

3

2

High flow 5 266/275

136/140

148/153

173/177

121/124

Number of detections/

number of samples

0.01

0.1

1

10

100

1,000

0 10 20 30 40 50 60 70 80 90 100

CUMULATIVE PERCENT

TOTAL VOC CONCENTRATION, IN MICROGRAMS PER LITER 

1st pentile Low flow

2nd pentile

3rd pentile

4th pentile

5th pentile High flow

Occurrence of Volatile Organic Compounds in Urban Streams 33
Figure 18. Relation between the percentage of urban stream samples and the number of volatile organic 

compounds (VOCs) detected by streamflow pentile at an assessment level of 0.02 microgram per liter, 

1995–2003.

0

25

50

75

100

1 3 5 7 9 11 13 15 17 19 21 23 25 27

NUMBER OF VOCs IN URBAN STREAM SAMPLES

PERCENTAGE OF URBAN STREAM SAMPLES WITH EQUAL 

OR GREATER NUMBER OF DETECTED VOCs 

1st pentile Low flow

2nd pentile

3rd pentile

4th pentile

5th pentile High flow

34 Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003

Volatile Organic Compound Groups

Gasoline hydrocarbons, solvents, THMs, and gasoline 

oxygenates occurred frequently in all streamflow pentiles, in 

contrast to the organic synthesis compounds, fumigants, and 

refrigerants that occurred less frequently in urban streams 

under all streamflow conditions (fig. 19). The detection 

frequencies of the VOC groups by streamflow pentiles were 

from statistically different distributions (contingency table 

χ2 = 31.5659, DF = 28, p-value = 0.2925). Furthermore, 

gasoline hydrocarbons were the most frequently detected VOC 

group in the first, second, third, and fifth streamflow pentiles, 

whereas solvents were the most frequently detected VOC 

group in the fourth streamflow pentile.

Within each individual VOC group, gasoline hydrocarbons occurred most frequently in the first and fifth streamflow 

pentiles and were from statistically different distributions 

in all pentiles (contingency table χ2 = 2.0672, DF = 4, 

p-value = 0.7234). The solvents occurred most frequently 

in the fifth streamflow pentile and were from statistically 

different distributions in all pentiles (contingency table 

χ2 = 1.321, DF = 4, p-value = 0.8578). THMs occurred 

most frequently in the fourth pentile and were from statistically different distributions in all pentiles (contingency table 

χ2 = 2.2276, DF = 4, p-value = 0.694). Gasoline oxygenates occurred most frequently in the second pentile and 

were from statistically different distributions in all pentiles 

(contingency table χ2 = 7.5864, DF = 4, p-value = 0.108). 

Organic synthesis compounds occurred most frequently in 

the fifth pentile and were from statistically different distributions in all pentiles (contingency table χ2 = 6.9012, DF = 4, 

p-value = 0.1412). Fumigants were from statistically different 

distributions in all pentiles (contingency table χ2 = 3.2795, 

DF = 4, p-value = 0.5122), and refrigerants were from statistically different distributions in all pentiles (contingency table 

χ2 = 0.8781, DF = 4, p-value = 0.9277).

Three general patterns of occurrence were evident 

within the VOC groups: (1) a general decrease in the detection frequency of gasoline hydrocarbons, THMs, and gasoline 

oxygenates was observed as the streamflow increases; (2) a 

general increase in the detection frequency of solvents and 

organic synthesis compounds was observed as the streamflow 

increases; and (3) no general pattern was observed for the 

fumigants and refrigerants. The detection frequency of the 

gasoline hydrocarbons, in general, decreased as flow increased 

until the fourth pentile, then increased from 68 to 83 percent 

from the fourth to fifth pentile. The detection frequency of 

the solvents increased as the streamflow increased from the 

first to the fifth pentile with a large increase (61 to 71 percent) 

between the first and second pentiles, then a small increase 

(71 to 74 percent) between the third and fourth pentiles. The 

detection frequency of the THMs generally decreased as the 
Figure 19. Detection frequencies of seven volatile organic compound (VOC) groups in urban stream samples by streamflow 

pentile at an assessment level of 0.02 microgram per liter, 1995–2003.

0 10 20 30 40 50 60 70 80 90 100

Gasoline hydrocarbons

Solvents

Trihalomethanes (THMs)

Gasoline oxygenates

Organic synthesis compounds

Fumigants

Refrigerants

VOC GROUP

DETECTION FREQUENCY, IN PERCENT

1st pentile Low flow

2nd pentile

3rd pentile

4th pentile

5th pentile High flow

Number of detections/

number of samples

104/124

133/177

123/153

95/140

229/275

76/124

126/177

109/153

103/140

204/275

73/124

97/177

82/153

90/140

139/275

55/124

89/177

66/153

50/140

88/275

13/124

24/177

12/153

20/140

48/275

7/124

13/177

5/153

10/140

13/275

5/124

9/177

6/153

8/140

11/275

Occurrence of Volatile Organic Compounds in Urban Streams 35

streamflow increased with the exception of the fourth pentile, 

which had the highest detection frequency of 64 percent. 

The detection frequency of the gasoline oxygenates also, 

in general, decreased as the streamflow increased with the 

exception of the second pentile, which had the largest detection frequency of 50 percent. The detection frequency of 

the organic synthesis compounds generally increased as the 

streamflow increased. The detection frequencies of the fumigants and refrigerants did not differ markedly as the streamflow increased.

Median total concentrations of detections for gasoline 

hydrocarbons, solvents, gasoline oxygenates, and organic 

synthesis compounds generally increased as streamflow 

increased. In contrast, median total concentrations of detections for THMs and fumigants generally decreased as streamflow increased. The median total concentrations of detections 

for refrigerants showed no pattern as streamflow increased 

(fig. 20).
Figure 20. Total volatile organic compound (VOC) concentrations of the seven VOC groups in urban stream 

samples by streamflow pentile at an assessment level of 0.02 microgram per liter, 1995–2003.

Low flow 1

2

3

4

High flow 5

0.01 0.1 1 10 100 1,000

Gasoline hydrocarbons

Solvents

Trihalomethanes

Gasoline 

oxygenates

Organic synthesis compounds

Fumigants

Refrigerants

Low flow 1

2

3

4

High flow 5

Low flow 1

2

3

4

High flow 5

Low flow 1

2

3

4

High flow 5

Low flow 1

2

3

4

High flow 5

Low flow 1

2

3

4

High flow 5

Low flow 1

2

3

4

High flow 5

Median of concentrations 

 greater than or equal to 

 the assessment level 

 (median concentrations 

 of the detections)

Total VOC concentration

 for a single sample

EXPLANATION

STREAMFLOW PENTILE

TOTAL VOC CONCENTRATION, IN MICROGRAMS PER LITER

Assessment level 

 

36 Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003
Occurrence of Volatile Organic Compounds in Urban Streams 37

Individual Volatile Organic Compounds

The detection frequencies of the 15 most frequently 

detected VOCs grouped by streamflow pentile are shown in 

figure 21. Two general occurrence patterns are evident for 

many of the 15 compounds: (1) the detection frequency of 

some compounds generally decreases as streamflow increases 

and (2) the detection frequency generally increases as streamflow increases. The first pattern may be from VOCs primarily 

entering the stream from groundwater inflows or small pointsource discharges that are diluted with increased streamflow. VOCs that have this general pattern include toluene, 

chloroform, MTBE, perchloroethene, and dichloromethane. 

The second pattern, compounds with increasing detection 

frequency as streamflow increases, also may have similar 

sources to the first pattern at smaller streamflow and have 

additional sources, such as stormwater runoff, contributing to 

the increased presence during larger streamflow conditions. 

VOCs that have this second pattern include trichloroethene, 

cis-1,2-dichloroethene, acetone, m- and p-xylene, benzene, 

chloromethane, 1,2,4-trimethylbenzene, o-xylene, and methyl 

isobutyl ketone.

The detection frequency of toluene generally decreased 

from the first to fourth pentile with a large increase from the 

fourth to fifth pentile. The detection frequency of chloroform 

generally decreased from the first to third pentile with a large 

increase from the third to fourth pentile, then a decrease from 

the fourth to fifth pentile, which is consistent with relatively 

stable sources (for example, contaminated groundwater entering the stream). The detection frequency of MTBE generally decreased from the first to fifth pentile with an increase 

from the first to second pentile. The detection frequencies 

of trichloroethene and cis-1,2-dichloroethene have similar 

patterns with an increase from the first to the second pentile, 

a small decrease to the third pentile, a small increase to the 

fourth pentile, and a decrease to the fifth pentile. The detection frequencies of m- and p-xylene, benzene, chloromethane, 

1,2,4-trimethylbenzene, o-xylene, and methyl isobutyl ketone 

increased as the streamflow increased, which is consistent with 

sources associated with increased rainfall runoff (for example, 

parking lot and street wash-off).

The concentrations of the 15 most frequently detected 

VOCs grouped by streamflow pentiles are shown in figure 22. 

The median concentrations of detections also are shown 

for each streamflow pentile on the figure. In general, three 

concentration patterns were evident for the 15 most frequently 

detected VOCs: (1) increasing median concentrations of 

detections as streamflow increased, (2) decreasing median 

concentrations of detections as streamflow increased, and 

(3) no marked difference in median concentrations of detections as streamflow increased. Median concentrations of 

detections for seven of the compounds (toluene, MTBE, 

acetone, benzene, chloromethane, o-xylene, dichloromethane, 

and methyl isobutyl ketone) generally increased as streamflow 

increased from the first pentile to the fifth pentile. Median 

concentrations of detections for chloroform, perchloroethene, 

and cis-1,2,-dichloroethene generally decreased as streamflow 

increased from the first pentile to the fifth pentile. Median 

concentrations of detections for trichloroethene, m- and 

p-xylene, 1,2,4-trimethylbenzene, and 1,1,1-trichloroethane 

had no marked change as streamflow increased from the first 

pentile to the fifth pentile. Of the 15 most frequently detected 

compounds, acetone had the largest increase in median 

concentrations of detections as streamflow increased, and the 

largest increase occurred between the fourth and fifth pentiles. 

The increase in acetone concentrations as streamflow increases 

may be attributed to atmospheric washout and runoff from 

impervious areas (Lopes and others, 2000).

The detection frequency of MTBE was at least three 

times larger in high MTBE-use areas than in low MTBE-use 

areas of the United States in all streamflow pentiles (fig. 23A). 

The detection frequency of MTBE generally decreased as 

streamflow increased in low MTBE-use areas and slightly 

increased as streamflow increased in high MTBE-use areas 

of the United States. In each streamflow pentile, concentrations of MTBE were statistically larger (Wilcoxon rank-sum 

Z > 6.8512, one-sided p-value <0.025) in high MTBE-use 

areas than in low MTBE-use areas. In high MTBE-use 

areas, concentrations generally increased as streamflow 

increased, with the largest median concentration of detections (0.49 μg/L) in the fifth pentile (fig. 23B). In contrast, 

concentrations in low MTBE-use areas generally decreased as 

streamflow increased, with the smallest median concentration 

of detections (0.05 μg/L) in the fifth pentile.

Occurrence Patterns of Volatile Organic 

Compounds by Season

The water quality of urban streams may vary with both 

season of the year and streamflow (base flow compared to 

stormflow). In addition to the VOC occurrence and concentration patterns observed by streamflow pentile, seasonal 

variability is expected for VOCs on the basis of prior studies 

(Lopes and Bender, 1998; Reiser and O’Brien, 1998; Lundgren and Lopes, 1999). This section describes the overall 

patterns of occurrence for VOCs in urban streams stratified 

by warmer (April through September) and cooler (October 

through March) months. The 869 samples from the 37 urban 

stream sites were stratified by warmer and cooler months. 

Occurrence of one or more VOCs, VOC groups, and individual VOCs at all sites is presented.

One or More Volatile Organic Compounds

The detection frequency of one or more VOCs and the 

median number of VOCs detected in samples by warmer 

and cooler months and streamflow pentile are summarized 

in table 8. One or more VOCs were frequently detected in 

both warmer (96 percent of 410 samples) and cooler months 

(98 percent of 459 samples). The detection frequencies were 

from statistically different distributions (contingency table 
Figure 21. Detection frequencies of the 15 most frequently detected volatile organic compounds in urban stream 

samples by streamflow pentile at an assessment level of 0.02 microgram per liter, 1995–2003.

0 10 20 30 40 50 60 70 80 90 100

DETECTION FREQUENCY, IN PERCENT

1st pentile Low flow

2nd pentile

3rd pentile

4th pentile

5th pentile High flow

Number of detections/

number of samples

Toluene

1,1,1-Trichloroethane

Chloroform

Methyl tert-butyl ether

Trichloroethene

Perchloroethene

cis-1,2-Dichloroethene

Acetone

m- and p-Xylene

Benzene

Chloromethane

1,2,4-Trimethylbenzene

o-Xylene

Dichloromethane

Methyl isobutyl ketone

101/123

130/177

114/153

92/140

211/274

29/142

65/177

56/153

55/140

89/275

44/124

75/177

66/153

48/140

36/124

68/177

53/153

54/140

88/275

55/124

89/177

66/153

50/140

88/275

73/124

97/177

82/153

90/140

138/275

21/123

57/175

39/149

29/139

115/270

21/123

35/175

30/149

43/139

110/270

15/124

29/177

34/153

38/140

78/275

11/124

16/177

16/153

19/140

78/275

2/124

13/177

13/153

14/140

64/275

5/123

15/177

13/149

15/139

49/270

17/124

24/177

17/153

17/140

20/275

11/124

21/177

24/153

17/140

21/275

4/123

15/175

6/149

16/139

41/270

64/275

38 Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003
Figure 22. Concentrations of the 15 most frequently detected volatile organic compounds in urban stream samples by streamflow pentile, 1995–2003.

0.001 0.01 0.1 1 10 100

TOLUENE CONCENTRATION, IN MICROGRAMS PER LITER

ELI TNEP WOLF MAERTS

12345

LowHigh

CHLOROFORM CONCENTRATION, IN MICROGRAMS PER LITER

METHYL tert-BUTYL ETHER CONCENTRATION, IN MICROGRAMS PER LITER

TRICHLOROETHENE CONCENTRATION, IN MICROGRAMS PER LITER

PERCHLOROETHENE CONCENTRATION, IN MICROGRAMS PER LITER

cis-1,2-DICHLOROETHENE CONCENTRATION, IN MICROGRAMS PER LITER

ACETONE CONCENTRATION, IN MICROGRAMS PER LITER

m- AND p-XYLENE CONCENTRATION, IN MICROGRAMS PER LITER

BENZENE CONCENTRATION, IN MICROGRAMS PER LITER

CHLOROMETHANE CONCENTRATION, IN MICROGRAMS PER LITER

1,2,4-TRIMETHYLBENZENE CONCENTRATION, IN MICROGRAMS PER LITER

o-XYLENE CONCENTRATION, IN MICROGRAMS PER LITER

DICHLOROMETHANE CONCENTRATION, IN MICROGRAMS PER LITER

1,1,1-TRICHOROETHANE CONCENTRATION, IN MICROGRAMS PER LITER

METHYL ISOBUTYL KETONE CONCENTRATION, IN MICROGRAMS PER LITER

0.001 0.01 0.1 1 10 100

ELI TNEP WOLF MAERTS

12345

LowHigh

0.001 0.01 0.1 1 10 100

ELI TNEP WOLF MAERTS

12345

LowHighLowHighLowHigh

0.001 0.01 0.1 1 10 100

ELI TNEP WOLF MAERTS

12345

0.001 0.01 0.1 1 10 100

ELI TNEP WOLF MAERTS

12345

LowHigh

0.001 0.01 0.1 1 10 100

ELI TNEP WOLF MAERTS

12345

LowHigh

0.001 0.01 0.1 1 10 100

ELI TNEP WOLF MAERTS

12345

0.001 0.01 0.1 1 10 100

ELI TNEP WOLF MAERTS

12345

LowHigh

0.001 0.01 0.1 1 10 100

ELI TNEP WOLF MAERTS

12345

LowHigh

0.001 0.01 0.1 1 10 100

ELI TNEP WOLF MAERTS

12345

LowHigh

0.001 0.01 0.1 1 10 100 1,000

ELI TNEP WOLF MAERTS

12345

LowHigh

0.001 0.01 0.1 1 10 100

ELI TNEP WOLF MAERTS

12345

LowHigh

0.001 0.01 0.1 1 10 100

ELI TNEP WOLF MAERTS

12345

LowHigh

0.001 0.01 0.1 1 10 100

ELI TNEP WOLF MAERTS

12345

LowHigh

0.001 0.01 0.1 1 10 100

ELI TNEP WOLF MAERTS

12345

LowHigh

Assessment level Median of concentrations greater than or equal to the assessment 

 level (median concentrations of the detections) 

Concentration greater than or equal to the assessment level Concentration less than the assessment level 

EXPLANATION

Occurrence of Volatile Organic Compounds in Urban Streams 39
Figure 23. Relation between (A) detection frequencies, and (B) concentrations of methyl tert-butyl ether (MTBE) in urban 

stream samples in low and high MTBE-use areas of the United States by streamflow pentile at an assessment level of 

0.02 microgram per liter, 1995–2003.

