In cooperation with the North Central Texas Council of Governments

Urban Stormwater Quality, Event-Mean Concentrations, 

and Estimates of Stormwater Pollutant Loads, 

Dallas-Fort Worth Area, Texas, 1992–93 

Water-Resources Investigations 

Report 98–4158

U.S. Department of the Interior

U.S. Geological Survey
Cover photograph: Stormwater monitoring site 08048505 Pylon Street Outfall at Meacham Road, Fort 

Worth, Photograph by Harry C. McWreath, U.S. Geological Survey.
Urban Stormwater Quality, Event-Mean Concentrations, 

and Estimates of Stormwater Pollutant Loads, 

Dallas-Fort Worth Area, Texas, 1992–93 

By Stanley Baldys III, T.H. Raines, B.L. Mansfield, and J.T. Sandlin 

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 98–4158

In cooperation with the North Central Texas Council of Governments

Austin, Texas

1998
ii

U.S. DEPARTMENT OF THE INTERIOR

Bruce Babbitt, Secretary

U.S. GEOLOGICAL SURVEY

Thomas J. Casadevall, Acting Director

Any use of trade, product, or firm names is for 

descriptive purposes only and does not imply 

endorsement by the U.S. Government.

For additional information write to: 

District Chief

U.S. Geological Survey

8011 Cameron Rd.

Austin, TX 78754–3898

Copies of this report can be purchased from:

U.S. Geological Survey

Branch of Information Services

Box 25286

Denver, CO 80225–0286
CONTENTS i

CONTENTS

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

Introduction .......................................................................................................................................................................... 1

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

Description of Study Area ........................................................................................................................................ 2

Previous Studies ........................................................................................................................................................ 2

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

Data Collection ..................................................................................................................................................................... 4

Instrumentation ......................................................................................................................................................... 5

Water-Quality Sampling ........................................................................................................................................... 5

Quality Assurance and Quality Control .................................................................................................................... 8

Urban Stormwater Quality ................................................................................................................................................... 8

Grab-Sample Properties and Constituents ................................................................................................................ 9

Bacteria ......................................................................................................................................................... 9

Volatile Organic Compounds ........................................................................................................................ 9

Flow-Weighted Properties and Constituents ............................................................................................................. 9

Nutrients ........................................................................................................................................................ 9

Biochemical and Chemical Oxygen Demand ............................................................................................... 11

Inorganic Constituents .................................................................................................................................. 12

Trace Elements .............................................................................................................................................. 13

Base/Neutral and Acid-Extractable Semivolatile Organic Compounds ........................................................ 13

Organochlorine Pesticides, Polychlorinated Biphenyls, and Diazinon ......................................................... 15

Event-Mean Concentrations ................................................................................................................................................. 16

Stormwater Pollutant Loads ................................................................................................................................................. 17

Computed Loads for Three Land Uses ..................................................................................................................... 17

Regression Analysis to Estimate Loads for All Gaged Basins in the Study Area .................................................... 18

Estimated Storm Loads ................................................................................................................................. 18

Estimated Mean Annual Loads ..................................................................................................................... 20

Summary .............................................................................................................................................................................. 20

Selected References ............................................................................................................................................................. 22

FIGURES

1. Map showing location of study area and sampling sites ...................................................................................... 3

2. Graph showing mean monthly rainfall at Love Field, Dallas, Texas, 1897–1989 ................................................ 4

3. Map showing drainage area for site 08047100 Clear Fork Trinity River Outfall at Oak Hill 

Circle, Fort Worth, Texas ...................................................................................................................................... 6

4. Hydrograph showing discharge and rainfall record of storm at site 08061510 Rowlett Creek Outfall at 

Willow Creek Park, Plano, Texas, April 14, 1993 ................................................................................................ 7

 5. Graph showing distributions of grab samples collected during storm runoff by land-use category .................... 8

 6. Boxplots showing ranges and distributions of fecal coliform and fecal streptococcus bacteria as a 

percentage of total storm runoff ........................................................................................................................... 10

7–8. Graphs showing: 

7. Distributions of volatile organic compound detections during storm runoff period by land-use 

category ...................................................................................................................................................... 11

 8. Volatile organic compound detections by land-use category ..................................................................... 11

9–12. Boxplots showing ranges and distributions of: 

9. Total nitrogen and total ammonia plus organic nitrogen concentrations by land-use category ................. 12

10. Total phosphorus and dissolved phosphorus concentrations by land-use category ................................... 13

11. Biochemical oxygen demand and chemical oxygen demand by land-use category .................................. 14

12. Suspended solids and dissolved solids concentrations by land-use category ............................................ 15
ii 

13–15. Graphs showing:

13. Base/neutral and acid extractable semivolatile organic compound detections by land-use 

category ...................................................................................................................................................... 16

14. Organochlorine pesticide detections by land-use category ........................................................................ 16

15. Estimated and measured biochemical oxygen demand storm loads .......................................................... 20

TABLES

1. Selected characteristics of surface-water and water-quality data-collection sites ................................................ 24

 2–3. Summary statistics for:

2. Physical properties (water temperature and pH) and total cyanide, phenols, and oil and grease by 

land-use category ....................................................................................................................................... 25

3. Bacteria by land-use category .................................................................................................................... 25

 4. Most frequent volatile organic compound detections by land-use category and sampling site ............................ 26

 5–9. Summary statistics for:

5. Volatile organic compounds by land-use category ..................................................................................... 26

 6. Nutrients in flow-composite samples by land-use category ....................................................................... 32

 7. Oxygen demand properties in flow-composite samples by land-use category .......................................... 33

 8. Inorganic constituents and specific conductance in flow-composite samples by land-use category ......... 34

 9. Trace-element concentrations in flow-composite samples by land-use category ...................................... 35

10. Most frequent base/neutral and acid-extractable semivolatile organic compound detections in flowcomposite samples by land-use category and sampling site ................................................................................. 36

11. Summary statistics for base/neutral and acid extractable semivolatile organic compounds in flowcomposite samples by land-use category .............................................................................................................. 37

12. Pesticide detections in flow-composite samples by land-use category and sampling site .................................... 42

13. Summary statistics for pesticides and polychlorinated biphenyls in flow-composite samples by land-use 

category ................................................................................................................................................................. 43

14. Mean and median event-mean concentrations by land-use category .................................................................... 46

15. Rainfall-runoff characteristics by land-use category ............................................................................................ 47

16. Computed loads per square mile for all sampled storms by land-use category .................................................... 48

17. Local regression equation coefficients for estimating loads of selected water-quality properties and 

constituents from individual storm-runoff events ................................................................................................. 49

18. Standard error and number of storms for local regression equations and Driver and Tasker regional 

regression equations .............................................................................................................................................. 50

19. Estimated annual loads for sites in all study basins using 1965 rainfall at Love Field and 1975 rainfall 

at Meacham Airport .............................................................................................................................................. 50

Abbreviations

Ah, ampere-hour

°C, degree Celsius

ft3/s, cubic foot per second

ft, foot

gal, gallon

in., inch

lb, pound

μg/L, microgram per liter

mi, mile

mi2, square mile

mg/L, milligram per liter

Acronyms

BCF, bias-correction factor

BNA, base/neutral and acid extractable semivolatile organic 

compound

BOD, biochemical oxygen demand

COD, chemical oxygen demand

DA, total contributing drainage area

EMC, event-mean concentration

EPA, U.S. Environmental Protection Agency

IA, impervious area

LUC, commercial land use

LUI, industrial land use

LUN, nonurban land use

LUR, residential land use

MRL, minimum reporting level

NCTCOG, North Central Texas Council of Governments

NPDES, National Pollutant Discharge Elimination System

NURP, Nationwide Urban Runoff Program

NWQL, National Water Quality Laboratory

PCB, polychlorinated biphenyl

QA/QC, quality assurance/quality control

R2, coefficient of determination

SE, standard error of estimate

TRN, total storm rainfall

USGS, U.S. Geological Survey

VOC, volatile organic compound

VWEMC, volume-weighted event-mean concentration
Abstract 1

Urban Stormwater Quality, Event-Mean Concentrations, 

and Estimates of Stormwater Pollutant Loads, 

Dallas-Fort Worth Area, Texas, 1992–93

By Stanley Baldys III, T.H. Raines, B.L. Mansfield, and J.T. Sandlin

Abstract

The quality of urban stormwater is characterized with respect to 188 properties and constituents. Event-mean concentrations and loads for 

three land uses (residential, industrial, commercial), and annual loads for 12 selected properties 

and constituents for 26 gaged basins in the DallasFort Worth study area are presented. During 

February 1992–June 1993, 182 water samples from 

the 26 gaged basins (each basin classified as primarily residential, industrial, or commercial) were 

collected and analyzed. Residential land-use basins 

had greater median concentrations of bacteria, 

nutrients, and total arsenic. Industrial land-use 

basins had greater median concentrations of suspended and dissolved solids, and total recoverable 

chromium, copper, nickel, and zinc. Diazinon was 

the most frequently detected pesticide in all three 

land-use basins. Diazinon was detected in 93 percent of samples from residential land-use basins, 

70 percent from commercial land-use basins, and 

33 percent from industrial land-use basins. Volatile 

organic compounds and base/neutral and acid 

extractable semivolatile organic compounds were 

detected more frequently in samples from industrial land-use basins than residential or commercial 

land-use basins. 

Event-mean concentrations (EMCs) were 

computed for each land use for biochemical oxygen demand; chemical oxygen demand; suspended 

and dissolved solids; total nitrogen and ammonia 

plus organic nitrogen; total and dissolved phosphorus; total recoverable copper, lead, and zinc; and 

total diazinon. The EMCs of chemical oxygen 

demand; total nitrogen and ammonia plus organic 

nitrogen; total and dissolved phosphorus; and total 

diazinon were greatest in samples from residential 

land-use basins. The EMCs of biochemical oxygen 

demand; suspended and dissolved solids; and total 

copper, lead, and zinc were greatest in samples 

from industrial land-use basins. 

Loads per square mile for the three land 

uses were estimated for the same properties and 

constituents from flow-weighted EMCs and runoff 

volume on the basis of seven sampled storms at 

each gaged site. Chemical oxygen demand and 

dissolved and suspended solids had the greatest 

mean loads per square mile. Mean loads per square 

mile were greatest for trace elements in industrial 

land-use basins and for total diazinon in residential 

land-use basins. Mean loads per square mile for 

total nitrogen in the three land-use basins were 

dissimilar. 

Local regression equations were developed 

to estimate loads produced by individual storms. 

Mean annual loads were estimated by applying the 

storm-load equations for all runoff-producing 

storms in an average climatic year and summing 

individual storm loads to determine the annual 

load. 

INTRODUCTION

The Federal Water Pollution Control Act amendments of 1972 and 1977, also known as the Clean Water 

Act, were passed to prohibit the discharge of any pollutant to the Nation’s waters from a point source unless 

authorized by a National Pollutant Discharge Elimination System (NPDES) permit (U.S. Environmental Protection Agency, 1991). Since implementation of the act, 

pollutant loads received by water bodies from point 

sources have been measurably reduced. 

Eutrophication rates in the Nation's lakes and 

reservoirs can be accelerated by pollutant loads from 

nonpoint sources. Nonpoint-pollutant loads in upstream 

river segments from a variety of sources, including 
2 Urban Stormwater Quality, Event-Mean Concentrations, and Estimates of Stormwater Pollutant Loads, Dallas-Fort Worth Area, 

Texas, 1992–93 

agricultural and urban lands, might adversely affect 

public water supplies. Urban areas have been identified 

as major contributors of nonpoint-pollutant loads (U.S. 

Environmental Protection Agency, 1990a). In 1987, 

Congress again amended the Clean Water Act to require 

the U.S. Environmental Protection Agency (EPA) to 

establish phased NPDES requirements for various 

classes of stormwater discharges, including discharges 

from municipal urban areas (U.S. Environmental Protection Agency, 1992).

According to the Clean Water Act amendments, 

cities with populations of 100,000 or greater must 

obtain permits to discharge stormwater into waters of 

the United States. One of the requirements for an 

NPDES permit is wet-weather sampling to characterize 

the quantity and quality of stormwater from watersheds 

within the city’s boundaries and to estimate pollutant 

concentrations and annual pollutant loads. In 1991, the 

U.S. Geological Survey (USGS), in cooperation with 

the North Central Texas Council of Governments 

(NCTCOG), began a study for the seven applicant cities 

in the Dallas-Fort Worth area (Arlington, Dallas, Fort 

Worth, Garland, Irving, Mesquite, and Plano) to do the 

sampling, stormwater characterization, and load estimation, and also to provide information about pollutant 

loads relative to land use in the metropolitan area.

Purpose and Scope

The purpose of this report is to present information about stormwater quality in the Dallas-Fort Worth 

area associated with several topics: (1) Characterization 

of stormwater quality with respect to 188 properties 

and constituents; (2) event-mean concentrations (EMC) 

for 12 properties and constituents (designated for 

NPDES load estimation by the EPA) for three land uses; 

(3) computed loads for the 12 properties and constituents for three land uses; and (4) estimated annual loads 

for the 12 properties and constituents for 26 gaged 

basins in the study area. Loads categorized by land use 

were computed from flow-weighted EMCs and runoff 

volumes for seven sampled storms in each gaged basin. 

Regression analysis was used to estimate loads for 

unsampled storms, which allowed annual loads to be 

estimated for an average climatic year. An average climatic year was selected for each of two climatic stations 

in the area on the basis of similarity of annual rainfall to 

1961–90 mean annual rainfall. Annual rainfall time 

series of each of the two average climatic years was 

used to estimate the mean annual loads for gaged sites. 

Proximity to a climatic station dictated which of the two 

annual rainfall time series was applied at each gaged 

site.

Description of Study Area

The approximately 1,700 mi2 Dallas-Fort Worth 

area (fig. 1) is in north-central Texas, about 70 mi 

south of the Red River, which forms most of the boundary between Oklahoma and Texas. The study area is 

within Collin, Dallas, and Tarrant Counties. Collin and 

Dallas Counties are in the Blackland Prairies physiographic region, and Tarrant County is in the Cross 

Timbers and Prairies physiographic regions (Kingston 

and Crawford, 1991). The metropolitan area has a population of about 3.3 million, according to the 1990 census (Keith Kennedy, North Central Texas Council of 

Governments, oral commun., 1992). Three cities, 

Arlington, Dallas, and Fort Worth, have populations 

greater than 250,000. Four cities, Garland, Irving, 

Mesquite, and Plano, have populations greater than 

100,000 but less than 250,000 (North Central Texas 

Council of Governments, 1993).

The study area is in the upper one-half of the 

Trinity River Basin. Three major tributaries to the main 

stem Trinity River—West Fork Trinity River, Elm Fork 

Trinity River, and East Fork Trinity River—meet in the 

Dallas-Fort Worth area (fig. 1). The average annual discharge at USGS streamflow-gaging station 08062500 

Trinity River near Rosser, approximately 40 mi downstream from the metropolitan area, is 2,921 ft3/s (U.S. 

Geological Survey, 1993).

The study area has varying climatic characteristics. Mean annual rainfall (1961–90) is 30.6 in., and 

mean minimum January temperature is 1.6 °C at 

Meacham Airport in Fort Worth. Mean annual rainfall 

(1961–90) is 33.6 in., and mean minimum January 

temperature is 2.2 °C at Love Field in Dallas. Mean 

monthly rainfall (1897–1989) at Love Field (fig. 2) is 

greatest in April and May (5.0 and 5.8 in., respectively) 

and least in January (2.8 in.).

Previous Studies

Driver and Tasker (1990) used data collected at 

173 urban basins nationwide during 1979–84 to develop 

four sets of regional multivariable regression models 

that can be used to estimate stormwater constituent 

loads. Hoos and Sisolak (1996) documented a procedure that uses local data to adjust the regional regression 

equations developed by Driver and Tasker. 
INTRODUCTION 3

MEACHAM AIRPORT

LOVE FIELD

TARRANT COUNTY

DALLAS COUNTY

DENTON COUNTY

COLLIN COUNTY

FORT WORTH

ARLINGTON

IRVING

DALLAS

PLANO

GARLAND

ME

I−30

I−820

I−35W

I−820 US 183

I−35W

I−35E

LOOP 12

I−635

I−820

STATE 121

I−20

I−30

STATE

121 US 75

I−635

LOOP 12

I−35E I−20 US 75

97 15’ 97

o

o

96 45’ o

o

o

97 30’

o 32 55’

32 40’

TRINITY RIVER

ELM

R.

EAS TRIN RIV

FORK

TRIN ITY

TRINITY

RIVER

FORK

WEST

8545

8510

8700

9360

9320

9220

9470

9590

6100

5570

6390

5590

7135

7310

7441

1525 1510

1530

1635

1690

16

1910

1915

1940

8505

7100

0 5 10 MILES

T

L

Boundary of study area

Surface-water, water-quality and climatic sampling sites—Number is last 4 digits of U.S. Geological Survey 8-digit site number. (See table 1)

EXPLANATION

8700

Base modified from U.S. GeologicalSurvey 1:250,000 quadranglesLambert Conformal Conic projectionStandard parallels 33 and 45 degrees

Figure 1. Location of study area and sampling sites.
4 Urban Stormwater Quality, Event-Mean Concentrations, and Estimates of Stormwater Pollutant Loads, Dallas-Fort Worth Area, 

Texas, 1992–93 

The EPA published the results of the Nationwide 

Urban Runoff Program (NURP) and the guidelines for 

sampling urban basins to meet NPDES requirements 

(U.S. Environmental Protection Agency, 1983, 1992). 

