U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2013–5227

Version 1.2, June 2014

Prepared in cooperation with the Capital Area Groundwater Conservation Commission;

the Louisiana Department of Transportation and Development, Public Works and Water 

Resources Division; and the City of Baton Rouge and Parish of East Baton Rouge

Simulation of Groundwater Flow in the “1,500-Foot” Sand 

and “2,000-Foot” Sand, with Scenarios to Mitigate

Saltwater Migration in the “2,000-Foot” Sand of the

Baton Rouge Area, Louisiana

Simulation of Groundwater Flow in the 

“1,500-Foot” Sand and “2,000-Foot” Sand, 

with Scenarios to Mitigate Saltwater 

Migration in the “2,000-Foot” Sand of the 

Baton Rouge Area, Louisiana

By Charles E. Heywood, Jason M. Griffith, and John K. Lovelace

Scientific Investigations Report 2013–5227

Version 1.2, June 2014

U.S. Department of the Interior

U.S. Geological Survey

Prepared in cooperation with the Capital Area Groundwater Conservation 

Commission; the Louisiana Department of Transportation and Development, 

Public Works and Water Resources Division; and the City of Baton Rouge and 

Parish of East Baton Rouge
U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia

First release: 2014, online

Revised: April 2014 (ver. 1.1), online

Revised: June 2014 (ver. 1.2), online

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Suggested citation:

Heywood, C.E., Griffith, J.M., and Lovelace, J.K., 2014, Simulation of groundwater flow in the “1,500-foot” sand and 

“2,000-foot” sand, with scenarios to mitigate saltwater migration in the “2,000-foot” sand of the Baton Rouge area, 

Louisiana (ver. 1.2, June 2014): U.S. Geological Survey Scientific Investigations Report 2013-5227, 63 p., 

http://dx.doi.org/10.3133/sir20135227.

ISSN 2328-031X (print)

ISSN 2328-0328 (online)

http://dx.doi.org/10.3133/sir20135227
iii

Acknowledgments

The authors would like to thank the many people who have contributed substantially to a 

better understanding of the hydrogeology and saltwater encroachment in the Baton Rouge area 

in southeastern Louisiana. Don C. Dial, Anthony J. Duplechin, Zahir “Bo” Bolourchi, and other 

members of the Capital Area Ground Water Conservation Commission provided guidance and 

assistance throughout this investigation.

v

Contents

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

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

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

Previous Investigations........................................................................................................................3

Study Area Description........................................................................................................................3

Horizontal Datum and Projection Systems.......................................................................................3

Hydrogeology..................................................................................................................................................5

Baton Rouge Fault.................................................................................................................................5

Occurrence and Movement of Saltwater.......................................................................................12

Hydrogeologic Framework................................................................................................................12

Groundwater Withdrawals.........................................................................................................................13

Simulation of Groundwater Flow and Movement of Saltwater............................................................14

Conceptual Model for Saltwater Transport....................................................................................17

Equations of Groundwater Flow and Transport.............................................................................17

Spatial Discretization .........................................................................................................................17

Internal Flow Package .......................................................................................................................20

Horizontal Flow Barriers...........................................................................................................20

Temporal Discretization.....................................................................................................................20

Boundary Conditions..........................................................................................................................22

No-Flow Boundaries .................................................................................................................22

Specified-Head Boundaries.....................................................................................................22

Head-Dependent Flux Boundaries..........................................................................................22

Specified-Concentration Boundaries

and Initial Conditions ...................................................................................................23

Hydraulic-Property Distribution .......................................................................................................23

Horizontal Interpolation of Hydraulic Conductivity ..............................................................23

Transport Properties..................................................................................................................26

Model Calibration.........................................................................................................................................26

Calibration Dataset.............................................................................................................................26

Water-Level Observations........................................................................................................26

Wellbore-Flow Observation .....................................................................................................27

Concentration Observations ...................................................................................................27

Water-Level Observation Errors..............................................................................................27

Weights........................................................................................................................................27

Calibration Assessment.....................................................................................................................27

Estimated Parameter Values....................................................................................................28

Parameter Sensitivities.............................................................................................................28

Residual Plot...............................................................................................................................28

Simulated Groundwater Conditions..........................................................................................................28

Simulated Water Levels.....................................................................................................................29

Simulated Connector-Well Flow Rate..............................................................................................36

Simulated Water Budget ...................................................................................................................36

Simulated Concentrations.................................................................................................................44
vi

Limitations and Appropriate Use of the Model.......................................................................................47

Hypothetical Groundwater-management Scenarios.............................................................................47

Scenario 1: Continued Groundwater Withdrawals at 2007 Rates ..............................................48

Scenario 2: Reduction of Groundwater Withdrawals from the “1,500-foot” Sand..................48

Scenario 3: Scavenger Well Withdrawal from the Base of the “2,000-foot” Sand .................53

Scenario 4: Reduction of Groundwater Withdrawals from the 

2,000-foot” Sand in the Baton Rouge Industrial District.................................................53

Scenario 5: Cessation of Groundwater Withdrawals from the

“2,000-foot” Sand in the Baton Rouge Industrial District...............................................53

Scenario 6: Scavenger Well Combined with a Reduction of 1.375 Million

Gallons Per Day of Industrial District Withdrawal from the

“2,000-foot” Sand ..................................................................................................................57

Summary........................................................................................................................................................60

Selected References...................................................................................................................................61

Figures

1. Map showing location of the study area, the Baton Rouge Fault,

stratigraphic control wells, and simulated groundwater-withdrawal wells

in southeastern Louisiana and southwestern Mississippi ....................................................4

2. Hydrogeologic section A-A’ in East Baton Rouge and East and

West Feliciana Parishes, southeastern Louisiana..................................................................7

3. Map showing simulated altitude of the top of the “1,500-foot” sand of the

Baton Rouge area in southeastern Louisiana and southwestern Mississippi...................8

4. Map showing simulated thickness of the “1,500-foot” sand of the

Baton Rouge area in southeastern Louisiana and southwestern Mississippi...................9

5. Map showing simulated altitude of the top of the “2,000-foot” sand of the

Baton Rouge area in southeastern Louisiana and southwestern Mississippi.................10

6. Map showing simulated thickness of the “2,000-foot” sand of the

Baton Rouge area in southeastern Louisiana and southwestern Mississippi.................11

7. Conceptual offset of hydrogeologic units at faults in the Baton Rouge area,

southeastern Louisiana .............................................................................................................13

8. Graph showing estimated withdrawals from the Baton Rouge sands,

1940–2007 .....................................................................................................................................15

9. Average daily withdrawal rate during 2007 at wells screened in the

“2,000-foot” sand of the Baton Rouge area and located at or near the

Baton Rouge industrial district in southeastern Louisiana..................................................16

10. Map showing the model finite-difference grid and locations of the

horizontal flow barrier in the “2,000-foot” sand of the Baton Rouge area

and simulated groundwater-withdrawal wells in southeastern Louisiana

and southwestern Mississippi..................................................................................................18

11. Map showing the finite-difference grid and locations of horizontal flow

barriers, simulated groundwater-withdrawal wells, and water-level

observation wells in the “1,000-foot,” “1,200-foot,” “1,700-foot,” “2,400-foot,”

and “2,800-foot” sands of the Baton Rouge area in the detailed model area

in southeastern Louisiana .........................................................................................................19

12. North-to-south cross section along model column 24 showing aquifers,

confining units, and finite-difference discretization.............................................................21
vii

13. Map showing pilot point locations and the simulated horizontal hydraulic

conductivity distribution within the “2,000-foot” sand of the

Baton Rouge area in the detailed model area in southeastern Louisiana........................25

14. Graph showing residuals as a function of simulated water level altitudes

for the “2,000-foot” sand and all other simulated aquifers. Residuals are

calculated by subtracting simulated water-level altitudes from observed

water-level altitudes...................................................................................................................29

15. Map showing simulated steady-state water levels within the“1,500-foot”

sand of the Baton Rouge area representing predevelopment conditions

before 1940 in southeastern Louisiana and southwestern Mississippi.............................30

16. Map showing simulated steady-state water-levels within the “2,000-foot”

sand of the Baton Rouge area representing predevelopment conditions

before 1940 in southeastern Louisiana and southwestern Mississippi.............................31

17A. Maps showing simulated 2007 water levels within the “1,500-foot” sand

of the Baton Rouge area in southeastern Louisiana and

southwestern Mississippi .........................................................................................................32

17B. Map showing simulated 2007 water levels within the “1,500-foot” sand

of the Baton Rouge area in the detailed model area in southeastern Louisiana.............33

18A. Map showing simulated 2007 water levels within the “2,000-foot” sand

of the Baton Rouge area in southeastern Louisiana and

southwestern Mississippi .........................................................................................................34

18B. Map showing simulated 2007 water levels within the “2,000-foot sand

of the Baton Rouge area in the detailed model area in southeastern Louisiana.............35

19. Graphs showing simulated and observed water levels within the “1,000-foot”

and “1,200-foot” sands of the Baton Rouge area in southeastern Louisiana ..................37

 20. Graphs showing simulated and observed water levels within the

“1,500-foot” sand of the Baton Rouge area in southeastern Louisiana............................38

21. Graphs showing simulated and observed water levels within the

“1,700-foot” sand of the Baton Rouge area in southeastern Louisiana............................39

22. Graphs showing simulated and observed water levels within the

“2,000-foot” sand of the Baton Rouge area in southeastern Louisiana............................40

23. Graphs showing simulated and observed water levels within the

“2,400-foot” sand of the Baton Rouge area in southeastern Louisiana............................42

24. Graph showing simulated and observed water levels within the

“2,800-foot” sand of the Baton Rouge area in southeastern Louisiana............................43

25. Graph showing simulated groundwater withdrawals and flows from

storage and specified-head boundaries.................................................................................44

26. Graph showing simulated and observed chloride concentrations at

observation wells within the “2,000-foot” sand of the Baton Rouge area

in southeastern Louisiana .........................................................................................................45

27. Map showing simulated 2007 water levels and chloride concentrations

at the base of the “2,000-foot” sand of the Baton Rouge area in the

detailed model area in southeastern Louisiana ....................................................................46

28. Map showing predicted 2047 water levels within the “1,500-foot” sand

of the Baton Rouge area in the detailed model area in southeastern Louisiana

after continued pumping at 2007 rates (scenario 1) .............................................................49

29. Map showing predicted 2047 water levels and chloride concentrations

at the base of the “2,000-foot” sand of the Baton Rouge area in the

detailed model area in southeastern Louisiana after continued pumping

at 2007 rates (scenario 1) ..........................................................................................................50
viii

30. Graphs showing predicted chloride concentrations at the base of the

“2,000-foot” sand after continued pumping at 2007 rates (scenario 1),

installation of a scavenger well (scenario 3 a,b), industrial-district withdrawal

reduction of 3.6 million gallons per day (scenario 4), cessation of industrialdistrict withdrawals from the “2,000-foot” sand (scenario 5), and a

scavenger well with withdrawal reductions (scenario 6) for: A, well EB-1028;

B, well EB-1150; C, well EB-630; D, well EB-781; E, well EB-807B; and

F, hypothetical well EB-X...........................................................................................................51

31. Map showing predicted 2047 water levels within the “1,500-foot” sand

of the Baton Rouge area in the detailed model area in southeastern

Louisiana following cessation of pumping from selected industrial wells

in the “1,500-foot” and “1,700-foot” sands beginning in 2015 (scenario 2).......................52

32. Map showing predicted 2047 water levels and chloride concentrations

at the base of the “2,000-foot” sand of the Baton Rouge area in the

detailed model area in southeastern Louisiana after pumping at a rate

of 2 million gallons per day from a simulated scavenger well located

in model row 57 and column 26 beginning in 2017 (scenario 3)..........................................54

33. Map showing predicted 2047 water levels and chloride concentrations

at the base of the “2,000-foot” sand of the Baton Rouge area in the

detailed model area in southeastern Louisiana after pumping at a rate

of 2 million gallons per day from a simulated scavenger well located

in model row 68 and column 30 starting in 2017 (scenario 3)..............................................55

34. Map showing predicted 2047 water levels and chloride concentrations

at the base of the “2,000-foot” sand of the Baton Rouge area in the

detailed model area in southeastern Louisiana after a 3.6 million gallon

per day reduction in pumping (from 2007 rates) at selected wells in the

Baton Rouge industrial district beginning in 2015 (scenario 4)...........................................56

35. Map showing predicted 2047 water levels and chloride concentrations

at the base of the “2,000-foot” sand of the Baton Rouge area in the

detailed model area in southeastern Louisiana following cessation

of pumping from the “2000-foot” sand in the Baton Rouge industrial

district beginning in 2015 (scenario 5).....................................................................................58

36. Map showing predicted 2047 water levels and chloride concentrations

at the base of the “2,000-foot” sand of the Baton Rouge area in the

detailed model area in southeastern Louisiana after 31 years of pumping

from a scavenger well located in model row 68 and column 30 beginning

in 2017 and reduced withdrawals at selected industrial and public supply

wells beginning in 2015 (scenario 6)........................................................................................59

Tables

1. Groundwater withdrawals (in million gallons per day) in the

Baton Rouge area, Louisiana, by parish and principal use, 2010 .........................................2

2. Aquifers and aquifer systems in southern Mississippi and southeastern

Louisiana and corresponding model layers .............................................................................6

3. Time discretization summary ....................................................................................................21

4. Parameter values and sensitivities for the calibrated groundwater-flow model ............24

5. Simulated steady-state and transient flow rates..................................................................43

6. Simulated plume areas and chloride concentrations ..........................................................48
ix

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square foot (ft2) 0.09290 square meter (m2)

square mile (mi2) 2.590 square kilometer (km2) 

acre 4,047 square meter (m2)

Volume

gallon (gal) 0.003785 cubic meter (m3) 

cubic foot (ft3) 0.02832 cubic meter (m3) 

Flow rate

cubic foot per day (ft3/d) 0.02832 cubic meter per day (m3/d)

gallon per minute (gal/min) 0.06309 liter per second (L/s)

gallon per day (gal/d) 0.003785 cubic meter per day (m3/d)

million gallons per day (Mgal/d) 0.04381 cubic meter per second (m3/s)

Density

pound per cubic foot (lb/ft3) 16.02 kilogram per cubic meter (kg/m3)

pound per cubic foot (lb/ft3) 0.01602 gram per cubic centimeter (g/cm3)

Hydraulic conductivity

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

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

°C=(°F-32)/1.8

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).

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

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

Abbreviations

City-Parish City of Baton Rouge and Parish of East Baton Rouge

Commission Capital Area Groundwater Conservation Commission

DOTD Louisiana Department of Transportation and Development

DNR Louisiana Department of Natural Resources

FHB Flow and Head Boundary package

gpm Gallons per minute

GIS Geographic information system

HOB Head Observation Package

HUF Hydrogeologic-Unit Flow package

IMT Integrated Mass Transport package

Mgal/d Million gallons per day

mg/L Milligram per liter

MNW2 Multi-Node Well package

NWIS National Water Information System

RASA Regional Aquifer System Analysis

TVD Total Variation Diminishing scheme

USGS U.S. Geological Survey

VDF Variable-Density Flow package

[M] Mass dimension

[L] Length dimension

[T] Time dimension
Simulation of Groundwater Flow in the “1,500-Foot” Sand

and “2,000-Foot” Sand, with Scenarios to Mitigate

Saltwater Migration in the “2,000-Foot” Sand of the

Baton Rouge Area, Louisiana

By Charles E. Heywood, Jason M. Griffith, and John K. Lovelace

Abstract

Groundwater withdrawals have caused saltwater to 

encroach into freshwater-bearing aquifers beneath Baton 

Rouge, Louisiana. Groundwater investigations in the 1960s 

identified a freshwater-saltwater interface located at the Baton 

Rouge Fault, across which abrupt changes in water levels 

occur. Aquifers south of the fault generally contain saltwater, 

and aquifers north of the fault contain freshwater, though 

limited saltwater encroachment has been detected within 7 of 

the 10 aquifers north of the fault. The 10 aquifers beneath the 

Baton Rouge area, which includes East and West Baton Rouge 

Parishes, Pointe Coupee Parish, and East and West Feliciana 

Parishes, provided about 167 million gallons per day (Mgal/d) 

for public supply and industrial use in 2010. Groundwater 

withdrawals from the “2,000-foot” sand in East Baton Rouge 

Parish have caused water-level drawdown as great as 356 

feet (ft) and induced saltwater movement northward across 

the fault. Saltwater encroachment threatens industrial wells 

that are located about 3 miles north of the fault. Constant and 

variable-density groundwater models were developed with 

the MODFLOW and SEAWAT groundwater modeling codes 

to evaluate strategies to control saltwater migration, including 

changes in the distribution of groundwater withdrawals and 

installation of “scavenger” wells to intercept saltwater before 

it reaches existing production wells.

Six hypothetical scenarios simulated the effects of 

different groundwater withdrawal options on groundwater 

levels within the “1,500-foot” sand and the “2,000-foot” 

sand and the transport of saltwater within the “2,000-foot” 

sand during 2008–47. Scenario 1 is considered a base case 

for comparison to the other five scenarios and simulates 

continuation of 2007 reported groundwater withdrawals. 

Scenario 2 simulates discontinuation of withdrawals from 

seven selected industrial wells located in the northwest corner 

of East Baton Rouge Parish and predicts that water levels 

within the “1,500-foot” sand will be about 10 to 12 ft higher 

with this withdrawal reduction than under scenario 1. Scenario 

3 simulates the effects of a scavenger well on water levels 

and chloride concentrations within the “2,000-foot” sand. 

The scavenger well, which withdraws water from the base of 

the “2,000-foot” sand at a rate of 2.0 Mgal/d, is simulated at 

two possible locations. In comparison to the concentrations 

simulated in scenario 1, operation of the scavenger well at 

the locations specified in scenario 3 reduces the chloride 

concentrations at all existing chloride-observation well 

locations. Scenario 4 simulates a 3.6 Mgal/d reduction in 

total groundwater withdrawals from selected wells screened 

in the “2,000-foot” sand that are located in the Baton Rouge 

industrial district. Under scenario 4, chloride concentrations 

decrease in the leading portion of the plume south of the 

industrial district but increase in areas farther east. Scenario 

5 simulates the effects of total cessation of withdrawals from 

the “2,000-foot” sand in the industrial district, which causes 

a change in the groundwater-flow direction toward municipal 

supply wells and increased chloride concentrations in the 

area where municipal supply wells are located. Scenario 6 

simulates the combined effect of withdrawal reductions from 

the “2,000-foot” sand and operation of a scavenger well and 

was most effective at decreasing the size of the plume area 

and median and mean chloride concentrations within the 

“2000-foot” sand in the Baton Rouge area.

Introduction

Fresh groundwater is a valuable resource in southeastern 

Louisiana and the five-parish Baton Rouge area (subsequently 

referred to as the “Baton Rouge area”), which includes 

East and West Baton Rouge, Pointe Coupee, and East and 

West Feliciana Parishes. In the Baton Rouge area, fresh 

groundwater in most aquifers is soft, sodium bicarbonate 

water with a dissolved-solids concentration of about 

200 milligrams per liter (mg/L) (Meyer and Turcan, 1955) and 

requires little treatment for potable use or industrial purposes 

(Stuart and others, 1994). Groundwater withdrawals in the 

Baton Rouge area since the 1940s have lowered water levels 
2 Simulation of Groundwater Flow in the “1,500-Foot” Sand and “2,000-Foot” Sand in the Baton Rouge Area, Louisiana

in the “2000-foot” sand as much as 356 feet (ft) and altered 

groundwater-flow directions in most of the 10 underlying 

freshwater-bearing aquifers. During 2010, about 196 million 

gallons per day (Mgal/d) of groundwater were withdrawn 

(table 1) in the Baton Rouge area (Sargent, 2011), mostly in 

East Baton Rouge Parish. Groundwater usage in 2010 was 

primarily for public supply and industry, which consumed 

about 94 Mgal/d and 73 Mgal/d, respectively. Withdrawals 

from “1,500-foot” and “2,000-foot” sands of the Baton 

Rouge area in 2010 were about 19.9 Mgal/d and 23.9 Mgal/d, 

or 10.2 percent and 12.2 percent of the total withdrawals, 

respectively (P. Sargent, U.S. Geological Survey, written 

commun., 2013). The drawdown of groundwater levels 

has caused saltwater to encroach into freshwater areas near 

Baton Rouge. Saltwater encroachment has been detected 

in seven aquifers, including the “1,500-foot” sand and 

the “2,000-foot” sand in East Baton Rouge Parish (Meyer 

and Turcan, 1955; Morgan, 1961; Tomaszewski, 1996; 

Lovelace, 2007). Saltwater threatens industrial wells which, 

in recent years, have typically accounted for about twothirds of the withdrawals from the “2,000-foot” sand in East 

Baton Rouge Parish.

 Water planners and managers need to have additional 

knowledge of the effects of groundwater withdrawals on 

the rate and pathways of saltwater migration and to assess 

possible management strategies that could control further 

saltwater encroachment in the Baton Rouge area. In response 

to this concern, the U.S. Geological Survey (USGS), in 

cooperation with the Capital Area Ground Water Conservation 

Commission (Commission), Louisiana Department of 

Transportation and Development (DOTD) Water Resources 

Office, and the City of Baton Rouge and Parish of East Baton 

Rouge (City-Parish), developed the groundwater-flow and 

saltwater-transport model of the Southern Hills regional 

aquifer system that is documented in this report. The model 

simulates the effects of reported groundwater withdrawals on 

groundwater flow in the “1,500-foot” sand and “2,000-foot” 

sand, and the movement of saltwater in the “2,000-foot” sand 

northward from the Baton Rouge Fault in East Baton Rouge 

Parish. The model simulates historical conditions (prior to 

2008) and six possible future pumping scenarios and can 

be used to evaluate possible strategies to mitigate saltwater 

encroachment in the “2,000-foot” sand in the Baton Rouge 

area. The model provides a tool for evaluation of the need, 

effectiveness, and possible locations of additional pumping, 

injection, or observation wells that may either mitigate or 

be used to monitor saltwater encroachment. The model also 

provides a framework for future studies of groundwater 

flow and saltwater encroachment in other aquifers within 

the groundwater-flow system. It could also facilitate study 

of possible saltwater-encroachment mitigation strategies and 

increase understanding of saltwater movement in similar 

hydrogeologic settings. A digital archive of the groundwater 

model is on file at the USGS office in Baton Rouge.

