U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 9

Ground-Water Flow in the Surficial Aquifer 

System and Potential Movement of 

Contaminants from Selected WasteDisposal Sites at Naval Station Mayport, 

Florida

Prepared in cooperation with the

Southern Division, 

Naval Facilities Engineering Command,

U.S. Navy

7-4262

By Keith J. Halford

Tallahassee, Florida

1998
U.S. DEPARTMENT OF THE INTERIOR

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY

Thomas J. Casadevall, Acting Director

For additional information write to: Copies of this report can be

purchased from:

U.S. Geological Survey

Branch of Information Services

Box 25286

Federal Center

Denver, CO 80225

The use of firm, trade, and brand names in this report is for identification purposes 

only and does not constitute endorsement by the U.S. Geological Survey.

District Chief

U.S. Geological Survey, WRD

Suite 3015

227 North Bronough Street

Tallahassee, FL 32301
Contents III

CONTENTS

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

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

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

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

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

Geohydrology ........................................................................................................................................................................ 4

Water Budget......................................................................................................................................................................... 5

Recharge ...................................................................................................................................................................... 16

Recharge Estimation by the Chloride Concentration Ratio Method ........................................................................... 17

Simulation of Ground-Water Flow in the Surficial Aquifer System..................................................................................... 18

Description of the Ground-Water Flow Model ........................................................................................................... 19

Hydraulic Characteristics .................................................................................................................................. 19

Tidal Effects and Surface-Water Features......................................................................................................... 25

Boundary Conditions......................................................................................................................................... 31

Model Calibration........................................................................................................................................................ 31

Parameter Estimation......................................................................................................................................... 34

Sensitivity Analysis ........................................................................................................................................... 40

Estimation of the Average Recharge Rate................................................................................................................... 42

Ground-Water Flow during the Calibration Period..................................................................................................... 42

Evolution of Mayport Peninsula and Surficial Aquifer System ............................................................................................ 44

Simulated Displacement of Saline Water.................................................................................................................... 48

Steady-State Displacement with 1996 Recharge Rates..................................................................................... 48

Transient Displacement ..................................................................................................................................... 50

Simulation of Movement of Contaminants ........................................................................................................................... 54

Contributing Areas and Ground-Water Age.......................................................................................................................... 61

Model Limitations ................................................................................................................................................................. 74

Summary................................................................................................................................................................................ 74

References ............................................................................................................................................................................. 77

Appendix A. Well information at NAVSTA Mayport .......................................................................................................... 80

Appendix B. A Simplified Approach to Simulating the Displacement of Saline Pore Water by Freshwater Recharge 

in a Reclaimed Salt Marsh....................................................................................................................................... 85

Appendix C. Time-Variant Hydraulic-Property Package...................................................................................................... 91

Appendix D. Example of Main Program to Use with the Time-Variant Hydraulic-Property Package ................................ 100

FIGURES

1. Map showing location of the study area, runways, dredge material holding areas, golf fairways and greens, 

SWMU-6/7, F-80 aquifer test and selected well sites, and traces of hydrogeologic sections................................. 3

2. Chart showing generalized geologic and geohydrologic units beneath NAVSTA Mayport .................................. 4

3-8. Maps showing:

3. Location of wells in the study area .................................................................................................................. 6

4. Altitude of base of the S-zone.......................................................................................................................... 9

5. Altitude of base of the I-zone .......................................................................................................................... 10

6. Thickness of the marsh-muck confining unit between the S-zone and the I-zone .......................................... 11

7. Average saturated thickness of the S-zone system .......................................................................................... 12

8. Thickness of the I-zone in the surficial aquifer system ................................................................................... 13

9. Generalized geohydrologic sections A-A′ and B-B′ in the study area.................................................................... 14

10. Graph showing annual cumulative rainfall for 1992 through 1996 and ground-water levels at wells 8-5S 

and 8-5I at NAVSTA Mayport during 1996 ........................................................................................................... 15

11. Schematic showing the water budget and its components within the study area.................................................... 16
IV Contents

12. Map showing active model grid.............................................................................................................................. 20

13. Graph showing relation between lateral hydraulic conductivity values estimated by single-well tests and 

multi-well tests........................................................................................................................................................ 23

14. Graph showing empirical and exponential variograms of log hydraulic conductivity in the S-zone 

and the I-zone.......................................................................................................................................................... 24

15-20. Maps showing:

15. Lateral hydraulic conductivity of the S-zone .................................................................................................. 26

16. Lateral hydraulic conductivity of the I-zone ................................................................................................... 27

17. Generalized land surface altitudes in the study area, surface-water observation sites, and vertical tidal

displacement measurement sites ..................................................................................................................... 29

18. Recharge area delineation based on recharge source ...................................................................................... 32

19. Simulated potentiometric surface of the S-zone on July 17, 1995.................................................................. 36

20. Simulated potentiometric surface of the I-zone on July 17, 1995................................................................... 39

21-23. Graphs showing:

21. Simulated and measured water levels for the calibrated model ...................................................................... 40

22. Model sensitivity to independent changes in selected calibration parameters................................................ 41

23. Relation between water levels measured in well 8-5I and effective recharge rate estimates for the 

unirrigated areas .............................................................................................................................................. 42

24. Schematic showing simulated volumetric flow budget for the three calibaration periods on July 17, 1995; 

July 31, 1996; and October 24, 1996 ...................................................................................................................... 43

25-30. Maps showing:

25. Simulated flow paths from areas where recharge occurs at rates greater than 45 in/yr to their 

respective discharge points during period 1.................................................................................... ................ 45

26. Simulated areas of discharge when the surficial aquifer system is recharged at 14 in/yr that are not 

discharge areas when the system is recharged at 6 in/yr................................................................................. 46

27. Areas that contribute recharge to the I-zone when the surficial aquifer system is recharged with the 

distribution from period 1 ............................................................................................................................... 47

28. Particle distributions in the I-zone after 50, 100, 150, and 200 years of travel simulated by the 

steady-state model using the average 1996 flow field .................................................................................... 49

29. Flushing of connate saltwater from the I-zone over a 200-year period simulated by the steady-state 

model using the average 1996 flow field ........................................................................................................ 51

30. Water table in the S-zone at selected times as simulated by the transient model ........................................... 53

31. Graph showing water levels in selected wells simulated by the transient model ................................................... 54

32-36. Maps showing:

32. Particle distributions in the I-zone after 50, 100, 150, and 200 years of travel simulated by the transient 

model from 1798 to 1997 ................................................................................................................................ 55

33. Flushing of connate saltwater from the I-zone over a 200-year period simulated by the transient model

from 1798 to 1997 ........................................................................................................................................... 56

34. Pathlines from selected sites at the water table to their discharge points simulated by the steady-state 

model using the average 1996 flow field ........................................................................................................ 57

35. Effects of variable recharge on the location of contributing points to an observation point .......................... 60

36. Particle traveltimes from the water table to the surface-water discharge point simulated by the 

steady-state model using the average 1996 flow field .................................................................................... 62

37. Schematic showing effects of variable recharge on the location of contributing points to an observation point... 63

38. Schematic showing effects of screen length, depth of screen below the water table, and variable recharge 

rates on the contributing area to an observation well.............................................................................................. 63

39-41. Maps showing:

39. Back-tracked particle paths from selected observation wells to contributing areas simulated by the 

steady-state model using the average 1996 flow field .................................................................................... 65

40. Age of water in the S-zone simulated by the steady-state model using the average 1996 flow field and 

with a uniform effective porosity of 40 percent.............................................................................................. 73

41. Age of water in the I-zone simulated by the steady-state model using the average 1996 flow field with 

a uniform effective porosity of 40 percent ..................................................................................... ................. 75
Contents V

TABLES

1. Annual atmospheric chloride deposition, ground-water chloride concentrations, and recharge estimate 

statistics for NAVSTA Mayport............................................................................................................................. 17

2. Lateral and vertical hydraulic conductivity estimates determined from multi-well aquifer tests .......................... 21

3. Lateral hydraulic conductivity estimates determined from single-well aquifer tests............................................. 22

4. Lateral hydraulic conductivity estimates determined from slug tests .................................................................... 23

5. Amplitude, phase shift, and wavelength of tidal signals in a one-dimensional, confined aquifer with 

different diffusivities driven by a source with a 1-foot amplitude ......................................................................... 30

6. Initial, calibrated, and alternative values of parameters estimated to calibrate the model ..................................... 34

7. Water-level error statistics by layer and synoptic-survey period from calibrated Mayport model results............. 35

8. Correlation coefficients between parameters from the calibrated model ............................................................... 40

9. Simulated recharge, irrigation, and discharge rates applied to the transient model of NAVSTA Mayport, 

1798 to 1997 ........................................................................................................................................................... 52

10. Approximate traveltimes of particle movement from selected sites to their respective discharge points as 

simulated by the steady-state model using the average 1996 flow field ................................................................ 61

11. Approximate length of contributing area, time period sampled, traveltimes from the top, midpoint, and 

bottom of the wetted screen estimated with the steady-state model using the average 1996 flow field, and 

the traveltime from the midpoint of the wetted screen estimated with the transient model................................... 68

VERTICAL DATUM AND TRANSMISSIVITY

Sea level: In this report, “sea level” refers to the National Geodetic Vertical Datum of 1929 (NGVD

of 1929)—a geodetic datum derived from a general adjustment of the first-order level nets of both

the United States and Canada, formerly called Sea Level Datum of 1929.

Transmissivity: The standard unit for transmissivity is cubic foot per day per square foot times foot

of aquifer thickness [(ft3

/d)/ft2]ft. In this report, the mathematically reduced form, foot squared per

day (ft2

/d), is used for convenience.
Abstract 1

Ground-Water Flow in the Surficial Aquifer System and 

Potential Movement of Contaminants from Selected 

Waste-Disposal Sites at Naval Station Mayport, Florida

By Keith J. Halford

Abstract

Ground-water flow through the surficial 

aquifer system at Naval Station Mayport near 

Jacksonville, Florida, was simulated with a 

two-layer finite-difference model as part of an 

investigation conducted by the U.S. Geological 

Survey. The model was calibrated to 229 

water-level measurements from 181 wells during 

three synoptic surveys (July 17, 1995; July 31, 

1996; and October 24, 1996). A quantifiable 

understanding of ground-water flow through the 

surficial aquifer was needed to evaluate 

remedial-action alternatives under consideration 

by the Naval Station Mayport to control the 

possible movement of contaminants from sites on 

the station. 

Multi-well aquifer tests, single-well tests, and 

slug tests were conducted to estimate the hydraulic 

properties of the surficial aquifer system, which 

was divided into three geohydrologic units—an 

S-zone and an I-zone separated by a marsh-muck 

confining unit. The recharge rate was estimated to 

range from 4 to 15 inches per year (95 percent 

confidence limits), based on a chloride-ratio 

method. Most of the simulations following model 

calibration were based on a recharge rate of 

8 inches per year to unirrigated pervious areas. 

The advective displacement of saline pore 

water during the last 200 years was simulated 

using a particle-tracking routine, MODPATH, 

applied to calibrated steady-state and transient 

models of the Mayport peninsula. The surficial 

aquifer system at Naval Station Mayport has been 

modified greatly by natural and anthropogenic 

forces so that the freshwater flow system is 

expanding and saltwater is being flushed from the 

system. A new MODFLOW package (VAR1) was 

written to simulate the temporal variation of 

hydraulic properties caused by construction activities at Naval Station Mayport. The transiently 

simulated saltwater distribution after 200 years of 

displacement described the chloride distribution in 

the I-zone (determined from measurements made 

during 1993 and 1996) better than the steady-state 

simulation. 

The advective movement of contaminants 

from selected sites within the solid waste management units to discharge points was simulated using 

MODPATH. Most of the particles were discharged 

to the nearest surface-water feature after traveling 

less than 1,000 feet in the ground-water system. 

Most areas within 1,000 feet of a surface-water 

feature or storm sewer had traveltimes of less than 

50 years, based on an effective porosity of 40 

percent.

Contributing areas, traveltimes, and pathlines 

were identified for 224 wells at Naval Station 

Mayport under steady-state and transient conditions by back-tracking a particle from the midpoint 

of the wetted screen of each well. Traveltimes to 

contributing areas that ranged between 15 and 

50 years, estimated by the steady-state model, 

differed most from the transient traveltime 

estimates. Estimates of traveltimes and pathlines 

based on steady-state model results typically were 

10 to 20 years more and about twice as long as 

corresponding estimates from the transient model. 
2 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected Waste-Disposal 

Sites at Naval Station Mayport, Florida

The models differed because the steady-state 

model simulated 1996 conditions when Naval 

Station Mayport had more impervious surfaces 

than at any earlier time. The expansion of the 

impervious surfaces increased the average 

distance between contributing areas and 

observation wells. 

INTRODUCTION

Inorganic and organic priority contaminants 

defined by the U.S. Environmental Protection Agency 

(USEPA, 1988) have been detected in surface water, 

sediment, and ground-water samples collected near 

abandoned waste-disposal sites at Naval Station 

(NAVSTA) Mayport. Concern exists that such contaminants may move with the underlying ground water 

into the base drainage, St. Johns River, and surrounding salt marshes. As part of the Installation Restoration 

Program, NAVSTA Mayport is considering 

remedial-action alternatives to control the movement 

of contaminants from those sites that may otherwise 

discharge to the surface. This effort requires a quantifiable understanding of the response of ground-water 

flow to current conditions and to any future stresses 

imposed on the surficial aquifer system. Numerical 

simulation provides the most tractable way of 

achieving this level of understanding. 

NAVSTA Mayport, located in northeast Duval 

County, Florida (fig. 1), provides all necessary support 

services for the surface fleet and aircraft stationed at or 

visiting Mayport. Industrial operations conducted at 

NAVSTA Mayport involve intermediate level maintenance for both ships and aircraft, and vehicle maintenance and repair. Any maintenance activities that can 

be conducted without putting a ship into dry-dock are 

considered intermediate (U.S. Department of the 

Navy, 1995). Wastes generated and disposed of at the 

station include waste oils, fuels, lubricants, solvents, 

paints, and general refuse associated with ship, 

aircraft, vehicle, and building maintenance activities 

(U.S. Department of the Navy, 1995). From 1942 to 

1979, all wastes were disposed of in landfills on the 

station or wastes were burned at the site to reduce their 

volume. From 1979 to 1994, all burnable wastes were 

incinerated in a carbonaceous fuel boiler. From 1979 

to 1985, the residual ash from the boiler, along with 

unburned debris, construction rubble, and large scrap 

materials were placed in onsite landfills (U.S. Department of the Navy, 1995). 

The dissolved and degraded constituents of 

fuels, lubricants, and solvents (benzene, dichlorobenzene, toluene, acetone, napthalene, and trichloroethene) are the primary contaminants that may be 

transported by ground water at NAVSTA Mayport. 

The movement of these dissolved constituents is 

similar to the advective flow of the ground water, as 

the solubility of these contaminants is usually low and 

the concentrations are not great enough to significantly alter the density of the ground water. These 

dissolved constituents sorb to the porous media of 

aquifers and confining units, which retards the rate of 

travel, but does not alter the direction of travel.

Purpose and Scope

The purpose of this report is to present the 

results of a study to analyze and quantify 

ground-water flow in the surficial aquifer system at 

NAVSTA Mayport (fig. 1) and describe the advective 

potential for the movement of ground-water contaminants. This report includes ground-water-level data, a 

description of the geohydrologic framework, an 

estimate of the water budget, and an estimate of the 

ground-water discharge to surface-water features. 

Model simulations were used to evaluate the hydrologic feasibility of several alternative approaches to 

site remediation. Simulation results are based on a 

calibrated, three-dimensional finite-difference, 

ground-water flow model of the NAVSTA Mayport 

area. A transient model was developed to simulate the 

expansion of the freshwater aquifer beneath the 

Mayport peninsula over the last 200 years. Estimates 

of ground-water movement from existing and 

potential sites of contamination to their discharge 

points were determined using particle tracking 

(Pollock, 1994). The contributing areas for 224 observation wells were identified by back-tracking particles 

from the wetted well screens. Results of 

cross-sectional model simulations are presented to 

support the locations of lateral model boundaries and 

the application of a uniform-density based analysis to 

the solution of a variable-density flow problem. 

Description of the Study Area

The study area is in northeastern Duval County 

at the mouth of the St. Johns River (fig. 1). Soils in the 

3.5 square miles (mi2) of non-marsh areas are fine 

sands with occurrences of shell or rock fragments 

(Stem and others, 1978). Most of the non-marsh areas
Introduction 3 Figure 1. Map showing location of the study area, runways, dredge material holding areas, golf fairways and greens, SW

selected well sites, and traces of hydrogeologic sections shown in figure 9.

0 2,500 

0 

Sherman

81° 26′ 

DREDGE 

HOLDING

RUNWAY

MATERIAL

 AREAS

HANGARS

Fairw

Fairways

M

a

i

n

e

St

.

Moale Ave.

Patrol Rd.

Patrol Rd.

Alpha Pier

Charlie Pier

Delta

Pier

Bravo

Pier

Echo

Pier

Foxtrot Pier

Bon Homme Richard

Chicopit Bay

M

Creek

30° 24′

30° 23′

FLORIDA

STUDY

AREA

ST. JOHNS RIVER

ST

TOWN OF

MAYPORT

STUDY

AREA

SWMU-6/7

TURNING

BASIN

8-5S,I

20-2S

B

W

W

B

A 

EXPLANATION

8-5S,I WELL AND

WELL NUMBER Bailey Ave.

A1A
4 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected Waste-Disposal 

Sites at Naval Station Mayport, Florida

are covered with deposits of dredge material except for 

the town of Mayport, the area between Alpha-Delta 

piers and Maine St., and the southeastern part of the 

study area (fig. 1). Topographic relief is minimal and 

land-surface slopes generally are 0 to 5 percent (Stem 

and others, 1978). The soils are typically well drained 

and require supplemental irrigation to grow lawn 

grasses and ornamental plants (Stem and others, 1978). 

The climate of Duval County is humid and 

subtropical. Average precipitation over the study area 

is about 52 inches per year (in/yr) with more than half 

falling from June to September (Owenby and Ezell, 

1992). The yearly potential evaporation rate from the 

study area has been estimated to be 48 inches (in.) 

(Farnsworth and others, 1982, map 3). The average 

yearly temperature is 79 °F (Owenby and Ezell, 1992). 

The geology and hydrology of the study area 

have been described in numerous reports as summarized in Spechler (1994), but most reports describe 

features at a county-wide scale and focus primarily on 

the Upper Floridan aquifer. Causey and Phelps (1978) 

described the extent and availability of water from the 

shallow-aquifer system in Duval County. The results 

of an aquifer test in the surficial aquifer system 

beneath NAVSTA Mayport are reported by Franks 

(1980). In addition to reporting the hydraulic characteristics, Franks (1980) describes the lithology to a 

depth of 100 feet (ft) below land surface near site F-80 

shown in figure 1. 

Acknowledgments

The author extends his appreciation to David 

Driggers, Southern Division Naval Facilities 

Engineering Command; Cheryl Mitchell, Staff Civil 

Engineering NAVSTA Mayport; Frank Lesene, ABB 

Environmental Services; and Larry Smith, ABB 

Environmental Services, for assistance provided 

during this study. 

GEOHYDROLOGY

The geologic units of interest in the study area 

include sediments of Holocene to Miocene age that 

extend from land surface to the top of the Hawthorn 

Group about 50 ft below land surface (fig. 2). Previous 

investigators have defined this sequence as the surficial 

aquifer system (Spechler, 1994). The surficial aquifer 

system consists of fine-grained sands near the surface 

interspersed with thin (less than 1 ft) clay lenses and 

generally grades to a mixture of sand and coarse shell 

fragments from 30 to 50 ft below land surface (Franks, 

1980). The base of the surficial aquifer system is the 

intermediate confining unit which, in the vicinity of 

NAVSTA Mayport, is a sequence of marine clays and 

discontinuous limestone stringers (Spechler, 1994). 

Thickness of the confining unit varies but averages about 

350 ft. 

Because this study is concerned with 

ground-water movement near land surface, the 

surficial aquifer system was further subdivided into 

three local geohydrologic units: the S-zone, the 

marsh-muck confining unit, and the I-zone (fig. 2). 

The S-zone consists of fine to medium sand with intermittent shell layers and clay lenses that are less than 

Series Formation Lithology

Geohydrologic unit

Model

Spechler layer

(1994) This report

Holocene 

to Upper

Miocene

Undiffer

entiated

 surficial 

deposits

Discontinuous sand, clay, 

and shell beds

Surficial 

aquifer 

system

S-zone 1

Marsh-muck confining 

unit --

I-zone 2

Miocene Hawthorn

Group

Clay and interbedded 

phosphatic sands

Intermediate

confining unit --

Figure 2. Generalized geologic and geohydrologic units beneath NAVSTA Mayport. (Modified from Spechler, 

1994.)
Water Budget 5

1 ft thick. The composition of the marsh-muck confining unit ranges from silty clays to dense, plastic clays 

and commonly includes a large fraction of organic 

material. The I-zone generally consists of well sorted 

sand and coarse shell fragments. 

The S-zone consists mostly of dredge material 

and is more heterogeneous than the other two geohydrologic units. The distribution of clay, silt, sand, and 

shell deposited by dredging operations is generally 

more variable than the distribution of these materials 

by natural accretion. Most of NAVSTA Mayport is 

covered with at least 5 ft of dredge material. More than 

30 ft of material is deposited in the dredge-material 

holding areas (U.S. Department of the Navy, 1995). 

The geohydrologic framework within the study 

area was defined by mapping the base of the S-zone 

and the I-zone and the thickness of the marsh-muck 

confining unit. The depths of the two bases and the 

thickness of the confining unit were estimated from 

geologists’ logs recorded for the more than 200 wells 

(fig. 3 and app. A) drilled as part of a remedial investigation (U.S. Department of the Navy, 1995). Control 

points were of sufficient areal density to permit 

estimates of the altitudes of the bases and the thickness 

of the marsh-muck confining unit by interpolation. 

Altitudes and thicknesses beneath the town of 

Mayport, in the marsh areas, and south of Lake 

Wonder Wood were extrapolated (figs. 4-6). The base 

of the S-zone usually is the contact between the buried 

saltmarsh areas and dredge material across much of 

the study area west of Maine St. (fig. 1) and typically 

is within 5 ft of sea level (fig. 4). The altitude of the 

base of the I-zone ranges from about 30 ft below sea 

level along the western edge of the study area to about 

60 ft below sea level towards the center of the study 

area (fig. 5). The saturated thickness of the S-zone was 

estimated by subtracting the altitude of the base of the 

S-zone from the altitude of the average water table 

(fig. 7). The S-zone ranges from less than 5 ft in 

thickness between the southern Patrol Road and the 

runway to more than 20 ft in thickness near Lake 

Wonder Wood. The thickness of the I-zone was 

estimated by subtracting the altitude of the base of the 

I-zone and the thickness of the marsh-muck confining 

unit from the altitude of the base of the S-zone (fig. 8). 

The I-zone (fig. 8) is thickest between Patrol Road and 

the eastern dredge material holding area (fig. 1) and is 

thinnest near Lake Wonder Wood (fig. 1). 

The marsh-muck confining unit is a significant 

geohydrologic feature that greatly retards the vertical 

movement of ground water where present (fig. 6). This 

unit is thickest beneath the southwestern runway. The 

marsh-muck confining unit occurs beneath most of 

NAVSTA Mayport (fig. 6) except in areas along the St. 

Johns River between the town of Mayport and Charlie 

pier, between Alpha-Delta piers and Moale Ave., and 

along the Atlantic Ocean (fig. 1). In addition to the 

controls shown, a geologist’s log indicated that the 

marsh-muck confining unit was absent along the 

Atlantic Ocean about 1,000 ft south of the study area 

(Brown and others, 1984). The confining unit was 

assumed to be absent if less than 1 ft of clayey material 

was reported in the geologist’s log (fig. 6). 

Compositing the S-zone, the marsh-muck 

confining unit, and the I-zone thicknesses (figs. 6-8) 

defines a geohydrologic framework which forms the 

structure of the ground-water flow system. Flow path 

directions and rates are influenced by variations in the 

unit thicknesses and lateral extent of the geohydrologic 

units. The variations in thickness and altitude of the 

three geohydrologic units in the surficial aquifer system 

are shown in section in figure 9. 

WATER BUDGET 

The rate of ground-water movement and solute 

transport through the surficial aquifer system is 

governed largely by aquifer recharge. A water budget 

details the total amount of water available within the 

study area and can be used to constrain recharge rates 

estimated during model calibration. A water budget for 

the study area can be described by the following 

equation: 

 , (1)

where

P is precipitation, in inches per year;

I is irrigation, in inches per year;

D is deep leakage from the Upper Floridan aquifer 

to the surficial aquifer system, in inches per 

year; 

Q is stream discharge, in inches per year, which is 

composed of 

QS surface runoff, in inches per year, and; 

QB base flow, in inches per year;

ET is evapotranspiration, in inches per year, and; 

∆S is change in storage, in inches per year, and is 

assumed to be negligible over the long term. 

PIDQ + + – – ET = ∆S ≅ 0
Sites at Naval Station Mayport, Florida

6 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected WasteDisposal Figure 3. Location of wells in the study area (U.S. Department of the Navy, 1995). 0 2,500 

0 

Sherman

81° 26′ 

DREDGE 

HOLDING

RUNWAY

MATERIAL

 AREAS

HANGARS

Fairwa

Fairways

A1A

Maine St.

Moale Ave.

Patrol Rd.

Patrol Rd.

Alpha Pier

Charlie Pier

Delta Pier

Bravo Pier

Echo Pier

Foxtrot Pier

Bailey Ave.

Chicopit Bay

Mas

L

Wo

W

Creek

30° 24′

30° 23′

STUDY

TURNING

BASIN

S

T

AREA

INSET B

INSET A

2-36S,I

15-P4

2-37S,I

2-35S,I

2-4S

2-3S

2-25S,I

2-26S,I 2-12S,I

2-11S,I

2-24S

2-P1

2-P9

2-P10

2-P11

2-P12

2-7S

2-P8

2-28S

2-27I

2-P7

B-1S,I

11-1S

11-2S

2-P2

2-17S,I

2-32S,I

2-29S

2-31S,I

2-P4

2-P3

EXPLANATION

WELL AND WELL NUMBER 2-P3

Bon Homme Richard
Water Budget 7

Figure 3. Inset A

0 1,000 2,000 FEET

0 500 METERS

81° 25′30′′ 81° 25′

30° 24′

30° 23′30′′

8-19S

8-17S

8-4S 8-3S

8-18S 8-2S

8-6S

8-1S

8-5S,I 8-P5

8-P1

8-P4

8-P6

10-P1

8-16S 8-11S

8-7S 8-8S

8-15S,I

8-14S

8-13S,I

8-12S

9-1S

9-2S 9-3S 16-2S

16-3S

8-9S

15-P1

28-1S

16-1I

16-4S 8-P3

8-P2

15-P2

15-5S,I

15-1S

15-3S

15-2S

2-38S,I 15-P3

2-34S,I

2-33S,I

2-30S

1406-8 1406-11

1406-7

13-P1

13-P6

2-P5

1406-23I

1406-17

13-8S

13-6S

13-1S

13-10S

13-5S

56-1S

13-2S 13-P4

13-4S

13-P5 13-3S

22-2S 26-1S

26-2S

2-18S,I 22-1S 26-4S

26-3S

2-9S,I 2-13S 2-10S

2-6S

2-19S

2-8S

2-15S,I 2-P6

2-21S

2-P13

2-2S

2-23S,I

2-16S

2-22S,I

2-20S

EXPLANATION 2-P13 WELL AND WELL NUMBER
Sites at Naval Station Mayport, Florida

8 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected WasteDisposal Figure 3. Inset B 0 1,000 

0 

81° 24′30′′ 81° 24′ 30° 23′45′′ 30° 23′30′′ TC-1I TC-2S TC-3S TC-4S TC-5S TC-6S 20-1S 20-2S 20-3S 21-1S 21-2S 21-3S 52-1S 17-2S 17-3S 17-1S 17-P1 17-P2 1406-15 1406-13 1406-2 CU-6S CU-5S CU-4S CU-8I CU-3S CU-2S 1-P2BQ-6S BQ-4S BQ-2S BQ-5S BQ-3S BE-2S BE-8I BE-3S BE-1S BE-7S 45-1S,I 44-1S,I 44-2S 1-1S,I 23-5S,I 45-2S 44-3S 23-6S 23-4S 1-P3 1-2S 23-7S 23-3S 24-1S 23-1S 23-2S 14-P1 

14

BE-5S 

1

Baseball Fields EXPLANATION 1406-15 WELL AND WELL NUMBER
Water Budget 9 Figure 4. Altitude of base of the S-zone (layer 1). 0 2,50

0 

Sherman

81° 26′ 

DREDGE 

HOLDING

RUNWAY

MATERIAL

 AREAS

HANGARS

Fairw

Fairways

A1A

Maine St.

Moale Ave.

Patrol Rd.

Patrol Rd.

Alpha Pier

Charlie Pier

Delta Pier

Bravo Pier

Echo Pier

Foxtrot Pier

Bailey Ave.

Bon Homme Richard

Chicopit Bay

Ma

W

W

Creek

30° 24′

30° 23′

EXPLANATION

SUBSURFACE CONTOUR--Shows approximate altitude of base of S-zone. Hachures indicate depression. Contour interval 5 feet. Datum is sea level CONTROL POINT-- Number is altitude, in feet

-3

-5 -4

-7

-4

-1

-5

-4 -2

-1

0 -2

1

-2

-2

3

5

0

1

2

-2

-8

0

-3

-6

-15

0

-1

-2

0 0

-4 -1

-1

-2

-2

-3

-1

-2

3

1

1

-3

-2 -2

-3

-1

-2

-2

-2

-5 -4

-3

-3

-5

0

-21

-22

-17

-

2

2 3

3

-1

1 1

-10

0

0

-5

0

0

-15

-20

TU

RNING

BASIN

ST. J

-4

-5

-10

-5

-5 -5

0

-5

-15

-15
Sites at Naval Station Mayport, Florida

10 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected WasteDisposal 0 2,5

0 

Sherman

81° 26′ 

DREDGE 

HOLDING

RUNWAY

MATERIAL

 AREAS

HANGARS

Fairw

Fairways

A1A

Maine St.

Moale Ave.

Patrol Rd.

Patrol Rd.

Alpha Pier

Charlie Pier

Delta Pier

Bravo Pier

Echo Pier

Foxtrot Pier

Bailey Ave.

Bon Homme Richard

Chicopit Bay

M

W

C

reek

30° 24′

30° 23′

STUDY

TURNING

BASIN

S

T

AREA

EXPLANATION

SUBSURFACE CONTOUR--Shows approximate altitude of base of I-zone. Hachures indicate depression. Contour interval 10 feet. Datum is sea levelCONTROL POINT-- Number is altitude, in feet

-42

-4

-48

-38

-41

-42

-42

-57 -48

-22

-24

-44

-62

-60

-50

-50

-40

-40

-30

-40

-50

Figure 5. Altitude of base of the I-zone (layer 2).
Water Budget 11 Figure 6. Thickness of the marsh-muck confining unit between the S-zone and the I-zone (between layers 1 and 2). 0 2

0 

Sherman

81° 26′ 

DREDGE 

HOLDING

MATERIAL

 AREAS

A1A

Chicopit Bay

Creek

30° 24′

30° 23′

STUDY

TURNING

BASIN

S

AREA

EXPLANATION

AREA WHERE MARSH-MUCK CONFINING UNIT GREATER THAN 1 FEET LINE OF EQUAL THICKNESS --Interval varies, in feetCONTROL POINT--Value in feet

4

5

5

5

4

2

6

2

3

0

15

10

1

12

2

0

5

10

10

2

5

2

2

1

1

4 7

8

5

3

12 4

1

2

3

5

5

5

7

5

0

0

1

0

3

0

1

0

0

0

0

0

0

0

0

0

1

0

0

0

2

2

1

4

4

8

8 

4

1

2

1

2

4

4

4

4

2

2

12

2

8
Sites at Naval Station Mayport, Florida

12 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected WasteDisposal Figure 7. Average saturated thickness of the S-zone (layer 1) system. 0 2,50

0 

Sherman

81° 26′ 

DREDGE 

HOLDING

RUNWAY

MATERIAL

 AREAS

HANGARS

Fairw

Fairways

A1A

Maine St.

Moale Ave.

Patrol Rd.

Patrol Rd.

Alpha Pier

Charlie Pier

Delta Pier

Bravo Pier

Echo Pier

Foxtrot Pier

Bailey Ave.

Bon Homme Richard

Chicopit Bay

Ma

W

W

Cr

eek

30° 24′

30° 23′

STUDY

TURNING

BASIN

ST

AREA

EXPLANATION

LINE OF EQUAL SATURATED THICKNESS OF THE S-ZONE-- Contour interval 5 feet 

15

5 10

10

5

20

10

2

0

15

10

10

5

10

5

5

10

5

10

-5
Water Budget 13 0 2,50

0 

Sherman

81°26′ 

DREDGE 

HOLDING

RUNWAY

MATERIAL

 AREAS

HANGARS

Fairw

Fairways

A1A

M

a

i

n

e

St

.

Moale Ave.

Patrol Rd.

Patrol Rd.

Alpha Pier

Charlie Pier

Delta

Pier

Bravo

Pier

Echo 

Pier

Foxtrot Pier

Bailey Ave.

