U.S. Department of the Interior

U.S. Geological Survey

oxygen demand (BOD), chemical 

oxygen demand (COD), suspended 

solids, dissolved solids, total nitrogen, 

total ammonia plus organic nitrogen, 

total phosphorus, dissolved 

phosphorus, total recoverable 

cadmium, total recoverable copper,

total recoverable lead, and total 

recoverable zinc. These estimates will 

be used by the municipalities to 

evaluate the magnitude of pollutant 

loadings and the ef ficiency of 

management strategies that are 

intended to reduce pollutant loads.

As part of a national synthesis of 

the study units in the U.S. Geological 

Survey (USGS) NPDES program, 

data were compiled on concentrations of the 12 properties and 

constituents required for load 

calculations. This report presents 

a comparison of these data. 

T

he U.S. Environmental 

Protection Agency, under 

section 402 (p) of the Water Quality 

Act of 1987, has required 

municipalities with populations of 

more than 100,000 to obtain National 

Pollutant Discharge Elimination 

System (NPDES) permits for urban 

stormwater discharge. This regulation 

is intended to minimize pollutant 

loadings from urbanized areas and 

preserve the quality of streams that 

receive stormwater. To apply for a 

NPDES permit, a municipality must 

monitor the chemistry of stormwater 

from basins having residential, 

commercial, and industrial land uses, 

and estimate storm- and annualpollutant loads and event-mean 

concentrations of 12 selected properties 

and constituents. The properties and 

constituents include biochemical

Comparison of NPDES Program

Findings for Selected Cities in

the United States

concrete pipes, lined ditches, and unlined 

channels. The drainage area of sampling 

sites typically was small and ranged from 

4.0 to 2,564 acres. Each site had a 

predominant land use —residential, 

commercial, or industrial (fig. 2). Flow 

and rainfall data either were collected on 

site or were estimated from nearby gages. 

Flow data are used to calculate loads from 

the concentration data. Samples were 

collected either by manually collecting 

discrete samples at timed intervals and 

flow-weighting volumes of these discrete 

samples or by collecting flow-weighted 

composite samples using an automatic 

sampler. Flow-weighted samples were 

collected during the first 3 hours of the 

storm or until the stream returned to prestorm levels. Samples were collected at 

a particular site about 30 or more days 

apart and after approximately 72 hours of 

less than 0.1 inch of rain.

Data Analysis

Analyses of the flow-weighted composite samples were done at the USGS 

National Water-Quality Laboratory with 

the exception of the Sioux Falls, South 

Dakota, and BOD analyses. These 

analyses were done at the individual 

USGS offices or at contract laboratories.

Nationwide Data Comparison

In an effort to compare storm loads 

for different land uses, concentration and 

flow data were compiled from study units 

in the USGS NPDES data bases. 

Concentration data and flow volumes 

were combined along with a unitconversion factor to obtain storm loads in 

pounds for each storm. The storm loads 

then were divided by the area of the 

individual basins to obtain storm load per 

unit area, in pounds per acre. Mean 

storm loads for all constituents then were 

calculated for the three land uses in each 

city or metropolitan area (table 1). This 

manipulation allows direct comparison of 

the storm loads for each land use.

Data Collection

The USGS, in cooperation with local 

agencies, sampled stormwater from 1991 

through 1996 in 13 cities and metropolitan 

areas that are required to obtain NPDES 

permits (fig. 1). For this comparison, 

permits (fig. 1). For this comparison, 

Birmingham and Montgomery, Alabama, 

were considered one study unit and 

designated as Birmingham/Montgomery, 

Alabama. Samples were collected from 

various conveyances, such as culverts, 

Phoenix,

Arizona

Denver,

Colorado

Omaha, Nebraska

Sioux Falls,

South

Dakota

Boise, Idaho

Figure 1. Cities and metropolitan areas where NPDES constiuents were sampled in 

urban stormwater, 1991–96.