Purpose and Scope

This report documents the hydrogeologic framework of 

the Southern Hills regional aquifer system in southeastern 

Louisiana and in southwestern Mississippi, the hydraulic 

properties of the aquifer system, groundwater-withdrawal 

rates, and the development and calibration of a groundwaterflow and saltwater-transport model that simulates groundwater 

flow in the “1,500-foot” sand and “2,000-foot” sand and 

migration of saltwater within the “2,000-foot” sand in the 

Baton Rouge area. The simulated effects of groundwater 

withdrawals on water levels and flow directions in the 

“2,000-foot” sand and “1,500-foot” sand and on the movement 

of saltwater in the “2,000-foot” sand are described. Six future 

scenarios are discussed that represent the effects of continued 

groundwater withdrawals and possible strategies to mitigate 

saltwater encroachment in the “2,000-foot” sand beneath the 

city of Baton Rouge.

Table 1. Groundwater withdrawals (in million gallons per day) in the Baton Rouge area, Louisiana, by parish and principal use, 2010 

(modified from Sargent, 2011).

Parish Public

supply

Industrial Power

generation

Rural 

domestic

Livestock Irrigation AquacultureTotal use

Rice General

East Baton 

Rouge

75.12 66.22 7.79 0.28 0.19 0.00 0.25 0.04 149.89 

East Feliciana 3.00 0.03 0.00 0.27 0.02 0.00 0.18 0.00 3.50 

Pointe Coupee 4.08 4.92 1.89 0.23 0.10 4.78 7.19 4.34 27.53 

West Baton 

Rouge

7.21 1.50 0.00 0.05 0.03 0.00 0.35 1.07 10.21 

West

Feliciana

4.15 0.41 0.02 0.10 0.00 0.00 0.00 0.00 4.68 

Total 93.56 73.08 9.70 0.93 0.34 4.78 7.97 5.45 195.81
Introduction 3

The model and scenarios in this report supercede those 

previously documented by Heywood and Griffith (2013). 

Differences from the previous version include the addition 

of water-level observations from 2008 to 2011, model 

modification and recalibration to improve simulation of the 

“1,500-foot” and “2,400-foot” sands, modification of the timing 

for all hypothetical groundwater management scenarios, and 

inclusion of an additional scenario.

The model domain encompasses an area of about 

6,600 square miles (mi2) in southeastern Louisiana and 

southwestern Mississippi; however, its primary focus is on 

the “1,500-foot” sand and “2,000-foot” sand in a 25-mi2

area in Baton Rouge where large groundwater withdrawals 

have occurred and where saltwater encroachment is of 

concern. Simulation of regional groundwater flow through all 

hydrogeologic units in the Southern Hills aquifer system helped 

assure reasonable simulated results within the primary area 

of concern.

Previous Investigations

Several previous reports included background data on 

the geologic, hydraulic, and water-quality characteristics of 

freshwater-bearing aquifers in the Baton Rouge area (Meyer 

and Turcan, 1955; Morgan, 1961). Morgan and Winner (1964) 

documented known areas of saltwater in aquifers underlying 

East and West Baton Rouge Parishes and estimated the rates 

of saltwater movement toward areas of large groundwater 

withdrawals in the industrial district and toward public-supply 

pumping stations. Whiteman (1979) included a detailed 

discussion of saltwater encroachment in the “600-foot” sand and 

“1,500-foot” sand and discussions of saltwater in other aquifers. 

Whiteman (1979) also documented the existence of the eastwest trending Baton Rouge Fault as a leaky hydrologic barrier 

that limits northward movement of saltwater in aquifers in the 

Baton Rouge area. Buono (1983) described the freshwaterbearing aquifers in the northern parishes of southeastern 

Louisiana (including those in the Baton Rouge area) and the 

up-dip equivalent aquifers in Mississippi as an interdependent 

system, which he named the “Southern Hills regional aquifer 

system” (table 1). Griffith (2003) presented hydrogeologic cross 

sections of the freshwater aquifers in southeastern Louisiana, 

which he described as a sequence of complexly interbedded, 

interconnected, lenticular (lens shaped), alluvial, freshwaterbearing, clayey, sandy, and graveliferous strata. Morgan and 

Winner (1964), Whitman (1979), Tomaszewski (1996), and 

Lovelace (2007) documented the occurrence of saltwater and 

increasing chloride concentrations within various aquifers in the 

Baton Rouge area.

In 1975, the USGS began a cooperative program with the 

DOTD and the Commission to analyze groundwater flow by 

using groundwater models of aquifers in the Baton Rouge area, 

including the “400-foot” sand, “600-foot” sand, “1,500-foot” 

sand, “1,700-foot” sand, and “2,000-foot” sand in the Baton 

Rouge area (Torak and Whiteman, 1982; Huntzinger and others, 

1985; Kuniansky, 1989; Halford and Lovelace, 1994). Under 

the USGS regional aquifer-system analysis (RASA) program, 

the hydrogeologic framework, groundwater chemistry, and 

regional flow patterns in the freshwater aquifers along the 

northern Gulf of Mexico Coast in Louisiana and parts of Texas 

and Mississippi were described, and groundwater-flow models 

were used to simulate regional flow patterns (Martin and 

Whiteman, 1990).

Study Area Description

The study area encompasses about 6,600 mi2 in 

southeastern Louisiana and southwestern Mississippi (fig. 1). 

The study area extends southward from about 25 miles (mi) 

north of the Mississippi state line to Gonzales, La., in the 

south and eastward from Breaux Bridge, La., in the west to 

Hammond, La., in the east. In southeastern Louisiana, all or 

parts of Ascension, Assumption, Avoyelles, Concordia, East 

and West Baton Rouge, East and West Feliciana, Iberville, 

Livingston, Pointe Coupee, St. Helena, St. Martin, St. Landry, 

and Tangipahoa Parishes are in the study area. In Mississippi, 

all or parts of Adams, Amite, Franklin, Lincoln, Pike, and 

Wilkinson Counties are in the study area.

The terrain in the study area varies from forested rolling 

hills in the north to flat lowlands and swamps in the south. 

The Mississippi River valley dominates the setting near the 

western and southern boundaries of the study area. Landsurface altitudes range from 0 ft to more than 450 ft (Calhoun 

and Frois, 1997). The climate is subtropical, warm, and 

temperate with an average annual temperature of 

68 °F (20 °C) and an average annual rainfall of 61 inches 

(National Oceanic and Atmospheric Administration, 1995). 

About 1 million people live within the study area, with 

largest populations in the Baton Rouge metropolitan area 

(U.S. Census Bureau, 2010). All of the public water supplied 

in the Baton Rouge area in 2010 was groundwater (Sargent, 

2011). Several industrial facilities, primarily located along 

the Mississippi River, also utilize the groundwater resources 

in the study area (table 1). In addition, groundwater supplies 

about 84 percent of agricultural water use in the study area 

(Sargent, 2011).

Horizontal Datum and Projection Systems

The geographic coordinates of database features, such as 

well-head locations, and geographic information system (GIS) 

data used in the model are referenced to the North American 

Datum of 1983 (NAD 83). To represent model-cell areas 

accurately, polygon and point GIS coverages of the model 

finite-difference cells and nodes, created with the program 

MODELGRID (Kernodle and Philip, 1988), were generated 

in a Lambert Conformal Conic projection system. The model 

finite-difference grid columns are oriented north-south in 

the Lambert Conformal Conic projection system. These GIS 

coverages were subsequently projected into the Universal 
Lake Maurepas MISSISSIPPI LOUISIANA WEST FELICIANA EAST FELICIANA ST. HELENA TANGIPAHOA LIVINGSTON EAST BATON ROUGE WEST BATON ROUGE POINTE COUPEE IBERVILLE ST. MARTIN ASCENSION ST. LANDRY AVOYELLES CONCORDIA WILKINSON AMITE PIKE BATON ROUGE BREAUX BRIDGE GONZALES HAMMOND ADAMS FRANKLIN LINCOLN Detailed model area (see fig. 11) 

A Base map modified from Louisiana Oil Spill Coordinator, Office of the Governor, Louisiana GIS CD: A Digital Map of the State, Version 2.0 Map Projection: North American Datum of 1983, Universal Transverse Mercator Zone 15 0 10 20 KILOMETERS 0 10 20 MILES 92°00' 91°45' 91°30' 91°15' 91°00' 90°45' 90°30' 31°15' 31°00' 30°45' 30°30' 30°15' See fig. 2 A' 

! ! A' 

§ ̈¦55 § ̈¦55 § ̈¦55 § ̈¦12 § ̈¦10 § ̈¦10 61 61 61 98 98 .71 .190 .190 .51.51

Figure 1. Map showing location of the study area, the Baton Rouge Fault, stratigraphic control wells, and simulated groundwater-withdrawal wells iand southwestern Mississippi.
Hydrogeology 5

Transverse Mercator (UTM) zone 15 coordinate system that was 

used for GIS coverages of wells, the hydrogeologic framework, 

and water levels. Consequently, the model finite difference grid 

appears slightly rotated in the UTM projection displayed in the 

map figures in this report. Projection and coordinate system 

details are contained in a file in the digital model archive. 

Hydrogeology

Aquifers containing freshwater in the Baton Rouge area 

are generally part of the Southern Hills regional aquifer system 

and include the Mississippi River alluvial aquifer, the shallow 

sands of the Baton Rouge area, the upland terrace aquifer, the 

“400-foot” sand, “600-foot” sand, “800-foot” sand, “1,000-

foot” sand, “1,200-foot” sand, “1,500-foot” sand, “1,700-foot” 

sand, “2,000-foot” sand, “2,400-foot” sand, and “2,800-foot” 

sand of the Baton Rouge area and the Catahoula aquifer (Meyer 

and Turcan, 1955; Morgan, 1961; Buono, 1983; Griffith, 2003). 

The Mississippi River alluvial aquifer and the shallow sands 

of the Baton Rouge area are the shallowest aquifers in the 

Baton Rouge area. Deeper aquifers in the Baton Rouge area 

include aquifers that are named for their depth of occurrence 

in the Baton Rouge industrial district (table 2; fig. 2) and the 

Catahoula aquifer. Aquifers in the Baton Rouge area have 

been correlated with aquifers in southern Mississippi and in 

Louisiana parishes east of the study area. The aquifers also 

have been grouped based on correlative units in southwestern 

and central Louisiana into the Chicot equivalent, Evangeline 

equivalent, Jasper equivalent, and Catahoula equivalent aquifer 

systems (Stuart and others, 1994). Although the Catahoula 

aquifer contains freshwater in some areas, it is generally too 

deep and contains too much saltwater to be an economically 

viable water resource in the Baton Rouge area (Griffith, 2003).

Freshwater-bearing aquifers in the Baton Rouge area 

range in composition from very fine to coarse sand with some 

pea-to-cobble-sized gravel (Griffith, 2003) and are sufficiently 

permeable to yield economically substantial quantities of water 

to wells (Bates and Jackson, 1984). The aquifers are separated 

by confining units composed of material ranging from solid 

clay to sandy and silty clay that limit vertical groundwater flow. 

The freshwater aquifers and intervening confining units in the 

Baton Rouge area, together with the up-dip equivalent units in 

southwestern Mississippi, form a thickening wedge that dips 

to the south and southwest toward the Gulf of Mexico and 

Mississippi River valley (fig. 2). The confining units generally 

pinch out northward, and deeper aquifers coalesce with 

overlying surficial aquifers.

The average annual precipitation over the study area 

is 54 to 60 inches, and precipitation in the northern part of 

the study area (fig. 1) and farther north in Mississippi is the 

primary source of recharge to the aquifer system. Because the 

aquifers are interconnected, precipitation that infiltrates through 

the shallow, surficial aquifers located in recharge areas flows 

southward into deeper aquifers. Kuniansky (1989) estimated a 

range from 0.2 to 4.6 inches per year (in/yr) for deep regional 

aquifer recharge. Groundwater velocities range from a few 

tens of feet per year to several hundreds of feet per year 

(Buono, 1983).

The “1,500-foot” sand and “2,000-foot” sand, like other 

freshwater aquifers in the study area, generally dip and thicken 

to the south and consist of single or multiple 65- to 95-ft thick 

intervals of fine to medium sand and 100 to 300 ft of medium 

sand. Where the aquifers contain multiple sand intervals, the 

intervals are separated by clays. The top of the “1,500-foot” 

sand is about 1,500 ft deep 1 mi north of the Baton Rouge 

Fault but is displaced deeper south of the fault (fig. 3). The 

“1,500-foot” sand is continuous throughout the study area 

except in parts of Avoyelles, East and West Baton Rouge, 

Iberville, Livingston, and Point Coupee Parishes and in most 

of Mississippi (fig. 4). The top of the “2,000-foot” sand is 

about 2,000 ft deep 1 mi north of the Baton Rouge Fault but 

is also displaced deeper south of the fault (fig. 5). The “2,000-

foot” sand is continuous throughout the study area (fig. 6). The 

location and thickness of the aquifers in Mississippi are based 

on the correlation of the “1,500-foot” sand and “2,000-foot” 

sand in the Baton Rouge area with up-dip units in southwestern 

Mississippi (Meyer and Turcan, 1955; Morgan, 1961; 

Newcome, 1975; Huntzinger and others, 1985; Griffith, 2003.)

Baton Rouge Fault

The Baton Rouge Fault extends across the southern part 

of the study area (fig. 2) and is part of a series of east-west 

trending faults in southern Louisiana (Murray, 1961; Hanor, 

1982; Griffith, 2003). The location of the Baton Rouge Fault 

was documented in the 1960s and 1970s after the importance 

of the fault as a barrier to groundwater flow in the aquifers 

in the Baton Rouge area became apparent (Meyer and Rollo, 

1965; Whiteman, 1979). McCulloh (1991) mapped the detailed 

location of the surface expression of faults through East Baton 

Rouge Parish. Within the study area, the Baton Rouge Fault 

dips to the south at angles between about 65 degrees and 

70 degrees (Durham and Peeples, 1956; Smith and Kazmann, 

1978; Whiteman, 1979; Roland and others, 1981; Hanor, 1982; 

McCulloh, 1991; Griffith, 2003, 2006).

Sediment deformation and displacement of sedimentary 

layers across the fault reduce the hydraulic connections between 

aquifers, thereby impeding horizontal groundwater flow, which 

causes substantial changes in both water levels and water 

quality across the fault. The displacement of aquifers across 

the Baton Rouge Fault ranges from about 20 ft near the ground 

surface to about 300 ft at altitudes of -1,600 to -3,000 ft (fig. 

2). In the Baton Rouge area, the displacement of the “1,500-

foot” sand and “2,000-foot” sand at the Baton Rouge Fault are 

about 235 and 250 ft, respectively (Durham and Peeples, 1956; 

Meyer and Rollo, 1965; Smith and Kazmann, 1978; Whiteman, 

1979; Roland and others, 1981; Hanor, 1982; McCulloh, 1991; 

Griffith, 2003, 2006).
6 Simulation of Groundwater Flow in the “1,500-Foot” Sand and “2,000-Foot” Sand in the Baton Rouge Area, Louisiana

??

? ?

Miocene

Oligocene

Quaternary ertiary T Pleistocene Pliocene Chicot equivalent aquifer system Evangeline equivalent aquifer system

Jasper equivalent  aquifer systemCatahoula equivalent  aquifer system

Southern Hills regional aquifer system

Citronelle  formationGraham  Ferry  formationPHattiesburg  formationCatahoula  formation

ascagoula 

 formation

Holocene Near-surface aquifers Alluvium

Series System

Aquifer system Aquifer1 unit

Southern 

Mississippi

Franklinton aquifer

Tchefuncte aquiferLower Hammond aquiferAmite aquiferRamsay aquifer

Ponchatoula 

 aquiferBig Branch aquiferKentwood aquifer

Upland terrace aquiferUpper 

Abita aquiferCovington aquiferSlidell aquifer

Ponchatoula 

 aquifer

“2,000-foot” sand“2,400-foot” sand“2,800-foot” sand

Catahoula aquifer

Layers 9–18

Layer 20

Layer 22

“800-foot” sand

“1,000-foot” sand“1,200-foot” sand“1,500-foot” sand“1,700-foot” sand

“400-foot” sand“600-foot” sand

Upland terrace

aquifer

Layer 1

Layer 3

Layer 5

Layer 7

No regionally extensive 

hydrogeologic units

Mississippi River 

alluvial aquifer

Shallow sands

Eastern Florida 

Parishes Baton Rouge area

Aquifer model layer2

Aquifer1 unit

Southeastern Louisiana

1Aquifers in southern Mississippi and southeastern Louisiana are separated by unnamed discontinuous confining units.2Aquifer model layers are separated by confining model layers except model layers 9–18. Model layer 22 is the bottom model layer. 

Table 2. Aquifers and aquifer systems in southern Mississippi and southeastern Louisiana and corresponding model layers (modified

from Buono, 1975; Stuart and others, 1994; Lovelace and Lovelace, 1995; and Griffith, 2003).
VERTICAL SCALE IS GREATLY EXAGGERATEDDatum is National Geodetic Vertical Datum of 1929 (NGVD 29)

0 10 MILES0 10 KILOMETERS

-400

NGVD 29

-600-800

-1,000-1,200-1,400-1,600-1,800

200

-2,000-2.200-2,400-2,600-2,800-3,000-3,200-3,400-3,600-3,800

400

-200

FEET

NORTH

A'

Figure 2. Hydrogeologic section A-A' in East Baton Rouge and East and West Feliciana Parishes, southeastern Louisiana. Figure modified from Griffith (2003).

Hydrogeologic framework layers—Shows the  location of hydrogeologic layers. Aquifer layers may  contain local confining beds. See figure 7 for conceptual diagram of hydrogeologic framework layers.

EXPLANATION

Hydrogeologic unit—Shows the  generalized location of the hydrogeologic  units. Layer 1—Mississippi River alluvial aquifer, shallow sands, upland terrace aquifer, and the “400-,” “600-,” and “800-foot” sands Layer 5—“1,500-foot” sandLayer 3—“1,000-” and “1,200-foot” sandsLayer 7—“1,700-foot” sandLayers 9 to 18—"2,000-foot" sandLayer 20—"2,400-foot" sandLayer 22—"2,800-foot" sand

BATON

ROUGE

GENERALIZED 

SURFACE PROFILE

FLOOD PLAIN 

BOUNDARIES

ST. FRANCISVILLE W. FELICIANA PARISH

E. FELICIANA PARISH

E. FELICIANA PARISH

E. BATON ROUGE PARISH

TEPETATE 

FAULT

I-10 HWY 19

WF-236

WF-242

WF-267

WF-269

WF-246

WF-44

EB-833

EB-645

EB-1268

EB-534

EB-1028

FLOOD PLAIN 

BOUNDARIES

Study 

area

Well—Shows name and location of well.Lithologic contact—Separates clay and sand  units. Dashed where approximate. Queried where  uncertain.

?

Hydrogeologic contact—defines boundary  between conjoined or merged aquifers.Fault

EB-534

Intervening confining unit layer

A

A'

Gulf of Mexico

TEXAS

LOUISIANA

MISSISSIPPI

ARKANSAS

“1,000-foot” 

sand

“1,700-foot” 

sand

“1,000-foot” sand

“1,500-foot” 

sand

“2,000-foot” sand

“1,500-foot” 

sand

“2,000-foot”

sand

“2,800-foot” 

sand

“400-foot” sand

“2,400-foot” sand

“2,800-foot” 

sand

“1,700-foot” sand

“2,000-foot” sand

“2,400-foot” 

sand “2,400-foot” 

sand

“1,200-foot” sand

Catahoula 

aquifer

“1,500-foot” 

sand

“1,200-foot” 

sand

“1,000-foot” 

sand

“1,700-foot” 

sand

“600-foot” sand

“400-foot” sand

“600-foot” 

sand

“800-foot” 

sand

Shallow aquifer Shallow aquifer

“1,700-foo

sand

“2,000-foot” san

“2,400-foot” sand

“2,400-foot” 

sand

“2,800-foot” 

sand

Catahoula 

aquifer

?

?

?

“2,800-foot” 

sand

?

?

?

?

?

?

? ?

“800-foot” 

sand Upland terrace aquifer

“800-foot” 

sand

?

Mississippi River alluvial aquifer 

Figure 2. Hydrogeologic section A-A’ in East Baton Rouge and East and West Feliciana Parishes, southeastern Louisiana. Figure modified from Griffi
Lake Maurepas MISSISSIPPI LOUISIANA WEST FELICIANA EAST FELICIANA ST. HELENA TANGIPAHOA LIVINGSTON EAST BATON ROUGE WEST BATON ROUGE POINTE COUPEE IBERVILLE ST. MARTIN ASCENSION ST. LANDRY AVOYELLES CONCORDIA WILKINSON AMITE PIKE BATON ROUGE BREAUX BRIDGE GONZALES HAMMOND ADAMS FRANKLIN LINCOLN 

Figure 3. Simulated altitude of the top of the "1,500-foot" sand of the Baton Rouge area in southeastern Louisianaand southwestern Mississippi.

Base map modified from Louisiana Oil Spill Coordinator, Office of theGovernor, Louisiana GIS CD: A Digital Map of the State, Version 2.0Map Projection: North American Datum of 1983, Universal Transverse Mercator Zone 15

0

-200

-800

-400

-600

-1800

-1000

-1200

-1400

-2000

-1600

200

-1200

-1800

-1400

0

-200

-800

-400

-600

-1800

-1000

-1200

-1400

-2000

-1600

200

-1200

-1800

-1400

§ ̈¦55

§ ̈¦55

§ ̈¦55

§ ̈¦12

§ ̈¦10 § ̈¦10

61

61

61

98

98

.71

.190

.190

.51

.51

0 10 20 KILOMETERS

0 10 20 MILES

92°00' 91°45' 91°30' 91°15' 91°00' 90°45' 90°30'

31°15'31°00'30°45'30°30'30°15'

Figure 3. Map showing simulated altitude of the top of the “1,500-foot” sand of the Baton Rouge area in southeastern Louisiana and southwestern M
LakeMaurepas

MISSISSIPPILOUISIANA

WEST

FELICIANA EAST FELICIANA ST. HELENA

TANGIPAHOA LIVINGSTON EAST BATON ROUGE

WEST

BATON

ROUGE

POINTE

COUPEE

IBERVILLE

ST. MARTIN

ASCENSION

ST. LANDRY

AVOYELLES

CONCORDIA

WILKINSON

AMITE

PIKE

BATONROUGE

BREAUX BRIDGE

GONZALES

HAMMOND

ADAMS FRANKLIN LINCOLN

Figure 4. Simulated thickness of the "1,500-foot" sand of the Baton Rouge area in southeastern Louisiana andsouthwestern Mississippi.