Kilpatrick and others (1985) documented and verified 

the formulas used to compute flow volumes in an 

enclosed storm sewer when a Palmer-Bowlus flume is 

used as the measuring device. Methods of collection 

and analysis of water-quality samples have been 

described by Wershaw and others (1987), Fishman and 

Friedman (1989), Ward and Harr (1990), and Wells and 

others (1990). RAINFALL, IN INCHES

1.0

2.0

3.0

4.0

5.0

6.0

JAN FEB MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC

Figure 2. Mean monthly rainfall at Love Field, Dallas, Texas, 1897–1989.

Acknowledgments

The authors express their gratitude to the following people for their cooperation and assistance with 

stormwater sampling during this study: Dr. James 

Caffey and Pete Cerone, City of Arlington; Larry 

McDaniel, City of Dallas; Gene Rattan and Brian 

Camp, City of Fort Worth; Philip Welsch and Mark 

Nelson, City of Garland; Fred Owen and Tyler Veak, 

City of Irving; Mike Jones, City of Mesquite; and Dale 

Hoelting, City of Plano.

DATA COLLECTION 

In accordance with an agreement between the 

EPA and the seven cities to use a regional approach 

to collect the data required by the NPDES regulations, 

26 storm-sewer drainage basins (table 1 at end of report) 

were selected by individuals from each city using a list 

of desirable site characteristics compiled by the USGS 

for rainfall and streamflow measurement and for waterquality sampling during seven storms. Under NPDES 

regulations, each city normally would be required to 

collect 3 samples at 5 to 10 sites, resulting in a maximum of 210 samples for the seven cities (U.S. Environmental Protection Agency, 1992). However, the EPA 

approved a reduced number of sites while maintaining 

the maximum number of samples. When the regional 

approach to data collection was established, 182 of the 

210 samples were designated for the seven municipal 

applicants, and the remaining 28 samples were reserved 

for an eighth NPDES applicant, later identified as the 

Texas Department of Transportation. Those 28 samples 

were collected in 1993 and 1994 and are not included in 

this report.

The basins and sampling sites were selected on 

the basis of catchment characteristics, hydraulic factors, 

accessibility, and safety. Catchment characteristics used 

to select drainage basins included a drainage area of 10 

to 500 acres and representative land use, where the predominant land use is residential, commercial, or industrial. These characteristics were verified by on-site 

inspection and by data from a geographic information 

system provided by NCTCOG.
DATA COLLECTION 5

Several hydraulic factors were considered in the 

selection of sampling sites. Storm-sewer pipes were 

limited to those with diameters between 4 and 6 ft. 

Box culverts were limited in size from 4 by 4 ft to 8 by 

8 ft. A straight and uniform pipe slope was required for 

the length of at least six pipe diameters upstream from 

the measuring device. Streamflow-gaging stations were 

installed at sites that were not affected by backwater 

conditions or unmeasured inflow from sanitary sewers. 

Adequate distance was maintained from upstream 

inflows to allow for complete mixing of the stormwater. 

There were no detected unauthorized connections in 

the storm-sewer system from which unregulated constituents could be contributed. Stations were located 

where there was less possibility of high-velocity flow 

conditions, sewer gases, vehicular traffic, poor lighting, 

and vandalism. Good accessibility to sampling sites 

required that the stations be located at outfalls or in 

pipes accessible through manholes. 

Of the 26 predominantly single land-use drainage 

basins, 11 are classified as residential, 6 as commercial, 

and 9 as industrial (table 1). Drainage-basin size ranges 

from 9.0 acres at site 08055590 Joe's Creek Outfall at 

Denton Drive, Dallas (industrial), to 160 acres at site 

08049320 River Legacy Park Outfall at Green Oaks 

Boulevard, Arlington (residential). The drainage basins 

are irregular in shape and generally do not follow topographic features. The drainage basin for site 08047100 

Clear Fork Trinity River Outfall at Oak Hill Circle, Fort 

Worth, typifies the irregularities common to urban 

basins in the study area (fig. 3).

Instrumentation

Stations were constructed with flow-control 

devices, either a V-notched or sharpcrested weir, or a 

Palmer-Bowlus flume. Water elevation (stage) was 

measured using one pressure transducer at weir stations 

and two pressure transducers at flume stations. The 

pressure transducers were connected to a gas bubbler 

system. Rainfall was recorded by a tipping-bucket rain 

gage measuring 0.01-in. increments. Water samples 

were collected with a portable automatic sampler powered by a 60-Ah battery. The sampling line to the sampler consisted of a stainless steel intake and Tefloncoated tubing. The automatic sampler contained four 

1-gal sample bottles that were cleaned using the protocols outlined in 40 Code of Federal Regulations Part 

136. Telephone communication was established to all 

stations except for 08048545 Dry Branch Outfall at 33d 

Street, Fort Worth. 

A data logger controlled the recording of streamflow and rainfall data and the activation of the sampler. 

Communication between the data logger and a computer in the office was provided by a modem and relay 

driver. A data-storage module powered by an 8-Ah 

battery and connected to the data logger provided a 

backup repository for the data in the event of power failure. A solar panel and voltage regulator were used to 

recharge the batteries for the automatic sampler and the 

data-storage module.

Water-Quality Sampling

Water-quality sampling was conducted when the 

following meteorologic criteria, defined in the NPDES 

stormwater regulations (U.S. Environmental Protection 

Agency, 1990b), were met:

• The storm was preceded by at least 72 hours of dry 

weather. 

• The depth of rainfall over the basin was greater than 

0.1 in. 

• Where feasible, the storm did not vary by more than 

50 percent from the average rainfall volume and 

duration for the area. 

On the basis of rainfall records at long-term 

climatic stations in Dallas and Fort Worth, the limits of 

0.20 and 0.90 in. of rainfall were established as the criteria for sampling. In October 1992, the upper limit was 

raised from 0.90 to 1.5 in., when permission to do so 

was requested by the NCTCOG and granted by the 

EPA. These limits were established to ensure a potential 

accumulation of pollutants during dry weather, adequate runoff from the storm for sampling, and a storm 

representative of the area in terms of intensity, amount, 

and duration.

The hydrograph in figure 4 shows a typical sampled storm with accumulated rainfall, instantaneous 

discharge, and sample activations (pulses) plotted 

against time. A sample pulse occurs when the data logger “instructs” the automatic sampler to collect a discrete sample that will be combined with other discrete 

samples to make a composite sample. The sample 

pulses are flow weighted and distributed throughout the 

hydrograph. 
6 Urban Stormwater Quality, Event-Mean Concentrations, and Estimates of Stormwater Pollutant Loads, Dallas-Fort Worth Area, 

Texas, 1992–93 

Hulen

Street

Lane

Oak Park

Circle

Oak Hill

Circle

Oak Hill

Trail

Trail

Trail

Trail

Trail

Hartwood Drive

Shady creek Drive

Hartwood Drive

Glenwood

Pebblebrook Court

Trail

Via Villani

Stonegate Blvd.

Bridge veiw Drive

South

Drive

POND

Clear

Fork

Trinity

River

0 0.1 0.2 0.3 0.4 0.5 MILE

Monitored storm drainage basin

U.S. Geological Survey sampling-site location

EXPLANATION

Base from U.S. Geological Survey

digital data, 1:100,000

State Plane North-Central Zone

Figure 3. Drainage area for site 08047100 Clear Fork Trinity River Outfall at Oak Hill Circle, Fort Worth, Texas.
DATA COLLECTION 7

0

20

2

4

6

8

10

12

14

16

18

DISCHARGE, IN CUBIC FEET PER SECOND

0

1.0

0.2

0.4

0.6

0.8

ACCUMULATED RAINFALL, IN INCHES

0620 0640 0700 0720 0740 0800 0820 0840 0900 0920 0940 1000 1020 1040 1100

14

April 1993

Accumulated rainfall

Discharge

Composite sample

Grab sample

Figure 4. Hydrograph showing discharge and rainfall record of storm at site 08061510 Rowlett Creek Outfall at 

Willow Creek Park, Plano, Texas, April 14, 1993.

Guidance for the collection of stormwater samples from small urban watersheds was provided in the 

NPDES Stormwater Sampling Guidance Document 

(U.S. Environmental Protection Agency, 1992). Samples were collected for properties and constituents that 

characterize physical, inorganic, organic, and microbiological characteristics of the stormwater. The EPA specified a suite of 138 properties and constituents for 

sampling and analysis using sampling, preservation, 

and analytical protocols identified in 40 Code of Federal 

Regulations Part 136. However, a total of 188 properties 

and constituents was analyzed for each sample because 

of the interest in concentrations of the additional 50 

properties and constituents by the cooperating agency 

and the cities involved in this study. 

Water-quality samples for analysis of 70 properties and constituents were collected using grabsampling techniques. The grab sample was collected 

primarily by hand dipping at the outflow, although 

some grab samples were collected using a peristaltic 

pump at sites where safety considerations prohibited 

hand-dipped samples. Grab-sampling techniques were 

used to prevent transformations, volatilization, or loss 

of aseptic conditions during compositing. For example, 

the volatile organic compound (VOC) sample was collected in specially treated glass-septum vials to prevent 

the compounds in solution from volatilizing. As shown 

in figure 4, the grab sample was collected, and the time 

of collection was plotted. 

Residual chlorine was analyzed on-site only to 

detect its presence in a sample. If residual chlorine was 

present, the VOC sample and biochemical oxygen 

demand (BOD) sample were preserved differently than 

if there was no residual chlorine. Residual chlorine was 

detected in only 2 of the 182 grab samples. Ascorbic 

acid was added to the VOC vials, and the BOD bottles 

were seeded with raw sewage for the two samples with 

detected residual chlorine that were collected early in 

the storms that occurred during summer 1992. The 

residual chlorine possibly resulted from storage in the 

storm-sewer system of chlorinated water recently 

released from the municipal water system or a swimming pool.

Grab samples were collected at various times during a storm. EPA guidelines recommend that the grab 

sample be collected within the first 15 minutes of the 

storm runoff or as soon thereafter as possible (U.S. 

Environmental Protection Agency, 1992). Storms in the 

Dallas-Fort Worth area can be characterized by short 

periods (less than 15 minutes) of rainfall during which 

the peak flow of the storm has occurred. To determine 

the distribution of grab samples collected during a 
8 Urban Stormwater Quality, Event-Mean Concentrations, and Estimates of Stormwater Pollutant Loads, Dallas-Fort Worth Area, 

Texas, 1992–93 

0–25 percent of total 

storm-runoff period

26–75 percent of total 

storm-runoff period

76–100 percent of total 

storm-runoff period

Grab sample collected during:

EXPLANATION

35

30

PLES

25

20

F SAMR O

15

EBNUM

10

5

0

RESIDENTIAL COMMERCIAL INDUSTRIAL

Figure 5. Distributions of grab samples collected during storm runoff by land-use category.

storm, the total storm-runoff period was divided into 

three intervals: 0 to 25, 26 to 75, and 76 to 100 percent 

of the total storm-runoff period. The distribution of the 

grab samples collected during each period and for each 

land use is plotted in figure 5. 

Automatic samplers were used to collect flowweighted composite samples for analysis of 118 other 

properties and constituents. Flow-weighted composite 

samples were collected for a minimum of the first 3 

hours of the storm discharge or for the entire discharge 

if the storm lasted less than 3 hours. 

Samples were shipped to the USGS National 

Water Quality Laboratory (NWQL) in Arvada, Colo., 

where most constituents were analyzed. Total concentrations of antimony, cyanide, silver, and thallium were 

determined at the Rocky Mountain Analytical Laboratory in Denver, Colo. Alkalinity, BOD, fecal coliform, 

and fecal streptococcus concentrations were determined 

at the USGS laboratory in Fort Worth. Temperature, 

pH, specific conductance, and the presence of residual 

chlorine were determined on-site from the grab sample.

Quality Assurance and Quality Control

Strict quality-assurance and quality-control 

(QA/QC) procedures were followed throughout the 

study. Chain-of-custody procedures were followed with 

each sample. Equipment blanks (organic-free water) for 

organic constituents were passed through the samplecollection equipment at randomly selected stations and 

analyzed at the NWQL. Organic spike mixtures (predetermined concentrations) for selected organic constituents were added to selected environmental samples in 

the field office and also at the NWQL to determine 

recovery rates. Field matrix spikes were used to determine the extent, if any, of sample-quality changes during shipping, and laboratory spikes were used to 

demonstrate laboratory recovery rates. Both types of 

spikes were used to determine the extent of matrix bias 

or interferences for constituent recovery. Reference 

samples (samples with known concentrations) for nutrient and inorganic constituents were submitted to the 

NWQL. Trip blanks (to determine if contamination of 

the VOC samples occurred during transit) and laboratory blanks (to determine if contamination of the 

organic samples occurred in the field laboratory during 

compositing) also were submitted to the NWQL. In 

addition to these QA/QC procedures, the NWQL followed similar in-house procedures (Friedman and 

Erdmann, 1982; Pritt and Raese, 1992).

URBAN STORMWATER QUALITY

Data from a grab sample provide the concentration of a constituent at a given point in time. Data from 

a composite sample provide the average concentration 

of a constituent over a period of time. 

Logarithmic plotting distribution estimation 

techniques (Helsel and Cohn, 1988) were used to compute statistics for constituent concentrations less than 

the laboratory analytical minimum reporting level 

(MRL). The logarithmic plotting distribution estimation 
URBAN STORMWATER QUALITY 9

technique also can be used for constituents with multiple MRLs (Helsel and Cohn, 1988), such as diazinon. 

The use of the robust probability-plot method has 

been shown to perform well for estimating summary 

statistics and reducing errors that would have been 

caused by simple substitution methods (Helsel and 

Hirsch, 1992).

Visual summaries of the distribution of constituent concentrations are shown using boxplots. Boxplots 

show the median, interquartile range (25th to 75th percentile), and outlying values. 

Grab-Sample Properties and Constituents

The properties and constituents determined from 

the grab sample were water temperature, pH, total cyanide, total phenols, total recoverable oil and grease, 

presence of residual chlorine, fecal coliforms, fecal 

streptococci, and 63 VOCs. 

Summary statistics for properties and constituents 

analyzed in the grab samples were computed for each 

land use. Water temperature ranged from 6.5 to 30.0 °C 

(table 2 at end of report). Water temperature might have 

been more dependent on ambient air temperature than 

on land use. Water temperature at sites in different parts 

of the Dallas-Fort Worth area for samples collected during the same storm event usually did not vary by more 

than 2 °C. pH ranged from 6.2 (acidic) 

to 9.9 (alkaline). The maximum pH was in a sample 

from a site in Garland that drained an area having roadconstruction activities during the sampling period. 

Total cyanide concentrations generally were 

less than the MRL. Total phenols concentrations ranged 

from 1.0 μg/L from all three types of land-use basins 

to 58 μg/L from an industrial land-use basin (site 

08061530). Total recoverable oil and grease concentrations generally were about or less than the MRL, 

although one sample from an industrial land-use basin 

had a concentration of 120 mg/L.

Bacteria

The two types of bacteria measured in this study, 

fecal coliforms and fecal streptococci (table 3 at end of 

report), are strains of bacteria that are present in the 

intestines or feces of warm-blooded animals. Fecal 

coliform bacteria are specified in State and Federal 

standards as indicators of the sanitary quality of the 

water (U.S. Environmental Protection Agency, 1990a). 

Median concentrations of fecal streptococci were 

equal to or greater than those of fecal coliforms except 

in those samples collected during 76 to 100 percent of 

the total storm runoff from industrial land-use basins 

(fig. 6). Median bacteria concentrations were greatest in 

residential land-use basins. Bacteria concentrations 

generally were greater during the first 25 percent of the 

total storm runoff than during the middle 50 percent and 

then increased during the last 25 percent. 

Volatile Organic Compounds

Samples from sites in industrial land-use basins 

had substantially more VOC detections than samples 

from sites in the two other land-use basins (fig. 7). Samples from sites in industrial land-use basins had about 

twice as many VOC detections during the first 25 percent of the total storm-runoff as during the remaining 

75 percent. The frequency of VOC detections in samples collected throughout the storm was similar for sites 

in residential and commercial land-use basins. Of 151 

VOC detections from sites in industrial land-use basins 

(fig. 8), 64 were from site 08048545 Dry Branch Outfall 

at 33d Ave., Fort Worth. 

The most frequently detected VOC was toluene 

(33 detections in 181 samples) (table 4 at end of report), 

the 27th largest volume chemical produced in the 

United States in 1985 (Sax and Lewis, 1987). Toluene 

is used for many purposes including aviation, gasoline, 

industrial solvents, thinner in nitrocellulose lacquers, 

and detergents. Benzene and substituted benzene 

(xylenes) were the next most frequently detected VOCs. 

Several other VOCs (table 5 at end of report) were 

detected at lesser frequencies and are not listed in table 

4. The greatest VOC concentration was 1,200 μg/L of 

cis-1,2-dichloroethene in a sample collected June 9, 

1993, from a site in an industrial land-use basin.