0.001 0.01 0.1 1 10 100 1,000

MTBE CONCENTRATION, IN MICROGRAMS PER LITER

B

0 10 20 30 40 50 60 70 80 90 100

DETECTION FREQUENCY OF MTBE, IN PERCENT

A

Number of detections/

number of samples

Number of detections/

number of samples

STREAMFLOW PENTILE

Low flow 1

2

3

4

High flow 5

STREAMFLOW PENTILE

2

3

4

19/80

36/44

20/101

69/76

21/96

45/57

17/103

33/37

27/205

61/70

19/80

36/44

20/101

69/76

21/96

45/57

17/103

33/37

27/205

61/70

Low flow 1

High flow 5

Low flow 1

High flow 5

Low MTBE-use areas

High MTBE-use areas

Assessment level

Low MTBE-use areas

High MTBE-use areas

Median of MTBE concentrations 

 greater than or equal to the 

 assessment level

MTBE concentration for a single 

 sample

EXPLANATION

EXPLANATION

40 Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003

χ2 = 0.0119, DF = 1, p-value = 0.9132) between warmer and 

cooler months, and generally the detection frequencies were 

larger in cooler months.

The concentration distributions by warmer and cooler 

months are shown in figure 24. The median total VOC concentration (table 8) was significantly larger (Wilcoxon rank-sum 

Z = -2.4774, one-sided p-value = 0.0066) in cooler months 

than in warmer months, with the median concentration of 

detections for cooler months (0.80 μg/L) about twice as large 

as the median concentration of detections for warmer months 

(0.41 μg/L).

The relation between the frequency and the number of 

VOCs detected in urban stream samples by warmer and cooler 

months at an assessment level of 0.02 microgram per liter is 

shown in figure 25. The median number of VOCs and the total 

number of VOCs detected in samples were statistically larger 

in cooler months than in warmer months (table 8; Wilcoxon 

rank-sum Z = -4.7285, p-value = 0).

Volatile Organic Compound Groups

In general, the detection frequency of most VOC groups 

was similar or larger in cooler months (October through 

March) than in warmer months with the exception of the 

THMs (fig. 26). The detection frequencies of the seven VOC 

groups, when analyzed individually between warmer and 

cooler months, were each from statistically different distributions (contingency table χ2

 < 3.8414 (critical value), DF = 1, 

p-value > 0.05) (for example, the detection frequencies for 

gasoline hydrocarbons for warmer and cooler months were 

from statistically different distributions). Similarly, the detection frequencies of the seven VOC groups, combined into 
0.01

0.1

1

10

100

1,000

0 10 20 30 40 50 60 70 80 90 100

CUMULATIVE PERCENT

TOTAL VOC CONCENTRATION, IN MICROGRAMS PER LITER 

Warmer months (number of samples = 410)

Cooler months (number of samples = 459)

Median total VOC concentration

0.80

0.41

Figure 24. Cumulative distribution of total volatile organic compound (VOC) concentrations in 869 samples 

from 37 urban stream sites by warmer (April through September) and cooler (October through March) 

months at an assessment level of 0.02 microgram per liter, 1995–2003.

Table 8. Detection frequency of one or more volatile organic compounds (VOCs) at all sites, total number of VOCs detected, median 

number of VOCs detected, the maximum number of VOCs detected, and median total concentration in urban stream samples in warmer 

and cooler months by streamflow pentile at an assessment level of 0.02 microgram per liter, 1995–2003.

Streamflow 

pentile

Number of 

samples

Number of 

samples 

with 

detections

Detection 

frequency 

(percent)

Total 

number of VOCs 

detected in all 

samples

Median 

number of VOCs 

detected per 

sample

Median 

concentration 

(micrograms 

per liter)

Warmer months (April through September)

Low flow 1 71 69 97.2 304 3 0.30

2 75 74 98.7 337 4 .73

3 65 62 95.4 235 3 .31

4 57 53 93.0 237 3 .26

High flow 5 142 137 96.5 744 5 .45

Totals 410 395 96.3 1,857 4 .41

Cooler months (October through March)

Low flow 1 53 52 98.1 250 4 0.48

2 102 99 97.1 584 5 1.1

3 88 86 97.7 515 4 .70

4 83 83 100 501 5 .61

High flow 5 133 129 97.0 913 6 1.1

Totals 459 449 97.8 2,763 5 .80

Occurrence of Volatile Organic Compounds in Urban Streams 41
Figure 25. Relation between the percentage of urban stream samples and the number of volatile organic 

compounds (VOCs) detected by warmer (April through September) and cooler (October through March) 

months at an assessment level of 0.02 microgram per liter, 1995–2003.

Warmer months

Cooler months

0

25

50

75

100

1 3 5 7 9 11 13 15 17 19 21 23 25 27

NUMBER OF VOCs IN URBAN STREAM SAMPLES

PERCENTAGE OF URBAN STREAM SAMPLES WITH EQUAL OR 

GREATER NUMBER OF DETECTED VOCs

42 Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003

a single analysis between warmer and cooler months, also 

were from statistically different distributions (contingency 

table χ2 = 9.9964, DF = 7, p-value = 0.1888). The gasoline 

hydrocarbons were the most frequently detected VOC group in 

both warmer and cooler months followed by solvents, THMs, 

gasoline oxygenates, organic synthesis compounds, fumigants, 

and refrigerants, which is the same order as the overall VOC 

group detection frequencies.

Three general patterns were evident for median concentrations of detections of the VOC groups: (1) larger median 

concentrations in the cooler months, (2) larger median 

concentrations in the warmer months, and (3) no difference in 

the median concentrations between the seasons (fig. 27). The 

first pattern includes the gasoline hydrocarbons, solvents, and 

gasoline oxygenates, with median concentrations of the detections for the gasoline hydrocarbons and gasoline oxygenates 

significantly larger in cooler months than in warmer months 

(Wilcoxon rank-sum Z > 2.8000, one-sided p-value <0.025). 

The second pattern includes the organic synthesis compounds 

and refrigerants, with the median concentration of the detections for organic synthesis compounds significantly larger in 

warmer months than in cooler months (Wilcoxon rank-sum 

Z = 3.1364, one-sided p-value = 0.0009). The third pattern 

includes the THMs and fumigants, with no significant difference in the median concentrations of the detections between 

the two seasons (Wilcoxon rank-sum Z > 0.3126, one-sided 

p-value > 0.025). The first pattern may be, in part, because 

the partitioning of VOCs between air and water is based on 

the Henry’s Gas Law, which favors VOCs staying in water as 

the temperature decreases meaning less volatilization during 

cooler months (Rathbun, 2000). The second pattern may be 

from VOCs primarily entering the stream from groundwater 

inflows or from small point-source discharges entering the 

stream during warmer months and possibly, from larger use in 

warmer months. The third pattern may indicate a consistent, 

year-round source for the compounds in these VOC groups.

Individual Volatile Organic Compounds

Two general patterns of occurrence for the 15 most 

frequently detected VOCs in warmer and cooler months 

were evident: (1) VOCs occur more frequently in cooler 

months, and (2) VOCs occur slightly more frequently 

in warmer months (fig. 28). The VOCs occurring more 

frequently in cooler months than in warmer months include 

11 of the 15 most frequently detected VOCs (toluene, 

MTBE, perchloroethene, acetone, m- and p-xylene, benzene, 

1,2,4-trimethylbenzene, o-xylene, dichloromethane, 

1,1,1-trichloroethane, and methyl isobutyl ketone). The VOCs 

occurring slightly more frequently in warmer months than in 

cooler months include 4 of the 15 most frequently detected 

VOCs (chloroform, trichloroethene, cis-1,2-dichloroethene, 

and chloromethane). Furthermore, more individual VOCs 
Figure 26. Detection frequencies of volatile organic compound (VOC) groups in urban stream samples in warmer (April through 

September) and cooler (October through March) months at an assessment level of 0.02 microgram per liter, 1995–2003.

0 20 40 60 80 100

Gasoline hydrocarbons

Solvents

Trihalomethanes (THMs)

Gasoline oxygenates

Organic synthesis compounds

Fumigants

Refrigerants

VOC GROUP

DETECTION FREQUENCY, IN PERCENT

Warmer months

Cooler months

300/410

384/459

292/410

326/459

231/410

250/459

148/410

200/459

45/410

72/459

18/410

30/459

14/410

25/459

Number of detections/

number of samples

Occurrence of Volatile Organic Compounds in Urban Streams 43

were detected in samples from cooler months (55 VOCs) than 

from warmer months (47 VOCs).

As noted previously, the first pattern may be, in part, 

because the partitioning of VOCs between air and water is 

more favorable to VOCs staying in water as the temperature 

decreases (Rathbun, 2000). The second pattern may be from 

VOCs primarily entering the stream from groundwater inflows 

or from small point-source discharges entering the stream 

during warmer months, and possibly from larger use during 

warmer months.

The concentrations of the 15 most frequently detected 

VOCs grouped by warmer and cooler months are shown in 

figure 29. A summary of the detection frequency and concentration distribution at an assessment level of 0.02 μg/L for all 

87 VOCs analyzed is provided in Appendix 2.

Three general patterns were evident in the median 

concentrations of detections for warmer and cooler months: 

(1) median concentrations were not different in warmer or 

cooler months, (2) median concentrations were larger in 

warmer months, and (3) median concentrations were larger 

in cooler months. Of the 15 most frequently detected VOCs, 

toluene, chloroform, perchloroethene, benzene, o-xylene, and 

methyl isobutyl ketone had no difference in median concentrations of detections between warmer and cooler months. Six 

of the 15 most frequently detected VOCs—trichloroethene, 

acetone, m- and p-xylene, 1,2,4-trimethylbenzene, dichloromethane, and 1,1,1-trichoroethane—had slightly larger median 

concentrations of detections in warmer months. Three of the 

15 most frequently detected VOCs—MTBE, cis-1,2-dichloroethene, and chloromethane—had larger median concentrations of detections in the cooler months. The concentrations 

for most of the compounds varied over at least two orders 

of magnitude, with the largest concentrations in the cooler 

months for most of the VOCs.

The median concentrations of detections for the 15 most 

frequently detected VOCs ranged from 0.03 to 4 μg/L in 

warmer months and from 0.03 to 3.8 μg/L in cooler months. 

The largest median concentrations of detections were associated with acetone, and the next largest median concentrations 

of detections were associated with methyl isobutyl ketone. 

Both acetone and methyl isobutyl ketone are oxygenated 

solvents and are highly soluble in water.

MTBE was detected more frequently in cooler months 

in both high MTBE-use areas and low MTBE-use areas of 

the United States (fig. 30). In addition, MTBE had statistically larger concentrations (Wilcoxon rank-sum Z = -3.5156, 

p-value = 0.0002) in cooler months compared to warmer 

months. The statistically largest concentrations of MTBE 

were in cooler months in high MTBE-use areas (Wilcoxon 

rank-sum Z > 6.0000, p-value < 0.025; fig. 30). The median 
Figure 27. Total volatile organic compound (VOC) concentrations in urban stream samples of the seven VOC 

groups in warmer (April through September) and cooler (October through March) months at an assessment level 

of 0.02 microgram per liter, 1995–2003.

Warmer months

Cooler months

EXPLANATION

0.01 0.1 1 10 100 1,000

TOTAL VOC CONCENTRATION, IN MICROGRAMS PER LITER

Warmer months

Cooler months

Warmer months

Cooler months

Warmer months

Cooler months

Warmer months

Cooler months

Warmer months

Cooler months

Warmer months

Cooler months

Gasoline hydrocarbons

Solvents

Trihalomethanes

Gasoline oxygenates

Organic synthesis compounds

Fumigants

Refrigerants

Median of concentrations 

 greater than or equal to the 

 assement level (median 

 concentrations of the 

 detections)

 Warmer months

 Cooler months

Total VOC concentration 

 for a single sample

44 Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003
Figure 28. Detection frequencies of the 15 most frequently detected volatile organic compounds in urban stream 

samples by warmer (April through September) and cooler (October through March) months at an assessment level of 

0.02 microgram per liter, 1995–2003.

0 20 40 60 80 100

Toluene

Chloroform

Methyl tert-butyl ether

Trichloroethene

Perchloroethene

cis-1,2-Dichloroethene

Acetone

m- and p-Xylene

Benzene

Chloromethane

1,2,4-Trimethylbenzene

o-Xylene

Dichloromethane

1,1,1-Trichloroethane

Methyl isobutyl ketone

DETECTION FREQUENCY, IN PERCENT

Warmer months

Cooler months

Number of detections/

number of samples

282/409

366/458

22/403

38/410

38/410

22/403

26/410

148/410

145/410

113/410

139/410

115/403

79/403

51/410

69/410

60/453

56/459

57/459

75/453

82/459

59/458

143/459

160/53

146/453

155/459

184/459

154/459

230/410

250/459

200/459

Occurrence of Volatile Organic Compounds in Urban Streams 45
Figure 29. Concentrations of the 15 most frequently detected volatile organic compounds in urban 

stream samples by warmer (April through September) and cooler (October through March) months at an 

assessment level of 0.02 microgram per liter, 1995–2003.

0.001 0.01 0.1 1 10 100 1,000

Toluene

Chloroform

Methyl tert-butyl ether

Trichloroethene

Perchloroethene

cis-1,2-Dichloroethene

Acetone

m- and p-Xylene

Benzene

Chloromethane

1,2,4-Trimethylbenzene

o-Xylene

Dichloromethane

1,1,1-Trichloroethane

Methyl isobutyl ketone

CONCENTRATION, IN MICROGRAMS PER LITER

Assessment level

Warmer month concentration

 less than the assessment 

 level

Cooler month concentration

 less than the assessment level

Cooler month concentration

 greater than or equal to the

 assessment level

Median of concentrations

 greater than or equal to the

 assessment level

Warmer month concentration 

 greater than or equal to the

 assessment level

282/409

366/458

22/403

38/410

38/410

22/403

26/410

148/410

145/410

113/410

139/410

115/403

79/403

51/410

69/410

60/453

56/459

57/459

75/453

82/459

59/458

143/459

160/453

146/453

155/459

184/459

154/459

230/410

250/459

200/459

Number of detections/

number of samples

46 Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003
Figure 30. Relation between (A) detection frequencies, and (B) concentrations of methyl tert-butyl ether (MTBE) in urban 

stream samples in low and high MTBE-use areas of the United States by warmer (April through September) and cooler 

(October through March) months at an assessment level of 0.02 microgram per liter, 1995–2003.

