Organic Waste Compounds as Contaminants in 

Milwaukee-Area Streams

During 2006–9, the U.S. Geological Survey (USGS), in 

cooperation with the Milwaukee Metropolitan Sewerage District (MMSD), conducted a study to investigate organic waste 

compounds (OWCs) in Milwaukee-area streams. OWCs are 

ingredients and by-products of common agricultural, industrial, 

and household substances that can contaminate our streams 

through sources like 

urban runoff, sewage 

overflows, and leaking 

septic systems. This 

fact sheet summarizes 

the major findings of 

this study; detailed 

information about this 

study and its results 

can be found in USGS 

Scientific Investigations 

Report 2013–5104.

This study will assist 

watershed managers in 

prioritizing management and remediation 

efforts by describing the occurrence, concentration, distribution, 

and toxicity of OWCs in Milwaukee-area streams.

Samples were collected at 12 sites (fig. 1). Three different sample types were collected: stream samples collected 

under normal flow conditions (base flow), water contained in 

the streambed (pore water), and the streambed sediment itself. 

Additionally, to investigate the effect of varying flow conditions, four stream sites representing varying degrees of urbanization were identified for stormflow sampling (stream samples 

collected during a storm)—Milwaukee River near Cedarburg 

(MRC, least urban); Oak Creek at South Milwaukee (OSM); 

Menomonee River at Wauwatosa (MRW); and Kinnickinnic 

River at South 11th Street, at Milwaukee (KRM, most urban). 

Each water sample was tested for 69 different OWCs; each sediment sample was tested for 57 different OWCs.

How Often Did We Find Organic Waste Compounds?

All of the 196 samples collected contained at least one OWC, 

with as many as 41 different compounds detected in a single sample. 

Of the 69 compounds analyzed, 

64 were detected at least once. The 

lowest detection rates were in baseflow samples, with a median of 12 

compounds detected per sample. 

Stormflow, pore-water, and sediment samples had roughly twice as 

many detections.

The compound classes with 

the highest detection rates were 

polycyclic aromatic hydrocarbons 

(PAHs), insecticides, herbicides, 

and dyes/pigments. PAHs were 

the most frequently detected class 

overall, occurring in 100 percent 

of the stormflow, pore-water, and 

sediment samples, and in 80 percent 

of the base-flow samples. Detection frequencies for all classes are 

shown in figure 2.

What Are Organic Waste Compounds (OWCs)?

OWCs are ingredients and by-products of common 

agricultural, industrial, and household substances. For this 

study, 69 individual compounds were aggregated into 15 

classes:

• Antioxidants

• Dyes/pigments

• Fire retardants

• Polycyclic aromatic 

hydrocarbons (PAHs)

• Plasticizers

• Fuels

• Solvents

• Herbicides

• Insecticides

• Antimicrobial disinfectants

• Detergent metabolites

• Flavors and fragrances

• Human drugs 

(nonprescription)

• Sterols

• Miscellaneous

OWCs enter the environment in many ways, including runoff from urban and agricultural areas, industrial 

discharges into the air or water, leaching into the groundwater from unlined landfills, discharges from wastewatertreatment plants, combined sewer overflows, leaking 

septic systems, and leaking municipal sanitary and storm 

sewer systems.

Many of these compounds are toxic at elevated concentrations and (or) are known to have endocrine-disrupting potential. Even low concentrations can impact aquatic 

organisms because exposure is often chronic, spanning 

entire life cycles and multiple generations. Furthermore, 

OWCs often occur as mixtures of multiple compounds, 

which can strengthen their effects. 

