GEOHYDROLOGY, WATER QUALITY, AND EFFECTS OF 

PUMPAGE ON THE NEW ORLEANS AQUIFER SYSTEM, 

NORTHERN JEFFERSON PARISH, LOUISIANA

By Don C. Dial and Dan J. Tcmaszewski

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 88-4097

Prepared in cooperation with the 

JEFFERSON PARISH, DEPARTMENT OF WATER

Baton Rouge, Louisiana 

1988
DEPARTMENT OF THE INTERIOR 

DONALD PAUL HODEL, Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

For additional information 

write to:

District Chief

U.S. Geological Survey

P.O. Box 66492

Baton Rouge, LA 70896

Telephone: (504) 389-0281

Copies of this report can be 

purchased from:

U.S. Geological Survey

Books and Open-File Reports Section

Federal Center, Building 810

Box 25425

Denver, CO 80225
CONTENTS

Page

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

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

Purpose, scope, and approach........................................ 2

Previous investigations ............................................. 4

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

Geohydrology............................................................. 5

Gramercy aquifer.................................................... 5

Nbrco aquifer ....................................................... 8

Gonzales-New Orleans aquifer ........................................ 8

Ground-water flow.............................................. 9

Water-level trends ............................................. 9

Water quality............................................................ 12

Gramercy aquifer.................................................... 12

Nbrco aquifer....................................................... 12

Gonzales-New Orleans aquifer ........................................ 15

Projected effects of pumpage ............................................. 17

Ground-water flow................................................... 19

Estimated movement of the freshwater-saltwater interface ............ 30

Land subsidence ..................................................... 31

Summary and conclusions .................................................. 32

Selected references ...................................................... 33

ILLUSTRATIONS

Figure 1. Map showing location of study area, geohydrologic sections,

and observation wells ...................................... 3

2. North-south geohydrologic section from Lake Pontchartrain

to the Mississippi River ................................... 6

3. East-west geohydrologic section near Lake Pontchartrain ...... 7

4. Map showing potentiometric surface of the Gonzales-New

Orleans aquifer, January 1987 .............................. 10

5. Hydrograph of water levels in observation wells JF-65 and 

JF-153 completed in the Gonzales-New Orleans aquifer at 

Kenner, Louisiana.......................................... 11

6. Map showing distribution of chloride concentration in water 

from selected wells completed in the Gonzales-New Orleans 

aquifer, 1987.............................................. 16

7. Map showing distribution of color in water from selected

wells completed in the Gonzales-New Orleans aquifer, 1987 .. 18 

8-11. Maps showing simulated potentiometric surface of the Gonzales-New Orleans aquifer after an additional pumpage of:

8. 25 million gallons per day for 7 days ................... 20

9. 25 million gallons per day for 30 days .................. 21

10. 25 million gallons per day for 20 years ................. 22

11. 50 million gallons per day for 1 year ................... 23

12. Graph showing the relation between water levels and historical and projected pumpage for the Gonzales-New Orleans 

aquifer in northern Jefferson Parish....................... 24

III
ILLUSTRATIONS Continued

Figure 13. Map showing simulated vertical leakage into the GonzalesNew Orleans aquifer for present-day pumpage (1986), after 

present-day pumpage continued for 20 years, and after an 

additional pumpage of 25 million gallons per day for 7 

days......................................................

14. Map showing simulated vertical leakage into the Gonzales-New 

Orleans aquifer after an additional pumpage of 25 million 

gallons per day for 20 years and after an additional 

pumpage of 50 million gallons per day for 1 year..........

Page

27

28

TABLES

Table 1. Chemical analyses of water from selected wells in northern

Jefferson Parish, 1986....................................... 13

2. Summary of estimated ground-water velocity near the freshwatersaltwater interface and simulated maximum water-level 

declines in the Gonzales-New Orleans aquifer at pumping 

nodes........................................................ 25

3. Water budgets from model simulations showing net groundwater inflow and outflow in the freshwater area of the 

Gonzales-New Orleans aquifer in northern Jefferson Parish.... 29

CONVERSION FACTORS AND ABBREVIATIONS

For the convenience of readers who prefer to use metric (International 

System) units rather than the inch-pound units used in this report, values may 

be converted by using the following factors:

Multiply inch-pound unit By To obtain metric unit

inch ( in. )

foot (ft)

foot per day (ft/d)

foot per year (ft/yr)

foot per mile (ft/mi)

square foot per day (ft2 /d)

mile (mi)

square mile (mi2 )

gallon per minute (gal/min)

million gallons per day

(Mgal/d)

25.40

0.3048

0.3048

0.3048

0.1894

0.0929

1.609

2.590

0.06309

0.04381

millimeter (mm)

meter (m)

meter per day (m/d)

meter per year (m/yr)

meter per kilometer (m/km)

square meter per day (m2 /d)

kilometer (km)

square kilometer (km2 )

liter per second (L/s)

cubic meter per second

(m3 /s)

Temperature in degrees Celsius (°C) can be converted to degrees Fahrenheit 

(°F) as follows: °F = 1.8 X °C + 32.

Sea level: In this report "sea level" refers to the National Geodetic 

Vertical Datum of 1929 (NGVD of 1929) a geodetic datum derived from a general 

adjustment of the first-order level nets of both the United States and Canada, 

formerly called "Sea Level Datum of 1929."

IV
GEOHYDROLOGY, WATER QUALITY, AND EFFECTS OF FUMPAGE ON THE NEW ORLEANS 

AQUIFER SYSTEM, NORTHERN JEFFERSON PARISH, LOUISIANA

By Don C. Dial and Dan J. Tomaszewski

ABSTRACT

The New Orleans aquifer system includes four areally extensive aquifers 

(the Gramercy, Norco, Gonzales-New Orleans, and "1,200-foot" aquifers) which 

are separated by beds of clay. Within the aquifer system din northern Jefferson Parish, only the Gonzales-New Orleans aquifer can be considered as a major 

source of freshwater; overlying and underlying aquifers generally contain 

saltwater (water with chloride concentration greater than 250 milligrams per 

liter). However, in northwestern Jefferson Parish the Gonzales-New Orleans 

aquifer contains saltwater. Color generally ranges between 50 and 120 platinum cobalt units in freshwater from the Gonzales-New Orleans aquifer. In 

1986, about 1 Mgal/d (million gallons per day) of water was withdrawn from the 

aquifer din northern Jefferson Parish; however, areally (including adjacent 

parishes) a total of about 40 Mgal/d was withdrawn from the Gonzales-New 

Orleans aquifer.

A three-dimensional finite-difference ground-water flow model was used to 

evaluate the effects of increased pumpage on water levels and flow patterns din 

the Gonzales-New Orleans aquifer. Model simulations included an additional 

pumpage of 25 Mgal/d over 1986 rates (40 Mgal/d) for 7 days, 30 days, and 20 

years, and an additional pumpage of 50 Mgal/d for 1 year. Pumpage was 

simulated din northeastern Jefferson Parish din areas with the most suitable 

combination of freshwater and low color, and as far as possible from the 

present (1987) freshwater-saltwater interface. Results of simulations 

indicate ground-water velocities at the present freshwater-saltwater interface 

near Kenner, Louisiana, will increase from the present average of 65 to 200 

feet per year and that water levels will decline as much as 166 feet at 

simulated well sites with an additional pumpage of 50 Mgal/d for 1 year. 

Increased pumpage would induce northward movement of saltwater about 4 miles 

south of the simulated pumping, and cause additional vertical leakage of 

saltwater through clay beds from overlying and underlying aquifers dLnto 

freshwater din the Gonzales-New Orleans aquifer.

INTRODUCTION

Jefferson Parish needs an alternative source of freshwater to supplement 

Mississippi River water, the regular source of supply. The parish generally 

uses about 50 Mgal/d (million gallons per day) of water from the Mississippi 

River for public supply (D.L. Lurry, U.S. Geological Survey, written comrnun., 

1986). However, because accidental spills of hazardous chemicals dLnto the 

river sometimes force the closure of water-supply intakes, Jefferson Parish, 

Department of Water, is interested din developing a contingency plan to 

withdraw 25 Mgal/d, or about 50 percent of present public water supply from a 

ground-water source for emergency use.
In 1986, about 1 Mgal/d of water was withdrawn from the Gonzales-New 

Orleans aquifer in northern Jefferson Parish; areal (including adjacent 

parishes) withdrawals totaled about 40 Mgal/d. However, water-quality 

problems have restricted the use of water from the aquifer. The most 

troublesome water-quality problems are high color, and concentrations of 

chloride that exceed the U.S. Environmental Protection Agency's (1975) 

recommended upper limit of 250 mg/L (milligrams per liter) for public supply. 

