U.S. Department of the Interior

U.S. Geological Survey

In cooperation with the Dallas/Fort Worth International Airport

Occurrence and Distribution of Fecal Indicator Bacteria, 

and Physical and Chemical Indicators of Water Quality 

in Streams Receiving Discharge From Dallas/Fort Worth 

International Airport and Vicinity, North-Central Texas, 2008

Scientific Investigations Report 2009–5103
Front cover:

Left, Cottonwood Creek at Bethel Rd., Grapevine, Tex., looking upstream, June 2, 2008.

Right, Airplane approaching Dallas/Fort Worth International Airport for landing from north side of 

airport, May 1, 2008.

Back cover:

Left, Little Bear Creek at State Highway 360, Euless, Tex., looking downstream from below State Highway 360 bridge, April 7, 2008.

Right, Grapevine Creek at North Airfield Dr., Grapevine, Tex., looking upstream from North Airfield Dr., 

February 20, 2008.
Occurrence and Distribution of Fecal 

Indicator Bacteria, and Physical and 

Chemical Indicators of Water Quality 

in Streams Receiving Discharge From 

Dallas/Fort Worth International Airport 

and Vicinity, North-Central Texas, 2008

By Glenn R. Harwell and Craig A. Mobley

In cooperation with the Dallas/Fort Worth International Airport

Scientific Investigations Report 2009–5103

U.S. Department of the Interior

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

KEN SALAZAR, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

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

This and other USGS information products are available at http://store.usgs.gov/

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U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Harwell, G.R., and Mobley, C.A., 2009, Occurrence and distribution of fecal indicator bacteria, and physical and 

chemical indicators of water quality in streams receiving discharge from Dallas/Fort Worth International Airport and 

vicinity, north-central Texas, 2008: U.S. Geological Survey Scientific Investigations Report 2009–5103, 44 p. 
iii

Contents

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

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

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

Description of Dallas/Fort Worth International Airport and Vicinity and Sampling Sites ........2

Acknowledgments ...............................................................................................................................5

Methods ..........................................................................................................................................................5

Sample Collection ................................................................................................................................5

Analytical Methods ..............................................................................................................................7

Quality Assurance ................................................................................................................................7

Statistical Tests ....................................................................................................................................8

Occurrence and Distribution of Fecal Indicator Bacteria in Receiving Streams ..............................8

Fecal Coliform and Escherichia Coli Counts During Low-Flow Conditions ................................8

West Fork Trinity River Watershed ..........................................................................................8

Elm Fork Trinity River Watershed ...........................................................................................10

Comparison of Escherichia Coli Counts for Airport and Non-Airport Discharge 

Sites ...............................................................................................................................14

Fecal Coliform and Escherichia Coli Counts During Stormflow Conditions .............................14

Physical and Chemical Indicators of Water Quality .............................................................................16

Water Temperature ...........................................................................................................................17

Dissolved Oxygen ...............................................................................................................................18

pH ..........................................................................................................................................................18

Specific Conductance and Dissolved Solids ................................................................................18

Ammonia ..............................................................................................................................................19

Total Suspended Solids .....................................................................................................................22

Chloride ................................................................................................................................................23

Summary .......................................................................................................................................................25

References ...................................................................................................................................................27

Appendix 1. Fecal Indicator Bacteria and Water-Quality Data Collected at Sampling Sites 

on Streams Receiving Discharge from Dallas/Fort Worth International Airport 

and Vicinity, North-Central Texas, 2008 ..........................................................................29

1.1. Fecal indicator bacteria and water-quality data for samples collected 

during low-flow conditions .....................................................................................31

1.2. Fecal indicator bacteria and water-quality data for samples collected 

during stormflow conditions ...................................................................................38

Appendix 2. Quality Assurance Data for Samples Collected at Sites on Streams Receiving 

Discharge from Dallas/Fort Worth International Airport and Vicinity, NorthCentral Texas, 2008 .............................................................................................................41

2.1. Total coliform and Escherichia coli laboratory duplicates ................................43

2.2. Ammonia, residue (total suspended solids), and total chloride split 

replicates ...................................................................................................................44
iv

Figures

1. Map showing location of Dallas/Fort Worth International Airport, north-central 

Texas, and sampling sites on streams receiving discharge from the airport and 

vicinity, 2008 ..................................................................................................................................3

2–5. Boxplots showing variability of:

2. Fecal coliform counts by site during low-flow conditions in streams in the 

lower West Fork Trinity River watershed that receive discharge from the 

Dallas/Fort Worth International (DFW) Airport and vicinity, north-central 

Texas, 2008 ...........................................................................................................................9

3. Escherichia coli counts by site during low-flow conditions in streams in the 

lower West Fork Trinity River watershed that receive discharge from the 

Dallas/Fort Worth International (DFW) Airport and vicinity, north-central 

Texas, 2008 .........................................................................................................................10

4. Fecal coliform counts by site during low-flow conditions in streams in the 

Elm Fork Trinity River watershed that receive discharge from the Dallas/Fort 

Worth International (DFW) Airport and vicinity, north-central Texas, 2008 ............11

5. Escherichia coli counts by site during low-flow conditions in streams in the 

Elm Fork Trinity River watershed that receive discharge from the Dallas/Fort 

Worth International (DFW) Airport and vicinity, north-central Texas, 2008 ............12

6. Map showing geometric mean Escherichia coli counts during low-flow conditions 

at all sampling sites that receive discharge from the Dallas/Fort Worth International 

Airport and vicinity, north-central Texas, 2008 .....................................................................13

7–17 Boxplots showing variability of:

7. Escherichia coli counts by watershed under low-flow conditions for airport 

sampling sites and non-airport sampling sites in streams that receive 

discharge from the Dallas/Fort Worth International (DFW) Airport and vicinity, 

north-central Texas, 2008 ................................................................................................14

8. Fecal coliform and Escherichia coli counts during stormflow conditions in 

2008 at integrator site BBC183, the most downstream of sampling sites in 

the lower West Fork Trinity River watershed that receive discharge from the 

Dallas/Fort Worth International Airport and vicinity, north-central Texas ..............15

9. Fecal coliform and Escherichia coli counts during stormflow conditions in 

2008 at integrator site EFT348, the most downstream of sampling sites in the 

Elm Fork Trinity River watershed that receive discharge from the Dallas/Fort 

Worth International Airport and vicinity, north-central Texas ..................................16

10. Water temperature by site in streams receiving discharge from the Dallas/

Fort Worth International Airport and vicinity, north-central Texas, 2008 ................17

11. Dissolved oxygen concentration by site in streams receiving discharge 

from the Dallas/Fort Worth International Airport and vicinity, north-central 

Texas, 2008 .........................................................................................................................19

12. pH by site in streams receiving discharge from the Dallas/Fort Worth 

International Airport and vicinity, north-central Texas, 2008 ....................................20

13. Specific conductance by site in streams receiving discharge from the 

Dallas/Fort Worth International Airport and vicinity, north-central Texas, 2008 ....21

14. Dissolved solids concentration (computed from specific conductance) by 

site in streams receiving discharge from the Dallas/Fort Worth International 

Airport and vicinity, north-central Texas, 2008 ............................................................22

15. Ammonia nitrogen concentration by site in streams receiving discharge from 

the Dallas/Fort Worth International Airport and vicinity, north-central Texas, 

2008 .....................................................................................................................................23
v

16. Total suspended solids concentration by site in streams receiving discharge 

from the Dallas/Fort Worth International Airport and vicinity, north-central 

Texas, 2008 .........................................................................................................................24

17. Chloride concentration by site in streams receiving discharge from the 

Dallas/Fort Worth International Airport and vicinity, north-central Texas, 

2008 .....................................................................................................................................25

Tables

1. Descriptive information for sampling sites on streams receiving discharge from 

Dallas/Fort Worth International Airport and vicinity, north-central Texas, 2008 ...............4

2. Size and land use of watershed areas upstream from sampling sites on streams 

receiving discharge from Dallas/Fort Worth International Airport and vicinity, 

north-central Texas, 2008 ...........................................................................................................5

3. Summary information for storms during which samples were collected at 

integrator sites BBC183 and EFT348 on streams receiving discharge from Dallas/

Fort Worth International Airport and vicinity, north-central Texas, 2008 ...........................5

Conversion Factors, Datums, and Water-Quality Units

SI to Inch/Pound

Multiply By To obtain

Length

kilometer (km) 0.6214 mile (mi)

meter (m) 3.281 foot (ft)

millimeter (mm) 0.03937 inch (in.)

Area

square kilometer (km2) 0.3861 square mile (mi2)

Flow rate

cubic meter per second (m3/s) 35.31 cubic foot per second (ft3/s)

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

 °F=(1.8×°C)+32

Inch/Pound to SI

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

Flow rate

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

Datums

Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 

(NGVD 29) and the North American Vertical Datum of 1988 (NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1927 (NAD 27) 

and the North American Datum of 1983 (NAD 83).

Water-Quality Units

μS/cm, microsiemens per centimeter at 25 degrees Celsius

mg/L, milligrams per liter

cfu/100 mL, colony-forming units per 100 milliliters

MPN/100 mL, most-probable number per 100 milliliters

psu, practical salinity units
Abstract

This report, done by the U.S. Geological Survey in cooperation with Dallas/Fort Worth International (DFW) Airport in 

2008, describes the occurrence and distribution of fecal indicator bacteria (fecal coliform and Escherichia [E.] coli), and the 

physical and chemical indicators of water quality (relative to 

Texas Surface Water Quality Standards), in streams receiving discharge from DFW Airport and vicinity. At sampling 

sites in the lower West Fork Trinity River watershed during 

low-flow conditions, geometric mean E. coli counts for five 

of the eight West Fork Trinity River watershed sampling sites 

exceeded the Texas Commission on Environmental Quality 

E. coli criterion, thus not fully supporting contact recreation. 

Two of the five sites with geometric means that exceeded the 

contact recreation criterion are airport discharge sites, which 

here means that the major fraction of discharge at those sites is 

from DFW Airport. At sampling sites in the Elm Fork Trinity River watershed during low-flow conditions, geometric 

mean E. coli counts exceeded the geometric mean contact 

recreation criterion for seven (four airport, three non-airport) 

of 13 sampling sites. Under low-flow conditions in the lower 

West Fork Trinity River watershed, E. coli counts for airport 

discharge sites were significantly different from (lower than) 

E. coli counts for non-airport sites. Under low-flow conditions 

in the Elm Fork Trinity River watershed, there was no significant difference between E. coli counts for airport sites and 

non-airport sites. During stormflow conditions, fecal indicator 

bacteria counts at the most downstream (integrator) sites in 

each watershed were considerably higher than counts at those 

two sites during low-flow conditions. When stormflow sample 

counts are included with low-flow sample counts to compute a 

geometric mean for each site, classification changes from fully 

supporting to not fully supporting contact recreation on the 

basis of the geometric mean contact recreation criterion. All 

water temperature measurements at sampling sites in the lower 

West Fork Trinity River watershed were less than the maximum criterion for water temperature for the lower West Fork 

Trinity segment. Of the measurements at sampling sites in the 

Elm Fork Trinity River watershed, 95 percent were less than 

the maximum criterion for water temperature for the Elm Fork 

Trinity River segment. All dissolved oxygen concentrations 

were greater than the minimum criterion for stream segments 

classified as exceptional aquatic life use. Nearly all pH measurements were within the pH criterion range for the classified 

segments in both watersheds, except for those at one airport 

site. For sampling sites in the lower West Fork Trinity River 

watershed, all annual average dissolved solids concentrations 

were less than the maximum criterion for the lower West Fork 

Trinity segment. For sampling sites in the Elm Fork Trinity 

River, nine of the 13 sites (six airport, three non-airport) had 

annual averages that exceeded the maximum criterion for that 

segment. For ammonia, 23 samples from 12 different sites had 

concentrations that exceeded the screening level for ammonia. 

Of these 12 sites, only one non-airport site had more than the 

required number of exceedances to indicate a screening level 

concern. Stormflow total suspended solids concentrations 

were significantly higher than low-flow concentrations at the 

two integrator sites. For sampling sites in the lower West Fork 

Trinity River watershed, all annual average chloride concentrations were less than the maximum annual average chloride 

concentration criterion for that segment. For the 13 sampling 

sites in the Elm Fork Trinity River watershed, one non-airport 

site had an annual average concentration that exceeded the 

maximum annual average chloride concentration criterion for 

that segment. 

Introduction

As required by the Federal Clean Water Act, the State of 

Texas must establish water-quality standards that describe how 

surface-water bodies are used and monitor the status of those 

water bodies relative to the standards. Texas Administrative 

Code, Title 30, Chapter 307, defines the Texas Surface Water 

Quality Standards (Texas Commission on Environmental 

Quality, 2008a). The designated uses for streams receiving 

discharge from Dallas/Fort Worth International (DFW) Airport 

Occurrence and Distribution of Fecal Indicator Bacteria, 

and Physical and Chemical Indicators of Water Quality 

in Streams Receiving Discharge From Dallas/Fort Worth 

International Airport and Vicinity, North-Central Texas, 2008

By Glenn R. Harwell and Craig A. Mobley
2 Fecal Indicator Bacteria and Water Quality in Streams, DFW International Airport, Texas, 2008

in north-central Texas are aquatic life, contact recreation, and 

fish consumption. Aquatic life standards are designed to 

protect plant and animal species that live in or around water. 

Contact recreation standards are designed to ensure that water 

is safe for swimming and other activities involving direct 

human contact with water. Fish consumption standards are 

designed to protect people from eating contaminated fish and 

shellfish. 

The Texas Commission on Environmental Quality 

(TCEQ) assesses water quality for these designated uses. 

When data indicate that a water body is not supporting a 

designated use, the water body is placed on the State 303(d) 

list (Texas Commission on Environmental Quality, 2008b), 

and the Total Maximum Daily Load (TMDL) program (Texas 

Commission on Environmental Quality, 2009a) works to 

improve water quality in the impaired water body. There are 

386 water bodies on the 2008 State 303(d) list with a total of 

543 impairments for all uses (Texas Commission on Environmental Quality, 2008c); 274 of those impairments are for 

nonsupport of the contact recreation use because of elevated 

bacteria in water. 

The Texas Surface Water Quality Standards adopted in 

2000 use Escherichia (E.) coli, a subgroup of fecal coliform 

bacteria, as the indicator bacteria to determine whether a 

freshwater body is impaired and does not meet the standard 

for contact recreation use (Texas Commission on Environmental Quality, 2008a). Fecal coliform bacteria, a subgroup 

of the total coliform group, are present in the intestinal tracts 

and feces of warm-blooded animals (Texas Commission on 

Environmental Quality, 2008a). The total coliform group is a 

large collection of different kinds of bacteria that exist in the 

environment (Washington State Department of Health, 2008). 

Total coliform, fecal coliform, and E. coli are all indicators of 

water quality. Fecal coliform and E. coli are the fecal indicator 

bacteria of this report.

Segments of the Trinity River receive flow from DFW 

tributaries (fig. 1) and are on the 2008 State 303(d) list 

because of fecal indicator bacteria. The listed segments are the 

lower West Fork Trinity River (Segment 0841) and the Elm 

Fork Trinity River below Lewisville Lake (Segment 0822) 

(Texas Commission on Environmental Quality, 2008b). In 

addition to flow from DFW tributaries, these segments receive 

municipal and industrial wastewater discharge and storm 

discharge from agricultural, industrial, and urban areas. In 

2008, the U.S. Geological Survey (USGS), in cooperation with 

DFW, did a study to address the occurrence and distribution of 

fecal indicator bacteria, and the physical and chemical indicators of water quality (relative to Texas Surface Water Quality 

Standards), in streams receiving discharge from DFW Airport 

and vicinity.

Purpose and Scope

The purpose of this report is to describe the occurrence 

and distribution of fecal indicator bacteria (fecal coliform 

and E. coli), and the physical and chemical indicators of 

water quality (relative to Texas Surface Water Quality Standards), in streams receiving discharge from DFW Airport 

and vicinity. The findings are intended to help DFW Airport 

management better understand the extent to which airport 

discharge is responsible for the 303(d) listing for bacteria 

of two segments of the Trinity River downstream from the 

airport. Occurrence and distribution are described for low-flow 

conditions on the basis of analysis of samples collected at 21 

sites (eight in the lower West Fork Trinity River watershed 

and 13 in the Elm Fork Trinity River watershed) in the 

tributaries on DFW Airport property and in streams receiving discharge at points upstream and downstream from DFW 

Airport property (which thus includes discharge from sources 

other than DFW Airport); and for stormflow conditions at 

two sites on streams receiving discharge at points downstream 

from DFW Airport property. Samples for low-flow conditions 

were collected almost monthly (10 times) from each of the 

21 sites (flow permitting) during February–December 2008, 

thus representing all seasons. Samples for stormflow conditions were collected from the two downstream sites during 

three storms in March, April, and August 2008, respectively. 

Eight samples were collected at each downstream site during the three storms. In addition to fecal indicator bacteria, 

samples were analyzed for total coliform. Total coliform 

results are tabulated but not described because total coliform 

is not primarily an indicator of fecal matter; values for total 

coliform frequently exceeded upper reporting levels and thus 

are qualified as greater-than values. Physical and chemical 

water-quality data (water temperature, dissolved oxygen [DO], 

pH, specific conductance, ammonia nitrogen (ammonia), 

total suspended solids [TSS], and chloride) obtained from the 

low-flow and stormflow samples are compared with waterquality criteria supporting the uses for the 303(d)-classified 

segments on the lower West Fork Trinity River and the Elm 

Fork Trinity River (Texas Commission on Environmental 

Quality, 2008b).

Description of Dallas/Fort Worth International 

Airport and Vicinity and Sampling Sites

The DFW Airport comprises a 77.2-square-kilometer 

(km2) area in north-central Texas that straddles the boundary 

between Tarrant and Dallas Counties (fig. 1). With respect to 

daily aircraft operations, DFW Airport is the third busiest airport in the world and the seventh busiest with respect to total 

number of passengers served (Dallas/Fort Worth International 

Airport, 2008).

Eight of the 21 sampling sites are on the west and south 

sides of DFW Airport on streams that ultimately flow into 

the lower West Fork Trinity River and thus are in the West 

Fork Trinity River watershed (fig. 1; table 1). These eight 

sites are in the Big Bear Creek watershed of the West Fork 

Trinity River watershed. Four of the eight sites are listed as 

“DFW Airport discharge sites” in table 1. Hereinafter, airport 

discharge sites, or airport sites, are those at which the major 
Introduction 3

Figure 1. Location of Dallas/Fort Worth International Airport, north-central Texas, and sampling sites on streams receiving discharge 

from the airport and vicinity, 2008. 

