and Fish in Mountain Creek Lake, 

Dallas, Texas, 1994–97

Water-Resources Investigations Report 03–4082

U.S. Department of the Interior

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

U.S. Geological Survey

Chemical Quality of Water, Sediment, 

and Fish in Mountain Creek Lake, 

Dallas, Texas, 1994–97

By P.C. Van Metre, S.A. Jones, J. Bruce Moring, B.J. Mahler, and 

Jennifer T. Wilson

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 03–4082

In cooperation with the Southern Division Naval Facilities 

Engineering Command

Austin, Texas

2003
ii

U.S. DEPARTMENT OF THE INTERIOR

Gale A. Norton, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

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

descriptive purposes only and does not imply 

endorsement by the U.S. Government.

For additional information write to

District Chief

U.S. Geological Survey

8027 Exchange Dr.

Austin, TX 78754–4733

E-mail: dc_tx@usgs.gov

Copies of this report can be purchased from

U.S. Geological Survey

Information Services

Box 25286

Denver, CO 80225–0286

E-mail: infoservices@usgs.gov
CONTENTS iii

CONTENTS

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

Introduction .......................................................................................................................................................................... 2

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

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

Methods ................................................................................................................................................................................ 4

Site Selection ............................................................................................................................................................ 4

Fish Taxa and Tissue Selection ................................................................................................................................. 7

Sampling Methods .................................................................................................................................................... 8

Analytical Methods .................................................................................................................................................. 9

Quality Control ......................................................................................................................................................... 10

Potential Sources of Contamination From Navy Facilities to Mountain Creek Lake .......................................................... 12

NWIRP Sources ........................................................................................................................................................ 12

NAS Sources ............................................................................................................................................................. 13

Chemical Quality of Water, Sediment, and Fish in Mountain Creek Lake .......................................................................... 15

Reference Concentrations ......................................................................................................................................... 15

Dating Sediment Cores ............................................................................................................................................. 19

Occurrence, Trends, and Sources of Metals ............................................................................................................. 22

Metals in Stormwater .................................................................................................................................... 22

Metals in Lake Water .................................................................................................................................... 23

Metals in Sediment ........................................................................................................................................ 23

Metals in Fish ................................................................................................................................................ 28

Sources of Metals .......................................................................................................................................... 30

Occurrence, Trends, and Sources of Volatile Organic Compounds ......................................................................... 33

VOCs in Stormwater ..................................................................................................................................... 33

VOCs in Lake Water ..................................................................................................................................... 36

VOCs in Sediment ......................................................................................................................................... 36

VOCs in Fish ................................................................................................................................................. 36

Sources of VOCs ........................................................................................................................................... 37

Occurrence, Trends, and Sources of Polycyclic Aromatic Hydrocarbons ............................................................... 37

PAHs in Stormwater and Lake Water ............................................................................................................ 37

PAHs in Sediment ......................................................................................................................................... 38

PAHs in Fish ................................................................................................................................................. 42

Sources of PAHs ........................................................................................................................................... 43

Pyrogenic Versus Uncombusted Fuel Sources .................................................................................. 43

Spatial Sources of PAHs .................................................................................................................... 46

Occurrence, Trends, and Sources of Organochlorine Pesticides .............................................................................. 48

Organochlorine Pesticides in Stormwater and Lake Water ........................................................................... 48

Organochlorine Pesticides in Sediment ........................................................................................................ 49

Organochlorine Pesticides in Fish ................................................................................................................. 50

Sources of Organochlorine Pesticides ........................................................................................................... 52

Occurrence, Trends, and Sources of Polychlorinated Biphenyls ............................................................................. 52

PCBs in Stormwater ...................................................................................................................................... 52

PCBs in Sediment ......................................................................................................................................... 53

PCBs in Fish .................................................................................................................................................. 55

Sources of PCBs ............................................................................................................................................ 56

Sediment and Contaminant Accumulation in Cottonwood Bay ............................................................................... 57

Summary .............................................................................................................................................................................. 59

References ............................................................................................................................................................................ 60
iv 

FIGURES

1–2. Maps showing: 

1. Locations of Phase I sampling sites and media collected at Mountain Creek Lake, Dallas, Texas ........... 3

2. Locations of Phase II sampling sites and media collected at Mountain Creek Lake, Dallas, Texas ......... 5

3–5. Boxplots showing: 

3. Percent recovery of laboratory spiked quality-control samples for polycyclic aromatic hydrocarbons 

in bottom sediment collected at Mountain Creek Lake, Dallas, Texas ...................................................... 10

4. Percent differences between environmental and replicate samples in lake bottom sediment collected 

at Mountain Creek Lake, Dallas, Texas ..................................................................................................... 11

5. Percent recovery of laboratory spiked quality-control samples for organochlorine pesticides in fish 

tissue collected at Mountain Creek Lake, Dallas, Texas ............................................................................ 12

6–8. Maps showing: 

6. Locations of selected buildings, groups, and solid-waste management units (SWMUs) on the Naval 

Air Station and Naval Weapons Industrial Reserve Plant, Dallas, Texas .................................................. 14

7. Place names of parts of Mountain Creek Lake used in this report ............................................................. 16

8. Locations of sites and range in selected constituents in bottom sediments for clusters ............................ 18

9. Graphs showing cesium-137 and organochlorine pesticide concentrations in M2.40 and MCL–4 cores ............ 20

10. Graphs showing age-depth indicators in Bay–13 core ......................................................................................... 21

11–15. Graphs showing: 

11. Ratios of Phase I metal concentrations in lake bottom sediment at selected sites to mean 

concentrations of main-lake reference sites ............................................................................................... 24

12. Ratios of Phase II metal concentrations in lake bottom sediment at selected sites to mean 

concentrations of main-lake reference sites ............................................................................................... 26

13. Trends in chromium, lead, and zinc concentrations in MCL–4, M2.40, and Bay–13 cores ...................... 27

14. Trends in heavy metals concentrations in Cottonwood Bay as indicated by the Bay–13 core .................. 29

15. Trends in mercury concentrations in the NAS inlet as indicated by the M2.40 core ................................. 30

16. Boxplots showing distribution of metal concentrations in fish tissues, Mountain Creek Lake ............................ 31

17. Graphs showing ratios of lake-bottom sediment and suspended sediment metal concentrations in the west 

lagoon and Cottonwood Bay to mean concentrations of mean-lake reference sites ............................................. 32

18. Graph showing percent detections of volatile organic compounds in composite samples collected at the 

fixed stormwater sites, Naval Air Station and Naval Weapons Industrial Reserve Plant ..................................... 34

19. Boxplots showing distribution of BTEX compound concentrations detected at NAS–2 stormwater site ............ 35

20. Graphs showing volatile organic compound concentrations in lake water samples ............................................. 36

21. Maps showing fluoranthene concentrations in top 3 centimeters of lake bottom sediments from (a) Phase I 

sampling; (b) Phase II sampling; (c) Phase II Cottonwood Bay sampling; and (d) Phase II NAS inlet 

sampling ................................................................................................................................................................ 39

22. Map showing total PAH concentrations in top 3 centimeters of surficial sediment from Phase II sampling ....... 40

23. Boxplots showing distribution of benzo(a)pyrene and benzo(b)fluoranthene concentrations in top 3 

centimeters of surficial sediment .......................................................................................................................... 41

24. Graphs showing trends in PAH concentrations in Bay–13, MCL–7, and MCL–4 cores ...................................... 42

25. Graphs showing trends in PAH concentrations in M2.40 core in the NAS inlet .................................................. 43

26. Boxplots showing longitudinal variation in total PAH and source indicator ratios for surficial sediment 

samples .................................................................................................................................................................. 45

27. Boxplots showing comparison of lake-bottom sediment and suspended sediment PAH concentrations in 

the east and west lagoons and Cottonwood Bay ................................................................................................... 47

28. Graphs showing mean concentrations of organochlorine pesticides detected in composite fish tissues 

sampled in Phase I ................................................................................................................................................ 50

29. Boxplots showing distribution of organochlorine pesticide concentrations detected in fish sampled in 

Phase II ................................................................................................................................................................. 51
CONTENTS v

30. Maps showing PCB concentrations in top 3 centimeters of lake bottom sediment from (a) Phase I sampling; 

(b) Phase II sampling; (c) Phase II Cottonwood Bay sampling; and (d) Phase II NAS inlet sampling ............... 54

31. Graphs showing trends in PCB concentrations in Mountain Creek Lake (cores MCL–4, M2.40, Bay–13) 

and in White Rock Lake, Dallas Texas ................................................................................................................. 55

32. Boxplots showing distribution of PCB concentrations in fish tissues .................................................................. 56

33. Map showing thickness of lacustrine sediment in central and east Cottonwood Bay .......................................... 58

34. Graphs showing mass accumulation rates of silver in Bay–13 core .................................................................... 59

TABLES

1. Type and number of samples analyzed for selected constituents at Mountain Creek Lake, Dallas, Texas .......... 6

2. Results of fishing-habits survey on Mountain Creek Lake .................................................................................. 7

3. Waste disposed of in the West Lagoon Naval Weapons Industrial Reserve Plant ................................................ 13

4. Sites included in cluster analysis .......................................................................................................................... 17

5. Summary of selected metal concentrations in sediment ....................................................................................... 28

6. Comparison of volatile organic compound concentrations at the Navy sites, Dallas, Texas, and at 

industrial sites in the Dallas-Fort Worth area ....................................................................................................... 35

7. Polycyclic aromatic hydrocarbon concentrations in stormwater suspended sediment samples ........................... 64

8. Diagnostic polycyclic aromatic hydrocarbon ratios for selected surficial sediment samples .............................. 66

9. Reported and estimated total polycyclic aromatic hydrocarbon concentrations for east and west lagoon 

sediment ................................................................................................................................................................ 66

10. Organochlorine pesticide and polychlorinated biphenyl concentrations in stormwater suspended 

sediment samples .................................................................................................................................................. 67

11. Summary of total polychlorinated biphenyl concentrations in sediment ............................................................. 68

12. Estimated total and annual contaminant mass accumulations in east and central Cottonwood Bay ................... 69
Abstract 1

Chemical Quality of Water, Sediment, 

and Fish in Mountain Creek Lake, 

Dallas, Texas, 1994–97

By P.C. Van Metre, S.A. Jones, J. Bruce Moring, B.J. Mahler, and Jennifer T. Wilson

Abstract

The occurrence, trends, and sources of 

numerous inorganic and organic contaminants 

were evaluated in Mountain Creek Lake, a reservoir in Dallas, Texas. The study, done in cooperation with the Southern Division Naval Facilities 

Engineering Command, was prompted by the 

Navy’s concern for potential off-site migration of 

contaminants from two facilities on the shore of 

Mountain Creek Lake, the Naval Air Station Dallas 

and the Naval Weapons Industrial Reserve Plant. 

Sampling of stormwater (including suspended 

sediment), lake water, bottom sediment (including 

streambed sediment), and fish was primarily in 

Mountain Creek Lake but also was in stormwater 

outfalls from the Navy facilities, nearby urban 

streams, and small streams draining the Air Station. 

Volatile organic compounds, predominantly 

solvents from the Reserve Plant and fuel-related 

compounds from the Air Station, were detected in 

stormwater from both Navy facilities. Fuel-related 

compounds also were detected in Mountain Creek 

Lake at two locations, one near the Air Station inlet 

where stormwater from a part of the Air Station 

enters the lake and one at the center of the lake. 

Concentrations of volatile organic compounds at 

the two lake sites were small, all less than 5 micrograms per liter.

Elevated concentrations of cadmium, chromium, copper, lead, mercury, nickel, silver, and 

zinc, from 2 to 4 times concentrations at background sites and urban reference sites, were 

detected in surficial bottom sediments in Cottonwood Bay, near stormwater outfalls from the 

Reserve Plant. 

Elevated concentrations of polycyclic aromatic hydrocarbons and polychlorinated biphenyls, 

compared to background and urban reference sites, 

were detected in surficial sediments in Cottonwood 

Bay. Elevated concentrations of polycyclic aromatic hydrocarbons, indicative of urban sources, 

also were detected in Cottonwood Creek, which 

drains an urbanized area apart from the Navy facilities. Elevated concentrations of polychlorinated 

biphenyls were detected in two inlets near the Air 

Station shoreline. Polycyclic aromatic hydrocarbon 

and heavy metal concentrations near the Air Station shoreline were not elevated compared to urban 

reference sites.

Much larger concentrations of selected 

heavy metals, polycyclic aromatic hydrocarbons, 

and polychlorinated biphenyls were detected in 

deeper, older sediments than in surficial sediments 

in Cottonwood Bay. The decreases in concentrations coincide with changes in wastewater discharge practices at the Reserve Plant. Elevated 

concentrations of polycyclic aromatic hydrocarbons and polychlorinated biphenyls also were 

detected in older sediments in the Air Station inlet.

On the basis of dated sediment cores and 

contaminant discharge histories, contaminant accumulation rates in Cottonwood Bay were much 

greater historically than recently. Most heavy 

metals, polycyclic aromatic hydrocarbons, and 

polychlorinated biphenyls that accumulated in the 

central and eastern parts of Cottonwood Bay 

appear to have come from the west lagoon on the 

Reserve Plant. Treated sewage and industrialprocess wastewater were discharged to the west 

lagoon from about 1941 to 1974. Estimated annual 

contaminant accumulation rates in Cottonwood 

Bay decreased by from 1 to 2 orders of magnitude 
2 Chemical Quality of Water, Sediment, and Fish in Mountain Creek Lake, Dallas, Texas, 1994–97 

after 1974, when most point-source discharges to 

the west lagoon ceased.

Polychlorinated biphenyls were detected in 

61 of 62 individual fish-tissue samples. The largest 

average concentrations were in eviscerated channel 

catfish and the smallest were in largemouth bass 

fillets. Polychlorinated biphenyl and selenium concentrations from analyses of this study were large 

enough to prompt the Texas State Department of 

Health to issue a fish-possession ban for Mountain 

Creek Lake in 1996.

Suspended sediments in stormwater at the 

lagoon outfalls and at sites on Cottonwood Creek 

were sampled and analyzed for major and trace 

elements, polycyclic aromatic hydrocarbons, 

organochlorine pesticides, and polychlorinated 

biphenyls. The suspended sediments from the outfalls contained about the same mixture of heavy 

metals and organic compounds, in elevated concentrations compared to reference sites, as bottom 

sediments from the lagoons and surficial bottom 

sediments in Cottonwood Bay. 

Diagnostic ratios of polycyclic aromatic 

hydrocarbons indicate that uncombusted fuel 

sources contribute to older sediments and that 

pyrogenic sources of polycyclic aromatic hydrocarbons dominate recently deposited sediments 

in Cottonwood Bay and along the Air Station 

shoreline. 

INTRODUCTION

Mountain Creek Lake is a reservoir on Mountain 

Creek in the southwestern part of Dallas, Tex. (fig. 1). 

The lake, impounded in 1929, is about 5 kilometers 

(km) long, 2 km wide, and about 7 meters (m) deep at 

the deepest point. The lake is owned by Texas Utilities, 

which uses the lake as a cooling reservoir for its oilfired electrical-power generating plant on the northeast 

shore. The lake is not used for water supply but is considered a potential water supply for the State of Texas 

and is used for recreation, including fishing. Two facilities of the U.S. Department of the Navy are on the 

northwestern shore of Mountain Creek Lake, the Naval 

Air Station Dallas (NAS) and the Naval Weapons 

Industrial Reserve Plant (NWIRP). As of 1998, a 

Resource Conservation and Recovery Act (RCRA) 

Facility Investigation (RFI) was being conducted at 

NWIRP and NAS, and base closure was underway at 

NAS (EnSafe/Allen & Hoshall, 1996a, b; 1997a, b). 

The NAS was established in 1928 as Hensley 

Field and has been expanded several times since. Major 

expansion occurred during World War II, and by 1945 

more than 4,000 personnel were stationed there. During 

1949–50 the main north-south runway was expanded on 

fill that separated Cottonwood Bay, a narrow arm of the 

lake at the mouth of Cottonwood Creek, from the main 

body of the lake. A canal connecting Cottonwood Bay 

to the lake was completed at that time to allow outflow 

from the Cottonwood Creek drainage. Cottonwood Bay 

is a part of Mountain Creek Lake. 

The NWIRP opened in 1941 as North American 

Aviation and remains an airplane manufacturing facility 

today. It is currently (1998) operated by Northrup 

Grumman.

In 1994, the U.S. Geological Survey (USGS), in 

cooperation with the Southern Division Naval Facilities 

Engineering Command, began a study to address the 

possibility of contamination in Mountain Creek Lake. 

The objective was to determine the occurrence and distribution of contaminants in Mountain Creek Lake. The 

information could be useful for indicating the potential 

for continuing contamination by stormwater runoff 

from either NAS or NWIRP and for evaluating humanhealth risks from consumption of fish from the lake. 

Because this investigation focused on the Navy 

facilities, more detailed definition of contaminant 

occurrence was obtained near the Navy facilities than in 

other areas of the lake. Furthermore, the work of the 

Navy and its contractors has resulted in a better understanding of occurrence and historical releases of contaminants on the Navy facilities than on other areas 

in the Mountain Creek Lake watershed. A detailed 

description of the occurrence and sources of all contaminants in all parts of the lake was not an objective of this 

investigation, although the objectives included defining 

the extent of contamination from the Navy facilities. To 

define the extent, sediments in the middle and upper 

parts of the lake and in the streambed and suspended 

sediments in Cottonwood Creek were sampled. 

Purpose and Scope

This report presents findings of the USGS study 

of Mountain Creek Lake and selected small tributaries 

and streams draining the Navy facilities. Specifically, 

the report presents and discusses the occurrence of all 

constituents analyzed for by compound or element 
INTRODUCTION 3

Florina Drive

US 80

Causeway

State 303

DAM

Bldg. 6 Bldg. 1

MOUNTAIN CREEK LAKE

Mountain Creek

Cottonwood Creek

West 

Lagoon East 

Lagoon

Cottonwood

Bay

0 0.5 1 KILOMETER

Base from EnSafe/Allen & Hoshall

written commun., 1996

Modified State Plane

Naval Weapons

Industrial Reserve

Plant

Naval

Air 

Station

Texas

Utilities

power

plant

96o59'

32o

44'

96o58' 96o

57'

32o

43'

32o

42'

Lake-bottom sediment sampling

site (surficial) and number

Lake-bottom sediment sampling

site (surficial and deeper) and

number 

Lake-water sampling site and number

Streambed sediment

sampling site and number

Fish sampling site and number

Stormwater sampling site and number

EXPLANATION

Boundary of Naval Weapons Industrial

Reserve Plant and Naval Air Station

NAS-1

MCL-4

MCL-1

MCL-2

Bay-13

NAS-3

MCL-4

MCL-2

MCL-1

MCL-3

MCL-12

MCL-11

MCL-10

MCL-8

MCL-5

MCL-6

MCL-13

MCL-7

Bay-13Bay-16

MCL-9

Bay-11

Bay-7

NAS-2

NAS-4

NAS-3

NAS-1

NWIRP-2

NWIRP-1

LOCATION MAP

Dallas

Study

 area

TEXAS

Fort Worth

Grand

 Prairie

Figure 1. Locations of Phase I sampling sites and media collected at Mountain Creek Lake, Dallas, Texas. 
4 Chemical Quality of Water, Sediment, and Fish in Mountain Creek Lake, Dallas, Texas, 1994–97 

group in each of the environmental phases sampled 

(stormwater [includes suspended sediment], lake water, 

bottom sediment [includes streambed sediment], and 

fish). On the basis of occurrence, selected contaminants 

are evaluated further. These evaluations include identification of temporal trends, estimation of mass fluxes, 

and identification of probable contaminant sources. 

Trends are identified using age-dated bottom-sediment 

cores. Mass fluxes are estimated using data from sediment cores, a sedimentation survey, and stormwater 

sampling. Probable sources are identified on the basis 

of (1) identification of a potential source or sources 

outside the lake, either in the urbanized parts of the 

watershed or on the Navy facilities; (2) description of a 

plausible transport pathway from the outside source(s) 

to the lake, and (3) relation of the source and pathway to 

the spatial and temporal distribution in the lake. Additionally, in the case of some groups of related organic 

compounds, chemical “signatures” are used to aid in 

source identification.

Data collected in this study for lake water, bottom 

sediment, and fish are presented in Jones and others 

(1997). Also included in that report are descriptions of 

the sampling design, collection methods (except for suspended sediment), and laboratory analytical methods. 

Stormwater data and loads of selected potential contaminants are presented in Raines and others (1997). Datacollection methods and analytical results for suspended 

sediment are presented in this report. 

Acknowledgments

The authors acknowledge the cooperation and 

assistance of EnSafe (formerly EnSafe/Allen & 

Hoshall), the Navy’s private consultant on the project. 

EnSafe provided its on-site facilities for USGS use and 

made all data previously collected during the RFI available to the USGS. The cooperation of personnel from 

the U.S. Navy and from Northrup Grumman also is 

acknowledged.

METHODS

Most methods of this study are described in Jones 

and others (1997) and Raines and others (1997) and are 

summarized briefly here. Methods for collection of suspended sediment samples are presented in more detail 

here because they are not included in the other reports. 

Details of a USGS-conducted fishing survey that 

contributed to the fish sampling approach also are presented here.

The study design, site selection, sampling and 

analytical methods, and quality-assurance procedures 

are described in a Sampling and Analysis Plan (SAP) 

provided to the Navy before sample collection (U.S. 

Geological Survey, written commun., 1995). Except 

where noted here, methods follow those described in the 

SAP.

Site Selection

The study was done in two phases (table 1). During Phase I (fig. 1), stormwater was sampled at five 

sites; lake water was sampled at four sites; lake bottom 

sediment was sampled at 17 sites; streambed sediment 

was sampled at three sites; and fish were sampled at 

three sites in the lake. During Phase II of the study 

(fig. 2), suspended sediment in stormwater was sampled 

at four sites; lake bottom sediment was sampled at 44 

sites; streambed sediment was sampled at four sites; and 

fish were sampled in 11 areas of the lake.

The five stormwater sampling sites established 

during Phase I—three on NAS and two on NWIRP 

(fig. 1)—were located to measure runoff from most of 

NWIRP and from the most developed parts of NAS. 

The four lake-water sampling sites (fig. 1) established during Phase I were located to measure water 

quality in areas near the two Navy facilities, in the main 

body of the lake, and at a reference site. Sites were colocated with sediment and fish sampling sites, where possible, to provide information on all three media at these 

locations.

The 17 lake-bottom sediment sampling sites 

established during Phase I (fig. 1) were selected to 

broadly cover the entire lake, including Cottonwood 

Bay, but to be more closely spaced near the Navy 

facilities. The selection of each sampling site for 

surficial (uppermost 3 centimeters [cm]) sediments 

was based on the results of reconnaissance sedimentcore sampling and on an understanding of sedimentation processes in reservoirs. Thirteen sites were located 

near potential contamination sources identified on NAS 

and NWIRP or near major stormwater outfalls from 

NAS and NWIRP to the lake. The four other lake sites 

were located in the main body of the lake. Three of 

the lake-bottom sediment sites were selected for sampling of deeper, older sediments in the lake for analysis 

of major and trace elements and hydrophobic organic 

compounds (fig. 1). Sediment pore water from deeper 

sediments also was analyzed for volatile organic 

compounds (VOCs) in a reconnaissance sampling of 
METHODS 5

Florina Drive

US 80

Causeway

State 303

DAM

Bldg. 6 Bldg. 1

MOUNTAIN CREEK LAKE

Mountain Creek

Cottonwood Creek

West 

Lagoon East 

Lagoon

Cottonwood

Bay

0 0.5 1 KILOMETER

Base from EnSafe/Allen & Hoshall

written commun., 1996

Modified State Plane

Naval Weapons

Industrial Reserve

Plant

Naval

Air 

Station

Texas

Utilities

power

plant

96o59' 96o

58' 96o

57'

32o

44'

32o

43'

32o

42'

M2.30 Lake-bottom sediment sampling

site (surficial) and number

Lake-bottom sediment sampling

site (surficial and deeper) and

number 

Streambed sediment sampling

site and number

EXPLANATION

Suspended sediment sampling

site and number

Boundary of Naval Weapons Industrial 

Reserve Plant and Naval Air Station

M2.11

M2.46

NWIRP-1

3 Fish sampling area and number

1

2

3

4

5

6

7

8

9

10

11

M2.30

M2.29

M2.32 M2.31 M2.35

M2.45

M2.34

M2.33

M2.36

M2.44

M2.43

M2.42 M2.41

M2.37

M2.38

M2.39 M2.40

M2.47

M2.46

M2.28

M2.27

M2.26

M2.25

M2.24

M2.22

M2.20 M2.21

M2.19 M2.18

M2.16

M2.17 M2.15

M2.12

M2.14

M2.13

M2.10

M2.11

NWIRP-1

M2.1

M2.7

M2.6

M2.2

M2.4

M2.5

NWIRP-2

M2.9

M2.3

M2.48

M2.23

M2.8

Figure 2. Locations of Phase II sampling sites and media collected at Mountain Creek Lake, Dallas, Texas. 
6 Chemical Quality of Water, Sediment, and Fish in Mountain Creek Lake, Dallas, Texas, 1994–97 

several sites in Cottonwood Bay (Jones and other, 

1997).

The three streambed sediment sampling sites 

established during Phase I near the NAS property 

boundary (fig. 1) were selected to determine chemical 

characteristics of bottom sediments in streams draining 

the facility. All three drainages contain possible contamination sources identified on the facility by EnSafe; 

however, all three drain to Mountain Creek downstream 

from Mountain Creek Lake and thus do not contribute 

flow to the lake.

The three fish sampling sites established 

during Phase I (fig. 1) were coincident with lakebottom sediment and lake-water sampling sites to 

help define the distribution of contaminants among 

media. Two sites were selected to measure potential 

contamination near the Navy facilities, and the third site 

was selected to describe background conditions in the 

lake; however, because of their mobility, fish from all 

parts of the lake could be affected by localized presence 

of contaminants. 

Four suspended sediment sampling sites were 

established during Phase II (fig. 2). Two of the four were 

new sites on Cottonwood Creek (one on the north fork, 

one on the south fork) selected to determine if hydrophobic contaminants from off-site urban areas were 

entering Mountain Creek Lake from Cottonwood 

Creek. The other two suspended sediment sampling 

sites, coincident with the two Phase I NWIRP stormwater sampling sites, were selected to determine if 

hydrophobic contaminants were entering the lake via 

runoff from NWIRP.

During Phase II, 44 additional lake-bottom 

sediment sampling sites (fig. 2) were established to 

enhance knowledge of the spatial and temporal distribution of contaminants in areas where contamination was 

found during Phase I and to help identify sources of 

bottom-sediment contamination. Eight of the 44 sites, 

each in Cottonwood Bay, were selected for sampling 

one or two deeper layers of sediment, and one site, 

M2.40, had numerous deeper layers analyzed to provide 

detailed contaminant trend information. Four streambed 

sediment sampling sites also were established (fig. 2).