0.001 0.01 0.1 1 10 100 1,000

MTBE CONCENTRATION, IN MICROGRAMS PER LITER

High MTBE-use areas

Low MTBE-use areas

109/137

135/147

39/273

65/312

B

0 10 20 30 40 50 60 70 80 90 100

High MTBE-use areas

Low MTBE-use areas

DETECTION FREQUENCY OF MTBE, IN PERCENT

39/273

65/312

109/137

135/147

A

Number of detections/

number of samples

Number of detections/

number of samples

Warmer months

Cooler months

Warmer months

Cooler months

Assessment level

Median of concentrations greater than

 or equal to the assessment level

Concentration for a single sample

EXPLANATION

Occurrence of Volatile Organic Compounds in Urban Streams 47

concentrations of detections were 0.09 μg/L in warmer 

and cooler months in low MTBE-use areas, and 0.21 and 

0.48 μg/L in warmer and cooler months, respectively, in 

high MTBE-use areas. The concentrations of MTBE ranged 

from 0.03 to 0.57 μg/L in warmer months and from 0.02 

to 0.77 μg/L in cooler months in low MTBE-use areas. In 

contrast, the concentrations of MTBE ranged from 0.04 to 

21 μg/L in warmer months and from 0.07 to 44 μg/L in cooler 

months in high MTBE-use areas.
48 Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003

Comparison of Volatile Organic 

Compound Concentrations to 

Benchmarks

In this section, VOC concentrations are compared to 

drinking-water and aquatic-life benchmarks to describe the 

significance of VOCs in urban streams to human health and 

aquatic life. The drinking-water benchmarks used for comparisons are USEPA’s drinking water MCLs (U.S. Environmental Protection Agency, 2006) and HBSLs developed by the 

USGS in collaboration with the USEPA, the New Jersey 

Department of Environmental Protection, and the Oregon 

Health & Science University (Toccalino and others, 2006). 

The aquatic-life criteria used for comparisons are Canadian 

Aquatic Guidelines (Canadian Council of Resource and 

Environment Ministers, 1991) and USEPA fresh-water chronic 

aquatic-life criteria (U.S. Environmental Protection Agency, 

1991). The Canadian Aquatic Guidelines were used because 

the United States aquatic guidelines currently (2009) are not 

available from USEPA for many of the VOCs. An aquatic 

guideline from USEPA was used if available. Ratios of the 

concentrations to the benchmarks were calculated by dividing the VOC concentration by the drinking-water benchmark 

or aquatic-life criteria. A concentration to benchmark ratio 

greater than one indicates that the concentration was greater 

than the benchmark. Concentration to benchmark ratios 

greater than 0.1 and less than 1 indicate that the concentration 

was within 10 percent of the drinking-water benchmark and 

(or) aquatic-life criteria. The compounds with concentration 

to benchmark ratios greater than 0.1 may warrant inclusion 

in low-concentration monitoring programs, like the NAWQA 

Program, to provide an indication of VOC concentrations 

approaching levels of potential concern for the beneficial 

use(s) of the stream.

No samples had concentrations greater than an MCL or 

HBSL (table 9). However, six compounds (trichloroethene, 

perchloroethene, cis-1,2-dichloroethene, dichloromethane, 

vinyl chloride, dibromochloropropane) had concentrations less than but within 10 percent of an MCL. Trichloroethene (37 samples), perchloroethene (54 samples), and 

dichloromethane (16 samples) accounted for the majority of 

the concentrations within 10 percent of an MCL. Acetone 

(1 sample), acrolien (3 samples), and 1,1,2,2-tetrachloroethane 

(2 samples), had concentrations less than but within 10 percent 

of an HBSL. Concentrations of MTBE in 59 samples were less 

than but within 10 percent of the lower limit of the USEPA 

Drinking Water Advisory (20 μg/L; U.S. Environmental 

Protection Agency, 1997), and concentrations in 5 samples 

were greater than or equal to this lower limit (table 9). These 

10 compounds may warrant inclusion in future low-concentration monitoring programs that focus on drinking-water 

sources.

Toluene (6 samples) and chloroform (2 samples) had 

stream concentrations greater than the aquatic-life criteria 

(table 9). Five additional compounds (trichloroethene, chlorobenzene, naphthalene, acrolien, and 1,2-dichlorobenzene) had 

concentrations less than but within 10 percent of aquatic-life 

criteria. Toluene and chloroform accounted for the majority of 

concentrations within 10 percent or greater than the aquaticlife criteria (table 9). These seven compounds may warrant 

inclusion in future low-concentration monitoring programs 

that focus on the protection of aquatic life.

Summary

The U.S. Geological Survey’s (USGS) National WaterQuality Assessment (NAWQA) Program was implemented 

in 1991. The primary goals of the NAWQA Program are 

to describe the status and trends of the water quality in the 

Nation’s water resources and identify natural and anthropogenic factors affecting the water quality. The NAWQA 

Program’s surface-water design includes, in part, monitoring 

the water-quality of streams draining relatively homogenous 

land uses and physiographic conditions. The objectives of 

monitoring at the urban indicator sites are to (1) characterize 

the stream quality from drainage basins with predominantly 

residential and commercial land use and (2) determine which 

natural and anthropogenic factors affect stream quality.

The NAWQA Program began collecting samples in 1995 

for analyses of volatile organic compounds (VOCs) in urban 

streams. The urban streams that were sampled have perennial 

streamflow, no major point-sources, and drain predominantly 

residential and commercial land uses. The occurrence of 

87 VOCs in 869 water samples collected between 1995 and 

2003 from 37 urban streams is summarized in this report. The 

occurrence of VOCs in urban streams is described for (1) all 

samples as a single dataset, (2) all samples grouped by streamflow pentiles, and (3) all samples grouped by warmer (April 

through September) and cooler (October through March) 

months by the detection frequency and (or) concentration of 

(a) any VOC, (b) VOC groups, and (c) individual compounds. 

Concentrations of VOCs were compared to (1) U.S. Environmental Protection Agency’s (USEPA) drinking-water 

Maximum Contaminant Levels (MCLs) or Drinking Water 

Advisories, (2) Health-Based Screening Levels (HBSLs) 

developed by the USGS in collaboration with USEPA and 

other agencies, and (3) USEPA and Canadian aquatic-life 

criteria. 

An assessment level of 0.02 microgram per liter (μg/L) 

was used to compute the detection frequencies and concentration statistics. The detection frequencies are considered 

minimum estimates because of the potential loss of information when using an assessment level. The use of an assessment 

level allowed for direct comparisons of occurrence information between VOC groups and individual VOCs.
Table 9. Summary by volatile organic compound of the number of samples with stream concentration-to-benchmark ratios greater 

than or equal to 0.1 and greater than or equal to 1 for drinking-water benchmarks or aquatic-life criteria listed in order of decreasing 

overall detection frequency, 1995–2003.—Continued

[DWB, drinking-water benchmark; μg/L, micrograms per liter; ≥, greater than or equal to; AQCR, aquatic-life criteria; MCL, Maximum Contaminant Level; 

CAN, Interim Canadian Aquatic Guideline; DWA, Drinking Water Advisory; HBSL, Health-Based Screening Level; FCH, U.S. Environmental Protection 

Agency fresh-water chronic aquatic-life criteria; --, no criteria or not applicable]

Compound name DWB 

type

DWB 

(μg/L)

Number of samples with 

concentration/DWB ratio AQCR 

source

AQCR 

(μg/L)

Number of samples with 

concentration/AQCR ratio

≥0.1 >1 ≥0.1 ≥1

Volatile organic compounds detected at an assessment level of 0.02 μg/L

Toluene MCL 11,000 0 0 CAN 22 205 6

Chloroform MCL 1,380 0 0 CAN 21.8 105 2

Methyl tert-butyl ether DWA 4

20 59 5 -- -- -- --

Trichloroethene MCL 15 37 0 CAN 221 3 0

Perchloroethene MCL 15 54 0 CAN 2111 0 0

cis-1,2-Dichloroethene MCL 1

70 4 0 -- -- -- --

Acetone HBSL 5700 1 0 -- -- -- --

m-and p-Xylene MCL 1,610,000 0 0 -- -- -- --

Benzene MCL 15 0 0 CAN 2370 0 0

Chloromethane HBSL 530 0 0 -- -- -- --

o-Xylene MCL 1,610,000 0 0 -- -- -- --

Dichloromethane MCL 15 16 0 CAN 298.1 0 0

1,1,1-Trichloroethane MCL 1200 0 0 -- -- -- --

Carbon disulfide HBSL 5700 0 0 -- -- -- --

Methyl ethyl ketone HBSL 54,000 0 0 -- -- -- --

Bromodichloromethane MCL 1,380 0 0 -- -- -- --

Ethylbenzene MCL 1700 0 0 CAN 290 0 0

Chlorobenzene MCL 1100 0 0 CAN 21.3 38 0

1,4-Dichlorobenzene MCL 175 0 0 CAN 226 0 0

Naphthalene HBSL 5100 0 0 CAN 21.1 18 0

1,1-Dichloroethene MCL 17 0 0 -- -- -- --

Dibromochloromethane MCL 1,380 0 0 -- -- -- --

Styrene MCL 1100 0 0 -- -- -- --

Trichlorotrifluoroethane HBSL 5200,000 0 0 -- -- -- --

Dichlorodifluoromethane HBSL 51,000 0 0 -- -- -- --

Tetrachloromethane MCL 15 0 0 CAN 213.3 0 0

Bromoform MCL 1,380 0 0 -- -- -- --

Diethyl ether HBSL 51,000 0 0 -- -- -- --

Vinyl chloride MCL 12 9 0 -- -- -- --

Acrolien HBSL 54 3 0 FCH 721 3 0

trans-1,2-Dichloroethene MCL 1

100 0 0 -- -- -- --

2-Chlorotoluene HBSL 5100 0 0 -- -- -- --

Trichlorofluoromethane HBSL 52,000 0 0 -- -- -- --

1,2-Dichloropropane MCL 15 0 0 -- -- -- --

1,1,2,2-Tetrachloroethane HBSL 5.3 2 0 -- -- -- --

Dibromochloropropane MCL 1.2 1 0 -- -- -- --

1,2-Dichlorobenzene MCL 1600 0 0 CAN 2.7 1 0

Summary 49
Table 9. Summary by volatile organic compound of the number of samples with stream concentration-to-benchmark ratios greater 

than or equal to 0.1 and greater than or equal to 1 for drinking-water benchmarks or aquatic-life criteria listed in order of decreasing 

overall detection frequency, 1995–2003.—Continued

[DWB, drinking-water benchmark; μg/L, micrograms per liter; ≥, greater than or equal to; AQCR, aquatic-life criteria; MCL, Maximum Contaminant Level; 

CAN, Interim Canadian Aquatic Guideline; DWA, Drinking Water Advisory; HBSL, Health-Based Screening Level; FCH, U.S. Environmental Protection 

Agency fresh-water chronic aquatic-life criteria; --, no criteria or not applicable]

Compound name DWB 

type

DWB 

(μg/L)

Number of samples with 

concentration/DWB ratio AQCR 

source

AQCR 

(μg/L)

Number of samples with 

concentration/AQCR ratio

≥0.1 >1 ≥0.1 ≥1

Volatile organic compounds detected at an assessment level of 0.02 μg/L—Continued

1,3-Dichlorobenzene HBSL 5600 0 0 CAN 2150 0 0

1,2-Dichloroethane MCL 15 0 0 CAN 2100 0 0

Isopropylbenzene HBSL 5700 0 0 -- -- -- --

Volatile organic compounds not detected at an assessment level of 0.02 μg/L

Acrylonitrile HBSL 50.06–6 0 0 -- -- -- --

Bromochloromethane HBSL 590 0 0 -- -- -- --

Bromomethane HBSL 5100 0 0 -- -- -- --

4-Chlorotoluene HBSL 5100 0 0 -- -- -- --

1,2-Dibromoethane MCL 10.05 0 0 -- -- -- --

cis-1,3-Dichloropropene HBSL 5,80.3–30 0 0 -- -- -- --

trans-1,3-Dichloropropene HBSL 5,80.3–30 0 0 -- -- -- --

Hexachlorobutadiene HBSL 50.9–90 0 0 CAN 21.3 0 0

Hexachloroethane HBSL 5.7 0 0 -- -- -- --

Methyl acrylonitrile HBSL 5.7 0 0 -- -- -- --

Methyl methacrylate HBSL 510,000 0 0 -- -- -- --

1,1,1,2-Tetrachloroethane HBSL 590 0 0 -- -- -- --

1,2,3-Trichlorobenzene -- -- -- -- CAN 28 0 0

1,2,4-Trichlorobenzene MCL 170 0 0 CAN 224 0 0

1,1,2-Trichloroethane MCL 15 0 0 -- -- -- --

1,2,3-Trichloropropane HBSL 540 0 0 -- -- -- --

Totals -- -- 186 5 -- -- 373 8

1

U.S. Environmental Protection Agency (2006).

2

Canadian Council of Resource and Environment Ministers (1991).

3

The MCL is for total trihalomethanes (TTHMs).

4

The value listed is the lower limit of the U.S. Environmental Protection Agency Drinking Water Advisory: Consumer acceptability advice and health effects 

analysis on methyl tert-butyl ether (MTBE; U.S. Environmental Protection Agency, 1997).

5

Toccalino and others (2006).

6

MCL is for total xylenes.

7

U.S. Environmental Protection Agency (1991).

8

HBSL range is for total 1,3-dichloropropene; the cis- and trans- isomers do not have individual HBSLs.

50 Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003
Summary 51

Overall Occurrence Patterns of Volatile Organic 

Compounds

One or more VOCs occurred frequently (97 percent of 

869 samples) in urban streams with a detection frequency 

ranging from 86 to 100 percent at the 37 urban stream sites. 

Twenty-seven of the sites had a detection frequency of 

100 percent for one or more VOCs. Total VOC concentrations ranged from not detected to 698 μg/L, with a median 

total VOC concentration of 0.57 μg/L. About 57 percent of the 

total VOC concentrations were less than or equal to 1 μg/L. 

The number of VOCs detected per sample ranged from 0 

to 27 VOCs, with a median of 4 VOCs per sample. About 

85 percent of the samples contained 2 or more VOCs, and 

about 25 percent of the samples contained 8 or more VOCs.

The seven VOC groups (gasoline hydrocarbons, solvents, 

trihalomethanes, gasoline oxygenates, organic synthesis 

compounds, fumigants, and refrigerants) had statistically 

different detection frequencies in urban stream samples. The 

gasoline hydrocarbons, solvents, trihalomethanes, and gasoline 

oxygenates were detected frequently (in more than 40 percent 

of the samples); in contrast, the organic synthesis compounds, 

fumigants, and refrigerants were detected less frequently. 

An individual VOC or several compounds usually accounted 

for most of the detections within a VOC group. The gasoline 

hydrocarbons were dominated by benzene, toluene, ethylbenzene, and o-, m- and p-xylene (collectively known as BTEX 

compounds). The solvents were dominated by trichloroethene, perchloroethene, cis-1,2-dichloroethene, and acetone. 

Trihalomethanes were dominated by chloroform, and gasoline oxygenates were dominated by methyl tert-butyl ether 

(MTBE). The gasoline oxygenates also had a larger detection 

frequency and concentrations in high MTBE-use areas of the 

United States. The larger solvent concentrations were influenced by the large concentrations of acetone in some samples. 

Median total concentrations of the VOC groups ranged from 

0.87 μg/L for the solvents to 0.03 μg/L for the organic synthesis compounds and fumigants.