Large withdrawals of ground water also could result din declining water levels, 

saltwater encroachment, vertical leakage of saltwater, and possibly landsurface subsidence.

In October 1985, the U.S. Geological Survey, in cooperation with 

Jefferson Parish, Department of Water, began a study to evaluate the effect of 

increased pumpage of freshwater from the Gonzales-New Orleans aquifer. The 

study area, about 50 mi2 (square miles), includes all of Jefferson Parish 

north of the Mississippi River (fig. 1) in southeastern Louisiana. Land surface is generally flat, and altitudes range from about 5 ft (feet) below to 5 

ft above sea level. At Kenner, Louisiana, the average annual temperature is 

about 20 °C (degrees Celsius), and average annual precipitation is about 60 

in. (inches) (National Oceanic and Atmospheric Administration, 1984).

Purpose, Scope, and Approach

The purpose of this report is to describe the geohydrology and water 

quality of the Gonzales-New Orleans aquifer, and to evaluate the effects on 

the aquifer of additional ground-water pumpage of 25 and 50 Mgal/d.

Physical properties of the New Orleans aquifer system, including extent, 

thickness, lithology, and hydraulic characteristics, are described. The 

potentiometric surface and water-level trends din the Gonzales-New Orleans 

aquifer at present (1987) and as anticipated in the event of several withdrawal scenarios, are defined.

Data for this study were collected, analyzed, and interpreted during 

October 1985 through March 1987. Water-well and test-hole data that include 

chemical analyses and electric, driller's, and geologic logs were compiled and 

used to define the geohydrologic setting. A reconnaissance of the study area 

was made and field data were collected from wells. In areas where data were 

not available or additional data were needed, test holes were drilled for 

collection of water-quality, electric-log, and lithologic data.

Five test holes were drilled as part of this study. Each test hole 

penetrated to the base of the Gonzales-New Orleans aquifer. Electric logs 

were made to interpret aquifer lithology, extent, thickness, and to determine 

the occurrence of saltwater in each aquifer. Confining units between aquifers 

also were identified from electric-log data. Sand samples from selected 

intervals in the test holes were collected for lithologic description. Water 

samples were collected from observation wells subsequently completed at each 

site to further define the water quality in the Gonzales-New Orleans and Norco 

aquifers.
90°15' 90°07'30'

OF LOUISIANA

A Jf-178 

Jf-186*

Jf-183*|i

Bi

NEW 

ORLEANS

EXPLANATION

Observation well and number. 

Asterick (*) indicates well was 

drilled for this study

Oil or gas well

Geohydrologic section (see 

figures 2 and 3) >

29°52'30

5 MILES 

_j

5 KILOMETERS

Figure 1. Location of study area, geohydrologic sections,

and observation wells.
Water quality of the Gonzales-New Orleans aquifer is discussed with 

emphasis on chloride and color, which also are mapped. Water quality of the 

Gramercy and Norco aquifers are only briefly described because they contain 

saltwater in most of the study area. As used in this report, saltwater 

refers to ground water with a chloride concentration greater than 250 mg/L. 

The "1,200-foot" aquifer, which underlies the Gonzales-New Orleans aquifer, 

contains saltwater and is only briefly mentioned because wells are not usually 

drilled to this depth.

A ground-water flow model developed for a previous study of the Greater 

New Orleans area (Dial and Sumner, 1989) was used to evaluate the waterresources potential of the area under study and to predict water-level 

declines and flow patterns in the Gonzales-New Orleans aquifer. Aquifer 

response to four pumpage scenarios was simulated: 25 Mgal/d for periods of 7 

days, 30 days, and 20 years, and 50 Mgal/d for 1 year, in addition to areal 

withdrawals of 40 Mgal/d in 1986 (determined from a water-use survey). 

Pumping nodes were distributed in areas that were known to have suitable water 

quality and located as far as possible from the freshwater-saltwater 

interface.

In this report, wells are identified by the parish abbreviation and 

sequential number. The abbreviation for Jefferson Parish is Jf. Numbers 

following this abbreviation indicate the sequential order in which the well 

was inventoried. Oil and gas wells are identified by a five- or six-digit 

serial number.

Previous Investigations

Data and published results from previous investigations were reviewed and 

used in this study. Two reports, a summary of well data for the Mississippi 

River parishes south of Baton Rouge (Cardwell and others, 1963) and a compilation of water-well and ground-water-quality information for aquifers in the 

Greater New Orleans area (Dial, 1983), contained information on the study 

area. Areal reports on ground-water resources in the New Orleans area 

(Eddards and others 1956; Rollo, 1966) presented the geohydrologic setting. 

Other ground-water studies on adjoining areas are described in reports on the 

Lake Pontchartrain area (Cardwell and others, 1967) and the Norco area 

(Bosnian, 1972). These reports include background data that were used to 

determine geologic, hydraulic, and water-quality characteristics of the 

aquifers. A complete list of references is given in the "Selected References" 

section.

Acknowledgments

Well owners in the area were especially cooperative in allowing collection of water-quality and water-level data from wells. Water well contractors 

supplied some of the driller's- and geophysical-log data used in this study. 

Special thanks are extended to the city of Kenner and the Jefferson Parish 

Drainage District for providing test-drilling sites.
GEDHYDROLOGY

The New Orleans aquifer system consists of an alternating series of 

lenticular clay and sand beds. The sand beds form four areally extensive 

aquifers which are, from youngest to oldest, the Gramercy, Nbrco, Gonzales-New 

Orleans, and "1,200-foot" aquifers. Beds of clay, which act as confining 

units, separate the individual aquifers and vary in thickness from a few feet 

to about 200 ft. Two generalized geohydrologic sections through the study 

area illustrate the complexity and show the relation of the aquifer and 

confining units to one another (figs. 2 and 3).

The Gonzales-New Orleans aquifer is overlain by localized shallow aquifers, the Gramercy aquifer, and the Nbrco aquifer. Shallow aquifers consist 

of point bars, distributary-channel deposits, and isolated near-surface beds 

of sand, (Rollo, 1966, p. 9-12). These localized shallow aquifers occur in a 

thick bed of clay (about 100 to 150 ft in thickness) which overlies the 

Gramercy aquifer. The shallow aquifers do not contain freshwater and are not 

areally extensive in the study area. The Gramercy and Nbrco aquifers are 

present in much of the study area; however, they are not developed because 

they generally contain saltwater. Locally, the Gramercy and Nbrco aquifers 

merge and are in direct hydraulic contact (fig. 3, wells Jf-175 and -176). A 

thick confining unit of clay separates the Gonzales-New Orleans aquifer from 

the overlying Nbrco aquifer. Interpretations of electric and driller's logs 

indicate the confining unit ranges from 50 to 200 ft in thickness and may be 

interbedded with sand beds (figs. 2 and 3).

The Gonzales-New Orleans aquifer also is separated from the underlying 

"1,200-foot" aquifer by a confining unit of clay. Interpretations of electric 

logs from two oil-test wells, 52513 and 56237 (fig. 1), indicate that the 

confining unit is about 50 and 150 ft in thickness, respectively, at these 

wells. Hydraulic connection between the Gonzales-New Orleans and "1,200-foot" 

aquifers has been proposed as an explanation for declines in water levels 

observed in the "1,200-foot" aquifer (Rollo, 1966, p. 48). The "1,200-foot" 

aquifer and underlying aquifers do not contain freshwater in the study area.

Gramercy Aquifer

The first extensive aquifer encountered below land surface in Jefferson 

Parish is the Gramercy aquifer, referred to in earlier reports as the "200- 

foot" sand of the New Orleans area (Eddards and others, 1956; Rollo, 1966). 

Locally the aquifer is sometimes missing or discontinuous as shown in figures 

2 and 3. The Gramercy aquifer averages about 100 ft in thickness, but ranges 

from 80 to 150 ft. Thickness values were determined by interpretation of 

electric and driller's logs. On the basis of interpretation of log data, the 

Gramercy aquifer ranges from 100 to 300 ft below sea level (figs. 2 and 3). 

Regionally the aquifer has a general southward dip and also thickens in a 

southward direction (Hosman, 1972, p. 19). Sand in the Gramercy aquifer 

ranges from fine to coarse (Hosman, 1972, p. 19).

