U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2014–1256

Changes in the Saltwater Interface Corresponding 

to the Installation of a Seepage Barrier Near Lake 

Okeechobee, Florida
Cover. Background photograph—Lake Okeechobee by U.S. Geological Survey, South Florida Information Access [SOFIA].

Inset photographs from left to right—Monitoring well used to collect water-quality data; technician measuring the water level in 

a well; collection of an electromagnetic induction log from a well (Jeffrey F. Robinson, U.S. Geological Survey).
Changes in the Saltwater Interface 

Corresponding to the Installation 

of a Seepage Barrier Near Lake 

Okeechobee, Florida

By Scott T. Prinosand Robert Valderrama

Open-File Report 2014–1256

U.S. Department of the Interior

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

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2015

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Suggested citation:

Prinos, S.T., and Valderrama, Robert, 2015, Changes in the saltwater interface corresponding to the installation of a 

seepage barrier near Lake Okeechobee, Florida: U.S. Geological Survey Open-File Report 2014–1256, 24 p., 

http://dx.doi.org/10.3133/ofr20141256.

ISSN 2331-1258 (online)
iii

Acknowledgments

The authors would like to acknowledge the substantial contributions of Mark Shafer and 

Hwai-Ping (Pearce) Cheng of the U.S. Army Corps of Engineers who provided data and insights 

that were crucial to understanding changes in the saltwater interface near the Herbert Hoover 

Dike, and differences in the quality of the information collected from short-screened, and longscreened wells. Substantive reviews of the report were also provided by Hwai-Ping (Pearce) 

Cheng, Mark Shafer, and Russ Weeks of the U.S. Army Corps of Engineers, and Mike Deacon, 

David Fitterman, emeritus, and Mike Wacker, of the U.S. Geological Survey. 

v

Contents

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

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

Methods...........................................................................................................................................................3

Results .............................................................................................................................................................8

Locations Without a Seepage Barrier...............................................................................................8

Locations With a Seepage Barrier ..................................................................................................12

Comparison of Information From Short-Screened and Long-Screened Wells ........................17

Conclusions ..................................................................................................................................................22

References Cited .........................................................................................................................................23

Appendix 1. Results of water samples from selected long-screened interval 

monitoring wells....................................................................http://pubs.usgs.gov/of/2014/1256/

Appendix 2. Results of water samples from selected short-screened interval 

monitoring wells....................................................................http://pubs.usgs.gov/of/2014/1256/

Figures

1. Map showing location of Lake Okeechobee, seepage barrier reaches, and 

monitoring wells installed to monitor the depth of the saltwater interface........................2

2. Idealized section through the Herbert Hoover Dike showing the freshwater/

saltwater mixing zone and the 1,000-milligram-per-liter isochlor........................................3

3. Diagram of short-screened interval monitoring wells used for water sampling 

and collection of time series electromagnetic-induction log datasets...............................6

4. Graphs showing chloride concentration of water samples from shallow, 

short-screened monitoring wells near Lake Okeechobee, Florida......................................9

5. Graph of time series electromagnetic-induction log (TSEMIL) dataset from 

monitoring well PB–1821, generally showing only minor temporal changes 

in the bulk conductivity of the aquifer.....................................................................................10

6. Graphs showing comparison of the time series electromagnetic-induction 

log (TSEMIL) dataset from monitoring well GL–332, and the total dissolved 

solids concentration of water samples collected from monitoring well 

HHD10–R2–MW4F ......................................................................................................................11

7. Graphs showing comparison of the time series electromagnetic-induction 

log (TSEMIL) dataset from well HE–1145, and the total dissolved solids 

concentration of water samples collected from well HHD10–R2–MW18F.......................13

8. Graphs showing comparison of the time series electromagnetic-induction 

log (TSEMIL) dataset from monitoring well PB–1822, and the total dissolved 

solids concentration of water samples collected from monitoring well 

HHD10–R3–MW18F ....................................................................................................................14

9. Graph showing time series electromagnetic-induction log dataset from 

monitoring well PB–1817 showing changes in the bulk conductivity of the 

aquifer...........................................................................................................................................15

10. Graph showing time series electromagnetic-induction log (TSEMIL) dataset 

from monitoring well PB–1815 showing changes in the bulk conductivity of 

the aquifer....................................................................................................................................16
vi

11. Graph showing time series electromagnetic-induction log (TSEMIL) dataset 

from monitoring well PB–1816 showing changes in the bulk conductivity of 

the aquifer....................................................................................................................................17

12. Graphs showing comparison of the time series electromagnetic-induction 

log (TSEMIL) dataset from well PB–1818, and the total dissolved solids 

concentration of water samples collected from well HHD08–R1C–MW8D, 

including detailed depictions of the TSEMIL dataset from 40–65 ft, and 75–100 ft .........18

13. Graph showing time series electromagnetic-induction log dataset from 

monitoring well PB–1819 showing changes in the bulk conductivity of 

the aquifer....................................................................................................................................19

14. Graph showing time series electromagnetic-induction log (TSEMIL) dataset

from monitoring well PB–1820 showing temporal changes in the bulk 

conductivity of the aquifer ........................................................................................................20

15. Graph showing total dissolved solids concentration of water samples collected 

from monitoring well HHD08–R1D–MW5D.............................................................................21

Tables

1. Design of monitoring wells, and depth and date of completion of seepage barrier.........4

2. Design of long-screened monitoring wells, and depth and date of completion of 

seepage barrier.............................................................................................................................7

Conversion Factors

Inch/Pound to International System of Units

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Electrical conductivity

siemens per meter (S/m) 1,000 millisiemens per meter (mS/m)

siemens per meter (S/m) 10,000 microsiemens per centimeter (μS/cm)

Electrical conductivity σ in siemens per meter [S/m] can be converted to electrical resistivity ρ

in ohm-meters [ohm m] as follows: ρ = 1/σ.

Electrical conductivity σ in millisiemens per meter [mS/m] can be converted to electrical 

resistivity ρ in ohm-meters [ohm m] as follows: ρ = 1,000/σ.

Electrical conductivity σ in microsiemens per centimeter [μS/cm] can be converted to electrical 

resistivity ρ in ohm-meters [ohm m] as follows: ρ = 10,000/σ.

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

°F = (1.8 × °C) + 32
vii

Datum

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

(NGVD 29).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Elevation, as used in this report, refers to distance above the vertical datum.

Supplemental Information

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius 

(μS/cm at 25 °C).

Concentrations of chemical constituents in water are given in milligrams per liter (mg/L).

Abbreviations

EMI electromagnetic induction

HHD Herbert Hoover Dike

IAG International Analytic Group

PVC polyvinyl chloride

TDS total dissolved solids

TSEMIL time series electromagnetic-induction log (dataset)

USACE U.S. Army Corps of Engineers

USGS U.S. Geological Survey 

Abstract 

In 2011, the U.S. Geological Survey and the U.S. Army 

Corps of Engineers began monitoring the saltwater interface 

near Lake Okeechobee to evaluate changes in interface depth 

that could possibly be related to the repair of the Herbert 

Hoover Dike. A seepage barrier (or cut-off wall), installed by 

the U.S. Army Corps of Engineers, is a wall of grout designed 

to protect the Herbert Hoover Dike from internal erosion 

caused by the piping of water. The seepage barrier prevents 

water from flowing through or immediately under the dike 

by diverting the flow below the dike, into the surficial aquifer 

system. The seepage barrier extends below the saltwater 

interface in some areas. Monitoring consisted of collecting 

water samples and time series electromagnetic-induction log 

(TSEMIL) datasets from 10 well clusters, each of which have 

1 shallow and 1 deep monitoring well, with 5- to 10-foot- (ft) 

long-screened intervals. The deep wells are 120 to 187 ft deep, 

and the shallow wells are 44 to 100 ft deep.

Changes in the depth of the saltwater interface were 

identified that correspond closely to the depth of the bottom of 

the seepage barrier. These changes may have been the consequence of changes in groundwater flow initiated by the seepage 

barrier installation. In areas of the dike where a seepage barrier 

had not been installed, or where the bottom of the seepage 

barrier is well above the saltwater interface, monitoring 

detected no changes in the depth of the saltwater interface. 

At five of the monitoring-well cluster locations, a 

long-screened well was also installed for monitoring and 

comparison purposes. These long-screened wells are 160 to 

200 ft deep, and have open intervals ranging from 145 to 

185 ft in length. Water samples were collected at depth 

intervals of about 5 to 10 ft, using 3-ft-long straddle packers 

to isolate each sampling interval. The results of monitoring 

conducted using these long-screened interval wells were 

generally too variable to identify any changes that might be 

associated with the seepage barrier. Samples from one of these 

long-screened interval wells failed to detect the saltwater 

interface evident in samples and TSEMIL datasets from a 

collocated well cluster. This failure may have been caused 

by downward flow of freshwater from above the saltwater 

interface in the well bore.