Fifty-seven of the 87 VOCs analyzed for this study were 

detected in at least one sample from the 37 urban streams 

sampled at an assessment level of 0.02 μg/L. Concentrations 

of 30 VOCs were less than the assessment level including 

16 organic synthesis compounds, 8 solvents, 5 fumigants, and 

1 gasoline hydrocarbon. Fifteen VOCs had detection frequencies greater than or equal to 10 percent at an assessment 

level of 0.02 μg/L. These 15 most frequently detected VOCs 

in urban streams included 6 gasoline related compounds 

(5 gasoline hydrocarbons—toluene, m- and p-xylene, benzene, 

1,2,4-trimethylbenzene, o-xylene—and the gasoline oxygenate, MTBE); 1 trihalomethane (chloroform); and 8 solvents 

(trichloroethene, perchloroethene, cis-1,2-dichloroethene, 

acetone, chloromethane, dichloromethane, 1,1,1-trichloroethane, and methyl isobutyl ketone). The median concentrations 

of detections of the 15 most frequently detected VOCs ranged 

from 0.03 to 3.9 μg/L and typically were less than or equal to 

0.10 μg/L, with the exceptions of those for MTBE (0.24 μg/L) 

and acetone (3.9 μg/L).

Occurrence Patterns of Volatile Organic 

Compounds by Streamflow Pentile

Many studies indicate that water quality in streams can 

vary with streamflow. Because many of the urban streams 

sampled are small and had short streamflow records, a simple 

and robust ratio method was used to estimate longer-term 

streamflow pentiles for each urban stream. The 869 samples 

were grouped into five streamflow pentiles (less than 20, 20 to 

less than 40, 40 to less than 60, 60 to less than 80, and greater 

than or equal to 80 percent of estimated annual long-term 

streamflow), providing a means to group and compare the 

water-quality results from the 37 sites on the basis of streamflow conditions.

The detection frequencies of one or more VOCs did not 

vary markedly between the streamflow pentiles and ranged 

from 96.7 to 97.7 percent. The median total VOC concentrations ranged from 0.39 to 1.0 μg/L for the pentiles. The 

median number of VOCs reported per sample was highest in 

the fifth pentile (largest streamflows), and the lowest was in 

the first and third pentiles. The fifth pentile also had the most 

VOCs present (27) in one sample. Two or more VOCs were 

present in more than 80 percent of samples in each of the 

pentiles.

Gasoline hydrocarbons, solvents, trihalomethanes, and 

gasoline oxygenates occurred frequently in all streamflow 

pentiles. In contrast, organic synthesis compounds, fumigants, and refrigerants occurred less frequently in all pentiles. 

Overall, the gasoline hydrocarbons occurred more frequently 

in the first and fifth pentiles, and the solvents occurred most 

frequently in the fifth pentile. The detection frequency of 

gasoline hydrocarbons generally decreased as the streamflow increased from the first to fourth pentile then increased 

from the fourth to fifth pentile. The detection frequency of 

the solvents and organic synthesis compounds increased as 

the streamflow increased from the first to the fifth pentile. In 

contrast, the detection frequency of the trihalomethanes and 

gasoline oxygenates generally decreased as the streamflow 

increased. The detection frequency of the fumigants and 

refrigerants did not differ markedly as streamflow increased.

Median concentrations of detections for gasoline hydrocarbons, solvents, gasoline oxygenates, and organic synthesis 

compounds generally increased as streamflow increased. 

Median concentrations of detections for trihalomethanes 

and fumigants generally decreased as streamflow increased. 

Median concentrations of detections for refrigerants showed 

no pattern as streamflow increased.

Two occurrence patterns were evident for most of the 

15 most frequently detected VOCs: (1) the detection frequency 

generally decreases as streamflow increases, and (2) the detection frequency generally increases as the streamflow increases. 

The first pattern may be from VOCs primarily entering the 
52 Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003

stream from groundwater inflows or from small point-source 

discharges that are diluted with increased streamflow, whereas 

some VOCs also may have additional sources, such as stormwater runoff, contributing to the increased presence during 

larger streamflow conditions in the second pattern. 

Toluene, chloroform, MTBE, perchloroethene, and 

dichloromethane generally had decreasing detection frequencies as the streamflow increased. In contrast, gasoline hydrocarbons—m- and p-xylene, benzene, 1,2,4-trimethylbenzene, 

and o-xylene—and the solvents—trichloroethene, cis-1,2-dichloroethene, chloromethane and methyl isobutyl ketone—had 

increasing detection frequencies as the streamflow increased.

Seven of the 15 most frequently detected VOCs (toluene, 

MTBE, acetone, chloromethane, o-xylene, dichloromethane, 

and methyl isobutyl ketone) had increasing median concentrations of detections as streamflow increased. In contrast, three 

VOCs (chloroform, perchloroethene, and cis-1,2-dichloroethene) showed a decrease in the median concentrations of detections as streamflow increased. The five other most frequently 

detected compounds had no significant change in the median 

concentrations of detections as streamflow increased.

concentrations in the warmer months, and (3) no difference 

in the median concentrations between the seasons. The first 

pattern included the gasoline hydrocarbons, solvents, and 

gasoline oxygenates, with median concentrations of detections 

for the solvents and gasoline oxygenates significantly larger 

in cooler months than in warmer months. The second pattern 

included the organic synthesis compounds and refrigerants, 

with median concentrations of detections for organic synthesis compounds significantly larger in warmer months than in 

cooler months. The third pattern included the trihalomethanes 

and fumigants, with no significant difference in the median 

concentrations of detections between the two seasons. The 

first pattern may be, in part, because the partitioning between 

air and water based on the Henry’s Gas Law is more favorable to VOCs staying in water as the temperature decreases 

meaning less volatilization during cooler months. The second 

pattern may be from VOCs primarily entering the stream from 

groundwater inflows or from small point-source discharges 

entering the stream during warmer months and, possibly, 

larger use in warmer months. The third pattern may indicate a 

consistent source for the compounds in these VOC groups.

Eleven (toluene, MTBE, perchloroethene, acetone, mand p-xylene, benzene, 1,2,4-trimethylbenzene, o-xylene, 

dichloromethane, 1,1,1-trichloroethane, and methyl isobutyl 

ketone) of the 15 most frequently detected VOCs occurred 

more frequently in cooler months than in warmer months. 

Four (chloroform, trichloroethene, cis-1,2-dichloroethene, 

and chloromethane) of the 15 most frequently detected VOCs 

occurred slightly more frequently in warmer months than 

in cooler months. More individual VOCs were detected in 

samples from cooler months (55 VOCs) than from warmer 

months (47 VOCs).

Of the 15 most frequently detected VOCs, 6 VOCs 

(toluene, chloroform, perchloroethene, benzene, o-xylene, 

and methyl isobutyl ketone) had median concentrations 

of detections that were not different in warmer or cooler 

months, 6 VOCs (trichloroethene, acetone, m- and p-xylene, 

1,2,4-trimethylbenzene, dichloromethane, and 1,1,1-trichloroethane) had median concentrations of detections that were 

slightly larger in warmer months, and 3 VOCs (MTBE, cis1,2-dicholoethene, and chloromethane) had median concentrations of detections that were larger in cooler months. The 

concentrations for most of the compounds varied over at least 

two orders of magnitude, with the largest concentrations typically in the cooler months for most of the VOCs.

None of the samples had concentrations greater than a 

U.S. Environmental Protection Agency Maximum Contaminant Level. However, six compounds (trichloroethene, 

perchloroethene, cis-1,2-dichloroethene, dichloromethane, 

vinyl chloride, dibromochloropropane) had concentrations 

within 10 percent of a Maximum Contaminant Level. Concentrations of MTBE in five samples were greater than or equal 

to the lower limit of the USEPA Drinking Water Advisory. 

Toluene and chloroform had concentrations greater than or 

equal to aquatic-life criteria. Five additional compounds had 

concentrations less than but within 10 percent of the aquaticlife criteria.

Occurrence Patterns of Volatile Organic 

Compounds by Season

Water quality of urban streams may vary with season 

of the year as well as with streamflow. The patterns of VOC 

occurrence described in this report were not markedly different between streamflow pentiles for one or more VOCs, 

VOC groups, and individual VOCs. Because a marked 

difference between the streamflow pentiles was not evident, 

the 869 samples from the 37 urban streams were stratified 

by warmer (April through September) and cooler (October 

through March) months to compare the effects of seasonality 

on water quality at these urban sites.

One or more VOCs were frequently detected in both 

warmer and cooler months and the detection frequencies for 

warmer and cooler months were not statistically different. 

However, median total VOC concentrations were significantly larger in cooler months than in warmer months, with 

the median total VOC concentration at least twice as large 

in cooler months. Furthermore, the median number and total 

VOCs detected in samples were statistically larger in cooler 

months than in warmer months. 

The detection frequencies of gasoline hydrocarbons, 

gasoline oxygenates, organic synthesis compounds, fumigants, 

and refrigerants generally were similar or larger in cooler 

months than in warmer months. However, the differences in 

the detection frequencies between warmer and cooler months 

within each VOC group were not significant. Gasoline hydrocarbons were the most frequently detected VOC group in both 

warmer and cooler months. 

Three general patterns were evident for the median 

concentrations of detections for the VOC groups: (1) larger 

median concentrations in the cooler months, (2) larger median 
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contamination by volatile organic compounds in surfaceand ground-water sampling procedures: U.S. Geological 

Survey Open-File Report 00–384, 36 p.

Terracciano, S.A., and O’Brien, A.K., 1997, Occurrence of 

volatile organic compounds in streams on Long Island, 

New York, and New Jersey—overview of available data 

and reconnaissance sampling: U.S. Geological Survey Fact 

Sheet 97–063, 4 p.

Thiros, S.A., 2000, Analysis of nitrate and volatile organic 

compound data for ground water in the Great Salt Lake 

Basins, Utah, Idaho, and Wyoming, 1980–98, National 

Water-Quality Assessment Program: U.S. Geological 

Survey Water-Resources Investigations Report 00–4043, 

20 p.

Toccalino, P.L., Norman, J.E., Booth, N.L., and Zogorski, J.S., 

2006, Health-Based Screening Levels—a tool for evaluating what water-quality data may mean to human health: 

U.S. Geological Survey, National Water-Quality Assessment 

Program, accessed February 2, 2007, at http://water.usgs.

gov/nawqa/HBSL/.

U.S. Environmental Protection Agency, 1982, Results of the 

nationwide urban runoff program, Volume II Appendices: 

U.S. Environmental Protection Agency, Water Planning 

Division, 862 p.

U.S. Environmental Protection Agency, 1983a, Results of the 

nationwide urban runoff program, Executive summary: U.S. 

Environmental Protection Agency, Water Planning Division, 

24 p.

U.S. Environmental Protection Agency, 1983b, Results of the 

nationwide urban runoff program, Volume I Final report: 

U.S. Environmental Protection Agency, Water Planning 

Division, 198 p.

U.S. Environmental Protection Agency, 1991, Water-quality 

criteria summary: Office of Water, Office of Science 

and Technology, Health and Ecological Effects Division 

(poster).

U.S. Environmental Protection Agency, 1997, Drinking-water 

advisory—consumer acceptability advice and health effects 

analysis on methyl tertiary-butyl ether (MtBE): Office of 

Water, EPA–822–F–97–009, 42 p.

U.S. Environmental Protection Agency, 1999a, Report to 

Congress on the Phase II stormwater regulations: 

U.S. Environmental Protection Agency, Office of Water, 

EPA 833–R–99–001, 40 p.

U.S. Environmental Protection Agency, 1999b, A review of 

contaminant occurrence in public water systems: Washington, D.C., EPA 816–R–99–006, 78 p.
56 Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003

U.S. Environmental Protection Agency, 2000a, Report to 

Congress on the Phase I stormwater regulations: 

U.S. Environmental Protection Agency, Office of Water, 

EPA 833–R–00–001 [variously paged].

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quality inventory, 1998 Report to Congress: Washington, 

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of the Drinking Water Standards and Health Advisories: 

Washington, D.C., EPA 822–R–06–013, 12 p.

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treatment of volatile organic compounds in water supplies: 

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relationships between discharge and water chemistry in 

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and Kuroda, Kouichi, 1997, Volatile organic compounds in 

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W.W., Moran, M.J., Rowe, B.L., Squillace, P.J., and 

Toccalino, P.L., 2006, The quality of our Nation’s water—

volatile organic compounds in the Nation’s ground water 

and drinking-water supply wells: U.S. Geological Survey 

Circular 1292, 101 p.
Glossary 57

Glossary

Assessment level A concentration selected 

by a scientist and applied to water-quality data 

that have variable laboratory reporting levels 

either for a specific compound or between 

individual compounds. The assessment level 

is applied to data received from the laboratory 

and is applied subsequent to the laboratory 

reporting level. Concentrations reported by 

the laboratory but less than the assessment 

level are considered as “non-detections” in 

the calculation of occurrence statistics. The 

primary purpose of the assessment level is for 

accurate comparison of detection frequencies 

and median concentrations between individual 

VOCs, groups of VOCs, and to previous 

studies.

Concentration The amount or mass of a 

substance present in a given volume or mass 

of sample. Concentrations in this report are 

expressed in micrograms per liter.

Fumigant A compound or mixture of 

compounds that produces a gas, vapor, 

fumes, or smoke intended to destroy, repel, or 

control organisms such as insects, bacteria, 

or rodents. Bromomethane is an example of 

a fumigant used for large-scale strawberry 

farming.

Gasoline hydrocarbon A straight, branched, 

and (or) cyclic structured organic compound 

containing only carbon and hydrogen atoms 

that is a common ingredient in gasoline 

and other petroleum product formulations. 

Benzene, toluene, ethylbenzene, and xylenes, 

commonly referred to as BTEX, are a subset 

of the gasoline hydrocarbons.

Gasoline oxygenate A compound that 

contains oxygen and added to gasoline in 

order to meet the requirements of the 1990 

Clean Air Act Amendments. As used in this 

report, gasoline oxygenates include the four 

ethers—MTBE, TAME, DIPE, and ETBE.

Health-Based Screening Level (HBSL) An 

estimate of concentration (for a noncarcinogen) or concentration range (for a carcinogen) 

in water that (1) may be of potential humanhealth concern, (2) can be used as a threshold 

value against which measured concentrations 

of contaminants in water samples can be 

compared, and (3) is consistent with USEPA 

Office of Water methodologies.

Low-level (analytical) method An enhanced 

gas chromatography/mass spectrometry 

(GC/MS) method for the analysis of VOCs 

in ambient water samples, USGS method 

0–4127–96, which was implemented by the 

USGS in 1996.

Major river basin (MRB) As used in this 

report, the major surface-water regions of 

the United States corresponding to the major 

hydrologic units within each basin.

Maximum Contaminant Level (MCL) As used 

in this report, a USEPA drinking-water standard that is legally enforceable, and that sets 

the maximum permissible level of a contaminant in water that is delivered to any user of a 

public water system.

Median concentration of detections As 

used in this report, the median concentration 

for the subset of samples that had concentrations equal to or greater than the assessment 

level of 0.02 microgram per liter.

Organic synthesis compound A compound 

that is used in the formation of other organic 

compounds. Vinyl chloride is an example of 

an organic synthesis compound used in the 

production of polyvinyl chloride plastics.

Pentile One of five segments of a distribution that has been divided into fifths, each 

being 20 percent of the range. As used in 

this report the cumulative distribution of 

streamflow was divided into fifths, each being 

20 percent of the streamflow at a site (for 

example, less than 20, 20 to less than 40, 40 

to less than 60, 60 to less than 80, and greater 

than or equal to 80 percent).

Refrigerant A compound used for producing 

refrigeration, either as a working substance in 

a refrigerator or by direct absorption of heat. 

The chlorofluorocarbons (CFCs) are classified 

as refrigerants for the purposes of this report.

Solvent A compound that is used to dissolve 

other substances. Two of the more common 

solvents are trichloroethene (TCE) and 

perchloroethene (PCE).
58 Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003

Study Unit A major hydrologic system of 

the United States in which NAWQA studies 

are focused, geographically defined by 

surface-water or groundwater features and 

usually encompassing more than 3,861 mi2

(10,000 km2) of land area. The NAWQA 

studies during the first decade of assessments 

included 51 of these systems, collectively 

covering a large part of the Nation, encompassing the majority of population and water 

use, and including diverse hydrologic settings 

that differ widely in the natural and human 

factors that affect water quality.