Base map modified from Louisiana Oil Spill Coordinator, Office of theGovernor, Louisiana GIS CD: A Digital Map of the State, Version 2.0Map Projection: North American Datum of 1983, Universal Transverse Mercator Zone 15

§ ̈¦55

§ ̈¦55

§ ̈¦55

§ ̈¦12

§ ̈¦10

§ ̈¦10

61

61

61

98

98

.71

.190

.190

.51

.51

0 10 20 KILOMETERS

0 10 20 MILES

92°00' 91°45' 91°30' 91°15' 91°00' 90°45' 90°30'

31°15'31°00'30°45'30°30'30°15'

Figure 4. Map showing simulated thickness of the “1,500-foot” sand of the Baton Rouge area in southeastern Louisiana and southwestern Mississip
Lake Maurepas MISSISSIPPI LOUISIANA W. FELICIANA E. FELICIANA ST. HELENA TANGIPAHOA LIVINGSTON E. BATON ROUGE W. BATON ROUGE POINTE COUPEE IBERVILLE ST. MARTIN ASCENSION ST. LANDRY AVOYELLES CONCORDIA WILKINSON AMITE PIKE BATON ROUGE BREAUX BRIDGE GONZALES HAMMOND ADAMS FRANKLIN LINCOLN 

Figure 5. Simulated altitude of the top of the "2,000-foot" sand of the Baton Rouge area in southeastern Louisianaand southwestern Mississippi.

Base map modified from Louisiana Oil Spill Coordinator, Office of theGovernor, Louisiana GIS CD: A Digital Map of the State, Version 2.0Map Projection: North American Datum of 1983, Universal Transverse Mercator Zone 15

0

-400

-600

-200

-800

-1400

-1600

-1000

-2200

-2400

-1800

-2000

-2600

-1200

200

-2800

-3000

-2400

-2800

0

-400

-600

-200

-800

-1400

-1600

-1000

-2200

-2400

-1800

-2000

-2600

-1200

200

-2800

-3000

-2400

-2800

§ ̈¦55

§ ̈¦55

§ ̈¦55

§ ̈¦12

§ ̈¦10

§ ̈¦10

61

61

61

98

98

.71

.190

.190

.51

.51

0 10 20 KILOMETERS

0 10 20 MILES

92°00' 91°45' 91°30' 91°15' 91°00' 90°45' 90°30'

31°15'31°00'30°45'30°30'30°15'

Figure 5. Map showing simulated altitude of the top of the “2,000-foot” sand of the Baton Rouge area in southeastern Louisiana and southwestern M
Lake Maurepas

MISSISSIPPILOUISIANA

WEST

FELICIANA EAST FELICIANA ST. HELENA

TANGIPAHOA LIVINGSTON EAST BATON ROUGE

WEST

BATON

ROUGE

POINTE

COUPEE

IBERVILLE

ST. MARTIN

ASCENSION

ST. LANDRY

AVOYELLES

CONCORDIA

WILKINSON

AMITE

PIKE

BATONROUGE

BREAUX BRIDGE

GONZALES

HAMMOND

ADAMS FRANKLIN LINCOLN 

Figure 6. Simulated thickness of the "2,000-foot sand of the Baton Rouge area in southeastern Louisianaand southwestern Mississippi.

Base map modified from Louisiana Oil Spill Coordinator, Office of theGovernor, Louisiana GIS CD: A Digital Map of the State, Version 2.0Map Projection: North American Datum of 1983, Universal Transverse Mercator Zone 15

§ ̈¦55

§ ̈¦55

§ ̈¦55

§ ̈¦12

§ ̈¦10

§ ̈¦10

61

61

61

98

98

.71

.190

.190

.51

.51

0 10 20 KILOMETERS

0 10 20 MILES

92°00' 91°45' 91°30' 91°15' 91°00' 90°45' 90°30'

31°15'31°00'30°45'30°30'30°15'

Figure 6. Map showing simulated thickness of the “2,000-foot” sand of the Baton Rouge area in southeastern Louisiana and southwestern Mississip
12 Simulation of Groundwater Flow in the “1,500-Foot” Sand and “2,000-Foot” Sand in the Baton Rouge Area, Louisiana

Occurrence and Movement of Saltwater

Groundwater investigations conducted during the 1960s 

identified a freshwater-saltwater interface located near the 

Baton Rouge Fault (Morgan and Winner, 1964; Rollo, 1969). 

Prior to groundwater development in the 1940s, freshwater 

flowed from recharge areas in Mississippi southward toward 

the fault, then upward to where it discharged at springs. 

This groundwater-flow pattern caused aquifers north of 

the fault to generally contain freshwater whereas they may 

contain saltwater south of the fault. Exceptions exist because 

freshwater is also found in some areas south of the Baton 

Rouge fault, such as West Baton Rouge Parish, where both the 

“1,500-foot” sand and “2,000-foot” sand contain freshwater 

areas. In the Baton Rouge area, the base of freshwater is 

between about 1,100 and 2,600 ft deeper on the north side of 

the fault than it is on the south side of the fault. The altitude 

of the base of freshwater ranges between about -1,500 ft and 

-3,500 ft north of the fault, and between -200 and -1,000 ft 

south of the fault (Smoot, 1988; Griffith, 2003). Aquifer tests 

conducted across the fault in the vicinity of Baton Rouge have 

indicated that the fault acts as a leaky barrier that impedes 

groundwater flow (Whiteman, 1979).

Large groundwater withdrawals north of the fault in 

Baton Rouge, primarily for public supply and industrial use, 

have lowered water levels and created gradients conducive 

to the movement of saltwater from the south side of the fault 

into previously freshwater areas north of the fault (Whiteman, 

1979; Tomaszewski, 1996). Except in the deeper “2,800-foot” 

sand and Catahoula aquifers, most saltwater currently north of 

the fault moved in response to the groundwater withdrawals 

in the Baton Rouge area. If groundwater withdrawals in the 

Baton Rouge area continue at rates similar to the historical 

rates, saltwater encroachment will probably continue to occur 

(Tomaszewski, 1996). 

Based on historical chloride-concentration data collected 

through 2005, saltwater and water containing chloride 

concentrations above background levels (10 mg/L or less) 

have been detected in all aquifers in the Baton Rouge area 

except the “800-foot” sand and “1,700-foot” sand (Lovelace, 

2007). Analyses of chloride-concentration measurements 

collected from wells prior to 1992 indicated that saltwater 

encroachment had occurred in the “600-foot” sand, “800-

foot” sand, “1,000-foot” sand, “1,500-foot” sand, and “2,000-

foot” sand (Morgan and Winner, 1964; Whiteman, 1979; 

Tomaszewski, 1996). Chloride concentration data collected 

from 1993 to 2003 indicated that chloride concentrations 

increased in the “1,000-foot” sand, “1,200-foot” sand, 

“1,500-foot” sand, “2,000-foot” sand, “2,400-foot” sand, and 

“2,800-foot” sand (Lovelace, 2007). Chloride concentrations 

measured during 2004 to 2005 exceeded background levels in 

one or more water samples from wells in East and West Baton 

Rouge Parishes north of the fault screened in the “600-foot” 

sand, “1,000-foot” sand, “1,200-foot” sand, “1,500-foot” 

sand, “1,700-foot” sand, “2,000-foot” sand, “2,400-foot” 

sand, and “2,800-foot” sand. Comparison of the 2004–5 data 

with historical data indicated that chloride concentrations 

north of the Baton Rouge Fault were increasing in all of 

those aquifers except the “1,700-foot” sand (Lovelace, 2007). 

Within the “2,000-foot” sand, chloride concentrations of about 

3,500 mg/L have been measured 3 mi east of the Mississippi 

River and about 500 feet north of the Baton Rouge Fault in 

observation well EB-781.

Hydrogeologic Framework

A three-dimensional hydrogeologic framework was 

constructed to delineate the extents and thicknesses of aquifers 

and confining units in the study area. The hydrogeologic 

framework represents the entire sequence of aquifers and 

confining units in the Southern Hills regional aquifer system 

above the Catahoula-equivalent aquifer system (table 2). 

The Catahoula-equivalent aquifer system was omitted from 

the framework because in the study area it contains mostly 

saltwater and is little used, and few data from stratigraphic 

control wells (fig. 1) were available to delineate the extent and 

thickness of the aquifers in the system. The hydrogeologic 

framework defines the top altitudes and thicknesses of the 

hydrogeologic units in the groundwater model documented 

in this report. Although the groundwater model was primarily 

developed to address concerns about declining groundwater 

levels in the “1,500-foot” sand and “2,000-foot” sand and 

saltwater encroachment in the “2,000-foot” sand, simulating 

groundwater flow in overlying and underlying aquifers 

improved the simulation of water-levels in the “1,500-foot” 

sand and “2,000-foot” sand aquifers. 

The top of the hydrogeologic framework is the ground 

surface and the base is the bottom of the “2,800-foot” sand. 

The aquifers and confining units are represented by 22 layers, 

numbered from the top toward the bottom (table 1). Layers 1, 

3, 5, 7, 9–18, 20, and 22 make up the aquifer layers. Layers 

2, 4, 6, 8, 19, and 21 make up confining units that separate 

the aquifer layers. Layers 1 and 3 represent multiple aquifers 

that have similar hydraulic characteristics and are likely 

interconnected. Layer 1 represents the Mississippi River 

alluvial aquifer, shallow sands, upland terrace aquifer, and 

the “400-foot” sand, “600-foot” sand, and “800-foot” sand. 

Layer 3 includes the “1,000-foot” sand and “1,200-foot” sand. 

The “2,000-foot” sand is represented by 10 layers numbered 

9 through 18. 

The location and thickness of aquifer and confining-unit 

layers in the hydrogeologic framework were specified on 

the basis of lithologic contacts at 192 stratigraphic control 

wells (fig. 1) and the previous work of Griffith (2003). About 

3,200 lithologic contacts were interpreted from borehole 

resistivity, spontaneous potential, nuclear, and (or) drillers’ 

lithologic logs on file at the USGS office in Baton Rouge 

for the stratigraphic control wells. Generally, aquifers and 

confining units less than 10 ft thick were not represented by 

discrete layers in the hydrogeologic framework.
Groundwater Withdrawals 13

Raster arrays of the top altitudes and thicknesses of 

all hydrogeologic framework layers were constructed with 

the VIEWLOG interpolation tool (Viewlog Systems, 2004). 

Hydrogeologic contacts interpreted from logs outside the study 

area were used to specify the hydrogeologic unit altitudes 

along the boundary of the study area. The hydrogeologic unit 

top altitudes interpolated with VIEWLOG were manually 

smoothed in areas where data were unavailable (generally 

near the margin of the study area). Contour maps illustrate the 

top altitudes and thicknesses of the hydrogeologic framework 

layers that represent the “1,500-foot” sand and the “2,000-

foot” sand (figs. 3, 4, 5, and 6).

The location and correlation of hydrogeologic units near 

the Baton Rouge Fault in the study area are uncertain (Griffith, 

2003), and the apparent displacement of units may be due 

to differences in sediment deposition on either side of the 

fault (Smith, 1979). By using previous reports (Durham and 

Peeples, 1956; Murray, 1961; Winner and others, 1968; Rollo, 

1969; Whiteman, 1979; Smith, 1979; Hanor, 1982; Smoot, 

1988; McCulloh, 1991; Griffith, 2003, 2006) and the lithologic 

contacts, separate representations of hydrogeologic unit layer 

top altitudes and thicknesses were generated for areas north 

and south of the Baton Rouge Fault. The separate north and 

south representations for each layer were linked at the fault to 

form a single representation for each layer so that differences 

in layer top altitudes across the Baton Rouge Fault represent 

the vertical fault displacement (fig. 7).

Groundwater Withdrawals

Withdrawals from 605 wells in Louisiana for the period 

of 1940 to 2007 were compiled from the digital databases 

and paper records of the USGS and the Commission. Most 

of these withdrawal records were reported by personnel at 

public supply and industrial facilities. Withdrawal rates for 

wells or facilities inventoried on a 5-year basis from 1960 to 

2005 were obtained from USGS water-use records. Sporadic 

annual withdrawal data from 1940 to 1975 for some facilities 

in the Baton Rouge area also were obtained from USGS 

water-use records. Annual withdrawal rates from wells in 

East and West Baton Rouge, East and West Feliciana, and 

Pointe Coupee Parishes from 1975 to 2007 were obtained 

from the Commission water-use database. Annual withdrawal 

rates from about 1988 to 2007 for facilities that withdraw 

an average of 1 Mgal/d or greater and are located in other 

parishes in the study area were obtained from USGS wateruse records. Groundwater withdrawals from all aquifers in 

the study area averaged 168.22 Mgal/d during 2007. 

Where only facility-specific withdrawals were available, 

well-specific rates were estimated by disaggregating the 

total withdrawal rate reported for the facility. Generally the 

disaggregated well-specific withdrawal rates were estimated 

by evenly distributing the withdrawals reported for each 

facility among the active wells at the respective facility. 

Aquifer hydrogeologic units

Layer 1—Mississippi River alluvial aquifer, shallow sands,

 upland terrace aquifer, and the “400-foot,” “600-foot,” and

 “800-foot” sands

Layer 5—“1,500-foot” sand

Layer 3—“1,000-foot” and “1,200-foot” sands

Layer 7—“1,700-foot” sand

Layers 9 to 18—"2,000-foot" sand

Layer 20—"2,400-foot" sand

Layer 22—"2,800-foot" sand

Fault

Confining hydrogeologic units

NORTH

SOUTH

Baton Rouge

DENHAM SPRINGSSCOTTLANDVILLE FAULT

BATON R0UGEFAULT

EXPLANATION

NOT TO SCALE

Figure 7. Conceptual offset of hydrogeologic 

units at faults in the Baton Rouge area, 

southeastern Louisiana.
14 Simulation of Groundwater Flow in the “1,500-Foot” Sand and “2,000-Foot” Sand in the Baton Rouge Area, Louisiana

Well registration, construction, and plugging or abandonment 

data from USGS, DOTD, Commission, and Louisiana 

Department of Natural Resources (DNR) databases were used 

to determine when specific wells were in use at the facilities 

where facility-specific withdrawals were reported. For some 

wells with intermittent data, annual withdrawals were estimated 

or interpolated to complete their pumpage records. In some 

cases, facilities were contacted to verify pumping rates and well 

activity during different periods.

Well-construction data including the borehole, screen, 

and casing diameters; screen intervals; pump depth; location; 

and land-surface altitude were obtained from USGS and 

State databases. Missing or inadequate information was 

estimated or adjusted by using ancillary information from 

topographic maps, well logs, the specifications of other nearby 

wells or wells with identical ownership, well schedules, 

and thickness data from the hydrogeologic framework. 

Some wells with inadequate well-construction information 

and probable withdrawal rates less than 0.01 Mgal/d were 

omitted. Wells with screen-interval records corresponding to 

confining-unit intervals in the hydrogeologic framework were 

assumed to be screened in aquifers and were assigned to the 

appropriate adjacent sand layer.

A graph of the withdrawals from the “400-foot,” “600-

foot,” “800-foot,” “1,000-foot,” “1,200-foot,” “1,500-foot,” 

“1,700-foot,” “2,000-foot,” “2,400-foot,” and “2,800-foot” 

sands, collectively referred to herein as the “Baton Rouge 

sands,” illustrates both increased total withdrawals and the 

withdrawal from deeper aquifers through time (fig. 8). Until the 

early 1950s, groundwater withdrawals were principally from 

the “400-foot” sand and the “600-foot” sand. Since that time, 

deeper aquifers such as the “1,200-foot” sand, “1,500-foot” 

sand, “2,000-foot” sand, “2,400-foot” sand, and “2,800-foot” 

sand have increasingly supplied most groundwater in the Baton 

Rouge area. In 2007, an estimated 180 Mgal/d were withdrawn 

from the Baton Rouge sands, including 23.7 Mgal/d from the 

“1,500-foot” sand and 25.3 Mgal/d from the “2,000-foot” sand. 

Withdrawals from other aquifers within the study area were 

37.7 Mgal/d. Industrial withdrawals, primarily in the Baton 

Rouge industrial district, accounted for 16.6 Mgal/d, or 66 

percent of the total water withdrawn from the “2,000-foot” 

sand during 2007. Figure 9 shows the average daily withdrawal 

rate during 2007 at wells screened in the “2,000-foot” sand and 

located at or near the Baton Rouge industrial district. 

Simulation of Groundwater Flow

and Movement of Saltwater

The modeling strategy was to initially construct a 

constant-density groundwater-flow model and calibrate the 

groundwater-flow model parameters to observed water levels 

throughout the aquifer system. Subsequently, the simulation 

of saltwater transport with a variable-density version of the 

groundwater-flow model was accomplished. Calibration of 

simulated concentrations to chloride concentrations observed 

in the Baton Rouge area required minor modification of some 

flow-model parameters and estimation of parameters that 

represented effective porosity and aquifer dispersivities. The 

highest observed chloride concentration north of the Baton 

Rouge Fault within the “2,000-foot” sand has been 3,500 

mg/L, implying that groundwater at that location has a density 

of about 62.71 pounds per cubic foot (lb/ft3), which is about 

0.45 percent greater than freshwater. Although the density of 

localized areas of brackish to saline groundwater (chloride 

concentration from 1,000 to 10,000 mg/L) may sufficiently 

contrast with adjacent fresher groundwater to affect flow in 

some areas, such as adjacent to the Baton Rouge Fault, density 

contrasts over larger areas are not thought to substantially 

affect regional groundwater flow. Because the constantdensity groundwater-flow code MODFLOW-2005 (Harbaugh, 

2005) can apportion specified pumpage withdrawals among 

multiple aquifers penetrated by a single well, which is 

important for simulating transient groundwater flow in the 

Baton Rouge area, it was used during the groundwater-flow 

model calibration process. After the groundwater-flow model 

had been calibrated, the optimal set of flow parameters and 

computed well fluxes were imported into the variable-density 

finite-difference code SEAWAT-2000 (Langevin and others, 

2003), hereinafter referred to as SEAWAT, which enabled 

simulation of saltwater transport. 

High concentrations of salt (sodium chloride) increase 

groundwater density and can affect the patterns and rates of 

groundwater flow if the density varies spatially. Although 

most chloride concentrations in the “2,000-foot” sand north 

of the Baton Rouge Fault are less than several hundred 

milligrams per liter, which is too low to substantially increase 

groundwater density, concentrations up to 3,500 mg/L near 

the north side of the fault have been observed and are likely 

higher in observed locations closer to the source of the salt. 

The effect of density contrasts on groundwater flow was 

simulated with the variable-density finite-difference code 

SEAWAT (Langevin and others, 2003), which integrates 

MODFLOW-2000 (Harbaugh and others, 2000) with 

MT3DMS (Zheng and Wang, 1999), a code that simulates 

solute transport. Because chloride is a conservative solute, 

chemical reactions were not simulated in the SEAWAT 

transport model. Temperature gradients within the Southern 

Hills aquifer system north of the Baton Rouge Fault are not 

substantial and are not known to affect groundwater flow 

within the “1,500-foot” sand and “2,000-foot” sand. The 

groundwater system was therefore modeled as isothermal, and 

temperature effects on groundwater density and viscosity were 

not simulated.

The model-inputs for SEAWAT and MODFLOW-2005 

are generally similar, but the multi-node well package, MNW2 

(Konikow and others, 2009), was not available with SEAWAT. 

Because the apportionment of withdrawals among aquifers 

from wells tapping multiple aquifers was important for 

groundwater-flow model calibration, the MODFLOW-2005 

code was used during the parameter estimation process. 

After the flow-model parameters had been optimized, an 

equivalent WEL package (Harbaugh and others, 2000) 
Figure 8. Estimated withdrawals from the Baton Rouge sands, 1940-2007.

Year

1940 1950 1960 1970 1980 1990 2

Annual withdrawal rate, in million gallons per day

0

10203040

50

"400-foot" sand"600-foot" sand"800-foot" sand"1,000-foot" sand"1,200-foot" sand"1,500-foot" sand"1,700-foot" sand"2,000-foot" sand"2,400-foot" sand"2,800-foot" sand

EXPLANATION

Figure 8. Graph showing estimated withdrawals from the Baton Rouge sands, 1940–2007
Mississippi River

Base map modified from Louisiana Oil Spill Coordinator, Office of theGovernor, Louisiana GIS CD: A Digital Map of the State, Version 2.0Map Projection: North American Datum of 1983, Universal Transverse Mercator Zone 15

Figure 9. Average daily withdrawal rate during 2007 at wells screened in the “2,000-foot” sand of theBaton Rouge area and located at or near the Baton Rouge industrial district in southeastern Louisiana.

0 0.5 1 2 MILES

0 0.5 1 2 KILOMETERS

EB-1323

EB-1317

EB-1313

EB-1309

EB-1253

EB-1227

EB-1151

EB-1150

EB-1030

EB- 962

EB- 884

EB- 878

EB- 874

EB- 856

EB- 855

EB- 851

EB- 814

EB- 810

EB- 785

EB- 774

EB- 737

EB- 733

EB- 656

EB- 630

EB- 587

EB- 151

EB- 788

EB- 722

75706560555045403530252080 15 20 25 30 35 40 45 50 55 60 65 70 75

§ ̈¦12

§ ̈¦110

§ ̈¦110

§ ̈¦10

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§ ̈¦10

61

67

946

986

986

76

73 1

1

61

61

30

37

.190

.90

.90

91°12'30" 91°10'00" 91°07'30" 91°05'00"

30°30'00"

30°27'30"

30°25'00"

Figure 9. Average daily withdrawal rate during 2007 at wells screened in the “2,000-foot” sand of the Baton Rouge area and located at or near the Bdistrict in southeastern Louisiana.
Simulation of Groundwater Flowand Movement of Saltwater 17

input was generated with MNW2 by using the parameter 

values optimized for the MODFLOW-2005 simulation. 

This computed WEL Package input was subsequently 

used to specify layer-variable groundwater fluxes for each 

withdrawal well in the SEAWAT simulation.

Conceptual Model for Saltwater Transport

Groundwater north of the Baton Rouge Fault 

is assumed to have been fresh prior to groundwater 

development. Groundwater entering the model domain in 

areas north of the Baton Rouge Fault is considered “fresh” 

with a zero salt concentration. Because sediments south 

of the Baton Rouge Fault are displaced downward, the 

source of saltwater south of the Baton Rouge Fault is likely 

within the “1,700-foot” sand, where its altitude is similar 

to that of the “2,000-foot” sand north of the fault. Although 

chloride concentrations south of the Baton Rouge Fault 

have been observed to vary spatially and some areas of 

freshwater are known to occur, a simple representation of 

the saltwater source is preferred to model transport north 

of the fault. This source was specified within the finitedifference cells adjacent to the south side of the fault that 

connect to the “2,000-foot” sand on the north side of the 

fault. As groundwater withdrawals cause aquifer water levels 

to decline north of the Baton Rouge Fault, higher pressure 

saltwater south of the fault seeps northward across the 

hydraulically resistive fault. 

Equations of Groundwater Flow and Transport

Whereas MODFLOW-2005 solves the constant-density 

groundwater-flow equation (Harbaugh, 2005), the SEAWAT 

(Langevin and others, 2003) code iteratively solves 

equations that represent variable-density groundwater flow 

and advective-dispersive mass transport. These equations are 

succinctly presented below, and the interested reader may 

refer to the referenced model-code documentation for further 

details.