Introduction 

Lake Okeechobee is one of the largest freshwater lakes 

in the United States (fig. 1) and is surrounded by the Herbert 

Hoover Dike (HHD). Modifications to the HHD are being 

made to prevent its failure. The U.S. Army Corps of Engineers 

(USACE) constructed the HHD during the 1930s to prevent 

hurricane-induced floods, like those in 1926 and 1928, that 

killed a combined estimated total of 2,400 to 3,400 people 

(Lloyd’s, 2010; U.S. Army Corps of Engineers, [n.d.]). The 

need for major repairs to the HHD became evident during 

2004 and 2005 when Hurricanes Frances, Jeanne, and Wilma 

damaged the levee through erosion and seepage of water 

through or under the dike (Abtew and Iricanin, 2008). When 

this seepage occurs, it can lead to internal erosion of the 

dike by piping, defined as the removal of sand- and silt-sized 

particles by water seeping through the dike. Piping can lead 

to cavity formation, which in turn, may eventually cause the 

dike to collapse. Concerning seepage through and beneath the 

HHD, Bromwell and others (2006) reported that the “Herbert 

Hoover Dike has narrowly escaped failure from this process 

on several occasions, and we suspect that its condition may 

be worsening.” The USACE began a project in 2007 to install 

a seepage barrier (or cut-off wall) to prevent water from 

seeping through or immediately under the dike (U.S. Army 

Corps of Engineers, 2013). The seepage barrier is a wall of 

grout that diverts the flow of water below the dike into the 

surficial aquifer system to prevent erosion by piping through 

the dike and immediately beneath it. The installation of the 

seepage barrier in the HHD around the lake is being done 

in stages over sections of the dike called “reaches” (fig. 1). 

Reaches 1A–1D of the seepage barrier were completed during 

October 2009–July 2012. Reaches 2 and 3 have not been 

installed at the time of this report.

Changes in the Saltwater Interface Corresponding 

to the Installation of a Seepage Barrier Near Lake 

Okeechobee, Florida

By Scott T. Prinosand Robert Valderrama
2 Changes in the Saltwater Interface Corresponding to the Installation of a Seepage Barrier Near Lake Okeechobee

Figure 1. Location of Lake Okeechobee, seepage barrier reaches, and monitoring wells installed to monitor the depth of the 

saltwater interface. [IAG, International Analytic Group; USACE, U.S. Army Corps of Engineers; USGS, U.S. Geological Survey]

#

#

#

##

#

#

# #

#

PB -1822

PB -1821

PB -1820

PB -1819

PB -1818 PB -1817

PB -1816

PB -1815

HE -1145

PB -1822S

PB -1820S

PB -1819S

PB -1818S

PB -1816S

PB -1815S

GL-332

HE -1145S

PB -1821S

PB -1817S

GL-332S

HHD10-R3-MW4F

HHD10-R2-MW4F

HHD10-R3-MW18F

HHD10-R2-MW18F

HHD08-R1D-MW5D

HHD08-R1A-MW11

HHD08-R1C-MW8D

L-47

L-1

L-65

L-1E

L-50

C-43

LD-1

L-64

C-19

L-8

L-63N

L-63S

C-2

3

LD-3

L306

C-21

L-41

Source: Esri, DigitalGlobe, GeoEye, i-cubed, USDA, USGS, AEX,

Getmapping, Aerogrid, IGN, IGP, swisstopo, and the GIS User Community

#

#

#

##

#

#

# #

*

*

*

**

*

*

* *

#

#

#

#

#

# Lake # Okeechobee

81°10’

27°10’

27°05’

27°00’

26°55’

26°50’

26°45’

26°40’

81°05’ 81°00’ 80°55’ 80°50’ 80°45’ 80°40’ 80°35’

Base from South Florida Water Management

and U.S. Geological Survey digital data

Source: Esri, DigitalGlobe, GeoEye, i-cubed, USDA, USGS, 

AEX, Getmapping, Aerogrid, IGN, IGP, swisstopo, and the 

GIS User Community

Lake Okeechobee

C–41A

C–40

C–41

C–41

L–62

C–38

LD–4

L–48

L–49

L–60

L–61

L–50

L–41

C–19

C–43

LD–3

LD–1

L–1

L–1E

L–8

L–47

L–65

L–64

L–63S

C–23

L–63N

C–21

L306

L–59

GL–332

GL–332S

HE–1145

HE–1145S

PB–1820S Torry Island

PB–1821

PB–1819S

PB–1819

PB–1818 PB–1817

PB–1816

PB–1816S

PB–1815

PB–1815S

PB–1817S PB–1818S

PB–1821S

PB–1822S

PB–1822

PB–1820

HHD10-R2-MW4F

HHD10-R2-MW18F

HHD10-R3-MW18F

HHD10-R3-MW4F

HHD08-R1D-MW5D

HHD08-R1C-MW8D

HHD08-R1A-MW11

EXPLANATION

Seepage barrier reaches

Reach 1A

Reach 1B

Reach 1C

Reach 1D

Reach 2 (not completed as of 2014)

Reach 3 (not completed as of 2014)

Herbert Hoover Dike

USACE/IAG monitoring wells

USGS monitoring wells

#

0 5 10 MILES

0 5 10 KILOMETERS
Methods 3

The surficial aquifer system is a source of freshwater 

that is used for private water supply in some areas near Lake 

Okeechobee. Near the southern edge of the Lake, in Glades, 

Hendry, and Palm Beach Counties, the freshwater in the 

aquifer transitions to saltwater beginning at depths of 30 to 

120 feet (ft). The ratios of strontium-87 to strontium-86 in 

water samples of this saltwater indicate that it is most likely 

residual invaded or relict seawater (Reese and Wacker, 2009). 

In some areas, the seepage barrier extends to a depth near 

or below that of the saltwater interface. Groundwater flow 

diverted by the seepage barrier in these areas could possibly 

alter the distribution of saltwater in the surficial aquifer (fig. 2) 

and cause saltwater to intrude into areas that were previously 

fresh (fig. 2B–C). 

Monitoring was initiated to determine if the interface 

was disturbed as groundwater flow was altered by the seepage 

barrier. A monitoring network was designed to detect changes 

in the depth and concentration of saltwater in the aquifer, 

using water samples to evaluate chloride concentration, and 

time series electromagnetic-induction log (TSEMIL) datasets 

to evaluate changes in bulk conductivity in the aquifer. 

Monitoring began in August 2011 and continues as of the 

writing of this report. 

This report documents changes in the saltwater interface, 

likely, resulting from installation of a seepage barrier 

near Lake Okeechobee, Florida. Monitoring results from 

August 2011 through January 2014 are summarized herein 

and compared between locations where the seepage barrier 

was present or absent to determine the sources of apparent 

variation in aquifer salinity. Monitoring results from long- and 

short-screened monitoring wells are compared to evaluate the 

well design that provides the most reliable results. 

Methods

The U.S. Geological Survey (USGS) monitored 

20 shallow and deep, short-screened interval monitoring wells 

installed at 10 sites (fig. 1; table 1). The shallow and deep 

monitoring wells of each monitoring-well cluster are generally 

installed within the same borehole (fig. 3). Monitoring wells 

are cased with polyvinyl chloride (PVC) pipe and have 5- to 

10-ft screened intervals. The deep wells are 2 inches (in.) 

in diameter and between 120 and 187 ft deep (table 1). The 

shallow wells are 0.75-in. in diameter and are used to collect 

water samples, generally from near the top of the saltwater 

interface. When monitoring began, the saltwater interface was 

about 1 to 7 ft below the bottom of the open intervals of wells 

GL–332S, PB–1819S, PB–1818S, PB–1821S, and PB–1822S, 

and 6 and 9 ft above the open interval of PB–1816S and 

PB–1817S, respectively (table 1). The top of the saltwater 

interface was about 27 to 67 ft below the bottom of the open 

intervals of wells HE–1145S, PB–1815S, and PB–1820S when 

monitoring began. Most of the shallow wells are between 

44 and 60 ft deep, but wells PB–1820S and PB–1821S are 

95 and 100 ft deep, respectively. Water samples and TSEMIL 

datasets were collected from each well. 

Figure 2. Idealized section through the Herbert Hoover 

Dike showing the freshwater/saltwater mixing zone and the 

1,000-milligram-per-liter isochlor (A) prior to the installation of 

the seepage barrier, and potential changes in the distribution of 

saltwater in the aquifer after installation of a seepage barrier that 

(B) extends to a depth near to or below the mixing zone, and (C) is 

completed to a depth well above that of the mixing zone. Diagram 

is not to scale.

Lake Okeechobee

Herbert 

Hoover 

Dike

Seepage

barrier

Saltwater 

Fresh 

water

Mixing 

Monitoring

well nest

1,000-mg/L 

isochlor

Before After

zone

Increased

water 

conductivity

Decreased

water 

conductivity

Lake Okeechobee

Herbert 

Hoover 

Dike

Saltwater 

Freshwater

Mixing zone 

Monitoring

well nest

1,000-mg/L 

isochlor

Groundwater flow

prior to seepage

barrier

Lake Okeechobee

Herbert 

Hoover 

Dike

Seepage

barrier

Saltwater 

Freshwater

Mixing zone 

Monitoring

well nest

Groundwater flow

diverted by seepage

barrier

1,000-mg/L 

isochlor

Before After

decreased

water conductivity

C

B

A

Groundwater flow

diverted by seepage

barrier

Unsaturated

zone

Unsaturated

zone

Unsaturated

zone
4 Changes in the Saltwater Interface Corresponding to the Installation of a Seepage Barrier Near Lake Okeechobee

Table 1. Design of monitoring wells, and depth and date of completion of seepage barrier. 