Phase II fish sampling areas (fig. 2) were selected 

to represent the entire range in expected contaminant 

concentrations in the lake and on the basis of the results 

of a fishing-habits survey described in the next section. 

Table 1. Type and number of samples analyzed for selected constituents at Mountain Creek Lake, Dallas, Texas

[--, not analyzed] 

Type of sample

(no. of sites/areas)

Constituent or property and no. of samples analyzed

Volatile

organic

compounds

Semivolatile

organic

compounds

Polycyclic

aromatic

hydrocarbons

Organochlorine

pesticides

Polychlorinated

biphenyls

Trace

elements

Cesium137Grain

size

Phase I

Stormwater (5 sites) 68 30 -- 30 30 68 -- --

Lake water (4 sites) 4 -- -- 4 -- 4 -- --

Lake bottom sediment (17 sites) 8 28 -- 41 41 79 23 80

Streambed sediment (3 sites) -- 3 -- 3 3 -- -- 3

Fish tissue (3 sites) -- -- -- 6 6 6 -- --

Phase II

Suspended sediment in stormwater (4 sites)-- -- 6 6 6 11 -- --

Lake bottom sediment (44 sites) -- -- 73 21 73 77 12 70

Streambed sediment (4 sites) -- -- 4 4 4 -- -- --

Fish tissue (11 areas) 5 5 -- 62 62 45 -- --
METHODS 7

Fish Taxa and Tissue Selection

Decisions on which fish taxa and tissue to sample 

were made on the basis of a survey of the habits of the 

lake fishermen. The survey was made over three consecutive Saturdays and one Friday in April and early 

May 1995. The full perimeter of the lake was visited 

three times each day by boat and vehicle approximately 

from sunrise until late morning, from early afternoon 

until mid-afternoon, and from late evening until onehalf hour after sunset. The 81 fishermen contacted during the survey were mostly from Dallas and surrounding 

communities.

Information on fish caught and consumed and on 

the nature of preparation was gathered in the survey 

(table 2). Channel catfish were the most frequently 

caught and the most frequently eaten. On average, about 

52 percent of fillets eaten were skin-off and about 35 

percent eaten were skin-on. Skin-off fillets were consumed more frequently than skin-on fillets for every 

species except sunfish. Sunfish and freshwater drum 

were the most frequently consumed eviscerated whole 

fish. On average, about 13 percent of fish eaten were 

eviscerated whole fish. 

Of the 81 fishermen surveyed, 51 (63 percent) 

said they fished most frequently in area 2, adjacent to 

the Texas Utilities power plant (fig. 2). Eleven (14 percent) fished most frequently in area 11 near NAS. Eight 

(10 percent) fished mostly in area 7 in the west end of 

Cottonwood Bay. Three (4 percent) indicated that their 

favorite fishing area was along the southeastern shoreline of the lake (area 3). Seventy-three (90 percent) of 

the 81 fishermen were bank fishermen, and eight (10 

percent) were boat fishermen. The majority of the boat 

fishermen interviewed said they usually release all the 

fish they catch. 

On the basis of the results of the survey and of 

fish habits, channel catfish (Ictalurus punctatus), largemouth bass (Micropterus salmoides), and common carp 

(Cyprinus carpio) were selected as target taxa. The 

most frequently caught and consumed species was the 

channel catfish, which is abundant throughout the lake. 

Largemouth bass were caught and consumed less frequently than various catfish and white crappie; however, 

largemouth bass were selected because of their more 

localized feeding and spawning habits thus providing 

more site-specific information on contaminants. Common carp were chosen because of their habit to exclusively bottom feed and their tendency to bioaccumulate 

sediment-borne contaminants. Samples of tissue media 

comprised (1) fillets, skin-off, for channel catfish, largemouth bass, and common carp; (2) fillets, skin-on, for 

channel catfish and largemouth bass; (3) eviscerated 

whole fish for channel catfish; and (4) fish livers for 

largemouth bass and common carp. 

Table 2. Results of fishing-habits survey on Mountain Creek Lake 

Note: Sum of fractions of all fish or of particular species might not equal 100 percent because of rounding.

Species

Fraction of all fish

caught represented

by particular species

(percent)

Fraction of all fish

eaten represented by

particular species

(percent)

Fraction of particular species

eaten prepared as:

Fillet,

skin-off

(percent)

Fillet

skin-on

(percent)

Eviscerated

whole fish

(percent)

Channel catfish 16 17 60 34 5.7

Blue catfish 14 15 60 33 6.6

White crappie 12 14 46 43 11

Yellow catfish 12 13 50 38 12

White bass 11 11 57 33 9.5

Bullhead catfish 10 11 57 38 4.8

Largemouth bass 10 10 52 37 11

Freshwater drum 7.4 6.0 45 27 27

Common carp 3.6 1.0 100 0 0

Sunfish species 3.2 1.0 0 50 50

Smallmouth buffalo 1.2 1.0 50 50 0
8 Chemical Quality of Water, Sediment, and Fish in Mountain Creek Lake, Dallas, Texas, 1994–97 

Sampling Methods

Stormwater samples were collected (Phase I) 

by automatic samplers that collect flow-weighted 

composite samples (Raines and others, 1997). Individual samples of equal volume were collected each time 

a specified volume of flow passed the flow-control 

structure. Hand-dipped composite samples were collected for volatile organic compound (VOC) analysis. 

Precipitation, in 0.25-millimeter (mm) increments, was 

measured by a tipping-bucket rain gage attached to the 

gage house. The water elevation (stage) in a culvert or 

drainage channel was measured by a pressure gage. Discharge was computed using the measured stage and a 

theoretical equation based on the type of flow-control 

structure. 

Suspended sediment samples for chemical analysis were collected (Phase II) during storms with a minimum of 2.5 mm of precipitation and 72 hours between 

storms. Sampling targeted the rising limb and the peak 

of the storm hydrograph. Because total suspended sediment (TSS) concentrations were small, from less than 

5 to 71 milligrams per liter (mg/L) in Phase I stormwater samples, suspended sediment from as much as 

200 liters (L) of water was required to provide the mass 

of sediment necessary for direct chemical analysis. During the early part of a storm, a high-volume peristaltic 

pump was used to pump water from the estimated centroid of flow through Teflon-lined tubing into a 200-L 

Teflon bag lining a plastic drum. Sand-size and larger 

particles (greater than 0.063 mm) were trapped by a 

polyester mesh and removed before water entered the 

drum. 

Silt- and clay-size particles were removed by filtration from the water in the 200-L drum. Pre-cleaned 

glass-fiber filters (293-mm diameter) with pore size of 

0.7-micrometer (μm) were held in stainless steel filter 

holders and used to trap as much as 3 grams (g) of sediment for analysis of organic compounds. Filters loaded 

with sediment were analyzed for target constituents 

using the same extraction, cleanup, and quantification 

procedures that were used for Phase II bottom sediments. Major and trace element samples were collected 

on 140-mm diameter, 0.5-μm pore size, Teflon filters 

held in acrylic filter holders. Loaded filters were placed 

in plastic bags with a small amount of distilled water to 

flush sediment off the filter. The sediment and distilled 

water then were transferred to plastic containers, and 

the sample was freeze-dried. A minimum of 300 milligrams (mg) of sediment was required for analysis of 

major and trace elements using the analytical methods 

of Lichte and others (1987) and Fishman (1993).

Lake-water sample collection (Phase I) began 

with vertical profiles of pH, temperature, specific conductance, and dissolved oxygen. These field properties 

were measured at 0.6-m intervals by lowering a sampling tube to the desired depth and pumping water to the 

surface where the field properties were measured using 

a Hydrolab. Because no thermocline or oxycline was 

indicated, one depth-integrated sample was collected at 

each site. Sample-processing (compositing, filtering, 

and treating samples) was done following USGS protocols (Ward and Harr, 1990).

Lake-bottom sediment samples were collected 

(Phase I and Phase II) from Mountain Creek Lake 

using box corers and gravity corers (Jones and others, 

1997) following methods of the USGS National Water 

Quality Assessment (NAWQA) program (Van Metre 

and Callender, 1997; Van Metre, Callender, and Fuller, 

1997). At sites where surficial samples were collected 

by box corer, a gravity core was collected first to determine the thickness and character of lacustrine sediments. A standard “surficial bottom sediment sample” 

was the top 3 cm of sediment from a box core. One or 

two deeper intervals, usually 3 to 9 cm and 9 to 15 cm, 

also were sampled from box cores at eight sites in 

Cottonwood Bay during Phase II (fig. 2). Gravity cores 

were collected at three sites during Phase I (fig. 1) and 

at one site (M2.40) during Phase II (fig. 2) for chemical 

analysis of deeper, older sediments. The cores were 

subsampled by vertically extruding the sample using a 

piston that fits inside the core liner, pushing the sample 

upward in the liner, and slicing off selected intervals 

with a thin stainless steel plate. 

Streambed sediment samples were collected 

(Phase I and Phase II) following the methods of Ward 

and Harr (1990). The surficial material from the streambed was collected and composited, then wet-sieved in 

the field using native water. Wet-sieving before analysis 

provides better comparability among samples because 

smaller grain size yields a greater specific surface area, 

and many trace contaminants adsorb to the surface of 

sediments. The silt and clay fraction less than 0.063 mm 

was retained for inorganics analyses. The fraction less 

than 2 mm was retained for organics analyses.

Fish samples were collected during Phase I using 

an electrofishing boat. Largemouth bass and common 

carp were placed in an onboard, aerated holding tank 

that contained water from the lake. Either four or five 

individual whole carp from each of three sites in the lake 
METHODS 9

were composited at the laboratory before analysis. Bass 

fillet samples were collected as whole, skinless fillets 

(Crawford and Luoma, 1993). Fillets from five fish 

from each of three sites were composited at the laboratory for analysis. Phase I analysis of major and trace elements in fish was done on fish livers from both carp and 

bass. Liver tissue weighing 3 to 5 g was excised from 

each of five fish collected from each site, with a minimum of 10 g (wet weight) required for a composite sample of each species. 

Individual fish were collected during Phase II 

using an electrofishing boat and gill nets. Phase II samples comprised channel catfish, largemouth bass, and 

common carp; sample types comprised fillets with skin 

off, fillets with skin on, and eviscerated whole fish. The 

target sample size of 10 fish of each species and tissue 

type was achieved, except for channel catfish with a 

sample size of nine whole-body, eviscerated fish. Size 

ranges for largemouth bass (304 to 352 mm) and common carp (420 to 496 mm) were within 25 percent of 

maximum size as planned. Three additional bass greater 

than 400 mm were submitted for analysis on the basis of 

a recommendation from the Texas Department of 

Health (Kirk Wiles, Texas Department of Health, oral 

commun., 1996). Difficulties in collecting channel catfish precluded meeting size requirements across all tissue sample types.

Analytical Methods

Methods of analysis of Phase I stormwater 

samples are documented in Raines and others (1997). 

Analyses of lake water samples were done using the 

procedures described in Fishman and Friedman (1989) 

and Fishman (1993). Major element concentrations 

were determined by colorimetric analysis, trace element 

concentrations were determined using inductively coupled plasma (ICP), and organic carbon concentrations 

were determined with a carbon analyzer. Pesticide concentrations were determined by gas chromatography/

mass spectrometry (GC/MS) and by high-pressure 

liquid chromatography. VOC analyses were done using 

GC/MS.

Lake-bottom sediment grain-size analyses 

were done at the USGS sediment laboratory in Iowa 

City, Iowa, using sieve and pipet methods (Carol 

Anderson, U.S. Geological Survey, written commun., 

1993). Phase I lake-bottom sediment pesticide and 

polychlorinated biphenyl (PCB) analyses were done 

by gas chromatography/electron capture detection 

(GC/ECD) (Wershaw and others, 1987). Phase I semivolatile organic compound (SVOC) analyses were done 

on organic-sediment extracts using GC/MS following 

the methods of Furlong and others (1996). Phase I major 

and trace element concentrations were determined 

on concentrated-acid digests (nitric-hydrofluoricperchloric acids) using ICP-atomic emission spectrometry (ICP–AES) (Lichte and others, 1987). Phase II 

polycyclic aromatic hydrocarbon (PAH) analyses were 

done following the extraction and cleanup procedures of 

Furlong and others (1996), with selected ion monitoring 

for PAHs by GC/MS (E.T. Furlong, U.S. Geological 

Survey, written commun., 1996). Pesticide and PCB 

analyses were done on organic-solvent extracts using 

the extraction procedures described by Foreman and 

others (1995) and the quantification procedures 

described by Wershaw and others (1987). PCBs and 

chlordane compounds were reported as Aroclors 1242, 

1254, and 1260, and as technical chlordane, respectively. Phase II analyses of major and trace elements 

included ICP–AES; chromium, lead, and zinc were 

determined by graphite-furnace atomic adsorption; 

mercury was determined by cold vapor; and selenium 

was determined by hydride generation (Lichte and 

others, 1987; Fishman, 1993). Suspended sediment 

samples (Phase II) were analyzed using the same 

methods as Phase II lake-bottom sediment samples. 

Fish samples analyzed for pesticides and PCBs 

were first homogenized to form a single composite 

sample (homogenate). A10-g homogenate subsample 

was extracted with organic solvents and gel permeation 

chromatography (GPC) procedures to concentrate 

and remove lipids from the extract. Percent lipid was 

determined for each sample to allow for normalization 

of data as needed. Prepared extracts were analyzed 

by GC/ECD (Leiker, 1995), and concentrations of 

individual compounds were quantified at a minimum 

reporting level (MRL) of 5.0 micrograms per kilogram 

(μg/kg) wet weight (U.S. Geological Survey, 1994). 

PCBs and chlordane compounds were reported as 

Aroclors 1242, 1254, and 1260, and as technical chlordane, respectively.

Liver tissues and fillets subsampled for trace 

element analysis were prepared by oven-drying to a 

constant weight, dissolution of the sample by acid 

digestion and the addition of hydrogen peroxide, 

and filtration of remaining insoluble materials (U.S. 

Geological Survey, 1993). Concentrations of trace 
10 Chemical Quality of Water, Sediment, and Fish in Mountain Creek Lake, Dallas, Texas, 1994–97 

elements were determined in the acid-digested 

biological material (Fishman and Friedman, 1989; 

Faires, 1993). Whole-body, eviscerated samples were 

homogenized using a stainless steel grinder; a 20-g 

subsample was retained for trace element analysis following the procedures described above. 

VOCs were analyzed using a method similar to 

the method recommended by the U.S. Environmental 

Protection Agency (USEPA) for analysis of VOCs in 

fish tissue (Easley and others, 1981). Ten milliliters of 

organic-free water and a spiked solution were added to 

each VOC subsample in a 1.9-cm-diameter glass test 

tube. The sample was then placed in an ice bath and 

subjected to a sonic disrupter for 2 minutes, then loaded 

into a Tekmar 2016 autosampler. The sampler is 

outfitted with a modified purge needle. The sample 

was heated to 70 degrees Celsius (°C) for 2 minutes 

before the purge cycle. The sample was desorbed into 

the gas chromatograph (GC), which is temperature programmed from -20 to 160 °C, and analyzed by electron 

impact mass spectrometry in the full-scan mode.

SVOCs in fish were analyzed using the extraction 

and cleanup procedures described in Leiker (1995) and 

the quantification procedures developed for sediment 

samples in Furlong and others (1996). 

Quality Control

Quality-control sample types and qualityassurance elements of the Mountain Creek Lake study 

are described in a written study plan provided to the 

Navy and regulatory agencies (USEPA and Texas Natural Resource Conservation Commission [TNRCC]) 

before sampling. Selected quality-control data for samples collected at Mountain Creek Lake are listed in 

Jones and others (1997). Quality-control data are used 

to estimate the bias and variability in environmental 

data. Bias is the systematic error inherent in a method or 

caused by some artifact of the measurement system. 

Variability is the degree of variation in independent 

measurements as the result of repeated application of 

the measurement process. Quality-assurance elements 

are specifications of methods of sample collection, 

procedures for sample processing, methods of laboratory analysis, and collection of field quality-control 

samples.

Spiked sediment samples were used to evaluate 

bias caused by analytical methods. The median percent 

recovery for 48 spikes (eight each for anthracene, 

benzo(a)pyrene, benzo(b)fluoranthene, fluoranthene, 

phenanthrene, and pyrene) was 71.5 percent during 

Phase II (fig. 3). Recoveries ranged from 50 to 98 percent, which met laboratory-established control limits. 

(8)

(8)

(8)

(8)

(8)

(8)

(48)

Anthracene

Benzo(a)pyrene

Benzo(b)fluoranthene

Fluoranthene

Phenanthrene

Pyrene

Combined

40 50 60 70 80 90 100

PERCENT RECOVERY

EXPLANATION

Minimum

25th percentile

Median (50th percentile)

75th percentile

Maximum

Number of samples

(8)

(8)

Figure 3. Percent recovery of laboratory spiked quality-control samples for polycyclic aromatic hydrocarbons in 

bottom sediment collected at Mountain Creek Lake, Dallas, Texas. 
METHODS 11

Replicate sediment samples were collected by 

splitting the environmental samples in the field. Replicate samples allow measurement of the variability in the 

analytical values produced by processing and transport 

of the samples and by the analytical method. Relative 

percent difference (RPD) between the environmental 

and replicate samples, which is defined as the difference 

divided by the average multiplied by 100, is a measure 

of this variability. 

Metals show the least variability as measured 

by the RPD (fig. 4). The median RPD for 32 replicate 

analyses of metals (eight samples each for chromium, 

copper, lead, and zinc) in bottom sediments collected 

during Phase I and Phase II was 4.3 percent. The median 

RPD for PAHs in 48 replicate samples (eight samples 

each for anthracene, benzo(a)pyrene, benzo(b)fluoranthene, fluoranthene, phenanthrene, and pyrene) in 

bottom sediments collected during Phase II was 19 percent. The median RPD for 20 organochlorine pesticide 

samples in bottom sediment collected during both 

phases was 11 percent (four samples each for chlordane, 

DDD, DDE, DDT, and dieldrin). Several of the pesticide environmental and replicate samples were below 

method detection limits, which resulted in an RPD of 

zero. The median RPD for PCBs in 27 replicate samples 

(nine samples each for Aroclors 1242, 1254, and 1260) 

collected in bottom sediment during both phases was 

21 percent. 

0 20 40 60 80 100 120

RELATIVE PERCENT DIFFERENCE

METALS

Chromium

Copper

Lead

Zinc

PAHs

Anthracene

Benzo(a)pyrene

Benzo(b)fluoranthene

Fluoranthene

Phenanthrene

Pyrene

ORGANOCHLORINE 

 PESTICIDES

PCBs

Aroclor 1242

Aroclor 1254

Aroclor 1260

(32)

(8)

(8)

(8)

(8)

(48)

(8)

(8)

(8)

(8)

(8)

(8)

(9)

(9)

(9)

(27)

(20)

EXPLANATION

(20)

Number of 

samples

Minimum

25th percentile

Median (50th percentile)

75th percentile

Maximum

Figure 4. Percent differences between environmental and replicate samples in lake bottom sediment collected at 

Mountain Creek Lake, Dallas, Texas. 
12 Chemical Quality of Water, Sediment, and Fish in Mountain Creek Lake, Dallas, Texas, 1994–97 

Stormwater and lake water samples collected during Phase I were monitored for field contamination 

from VOCs and trace elements by collecting field 

blanks and by including trip blanks (VOCs only) in 

coolers with environmental samples. Blank and spike 

solutions were analyzed in the laboratory along with 

each batch of water samples analyzed. The qualitycontrol data were within acceptable ranges, except for 

stormwater samples collected by automatic sampler at 

one site in which blank contamination for VOCs 

occurred (Raines and others, 1997). It was determined 

that contamination of the pump tubing had occurred 

during the previous storm. To avoid additional sample 

contamination, pump tubing was replaced after each 

use. 

Laboratory blanks and spikes also were run for 

fish-tissue samples (Jones and others, 1997). Median 

percent recovery for 40 spikes for organochlorine 

pesticides (eight each for chlordane, DDD, DDE, DDT, 

and dieldrin) was 94 percent during Phase II (fig. 5). 

The spike recovery range of 70 to 105 percent met 

laboratory-established control limits.

POTENTIAL SOURCES OF CONTAMINATION FROM NAVY FACILITIES TO 

MOUNTAIN CREEK LAKE

Contaminants could reach Mountain Creek Lake 

from several sources and by several pathways. Pathways 

include wash-off of contaminants from surrounding 

areas by stormwater, direct (point-source) discharges of 

wastewater, and inflow of ground water to the lake. 

Wash-off, direct discharges, and ground-water inflows 

could come from several industrial facilities in the 

Mountain Creek Lake watershed including the Navy 

facilities and commercial or urbanized areas of the 

Cottonwood Creek watershed. Some contaminants, lead 

and mercury for example, also can reach lakes from 

local and regional atmospheric sources. 

This section briefly summarizes the current 

(1998) understanding of historical releases and presentday occurrence of contaminants on Navy facilities. In 

some cases, more detailed information of the on-site 

occurrence of some contaminants is presented in following sections, which discuss potential sources of 

specific elements and compounds. The information in 

this section is from the Navy and its contractors, primarily EnSafe. Selected information on recent inputs of 

containments from the Cottonwood Creek watershed 

obtained during this investigation is presented with 

other chemical results.

NWIRP Sources

During 1941–74, the NWIRP facility discharged 

stormwater runoff, treated sanitary sewage, and industrial process wastewater into the west and east lagoons 

(fig. 1). Waste disposal into the west lagoon, which 

(8)

(8)

(8)

(8)

(8)

(40)

Chlordane

Dieldrin

DDE

DDD

DDT

Combined

60 70 80 90 100 110

PERCENT RECOVERY

EXPLANATION

Minimum

25th percentile

Median (50th percentile)

75th percentile

Maximum

Number of samples

(8)

Figure 5. Percent recovery of laboratory spiked quality-control samples for organochlorine pesticides in fish tissue 

collected at Mountain Creek Lake, Dallas, Texas. 
POTENTIAL SOURCES OF CONTAMINATION FROM NAVY FACILITIES TO MOUNTAIN CREEK LAKE 13

flows into Cottonwood Bay, was estimated as 1,300 

m3

/d (cubic meters per day) including an undetermined 

amount of waste petroleum, oil, and lubricants mixed 

with storm runoff. Of the 1,300 m3

/d, about 1,150 m3/d 

is attributed to facility processes (table 3) (EnSafe/Allen 

& Hoshall, 1996a). Beginning in 1974, sewage generated on the facility was discharged to the City of Dallas 

sanitary sewer system, and much of the facility’s process wastewater was routed to the industrial waste treatment plant (IWTP) for treatment before discharge to 

the sanitary sewer. A control system was built in 1974 

to reduce the amount of flow entering Cottonwood 

Bay from the west lagoon. The system diverts 110 to 

190 m3/d to the IWTP for treatment before discharge to 

the sanitary sewer system. During 1974–84 the west 

lagoon received about 570 to 760 m3/d of flow from 

unspecified sources. In March 1992, miscellaneous and 

previously unidentified wastewater lines discharging 

into the lagoon were disconnected. Dry-weather flow to 

west lagoon now ranges from 110 to 190 m3

/d and still 

contains some process wastewater, most of which is 

captured by the diversion system to the IWTP (EnSafe/

Allen & Hoshall, 1996a).

During 1941–74 the east lagoon received an 

unknown quantity of treated sanitary sewage. Since 

1974 the lagoon has received primarily stormwater runoff. This runoff contained about 0.4 cubic meter per 

year (m3

/yr) of spilled fuel and oil from aircraft fueling 

and maintenance areas in the east lagoon drainage area. 

In 1971 an oil-spill recovery system was installed at the 

southern end of the lagoon to reduce the fuel and oil discharge into Cottonwood Bay.

In addition to the waste disposal in the lagoons, 

the large manufacturing buildings (1 and 6, fig. 6) house 

degreaser vats which historically used trichloroethene 

(TCE) as a degreasing solvent. A large TCE groundwater plume is present at the site. An off-site source 

west of the NWIRP might also contribute to the plume 

at the site. A recently developed ground-water-flow 

model indicates that about 70 m3

/d of ground water is 

discharging to the east and west lagoons (Barker and 

Braun, 2000). 

NAS Sources

Six identified solid-waste management units 

(SWMUs) (Groups 9, 12, and 14 and buildings 43, 51, 

and 178 in fig. 6) are located in the drainage area of the 

NAS–1 stormwater site (fig. 1). Documented petroleum, oil, and lubricant (POL) spills have occurred. 

Table 3. Waste disposed of in the west lagoon, Naval Weapons Industrial Reserve Plant

[From Ensafe/Allen & Hoshall, 1996a] 

Period Waste type

Total

discharge

(cubic meters)

Average daily

discharge

(cubic meters 

per day)

Sources

1941–74 Metal plating solutions containing magnesium 

(Mg), nickel (Ni), titanium (Ti), copper (Cu), 

cadmium (Cd), chromium (Cr), and zinc (Zn)

42 0.003 Plating shops

1941–74 Metal plating rinse water 2,800,000 220 Plating shops

1941–74 Neutralized acid solutions (sulfuric, nitric, 

chromic, phosphoric, hydrofluoric)

170 .014 Plating shops

1941–74 Alkaline cleaning solutions 38 .003 Plating shops

1941–74 Waste petroleum, oil, and lubricants and plantwide stormwater runoffUndetermined Undetermined Plant-wide storm runoff and 

shop floor washdown water

1941–74 Solvents (acetone, methyl ethyl ketone, 

isopropanol)

25 .002 Bond shop

1941–74 Treated effluent from the sewage treatment plant 11,000,000 910 Plant-wide

1941–74 Boiler and cooling tower blowdown 98,000 7.9 Plant-wide

1967–74 Phenolic stripper rinse water 11,000 .9 Aluminum parts stripper shop

1974–84 Herbicide rinse water 5 .0003 Herbicide formulation
14 Chemical Quality of Water, Sediment, and Fish in Mountain Creek Lake, Dallas, Texas, 1994–97 

US 80

MOUNTAIN CREEK LAKE

Creek

West 

Lagoon East 

Lagoon

Cottonwood

Cot

Bay tonwood

0 0.5 1 KILOMETER

Base from EnSafe/Allen & Hoshall

written commun., 1996

Modified State Plane

Naval Weapons

Industrial Reserve

Plant

Naval

Air 

Station

96o59'

32o

44'

96o

58' 96o

57'

32o

42'

EXPLANATION

Boundary of Naval Weapons Industrial

Reserve Plant and Naval Air Station

Building of interest

Group of interest

SWMU of interest

Group 14

Group 12

Bldg. 20

Group 9

Bldg. 43

Bldg. 51

Bldg. 178

Bldg. 6 Bldg. 1

SWMU 81

SWMU 20

SWMU 29

SWMU 14

SWMU 6

SWMU 1

SWMU 2P

Group 11

SWMU 26P

SWMU 79

Figure 6. Locations of selected buildings, groups, and solid-waste management units (SWMUs) on the Naval Air 

Station and Naval Weapons Industrial Reserve Plant, Dallas, Texas. 
CHEMICAL QUALITY OF WATER, SEDIMENT, AND FISH IN MOUNTAIN CREEK LAKE 15

A fuel farm is located just north of building 20. Group 

12 currently (1998) houses the Public Works storage 

area, but formerly contained a sewage treatment plant 

and possibly a sludge-drying bed. No VOC contamination is suspected from this area. Group 14 is located 

nearest the NAS–1 stormwater site. A 38-cubic meter 

(m3

) steel storage tank located in this group is suspected 

of being the source of an on-site TCE ground-water 

plume mapped by EnSafe. Additional sources in this 

area include a former aircraft wash area (where solvents 

were used) and a drum storage area (EnSafe/Allen & 

Hoshall, 1996b).