§ ̈¦635

§ ̈¦35E

Æÿ183 Æÿ183

Æÿ121

Æÿ114

Æÿ114

Æÿ161

Æÿ121

TL

97°06' 97°03' 97°00' 96°57'

33°00'

32°57'

32°54'

32°51'

DENTON COUNTY DALLAS COUNTY

TARRANT COUNTY

0 2.5 5 KILOMETERS

LOCATION MAP 

Elm Fork Trinity River

 watershed

West Fork

Trinity River

 watershed

Study area

TEXAS

Base from Dallas Fort Worth International Airport,

Texas Department of Transportation,

USGS National Hydrography Dataset,

Texas Natural Resources Information System

EXPLANATION

Dallas Fort Worth International

(DFW) Airport property

Lower West Fork Trinity River watershed

Elm Fork Trinity River watershed

Sampling site and field identifier, by watershed

Lower West Fork Trinity River

Elm Fork Trinity River

BBC183

EFT348

CCBR

GCRR

CCTTR

GCNAD

TRIBMD

TRIBEG

BBC121

OF25

LBC360

BBC183

OF19

CCDTR

GCDTR

HCCER HCMSC

MSC

SHCHPR

HCLR

SHCBLR

EFT348

Segment 0841

Segment 0822

Mud Springs Creek Hackberry

Creek

Creek

Sout

Hackberry

h

Elm

Fork River

Trinity

Creek

Grapevine Creek

Cotto

Cr

nwood eek

Denton

Creek

Cottonwood

Creek

Little

Bear

Creek

Bear

Big

Branch

Dudley

North

Lake

Lake

Grapevine

River

Trinity

West

Fork
4 Fecal Indicator Bacteria and Water Quality in Streams, DFW International Airport, Texas, 2008

fraction of discharge is from DFW Airport. Upstream from 

the most downstream (integrator) sampling site on Big Bear 

Creek (BBC183), Big Bear Creek watershed is 199 km2, predominantly urban (table 2), and extends westward from DFW 

Airport. The watersheds of the four airport discharge sites that 

contribute flow at BBC183 (TRIBEG, OF25, OF19, and TL) 

account for 11 percent of the contributing area to BBC183, 

and these watersheds are greater than 50-percent urban. A 

major contributor to flow at BBC183 is Little Bear Creek. 

The watershed of sampling site LBC360 on Little Bear Creek 

accounts for 31 percent of the contributing area to BBC183, 

and this watershed is 75-percent urban. Sampling site BBC121 

is the most upstream site on Big Bear Creek and likely is not 

affected by airport discharge. Its watershed accounts for 45 

percent of the contributing area to BBC183 and is 62-percent 

urban. BBC121 was selected because it provides an indication 

of conditions in Big Bear Creek before airport influence.

Thirteen of the 21 sites are on the east and north sides of 

DFW Airport; 12 of those sites are on streams that flow into 

the Elm Fork Trinity River and thus are in the Elm Fork Trinity River watershed (fig. 1; table 1). Seven of the 13 sites are 

listed as “DFW Airport discharge sites” in table 1. As for the 

lower West Fork Trinity River sites, airport discharge sites, or 

airport sites, are those at which the major fraction of discharge 

is from DFW Airport. The most downstream (integrator) of 

the 13 sampling sites (EFT348) is on Elm Fork Trinity River. 

Contributing area to EFT348 is 6,570 km2 and includes Lake 

Grapevine and Lake Lewisville (a 94-km2 reservoir about 15 

kilometers northeast of Lake Grapevine [not shown in fig. 1]). 

The contributing areas to Lake Grapevine and Lake Lewisville are 1,800 and 4,300 km2

, respectively. Flow at EFT348 

depends on dam releases from these two lakes and the remaining 470 km2

 that is downstream from the two lakes. The 12 

sampling sites are on smaller creeks, including Cottonwood 

Creek (CCTTR, CCBR, CCDTR), Grapevine Creek (GCNAD, 

GCRR, GCDTR), Hackberry Creek (HCCER, HCMSC, 

HCLR), Mud Springs Creek (MSC), and South Fork Hackberry Creek (SHCBLR, SHCHPR); these creeks ultimately 

Table 1. Descriptive information for sampling sites on streams receiving discharge from Dallas/Fort Worth International Airport and 

vicinity, north-central Texas, 2008.

[USGS, U.S. Geological Survey; DFW, Dallas/Fort Worth International; latitude/longitude, datum is NAD 27 unless otherwise specified]

Field 

identifier 

(fig. 1)

USGS site 

identifier USGS site name

DFW 

Airport 

discharge 

site

Latitude 

(decimal 

degrees)

Longitude 

(decimal 

degrees)

Lower West Fork Trinity River watershed

BBC121 0804955100 Big Bear Creek at State Highway 121, Euless, Tex. No 32.90178 097.09972

TRIBMD 0804955150 Unnamed Bear Creek tributary at Mustang Dr., Grapevine, Tex. No 32.91777 097.08453

TRIBEG 0804955175 Unnamed Bear Creek tributary at Euless Grapevine Rd., Grapevine, Tex. Yes 32.90492 097.09232

OF25 08049555 DFW Airport Outfall 25 at Glade Rd., Euless, Tex. Yes 32.88095 097.06650

OF19 08049556 Unnamed tributary to Big Bear Creek (Outfall 19), Euless, Tex. Yes 132.87194 1097.05667

LBC360 08049558 Little Bear Creek at State Highway 360, Euless, Tex. No 32.86045 097.06357

TL 0804956750 Trigg Lake Outfall tributary upstream of Bear Creek, Euless, Tex. Yes 32.84353 097.04180

BBC183 08049569 Big Bear Creek at State Highway183, Euless, Tex. No 132.83556 1097.03583

Elm Fork Trinity River watershed

CCTTR 08055100 Cottonwood Creek at Texan Trail Rd., Grapevine, Tex. No 32.92762 097.06008

CCBR 08055120 Cottonwood Creek at Bethel Rd., Grapevine, Tex. Yes 32.95549 097.03497

CCDTR 08055140 Cottonwood Creek at Denton Tap Rd., Grapevine, Tex. No 32.97820 096.99302

GCNAD 08055510 Grapevine Creek at North Airfield Dr., Grapevine, Tex. Yes 32.92555 097.03337

GCRR 08055512 Grapevine Creek at railroad bridge, Irving, Tex. Yes 32.93782 097.02153

GCDTR 08055514 Grapevine Creek at Denton Tap Rd., Irving, Tex. No 32.95554 096.99293

HCCER 08055520 Hackberry Creek upstream of Cabell and Esters Rd., Irving, Tex. Yes 32.90795 097.00945

HCMSC 08055524 Hackberry Creek upstream of Mud Springs Creek, Irving, Tex. Yes 32.90151 096.99439

MSC 08055526 Mud Springs Creek upstream of Hackberry Creek, Irving, Tex. Yes 32.90126 096.99459

SHCBLR 08055530 South Hackberry Creek at Belt Line Rd., Irving, Tex. Yes 32.88523 096.99124

SHCHPR 08055534 South Hackberry Creek at High Point Rd., Irving, Tex. No 32.89050 096.96965

HCLR 08055538 Hackberry Creek at Love Rd., Irving, Tex. No 32.88874 096.95426

EFT348 08055560 Elm Fork Trinity River at Spur 348, Irving, Tex. No 132.87333 1096.93056

1

 Datum is NAD 83. 
Methods 5

flow into the Elm Fork Trinity River. The contributing area 

upstream from the most downstream sampling sites on Cottonwood Creek (CCDTR), Grapevine Creek (GCDTR), and 

Hackberry Creek (HCLR) is about 74 km2. Of all the sampling-site watersheds contributing to flow at EFT348, only the 

watershed upstream from CCBR on Cottonwood Creek is less 

than 50-percent urban (48 percent). DFW Airport discharge 

sites that contribute to flow at EFT348 are CCBR, GCNAD, 

GCRR, HCCER, HCMSC, MSC, and SHCBLR.

Acknowledgments

The authors thank DFW Airport Environmental Affairs 

Department staff for their interest in the study and assistance 

with site selection, access to sampling sites, and sampling 

logistics. 

Methods

Data were collected in accordance with the USGS 

“National Field Manual for the Collection of Water Quality Data” (U.S. Geological Survey, variously dated) and the 

TCEQ “Surface Water Quality Monitoring Procedures, Volume 1—Physical and Chemical Monitoring Methods” (Texas 

Commission on Environmental Quality, 2009b).

Sample Collection

Samples for low-flow conditions were collected almost 

monthly (10 times) from each of the 21 sites (flow permitting) 

during February–December 2008 (appendix 1.1). Samples for 

stormflow conditions were collected at the most downstream 

(integrator) sites in the West Fork Trinity River watershed (BBC183) and the Elm Fork Trinity River watershed

(EFT348) during three storms in March, April, and August 

2008 (table 3). Eight samples were collected at each downstream site during the three storms (appendix 1.2). Sampled 

storms were different with respect to the total amounts of 

Table 2. Size and land use of watershed areas upstream from 

sampling sites on streams receiving discharge from Dallas/Fort 

Worth International Airport and vicinity, north-central Texas, 2008. 

Field 

identifier 

(fig. 1)

Area 

(square 

kilometers)

Land-use category 

(percentage of watershed area)

Urban

Sum of 

agriculture, 

range, 

and forest

Water Wetland

Barren 

land

Lower West Fork Trinity River watershed

BBC121 90.1 61.6 38.1 0.28 0 0

TRIBMD 1.27 96.5 3.54 0 0 0

TRIBEG 4.14 52.0 47.9 .13 0 0

OF25 2.82 89.0 11.0 0 0 0

OF19 2.70 87.1 12.9 0 0 0

LBC360 61.5 75.4 24.2 .18 .08 .16

TL 11.9 67.1 31.2 1.6 .10 0

BBC183 199 66.1 33.4 .30 .10 .10

Elm Fork Trinity River watershed

CCTTR 3.26 77.9 22.2 0 0 0

CCBR 9.29 48.2 51.1 .25 .52 0

CCDTR 16.8 57.7 41.9 .14 .29 0

GCNAD 6.26 81.2 18.8 0 0 0

GCRR 9.22 67.2 32.7 0 0 .12

GCDTR 22.0 73.6 26.3 0 .05 .06

HCCER 2.40 85.8 14.2 0 0 0

HCMSC 4.35 70.2 29.8 0 0 0

MSC 8.16 67.0 32.9 .12 0 0

SHCBLR 2.92 52.2 47.8 0 0 0

SHCHPR 7.01 58.0 42.0 0 0 0

HCLR 34.7 72.4 27.5 .07 .05 0

EFT348 6,570 14.5 80.3 4.6 .50 .10

Table 3. Summary information for storms during which samples were collected at integrator sites BBC183 and EFT348 on streams 

receiving discharge from Dallas/Fort Worth International Airport and vicinity, north-central Texas, 2008.

[Dry days prior to storm is number of days with less than 2.54 millimeters of precipitation prior to sampled storm; DFW, Dallas/Fort Worth International; 

>, greater than; NA, not available]

Storm

Total precipitation, 

DFW Airport 

(millimeters)

Dry days prior 

to storm

Peak stage 

(meters above datum)

Maximum discharge 

(cubic meters per second) 

BBC1831 EFT3482 BBC183 EFT348

March 2008 67.8 7 >4.04 7.32 NA 200

April 2008 6.35 4 2.52 5.55 NA 114

August 2008 47.3 3 3.65 4.15 NA 40.0

1

 Datum is 146.3 meters above NGVD 29.

2

 Datum is 121.9 meters above NAVD 88.
6 Fecal Indicator Bacteria and Water Quality in Streams, DFW International Airport, Texas, 2008

precipitation and the period over which the storm occurred. 

The March 2008 storm had the most precipitation (67.8 millimeters [mm]) and occurred over a period of about 1 day. The 

April 2008 storm had the least amount of precipitation (6.35 

mm) and occurred over a 4-hour period. The August 2008 

storm had 47.3 mm of precipitation. During this storm, 23.9 

mm of precipitation fell over a 7-hour period on August 15; 

after 2 days without appreciable precipitation, 15.0 mm fell on 

August 18 over a 12-hour period; and the remaining 8.38 mm 

of precipitation fell over the next 2 days.

All samples (low-flow and stormflow) were collected for 

analysis of total coliform, fecal coliform, E. coli, ammonia, 

TSS, and chloride. Instantaneous water-quality measurements 

were made at the time of sample collection for water temperature, DO, pH, and specific conductance using multiparameter 

water-quality monitors. Monitors were calibrated and operated 

according to USGS protocols (U.S. Geological Survey, variously dated). Post calibration also was done to comply with 

requirements of the TCEQ “Surface Water Quality Monitoring 

Procedures” (Texas Commission on Environmental Quality, 

2009b). Salinity was estimated from specific conductance 

measurements (Wagner and others, 2006).

During low-flow sample collection, streamflow was 

estimated either as the product of surface-water velocity and 

cross-sectional flow area or using professional judgment. 

Estimates based on judgment were reported as less than a 

specified amount. The goal of estimating streamflow was to 

document that sampling was done during low-flow conditions and was indicative of periods following 72 hours without 

substantial precipitation. Site EFT348 is a USGS real-time 

streamflow-gaging station (08055560, Elm Fork Trinity River 

at Spur 348, Irving, Tex.) with an established stage-discharge 

relation (rating). At this site, stage was measured during 

sample collection for both low-flow and stormflow conditions, 

and streamflow was obtained from the rating.

Ancillary data collected at the time of all sampling 

included weather conditions, odor, bank vegetation, presence 

or absence of visible algae, upstream construction activities, 

water depth at sampling site, and sampling site description. 

Also, a photograph was taken of the sampling conditions.

All samples were collected as discrete grab samples at 

the estimated centroid of flow whenever possible. For water 

depths greater than 0.46 meter (m) (1.50 feet), samples were 

collected at 0.30 m (1.00 foot) below the water surface. For 

water depths less than 0.46 m, samples were collected at 

one-third of the water depth measured from the water surface. 

Samples were collected at or just below the water surface if 

the water depth was so shallow that bottom sediment would be 

disturbed if the sample were collected at one-third of the water 

depth. Every effort was made to not collect the sample from 

the surface, although some shallow sampling depths prevented 

collection below the water surface.

Fecal indicator bacteria samples were collected using 

sterile single-use Whirlpak® bags. The bags were not fieldrinsed with native water. The bags were filled by submerging 

below the water surface with the top facing upstream and tilted 

slightly upward. The perforated top parts of the bags were 

removed before they were submerged, but the bags were 

held closed until they were at the depth of sample collection to 

prevent collection of surface water. When the stream velocity was low and water would not flow easily into the bags, 

they were held open at the proper depth and moved slowly 

upstream until full. Immediately after the bags were filled, 

some water was squeezed out to leave airspace to aid in mixing the water before decanting into separate sterile bottles for 

fecal coliform and E. coli analyses. The bags were shaken 

periodically while decanting into separate sterile bottles to 

keep the water well-mixed. Two sterile fecal coliform bottles 

(supplied by the analyzing laboratory) and one or two sterile 

IDEXX®-supplied bottles (depending on the number of dilutions to run) were filled to the 100-milliliter (mL) line immediately after collection in the sterile bags. All sample bottles 

for fecal coliform and E. coli analyses were pretreated with 

sodium thiosulfate in the event that residual chlorine was present. Bottles were put in coolers and placed on ice immediately 

after collection.

Ammonia, TSS, and chloride sample water was collected 

in two unused, 500-mL, clear polyethylene bottles supplied by 

the analyzing laboratory. One 500-mL bottle was collected for 

TSS and chloride analysis. Water for ammonia analysis was 

collected in a separate bottle. The bottles were dipped to the 

proper depth and filled but left with a small airspace. Sampling during low-flow conditions made the use of isokinetic 

samplers impractical. At most of the sampling sites during 

low-flow conditions, the depth of water was less than or equal 

to the unsampled zone of an isokinetic sampler. Water for 

ammonia analysis was preserved with 2.0 mL of concentrated 

sulfuric acid. After adding the acid, the bottle was inverted to 

mix the acid. All bottles were placed on ice immediately after 

collection. 

The bottles were not field-rinsed with native water (as 

required by the USGS “National Field Manual for the Collection of Water Quality Data”) before sample collection because 

they were identified as clean bottles by the analyzing laboratory, and because the TCEQ “Surface Water Quality Monitoring Procedures” require that bottles not be rinsed with native 

water. To account for both requirements, bottle lot numbers 

were recorded for all samples, and blank samples (deionized 

reagent-grade water from the USGS National Water Quality Laboratory [NWQL]) were put in the laboratory-supplied 

sample bottles and analyzed for ammonia, TSS, and chloride 

at the beginning of the study. Blank samples were handled in 

the same manner as environmental samples. 

Sample bottles were labeled with field identifier, collection date and time, type of analysis requested, name of person 

collecting the sample, and preservation method. Samples for 

total coliform and E. coli were transported to the USGS Texas 

Water Science Center in Fort Worth for analysis by USGS 

staff. Samples for fecal coliform, ammonia, TSS, and chloride 

analyses were given to a courier for transport to the analyzing 

laboratory. Chain-of-custody forms were used to document the 

transport of samples.
Methods 7

Analytical Methods

Xenco Laboratories, Dallas, analyzed samples for ammonia, TSS, and chloride. Xenco also analyzed samples for fecal 

coliform, except for one suite of low-flow samples (December 

2008) that was analyzed by Armstrong Forensic Laboratory, 

Inc., Arlington, Tex. 

Total coliform and E. coli analyses were done by USGS 

staff using the IDEXX Colilert-24® method with the QuantiTray/2000 (Eaton and others, 2005; IDEXX Laboratories, 

2009). This method is a 24-hour test that detects and quantifies total coliform and E. coli bacteria in water. After 24 hours 

of incubation at 35.0 (±0.5) degrees Celsius (°C), the sample 

should turn yellow if coliform bacteria are present. The sample 

also should fluoresce when exposed to ultraviolet light with 

a wavelength ranging from 365 to 366 nanometers if E. coli

are present. Results (estimated values) are reported as mostprobable number per 100 mL (MPN/100 mL). The range 

in reporting level for the method depends on sample dilutions. For an undiluted sample, the lowest reporting level is 

1.0 MPN/100 mL, and the highest reporting level is 2,400 

MPN/100 mL. Dilutions (1:10 and 1:100) were run to quantify 

results greater than 2,400 MPN/100 mL. 