[--, no information; ft, foot; ID, Identifier; LS, land surface; HHD, Herbert Hoover Dike; NAD 83, North American Datum of 1983]

Longitude 

(decimal 

degree, 

NAD 83)

Latitude 

(decimal 

degree, 

NAD 83)

Deep well 

name

Deep well 

USGS ID

Depth 

of well 

(ft 

below 

LS)

Depth 

of top 

of open 

interval 

(ft below 

LS)

Depth of 

bottom 

of open 

interval 

(ft below 

LS)

Shallow 

well name

Shallow well 

USGS ID

Depth of 

well 

(ft below 

LS)

-81.046 26.820 GL-332 264912081024601 131 120 125 GL-332S 264912081024602 60

-80.916 26.759 HE-1145 264532080545901 161 145 150 HE-1145S 264532080545902 60

-80.614 26.922 PB-1815 265519080364901 120 108 118.4 PB-1815S 265519080364902 44

-80.613 26.908 PB-1816 265428080364501 128 115 120 PB-1816S 265428080364502 55

-80.628 26.862 PB-1817 265142080374201 131 110 120 PB-1817S 265142080374202 55

-80.633 26.861 PB-1818 265138080375801 146 135 140 PB-1818S 265138080375802 45

-80.695 26.804 PB-1819 264814080414301 135 125 130 PB-1819S 264814080414302 60

-80.703 26.726 PB-1820 264332080421101 134 125 130 PB-1820S 264332080421102 95

-80.715 26.706 PB-1821 264222080425401 136 125 130 PB-1821S 264222080425402 100

-80.801 26.698 PB-1822 264154080480301 187 180 185 PB-1822S 264154080480302 60
Methods 5

Table 1. Design of monitoring wells, and depth and date of completion of seepage barrier.—Continued

[--, no information; ft, foot; ID, Identifier; LS, land surface; HHD, Herbert Hoover Dike; NAD 83, North American Datum of 1983]

Depth 

of top 

of open 

interval 

(ft below 

LS)

Depth of 

bottom 

of open 

interval 

(ft below 

LS)

Depth of 

seepage 

barrier near 

cluster 

(ft below 

LS)

Approximate 

depth of the top 

of the saltwater 

interface at 

beginning of 

monitoring 

(ft below LS)

Date of 

completion 

of seepage 

barrier

Approximate 

distance and 

direction from 

center line of 

HHD

Notes

55 60 -- 62 -- 290 ft south Well cluster is immediately south of the 

LD-1 Canal and on the landward side of the 

HHD. No seepage barrier at this location.

55 60 -- 127 -- 80 ft southwest Well cluster is on the landward side the HHD 

and on its slope. No seepage barrier at this 

location.

34 44.5 46 70 May 2010 85 ft east Well cluster is on landward side of the HHD and 

adjacent to the HHD toe ditch. The bottom 

of seepage barrier is just above saltwater 

interface.

50 55 57 44 January 2011 200 ft east Well cluster is on the landward side of the HHD. 

The seepage barrier extends into the saltwater 

interface at this location.

50 55 55 41 August 2012 

and February 

2011

1,550 ft 

southeast1

Well cluster is on the landward side of the HHD, 

and is immediately north of the West Palm 

Beach Canal. In reaches 1B and 1C the seepage barrier extends into the saltwater interface, 

but there is 500-ft gap in the seepage barrier 

at this location. The seepage barrier 350 ft to 

the north was constructed in August 2012, and 

the seepage barrier 150 ft to the south was 

constructed in February 2011.

40 45 57 46 March 2011 720 ft southeast Well cluster is on the landward side of the HHD 

and is about 1,000 ft south of the L-10 Canal. 

The seepage barrier extends into the saltwater 

interface.

55 60 57 63 April 2012 80 ft southeast Well cluster is located on the landward side slope 

of the HHD. The seepage barrier extends into 

the saltwater interface.

90 95 47 122 October 2009 130 ft southeast Well is on the landward side of the HHD and 

adjacent to the HHD toe ditch. The bottom 

of seepage barrier is about 75 ft above top of 

seepage barrier.

95 100 61 107 July 2012 940 ft west2 Well is 1,150 ft south of the end of the seepage barrier and on Torry Island on the Lake 

Okeechobee side of the HHD.

55 60 -- 64 -- 90 ft south Well is on the landward side slope of the HHD. 

There is no seepage barrier at this location.

1

There is a 500-ft gap in the seepage barrier.

2

Well cluster is on the lake side of the HHD.
6 Changes in the Saltwater Interface Corresponding to the Installation of a Seepage Barrier Near Lake Okeechobee

Figure 3. Diagram of short-screened interval monitoring wells used for water sampling and collection of time 

series electromagnetic-induction log datasets. [PVC, polyvinyl chloride]

Filter pack

Annular seal 

Shallow well

Screen

Saltwater 

Freshwater

Base of aquifer Additional casing is 

added to accommodate 

logging equipment

 Sand seal 

Bentonite 

pellet seal 

Metal protective 

well cover 

Sand to allow 

drainage of 

well cover

Annular seal

Filter pack

PVC well casing 

Bentonite pellet seal 

 Sand seal 

Top of saltwater

interface (depth varies

temporally and spatially)

Cement well pad 

Well cap

Screen
Methods 7

The USACE and the International Analytic Group (IAG) 

monitored seven long-screened interval wells to aid in the 

evaluation of changes that might be related to installation 

of the seepage barrier. Five of these long-screened wells 

are located near the short-screened wells monitored by the 

USGS (fig. 1 and table 2). These five long-screened wells 

are 160 to 200 ft deep, and have open intervals ranging from 

145 to 185 ft in length. Data from these five wells were used 

to help evaluate differences between water samples obtained 

from long-screened wells and the water samples and TSEMIL 

datasets collected in short-screened wells. 

TSEMIL datasets, collected by the USGS, consist of 

a series of electromagnetic-induction (EMI) logs collected 

through time. Generally the individual EMI logs of the 

TSEMIL datasets were collected on a monthly or bimonthly 

basis for this project. EMI logs measure the bulk conductivity 

of the aquifer, which is a function of the electrical conductivity 

of the pore water and the characteristics of the rock matrix, 

including pore structure, shape, and total porosity. Changes 

in the bulk conductivity can be detected, even through PVC 

well casings. TSEMIL datasets depict temporal changes 

in the conductivity of the water in the aquifer, because the 

characteristics of the rock matrix generally do not change 

appreciably during the period of monitoring. Individual EMI 

logs in the TSEMIL dataset are color coded by collection 

date in the red, orange, yellow, green, blue, indigo, and 

violet color sequence. The most recent log is colored black. 

If all of the individual EMI logs plot directly on top of each 

other, the water conductivity is not changing. A monotonic 

increase or decrease in water conductivity through time results 

in a set of curves or curve segments that follow the above 

mentioned color sequence. TSEMIL datasets were processed 

as described in Prinos and others (2014). EMI logs collected 

between August 2012 and April 2013 showed an increase in 

measurement noise, relative to preceding and subsequent logs. 

A 5-point moving average was used to smooth the data in those 

logs where the noise obscured the changes in bulk conductivity.

Prinos and others (2014) established the relation between 

bulk conductivity from EMI logs and chloride concentrations 

of water samples collected in the Biscayne aquifer of MiamiDade County, Florida, which showed that parts of the aquifer 

containing saltwater with 1,000 milligrams (mg/L) of chloride 

Table 2. Design of long-screened monitoring wells, and depth and date of completion of seepage barrier.

[--, no information; ft, foot; LS, land surface; NGVD 29, National Geodetic Vertical Datum of 1929]

Longitude Latitude Well name

Depth 

of top 

of open 

interval 

(ft below 

LS)

Depth of 

bottom 

of open 

interval 

(ft below 

LS)

Proximal 

USGS 

monitored 

sites

Depth of 

seepage 

barrier 

near well 

(ft below 

LS)

Date of 

completion of 

seepage 

barrier 

(ft below 

LS)

Notes

-80.610 26.956 HHD08-R1A-MW11 32 126 None -- June 2010 Elevation of bottom of 

seepage barrier is 20 ft 

below NGVD 29.

-80.633 26.861 HHD08-R1C-MW8D 32 183 PB-1818, 

PB-1818S

57 March

2011

Seepage barrier extends 

into the saltwater 

interface.

-80.703 26.726 HHD08-R1D-MW5D 15 160 PB-1820, 

PB-1820S

47 October

2009

The proximal USGS 

site, indicates that the 

seepage barrier is about 

75 ft above top of the 

saltwater interface at this 

location.

-80.916 26.759 HHD10-R2-MW18F 10 180 HE-1145, 

HE-1145S

-- -- No seepage barrier at this 

location.

-81.046 26.820 HHD10-R2-MW4F 15 200 GL-332, 

GL-332S

-- -- No seepage barrier at this 

location.

-80.801 26.698 HHD10-R3-MW18F 25 190 PB-1822, 

PB-1822S

-- -- No seepage barrier at this 

location.

-80.725 26.690 HHD10-R3-MW4F 32 185 None -- -- No seepage barrier at this 

location.
8 Changes in the Saltwater Interface Corresponding to the Installation of a Seepage Barrier Near Lake Okeechobee

or greater have formation conductivity values of about 

100 millisiemens per meter (mS/m) or greater (equivalent to a 

bulk resistivity of about 10 ohm-m or less). For the purposes 

of this study, the shallowest depth at which an EMI log indicated a bulk conductivity of 100 mS/m was generally considered to be the top of the saltwater interface, except where EMI 

logs may have been affected by variations in water saturation 

of the unsaturated zone, or where layers of conductive clay 

resulted in greater than normal bulk conductivity. 

Water samples were collected by the USGS from the 

shallow and deep short-screened interval monitoring wells to 

evaluate the chloride concentration and specific conductance 

of water in the aquifer. Wells were sampled, monthly or 

bimonthly, to evaluate temporal changes in salinity. Water 

samples were collected from the wells, following the removal 

of 3 to 5 well volumes of water, to ensure that the samples 

were representative of water in the aquifer rather than in the 

well bore. Samples were not filtered prior to analysis. The 

chloride concentration of water samples was determined by 

the USGS using a Seal Analytical AQ1 discrete analyzer. 

Specific conductance was measured using a Mettler Toledo 

Seven Easy conductivity meter. 