Stormwater site NAS–2 (fig. 1) is located on the 

part of NAS that houses the administrative, recreational, 

and residential areas of the base, but the drainage area 

includes the main fuel farm (SWMU 79) for the facility. 

NAS–2 receives flow from stormwater and sanitary 

sewers in addition to surface runoff. Fuel spills historically have been routed to the fuel farm storm sewers and 

tanks (EnSafe/Allen & Hoshall, 1997b). 

Stormwater site NAS–3 (fig. 1) is located in the 

northeastern corner of NAS in the oldest developed part 

of the facility. The area currently (1998) is used by the 

Texas Air National Guard (TANG), Marine Air Group 

41, Navy vehicle maintenance, and fire department. The 

TANG storm sewers discharge to an unlined ditch near 

NAS–3. These storm sewers collect spills and wash 

water from the TANG maintenance hanger, aircraft 

maintenance hanger, transport hanger, and aircraft wash 

rack. Chemicals released to the storm sewers include 

solvents, cleaning compounds, detergents, degreasers, 

hydraulic oils, motor oils, and kerosene. The Navy 

transformer station is directly north of NAS–3.

CHEMICAL QUALITY OF WATER, 

SEDIMENT, AND FISH IN MOUNTAIN 

CREEK LAKE

The occurrence, trends, and sources of chemical 

constituents presented and discussed in this section are 

organized by chemical groups, which comprise metals, 

VOCs, PAHs, organochlorine pesticides, and PCBs. 

Within each chemical group, discussions are organized 

by environmental phase, as applicable, including stormwater, lake water, sediment, and fish. 

Discussions of spatial occurrence require a common locational reference for the lake and surrounding 

areas. Three sets of locations typically are referred 

to: Phase I sampling sites (fig. 1), Phase II sampling 

sites/areas (fig. 2), and place names associated with the 

lake (fig. 7). Some of the place names in figure 7 are 

official; others are used only in this report and have been 

established to facilitate discussion. 

Reference Concentrations

Comparisons of concentrations in any given sample to reference concentrations can indicate the magnitude of a land-use-related effect of interest. Two types of 

reference concentrations were used: (1) main lake and 

(2) urban. Main lake reference concentrations are typical of the main body of Mountain Creek Lake remote 

from the Navy facilities at sites not directly affected by 

runoff of contaminants from either the Navy facilities or 

the nearby urban areas of Dallas or Grand Prairie. Urban 

reference concentrations are of interest because much of 

the activity at the Navy facilities is similar to urban 

areas in general, for example the large parking areas and 

associated automobile traffic. Three sites were chosen 

on the basis of watershed land-use characteristics to 

provide urban reference concentrations. Two sites sampled in this study are on the north and south forks of 

Cottonwood Creek. Cottonwood Creek drains parts of 

Grand Prairie and does not receive drainage from Navy 

facilities. The third site is White Rock Lake in northeastern Dallas, a reservoir with an urbanized watershed 

in a geologic setting similar to that of Mountain Creek 

Lake. Age-dated sediment cores were collected from 

White Rock Lake in 1994 and 1996 and interpreted to 

describe trends in water quality using methods similar 

to those used at Mountain Creek Lake (Van Metre and 

Callender, 1997; Van Metre and others, 2000). 

A reproducible, statistically based method for 

describing reference concentrations of possible contaminants can reduce the potential for bias in interpretation 

of environmental data. The largest datasets generated 

by this study are for sediments and fish tissues. Because 

fish are able to move around the lake, their exposure 

history to site specific inputs is unknown; therefore, 

no attempt was made to describe reference concentrations of contaminants in fish. The same is also true of 

water. Sediments, however, generally remain in place 

after deposition on the bottom of a lake, except in 

near-shore areas where wave action can cause resuspension. The stability of lake sediment deposits over time is 

demonstrated by age-dated sediment cores from lakes 

(Van Metre and others, 1998). Therefore, only main 

lake reference concentrations were computed and used 

in this report for bottom sediment data.
16 Chemical Quality of Water, Sediment, and Fish in Mountain Creek Lake, Dallas, Texas, 1994–97 

Florina Drive

US 80

Causeway

State 303

DAM

Bldg. 6 Bldg. 1

MOUNTAIN CREEK LAKE

Mountain Creek

Cottonwood Creek

West 

Lagoon East 

Lagoon

Cottonwood

Bay

0 0.5 1 KILOMETER

Base from EnSafe/Allen & Hoshall

written commun., 1996

Modified State Plane

Naval Weapons

Industrial Reserve

Plant

Naval

Air 

Station

Texas

Utilities

power

plant

96o59'

32o

44'

96o58' 96o

57'

32o

43'

32o

42'

EXPLANATION

Boundary of Naval Weapons Industrial

Reserve Plant and Naval Air Station

Boundary between parts of Mountain

Creek Lake

MAIN LAKE

UPPER LAKE

NAS 

INLET

RUNWAY

INLET

CANAL

WEST

BAY

CENTRAL

BAY

EAST

BAY

EAST

LAGOON WEST

LAGOON

PLACE NAME SITES INCLUDED

UPPER LAKE Phase I: MCL–1

MAIN LAKE Phase I: MCL–2, MCL–3, MCL–4

Phase II: M2.28, M2.29, M2.30,

M2.33, M2.34, M2.35, M2.36,

M2.44, M2.45

NAS INLET Phase I: MCL–11, MCL–12,

NAS–1, NAS–2, NAS–3

Phase II: M2.37, M2.38, M2.39,

M2.40, M2.41, M2.42, M2.43

RUNWAY INLET Phase I: MCL–10

Phase II: M2.31, M2.32 

CANAL Phase I: MCL–8

Phase II: M2.24, M2.25, M2.26,

M2.27

WEST BAY Phase I: MCL–5, MCL–6

Phase II: M2.19, M2.20, M2.21,

M2.22

CENTRAL BAY Phase I: MCL–7, MCL–13

Phase II: M2.10, M2.11, M2.12,

M2.13, M2.14, M2.15, M2.16,

M2.17, M2.18

EAST BAY Phase I: MCL–9, Bay–7, Bay–11,

Bay–13, Bay–16

Phase II: M2.1, M2.2, M2.3, M2.4,

M2.5, M2.6, M2.7, M2.8, M2.9

WEST LAGOON NWIRP–1

EAST LAGOON NWIRP–2

Figure 7. Place names of parts of Mountain Creek Lake used in this report. 
CHEMICAL QUALITY OF WATER, SEDIMENT, AND FISH IN MOUNTAIN CREEK LAKE 17

Cluster analysis was used to group data on the 

basis of similar characteristics. Clustering forms groups 

of cases (sampling sites) on the basis of a distance measure between each case. In this application, the distance 

measure is based on relative concentrations of indicator 

contaminants. As nearby cases are grouped to form 

clusters, the distance to each new case is based on the 

centroid of cases in the group. The resulting number of 

clusters formed is controlled by the analyst. After cases 

are grouped, each cluster can be evaluated by the analyst 

to determine what part of the overall dataset the cluster 

represents. For example, one cluster could include only 

sampling sites from the upper part of the lake, whereas 

another could include only sites in Cottonwood Bay. 

Although the clustering procedure is statistically 

based and reproducible, several judgment decisions 

were made that can affect the outcome. The first of these 

is the choice of what sites and what variables to include. 

All of the Phase I (except Bay–16) and Phase II surficial 

(0 to 3 cm) lake-bottom sediment sampling sites (one 

sample per site) were included. Three chemical concentration variables were chosen as indicator contaminants: 

chromium, total PAHs (T-PAH), and PCBs. These three 

were chosen because each varied greatly in Mountain 

Creek Lake sediment, each represents a different group 

of potential contaminants with different sources and 

environmental behaviors, and each has sources on Navy 

facilities (EnSafe/Allen & Hoshall, 1996a, b) and from 

other industrial and urban activities (Hites and others, 

1981; Hem, 1985). Before clustering, concentrations 

were converted to logarithms and normalized by dividing each (log) concentration by the largest (log) concentration. The log transformations were done because 

the clustering is based on distance (measured in concentration difference) between cases. Chemical concentrations in the environment usually are log-normally 

distributed, so a log transformation moves large concentrations relatively closer to each other and spreads small 

and medium concentrations relatively farther apart. 

Normalization of each constituent to its largest concentration was done because the relative magnitudes of 

the concentrations are quite different. Thus normalization evens the weighting (or influence on the outcome) 

of chromium concentrations (21 to 360 μg/g [micrograms per gram]) and T-PAH concentrations (97 to 

225,000 μg/kg).

Six clusters were formed (fig. 8; table 4). Clusters 

4 and 6 have only one site each, M2.42 and MCL–9, 

respectively (table 4). Site M2.42 has unusually small 

chromium and large PCB concentrations, making it an 

outlier relative to the other sites. Site MCL–9 has 

unusually large chromium and small PCB concentrations, making it an outlier as well. The remaining sites 

were grouped into four clusters. Twenty-three of the 

Table 4. Sites included in cluster analysis

[NAS, Naval Air Station] 

Cluster Location Sites included in cluster

1 Cottonwood Bay Phase I: MCL–7, MCL–13, Bay–7

Phase II: M2.1, M2.2, M2.3, M2.4, M2.5, M2.6, M2.7, M2.8, M2.9, M2.10, M2.11, 

M2.12, M2.13, M2.14, M2.15, M2.16, M2.17, M2.18, M2.20, M2.21, M2.37, 

M2.39

2 Canal/runway Phase I: MCL–5, MCL–6, MCL–8, MCL–10, MCL–11

Phase II: M2.19, M2.22, M2.24, M2.25, M2.26, M2.27, M2.28, M2.29, M2.30, 

M2.33, M2.34, M2.35, M2.36, M2.41, M2.45

3 Runway inlet/NAS 

inlet

Phase I: MCL–12

Phase II: M2.31, M2.32, M2.38

4 NAS inlet, outlier Phase II: M2.42

5 Main-lake reference Phase I: MCL–1, MCL–2, MCL–3, MCL–4

Phase II: M2.43, M2.44

6 Cottonwood Bay, 

outlier

Phase I: MCL–9
18 Chemical Quality of Water, Sediment, and Fish in Mountain Creek Lake, Dallas, Texas, 1994–97 

Cluster 2, Canal/runway

Cluster 3, Runway inlet/NAS inlet

Cluster 1, Cottonwood Bay

Cluster 4, NAS inlet outlier

Cluster 6, Cottonwood Bay outlier

Cluster 5, Main-lake reference

MOUNTAIN CREEK LAKEMOUNTAIN CREEK LAKE

EXPLANATION

Cluster 1,

Cottonwood

Bay

Cluster 2,

Canal/runway

Cluster 3,

Runway inlet/

NAS inlet

Cluster 4,

NAS inlet outlier

Cluster 5,

Main-lake 

reference

Cluster 6,

Cottonwood Bay

outlier

CHROMIUM CONCENTRATION,

IN MICROGRAMS PER GRAM

0 100 200 300 400 1 10 100 1,000

PCB CONCENTRATION,

IN MICROGRAMS PER KILOGRAM

5 500 50,000

TOTAL PAH CONCENTRATION,

IN MICROGRAMS PER KILOGRAM

EXPLANATION

(20)

Number of

samples

75th percen

Maximum

tile

Median (50th

percentile)

25th percentile

Minimum

(25)

(20)

(4)

(1)

(6)

(1)

Figure 8. Locations of sites and range in selected constituents in bottom sediments for clusters.
CHEMICAL QUALITY OF WATER, SEDIMENT, AND FISH IN MOUNTAIN CREEK LAKE 19

25 sites in cluster 1 are located in Cottonwood Bay. The 

other two sites, M2.37 and M2.39, are located in the 

NAS inlet. Of the four multisite clusters, cluster 1 has 

the largest concentrations of all three indicator variables 

(chromium, T-PAHs, and PCBs) that the clusters were 

based on. Cluster 2 has 20 sites. These sites are located 

in the west end of Cottonwood Bay, in the canal connecting to the main lake, along the west side of the runway, in the main lake, in the runway inlet, and in the 

NAS inlet. Concentrations of all three indicator variables are intermediate for this cluster. Cluster 3 has four 

sites, two in the runway inlet and two in the NAS inlet. 

These sites have relatively small chromium and T-PAH 

concentrations and relatively large PCB concentrations. 

Cluster 5 has six sites, one in the NAS inlet and the other 

five in the main and upper parts of the lake. With the 

exception of the anomalously small chromium concentration at site M2.42 (cluster 4), cluster 5 has the smallest concentrations of all three variables. It was thus 

designated as “main-lake reference.” 

Dating Sediment Cores

Historical trends in many persistent, hydrophobic contaminants can be identified by analyzing cores 

of bottom sediment from lakes and reservoirs (for 

example, Eisenreich and others, 1989; Callender and 

Van Metre, 1994; Van Metre and Callender, 1996, 

1997). During storms, sediment is washed off the land 

surface and deposited in the lake. Over time, sediment 

accumulates in a thick layer on the bottom. More than 

2 m of sediment has been deposited in the deepest part 

of Mountain Creek Lake since it was built in 1929. Coring through the sediment and analyzing discrete slices 

from the cores can allow a partial reconstruction of historical inputs of contaminants. 

Gravity cores of deeper, older sediment were 

collected from two sites in Mountain Creek Lake 

(MCL–4 and M2.40) and two sites in Cottonwood Bay 

(MCL–7 and Bay–13) (figs. 1, 2). Cores were described 

visually on-site for color, texture, odor, and identification of the pre-reservoir land surface. The lacustrine 

(lake-deposited) sediments were characterized by uniform, fine-textured, olive-gray (5Y 4/1 on the Munsell 

rock color chart; Geological Society of America, 1991) 

and olive-black (5Y 2/1) clay-size material that oxidized to a dark yellowish brown (10YR 4/2) on exposure to air. Several black (N2 and N1) layers that had a 

strong hydrocarbon odor were noted in numerous 

reconnaissance cores and in cores from MCL–7 and 

Bay–13 in Cottonwood Bay. Lacustrine sediment was 

more than 99 percent silt and clay (less than 0.062 mm) 

with a median of 86 percent clay-size (less than 0.004 

mm) particles. Organic carbon concentrations, in 

weight percent, ranged from 1.1 to 3.4 (median 2.0, 

interquartile range 0.4) in gravity cores from sites 

MCL–4 and M2.40 in the main lake and were as large 

as 6.6 in samples from Cottonwood Bay. 

Four approaches were used to assign deposition 

dates to individual sample intervals in gravity cores: 

(1) core lithology, specifically the visual and chemical 

identification of the pre-reservoir land surface in the 

core; (2) cesium-137 (137Cs) concentrations; (3) concentrations of DDT and dieldrin in relation to their historical uses; and (4) down-core sediment chemistry in 

relation to the discharge history of the west lagoon on 

NWIRP. 

Lacustrine sediment begins to accumulate soon 

after a reservoir is impounded. The pre-reservoir land 

surface is easily identified in reservoir cores by the 

change in grain size and chemistry of sediments and by 

the presence of vegetative root hairs and other woody 

debris. Lacustrine sediment in Mountain Creek Lake 

immediately above the pre-reservoir material in a core, 

therefore, was assigned the date of reservoir impoundment, 1929. Because sediment continues to accumulate 

over time, the top of a core is assigned the sampling 

date. 

Dating information was obtained at two coring 

locations by analyzing 137Cs. A by-product of nuclear 

weapons testing, 137Cs has a half-life of 30.8 years. 

Appreciable concentrations of 137Cs in the atmosphere 

first occurred in about 1952 with the advent of largescale weapons testing; atmospheric concentrations had 

a minor peak in 1958 and a major peak during 1963–64. 

Because 137Cs sorbs strongly to fine-grained sediment, 

it is useful for dating sediment exposed to atmospheric 

fallout (Durrance, 1986). 

137Cs was detected in the deepest lacustrine sample (44- to 48-cm interval) and in the first sample of 

pre-reservoir material (48 to 52 cm) from the M2.40 

core and peaked in the 40- to 44-cm interval (fig. 9), 

indicating that the assumption of continuous sedimentation since impoundment in 1929 was not valid at this 

site. Sediment deposited there from 1929 until the early 

1950s apparently was eroded, possibly because this site 

is relatively shallow and near shore and because lake 

levels have fluctuated historically. The 137Cs peak and 

the shape of the 137Cs profile in the upper part of the 
20 Chemical Quality of Water, Sediment, and Fish in Mountain Creek Lake, Dallas, Texas, 1994–97 

core indicate that continuous sedimentation has 

occurred since the 1950s. 

The 137Cs dating interpretation in the M2.40 core 

is supported by the total DDT (p,p'-DDE + p,p'-DDD + 

p,p'-DDT) profile in a second core from the same site 

(fig. 9). Use of DDT peaked in the United States in the 

early 1960s (Rapaport and others, 1985). Total DDT 

profiles in reservoir sediment cores reflect this use history with peaks in total DDT concentrations consistently in the early 1960s and exponential decreases in 

concentrations to the tops of cores (Van Metre and 

Callender, 1997; Van Metre, Callender, and Fuller, 

1997). Total DDT concentrations were largest in the 

35- to 40-, 40- to 45-, and 45- to 50-cm intervals in the 

“organics” core from site M2.40 indicating late-1950s 

and early 1960s. (Separate cores were used for organics 

[organochlorine pesticides, PAHs, and PCBs] and inorganics [137Cs and major and trace elements] analyses 

from this site.) 

One additional piece of information was available 

to provide an approximate date of the sediment. Dieldrin, an organochlorine pesticide, was detected in most 

samples in the M2.40 core down through the 60- to 

65-cm interval (fig. 9). Dieldrin is a breakdown product 

EXPLANATION

Cesium-137

Total DDT (DDE+DDD+DDT) 

p,p'-DDE

p,p'-DDD

p,p'-DDT

Dieldrin

Below method detection limit

0 5 10

0

160

20

40

60

80

100

120

140

 DDTs

0 0.2 0.4 0.6 0.8 0 0.5 1.0

0

80

20

40

60

0 20 40

DEPTH, IN CENTIMETERS

CESIUM-137 DDTs DIELDRIN

ACTIVITY, IN 

PICOCURIES

PER GRAM

First occurrence,

early 1950s

CONCENTRATION, IN

MICROGRAMS

PER KILOGRAM

CONCENTRATION, IN

MICROGRAMS

PER KILOGRAM

M2.40 core MCL–4 core 

CONCENTRATION, IN

MICROGRAMS

PER KILOGRAM

First occurrence,

early 1950s

Peak,

1964

Peak,

early 

1960s

Top of core, 1994

Peak,

early 

1960s

Pre-reservoir surface

Figure 9. Cesium-137 and organochlorine pesticide concentrations in M2.40 and MCL–4 cores. 
CHEMICAL QUALITY OF WATER, SEDIMENT, AND FISH IN MOUNTAIN CREEK LAKE 21

of aldrin. Aldrin was synthesized in 1948 and first 

produced commercially in 1951; therefore, the 60- to 

65-cm interval cannot be older than the early 1950s. The 

total DDT peak is consistent with the 137Cs peak at 40 

to 44 cm; however, the organics core extended to 72 cm 

before encountering pre-reservoir material compared to 

48 cm in the inorganics core. Variability in lengths of 

cores and in thickness of lacustrine sediments between 

nearby sites is not uncommon (Van Metre, Callender, 

and Fuller, 1997). Variability between cores probably is 

caused by movement of the boat between core collections and uneven pre-reservoir surface elevations leading to uneven sedimentation and erosion. On the basis of 

the total DDT profile, dieldrin detections, linear sedimentation rates for the upper parts of the two cores, and 

relative lengths of the cores, the lacustrine sedimentary 

record in the organics core probably begins about 1940.

Samples from the MCL–4 core were not analyzed 

for 137Cs; however, the location of the site in deep water 

at the center of the lake and the total DDT profile in the 

core indicate a complete sedimentary record from 1929 

until 1994 when the cores were collected (fig. 9). Lacustrine sediments in the MCL–4 organics core were 128 

cm thick, and total DDT peaked in the 50- to 60-cm 

interval at 5.9 μg/kg. DDT and its breakdown products 

were not detected below 100 cm, indicating that this 

core probably does date from 1929. 

Samples from the Bay–13 core were dated 

(fig. 10) on the basis of core lithology, 137Cs results, and 

phosphorus and trace element trends in relation to historical discharges from the west lagoon. Dates for two 

deeper samples from the MCL–7 core in Cottonwood 

Bay were assigned on the basis of comparison to the 

Bay–13 core. The lacustrine sediment at MCL–7 was 

84 cm thick compared to 161 cm in the 137Cs core (and 

160 cm in the organics core) at Bay–13. The first occurrence of 137Cs in the Bay–13 core was in the 91- to 

98-cm interval, a minor peak occurred in the 84- to 

0 3 1 2

0

150

50

100

DEPTH, IN CENTIMETERS

0 0.4 0.2 0 40 20

CESIUM-137 PHOSPHORUS SILVER

DATE BASED ON

1995—Core lithology

1974—Sewage discharge history

1964—Cesium-137 profile

1995

1974

1964

1958

1953

1941

1929 at 160 centimeters

SEDIMENTATION RATE 

 Centimeters Grams per

1.0 0.4

4.2 2.2

2.9 1.8

2.7 1.6

ACTIVITY, IN

PICOCURIES

PER GRAM

CONCENTRATION, 

IN WEIGHT

PERCENT

CONCENTRATION, 

IN MICROGRAMS 

PER GRAM

 per year square centimeter

 per year

Nondetections

Figure 10. Age-depth indicators in Bay–13 core. 
22 Chemical Quality of Water, Sediment, and Fish in Mountain Creek Lake, Dallas, Texas, 1994–97 

91-cm interval, and the maximum concentration was 

in the 63- to 70-cm interval. Therefore, 98 cm was 

assigned a date of 1953, 87.5 cm a date of 1958, and 

66.5 cm a date of 1964. A dark black layer with a strong 

hydrocarbon odor occurs at 13 to 25 cm, and relatively 

large concentrations of phosphorus were measured in 

the 14- to 25-cm interval in the MCL–7 core. Phosphorus concentrations, in weight percent, increased from 

0.09 to 0.30 from the 15- to 20-cm interval to the 20- to 

25-cm interval in Bay–13 and increased from 0.08 to 

0.21 from the 0- to 3-cm interval to the 14- to 25-cm 

interval in MCL–7. The change in phosphorus concentrations in the MCL–7 and Bay–13 cores provides a 

time marker matching the end of sewage effluent discharges to the west lagoon from NWIRP in 1974. Basing the 1974 date at 20 cm down core in Bay–13 on 

phosphorus concentrations and on cessation of sewage 

effluent discharges is supported by decreases in trace 

element concentrations at the same level in the core, for 

example silver (fig. 10). Large reductions in pointsource discharges containing metals to the west lagoon 

occurred in 1974. Cadmium, chromium, and copper 

concentrations decreased from 72 to 9.0 μg/g, 4,300 to 

550 μg/g, and 180 to 62 μg/g, respectively, between the 

20- to 25-cm and 15- to 20-cm intervals in the core. Six 

date-depth markers thus are available for the Bay–13 

core: 1995 at 0 cm, 1974 at 20 cm, 1964 at 66.5 cm, 

1958 at 87.5 cm, 1953 at 98 cm, and 1929 at 160 cm 

(fig. 10). An additional date, 1941, was inferred from 

chemical changes in the core that probably are related to 

the opening of the NWIRP facility. 

Occurrence, Trends, and Sources of Metals

Metals in Mountain Creek Lake come from natural as well as anthropogenic sources. Metals that are naturally introduced to the lake come from weathering of 

rocks, soil erosion, or dissolution of salts. Metals that 

are artificially introduced come from a variety of human 

activities. In the drainage of Mountain Creek Lake, 

these include industrial releases; urban runoff from 

roads, buildings, and parking lots; fallout from local and 

regional atmospheric sources; and agricultural runoff of 

pesticides.

The metallic elements can be categorized into two 

groups. Heavy metals are those with densities more than 

five times the density of water, and light metals are 

those with lesser densities. Heavy metals, which include 

cadmium, chromium, copper, lead, mercury, nickel, silver, and zinc, are frequently associated with industrial 

and urban sources and are the focus of the interpretations presented here. Additionally, this section discusses 

other selected major and trace elements, including the 

non-metallic trace elements arsenic and selenium.

Metals in Stormwater

Runoff from six storms was sampled at each of 

three sites on NAS and two sites on NWIRP during 

1994–96; however, the same six storms were not sampled concurrently at all sites (Raines and others, 1997). 

Samples were collected by automated samplers and by 

hand-dipping and were composited over storm hydrographs to allow storm loads to be computed for selected 

constituents. Unfiltered water samples were extracted to 

obtain “total recoverable” metals concentrations. 

Several metals were detected in stormwater samples from the five sites at NAS and NWIRP. The most 

commonly detected metals—iron, manganese, and 

zinc—were detected in all composite samples in which 

they were analyzed (iron and manganese not analyzed 

for all storms at some sites). Aluminum also was 

detected in a majority of the samples. Generally, the 

greater the TSS concentration, the greater the metals 

concentrations. This relation is expected because sediments contain much greater concentrations of metals 

than water. These analyses are of unfiltered water; 

therefore, the more sediment in the sample (larger TSS 

concentration), the larger the expected metals concentrations in the sample. 

In addition to sampling unfiltered water during 

1994–96, large-volume stormwater samples were collected and dewatered to obtain suspended sediment for 

direct chemical analysis in 1997. Filtered (0.5-μm pore 

size) samples were collected for dissolved metal analyses concurrently with the suspended sediment samples. 