Bon Homme Richard

Chicopit Bay

Ma

L

Wo

W

Creek

30°24′

30°23 ′

STUDY

TURNING

BASIN

ST

AREA

50

40 30

20

30

20

30

40

40

50

20

10

EXPLANATION

LINE OF EQUAL THICKNESS

Contour interval 10 feet

30 OF THE I-ZONE--

Figure 8. Thickness of the I-zone (model layer 2) in the surficial aquifer system.
Sites at Naval Station Mayport, Florida

14 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected WasteDisposal Figure 9. Generalized geohydrologic sections A-A′ and B-B′ in the study area. (Traces shown in Fig. 24). VERTICAL EXAGG

0 0 

25SEA LEVEL 255075 

25 SEA LEVEL25507525 SEA LEVEL255075 LAND S-ZONE (1)

B

B St. Johns

TURNING

BASIN

WATER 

A

LAND SURFACE WATER TABLE

Dredge Material

I-ZONE (2)

S-ZONE (1)

I-ZONE (2)

River

Sherman

Creek

RUNWAY

RUNWAY

MARSH MUCK

MARSH MUCK

St. Johns

River

Holding Area SURFACE TABLE

FEET

FEET

INTERMEDIATE CONFINING UNIT

INTERMEDIATE CONFINING UNIT

S

U

RFICIAL A

Q

UIFER

S

Y

S

TEM

S

U

A

Q

S

Y

B-B

A-A
Water Budget 15

Precipitation, irrigation, and deep leakage add 

water to the budget of the study area. Precipitation is 

the dominant and most variable source of water. The 

long-term average precipitation rate is about 51 in/yr 

(Owenby and Ezell, 1992). The average annual precipitation between 1992 and 1996 was 56 in/yr but the 

extremes during that same 5-year period ranged from 

44 in. in 1996 to 68 in. in 1995 (fig. 10). The application of irrigation water pumped from the Upper 

Floridan aquifer and the public utility adds about 

5 in/yr, in total, to the study area, but because of the 

localized nature of irrigation, application rates at 

individual sites are considerably higher than the 

average rate. Most of the irrigation in the study area is 

applied to the fairways and greens of the golf course 

(fig. 1) at rates between 150 and 300 in/yr. Other areas 

of intensive irrigation include the baseball fields, 

ornamental plants around most of the buildings 

constructed after 1980, and landscaped areas along 

Masset Ave. and Baltimore St. Deep leakage previFigure 10. Annual cumulative rainfall for 1992 through 1996 and ground-water levels at wells 8-5S and 

8-5I at NAVSTA Mayport during 1996.

JFMAMJJASOND

WATER LEVEL, IN FEET

ABOVE SEA LEVEL

0

70

10

20

30

40

50

60

1992

1993

1994

1995

1996

14

4

6

8

10

12

8-5S

8-5I

2

1996

CUMULATIVE RAINFALL,

IN INCHES

ously was estimated to be less than 0.5 in/yr (Krause 

and Randolph, 1989) and, for the purposes of this study, 

is not a significant component of the water budget. 

Stream discharge and evapotranspiration remove 

water from the budget of the study area and are difficult 

to quantify at NAVSTA Mayport. Stream discharge 

generated within the study area cannot be measured 

directly because it is a very small component of the total 

surface-water movement. The evapotranspiration 

estimate typically is the residual that remains after 

summing all other components of the water budget and 

balances the budget. This approach assumes the other 

components are measurable. Micrometeorological 

methods provide a method of independently measuring 

evapotranspiration but are minimally accurate (only 

within about 10 percent of actual rates; Bidlake and 

others, 1993; Sumner, 1996). Pumpage is another 

typical discharge component of a ground-water budget 

but was not considered because none of the supply 
16 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected Waste-Disposal 

Sites at Naval Station Mayport, Florida

wells in the study area extract water from the surficial 

aquifer system (U.S. Department of the Navy, 1995).

Measurement of stream discharge generated 

within the study area is obscured by discharge from 

the entire St. Johns River Basin (8,850 mi2

) passing 

through the study area (4 mi2). In addition, tidal 

forcing generates large peak positive discharges in the 

St. Johns River that typically range from 100,000 to 

140,000 cubic feet per second (ft3

/s) at Jacksonville 

Station 02246500 compared to an average discharge of 

about 6,100 ft3

/s (U.S. Geological Survey, 1996). 

Surface-water movement in Chicopit Bay, Sherman 

Creek, and the unnamed canals that drain Lake 

Wonder Wood and the golf course area along Patrol 

Road also is predominately influenced by tidal effects. 

Although stream discharge generated within the 

study area cannot be measured directly, it can be 

extrapolated from a nearby basin. The average annual 

stream discharge from the study area can be approximated by the stream discharge from Pablo Creek at 

Jacksonville 02246828 which averaged about 19 in/yr 

between 1974 and 1996 (U.S. Geological Survey, 

1996). The drainage area of Pablo Creek is 26 mi2

 and 

is about 5 miles (mi.) south of NAVSTA Mayport. The 

topography, land use, and climate of the Pablo Creek 

drainage are similar to those in the study area. 

Figure 11. The water budget and its components within the study area.

I = 5 in/yr

ET = 37 in/yr

QS

Q = 19 in/yr

EXPLANATION

P PRECIPITATION

I IRRIGATION

ET EVAPOTRANSPIRATION

N RECHARGE

QS SURFACE RUNOFF

Q STREAM DISCHARGE

QB BASE FLOW

D DEEP LEAKAGE

D < 0.5 in/yr

P = 51 in/yr

N

SURFICIAL

SYSTEM

AQUIFER

INTERMEDIATE CONFINING UNIT

QB

If stream discharge is generated from the study area at 

a rate of 19 in/yr, then the annual mean stream 

discharge would be about 6 ft3/s. This is about 0.1 

percent of the annual mean stream discharge and about 

0.004 percent of the typical peak discharge of the St. 

Johns River. Assuming that stream discharge is 19 

in/yr, evapotranspiration from the study area would 

then be 37 in/yr to balance the water budget. 

Recharge 

Recharge (N) is the subcomponent of the water 

budget that drives ground-water flow through the 

surficial aquifer system (fig. 11) and can be defined 

as: or . The 

surficial aquifer system is recharged when applied 

water exceeds evapotranspirative losses and 

overcomes capillary effects in the unsaturated zone. 

Surface runoff (QS) occurs when the infiltration 

capacity of the soil is exceeded and additional precipitation or applied irrigation water drains directly to 

local streams or depressions without infiltrating the 

subsurface (fig. 11). Of the water that crosses the 

water table, recharge (N) is the fraction that is not 

immediately extracted by evapotranspiration and 

moves downgradient. Discharge from the surficial 

N P ET – QS = – N QQS = – + D
Water Budget 17

aquifer system occurs as either evapotranspiration or 

stream discharge (fig. 11). 

Recharge is practically impossible to measure 

directly or correlate to a measurable parameter, such as 

precipitation or stream discharge, owing to the 

complexity of interactions between evapotranspiration, the unsaturated zone, precipitation, surface 

runoff, and stream discharge. Recharge events that 

correspond with periods of intense rainfall (more than 

4 in. over a 2- to 3-day period) are easily discernible 

by water-level responses in either the S-zone or I-zone 

of the surficial aquifer system (fig. 10). Effects from 

the majority of rainfall events are not as clearly 

reflected in the ground-water hydrographs, if at all 

(fig. 10). 

Recharge usually is indirectly estimated as a 

calibration parameter in a ground-water flow model 

because of the complexity and interdependence of the 

controlling processes. Recharge rates have been 

estimated in this manner at NAS Jacksonville and 

NAS Cecil Field, about 15 and 35 mi west of 

NAVSTA Mayport, respectively. Recharge rates at 

NAS Jacksonville and NAS Cecil Field were 

estimated to be 7 in/yr (Davis and others, 1996) and 

6 in/yr (Halford, 1998), respectively. Both of these 

estimates probably are biased below the actual 

recharge rates because differentially higher rates of 

riparian evapotranspiration were neglected in both 

studies. 

Recharge Estimation by the Chloride 

Concentration Ratio Method

Recharge rates can be estimated by comparing 

the atmospherically deposited chloride concentration 

to the ground-water chloride concentration (Krulikas 

and Giese, 1995): 

, (2)

where 

Clatmos is the concentration of the atmospherically 

deposited chloride, in milligrams per liter, 

which is the mass of chloride deposited by 

dry fall and wet fall divided by the precipitation during the collection period; 

ClGW is the concentration of the chloride in ground 

water, in milligrams per liter; and 

P-QS is precipitation minus surface runoff, in 

inches per year. 

The chloride concentration ratio method 

assumes that chloride is a conservative constituent, the 

N

Clatmos

ClGW

-----------------     P QS = ( ) –

ground-water samples are from a recharge zone, the 

chloride concentration of the surface runoff is the same 

as in the water that infiltrates the ground, and the 

chloride concentration increase from Clatmos to ClGW is 

due to evapotranspiration alone, not a mineral fraction 

or connate water. Most of these assumptions are not 

overly restrictive and are met by the conditions at 

NAVSTA Mayport. 

Conceptually, the chloride concentration ratio 

method is straightforward, but it is complicated by the 

spatial and temporal variability of the chloride concentration measurements. The concentration of atmospherically deposited chloride is not spatially uniform and can 

exhibit a high degree of annual variability (table 1), 

especially in a coastal setting. For example, the average 

atmospheric chloride concentration at National 

Atmospheric Deposition Program (NADP) station 

100380 (located at the Kennedy Space Center, fig. 1) 

was 2.2 milligrams per liter (mg/L) between 1985 and 

1994. However, the annual concentration would be 

expected to range from 1.5 to 3.0 mg/L within a 

90 percent confidence interval. The confidence interval 

can be reduced from 1.5 mg/L to 0.5 mg/L by increasing the averaging period from 1 to 2 years. However, 

the confidence intervals are not quite comparable 

because they are based on small distributions of 10 and 

5 samples, respectively. 

Table 1. Annual atmospheric chloride deposition, 

ground-water chloride concentrations, and recharge estimate 

statistics for NAVSTA Mayport

[n, number of samples; mg/L, milligrams per liter; in/yr, inches per year]

Parameter n Minimum

MaximumAverage

Standard

deviation

95 percent

confidence 

limits

Lower Upper

Clatmos, mg/La

1-year average

10 1.7 2.7 2.2 0.37 1.5 3.0

Clatmos, mg/La

2-year average

5 2.1 2.4 2.2 .13 2.0 2.5

ClGW, mg/Lb 22 7 20 14 4 6 22

ln(Recharge)c 220 1.28 2.92 1.98 .35 1.29 2.67

Recharge, in/yr 220 4 19 7 -- 4 14

a Estimates are extrapolated from the 1985 to 1994 precipitation measurements at NADP/NTN station 100380 (located at the Kennedy Space 

Center) and adjusted to the combined wet and dry amount by the 

dry-fall:wet-fall ratio of 0.42 estimated for Florida by Baker (1991). b Chloride concentrations determined from samples collected during 

January 1993 (U.S. Department of the Navy, 1995). c Recharge estimate statistics are based on a 1-year averaging period of 

the atmospheric chloride deposition data. Infiltration was assumed to be 

44 in/yr (precipitation + irrigation - stream discharge + recharge). 
18 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected Waste-Disposal 

Sites at Naval Station Mayport, Florida

Ground-water chloride measurements are more 

spatially variable than atmospheric chloride measurements (table 1), partly because the depth of samples 

and, hence, the traveltime from the point of recharge to 

the sampled well can significantly vary. The rate of 

infiltration through the unsaturated zone also affects 

opportunities for the enrichment of chloride in ground 

water and depends on the thickness of the zone, 

antecedent conditions, and the porosity of the unsaturated media. Accordingly, the time period sampled is 

dependent on the well construction, the rate and 

frequency of recharge events, and the porosity. The 

time period sampled affects the magnitude and uncertainty of the Clatmos estimate used to estimate the 

recharge rate. Where the aquifer is homogeneous, the 

traveltime through the unsaturated zone is negligible, 

and the aquifer is thick relative to the length of the 

well screen, the time period sampled by shallow wells 

in a recharge area can be approximated by:

, (3)

where

LScreen is the contributing screen length, in feet; 

N is the recharge rate, in feet per year; and 

θ is the effective porosity, dimensionless.

As equation 3 shows, determining the time 

period sampled is difficult because it is dependent on 

the estimate of annual recharge rates. The time periods 

sampled at NAVSTA Mayport typically range from 0.3 

to 6 years based on contributing screen lengths 

ranging between 3 and 8 ft, recharge rates between 6 

and 12 in/yr (0.5 and 1 foot per year (ft/yr)), and 

effective porosities between 10 and 40 percent. 

Chloride concentrations in water from most of 

the observation wells at NAVSTA Mayport cannot be 

used to estimate the ground-water recharge rate, 

except for chloride concentrations in samples from 

wells in the vicinity of well 8-5S and Solid Waste 

Management Unit-6/7 (SWMU-6/7). The chloride 

concentration in these areas represents mostly 

atmospheric sources because it is part of the older 

upland areas and has been flushed by freshwater 

recharge many times. The chloride deposition rate east 

of Maine St. (fig. 1) is largely unknown because the 

area is recharged by a mixture of precipitation and 

unmetered irrigation from Upper Floridan supply 

wells and the public utility. The ground-water chloride 

concentrations in the hangar areas, along the 

southwest runway, and in the areas south of the Patrol 

t ∆ Sample

LScreen

N = ----------------θ

Road are elevated (as much as 25,000 mg/L) and are 

indicative of the incomplete flushing of a recently 

reclaimed salt marsh. 

A recharge rate of 7 in/yr (table 1) was 

estimated using an average of 22 ground-water 

chloride measurements (14 mg/L) made during 

January 1993 (U.S. Department of the Navy, 1995) at 

14 wells in the vicinity of well 8-5S and SWMU-6/7. 

These 14 wells were considered appropriate for use in 

the analyses because the primary land cover is unirrigated grasses. The annual atmospheric chloride 

deposition rate was extrapolated from NADP station 

100380. An average atmospheric deposition rate of 

2.24 mg/L corresponds to most of the time periods 

sampled by the wells. Infiltration was assumed to be 

44 in. during 1992 based on the total precipitation 

(58 in.) minus the surface discharge from Pablo Creek 

(21 in.) plus the recharge at NAS Jacksonville (7 in.). 

Recharge rates estimated using the chloride 

concentration ratio method are associated with a large 

uncertainty. For example, if all of the assumptions of 

the method are met and the infiltration rate is known, 

the recharge rate can range from 4 to 15 in/yr based on 

a 95 percent confidence interval (table 1). A reduction 

of the confidence interval to 50 percent still yields a 

range in recharge rates from 5 to 9 in/yr. 

The water-budget analysis and recharge rate 

estimates provide a general idea of how much water 

passes through the surficial aquifer system, but cannot 

indicate what fraction of flow passes through the 

S-zone or the I-zone of the surficial aquifer system. 

The direction and velocity of the movement of 

contaminants from specific sites are also not determined through a water-budget analysis. A 

ground-water flow model is needed to address these 

more specific questions. 

SIMULATION OF GROUND-WATER FLOW 

IN THE SURFICIAL AQUIFER SYSTEM

A three-dimensional numerical model was used 

to quantitatively analyze ground-water flow and the 

advective transport of contaminants through the 

surficial aquifer system. The McDonald and Harbaugh 

(1988) modular finite-difference model (MODFLOW) 

was used to simulate flow in the surficial aquifer 

system and to solve the governing equation: 
Simulation of Ground-Water Flow in the Surficial Aquifer System 19

, (4)

where 

∇ is del, the vector differential operator; 

K is hydraulic conductivity, in feet per day; 

b is thickness, in feet; 

h is hydraulic head, in feet; 

q is a source or sink, in feet per day; 

P-QS is precipitation minus surface runoff, in feet 

per day; 

ET is evapotranspiration, in feet per day; 

S is storage coefficient in confined aquifers and 

the specific yield in unconfined aquifers, 

dimensionless; and

t is time, in days.

Description of the Ground-Water Flow Model 

To implement a finite-difference model, the 

study area was discretized into a rectangular grid of 

cells by row and column. The active model grid 

covered an area of about 4.4 mi2 and was divided into 

107 rows of 152 columns (fig. 12). Uniform, square 

cells that measured 100 ft on a side were used throughout the simulated area. Of the 32,528 model cells, 

8,126 cells were inactive beyond the study area and in 

areas covered by the St. Johns River, the turning basin, 

and the Atlantic Ocean. 

The grid was oriented along a north-south axis 

for convenience. Neither a majority of known stresses 

or boundary conditions were aligned along any particular axis. No measurements of anisotropy were 

available and a lateral anisotropy ratio of 1:1 was used 

for simulation. Values of aquifer and confining-unit 

hydraulic properties were assigned to the center of 

each cell, defined as a node, by interpolation from 

observed point values. 

The model was vertically discretized into two 

layers to simulate the S-zone and I-zone of the 

surficial aquifer system (fig. 9). Vertical impedance to 

flow within the surficial aquifer system was simulated 

by assigning leakance values at each cell between 

model layers. The leakance is the average vertical 

hydraulic conductivity of the aquifer or confining unit 

material between nodes divided by the vertical 

distance between corresponding nodes in adjacent 

model layers and is in units of feet per day per 

foot (d-1). Leakage between the S-zone and the I-zone 

primarily is controlled by the thickness of the 

marsh-muck confining unit in areas where the 

∇ ⋅ ( ) Kb∇h q PQS + + ( ) – – ET S

∂t

∂h = confining unit is more than 1 ft thick. Vertical 

movement of water was assumed to be controlled by the 

vertical hydraulic conductivity of the aquifer where the 

confining unit is 1 ft thick or less.

Hydraulic Characteristics

Multi-well aquifer tests, single-well aquifer tests, 

and slug tests were conducted at NAVSTA Mayport to 

estimate the hydraulic properties of the surficial aquifer 

system. The lateral hydraulic conductivities estimated 

by these tests were the final values used in the 

ground-water flow model. Because there is no pumpage 

from the surficial aquifer and the surface-water features 

are tidally influenced, ground-water discharge could not 

be independently quantified and the lateral hydraulic 

conductivity distribution could not be reasonably 

estimated by model calibration. 

An aquifer test consists of applying a known 

stress to an aquifer; measuring the change in water 

level, drawdown or recovery, due to that stress; and 

inferring the hydraulic properties of the aquifer. For the 

multi-well and the single-well aquifer tests, the aquifer 

was stressed by pumping at a constant, known rate. The 

principal difference between the multi-well tests and the 

single-well tests is the measurement of drawdowns in 

observation wells in addition to the pumped well. For 

slug tests, the aquifer was stressed by removing a 

known volume from a well and measuring the water 

level recovery. 

Lateral hydraulic conductivity estimates from 

multi-well tests are considered most representative of 

aquifer hydraulic characteristics because the amount of 

water exchanged and, therefore, the volume of aquifer 

affected usually are greater than during slug tests or 

single-well tests. The median volumes removed during 

the multi-well, single-well, and slug tests at NAVSTA 

Mayport were about 900, 40, and 0.4 gallons (gal), 

respectively. Hydraulic conductivity estimates generally 

are averaged over a greater volume of aquifer by the 

inclusion of drawdown measurements from several 

observation wells. An increased number of observation 

well locations also increases the uniqueness of 

hydraulic conductivity estimates, even when fitting the 

test data to more complex models that account for 

unconfined conditions and vertical flow within the 

aquifer. 

In addition to multi-well aquifer tests, single-well 

tests and slug tests were used to estimate lateral 

hydraulic conductivities. Although the multi-well 

aquifer tests provide the most representative estimates 
Sites at Naval Station Mayport, Florida

20 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected WasteDisposal Figure 12. Active model grid. 0 2,500 

0 

Sherman

81° 26′ 

DREDGE 

HOLDING

MATERIAL

 AREAS

A1A

Chicopit Bay

Creek

30° 24′

30° 23′

STUDY

TURNING

BASIN

S

T

AREA

EXPLANATION

MODEL GRID
Simulation of Ground-Water Flow in the Surficial Aquifer System 21

of lateral hydraulic conductivity estimates, the singlewell tests and slug tests can be executed in less time and 

at a lower cost than the multi-well aquifer tests. About 

15 to 20 single-well tests were conducted and analyzed 

in the same amount of time it took to conduct one 

multi-well aquifer test at NAVSTA Mayport. Although 

greater uncertainty is associated with estimates based 

on data collected during single-well tests and slug tests, 

the improved efficiencies associated with these tests 

facilitate an increase in spatial coverage and provide a 

better description of the spatial variability of the lateral 

hydraulic conductivity. 

Lateral hydraulic conductivities were estimated 

from the multi-well aquifer tests by fitting a model to 

the measured drawdowns. The appropriate flow model 

was dictated by the geology and ground-water flow 

conditions at the site and the configuration of the 

pumped well and observation wells. The drawdown 

response in a single, confined aquifer can be described 

by the analytical Theis (1935) model. The Theis model 

was used to analyze the drawdown in well 8-3 which 

was affected by a nearby sump screened across both 

the S-zone and the I-zone (table 2). Most of the other 

multi-well aquifer tests were better described by the 

numerical model VS2DT (Lappala and others, 1987; 

Healy, 1990) that accounts for an unconfined aquifer 

and vertical flow within the aquifer. Six of the 

multi-well aquifer tests were analyzed by fitting 

results computed with a variably saturated, radially 

symmetric, numerical model, VS2DT, to the measured 

drawdowns (Halford, 1997). Aquifer tests conducted 

at wells B-1S and B-1I were analyzed with a 

three-dimensional MODFLOW model to account for 

the asymmetric effects of Lake Wonder Wood and a 

nearby drainage canal. 

Where the marsh-muck confining unit was 

about 1 ft thick or less at the test site, the aquifer-test 

model (either VS2DT or MODFLOW) spanned both 

the S-zone and the I-zone of the surficial aquifer 

system. The entire vertical section was simulated for 

these tests to avoid prescribing boundary conditions 

within the section. Where the marsh-muck confining 

unit was more than 1 ft thick, vertical leakage across 

the confining unit was generally ignored. 

Lateral hydraulic conductivity estimates were 

constrained in all aquifer test analyses by assuming 

that one value could characterize the entire thickness 

of either the S-zone or the I-zone at the test site. 

Table 2. Lateral and vertical hydraulic conductivity estimates determined from multi-well aquifer tests

[Well locations are shown in figure 3; ft/d, feet per day; gpm, gallons per minute; ft, feet; <, less than; --, not applicable] 

Well

identifiera

Lateral hydraulic

conductivity (KXY), ft/d

Vertical 

hydraulic 

conductivity (Kz) , 

ft/d

Vertical 

anisotropy

 (KZ/KXY) 

Flow 

rate,

gpm

Test 

duration

hour:minute

Maximum 

drawdown, 

ft

Initial 

wetted

screen, 

ft

Aquifer 

thickness, ft

Marsh-muck

confining unit

Multi- thickness, ft

well

Single

wellb

Slug

testc

2-17S 8 15 11 8 1 4.6 6:45 4.0 9 18 4

2-38S 80 135 65 12

< 0.002f 0.15 5.0 2:15 3.5 10 6 10

8-3Sd 15 -- -- -- .13 1.0 5:00 -- 25 40 0

13-5S 13 33 -- 13 1 1.9 7:15 4.0 9 7 1

20-2S 27 35 27 10 0.38 1.7 5:30 2.4 8 8 4

B-1Se 30 41 -- -- -- 5.4 6:00 3.0 9 24 2

BE-7S 32 58 -- 3 .09 4.5 3:10 2.3 8 49 0

B-1Ie 70 -- -- < 1f -- 5.4 6:00 1.2 5 18 2

F-80Ig 34 48 -- 2 .07 20 5:00 12.2 10 49 0

a Suffix denotes zone tested. 

b All single-well tests were analyzed with no more than the first hour of drawdown data. 

c Lateral hydraulic conductivity estimates from slug tests were reported in U.S. Department of the Navy (1995).

d Aquifer was stressed by a 4-ft diameter sump with 25 ft of screen. The drawdown response was simulated with the Theis (1935) solution. Vertical 

anisotropy was determined by a nearby test in the unsaturated zone. An unspecified air flow rate was induced near the water table (about 7 ft below land 

surface) and six drawdowns were measured at 10, 20, and 30 ft from the pumped well and 2 and 4 ft below land surface. The maximum drawdown was 

equivalent to 0.58 ft of water and the compressibility effects of air could be ignored. e Observed drawdowns were fitted to a three-dimensional model that accounted for the effects of Lake Wonder Wood and a nearby canal. The model 

was simulated with the MODFLOW code. f Maximum vertical hydraulic conductivity of the marsh-muck confining unit at test sites. Based on both the S-zone and I-zone tests. g Aquifer test was performed in 1979 and originally reported by Franks (1980).
22 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected Waste-Disposal 

Sites at Naval Station Mayport, Florida

Table 3. Lateral hydraulic conductivity estimates determined from 

single-well aquifer tests

[Well locations are shown in figure 3; gpm, gallons per minute; ft, feet; --, not applicable]

Well

identifiera

Lateral hydraulic 

conductivity, ft/d

Flow rate,

gpm

Test duration

hour:minute

Maximum 

drawdown, ft

Initial wetted

screen, ft

Aquifer 

thickness, ft

Marsh-muck

confining unit

thickness, ft

Corrected

singlewell b

Single

well

Slug

test c

2-32S 58 98 -- 1.9 0:09 1.0 76 7

2-34S 28 48 -- 2.1 0:08 2.4 6 6 14

2-35S 9 15 -- 1.2 2:45 6.2 77 5

2-36S 15 25 54 3.5 0:06 4.9 9 6 10

2-37S 1 2 -- 1.8 0:04 3.0 10 13 10

8-5S 2 4 1.2 0.7 0:06 3.6 97 1

15-P2 5 9 5.5 2.0 0:07 2.3 10 50 0

16-4S 34 58 -- 1.8 0:16 0.8 4 10 1

23-3S 6 11 2 1.8 0:18 5.1 89 5

23-5Sd 7 12 9 2.0 0:15 .8 8 21 11

23-7S 8 14 1.5 .9 0:16 3.0 86 4

CU-4S 5 8 -- 1.8 0:14 1.0 6 49 0

1-1I 9 16 -- 4.6 0:11 5.0 5 41 2

2-11I 55 92 -- 4.6 0:13 2.4 5 44 6

2-12I 47 79 45 5.0 0:15 2.4 5 42 5

2-17I 72 120 93 4.3 2:35 4.6 5 25 4

2-18I 13 22 29 4.8 5:00 2.2 5 58 1

2-23I 49 83 -- 4.5 0:21 2.4 5 48 6

2-32I 14 25 -- 4.8 0:07 1.0 5 40 7

2-34Ie -- -- -- .6 0:07 26.0 5 45 14

2-35I 10 18 -- 4.8 6:15 4.0 5 21 5

2-36I 70 117 46 4.8 0:13 2.0 5 13 10

2-37I 3 5 -- 1.8 0:12 2.6 5 28 10

2-38I .6 1.1 1.4 2.4 2:00 19.0 5 46 10

8-5I 14 24 -- 4.6 0:11 3.3 5 40 1

16-1I 56 95 -- 4.5 0:15 1.9 5 42 0

23-5I 1.1 2 1.3 1.6 0:18 7.8 5 17 11

CU-8I 15 26 -- 4.0 0:17 2.9 5 49 0 a Suffix denotes zone tested. 

b The single-well lateral hydraulic conductivity estimates were corrected by 

equation 6. c Lateral hydraulic conductivity estimates from slug tests were reported in U.S. 

Department of the Navy (1995). d Pumped for 15 minutes but only the first minute was analyzed due to proximity of 

St. Johns River. e Specific capacity was less than 0.02 gallon per minute per foot. 

Estimates of vertical hydraulic conductivity 

across the marsh-muck confining unit or 

within the S-zone were similarly constrained. Preliminary results of aquifer tests 

in vertically adjacent zones were applied 

iteratively until “best fit” results were 

achieved for tests in both zones (table 2).

The single-well aquifer tests were 

analyzed with the Cooper-Jacob (1946) 

approximation of the Theis solution. The 

Cooper-Jacob model of aquifer response 

can be described by a straight line on a plot 

of drawdown as a function of the logarithm 

of time. Lateral hydraulic conductivity (K) 

values are estimated from flow rate and 

drawdown measurements by: 

, (5)

where

QPump is the rate the well is pumped, in 

cubic feet per day; 

b is the thickness of the aquifer, in 

feet; and

slog cycle is the measured rate of drawdown 

increase, in feet per log-cycle. 

For all of the aquifer tests conducted 

at NAVSTA Mayport, the drawdowns 

observed in the pumped wells increased 

semi-logarithmically after the initial 

well-bore effects dissipated. Using 

equation 5, a lateral hydraulic conductivity 

estimate was determined at most of the 

single-well aquifer test sites (table 3). The 

limited drawdown data could have been 

fitted to more sophisticated models but no 

K

2.3QPump

4πbslogcycle

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

more than one hydraulic characteristic could have 

been reasonably estimated. 

Although the Cooper-Jacob method provides a 

simple method of analysis, many of the inherent 

assumptions of the method are not met or are only 

partially satisfied at NAVSTA Mayport because a 

leaky confining unit is present and the surficial aquifer 

system is unconfined. The combined result of neglecting these factors was that lateral hydraulic conductivity estimates based on single-well tests, Ksingle, were 

consistently greater than corresponding estimates 

based on multi-well tests, Kmulti (table 2).

A log-log graph of Kmulti versus Ksingle suggests 

a linear relation exists between the logarithms of the 

two variables (fig. 13), which can be described by: 

 . (6)

Equation 6 adequately corrects the initial 

estimates from single-well aquifer tests, as indicated 

by the regression coefficient (r2 = 0.89), and is considered to provide the best estimate of lateral hydraulic 

conductivity at NAVSTA Mayport. The corrected 

values of lateral hydraulic conductivity from the 

single-well tests were used in the calibrated model 

(table 3). 

KMulti 0.53KSingle

1.03 =
Simulation of Ground-Water Flow in the Surficial Aquifer System 23

Additional lateral hydraulic conductivity 

estimates at NAVSTA Mayport were determined from 

slug tests (U.S. Department of the Navy, 1995), 59 in 

the S-zone and 5 in the I-zone (table 4). The slug tests 

were analyzed by the Bouwer and Rice (1976) method 

which empirically corrects for the effects of partially 

penetrating wells in an unconfined aquifer. 

Table 4. Lateral hydraulic conductivity estimates 

determined from slug tests

[Lateral hydraulic conductivity in feet per day; all other values in feet; 

<, less than; well locations are shown in figure 3]

Well

identifiera

Lateral hydraulic 

conductivityb

Initial 

wetted

screen

Aquifer 

thickness

Marsh-muck

confining unit

thickness

1-P1 20 5 18 3

1-P2 25 5 15 1

1-P3 18 8 14 7

2-18S 5 10 8 1

2-22S 7 10 6 3

2-25S 3 10 18 5

2-26S 10 10 18 5

2-31S 29 10 9 11

2-33S 34 10 9 5

2-P11 8 4 7 2

2-P2 8 5 11 3

2-P4 13 5 10 4

2-P5 6 5 6 2

2-P6 6 5 2 3

2-P8 5 5 5 5

a Suffix denotes zone tested. 

b Lateral hydraulic conductivity estimates were reported in U.S. 

Department of the Navy (1995).

Figure 13. Relation between lateral hydraulic conductivity 

values estimated by single-well tests and multi-well tests.

10 20 50 100 200

100

5

10

20

50

MULTI-WELL 

 ESTIMATE, IN FEET PER DAY

HYDRAULIC CONDUCTIVTY

 ESTIMATE, IN FEET PER DAY

SINGLE-WELL HYDRAULIC CONDUCTIVTY

r

2 = 0.89

K Multi 0.53KSingle

1.03 =

Regression Line

2-P9 18 5 9 1

8-4S 7 6 43 0

8-6S 2 7 44 0

8-7S 2 7 44 0

8-8S 1.0 6 8 < 1

8-P2 7 5 44 0

8-P3 0.8 5 45 < 1

8-P4 10 7 10 3

13-8S 45 10 7 5

13-P1 18 5 8 5

13-P4 16 5 61 0

13-P5 1.3 5 4 3

14-3S 13 9 47 0

14-4S 10 9 47 0

14-5S 11 8 47 0

14-6S 11 9 47 0

14-7S 8 9 47 0

14-8S 11 8 47 0

14-9S 8 9 47 0

14-10S 18 9 47 0

14-11S 21 9 48 0

14-12S 14 6 48 0

14-13S 9 9 47 0

14-14S 13 9 47 0

14-P1 12 5 47 0

14-P2 22 5 46 0

15-1S 3 9 9 1

15-P3 6 10 9 3

16-2S 5 7 43 0

17-P2 23 5 51 0

18-1S 14 8 48 0

18-2S 9 8 47 0

18-3S 17 8 47 0

23-1S 2 9 8 3

23-2S 1.0 10 8 4

23-4S 5 9 15 8

23-6S 3 7 12 5

24-1S 2 10 8 3

44-1S 5 7 14 3

44-2S 1.0 6 12 3

44-3S 5 7 17 7

45-2S 8 8 19 9

56-1S 36 10 5 3

CU-5S 6 6 47 0

2-15I 12 10 50 5

2-25I 50 5 46 5

2-31I 9 5 23 11

2-33I 7 5 49 5

15-5I 15 5 55 0

Table 4. Lateral hydraulic conductivity estimates 

determined from slug tests--(Continued)

[Lateral hydraulic conductivity in feet per day; all other values in feet; 

<, less than; well locations are shown in figure 3]

Well

identifiera

Lateral hydraulic 

conductivityb

Initial 

wetted

screen

Aquifer 

thickness

Marsh-muck

confining unit

thickness

a Suffix denotes zone tested. 

b Lateral hydraulic conductivity estimates were reported in U.S. 

Department of the Navy (1995).
24 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected Waste-Disposal 

Sites at Naval Station Mayport, Florida

Lateral hydraulic conductivity estimates based on slug 

test results are reported to be within 25 percent of actual 

value (Bouwer and Rice, 1976) under ideal conditions, 

but the discrepancy is expected to be greater in practice. 

Lateral hydraulic conductivity values were 

estimated using results from pumping tests and slug 

tests at 15 wells. Values based on the pumping tests 

and slug tests ranged from 0.4 to 80 feet per day (ft/d) 

and from 1.2 to 93 ft/d, respectively. The geometric 

averages of the two sets of estimates are the same 

(10 ft/d) but the median discrepancy between any two 

estimates was about 50 percent of the greater estimate. 

The maximum discrepancies between values at a 

single site resulted from tests at wells 23-7S and 

2-36S. The slug test underestimated the single-well 

test results at 23-7S by a factor of 4 (1.5 ft/d compared 

to 7 ft/d), and overestimated the single-well test results 

at 2-36S by a factor of 4 (54 ft/d compared to 13 ft/d). 