IAG collected water samples from the long-screened 

interval wells at depth intervals of about 5 to 10 ft using 

straddle packers to isolate each sampling interval. Each packer 

was 3 ft long, and a bladder pump located between the packers 

was used to collect the water samples. A YSI multi-parameter 

meter was used to measure field water-quality parameters. 

Water samples were analyzed by the TestAmerica laboratory. 

Quality assurance samples including method blanks were 

also collected. Method blanks were used to determine if the 

equipment cleaning procedures designed to prevent cross 

contamination between wells had successfully removed all 

traces of the analyte for which sampling is conducted. Detections of the analyte in method blanks are noted in the figures 

and appendixes of this report.

Results

Monitoring results from locations where the seepage 

barrier was installed can be compared to those from locations without it to understand whether apparent changes in 

aquifer salinity are caused by natural variation, ambiguity in 

results, or the barrier. Sample results from the shallow well 

of each short-screened well cluster, for example, generally 

showed increases in chloride concentration where the seepage 

barrier was installed to a depth near or below that of the 

saltwater interface (fig. 4D–G; table 1), and there was little 

or no change where the seepage barrier was not installed 

(fig. 4A, B, and J; table 1) or where the seepage barrier was 

well above the saltwater interface (fig. 4C, H, and I; table 1). 

Monitoring results at locations without the seepage barrier and 

those with it are discussed in greater detail in the “Locations 

Without a Seepage Barrier” and “Locations With a Seepage 

Barrier” sections of this report. 

Sample results from five of the long-screened wells 

monitored by IAG are compared to those of water samples 

and TSEMIL datasets collected from the collocated shortscreened well clusters in the “Comparison of Information 

From Short-Screened and Long-Screened Wells” section of 

this report. IAG sample results were provided by the USACE 

(appendix 1; Mark Shafer, U.S. Army Corps of Engineers, 

written commun., April 25, 2011). Long-screened wells, like 

those monitored by IAG during this study, are commonly used 

to monitor salinity in Florida, as well as in other states and 

countries. Well-bore flow under ambient conditions, however, 

has been shown to alter the distribution of salinity in the well 

relative to that in the aquifer (Reilly and others, 1989; Johnson 

and others, 2002; Shapiro, 2002; Oki and Presley, 2008; 

Runkel and others, 2008; and Shalev and others, 2009). Information collected from the short-screened and long-screened 

wells can be compared to evaluate any differences that may 

have resulted from flow within the well bore.

TSEMIL datasets from most monitoring wells indicated 

temporal changes in bulk conductivity near the water table. 

The maximum depth of the water table in well PB–1821, for 

example, was 10.42 ft below land surface (fig. 5). The induction logging probe is 5.2 ft long, and in this instance, would 

not be fully submerged until it reached a depth of 15.6 ft. Bulk 

conductivity values in the TSEMIL dataset for the interval 0 to 

16 ft could possibly be influenced by temporal variations in 

the water saturation in the unsaturated zone above the depth of 

the water table and by incomplete submergence of the probe. 

Although the delineation of these changes was not the focus of 

this study, the maximum water table depth and depth at which 

the probe is fully submerged are depicted on some of the 

graphs of the TSEMIL datasets for informational purposes. 

Locations Without a Seepage Barrier

Water sample results and TSEMIL datasets generally 

did not indicate large changes in bulk conductivity or salinity 

near the depth of the saltwater interface at locations where 

the seepage barrier had not been installed. At the time of this 

study, reaches 2 and 3 of the barrier had not been installed 

near well clusters GL–332S/GL–332, HE–1145S/HE–1145, 

and PB–1822S/PB–1822 (fig. 1). The monitoring-well cluster 

PB–1821/PB–1821S is located 1,150 ft south of the end of 

reach 1D of the seepage barrier on Torry Island, 940 ft west 

of the HHD (table 1); this is the only well cluster on the Lake 

Okeechobee side of the HHD. Throughout most of the depth 

interval of well PB–1821, except near the water table, the 

10 individual logs of the TSEMIL dataset plot directly or 

almost directly on top of each other, which indicates little or 

no change in bulk conductivity through time (fig. 5). Changes 

of only 1 to 5 mS/m in the depth intervals 14 to 28 ft, 71 to 

91 ft, and 109 to 134 ft were observed. The depth of the top 

of the saltwater interface increased by 0.8 ft during the study. 

The open interval of the shallow well PB–1821S is about 7 ft 

above the saltwater interface (fig. 5; table 1). The chloride 
Results 9

8,000

9,000

10,000

11,000

12,000

4,000

4,500

5,000

5,500

6,000

6,500

7,000

A B

E

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

C

0

200

400

600

800

1,000

1,200

1,400

1,600

1,800

D

Jun 2014

0

50

100

150

200

250

Dec 2010

Mar 2011

Jun 2011

Aug 2011Dec 2011

Mar 2012

May 2012

Aug 2012Nov 2012

Mar 2013

Jun 2013

Aug 2013Nov 2013

Mar 2014

Date

400

450

500

550

600

650

700

750

800

Chloride concentration,

 in milligrams per liter

HE–1145S

PB–1816S

PB–1818S

PB–1820S

PB–1822S

PB–1815S

PB–1817S

PB–1821S

PB–1819S

GL–332S

0

50

100

150

200

250

F

G H

Jun 2014

0

50

100

150

200

250

Dec 2010

Mar 2011

Jun 2011

Aug 2011Dec 2011

Mar 2012

May 2012

Aug 2012Nov 2012

Mar 2013

Jun 2013

Aug 2013Nov 2013

Mar 2014

0

50

100

150

200

250

0

50

100

150

200

250

Date

I J

Chloride concentration,

 in milligrams per liter

Chloride concentration,

 in milligrams per liter

Chloride concentration,

 in milligrams per liter

Chloride concentration,

 in milligrams per liter

No seepage barrier

Seepage barrier completed

May 2010 to a depth 24 feet

above saltwater interface

Seepage barrier completed

January 2011 to a depth 14 feet

below saltwater interface

Seepage barrier is 13 feet

below saltwater interface

Seepage barrier 150 feet

south of well, completed

February 2012

Seepage barrier 350 feet

north of well, completed

August 2012

Seepage barrier completed

April 2012 to a depth 6 feet

above saltwater interface

Seepage barrier ends 

1,150 feet north of well 

and was completed

in July 2012

Seepage barrier completed

October 2009 to a depth 

75 feet above saltwater 

interface

No seepage barrier 

Seepage barrier completed

March 2011 to a depth 11 feet

below saltwater interface

No seepage barrier

Figure 4. Chloride concentration of water samples from shallow, short-screened monitoring wells near Lake 

Okeechobee, Florida. (See fig. 1 for well locations.) Vertical lines, if present, indicate the date of installation of the 

seepage barrier.
10 Changes in the Saltwater Interface Corresponding to the Installation of a Seepage Barrier Near Lake Okeechobee

concentration of water samples from PB–1821S confirm 

that only minor changes in salinity have occurred at its open 

interval. Chloride concentrations of samples from this well 

ranged from 210 to 240 mg/L during the study (fig. 4I). The 

deep well, PB–1821, is open to the aquifer about 18 ft below 

the top of the saltwater interface. Water samples from this 

well indicate that the chloride concentration has been fairly 

constant. Nine of the 11 water samples from PB–1821 have a 

chloride concentration of 3,900 mg/L (appendix 2). 

The TSEMIL datasets from wells GL–332, HE–1145, 

and PB–1822 indicated little or no change in the depth of the 

saltwater interface during this study (figs. 6A, 7A, and 8A). 

The TSEMIL dataset from well GL–332 (fig. 6A) indicated 

variations in bulk conductivity through time in the depth 

interval 20 to 30 ft. These variations are almost entirely above 

a greenish clay and silt layer that extends from about 28 to 

44 ft below land surface. Clay typically has a higher electrical 

conductivity than sand or limestone (U.S. Environmental 

Protection Agency, 2014a). This clay and silt layer is indicated 

within the depth interval 32 to 42 ft of the TSEMIL dataset 

by bulk conductivities that are up to 130 mS/m and relatively 

constant through time. The saltwater interface, inferred from 

the TSEMIL dataset, begins below this clay and silt layer, at 

a depth of 62 ft. Just above the saltwater interface, there was 

a minor 6-mS/m increase in bulk conductivity through time. 