Total VOC concentration The sum of all 

quantified concentrations for all VOCs 

analyzed in a sample.

Trihalomethane As used in this report, a 

compound belonging to a group of VOCs that 

includes bromodichloromethane, bromoform, 

chloroform, and dibromochloromethane. 

These compounds are known by-products of 

water chlorination.

Volatile organic compound (VOC) An 

organic chemical that has a high vapor pressure relative to its water solubility. VOCs 

include components of gasoline, fuel oils, and 

lubricants, as well as organic solvents, fumigants, some inert ingredients in pesticides, 

refrigerants, some compounds used in organic 

synthesis, and some by-products of water 

chlorination.
Appendix 1
60 Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003

Appendix 1. Figures showing streamflow and statistics for all sites (linked to 

Streamflow Record Extension section)

Figure A1.1. Daily streamflow and 20-year pentiles of flow, in cubic feet per second, at station 01102500, 

Aberjona River at Winchester, Mass., from May 1999 to March 2000.

1

10

100

1,000

May 1999 Jun 1999 Jul 1999 Aug 1999 Sep 1999 Oct 1999 Nov 1999 Dec 1999 Jan 2000 Feb 2000 Mar 2000 Apr 2000

MONTH-YEAR

STREAMFLOW, IN CUBIC FEET PER SECOND

Sample Q Daily Q 20-yr 80% of Q

20-yr 60% of Q 20-yr 40% of Q 20-yr 20% of Q

[Sample Q, streamflow during sampling; Daily Q, mean daily streamflow; 20-yr 80% of Q, 80th percentile of streamflow based on 20-years of 

mean daily streamflow; 20-yr 60% of Q, 60th percentile of streamflow based on 20-years of mean daily streamflow; 20-yr 40% of Q, 40th percentile of streamflow based on 20-years of mean daily streamflow; 20-yr 20% of Q, 20th percentile of streamflow based on 20-years of mean daily 

streamflow]
Appendix 1 61

Figure A1.2. Daily streamflow and 20-year pentiles of flow, in cubic feet per second, at station 01209710, Norwalk River at 

Winnipauk, Conn., from November 2001 to September 2002.

Figure A1.3. Daily streamflow and 20-year pentiles of flow, in cubic feet per second, at station 01390500, Saddle River at 

Ridgewood, N.J., from May 1996 to January 1997.

1

10

100

1,000

MONTH-YEAR

STREAMFLOW, IN CUBIC FEET PER SECOND

Sample Q Daily Q 20-yr 80% of Q

20-yr 60% of Q 20-yr 40% of Q 20-yr 20% of Q

Nov 2001 Dec 2001 Jan 2002 Feb 2002 Mar 2002 Apr 2002 May 2002 Jun 2002 Jul 2002 Aug 2002 Sep 2002 Oct 2002

[Sample Q, streamflow during sampling; Daily Q, mean daily streamflow; 20-yr 80% of Q, 80th percentile of streamflow based on 20-years of mean daily 

streamflow; 20-yr 60% of Q, 60th percentile of streamflow based on 20-years of mean daily streamflow; 20-yr 40% of Q, 40th percentile of streamflow based 

on 20-years of mean daily streamflow; 20-yr 20% of Q, 20th percentile of streamflow based on 20-years of mean daily streamflow]

1

10

100

1,000

MONTH-YEAR

STREAMFLOW, IN CUBIC FEET PER SECOND

Sample Q Daily Q 20-yr 80% of Q

20-yr 60% of Q 20-yr 40% of Q 20-yr 20% of Q

Apr 1996 May 1996 Jun 1996 Jul 1996 Aug 1996 Sep 1996 Oct 1996 Nov 1996 Dec 1996 Jan 1997 Feb 1997

[Sample Q, streamflow during sampling; Daily Q, mean daily streamflow; 20-yr 80% of Q, 80th percentile of streamflow based on 20-years of mean daily 

streamflow; 20-yr 60% of Q, 60th percentile of streamflow based on 20-years of mean daily streamflow; 20-yr 40% of Q, 40th percentile of streamflow based 

on 20-years of mean daily streamflow; 20-yr 20% of Q, 20th percentile of streamflow based on 20-years of mean daily streamflow]
62 Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003

Figure A1.4. Daily streamflow and 20-year pentiles of flow, in cubic feet per second, at station 01403900, Bound Brook 

at Middlesex, N.J., from April 1996 to July 2002.

Figure A1.5. Daily streamflow and 20-year pentiles of flow, in cubic feet per second, at station 01410784, Great Egg 

Harbor River near Sicklerville, N.J., from April 1996 to March 1998.

1

10

100

10,000

1,000

MONTH-YEAR

STREAMFLOW, IN CUBIC FEET PER SECOND

Sample Q Daily Q 20-yr 80% of Q

20-yr 60% of Q 20-yr 40% of Q 20-yr 20% of Q

Mar 1996 Sep 1996 Mar 1997 Sep 1997 Mar 1998 Sep 1998 Mar 1999 Sep 1999 Mar 2000 Sep 2000 Mar 2001 Sep 2001 Mar 2002 Sep 2002

[Sample Q, streamflow during sampling; Daily Q, mean daily streamflow; 20-yr 80% of Q, 80th percentile of streamflow based on 20-years of mean daily 

streamflow; 20-yr 60% of Q, 60th percentile of streamflow based on 20-years of mean daily streamflow; 20-yr 40% of Q, 40th percentile of streamflow based 

on 20-years of mean daily streamflow; 20-yr 20% of Q, 20th percentile of streamflow based on 20-years of mean daily streamflow]

1

10

100

MONTH-YEAR

STREAMFLOW, IN CUBIC FEET PER SECOND

Sample Q Daily Q 20-yr 80% of Q

20-yr 60% of Q 20-yr 40% of Q 20-yr 20% of Q

Mar 1996 May 1996 Jul 1996 Sep 1996 Nov 1996 Jan 1997 Mar 1997 May 1997 Jul 1997 Sep 1997 Nov 1997 Jan 1998 Mar 1998

[Sample Q, streamflow during sampling; Daily Q, mean daily streamflow; 20-yr 80% of Q, 80th percentile of streamflow based on 20-years of mean daily 

streamflow; 20-yr 60% of Q, 60th percentile of streamflow based on 20-years of mean daily streamflow; 20-yr 40% of Q, 40th percentile of streamflow based 

on 20-years of mean daily streamflow; 20-yr 20% of Q, 20th percentile of streamflow based on 20-years of mean daily streamflow]
Appendix 1 63

0.1

1

10

10,000

100

1,000

MONTH-YEAR

STREAMFLOW, IN CUBIC FEET PER SECOND

Sample Q Daily Q 20-yr 80% of Q

20-yr 60% of Q 20-yr 40% of Q 20-yr 20% of Q

Nov 1998 Jan 1999 Mar 1999 May 1999 Jul 1999 Sep 1999 Nov 1999 Jan 2000 Mar 2000 May 2000 Jul 2000 Sep 2000 Nov 2000

[Sample Q, streamflow during sampling; Daily Q, mean daily streamflow; 20-yr 80% of Q, 80th percentile of streamflow based on 20-years of mean daily 

streamflow; 20-yr 60% of Q, 60th percentile of streamflow based on 20-years of mean daily streamflow; 20-yr 40% of Q, 40th percentile of streamflow based 

on 20-years of mean daily streamflow; 20-yr 20% of Q, 20th percentile of streamflow based on 20-years of mean daily streamflow]

Figure A1.6. Daily streamflow and 20-year pentiles of flow, in cubic feet per second, at station 01464907, Little Neshaminy 

Creek at Valley Road near Neshaminy, Pa., from February 1999 to October 2000.

Figure A1.7. Daily streamflow and 20-year pentiles of flow, in cubic feet per second, at station 01467150, Cooper River at 

Haddonfield, N.J., from December 1998 to October 2000.

0.1

1

10

10,000

100

1,000

MONTH-YEAR

STREAMFLOW, IN CUBIC FEET PER SECOND

Sample Q Daily Q 20-yr 80% of Q

20-yr 60% of Q 20-yr 40% of Q 20-yr 20% of Q

Jan 1999 Mar 1999 May 1999 Jul 1999 Sep 1999 Nov 1999 Jan 2000 Mar 2000 May 2000 Jul 2000 Sep 2000 Nov 2000

[Sample Q, streamflow during sampling; Daily Q, mean daily streamflow; 20-yr 80% of Q, 80th percentile of streamflow based on 20-years of mean daily 

streamflow; 20-yr 60% of Q, 60th percentile of streamflow based on 20-years of mean daily streamflow; 20-yr 40% of Q, 40th percentile of streamflow based 

on 20-years of mean daily streamflow; 20-yr 20% of Q, 20th percentile of streamflow based on 20-years of mean daily streamflow]
64 Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003

0.01

0.1

1

10

100

1,000

MONTH-YEAR

STREAMFLOW, IN CUBIC FEET PER SECOND

Sample Q Daily Q 20-yr 80% of Q

20-yr 60% of Q 20-yr 40% of Q 20-yr 20% of Q

Oct 2001 Nov 2001 Dec 2001 Jan 2002 Feb 2002 Mar 2002 Apr 2002 May 2002 Jun 2002 Jul 2002 Aug 2002 Sep 2002 Oct 2002

[Sample Q, streamflow during sampling; Daily Q, mean daily streamflow; 20-yr 80% of Q, 80th percentile of streamflow based on 20-years of mean daily 

streamflow; 20-yr 60% of Q, 60th percentile of streamflow based on 20-years of mean daily streamflow; 20-yr 40% of Q, 40th percentile of streamflow based 

on 20-years of mean daily streamflow; 20-yr 20% of Q, 20th percentile of streamflow based on 20-years of mean daily streamflow]

Figure A1.8. Daily streamflow and 20-year pentiles of flow, in cubic feet per second, at station 01571490, Cedar Run at 

Eberlys Mill, Pa., from January 1994 to August 1995.

Figure A1.9. Daily streamflow and 20-year pentiles of flow, in cubic feet per second, at station 01654000, Accotink Creek 

near Annandale, Va., from October 2001 to September 2002.

1

10

100

1,000

MONTH-YEAR

STREAMFLOW, IN CUBIC FEET PER SECOND

Sample Q Daily Q 20-yr 80% of Q

20-yr 60% of Q 20-yr 40% of Q 20-yr 20% of Q

Dec 1993 Feb 1994 Apr 1994 Jun 1994 Aug 1994 Oct 1994 Dec 1994 Feb 1995 Apr 1995 Jun 1995 Aug 1995

[Sample Q, streamflow during sampling; Daily Q, mean daily streamflow; 20-yr 80% of Q, 80th percentile of streamflow based on 20-years of mean daily 

streamflow; 20-yr 60% of Q, 60th percentile of streamflow based on 20-years of mean daily streamflow; 20-yr 40% of Q, 40th percentile of streamflow based 

on 20-years of mean daily streamflow; 20-yr 20% of Q, 20th percentile of streamflow based on 20-years of mean daily streamflow]
Appendix 1 65

1

10

100

10,000

1,000

MONTH-YEAR

STREAMFLOW, IN CUBIC FEET PER SECOND

Jan 1996 Mar 1996 May 1996 Jul 1996 Sep 1996 Nov 1996 Jan 1997 Mar 1997 May 1997 Jul 1997 Sep 1997 Nov 1997 Jan 1998 Mar 1998

Sample Q Daily Q 20-yr 80% of Q

20-yr 60% of Q 20-yr 40% of Q 20-yr 20% of Q

[Sample Q, streamflow during sampling; Daily Q, mean daily streamflow; 20-yr 80% of Q, 80th percentile of streamflow based on 20-years of mean daily 

streamflow; 20-yr 60% of Q, 60th percentile of streamflow based on 20-years of mean daily streamflow; 20-yr 40% of Q, 40th percentile of streamflow based 

on 20-years of mean daily streamflow; 20-yr 20% of Q, 20th percentile of streamflow based on 20-years of mean daily streamflow]

Figure A1.10. Daily streamflow and 20-year pentiles of flow, in cubic feet per second, at station 02087580, Swift Creek 

near Apex, N.C., from October 2001 to July 2003.

Figure A1.11. Daily streamflow and 20-year pentiles of flow, in cubic feet per second, at station 02169570, Gills Creek at 

Columbia, S.C., from February 1996 to March 1998.

0.01

0.1

1

10

100

1,000

MONTH-YEAR

STREAMFLOW, IN CUBIC FEET PER SECOND

Sample Q Daily Q

20-yr 80% of Q 20-yr 60% of Q

20-yr 40% of Q 20-yr 20% of Q

Sep 2001 Nov 2001 Jan 2002 Mar 2002 May 2002 Jul 2002 Sep 2002 Nov 2002 Jan 2003 Mar 2003 May 2003 Jul 2003

[Sample Q, streamflow during sampling; Daily Q, mean daily streamflow; 20-yr 80% of Q, 80th percentile of streamflow based on 20-years of mean daily 

streamflow; 20-yr 60% of Q, 60th percentile of streamflow based on 20-years of mean daily streamflow; 20-yr 40% of Q, 40th percentile of streamflow based 

on 20-years of mean daily streamflow; 20-yr 20% of Q, 20th percentile of streamflow based on 20-years of mean daily streamflow]
66 Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003

Figure A1.12. Daily streamflow and 20-year pentiles of flow, in cubic feet per second, at station 02306774, Rocky Creek at 

State Highway 587 at Citrus Park, Fla., from January 2002 to July 2003.

Figure A1.13. Daily streamflow and 20-year pentiles of flow, in cubic feet per second, at station 02335870, Sope Creek near 

Marietta, Ga., from October 2001 to September 2002.

0.001

1

0.1

0.01

10

100

1,000

MONTH-YEAR

STREAMFLOW, IN CUBIC FEET PER SECOND

Sample Q Daily Q 20-yr 80% of Q

20-yr 60% of Q 20-yr 40% of Q 20-yr 20% of Q

Jan 2002 Mar 2002 May 2002 Jul 2002 Sep 2002 Nov 2002 Jan 2003 Mar 2003 May 2003 Jul 2003

[Sample Q, streamflow during sampling; Daily Q, mean daily streamflow; 20-yr 80% of Q, 80th percentile of streamflow based on 20-years of mean daily 

streamflow; 20-yr 60% of Q, 60th percentile of streamflow based on 20-years of mean daily streamflow; 20-yr 40% of Q, 40th percentile of streamflow based 

on 20-years of mean daily streamflow; 20-yr 20% of Q, 20th percentile of streamflow based on 20-years of mean daily streamflow]

1

10

100

1,000

MONTH-YEAR

STREAMFLOW, IN CUBIC FEET PER SECOND

Sample Q Daily Q 20-yr 80% of Q

20-yr 60% of Q 20-yr 40% of Q 20-yr 20% of Q

Sep 2001 Oct 2001 Nov 2001 Dec 2001 Jan 2002 Feb 2002 Mar 2002 Apr 2002 May 2002 Jun 2002 Jul 2002 Aug 2002 Sep 2002 Oct 2002

[Sample Q, streamflow during sampling; Daily Q, mean daily streamflow; 20-yr 80% of Q, 80th percentile of streamflow based on 20-years of mean daily 

streamflow; 20-yr 60% of Q, 60th percentile of streamflow based on 20-years of mean daily streamflow; 20-yr 40% of Q, 40th percentile of streamflow based 

on 20-years of mean daily streamflow; 20-yr 20% of Q, 20th percentile of streamflow based on 20-years of mean daily streamflow]
Appendix 1 67

Figure A1.14. Daily streamflow and 20-year pentiles of flow, in cubic feet per second, at station 02419977, Three Mile Branch 

at North Boulevard at Montgomery, Ala., from January 1999 to June 2001.

