U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2015–5083

Version 1.1, September 2015

Simulation of Groundwater Flow and Chloride Transport in 

the “1,200-Foot” Sand With Scenarios To Mitigate Saltwater 

Migration in the “2,000-Foot” Sand in the Baton Rouge Area, 

Louisiana

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 and 

Chloride Transport in the “1,200-Foot” 

Sand With Scenarios To Mitigate Saltwater 

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

Baton Rouge Area, Louisiana

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

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

Scientific Investigations Report 2015–5083

Version 1.1, September 2015

U.S. Department of the Interior

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

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

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

First release: 2015

Revised: September 2015 (ver. 1.1)

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Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials 

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Suggested citation:

Heywood, C.E., Lovelace, J.K., and Griffith, J.M., 2015, Simulation of groundwater flow and chloride transport in the 

“1,200-foot” sand with scenarios to mitigate saltwater migration in the “2,000-foot” sand in the Baton Rouge area, 

Louisiana (ver. 1.1, September 2015): U.S. Geological Survey Scientific Investigations Report 2015–5083, 69 p.,

http://dx.doi.org/10.3133/sir20155083.

ISSN 2328-031X (print)

ISSN 2328-0328 (online)

ISBN 978-1-4113-3927-9
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 members 

of the Capital Area Groundwater Conservation Commission provided guidance and assistance 

throughout this investigation.

v

Contents

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

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

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

Previous Investigations .......................................................................................................................2

Study Area Description .......................................................................................................................4

Horizontal Datum and Projection Systems ......................................................................................4

Hydrogeology .................................................................................................................................................4

Baton Rouge Fault ................................................................................................................................6

Occurrence and Movement of Saltwater ........................................................................................6

Hydrogeologic Framework .................................................................................................................9

Groundwater Withdrawals ..........................................................................................................................9

Simulation of Groundwater Flow and Chloride Transport ....................................................................10

Conceptual Model for Solute Transport .........................................................................................11

Equations of Groundwater Flow and Transport ............................................................................14

Spatial Discretization ........................................................................................................................14

Internal Flow Package ......................................................................................................................17

Horizontal Flow Barriers ...................................................................................................................17

Time Discretization ............................................................................................................................17

Boundary Conditions .........................................................................................................................18

No-Flow Boundaries ................................................................................................................18

Specified-Head Boundaries ....................................................................................................18

Head-Dependent Flux Boundaries .........................................................................................21

Specified-Concentration Boundaries and Initial Conditions .............................................21

Hydraulic-Property Distribution ......................................................................................................21

Model Calibration ........................................................................................................................................23

Calibration Dataset ............................................................................................................................23

Water-Level Observations .......................................................................................................23

Chloride-Concentration Observations ...................................................................................24

Observation and Prior-Information Weights ........................................................................24

Calibration Assessment ....................................................................................................................24

Estimated Parameter Values ...................................................................................................24

Parameter Sensitivities ............................................................................................................25

Simulated Groundwater Conditions .........................................................................................................26

Simulated Water Levels ....................................................................................................................26

Simulated Water Budget ..................................................................................................................26

Simulated Concentrations ................................................................................................................31

Limitations and Appropriate Use of the Model ......................................................................................31

Scenarios To Mitigate Saltwater Migration ...........................................................................................35

Scenario 1: Continued Groundwater Withdrawals at 2012 Rates .............................................35

Scenario 2: Increased Groundwater Withdrawals From the “1,200-Foot” Sand ....................43

Scenario 3: Modification of Groundwater Withdrawals From the “2,000-Foot” Sand ...........43
vi

Scenario 4: Modification of Groundwater Withdrawals With Installation of a Scavenger 

Well in the “2,000-Foot” Sand ............................................................................................48

Scenario 5: Reduction of Industrial Withdrawals From the “2,000-Foot” Sand ......................54

Scenario 6: Extensive Reduction of Industrial and Public-Supply Withdrawals From the 

“2,000-Foot” Sand .................................................................................................................54

Scenario 7: Extensive Reduction of Industrial and Public-Supply Withdrawals With 

Installation of a Scavenger Well in the “2,000-Foot” Sand ...........................................59

Scenario Comparison ........................................................................................................................59

Summary .......................................................................................................................................................65

References ...................................................................................................................................................67

Figures

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

control wells, and simulated groundwater-withdrawal wells in southeastern 

Louisiana and southwestern Mississippi ................................................................................5

2. Map showing location of the finite-difference grid and simulated altitude of the 

top of the “1,200-foot” sand of the Baton Rouge area in southeastern Louisiana 

and southwestern Mississippi ...................................................................................................7

3. Map showing simulated thickness of the “1,200-foot” sand of the Baton Rouge 

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

4. Graph showing estimated withdrawals from the Baton Rouge sands, 1940–2012 ........11

5. Map showing average daily withdrawal rate during 2012 at wells screened in 

the “1,200-foot” sand of the Baton Rouge area and located at or near the 

Baton Rouge industrial district in southeastern Louisiana .................................................12

6. Map showing average daily withdrawal rate during 2012 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 and location of hypothetical 

supply well screened in the “2,000-foot” sand .....................................................................13

7. Map showing the finite-difference grid, locations of horizontal flow barriers, 

and selected water-level and chloride observation wells screened in the 

“1,200-foot” sand of the Baton Rouge area in the detailed model area in 

southeastern Louisiana ............................................................................................................15

8. Map showing north-to-south cross section along model column 24 showing 

aquifers, confining units, and finite-difference discretization ...........................................16

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

conductivity distribution within the “1,200-foot” sand of the Baton Rouge area 

in the detailed model area in southeastern Louisiana ........................................................22

10. Graph showing water-level residuals as a function of simulated water-level 

altitudes .......................................................................................................................................25

11. Map showing simulated steady-state water levels within the “1,200-foot” sand 

of the Baton Rouge area representing predevelopment conditions (before 1940) in 

southeastern Louisiana and southwestern Mississippi ......................................................27

12. Map showing simulated 2012 water levels and chloride concentrations in the 

“1,200-foot” sand of the Baton Rouge area in the detailed model area in 

southeastern Louisiana ............................................................................................................28
vii

13. Graphs showing simulated and observed water-level altitudes within the 

“1,200-foot” sand of the Baton Rouge area in southeastern Louisiana ...........................29

14. Graph showing simulated groundwater withdrawals and flows from storage 

and specified-head boundaries ..............................................................................................30

15. Graphs showing simulated and observed chloride concentrations at 

observation wells within the “1,200-foot” sand of the Baton Rouge area in 

southeastern Louisiana ............................................................................................................32

16. Graphs showing simulated and observed chloride concentrations at 

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

southeastern Louisiana ............................................................................................................33

17. Map showing simulated 2012 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 ...............................................................................................34

18. Map showing predicted 2047 water levels and chloride concentrations in the 

“1,200-foot” sand of the Baton Rouge area in the detailed model area in 

southeastern Louisiana after continued pumping at 2012 rates (scenario 1) .................36

19. Map showing predicted 2112 water levels and chloride concentrations in the 

“1,200-foot” sand of the Baton Rouge area in the detailed model area in 

southeastern Louisiana after continued pumping at 2012 rates (scenario 1) .................37

20. 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 2012 rates (scenario 1) .............38

21. Map showing predicted 2112 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 2012 rates ..........................40

22. Graphs showing observed and predicted chloride concentrations at the base 

of the “2,000-foot” sand resulting from pumping rates specified for scenarios 

1, 3, 4a, 4b, 5, 6, 7a, and 7b for observation wells and a scavenger well in the 

detailed model area in the Baton Rouge area in southeastern Louisiana .......................41

23. Map showing predicted 2047 water levels and chloride concentrations in the 

“1,200-foot” sand of the Baton Rouge area in the detailed model area in 

southeastern Louisiana after a pumping increase (from 2012 rates) of 2 million 

gallons per day at selected wells in the Baton Rouge industrial district beginning 

in 2015 (scenario 2) ....................................................................................................................44

24. Map showing predicted 2112 water levels and chloride concentrations in the 

“1,200-foot” sand of the Baton Rouge area in the detailed model area in 

southeastern Louisiana after a pumping increase (from 2012 rates) of 2 million 

gallons per day at selected wells in the Baton Rouge industrial district beginning 

in 2015 (scenario 2) ....................................................................................................................45

25. 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 is turned off at selected industrial 

and public-supply wells and a hypothetical public-supply well located north of 

the detailed model area in model row 22 and column 34 is turned on starting in 

2015 (scenario 3) ........................................................................................................................46

26. Map showing predicted 2112 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 is turned off at selected industrial 

and public-supply wells and a hypothetical public-supply well located north of 

the detailed model area in model row 22 and column 34 is turned on starting in 

2015 (scenario 3) ........................................................................................................................47
viii

27. 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 is turned off at selected industrial 

and public-supply wells, a hypothetical public-supply well located north of the 

detailed model area in model row 22 and column 34 is turned on in 2015, and a 

scavenger well located in row 64 and column 29 pumps at 2.5 million gallons 

per day beginning in 2017 (scenario 4) ...................................................................................49

28. Map showing predicted 2112 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 is turned off at selected industrial 

and public-supply wells, a hypothetical public-supply well located north of the 

detailed model area in model row 22 and column 34 is turned on in 2015, and a 

scavenger well located in row 64 and column 29 pumps at 2.5 million gallons 

per day beginning in 2017 (scenario 4) ...................................................................................50

29. Graph showing simulated inflow across fault, outflow to wells, and net change 

of salt mass in the “2,000-foot” sand of the Baton Rouge area north of the Baton 

Rouge Fault, 1940–2012, and predicted changes in salt mass, 2013–2112, after 

pumping changes are made at selected industrial and public-supply wells in 

2015 and pumping at a rate of 2.5 million gallons per day from a simulated 

scavenger well begins in 2017 (scenario 4a) ........................................................................51

30. 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 is turned off at selected industrial 

and public-supply wells, a hypothetical public-supply well located north of the 

detailed model area in model row 22 and column 34 is turned on in 2015, and a 

scavenger well located in row 64 and column 29 pumps at 1.25 million gallons 

per day beginning in 2017 (scenario 4b) ................................................................................52

31. Map showing predicted 2112 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 is turned off at selected industrial and 

public-supply wells, a hypothetical public-supply well located in model row 22 

and column 34 is turned on in 2015, and a scavenger well located in row 64 and 

column 29 begins pumping at 1.25 million gallons per day in 2017 (scenario 4b) ...........53

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 is turned off at selected industrial and 

public-supply wells and a hypothetical public-supply well located north of the 

detailed model area in model row 22 and column 34 is turned on starting in 

2015 (scenario 5) ........................................................................................................................55

33. Map showing predicted 2112 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 is turned off at selected industrial and 

public-supply wells and a hypothetical public-supply well located north of the 

detailed model area in model row 22 and column 34 is turned on starting in 

2015 (scenario 5) ........................................................................................................................56

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 pumping is turned off at selected industrial 

and public-supply wells and a hypothetical public-supply well located north of 

the detailed model area in model row 22 and column 34 is turned on starting in 

2015 (scenario 6) ........................................................................................................................57
ix

35. Map showing predicted 2112 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 is turned off at selected industrial 

and public-supply wells and a hypothetical public-supply well located north of 

the detailed model area in model row 22 and column 34 is turned on starting in 

2015 (scenario 6) ........................................................................................................................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 pumping is turned off at selected industrial 

and public-supply wells, a hypothetical public-supply well located north of the 

detailed model area in model row 22 and column 34 is turned on in 2015, and a 

scavenger well located in row 64 and column 29 pumps at 2.5 million gallons 

per day beginning in 2017 (scenario 7a) ................................................................................60

37. Map showing predicted 2112 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 is turned off at selected industrial 

and public-supply wells, a hypothetical public-supply well located north of the 

detailed model area in model row 22 and column 34 is turned on in 2015, and a 

scavenger well located in row 64 and column 29 pumps at 2.5 million gallons 

per day beginning in 2017 (scenario 7a) ................................................................................61

38. 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 is turned off at selected industrial 

and public-supply wells, a hypothetical public-supply well located north of the 

detailed model area in model row 22 and column 34 is turned on in 2015, and a 

scavenger well located in row 64 and column 29 pumps at 1.25 million gallons 

per day beginning in 2017 (scenario 7b) ................................................................................62

39. Map showing predicted 2112 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 is turned off at selected industrial 

and public-supply wells, a hypothetical public-supply well located north of the 

detailed model area in model row 22 and column 34 is turned on in 2015, and a 

scavenger well located in row 64 and column 29 pumps at 1.25 million gallons 

per day beginning in 2017 (scenario 7b) ................................................................................63

40. Graph showing simulated salt mass in the “2,000-foot” sand of the Baton Rouge 

area north of the Baton Rouge Fault, 1940–2012, and predicted salt mass during 

eight hypothetical pumping scenarios, 2013–2112 ...............................................................64

41. Graph showing predicted changes in salt mass in the “2,000-foot” sand of the 

Baton Rouge area north of the Baton Rouge Fault, 1940–2012, and predicted 

changes in salt mass during eight hypothetical pumping scenarios, 2013–2112 ...........64
x

Tables

1. Aquifers and aquifer systems in southern Mississippi and southeastern Louisiana 

and corresponding model layers ..............................................................................................3

2. Discretization of the years 1900–2112 simulated in the model of the Southern Hills 

regional aquifer system ............................................................................................................17

3. Calibrated parameter values and sensitivities of the groundwater-flow model..............19

4. Simulated steady-state and transient water budgets .........................................................30

5. Plume area and average chloride concentrations simulated for 2012 and 

predicted for 2047 at the base of the “2,000-foot” sand (layer 20) ....................................39

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 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).
xi

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

GIS geographic information system

HFB horizontal flow barrier

HUF Hydrogeologic-Unit Flow package

IMT Integrated Mass Transport package

[L] length dimension

[M] mass dimension

MNW2 multinode well package

RMSE root-mean-square error

[T] time dimension

USGS U.S. Geological Survey

UTM Universal Transverse Mercator

Simulation of Groundwater Flow and Chloride Transport 

in the “1,200-Foot” Sand With Scenarios To Mitigate 

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

Rouge Area, Louisiana

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

Abstract

Groundwater withdrawals have caused saltwater to 

encroach into freshwater-bearing aquifers beneath Baton 

Rouge, Louisiana. 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 184.3 million gallons per day (Mgal/d) 

for public supply and industrial use in 2012. Groundwater 

withdrawals from the “1,200-foot” sand in East Baton 

Rouge Parish have caused water-level drawdown as large 

as 177 feet (ft) north of the Baton Rouge Fault and limited 

saltwater encroachment from south of the fault. The recently 

developed groundwater model for simulating transport in the 

“2,000-foot” sand was rediscretized to also enable transport 

simulation within the “1,200-foot” sand and was updated 

with groundwater withdrawal data through 2012. The model 

was recalibrated to water-level observation data through 2012 

with the parameter-estimation code PEST and calibrated to 

observed chloride concentrations at observation wells within 

the “1,200-foot” sand and “2,000-foot” sand. The model is 

designed 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.

