Fate and Transport Modeling of

Selected Chlorinated Organic Compunds

at Hangar 1000, U.S. Naval Air Station,

Jacksonville, Florida

U.S. Geological Survey

Water Resources Investigations Report 03-4089

Prepared as part of the

U.S. Navy, Southern Division,

Naval Facilities Engineering Command
Fate and Transport Modeling of 

Selected Chlorinated Organic Compounds 

at Hangar 1000, U.S. Naval Air Station, 

Jacksonville, Florida

By J. Hal Davis

U.S. Geological Survey

Water-Resources Investigations Report 03-4089

Prepared in cooperation with the

U.S. NAVY, SOUTHERN DIVISION, 

NAVAL FACILITIES ENGINEERING COMMAND

Tallahassee, Florida

2003
U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

Use of trade, product, or firm names in this publication is for descriptive purposes only 

and does not imply endorsement by the U.S. Geological Survey

For additional information 

write to: 

U.S. Geological Survey

2010 Levy Avenue

Tallahassee, FL 32310

Additional information about water resources in Florida is available on the internet 

at http://fl.water.usgs.gov

Copies of this report can be 

purchased from:

U.S. Geological Survey

Branch of Information Services

Box 25286

Denver, CO 80225-0286

888-ASK-USGS
Contents III

CONTENTS

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

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

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

Previous Modeling at the Jacksonville Naval Air Station .......................................................................... 5

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

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

Hydrologic Setting............................................................................................................................................... 5

Occurrence and Factors Affecting the Movement of Trichloroethene, Dichloroethene, and 

Vinyl Chloride ................................................................................................................................................. 15

Ground-Water Flow Simulation at the Station .................................................................................................... 22

Original Subregional Model ....................................................................................................................... 22

Recalibration of the Subregional Model..................................................................................................... 23

Ground-Water Budget................................................................................................................................. 30

Sensitivity Analysis .................................................................................................................................... 31

Ground-Water Flow Model Limitations ..................................................................................................... 33

Fate and Transport Simulations of Trichloroethene, Dichloroethene, and Vinyl Chloride 

Movement at Hangar 1000 .............................................................................................................................. 33

Model Construction .................................................................................................................................... 33

Flow Path Analysis ..................................................................................................................................... 33

Fate and Transport Modeling Overview ..................................................................................................... 33

Calibration to Current Distribution Trichloroethene, Dichloroethene, and Vinyl Chloride ....................... 36

Predicted Movement of Trichloroethene, Dichloroethene, and Vinyl Chloride Assuming 

Source Reduction of 50 Percent.............................................................................................................. 40

Predicted Movement of Trichloroethene, Dichloroethene, and Vinyl Chloride Assuming 

Source Reduction of 100 Percent............................................................................................................ 40

Measurement Error and Effect of Parameter Variation on Fate and Transport Modeling Results ............. 40

Summary.............................................................................................................................................................. 49

References ........................................................................................................................................................... 50

FIGURES

1. Map showing the location of the Jacksonville Naval Air Station ............................................................ 3

2. Map showing the subregional and regional model areas with particle pathlines..................................... 4

3. Chart showing geologic units, hydrologic units, and equivalent layers used in the computer model ..... 5

4. Generalized hydrogeologic section through the subregional study area.................................................. 6

Figures 5-19 are maps showing the:

5. Extent and thickness of the clay layer that separates the upper and intermediate layers 

of the surficial aquifer .............................................................................................................................. 7

6. Top of the Hawthorn Group ..................................................................................................................... 7

7. Wells completed in the upper layer of the surficial aquifer within the subregional study area ............... 8

8. Wells completed in the intermediate layer of the surficial aquifer within the subregional study area ....10

9. Water-table surface for the upper layer of the surficial aquifer on April 4, 2001....................................11

10. Stormwater-drainage system at the Jacksonville Naval Air Station ........................................................12
IV Contents

11. Location of sewer sections in the vicinity of Hangar 1000..................................................................... 13

12. Water-table surface for the upper layer of the surficial aquifer on April 4, 2001, in the vicinity of 

Hangar 1000............................................................................................................................................ 14

13. Potentiometric surface for the intermediate layer of the surficial aquifer on April 4, 2001 ................... 15

14. Water-level fluctuations in the surficial aquifer from 1993 to 2001 ....................................................... 16

15. Location of wells where ground-water quality samples were taken. ...................................................... 17

16. Distribution of trichloroethene contamination in the ground water of the surficial 

aquifer at Hangar 1000 on January 17, 2001 .......................................................................................... 18

17. Distribution of dichloroethene contamination in the ground water of the surficial 

aquifer at Hangar 1000 on January 17, 2001 .......................................................................................... 20

18. Distribution of vinyl chloride contamination in the ground water of the surficial aquifer at 

Hangar 1000 on January 17, 2001........................................................................................................... 21

19. Location and orientation of the subregional model finite-difference grid .............................................. 23

20. Generalized hydrologic section for the recalibrated subregional model................................................. 24

21. Graphs showing comparison of measured and simulated heads for the subregional model................... 25

Figures 22-44 are maps showing the:

22. Simulated recharge rates for the recalibrated subregional model ........................................................... 26

23. Simulated horizontal hydraulic conductivity of the upper layer of the recalibrated subregional 

model....................................................................................................................................................... 26

24. Simulated horizontal hydraulic conductivity of layer 2 of the recalibrated subregional model ............. 27

25. Simulated thickness of layer 2 of the recalibrated subregional model.................................................... 27

26. Simulated horizontal hydraulic conductivity of layer 3 of the subregional model ................................. 28

27. Simulated thickness of layer 3 of the recalibrated subregional model.................................................... 28

28. Simulated horizontal hydraulic conductivity of layer 4 of the recalibrated subregional model ............. 29

29. Simulated thickness of layer 4 of the recalibrated subregional model.................................................... 29

30. Simulated water-table surface of the upper layer of the recalibrated subregional model ....................... 30

31. Simulated potentiometric surface of the intermediate layer of the recalibrated subregional model....... 31

32. Location and orientation of the Hangar 1000 model .............................................................................. 32

33. Particle pathlines representing ground-water flow directions in the upper layer of the 

surficial aquifer at Hangar 1000.............................................................................................................. 33

34. Simulated trichloroethene concentrations in layer 1 after 16 years ........................................................ 37

35. Simulated dichloroethene concentrations in layer 1 after 14 years......................................................... 38

36. Simulated vinyl chloride concentrations in layer 1 after 12 years .......................................................... 39

37. Simulated trichloroethene concentrations in layer 1 after 8 years .......................................................... 41

38. Simulated trichloroethene concentrations in layer 1 after 8 years assuming 50 percent 

source reduction ...................................................................................................................................... 42

39. Simulated dichloroethene concentrations in layer 1 after 8 years assuming 50 percent 

source reduction ...................................................................................................................................... 43

40. Simulated vinyl chloride concentrations in layer 1 after 8 years assuming 50 percent 

source reduction ...................................................................................................................................... 44

41. Simulated trichloroethene concentrations in layer 1 after 8 years assuming 100 percent 

source reduction ...................................................................................................................................... 45

42. Simulated dichloroethene concentrations in layer 1 after 8 years assuming 100 percent 

source reduction ...................................................................................................................................... 46

43. Simulated vinyl chloride concentrations in layer 1 after 8 years assuming 100 percent source

reduction.................................................................................................................................................. 47

44. Simulated trichloroethene concentrations in layer 1 after 16 years assuming 100 percent 

source reduction ...................................................................................................................................... 48
Contents V

TABLES

1. Monitoring wells completed in the upper layer of the surficial aquifer .................................................. 9

2. Monitoring wells completed in the intermediate layer of the surficial aquifer .......................................10

3. Distribution of partitioning coefficients and retardation factors for trichloroethene,

dichloroethene, and vinyl chloride for the upper layer of the surficial aquifer .......................................22

4. Simulated ground-water inflows and outflows for the recalibrated subregional model..........................31

5. Summary of sensitivity analyses for the recalibrated subregional model ...............................................32

CONVERSION FACTORS, DATUMS, AND ABBREVIATIONS

ACRONYMS AND ABBREVIATIONS

Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 (NGVD29); 

horizontal coordinate information is referenced to the North American Datum of 1927 (NAD27).

Multiply By To obtain

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

inch per year (in/yr) 25.4 millimeter per year (mm/yr)

square foot (ft2) 0.09290 square meter (m2)

square mile (mi2) 2.59 square kilometer (km2)

foot per day (ft/d) 0.3048 meter per day (m/d)

foot squared per day (ft2/d) 0.0929 meter squared per day (m2

/d)

cubic foot per day (ft3/d) 0.028317 cubic meter per day (m3

/d)

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

foot per year (ft/yr) 0.3048 meter per year (m/yr)

DCE Dichloroethene

g/cm3 grams per cubic centimeter

μg/L micrograms per liter

MODFLOW Modular Three-Dimensional Finite-Difference Ground-Water Flow Model

OU1 Operable Unit 1

RT3D Reactive Transport in Three Dimensions

TCE Trichloroethene

USEPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey

VC Vinyl Chloride
Abstract 1

Fate and Transport Modeling of 

Selected Chlorinated Organic Compounds 

at Hangar 1000, U.S. Naval Air Station, 

Jacksonville, Florida

By J. Hal Davis

ABSTRACT

The Jacksonville Naval Air Station occupies 3,800 acres adjacent to the St. Johns River in Jacksonville, 

Florida. Two underground storage tanks at Hangar 1000 contained solvents from the late 1960s until they were 

removed in 1994. Ground-water samples at one of the tank sites had levels of trichloroethene (TCE) and total 

dichloroethene (DCE) of 8,710 micrograms per liter (μg/L) and 4,280 μg/L, respectively. Vinyl chloride (VC) at 

the site is the result of the biodegradation of DCE. Ground water beneath Hangar 1000 flows toward a storm 

sewer. TCE and DCE plumes travel with the ground water and presumably have reached the storm sewer, which 

discharges to the St. Johns River.

Simulation of solute transport indicates that the traveltime from the storage tank site to the storm sewer is 

16, 14, and 12 years for TCE, DCE, and VC respectively. TCE has the longest traveltime because it has the highest retardation factor at 2.5, DCE takes less time with a retardation factor of 2.0, and VC has the quickest traveltime because it has the lowest retardation factor of 1.7. Based on modeling results, the release of contaminants in 

the aquifer occurred more than 16 years ago. 

Model-derived dispersivity values at Hangar 1000 were: longitudinal 1.5 feet (ft), transverse 0.27 ft, and 

vertical 0.27 ft. The model-derived first order decay rates for biodegradation of TCE, DCE, and VC were 

0.0002 per day (d-1), 0.0002 d-1, and 0.06 d-1, respectively. These rates are equivalent to half-lives of 13.7 years 

for TCE and DCE and 17 days for VC.

Source area reductions in contaminant concentrations of 50 and 100 percent were modeled to simulate 

remediation. As expected, reducing the source concentration by 50 percent resulted in eventual TCE, DCE, and 

VC concentrations that were half of the original concentrations. About 16 years were needed for new steady-state 

TCE concentrations to develop, about 14 years for DCE, and about 12 years for VC. Reducing the source area 

concentrations by 100 percent in the model eventually resulted in zero concentrations of TCE, DCE, and VC. The 

modeled period of time for the contaminants to be removed from the aquifer once the source was removed was 

about 17 years for TCE, 15 years for DCE, and 13 years for VC.
2 Fate and Transport Modeling of Selected Chlorinated Organic Compounds at Hangar 1000, 

U.S. Naval Station, Jacksonville, Florida

INTRODUCTION

The U.S. Naval Air Station, (referred to as the 

Station) occupies 3,800 acres adjacent to the St. Johns 

River in Jacksonville, Fla. (fig. 1). The mission of the 

Station is to provide aerial anti-submarine warfare 

support, aviator training, and aircraft maintenance. 

Support facilities at the Station include an airfield, a 

maintenance depot, a Naval hospital, a Naval supply 

center, and recreational and residential facilities. 

Military activities have been conducted at the Station 

since 1909; the Station presently employs about 

15,000 people.

The Station was placed on the U.S. Environmental 

Protection Agency’s (USEPA) National Priorities List 

in December 1989, and is participating in the 

U.S. Department of Defense Installation Restoration 

Program, which serves to identify and remediate 

environmental contamination in compliance with the 

Comprehensive Environmental Response, Compensation, and Liability Act and the Superfund Amendments and Reauthorization Act of 1980 and 1985, 

respectively. On October 23, 1990, the Station entered 

into a Federal Facility Agreement with the USEPA and 

the Florida Department of Environmental Protection, 

which designated Operable Units 1, 2, and 3 at the 

Station (U.S. Navy, 1994a). Operable Units (fig. 1) 

were designated in areas where several sources of 

similar contamination existed in close proximity, thus 

allowing the contaminated areas to be addressed in 

one coordinated effort. Operable Unit 1 (OU1) was the 

Station landfill; this site has been discussed in previous studies (Davis and others, 1996). Operable Unit 2 

(OU2) was the wastewater treatment plant, which has 

been remediated. Operable Unit 3 (OU3) was the 

Naval Aviation Depot; this site has been discussed in 

previous studies (Davis, 1998; 2000). Since entering 

into the Federal Facility Agreement, several additional 

operable units have been designated, including Operable Unit 6 (OU6), also known as Hangar 1000, which 

is the subject of this report.