Colorado

Springs,

Colorado

Davenport,

Iowa

Independence,

Missouri

Little Rock,

Arkansas Birmingham /

Montgomery,

Alabama

San Antonio, Texas Baton

Rouge,

Louisiana

Dallas/Ft. Worth,

Texas
Biochemical

oxygen

demand

—

0.30

.41

.75

.60

.08

—

.57

.49

.23

.09

.22

.46

7.3 

1.6 

2.6 

2.0 

2.4 

.36

— 

5.5 

3.0 

1.1 

.35

2.9 

6.8 

1.1 

4.1 

11 

3.1 

5.9 

.28

—

63 

6.3 

2.6 

1.5 

3.3 

12 

1.2 

1.2 

1.2 

 .86

1.6 

.17

—

4.3 

2.4 

1.1 

1.3 

2.8 

3.8 

5.1x10–2

2.7x10–4

1.9x10–4

8.3x10–5

6.0x10–4

3.1x10–5

— 

2.8x10–3

9.4x10–4

1.5x10–4

ND 

2.7x10–4

7.6x10–4

1.3x10–4

6.0x10–4

4.2x10–4

5.6x10–4

6.6x10–5

8.3x10–5

— 

1.1x10–2

1.2x10–3

3.5x10–4

ND 

5.8x10–4

2.6x10–3

9.6x10–4

3.0x10–3

1.5x10–3

1.3x10–3

2.9x10–3

4.4x10–4

— 

2.6x10–2

4.8x10–3

1.4x10–3

6.2x10–4

2.3x10–3

8.9x10–3

Suspended

solids

Study

unit

Dissolved

solids

Total

nitrogen

Residential land use

Total ammonia

plus organic

nitrogen

Total

phosphorus

Dissolved

phosphorus

Total

recoverable

copper

Total

recoverable

zinc

Total

recoverable

lead

Chemical

oxygen

demand

Birmingham /

 Montgomery,

 Alabama

Phoenix,

 Arizona

Little Rock,

 Arkansas

Colorado Springs,

 Colorado

Denver,

 Colorado

Boise,

 Idaho

Davenport,

 Iowa

Baton Rouge,

 Louisiana

Independence ,

 Missouri

Omaha,

 Nebraska

Sioux Falls,

 South Dakota

Dallas/Fort Worth,

 Texas

San Antonio,

 Texas

Commercial land use

Birmingham /

 Montgomery,

 Alabama

Phoenix,

 Arizona

Little Rock,

 Arkansas

Colorado Springs,

 Colorado

Denver,

 Colorado

Boise,

 Idaho

Davenport,

 Iowa

Baton Rouge,

 Louisiana

Independence ,

 Missouri

Omaha,

 Nebraska

Sioux Falls,

 South Dakota

Dallas/Fort Worth,

 Texas

San Antonio,

 Texas

Industrial land use

Birmingham /

 Montgomery,

 Alabama

Phoenix,

 Arizona

Little Rock,

 Arkansas

Colorado Springs,

 Colorado

Denver,

 Colorado

Boise,

 Idaho

Davenport,

 Iowa

Baton Rouge,

 Louisiana

Independence ,

 Missouri

Omaha,

 Nebraska

Sioux Falls,

 South Dakota

Dallas/Fort Worth,

 Texas

San Antonio,

 Texas

0.034 

.061 

.091 

.025 

.068 

.0013

.013 

.36 

.032 

.042 

.030 

.068 

.11 

 0.025 

.050 

.060 

.022 

.052 

.0064

.0085

.34 

.020 

.028 

.025 

.047 

.092 

0.022 

.0067

.017 

 .0048

.013 

.0009

.0027

.059 

.0074

.0083

.0030

.013 

.022 

0.022

.0030

.011 

.0018

.0035

.0006

.0028

.021 

.0024

.0035

.0010

.0089

.012 

—

2.2 

.81

.89

10 

1.4 

—

1.8 

1.8 

.43

.23

.49

.73

4.9 

14 

4.4 

6.3 

15 

3.6 

— 

14 

14 

1.6 

.49

4.7 

8.9 

.45

6.7 

5.1 

8.8 

4.5 

2.2 

—

33 

11 

4.5 

1.3 

4.0 

15 

.74

7.2 

1.8 

2.8 

3.2 

.68

—

12 

3.1 

1.8 

1.6 

4.8 

5.5 

1.4x10–4

1.1x10–3

6.8x10–4

3.6x10–4

2.7x10–3

6.3x10–4

— 

2.4x10–3

1.1x10–3

2.1x10–4

ND 

8.9x10–4

1.2x10–3

2.0x10–4