Fecal coliform analyses were done by the contract 

laboratories using the membrane filtration method with a 

0.45-micrometer filter (Eaton and others, 2005). For this 

method, a 100-mL volume of sample water is passed through 

the filter. The fecal coliform bacteria present in the water 

remain on the filter. The filter is then placed in a petri dish 

containing the appropriate growth medium (M-FC) and incubated for 24 hours at 44.5 (±0.2) °C. During incubation the 

bacteria on the filter grow into separate colonies, which are 

then directly counted and reported as the number of colonyforming units per 100 mL (cfu/100 mL). Dilutions were run 

to try to achieve an ideal colony-counting range, as the range 

in reporting level for the method depends on sample dilutions. 

For an undiluted sample, the lowest reporting level is 1.00 

cfu/100 mL, and the highest reporting level depends on the 

countability of the individual colonies after incubation; when 

it is not possible to count the colonies, results are reported as 

too numerous to count (TNTC).

The reporting units of most-probable number (for the 

IDEXX method in this report) are estimates, and the reporting units of colony-forming units (for the membrane filtration 

method in this report) are direct counts of cells on a plate. On 

the basis of the respective methods, total coliform and E. coli

are reported here in terms of most-probable number, and fecal 

coliform are reported in terms of colony-forming units. Also, 

as noted in the section, “Occurrence and Distribution of Fecal 

Indicator Bacteria in Receiving Streams,” the TCEQ E. coli

criterion for classifying a stream segment as not fully supporting contact recreation is in colony-forming units. The units 

of most-probable number for the IDEXX method and colonyforming units are considered comparable.

Ammonia analyses were done using U.S. Environmental Protection Agency (1993) methods 350.1 and 350.3 with 

a lowest reporting level of 0.100 milligram per liter (mg/L). 

Total ammonia concentrations are reported as equivalent 

amounts of elemental nitrogen. TSS analyses were done 

using method SM2540D (Eaton and others, 2005) with lowest 

reporting levels of 4.00 and 5.00 mg/L. Chloride analyses 

were done using U.S. Environmental Protection Agency 

method 325.3 (National Environmental Methods Index, 2008) 

with a lowest reporting level of 5.00 mg/L.

Quality Assurance

Quality assurance was provided by blanks (laboratory 

and field), laboratory duplicates, split replicates, and field 

duplicates (E. coli samples collected from the same site using 

the same method). Blanks were analyzed to identify contamination, if any, during sample collection, transport, and 

analysis. Laboratory duplicate analyses for E. coli samples 

were done to test the reproducibility of analytical results for 

the IDEXX Colilert-24® method for E. coli. Split replicate 

analyses for ammonia, TSS, and chloride samples were done 

to assess the variability in results associated with sample 

preservation, handling, shipping, and analysis. Results of 

quality-assurance analyses of laboratory duplicates and split 

replicates are in appendixes 2.1 and 2.2, respectively. Field 

duplicate E. coli samples were analyzed for low-flow samples 

only to assess environmental variability in E. coli counts. 

Results of quality-assurance analyses of field duplicates are in 

appendix 1.1.

For fecal coliform bacteria blanks, IDEXX®-supplied 

sterile water was pipetted (with individually packaged sterile 

pipettes used to make dilutions) into a Whirlpack® bag. The 

water was transferred from the bag to the laboratory-supplied 

fecal coliform bacteria bottles used during environmental sample collection. The bottles were transported as environmental 

samples and analyzed for fecal coliform bacteria. Analytical 

results for fecal coliform bacteria blank samples were less than 

laboratory reporting levels. 

Each new lot number of IDEXX®-supplied sterile water 

and IDEXX®-supplied sample bottles were tested for sterility. The sterile water was poured into a sample bottle and the 

sample was analyzed as an environmental sample. Analytical 

results for sterile water blank samples were less than reporting 

levels.

For other blank samples, deionized reagent-grade water 

from the NWQL was poured into a 1-liter (L) polyethylene 

bottle from the NWQL. This water was used to fill two of 

the 500-mL sample bottles supplied by the analyzing laboratory. Bottles were preserved and transported as environmental 

samples and analyzed for ammonia, TSS, and chloride. All 

analytical results for these samples were less than laboratory 

reporting levels. 

Laboratory duplicate samples of E. coli samples were 

created by removing (using individually packaged sterile 

pipettes) a volume of water from a bottle of IDEXX®-

supplied sterile water and replacing it with the same volume of 

environmental sample. This was done in duplicate to compare 
8 Fecal Indicator Bacteria and Water Quality in Streams, DFW International Airport, Texas, 2008

two results of the same dilution factor, typically 1:10 and 

1:100, indicating 10 and 1.0 mL, respectively, of environmental sample water. Thirty-five laboratory duplicates were 

run on 31 samples (appendix 2.1), 12.7 percent of the 244 

samples collected. Duplicate dilutions were analyzed for some 

samples, for example two 1:10-mL dilutions and two 1:100-

mL dilutions. Laboratory duplicate results indicate that when 

the total number of cells that were yellow and fluoresced was 

within the recommended range of 30 to 80 (Texas Commission 

on Environmental Quality, 2009, p. 4–8), the average percentage difference between duplicate pairs for E. coli was 16.2. 

Split replicates were collected by filling a 1-L polyethylene sample bottle from the NWQL in the field with stream 

water and decanting 500 mL into two sample bottles for 

ammonia analyses. The process was repeated to make replicates for TSS and chloride analyses. Split replicates were run 

on 24 samples (appendix 2.2), 9.8 percent of the 244 samples 

collected. For the split replicate samples, the average relative 

percentage difference is 10.6 for ammonia, 18.6 for TSS, and 

10.3 for chloride. 

Field duplicates were run on 11 samples for E. coli during low-flow conditions (appendix table 1.1), or 5.6 percent 

of the 196 low-flow samples collected. Average percentage 

difference between duplicate pairs was 27.3.

Reagent checks, positive control checks, and comparison count checks also were done. Reagent checks were done 

to test for E. coli contamination of the reagents. All sterility 

checks on sterile water and reagents were negative for presence of E. coli. Positive control checks were done to check the 

productivity of the reagent. Each new lot of reagent was tested 

for productivity with Quanti-cult® quality control test kits 

(U.S. Geological Survey, variously dated). All positive control 

checks yielded expected results for productivity of reagent. 

Comparison count checks were done on 36 different samples. 

Replicate counts between analysts averaged 7.8 percent.

Of the 244 samples analyzed for fecal coliform, 15 (6.1 

percent) had holding times that exceeded 8 hours and 50 

(20.5 percent) had holding times between 6 and 8 hours. The 

longest holding time for fecal coliform analysis was 9 hours 

5 minutes. Of the 244 samples analyzed for E. coli, none had 

holding times that exceeded 8 hours, and five (2.0 percent) 

had holding times between 6 and 8 hours. USGS recommended holding times for total coliform, fecal coliform, and 

E. coli bacteria are 6 hours for nonpotable water collected 

for compliance purposes and 24 hours for noncompliance 

purposes (Myers and others, 2007). TCEQ recommends that 

bacteriological samples be analyzed within 8 hours of sample 

collection. The holding time for E. coli may be extended to 48 

hours when samples are analyzed using the IDEXX Colilert 

Quanti-Tray/2000 (Texas Commission on Environmental 

Quality, 2008a).

Statistical Tests

Nonparametric methods were used to test for differences 

between groups (datasets) of analytical results for selected 

sampling sites. Comparisons between sites were made 

using the Mann-Whitney (Wilcoxon rank-sum) test. The 

Mann-Whitney test indicates whether one group tends to 

produce larger observations than a second group (Helsel and 

Hirsch, 1992). No assumptions are made about the distributions of the data in either group, and the two groups do not 

need to have the same distribution. For this report, differences 

between groups are considered significant at the .05 level 

(p-value less than or equal to .05).

Occurrence and Distribution of Fecal 

Indicator Bacteria in Receiving 

Streams

Results of analyses for fecal indicator bacteria (fecal coliform and E. coli) are listed in appendixes 1.1 and 1.2. All fecal 

coliform and E. coli data are included in the data analyses and 

graphical data presentation. E. coli counts are compared with 

contact recreation criteria. Water bodies are classified as fully 

supporting contact recreation if geometric mean E. coli counts 

are less than or equal to 126 cfu/100 mL (or MPN/100 mL) 

and 25 percent or less of the samples exceed the single-sample 

criterion of 394 cfu/100 mL (or MPN/100 mL). They are 

classified as not fully supporting contact recreation if either 

the geometric mean exceeds 126 cfu/100 mL or more than 25 

percent of the samples exceed 394 cfu/100 mL (Texas Commission on Environmental Quality, 2008a).

Fecal Coliform and Escherichia Coli Counts 

During Low-Flow Conditions

Variability of fecal coliform and E. coli counts at all sampling sites during low-flow conditions is shown by boxplots 

(figs. 2–5). Boxplots for sites in the lower West Fork Trinity 

River watershed are shown in figures 2 and 3, and boxplots 

for sites in the Elm Fork Trinity River watershed are shown in 

figures 4 and 5.

West Fork Trinity River Watershed

At sampling sites in the lower West Fork Trinity River 

watershed during low-flow conditions, fecal coliform counts 

ranged from 4.00 to 8,500 cfu/100 mL (fig. 2), and E. coli

counts ranged from 1.0 to 4,900 MPN/100 mL (fig. 3). Fecal 

coliform counts were reported by the laboratory as TNTC for 

five of the 70 West Fork Trinity River watershed low-flow 

samples; one for non-airport site BBC121 and two each 

for non-airport site TRIBMD and airport site OF25. Geometric mean E. coli counts1

 for five of the eight West Fork 

1

IDEXX analytical results (most-probable number) are reported to two significant figures. However, because the TCEQ criterion for contact recreation 

use based on E. coli counts (126 cfu/100 mL [or MPN/100 mL]) contains 

three significant figures (and geometric mean is a computed value), geometric 

mean E. coli counts are reported here to three significant figures.
Occurrence and Distribution of Fecal Indicator Bacteria in Receiving Streams 9

Trinity River watershed sampling sites (BBC121 [non-airport], 

TRIBMD [non-airport], TRIBEG [airport], OF25 [airport], 

and LBC360 [non-airport]) were greater than 126 MPN/100 

mL (fig. 6), thus not fully supporting contact recreation on the 

basis of the TCEQ criterion. 

Maximum fecal indicator bacteria counts were measured 

at non-airport site TRIBMD, on the northwest side of DFW 

Airport property (fig. 1). It is the smallest sampled watershed 

at 1.3 km2 and classified as 96.5-percent urban. The contributing area is mostly covered by office buildings and parking lots. 

The geometric mean E. coli count at TRIBMD (809 MPN/100 

mL) exceeded the geometric mean criterion for support of 

contact recreation (fig. 6). Samples collected downstream from 

TRIBMD (after flow crosses DFW Airport property) at airport 

site TRIBEG had lower fecal indicator bacteria concentrations, 

but the geometric mean E. coli count (174 MPN/100 mL) 

still exceeded geometric mean criterion for support of contact 

recreation. Airport site OF25 represents a small watershed on 

DFW Airport property. The geometric mean E. coli count for 

OF25 was 209 MPN/100 mL, also greater than the geometric mean criterion for support of contact recreation. Sanitary 

sewer lines adjacent to the OF25 outfall creek and kennels for 

DFW Airport police dogs are in the watershed upstream from 

OF25. The sewer lines and kennels are potential sources of 

bacteria, but additional data from upstream of those potential 

sources would be needed for confirmation. Geometric mean 

Figure 2. Boxplots showing variability of fecal coliform counts by site during low-flow conditions in streams in the lower West Fork 

Trinity River watershed that receive discharge from the Dallas/Fort Worth International (DFW) Airport and vicinity, north-central Texas, 

2008. 

BBC121 TRIBMD TRIBEG OF25 OF19 LBC360 TL BBC183

SAMPLING SITES (FIG. 1)

9,000

8,000

7,000

6,000

5,000

4,000

3,000

2,000

1,000

0

FECAL COLIFORM COUNTS, IN COLONY FORMING UNITS

PER 100 MILLILITERS

EXPLANATION

Sample size

Data value greater than or equal to 1.5 times 

the IQR outside the box

Largest data value within 1.5 times 

the IQR above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times 

the IQR below the box

7

Interquartile

range (IQR) {

Non-airport site—Receives major fraction of discharge from DFW Airport

Airport site—Receives major fraction of discharge from DFW Airport

Laboratory reporting level at 4.0 colony-forming units per 100 milliliters

8

5

7

3

9

9

5

9
10 Fecal Indicator Bacteria and Water Quality in Streams, DFW International Airport, Texas, 2008

E. coli counts for airport sites OF19 and TL were less than the 

geometric mean criterion for support of contact recreation; and 

geometric mean E. coli counts for integrator site BBC183, the 

most downstream of the West Fork Trinity River watershed 

sites, also were less than the contact recreation criterion during 

low-flow conditions.

Non-airport sampling sites BBC121 and LBC360 represent relatively large urban watersheds (table 2) and no contributing area from DFW Airport property. Geometric mean 

E. coli counts for these two sites exceeded the criterion for 

support of contact recreation (fig. 6). Low-flow E. coli counts 

for these two sites were not significantly different from each 

other but were significantly different from counts at integrator 

site BBC183 on the basis of the Mann-Whitney test. 

Elm Fork Trinity River Watershed

At sampling sites in the Elm Fork Trinity River watershed during low-flow conditions, fecal coliform counts ranged 

from 1.00 to 2,160 cfu/100 mL (fig. 4), and E. coli counts 

ranged from less than 1.0 to 2,000 MPN/100 mL (fig. 5). Fecal 

coliform counts were reported by the laboratory as TNTC 

for three of 126 Elm Fork Trinity River watershed low-flow 

samples; one each for non-airport site CCDTR, airport site 

GCNAD, and integrator site EFT348. Of the 13 sampling 

sites in the Elm Fork Trinity River watershed, geometric 

mean E. coli counts exceeded the geometric mean contact 

recreation criterion of 126 cfu/100 mL (or MPN/100 mL) for 

seven sites—non-airport CCTTR, airport CCBR, non-airport 

Figure 3. Boxplots showing variability of Escherichia coli counts by site during low-flow conditions in streams in the lower West Fork 

Trinity River watershed that receive discharge from the Dallas/Fort Worth International (DFW) Airport and vicinity, north-central Texas, 

2008. 

BBC121 TRIBMD TRIBEG OF25 OF19 LBC360 TL BBC183

SAMPLING SITES (FIG. 1)

4,500

4,000

3,500

3,000

2,500

2,000

1,500

1,000

500

0

5,000

ESCHERICHIA COLI COUNTS, IN MOST-PROBABLE 

NUMBER PER 100 MILLILITERS 

EXPLANATION

Sample size

Data value greater than or equal to 1.5 times 

the IQR outside the box

Largest data value within 1.5 times

the IQR above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times 

the IQR below the box

10

Interquartile

range (IQR) {

Non-airport site—Receives major fraction of discharge from DFW Airport

Airport site—Receives major fraction of discharge from DFW Airport

Laboratory reporting level at 1.0 most-probable number per 100 milliliters

10

5

10

6

10

12

6 10
Occurrence and Distribution of Fecal Indicator Bacteria in Receiving Streams 11

CCDTR, airport GCNAD, airport GCRR, non-airport

GCDTR, and airport SHCBLR (fig. 6). These seven sites 

include all of the sampling sites on Cottonwood Creek and 

Grapevine Creek and one site on South Hackberry Creek. 

Fecal indicator bacteria counts at the three sampling sites 

on Cottonwood Creek (non-airport CCTTR, airport CCBR, 

and non-airport CCDTR) generally increase from upstream to 

downstream (figs. 4, 5). There were no statistically significant 

differences between counts at these three sites, despite the fact 

that the geometric mean E. coli count at the most downstream 

sampling site on Cottonwood Creek (non-airport CCDTR) 

was 1.6 to 1.8 times greater than geometric mean counts at the 

upstream sampling sites. However, small sample sizes (8–10 

per site) likely reduced the power of the Mann-Whitney test to 

indicate differences. In general, small sample sizes reduce the 

power of a statistical test to indicate a difference, if one exists 

(Park, 2004). 

Fecal indicator bacteria counts at the three sampling sites 

on Grapevine Creek (airport GCNAD, airport GCRR, and nonairport GCDTR) decrease from the two upstream sites to the 

most downstream site (figs. 4, 5). There were no statistically 

significant differences between counts at these sites, despite 

the fact that the geometric mean E. coli count at the most 

downstream sampling site on Grapevine Creek (non-airport 

GCDTR) was 1.6 to 1.7 times less than geometric mean counts 

at the upstream sampling sites; but again, small sample sizes 

Figure 4. Boxplots showing variability of fecal coliform counts by site during low-flow conditions in streams in the Elm Fork Trinity 

River watershed that receive discharge from the Dallas/Fort Worth International (DFW) Airport and vicinity, north-central Texas, 

2008. 

CCBR

GCNAD

CCTTR

CCDTR

SAMPLING SITES (FIG. 1)

GCDTR

HCMSC

GCRR

HCCER

MSC

SHCHPR

EFT348

SHCBLR

HCLR

2,000

1,500

1,000

500

0

FECAL COLIFORM COUNTS, IN COLONY FORMING UNITS

PER 100 MILLILITERS

EXPLANATION

Sample size

Data value greater than or equal to 1.5 times 

the IQR outside the box

Largest data value within 1.5 times 

the IQR above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times 

the IQR below the box

5

Interquartile

range (IQR) {

Non-airport site—Receives major fraction of discharge from DFW Airport

Airport site—Receives major fraction of discharge from DFW Airport

Laboratory reporting level at 4.0 colony-forming units per 100 milliliters

8

9

8

8

9

5

9

9

8 9 8

5 8
12 Fecal Indicator Bacteria and Water Quality in Streams, DFW International Airport, Texas, 2008

likely reduced the power of the Mann-Whitney test to indicate 

differences.

The differences in geometric mean E. coli counts between 

the upstream and downstream sites on Cottonwood Creek and 

Grapevine Creek results are relatively large; but the statistical 

tests indicate no significant differences in the counts, although 

the test results here are questionable because of small sample 

sizes. If sample sizes had been larger than 8–10 per site, 30–50 

for example, the statistical tests would have been more definitive. In general, statistical tests using adequate sample sizes 

offer a more defensible basis for comparison of bacteria counts 

between sites than geometric mean values.