Aircraft are serviced and repaired at Hangar 

1000. To contain the solvents used at the hangar, two 

underground storage tanks were operated from the late 

1960s until their use was discontinued in 1994. One 

tank was a 750-gallon concrete tank used as a solvent 

and water separator. The other was a 2,000-gallon 

steel tank, which received solvent overflow from the 

first tank as well as waste oils and solvents discharged 

from other operations at the facility. Both tanks, associated piping systems, and visually contaminated soils 

were excavated and removed in March 1994. After 

removal, contamination levels in the wells near the 

removal site fluctuated, indicating that tank removal 

may have spread the contamination (U.S. Navy, in 

press.) Floor drains and their associated pipes were 

abandoned intact at the time of the tank removals.

The Navy has documented the occurrence and 

distribution of contamination at Hangar 1000 through 

a contractor, Tetra Tech NUS, Inc. (Tetra Tech). 

Currently, Tetra Tech is determining whether the 

contamination poses a risk to human health or the 

environment. To better understand the fate and 

transport and consequences of future remedial actions 

on contamination at Hanger 1000, the U.S. Geological 

Survey (USGS) conducted a study to simulate the 

movement of contaminated ground water from the old 

storage tank site to ground-water discharge areas. 

Purpose and Scope

A computer model capable of simulating the 

ground-water flow and the fate and transport of 

trichloroethene (TCE), dichloroethene (DCE), and 

vinyl chloride (VC) in the ground water at Hangar 

1000 was needed by the Navy to aid in remedial decisions. The purpose of this report is to document the 

development of this model, which simulates groundwater flow and solute transport, and present the results 

of the model predictions. The computer modeling 

effort consisted of: (1) updating an existing large-scale 

ground-water model to simulate ground-water flow in 

the vicinity of Hangar 1000, (2) establishing boundary 

conditions for a site-specific model with the largescale model, and (3) predicting the movement of contaminants at Hangar 1000 through solute transport 

simulation using the site-specific model.

Previous Modeling at the Jacksonville 

Naval Air Station

The USGS previously developed and calibrated 

a one-layer regional ground-water flow model that 

simulated steady-state flow in the surficial aquifer that 

underlies the site (Davis and others, 1996). This model 

used the USGS Modular Three-Dimensional FiniteDifference Ground-Water Flow Model (MODFLOW) 

software as described in McDonald and Harbaugh 

(1988). The regional model had 240 rows and 

290 columns with a uniform cell size of 100 by 
Introduction 3

OPERABLE UNIT LOCATION AND NUMBER

EXPLANATION

OU1

St. Johns River

Ortega River

NAVAL AIR STATION,

JACKSONVILLE

17

17

OU2

OU3

OU1

30°12′30′′

30°15′

81°42′30′′ 81°40′

Timuquana

Country Club

295

ATLANTIC

OCEAN

30°30′

30°15′

82°00′ 81°30′ 45′

Nassau River

DUVAL COUNTY

CLAY COUNTY

ST. JOHNS

COUNTY

NASSAU COUNTY

BAKER COUNTY

10

95

295

10

90

A1A

JACKSONVILLE

Naval Air Station,

Jacksonville

GEORGIA

FLORIDA

95

St. Johns River

Hangar 1000

and OU6

0 0.5 1 MILE

0 0.5 1 KILOMETER

0 10 MILES

0 10 KILOMETERS

DUVAL

COUNTY

0 50 MILES

0 50 KILOMETERS

Figure 1. Location of the Jacksonville Naval Air Station.
4 Fate and Transport Modeling of Selected Chlorinated Organic Compounds at Hangar 1000, 

U.S. Naval Station, Jacksonville, Florida

100 feet (ft), and simulated steady-state flow at 

the entire Station and some surrounding areas 

(fig. 2). The model was used to determine the direction 

and velocity of ground-water flow throughout the 

Station as well as to evaluate the effect of proposed 

remediation scenarios on ground-water flow at OU1. 

Later, this model was used to establish boundary 

conditions for a smaller subregional model centered 

at OU3.

The subregional ground-water flow model 

(Davis, 1998) was developed to investigate steadystate ground-water flow at OU3. Boundaries for the 

regional and subregional model are shown in figure 2. 

The subregional model had 2 layers with 78 rows and 

148 columns and a uniform cell size of 100 by 100 ft. 

This model was used to establish the boundary conditions and aquifer properties for a site-specific solutetransport model at OU3 (Davis, 2000), and to predict 

S t . J o

h n

s

R

i

v

e

r

Or e te v

g i a

R r

295

30°12′30′′

30°15′

81°42′30′′ 81°40′

EXPLANATION

CREEKS AND DITCHES

PARTICLE PATHLINES Shows simulated ground-water

flow paths

−

GROUND-WATER FLOW ARROW Shows direction of

ground-water flow along pathlines

−

SUBREGIONAL STUDY AREA AND SUBREGIONAL

MODEL BOUNDARY

REGIONAL STUDY AREA AND REGIONAL MODEL

BOUNDARY

NAVAL AIR STATION,

JACKSONVILLE

OPERABLE UNITS

17

OU2

OU3

OU1

Hangar

1000

17

0 0.5 1 MILE

0 0.5 1 KILOMETER

Figure 2. Subregional and regional model areas with particle pathlines.
Hydrologic Setting 5

the movement of TCE, DCE, and VC from OU3 to the 

ultimate discharge points in the St. Johns River. The 

solute transport modeling was conducted using the 

Modular Three-Dimensional Multi-Species Transport 

Model (Zheng and Wang, 1998) computer software.

Acknowledgments

The author expresses appreciation to Dana 

Gaskins, Cliff Casey, and Anthony Robinson of U.S. 

Navy, Southern Division, Naval Facilities Engineering 

Command for providing information and funding; Tim 

Curtin and Jane Beason of the Station for helping 

provide access to Station facilities; and Greg Roof and 

Mark Peterson of Tetra Tech for providing technical 

assistance and data.

Methods

For this study, a ground-water flow model 

previously developed to simulate ground-water flow at 

OU3 was updated and used to simulate ground-water 

flow at Hangar 1000. This model was documented by 

Davis (2000). The updated model was then used to set 

the boundary conditions for a site-specific solute 

transport model. All of the models referenced were 

based on previous work conducted by the USGS. All 

of the water-quality sampling data was collected by 

Tetra Tech, and thus, the discussion of contamination 

distribution, history, and movement is based on Tetra 

Tech data. For a more complete discussion of the 

methods and results determined by Tetra Tech, see 

U.S. Navy (in press).

HYDROLOGIC SETTING

The climate for Jacksonville is humid subtropical, 

with an average annual rainfall and temperature for 

1967-96 of 60.63 inches and 78 °F, respectively. Most 

of the annual rainfall occurs in late spring and early 

summer (Fairchild, 1972). Rainfall distribution is 

highly variable because most comes from scattered 

convective thunderstorms during the summer. Winters 

are mild and dry with occasional frost from November 

through February (Fairchild, 1972).

 Land-surface topography consists of gently 

rolling hills with elevations ranging from about 30 ft 

above sea level on hilltops to 1 ft above sea level at the 

shorelines of the St. Johns and Ortega Rivers (fig. 1).

The Naval Air Station is located in the Dinsmore Plain 

of the Northern Coastal Strip of the Sea Island District 

SYSTEM

SERIES

QUATERNARY TERTIARY

MIOCENE PLIOCENE HOLOCENE PLEISTOCENE

FORMATION

MODEL LAYERS

HYDROGEOLOGIC

UNIT

Undifferentiated

terrace and

shallow marine

deposits

Hawthorn

Group

Surficial aquifer

Confining unit No-flow

boundary

No-flow

boundary

No-flow

boundary

Layer 1

Layer 1

Layer 1 (Upper layer)

(Upper layer)

Layer 2

(Clay layer)

Layer 2

(Intermediate layer)

Layer 3

(Intermediate layer)

Layer 4

(Intermediate layer)

REGIONAL

MODEL

PREVIOUS

SUBREGIONAL MODEL

DOCUMENTED BY

DAVIS (1998)

HANGER 1000

SUBREGIONAL MODEL,

OU3 SUBREGIONAL MODEL,

AND HANGER 1000

SITE-SPECIFIC SOLUTE

TRANSPORT MODEL

Note A: The clay between layers 1 and 2 was simulated

by a low vertical conductance. SURFICIAL AQUIFER

EXPLANATION

See Note "A"

Figure 3. Geologic units, hydrologic units, and equivalent layers used in the computer model.
6 Fate and Transport Modeling of Selected Chlorinated Organic Compounds at Hangar 1000, 

U.S. Naval Station, Jacksonville, Florida

in the Atlantic Coastal Plain Section (Brooks, 1981). 

The Dinsmore Plain is characterized by low-relief, 

clastic terrace deposits of Pleistocene to Holocene age 

(Brooks, 1981).

The surficial aquifer is exposed at land surface 

and forms the uppermost permeable unit at the Station. 

The aquifer is composed of sedimentary deposits of 

Pliocene to Holocene age (fig. 3), and consists of 30 to 

100 ft of tan to yellow, medium to fine unconsolidated 

silty sands interbedded with lenses of clay, silty clay, 

and sandy clay (U.S. Navy, 1994a). The Pleistoceneage sedimentary deposits in Florida were deposited in 

a series of terraces formed during marine transgressions and regressions associated with glacial and 

interglacial periods (Miller, 1986).

The surficial aquifer is composed of three 

distinct layers in the vicinity of Hangar 1000 and 0U3 

(fig. 4). The upper layer is unconfined and extends 

from land surface to depths of about 15 to 35 ft below 

land surface (Navy, 1998). Beneath the upper layer (in 

most areas) is a low-permeability clay layer (figs. 4 

and 5). This clay layer, where present, separates the 

upper layer of the surficial aquifer from the intermediate layer. In areas where this clay layer is 5 to 30 ft 

thick (fig. 5), it is almost exclusively clay; where the 

layer is greater than 30 ft thick, it grades into a silt and 

clay mixture at depth. The extent of the clay is well 

known at OU3 because of the extensive wells and 

direct push drilling that was conducted in association 

with contaminant delineation. The westward extent of 

the clay toward Hangar 1000 is less well known; however, a relatively thick clay (5 to 20 ft) is present at 

Hangar 1000. For this reason, it is speculated that the 

clay at Hangar 1000 and OU3 are connected. In any 

event, the relatively thick, dense clay at Hangar 1000 

separates the surficial aquifer into two separate flow 

zones at the site.

The confined intermediate layer (fig. 4) extends 

below the clay downward to the top of the Hawthorn 

Group. The base of the surficial aquifer is formed by the 

top of the Miocene-age Hawthorn Group (figs. 4 and 6), 

which is mainly composed of low-permeability clays 

(Scott, 1988). 

30

20

10

10

20

30

40

50

60

70

80

90

Sea

Level

FEET

St.

Johns

River

Hangar

1000

Vertical scale greatly exaggerated

A

Seawall

OU3

0 2,000 FEET

A

St. Johns River

Upper layer

Clay

Intermediate

layer

Hawthorn Group

?

?

SURFICIAL

AQUIFER

EXPLANATION

A

A

0 0.5 1 MILE

0 0.5 1 KILOMETER

Figure 4. Generalized hydrogeologic 

section through the subregional study 

area.
Hydrologic Setting 7

OU3

0 1,000 2,000 FEET

St. Johns River

Hangar 1000

EXPLANATION

LINE OF EQUAL THICKNESS OF CLAY LAYER In feet

above NGVD of 1929. Contour interval 5 and 10 feet

5 −

5

20

10

50

30 40

Figure 5. Extent and thickness of the clay layer that separates the upper and intermediate layers of the surficial aquifer.

OU3

EXPLANATION

S t . J o

h n

s

Ri v e r

-13

STRUCTURE CONTOUR Shows altitude of the top of the Hawthorn Group.

Contour interval is 25 feet. Datum is NGVD of 1929

WELL Number is the altitude of the top of the Hawthorn Group

in feet below NGVD of 1929

−

−

-25

Hangar

1000

0 1,000 2,000 FEET

-96

-77 -91

-88 -84

-85

-85

-69

-13

-10

-7

-75

-25

-50

Figure 6. Top of the Hawthorn Group.
8 Fate and Transport Modeling of Selected Chlorinated Organic Compounds at Hangar 1000, 

U.S. Naval Station, Jacksonville, Florida

The top of the Hawthorn Group ranges from 35 to 

100 ft below land surface at the Station and is about 

60 ft below land surface at Hangar 1000. The Hawthorn 

Group is approximately 300 ft thick and composed of 

dark gray and olive-green sandy to silty clay, clayey 

sand, clay, and sandy limestone, all containing moderate to large amounts of black phosphatic sand, 

granules, or pebbles (Fairchild, 1972; Scott, 1988).

Wells used to define the water-table surface are 

shown in figure 7 and listed in table 1; wells used to 

define the potentiometric surface in the intermediate 

layer are shown in figure 8 and listed in table 2. The 

water-table surface on April 4, 2001, is shown in 

figure 9. In general, the water table slopes eastward 

toward the St. Johns River. However, this eastward 

slope is modified by the presence of leaky storm 

drains throughout the study area and two small ditches 

south of Hanger 1000.

An extensive stormwater-drainage system is 

present at the Station (fig. 10). The maintenance staff 

and consultants performed photographic surveys at 

OU3 documenting that ground-water seeps into the 

drains through joints and cracks in the drainage pipes 

(U.S. Navy, written commun., 1999.) Visual 

inspection of the drains by Navy personnel indicated 

that the leakage is generally confined to high motortraffic areas. Drain depths vary, but generally range 

from 5 to 10 ft below land surface. All drains are in 

the upper layer of the aquifer. 