The areal distribution of lateral hydraulic 

conductivity in the S-zone (layer 1) and the I-zone 

(layer 2) were estimated by kriging the log of the test 

estimates of hydraulic conductivity. Ordinary kriging 

was used to interpolate and extrapolate from the test 

site locations (point values) to the model nodes because 

it provides the best linear, unbiased estimate (Isaaks 

and Srivastava, 1989). Ordinary kriging can be used 

because no spatial trends exist in the log-hydraulic conductivity values of either the S-zone or the I-zone. 

Spatial interpolation by kriging is based on the 

internal structure of the data set (autocorrelation). This 

structure, if present, is examined by plotting the squared 

difference in measured values, γij, against the distance 

between locations i and j. A scatter plot of γij as a function 

of distance will show a general increase in γij as pairs 

become further apart. An overall structure, however, is 

hard to determine because of the variability which exists 

at any given point (Isaaks and Srivastava, 1989). 

An underlying internal structure is made more 

apparent by averaging γij over intervals (lags) to obtain: 

, (7)

where

h is the average distance between log-hydraulic 

conductivity values in an interval; 

N(h) is the number of pairs in an interval; and 

Y is a measured log-hydraulic conductivity value. 

A plot of γ(h) versus h produces an empirical 

variogram (fig. 14). Variograms of log-hydraulic 

conductivity differences showed little uncertainty 

γ( ) h 1

2N h( ) --------------- Yi Yj ( ) – 2

( ) i j , hij ≈ h

= ∑

(nugget effect) associated with the measured values 

relative to the variance of Y in either the S-zone or the 

I-zone (fig. 14). For about the first 1,000 to 1,500 ft, 

γ(h) increased rapidly with distance. Beyond about 

4,000 ft, γ(h) remained near the variance of Y in both 

the S-zone and the I-zone which was 0.25 and 0.62 log 

(ft/d)2, respectively (fig. 14). The variability in γij as a 

function of data pair orientation was not considered 

because the available data were insufficient to define 

anisotropic variograms. 

Exponential variograms (fig. 14) provide the 

functional form of the relation between γ(h) and 

distance. The empirical variograms of Y in the S-zone 

and the I-zone were approximated by: 

, (8)

where

σ2 is the variance of log-hydraulic conductivity, in 

log (ft/d)2, and 

a is the range, in feet. 

Range is the primary variogram parameter that 

affects kriging estimates. As range increases, more 

measured values influence the estimate. Both the 

S-zone and the I-zone exponential variograms were 

defined by a range of 3,000 ft. 

Figure 14. Empirical and exponential variograms of log 

hydraulic conductivity in the S-zone (layer 1) and the I-zone 

(layer 2). 

Empirical Exponential

S-zone

I-zone

0 6,000 0 2,000 4,000

DISTANCE, IN FEET

0

0.75

0.25

0.50

γij, IN LOG (FEET PER DAY)2

γ ̃ij σ

2 1 –3h

a – exp ---------     =
Simulation of Ground-Water Flow in the Surficial Aquifer System 25

Kriging estimates for each model node were 

generated from a weighted linear combination of the 

point estimates of log-hydraulic conductivity. The 

weights were determined by solving the kriging 

system of equations that minimizes the estimation 

error, subject to the constraints of unbiasedness (Isaaks 

and Srivastava, 1989). When solving the kriging 

system of equations, the exponential variogram placed 

more emphasis on measurements (point values) that 

were closer to a node location. 

The hydraulic conductivity distribution of the 

S-zone (layer 1) was kriged from 79 measurements 

(7 multi-well aquifer tests, 13 single-well tests, and 

59 slug tests) and the S-zone exponential variogram 

(fig. 14). Many measurements were along the runways 

and north of the golf course (fig. 15). A few measurements were near the dredge material holding areas; no 

measurements were available south of Lake Wonder 

Wood. Three principal areas of relatively low 

hydraulic conductivity in the S-zone were identified 

near SWMU-6/7, between the hangars and the eastern 

dredge material holding area, and north of the baseball 

fields (fig. 15). 

The hydraulic conductivity distribution of the 

I-zone (layer 2) was kriged from 23 point estimates 

from 2 multi-well aquifer tests, 15 single-well tests, 

5 slug tests, and a specific capacity test. The specific 

capacity test was less than 0.02 gallons per minute per 

foot (gal/min)/ft at well 2-34I and a hydraulic conductivity of 0.1 ft/d was assigned to this site. The I-zone 

exponential variogram (fig. 14) described the spatial 

structure of the lateral hydraulic conductivity measurements. Most of the measurements were near the 

runways and around the eastern dredge material 

holding area (fig. 16). There were no measurements 

beneath the golf course areas, along the Atlantic 

Ocean, or south of Lake Wonder Wood. Two areas of 

relatively low hydraulic conductivity in the I-zone 

were identified near the center of the runways and near 

Foxtrot pier (fig. 16). 

The transmissivity (T) distribution of the I-zone 

(layer 2) was used in place of the hydraulic conductivity distribution in the flow model because the 

thickness of the I-zone is not a function of the water 

table. The transmissivity distribution of the I-zone was 

calculated by multiplying the lateral hydraulic conductivity distribution (fig. 16) by the corresponding 

thickness for layer 2 (fig. 8). 

The initial areal distribution of leakance 

between layers 1 and 2 was defined by the presence or 

absence of the marsh-muck confining unit. Where the 

marsh-muck confining unit was 1 ft thick or greater 

(fig. 6), the marsh-muck confining unit was assumed to 

control the vertical movement of water. The initial 

leakance estimate for these areas was calculated by 

dividing the preliminary estimate of vertical hydraulic 

conductivity of the confining unit (0.001 ft/d) by the 

thickness of the marsh-muck confining unit (fig. 6). The 

vertical hydraulic conductivity of the aquifer was 

assumed to control the vertical movement of water 

where the marsh-muck confining unit was less than 1 ft 

thick (fig. 6). The initial leakance estimate for areas 

where the marsh-muck confining unit was thin or 

missing was calculated by multiplying the lateral 

hydraulic conductivity of the S-zone (fig. 15) by the 

vertical anisotropy determined from multi-well test 

results (table 2) and dividing it by the average internode 

distance between layers 1 and 2 (30 ft). A vertical 

anisotropy of KZ/KXY = 0.1 was applied consistently 

and is the rounded average of the non-unity values 

listed in table 2. 

Different vertical leakances were assigned 

beneath Sherman Creek and Lake Wonder Wood. 

Sherman Creek is about 10 ft deep at SR A1A and was 

dredged between 1969 and 1972 from south of the 

dredge material holding areas to the canal along Patrol 

Road (fig. 1). Because the marsh-muck confining unit 

was assumed to be breached along the length of 

Sherman Creek, the leakance beneath the creek was 

arbitrarily set 1,000 times greater than the leakance of 

the surrounding marsh-muck confining unit in order to 

simulate the breach. Lake Wonder Wood, created 

between 1960 and 1965, was dredged to about 20 ft 

below sea level, and is well connected with the I-zone. 

Leakance below the lake was estimated during model 

calibration. 

Tidal Effects and Surface-Water Features 

The dominant surface-water features surrounding NAVSTA Mayport are the St. Johns River and the 

Atlantic Ocean along the northern and eastern edges, 

respectively (fig. 1). Both features are deep, 

tidally-influenced, saltwater bodies that communicate 

directly with the S-zone and the I-zone of the surficial 

aquifer system. The typical tidal range is about 6 ft but 

can be as much as 10 ft (U.S. Department of the Navy, 

1995). The average stage of the St. Johns River and the 

Atlantic Ocean near NAVSTA Mayport is about 1 ft 

above sea level. 
Sites at Naval Station Mayport, Florida

26 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected WasteDisposal Figure 15. Lateral hydraulic conductivity of the S-zone (layer 1). 0 2,50

0 

Sherman

81° 26′ 

DREDGE 

HOLDING

RUNWAY

MATERIAL

 AREAS

HANGARS

Fairw

Fairways

A1A

Maine St.

Moale Ave.

Patrol Rd.

Patrol Rd.

Alpha Pier

Charlie Pier

Delta Pier

Bravo Pier

Echo Pier

Foxtrot

Pier

Bailey Ave.

Bon Homme Richard

Chicopit Bay

Ma

L

W

W

Creek

30° 24′

30° 23′

5

3

6

2 1 2

15

7

2

10

3

5 4

80 28

45

18 15

58

15

9

18 8

8

7

29

13

5

3

6

10

5

1

16

36

6

1

7

8

5

20

6

2

5 3 7

1 2

8 

28

23

30

TU

RNING

BASIN

ST. 

2

0

10

1

0

5

10

5

10

20

20

5

5

EXPLANATION

LINE OF EQUAL LATERAL HYDRAULIC CONDUCTIVITY--Interval variable, in feet per day. Hachures indicate lesser values

HYDRAULIC CONDUCTIVITY--All values in feet per day

MULTI-WELL TESTSINGLE-WELL TESTSLUG TEST

3226

45

5

5

20

5

10

8

34

13
Simulation of Ground-Water Flow in the Surficial Aquifer System 27Figure 16. Lateral hydraulic conductivity of the I-zone (layer 2). 0 2,5

0 

Sherman

81° 26′ 

DREDGE 

HOLDING

RUNWAY

MATERIAL

 AREAS

HANGARS

Fairw

Fairways

A1A

Maine St.

Moale Ave.

Patrol Rd.

Patrol Rd.

Alpha Pier

Charlie Pier

Delta Pier

Bravo Pier

Echo Pier

Foxtrot Pier

Bailey Ave.

Bon Homme Richard

Chicopit Bay

M

W

W

Cr

eek

30° 24′

30° 23′

STUDY

TURNING

BASIN

S

T

AREA

70

20 10

3

0.6

7

14 13

1

5

15

10

14

15

20

6

12

20

49

50 55

47

72

9

70

50

1

9 5

20

20

50

10

20

5

10

5

EXPLANATION

SPECIFIC CAPACITY isless than 0.02 gpm/ft

LINE OF EQUALLATERAL HYDRAULICCONDUCTIVITY --Interval variable, in feet perday. Hachures indicatelesser values

32

26

4

MULTI-WELL TEST

SINGLE-WELL TEST

SLUG TESTAll values in feet per day

HYDRAULIC CONDUCTIVITY

10
28 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected Waste-Disposal 

Sites at Naval Station Mayport, Florida

Chicopit Bay, Sherman Creek, and the unnamed 

canals that drain Lake Wonder Wood and the golf 

course area along Patrol Road also are tidallyinfluenced. The tidal range varies from about 6 ft at 

Sherman Creek and SR A1A to about 2 ft at the far 

reaches of the unnamed canals that drain Lake Wonder 

Wood and the golf course area along Patrol Road. The 

average stage of these features is also about 1 ft above 

sea level. 

Measurable tidal effects propagate throughout 

most of the surficial aquifer system (fig. 17). Within 

200 ft of the St. Johns River, vertical tidal displacements of 0.5 ft or more were observed in the S-zone 

near SWMU-6/7 and in the I-zone east of the turning 

basin. Tidal displacements decreased away from the 

shoreline but were still measurable in wells 8-5S and 

8-5I by the runways and near the F-80 aquifer test site 

(fig. 17). East of the dredge material holding area and 

west of Lake Wonder Wood, ground-water displacements of more than 0.1 ft were responses to tidal 

fluctuations in the adjacent canals, not in the St. Johns 

River or the Atlantic Ocean (fig. 17). 

The tidal displacement data can be used to 

independently evaluate the lateral hydraulic conductivity of the surficial aquifer system. If the tidal 

displacements do not significantly change the 

saturated thickness, then an analytical solution that 

describes the displacements in a one-dimensional, 

confined aquifer due to tidal forcing (Cooper and 

others, 1964) can be described by:

, (9)

where

h0 is the amplitude of the tidal signal, in feet; 

x is the distance from the tidal signal, in feet; 

t0 is the period of the tidal cycle, in days (about 

0.52 day or 12.5 hours); and 

t is the elapsed time since the beginning of a tidal 

cycle. 

Equation 9 shows that the amplitude of 

water-level displacement in a given well is a function 

of the distance from the tidal signal and of the aquifer 

diffusivity, Kb/S. 

Hydraulic characteristic estimates imposed by 

equation 9 tend to be qualitative because the appropriate specific yield or storage coefficient is unknown 

and can vary over three orders of magnitude or more. 

Specific yield estimates from multi-well aquifer tests 

h∆ Tide

h0

2

---- e

x πS

t0Kb – -----------

2π

t

t0

--- x

πS

t0Kb – -----------     = sin

of the S-zone ranged from 0.04 to 0.12 at clean sites 

and was about 0.004 near SWMU-6/7, where free 

product occurs at the water table. Storage coefficient 

estimates from multi-well tests of the I-zone ranged 

from to . Quantitative analysis is 

further complicated by the vertical transmission of the 

tidal signal between the I-zone and S-zone which 

causes diffusivity estimates from equation 9 to reflect 

a composite storage coefficient for both zones. 

Relative differences between lateral and vertical 

hydraulic conductivity can be inferred between sites if 

the spatial variability of specific yield and storage 

coefficient are assumed to be minimal. Average diffusivities in the areas near wells 8-5S, 8-5I, and the F-80 

aquifer test site (fig. 17) are about 500,000 feet 

squared per day (ft2

/d) based on an attenuation of the 

tidal amplitude to about 0.01 of the source and 

distances of between 1,000 and 1,500 ft (table 5). The 

differences in tidal displacements in the S-zone and 

I-zone at these three sites suggest that the vertical 

hydraulic conductivity near wells 8-5S and 8-5I is 

much less than near the F-80 aquifer-test site (fig. 17). 

The diffusivity of the area between the southwestern 

end of the runway and the St. Johns River is about 

100,000 ft2/d which suggests the transmissivity of the 

surficial aquifer system in this area should be about 

five times less than near well 8-5I or the F-80 

aquifer-test site.

Vertical ground-water displacements were 

greater in the S-zone than in the I-zone east of the 

dredge material holding area and west of Lake Wonder 

Wood because the tidal signal originated in the 

adjacent canals (fig. 17). The vertical displacement in 

the I-zone at these sites probably was the result of the 

loading effect of the canals on the marsh-muck 

confining unit. The similar range of displacement in 

the S-zone and I-zone east of the dredge material 

holding area suggests that the leakance between the 

two zones is less in this area than west of Lake Wonder 

Wood. 

Tidal fluctuation affects ground-water 

movement but does not affect the average 

ground-water flow rate or direction. Tidal fluctuation 

increases the potential for dispersion when the 

maximum tidally driven component of flow is greater 

than the topographically driven component of lateral 

ground-water flow. In areas near the shoreline, flow 

paths and dispersion are increased because shallow 

flow paths can be reversed and deeper flow paths 

along the freshwater/saltwater interface oscillate. 

Away from the shoreline and canals, the maximum 

3 –4

×10 6 –4×10
Simulation of Ground-Water Flow in the Surficial Aquifer System 29Figure 17. Generalized land surface altitudes in the study area, surface-water observation sites, and vertical tidal displace

0 2,50

0 

Sherman

81° 26′ 

A1A

Chicopit Bay

C

reek

30° 24′

30° 23′

STUDY

TURNING

BASIN

S

T

AREA

EXPLANATION

AREA WHERE LAND SURFACE IS GREATER THAN: 10 feet above sea level20 feet above sea levelVERTICAL TIDALDISPLACEMENT--Upper value is in theS-zone. Lower value is the I-zone. Values in feetNO DATASURFACE WATEROBSERVATION SITE

0.030.12

< 0.02

0.04

0.051.5

0.150.05

0.6

--

0.02

--

0.220.18

0.030.12

 0.02

< 0.02

< 0.01

--

0.4

--

0.9

--

0.4

--

0.15

--

--
30 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected Waste-Disposal 

Sites at Naval Station Mayport, Florida

tidally driven component of velocity is small relative to 

the topographically driven component of lateral 

ground-water flow, thus producing a periodic increase 

and decrease in the ground-water flow rate but not 

lengthening the flow path. 

Interaction between the S-zone (layer 1) of the 

surficial aquifer system and the St. Johns River and the 

Atlantic Ocean was simulated by specified heads at a 

stage of 1 ft above sea level. Tidal fluctuations were 

not simulated. Interaction between the I-zone (layer 2) 

and the St. Johns River and the Atlantic Ocean was 

simulated using drains with high conductances. This 

interaction could have been simulated with specified 

heads instead of drains and, as such, could add water 

to the volumetric budget. This additional water would 

account for the flow of saltwater along the freshwater/saltwater interface but would not be part of the 

freshwater flow system. The outlet head at each drain 

node was set to 1.75 ft (the average stage of the St. 

Johns River and the Atlantic Ocean plus the differential hydrostatic head between 30 ft columns of 

seawater and freshwater). The length of the column, 

30 ft, represents the typical depth to the 

middle-to-upper I-zone below the St. Johns River and 

the Atlantic Ocean. This approximation of the freshwater/saltwater interface adequately simulates the 

freshwater flow system (app. B). 

The distribution and altitude of surface-water 

features controls the direction and rate of 

Table 5. Amplitude, phase shift, and wavelength of tidal 

signals in a one-dimensional, confined aquifer with different

diffusivities driven by a source with a 1-foot amplitude

[Diffusivity: upper value is amplitude, in feet; lower value is the

difference in phase in hours:minutes, assuming a 12.5-hour cycle]

Distance 

from 

source, 

in feet

 Diffusivity, Kb/S, in feet squared per day 

10,000 50,000 100,000 500,000 1,000,000

50 0.293 

2:26

0.577

1:05

0.678 

0:46

0.841

0:20

0.884

0:14

100 0.086 

4:53

0.333

2:11

0.460 

1:32

0.707

0:41

0.782 

0:29

250 0.002

12:12

0.064

5:27

0.143 

3:51

0.420

1:43

0.541

1:13

500 0.000

11:55

0.004

10:55

0.021 

7:43

0.176

3:27

0.293

2:26

1,000 0.000

9:21

0.000

2:57

0.031

6:54

0.086

4:53

1,500 0.005

10:21

0.025

7:19

Wavelength, 

in feet 256 572 809 1,810 2,560

ground-water flow in the surficial aquifer system. The 

distribution of surface-water features was determined 

from aerial photographs and plans of NAVSTA 

Mayport (C. Mitchell, Staff Civil Engineer Mayport, 

U.S. Navy, written commun., 1996). The elevations of 

the canals, creeks, lakes, and ponds were interpolated 

from the surveyed elevations at the surface-water 

observation sites shown in figure 17. The base of 

storm sewers typically was about 5 ft below land 

surface. 

Interaction between the surficial aquifer system 

and the canals, creeks, marshes, storm sewers, lakes 

and ponds was simulated by river nodes. The 

simulated flow rate in or out of the aquifer at a river 

node was defined by: 

, (10)

where

CRB is the hydraulic conductance of the 

riverbed, in feet squared per day; 

HRIVER is the average stage of the river or lake, 

in feet; and 

HAQUIFER is the head in the aquifer beneath the 

river, in feet. 

Equation 10 only applies if HAQUIFER is greater 

than or equal to the assigned elevation of the bottom of 

the surface-water feature. 

A riverbed conductance of 100,000 ft2

/d was 

used for all river nodes and was not estimated. The 

results of model simulations of similar aquifer conditions at Cecil Field NAS (Halford, 1998) indicated that 

model results would not be sensitive to changes in 

riverbed conductance. The ground-water flow model 

at Cecil Field NAS was insensitive to increasing 

riverbed conductance and estimates of riverbed 

conductance were highly correlated with estimates of 

lateral hydraulic conductivity of the surficial aquifer, a 

more sensitive parameter than the riverbed conductance. This result implies that surface-water interaction is controlled by the hydraulic conductivity of 

the surficial aquifer rather than the riverbed conductance; model calibration at NAVSTA Mayport was 

conducted accordingly. 

All canals, creeks, marshes, storm sewers, lakes 

and ponds shown in figure 1 were represented in the 

model. A total of 3,197 river nodes was assigned to 

layer 1 of which 2,222 simulated the marsh in the 

southwestern part of the study area. The river bottom 

elevation for all canals, creeks, marshes, and storm 

sewers was set equal to the river stage to ensure all 

QB CRB HRIVER HAQUIFER = ( ) –
Simulation of Ground-Water Flow in the Surficial Aquifer System 31

simulated reaches were either gaining or inactive. For 

the lakes and ponds, the river bottom was set far below 

the altitude of the water surface so water could be 

gained or lost from these features. 

Ground water is diffusely discharged in areas 

between the southwestern runway and the St. Johns 

River, northeast of the dredge material holding areas, 

and over much of the golf course. These diffuse 

discharge areas can shrink or expand depending on the 

frequency and intensity of rainfall or irrigation events. 

All land areas not occupied by a visible surface-water 

feature were simulated as drains with high conductances and outlet heads set at land surface. If the water 

table rises to land surface, the drains behave as 

specified heads and simulate the removal of water 

from the S-zone (layer 1); otherwise they have no 

effect. Conceptually, the drain nodes simulated the 

effects of relatively high evapotranspiration and 

ground-water discharge in these areas. 

Boundary Conditions

Proper representation of model boundary conditions is one of the most important aspects in the 

simulation of an aquifer system. Model boundaries are 

assigned to represent the actual hydrologic boundaries 

as accurately as possible. If model boundaries are 

generalized, they are placed far enough away from the 

influence of hydrologic stresses in the model area to 

minimize their influence on simulation results.

The upper boundary, layer 1, is the water table 

and is represented in MODFLOW as a free surface 

except where the water table intersects land surface. 

Six zones of spatially uniform recharge rates were 

applied to this boundary in all simulations (fig. 18). 

The predominant areas were unirrigated, pervious 

surfaces. The dredge material holding areas were 

differentiated from the other unirrigated recharge areas 

because they are elevated (fig. 17) and have diked 

perimeters that impede surface runoff (fig. 9). Areas 

identified as golf-course irrigation were assigned only 

to the fairways and greens (fig. 18). The underflow 

recharge areas are those where water moves beneath 

impervious surfaces and enters into storage after 

recharge events. This water then is later released from 

storage as drainage. The flux across the water table 

was not uniform in each area due to rejection of water 

where the water table was near or at land surface. 

The lower model boundary is the contact 

between the surficial aquifer system and the intermediate confining unit and is simulated as a no-flow 

boundary. The potential flow across this boundary is 

upward from the Upper Floridan aquifer to the 

surficial aquifer system because of the upward 

gradient between the two aquifers. The potentiometric 

surface of the Upper Floridan beneath NAVSTA 

Mayport is about 25 to 30 ft above sea level (Halford 

and others, 1993) and water levels in the surficial 

aquifer system typically range from 1 to 10 ft above 

sea level.

The lateral model boundaries in both layers 1 

and 2 are no-flow boundaries that coincide with 

surface-water features. The northern and eastern edges 

of the study area lie within the St. Johns River and the 

Atlantic Ocean, respectively. Two-thirds of the 

southern boundary and the western boundary pass 

through marsh along Sherman Creek and Chicopit Bay 

(fig. 1). Flow does not cross these boundaries because 

no hydraulic gradient exists transverse to the boundaries. The eastern one-third of the southern boundary 

crosses the coastal ridge perpendicularly (fig. 17). 

This divide constitutes a no-flow boundary because 

water flows parallel to the boundary. The boundary 

along the turning basin perimeter is a no-flow 

boundary because the retaining walls beneath the piers 

are made of two layers of interlocking sheet pile with a 

grout fill (U.S. Department of the Navy, 1995) and are 

assumed to be impervious except where breached by 

storm sewers. 

Model Calibration

Calibration is the attempt to reduce the difference between model results and measured data by 

adjusting model input. Calibration was accomplished 

in this study by adjusting input values of vertical 

hydraulic conductivity and recharge until an acceptable calibration criterion was achieved. The 

“goodness” or improvement of the calibration is based 

on the differences between simulated and measured 

ground-water levels and stream discharges. Simulated 

water levels and discharges from a calibrated, deterministic ground-water model commonly depart from 

measured water levels and discharges, even after a 

diligent calibration effort. The discrepancy between 

model results and measurements (model error) 

commonly is the cumulative result of simplification of 

the conceptual model, grid scale, and the difficulty in 

obtaining sufficient measurements to account for all of 

the spatial variation in hydraulic properties and 

recharge throughout the model area. 
Sites at Naval Station Mayport, Florida

32 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected WasteDisposal Figure 18. Recharge area delineation based on recharge source. 0 2,500 

0 

Sherm

an

81° 26′ 

A1A

Chicopit Bay

Creek

30° 24′

30° 23′

STUDY

TURNING

BASIN

ST

AREA

EXPLANATION

Unirrigated

Golf-CourseDredge Material

Underflow

Sports Facilities

Ornamental

RECHARGE AREAS

Irrigation

Plant Irrigation

Irrigation
Simulation of Ground-Water Flow in the Surficial Aquifer System 33

The ground-water flow model was calibrated to 

229 water-level measurements from 181 wells. 

Water-level data were obtained from three synoptic 

surveys conducted during July 17, 1995, to October 

24, 1996. Synoptic water-level measurements were 

affected by factors not accounted for by the model. 

Some water-level measurements near SWMU-6/7 

were rejected for calibration purposes because of 

obvious tidal effects. Other water-level measurements 

along the periphery of the western dredge material 

holding area were not used due to discretization effects 

and steep gradients in close proximity to a drainage 

feature. The synoptic surveys were treated as independent “snapshots” of the ground-water system taken at 

various times (Halford, 1998). 

The data from these surveys were fitted to the 

simpler steady-state equation: 

, (11)

where 

N ′ is the effective recharge rate during a given survey, in feet per day, which is the summation of 

precipitation, surface runoff, evapotranspiration, and water released from storage and can 

be summarized by 

. (12)

Although the effective recharge rates, N ′, 

estimated for each synoptic survey period are not 

estimates of the average recharge rate, estimates 

obtained during extreme conditions can bracket the 

average recharge rate (Halford, 1998). 

Some stresses must be known to calibrate a 

model if both recharge rates and hydraulic conductivities are simultaneously adjusted. When the use of 

equation 11 is appropriate, the stresses and recharge 

rates are proportional to the hydraulic conductivity. 

Usually, the lateral and vertical hydraulic conductivities are estimated when calibrating ground-water 

flow models of a surficial aquifer system. Commonly, 

stream discharge during baseflow conditions is 

assumed to represent the recharge rate to the aquifer 

during a specified period. At NAVSTA Mayport, 

ground-water discharge from the surficial aquifer 

system is an insignificant and unmeasureable contribution (less than 10 ft3/s) relative to the tidal flow 

(more than 100,000 ft3

/s). 

In a coastal setting like the one at NAVSTA 

Mayport, a successful calibration strategy is based on 

knowing the lateral hydraulic conductivity distributions of the flow zones and estimating recharge rates 

during model calibration. Ground-water flow rates 

estimated with this approach are not dependent on the 

quality of stream discharge measurements and 

assumptions about baseflow. Instead, the accuracy of 

flow-rate estimates is dependent on the quality of 

lateral hydraulic conductivity estimates. 

Calibration improvement was determined by 

decreases in the sum-of-squares (SS) error which is 

defined by 

 , (13)

where

 is the kth simulated water level, in feet;

hk is the kth measured water level, in feet; 

nwl is the number of water-level comparisons; and 

wk is the kth weight which was subjectively used to 

reduce the bias towards periods with more 

water levels. Weights of 1, 2, and 4 were 

applied to observations in synoptic-survey 

periods 1, 2, and 3 which had 180, 40, and 

9 observations, respectively. 

Although the sum-of-squares error serves as the 

objective function, root-mean-square (RMS) error is 

reported instead because RMS error is more directly 

comparable to actual values and serves as a composite 

of the average and the standard deviation of a set. 

Root-mean-square error is related to the 

sum-of-squares error by 

 . (14)

Because measured water levels rarely coincide 

with the center of a cell, simulated water levels were 

interpolated laterally to points of measurement from 

the centers of surrounding cells. Simulated water 

levels were interpolated because they were assumed to 

be part of a continuous distribution. Vertical interpolation was not considered because of the discontinuity 

and associated refraction of potential fields from an 

aquifer across a confining unit. 

∇•( ) Kb∇h + + q N' = 0

N ′ P Qo ( ) – – ET Sy∂t

∂h = –

SS hˆ

k hk ( ) – wk [ ]

2

k = 1

nwl

= ∑

h

ˆ

k

RMS SS

wl

2

l = 1

nwl

∑

= ---------------
34 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected Waste-Disposal 

Sites at Naval Station Mayport, Florida

Parameter Estimation

Model calibration is facilitated by a parameter 

estimation program (Halford, 1992). The parameter 

estimation process is initialized by using the model to 

establish the initial differences between simulated and 

measured water levels. These differences, or residuals, 

are then minimized by the parameter estimation 

program. To implement parameter estimation, the sensitivity coefficients (the derivatives of simulated water 

level change with respect to parameter change) are 

calculated by the influence coefficient method using the 

initial model results (Yeh, 1986). Each parameter is 

changed a small amount and MODFLOW is used to 

compute new water levels for each perturbed parameter. 

The current arrays of sensitivity coefficients and 

residuals are used by a quasi-Newton procedure (Gill 

and others, 1981, p. 137) to compute the parameter 

changes that should improve the model. The model is 

updated to reflect the latest parameter estimates and a 

new set of residuals is calculated. The entire process of 

Table 6. Initial, calibrated, and alternative values of parameters 

estimated to calibrate the model 

[ft/d, feet per day; in/yr, inches per year; ft, feet]

Estimated parameter Initial Calibrated

I-zone

transmissivitya

Halved Doubled

KZ/KXY aquifer, dimensionless 0.1 0.05 0.03 0.06

KZ marsh-muck confining unit, ft/d .001 .0003 .0001 .001

KZ Lake Wonder Woodb, ft/d .1 .02 .02 .02

N ′unirrigated, period 1, in/yr 10 8.2 5.5 12.2

N ′Golf-Course, period 1, in/yr 10 69 69 74

N ′Dredge Material, period 1, in/yr 10 21 21 21

N ′Underflow, periods 1 and 3, in/yr .1 .8 .7 .8

N ′Sports Facilities, periods 1and 3, in/yr 10 46 40 64

N ′Ornamental Plant Irrigation, in/yr 10 18 13 26

N ′unirrigated, period 2, in/yr 10 5.8 3.9 7.9

N ′Golf-Course, period 2, in/yr 10 59 57 63

N ′Dredge Material, period 2, in/yr 10 13 12 12

N ′Sports Facilities, period 2, in/yr 10 25 24 33

N ′Underflow, period 2, in/yr .1 1.2 1.1 1.3

N ′unirrigated, period 3, in/yr 10 14.1 8.8 24

N ′Golf-Course, period 3, in/yr 10 114 117 113

Weighted RMS error, in ft 1.82 .76 .78 .83

a The calibrated parameter estimates were used as initial estimates for both alternative models. The initial weighted RMS errors of the halved and doubled models were 1.20 

and 1.11 feet, respectively. b The vertical leakance below Lake Wonder Wood was estimated by dividing this 

value by the thicknesses shown in figure 6. 

changing a parameter in the model, calculating new 

residuals, and computing a new value for the parameter 

is continued iteratively until model error or 

model-error change is reduced to a specified level or 

until a specified number of iterations are made 

(Halford, 1992).

Logs of the parameters are estimated because 

vertical hydraulic conductivities are usually 

log-normally distributed (Domenico and Schwartz, 

1990). Log-parameters also are better behaved from a 

numerical perspective because the estimates are 

restricted to positive values and are scaled to some 

degree. Log-recharge rates also are used, thus ensuring 

that all estimated values of ′ are positive. 

Sixteen parameters (table 6) were used as global 

multipliers that changed the value of either vertical 

hydraulic conductivity or effective recharge rates by a 

fixed amount throughout specific zones. The initial 

values of vertical hydraulic conductivity in the 

marsh-muck confining unit were derived directly from 

N
Simulation of Ground-Water Flow in the Surficial Aquifer System 35

the multi-well test results. An initial effective recharge 

rate of 10 in/yr was used for all three synoptic-survey 

periods. Final parameter estimates were not sensitive to 

the initial parameter estimates. 

 The unweighted minimum, maximum, 

average, and RMS errors of the calibrated model 

were -2.78, 1.92, 0.00, and 0.82 ft, respectively. A 

more detailed listing of the error statistics by layer 

and synoptic-survey period is provided in table 7. 

The greater number of water-level measurements 

available during synoptic-survey period 1 did not 

overly bias model calibration toward that period 

(table 7). The water-level residuals did not exhibit 

any apparent trend across the study area during any 

of the synoptic-survey periods (figs. 19-20). 

Simulated potentiometric surfaces and water-level 

residuals are only shown for synoptic-survey period 

1 because the distribution of residuals is similar in 

all periods. 

Simulated water levels for the three synoptic-survey periods approximated the measured 

levels throughout the approximately 12-ft range 

observed in the study area (fig. 21). The measured 

water level range from 1 to 13 ft above sea level is 

similar to the simulated water level range from 1 to 

20 ft above sea level in the surficial aquifer system. 

Water levels probably are greater than 13 ft above 

sea level towards the centers of the dredge material 

holding areas, but no wells existed to measure water 

levels. The water-level residuals were normally 

Table 7. Water-level error statistics by layer and synoptic-survey period from calibrated Mayport model results

[N′unirrigated, effective recharge rate estimate; in/yr, inches per year; n, number of samples; maximum, minimum, average, and RMS in feet]

SYNOPTIC-SURVEY PERIOD

Zone 

(Layer)

(1) (2) (3)

July 17, 1995 July 31, 1996 October 24, 1996

N′unirrigated = 8.2 in/yr N′unirrigated = 5.8 in/yr N′unirrigated = 14.1 in/yr

MinimumMaximumAverage

RMS n Minimum

MaximumAverage

RMS n Minimum

MaximumAverage

RMS n

S (1) -2.78 1.92 0.02 0.86 156 -1.84 1.26 -0.04 0.74 29 -2.23 0.75 -0.35 1.10 7

I (2) -1.67 1.03 .02 .65 24 -1.62 .47 -.15 .64 11 -.08 -.08 -.08 .08 2

All -2.78 1.92 .02 .84 180 -1.84 1.26 -.07 .71 40 -2.23 .75 -.29 .97 9

 Composite water level statistics for all periods -2.78 1.92 .00 .82 229

distributed and 78 percent of the simulated water 

levels were within 1 ft of the measured water levels. 