All sampling sites on Hackberry Creek, Mud Springs 

Creek, and South Fork Hackberry Creek (except airport site 

SHCBLR) and integrator site EFT348 on Elm Fork Trinity 

River had geometric mean E. coli counts less than the geometric mean contact recreation criterion (fig. 6). SHCBLR drains 

a small watershed (2.9 km2) with about 52 percent of its area 

classified as urban and the remainder classified as agriculture, 

range, or forest (table 2). Airport site SHCBLR site is downstream from a forested area and park that provide habitat for 

small animals. E. coli counts at SHCBLR were significantly 

higher than those at the downstream sampling site on South 

Hackberry Creek (non-airport site SHCHPR).

Figure 5. Boxplots showing variability of Escherichia coli counts by site during low-flow conditions in streams in the Elm Fork Trinity 

River watershed that receive discharge from the Dallas/Fort Worth International (DFW) Airport and vicinity, north-central Texas, 2008. 

CCBR

GCNAD

CCTTR

CCDTR

SAMPLING SITES (FIG. 1)

GCDTR

HCMSC

GCRR

HCCER

MSC

SHCHPR

EFT348

SHCBLR

HCLR

2,000

1,500

1,000

500

0

ESCHERICHIA COLI COUNTS, IN MOST-PROBABLE 

NUMBER PER 100 MILLILITERS 

EXPLANATION

Sample size

Data value greater than or equal to 1.5 times 

the IQR outside the box

Largest data value within 1.5 times 

the IQR above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times 

the IQR below the box

10

Interquartile

range (IQR) {

Non-airport site—Receives major fraction of discharge from DFW Airport

Airport site—Receives major fraction of discharge from DFW Airport

Laboratory reporting level at 1.0 most-probable number per 100 milliliters

10

12

10

9

11

6

10

13

9

9

10

6

10
Occurrence and Distribution of Fecal Indicator Bacteria in Receiving Streams 13

Figure 6. Geometric mean Escherichia coli counts during low-flow conditions at all sampling sites that receive discharge from the 

Dallas/Fort Worth International Airport and vicinity, north-central Texas, 2008. 

DENTON COUNTY

TARRANT COUNTY

§ ̈¦635

§ ̈¦35E

Æÿ183 Æÿ183

Æÿ121

Æÿ114

Æÿ114

Æÿ161

Æÿ121

DALLAS COUNTY

97°06' 97°03' 97°00' 96°57'

33°00'

32°57'

32°54'

32°51'

0 2.5 5 KILOMETERS

Base from Dallas Fort Worth International Airport,

Texas Department of Transportation,

USGS National Hydrography Dataset,

Texas Natural Resources Information System

EXPLANATION

Dallas Fort Worth International (DFW) Airport property

Sampling site and field identifier/geometric mean Escherichia (E.) coli count, in most-probable

number per 100 milliliters—Red font indicates site receives major fraction of discharge from DFW 

Airport. Filled symbol indicates E. coli count greater than and open symbol indicates E. coli count 

less than or equal to Texas Commisssion on Environmental Quality (2008a) contact recreation

criterion (126 colony-forming units [or most-probable number] per 100 milliliters)

CCBR

194

CCBR

194

GCRR

293

CCTTR

211 GCNAD

273

TRIBMD

809

TRIBEG

174

BBC121

189

OF25

209

LBC360

138

BBC183

38

OF19

21.0

CCDTR

356

GCDTR

171

HCCER

62.0

HCMSC

86.0

MSC

4.00

SHCHPR

67

HCLR

60

SHCBLR

185

EFT348

53

TL

66

Mud Springs Creek Hackberry

Creek

Creek

Hackberry

South

Elm

Fork

River Trinity

Creek

Grapevine Creek

Cotto

Cr

nwood eek

Denton

Creek

Cottonwood

Creek

Little

Bear

Creek

Bear

Big

Branch

Dudley

North

Lake

Lake

Grapevine

River

Trinity

West

Fork
14 Fecal Indicator Bacteria and Water Quality in Streams, DFW International Airport, Texas, 2008

Comparison of Escherichia Coli Counts for 

Airport and Non-Airport Discharge Sites

E. coli counts under low-flow conditions for airport 

discharge sites in the lower West Fork Trinity River and Elm 

Fork Trinity River watersheds were compared with counts for 

non-airport discharge sites (fig. 7). E. coli counts for airport 

sites in the lower West Fork Trinity River watershed were 

significantly different from (lower than) E. coli counts for nonairport sites in the lower West Fork Trinity River watershed. 

There was no significant difference between E. coli counts for 

airport sites in the Elm Fork Trinity River watershed and E. 

coli counts for non-airport sites in the Elm Fork Trinity River 

watershed. 

Fecal Coliform and Escherichia Coli Counts 

During Stormflow Conditions

Fecal indicator bacteria counts at downstream integrator sites BBC183 (fig. 8) and EFT348 (fig. 9) during stormflow conditions ranged from 20 to 39,800 cfu/100 mL for 

AIRPORT SITES NON-AIRPORT SITES

5,000

4,500

4,000

3,500

3,000

2,500

2,000

1,500

1,000

500

E. COLI

0

 COUNTS, IN MOST PROBABLE NUMBER PER 100 MILLILITERS 

EXPLANATION

Sample size

Data value greater than or equal to 1.5 times 

the IQR outside the box

Largest data value within 1.5 times 

the IQR above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times 

the IQR below the box

27

Interquartile

range (IQR) {

Lower West Fork Trinity River watershed

Elm Fork Trinity River watershed

Laboratory reporting level at 1.0 most probable

number per 100 milliliters

Airport site—Receives major fraction of discharge from DFW Airport

Non-airport site—Receives major fraction of discharge from DFW Airport

27

63

42

62

Figure 7. Variability of Escherichia coli counts by watershed under low-flow conditions for airport sampling sites and non-airport 

sampling sites in streams that receive discharge from the Dallas/Fort Worth International (DFW) Airport and vicinity, north-central 

Texas, 2008. 
Occurrence and Distribution of Fecal Indicator Bacteria in Receiving Streams 15

fecal coliform and 25 to 43,000 MPN/100 mL for E. coli. 

Maximum counts for both fecal coliform and E. coli

were from samples collected at BBC183. For BBC183, 

median fecal coliform counts and E. coli counts were 4,800 

cfu/100 mL and 4,250 MPN/100 mL, respectively. In contrast, during low-flow conditions median fecal coliform and 

E. coli counts were 58 cfu/100 mL and 57 MPN/100 mL, 

respectively. For EFT348, median fecal coliform and E. coli

counts were 350 cfu/100 mL and 225 MPN/100 mL, respectively. During low-flow conditions, median fecal coliform and 

E. coli counts were 115 cfu/100 mL and 59 MPN/100 mL, 

respectively. 

Counts of fecal indicator bacteria in stormflow samples 

can strongly influence descriptive statistics used to characterize counts in surface water. Geometric mean E. coli counts 

at integrator sites BBC183 and EFT348 during low-flow 

conditions were 38 and 53 MPN/100 mL, respectively (fig. 6). 

Geometric mean E. coli counts at these two sites were 645 

and 203 MPN/100 mL, respectively, when stormflow samples 

were included, which changes the stream-segment classification from fully supporting to not fully supporting contact 

recreation.

The high counts of fecal indicator bacteria in stormflow 

samples at BBC183 and EFT348 are typical of counts at 

other urban sites in the Dallas/Fort Worth area. Stormflow 

samples analyzed for fecal coliform bacteria from small 

watersheds (less than 1.0 km2) during February 1992–June 

1993 had median counts of 20,000 cfu/100 mL in residential 

Figure 8. Variability of fecal coliform and Escherichia coli counts during stormflow conditions in 2008 at integrator site BBC183, the 

most downstream of sampling sites in the lower West Fork Trinity River watershed that receive discharge from the Dallas/Fort Worth 

International Airport and vicinity, north-central Texas. 

FECAL COLIFORM ESCHERICHIA COLI

40,000

30,000

20,000

10,000

0

FECAL COLIFORM COUNTS, IN COLONY FORMING UNITS PER 100 MILLILITERS,

AND E. COLI COUNTS, IN MOST-PROBABLE NUMBER PER 100 MILLILITERS 

EXPLANATION

Sample size

Data value greater than or equal to 1.5 times 

the IQR outside the box

Largest data value within 1.5 times 

the IQR above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times 

the IQR below the box

24

Interquartile

range (IQR) {

23

24
16 Fecal Indicator Bacteria and Water Quality in Streams, DFW International Airport, Texas, 2008

watersheds, 6,900 cfu/100 mL in commercial watersheds, and 

9,700 cfu/100 mL in industrial watersheds (Baldys and others, 

1998, table 3). Maximum fecal coliform bacteria counts in 

these watersheds were 600,000, 810,000, and 290,000 cfu/100 

mL, respectively. At sites monitoring flow from two relatively 

large watersheds, 08048542 Sycamore Creek at Scott Avenue, 

Fort Worth, Tex. (88 km2) and 08049240 Rush Creek at Woodland Park Boulevard, Arlington, Tex. (69 km2

), stormflow 

samples were collected during December 1997–May 2000 

and analyzed for fecal coliform bacteria. Median counts were 

17,000 and 13,000 cfu/100 mL, respectively, and maximums 

were as high as 150,000 cfu/100 mL (U.S. Geological Survey, 

2008).

Physical and Chemical Indicators of 

Water Quality

The physical and chemical water-quality indicators, 

water temperature, DO, pH, specific conductance, ammonia, 

TSS, and chloride, for the classified segments on the lower 

West Fork Trinity River (0841) and the Elm Fork Trinity 

River (0822) were compared with numerical criteria for sitespecific uses (if applicable) in the “2000 Texas Surface Water 

Quality Standards” (Texas Commission on Environmental 

Quality, 2008a). The stream segments sampled for this report 

(except segment 0822 that contains EFT348) are not segments 

Figure 9. Variability of fecal coliform and Escherichia coli counts during stormflow conditions in 2008 at integrator site EFT348, 

the most downstream of sampling sites in the Elm Fork Trinity River watershed that receive discharge from the Dallas/Fort Worth 

International Airport and vicinity, north-central Texas. 

FECAL COLIFORM ESCHERICHIA COLI

8,000

6,000

4,000

2,000

0

FECAL COLIFORM COUNTS, IN COLONY FORMING UNITS PER 100 MILLILITERS,

AND E. COLI COUNTS, IN MOST-PROBABLE NUMBER PER 100 MILLILITERS 

1,000

9,000

7,000

5,000

3,000

EXPLANATION

Sample size

Data value greater than or equal to 1.5 times 

the IQR outside the box

Largest data value within 1.5 times 

the IQR above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times 

the IQR below the box

24

Interquartile

range (IQR) {

23

24
Physical and Chemical Indicators of Water Quality 17

classified by the TCEQ, but they discharge to either segment 

0841 or 0822. Physical and chemical water-quality data are in 

appendixes 1.1 and 1.2.

Water Temperature

Water temperature at all sites ranged from 4.8 °C in 

December to 37.2 °C in July. The distributions and the wide 

interquartile ranges reflect the seasonal variability of water 

temperature measured at all sampling sites (fig. 10). The 

highest water temperature was at airport site MSC, which 

likely is because of channel conditions at this site. MSC 

has a relatively wide, exposed concrete trapezoidal channel. 

The tops of the right and left banks are covered with grasses 

that provide little or no shade. Some of the distributions 

are influenced by a lack of samples during summer. For example, at airport sites OF25, TL, and SHCBLR samples were 

not collected during some summer months because there 

was no flow at these sites at the time of sample collection. 

Figure 10. Variability of water temperature by site in streams receiving discharge from the Dallas/Fort Worth International Airport and 

vicinity, north-central Texas, 2008. 

CCBR

GCNAD

CCTTR

CCDTR

GCDTR

HCMSC

GCRR

HCCER

MSC

SHCHPR

EFT348

SHCBLR

HCLR

TRIBMD

OF25

BBC121

TRIBEG

LBC360

BBC183

OF19

TL

SAMPLING SITES (FIG. 1)

40

30

20

10

0

WATER TEMPERATURE, IN DEGREES CELSIUS 

EXPLANATION

Sample size

Largest data value within 1.5 times 

the IQR above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times 

the IQR below the box

10

Interquartile

range (IQR) {

Sampling site, low-flow conditions

Sampling site, stormflow conditions

Maximum water temperature criterion 35.0 degrees Celsius, lower West Fork Trinity River

watershed (Texas Commission on Environmental Quality, 2008a, p. 59–60)

Maximum water temperature criterion 32.2 degrees Celsius, Elm Fork Trinity River

watershed (Texas Commission on Environmental Quality, 2008a, p. 59–60)

LOWER WEST FORK

TRINITY RIVER WATERSHED

ELM FORK

TRINITY RIVER WATERSHED

10

6

5

11

10

10

6

12

24 10

9

10

12

11 6

10

13

9

9

10

6

10

24
18 Fecal Indicator Bacteria and Water Quality in Streams, DFW International Airport, Texas, 2008

Thus their distributions do not include the high temperatures 

that likely would have been measured had the streams been 

flowing. 

Maximum water temperature criteria for the lower 

West Fork Trinity and the Elm Fork Trinity River segments 

are 35.0 and 32.2 °C, respectively (Texas Commission on 

Environmental Quality, 2008a, p. 59–60). All water temperature measurements at sampling sites in the lower West Fork 

Trinity River watershed were less than the maximum criterion. 

Of the water temperature measurements at sampling sites 

in the Elm Fork Trinity River watershed, 95 percent were 

less than the maximum criterion. Seven measurements were 

greater than 32.2 °C, and more than one-half of those were at 

airport site MSC during June–September 2008.

Dissolved Oxygen

DO concentrations ranged from 4.4 mg/L at non-airport 

site TRIBMD to 17.4 mg/L at non-airport site CCTTR 

(fig. 11). TRIBMD is on the northwest side of DFW Airport 

property, although the contributing area for this site does not 

include airport property (fig. 1). The TRIBMD watershed is 

the smallest sampled at 1.3 km2. he watershed is 96.5-percent 

urban and comprises mostly office buildings and parking 

lots.

Although non-airport site CCTTR had the highest 

measured DO concentration at 17.4 mg/L, the boxplot (fig. 11) 

shows this value as an outlier. DO concentrations at airport 

site MSC frequently were higher than at other sites. Channel 

conditions at CCTTR and MSC likely are responsible for these 

elevated DO concentrations. The concrete trapezoidal channel at MSC usually was covered with a thin layer of algae. 

Samples were collected during daylight when photosynthesis 

was taking place and DO concentrations were elevated. 

DO criteria for classified freshwater stream segments are 

given in terms of minimum averages over a 24-hour period 

and absolute minimums. For this report, point measurements 

were made at the time of sample collection, thus comparisons 

with minimum 24-hour average criteria are not relevant. All 

DO concentrations at all sampling sites during low-flow and 

stormflow conditions were greater than the minimum criterion 

of 4.0 mg/L for stream segments classified as exceptional 

aquatic life use (Texas Commission on Environmental Quality, 

2008d, p. 3–5).

pH

Measurements of pH ranged from a low of 6.1 at integrator site BBC183 to a high of 10.1 at airport site MSC 

(fig. 12). Elevated pH at MSC is consistent with elevated temperature and DO. During photosynthesis, algae use sunlight 

to consume inorganic carbon (carbon dioxide, carbonate, and 

bicarbonate) from solution and increase the pH of the water 

(Snoeyink and Jenkins, 1980). MSC was characterized by the 

presence of algae, elevated temperatures, oxygen production 

during photosynthesis, and elevated pH.

The pH criterion listed in the “2000 Texas Surface Water 

Quality Standards” for the classified segments in the lower 

West Fork Trinity River and the Elm Fork Trinity River is the 

range 6.5–9.0 (Texas Commission on Environmental Quality, 2008a, p. 59–60). One pH measurement, at integrator 

site BBC183 during stormflow conditions, was less than the 

minimum of the criterion range. Most pH measurements at airport site MSC were greater than the maximum of the criterion 

range. All other pH measurements were within the criterion 

range. Ecological consequences can occur as a result of low 

pH (Baker and others, 1996): When pH is between 6.0 and 

6.5, loss of sensitive benthic invertebrates can occur. Between 

5.5 and 6.0, acid-sensitive fish can die or reproduce at reduced 

rates. When surface-water pH is greater than 6.5, there are no 

adverse effects due to acidity.

Specific Conductance and Dissolved Solids

Specific conductance measurements ranged from 251 

microsiemens per centimeter (μS/cm) at integrator site 

BBC183 to 2,020 μS/cm at non-airport site CCTTR (fig. 13). 

Empirical data have demonstrated a strong linear relation 

between specific conductance and dissolved solids concentration, with coefficients mostly between 0.55 and 0.75 (Hem, 

1985, p. 67). If dissolved solids concentration is not available, 

TCEQ currently (2009) uses a coefficient of 0.65 to estimate 

dissolved solids concentrations (in milligrams per liter) from 

specific conductance (in microsiemens per centimeter) (Texas 

Commission on Environmental Quality, 2008d, p. 3–33). 

Boxplots of dissolved solids concentrations thus computed are shown in figure 14. The dissolved solids criteria 

for classified stream segments are given in terms of annual 

averages and are 850 mg/L for the lower West Fork Trinity 

River segment and 500 mg/L for the Elm Fork Trinity 

River segment (Texas Commission on Environmental 

Quality, 2008a, p. 59–60). For sampling sites in the lower 

West Fork Trinity River watershed, all annual averages 

were less than 850 mg/L. For the 13 sampling sites in the 

Elm Fork Trinity River watershed, nine sites (six airport, 

three non-airport) had annual averages that exceeded 500 

mg/L; airport site GCNAD, non-airport site SHCHPR, nonairport site HCLR, and integrator site EFT348 had annual 

averages less than 500 mg/L. Specific conductance, and therefore dissolved solids concentration, typically is higher during 

low-flow conditions, which was more the case for BBC183 

than for EFT348. Dissolved solids concentrations during 

low-flow conditions were significantly higher than concentrations during stormflow conditions on the basis of the MannWhitney test. For EFT348 there was no significant difference 

between low-flow and stormflow dissolved solids concentrations. Discharge at EFT348 depends on dam releases from 

two lakes. Dilution of stormflows through the lakes and lake 

releases likely account for no significant difference between 

the two groups.
Physical and Chemical Indicators of Water Quality 19

Ammonia

Ammonia is a common surface-water constituent. 