Suspended sediment samples were collected at the west 

and east lagoon outfalls from NWIRP (NWIRP–1 

and NWIRP–2, respectively) and on the north fork of 

Cottonwood Creek. One storm was sampled at the east 

lagoon outfall. Two storms were sampled at the west 

lagoon outfall and the north fork of Cottonwood Creek; 

however, small sediment recovery in the west lagoon 

outfall samples led to a decision to composite sediment 

from the two storms to obtain more reliable analyses of 

metals concentrations. Sufficient mass was available in 

split samples from each of the two west lagoon storms 

for analysis of organic compounds (PAHs, organochlorine pesticides, and PCBs). 
CHEMICAL QUALITY OF WATER, SEDIMENT, AND FISH IN MOUNTAIN CREEK LAKE 23

Metals concentrations in suspended sediment 

were highly variable with larger concentrations in samples from the NWIRP lagoons than in the north fork of 

Cottonwood Creek. Concentrations of selected heavy 

metals, including cadmium, chromium, copper, lead, 

mercury, and zinc, are notably larger in the lagoon samples relative to the urban (north fork) site on Cottonwood Creek. 

As has been demonstrated elsewhere (for example, Meade, 1995), concentrations of heavy metals are 

much greater in suspended and bottom sediment than in 

filtered water. For example, the concentration of lead in 

three filtered stormwater samples from the NWIRP 

lagoons (one from the east lagoon and two from the 

west lagoon) were all less than 0.5 μg/L (or parts per 

billion). In comparison, the concentrations of lead in 

suspended sediment samples from the same storms 

were 370 μg/g (or parts per million [ppm]) in the east 

lagoon storm sample and 250 μg/g in the composite of 

suspended sediment samples from the two west lagoon 

storms. On a per-mass basis, the lead concentrations 

were at least 740,000 and 500,000 times greater in suspended sediments than in filtered water, respectively. 

Large ratios also occur for other heavy metals, for 

example zinc. Zinc in a filtered water sample from the 

west lagoon was 12 μg/L compared to 2,130 μg/g in a 

suspended sediment sample. Converting both to parts 

per million yields 0.012 ppm in filtered water compared 

to 2,130 ppm in suspended sediment or 178,000 times 

more zinc in the equivalent mass of sediment than in 

water.

Even though the dissolved concentrations are 

much smaller than the suspended concentrations, a 

much larger mass of water than sediment is transported 

to the lake by storms. The proportion of the load of metals transported to the lake in stormwater and associated 

with the suspended and dissolved phases can be evaluated for these sampled storms. The mass of metal in a 

liter of filtered stormwater is reported directly in micrograms per liter. The mass of metal in the suspended sediment in a liter of stormwater can be determined by 

multiplying the mass of metal per gram of sediment 

times the TSS, in grams per liter. TSS concentrations 

in the two storms sampled at the west lagoon outfall 

were 8.0 and 3.3 mg/L or 0.0080 and 0.0033 grams per 

liter (g/L). Averaging those two concentrations, because 

the suspended sediment metals analysis was a composite of sediment from the two storms, yields 0.0056 g/L. 

Multiplying TSS times the zinc concentration in the 

suspended sediment sample, 2,130 μg/g, yields 12 μg/L 

of zinc in the suspended fraction of stormwater, equal 

to the 12 μg/L measured in the filtered fraction. Therefore, even though the concentration in sediment was 

178,000 times greater, about the same mass load of zinc 

was moving to the lake in the water phase as was moving to the lake in the suspended sediment phase. A similar calculation for lead, 370 μg/g times 0.0056 g/L, 

yields an estimated 2.1 μg/L in the sediment phase versus less than 0.5 μg/L in the filtered water. Even though 

the TSS concentrations are small, at least 80 percent of 

the lead and about 50 percent of the zinc were transported in the suspended phase.

Metals in Lake Water

Lake water samples were collected from four 

sites (fig. 1) on October 12, 1994. Major and trace 

element concentrations were measured in filtered 

(0.45-μm pore size) water. Metals detected were barium, iron, lithium, strontium, and zinc (Jones and 

others, 1997, p. I–33). Except for the one detection of 

zinc at site MCL–12, none of the industrial heavy metals with elevated concentrations in suspended sediments 

(cadmium, chromium, copper, lead, mercury, and zinc) 

were detected in lake water. 

Metals in Sediment

Metal concentrations vary greatly in bottom 

sediment from Mountain Creek Lake. For example, 

chromium concentrations in Phase I samples range 

from 69 μg/g at site MCL–11 to 4,400 μg/g in a deeper 

interval from site Bay–13 (Jones and others, 1997; 

p. I–25, I–22). Ratios of concentrations in White Rock 

Lake in Dallas, in MCL–7 (central bay), and in 

MCL–12 (NAS inlet) to mean concentrations of mainlake reference sites (table 4) were computed to show 

which metals, if any, have elevated concentrations in 

Mountain Creek Lake bottom sediment (fig. 11). Ratios 

were computed for selected metals commonly associated with urban and industrial sources. Main-lake 

reference concentrations are the mean concentrations of 

six sites grouped by cluster analysis (table 4). White 

Rock Lake is considered typical of urban-influenced 

lakes in the Dallas area. MCL–7 is influenced by runoff 

from the west lagoon and NWIRP. MCL–12 is influenced by runoff from the NAS hanger area, roads, parking areas, and fuel farm.

As a general guideline, a ratio greater than 2 

(concentration more than double the reference concentration) is considered an indication of an elevated 
24 Chemical Quality of Water, Sediment, and Fish in Mountain Creek Lake, Dallas, Texas, 1994–97 

360

350

360

210

83

130

310

96

110

120 110

75

69 100

80

Aluminum

Arsenic

Cadmium1

Chromium

Copper

Lead

Nickel

Silver1

Zinc

RATIO OF SITE CONCENTRATION TO MEAN CONCENTRATION OF MAIN-LAKE REFERENCE SITES (table 4)

WHITE ROCK LAKE

MCL–7, 0–3 centimeter MCL–7, 14–25 centimeter MCL–12, 0–3 centimeter

COTTONWOOD BAY NAS INLET

0 1 2 3 4 0 1 2 3 4 0 50 10 20 30 40 0 1 2 3 4

depth interval depth interval depth interval

EXPLANATION

110 Chromium concentration,

in micrograms per gram,

at Phase I lake-bottom

sediment sampling site

MCL-12

MCL-7

CHROMIUM

 Cadmium and silver concentrations below method detection limits at main-lake reference sites; mean method detection limit, 

2 micrograms per gram for both, used to compute ratios.

1

5 5 5

Figure 11. Ratios of Phase I metal concentrations in lake bottom sediment at selected sites to mean 

concentrations of main-lake reference sites. 
CHEMICAL QUALITY OF WATER, SEDIMENT, AND FISH IN MOUNTAIN CREEK LAKE 25

concentration, and a ratio greater than 10 is considered 

an indication of a greatly elevated concentration. Aluminum concentrations are shown (fig. 11) because aluminum is a major element in clay minerals and thus can 

be used to normalize sediment data for comparison of 

trace metal concentrations among samples (Van Metre 

and Callender, 1996). Aluminum concentration ratios 

are about 1.0, indicating slightly more aluminum at reference sites than at the other sites. The range in aluminum concentration ratios also indicates that elevated 

concentrations of trace metals at some sites are not a 

sampling artifact related to greater clay content in those 

samples. 

In general, ratios are near unity in the samples 

from site MCL–12 and White Rock Lake (fig. 11), 

suggesting these sites do not have elevated metals concentrations. Ratios greater than unity for lead and zinc 

at White Rock Lake and lead at MCL–12 are exceptions. Lead enrichment at both sites probably results 

from urban and, in particular, automobile-related lead 

sources. Lead concentrations in urban lakes greatly 

increased coincident with urbanization and lead 

use in gasoline prior to the mid-1970s (Callender and 

Van Metre, 1997). Although concentrations have 

decreased substantially since then, they remain about 

double pre-urban levels in many urban lakes including 

White Rock Lake. Ratios greater than 2 and, in one case, 

as large as 33 were computed for the samples from site 

MCL–7, with larger ratios in the 14- to 25-cm interval 

than in the 0- to 3-cm interval. Of the eight metals 

shown in figure 11, only arsenic, with concentration 

ratios of 0.92 to 1.10, was not elevated in any of the 

three MCL samples. Copper, nickel, and zinc are elevated in MCL–7 (0 to 3 cm and 14 to 25 cm), with 

maximum ratios of 3.5, 2.7, and 4.4, respectively. Concentrations of cadmium, chromium, and silver were 

greatly elevated in the 14- to 25-cm interval from 

MCL–7, with ratios of 26, 33, and 24, respectively. 

The actual ratio for silver could be greater than 24 

because silver was not detected at an MRL of 2 μg/g at 

any site outside of Cottonwood Bay but was 48 μg/g in 

the 14- to 25-cm interval from MCL–7. The ratio of 24 

is based on the MRL of 2 μg/g at the reference sites. 

Ratios of concentrations at four Phase II sites to 

main-lake reference concentrations were computed for 

selected metals (fig. 12) that showed elevated concentrations relative to reference concentrations at Phase I 

sites, with the exception of cadmium (not measured in 

Phase II) and with the addition of mercury (Jones and 

others, 1997, p. II–22). Sites compared to reference 

concentrations were M2.22 (west bay) near the mouth 

of Cottonwood Creek, M2.11 (central bay) near site 

MCL–7 in front of the west lagoon outfall, M2.2 (east 

bay) near the east lagoon outfall from NWIRP, and 

M2.40 (NAS inlet). As in figure 11, main-lake reference 

concentrations are the mean concentrations of six sites 

grouped by cluster analysis (table 4). 

Phase II metals compared in figure 12 confirm 

several conclusions from the Phase I comparison. Concentrations of chromium, lead, mercury, and zinc were 

elevated in the central and eastern parts of Cottonwood 

Bay. Chromium, lead, and zinc enrichment factors for 

surficial sediments (fig. 12) are similar to those for 

Phase I (fig. 11). Most metals were not elevated at 

M2.40, the NAS inlet, with the possible exceptions of 

lead and mercury. The ratio of lead at M2.40 to the mean 

main-lake reference for lead is 1.9, and the ratio of mercury is 2.0. Mercury also was somewhat elevated at the 

western end of Cottonwood Bay (M2.22; ratio of 1.9) 

and was elevated in the east bay (M2.2; ratio of 5.7) and 

the central bay (M2.11; ratio of 7.7). 

Selenium was identified by the Texas Department 

of Health as a possible human health concern in 

fish-tissue samples (Kirk Wiles, Texas Department of 

Health, written commun., 1996). Selenium concentrations were measured in 19 Phase II surficial sediment 

samples and ranged from 0.5 to 1.0 μg/g (Jones and 

others, 1997). The narrow range and lack of a distinct 

spatial pattern as a function of land use indicates that the 

selenium in sediments is from natural sources.

The spatial pattern in chromium concentrations 

and other heavy metals with elevated concentrations 

was similar—larger concentrations in Cottonwood Bay, 

with the largest near the west lagoon outfall, and smaller 

concentrations in the main lake and NAS inlet. Concentrations of the four heavy metals in Phase II bottom sediment samples are summarized in table 5 for five areas 

of the lake. Summary statistics were computed for surficial samples (0 to 3 cm) in each area. Concentrations 

are largest in the eastern and central parts of Cottonwood Bay, decrease in the west bay and the canal, and 

are smallest in the main lake. The main lake includes the 

NAS inlet because concentrations in the NAS inlet 

are not appreciably greater than in other parts of the 

main lake. As shown by the site comparisons (fig. 12), 

concentrations of these metals in the central and east 

bay are 2 to 4 times greater than in the main part of 

Mountain Creek Lake.

Trends in chromium, lead, and zinc in sediment 

cores (fig. 13) in the main lake (MCL–4) and NAS 
26 Chemical Quality of Water, Sediment, and Fish in Mountain Creek Lake, Dallas, Texas, 1994–97 

M2.11, 0–3 centimeter

COTTONWOOD BAY NAS INLET

Aluminum

Arsenic

Chromium

Copper

Lead

Mercury1

Nickel

Zinc

M2.22, 0–3 centimeter M2.2, 0–3 centimeter M2.40, 0–3 centimeter

RATIO OF SITE CONCENTRATION TO MEAN CONCENTRATION OF MAIN-LAKE REFERENCE SITES (table 4)

0 2 4 6 0 2 4 6 0 2 4 6 0 2 4 6

depth interval depth interval depth interval depth interval

<0.040

0.042

<0.040

0.056 0.057

0.060

0.052

0.044

0.044

<0.040

0.042

<0.020

<0.020

0.043

0.046

0.420 0.060 M2.40

<0.040

0.058

0.063

0.057

0.069

M2.22 0.057

0.100 0.120

0.072 0.220

0.110

0.110 0.210

0.290

0.140

0.160

0.420

M2.11 0.230

0.055

0.220

0.160

0.170 M2.2

0.170

0.160

0.180

0.170 0.100

0.110 Mercury concentration, 

in micrograms per gram, 

at Phase II lake-bottom 

sediment sampling site

MERCURY

8 88 8

 Cadmium and silver concentrations below method detection limits at main-lake reference sites; mean method detection limit, 

2 micrograms per gram for both, used to compute ratios.

1

Figure 12. Ratios of Phase II metal concentrations in lake bottom sediment at selected sites to mean 

concentrations of main-lake reference sites. 
CHEMICAL QUALITY OF WATER, SEDIMENT, AND FISH IN MOUNTAIN CREEK LAKE 27

50 200 100 150 0 5,000 0 2,500 1920

2000

1940

1960

1980

DATE

100 200 100 150

CHROMIUM CONCENTRATION, IN MICROGRAMS PER GRAM

10 40 20 30 1920

2000

1940

1960

1980

DATE

10 40 20 30

LEAD CONCENTRATION, IN MICROGRAMS PER GRAM

0 300 100 200

80 140 100 120 1920

2000

1940

1960

1980

DATE

60 120 80 100

ZINC CONCENTRATION, IN MICROGRAMS PER GRAM

0 1,000 0 500

MAIN LAKE NAS INLET

M2.40

COTTONWOOD BAY

MCL–4 BAY–13

Figure 13. Trends in chromium, lead, and zinc concentrations in MCL–4, M2.40, and Bay–13 cores.
28 Chemical Quality of Water, Sediment, and Fish in Mountain Creek Lake, Dallas, Texas, 1994–97 

inlet (M2.40) generally are similar to trends in White 

Rock Lake (Van Metre and Callender, 1997) and in 

urban reservoirs in Georgia and Virginia (for lead, 

Callender and Van Metre, 1997; for chromium and zinc, 

Edward Callender, U.S. Geological Survey, unpub. data, 

1997). Characteristics of these trends are maximum 

chromium concentrations in the 1960s and early 1970s, 

lead peaks in the mid-1970s coincident with maximum 

use of lead in gasoline, and increases in zinc concentrations with urban growth. The notable exception to 

these trends is the lack of a 1970s lead peak in the mainlake core (MCL–4). Lead concentrations in the mainlake core increase from the 1930s to the 1970s, as 

observed in other urbanizing areas; however, the lack 

of a decrease after the introduction of unleaded gasoline 

in the mid-1970s has not been observed elsewhere 

(Callender and Van Metre, 1997) and suggests some 

other source or sources of lead could be contributing to 

the continuing increase. The decreasing trends in both 

the NAS inlet (M2.40) and Cottonwood Bay (Bay–13) 

indicate that the Navy facilities are not the source of 

recent increases in lead concentrations in the main lake. 

The Bay–13 core from Cottonwood Bay shows 

very large peaks in all three metals in comparison to 

concentrations in the other two cores (note the scale 

differences on graphs in fig. 13). Maximum lead and 

zinc concentrations are about 10 times greater than at 

the other sites, and the maximum chromium concentration is about 20 times greater. The largest concentrations of these three metals are in a sample deposited in 

about 1960. Smaller peaks occur in the early 1940s and 

the early 1970s. Lead and chromium concentrations 

decrease substantially after 1974 with the reduction in 

point-source discharges to the west lagoon; zinc concentrations have remained relatively stable since the 

mid-1960s. 

All seven heavy metals that had elevated concentrations in Phase I surficial sediments in Cottonwood 

Bay (fig. 11) have pronounced historical trends in the 

Bay–13 core from Cottonwood Bay (fig. 14). Cadmium, 

as was the case for chromium, lead, and zinc, peaked in 

about 1960, was high throughout the 1960s, and had 

secondary peaks in the mid-1940s and mid-1970s. 

Neither copper nor nickel had a large peak in 1960 or a 

secondary peak in the 1940s. Both had maximum concentrations during the mid- to late-1960s and had 

slightly smaller peaks in about 1974. Silver had yet 

another temporal pattern with three large peaks in the 

early 1940s, mid-1960s, and mid-1970s. The largest 

silver peak was 37 μg/g in the early 1940s. Silver was 

not detected at an MRL of 2 μg/g in any samples from 

White Rock Lake (P.C. Van Metre, U.S. Geological Survey, unpub. data, 1997) or in any samples from the main 

part of Mountain Creek Lake (Jones and others, 1997). 

The differences in trends between metals indicate some 

differences in input histories.

Mercury was not measured in Phase I bottom 

sediment samples including the Bay–13 core; however, 

it was measured in Phase II samples including surficial 

sediments in Cottonwood Bay and in the M2.40 gravity 

core from the NAS inlet (fig. 15). Mercury concentrations are increasing in the NAS inlet, which is consistent with regional increases in mercury observed in 

cores from other reservoirs (Van Metre, Mahler, and 

Callender, 1997) and lakes (Swain and others, 1992). 

Metals in Fish

Composite samples of fish-liver tissue from 

either four or five fish from three areas of the lake were 

analyzed for major and trace elements during Phase I 

(Jones and others, 1997, p. I–42). Several common 

Table 5. Summary of selected metal concentrations in sediment

[In micrograms per gram; s.d., standard deviation; NAS, Naval Air Station] 

Metal

East

Cottonwood Bay

mean (s.d.)

of 9 samples

Central

Cottonwood Bay

mean (s.d.)

of 9 samples

West

Cottonwood Bay

mean (s.d.)

of 4 samples

Canal

mean (s.d.)

of 4 samples

Main lake

(includes NAS inlet)

mean (s.d.)

of 18 samples

Chromium 240.(19) 210.(53) 140.(40) 150.(4.0) 100.(41)

Lead 90.(10.4) 74.(20.6) 54.(14.5) 30.(5.2) 23.(10.3)

Mercury .15 (.048) .21 (.099) .09 (.028) .06 (.005) .05 (.007)

Zinc 330.(79) 350.(54) 240.(86) 130.(26) 120.(56)
CHEMICAL QUALITY OF WATER, SEDIMENT, AND FISH IN MOUNTAIN CREEK LAKE 29

industrial heavy metals—copper, cadmium, chromium, 

lead, nickel, and zinc—were detected in bass and common carp liver tissue samples (fig. 16). Iron, manganese, and strontium also were detected. Neither the 

detections nor concentrations of specific elements in 

bass and common carp liver tissue indicate a spatial pattern for the elements in the reservoir. 

Fillet subsamples from individual fish were 

analyzed for major and trace elements during Phase II 

(Jones and others, 1997, p. II–40). Commonly detected 

elements in Phase II tissue samples were chromium, 

copper, mercury, selenium, and zinc (fig. 16). Selenium 

concentrations generally were larger than those of other 

“bioavailable” trace elements (fig. 16), a group that 

includes arsenic, mercury, and selenium. These three 

trace elements are termed bioavailable because they 

accumulate in the axial muscles of fish and often occur 

in fillets at concentrations comparable to whole-body 

0 200 100

1920

2000

1940

1960

1980

0 300 150

0 200 100 0 40 20

0 5,000 2,500

1920

2000

1940

1960

1980

0 300 150

0 1,000 500

DATE DATE

Period of 

Discharge

Effluent

Period of 

Discharge

Effluent

CONCENTRATION, IN MICROGRAMS PER GRAM

Cadmium Copper

Silver

Chromium Lead

Zinc

CONCENTRATION, IN MICROGRAMS PER GRAM

Nickel

Figure 14. Trends in heavy metals concentrations in Cottonwood Bay as indicated by the Bay–13 core.
30 Chemical Quality of Water, Sediment, and Fish in Mountain Creek Lake, Dallas, Texas, 1994–97 

concentrations of the same species (Schmitt and Finger, 

1987). Median selenium concentrations by fish type 

ranged from 1.2 milligrams per kilogram (mg/kg) in 

channel catfish fillets to 2.4 mg/kg in common carp fillets. The median selenium concentration in whole-body, 

eviscerated channel catfish was only 0.18 mg/kg greater 

than the average fillet concentration for the same species. Concentrations of these bioaccumulating trace elements in fish tissue reportedly are strongly associated 

with sediment concentrations and less so with overlying 

water concentrations (Eisler, 1985). Selenium is the 

only trace element in edible fish tissue from Mountain 

Creek Lake for which the Texas Department of Health 

has expressed concern with respect to human consumption of fish (Kirk Wiles, Texas Department of Health, 

written commun., 1996). 

Sources of Metals

Many of the heavy metals discussed in the previous sections have industrial uses (Hem, 1985). Cadmium is used for electroplating and for pigments used 

in paint, printing ink, and plastics. It also is used as a 

stabilizer for PVC plastic and in electrical batteries. 

Chromium is used in a variety of industrial applications 

including metal plating. Copper is used for a variety of 

applications including pipes and wiring. Nickel is used 

in stainless steel and other corrosion-resistant alloys. 

Silver is used extensively in photography and is a common minor constituent of industrial wastes. Zinc is used 

in metallurgy, principally as a constituent of brass or 

bronze, and for galvanizing. It also is used in rubber and 

as a white pigment in paint. The use of lead that has had 

the greatest environmental effect was the addition of 

tetraethyl lead to gasoline before the mid-1970s.

From 1941 until the late-1950s, the west lagoon 

was open directly to Cottonwood Bay along the western 

side of the north-south causeway and bridge across the 

bay. An earth berm with two 1.3-m (48-inch) pipes open 

to the bay was installed in the late-1950s to create a settling pond that is the present west lagoon. In 1971 an 

oil-spill recovery system was built across the southern 

end of the lagoon. As of 1998, water from the west 

lagoon reached Cottonwood Bay only during storms 

that resulted in flow through the stormwater outflow 

pipes from the west lagoon to Cottonwood Bay. 

An additional factor could affect sedimentation 

and contaminant movement into Cottonwood Bay. The 

natural channel of Cottonwood Creek crossed what is 

now the main runway of NAS before 1949. During 

1949–50, fill was used to extend the main runway and 

expand NAS, closing off the natural outflow from Cottonwood Creek. The canal connecting Cottonwood Bay 

to the lake was dug at that time to provide an outlet for 

flow from Cottonwood Creek. Therefore, the central 

and eastern parts of Cottonwood Bay would have 

received sediment from all of the Cottonwood Creek 

watershed before 1950. After 1950, the central and east 

bay areas became a “dead end” embayment with only 

the immediate areas of NAS and NWIRP draining to 

them. 

To indicate the association between metals 

concentrations in sediment of the west lagoon and 

Cottonwood Bay, thus the likelihood of the west lagoon 

as a source of the metals in Cottonwood Bay, concentrations of selected metals in sludge samples from the 

west lagoon (EnSafe/Allen & Hoshall, 1996a), in suspended sediment samples from the west lagoon outfall 

(NWIRP–1), and in bottom sediment samples from 

Cottonwood Bay are compared to mean concentrations 

of main-lake reference sites (fig. 17). The comparisons 

indicate that (1) heavy metals generally are at greatly 

elevated concentrations in the west lagoon sediment, 

and (2) the same heavy metals also are at elevated concentrations in Cottonwood Bay sediment (fig. 17).

Historical point-source discharges are a source of 

heavy metals to the west lagoon. Much of the waste disposed of in the west lagoon during 1941–74 (table 3) 

0 0.08 0.04

1940

2000

1960

1980

DATE

CONCENTRATION, IN

MICROGRAMS PER GRAM

Figure 15. Trends in mercury concentrations in the 

NAS inlet as indicated by the M2.40 core.
CHEMICAL QUALITY OF WATER, SEDIMENT, AND FISH IN MOUNTAIN CREEK LAKE 31

1.5

0

0.5

1.0

0.8

0

0.2

0.4

0.6

6

0

2

4

8

0

2

4

6

0.1

100

1

10

0.5

0

0.1

0.2

0.3

0.4

Phase I Phase II Phase II Phase II Phase II

1.5

0

0.5

1.0

10

1,000

100

(5) (11) (10) (9) (15)

0

2

1

liver 

tissue

bass

fillets

carp

fillets

catfish

fillets

catfish

whole body

eviscerated

(5) (11) (10) (9) (15)

EXPLANATION

Minimum

25th percentile

Median (50th percentile)

75th percentile

Maximum

(5) Number of samples

Phase I Phase II Phase II Phase II Phase II

liver 

tissue

bass

fillets

carp

fillets

catfish

fillets

catfish

whole body

eviscerated

Arsenic

Mercury

Chromium Copper

Lead

Nickel

Zinc

Cadmium

Selenium

CONCENTRATION, IN MICROGRAMS PER GRAMCONCENTRATION, IN MICROGRAMS PER GRAM

Figure 16. Distribution of metal concentrations in fish tissues, Mountain Creek Lake. 
32 Chemical Quality of Water, Sediment, and Fish in Mountain Creek Lake, Dallas, Texas, 1994–97 

Figure 17. Ratios of lake-bottom sediment and suspended sediment metal concentrations in the west lagoon and Cottonwconcentrations of mean-lake reference sites. 

0 

NOT 

0 2 4 6 8

NOT MEASURED

0 2 4 6 8 10

Aluminum

Arsenic

Cadmium1

Chromium

Copper

Lead

Mercury1

Nickel

Silver1

Zinc

RATIO OF SITE CONCENTRATION TO MEAN CONCENTRATION OF MAIN-LAKE REFERENCE SITES 

WEST LAGOONBOTTOM SEDIMENT0–60 centimeters SUSPENDED COTTONWOOD BAY

BOTTOM SEDIMENTMCL–7 0–3 centimeters

COTTBOTTMCL–

West

Cottonwood

NWIRP-1

Bay

 lagoon

Stormwater outfall pipes

NWIRP–1

0 20 40 0 20 40

NOT MEASURED

1 Cadmium, mercury, and silver concentrations below method detection limits at main-lake reference sites; mean method detection limits of 2.0, 0.03, and 2.0 micr

per gram, respectively, used to compute ratios.

COTTONWOOD BAYBOTTOM SEDIMENTM2.11 0–3 centimeters

WEST LAGOON OUTFALLSEDIMENT

NOT MEASURED

NOT MEASURED

 (EnSafe/Allen & Hoshall, 1996a)

60 60 10
CHEMICAL QUALITY OF WATER, SEDIMENT, AND FISH IN MOUNTAIN CREEK LAKE 33

was from the plating shops and likely contained the 

metals that were found at elevated concentrations in 

the lagoon and Cottonwood Bay sediment. The greatly 

elevated mercury concentrations in bottom sediment in 

the west lagoon and in suspended sediment in the west 

lagoon outfall and the elevated concentrations in bottom 

sediment in Cottonwood Bay cannot be attributed to 

regional atmospheric sources. 