Groundwater systems without significant chemical 

reactions or temperature gradients are governed by equations 

for variable-density flow:

−∇ ⋅ + = ∂

∂

+

∂

∂

∂

∂ ( ) ρ ρ ρ θ  ρ

q q S

P

t C

C

t s p (1)

and mass transport:

 

∂ 

∂

= ∇⋅ ∇ ( ) − ∇⋅





 



 − C

t

D C q C

q

s C

s



θ θ (2)

where

∇

ρ

ρ

θ



q

S

P

t

C

q

s

D

Cs

p

is the gradient operator,

is fluid density [ML-3],

is specific discharge [LT-1],

is source or sink fluid density [ML-3],

is flow rate per unit volume representing 

 sources or sinks [T-1],

is specific storage in pressure terms [M-1LT2],

is fluid pressure [ML-1T-2], 

 is time [T],

 is effective porosity,

 is solute concentration [ML-3],

is the dispersion coefficient [L2T-1], and

 is source or sink solute concentration [ML-3]. 

These groundwater flow and transport equations are coupled 

by the specific discharge ( q



) and concentration ( C ) terms. 

The dependence of fluid density on concentration can be 

approximated by a linear equation of state: 

ρ ρ ρ = +

∂

∂ f C

C 

(3)

where ρf is the density of freshwater. The SEAWAT (Langevin 

and others, 2003) code iteratively solves finite-difference 

versions of these variable-density flow and mass transport 

equations for every transport time step, thereby coupling the 

flow and transport equations. Because this solute-transport 

problem was advection-dominated, the advection-dispersion 

(equation 2) was numerically solved with the third-order 

total-variation-diminishing (TVD) scheme to reduce numerical 

dispersion (Zheng and Wang, 1999).

Spatial Discretization

The three-dimensional finite-difference groundwater model 

grid (fig. 10) was designed with variable grid-cell spacing to 

(1) provide sufficient spatial resolution in a 25-mi2 area (the 

detailed model area) where significant saltwater migration either 

has occurred or could occur in the future (fig. 11), (2) locate 

model boundaries sufficiently far from the detailed model area 

to minimize the effects of boundary conditions on simulated 

heads in the area, and (3) limit execution times to enable 

numerous model simulations to be conducted during calibration 

through parameter estimation. The total area encompassed 

by the model domain is 6,529.23 mi2 and contains 158,950 

active finite difference cells. The areas encompassed by the 

finite-difference cells range from 2.5x105 ft2 (5.74 acres) in the 

detailed model area to a maximum of 3x109 ft2 (68,870 acres) at 

the northwest corner of the model domain.

The variable grid spacing creates a large finite-differencecell aspect ratio, or differences in the north-south versus eastwest dimensions, in some areas of the model grid. Although 

numerical inaccuracies can occur in such areas (de Marsily, 

1986), they are located in areas of the model grid where high 

computational accuracy is not required.

∇

ρ

ρ

θ



q

S

P

t

C

q

s

D

Cs

p
MISSISSIPPI LOUISIANA WEST FELICIANA EAST FELICIANA ST. HELENA TANGIPAHOA LIVINGSTON EAST BATON ROUGE WEST BATON ROUGE POINTE COUPEE IBERVILLE ST. MARTIN ASCENSION ST. LANDRY AVOYELLES CONCORDIA WILKINSON AMITE PIKE BATON ROUGE BREAUX BRIDGE GONZALES HAMMOND ADAMS FRANKLIN LINCOLN Detailed model area (see fig. 11) 

8

Perimeter of model domain

Figure 10. The model finite-difference grid and locations of the horizontal flow barrier in the "2,000-foot" sand of theBaton Rouge area and simulated groundwater-withdrawal wells in southeastern Louisiana and southwestern Mississip

Base map modified from Louisiana Oil Spill Coordinator, Office of theGovernor, Louisiana GIS CD: A Digital Map of the State, Version 2.0Map Projection: NAD 1983, UTM Zone 15

5

10

15

20

8085 5 10 75 80 85

1

1

0 10 20 KILOMETERS

0 10 20 MILES

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92°00' 91°45' 91°30' 91°15' 91°00' 90°45' 90°30'

31°15'31°00'30°45'30°30'30°15'

Figure 10. Map showing the model finite-difference grid and locations of the horizontal flow barrier in the “2,000-foot” sand of the Baton Rouge area groundwater-withdrawal wells in southeastern Louisiana and southwestern Mississippi.
Mississippi River

25

3540

45

5055606570

7530

15 20 25 30 35 40 45 50 55 60 65 70

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EB-1293

"

"

"

"

"

EB - 807B

EB - 1028

EB - 781

EB - 1150 EB - 630

!

!

!

!

"

"

"

"

"

"

"

"

"

"

"

"

""

"

" "

"

"

EB - 944

EB - 794

WBR- 100B

EB - 806B

WBR- 147

WBR- 104

WBR- 37

WBR- 36

WBR- 5

EB - 946

EB - 327

EB - 323

EB - 301

EB - 299 EB - 298

EB - 146

EB - 117

EB - 28

EB - 782A

EB - 780A

WBR- 81

WBR- 100A

EB - 792A ! EB - 917

0 0.5 1 2 KILOMETERS0 0.5 1 2 MILES

Figure 11. The finite-difference grid and locations of horizontal flow barriers, simulated groundwater-withdrawal wells,and water-level observation wells in the "1,000-foot," "1,200-foot," "1,700-foot," "2,400-foot," and "2,800-foot" sandsof the Baton Rouge area in the detailed model area in southeastern Louisiana.

91°12'30" 91°10'00" 91°07'30"

30°30'00"30°27'30"30°25'00"

EB-1WBREB-7EB-9

70

EB-1

EB - 63

Base map modified from Louisiana Oil Spill Coordinator, Office of theGovernor, Louisiana GIS CD: A Digital Map of the State, Version 2.0Map Projection: North American Datum of 1983, Universal Transverse Mercator Zone 15

§ ̈¦12

§ ̈¦110

§ ̈¦110

§ ̈¦10

§ ̈¦10

§ ̈¦10

61

67

986

986

76

73

1

1

19

30

37

.190

Government Street pumping station

Lafayette Street pumping station

Figure 11. Map showing the finite-difference grid and locations of horizontal flow barriers, simulated groundwater-withdrawal wells, and water-leve“1,000-foot,” “1,200-foot,” “1,700-foot,” “2,400-foot,” and “2,800-foot” sands of the Baton Rouge area in the detailed model area in southeastern Louis
20 Simulation of Groundwater Flow in the “1,500-Foot” Sand and “2,000-Foot” Sand in the Baton Rouge Area, Louisiana

The model grid consists of 22 variable-thickness layers, 

each of which is a rectangular array containing 85 rows and

85 columns of finite-difference cells. For a subset of the model 

grid, 50 rows by 55 columns, horizontal grid spacing of 500 ft, 

and vertical layer spacing of about 20 ft within the “2,000-

foot” sand were specified within the 25-mi2 detailed model 

area based on preliminary simulations along two-dimensional 

cross-sections throughout the Baton Rouge area. Transport of 

saltwater was only simulated within the detailed model area to 

limit model execution times.

The altitude of the top of each model layer on the north 

side of the Baton Rouge Fault was assigned the altitude of 

the top of hydrogeologic framework unit represented by the 

layer (table 2). South of the Baton Rouge Fault, the altitudes 

of the top of each finite-difference layer do not correspond to 

the tops of hydrogeologic framework units and are constant 

along columns of finite-difference cells (that is, in the northsouth direction). This geometry facilitated simulation of flow 

across the Baton Rouge Fault and is explained in further 

detail in the “Internal Flow Package” section. The north-south 

cross-sectional view of the model grid (fig. 12) along column 

24 illustrates the variable thickness and “pinching out” of 

hydrogeologic units north of the Baton Rouge Fault, the offset 

of hydrogeologic units at the fault, and the discordance between 

hydrogeologic units and finite-difference cells south of the fault.

In comparison to numerical solution of the transient 

groundwater-flow equation, numerical solution of the transient 

solute-transport equation is computationally intensive. It is 

therefore generally desirable to limit the size of the numerical 

solute-transport problem when possible. Because simulation of 

saltwater encroachment is needed in only a small portion of the 

flow-model domain, a subset of the groundwater-flow model 

grid was identified for simulation of solute transport. This 

solute-transport domain is the previously described “detailed 

model area” that has a 500-ft cell spacing (fig. 11). Within this 

area, the solute transport equation was numerically solved in all 

model layers but was calibrated only for model layers 9 through 

18, which correspond to the “2,000-foot” sand on the north side 

of the Baton Rouge Fault.

Internal Flow Package

Offsets of hydrogeologic units at the Baton Rouge Fault 

may enable flow from stratigraphically younger hydrogeologic 

units south of the fault into stratigraphically older and 

horizontally juxtaposed units north of the fault. This flow 

between hydrogeologic units was simulated by using the 

Hydrogeologic-Unit Flow Package (HUF) (Anderman and Hill, 

2000), which represents the thickness of hydrogeologic units 

independently from that of the model finite-difference-grid-cell 

layers and calculates storage and intercell conductance terms for 

each cell from the hydraulic property distributions assigned to 

individual hydrogeologic units present within that cell. In this 

model, the altitudes of the finite-difference layers correspond to 

the tops and bottoms of the aquifers and intervening confining 

units defined in the hydrogeologic framework only for the 

portion of the model domain north of the Baton Rouge Fault 

(fig. 12). South of the Baton Rouge Fault, the finite-differencelayer altitudes within each model-grid column are “flat,” 

with altitudes equal to those at the simulated fault location. 

The finite-difference layers do not correspond to specific 

hydrogeologic units south of the Baton Rouge Fault. Because 

of this lack of correspondence, different hydrogeologic units 

are contained within each finite-difference layer on the north 

versus south sides of the fault, which allows simulated flow 

and transport within finite-difference layers between different 

aquifers that are horizontally juxtaposed at the fault. For 

example, the “1,700-foot” sand on the south side of the fault 

may be connected to the “2,000-foot” sand on the north side of 

the fault along some portions of the fault. Because of accuracy 

limitations in the digital representation of the hydrogeologic 

framework near the fault, this connection was initially not 

adequately represented within model finite-difference layers 

9 through 18 where saltwater is thought to cross the fault. To 

compensate for this limitation, a portion of the hydrogeologic 

unit layer which generally represents the confining unit above 

the “2,000-foot” sand was assigned to the overlying “1,700-

foot” sand in cells on the south side of the Baton Rouge fault 

between columns 38 and 48 (fig. 11).

Horizontal Flow Barriers

The resistance to groundwater flow at the Baton 

Rouge Fault as a consequence of sediment deformation 

and displacement of sedimentary layers was simulated with 

horizontal flow barriers (HFB) (Hsieh and Freckleton, 1993), 

which were specified along the vertical faces of cells closest 

to the fault. The decrease of each HFB to the conductance 

between adjacent model cells is specified with a “hydraulic 

characteristic” that is dimensionally equivalent to the hydraulic 

conductivity of the fault zone (in the direction perpendicular 

to the fault plane) divided by the width of the fault zone. 

HFBs were defined for all model layers that simulated aquifers 

except model layer 1.

Because the Baton Rouge Fault plane dips to the south at 

65 to 70 degrees, the fault dip was represented by offsetting 

the fault to the south in deeper framework layers. In layers 2 

through 7 the fault is represented 500 ft south of its surface 

location as indicated in figure 1, whereas in layers 8 through 

22 the fault is offset 1,000 ft south of its surface location.

Temporal Discretization

Because groundwater withdrawals from the Southern 

Hills aquifer system were relatively minor prior to about 

1940, a single steady-state stress period was used to simulate 

predevelopment conditions in the groundwater-flow system 

(table 3). Sixty-eight annual stress periods simulated the 

time from January 1, 1940, through December 31, 2007. 
Simulation of Groundwater Flowand Movement of Saltwater 21

Row

79

Row

16

11.35 miles

VERTICAL EXAGGERATION x10

Baton Rouge Fault

Figure 11. North-to-south cross section along model column 24 showing aquifers, confining units, and finite-difference

discretization. The location of column 24 is shown on figure 10. 2,700 feet

Layer 1

Layer 22

NORTH SOUTH

EXPLANATION

Cells other than red or blue contain

both aquifers and confining units

Aquifer

Confining unit

Figure 12. North-to-south cross section along model column 24 showing aquifers, confining units, and finite-difference discretization.

Table 3. Time discretization summary.

Stress

Period

Groundwater flow 

model solution Years represented

Flow time steps

per stress period in 

groundwater model

Transport time steps in 

solute-transport model

Duration of first

flow time step

1 Steady state 1900–39 1 1,790 Not applicable

2–69 Transient 1940–2007 5 14,761 33.4 days

70 Transient 2008–14 11 572 25.9 days

71 Transient 2015–16 11 2108–174 7.4 days

72 Transient 2017–27 11 2314 – 2,510 40.7 days

73 Transient 2028–47 11 2674 – 4,564 74.0 days

1

Total number of transport time steps simulating 1940 through 2007.

2

Number of transport time steps varied among scenarios 1 through 6.
22 Simulation of Groundwater Flow in the “1,500-Foot” Sand and “2,000-Foot” Sand in the Baton Rouge Area, Louisiana

Each stress period was discretized into five time steps that 

geometrically increase in duration by a factor of 1.4, such that 

the first time step of each stress period simulated about 33 

days. Hypothetical scenarios used four transient stress periods 

of various lengths that represented January 1, 2008, through 

December 31, 2047, each of which were discretized into 11 

time steps that also geometrically increase in duration by a 

factor of 1.4. The geometric progression of increasing time-step 

length provided good temporal discretization for simulation of 

transient changes in groundwater levels. In the solute-transport 

simulations, flow time steps are further subdivided into transport 

time steps (table 3). The number of transport time steps was 

computed internally on the basis of the flow velocity to maintain 

numerical stability and varied with the specified effective 

porosity and boundary conditions, such as specified groundwater 

withdrawal rates. Smaller transport time steps are required as the 

flow velocity increases.

Boundary Conditions

Boundary conditions were specified at the boundaries of 

the groundwater-flow system and within the model domain 

where they simulate groundwater-withdrawal wells. Three types 

of boundary conditions were specified for the groundwaterflow model: no-flow, specified head, and head-dependent flux. 

Constant concentration boundaries were also specified at the 

lateral boundaries of the solute-transport model.

No-Flow Boundaries

The north, east, and west sides and the top 21 layers of the 

southern side of the groundwater-flow model domain (fig. 10) 

are located where negligible groundwater flow is presumed to 

enter or exit the model domain and were accordingly considered 

no-flow boundaries. The southernmost row of the lowest model 

layer (row 85, layer 22) contains a specified-head boundary. The 

model-domain perimeter was located sufficiently far from the 

Baton Rouge area to minimize any effect on simulated water 

levels in that area from possible inaccuracy of the no-flow 

boundary-condition specification. The bottom model boundary 

at the base of layer 22 is also no-flow and corresponds to the top 

of a confining unit located above the Catahoula Formation (table 

2), which restricts vertical groundwater flow.

Specified-Head Boundaries

Water levels in the top model layer (layer 1), which 

represents the “400-foot” sand, “600-foot” sand, and “800-foot” 

sand, were specified with the Flow and Head Boundary (FHB) 

package (Leake and Lilly, 1997). Water-level distributions that 

represent the years 1944, 1980, 1984, 1990, 1998, 1999, and 

2004 were constructed from existing data. Water levels for times 

between these years were linearly interpolated for each model 

cell in the top layer. Steady-state (predevelopment) water levels 

were specified at the 1944 levels and water levels for times 

after 2004 were specified at the 2004 levels.

Water-level maps were digitized from previous reports: 

predevelopment (1944) (Kuniansky, 1989), 1980 (Martin and 

Whiteman, 1985; Boswell and Arthur, 1988), 1984 (Boswell 

and Arthur, 1988; Kuniansky, 1989), and 1990 (Tomaszewski, 

1996). The water-level map for 2004 was created by using 

water-level data collected by the USGS in cooperation with 

the Commission and DOTD. Water-level maps for 1998 and 

1999 were created by modification of the 1990 and 2004 

water-level maps using water-level data collected at selected 

wells during 1998 and 1999 to more accurately specify water 

levels near the Commission’s “connector well,” EB-1293 

(fig. 11), which was installed in 1998 and screened in the 

“800-foot” sand and “1,500-foot” sand (Dial and Cardwell, 

1999). Because little water-level change has occurred within 

the model domain in Mississippi, interpreted water levels in 

Mississippi during 1982 (Boswell and Arthur, 1988) were 

incorporated into all of the water-level maps used to specify 

transient water levels with the FHB package. Historic waterlevel observations were used to modify the predevelopment 

water-level map (Kuniansky, 1989) in some areas.

A specified-head boundary was defined for the 

southern boundary of the bottom model layer (row 85, layer 

22) to simulate groundwater underflow out of the model 

domain under predevelopment conditions. The water level 

specified for this boundary was estimated during the model 

calibration process.

Head-Dependent Flux Boundaries

The previously described groundwater withdrawals were 

simulated with the revised MNW2 package of MODFLOW 

(Konikow and others, 2009), which was used because the 

screen intervals of many withdrawal wells span multiple 

model layers. The MNW2 package computes a layer-bylayer distribution of withdrawal for each well based on the 

hydraulic conductivities and simulated water levels in each 

finite-difference cell connected to the simulated well-screen 

interval. For each annual stress period, the average daily 

withdrawal from each well was specified in cubic feet per day 

(ft3/d). In some wells, water may flow between model layers 

when the water level simulated in a connected finite-difference 

cell is less than that simulated in the well. The effects of 

turbulent-flow head losses near the well and flow through 

drilling-damaged formation, gravel pack, or the well screen 

were not simulated.

Groundwater withdrawals from wells screened in the top 

model layer (layer 1) corresponding to the Mississippi River 

alluvial aquifer, shallow sands, upland terrace aquifer, “400-

foot” sand, “600-foot” sand, and “800-foot” sand were not 

simulated because water levels in this layer were a specified 

boundary condition. One exception was the “connector well” 

(EB-1293) (Dial and Cardwell, 1999) near Baton Rouge 

Water Company’s Government Street pumping station (fig. 

11), where the water level for the top model layer (layer 1) 
Simulation of Groundwater Flowand Movement of Saltwater 23

was not specified. At this location, the MNW2 package was 

used to simulate flow through the “connector well,” which has 

screens that intersect the “800-foot” sand (model layer 1) and 

the “1,500-foot” sand (model layer 5). Exclusion of layer 1 

withdrawals, which accounted for about 49 Mgal/d in 2007, 

reduced the total withdrawals simulated in the model in 2007 to 

169 Mgal/d.

Specified-Concentration Boundaries

and Initial Conditions

Model cells within the solute-transport domain adjacent 

to the south side of the Baton Rouge Fault were specified as 

constant-concentration boundaries and therefore retain the 

initially assigned concentration throughout the simulation. 

The saltwater source was simulated on the south side of the 

Baton Rouge Fault in model-grid columns 30 through 70 

(fig. 11), corresponding to a 4-mile long region east of the 

Mississippi River. Within this region, the specified source 

concentration increases linearly from zero above model-grid 

layer 9 to a maximum at the base of layer 18. Model cells south 

of the Baton Rouge Fault and west of column 30 have zero 

concentration, corresponding to freshwater. Model-grid layers 

1 through 8 and 19 through 22 were specified with zero initial 

concentration. The concentration of simulated water flowing 

from surrounding areas into the solute-transport domain is 

specified as zero, corresponding to freshwater.

North of the Baton Rouge Fault, initial concentrations 

were specified as zero (corresponding to freshwater), and 

variable concentrations were simulated within the “detailed 

model area.” Simulated concentrations were normalized to 

the maximum specified source concentration, which was 

parameterized and estimated through model calibration to be 

10,000 mg/L of chloride.

Hydraulic-Property Distribution

The simulated horizontal hydraulic conductivities (Kh) 

within the hydrogeologic units that represent aquifers including 

the “400-foot” sand, “600-foot” sand, and “800-foot” sand; 

the “1,000-foot” sand and “1,200-foot” sand; the “1,700-foot” 

sand; the “2,400-foot” sand; and the “2,800-foot” sand were 

parameterized and estimated during model calibration. Areas 

within the “1,500-foot” sand and “1,700-foot” sand where 

those units “pinched out” were assigned the Kh that was used 

for all of the confining unit layers. Because the specified 

thickness of each of these hydrogeologic units is spatially 

variable, simulated transmissivity is spatially variable within 

each hydrogeologic unit. Variability of Kh within the “1,500-

foot” sand was simulated with three zones within which Kh was 

uniform. The spatial variation of Kh within the “2,000-foot” 

sand was interpolated by using pilot-points, as discussed in 

the following section. The vertical hydraulic conductivity (Kv) 

for each of the hydrogeologic units representing the confining 

units (model layers 2, 4, 6, 8, 19, and 21 on the north side of 

the Baton Rouge Fault, subsequently referred to as “confiningunit layers”) that separate the aquifer layers was estimated 

separately. Distinct spatial zones within the “2,400-foot” 

sand and the lowest confining unit (layer 21) were delineated 

north of the Baton Rouge fault between columns 32 and 70 

to simulate greater vertical conductance between the “2,800-

foot” sand and the “2,400-foot” sand and increase simulated 

water levels within the “2,400-foot” sand in the vicinity of 

the Government Street pumping station (fig. 11). The Kv of 

all aquifers and Kh of all confining units were specified with a 

single parameter for each of these two types of hydrogeologic 

units (table 4), which were relatively insensitive during initial 

parameter estimation, and subsequently fixed at reasonable 

values. Separate parameters were defined to represent specific 

storage (Ss) within each aquifer and confining-unit layer. 

Because water levels were specified for the top model layer 

(layer 1), Ss for model layer 1, representing the “400-foot” 

sand, “600-foot” sand, and “800-foot” sand, had no effect on 

simulated water levels.

Because of the importance of fault-zone conductance in 

controlling the transport of saltwater across the Baton Rouge 

Fault, distinct hydraulic characteristics were estimated for six 

lateral segments of the Baton Rouge Fault within the 10 model 

layers (layers 9–18) representing the “2,000-foot” sand north 

of the fault. A single hydraulic characteristic was estimated 

for each of the other model layers (layers 3, 5, 7, 20, and 22) 

that contain aquifers north of the fault. The calibrated values 

of the hydraulic properties for the groundwater-flow model are 

summarized in table 4.

Horizontal Interpolation of Hydraulic Conductivity

Heterogeneity of horizontal hydraulic conductivity within 

the “2,000-foot” sand was interpolated by estimating values 

at 142 “pilot points” (Doherty, 2003) that were specified at 

selected well locations where borehole lithologic and (or) 

electric logs were available to constrain the estimated values. 