Sources of ammonia in surface water include industrial and 

municipal wastewater discharges, agricultural runoff of 

fertilizers, confined animal feeding operations, leaking septic systems, raw sewage spills, urban runoff of fertilizers and 

cleaners, and accidental spills (Texas Commission on Environmental Quality, 2005). Background ammonia concentrations 

are those that can be expected in the absence of substantial 

human influence and are usually less than 0.1 mg/L (Mueller and others, 1995). Ammonia concentrations in untreated 

sewage might exceed 30 mg/L and might approach 5 mg/L 

downstream from wastewater discharges in small streams 

(Maidment, 1993, p. 11.48–11.49). Ammonia toxicity depends 

on pH and water temperature. Its toxicity increases as pH 

and water temperature increase. In alkaline water at high 

temperatures, chronic-exposure criteria can be exceeded by 

CCBR

GCNAD

CCTTR

CCDTR

GCDTR

HCMSC

GCRR

HCCER

MSC

SHCHPR

EFT348

SHCBLR

HCLR

TRIBMD

OF25

BBC121

TRIBEG

LBC360

BBC183

OF19

TL

SAMPLING SITES (FIG. 1)

19

17

13

11

5

DISSOLVED OXYGEN, IN MILLIGRAMS PER LITER 

7

9

15

EXPLANATION

Sample size

Data value greater than or equal to 1.5 times 

the IQR outside the box

Largest data value within 1.5 times 

the IQR above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times 

the IQR below the box

10

Interquartile

range (IQR) {

Sampling site, low-flow conditions

Sampling site, stormflow conditions

Maximum 24-hour average dissolved oxygen criterion 4.0 milligrams per liter for

stream segments 303(d) classified as exceptional aquatic life use (Texas Commission

on Environmental Quality, 2008d, p. 3–5)

LOWER WEST FORK

TRINITY RIVER WATERSHED

ELM FORK

TRINITY RIVER WATERSHED

10 6

5

11

10

10

6

12

24

10

9

10

12 11 6

10

13

9

9

10

6

10

24

Figure 11. Variability of dissolved oxygen concentration by site in streams receiving discharge from the Dallas/Fort Worth International 

Airport and vicinity, north-central Texas, 2008. 
20 Fecal Indicator Bacteria and Water Quality in Streams, DFW International Airport, Texas, 2008

total ammonia concentrations less than 0.1 mg/L (Mueller 

and others, 1995). The screening level for ammonia in 

freshwater streams to support the general uses for unclassified 

water bodies is 0.33 mg/L (Texas Commission on Environmental Quality, 2008d, table 3–10). A water-quality concern is 

identified if this screening level is exceeded more than 

20 percent of the time using the binomial method, based 

on the number of exceedances for a given sample size 

(Texas Commission on Environmental Quality, 2008d, 

p. 3–33).

Ammonia concentrations ranged from less than 0.100 

to 0.809 mg/L (fig. 15). For the boxplots in figure 15, all 

nondetections were set equal to values less than the laboratory 

reporting level so that detected values are represented correctly 

by the boxplot and no information is lost (Helsel, 2005). 

The proportion of the censored data is represented by the 

Figure 12. Variability of pH by site in streams receiving discharge from the Dallas/Fort Worth International Airport and vicinity, northcentral Texas, 2008.

SAMPLING SITES (FIG. 1)

CCBR

GCNAD

CCTTR

CCDTR

GCDTR

HCMSC

GCRR

HCCER

MSC

SHCHPR

EFT348

SHCBLR

HCLR

TRIBMD

OF25

BBC121

TRIBEG

LBC360

BBC183

OF19

TL

9.5

9.0

8.0

7.5

6.0

pH, IN STANDARD UNITS 

6.5

7.0

8.5

10.0

EXPLANATION

Sample size

Data value greater than or equal to 1.5 times 

the IQR outside the box

Largest data value within 1.5 times 

the IQR above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times 

the IQR below the box

10

Interquartile

range (IQR) {

Sampling site, low-flow conditions

Sampling site, stormflow conditions

pH criterion 6.5–9.0 for 303(d)-classified stream segments in lower West Fork Trinity River and Elm Fork

Trinity River watersheds (Texas Commission on Environmental Quality, 2008d, p. 59–60)

LOWER WEST FORK

TRINITY RIVER WATERSHED

ELM FORK

TRINITY RIVER WATERSHED

10

6

5

11 10 12 6 10

24

10 9

10

12

11 6

10

13

9

9

10

6

10

24
Physical and Chemical Indicators of Water Quality 21

amount of data below the reference line. For example, the 

median line for airport site HCCER is not visible in the box; 

therefore, between 50 and 75 percent of the ammonia concentrations were less than 0.100 mg/L. Ammonia concentrations for one storm each at integrator sites BBC183 and 

EFT348 were all less than the laboratory reporting level of 

1.00 mg/L (appendix 1.2); those data were not included in the 

boxplots.

Of 216 low-flow and stormflow samples, 23 samples 

from 12 different sites had concentrations that exceeded 

the screening level for ammonia of 0.33 mg/L. Of these 12 

sites, only one (non-airport site TRIBMD) had more than the 

required number of exceedances to indicate a screening level 

concern. Nine of the 12 sites had only one sample that was 

greater than 0.33 mg/L. 

For the integrator sites BBC183 and EFT348 at 

which stormflow samples were collected in addition to 

low-flow samples, variability of stormflow concentrations 

appears substantially greater than variability of low-flow 

concentrations (fig. 15); but Mann-Whitney tests indicated no 

Figure 13. Variability of specific conductance by site in streams receiving discharge from the Dallas/Fort Worth International Airport 

and vicinity, north-central Texas, 2008. 

SAMPLING SITES (FIG. 1)

CCBR

GCNAD

CCTTR

CCDTR

GCDTR

HCMSC

GCRR

HCCER

MSC

SHCHPR

EFT348

SHCBLR

HCLR

TRIBMD

OF25

BBC121

TRIBEG

LBC360

BBC183

OF19

TL

1,500

1,000

0

SPECIFIC CONDUCTANCE, IN MICROSIEMENS PER 

CENTIMETER AT 25 DEGREES CELSIUS

500

2,000

EXPLANATION

Sample size

Data value greater than or equal to 1.5 times 

the IQR outside the box

Largest data value within 1.5 times 

the IQR above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times 

the IQR below the box

10

Interquartile

range (IQR) {

Sampling site, low-flow conditions

Sampling site, stormflow conditions

LOWER WEST FORK

TRINITY RIVER WATERSHED

ELM FORK

TRINITY RIVER WATERSHED

10

6

5

11

10

10

6

12

24

10

9

10

12

11 6 10 13

9

9

10

6

10 24
22 Fecal Indicator Bacteria and Water Quality in Streams, DFW International Airport, Texas, 2008

significant difference between low-flow and stormflow concentrations for either site. 

Total Suspended Solids

Possible sources of elevated TSS concentrations include 

sewage bypasses, agricultural runoff, urban runoff, and 

construction runoff (Texas Commission on Environmental 

Quality, 2005). TSS concentrations ranged from less than 

4.00 to 851 mg/L (fig. 16). There were two laboratory 

reporting levels for analysis of TSS samples for this report, 

4.00 and 5.00 mg/L; the higher of the two is shown on the 

boxplots of figure 16, which is the reason some values are 

below the reporting-level line. 

Figure 14. Variability of dissolved solids concentration (computed from specific conductance) by site in streams receiving discharge 

from the Dallas/Fort Worth International Airport and vicinity, north-central Texas, 2008. 

SAMPLING SITES (FIG. 1)

CCBR

GCNAD

CCTTR

CCDTR

GCDTR

HCMSC

GCRR

HCCER

MSC

SHCHPR

EFT348

SHCBLR

HCLR

TRIBMD

OF25

BBC121

TRIBEG

LBC360

BBC183

OF19

TL

1,200

1,000

0

DISSOLVED SOLIDS, IN MILLIGRAMS PER LITER

200

1,400

400

600

800

EXPLANATION

Sample size

Data value greater than or equal to 1.5 times 

the IQR outside the box

Largest data value within 1.5 times 

the IQR above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times 

the IQR below the box

10

Interquartile

range (IQR) {

Sampling site, low-flow conditions

Sampling site, stormflow conditions

Dissolved solids criterion 850 milligrams per liter for 303(d)-classified stream segments in lower 

West Fork Trinity River watershed (Texas Commission on Environmental Quality, 2008a, p. 59–60)

Dissolved solids criterion 500 milligrams per liter for 303(d)-classified stream segments in

Elm Fork Trinity River watershed (Texas Commission on Environmental Quality, 2008a, p. 59–60)

LOWER WEST FORK

TRINITY RIVER WATERSHED

ELM FORK

TRINITY RIVER WATERSHED

10

6

5

11

10

10

6

12

24

10

9

10

12

11 6 10 13

9

9

10

6

10 24
Physical and Chemical Indicators of Water Quality 23

All samples collected during low-flow conditions had 

TSS concentrations less than 86 mg/L, and 75 percent were 

less than or equal to 13 mg/L. At the scale of the graph in 

figure 16 (necessitated by a few anomalously large stormflow 

concentrations at integrator site BBC183), the low-flow 

distributions are not visible, but the main point of the boxplots in figure 16 is to show that TSS concentrations during 

low-flow conditions were lower than during stormflow conditions and typical of TSS concentrations in streams and rivers 

nationwide, which commonly range from 10 to 110 mg/L 

(Maidment, 1993, p. 11.13). Mann-Whitney tests indicated 

that stormflow TSS concentrations were significantly higher 

than low-flow concentrations at both BBC183 and EFT348. 

Chloride

Chloride concentrations ranged from less than 5.00 to 

154 mg/L (fig. 17). Chloride criteria for classified stream 

Figure 15. Variability of ammonia nitrogen concentration by site in streams receiving discharge from the Dallas/Fort Worth 

International Airport and vicinity, north-central Texas, 2008. 

SAMPLING SITES (FIG. 1)

CCBR

GCNAD

CCTTR

CCDTR

GCDTR

HCMSC

GCRR

HCCER

MSC

SHCHPR

EFT348

SHCBLR

HCLR

TRIBMD

OF25

BBC121

TRIBEG

LBC360

BBC183

OF19

TL

0.8

0.7

0

AMMONIA, IN MILLIGRAMS PER LITER

0.3

0.9

0.4

0.5

0.6

0.2

0.1

EXPLANATION

Sample size

Data value greater than or equal to 1.5 times 

the IQR outside the box

Largest data value within 1.5 times 

the IQR above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times 

the IQR below the box

10

Interquartile

range (IQR) {

Sampling site, low-flow conditions

Sampling site, stormflow conditions

Screening level 0.33 milligram per liter for ammonia nitrogen in freshwater streams to support

general uses for unclassified water bodies (Texas Commission on Environmental Quality,

2008a, table 3–10)

Laboratory reporting level

LOWER WEST FORK

TRINITY RIVER WATERSHED

ELM FORK

TRINITY RIVER WATERSHED

10

6

5

10

10

10

6

10

16

9 10

9

10 10

6

9

10 9

9

10

6

10

16
24 Fecal Indicator Bacteria and Water Quality in Streams, DFW International Airport, Texas, 2008

segments are given in terms of annual averages. Maximum 

annual average chloride concentration criteria for the lower 

West Fork Trinity and the Elm Fork Trinity River segments 

are 175 and 80 mg/L, respectively (Texas Commission on 

Environmental Quality, 2008a, p. 59–60). For sampling sites 

in the lower West Fork Trinity River watershed, all annual 

averages were below 175 mg/L. For sampling sites in the Elm 

Fork Trinity River watershed, one of the 13 (non-airport site 

CCDTR) had an annual average concentration that exceeded 

80 mg/L. 

Similar to specific conductance and dissolved solids 

concentrations, higher chloride concentrations are common 

during low-flow conditions. Chloride concentrations during 

low-flow conditions at BBC183 were significantly higher than 

concentrations during stormflow conditions. At EFT348, there 

was no significant difference between low-flow and stormflow 

chloride concentrations. 

Figure 16. Variability of total suspended solids concentration by site in streams receiving discharge from the Dallas/Fort Worth 

International Airport and vicinity, north-central Texas, 2008.

SAMPLING SITES (FIG. 1)

CCBR

GCNAD

CCTTR

CCDTR

GCDTR

HCMSC

GCRR

HCCER

MSC

SHCHPR

EFT348

SHCBLR

HCLR

TRIBMD

OF25

BBC121

TRIBEG

LBC360

BBC183

OF19

TL

800

700

0

TOTAL SUSPENDED SOLIDS, IN MILLIGRAMS PER LITER

300

900

400

500

600

200

100

EXPLANATION

Sample size

Data value greater than or equal to 1.5 times 

the IQR outside the box

Largest data value within 1.5 times 

the IQR above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times 

the IQR below the box

10

Interquartile

range (IQR) {

Note: Laboratory reporting level 5.00 milligrams per liter; 4.00 milligrams per liter for some analyses

Sampling site, low-flow conditions

Sampling site, stormflow conditions

Laboratory reporting level

LOWER WEST FORK

TRINITY RIVER WATERSHED

ELM FORK

TRINITY RIVER WATERSHED

10 6 5

10

10 6 10

10

24

10

9

9 10 10

6

10 9 9

9 10

6

10

24
Summary 25

Summary

This report, done by the U.S. Geological Survey in 

cooperation with Dallas/Fort Worth International (DFW) 

Airport in 2008, describes the occurrence and distribution of 

fecal indicator bacteria (fecal coliform and Escherichia [E.] 

coli), and the physical and chemical indicators of water quality 

(relative to Texas Surface Water Quality Standards), in streams 

receiving discharge from DFW Airport and vicinity. The findings are intended to help DFW Airport management better 

understand the extent to which airport discharge is responsible 

for the State 303(d) listing for bacteria of two segments of the 

Trinity River downstream from the airport. Occurrence and 

distribution are described for low-flow conditions on the basis 

of analysis of samples collected at 21 sites, eight in the lower 

West Fork Trinity River watershed and 13 in the Elm Fork 

Trinity River watershed. Four of the eight lower West Fork 

Figure 17. Variability of chloride concentration by site in streams receiving discharge from the Dallas/Fort Worth International Airport 

and vicinity, north-central Texas, 2008. 

SAMPLING SITES (FIG. 1)

CCBR

GCNAD

CCTTR

CCDTR

GCDTR

HCMSC

GCRR

HCCER

MSC

SHCHPR

EFT348

SHCBLR

HCLR

TRIBMD

OF25

BBC121

TRIBEG

LBC360

BBC183

OF19

TL

175

150

0

CHLORIDE, IN MILLIGRAMS PER LITER

50

200

75

100

125

25

EXPLANATION

Sample size

Data value greater than or equal to 1.5 times 

the IQR outside the box

Largest data value within 1.5 times 

the IQR above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times 

the IQR below the box

10

Interquartile

range (IQR) {

Sampling site, low-flow conditions

Sampling site, stormflow conditions

Maximum annual average chloride concentration criterion 175 milligrams per liter, lower West Fork

Trinity River watershed (Texas Commission on Environmental Quality, 2008a, p. 59–60)

Maximum annual average chloride concentration criterion 80 milligrams per liter, Elm Fork Trinity River

watershed (Texas Commission on Environmental Quality, 2008a, p. 59–60)

LOWER WEST FORK

TRINITY RIVER WATERSHED

ELM FORK

TRINITY RIVER WATERSHED

Laboratory reporting level

10

6

5

10

10

10

6

10

24

10

9

9

10

10

6

9

10

9

10 9

6

10

24
26 Fecal Indicator Bacteria and Water Quality in Streams, DFW International Airport, Texas, 2008

Trinity River watershed sites and seven of the 13 Elm Fork 

Trinity River watershed sites are airport discharge sites, or 

airport sites, which for this report means the major fraction of 

discharge at those sites is from DFW Airport. For stormflow 

conditions, occurrence and distribution are described on the 

basis of analysis of samples collected at the two most downstream (integrator) sites in each watershed, each downstream 

from DFW Airport property.

Samples for low-flow conditions were collected almost 

monthly from each of the 21 sites (flow permitting) during 

February–December 2008. Samples for stormflow conditions were collected from the two integrator sites during three 

storms in March, April, and August 2008, respectively. Eight 

samples were collected at each downstream site during the 

three storms. Physical and chemical water-quality data (water 

temperature, dissolved oxygen, pH, specific conductance, 

ammonia nitrogen, total suspended solids [TSS], and chloride) obtained from the low-flow and stormflow samples are 

compared with water-quality criteria supporting the uses for 

the 303(d)-classified segments on the lower West Fork Trinity 

River and the Elm Fork Trinity River.

At sampling sites in the lower West Fork Trinity River 

watershed during low-flow conditions, geometric mean E. coli 

counts for five of the eight West Fork Trinity River watershed sampling sites exceeded the TCEQ E. coli criterion (126 

cfu/100 mL [or MPN/100 mL]), thus not fully supporting contact recreation. Two of the five sites with geometric means that 

exceeded the contact recreation criterion are airport discharge 

sites. Maximum fecal indicator bacteria counts were measured 

for non-airport site TRIBMD on the northwest side of DFW 

Airport property, the contributing area for which does not 

include DFW Airport property. Samples collected downstream 

(after flowing across DFW Airport property) from TRIBMD 

had lower fecal indicator bacteria counts, but geometric mean 

E. coli counts still exceeded the geometric mean contact recreation criterion. One airport site (OF25) on the western side of 

the airport with geometric mean E. coli counts that exceeded 

the geometric mean contact recreation criterion has sanitary 

sewer lines adjacent to the creek and kennels for DFW Airport 

police dogs. Geometric mean E. coli counts at three sites in 

the lower West Fork Trinity River watershed were less than the 

geometric mean contact recreation criterion during low-flow 

conditions. Two of the three are airport sites, and one is the 

most downstream (integrator) site. 

At sampling sites in the Elm Fork Trinity River watershed 

during low-flow conditions, geometric mean E. coli counts 

exceeded the geometric mean contact recreation criterion for 

seven of the 13 sampling sites; of the seven, four were airport 

sites and three were non-airport sites. The seven exceedance 

sites include all sites on Cottonwood Creek (three) and Grapevine Creek (three) and one site on South Hackberry Creek. 

Fecal indicator bacteria counts at the three sampling 

sites on Cottonwood Creek (non-airport, airport, non-airport 

in downstream order) generally increase from upstream 

to downstream; and fecal indicator bacteria counts at the 

three sampling sites on Grapevine Creek (two airport, one 

non-airport in downstream order) decrease from the two 

upstream sites to the most downstream site. For each creek, 

there were no statistically significant differences between 

counts at the three sites, despite the fact that the geometric 

mean E. coli count at the most downstream sampling site on 

each creek was substantially different from geometric mean 

counts at the upstream sampling sites. Small sample sizes 

(8–10 per site) likely reduced the power of the statistical test 

applied (Mann-Whitney) to indicate differences. In general, 

statistical tests using adequate sample sizes offer a more 

defensible basis for comparison of bacteria counts between 

sites than geometric mean values.