Although the model can simulate the 

ground-water flow system beneath NAVSTA 

Mayport fairly well, there are a few areas where 

model results may be deficient. The simulated water 

table south of the runway and north of the western 

dredge material holding area is 2 to 3 ft less than the 

measured water table, probably because lateral 

hydraulic conductivity of the S-zone was overestimated (note the residuals of -3 and -2 ft in fig. 19). 

The simulated potentiometric surface of the I-zone is 

about 2 ft less than the measured surface near 

Baltimore St. and Masset Ave. (fig. 20). These differences could indicate that either the recharge rate in 

this area was underestimated or the transmissivity 

between this area and the Atlantic Ocean was overestimated. 

Estimated parameters were not highly correlated (table 8). Recharge from golf course irrigation 

and sports facilities irrigation during synoptic-survey 

period 2 was the most highly correlated pair of 

parameters (0.72). The vertical anisotropy of the 

aquifer, KZ/KXY, was somewhat correlated (-0.69) 

with the effective recharge rate of the unirrigated 

areas for period 3. Very little correlation existed 

between the vertical anisotropy of the aquifer and 

any of the other recharge rate estimates during 

periods 1 and 2 (table 8), during which many more 

water levels were measured. 
Sites at Naval Station Mayport, Florida

36 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected WasteDisposal Figure 19. Simulated potentiometric surface of the S-zone (layer 1) on July 17, 1995. 0 2,500 

0 

Sherman

81° 26′ 

DREDGE 

HOLDING

RUNWAY

MATERIAL

 AREAS

HANGARS

Fairwa

Fairways

A1A

Maine St.

Moale Ave.

Patrol Rd.

Patrol Rd.

Alpha Pier

Charlie Pier

Delta Pier

Bravo Pier

Echo Pier

Foxtrot Pier

Bailey Ave.

Bon Homme Richard

Chicopit Bay

Mas

Cr

eek

30° 24′

30° 23′

STUDY

ST. 

AREA

EXPLANATION

POTENTIOMETRIC CONTOUR--Shows altitude at which water level would have stood in tightly cased wells. Contour interval 2 feet. Datum is sea level RESIDUAL--Difference between simulated and measured water levels, in feetWELL USED IN:Two synoptic-surveysThree synoptic-surveys

2

0

6

6

4

2

-1 -3 -0

-0

-1

-0

1

0

0 0

14

12 10

8

6 4

6

8

4

4

4

6 2

2

8

10 1214

16

18

20 0

1

4 2

2

1

1

0

0

0

4

2

4

6

8

10

6

0

-1

0

Lake

Wonder

Wood

INSET B

INSET A

2

12

6
Simulation of Ground-Water Flow in the Surficial Aquifer System 37

0 1,000 2,000 FEET

0 500 METERS

81° 25′30′′ 81° 25′

30° 24′

30° 23′30′′

1

-1

1 1

1

1

1

0 0

-3

1 1 1 2

1

1

1

0

0

-1 -1 -1

0

0

1

0

-1

-2 -1

2 0

1

0

0 0 1

1 0 1

0

0

0 1

1

1

2 1

2 -1

2 1

1

0

0 0

-1

EXPLANATION

POTENTIOMETRIC 

CONTOUR--

Shows altitude at which 

water level would have 

stood in tightly cased wells. 

Contour interval 2 feet. 

Datum is sea level 

RESIDUAL--Difference 

between simulated and 

measured water levels, in 

feet

WELL USED IN:

Two synoptic-surveys

Three synoptic-surveys

0 4

6

8

6

8

6

4

4

4

4

6

8

INSET A

2

2

2

2

2

10

14 12

16

18

4

4

6

6

1 0

1

-1

Figure 19. Inset A.
Sites at Naval Station Mayport, Florida

38 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected WasteDisposal Figure 19. Inset B. 0 1,000 

0 

81° 24′30′′ 81° 24′ 30° 23′45′′ 30° 23′30′′ Baseball Fields

0

-1

0

0

0

-1

-1

1

-1 1 -1

1

1

1

1

-1

-1 

0

0

0 0

0

2

0 0

0

-1

-1

-1 0

-1

-1

-1

-1

1

1 0 1

0 0

0 0

0

0 0

-2

-1 -1 -1

EXPLANATION

POTENTIOMETRIC CONTOUR--Shows altitude at which water level would have stood in tightly cased wells. Contour interval 2 feet. Datum is sea level RESIDUAL--Difference between 

simulated and measured water levels, in feet

WELL USED IN:Two synoptic-surveysThree synoptic-surveys

2

0

-1

0

12

10

8

8

6

6

4

2

4

4

2

2

2
Simulation of Ground-Water Flow in the Surficial Aquifer System 39 Figure 20. Simulated potentiometric surface of the I-zone (layer 2) on July 17, 1995. 0 2,500 

0 

Sherman

81° 26′ 

DREDGE 

HOLDING

RUNWAY

MATERIAL

 AREAS

HANGARS

Fairwa

Fairways

A1A

Maine St.

Moale Ave.

Patrol Rd.

Patrol Rd.

Alpha Pier

Charlie Pier

Delta Pier

Bravo Pier

Echo Pier

Foxtrot Pier

Bailey Ave.

Bon Homme Richard

Chicopit Bay

Mas

La

Won

Wo

Creek

30° 24′

30° 23′

STUDY

TURNING

BASIN

ST

. 

AREA

EXPLANATION

POTENTIOMETRIC CONTOUR-- Shows altitude at which water level would have stood in tightly cased wells. Contour interval 2 feet with supplemental 3 foot contour. Datum is sea level RESIDUAL-- Difference between simulated and measured water levels, in feetWELL USED IN:Two synoptic-surveysThree synoptic-surveys

0

0

1

-1 

-1

1

1

1

1 1 1

0

0

0

0 0

0

0

0

0

6

4

0

-1

2

0

2

4

0

0

3

3

4

3

3

2

6

3

3

2
40 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected Waste-Disposal 

Sites at Naval Station Mayport, Florida

0

15

5

10

0 15 5 10

MEASURED WATER LEVEL, IN FEET

SIMULATED WATER LEVEL, IN FEET

Figure 21. Simulated and measured water levels for the 

calibrated model. 

Table 8. Correlation coefficients between parameters from the calibrated model

[--, not applicable]

Estimated parameters Correlation coefficients, 

N ′unirrigated, period 3 1.00 -- -- -- -- -- -- -- -- -- -- -- -- -- -- --

N ′unirrigated, period 1 0.00 1.00 -- -- -- -- -- -- -- -- -- -- -- -- -- --

N ′

unirrigated, period 2 .00 0.00 1.00 -- -- -- -- -- -- -- -- -- -- -- -- --

N ′Golf-Course, period 2 .00 .00 0.18 1.00 -- -- -- -- -- -- -- -- -- -- -- --

N ′Golf-Course, period 1 .00 .14 .00 0.00 1.00 -- -- -- -- -- -- -- -- -- -- --

KZ/KXY aquifer -.69 -.21 -.20 -.09 -0.08 1.00 -- -- -- -- -- -- -- -- -- --

N ′Golf-Course, period 3 .02 .00 .00 .00 .00 -0.02 1.00 -- -- -- -- -- -- -- -- --

N ′

Ornamental Plant Irrigation .01 .27 .29 .35 .26 -.22 0.10 1.00 -- -- -- -- -- -- -- --

N ′Dredge Material, period 1 .00 .10 .00 .00 .01 .00 .00 0.03 1.00 -- -- -- -- -- -- --

KZ marsh-muck confining unit -.31 -.04 .04 -.15 -.06 .19 -.04 .00 0.03 1.00 -- -- -- -- -- --

N ′

Sports Facilities, periods 1and 3 .00 .29 .00 .00 .32 -.10 .13 .29 .00 -0.10 1.00 -- -- -- -- --

N ′Sports Facilities, period 2 .00 .00 .29 .72 .00 -.11 .00 .40 .00 -.12 0.00 1.00 -- -- -- --

N ′

Underflow, period 2 .00 .00 .70 .28 .00 -.14 .00 .37 .00 -.03 .00 0.64 1.00 -- -- --

N ′

Underflow, periods 1 and 3 .00 .57 .00 .00 .15 -.13 .00 .37 .02 -.14 .60 .00 0.00 1.00 -- --

KZ Lake Wonder Wood .00 -.09 -.13 -.18 -.14 .10 -.03 -.28 .00 .00 -.16 -.20 -.15 -0.10 1.00 --

N ′Dredge Material, period 2 .15 .00 .14 .02 .00 -.11 .00 .06 .00 .30 .00 .01 .08 .00 -0.01 1.00

N ′unirrigated, period 3N ′unirrigated, period 1N ′unirrigated, period 2

N ′Golf-Course, period 2N ′Golf-Course, period 1

KZ/KXY aquifer

N ′Golf-Course, period 3

N ′Ornamental Plant Irrigation

N ′Dredge Material, period 1

KZ marsh-muck confining unit

N ′Sports Facilities, periods 1and 3

N ′Sports Facilities, period 2

N ′Underflow, period 2

N ′Underflow, periods 1and 3

KZ Lake Wonder Wood

N ′Dredge Material, period 2

Normalized main diagonal 1.00 .47 .38 .34 .29 .29 .19 .19 .17 .17 .16 .14 .06 .06 .02 .01

ρi j ,

ρi j ,

Ci j ,

Ci i , Cj j ,

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

Ci i ,

C1 1,

----------

Sensitivity Analysis

To determine how model parameters affected 

simulation results, each estimated parameter (except for 

KZLake Wonder Wood) was varied independently from 

0.2 to 5 times their calibrated value. This range was 

greater than the uncertainties associated with the parameters, but provided a more complete perspective on 

parameter sensitivity. Model sensitivity was described 

in terms of weighted RMS error. The sensitivity of 

model results to changing one parameter while all 

others are held at their calibrated values is shown in 

figure 22. Model error was determined to be most 

sensitive to changes in effective recharge rates to the 

unirrigated and golf-course irrigation areas and the 

vertical anisotropy of the aquifer. The model was least 

sensitive to changes in the effective recharge rate of the 

underflow areas and was more sensitive to overestimation of this parameter (fig. 22). 

Although the lateral hydraulic conductivity distributions of the S-zone (layer 1) and the I-zone (layer 2) 

were not changed during model calibration, 
Simulation of Ground-Water Flow in the Surficial Aquifer System 41

estimates of these distributions affect effective 

recharge rate and vertical hydraulic conductivity estimates. These effects were investigated by estimating 

the same parameters listed in table 6 with two alternative models. The lateral hydraulic conductivity of the 

I-zone was assumed to be half of the best estimate for 

one alternative model and double the best estimate for 

the other alternative model. The lateral hydraulic conductivity of the I-zone was varied because it is less well 

known than the lateral hydraulic conductivity of the 

S-zone. 

Effective recharge rates to the unirrigated areas 

and vertical hydraulic conductivity estimates of the 

alternative models differed most from the calibrated 

Figure 22. Model sensitivity to independent changes in selected calibration parameters. ROOT-MEAN-SQUARE ERROR, IN FEET

0.7

0.8

0.9

1

1.5

0.2 0.3 0.4 0.5 0.7 1 2 3 4 5

0.75

1

0.8

0.9

N′

Unirrigated

N′

Golf-course

KZ / KXY aquifer

N′

Underflow

N′

Ornamental plant irrigation

N′

Dredge material

KZ Marsh-muck confining unit

N′

Sports facilities 

N′

Underflow

MULTIPLIER OF CALIBRATED VALUE
42 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected Waste-Disposal 

Sites at Naval Station Mayport, Florida

model. Effective recharge rate estimates from the 

calibrated model decreased 33 percent in the halved 

model and increased 50 percent in the doubled model. 

The vertical hydraulic conductivity of the marsh-muck 

confining unit was decreased 70 percent in the halved 

model and increased by a factor of three in the doubled 

model. The RMS errors of the halved and doubled 

models, 0.78 and 0.83 ft, were slightly greater than the 

RMS error of the calibrated model, 0.75 ft. The alternative models show that a relatively small RMS error 

alone does not assure a well calibrated model and 

either some stresses or hydraulic conductivities must 

be known. 

Estimation of the Average Recharge Rate

Instead of conceptualizing the effective recharge 

rates estimated for each synoptic survey period as 

volumetric rates, they can be thought of as measures of 

the energy release rate or discharge from the flow 

system during each period. Rising or declining water 

levels represent increasing or decreasing rates of 

discharge from the surficial aquifer system. Discharge 

rates increase even as the surficial aquifer system is 

recharged, analogous to the increase in discharge from 

a leaky bucket as it is filled. 

The relation between water level and effective 

recharge rate (eq. 12) is expected to be linear and can 

be used to estimate the daily aquifer discharge rate. 

The effective recharge rates that were applied to the 

unirrigated areas for periods 1, 2, and 3 were regressed 

against the water levels in well 8-5I during the respective periods. The effective recharge rates were correlated with the water levels (fig. 23) and could be 

estimated on a daily basis using the hydrograph for 

well 8-5I (fig. 10). 

The recharge rate over the period of water-level 

record (fig. 10) was 7.6 in/yr and was estimated by 

averaging the effective recharge rate (estimated from the 

relation in fig. 23). The recharge rate for 1996 was 

probably closer to 7 in/yr because the first 3 months of 

the year (without water-level record) were comparatively drier (fig. 10). The recharge rate over the last 

36 years is probably closer to 8 in/yr because 1996 was a 

relatively dry year (44 in. compared to an average 

precipitation rate of 51 in/yr between 1961 and 1996). 

The median recharge rate (6.6 in/yr) is lower 

than the average rate (7.6 in/yr) because recharge is 

not uniformly distributed throughout the year. 

Recharge events were of a smaller magnitude from 

winter through early summer (fig. 10) and the daily 

effective recharge rate (estimated from the relation in 

fig. 23) ranged from about 5 to 8 in/yr during this 

period. Intense precipitation events in the fall 

produced effective recharge rates as great as 22 in/yr. 

The effective recharge rate remained greater than the 

average rate for almost 2 months after a 12-in. precipitation event in early October. 

Ground-Water Flow during the Calibration 

Period 

The analysis of ground-water flow and potential 

movement of contaminants within the surficial aquifer 

system was addressed using the calibrated model 

driven by the recharge rate distribution estimated for 

period 1. This recharge rate distribution was assumed 

to be representative of the average rate of water application to the surficial aquifer system because the 

recharge rate to the unirrigated areas was about 8 in/yr. 

The response of the ground-water system to recharge 

rates that are lower than average is discussed because 

the effective recharge rate on any given day is less 

than the average amount of recharge received during a 

year. Flow conditions related to higher-than-average 

recharge rates also are discussed because the locations 

of discharge points of ground-water flow paths and the 

rate of contaminant travel to those discharge locations 

vary according to changes in recharge rates. 

Figure 23. Relation between water levels measured 

in well 8-5I and effective recharge rate estimates for 

the unirrigated areas. 

2 7 3 4 5 6

WATER LEVEL, IN FEET

0

15

5

10

EFFECTIVE RECHARGE RATE, 

IN INCHES PER YEAR

Regression Line

ABOVE SEA LEVEL

N ′

Unirrigated = 3.3h - 6.7
Simulation of Ground-Water Flow in the Surficial Aquifer System 43

The water table configuration is strongly influenced by drainage features. The simulated lateral flow 

direction in the S-zone commonly is perpendicular to 

the nearest drainage feature (fig. 19). One exception is 

in the area near well 8-5I, where the lateral flow 

direction is affected by the spatial variability in 

hydraulic conductivity and the predominant flow 

direction is downward. The simulated potentiometric 

surface of the I-zone is strongly influenced by the 

larger surface-water features (fig. 20). 

Schematics of the simulated volumetric flow 

budgets for the three synoptic survey periods are 

presented in figure 24. The volumetric budget for 

period 1 is most representative of estimated average 

S-ZONE (1) 0.67

1.33

I-ZONE (2)

EXPLANATION

FLOW ACROSS A BOUNDARY

1.33 FLOW RATE, IN CUBIC FEET PER SECOND

(2) MODEL LAYER

IRRIGATION UNDERFLOW

UNIRRIGATED

0.48 0.43 0.04

0.36

0.07

0.44

0.18 1.34 0.11

0.00 0.05

SHERMAN

0.14

0.18 0.06

CREEK CANALS

LAKE

WONDER

WOOD SEEPAGE

ST. JOHNS

AND

ATLANTIC

Period 1: July 17, 1995

S-ZONE (1) 0.55

0.94

I-ZONE (2)

DREDGE

0.30 0.36 0.05

0.31

0.04

0.36

0.15 0.94 0.09

0.00 0.04

SHERMAN

0.07

0.15 0.05

CREEK CANALS

LAKE

WONDER

WOOD SEEPAGE

Period 2: July 31, 1996

S-ZONE (1) 0.89

2.29

I-ZONE (2)

0.33 0.58 0.04

0.43

0.19

0.56

0.19 1.78 0.16

0.00 0.08

SHERMAN

0.36

0.19 0.08

CREEK CANALS

LAKE

WONDER

WOOD SEEPAGE

Period 3: October 24, 1996

UNDERFLOW

UNDERFLOW

MATERIAL

DREDGE

MATERIAL

DREDGE

MATERIAL

IRRIGATION

IRRIGATION

RECHARGE

UNIRRIGATED

RECHARGE

UNIRRIGATED

RECHARGE

OCEAN

RIVER

ST. JOHNS

AND

ATLANTIC

OCEAN

RIVER

ST. JOHNS

AND

ATLANTIC

OCEAN

RIVER

Figure 24. Simulated volumetric flow budget for the three calibaration periods on July 17, 1995; July 31, 1996; and 

October 24, 1996.
44 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected Waste-Disposal 

Sites at Naval Station Mayport, Florida

ground-water flow rates because the effective recharge 

rate to the unirrigated areas is about equal to the 

average amount of recharge received during a year. 

The total flow through the surficial aquifer system 

averaged 2.3 ft3

/s (period 1) and ranged from 1.7 ft3/s 

(period 2) to 3.2 ft3

/s (period 3, fig. 24). For the 

extreme effective recharge rates estimated from the 

hydrograph for well 8-5I (fig. 10), the range in total 

simulated flow through the surficial aquifer system is 

about 1 to 4 ft3

/s. 

Irrigation accounts for about 20 percent of the 

water that circulates through the surficial aquifer 

system during all three periods (fig. 24). Most of the 

irrigation water is applied to the golf greens and 

fairways and the sports facilities north of the golf 

course. Much of the golf-course irrigation water 

passes through the I-zone and is discharged to 

Sherman Creek and Lake Wonder Wood (fig. 25). The 

sharp bends and sudden changes in particle direction 

are the effects of movement between the S-zone and 

the I-zone. Golf-course irrigation supplies about 

0.06 ft3

/s (33 percent) of the ground-water discharge 

to Sherman Creek and about 0.04 ft3/s (35 percent) of 

the ground-water discharge to Lake Wonder Wood. 

As the recharge rate increases, the water table 

rises and diffuse discharge seeps from areas that 

formerly were recharge areas. These areas mostly are 

between the southwest runway and Patrol Rd., 

northeast of the dredge material holding areas, and 

over the baseball fields (fig. 26). Simulation of 

advective transport of contaminants based on an 

average recharge rate is problematic in these areas. A 

contaminant being transported near the water table in 

one of these areas could be discharged from the 

surficial aquifer system earlier and in a different 

location than expected based on the average recharge 

rate. For example, an intense recharge event could 

cause contaminants to be discharged along the 

southwest runway 200 to 400 ft upgradient of the 

perennial drains and 5 to 20 years sooner than 

predicted by a steady-state simulation. 

As recharge rates increase, the absolute quantity 

of water circulating through the I-zone increases, but 

the fraction of ground-water flow circulating through 

the I-zone decreases compared to the total 

ground-water flow through the surficial aquifer system 

(fig. 24). The I-zone transmitted between 0.55 and 

0.89 ft3

/s (33 and 27 percent of the ground-water flow) 

during periods 2 and 3, respectively. 

Most of the I-zone is recharged in areas where 

the marsh-muck confining unit is less than 1 ft thick 

(fig. 6). Recharge from the dredge material holding 

areas (where the marsh-muck confining unit is more 

than 1 ft thick) to the I-zone is an exception because of 

head differences of about 15 ft between the water table 

and the I-zone. Localized areas of higher recharge 

rates to the I-zone from irrigation-augmented recharge 

appear as denser patches of particles in figure 27. 

Contaminants migrating from areas that recharge the 

I-zone generally will have longer flow paths and 

residence times than those that migrate exclusively 

through the S-zone. 

EVOLUTION OF MAYPORT PENINSULA 

AND SURFICIAL AQUIFER SYSTEM

The surficial aquifer system at NAVSTA 

Mayport is a dynamic system that has been modified 

by natural and anthropogenic forces over the last 

200 years. The freshwater flow system is expanding 

and entrained saltwater continues to be flushed from 

the system. The chloride concentration in many of the 

wells screened about 20 ft below sea level range from 

about 20 to 25,000 mg/L. Concentrations in excess of 

typical sea water values (19,400 mg/L) indicate that 

the original water from the salt marshes has not yet 

been displaced. Water levels of about 3 to 6 ft above 

the average level of the St. Johns River also indicate 

that the freshwater lens is still developing. If the 

Ghyben-Herzberg approximation is applied, the water 

levels in these same wells would suggest that the 

interface should be more than 100 ft below the well 

screens. 

Anthropogenic activities associated with the 

construction and modification of NAVSTA Mayport 

since 1942 have caused the majority of change to the 

surficial aquifer system. More than 1 mi2

 of salt marsh 

and tidally-affected areas have been reclaimed by the 

construction of runways, building of support facilities, 

and maintenance of the turning basin. In addition to 

expanding the domain of the surficial-aquifer system, 

recharge rates have been dramatically increased by 

intensive irrigation. 

The extent and morphology of the Mayport 

peninsula has been documented sporadically since the 

early 1800’s (U.S. Department of the Navy, 1995). The 

earliest maps of the Mayport peninsula were 

developed during British occupation in 1822 (U.S. 

Department of the Navy, 1995). A U.S. Coast Survey
Evolution of Mayport Peninsula and Surficial Aquifer System 45Figure 25. Simulated flow paths from areas where recharge occurs at rates greater than 45 in/yr to their respective d

period 1. 0 2,50

0 

Sherman

81° 26′ 

DREDGE 

HOLDING

RUNWAY

MATERIAL

 AREAS

HANGARS

Fairw

Fairways

A1A

Maine St.

Moale Ave.

Patrol Rd.

Patrol Rd.

Alpha Pier

Charlie Pier

Delta Pier

Bravo Pier

Echo Pier

Foxtrot Pier

Bailey Ave.

Bon Homme Richard

Chicopit Bay

Ma

L

Wo

W

Creek

30° 24′

30° 23′

STUDY

TURNING

BASIN

S

T

AREA

EXPLANATION

PATHLINE--Shows path of a particle transported by advection through:

the S-zonethe I-zoneDirection of flow
Sites at Naval Station Mayport, Florida

46 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected WasteDisposal 0 2,50

0 

Sherman

81° 26′ 

DREDGE 

HOLDING

RUNWAY

MATERIAL

 AREAS

HANGARS

Fairw

Fairways

A1A

Maine St.

Moale Ave.

Patrol Rd.

Patrol Rd.

Alpha Pier

Charlie Pier

Delta Pier

Bravo Pier

Echo Pier

Foxtrot Pier

Bailey Ave.

Bon Homme Richard

Chicopit Bay

Ma

L

Wo

W

Creek

30° 24′

30° 23′

STUDY

TURNING

BASIN

S

T

AREA

EXPLANATION

DISCHARGE AREAS / RECHARGE AREAS -- Areas of discharge when recharge rate is 14 in/yr. Areas of recharge when recharge rate is 6 in/yr

Figure 26. Simulated areas of discharge when the surficial aquifer system is recharged at 14 in/yr that are not discharge a

recharged at 6 in/yr.
Evolution of Mayport Peninsula and Surficial Aquifer System 47 0 2,

0 

Sherman

81° 26′ 

DREDGE 

HOLDING

RUNWAY

MATERIAL

 AREAS

HANGARS

Fa

Fairways

A1A

Maine St.

Moale Ave.

Patrol Rd.

Patrol Rd.

Alpha Pier

Charlie Pier

Delta Pier

Bravo Pier

Echo Pier

Foxtrot Pier

Bailey Ave.

Chicopit Bay

Creek

30° 24′

30° 23′

STUDY

TURNING

BASIN

S

AREA

EXPLANATION

AREA CONTRIBUTING RECHARGE TO THE I-ZONE -- Areal density is approximately proportional to the recharge rate

Figure 27. Areas that contribute recharge to the I-zone when the surficial aquifer system is recharged with the distributio
48 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected Waste-Disposal 

Sites at Naval Station Mayport, Florida

map from 1853 was the first to document the large salt 

marsh west of the coastal sand dunes. The shoreline, 

extent of marsh, and drainage features that existed in 

1918 and 1940 were depicted by maps from the U.S. 

Geological Survey and NAVSTA Mayport historians, 

respectively (U.S. Department of the Navy, 1995). 

Further changes in the extent and morphology of the 

peninsula were documented by aerial photographs of 

NAVSTA Mayport taken since 1952. 

The surficial aquifer system has been strongly 

affected by the rapidly changing morphology of the 

peninsula. Expansion of land mass by either natural 

accretion or anthropogenic activities has increased the 

lateral and vertical extent of the fresh ground-water 

flow system. Natural accretion gradually moves the 

freshwater/saltwater interface seaward, whereas the 

reclamation projects are more analogous to a sudden 

uplift causing commensurate changes in the rates and 

distribution of recharge to and discharge from the 

surficial aquifer system. The typical reclamation project 

at NAVSTA Mayport raised about a 0.25-mi2

 area from 

1 to 12 ft above sea level over a 5-year period. 

Prior to land being accreted or reclaimed, 

ground-water flow in the offshore and salt marsh areas 

was negligible. As the land mass expanded and the 

altitude of the land surface increased, additional 

surfaces became available for freshwater recharge. 

The additional freshwater recharge increased the 

ground-water flow rate and began displacing the 

entrained saline pore water.

Simulated Displacement of Saline Water 

The advective displacement of saline pore water 

was simulated using a particle-tracking routine, 

MODPATH (Pollock, 1994). The density contrast 

between saline and freshwater zones was assumed to 

have a negligible effect on the flow system and was 

not simulated. A comparison between density-dependent and uniform-density simulations of generalized 

cross-sections through NAVSTA Mayport showed that 

the displacement of saline pore water by freshwater 

recharge can be adequately simulated as a 

uniform-density flow field (app. B) because the 

topographically driven gradients are several times 

greater than the density-driven gradients. 

Particle traveltimes and advective displacement 

rates are proportional to the effective porosity 

estimates. If effective porosity estimates are doubled, 

ground-water velocities will be halved and traveltimes 

will double. Porosity measurements from cores 

collected in the unsaturated zone near Lake Wonder 

Wood and north of the southwest runways ranged from 

45 to 51 percent. The porosity of these samples is 

suspected of being biased upward by the measurement 

method (the volume of the cores was determined by 

drying and weighing the samples). The measured 

porosities also are not entirely representative of the 

aquifer matrix because the matrix contains oyster 

shells and debris that were too large to be collected in 

the cores. A lower effective porosity of 40 percent was 

used for all particle-tracking simulations because the 

core porosities, as measured, represent the total 

porosity. Effective porosity differs from total porosity 

in that only the interconnected pore spaces are 

included. 

The connate pore water was approximated by a 

uniform array of particles placed in the middle of the 

I-zone. Particles were not placed in the S-zone because 

water quickly moves through the S-zone to discharge 

at the surface or enters the I-zone. The average 

residence time in the S-zone was about 12 years under 

average 1996 conditions and an effective porosity of 

40 percent. 

The dilution of connate saltwater by freshwater 

recharge was depicted by particle spreading within the 

I-zone and removal at simulated surface-water 

features. Graphically approximating the relative 

concentration of saltwater in the I-zone with a single 

layer of particles can be locally deceptive because the 

areal particle concentration is decreased or increased 

by factors other than freshwater recharge. Vertical 

movement near discharge areas causes the areal 

concentration of particles to increase. This effect is 

more pronounced when the recharge is diffuse and the 

discharge is focused. Increases in aquifer thickness or 

effective porosity will cause the areal concentration of 

particles to increase whereas decreases in either 

aquifer property will have the opposite effect. 

Steady-State Displacement with 1996 Recharge 

Rates

Saltwater displacement initially was simulated 

with the steady-state model driven by the recharge 

rates that were estimated for 1996 (period 1). The 

saltwater displacement patterns in the I-zone are 

shown in figure 28 at the end of 50-year intervals for 

the 200-year simulation period. Initial pore-water 

distributions were assumed to be 100 percent fresh in 

the S-zone and 100 percent saline in the I-zone. 
Evolution of Mayport Peninsula and Surficial Aquifer System 49

1847 18971947 1997

Figure 28. Particle distributions in the I-zone after 50, 100, 150, and 200 years of travel simulated by the steady-state model us

0 

0 

EXPLANATION

APPROXIMATE EXTENT OF PARTICLE DISTRIBUTION
50 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected Waste-Disposal 

Sites at Naval Station Mayport, Florida

Saltwater displacement was complete and rapid 

in the vicinity of recharge areas to the I-zone (fig. 27). 

Saltwater was completely displaced between well 

8-5S and the St. Johns River, beneath the golf course, 

and along the Atlantic Ocean in 50 years or less 

(fig. 28). More moderate rates of saltwater displacement occurred beneath and south of the dredge 

material holding areas. Dilution and spreading of the 

connate water is apparent after 50 years of freshwater 

recharge and is nearly complete beneath the western 

dredge material holding area after 200 years. 

Very little saltwater was displaced near the 

hangars, north of the dredge material holding areas, 

and along the southwestern runway during the 

200-year simulation period (fig. 28). Ground-water 

flow and saltwater displacement in the I-zone were 

restricted by the marsh-muck confining unit (fig. 6) 

and an area of low transmissivity northwest of the 

hangars in the I-zone (fig. 16). Another pocket of 

reduced saltwater displacement existed between Echo 

pier and Bon Homme Richard St. (figs. 1 and 28). In 

addition to the presence of the marsh-muck confining 

unit and an area of low transmissivity along the St. 

Johns River, ground-water movement in the I-zone 

was further restricted by Echo and Foxtrot piers. 

The veracity of the steady-state, saltwater 

displacement simulation was assessed by comparing 

the final particle distribution (200 year) to chloride 

concentrations measured in 1993 (U.S. Department of 

the Navy, 1995) and 1996 from the I-zone (fig. 29). 

Areas of little saltwater displacement should have 

chloride concentrations of about 19,400 mg/L, which 

is the typical chloride concentration of seawater. Areas 

that have passed many pore volumes of freshwater 

should have chloride concentrations of less than 

100 mg/L. The simulated saltwater distribution after 

200 years of displacement did not consistently 

describe the measured chloride distribution in the 

I-zone (fig. 29). Measured chloride values and the 

simulated saltwater distribution agreed in the areas 

between well 8-5S and the St. Johns River, north of the 

dredge material holding areas, and along the Atlantic 

Ocean. The simulated saltwater distribution did not 

reflect the measured chloride concentrations beneath 

and to the south of the dredge material holding areas, 

between the eastern dredge material holding area and 

the golf course, or along the southwestern runway 

(fig. 29). 

The changes in stresses, boundary conditions, 

and hydraulic properties of the Mayport peninsula 

have been great enough that no one, steady-state, flow 

field can adequately simulate the saltwater displacement from the surficial aquifer system. Even if the 

50-year displacement pattern were compared instead 

of the 200-year pattern, many discrepancies would 

exist between the simulated pattern and the measured 

chloride values. Greater saltwater displacement was 

simulated south of the western golf course than the 

chloride measurements indicate (figs. 28-29). Insufficient displacement was simulated north of Moale Ave. 

and to the east of Echo pier and does not adequately 

account for the measured chloride concentrations of 

less than 200 mg/L. 

Transient Displacement 

A transient model of the Mayport peninsula was 

developed that accounted for the known changes in 

hydraulic properties, boundary conditions, and stresses 

over the last 200 years. The transient flow field of the 

surficial aquifer system was simulated with 10 stress 

periods that approximated the shifting morphology 

and changing boundaries that occurred between 1798 

and 1997. 

Stress periods were based primarily on changes 

in surface-water features and data availability. The 

surface-water features were allowed to expand, 

contract, or move as needed between stress periods. 

The distribution and extents of surface-water features 

were determined from maps of the Mayport peninsula 

for the years 1822, 1853, 1918, 1940, and 1964 (U.S. 

Department of the Navy, 1995) and aerial photographs 

taken during 1952, 1962, 1972, 1977, 1982, 1989, and 

1995 (Cheryl Mitchell, Staff Civil Engineer Mayport, 

U.S. Navy, written commun., 1996). The division of 

the simulation period into stress periods and the significant hydrologic changes between periods are listed in 

table 9.

Hydraulic properties of the surficial aquifer 

system were modified over time by anthropogenic 

activities at NAVSTA Mayport. For example, the 

addition of dredge material locally increased the 

thickness of the marsh-muck confining unit and 

elevated the base of the S-zone; the dredging of 

Sherman Creek and Lake Wonder Wood breached the 

marsh-muck confining unit; and the construction of 

quay walls has introduced impermeable barriers 

between the surficial aquifer system and the turning 

basin. MODFLOW does not simulate time-variant 

hydraulic properties (McDonald and Harbaugh, 1988), 

so a new MODFLOW package (VAR1, app. C) was 
Evolution of Mayport Peninsula and Surficial Aquifer System 51Figure 29. Flushing of connate saltwater from the I-zone over a 200-year period simulated by the steady-state model usi

0 2,

0 

Sherman

81° 26′ 

DREDGE 

HOLDING

RUNWAY

MATERIAL

 AREAS

HANGARS

Fa

Fairways

A1A

Maine St.

Moale Ave.

Patrol Rd.

Patrol Rd.

Alpha Pier

Charlie Pier

Delta Pier

Bravo Pier

Echo Pier

Foxtrot Pier

Bailey Ave.