Flow-Weighted Properties and Constituents

Flow-weighted composite samples were analyzed 

for the following groups of properties and constituents: 

nutrients (8), oxygen demand (2), inorganics (10), trace 

elements (13), base/neutral and acid extractable semivolatile organic compounds (BNAs) (57), organochlorine pesticides and polychlorinated biphenyls (PCBs) 

(27), and diazinon, an organophosphorus insecticide.

Nutrients

Median concentrations of total nitrogen and total 

ammonia plus organic nitrogen in samples from sites in 

residential land-use basins were greater (about 0.5 mg/L 

as nitrogen) than median concentrations in commercial 
10 Urban Stormwater Quality, Event-Mean Concentrations, and Estimates of Stormwater Pollutant Loads, Dallas-Fort Worth Area, 

Texas, 1992–93 

(31)

Smallest data value within 1.5 

times the IQR below the box

Number of samples

Outside data value 1.5 to 3.0 

times the IQR outside the box

Outside data value greater than 

3.0 times the IQR outside the box

25th percentile

Largest data value within 1.5 

times the IQR above the box

75th percentile

Median (50th 

percentile)

EXPLANATION

Interquartile 

range (IQR)

100

10

1,000

10,000

100,000

1,000,000

COMMERCIAL

(18)

(18) (13)

(13) (11)

(11)

COLONIES PER 100 MILLILITERS

PERCENTAGE OF TOTAL STORM RUNOFF

0–25 26–75 76–100

FECAL

COLIFORMS

FECAL

COLIFORMS

FECAL

COLIFORMS

FECAL

STREPTOCOCCI

FECAL

STREPTOCOCCI

FECAL

STREPTOCOCCI

100

1,000

10,000

100,000

1,000,000

10

INDUSTRIAL

(22)

(22)

(13)

(13)

(28)

(27)

100

1,000

10,000

100,000

1,000,000

RESIDENTIAL

(31)

(31)

(21)

(21)

(25)

(25)

Figure 6. Ranges and distributions of fecal coliform and fecal streptococcus bacteria as a percentage of total 

storm runoff. 
URBAN STORMWATER QUALITY 11

0–25 percent of total 

storm-runoff period

26–75 percent of total 

storm-runoff period

76–100 percent of 

total storm-runoff 

period

Sample collected during:

EXPLANATION

0

10

20

30

40

50

60

70

80

90

100

RESIDENTIAL COMMERCIAL INDUSTRIAL

NUMBER OF DETECTIONS

Figure 7. Distributions of volatile organic compound detections during storm runoff period by land-use category.

(77) (77)

(

177)

(41) (41)

(

141)

(63) (63)

(

163)

0

20

40

60

80

100

120

140

160

RESIDENTIAL COMMERCIAL INDUSTRIAL

NUMBER OF DETECTIONS

(77) Number of samples 

analyzed

Toluene

Xylene

Total detections, all 

VOCs

For most VOCs; see 

table 5

1

EXPLANATION

Figure 8. Volatile organic compound detections by land-use category.

and industrial land-use basins (fig. 9). Fertilizer applications to lawns and ornamental plants might be the cause 

of the greater nitrogen concentrations. Median phosphorus concentrations (total and dissolved) also were 

greater in samples from sites in residential land-use 

basins than in commercial or industrial land-use basins 

(fig. 10). Phosphorus concentrations in samples from 

sites in commercial and industrial land-use basins were 

not substantially different. The median total organic 

carbon concentration was 18.0 mg/L in samples from 

sites in residential and industrial land-use basins and 

12.0 mg/L in commercial land-use basins (table 6 at end 

of report). 

Biochemical and Chemical Oxygen Demand

Two types of oxygen demand analyses were done 

on the collected samples, BOD and chemical oxygen 

demand (COD). Samples from sites in industrial landuse basins had a greater median BOD (7.5 mg/L) than 

in the other types of land-use basins (fig. 11, table 7 at 

end of report). Samples from sites in residential landuse basins had a greater median COD (70.0 mg/L) than 
12 Urban Stormwater Quality, Event-Mean Concentrations, and Estimates of Stormwater Pollutant Loads, Dallas-Fort Worth Area, 

Texas, 1992–93 

(77)

Smallest data value within 1.5 

times the IQR below the box

Number of samples

Outside data value 1.5 to 3.0 

times the IQR outside the box

Outside data value greater than 

3.0 times the IQR outside the 

box

25th percentile

Largest data value within 1.5 

times the IQR above the box

75th percentile

Median (50th 

percentile)

EXPLANATION

Interquartile 

range (IQR)

TOTAL NITROGEN CONCENTRATION, 

IN MILLIGRAMS PER LITER

TOTAL AMMONIA PLUS ORGANIC NITROGEN

CONCENTRATION, IN MILLIGRAMS

0

2

4

6

8

RESIDENTIAL COMMERCIAL INDUSTRIAL

0

2

4

6

8

10

(77)

(77)

(42)

(42)

(63)

(63)

PER LITER AS NITROGEN

Figure 9. Ranges and distributions of total nitrogen and total ammonia plus organic nitrogen concentrations by 

land-use category.

samples from sites in industrial (66.0 mg/L) or commercial (56.5 mg/L) land-use basins. 

Inorganic Constituents

The median suspended solids concentration 

in samples from sites in industrial land-use basins 

(104 mg/L) was substantially greater than in residential 

(78.0 mg/L) or commercial (42.0 mg/L) land-use 

basins (fig. 12, table 8 at end of report). The median 

dissolved solids concentration was greater in samples 

from sites in industrial land-use basins (69.0 mg/L) than 

in residential (59.0 mg/L) or commercial (50.0 mg/L) 

land-use basins. Mean suspended solids and dissolved 

solids concentrations differ substantially from respective median concentrations. For example, the mean 

suspended solids concentration for industrial land-use 

basins (222 mg/L) is more than twice the median 

(table 8). 

The dominant water type for all three land uses is 

calcium carbonate. Alkalinity concentrations in stormwater samples were very unstable. Concentrations 

could increase as much as 50 percent from the time of 

analysis immediately after sample collection until the 

sample was reanalyzed by the NWQL. The alkalinity 

values reported in table 8 are those determined nearest 

to the times of sample collection. 
URBAN STORMWATER QUALITY 13

(77)

Smallest data value within 1.5 

times the IQR below the box

Number of samples

Outside data value 1.5 to 3.0 

times the IQR outside the box

Outside data value greater than 

3.0 times the IQR outside the box

25th percentile

Largest data value within 1.5 

times the IQR above the box

75th percentile

Median (50th 

percentile)

EXPLANATION

Interquartile 

range (IQR)

DISSOLVED PHOSPHORUS CONCENTRATION,

IN MILLIGRAMS PER LITER

TOTAL PHOSPHORUS CONCENTRATION,

IN MILLIGRAMS PER LITER

0

0.2

0.4

0.6

0.8

1.0

RESIDENTIAL COMMERCIAL INDUSTRIAL

0

0.2

0.4

0.6

0.8

1.0

(77)

(77)

(42)

(42)

(63)

(63)

Figure 10. Ranges and distributions of total phosphorus and dissolved phosphorus concentrations by land-use 

category.

Trace Elements

Median concentrations of total recoverable chromium, copper, nickel, and zinc in samples from sites in 

industrial land-use basins were greater than in the two 

other land-use basins (table 9 at end of report). The 

median total arsenic concentration in samples from sites 

in residential land-use basins (3.0 μg/L) was greater 

than in industrial (2.0 μg/L) or commercial (1.0 μg/L) 

land-use basins. One residential land-use basin in particular (site 08061915 South Mesquite Creek Outfall at 

South Parkway, Mesquite) had relatively large total 

arsenic concentrations, ranging from 11.0 to 35.0 μg/L, 

and a mean of 22.6 μg/L. One industrial land-use basin 

(site 08061530 Spring Creek Outfall at Avenue F, 

Plano) had very large mean concentrations of total 

recoverable copper (732 μg/L), lead (133 μg/L), and 

zinc (296 μg/L).

Base/Neutral and Acid-Extractable Semivolatile 

Organic Compounds

Each of approximately1 182 composite storm 

samples was analyzed for 57 BNAs. The most detec1 “Approximately” because 1 or 2 analyses for a few of the 

57 compounds were missing. 
14 Urban Stormwater Quality, Event-Mean Concentrations, and Estimates of Stormwater Pollutant Loads, Dallas-Fort Worth Area, 

Texas, 1992–93 

(74)

Smallest data value within 1.5 

times the IQR below the box

Number of samples

Outside data value 1.5 to 3.0 

times the IQR outside the box

Outside data value greater 

than 3.0 times the IQR outside 

the box

25th percentile

Largest data value within 1.5 

times the IQR above the box

75th percentile

Median (50th 

percentile)

EXPLANATION

Interquartile 

range (IQR)

CHEMICAL OXYGEN DEMAND,

IN MILLIGRAMS PER LITER

BIOCHEMICAL OXYGEN DEMAND,

IN MILLIGRAMS PER LITER

10

100

1,000

10,000

RESIDENTIAL COMMERCIAL INDUSTRIAL

0

5

10

15

20

25

30

(74)

(77)

(40)

(42)

(61)

(62)

Figure 11. Ranges and distributions of biochemical oxygen demand and chemical oxygen demand by land-use 

category.

tions of BNAs (98) were in 63 samples from sites in 

industrial land-use basins (fig. 13). The fewest BNA 

detections (37) were in samples from 77 sites in residential land-use basins. The most frequently detected BNA 

from all land-use basins was bis(2-ethylhexyl)phthalate 

(79 detections in 181 samples) (table 10 at end of 

report). This compound is used as a plasticizer, added 

to a high-density polymer to facilitate processing and 

to increase the flexibility and toughness of the final 

product by solvation of the polymer molecule (Sax 

and Lewis, 1987). Bis(2-ethylhexyl)phthalate also is a 

common laboratory contaminant, and concentrations 

less than or equal to 10 times the concentration in any 

associated laboratory blank should not be used without 

qualification (R.D. Brock, U.S. Geological Survey, 

written commun., 1994). Concentrations of bis(2-ethylhexyl)phthalate were less than 5.0 μg/L for laboratory 

blanks. The BNAs such as fluoranthene, phenanthrene, 

and pyrene are derived from coal tar (Sax and Lewis, 

1987) and might be an indicator of leaching from road 

surfaces or roofing materials. Several other BNAs were 

detected but not as frequently as those listed in table 10. 

The greatest BNA concentration detected was 280 μg/L 

of benzo(k)fluoranthene in a sample from a site in a 

residential land-use basin (table 11 at end of report). 
URBAN STORMWATER QUALITY 15

(72)

Smallest data value within 1.5 

times the IQR below the box

Number of samples

Outside data value 1.5 to 3.0 

times the IQR outside the box

Outside data value greater than 

3.0 times the IQR outside the 

box

25th percentile

Largest data value within 1.5 

times the IQR above the box

75th percentile

Median (50th 

percentile)

EXPLANATION

Interquartile 

range (IQR)

DISSOLVED SOLIDS CONCENTRATION, 

IN MILLIGRAMS PER LITER

SUSPENDED SOLIDS CONCENTRATION, 

IN MILLIGRAMS PER LITER

10

100

1,000

RESIDENTIAL COMMERCIAL INDUSTRIAL

10

100

1,000

1

10,000

(72) (38)

Note: Concentrations less than 1.0

 not shown 

(60)

(72) (37)

(60)

Organochlorine Pesticides, Polychlorinated 

Biphenyls, and Diazinon

Analyses were done for 27 organochlorine pesticides and PCBs (as aroclors) and 1 organophosphorus 

pesticide, diazinon. Chlordane was reported as “technical” and as two of its isomers. Diazinon was the most 

frequently detected pesticide (fig. 14, table 12 at end of 

report)—71 detections in 76 samples from sites in residential land-use basins, 28 detections in 40 samples 

from commercial land-use basins, and 21 detections in 

63 samples from industrial land-use basins. Diazinon 

is used extensively in the Dallas-Fort Worth area to 

control fire ants and other insects. Chlordane and dieldFigure 12. Ranges and distributions of suspended solids and dissolved solids concentrations by land-use 

category.

rin were the next most frequently detected pesticides. 

Chlordane was banned for all uses by the EPA in 1988 

(Agency for Toxic Substances and Disease Registry, 

1994). Between July 1, 1983, and April 14, 1988, the 

only approved use for chlordane in the United States 

was for underground termite control (R.D. Brock, U.S. 

Geological Survey, written commun., 1993). Since 

April 14, 1988, however, all commercial use of chlordane in the United States has been banned by the EPA 

(Howard and others, 1991). Dieldrin is an insecticide 

that is restricted to nonagricultural applications.

Although most pesticide detections are expected 

during April to September when pesticide application 
16 Urban Stormwater Quality, Event-Mean Concentrations, and Estimates of Stormwater Pollutant Loads, Dallas-Fort Worth Area, 

Texas, 1992–93 

(

163)

(77)

(

177)

(77) (41) (63)

(63)

(42)

(77)

Number of samples 

analyzed

Bis(2–Ethylhexyl) 

phthalate

Pyrene

Total BNA detections, all compounds

(

142)

1

For most BNAs; see 

table 11

EXPLANATION

100

90

80

70

60

F DETECTIONS

50

R O

40

EBNUM30

20

10

0

RESIDENTIAL COMMERCIAL INDUSTRIAL

Figure 13. Base/neutral and acid extractable semivolatile organic compound detections by land-use category.

(

177)

(76)

(76)

(40)

(63) (77)

(42) (63)

Diazinon

Chlordane

Total detections, 

all pesticides

(

142)

1 For most pesticides; 

see table 13

EXPLANATION

(63)

Number of samples 

analyzed

120

 DETECTIONS

100

80

60

FBER O

40

NUM

20

0

RESIDENTIAL COMMERCIAL INDUSTRIAL

Figure 14. Organochlorine pesticide detections by land-use category.

rates are greater because of the increased activity of fire 

ants, more pesticides were detected during October to 

March. This anomaly is explained by the greater number of samples collected in fall and winter, when storms 

occur with greater frequency and duration than in summer. Median total diazinon concentrations in samples 

from sites in residential land-use basins (0.50 μg/L) 

were 500 percent greater than in commercial land-use 

basins (0.10 μg/L) (table 13 at end of report). The 

median total diazinon concentration for industrial landuse basins was less than the MRL. The largest total 

diazinon concentration, 25.0 μg/L, was measured at a 

site in a residential land-use basin.

EVENT-MEAN CONCENTRATIONS

The EPA designated 12 properties and constituents for load estimation. EMCs for BOD; COD; 

suspended and dissolved solids; total nitrogen and 

ammonia plus organic nitrogen; total and dissolved 

phosphorus; and total recoverable copper, lead, and zinc 

were computed from the flow-weighted composite samples for each land use by three methods—volumeweighted mean concentration, logarithmic-transformed 

mean concentration, and arithmetic mean concentration 

(table 14 at end of report). EMCs for total recoverable 

cadmium were not computed because concentrations 
STORMWATER POLLUTANT LOADS 17

were greater than the MRL (1.0 μg/L) in samples from 

only a few storms. In addition, EMCs were computed 

for diazinon (not designated by EPA) because of its 

numerous detections in the Dallas-Fort Worth area. A 

median concentration for each constituent by land use 

also was determined. 

Volume-weighted event-mean concentration 

(VWEMC) was computed for each land use by the 

equation

, (1)

where 

VWEMC = volume-weighted event-mean concentration of constituent (in milligrams per 

liter or micrograms per liter) for a landuse basin;

EMCi = event-mean concentration of constituent 

(in milligrams per liter or micrograms 

per liter) for storm i; and

RVi = runoff volume (in cubic feet) for storm i.

The logarithmic-transformed mean concentration 

was computed by transforming individual storm mean 

concentrations (measured) to base 10 logarithms, summing the values, and dividing by the number of storms. 

This value was then retransformed and reported in table 

14. The arithmetic mean was computed by summing the 

EMC for each sampled storm and then dividing the 

summation by the total number of storms. The median 

for each constituent by land use is the 50th percentile 

(central value) for each data set. Industrial land-use 

median EMCs were not determined during the NURP 

study (U.S. Environmental Protection Agency, 1983) 

and therefore were not reported.

The EMCs of COD; total nitrogen and ammonia 

plus organic nitrogen; total and dissolved phosphorus; 

and total diazinon were greatest in samples from sites in 

the residential land-use basins. The EMCs of BOD; suspended and dissolved solids; and total recoverable copper, lead, and zinc were greatest in samples from sites in 

the industrial land-use basins. The median EMCs computed for this study are substantially less than NURP 

medians for BOD, total ammonia plus organic nitrogen, 

and total copper, lead, and zinc.

The question arises as to which value is the best 

estimator of central tendency for the sample population—mean concentrations or median concentrations. 

Tests for normality of distributions done on the 12 

constituents indicate that the populations are not normally distributed. Therefore, the median and the logtransformed mean are better estimators of the central 

tendency for these constituents than the arithmetic mean 

and the volume-weighted mean.

STORMWATER POLLUTANT LOADS

Stormwater pollutant loads for 11 of the 12 designated properties and constituents, plus diazinon, were 

estimated using two methods: Computing loads directly 

from measured data and estimating loads using statistical methods. Twelve constituents are required by the 

EPA for load estimation—BOD; COD; suspended and 

dissolved solids; total nitrogen and ammonia plus 

organic nitrogen; total and dissolved phosphorus; and 

total recoverable cadmium, copper, lead, and zinc. 