No quantitative data on aquifer hydraulic properties are available in the 

study area. Transmissivities determined from two aquifer tests, a few miles 

southeast of the study area, were 2,600 and 5,300 ft2 /d (feet squared per 

day), and hydraulic conductivities were 30 and 50 ft/d (feet per day) (Rollo, 

1966, p. 15). These hydraulic properties are much lower than those reported
FEET

SEA 

LEVEL

100 -

200 -

300 -

400 -

500 -

600 -

700 -

800 -

900 -

1,000 -1

NORTH

A

LAKE 

PONTCHARTRAIN

Jf-186 Jf-182 Jf-184 Jf-185

SOUTH A'

MISSISSIPPI 

RIVER

56237

NEW ORLEANS 

AQUIFER

EXPLANATION 

[] MOSTLY CLAY 

I FRESHWATER SAND 

E SALTWATER SAND

ul

See figure 1 for location of section

FEET

- SEA 

LEVEL

- 100

- 200

- 300

- 400

- 500

- 600

- 700

- 800

i- 900

L- 1,000

4 MILES

1 I T I I

01234 KILOMETERS

Figure 2. North-south geohydrologic section from Lake Pontchartrain

to the Mississippi River.
WEST p

Jf-183 Jf-186 Jf-177 JfFEET

SEA LEVEL "" 

100 -

200 - 

300 - 

400 - 

500 - 

600 -

700 ~ 

800 -

- 

 = 

 . 

""""^

0 1

I 1 ' ,

GRAMERCY 

AQUIFER

|

\£k

«f"

<^_

^

-^H

2 3 

i i

NORCO 

AQUIFER

<!> "«

^ tf> 

V^ "^ *".4

-«^1b_

\

^^

4 MILES

1 1 1 1 1

GRAMERCY 

AQUIFER

^

r^

-^-

i GONZALESNEW

^^~

~^~

EAST R' 