Temporal changes in bulk conductivity near the saltwater 

interface are probably not related to temporal changes in the 

depth interval 20 to 30 ft because the clay unit between them 

likely restricts vertical flow in the aquifer. There was little or 

no temporal change in bulk conductivity in the interval 60 to 

108 ft and a minor increase in the interval 108 to 129 ft. The 

chloride concentration of water samples from the shallow 

Seepage barrier was installed in July 2012, and ends 1,150 ft to the north of this well

0

10

20

30

40

50

60

70

80

90

100

110

120

130

0 50 100 150 200 250 300

Depth, in feet below land surface

Bulk conductivity, in millisiemens per meter

Maximum depth of water table

Probe may be partially out of water

Little or no change in bulk

conductivity through time

from 28 to 130 feet

Slight increase in bulk 

conductivity from 14 to 28 feet

PB–1821,

screened 

125–130 feet

PB–1821S,

screened 

95–100 feet

0.8-foot increase in the 

depth of the top of 

the saltwater interface

EXPLANATION

PB–1821

 electromagnetic-

 induction logs 

 08/11/2011 

 10/25/2011 

 12/14/2011 

 02/24/2012 

 04/24/2012 

 08/28/2012 

 10/22/2012 

 12/19/2012 

 02/25/2013 

 04/15/2013 

Figure 5. Time series electromagnetic-induction log (TSEMIL) dataset from monitoring well PB–1821, 

generally showing only minor temporal changes in the bulk conductivity of the aquifer. Circle shows 

depth of the top of the saltwater interface inferred from TSEMIL dataset, as a bulk conductivity of 

100 mS/m. [ft, foot; mg/L milligrams per liter; %, percent; mS/m, millisiemens per meter]
Results 11

0

102030405060708090

100110120130

0 50 100 150 200 250 300

Bulk conductivity, in millisiemens per meter

EXPLANATION

0

102030405060708090

100110120130

0 2,000 4,000 6,000 8,000 10,000 12,000

Depth, in feet below land surface

Total dissolved solids concentration, in milligrams per liter

04/26/2012*06/26/201208/25/201210/19/201211/18/201201/26/2013

HHD10-R2-MW4F is

screened 15–200 ft

Total dissolved solids of samples collected at 90 and 120 ft varied by 80–83%of the maximum value sampled

Water samples 

GL–332 isscreened 120–125 ft

from well GL-332S,increased by 90 mg/Loverall

Bulk conductivityvaried throughtime in the interval 20–30 ft

Little or no change in bulkconductivity through timefrom 60 to 108 ft

Minor temporal variations in bulk conductivity from45 to 60 ft. Increaseof about 6 mS/m overall

Minor 5-mS/m temporal increase in bulk conductivity from 108 to 129 ft between August and October 2011.Little or no change after this

This variation is much greater than that observed in samples and logs from the short-screened wells

* Analyte detected

in sample and method blank

Total dissolved solids of samples collected at 60 ft were variable, but increasedby 3,210 mg/L between August 2012 and January 2013

Depth, in feet below land surface

A B

Greenish clay and silt layer

No change in the depth of the saltwater interface

08/10/201110/19/201112/15/201102/28/201204/26/2012 06/19/2012 08/30/2012 10/23/2012 12/18/2012 02/26/2013 04/16/2013 

GL–332 electromagnetic- induction logs

HHD10-R2-MW4F

sample dates

EXPLANATION

Figure 6. Comparison of the (A) time series electromagnetic-induction log (TSEMIL) dataset from monitoring well GL–332, and the (B) total dissolved solids concentration of water samples collected from monitoring well HHD10–R2–MW4F. Circle shows depth of the top of the saltwater interface, defined as 100 mS/m. [ft, foot; mg/L, milligrams per liter; mS/m, millisiemens per meter; %, percent]
12 Changes in the Saltwater Interface Corresponding to the Installation of a Seepage Barrier Near Lake Okeechobee

well, GL–332S, screened from 55 to 60 ft, varied through time 

but increased by 90 mg/L overall during the study (fig. 4A). 

The drawdown induced by well sampling in well GL–332 

was so great that a sample could not readily be collected. 

The TSEMIL dataset from well HE–1145 indicated minor 

temporal variations in bulk conductivity above the saltwater 

interface but no change in the depth of the interface (fig. 7A). 

During the study, the chloride concentration of samples 

from well HE–1145S only varied by 20 mg/L (fig. 4B). 

The TSEMIL dataset from well PB–1822 indicated a minor 

14-mS/m variation in bulk conductivity in the depth interval 

55 to 60 ft, which is a few feet above the top of the saltwater 

interface (fig. 8A). Water samples from the shallow well, 

PB–1822S, screened at the same depth as this variation in bulk 

conductivity, indicated that chloride concentration at this depth 

varied by about 24 mg/L (fig. 4J). The chloride concentration 

of water samples from the deep well, PB–1822, only varied by 

10 percent during the project (appendix 2). 

Monitoring-well cluster PB–1817/PB–1817S is farther 

away from the HHD than the other wells. The cluster is 

located adjacent to the West Palm Beach Canal and 1,550 ft 

southeast of the centerline of the HHD, and there is a 500-ft 

gap in the seepage barrier at this location (table 1). The 

seepage barrier south of this location was completed in 

February 2011, and the barrier to the north was completed 

in August 2012. The chloride concentration of samples from 

well PB–1817S increased after the completion of the seepage 

barrier to the south, but decreased briefly after completion 

of the northern seepage barrier before resuming an overall 

increase of 800 mg/L, relative to the initial chloride concentration (fig. 4E). In the depth interval 50 to 70 ft, near the depth 

of the bottom of the seepage barrier, the bulk conductivity of 

EMI logs increased, but the depth to the top of the saltwater 

interface only oscillated up and down slightly through time 

(fig. 9). Generally, bulk conductivity increased overall in the 

depth interval 81 to 110 ft, but these changes varied through 

time and with depth.

Locations With a Seepage Barrier

The TSEMIL datasets from the wells PB–1815, 

PB–1816, PB–1818, and PB–1819, where the seepage barrier 

extends near to or below the top of the saltwater interface, 

indicated changes in the depth and bulk conductivity of the 

interface (figs. 10; 11; 12A, C, D; and 13). The TSEMIL 

datasets from these wells indicated (1) decreases in the depth 

of the saltwater interface, through time, of 2.4 to 18.7 ft; 

(2) increases in bulk conductivity through time from depths of 

0 to 29 ft above to 0 to 18 ft below the bottom of the seepage 

barrier; and (3) decreases in bulk conductivity, through time, 

in the aquifer, beginning at depths of 11 to 18 ft below the 

bottom of the seepage barrier and extending to depths of 34 to 

73 ft below the bottom of the seepage barrier. 

The TSEMIL dataset from well PB–1815 indicated 

temporal changes in bulk conductivity that corresponded 

closely with the depth of the bottom of the seepage barrier, 

46 ft, which was completed in May 2010 (fig.10; table 1). 

This dataset consists of 21 EMI logs that were collected on a 

monthly basis. Between August 2011, when the first log was 

collected, and April 2013, the bulk conductivity of the aquifer 

increased by as much as 25 mS/m in the depth interval 46 to 

74 ft, and the depth of the saltwater interface decreased by 

2.4 ft. Bulk conductivity decreased in the depth interval 74 to 

80 ft. Bulk conductivity had initially increased in the depth 

interval 64 to 74 ft but started decreasing in September 2012. 

The saltwater interface, therefore, may be gradually beginning 

to return to its initial depth. Below a depth of about 87 ft, 

the TSEMIL dataset indicated little or no change in bulk 

conductivity. Analyses of water samples at well PB–1815S 

did not indicate an increase in chloride concentration because 

the bottom of the well’s intake was 25.4 to 23 ft above the 

saltwater interface during this study (fig. 10). All but one 

of the water samples from the deep well, PB–1815, have a 

chloride concentration of 13,000 mg/L (appendix 2). 

Most of the reaches of the seepage barrier (fig. 1) were 

completed before monitoring began at the well clusters. 

The seepage barrier near monitoring-well cluster PB–1816/

PB–1816S, for example, was completed in January 2011, 

about 8 months before monitoring began. In the depth interval 

36 to 68 ft, which brackets the depth of the seepage barrier, 

the TSEMIL dataset from PB–1816 indicated increasing bulk 

conductivity during August 2011–January 2014 (fig. 11); the 

depth of the saltwater interface decreased 5.5 ft during this 

period. The chloride concentration of water samples collected 

from well PB1816S increased from 8,600 to 11,000 mg/L 

between October 26, 2011, and January 30, 2014 (fig. 4D). 

Beginning about 11 ft below the bottom of the seepage barrier, 

bulk conductivity in the depth interval 68 to 104 ft decreased, 

and there was little or no change in bulk conductivity below 

a depth of 106 ft. The chloride concentration of samples 

from the deep well, PB–1816, varied between 14,000 and 

16,000 mg/L (appendix 2).

The TSEMIL dataset collected in monitoring well 

PB–1818 indicated (1) a temporal decrease in the depth of 

the saltwater interface of 3.7 ft during the study period; (2) a 

temporal increase in bulk conductivity from about 29 ft above 

to 8 ft below the bottom of the seepage barrier; (3) a temporal 

decrease in bulk conductivity from 18 to 49 ft below the 

bottom of the seepage barrier (fig. 12D); and (4) a temporal 

increase in bulk conductivity from about 70 to 77 ft below 

the bottom of the seepage barrier, which corresponds to the 

depth interval 127 to 134 ft (fig. 12A). Water samples collected 

from the deep well, PB–1818, which is open from 135 to 

140 ft (table 1), indicated a variation in chloride concentration of 2,000 mg/L (appendix 2). Water samples from the 

shallow well, PB–1818S, indicated an increase in chloride 

concentration of 2,500 mg/L (fig. 4F). 