Loads were not estimated for cadmium because of the 

low frequency of detections (less than 50 percent in 

samples from sites in industrial land-use basins and 

less than 5 percent in samples from commercial and 

residential land-use basins). However, loads for total 

diazinon were estimated because of its known presence 

in stormwater in the Dallas-Fort Worth area.

The first method, direct computation from measured data, is basin specific. Measured data from seven 

storms at each of the 26 sites were used to directly compute storm loads for that site. The second method, a 

statistical method (regression analysis), was used to 

estimate storm and annual loads for sites on a regional 

basis by using the information generated from the basinspecific computations. 

Computed Loads for Three Land Uses

Pollutant loads for an individual storm were computed from measured flow-weighted EMCs and runoff 

volume. The runoff volume is an important factor in the 

variation of loads. For each land use, the drainage 

basins with the largest areas generally produced the 

greatest pollutant loads. A load for a given storm (i) is 

computed by the equation

, (2)

where 

= pollutant load (in pounds) for storm i;

= event-mean concentration of constituent 

(in milligrams per liter or micrograms per 

liter) for storm i;

= runoff volume (in cubic feet) for storm i; and

VWEMC

Σ EMCi RVi ( ) ×

ΣRVi

= ----------------------------------------

LOADi EMCi RVi = × × CF

LOADi

EMCi

RVi
18 Urban Stormwater Quality, Event-Mean Concentrations, and Estimates of Stormwater Pollutant Loads, Dallas-Fort Worth Area, 

Texas, 1992–93 

CF = conversion factor (6.2382-5 if constituent 

is in milligrams per liter or 6.2382-8 if 

constituent is in micrograms per liter).

Statistics for rainfall, runoff volume, and percent 

runoff for each land-use category were computed (table 

15 at end of report). The median rainfall was 0.44 in. for 

commercial land-use basins and 0.45 in. for residential 

and industrial land-use basins. However, commercial 

and industrial land-use basins had substantially greater 

median runoff volume and median percent runoff. The 

amount of impervious area in a basin had a substantial 

effect on percent runoff. Those land-use basins identified earlier with larger impervious areas (table 1) had 

greater percent runoff volumes than those with smaller 

impervious areas.

Loads for the properties and constituents for each 

land-use category on the basis of seven sampled storms 

at each site, were computed using equation 2. The loads 

were divided by the contributing drainage area to allow 

comparison between the three land-use categories. 

Mean loads per square mile were greatest for COD and 

suspended and dissolved solids for all land uses (table 

16 at end of report). Mean loads per square mile were 

greatest for trace elements at sites in industrial land-use 

basins and for total diazinon at sites in residential landuse basins. Mean loads per square mile for total nitrogen 

from the three types of land-use basins were dissimilar, 

ranging from about 44 lb for residential to slightly more 

than 70 lb for commercial and industrial. 

An analysis of covariance (parametric test) 

using quantitative and qualitative variables (Thomas, 

1982) was done on the loads computed for each 

constituent by land use to determine if significant differences (at the 95-percent confidence level) existed. Suspended solids loads for commercial land-use basins 

were not significantly different from loads for the two 

other land-use basins. Loads for total ammonia plus 

organic nitrogen and total and dissolved phosphorus did 

not differ significantly among land-use basins, although 

median concentrations were significantly different 

among land-use basins. Loads for the remaining constituents were significantly different among the three land 

uses.

These results were confirmed by Kruskal-Wallis 

tests (Iman and Conover, 1983), nonparametric analysis 

of variance tests on the ranks of the data. The results of 

the Kruskal-Wallis tests indicate no significant differences in loads among land uses for total ammonia plus 

organic nitrogen, total phosphorus, and dissolved phosphorus but do indicate significant differences in loads 

for the remaining constituents.

Regression Analysis to Estimate Loads for All 

Gaged Basins in the Study Area

Stormwater pollutant loads can be estimated 

for periods without field data by using statistical procedures (regression analysis) or deterministic models. 

Regression analysis to estimate loads involves developing a relation between load and a series of quantifiable 

physical and land-use characteristics (explanatory variables). Deterministic models estimate loads by attempting to simulate the physical processes using measured 

data to calibrate model parameters. Regression equations were developed as part of this study to estimate 

loads for gaged basins. 

Estimated Storm Loads

Local regression equations were developed to 

estimate the load produced by individual storms for 

each of the 12 properties and constituents identified for 

load computations. Possible explanatory variables were 

identified on the basis of being easily estimated with 

available physical, land-use, and climatic data. A subset 

of the variables used by Driver and Tasker (1990) was 

selected for the regression analysis. The seven explanatory variables are total storm rainfall (TRN), in inches; 

total contributing drainage area (DA), in square miles; 

impervious area (IA), as a percentage of DA; industrial 

land use (LUI), as a percentage of DA; commercial land 

use (LUC), as a percentage of DA; residential land use 

(LUR), as a percentage of DA; and nonurban land use 

(LUN), as a percentage of DA. The physical and landuse characteristics for the 26 sites in the study basins are 

listed in table 1 (IA in percent; and LUI, LUC, and 

LUN in acres). Regional regression equations derived 

by Driver and Tasker (1990) and the adjustment procedure developed by Hoos and Sisolak (1996) were not 

used for the following reasons: (1) The EMCs computed 

from NURP data varied substantially from the EMCs 

computed from data collected during this study; 

(2) there was an extensive time span (about 10 years) 

between the NURP data-collection period and the 

data-collection period of this study, during which 

sampling-equipment technology improved and factors 

that change environmental conditions occurred—for 

example, the discontinuance of leaded gasoline; and 

(3) the size of the data set compiled from this study 
STORMWATER POLLUTANT LOADS 19

allowed new regression equations to be developed with 

confidence. 

The form of the regression equation, using a logarithmic transformation (log base-10) of the response 

and explanatory variables, is given by

(3)

When equation 3 is detransformed it becomes

(4)

where 

= .

Unity (+1) is added to the IA and land-use percentages 

to avoid the logarithm of zero, which is undefined.

The detransformation of a regression model 

provides a consistent estimator of median response 

but systematically underestimates the mean response 

(Miller, 1984). A bias-correction factor (BCF) is 

included to obtain an unbiased estimate of the mean 

response computed using a parametric method (Miller, 

1984) defined by

, (5)

where 

SE = standard error of estimate (in log units) of the 

regression equation.

The SE is a measure of deviation about the regression. 

The final form of the detransformed equation becomes

(6)

The explanatory variables for each equation 

were selected with stepwise regression. A regression 

coefficient was retained in the equation if it was significantly different from zero at the 5-percent confidence 

level (p = 0.05). The SE and the adjusted coefficient of 

determination (R2) were also used as means of evaluating the use of a specific explanatory variable. The SE is 

a measure of the error about the regression. A smaller 

SE corresponds to a more precise prediction. The R2

measures the proportion of variation of the response 

variable (load) explained by the explanatory variables. 

It depends on the number of parameters in the model 

and is used to judge the fit of the regression model to the 

data. A greater R2

 indicates a better fit. In addition, the 

residuals, the difference between estimated and measured values, were plotted to check the assumptions that 

the residuals are normally distributed with a mean of 

zero and have a constant variance over the range of 

explanatory variables. An example of the estimated 

loads plotted against the measured loads for BOD is 

shown in figure 15 for all sampled storms.

Two additional climatic variables, antecedent dry 

days and maximum 5-minute intensity, were identified 

as possible variables that would explain substantially 

more variation in the regression equations. However, 

because no increase in R2 or decrease in SE was 

observed, the two explanatory variables were not used 

in the regression equations.

The significant explanatory variables, coefficients, BCF, SE, and adjusted R2

 for each local regression equation are listed in table 17 (at end of report). 

The SE ranges from 48.7 to 210 percent, and the 

adjusted R2

 ranges from 40.6 to 65.3 percent for the 

local regression equations. The SE and number of 

storms for the local regression equations and regional 

regression equations (Driver and Tasker, 1990) are 

listed in table 18 (at end of report). For each property or 

constituent, the local regression equations have a 

smaller SE than the regional regression equations.

The following example illustrates the computation of a storm load for BOD at site 08049470 

Tributary to Johnson Creek Outfall at I–30 East, 

Arlington:

(7)

Using a TRN of 0.40 in., the values for the explanatory 

variables determined from table 1 (0.134-mi2

 DA, 

log (LOAD) bo b1 ( ) TRN b = + log + 2log( ) DA

+ b3log( ) IA 1 +

b4 + log( ) LUI 1 +

b5 + log( ) LUC 1 +

b6 + log( ) LUR 1 +

b7 + log( ) LUN 1 + .

LOAD bo' ( ) TRN

b1 ( ) DAb2 = × ×

( ) IA 1 +

b3 ( ) LUI 1 +b4

× ×

( ) LUC 1 +

b5 ( ) LUR 1 +b6

× ×

( ) LUN 1 +

b7

× ,

bo' 10

bo

BCF 10 1.1515 SE ( )2 ( ) =

LOAD bo' ( ) TRN

b1 ( ) DAb2 = × ×

( ) IA 1 +

b3 ( ) LUI 1 +b4

× ×

( ) LUC 1 +

b5 ( ) LUR 1 +b6

× ×

( ) LUN 1 +

b7

× × BCF.

BOD bo' ( ) TRN

b1 ( ) DAb2 = × ×

( ) IA 1 +

b3 ( ) LUI 1 +b4

× ×

( ) LUC 1 +

b5

× × BCF.
20 Urban Stormwater Quality, Event-Mean Concentrations, and Estimates of Stormwater Pollutant Loads, Dallas-Fort Worth Area, 

Texas, 1992–93 

80.9-percent IA, 91-percent LUI, and 9.0-percent 

LUC), and a BCF of 1.11 from table 17, then

BOD 9.01 0.40 ( )0.879 ( ) 0.134 0.725 = × ×

( ) 80.9 1 +

0.656 ( ) 91.0 1.0 +0.104

× ×

( ) 9.0 1.0 +

0.085

× × 1.11,

BOD 36.5 lbs. =

Estimated Mean Annual Loads

Mean annual loads were estimated by applying 

the storm-load equations for all runoff-producing 

storms in an average climatic year (a year in which 

annual rainfall is about the same as mean annual rainfall) and summing individual storm loads to determine 

the annual load. This procedure requires a time series of 

rainfall totals for storms that are representative of the 

mean annual rainfall for each site. To obtain the time 

series, an average climatic year was selected for each 

of two climatic stations in the area—Love Field and 

Meacham Airport—on the basis of similarity of annual 

rainfall to 1961–90 mean annual rainfall. The mean 

annual rainfall for 1961–90 was 33.6 in. for Love Field 

and 30.6 in. for Meacham Airport. The most similar 

annual rainfall to mean annual rainfall for Love Field 

was 33.1 in. during 1965; the most similar annual rainfall to mean annual rainfall for Meacham Airport was 

30.4 in. during 1975. Either the 1965 annual rainfall 

time series or the 1975 annual rainfall time series was 

applied at each of the 26 gaged sites in the study basins 

to estimate mean annual loads, depending on which of 

the two climatic stations the gaged site was closest to. 

The estimated mean annual loads for the 12 properties 

and constituents of interest at the 26 sites in the study 

basins are listed in table 19 (at end of report). 

SUMMARY

EPA regulations require cities with populations 

of 100,000 and greater to obtain NPDES permits to 

discharge stormwater into U.S. waters. Part of the permit-application process requires each city to conduct 

wet-weather sampling to characterize the quantity and 

quality of stormwater from watersheds within the city's 

boundaries and to estimate pollutant concentrations 

and annual pollutant loads. To address this requirement, 

the USGS, in cooperation with the NCTCOG, established a wet-weather sampling network in seven 

cities—Arlington, Dallas, Fort Worth, Garland, Irving, 

Mesquite, and Plano—to collect data to characterize the 

quality of urban stormwater, compute EMCs, and estimate annual stormwater pollutant loads from predominantly single land-use urban drainage basins for 12 

properties and constituents designated by the EPA.

From February 1992 through June 1993, 26 sites 

in urban stormwater drainage basins were sampled 

0 10 20 30 40 50 60 70 80 90 100

0

10

20

30

40

50

60

70

80

90

100

ESTIMATED BIOCHEMICAL OXYGEN DEMAND

MEASURED BIOCHEMICAL OXYGEN DEMAND LOADS (IN POUNDS)

LOADS (IN POUNDS)

Figure 15. Estimated and measured biochemical oxygen demand storm loads.
SUMMARY 21

seven times during storms, for a total of 182 waterquality samples. Of the 26 basins, 11 are predominantly 

residential land use, 6 are predominantly commercial 

land use, and 9 are predominantly industrial land use. 

Water-quality sampling was conducted when 

meteorologic criteria described in the EPA NPDES 

stormwater regulations were met. On-site sampling 

methods, equipment maintenance, sample preservation 

and shipping procedures, laboratory analyses, and quality assurance/quality control sampling followed protocols described in 40 Code of Federal Regulations Part 

136. 

Laboratory analyses were conducted on each 

sample for 188 properties and constituents, of which 

138 properties and constituents were specified by EPA 

NPDES stormwater regulations. Analyses for 70 constituents were conducted on discrete samples collected 

by grab methods. Analyses for the remaining 118 constituents were conducted on flow-weighted composite 

samples collected by automatic sampler. 

Grab samples were collected at various times during a storm. Summary statistics for constituent concentrations in the grab samples were computed for each 

land use. Total cyanide concentrations generally were 

less than the MRL. Total phenols concentrations ranged 

from 1.0 μg/L from all three types of land-use basins to 

58 mg/L from an industrial land-use basin. Total recoverable oil and grease concentrations generally were 

about or less than the MRL, although one sample from 

a site in an industrial land-use basin had a concentration 

of 120 mg/L. Median bacteria concentrations were 

greatest in samples from sites in residential land-use 

basins. Samples from sites in industrial land-use basins 

had substantially more VOC detections than samples 

from sites in the two other types of land-use basins. The 

most frequently detected VOC was toluene.

Flow-weighted composite samples were collected for a minimum of the first 3 hours of the storm 

discharge or for the entire discharge if the storm duration was less than 3 hours. Flow-weighted composite 

samples were analyzed for the following groups of 

properties and constituents: nutrients (8), oxygen 

demand (2), inorganics (10), trace elements (13), 

base/neutral and acid extractable semivolatile organic 

compounds (BNAs) (57), organochlorine insecticides 

and polychlorinated biphenyls (PCBs) (27), and diazinon, an organophosphorus insecticide.

Median concentrations of total nitrogen and total 

ammonia plus organic nitrogen in samples from sites in 

residential land-use basins were greater than in the two 

other types of land-use basins. Median phosphorus concentrations (total and dissolved) also were greater in 

samples from sites in residential land-use basins.

Samples from sites in industrial land-use basins 

had greater median BOD concentrations than samples 

from sites in the two other land-use basins. Samples 

from sites in residential land-use basins had greater 

median COD concentrations. 

Median concentrations of suspended solids were 

substantially greater in samples from sites in industrial 

land-use basins than in the two other land-use basins. 

Median dissolved solids concentrations were greater in 

samples from sites in industrial land-use basins.

Median concentrations of total recoverable chromium, copper, nickel, and zinc were greater in samples 

from sites in industrial land-use basins than in the two 

other land-use basins. The median total arsenic concentration was greater in samples from sites in residential 

land-use basins.

The most BNA detections (98) were in 63 samples from sites in industrial land-use basins, and the 

fewest detections (37) were in 77 samples from sites in 

residential land-use basins. The most commonly 

detected BNA from all land-use basins was bis(2-ethylhexyl)phthalate (79 detections in 181 samples).

Diazinon was the most frequently detected pesticide—71 detections in 76 samples (93 percent) from 

sites in residential land-use basins, 28 detections in 40 

samples (70 percent) from commercial land-use basins, 

and 21 detections in 63 samples (33 percent) from 

industrial land-use basins. Chlordane and dieldrin were 

the next most frequently detected pesticides.

EMCs for the 12 properties and constituents 

(except total recoverable cadmium) designated by the 

EPA for load estimation (BOD; COD; suspended and 

dissolved solids; total nitrogen and ammonia plus 

organic nitrogen; total and dissolved phosphorus; and 

total recoverable copper, lead, and zinc) were computed 

from the flow-weighted composite samples for each 

land use by three methods—volume-weighted mean 

concentration, logarithmic-transformed mean concentration, and arithmetic mean concentration. EMCs for 

cadmium were not computed because concentrations 

were greater than the MRL (1.0 μg/L) in samples 

from only a few storms. EMCs also were computed for 

total diazinon because of its numerous detections in the 

Dallas-Fort Worth area.

The EMCs of COD, total nitrogen, total ammonia 

plus organic nitrogen, total phosphorus, dissolved solids, and total diazinon were greatest in samples from 
22 Urban Stormwater Quality, Event-Mean Concentrations, and Estimates of Stormwater Pollutant Loads, Dallas-Fort Worth Area, 

Texas, 1992–93 

sites in residential land-use basins. The EMCs of BOD, 

suspended solids, dissolved solids, and total recoverable copper, lead, and zinc were greatest in samples 

from sites in industrial land-use basins. The median 

EMCs computed for this study are substantially less 

than NURP medians for BOD, total ammonia plus 

organic nitrogen, and total copper, lead, and zinc.

Stormwater pollutant loads for 11 of the 12 designated properties and constituents, plus diazinon, were 

estimated using two methods—computing loads 

directly from measured data and estimating loads using 

statistical methods (regression analysis). 