The locations of sewer sections that drain 

ground water from the surficial aquifer are shown in 

figure 11, and the water-table surface in the vicinity of 

Hangar 1000 on April 4, 2001, is shown in 

figure 12. The water table in the vicinity of Hangar 

1000 slopes southeastward toward storm drains. The 

ground-water contours wrap around sewer section 4 

(fig. 12), indicating that ground water from the 

surficial aquifer is discharging to the storm drain from 

both sides. South of Hanger 1000, the water table 

slopes toward the small ditch southeast of 

Hangar 1000, indicating that water is discharging from 

the aquifer to the ditch from both sides. These ditches 

were concrete-lined in the 1940s by German prisoners 

of war; however, the linings presently contain 

numerous cracks and openings. 

OU3

0 1,000 2,000 FEET

39

EXPLANATION

UPPER LAYER WELL WITH NUMBER Number corresponds to map number in table 1 −

St. Johns River

Hangar 1000

39

7

3 2 1

4

5

8

9

24

26

11

32

30, 31

29 28

27

25 23

22

21

20 19

18

17

16

15

14

13

12

10

33 34

35

36 37

38

6

Figure 7. Wells completed in the upper layer of the surficial aquifer within the subregional study area.
Hydrologic Setting 9

Table 1. Monitoring wells completed in the upper layer of the surficial aquifer

 Map number

(see figure 7) Well name

Altitude of top of 

casing,

in feet

Well depth,

in feet

Altitude of head on 

April 4, 2001, 

in feet

1 MW-16 20.68 12.00 15.50

2 PZ-1 19.15 14.00 15.16

3 PZ-6 19.13 15.90 10.57

4 JAX-TF-MW27 6.20 9.00 4.53

5 JAX-HA-MW03 10.04 12.00 6.79

6 JAX-TF-MW14 8.65 11.00 4.46

7 MW41-R 21.29 18.40 16.28

8 JAX-HA-MW05 11.11 12.00 7.96

9 JAX-HA-MW06 10.23 12.00 7.14

10 H10-MW10 16.37 14.00 9.72

11 H10-MW07 16.93 14.00 9.48

12 H10-MW08 16.46 14.00 9.54

13 H10-MW06 16.96 14.00 9.36

14 H10-MW02 16.19 14.00 9.47

15 H10-MW05 16.93 14.00 9.28

16 H10-MW15 15.67 15.00 9.00

17 H10-MW20 12.28 11.00 10.48

18 H10-MW14 16.35 15.00 8.93

19 H10-MW03 16.40 14.00 9.30

20 H10-MW13 16.56 15.00 9.17

21 H10-MW18 14.48 21.00 8.88

22 H10-MW22 14.17 11.70 8.27

23 H10-MW17 14.13 21.00 7.82

24 PZOO4 5.64 14.00 1.95

25 H10-MW19 14.24 12.00 6.74

26 PZO26 10.86 13.50 4.96

27 H10-MW23 12.62 15.00 5.73

28 H10-MW25 16.38 11.00 9.00

29 H10-MW24 17.01 14.50 8.38

30 H10-MW26 9.50 25.00 5.90

31 H10-MW27 9.70 14.00 6.47

32 MW-122 13.67 13.50 10.04

33 PZO17 10.77 14.00 3.76

34 PZO12 9.22 15.00 2.09

35 MW-47 20.99 14.50 14.42

36 MW-45 27.45 16.00 20.07

37 MW-49 22.11 25.50 1.81

38 MW-121 11.47 13.50 7.09

39 MW-52 27.76 16.00 18.18
10 Fate and Transport Modeling of Selected Chlorinated Organic Compounds at Hangar 1000, 

U.S. Naval Station, Jacksonville, Florida

OU3

EXPLANATION

St. Johns River

Hangar

1000

46 INTERMEDIATE LAYER WELL WITH NUMBER Number corresponds to map number in table 2 −

0 1,000 2,000 FEET

42

43

44

45

46

41 40

Figure 8. Wells completed in the intermediate layer of the surficial aquifer within the subregional study area. 

Table 2. Monitoring wells completed in the intermediate layer of the surficial aquifer

 Map number

(see figure 8) Well name

Altitude of top of 

casing,

in feet

Well depth,

in feet

Altitude of head on 

April 4, 2001, 

in feet

40 JAX-TF-MW48D 8.36 36.50 2.23

41 H10-MW11 16.35 39.00 9.87

42 PZOO3 5.71 63.70 3.65

43 PZO25 10.69 85.50 5.85

44 PZO16 10.80 54.00 2.64

45 PZO11 9.27 93.00 2.01

46 MW-50 21.96 92.00 1.96
Hydrologic Setting 11

Storm sewer section 2 has several steel grates 

that allow observation of the sewer. In some parts of 

the sewer, sand boils can be seen at joints where 

ground water is leaking in. The drains were observed 

during dry periods; however, not all of the water flowing in the drains could be attributed to ground-water 

leakage, because parts of sewer section 2 are 

connected to overflow-underflow weirs that are 

connected to wash racks that drain to section 2. Other 

drains were difficult to observe except at a few 

occasional manholes. Sections 1 and 5 were almost 

completely unobservable; however, some observations 

of the sewer could be made at section 4 through the 

manholes. Observations through a manhole at the 

junction of sections 2, 4, and 5 indicated that water in 

the drain flowed southward but did not enter section 4 

because a small berm blocked the flow. Further eastward, a small flow was observed through other 

manholes along section 4, presumably from groundwater inflow to the drain system. However, no direct 

evidence such as sand boils were observed. Fairly 

deep standing water (approximately 1-2 ft) at the 

junction of sections 1 and 4 with the small ditch 

(fig. 11) made it impossible to observe the flow 

discharging from of section 4. 

Surface-water flow in the ditches was measured 

at the same time the water levels were measured in 

the wells (April 4, 2001), and the locations of these 

flow measurements are shown in figure 9. The 

measured flows were 0.23 cubic feet per second (ft3

/s) 

at location 1 and 0.11 ft3

/s at location 2. Since the 

flows in the ditches contain water other than ground 

water, they should be considered an upper limit for 

ground-water leakage to the storm sewers and ditches. 

The measured flow at location 2 was lower than at 

location 1, probably because location 2 had less 

influence from outside sources of water. 

Figure 9. Water-table surface for the upper layer of the surficial aquifer on April 4, 2001.

OU3

0 1,000 2,000 FEET

S t . J o

h n

s

Ri v e r

EXPLANATION

Hangar

1000

10

4

2

16

8

6

4

2

1

WATER-TABLE CONTOUR Shows level to which water would

have stood in tightly cased wells tapping the upper layer of the

surficial aquifer. Contour interval 1 foot. Datum is NGVD of 1929

STORMWATER DRAINS THAT MAY BE DRAINING GROUND

WATER From the upper layer of the surficial aquifer

MONITORING WELL LOCATION

SURFACE-WATER MEASUREMENT LOCATION

−

−

2

1

14

12

10

14

12

10

8

6

16
12 Fate and Transport Modeling of Selected Chlorinated Organic Compounds at Hangar 1000, 

U.S. Naval Station, Jacksonville, Florida

An attempt was made to measure the flow in sewer 

section 4 at several locations. At manhole locations 1 

and 2 (fig. 11), the flow was not deep enough to submerge a pygmy meter, and the presence of rocks and 

debris made measurement impossible even though 

flow was observed. At the sewer outfall location 3 

(fig. 11, where sections 1, 4, and the small ditch meet) 

water was 1-2 ft deep and the velocity was too low to 

measure.

The potentiometric surface of the intermediate 

layer shows that ground-water flow is generally eastward toward the St. Johns River (fig. 13). The eastward movement of ground water is partially redirected 

southward by clay deposits underlying OU3. The 

horizontal and vertical distribution of this clay deposit 

is based on extensive drilling at OU3 by Navy 

consultants (U.S. Navy, 1998); additional discussion 

of the clay and its effect on ground-water flow was 

documented in ground-water modeling studies by 

Davis (1998; 2000).

The surficial aquifer is not used for water supply 

at the Station or surrounding areas, so ground-water 

level fluctuations are due to natural variations in 

recharge, evapotranspiration, and discharge to creeks 

and rivers. Water-level fluctuations in the surficial 

aquifer from 1993 to 2001 are shown in figure 14. 

As shown in the figure, water levels fluctuate 

seasonally but show no long-term trend. No systematic collection of water-level data has occurred since 

1997. Only well MW-45 has had a recent water-level 

measurement and that was taken on April 4, 2001. 

This measurement was at the low end of the 

previously observed range but was taken during an 

extended period of low rainfall. Since water levels 

at the Station show no long-term trends, the system 

could be analyzed assuming steady-state conditions.

OU3 S t . J o

h n

s

Ri v e r

Hangar

1000

0 1,000 2,000 FEET

EXPLANATION

STORMWATER DRAINS THAT ARE NOT DRAINING

GROUND WATER From the upper layer of the surficial aquifer

STORMWATER DRAINS THAT ARE DRAINING

GROUND WATER From the upper layer of the surficial aquifer

−

−

Figure 10. Stormwater-drainage system at the Jacksonville Naval Air Station.
Hydrologic Setting 13

Hangar 1000

No

Flow

Section

2

Section 1

Section

3

Section

4

Section

5

STORMWATER DRAINS THAT ARE NOT DRAINING GROUND

WATER From the upper layer of the surficial aquifer

STORMWATER DRAINS THAT ARE DRAINING GROUND WATER From

the upper layer of the surficial aquifer

DIRECTION OF WATER FLOW In storm drain or ditch

STORM SEWER SAMPLING LOCATION Locations 1 and 2 are at manholes,

location 3 is at the storm sewer outfall

SAMPLING LOCATION FOR TOTAL ORGANIC CARBON

−

−

−

−

EXPLANATION

1

2 3

1

Figure 11. Location of sewer sections in the vicinity of Hangar 1000.
14 Fate and Transport Modeling of Selected Chlorinated Organic Compounds at Hangar 1000, 

U.S. Naval Station, Jacksonville, Florida

12

11

9

8

7

14

13

10

9

6

14

13

10

12

11

10

10

WATER-TABLE SURFACE CONTOUR Showing the surface of the

water table in feet above NGVD of 1929. Contour interval is 1 foot

STORMWATER DRAINS THAT ARE NOT DRAINING GROUND

WATER From the upper layer of the surficial aquifer

STORMWATER DRAINS THAT ARE DRAINING GROUND WATER From

the upper layer of the surficial aquifer

DIRECTION OF WATER FLOW In storm drain or ditch

MONITORING WELL LOCATION

−

−

−

−

10

EXPLANATION

Hangar 1000

Figure 12. Water-table surface for the upper layer of the surficial aquifer on April 4, 2001, in the vicinity of 

Hangar 1000.
Occurrence and Factors Affecting the Movement of TCE, DCE, and VC 15

OCCURRENCE AND FACTORS 

AFFECTING THE MOVEMENT OF 

TRICHLOROETHENE, DICHLOROETHENE, AND VINYL CHLORIDE 

The ground-water contaminants of concern at 

Hangar 1000 are TCE, DCE, and VC. The present 

distribution of these chemicals in the ground water, 

and the factors affecting their future movement are 

discussed in this section. The current extent of the 

contaminant plumes is based on data collected by 

Tetra Tech and is more fully discussed in Navy 

documentation on Hanger 1000 (U.S. Navy, written 

commun., 2002). The location of monitoring wells 

used to define the plumes is shown in figure 15.

TCE, DCE, and VC are known to degrade in 

natural environments due to reductive dehalogenation 

(Zheng and Bennett, 1995). TCE degrades to DCE which 

degrades to VC, which can further degrade to ethene. 

Degradation occurs when a chlorine molecule is 

removed and replaced by a hydrogen molecule. The 

rate of degradation can be extremely variable even 

over small distances and depends on the particular 

compound and the micro-environments within the 

aquifer. Conditions at Hangar 1000 are generally 

favorable for anaerobic processes due to several 

reduction pathways including iron reduction, sulfate 

reduction, and methanogenesis (U.S. Navy, in press). 

The distribution of TCE in the ground water at 

Hangar 1000 is shown in figure 16. All of the 

contamination associated with the previously removed 

storage tanks is located in the upper layer of the 

surficial aquifer. The highest concentration of TCE, 

8,710 μg/L, was measured in a well installed in the 

location where the TCE storage tanks had been 

removed suggesting that free product is present 

because of the high levels. The TCE is migrating from 

the source area toward storm sewer section 4. As 

discussed earlier, ground water is leaking into the 

storm sewer in this area, so it is likely that the sewer is 

the discharge point for the contaminated ground water; 

TCE was not detected in monitoring wells south of the 

storm sewer. 