The values of 142 parameters, each representing Kh at a 

single pilot point, were estimated during model calibration. 

The spatial interpolation between pilot-point locations was 

computed by ordinary kriging with an isotropic spherical 

variogram. The interpolated Kh distributions in the “2,000-

foot” sand were smoothed to avoid “over fitting” and to 

constrain estimated values within a reasonable range by 

using two “regularization” methods (Doherty, 2003). The 

first method minimized the difference between pilot-point 

parameter values among neighboring pilot points, whereas 

“prior information” (Hill and Tiedeman, 2007) was assigned 

to the pilot points in the second method. The second method 

was deemed more appropriate and used Kh values of 100 feet 

per day (ft/day) based on aquifer-pumping tests (Meyer and 

Turcan, 1955; Morgan, 1961, 1963). Parameter values at pilotpoint locations where an aquifer “pinched out” were fixed with 

Kh equal to 1 ft/day. The simulated hydraulic conductivity 

distribution resulting from the calibrated model parameters for 

the “2,000-foot” sand is illustrated in figure 13.
24 Simulation of Groundwater Flow in the “1,500-Foot” Sand and “2,000-Foot” Sand in the Baton Rouge Area, Louisiana

Table 4. Parameter values and sensitivities for the calibrated groundwater-flow model.

[ft, foot or feet; numbers in parameter names correspond to aquifer name or layer number (see table 2); 2k, “2,000-foot” sand. The fault hydraulic characteristic 

of the “2,000-foot” sand was specified for 6 fault segments: fault_2k, fault_2kmid, fault_2ka, fault_2kb, fault_2kc, and fault_2kw.]

Parameter type Units Parameter name Calibrated value Composite sensitivity

Specified head ft bound_head 121.0 1.80

Horizontal hydraulic conductivity ft/day k_468sand 30.0 fixed

k_1200sand 34.1 1.00

k_1500sand 240.0 0.07

k_1500neas 63.1 0.52

k_1500falt 149.0 0.04

k_1700sand 6.3 0.32

k_2000sand1 See figure 13 various

k_2400sand 10.0 0.38

k_2400sand2 40.0 fixed

k_2800sand 35.8 0.88

k_clay 1.E-5 fixed

Vertical hydraulic conductivity ft/day vk_sands 0.71 fixed

vk_2con 2.0E-5 0.14

vk_4con 1.3E-4 0.09

vk_6con 1.0E-5 0.07

vk_8con 2.1E-3 0.28

vk_19con 6.8E-4 0.26

vk_21con 1.2E-5 0.27

vk_gov 6.0E-4 fixed

Specific storage ft1 ss_sand 1.0E-5 0.09

ss_15 1.0E-6 0.04

ss_17 8.0E-6 0.14

ss_24 4.6E-6 0.07

ss_28 2.2E-6 0.06

ss_2ksand 5.5E-6 0.11

ss_clay2 1.1E-6 0.01

ss_clay4 1.8E-6 0.04

ss_clay6 1.0E-6 0.04

ss_clay8 5.2E-6 0.11

ss_clay19 1.2E-6 0.04

ss_clay21 1.0E-6 0.04

Fault hydraulic characteristic day1 fault_lay_3 1.2E-4 0.03

fault_ lay_5 9.4E-6 0.01

fault_ lay_7 1.4E-3 0.07

fault_2k 6.0E-4 0.02

fault_2kmid 8.0E-5 0.02

fault_2ka 3.0E-5 0.02

fault_2kb 3.0E-5 0.02

fault_2kc 3.0E-5 0.02

fault_2kw 1.0E-3 0.02

fault_ lay_20 1.0E-06 0.01

fault_ lay_22 4.2E-3 0.02

1

142 additional parameters represented horizontal hydraulic conductivity at pilot points in these aquifers.
Mississippi River

§ ̈¦12

§ ̈¦110

§ ̈¦110

§ ̈¦10

§ ̈¦10

§ ̈¦10

61 67

986

986

76

73

1

1

19

30

37

.190

WBR-97

WBR-33

EB-972

EB-939

EB-884

EB-855

EB-813

EB-807

EB-806

EB-794

EB-790

EB-789

EB-783

EB-778

EB-751

EB-674

EB-534

EB-514

EB-378

EB-133

WBR-128

WBR-111

WBR-104

WBR-103

WBR-100 EB-1253 EB-1252

EB-1028

P136823

91°12'30" 91°10'00" 91°07'30"

30°30'00"30°27'30"30°25'00"

0 0.5 1 2 KILOMETERS0 0.5 1 2 MILES

Figure 13. Pilot point locations and simulated horizontal hydraulic conductivity distribution within the "2,000-foot" sandof the Baton Rouge area in the detailed model area in southeastern Louisiana.

EB

Base map modified from Louisiana Oil Spill Coordinator, Office of theGovernor, Louisiana GIS CD: A Digital Map of the State, Version 2.0Map Projection: North American Datum of 1983, Universal Transverse Mercator Zone 15

Figure 13. Map showing pilot-point locations and the simulated horizontal hydraulic conductivity distribution within the “2,000-foot” sand of the Batodetailed model area in southeastern Louisiana.
26 Simulation of Groundwater Flow in the “1,500-Foot” Sand and “2,000-Foot” Sand in the Baton Rouge Area, Louisiana

Transport Properties

Solution of the advection-dispersion equation with 

SEAWAT required definition of the spatial distribution of the 

longitudinal, transverse, and vertical dispersivities, diffusion 

coefficient, and effective porosity of the aquifer system within 

the solute-transport domain. A homogeneous distribution 

for each of these properties was specified. The longitudinal, 

transverse, and vertical dispersivities and effective porosity 

were estimated during calibration of simulated-to-observed 

chloride concentrations. Because the simulated transport 

processes are dominated by advection, diffusion is negligible, 

and the diffusion coefficient was specified equal to zero. The 

calibrated values of these parameters are summarized in the 

“Estimated Parameter Values” section of this report.

Model Calibration

The groundwater-flow model was calibrated to obtain 

the best overall agreement between measured heads and their 

corresponding values simulated with MODFLOW. Although 

water-level measurements were used as observations in 

the model-calibration regression, groundwater fluxes were 

constrained by specification of well withdrawals. By using the 

parameter-estimation code PEST (Doherty, 2004), the values of 

185 parameters, which include 142 pilot-point parameters and 

the others summarized in table 4, were adjusted to minimize 

the objective function:

(4)

In equation 4, symbols in the first summation are 

associated with water levels:

H is the measured water level for observation k,

H′ is the simulated-equivalent water level for 

 observation k,

b is the vector of 185 model parameters,

ωk is the weight applied to water-level 

 observation k, and

N is the number of water-level observations 

 (3,612).

Symbols in the second summation are associated with the 

“prior information” equations used for the regularization 

previously described in the “Horizontal Interpolation of 

Hydraulic Conductivity” section of this report: Pi is the ith 

prior estimate, P’i is the ith simulated value, ωi is the weight 

applied to the ith prior estimate, and NPR is the number of 

prior equations used to regularize the Kh distributions specified 

for the “2,000-foot” sand in the regression, which equaled 138.

( ) ( )

2

1

2 3,612

1

∑ ' ( ) ∑ ' ( ) = =

− + −

NPR

i

i i i i

k

ωkHk ωkH k b ω P ω P b

Calibration Dataset

The model calibration dataset consisted of observations 

of groundwater levels, connector-well flow, and chloride 

concentrations. PEST was used to calibrate the water levels 

simulated with the constant-density MODFLOW model to 

observed water-levels. The observed borehole flow through 

the “connector well” (fig. 11) was compared to the value 

simulated for the time of the observation, which assisted 

manual calibration of the Kh specified in the top model layer. 

Observations of chloride concentrations were used to calibrate 

the transport model parameters. The flow model was calibrated 

through parameter estimation with PEST whereas the transport 

model was manually calibrated through trial and error. 

Water-Level Observations

A total of 4,857 water levels measured during the period 

between 1940 and 2011 from 161 wells in Louisiana were 

utilized for the groundwater-flow model. These measurements 

were from wells with at least six annual measurements, 

and only one measurement per year from any well was 

incorporated into the calibration database. About 74 percent 

(3,612) of these measurements from 137 wells that were 

measured before 2008 in aquifers beneath the “800-foot” 

sand were used to estimate parameters in the flow-model 

calibration. About 21 percent (1,012) was used to evaluate the 

accuracy of transient water levels specified in the top model 

layer. The remaining 5 percent (233) that was measured during 

the period from 2008 through 2011 in aquifers beneath the 

“800-foot” sand were used to evaluate model fit during that 

period. In locations where multiple wells with overlapping 

periods of record exist, wells with the longest periods of 

continuous water-level record generally were selected 

for the compilation. Measured water-level altitudes were 

between 248 and -292 ft. Measured water levels from the 

deeper observation wells used for estimation of flow-model 

parameters were between 215 and -292 ft, a range of 507 ft.

Well location and construction information from USGS, 

DOTD, and DNR records were used to specify the screen 

intervals and locations of the observation wells. Water-level 

observations from wells screened within the “400-foot” sand, 

“600-foot” sand, and “800-foot” sand were assigned zero 

weights because water levels within layer 1 were specified 

throughout the simulation. Although effectively removed from 

the parameter-estimation regression, these observations were 

retained in the calibration dataset for evaluation of the waterlevel specification accuracy within layer 1.

Most (4,068) water-level observations were measured 

in wells with screen intervals corresponding to a single 

model layer, but 789 observations were measured in wells 

with either long or multiple screens that correspond to more 

than one model layer. In the latter cases, the measured water 

levels represent a composite of the actual head conditions 

in the various aquifer-depth intervals in which the well is 

screened. The majority of these multilayer observations were 
Model Calibration 27

measured in wells screened in the “2,000-foot” sand, which is 

represented by 10 model layers with identical Kh distributions. 

The composite water level simulated for each multilayer well 

was computed by averaging the water levels simulated in all 

the model layers intersected by the well screen.

Because of the paucity of water level measurements 

within the “2,400-foot” sand in the Baton Rouge area, 

several solitary water level measurements documented by 

Tomaszewski and Accardo (2004) that were not included in 

the water-level observation during the parameter-estimation 

regression were subsequently utilized to manually calibrate 

water levels within that sand.

Wellbore-Flow Observation

Following installation and initial development of well 

EB-1293, which is the “connector well” (fig. 11) providing a 

conduit between the “800-foot” sand and “1,500-foot” sand, 

a flow rate of about 475 gallons per minute (gpm) from the 

“800-foot” sand to the “1,500-foot” sand was measured with 

a calibrated flow meter during December 1998 (Dial and 

Cardwell, 1999). The simulated flow through the “connector 

well” was fitted to the measured flow by adjusting the Kh

for model layer 1, which represents the “400-foot” sand, 

“600-foot” sand, and “800-foot” sand. Because further well 

development was conducted before the well was officially 

placed in service on April 6, 1999, it is possible that the 

ambient flow though the “connector well” since that time 

has been greater than the initial measurement. Multiple 

measurements of water levels in EB-1293 were also used for 

model calibration with PEST. 

Concentration Observations 

Two hundred eighty-three chloride-concentration 

observations from 16 wells within the “2,000-foot” sand were 

compiled from the USGS National Water Information System 

(NWIS) (U.S. Geological Survey, 2013) for calibration of the 

transport simulation. Five wells (EB-781, EB-1028, EB-1150, 

EB-630, and EB-807B; fig. 11) were located in the area of 

saltwater encroachment and had sufficiently long periods of 

record to be useful calibration targets.

Water-Level Observation Errors

Quantification of the various sources of error that 

contribute to the uncertainty of water-level measurements 

is desirable for calculation of the measurement weights in 

the regression equations used during model calibration. The 

sources of water-level measurement error in the calibration 

dataset were categorized as follows: (1) errors in the measured 

location and altitude of the observation-well measurement 

point and (2) errors in depth-to-water measurements. The 

altitudes of the measurement points of most water-level 

observation wells were interpolated from local USGS 

7.5-minute quadrangle topographic maps that have a 5-ft 

contour interval. The uncertainty of each altitude determined 

from these maps is within one half of the contour interval, or 

2.5 ft. Most depth-to-water level measurements used for model 

calibration were made by using steel or electrical tapes with 

an estimated accuracy of 0.01 ft. Water levels at flowing wells, 

where the water level was above land surface, were measured 

using calibrated pressure gages with an estimated accuracy of 

0.1 ft. Because the vast majority of water-level measurements 

used in the model were from wells in the Baton Rouge area 

which have not flowed since the 1940s, the average error 

associated with the depth-to-water measurements is assumed 

to be 0.01 ft. Transient water-level fluctuations caused by 

processes not simulated by the model, such as atmospheric 

pressure fluctuations, earth tides, or unreported groundwater 

withdrawals are termed “nonsimulated transient-stress errors.” 

Although it can be advantageous to estimate the “error” 

associated with such nonsimulated transient stresses to 

appropriately weight measurements from “noisy” water-level 

records, the magnitude of these errors was not quantified. The 

total error for water-level measurements was estimated as 

the sum of errors in measurement-point altitude and depth to 

water, which is about 2.5 ft.

Weights

The uncertainties associated with measurement of wellhead altitudes and the depth to water in the observation well 

were converted to variances and summed to obtain an error 

variance associated with each water-level measurement (Hill 

and Tiedeman, 2007). The inverse of this composite variance 

can be used to assign a measurement weight in the modelcalibration regression. Because all well-head altitude and 

depth-to-water measurement errors in the calibration dataset 

were deemed to be similar, the resulting observation weights 

were normalized for observations used in the regression. 

Because well-withdrawal data from 2007 was extrapolated 

to simulate the period from 2008 through 2011, waterlevel measurements from that period are likely affected by 

withdrawals that are not accurately simulated by the model (a 

“nonsimulated transient stress error”). Accordingly, waterlevel observations from the period 2008 through 2011 were 

assigned zero weight, as were observations corresponding 

to specified head boundaries. Because PEST automatically 

adjusts the weight of the set of prior information equations 

with respect to the set of observations during the parameterestimation process, the relative weight assigned to the set of 

prior information equations versus the set of observations was 

not important.

Calibration Assessment

The quality of the model calibration was evaluated on the 

basis of the reasonableness of the estimated parameter values, 

the overall fit of simulated-to-observed water levels measured 
28 Simulation of Groundwater Flow in the “1,500-Foot” Sand and “2,000-Foot” Sand in the Baton Rouge Area, Louisiana

by the objective function, the fit of simulated-to-observed 

chloride values, and the lack of bias in the distribution 

of positive and negative water-level residuals. Summary 

statistics were calculated for the residuals (simulated minus 

observed water levels) of the 3,612 water-level observations 

used in the regression. The mean magnitude of the waterlevel residuals was 12 ft. The standard error of the regression 

(Draper and Smith, 1998) was 16.28 ft. The root-meansquare error (RMSE) was calculated as the square root of the 

mean of the unweighted squared residuals:

(5)

where

H is the measured water level for observation

 k, and

H′ is the simulated-equivalent water level

 for observation k.

The RMSE and the standard deviation of the residuals were 

both 15.85 ft. The normalized root-mean-square deviation 

is 0.031 and was obtained by dividing the RMSE of the 

residuals by the 507 ft range of observed water levels. 

Because the RMSE is about 3 percent of the observed 

measurement range, the model is adequately calibrated for 

the purpose of this study.

Estimated Parameter Values

Parameter values were constrained within “reasonable 

limits” during the model calibration process with PEST. 

Several relatively insensitive model parameters drifted 

toward their respective limiting constraints between 

successive parameter-estimation iterations but were 

not allowed to exceed those limits. Consequently, all of 

the groundwater-model parameters in the “calibrated” 

MODFLOW-2005 and SEAWAT simulations (table 4) are 

considered reasonable. 

Whereas the groundwater-flow model parameters were 

formally estimated by minimization of the objective function 

(equation 4), parameters representing the longitudinal, 

transverse, and vertical dispersivities and effective porosity 

in the solute transport model were estimated by manual 

calibration of simulated-to-observed chloride concentrations. 

The longitudinal component of the aquifer dispersivity 

was specified homogeneously at 300 ft, the transverse 

at 30 ft, and the vertical at 3 ft. Effective porosity was 

homogeneously specified at 15 percent. These values are 

within the range of reasonable values for these transport 

parameters (Zheng and Bennett, 1995).

( )

3612

'

2 3,612

1

∑=

−

= k

Hk H k

RMSE

Parameter Sensitivities

The composite parameter sensitivity reflects the 

total amount of information provided by the water-level 

observations for the estimation of the model parameter 

(Hill and Tiedeman, 2007). PEST computes a “composite 

sensitivity” (Doherty, 2004) of each model parameter 

with respect to all the weighted simulated heads (h′

i

). 

The composite sensitivities of parameters included in 

the regression computed at the final parameter values 

are summarized in table 4. In general, parameters with 

sensitivities greater than about 0.1 were well estimated 

and have correspondingly smaller confidence intervals. 

Parameters with composite scaled sensitivities smaller than 

about 0.1 were more difficult to estimate and (or) have larger 

confidence intervals.

Residual Plot

A graph of the water-level residuals (measured water 

levels minus simulated water levels) plotted as a function of 

the simulated water levels can be useful for detecting trends 

in the distribution of residuals, which may indicate model 

bias. Residuals for water levels measured north of the Baton 

Rouge Fault in the “2,000-foot” sand and in other aquifers are 

plotted with separate symbols in figure 14. The residuals for 

these observation groups are randomly distributed about the 

horizontal residual=0 abscissa, suggesting a lack of systematic 

model bias in simulated water levels.

Simulated Groundwater Conditions

In areas of constant groundwater density, the horizontal 

component of groundwater flow is generally in the direction 

of decreasing simulated water levels. Because the simulated 

chloride concentrations are relatively high in some areas 

adjacent to the Baton Rouge Fault, the contours of simulated 

water levels should not be used to infer the direction of 

groundwater flow in this area. The simulated water levels 

depicted as contour maps in this report represent conditions 

on December 31 of the indicated year. Comparisons between 

contour maps generated for different simulated times can 

be used to quantify water-level changes, and hydrographs 

of simulated and observed water levels at observation well 

locations can also be used to visualize water-level changes 

at various locations and depths within the aquifer system. 

Water levels simulated with SEAWAT that are presented in 

hydrographs in this report were computed with the Head 

Observation Package (HOB), which spatially and temporally 

interpolates simulated water levels at the location and time of 

each specified water-level observation. Changes in observed 

chloride concentration with time (chlorographs) and the 

corresponding concentrations simulated with SEAWAT are 

also presented in this report for selected wells.
Simulated Groundwater Conditions 29

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

10

20

30

40

50

60

70

80

90

100

-300 -200 -100 0 100 200

Residual, in feet

Simulated water level altitude, in feet

Figure 14. Residuals as a function of simulated water level altitudes for the "2,000 foot s-and of the Baton Rouge area and all other

simulated aquifers. Residuals are calculated by subracting simulated water level altitudes from observed water-level altitudes.

EXPLANATION

Other aquifers

“2000-foot” sand north of fault

Figure 14. Graph showing residuals as a function of simulated water level altitudes for the “2,000-foot” sand and all other simulated 

aquifers. Residuals are calculated by subtracting simulated water-level altitudes from observed water-level altitudes.

Simulated Water Levels

Simulated groundwater flow within the “1,500-foot” 

sand during the “predevelopment” steady-state period 

prior to 1940 generally flowed from up-dip areas near the 

Louisiana-Mississippi border southward and southwestward 

toward the Baton Rouge area (fig. 15). Contours of simulated 

steady-state predevelopment water levels within the “2,000-

foot” sand suggest that groundwater flowed southward and 

southwestward toward Baton Rouge in areas east of the 

Mississippi River and may have flowed in a more westerly 

direction in areas west of the Mississippi River (fig. 16). 

Simulated groundwater flow within the “2,000-foot” sand and 

“1,500-foot” sand that flows toward the northwest corner of 

the model domain discharges upward toward the specifiedhead boundary that represents the surficial aquifers.

After 68 years of groundwater withdrawals (1940–2007), 

simulated groundwater levels in much of the study area 

declined from their predevelopment levels. Groundwater 

currently flows toward the Baton Rouge area where 

withdrawals from most of the simulated aquifers have caused 

substantial drawdown of water levels (fig. 17A). Within the 

“1,500-foot” sand, a simulated “cone of depression” (area 

of groundwater drawdown) is centered about 0.3 mi east of 

Interstate 110, where the minimum simulated water-level 

altitude is -130 ft (figs. 17A and 17B). Within the “2,000-foot” 

sand, the area of greatest simulated drawdown is located in 

the industrial district northeast of well EB-367, where the 

minimum simulated water-level altitude is -235 ft (figs. 18A

and 18B). Lower water levels within the “2,000-foot” sand 

were simulated for years before 2007. For example, the water 

level simulated at the location of observation well EB-367, 

in which a water-level drawdown of 338 ft was measured 

between 1937 and 1972, is about -281 ft for the year 1972.

Hydrographs that depict the fit of simulated and observed 

water levels for wells in the detailed model area (see figs. 11, 

17, and 18 for well locations) also show the history of waterlevel changes in the various aquifers (figs. 19–24). Simulated 

water levels depicted in the hydrographs were computed with 

the HOB package, which interpolated heads between model 

nodes for the well location and observation time, and averaged 

simulated heads for multilayer observations. A spreadsheet and 
Lake Maurepas WEST FELICIANA EAST FELICIANA ST. HELENA TANGIPAHOA LIVINGSTON EAST BATON ROUGE WEST BATON ROUGE POINTE COUPEE IBERVILLE ST. MARTIN ASCENSION ST. LANDRY AVOYELLES CONCORDIA WILKINSON AMITE PIKE BATON ROUGE BREAUX BRIDGE GONZALES HAMMOND ADAMS FRANKLIN LINCOLN MISSISSIPPI LOUISIANA 

Figure 15. Simulated steady-state water levels within the "1,500-foot" sand of the Baton Rouge area representingpredevelopment conditions before 1940 in southeastern Louisiana and southwestern Mississippi.