Kayakers explore the 

Milwaukee Estuary, 

Milwaukee, Wisconsin

100%

of the 196 samples 

had detections of one 

or more compounds

93%

of the 69 compounds 

were detected at 

least once

Maximum number of 

compounds detected 

in a single sample:

41

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2015–3056

September 2015

ISSN 2327-6916 (print) ISSN 2327-6932 (online)

http://dx.doi.org/10.3133/fs20153056
Figure 1. Summary of the distribution of organic waste compounds for 12 sites in the Milwaukee Metropolitan Sewerage District (MMSD) 

planning area, Wisconsin. (μg/L, micrograms per liter; μg/kg, micrograms per kilogram)

NA

NA

NA NA

NA NA

NA

NA

NA NA

NA

NA

NA

NA

Honey Creek Milwaukee 

River at 

Wauwatosa

(MRW)

Milwauke

at Jone

Kinnick

River (KR

Milwaukee Harbor

(outside breakwater)

Milwaukee Harbor

(inside breakwater)

Oak Creek (OSM)

Honey Creek

Underwood Creek

Milwaukee River

at Jones Island

Kinnickinnic

River (KRM)

Little Menomonee

River

Root River

Milwaukee 

River at 

Wauwatosa

(MRW)

Milwaukee River

near Cedarburg (MRC)

Lake Michigan

Lincoln Creek

Menomonee

River Basin

Kinnickinnic

River Basin

Oak Creek Basin

Root River

Basin

Milwaukee River Basin

Oak Creek Basin

Kinnickinnic

River Basin

Menomonee

River Basin

Milwaukee

West Allis

Franklin

Menomonee

Falls

Brown

Deer

Milwaukee

Franklin

Menomonee

Falls

West Allis

Brown

Deer

Base composited from U.S. Geological Survey National Land Cover Database 2011, 30-meter, 2011 (Jin and others, 2013); Southeastern Wisconsin Regional Planning Commission regional base map, 

1:2,000, 1995; U.S. Geological Survey digital line graph hydrography, 1:100,000, 1989; Wisconsin Department of Natural Resources version 2 hydrography, 1:24,000, 2002. 

Wisconsin Transverse Mercator projection, referenced to North American Datum of 1983, 1991 adjustment

WISCONSIN

MICHIGAN

ILLINOIS

IOWA

MINNESOTA

MMSD

planning area

EXPLANATION

Water

High- and medium-intensity 

urban development

Low-intensity urban 

development

Area within the MMSD 

planning area

Area outside of the MMSD 

planning area

Watershed boundary

Subwatershed boundary

Stream

Sampling site and name

Less than 40.0

40.0–49.9

50.0–59.9

60.0–69.9

70.0–79.9

Circle size—Percent of sampled

compounds detected at 

least once

base

flow

pore

water

stormflow

sediment

Sample type:

NA Sample type not collected

Circle color—Sum of detected 

concentrations

Less than 5.0

5.0–24.9

25.0–44.9

45.0–64.9

More than 65.0

Less than 5,000

5,000–16,999

17,000–28,999

29,000–40,999

More than 41,000 

Water (μg/L) Sediment (μg/kg)

0 2 4 MILES

0 2 4 KILOMETERS

ID

88°10' 87°50'

42°50'

43°10'
How Much Did We Find?

The OWC classes with the highest concentrations were 

PAHs and herbicides. Maximum concentration values for each 

class can be seen below in figure 2.

Concentrations of most compounds were higher in stormflow and pore-water samples than in base-flow samples; this was 

especially true of PAHs, dyes/pigments, and solvents. Stormflow 

sample concentrations were higher than base-flow concentrations by a factor of 2 or more for 23 compounds and by a factor 

of 10 or more for 5 compounds (3 PAHs, 1 solvent, and 1 flavor 

and fragrance). This indicates that nonpoint-source runoff and 

(or) wastewater leakage associated with storm events may be 

important sources of OWCs to the streams.

Domestic Wastewater Indicators

To identify domestic human wastewater OWC sources 

(for example, from leaking sanitary sewers and septic systems), a subset of 20 indicator 

compounds was analyzed. This 

group included all fire retardants 

and detergent metabolites, most 

flavors/fragrances, and triclosan (a common antimicrobial 

disinfectant).