Pollutant loads for the properties and constituents 

for each of the three land-use categories were computed, on the basis of seven sampled storms at each site, 

from measured flow-weighted EMCs and runoff volume. COD and suspended and dissolved solids had the 

greatest mean loads per square mile. Mean loads per 

square mile for trace elements were greatest in industrial land-use basins. Mean loads per square mile for 

diazinon were greatest in residential land-use basins. 

Mean loads per square mile for total nitrogen were dissimilar among the three types of land-use basins.

An analysis of covariance was done on the 

loads for each constituent by land use to determine if 

significant differences (at the 95-percent confidence 

level) existed. Suspended solids loads for commercial 

land-use basins were not significantly different from 

loads for the two other land-use basins. Loads for total 

ammonia plus organic nitrogen, total phosphorus, and 

dissolved phosphorus did not differ significantly among 

land uses, although median concentrations were significantly different among land uses. Loads for the remaining constituents were significantly different among the 

three land uses. 

Local regression equations were developed to 

estimate loads produced by individual storms. For each 

property or constituent, the local regression equations 

have a smaller standard error of estimate than regional 

regression equations developed as a part of a previous 

nationwide study to develop methods to estimate stormwater constituent concentrations. Mean annual loads for 

gaged basins were estimated by applying the storm-load 

equations for all runoff-producing storms in an average 

climatic year and summing individual storm loads to 

determine the annual load. 

SELECTED REFERENCES

Agency for Toxic Substances and Disease Registry, 1994, 

Toxicological profile for chlordane (update): Atlanta, 

Ga., U.S. Department of Health and Human Services, 

Public Health Service 

URL: <http://atsdr1.atsdr.cdc.gov:8080/tfacts31.html>.

Driver, N.E., and Tasker, G.D., 1990, Techniques for estimation of storm-runoff loads, volumes, and selected 

constituent concentrations in urban watersheds in the 

United States: U.S. Geological Survey Water-Supply 

Paper 2363, 44 p.

Fishman, M.J., and Friedman, L.C., eds., 1989, Methods 

for determination of inorganic substances in water and 

fluvial sediments: U.S. Geological Survey Techniques 

of Water-Resources Investigations, book 5, chap. A1, 

545 p.

Friedman, L.C., and Erdmann, D.E., 1982, Quality assurance 

practices for chemical and biological analyses of water 

and fluvial sediments: U.S. Geological Survey Techniques of Water-Resources Investigations, book 5, 

chap. A6, 181 p.

Helsel, D.R., and Cohn, T.A., 1988, Estimation of descriptive 

statistics for multiple censored water quality data: Water 

Resources Research, v. 24, no. 12, p. 1,997–2,004.

Helsel, D.R., and Hirsch, R.M., 1992, Studies in environmental science 49—Statistical methods in water resources: 

Amsterdam, Elsevier, 522 p.

Hoos, A.B., and Sisolak, J.K., 1996, Procedures for adjusting 

regional regression models of urban-runoff quality 

using local data: U.S. Geological Survey Water-Supply 

Paper 2428, 33 p.

Howard, P.H., Michalenko, E.M., Sage, G.W., Jarvis, W.F., 

Meylon, W.M., Basu, D.K., Beauman, J.A., and Gray, 

D.A., 1991, Handbook of environmental fate and exposure data for organic chemicals, V. III, Pesticides: 

Chelsea, Mich., Lewis Publishers, Inc., 684 p. 

Iman, R.L., and Conover, W.J., 1983, A modern approach to 

statistics: New York, John Wiley, 497 p.

Kilpatrick, F.A., Kaehrle, W.R., Hardee, Tuck, Cordes, 

E.H., and Landers, M.N., 1985, Development and testing of highway storm-sewer flow measurement and 

recording system: U.S. Geological Water-Resources 

Investigations Report 85–4111, 98 p.

Kingston, Mike, and Crawford, M.G., 1991, 1992–93 Texas 

almanac: Houston, Gulf Publishing Co., 656 p.

Miller, D.H., 1984, Reducing transformation bias in curve 

fitting: The American Statistician, v. 38, no. 2, 

p. 124–126.

North Central Texas Council of Governments, 1993, 1993 

Current population estimates: North Central Texas 

Council of Governments, April Bulletin, 4 p.
SELECTED REFERENCES 23

Pritt, J.W., and Raese, J.W., eds., 1992, Quality assurance/

quality control manual—National Water-Quality 

Laboratory: U.S. Geological Survey Open-File Report 

92–495, 33 p.

Sax, N.I., and Lewis, R.J., 1987, Hawley's condensed 

chemical dictionary (11th ed.): Van Nostrand Reinhold 

Co. Inc., p. 1,288.

Sutherland, R.C., Jelen, S.L., and Green, D.L., 1992, 

Simplified particulate transport model, version 3.1: 

Lake Oswego, Ore., Otak, Inc., 72 p.

Tasker, G.D., Gilroy, E.J., and Jennings, M.E., 1990, 

Estimation of mean urban stormwater loads at 

unmonitored sites by regression, in Symposium on 

Urban Hydrology, Denver, Colo., Nov. 4–8, 1990, 

Proceedings: American Water Resources Association, 

p. 127–137. 

Thomas, W.O., Jr., 1982, Use of qualitative variables in 

regression analysis: U.S. Geological Survey, WRD 

Bulletin, May–Aug. 1982, p. 19–23.

U.S. Environmental Protection Agency, 1983, Results of the 

Nationwide Urban Runoff Program—Executive summary: U.S. Environmental Protection Agency, Water 

Planning Division, National Technical Information 

Service PB84–185545, 24 p.

______1990a, Drinking water regulations and health advisories: U.S. Environmental Protection Agency, Office of 

Drinking Water, 10 p. 

______1990b, National Pollutant Discharge Elimination 

System permit application regulations for stormwater 

discharges—Final rule: U.S. Federal Register, v. 55, 

no. 222, p. 47,989–48,091.

______1991, Guidance manual for the preparation of part 1 

of the NPDES permit applications for discharges 

from municipal separate storm sewer systems: U.S. 

Environmental Protection Agency, Permits Division, 

EPA–505/8–91–003A, 106 p.

______1992, NPDES storm water sampling guidance document: U.S. Environmental Protection Agency, 121 p.

U.S. Geological Survey, 1993, Water resources data for 

Texas, water year 1992, v. 1: U.S. Geological Survey 

Water-Data Report TX–92–1, 617 p.

University of Texas, Bureau of Economic Geology, 1987, 

Geologic atlas of Texas, Dallas sheet: Austin, 1 sheet, 

scale 1:250,000.

Ward, J.R., and Harr, C.A., eds., 1990, Methods for collection and processing of surface-water and bed-material 

samples for physical and chemical analyses: U.S. 

Geological Survey Open-File Report 90–140, 71 p.

Wells, F.C., Gibbons, W.J., and Dorsey, M.E., 1990, Guidelines for collection and field analysis of water-quality 

samples from streams in Texas: U.S. Geological Survey 

Open-File Report 90–127, 79 p.

Wershaw, R.L., Fishman, M.J., Grabbe, R.R., and Lowe, 

L.E., 1987, Methods for the determination of organic 

substances in water and fluvial sediments: U.S. 

Geological Survey Techniques of Water-Resources 

Investigations, book 5, chap. A3, 80 p.
24 Urban Stormwater Quality, Event-Mean Concentrations, and Estimates of Stormwater Pollutant Loads, Dallas-Fort Worth Area, 

Texas, 1992–93 Table 1

Table 1. Selected characteristics of surface-water and water-quality data-collection sites 

Site no.

(fig. 1)

Site name

Land-use

classification

Total

drainage

area

(acres)

Impervious

area

(percent)

Residential C

Arlington

08049220 The Parks Mall Outfall at I–20 West Commercial 38.8 76.2 0 08049320 River Legacy Park Outfall at Green Oaks Boulevard Residential 160 47.4 139 08049360 Tributary to West Fork Trinity River Outfall at Baird’s Farm Road Residential 77.0 89.0 70.5 08049470 Tributary to Johnson Creek Outfall at I–30 East Industrial 85.5 80.9 0 

Dallas

08055590 Joe's Creek Outfall at Denton Drive Industrial 9.0 80.0 0 08056390 Bastille Street Outfall at La Reunion Parkway Industrial 49.5 80.0 0 08057135 White Rock Creek Outfall at Preston Road Commercial 59.1 84.5 .9 08057310 Ash Creek Outfall at Whittier Street Residential 71.3 50.0 71.3 08057441 Newton Creek Outfall at Tioga Street Residential 38.9 44.9 33.9 

Fort Worth

08047100 Clear Fork Trinity River Outfall at Oak Hill Circle Residential 61.7 21.9 13.2 08048505 Pylon Street Outfall at Meacham Road Industrial 151 27.7 0 08048510 West Fork Trinity River Outfall at Highway 121 Commercial 136 66.5 59.7 08048545 Dry Branch Outfall at 33d Street Industrial 73.7 79.3 0 08048700 Eastern Hills High School Outfall at Weiler Drive Residential 151 61.4 97.2 

Garland

08061635 Tributary to Duck Creek Outfall at Hightower Road Industrial 33.9 67.3 0 08061660 Sleepy Hollow Street Outfall at Northwest Highway Residential 67.3 55.1 58.7 08061690 I–635 Outfall at Centerville Road Commercial 36.2 84.6 11.3 

Irving

08049590 Bear Creek Outfall at Shady Grove Road Residential 65.3 41.9 50.4 08055570 Hereford Road Outfall at Walnut Hill Road Industrial 43.4 77.3 0 08056100 Tributary to Elm Fork Trinity River Outfall at Cascade Street Industrial 43.9 77.8 0 

Mesquite

08061910 South Mesquite Creek Outfall at I–635 Commercial 45.9 89.4 0 08061915 South Mesquite Creek Outfall at South Parkway Residential 45.4 49.8 44.8 08061940 South Mesquite Creek Outfall at Bruton Road Residential 46.2 49.9 46.1 

Plano

08061510 Rowlett Creek Outfall at Willow Creek Park Residential 51.4 54.3 44.7 08061525 Spring Creek Outfall at Park Boulevard Commercial 22.7 73.5 0 08061530 Spring Creek Outfall at Avenue F Industrial 49.0 81.6 5.1 
Table 3 25

Table 3

Table 2

Table 2. Summary statistics for physical properties (water temperature and pH) and total cyanide, phenols, and oil 

and grease by land-use category

[°C, degrees Celsius; mg/L, --, no data or not applicable; mg/L, milligrams per liter; μg/L, micrograms per liter; ND, 

nondetection] 

Table 3. Summary statistics for bacteria by land-use category

[In colonies per 100 milliliters.] 

Property or

constituent

Laboratory minimum reporting

level if nondetections present

No.

of

samples

MaximumMinimum Mean

95th

percentile

75th

percentile

Median

50th

percentile

25th

percentile

5th

percentile

Water temperature1 (°C) --

Residential 77 29.0 8.0 17.7 26.6 22.5 17.0 13.2 9.5

Commercial 41 24.5 6.5 15.9 23.9 20.5 15.0 13.0 8.0

Industrial 63 30.0 8.5 18.3 27.0 24.0 18.5 13.0 9.0

pH1 (standard units)

1 Property or constituent mandated by U.S. Environmental Protection Agency (1992).

--

Residential 77 9.9 6.2 (

2

)

2 Mean for pH not reported.

9.0 8.2 7.8 7.4 6.7

Commercial 41 8.7 6.3 (

2

) 8.5 8.1 7.8 7.6 6.8

Industrial 63 9.2 6.5 (

2) 8.9 8.3 8.0 -- --

Cyanide, total1 (mg/L) 0.01

Residential 76 .08 ND -- .01 ND ND ND ND

Commercial 42 .08 ND -- .01 ND ND ND ND

Industrial 62 .04 ND -- .01 ND ND ND ND

Phenols, total1 (μg/L) --

Residential 77 21.0 1.0 4.4 11.0 5.0 4.0 3.0 1.0

Commercial 42 17.0 1.0 5.4 14.7 7.0 4.0 2.0 1.0

Industrial 63 58.0 1.0 6.2 17.4 6.0 4.0 3.0 1.2

Oil and grease, total recoverable

gravimetric1 (mg/L) 1.0 

Residential 76 19.0 ND 32.2

3 Mean values calculated for censored data by logarithmic probability regression method (Helsel and Cohn, 1988).

8.0 2.0 1.0 ND ND

Commercial 42 8.0 ND 32.3 6.0 3.0 2.0 ND ND

Industrial 63 120 ND 33.5 6.0 2.0 ND ND ND

Bacteria

No. of

samples

MaximumMinimum Mean 95th

percentile

75th

percentile

Median

50th

percentile

25th

percentile

5th

percentile

Fecal coliforms1

1 Constituent mandated by U.S. Environmental Protection Agency (1992).

Residential 77 600,000 150 70,000 290,000 75,000 20,000 5,600 1,000

Commercial 42 810,000 67 48,000 400,000 36,000 6,900 970 200

Industrial 63 290,000 70 20,000 100,000 19,000 9,700 2,400 900

Fecal streptococci1

Residential 77 670,000 2,600 120,000 430,000 190,000 56,000 24,000 7,000

Commercial 42 350,000 1,400 50,000 320,000 47,000 18,000 7,100 1,600

Industrial 62 210,000 33 25,000 150,000 20,000 10,000 6,100 1,900
26 Urban Stormwater Quality, Event-Mean Concentrations, and Estimates of Stormwater Pollutant Loads, Dallas-Fort Worth Area, 

Texas, 1992–93 

Table 4. Most frequent volatile organic compound detections by land-use category and sampling site 

1 Compounds with detections less than 10 percent not listed.

Volatile organic

compound

Laboratory minimum reporting

level(s) if nondetections present

No.

of

samples

MaximumMinimum

95th

percentile

75th

percentile

Median

50th percentile

25th

percentile

5th

percentile

Acrolein1 1,000; 500; 20

Residential 77 ND ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

Acrylonitrile1 1,000; 500; 20

Residential 77 ND ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

Footnote at end of table.

Table 5. Summary statistics for volatile organic compounds by land-use category

[In micrograms per liter. --, no data; ND, nondetection]

Land-use category Detected volatile organic compound1

Percent detected, all sites

in land-use category

(no. of detections)

Sampling site(s) with

most detections

(no. of detections)

Residential Trimethylbenzene 14 (11) 08049590 (3)

Xylene 14 (11) 08049590 (3)

Toluene 13 (10) 08048700 (3)

Chloroform 10 (8) 08048700 (4)

Commercial Toluene 29 (12) 08061690 (7)

Xylene 21 (9) 08061690 (7)

Benzene 19 (8) 08061690 (6)

Ethylbenzene 17 (7) 08061690 (6)

Industrial Trichloroethylene 22 (14) 08048545 (7)

08061530 (5)

Chloroform 21 (13) 08056100 (7)

trans-1,2-Dichloroethylene 14 (9) 08061530 (6)

08048545 (3)

Tetrachloroethylene 13 (8) 08048545 (7)

1,1,1-Trichloroethylene 13 (8) 08048545 (7)

cis-1,2-Dichloroethylene 22 (14) 08048545 (7)

08061530 (7)

Toluene 17 (11) 08048545 (3)

08049470 (3)

08061530 (3)

Xylene 16 (10) 08061530 (4)

1,2,4-Trimethylbenzene 13 (8) 08061530 (4)

08056100 (3)
Table 5 27

Table 5

Benzene1 10; 5.0; 0.20

Residential 77 0.30 ND ND ND ND ND ND

Commercial 41 .80 ND 0.60 ND ND ND ND

Industrial 63 .60 ND ND ND ND ND ND

Bromobenzene 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

Bromochloromethane 10; 5.0; 0.20

Residential 49 .20 ND ND ND ND ND ND

Commercial 29 ND ND ND ND ND ND ND

Industrial 25 ND ND ND ND ND ND ND

Bromodichloromethane1 10; 5.0; 0.20

Residential 77 .20 ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND

Industrial 63 .50 ND ND ND ND ND ND

Bromoform1 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

n-Butylbenzene 10; 5.0; 0.20

Residential 77 .20 ND ND ND ND ND ND

Commercial 38 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

sec-Butylbenzene 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 38 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

tert-Butylbenzene 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 38 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

Carbon tetrachloride1 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

Chlorobenzene1 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

Chloroethane1 10; 5.0; 0.20

Residential 77 .20 ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

Table 5. Summary statistics for volatile organic compounds by land-use category—Continued

Volatile organic

compound

Laboratory minimum reporting

level(s) if nondetections present

No.

of

samples

MaximumMinimum

95th

percentile

75th

percentile

Median

50th percentile

25th

percentile

5th

percentile

Footnote at end of table.
28 Urban Stormwater Quality, Event-Mean Concentrations, and Estimates of Stormwater Pollutant Loads, Dallas-Fort Worth Area, 