Seven hypothetical scenarios predict the effects of 

different groundwater withdrawal options on groundwater 

levels and the transport of chloride within the “1,200-foot” 

sand and the “2,000-foot” sand during 2015–2112. The 

predicted water levels and concentrations for all scenarios 

are depicted in maps for the years 2047 and 2112. The 

first scenario is a base case for comparison to the six other 

scenarios and simulates continuation of 2012 reported 

groundwater withdrawals through 2112 (100 years). The 

second scenario that simulates increased withdrawals from 

industrial wells in the “1,200-foot” sand predicts that water 

levels will be 12–25 ft lower by 2047 and that there will 

be a negligible difference in chloride concentrations within 

the “1,200-foot” sand. The five other scenarios simulate the 

effects of various withdrawal schemes on water levels and 

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

these five other scenarios, three of the scenarios simulate 

only various withdrawal reductions, whereas the two others 

also incorporate withdrawals from a scavenger well that is 

designed to extract salty water from the base of the “2,000-

foot” sand. Two alternative pumping rates (2.5 Mgal/d and 

1.25 Mgal/d) are simulated in each of the scavenger-well 

scenarios. For the “2,000-foot” sand scenarios, comparison 

of the predicted effects of the scenarios is facilitated by 

graphs of predicted chloride concentrations through time at 

selected observation wells, plots of salt mass in the aquifer 

through time, and a summary of the predicted plume area and 

average concentration. In all scenarios, water levels essentially 

equilibrate by 2047, after 30 years of simulated constant 

withdrawal rates. Although predicted water-level recovery 

within the “2,000-foot” sand is greatest for the scenario with 

the greatest reduction in groundwater withdrawal from that 

aquifer, the scavenger-well scenarios are most effective in 

mitigating the future extent and concentration of the chloride 

plume. The simulated scavenger-well withdrawal rate has 

more influence on the plume area and concentration than 

do differences among the scenarios in industrial and publicsupply withdrawal rates.

Introduction

Fresh groundwater is valued for public and industrial 

supply in southeastern Louisiana and the greater 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 total dissolved-solids concentration 

of less than 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 and altered groundwater-flow 

directions in most of the 10 underlying freshwater-bearing 
2 Simulation of Groundwater Flow and Chloride Transport in the “1,200-Foot” Sand, Baton Rouge Area, Louisiana

aquifers. During 2010, about 196 million gallons per day 

(Mgal/d) of groundwater were withdrawn in the Baton Rouge 

area (Sargent, 2011), mostly in East Baton Rouge Parish. 

Groundwater usage in 2010 was primarily for public and 

industrial supply, which consumed about 94 Mgal/d and 

73 Mgal/d, respectively. The drawdown of groundwater levels 

has caused saltwater1 to encroach into freshwater areas near 

Baton Rouge. Saltwater encroachment has been detected in 

seven aquifers, including the “1,200-foot” sand and “2,000-

foot” sand in East Baton Rouge Parish (Lovelace, 2007). 

Water planners and managers need additional knowledge 

of the effects of groundwater withdrawals on the rate and 

pathways of saltwater migration and a tool to assess possible 

management strategies that could control further saltwater 

encroachment in the Baton Rouge area. In response to this 

need, the U.S. Geological Survey (USGS), in cooperation 

with the Capital Area Groundwater Conservation Commission 

(Commission), the Louisiana Department of Transportation 

and Development (DOTD) Public Works and Water Resources 

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

Baton Rouge (City-Parish), developed the groundwaterflow and saltwater-transport model of the Southern Hills 

regional aquifer system (Buono, 1983) that is documented 

in this report. The model simulates the effects of reported 

groundwater withdrawals on groundwater flow in the regional 

aquifer system and the movement of saltwater northward from 

the Baton Rouge Fault in the “1,200-foot” sand and “2,000-

foot” sand in East Baton Rouge Parish. The model simulates 

historical conditions (prior to 2013) and six possible future 

pumping scenarios. The model provides a tool for evaluation 

of the effectiveness of modified pumping rates that may affect 

saltwater encroachment. A digital archive of the groundwater 

model is on file at the USGS Lower Mississippi-Gulf Water 

Science Center 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 a groundwater model that simulates flow in the 

regional aquifer system and chloride transport in the “1,200-

foot” sand and the “2,000-foot” sand in the Baton Rouge area. 

The simulated effects of groundwater withdrawals on water 

levels, flow directions, and the movement of saltwater in the 

“1,200-foot” sand are described. Because the simulated effects 

of groundwater withdrawals on water levels, flow directions, 

1

For the purposes of this report, saltwater is defined as water containing 

greater than 250 mg/L chloride. Concentrations of chloride greater than 

250 mg/L exceed the Secondary Maximum Contaminant Level (SMCL) for 

drinking water (U.S. Environmental Protection Agency, 2006). SMCLs are 

established for contaminants that can adversely affect the aesthetic quality of 

drinking water. At high concentrations or values, health implications, as well 

as aesthetic degradation, also may exist. SMCLs are not federally enforceable 

but are intended as guidelines for the States.

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

described in a previous report (Heywood and others, 2014), 

only new scenarios for managing pumpage and saltwater 

movement within the “2,000-foot” sand are described. 

Seven hypothetical groundwater-management scenarios that 

represent the effects of continued groundwater withdrawals 

at 2012 rates and various modifications to withdrawal rates 

and (or) installation of a “scavenger well” that could affect 

saltwater encroachment in the “1,200-foot” sand or “2,000-

foot” sand beneath the city of Baton Rouge are simulated and 

discussed.

The model documented in this report is a modified 

version of the model previously documented by Heywood and 

others (2014). Differences from the previous version include 

refinement of the hydrogeologic framework to represent the 

“1,000-foot” sand and “1,200-foot” sand as separate aquifers, 

refinement of the horizontal and vertical finite-difference 

discretization to provide more detail in the area of transport 

within the “1,200-foot” sand, specification of reported annual 

groundwater withdrawals from 2008 through 2012, and 

recalibration of model parameters to water levels observed 

through 2012. 

The model domain encompasses an area of 6,529 square 

miles (mi2) in southeastern Louisiana and southwestern 

Mississippi; however, its primary focus is on the “1,200-foot” 

sand and “2,000-foot” sand in a 48-mi2 area in the Baton 

Rouge area (the detailed model area) 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 regional 

aquifer system helped ensure reasonable simulated results 

within the primary area of concern.

Previous Investigations

Several previous reports have 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 east-west 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 freshwater-bearing aquifers in the northern 

parishes of southeastern Louisiana (including those in the 

Baton Rouge area) and the updip 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 
Table 1. Aquifers and aquifer systems in southern Mississippi and southeastern Louisiana and corresponding model layers (modified from Buono, 19Lovelace and Lovelace, 1995; and Griffith, 2003).

??? ?

Oligocene

Miocene

Tertiary Quaternary Pleistocene Pliocene

Catahoula  aquifer system

equivalent 

Jasper equivalent  aquifer system

Evangeline equivalent  aquifer systemChicot equivalent  aquifer system

Southern Hills regional aquifer system

Catahoula  formationHattiesburg  formationCitronelle  formationGraham  ferry  formationPascagoula  formation

Holocene Alluvium Near-surface aquifers

System Series

Aquifer system Aquifer1 unit

Southern 

Mississippi

Franklinton aquifer

Tchefuncte aquiferHammond aquiferAmite aquiferRamsay aquiferLower 

Ponchatoula 

 aquiferBig Branch aquiferKentwood aquiferAbita aquiferCovington aquiferSlidell aquifer

Upland terrace aquiferUpper 

Ponchatoula 

 aquifer

Catahoula aquifer

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

“800-foot” sand

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

“600-foot” san“400-foot” san

Upland terrace

aquifer

No regionally extensive 

hydrogeologic units

Mississippi River 

alluvial aquifer

Shallow sands

Eastern Florida 

Parishes Baton Rouge area

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 11–20. Model layer 24 is the bottom model layer.
4 Simulation of Groundwater Flow and Chloride Transport in the “1,200-Foot” Sand, Baton Rouge Area, Louisiana

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), Whiteman (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 and “600-foot” 

sand (Kuniansky, 1989), the “1,200-foot” sand (Halford and 

Lovelace, 1994), the “1,500-foot” sand and “1,700-foot” 

sand (Huntzinger and others, 1985), and the “2,000-foot” 

sand (Torak and Whiteman, 1982) in the Baton Rouge area. 

Under the USGS regional aquifer-system analysis program, 

the hydrogeologic framework, groundwater chemistry, and 

regional flow patterns in the freshwater aquifers along the 

northern coast of the Gulf of Mexico in Louisiana and parts of 

Texas and Mississippi were described, and groundwater-flow 

models were developed to simulate regional flow patterns 

(Martin and Whiteman, 1990). Heywood and others (2014) 

developed a groundwater-flow model of the aquifers in the 

Baton Rouge area, and much of the background information 

presented herein is from that report.

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, Avoyelles, Concordia, East and West 

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

Pointe Coupee, St. Helena, St. Landry, St. Martin, 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 zero to more than 450 feet 

(ft) (Calhoun and Frois, 1997). The climate is subtropical, 

warm, and temperate, with an average annual temperature of 

68 degrees Fahrenheit (°F) (20 degrees Celsius [°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 

the largest population 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. 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 

Transverse Mercator (UTM) zone 15 coordinate system that 

was used for GIS coverages of wells, the hydrogeologic 

framework, and water levels. Consequently, the model finitedifference grid appears slightly rotated in the UTM projection 

displayed in the map figures in this report. Projection and 

coordinate system details are included 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, and 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 1) 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 on the basis of 

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).
Detailed

model 

area

LakeMaurepas

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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 2.0Universal Transverse Mercator projection, zone 15North American Datum of 1983 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'

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

ADAMS FRANKLIN LINCOLN

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Breaux Bridge

Gonzales

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Figure 1. Location of the study area, the Baton Rouge Fault, geophysical control wells, and simulated groundwater-withdrawal wells in southeastern southwestern Mississippi.
6 Simulation of Groundwater Flow and Chloride Transport in the “1,200-Foot” Sand, Baton Rouge Area, Louisiana

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 materials 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 

updip equivalent units in southwestern Mississippi, form a 

thickening wedge that dips to the south and southwest toward 

the Gulf of Mexico. The confining units generally pinch 

out northward, and deeper aquifers coalesce with overlying 

surficial aquifers.

Precipitation in the northern part of the study area and 

farther north in Mississippi is the primary source of recharge 

to the aquifer system. Because the aquifers are interconnected, 

precipitation that infiltrates 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 in the Baton 

Rouge area. Groundwater velocities range from a few tens 

of feet per year to several hundreds of feet per year (Buono, 

1983).

The “1,200-foot” sand, like other freshwater aquifers in 

the study area, generally dips and thickens to the south and 

consists 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 

aquifer contains multiple sand intervals, the sand intervals are 

separated by clays. The top of the “1,200-foot” sand is about 

1,200 ft below land surface north of the Baton Rouge Fault 

but is displaced downward about 300 ft at the fault (fig. 2). 

The “1,200-foot” sand is continuous throughout the study area 

except in parts of Avoyelles, Concordia, and Point Coupee 

Parishes and in most of Mississippi (fig. 3).

Baton Rouge Fault

The Baton Rouge Fault extends across the southern part 

of the study area (fig. 1) 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 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 Baton Rouge 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 fault ranges from about 

20 ft near the ground surface to about 300 ft at altitudes of 

-1,600 to -3,000 ft.

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, fresh 

groundwater flowed from recharge areas in Mississippi 

southward toward the fault and then upward to discharge 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 

the “2,000-foot” sand contains 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 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 

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). Groundwater withdrawals from 

the “2,000-foot” sand have resulted in measured water-level 

drawdowns as great as 356 ft. Except in the deeper “2,800-

foot” sand and Catahoula aquifers, most saltwater currently 

north of the fault moved there in response to the groundwater 

withdrawals in the Baton Rouge area. Within the “2,000-

foot” sand, saltwater threatens industrial wells located about 

3 mi north of the fault. 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). 
LOUIS

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model domain

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

WEST

FELICIANA

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TANGIPAHOA LIVINGSTON EAST BATON ROUGE

WEST

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Figure 2. Location of the finite-difference grid and simulated altitude of the top of the “1,200-foot” sand of the Baton Rouge area in southeastern LouMississippi.
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30 

Base map modified from Louisiana Oil Spill Coordinator, Office of the Governor, Louisiana GIS CD: A Digital Map of the State, Version 2.0 Universal Transverse Mercator projection, zone 15 North American Datum of 1983 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' WEST FELICIANA EAST FELICIANA ST HELENA TANGIPAHOA LIVINGSTON EAST BATON ROUGE WEST BATON ROUGE POINTE COUPEEIBERVILLE ST MARTIN ASCENSION ST LANDRY AVOYELLES CONCORDIA WILKINSON AMITE PIKE ADAMS FRANKLIN LINCOLN Baton Rouge Gonzales Hammond Breaux Bridge Lake Maurepas Mississippi River Lake Maurepas 180 150 120 270 90 60 30 180 150210 240 240 300 270 300 6030 240 210 210 90 180 30 300 330 90240 90 330 90120 180 270 120 120 150 30 240 90 6060 60 30 30 180 150210 240 240 330330 300 240 300 6030 240 210 210 90 90 180 180 180 180 180 180 180 180 180 150 150 150 150 150 30 210 210 210 120 210 210 300 330 90240 240270 120 90 330 90 90 90 120 120 120 240 240 180 270 270 270 270 120 120 120 150 150 150 30 240 240 240 210 270 300 240 120

Figure 3. Simulated thickness of the “1,200-foot” sand of the Baton Rouge area in southeastern Louisiana and southwestern Mississippi.
Groundwater Withdrawals 9

On the basis of geophysical log data and analyses of 

water samples collected through 2005, saltwater or water 

containing chloride concentrations above background levels 

(10 mg/L or less) has been detected north of the Baton 

Rouge Fault in all 10 sands in the Baton Rouge area (Rollo, 

1969; Whiteman, 1979; Tomaszewski, 1996; Lovelace, 

2007). Analyses of chloride-concentration measurements 

collected from wells prior to 1992 indicated that saltwater 

encroachment had occurred in the “600-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 over this 

period 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 2004–05 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 2004–05 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 

“1,200-foot” sand, chloride concentrations of about 157 mg/L 

have been measured 6.5 mi east of the Mississippi River and 

about 300 ft north of the Baton Rouge Fault.

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 1). 

The Catahoula equivalent aquifer system was omitted from 

the framework because in the study area it contains mostly 

saltwater and is little used and because few geophysical logs 

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 

simulated in the groundwater model documented in this 

report. Although the groundwater model documented herein 

was primarily developed to address concerns about declining 

groundwater levels and saltwater encroachment in the “1,200-

foot” and “2,000-foot” sands, simulating groundwater flow in 

overlying and underlying aquifers improved the simulation of 

water levels in the aquifers of concern. 

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 24 layers, 

numbered from the top to the bottom (table 1). Layers 1, 3, 

5, 7, 9, 11–20, 22, and 24 make up the aquifer layers. Layers 

2, 4, 6, 8, 10, 21, and 23 make up confining-unit layers that 

separate the aquifer layers. Layer 1 represents multiple 

aquifers that have similar hydraulic characteristics and are 

likely interconnected, including the Mississippi River alluvial 

aquifer, shallow sands, Upland terrace aquifer, and the “400-

foot” sand, “600-foot” sand, and “800-foot” sand. Layer 5 

represents the “1,200-foot” sand.

The location and thickness of aquifer and confining-unit 

layers in the hydrogeologic framework were specified from 

lithologic contacts interpreted from 202 borehole resistivity, 

spontaneous potential, nuclear, and drillers’ lithologic logs and 

the previous work of Griffith (2003). Generally, aquifers and 

confining units less than 10 ft thick were not represented by 

discrete layers in the hydrogeologic framework. 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; Smith, 

1979; Whiteman, 1979; Hanor, 1982; Smoot, 1988; McCulloh, 

1991; Griffith, 2003, 2006) and the lithologic contacts, 

separate representations of the top altitudes and thicknesses of 

the hydrogeologic-unit layers were generated for areas north 

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

south representations for each layer were merged at the fault to 

form a single representation for each layer so that differences 

in top altitudes of layers across the Baton Rouge Fault 

represent the vertical fault displacement.

The top altitudes and thicknesses of all hydrogeologic 

framework layers were initially constructed with VIEWLOG 

(Viewlog Systems, 2004) for the entire model domain. 

Subsequent analysis indicated that the defined top and bottom 

altitudes of the “1,200-foot” sand were inadequate in a portion 

of the model domain in the eastern Baton Rouge area. The 

lithologic contacts were reinterpreted from borehole resistivity 

logs in this area, and linear interpolation between borehole 

locations was used to define the top and bottom altitudes of 

the “1,200-foot” sand. Contour maps depict the top altitude 

and thickness of the “1,200-foot” sand (figs. 2 and 3) in the 

groundwater model.