Figure A1.15. Daily streamflow and 20-year pentiles of flow, in cubic feet per second, at station 0242354750, Cahaba 

Valley Creek at Cross Creek Road at Pelham, Ala., from January 1999 to June 2001.

1

10

100

1,000

MONTH-YEAR

STREAMFLOW, IN CUBIC FEET PER SECOND

Sample Q Daily Q 20-yr 80% of Q

20-yr 60% of Q 20-yr 40% of Q 20-yr 20% of Q

Dec 1998 Feb 1999 Apr 1999 Jun 1999 Aug 1999 Oct 1999 Dec 1999 Feb 2000 Apr 2000 Jun 2000 Aug 2000 Oct 2000 Dec 2000 Feb 2001 Apr 2001 Jun 2001

[Sample Q, streamflow during sampling; Daily Q, mean daily streamflow; 20-yr 80% of Q, 80th percentile of streamflow based on 20-years of mean daily 

streamflow; 20-yr 60% of Q, 60th percentile of streamflow based on 20-years of mean daily streamflow; 20-yr 40% of Q, 40th percentile of streamflow based 

on 20-years of mean daily streamflow; 20-yr 20% of Q, 20th percentile of streamflow based on 20-years of mean daily streamflow]

1

10

100

10,000

1,000

MONTH-YEAR

STREAMFLOW, IN CUBIC FEET PER SECOND

Sample Q Daily Q 20-yr 80% of Q

20-yr 60% of Q 20-yr 40% of Q 20-yr 20% of Q

Dec 1998 Apr 1999 Aug 1999 Dec 1999 Apr 2000 Aug 2000 Dec 2000 Apr 2001

[Sample Q, streamflow during sampling; Daily Q, mean daily streamflow; 20-yr 80% of Q, 80th percentile of streamflow based on 20-years of mean daily 

streamflow; 20-yr 60% of Q, 60th percentile of streamflow based on 20-years of mean daily streamflow; 20-yr 40% of Q, 40th percentile of streamflow based 

on 20-years of mean daily streamflow; 20-yr 20% of Q, 20th percentile of streamflow based on 20-years of mean daily streamflow]
68 Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003

Figure A1.16. Daily streamflow and 20-year pentiles of flow, in cubic feet per second, at station 03049646, Deer Creek 

near Dorseyville, Pa., from January 1997 to August 1998.

Figure A1.17. Daily streamflow and 20-year pentiles of flow, in cubic feet per second, at station 03353637, Little Buck Creek 

near Indianapolis, Ind., from March 2001 to September 2002.

0.01

1

0.1

10

100

1,000

MONTH-YEAR

STREAMFLOW, IN CUBIC FEET PER SECOND

Sample Q Daily Q 20-yr 80% of Q

20-yr 60% of Q 20-yr 40% of Q 20-yr 20% of Q

Feb 1997 Apr 1997 Jun 1997 Aug 1997 Oct 1997 Dec 1997 Feb 1998 Apr 1998 Jun 1998 Aug 1998

[Sample Q, streamflow during sampling; Daily Q, mean daily streamflow; 20-yr 80% of Q, 80th percentile of streamflow based on 20-years of mean daily 

streamflow; 20-yr 60% of Q, 60th percentile of streamflow based on 20-years of mean daily streamflow; 20-yr 40% of Q, 40th percentile of streamflow based 

on 20-years of mean daily streamflow; 20-yr 20% of Q, 20th percentile of streamflow based on 20-years of mean daily streamflow]

0.01

1

0.1

10

100

10,000

1,000

MONTH-YEAR

STREAMFLOW, IN CUBIC FEET PER SECOND

Sample Q Daily Q 20-yr 80% of Q

20-yr 60% of Q 20-yr 40% of Q 20-yr 20% of Q

Feb 2001 Apr 2001 Jun 2001 Aug 2001 Dec 2001 Feb 2002 Apr 2002 Jun 2002 Aug 2002 Oct 2002

[Sample Q, streamflow during sampling; Daily Q, mean daily streamflow; 20-yr 80% of Q, 80th percentile of streamflow based on 20-years of mean daily 

streamflow; 20-yr 60% of Q, 60th percentile of streamflow based on 20-years of mean daily streamflow; 20-yr 40% of Q, 40th percentile of streamflow based 

on 20-years of mean daily streamflow; 20-yr 20% of Q, 20th percentile of streamflow based on 20-years of mean daily streamflow]

Oct 2001
Appendix 1 69

Figure A1.18. Daily streamflow and 20-year pentiles of flow, in cubic feet per second, at station 393944084120700, Holes Creek 

in Huffman Park at Kettering, Ohio, from March 1999 to September 2002.

Figure A1.19. Daily streamflow and 20-year pentiles of flow, in cubic feet per second, at station 040869415, Lincoln Creek at 

47th Street at Milwaukee, Wis., from November 2001 to September 2002.

1

0.1

10

100

1,000

MONTH-YEAR

STREAMFLOW, IN CUBIC FEET PER SECOND

Sample Q Daily Q 20-yr 80% of Q

20-yr 60% of Q 20-yr 40% of Q 20-yr 20% of Q

Feb 1999 May 1999 Aug 1999 Nov 1999 Feb 2000 May 2000 Aug 2000 Nov 2000 Feb 2001 May 2001 Aug 2001 Nov 2001 Feb 2002 May 2002 Aug 2002

[Sample Q, streamflow during sampling; Daily Q, mean daily streamflow; 20-yr 80% of Q, 80th percentile of streamflow based on 20-years of mean daily 

streamflow; 20-yr 60% of Q, 60th percentile of streamflow based on 20-years of mean daily streamflow; 20-yr 40% of Q, 40th percentile of streamflow based 

on 20-years of mean daily streamflow; 20-yr 20% of Q, 20th percentile of streamflow based on 20-years of mean daily streamflow]

1

0.1

10

100

10,000

1,000

MONTH-YEAR

STREAMFLOW, IN CUBIC FEET PER SECOND

Sample Q Daily Q 20-yr 80% of Q

20-yr 60% of Q 20-yr 40% of Q 20-yr 20% of Q

Nov 2001 Dec 2001 Jan 2002 Feb 2002 Mar 2002 Apr 2002 May 2002 Jun 2002 Jul 2002 Aug 2002 Sep 2002 Oct 2002

[Sample Q, streamflow during sampling; Daily Q, mean daily streamflow; 20-yr 80% of Q, 80th percentile of streamflow based on 20-years of mean daily 

streamflow; 20-yr 60% of Q, 60th percentile of streamflow based on 20-years of mean daily streamflow; 20-yr 40% of Q, 40th percentile of streamflow based 

on 20-years of mean daily streamflow; 20-yr 20% of Q, 20th percentile of streamflow based on 20-years of mean daily streamflow]
70 Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003

Figure A1.21. Daily streamflow and 20-year pentiles of flow, in cubic feet per second, at station 05288705, Shingle Creek 

at Queen Avenue in Minneapolis, Minn., from August 1996 to November 1998.

Figure A1.20. Daily streamflow and 20-year pentiles of flow, in cubic feet per second, at station 04161820, Clinton River 

at Sterling Heights, Mich., from October 1996 to June 1998.

10

100

10,000

1,000

MONTH-YEAR

STREAMFLOW, IN CUBIC FEET PER SECOND

Sample Q Daily Q 20-yr 80% of Q

20-yr 60% of Q 20-yr 40% of Q 20-yr 20% of Q

Oct 1996 Dec 1996 Feb 1997 Apr 1997 Jun 1997 Aug 1997 Oct 1997 Dec 1997 Feb 1998 Apr 1998 Jun 1998

[Sample Q, streamflow during sampling; Daily Q, mean daily streamflow; 20-yr 80% of Q, 80th percentile of streamflow based on 20-years of mean daily 

streamflow; 20-yr 60% of Q, 60th percentile of streamflow based on 20-years of mean daily streamflow; 20-yr 40% of Q, 40th percentile of streamflow based 

on 20-years of mean daily streamflow; 20-yr 20% of Q, 20th percentile of streamflow based on 20-years of mean daily streamflow]

MONTH-YEAR

STREAMFLOW, IN CUBIC FEET PER SECOND

Sample Q Daily Q 20-yr 80% of Q

20-yr 60% of Q 20-yr 40% of Q 20-yr 20% of Q

Jul 1996 Sep 1996 Nov 1996 Jan 1997 Mar 1997 May 1997 Jul 1997 Sep 1997 Nov 1997 Jan 1998 Mar 1998 May 1998 Jul 1998 Sep 1998 Nov 1998

[Sample Q, streamflow during sampling; Daily Q, mean daily streamflow; 20-yr 80% of Q, 80th percentile of streamflow based on 20-years of mean daily 

streamflow; 20-yr 60% of Q, 60th percentile of streamflow based on 20-years of mean daily streamflow; 20-yr 40% of Q, 40th percentile of streamflow based 

on 20-years of mean daily streamflow; 20-yr 20% of Q, 20th percentile of streamflow based on 20-years of mean daily streamflow]

0.1

10

1

100

1,000
Appendix 1 71

Figure A1.22. Daily streamflow and 20-year pentiles of flow, in cubic feet per second, at station 05330902, Nine Mile Creek 

near James Circle at Bloomington, Minn., from January 1997 to December 1997.

Figure A1.23. Daily streamflow and 20-year pentiles of flow, in cubic feet per second, at station 05531500, Salt Creek at 

Western Springs, Ill., from March 1999 to March 2000.

0.1

10

1

100

1,000

MONTH-YEAR

STREAMFLOW, IN CUBIC FEET PER SECOND

Sample Q Daily Q 20-yr 80% of Q

20-yr 60% of Q 20-yr 40% of Q 20-yr 20% of Q

Jan 1997 Feb 1997 Mar 1997 Apr 1997 May 1997 Jun 1997 Jul 1997 Aug 1997 Sep 1997 Oct 1997 Nov 1997 Dec 1997 Jan 1998

[Sample Q, streamflow during sampling; Daily Q, mean daily streamflow; 20-yr 80% of Q, 80th percentile of streamflow based on 20-years of mean daily 

streamflow; 20-yr 60% of Q, 60th percentile of streamflow based on 20-years of mean daily streamflow; 20-yr 40% of Q, 40th percentile of streamflow based 

on 20-years of mean daily streamflow; 20-yr 20% of Q, 20th percentile of streamflow based on 20-years of mean daily streamflow]

10

1

100

10,000

1,000

MONTH-YEAR

STREAMFLOW, IN CUBIC FEET PER SECOND

Sample Q Daily Q 20-yr 80% of Q

20-yr 60% of Q 20-yr 40% of Q 20-yr 20% of Q

Feb 1999 Mar 1999 Apr 1999 May 1999 Jun 1999 Jul 1999 Aug 1999 Sep 1999 Oct 1999 Nov 1999 Dec 1999 Jan 2000 Feb 2000 Mar 2000 Apr 2000

[Sample Q, streamflow during sampling; Daily Q, mean daily streamflow; 20-yr 80% of Q, 80th percentile of streamflow based on 20-years of mean daily 

streamflow; 20-yr 60% of Q, 60th percentile of streamflow based on 20-years of mean daily streamflow; 20-yr 40% of Q, 40th percentile of streamflow based 

on 20-years of mean daily streamflow; 20-yr 20% of Q, 20th percentile of streamflow based on 20-years of mean daily streamflow]
72 Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003

Figure A1.24. Daily streamflow and 20-year pentiles of flow, in cubic feet per second, at station 06713500, Cherry Creek at 

Denver, Colo., from October 2001 to September 2002.

Figure A1.25. Daily streamflow and 20-year pentiles of flow, in cubic feet per second, at station 07031692, Fletcher 

Creek at Sycamore View Road at Memphis, Tenn., from October 1996 to September 1997.

10

1

100

1,000

MONTH-YEAR

STREAMFLOW, IN CUBIC FEET PER SECOND

Sample Q Daily Q 20-yr 80% of Q

20-yr 60% of Q 20-yr 40% of Q 20-yr 20% of Q

Oct 2001 Nov 2001 Dec 2001 Jan 2002 Feb 2002 Mar 2002 Apr 2002 May 2002 Jun 2002 Jul 2002 Aug 2002 Sep 2002 Oct 2002

[Sample Q, streamflow during sampling; Daily Q, mean daily streamflow; 20-yr 80% of Q, 80th percentile of streamflow based on 20-years of mean daily 

streamflow; 20-yr 60% of Q, 60th percentile of streamflow based on 20-years of mean daily streamflow; 20-yr 40% of Q, 40th percentile of streamflow based 

on 20-years of mean daily streamflow; 20-yr 20% of Q, 20th percentile of streamflow based on 20-years of mean daily streamflow]

10

1

0.1

0.01

100

10,000

1,000

MONTH-YEAR

STREAMFLOW, IN CUBIC FEET PER SECOND

Sample Q Daily Q 20-yr 80% of Q

20-yr 60% of Q 20-yr 40% of Q 20-yr 20% of Q

Sep 1996 Oct 1996 Nov 1996 Dec 1996 Jan 1997 Feb 1997 Mar 1997 Apr 1997 May 1997 Jun 1997 Jul 1997 Aug 1997 Sep 1997 Oct 1997

[Sample Q, streamflow during sampling; Daily Q, mean daily streamflow; 20-yr 80% of Q, 80th percentile of streamflow based on 20-years of mean daily 

streamflow; 20-yr 60% of Q, 60th percentile of streamflow based on 20-years of mean daily streamflow; 20-yr 40% of Q, 40th percentile of streamflow based 

on 20-years of mean daily streamflow; 20-yr 20% of Q, 20th percentile of streamflow based on 20-years of mean daily streamflow]
Appendix 1 73

Figure A1.26. Daily streamflow and 20-year pentiles of flow, in cubic feet per second, at station 07379960, Dawson Creek at 

Bluebonnet Boulevard near Baton Rouge, La., from January 1999 to February 2001.

Figure A1.27. Daily streamflow and 20-year pentiles of flow, in cubic feet per second, at station 08057200, White Rock 

Creek at Greenville Avenue, Dallas, Tex., from October 2001 to September 2002.

10

1

0.1

100

1,000

MONTH-YEAR

STREAMFLOW, IN CUBIC FEET PER SECOND

Sample Q Daily Q 20-yr 80% of Q

20-yr 60% of Q 20-yr 40% of Q 20-yr 20% of Q

Dec 1998 Feb 1999 Apr 1999 Jun 1999 Aug 1999 Oct 1999 Dec 1999 Feb 2000 Apr 2000 Jun 2000 Aug 2000 Oct 2000 Dec 2000 Feb 2001

[Sample Q, streamflow during sampling; Daily Q, mean daily streamflow; 20-yr 80% of Q, 80th percentile of streamflow based on 20-years of mean daily 

streamflow; 20-yr 60% of Q, 60th percentile of streamflow based on 20-years of mean daily streamflow; 20-yr 40% of Q, 40th percentile of streamflow based 

on 20-years of mean daily streamflow; 20-yr 20% of Q, 20th percentile of streamflow based on 20-years of mean daily streamflow]

10

1

100

10,000

1,000

MONTH-YEAR

STREAMFLOW, IN CUBIC FEET PER SECOND

Sample Q Daily Q 20-yr 80% of Q

20-yr 60% of Q 20-yr 40% of Q 20-yr 20% of Q

Oct 2001 Nov 2001 Dec 2001 Jan 2002 Feb 2002 Mar 2002 Apr 2002 May 2002 Jun 2002 Jul 2002 Aug 2002 Sep 2002 Oct 2002

[Sample Q, streamflow during sampling; Daily Q, mean daily streamflow; 20-yr 80% of Q, 80th percentile of streamflow based on 20-years of mean daily 

streamflow; 20-yr 60% of Q, 60th percentile of streamflow based on 20-years of mean daily streamflow; 20-yr 40% of Q, 40th percentile of streamflow based 

on 20-years of mean daily streamflow; 20-yr 20% of Q, 20th percentile of streamflow based on 20-years of mean daily streamflow]
74 Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003

Figure A1.28. Daily streamflow and 20-year pentiles of flow, in cubic feet per second, at station 08178800, Salado Creek at 

Loop 13 at San Antonio, Tex., from January 1997 to January 1998.