OU3 S t . J o

h n

s

Ri v e r

0 1,000 2,000 FEET

Hangar 1000

2

3

5

4

7

6

8

10

9

2

3

EXPLANATION

CLAY DEPOSITS

POTENTIOMETRIC CONTOUR Shows level to which water would

have stood in tightly cased wells tapping the intermediate layer

of the surficial aquifer. Contour interval 1 foot. Datum is NGVD of 1929

MONITORING WELL LOCATION

2 −

Figure 13. Potentiometric surface for the intermediate layer of the surficial aquifer on April 4, 2001.
16 Fate and Transport Modeling of Selected Chlorinated Organic Compounds at Hangar 1000, 

U.S. Naval Station, Jacksonville, Florida

1993 1995 1996 1998 2000

TIME, IN YEARS

GROUND-WATER ELEVATION, IN FEET ABOVE NGVD OF 1929

0

5

10

15

20

25

1994 1997 1999 2001

MW-45

PZ 2

MW-115

MW-82

S t . J o h n s R i v e r

Ortega River

NAVAL AIR STATION,

JACKSONVILLE

17

17

OU2

OU3

OU1

30°12′30′′

30°15′

81°42′30′′ 81°40′

0 0.5 1 MILE

Hangar 1000

and OU6

PZ 2

MW-45

MW-115

MW-82

MW-115

WELL LOCATION

AND NAME For

wells shown in

graph below

−

EXPLANATION

Figure 14. Water-level fluctuations in the surficial aquifer from 1993 to 2001.
Occurrence and Factors Affecting the Movement of TCE, DCE, and VC 17

EXPLANATION

0 100 FEET

Tarmac

21

21

12

12

12

11

11

15

15

15

15

15

15

14

14

14

14

14

14

14 14 14

Parking

Hangar

1000

Yorktown Avenue

14

STORMWATER DRAINS THAT ARE NOT DRAINING

GROUND WATER From the upper layer of the surficial aquifer

STORMWATER DRAINS THAT ARE DRAINING

GROUND WATER From the upper layer of the surficial aquifer

MONITORING WELL LOCATION AND DEPTH In feet

−

−

−

Building Parking

Grass

Figure 15. Location of wells where ground-water quality samples were collected.
18 Fate and Transport Modeling of Selected Chlorinated Organic Compounds at Hangar 1000, 

U.S. Naval Station, Jacksonville, Florida

EXPLANATION

0 100 FEET

Tarmac

1.0

578.0

229.0

94.5

3.1 ND

0.0

18.5

1610.0

36.2

7.8

25.3

8710.0

1.0

Parking

Hangar

1000

Parking

Yorktown Avenue

10

100

1,000

266.0

29.5 48.1

LINE OF EQUAL CONCENTRATION OF TRICHLOROETHENE (TCE) In

micrograms per liter. Contour interval is variable

STORMWATER DRAINS THAT ARE NOT DRAINING

GROUND WATER From the upper layer of the surficial aquifer

STORMWATER DRAINS THAT ARE DRAINING

GROUND WATER From the upper layer of the surficial aquifer

MONITORING WELL LOCATION AND TCE CONCENTRATION In

micrograms per liter. “ND” indicates no detection

DIRECTION OF WATER FLOW In storm drain or ditch

−

−

−

−

−

1.0

10

ND ND

ND ND

ND

Building

Grass

Section 4

Figure 16. Distribution of trichloroethene (TCE) contamination in the ground water of the surficial 

aquifer at Hangar 1000 on January 17, 2001.
Occurrence and Factors Affecting the Movement of TCE, DCE, and VC 19

Tetra Tech sampled the water flowing in the 

storm sewer at the three locations shown in figure 11. 

No TCE was detected in any of these samples. This 

would be expected in locations 1 and 2 because they 

are upstream of the area where contaminated water 

would be expected to discharge to the storm sewer, but 

not in location 3. If the sewer is receiving the contaminated ground water, then the lack of detection at location 3 could be the result of several factors. First, 

videos taken in the storm sewers at OU3 showed that 

water entering the sewers at joints and cracks commonly runs down the pipes as film flow, thus allowing 

a substantial amount of volatilization. Second, the 

flow in the sewer pipe is small and essentially sheet 

flow, thus allowing more volatilization. Third, dilution 

in the standing water at the sewer outfall is occurring 

due to flow that can be observed coming from the 

sewer to the north.

If the contaminated ground water is passing 

beneath the sewer, then it would probably discharge 

directly to the small ditch to the southeast. However, 

no contaminants have been detected in the 

monitoring wells south of sewer section 4.

The distribution of DCE in the ground water is 

shown in figure 17. The source of DCE contamination 

is probably the result of reductive dehalogenation of 

TCE and leakage from the tanks. Concentrations of 

DCE at Hangar 1000 are roughly the same as that of 

TCE. The distribution of VC in ground water is 

shown in figure 18. Concentrations of VC are low, 

indicating either that the dehalogenation of DCE to 

VC is occurring relatively slowly or more likely that 

the destruction of VC is occurring relatively rapidly. 

Contaminants dissolved in ground water will 

move by advection in the direction of flow. However, 

other natural processes can modify the movement 

of contaminants, causing the concentrations to 

change or causing contaminants to move at different 

rates than the ground water. Major processes 

affecting contaminant movement are advection, 

hydrodynamic dispersion, biodegradation, and 

retardation due to sorption to the sediments. 

The most important factor affecting contaminant 

movement is advection, which is the transport of 

dissolved constituents with the velocity and direction 

of ground-water flow. Most of the surficial ground 

water (containing the contaminants) at Hangar 1000 

probably discharges to the storm drains, which then 

discharges to a small creek that flows to the St. Johns 

River. 

Hydrodynamic dispersion occurs due to 

the mechanical mixing of moving ground water 

and molecular diffusion of the dissolved chemical. 

Dispersion will cause a contaminant plume to 

spread, resulting in lower solute concentrations 

away from the plume center. Dispersion is usually 

difficult to accurately quantify in the field. Gelhar 

and others (1992) performed a critical review of fieldscale dispersion studies to define reasonable 

dispersivity values. Using data that Gelhar and 

others (1992) described as the most reliable, a high 

value for longitudinal dispersivity (in the direction 

of the flow axis) was 5.6 ft for sites similar to 

Hangar 1000 and a low value was 0.98 ft. A high 

value for transverse dispersivity (perpendicular to 

the flow axis) was 0.30 ft and a low value was 

0.033 ft. When simulating solute movement, low 

values of dispersivity will result in the highest 

predicted concentrations.

The rate of movement of a dissolved chemical 

depends on the ground-water flow velocity and the 

retardation factor of the particular chemical. The 

retardation factor is the ratio of the velocity of 

ground water to the velocity of the chemical. For 

example, a retardation factor of 1.5 means that 

ground water moves 1.5 times faster than the 

dissolved chemical. Retardation of TCE, DCE, and 

VC occurs because these chemicals are nonpolar, 

which causes them to partition to the organic matter 

in the aquifer sediments. Therefore, retardation and 

retardation factors are a function of the fraction of 

organic carbon content (foc) of the aquifer. 

Partitioning is a reversible process; molecules that 

have partitioned to the organic matter will move 

back into the ground water as relative concentrations 

change.

The organic carbon content in the upper layer 

of the surficial aquifer at Hangar 1000 was measured 

at three locations (fig. 11). The measured values were 

of 1,200 milligramsorganic carbon per kilogramssoil 

(mgoc/kgsoil), 1,200 mgoc/kgsoil and 3,280 mgoc/kgsoil. 

The average of these is 1,893 mgoc/kgsoil or an 

average foc of 1.893 ×10-3 mgoc/kgsoil (the foc is 

calculated by dividing the organic carbon content 

by 1,000,000). The distribution coefficient (Kd) 

relates the mass of contaminant dissolved in the 

ground water to the mass sorbed to the sediments. 
20 Fate and Transport Modeling of Selected Chlorinated Organic Compounds at Hangar 1000, 

U.S. Naval Station, Jacksonville, Florida

LINE OF EQUAL CONCENTRATION OF Dichloroethene (DCE) In

micrograms per liter. Contour interval is variable

STORMWATER DRAINS THAT ARE NOT DRAINING

GROUND WATER From the upper layer of the surficial aquifer

STORMWATER DRAINS THAT ARE DRAINING

GROUND WATER From the upper layer of the surficial aquifer

MONITORING WELL LOCATION AND DCE CONCENTRATION In micrograms per liter.

“ND” indicates no detection

DIRECTION OF WATER FLOW In storm drain or ditch

−

−

−

−

−

EXPLANATION

0 100 FEET

Tarmac

ND

ND

176.4

190.0

ND ND

ND

ND

ND

ND

ND

19.6

2046.0

ND

ND

ND

4280.0

ND

Parking

Hangar

1000

Parking

Yorktown Avenue

1.0

10

100

1,000

424.0

42.6 47.4

133.0

10

Building

Grass

Figure 17. Distribution of dichloroethene (DCE) contamination in the ground water of the surficial 

aquifer at Hangar 1000 on January 17, 2001.
Occurrence and Factors Affecting the Movement of TCE, DCE, and VC 21

0 100 FEET

EXPLANATION

Tarmac

Parking

Hangar

1000

Parking

Yorktown Avenue

15.9 1.4

4.7

3.3

ND

STORMWATER DRAINS THAT ARE NOT DRAINING

GROUND WATER From the upper layer of the surficial aquifer

STORMWATER DRAINS THAT ARE DRAINING

GROUND WATER From the upper layer of the surficial aquifer

MONITORING WELL LOCATION AND VINYL CHLORIDE (VC)

CONCENTRATION In micrograms per liter. “ND” indicates no detection

DIRECTION OF WATER FLOW In storm drain or ditch

−

−

−

−

1.4

Building

Grass

ND

ND ND

ND

ND

ND

ND

ND ND

ND

ND ND

ND

ND

ND

ND

ND

Figure 18. Distribution of vinyl chloride (VC) contamination in the ground water of the surficial aquifer 

at Hangar 1000 on January 17, 2001.
22 Fate and Transport Modeling of Selected Chlorinated Organic Compounds at Hangar 1000, 

U.S. Naval Station, Jacksonville, Florida

Partitioning coefficients were calculated using the 

following equation with resulting values given in 

table 3:

Kd = Kocfoc ,

where

The retardation factor for the upper layer was 

calculated using the following equation, with the 

results given in table 3. Reasonable values for bulk 

density of 1.6 grams per cubic centimeter (g/cm3

) and 

total porosity of 25 percent (Hillel, 1980) were 

assumed for the aquifer sediments.

,

where

Table 3. Distribution of partitioning coefficients and 

retardation factors for trichloroethene (TCE), dichloroethene 

(DCE), and vinyl chloride (VC) for the upper layer of the 

surficial aquifer

[foc, fraction organic carbon; mLwater, milliliters water; gsoil, grams soil; 

Koc, partition coefficient; goc, grams organic carbon; Kd, distribution 

coefficient]

GROUND-WATER FLOW SIMULATION AT 

THE STATION

Several ground-water flow models have been 

developed, each designed to satisfy a particular need 

of the Station. Because of the contaminant plumes of 

TCE, DCE, and VC identified in the area of Hangar 

1000, a model was needed to simulate the contaminant 

concentration and movement of these chemicals. 

Before solute transport modeling could be performed, 

ground-water flow had to be simulated. This section 

discusses the simulation of ground-water flow and the 

next section discusses the solute transport modeling at 

Hangar 1000.

Original Subregional Model

The original subregional OU3 model (Davis, 

1998) was calibrated to the head data collected on 

October 29 and 30, 1996, and steady-state groundwater flow conditions were assumed. The calibration 

strategy was to match simulated heads in the upper 

and intermediate layers to within 1 ft of the measured 

values. After calibration, all of the model simulated 

heads matched the measured heads within the calibration criterion of 1 ft, and 48 of 67 simulated heads 

(72 percent) were within 0.5 ft of the corresponding 

measured values.

The original model contained 78 rows and 

148 columns of active model cells; all cells were 

100 ft on each side. Vertically, the surficial aquifer was 

divided into two layers. The upper model layer 

represented the upper layer of the surficial aquifer and 

extended from land surface down to 15 ft below sea 

level (sea level refers to the National Geodetic Vertical 

Datum of 1929 (NGVD29)); this layer was modeled as 

unconfined. The lower model layer represented the 

intermediate layer and extended from the bottom of 

the upper layer down to the top of the Hawthorn 

Group; this layer was modeled as confined. The clay 

layer separating the upper and intermediate layers 

was simulated through the vertical leakance term. A 

seawall at OU3 was simulated using the HorizontalFlow Barrier Package documented by Hseih and 

Freckleton (1993).

The northern, western, and southern boundaries 

of the model were simulated as no flow and were positioned along ground-water divides delineated using 

both water-table maps and particle tracking with the 

regional model (fig. 2). The eastern model boundary 

also is no-flow and is positioned near the center of the 

Kd = distribution coefficient, milliliters water per 

gramssoil (mLwater/gsoil),

Koc= partition coefficient, mLwater/goc, and

foc = fraction organic carbon, in gramsorganic carbon per 

gramssoil (goc/gsoil).

R = retardation factor, no units,

ρ = bulk density of aquifer material, in g/cm3,

Kd = distribution coefficient, mLwater/gsoil, and

= aquifer porosity, milliliterswater per cubic 

centimetersoil (mLwater/cm3

soil).

TCE DCE VC

Average foc

(mLwater/gsoil)

 1.893×10-3 1.893×10-3 1.893×10-3

Koc (mLwater/goc) 126a 86a 57a

Kd (mLwater/gsoil) 0.2386 0.1628 0.1079

Retardation factor 

(no units)

2.5 2.0 1.7

a

 Mercer and others, 1990.

R 1 ( ) ρ Kd ( )

φ = + -------------------

φ
Ground-Water Flow Simulation at the Station 23

St. Johns River. This boundary was positioned away 

from the shoreline so that the model could simulate the 

upward seepage of ground water through the bottom 

of the river. The base of the surficial aquifer was simulated as a no-flow boundary because it is underlain by 

the low-permeability sediments of the Hawthorn 

Group. There is little, if any, vertical flow between the 

surficial aquifer and the Hawthorn Group.

The MODFLOW River Package was used to 

simulate, in the upper layer of the model, the presence 

of the St. Johns River and two small ditches. The riverbed conductance for the St. Johns River was calculated 

using a riverbed thickness of 1 ft over the entire area 

of each cell and a riverbed hydraulic conductivity of 

8 feet per day (ft/d). The altitude of the bottom of the 

river was taken from USGS topographic maps and a 

stage of 1 ft above sea level (NVGD29). Conductance 

for two small ditches was calculated using a thickness 

of 1 ft, a width of 10 ft, and a hydraulic conductivity of 

4 ft/d. The altitude of the stage and bottom of the two 

ditches were estimated from the topographic maps and 

field observations.