Texas, 1992–93 

2-Chloroethyl vinyl ether1 50; 30; 2.5; 1.0

Residential 77 ND ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

Chloroform1 0.20

Residential 77 0.70 ND 0.20 ND ND ND ND

Commercial 41 1.10 ND ND ND ND ND ND

Industrial 63 .70 ND .50 ND ND ND ND

Chloromethane1 10; 5.0; 0.20

Residential 77 .40 ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

1,2-Chlorotoluene 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND

Industrial 63 .20 ND ND ND ND ND ND

1,4-Chlorotoluene 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND

Industrial 63 .20 ND ND ND ND ND ND

Dibromochloromethane 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

Dibromochloropropane1 50; 25; 1.0

Residential 77 ND ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

1,2-Dibromoethane 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

Dibromomethane 5.0; 0.20

Residential 77 .20 ND ND ND ND ND ND

Commercial 41 .40 ND ND ND ND ND ND

Industrial 63 .70 ND ND ND ND ND ND

1,2-Dichlorobenzene 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

1,3-Dichlorobenzene 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

Table 5. Summary statistics for volatile organic compounds by land-use category—Continued

Volatile organic

compound

Laboratory minimum reporting

level(s) if nondetections present

No.

of

samples

MaximumMinimum

95th

percentile

75th

percentile

Median

50th percentile

25th

percentile

5th

percentile

Footnote at end of table.
Table 5 29

1,4-Dichlorobenzene 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

Dichlorodifluoromethane 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

1,1-Dichloroethane1 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND

Industrial 63 8.3 ND 0.50 ND ND ND ND

1,2-Dichloroethane1 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

1,1-Dichlorethylene1 10; 5.0; 0.20

Residential 77 5.9 ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND

Industrial 63 13.0 ND .50 ND ND ND ND

cis-1,2-Dichloroethene 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND

Industrial 63 1,200 ND 76.0 ND ND ND ND

trans-1,2-Dichlorolethylene1 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND

Industrial 63 27.0 ND 2.3 ND ND ND ND

1,2-Dichloropropane1 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

1,3-Dichloropropane 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

2,2-Dichloropropane 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

1,1-Dichloropropene 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

Table 5. Summary statistics for volatile organic compounds by land-use category—Continued

Volatile organic

compound

Laboratory minimum reporting

level(s) if nondetections present

No.

of

samples

MaximumMinimum

95th

percentile

75th

percentile

Median

50th percentile

25th

percentile

5th

percentile

Footnote at end of table.
30 Urban Stormwater Quality, Event-Mean Concentrations, and Estimates of Stormwater Pollutant Loads, Dallas-Fort Worth Area, 

Texas, 1992–93 

cis-1,3-Dichloropropene1 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

trans-1,3-Dichloropropene1 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

Ethylbenzene1 10; 5.0; 0.20

Residential 77 0.60 ND ND ND ND ND ND

Commercial 41 .60 ND 0.40 ND ND ND ND

Industrial 63 1.5 ND ND ND ND ND ND

Hexachlorobutadiene 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

Isopropylbenzene 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 38 ND ND ND ND ND ND ND

Industrial 63 4.6 ND ND ND ND ND ND

4-Isopropyltoluene 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 38 .90 ND ND ND ND ND ND

Industrial 63 .20 ND ND ND ND ND ND

Methyl bromide1 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

Methyl-tert-butyl ether 50; 25; 1.0

Residential 49 ND ND ND ND ND ND ND

Commercial 41 8.7 ND 8.30 ND ND ND ND

Industrial 25 5.4 ND ND ND ND ND ND

Methylene chloride1 5.0; 0.20

Residential 77 .80 ND ND ND ND ND ND

Commercial 41 .30 ND ND ND ND ND ND

Industrial 63 3.30 ND .30 ND ND ND ND

Naphthalene 5.0; 0.20

Residential 77 .60 ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND

Industrial 63 1.3 ND ND ND ND ND ND

n-Propylbenzene 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 38 ND ND ND ND ND ND ND

Industrial 63 .50 ND ND ND ND ND ND

Table 5. Summary statistics for volatile organic compounds by land-use category—Continued

Volatile organic

compound

Laboratory minimum reporting

level(s) if nondetections present

No.

of

samples

MaximumMinimum

95th

percentile

75th

percentile

Median

50th percentile

25th

percentile

5th

percentile

Footnote at end of table.
Table 5 31

Styrene 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 41 0.60 ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

1,1,1,2-Tetrachloroethane 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

1,1,2,2-Tetrachloroethane1 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

Tetrachloroethylene1 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND

Industrial 63 42.0 ND 4.90 ND ND ND ND

Toluene1 0.20

Residential 77 1.8 ND .20 ND ND ND ND

Commercial 41 2.4 ND 1.2 0.20 ND ND ND

Industrial 63 1.8 ND .30 ND ND ND ND

1,2,3-Trichlorobenzene 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 38 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

1,2,4-Trichlorobenzene 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

1,1,1-Trichloroethane1 5.0; 0.20

Residential 77 .30 ND ND ND ND ND ND

Commercial 41 .20 ND ND ND ND ND ND

Industrial 63 5.4 ND 2.5 ND ND ND ND

1,1,2-Trichloroethane1 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND

Industrial 63 .20 ND ND ND ND ND ND

Trichloroethylene1 10; 5.0; 0.20

Residential 77 .20 ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND

Industrial 63 28.0 ND 7.6 ND ND ND ND

Trichlorofluoromethane 25; 13; 0.50

Residential 49 ND ND ND ND ND ND ND

Commercial 30 ND ND ND ND ND ND ND

Industrial 25 ND ND ND ND ND ND ND

Table 5. Summary statistics for volatile organic compounds by land-use category—Continued

Volatile organic

compound

Laboratory minimum reporting

level(s) if nondetections present

No.

of

samples

MaximumMinimum

95th

percentile

75th

percentile

Median

50th percentile

25th

percentile

5th

percentile

Footnote at end of table.
32 Urban Stormwater Quality, Event-Mean Concentrations, and Estimates of Stormwater Pollutant Loads, Dallas-Fort Worth Area, 

Texas, 1992–93 

Table 6. Summary statistics for nutrients in flow-composite samples by land-use category—Continued

Nutrient

No. of

samples

MaximumMinimum Mean

95th

percentile

75th

percentile

Median

50th percentile

25th

percentile

5th

percentile

Nitrogen, total1, as nitrogen2

Residential 77 8.4 0.92 2.09 4.8 2.4 1.7 1.4 1.1

Commercial 42 5.4 .64 1.54 3.0 1.8 1.2 1.0 .79

Industrial 63 3.8 .60 1.55 2.6 1.9 1.4 1.2 .92

Nitrogen, total1 ammonia

Residential 42 .65 .06 .21 .54 .32 .18 .13 .09

Commercial 20 .73 .08 .28 .73 .43 .18 .12 .08

Industrial 47 .34 .02 .16 .33 .19 .14 .11 .07

Table 6

1 Constituent mandated by U.S. Environmental Protection Agency (1992).

Table 6. Summary statistics for nutrients in flow-composite samples by land-use category

[In milligrams per liter.] 

1,2,3-Trichloropropane 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

Trichlorotrifluoromethane 10; 5.0; 0.20

Residential 77 0.40 ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND

Industrial 63 .30 ND ND ND ND ND ND

1,2,4-Trimethylbenzene 5.0; 0.20

Residential 77 2.0 ND 0.60 ND ND ND ND

Commercial 38 .40 ND .40 ND ND ND ND

Industrial 63 15.0 ND .60 ND ND ND ND

1,3,5-Trimethylbenzene 10; 5.0; 0.20

Residential 77 .30 ND .20 ND ND ND ND

Commercial 38 ND ND ND ND ND ND ND

Industrial 63 6.30 ND .30 ND ND ND ND

Vinyl chloride1 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND

Industrial 63 ND ND 4.80 ND ND ND ND

Xylene, total 5.0; 0.20

Residential 77 3.70 ND .90 ND ND ND ND

Commercial 41 1.90 ND 1.0 ND ND ND ND

Industrial 63 10.0 ND 1.50 ND ND ND ND

Table 5. Summary statistics for volatile organic compounds by land-use category—Continued

Volatile organic

compound

Laboratory minimum reporting

level(s) if nondetections present

No.

of

samples

MaximumMinimum

95th

percentile

75th

percentile

Median

50th percentile

25th

percentile

5th

percentile

Footnotes at end of table.
Table 7 33

Table 7

Table 7. Summary statistics for oxygen demand properties in flow-composite samples by land-use category

[In milligrams per liter.]

Nitrogen, total1 ammonia plus organic2

Residential 77 7.8 0.60 1.45 3.60 1.75 1.1 0.80 0.60

Commercial 42 4.2 .30 .96 2.14 1.05 .80 .60 .40

Industrial 63 2.0 .30 .86 1.66 1.00 .80 .60 .40

Nitrogen, total1 nitrate

Residential 42 .15 .02 .06 .12 .07 .05 .03 .02

Commercial 20 .12 .02 .06 .12 .08 .06 .03 .02

Industrial 47 .26 .02 .06 .15 .08 .05 .03 .02

Nitrogen, total1 nitrite plus nitrate2

Residential 77 1.70 .27 .64 1.20 .80 .58 .42 .31

Commercial 42 1.50 .23 .58 1.28 .73 .52 .39 .24

Industrial 63 2.70 .26 .69 1.18 .79 .63 .49 .30

Phosphorus, total1, 2

Residential 77 1.0 .16 .38 .81 .48 .33 .24 .17

Commercial 42 .74 .05 .18 .53 .28 .14 .09 .05

Industrial 63 .92 .05 .28 .71 .38 .21 .16 .06

Phosphorus, dissolved2, 3

Residential 77 .84 .04 .25 .48 .34 .21 .17 .08

Commercial 42 .47 .01 .09 .30 .11 .06 .04 .01

Industrial 63 .45 .03 .14 .39 .20 .09 .06 .04

Carbon, total1 organic 

Residential 77 370 8.2 25.5 51.9 25.0 18.0 12.0 9.08

Commercial 42 48.0 5.8 16.0 45.8 18.2 12.0 9.3 6.56

Industrial 63 58.0 6.9 19.9 44.2 26.0 18.0 13.0 8.00

1 “Total” is the total amount of a given constituent in a representative water sample regardless of the physical or chemical form of the constituent.

2 Constituent mandated by U.S. Environmental Protection Agency (1992).

3 “Dissolved” refers to that material in a representative water sample that passes through a 0.45-millimeter membrane filter.

Property No. of

samples

MaximumMinimum Mean

95th

percentile

75th

percentile

Median

50th percentile

25th

percentile

5th

percentile

Biochemical oxygen demand1

1 Property mandated by U.S. Environmental Protection Agency (1992).

Residential 74 19.0 3.4 7.2 12.3 8.0 7.3 5.2 3.9

Commercial 40 17.0 2.7 6.8 16.0 7.7 6.6 4.6 2.8

Industrial 61 27.0 2.7 7.5 12.7 8.5 7.5 5.5 3.6

Chemical oxygen demand1

Residential 77 1,300 29.0 95.0 220 96.0 70.0 48.0 33.8

Commercial 42 180 23.0 70.0 160 91.5 56.5 41.0 23.4

Industrial 62 250 10.0 76.3 190 89.0 66.0 42.8 12.2

Table 6. Summary statistics for nutrients in flow-composite samples by land-use category—Continued

Nutrient

No. of

samples

MaximumMinimum Mean

95th

percentile

75th

percentile

Median

50th percentile

25th

percentile

5th

percentile
34 Urban Stormwater Quality, Event-Mean Concentrations, and Estimates of Stormwater Pollutant Loads, Dallas-Fort Worth Area, 

Texas, 1992–93 

Table 8

Table 8. Summary statistics for inorganic constituents and specific conductance in flow-composite samples by 

land-use category

[In milligrams per liter except as indicated. ND, nondetection at 1.0 milligram per liter minimum reporting level; μS/cm, 

microsiemens per centimeter at 25 degrees Celsius] 

Property or

constituent

No. of

samples

MaximumMinimum Mean

95th

percentile

75th

percentile

Median

50th percentile

25th

percentile

5th

percentile

Calcium, dissolved1

1 “Dissolved” refers to that material in a representative water sample that passes through a 0.45-millimeter membrane filter.

Residential 72 33.0 5.4 12.8 24.0 14.8 12.0 9.4 6.8

Commercial 38 32.0 5.5 13.0 25.4 15.5 11.5 9.4 6.5

Industrial 60 59.0 5.1 16.1 35.6 18.8 14.0 11.0 6.1

Chloride, dissolved1

Residential 72 15.0 .60 3.5 9.7 4.5 2.6 1.6 .66

Commercial 37 11.0 .50 2.5 9.6 2.6 1.9 1.0 .59

Industrial 60 50.0 .60 5.3 21.7 5.2 3.0 1.8 .80

Magnesium, dissolved1

Residential 72 5.1 .20 .79 2.7 .86 .55 .33 .21

Commercial 38 1.8 .12 .48 1.8 .53 .37 .26 .14

Industrial 60 2.6 .11 .68 1.6 .90 .60 .37 .14

Potassium, dissolved1

Residential 72 8.6 .70 3.5 5.7 4.1 3.2 2.6 1.9

Commercial 38 4.8 .70 1.8 4.6 2.2 1.6 .98 .70

Industrial 60 3.9 .70 1.9 3.5 2.2 1.8 1.4 .90

Sodium, dissolved1

Residential 72 17.0 .90 3.3 9.8 3.7 2.3 1.5 .90

Commercial 38 20.0 .20 2.8 9.2 3.0 2.0 1.3 .67

Industrial 60 41.0 .70 5.4 18.6 6.2 3.7 2.4 1.0

Sulfate, dissolved1

Residential 72 48.0 2.1 8.6 27.0 10.4 5.5 4.1 2.7

Commercial 38 18.0 .10 6.6 17.0 7.7 5.7 3.5 2.3

Industrial 60 57.0 2.2 11.8 26.8 15.0 10.4 6.2 3.2

Suspended2 solids3

2 “Suspended” refers to the amount of a given constituent in the part of a water sample that is retained by a 0.45 millimeter-membrane 

filter.

3 Constituent mandated by U.S. Environmental Protection Agency (1992).

Residential 72 686 1.0 130 528 151 78.0 41.8 10.2

Commercial 38 156 ND 55.5 146 80 42.0 24.0 ND

Industrial 60 2,490 15.0 222 842 218 104 62.5 23.1

Dissolved1 solids3

Residential 72 959 29.0 78.8 148 73.8 59.0 49.2 35.6

Commercial 37 249 23.0 64.0 161 70.5 50.0 39.0 28.4

Industrial 60 318 21.0 78.1 162 92.0 69.0 54.5 30.0

Alkalinity, total as CaCO3

Residential 75 66.0 11.0 29.9 54.4 36.0 28.0 23.0 15.8

Commercial 41 61.0 11.0 28.4 44.9 33.0 27.0 22.0 12.4

Industrial 62 140 9.8 33.3 58.7 38.0 28.5 23.0 15.4

Specific conductance (μS/cm)

Residential 72 334 58.0 140 265 184 110 99.2 73.3

Commercial 38 258 61.0 114 255 123 106 84.8 70.5

Industrial 60 539 66.0 164 264 201 153 121 83.2
Table 9 35

Table 9 Table 9. Summary statistics for trace-element concentrations in flow-composite samples by land-use category—

Continued

Trace element

Laboratory

minimum

reporting

level(s), if

nondetections present

No.

of

samples

MaximumMinimum Mean

95th

percentile

75th

percentile

Median

50th percentile

25th

percentile

5th

percentile

Antimony, total1 20; 10

Residential 77 ND ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND ND

Industrial 63 53.0 ND 4.9 ND ND ND ND ND

Arsenic, total1 1.0

Residential 76 45.0 1.0 5.6 25.2 5.0 3.0 2.0 1.0

Commercial 41 25.0 ND 1.8 3.0 2.0 1.0 ND ND

Industrial 62 7.0 ND 2.0 5.0 2.0 2.0 1.0 ND

Beryllium, total recoverable1 1.0

Residential 77 ND ND -- ND ND ND ND ND

Commercial 40 ND ND -- ND ND ND ND ND

Industrial 63 ND ND -- ND ND ND ND ND

Cadmium, total recoverable1 1.0

Residential 77 1.0 ND -- ND ND ND ND ND

Commercial 40 1.0 ND -- ND ND ND ND ND

Industrial 63 8.0 ND .92 3.0 1.0 ND ND ND

Chromium, total recoverable1 1.0

Residential 76 26.0 ND 5.6 15.0 7.0 4.0 3.0 ND

Commercial 40 100 ND 7.1 11.0 7.0 4.0 2.0 ND

Industrial 62 100 1.0 12.9 43.3 16.0 9.0 4.0 2.0

Copper, total recoverable1 --

Residential 76 86.0 1.0 9.7 16.2 12.0 8.0 5.0 3.8

Commercial 38 82.0 2.0 11.4 34.5 11.2 8.0 6.0 3.0

Industrial 61 1,300 4.0 95.4 1,060 19.5 12.0 7.0 4.0

Lead, total recoverable1 --

Residential 76 89.0 1.0 21.4 58.4 29.8 13.0 7.0 4.0

Commercial 40 130 5.0 33.2 98.7 46.8 29.5 13.5 6.0

Industrial 62 320 1.0 53.7 240 60.5 29.0 14.0 6.2

Mercury, total recoverable1 0.10

Residential 76 .40 ND -- .10 ND ND ND ND

Commercial 40 .10 ND -- .10 ND ND ND ND

Industrial 62 9.2 ND -- .20 ND ND ND ND

Nickel, total recoverable1 1.0

Residential 76 18.0 1.0 5.2 16.0 6.0 4.0 3.0 1.0

Commercial 40 9.0 ND 3.5 8.0 4.0 3.0 2.0 ND

Industrial 62 59.0 1.0 8.1 22.4 9.2 6.0 3.8 2.0

Selenium, total1 2.0; 1.0

Residential 76 2.0 ND ND ND ND ND ND ND

Commercial 41 ND ND ND ND ND ND ND ND

Industrial 63 2.0 ND ND ND ND ND ND ND

Table 9. Summary statistics for trace-element concentrations in flow-composite samples by land-use category