E. coli counts under low-flow conditions for airport 

discharge sites in the lower West Fork Trinity River and Elm 

Fork Trinity River watersheds were compared with counts for 

non-airport discharge sites. E. coli counts for airport sites in 

the lower West Fork Trinity River watershed were significantly 

different from (lower than) E. coli counts for non-airport sites 

in the lower West Fork Trinity River watershed. There was no 

significant difference between E. coli counts for airport sites 

in the Elm Fork Trinity River watershed and E. coli counts for 

non-airport sites in the Elm Fork Trinity River watershed. 

During stormflow conditions, fecal indicator bacteria 

counts at the two downstream integrator sites (BBC183 and 

EFT348) were considerably higher than counts at those sites 

during low-flow conditions. When stormflow sample counts 

are included with low-flow sample counts to compute a geometric mean for each site, classification changes from fully 

supporting to not fully supporting contact recreation on the 

basis of the geometric mean contact recreation criterion.

All water temperature measurements at sampling sites in 

the lower West Fork Trinity River watershed were less than 

the maximum criterion for water temperature for the lower 

West Fork Trinity segment (35 °C). Of the measurements at 

sampling sites in the Elm Fork Trinity River watershed, 95 

percent were less than the maximum criterion for water temperature for the Elm Fork Trinity River segment (32.2 °C). All 

measured DO concentrations were greater than the minimum 

criterion of 4.0 mg/L for stream segments classified as exceptional aquatic life use. One pH measurement, at integrator 

site BBC183 during stormflow conditions, was less than the 

minimum of the pH criterion range for the classified segments 

in both watersheds (6.5–9.0). Most pH measurements at airport site MSC were greater than the maximum of the criterion 

range; all other pH measurements were within the range. For 

sampling sites in the lower West Fork Trinity River watershed, 

all annual average dissolved solids concentrations were less 

than the maximum criterion for the lower West Fork Trinity segment (850 mg/L). For sampling sites in the Elm Fork 

Trinity River, nine of the 13 (six airport, three non-airport) had 

annual average dissolved solids concentrations that exceeded 

the maximum criterion for the Elm Fork Trinity segment (500 

mg/L). For ammonia, 23 samples from 12 different sites had 

concentrations that exceeded the screening level for ammonia (0.33 mg/L). Of these 12 sites, only one (non-airport site 

TRIBMD) had more than the required number of exceedances 
References 27

to indicate a screening level concern. Nine of the 12 sites had 

only one sample that exceeded the screening level. MannWhitney tests indicated that stormflow TSS concentrations 

were significantly higher than low-flow concentrations at the 

two integrator sites (BBC183 and EFT348) where both lowflow and stormflow samples were collected. For sampling sites 

in the lower West Fork Trinity River watershed, all annual 

average chloride concentrations were less than the maximum 

annual average chloride concentration criterion for the lower 

West Fork Trinity segment (175 mg/L). For sampling sites in 

the Elm Fork Trinity River watershed, one of the 13 (nonairport site CCDTR) had an annual average concentration that 

exceeded the maximum annual average chloride concentration 

criterion for the Elm Fork Trinity segment (80 mg/L).

References

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Appendix 1—Fecal Indicator Bacteria and Water-Quality Data 

Collected at Sampling Sites on Streams Receiving Discharge 

from Dallas/Fort Worth International Airport and Vicinity, NorthCentral Texas, 2008
Blank Page
Appendix 1.1 31

Appendix 1.1. Fecal indicator bacteria and water-quality data for samples collected during low-flow conditions—Continued.

Field 

identifier 

(fig. 1)

Sample date 

and time

Total 

coliforms1

(MPN/100 

mL)

Fecal 

coliforms1

(cfu/100 mL)

E. coli 1

(MPN/100 

mL)

Ammonia, as 

nitrogen 

(mg/L)

Residue 

(TSS) 

(mg/L)

Total 

chloride 

(mg/L)

Water 

temperature 

(oC)

Dissolved 

oxygen2

(mg/L)

pH 

(standard 

units)

Specific 

conductance 

(μS/cm)

Salinity3

(psu)

Discharge 

(ft3/s)

Stage

(ft)

Lower West Fork Trinity River watershed

BBC121 2/20/2008 11:05 >2,400 TNTC 370 0.170 11.0 26.5 10.6 9.9 7.6 560 0.253 E20 NABBC121 4/7/2008 15:15 >2,400 80.0 140 .139 14.0 83.0 19.5 10.2 7.8 826 .383 E20 NABBC121 5/1/2008 12:25 >2,400 E1,200 1,300 .210 18.0 74.5 19.7 7.9 7.8 852 .396 E15 NABBC121 6/2/2008 12:30 16,000 144 220 .120 10.0 61.5 26.9 6.0 7.8 669 .306 E15 NABBC121 7/7/2008 9:45 8,400 E100 66 .194 17.0 68.0 27.4 4.8 7.6 697 .320 E1.5 NABBC121 8/5/2008 9:10 >2,400 E300 260 <.100 18.0 68.5 28.1 6.2 7.8 668 .305 E1 NABBC121 9/22/2008 10:30 >2,400 E100 130 .155 10.0 63.0 21.7 5.8 7.6 587 .266 E10 NABBC121 10/29/2008 10:25 1,700 50.0 72 .333 6.00 52.0 12.0 6.0 7.1 594 .270 E8 NABBC121 11/18/2008 10:35 >2,400 NA 120 .206 9.00 52.0 11.3 9.4 7.7 579 .262 E13 NABBC121 12/2/2008 10:55 >2,400 E160 200 <.100 5.00 36.0 7.5 9.8 7.8 603 .274 E13 NATRIBMD 2/20/2008 11:30 1,600 8.00 1.0 .622 48.0 31.0 12.9 6.9 7.7 890 .415 <.3 NATRIBMD 4/7/2008 17:20 >2,400 TNTC 1,100 .691 <5.00 65.5 18.1 7.3 7.6 747 .344 <.2 NATRIBMD 5/1/2008 12:55 >2,400 TNTC >2,400 .484 6.50 70.8 19.8 6.8 7.8 1,130 .535 E1 NATRIBMD 6/2/2008 13:05 31,000 3,000 4,100 .274 7.00 71.3 24.1 5.9 7.7 1,200 .570 E1 NATRIBMD 7/7/2008 10:15 79,000 8,500 4,900 .459 11.0 87.5 24.3 4.4 7.9 1,270 .605 <1 NATRIBMD 8/5/2008 9:35 120,000 4,100 3,200 <.100 <4.00 69.5 25.4 5.8 7.7 1,140 .540 <1 NATRIBMD 9/22/2008 11:05 73,000 E2,600 1,400 .133 5.00 55.0 22.6 6.4 8.0 836 .388 <1 NATRIBMD 10/29/2008 10:45 460 2,600 740 .354 <4.00 64.5 13.4 7.2 7.2 914 .427 <1 NATRIBMD 11/18/2008 11:00 39,000 NA 1,900 .384 4.00 81.5 13.6 7.0 7.8 1,080 .509 <1 NATRIBMD 11/18/2008 11:01 55,000 NA 2,200 NA NA NA 13.6 7.0 7.8 1,080 .509 <1 NATRIBMD 12/2/2008 11:25 2,200 260 390 .457 14.5 31.5 12.9 8.8 7.9 681 .312 <1 NATRIBEG 2/20/2008 10:45 1,600 68.0 100 <.100 <5.00 33.0 12.4 12.6 8.2 510 .229 E.3 NATRIBEG 4/7/2008 14:58 >2,400 79.0 120 .136 7.00 41.0 23.0 10.9 7.8 699 .321 E4 NATRIBEG 5/1/2008 12:03 >2,400 E216 290 <.100 <5.00 45.0 21.1 9.8 7.6 773 .357 E2 NATRIBEG 6/2/2008 12:05 >2,400 180 160 .809 7.00 70.5 26.5 6.1 6.9 1,610 .779 <1 NATRIBEG 12/2/2008 10:35 >2,400 E150 290 <.100 9.00 45.0 11.0 4.9 6.9 1,180 .560 E1.5 NAOF25 2/20/2008 10:20 >2,400 172 150 .202 23.0 53.5 10.1 9.3 7.4 925 .432 <1 NAOF25 4/7/2008 14:20 >2,400 TNTC 530 .104 9.50 42.8 19.0 9.5 7.6 1,170 .555 E3 NA

Appendix 1.1 Appendix 1.1. Fecal indicator bacteria and water-quality data for samples collected during low-flow conditions. [Bold font indicates field duplicate; MPN/100 mL, most-probable number per 100 milliliters; cfu/100 mL, colony-forming units per 100 milliliters; E., Escherichia; mg/L, milligrams per liter; TSS, total sus- pended solids; °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 degrees Celsius; psu, practical salinity units; ft3/s, cubic feet per second; ft, feet; >, greater than; TNTC, too numerous to count; E, 

estimated; NA, not available; <, less than laboratory reporting level] 
32 Fecal Indicator Bacteria and Water Quality in Streams, DFW International Airport, Texas, 2008 Appendix 1.1. Fecal indicator bacteria and water-quality data for samples collected during low-flow conditions—Continued. Field identifier (fig. 1) Sample date and time Total coliforms1 (MPN/100 mL) Fecal coliforms1 (cfu/100 mL) E. coli 1 (MPN/100 mL) Ammo- nia, as nitrogen (mg/L) Residue (TSS) (mg/L) Total chloride (mg/L) Water tempera- ture (oC) Dis- solved oxygen2 (mg/L) pH (standard units) Specific conduc- tance (μS/cm) Salinity3 (psu) Discharge (ft3/s) Stage (ft) Lower West Fork Trinity River watershed—Continued OF25 5/1/2008 11:25 >2,400 TNTC 1,200 0.131 5.00 45.8 18.7 7.6 7.4 1,290 0.616 E4 NA OF25 6/2/2008 11:35 18,000 416 860 .103 <5.00 47.0 24.5 7.1 7.7 1,180 .560 E2 NA OF25 11/18/2008 10:05 920 NA 8.5 .568 9.00 45.0 10.1 10.0 7.7 1,110 .525 <1 NA OF25 12/2/2008 10:15 2,400 E110 120 <.100 <4.00 <5.00 6.1 10.5 7.7 684 .313 E2 NA OF19 2/20/2008 9:15 1,400 E20.0 9.8 .137 <5.00 17.0 11.1 11.4 8.0 1,230 .585 <1 NA OF19 4/7/2008 13:00 >2,400 22.0 18 <.100 <5.00 19.0 21.0 13.5 7.9 1,170 .555 E3 NA OF19 5/1/2008 9:57 >2,400 E26.0 19 <.100 <5.00 21.0 20.3 9.3 7.8 1,190 .565 E3 NA OF19 6/2/2008 10:20 2,000 8.00 18 .113 <5.00 27.5 26.6 8.4 7.9 1,380 .661 E1 NA OF19 7/7/2008 8:15 8,100 E120 58 .106 8.00 30.0 27.0 6.1 7.6 1,350 .646 <1 NA OF19 8/5/2008 7:45 >2,400 E56.0 74 <.100 8.00 23.5 28.2 6.5 7.4 1,040 .489 <1 NA OF19 9/22/2008 9:15 >2,400 20.0 9.8 <.100 <4.00 35.0 21.6 7.9 7.7 877 .408 E1 NA OF19 10/29/2008 9:10 >2,400 4.00 5.2 .168 <4.00 33.5 11.4 11.3 7.0 1,560 .754 <1 NA OF19 11/18/2008 8:50 >2,400 NA 40 <.100 5.00 21.8 10.5 10.1 7.8 1,390 .667 <1 NA OF19 12/2/2008 9:00 >2,400 E140 37 <.100 12.0 16.0 6.3 10.6 7.8 935 .437 <1 NA LBC360 2/20/2008 10:00 >2,400 218 240 .202 6.00 56.5 11.0 10.6 7.6 659 .301 E8 NA LBC360 4/7/2008 13:58 >2,400 88.0 67 .151 5.00 99.5 21.2 12.6 8.0 1,000 .469 E17 NA LBC360 5/1/2008 10:50 >2,400 E148 140 .298 32.0 79.5 20.2 10.1 7.8 875 .407 E10 NA LBC360 6/2/2008 11:10 >2,400 144 200 .152 <5.00 62.5 26.6 9.3 7.9 681 .312 E10 NA LBC360 7/7/2008 8:55 >2,400 E260 250 .105 5.00 63.5 26.3 7.4 7.7 671 .307 <1 NA LBC360 8/5/2008 8:20 11,000 E134 130 <.100 <4.00 57.5 27.4 6.2 7.6 692 .317 E1 NA LBC360 8/5/2008 8:24 6,800 NA 140 NA NA NA 27.4 6.2 7.6 692 .317 E1 NA LBC360 9/22/2008 9:50 >2,400 600 390 .186 <4.00 57.0 22.4 9.6 7.9 338 .148 E8 NA LBC360 10/29/2008 9:45 1,500 44.0 52 .213 42.0 70.0 11.3 11.2 7.3 853 .396 E5 NA

LBC360 10/29/2008 9:46 1,600 NA 38 NA NA NA 11.3 11.2 7.3 853 .396 E5 NALBC360 11/18/2008 9:45 >2,400 NA 200 .423 4.00 77.0 11.5 9.5 7.6 737 .339 E7 NALBC360 12/2/2008 9:50 >2,400 E100 150 <.100 4.00 52.0 7.4 10.5 7.7 585 .265 E7 NATL 2/20/2008 9:45 2,400 48.0 50 .123 <5.00 19.5 10.3 9.5 7.6 515 .232 <1 NATL 4/7/2008 13:28 >2,400 105 120 .135 9.00 17.5 18.4 8.4 7.7 619 .282 E2 NATL 5/1/2008 10:25 >2,400 E44.0 53 .111 6.00 16.0 19.0 7.5 7.6 657 .300 E2 NATL 6/2/2008 10:45 >2,400 68.0 140 .164 <5.00 16.0 25.4 5.0 7.8 478 .214 E1 NATL 11/18/2008 9:20 >2,400 NA 32 .332 8.00 17.0 10.9 8.6 8.0 371 .163 <1 NATL 12/2/2008 9:25 2,000 E30 60 <.100 <4.00 15.0 7.4 9.4 7.8 482 .216 E1.5 NA
Appendix 1.1 33

Appendix 1.1. Fecal indicator bacteria and water-quality data for samples collected during low-flow conditions—Continued.

Field 

identifier 

(fig. 1)

Sample date 

and time

Total 

coliforms1

(MPN/100 

mL)

Fecal 

coliforms1

(cfu/100 mL)

E. coli 1

(MPN/100 

mL)

Ammonia, as 

nitrogen 

(mg/L)

Residue 

(TSS) 

(mg/L)

Total 

chloride 

(mg/L)

Water 

temperature 

(oC)

Dissolved 

oxygen2

(mg/L)

pH 

(standard 

units)

Specific 

conductance 

(μS/cm)

Salinity3

(psu)

Discharge 

(ft3/s)

Stage

(ft)

Lower West Fork Trinity River watershed—Continued

BBC183 2/20/2008 8:40 >2,400 E400 210 0.266 8.00 60.0 9.8 10.4 7.7 601 0.273 E20 6.22

BBC183 4/7/2008 12:25 >2,400 67.0 64 .146 9.00 78.0 18.9 10.2 8.0 860 .400 E45 6.07BBC183 5/1/2008 9:30 >2,400 E58.0 71 <.100 5.00 65.5 19.6 8.6 8.0 858 .399 E15 6.26BBC183 6/2/2008 9:45 >2,400 E40.0 120 .118 11.0 57.0 26.7 6.7 7.9 649 .296 E15 5.80BBC183 7/7/2008 7:45 >2,400 E38.0 19 .111 12.0 75.5 28.0 5.4 7.4 780 .360 E3 5.41BBC183 8/5/2008 7:10 >2,400 E98.0 19 <.100 5.00 48.5 29.2 6.0 6.8 581 .263 E1 NABBC183 9/22/2008 8:40 >2,400 10.0 13 .173 16.0 46.0 23.5 7.4 7.8 497 .223 E12 NABBC183 10/29/2008 8:45 550 7.00 3.1 .203 <4.00 43.0 12.7 8.3 6.6 587 .266 E4 5.50BBC183 11/18/2008 8:20 >2,400 NA 50 .234 12.0 44.0 11.7 9.6 7.6 596 .271 E8 5.06BBC183 12/2/2008 8:30 >2,400 E200 81 <.100 4.00 58.0 7.1 11.0 7.4 688 .315 E11 5.71