Monitoring-well cluster PB–1819/PB–1819S was the only 

cluster monitored before the seepage barrier was completed in 

its vicinity. Monitoring at this cluster began in August 2011, 
Results 13

0

102030405060708090

100110120130140150160

300 400 500 600 700 800

Depth, in feet below land surface

Total dissolved solids concentration, in milligrams per liter

0

102030405060708090

100110120130140150160

0 50 100 150 200 250 300

Depth, in feet below land surface

Bulk conductivity, in millisiemens per meter

HHD10-R3-MW18F screened from 10 to 180 ft

HE–1145S

HE–1145

Minor oscillation in bulk conductivity of about 5 mS/m in the interval 94 to 116 ft

No change in the depthof the saltwater interface

Little or no changein bulk conductivityfrom 40 to 68 ftand no change inchloride in wellHE–1145S

Little or no changein bulk conductivityfrom 116 to 160 ft

15-mS/m increasein bulk conductivity

15-mS/m decreasein bulk conductivity

Water table

Probe partially out of water

Total dissolved solids of samples collected at 60 ft varied from 420 to 580 mg/L or about 28%of the maximum concentration at this depth

A

B

Alternatingsand and clay layers

EXPLANATION

 04/24/2012 06/25/2012 08/25/2012 10/18/2012 11/17/2012 01/25/2013

HHD10-R2-MW18F

sample dates

EXPLANATION

HE–1145 electromagnetic-  induction logs 

 08/09/2011 10/19/2011 12/15/2011 02/24/2012 04/24/2012 06/19/2012 08/30/2012 10/23/2012 12/18/2012 02/26/2013 04/16/2013

Figure 7. Comparison of the (

A) time series electromagnetic-induction log (TSEMIL) dataset from well HE–1145, and the (

B) total dissolved solids concentration 

of water samples collected from well HHD10–R2–MW18F. Circle shows depth of the top of the saltwater interface inferred from TSEMIL dataset, as a bulk conductivity of 100 mS/m. [ft, foot; mg/L, milligrams per liter; %, percent; mS/m, millisiemens per meter]
14 Changes in the Saltwater Interface Corresponding to the Installation of a Seepage Barrier Near Lake Okeechobee

0

102030405060708090

100110120130140150160170180190

0 200 400 600 800

Bulk conductivity, in millisiemens per meter

0

102030405060708090

100110120130140150160170180190

0 5,000 10,000 15,000 20,000

Depth, in feet below land surface

Total dissolved solids concentration, in milligrams per liter

Water table

Probe partially out of water

No change in the depthof the saltwater interface

Depth, in feet below land surface Little or no change in bulk conductivity from 65 to 185 ft

Total dissolved solids of samples collected at 90 ft varied from 7,200 to 11,000 mg/L or about 35%of the maximum concentration at this depth

A

B

HHD10-R3-MW18F screened from 25 to 190 ft

PB–1822SPB–1822

4/23/2012*6/25/20128/25/201210/18/201211/17/20121/25/2013

Analysis of sampledelayed beyond the acceptable period

*

EXPLANATION

HHD10-R3-MW18F

sample dates

EXPLANATION

08/09/2011 10/19/2011 12/15/2011 02/24/2012 04/24/2012 06/19/2012 08/28/2012 10/22/2012 12/19/2012 02/26/2013 04/15/2013 10/30/2013 01/29/2014

PB–1822 electromagnetic-  induction logs 

Minor oscillations in bulk conductivity in the interval 24–63 ft. Chloride concentration of water samples from well PB–1822S varied by only 24 mg/L

Figure 8. Comparison of the (

A) time series electromagnetic-induction log (TSEMIL) dataset from monitoring well PB–1822, and the (

B) total dissolved solids 

concentration of water samples collected from monitoring well HHD10–R3–MW18F. Circle shows depth of the top of the saltwater interface inferred from TSEMIL dataset, as a bulk conductivity of 100 mS/m [ft, foot; mg/L, milligrams per liter; %, percent; mS/m, millisiemens per meter]
Results 15

8 months before the seepage barrier was completed. The 

TSEMIL dataset from well PB–1819 indicated that prior to 

completion of the seepage barrier, there was little or no change 

in the bulk conductivity of aquifer materials. The first EMI log 

collected after the seepage barrier was completed in April 2012 

indicated an increase in bulk conductivity through time in the 

depth interval 50 to 60 ft, near the depth of the bottom of the 

seepage barrier (fig. 13). Subsequent EMI logs indicated an 

increase of as much as 98-mS/m in bulk conductivity from 

15 ft above to 8 ft below the bottom of the seepage barrier, 

decreases in bulk conductivity from 11 to 73 ft below the 

bottom of the seepage barrier, and a decrease of 18.7 ft in the 

depth of the saltwater interface. After the seepage barrier was 

completed, the chloride concentration of the water samples 

from the shallow well, PB–1819S, increased from 210 to 

1,600 mg/L between March 28, 2012, and June 18, 2012 

(fig. 4G). The chloride concentration of water samples 

from the deep well, PB–1819, varied between 5,600 and 

6,000 mg/L (appendix 2). 

A seepage barrier was installed near monitoring well 

PB–1820 in October 2009. The bottom of the seepage barrier 

is 75 ft above the top of the saltwater interface at this location 

(fig. 14). The chloride concentration of water samples from 

well PB–1820S, which is about 27 ft above the top of the saltwater interface, only varied by 20 mg/L (fig. 4H). The TSEMIL 

dataset indicated an increase of 0.5 ft in the depth of the 

saltwater interface at this location and as much as a 10-mS/m 

decrease in bulk conductivity in the depth interval 108 to 

121 ft, which is just above the interface. Between October 2011 

and April 2013, the chloride concentration of samples from 

the wells PB–1820 decreased from 1,900 to 1,800 mg/L 

(appendix 2). Bulk conductivity increased as much as 18 mS/m 

from 13 to 32 ft above the top of the seepage barrier.

0

10

20

30

40

50

60

70

80

90

100

110

120

130

0 100 200 300 400 500 600 700 800 900

Depth, in feet below land surface

Bulk conductivity, in millisiemens per meter

Depth of bottom of

seepage barrier

Bulk conductivity 

gradually increased 

by about 40 mS/m 

from 50 to 70 ft

Water table

Probe partially out of water

Bulk conductivity 

generally increased

but is variable

from 81 to 110 ft

Only slight oscillations in the depth

of the saltwater interface

EXPLANATION

PB–1817

 electromagnetic-

 induction logs 

08/15/2011 

10/26/2011 

12/13/2011 

02/23/2012 

04/25/2012 

06/18/2012 

08/30/2012 

10/23/2012 

12/19/2012 

02/26/2013

04/16/2013 

10/29/2013 

01/29/2014 

PB–1817

PB–1817S

Figure 9. Time series electromagnetic-induction log dataset from monitoring well PB–1817 

showing changes in the bulk conductivity of the aquifer. Circle shows depth of the top of the 

saltwater interface inferred from TSEMIL dataset, as a bulk conductivity of 100 mS/m. [ft, foot; mS/m, 

millisiemens per meter]
16 Changes in the Saltwater Interface Corresponding to the Installation of a Seepage Barrier Near Lake Okeechobee

0

10

20

30

40

50

60

70

80

90

100

110

120

0 100 200 300 400 500 600 700 800 900 1,000

Depth, in feet below land surface

Bulk conductivity, in millisiemens per meter

Depth of bottom

of seepage barrier

Depth of bottom

of seepage barrier

40

45

50

55

60

65

70

75

80

0 50 100 150 200 250 300

Bulk conductivity initially

increased in the depth 

interval 64–74 ft, but is 

now decreasing

Bulk conductivity is 

decreasing in the depth 

interval 74–80 ft

No change in bulk

conductivity below

87 ft

Bulk conductivity is

increasing in the depth 

interval 46–64 ft

Depth of the 

saltwater interface 

decreased by 2.4 ft

Water table

Probe partially

out of water

PB–1815

PB–1815S

PB–1815S

EXPLANATION

PB–1815

 electromagnetic-

 induction logs 

08/15/2011 

09/13/2011 

10/26/2011 

11/15/2011 

12/13/2011 

01/24/2011 

02/23/2012 

03/28/2012 

04/25/2012 

05/24/2012 

06/18/2012 

07/17/2012 

08/29/2012 

09/25/2012 

10/24/2012 

11/20/2012 

12/17/2012 

01/29/2013 

02/27/2013 

03/19/2013 

04/17/2013 

Figure 10. Time series electromagnetic-induction log (TSEMIL) dataset from monitoring well PB–1815 

showing changes in the bulk conductivity of the aquifer. Circle shows depth of the top of the saltwater 

interface inferred from TSEMIL dataset, as a bulk conductivity of 100 mS/m. [ft, foot; mS/m, millisiemens 

per meter]
Results 17

Comparison of Information From Short-Screened 

and Long-Screened Wells

The results of monitoring of the long-screened interval 

wells were probably affected by flow within the well bore 

and were frequently too temporally variable to be used to 

evaluate changes in aquifer salinity that could be related 

to installation of the seepage barrier. The concentration of 

total dissolved solids (TDS) of water samples collected 

from the long-screened monitoring wells HHD08–

R1D–MW5D (fig. 15), HHD10–R2–MW18F (fig. 7B), 

HHD10–R3–MW18F (fig. 8B), and HHD10–R2–MW4F 

(fig. 6B) varied over time to a greater extent than the results 

of water sampling and electromagnetic-induction logging 

in the respective, collocated, short-screened well clusters, 

PB–1820S/PB–1820 (figs. 4H and 14), HE–1145S/HE–1145 

(figs. 4B and 7A), PB–1822S/PB–1822 (figs. 4J and 8A), and 

GL–332S/GL–332 (figs. 4A and 6A). The TDS and chloride 

concentrations of water samples from a depth of 130 ft in 

well HHD08–R1D–MW5D, for example, varied by 34 and 

43 percent, respectively, of the maximum concentrations 

sampled at this depth (appendix 1; fig. 15). The chloride 

concentration of water samples from well PB–1820, which 

is collocated with well HHD08–R1D–MW5D and open to 

the aquifer in the depth interval 125 to 130 ft, decreased by 

only 5 percent, from 1,900 to 1,800 mg/L (appendix 2). The 

TSEMIL dataset from well PB–1820 indicated only a slight 

decrease in bulk conductivity at 130 ft (fig. 14). 