[In micrograms per liter. ND, nondetection; --, no data or not applicable; <, less than] 

Footnote at end of table.
36 Urban Stormwater Quality, Event-Mean Concentrations, and Estimates of Stormwater Pollutant Loads, Dallas-Fort Worth Area, 

Texas, 1992–93 

Table 10

Table 10. Most frequent base/neutral and acid-extractable semivolatile organic compound detections in flowcomposite samples by land-use category and sampling site 

1 Compounds with detections less than 13 percent not listed.

Silver, total recoverable1 1.0

Residential 77 ND ND -- ND ND ND ND ND

Commercial 40 ND ND -- ND ND ND ND ND

Industrial 63 ND ND -- ND ND ND ND ND

Thallium, total1 1,000; 500; 50; 

25; 10; 5.0

Residential 77 ND ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND ND

Zinc, total recoverable1

Residential 76 230 20.0 77.6 170 100 60.0 40.0 30.0

Commercial 40 290 30.0 103 260 130 80.0 52.5 40.0

Industrial 62 1,400 20.0 206 686 230 140 97.5 50.0

1 Constituent mandated by U.S. Environmental Protection Agency (1992).

Land-use category Detected compound1

Percent detected, all sites

in land-use category

(no. of detections)

Sampling site(s) with

most detections

(no. of detections)

Residential bis(2-Ethylhexyl)phthalate 36 (28) 08061510 (7)

08057441 (4)

08061660 (4)

Commercial bis(2-Ethylhexyl)phthalate 61 (25) 08061690 (6)

08049220 (5)

08057135 (4)

Pyrene 13 (8) 08061690 (5)

Industrial bis(2-Ethylhexyl)phthalate 41 (26) 08061530 (7)

08048545 (6)

08061635 (5)

08055570 (4)

Fluoranthene 24 (15) 08061635 (6)

Pyrene 22 (14) 08061635 (6)

Phenanthrene 21 (13) 08061635 (6)

08055570 (4)

Table 9. Summary statistics for trace-element concentrations in flow-composite samples by land-use category—

Continued

Trace element

Laboratory

minimum

reporting

level(s), if

nondetections present

No.

of

samples

MaximumMinimum Mean

95th

percentile

75th

percentile

Median

50th percentile

25th

percentile

5th

percentile
Table 11 37

Table 11. Summary statistics for base/neutral and acid extractable semivolatile organic compounds in flowcomposite samples by land-use category—Continued

Compound

Laboratory minimum

reporting level(s) if

nondections present

No. of

samples

MaximumMinimum

95th

percentile

75th

percentile

Median

50th percentile

25th

percentile

5th

percentile

Acenaphthene1 5.0

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

Acenaphthylene1 5.0

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

Anthracene1 5.0

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 7.0 ND ND ND ND ND ND

Benzidine1 40

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

Benzo(a)anthracene1 10

Residential 77 ND ND ND ND ND ND ND

Commercial 42 13.0 ND ND ND ND ND ND

Industrial 63 26.0 ND ND ND ND ND ND

Benzo(a)pyrene1 10

Residential 77 ND ND ND ND ND ND ND

Commercial 42 11.0 ND ND ND ND ND ND

Industrial 63 20.0 ND ND ND ND ND ND

Benzo(b)fluoranthene1 10

Residential 77 ND ND ND ND ND ND ND

Commercial 42 15.0 ND ND ND ND ND ND

Industrial 63 23.0 ND 11.0 ND ND ND ND

Benzo(g,h,i)perylene1 10

Residential 77 ND ND ND ND ND ND ND

Commercial 42 15.0 ND ND ND ND ND ND

Industrial 63 25.0 ND 11.0 ND ND ND ND

Benzo(k)fluoranthene1 10

Residential 77 280 ND ND ND ND ND ND

Commercial 42 13.0 ND ND ND ND ND ND

Industrial 63 22.0 ND ND ND ND ND ND

4-Bromophenyl phenyl ether1 5.0

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

Table 11

Table 11. Summary statistics for base/neutral and acid extractable semivolatile organic compounds in flowcomposite samples by land-use category

[In micrograms per liter. ND, nondetection; --, no data]

Footnote at end of table.
38 Urban Stormwater Quality, Event-Mean Concentrations, and Estimates of Stormwater Pollutant Loads, Dallas-Fort Worth Area, 

Texas, 1992–93 

Butyl benzyl phthalate1 5.0

Residential 77 10.0 ND ND ND ND ND ND

Commercial 42 8.0 ND ND ND ND ND ND

Industrial 63 14.0 ND ND ND ND ND ND

4-Chloro-3-methylphenol1 30

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

bis(2-Chloroethoxy)methane1 5.0

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

bis(2-Chloroethyl)ether1 5.0

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

bis(2-Chloroisopropyl)ether1 5.0

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

2-Chloronaphthalene1 5.0

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

2-Chlorophenol1 5.0

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

4-Chlorophenyl phenyl ether1 5.0

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

Chrysene1 10

Residential 77 ND ND ND ND ND ND ND

Commercial 42 23.0 ND 12.0 ND ND ND ND

Industrial 63 49.0 ND 16.0 ND ND ND ND

Dibenzanthracene1 10

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

Table 11. Summary statistics for base/neutral and acid extractable semivolatile organic compounds in flowcomposite samples by land-use category—Continued

Compound

Laboratory minimum

reporting level(s) if

nondections present

No. of

samples

MaximumMinimum

95th

percentile

75th

percentile

Median

50th percentile

25th

percentile

5th

percentile

Footnote at end of table.
Table 11 39

1,2-Dichlorobenzene1 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

1,3-Dichlorobenzene1 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

1,4-Dichlorobenzene1 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

3,3'-Dichlorobenzidine1 20

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

2,4-Dichlorophenol1 5.0

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

Diethyl phthalate1 5.0

Residential 77 ND ND ND ND ND ND ND

Commercial 42 6.0 ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

2,4-Dimethylphenol1 5.0

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

Dimethylphthalate1 5.0

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

Di-n-butyl phthalate1 5.0

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

4,6-Dinitro-2-methylphenol1 30

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

Table 11. Summary statistics for base/neutral and acid extractable semivolatile organic compounds in flowcomposite samples by land-use category—Continued

Compound

Laboratory minimum

reporting level(s) if

nondections present

No. of

samples

MaximumMinimum

95th

percentile

75th

percentile

Median

50th percentile

25th

percentile

5th

percentile

Footnote at end of table.
40 Urban Stormwater Quality, Event-Mean Concentrations, and Estimates of Stormwater Pollutant Loads, Dallas-Fort Worth Area, 

Texas, 1992–93 

2,4-Dinitrophenol1 20

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

2,4-Dinitrotoluene1 5.0

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

2,6-Dinitrotoluene1 5.0

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

Di-n-octylphthalate1 10

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

1,2-Diphenyl hydrazine1 5.0

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

bis(2-Ethylhexyl)phthalate1 5.0

Residential 77 24.0 ND 14.0 8.0 ND ND ND

Commercial 41 20.0 ND 13.0 8.0 6.0 ND ND

Industrial 63 130 ND 16.0 7.0 ND ND ND

Fluoranthene1 5.0

Residential 77 13.0 ND ND ND ND ND ND

Commercial 42 23.0 ND 12.0 ND ND ND ND

Industrial 63 52.0 ND 23.0 ND ND ND ND

Fluorene1 5.0

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

Hexachlorobenzene1 5.0

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

Hexachlorobutadiene1 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

Table 11. Summary statistics for base/neutral and acid extractable semivolatile organic compounds in flowcomposite samples by land-use category—Continued

Compound

Laboratory minimum

reporting level(s) if

nondections present

No. of

samples

MaximumMinimum

95th

percentile

75th

percentile

Median

50th percentile

25th

percentile

5th

percentile

Footnote at end of table.
Table 11 41

Hexachlorocyclopentadiene1 5.0

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

Hexachloroethane1 5.0

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

Indeno(1,2,3-cd)pyrene1 10

Residential 77 ND ND ND ND ND ND ND

Commercial 42 15.0 ND ND ND ND ND ND

Industrial 63 27.0 ND 11.0 ND ND ND ND

Isophorone1 5.0

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

Naphthalene1 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

Nitrobenzene1 5.0

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

2-Nitrophenol1 5.0

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

4-Nitrophenol1 30

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

N-nitrosodi-n-propylamine1 5.0

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

N-nitrosodiphenylamine1 5.0

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

Table 11. Summary statistics for base/neutral and acid extractable semivolatile organic compounds in flowcomposite samples by land-use category—Continued

Compound

Laboratory minimum

reporting level(s) if

nondections present

No. of

samples

MaximumMinimum

95th

percentile

75th

percentile

Median

50th percentile

25th

percentile

5th

percentile

Footnote at end of table.
42 Urban Stormwater Quality, Event-Mean Concentrations, and Estimates of Stormwater Pollutant Loads, Dallas-Fort Worth Area, 

Texas, 1992–93 

Table 12

N-nitrosodimethlyamine1 5.0

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

Pentachlorophenol1 30

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

Phenanthrene1 5.0

Residential 77 10.0 ND ND ND ND ND ND

Commercial 42 10.0 ND 6.0 ND ND ND ND

Industrial 63 33.0 ND 13.0 ND ND ND ND

Phenol1 5.0

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

Pyrene1 5.0

Residential 77 10.0 ND ND ND ND ND ND

Commercial 42 18.0 ND 10.0 ND ND ND ND

Industrial 63 43.0 ND 18.0 ND ND ND ND

1,2,4-Trichlorobenzene1 10; 5.0; 0.20

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

2,4,6-Trichlorophenol1 20

Residential 77 ND ND ND ND ND ND ND

Commercial 42 ND ND ND ND ND ND ND

Industrial 63 ND ND ND ND ND ND ND

1 Compound mandated by U.S. Environmental Protection Agency (1992).

Table 12. Pesticide detections in flow-composite samples by land-use category and sampling site 

Land-use

category

Detected

pesticide1 Percent detected, all sites in land-use category(no. of detections)

Sampling site(s) with most detections

(no. of detections)

Residential Diazinon 93 (71) All

Chlordane 22 (17) 08048700 (4)

08049590 (4)

Dieldrin 12 (9) 08057310 (5)

Commercial Diazinon 70 (28) All

Chlordane 21 (9) 08061690 (6)

Industrial Diazinon 33 (21) All

Chlordane 10 (6) 08061530 (5)

Table 11. Summary statistics for base/neutral and acid extractable semivolatile organic compounds in flowcomposite samples by land-use category—Continued

Compound

Laboratory minimum

reporting level(s) if

nondections present

No. of

samples

MaximumMinimum

95th

percentile

75th

percentile

Median

50th percentile

25th

percentile

5th

percentile

1 Pesticides with detections less than 10 percent not listed.
Table 13 43

Table 13. Table 13 Summary statistics for pesticides and polychlorinated biphenyls in flow-composite samples by land-use 

category—Continued

Compound

Laboratory minimum reporting

level(s) if nondetections present

No.

of

samples

MaximumMinimum Mean

95th

percentile

75th

percentile

Median

50th

percentile

25th

percentile

5th

percentile

Aldrin, total1 0.08; 0.04

Residential 77 ND ND -- ND ND ND ND ND

Commercial 42 ND ND -- ND ND ND ND ND

Industrial 63 ND ND -- ND ND ND ND ND

alpha-BHC, total1 0.05; 0.03

Residential 77 0.03 ND -- ND ND ND ND ND

Commercial 42 .03 ND -- ND ND ND ND ND

Industrial 63 ND ND -- ND ND ND ND ND

beta-BHC, total1 0.40; 0.03

Residential 77 ND ND -- ND ND ND ND ND

Commercial 42 ND ND -- ND ND ND ND ND

Industrial 63 ND ND -- ND ND ND ND ND

delta-BHC, total1 0.20; 0.09

Residential 77 ND ND -- ND ND ND ND ND

Commercial 42 ND ND -- ND ND ND ND ND

Industrial 63 ND ND -- ND ND ND ND ND

gamma-BHC (Lindane), 

total1

0.03

Residential 77 .21 ND -- ND ND ND ND ND

Commercial 42 .03 ND -- ND ND ND ND ND

Industrial 63 ND ND -- ND ND ND ND ND

Chlordane, total1 0.10

Residential 77 1.2 ND -- 0.50 ND ND ND ND

Commercial 42 .50 ND -- .20 ND ND ND ND

Industrial 63 .10 ND -- .10 ND ND ND ND

cis-Chlordane, total1 0.10

Residential 77 .10 ND -- ND ND ND ND ND

Commercial 42 ND ND -- ND ND ND ND ND

Industrial 63 ND ND -- ND ND ND ND ND

trans-Chlordane, total1 0.10

Residential 77 .10 ND -- ND ND ND ND ND

Commercial 42 .10 ND -- ND ND ND ND ND

Industrial 63 ND ND -- ND ND ND ND ND

DDD, total (4,4'-Dichlorodiphenyldichloroethane)1

0.20; 0.10

Residential 77 ND ND -- ND ND ND ND ND

Commercial 44 ND ND -- ND ND ND ND ND

Industrial 63 ND ND -- ND ND ND ND ND

Table 13. Summary statistics for pesticides and polychlorinated biphenyls in flow-composite samples by land-use 

category

[In micrograms per liter. ND, nondetection; --, no data]

Footnotes at end of table.
44 Urban Stormwater Quality, Event-Mean Concentrations, and Estimates of Stormwater Pollutant Loads, Dallas-Fort Worth Area, 

Texas, 1992–93 

DDE, total (4,4'-Dichlorodiphenyldichloroethylene)1

0.08; 0.04

Residential 77 ND ND -- ND ND ND ND ND

Commercial 42 ND ND -- ND ND ND ND ND

Industrial 63 ND ND -- ND ND ND ND ND

DDT, total (4,4'-Dichlorodiphenyltrichloroethane)1

0.20; 0.10

Residential 77 ND ND -- ND ND ND ND ND

Commercial 42 ND ND -- ND ND ND ND ND

Industrial 63 ND ND -- ND ND ND ND ND

Dieldrin, total1 0.20

Residential 77 0.06 ND -- 0.04 ND ND ND ND

Commercial 42 ND ND -- ND ND ND ND ND

Industrial 63 ND ND -- ND ND ND ND ND

Endosulfan I, total1 0.20; 0.10

Residential 77 ND ND -- ND ND ND ND ND

Commercial 42 ND ND -- ND ND ND ND ND

Industrial 63 ND ND -- ND ND ND ND ND

Endosulfan II, total1 0.08; 0.04

Residential 77 ND ND -- ND ND ND ND ND

Commercial 42 ND ND -- ND ND ND ND ND

Industrial 63 ND ND -- ND ND ND ND ND

Endosulfan sulfate, total1 1.0; 0.60

Residential 77 ND ND -- ND ND ND ND ND

Commercial 42 ND ND -- ND ND ND ND ND

Industrial 63 ND ND -- ND ND ND ND ND

Endrin, recoverable1 0.10; 0.06

Residential 77 ND ND -- ND ND ND ND ND

Commercial 42 ND ND -- ND ND ND ND ND

Industrial 63 ND ND -- ND ND ND ND ND

Endrin aldehyde, total1 0.40; 0.20

Residential 77 ND ND -- ND ND ND ND ND

Commercial 42 ND ND -- ND ND ND ND ND

Industrial 63 ND ND -- ND ND ND ND ND

Heptachlor, total1 0.03

Residential 77 .20 ND -- ND ND ND ND ND

Commercial 42 ND ND -- ND ND ND ND ND

Industrial 63 ND ND -- ND ND ND ND ND

Table 13. Summary statistics for pesticides and polychlorinated biphenyls in flow-composite samples by land-use 

category—Continued

Compound

Laboratory minimum reporting

level(s) if nondetections present

No.