Chicopit Bay

Creek

30° 24′

30° 23′

STUDY

TURNING

BASIN

S

AREA

120

26

15

14,000

18,700

8,700

14,000

16,200

19,800

13,400

17,000

19,800

4,700

25,500

14,000

19,000

350

34

52

1,100

EXPLANATION

FINAL CONNATE PARTICLE POSITIONS--Initially uniform, lateral spacing of 125 ft and vertically centered in the middle of the I-zone. Areas with less particles represent zones of greater saltwater flushingCHLORIDE CONCENTRATION--measured during 1996, in milligrams per literCHLORIDE CONCENTRATION--measured during 1993, in milligrams per liter. Seawater is about 19,400 mg/L

34

15

19,500
52 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected Waste-Disposal 

Sites at Naval Station Mayport, Florida

written to accommodate the time-variant hydraulic 

properties. This package is not a major modification of 

MODFLOW and is documented in appendix C. Away 

from Sherman Creek, Lake Wonder Wood, and the 

areas where the base of the S-zone was elevated above 

sea level, it was assumed that the hydraulic property 

estimates from the calibrated model were adequate and 

did not change. A uniform specific yield of 0.1 and 

storage coefficient of were assumed for the 

S-zone and I-zone, respectively. 

Historical recharge rate estimates were speculative but were extrapolated from 1996 estimates. A 

spatially uniform recharge rate of 5 in/yr was applied 

during stress periods 1, 2, and 3 (1800 to 1945) and 

was extrapolated from the smaller estimates during 

1996. The estimates were constrained by assuming the 

elevation of the land surface was lower prior to 1945 

than in 1996 and assuming that the surficial aquifer 

system lacked the storage capacity to retain water after 

intense precipitation events. Spatial recharge variation 

due to impervious surfaces was simulated in stress 

periods 4 through 10 (1946 to 1997) and was based on 

aerial photographs. The recharge rate to unirrigated 

areas was increased to 6 and 8 in/yr in stress periods 6 

and 8 (table 9), respectively, to reflect the increasing 

storage capacity of the surficial aquifer system. The 

effect of irrigation projects was simulated in stress 

periods 7 through 10 (1973 to 1997). 

The effects of the shifting morphology, 

changing boundaries, and increasing recharge rates are 

shown by changes in the water table extent, elevation, 

and configuration (fig. 30). Prior to 1880, the freshwater flow system was confined to a thin finger of land 

that covered less than 1 mi2. By 1945, the upland area 

had increased to about 2 mi2, mostly due to natural 

accretion. The ground-water flow system was immediately modified after the establishment of NAVSTA 

Mayport as evidenced by the filling of Ribault Bay, the 

extending of the runways to the southwest, and the 

redirecting of the creek that flows through present day 

Lake Wonder Wood. Between 1952 and 1972, about 

1 mi2

 of marsh was converted to an upland area south 

of the runways and the inlet for Delta pier, Sherman 

Creek, and Lake Wonder Wood was dredged. Between 

1972 and 1977, the effects of irrigation associated with 

the addition of the golf course are shown by the 

expanded 5-ft contour (fig. 30). The addition of 

irrigated sports facilities and ornamental plants 

between 1978 and 1994 caused the water table to rise 

to more than 10 ft above sea level east of Maine St. 

During this same period, the altitude of the dredge 

material holding areas exceeded 30 ft, thus these areas 

could sustain higher recharge rates (fig. 30). 

Table 9. Simulated recharge, irrigation, and discharge rates applied to the transient model of NAVSTA Mayport, 

1798 to 1997 

[mi2, square miles; in/yr, inches per year; recharge, irrigation, and discharge in cubic feet per second; --, not applicable]

Stress

period

Last 

year of 

stress 

period

Upland 

area, 

mi2

Natural 

recharge 

rate, 

in/yr

Recharge 

and 

irrigation

Discharge

Percent 

of 1996 

rate

Significant change from 

previous stress period

Canals, 

lakes, 

and 

seepage

St. Johns 

River and 

Atlantic 

Ocean

1 1880 0.91 5 0.34 0.18 0.16 15 --

2 1920 1.54 5 .57 .27 .30 25 Mayport peninsula expanded by natural

 accretion.

3 1945 2.01 5 .74 .24 .50 33 Ribault Bay formed; NAVSTA Mayport 

commissioned in 1942.

4 1952 2.75 5 .89 .49 .40 39 Alpha, Beta, and Charlie piers were built. 

5 1962 2.99 5 .98 .56 .42 43 Delta pier added and southwest runways 

extended.

6 1972 2.99 6 1.11 .73 .39 49 Lake Wonder Wood dredged. 

7 1977 3.41 6 1.67 1.21 .47 73 Golf course irrigation started; Sherman 

Creek dredged.

8 1982 3.41 8 1.71 1.23 .48 75 Sports facility irrigation started.

9 1994 3.42 8 2.28 1.77 .51 100

Echo pier and hangars added; ornamental 

plant irrigation started; dredge material 

holding area exceeded 30 feet above sea 

level.

10 1997 3.42 8 2.28 1.77 .51 100 Foxtrot pier added. 

5 –5×10
Evolution of Mayport Peninsula and Surficial Aquifer System 53

Ribault Bay

EXPLANATION

WATER TABLE CONTOUR--Shows altitude 

of water table. Contour interval 5 feet with 

supplemental 2 foot contour. 

Datum is sea level 

Present day shoreline

(Shorelines and marsh extents modified from U.S. 

Department of Navy, 1995)

2

1880

1945

1972

1994

1920

1952

1977

0 4,000 FEET

0 1,000 METERS

2,000

500

Figure 30. Water table in the S-zone (layer 1) at selected times as simulated by the transient model.

SHORELINE 5

2

2

5

5

5

5

5

2

5

10

5

5

10

10 15

5

10

5

2

5

2

5

10

5

2

5

5

2

5

2 5

2

2

2

2

2

5

5

2

2

5

2

5

2

2

2

5

2

5

2

2

2

2

2

5

5
54 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected Waste-Disposal 

Sites at Naval Station Mayport, Florida

Natural accretion and land reclamation projects 

have expanded the upland area of the Mayport 

peninsula and increased the amount of flow through 

the surficial aquifer system (table 9). The simulated 

flow through the system increased more than sixfold 

from 0.34 to 2.28 ft3

/s between 1880 and 1996 (table 

9). Irrigation has also increased the flow through the 

system as evidenced by the increase in simulated flow 

from 1.11 to 1.67 ft3

/s following the commencement 

of golf course irrigation between 1972 and 1977. 

Water levels rose as the upland area expanded 

and recharge to the surficial aquifer system increased 

(fig. 31). Part of the water-level rise was due to the 

increased length of the flow paths between recharge 

and discharge points. Shortening the flow paths will 

lower water levels as was done by dredging the inlet 

for Delta pier near well 20-2S between 1953 and 1962. 

The second water-level decline between 1963 and 

1972 near well 20-2S was caused by the dredging of 

Lake Wonder Wood. Most of the water-level rise 

simulated between 1973 and 1997 was due to recharge 

induced by golf course irrigation.

Saltwater displacement from the I-zone was 

confined to a relatively narrow strip that paralleled 

Maine St. and extended to the town of Mayport during 

the first 100 years (fig. 32). An area of unflushed 

connate water existed for the first 150 years beneath 

the creek that was rerouted from the St. Johns River to 

the western marsh. This unflushed connate water 

began to dissipate in the ensuing 50 years after intense 

irrigation altered the previous flow paths (fig. 32). 

The transient simulation showed less saltwater 

displacement than the steady-state simulation around 

the dredge material holding areas, west of the golf 

course, and along the southwestern runways (fig. 32). 

The simulations differed because the principal stresses 

that displaced the saltwater more thoroughly in the 

steady-state simulation have existed only for the last 

25 to 50 years. The transient simulation indicated that 

more saltwater displacement occurred between Echo 

pier and Bon Homme Richard St. when compared to 

simulation results from the steady-state model. The 

transient simulation indicates that additional displacement also occurred because Echo and Foxtrot piers did 

not exist until 1983 and 1995, respectively. 

The simulated saltwater distribution after 

200 years of transient displacement described the 

measured chloride distribution in the I-zone better 

than the steady-state simulation (fig. 33). The greatest 

discrepancy between the simulated saltwater distribution and the measured chloride concentrations 

occurred between the hangars and the runway; the 

particle distribution suggests very little displacement, 

but the measured chloride concentration in this area is 

4,700 mg/L. The difference probably was due to 

over-extrapolation of the extent of the marsh-muck 

confining unit to the north of well 2-34I (location 

shown in fig. 3a). The discrepancy also may have 

resulted from neglecting variable-density and dispersive effects, given the proximity to the internal freshwater/saltwater interface (app. B).

SIMULATION OF MOVEMENT OF 

CONTAMINANTS

The advective movement of conservative 

contaminants from selected sites within the SWMUs 

to discharge points was simulated with MODPATH 

(Pollock, 1994). Contaminant movement was 

simulated by the steady-state model driven by the 

recharge rates that were estimated for 1996 (period 1). 

Particles were released at the water table to approximate the initial position of contaminants at selected 

sites. Most of the particles were discharged to the 

nearest surface-water feature and traveled less than 

1,000 ft before being discharged from the 

ground-water system (fig. 34). Particles that traversed 

longer flow paths migrated through the I-zone (sites 

4b, 5d, 13a, 13b, 13c, and 15 in fig. 34). 

10

8

6

4

2

1900 1925 1950 1975 2000

0

YEAR

WATER LEVEL, IN FEET

 ABOVE SEA LEVEL

Figure 31. Water levels in selected wells simulated by the 

transient model (Well locations are shown in fig. 1).

8-5S

8-5I

20-2S
Evolution of Mayport Peninsula and Surficial Aquifer System 55Figure 32. Particle distributions in the I-zone after 50, 100, 150, and 200 years of travel simulated by the transient model from 

1847 18971947 1997

0 

0 

EXPLANATION

APPROXIMATE EXTENT OF PARTICLE DISTRIBUTION
Sites at Naval Station Mayport, Florida

56 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected Waste-Disposal Figure 33. Flushing of connate saltwater from the I-zone over a 200-year period simulated by the transient mod

0 2,50

0 

Sherman

81° 26′ 

DREDGE 

HOLDING

RUNWAY

MATERIAL

 AREAS

HANGARS

Fairw

Fairways

A1A

Maine St.

Moale Ave.

Patrol Rd.

Patrol Rd.

Alpha Pier

Charlie Pier

Delta Pier

Bravo Pier

Echo Pier

Foxtrot Pier

Bailey Ave.

Bon Homme Richard

Chicopit Bay

Ma

L

Wo

W

Creek

30° 24′

30° 23′

STUDY

TURNING

BASIN

S

T

AREA

EXPLANATION

FINAL CONNATE PARTICLE POSITIONS -- Initially uniform, lateral spacing of 125 ft and vertically centered in the middle of the I-zone. Areas with less particles represent zones of greater saltwater flushingCHLORIDE CONCENTRATION-- measured during 1996, in milligrams per literCHLORIDE CONCENTRATION-- measured during 1993, in milligrams per liter. Seawater is about 19,400 mg/L

34

15

120

180

26

4

15

14,000

18,700 14,900

8,700

14,000

19,800

11,900 13,400

17,000

19,800

4,700

25,500

14,000

19,000

350

34

52

1,100

50

16,200

19,500
Evolution of Mayport Peninsula and Surficial Aquifer System 57 0 2,50

0 

Sherman

81° 26′ 

DREDGE 

HOLDING

RUNWAY

MATERIAL

 AREAS

HANGARS

Fairw

Fairways

A1A

Maine St.

Moale Ave.

Patrol Rd.

Patrol Rd.

Alpha Pier

Charlie Pier

Delta Pier

Bravo Pier

Echo Pier

Foxtrot Pier

Bailey Ave.

Bon Homme Richard

Chicopit Bay

Ma

L

Wo

W

Creek

30° 24′

30° 23′

STUDY

TURNING

BASIN

ST

AREA

INSET B

INSET A

13c

56 13b

13a

26b

22

26a

2

50k 50j

5a

5d 5b 5c

50f

50i

50h

50g

4a 4b

50e

50d

50c 50a

50b

29

52

17

46

21

20

45

44

1

24

25

Figure 34. Pathlines from selected sites at the water table to their discharge points simulated by the steady-state model u

15

28a

28b

6 7

28c

11

10 9

16

17

EXPLANATION

PATHLINE -- Shows pathof a particle transportedby advection through:

the S-zone

the I-zone

PARTICLE ORIGIN ANDSWMU ID
58 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected Waste-Disposal 

Sites at Naval Station Mayport, Florida

0 1,000 2,000 FEET

0 500 METERS

81° 25′30′′ 81° 25′

30° 24′

30° 23′30′′

16

11

10

9

28c

7 6

28b

28a

15

29

13c

56 13b

13a

22

26b

26a

5a

5d

2

50k 50j

5b 5c

INSET A

17

EXPLANATION

PATHLINE -- Shows path

of a particle transported

by advection through:

the S-zone

the I-zone

PARTICLE ORIGIN AND

SWMU ID

Figure 34. Inset A.
Evolution of Mayport Peninsula and Surficial Aquifer System 59Figure 34. Insert B. 0 1,000 

0 

81° 24′30′′ 81° 24′

30° 23′45′′30° 23′30′′ Baseball

Fields

52

17

21

20

25

23

24

1

44

45

17

EXPLANATION

PATHLINE -- Shows pathof a particle transportedby advection through:

the S-zone

the I-zone

PARTICLE ORIGIN ANDSWMU ID

46
60 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected Waste-Disposal 

Sites at Naval Station Mayport, Florida

Differences in the direction of the lateral hydraulic 

gradient exist between the S-zone and the I-zone over 

much of the study area where the marsh-muck confining 

unit is present (fig. 6). In areas where the difference is 

great, sharp bends and sudden changes in particle 

direction are exhibited by the flow paths, as particles 

move between the S-zone and the I-zone (sites 4b, 5d, 

and 13a in fig. 34). Particle movement from the S-zone to 

the I-zone along paths 4b and 5d are the most extreme 

examples, where the direction of the lateral hydraulic 

gradients differ by about 180 degrees. For both particles, 

initial movement in the S-zone is north towards the Patrol 

Road canal and downward (fig. 34). After crossing the 

marsh-muck confining unit and entering the I-zone, the 

particles reverse direction and head south towards 

Sherman Creek. 

Most of the water that crosses the marsh-muck 

confining unit to enter the I-zone originates at or near a 

ground-water divide or mound. The flow field around a 

ground-water divide or mound is divergent and the 

dominant hydraulic gradient is downwards. Small 

displacements at the locations of particle release can 

greatly alter the particle paths and points of discharge. 

The effects of the divergent flow field are best 

illustrated by tracing a north-south transect of particles 

across the water table beneath the western dredge 

material holding area and examining their paths in 

plan and section (fig. 35). Of the 15 particles released, 

0 1,000 FEET

0 250 METERS

Sherman

Creek

A1A

25SEALEVEL2550

25

SEA

LEVEL

2550

LAND 

C

WATER 

Dredge Material Holding Area

S-ZONE

I-ZONE

Sherman

Creek

MARSH MUCK

TABLE

SURFACE

C C

C

AREA OF

DETAIL

N

VERTICAL EXAGGERATION 34X

EXPLANATION

PATHLINE OF A PARTICLE TRANSPORTED

BY ADVECTION THROUGH THE I-ZONE FEET

INTERMEDIATE

CONFINING UNIT

SURFICIAL

AQUIFER

SYSTEM

Figure 35. Effects of variable recharge on the location of contributing points to an observation point.
Contributing Areas and Ground-Water Age 61

12 particles traveled exclusively through the S-zone 

and were discharged along the flanks of the dredge 

material holding area (fig. 35). The three remaining 

particles were released within 300 ft of the groundwater divide and moved downward into the I-zone 

(fig. 35). The effect of opposing lateral hydraulic 

gradients in the S-zone and the I-zone on particle paths 

are clearly seen in section C-C′ (fig. 35). 

The traveltimes from the selected sites shown in 

figure 34 to their respective discharge points were 

estimated using an effective porosity of 40 percent 

(table 10). About 45, 80, and 90 percent of the traveltimes were less than 10, 50, and 100 years, respectively. Short traveltimes of less than a year for sites 2, 

26b, and 29 are the result of these sites being located 

in discharge areas. Traveltimes of more than 100 years 

were associated with the longer flow paths from sites 

4b, 5d, 13a, 13b, and 15 (table 10). Traveltimes 

reported for the selected sites in figure 34 are not 

representative of the traveltimes over the entire study 

area.

A generalized map of traveltimes was 

constructed for the study area by releasing a particle at 

each of the nodes in layer 1 and calculating the traveltime from the water table to the particle’s discharge 

point (fig. 36). Most areas within 1,000 ft of a 

surface-water feature or a storm sewer had traveltimes 

of less than 50 years. Flow paths with traveltimes of 

more than 500 years mostly originated from 

ground-water divides near the hangars and runways, in 

the dredge material holding areas, and near the intersection of Bailey Ave. and Bon Homme Richard St. 

CONTRIBUTING AREAS AND 

GROUND-WATER AGE

To assess the extent of ground-water contamination and the potential migration of contaminants, the 

origins of ground-water samples need to be identified. 

The contributing point for an observation point can be 

identified by back-tracking a particle from the observation point to the water table (fig. 37). If the recharge 

to the surficial-aquifer system always equalled the 

average rate, a steady-state flow field would exist and 

each observation point would correspond to only one 

contributing point at the water table. This one contributing point would supply water to the same observation point continuously. 

Table 10. Approximate traveltimes of particle movement 

from selected sites to their respective discharge points as 

simulated by the steady-state model using the average 1996 

flow field

[Associated particle paths are displayed in figure 34; <, less than] 

Site

identifier

Approximate

 traveltime, in years, 

for particles released 

at the water tablea

1 44

2 < 1

4a 2

4b 560

5a 3

5b 17

5c 10

5d 270

6 13

7 22

9 16

10 25

11 10

13a 230

13b 200

13c 88

14 33

15 130

16 53

17 4

18 32

20 24

21 25

22 6

23 21

24 59

25 38

26a 2

26b < 1

28a 96

28b 76

28c 26

29 < 1

44 19

45 5

46 1

50a 4

50b 5

50c 10

50d 6

50e 3

50f 4

50g 5

50h 11

50i 8

50j 6

50k 2

52 6

56 11

a

 Traveltimes are based on an effective porosity of 40 percent 

throughout the study area. 
Sites at Naval Station Mayport, Florida

62 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected Waste-Disposal Figure 36. Particle traveltimes from the water table to the surface-water discharge point simulated by the steady-state mo

flow field. 0 2,5

0 

Sherman

81° 26′ 

DREDGE 

HOLDING

MATERIAL

 AREAS

A1A

Chicopit Bay

C

reek

30° 24′

30° 23′

STUDY

TURNING

BASIN

ST

AREA

EXPLANATION

AREA WHERE TRAVELTIME FROM THE WATER TABLE IS GREATER THAN:

5 years50 years500 years

All times based on a uniform porosity of 0.4 
Contributing Areas and Ground-Water Age 63

The flow field of the surficial-aquifer system 

beneath NAVSTA Mayport is not under steady-state 

conditions because recharge rates are variable. The 

effective recharge rate in the unirrigated areas 

typically ranges from 5 to 7 in/yr but can exceed 

20 in/yr after intense precipitation events. Irrigation 

induced recharge can also vary on a seasonal basis 

over a range of more than 50 in/yr. 

In a variable flow field, many points exist at the 

water table for each observation point, because these 

points on the water table each contribute water to the 

observation point a fraction of the time. Contributing 

points under the average recharge rate will supply 

water to the observation point much more frequently 

than points under the minimum or maximum recharge 

rates (fig. 37). The maximum frequency of contribution for observation points at NAVSTA Mayport 

occurs between the average and minimum recharge 

rates because the median recharge rate is less than the 

average recharge rate. 

Ground-water samples are collected from observation wells, not points. Unlike an observation point, 

the screen of an observation well has a finite, 

cross-sectional area through which many pathlines 

pass. The finite area of a well screen translates to a 

finite contributing area at the water table even in a 

steady-state flow field. For a steady-state flow field, 

the ratio of cross-sectional screen area to contributing 

area can be approximated by the ratio of the average, 

lateral ground-water velocity at the screen to the 

recharge rate in the contributing area. In actuality, the 

contributing area is larger and more diffuse because of 

the effects of variable recharge rates (fig. 38). 

Ground-water samples represent the average 

water quality of the aquifer over a period of time. The 

time period sampled represents the range of traveltimes along flowpaths from contributing areas to the 

open interval of the sampled well and is proportional 

to the wetted length of the well screen. For example, 

the time period sampled from a well screened across 

the water table can be approximated by equation 3, 

which assumes the age of the sampled water ranges 

from 0 to ∆tSample years. The time period sampled by a 

typical well screened across the water table at 

NAVSTA Mayport would be about 5 years based on a 

wetted screen length of 8 ft, a recharge rate of 8 in/yr, 

and an effective porosity of 40 percent. 

NOT TO SCALE

Water Table

Base of Aquifer

Pathlines

Figure 37. Effects of variable recharge on the location of 

contributing points to an observation point. 

FLOW

Contributing Points

Observation

Point

Average

Maximum

Minimum

Recharge

Rates

NOT TO SCALE

Contributing Area*

Water Table Observation Well

Base of Aquifer

Pathlines

Screen

* Darker areas contribute water to the 

observation well more frequently

FLOW

FLOW

Figure 38. Effects of screen length, depth of screen below the water table, and variable recharge rates on the 

contributing area to an observation well.
64 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected Waste-Disposal 

Sites at Naval Station Mayport, Florida

The time period sampled by wells screened 

across the water table is variable because the wetted 

screen length fluctuates with time. This causes the 

contributing area to be skewed towards the observation well (fig. 38). Spatial variations in the recharge 

rate, such as the difference between the golf greens 

and the unirrigated areas or between the pervious and 

impervious areas, will also skew the time period 

sampled. The contributing area and associated time 

period sampled will be large but most of the water will 

come from the area with the higher recharge rate, 

which weights the time period sampled to a much 

smaller subperiod. 

Commonly, the youngest water enters the top of 

the screen and the oldest water enters the bottom of the 

screen. However, this pattern can be reversed if the 

flow paths reverse direction as they did at sites 4b and 

5d (fig. 34). Under similar flow conditions, if a well 

samples water from multiple contributing areas, the 

oldest water could enter the well anywhere along the 

screen length. 

The contributing areas for 224 wells at 

NAVSTA Mayport were identified by back-tracking a 

particle from the midpoint of the wetted screen using 

the steady-state model and the average 1996 flow 

field. For most wells, the centroid of the contributing 

area is located at the end of the pathline back-tracked 

from the well (fig. 39); however, this is not the case if 

the well intercepts multiple contributing areas. The 

traveltimes from the midpoint of the wetted screens to 

the centroid of the contributing areas are listed in 

table 11. 

The length of the contributing area for each well 

was approximated by the lateral distance between 

contributing points to the top and bottom of the wetted 

well screen (table 11). The estimate assumed the 

length of the contributing area was relatively short and 

only one contributing area existed for each well; this is 

the case for many of the wells. These estimates were 

appropriate when the traveltime to the midpoint was 

about the same as the average traveltime to the top and 

bottom of the wetted screen (table 11). 

Contributing area estimates for some wells were 

inappropriate because the well screens intercepted 

multiple contributing areas. If the traveltime to the 

midpoint of the screen does not fall between the 

traveltimes to the top and bottom of the screen, the 

well has multiple contributing areas. For example, the 

pathline for well 2-17I (figs. 3 and 39) indicates the 

contributing area is in the eastern dredge material 

holding area. However, the traveltime from the 

midpoint of 2-17I (61 years) does not fall between the 

traveltimes to the top and bottom of the well screen 

(86 and 73 years, respectively). Therefore, well 2-17I 

has multiple contributing areas and receives water 

from both the eastern and western dredge material 

holding areas. 

Other contributing area estimates were misleading because the well screens were supplied by areas 

with different recharge rates. If the traveltime to the 

midpoint of the open interval is close to either the top 

or bottom traveltimes, the sample does not represent 

an average of the sample period because it has been 

skewed towards the higher recharge rate in the contributing area. Contributing areas to wells 14-1S and 

14-2S (northeast corner of fig. 3b) are supplied by 

recharge from unirrigated areas and underflow from 

beneath the impervious area. Most of the water 

received by well 14-2S originates from the far end of 

its contributing area whereas well 14-1S is supplied 

mostly by the contributing area close to the well 

(table 11). 

The contributing areas of the wells also were 

affected by the historical landscape changes at 

NAVSTA Mayport. The effects of the landscape 

changes were investigated by back-tracking particles 

from the midpoint of the wetted screens using the 

transient model for the period from 1798 to 1997. The 

pathlines and traveltimes from the transient model 

were compared to corresponding pathlines and traveltimes based on steady-state results. Contributing areas 

for about 65 percent of the wells were the same 

because traveltimes were less than 15 years for both 

models (table 11). The stresses and boundary conditions of both models were very similar during the 

period from 1982 to 1997 so substantial differences in 

contributing areas would not be expected. 

Both transient and steady-state models produced 

the same results for the origin of ground-water from 

wells located in areas of reclaimed marsh and screened 

in the I-zone. Although the contributing areas and 

traveltimes varied, all of the contributing areas were in 

the former salt marsh area and the traveltimes were 

about 100 years or greater. The water sampled from 

these wells represents connate water which agrees 

with the chloride measurements. These wells account 

for about 10 percent of the observation wells in 

NAVSTA Mayport. 
Contributing Areas and Ground-Water Age 65 0 2,500 

0 

Sherman

81° 26′ 

DREDGE 

HOLDING

RUNWAY

MATERIAL

 AREAS

HANGARS

Fairway

Fairways

A1A

Maine St.

Moale Ave.

Patrol Rd.

Patrol Rd.

Alpha Pier

Charlie Pier

Delta Pier

Bravo Pier

Echo Pier

Foxtrot Pier

Bailey Ave.

Bon Homme Richard

Chicopit Bay

Mass

Lak

Won

Woo

Creek

30° 24′

30° 23′

STUDY

TURNING

BASIN

S

T

. J

AREA

INSET A

INSET B

Figure 39. Back-tracked particle paths from selected observation wells to contributing areas simulated by the steady-state flow field.

EXPLANATION

Pthaline

PATHLINE -- Shows path of a particletransported by advection through:

the S-zone

the I-zone

OBSERVATION WELL
66 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected Waste-Disposal 

Sites at Naval Station Mayport, Florida

0 1,000 2,000 FEET

0 500 METERS

81° 25′30′′ 81° 25′

30° 24′

30° 23′30′′

INSET A EXPLANATION

PATHLINE -- Shows

path of a particle

trasported by

advection through:

the S-zone

the I-zone

OBSERVATION WELL

Figure 39. Inset A.
Contributing Areas and Ground-Water Age 67 0 1,000 

0 

81° 24′30′′ 81° 24′

30° 23′45′′30° 23′30′′ Baseball

Fields

EXPLANATION

PATHLINE--Shows path of a the S-zonethe I-zoneOBSERVATION WELLparticle transported by advectionthrough:

Figure 39. Inset B.
68 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected Waste-Disposal 

Sites at Naval Station Mayport, Florida

Steady-state estimates of traveltimes to contributing areas that ranged 

between 15 and 50 years differed most 

from the transient estimates. 

Estimates of traveltimes and pathlines 

from the transient model typically 

were 10 to 20 years less and about 

half as long as estimates based on 

steady-state model results for this 

subset of wells. About 90 percent of 

the 45 affected wells are screened in 

the S-zone east of Maine St. The 

results from the steady-state and 

transient models differ because many 

buildings, streets, and parking lots 

were built east of Maine St. between 

1972 and 1994. The expanded impervious area increased the average 

distance between contributing areas 

and observation wells. 

Generalized maps of 

ground-water age were constructed 

for the S-zone and I-zone by 

back-tracking particles from all of the 

nodes in layers 1 and 2 and calculating the traveltimes to their respective 

contributing points at the water table. 

The maps are generalized because 

average traveltimes for volumes that 

range from 30,000 to 700,000 ft3

 are 

being approximated with one pathline. 

The traveltimes were estimated with 

the steady-state model, using average 

1996 flow field conditions, and a 

uniform effective porosity of 40 

percent. Residence time in the unsaturated zone was neglected. 

Results of the simulations 

indicate that most of the water in the 

S-zone is less than 5 years old 

(fig. 40). Water in the S-zone that is 

between 5 and 50 years old is present 

beneath impervious areas, canals and 

lakes, and south of Lake Wonder 

Wood, where the S-zone is thicker. 

The oldest water in the S-zone is in 

the salt marsh south and east of the 

dredge material holding areas 

(fig. 40). Water from the I-zone 

diffusely discharges to the S-zone in 

these areas. 

Table 11. Approximate length of contributing area, time period sampled, 

traveltimes from the top, midpoint, and bottom of the wetted screen estimated 

with the steady-state model using the average 1996 flow field, and the 

traveltime from the midpoint of the wetted screen estimated with the transient 

model

 [Well locations are shown in figure 3; parentheses indicate that the traveltime to the top of 

the screen was greater than to the bottom of the screen; ft, feet; <, less than; >, greater than]

Well

identifier

Approximate 

length of 

contributing 

area, in fta

Period 

sampled, 

in years 

Steady-state traveltime, 

in years from the screen

Transient 

traveltime

from

midpoint

Top Midpoint Bottom

1-1I 18 20 89 101 108 55 

1-1S 31 < 1 54 55 55 12 

1-2S 9 < 1 62 62 62 10 

1-P1 297 3 < 1 3 4 3 

1-P2 131 2 2 3 3 3 

1-P3 167 5 9 11 14 11 

2-1S 224 6 7 9 12 9 

2-2S 502 13 < 1 2 13 2 

2-3S 365 4 < 1 2 4 2 

2-4S 593 13 < 1 6 13 6 

2-6S 112 9 < 1 3 9 3 

2-7S 149 3 < 1 1 3 1 

2-8S 100 6 < 1 2 6 2 

2-9I 28 48 27 49 74 37 

2-9S 53 6 < 1 2 6 2 

2-10S 25 6 < 1 3 7 3 

2-11I 1,462 41 131 173 173 > 200

2-11S 651 18 < 1 9 18 9 

2-12I 230 (49) 120 66 71 > 200

2-12S 960 13 < 1 5 13 5 

2-13S 302 10 < 1 4 10 4 

2-15I 325 (18) 76 58 59 > 200

2-15S 1,454 150 10 18 160 18 

2-16S 888 11 < 1 7 11 7 

2-17I 1,826 (12) 86 61 73 > 200

2-17S 613 8 < 1 3 9 3 

2-18I 9 64 745 768 810 > 200

2-18S 199 9 < 1 6 10 6 

2-19S 444 8 2 4 10 4 

2-20S 317 8 3 8 11 8 

2-21S 261 11 1 11 12 11 

2-22I 37 84 186 219 270 > 200

2-22S 230 5 5 8 9 8 

2-23I 41 < 1 42 43 43 > 200

2-23S 304 10 < 1 10 10 10 

2-24S < 1 < 1 < 1 < 1 < 1 < 1

2-25I 258 7 135 115 142 > 200

2-25S 288 9 3 6 12 6 

2-26I 99 15 49 56 63 > 200

2-26S 358 9 4 8 13 8 

2-27I 118 11 69 74 80 > 200

2-28S 195 3 < 1 2 3 2 

2-29S 844 31 < 1 8 31 8 

2-30S 601 15 < 1 5 15 5 

2-31I 75 139 306 362 445 > 200

2-31S 581 27 < 1 4 27 4 

2-32I 272 103 355 407 458 > 200

a The length of the contributing area for each well was approximated by the lateral distance between contributing points to the top and bottom of the wetted well screen. This estimate is inappropriate if the traveltime to the midpoint is not close to halfway between the top 

and bottom estimates.
Contributing Areas and Ground-Water Age 69

2-32S 549 80 < 1 80 80 16 

2-33I 224 72 175 207 247 > 200

2-33S 230 30 < 1 4 30 4 

2-34I 3 156 533 608 689 > 200

2-34S 106 11 1 12 12 12 

2-35I 150 302 304 429 606 > 200

2-35S 102 7 5 12 12 12 

2-36I 1,511 718 452 656 1,170 > 200

2-36S 648 71 < 1 5 71 5 

2-37I 77 40 319 312 359 > 200

2-37S 93 11 19 23 30 6 

2-38I 22 48 237 260 285 > 200

2-38S 866 21 < 1 16 21 16 

2-P1 398 7 7 10 14 10 

2-P10 612 6 < 1 4 6 4 

2-P11 383 3 < 1 1 3 1 

2-P12 39 < 1 < 1 < 1 < 1 < 1

2-P13 58 5 3 5 8 5 

2-P2 106 2 7 8 9 8 

2-P3 299 3 1 3 4 3 

2-P4 407 5 2 3 7 3 

2-P5 149 11 2 5 13 5 

2-P6 424 65 4 69 69 > 200

2-P7 60 2 14 16 16 16 

2-P8 1,118 20 2 21 22 9 

2-P9 532 6 2 4 8 4 

8-1S 17 7 < 1 3 7 3 

8-2S 47 3 < 1 1 3 1 

8-3S 76 3 < 1 1 3 1 

8-4S 124 5 < 1 2 5 2 

8-5I 72 4 10 11 13 11 

8-5S 43 4 < 1 2 4 2 

8-6S 29 4 4 6 8 6 

8-7S 50 5 < 1 2 5 2 

8-8S 22 3 3 4 5 4 

8-9S 387 28 < 1 3 28 3 

8-11S 62 4 < 1 2 4 2 

8-12S 32 5 < 1 3 5 3 

8-13I 131 2 47 47 49 67 

8-13S 41 4 5 7 9 7 

8-14S 15 5 28 28 32 26 

8-15I 151 5 34 39 39 52 

8-15S 202 10 < 1 9 10 9 

8-16S 202 10 < 1 9 10 9 

8-17S 176 6 < 1 3 6 3 

8-18S 119 8 < 1 3 8 3 

8-19S 257 12 < 1 7 13 7 

8-P1 98 4 10 12 14 12 

Table 11. Approximate length of contributing area, time period sampled, 

traveltimes from the top, midpoint, and bottom of the wetted screen estimated 

with the steady-state model using the average 1996 flow field, and the 

traveltime from the midpoint of the wetted screen estimated with the transient 

model--(Continued)