Elm Fork Trinity River watershed

CCTTR 2/20/2008 12:00 >2,400 66.0 42 .147 6.00 45.5 16.9 17.4 8.3 1,580 .764 <1 NACCTTR 4/7/2008 16:50 >2,400 192 200 .134 <5.00 66.0 22.4 10.4 8.1 1,870 .914 <.2 NACCTTR 5/1/2008 15:44 >2,400 38.0 150 .130 22.0 50.5 23.5 9.2 8.0 1,610 .779 E.8 NACCTTR 6/2/2008 13:30 >2,400 116 250 .160 8.00 68.0 31.5 9.0 8.0 2,020 .992 <.2 NACCTTR 7/7/2008 10:47 17,000 700 860 <.100 10.0 59.0 31.4 11.2 8.0 1,660 .805 <.2 NACCTTR 9/22/2008 13:28 18,000 200 610 <.100 <4.00 46.0 27.0 10.0 7.9 1,680 .816 <.2 NACCTTR 10/29/2008 12:35 5,000 218 190 .161 4.00 69.0 15.4 11.0 7.9 1,490 .718 <.2 NACCTTR 11/18/2008 14:00 4,100 NA 310 .154 <4.00 60.0 13.7 12.1 8.0 1,870 .914 <.2 NACCTTR 11/18/2008 14:02 1,100 NA 140 NA NA NA 13.7 12.1 8.0 1,870 .914 <.2 NACCTTR 12/2/2008 14:15 3,300 360 130 <.100 <4.00 52.0 10.7 E11.9 8.1 1,600 .774 <.2 NACCBR 2/20/2008 13:30 >2,400 50.0 96 .111 6.00 21.0 13.0 11.2 7.4 745 .343 E.2 NACCBR 4/7/2008 15:06 >2,400 57.0 62 <.100 5.00 35.0 21.8 10.3 7.7 990 .464 <.2 NACCBR 5/1/2008 13:19 >2,400 100 210 .276 49.0 34.5 20.6 9.4 7.8 1,200 .570 E.2 NACCBR 6/2/2008 13:00 >2,400 572 1,300 .164 9.00 49.5 28.9 10.5 7.3 1,230 .585 <.2 NACCBR 7/7/2008 10:22 46,000 282 300 .183 16.0 52.5 28.1 7.8 7.3 1,020 .479 <.2 NACCBR 9/22/2008 11:17 6,200 E120 60 <.100 <4.00 35.0 22.7 7.1 7.9 751 .346 <.2 NACCBR 10/29/2008 13:05 6,400 196 230 .111 <4.00 28.8 12.9 7.8 7.7 767 .354 <.2 NACCBR 11/18/2008 13:40 1,100 NA 61 .230 <4.00 25.0 12.3 6.9 7.6 747 .344 <.2 NACCBR 12/2/2008 13:50 11,000 1,600 960 <.100 6.00 22.0 10.5 E8.2 7.7 634 .289 <.2 NA
34 Fecal Indicator Bacteria and Water Quality in Streams, DFW International Airport, Texas, 2008 Appendix 1.1. Fecal indicator bacteria and water-quality data for samples collected during low-flow conditions—Continued. Field identifier (fig. 1) Sample date and time Total coliforms1 (MPN/100 mL) Fecal coliforms1 (cfu/100 mL) E. coli 1 (MPN/100 mL) Ammo- nia, as nitrogen (mg/L) Residue (TSS) (mg/L) Total chloride (mg/L) Water tempera- ture (oC) Dis- solved oxygen2 (mg/L) pH (standard units) Specific conduc- tance (μS/cm) Salinity3 (psu) Discharge (ft3/s) Stage (ft) Elm Fork Trinity River watershed—Continued CCDTR 2/20/2008 14:00 >2,400 98.0 73 <.100 5.00 102 14.1 10.3 7.8 1,470 0.707 E4 NA CCDTR 4/7/2008 14:05 >2,400 TNTC 1,400 .256 <5.00 15.5 18.8 9.7 7.9 1,620 .785 E5 NA CCDTR 5/1/2008 12:47 >2,400 1,300 1,100 .129 25.0 115 19.2 8.5 7.9 1,570 .759 E6 NA CCDTR 6/2/2008 12:15 31,000 1,000 910 .113 13.0 108 24.0 7.3 7.9 1,490 .718 E2.5 NA CCDTR 7/7/2008 9:43 5,500 E264 310 .104 8.50 131 25.2 6.0 7.6 1,700 .826 E3 NA CCDTR 8/5/2008 9:38 5,000 178 260 <.100 <4.00 154 27.0 5.4 7.5 1,740 .847 E1 NA CCDTR 9/22/2008 10:50 7,600 E100 170 <.100 <4.00 115 22.6 7.4 7.8 872 .406 E2 NA CCDTR 10/29/2008 10:40 5,300 96.0 70 .113 <4.00 128 13.0 9.5 7.7 1,520 .733 E2 NA CCDTR 11/18/2008 13:15 920 NA 350 <.100 5.00 119 12.7 9.5 8.0 1,520 .733 E2 NA CCDTR 12/2/2008 13:25 4,900 1,280 960 <.100 13.0 101 8.9 E10.0 7.9 1,420 .682 E5 NA GCNAD 2/20/2008 12:20 >2,400 17.0 31 .115 <5.00 19.0 14.3 11.7 7.7 944 .441 E2 NA GCNAD 4/7/2008 15:45 >2,400 TNTC 170 .103 20.0 18.0 24.2 10.9 7.7 879 .409 E2 NA GCNAD 4/7/2008 15:46 >2,400 136 160 NA NA NA 24.2 10.9 7.7 879 .409 E2 NA GCNAD 5/1/2008 13:30 >2,400 280 550 .253 8.00 21.5 21.2 8.2 7.5 860 .400 E5 NA GCNAD 6/2/2008 13:40 16,000 100 190 <.100 11.0 19.5 29.5 5.5 7.4 1,250 .595 <1 NA GCNAD 7/7/2008 10:50 7,000 64.0 61 .107 15.0 10.0 26.6 5.1 7.4 673 .308 <.5 NA GCNAD 8/5/2008 10:15 14,000 800 540 <.100 23.0 7.50 28.7 7.0 7.5 574 .260 <1 NA GCNAD 9/22/2008 11:37 17,000 E1,800 660 .130 <4.00 22.5 22.6 6.6 7.6 316 .138 <1 NA GCNAD 9/22/2008 11:40 14,000 NA 690 NA NA NA 22.6 6.6 7.6 316 .138 <1 NA GCNAD 10/29/2008 11:15 2,900 500 280 .324 11.0 6.50 10.8 6.3 7.1 443 .197 <1 NA GCNAD 11/18/2008 11:35 5,300 NA 1,100 .199 15.0 20.0 10.5 8.0 7.6 868 .404 <1 NA GCNAD 12/2/2008 11:55 16,000 460 420 <.100 12.0 12.0 6.0 8.4 7.6 547 .247 E1 NA GCRR 2/20/2008 13:05 >2,400 E52.0 50 .106 8.00 25.5 17.4 11.6 8.1 716 .329 E.6 NA

GCRR 4/7/2008 15:34 >2,400 73.0 110 .203 5.50 28.5 27.6 8.5 8.1 692 .317 E.2 NAGCRR 5/1/2008 15:06 >2,400 112 260 .145 35.0 21.5 26.3 9.1 8.2 739 .340 E1 NAGCRR 6/2/2008 15:22 >2,400 116 120 .142 6.00 28.5 32.7 8.7 8.1 498 .223 E.2 NAGCRR 7/7/2008 12:18 11,000 1,300 750 .155 11.0 47.5 29.4 8.5 7.7 871 .405 E.2 NAGCRR 8/5/2008 10:10 19,000 600 290 <.100 4.00 51.5 27.4 6.7 7.5 824 .382 E.2 NAGCRR 9/22/2008 14:05 8,600 500 340 .294 11.0 46.5 25.1 9.3 8.0 933 .436 <.2 NAGCRR 9/22/2008 14:07 15,000 NA 340 NA NA NA 25.1 9.3 8.0 933 .436 <.2 NAGCRR 10/29/2008 13:30 14,000 500 530 .131 <4.00 58.0 13.9 9.7 7.8 1,120 .530 <.2 NAGCRR 11/18/2008 14:30 8,100 NA 310 .147 4.00 47.0 12.5 10.3 7.9 890 .415 <.2 NAGCRR 12/2/2008 11:10 20,000 2,160 1,900 <.100 16.0 19.0 6.3 E10.2 7.8 661 .302 E.5 NA
Appendix 1.1 35

Appendix 1.1. Fecal indicator bacteria and water-quality data for samples collected during low-flow conditions—Continued.

Field 

identifier 

(fig. 1)

Sample date 

and time

Total 

coliforms1

(MPN/100 

mL)

Fecal 

coliforms1

(cfu/100 mL)

E. coli 1

(MPN/100 

mL)

Ammonia, as 

nitrogen 

(mg/L)

Residue 

(TSS) 

(mg/L)

Total 

chloride 

(mg/L)

Water 

temperature 

(oC)

Dissolved 

oxygen2

(mg/L)

pH 

(standard 

units)

Specific 

conductance 

(μS/cm)

Salinity3

(psu)

Discharge 

(ft3/s)

Stage

(ft)

Elm Fork Trinity River watershed—Continued

GCDTR 2/20/2008 14:25 2,000 56.0 63 0.110 <5.00 16.0 16.2 12.0 7.6 875 0.407 E4 NAGCDTR 4/7/2008 14:43 >2,400 21.0 390 .158 <5.00 49.0 23.3 10.9 7.7 1,040 .489 E5 NAGCDTR 5/1/2008 12:11 9,700 357 370 .210 <5.00 53.3 21.6 10.8 7.6 1,050 .494 E4 NAGCDTR 6/2/2008 11:38 >2,400 180 300 .102 <5.00 59.5 27.9 10.0 7.7 1,010 .474 E2 NAGCDTR 6/2/2008 11:39 11,000 NA 240 NA NA NA 27.9 10.0 7.7 1,010 .474 E2 NAGCDTR 7/7/2008 9:12 8,100 E174 250 .121 5.00 45.5 25.5 7.3 7.2 855 .397 E2 NAGCDTR 8/5/2008 9:15 10,000 E144 68 <.100 <4.00 44.5 27.1 6.7 7.0 815 .378 E2 NAGCDTR 9/22/2008 10:20 7,000 E104 92 <.100 6.00 54.0 22.9 10.1 7.5 999 .469 E2 NAGCDTR 9/22/2008 10:22 5,900 NA 34 NA NA NA 22.9 10.1 7.5 999 .469 E2 NAGCDTR 10/29/2008 10:15 3,900 280 410 .107 <4.00 56.0 13.0 11.8 7.5 966 .452 E3 NAGCDTR 10/29/2008 10:17 1,400 NA 310 NA NA NA 13.0 11.8 7.5 966 .452 E3 NAGCDTR 11/18/2008 12:55 3,300 NA 110 .117 <4.00 52.0 13.5 11.4 7.6 689 .316 E5 NAGCDTR 12/2/2008 13:00 1,300 150 220 <.100 <4.00 40.0 9.6 E11.4 7.6 857 .398 E5 NAHCCER 2/20/2008 15:00 1,400 4.00 6.3 <.100 <5.00 14.5 15.8 10.3 7.8 1,000 .469 E1 NAHCCER 4/7/2008 17:50 2,000 10.0 9.7 <.100 <5.00 21.5 23.2 8.7 7.8 1,080 .509 E.2 NAHCCER 5/1/2008 17:12 >2,400 74.0 91 .152 <5.00 16.5 23.9 8.1 7.9 1,070 .504 E.2 NAHCCER 5/1/2008 17:14 >2,400 68.0 110 NA NA NA 23.9 8.1 7.9 1,070 .504 E.2 NAHCCER 6/2/2008 15:56 >2,400 1,900 2,000 .147 <5.00 23.5 33.2 5.9 7.8 1,090 .514 E.2 NAHCCER 7/7/2008 12:44 7,100 10.0 10 .125 <4.00 24.5 31.9 9.9 7.9 1,090 .514 <.2 NAHCCER 9/22/2008 14:35 13,000 150 340 <.100 <4.00 13.0 26.8 8.0 7.9 850 .395 <.2 NAHCCER 10/29/2008 13:55 >2,400 168 170 .107 7.00 22.0 16.4 8.2 7.8 926 .432 <.2 NAHCCER 11/18/2008 11:10 2,400 NA 60 <.100 <4.00 23.0 14.2 9.4 7.9 1,020 .479 <.2 NAHCCER 12/2/2008 10:45 >2,400 E90 20 <.100 12.0 11.5 7.3 E10.3 7.9 849 .394 <.2 NAHCMSC 2/20/2008 15:25 2,400 14.0 22 <.100 6.00 30.5 16.1 10.5 7.9 952 .445 E2 NAHCMSC 4/7/2008 18:23 >2,400 42.0 54 .179 5.00 19.0 25.2 8.6 8.0 1,020 .479 <.2 NAHCMSC 5/1/2008 16:20 >2,400 104 110 .165 52.0 19.5 27.2 8.3 8.0 888 .414 E.8 NAHCMSC 6/2/2008 16:40 >2,400 68.0 110 .521 86.0 33.0 32.8 6.4 8.2 648 .296 E.2 NAHCMSC 11/18/2008 10:30 >2,400 NA 96 <.100 <4.00 31.0 9.7 10.6 7.9 1,140 .540 <.2 NAHCMSC 12/2/2008 10:00 >2,400 E190 290 <.100 <4.00 19.0 4.8 E12.0 7.9 853 .396 <.2 NAMSC 2/20/2008 15:45 >2,400 8.00 9.8 .141 12.0 15.5 20.1 15.7 9.0 945 .442 E.5 NAMSC 4/7/2008 18:38 1,300 15.0 16 .217 <5.00 29.5 26.6 12.3 10.0 1,290 .616 E1.5 NA
36 Fecal Indicator Bacteria and Water Quality in Streams, DFW International Airport, Texas, 2008 Appendix 1.1. Fecal indicator bacteria and water-quality data for samples collected during low-flow conditions—Continued. Field identifier (fig. 1) Sample date and time Total coliforms1 (MPN/100 mL) Fecal coliforms1 (cfu/100 mL) E. coli 1 (MPN/100 mL) Ammo- nia, as nitrogen (mg/L) Residue (TSS) (mg/L) Total chloride (mg/L) Water tempera- ture (oC) Dis- solved oxygen2 (mg/L) pH (standard units) Specific conduc- tance (μS/cm) Salinity3 (psu) Discharge (ft3/s) Stage (ft) Elm Fork Trinity River watershed—Continued MSC 5/1/2008 16:40 370 <2.00 1.0 .177 <5.00 23.0 31.0 11.8 10.1 1,300 .621 E2 NA MSC 6/2/2008 16:50 310 <4.00 <1.0 0.212 <5.00 34.5 35.6 11.8 10.0 1,410 0.677 E.2 NA MSC 7/7/2008 13:20 46 <2.00 <1.0 .248 6.00 40.0 37.2 11.8 9.7 834 .387 E.2 NA MSC 8/5/2008 12:12 >2,400 <2.00 <1.0 <.100 4.00 47.5 36.6 12.5 9.4 1,440 .692 E.2 NA MSC 9/22/2008 15:00 980 1.00 1.0 .157 8.00 28.0 33.0 13.3 9.9 1,290 .616 <.2 NA MSC 10/29/2008 14:30 NA NA NA NA NA NA NA NA NA NA NA E14 NA MSC 11/18/2008 10:40 2,400 NA 82 .170 <4.00 33.5 14.6 17.3 8.8 838 .389 <.3 NA MSC 12/2/2008 10:15 >2,400 E170 96 <.100 <4.00 28.0 9.1 E17.1 8.6 873 .406 <.2 NA SHCBLR 2/20/2008 16:20 >2,400 30.0 60 .467 8.00 20.0 15.3 12.0 7.9 1,560 .754 E.2 NA SHCBLR 4/7/2008 12:22 >2,400 89.0 180 .190 18.0 52.5 18.9 8.4 7.6 1,830 .893 <.2 NA SHCBLR 5/1/2008 9:40 >2,400 E250 180 .150 12.0 87.0 19.6 8.6 7.6 1,400 .672 <.2 NA SHCBLR 10/29/2008 8:35 >2,400 400 210 .129 9.00 44.0 10.6 5.5 7.4 1,170 .555 <.2 NA SHCBLR 11/18/2008 8:35 >2,400 NA 170 .233 10.5 67.5 9.9 7.9 7.6 1,430 .687 <.2 NA SHCBLR 12/2/2008 8:22 >2,400 E540 580 <.100 <4.00 73.0 5.4 E12.7 7.7 1,850 .904 <.2 NA SHCHPR 2/25/2008 14:20 2,600 29.0 36 .296 25.0 19.5 16.8 8.5 7.2 706 .324 E.2 NA SHCHPR 4/7/2008 12:45 2,400 169 41 .151 15.0 21.5 18.9 9.9 8.2 749 .345 <.5 NA SHCHPR 5/1/2008 10:24 >2,400 E21.7 38 .324 15.0 13.8 20.8 9.2 8.4 527 .237 <.2 NA SHCHPR 6/2/2008 9:42 >2,400 E72.0 150 .179 12.0 17.5 28.0 8.1 8.4 526 .237 <.2 NA SHCHPR 7/7/2008 7:55 >2,400 E42.0 33 .168 11.0 30.5 29.1 6.3 7.0 644 .294 E.2 NA SHCHPR 8/5/2008 7:18 2,000 E200 99 <.100 5.00 33.5 30.8 7.3 7.1 659 .301 <.2 NA SHCHPR 9/22/2008 8:55 >2,400 E200 53 .236 <4.00 31.5 24.7 6.9 7.6 559 .253 <.2 NA SHCHPR 10/29/2008 9:00 1,600 70.0 45 .111 7.00 18.5 15.3 8.6 7.9 482 .216 <.5 NA SHCHPR 11/18/2008 9:00 >2,400 NA 690 .392 46.0 12.0 13.2 6.6 7.7 412 .183 <.5 NA

SHCHPR 12/2/2008 8:45 2,400 E30 41 <.100 13.0 13.0 8.8 E10.6 8.0 504 .226 <.2 NAHCLR 2/20/2008 17:10 >2,400 230 160 .199 52.0 18.5 10.7 9.1 7.6 318 .139 E6 NAHCLR 4/7/2008 13:10 >2,400 102 170 .164 30.0 9.50 19.9 9.1 8.1 426 .189 E1 NAHCLR 5/1/2008 10:48 >2,400 E100 73 .487 71.0 10.5 20.6 7.7 7.7 412 .183 E1 NAHCLR 6/2/2008 10:14 >2,400 76.0 210 .145 14.0 19.0 25.8 5.6 7.8 292 .127 <.2 NAHCLR 8/5/2008 7:57 >2,400 E6.00 4.1 <.100 14.0 33.5 30.3 5.8 7.4 637 .290 E1.3 NAHCLR 9/22/2008 9:18 >2,400 E100 5.2 .127 14.0 33.0 24.6 7.4 8.2 543 .245 E.5 NAHCLR 10/29/2008 9:20 2,400 54.0 76 .174 22.0 26.0 15.1 8.8 7.8 541 .244 E5 NA
Appendix 1.1 37

Appendix 1.1. Fecal indicator bacteria and water-quality data for samples collected during low-flow conditions—Continued.