Groundwater Withdrawals

Withdrawal records for 636 wells in Louisiana from 

the period 1940 through 2012 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 (B. Pierre Sargent, U.S. Geological Survey, 

written commun., 2013). Sporadic annual withdrawal data 

from 1940 to 1975 for some facilities in the Baton Rouge area 
10 Simulation of Groundwater Flow and Chloride Transport in the “1,200-Foot” Sand, Baton Rouge Area, Louisiana

also were obtained from USGS water-use records (B. Pierre 

Sargent, U.S. Geological Survey, written commun., 2013). 

Annual withdrawal rates from wells in East and West Baton 

Rouge, East and West Feliciana, and Pointe Coupee Parishes 

from 1975 through 2012 were obtained from the Commission 

water-use database (Shawn Scallan, Capital Area Groundwater 

Conservation Commission, written commun., 2013). Annual 

withdrawal rates from about 1988 through 2012 for facilities 

that withdrew an average of 1 Mgal/d or greater and were 

located in other parishes in the study area were obtained from 

USGS water-use records. Specified groundwater withdrawals 

from simulated aquifers in the study area (not including the 

Mississippi River alluvial aquifer, shallow sands, Upland 

terrace aquifer, “400-foot” sand, “600-foot” sand, and “800-

foot” sand represented in layer 1) totaled 171.3 Mgal/d during 

2012. 

Where only facility-specific withdrawals were available, 

well-specific rates were typically estimated by evenly 

distributing the withdrawals reported for each facility among 

the active wells at that facility. 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 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 aquifer 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 hereinafter as the “Baton Rouge 

sands,” illustrates both increased total withdrawals and the 

withdrawal from deeper aquifers through time (fig. 4). 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 of the groundwater used 

in the Baton Rouge area. In 2012, an estimated 184.3 Mgal/d 

were withdrawn from the Baton Rouge sands for public supply 

and industrial use, including 24.1 Mgal/d from the “400-foot,” 

“600-foot,” and “800-foot” sands that were not specified in the 

model. Specified withdrawals from aquifers within the study 

area but outside of the Baton Rouge area that correlate with 

the Baton Rouge sands totaled 11.1 Mgal/d. 

Figures 5 and 6 depict the average daily withdrawal 

rate during 2012 at wells screened in the “1,200-foot” sand 

(fig. 5) and the “2,000-foot” sand (fig. 6) and located at 

or near the Baton Rouge industrial district. Withdrawals 

from the “1,200-foot” sand in the Baton Rouge area in 

2012 (fig. 5) totaled 23.33 Mgal/d, which were split nearly 

evenly between public supply (11.79 Mgal/d) and industry 

(11.54 Mgal/d). Withdrawals from the “2,000-foot” sand in 

the Baton Rouge area in 2012 (fig. 6) totaled 28.5 Mgal/d, and 

industrial withdrawals, primarily in the Baton Rouge industrial 

district, accounted for 16.1 Mgal/d, or 57 percent of the total 

withdrawn.

Simulation of Groundwater Flow and 

Chloride Transport

The modeling strategy involved an update of the 

groundwater model previously documented by Heywood and 

others (2014). The finite-difference grid was rediscretized 

to separate the “1,000-foot” sand from the “1,200-foot” 

sand and increase horizontal resolution (with smaller finitedifference cells) in the area where chloride transport within 

the “1,200-foot” sand is of concern. Specified groundwater 

withdrawals were updated through 2012, and the model 

parameters were recalibrated to water levels measured 

throughout the aquifer system through 2012. Subsequently, 

saltwater transport was simulated with the variable density 

groundwater-flow model SEAWAT (Langevin and others, 

2003). Calibration of simulated chloride concentrations to 

chloride concentrations measured in the Baton Rouge area 

required minor modification of parameters representing 

the hydraulic characteristics along segments of the Baton 

Rouge Fault. Estimates of effective porosity and aquifer 

dispersivities utilized in the previous model documented by 

Heywood and others (2014) provided a good fit of simulated 

to measured chloride concentrations in both the “1,200-

foot” sand and the “2,000-foot” sand. The highest observed 

chloride concentration north of the Baton Rouge Fault within 

the “1,200-foot” sand has been 157 mg/L, implying that 

groundwater at that location has a density not substantially 

greater than freshwater. Because the multinode well package, 

MNW2 (Konikow and others, 2009), of the constant-density 

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, MODFLOW-2005 was used during the groundwaterflow model calibration process. After the groundwater-flow 
Simulation of Groundwater Flow and Chloride Transport 11

Year

1940 1950 1960 1970 1980 1990 2000 2010 2020

Annual withdrawal rate, in million gallons per day

0

10

20

30

40

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

Estimated withdrawals from

the Baton Rouge sands

Figure 4. Estimated withdrawals from the Baton Rouge sands, 1940–2012.

model parameters had been estimated, the calibrated set of 

flow parameters and computed well fluxes were specified in 

the SEAWAT model, which enabled simulation of saltwater 

transport. An equivalent Well (WEL) package (Harbaugh and 

others, 2000) input was generated by the MODFLOW-2005 

simulation to specify the layer-variable groundwater fluxes for 

each withdrawal well in the subsequent SEAWAT simulation.

Conceptual Model for Solute Transport

A simple conceptual model was used for defining initial 

and boundary conditions within the detailed model area 

that corresponds to the solute-transport model domain. In 

this model, groundwater north of the Baton Rouge Fault is 

assumed to have been fresh prior to groundwater development. 

Groundwater entering the solute-transport model domain from 

areas north of the Baton Rouge Fault is simulated to have 

zero salt concentration. Although the origin of the saltwater 

encroaching into the “1,200-foot” sand is unknown, it likely 

flows through permeable sediments that are adjacent on the 

south side of the Baton Rouge Fault. Because sediments 

south of the Baton Rouge Fault are displaced downward, 

the saltwater may flow from the “1,000-foot” sand south 

of the Baton Rouge Fault, where its altitude is similar to 

that of the “1,200-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 finite-difference 

cells adjacent to the south side of the fault that connect 

to the “1,200-foot” sand on the north side of the fault. As 

groundwater withdrawals cause water levels to decline in 

aquifers north of the Baton Rouge Fault, saltwater under 

higher pressure south of the fault seeps northward across the 

hydraulically resistive fault. 
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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 2.0Universal Transverse Mercator projection, zone 15North American Datum of 1983

Figure 5. Average daily withdrawal rate during 2012 at wells screened in the “1,200-foot” sand of the Baton Rouge area and located at or near the B

district in southeastern Louisiana.
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Figure 6. Average daily withdrawal rate during 2012 at wells screened in the “2,000-foot” sand of the Baton Rouge area and located at or near the B

district in southeastern Louisiana and location of hypothetical supply well screened in the “2,000-foot” sand.
14 Simulation of Groundwater Flow and Chloride Transport in the “1,200-Foot” Sand, Baton Rouge Area, Louisiana

Equations of Groundwater Flow and Transport

Whereas MODFLOW-2005 solves the constantdensity groundwater-flow equation (Harbaugh, 2005), the 

SEAWAT-2000 (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,

( ) s p

P ρ C

ρq ρq ρS θ

t C t

∂ ∂ ∂ −∇ ⋅ + = +

∂ ∂ ∂

 , (1)

and mass transport,

( ) s

q C q s D C C C

t θ θ

∂   = ∇ ⋅ ∇ − ∇ ⋅ −   ∂  



, (2)

where

∇ is the gradient operator, 

ρ is fluid density [ML-3], 

q

 is specific discharge [LT-1], 

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

q

s

is flow rate per unit volume representing 

sources or sinks [T-1], 

Sp is specific storage in pressure terms 

[M-1LT2], 

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

t is time [T], 

θ is effective porosity, 

C is solute concentration [ML-3], 

D is the dispersion coefficient [L2

T-1], and 

Cs is source or sink solute concentration 

[ML-3]. 

These groundwater-flow and mass-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: 

f

ρ ρ ρ C

C

∂

= +

∂ , (3)

where 

f ρ is the density of freshwater. 

The SEAWAT-2000 (Langevin and others, 2003) code 

iteratively solves finite-difference versions of these variabledensity groundwater-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 mass transport 

(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 was designed with variable grid-cell spacing 

to (1) provide sufficient spatial resolution in a 48-mi2 area 

(the detailed model area) (fig. 7) where substantial saltwater 

migration either has occurred or could occur in the future, 

(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 mi2 and contains 

273,600 active finite-difference cells. The areas encompassed 

by the finite-difference cells range from 2.5×105 square feet 

(ft2) (5.74 acres) in the detailed model area to a maximum of 

3×109 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 (Marsily, 

1986), cells with large aspect ratios are located in areas of 

the model grid where high computational accuracy is not 

required.

The model grid consists of 24 layers of variable 

thickness, each of which is a rectangular array containing 

95 rows and 120 columns of finite-difference cells. For a 

subset of the model grid, 60 rows by 90 columns, a horizontal 

grid spacing of 500 ft was specified within the 48-mi2 detailed 

model area.

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 the hydrogeologic framework unit represented by the 

layer (table 1). South of the Baton Rouge Fault, the altitudes 

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

to the hydrogeologic framework units and are constant along 

columns of finite-difference cells (that is, in the north-south 

direction). This geometry facilitated simulation of flow across 

the Baton Rouge Fault and is explained in further detail in the 

“Internal Flow Package” section of this report. The north-tosouth cross-sectional view of the model grid (fig. 8) 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 
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Figure 7. The finite-difference grid, locations of horizontal flow barriers, and selected water-level and chloride observation wells screened in the “1

Rouge area in the detailed model area in southeastern Louisiana.
laf15-ESSF-0686_Heywood_figure 8

Row

87

Row

16

11.35 miles

VERTICAL EXAGGERATION x10

BATON ROUGE FAULT

2,700 feet

AquiferConfining unit

North South

EXPLANATION

Cells other than red or blue containboth aquifers and confining units

Figure 8. North-to-south cross section along model column 24 showing aquifers, confining units, and finite-difference discretization.
Simulation of Groundwater Flow and Chloride Transport 17

solute-transport problem when possible. Because simulation 

of saltwater encroachment is needed in only a small portion 

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

groundwater-flow model grid was identified for simulation 

of solute transport. This solute-transport model domain is the 

previously described “detailed model area” that has a 500-

ft cell spacing (fig. 7). Within this area, the solute-transport 

equation was numerically solved in all model layers but only 

calibrated for model layer 5 and model layers 11–20, which 

correspond to the “1,200-foot” sand and “2,000-foot” sand on 

the north side of the Baton Rouge Fault, respectively.

Internal Flow Package

Offsets of aquifers at the Baton Rouge Fault may 

enable flow from stratigraphically younger aquifers south 

of the fault into stratigraphically older and horizontally 

juxtaposed aquifers north of the fault. Horizontal flow between 

juxtaposed hydrogeologic units was enabled by representing 

the stratigraphy with the Hydrogeologic-Unit Flow package 

(HUF) (Anderman and Hill, 2000), which represents the 

thickness of hydrogeologic units independently from that 

of the finite-difference-grid layers. HUF calculates the 

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 for only the portion 

of the model domain north of the Baton Rouge Fault. South 

of the Baton Rouge Fault, the altitudes of the finite-difference 

layers within each model column are flat, with altitudes 

equal to that at the fault. 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 “1,000-foot” sand on the south side 

of the fault may be connected to the “1,200-foot” sand on the 

north side of the fault along some portions of the fault.

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 (HFBs) (Hsieh and Freckleton, 1993), 

which were specified along the vertical faces of cells closest 

to the fault. The increased resistance between adjacent model 

cells is specified with a hydraulic characteristic for each HFB 

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, for which water levels were specified.

Because the Baton Rouge Fault plane dips to the 

south between about 65 and 70 degrees, the fault dip was 

represented by offsetting the fault to the south in deeper 

framework layers. In layers 3 and 5, the fault is represented 

500 ft south of its surface location as indicated in figure 1, 

whereas in layers 7 through 24, the fault is offset 1,000 ft 

south of its surface location.

Time Discretization

Because groundwater withdrawals from the Southern 

Hills regional aquifer system were minor prior to about 

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

predevelopment conditions in the groundwater-flow system 

(table 2). Seventy-three annual stress periods simulated the 

time for which annual groundwater-withdrawal data were 

available between January 1, 1940, and December 31, 2012. 

Each annual stress period was discretized into five time 

steps that geometrically increased in duration by a factor 

of 1.4 such that the first time step of each stress period 

Table 2. Discretization of the years 1900–2112 simulated in the model of the Southern Hills regional aquifer system.

Stress 

period

Groundwater-flow 

model solution

Years 

represented

Flow time steps

per stress period in 

groundwater model

Number of transport 

time steps

Duration of first

flow time step

1 Steady state 1900–39 1 2 Not applicable

2–74 Transient 1940–2012 5 *

4,785 33.4 days

75 Transient 2013–14 7 239 30.6 days

76 Transient 2015–16 7 **236 30.6 days

77 Transient 2017–47 15 **3,991 29.3 days

78 Transient 2048–2112 15 **8,473 61.4 days

*

Total number of transport time steps simulating 1940 through 2012.

**Number of transport time steps differed among scenarios.
18 Simulation of Groundwater Flow and Chloride Transport in the “1,200-Foot” Sand, Baton Rouge Area, Louisiana

simulated 33.4 days. The hypothetical scenarios simulate 

100 additional years (2013 through 2112) with four additional 

stress periods, each divided into either 7 or 15 time steps. A 

2-year stress period from 2013 through 2014 utilizes 2012 

groundwater-withdrawal rates. Another 2-year stress period 

encompasses 2015 through 2016, during which groundwaterwithdrawal rates were modified for some scenarios. A 31-year 

stress period that encompasses January 1, 2017, through 

December 31, 2047, and a final 65-year stress period that 

encompasses January 1, 2048, through December 31, 2112, 

simulate identical pumpage stresses but are separated to save 

simulated results for December 31, 2047. 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. 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 

groundwater-flow model: no flow, specified head, and headdependent 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 23 layers 

of the southern side of the groundwater-flow model domain 

(fig. 1) are located where negligible groundwater flow 

is presumed to enter or exit the model domain and were 

accordingly considered no-flow boundaries. The modeldomain 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 boundarycondition specification. The bottom model boundary at the 

base of layer 24 is also no flow and corresponds to the top 

of a confining unit located above the Catahoula Formation 

(table 1), 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). Waterlevel distributions that represent the years 1944, 1980, 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. Steadystate (predevelopment) water levels were specified at the 

1944 levels, and water levels for times after 2004 were 

specified at the 2004 levels. The accuracy of these water-level 

specifications was verified by calculating the differences 

between the specified water levels and 1,016 water levels 

measured in wells screened within the “400-foot” sand, “600-

foot” sand, or “800-foot” sand. The mean magnitude of the 

water-level residuals (measured minus simulated water level) 

was 8.5 ft, and the standard deviation of the residuals was 

13.0 ft.

Water-level maps were digitized from previous reports: 

predevelopment (1944) (Kuniansky, 1989), 1980–84 (Martin 

and Whiteman, 1985; Boswell and Arthur, 1988; Kuniansky, 

1989), and 1990 (Tomaszewski, 1996). Historical waterlevel observations were used to enhance the predevelopment 

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

maps for 1998 and 1999 were created through modification 

of the 1990 and 2004 water-level maps by using water-level 

data collected at selected wells during 1998 and 1999 to 

more accurately specify water levels near the Commission’s 

“connector well,” which was installed in 1998 and screened in 

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

1999). The water-level map for 2004 was created by using 

water-level data collected by the USGS in cooperation with 

the Commission and the DOTD. 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. 