of

samples

MaximumMinimum Mean

95th

percentile

75th

percentile

Median

50th

percentile

25th

percentile

5th

percentile

Footnotes at end of table.
Table 13 45

Heptachlor epoxide, total1 2.0; 0.80

Residential 77 ND ND -- ND ND ND ND ND

Commercial 42 ND ND -- ND ND ND ND ND

Industrial 63 ND ND -- ND ND ND ND ND

Toxaphene, total1 4.0; 2.0

Residential 77 ND ND -- ND ND ND ND ND

Commercial 42 ND ND -- ND ND ND ND ND

Industrial 63 ND ND -- ND ND ND ND ND

Aroclor 1016, PCB, total1 0.20; 0.10

Residential 77 ND ND -- ND ND ND ND ND

Commercial 42 ND ND -- ND ND ND ND ND

Industrial 63 ND ND -- ND ND ND ND ND

Aroclor 1221, PCB, total1 2.0; 1.0

Residential 77 ND ND -- ND ND ND ND ND

Commercial 42 ND ND -- ND ND ND ND ND

Industrial 63 ND ND -- ND ND ND ND ND

Aroclor 1232, PCB, total1 0.20; 0.10

Residential 77 ND ND -- ND ND ND ND ND

Commercial 42 ND ND -- ND ND ND ND ND

Industrial 63 ND ND -- ND ND ND ND ND

Aroclor 1242, PCB, total1 0.20; 0.10

Residential 77 ND ND -- ND ND ND ND ND

Commercial 42 ND ND -- ND ND ND ND ND

Industrial 63 0.20 ND -- ND ND ND ND ND

Aroclor 1248, PCB, total1 0.20; 0.10

Residential 77 ND ND -- ND ND ND ND ND

Commercial 42 ND ND -- ND ND ND ND ND

Industrial 63 ND ND -- ND ND ND ND ND

Aroclor 1254, PCB, total1 0.20; 0.10

Residential 77 ND ND -- ND ND ND ND ND

Commercial 42 ND ND -- ND ND ND ND ND

Industrial 63 .80 ND -- ND ND ND ND ND

Aroclor 1260, PCB, total1 0.20; 0.10

Residential 77 ND ND -- ND ND ND ND ND

Commercial 42 ND ND -- ND ND ND ND ND

Industrial 63 .10 ND -- ND ND ND ND ND

Diazinon, total 0.10; 0.05; 0.01

Residential 76 25.0 ND 21.8 7.4 1.6 0.50 0.20 ND

Commercial 40 4.4 ND 2.27 .40 .20 .10 ND ND

Industrial 63 1.8 ND 2.12 .50 .10 ND ND ND

1 Pesticide mandated by U.S. Environmental Protection Agency (1992).

2 Mean values calculated for censored data by logarithmic probability regression method (Helsel and Cohn, 1988).

Table 13. Summary statistics for pesticides and polychlorinated biphenyls in flow-composite samples by land-use 

category—Continued

Compound

Laboratory minimum reporting

level(s) if nondetections present

No.

of

samples

MaximumMinimum Mean

95th

percentile

75th

percentile

Median

50th

percentile

25th

percentile

5th

percentile
46 Urban Stormwater Quality, Event-Mean Concentrations, and Estimates of Stormwater Pollutant Loads, Dallas-Fort Worth Area, 

Texas, 1992–93 

Table 14. Mean and median event-mean concentrations by land-use category—Continued

Property or constituent

No. of

samples1

Event-mean concentration

NURP median

event-mean

concentration

Volumeweighted

mean

Logtransformed

mean

Arithmetic

mean1 Median1

Residential (11 sites)

Biochemical oxygen demand, mg/L 72 6.7 6.6 7.0 7.3 10

Chemical oxygen demand, mg/L 76 77 71 85 70 73

Suspended solids, mg/L 69 110 83 127 78 101

Dissolved solids, mg/L 70 64 62 66 58 --

Total nitrogen, mg/L 77 2.0 1.9 2.1 1.7 --

Total ammonia plus organic nitrogen, mg/L 77 1.3 1.2 1.5 1.1 1.90

Total phosphorus, mg/L 77 .39 .34 .38 .33 .38

Dissolved phosphorus, mg/L 77 .27 .22 .25 .21 .14

Total recoverable cadmium, μg/L 76 -- -- -- -- --

Total recoverable copper, μg/L 74 8.2 8.0 9.6 8.0 33

Total recoverable lead, μg/L 74 17 15 21 13 144

Total recoverable zinc, μg/L 75 67 66 76 60 135

Total diazinon, μg/L 76 1.8 .54 1.8 .55 --

Commercial (6 sites)

Biochemical oxygen demand, mg/L 38 7.0 6.2 6.5 6.6 9.3

Chemical oxygen demand, mg/L 42 65 59 68 56 57

Suspended solids, mg/L 35 61 45 60 52 69

Dissolved solids, mg/L 37 59 55 64 50 --

Total nitrogen, mg/L 42 1.5 1.4 1.5 1.2 --

Total ammonia plus organic nitrogen, mg/L 42 .92 .83 .96 .80 1.18

Total phosphorus, mg/L 42 .18 .14 .18 .14 .20

Dissolved phosphorus, mg/L 42 .10 .06 .09 .06 .08

Total recoverable cadmium, μg/L 40 -- -- -- -- --

Total recoverable copper, μg/L 38 12 8.6 11 8.0 29

Total recoverable lead, μg/L 40 36 25 33 30 104

Total recoverable zinc, μg/L 40 102 88 103 80 226

Total diazinon, μg/L 40 .30 .12 .27 .10 --

Table 14

Table 14. Mean and median event-mean concentrations by land-use category

[NURP, Nationwide Urban Runoff Program (U.S. Environmental Protection Agency, 1983); mg/L, milligrams per liter; --, not 

calculated; μg/L, micrograms per liter]

Footnote at end of table.
Table 15 47

Table 15

Table 15. Rainfall-runoff characteristics by land-use category 

Industrial (9 sites)

Biochemical oxygen demand, mg/L 61 7.1 7.0 7.5 7.5 --

Chemical oxygen demand, mg/L 59 77 69 80 67 --

Suspended solids, mg/L 60 259 121 222 104 --

Dissolved solids, mg/L 60 73 70 78 69 --

Total nitrogen, mg/L 63 1.5 1.5 1.5 1.4 --

Total ammonia plus organic nitrogen, mg/L 63 .83 .80 .86 .80 --

Total phosphorus, mg/L 63 .26 .23 .28 .21 --

Dissolved phosphorus, mg/L 63 .12 .11 .14 .09 --

Total recoverable cadmium, μg/L 63 -- -- -- -- --

Total recoverable copper, μg/L 61 100 17 95 12 --

Total recoverable lead, μg/L 61 64 32 55 29 --

Total recoverable zinc, μg/L 59 173 139 168 130 --

Total diazinon, μg/L 62 .14 .07 .14 .05 --

1 Values might not match those in tables 6, 7, 8, 9, or 13 because of different computation methods for nondetections.

Land-use category

Rainfall

(inches)

Runoff volume

(cubic feet)

Percent runoff

Residential

Mean 0.51 36,200 27.2

Median .45 28,300 24.0

Minimum .19 7,270 10.8

Maximum 1.30 175,000 54.6

Commercial

Mean .50 62,800 71.6

Median .44 49,800 76.5

Minimum .20 13,500 22.3

Maximum 1.50 189,000 96.5

Industrial

Mean .51 58,400 65.2

Median .45 49,400 73.6

Minimum .20 6,260 10.9

Maximum 1.38 190,000 97.3

Table 14. Mean and median event-mean concentrations by land-use category—Continued

Property or constituent

No. of

samples1

Event-mean concentration

NURP median

event-mean

concentration

Volumeweighted

mean

Logtransformed

mean

Arithmetic

mean1 Median1
48 Urban Stormwater Quality, Event-Mean Concentrations, and Estimates of Stormwater Pollutant Loads, Dallas-Fort Worth Area, 

Texas, 1992–93 

Table 16

Table 16. Computed loads per square mile for all sampled storms by land-use category

[<, less than]

Land-use

category

Load (pounds per square mile)

Biochemical

oxygen demand

Chemical

oxygen demand

Suspended

solids

Dissolved

solids

Total

nitrogen

Total ammonia plus

organic nitrogen

Residential

Mean 138 1,830 2,120 1,790 43.7 30.2

Median 121 1,070 1,440 990 31.4 20.2 

Minimum 28.3 333 .56 324 8.16 4.47

Maximum 451 16,100 8,302 32,100 214 155

Commercial

Mean 316 3,000 2,580 3,070 70.9 43.2

Median 245 2,300 2,000 2,320 62.1 34.5

Minimum 74.4 972 .60 1,090 21.6 9.48

Maximum 1,000 10,800 7,850 12,000 232 149

Industrial 

Mean 337 3,577 12,000 3,460 72.9 41.3

Median 294 2,877 4,430 2,570 63.2 31.9

Minimum 40.0 95.40 110 629 7.67 2.40

Maximum 1,241 13,810 125,000 13,800 202 124

Land-use

category

Load (pounds per square mile)

Total

phosphorus

Dissolved

phosphorus

Total

recoverable copper

Total

recoverable lead

Total

recoverable zinc

Total 

diazinon

Residential

Mean 8.29 5.72 0.17 0.37 1.46 0.05

Median 4.96 3.56 .13 .27 1.09 .01

Minimum 1.19 .30 <.01 <.01 .19 <.01

Maximum 47.0 41.9 .62 1.91 5.69 .73

Commercial

Mean 7.85 3.72 .57 1.52 4.60 .01

Median 6.23 2.88 .39 1.06 3.88 <.01

Minimum 1.90 .22 .09 .17 1.19 <.01

Maximum 29.8 16.5 5.08 5.39 13.6 .10

Industrial 

Mean 12.6 6.48 4.81 3.08 9.74 .01

Median 8.50 4.19 .47 1.18 6.48 <.01

Minimum .48 .29 .02 <.01 .10 <.01

Maximum 55.9 46.6 69.2 24.8 60.5 .10
Table 17 49

Table 17

Table 17. Local regression equation coefficients for estimating loads of selected water-quality properties and 

constituents from individual storm-runoff events—Continued

Property or constituent bo' b1 b2 b3 b4 b5

Biochemical oxygen demand 9.01 0.879 0.725 0.656 0.104 0.085

Chemical oxygen demand 10.2 .711 .593 .961 .176 .123

Suspended solids 5.85 .889 .544 .913 .463 .170

Dissolved solids 104 .764 .745 .568 .131 .124

Total nitrogen 1.14 .838 .597 .725 .072 .056

Total ammonia plus organic nitrogen .666 .878 .544 .716 .045 .037

Total phosphorus .955 .932 .475 -- .286 .176

Dissolved phosphorus .546 1.05 .477 -- .281 .121

Total recoverable copper .0023 .894 .623 .996 .138 .057

Total recoverable lead .00000086 1.21 .500 2.55 .371 .210

Total recoverable zinc .00020 .905 .520 1.85 .363 .198

Total diazinon .0013 1.47 .305 -- -- --

Property or constituent b6 b7 BCF SE R2 adj

Biochemical oxygen demand -- -- 1.11 48.7 64.0

Chemical oxygen demand 0.130 -- 1.16 58.5 53.6

Suspended solids .328 -- 1.52 115 42.0

Dissolved solids -- -- 1.13 52.3 59.2

Total nitrogen .052 -- 1.15 57.1 49.9

Total ammonia plus organic nitrogen .077 -- 1.18 63.0 45.0

Total phosphorus .272 -- 1.20 66.2 51.5

Dissolved phosphorus .333 -- 1.25 75.7 52.7

Total recoverable copper .012 -- 1.24 72.8 49.2

Total recoverable lead .274 0.265 1.41 99.5 58.8

Total recoverable zinc .201 .266 1.20 65.8 65.3

Total diazinon .374 -- 2.32 210 40.6

Table 17. Local regression equation coefficients for estimating loads of selected water-quality properties and 

constituents from individual storm-runoff events

[LOAD, storm-runoff load of property or constituent, in pounds; bo', intercept in regression model; b1, coefficient for variable 

TRN (total storm rainfall), in inches; b2, coefficient for variable DA (drainage area), in square miles; b3, coefficient for 

variable IA (impervious area), as percentage of DA; b4, coefficient for variable LUI (industrial land use), as percentage of DA; 

b5, coefficient for variable LUC (commercial land use), as percentage of DA; b6, coefficient for variable LUR (residential land 

use), as percentage of DA; b7, coefficient for variable LUN (nonurban land use), as percentage of DA; BCF, bias correction 

factor; SE, standard error of regression equation, in percent; R2

 adj, adjusted coefficient of determination, in percent; --, 

variable not included. Equation form is: 

LOAD bo' TRN .] ( )

b1 ( ) DAb2 ( ) IA 1 +b3 ( ) LUI 1 +b4

× ( ) LUC 1 +

b5

× ( ) LUR 1 +

b6

× ( ) LUN 1 +

b7 = × × × × × BCF
50 Urban Stormwater Quality, Event-Mean Concentrations, and Estimates of Stormwater Pollutant Loads, Dallas-Fort Worth Area, 

Texas, 1992–93 

Table 

Table 19 Table 19. Estimated annual loads for sites in all study basins using 1965 rainfall at Love Field and 1975 rainfall at 

Meacham Airport—Continued City

Site no.

(fig. 1)

Load (pounds)

Biochemical

oxygen

demand

Chemical

oxygen

demand

Suspended

solids

Dissolved

solids

Total

nitrogen

Total

ammonia

plus

organic

nitrogen

Total

phosphorus

Dissolved

phosphorus

Total

recoverable

copper

Total

recoverable

lead

Total

recoverable

zinc

Total

diazinon

Computed using 1965 rainfall at Love Field (33.1 inches)

Dallas

08055590 426 4,710 13,300 3,530 112 71.7 18.5 11.0 0.970 4.26 11.1 0.03

08056390 1,490 13,300 35,000 12,900 314 182 43.3 25.6 2.85 10.7 28.3 .06

08057135 1,580 13,400 13,700 14,200 350 215 35.1 17.7 2.30 7.84 18.4 .09

08057310 871 8,310 14,400 6,890 252 184 46.1 37.5 1.24 2.36 6.53 .36

08057441 529 5,240 9,420 4,190 162 122 34.3 27.6 .780 2.60 6.73 .29

Garland

08061635 974 8,460 21,300 8,360 216 129 32.7 19.6 1.82 10.9 27.7 .05

08061660 1,110 12,000 22,800 9,650 300 208 68.7 48.0 1.53 4.86 12.4 .34

08061690 1,070 13,300 22,600 9,440 292 198 51.8 31.1 1.72 11.5 22.1 .19

Irving

08049590 783 7,160 12,400 6,490 218 157 47.8 36.5 1.03 3.66 9.79 .32

08055570 1,690 16,700 45,100 16,500 332 184 64.8 31.8 2.89 15.8 42.0 .06

08056100 1,630 15,900 45,100 15,600 324 181 61.7 31.5 2.87 16.4 43.0 .06

Table 18. Standard error and number of storms for local regression equations and Driver and Tasker regional 

regression equations

[SE, standard error of estimate for regression equation; --, equation not developed for property or constituent]

1 Driver and Tasker, 1990.

Table 19. Estimated annual loads for sites in all study basins using 1965 rainfall at Love Field and 1975 rainfall at 

Meacham Airport 

Property or constituent

Local regression equations Driver and Tasker regional regression equations1

SE

(percent)

No. of

storms

SE

(percent)

No. of

storms

Biochemical oxygen demand 48.7 172 -- --

Chemical oxygen demand 58.5 177 97 793

Suspended solids 115 164 165 964

Dissolved solids 52.3 167 69 281

Total nitrogen 57.1 182 97 574

Total ammonia plus organic nitrogen 63.0 182 106 859

Total phosphorus 66.2 182 116 1,091

Dissolved phosphorus 75.7 182 119 469

Total recoverable copper 72.8 167 123 298

Total recoverable lead 99.5 175 131 943

Total recoverable zinc 65.8 174 160 357

Total diazinon 210 179 -- --
Table 19 51

Computed using 1965 rainfall at Love Field (33.1 inches)—Continued

Mesquite

08061910 1,360 10,800 9,200 12,200 298 182 24.0 11.4 2.06 6.89 16.2 0.06

08061915 652 6,700 12,100 5,210 197 146 40.3 31.9 .960 2.28 6.14 .31

08061940 636 6,410 11,400 4,990 194 145 37.5 30.5 .950 1.94 5.33 .32

Plano

08061510 897 9,910 19,000 7,720 251 177 59.2 41.6 1.27 4.88 12.0 .31

08061525 708 5,750 5,090 6,300 168 107 16.1 7.98 1.08 5.46 12.8 .05

08061530 1,810 23,500 80,900 17,600 406 242 112 62.5 3.07 29.5 62.7 .14

Computed using 1975 rainfall at Meacham Airport (30.4 inches)

Arlington

08049220 1,130 9,510 7,840 10,300 255 155 20.6 9.58 1.73 5.86 14.4 .05

08049320 1,590 14,300 23,600 13,800 398 269 75.4 55.7 1.96 6.44 17.2 .38

08049360 1,380 16,600 29,400 11,800 382 262 64.6 45.2 2.10 10.2 21.1 .31

08049470 2,480 23,100 60,700 24,100 465 251 73.0 37.7 4.22 18.9 52.1 .06

Fort Worth

08047100 504 3,510 4,900 4,690 125 85.6 35.8 23.6 .520 .740 3.50 .17

08048505 1,520 8,370 14,500 15,300 264 147 55.5 30.3 1.67 2.72 13.6 .07

08048510 2,200 22,900 37,200 20,600 515 327 93.6 57.2 2.86 17.5 38.3 .28

08048545 1,820 15,900 38,600 16,200 371 210 46.4 27.2 3.34 12.4 34.1 .06

08048700 2,150 22,300 38,000 20,000 513 330 99.5 64.0 2.75 14.9 34.1 .34

Table 19. Estimated annual loads for sites in all study basins using 1965 rainfall at Love Field and 1975 rainfall at 

Meacham Airport—Continued City

Site no.

(fig. 1)

Load (pounds)

Biochemical

oxygen

demand

Chemical

oxygen

demand

Suspended

solids

Dissolved

solids

Total

nitrogen

Total

ammonia

plus

organic

nitrogen

Total

phosphorus

Dissolved

phosphorus

Total

recoverable

copper

Total

recoverable

lead

Total

recoverable

zinc

Total

diazinon