iSTREEM® 

A Web-based River Chemical 

Concentration Estimation Model

Dr. Xinhao Wang

University of Cincinnati

EPA Exposure Modeling Public Meeting

March 19, 2013

1
Who are we?

The 120-member trade association of the 

$30 billion US cleaning products industry

2
Onsite Treatment

Municipal Waste Water

Treatment Plants

Soils Surface waters

Sludge Effluent

Ground water

Drinking water

Direct

Discharge

Household

Wastewater

Fate of Consumer Product Ingredients

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iSTREEM® - What is it?

• Environmental exposure model for down-thedrain consumer products

• Estimates chemical concentration in the effluent 

of >10,000 municipal WWTPs in the U.S.

• Estimates in-stream concentrations for 30,000 

effluent-impacted perennial streams in the U.S.

• Estimates raw drinking water concentrations at 

surface water intakes (∼1,700)

4
Model Algorithm

U.S. rivers are segmented, and modeled downstream flow

Losses within segment

• Biodegradation

• Downstream Transport

• Drinking water intake

Sources to segment

• WWTP Effluent

• Upstream Input

• Tributary Input

• Industrial Loads

WWTP Effluent

Calculates effluent concentration

Influent to WWTP

(per capita use x population served)

Calculates concentration at drinking water intake

Calculates concentration for effluent-impacted streams

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User Inputs

• Chemical per capita use rate (national or 

regional)

• Chemical fate parameters

– Primary treatment efficiency

– Secondary treatment efficiency (activated sludge, 

lagoon, oxidation ditch, RBC, trickling filter)

– In-stream loss (first order)

• Geographic scope (national or regional)

6
Chemical Fate Parameters

In-stream 1st order loss (e.g., sorption, 

biodegradation, etc.)

Secondary treatment

Present Pop = 2004, Future Pop = 2008

Mean River Flow or 

Low Flow (7Q10, worse-case, sometimes 

100% effluent)
U.S. EPA Data Sets 

• Enhanced-River Reach File 1 – 1:500,000 scale; Contains 

stream data such as reach number, type, name, length, slope, 

annual/monthly mean and low flows and flow velocities

• Reach File 3 and National Hydrography Dataset (NHD+) –

1:100,000 scale, used initially to locate WWTPs on RF1 reach

• Clean Watersheds Needs Survey – WWTP data includes 

NPDES permit numbers, treatment type information, 

population data, effluent flow, and location data for 2008

• Drinking Water Supply File – Contains data for U.S. drinking 

water facilities: Includes facility code, production volumes, 

population served, and locations for plant intakes and sources 

(SDWIS – 2004), also found in BASINS model

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Wastewater Treatment Plants

Type Description Count % Pop. % Flow

S Activated Sludge 4,866 79.4% 81.1%

L Lagoon 3,360 6.2% 5.9%

O Oxidation Ditch 1,052 5.8% 4.9%

F Trickling Filter 802 6.7% 6.3%

R Rotating Biological Contactor 319 1.9% 1.8%

P Primary 15 0.01% 0.01%

Total Public WWTPs in US 10,414 100% 100%

(US EPA Clean Watersheds Needs Survey – 2008)

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Three-Panel Main User Interface 

Map Display Window Operation 

Panel

Map 

Control 

Panel

Navigation bar
(Comparison of predicted to observed response yields ratios ranging from 0.53-1.25)

Model Verification

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Model Verification 1

2

3

4

5

6

Minneapolis

Moline

St. Louis

Memphis

Baton Rouge New Orleans

Model Verification (cont.)

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Model Verification (cont.)