 [Well locations are shown in figure 3; parentheses indicate that the traveltime to the top of 

the screen was greater than to the bottom of the screen; ft, feet; <, less than; >, greater than]

Well

identifier

Approximate 

length of 

contributing 

area, in fta

Period 

sampled, 

in years 

Steady-state traveltime, 

in years from the screen

Transient 

traveltime

from

midpoint

Top Midpoint Bottom

a The length of the contributing area for each well was approximated by the lateral distance between contributing points to the top and bottom of the wetted well screen. This estimate is inappropriate if the traveltime to the midpoint is not close to halfway between the top 

and bottom estimates.
70 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected Waste-Disposal 

Sites at Naval Station Mayport, Florida

8-P2 27 3 < 1 2 3 2 

8-P3 38 2 1 2 3 2 

8-P4 500 14 < 1 10 14 10 

8-P5 72 11 < 1 5 11 5 

8-P6 585 46 < 1 45 46 3 

9-1S 32 5 < 1 2 5 2 

9-2S 36 3 < 1 1 3 1 

9-3S 180 23 < 1 22 23 2 

10-P1 18 5 2 7 7 7 

11-1S 571 (69) 145 145 76 27 

11-2S 537 (112) 152 170 40 49 

11-3S 539 (97) 135 78 38 30 

13-1S 79 < 1 < 1 < 1 < 1 < 1

13-2S 191 3 < 1 < 1 3 < 1

13-3S 25 2 < 1 < 1 2 < 1

13-4S 452 6 < 1 2 6 2 

13-5S 268 7 < 1 2 7 2 

13-6S 297 7 14 17 21 17 

13-8S 368 11 7 13 18 13 

13-10S 404 9 14 17 23 17 

13-P1 260 6 < 1 3 7 3 

13-P4 45 < 1 6 6 7 6 

13-P5 1,379 28 < 1 28 28 8 

13-P6 84 5 9 12 14 12 

14-1S 826 45 < 1 2 45 2 

14-2S 614 35 < 1 34 35 9 

14-3S 83 4 27 29 31 18 

14-4S 35 2 41 41 42 17 

14-5S 10 < 1 56 57 57 17 

14-6S 563 33 < 1 32 33 5 

14-7S 89 4 23 25 27 18 

14-8S 11 < 1 47 48 48 17 

14-9S 69 3 22 24 26 17 

14-10S 23 1 15 16 17 16 

14-11S 56 3 20 21 23 17 

14-12S 60 3 8 9 11 9 

14-13S 69 3 29 31 33 18 

14-14S 38 2 38 38 39 17 

14-P1 143 4 < 1 2 4 2 

14-P2 83 4 1 3 5 3 

1406-2 < 1 < 1 122 122 122 121 

1406-7 7 1 209 210 210 78 

1406-8 5 2 4 6 6 6 

1406-11 < 1 < 1 < 1 < 1 < 1 < 1

1406-13 7 < 1 17 17 17 17 

1406-15 153 (11) 45 34 34 69 

1406-17 674 66 < 1 66 66 55 

1406-23I < 1 < 1 8 8 8 8 

Table 11. Approximate length of contributing area, time period sampled, 

traveltimes from the top, midpoint, and bottom of the wetted screen estimated 

with the steady-state model using the average 1996 flow field, and the 

traveltime from the midpoint of the wetted screen estimated with the transient 

model--(Continued)

 [Well locations are shown in figure 3; parentheses indicate that the traveltime to the top of 

the screen was greater than to the bottom of the screen; ft, feet; <, less than; >, greater than]

Well

identifier

Approximate 

length of 

contributing 

area, in fta

Period 

sampled, 

in years 

Steady-state traveltime, 

in years from the screen

Transient 

traveltime

from

midpoint

Top Midpoint Bottom

a The length of the contributing area for each well was approximated by the lateral distance between contributing points to the top and bottom of the wetted well screen. This estimate is inappropriate if the traveltime to the midpoint is not close to halfway between the top 

and bottom estimates.
Contributing Areas and Ground-Water Age 71

15-1S 43 5 < 1 3 5 3 

15-2S 311 10 < 1 3 10 3 

15-3S 73 4 < 1 3 5 3 

15-5I 68 3 11 13 14 13 

15-5S 29 5 1 4 6 4 

15-P1 19 3 2 3 4 3 

15-P2 28 3 < 1 2 4 2 

15-P3 553 21 2 20 23 10 

15-P4 254 9 < 1 6 10 6 

16-1I 116 3 12 14 15 14 

16-1S 177 4 9 14 14 14 

16-2S 35 4 2 4 6 4 

16-3S 32 5 < 1 2 5 2 

16-4S 124 2 3 4 5 4 

17-1S 107 10 < 1 3 11 3 

17-2S 103 4 < 1 3 4 3 

17-3S 169 14 6 19 20 19 

17-P1 14 1 < 1 < 1 1 < 1

17-P2 1,207 (5) 65 60 60 81 

18-1S 46 3 < 1 1 3 1 

18-2S 48 3 < 1 1 3 1 

18-3S 55 2 < 1 2 3 2 

20-1S 178 2 6 7 8 7 

20-2S 32 2 2 2 4 2 

20-3S 529 5 < 1 4 6 4 

21-1S 200 3 2 3 5 3 

21-2S 184 3 2 3 4 3 

21-3S 158 2 3 4 5 4 

22-1S 277 13 < 1 5 13 5 

22-2S 317 13 < 1 7 14 7 

23-1S 75 2 41 42 43 19 

23-2S 121 4 37 39 40 23 

23-3S 120 3 27 29 30 19 

23-4S 106 2 45 46 48 22 

23-5I 36 47 242 262 289 > 200

23-5S 822 47 < 1 47 48 18 

23-6S 14 1 26 27 27 22 

23-7S 91 3 43 44 46 20 

24-1S 111 3 26 28 29 20 

26-1S 176 10 5 9 15 9 

26-2S 253 12 < 1 5 13 5 

26-3S 178 11 < 1 5 11 5 

26-4S 201 12 < 1 5 12 5 

28-1S 41 6 < 1 3 6 3 

44-1I 164 36 90 109 126 > 200

44-1S 43 1 4 4 5 4 

44-2S 24 1 8 9 10 9 

44-3S 10 < 1 35 36 36 20 

Table 11. Approximate length of contributing area, time period sampled, 

traveltimes from the top, midpoint, and bottom of the wetted screen estimated 

with the steady-state model using the average 1996 flow field, and the 

traveltime from the midpoint of the wetted screen estimated with the transient 

model--(Continued)

 [Well locations are shown in figure 3; parentheses indicate that the traveltime to the top of 

the screen was greater than to the bottom of the screen; ft, feet; <, less than; >, greater than]

Well

identifier

Approximate 

length of 

contributing 

area, in fta

Period 

sampled, 

in years 

Steady-state traveltime, 

in years from the screen

Transient 

traveltime

from

midpoint

Top Midpoint Bottom

a The length of the contributing area for each well was approximated by the lateral distance between contributing points to the top and bottom of the wetted well screen. This estimate is inappropriate if the traveltime to the midpoint is not close to halfway between the top 

and bottom estimates.
72 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected Waste-Disposal 

Sites at Naval Station Mayport, Florida

45-1I 197 38 110 127 148 > 200

45-1S 297 3 < 1 3 3 3 

45-2S 19 < 1 23 24 24 17 

52-1S 39 24 23 23 47 23 

56-1S 999 27 < 1 27 27 6 

B-1I 329 (2) 35 33 33 36 

B-1S 255 7 < 1 3 7 3 

BE-1S 85 2 2 3 4 3 

BE-2S 119 2 < 1 1 2 1 

BE-3S 75 2 1 2 3 2 

BE-4S 98 2 2 3 4 3 

BE-7S 85 2 2 3 4 3 

BE-8I 148 2 10 12 12 12 

BE-9S 68 2 2 3 4 3 

BQ-2S 148 3 3 4 5 4 

BQ-3S 142 3 3 5 6 5 

BQ-4S 37 < 1 < 1 < 1 < 1 < 1

BQ-5S 51 < 1 < 1 < 1 < 1 < 1

BQ-6S 34 < 1 < 1 < 1 < 1 < 1

CU-1S 60 1 5 6 6 6 

CU-2S 96 2 4 5 6 5 

CU-3S 38 1 7 8 8 8 

CU-4S 34 < 1 10 10 10 10 

CU-5S 16 < 1 13 14 14 14 

CU-6S 2 < 1 40 40 40 14 

CU-7S 52 1 7 7 8 7 

CU-8I 34 3 19 20 22 17 

TC-1I 5 < 1 4 5 5 5 

TC-2S 191 < 1 1 2 2 2 

TC-3S 22 < 1 2 2 2 2 

TC-4S 491 4 1 5 6 5 

TC-5S 445 3 < 1 3 4 3 

TC-6S 582 5 < 1 3 5 3 

Table 11. Approximate length of contributing area, time period sampled, 

traveltimes from the top, midpoint, and bottom of the wetted screen estimated 

with the steady-state model using the average 1996 flow field, and the 

traveltime from the midpoint of the wetted screen estimated with the transient 

model--(Continued)

 [Well locations are shown in figure 3; parentheses indicate that the traveltime to the top of 

the screen was greater than to the bottom of the screen; ft, feet; <, less than; >, greater than]

Well

identifier

Approximate 

length of 

contributing 

area, in fta

Period 

sampled, 

in years 

Steady-state traveltime, 

in years from the screen

Transient 

traveltime

from

midpoint

Top Midpoint Bottom

a The length of the contributing area for each well was approximated by the lateral distance between contributing points to the top and bottom of the wetted well screen. This estimate is inappropriate if the traveltime to the midpoint is not close to halfway between the top 

and bottom estimates.
Contributing Areas and Ground-Water Age 73 Figure 40. Age of water in the S-zone simulated by the steady-state model using the average 1996 flow field and with a 

40 percent. 0 2,5

0 

Sherman

81° 26′ 

DREDGE

HOLDING

MATERIAL

 AREAS

A1A

Chicopit Bay

Creek

30° 24′

30° 23′

STUDY

TURNING

BASIN

ST

AREA

EXPLANATION

 AREA WHERE AGE OF WATER IS 

GREATER THAN--

5 years50 years500 years
74 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected Waste-Disposal 

Sites at Naval Station Mayport, Florida

All of the water in the I-zone, except for a small 

area beneath golf greens near well 20-2S, is more than 

5 years old (fig. 41). Most of the water in the I-zone 

between 5 and 50 years old is in an area where the 

marsh-muck confining unit is absent and beneath part 

of the western dredge material holding area. The 

oldest water in the I-zone is in stagnant zones beneath 

the hangars and runways and east of Echo and Foxtrot 

piers (fig. 41). 

MODEL LIMITATIONS

The flow model addresses questions about the 

advective movement of contaminants through the 

surficial aquifer system beneath NAVSTA Mayport 

fairly well, but it cannot mimic the true system 

exactly. This model, or any other model, is limited by 

simplification of the conceptual model, discretization 

effects, difficulty in obtaining sufficient measurements 

to account for all of the spatial variation in hydraulic 

properties throughout the model area, and limitations 

in the accuracy of land surface altitude measurements. 

The conceptual model has been simplified by 

assuming most of the current questions raised by site 

assessments and remediation plans can be addressed with 

either a steady-state ground-water flow model or a 

transient model that considers gross changes over periods 

of 5 years or more. However, available data indicate that 

during 1996, water-levels fluctuated seasonally as much 

as 8 ft, and the surficial aquifer system infrequently 

approaches, at best, a quasi-steady state condition. Both 

the steady-state and transient models were adequate to 

estimate the advective movement of dissolved constituents over a few years or more, but are not adequate to 

estimate the advective movement of contaminants over a 

couple of years or less.

Estimates of future contaminant migration are 

limited by future land uses at NAVSTA Mayport and 

the reactive nature of the contaminants. Historical land 

use changes at NAVSTA Mayport indicate that the 

stresses identified for 1996 are unlikely to remain the 

same and future ground-water movement beneath 

NAVSTA Mayport will be affected by changes in land 

use. Many of the contaminants that were identified at 

NAVSTA Mayport are sorbtive which retards their 

movement and the contaminants move at velocities 

less than the surrounding ground water. 

Lateral discretization of the study area into a 

rectangular grid of cells and vertical discretization into 

layers forced an averaging of hydraulic properties. 

Each cell represents a homogeneous block or some 

volumetric average of the aquifer medium. Discretization errors occurred in even the smallest model cells, 

which were 100 ft on a side and about 3 ft thick, 

because the S-zone contains clay lenses that are less 

than 1 ft thick interbedded in the more permeable 

sands. Due to the averaging of the hydraulic properties, the model cannot simulate the dispersive effects 

on flow caused by aquifer heterogeneity. 

The model of a heterogeneous aquifer system 

was simplified further by the methods used to describe 

the spatial variability of the hydraulic conductivity 

distributions. The lateral hydraulic conductivity distributions of the S-zone and I-zone of the surficial 

aquifer system were assumed to be log-normally 

distributed. The vertical hydraulic conductivity of the 

marsh-muck confining unit and the vertical anisotropy 

of the S-zone were uniform multipliers that changed 

by fixed amounts throughout each area. The lack of 

sufficient measurements to account for all of the 

spatial variation in hydraulic properties throughout the 

model area necessitated these simplifications. Simplifying the model to this degree does not invalidate the 

model results, but does mean that model results should 

be interpreted at scales larger than the representative 

elemental volume of hydraulic conductivity. 

SUMMARY

As part of the Installation Restoration Program, 

NAVSTA Mayport is considering remedial-action 

alternatives to control the movement of contaminants 

from sites that may otherwise discharge to the surface. 

The evaluation of remedial-action alternatives requires 

a quantifiable understanding of how the ground-water 

flow system responds to current conditions and how 

the system will respond to future stresses imposed on 

the system. Numerical simulation provides the most 

tractable way of achieving this level of understanding. 

The geologic units of interest in the study area 

consist of sediments of Holocene to Miocene age that 

extend from land surface to the top of the Hawthorn 

Group. Previous investigators have defined this 

sequence as the surficial aquifer system. Because this 

study is concerned with ground-water movement near 

the surface, this sequence has been further subdivided 

into three local geohydrologic units: the S-zone, the 

marsh-muck confining unit, and the I-zone. The geohydrologic structure within the study area was defined by 

depth and thickness data from geologists’ logs. 
Summary 75Figure 41. Age of water in the I-zone simulated by the steady-state model using the average 1996 flow field with a uniform 

0 2,5

0 

Sherman

81° 26′ 

DREDGE 

HOLDING

MATERIAL

 AREAS

A1A

Chicopit Bay

Creek

30° 24′

30° 23′

STUDY

TURNING

BASIN

ST

AREA

EXPLANATION

 AREA WHERE AGE OF WATER IS 

GREATER THAN--

5 years50 years500 years
76 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected Waste-Disposal 

Sites at Naval Station Mayport, Florida

The chloride-ratio method was used to estimate 

the recharge rate in the study area. The recharge rate 

and associated uncertainty were estimated with annual 

atmospheric chloride deposition rates between 1985 

and 1994 and 22 ground-water chloride measurements 

from the surficial-aquifer system beneath NAVSTA 

Mayport. The recharge rate was estimated to be 

7 in/yr. The range in recharge rate for a 95 percent 

confidence interval is 4 to 15 in/yr. 

Ground-water flow through the surficial aquifer 

system was simulated with a two-layer, finite-difference model that extended vertically from the water 

table to the top of the intermediate confining unit. 

Multi-well aquifer tests, single-well aquifer tests, and 

slug tests were conducted at NAVSTA Mayport to 

estimate the hydraulic properties of the surficial 

aquifer system. The lateral hydraulic conductivities 

estimated by these tests were the final values used in 

the ground-water flow model because ground-water 

discharge could not be quantified. The lateral 

hydraulic conductivity distributions of the S-zone 

(layer 1) and the I-zone (layer 2) were estimated by 

kriging the log-hydraulic conductivities from the 

aquifer tests. 

The dominant surface-water features adjacent to 

NAVSTA Mayport are the St. Johns River and the 

Atlantic Ocean; these features communicate directly 

with both the S-zone and I-zone of the surficial aquifer 

system. The distribution of surface-water features was 

determined from aerial photographs and plans of 

NAVSTA Mayport. All lateral model boundaries in 

each layer were assumed to be no-flow boundaries that 

coincided with either surface-water features or were 

parallel to ground-water flow paths. 

The effective-recharge approach was used to 

calibrate a series of independent steady-state models 

to the available data which consisted of “snapshot” 

images of a transient system. The model was 

calibrated to 229 water-level measurements from 

181 wells during three synoptic surveys (July 17, 

1995; July 31, 1996; and October 24, 1996). Model 

calibration was facilitated by a parameter estimation 

program that estimated the effective recharge rates and 

the vertical hydraulic conductivities. 

The unweighted minimum, maximum, average, 

and RMS errors in water levels from the calibrated 

model were -2.78, 1.92, 0.00, and 0.82 ft, respectively, 

and did not exhibit any apparent trend across the study 

area. Most of the estimated parameters are not highly 

correlated. Model error was determined to be most 

sensitive to changes in recharge rates to the unirrigated 

areas and golf course irrigation. 

The analysis of ground-water flow and potential 

movement of contaminants within the surficial aquifer 

system primarily was addressed using the calibrated 

model driven by the effective recharge rate distribution estimated for period 1. This recharge rate distribution was assumed to be representative of the average 

rate of water application to the surficial aquifer system 

because the effective recharge rate to the unirrigated 

areas was about 8 in/yr. The total flow through the 

surficial aquifer system averaged 2.3 ft3/s and ranged 

from 1 to 4 ft3

/s during 1996. Irrigation accounts for 

about 20 percent of the water that circulates through 

the surficial aquifer system. Most of the I-zone is 

recharged by areas where the marsh-muck confining 

unit is less than 1 ft thick. Contaminants migrating 

from areas that recharge the I-zone will have longer 

flow paths and residence times than those that exclusively migrate through the S-zone. 

The surficial aquifer system at NAVSTA 

Mayport is a dynamic system and has been modified 

greatly by natural and anthropogenic forces over the 

last 100 years. The freshwater flow system is 

expanding and entrained saltwater is still being 

flushed from the system. The advective displacement 

of the saline pore water initially was simulated as 

discrete particles being flushed by a steady-state flow 

field. The simulated saltwater distribution after 

200 years of displacement did not consistently 

describe the chloride distribution in the I-zone 

measured during 1993 and 1996. 

A transient model of the Mayport peninsula was 

developed to better approximate the saltwater 

displacement and accounted for the known changes in 

hydraulic properties, boundary conditions, and stresses 

over the last 200 years. The transient flow field of the 

surficial aquifer system was simulated with 10 stress 

periods that approximated the shifting morphology 

and changing boundaries between 1798 and 1997. A 

new MODFLOW package (VAR1) was written to 

simulate the temporal variation of hydraulic properties 

caused by construction activities at NAVSTA 

Mayport. The simulated saltwater distribution after 

200 years of transient displacement described the 

measured chloride distribution in the I-zone better 

than the steady-state simulation. 

The advective movement of conservative 

contaminants from selected sites within the solid 

waste management units to discharge points was 
References 77

simulated with MODPATH. Particles were released at 

the water table to approximate the initial position of 

contaminants at selected sites. Most of the particles 

were discharged to the nearest surface-water feature 

and traveled less than 1,000 ft before being discharged 

from the ground-water system. The traveltimes were 

estimated using an effective porosity of 40 percent. A 

generalized map of traveltimes showed most areas 

within 1,000 ft of a surface-water feature or a storm 

sewer had traveltimes of less than 50 years. 

The contributing areas for 224 wells at 

NAVSTA Mayport were identified by back-tracking a 

particle from the midpoint of the wetted screen with 

the steady-state model. Some of the contributing area 

estimates were inappropriate or misleading because 

the well screens intercepted multiple contributing 

areas or were supplied by areas of different recharge 

rates. 

The effect of the historical changes at NAVSTA 

Mayport on contributing areas to wells was investigated. Particles were back-tracked from the midpoint 

of the wetted screens with the transient model and 

compared to the steady-state results. Traveltimes to 

contributing areas that ranged between 15 and 50 

years as estimated by the steady-state model differed 

most from the transient estimates. Estimates of traveltimes and pathlines from the transient model typically 

were 10 to 20 years less and about half as long as 

estimates from the steady-state model. The difference 

is attributed to the increase in the average distance 

between contributing areas and observation wells 

resulting from the expansion of the impervious 

surfaces near the affected wells. 

REFERENCES

Baker, L.A., 1991, Appendix B, Regional estimates of 

atmospheric dry deposition, in Acidic Deposition and 

Aquatic Ecosystems—Regional Case Studies: New 

York, Springer-Verlag, p. 645-652. 

Bidlake, W.R., Woodham, W.M., and Lopez, M.A., 1993, 

Evapotranspiration from areas of native vegetation in 

west-central Florida: U.S. Geological Survey 

Open-File Report 84-143, 35 p. 

Bouwer, Herman, and Rice, R.C., 1976, A slug test for 

determining hydraulic conductivity of unconfined 

aquifers with completely or partially penetrating wells: 

Water Resources Research, 12 (3), p. 423-428.

Brown, D.P., Johnson, R.A., Baker, J.S., 1984, Hydrogeologic data from a test well at Kathryn Abbey Hanna 

Park, City of Jacksonville, Florida: U.S. Geological 

Survey Open-File Report 84-143, 27 p.

Causey, L.V., and Phelps, G.G., 1978, Availability and 

quality of water from shallow aquifers in Duval County, 

Florida: U.S. Geological Survey Water-Resources 

Investigations Report 78-92, 36 p. 

Cooper, H.H., Jr., and Jacob, C.E., 1946, A generalized 

graphical method for evaluating formation constants 

and summarizing well field history: Transactions of the 

American Geophysical Union, v. 27, p. 526-534.

Cooper, H.H., Jr., Kohout, F.A., Glover, R.E., and Henry, 

H.R., 1964, Sea water in coastal aquifers: U.S. Geological Survey Water Supply Paper 1613-C, p. 6-11.

Davis, J.H., Planert, M., and Andrews, W.J., 1996, Simulation of ground-water flow at the U.S. Naval Air Station 

Jacksonville, Florida, with an evaluation of changes to 

ground-water movement caused by proposed remedial 

designs at operable unit 1: U.S. Geological Survey 

Open-File Report 96-597, 47 p. 

Domenico, P.A., and Schwartz, F.W., 1990, Physical and 

chemical hydrogeology: New York, John Wiley and 

Sons, Inc., 824 p. 

Farnsworth, R.K., Thompson, E.S., and Peck, E.L., 1982, 

Evaporation atlas for the contiguous 48 United States: 

National Oceanographic and Atmospheric Administration Technical Report, NWS-33, 26 p.

Franks, B.J., 1980, The surficial aquifer at the U.S. Naval 

Station near Mayport, Florida: U.S. Geological Survey 

Open-File Report 80-765, 13 p.

Gill, T.E., Murray, W., and Wright, M.H., 1981, Practical 

optimization: Orlando, Fla., Academic Press Inc., 

401 p. 

Halford, K.J., 1992, Incorporating reservoir characteristics 

for automatic history matching: Baton Rouge, La., 

Louisiana State University, Ph.D. dissertation, 150 p.

———1997, Effects of unsaturated zone on aquifer 

test analysis in a shallow-aquifer system: Ground 

Water, v. 35, no. 3, p. 512-522. 

———1998, Ground-water flow in the surficial aquifer system and potential movement of contaminants from selected waste-disposal sites at Cecil 

Field Naval Air Station, Jacksonville, Florida: 

U.S. Geological Survey Water-Resources Investigations Report 97-4278.

Halford, K.J., Murray, L.C., Jr., Spechler, R.M., Phelps, 

G.G., and Bradner, L.A., 1993, Potentiometric surface 

of the Upper Floridan aquifer in the St. Johns River 

Water Management District and vicinity, May 1993: 

U.S. Geological Survey Open-File Report 93-451, 

1 sheet. 

Healy, R.W., 1990, Simulation of solute transport in variably 

saturated porous media with supplemental information 

on modifications to the U.S. Geological Survey’s 
78 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected Waste-Disposal 

Sites at Naval Station Mayport, Florida

computer program VS2D: U.S. Geological Survey 

Water-Resources Investigations Report 90-4025, 125 p.

Isaaks, E.H., and Srivastava, R.H., 1989, Applied geostatistics: New York, Oxford University Press, 561 p.

Krause, R.E., and Randolph, R.B., 1989, Hydrology of the 

Floridan aquifer system in southeast Georgia and 

adjacent parts of Florida and South Carolina: 

U.S. Geological Survey Professional Paper 1403-D, 

65 p.

Krulikas, R.K., and Giese, G.L., 1995, Recharge to the 

surficial aquifer system in Lee and Hendry Counties, 

Florida: U.S. Geological Survey Water-Resources 

Investigations Report 95-4003, 21 p. 

Lappala, E.G., Healy, R.W., and Weeks, E.P., 1987, Documentation of computer program VS2D to solve the 

equations of fluid flow in variably saturated porous 

media: U.S. Geological Survey Water-Resources Investigations Report 83-4009, 184 p.

McDonald, M.G., and Harbaugh, A.W., 1988, A modular 

three-dimensional finite-difference ground-water flow 

model: U.S. Geological Survey Techniques of 

Water-Resources Investigations, book 6, chap. A1, 

576 p. 

National Atmospheric Deposition Program, NADP/NTN 

annual data summary-precipitation chemistry in the 

United States: 1985-1994. 

Owenby, J.R., and Ezell, D.S., 1992, Monthly station 

normals of temperature, precipitation, and heating and 

cooling degree days 1961-90—Florida: National 

Oceanographic and Atmospheric Administration 

Climatography of the United States, no. 81, 26 p.

Pollock, D.W., 1994, User's guide for MODPATH/MODPATH-PLOT, version 3: A particle tracking postprocessing package for MODFLOW, the U.S. 

Geological Survey finite-difference ground-water flow 

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

94-464 [variously paged]. 

Spechler, R.M., 1994, Saltwater intrusion and quality of 

water in the Floridan aquifer system, northeastern 

Florida: U.S. Geological Survey Water-Resources 

Investigations Report 92-4174, 76 p. 

Stem, L.T., Dollar, H.D., Howell, D.A., Lewis, D.L., 

Wettstein, C.A., and Yamataki, H., 1978, Soil survey of 

city of Jacksonville, Duval County, Florida: U.S. 

Department of Agriculture, Soil Conservation Service, 

113 p.

Sumner, D.M., 1996, Evapotranspiration from successional 

vegetation in a deforested area of the Lake Wales 

Ridge, Florida: U.S. Geological Survey 

Water-Resources Investigations Report 96-4244, 38 p. 

Theis, C.V., 1935, The relation between the lowering of the 

piezometric surface and the rate and duration of 

discharge of a well using ground-water storage: 

Transactions of the American Geophysical Union, v. 

16, p. 519-524.

U.S. Department of the Navy, Southern Division Naval 

Facilities Engineering Command, 1995, Resource 

Conservation and Recovery Act (RCRA) corrective 

action program general information report, Naval 

Station, Mayport, Florida: UIC No. N60201, SouthDiv 

Contract N62467-89-D-0317/028, July 1995, 286 p.

U.S. Environmental Protection Agency, 1988, Ambient 

water quality criteria: Office of Water, Regulations, and 

Standards Division, EPA-440/5-86-008, 256 p. 

U.S. Geological Survey, 1996, Water resources data for 

Florida, water year 1995: v. 1A, Northeast Florida 

surface water, 357 p. 

Yeh, W.W.-G., 1986, Review of parameter identification 

procedures in groundwater hydrology: Water Resources 

Research, v. 22, no. 2, p. 95-108.
APPENDIXES
80 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected Waste-Disposal 

Sites at Naval Station Mayport, Florida

Appendix A. Well information at NAVSTA Mayport

[All measurements are in feet, except as noted]

Well ID Eastinga Northinga Top of 

casing

Casing

length

Screen 

length

Depth to 

water

Base 

of 

S-zone

Base 

of 

I-zone

Thickness

Lateral

hydraulic

conductivity,

in ft/d

Marshmuck 

confining unit

I-zone S-zone I-zone

1-1I 372,827 2,202,318 14.09 30 5 7 12 55 2 41 2 10

1-1S 372,829 2,202,287 16.96 5 10 9 15 58 2 41 3 10

1-2S 372,520 2,202,618 16.89 5 10 11 22 59 5 32 5 4

1-P1 372,912 2,203,345 7.11 5 5 5 23 49 3 23 16 3

1-P2 373,339 2,202,891 11.77 10 5 8 23 54 1 30 16 12

1-P3 372,166 2,202,846 11.04 5 10 7 20 56 7 28 14 3

2-1S 365,499 2,199,298 10.33 3 7 5 10 63 2 50 8 35

2-2S 368,574 2,199,856 7.56 3 7 4 10 63 3 50 7 42

2-3S 364,605 2,199,039 17.20 5 10 9 20 60 4 36 12 20

2-4S 365,011 2,199,897 8.29 3 10 4 10 59 4 45 15 18

2-6S 365,493 2,199,780 9.43 3 7 3 10 65 3 51 8 24

2-7S 365,927 2,197,406 10.49 4 7 7 22 55 5 28 8 69

2-8S 365,839 2,200,145 10.55 3 7 4 11 72 2 59 6 20

2-9I 366,128 2,200,339 10.49 15 10 4 11 72 2 59 4 16

2-9S 366,127 2,200,346 10.50 3 7 4 11 72 2 59 4 16

2-10S 366,392 2,200,334 10.02 5 5 4 12 72 3 57 4 15

2-11I 368,640 2,198,821 5.77 25 5 3 9 59 6 44 7 53

2-11S 368,644 2,198,830 5.73 2 10 3 9 59 6 44 7 53

2-12I 368,320 2,198,212 5.42 14 5 3 10 57 5 42 7 45

2-12S 368,318 2,198,210 5.51 2 10 3 10 57 5 42 7 45

2-13S 365,693 2,200,320 7.57 2 10 3 10 70 3 57 9 16

2-15I 367,585 2,200,458 6.89 15 10 3 11 66 5 50 4 14

2-15S 367,585 2,200,461 6.65 5 10 3 10 65 5 50 4 14

2-16S 365,475 2,200,289 6.73 2 10 2 9 67 5 54 12 17

2-17I 365,768 2,197,417 7.83 25 5 4 22 52 4 25 8 70

2-17S 365,775 2,197,410 7.73 3 10 4 22 52 4 25 8 70

2-18I 366,069 2,200,556 6.51 25 5 1 9 68 1 58 5 14

2-18S 366,070 2,200,556 6.37 2 10 1 9 68 1 58 5 14

2-19S 366,211 2,200,026 32.50 25 10 23 34 93 3 56 4 22

2-20S 366,631 2,199,689 32.09 25 10 19 31 91 6 53 4 35

2-21S 367,897 2,200,052 7.56 3 10 1 8 65 3 54 5 28

2-22I 365,528 2,199,563 7.19 25 5 2 8 62 3 52 7 30

2-22S 365,528 2,199,568 8.09 2 10 2 9 63 3 52 7 30

2-23I 368,951 2,199,409 5.36 25 5 2 5 59 6 48 8 50

2-23S 368,954 2,199,414 5.22 3 10 2 5 59 6 48 8 50

2-24S 365,637 2,199,026 32.29 4 10 23 33 84 2 50 7 44

2-25I 367,458 2,198,859 31.78 50 5 18 35 86 5 46 3 51

2-25S 367,453 2,198,864 32.07 25 10 18 36 87 5 46 3 51

2-26I 367,495 2,198,092 32.35 50 5 20 37 84 5 41 9 48

2-26S 367,500 2,198,100 32.41 30 10 20 38 84 5 41 9 48

2-27I 366,592 2,197,396 7.99 25 5 4 10 55 6 39 7 57

2-28S 364,987 2,198,675 17.36 4 10 6 22 62 3 37 10 28

2-29S 364,775 2,199,943 9.43 2 10 5 9 54 4 41 22 14

2-30S 365,514 2,200,721 8.91 3 10 5 11 68 4 52 15 12

2-31I 364,247 2,199,945 9.08 25 5 2 12 45 11 23 26 10

2-31S 364,241 2,199,940 9.14 2 10 2 12 45 11 23 26 10

2-32I 364,817 2,200,580 9.10 25 5 3 7 54 7 40 46 14

2-32S 364,813 2,200,576 9.10 2 10 3 7 54 7 40 46 14

2-33I 365,496 2,201,368 9.33 25 5 2 10 64 5 49 27 8

2-33S 365,491 2,201,362 9.47 2 10 2 11 63 5 47 27 8

2-34I 366,614 2,202,542 10.81 25 5 1 7 66 14 45 27 0.1

2-34S 366,609 2,202,537 10.46 2 10 0 6 65 14 45 27 0.1

2-35I 363,450 2,200,286 7.40 24 5 0 7 32 5 21 10 10

2-35S 363,445 2,200,281 7.36 2 10 0 7 32 5 21 10 10
Appendix A 81

2-36I 364,162 2,200,982 7.57 25 5 2 9 32 10 13 17 51

2-36S 364,158 2,200,977 7.58 2 10 2 9 32 10 13 17 51

2-37I 364,907 2,201,740 6.84 25 5 1 14 51 10 28 1 4

2-37S 364,902 2,201,736 6.93 2 10 1 14 51 10 28 1 4

2-38I 365,577 2,202,418 8.16 25 5 2 9 64 10 46 58 1

2-38S 365,563 2,202,403 8.14 2 10 2 9 64 10 46 58 1

2-P1 365,497 2,199,064 7.75 3 5 2 8 59 2 49 8 39

2-P10 363,416 2,195,900 32.02 30 5 31 33 68 1 33 10 21

2-P11 364,396 2,196,199 31.85 30 5 31 37 70 2 31 8 30

2-P12 365,157 2,196,870 32.75 25 5 29 43 74 3 28 8 47

2-P13 367,409 2,199,403 11.87 5 5 1 14 69 5 50 3 46

2-P2 365,498 2,198,464 7.97 4 5 3 14 56 3 39 8 42

2-P3 363,421 2,198,075 31.93 27 5 23 36 66 2 28 14 11

2-P4 364,241 2,198,967 32.74 30 5 26 36 71 4 31 13 15

2-P5 366,453 2,201,087 7.15 6 5 4 10 68 2 55 5 5

2-P6 367,965 2,200,322 5.10 5 5 4 7 62 3 53 6 19

2-P7 366,597 2,197,397 7.95 5 5 4 9 55 7 40 7 57

2-P8 367,732 2,197,417 6.35 5 5 3 8 55 5 42 5 39

2-P9 362,978 2,197,566 32.18 30 5 26 35 65 1 29 17 13

8-1S 366,285 2,204,731 10.19 6 10 6 15 51 1 35 2 17

8-2S 366,262 2,204,968 13.93 5 10 10 19 54 0 34 3 16

8-3S 366,363 2,205,070 13.72 5 10 11 19 54 0 34 6 16

8-4S 366,255 2,205,098 11.90 5 10 9 18 52 0 34 5 16

8-5I 366,645 2,203,938 13.34 25 5 7 15 56 1 40 2 11

8-5S 366,640 2,203,929 13.00 5 10 6 14 56 1 40 2 11

8-6S 366,149 2,204,829 11.57 5 10 8 17 52 0 35 2 17

8-7S 366,601 2,205,103 11.73 5 10 8 17 52 0 35 3 19

8-8S 366,883 2,205,161 13.12 5 10 9 17 53 1 35 1 26

8-9S 366,890 2,204,961 12.55 5 10 6 16 53 1 35 2 24

8-11S 366,493 2,205,204 11.46 5 10 9 18 51 0 33 6 17

8-12S 366,970 2,205,290 12.93 8 10 9 17 53 1 36 1 30

8-13I 366,853 2,205,390 11.33 35 5 8 15 51 0 36 1 29

8-13S 366,853 2,205,390 11.33 5 10 8 15 51 0 36 1 29

8-14S 366,701 2,205,362 10.72 5 10 8 15 51 0 35 2 23

8-15I 366,579 2,205,347 9.96 34 5 7 16 50 0 34 3 21

8-15S 366,394 2,205,227 10.03 5 10 8 17 50 0 33 9 16

8-16S 366,394 2,205,227 10.03 5 10 8 17 50 0 33 9 16

8-17S 366,230 2,205,126 10.89 5 10 8 17 51 0 34 7 16

8-18S 366,161 2,205,002 8.80 5 10 6 15 49 0 34 3 16

8-19S 366,196 2,205,169 5.24 4 10 3 11 45 0 34 5 17

8-P1 367,186 2,204,937 12.89 10 5 7 16 54 1 36 4 31

8-P2 368,584 2,205,241 12.70 5 10 10 18 54 0 36 5 38

8-P3 368,104 2,205,052 13.17 5 10 10 18 55 0 37 2 41

8-P4 367,808 2,204,485 14.67 5 10 8 18 58 3 37 9 21

8-P5 367,286 2,203,956 14.00 5 10 4 16 58 2 41 6 8

8-P6 366,740 2,203,360 14.87 5 10 6 14 63 2 48 7 2

9-1S 367,081 2,205,219 14.42 8 10 11 18 55 1 36 2 34

9-2S 367,012 2,205,466 13.39 5 10 10 17 53 0 36 2 36

9-3S 367,183 2,205,508 11.53 5 10 9 15 51 0 37 3 40

10-P1 365,964 2,204,746 10.68 10 10 7 15 51 0 36 2 18

11-1S 369,851 2,205,131 12.16 10 10 11 21 55 0 33 9 20

11-2S 369,902 2,205,332 10.42 10 10 9 20 52 0 32 9 21

11-3S 369,803 2,205,343 9.97 7 10 9 19 52 0 33 9 23

13-1S 368,004 2,202,052 13.06 3 7 7 12 67 0 55 21 2

Appendix A. Well information at NAVSTA Mayport--(Continued)