-176 Jf-175

FEET

SEA

.SHALLOW 

/AQUIFER

"%

^ _

"5

ORLEANS 

AQUIFER

 ^

 ~~~ » -

AQUIFER

 . 

EXPLANATION 

Q MOSTLY CLAY 

0 FRESHWATER SAND 

0 SALTWATER SAND

LEVEL 

- 100 

- 200 

- 300 

- 400 

- 500 

- 600

700 

- 800

See figure 1 for location of section

Figure 3. East-west geohydrologic section near Lake Pontchartrain.
in the Gramercy area where transmissivities from two tests were 9,000 and 

30,000 ft2 /d, and hydraulic conductivities were about 100 and 250 ft/d (Dial 

and Kilburn, 1980, p. 14).

Nbrco Aquifer

The Nbrco aquifer, previously named the "400-foot" sand of the New 

Orleans area (Eddards and others, 1956), underlies the Gramercy aquifer. The 

Nbrco aquifer generally is continuous in the study area, but may be missing 

locally. The aquifer thins and pinches out north of the study area under Lake 

Pontchartrain and a few miles east of the Jefferson-Orleans Parish line 

(Hosman, 1972, p. 28). Interpretations of electric and driller's logs 

indicate that the Nbrco aquifer ranges from about 75 to 130 ft in thickness in 

the study area. The aquifer ranges between 225 and 350 ft below sea level 

near Lake Pontchartrain. The aquifer is deepest at the south end of the study 

area near Harahan where it is present between about 400 and 500 ft below sea 

level.

The Nbrco aquifer is composed of fine to medium sand as determined by 

sieve analyses of samples collected from test holes for wells Jf-184 and 

Jf-186. Estimations from specific-capacity data collected south of Kenner 

indicate the transmissivity of the Nbrco aquifer is about 6,700 ft2 /d (Rollo, 

1966, p. 19, 20). In the Nbrco area estimates of transmissivity and hydraulic 

conductivity of 27,000 ft2 /d and 200 ft/d, respectively, were reported by 

Hosman (1972, p. 41).

Gonzales-New Orleans Aquifer

The Gonzales-New Orleans aquifer extends throughout the study area and 

into the parishes of Orleans and St. Charles, and under Lake Pontchartrain. 

The top of the aquifer occurs about 450 to 500 ft below sea level near Lake 

Pontchartrain. Southward along U.S. Highway 61, the top of the aquifer is 

about 600 to 650 ft below sea level. Regional dip of the aquifer is 25 to 50 

ft/mi (feet per mile) to the south (Hosman, 1972, p. 47).

Interpretations of electric and driller's logs indicate thickness of the 

aquifer ranges from 100 to 300 ft in the study area. Average thickness of the 

aquifer is slightly greater than 200 ft. A geohydrologic section (fig. 3) 

shows that the Gonzales-New Orleans aquifer thins to less than 150 ft in 

northeast Jefferson Parish at the locations of wells Jf-175 and Jf-176. 

Maximum thickness is about 300 ft near the Mississippi River at oil-test well 

56237 (figs. 1 and 2).

Sieve analyses of samples collected from test holes Jf-182, Jf-184, and 

Jf-185 (fig. 1) indicate sand in the aquifer is fine- to medium-grained. At 

aquifer-test sites in the study area and Orleans Parish transmissivity ranges 

from 12,000 to 24,000 ft2 /d, and hydraulic conductivity ranges from 85 to 110 

ft/d (Rollo, 1966, table 3).
Ground-Water Flow

Ground-water movement in the New Orleans aquifer system is part of a 

regional flow system (Dial and Sumner, 1989). Recharge from precipitation and 

seepage enters the New Orleans aquifer system in subcrop or outcrop areas, 

which approximately extend from the northern shore of Lake Pontchartrain 

northward into Tangipahoa and St. Tammany Parishes. Prior to development, 

ground water in the aquifer system flowed south or southwesterly into and 

through the study area and eventually discharged into the overlying 

Mississippi River alluvial aquifer southwest of the study area or coastal 

marshes.

Ground-water flow in the Gonzales-New Orleans aquifer is, at present, 

eastward toward pumping centers in New Orleans. Figure 4 is a potenticmetric 

map showing the water-level surface of the Gonzales-New Orleans aquifer in 

January 1987. The significant decline in water levels toward New Orleans 

indicates that ground-water flow is primarily eastward as ground-water flow is 

generally perpendicular to the potenticmetric contours.

Development of the Gonzales-New Orleans aquifer in the New Orleans area 

has altered the predevelopment flow direction in the aquifer system. Recharge 

to the New Orleans aquifer system has increased with increased potenticmetric 

gradients induced by pumpage. Additional recharge to the Gonzales-New Orleans 

aquifer occurs as leakage through overlying and underlying confining units. 

Water from the overlying Norco aquifer and the underlying "1,200-foot" aquifer 

flows through confining units into the Gonzales-New Orleans aquifer in 

response to the head difference between the aquifers. Because most of the 

pumpage in the study area and nearby New Orleans area is from the Gonzales-New 

Orleans aquifer, hydraulic head in this aquifer is significantly lower than in 

the Norco and "1,200-foot" aquifers.

In the study area, water levels in the Gonzales-New Orleans aquifer range 

from about 30 to 70 ft below sea level in January 1987 (fig. 4). The velocity 

of ground-water flow in the study area can be approximated from Darcy's law 

and estimation of the potenticmetric gradient from figure 4. In the western 

part of the study area, the potenticmetric surface has a small gradient of 

about 1.5 ft/mi. In the eastern part of the study area, the potenticmetric 

gradient increases to between 4.5 and 10 ft/mi. Ground-water velocity in the 

study area may range from 40 to 250 ft/yr (feet per year), assuming that the 

effective porosity of the aquifer is 30 percent and the hydraulic conductivity 

is 110 ft/d. Ground-water velocities are smallest near the St. Charles Parish 

boundary and greatest near the Orleans Parish boundary.

Water-Level Trends

Water-level trends of the Gonzales-New Orleans aquifer are represented by 

the hydrograph for wells Jf-65 and Jf-153 shown in figure 5. (See fig. 1 for 

well locations.) At well Jf-65 water levels declined an average of about 2 

ft/yr from 1959 to 1974. From 1974 to 1983, water levels rose about 2 ft/yr 

at well Jf-65. Since 1983, water levels at well Jf-153 appear to be fluctuating only slightly. The general trend shown by these data reflects areal 

trends (rises and declines) in water levels caused by pumpage from the 

aquifer, primarily in Orleans Parish. Periods of greatest pumpage generally
OS 

O 

O 

O 

O
20

fLU 

LU 

U.

LU 

>

UJ

UJ 

CO

o_l

UJ 

CD

UJ

UJ

_l

cc

UJhLL 

O

UJ 

Q

WELL: Jf-65 

DEPTH: 698 FEET

Bar graph indicates total pumpage in 

million gallons per day from the 

Gonzales-New Orleans aquifer in 

Jefferson and Orleans Parishes 

(Dial, 1983 p. 7; D.L. Lurry, U.S. 

Geological Survey, written commun. 

1986)

WELL: Jf-153 

DEPTH: 670 FEET

40

60

1960 1965 1970 1975 1980 1985

Figure 5. Hydrograph of v/ater levels in observation wells Jf-65 

and Jf-153 completed in the Gonzales-New Orleans aquifer at 

Kenner, Louisiana.

11
coincide with declines in water levels, and periods of least pumpage or 

declines in pumpage when compared to previous years coincide with rises or 

higher water levels in the aquifer. Because pumpage from the aquifer varies 

seasonally, hydrographs of wells show an annual decline and recovery that is 

superimposed on the long-term trends.

WATER QUALITY

The greatest deterrent to ground-water use for public supply in northern 

Jefferson Parish is the occurrence of saltwater in the aquifers. Saltwater 

generally occurs in aquifers overlying and underlying the Gonzales-New Orleans 

aquifer. However, in most of the study area the Gonzales-New Orleans aquifer 

contains freshwater. In northwestern Jefferson Parish freshwater is locally 

available in the Norco aquifer.

Gramercy Aquifer

Interpretation of electric logs and chemical analyses of ground water 

collected during this study indicate that the Gramercy aquifer contains 

saltwater throughout the study area. Although the Gramercy aquifer in northwestern Jefferson Parish has been described as containing freshwater (Rollo, 

1966, p. 15), subsequent test-drilling and electric-log data collected during 

this study indicate that the aquifer contains saltwater only. In previous 

reports (Dial, 1983; Rollo, 1960), wells identified as being screened in the 

Gramercy aquifer had actually been screened in the Norco aquifer. Because the 

Gramercy aquifer contains saltwater, wells are not completed in this aquifer, 

and chemical data are limited.

Norco Aquifer

Water from the Norco aquifer generally is saltwater. In most of the 

study area chloride concentrations range from 250 to less than 1,000 mg/L 

(Dial, 1983, tables 3 and 4). However, in northwestern Jefferson Parish, data 

collected during test drilling at well Jf-186 (fig. 1) indicate freshwater is 

locally available. Chemical analyses of water collected from the Norco 

aquifer at test well JF-186 indicate a chloride concentration of 130 mg/L 

(table 1). Water sampled from well Jf-186 was moderately hard, 95 mg/L, and 

concentrations of iron and manganese were 420 and 36 ug/L (micrograms per 

liter), respectively. Dissolved solids were about 700 mg/L, and color was 40 

platinum cobalt units.