The southernmost row of the bottom model layer 

(row 95 in layer 24) contains a specified-head boundary to 

simulate groundwater underflow out of the model domain 

under predevelopment conditions. The water level for 

this boundary was specified by estimating the value of the 

associated parameter “bound_head” (table 3) during the model 

calibration process.
Simulation of Groundwater Flow and Chloride Transport 19

Table 3. Calibrated parameter values and sensitivities of the 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 three fault segments: fault_2k, fault_2kmid, and fault_2kw]

Parameter type Units Parameter 

name 

 Calibrated 

value 

Composite 

sensitivity

Specified head ft bound_head 111.3 1.83

Horizontal hydraulic conductivity ft/day k_468sand 40.0 fixed

k_1000sand 10.0 0.15

k_1200s01 117 0.02

k_1200s02 6.9 0.03

k_1200s03 83.6 0.08

k_1200s04 74.5 0.02

k_1200s05 15.8 0.02

k_1200s06 134 0.12

k_1200s07 46.2 0.03

k_1200s08 58.3 0.14

k_1200s09 21.3 0.09

k_1200s10 5 0.02

k_1200s11 91.7 0.02

k_1200s12 36.9 0.07

k_1200s13 5.28 0.03

k_1200s14 119 0.10

k_1200s15 143 0.03

k_1200s16 163 0.03

k_1200s17 11.4 0.05

k_1200s18 183 0.05

k_1200s19 54.4 0.06

k_1200s20 88.1 0.07

k_1200s21 200 0.05

k_1200s22 5 0.02

k_1200s23 200 0.11

k_1500sand 281 0.08

k_1500neas 53.0 0.48

k_1500falt 300 0.05

k_1700sand 7.4 0.36

k_2000sand1 various various

k_2400sand 12.1 0.29

k_2400sand2 13.3 0.19

k_2800sand 34.0 0.78

k_clay 2.4×10-5 0.03
20 Simulation of Groundwater Flow and Chloride Transport in the “1,200-Foot” Sand, Baton Rouge Area, Louisiana

Table 3. Calibrated parameter values and sensitivities of the groundwater-flow model.—Continued

[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 three fault segments: fault_2k, fault_2kmid, and fault_2kw]

Parameter type Units Parameter 

name 

 Calibrated 

value 

Composite 

sensitivity

Vertical hydraulic conductivity ft/day vk_sands 0.1 0.1

vk_2con 4.5×10-5 0.02

vk_4con 1.6×10-4 0.09

vk_6con 1×10-5 0.07

vk_8con 3.0×10-3 0.30

vk_19con 6.8×10-4 0.22

vk_21con 1.2×10-5 0.17

vk_neocon 3.2×10-4 0.11

vk_gov 1.5×10-3 0.38

Specific storage ft-1 ss_sand 2.3×10-6 0.02

ss_12 1×10-6 0.02

ss_15 1×10-6 0.02

ss_17 1.3×10-6 0.02

ss_24 2.8×10-6 0.03

ss_28 4.5×10-6 0.10

ss_neocon 4.4×10-6 0.02

ss_2ksand 3.1×10-6 0.05

ss_clay2 1.2×10-6 0.02

ss_clay4 2.6×10-5 0.22

ss_clay6 1×10-6 0.03

ss_clay8 1.5×10-5 0.27

ss_clay19 1×10-6 0.03

ss_clay21 1.4×10-6 0.02

Fault hydraulic characteristic day-1 hfb_1000ft 1.2×10-5 0.02

hfb_1200ft 1.6×10-6 0.02

hfb_1500ft 2.3×10-5 0.02

hfb_1700ft 3.3×10-5 0.02

fault_2k 5.9×10-4 0.03

fault_2kmid 1.5×10-4 fixed

fault_2kw 8.4×10-4 0.03

fault_ 24 1×10-6 0.02

fault_28 1.4×10-3 0.02

1

This parameter name represents 142 parameter values at pilot points in the “2,000-foot” sand documented in Heywood and others (2014). 
Simulation of Groundwater Flow and Chloride Transport 21

Head-Dependent Flux Boundaries

The previously described groundwater withdrawals were 

simulated with the revised MNW2 of MODFLOW (Konikow 

and others, 2009) because the screen intervals of many 

withdrawal wells span multiple model layers. The MNW2 

package computes a layer-by-layer distribution of withdrawal 

for each well on the basis of 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. 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 cell 

containing the connector well (EB-1293) (Dial and Cardwell, 

1999), where the water level for the top model layer (layer 1) 

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 7), so that calculated 

flow through the “connector well” could be compared to 

that measured by Dial and Cardwell (1999). Exclusion of 

withdrawals from the “400-foot” sand, “600-foot” sand, and 

“800-foot” sand, which amounted to about 24 Mgal/d in the 

Baton Rouge area during 2012, reduced the total withdrawals 

simulated in the model during 2012 to 171.3 Mgal/d.

Specified-Concentration Boundaries and Initial 

Conditions

The source of saltwater to the “2,000-foot” sand was 

simulated on the south side of the Baton Rouge Fault in model 

columns 16 through 53 (fig. 7), corresponding to a 3.6-mi-long 

region extending east from the Mississippi River. Within this 

region, the specified concentration increases linearly from 

zero above model layer 11 to a maximum of 10,000 mg/L of 

chloride at the base of layer 20. Constant-concentration cells 

in the two rows south of the Baton Rouge Fault within each 

column represent this source.

For the “1,200-foot” sand, the saltwater source is 

simulated as a constant-concentration boundary of 5,300 mg/L 

two model rows south of the simulated location of the Baton 

Rouge Fault in model-grid layer 5, columns 16 through 104, 

corresponding to an 8.6-mi-long region east of the Mississippi 

River. Offsetting of the concentration boundary 1,000 ft south 

of the fault improved calibration to observed concentrations 

north of the fault by simulating transport during a time period 

prior to salt crossing the fault. This location approximately 

corresponds to the simulated location of the Baton Rouge 

Fault in the underlying “2,000-foot” sand. The 5,300-mg/L 

chloride concentration and distance south of the fault of this 

boundary were determined by trial and error calibration of the 

transport simulation.

Within the solute-transport model domain (the “detailed 

model area”) north of the Baton Rouge Fault, the initial 

specified concentrations were zero (corresponding to 

freshwater) and were subsequently calculated by solution 

of the advective-dispersive equation (2). Model cells south 

of the Baton Rouge Fault and west of column 16 have zero 

concentration in all model layers, corresponding to freshwater. 

Model-grid layers 1 through 4, 6 through 10, and 21 through 

24 were specified with zero initial concentration in all areas 

because simulation of transport in the hydrogeologic units 

corresponding to those layers is not within the scope of the 

current modeling effort, and therefore transport was not 

calibrated in those layers. The concentration of simulated 

water flowing from surrounding areas to the north, east, and 

west into the solute-transport model domain is specified as 

zero, corresponding to freshwater.

Hydraulic-Property Distribution

The simulated horizontal hydraulic conductivities (Kh) 

within the top specified-head model layer that represents 

shallow aquifers including the “400-foot” sand, “600-foot” 

sand, and “800-foot” sand were uniformly fixed at 40 ft per 

day, the value estimated in the previous model (Heywood 

and others, 2014). The Kh for aquifer hydrogeologic units 

representing the “1,000-foot” sand (layer 3), the “1,700-foot” 

sand (layer 9), and the “2,800-foot” sand (layer 24) were 

each represented with single parameters that were estimated 

during model calibration. Because the specified thickness 

of each of these hydrogeologic units is spatially variable, 

simulated transmissivity varies spatially within these aquifers. 

Variability of Kh within the “1,200-foot” sand (layer 5) was 

simulated with 23 spatial zones within which Kh

 was uniform. 

These zones are Thiessen polygons constructed with centroids 

corresponding to the location of water-level observation wells 

screened within the “1,200-foot” sand (fig. 9). Variability of 

Kh within the “1,500-foot” sand (layer 7) was simulated with 

three zones within which Kh was uniform. Heterogeneity 

of Kh within the “2,000-foot” sand (layers 11–20) was 

simulated by estimating values at 142 locations as described 

by Heywood and others (2014), and the specified values of Kh

at those locations were updated. Variability of Kh within the 

“2,400-foot” sand (layer 22) was simulated with two zones 

within which Kh was uniform. Areas where the “1,500-foot” 

sand (layer 7) and “1,700-foot” sand (layer 9) do not exist 

because those units pinched out were assigned the Kh used for 

confining-unit layers within their respective hydrogeologicunit layers. The simulated vertical hydraulic conductivity (Kv

) 

within each hydrogeologic unit that represents a confining unit 

(model layers 2, 4, 6, 8, 10, 21, and 23 on the north side of the 
! ! ! ! ! ! ! ! ! ! ! 30 90 73 67 37 61 946 61 61 90 37 § ̈¦12 § ̈¦10 § ̈¦10 § ̈¦10 § ̈¦10 

! 0 1 2 KILOMETERS 0.5 0 0.5 1 2 MILES Base map modified from Louisiana Oil Spill Coordinator, Office of the Governor, Louisiana GIS CD: A Digital Map of the State, Version 2.0 Universal Transverse Mercator projection, zone 15 North American Datum of 1983 91°10' 91°07'30" 91°05' 30°30' 30°27'30" 30°25'

Figure 9. Pilot point locations and the simulated horizontal hydraulic conductivity distribution within the “1,200-foot” sand of the Baton Rouge area i

southeastern Louisiana.
Model Calibration 23

Baton Rouge Fault, subsequently referred to as “confining-unit 

layers”) was uniform within each confining unit and estimated 

separately. 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 3). Separate parameters 

that represent specific storage (Ss) within each aquifer and 

confining-unit layer were estimated during model calibration 

(except for the top specified-head model layer).

Distinct hydraulic characteristics were estimated for three 

lateral segments of the Baton Rouge Fault within the 10 model 

layers representing the “2,000-foot” sand north of the fault 

(layers 11–20). A single hydraulic characteristic was estimated 

for other model layers that contain aquifers north of the fault 

(layers 3, 5, 7, 9, 22, and 24). Horizontal flow barriers were 

simulated for confining-unit layers that separate the “1,000-

foot” sand from the “1,200-foot” sand and the “1,200-foot” 

sand from the “1,500-foot” sand. The calibrated values of 

the hydraulic properties for the groundwater-flow model are 

summarized in table 3.

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 model domain. A homogeneous 

distribution for each of these properties was specified. 

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 and in table 3.

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 levels 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 212 parameters, including 142 parameters representing 

Kh at pilot points in the “2,000-foot” sand, 23 parameters 

representing Kh within zones of the “1,200-foot” sand, and 

other parameters summarized in table 3, were adjusted to 

minimize the objective function: 

( ) ( )

4,911 2 2

1 1

' ( ) ' ( )

NPR

k k k k i i i i

k i

ω ω H H ω ω P P = =

∑ − b + − ∑ b (4)

In equation 4, symbols in the first summation are associated 

with water levels where

4,911 is the number of water-level observations, 

ωk is the weight applied to water-level 

observation k, 

Hk is the measured water level for observation k, 

H′

k is the simulated-equivalent water level for 

observation k, and 

b is the vector of 212 model parameters. 

Symbols in the second summation are associated with the 

“prior information” equations used for the regularization and 

described by Heywood and others (2014) where

NPR equals 138, the number of prior equations 

used to regularize the Kh distributions 

specified for the “2,000-foot” sand in the 

regression; 

ωi is the weight applied to the ith prior estimate; 

Pi is the ith prior estimate; and 

P′

i is the ith simulated value.

Calibration Dataset

The model calibration dataset consisted of groundwaterlevel observations, 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. Observations of chloride concentrations 

were used to calibrate the solute-transport model parameters. 

The groundwater-flow model was calibrated through 

parameter estimation with PEST, whereas the solute-transport 

model was manually calibrated through trial and error. 

Water-Level Observations

A total of 4,911 water levels measured during the period 

from 1916 through 2012 from 161 wells in Louisiana were 

utilized in the groundwater-flow model calibration. These 

measurements were from wells with at least six annual 

measurements; one measurement per year from any well 

was incorporated into the calibration database. About 79 

percent (3,895) of the measurements made before 2013 in 

aquifers beneath the “800-foot” sand were used to estimate 

parameters in the groundwater-flow model calibration. About 

21 percent (1,016) were used to evaluate the accuracy of the 

transient water levels specified for the top model layer from 

interpolation of historical water-level maps. In locations 

where multiple observation wells within a single model cell 

had overlapping periods of record, wells with the longest 

periods of continuous water-level record were selected for 

the compilation. Observed water-level altitudes were between 

248 and -292 ft. Observed water levels from the wells 

screened beneath model layer 1 that were used for estimation 

of groundwater-flow model parameters were between 215 

and -292 ft, a range of 507 ft. Within the “1,200-foot” sand, 

a decrease in water level of 177 ft has been observed in well 

EB-146 during the years from 1916 through 2011.

Well location and construction information from 

USGS, DOTD, and DNR records was used to specify the 

screen intervals and locations of the observation wells. Most 
24 Simulation of Groundwater Flow and Chloride Transport in the “1,200-Foot” Sand, Baton Rouge Area, Louisiana

(4,162) water-level observations were measured in wells with 

screen intervals corresponding to a single model layer, but 

749 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 aquiferdepth intervals in which the well is screened. The majority of 

these multilayer observations were measured in wells screened 

in the “2,000-foot” sand, which is represented by 10 model 

layers with identical Kh distributions. MODFLOW computed 

the composite water level for each multilayer well by 

averaging the water levels simulated in all of the model layers 

intersected by the well screen.

Chloride-Concentration Observations 

Chloride-concentration observations from wells within 

the “1,200-foot” sand and “2,000-foot” sand were compiled 

from the USGS National Water Information System (http://

waterdata.usgs.gov/nwis/qw). Observed concentrations from 

five wells located in the area of saltwater encroachment (EB781, EB-1028, EB-1150, EB-630, and EB-807B) were used 

as calibration targets for the simulation of transport within 

the “2,000-foot” sand. Of the four wells useful as transportcalibration targets for the “1,200-foot” sand (EB-618, EB-621, 

EB-1287, and EB-1297) (fig. 7), only one (EB-621) had a 

record of chloride concentrations that had risen substantially 

above background levels. Measured chloride concentrations 

between 2 and 10 mg/L in the other three observation wells 

within the “1,200-foot” sand also constrained the extent of the 

simulated chloride plume.

Observation and Prior-Information Weights

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

were described in a previous report (Heywood and others, 

2014). The total error for water levels was estimated as 

the sum of errors in measurement-point altitude and depth 

to water, which is about 2.5 ft, referred to herein as the 

“composite variance.” The inverse of this composite variance 

can be used to assign a measurement weight in the modelcalibration regression. Because well-head altitude and depthto-water measurement errors were similar for all observations, 

observation weights were set equal for water levels measured 

in aquifers beneath the “800-foot” sand (layer 1). Waterlevel observations from wells screened within the “400-foot” 

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

zero weight because those aquifers are represented by the 

specified heads within layer 1. Although effectively removed 

from the parameter-estimation regression, these observations 

were retained in the calibration dataset to evaluate the 

accuracy of the water-level specification within layer 1. PEST 

automatically adjusts the weight of the set of prior information 

equations with respect to the set of observations during the 

parameter-estimation process.

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 computed 

by the objective function, the fit of simulated to observed 

chloride values, and the amount of bias in the distribution of 

positive and negative water-level residuals. Residuals were 

calculated by subtracting simulated water-level altitudes from 

the observed water-level altitudes. A graph of the water-level 

residuals plotted as a function of the simulated water-level 

altitudes (fig. 10) indicates that the residuals are randomly 

distributed around the horizontal (residual=0) abscissa, 

suggesting a lack of systematic model bias in simulated water 

levels.

Summary statistics were calculated for the residuals of 

the 3,895 water-level observations used in the regression. The 

mean magnitude of the water-level residuals was 11.7 ft. The 

standard error of the residuals was 15.78 ft. The root-meansquare error (RMSE) was calculated as the square root of the 

mean of the unweighted squared residuals:

( )

2 3,895

1

'

3,895

k k

k

H H

RMSE =

−

=

∑

(5)

where 

Hk is the measured water level for observation k, 

and 

H′k is the simulated-equivalent water level for 

observation k. 