The concentrations of TDS and chloride in water samples 

from well HHD10–R2–MW18F, varied by 28 and 59 percent, 

respectively, of the maximum sampled at 60 ft (fig. 7B and 

appendix 1). The chloride concentration of samples from well 

HHD10–R2–MW18F at a depth of 60 ft ranged from 24 to 

59 mg/L, whereas the chloride concentration of water samples 

PB–1816

PB–1816S

0

10

20

30

40

50

60

70

80

90

100

110

120

0 100 200 300 400 500 600 700 800 900 1,000

Depth, in feet below land surface

Bulk conductivity, in millisiemens per meter

Depth of bottom of seepage barrier

Increasing bulk 

conductivity

36–68 ft

Decreasing bulk 

conductivity

68–104 ft

Little or no change 

below 106 ft

Water table

Probe partially out of water

Depth of the 

saltwater interface 

decreased by 5.5 ft

08/16/2011 

10/26/2011 

12/13/2011 

02/23/2012 

04/24/2012 

07/17/2012 

08/20/2012 

10/24/2012 

12/17/2012 

02/23/2013 

04/17/2013 

10/28/2013 

01/30/2014 

EXPLANATION

PB–1816

 electromagnetic-

 induction logs 

Figure 11. Time series electromagnetic-induction log (TSEMIL) dataset from monitoring well PB–1816 

showing changes in the bulk conductivity of the aquifer. Circle shows depth of the top of the saltwater 

interface inferred from TSEMIL dataset, as a bulk conductivity of 100 mS/m. [ft, foot; mS/m, millisiemens 

per meter]
18 Changes in the Saltwater Interface Corresponding to the Installation of a Seepage Barrier Near Lake Okeechobee

Water table

Probe partially out of water

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

0 200 400 600 800 1,000

Bulk conductivity, in millisiemens per meter

Increased bulk 

conductivity

28–65 ft

Decreased bulk 

conductivity

75–106 ft

Increased bulk 

conductivity 

127–134 ft

PB–1818 is screened 

from 135 to 140 ft

PB-1818S is screened 

from 40 to 45 ft

40

45

50

55

60

65

425 475 525 575 625 675

January 2014

August 

2011

Increased bulk 

conductivity

75

85

95

450 490 530 570 610 650

January 2014

February 2012

Decreased bulk 

conductivity

Depth, in feet below land surfaceDepth, in feet below land surface

Bulk conductivity, in millisiemens per meter Bulk conductivity, in millisiemens per meter

Depth, in feet below land surface

A

C D

D

C

PB–1818

Electromagneticinduction logs

(see A for explanation) 

PB–1818

Electromagneticinduction logs

(see A for explanation) 

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

0 10,000 20,000 30,000 40,000

Depth, in feet below land surface

Total dissolved solids concentration, in milligrams per liter HHD08-R1C-MW8D is screened 32–183 ft

B

Total dissolved solids of 

samples collected at 50 ft 

increased from 16,000 to 

19,000 mg/L 

Total dissolved solids of 

samples collected at 130 ft 

oscillated between 22,000 to 

27,000 mg/L or 19% of the 

maximum concentration 

at this depth

Depth of bottom of

seepage barrier

Depth of bottom of

seepage barrier

Depth of bottom of

seepage barrier

Depth of the 

saltwater interface 

decreased by 3.7 ft

EXPLANATION

08/15/2011 

10/26/2011 

12/13/2011 

02/23/2012 

04/24/2012 

06/19/2012 

08/29/2012 

10/23/2012 

12/18/2012 

02/27/2013 

04/16/2013 

10/29/2013 

01/29/2014

PB–1818

 electromagnetic-

 induction logs 04/26/2012*

06/26/2012

08/26/2012

10/21/2012

11/16/2012

01/27/2013

* Analyte detected

in sample and 

method blank

EXPLANATION

HHD08-R1C-MW8D

 sample dates

Figure 12. Comparison of the (A) time series electromagnetic-induction log (TSEMIL) dataset from well PB–1818, and the 

(B) total dissolved solids concentration of water samples collected from well HHD08–R1C–MW8D, including detailed 

depictions of the TSEMIL dataset from (C) 40–65 ft, and (D) 75–100 ft. Circle shows depth of the top of the saltwater interface 

inferred from TSEMIL dataset, as a bulk conductivity of 100 mS/m. [ft, foot; mg/L milligrams per liter; %, percent; mS/m, 

millisiemens per meter] 
Results 19

35

40

45

50

55

60

0 50 100 150 200

Bulk conductivity

increased in 

the first log 

collected after

installation of 

the seepage

barrier

The first 8 logs 

(8/2011-3/2012)

show no changes

0

10

20

30

40

50

60

70

80

90

100

110

120

130

0 50 100 150 200 250 300 350 400 450 500

Depth, in feet below land surface

Bulk conductivity, in millisiemens per meter

Depth of bottom of seepage barrier

Increasing bulk 

conductivity 42–65 ft

Decreasing bulk conductivity 

68–130 ft

Depth of the 

saltwater 

interface 

decreased 

by 18.7 ft

Water table

Probe partially 

out of water

PB–1819

PB–1819S

Seepage

barrier in 

this area 

was 

completed

in 

April 2012

08/12/2011 

09/13/2011

10/25/2011

11/15/2011 

12/14/2011 

01/24/2012 

02/28/2012 

03/28/2012 

04/26/2012 

05/24/2012 

06/18/2012 

07/18/2012 

08/29/2012 

09/25/2012 

10/22/2012 

11/20/2012 

12/18/2012 

01/29/2013 

02/25/2013 

03/19/2013

04/15/2013 

10/29/2013 

01/30/2014 

EXPLANATION

PB–1819

 electromagnetic-

 induction logs 

Figure 13. Time series electromagnetic-induction log (TSEMIL) dataset from monitoring well PB–1819 showing 

changes in the bulk conductivity of the aquifer. Arrow shows change in depth of the top of the saltwater interface 

inferred from TSEMIL dataset, as a bulk conductivity of 100 mS/m. [ft, foot; mS/m, millisiemens per meter]
20 Changes in the Saltwater Interface Corresponding to the Installation of a Seepage Barrier Near Lake Okeechobee

EXPLANATION

PB–1820

 electromagnetic-

 induction logs 

08/12/2011 

10/25/2011

12/14/2011

02/24/2012 

04/24/2012 

06/20/2012 

08/28/2012 

10/22/2012 

12/17/2012 

02/25/2013 

04/15/2013 

PB–1820

PB–1820S

0

10

20

30

40

50

60

70

80

90

100

110

120

130

0 50 100 150 200 250 300

Depth, in feet below land surface

Bulk conductivity, in millisiemens per meter

Depth of 

bottom

of seepage

barrier

90

95

100

105

110

115

120

12520 30 40 50 60 70 80 90 100

Depth, in feet below land surface

Bulk conductivity, in millisiemens per meter

Decreasing bulk 

conductivity

108–121 ft

Increasing 

bulk 

conductivity

13–32 ft

Slight increase 

of 0.5 ft in the depth 

of the saltwater 

interface

Figure 14. Time series electromagnetic-induction log (TSEMIL) dataset from monitoring well PB–1820 showing 

temporal changes in the bulk conductivity of the aquifer. Circle shows depth of the top of the saltwater interface 

inferred from TSEMIL dataset, as a bulk conductivity of 100 mS/m. [ft, foot; mS/m, millisiemens per meter]
Results 21

The saltwater interface evident in information from well 

cluster HE–1145/HE–1145S is not evident in the information 

from well HHD10–R2–MW18F. Water samples from well 

cluster HE–1145S/HE–1145 indicated chloride concentrations 

of 130 to 150 mg/L at 55 to 60 ft, and 930 to 990 mg/L at 

145 to 150 ft (appendix 2; table 1). The TSEMIL dataset 

from well HE–1145 indicated that bulk conductivity gradually increased with depth from 80 to 158 ft (fig. 7A). The 

maximum chloride concentration of samples from collocated 

well HHD10–R2–MW18F was only 71 mg/L (appendix 1), 

which is well below the U.S. Environmental Protection 

Agency secondary drinking water standard of 250 mg/L (U.S. 

Environmental Protection Agency, 2014b). The TDS concentration of water samples from well HHD10–R2–MW18F 

was generally greater at the depths of 60 or 90 ft than at 

0

20

40

60

80

100

120

140

160

0 5,000 10,000 15,000 20,000

Depth, in feet below land surface

Total dissolved solids concentration, in milligrams per liter

4/23/2012

6/26/2012

8/26/2012

10/21/2012

11/18/2012

1/26/2013

HHD08-R1D-MW5D isscreened 15–160 ft

EXPLANATION

HHD08-R1D-MW5D

sample dates

Figure 15. Total dissolved solids concentration of water samples 

collected from monitoring well HHD08–R1D–MW5D.

from collocated well HE–1145S, which is open to the aquifer 

from 55 to 60 ft, ranged from 130 to 150 mg/L and varied 

by only 13 percent of the maximum (fig. 4B; appendix 2). 

Although, some erroneous data in the TSEMIL dataset from 

well HE–1145, in the depth interval 59 to 62 ft, had to be 

deleted, there was little or no change in the depth interval 

55 to 59 ft (fig. 7A). The concentrations of TDS and chloride 

in water samples from well HHD10–R2–MW18F varied, 

respectively, by 19 and 53 percent at 90 ft, 18 and 36 percent 

at 120 ft, and 16 and 49 percent at 150 ft (appendix 1), yet 

the TSEMIL dataset from well HE–1145 indicated little or 

no change at these depths. Water samples from the deep well 

HE–1145, open to the aquifer from 145 to 150 ft averaged 

about 960 mg/L and varied by 60 mg/L, which is only about 

6 percent of the maximum concentration (appendix 2). 
22 Changes in the Saltwater Interface Corresponding to the Installation of a Seepage Barrier Near Lake Okeechobee

150 or 180 ft (appendix 1; fig. 7B). It is likely that downward 

freshwater flow within the bore of well HHD10–R2–MW18F 

diluted samples. 