Interpretations of electric log data collected during this study, and 

review of previously collected chemical data indicate freshwater in the Norco 

aquifer extends only 1 or 2 mi south of the shore of Lake Pontchartrain (figs. 

1 and 2) and extends east from well Jf-186 to well Jf-177 (fig. 3). East of 

well Jf-177 the Norco aquifer pinches out and is locally replaced by clay 

(fig. 3, well Jf-176); however, underlying the clay is a freshwater bed of 

sand. This bed of sand may be in hydraulic contact with the Norco aquifer 

west of well Jf-177. In northeastern Jefferson Parish, the Norco aquifer 

contains saltwater.

12
Table 1.--Chemical analyses of water from selected wells in northern Jefferson Parish, 1986

[uS/cm, microsiemens per centimeter; °C, degrees Celsius; mg/L, milligrams per liter;

ug/L, micrograms per liter]

Well 

number

Latitude

Longitude

Depth 

of well, 

total Date 

(feet)

Specific 

conductance 

(uS/cm)

Gonzales-New Orleans

Jf- 64

Jf-141

Jf-149

Jf-162

Jf-163

Jf-168

Jf-169

Jf-170

Jf-171

Jf-172

Jf-175

Jf-176

Jf-177

Jf-178

Jf-180

Jf-182

Jf-183

Jf-184

Jf-185

295831

OQC COC

Z 7OOZO

295832

300135

295545

295940

300000

300011

300210

300040

300110

300111

300154

300222

295738

300025

300206

295926

295823

90164601

90111701

90080301

90151401

90123001

90110801

90103501

90123801

90141501

90104501

90083601

90104701

90130001

90144601

90084701

90143901

90163101

90143201

90123601

719

740

749

628

768

744

740

737

557

628

640

610

650

700

730

605

612

704

766

6-18-86

1 - J.-OD 1 Q£

5-19-86

5- 8-86

5-19-86

1-16-86

1-16-86

1-16-86

1-17-86

5- 8-86

5- 7-86

1-17-86

5- 7-86

5- 7-86

5-14-86

10- 3-86

10- 2-86

9-26-86

9-25-86

1,730

971

5,060

920

701

641

621

1,450

702

719

672

622

3,660

869

691

7,850

661

769

Color 

Specific pH (platconduct- (stand- Temper- inumance, lab ard ature cobalt 

(uS/cm) units) (°C) units)

Aquifer

1,

,

4,

1,

3,

7,

720

910

970

980

926

722

663

617

460

691

723

684

623

700

853

680

340

644

772

8.10

8.40

7.80

8.30

8.10

8.30

8.20

7.90

8.30

8.40

8.20

8.60

8.10

8.40

8.70

____

9.10

8.50

25.5

25.5

24.5

24.5

25.0

25.0

25.0

24.5

25.0

25.5

24.0

25.0

26.0

25.0

24.0

24.0

24.0

24.0

20

Q f\ oU 

120

5

100

80

80

100

5

60

60

50

70

5

120

20

5

30

100

Norco Aquifer

Jf-186

Well

number

300223

Hardness

(mg/L

as

CaCOJ

90144601

Hardness,

noncarb

wh wat

tot fid

(mg/L as

CaC0 3 )

325

Calcium

dissolved

(mg/L

as Ca)

10- 2-86

Magnesium,

dissolved

(mg/L

as Mg)

1,190

Sodium,

dissolved

(mg/L

as Na)

Gonzales-New Orleans

Jf- 64

Jf-141

Jf-149

Jf-162

Jf-163

Jf-168

Jf-169

Jf-170

Jf-171

Jf-172

Jf-175

Jf-176

Jf-177

Jf-178

Jf-180

Jf-182

Jf-183

Jf-184

Jf-185

74

___

15

___

13

9

9

9

43

___

9

___

___

11

19

260

22

14

__

--

0

--

0

0

0

0

0

__

0

--

--

0

--

1

--

--

19

____

3.4

____

3.2

2.6

2.7

2.8

12

____

.4

____

.6

.9

55

.9

3.8

6.5

____

1.5

____

1.3

.7

.6

.6

3.2

____

.7

____

1.1

.3

29

.5

1.1

300

____

200

____

200

160

140

140

280

____

160

____

____

180

140

1600

140

180

1, 180

Percent

sodium

7.80

PotasSodium, sium.

adsorp- distion solved

ratio (mg/L

as K)

23.0

Alkalinity,

wh wat

total

field

(mg/L as

CaCOJ

40

Alkalinity,

lab

(mg/L

as

CaC0 3 )

Aquifer

__

--

96

--

96

97

97

96

93

__

97

--

--

97

93

93

92

96

16

___

23 3.5

___

25 2.5

24 1.7

21 1.4

21 1.6

19 4.4

_ _ _ _ _

24 2.0

__

___

24 2.2

15 2.9

45 9.5

14 4.1

22 1.8

___

317

___

288

250

244

259

181

_ _ _

221

___

___

299

207

___

240

277

198

___

319

___

292

253

245

261

179

___

220

___

___

298

202

256

235

271

Norco Aquifer

Jf-186 95 0 15 14 220 82 10 8.0 438 420

13
Table 1.--Chemical analyses of water from selected wells

in northern Jefferson Parish, 1986--Continued

Well

number

Sulfate,

dissolved

(mg/L

as SO ) 

4

Chloride,

dissolved

(mg/L

as Cl)

Fluoride.

dissolved

(mg/L

as F)

Silica,

dissolved

(mg/L

as Si0 2 )

Solids, NitroSolids. sum of gen.

Nitrogen,

residue consti- nitrate nitrite

at 180 tuents, dis-

°C dis- dis- solved

solved solved (mg/L

(mg/L) (mg/L) as N)

dissolved

(mg/L

as N)

Nitrogen,

No +No 3

dissolved

(mg/L

as N)

Gonzales-New Orleans Aquifer

Jf- 64

Jf-141 

Jf-149 

Jf-162

Jf-163

Jf-168

Jf-169

Jf-170

Jf-171

Jf-172 

Jf-175

Jf-176

Jf-177

Jf-178

Jf-180

Jf-182

Jf-183

Jf-184

Jf-185

0.2

.2

.4

.8

1.0

.6

.4

.4

.2

4.9

22

7.5

11

410

740

120 

1,500

120

78

60

48

340

O A 84 

100

88

59

1,100

96

93

2,400

63

87

___

0.9

.8

.6

.7

.7

.3

.5

1.0

.3

.8

.3

.6

__

28

29

28

28

28

29

28

28

--

--

--

--

899 

579 550 0.64

549 530 .62

431 420 .28

401 380 .25

405 380 .26

602 780 .56

414 420 .33

519 490 .59

413 --- 

4,510 ----

425

455 

____

0.01

<.01

<.0l

<.0l

<.01

<.01

<.0l

.01

____

____

____

----

____

0.65

.63

.29

.26

.27

.57

.34

.60

<.10

____

.61

.42

Norco Aquifer

Jf-186

Well

number

1.2

Aluminum,

dissolved

(ug/L

as Al)

130

Antimony,

dissolved

(wg/L

as Sb)

.6

Arsenic

dissolved

(wg/L

as As)

--

, Barium,

dissolved

(ug/L

as Ba)

697 

Beryl- Chrolium. Cadmium, mium. Copper,

dis- dis- dis- dissolved solved solved solved

(ug/L (ug/L (ug/L (ug/L

as Be) as Cd) as Cr) as Cu)

 

Iron,

dissolved

(ug/L

as Fe)

 

Gonzales-New Orleans Aquifer

Jf- 64

Jf-141

Jf-149

Jf-162

Jf-163

Jf-168

Jf-169

Jf-170

Jf-171

Jf-172

Jf-175

Jf-176

Jf-177

Jf-178

Jf-180

Jf-182

Jf-183

Jf-184

Jf-185

__

--

--

--

--

--

--

--

--

--

--

--

--

--

30

--

90

20

__

--

__

__

--

__

__

--

--

--

--

--

--

--

--

<1

--

<1

<1

__

--

--

--

--

--

--

--

--

--

--

--

--

--

<1

--

1

<1

___

___

___

___

___

___

___

___

___

___

___

___

___

66

___

110

110

____ __ ___

____ __ ___

___

____ __ ___

____ __ ___

____ __ ___

___

____ __ ___

____ __ ___

____ __ ___

____ __ ___

____ __ ___

____ __ ___

____ __ ___

____ __ ___

<0.5 <1 <10 1

____ __ ___

<.5 <1 <10 2

<.5 <1 <10 <1

190

___

87

200

71

64

72

75

110

89

71

77

59

180

100

34

___

75

340

Norco Aquifer

Jf-186 -- -- -- 420

14
Table 1.--Chemical analyses of water from selected wells

in northern Jefferson Parish, 1986--Continued

Well

number

Lead, 

dissolved

(pg/L 

as Pb)

Manga 

nese, 

dissolved

(pg/L 

as Mn)

Mercury, 

dissolved

(pg/L 

as Hg)

Nickel, 

dissolved

(pg/L 

as Ni)

Selenium, 

dissolved

(pg/L 

as Se)

Silver, 

dissolved

(pg/L 

as Ag)

Zinc, 

dissolved

(pg/L 

as Zn)

Carbon, 

organic 

total

(mg/L 

as C)

Carbon, 

organic 

dissolved

(mg/L 

as C)

Jf- 64 

Jf-141 

Jf-149 

Jf-162 

Jf-163 

Jf-168 

Jf-169 

Jf-170 

Jf-171 

Jf-172 

Jf-175 

Jf-176 

Jf-177 

Jf-178 

Jf-180 

Jf-182 

Jf-183 

Jf-184 

Jf-185

Jf-186

<5

<5 

<5

90

20

350

20

10

10

30

110

18

20

20

32

120

20

3

3

19

36

Gonzales-New Orleans Aquifer

<1 <1

Norco Aquifer

4.0 

4.8

1.7

2.5

2.6 

5.6

5.4 

4.0 

4.8 

5.0 

1.4

2.5

6.1 

2.0

2.4 

4.8

Gonzales-New Orleans Aquifer

Fresh ground water in the Gonzales-New Orleans aquifer generally is a 

mixed sodium bicarbonate-chloride type. The freshwater is soft; hardness 

ranges between 9 and 22 mg/L (table 1). Field determined pH values, measured 

during this study, range from 8.1 to 9.1 standard units for freshwater. 

Concentrations of iron and manganese generally are less than 100 ug/L in 

freshwater but locally may exceed this concentration (well Jf-185, table 1). 

Dissolved-solids concentrations range between 400 and 600 mg/L (table 1) in 

freshwater, and concentrations of sodium range between 140 and 200 mg/L.

Chloride concentrations range from 48 to 2,400 mg/L in water from the 

Gonzales-New Orleans aquifer (table 1). On the basis of available sampling 

sites and electric-log interpretations, about one-fifth of the study area 

(10 mi2 in northwestern Jefferson Parish) is underlain by saltwater in the 

Gonzales-New Orleans aquifer (fig. 6). The aquifer contains freshwater 

throughout northern Jefferson Parish except for the area approximately located 

within 2 mi (miles) of the Jefferson and St. Charles Parishes border. Freshwater in the Gonzales-New Orleans aquifer extends northward under Lake 

Pontchartrain and eastward into Orleans Parish. Chloride concentration in 

freshwater from the aquifer generally is less than 150 mg/L; however, this 

concentration may be exceeded near the freshwater-saltwater interface (figs. 

2, 3, and 6). As shown in figures 2 and 3, the freshwater-saltwater interface 

resembles a wedge extending from the main body of saltwater (areas where the

15
90°15'00" 90°07'30"

29°52'30"

1000

Jf-170

48

LINE OF EQUAL CHLORIDE 

CONCENTRATION IN WATER 

FROM WELLS COMPLETED IN THE 

GONZALES-NEW ORLEANS AQUIFER. 

Interval is milligrams per liter (mg/l)

OBSERVATION WELL. Top number 

with letter prefix identifies well. 

Bottom number is chloride 

concentration in (mg/l)

Simulated pumping node

5 MILES

5 KILOMETERS

Figure 6. Distribution of chloride concentration in water from selected 