Domestic wastewater indicators were detected in 100 percent of stormflow and pore-water 

samples, 79 percent of base-flow 

samples, and 89 percent of sediment samples. For base-flow and 

stormflow samples, the site with the highest median total concentration was KRM. Most samples showed a trend of increasing 

total concentrations with increasing urban area.

Did We Find Potentially Toxic Amounts of Organic 

Waste Compounds?

Of the 69 OWCs evaluated, 25 have known aquatic-toxicity 

benchmarks, and samples that exceed these benchmarks are 

considered potentially toxic. A benchmark indicates the value 

above which there is potential harm to humans or animals, but 

it is not a regulatory standard (U.S. Environmental Protection 

Agency, 2015). It is important to note that these benchmarks are 

based on individual compounds, 

rather than the complex mixtures 

of 20 to 40 different compounds 

observed in this study. Likewise, 

benchmarks commonly are based 

on exposure times of 10 days or 

less, whereas environmental exposure to these compounds may be 

measured in weeks or months. For 

these reasons, these single-compound benchmarks may underestimate the potential for adverse 

effects on aquatic organisms.

In the samples collected during this study, 13 of the 25 known 

benchmarks were exceeded. The 

compounds with the greatest 

benchmark exceedances were 

PAHs, both in terms of exceedance frequency (up to 93 percent 

in sediment) and magnitude (concentrations up to 1,024 times 

higher than the benchmark value). Other compounds with toxicity-benchmark exceedances include individual compounds from 

the plasticizers, fuels, antimicrobial disinfectants, and detergent 

metabolites categories. Benchmark exceedances for 7 of the 

13 compounds in water samples and sediment samples indicate 

that OWCs likely enter the stream and collect in the streambed 

sediments.

Figure 2. Detection frequency and maximum concentration by class for the four stormflow sampling sites in the Milwaukee area 

representing a gradient of low to high urban land use. (<, less than; ≥ greater than or equal to; μg/L, micrograms per liter; μg/kg, micrograms 

per kilogram)

Sites 

(least to most 

urban, top to 

bottom)

MRC

KRM

MRW

OSM

Polycyclic aromatichydrocarbons (PAH)

Insecticides

Sterols

.

Dyes/pigments

Fuels

Antimicrobialdisinfectants

DetergentmetabolitesFlavors andfragrances

.Antioxidants .

Plasticizers .

Fire retardants .

.

Solvents .

Herbicides .

.

.

.

Human drugs,nonprescription

.

.

.

.

.Miscellaneous .

.

Sediment samples

KRM

MRC

MRW

OSM

Stormflow samples

80−100

60−79

40−59

20−39

<100

100−999

1,000−9,999

≥10,000

0

<0.99

1.0−9.99

10.0−99.9

≥100.0

Maximum concentration

Sediment

(μg/kg)

Stormflow

(μg/L)

Detection frequency,

in percent

.

EXPLANATION

100%

of stormflow and 

pore-water samples 

contained domestic 

wastewater indicators

One urban PAH sample 

was 1,024

times higher than the 

toxicity benchmark

Number of aquatictoxicity benchmarks 

exceeded:

13 of the 25 

known

benchmarks
Featured Result: Polycyclic Aromatic Hydrocarbons 

(PAHs)

PAHs enter the environment through emissions from 

vehicles and power plants, tire particles, motor oil, creosotetreated lumber, roofing tar, coal-tar-based pavement sealants, 

and other sources. They break down slowly, accumulate in 

stream and lake sediments, and stay in the environment for 

long periods of time.

The PAHs were the most frequently detected class 

overall, occurring in 100 percent of stormflow, pore-water, 

and sediment samples, and 

in 80 percent of base-flow 

samples. 

In stormflow samples, 

PAH concentrations were 

directly related to the 

percentage of the basin in 

urban land use. The median 

total PAH concentration 

from stormflow samples at the most urban site (KRM) was 

83 times higher than at the least urban site (MRC)(fig. 3).