Base map modified from Louisiana Oil Spill Coordinator, Office of theGovernor, Louisiana GIS CD: A Digital Map of the State, Version 2.0Map Projection: North American Datum of 1983, Universal Transverse Mercator Zone 15

§ ̈¦55

§ ̈¦55

§ ̈¦55

§ ̈¦12

§ ̈¦10 § ̈¦10

61

61

61

98

98

.71

.190

.190

.51

.51

0 10 20 KILOMETERS

0 10 20 MILES

1 2 0

11 0

9 0

1 0 0

1 3 0

1 4 0

1 5 0

1 6 0

1 7 0

8 0 1 8 0

70

5060 4 0

3 1 9 0 0

2 1 0

1 9 0

1 6 0

50

8 0 6 0

9 0

70

1 0 0

11 0

1 3 0

7 0

7 0

7 0

1 5 0

8 0

8 0

8 0

9 0

1 4 0

6 0

92°00' 91°45' 91°30' 91°15' 91°00' 90°45' 90°30'

31°15'31°00'30°45'30°30'30°15'

Figure 15. Map showing simulated steady-state water levels within the “1,500-foot” sand of the Baton Rouge area representing predevelopment cosoutheastern Louisiana and southwestern Mississippi.
Lake Maurepas

MISSISSIPPILOUISIANA

WEST

FELICIANA EAST FELICIANA ST. HELENA

TANGIPAHOA LIVINGSTON EAST BATON ROUGE

WEST

BATON

ROUGE

POINTE

COUPEE

IBERVILLE

ST. MARTIN

ASCENSION

ST. LANDRY

AVOYELLES

CONCORDIA

WILKINSON

AMITE

PIKE

BATONROUGE

BREAUX BRIDGE

GONZALES

HAMMOND

ADAMS FRANKLIN LINCOLN

92°00' 91°45' 91°30' 91°15' 91°00' 90°45' 90°30'

31°15'31°00'30°45'30°30'30°15'

Figure 16. Simulated steady-state water levels within the "2,000-foot" sand of the Baton Rouge area representingpredevelopment conditions before 1940 in southeastern Louisiana and southwestern Mississippi.

Base map modified from Louisiana Oil Spill Coordinator, Office of theGovernor, Louisiana GIS CD: A Digital Map of the State, Version 2.0Map Projection: North American Datum of 1983, Universal Transverse Mercator Zone 15

§ ̈¦55

§ ̈¦55

§ ̈¦55

§ ̈¦12

§ ̈¦10

§ ̈¦10

61

61

61

98

98

.71

.190

.190

.51

.51

0 10 20 KILOMETERS

0 10 20 MILES

1

5 0

1 6 0

1

4 0

1

3

0

9 0

1 7 0

1

2

0

1

1

0

1 8 0

1

0 0

8 0

1 9 0

2 0 0

7 0

2 1 0

6 0

2 2 0

2 3 0

2 4 0

2 5 0

2 6 0 2 7 0

2 8 0 2 9 0 5 0 3 0 0 3 1 0 3 2 0 3 3 0 3 4 0

3 5 0 3 6 0 2 9 0

Figure 16. Map showing simulated steady-state water-levels within the “2,000-foot” sand of the Baton Rouge area representing predevelopment consoutheastern Louisiana and southwestern Mississippi.
Lake Maurepas MISSISSIPPI LOUISIANA WEST FELICIANA EAST FELICIANA ST. HELENA TANGIPAHOA LIVINGSTON EAST BATON ROUGE WEST BATON ROUGE POINTE COUPEE IBERVILLE ST. MARTIN ASCENSION ST. LANDRY AVOYELLES CONCORDIA WILKINSON AMITE PIKE BATON ROUGE BREAUX BRIDGE GONZALES HAMMOND ADAMS FRANKLIN LINCOLN

Figure 17A. Simulated 2007 water levels within the "1,500-foot" sand of the Baton Rouge area in southeasternLouisiana and southwestern Mississippi.

T

Base map modified from Louisiana Oil Spill Coordinator, Office of theGovernor, Louisiana GIS CD: A Digital Map of the State, Version 2.0Map Projection: North American Datum of 1983, Universal Transverse Mercator Zone 15

§ ̈¦55

§ ̈¦55

§ ̈¦55

§ ̈¦12

§ ̈¦10

§ ̈¦10

61

61

61

98

98

.71

.190

.190

.51

.51

0 10 20 KILOMETERS

0 10 20 MILES

4 0

0

6 0

8 0

2 0

1 0 0

1 2 0

-2 0

1 4 0

-4 0

1 6 0

-6 0

-8 0

1 8 0

-1 0 0

2 0 0

-1 2 0

2 4 0

-8 0

2 0

4 0 -1 2 0

-4 0

1 6 0

-4 0

1 2 0

6 0

2 0

1 0 0

0

-2 0

0

8 0

PC-39 EF-27

WBR-23

TA-454

LI-26B

EB-918

EB-652

EB-585

EB-392

EB-168

WBR-97B

EB-803A

92°00' 91°45' 91°30' 91°15' 91°00' 90°45' 90°30'

31°15'31°00'30°45'30°30'30°15'

Figure 17A. Simulated 2007 water levels within the “1,500-foot” sand of the Baton Rouge area in southeastern Louisiana and southwestern Mississi
Mississippi River

§ ̈¦12

§ ̈¦10

§ ̈¦10

§ ̈¦110

§ ̈¦110

§ ̈¦10

.190

61

67

19

1

1 30

73

76

37

986

986

0 0.5 1 2 KILOMETERS0 0.5 1 2 MILES

Figure 17B. Simulated 2007 water levels within the "1,500-foot" sand of the Baton Rouge area in the detailed model arein southeastern Louisiana.

EB-918

EB-168

WBR-173

WBR-132

WBR-97B

EB-1293

EB-807A

EB-783A EB-789B

EB-782B

EB-780B

91°12'30" 91°10'00" 91°07'30"

30°30'00"30°27'30"30°25'00"

EB

Base map modified from Louisiana Oil Spill Coordinator, Office of theGovernor, Louisiana GIS CD: A Digital Map of the State, Version 2.0Map Projection: North American Datum of 1983, Universal Transverse Mercator Zone 15

-1 0 5

-1 1 0

-

1

1

5

-1 2 0

-9 5

-1 2 5

-

8

0

-

8

5

-

9

0

-

7

5

-

7 0

-1 3 0

-

1

0

5

-

9

5

-

1

0 0

-

1

1

5

-

1

1

0

-1 2 0

Figure 17B. Simulated 2007 water levels within the “1,500-foot” sand of the Baton Rouge area in the detailed model area in southeastern Louisiana.
Lake Maurepas MISSISSIPPI LOUISIANA WEST FELICIANA EAST FELICIANA ST. HELENA TANGIPAHOA LIVINGSTON EAST BATON ROUGE WEST BATON ROUGE POINTE COUPEE IBERVILLE ST. MARTIN ASCENSION ST. LANDRY AVOYELLES CONCORDIA WILKINSON AMITE PIKE BATON ROUGE BREAUX BRIDGE GONZALES HAMMOND ADAMS FRANKLIN LINCOLN 

E

E

Figure 18A. Simulated 2007 water levels within the "2,000-foot" sand of the Baton Rouge area in southeastern Louisianaand southwestern Mississippi.

Base map modified from Louisiana Oil Spill Coordinator, Office of theGovernor, Louisiana GIS CD: A Digital Map of the State, Version 2.0Map Projection: North American Datum of 1983, Universal Transverse Mercator Zone 15

§ ̈¦55

§ ̈¦55

§ ̈¦55

§ ̈¦12

§ ̈¦10

§ ̈¦10

61

61

61

98

98

.71

.190

.190

.51

.51

0 10 20 KILOMETERS

0 10 20 MILES

92°00' 91°45' 91°30' 91°15' 91°00' 90°45' 90°30'

31°15'31°00'30°45'30°30'30°15'

4 0

6 0

8

0

0

1 0 0

2 0

1 2 0

1

4

0

1 6 0

1 8 0

2 0 0

2 2 0

2 4 0

-2 0

2 6 0 2 8 0

-4 0

-6 0

3 0 0 3 2 0

-8 0

3 4 0

-1 0 0

3 6 0

-

1

2

0

-

1 4 0

-1 6 0

-

1

8 0

-2 0 0

4 0

EB-322

WF-40

PC-66

LI-61 LI-55

LI-54

IB-29

EB-90

WBR-50

WBR-10

TA-343

TA-273

TA-268

PC-144

PC-138

EB-781

EB-778

EB-575

EB-315

EB-304

WBR-111 EB-807B EB-803B

Figure 18A. Simulated 2007 water levels within the “2,000-foot” sand of the Baton Rouge area in southeastern Louisiana and southwestern Mississi
Mississippi River

§ ̈¦12

§ ̈¦110

§ ̈¦110

§ ̈¦10

§ ̈¦10

§ ̈¦10

67 61

986

986

76

73

1

1

19

30

37

.190

0 0.5 1 2 KILOMETERS0 0.5 1 2 MILES

Figure 18B. Simulated 2007 water levels within the "2,000-foot sand of the Baton Rouge area in the detailed model arein southeastern Louisiana.

EB-90

WBR-50

WBR-10

EB-781

EB-778

EB-367

EB-112

WBR-111

WBR-106

EB-1028

EB-807B

EB-792B

EB-783B

91°12'30" 91°10'00" 91°07'30"

30°30'00"30°27'30"30°25'00"

Base map modified from Louisiana Oil Spill Coordinator, Office of theGovernor, Louisiana GIS CD: A Digital Map of the State, Version 2.0Map Projection: North American Datum of 1983, Universal Transverse Mercator Zone 15

-

1

4

0

-

1

3 5

-

1

6

5

-

1

6

0

-

1

5

5

-

1

5

0

-

1

4

5

-

1

8

0

-

1

7

0

-

1

7

5

-

1

8

5

-

1

9

0

-1 9 5

-2 0 0

-

2

0

5

-

1 3 - 0 2 1

0-2

1

5

-2 2 0

-

1 2 5

-2 2 5

-1 9 5

-1 8 5

-1 9 0

-1 8 5 -1 8 5

-

2

2

5

Figure 18B. Simulated 2007 water levels within the “2,000-foot sand of the Baton Rouge area in the detailed model area in southeastern Louisiana.
36 Simulation of Groundwater Flow in the “1,500-Foot” Sand and “2,000-Foot” Sand in the Baton Rouge Area, Louisiana

database containing hydrograph information for all observed 

and simulated water-levels are included with the digital archive 

of this groundwater model that is on file at the USGS office 

in Baton Rouge. 

Water levels in the “1,000-foot” sand and “1,200-foot” 

sand are simulated by model layer 3 north of the fault. Although 

a uniform hydraulic conductivity was estimated for this model 

layer, the simulated transmissivity is variable because the 

model-layer thickness is variable. The fit of simulated-toobserved water levels shown in hydrographs (fig. 19) is good, 

and the 177 ft of drawdown observed in well EB-146, (located 

about 0.9 mi east of Interstate 110 in Baton Rouge), is well 

simulated. Simulated water levels at some wells (EB-146, 

EB-299, and EB-301) are lower than observed during the 1960s 

and early 1970s, possibly as a result of inaccurate pumpage 

specified within this layer for those periods.

Water levels in the “1,500-foot” sand north of the fault 

were simulated by model layer 5 by using four spatial zones 

of horizontal hydraulic conductivity. The hydrograph for well 

EB-807A documents 82 ft of drawdown between the years 1967 

and 1992, which was the largest observed water-level change in 

the “1,500-foot” sand (fig. 20).

Water levels in the “1,700-foot” sand north of the fault 

were simulated with model layer 7 with a homogeneous 

horizontal hydraulic conductivity distribution. Although most 

observed water levels are well simulated, the water-level 

recovery at well EB-792A during the early 1970s was not (fig. 

21), possibly as a result of inaccurate pumpage specified within 

this layer in the vicinity of EB-792A for that period.

Water levels in the “2,000-foot” sand were simulated by 

model layers 9 through 18, each of which has an identical, 

complex distribution of simulated horizontal hydraulic 

conductivity (fig. 13). Observations of water levels in the 

“2,000-foot” sand are closely simulated throughout most of 

the model domain, particularly in the detailed model area. 

Locations of wells that are screened within the “2,000-foot” 

sand in the detailed model area that were used for model 

calibration are shown on figure 18B. A 368-ft water-level 

drawdown measured in well EB-112 between 1930 and 1973 

is well simulated (fig. 22B). Water-level drawdowns of similar 

magnitude measured in other wells in the detailed model area 

are also well simulated by the model.

Water levels in the “2,400-foot” sand were simulated 

by model layer 20 by using two spatial zones of horizontal 

hydraulic conductivity. Water levels measured in two wells 

within the detailed model area, EB-794 and EB-806B (fig. 

11), document about 100 ft of water-level drawdown between 

1965 and 2007 (figs. 23B,C). Considering the relatively simple 

hydraulic conductivity distribution used to simulate the “2,400-

foot” sand, water levels throughout the model domain are 

well simulated.

Because chloride concentrations in the “2,800-foot” 

sand are relatively high in the Baton Rouge area, only one 

well screened in the “2,800-foot” sand, EB-944 (fig. 24), was 

available to depict water levels in the detailed model area 

(fig. 11). Despite the scarcity of observation wells screened 

in the “2,800-foot” sand in the detailed model area, 15 other 

hydrographs within the “2,800-foot” sand outside of the 

detailed model area (not shown) also depict good model fit.

Simulated Connector-Well Flow Rate

The simulated transient flow through the “connector 

well,” EB-1293, was compared with the previously described 

wellbore-flow observation during model calibration. The 

simulated flow rate of 480 gpm (0.69 Mgal/d) through this 

well during December 1998 is a good fit to the measured 

value of 475 gpm reported by Dial and Cardwell (1999). The 

flow simulated through this “connector well” increases after 

December 1999 because simulated water levels within the 

“1,500-foot” sand generally decline faster than water levels 

specified for the “800-foot” sand, which increases the hydraulic 

gradient between those aquifers at that location. The maximum 

simulated flow rate of 660 gpm occurred after installation of the 

connector well during early 1998, and before simulated water 

level differences between the “800-foot” sand and “1,500-foot” 

sand near EB-1293 had sufficient time to begin equilibration. 

Simulated Water Budget

Under predevelopment (steady-state) conditions, the 

simulated water budget indicates that about 70 Mgal/d of water 

entered (and exited) the groundwater-flow model domain (table 

5). The majority of the inflow (97.5 percent) was from the top 

model layer, which is a specified head boundary that represents 

the “400-foot” sand, “600-foot” sand, and “800-foot” sand 

aquifers. A small amount of inflow and outflow was simulated 

entering and exiting the model domain through the constanthead boundary along the southernmost row (row 85) of the 

deepest model layer (layer 22). By the end of the transient 

historical simulation (December 31, 2007), substantial net 

groundwater withdrawals (168.22 Mgal/d during 2007) had 

caused water-level declines that increased simulated infiltration 

from layer 1 by 67 percent, to 115.2 Mgal/d. Water that flows 

into a model layer through a multi-node well comes out from 

another model layer connected to the same well. Specified 

water-level changes in the top model layer account for processes 

not explicitly simulated by the model, including storage changes 

in the upper “400-foot” sand, “600-foot” sand, and “800-foot” 

sand aquifers; evapotranspiration; and recharge. As such, 

recharge and discharge to the upper aquifers are not represented 

in the simulated water budget. Inflows from storage simulated 

in model layers 2–22 are from aquifer-matrix compression and 

water expansion.

A graph of the changes in the contributions from the three 

major sources and sinks of water during the transient historical 

groundwater simulation illustrates the effect of groundwater 

withdrawals on the simulated water budget (fig. 25). Following 

the steady-state stress period that simulates “predevelopment” 

conditions prior to 1940, groundwater withdrawals are initially 

mostly supplied by the elastic release of water from storage. 
Simulated Groundwater Conditions 37

A. EB-146

-100

-50

0

50

100

Simulated

Observed

B. EB-299

-100

-50

0

50

100

Simulated

Observed

C. EB-301

Water-level altitude, in feet

-100

-50

0

50

100

Simulated

Observed

D. EB-327

-150

-100

-50

0

50

Simulated

Observed

E. EB-782A

Year

1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 2020

-100

-50

0

50

100

Simulated

Observed

Figure 19. Simulated and observed water levels within the "1,000-foot" and "1,200-foot" sands of the

Baton Rouge area in southeastern Louisiana (see fig. 10 for well locations).

EXPLANATION

EXPLANATION

EXPLANATION

EXPLANATION

EXPLANATION

Figure 19. Graphs showing simulated and observed water levels within the “1,000-foot” and “1,200-foot” sands of the Baton Rouge 

area in southeastern Louisiana.
38 Simulation of Groundwater Flow in the “1,500-Foot” Sand and “2,000-Foot” Sand in the Baton Rouge Area, Louisiana

A. EB-782B

-120

-100

-80

-60

-40

-20

Simulated

Observed

B. EB-807A

-120

-100

-80

-60

-40

-20

Simulated

Observed

C. EB-918

Water-level altitude, in feet -140

-120

-100

-80

-60

-40

Simulated

Observed

D. EB-1293

Year

1960 1970 1980 1990 2000 2010 2020

-120

-100

-80

-60

-40

-20

Simulated

Observed

Figure 20. Simulated and observed water levels within the "1,500-foot" sand of the Baton Rouge area

in southeastern Louisiana (see fig. 10 for well locations).

EXPLANATION

EXPLANATION

EXPLANATION

EXPLANATION

Figure 20. Graphs showing simulated and observed water levels within the “1,500-foot” sand of the Baton Rouge area in 

southeastern Louisiana.
Simulated Groundwater Conditions 39

A. EB-792A

-140

-100

-60

-20

20

Simulated

Observed

B. EB-917

Water-level altitude, in feet -160

-120

-80

-40

0

Simulated

Observed

C. WBR-81

0

40

80

120

160

Simulated

Observed

Figure 21. Simulated and observed water levels within the "1,700-foot" sand of the Baton Rouge area

in southeastern Louisiana (see fig. 10 for well locations).

D. WBR-100A

Year

1950 1960 1970 1980 1990 2000 2010 2020

-160

-120

-80

-40

0

Simulated

Observed

EXPLANATION

EXPLANATION

EXPLANATION

EXPLANATION

Figure 21. Graphs showing simulated and observed water levels within the “1,700-foot” sand of the Baton Rouge area in 

southeastern Louisiana.
40 Simulation of Groundwater Flow in the “1,500-Foot” Sand and “2,000-Foot” Sand in the Baton Rouge Area, Louisiana

A. EB-90

-260

-180

-100

-20

60

140

Simulated

Observed

B. EB-112

-260

-180

-100

-20

60

140

Simulated

Observed

C. EB-367

Water-level altitude, in feet -320

-240

-160

-80

0

80

Simulated

Observed

D. EB-781

-300

-220

-140

-60

20

100

Simulated

Observed

E. EB-792B

Year

1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 2020

-300

-220

-140

-60

20

100

Simulated

Observed

Figure 22. Simulated and observed water levels within the "2,000-foot" sand of the Baton Rouge area

in southeastern Louisiana (see fig. 17 B for well locations).

EXPLANATION

EXPLANATION

EXPLANATION

EXPLANATION

EXPLANATION

Figure 22. Graphs showing simulated and observed water levels within the “2,000-foot” sand of the Baton Rouge area in 

southeastern Louisiana.
Simulated Groundwater Conditions 41

F. EB-807B

-300

-220

-140

-60

20

100

Simulated

Observed

H. WBR-10

-200

-120

-40

40

120

200

Simulated

Observed

I. WBR-50

-340

-260

-180

-100

-20

60

Simulated

Observed

J. WBR-111

Year

1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 2020 -200

-120

-40

40

120

200

Simulated

Observed

Figure 22. Simulated and observed water levels within the "2,000-foot" sand of the Baton Rouge area

in southeastern Louisiana (see fig. 17 B for well locations).

G. EB-1028

-300

-220

-140

-60

20

100

Simulated

Observed

Water-level altitude, in feet

EXPLANATION

EXPLANATION

EXPLANATION

EXPLANATION

EXPLANATION

Figure 22. Graphs showing simulated and observed water levels within the “2,000-foot” sand of the Baton Rouge area in 

southeastern Louisiana.—Continued
42 Simulation of Groundwater Flow in the “1,500-Foot” Sand and “2,000-Foot” Sand in the Baton Rouge Area, Louisiana

A. EB-322

-100

-50

0

50

100

Simulated

Observed

B. EB-794

-200

-150

-100

-50

0

Simulated

Observed

C. EB-806B

Water-level altitude, in feet

-200

-150

-100

-50

0

Simulated

Observed

D. WBR-100B

Year

1950 1960 1970 1980 1990 2000 2010 2020

-200

-150

-100

-50

0

Simulated

Observed

Figure 23. Simulated and observed water levels within the "2,400-foot" sand of the Baton Rouge area

in southeastern Louisiana (see figs. 10 and 17 A for well locations).

EXPLANATION

EXPLANATION

EXPLANATION

EXPLANATION

Figure 23. Graphs showing simulated and observed water levels within the “2,400-foot” sand of the Baton Rouge area in 

southeastern Louisiana.
Simulated Groundwater Conditions 43

A. EB-944

1960 1970 1980

Year

1990 2000 2010 2020

Water-level altitude, in feet -20

0

20

40

60

Simulated

Observed

Figure 24. Simulated and observed water levels within the "2,800-foot" sand of the Baton Rouge area

in southeastern Louisiana (see figs. 10 for well location).

EXPLANATION

Table 5. Simulated steady-state and transient flow rates.

[SP, stress period; TS, time step; ft3/d, cubic feet per day; Mgal/d, million gallons per day]

Budget component Steady-state SP 1 (pre-1940) Transient SP 69, TS 5 (Dec. 31, 2007)

ft3/d Mgal/d ft3/d Mgal/d

In Specified-head layer 1 9.2018x106 68.83 1.5399x107 115.2

South row of layer 22 2.3632 x105 1.77 7.6428x106 57.17

Storage 0 0 2.5449x106 19.04

Multi-node wells 0 0 2.3474x105 1.76

Out Specified-head layer 1 8.9847x106 67.21 2.4214x106 19.23

South row of layer 22 4.5359x105 3.39 0 0

Storage 0 0 5.2941x104 3.96

Multi-node wells 0 0 2.2723x107 169.98

Figure 24. Graph showing simulated and observed water levels within the “2,800-foot” sand of the Baton Rouge area in 

southeastern Louisiana.
44 Simulation of Groundwater Flow in the “1,500-Foot” Sand and “2,000-Foot” Sand in the Baton Rouge Area, Louisiana

-10

10

30

50

70

90

110

130

150

170

1940 1950 1960 1970 1980 1990 2000

Million gallons per day

Year

Figure. 25 - Simulated groundwater withdrawals, and flows from storage and specified -head boundaries.

Simulated groundwater withdrawals

Net flow from storage

Net flow from specified-head boundaries

EXPLANATION

Over time, vertical hydraulic gradients caused by groundwater 

withdrawals from the deeper model layers cause increasing 

downward flow from the top model layer specified-head 

boundary that represents the upper aquifers. Flow from storage 

continues to respond to shorter term changes in the pumpage 

stress. Flow from specified-head boundaries is relatively 

smooth through time (fig. 25) because it is computed during 

every time step. In contrast, groundwater withdrawals are 

specified by stress periods composed of multiple time steps, 

and flow from storage responds to these specified withdrawals.