The RMSE and the standard deviation of the residuals were 

16.08 and 16.07 ft, respectively. The normalized RMSE was 

0.032 and was obtained by dividing the RMSE of the residuals 

by the 507-ft range of observed water levels. Because the 

RMSE is only 3 percent of the observed measurement range, 

the model adequately simulates observed water levels.

Estimated Parameter Values

Parameter values were constrained within reasonable 

limits on the basis of local knowledge and literature values 

during the model calibration process with PEST. Several 

relatively insensitive model parameters drifted toward their 

respective limiting constraints between successive parameterestimation 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 3) are considered reasonable. 
Model Calibration 25

-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

Water-level residual, in feet

Simulated water-level altitude, in feet

Figure 10. Water-level residuals as a function of simulated water-level altitudes.

Whereas the groundwater-flow model parameters 

were formally estimated by minimization of the objective 

function (equation 4), the values of parameters representing 

the longitudinal, transverse, and vertical dispersivities 

and effective porosity that were used in the previously 

documented version of the model (Heywood and others, 

2014) were reevaluated by manual calibration of simulated to 

observed concentrations, and the previously specified values 

were retained. 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).

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 of 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 3. 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. The parameter “bound_head,” 

which controls the specified water level in the bottom row at 

the south end of the model that represents the groundwater 

base level (Kafri and Yechieli, 2010) south of the study 

area, has the highest composite sensitivity, indicating that, 

in general, simulated water levels are most sensitive to this 

parameter.
26 Simulation of Groundwater Flow and Chloride Transport in the “1,200-Foot” Sand, Baton Rouge Area, Louisiana

Simulated Groundwater Conditions

In areas where the density of groundwater does not vary 

spatially, groundwater flows from areas with higher water 

levels to areas with lower water levels. Because the simulated 

chloride concentrations and associated groundwater densities 

are relatively high adjacent to some areas along the Baton 

Rouge Fault, however, the direction of groundwater flow may 

not coincide with the gradient of water levels simulated by 

SEAWAT 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 in the aquifer system. Hydrographs of simulated water 

levels presented in this report were computed with the Head 

Observation Package of MODFLOW, 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 Water Levels

Simulated groundwater flow within the “1,200-foot” 

sand during the predevelopment steady-state period prior to 

1940 generally flowed from updip areas near the LouisianaMississippi border southward and southwestward toward 

the Baton Rouge area (fig. 11). Simulated groundwater flow 

within the “1,200-foot” sand that flows toward the northwest 

corner of the model domain discharges upward toward the 

specified-head boundary that represents the surficial aquifers. 

Because the simulated effects of groundwater withdrawals on 

water levels and flow directions in the “2,000-foot” sand and 

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

described in a previous report (Heywood and others, 2014), 

only new scenarios for managing pumpage and saltwater 

movement within the “2,000-foot” sand are described.

After 73 years of groundwater withdrawals (1940–2012), 

simulated groundwater levels in much of the study area 

declined from their predevelopment levels. Groundwater 

currently flows toward the industrial district in the Baton 

Rouge area where withdrawals have substantially decreased 

water levels (fig. 12). Within the “1,200-foot” sand, a 

simulated “cone of depression” (area of groundwater 

drawdown) is centered over the industrial district, where the 

minimum simulated water-level altitude is about -135 ft.

Hydrographs depict the fit of simulated and observed 

water levels for wells in the detailed model area (see fig. 7 for 

well locations) and show the history of water-level changes 

in the “1,200-foot” sand (fig. 13). A spreadsheet and database 

containing hydrograph information for all observed and 

simulated water levels are included with the model archive 

that is available from the USGS Lower Mississippi-Gulf Water 

Science Center.

Water levels in the “1,200-foot” sand are simulated by 

model layer 5 north of the fault with a complex hydraulic 

conductivity distribution (fig. 9). Simulated water levels 

correspond closely with water levels observed in wells 

screened in the “1,200-foot” sand, and the 177 ft of drawdown 

in well EB-146, located about 0.9 mi east of Interstate 10 in 

Baton Rouge, is accurately simulated (fig. 13A). Simulated 

water levels at two wells (EB-146 and EB-301) are slightly 

lower than observed water levels during the 1960s and early 

1970s, possibly as a result of inaccurate pumpage specified 

within this layer for those periods.

Simulated Water Budget

Under predevelopment conditions, the simulated steadystate water budget indicates that about 67.46 Mgal/d of water 

entered and exited the groundwater-flow model domain 

(table 4). Net inflow of 3.35 Mgal/d from the top specifiedhead model layer that represents the “400-foot” sand, “600-

foot” sand, “800-foot” sand, Mississippi River alluvial aquifer, 

Upland terrace aquifer, and other shallow sands into the 

underlying model layer is balanced by net outflow through 

the constant-head boundary along the southernmost row 

(row 95) of the deepest model layer (layer 24). By the end 

of the transient historical simulation (December 31, 2012), 

substantial net groundwater withdrawals (171.31 Mgal/d 

during 2012) had caused water-level declines that 

substantially increased net simulated infiltration from layer 

1 to 92.93 Mgal/d. Specified water-level changes in the top 

model layer account for processes not explicitly simulated by 

the model, including storage changes in the “400-foot” sand, 

“600-foot” sand, and “800-foot” sand; 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 2–24 represent 

water 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. 14). After the steady-state stress period that simulates 

predevelopment conditions (conditions prior to 1940), 

groundwater withdrawals are initially mostly supplied by 

the elastic release of water from storage. Over time, vertical 

hydraulic gradients caused by groundwater withdrawals from 

the deeper model layers cause increasing downward flow 

from the top specified-head model layer that represents the 

upper aquifers. Flow from storage continues to respond to 

shorter term changes in the pumpage stress. The plot of flow 

from specified-head boundaries in figure 14 appears relatively 

smooth through time 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.
LOUISI

Studyarea

LakeMaurepas

§ ̈¦55

§ ̈¦55

§ ̈¦55

§ ̈¦12

§ ̈¦10

§ ̈¦10

61

61

61

98

98

.71

.190

.190

.51

MISSISSIPPI .51

LOUISIANA

UrBaSim

360

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

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

ADAMS FRANKLIN LINCOLN

BatonRouge

Gonzales

Hammond

Breaux Bridge

Mississippi

River

90

80

70

60

50

40

100

110

120

130

140

150

160

170

180

190

200

210 220

230

240 250

260 270

280

290

300

310320

330

30

340

350 36 1 0 50 360

270

250

290

340

220

350

260

240

300

290

230

90

90

80

80

70

70

60

60

50

50

40

40

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100

110

110

120

120

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150

160

160

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180

180

190

190 200

200 210

210

220

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240 250

260 270

280

290

290 300

310320

330

30

340

350 360 150 360

270

250 290

340

220

350

260

240

300 290

230

Figure 11. Simulated steady-state water levels within the “1,200-foot” sand of the Baton Rouge area representing predevelopment conditions (befor

Louisiana and southwestern Mississippi.
30 90 73 37 67 61 946 61 61 90 37 § ̈¦12 § ̈¦10 § ̈¦10 § ̈¦10 § ̈¦10 

InSi

10 2481632641,2,5,

!( S

W

-60 B

0 0.5 1 2 KILOMETERS 0 0.5 1 2 MILES Base map modified from Louisiana Oil Spill Coordinator, Office of the Governor, Louisiana GIS CD: A Digital Map of the State, Version 2.0 Universal Transverse Mercator projection, zone 15 North American Datum of 1983 91°10' 91°07'30" 91°05' 30°30' 30°27'30" 30°25' !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !(!( !( !(!(!( !( -65 -70-75 -95 -80-85 -90 -100 -105 -110 -60-115-120 -125 -55 -55 -130 -90 -75 -65 -70-75 -95 -80-85 -90 -100 -105 -110 -60 -60 -115-120 -125 -55 -55 -130 -90 -75 Mississippi River

Figure 12. Simulated 2012 water levels and chloride concentrations in the “1,200-foot” sand of the Baton Rouge area in the detailed model area in s
Simulated Groundwater Conditions 29

-100

-60

-20

20

60

100

C. Well EB-301

-100

-60

-20

20

60

100

D. Well EB-327

-100

-60

-20

20

60

100

B. Well EB-299

-100

-50

0

50

100

A. Well EB-146

Simulated

Observed

Water-level altitude, in feet

EXPLANATION

-110

-60

-10

40

90

F. Well EB-653

-110

-60

-10

40

90

1915 1925 1935 1945 1955 1965 1975 1985 1995 2005

G. Well EB-756

E. Well EB-782A

-100

-60

-20

20

60

100

Year

Figure 13. Simulated and observed water-level altitudes within the “1,200-foot” sand of the Baton Rouge area in southeastern 

Louisiana. A, Well EB-146. B, Well EB-299. C, Well EB-301. D, Well EB-327. E, Well EB-782A. F, Well EB-653. G, Well EB-756.
30 Simulation of Groundwater Flow and Chloride Transport in the “1,200-Foot” Sand, Baton Rouge Area, Louisiana

Table 4. Simulated steady-state and transient water budgets.

[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 74, TS 5 

(December 31, 2012)

ft3

/d Mgal/d ft3/d Mgal/d

In Specified-head layer 1 8.7647×106 65.56 1.4497×107 108.45

South row of layer 24 2.5432×105 1.90 8.6547×106 64.74

Storage 0 0 1.8262×106 13.66

Multinode wells 0 0 1.0499×105 0.79

Out Specified-head layer 1 8.3168×106 62.21 2.0746×106 15.52

South row of layer 24 7.0176×105 5.25 0 0

Storage 0 0 2.4519×103 0.02

Multinode wells 0 0 2.3006×107 172.10

-10

10

30

50

70

90

110

130

150

170

1940 1950 1960 1970 1980 1990 2000 2010

Million gallons per day

Year

Simulated groundwater withdrawals

Net flow from storage

Net flow from specified-head 

boundaries

EXPLANATION

Figure 14. Simulated groundwater withdrawals and flows from storage and specified-head boundaries.
Limitations and Appropriate Use of the Model 31

Simulated Concentrations

The concentration of the chloride source to the “1,200-

foot” sand is unknown and was estimated during model 

calibration. A simulated chloride-source concentration 

of 5,300 mg/L produced the best overall fit of simulated 

concentrations to concentrations observed in the “1,200-

foot” sand. Simulated chloride concentrations at the centers 

of model cells containing chloride observation well screens 

were used to generate the simulated chlorographs (fig. 15). 

Two factors complicated simulation of the concentrations 

observed in observation well EB-621 (fig. 15D), the screen 

of which is located about 100 ft north of the Baton Rouge 

Fault. First, although the precise location of the Baton Rouge 

Fault at the “1,200-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 among the four model 

cells surrounding the simulated location of observation well 

EB-621. Therefore, the concentrations simulated for the 

four cells around observation well EB-621 were averaged to 

generate the simulated concentration for this well (fig. 15D). 

Among the chloride observation wells in the “2,000-

foot” sand, EB-1150 and EB-630 are production wells. Well 

EB-1150 has a screen-interval length of 56 ft, and EB-630 

has two screened intervals that are 50 ft and 105 ft in length. 

The measured chloride-concentration fluctuations over time 

in both of these wells (fig. 16) are difficult to simulate while 

maintaining relatively parsimonious initial and boundary 

conditions and transport-model parameter distributions. The 

simulated concentrations at these locations were therefore 

fit in the middle of the range of the observed concentration 

fluctuations. Although the most recent chloride-concentration 

observation in well EB-807B, located about 0.7 mi 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 immediately north of the fault are as high as 

5,120 mg/L and rapidly decline to the north between wells 

EB-781 and EB-807B (fig. 17).

Limitations and Appropriate Use of

the Model

The groundwater model was designed and calibrated 

primarily to simulate groundwater flow and saltwater transport 

in the “1,200-foot” sand and “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, “1,500-foot” 

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

foot” sand is also reasonably well simulated. It is possible 

to simulate the effects of potential 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 “1,200-foot” sand and “2,000-foot” sand that 

might result from changes such as those described in the 

“Scenarios To Mitigate Saltwater Migration” section of this 

report are examples of appropriate uses of the model. The 

predevelopment 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 “1,200-foot” sand 

and “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 simulated. 

Predictions of changes in chloride concentrations within either 

the “1,200-foot” sand or the “2,000-foot” sand that might 

result from changes such as those described in the “Scenarios 

To Mitigate Saltwater Migration” section of this report are 

an appropriate use of the model. Predictions of changes 

in chloride concentrations within other aquifers are not 

appropriate because the model was not calibrated to chlorideconcentration 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.
32 Simulation of Groundwater Flow and Chloride Transport in the “1,200-Foot” Sand, Baton Rouge Area, Louisiana

0

25

50

75

100

125

150

Year

0

25

50

75

100

125

150

0

25

50

75

100

125

150

1952 1962 1972 1982 1992 2002 2012 1952 1962 1972 1982 1992 2002 2012

Year

Simulated concentration

Baton Rouge Water Company

Observed concentration

B. EB-1297

C. EB-618

E. EB-1016B

Chloride concentration, in milligrams per liter

EXPLANATION

A. EB-1287

D. EB-621

F. EB-990

Figure 15. Simulated and observed chloride concentrations at observation wells within the “1,200-foot” sand of the Baton Rouge area 

in southeastern Louisiana. A, Well EB-1287. B, Well EB-1297. C, Well EB-618. D, Well EB-621. E, Well EB-1016B. F, Well EB-990.
Limitations and Appropriate Use of the Model 33

0

100

200

300

400

500

0

100

200

300

400

500

0

1,000

2,000

3,000

4,000

5,000

Observed

Simulated

0

100

200

300

400

500

1965 1975 1985 1995 2005

Year

0

100

200

300

400

500

Chloride concentration, in milligrams per liter

A. Well EB-781 EXPLANATION

B. Well EB-807B

D. Well EB-1150

E. Well EB-630

C. Well EB-1028

Figure 16. Simulated and observed chloride concentrations at observation wells within the “2,000-foot” sand of the Baton Rouge area 

in southeastern Louisiana. A, Well EB-781. B, Well EB-807B. C, Well EB-1028. D, Well EB-1150. E, Well EB-630.
Mississippi River

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

0 0.5 1 2 KILOMETERS0 0.5 1 2 MILES

laf15-ESSF-0686_Heywood_figure 17

!

Wel s

Sim con mil

EB-781

.

.

EB-X

-180

Indu

10 to 

5,121 2,561 1,281 641 to 321 to 161 to 81 to 41 to 21 to 

BatoSim a s in G

Wat “ s

Hyp c

-

1

45

-

1

40-135

-

1

55

-

1

50

-

1

60

-

1

80

-

1

7

5

-

1

7

0

-

1

6

5

-

1

8

5

-

1

9

- 0195

-130

-200

-205

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-180

-

2

1

5

-175

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-180

-185

-180

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-225

-215

!

!

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!

!

!

!

!

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!!

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!

!

!

!

.

.

.

.

.

.