The MODFLOW Drain Package was used to 

simulate the presence of the stormwater drains in the 

upper model layer. The altitude, relative to the 

NGVD29, of the bottom of the drains was determined 

where manholes allowed access. Altitudes between 

manholes were extrapolated from the 

measured values. 

The distribution of recharge ranged from 

13.0 inches per year (in/yr) in irrigated areas to 

0.4 in/yr in relatively impervious areas. The 

horizontal hydraulic conductivity for the upper layer 

ranged from 0.5 to 7.5 ft/d, while the horizontal 

hydraulic conductivity in the intermediate layer 

ranged from 20 ft/d in a sandy area to 0.2 ft/d within 

the low-permeability silt and clay deposits.

Recalibration of the Subregional Model

The recalibrated model used the same 

grid location and discretization of 78 rows and 

148 columns of active model cells (measuring 100 ft 

on each side, fig. 19) as the original subregional 

OU3

BOUNDARY OF ACTIVE CELLS FOR

BOTH MODEL LAYERS

DRAIN CELLS

NOTE: The St. Johns River was modeled using river cells

EXPLANATION

MODEL GRID

Columns

Rows

1

1

82

158

RIVER CELLS

0 1,000 2,000 FEET

St. Johns River

Docking

facility

Sea wall

Hangar

1000

Figure 19. Location and orientation of the subregional model finite-difference grid.
24 Fate and Transport Modeling of Selected Chlorinated Organic Compounds at Hangar 1000, 

U.S. Naval Station, Jacksonville, Florida

model. The lateral boundaries and extent of the 

recalibrated model are the same as the original model. 

The surficial aquifer was divided into four layers 

(instead of the two layers in the original model) to 

more accurately simulate the complex hydrology 

(fig. 20). Layer 1 of the original model was split into 

layers 1 and 2; layers 3 and 4 are the result of 

splitting layer 2 of the original model. Model layer 1 

represents the upper layer of the surficial aquifer 

and extends from land surface down to about 15 ft 

below land surface; this layer was modeled as 

unconfined. Layer 2 represents most of the clay layer 

shown in figure 5 (the deeper parts of the clay are 

simulated in layers 3 and 4). Model layers 3 and 4 

represent the intermediate layer of the surficial 

aquifer and were modeled as confined. The top of 

the Hawthorn Group forms the base of the surficial 

aquifer. A seawall, located at OU3, was simulated 

using the Horizontal-Flow Barrier Package 

documented by Hseih and Freckleton (1993). The 

initial aquifer parameters, before recalibration, were 

all taken directly from the original model. The 

hydraulic conductivity of the clay layer (which was 

not explicitly modeled in the original model) was 

estimated using the vertical conductance 

and thickness.

The model was calibrated to the head data 

collected on April 4, 2001. Water levels were 

collected across the entire northern part of the Station 

and contoured to verify that the ground-water divides 

(which established the model boundaries) were the 

same as for the original model. The relatively thin 

aquifer and numerous small creeks draining ground 

water tend to stabilize ground-water levels and the 

locations of ground-water divides. During 

recalibration, the following parameters were varied: 

horizontal and vertical hydraulic conductivities of all 

layers, the recharge rates, and riverbed conductances. 

The parameter changes during recalibration were 

generally minor, so the recalibrated model is similar to 

the original model.

Steady-state ground-water flow conditions were 

assumed. The calibration strategy was to match 

simulated heads in the upper and intermediate layers 

to within 1.5 ft of the measured values. When 

calibration was completed, 45 of the 46 modelsimulated heads matched the measured heads to within 

the 1.5-ft calibration criterion, 41of 46 simulated 

heads (89 percent) were within 1.0 ft, and 27 of 

46 simulated heads (59 percent) were within 0.5 ft of 

the corresponding measured values. Figure 21 shows a 

comparison of the measured and simulated heads. If 

the model-simulated heads had matched the measured 

values exactly, then all the points would lie on the 

45 degree line (line of equality).

The simulated recharge rate for the recalibrated 

model is shown in figure 22. Recharge ranged from a 

low of 0.1 in/yr largely in paved areas to 13 in/yr in 

irrigated areas. Most of the small, irregularly shaped, 

high recharge areas represent grassy areas within 

otherwise paved surfaces: the locations of these high 

recharge areas were determined from aerial 

photographs. The most significant changes in recharge 

occured in the grassy areas with higher recharge 

southeast of Hangar 1000.

30

20

10

10

20

30

40

50

60

70

80

90

Sea

Level

FEET

St.

Johns

River

Hangar

1000

Layer 1

Layer 4

Layer 3

No-flo

Layer 2

w boundar

y

Vertical scale greatly exaggerated

A

Seawall

OU3

0 2,000 FEET

A

St. Johns River

Upper layer

Clay

Intermediate

layer

Hawthorn Group

SURFICIAL AQUIFER

EXPLANATION

?

?

CONFINING UNIT “ ” indicates lateral extent not known − ?

0 1 MILE

A

A

Figure 20. Generalized hydrologic section for the 

recalibrated subregional model.
Ground-Water Flow Simulation at the Station 25

The model-simulated horizontal hydraulic 

conductivity distribution for the upper layer is shown 

in figure 23. In the central part of the model area, the 

hydraulic conductivity is 0.5 ft/d, which is very nearly 

the value of 0.6 ft/d determined from a multiple-well 

aquifer test (Davis, 1996a,b) conducted at a contaminated site (the test was located approximately at the 

center of the 0.5-ft/day conductivity area.) The 0.5-ft/d 

conductivity area has been reduced in size from the 

original subregional model. The hydraulic conductivity in the southern part of the model area is 1.0 ft/d 

and was determined during the calibration of the 

original subregional model. In the remainder of the 

model area, the simulated hydraulic conductivity was 

7.5 ft/d. Aquifer testing of two wells in the upper layer 

of the surficial aquifer at Hangar 1000 (wells 

numbered 10 and 19 on figure 7) gave hydraulic 

conductivities of 4 ft/d and 8 ft/d, respectively 

(Davis, 2001). The hydraulic conductivity of the 

surficial aquifer in the original subregional model was 

7.5 ft/d; this value was used in the recalibrated model 

because it gave the best calibration and because it fell 

between the measured values. The 7.5-ft/d conductivity area has increased in size from the original model. 

The vertical hydraulic conductivity for this, and all the 

other layers, is one order of magnitude lower than the 

horizontal hydraulic conductivity. 

The model-simulated horizontal hydraulic conductivity distribution for layer 2 is shown in figure 24. 

The hydraulic conductivity ranged from a low of 

5.0x10-6 ft/d in the thicker part of the clay layer to a 

high of 4.3x10-1 ft/d in the area around the old fuel 

barge dock, where dredging has removed or disturbed 

the clay. The simulated thickness of layer 2 is shown 

in figure 25. As seen in the figure, the clay layer is 

thickest near the center of the model and thins toward 

the edges.

The model-simulated horizontal hydraulic 

conductivity distribution for layer 3 is shown in 

figure 26. The simulated hydraulic conductivity over 

most of the model area was 7.5 ft/d. The higher 20-ft/d 

conductivity area at OU3 was based on a multi-well 

aquifer test (Davis, 1996a,b). The hydraulic conductivity of 0.4 ft/d represents low-permeability silt 

and clay deposits, and was taken from earlier 

modeling studies (Davis, 1998). The thickness of 

layer 3 ranges from 15-20 ft at Hangar 1000 

(fig. 27). Near the center of the model, layer 3 

thins to about 5 ft, which is due to the thickening 

of the overlying clay represented by layer 2.

The model-simulated horizontal hydraulic 

conductivity distribution for layer 4 is shown in 

figure 28. The distribution is the same as for layer 3 

and for the same reasons, except that layer 4 does not 

extend as far westward as layer 3. The simulated 

thickness of layer 4 is shown in figure 29. The 

increase in thickness from west to east is a result of 

the thinning of the top of the Hawthorn Group which 

forms the base of layer 4. 

The riverbed conductance for the St. Johns 

River was 8 square feet per day (ft2

/d), except in 

the area of the docking facility where the conductance was 60 ft2/d to reflect the disturbance and 

removal of riverbed sediments during dredging. The 

conductance of the small ditches was of 4 ft2

/d. 

LINE OF

EQUALITY

+1 FOOT

-1.5 FOOT

LINE OF

EQUALITY

+1.5 FOOT

-1.5 FOOT

0 5 10 15 20

UPPER LAYER MEASURED HEADS,

IN FEET ABOVE NGVD OF 1929

0

5

10

15

20

UPPER LAYER SIMULATED HEADS,

IN FEET ABOVE NGVD OF 1929

0 5 10 15 20

INTERMEDIATE LAYER MEASURED HEADS,

IN FEET ABOVE NGVD OF 1929

0

5

10

15

20

UPPER LAYER SIMULATED HEADS,

IN FEET ABOVE NGVD OF 1929

Figure 21. Comparison of measured and simulated 

heads for the recalibrated subregional model.
26 Fate and Transport Modeling of Selected Chlorinated Organic Compounds at Hangar 1000, 

U.S. Naval Station, Jacksonville, Florida

0 1,000 2,000 FEET

S t . J o

h n

s

Ri v e r

Hangar

1000

EXPLANATION

SUBREGIONAL STUDY AREA AND SUBREGIONAL MODEL BOUNDARY

BOUNDARY OF MODEL-SIMULATED HORIZONTAL HYDRAULIC

CONDUCTIVITY In the upper layer

MODEL-SIMULATED HORIZONTAL HYDRAULIC CONDUCTIVITY In the

upper layer, in feet per day

−

1.0 −

7.5

0.5

1.0

Figure 23. Simulated horizontal hydraulic conductivity of the upper layer of the recalibrated subregional model.

0 1,000 2,000 FEET

S t . J o

h n

s

Ri v e r

Hangar

1000

EXPLANATION

SUBREGIONAL STUDY AREA AND SUBREGIONAL MODEL BOUNDARY

BOUNDARY OF RECHARGE ZONES IN MODEL

2.5 RECHARGE RATES Model simulated, values in inches per year −

5

5

2.5

2.5

10 10

10

10

13

0.1

0.1 2.5

5.0

10

Figure 22. Simulated recharge rates for the recalibrated subregional model.
Ground-Water Flow Simulation at the Station 27

0 1,000 2,000 FEET

S t . J o

h n

s

Ri v e r

Hangar

1000

EXPLANATION

SUBREGIONAL STUDY AREA AND SUBREGIONAL MODEL BOUNDARY

LINE OF EQUAL SIMULATED THICKNESS OF LAYER 2 Of the

subregional model, in feet.

20 −

5

20

25

15

10

Figure 25. Simulated thickness of layer 2 of the recalibrated subregional model.

0 1,000 2,000 FEET

S t . J o

h n

s

Ri v e r

Hangar

1000

EXPLANATION

SUBREGIONAL STUDY AREA AND SUBREGIONAL MODEL BOUNDARY

BOUNDARY OF MODEL-SIMULATED HORIZONTAL HYDRAULIC

CONDUCTIVITY Of layer 2

MODEL-SIMULATED HORIZONTAL HYDRAULIC CONDUCTIVITY Of

layer 2, in feet per day

−

− 2.5 x 10-3

2.5 x 10-3

5.0 x 10-6

4.3 x 10-1

Figure 24. Simulated horizontal hydraulic conductivity of layer 2 of the recalibrated subregional model.
28 Fate and Transport Modeling of Selected Chlorinated Organic Compounds at Hangar 1000, 

U.S. Naval Station, Jacksonville, Florida

SUBREGIONAL STUDY AREA AND SUBREGIONAL MODEL BOUNDARY

LINE OF EQUAL SIMULATED THICKNESS OF LAYER 3 Of the

subregional model, in feet.

5 −

0 1,000 2,000 FEET

S t . J o

h n

s

Ri v e

Hangar 1000 r

EXPLANATION

5

30

15

20

25

10

15

10

5

Figure 27. Simulated thickness of layer 3 of the recalibrated subregional model.

S t . J o

h n

s

Ri v e r

Hangar

1000

EXPLANATION

SUBREGIONAL STUDY AREA AND SUBREGIONAL MODEL BOUNDARY

BOUNDARY OF MODEL-SIMULATED HORIZONTAL HYDRAULIC

CONDUCTIVITY Of layer 3

MODEL-SIMULATED HORIZONTAL HYDRAULIC CONDUCTIVITY Of

layer 3, in feet per day

−

− 20.0

20.0

20.0

0.4

7.5

0 1,000 2,000 FEET

Figure 26. Simulated horizontal hydraulic conductivity of layer 3 of the recalibrated subregional model.
Ground-Water Flow Simulation at the Station 29

0 1,000 2,000 FEET

S t . J o

h n

s

Ri v e r

Hangar

1000

EXPLANATION

SUBREGIONAL STUDY AREA AND SUBREGIONAL MODEL BOUNDARY

LINE OF EQUAL SIMULATED THICKNESS OF LAYER 4 Of the

subregional model, in feet.

5 −

10

5

15

20

25

30

35

40

45

50

55

60

Figure 29. Simulated thickness of layer 4 of the recalibrated subregional model.