Figure A1.29. Daily streamflow and 20-year pentiles of flow, in cubic feet per second, at station 094196783, Las Vegas 

Wash below Flamingo Wash confluence near Las Vegas, Nev., from October 2001 to August 2002.

10

1

0.1

0.01

100

10,000

100,000

1,000

MONTH-YEAR

STREAMFLOW, IN CUBIC FEET PER SECOND

Sample Q Daily Q 20-yr 80% of Q

20-yr 60% of Q 20-yr 40% of Q 20-yr 20% of Q

Jan 1997 Feb 1997 Mar 1997 Apr 1997 May 1997 Jun 1997 Jul 1997 Aug 1997 Sep 1997 Oct 1997 Nov 1997 Dec 1997 Jan 1998 Feb 1998

[Sample Q, streamflow during sampling; Daily Q, mean daily streamflow; 20-yr 80% of Q, 80th percentile of streamflow based on 20-years of mean daily 

streamflow; 20-yr 60% of Q, 60th percentile of streamflow based on 20-years of mean daily streamflow; 20-yr 40% of Q, 40th percentile of streamflow based 

on 20-years of mean daily streamflow; 20-yr 20% of Q, 20th percentile of streamflow based on 20-years of mean daily streamflow]

10

1

100

MONTH-YEAR

STREAMFLOW, IN CUBIC FEET PER SECOND

Sample Q Daily Q 20-yr 80% of Q

20-yr 60% of Q 20-yr 40% of Q 20-yr 20% of Q

Sep 2001 Oct 2001 Nov 2001 Dec 2001 Jan 2002 Feb 2002 Mar 2002 Apr 2002 May 2002 Jun 2002 Jul 2002 Aug 2002 Sep 2002

[Sample Q, streamflow during sampling; Daily Q, mean daily streamflow; 20-yr 80% of Q, 80th percentile of streamflow based on 20-years of mean daily 

streamflow; 20-yr 60% of Q, 60th percentile of streamflow based on 20-years of mean daily streamflow; 20-yr 40% of Q, 40th percentile of streamflow based 

on 20-years of mean daily streamflow; 20-yr 20% of Q, 20th percentile of streamflow based on 20-years of mean daily streamflow]
Appendix 1 75

Figure A1.30. Daily streamflow and 20-year pentiles of flow, in cubic feet per second, at station 10168000, Little 

Cottonwood Creek at Jordan River near Salt Lake City, Utah, from March 1999 to April 2000.

Figure A1.31. Daily streamflow and 20-year pentiles of flow, in cubic feet per second, at station 11060400, Warm Creek 

near San Bernardino, Calif., from November 1998 to June 2002.

10

0.1

1

1,000

100

MONTH-YEAR

STREAMFLOW, IN CUBIC FEET PER SECOND

Sample Q Daily Q 20-yr 80% of Q

20-yr 60% of Q 20-yr 40% of Q 20-yr 20% of Q

Mar 1999 Apr 1999 May 1999 Jun 1999 Jul 1999 Aug 1999 Sep 1999 Oct 1999 Nov 1999 Dec 1999 Jan 2000 Feb 2000 Mar 2000 Apr 2000 May 2000

[Sample Q, streamflow during sampling; Daily Q, mean daily streamflow; 20-yr 80% of Q, 80th percentile of streamflow based on 20-years of mean daily 

streamflow; 20-yr 60% of Q, 60th percentile of streamflow based on 20-years of mean daily streamflow; 20-yr 40% of Q, 40th percentile of streamflow based 

on 20-years of mean daily streamflow; 20-yr 20% of Q, 20th percentile of streamflow based on 20-years of mean daily streamflow]

10

0.01

0.1

1

1,000

100

MONTH-YEAR

STREAMFLOW, IN CUBIC FEET PER SECOND

Sample Q Daily Q 20-yr 80% of Q

20-yr 60% of Q 20-yr 40% of Q 20-yr 20% of Q

Oct 1998 Jan 1999 Apr 1999 Jul 1999 Oct 1999 Jan 2000 Apr 2000 Jul 2000 Oct 2000 Jan 2001 Apr 2001 Jul 2001 Oct 2001 Jan 2002 Apr 2002

[Sample Q, streamflow during sampling; Daily Q, mean daily streamflow; 20-yr 80% of Q, 80th percentile of streamflow based on 20-years of mean daily 

streamflow; 20-yr 60% of Q, 60th percentile of streamflow based on 20-years of mean daily streamflow; 20-yr 40% of Q, 40th percentile of streamflow based 

on 20-years of mean daily streamflow; 20-yr 20% of Q, 20th percentile of streamflow based on 20-years of mean daily streamflow]
76 Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003

Figure A1.32. Daily streamflow and 20-year pentiles of flow, in cubic feet per second, at station 11447360, Arcade Creek 

near Del Paso Heights, Calif., from March 1996 to April 1998.

Figure A1.33. Daily streamflow and 20-year pentiles of flow, in cubic feet per second, at station 12128000, Thornton Creek 

near Seattle, Wash., from March 1996 to May 1998.

10

0.01

0.1

1

10,000

1,000

100

MONTH-YEAR

STREAMFLOW, IN CUBIC FEET PER SECOND

Sample Q Daily Q 20-yr 80% of Q

20-yr 60% of Q 20-yr 40% of Q 20-yr 20% of Q

Feb 1996 Apr 1996 Jun 1996 Aug 1996 Oct 1996 Dec 1996 Feb 1997 Apr 1997 Jun 1997 Aug 1997 Oct 1997 Dec 1997 Feb 1998 Apr 1998

[Sample Q, streamflow during sampling; Daily Q, mean daily streamflow; 20-yr 80% of Q, 80th percentile of streamflow based on 20-years of mean daily 

streamflow; 20-yr 60% of Q, 60th percentile of streamflow based on 20-years of mean daily streamflow; 20-yr 40% of Q, 40th percentile of streamflow based 

on 20-years of mean daily streamflow; 20-yr 20% of Q, 20th percentile of streamflow based on 20-years of mean daily streamflow]

10

0.1

1

1,000

100

MONTH-YEAR

STREAMFLOW, IN CUBIC FEET PER SECOND

Sample Q Daily Q 20-yr 80% of Q

20-yr 60% of Q 20-yr 40% of Q 20-yr 20% of Q

Feb 1996 Apr 1996 Jun 1996 Aug 1996 Oct 1996 Dec 1996 Feb 1997 Apr 1997 Jun 1997 Aug 1997 Oct 1997 Dec 1997 Feb 1998 Apr 1998 Jun 1998

[Sample Q, streamflow during sampling; Daily Q, mean daily streamflow; 20-yr 80% of Q, 80th percentile of streamflow based on 20-years of mean daily 

streamflow; 20-yr 60% of Q, 60th percentile of streamflow based on 20-years of mean daily streamflow; 20-yr 40% of Q, 40th percentile of streamflow based 

on 20-years of mean daily streamflow; 20-yr 20% of Q, 20th percentile of streamflow based on 20-years of mean daily streamflow]
Appendix 1 77

Figure A1.34. Daily streamflow and 20-year pentiles of flow, in cubic feet per second, at station 12424500, Spokane River 

at 7 Mile Bridge near Spokane, Wash., from February 1999 to October 1999.

Figure A1.35. Daily streamflow and 20-year pentiles of flow, in cubic feet per second, at station 14206950, Fanno Creek at 

Durham, Oreg., from October 2001 to September 2002.

100

1,000

100,000

10,000

MONTH-YEAR

STREAMFLOW, IN CUBIC FEET PER SECOND

Sample Q Daily Q 20-yr 80% of Q

20-yr 60% of Q 20-yr 40% of Q 20-yr 20% of Q

Jan 1999 Feb 1999 Mar 1999 Apr 1999 May 1999 Jun 1999 Jul 1999 Aug 1999 Sep 1999 Oct 1999 Nov 1999

[Sample Q, streamflow during sampling; Daily Q, mean daily streamflow; 20-yr 80% of Q, 80th percentile of streamflow based on 20-years of mean daily 

streamflow; 20-yr 60% of Q, 60th percentile of streamflow based on 20-years of mean daily streamflow; 20-yr 40% of Q, 40th percentile of streamflow based 

on 20-years of mean daily streamflow; 20-yr 20% of Q, 20th percentile of streamflow based on 20-years of mean daily streamflow]

1

10

1,000

100

MONTH-YEAR

STREAMFLOW, IN CUBIC FEET PER SECOND

Sample Q Daily Q 20-yr 80% of Q

20-yr 60% of Q 20-yr 40% of Q 20-yr 20% of Q

Oct 2001 Nov 2001 Dec 2001 Jan 2002 Feb 2002 Mar 2002 Apr 2002 May 2002 Jun 2002 Jul 2002 Aug 2002 Sep 2002 Oct 2002

[Sample Q, streamflow during sampling; Daily Q, mean daily streamflow; 20-yr 80% of Q, 80th percentile of streamflow based on 20-years of mean daily 

streamflow; 20-yr 60% of Q, 60th percentile of streamflow based on 20-years of mean daily streamflow; 20-yr 40% of Q, 40th percentile of streamflow based 

on 20-years of mean daily streamflow; 20-yr 20% of Q, 20th percentile of streamflow based on 20-years of mean daily streamflow]
Figure A1.36. Daily streamflow and 20-year pentiles of flow, in cubic feet per second, at station 15275100, Chester Creek at 

Arctic Boulevard at Anchorage, Alaska, from January 1999 to September 1999.

Figure A1.37. Daily streamflow and 20-year pentiles of flow, in cubic feet per second, at station 16242500, Manoa Stream at 

Kanewai Field, Honolulu, Oahu, Hawaii, from July 1999 to June 2000.

1

10

1,000

100

MONTH-YEAR

STREAMFLOW, IN CUBIC FEET PER SECOND

Sample Q Daily Q 20-yr 80% of Q

20-yr 60% of Q 20-yr 40% of Q 20-yr 20% of Q

Jan 1999 Feb 1999 Mar 1999 Apr 1999 May 1999 Jun 1999 Jul 1999 Aug 1999 Sep 1999 Oct 1999

[Sample Q, streamflow during sampling; Daily Q, mean daily streamflow; 20-yr 80% of Q, 80th percentile of streamflow based on 20-years of mean daily 

streamflow; 20-yr 60% of Q, 60th percentile of streamflow based on 20-years of mean daily streamflow; 20-yr 40% of Q, 40th percentile of streamflow based 

on 20-years of mean daily streamflow; 20-yr 20% of Q, 20th percentile of streamflow based on 20-years of mean daily streamflow]

1

10

1,000

100

MONTH-YEAR

STREAMFLOW, IN CUBIC FEET PER SECOND

Sample Q Daily Q 20-yr 80% of Q

20-yr 60% of Q 20-yr 40% of Q 20-yr 20% of Q

Jul 1999 Aug 1999 Sep 1999 Oct 1999 Nov 1999 Dec 1999 Jan 2000 Feb 2000 Mar 2000 Apr 2000 May 2000 Jun 2000 Jul 2000

[Sample Q, streamflow during sampling; Daily Q, mean daily streamflow; 20-yr 80% of Q, 80th percentile of streamflow based on 20-years of mean daily 

streamflow; 20-yr 60% of Q, 60th percentile of streamflow based on 20-years of mean daily streamflow; 20-yr 40% of Q, 40th percentile of streamflow based 

on 20-years of mean daily streamflow; 20-yr 20% of Q, 20th percentile of streamflow based on 20-years of mean daily streamflow]
Appendix 2
80 Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003

Appendix 2. Summary of the detection frequency and concentrations by warmer (April through September) and cooler (October 

through March) months for individual volatile organic compounds at an assessment level of 0.02 microgram per liter, 1995–2003.—

Continued

[VOC, volatile organic compound; USGS, U.S. Geological Survey; F, fumigant; GH, gasoline hydrocarbon; GO, gasoline oxygenate; O, organic synthesis 

compound; R, refrigerant; S, solvent; T, trihalomethane; <, less than; E, estimated concentration below the long-term method detection level; --, not applicable]

Compound name VOC 

group

USGS 

parameter 

code

Warmer months (April through September) 

Number 

of 

samples

Number 

of 

samples 

with 

detected 

VOCs

Detection 

frequency 

(percent)

Statistical summary for concentrations 

(micrograms per liter) 

Minimum 25th 

percentile Median 75th percentile Maximum 

Toluene GH 34010 409 282 69 <0.04 <0.04 0.04 0.09 3.5 

Chloroform T 32106 410 230 56 <.02 <.02 .02 .04 1.9 

Methyl tert-butyl 

ether

GO 78032 410 148 36 <.11 <.11 <.11 .10 21 

Trichloroethene S 39180 410 145 35 <.04 <.04 <.04 .05 .57 

Perchloroethene S 34475 410 113 28 <.03 <.03 <.03 .02 1.1 

cis-1,2-Dichloroethene

S 77093 410 139 34 <.02 <.02 <.02 .04 1.5 

Acetone S 81552 403 115 29 <4.9 <4.9 <4.9 E1.5 45 

m- and p-Xylene GH 85795 403 79 20 <.06 <.06 <.06 <.06 .69 

Benzene GH 34030 410 51 12 <.02 <.02 <.02 <.02 .21 

Chloromethane S 34418 410 69 17 <.17 <.17 <.17 <.17 .20 

1,2,4-TrimethylbenzeneGH 77222 410 26 6.3 <.06 <.06 <.06 <.06 .66 

o-Xylene GH 77135 403 22 5.5 <.04 <.04 <.04 <.04 .36 

Dichloromethane S 34423 410 38 9.3 <.06 <.06 <.06 <.06 1.4 

1,1,1-TrichloroethaneS 34506 410 38 9.3 <.03 <.03 <.03 <.03 1.3 

Methyl isobutyl 

ketone

S 78133 403 22 5.5 <.37 <.37 <.37 <.37 1.1 

Carbon disulfide O 77041 403 37 9.2 <.04 <.04 <.04 <.04 .2 

Methyl ethyl ketone S 81595 403 27 6.7 <1.6 <1.6 <1.6 <1.6 5.7 

BromodichloromethaneT 32101 410 34 8.3 <.03 <.03 <.03 <.03 .48 

4-Isopropyltoluene GH 77356 410 31 7.6 <.07 <.07 <.07 <.07 1.4 

1,1-Dichloroethane S 34496 410 29 7.1 <.03 <.03 <.03 <.03 .11 

Ethylbenzene GH 34371 410 13 3.2 <.03 <.03 <.03 <.03 .13 

Chlorobenzene S 34301 410 21 5.1 <.03 <.03 <.03 <.03 .33 

1,4-DichlorobenzeneF 34571 410 17 4.2 <.03 <.03 <.03 <.03 .05 

tert-Amyl methyl 

ether

GO 50005 403 8 2.0 <.08 <.08 <.08 <.08 .09 

Naphthalene GH 34696 410 2 .49 <.25 <.25 <.25 <.25 E.06 

1,1-Dichloroethene O 34501 410 8 2.0 <.02 <.02 <.02 <.02 .05 

DibromochloromethaneT 32105 410 15 3.7 <.1 <.1 <.1 <.1 .36 
Appendix 2 81

Cooler months (October through March)

Number 

of 

samples

Number 

of 

samples 

with 

detected 

VOCs

Detection 

frequency 

(percent)

Statistical summary for concentrations 

(micrograms per liter)