The primary source of the elevated levels of 

heavy metals in sediment in east and central Cottonwood Bay is the west lagoon on NWIRP. This conclusion is based on the following evidence: 

1. There is spatial proximity between the lagoon outfall and the sites of largest metal concentrations 

in Mountain Creek Lake bottom sediment; and 

concentrations decrease with distance from the 

outfall. 

2. Documented historical discharges of metals to the 

west lagoon coincide temporally with large 

metal concentrations identified in lake sediment 

cores. 

3. Elevated concentrations of the same metals are in 

bottom sediments in the west lagoon and in suspended sediments in stormwater flowing from 

the west lagoon into Cottonwood Bay. 

4. Stormwater runoff and historical point-source 

discharges provide logical transport mechanisms from the lagoon to the bay. 

5. Urban sources represented by sediment from the 

western end of Cottonwood Bay, bottom sediment from White Rock Lake, and bottom and 

suspended sediment from Cottonwood Creek 

have much smaller concentrations of heavy 

metals and cannot account for the concentrations in Cottonwood Bay sediments. 

Concentrations of heavy metals in the NAS 

inlet are similar to those of main-lake and urban reference sites and indicate that large releases of metals 

from the NAS to Mountain Creek Lake have not 

occurred.

Occurrence, Trends, and Sources of Volatile 

Organic Compounds

VOCs present in the environment come from a 

variety of sources. The two categories of VOCs that 

are of concern at Mountain Creek Lake are those contained in fuels (for example, the BTEX compounds—

benzene, methylbenzene [toluene], ethylbenzene, and 

xylenes) and chlorinated solvents (for example, TCE). 

The VOCs from fuels present on the Navy facilities are 

primarily from spills related to storage and refueling of 

aircraft and motor vehicles, and the VOCs from chlorinated solvents present are primarily from leaks in 

degreasing tanks (EnSafe/Allen & Hoshall, 1996a, b).

The major components of gasoline are the saturated hydrocarbons—paraffins and alkanes. Other 

components in gasoline include the unsaturated hydrocarbons—olefins, aromatics, acetylenes, and PAHs. 

Although gasoline mixtures vary greatly, aromatics 

such as the BTEX compounds make up about 30 to 

35 percent of the gasoline mixture, and paraffins usually 

make up more than 50 percent. Oxygenates such as 

methyl tert-butyl ether (MTBE) can contribute as much 

as 15 percent of the volume of the gasoline mixture. 

Because of the greater solubility of BTEX compounds, 

they can compose more than 60 percent of the mass that 

goes into solution when gasoline is mixed with water 

(Barbaro and others, 1992). MTBE solubilities are 1 to 

2 orders of magnitude larger than solubilities of BTEX 

compounds.

Chlorinated-solvent volatilities often result in 

their quick removal from surface-water bodies, primarily by evaporation. Measured and estimated half-lives 

for the chlorinated compounds of interest at Mountain 

Creek Lake, dichloroethene, TCE, tetrachloroethene, 

trichloroacetic acid, and vinyl chloride, range from as 

little as 3 hours to as much as 25 days (Howard, 1990). 

Chlorinated-solvent solubilities make the compounds a 

major concern in ground water because they quickly 

pass through soils because of their low adsorption coefficients (Howard, 1990). 

VOCs in Stormwater

Fuel-related and chlorinated VOCs were detected 

in stormwater samples collected at NAS and NWIRP 

sites (Raines and others, 1997). The most commonly 

detected compounds at NAS sites were fuel-related 

VOCs, and the most commonly detected compounds 

at NWIRP sites were chlorinated solvents (fig. 18). 

Although fuel-related VOCs were more common at 

NAS sites, some chlorinated compounds also were 

detected at NAS–1. Chlorinated compounds occur 

as soil and ground-water contaminants near NAS–1 

(EnSafe/Allen & Hoshall, 1996b). Fuel-related 

compounds were the only VOCs detected in stormwater 

at NAS–2 and NAS–3, except methylene chloride and 
34 Chemical Quality of Water, Sediment, and Fish in Mountain Creek Lake, Dallas, Texas, 1994–97 

acetone (NAS–2 only). BTEX compounds were 

detected for all six storms at NAS–2 (fig. 19). Xylenes 

were the only BTEX compounds detected at NAS–3, 

but several other fuel-related compounds were detected 

at this site. MTBE was analyzed only in storms 5 and 6 

and was detected in samples from both storms at all 

NAS sites. 

Chlorinated compounds were detected in four 

storms at the west lagoon outfall (NWIRP–1) and in five 

storms at the east lagoon outfall (NWIRP–2) (fig. 18). 

0 20 40 60 80 100

PERCENT DETECTION

Chloromethane

Chloroethane

Methylene chloride

Chloroform

Vinyl chloride

cis-1,2-Dichloroethylene

Trichloroethylene

Trichloroethane

Trichlorotrifluoroethane

Naphthalene

Benzene

Toluene

Ethylbenzene

Xylenes

Methyl tert-butyl ether

1,2,4-Trimethylbenzene

1,3,5-Trimethylbenzene

Isopropylbenzene

n-Propylbenzene

n-Butylbenzene

sec-Butylbenzene

p-Isopropyltoluene EXPLANATION

NAS–1

NAS–2

NAS–3

NWIRP–1

NWIRP–2

FUEL RELATED COMPOUNDS CHLORINATED COMPOUNDS

Figure 18. Percent detections of volatile organic compounds in composite samples collected at the fixed 

stormwater sites, Naval Air Station and Naval Weapons Industrial Reserve Plant. 
CHEMICAL QUALITY OF WATER, SEDIMENT, AND FISH IN MOUNTAIN CREEK LAKE 35

MTBE was detected in all samples from both storms 

(storms 5 and 6) at NWIRP–2. 

Minimum and maximum VOC concentrations 

and percent detections at the Navy facilities were compared to VOCs in stormwater from industrial sites in the 

Dallas-Fort Worth area that were measured as part of the 

National Pollutant Discharge Elimination System 

(NPDES) Program (table 6) (Baldys and others, 1998). 

The NPDES samples are from seven storms at each of 

10 sites, all of generally similar drainage size as the 

Navy sites. Sampling methods of the two studies were 

similar, and the analytical method for VOCs was the 

same for the last two storms at the Navy sites. Maximum concentrations of the BTEX compounds and 

MTBE are 1 to 2 orders of magnitude larger at the 

Navy sites than at the NPDES sites. All of the maximum 

concentrations at the Navy sites occurred at NAS–2. 

Conversely, maximum concentrations of the ethene 

(6)

(6)

(6)

(6)

0

300

100

200

CONCENTRATION, IN 

EXPLANATION

Method detection limit 

Minimum

25th percentile

Median (50th percentile)

75th percentile

Maximum

(6) Number of storms

BENZENE METHYL- ETHYLBENZENE BENZENE

MICROGRAMS PER LITER

TOTAL

XYLENES

(5 micrograms per liter)

Figure 19. Distribution of BTEX compound concentrations detected at NAS–2 stormwater site. 

Table 6. Comparison of volatile organic compound concentrations at the Navy sites, Dallas, Texas, and at 

industrial sites in the Dallas-Fort Worth area

[NWIRP, Naval Weapons Industrial Reserve Plant; NAS, Naval Air Station; μg/L, micrograms per liter; NPDES, National 

Pollutant Discharge Elimination System; <, less than] 

1 Baldys and others, 1998.

Volatile organic

compound

NWIRP and NAS NPDES1

Minimum 

concentration

(μg/L)

Maximum 

concentration

(μg/L)

Percent

detection

Minimum 

concentration

(μg/L)

Maximum 

concentration

(μg/L)

Percent

detection

Benzene <0.2 73 20 <0.2 0.6 <10

Toluene <.2 120 20 <.2 1.8 17

Ethylbenzene <.2 30 20 <.2 1.5 <10

Total xylenes <.2 270 27 <.2 10 16

Methyl tert-butyl ether <1 55 80 <1 5.4 <10

Trichloroethene <.2 25 40 <.2 28 13

cis-1,2-dichloroethene <.2 3.5 13 <.2 1,200 22

Vinyl chloride <.2 9 13 <.2 110 <10
36 Chemical Quality of Water, Sediment, and Fish in Mountain Creek Lake, Dallas, Texas, 1994–97 

compounds and vinyl chloride at the Navy sites are similar to or much smaller than maximum concentrations at 

the NPDES sites.

VOCs in Lake Water

VOCs were detected at two of the four lake-water 

sampling sites (fig. 1) in Mountain Creek Lake in 1994 

(Jones and others, 1997). Lake water samples from 

MCL–4 and MCL–12 contained small concentrations 

of BTEX, MTBE, and other fuel-related compounds but 

no chlorinated solvents (fig. 20). MCL–12 is in the NAS 

inlet near the NAS–1 stormwater outfall, and MCL–4 is 

southeast of MCL–12 near the middle of the lake. 

Of the fuel-related compounds, only the aromatics were detected in lake water samples. Volatilization 

is the primary process for degradation of fuel-related 

VOCs in surface waters. The half-life of most aromatic 

hydrocarbons in lakes is on the order of 3 hours to 

25 days (Howard, 1990). Half-lives of VOCs in streams 

vary as a function of Henry’s Law constant, water 

velocity, wind speed, temperature, distance, and depth 

(Pankow and others, 1996). Concentrations of BTEX 

compounds in the NAS inlet (MCL–12) were 2.3 to 3 

times greater than the concentrations near the middle of 

the lake (MCL–4). The difference in concentrations 

between sites could be caused by several factors including dilution and loss by volatilization. 

VOCs in Sediment

Three sampling sites were selected for collection 

of VOCs in lake bottom sediment, Bay–7, Bay–11, and 

Bay–13 (fig. 1). VOCs were detected at Bay–11 (95 to 

100 cm) and Bay–13 (76 to 86 cm) (Jones and others, 

1997, p. I–2). As many as five fuel-related compounds 

were detected in deeper sediment layers that were black 

and smelled of hydrocarbons. Chlorinated solvents, 

found in ground water at NWIRP, were not detected. 

VOCs in Fish

Five channel catfish skin-off fillet samples analyzed for VOCs included two fish from Cottonwood 

Bay (one each from areas 7 and 8) and three fish from 

Mountain Creek Lake (two from area 10 and one from 

area 2) (fig. 2). Acetone, benzene, and 2-Butanone 

were detected at low levels (1,000, 6.9, and 220 μg/kg, 

respectively); however, sample contamination from 

handling in the field and at the USGS National Water 

Quality Laboratory is suspected (D.L. Rose, U.S. Geological Survey, oral commun., 1996). VOCs have high 

vapor pressures and water solubilities compared to 

organochlorine compounds and PAHs; therefore, VOCs 

generally do not accumulate in fish tissue. The Texas 

Department of Health (Kirk Wiles, Texas Department of 

Health, oral commun., 1996) concluded that VOCs in 

edible fish tissue are not a human health concern for the 

consumption of fish tissue.

0 0.5 1.0 1.5 2.0

EXPLANATION

Benzene

Methylbenzene

Ethylbenzene

Total xylenes

Methyl tert-butyl ether

Naphthalene

1,2,4-Trimethylbenzene

1,3,5-Trimethylbenzene

n-Propylbenzene

Method

detection limit

(0.2 microgram

per liter)

MCL–12

0 5.0 1.0 2.0 3.0 4.0

MCL–4

CONCENTRATION, IN MICROGRAMS PER LITER

Figure 20. Volatile organic compound concentrations in lake water samples. 
CHEMICAL QUALITY OF WATER, SEDIMENT, AND FISH IN MOUNTAIN CREEK LAKE 37

Sources of VOCs

Aircraft fuels used at both facilities include JP–4, 

JP–5 and AVGAS; gasoline, hydraulic fluid, and lubrication oils also are used (EnSafe/Allen & Hoshall, 

1996a, b). BTEX compounds, which are components of 

fuel, have been found in soil and ground-water samples 

at NWIRP but are not considered a major concern 

except in local areas (Jeffery James, EnSafe/Allen & 

Hoshall, written commun., 1996). The primary compounds of concern at NWIRP are chlorinated solvents in 

ground water. A plume of chlorinated solvents is present 

in ground water beneath most of NWIRP. Large 

degreaser vats in buildings 1 and 6 (fig. 6) are likely 

sources for the chlorinated ground-water contamination 

on NWIRP. An off-site source west of NWIRP also 

probably contributes to the on-site plume. Several areas 

have been identified on NAS where fuel and chlorinated 

compounds have been found in soil and ground water 

(EnSafe/Allen & Hoshall, 1996b, 1997a).

Documented petroleum, oil, and lubricant spills 

have occurred on NAS (EnSafe/Allen & Hoshall, 

1996b). Leaking storage tanks are the source of many of 

the soil and ground-water problems at the site. The 

NAS–1 drainage area includes six identified SWMUs 

(fig. 6). A 38-m3

 steel storage tank located near NAS–1 

is suspected of being the source of an on-site TCE 

ground-water plume mapped by EnSafe. Additional 

sources in this area include a former aircraft wash area 

where solvents were used and a drum storage area. 

NAS–2 receives flow from stormwater and sanitary sewers in addition to surface runoff. The main fuel 

farm (fig. 6) for NAS is in the drainage area for NAS–2. 

Fuel spills historically have been routed to the fuel farm 

storm sewers and tanks (EnSafe/Allen & Hoshall, 

1997b). Fuel-related VOCs consistently were detected 

in stormwater at NAS–2, and the largest concentrations 

of the BTEX compounds in this study were measured at 

NAS–2. The fuel farm is a likely source of the VOCs 

detected at NAS–2. 

NAS–3 is located in an area of NAS occupied by 

the Texas Air National Guard. Spills and wash water 

from hangers and maintenance buildings historically 

have been washed into grated areas on the floors of the 

buildings, which connect to the storm sewer. The storm 

sewer discharges to an unlined ditch near NAS–3. 

Thus, there are potential sources of chlorinated 

solvents to the NWIRP stormwater sites and potential 

sources of fuel-related compounds and solvents to the 

NAS sites. Because the drainage areas to all five stormwater sites are confined to the Navy facilities, and 

because known sources of the VOCs detected are there, 

the sources are attributed to the facilities. 

Occurrence, Trends, and Sources of 

Polycyclic Aromatic Hydrocarbons

PAHs are organic chemicals that are relatively 

unreactive and thus persistent in the environment. PAHs 

are very hydrophobic and sorb readily to sediments. 

Unsubstituted, or parent, compounds consist only of 

carbon and hydrogen (carbon-benzene rings with 

hydrogens attached). Substituted compounds are those 

PAHs in which one or more of the attached hydrogens 

have been replaced by alkyl groups. Hydrophobicity 

and resistance of PAHs to degradation increase with 

increasing number of rings and, within a homologous 

series, with increasing alkylation. A homologous series 

comprises compounds with the same benzene ring 

structure but with varying numbers of alkyl substitutions. The presence and distribution of PAHs in the 

environment largely is caused by incomplete combustion of coal, oil, wood, and petroleum. The largest 

concentrations of PAHs generally are detected in urbanized areas where the potential sources include atmospheric deposition, surface runoff, sewage effluents, 

industrial effluents, and spills and leakage of fossil fuels 

(Eganhouse and Gossett, 1991). Other sources include 

natural seepage of hydrocarbons, erosion of exposed 

shales and coal seams (Eganhouse and Gossett, 1991), 

and forest and prairie fires (Blumer and Youngblood, 

1975).

PAHs are an environmental concern because 

some of these compounds are toxic or mutagenic or are 

known or suspected carcinogens. Sixteen PAHs are on 

the USEPA Priority Pollutant list (U.S. Environmental 

Protection Agency, 1995). Among the PAHs detected in 

Mountain Creek Lake are two compounds included in 

the first 10 of the USEPA list of the top 20 hazardous 

substances: benzo(a)pyrene and benzo(b)fluoranthene 

(Agency for Toxic Substances and Disease Registry, 

1994). 

PAHs in Stormwater and Lake Water

Only two PAHs were detected in the 30 stormwater samples collected during 1995–96 (Raines and 

others, 1997). Naphthalene was detected in two samples 

from NAS–2, and fluoranthene was detected in one 

sample from NAS–3. The MRL for the analytical 

method was either 5.0 or 10 μg/L depending on which 
38 Chemical Quality of Water, Sediment, and Fish in Mountain Creek Lake, Dallas, Texas, 1994–97 

PAH was measured. A common measure of the degree 

of hydrophobicity of organic compounds is the 

octanol/water partition coefficient (Kow). It is the 

measure of the distribution of a given compound in two 

phases, generally n-octanol and water, expressed as the 

logarithm of the concentration ratio. The Kow values 

for PAHs range from 3.46 for naphthalene (two rings) 

to 5.91 for benz(a)anthracene (four rings) to 7.10 for 

benzo(ghi)perylene (six rings) (Lucius and others, 

1992; Knox and others, 1993). A Kow of 7.1 means that 

107.1 times (12.6 million) more of the compound, at 

equilibrium, was measured in the n-octanol phase than 

in the water phase. The hydrophobicity of these compounds causes them to partition strongly into sediment, 

and lack of detection of PAHs in the aqueous phase (for 

example, in stormwater samples) is not unusual. 

In contrast to the water-sampling results, numerous PAHs were detected in suspended sediment samples 

in stormwater from the west and east lagoon outfalls 

(NWIRP–1 and NWIRP–2, respectively) and from the 

north and south forks of Cottonwood Creek (table 7, at 

end of report). PAH concentrations were larger in samples from NWIRP than in samples from Cottonwood 

Creek, with the largest concentrations at NWIRP–1. 

Concentrations of PAHs were relatively small on the 

more rural south fork of Cottonwood Creek. No suspended sediment samples were collected from the NAS 

stormwater sites.

Most PAHs were not analyzed in samples from 

the four lake-water sampling sites; however, naphthalene was analyzed in lake water as part of the VOC analytical schedule and was detected at site MCL–12 in the 

NAS inlet (Jones and others, 1997). That site is adjacent 

to stormwater site NAS–1, where other fuel-related 

VOCs were detected but not naphthalene. The two sites 

where PAHs were detected in stormwater, NAS–2 and 

NAS–3, do not drain to the lake but drain to Mountain 

Creek downstream from the dam.

PAHs in Sediment

PAHs were detected in all surficial (top 3 cm) bottom sediment samples collected from Mountain Creek 

Lake (Jones and others, 1997, p. I–4, II–6). The smallest 

concentrations were in the upper part of the lake where 

all individual PAH concentrations were less than 50 

μg/kg. Fluoranthene was the PAH with the largest concentration in all Phase I sediment samples. The fluoranthene concentration at MCL–1 in the upper lake was 

relatively small, 37 μg/kg (fig. 21a). Small concentrations in the upper lake reflect the more rural watershed 

of Mountain Creek south of the Dallas area. In comparison, fluoranthene concentrations in sediment collected 

from Cottonwood Bay (fig. 21c) were from 1 to 3 orders 

of magnitude larger and an order of magnitude larger 

than those collected from the lake along the eastern 

shoreline of NAS (fig. 21d). 

Phase II bottom sediment samples were analyzed 

for a larger number of PAH compounds and at lower 

method detection limits than Phase I samples (Jones and 

others, 1997). T-PAH concentrations in Phase II samples from east Cottonwood Bay ranged from 17,800 to 

27,900 μg/kg, except for one sample of 218,000 μg/kg 

(fig. 22). T-PAH concentrations in samples from central 

and west Cottonwood Bay ranged from 4,750 to 

28,800 μg/kg. All concentrations in samples from the 

main body of Mountain Creek Lake were less than 

2,800 μg/kg, and the median concentration of the mainlake sites was 1,210 μg/kg. For comparison, the T-PAH 

concentration in surficial sediment from White Rock 

Lake was 2,790 μg/kg (Van Metre and others, 2000). A 

streambed sediment sample collected from Cottonwood 

Creek where Eighth Street crosses it west of Cottonwood Bay (M2.23) had a T-PAH concentration of 

20,600 μg/kg, reflecting urban land use and possibly 

additional enrichment from proximity to Eighth Street. 

This concentration is comparable to concentrations in 

the western and central parts of Cottonwood Bay.

The largest concentrations of the two PAHs 

ranked in the first 10 of the USEPA list of top 20 

hazardous substances (Agency for Toxic Substances 

and Disease Registry, 1994), benzo(a)pyrene and 

benzo(b)fluoranthene, were in bottom sediments from 

east Cottonwood Bay (fig. 23). The median concentration of benzo(a)pyrene in the 0- to 3-cm interval from 

Phase II samples in east Cottonwood Bay was 1,570 

μg/kg, and the maximum concentration was 11,100 

μg/kg; the median concentration in main-lake sites was 

97.3 μg/kg. Benzo(a)pyrene was not detected (less than 

150 μg/kg) at MCL–1 in the upper part of the lake during Phase I. The median benzo(b)fluoranthene concentration in east Cottonwood Bay was 1,850 μg/kg, and 

the maximum was 13,000 μg/kg; the main-lake median 

was 98.2 μg/kg.

Concentrations of PAHs in the NAS inlet generally were larger than in the main lake but smaller 

than in Cottonwood Bay (figs. 21, 22). The median 

benzo(a)pyrene concentration in Phase II samples from 

the NAS inlet was 411 μg/kg compared to a median of 

98.2 μg/kg in samples farther from shore in the main 
CHEMICAL QUALITY OF WATER, SEDIMENT, AND FISH IN MOUNTAIN CREEK LAKE 39

110

91

37

94

400

690

180

1,700

740

1,800

3,300

5,100 2,9003,000

4,800 3,600 4,000

860

36,000

MOUNTAIN CREEK LAKEMOUNTAIN CREEK LAKE

337

461

134 201 1

128

9

788

203

725

1,740 3

2,620

MOUNTAIN CREEK LAMOUNTAIN CREEK LA

Area enlargedin (d)

Area enlargedin (c)

2,510

2,430 1,960

1,600 2,200

697

4,010 3,760

1,390

1,740 2,280

3,900 3,580

2,570

1,940

29,200

2,570

1,770 175

2,630

2,120

1,820

3,0802,080 1,320

5

325

1,290 

832

(a) (b)

(c) (d)

37 Fluoranthene

concentration,in microgramsper kilogram 337 Fluoranthene concentration, in micrograms per kilogram

186 Fluoranthene concentration,

in micrograms per kilogram

175 Fluoranthene concentration,

in microgramsper kilogram

MOUNTAIN MOUNTAIN 

COTTONWOOD BAY COTTONWOOD BAY

Figure 21. Fluoranthene concentrations in top 3 centimeters of lake bottom sediments from (a) Phase I sampling; (b) Phas(c) Phase II Cottonwood Bay sampling; and (d) Phase II NAS inlet sampling. 
40 Chemical Quality of Water, Sediment, and Fish in Mountain Creek Lake, Dallas, Texas, 1994–97 

lake (fig. 23). T-PAH concentrations in the NAS inlet 

ranged from 216 to 15,600 μg/kg compared to T-PAH 

concentrations of 63 to 3,740 μg/kg in main-lake 

samples (fig. 22). 

PAHs were measured in three Phase I and two 

Phase II sediment samples from small streams draining 

the northeastern part of NAS to Mountain Creek downstream from the dam (figs. 1, 2). One of those samples, 

from a stream known locally as the TANG Canal (site 

NAS–3), had large PAH concentrations with a T-PAH of 

159,000 μg/kg. Moderately elevated T-PAH concentrations compared to the main-lake sites were detected in 

sediment samples from two nearby streambeds: NAS–2 

and NAS–4 had detections of 21,400 and 4,730 μg/kg, 

respectively. T-PAH concentrations in two samples collected farther downstream at Phase II sites M2.46 and 

M2.47 also were moderately elevated at 6,330 and 

11,500 μg/kg, respectively (fig. 22), similar to concentrations at the Cottonwood Creek urban reference site 

and the NAS inlet sites. 

T-PAH concentrations in the MCL–4 gravity 

core, at the center of Mountain Creek Lake, increased 

from less than 100 μg/kg at the bottom of the core to 

910 μg/kg in the most recently deposited sediment 

(fig. 24). Similar temporal patterns occur in sediment 

cores from White Rock Lake and from Lake Anne in 

Reston, Va. (Van Metre and others, 2000). These trends 

probably result from increased population growth and 

automobile use in the watersheds of these reservoirs. 

In contrast to gradually increasing trends in the main 

2,780

3,740

1,280 1,740 1,100

1,170

1,240

63

11,500

6,330

1,590

5,480

40 12,400

20,600

MOUNTAIN CREEK LAKEMOUNTAIN CREEK LAKE

1,440

1,730

3,620

7,380

10,500

15,600

216

4,810

16,950

20,100 11,390

16,200 12,100

5,430 20,800

12,300

12,700

27,400

25,300

25,400

4,780

28,800

22,600

218,000

25,600

25,600

26,000

27,900

26,800

17,800

27,000

8th Street

COTTONWOOD COTTONWOOD BAY BAY

40 Total PAH concentration,

in micrograms per kilogram

21,500

Figure 22. Total PAH concentrations in top 3 centimeters of surficial sediment from Phase II sampling. 
CHEMICAL QUALITY OF WATER, SEDIMENT, AND FISH IN MOUNTAIN CREEK LAKE 41

part of the lake, T-PAH trends in Cottonwood Bay are 

decreasing from larger historical levels. The largest 

T-PAH concentrations in the MCL–7 core (central bay) 

were detected in sediment deposited in the 1950s. These 

concentrations are about 60 percent larger than concentrations in sediment deposited during the same time 

period in the Bay–13 core (east bay) (fig. 24). T-PAH 

concentrations at Bay–13 increased from slightly 

less than 6,000 μg/kg in sediments deposited in the 

1930s to 43,100 μg/kg in sediments deposited in about 

1 100,000 10 100 1,000 10,000

Benzo(a)pyrene

East 

Central 

West Cottonwood 

Cottonwood 

Main lake

NAS inlet

SITE

EXPLANATION

Minimum

25th percentile

Median (50th percentile)

75th percentile

Maximum

1 100,000 10 100 1,000 10,000

Benzo(b)fluoranthene

East 

Central 

West Cottonwood 

Cottonwood 

Main lake

NAS inlet

Cottonwood Bay

Cottonwood Bay

Bay and Canal

Creek

Cottonwood Bay

Cottonwood Bay

Bay and Canal

Creek

CONCENTRATION, IN MICROGRAMS PER KILOGRAM

Number of

(9)

(9)

(8)

(2)

(11)

(7)

(9)

(9)

(8)

(2)

(11)

(7)

samples

(9)

Datapoint shown for 

detections at two sites

Figure 23. Distribution of benzo(a)pyrene and benzo(b)fluoranthene concentrations in top 3 centimeters of 

surficial sediment.
42 Chemical Quality of Water, Sediment, and Fish in Mountain Creek Lake, Dallas, Texas, 1994–97 

1950. Concentrations then decreased to 24,700 μg/kg 

in recently deposited sediments, similar to those in 

recently deposited sediments at MCL–7.