0 1,000 2,000 FEET

S t . J o

h n

s

Ri v e r

Hangar

1000

EXPLANATION

SUBREGIONAL STUDY AREA AND SUBREGIONAL MODEL BOUNDARY

BOUNDARY OF MODEL-SIMULATED HORIZONTAL HYDRAULIC

CONDUCTIVITY Of layer 4

MODEL-SIMULATED HORIZONTAL HYDRAULIC CONDUCTIVITY Of

layer 4, in feet per day

−

− 20.0

7.5

20.0

20.0

0.4

Figure 28. Simulated horizontal hydraulic conductivity of layer 4 of the recalibrated subregional model.
30 Fate and Transport Modeling of Selected Chlorinated Organic Compounds at Hangar 1000, 

U.S. Naval Station, Jacksonville, Florida

The calibrated conductances of the stormwater drains 

ranged from 0.1 to 2 ft2

/d. All of these values are the 

same as the values used in the original subregional 

model except the stormwater drains, which had a 

lower conductance.

The simulated water table for the upper layer is 

shown in figure 30. The water table slopes toward the 

St. Johns River except in areas that are influenced by 

the leaking stormwater drains. Almost all of the simulated drains caused some depression in the water-table 

surface because they are removing ground water from 

the upper layer of the aquifer. The presence of the seawall causes elevated heads to occur directly adjacent 

to the St. Johns River in the central and northern parts 

of OU3. The heads are relatively higher in this area 

because the seawall extends downward into the clay 

and prevents ground water from moving easily under 

the seawall and discharging to the St. Johns River. 

The simulated potentiometric surface for the 

intermediate layer slopes toward the St. Johns River 

(fig. 31). The presence of the low-permeability 

deposits is reflected in the bending of the contours in 

the central part of OU3; the result is a steeper slope of 

the potentiometric surface in the northern half of OU3 

than in the southern half. 

Ideally, there would also be a match of 

simulated flows to field measurements. Two streamflow measurements were taken within the study area 

(fig. 9); however, as discussed earlier, these creeks 

receive both ground-water seepage and flow from 

other sources, and thus could only be used as an upper 

limit for comparison with model-simulated values 

which were substaintially below the measured values. 

The regional, Station-wide ground-water model was 

calibrated to measured stream flows (due to numerous 

creeks at the Station) and the same recharge rates 

determined in adjacent watersheds were applied to the 

recalibrated modeled watershed to ensure reasonable 

recharge rates. 

Ground-Water Budget

The model-simulated inflows and outflows for 

the subregional model area are shown in table 4. The 

total rate of recharge to the subregional model was

0 1,000 2,000 FEET

S t . J o

h n

s

Ri v e r

Hangar

1000

EXPLANATION

SUBREGIONAL STUDY AREA AND SUBREGIONAL MODEL BOUNDARY

SIMULATED WATER-TABLE CONTOUR Shows model-simulated head in

the upper layer. Contour interval 1 foot. Datum is NGVD of 1929

SIMULATED LEAKING STORMWATER DRAINS

5 −

2

2

3

3

4

4

5

4

5

7

6

9

8

13 12

11

10

14

15

16

17

10

16

1918

17

9

8

7

8

7

7

Figure 30. Simulated water-table surface of the upper layer of the recalibrated subregional model.
Ground-Water Flow Simulation at the Station 31

0.189 ft3/s. Discharge rates were 0.071 ft3/s to the 

St. Johns River, 0.055 ft3/s to the ditches, and 

0.063 ft3/s to the stormwater drains.

Sensitivity Analysis

Sensitivity tests were conducted to determine the 

effect of changes in model input parameters on the 

model calibration. Tests were conducted by increasing 

(or decreasing) each parameter by 50 percent while 

other parameters were unchanged. Parameter changes 

resulted in the simulation of a new distribution of 

heads, and the effect of the parameter change was 

judged by determining the number of simulated heads 

that no longer remained within 1.5 ft of the measured 

values (table 5). Input parameters tested were 

recharge, riverbed conductance, storm drain conductance, horizontal hydraulic conductivity of the upper 

layer, horizontal hydraulic conductivity of the clay 

layer, horizontal hydraulic conductivity of the 

intermediate layer, and vertical hydraulic conductivity.

The model was sensitive to recharge rate 

changes because recharge was the only source of 

water to the model. Decreasing the recharge rate by 

50 percent caused the simulated heads to drop and 

the number of simulated heads exceeding the error 

criterion to increase from 1 to 6 (out of 46). Increasing 

the recharge rate by 50 percent caused the model heads 

to rise and the number of heads exceeding the error 

criterion to increase from 1 to 10. 

Decreasing the riverbed conductance caused the 

simulated heads to rise, because a larger gradient was 

necessary to move water from the aquifer to the river. 

A decrease of 50 percent caused the total number of 

simulated heads exceeding the error criterion to 

increase from 1 to 5. In contrast, the model was not 

Table 4. Simulated ground-water inflows and outflows for 

the recalibrated subregional model

[ft3/s, cubic feet per second]

Ground-water 

source or sink

Flow rate into 

the model

(ft3/s)

Flow rate out 

of the model

(ft3/s)

Recharge 0.189 0

St. Johns River 0 0.071

Ditches 0 0.055

Stormwater drains 0 0.063

Total 0.189 0.189

0 1,000 2,000 FEET

S t . J o

h n

s

Ri v e r

Hangar

1000

EXPLANATION

SUBREGIONAL STUDY AREA AND SUBREGIONAL MODEL BOUNDARY

SIMULATED POTENTIOMETRIC CONTOUR Shows model-simulated head in

the upper layer. Contour interval 1 foot. Datum is NGVD of 1929

5 −

2

3

6

5

8

7

9

10

11

4

Figure 31. Simulated potentiometric surface of the intermediate layer of the recalibrated subregional model.
32 Fate and Transport Modeling of Selected Chlorinated Organic Compounds at Hangar 1000, 

U.S. Naval Station, Jacksonville, Florida

sensitive to increases in riverbed conductance. An 

increase of 50 percent caused the number of simulated 

heads exceeding the error criterion to increase from 

1 to 3.

Decreasing the storm drain conductance caused 

simulated heads in the vicinity of the drains to rise, 

because a larger vertical gradient developed between 

the drains and the aquifer. A decrease of 50 percent 

caused the number of simulated heads exceeding the 

error criterion to increase from 1 to 5 in the upper 

layer. The model was not sensitive to an increase in 

drain conductance. An increase of 50 percent caused 

the number of simulated heads exceeding the error 

criterion in the upper layer to increase from 1 to 3. 

As expected, varying the drain conductance had little 

effect on the heads in the intermediate layer.

Decreasing the horizontal hydraulic conductivity 

in the upper layer by 50 percent caused no change in 

the number of heads that exceeded the error criterion. 

This is probably because most of the wells are near 

storm drains, which reduce the fluctuations of the 

water levels in the aquifer in their vicinity. An increase 

of 50 percent also caused no change in the quality of 

the calibration for the same reason. 

Increasing or decreasing the horizontal hydraulic 

conductivity in the clay layer by 50 percent also 

caused no change in the number of heads that 

exceeded the error criterion. This is probably because 

the clay layer had a low conductivity (especially in the 

thicker areas) and varying this low conductivity did 

not substantially change the volume of water moving 

through it. 

Decreasing the horizontal hydraulic conductivity 

in the intermediate layer (layers 3 and 4 combined) 

caused the simulated heads in the intermediate layer to 

rise, causing a corresponding rise in the upper layer. A 

decrease of 50 percent caused the total number of 

simulated heads that exceeded the error criterion to 

increase from 1 to 6. The model was not sensitive to an 

increase in horizontal hydraulic conductivity. An 

increase of 50 percent caused no change in the quality 

of the calibration.

Decreasing the vertical hydraulic conductivity 

by 50 percent caused simulated heads in layer 1 to rise 

and the total number of simulated heads that exceeded 

the error criterion to increase from 1 to 9. An increase 

of 50 percent caused no change in the quality of the 

calibration.

Table 5. Summary of sensitivity analyses for the recalibrated subregional model

[*, indicates parameter is multiplied by the number to the right.]

Parameter changed

Number of simulated 

heads in the upper 

layer that 

exceeded the 

calibration 

criterion of 1.5 foot

Number of 

simulated heads in 

the intermediate 

layer that exceeded 

the calibration 

criterion of 1.5 foot

Total

Calibrated Model 1 0 1

Recharge * 0.5 4 2 6

Recharge * 1.5 8 2 10

Riverbed conductance * 0.5 4 1 5

Riverbed conductance * 1.5 1 2 3

Drain conductance * 0.5 5 0 5

Drain conductance * 1.5 3 0 3

Horizontal hydraulic conductivity of upper layer * 0.5 1 0 1

Horizontal hydraulic conductivity of upper layer * 1.5 1 0 1

Horizontal hydraulic conductivity of clay layer * 1.5 1 0 1

Horizontal hydraulic conductivity of clay layer * 1.5 1 0 1

Horizontal hydraulic conductivity of intermediate layer * 0.5 6 0 6

Horizontal hydraulic conductivity of intermediate layer * 1.5 1 0 1

Vertical hydraulic conductivity of all layers * 0.5 8 1 9

Vertical hydraulic conductivity of all layers * 1.5 1 0 1
Modeling Ground-Water Flow and the Fate and Transport of Contaminants 33

Ground-Water Flow Model Limitations

The subregional model simulated ground-water 

flow by assuming steady-state conditions. The 

surficial aquifer is assumed to be under steady-state 

conditions because water levels in wells showed no 

long-term trend (but did show seasonal variation). The 

water table is generally close to the land surface, and 

there is little capacity for a substantial rise in water 

levels. If higher than average rainfall occurred, greater 

runoff would probably result without inducing a 

substantially higher water table. However, an extended 

drought could reduce water levels to below those that 

were used to calibrate the model, which would result 

in simulated ground-water flow velocities that are 

slower than actual velocities. 

Since there were no discharge measurements for 

direct calibration of the model, model-derived 

recharge rates from the Station-wide model (which did 

have discharge measurements) were used because they 

were considered to be the best estimates. If these rates 

were too low, then this would result in ground-water 

flow velocities that were too low. Conversely, if these 

recharge rates were too high, then the velocities would 

be too high.

FATE AND TRANSPORT SIMULATIONS 

OF TRICHLOROETHENE, DICHLOROETHENE, AND VINYL CHLORIDE 

MOVEMENT AT HANGAR 1000

This section describes site-specific ground-water 

flow and fate and transport modeling conducted at 

Hangar 1000. The previously discussed subregional 

flow model was used to establish layering and 

boundary conditions for the site-specific ground-water 

flow model. Fate and transport modeling was 

conducted using the site-specific ground-water flow 

model and the computer code, Reactive Transport in 

Three Dimensions (RT3D), developed by Clement 

(1997). This code was used because it can simulate the 

degradation of TCE to DCE to VC. This model is 

herein referred to as the Hangar 1000 model.

Model Construction

The Hangar 1000 model contains 161 rows and 

149 columns of model cells. All cells are 5 ft long on 

each side. The location and orientation of the finitedifference grid for the Hanger 1000 model is shown in 

figure 32. The model simulates the same four layers as 

the subregional model (fig. 20.) The perimeter of the 

Hangar 1000 model consists of constant head cells; the 

assigned head at these cells was taken from the 

calibrated subregional model described in the previous 

section. All other modeling and aquifer parameters 

were the same as those used for the subregional model, 

except for the cell size.

Flow Path Analysis

The direction and rate of ground-water 

movement in the upper layer of the aquifer was 

computed by using the USGS program MODPATH 

(Pollock, 1989), and the results of this analysis are 

shown in figure 33. Particle tracking was simulated in 

layer 1 because this is where contaminants are present. 

The very low-permeability clay layer (layer 2 of the 

model) essentially prevents contaminate ground water 

from moving downward into the intermediate layer 

(layers 3 and 4 of the model) in the study area. Thus, 

contamination is transported only in layer 1 of the 

model. The ground-water flow velocity averaged 

about 75 feet per year (ft/yr) and took about 6 years for 

particles to move the 450 ft to the storm drain, 

assuming a porosity of 25 percent. Other porosities 

would give exactly the same direction of ground-water 

flow, but the rate of movement would be inversely 

proportional to the porosity. Reducing the simulated 

porosity by one half would double the simulated 

velocity. Likewise, doubling the simulated porosity 

would decrease the simulated velocity by one half.

Fate and Transport Modeling Overview

The objective of the fate and transport modeling 

calibration was to match, as closely as possible, the 

known distribution of TCE, DCE, and VC. Because 

of the high levels of contamination at the tank removal 

site, free product is suspected to be present. To 

simulate this free product source, two cells (creating 

a 5 by 10 ft area) were designated as constant 

chemical concentration cells; the concentration in 

these two cells was varied during calibration. When 

a simulation began, RT3D assigned particles to 

constant concentration model cells; each particle 

represented a cell volume-weighted mass of 

contamination. The movement of particles was 

tracked during each step in the simulation. 
34 Fate and Transport Modeling of Selected Chlorinated Organic Compounds at Hangar 1000, 

U.S. Naval Station, Jacksonville, Florida

0 100 FEET

EXPLANATION

Tarmac

Parking

Hangar

1000

Parking

Yorktown Avenue

STORMWATER DRAINS THAT ARE NOT DRAINING GROUND

WATER

STORMWATER DRAINS CELLS IN LAYER 1

CONSTANT HEAD CELLS

MONITORING WELL LOCATION

−From the upper layer of the surficial aquifer

Column

1

Column

160

Row 1

Row 170

Figure 32. Location and orientation of the Hangar 1000 model.
Fate and Transport Simulations of TCE, DCE, and VC Movement at Hangar 1000 35

0 100 FEET

EXPLANATION

STORMWATER DRAINS THAT ARE DRAINING

GROUND WATER From the upper layer of the surficial aquifer −

PARTICLE PATHLINE Shows simulated ground-water flow path in the

upper layer. Distance between dots represents a traveltime of 1 year

−

Tarmac

Parking

Hangar

1000

Parking

Yorktown Avenue

MONITORING WELL LOCATION

STORMWATER DRAINS THAT ARE NOT DRAINING GROUND

WATER−From the upper layer of the surficial aquifer

Figure 33. Particle pathlines representing ground-water flow directions in the upper layer of the 

surficial aquifer at Hangar 1000.
36 Fate and Transport Modeling of Selected Chlorinated Organic Compounds at Hangar 1000, 

U.S. Naval Station, Jacksonville, Florida

The sum of the masses of all the particles in a cell 

equaled the total mass of contamination for that cell. 