Simulated Concentrations

Because the chloride-source concentration is unknown, 

it was parameterized and estimated during model calibration. 

To facilitate calibration to observed concentrations, simulated 

concentrations were normalized to the source concentration. 

A chloride-source concentration of 10,000 mg/L produced 

the best overall fit of simulated-to-observed chloride 

concentrations. Simulated chloride concentrations at the 

centers of model cells containing chloride-observation well 

screens were used to generate the simulated chlorographs 

(fig. 26), the locations of which are mapped in figure 27. 

Wells EB-1150 and EB-630 have long screens that span 

more than one model layer within the “2,000-foot” sand; 

simulated chloride concentrations from multiple vertically 

adjacent model cells were averaged to calculate the simulated 

concentrations for these wells.

Two factors complicated simulation of the concentrations 

observed in observation well EB-781, the screen of which is 

located about 250 ft north of the Baton Rouge Fault. First, 

although the precise location of the Baton Rouge Fault at 

the “2,000-foot” sand depth is somewhat uncertain, it was 

defined along the finite-difference cell interfaces nearest 

to its presumed location. Because the finite-difference grid 

cell spacing is 500 ft in this area, the error inherent in the 

simulated fault location is likely on the order of 250 ft. 

Second, the steep, simulated concentration gradient near the 

north side of the Baton Rouge Fault causes a large difference 

in simulated concentration between the model cell north of 

and adjacent to the fault and its neighboring cell to the north. 

The concentrations simulated for the two cells north of the 

fault in rows 72 and 73, both in column 46 and layer 18, were 

averaged to generate the simulated concentration for well 

EB-781 (fig. 26).

Figure 25. Graph showing simulated groundwater withdrawals and flows from storage and specified-head boundaries.
Simulated Groundwater Conditions 45

Chloride concentration, in milligrams per liter

1965 1975 1985 1995 2005

Year

0

1000

2000

3000

4000

A. Well EB-781

observed

simulated

EXPLANATION

0

100

200

300

400

500

B. Well EB-807B

observed

simulated

EXPLANATION

observed

simulated

EXPLANATION

observed

simulated

EXPLANATION

observed

simulated

EXPLANATION

0

100

200

300

400

500

C. Well EB-1028

0

100

200

300

400

500

D. Well EB-1150

0

100

200

300

400

500

E. Well EB-630

Figure 26. Graph showing simulated and observed chloride concentrations at observation wells within the “2,000-foot” sand of the 

Baton Rouge area in southeastern Louisiana.
Mississippi River

§ ̈¦12

§ ̈¦110

§ ̈¦110

§ ̈¦10

§ ̈¦10

§ ̈¦10

61 67

986

986

76

73

1

1

19

30

37

.190

91°12'30" 91°10'00" 91°07'30"

30°30'00"30°27'30"30°25'00"

0 0.5 1 2 KILOMETERS0 0.5 1 2 MILES

Figure 27. Simulated 2007 water levels and chloride concentrations at the base of the "2,000-foot" sand of theBaton Rouge area in the detailed model area in southeastern Louisiana.

EX

EB-781

EB-X

-180

EB-781

EB-X

EB-807B

EB-1028

EB-630 EB-1150

EB-874

-

1

4

0

-

1 3 5

-

1

6

5

-

1

6

0

-

1

5

5

-

1

5

0

-

1

4

5

-

1

8

0

-

1

7

0

-

1

7

5

-

1

8

5

-

1

9

0

-1 9 5

-2 0 0

-

2

0

5

-

1 3 - 0 2 1

0-2

1

5

-2 2 0

-

1 2 5

-2 2 5

-1 9 5

-1 8 5

-1 9 0

-1 8 5 -1 8 5

-2 2 5

Base map modified from Louisiana Oil Spill Coordinator, Office of theGovernor, Louisiana GIS CD: A Digital Map of the State, Version 2.0Map Projection: North American Datum of 1983, Universal Transverse Mercator Zone 15

Figure 27. Map showing simulated 2007 water levels and chloride concentrations at the base of the “2,000-foot” sand of the Baton Rouge area in the southeastern Louisiana.
Hypothetical Groundwater-management Scenarios 47

Although the most recent chloride concentration 

observation in well EB-807B (located about 0.7 mile north 

of well EB-871) was made in 1998, the relatively low 

concentrations measured before that time provide a useful 

constraint on model parameters affecting the transport of the 

saline water in a northerly direction away from source areas 

near EB-781 and the Baton Rouge Fault.

Chloride concentrations measured in wells EB-1150 and 

EB-630 (figs. 26D and 26E) have fluctuated over the period 

of the observation record. These fluctuations are difficult to 

simulate while maintaining relatively parsimonious initial 

and boundary conditions and transport-model parameter 

distributions. Consequently, simulated chlorographs for these 

wells are a reasonable fit to intermediate values within the 

range of fluctuations in the observed concentrations.

Limitations and Appropriate Use

of the Model

The groundwater model was designed and calibrated 

primarily to simulate groundwater flow in the “1,500-foot” 

sand and “2,000-foot” sand and saltwater transport within 

the “2,000-foot” sand of the Baton Rouge area. Because the 

model layering was designed to represent the most important 

hydrogeologic units of the aquifer system and water-level 

observations from all aquifers in the Baton Rouge area were 

used for model calibration, groundwater flow within the 

“1,000-foot” sand and “1,200-foot” sand, “1,500-foot” sand, 

“1,700-foot” sand, “2,400-foot” sand, and “2,800-foot” sand 

is reasonably well simulated. It is possible to simulate the 

effects of future changes in groundwater withdrawals on 

groundwater levels in each of these sands in the Baton Rouge 

area. Predictions of changes in water levels in the “1,500-

foot” sand and “2,000-foot” sand that might result from 

changes such as those described in the subsequent section on 

hypothetical groundwater management scenarios are examples 

of appropriate uses of the model. The period before 1940 was 

simulated with a steady-state solution of the flow equation, 

during which transient effects of any minor groundwater 

withdrawals were not simulated.

Chloride concentrations within the “2,000-foot” sand 

in the Baton Rouge area were used to calibrate the model; 

consequently, saltwater encroachment in other aquifers in the 

Baton Rouge area is not accurately simulated. Predictions of 

changes in chloride concentrations within the “2,000-foot” 

sand that might result from changes such as those described 

in the subsequent section on hypothetical groundwater 

management scenarios is an appropriate use of the model. 

Predictions of changes in chloride concentrations within 

the “1,500-foot” sand or other aquifers are not appropriate 

because the model was not calibrated to chloride-concentration 

observations within other aquifers.

The variably spaced, finite-difference model grid enabled 

fine discretization with greater numerical accuracy in the 

Baton Rouge area and coarse and large aspect-ratio (long side 

divided by short side) with less numerical accuracy in the 

surrounding areas. Water levels predicted for areas with either 

very coarse or very large aspect-ratio model cells will be less 

accurate and should be used judiciously.

Hypothetical Groundwatermanagement Scenarios

Six hypothetical groundwater-management scenarios 

were formulated to predict the effects of modifying 

groundwater withdrawals on future groundwater levels and 

saltwater concentrations. All of the scenarios used the 2007 

groundwater-withdrawal rate for the 7-year period from 

2008 through 2014. As previously discussed, simulated 2007 

withdrawal rates totaled 169 Mgal/d after layer 1 withdrawals 

were excluded. Simulated 2007 withdrawals from layer 5 

north of the fault were 27.5 Mgal/d and included 23.7 Mgal/d 

from the “1,500-foot” sand. Simulated 2007 withdrawals from 

layers 9 through 18 north of the fault were 30.2 Mgal/d and 

included 25.3 Mgal/d from the “2,000-foot” sand. Of the 25.3 

Mgal/d withdrawn from the “2,000-foot” sand, 16.6 Mgal/d 

were withdrawn in the industrial district. Scenario 1 simulates 

continuation of the 2007 pumping rate through 2047 and is a 

benchmark for comparison of water levels and (or) chloride 

concentrations simulated in the other five scenarios. Scenario 

2 simulated the effect of reducing groundwater withdrawals 

from seven selected industrial wells by 10.8 Mgal/d beginning 

in 2015 on water levels in the “1,500-foot” sand. Scenarios 

3, 4, 5, and 6 simulate alternative strategies for mitigating the 

northward migration of saltwater within the “2,000-foot” sand. 

Scenarios 3a and 3b simulate a 2.0 Mgal/d withdrawal from 

a scavenger well beginning in 2017 at the base of the “2,000-

foot” sand, scenario 4 simulates a 3.6 Mgal/d reduction in 

withdrawals from the “2,000-foot” sand at selected industrial 

wells beginning in 2015, and scenario 5 simulates cessation of 

withdrawals from the “2,000-foot” sand within the industrial 

district beginning in 2015 (16.625 Mgal/d reduction in 

withdrawals). Scenario 6 simulates the combined effect of a 

1.375 Mgal/d reduction in withdrawals from the “2,000-foot” 

sand in 2015 with a 2.5 Mgal/d withdrawal from a “scavenger 

well couple” accompanied by a 1.5 Mgal/d reduction in 

withdrawals from public-supply wells beginning in 2017.

In addition to the existing observation wells, the chloride 

concentration at hypothetical observation well “EB-X,” 

located south of the industrial district (fig. 27), is simulated 

for each scenario. The “plume area,” defined as an area with 

a simulated chloride concentration greater than 10 mg/L in 

model layer 18 (the base of the “2,000-foot” sand) north 

of the Baton Rouge Fault, and the mean and median cell 

concentrations within that area in 2047 for each scenario as 

well as 2007 are summarized in table 6.
48 Simulation of Groundwater Flow in the “1,500-Foot” Sand and “2,000-Foot” Sand in the Baton Rouge Area, Louisiana

Table 6. Simulated plume areas and chloride concentrations.

[mg/L, milligrams per liter]

Date and/or scenario Plume area

(square miles)

Mean layer 18 cell

concentration (mg/L)

median layer 18 cell

concentration (mg/L)

2007: 5.42 883 340

2047: scenario 1 7.17 958 311

2047: scenario 3a: 6.01 1,023 362

2047: scenario 3b: 5.61 765 138

2047: scenario 4 7.20 954 308

2047: scenario 5 6.54 755 216

2047: scenario 6 5.25 730 130

Scenario 1: Continued Groundwater 

Withdrawals at 2007 Rates

Continuation of the “status quo” groundwater 

withdrawals was simulated by using the simulated 2007 

withdrawal rates for an additional 40 years (2008–47). 

Contours of predicted water-levels within the “1,500-foot” 

sand (fig. 28) for 2047 are similar to those simulated for 2007 

(fig. 17 A, B) but are consistently about 5 ft lower throughout 

the Baton Rouge area. The lowest water-level altitudes 

of about -140 ft are simulated 1.6 mi north-northwest of 

observation well EB-1293.

Continued groundwater withdrawals at 2007 rates are 

predicted to cause further decline of groundwater levels within 

the “2,000-foot” sand. Although the shape of contours of 

predicted water levels within the “2,000-foot” sand (fig. 29) 

for 2047 are similar to those for 2007 (figs. 18A,B), the water 

levels are about 13 ft lower in the Baton Rouge area. The 

lowest water-level altitudes of about -245 ft are simulated in 

the industrial district.

Comparison of the simulated chloride concentration 

distributions in layer 18 for years 2047 (fig. 29) and 2007 (fig. 

27) indicates that the portion of the saltwater plume containing 

chloride concentrations in the 161–320 mg/L range at the base 

of the “2,000-foot” sand would migrate approximately 0.6 mi 

northward toward the industrial district. The plume area at 

the base of the “2,000-foot” sand north of the Baton Rouge 

Fault with concentrations above background levels (10 mg/L) 

would increase by about 32 percent (table 6). Concentrations 

at most existing observation wells would increase, and the 

concentration at EB-X, near the center of the plume south of 

the industrial district (fig. 29), is predicted to increase from 

about 20 mg/L to about 180 mg/L within about 30 years (fig. 

30F). Concentrations at observation well EB-630 are predicted 

to decrease because groundwater flow at that location is from 

the south where the aquifer south of the fault may be fresh and 

the saltwater source is not simulated.

Scenario 2: Reduction of Groundwater 

Withdrawals from the “1,500-foot” Sand

Saltwater encroachment is also a concern within the 

“1,500-foot” sand in the Baton Rouge area. Similar to the 

saltwater encroachment problem within the “2,000-foot” sand, 

this encroachment is caused by water-level drawdown that 

is due to withdrawals from the “1,500-foot” sand. Although 

chloride concentrations within the “1,500-foot” sand were 

not calibrated, simulation of transient water levels within 

the “1,500-foot” sand enabled assessment of a possible 

groundwater-withdrawal reduction on water levels in the 

“1,500-foot” sand. Of particular interest is the contribution to 

future water-level drawdown in the “1,500-foot” sand caused 

by withdrawals from selected industrial wells in the northwest 

corner of East Baton Rouge Parish (fig. 11). This contribution 

was assessed as the difference between the 2047 water levels 

simulated with scenario 1 and the 2047 water levels simulated 

with the selected industrial wells turned off from 2015 through 

2047. For scenario 2, zero withdrawal rates were specified 

from seven industrial wells in model row 10 and column 10 

(fig. 10) that have screens either in the “1,500-foot” sand or 

an adjacent sand, simulating a withdrawal reduction of 10.8 

Mgal/d. Two wells (EB-963 and PC-343) have simulated 

screen intervals only within the “1,500-foot” sand. Four wells 

(EB-835, EB-837, EB-1248, and EB-1277) have simulated 

screen intervals within both the “1,500-foot” sand and the 

“1,700-foot” sand. The remaining well (EB-838) is screened 

entirely within the “1,700-foot” sand.

Comparison of the contours of water levels predicted 

for 2047 within the “1,500-foot” sand for scenarios 1 and 2 

(figs. 28 and 31) indicated that 2047 water-level altitudes for 

scenario 2 are generally about 10 to 12 ft higher in the Baton 

Rouge area than those predicted for scenario 1. The lowest 

predicted water-level altitudes of about -125 ft are around 

municipal supply wells located about 2 mi southeast of the 

industrial district.
Mississippi River

§ ̈¦12

§ ̈¦110

§ ̈¦110

§ ̈¦10

§ ̈¦10

§ ̈¦10

61 67

986

986

76

73

1

1

19

30

37

.190

0 0.5 1 2 KILOMETERS0 0.5 1 2 MILES

Figure 28. Predicted 2047 water-levels within the "1,500-foot" sand of the Baton Rouge area in the detailed modelarea in southeastern Louisiana after continued pumping at 2007 rates (scenario 1).

EB-918

EB-168

WBR-173

WBR-132

WBR-97B

EB-1293

EB-807A

EB-783A EB-789B

EB-782B

EB-780B

91°12'30" 91°10'00" 91°07'30"

30°30'00"30°27'30"30°25'00"

Base map modified from Louisiana Oil Spill Coordinator, Office of theGovernor, Louisiana GIS CD: A Digital Map of the State, Version 2.0Map Projection: North American Datum of 1983, Universal Transverse Mercator Zone 15

EB-807A

-95

-1 1 5

-1 2 0

-1 2 5

-1 1 0

-1 0 5

-1 3 0

-8

5

-

9

0

-

9

5-8 0

-

1

0

0

-7 5

-1 3 5

-

1

1

0

-

1

1

5

-

1

0 5

-

1

3

0

-

1

2

0

-1 2 5

-1 0 0

Figure 28. Map showing predicted 2047 water levels within the “1,500-foot” sand of the Baton Rouge area in the detailed model area in southeasterpumping at 2007 rates (scenario 1).
Mississippi River

§ ̈¦12

§ ̈¦110

§ ̈¦110

§ ̈¦10

§ ̈¦10

§ ̈¦10

61

67

986

986

76

73

1

1

19

30

37

.190

-

1

5

5

-

1

5 0

-

1

8

0

-

1

7

5

-

1

7

0

-

1

6

5

-

1

6

0

-

1

9

5

-

1

9

0

-

1

8-

5

2

0

0

-

2

0

5

-

2

1

0

-

2

1

5

-

1

4 5

-

2

2

0

-2 2 5

-2 3 0

-

1 4 0

-2 3 5

-2 4 0

-1 9 5

-2 0 0

-2 0 5

-1 9 5

-2 1 0

91°12'30" 91°10'00" 91°07'30"

30°30'00"30°27'30"30°25'00"

0 0.5 1 2 KILOMETERS0 0.5 1 2 MILES

Figure 29. Predicted 2047 water levels and chloride concentrations at the base of the "2,000-foot" sand of theBaton Rouge area in the detailed model area in southeastern Louisiana after continued pumping at 2007 rates(scenario 1).

EB-781

EB-807B

EB-1028

EB-630 EB-1150

EB-874

EB-X

Base map modified from Louisiana Oil Spill Coordinator, Office of theGovernor, Louisiana GIS CD: A Digital Map of the State, Version 2.0Map Projection: North American Datum of 1983, Universal Transverse Mercator Zone 15

EXPLA

EB-781

EB-X

-180

Figure 29. Map showing predicted 2047 water levels and chloride concentrations at the base of the “2,000-foot” sand of the Baton Rouge area in the southeastern Louisiana after continued pumping at 2007 rates (scenario 1).
Observed Scenario 1: status quo Scenario 3a: scavenger row 57 col 26 Scenario 3b: scavenger row 68 col 30 Scenario 4: 3.6 Mgal/d reduction Scenario 5: industrial district cessation Scenario 6: scavenger with reductions EXPLANATION

1960 1970 1980 1990 2000 2010 2020 2030 2040

Year

0

200400600

800

1,0001,2001,4001,6001,8002,000

Chloride concentration, in milligramsper literA. Well EB-1028

0

100200300400500

1960 1970 1980 1990 2000 2010 2020 2030 2040

Chloride concentration,inmilligramsper liter

Year

B. Well EB-1150

0

100200300400500

1960 1970 1980 1990 

Chloride concentration,inmilligramsper liter

C. Well EB-630

0

1,0002,0003,0004,000

1960 1970 1980 1990 2000 2010 2020 2030 2040

Chloride concentration,inmilligramsper liter

Year

D. Well EB-781

0

100200300400500600700800900

1,000

1960 1970 1980 1990 2000 2010 2020 2030 2040

Chloride concentration, inmilligrams per liter

Year

E. Well EB-807B

0

100200

1960 1970 1980 1990 

Chloride concentration, in milligrams per liter

F. Well EB-X

Figure 30. Graphs showing predicted chloride concentrations at the base of the “2,000-foot” sand after continued pumping at 2007 rates (scenario 1)well (scenario 3 a,b), industrial district withdrawal reduction of 3.6 million gallons per day (Mgal/d) (scenario 4), cessation of industrial district withdrawsand (scenario 5), and a scavenger well with withdrawal reductions (scenario 6) for: A, well EB-1028; B, well EB-1150; C, well EB-630; D, well EB-781; E

F, hypothetical well EB-X.
Mississippi River

§ ̈¦12

§ ̈¦110

§ ̈¦110

§ ̈¦10

§ ̈¦10

§ ̈¦10

61 67

986

986

76

73

1

1

19

30

37

.190

0 0.5 1 2 KILOMETERS0 0.5 1 2 MILES

Figure 31. Predicted 2047 water levels within the "1,500-foot" sand of the Baton Rouge area in the detailed model areain southeastern Louisiana following cessation of pumping from selected industrial wells in the "1,500-foot" and"1,700-foot" sands beginning in 2015 (scenario 2).

EB-918

EB-168

WBR-173

WBR-132

WBR-97B

EB-1293

EB-807A

EB-789B EB-783A

EB-782B

EB-780B

-1 0 5

-

1

1

0

-9 5

-1 0 0

-1 1 5

-9 0

-

7

5

-

8

0

-

8

5

-1 2 0

-7 0

-6 5

-1 2 5

-

1

0 5

-

9

0

-

1

1

0

-9 5

-1 1 5

-8 5

-

1

0

0

-

1

2

0

91°12'30" 91°10'00" 91°07'30"

30°30'00"30°27'30"30°25'00"

Base map modified from Louisiana Oil Spill Coordinator, Office of theGovernor, Louisiana GIS CD: A Digital Map of the State, Version 2.0Map Projection: North American Datum of 1983, Universal Transverse Mercator Zone 15

Figure 31. Map showing predicted 2047 water levels within the “1,500-foot” sand of the Baton Rouge area in the detailed model area in southeastercessation of pumping from selected industrial wells in the “1,500-foot” and “1,700-foot” sands beginning in 2015 (scenario 2).
Hypothetical Groundwater-management Scenarios 53

Scenario 3: Scavenger Well Withdrawal from 

the Base of the “2,000-foot” Sand

One proposed strategy to mitigate the northward 

migration of the saltwater plume is the installation and 

operation of a “scavenger” well that is screened at the base 

of the “2,000-foot” sand, where multidepth observations of 

chloride concentrations within the aquifer have indicated 

that higher concentrations exist (Tomaszewski, 1996). The 

scavenger well would withdraw the higher-concentration 

groundwater from the base of the aquifer, which would 

subsequently require desalinization and (or) disposal. For 

scenario 3, the effects of pumping 2.0 Mgal/d from the 

bottom (layer 18) of the “2,000-foot” sand on water levels 

and chloride concentrations were simulated for two possible 

scavenger well locations. In scenario 3, total simulated 

withdrawals from the “2,000-foot” sand north of the fault 

remained at 25.3 Mgal/d during 2007–16 but increased to 

27.3 Mgal/d during 2017–47. The effects of scavenger well 

activation in 2017 at each location was simulated separately.

Because of the additional 2 Mgal/d withdrawal from the 

scavenger well, water-levels simulated for 2047 in the “2,000-

foot” sand for both scavenger well locations are generally 

about 10 to 15 ft lower than those predicted for scenario 1 

(the “status quo” simulation), and the lowest water-levels are 

predicted in the same locations of the industrial district as in 

scenario 1 (figs. 32 and 33). Water-level contours depict the 

drawdown around each of the scavenger wells, where 2047 

water-level altitudes of about -260 ft are simulated.

For scenario 3a, the scavenger well was simulated in 

model row 57, column 26 (fig. 32). Predicted 2047 chloride 

concentrations in layer 18 (the base of the “2,000-foot” sand) 

indicate that although the lowest-concentration front of the 

saltwater plume continues to migrate northward toward the 

industrial district, the concentrations between the scavenger 

well and the industrial district are lower than in scenario 1 (fig. 

27). Higher chloride concentrations within the central portion 

of the plume between the scavenger well and the Baton Rouge 

Fault might result from more movement of saltwater because 

of the larger hydraulic gradients generated by the 2 Mgal/d 

withdrawal from the scavenger well.