wells completed in the Gonzales-New Orleans aquifer, 1987.

16
aquifer contains saltwater vertically from the base to the top) into freshwater parts of the aquifer. This wedge is variable in width and possibly 

extends from 1 to several miles under the freshwater in the aquifer. Along 

this wedge the transition from freshwater to water having very high chloride 

concentrations (19,000 mg/L or more) in the study area and surrounding areas 

is gradual. Chloride concentrations are less than 1,000 mg/L in most saltwater wells in the study area and surrounding areas (Dial and Sumner, 1989).

Color in water from the Gonzales-New Orleans aquifer ranges from 5 to 120 

units (fig. 7). Low color (less than 30 units) is contained in saltwater or 

areas near the freshwater-saltwater interface (fig. 7). Color from 50 to 120 

units can generally be expected in freshwater from the Gonzales-New Orleans 

aquifer.

Color in natural water usually results from leaching of organic materials 

and is usually reported in units as determined by the platinum-cobalt methods 

(Hem, 1985, p. 152-153). However, no direct connection is associated with the 

amount of organic material causing the color and the color value. Effects of 

color on public water supplies are generally aesthetic. Color below 10 units 

is usually not noticeable. Recommended color of 15 units or less was established by the Public Health Service in 1962 (U.S. Environmental Protection 

Agency, 1977, p. 52). Coagulation, sedimentation, and filtration can be used 

to reduce color to 15 units or less when the color of the source water does 

not exceed 75 units (U.S. Environmental Protection Agency, 1977, p. 52).

PROJECTED EFFECTS OF PUMPAGE

A three-dimensional ground-water flow model, documented by McDonald and 

Harbaugh (1984), of the New Orleans aquifer system was constructed for a previous study of the Greater New Orleans area (Dial and Sumner, 1989). The 

aquifer system was simulated in the model by four layers that represented the 

Gramercy, Norco, Gonzales-New Orleans, and "1,200-foot" aquifers. The 

resistance to flow of the intervening confining units was incorporated in the 

model. The modeled area, of which the study area is only a small part, covers 

much of southeastern Louisiana and southern Mississippi. The preparation of 

the model included a conceptualization of the aquifer system, calibration of 

the model by comparison of model output with observed data, and application of 

the model for predictive purposes. Different pumping stresses were simulated 

to evaluate possible future water-level declines and flow patterns.

The New Orleans model was predesigned so that the smallest grid blocks 

(cells) were in Orleans and Jefferson Parishes where detailed resolution was 

desired. The grid blocks range from 1.0 mi2 (1 mi on a side) in the study 

area to a maximum of 281 mi2 (25 mi X 11.25 mi) at the model boundaries. 

Therefore, the New Orleans model is well suited to the present study which is 

near the center of the modeled area and far from any boundary conditions.

17
9Q°15'00' 90°G7'3Q'

30°00'

29°52'30'

PQNTCHARTRAIN

700

Jf-170 

100

VSX

X

throughout entire thickness

LINE OF EQUAL COLOR OF WATER FROM 

WELLS COMPLETED IN THE GONZALES-NEW 

ORLEANS AQUIFER. Interval 25 platinum 

cobalt units

OBSERVATION WELL. Top number with letter 

prefix identifies well. Bottom number is 

color in platinum cobalt units

Simulated pumping node

____/-_ i__ ^

5 MILES

5 KILOMETERS

Figure 7. Distribution of color in water from selected wells completed in 

the Gonzales-New Orleans aquifer, 1987.

18
Simulations for this study were done to evaluate the effects on waterlevel declines and the movement of the freshwater-saltwater interface in the 

Gonzales-New Orleans aquifer in response to several ground-water pumpage scenarios. These scenarios included an additional pumpage of 25 Mgal/d from the 

Gonzales-New Orleans aquifer for periods of 7 days, 30 days, and 20 years, and 

an additional pumpage of 50 Mgal/d for a 1-year period. The pumping rates 

were added to the current (1986) areal ground-water pumpage of 40 Mgal/d from 

the Gonzales-New Orleans aquifer. The simulated 25 Mgal/d was evenly distributed in three locations in Jefferson Parish (figs. 8, 9, and 10). The 

simulated 50 Mgal/d was evenly distributed in six locations in Jefferson 

Parish (fig. 11). The locations of the simulated pumpage (nodes) are in the 

center of the finite-difference blocks used in modeling. Each block in the 

study area had an area of 1 mi2 , and total simulated pumpage at each node was 

about 6,000 gal/min (gallons per minute). Distribution of simulated pumpage 

in the Gonzales-New Orleans aquifer was determined by mapping areas where 

freshwater is available and has relatively low color. The best combination of 

freshwater (less than 250 mg/L) and color (less than 100 units) appears to be 

in the northeastern part of Jefferson Parish (figs. 6 and 7). Therefore, 

simulated node sites were located In that area as far as possible from the 

area underlain by saltwater to minimize the rate of saltwater encroachment 

toward the pumping centers (fig. 8).

The node distribution was the same for each simulation involving an additional pumpage of 25 Mgal/d. Thus, the potentiometric surfaces produced by 

these three pumpage scenarios are similar In configuration because only the 

duration of pumping was variable. The potentiometric surfaces of the 

Gonzales-New Orleans aquifer that represent water-level surfaces after an 

additional pumpage of 25 Mgal/d for 7 days, 30 days, and 20 years are shown In 

figures 8, 9, and 10, respectively. Maximum water-level declines at simulated 

pumping nodes are shown in figure 12 and table 2. Localized drawdowns in 

individual wells or well fields would be greater than shown in the table 

because the simulated water levels are averages of the whole block.

The locations of the simulated pumping nodes and the potentiometric 

surface of the Gonzales-New Orleans aquifer after pumping 1 year at 50 Mgal/d 

are shown in figure 11. The greatest water-level decline in the study area 

was 166 ft (table 2).

Ground-Water Flow

A comparison of the simulated potentiometric surfaces (figs. 8-11) with 

the 1987 potentiometric map (fig. 4) indicates an additional 25 and 50 Mgal/d 

pumpage will alter present-day ground-water flow in the study area and 

adjacent areas. As shown by the simulated potentiometric surfaces, a cone of 

depression becomes centered around the simulated pumping nodes. This would 

result in radial flow of ground water from inside and outside the study area 

toward the simulated pumping nodes. A significant change in direction of 

ground-water flow would occur south of the pumping nodes with the additional 

25 and 50 Mgal/d pumpage. Ground water south of the pumping nodes would begin 

to move northward toward the pumping nodes.

19
90°15'00' 90°07'30*

30°00'

29°52'30"

-80 PONTENTIOMETRIC CONTOUR 

Shows altitude at which water 

level would have stood in tightly 

cased wells. Contour interval 

is 20 feet. Datum is sea level

Simulated node pumping 6,000 

gallons per minute

5 MILES

5 KILOMETERS

Figure 8. Simulated potenticmetric surface of the Gonzales-New Orleans 

aquifer after an additional pumpage of 25 million gallons per day for 

7 days.

20
90°15'GCr 90°07'30'

EXPLANATION

PONTENTIOMETRIC CONTOURShows altitude at which water 

level would have stood in tightly 

cased wells. Contour interval is 

20 feet. Datum is sea level

Simulated node pumping 6,000 

gallons per minute

29°52'30"

MILES

Figure 9. Simulated potentiometric surface of the Gonzales-New Orleans 

aquifer after an additional pumpage of 25 million gallons per day for 

30 days.

21
90°15'00

30°00' -

29°52'3(r

CHARTRAIN

EXPLANATION

PONTENTIOMETRIC CONTOURShows altitude at which water 

level would have stood in tightly 

cased wells. Contour interval 

is 20 feet. Datum is sea level

Simulated node pumping 6,000 

gallons per minute

5 MILES

0 5 KILOMETERS

Figure 10. Simulated potentionetric surface of the Gonzales-New Orleans 

aquifer after an additional pumpage of 25 million gallons per day for 20 

years.

22
90°15'00' 9Q°Q7'3Cr

30°00' -

29°52'30" -

EXPLANATION

PONTENTIOMETRIC CONTOUR-- 

Shows altitude at which water 

level would have stood in tightly 

cased wells. Contour interval 

is 20 feet. Datum is sea level

Simulated node pumping 6,000 

gallons per minute

/

5 MILES

5 KILOMETERS

Figure 11. Simulated potenticmetric surface of the Gonzales-New Orleans 

aquifer after an additional pumpage of 50 million gallons per day for 

1 year.

23
c-o

hLU 

LU

LU 

>

LU

LU 

CO

LU 

CO

_J 

LJJ

>

LJJ

_J

CC 

LLI

o

25

50

75

100

125

150

175

200

225

25 Mgal/d for 7 days25 Mgal/d for 30 days

50 Mgal/d for 1 year 

 Com

proj

 Com

Bar grap

pumpage 

per day 

Gonzale

Recove

50 Mg

Recov

25 Mg

I I ^25 Mg

i' 

\l

1953 1963 1969 1975 1981 1986

Filgure 12. The relation between water levels and historical and pr

Gonzales-New Orleans aquifer in northern Jefferson 
Table 2. Summary of estimated ground-water velocity near the freshwatersaltwater interface and simulated maximum water-level declines in the 