Advection of ground water is the most important 

factor governing the transport of these chemical 

compounds. The direction of ground-water flow was 

determined from the intercell flow velocities, which 

were part of the output from MODFLOW. The intercell flow velocities were divided by the effective 

porosity to get the ground-water velocity. In addition 

to advection, the effects of retardation, hydrodynamic 

dispersion, and chemical decay were added to the 

simulation. The effects of retardation due to sorption 

caused the contaminant to move slower than the 

ground water, and these effects were specified by the 

retardation factor. The effect of hydrodynamic 

dispersion, as specified by the dispersivity, caused the 

plume to spread. Chemical decay, as specified by a 

half-life, dictated how rapidly the compounds 

degraded naturally in the aquifer. TCE degrades into 

DCE; DCE degrades into VC; and VC can degrades 

into ethene (or VC could be biodegraded to other nonhazardous compounds). For a more complete 

discussion of contaminant transport, see Zheng and 

Bennett (1995).

The calibration strategy was to vary the 

effective porosity, dispersivity, retardation, chemical 

decay rate, and chemical concentrations in two 

constant chemical concentration cells (that represented 

the source area) until modeled concentrations matched 

measured values as closely as possible. For this 

simulation, it was assumed that the flow field is 

constant in time, degradation and sorption are constant 

along a flow path, and that degradation occurs in both 

the dissolved and sorbed phase.

After the fate and transport model was 

calibrated, it was used to simulate future concentrations. The Navy has begun pilot tests to reduce the 

concentrations at the tank removal site. To simulate 

this result the concentration in the constant concentration cells was reduced by 50 percent and the 

model was run to predict the effect. This scenerio was 

then repeated assuming a 100 percent reduction at 

the source.

Calibration to Current Distributions 

of Trichloroethene, Dichloroethene, 

and Vinyl Chloride 

As discussed earlier, the simulated source of 

contamination is the two constant chemical concentration cells (creating a source area of 5 by 10 ft) 

located where the leaking chemical storage tank and 

associated piping existed before removal. The 

calibrated values for the two constant chemical concentration cells were 11,000 and 20,000 μg/L for TCE; 

5,400 and 10,000 μg/L for DCE; and 0 and 0 μg/L for 

VC. Figure 34 shows the simulated TCE distribution 

16 years after the initial release. The spilled product 

acts as an ongoing source by slowly leaching into the 

ground water. TCE then continues moving toward, and 

discharging into, the stormwater sewer to the southeast. It is not known when the release of TCE actually 

began, but the tanks were installed in the late 1960s, 

approximately 35 years ago. After simulating 16 years 

into the future, TCE concetrations reach steady-state 

conditions; that is, the concentrations do not change if 

additional years are simulated. Since these steady-state 

concentrations result in the best match to the measured 

data, it is speculated that the initial leak occurred more 

than 16 years ago. If the contamination source area 

changed sunstantially during tank removal in 1994, 

then some concentration changes may still be migrating through the system. DCE concentrations reached 

steady-state conditions in 14 years (fig. 35) and VC 

concentrations reached steady-state concentrations in 

12 years (fig 36). The VC concentrations reached 

steady-state conditions first because the retardation 

factor for VC is the lowest of the three chemicals, thus 

allowing VC to be transported faster; DCE was intermediate in reaching steady-state conditions because its 

retardation factor is intermediate to TCE and VC.

At monitoring well H10-MW08 (map number 

12) located directly south of the simulated source area, 

the model-simulated and measured TCE concentrations are 8,609 and 8,710 μg/L (fig. 34), respectively; 

the model-simulated and measured DCE concentrations are 3,779 and 4,280 μg/L (fig. 35), respectively. 

Matching the concentrations at this well was used as 

the basis for determining the concentration level in the 

two constant chemical concentration cells. The 

concentration for VC was set at 0 μg/L in the source 

area because VC is a degradation product of DCE. 

Matching the measured concentration values in the 

other wells was accomplished by varying the 

dispersivity and first order decay rates of TCE, DCE, 

and VC. The dispersivity values that gave the best 

match were: longitudinal 1.5 ft, transverse 0.27 ft, 

and vertical 0.27 ft. These dispersivity values fall 

within the expected range (0.98 to 5.6 ft for 

longitudinal and 0.033 to 0.3 ft for transverse 

dispersivity) described by Gelhar and others (1992). 
Fate and Transport Simulations of TCE, DCE, and VC Movement at Hangar 1000 37

0 100 FEET

EXPLANATION

Tarmac

Parking

Hangar

1000

Parking

Yorktown Avenue

(H10-MW15)

356.5/578.0

(H10-MW14)

652.6/266.0

(H10-MW18)

0.8/8.6

(H10-MW22)

2396.0/1610.0

(H10-MW19)

1077.8/229.0

(H10-MW12)

596.4/94.5

(H10-MW06)

231.6/36.2

(H10-MW07)

4.2/25.3

(H10-MW08)

8608.5/8710.0

(H10-MW16)

47.2/48.1

10

STORMWATER DRAINS THAT ARE DRAINING

GROUND WATER From the upper layer of the surficial aquifer −

LINE OF EQUAL SIMULATED TCE CONCENTRATION In

micrograms per liter. Interval is variable

−

MONITORING WELL LOCATION

(WELL NAME)

SIMULATED/OBSERVED CONCENTRATION In micrograms per liter −

(H10-MW16)

47.2/48.1

(H10-MW17)

16.3/29.5

(H10-MW03)

0.0/3.1

(H10-MW13)

0.0/0.0

(H10-MW05)

0.0/18.5

(H10-MW02)

0.0/1.0

(H10-MW01)

19.8/7.8

(H10-MW10)

0.0/1.0

10,000

10

100

1,000

STORMWATER DRAINS THAT ARE NOT DRAINING GROUND

WATER−From the upper layer of the surficial aquifer

Figure 34. Simulated trichloroethene (TCE) concentrations in layer 1 after 16 years.
38 Fate and Transport Modeling of Selected Chlorinated Organic Compounds at Hangar 1000, 

U.S. Naval Station, Jacksonville, Florida

0 100 FEET

Tarmac

Parking

Hangar

1000

Parking

Yorktown Avenue

(H10-MW15)

272.2/176.4

(H10-MW14)

386.6/424.0 (H10-MW18)

0.4/0.0

(H10-MW22)

1598.8/2046.0

(H10-MW19)

1220.5/190.0

(H10-MW12)

596.4/94.5

(H10-MW06)

1292.8/0.0

(H10-MW07)

1.8/0.0

(H10-MW08)

3779.3/4280.0

(H10-MW16)

29.9/47.4

(H10-MW17)

11.7/42.6

(H10-MW03)

0.0/0.0

(H10-MW13)

0.0/0.0

(H10-MW05)

0.0/19.6

(H10-MW02)

0.0/0.0

(H10-MW01)

21.3/0.0

(H10-MW10)

0.0/0.0

EXPLANATION

STORMWATER DRAINS THAT ARE DRAINING

GROUND WATER From the upper layer of the surficial aquifer −

LINE OF EQUAL SIMULATED DCE CONCENTRATION In

micrograms per liter. Interval is variable

10 −

(H10-MW19)

1220.5/190.0

MONITORING WELL LOCATION

(WELL NAME)

SIMULATED/OBSERVED CONCENTRATION In micrograms per liter −

10

100

1,000

STORMWATER DRAINS THAT ARE NOT DRAINING GROUND

WATER−From the upper layer of the surficial aquifer

Figure 35. Simulated dichloroethene (DCE) concentrations in layer 1 after 14 years.
Fate and Transport Simulations of TCE, DCE, and VC Movement at Hangar 1000 39

0 100 FEET

Tarmac

Parking

Hangar

1000

Parking

Yorktown Avenue

(H10-MW15)

0.6/4.7

(H10-MW14)

0.8/0.0

(H10-MW18)

0.0/0.0

(H10-MW22)

3.6/3.3

(H10-MW19)

2.6/0.0

(H10-MW12)

0.9/0.0

(H10-MW06)

2.7/0.0

(H10-MW07)

0.0/0.0

(H10-MW08)

2.4/0.0

(H10-MW16)

0.0/0.0

(H10-MW17)

0.0/0.0

(H10-MW03)

0.0/1.4

(H10-MW05)

0.0/0.0

(H10-MW02)

0.0/0.0

(H10-MW01)

0.0/0.0

(H10-MW10)

0.0/0.0

EXPLANATION

STORMWATER DRAINS THAT ARE DRAINING

GROUND WATER From the upper layer of the surficial aquifer −

LINE OF EQUAL SIMULATED VC CONCENTRATION In

micrograms per liter. Interval is variable

10 −

MONITORING WELL LOCATION

(WELL NAME)

SIMULATED/OBSERVED CONCENTRATION In micrograms per liter −

(H10-MW19)

2.6/0.0

(H10-MW13)

0.0/15.9

1

10 1

STORMWATER DRAINS THAT ARE NOT DRAINING

GROUND WATER From the upper layer of the surficial aquifer −

Figure 36. Simulated vinyl chloride (VC) concentrations in layer 1 after 12 years.
40 Fate and Transport Modeling of Selected Chlorinated Organic Compounds at Hangar 1000, 

U.S. Naval Station, Jacksonville, Florida

Because the discharge point was close to the source 

(about 450 ft), the model was relatively insensitive to 

dispersivity. Dispersivity has the greatest effect on 

contaminant concentrations when the contamination 

has a long distance to travel and thus has a long period 

to affect the plume.

The first order decay rate for TCE that resulted 

in the best match was 0.0002 d-1. At a similar site at 

OU3 (the contamination was near the water table and 

the site was paved), 10 years of measuring TCE concentrations gave first order decay rates of 0.0007 to 

0.0002 d-1 (U.S. Navy, 1998). The expected range of 

values for TCE is 0.0002 to 0.08 d-1 (U.S. 

Environmental Protection Agency, 1998). At this 

site, the simulated degradation rate of TCE that 

gave the best match was at the slow end of the 

expected range. The calibrated first order decay rate 

was a 0.0002 for DCE and 0.06 d-1 for VC. The 

expected range of values for VC is 0.0006 to 0.08 d-1

(U.S. Environmental Protection Agency, 1998). A 

relatively high decay rate (but still within the expected 

range) for VC was required to match the low concentration values observed at the site. At Cecil Field, 

located about 10 miles west of the Jacksonville Naval 

Air Station, a low TCE decay rate and a high VC 

decay rate also were observed and attributed to the 

mildly oxidizing conditions (Frank Chapelle, 

U.S. Geological Survey written commun., 2002).

Figure 37 shows the simulated TCE distribution 

8 years after the initial release of contamination. As 

shown in figure 37, the TCE plume has moved only 

about one-half of the distance to the storm sewer. 

Predicted Movement of Trichloroethene, 

Dichloroethene, and Vinyl Chloride 

Assuming Source Reduction of 

50 Percent

The effect of the reduction in the concentration 

of contamination at the source was simulated. For 

these simulations, the source was reduced by 

50 percent. Figure 38 shows the simulated distribution 

of TCE 8 years after the source reduction. The 

3,000-μg/L concentration contour near the center 

of the plume represents the last of the higher concentrations of TCE contamination that left the source 

and have traveled about one-half of the distance to the 

storm sewer. For all of the contaminants, the new 

steady-state concentrations were one-half of the 

original concentrations. 

Figures 39 and 40 show the simulated 

distribution of DCE and VC, respectively, 8 years after 

the source reduction. The 2,000-μg/L concentration 

contour (fig. 39) near the center of the plume 

represents the last of the higher concentrations of DCE 

contamination that left the source and have traveled 

about one-half of the distance to the storm sewer.

Predicted Movement of Trichloroethene, 

Dichloroethene, and Vinyl Chloride 

Assuming Source Reduction of 

100 Percent

In these simulations, the reduction in the 

concentration of contamination at the source was 

100 percent. Figures 41- 43 show the simulated 

distributions of TCE, DCE, and VC, respectively, 

8 years after the source was eliminated. As shown in 

these figures, TCE, DCE, and VC are absent from 

ground water in the area where the tanks were located, 

and the remainder of the contaminant plumes have 

moved toward the storm sewer.

Figure 44 shows the simulated distribution of 

TCE 16 years after source elimination. The TCEcontaminated ground water has been flushed almost 

completely from the aquifer. Since TCE was not 

completely removed from the aquifer after 16 years, 

it apparently takes slightly longer for the contaminant 

to be flushed from the aquifer than it did for the initial 

concentrations to reach the storm sewer after the initial 

release. The simulated period of time for the contaminants to be removed from the aquifer once the 

source was removed was about 17 years for TCE, 

15 years for DCE, and 13 years for VC.