Minimum 25th 

percentile Median 75th percentile Maximum

458 366 80 <0.04 0.02 0.05 0.10 11

459 250 54 <.02 <.02 .02 .04 1.9

459 200 44 <.11 <.11 <.11 .25 44

459 154 34 <.04 <.04 <.04 .04 1.5

459 184 40 <.03 <.03 <.03 .06 .78

459 155 34 <.02 <.02 <.02 .04 7.6

453 146 32 <4.9 <4.9 <4.9 E1.9 698

453 160 35 <.06 <.06 <.06 .03 .67

459 143 31 <.02 <.02 <.02 .02 .20

458 59 13 <.17 <.17 <.17 <.17 .30

459 82 18 <.06 <.06 <.06 <.06 .99

453 75 17 <.04 <.04 <.04 <.04 .35

459 57 12 <.06 <.06 <.06 <.06 .99

459 56 12 <.03 <.03 <.03 <.03 .30

453 60 13 <.37 <.37 <.37 <.37 1.5

453 44 9.7 <.04 <.04 <.04 <.04 .11

452 51 11 <1.6 <1.6 <1.6 <1.6 4.3

459 43 9.4 <.03 <.03 <.03 <.03 .88

459 43 9.4 <.07 <.07 <.07 <.07 2.1

459 37 8.1 <.03 <.03 <.03 <.03 .16

459 47 10 <.03 <.03 <.03 <.03 .09

459 25 5.5 <.03 <.03 <.03 <.03 .37

458 28 6.1 <.03 <.03 <.03 <.03 .26

453 36 8.0 <.08 <.08 <.08 <.08 .17

459 36 7.8 <.25 <.25 <.25 <.25 .30

459 23 5.0 <.02 <.02 <.02 <.02 .06

458 14 3.1 <.1 <.1 <.1 <.1 .50
82 Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003

Appendix 2. Summary of the detection frequency and concentrations by warmer (April through September) and cooler (October 

through March) months for individual volatile organic compounds at an assessment level of 0.02 microgram per liter, 1995–2003.—

Continued

[VOC, volatile organic compound; USGS, U.S. Geological Survey; F, fumigant; GH, gasoline hydrocarbon; GO, gasoline oxygenate; O, organic synthesis 

compound; R, refrigerant; S, solvent; T, trihalomethane; <, less than; E, estimated concentration below the long-term method detection level; --, not applicable]

Compound name VOC 

group

USGS 

parameter 

code

Warmer months (April through September) 

Number 

of 

samples

Number 

of 

samples 

with 

detected 

VOCs

Detection 

frequency 

(percent)

Statistical summary for concentrations 

(micrograms per liter) 

Minimum 25th 

percentile Median 75th percentile Maximum 

1,2,3-TrimethylbenzeneGH 77221 403 7 1.7 <0.06 <0.06 <0.06 <0.06 0.17 

Styrene GH 77128 410 12 2.9 <.04 <.04 <.04 <.04 .04 

TrichlorotrifluoroethaneR 77652 410 10 2.4 <.03 <.03 <.03 <.03 .10 

1,3,5-TrimethylbenzeneGH 77226 410 7 1.7 <.04 <.04 <.04 <.04 .17 

2-Ethyltoluene GH 77220 403 5 1.2 <.06 <.06 <.06 <.06 .10 

Tetrahydrofuran S 81607 403 12 3.0 <1.2 <1.2 <1.2 <1.2 3.3 

1,2,3,5-TetramethylbenzeneGH 50000 403 4 .99 <.14 <.14 <.14 <.14 .14 

Chloroethane S 34311 410 7 1.7 <.12 <.12 <.12 <.12 .10 

DichlorodifluoromethaneR 34668 410 4 .98 <.1 <.1 <.1 <.1 .50 

Tetrachloromethane S 32102 410 3 .73 <.06 <.06 <.06 <.06 .04 

Diisopropyl ether GO 81577 351 2 .57 <.1 <.1 <1 <.1 E.02 

Bromoform T 32104 410 4 .98 <.06 <.06 <.06 <.06 .54 

n-Propylbenzene S 77224 410 3 .73 <.04 <.04 <.04 <.04 .05 

Diethyl ether S 81576 403 8 2.0 <.08 <.08 <.08 <.08 .43 

1,2,3,4-TetramethylbenzeneGH 49999 403 0 -- <.14 <.14 <.14 <.14 <.14 

Vinyl chloride O 39175 410 3 .73 <.06 <.06 <.06 <.06 .80 

Acrolein O 34210 154 2 1.3 <1.5 <1.5 <1.5 <1.5 2.1 

trans-1,2-Dichloroethene

S 34546 410 1 .24 <.03 <.03 <.03 <.03 .03 

n-Butylbenzene GH 77342 410 0 -- <.12 <.12 <.12 <.12 <.12 

2-Chlorotoluene S 77275 410 2 .49 <.03 <.03 <.03 <.03 .05 

1,2-DichloropropaneF 34541 410 0 -- <.03 <.03 <.03 <.03 <.03 

1,1,2,2-TetrachloroethaneS 34516 410 0 -- <.09 <.09 <.09 <.09 <.09 

TrichlorofluoromethaneR 34488 410 0 -- <.03 <.03 <.03 <.03 <.03 

Ethyl tert-butyl 

ether

GO 50004 403 0 -- <.05 <.05 <.05 <.05 <.05 

sec-Butylbenzene GH 77350 410 0 -- <.03 <.03 <.03 <.03 <.03 
Appendix 2 83

Cooler months (October through March)

Number 

of 

samples

Number 

of 

samples 

with 

detected 

VOCs

Detection 

frequency 

(percent)

Statistical summary for concentrations 

(micrograms per liter)

Minimum 25th 

percentile Median 75th percentile Maximum

453 21 4.6 <0.06 <0.06 <0.06 <0.06 0.22

459 15 3.3 <.04 <.04 <.04 <.04 .10

459 17 3.7 <.03 <.03 <.03 <.03 .15

459 17 3.7 <.04 <.04 <.04 <.04 .25

453 17 3.8 <.06 <.06 <.06 <.06 .18

453 10 2.2 <1.2 <1.2 <1.2 <1.2 1.5

453 10 2.2 <.14 <.14 <.14 <.14 .10

459 7 1.5 <.12 <.12 <.12 <.12 .09

459 7 1.5 <.1 <.1 <.1 <.1 .58

459 8 1.7 <.06 <.06 <.06 <.06 .04

412 7 1.7 <.1 <.1 <.1 <.1 .05

459 6 1.3 <.06 <.06 <.06 <.06 .13

459 7 1.5 <.04 <.04 <.04 <.04 .08

453 1 .22 <.08 <.08 <.08 <.08 .07

453 9 2.0 <.14 <.14 <.14 <.14 .35

459 6 1.3 <.06 <.06 <.06 <.06 .94

154 1 .65 <1.5 <1.5 <1.5 <1.5 3.4

459 5 1.1 <.03 <.03 <.03 <.03 3.52

459 5 1.1 <.12 <.12 <.12 <.12 E.04

459 2 .44 <.03 <.03 <.03 <.03 .07

459 2 .44 <.03 <.03 <.03 <.03 .03

459 2 .44 <.09 <.09 <.09 <.09 .08

459 2 .44 <.03 <.03 <.03 <.03 .08

453 1 .22 <.05 <.05 <.05 <.05 E.02

459 1 .22 <.03 <.03 <.03 <.03 .02
84 Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003

Appendix 2. Summary of the detection frequency and concentrations by warmer (April through September) and cooler (October 

through March) months for individual volatile organic compounds at an assessment level of 0.02 microgram per liter, 1995–2003.—

Continued

[VOC, volatile organic compound; USGS, U.S. Geological Survey; F, fumigant; GH, gasoline hydrocarbon; GO, gasoline oxygenate; O, organic synthesis 

compound; R, refrigerant; S, solvent; T, trihalomethane; <, less than; E, estimated concentration below the long-term method detection level; --, not applicable]

Compound name VOC 

group

USGS 

parameter 

code

Warmer months (April through September) 

Number 

of 

samples

Number 

of 

samples 

with 

detected 

VOCs

Detection 

frequency 

(percent)

Statistical summary for concentrations 

(micrograms per liter) 

Minimum 25th 

percentile Median 75th percentile Maximum 

DibromochloropropaneF 82625 410 1 0.24 <0.21 <0.21 <0.21 <0.21 E0.09 

1,2-DichlorobenzeneS 34536 410 0 -- <.05 <.05 <.05 <.05 <.05 

1,3-DichlorobenzeneS 34566 410 0 -- <.03 <.03 <.03 <.03 <.03 

1,2-Dichloroethane S 32103 410 1 .24 <.13 <.13 <.13 <.13 E.03 

Isopropylbenzene GH 77223 410 0 -- <.03 <.03 <.03 <.03 <.03 

Acrylonitrile O 34215 404 0 -- <1.2 <1.2 <1.2 <1.2 <1.2 

Bromobenzene S 81555 410 0 -- <.03 <.03 <.03 <.03 <.03 

BromochloromethaneO 77297 410 0 -- <.04 <.04 <.04 <.04 <.04 

Bromomethane F 34413 410 0 -- <.15 <.15 <.15 <.15 <.15 

tert-Butylbenzene GH 77353 410 0 -- <.05 <.05 <.05 <.05 <.05 

3-Chloro-1-propene O 78109 403 0 -- <.07 <.07 <.07 <.07 <.07 

4-Chlorotoluene S 77277 410 0 -- <.05 <.05 <.05 <.05 <.05 

Dibromomethane S 30217 410 0 -- <.05 <.05 <.05 <.05 <.05 

trans-1,4-Dichloro2-butene

O 73547 403 0 -- <.7 <.7 <.7 <.7 <.7 

1,3-DichloropropaneO 77173 410 0 -- <.06 <.06 <.06 <.06 <.06 

2,2-DichloropropaneO 77170 410 0 -- <.05 <.05 <.05 <.05 <.05 

1,1-DichloropropeneO 77168 410 0 -- <.03 <.03 <.03 <.03 <.03 

cis-1,3-Dichloropropene

F 34704 410 0 -- <.05 <.05 <.05 <.05 <.05 

trans-1,3-Dichloropropene

F 34699 410 0 -- <.09 <.09 <.09 <.09 <.09 

Ethylene dibromide F 77651 410 0 -- <.04 <.04 <.04 <.04 <.04 

Ethyl methacrylate O 73570 403 0 -- <.18 <.18 <.18 <.18 <.18 

HexachlorobutadieneO 39702 410 0 -- <.14 <.14 <.14 <.14 <.14 

Hexachloroethane S 34396 404 0 -- <.14 <.14 <.14 <.14 <.14 

Iodomethane O 77424 403 0 -- <.08 <.08 <.08 <.08 <.08 

Methyl acrylate O 49991 403 0 -- <.6 <.6 <.6 <.6 <.6 
Appendix 2 85

Cooler months (October through March)

Number 

of 

samples

Number 

of 

samples 

with 

detected 

VOCs

Detection 

frequency 

(percent)

Statistical summary for concentrations 

(micrograms per liter)

Minimum 25th 

percentile Median 75th percentile Maximum

459 0 -- <0.21 <0.21 <0.21 <0.21 <0.21

459 1 0.22 <.05 <.05 <.05 <.05 .18

459 1 .22 <.03 <.03 <.03 <.03 .02

459 0 -- <.13 <.13 <.13 <.13 <.13

459 1 .22 <.03 <.03 <.03 <.03 .03

454 0 -- <1.2 <1.2 <1.2 <1.2 <1.2

459 0 -- <.03 <.03 <.03 <.03 <.03

459 0 -- <.04 <.04 <.04 <.04 <.04

459 0 -- <.15 <.15 <.15 <.15 <.15

459 0 -- <.05 <.05 <.05 <.05 <.05

453 0 -- <.07 <.07 <.07 <.07 <.07

459 0 -- <.05 <.05 <.05 <.05 <.05

459 0 -- <.05 <.05 <.05 <.05 <.05

453 0 -- <.7 <.7 <.7 <.7 <.7

459 0 -- <.06 <.06 <.06 <.06 <.06

459 0 -- <.05 <.05 <.05 <.05 <.05

459 0 -- <.03 <.03 <.03 <.03 <.03

459 0 -- <.05 <.05 <.05 <.05 <.05

459 0 -- <.09 <.09 <.09 <.09 <.09

459 0 -- <.04 <.04 <.04 <.04 <.04

453 0 -- <.18 <.18 <.18 <.18 <.18

459 0 -- <.14 <.14 <.14 <.14 <.14

453 0 -- <.14 <.14 <.14 <.14 <.14

453 0 -- <.08 <.08 <.08 <.08 <.08

453 0 -- <.6 <.6 <.6 <.6 <.6
86 Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003

Appendix 2. Summary of the detection frequency and concentrations by warmer (April through September) and cooler (October 

through March) months for individual volatile organic compounds at an assessment level of 0.02 microgram per liter, 1995–2003.—

Continued

[VOC, volatile organic compound; USGS, U.S. Geological Survey; F, fumigant; GH, gasoline hydrocarbon; GO, gasoline oxygenate; O, organic synthesis 

compound; R, refrigerant; S, solvent; T, trihalomethane; <, less than; E, estimated concentration below the long-term method detection level; --, not applicable]

Compound name VOC 

group

USGS 

parameter 

code

Warmer months (April through September) 

Number 

of 

samples

Number 

of 

samples 

with 

detected 

VOCs

Detection 

frequency 

(percent)

Statistical summary for concentrations 

(micrograms per liter) 

Minimum 25th 

percentile Median 75th percentile Maximum 

Methyl acrylonitrile O 81593 403 0 -- <0.6 <0.6 <0.6 <0.6 <0.6 

Methyl butyl 

ketone

S 77103 403 0 -- <.7 <.7 <.7 <.7 <.7 

Methyl methacrylateO 81597 403 0 -- <.35 <.35 <.35 <.35 <.35 

1,1,1,2-TetrachloroethaneS 77562 410 0 -- <.03 <.03 <.03 <.03 <.03 

1,2,3-TrichlorobenzeneO 77613 410 0 -- <.27 <.27 <.27 <.27 <.27 

1,2,4-TrichlorobenzeneS 34551 410 0 -- <.07 <.07 <.07 <.07 <.07 

1,1,2-TrichloroethaneS 34511 410 0 -- <.06 <.06 <.06 <.06 <.06 

1,2,3-TrichloropropaneF 77443 410 0 -- <.07 <.07 <.07 <.07 <.07 

Vinyl acetate O 77057 95 0 -- <5 <5 <5 <5 <5 

Vinyl bromide O 50002 403 0 -- <.1 <.1 <.1 <.1 <.1 
Appendix 2 87

Cooler months (October through March)

Number 

of 

samples

Number 

of 

samples 

with 

detected 

VOCs

Detection 

frequency 

(percent)

Statistical summary for concentrations 

(micrograms per liter)

Minimum 25th 

percentile Median 75th percentile Maximum

453 0 -- <0.6 <0.6 <0.6 <0.6 <0.6

453 0 -- <.7 <.7 <.7 <.7 <.7

453 0 -- <.35 <.35 <.35 <.35 <.35

459 0 -- <.03 <.03 <.03 <.03 <.03

459 0 -- <.27 <.27 <.27 <.27 <.27

459 0 -- <.07 <.07 <.07 <.07 <.07

459 0 -- <.06 <.06 <.06 <.06 <.06

459 0 -- <.07 <.07 <.07 <.07 <.07

106 0 -- <5 <5 <5 <5 <5

453 0 -- <.1 <.1 <.1 <.1 <.1
Publishing support provided by:

Denver Publishing Service Center

For more information concerning this publication, contact:

Director, USGS South Dakota Water Science Center

1608 Mt. View Rd.

Rapid City, SD 57702

(605) 394–3200

Or visit the South Dakota Water Science Center Web site at:

http://sd.water.usgs.gov

Bender and others— Occurrence of Volatile Organic Compounds in Selected Urban Streams in the United States, 1995–2003—SIR 2009–5203

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