Gonzales-New Orleans aquifer at pumping nodes

_ . , , Estimated average linear _. _ , , Pump^g rate and ground-water velocity (feet S^nulated maximn,

penod of mtti- ^ simulated water-level decline

drawal (mllicn ^rnpage (near p^^t fresh- (feet) !* s"^Lafed

gallons per day) *- *- » _. , . . ,. , pumping nodes ^ *~ J ' water-saltwater interface) f ** »

South of Near 

pumping nodes Kenner

Present (1986) 65 

Present pumpage con- 60 none 

tinued for 20 years.

Present pumpage and 150 80 57 

additional 25 Mgal/d 

for 7 days.

Present pumpage and 150 170 74 

additional 25 Mgal/d 

for 30 days.

Present pumpage and 230 170 99 

additional 25 Mgal/d 

for 20 years.

Present pumpage and 500 200 166 

additional 50 Mgal/d 

for 1 year.

Declines are the differences between simulated water levels for 1986 and 

the end of each pumpage scenario.

Short periods of additional pumpage, such as the simulated 7- and 30-day 

periods (figs. 8 and 9) would not have long-term effects on ground-water flow 

in the Gonzales-New Orleans aquifer. At the end of the 7- and 30-day periods, 

when the additional 25 Mgal/d pumpage is ceased, ground-water levels would 

begin to recover to levels prior to the simulated pumpage (cones of depression 

would diminish) and the present-day flow regime would be reestablished. 

Longer periods of simulated pumpage, 20 years with an additional 25 Mgal/d and 

1 year with an additional 50 Mgal/d, would cause the formation of deeper cones 

of depression (figs. 10 and 11) when compared to shorter periods (figs. 8 and 

9). Larger periods would cause the hydraulic gradient to steepen in the 

direction of the pumping nodes. In the Gonzales-New Orleans aquifer, the 

present-day freshwater-saltwater interface would move toward the simulated 

pumping nodes and the volume of saltwater entering the aquifer by vertical 

leakage across overlying and underlying clays may increase.

25
The present-day net ground-water inflow and outflow in the freshwater 

area of the Gonzales-New Orleans aquifer in northern Jefferson Parish and the 

effects of simulated pumpage on this flow are shown in table 3. At present 

pumpage rates, lateral inflow of saltwater from western parts of the study 

area and areas south of the Mississippi River into the freshwater area totals 

about 3.9 Mgal/d (59 percent of the net ground-water inflow). Additional 

freshwater, 1.7 Mgal/d (27 percent of the net inflow), enters the study area 

by lateral flow from north and east of the study area. Vertical leakage 

through confining units from the overlying and underlying aquifers at present 

supplies about 0.8 Mgal/d (14 percent of the net inflow) of water daily. 

Discharge (net outflow) from the freshwater parts of the study area is by 

pumping and lateral outflow east and south. Present-day pumpage if continued 

for 20 years would not alter the present flow pattern. As shown in table 3, 

there is no change in water taken from or going to storage in the Gonzales-New 

Orleans aquifer. Therefore, the aquifer under present (1986) pumping conditions is in steady state.

The effects of additional pumpage of 25 Mgal/d and 50 Mgal/d on the net 

inflow and outflow on the freshwater area of the Gonzales-New Orleans aquifer 

can be seen in table 3. For example, with an additional pumpage of 50 Mgal/d 

for 1 year about 17.2 Mgal/d (30 percent of the net inflow) is from lateral 

flow of saltwater from the Gonzales-New Orleans aquifer in the western part of 

the study area and south of the Mississippi River. Lateral flow of freshwater 

from the Gonzales-New Orleans aquifer north and east of the study area would 

supply a total of 35.7 Mgal/d (63 percent of the net inflow). Vertical leakage from overlying and underlying aquifers would total about 3.5 Mgal/d (6 

percent of the total net inflow). About 0.3 Mgal/d (less than 1 percent of 

the net inflow) would come from aquifer storage. Outflow of freshwater does 

not change significantly during the simulations except for additional pumpage 

from the simulated pumping nodes.

Vertical leakage through overlying and underlying confining units into 

freshwater in the Gonzales-New Orleans aquifer is important because it is a 

possible source of saltwater. The net inflow of saltwater from vertical leakage would increase with additional pumpage rates and the duration of pumpage 

(figs. 13 and 14, table 3). Although the increased vertical leakage appears 

to be small when compared to increased inflow from lateral flow, it is important to determine where the vertical leakage may be concentrated. A series of 

vertical leakage maps shown in figures 13b, 13d, 14b, and 14d indicate most of 

the vertical leakage into the Gonzales-New Orleans aquifer from overlying 

aquifers would be concentrated in the northeastern quarter of the study area. 

Present-day vertical leakage from overlying aquifers is concentrated here 

because of nearby pumpage in Orleans Parish. Selected vertical leakage maps 

for model simulations of 25 Mgal/d for 7 days and 30 days, and 50 Mgal/d for 1 

year indicate additional pumpage would increase vertical leakage from overlying aquifers in this area. To determine how additional pumpage will affect 

the amount of vertical leakage from overlying or underlying aquifers one may 

refer to table 3 and figures 13 and 14. For example, table 3 indicates that 

an additional pumpage of 50 Mgal/d for 1 year will increase inflow (vertical 

leakage) from overlying aquifers from 0.4 Mgal/d at present to 1.9 Mgal/d 

(about five times the present rate). The leakage map shown in figure 13b 

indicates that vertical leakage from overlying aquifers at present is about 

0.020 (Mgal/d)/mi2 at simulated pumping nodes. With an additional pumpage of 

50 Mgal/d for 1 year, vertical leakage from overlying aquifers (fig. 14d) 

would increase to about 0.10 (Mgal/d)/mi2 (five times the present-day rate).

26
90°15 00" 90°07'30"

a. Leakage from underlying aquifers present 

day (1986) and after present day pumpage 

continued for 20 years.

b. Leakage from overlying aquifers present 

day (1986) and after present day pumpkge 

continued for 20 years.

90°15'DO" 90°07'30*

c. Leakage from underlying aquifers after 

additional pumpage of 25 Mgal/d for 7 days.

d. Leakage from overlying aquifers after 

additional pumpage of 25 Mgal/d for 7 days.

EXPLANATION

 0.020 Line of equal vertical flow at end of simulation period.

Interval is 0.005 million gallons per day (Mgal/d) per square mile

-^- Simulated pumping node

5 MILES

0 5 KILOMETERS

Figure 13. Simulated vertical leakage into the Gonzales-New Orleans aquifer 

for present-day punpage (1986), after present-day punpage continued for 20 

years, and after an additional punpage of 25 million gallons per day for 7 

days.

27
°- 025

a. Leakage from underlying aquifers after 

additional pumpage of 25 Mgal/d for 20 

years.

b. Leakage from overlying aquifers after 

additional pumpage of 25 Mgal/d for 20 

years.

c. Leakage from underlying aquifers after 

additional pumpage of 50 Mgal/d for 1 year.

d. Leakage from overlying aquifers after 

additional pumpage of 50 Mgal/d for 1 year.

EXPLANATION

 0.020 Line of equal vertical flow at end of simulation period.

Interval is 0.005 million gallons per day (Mgal/d) per square mile

-^- Simulated pumping node

0 5 MILES

0 5 KILOMETERS

Figure 14. Simulated vertical leakage into the Gonzales-New Orleans aquifer 

after an additional pumpage of 25 million gallons per day for 20 years and 

after an additional pumpage of 50 million gallons per day for 1 year.

28
Table 3---Water budgets from model simulations showing net ground-water inflow and outflow 

of the Gonzales-New Orleans aquifer in northern Jefferson Parish

[Rates given in million gallons per day Mgal/d at end of model simulation: number in parenthesis

Pumping rate and period

Present rate 

1986

Present rate

continued for

20 years

Additional 25 Mgal/d, continued 

7 days 30 days 20 

Inflow (recharge)

Overlying aquifers ------ Q.4 (7)

Gonzales-New Orleans 

aquifer north and 

east of study area----- 1.7 (27)

Gonzales-New Orleans 

aquifer in north 

western Jefferson 

Parish and south of i 

the Mississippi River - 3.9 (59)

Underlying aquifers ----- .4 (7) 

Aquifer storage---------- .0 (0)

Net inflow--------------- 6.4

Pumpage------------------ 1.1 (17)

Gonzales-New Orleans 

aquifer east of 

study area------------- 3.2 (50)

Gonzales-New Orleans 

aquifer south of 

study area------------- 2.1 (33)

Aquifer storage---------- .0 (0)

Net outflow-------------- 6.4

1

Indicates saltwater.

0.4 (7)

1.7 (27)

3-9 (59)

 4 (7)

.0 (0)

6.4

0.8 (3)

14.6 (49)

6.9 (23)

 7 (2)

6.7 (23)

29-7

1.0 (3)

16.4 (55)

9-7 (33)

 9 (3)

1.8 (6)

1-

16.

10.

l.

29-

Outflow (discharge)

1.1 (17) 

3-2 (50)

2.1 (33) 

 0 (0)

6.4

26.1 (88) 

1.9 (6)

1-7 (6) 

.0 (0)

29-7

26.1 (88)

2.1 (7)

1.6 (5)

.0 (0)

26.

2.

1-

-

29-
Vertical leakage frcm underlying saltwater aquifers at the present rate 

of pumping is concentrated in the eastern half of the study area as shown in 

figure 13a. Figures 13c and 14a show that an additional pumpage of 25 Mgal/d 

for 7 days and 20 years would increase vertical leakage throughout the study 