EB-781

EB-X

EB-807B

EB-1028

EB-630

EB-874

EB-1150

§ ̈¦10

§ ̈¦110

§ ̈¦110

§ ̈¦10

§ ̈¦10

§ ̈¦12

61

67

19

1

1

30

73

37

986

986

76 190

91°12'30" 91°10' 91°07'30"

30°30'

30°27'30"

30°25'

Figure 17. Simulated 2012 water levels and chloride concentrations at the base of the “2,000-foot” sand of the Baton Rouge area in the detailed modLouisiana.
Scenarios To Mitigate Saltwater Migration 35

Scenarios To Mitigate Saltwater 

Migration

Seven hypothetical groundwater-management scenarios 

were formulated to evaluate the effects of modifying 

groundwater withdrawals on future groundwater levels and 

saltwater concentrations from 2013 through 2112. Maps 

showing predicted water levels and chloride concentrations 

in 2047 and 2112 are presented for each scenario. The first 

(scenario 1) represents the effects of continued, or “status 

quo,” groundwater withdrawals at 2012 rates and serves 

as a base case for comparison with the other scenarios in 

which various changes were simulated. Scenario 2 predicts 

the effects of increased withdrawals from selected wells 

screened in the “1,200-foot” sand on future groundwater 

levels and chloride concentrations in that sand. The remaining 

five scenarios, 3 through 7, simulate the effects of various 

pumping schemes on future groundwater levels and chloride 

concentrations in the “2,000-foot” sand and incorporate a 

hypothetical new public-supply well within the industrial 

district withdrawing 1.9 Mgal/d. In all of the scenarios, 

2012 groundwater-withdrawal rates are specified for the 

2-year period from 2013 through 2014. All modifications to 

simulated pumping rates begin in 2015, with the exception of 

withdrawals simulated to begin in 2017 from the “scavenger 

well” that is designed to extract salty water from the base of 

the “2,000-foot” sand. Two alternative pumping rates from the 

scavenger well are simulated in scenarios 4 and 7, which are 

denoted with the suffix “a” or “b” in their respective scenario 

descriptions and associated figures. Water levels at specifiedhead boundaries in the top model layer remained at the 2004 

levels until 2112 in all of the scenarios.

Scenario 1: Continued Groundwater 

Withdrawals at 2012 Rates

Continuation of the “status quo” groundwater withdrawals 

was simulated by using the 2012 withdrawal rates for an 

additional 100 years (2013–2112). Contours of predicted 

water levels within the “1,200-foot” sand for 2047 (fig. 18) 

are similar to those simulated for 2012 (fig. 12) but are about 

10 ft lower in the industrial district and about 5 ft lower in 

other parts of the detailed model area. The leading edge of the 

saltwater plume is predicted to migrate a maximum of about 1 

mi north of the Baton Rouge Fault in 35 years.

By 2112, predicted water levels within the “1,200-foot” 

sand (fig. 19) are almost identical to the 2047 levels (fig. 18), 

indicating that the simulated groundwater system was close to 

hydraulic equilibrium by 2047. Between 2047 and 2112, the 

plume of saltwater continued to migrate northward toward the 

cone of depression in the industrial area, and the leading edge 

reached a distance of about 2 mi north of the Baton Rouge 

Fault.

In the “2,000-foot” sand, water levels for 2047 (fig. 20) 

are generally about 8 ft lower than during 2012 (fig. 17) in 

the detailed model area. The lowest water-level altitudes, 

about -240 ft, are predicted in the industrial district for 2047 

compared to about -235 in the 2012 simulation. Comparison 

of the predicted chloride-concentration distributions in 

layer 20 for years 2047 (fig. 20) and 2012 (fig. 17) indicates 

that the portion of the saltwater plume containing chloride 

concentration in the 161- to 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 area of the plume 

containing concentrations above background levels (10 mg/L) 

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

Fault would increase by about 20 percent (table 5). 

By 2112, predicted water levels within the “2,000-

foot” sand (fig. 21) are within about a foot of the 2047 levels 

(fig. 20), indicating that the simulated groundwater system 

was close to hydraulic equilibrium by 2047. Between 2047 

and 2112, the saltwater plume continues to migrate northward 

toward the cone of depression in the industrial area, and 

chloride concentrations increase at most observation wells 

(fig. 22), except possibly near well EB-807B.
!( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !(!( !( !(!(!( !( 30 90 73 37 67 61 946 61 61 90 37 § ̈¦12 § ̈¦10 § ̈¦10 § ̈¦10 § ̈¦10 Indu

Pred

i

10 t21 t41 t81 t161 321 641 1,282,565,12

!( Pre

Wa

-60 Bat

0 0.5 1 2 KILOMETERS

0 0.5 1 2 MILES Base map modified from Louisiana Oil Spill Coordinator, Office of the

Governor, Louisiana GIS CD: A Digital Map of the State, Version 2.0Universal Transverse Mercator projection, zone 15North American Datum of 1983

91°10' 91°07'30" 91°05'

30°30'

30°27'30"

30°25'

-70

-

75

-80

-85

-90

-

95

-

105

-100

-

110

-

115

-

120 -125

-65

-

130-

135

-60

-

140

-75

-115

-95

-140

-70

-

75

-80

-85

-90

-

95

-

105

-100

-

110

-

115

-

120 -125

-65

-65

-

130-

135

-60

-

140

-75

-115

-95

-140

Mississippi River

Figure 18. Predicted 2047 water levels and chloride concentrations in the “1,200-foot” sand of the Baton Rouge area in the detailed model area in socontinued pumping at 2012 rates (scenario 1).
30

90

73

37 67

61

946

61

61

90

37

§ ̈¦12

§ ̈¦10

§ ̈¦10

§ ̈¦10

§ ̈¦10

Indu

Pred

10 21 41 81 161 321 641 1,22,55,1

!(

PreWa

-60

Ba

0 0.5 1 2 KILOMETERS

0 0.5 1 2 MILES Base map modified from Louisiana Oil Spill Coordinator, Office of the

Governor, Louisiana GIS CD: A Digital Map of the State, Version 2.0Universal Transverse Mercator projection, zone 15North American Datum of 1983

91°10' 91°07'30" 91°05'

30°30'

30°27'30"

30°25'

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(!(

!(

!(

!(!(

!(

-70

-75

-80 -85

-90

-

95

-

105

-100

-

110

-

115

-

120

-

125

-65

-

130 -

135

-60

-

140

-115

-95

-140

-70

-75

-80 -85

-90

-

95

-

105

-100

-

110

-

115

-

120

-

125

-65

-65

-

130 -

135

-60

-

140

-115

-95

-140

Mississippi River

Figure 19. Predicted 2112 water levels and chloride concentrations in the “1,200-foot” sand of the Baton Rouge area in the detailed model area in socontinued pumping at 2012 rates (scenario 1).
Mississippi River

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

190

67

73

76

1

19

1 986

986

61

30

§ ̈¦12

§ ̈¦10

§ ̈¦110

§ ̈¦110

§ ̈¦10

InduPre

10 t21 t41 t81 t161 321 641 1,282,565,12

PreWaHyWeBa

!

.

.

EB-1028

EB-X

-130

91°12'30" 91°10' 91°07'30"

30°30'

30°27'30"

30°25'

0 0.5 1 2 KILOMETERS0 0.5 1 2 MILES

!

!

!

!

!

!

!

!

!

!

!

!

!

!

!

!

!!

!

!

!

!

!

!

.

.

.

.

.

.

EB-781

EB-X

EB-807B

EB-1028

EB-630

EB-1150

EB-874

-215

-

170 -1

75

-210

-

140

-

150

-

145 -

155 -165 -160

-

1

90-185 -18-0 19- 5200

-205

-

135

-220

-225

-130

-230

-235

-230

-180

-200

-190

-185

-185

-190

-195

-

140

-

150

-

145 -

155 -165 -160

-

1

90-185

-

170

-

180

-

1

75

-

1

9

- 5200

-205

-210

-215

-

135

-135

-220

-225

-130

-230

-235

-230

-180

-200

-190

-185 -185

-185

-190

-195

-225

Figure 20. Predicted 2047 water levels and chloride concentrations at the base of the “2,000-foot” sand of the Baton Rouge area in the detailed modLouisiana after continued pumping at 2012 rates (scenario 1).
Scenarios To Mitigate Saltwater Migration 39

Table 5. Plume area and average chloride concentrations simulated for 2012 and predicted for 2047 at the base of the “2,000-foot” 

sand (layer 20).

[mi2, square miles; mg/L, milligrams per liter]

Date and (or) scenario Plume area

(mi2)

Mean layer 20 cell

chloride concentration 

(mg/L)

Median layer 20 cell

chloride concentration 

(mg/L)

2012 4.84 575 253

2047: Scenario 1 5.84 626 302

2047: Scenario 3 5.26 656 357

2047: Scenario 4a 4.32 600 178

2047: Scenario 4b 4.65 637 296

2047: Scenario 5 5.19 663 348

2047: Scenario 6 5.19 675 325

2047: Scenario 7a 4.29 597 109

2047: Scenario 7b 4.62 631 189
Mississippi River

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

190

67

73

76

1

19

1 986

986

61

30

§ ̈¦12

§ ̈¦10

§ ̈¦110

§ ̈¦110

§ ̈¦10

InduPre

10 t21 t41 t81 t161 321 641 1,282,565,12

PreWaHyWeBa

!

.

.

EB-1028

EB-X

-130

91°12'30" 91°10' 91°07'30"

30°30'

30°27'30"

30°25'

0 0.5 1 2 KILOMETERS0 0.5 1 2 MILES

!

!

!

!

!

!

!

!

!

!

!

!

!

!

!

!

!!

!

!

!

!

!

!

.

.

.

.

.

.

EB-781

EB-X

EB-807B

EB-1028

EB-630

EB-1150

EB-874

-

150

-

145

-

15- 5165 -160

-

1

70

-

190

-

185

-

180

-

1

75

-195

-200

-205

-

140

-210

-215

-

135

-220

-225

-130

-230

-235

-185

-185

-180

-190

-225

-185 -185

-190

-190

-

150

-

145

-

15- 5165 -160

-

1

70

-

190

-

185

-

180

-

1

75

-195

-

195

-200

-205

-

140

-210

-215

-

135

-

140

-

135

-

140

-

135

-220

-225

-130

-230

-235

-185

-185

-180

-190

-225

-185 -185

-190

-190

Figure 21. Predicted 2112 water levels and chloride concentrations at the base of the “2,000-foot” sand of the Baton Rouge area in the detailed modLouisiana after continued pumping at 2012 rates.
Scenarios To Mitigate Saltwater Migration 41

0

200

400

600

800

1,000

1,200

1,400

1960 1980 2000 2020 2040 2060 2080 2100

A. Well EB-1028

0

100

200

300

400

500

1960 1980 2000 2020 2040 2060 2080 2100

C. Well EB-630

1,000

2,000

3,000

4,000

1960 1980 2000 2020 2040 2060 2080 2100

D. Well EB-781

0

100

200

300

400

500

1960 1980 2000 2020 2040 2060 2080 2100

B. Well EB-1150

Scenario 1

Scenario 3

Scenario 4a

Scenario 4b

Scenario 5

Scenario 6

Scenario 7a

Scenario 7b

Observed

EXPLANATION

Year Year

Chloride concentration, in milligrams per liter

Figure 22. Observed and predicted chloride concentrations at the base of the “2,000-foot” sand resulting from pumping rates 

specified for scenarios 1, 3, 4a, 4b, 5, 6, 7a, and 7b for observation wells and a scavenger well in the detailed model area in the Baton 

Rouge area in southeastern Louisiana. A, Well EB-1028. B, Well EB-1150. C, Well EB-630. D, Well EB-781. E, Well EB-807B. F, Well EB-X. 

G, Scavenger well.
42 Simulation of Groundwater Flow and Chloride Transport in the “1,200-Foot” Sand, Baton Rouge Area, Louisiana

0

100

200

300

400

500

1960 1980 2000 2020 2040 2060 2080 2100

0

100

200

300

400

500

600

700

800

900

1,000

1960 1980 2000 2020 2040 2060 2080 2100

Year

Year

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Scenario 3

Scenario 4a

Scenario 4b

Scenario 5

Scenario 6

Scenario 7a

Scenario 7b

0

100

200

300

400

500

1960 1980 2000 2020 2040 2060 2080 2100

E. Well EB-807B F. Well EB-X

G. Scavenger well

Chloride concentration, in milligrams per liter

Observed

EXPLANATION

Figure 22. Observed and predicted chloride concentrations at the base of the “2,000-foot” sand resulting from pumping rates 

specified for scenarios 1, 3, 4a, 4b, 5, 6, 7a, and 7b for observation wells and a scavenger well in the detailed model area in the Baton 

Rouge area in southeastern Louisiana. A, Well EB-1028. B, Well EB-1150. C, Well EB-630. D, Well EB-781. E, Well EB-807B. F, Well EB-X. 

G, Scavenger well.—Continued
Scenarios To Mitigate Saltwater Migration 43

Scenario 2: Increased Groundwater 

Withdrawals From the “1,200-Foot” Sand

A net increase of 2.0 Mgal/d in groundwater withdrawals 

from the “1,200-foot” sand within the industrial district was 

simulated by increasing pumpage from two industrial-area 

wells (EB-567 and EB-1304) (see fig. 5 for well locations) 

by 1.0 Mgal/d, each beginning in 2015 while maintaining 

all other well withdrawals at the 2012 rates. Referenced to 

2012 water levels (fig. 12), simulated water levels within the 

“1,200-foot” sand decline about 25 ft in the industrial district 

and about 10–15 ft elsewhere by 2047 (fig. 23). The migration 

of saltwater north of the Baton Rouge Fault within the “1,200-

foot” sand is essentially the same as that predicted under 

scenario 1 for 2047 (fig. 18).

By 2112, predicted water levels within the “1,200-foot” 

sand (fig. 24) remain approximately equal to the 2047 levels 

(fig. 23), indicating that the groundwater system approached 

hydraulic equilibrium by 2047 under scenario 2. Between 

2047 and 2112, the northward migration of the saltwater 

plume toward the cone of depression in the industrial area is 

similar to that of scenario 1 (fig. 19).

Scenario 3: Modification of Groundwater 

Withdrawals From the “2,000-Foot” Sand

A net decrease of 0.696 Mgal/d in groundwater 

withdrawals from the “2,000-foot” sand was simulated by 

discontinuing 1.889 Mgal/d of withdrawals from two publicsupply wells (EB-151 and EB-733), commencing equivalent 

withdrawals from the “2,000-foot” sand at a hypothetical 

new public-supply well located north of the detailed model 

area in row 22 and column 34, discontinuing 0.696 Mgal/d of 

withdrawals from three industrial wells (EB-810, EB-851, and 

EB-884) (see fig. 6 for well locations), and keeping all other 

well withdrawals at the 2012 rates. Despite these withdrawal 

reductions, water levels are predicted to decline about 10 

ft in the industrial district from 2012 levels (fig. 17) and 

about 5 ft in other parts of the detailed model area by 2047 

(fig. 25). The predicted concentration of the chloride plume 

generally increases and continues to migrate northward, with 

concentrations up to about 80 mg/L predicted in the industrial 

district by 2047. The eastern edge of the chloride plume 

recedes about 0.2 mi westward, away from the location of the 

discontinued public-supply withdrawals. The predicted area 

of the plume for 2047 with a concentration above background 

levels (10 mg/L) is about 10 percent less than in scenario 1, and 

the median and mean cell concentrations within that area are 

slightly greater than those in scenario 1 (table 5).

By 2112, predicted water levels are less than 1 ft lower than 

the 2047 levels (figs. 25 and 26). The predicted concentration 

within the chloride plume increases, and the leading edge of the 

plume migrates about 1 mi further north into industrial district. 