6.8x10–4

1.5x10–3

3.1x10–3

1.5x10–3

9.0x10–4

— 

9.1x10–3

4.6x10–3

5.1x10–4

ND 

2.4x10–3

4.9x10–3

2.0x10–3

1.3x10–2

7.6x10–3

6.1x10–3

7.7x10–3

4.6x10–3

— 

4.2x10–2

1.4x10–2

2.3x10–3

1.1x10–3

7.2x10–3

1.8x10–2

.019 

.33 

.076 

.075 

.099 

.21 

.030 

.32 

.13 

.046 

.024 

.11 

.15 

.014 

.26 

.049

.050 

.065 

.21 

.020

.25 

.094

.028

.019

.068

.12 

.0031

.034

 .0097

 .0081

 .0082

.0079

.0033

.034 

.018 

.0061

.0022

.012 

.028 

.0020

.027 

.0072

.0036

.0037

.0043

.0041

.017 

.0059

.0037

.0012

.0058

.012 

—

5.9 

.88

.25

5.4 

—

—

2.9 

3.1 

1.7 

.05

.53

.50

3.4 

5.8 

4.6 

1.4 

9.2 

— 

— 

37 

5.5 

6.7 

.17

5.6 

6.3 

2.2 

7.7 

3.0 

3.1 

22 

—

— 

41 

20 

66 

.62

19 

10 

1.5 

2.2 

2.3 

 .52

2.4 

— 

—

33 

250 

6.5 

.52

5.4 

6.0 

9.9x10–4

1.4x10–3

5.3x10–4

2.0x10–4

5.9x10–3

— 

— 

6.3x10–3

8.8x10–4

2.2x10–3

ND 

7.5x10–3

7.4x10–4

1.7x10–3

1.6x10–3

1.1x10–3

1.0x10–3

1.2x10–2

— 

— 

3.9x10–2

1.5x10–2

5.3x10–3

ND 

4.8x10–3

1.1x10–3

7.2x10–3

7.2x10–3

9.4x10–3

3.7x10–3

4.0x10–2

— 

— 

8.3x10–2

1.1x10–1

2.2x10–2

4.9x10–4

1.5x10–2

1.5x10–2

.024 

.099 

.22 

.016 

.13 

— 

.036 

.54 

.033 

.16 

.017 

.11 

.10 

 .017 

.062 

.19 

.011 

.092

— 

.034 

.43 

.019 

.11 

.013 

.064 

.061 

.0067

.014 

.047 

 .0017

.021 

—

.0009

.074 

.014 

.025 

.0027

.020 

.025 

.0045

.0050

.016 

.0010

.0084

—

.0001

.044 

.0024

.012 

.0010

.010 

.018 

Table 1. Mean storm loads in pounds per acre for 11 NPDES properties and constituents in the United States, 1991–96

[—, not analyzed for; ND, 50 percent or more of values below detection limit] 
Physical Properties

BOD, COD, suspended solids, and 

dissolved solids were compared for all 

the cities with the exception of 

Davenport, Iowa; Boise, Idaho; and 

Birmingham/Montgomery, Alabama. 

Samples from Davenport, Iowa, were not 

analyzed for these properties and 

constituents. An industrial land-use basin 

was not sampled in Boise, Idaho. 

Samples from Birmingham/ 

Montgomery, Alabama, were not 

analyzed for BOD.

BOD and COD are determined by 

measurement of the quantity of oxygen 

utilized by organic matter and chemicals 

in stormwater samples and are used to 

indicate pollution (Hem, 1992). Mean 

storm loads of BOD varied by two orders 

of magnitude, from 0.05 to 10 pounds per 

acre. The largest mean storm loads of 

BOD were associated with industrial 

land-use basins, except for the maximum 

that occurred in commercial land-use 

basins in Denver, Colorado. Mean storm 

loads of COD varied by two orders of 

magnitude, from 0.17 to 37 pounds per 

acre. The largest mean storm loads of 

COD were associated with commercial 

land-use sites, except for the maximum 

that occurred in industrial land-use 

basins in Baton Rouge, Louisiana.