[All measurements are in feet, except as noted]

Well ID Eastinga Northinga Top of 

casing

Casing

length

Screen 

length

Depth to 

water

Base 

of 

S-zone

Base 

of 

I-zone

Thickness

Lateral

hydraulic

conductivity,

in ft/d

Marshmuck 

confining unit

I-zone S-zone I-zone
82 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected Waste-Disposal 

Sites at Naval Station Mayport, Florida

13-2S 367,476 2,201,307 12.79 3 7 6 11 71 2 58 13 3

13-3S 367,741 2,200,862 10.41 3 7 6 12 68 2 54 6 8

13-4S 367,688 2,201,086 9.88 2 10 5 10 68 1 56 7 5

13-5S 367,719 2,201,499 10.04 3 10 4 11 67 1 55 13 3

13-6S 367,684 2,201,905 9.66 2 10 2 10 65 2 53 28 1

13-8S 367,394 2,202,014 10.47 2 10 2 10 66 5 52 42 1

13-10S 367,455 2,201,732 9.65 2 10 2 10 66 3 54 31 1

13-P1 366,076 2,201,716 11.04 5 5 3 12 69 5 52 18 1

13-P4 368,069 2,201,301 9.31 5 5 5 11 65 0 54 15 4

13-P5 367,115 2,200,912 6.45 5 5 4 8 66 3 55 2 5

13-P6 366,880 2,202,120 10.16 5 5 1 8 67 9 50 28 0

14-1S 374,860 2,203,771 7.56 3 9 6 20 53 0 32 13 23

14-2S 374,681 2,203,726 8.64 3 10 7 22 54 0 32 12 21

14-3S 374,653 2,203,661 6.17 3 10 4 19 51 0 32 8 22

14-4S 374,826 2,203,692 6.37 3 10 4 19 51 0 33 14 24

14-5S 374,934 2,203,729 7.42 3 10 5 20 52 0 32 11 24

14-6S 374,997 2,203,839 5.97 3 10 4 18 51 0 32 11 23

14-7S 374,640 2,203,604 5.96 3 10 4 19 51 0 32 8 22

14-8S 374,926 2,203,629 6.58 3 10 5 19 52 0 33 15 25

14-9S 374,694 2,203,500 6.38 3 10 4 19 52 0 32 10 23

14-10S 374,927 2,203,515 5.77 3 10 4 18 51 0 33 13 26

14-11S 374,732 2,203,341 6.88 3 10 4 19 52 0 33 18 26

14-12S 374,688 2,203,072 9.92 3 10 7 21 55 0 34 15 29

14-13S 374,708 2,203,608 5.68 3 10 4 18 51 0 32 10 23

14-14S 374,852 2,203,650 6.55 3 10 4 19 52 0 33 14 24

14-P1 374,025 2,203,676 6.50 5 5 4 21 51 0 30 13 14

14-P2 375,562 2,204,016 5.71 6 5 4 18 50 0 33 21 24

1406-2 370,014 2,202,496 6.80 3 10 4 10 55 0 45 14 9

1406-7 369,366 2,202,734 7.69 3 10 6 10 56 0 46 13 8

1406-8 368,855 2,202,872 7.50 3 10 5 8 56 0 48 13 6

1406-11 369,122 2,202,827 7.67 3 10 6 9 56 0 46 13 7

1406-13 369,768 2,202,491 6.82 3 10 4 9 55 0 46 14 9

1406-15 369,572 2,202,595 5.93 3 10 3 8 54 0 46 13 8

1406-17 369,381 2,202,518 7.24 4 10 5 9 56 0 47 14 7

1406-23I 369,494 2,202,660 7.40 50 5 6 10 56 0 46 13 8

15-1S 365,726 2,203,211 12.14 5 10 6 14 62 1 47 4 5

15-2S 365,942 2,202,905 11.77 3 10 3 13 65 1 51 7 1

15-3S 365,641 2,203,087 11.26 6 10 5 14 63 1 47 7 3

15-5I 365,767 2,203,379 12.45 25 5 6 16 61 0 45 3 8

15-5S 365,772 2,203,377 12.37 8 10 6 15 61 0 45 3 8

15-P1 365,689 2,204,182 13.28 10 5 6 16 56 0 40 3 17

15-P2 365,420 2,203,729 10.83 5 10 5 13 56 0 43 5 16

15-P3 365,854 2,202,424 10.07 5 10 2 11 67 3 52 9 0

15-P4 362,689 2,199,535 10.51 5 10 3 12 37 2 23 11 9

16-1I 367,542 2,205,254 12.64 25 5 10 16 53 0 37 11 51

16-1S 368,463 2,203,118 12.45 10 10 8 13 61 1 47 13 5

16-2S 367,483 2,205,468 10.65 5 10 8 14 51 0 37 5 52

16-3S 367,599 2,205,439 11.19 5 10 8 15 52 0 37 6 55

16-4S 367,679 2,204,979 14.65 5 10 11 18 56 1 37 20 38

17-1S 370,214 2,201,128 8.60 3 10 6 10 59 0 48 19 21

17-2S 370,144 2,201,319 8.34 3 10 5 10 58 0 48 18 18

17-3S 370,349 2,201,346 8.17 4 10 5 10 58 0 48 19 17

17-P1 369,942 2,201,071 7.97 5 5 4 9 59 0 50 16 23

17-P2 370,630 2,201,114 7.72 7 5 6 10 57 0 47 22 18

Appendix A. Well information at NAVSTA Mayport--(Continued)

[All measurements are in feet, except as noted]

Well ID Eastinga Northinga Top of 

casing

Casing

length

Screen 

length

Depth to 

water

Base 

of 

S-zone

Base 

of 

I-zone

Thickness

Lateral

hydraulic

conductivity,

in ft/d

Marshmuck 

confining unit

I-zone S-zone I-zone
Appendix A 83

18-1S 374,966 2,203,261 7.42 3 10 5 19 53 0 34 15 29

18-2S 375,011 2,203,400 6.82 3 10 5 19 52 0 33 11 27

18-3S 375,236 2,203,510 7.49 3 10 5 19 52 0 33 16 27

20-1S 372,101 2,200,764 13.49 5 10 4 14 57 4 39 26 23

20-2S 372,164 2,200,732 13.68 4 10 4 14 57 4 39 27 23

20-3S 371,946 2,200,862 12.01 3 10 4 13 57 3 41 24 21

21-1S 372,202 2,200,875 13.21 5 10 3 12 57 5 40 27 21

21-2S 372,370 2,200,897 12.79 5 10 3 12 56 4 40 21 21

21-3S 372,380 2,200,826 12.36 5 10 2 12 56 4 40 21 21

22-1S 366,583 2,200,639 7.15 2 10 1 10 68 2 56 3 9

22-2S 366,541 2,200,765 6.70 3 10 1 10 68 2 56 3 8

23-1S 372,595 2,202,382 13.59 5 10 6 14 55 3 38 2 7

23-2S 372,450 2,202,388 12.86 5 10 5 14 55 4 38 1 6

23-3S 372,221 2,202,449 12.72 4 10 6 16 56 5 35 4 5

23-4S 372,225 2,202,900 9.72 5 10 6 21 54 8 26 7 2

23-5I 372,563 2,203,212 7.45 39 5 5 26 54 11 17 6 1

23-5S 372,558 2,203,212 7.42 3 10 5 26 54 11 17 6 1

23-6S 372,660 2,202,788 12.78 5 10 8 20 54 5 30 3 4

23-7S 372,535 2,202,458 13.65 5 10 7 15 55 4 37 2 6

24-1S 372,501 2,202,232 12.51 5 10 4 12 54 3 39 2 7

26-1S 366,352 2,200,738 5.85 2 10 1 10 67 2 56 4 9

26-2S 366,292 2,200,621 6.88 2 10 2 11 69 2 56 4 11

26-3S 366,204 2,200,520 7.05 2 10 1 10 69 2 57 4 14

26-4S 366,329 2,200,554 7.21 2 10 1 10 69 2 57 4 12

28-1S 365,616 2,204,661 11.85 8 10 8 16 53 0 36 3 18

44-1I 372,909 2,202,904 11.69 32 5 8 22 50 3 25 3 5

44-1S 372,906 2,202,902 11.78 5 10 8 22 50 3 25 3 5

44-2S 372,883 2,202,762 13.79 5 10 9 20 54 3 30 2 5

44-3S 372,629 2,203,003 10.87 5 10 8 25 54 7 22 4 2

45-1I 372,912 2,203,340 7.24 30 5 5 23 49 3 23 16 3

45-1S 372,912 2,203,345 7.14 5 5 5 23 49 3 23 16 3

45-2S 372,691 2,203,107 9.12 4 10 6 25 53 9 19 6 2

52-1S 370,281 2,201,849 7.48 3 10 5 10 57 0 47 16 12

56-1S 367,378 2,201,436 8.97 2 10 2 7 67 3 57 21 2

B-1I 372,332 2,199,058 7.19 33 5 6 30 49 2 18 27 66

B-1S 372,331 2,199,065 7.19 5 10 6 30 49 2 18 27 66

BE-1S 373,798 2,202,376 9.38 4 10 5 19 55 0 36 24 29

BE-2S 373,766 2,202,420 10.35 4 10 6 20 56 0 35 29 31

BE-3S 373,757 2,202,314 9.98 4 10 6 19 55 0 36 24 29

BE-4S 373,768 2,202,347 9.27 4 10 5 18 54 0 36 24 29

BE-7S 373,792 2,202,351 9.73 4 10 6 19 55 0 36 24 29

BE-8I 373,783 2,202,360 9.93 30 5 6 19 55 0 36 24 29

BE-9S 373,781 2,202,323 9.80 4 10 6 19 55 0 36 24 29

BQ-2S 373,723 2,202,645 10.18 4 10 6 22 56 1 34 27 31

BQ-3S 373,764 2,202,658 8.63 3 10 5 20 54 1 34 27 31

BQ-4S 373,712 2,202,700 11.95 4 10 8 24 57 1 33 26 27

BQ-5S 373,751 2,202,705 10.58 4 10 7 22 56 1 33 26 27

BQ-6S 373,691 2,202,720 12.27 4 10 8 24 57 1 32 24 23

CU-1S 373,313 2,201,477 11.28 3 10 7 13 54 0 41 6 16

CU-2S 373,275 2,201,426 11.28 3 10 6 12 54 1 41 5 15

CU-3S 373,390 2,201,482 11.29 3 10 7 13 54 0 41 6 16

CU-4S 373,369 2,201,431 11.54 3 10 7 13 54 0 41 6 16

CU-5S 373,410 2,201,387 11.71 3 10 7 14 55 0 40 7 18

CU-6S 373,522 2,201,514 11.05 3 10 7 14 54 0 41 7 18

Appendix A. Well information at NAVSTA Mayport--(Continued)

[All measurements are in feet, except as noted]

Well ID Eastinga Northinga Top of 

casing

Casing

length

Screen 

length

Depth to 

water

Base 

of 

S-zone

Base 

of 

I-zone

Thickness

Lateral

hydraulic

conductivity,

in ft/d

Marshmuck 

confining unit

I-zone S-zone I-zone
84 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected Waste-Disposal 

Sites at Naval Station Mayport, Florida

CU-7S 373,328 2,201,442 11.33 3 10 7 13 54 0 41 6 16

CU-8I 373,390 2,201,460 11.37 25 5 7 13 54 0 41 6 16

TC-1I 371,600 2,200,675 9.60 35 5 4 13 55 1 41 22 24

TC-2S 371,527 2,200,595 10.89 4 10 6 15 57 1 41 22 26

TC-3S 371,427 2,200,587 8.68 3 10 4 13 55 0 41 22 26

TC-4S 371,652 2,200,865 8.78 3 10 4 11 54 0 43 22 20

TC-5S 371,627 2,200,926 8.73 3 10 4 11 54 0 43 21 19

TC-6S 371,773 2,200,942 9.84 3 10 4 11 55 1 42 21 19

a

 Florida State Plane Coordinate System.

Appendix A. Well information at NAVSTA Mayport--(Continued)

[All measurements are in feet, except as noted]

Well ID Eastinga Northinga Top of 

casing

Casing

length

Screen 

length

Depth to 

water

Base 

of 

S-zone

Base 

of 

I-zone

Thickness

Lateral

hydraulic

conductivity,

in ft/d

Marshmuck 

confining unit

I-zone S-zone I-zone
Appendix B 85

APPENDIX B. A SIMPLIFIED APPROACH TO SIMULATING THE DISPLACEMENT OF SALINE PORE WATER BY FRESHWATER RECHARGE IN A 

RECLAIMED SALT MARSH

The density difference between the freshwater 

recharge and the saline pore water can complicate 

analysis of the ground-water flow system in a setting 

with land being accreted. The frequently used assumption (Anderson and Woessner, 1992) that the saline 

zones are not part of the active flow system is 

inadequate. Exclusion of the saline zones assumes that 

the freshwater/saltwater interfaces are in equilibrium 

which is not so when land is being accreted. 

The displacement of saline pore water and 

associated dissolved solids by freshwater recharge can 

be simulated explicitly, accounting for 

variable-density effects. This approach is deterministic 

but, nonetheless, many “reasonable” assumptions must 

be invoked. The data requirements for this approach 

also are large. A history of the natural accretion and 

marsh reclamation is needed, in addition to knowledge 

of its current state. In addition to knowing the 

hydraulic stresses and boundaries of the system, the 

distribution of solute sources and sinks and the initial 

solute distribution must be known in order to 

adequately simulate solute transport. 

The density contrast between the saline and 

freshwater zones can be assumed to have a negligible 

effect on the flow system and negated from the simulation. The effectiveness of this approach assumes that 

ground-water flow gradients caused by topographic 

effects are substantially larger than density gradients 

within the flow field. This assumption improves as the 

recharge rates increase, the hydraulic conductivity 

decreases, and the thickness of the flow system 

decreases. 

Purpose and Scope

The purpose of this appendix is to demonstrate 

that the displacement of saline pore water by freshwater recharge in a shallow, coastal aquifer, such as 

the surficial aquifer system at NAVSTA Mayport, can 

be adequately simulated as a uniform-density flow 

field. This is achieved by comparing density-dependent and uniform-density simulations of generalized 

cross-sections through NAVSTA Mayport, which are 

typical of reclaimed land in a salt-marsh environment. 

Cross-Sectional Models

The significance of simulating densitydependent flow in a ground-water flow system with 

land being accreted and freshwater recharge flushing a 

saltwater aquifer was investigated by comparing two 

cross-sectional models. The density-dependent section 

was simulated with SUTRA (Voss, 1984) and the 

uniform-density section was simulated with 

MODFLOW (McDonald and Harbaugh, 1988). While 

the uniform-density section could have been simulated 

with SUTRA, MODFLOW typically is used to solve 

for the uniform-density flow field. 

The geohydrologic framework for investigating 

density-dependent effects was a 500 m long by 20 m 

thick generalized section through NAVSTA Mayport 

(fig. B1). The upper 10 m represented the gross 

thickness of the surficial aquifer system and the lower 

10 m approximated the top of the intermediate 

confining unit. The left boundary represented a 

no-flow boundary through a ground-water divide. The 

right boundary approximated the edge of a deep 

saltwater body that was in communication with the 

surficial aquifer system. 

Ground-water flow and saltwater displacement 

at NAVSTA Mayport are strongly affected by the 

occurrence and extent of the marsh-muck confining 

unit which is characterized by a relatively low 

hydraulic conductivity ( m/d) compared to the 

S-zone and I-zone aquifers (5 m/d). The effect of the 

marsh-muck confining unit was investigated with 

three geohydrologic sections (cases one, two, and 

three); (1) the marsh-muck confining unit is absent; 

(2) the 2.5 m thick marsh-muck confining unit extends 

250 m from the left boundary; and (3) the marsh-muck 

confining unit exists across the entire section. 

The uniform-density and variable-density 

models of each section were discretized into 

101 nodes laterally and 26 nodes vertically. Slight 

differences existed between the discretization of the 

two models because the uniform-density section was 

simulated with a block-centered, finite-difference 

model (MODFLOW; McDonald and Harbaugh, 1988) 

and the density-dependent section was simulated with 

a finite-element model (SUTRA; Voss, 1984). The 

1 –3

×10
86 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected Waste-Disposal 

Sites at Naval Station Mayport, Florida

MODFLOW model laterally was discretized into 

101 columns that are 5 m wide except for the first and 

last columns which were 2.5 m wide. Vertically, the 

MODFLOW model was discretized into 20 rows 

(0.5 m high) in the upper 10 m and 6 rows that 

expanded with a uniform multiplier to cover the lower 

10 m. The SUTRA model was discretized into 

2500 rectangular elements that were 5 m wide by 

0.5 m high in the upper 10 m and were of variable 

height in the lower 10 m, similar to the heights used in 

the MODFLOW model. 

The deep saltwater body (the right edge of the 

model) was simulated as a specified pressure and 

concentration boundary that was set to the hydrostatic 

pressure of a column of seawater (ρ = 1.025 g/cc). 

Seawater hydrostatic pressures were assigned in both 

the density-dependent and uniform-density simulations. A uniform concentration of 0.0357 

kgsolute/kgfluid was assigned to the deep saltwater body 

nodes in the density-dependent simulations. The 

ground-water divide (the left edge of the model) was 

simulated as a no-flow boundary. 

The initial conditions of the density-dependent 

problems (SUTRA) were steady-state solutions of 

uniform saltwater flow. These solutions were driven 

by a uniform recharge rate of 0.5 mm/d of saltwater

(ρ = 1.025 g/cc and C = 0.0357 kgsolute/kgfluid) applied 

to the upper boundary. The 0.5 mm/d recharge was 

maintained throughout the saltwater displacement 

simulation but the saltwater was replaced with freshwater (ρ = 1.000 g/cc and C = 0.000 kgsolute/kgfluid). 

In addition to specifying initial and boundary 

solute concentrations, the longitudinal and transverse 

dispersivities of the surficial aquifer system must be 

defined to solve the associated solute transport 

problem. Longitudinal and transverse dispersivities of 

1 and 0.2 m, respectively, were used for all of the 

transport problems investigated. Sanford and Konikow 

(1989) found these values adequately described the 

mixing along a freshwater/saltwater interface. 

The water table was not simulated as a free 

surface and the transmissivity of the S-zone was based 

on a 3 m thickness for all simulations. The free surface 

upper boundary was ignored because SUTRA does not 

actively solve for this boundary. The simulation of the 

water table was not the most accurate for any of the 

problems but all of the solutions were adequate for 

comparing density-dependent to uniform-density 

flushing. The third case simulated, accounting for the 

effects of a continuous marsh-muck confining unit, 

produced the highest water table which had a 

maximum elevation of about 3.2 m (fig. B2) and 

would have been closer to 2.8 m with the correct 

solution. 

Saltwater Displacement

The advective displacement of saline pore water 

was simulated using a particle-tracking routine, 

MODPATH (Pollock, 1994) and an effective porosity 

of 40 percent. The connate pore water was approximated by a uniform array of particles placed within the 

volume of the surficial aquifer system (fig. B3). The 

displacement and dilution of connate saltwater by 

freshwater recharge was depicted by particle spreading 

and discharging to the deep saltwater body. 

KXY = 5 m/d 

KXY / KZ = 5

αL = 1 m

αT = 0.2 m

n = 0.4

KXY = 5 x 10-4 m/d 

KXY = 1x 10-3 m/d

N = 0.5 mm/d

SPECIFIED PRESSURE AND

NO FLOW

CONCENTRATION

TOP OF INTERMEDIATE CONFINING UNIT

S-ZONE

MARSH-MUCK

I-ZONE

 CONFINING UNIT

Ground-Water

Divide

Deep Saltwater

Body

DEPTH BELOW DATUM, IN METERS 20

10

0

Figure B1. Cross-section showing geohydrologic framework, hydraulic properties, and boundary conditions of a generalized 

section through the surficial aquifer system at NAVSTA Mayport.
Appendix B 87

Figure B2. Steady-state, uniform-density, water table profiles along 3 hypothetical cross-sections through 

NAVSTA Mayport that are driven by a recharge rate of 0.5 mm/d. 

500 400 300 200 100 0

3

2

1

0

DISTANCE FROM SHORE, IN METERS

WATER LEVEL,

IN METERS

ABOVE DATUM

marsh-muck confining unit absent

marsh-muck confining unit present throughout

marsh-muck confining unit present

from 250 to 500 m from the shore

Figure B3. Initial particle distributions in generalized section experiments for NAVSTA Mayport.

500 400 300 200 100 0

DISTANCE FROM SHORE, IN METERS

DEPTH BELOW DATUM,

10

8

6

4

2

0

 IN METERS
88 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected Waste-Disposal 

Sites at Naval Station Mayport, Florida

Saltwater displacement was fastest from the 

section without the marsh-muck confining unit 

because the entire thickness was available for 

conveying the recharge to the seaward outlet (fig. B4). 

Density-dependent effects were minimal throughout 

most of this section because strong density contrasts 

never formed, except at the seaward outlet. This can 

be seen by examining any 20 m wide column within 

the section and noting the similarity between adjacent 

vertical concentration profiles. 

Density-dependent effects were the most 

pronounced for the second case, with the marsh-muck 

confining unit extended partially across the section. 

Density gradients were greatest in the middle of the 

geohydrologic section at the end of the marsh-muck 

confining unit (fig. B5). The density effects are shown 

by the relative concentration decrease just below the 

tip of the marsh-muck confining unit and the relative 

concentration bulge between 8 and 10 m below the 

datum. Density-dependent effects appear because the 

strong downward flow from the marsh-muck 

confining unit maintains a 4 m long vertical interface 

with a strong solute concentration contrast. 

The third case, with the marsh-muck confining 

unit present throughout the entire section, flushed the 

lower zone faster than noted in case 2. Simulations of 

the density-dependent and uniform-density conditions 

were quite similar (fig. B6). The continuous confining 

unit reduced the effective thickness of the flow system 

and the resulting higher water table caused more water 

to flow across the marsh-muck confining unit 

(fig. B2). Density-dependent effects were largely 

absent because the system was horizontally stratified 

and sharp vertical concentration profiles could not 

develop. 

Figure B4. Comparison between density-dependent (SUTRA) and uniform-density (MODFLOW) simulations 

of saltwater displacement from a generalized section of NAVSTA Mayport with the marsh-muck confining unit 

absent.

500 400 300 200 100 0

10

8

6

4

DISTANCE FROM SHORE, IN METERS

DEPTH BELOW DATUM, IN METERS

500 400 300 200 100 0

2

0

10

8

6

4

2

0

10

8

6

4

2

0

DENSITY-DEPENDENT DISPLACEMENT (SUTRA) UNIFORM-DENSITY DISPLACEMENT (MODFLOW)

0.3

0.5

0.8

0.3

0.5 0.8

0.5 0.8

0.3

EXPLANATION

LINE OF EQUAL SOLUTE FRACTION--

Interval variable

0.8

25 YEARS

50 YEARS

75 YEARS
Appendix B 89

Conclusions

A comparison between density-dependent 

(SUTRA) and uniform-density (MODFLOW) simulations in generalized sections through NAVSTA 

Mayport showed that the effects of density differences 

on the flow system are minor. The uncertainty of the 

hydraulic conductivity distribution and the lateral 

extent of the marsh-muck confining unit introduce 

greater errors than those associated with neglecting 

density differences. These results indicate that 

density-dependent effects can be neglected and that 

flushing of the aquifer system can be simulated 

adequately with MODFLOW. 

Density-dependent effects were most 

pronounced where the marsh-muck confining unit 

extended through half of the section. Ignoring density 

effects caused a relatively sharp interface in the center 

of the section but displaced the interface by less than 

30 m. Topographic gradients were much greater than 

any density gradients and dominated the flow field. 

While density-dependent effects control the 

seaward freshwater/saltwater interface, the effects can 

be approximated well with a uniform-density simulation by specifying the hydrostatic head due to the 

density difference between the freshwater and 

saltwater bodies. This approximation works because 

the concentration of dissolved solids in the saltwater 

body does not change and is not diluted over time. 

EXPLANATION

LINE OF EQUAL 

SOLUTE 

FRACTION--

Interval variable

0.8

Figure B5. Comparison between density-dependent (SUTRA) and uniform-density (MODFLOW) simulations 

of saltwater displacement from a generalized section of NAVSTA Mayport with the marsh-muck confining unit 

present through 250 m of the 500 m long section.

500 400 300 200 100 0

10

8

6

4

DISTANCE FROM SHORE, IN METERS

DEPTH BELOW DATUM, IN METERS

500 400 300 200 100 0

2

0

10

8

6

4

2

0

10

8

6

4

2

0

DENSITY-DEPENDENT DISPLACEMENT (SUTRA) UNIFORM-DENSITY DISPLACEMENT (MODFLOW)

0.5

0.8

0.3

0.5

0.8

0.3

0.5

0.8

0.3

25 YEARS

50 YEARS

75 YEARS
90 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected Waste-Disposal 

Sites at Naval Station Mayport, Florida

The contribution of dissolved solids from the 

top of the intermediate confining unit was negligible. 

These results indicate that both the ground-water flow 

and geochemical-reaction paths within the surficial-aquifer system can be explained by treating the 

lower confining unit as an inert, impervious boundary. 

It also suggests that the water quality at or near the top 

of the intermediate confining unit is more indicative of 

that unit’s depositional history and development than 

the development of the surficial aquifer system. 

REFERENCES

Anderson, M. P., and Woessner, W. W., 1992, Applied 

groundwater modeling: Simulation of flow and advective transport: San Diego, Academic Press, Inc., 381 p. 

McDonald, M.G., and Harbaugh, A.W., 1988, A modular 

three-dimensional finite-difference ground-water flow 

model: U.S. Geological Survey Techniques of 

Water-Resources Investigations, book 6, chap. A1, 

576 p.

Pollock, D.W., 1994, User’s guide for MODPATH/MODPATH-PLOT, version 3: A particle tracking postprocessing package for MODFLOW, the U.S. 

Geological Survey finite-difference ground-water flow 

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

94-464 [variously paged]. 

Sanford, W.E., and Konikow, L.F., 1989, Simulation of 

calcite dissolution and porosity changes in saltwater 

mixing zones in coastal aquifers: Water Resources 

Research, v. 25 (4), p. 655-667. 

Voss, C.I., 1984, SUTRA A finite-element simulation 

model for saturated-unsaturated, fluid-densitydependent ground-water flow with energy transport or 

chemically-reactive single-species solute transport: 

Water-Resources Investigations Report 84-4369, 409 p.

Figure B6. Comparison between density-dependent (SUTRA) and uniform-density (MODFLOW) 

simulations of saltwater displacement from a generalized section of NAVSTA Mayport with the marsh-muck 

confining unit present throughout the entire section. 

500 400 300 200 100 0

10

8

6

4

DISTANCE FROM SHORE, IN METERS

DEPTH BELOW DATUM, IN METERS

500 400 300 200 100 0

2

0

10

8

6

4

2

0

10

8

6

4

2

0

DENSITY-DEPENDENT DISPLACEMENT (SUTRA) UNIFORM-DENSITY DISPLACEMENT (MODFLOW)

0.3

0.5 0.8

0.5

0.8

0.3 0.5

0.8

0.3

EXPLANATION

LINE OF EQUAL SOLUTE FRACTION--

Interval variable

0.8

25 YEARS

50 YEARS

75 YEARS
Appendix C 91

Appendix C. Time-Variant Hydraulic-Property Package

The Time-Variant Hydraulic-Property Package was developed to accommodate temporal changes in 

inter-node conductance, hydraulic conductivity, the top and bottom elevations of model layers, and the primary 

and secondary storage coefficients. The package allows hydraulic properties to be modified step-wise from one 

stress period to the next. The hydraulic properties of a cell are modified by either being multiplied or replaced. 

The Time-Variant Hydraulic-Property Package does not alter the formulation of the finite-difference equations 

in MODFLOW (McDonald and Harbaugh, 1988). Because the package is not a complex modification of 

MODFLOW, documentation in this appendix is the minimum amount required to implement the package. 

Modifications to the main program to implement the Time-Variant Hydraulic-Property package are given in 

Appendix D.
92 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected Waste-Disposal 

Sites at Naval Station Mayport, Florida

Input Instructions

Input for the Time-Variant Hydraulic-Property Package is read from the unit in IUNIT(21) specified in the 

basic package input (see McDonald and Harbaugh, 1988, chap. 4, p. 9-11).

FOR EACH SIMULATION

VAR1AL

1. Data: MXVAR

Format: I10

FOR EACH STRESS PERIOD 

VAR1RP

2. Data: ITMP

Format: I10

3. Data: Layer Row Column Modifier Property Action (optional)

Format: I10 I10 I10 F10.0 A10 A78

(Input item 3 normally consists of one record for each time-variant hydraulic-property cell modified. If ITMP 

is zero or less, item 3 is not read.)

Explanation of Fields Used in Input Instructions

MXCHD is the maximum number of time-variant hydraulic-property cells to be modified. 

ITMP is a flag. 

If , hydraulic-property data from a previous stress period will be reused and input from 

item 3 will not be read. 

If , it is the number of records of hydraulic-property data that will be read for the current 

stress period. 

Layer is the layer number of the cell affected by the modification of the hydraulic property. 

Row is the row number of the cell affected by the modification of the hydraulic property. 

Column is the column number of the cell affected by the modification of the hydraulic property. 

Modifier is the multiplier or replacement value of the hydraulic property to be modified. 

Property identifies which hydraulic property is to be modified. The properties are identified by the keys listed in 

table C1.

Action specifies if the hydraulic property is to be multiplied or replaced by the modifier. If the string 

“REPLACE” (case insensitive) is detected, the modifier will replace the old value. Otherwise, the old 

value will be multiplied by the modifier. 

ITMP ≤ 0

ITMP > 0
Appendix C 93

Table C1. Hydraulic properties modified by VAR1 and the property keys that

 identify the properties to be modified. 