T-PAH concentrations in sediment samples collected during Phase II from core M2.40 in the NAS inlet 

ranged from 527 to 5,500 μg/kg (fig. 25). The smallest 

concentration was in sediments at the bottom of the 

core; these sediments were deposited in about 1940. 

Sediments deposited in the 1940s and 1950s showed 

increasing amounts of T-PAH, culminating in sediment 

deposited in the mid-1950s (50- to 55-cm interval) with 

5,500 μg/kg, about 3 times the T-PAH concentration 

as in sediment samples above and below that interval. 

Concentrations then decreased and remained somewhat 

constant at 1,500 to 2,000 μg/kg to the top of the core. 

The increase in T-PAH concentrations from the 1940s 

into the 1950s is coincident with increasing activities on 

NAS and probably indicates an effect of those activities 

on the quality of water and sediment discharging into 

the inlet. Concentrations at the NAS inlet, however, 

were small compared to those in Cottonwood Bay and 

the north fork of Cottonwood Creek.

PAHs in Fish

Five channel catfish skin-off fillet samples 

analyzed for PAHs (Jones and others, 1997, p. II–32) 

included two fish from Cottonwood Bay (one each 

from areas 7 and 8) and three fish from Mountain Creek 

Lake (two from area 10 and one from area 2) (fig. 2). 

Only five samples were analyzed because, unlike 

0 80,000 0 40,000

Total PAH

1930

2000

1940

1950

1960

1970

1980

1990

DEPOSITION DATE

0 1,000 500

Total PAH

0 1

Fluoranthene/pyrene

EXPLANATION

Bay–13, in east bay

MCL–7, in central bay

MCL–4, in main lake

0 2

2- & 3-ringed/4- & 5-ringed

PAH compounds

Nondetection

CONCENTRATION, IN MICROGRAMS PER KILOGRAM RATIO OF PAH COMPOUNDS

2 4

Figure 24. Trends in PAH concentrations in Bay–13, MCL–7, and MCL–4 cores. 
CHEMICAL QUALITY OF WATER, SEDIMENT, AND FISH IN MOUNTAIN CREEK LAKE 43

organochlorine pesticides and PCBs, PAHs that are 

taken up across gill membranes or ingested are metabolized by the fish’s mixed-oxidase system to form metabolites that are excreted (Eisler, 1987). Of the 16 PAHs 

on the USEPA Priority Pollutant list (U.S. Environmental Protection Agency, 1995), only fluoranthene and 

pyrene were detected in the channel catfish fillets. Fluoranthene concentrations ranged from one nondetection 

to 39 μg/kg, and pyrene concentrations ranged from two 

nondetections to 32 μg/kg. The Texas Department of 

Health (Kirk Wiles, Texas Department of Health, oral 

commun., 1996) concluded that PAHs in edible fish tissues are not a human health concern for the consumption of fish tissues. 

Sources of PAHs

The sources of PAHs in sediment from Mountain 

Creek Lake, in suspended sediment, and in sediment 

from nearby streams are discussed in two sections. The 

chemical origin of PAHs (pyrogenic versus uncombusted fuel sources) on the basis of relative abundance 

of selected PAHs is presented first. An evaluation of 

physical locations (spatial sources) where PAHs might 

have originated on the Navy facilities or urban areas 

around the lake is presented second.

Pyrogenic Versus Uncombusted Fuel Sources

The relative abundance of selected PAHs can 

indicate whether they are derived from pyrogenic (combustion related) or uncombusted fuel sources. Crude 

oil and refined petroleum contain predominantly 2- and 

3-ringed PAH compounds, whereas combustion results 

in predominantly 4- and 5-ringed compounds (Hites and 

others, 1981; Eganhouse and Gossett, 1991). PAHs produced by combustion are characterized by the predominance of fluoranthene over pyrene (Eganhouse and 

Gossett, 1991) or phenanthrene over anthracene (Heit, 

1985), and they tend to contain 4-ringed compounds 

(fluoranthene and pyrene and C1–3 alkylated homologues) as a large proportion of the T-PAH (Sporstøl and 

others, 1983). A typical characteristic of a petroleum 

source is enrichment of the alkylated homologues relative to the parent compounds. For example, samples of 

wastewater effluent from the Los Angeles County 

Sanitation District in California, which receives petrochemical waste in its influent, had a fluoranthene/

pyrene ratio of about 0.5 indicating uncombusted fuel 

sources (Eganhouse and Gossett, 1991). In contrast, 

sediments from Cayuga Lake in New York, which 

receives regional atmospheric deposition from pyrogenic sources (for example power plants), had a fluoranthene/pyrene ratio of 12 or more (Heit, 1985).

0 2,000 4,000 6,000

Total PAH

1930

2000

1940

1950

1960

1970

1980

1990

DEPOSITION DATE

0.6 0.8 1.0 1.2 1.4

Fluoranthene/pyrene

0 3 1 2

2- & 3-ringed/4- & 5-ringed

PAH compounds

0 1 2

Phenanthene/

anthracene

0 1 2 3

C1-Phenanthrene/

phenanthrene

CONCENTRATION, RATIO OF PAH COMPOUNDS

IN MICROGRAMS

PER KILOGRAM

RATIO OF PAH COMPOUNDS

3 4

Figure 25. Trends in PAH concentrations in M2.40 core in the NAS inlet. 
44 Chemical Quality of Water, Sediment, and Fish in Mountain Creek Lake, Dallas, Texas, 1994–97 

PAHs in surficial sediment in Mountain Creek 

Lake near NWIRP (sites M2.1 through M2.22), in and 

near the canal (sites M2.24 through M2.30), and offshore from the NAS inlet (sites M2.31 through M2.45) 

appear to be predominantly from pyrogenic sources 

rather than uncombusted fuel sources (fig. 26; table 8, at 

end of report). The pyrogenic source is indicated by a 

fluoranthene/pyrene ratio greater than 1.0; enrichment 

of 4- and 5-ringed compounds relative to 2- and 3-

ringed; predominance of parent phenanthrene over the 

singly-alkylated homologue; and large percentage of 

T-PAH composed of the 3-ringed series and their C1–3

alkylated homologues. The composition of the PAHs 

found in the sediment offshore of NAS differs significantly from those near NWIRP (t-test p-value less than 

.001). Although samples from both locations are 

predominantly pyrogenic in origin, NAS offshore samples are relatively more fuel-related (table 8). VOCs in 

stormwater samples were predominantly fuel-related 

from NAS and solvent-related from NWIRP, which 

indicates relatively more fuel-related releases to the 

NAS inlet than to Cottonwood Bay.

The two diagnostic ratios that can be computed 

for east lagoon surficial sediment on NWIRP have a 

relatively strong pyrogenic signal: The fluoranthene/

pyrene ratio is 1.33 or greater for five of the six sludge 

samples, and the phenanthrene/anthracene ratio is 6.8 or 

greater for three of the six sludge samples. The suspended sediment sample from the east lagoon has a 

similarly strong pyrogenic signal with a fluoranthene/

pyrene ratio of 1.27 and a phenanthrene/anthracene 

ratio of 6.9. 

Bottom and suspended sediments from the west 

lagoon also have pyrogenic signals. The median fluoranthene/pyrene ratio in five west lagoon surficial sediment samples is 1.24, and the median phenanthrene/

anthracene ratio 4.75 (fig. 26). The fluoranthene/pyrene 

ratios in the two suspended sediment samples are 1.15 

and 1.19, and the phenanthrene/anthracene ratios are 6.6 

and 8.3, all indicating pyrogenic sources. 

At the southwestern end of Cottonwood Bay the 

PAH compositions reflect the probable contribution of 

sediment from Cottonwood Creek. The north fork of 

Cottonwood Creek has a relatively large phenanthrene/

anthracene ratio of 6.36 in bottom sediment (site M2.23, 

fig. 26) and 9.3 and 11 in suspended sediments, indicating pyrogenic origin. Site M2.20 (west bay) near the 

canal has a relatively large phenanthrene/anthracene 

ratio of 6.17. Moving down the canal toward the main 

body of the lake, T-PAH concentrations decrease to a 

concentration of 3,000 μg/kg in sediment at site M2.30 

in the main lake. As T-PAH concentrations decrease 

down the canal, phenanthrene/anthracene ratios 

decrease and C1-phenanthrene/phenanthrene ratios 

increase, indicating increased contribution from uncombusted fuel sources. Because main-lake reference site 

PAHs tend to be from uncombusted fuel sources, this 

shift from pyrogenic to fuel-related sources could be 

caused by smaller inputs of pyrogenic PAHs rather than 

from greater inputs of fuels.

Large concentrations of PAHs were detected in 

samples collected during Phase I in a small streambed in 

the northeastern part of NAS (site NAS–3). The laboratory analysis of Phase I samples did not include the full 

suite of 64 PAH compounds that the Phase II analyses 

included, thus the computed T-PAH concentration from 

the laboratory analysis of 159,000 μg/kg underestimates 

the actual T-PAH concentration. Source indicators at 

NAS–3 that are based on PAH composition are ambiguous: Although the sample has a fairly large fluoranthene/pyrene ratio of 1.38, indicating a pyrogenic 

origin, the very small phenanthrene/anthracene ratio of 

2.08 indicates a fuel origin. Several SWMUs in the 

immediate vicinity could be sources of PAHs, including 

floor drains conveying motor and hydraulic oil from 

spills, oil-water separators, and two underground storage tanks containing waste petroleum (EnSafe/Allen & 

Hoshall, 1995).

Temporal trends in PAH source indicators also 

occur. The fluoranthene/pyrene ratio in the Bay–13 core 

increased from 0.5 in sediments deposited in the 1930s 

and 1940s to more than 1.0 in sediments deposited from 

the late 1960s to the present (fig. 24). The 2- and 3-

ringed/4- and 5-ringed ratio decreased from about 1.6 in 

the lower part of the core to less than 0.5 in recently 

deposited sediments. At Bay–13, both of these indicators point to a change from uncombusted fuel sources to 

pyrogenic sources.

Four different indicators suggest that PAHs in the 

M2.40 core in the NAS inlet shifted from uncombusted 

fuel sources in the 1940s toward more pyrogenic, typically urban sources in the 1960s and later (fig. 25). The 

ratio of fluoranthene to pyrene, less than 1.0 in sediments deposited from the 1940s (except for 1.2 in 1940) 

through the 1960s at M2.40, increases to greater than 

1.0 in sediments deposited from about 1970 to the 

present. Similarly, the 2- and 3-ringed/4- and 5-ringed 

ratio is greater than 1.0 in sediments deposited from the 

1940s through the 1960s and less than 1.0 in sediments 

deposited after 1970. Relative amounts of phenanthrene 
CHEMICAL QUALITY OF WATER, SEDIMENT, AND FISH IN MOUNTAIN CREEK LAKE 45

(6)

(5)

1,000

10,000,000

10,000

100,000

1,000,000

TOTAL PAH CONCENTRATION,

EXPLANATION

Minimum

25th percentile

Median (50th percentile)

75th percentile

Maximum

(6) Number of samples

East bay

Central bay

West bay

Canal to lake

1.6

0.8

1.0

1.2

1.4

FLUORANTHENE/PYRENE

East

M2.1M2.4

West

M2.11M2.14M2.17M2.20M2.23M2.25M2.26M2.27M2.29M2.30

0

10

2

4

6

8

PHENANTHRENE/ANTHRACENE

lagoonlagoon

North fork Cottonwood Creek

IN MICROGRAMS PER KILOGRAM

(6)

(6)

(5)

(5)

Datapoint shown for detection at one site

PLACE NAME OR SITE NUMBER

Figure 26. Longitudinal variation in total PAH and source indicator ratios for surficial sediment samples. 
46 Chemical Quality of Water, Sediment, and Fish in Mountain Creek Lake, Dallas, Texas, 1994–97 

and anthracene also are indicative of a shift from fuel 

sources to pyrogenic sources. The phenanthrene/

anthracene ratio, about 2.0 in sediments deposited in the 

1940s, decreases to less than 1.0 in sediments deposited 

in the mid-1950s to the mid-1960s, then increases in 

sediments deposited from the mid-1960s until the 

present, reaching its 1994 value of just less than 3.0. The 

smallest ratios of phenanthrene/anthracene are in petroleum products. Urban runoff, which usually contains 

pyrogenic PAHs with some petroleum product, generally has a phenanthrene/anthracene ratio of 3 to 5, and 

ratios greater than 10 are found at remote sites where the 

source of PAHs is atmospheric deposition (Gschwend 

and Hites, 1981). Finally, enrichment in the alkylated 

homologue relative to the parent PAH in sediments 

deposited at the site from the 1940s to the 1960s, indicative of a fossil-fuel origin, is illustrated by the C1-

phenanthrene/phenanthrene ratio in figure 25. This ratio 

peaks at 3.3 for sediments deposited in about 1960 and 

decreases to about 1.0 for sediments deposited in the 

mid-1970s. A ratio of 0.76, indicative of a pyrogenic 

origin, was computed for the most recently deposited 

sediments.

Spatial Sources of PAHs

T-PAH concentrations in two suspended sediment 

samples collected in 1997 from the north fork of Cottonwood Creek were 3,000 and 1,000 μg/kg, about onetenth the concentration in the streambed sample from 

the site. The difference could indicate enrichment of the 

bottom sediment from local runoff from the bridge and 

road. The T-PAH concentration in a suspended sediment 

sample from the south fork of Cottonwood Creek was 

890 μg/kg, smaller than the north fork concentrations 

but about 10 times greater than the very small concentration in the streambed sample from the site. These 

concentrations indicate that some PAHs are transported 

to Cottonwood Bay by the north and south forks of Cottonwood Creek. 

Analyses were done to indicate whether the east 

and west lagoons were sources of PAHs. PAHs were 

measured in the sediment samples collected in the east 

and west lagoons by EnSafe/Allen & Hoshall (1996a); 

however, analyses of lagoon sediments included only 

16 of the 64 compounds that were analyzed in the USGS 

Phase II Mountain Creek Lake samples. The EnSafe/

Allen & Hoshall (1996a) analyses included primarily 

parent PAH compounds and excluded most of the 

alkylated homologues. The 16 compounds account for 

17 to 80 percent of the T-PAH in USGS Phase II samples; this wide range is caused by variations in the 

relative concentrations of various PAH compounds. 

T-PAH concentrations for the lagoon sediment were 

estimated by linear regression. The regression equation 

was developed using Phase II results in Cottonwood 

Bay by relating measured T-PAH to the sum of concentrations of 10 of the compounds analyzed by 

EnSafe: pyrene, 9H-fluorene, chrysene, acenaphthalene, fluoranthene, benzo(a)anthracene, benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(a)pyrene, and 

benzo(ghi)perylene. The coefficient of regression (r2

) 

was 0.999, the regression was significant (p-value = 

.001), and the standard error of the estimate (SE) was 

1,420 μg/kg. The regression equation was used with 

data from EnSafe/Allen & Hoshall (1996a) to estimate 

T-PAH in the lagoon sediments (table 9, at end of 

report). Estimated T-PAH concentrations in the upper 

60 cm of sediments from the east lagoon range from 

88,100 to 4,720,000 μg/kg, and estimated concentrations in the upper 60 cm of sediments from the west 

lagoon range from 21,400 to 540,000 μg/kg.

The T-PAH concentration in a stormwater 

suspended sediment sample collected at the east lagoon 

outfall in 1997 was 5,500 μg/kg, smaller than the 

concentrations in lagoon bottom sediment or in surficial bottom sediment in Cottonwood Bay (fig. 26). 

T-PAH concentrations in two suspended sediment 

samples from the west lagoon outfall were 26,000 and 

22,000 μg/kg, comparable to average surficial sediment 

concentrations in central and east Cottonwood Bay. 

The mixture of individual PAH compounds and the 

magnitude of concentrations detected in the suspended 

sediment samples from the west lagoon (fig. 27) are 

similar to PAHs in west lagoon and central bay bottom 

sediments. 

Sources of PAHs in east and central Cottonwood 

Bay are most likely the east and west lagoons. The large 

concentration of PAHs in the east lagoon and the proximity of the outfall from the lagoon to site M2.1, where 

the T-PAH concentration was 218,000 μg/kg (fig. 26) 

indicate that the east lagoon is the most likely source 

of the PAH contamination in the eastern end of the bay. 

At site M2.4, about 260 m from the outfall, the T-PAH 

concentration was 27,000 μg/kg (fig. 26). The relatively 

small PAH concentration in the east lagoon outfall suspended sediment sample suggests current transport of 

the more highly contaminated sediments in the east 

lagoon is not occurring. The T-PAH concentration was 

slightly larger at site M2.11, which is near the outfall 
CHEMICAL QUALITY OF WATER, SEDIMENT, AND FISH IN MOUNTAIN CREEK LAKE 47

from the west lagoon. T-PAH concentrations decrease 

along the length of Cottonwood Bay to the canal. At the 

canal, T-PAH concentrations again increase, possibly 

because of the contribution of sediments from urban 

sources in the Cottonwood Creek watershed. A relatively large concentration of T-PAH was found in a 

streambed sediment sample from the urbanized north 

fork of Cottonwood Creek (site M2.23, 20,600 μg/kg) 

and a very small concentration of T-PAH was found in 

the less-urban south fork (site M2.48, 40 μg/kg). The 

north fork of Cottonwood Creek drains a residential and 

commercial area of Grand Prairie, Tex.; additionally, 

the sampling site is beneath a four-lane bridge. 

Several SWMUs on NAS along the canal might 

be sources of petroleum-derived PAHs. SWMU 81 

(fig. 6) is a storm sewer that discharges petroleumcontaminated wastewater runoff, spent solvents, waste 

petroleum, and waste oil and sludge; SWMU 20 and 29 

are underground storage tanks containing waste petroleum; SWMU 14 and 6 are firefighter training areas 

contaminated with jet fuel, aviation gasoline, and waste 

petroleum; and SWMU 1 is a landfill contaminated with 

waste oil and sludge (EnSafe/Allen & Hoshall, 1995). 

Decreasing T-PAH concentrations along the canal, however, indicate that any contributions from these SWMUs 

must be relatively small. 

PAHs at the NAS inlet are most likely the result 

of the presence of a fuel farm and other fuel-related 

SWMUs (EnSafe/Allen & Hoshall, 1996b) combined 

with runoff from roads and parking areas. Sediment 

3,000

0

1,0002,000

 REFERENCE 

Bottom sediment 

M2.30 0–3 centimeters

0525,000

,000

10,00015,00020,000

Anthracene

Benz(a)anthracene

Benzo(a)pyrene

Benzo(b)fluoranthene

Chyrsene

Fluoranthene

Fluorene

Naphthalene

Phenanthrene

Pyrene

0150,00050,000100,000

Anthracene

Benz(a)anthracene

Benzo(a)pyrene

Benzo(b)fluoranthene

Chyrsene

Fluoranthene

Fluorene

Naphthalene

Phenanthrene

Pyrene

 WEST LAGOON

Bottom sediment

0–60 centimeters

 EAST LAGOON

Bottom sediment

0–60 centimeters

3,000

0

1,0002,000

6,00002,0004,000

WEST LAGOON OUTFALL

Suspended sediment

NWIRP–1

EAST LAGOON OUTFALL

Suspended sediment

NWIRP–2

PAH CONCENTRATION, IN MICROGRAMS PER KILOGRAM

3,000

0

1,0002,000

06,0002,0004,000

WEST COTTONWOOD BAY

Bottom sediment

EAST COTTONWOOD BAY

Bottom sediment 

M2.1–M2.9 0–3 centimeters

M2.10–M2.18 0–3 centimeters

Figure 27. Comparison of lake-bottom sediment and suspended sediment PAH concentrations in the east and 

west lagoons and Cottonwood Bay.
48 Chemical Quality of Water, Sediment, and Fish in Mountain Creek Lake, Dallas, Texas, 1994–97 

from several SWMUs near the lake contained PAHs. 

For example samples from Group 12, a 7.6-m3 tanker 

truck, contained benzo(a)anthracene, benzo(z)pyrene, 

benzo(b)fluoranthene, benzo(k)fluoranthene, chrysene, 

fluoranthene, indeno(1,2,3-cd)pyrene, phenanthrene, 

and pyrene; samples from SWMU 2P, a former paint 

disposal area, contained fluoranthene, pyrene, and 

naphthalene; and samples from Group 11, SWMU 26P, 

an underground storage tank, contained anthracene, 

benzo(a)anthracene, chrysene, fluoranthene, phenanthrene, and pyrene. These SWMUs could be sources of 

petroleum-derived PAHs along the NAS inlet shoreline.

Occurrence, Trends, and Sources of 

Organochlorine Pesticides

Organochlorine pesticides include well-known 

compounds such as DDT, chlordane, and dieldrin, all of 

which were detected in Mountain Creek Lake sediment 

and fish. DDT was first synthesized in 1874 and was 

used as an insecticide starting in 1939 (U.S. Environmental Protection Agency, 1983). Use of DDT peaked 

in the United States in the early 1960s (Rapaport and 

others, 1985) and was banned nationwide in 1972 

(Smith and others, 1988). DDT is not long-lived in the 

natural environment, and it readily breaks down into 

two metabolites, DDD and DDE, both of which are 

resistant to further breakdown.

The insecticidal properties of chlordane were first 

identified in 1945 (Smith and others, 1988); chlordane 

was first produced commercially in the United States in 

1947 (U.S. Environmental Protection Agency, 1983). 

Agricultural use of chlordane principally was on corn, 

and nationwide agricultural use in 1971 was an estimated 857,000 kg of active ingredient (U.S. Department 

of Agriculture, 1974). Limited use of chlordane, following USEPA restrictions in 1983, continued as a termiticide and for control of fire ants until virtually all uses 

were banned in 1988 because of environmental concerns. After 1988, the only permitted uses of chlordane 

were for fire ant control in power transformers and for 

the use of existing stocks in the possession of homeowners (U.S. Environmental Protection Agency, 1990). 

Home and garden use of chlordane was an estimated 

524,000 kg in 1990 (Whitmore and others, 1992), which 

indicates relatively large recent use in some urban areas. 

Dieldrin is an insecticide and also a metabolite 

of the insecticide aldrin. Aldrin and dieldrin were synthesized in the laboratory in 1948 and registered for 

commercial production in 1951 (U.S. Environmental 

Protection Agency, 1983). Aldrin and dieldrin were 

used to control pests on corn until farm uses were 

banned in 1974. Subsurface ground insertion for termite 

control, dipping of non-food roots and tops, and mothproofing by manufacturing processes in closed systems 

were allowed to continue (U.S. Environmental Protection Agency, 1983). Aldrin and dieldrin use was banned 

in all products in May 1987 (U.S. Environmental Protection Agency, 1990). Unlike chlordane, no home and 

garden use of aldrin or dieldrin was reported in 1990 

(Whitmore and others, 1992).

Organochlorine Pesticides in Stormwater and Lake 

Water

Organochlorine pesticides were not detected in 

any of the 30 stormwater samples (Raines and others, 

1997) or the four lake water samples (Jones and others, 

1997). The MRL of the analytical method used for 

stormwater was 0.1 μg/L for DDT and its metabolites, 

0.5 μg/L for chlordane, and 0.05 μg/L for dieldrin. The 

MRL of the analytical method used for lake water was 

0.006 μg/L for DDE, 0.002 μg/L for chlordane, and 

0.001 μg/L for dieldrin. The ranges of log Kow values 

reported for DDT, chlordane, and dieldrin are 3.98 to 

6.19, 2.78 to 6.00, and 3.54 to 5.16, respectively (Lucius 

and others, 1992). The Kow values indicate that these 

compounds are hydrophobic and will partition strongly 

into sediment. Concentrations of DDT, chlordane, and 

dieldrin in water therefore are expected to be small. 

Although organochlorine pesticides were not 

detected in stormwater samples, several were detected 

in suspended sediment samples from the urban reference site on Cottonwood Creek (table 10, at end of 

report). Chlordane had the largest concentrations at 

13 and 11 μg/kg in the two samples from the north 

fork of Cottonwood Creek. Chlordane was not detected 

in any of the other four samples; however, the MRLs 

for chlordane in those samples were relatively large 

because of the small sample masses analyzed. Dieldrin, 

p,p'-DDE, and p,p'-DDT also were detected in suspended sediment samples from the north fork of Cottonwood Creek. Although organochlorine pesticides are 

not detected frequently in urban stormwater (Baldys 

and others, 1998), they are detected frequently in reservoir bottom sediments from urban areas (Van Metre and 

Callender, 1997; Van Metre, Callender, and Fuller, 

1997).
CHEMICAL QUALITY OF WATER, SEDIMENT, AND FISH IN MOUNTAIN CREEK LAKE 49

Organochlorine Pesticides in Sediment

The same group of organochlorine pesticides 

detected in Cottonwood Creek suspended sediment—

chlordane, dieldrin, p,p'-DDT, and p,p'-DDE—also 

was detected in Mountain Creek Lake bottom sediment 

(Jones and others, 1997, p. I–14–II–18). Concentrations 

in the surficial (top 3 cm) sediment generally were small 

throughout the main body of the lake and Cottonwood 

Bay and larger in the NAS inlet. For example, total DDT 

concentrations in Phase I samples from the main lake 

and Cottonwood Bay ranged from 0.4 to 3.1 μg/kg compared to 0.4 to 18 μg/kg in the NAS inlet. The distribution of pesticides was similar—small concentrations in 

Cottonwood Bay and some relatively larger concentrations in the NAS inlet—for total DDT, chlordane, and 

dieldrin. Two larger concentrations of chlordane in 

Cottonwood Bay, 16.0 μg/kg in MCL–6 and 10.5 μg/kg 

in MCL–7, were similar to concentrations in suspended 

sediments from the north fork of Cottonwood Creek.

Phase II sediment analyses of organochlorine pesticides were limited to the seven sites in the NAS inlet. 

Samples from the inlet had a median total DDT concentration of 3.7 μg/kg. Site M2.39 had the largest total 

DDT concentration, 18.0 μg/kg. Concentrations of 

p,p'-DDE in the inlet ranged from 0.2 to 6.4 μg/kg with 

a median of 1.7 μg/kg; and p,p'-DDD ranged from 0.15 

to 11 μg/kg with a median of 1.8 μg/kg. Six of seven 

samples had detectable concentrations of p,p'-DDT 

with a range of less than 0.1 to 3.5 μg/kg and a median 

of 0.48 μg/kg. These concentrations are similar to concentrations of organochlorine pesticides measured in 

other urban and agricultural reservoirs in the southeastern states (Van Metre and Callender, 1997; Van Metre, 

Callender, and Fuller, 1997).