PAH compounds were determined to be potentially 

toxic at 3 of 4 stormflow sites, at 4 of 9 pore-water sites, and 

at 7 of 9 sediment sites; but base-flow samples showed low 

potential for PAH toxicity. This determination indicates that 

PAHs are likely entering the stream through urban nonpoint 

runoff during storm events and accumulating in the streambed 

sediments.

Featured Result: Urbanization and Storm Runoff

Urbanization increases the amount of impervious surfaces like roads and rooftops, which funnel stormwater runoff 

into storm sewers and prevent it from infiltrating into the 

ground. Structures like sanitary sewers and septic systems 

can suffer storm-related overflows and leaks.

To investigate the relation between OWCs, flow condition, and urbanization, we compared base-flow and stormflow 

samples at four sites representing an increasing gradient of 

urban land use. The results indicate that urban runoff and 

other storm-related inputs are an important source of OWCs 

to Milwaukee area streams:

• Compared with rural sites, urban sites exhibited higher 

detection frequencies, concentrations, and toxicity 

benchmark exceedances.

• Compared to base-flow samples, concentrations in 

stormflow samples were as much as 10 times higher.

• Stormflow detection frequencies averaged 1.3 to 

2.0 times higher than those in base-flow samples.

• Kinnickinnic River, the most urbanized site, had the highest 

detection rates and concentrations of all sampled sites.

Many of these conclusions can be visualized by looking at the 

results for the PAH base-flow and stormflow samples (fig. 3).

Figure 3. Polycyclic aromatic hydrocarbon (PAH) 

potential toxicity for base-flow and stormflow samples for 

the four stormflow sampling sites in the Milwaukee Area, 

representing a gradient of low to high urban land use.

MRC

(least urban)

10

1

0.1

0.01

KRM

(most urban)

OSM MRW

Potentially toxic

above line

A. Chronic potential toxicity (long-duration) in base-flow samples

B. Acute potential toxicity (short-duration) in stormflow samples Potential toxicity for all PAH compounds Potential toxicity for all PAH compounds

Potentially toxic

above line

1.2

1.0

0.8

0.6

0.4

0.2

0.0

MRC

(least urban)

KRM

(most urban)

OSM MRW

Stream sites

75th percentile

Median

25th percentile

Adjacent

adjacent

References Cited EXPLANATION

Jin, S., Yang, L., Danielson, P., Homer, C., Fry, J., and Xian, G., 

2013, A comprehensive change detection method for updating the National Land Cover Database to circa 2011: Remote 

Sensing of Environment, v. 132, p. 159–175.

U.S. Environmental Protection Agency, 2015, Water Quality 

Benchmarks for Aquatic Life, accessed June 19, 2015, at 

http://www.epa.gov/bpspill/water-benchmarks.html.

100%

of stormflow, pore-water, 

and sediment samples 

contained PAHs

USGS Scientific Investigations Report 2013–5104, 

Organic Waste Compounds in Streams: Occurrence and Aquatic Toxicity in Different Stream 

Compartments, Flow Regimes, and Land Uses in 

Southeast Wisconsin, 2006–9 

http://pubs.usgs.gov/sir/2013/5104/

For more information about this study, the methods used, 

the data collected, and references cited, please see the 

following report:

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2013–5104

Prepared in cooperation with the 

Milwaukee Metropolitan Sewerage District

Organic Waste Compounds in Streams: Occurrence and 

Aquatic Toxicity in Different Stream Compartments, Flow 

Regimes, and Land Uses in Southeast Wisconsin, 2006–9

By Austin K. Baldwin,1 Steven R. Corsi,1 Christopher Magruder,2

Matthew Magruder,2

 and Jennifer L. Bruce1

1

U.S. Geological Survey

2

Milwaukee Metropolitan Sewerage District