The predicted chloride concentration is between 80 and 160 

mg/L near the southernmost industrial wells.
30 90 73 37 67 61 946 61 61 90 37 § ̈¦12 § ̈¦10 § ̈¦10 § ̈¦10 § ̈¦10 

IndPr

10 21 41 81 1632641,22,55,

!( P

W

-60 B

0 0.5 1 2 KILOMETERS 0 0.5 1 2 MILES Base map modified from Louisiana Oil Spill Coordinator, Office of the Governor, Louisiana GIS CD: A Digital Map of the State, Version 2.0 Universal Transverse Mercator projection, zone 15 North American Datum of 1983 91°10' 91°07'30" 91°05' 30°30' 30°27'30" 30°25' !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !( !(!( !( !(!(!( !( -75 -80 -85-90 -95 -115 -110 -105 -100 -120 -12-1530 -135 -70 -14-0145 -150 -65 -70 -155 -160 -125 -75 -80 -85-90 -95 -115 -110 -105 -100 -120 -12-1530 -135 -70 -14-0145 -150 -65 -60 -70 -155 -160 -125 Mississippi River

Figure 23. Predicted 2047 water levels and chloride concentrations in the “1,200-foot” sand of the Baton Rouge area in the detailed model area in soa pumping increase (from 2012 rates) of 2 million gallons per day at selected wells in the Baton Rouge industrial district beginning in 2015 (scenario 2)
30

90

73

37

67

61

946

61

61

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37

§ ̈¦12

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0 0.5 1 2 KILOMETERS

0 0.5 1 2 MILES Base map modified from Louisiana Oil Spill Coordinator, Office of the

Governor, Louisiana GIS CD: A Digital Map of the State, Version 2.0Universal Transverse Mercator projection, zone 15North American Datum of 1983

91°10' 91°07'30" 91°05'

30°30'

30°27'30"

30°25'

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Mississippi River

Figure 24. Predicted 2112 water levels and chloride concentrations in the “1,200-foot” sand of the Baton Rouge area in the detailed model area in soa pumping increase (from 2012 rates) of 2 million gallons per day at selected wells in the Baton Rouge industrial district beginning in 2015 (scenario 2)
Mississippi River

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

InduPre

10 t21 t41 t81 t161 321 641 1,282,565,12

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EB-1028

EB-X

-130

91°12'30" 91°10' 91°07'30"

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0 1 2 KILOMETERS 0.50 0.5 1 2 MILES

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.

EB-781

EB-X

EB-807B

EB-1028

EB-630

EB-1150

EB-874

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19

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986

61

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Figure 25. Predicted 2047 water levels and chloride concentrations at the base of the “2,000-foot” sand of the Baton Rouge area in the detailed mod

Louisiana after pumping is turned off at selected industrial and public-supply wells and a hypothetical public-supply well located north of the detailed and column 34 (see fig. 6) is turned on starting in 2015 (scenario 3).
Mississippi River

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

190

67

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986

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10 t21 t41 t81 t161 321 641 1,282,565,12

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EB-1028

EB-X

-130

91°12'30" 91°10' 91°07'30"

30°30'

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30°25'

0 1 2 KILOMETERS 0.50 0.5 1 2 MILES

!

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EB-781

EB-X

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Figure 26. Predicted 2112 water levels and chloride concentrations at the base of the “2,000-foot” sand of the Baton Rouge area in the detailed mod

Louisiana after pumping is turned off at selected industrial and public-supply wells and a hypothetical public-supply well located north of the detailed and column 34 (see fig. 6) is turned on starting in 2015 (scenario 3).
48 Simulation of Groundwater Flow and Chloride Transport in the “1,200-Foot” Sand, Baton Rouge Area, Louisiana

Scenario 4: Modification of Groundwater 

Withdrawals With Installation of a Scavenger 

Well in the “2,000-Foot” Sand

The installation of a scavenger well couplet was 

simulated in model row 64 and column 29 (fig. 6) with two 

wells: one screened in the upper portion and one screened 

in the bottom of the “2,000-foot” sand. The bottom well 

(screened in model layer 20) of the scavenger-well couplet is 

screened at the base of the “2,000-foot” sand where the saltier, 

denser water is simulated, and the upper well (screened in 

model layers 11–13) is screened toward the top of the aquifer 

where it may extract better quality water. Simultaneous 

withdrawals from both of these aquifer intervals preserve 

horizontal flow toward the scavenger-well couplet, thereby 

maintaining separation of the saltier and fresher fractions of 

water in that area of the aquifer. Two alternative total pumping 

rates from the scavenger-well couplet were simulated: 2.5 

Mgal/d (scenario 4a) and 1.25 Mgal/d (scenario 4b). In 

scenario 4a, the withdrawals from the upper and lower wells 

were specified at 1.5 Mgal/d and 1.0 Mgal/d, respectively. The 

scavenger-well withdrawal rates were reduced by 50 percent 

for scenario 4b; withdrawals from the upper and lower wells 

were specified at 0.75 Mgal/d and 0.5 Mgal/d, respectively. 

The withdrawal rates from other industrial and public-supply 

wells were identical to those of scenario 3. 

By 2047, the scavenger well had pumped at 2.5 Mgal/d 

for 31 years, and water levels are predicted to decline 20–25 

ft in the industrial district and 15–20 ft (fig. 27) in other parts 

of the detailed model area compared to 2012 (fig. 20), except 

near the scavenger well, where a distinct cone of depression 

forms. Predicted chloride concentrations decrease in the plume 

north of the scavenger well, but the leading edge of the plume 

continues to migrate northward into the industrial district. In 

comparison to scenario 1, the plume recedes westward about 

0.5 mi away from the area where public-supply withdrawals 

were reduced. Chloride concentrations increase within the 

plume between the scavenger well and the Baton Rouge 

Fault because the increased hydraulic gradient created by the 

scavenger-well pumping stress increases simulated advective 

transport of chloride. Overall, the plume area decreases about 

10 percent in comparison to its 2012 extent, causing the mean 

plume concentration to rise about 4 percent, yet the median 

cell concentration decreases by almost 30 percent (table 5).

By 2112, water levels remain at 2047 levels (figs. 27 and 

28). The leading edge of the plume recedes southward more 

than 1 mi, and concentrations north of the scavenger well 

continue to decline compared to 2047 (fig. 27). Concentrations 

between the scavenger well and the Baton Rouge Fault remain 

similar to the concentrations predicted for 2047.

The rate of salt mass transport across the Baton Rouge 

Fault into the “2,000-foot” sand, the rate of extraction 

of salt mass through wells screened in this aquifer, and 

the net change of salt mass in the aquifer are affected by 

withdrawals from public-supply wells and the scavenger well 

(fig. 29). Beginning around 1980, some salt is withdrawn by 

wells pumping from the “2,000-foot” sand. The increased 

hydraulic gradient caused by commencement of scavengerwell withdrawals in 2017 initially increases the rate of salt 

transport across the fault; both the hydraulic gradient and 

transport rate decrease in subsequent years as hydraulic 

equilibrium is approached. The simulated scavenger well 

effectively withdraws salt from the aquifer and causes an order 

of magnitude decrease in the rate of salt accumulation in the 

aquifer.

For scenario 4b, the withdrawals from the scavenger 

well were one-half that of scenario 4a (1.25 Mgal/d). By 

2047, predicted water levels within the “2,000-foot” sand are 

generally about 10 ft higher (fig. 30) than under scenario 4a 

(fig. 27) in the Baton Rouge area. The plume area remains 

about 8 percent larger than under scenario 4a for 2047 

(table 5), within which the mean and median predicted 

chloride concentrations are also higher. 

By 2112, predicted water levels have declined an 

additional 2 ft near the scavenger well but elsewhere are very 

close to their 2047 levels (figs. 30 and 31). In comparison to 

the effect of the higher scavenger-well pumping of scenario 

4a, predicted water levels are about 10 ft higher in the Baton 

Rouge area, but higher chloride concentrations remain in the 

aquifer north of the scavenger well. 
Mississippi River

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

190

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i

10 to 21 to 41 to 81 to 161 321 641 1,282,565,12

PreWaHypScaWeBat

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EB-X

-140

91°12'30" 91°10' 91°07'30"

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0 1 2 KILOMETERS 0.50 0.5 1 2 MILES

!

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EB-781

EB-X

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Figure 27. Predicted 2047 water levels and chloride concentrations at the base of the “2,000-foot” sand of the Baton Rouge area in the detailed mod

Louisiana after pumping is turned off at selected industrial and public-supply wells, a hypothetical public-supply well located north of the detailed moand column 34 (see fig. 6) is turned on in 2015, and a scavenger well located in row 64 and column 29 pumps at 2.5 million gallons per day beginning in 
Mississippi River

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

190

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10 t21 t41 t81 t161 321 641 1,282,565,12

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91°12'30" 91°10' 91°07'30"

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30°25'

0 1 2 KILOMETERS 0.50 0.5 1 2 MILES

!

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EB-781

EB-X

EB-807B

EB-1028

EB-630

EB-1150

EB-874

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Figure 28. Predicted 2112 water levels and chloride concentrations at the base of the “2,000-foot” sand of the Baton Rouge area in the detailed mod

Louisiana after pumping is turned off at selected industrial and public-supply wells, a hypothetical public-supply well located north of the detailed moand column 34 (see fig. 6) is turned on in 2015, and a scavenger well located in row 64 and column 29 pumps at 2.5 million gallons per day beginning in 
Scenarios To Mitigate Saltwater Migration 51

-24

-16

-8

0

8

16

24

1940 1960 1980 2000 2020 2040 2060 2080 2100

Thousands of pounds per day

Outflow to wells

Simulated inflow

across fault

Net change

Salt mass flow

EXPLANATION

Year

Figure 29. Simulated inflow across fault, outflow to wells, and net change of salt mass in the “2,000-foot” sand of the Baton Rouge 

area north of the Baton Rouge Fault, 1940–2012, and predicted changes in salt mass, 2013–2112, after pumping changes are made at 

selected industrial and public-supply wells in 2015 and pumping at a rate of 2.5 million gallons per day from a simulated scavenger well 

begins in 2017 (scenario 4a).
Mississippi River

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

190

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91°12'30" 91°10' 91°07'30"

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EB-781

EB-X

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Figure 30. Predicted 2047 water levels and chloride concentrations at the base of the “2,000-foot” sand of the Baton Rouge area in the detailed mod

Louisiana after pumping is turned off at selected industrial and public-supply wells, a hypothetical public-supply well located north of the detailed moand column 34 (see fig. 6) is turned on in 2015, and a scavenger well located in row 64 and column 29 pumps at 1.25 million gallons per day beginning i
Mississippi River

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

190

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91°12'30" 91°10' 91°07'30"

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0 1 2 KILOMETERS 0.50 0.5 1 2 MILES

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EB-781

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140

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-225

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1

35

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140

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-240

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-250

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-195

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-140

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-240 -130 -245 -135 -250 -2505

-195 -195

-195

-210

-215

-185 -180

-195

-190

-230

Figure 31. Predicted 2112 water levels and chloride concentrations at the base of the “2,000-foot” sand of the Baton Rouge area in the detailed mod

Louisiana after pumping is turned off at selected industrial and public-supply wells, a hypothetical public-supply well located in model row 22 and coland a scavenger well located in row 64 and column 29 begins pumping at 1.25 million gallons per day in 2017 (scenario 4b). 
54 Simulation of Groundwater Flow and Chloride Transport in the “1,200-Foot” Sand, Baton Rouge Area, Louisiana

Scenario 5: Reduction of Industrial Withdrawals 

From the “2,000-Foot” Sand

For scenario 5, the changes to groundwater withdrawals 

are similar to scenario 3, but an additional 1.678 Mgal/d of 

withdrawal reductions were specified from industrial wells by 

discontinuing withdrawals from three wells (EB-722, EB-856, 

and EB-587) while maintaining withdrawal from EB-851 at 

the 2012 rate (see fig. 6 for well locations), resulting in a net 

decrease of 2.222 Mgal/d from the total 2012 withdrawal 

rate. Overall, the predicted conditions are similar to those 

predicted under scenario 3. By 2047, predicted water levels 

increase about 15 ft throughout much of the detailed model 

area (fig. 32) compared to scenario 1 (fig. 20). The leading 

edge of the plume continues to migrate northward and reaches 

the southernmost industrial well but at a slower rate than in 

scenario 1, resulting in a plume area that is 11 percent smaller 

than scenario 1 in 2047 (table 5).

By 2112, water levels remain near 2047 levels (figs. 32 

and 33). The chloride plume continues to migrate northward, 

but at a slightly lower rate than predicted in scenario 3 

(fig. 25). 

Scenario 6: Extensive Reduction of Industrial 

and Public-Supply Withdrawals From the 

“2,000-Foot” Sand

A net reduction of 7.344 Mgal/d in groundwater 

withdrawals from the “2,000-foot” sand with respect to 2012 

rates was predicted by discontinuing withdrawals from two 

public-supply wells (EB-151 and EB-733) and seven industrial 

wells (EB-1317, EB-1323, EB-1313, EB-1309, EB-1151, 

EB-788, and EB-1227) and by commencing 1.889 Mgal/d of 

withdrawal from a hypothetical public-supply well located 

north of the detailed model area in model row 22 and column 

34 (see fig. 6 for well locations). 

By 2047, predicted water levels recover from 2012 levels 

(fig. 17) and are about 50 ft higher (fig. 34) in the industrial 

district and 35–40 ft higher in other parts of the detailed model 

area. Nevertheless, the leading edge of the plume continues to 

migrate northward, and low chloride concentrations (less than 

40 mg/L) are predicted near the southernmost industrial wells. 

The area and average concentration of the predicted plume are 

similar to those in scenario 5 (table 5).

By 2112, predicted water levels remain very close to the 

predicted 2047 levels (figs. 34 and 35), indicating that the 

simulated system approached hydraulic equilibrium by 2047. 

Chloride concentrations do not change substantially near the 

industrial district, though concentrations closer to the Baton 

Rouge Fault continue to increase.
Mississippi River

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EB-1028

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EB-781

EB-X

EB-807B

EB-1028

EB-630 EB-1150

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-160-155-185-190 -195 -200

-125

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-205

-210 -120 -215 -220

-170 -165

-175

-170

-170

-225

Figure 32. Predicted 2047 water levels and chloride concentrations at the base of the “2,000-foot” sand of the Baton Rouge area in the detailed mod

Louisiana after pumping is turned off at selected industrial and public-supply wells and a hypothetical public-supply well located north of the detailed and column 34 (see fig. 6) is turned on starting in 2015 (scenario 5).
Mississippi River

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

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a

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EB-1028

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EB-781

EB-X

EB-807B

EB-1028

EB-630

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-160-155-185-190 -195 -200

-125

-125

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-210 -120 -215 -220

-170 -165

-175

-170

-170

-225

Figure 33. Predicted 2112 water levels and chloride concentrations at the base of the “2,000-foot” sand of the Baton Rouge area in the detailed mod

Louisiana after pumping is turned off at selected industrial and public-supply wells and a hypothetical public-supply well located north of the detailed and column 34 (see fig. 6) is turned on starting in 2015 (scenario 5).
Mississippi River

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

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10 to 21 to 41 to 81 to 161 to 321 to 641 to 1,281 2,561 5,121 

Pred

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Well 

a

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EB-1028

EB-X

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91°12'30" 91°10' 91°07'30"

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.

.

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.

EB-781

EB-X

EB-807B

EB-1028

EB-630 EB-1150

EB-874

-115

-125 -120

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-130

-145

-150

-155

-155

-110

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185

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-140 -145

-140

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Figure 34. Predicted 2047 water levels and chloride concentrations at the base of the “2,000-foot” sand of the Baton Rouge area in the detailed mod

Louisiana after pumping is turned off at selected industrial and public-supply wells and a hypothetical public-supply well located north of the detailed and column 34 (see fig. 6) is turned on starting in 2015 (scenario 6).
Mississippi River

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10 to 21 to 41 to 81 to 161 t321 t641 t1,282,565,12

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91°12'30" 91°10' 91°07'30"

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EB-781

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145 -

-140

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-190

Figure 35. Predicted 2112 water levels and chloride concentrations at the base of the “2,000-foot” sand of the Baton Rouge area in the detailed mode

Louisiana after pumping is turned off at selected industrial and public-supply wells and a hypothetical public-supply well located north of the detailed and column 34 (see fig. 6) is turned on starting in 2015 (scenario 6).
Scenarios To Mitigate Saltwater Migration 59

Scenario 7: Extensive Reduction of Industrial 

and Public-Supply Withdrawals With 

Installation of a Scavenger Well in the 

“2,000-Foot” Sand

In scenarios 7a and 7b, the reductions to groundwater 

withdrawals from the “2,000-foot” sand are identical to 

those in scenario 6, but installation of a scavenger well 

was also predicted in model row 64, column 29 (the same 

location as scenario 4). Two alternative total pumping rates 

from the scavenger-well couplet were predicted: 2.5 Mgal/d 

(scenario 7a) and 1.25 Mgal/d (scenario 7b). In scenario 7a, 

the withdrawals from the upper and lower wells were specified 

at 1.5 Mgal/d and 1.0 Mgal/d, respectively. In scenario 7b, 

withdrawals from the upper and lower wells were specified 

at 0.75 Mgal/d and 0.5 Mgal/d, respectively. The withdrawal 

rates from other industrial and public-supply wells were 

identical to those of scenario 6.