Concentrations of suspended solids 

and dissolved solids are measures of 

solids loads in stormwater and also may 

be used as indicators of pollution. Mean 

storm loads of suspended solids varied 

by more than two orders of magnitude, 

from 0.28 to 66 pounds per acre. The 

largest mean storm loads of suspended 

solids were associated with the industrial 

land-use basins; the maximum occurred 

in Omaha, Nebraska. Mean storm loads 

of dissolved solids varied by more than 

three orders of magnitude, from 0.17 to 

250 pounds per acre. The lar gest mean 

storm loads of dissolved solids were 

associated with industrial land-use 

basins; the maximum occurred in 

Independence, Missouri.

Nutrients

Four nutrient constituents —total 

nitrogen, total ammonia plus or ganic 

nitrogen, total phosphorus, and 

dissolved phosphorus —are being 

analyzed by the USGS NPDES program. 

These constituents were compared for all 

land uses in selected cities, with the 

exception of industrial land-use basins in 

Boise, Idaho. An industrial land-use basin 

was not part of the sampling program in 

Boise.

Nutrients are essential components in 

plant growth; however, an overabundance 

of these constituents will cause undesirable algal blooms in bodies of water that 

are used for urban drinking -water supplies (Hem, 1992). These algal blooms 

cause adverse effects on the taste and 

odor of drinking water and have the 

potential to cause more serious health 

problems. 

Mean storm loads of total nitrogen 

varied by more than two orders of magnitude, from 0.0013 to 0.54 pounds per 

acre. The largest mean storm loads of 

total nitrogen are associated with industrial land -use basins; the maximum 

occurred in Baton Rouge, Louisiana. 

Mean storm loads of total ammonia 

plus organic nitrogen varied by almost 

two orders of magnitude, from 0.0064 to 

0.43 pounds per acre. The largest mean 

storm loads of total ammonia plus 

organic nitrogen were associated with 

industrial and commercial land-use 

basins; the maximum occurred in Baton 

Rouge, Louisiana.

Mean storm loads of total phosphorus 

varied by almost two orders of magnitude, from 0.0009 to 0.074 pounds per 

acre. The largest mean storm loads of 

total phosphorus were associated with 

industrial land-use basins; the maximum 

occurred in Baton Rouge, Louisiana. 

Mean storm loads of dissolved phosphorus varied by more than three orders of 

magnitude, from 0.0001 to 0.044 pounds 

per acre. The largest mean storm loads of 

dissolved phosphorus were associated with 

industrial land-use basins; the maximum 

occurred in Baton Rouge, Louisiana. 

Figure 2. National Pollutant Discharge Elimination System (NPDES) residential landuse site at Glendale, Arizona.
Trace Metals

Concentrations of four trace -metal 

constituents—total recoverable copper, 

total recoverable zinc, total recoverable 

cadmium, and total recoverable lead are 

being analyzed by the USGS NPDES 

program. These constituents were 

compared for all land uses in the selected 

cities with the exception of Davenport, 

Iowa, and Boise, Idaho. Concentrations 

of these constituents were not determined 

in Davenport, Iowa, and an industrial landuse basin was not sampled in Boise, Idaho.

Copper and zinc are essential to plant 

and animal metabolism and are needed in 

small amounts by all plants and animals. 

Large amounts of these metals in drinking 

water, however, can cause adverse effects 

on the taste and odor of drinking water. 

Mean storm loads of total recoverable 

copper varied by more than three orders 

of magnitude, from 3.1 x10 -5 to 5.1x102 

pounds per acre. The largest mean storm 

loads of total recoverable copper were 

associated with commercial and 

industrial land-use basins. The exception was the maximum that occurred 

in a residential land - use basin in 

Birmingham/Montgomery, Alabama.

Mean storm loads of total 

recoverable zinc varied by almost three 

orders of magnitude, from 4.4 x10- 4 to

1.1x10-1 pounds per acre (fig. 3).

USGS Fact Sheet

January 1998 FS-192-97

Figure 3. Mean storm loads of total recoverable zinc. 