Measurement Error and Effect of 

Parameter Variation on Fate and Transport 

Modeling Results

The simulation of future contaminant 

concentration values and the times of arrival at 

the storm sewer are subject to three major sources of 

error. First, the simulated ground-water flow velocities 

may not accurately reflect the actual flow velocities; 

second, the measured concentrations may not fully 

characterize the contaminant concentrations in the 

aquifer; and third, the model input parameters may not 

accurately characterize the transport mechanisms.
Fate and Transport Simulations of TCE, DCE, and VC Movement at Hangar 1000 41

0 100 FEET

Tarmac

Parking

Hangar

1000

Parking

Yorktown Avenue

EXPLANATION

STORMWATER DRAINS THAT ARE DRAINING

GROUND WATER From the upper layer of the surficial aquifer −

LINE OF EQUAL SIMULATED TCE CONCENTRATION In

micrograms per liter. Interval is variable

10 −

10 100

1,000 10,000

STORMWATER DRAINS THAT ARE NOT DRAINING GROUND

WATER−From the upper layer of the surficial aquifer

MONITORING WELL LOCATION

Figure 37. Simulated trichloroethene (TCE) concentrations in layer 1 after 8 years.
42 Fate and Transport Modeling of Selected Chlorinated Organic Compounds at Hangar 1000, 

U.S. Naval Station, Jacksonville, Florida

0 100 FEET

EXPLANATION

Tarmac

Parking

Hangar

1000

Parking

Yorktown Avenue

MONITORING WELL LOCATION

10

3,000

3,000

1,000 100

10

STORMWATER DRAINS THAT ARE NOT DRAINING GROUND

WATER−From the upper layer of the surficial aquifer

STORMWATER DRAINS THAT ARE DRAINING

GROUND WATER From the upper layer of the surficial aquifer −

LINE OF EQUAL SIMULATED TCE CONCENTRATION In

micrograms per liter. Interval is variable

−

Figure 38. Simulated trichloroethene (TCE) concentrations in layer 1 after 8 years assuming 

50 percent source reduction.
Fate and Transport Simulations of TCE, DCE, and VC Movement at Hangar 1000 43

0 100 FEET

Tarmac

Parking

Hangar

1000

Parking

Yorktown Avenue

EXPLANATION

STORMWATER DRAINS THAT ARE DRAINING

GROUND WATER From the upper layer of the surficial aquifer −

LINE OF EQUAL SIMULATED DCE CONCENTRATION In

micrograms per liter. Interval is variable

10 −

100

2,000

1,000

10

STORMWATER DRAINS THAT ARE NOT DRAINING GROUND

WATER−From the upper layer of the surficial aquifer

MONITORING WELL LOCATION

Figure 39. Simulated dichloroethene (DCE) concentrations in layer 1 after 8 years assuming 

50 percent source reduction.
44 Fate and Transport Modeling of Selected Chlorinated Organic Compounds at Hangar 1000, 

U.S. Naval Station, Jacksonville, Florida

0 100 FEET

Tarmac

Parking

Hangar

1000

Parking

Yorktown Avenue

EXPLANATION

LINE OF EQUAL SIMULATED VC CONCENTRATION In

micrograms per liter

1 −

1

4

4

STORMWATER DRAINS THAT ARE DRAINING

GROUND WATER From the upper layer of the surficial aquifer −

STORMWATER DRAINS THAT ARE NOT DRAINING

GROUND WATER From the upper layer of the surficial aquifer −

MONITORING WELL LOCATION

Figure 40. Simulated vinyl chloride (VC) concentrations in layer 1 after 8 years assuming 50 percent 

source reduction.
Fate and Transport Simulations of TCE, DCE, and VC Movement at Hangar 1000 45

0 100 FEET

Tarmac

Parking

Hangar

1000

Parking

Yorktown Avenue

EXPLANATION

LINE OF EQUAL SIMULATED TCE CONCENTRATION In

micrograms per liter. Interval is variable

10 −

10

100 1,000

STORMWATER DRAINS THAT ARE DRAINING

GROUND WATER From the upper layer of the surficial aquifer −

STORMWATER DRAINS THAT ARE NOT DRAINING

GROUND WATER−From the upper layer of the surficial aquifer

MONITORING WELL LOCATION

Figure 41. Simulated trichloroethene (TCE) concentrations in layer 1 after 8 years assuming 

100 percent source reduction.
46 Fate and Transport Modeling of Selected Chlorinated Organic Compounds at Hangar 1000, 

U.S. Naval Station, Jacksonville, Florida

0 100 FEET

Tarmac

Parking

Hangar

1000

Parking

Yorktown Avenue

EXPLANATION

LINE OF EQUAL SIMULATED DCE CONCENTRATION In

micrograms per liter. Interval is variable

10 −

1,000

100

10

STORMWATER DRAINS THAT ARE DRAINING

GROUND WATER From the upper layer of the surficial aquifer −

STORMWATER DRAINS THAT ARE NOT DRAINING

GROUND WATER−From the upper layer of the surficial aquifer

MONITORING WELL LOCATION

Figure 42. Simulated dichloroethene (DCE) concentrations in layer 1 after 8 years assuming 

100 percent source reduction.
Fate and Transport Simulations of TCE, DCE, and VC Movement at Hangar 1000 47

0 100 FEET

Tarmac

Parking

Hangar

1000

Parking

Yorktown Avenue

EXPLANATION

LINE OF EQUAL SIMULATED VC CONCENTRATION In

micrograms per liter

1 −

1

STORMWATER DRAINS THAT ARE DRAINING

GROUND WATER From the upper layer of the surficial aquifer −

STORMWATER DRAINS THAT ARE NOT DRAINING

GROUND WATER From the upper layer of the surficial aquifer −

MONITORING WELL LOCATION

Figure 43. Simulated vinyl chloride (VC) concentrations in layer 1 after 8 years assuming 

100 percent source reduction.
48 Fate and Transport Modeling of Selected Chlorinated Organic Compounds at Hangar 1000, 

U.S. Naval Station, Jacksonville, Florida

0 100 FEET

Tarmac

Parking

Hangar

1000

Parking

Yorktown Avenue

EXPLANATION

LINE OF EQUAL SIMULATED TCE CONCENTRATION In

micrograms per liter. Interval is variable

10 −

100

10

STORMWATER DRAINS THAT ARE DRAINING

GROUND WATER From the upper layer of the surficial aquifer −

STORMWATER DRAINS THAT ARE NOT DRAINING

GROUND WATER−From the upper layer of the surficial aquifer

MONITORING WELL LOCATION

Figure 44. Simulated trichloroethene (TCE) concentrations in layer 1 after 16 years assuming 

100 percent source reduction.
Summary 49

If the actual ground-water velocities are greater 

than the simulated velocities, then the contaminants 

will move to the storm sewer faster than predicted; if 

the simulated velocities are slower, then the contaminants will remain in the aquifer longer and arrive at the 

sewer later than predicted. Ground-water velocity 

probably is the most important factor when predicting 

the traveltime from the source area to the storm sewer.

Simulated contaminant concentrations discharging to the sewer are related directly to initial concentrations at the source. The simulation will underpredict concentrations discharging to the sewer if 

measured concentrations in the source area are 

substantially higher than concentrations sampled from 

the wells. However, the plumes, which were generally 

well-defined laterally and vertically, were characterized using data from several wells, thus making it 

unlikely that higher concentrations existed.

Model parameters such as retardation, 

hydrodynamic dispersion, porosity, and chemical 

degradation have a strong influence on the simulated 

movement and concentration of contaminants. 

Variations in each of the these parameters can affect 

the model-simulated fate and transport of contaminants. As discussed previously, the organic carbon 

content was measured at three locations in the upper 

layer of the surficial aquifer. The organic carbon content was averaged to determine retardation factors 

used in model simulations. With only three samples, 

the actual range of values in the aquifer may not be 

well characterized and could vary from the values 

used. The effect of retardation on contaminant movement is straightforward. If the retardation factor is 

doubled, then the rate of travel of the contaminant is 

halved. Conversely, if the retardation factor is halved, 

then the rate of travel is doubled. For example, simulated concentrations of TCE at a traveltime of 8 years 

are shown in figure 37. If the retardation factor for this 

simulation were doubled, then the TCE would have 

traveled only one quarter of the distance to the storm 

sewer. Conversely, if the retardation factor were halved, 

then the plume would have reached the storm sewer.

Similar to the retardation factor, the effective 

porosity affects the movement of contaminants, but in 

a linear fashion. If the porosity is doubled, then the 

traveltime of the contaminants also is doubled. If the 

porosity is halved, then the traveltime is halved. For 

example, in figure 37, if the porosity for this simulation had been halved, then the contaminant plume 

would have reached the sewer. Conversely, if the 

porosity had been doubled, then the contaminant 

plume would have traveled only one quarter of the 

way to the sewer. Effective porosity is difficult to 

quantify in the field. The value used in this model was 

25 percent, and could reasonably be expected to vary 

from about 12.5 percent up to about 30 percent.

The simulated first order rates of chemical 

degradation were 0.0002, 0.0002, and 0.06 d-1 for 

TCE, DCE, and VC, respectively. Because a similar 

rate of degradation for TCE was documented at a 

similar site nearby (U.S. Navy, 1998), using this rate 

has some justification. The rates for DCE and VC, 

however, are simply model-calibration parameters 

(although they fall within expected values) that 

resulted in the best calibration for the model. If the 

actual rates of degradation are substanially different 

(or if they vary over time), then the simulated concentration values also could vary substantially. In 

addition, the initial concentrations and simulated 

concentrations in the aquifer are correlated, thus 

making a unique prediction more difficult. For 

example, if the initial concentration were too high and 

the first order decay rate too low, then a match to the 

measured values might still be possible. 

SUMMARY

The Jacksonville Naval Air Station occupies 

3,800 acres adjacent to the St. Johns River in 

Jacksonville, Florida. Hangar 1000, in the northcentral part of the Station is an area where aircraft are 

serviced and repaired. Two underground storage tanks 

containing solvents were operated from the late 1960s 

until they were closed in 1994. One tank was a 

750-gallon concrete tank used as a solvent and water 

separator. The other was a 2,000-gallon steel tank that 

received solvent overflow from the first tank, and 

waste oils and solvents discharged from other 

operations at the facility. Both tanks, associated piping 

systems, and visually identified contaminated soils 

were excavated and removed in March 1994. 

However, tests indicated that solvents had previously 

leaked from the tanks into the ground-water system.

Ground-water samples at one of the tank sites 

had levels of trichloroethene (TCE) and dichloroethene (DCE) of 8,710 and 4,280 μg/L, respectively. 

Some of the DCE at the site is from the biodegradation 

of TCE, and all of the vinyl chloride (VC) at the site is 

derived from the biodegradation of DCE. Ground 

water at Hangar 1000 flows toward a storm sewer that 
50 Fate and Transport Modeling of Selected Chlorinated Organic Compounds at Hangar 1000, 

U.S. Naval Station, Jacksonville, Florida

drains ground water from the aquifer. Analyses 

indicate that TCE, DCE, and VC plumes are traveling 

with the ground water and have reached the storm 

sewer. The sewer discharges to a small creek, which 

discharges to the St. Johns River.

A subregional model was calibrated to simulate 

the ground-water flow in the region around Hangar 

1000 using the Modular Three-Dimensional FiniteDifference Ground-Water Flow Model (MODFLOW). 

This model was then used to establish the boundary 

conditions for a site-specific ground-water flow model 

and a fate and transport model using the computer 

code, Reactive Transport in Three Dimensions (RT3D). 

Model results indicate that the ground-water 

flow velocity averaged about 75 ft/yr and it took about 

6 years for the ground water to travel from the tank 

removal site to the storm sewer. Modeling results also 

indicate that the traveltime from the tank removal site 

to the storm sewer is 16, 14, and 12 years for TCE, 

DCE, and VC respectively. TCE has the longest 

traveltime because it has the highest retardation factor 

of 2.5; DCE takes less time with a retardation factor of 

2.0; and VC has the the fastest traveltime because it 

has the lowest retardation factor of 1.7. Modeling 

results indicate that the release of contamination in the 

aquifer occurred more than 16 years ago, and currently 

all three contaminants are at steady-state conditions; 

thus, plume locations and concentrations are not 

changing substantially at this time.

Model-derived dispersivity values for Hangar 

1000 were: longitudinal 1.5 ft, transverse 0.27 ft, and 

vertical 0.27 ft. Because the discharge point was close 

to the source (about 450 ft), the model was relatively 

insensitive to dispersivity. This is because dispersivity 

has the greatest effect on contaminant concentrations 

over long distances. The model-derived first order 

decay rate for TCE at Hangar 1000 was 0.0002 d-1. In 

a previous study at a similar nearby site, first order 

decay rates of 0.0007 to 0.0002 d -1 were determined. 

The calibrated first order decay rate was 0.0002 d-1 for 

DCE and 0.06 d-1 for VC. The expected range of 

values for VC is 0.002 to 0.08 d-1. 

The Navy has begun pilot tests to reduce the 

TCE and DCE concentrations at the tank removal site. 

Source reductions of 50 percent and 100 percent were 

simulated. As expected, reducing the contaminant 

source by 50 percent resulted in TCE, DCE, and VC 

concentrations that were half of their original concentrations. It took about 16 years for new steady-state 

TCE concentrations to develop, about 14 years for 

DCE, and about 12 years for VC. Reducing the source 

area concentrations by 100 percent in the model 

eventually resulted in the total elimination of TCE, 

DCE, and VC in the aquifer. The simulated period of 

time for the contamination to be removed from the 

aquifer once the source was removed was about 

17 years for TCE, 15 years for DCE, and 13 years 

for VC.

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Clement, T.P., 1997, A modular computer code for 

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PNNL-SA-28967

Davis, J.H., 2001, Documentation of three aquifer tests 

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pump-and-treat ground-water remediation 

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