For scenario 3b, a scavenger well was simulated in 

model row 68, column 30 (fig. 33). Predicted 2047 chloride 

concentrations in layer 18 indicate that the saltwater plume 

would also continue to migrate northward toward withdrawal 

wells in the industrial district with concentrations lower than 

in scenario 1. Predicted chloride concentration within the 

central portion of the plume between this scavenger well 

location and observation wells EB-630 and EB-1150 are lower 

than those predicted for either scenario 1 or scenario 3a (the 

other scavenger well location).

 In comparison to the concentrations simulated in 

scenario 1, operation of the scavenger well in the locations 

specified in scenarios 3a and 3b reduces the chloride 

concentrations at all existing chloride-observation well 

locations (fig. 30). At EB-X, the hypothetical observation 

location near the leading-edge of the plume, predicted 2047 

chloride concentrations decrease from the 187 mg/L predicted 

in scenario 1 to 50 mg/L and 80 mg/L for scenarios 3a and 3b, 

respectively (fig. 30F). 

Scenario 4: Reduction of Groundwater 

Withdrawals from the “2,000-foot” Sand in the 

Baton Rouge Industrial District

Reduction of groundwater withdrawals from the “2,000-

foot” sand in the Baton Rouge industrial district would 

decrease the hydraulic gradient toward that area and limit the 

northward advective transport of saltwater. A reduction of 3.6 

Mgal/d from selected wells screened in the “2,000-foot” sand 

in the industrial district was simulated beginning in 2015. 

In scenario 4, total simulated withdrawals from the “2,000-

foot” sand north of the fault remained at 25.3 Mgal/d during 

2007–14 but decreased to 21.7 Mgal/d during 2015–47. 

Contours of water levels predicted within the “2,000-

foot” sand (fig. 34) for 2047 illustrate similar groundwater 

flow to that predicted for scenario 1 but are generally between 

20 and 35 ft higher in the Baton Rouge area. The lowest waterlevel altitude of about -215 ft is predicted within the industrial 

district in the same location as that predicted for scenario 1.

The map of simulated chloride concentrations for 2047 

at the base of the “2,000-foot” sand (fig. 34) indicates that 

although the saltwater plume would continue to migrate 

northward toward the industrial district withdrawal wells 

following a 3.6 Mgal/d withdrawal reduction, concentrations 

in the leading portion of the plume would be lower. The 

simulated concentration at EB-X is 85 mg/L (fig. 30F), 

which is less than half of the concentration predicted for 

scenario 1. In contrast, concentrations at observation wells 

EB-1028 and EB-807B increase with respect to scenario 1 

because decreased flow toward the industrial district results in 

relatively more flow toward the area of municipal withdrawals 

1 mi north of EB-807B. The area with a chloride concentration 

greater than 10 mg/L is similar to that predicted in scenario 1, 

as are the median and mean plume concentrations (table 6).

Scenario 5: Cessation of Groundwater 

Withdrawals from the “2,000-foot” Sand in the 

Baton Rouge Industrial District

Zero withdrawals from all 19 production wells screened 

in the “2,000-foot” sand in the industrial district (fig. 9) 

were specified beginning in 2015 to simulate cessation of 

withdrawals in the industrial district. In scenario 5, total 

simulated withdrawals from the “2,000-foot” sand north of 

the fault remained at 25.3 Mgal/d during 2007–14 but were 

reduced by 16.6 Mgal/d to 8.7 Mgal/d during 2015–47. In 

comparison to scenario 1, this scenario simulated the largest 

increase in water levels and change in chloride concentrations 

within the “2,000-foot” sand. The simulated 2047 water-level 
Mississippi River

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Figure 32. Predicted 2047 water levels and chloride concentrations at the base of the "2,000-foot" sand of theBaton Rouge area in the detailed model area in southeastern Louisiana after pumping at a rate of 2 million gallonsper day from a simulated scavenger well located in model row 57 and column 26 beginning in 2017 (scenario 3).

EB-781

EB-807B

EB-1028

EB-630 EB-1150

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In

BP     W  W H S 

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EB-781

EB-X

-180

102141811632641,2,5,

91°12'30" 91°10'00" 91°07'30"

30°30'00"30°27'30"30°25'00"

Base map modified from Louisiana Oil Spill Coordinator, Office of theGovernor, Louisiana GIS CD: A Digital Map of the State, Version 2.0Map Projection: North American Datum of 1983, Universal Transverse Mercator Zone 15

Figure 32. Map showing predicted 2047 water levels and chloride concentrations at the base of the “2,000-foot” sand of the Baton Rouge area in the southeastern Louisiana after pumping at a rate of 2 million gallons per day from a simulated scavenger well located in model row 57 and column 26 be
Mississippi River

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Figure 33. Predicted 2047 water levels and chloride concentrations at the base of the "2,000-foot" sand of theBaton Rouge area in the detailed model area in southeastern Louisiana after pumping at a rate of 2 million gallonsper day from a simulated scavenger well located in model row 68 and column 30 starting in 2017 (scenario 3).

EB-781

EB-807B EB-1028

EB-630

EB-1150

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EB-874

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10–21–41–81–1613216411,22,55,1

91°12'30" 91°10'00" 91°07'30"

30°30'00"30°27'30"30°25'00"

Base map modified from Louisiana Oil Spill Coordinator, Office of theGovernor, Louisiana GIS CD: A Digital Map of the State, Version 2.0Map Projection: North American Datum of 1983, Universal Transverse Mercator Zone 15

Figure 33. Map showing predicted 2047 water levels and chloride concentrations at the base of the “2,000-foot” sand of the Baton Rouge area in the southeastern Louisiana after pumping at a rate of 2 million gallons per day from a simulated scavenger well located in model row 68 and column 30 st
Mississippi River

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Figure 34. Predicted 2047 water levels and chloride concentrations at the base of the "2,000-foot" sand of theBaton Rouge area in the detailed model area in southeastern Louisiana after a 3.6 million gallon per day reductionin pumping (from 2007 rates) at selected wells in the Baton Rouge industrial district beginning in 2015 (scenario 4).

Ind

BaPre     Wa  We Hy 

Pre 

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91°12'30" 91°10'00" 91°07'30"

30°30'00"30°27'30"30°25'00"

Base map modified from Louisiana Oil Spill Coordinator, Office of theGovernor, Louisiana GIS CD: A Digital Map of the State, Version 2.0Map Projection: North American Datum of 1983, Universal Transverse Mercator Zone 15

Figure 34. Map showing predicted 2047 water levels and chloride concentrations at the base of the “2,000-foot” sand of the Baton Rouge area in the in southeastern Louisiana after a 3.6 million gallon per day reduction in pumping (from 2007 rates) at selected wells in the Baton Rouge industrial distr(scenario 4).
Hypothetical Groundwater-management Scenarios 57

altitudes within the “2,000-foot” sand (fig. 35) are 95 to 

165 ft higher than those in scenario 1, and the direction of 

groundwater flow in the Baton Rouge area differs. In scenarios 

1 through 4, groundwater flow in the “2,000-foot” sand is 

generally toward the area of water-level drawdown under the 

industrial district, whereas in scenario 5, groundwater flows 

toward an area of water-level drawdown about 0.5 mi north 

of EB-807B (fig. 35). Minimum groundwater levels of about 

-114 ft reflect the continued municipal withdrawals from the 

“2,000-foot” sand in this area.

The simulated chloride-concentration distribution (fig. 

35) in this scenario reflects the change in groundwater-flow 

direction. Although some saltwater would continue to cross 

the Baton Rouge Fault and encroach toward municipal 

supply wells in the area of drawdown about 0.5 mi north of 

EB-807B, further encroachment toward the industrial district 

would be abated. Saltwater within the “2,000-foot” sand 

that is presently encroaching south of the industrial district 

(fig. 27) would be replaced by freshwater flowing from the 

northwest. The simulated chloride concentration at the base 

of the “2,000-foot” sand at EB-X decreases to “background 

concentrations” below 10 mg/L by 2047 (fig. 30F). Because 

saltwater is no longer transported toward the industrial district 

in this scenario, relatively more of it is transported toward 

the area of municipal groundwater withdrawals north of 

EB-807B. Consequently, the simulated chloride concentration 

at well EB-807B is about twice that simulated in scenario 1. 

Simulated chloride concentrations at EB-1028 and EB-1150 

initially increase as higher-concentration water west of those 

observation wells begins to flow eastward but subsequently 

decline as it is replaced by fresher water from west of the 

plume. Concentrations simulated in well EB-781 remain 

similar to the other scenarios because it is close to the salt 

source where concentrations are less sensitive to the simulated 

pumping distribution.

Scenario 6: Scavenger Well Combined with a 

Reduction of 1.375 Million Gallons Per Day of 

Industrial District Withdrawal from the “2,000-

foot” Sand

Analysis of the preceding scenarios suggested an additional 

scenario in which industrial district withdrawal reductions from 

the “2,000-foot” sand beginning in 2015 are combined with the 

activation of a “scavenger well couple” in 2017 at the location 

simulated in scenario 3b (row 68, column 30). In scenario 6, 

withdrawals from EB-810, EB-851, and EB-884, all located 

in the industrial district and screened in the “2,000-foot” sand 

(fig. 9), were reduced by a total of 1.4 Mgal/d from their 2007 

withdrawal rates. The “scavenger well couple” consists of 

a lower well that withdraws 1 Mgal/d from the base of the 

“2000-foot” sand (layer 18) and an upper well that withdraws 

1.5 Mgal/d from the upper third of the “2000-foot” sand (layers 

9–11). Because the 1.5 Mgal/d withdrawn from the upper well 

may be usable for public supply, 1.5 Mgal/d of compensating 

withdrawal reductions (with respect to 2007 rates) were 

specified from five public supply wells, including EB-151, 

EB-630, EB-774, EB-814, and EB-1150 (fig. 9). Well EB-151 

is screened in both the “2,000-foot” sand and the “2,400-foot” 

sand. Because zero withdrawals were specified from well 

EB-151 in scenario 6, where water levels within the “2,400-

foot” sand are higher than within the “2,000-foot” sand, up to 

0.35 Mgal/d (242 gpm) of water flows through EB-151 from 

the “2,400-foot” sand into the “2,000-foot” sand after 2017. In 

scenario 6, total simulated withdrawals from the “2,000-foot” 

sand north of the fault remained at 25.3 Mgal/d during 2007–14, 

decreased to 23.9 Mgal/d during 2015–16, then increased to 

24.9 Mgal/d during 2017–47. 

The saltwater plume continues to migrate toward the 

industrial district in scenario 6 (fig. 36), but the concentrations 

within the plume are lower than those simulated for scenario 

1. The chloride concentration simulated for 2047 is reduced 

from 187 to 115 mg/L at well EB-X (fig. 30), which is a smaller 

reduction than those simulated for scenarios 3, 4, or 5. Scenario 

6 predicts the smallest plume area and lowest mean and median 

chloride concentration in 2047 (table 6), which suggests it is 

more effective in reducing saltwater concentrations within the 

“2,000-foot” sand in the Baton Rouge area. 
Mississippi River

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Figure 35. Predicted 2047 water levels and chloride concentrations at the base of the "2,000-foot" sand of theBaton Rouge area in the detailed model area in southeastern Louisiana following cessation of pumping from the2000-ft sand in the Baton Rouge industrial district beginning in 2015 (scenario 5).

In

BP    W  W H 

P 

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91°12'30" 91°10'00" 91°07'30"

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Base map modified from Louisiana Oil Spill Coordinator, Office of theGovernor, Louisiana GIS CD: A Digital Map of the State, Version 2.0Map Projection: North American Datum of 1983, Universal Transverse Mercator Zone 15

Figure 35. Map showing predicted 2047 water levels and chloride concentrations at the base of the “2,000-foot” sand of the Baton Rouge area in the southeastern Louisiana following cessation of pumping from the “2000-foot” sand in the Baton Rouge industrial district beginning in 2015 (scenario 5)
Mississippi River

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Figure 36. Predicted 2047 water levels and chloride concentrations at the base of the "2,000-foot" sand of theBaton Rouge area in the detailed model area in southeastern Louisiana after pumping from a scavenger welllocated in model row 68 and column 30 beginning in 2017 and reduced withdrawals at selected industrial andpublic supply wells beginning in 2015 (scenario 6).

EB-781

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BaPr    W  W Hy Sc 

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102141811632641,22,55,1

91°12'30" 91°10'00" 91°07'30"

30°30'00"30°27'30"30°25'00"

Base map modified from Louisiana Oil Spill Coordinator, Office of theGovernor, Louisiana GIS CD: A Digital Map of the State, Version 2.0Map Projection: North American Datum of 1983, Universal Transverse Mercator Zone 15

Figure 36. Map showing predicted 2047 water levels and chloride concentrations at the base of the “2,000-foot” sand of the Baton Rouge area in the southeastern Louisiana after 31 years of pumping from a scavenger well located in model row 68 and column 30 beginning in 2017 and reduced withdand public supply wells beginning in 2015 (scenario 6).
60 Simulation of Groundwater Flow in the “1,500-Foot” Sand and “2,000-Foot” Sand in the Baton Rouge Area, Louisiana

Summary

Groundwater withdrawals in the Baton Rouge area since 

the 1940s have lowered water levels and altered groundwaterflow directions in the freshwater aquifers of the Southern Hills 

aquifer system. Generally, aquifers south of the Baton Rouge 

Fault contain saltwater, and aquifers north of the fault contain 

freshwater. The drawdown of groundwater levels has caused 

saltwater to encroach into previously freshwater areas in the 

Baton Rouge area. Saltwater encroachment has been detected 

north of the Baton Rouge Fault in East Baton Rouge Parish 

in 7 of the 10 Baton Rouge sands, including the “1,500-foot” 

sand and “2,000-foot” sand. The 10 aquifers that underlie the 

Baton Rouge area, which includes East and West Baton Rouge 

Parishes, Pointe Coupee Parish, and East and West Feliciana 

Parishes, provided about 167 million gallons per day (Mgal/d) 

for public supply and industrial use in 2010. Groundwater 

withdrawals from the “2,000-foot” sand, which totaled 23.9 

Mgal/d during 2010, have resulted in measured water-level 

drawdowns as great as 356 feet (ft) and saltwater migration 

from south of the fault into the “2,000-foot” sand. This 

saltwater threatens industrial wells located about 3 miles (mi) 

north of the fault. A groundwater flow and saltwater transport 

model was constructed to assess the effects of groundwater 

withdrawals on the rate and pathways of saltwater migration.

Because density differences between groundwater 

areas with contrasting saltwater concentrations may affect 

groundwater flow between those areas, both constant- and 

variable-density simulations of groundwater flow were 

utilized. The groundwater-flow simulation was initially 

constructed with MODFLOW and calibrated to observed 

water levels with PEST. The calibrated groundwater-flow 

model parameters were subsequently utilized for the variabledensity SEAWAT version of the model, which simulated both 

groundwater flow and solute transport. Although much of the 

model input for SEAWAT is identical to MODFLOW input, 

withdrawal fluxes previously computed with the MODFLOW 

multi-node well package were used to specify WEL package 

input for SEAWAT. Additional input was constructed to define 

transport boundary and initial conditions, transport properties, 

and specification of the equation of state relating solute 

concentration to groundwater density. The groundwater flow 

and solute-transport equations are coupled because SEAWAT 

iteratively solves each equation for every transport time step 

such that computed concentrations affect groundwater density 

and can therefore influence groundwater velocities. 

A three-dimensional hydrogeologic framework was 

constructed to define the extents and thicknesses of the 

aquifers and confining units in the study area. The framework 

consists of 22 layers that represent the entire sequence of 

sands and clays from land surface to the base of the “2,800-

foot” sand. Layers 1, 3, 5, 7, 9–18, 20, and 22 compose the 

aquifer layers. Layers 2, 4, 6, 8, 19, and 21 compose the 

confining units that separate aquifer layers. Layers 1 and 

3 represent multiple aquifers that have similar hydraulic 

characteristics and are likely interconnected. Layer 1 

represents the Mississippi River alluvial aquifer, shallow 

sands, upland terrace aquifer, and the “400-foot” sand, “600-

foot” sand, and “800-foot” sand. Layer 3 includes the “1,000-

foot” sand and “1,200-foot” sand. The “2,000-foot” sand is 

represented by 10 layers numbered 9 through 18.

A finite-difference grid with lateral cell dimensions of 

500 by 500 ft in the Baton Rouge area has increasing cell 

spacing toward the model-domain boundaries so that the 

entire 6,529 square mile study area is discretized with 85 

rows and 85 columns of finite-difference cells. Vertical finitedifference discretization was defined such that model-cell 

layers correspond to the tops of hydrogeologic framework 

units north of the Baton Rouge Fault and are horizontal along 

columns from the fault southward. Because the Hydrogeologic 

Unit-Flow Package was used to define the hydrogeologic 

framework geometry independently from finite-difference 

discretization, this discretization scheme facilitated simulation 

of flow between hydrogeologic units where they are 

juxtaposed at the Baton Rouge Fault. Additional resistance 

to flow across the Baton Rouge Fault was simulated with 

horizontal flow barriers. Following an initial steady-state 

stress period that simulated predevelopment conditions prior 

to 1940, 68 annual transient stress periods simulated time 

from 1940 through 2007. The period from 2008 through 2011 

was simulated with 2007 withdrawal rates. Three additional 

stress periods were used for scenarios that simulate future 

conditions through 2047.

Boundary conditions utilized for the groundwater-flow 

simulation included specified flux, specified head, and headdependent flux types. Transient water levels within the top 

model layer, which represents the “400-foot” sand, “600-

foot” sand, and “800-foot” sand, were specified by linear 

interpolation between levels constructed for 1944, 1980, 

1984, 1990, 1998, 1999, and 2004. Water levels in the top 

model layer for simulated times before 1944 and after 2004 

were specified at the 1944 and 2004 levels, respectively. A 

constant-head boundary was specified along row 85 in the 

bottom model layer, which corresponds to the southernmost 

extent of the “2,800-foot” sand. The water-level for this 

boundary, which was estimated as a parameter during model 

calibration, enabled simulation of underflow to and from areas 

south of the simulated aquifer system. The remaining lateral 

and lower boundaries of the flow domain were simulated as 

no-flow boundaries. The layer-by-layer withdrawals simulated 

by the MODFLOW multi-node well package depend upon 

water levels simulated in the model layers in which wells 

have screens and are therefore head-dependent fluxes. The 

equivalent fluxes specified using the WEL package in the 

SEAWAT simulation are the specified-flux type.

Average daily withdrawal rates were specified for 605 

wells with the multi-node well package for each annual stress 

period from 1940 through 2007. After calibration of the 

MODFLOW model, the simulated layer-by-layer fluxes in and 

out of each well were specified as WEL package input for the 

SEAWAT simulation.
Selected References 61

The area in which solute transport was simulated 

with SEAWAT is a subset of the flow model domain and 

corresponds to the 50 row by 55 column portion of the grid 

with 500 by 500 ft finite-difference cells in the Baton Rouge 

area. Model-grid cells within this area south of the Baton 

Rouge Fault are constant-concentration boundaries; cells 

north of the fault are variable-concentration cells for which a 

concentration was calculated for each transport time step.

The initial chloride concentration within model-grid 

cells adjacent to the south side of the Baton Rouge Fault, 

east of column 30, and from model-grid layers 9 through 18 

(inclusive) was specified to increase linearly with depth from 

zero to a maximum concentration, which was parameterized 

and estimated during model calibration to be 10,000 

milligrams per liter (mg/L). These model grid layers are 

laterally connected to the 10 layers that simulate the “2,000-

foot” sand north of the fault. All other portions of the solute 

transport domain were assigned a zero initial concentration.

The groundwater-flow model was calibrated to 3,612 

water levels measured between 1940 and 2007 from 137 

observation wells with the parameter-estimation code PEST. 

Additional water levels were used to evaluate the accuracy of 

the specified-head boundaries in the top model layer and the fit 

of simulated-to-observed water levels during the period 2008 

through 2011. The estimated values of hydraulic property 

parameters were all within the range considered reasonable. 

Six hypothetical scenarios simulated the effects of 

different groundwater withdrawal options on groundwater 

levels within the “1,500-foot” sand and the “2,000-foot” sand 

and the transport of saltwater within the “2,000-foot” sand. All 

scenarios simulated 2007 withdrawal rates for a 7-year period 

from 2008 through 2014 and various withdrawal options 

during three subsequent periods that simulate 2015 through 

2047. Scenario 1 is considered a base case for comparison to 

the other five scenarios and simulates continuation of 2007 

reported groundwater withdrawals. Scenario 2 simulates 

discontinuation of withdrawals from seven selected industrial 

wells located in the northwest corner of East Baton Rouge 

Parish that are screened either in the “1,500-foot” sand or 

an adjacent aquifer. Water levels within the “1,500-foot” 

sand were predicted to be about 10 to 12 ft higher under this 

withdrawal scenario than under scenario 1. 

Four other scenarios test various groundwater 

withdrawal options on the water levels and predicted chloride 

concentrations within the “2,000-foot” sand. Scenario 3a and 

3b simulate the effects of a scavenger well that withdraws 

2.0 Mgal/d from the base of the “2,000-foot” sand at two 

possible locations on water levels and concentrations within 

the “2,000-foot” sand. Scenario 4 simulates a 3.6 Mgal/d 

reduction in total groundwater withdrawals from selected 

wells screened in the “2,000-foot” sand that are located in 

the Baton Rouge industrial district. Scenario 5 simulates the 

effect of total cessation of groundwater withdrawals from 

the “2,000-foot” sand in the industrial district. Scenario 6 

simulates the combined effect of a 1.4 Mgal/d withdrawal 

reduction from the industrial district, a scavenger well that 

withdraws 1.0 Mgal/d from the base of the “2000-foot” sand, 

a well that withdraws 1.5 Mgal/d from the upper third of the 

“2000-foot” sand at the scavenger location, and 1.5 Mgal/d 

of total withdrawal reductions from other public-supply wells 

screened in the “2000-foot” sand.

In comparison to the concentrations simulated in 

scenario 1, operation of the scavenger well in the locations 

specified in scenario 3 reduces the chloride concentrations at 

all existing chloride-observation well locations. In scenario 

4, the concentration decreased in the leading portion of the 

plume south of the industrial district but increased in other 

areas; the size of the plume area and median, and mean 

chloride concentrations are similar to scenario 1. The chlorideconcentration distribution in scenario 5 reflects the change in 

groundwater-flow direction toward municipal supply wells in 

the area of drawdown about 1.5 mi north of the Baton Rouge 

fault, where chloride concentrations increased in comparison 

to scenario 1. Although scenario 6 simulated a smaller 

concentration reduction at EB-X (south of the industrial 

district), it was most effective at decreasing the size of the 

plume area and median and mean chloride concentrations 

within the “2000-foot” sand in the Baton Rouge area.

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