0.0001

Residential

Commercial

Industrial

0.001

MEAN STORM LOAD OF TOTAL RECOVERABLE ZINC,

IN POUNDS PER ACRE

0.01

0.1

1.0

Selected References

Baldys Stanley, III, Raines, T.H., Mansfield, 

B.L., and Sandlin, J.T., 1997, Hydrologic 

data for urban stormwater studies in the 

Dallas-Fort Worth area, Texas, 1992–94: 

U.S. Geological Survey Open-File Report 

96–482, 254 p.

Barks, C.J., 1995, Verification and adjustment of regional regression models for 

urban storm-runoff quality using data 

collected in Little Rock, Arkansas: U.S. 

Geological Survey Water-Resources 

Investigations Report 94–4216, 36 p.

Fossum, K.D., and Davis, R.G., 1996, 

Physical, chemical, biological, and 

toxicity data from the study of urban 

stormwater and ephemeral streams, 

Maricopa County, Arizona, water years 

1992–95: U.S. Geological Survey OpenFile Report 96–394, 71 p.

Guerard, P.V., and Weiss, W.B., 1995, Water 

quality of storm runoff and comparison 

of procedures for estimating storm-runoff 

loads, volume, event-mean concentrations, and the mean load for a storm 

for selected properties and constituents 

for Colorado Springs, southeastern 

Colorado, 1992: U.S. Geological Survey 

Water-Resources Investigations Report 

94–4194, 68 p.

Hem, J.D., 1992, Study and interpretation of 

the chemical characteristics of natural 

water: U.S. Geological Survey WaterSupply Paper 2254, 263 p.

Kjelstrom, L.C., 1995, Data for and adjusted 

regional regression models of volume 

and quality of urban storm-water runof f 

in Boise and Garden City , Idaho, 

1993–94: U.S. Geological Survey WaterResources Investigations Report 

95–4228, 36 p.

Niehus, C.A., 1997, Characterization of 

stormwater runoff in Sioux Falls, South 

Dakota, 1995 – 96: U.S. Geological 

Survey Water-Resources Investigations 

Report 97–4070, 62 p.

Pearman, J.L., Sedberry, V.E., Stricklin,V.E., 

and Cole, P.W., 1993, Water-resources 

data for Alabama, water year 1993: U.S. 

Geological Survey Water-Data Report 

AL–93–1, 518 p.

Schalk, G.K., 1994, Quantity and quality of 

base flow and storm water runoff in 

Independence, Missouri—October 1991 to 

February 1993: U.S. Geological Survey 

Open-File Report 93–495, 69 p.

For more information contact:

District Chief

U.S. Geological Survey

520 N. Park Ave., Suite 221

Tucson, Arizona 85719-5035

(520) 670-6671

http://wwwdaztcn.wr.usgs.gov

Birmingham/ Montgomery, Alabama

Phoenix,

 Arizona

Little Rock,

 Arkansas

Colorado Springs, Colorado

Denver,

 Colorado

Boise,

 Idaho

Davenport,

 Iowa

Baton Rouge, Louisiana

Independence, Missouri

Omaha,

 Nebraska

Sioux Falls,

 South Dakota

Dallas/Fort 

Worth,

 Texas

San Antonio,

 Texas

The largest mean storm loads of total 

recoverable zinc were associated with 

industrial land-use basins; the maximum 

occurred in Independence, Missouri.

Cadmium and lead tend to 

bioaccumulate in plants and animals. 

Large concentrations of these metals lead 

to toxicity and health problems in plants 

and humans (Hem, 1992).

Concentrations of total recoverable 

cadmium were considered in this analysis 

of data, but more than 70 percent of the 

analyses were below detection limits. No 

mean storm loads of cadmium were 

included in the data tables.

Mean storm loads of total recoverable 

lead varied by almost three orders of 

magnitude, from 8.3x10-5 to 3.9x10-2 

pounds per acre. The largest mean storm 

loads of total recoverable lead were 

associated with industrial land-use basins; 

the maximum occurred in Baton Rouge, 

Louisiana.

The majority of minimum mean storm 

loads occurred in residential land-use 

basins and the majority of maximum 

mean storm loads occurred in industrial 

land-use basins. The information 

contained in this fact sheet is part of 

ongoing studies and may be updated upon 

completion of the NPDES program.

—Kenneth D. Fossum and Dawn S. 

McDoniel