Phase I concentrations of chlordane in surficial 

sediments were less than method detection limits in 

samples from four of eight sites in the main body of 

the lake (Jones and others, 1997). The concentration 

was 7.0 μg/kg at site MCL–12 in the NAS inlet. Concentrations in Cottonwood Bay ranged from less than 

2.0 to 16.0 μg/kg with detections at seven of eight sites. 

Phase II samples from the NAS inlet had chlordane concentrations that ranged from less than 0.1 to 22.0 μg/kg 

with a median of 9.3 μg/kg and detections at six of 

seven sites. 

Phase I dieldrin concentrations were below the 

method detection limit of 0.1 μg/kg in five of eight 

samples in the main body of the lake. The three sites 

where dieldrin was detected had concentrations of 0.2 

to 0.5 μg/kg. Four of eight sites in Cottonwood Bay 

had measurable amounts of dieldrin with maximum 

concentrations of 1.7 and 2.4 μg/kg at sites MCL–6 and 

MCL–7, respectively. Phase II dieldrin concentrations 

in the NAS inlet ranged from 0.22 to 0.55 μg/kg with 

detections at six of seven sites. In comparison, dieldrin 

concentrations in recently deposited sediments in White 

Rock Lake on the north side of Dallas ranged from 0.3 

to 0.7 μg/kg (Van Metre and Callender, 1997). 

Streambed sediment was collected during both 

sampling phases for organochlorine pesticide analysis. 

Sediment from three sites, one each on three small 

streams along the northeastern boundary of NAS, was 

sampled during Phase I (fig. 1; NAS–2, NAS–3, and 

NAS–4). Four streambed sediment sites were sampled 

during Phase II, two downstream from two Phase I sites 

on the streams along the NAS boundary and the remaining two on the north and south forks of Cottonwood 

Creek (fig. 2; M2.46 and M2.47; M2.23 and M2.48). 

Organochlorine pesticide concentrations were relatively 

large for the sites on and near NAS and on the north 

fork of Cottonwood Creek, similar to concentrations in 

lake bottom sediments in the NAS inlet and to suspended sediment concentrations from the north fork of 

Cottonwood Creek. No organochlorine pesticides were 

detected in the more rural south fork of Cottonwood 

Creek. Chlordane concentrations for streambed sediment sampling sites on and near the NAS ranged from 

6.8 to 31 μg/kg with the largest value at NAS–4. The 

chlordane concentration for the north fork of Cottonwood Creek was 36 μg/kg, and the concentration for 

the south fork was below the method detection limit of 

1.0 μg/kg. The difference in concentrations between 

the two sites reflects the different land uses within 

the watersheds and the largely urban sources of chlordane that contribute to recent sediment (Van Metre, 

Callender, and Fuller, 1997). Dieldrin concentrations 

were less than method detection limits for the three 

Phase I samples. Dieldrin was detected in two Phase II 

samples downstream from NAS at a concentration of 

0.5 μg/kg in both samples and in one sample from the 

north fork of Cottonwood Creek at a concentration of 

1.1 μg/kg.

Gravity cores MCL–4, Bay–13, and M2.40 were 

analyzed for organochlorine pesticides. Total DDT 

concentrations in MCL–4 peaked at a concentration of 

5.9 μg/kg in a sample deposited in about 1966 and 

decreased to less than 0.7 μg/kg (p,p'-DDE, 0.3 μg/kg; 

p,p'-DDT, less than 0.2 μg/kg; and p,p'-DDD, less than 

0.2 μg/kg) in the most recent sample. Bay–13 (east 
50 Chemical Quality of Water, Sediment, and Fish in Mountain Creek Lake, Dallas, Texas, 1994–97 

Cottonwood Bay) had a maximum total DDT concentration of 37 μg/kg in a sample deposited in about 

1967. The total DDT concentration in surficial sediments at Bay–13 was less than 10 μg/kg. The maximum 

total DDT concentration in M2.40 (NAS inlet) was 

21.4 μg/kg in a sample deposited in about 1960. Concentrations decrease to 2.1 μg/kg in the most recent 

sample. Temporal patterns and the magnitude of concentrations of total DDT at all three sites are similar 

to other reservoirs in the southeastern United States 

(Van Metre, Callender, and Fuller, 1997).

Chlordane and dieldrin were detected less frequently in the Mountain Creek Lake cores than the 

DDT degradation products p,p'-DDD and p,p'-DDE. 

Chlordane was not detected in any of 13 samples from 

MCL–4 or in any of seven samples from Bay–13. Chlordane was detected in the six most recently deposited 

samples from M2.40, beginning at 25 to 30 cm and 

continuing to the surface, representing deposition since 

about 1975. The chlordane concentration peaked at 

4.8 μg/kg in the 5- to 10-cm interval, deposited in about 

1990. A similar chlordane trend was reported for White 

Rock Lake (Van Metre and Callender, 1997). Dieldrin 

was not detected in any of the samples from MCL–4 

and Bay–13. Core M2.40 had dieldrin concentrations 

greater than method detection limits for 12 of 15 sampling intervals, although concentrations were consistently small, ranging from 0.14 to 0.51 μg/kg. 

Organochlorine Pesticides in Fish

The most commonly detected organochlorine 

pesticides in fish tissue from Mountain Creek Lake 

were DDT degradation products and various components of technical chlordane (Jones and others, 1997, 

p. I–41, II–34). In composite samples from Phase I, 

organochlorine pesticides were detected more frequently and at larger concentrations in common carp 

than in largemouth bass (fig. 28). Seven organochlorine 

pesticides were detected in whole-body common carp 

samples, and three organochlorine pesticides were 

detected in the largemouth bass fillets, which probably 

reflects the lower lipid content of the fillets. Mean p,p'-

DDD and p,p'-DDE concentrations in whole-body 

common carp were larger than those of any of the other 

organochlorines. DDE, like other organochlorine pesticides, has low water solubility (0.040 mg/L at 20 °C) 

but high lipid solubility. Water-to-fish-tissue bioconcentration factors (BCF) for DDE are as high as 11,000 

(Verschueren, 1983). The chlordane isomers, cis- and 

trans-nonachlor occurred at larger concentrations in 

whole-body common carp than largemouth bass, and 

cis- and trans-chlordane were detected only in wholebody common carp in Phase I. 

All of the organochlorine pesticides detected in 

Phase I composite tissue samples also were detected in 

the individual tissue samples in Phase II. The number of 

detections ranged from two organochlorine pesticides in 

largemouth bass fillets to eight in eviscerated channel 

o,p'-DDE

p,p'-DDE

p,p'-DDD

0 100 20 40 60 80

BASS FILLETS

CONCENTRATION, IN MICROGRAMS PER KILOGRAM

20 40 60 80 100

trans-Chlordane

cis-Chlordane

trans-Nonachlor

cis-Nonachlor

ORGANOCHLORINE PESTICIDE

CARP, WHOLE BODY

0

Figure 28. Mean concentrations of organochlorine pesticides detected in composite fish tissues sampled in 

Phase I. 
CHEMICAL QUALITY OF WATER, SEDIMENT, AND FISH IN MOUNTAIN CREEK LAKE 51

catfish fillets. Dieldrin commonly was detected in 

tissue samples from Phase II. Technical chlordane 

was added as a separate constituent for analysis in 

Phase II and occurred at the largest average concentrations of any organochlorine pesticide in all four tissues 

media. Median concentrations of technical chlordane 

ranged from 11.2 μg/kg in bass fillets to 144 μg/kg in 

eviscerated channel catfish. Major components of technical chlordane include cis-chlordane (19 percent), 

trans-chlordane (24 percent), cis- and trans-nonachlor 

(7 percent each), and heptachlor epoxide (10 percent) 

(Irwin, 1988). Median and maximum concentrations 

of detected organochlorine pesticides were greater in 

catfish fillets or eviscerated whole-body catfish than 

in common carp or largemouth bass fillets (fig. 29). 

Some of the difference in concentrations of these 

(22) (22) (10) (8)

0

600

200

400

Technical

EXPLANATION

Minimum

25th percentile

Median (50th percentile)

75th percentile

Maximum

(22) Number of samples

50

0

10

20

30

40 cis-Chlordane

30

0

10

20

trans-Chlordane

(22) (22) (10) (8)

30

 0

10

20

cis-Nonachlor

100

 0

20

40

60

80

50

 0

10

20

30

40 Dieldrin

Bass Carp Catfish Catfish

200

0

50

100

150

p,p’-DDE

fillets fillets fillets whole body,

eviscerated

Bass Carp Catfish Catfish

fillets fillets fillets whole body,

eviscerated

chlordane

trans-Nonachlor

CONCENTRATION, IN MICROGRAMS PER KILOGRAM

CONCENTRATION, IN MICROGRAMS PER KILOGRAM

Figure 29. Distribution of organochlorine pesticide concentrations detected in fish sampled in Phase II. 
52 Chemical Quality of Water, Sediment, and Fish in Mountain Creek Lake, Dallas, Texas, 1994–97 

organochlorine pesticides among fish samples could 

be attributed to the larger lipid content in the channel 

catfish whole-body and fillet samples than in the bass 

or common carp fillets. Mean or median lipid content 

was 3.9 percent in whole-body channel catfish, 3.0 percent in channel catfish fillets, 1.5 percent in common 

carp fillets, and 0.56 percent in largemouth bass fillets. 

Organochlorine pesticides are more lipid soluble than 

water soluble, and as such, organochlorine pesticide 

concentrations generally are larger in tissue with a 

larger lipid content.

Sources of Organochlorine Pesticides

Organochlorine pesticides detected in Mountain 

Creek Lake are widespread in the environment and frequently detected at similar or greater levels in urban 

lakes or reservoirs (Eisenreich and others, 1989; Van 

Metre, Callender, and Fuller, 1997). Additionally, a possible source of pesticides for the NAS–1 drainage area 

is a site identified by EnSafe/Allen & Hoshall (1996b) 

as Group 12. Group 12 once contained a sewage treatment plant and possibly a sludge-drying bed. An area of 

soil and ground water at the site contaminated with pesticides has been mapped by EnSafe. The pesticides 

detected that exceeded the Risk Reduction Standard 

2-Industrial (RRS2–IND) are dieldrin, aldrin, DDT, 

DDD, and DDE. (EnSafe/Allen & Hoshall, 1996b). 

Occurrence, Trends, and Sources of 

Polychlorinated Biphenyls

PCBs were first synthesized in the laboratory in 

1929, and from 1930 to 1974 an estimated 5.94 X 108

kilograms (kg) were produced (National Academy of 

Sciences, 1979). Annual PCB sales in the United States 

peaked at 36,530 metric tons in 1970 and declined to 

about one-half that amount by 1973 following the 

voluntary ban on PCB use in open systems in 1971 

(Peakall, 1975). In 1979 all new uses of PCBs were 

banned (National Academy of Sciences, 1979). PCBs 

have been used as plasticizers, as hydraulic lubricants 

in gas turbines and vacuum pumps, in heat-transfer 

systems, and as dielectric fluids in electrical capacitors 

and transformers. A biphenyl is two carbon rings 

attached by a carbon-carbon bond. There are 209 possible combinations in which chlorine atoms can attach to 

the biphenyls. Each of these unique configurations is 

known as a PCB congener; congeners differ in their 

physical and chemical characteristics (National Academy of Sciences, 1979). PCBs were formulated and sold 

as Aroclors, which are complex mixtures of as many as 

60 to 80 congeners at analytically detectable levels 

(Bedard and others, 1987). PCBs generally are highly 

resistant to chemical or biological transformation. 

Reductive dechlorination of PCBs has been demonstrated (Alder and others, 1993); however, it proceeds 

very slowly, particularly with the more highly chlorinated congeners. 

PCBs in Stormwater

PCBs were not detected in any of the 30 stormwater samples at an MRL of 1.0 μg/L (Raines and 

others, 1997). PCBs were not analyzed at the four 

lake-water sampling sites. Lack of detections of PCBs 

in stormwater is common (for example, Baldys and others, 1998) because PCBs are very hydrophobic. Kow

values reported for PCBs are 2.8 for the less chlorinated 

Aroclor 1221, 6.11 for the intermediate chlorinated 

Aroclor 1248, and 6.91 for the more chlorinated Aroclor 

1260 (Montgomery, 1991). For Aroclor 1260, a Kow of 

6.91 means that about 8 million times more PCB was 

measured in the n-octanol phase than in the water phase. 

The more chlorinated PCBs are both more persistent 

and more hydrophobic. It is, therefore, expected that 

PCBs will partition strongly to sediment organic matter 

and biota and that water concentrations will be small.

PCBs were detected in stormwater suspended 

sediment samples from the east and west lagoons 

(table 11, at end of report). Concentrations of total 

PCBs (the three Aroclors quantified, Aroclors 1242 + 

1254 + 1260; for computation of total PCBs, nondetections of one or more Aroclors were treated as zero values) in the two west lagoon outfall samples were 650 

and 248 μg/kg. The concentration in a suspended sediment sample from the east lagoon outfall was 45 μg/kg, 

and PCBs were not detected in suspended sediment 

samples from the north and south forks of Cottonwood 

Creek. The MRLs varied among samples and were relatively high; for example, the MRLs for three PCB Aroclors in suspended sediment were all 25 μg/kg in the 

south fork sample. The variability in MRLs is a consequence of variable sample masses recovered from 

stormwater. Despite the variability in MRLs, it is still 

apparent that larger concentrations of PCBs occurred in 

suspended sediments from NWIRP, particularly the 

west lagoon, than from the reference sites on Cottonwood Creek.
CHEMICAL QUALITY OF WATER, SEDIMENT, AND FISH IN MOUNTAIN CREEK LAKE 53

PCBs in Sediment

PCBs were detected in all surficial (top 3 cm) 

lake-bottom sediment samples collected from Mountain 

Creek Lake (Jones and others, 1997, p. I–14, II–18). 

PCB concentrations in surficial bottom sediments in 

Cottonwood Bay and in the NAS inlet are about 1 to 2 

orders of magnitude larger than in the middle and upper 

parts of the lake (fig. 30). Concentrations in Phase I 

samples in the central and east bay ranged from 31 to 

110 μg/kg in samples collected in June 1994 and analyzed using the method of Wershaw and others (1987). 

Concentrations in samples collected in October and 

November 1994 in the same area ranged from 64 to 800 

μg/kg using the method of Foreman and others (1995). 

Part of the explanation for the large concentrations in 

the second set of samples could be that the second 

method uses a more aggressive chemical extraction procedure. Concentrations in the west end of Cottonwood 

Bay and in the main body of the lake are 20 μg/kg or less 

in Phase I samples, except at site MCL–12 (99 μg/kg) 

near the NAS shoreline in the NAS inlet (fig. 30).

Phase II sampling added more spatial detail in 

Cottonwood Bay and along the NAS shoreline. PCB 

concentrations in various sediment samples are summarized in table 11. The largest concentrations in the lake 

were in central and east Cottonwood Bay and in the 

NAS inlet. Concentrations decreased down Cottonwood 

Bay (to the southwest) and in the canal and were the 

lowest in the main part of Mountain Creek Lake and in 

Cottonwood Creek streambed sediment samples. The 

mean concentrations of PCBs in east and central Cottonwood Bay were 271 and 313 μg/kg, respectively, 

compared to a mean of 20 μg/kg in samples from the 

main lake, excluding samples from near the NAS shoreline, indicating that concentrations were elevated by a 

factor of about 15 in east and central Cottonwood Bay 

compared to the main part of the lake. The PCB concentration in the north fork of Cottonwood Creek 

was 5.8 μg/kg. PCBs were not detected at an MRL of 

1.0 μg/kg for each of the three Aroclors in the sample 

from the south fork of Cottonwood Creek. In comparison, the PCB concentration in a surficial sediment 

sample from White Rock Lake collected in 1996 was 

14 μg/kg. PCB concentrations in White Rock Lake, 

Cottonwood Creek, and the main part of Mountain 

Creek Lake indicate that about 20 μg/kg is typical for 

recent lake sediments in urban Dallas. 

Concentrations of PCBs in the NAS inlet ranged 

from less than 3.5 μg/kg (Aroclor 1260 = 1.5, Aroclor 

1254 and Aroclor 1242 less than 1.0 μg/kg) to 700 

μg/kg (fig. 30b, d). Four of six Phase II surficial sediment samples from the NAS inlet had PCB concentrations greater than 100 μg/kg. Unexpectedly, PCB 

concentrations did not correlate with percent finegrained material; the largest concentration was in a sample that was mostly sand (M2.42), and concentrations 

varied greatly regardless of percent fine-grained material. Concentrations in seven Phase II surficial sediment 

samples that were 100 to 300 m from shore ranged from 

less than 4.6 to 700 μg/kg with a median of 110 μg/kg. 

Another small area with larger PCB concentrations is the inlet just east of the main runway (the 

runway inlet) where concentrations were 220 and 

120 μg/kg in two samples (fig. 30b). Concentrations 

decrease rapidly with distance from shore as indicated 

by a Phase I concentration of 7.0 μg/kg at site MCL–10, 

about 100 m south of the shoreline (fig. 30a). 

Historical trends in PCBs at core MCL–4 in the 

middle of Mountain Creek Lake (fig. 31) are similar to 

historical trends in sediment cores from White Rock 

Lake (Van Metre and Callender, 1997). The maximum 

PCB concentration in the White Rock Lake core was 

21 μg/kg in a sample deposited in about 1970, when 

PCB use in the United States peaked. The maximum 

concentration in MCL–4 was 11 μg/kg, also in a sample 

deposited in about 1970. Concentrations in both cores 

since 1970 follow a characteristic decreasing trend 

observed in other reservoirs (Van Metre and others, 

1998).

Maximum PCB concentrations in three samples 

from the middle part of core Bay–13 from Cottonwood 

Bay (fig. 31) are 2,100 to 4,000 μg/kg, greatly exceeding historical concentrations in the other sediment cores 

and surficial concentrations in all parts of Mountain 

Creek Lake. Recently deposited sediments (the top of 

the cores) had much smaller concentrations, 3 μg/kg in 

the core from the main body of the lake (MCL–4) and 

300 μg/kg in the core from Cottonwood Bay (Bay–13). 

These trends indicate very large historical PCB inputs 

and large decreases in PCB inputs in recent years. Three 

samples from core MCL–7 show a similar temporal 

trend in PCBs as indicated at Bay–13 (fig. 31). The temporal record is less complete for PCBs than for heavy 

metals in the Cottonwood Bay cores (fewer samples 

were analyzed); however, similar general trends are 

indicated, with the largest concentrations of PCBs in 

sediments coincident with the time period of pointsource discharges to the west lagoon (pre-1974) and a 

large decrease in concentrations in recent sediments. 
54 Chemical Quality of Water, Sediment, and Fish in Mountain Creek Lake, Dallas, Texas, 1994–97 2.0 3.0 2.0 3.0 99 14 7.0 6.0 6.020 220 110 300 31190 210 <50 <50 3,200

MOUNTAIN CREEK LAKEMOUNTAIN CREEK LAKE

23

16

220 120 1

18

<3.5

<13

14

15

<3.0 24

5.8

MOUNTAIN CREEK LAKMOUNTAIN CREEK LAK

Area enlargedin (d)

Area enlargedin (c)

28

48 50

170 220

38

420 350

98

140 490

330 230

250

360

170

280

320 510

300

270

270

140

320 21

40

110

700 

120

3

(a) (b)

(c) (d)

(0-12 cm)

220

120

220 37

PCB concentration,in micrograms perkilogram PCB concentration, in micrograms per

kilogram

PCB concentration,in micrograms perkilogram

PCB concentration,in micrograms perkilogram

Figure 30. PCB concentrations in top 3 centimeters of lake bottom sediment from (a) Phase I sampling; (b) Phase II sampCottonwood Bay sampling; and (d) Phase II NAS inlet sampling. 
CHEMICAL QUALITY OF WATER, SEDIMENT, AND FISH IN MOUNTAIN CREEK LAKE 55

A more complete PCB record is available for core 

M2.40 in the NAS inlet sampled during Phase II (fig. 

31). PCB concentrations were small (4 and 10 μg/kg) at 

the bottom of the core in samples deposited in the mid1940s. Concentrations increased dramatically in the 

early 1950s to a peak of 391 μg/kg in about 1952 and 

generally remained above 100 μg/kg until about 1970. 

The mean concentration of the seven samples deposited 

from about 1952 to 1970 is 188 (+113) μg/kg. The concentration has decreased since 1970 and was 32 μg/kg 

in the most recent sample at M2.40. The pattern at 

M2.40 is a fairly typical temporal trend that is consistent 

with historical use and restrictions on use of PCBs. 

Although the concentrations at M2.40 are much larger 

than those in White Rock Lake sediments, they are comparable to concentrations in reservoir cores from Lakes 

West Point and Harding downstream from Atlanta, Ga., 

on the Chattachoochee River (Van Metre, Callender, 

and Fuller, 1997). 

Large concentrations of PCBs were reported 

for surficial (0- to 60-cm interval) sediments from the 

west lagoon on NWIRP (table 11). PCBs also occur in 

bottom sediments in the east lagoon—concentrations 

were highly variable with two detections, 760 and 720 

μg/kg, and four nondetections. Concentrations in the 

lagoons are similar to, or larger than, concentrations in 

deeper (older) sediments in cores Bay–13 and MCL–7. 

Although no PCBs were detected in 1994–96 stormwater samples at the lagoon outfalls (Raines and others, 

1997), relatively large concentrations were measured in 

suspended sediment samples collected during storms in 

1997. PCB concentrations in suspended sediment from 

the west lagoon (650 and 248 μg/kg) and from the east 

lagoon (45 μg/kg) are in the same magnitude range as 

surficial sediment concentrations in east and central 

Cottonwood Bay (table 10). Concentrations decreased 

systematically from the central bay to the west bay to 

Cottonwood Creek and from the west bay through the 

canal to the main lake (fig. 30; table 11). 

PCBs in Fish

PCBs were detected in all fish-tissue composite 

samples from Phase I and in 61 of 62 individual fishtissue samples from Phase II (Jones and others, 1997, 

p. I–41, II–34). Concentrations of total PCBs in fish 

from Phase I ranged from 63 μg/kg in a largemouth bass 

fillet composite sample from the upper lake to 4,200 

μg/kg for a carp composite sample from the NAS inlet. 

Total PCB concentrations were larger in largemouth 

Bay–13

Cottonwood Bay

0 15 5 10 1920

2000

1940

1960

1980

DATE

0 500 250 0 5,000 0 2,500 0 10 20 30

M2.40 

NAS inlet

WHITE ROCK LAKE

MCL–4 

Main lake

CONCENTRATION, IN MICROGRAMS PER KILOGRAM

Nondetections

Nondetections

MOUNTAIN CREEK LAKE

Figure 31. Trends in PCB concentrations in Mountain Creek Lake (cores MCL–4, M2.40, Bay–13) and in White 

Rock Lake, Dallas Texas. 
56 Chemical Quality of Water, Sediment, and Fish in Mountain Creek Lake, Dallas, Texas, 1994–97 

bass fillets and whole-body common carp from the NAS 

inlet and Cottonwood Bay than from the upper lake. 

Concentrations in samples from NAS inlet, Cottonwood 

Bay, and upper lake differed by as little as a factor of 2 

to as much as a factor of 9. 

PCB Aroclors 1242, 1254, and 1260 were quantified in fish-tissue samples from Phase II. Aroclor 1260 

concentration was larger than the other Aroclors in 

every tissue sample from Phase II; and for every sample 

with detections of the three Aroclors, the order of concentration from largest to smallest was always 1260, 

1254 and 1242. Concentrations of Aroclor 1260 in individual samples ranged from 2,200 μg/kg for an eviscerated channel catfish collected in Cottonwood Bay to a 

nondetection for a skin-off channel catfish fillet from 

the upper lake. Concentrations of Aroclor 1254 ranged 

from 11 nondetections distributed across all tissue sample types and representing all areas of the lake to a 

maximum of 470 μg/kg in a common carp fillet from 

near the runway inlet. Concentrations of Aroclor 1242 

ranged from nondetections in more than one-half the 

samples to 33 μg/kg in a channel catfish fillet from the 

upper lake. Median concentrations of Aroclors 1260 

and 1254 were greatest in eviscerated channel catfish; 

the maximum average concentration of Aroclor 1242 

was in common carp fillets. 

Total PCB concentrations (the sum of Aroclors 

1242, 1254, and 1260) were not significantly different 

between skin-on and skin-off largemouth bass fillets 

(Wilcoxon rank-sum test [Helsel and Hirsch, 1992]; p 

>.05) or between skin-on and skin-off channel catfish 

fillets (p >.05; fig. 32). Total PCB concentrations were 

significantly different in fillets from all species versus 

eviscerated channel catfish (multiple stage KruskalWallis test [Helsel and Hirsch, 1992]; p <.05). 

Sources of PCBs

As with the heavy metals, all conditions 

necessary to identify source have been demonstrated 

for PCBs in Cottonwood Bay. PCB concentrations 

in Cottonwood Bay are elevated relative to those in 

the main lake and to those at urban reference sites. 

PCB concentrations in the west and east lagoons on 

NWIRP are similar to, or greater than, those in the 

bay. Greater concentrations in dated sediment cores are 

coincident in time with large point-source discharges to 

the west lagoon. PCBs were not identified as a component of those discharges; however, PCBs commonly are 

in waste oil and petroleum products, one of the discharge categories identified (table 3). Additionally, the 

high (particulate) organic carbon content of sewage 

effluent provides an excellent transport medium for 

hydrophobic organic contaminants like PCBs. Finally, 

PCB concentrations in three suspended sediment samples collected in 1997 from the west and east lagoon 

outfalls were similar to concentrations in surficial bottom sediments in the bay and directly demonstrate 

transport to the bay. Therefore, the NWIRP lagoons, 

principally the west lagoon, are indicated as the source 

of the elevated levels of PCBs in bottom sediments in 

Cottonwood Bay. 

Bass Bass Carp Catfish Catfish

EXPLANATION

Minimum

25th percentile

Median (50th percentile)

75th percentile

Maximum

(10) Number of samples (10)

(11)

(9)

(13)

(10)

(9)

0

3,000

500

1,000

1,500

2,000

2,500

CONCENTRATION, IN

MICROGRAMS PER KILOGRAM

fillets, fillets, fillets, fillets, fillets,

skin-off skin-on skin-off skin-off skin-on

whole body,

Catfish

eviscerated

Figure 32. Distribution of PCB concentrations in fish tissues. 
CHEMICAL QUALITY OF WATER, SEDIMENT, AND FISH IN MOUNTAIN CREEK LAKE 57

Two other areas of Mountain Creek Lake had 

elevated PCB concentrations in bottom sediments. 

PCB concentrations in the NAS inlet had a mean of 

226 μg/kg and ranged from less than 3.5 to 700 μg/kg. 