With the scavenger-well couplet withdrawing 2.5 

Mgal/d, predicted water levels in the “2,000-foot” sand 

recover from their 2012 levels and are about 40 ft higher in 

the industrial district and about 20 ft higher in other parts of 

the detailed model area than they were in 2012 (figs. 17 and 

36). A groundwater divide formed at latitude 30 degrees 27 

minutes 30 seconds, approximately beneath the east-west 

portion of Interstate 110. This groundwater divide is the 

northern extent of the scavenger well’s capture zone, which 

prevents continued migration of the chloride plume toward 

the industrial district. By 2047, the plume area decreases 

and is 27 percent smaller than that predicted for scenario 1 

(table 5). The median cell concentration is substantially lower 

than in 2012 or scenario 1, though the mean cell concentration 

remains slightly higher than it was in 2012 because of higher 

chloride concentrations between the scavenger well and the 

Baton Rouge Fault. 

By 2112, predicted water levels remain at the 2047 

levels (figs. 36 and 37). The size of the plume is dramatically 

reduced in extent, and the plume has been diluted to 

freshwater in areas it previously occupied to the north of the 

scavenger well within the “2,000-foot” sand.

In scenario 7b, with the scavenger-well couplet 

withdrawing only 1.25 Mgal/d, predicted water levels in the 

“2,000-foot” sand make a greater recovery than in scenario 

7a and by 2047 are simulated to be about 45 ft higher in the 

industrial district and about 30 ft higher in other parts of the 

detailed model area than they were during 2012 (figs. 17, 37, 

and 38). Because the scavenger-well withdrawals are half 

those in scenario 7a, the chloride plume area remains larger, 

and average concentrations remain somewhat higher than they 

were in scenario 7a (table 5).

By 2112, predicted water levels remain at the levels 

predicted for 2047 under scenario 7b (figs. 38 and 39). 

The predicted extent of the chloride plume has reduced from 

its 2047 extent but not as dramatically as it had with the 

greater withdrawal rate simulated in scenario 7a (figs. 37, 38, 

and 39).

Scenario Comparison

In all scenarios, water levels essentially equilibrate by 

2047, after 31 years of simulated constant withdrawal rates. 

Table 5 provides a quantitative comparison of the relative 

effectiveness of the various groundwater-withdrawal scenarios 

in mitigating the areal extent and average concentration of the 

chloride plume in the “2,000-foot” sand. Comparison of the 

total salt mass in the “2,000-foot” sand provides an additional 

metric of the effectiveness of the scenarios. Although the total 

mass indicated in figure 40 is uncertain because of uncertainty 

in the concentration and extent of the salt source near the 

Baton Rouge Fault, the relative magnitudes of the curves 

provide a useful comparison among the scenarios. As a group, 

the scavenger-well scenarios (4a, 4b, 7a, and 7b) simulate 

the lowest total salt mass, plume area, and median cell 

concentration, with the higher scavenger-well withdrawal-rate 

scenarios (4a and 7a) being most effective by these metrics. 

The simulated scavenger-well withdrawal rate is likely more 

influential in chloride plume mitigation than other differences 

among the scenarios in industrial and public-supply 

withdrawal rates. The relatively minor withdrawal reduction 

in scenario 3 predicts a greater total salt mass and average 

concentrations than scenario 1, though the smaller area and 

distribution of the chloride plume may be advantageous 

over that predicted by continuation of the 2012 pumping 

rates. Scenarios 5 and 6, which predict the effects of greater 

withdrawal-rate reductions and redistributions, are somewhat 

more effective in plume area and concentration reduction but 

are not as effective as the scavenger-well scenarios. 

Differences among the scenarios in the rates of salt 

mass accumulation in the “2,000-foot” sand are more evident 

in figure 41, which is similar to figure 29 discussed under 

scenario 4, but depicts only the net mass for each scenario. 

The slope of the scenario curves after 2015 could be used 

to evaluate the rapidity with which various scenarios affect 

aquifer remediation. By this metric, scenarios 3 and 5 may be 

least effective in reducing salt accumulation. Scenarios 3 and 5 

also predict increasing concentrations in the central portion of 

the plume, near public-supply well EB-630 (fig. 22C). 

The chlorographs are useful for discerning differences 

among predictions of the scenarios in specific areas that are 

not readily apparent from the summary statistics or aquifermass plots. For example, among the scavenger-well scenarios, 

scenario 4a, which simulates greater groundwater withdrawals 

than scenario 7a, predicts slightly greater reduction in chloride 

concentration in the vicinity of well EB-1028 (fig. 22A).
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 the Baton Rouge area in the detailed mod

Louisiana after pumping is turned off at selected industrial and public-supply wells, a hypothetical public-supply well located north of the detailed moand column 34 (see fig. 6) is turned on in 2015, and a scavenger well located in row 64 and column 29 pumps at 2.5 million gallons per day beginning in 
Mississippi River

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Figure 37. Predicted 2112 water levels and chloride concentrations at the base of the “2,000-foot” sand of the Baton Rouge area in the detailed mod

Louisiana after pumping is turned off at selected industrial and public-supply wells, a hypothetical public-supply well located north of the detailed moand column 34 is turned on in 2015, and a scavenger well located in row 64 and column 29 (see fig. 6) pumps at 2.5 million gallons per day beginning in 
Mississippi River

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Figure 38. Predicted 2047 water levels and chloride concentrations at the base of the “2,000-foot” sand of the Baton Rouge area in the detailed mod

Louisiana after pumping is turned off at selected industrial and public-supply wells, a hypothetical public-supply well located north of the detailed moand column 34 is turned on in 2015, and a scavenger well located in row 64 and column 29 (see fig. 6) pumps at 1.25 million gallons per day beginning i
Mississippi River

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-145

-150

Figure 39. Predicted 2112 water levels and chloride concentrations at the base of the “2,000-foot” sand of the Baton Rouge area in the detailed mod

Louisiana after pumping is turned off at selected industrial and public-supply wells, a hypothetical public-supply well located north of the detailed moand column 34 (see fig. 6) is turned on in 2015, and a scavenger well located in row 64 and column 29 pumps at 1.25 million gallons per day beginning i
64 Simulation of Groundwater Flow and Chloride Transport in the “1,200-Foot” Sand, Baton Rouge Area, Louisiana

0

100

200

300

400

500

600

1940 1949 1960 1969 1980 1989 2000 2009 2020 2029 2040 2049 2060 2069 2080 2089 2100 2110

Millions of pounds of salt

Scenario 7b

Scenario 7a

Scenario 6

Scenario 5

Scenario 4b

Scenario 4a

Scenario 3

Scenario 1

EXPLANATION

Year

Figure 40. Simulated salt mass in the “2,000-foot” sand of the Baton Rouge area north of the Baton Rouge Fault, 1940–2012, and 

predicted salt mass during eight hypothetical pumping scenarios, 2013–2112.

-3

0

3

6

9

12

15

18

1940 1950 1960 1970 1980 1990 2000 2010 2020 2030 2040 2050 2060 2070 2080 2090 2100 2110

Change in salt mass, in thousands of pounds per day

Scenario 7b

Scenario 7a

Scenario 6

Scenario 5

Scenario 4b

Scenario 4a

Scenario 3

Scenario 1

EXPLANATION

Year

Figure 41. Predicted changes in salt mass in the “2,000-foot” sand of the Baton Rouge area north of the Baton Rouge Fault, 1940–2012, 

and predicted changes in salt mass during eight hypothetical pumping scenarios, 2013–2112.
Summary 65

Summary

Groundwater withdrawals in the Baton Rouge area since 

development in the 1940s have lowered water levels and 

altered groundwater-flow directions in the freshwater aquifers 

of the Southern Hills regional 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 “1,200-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 

184.3 million gallons per day (Mgal/d) for public supply and 

industrial use in 2012. Groundwater withdrawals from the 

“1,200-foot” sand, which totaled 23.33 Mgal/d during 2012, 

have resulted in measured water-level drawdowns as great 

as 177 feet (ft) and the potential for saltwater migration from 

south of the Baton Rouge Fault. Groundwater withdrawals 

from the “2,000-foot” sand, which totaled 28.5 Mgal/d during 

2012, have resulted in measured water-level drawdowns as 

great as 356 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 in both the 

“1,200-foot” sand and the “2,000-foot” sand.

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 the constant-density groundwater-flow 

simulation code MODFLOW and calibrated to observed 

water levels with the parameter-estimation code PEST. 

The calibrated groundwater-flow model parameters were 

subsequently utilized for the variable-density SEAWAT 

version of the model. Although much of the model input for 

SEAWAT is identical to MODFLOW input, withdrawal fluxes 

computed with the MODFLOW multinode well (MNW2) 

package were used to specify Well (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, 

so computed concentrations affect groundwater density and 

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 24 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, 11–20, 22, and 24 compose the 

aquifer layers. Layers 2, 4, 6, 8, 10, 21, and 23 compose the 

confining units that separate aquifer layers. 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 5 represents the “1,200-foot” sand. 

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

11 through 20.

The finite-difference grid with lateral cell dimensions 

of 500 by 500 ft in the Baton Rouge area incorporates 

increasing cell spacing toward the model-domain boundaries 

so that the entire 6,529-square-mile study area is contained 

within 95 rows and 120 columns of finite-difference cells. 

Vertical finite-difference 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 finitedifference 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. After an initial steady-state stress 

period that simulated predevelopment conditions prior to 

1940, 73 annual transient stress periods simulated time from 

1940 through 2012. The period from 2013 through 2014 was 

simulated with 2012 withdrawal rates. Three additional stress 

periods were used for scenarios that predict future conditions 

through 2112.

Boundary conditions utilized for the groundwater-flow 

simulation included no flow, 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, 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 95 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 

MNW2 depend upon water levels simulated in the model 

layers in which wells have screens and are therefore headdependent fluxes. The equivalent fluxes specified by using the 

WEL package in the SEAWAT simulation are the specifiedflux type.
66 Simulation of Groundwater Flow and Chloride Transport in the “1,200-Foot” Sand, Baton Rouge Area, Louisiana

Average daily withdrawal rates were specified for 636 

wells for each annual stress period from 1940 through 2012. 

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.

The area in which solute transport was simulated with 

SEAWAT is a subset of the groundwater-flow model domain 

and corresponds to the 60-row by 90-column portion of the 

grid with 500-ft by 500-ft finite-difference cells in the Baton 

Rouge area. Model 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 

sources of saltwater to the “1,200-foot” sand and “2,000-foot” 

sand are simulated as constant-concentration boundaries on 

the south side of the Baton Rouge Fault. For the “1,200-foot” 

sand, the constant-concentration boundary of 5,300 milligrams 

per liter (mg/L) is in model layer 5 and extends 8.6 mi east 

from the Mississippi River. For the “2,000-foot” sand, the 

concentration of the boundaries increases linearly with depth 

in model layers 10 through 20 (inclusive) from zero to a 

maximum concentration of 10,000 mg/L within a region that 

extends 3.6 mi east from the Mississippi River and is 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 3,895 

water levels measured between 1940 and 2011 with PEST. 

Additional water levels were used to evaluate the accuracy 

of the specified-head boundaries in the top model layer. The 

estimated values of hydraulic property parameters were all 

within the range considered reasonable. 

Seven hypothetical scenarios predicted the effects of 

different groundwater-withdrawal options on groundwater 

levels and the transport of saltwater within the “1,200-foot” 

sand and the “2,000-foot” sand during 2015–2112. In all of the 

scenarios, 2012 groundwater-withdrawal rates are specified 

for the 2-year period from 2013 through 2014. Modifications 

to pumping rates are simulated to begin in 2015, except that 

withdrawals from a scavenger well are simulated to begin in 

2017. Scenario 1 is the base case for comparison to the other 

scenarios and predicts the effects of 100 years (through 2112) 

of continued withdrawals at 2012 rates. Scenario 2 simulates 

increased withdrawals from industrial wells in the “1,200-

foot” sand and predicts water levels 10–25 ft lower by 2047 

and a negligible difference in chloride concentrations within 

the “1,200-foot” sand. Scenarios 3 through 7 predict the effects 

of various pumping schemes on future groundwater levels 

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

all incorporate a new hypothetical public-supply well within 

the industrial district withdrawing 1.9 Mgal/d. Scenario 3 

simulates redistribution and a relatively modest 0.696-Mgal/d 

net decrease of withdrawals from the “2,000-foot” sand. 

Scenario 4 simulates the same withdrawal modifications as 

those under scenario 3, with additional withdrawals from a 

scavenger well that withdraws salty water from the base of 

“2,000-foot” sand and presumably fresher water from the top 

of that aquifer at the same location. Two alternative pumping 

rates from the scavenger well, 2.5 Mgal/d and 1.25 Mgal/d, are 

simulated in each of scenarios 4 and 7. Scenario 5 is similar 

to scenario 3 but simulates additional withdrawal reductions 

from different wells than scenario 3, with the net reduction 

about four times greater (2.2 Mgal/d). Scenario 6 simulates the 

net largest reduction (7.3 Mgal/d) of groundwater withdrawals 

from the “2,000-foot” sand. Scenario 7 simulates the scenario 

6 withdrawal modifications with the addition of scavengerwell withdrawals at the same rates and location as in scenario 

4. The effects of all scenarios are illustrated by maps of 

predicted water levels and concentrations for the years 2047 

and 2112 and chlorographs at observation wells within the 

“1,200-foot” sand and “2,000-foot” sand. For the “2,000-

foot” sand scenarios, comparison of the predicted effects of 

the scenarios is facilitated by observation-well chlorographs, 

plots of salt mass in the aquifer through time, and a summary 

of the predicted plume area and average concentration. In all 

scenarios, water levels essentially equilibrate by 2047, after 

31 years of simulated constant withdrawal rates. In scenario 

2, water levels decline an additional 10–25 ft from 2012 

levels in the “1,200-foot” sand, but the additional withdrawal 

stress does not substantially increase chloride concentrations 

north of the Baton Rouge Fault. In scenario 3, predicted 

water levels decline an additional 5–10 ft from 2012 levels 

in the “2,000-foot” sand despite the reduced withdrawal 

stress, and the chloride plume continues to migrate toward 

the industrial district but recedes from areas to the east where 

public-supply withdrawals were curtailed. In scenario 4, the 

additional scavenger-well withdrawals contribute to 15–25 ft 

of drawdown in the “2,000-foot” sand from 2012 levels, with 

greater drawdown near the scavenger well and reductions of 

chloride concentrations north of the scavenger well, which 

are more pronounced at the higher simulated scavenger-well 

withdrawal rate of 2.5 Mgal/d. In scenario 5, reductions 

in groundwater withdrawals cause about a 5-ft recovery 

from 2012 water levels in the “2,000-foot” sand and both 

lower concentrations and a slower rate of northward plume 

migration in comparison to scenario 1. In scenario 6, extensive 

reductions in groundwater withdrawals cause 35–50 ft of 

recovery from 2012 water levels and the smallest plume area 

and lowest median cell concentration among the scenarios that 

do not simulate a scavenger well. In scenario 7, the additional 

scavenger-well withdrawals dampen water-level recovery 

because of the scenario 6 reductions to the 20- to 45-ft range 

but enable marked decreases in the chloride plume area and 

concentration. Similar to scenario 4, the decreases in plume 

area and concentration are most pronounced at the higher 

simulated scavenger-well withdrawal rate of 2.5 Mgal/d. 
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Publishing support provided by

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Heywood and others—Simulation of Groundwater Flow and Chloride Transport in the “1,200-Foot” Sand, Baton Rouge Area, Louisiana—SIR 2015–5083 , ver. 1.1

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