Hydraulic property Keya MODFLOW arrayb

Inter-node conductance along rowsc X-conductance CR

Inter-node conductance along columnsc Y-conductance CC

Inter-node conductance between layersc Z-conductance CV

Inter-node conductances along rows and columnsc XY-conductance CR, CC

Inter-node conductances along columns and 

between layersc

YZ-conductance CC, CV

Inter-node conductances along rows and between 

layersc

XZ-conductance CR, CV

Inter-node conductances along rows and columns 

and between layersc

XYZ-conductance CR, CC, CV

Hydraulic conductivity of layer 1 HYd. conductivity HY

Elevation of the layer top TOP of layer TOP

Elevation of the layer bottom BOTtom of layer BOT

Primary storage coefficient SC1 SC1

Secondary storage coefficient SC2 SC2

a Only the underlined fragment of the key is needed. 

b See McDonald and Harbaugh (1988) for further description of the arrays.

c Inter-node conductances modified by the X-conductance, Y-conductance, and Z-conductance keys when applied to the <i,j,k> node are shown below: 

i, j, k

i, j+1, k

i+1, j, k

X-conductance

i j

k

i, j, k

i, j, k+1

Z-conductance Y-conductance
94 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected Waste-Disposal 

Sites at Naval Station Mayport, Florida

Program Listing for Module VAR1AL

 SUBROUTINE var1AL(ISUM,LENX,MXvar,IN,IOUT)

C 

C-----VERSION 1.000 12-14-96

C

C ******************************************************************

C ALLOCATE ARRAY STORAGE FOR time dependent changes in conductance

c and storage ...........

C ******************************************************************

C 

C SPECIFICATIONS: 

C ------------------------------------------------------------------

C ------------------------------------------------------------------

C 

C1------IDENTIFY PACKAGE AND INITIALIZE # OF BCF Cells........

 WRITE(IOUT,1) 

 1 FORMAT(1H0,’var1 -- var PACKAGE, VERSION 1, 12/14/96’) 

 Nvars=0 

C 

C2------READ AND PRINT MXBND AND IvarCB (MAX # OF BOUNDS AND UNIT 

C2------FOR CELL-BY-CELL FLOW TERMS FOR var) 

 READ(IN,’(i10)’) MXvar

 WRITE(IOUT,3) MXvar

 3 FORMAT(1H ,’MAXIMUM OF’,I6,’ BCF properties can be updated.’) 

c

 ISP = 0 

 ISUM = ISUM+ISP 

C 

C5------PRINT AMOUNT OF SPACE USED BY THE var PACKAGE 

 WRITE(IOUT,4) ISP 

 4 FORMAT(1X,I5,’ ELEMENTS IN X ARRAY ARE USED FOR time-dependent’, 

 1 ’ BCF updates.’) 

 ISUM1 = ISUM-1 

 WRITE(IOUT,5) ISUM1,LENX 

 5 FORMAT(1X,I6,’ ELEMENTS OF X ARRAY USED OUT OF’,I7) 

 IF(ISUM1.GT.LENX) WRITE(IOUT,6) 

 6 FORMAT(1X,’ ***X ARRAY MUST BE DIMENSIONED LARGER***’) 

C 

C6------RETURN 

 RETURN 

 END 

c..........................................................................

c
Appendix C 95

Program Listing for Module VAR1RP

c

 SUBROUTINE var1RP(mxvar,IBOUND,SC1,HY,CR,CC,CV,DELR,DELC,

 + BOT,TOP,SC2,ISS,NCOL,NROW,NLAY,in,iout)

C

C-----VERSION 1.000 12-14-96

C

C ******************************************************************

C READ AND MODIFY BLOCK-CENTERED FLOW PACKAGE DATA BY STRESS PERIOD

C ******************************************************************

C

c The following arrays can be modified: 

c CR( i, j, k) ------> CR i + 1/2

c CC( i, j, k) ------> CC j + 1/2

c CV( i, j, k) ------> CV k + 1/2

c HY, BOT, TOP, SC1, SC2 are block centered values

c

c Specify quantity to vary using the following keys ......

c data keys/’X-??’,’Y-??’,’Z-??’,’XY-?’,’YZ-?’,’XZ-?’,’XYZ-’,

c + ’HY??’,’BOT?’,’SC1?’,’SC2?’,’TOP?’/

c

c Default assumption is to modify value by multiplication, unless the 

c identifier ’REPLACE’ is on the line...............

c

C SPECIFICATIONS:

C ------------------------------------------------------------------

 DIMENSION SC1(NCOL,NROW,NLAY),HY(NCOL,NROW,NLAY),

 + CR(NCOL,NROW,NLAY),CC(NCOL,NROW,NLAY),CV(NCOL,NROW,NLAY),

 + DELR(NCOL),DELC(NROW),BOT(NCOL,NROW,NLAY),TOP(NCOL,NROW,NLAY),

 + SC2(NCOL,NROW,NLAY),IBOUND(NCOL,NROW,NLAY)

 dimension nvkey(12) 

 character*4 keys(12) 

 character*10 action

 character*128 txt

C ------------------------------------------------------------------

 data nvkey/2,2,2,3,3,3,4,2,3,3,3,3/

 data keys/’X-??’,’Y-??’,’Z-??’,’XY-?’,’XZ-?’,’YZ-?’,’XYZ-’,

 + ’HY??’,’BOT?’,’SC1?’,’SC2?’,’TOP?’/ 

C 

C1------READ ITMP(# OF HEAD updates OR FLAG TO REUSE DATA.) 

 READ(IN,’(i10)’) ITMP

C 

C2------TEST ITMP 

 IF(ITMP.lt.0) then 

C 

C2A-----IF ITMP<0 THEN REUSE DATA FROM LAST STRESS PERIOD 

 WRITE(IOUT,7) 

 7 FORMAT(1H0,’REUSING BCF-updates FROM LAST STRESS’, 

 1 ’ PERIOD’) 

 else 

C 
96 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected Waste-Disposal 

Sites at Naval Station Mayport, Florida

C3------IF ITMP=>0 THEN IT IS THE # OF HYDRAULIC PROPERTIES 

 Nvars = ITMP 

C 

C4------IF MAX NUMBER OF BCF values IS EXCEEDED THEN STOP 

 if( nvars .gt. mxvar ) then

 WRITE(IOUT,99) Nvars,MXvar 

 99 FORMAT(1H0,’NBOUND(’,I4,’) IS GREATER THAN MXvar(’,I4,’)’) 

C 

C4A-----ABNORMAL STOP 

 STOP’ Abnormal Stop!!!!!!!’

 endif

C 

C5------PRINT # OF BCF Nodes altered THIS STRESS PERIOD 

 WRITE(IOUT,1) nvars

 1 FORMAT(1H0,//1X,I6,’ TIME-DEPENDENT BCF NODES’) 

C 

C6------IF THERE ARE NO HYDRAULIC PROPERTIES THEN RETURN. 

 IF(nvars.EQ.0) return 

C 

C7------READ, modify, & echo BCF info to main output file 

 WRITE(IOUT,3) 

 3 FORMAT(1H0,1X,’LAYER’,5X,’ROW’,5X 

 1,’COL OLD VAL NEW BOUND NO.’/1X,15X,60(’-’)) 

 DO II = 1, nvars 

 READ (IN,’(a128)’) txt

 call caps( txt, 128 )

 ireplc = index(txt,’REPLACE’) 

 READ (txt,’(3I10,F10.0)’) K,I,J,rmodfy

 icho = 0

c data keys/’X-??’,’Y-??’,’Z-??’,’XY-?’,’YZ-?’,’XZ-?’,’XYZ-’,

c + ’HY??’,’BOT?’,’SC1?’,’SC2?’,’TOP?’/

 action = txt(41:50)

 do nop = 1, 12

 if( index(action,keys(nop)(1:nvkey(nop))).gt.0 ) then

 icho = nop

 endif

 enddo

c

 if( icho.eq.1 ) then

 varold = cr(j,i,k) 

 varnew = varold * rmodfy 

 if( ireplc.gt.0 ) varnew = rmodfy 

 cr(j,i,k) = varnew

 elseif( icho.eq.2 ) then

 varold = cc(j,i,k) 

 varnew = varold * rmodfy 

 if( ireplc.gt.0 ) varnew = rmodfy 

 cc(j,i,k) = varnew

 elseif( icho.eq.3 ) then

 varold = cv(j,i,k) 

 varnew = varold * rmodfy 

 if( ireplc.gt.0 ) varnew = rmodfy 

 cv(j,i,k) = varnew
Appendix C 97

 elseif( icho.eq.4 ) then

 varold = cr(j,i,k) 

 varnew = varold * rmodfy 

 if( ireplc.gt.0 ) varnew = rmodfy 

 cr(j,i,k) = varnew

 action(10:10) = ’X’

 WRITE (IOUT,’(1x,I4,I9,I8,G13.4,G14.4,I8,a10)’) 

 + K,I,J,varold,varnew,II,action 

 varold = cc(j,i,k) 

 varnew = varold * rmodfy 

 if( ireplc.gt.0 ) varnew = rmodfy 

 cc(j,i,k) = varnew

 action(10:10) = ’Y’

 elseif( icho.eq.5 ) then

 varold = cr(j,i,k) 

 varnew = varold * rmodfy 

 if( ireplc.gt.0 ) varnew = rmodfy 

 cr(j,i,k) = varnew

 action(10:10) = ’X’

 WRITE (IOUT,’(1x,I4,I9,I8,G13.4,G14.4,I8,a10)’) 

 + K,I,J,varold,varnew,II,action 

 varold = cv(j,i,k) 

 varnew = varold * rmodfy 

 if( ireplc.gt.0 ) varnew = rmodfy 

 cv(j,i,k) = varnew

 action(10:10) = ’Z’

 elseif( icho.eq.6 ) then

 varold = cc(j,i,k) 

 varnew = varold * rmodfy 

 if( ireplc.gt.0 ) varnew = rmodfy 

 cc(j,i,k) = varnew

 action(10:10) = ’Y’

 WRITE (IOUT,’(1x,I4,I9,I8,G13.4,G14.4,I8,a10)’) 

 + K,I,J,varold,varnew,II,action 

 varold = cv(j,i,k) 

 varnew = varold * rmodfy 

 if( ireplc.gt.0 ) varnew = rmodfy 

 cv(j,i,k) = varnew

 action(10:10) = ’Z’

 elseif( icho.eq.7 ) then

 varold = cr(j,i,k) 

 varnew = varold * rmodfy 

 if( ireplc.gt.0 ) varnew = rmodfy 

 cr(j,i,k) = varnew

 action(10:10) = ’X’

 WRITE (IOUT,’(1x,I4,I9,I8,G13.4,G14.4,I8,a10)’) 

 + K,I,J,varold,varnew,II,action 

 varold = cc(j,i,k) 

 varnew = varold * rmodfy 

 if( ireplc.gt.0 ) varnew = rmodfy 

 cc(j,i,k) = varnew

 action(10:10) = ’Y’

 WRITE (IOUT,’(1x,I4,I9,I8,G13.4,G14.4,I8,a10)’) 
98 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected Waste-Disposal 

Sites at Naval Station Mayport, Florida

 + K,I,J,varold,varnew,II,action 

 varold = cv(j,i,k) 

 varnew = varold * rmodfy 

 if( ireplc.gt.0 ) varnew = rmodfy 

 cv(j,i,k) = varnew

 action(10:10) = ’Z’

 elseif( icho.eq.8 ) then

 varold = hy(j,i,k) 

 varnew = varold * rmodfy 

 if( ireplc.gt.0 ) varnew = rmodfy 

 hy(j,i,k) = varnew

 elseif( icho.eq.9 ) then

 varold = bot(j,i,k) 

 varnew = varold * rmodfy 

 if( ireplc.gt.0 ) varnew = rmodfy 

 bot(j,i,k) = varnew

 elseif( icho.eq.10 .and. iss.eq.0 ) then

 varold = sc1(j,i,k) 

 varnew = varold * rmodfy 

 if( ireplc.gt.0 ) varnew = rmodfy 

 sc1(j,i,k) = varnew

 elseif( icho.eq.11 .and. iss.eq.0 ) then

 varold = sc2(j,i,k) 

 varnew = varold * rmodfy 

 if( ireplc.gt.0 ) varnew = rmodfy 

 sc2(j,i,k) = varnew

 elseif( icho.eq.12) then

 varold = top(j,i,k) 

 varnew = varold * rmodfy 

 if( ireplc.gt.0 ) varnew = rmodfy 

 top(j,i,k) = varnew

 else

 endif

 WRITE (IOUT,’(1x,I4,I9,I8,G13.4,G14.4,I8,a10)’) 

 + K,I,J,varold,varnew,II,action 

 enddo

 endif

c

C8------RETURN 

 RETURN 

 END 
Appendix C 99

Program Listing for Module CAPS

 subroutine caps(a1,n)

 character*1 lc(26), uc(26)

 character*128 a1

 data lc /’a’,’b’,’c’,’d’,’e’,’f’,’g’,’h’,’i’,’j’,’k’,’l’,’m’,’n’,

 . ’o’,’p’,’q’,’r’,’s’,’t’,’u’,’v’,’w’,’x’,’y’,’z’/

 data uc /’A’,’B’,’C’,’D’,’E’,’F’,’G’,’H’,’I’,’J’,’K’,’L’,’M’,’N’,

 . ’O’,’P’,’Q’,’R’,’S’,’T’,’U’,’V’,’W’,’X’,’Y’,’Z’/

 do 10 i=1,n

 do 20 j=1,26

 if(a1(i:i).ne.lc(j)) goto 20

 a1(i:i)=uc(j)

 goto 10

 20 continue

 10 continue

 return

 end
100 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected Waste-Disposal 

Sites at Naval Station Mayport, Florida

Appendix D. Example of Main Program to Use with the Time-Variant Hydraulic-Property 

Package

The following main program has been modified to allow use of the Time-Variant Hydraulic-Property 

Package. The additions to the code specify that input data for the Time-Variant Hydraulic-Property Package are to 

be read from the unit number stored in element 21 of the IUNIT array. In the following program listing, records 

added to access the Time-Variant Hydraulic-Property Package are identified with the characters “VAR1” in 

rightmost columns. This identifier is not necessary but can only be added after column 72. 

Program Listing

C ******************************************************************

C MAIN CODE FOR MODULAR MODEL -- 6/1/83

C BY MICHAEL G. MCDONALD AND ARLEN W. HARBAUGH

C-----VERSION 1116 28DEC1983 MAIN1

C ******************************************************************

C

C SPECIFICATIONS:

C ------------------------------------------------------------------

 parameter (LENX=2000000)

 COMMON X(lenx)

 DIMENSION HEADNG(32),VBNM(4,20),VBVL(4,20),IUNIT(24)

 DOUBLE PRECISION DUMMY

 EQUIVALENCE (DUMMY,X(1))

c

C ------------------------------------------------------------------

C

C1------SET SIZE OF X ARRAY. REMEMBER TO REDIMENSION X.

C

C2------ASSIGN BASIC INPUT UNIT AND PRINTER UNIT.

 INBAS=5

 IOUT=6

C

C3------DEFINE PROBLEM__ROWS,COLUMNS,LAYERS,STRESS PERIODS,PACKAGES

 CALL BAS1DF(ISUM,HEADNG,NPER,ITMUNI,TOTIM,NCOL,NROW,NLAY,

 1 NODES,INBAS,IOUT,IUNIT)

C

C4------ALLOCATE SPACE IN "X" ARRAY.

 CALL BAS1AL(ISUM,LENX,LCHNEW,LCHOLD,LCIBOU,LCCR,LCCC,LCCV,

 1 LCHCOF,LCRHS,LCDELR,LCDELC,LCSTRT,LCBUFF,LCIOFL,

 2 INBAS,ISTRT,NCOL,NROW,NLAY,IOUT)

 IF(IUNIT(1).GT.0) CALL BCF1AL(ISUM,LENX,LCSC1,LCHY,

 1 LCBOT,LCTOP,LCSC2,LCTRPY,IUNIT(1),ISS,

 2 NCOL,NROW,NLAY,IOUT,IBCFCB)

 IF(IUNIT(2).GT.0) CALL WEL1AL(ISUM,LENX,LCWELL,MXWELL,NWEL,

 1 IUNIT(2),IOUT,IWELCB)

 IF(IUNIT(3).GT.0) CALL DRN1AL(ISUM,LENX,LCDRAI,NDRAIN,MXDRN,

 1 IUNIT(3),IOUT,IDRNCB)

 IF(IUNIT(8).GT.0) CALL RCH1AL(ISUM,LENX,LCIRCH,LCRECH,NRCHOP,

 1 NCOL,NROW,IUNIT(8),IOUT,IRCHCB)

 IF(IUNIT(5).GT.0) CALL EVT1AL(ISUM,LENX,LCIEVT,LCEVTR,LCEXDP,
Appendix D 101

 1 LCSURF,NCOL,NROW,NEVTOP,IUNIT(5),IOUT,IEVTCB)

 IF(IUNIT(4).GT.0) CALL RIV1AL(ISUM,LENX,LCRIVR,MXRIVR,NRIVER,

 1 IUNIT(4),IOUT,IRIVCB)

 IF(IUNIT(14).GT.0) CALL STR1AL(ISUM,LENX,LCSTRM,ICSTRM,MXSTRM,

 1 NSTREM,IUNIT(14),IOUT,ISTCB1,ISTCB2,NSS,NTRIB,

 2 NDIV,ICALC,CONST,LCTBAR,LCTRIB,LCIVAR,LCFGAR)

 IF(IUNIT(7).GT.0) CALL GHB1AL(ISUM,LENX,LCBNDS,NBOUND,MXBND,

 1 IUNIT(7),IOUT,IGHBCB)

 IF(IUNIT(9).GT.0) CALL SIP1AL(ISUM,LENX,LCEL,LCFL,LCGL,LCV,

 1 LCHDCG,LCLRCH,LCW,MXITER,NPARM,NCOL,NROW,NLAY,

 2 IUNIT(9),IOUT)

 IF(IUNIT(13).GT.0) CALL PCG2AL(ISUM,LENX,LCV,LCSS,LCP,LCCD,

 1 LCHCHG,LCLHCH,LCRCHG,LCLRCH,MXITER,ITER1,NCOL,NROW,NLAY,

 2 IUNIT(13),IOUT,NPCOND)

 IF(IUNIT(20).GT.0) CALL CHD1AL(ISUM,LENX,LCCHDS,NCHDS,MXCHD,

 1 IUNIT(20),IOUT)

 IF(IUNIT(21).GT.0) CALL var1AL(ISUM,LENX,MXvar,Iunit(21), IOUT ) VAR1

C

C5------IF THE "X" ARRAY IS NOT BIG ENOUGH THEN STOP.

 IF(ISUM-1.GT.LENX) STOP

C

C6------READ AND PREPARE INFORMATION FOR ENTIRE SIMULATION.

 CALL BAS1RP(X(LCIBOU),X(LCHNEW),X(LCSTRT),X(LCHOLD),

 1 ISTRT,INBAS,HEADNG,NCOL,NROW,NLAY,NODES,VBVL,X(LCIOFL),

 2 IUNIT(12),IHEDFM,IDDNFM,IHEDUN,IDDNUN,IOUT)

 IF(IUNIT(1).GT.0) CALL BCF1RP(X(LCIBOU),X(LCHNEW),X(LCSC1),

 1 X(LCHY),X(LCCR),X(LCCC),X(LCCV),X(LCDELR),

 2 X(LCDELC),X(LCBOT),X(LCTOP),X(LCSC2),X(LCTRPY),

 3 IUNIT(1),ISS,NCOL,NROW,NLAY,NODES,IOUT)

 IF(IUNIT(9).GT.0) CALL SIP1RP(NPARM,MXITER,ACCL,HCLOSE,X(LCW),

 1 IUNIT(9),IPCALC,IPRSIP,IOUT)

 IF(IUNIT(13).GT.0) CALL PCG2RP(MXITER,ITER1,HCLOSE,RCLOSE,

 1 NPCOND,NBPOL,RELAX,IPRPCG,IUNIT(13),IOUT,MUTPCG,IPCGCD)

C

C7------SIMULATE EACH STRESS PERIOD.

 DO 300 KPER=1,NPER

C

C7A-----READ STRESS PERIOD TIMING INFORMATION.

 CALL BAS1ST(NSTP,DELT,TSMULT,PERTIM,KPER,INBAS,IOUT)

C

C7B-----READ AND PREPARE INFORMATION FOR STRESS PERIOD.

 IF(IUNIT(2).GT.0) CALL WEL1RP(X(LCWELL),NWEL,MXWELL,IUNIT(2),

 1 IOUT)

 IF(IUNIT(3).GT.0) CALL DRN1RP(X(LCDRAI),NDRAIN,MXDRN,IUNIT(3),

 1 IOUT)

 IF(IUNIT(8).GT.0) CALL RCH1RP(NRCHOP,X(LCIRCH),X(LCRECH),

 1 X(LCDELR),X(LCDELC),NROW,NCOL,NLAY,IUNIT(8),IOUT)

 IF(IUNIT(5).GT.0) CALL EVT1RP(NEVTOP,X(LCIEVT),X(LCEVTR),

 1 X(LCEXDP),X(LCSURF),X(LCDELR),X(LCDELC),NCOL,NROW,

 1 NLAY,IUNIT(5),IOUT)

 IF(IUNIT(4).GT.0) CALL RIV1RP(X(LCRIVR),NRIVER,MXRIVR,IUNIT(4),

 1 IOUT)

 IF(IUNIT(14).GT.0) CALL STR1RP(X(LCSTRM),X(ICSTRM),NSTREM,
102 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected Waste-Disposal 

Sites at Naval Station Mayport, Florida

 1 MXSTRM,IUNIT(14),IOUT,X(LCTBAR),NDIV,NSS,

 1 NTRIB,X(LCIVAR),ICALC,IPTFLG)

 IF(IUNIT(7).GT.0) CALL GHB1RP(X(LCBNDS),NBOUND,MXBND,IUNIT(7),

 1 IOUT)

 IF(IUNIT(20).GT.0) CALL CHD1RP(X(LCCHDS),NCHDS,MXCHD,CHDEXP,

 + x(lcibou),ncol,nrow,nlay,perlen,delt,nstp,tsmult,IUNIT(20),iout)

 IF(IUNIT(21).GT.0) CALL VAR1RP(mxvar,X(LCIBOU),X(LCSC1),X(LCHY), VAR1

 + X(LCCR),X(LCCC),X(LCCV),X(LCDELR),X(LCDELC),X(LCBOT),X(LCTOP), VAR1

 + X(LCSC2),ISS,NCOL,NROW,NLAY,IUNIT(21),iout) VAR1

C

C7C-----SIMULATE EACH TIME STEP.

 DO 200 KSTP=1,NSTP

C

C7C1----CALCULATE TIME STEP LENGTH. SET HOLD=HNEW..

 CALL BAS1AD(DELT,TSMULT,TOTIM,PERTIM,X(LCHNEW),X(LCHOLD),KSTP,

 1 NCOL,NROW,NLAY)

 IF(IUNIT(20).GT.0)

 . CALL CHD1FM(NCHDS,MXCHD,CHDEXP,X(LCCHDS), x(lcibou),x(lchnew),

 . x(lchold),perlen,pertim,delt,ncol,nrow,nlay,iout)

C7C2----ITERATIVELY FORMULATE AND SOLVE THE EQUATIONS.

 DO 100 KITER=1,MXITER

C

C7C2A---FORMULATE THE FINITE DIFFERENCE EQUATIONS.

 CALL BAS1FM(X(LCHCOF),X(LCRHS),NCOL,NROW,NLAY,NODES)

 IF(IUNIT(1).GT.0) CALL BCF1FM(X(LCHCOF),X(LCRHS),X(LCHOLD),

 1 X(LCSC1),X(LCHNEW),X(LCIBOU),X(LCCR),X(LCCC),X(LCCV),

 2 X(LCHY),X(LCTRPY),X(LCBOT),X(LCTOP),X(LCSC2),

 3 X(LCDELR),X(LCDELC),DELT,ISS,KITER,KSTP,KPER,NCOL,

 4 NROW,NLAY,IOUT)

 IF(IUNIT(2).GT.0) CALL WEL1FM(NWEL,MXWELL,X(LCRHS),X(LCWELL),

 1 X(LCIBOU),NCOL,NROW,NLAY,iout)

 IF(IUNIT(3).GT.0) CALL DRN1FM(NDRAIN,MXDRN,X(LCDRAI),X(LCHNEW),

 1 X(LCHCOF),X(LCRHS),X(LCIBOU),NCOL,NROW,NLAY,iout)

 IF(IUNIT(8).GT.0) CALL RCH1FM(NRCHOP,X(LCIRCH),X(LCRECH),

 1 X(LCRHS),X(LCIBOU),NCOL,NROW,NLAY,iout)

 IF(IUNIT(5).GT.0) CALL EVT1FM(NEVTOP,X(LCIEVT),X(LCEVTR),

 1 X(LCEXDP),X(LCSURF),X(LCRHS),X(LCHCOF),X(LCIBOU),

 1 X(LCHNEW),NCOL,NROW,NLAY,iout)

 IF(IUNIT(4).GT.0) CALL RIV1FM(NRIVER,MXRIVR,X(LCRIVR),X(LCHNEW),

 1 X(LCHCOF),X(LCRHS),X(LCIBOU),NCOL,NROW,NLAY)

 IF(IUNIT(14).GT.0) CALL STR1FM(NSTREM,X(LCSTRM),X(ICSTRM),

 1 X(LCHNEW),X(LCHCOF),X(LCRHS),X(LCIBOU),

 2 MXSTRM,NCOL,NROW,NLAY,IOUT,NSS,X(LCTBAR),

 3 NTRIB,X(LCTRIB),X(LCIVAR),X(LCFGAR),ICALC,CONST)

 IF(IUNIT(7).GT.0) CALL GHB1FM(NBOUND,MXBND,X(LCBNDS),X(LCHCOF),

 1 X(LCRHS),X(LCIBOU),NCOL,NROW,NLAY,iout)

C

C7C2B---MAKE ONE CUT AT AN APPROXIMATE SOLUTION.

 IF(IUNIT(9).GT.0) CALL SIP1AP(X(LCHNEW),X(LCIBOU),X(LCCR),X(LCCC),

 1 X(LCCV),X(LCHCOF),X(LCRHS),X(LCEL),X(LCFL),X(LCGL),X(LCV),

 2 X(LCW),X(LCHDCG),X(LCLRCH),NPARM,KITER,HCLOSE,ACCL,ICNVG,

 3 KSTP,KPER,IPCALC,IPRSIP,MXITER,NSTP,NCOL,NROW,NLAY,NODES,

 4 IOUT)
Appendix D 103

C

C ADD AFTER CALL SOR1AP

C . . . . . . . . . . EXECUTE MULTIPLE INNER ITERATIONS OR . . .

 KPER1=KPER

 KSTP1=KSTP

 MX1=MXITER

 ITER11=ITER1

 IF(IUNIT(15).NE.0) THEN

 KPER1=IP

 KSTP1=KPER-1

 ENDIF

 IF(IUNIT(13).GT.0) CALL PCG2AP(X(LCHNEW),X(LCIBOU),X(LCCR),

 1 X(LCCC),X(LCCV),X(LCHCOF),X(LCRHS),X(LCV),X(LCSS),X(LCP),

 2 X(LCCD),X(LCHCHG),X(LCLHCH),X(LCRCHG),X(LCLRCH),

 3 KKITER,NITER,HCLOSE,RCLOSE,ICNVG,KSTP1,KPER1,IPRPCG,

 4 MX1,ITER11,NPCOND,NBPOL,NSTP,NCOL,NROW,NLAY,NODES,

 5 RELAX,IOUT,MUTPCG,IUNIT(15),IP,SN,SP,SR)

C

C7C2C---IF CONVERGENCE CRITERION HAS BEEN MET STOP ITERATING.

 IF(ICNVG.EQ.1) GO TO 110

 100 CONTINUE

 KITER=MXITER

 110 CONTINUE

C

C7C3----DETERMINE WHICH OUTPUT IS NEEDED.

 CALL BAS1OC(NSTP,KSTP,KPER,ISTRT,ICNVG,X(LCIOFL),NLAY,

 1 IBUDFL,ICBCFL,IHDDFL,IUNIT(12),IOUT)

C

C7C4----CALCULATE BUDGET TERMS. SAVE CELL-BY-CELL FLOW TERMS.

 MSUM=1

 IF(IUNIT(1).GT.0) CALL BCF1BD(VBNM,VBVL,MSUM,X(LCHNEW),

 1 X(LCIBOU),X(LCHOLD),X(LCSC1),X(LCCR),X(LCCC),X(LCCV),

 2 X(LCTOP),X(LCSC2),DELT,ISS,NCOL,NROW,NLAY,KSTP,KPER,

 3 IBCFCB,ICBCFL,X(LCBUFF),IOUT)

 IF(IUNIT(2).GT.0) CALL WEL1BD(NWEL,NWELL,VBNM,VBVL,MSUM,X(LCWELL),

 1 X(LCIBOU),DELT,NCOL,NROW,NLAY,KSTP,KPER,IWELCB,ICBCFL,

 1 X(LCBUFF),IOUT)

 IF(IUNIT(3).GT.0) CALL DRN1BD(NDRAIN,MXDRN,VBNM,VBVL,MSUM,

 1 X(LCDRAI),DELT,X(LCHNEW),NCOL,NROW,NLAY,X(LCIBOU),KSTP,KPER,

 2 IDRNCB,ICBCFL,X(LCBUFF),IOUT)

 IF(IUNIT(8).GT.0) CALL RCH1BD(NRCHOP,X(LCIRCH),X(LCRECH),

 1 X(LCIBOU),NROW,NCOL,NLAY,DELT,VBVL,VBNM,MSUM,KSTP,KPER,

 2 IRCHCB,ICBCFL,X(LCBUFF),IOUT)

 IF(IUNIT(5).GT.0) CALL EVT1BD(NEVTOP,X(LCIEVT),X(LCEVTR),

 1 X(LCEXDP),X(LCSURF),X(LCIBOU),X(LCHNEW),NCOL,NROW,NLAY,

 2 DELT,VBVL,VBNM,MSUM,KSTP,KPER,IEVTCB,ICBCFL,X(LCBUFF),IOUT)

 IF(IUNIT(4).GT.0) CALL RIV1BD(NRIVER,MXRIVR,X(LCRIVR),X(LCIBOU),

 1 X(LCHNEW),NCOL,NROW,NLAY,DELT,VBVL,VBNM,MSUM,

 2 KSTP,KPER,IRIVCB,ICBCFL,X(LCBUFF),IOUT)

 IF(IUNIT(14).GT.0) CALL STR1BD(NSTREM,X(LCSTRM),X(ICSTRM),

 1 X(LCIBOU),MXSTRM,X(LCHNEW),NCOL,NROW,NLAY,DELT,VBVL,VBNM,MSUM,

 2 KKSTP,KKPER,ISTCB1,ISTCB2,ICBCFL,X(LCBUFF),IOUT,NTRIB,NSS,

 3 X(LCTRIB),X(LCTBAR),X(LCIVAR),X(LCFGAR),ICALC,CONST,IPTFLG)
104 Ground-Water Flow in the Surficial Aquifer System and Potential Movement of Contaminants from Selected Waste-Disposal 

Sites at Naval Station Mayport, Florida

 IF(IUNIT(7).GT.0) CALL GHB1BD(NBOUND,MXBND,VBNM,VBVL,MSUM,

 1 X(LCBNDS),DELT,X(LCHNEW),NCOL,NROW,NLAY,X(LCIBOU),KSTP,KPER,

 2 IGHBCB,ICBCFL,X(LCBUFF),IOUT)

C

C------SAVE CELL-BY-CELL FLOW TERMS FOR USE IN MT3D

 IMT3D=IUNIT(22)

 IF(IMT3D.ne.0) then

 CALL BAS1MT(X(LCHNEW),X(LCIBOU),

 2 NCOL,NROW,NLAY,KSTP,KPER,X(LCBUFF),IMT3D)

 IF(IUNIT(1).GT.0) CALL BCF1MT(X(LCHNEW),X(LCIBOU),X(LCCR),

 1 X(LCCC),X(LCCV),X(LCTOP),NCOL,NROW,NLAY,KSTP,KPER,

 3 X(LCBUFF),IMT3D)

 IF(IUNIT(2).GT.0) CALL WEL1MT(NWELLS,MXWELL,

 1 X(LCWELL),X(LCIBOU),NCOL,NROW,NLAY,KSTP,KPER,IMT3D)

 IF(IUNIT(3).GT.0) CALL DRN1MT(NDRAIN,MXDRN,

 1 X(LCDRAI),X(LCHNEW),NCOL,NROW,NLAY,X(LCIBOU),KSTP,

 2 KPER,IMT3D)

 IF(IUNIT(8).GT.0) CALL RCH1MT(NRCHOP,X(LCIRCH),X(LCRECH),

 1 X(LCIBOU),NROW,NCOL,NLAY,KSTP,KPER,X(LCBUFF),IMT3D)

 IF(IUNIT(5).GT.0) CALL EVT1MT(NEVTOP,X(LCIEVT),X(LCEVTR),

 1 X(LCEXDP),X(LCSURF),X(LCIBOU),X(LCHNEW),NCOL,NROW,NLAY,

 2 KSTP,KPER,X(LCBUFF),IMT3D)

 IF(IUNIT(4).GT.0) CALL RIV1MT(NRIVER,MXRIVR,X(LCRIVR),X(LCIBOU),

 1 X(LCHNEW),NCOL,NROW,NLAY,KSTP,KPER,IMT3D)

 IF(IUNIT(7).GT.0) CALL GHB1MT(NBOUND,MXBND,

 1 X(LCBNDS),X(LCHNEW),NCOL,NROW,NLAY,X(LCIBOU),KSTP,

 2 KPER,IMT3D)

 endif

C

C7C5---PRINT AND OR SAVE HEADS AND DRAWDOWNS. PRINT OVERALL BUDGET.

 CALL BAS1OT(X(LCHNEW),X(LCSTRT),ISTRT,X(LCBUFF),X(LCIOFL),

 1 MSUM,X(LCIBOU),VBNM,VBVL,KSTP,KPER,DELT,

 2 PERTIM,TOTIM,ITMUNI,NCOL,NROW,NLAY,ICNVG,

 3 IHDDFL,IBUDFL,IHEDFM,IHEDUN,IDDNFM,IDDNUN,IOUT)

C

 200 CONTINUE

 300 CONTINUE

C

C8------END PROGRAM

c ENDFILE (UNIT=IOUT)

 STOP

C

 END

C