PCB concentrations decrease rapidly with increasing 

distance from shore. SWMU Group 12 is a possible 

source for the PCB contamination in the NAS inlet, with 

reported soil concentrations of Aroclor 1260 of 95 and 

1,100 μg/kg (EnSafe/Allen & Hoshall, 1996b). The second area of large PCB concentrations near NAS is the 

runway inlet, where concentrations were 220 and 120 

μg/kg in two samples. A likely source is a former transformer storage site (SWMU 85) identified on NAS just 

north of site M2.31, with reported soil concentrations of 

Aroclor 1260 of 22, 400, and 3,400 μg/kg (EnSafe/

Allen & Hoshall, 1996b). Concentrations decrease rapidly with distance from shore. 

The transport pathway from the two NAS on-site 

PCB sources to the areas with elevated concentrations in 

bottom sediments at the NAS and runway inlets presumably is erosion and transport of contaminated soils 

by stormwater runoff. This transport pathway is difficult 

to verify because, unlike the NWIRP lagoons, flow 

from these contaminated areas to the lake is not in 

defined channels and does not pass any of the stormwater monitoring stations where suspended sediments 

were collected. On the basis of spatial proximity, temporal trends in core M2.40 of large historical concentrations and stable sedimentation patterns over a long time 

period, the presence of on-site sources, and the lack of 

plausible alternative sources, NAS is identified as the 

source of PCBs in bottom sediments at the NAS and 

runway inlets. 

Sediment and Contaminant Accumulation in 

Cottonwood Bay

The largest concentrations of contaminants in 

surficial sediments in Mountain Creek Lake, which 

include heavy metals (cadmium, chromium, copper, 

lead, mercury, nickel, silver, zinc), PAHs, and PCBs, 

were in Cottonwood Bay. Because of the occurrence of 

these contaminants in the bay, a sedimentation survey 

was done to estimate the total mass of sediment and 

(using measured concentrations) to estimate the mass of 

contaminants in storage in the bay. The total thickness 

of lacustrine sediments was determined at each of the 

Phase I and II sediment sampling sites using gravity 

cores during sampling. Sediment thickness was determined at selected additional sites using metal bars 

pushed through the sediments and using gravity cores 

during July and August 1996. Thicknesses were contoured (fig. 33), constrained by a zero-thickness contour 

near shore, and converted to sediment volume by a 

computer program. Sediment volume was converted to 

mass using the bulk density calculated from measured 

porosities in selected cores. An estimated 38,000,000 kg 

of sediment accumulated in east Cottonwood Bay from 

1928, when the dam to form Mountain Creek Lake was 

built, to 1995. An estimated 29,000,000 kg accumulated 

in central Cottonwood Bay over the same time period. 

Contaminant accumulation rates in a core can 

be estimated by multiplying the mass accumulation 

rate of sediment for a given time interval times the 

concentration of the contaminant in the interval. This 

method is illustrated in figure 34 using silver in core 

Bay–13. Because both the sedimentation rate and the 

silver concentration decreased after 1974, the product 

of the two, silver accumulation rate, decreased 

substantially. 

Masses of selected contaminants in storage in 

bottom sediments in east and central Cottonwood Bay 

were estimated for two time periods, 1940–74 and 

1974–95. The estimates were made for the earlier 

period by (1) multiplying the fraction of core mass 

accumulated during the 1940–74 interval for core 

Bay–13 (73 percent of the core) times the total mass of 

sediment in each part of the bay, then (2) multiplying the 

mean concentration of the selected contaminant in the 

1940–74 period of cores MCL–7 and Bay–13 times the 

sediment mass. The first step assumes that the temporal 

pattern in sedimentation at core Bay–13 is representative of sedimentation over east and central Cottonwood 

Bay. The second step in the calculation assumes that the 

contaminant concentrations in the deeper sediment layers over the whole upper bay are equal to the average 

concentrations at MCL–7 and Bay–13. Both of these 

assumptions lead to considerable uncertainty in the estimates of total contaminant masses in storage in the 

older sediment interval. 

The estimated mass of sediment in storage for the 

latter time period, 1974–95, was made by multiplying 

the fraction of core mass accumulated during the interval in core Bay–13 (9 percent of the core) times the total 

mass of sediment in each part of the bay. This step 

makes the same assumptions as the comparable step for 

the earlier time period. Contaminant masses in these 

sediment intervals then were estimated by multiplying 

the mean contaminant concentrations in surficial sediment samples times the sediment mass in each part of 
58 Chemical Quality of Water, Sediment, and Fish in Mountain Creek Lake, Dallas, Texas, 1994–97 

the bay. This step should lead to more accurate estimates than the comparable step for the earlier time 

period because the surficial samples were more numerous and more uniformly distributed over each area of 

the bay. The comparable step for the earlier period used 

concentrations at only two locations, Bay–13 and 

MCL–7. 

Masses of contaminants in storage then were 

divided by the time interval represented to estimate 

annual contaminant accumulation rates (table 12, at end 

of report). Two conclusions are apparent from table 12. 

The first is that most of the contaminant accumulation 

to Cottonwood Bay occurred before 1974 when active 

waste discharge to the NWIRP lagoons was occurring. 

Total contaminant mass accumulations typically are 1 to 

2 orders of magnitude greater for the 1940–74 period 

than the 1974–95 period. The second conclusion is that 

although contaminant accumulation rates have been 

greatly reduced, some contaminant movement to the 

bay is still occurring. The primary source of most of the 

contaminants to bay sediments is stormwater runoff 

passing through the east and west lagoons on NWIRP. 

In the case of PAHs, transport from urban areas by way 

of Cottonwood Creek also is a contributor. Continuing 

off-site transport was verified by measured chemical 

concentrations in suspended sediments collected during 

stormflow from the east and west lagoons.

SEDIMENT THICKNESS

Less than 0.5 meter

0.5 to 1.0 meter

1.0 to 1.5 meters

Greater than 1.5 meters

CENTRAL BAY

EAST BAY

COTTONWOOD BAY

0 100 200 METERS

N

EXPLANATION

Figure 33. Thickness of lacustrine sediment in central and east Cottonwood Bay. 
SUMMARY 59

SUMMARY

The occurrence, trends, and sources of numerous 

inorganic and organic contaminants were assessed in 

Mountain Creek Lake, a reservoir in Dallas, Tex. The 

study was done in cooperation with the Southern Division Naval Facilities Engineering Command and was 

prompted by the Navy’s concern for potential off-site 

migration of contaminants from two facilities, the NAS 

and NWIRP. Both facilities are on the shores of Mountain Creek Lake. The objective was to determine the 

occurrence and distribution of contaminants in Mountain Creek Lake. Sampling primarily was in Mountain 

Creek Lake (including Cottonwood Bay) but also was 

done in stormwater outfalls from the Navy facilities, 

nearby urban streams, and small streams draining NAS. 

This report presents and discusses the occurrence 

of constituents sampled in each of the environmental 

phases sampled (stormwater [includes suspended sediment], lake water, bottom sediment [includes streambed 

sediment], and fish tissue). Temporal trends, mass 

fluxes, and sources are evaluated for selected elements 

and compounds including heavy metals, VOCs, PAHs, 

organochlorine pesticides, and PCBs. Trends were 

identified using dated bottom-sediment cores. Mass 

fluxes were estimated using data from sediment cores 

and a sedimentation survey. Potential sources of contaminants in the lake were identified on the basis of 

(1) identification of a potential source or sources in 

either the urbanized parts of the watershed or at the 

Navy facilities; (2) description of a plausible transport 

pathway from the source(s) to the lake supported, in 

some cases, by stormwater sampling results; and 

(3) relation of the source and pathway to the spatial 

and temporal distribution in the lake. Additionally, 

in the case of some groups of related organic compounds, chemical “signatures” are used to aid in source 

identification.

Major findings of this study are:

• Concentrations of selected heavy metals in surficial 

bottom sediments in Cottonwood Bay were 

2 to 4 times greater than main lake and urban 

reference site concentrations, with the largest 

concentrations near the NWIRP outfalls. The 

metals included cadmium, chromium, copper, 

lead, mercury, nickel, silver, and zinc. Suspended 

sediments from the NWIRP outfalls contained 

about the same mixture of heavy metals, in 

elevated concentrations compared to reference 

0

150

50

100

DEPTH, IN CENTIMETERS

20 40

SILVER

MICROGRAMS PER GRAM

1995

1974

1963

1952

1941

 SEDIMENTATION 

 RATE

1.0 0.4

4.2 2.2

2.9 1.8

2.7 1.6

DEPOSITION

 7.0

 20

 11

 20

 SILVER 

ACCUMULATION RATE

 59 2.8

480 44

220 20

350 32

 DATE

 MEAN SILVER 

CONCENTRATION

Centimeters

 per year

 Grams per

square centimeter

 per year

Micrograms

 per gram

Micrograms

 per square

 Micrograms per

square centimeter

 centimeter per year

0

Figure 34. Mass accumulation rates of silver in Bay–13 core. 
60 Chemical Quality of Water, Sediment, and Fish in Mountain Creek Lake, Dallas, Texas, 1994–97 

sites, as bottom sediments in the NWIRP lagoons 

and surficial bottom sediments in Cottonwood 

Bay. These same metals were elevated in 

deeper sediments deposited historically in 

Cottonwood Bay, with concentrations of cadmium, chromium, and silver more than 20 times 

reference concentrations.

• VOCs were detected in stormwater from both Navy 

facilities, predominantly solvents from NWIRP 

and fuel-related compounds from NAS. Fuelrelated compounds also were detected in Mountain Creek Lake at two locations, one near the 

NAS inlet where stormwater from a part of NAS 

enters the lake and one at the center of the lake. 

Concentrations at the two lake sites were small, 

all less than 5 μg/L. 

• Elevated concentrations of PAHs compared to main 

lake and urban reference sites, were detected in 

surficial sediments in Cottonwood Bay. Elevated 

concentrations of PAHs, indicative of urban 

sources, also were detected in Cottonwood Creek, 

which drains an urbanized area apart from the 

Navy facilities. PAH concentrations near the NAS 

shoreline were not elevated compared to urban 

reference sites. Larger concentrations of PAHs 

were detected in deeper, older sediments in 

Cottonwood Bay than in surficial sediments, indicating historical contaminant inputs were greater. 

Larger concentrations are associated with the 

period before improvements in wastewater discharge practices at NWIRP were made. Diagnostic ratios of PAHs indicate that uncombusted fuel 

sources contribute PAHs to older sediments and 

that pyrogenic sources of PAHs dominate 

recently deposited sediments.

• Concentrations of organochlorine pesticides in 

sediments were small and similar to relatively 

uncontaminated urban sites like White Rock Lake 

in Dallas. Fish tissue concentrations also were 

relatively small.

• PCBs were detected in all surficial bottom sediment 

samples and in 61 of 62 individual fish tissue 

samples. PCB concentrations, like some of the 

heavy metals and PAHs, were largest in surficial 

sediment samples in Cottonwood Bay near the 

west and east lagoon outfalls from NWIRP. The 

mean concentration in surficial sediments of 

about 300 μg/kg was about an order of magnitude 

smaller than the concentrations in deeper sediments, deposited in the 1960s or early 1970s, 

and 1 to 2 orders of magnitude greater than 

surficial sediment concentrations in main-lake 

reference sites. PCBs were also elevated in 

selected samples along the NAS shoreline. PCBs 

were detected in suspended sediments in stormwater flowing from the east and west lagoons 

indicating transport to the lake was still occurring 

in 1997. PCB and selenium concentrations from 

analyses of this study were large enough to 

prompt the Texas State Department of Health to 

issue a fish-possession ban for Mountain Creek 

Lake in 1996.

• On the basis of dated sediment cores and contaminant discharge histories, contaminant accumulation rates in Cottonwood Bay were much greater 

historically than recently. Most heavy metals, 

PAHs, and PCBs that accumulated in the central 

and eastern parts of Cottonwood Bay appear to 

have come from the west lagoon on NWIRP. 

Treated sewage and industrial process wastewater 

were discharged to the west lagoon from about 

1941 to 1974. Estimated annual contaminant 

accumulation rates in Cottonwood Bay decreased 

by 1 to 2 orders of magnitude after 1974, when 

most point-source discharges to the west lagoon 

ceased.

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64 Chemical Quality of Water, Sediment, and Fish in Mountain Creek Lake, Dallas, Texas, 1994–97 Table 7 Table 7. Polycyclic aromatic hydrocarbon concentrations in stormwater suspended sediment samples [In micrograms per kilogram. NWIRP, Naval Weapons Industrial Reserve Plant; E, estimated; <, less than; QA/QC, quality assurance/q

Site Date Phenol

pCresol

C8-

Alkylphenol Naph- thalene C1-128 Isomers 2-Ethyl- naph- thalene 2,6-Di- methyl- naph- thalene 1,6-Di- methyl- naph- thalene C2-128 Isomers Ace

thy

NWIRP-1 outfall 03–25–97

04–04–97

428188

159

66.2

E 88.5E 38.1

E 92.7

62.8

594394

<100

<50

E 55.9

17.7

<100

E 9.54

<100

79.5

E 4E 1

NWIRP-2 outfall 03–25–97 71.4 E 27.2 E 18.8 E 36.5 226 <50 E 5.34 E 3.89 E 40.6 E 1North fork Cottonwood Creek at 

Beltline Rd.

02–12–9702–24–97

E 16.9E 37.2

E 7.27

E 12.9

E 4.97

<50

E 6.03

E 14.0

51.384.7

<20<50

E 5.52

<50

E 1.47E 1.74

E 19.7E 25.4

E 

<5

South fork Cottonwood Creek

at Marshall Dr.

04–25–97 113 <80 <80 34.0 326 <80 E 8.72 E 3.82 E 51.4 <8

Fort Worth Subdistrict lab, 

QA/QC filter check

04–11–97 E 3.88 E .829 <50 E .381 <5 <5 <5 <5 <5 <

Site Date C3-128 Isomers

2,3,6-Trimethylnaphthalene 9H- Fluorene C4-128 Isomers 1-Methyl- 9H- fluorene C1-166 Isomers Dibenzo- thio- phene Phenan- threne Anthra- cene 

NWIRP-1 outfall 03–25–97

04–04–97

<100

69.1

<100

E 4.72

E 74.6E 68.3

<100<250

454

E 4.43

<100

65.9

E 43.1

52.9

880

1,050

133127

NWIRP-2 outfall 03–25–97 E 24.3 <50 E 27.6 <50 E 0.641 E 45.4 E 9.51 249 E 35.8 North fork Cottonwood Creek 

at Beltline Rd.

02–12–9702–24–97

E 14.2

E 8.14

E .868

<50

E 10.6

E 8.70

E 16.6

<50

E .755

<50

E 7.36

<50

E 5.96E 1.08

128

58.8

E 13.7

E 5.53

South fork Cottonwood Creek 

at Marshall Dr.

04–25–97 <80 <80 <80 <80 E 29.2 <80 <80 E 31.8 E 4.5 

Fort Worth Subdistrict lab, 

QA/QC filter check

04–11–97 <5 <5 <5 <5 <5 <5 <5 E 0.274 E 0.151 

Site Date C5-128 Isomers C2-166 Isomers 2-Methyl- anthracene 4,5- Methylene- phenan- threne C1-178 Isomers 1-Methyl- phenan- threne C3-166 Isomers C2-178 Isomers Fluo- ran- thene P

NWIRP-1 outfall 03–25–97

04–04–97

<100

165

<100

103

E 45.9E 19.0

E 88.6

83.7

582342

E 50.0E 47.0

<100

75

1,180

352

2,6302,370

21

NWIRP-2 outfall 03–25–97 <50 E 35.0 E 7.63 E 19.4 116 E 12.7 <50 110 510 North fork Cottonwood 

Creek at Beltline Rd.

02–12–9702–24–97

<20<50

<20<50

E 2.68E 1.31

E 12.7

E 3.54

53.8

E 17.0

E 8.04E 0.119

<20<50

50.7

E 23.4

310106

South fork Cottonwood 

Creek at Marshall Dr.

04–25–97 <80 <80 E 3.12 <80 E 50.0 <80 <80 126 119 

Fort Worth Subdistrict lab, 

QA/QC filter check

04–11–97 <5 <5 <5 <5 E 1.13 <5 <5 5.06 <5 
Table 7 65

Table 7. Polycyclic aromatic hydrocarbon concentrations in stormwater suspended sediment samples—Continued

Site Date 1-Methylpyrene C1-202 Isomers C2-202 Isomers C5-178 Isomers Benz(a)- anthracene Chrysene C3-202 Isomers C1-228 Isomers C4-

 Iso

NWIRP-1 outfall 03–25–97

04–04–97

138

66.6

727707

1,1201,270

<100

<50

667626

1,6601,290

587504

600563

<10

55

NWIRP-2 outfall 03–25–97 E 17.6 236 452 <50 167 318 190 156 15North fork Cottonwood Creek

at Beltline Rd.

02–12–9702–24–97

E 9.07E 1.31

105

E 32.8

169

65.7

46.6

<50

93.4

E 20.5

192

E 43.5

55.0

E 24.4

57.9

E 14.2

6

E 2

South fork Cottonwood Creek

at Marshall Dr.

04–25–97 E 2.02 E 38.6 131 <80 E 17.0 E 70.0 E 70.4 E 40.8 <8

Fort Worth Subdistrict lab,

QA/QC filter check

04–11–97 <5 <5 <5 <5 <5 <5 <5 <5 <

Site Date Benzo(b)- fluoranthene Benzo(k)- fluoranthene Benzo(e)- pyrene Benzo(a)- pyrene Perylene C1-252 Isomers C3-228 Isomers C2-2

Isom

NWIRP-1 outfall 03–25–97

04–04–97

2,4901,360

379985

1,250

982

1,030

878

209197

<550

518

<250

E 23.9

308274

NWIRP-2 outfall 03–25–97 264 234 207 188 E 29.1 104 E 2.96 77North fork Cottonwood Creek

at Beltline Rd.

02–12–9702–24–97

185

E 28.5

164

E 25.2

137

E 21.1

126

E 20.9

26.9

<50

46.3

E 10.0

E 3.13

<50

E 15

<50

South fork Cottonwood Creek

at Marshall Dr.

04–25–97 E 41.8 E 22.8 E 20.8 E 15.6 <80 E 16.72 <80 E 4

Fort Worth Subdistrict lab,

QA/QC filter check

04–11–97 <5 <5 <5 <5 <5 <5 <5 <5 

Site Date

Indeno-

 (1,2,3-c,d)-

pyrene

Dibenzo(a,h)-

anthracene

C3-252

Isomers

C4-252

 Isomers

C5-228

 Isomers

 

NWIRP-1 outfall 03–25–97

04–04–97

1,160

868

171159

<350

57.9

<350

E 21.7

<100

<50

NWIRP-2 outfall 03–25–97 169 E 32.1 <50 <50 <50 North fork Cottonwood Creek at 

Beltline Rd.

02–12–9702–24–97

129

E 22.5

23.7

E 3.03

<20<50

<20<50

<20<50

South fork Cottonwood Creek at 

Marshall Dr.

04–25–97 E 31.0 <80 <80 <80 <80 

Fort Worth Subdistrict lab, 

QA/QC filter check

04–11–97 <5 <5 <5 <5 <5 
66 Chemical Quality of Water, Sediment, and Fish in Mountain Creek Lake, Dallas, Texas, 1994–97 

Table 9

Table 8

Table 8. Diagnostic polycyclic aromatic hydrocarbon ratios for selected surficial sediment samples

[Fluoranthene/pyrene ranges from 1.077 to 1.400; C1-phenanthrene/phenanthrene ranges from 0.447 to 0.961; and 

phenanthrene + . . ./T-PAH ranges from 2.292 to 4.153 for the main lake sites when the concentrations are greater than method 

detection limits. PAH, polycyclic aromatic hydrocarbon; NAS, Naval Air Station; NWIRP, Naval Weapons Industrial Reserve 

Plant; T-PAH, total polycyclic aromatic hydrocarbons] 

Table 9. Reported and estimated total polycyclic aromatic 

hydrocarbon concentrations for east and west lagoon sediment

[All samples from upper 60 centimeters; in micrograms per kilograms. 

PAHs, polycyclic aromatic hydrocarbons] 

Diagnostic PAH ratio

Mean diagnostic

ratio in sediments

(standard deviation)

Interpretation

guideline Interpretation

NAS NWIRP

Fluoranthene/pyrene 1.16 (0.06) 1.27 (0.07) Pyrogenic sources 

enriched in fluoranthene 

Both predominantly 

pyrogenic; however, 

NAS more fuelrelated than NWIRP

2- and 3-ringed compounds/

4- and 5-ringed compounds

.59 (.27) .35 (.06) Fuel sources enriched in 

di- and tri-cyclic species 

Same

C1-phenanthrene/phenanthrene .75 (.26) .45 (.19) Fuel sources enriched in 

alkylated homologues

Same

Phenanthrene + anthracene 

+ C1–3 homologues/T-PAH 

(X 100)

25.1 (4.0) 28.1 (3.0) Pyrogenic sources 

enriched in 4-ringed 

compounds

Same

Site no.

Sum of reported PAHs

(EnSafe/Allen & Hoshall, 

1996a)

Estimated

total PAHs

West lagoon

W01–S01 12,600 21,400

W01–S02 128,000 189,000

W01–S03 351,000 540,000

W01–S04 77,800 139,000

W01–S05 57,000 75,200

East lagoon

W02–S01 3,070,000 4,720,000

W02–S02 121,000 118,000

W02–S03 88,200 115,000

W02–S06 57,600 88,100
Table 10 67

Table 10

Table 10. Organochlorine pesticide and polychlorinated biphenyl concentrations in stormwater suspended sediment samp[In micrograms per kilogram. NWIRP, Naval Weapons Industrial Reserve Plant; <, less than; E, estimated; QA/QC, quality assurance/q

Site Date Lindane Hepta- chlor Aldrin Heptachlor epoxide Chlor- dane Endo- sulfan I Dield

NWIRP–1 outfall 03–25–97

04–04–97

<7.0<3.8

<7.0<3.8

<7.0<3.8

<7.0<3.8

<70<38

<7.0<3.8

<7<3

NWIRP–2 outfall 03–25–97 <2.0 <2.0 <2.0 <2.0 <20 <2.0 <2North fork Cottonwood Creek at Beltline Rd. 02–12–97

02–24–97

<.5

<1.4

<.5

<1.4

<.5

<1.4

<.5

<1.4

13

E11

<.1

<1.4

E1

South fork Cottonwood Creek at Marshall Dr. 04–25–97 <2.5 <2.5 <2.5 <2.5 <25 <2.5 <2Fort Worth Subdistrict lab, QA/QC filter check 04–11–97 <2.5 <2.5 <2.5 <2.5 <25 <2.5 <2

Site Date Perthane p,p'- DDD p,p'- DDT p,p'- Meth- oxychlor Mirex Toxa- phene PC

Aroc

124

NWIRP–1 outfall 03–25–97

04–04–97

<70<38

<7.0<4.8

<7.0<3.8

<55<31

<7.0<3.8

<700<380

<70<38

NWIRP–2 outfall 03–25–97 <20 <2.0 <2.8 <16 <2.0 <200 <22 North fork Cottonwood Creek at Beltline Rd. 02–12–97

02–24–97

<5.0

<14

<.6

<1.4

.88

E1.1

<4.0

<11

<.5

<1.4

<50

<140

<5

<14

South fork Cottonwood Creek at Marshall Dr. 04–25–97 <25 <2.5 <2.5 <20 <2.5 <250 <25 Fort Worth Subdistrict lab, QA/QC filter check 04–11–97 <25 <2.5 <2.5 <20 <2.5 <250 <25 
68 Chemical Quality of Water, Sediment, and Fish in Mountain Creek Lake, Dallas, Texas, 1994–97 

Table 11

Table 11. Summary of total polychlorinated biphenyl concentrations in sediment 

[n, no. samples; μg/kg, micrograms per kilogram; NWIRP, Naval Weapons Industrial Reserve Plant; cm, centimeters; --, not 

sampled; ND, nondetections; NAS, Naval Air Station] 

1 Sum of Aroclors 1254 and 1260; Aroclor 1242 not detected.

Location

(depth interval for

bottom sediments; n)

Total PCB concentrations

(μg/kg)

(mean concentration if n > 2; +1 standard deviation)

EnSafe/Allen

& Hoshall

(1996a)

USGS

Phase I Phase II Suspended

sediments

NWIRP

West lagoon (0–60 cm; n = 5) 5,600 (+5,400) -- -- --

West lagoon outfall (n = 2) -- -- -- 1

650, 1248

East lagoon (0–60 cm; n = 6) 760, 720, 4 ND -- -- --

East lagoon outfall (n = 1) -- -- -- 1

45

Cottonwood Bay, Creek, and Canal

Bay-13 (0–12 cm; n = 1) -- 300 -- --

Bay-13 (51–58 cm; n = 1) -- 3,500 -- --

MCL-7 (0–3 cm; n = 2) -- 110, 800 -- --

MCL-7 (14–25 cm; n = 1) -- 2,000 -- --

East Cottonwood Bay (0–3 cm; n = 9) -- -- 271 (+71) --

Central Cottonwood Bay (0–3 cm; n = 9) -- -- 313 (+146) --

West Cottonwood Bay (0–3 cm; n = 4) -- -- 119 (+ 90) --

North fork and south fork Cottonwood 

Creek (0–3 cm; n = 2)

-- -- 5.8, <3.0 --

Canal (0–3 cm; n = 4) -- -- 29 (+15) --

Mountain Creek Lake and NAS

Main lake (0–3 cm; n = 9) -- -- 20 (+10) --

Group 12 (Aroclor 1260) 95, 1,100 -- -- --

NAS inlet (0–3 cm; n = 6) -- -- 226 (+272) --

Runway inlet (0–3 cm; n = 2) -- -- 224, 118 --
Table 12 69

Table 12

Table 12. Estimated total and annual contaminant mass accumulations in east and central Cottonwood Bay

[μg/g, micrograms per gram; μg/kg, micrograms per kilogram; PAH, polycyclic aromatic hydrocarbon; PCB, polychlorinated 

biphenyl; kg, kilograms; kg/yr, kilograms per year] 

Contaminant

Part of

Cottonwood

Bay

Mean contaminant

concentration in sediments

(metals μg/g;

PAHs and PCBs, μg/kg)

Total contaminant

mass accumulation

(kg)

Annual contaminant

mass accumulation

(kg/yr)

1940–74 1974–95 1940–74 1974–95 1940–74 1974–95

Chromium East 2,420 240 67,000 820 2,000 39

Central 2,420 210 51,000 550 1,500 26

Lead East 128 90 3,500 310 100 15

Central 128 74 2,700 190 79 9.0

Zinc East 430 330 12,000 1,100 350 52

Central 430 350 9,000 910 260 43

Total PAHs East 40,000 26,000 1,100 89 32 4.2

Central 40,000 21,000 840 55 25 2.6

Total PCBs East 2,600 271 72 .93 2.1 .044

Central 2,600 313 55 .82 1.6 .039