The saltwater interface is evident in the TDS concentration 

samples collected from well HHD10–R3–MW18F (fig. 8B). 

The slope of increasing TDS concentration with depth in 

well HHD10–R3–MW18F is somewhat similar to the slope 

of increasing bulk conductivity with depth in the collocated 

well PB–1822 (fig. 8A); however, there is generally greater 

temporal variation in the results of TDS samples from 

HHD10–R3–MW18F, than in bulk conductivity in well 

PB–1822. Water samples collected at a depth of 90 ft in 

monitoring well HHD10–R3–MW18F, for example, indicated 

that the TDS and chloride concentrations varied by 35 percent 

(appendix 1), yet at this same depth, the TSEMIL dataset 

from well PB–1822 indicated no temporal change in bulk 

conductivity during April 2012–February 2013. 

The TDS and chloride concentrations of water 

samples from a depth of 60 ft in the long-screened well 

HHD10–R2–MW4F varied by 76 and 75 percent, respectively (appendix 1; fig. 6B), yet the chloride concentration 

of water samples from collocated well GL–332S varied 

through time by only about 16 percent in the depth interval 

55 to 60 ft (fig. 4A; appendix 2). At a depth of 90 ft, water 

samples from well HHD10–R2–MW4F indicated that TDS 

and chloride concentrations varied by 80 and 89 percent, 

respectively, yet the TSEMIL dataset from well GL–332 

indicated little or no temporal change in bulk conductivity 

at this depth (fig. 6A–B). The TDS concentration of the 

sample collected at a depth of 120 ft in January 2013 in well 

HHD10–R2–MW4F was about 6 times that of the sample 

collected in August 2012, yet the TSEMIL dataset from well 

GL–332 indicated only a minor increase in bulk conductivity 

during the study (fig. 6A–B). A possible explanation for this 

difference is dilution of the August 2012 sample from well 

HHD10–R2–MW4F by downward flow of less saline water 

within the open well bore.

Water samples collected during April 2012–January 2013 

from the long-screened monitoring well HHD08–R1C–MW8D 

indicated an increase of 3,000 mg/L in the TDS concentration 

at a depth of 50 ft and a variation in TDS concentration of 

22,000 to 27,000 mg/L at 130 ft (appendix 1; fig. 12B). These 

depths do not correspond to the depths sampled in collocated 

well cluster PB–1818S/PB–1818, therefore, water sample 

results cannot be compared. The TSEMIL dataset from well 

PB–1818 indicated increases in bulk conductivity at 50 and 

130 ft during this period (fig. 12A). Although the changes 

in TDS samples from HHD08–R1C–MW8D corresponded 

to changes in the TSEMIL dataset from the collocated well 

PB–1818, these changes are much smaller than some of the 

changes observed in other long-screened wells at locations 

where no seepage barrier had been installed. The data from the 

collocated well clusters showed little or no changes; therefore, 

it would be difficult to evaluate any effects that might have 

resulted from the installation of the seepage barriers using data 

from the long-screened wells alone.

Conclusions 

A seepage barrier is being installed along the Herbert 

Hoover Dike (HHD), around Lake Okeechobee, to prevent its 

failure. Monitoring was initiated to determine if the saltwater 

interface was disturbed as groundwater flow was altered by 

the seepage barrier. The monitoring network consisted of 

20 shallow and deep, short-screened interval monitoring wells 

installed at 10 sites, from which water samples and timeseries-electromagnetic-induction-log (TSEMIL) datasets were 

collected. Water samples were collected from the monitoring 

wells, following the removal of 3 to 5 well volumes of water 

to ensure that the samples were representative of water in 

the aquifer rather than that within the well bore. At five of 

the locations monitored by the U.S. Geological Survey, the 

U.S. Army Corps of Engineers and the International Analytic 

Group monitored collocated long-screened interval wells by 

collecting water samples using a straddle packer system.

Monitoring results indicate that the seepage barrier 

may be altering groundwater flow and disturbing the layer 

of saltwater within the surficial aquifer. Changes in bulk 

conductivity values in the TSEMIL datasets, closely associated with the depth of the seepage barrier, were evident at all 

of the monitoring locations where the seepage barrier was 

installed to a depth near to, or below, that of the top of the 

saltwater interface. The TSEMIL datasets collected from deep 

monitoring wells PB–1815, PB–1816, PB–1818, and PB–1819 

showed (1) decreases in the depth of the saltwater interface of 

2 to 19 feet (ft), (2) increases in bulk conductivity extending 

from depths 0 to 29 ft above to 0 to 18 ft below the bottom 

of the seepage barrier, and (3) dilution of the saltwater in the 

aquifer extending from depths of 11 to 18 ft to 34 to 73 ft 

below the bottom of the seepage barrier. These changes are 

probably the result of the diversion of groundwater flow under 

the seepage barrier, where it is causing saltwater from deeper 

in the aquifer to move upward at the monitoring locations. 

This groundwater flow also appears to be diluting saltwater in 

the aquifer at depths well below the seepage barrier. 

The TSEMIL dataset from monitoring well PB–1817 

indicated slight increases in bulk conductivity, but the depth to 

the top of the saltwater interface has not changed substantially. 

The lack of change may be related to the monitoring well 

location, because it is 1,750 ft from the HHD, adjacent to the 

West Palm Beach Canal, and located near a 500-ft gap in the 

seepage barrier. Seepage of freshwater from the canal may 

have been a factor in preventing decreases in the depth of 

the saltwater interface at this location. A potential increase in 

groundwater flow through the seepage barrier gap could have 

transported more saline groundwater from the north and south 

to well PB–1817 without establishing an upward groundwater 

flow gradient at the well location that could cause the saltwater 

interface to become shallower. 

At monitoring well location PB–1820, where the depth of 

the saltwater interface is 75 ft below the bottom of the seepage 

barrier, there was a slight increase in the depth of the saltwater 

interface and a slight decrease in bulk conductivity just above 
References Cited 23

the interface. These changes may have been caused by deeper 

circulation of fresh groundwater resulting from the installation of the seepage barrier. Where the seepage barrier was 

not installed, the changes in bulk conductivity and chloride 

concentration were generally minor. At these locations, 

therefore, water conductivity does not appear to have changed 

substantially in the aquifer.

At the locations of monitoring wells GL–332, HE–1145, 

PB–1821, and PB–1822, where a seepage barrier had not been 

installed, there was little or no change in the depth of the saltwater interface through time. The TSEMIL dataset from well 

PB–1821 indicated virtually no change in bulk conductivity, 

except near the water table. The seepage barrier ends 1,150 ft 

north of this well, and the well is located 1,050 ft west of the 

HHD and on the Lake Okeechobee side of the dike. 

The results of water sampling to evaluate the 

concentration of total dissolved solids in monitoring 

wells HHD10–R2–MW4F, HHD10–R2–MW18F, and 

HHD10–R3–MW18F varied by as much as 20 to 85 percent, 

respectively, even though a seepage barrier had not been 

installed at these well locations. These variations were 

much greater than those indicated by chloride concentration sampling and electromagnetic-induction logging 

in collocated short-screened monitoring-well clusters 

PB–1822S/PB–1822 and GL–332S/GL–332. The saltwater 

interface evident in samples and TSEMIL datasets from 

well cluster HE–1145S/HE–1145 could not be identified 

in the information collected from the collocated well 

HHD10–R2–MW18F.

The variability of water-sample results from the 

long-open-interval wells could be explained by well-bore flow 

under ambient conditions, which has been shown to alter the 

distribution of salinity in the well relative to that in the aquifer. 

Even though the long-screened wells were purged prior to 

sampling, it is unlikely that this would remove all water 

that might have flowed through the well bore and into the 

aquifer. It is also possible that when the well is pumped during 

sampling, water may flow vertically through the annulus 

between the well screen and wall of the borehole, because 

there are no seals to prevent this flow.

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on south Florida water management system—A case study 

of Hurricane Wilma of October 2005: Journal of Spatial 

Hydrology, v. 8, no. 1, 21 p. 

Bromwell, L.G., Dean, R.G., and Vick, S.V., 2006, Report 

of expert review panel—Technical evaluation of Herbert 

Hoover Dike, Lake Okeechobee, Florida: BCI Engineers & 

Scientists, Inc., 77 p.

Johnson, C.D., Haeni, F.P., Lane, J.W., and White, E.A., 2002, 

Borehole-geophysical examination of the University of 

Connecticut landfill, Storrs, Connecticut: U.S. Geological 

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42 p.

Lloyd’s, 2010, The Herbert Hoover Dike, a discussion of 

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www.lloyds.com/~/media/Lloyds/Reports/360/360%20

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24 Changes in the Saltwater Interface Corresponding to the Installation of a Seepage Barrier Near Lake Okeechobee

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Manuscript approved December 18, 2014

Prepared by the Raleigh Publishing Service Center

Michael Deacon, Editor

Kimberly Swidarski, Illustrations and layout

For more information about this publication, contact:

Director 

U.S. Geological Survey

Caribbean-Florida Water Science Center

4446 Pet Lane, Suite 108

Lutz, FL 33559

(813) 498-5000

or visit our Web site at

http://fl.water.usgs.gov
Prinos and Valderrama—Changes in the Saltwater Interface Corresponding to the Installation of a Seepage Barrier Near Lake Okeechobee, Florida—Open-File Report 2014–1256

ISSN 2331-1258 (online)

http://dx.doi.org/10.3133/ofr20141256