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Model Results

15
View of Model Results

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Comparing Model Simulations to 

Regulatory and Effects Thresholds

• Compare iSTREEM® effluent predictions to Oregon DEQ plant 

initiation levels under their Priority Persistent Pollutant 

program

o Triclosan: 70 ug/L

• Compare iSTREEM® in-stream predictions to effects threshold

o HC5 for Triclosan: 0.8 ug/L for aquatic species (Capdevielle et al., 2008)

o EU PNEC for DEET: 43 ug/L for freshwater aquatic species (EU 

Assessment Report, 2010)

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National Simulation Parameters

Ingredient Triclosan1 LAS1 AE1 AES1 DEET2

Oxidation Ditch 95 99 99 98 56.9

Activated Sludge 95 99 99 98 56.9

Lagoon 95 98 99 98 56.9

Trickling Filter 80 80 96 93 56.9

Rotating Biological Contactor 95 98 99 98 56.9

Primary 30 27 18.9 0 0

Decay (d-1) 0.264 0.7 31.2 24 0.0234

River Temperature 20 20 20 20 20

Scenario Present Pop Present Pop Present Pop Present Pop Present Pop

National Loading factor 

(g/capita/day) 0.0062 3.1365 1.4675 2.7708 0.0241

1 De Zwart, D., S.D. Dyer, L. Posthuma, C.P. Hawkins. 2006. Use of predictive models to attribute potential effects of 

mixture toxicity and habitat alteration on the biological condition of fish assemblages. Ecol. Applications 16: 1295-1310.

2 Aronson, D., J. Weeks, B. Meylan, P.D. Guiney, P.H. Howard. 2012. Environmental release, environmental 

concentrations and ecological risk of N,N-diethyl-m-toluamide (DEET). Integr. Environ. Assess. Manag. 8: 135-166. 

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Triclosan concentration in effluent

0%

20%

40%

60%

80%

100%

0.01 0.1 1 10 100

Cumulative Percentage of Facilities

Log Concentration (ug/L)

National effluent-simulated Measured effluent

Oregon DEQ initiation 

level/detection limit 

(70 ug/L)

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Predicted In-stream Concentration: 

Triclosan

0%

20%

40%

60%

80%

100%

0.001 0.01 0.1 1 10

Cumulative Percentage River Reaches

Log Concentration (ug/L)

HC5 for Triclosan 

(0.8 ug/L)

Low flow (7Q10)

Mean flow

20
DEET concentration in effluent

0%

20%

40%

60%

80%

100%

0.1 1 10 100

Cumulative Percentage of Facilities

Log concentration (ug/L)

National effluent-simulated Measured data

Observed effluent concentrations 

(from Aronson et al., 2012)

21
Predicted In-stream Concentration: DEET

0%

20%

40%

60%

80%

100%

0.01 0.1 1 10 100

Cumulative Percentage River Reaches

Log Concentration (ug/L)

PNEC for DEET 

(43 ug/L)

Mean flow Low flow (7Q10)

Observed surface water concentrations 

(from Aronson et al., 2012)

22
Conclusions

• iSTREEM® provides ability to predict in-stream 

concentrations of user-defined chemicals on a national 

scale or a watershed scale

• Model verified for broadly discharged chemical

• GIS/Internet platform enables universal access to 

exposure model, ease-of-use

• GIS functionality-spatially-varied input, analysis on 

variety of scales (e.g. watershed/regional/national) 

lends to new insights

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For More Information

• Go to the ACI Science website: 

http://www.aciscience.org/iSTREEM.aspx

• Log in to iSTREEM® directly: 

http://gis2.uc.edu/iSTREEM

References

Wang et al. 2005. A river water quality model integrated with a web-based 

geographic information system. J. Environ. Mgmt., 75: 219-228.

Wang et al. 2000. GIS-ROUT: a river model for watershed planning. 

Environment and Planning B: Planning and Design, Vol 27(2): 231–246.

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Contact Information

Dr. Xinhao Wang

Schools of Planning

University of Cincinnati

Cincinnati, OH 45221-0016

513-556-0497

xinhao.wang@uc.edu

Dr. Paul C. DeLeo

American Cleaning Institute

1331 L Street, N.W., Suite 650

Washington, D.C. 20005

202-662-2516

pdeleo@cleaninginstitute.org

http://www.aciscience.org

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