Field 

identifier 

(fig. 1)

Sample date 

and time

Total 

coliforms1

(MPN/100 

mL)

Fecal 

coliforms1

(cfu/100 mL)

E. coli 1

(MPN/100 

mL)

Ammonia, as 

nitrogen 

(mg/L)

Residue 

(TSS) 

(mg/L)

Total 

chloride 

(mg/L)

Water 

temperature 

(oC)

Dissolved 

oxygen2

(mg/L)

pH 

(standard 

units)

Specific 

conductance 

(μS/cm)

Salinity3

(psu)

Discharge 

(ft3/s)

Stage

(ft)

Elm Fork Trinity River watershed—Continued

HCLR 11/18/2008 9:33 >2,400 NA 160 .181 51.0 10.0 13.6 9.4 8.1 264 .114 E5 NAHCLR 12/2/2008 9:10 13,000 E100 89 .216 13.0 10.0 8.6 E11.5 8.2 363 .160 E3 NAEFT348 2/20/2008 17:35 >2,400 350 140 0.190 37.0 77.5 10.8 9.4 7.6 399 0.176 123 11.70EFT348 4/7/2008 13:35 >2,400 TNTC 44 .250 37.0 19.5 16.6 9.6 8.0 365 .160 3,279 17.00EFT348 5/1/2008 11:20 >2,400 E100 68 .257 42.0 18.0 19.4 9.2 8.0 362 .159 3,445 17.27EFT348 6/2/2008 11:00 >2,400 48.0 50 .198 34.0 25.0 27.5 8.7 8.0 411 .182 286 12.09EFT348 7/7/2008 8:38 >2,400 E10.0 11 .179 27.0 26.5 28.5 7.0 7.5 403 .178 172 11.83EFT348 8/5/2008 8:27 >2,400 E42.0 7.3 <.100 27.0 24.5 31.3 10.4 7.6 354 .155 197 11.89EFT348 9/22/2008 9:42 >2,400 E200 17 <.100 29.0 40.0 25.5 10.0 8.6 422 .187 232 11.97EFT348 10/29/2008 9:45 2,400 600 270 .181 23.0 29.5 17.2 8.8 7.9 410 .182 156 11.79EFT348 11/18/2008 10:00 >2,400 NA 240 .310 33.0 17.0 14.5 7.5 7.9 334 .146 35.5 11.39EFT348 12/2/2008 9:30 >2,400 E130 100 <.100 22.0 21.0 10.9 E9.6 7.8 422 .187 255 12.02

1 Estimated if holding time greater than 6 hours.2 Estimated if rated as fair (+0.5 to 0.8 mg/L) or poor (>+0.8 mg/L).3 Calculated from specific conductance. 
38 Fecal Indicator Bacteria and Water Quality in Streams, DFW International Airport, Texas, 2008 Appendix 1.2. Fecal indicator bacteria and water-quality data for samples collected during stormflow conditions—Continued. Field identi- fier (fig. 1) Sample date and time Total coliforms1 (MPN/100 mL) Fecal coliforms1 (cfu/100 mL) E. coli 1 (MPN/100 mL) Ammonia, as nitrogen (mg/L) Residue (TSS) (mg/L) Total chloride (mg/L) Water tempera- ture 

(°C)

Dissolved 

oxygen2

(mg/L)

pH 

(standard 

units)

Specific 

conductance 

(μS/cm)

Salinity3 

(psu)

Discharge 

(ft3/s)

Stage 

(ft)

Lower West Fork Trinity River watershed

BBC183 3/17/2008 14:20 2,400 20.0 48 <1.00 9.00 76.5 18.6 11.3 8.1 902 0.421 NA 6.27BBC183 3/18/2008 9:54 E15,000 E1,200 E1,400 <1.00 149 65.5 17.7 8.4 7.8 774 .357 NA 7.00BBC183 3/18/2008 11:52 92,000 4,800 4,900 <1.00 426 20.0 16.3 9.0 7.8 306 .133 NA 13.24BBC183 3/19/2008 10:00 130,000 E6,200 5,200 <1.00 296 16.5 12.3 9.7 7.6 259 .111 NA 12.92BBC183 3/19/2008 12:00 46,000 6,400 4,600 <1.00 226 17.5 12.7 9.9 7.7 272 .117 NA 11.71BBC183 3/19/2008 13:46 120,000 6,100 4,600 <1.00 132 19.5 13.2 10.0 7.4 287 .124 NA 10.80BBC183 3/20/2008 9:28 58,000 2,350 2,100 <1.00 54.0 30.5 12.5 10.1 7.5 444 .198 NA 7.41BBC183 3/20/2008 11:16 44,000 1,900 1,400 <1.00 74.0 29.5 13.3 10.2 7.5 458 .204 NA 7.33BBC183 4/3/2008 18:23 >2,400 TNTC 55 .481 22.0 58.0 20.8 10.4 8.3 728 .335 NA 6.29BBC183 4/4/2008 8:11 120,000 E7,000 7,600 .349 106 49.5 17.8 9.0 7.7 625 .285 NA 7.96BBC183 4/4/2008 10:12 200,000 E9,900 7,600 .415 56.0 45.5 17.5 8.9 7.9 597 .271 NA 7.30BBC183 4/4/2008 10:34 200,000 E7,400 6,500 .350 57.0 46.5 17.6 8.5 7.9 630 .287 NA 7.28BBC183 4/4/2008 14:00 E>240,000 6,900 E6,500 .239 43.0 42.0 18.9 9.9 7.9 576 .261 NA 7.15BBC183 4/4/2008 15:30 240,000 8,200 6,900 .269 45.0 44.5 19.4 9.6 8.0 601 .273 NA 7.10BBC183 4/4/2008 16:55 >240,000 6,900 6,900 .237 42.0 43.5 19.3 9.6 8.0 623 .284 NA 7.10BBC183 4/5/2008 10:15 61,000 1,140 1,300 .315 22.0 67.5 16.4 E8.6 8.0 710 .326 NA 6.69BBC183 8/15/2008 10:43 >240,000 E19,200 18,000 .147 834 26.0 24.5 E6.3 6.1 317 .138 NA 11.45BBC183 8/15/2008 12:44 >240,000 39,800 43,000 .125 851 23.8 24.6 E6.2 7.0 251 .108 NA 11.46BBC183 8/18/2008 13:07 130,000 2,250 1,700 .129 200 30.5 25.3 7.4 6.6 419 .186 NA 7.57BBC183 8/19/2008 11:30 140,000 4,100 3,900 <.100 100 34.5 25.1 7.4 7.0 406 .180 NA 6.98BBC183 8/19/2008 13:38 98,000 2,700 2,300 <.100 61.0 35.0 25.7 7.5 7.3 408 .181 NA 6.84BBC183 8/20/2008 10:30 17,000 E400 220 <.100 29.0 34.5 25.1 E6.6 6.8 420 .186 NA 6.38BBC183 8/20/2008 11:55 22,000 100 130 <.100 27.0 34.5 25.6 E6.9 7.2 425 .189 NA 6.35BBC183 8/20/2008 13:26 14,000 200 170 <.100 27.0 35.5 26.3 E7.0 7.3 430 .191 NA 6.27

Elm Fork Trinity River watershed

EFT348 3/17/2008 15:30 2,000 27.0 37 <1.00 37.0 17.5 13.2 10.7 7.8 358 .157 2,881 16.35EFT348 3/18/2008 10:55 E4,100 E90.0 E230 <1.00 73.0 16.5 14.2 9.7 7.9 347 .152 3,180 16.84EFT348 3/18/2008 13:40 87,000 1,120 1,600 <1.00 268 13.5 14.8 9.4 7.9 343 .150 5,458 20.92EFT348 3/18/2008 14:34 52,000 1,450 1,700 <1.00 242 15.0 14.5 9.6 8.0 337 .147 5,853 21.63EFT348 3/19/2008 11:00 E100,000 E8,550 E5,400 <1.00 170 11.5 13.7 8.8 7.7 285 .123 6,918 23.53

Appendix 1.2. Fecal indicator bacteria and water-quality data for samples collected during stormflow conditions.[MPN/100 mL, most-probable number per 100 milliliters; cfu/100 mL, colony-forming units per 100 milliliters; E., Escherichia; mg/L, milligrams per liter; TSS, total suspended solids; °C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 degrees Celsius; psu, practical salinity units; ft3/s, cubic feet per second; ft, feet; <, less than laboratory reporting level; NA, not available; E, estimated; >, greater than; TNTC, too numerous to count]

Appendix 1.2
Appendix 1.2 39

Appendix 1.2. Fecal indicator bacteria and water-quality data for samples collected during stormflow conditions—Continued. 

Field 

identifier 

(fig. 1)

Sample date 

and time

Total 

coliforms1

(MPN/100 mL)

Fecal 

coliforms1

(cfu/100 mL)

E. coli 1

(MPN/100 mL)

Ammonia, 

as nitrogen 

(mg/L)

Residue 

(TSS) 

(mg/L)

Total 

chloride 

(mg/L)

Water 

temperature 

(°C)

Dissolved 

oxygen2

(mg/L)

pH 

(standard 

units)

Specific 

conductance 

(μS/cm)

Salinity3 

(psu)

Discharge 

(ft3/s)

Stage 

(ft)

Elm Fork Trinity River watershed—Continued

EFT348 3/19/2008 12:57 130,000 7,500 5,100 <1.00 246 12.0 13.7 9.0 7.5 284 .123 6,828 23.37EFT348 3/20/2008 10:18 77,000 5,300 4,600 <1.00 65.0 13.0 13.7 8.7 7.4 330 .144 3,236 16.93EFT348 3/20/2008 12:13 87,000 4,600 4,900 <1.00 78.0 14.5 13.8 8.8 7.3 336 .147 2,791 16.20EFT348 4/3/2008 19:07 >2,400 TNTC 64 .600 43.0 20.0 16.2 9.6 8.0 367 .161 3,340 17.10EFT348 4/4/2008 9:23 6,100 E110 93 .301 45.0 20.0 16.0 9.4 8.1 364 .160 3,606 17.53EFT348 4/4/2008 11:26 5,600 240 130 .379 47.0 19.0 15.9 9.8 8.1 370 .163 3,750 17.76EFT348 4/4/2008 12:07 14,000 100 190 .327 52.0 20.5 16.0 8.7 8.1 373 .164 3,794 17.83EFT348 4/4/2008 14:43 E46,000 760 E580 .347 63.0 24.0 16.3 10.1 8.0 393 .174 3,932 18.06EFT348 4/4/2008 16:10 19,000 940 580 .327 88.0 23.5 16.4 10.1 8.0 401 .177 3,970 18.13EFT348 4/5/2008 9:30 21,000 760 830 .295 44.0 21.0 15.8 E9.1 8.0 377 .166 3,819 17.87EFT348 4/5/2008 10:52 25,000 640 720 .308 47.0 20.5 15.9 E8.7 8.0 376 .166 3,794 17.83EFT348 8/15/2008 11:27 9,900 173 25 .125 38.0 26.0 28.1 E6.2 7.4 386 .170 933 13.20EFT348 8/15/2008 13:31 12,000 200 26 .130 44.0 25.0 28.3 E6.0 7.3 388 .171 1,134 13.51EFT348 8/19/2008 10:45 19,000 200 250 <.100 39.0 26.5 26.7 5.1 6.7 405 .179 503 12.49EFT348 8/19/2008 12:55 18,000 300 200 <.100 39.0 24.5 26.8 5.4 6.8 404 .179 450 12.40EFT348 8/19/2008 14:20 20,000 800 170 <.100 35.0 26.5 26.9 5.5 7.2 401 .177 421 12.35EFT348 8/20/2008 11:15 16,000 350 220 <.100 55.0 32.5 26.6 E5.2 7.0 433 .193 576 12.61EFT348 8/20/2008 12:35 13,000 100 200 <.100 49.0 35.5 26.7 E5.4 7.1 429 .191 545 12.56EFT348 8/20/2008 14:05 15,000 100 160 <.100 53.0 26.5 27.0 E5.7 7.2 426 .189 515 12.51

1 Estimated if holding time greater than 6 hours. 2 Estimated if rated as fair (+0.5 to 0.8 mg/L) or poor (>+0.8 mg/L). 3 Calculated from specific conductance. 
Blank Page
Appendix 2—Quality Assurance Data for Samples Collected at 

Sites on Streams Receiving Discharge from Dallas/Fort Worth 

International Airport and Vicinity, North-Central Texas, 2008
Blank Page
Appendix 2.1 43

Appendix 2.1. Total coliform and Escherichia coli laboratory duplicates.

[MPN/100 mL, most-probable number per 100 milliliters; E., Escherichia; >, greater than; <, less than]

Field 

identifier 

(fig. 1)

Sample date 

and time

Total coliforms1

(MPN/100 mL)

E. coli 1

(MPN/100 mL) E. coli laboratory duplicates 

(percentage difference2) Duplicate 1 Duplicate 2 Duplicate 1 Duplicate 2

Lower West Fork Trinity River watershed

BBC121 7/7/08 9:45 9,200 11,000 120 98

TRIBMD 5/1/08 12:55 >2,400 >2,400 >2,400 >2,400

TRIBMD 11/18/08 11:01 >24,000 >24,000 2,100 2,200 4.7

TRIBMD 12/2/08 11:25 2,200 7,300 280 270

OF25 4/7/08 14:20 >2,400 >2,400 520 550 5.6

OF25 5/1/08 11:25 >2,400 >2,400 1,200 1,100

OF19 7/7/08 8:15 10,000 14,000 52 63

LBC360 8/5/08 8:20 20,000 17,000 135 109

LBC360 8/5/08 8:24 8,200 6,100 75 63

LBC360 10/29/08 9:45 1,200 1,700 41 52

BBC183 3/18/08 11:52 >24,000 >24,000 4,600 5,200 12.2

BBC183 4/4/08 8:11 >48,000 >48,000 9,800 6,300 43.5

BBC183 8/15/08 12:44 >24,000 >24,000 >24,000 >24,000

BBC183 8/15/08 12:44 >240,000 >240,000 49,000 37,000 27.9

Elm Fork Trinity River watershed

CCTTR 11/18/08 14:00 4,400 3,700 350 250

CCDTR 7/7/08 9:43 12,000 2,000 290 110

GCNAD 9/22/08 11:37 14,000 20,000 730 580 22.9

GCNAD 9/22/08 11:40 20,000 24,000 710 650 8.8

GCNAD 9/22/08 11:40 7,700 11,000 690 720 4.3

GCRR 4/7/08 15:34 >2,400 >2,400 81 130 46.4

GCRR 9/22/08 14:05 12,000 8,700 410 330

GCRR 9/22/08 14:07 17,000 20,000 290 340

GCRR 9/22/08 14:07 17,000 14,000 300 390

GCDTR 5/1/08 12:11 >9,700 9,700 430 420 2.4

GCDTR 9/22/08 10:20 6,100 7,700 97 31

GCDTR 9/22/08 10:22 6,500 6,900 41 31

GCDTR 10/29/08 10:15 3,900 400 290 230

HCCER 12/2/08 10:45 >2,400 >2,400 24 16

SHCHPR 2/25/08 14:20 2,600 2,600 34 43

SHCHPR 5/1/08 10:24 >2,400 >2,400 40 37

HCLR 12/2/08 9:10 7,300 11,200 31 160

EFT348 3/18/08 13:40 >24,000 >24,000 1,600 1,600 0

EFT348 4/4/08 9:23 5,000 8,700 62 150

EFT348 8/15/08 13:31 16,000 16,000 31 30

EFT348 8/15/08 13:31 15,000 10,000 100 <100

Average percentage difference 16.2

1

 Normal font indicates counts with number of cells that were yellow and fluoresced within recommended 30 to 80 range (Texas Commission on Environmental Quality, 2009, p. 4–8); bold font indicates counts not within recommended 30 to 80 range.

2

 Percentage difference listed for counts within recommended 30 to 80 range (Texas Commission on Environmental Quality, 2009, p. 4–8). 
44 Fecal Indicator Bacteria and Water Quality in Streams, DFW International Airport, Texas, 2008 Appendix 2.2. Ammonia, residue (total suspended solids), and total chloride split replicates. [mg/L, milligrams per liter; TSS, total suspended solids; <, less than laboratory reporting level; NA, not applicable] Field identifier (fig. 1) Sample date Ammonia, as nitrogen, (mg/L) Ammonia replicates (relative percent- age difference1

)

Residue (TSS) 

(mg/L)

TSS replicates 

(relative 

percentage 

difference1

)

Total chloride

(mg/L) Chloride replicates (relative percentage 

difference1

) Replicate 1 Replicate 2 Replicate 1 Replicate 2 Replicate 1 Replicate 2

Lower West Fork Trinity River watershed

BBC121 7/7/2008 0.180 0.207 14.0 16.0 18.0 11.8 73.5 62.5 16.2TRIBMD 5/1/2008 .470 .497 5.6 7.00 6.00 15.4 70.5 71.0 .7TRIBMD 6/2/2008 .267 .280 4.8 <5.00 7.00 NA 71.5 71.0 .7TRIBMD 12/2/2008 .462 .452 2.2 13.0 16.0 20.7 31.0 32.0 3.2OF25 4/7/2008 .104 <.100 NA 11.0 8.00 31.6 43.5 42.0 3.5OF25 5/1/2008 <.100 .131 NA <5.00 5.00 NA 44.5 47.0 5.5OF19 11/18/2008 <.100 <.100 NA 5.00 <4.00 NA 22.5 21.0 6.9LBC360 8/5/2008 <.100 <.100 NA <4.00 <4.00 NA 57.5 57.5 0BBC183 4/4/2008 .302 .315 4.2 101 105 3.9 50.5 48.5 4.0BBC183 8/15/2008 .128 .121 5.6 840 862 2.6 25.5 22.0 14.7

Elm Fork Trinity River watershed

CCBR 10/29/2008 .116 .105 10.0 <4.00 <4.00 NA 25.5 32.0 22.6CCDTR 6/2/2008 <.100 .113 NA 10.0 16.0 46.2 106 109 2.8CCDTR 7/7/2008 .100 .108 7.7 8.00 9.00 11.8 127 135 6.1GCNAD 9/22/2008 <.100 .130 NA <4.00 <4.00 NA 17.0 28.0 48.9GCRR 4/7/2008 .200 .205 2.5 5.00 6.00 18.2 27.5 29.5 7.0GCRR 9/22/2008 .291 .297 2.0 <4.00 11.0 NA 43.0 50.0 15.1GCDTR 5/1/2008 .210 <.100 NA <5.00 <5.00 NA 53.5 53.0 .9GCDTR 9/22/2008 <.100 <.100 NA 6.00 <4.00 NA 60.0 48.0 22.2HCCER 10/29/2008 .107 <.100 NA 7.00 <4.00 NA 21.0 23.0 9.1HCCER 12/2/2008 <.100 <.100 NA 12.0 <4.00 NA 12.0 11.0 8.7SHCBLR 11/18/2008 .158 .308 64.4 7.00 14.0 66.7 54.0 81.0 40.0SHCHPR 5/1/2008 .353 .295 17.9 15.0 15.0 0 14.0 13.5 3.6EFT348 4/4/2008 .337 .346 2.6 48.0 44.0 8.7 19.0 19.0 0EFT348 8/15/2008 .133 .127 4.6 43.0 45.0 4.5 25.5 24.5 4.0Average relative percentage difference 10.6 18.6 10.3

1 Relative percentage difference between replicate sample concentrations (C) computed as

C C

C C

1 2

1 2 2

−

+ ( ) /

X 100 .
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Harwell and Mobley—Fecal Indicator Bacteria and Water Quality in Streams, DFW International Airport, Texas, 2008—SIR 2009–5103

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