area; however, vertical leakage from underlying aquifers would still be 

concentrated in the eastern half. With an additional pumpage of 50 Mgal/yr 

for 1 year vertical leakage from underlying aquifers would be concentrated 

around the pumping nodes (fig. 14c).

Estimated Movement of the Freshwater-Saltwater Interface

The main problem in the development of the Gonzales-New Orleans aquifer 

as an alternative water supply is the occurrence of saltwater in the western 

part of the study area and south of the Mississippi River (fig. 6). Additional pumpage in eastern Jefferson Parish would increase the eastward rate of 

movement of the freshwater-saltwater interface in the western part of the 

study area and cause the freshwater-saltwater interface about 4 miles south of 

the simulated pumping nodes to begin to move north. The velocity of groundwater flow can be estimated by application of Darcy's law, which is given as:

KI 

V = 9

where V = ground-water velocity, in feet per day;

K = aquifer hydraulic conductivity, in feet per day; 

I = potentiometric gradient, in feet per foot; 

9 = aquifer porosity, dimensionless.

Application of Darcy's law to estimate the rate of movement of the 

freshwater-saltwater interface assumes no dispersion and density effects. 

These assumptions were tested in the New Orleans area by a comparison of 

historically observed rates of saltwater encroachment and those estimated by 

Darcy's law. The results showed that Darcy's law gave close estimates of 

observed rates of saltwater encroachment (Dial and Sumner, 1989). Thus, in 

the present analysis, Darcy's law is applied to the various pumpage scenarios 

to arrive at estimates of anticipated rates of saltwater encroachment. These 

estimates, based on assumed values of aquifer hydraulic conductivity and 

porosity of 110 ft/d and 0.30, respectively, are summarized in table 2.

Short durations of increased pumpage, 7 days and 30 days, would have 

little effect on the present freshwater-saltwater interface as the average 

linear ground-water velocity at the interface would slow and return to or 

nearly to steady-state conditions when the additional pumpage is ceased. 

Table 2 shows a comparison of ground-water velocities at 1986 pumping 

conditions with the added pumping rates of 25 and 50 Mgal/d. The present 

velocity near the freshwater-saltwater interface in western Jefferson Parish 

near Kenner is about 65 ft/yr. If an additional 25 Mgal/d were added to the 

present pumpage for a 20-year period, the velocity at the interface near 

Kenner would increase to about 170 ft/yr. However, the average velocity of 

ground water would be about 230 ft/yr at the freshwater-saltwater interface 

about 4 mi south of the simulated pumpage. Assuming no dispersion or diffusion, the freshwater-saltwater interface would travel northward about 0.9 mi

30
by the end of the 20-year period. The interface in western Jefferson Parish 

would travel about 0.6 mi in an eastward direction by the end of the 20 year 

pumping period. If an additional 50 Mgal/d were added to the present pumpage 

for 1 year, the average velocity would be about 500 ft/yr at the freshwatersaltwater interface south of the pumping nodes. However at the end of the 1- 

year pumping period when simulated pumpage is ended, water levels in the 

Gonzales-New Orleans aquifer would begin to recover and the ground-water 

velocity at the freshwater-saltwater interface would slow. The location of 

well sites in the eastern part of the study area would allow the maximum time 

before saltwater would reach the wells.

Land Subsidence

Much of the land subsidence in Jefferson Parish has been relatively 

recent, occurring after the marshland was drained and urbanization began. The 

three most probable causes of subsidence in the study area are related to (1) 

secLLment loading and associated compaction of sediments as they become more 

deeply buried, (2) dewatering of marshy areas where surf icial materials were 

formerly saturated, and (3) pumpage of ground water in the New Orleans area. 

Because pumpage of ground water is related to subsidence, the development of 

ground water as a public-supply source can only be evaluated by monitoring 

pumpage and subsidence concurrently.

The first two causes, sediment loading and dewatering, have been investigated by Saucier (1963) and Snowden and others (1977); the reader is referred 

to these sources for additional information. The natural subsidence resulting 

from sediment loading is area wide in scope, and its effects locally are not 

believed significant. Saucier (1963, p. 13) estimated a subsidence rate of 

0.39 foot per century in the Lake Ponlxhartrain basin. This subsidence is 

attributed mostly to the combined effects of sediment loading, compaction, and 

faulting. The drainage of swamps and marshy areas for development of suburban 

areas in Jefferson Parish has caused the most dramatic short-term problem of 

land subsidence. Differential subsidence of up to 3.3 ft was reported in some 

areas by Snowden and others (1977, p. 173).

Because this study involves increased ground-water pumpage, an evaluation 

of its effects on subsidence would be useful. Increased pumpage of ground 

water in Jefferson Parish would cause some subsidence, but no records are 

available to determine how much. In the downtown area of New Orleans, land 

subsidence of 1.7 ft was reported between 1938 and 1964 on the basis of 

published bench-mark records (Kazmann and Heath, 1968, p. 111). They attributed most of the subsidence to water-level decline in the Gonzales-New 

Orleans aquifer. They concluded that the ratio of land subsidence to waterlevel decline was 1 ft of subsidence for every 50 ft of water-level decline, 

assuming the bench-mark data were valid. Since the early 1970's, pumpage in 

the New Orleans area has declined and water levels have been recovering. 

Information is not available to determine whether water-level recovery in the 

New Orleans area has been accompanied by a rise in altitude of land surface.

In the Baton Rouge area where local subsidence was monitored with 

extensometers from 1975 to 1979, only a small amount of permanent compaction 

occurred during the period when water-level recoveries occurred in the "600- 

foot" aquifer (Whiteman, 1980, p. 11-12). However, more than 1 ft of

31
subsidence in the Baton Rouge area occurred during the period 1934-76 and is 

believed to be mostly permanent. This subsidence was a result of irreversible 

compaction of clays primarily caused by ground- water pumpage (Whiteman, 1980, 

p. 1-2). It is reasonable to assume that conditions of subsidence and 

recovery would be similar in the aquifer system in the study area. Thus, 

short periods of small rates of pumping would probably cause a minimal 

subsidence effect when compared to long continuous periods of large pumpage.

SUMMARY AND CONCLUSIONS

The New Orleans aquifer system is composed of a complex series of alternating interbedded clay and sand beds which form four areally extensive 

aquifers. From youngest to oldest, they are the Gramercy, Norco, Gonzales-New 

Orleans, and "1,200-foot" aquifers. Generally, these aquifers are separated 

by confining units of clay. Although freshwater is locally available near the 

shore of Lake Pontchartrain in northwestern Jefferson Parish from the Norco 

aquifer, the Gonzales-New Orleans aquifer is the only major source of fresh 

ground water.

Because the public-water supply from the Mississippi River is sometimes 

interrupted, planners and managers have begun to consider the Gonzales-New 

Orleans aquifer as an alternative source of water. However, about one-fifth 

of the study area is underlain by saltwater in the Gonzales-New Orleans 

aquifer. Saltwater generally occurs in the western part of the study area. 

Color, although its effects are mostly aesthetic, also generally exceeds 15 

platinum-cobalt units. Color generally ranges between 50 to 120 units where 

the aquifer contains freshwater (all of the study area except the western onefifth).

Freshwater from the Gonzales-New Orleans aquifer is generally a mixed 

sodium bicarbonate-chloride type. The ground water is soft, and pH generally 

ranges from 8.1 to 9.1 standard units. Both iron and manganese generally are 

less than 100 ug/L. Dissolved-solids concentrations range between 400 and 600 

mg/L. Sodium concentrations range between 140 and 200 mg/L in freshwater from 

the Gonzales-New Orleans aquifer.

Analysis of sand, collected from the Gonzales-New Orleans aquifer, 

indicates grain size ranges from fine to medium. Transmissivity and hydraulic 

conductivity ranging from 12,000 to 24,000 ft2 /d and 85 to 110 ft/d, respectively, have been determined from aquifer tests in the study area and nearby 

areas. The aquifer averages slightly greater than 200 ft in thickness.

By use of a three-dimensional finite-difference ground-water flow model, 

an additional pumpage of 25 Mgal/d of water for 7 days, 30 days, and 20 years, 

and a pumpage of 50 Mgal/d for 1 year from the Gonzales-New Orleans aquifer 

were simulated to evaluate the effect on water levels and flow patterns. The 

simulated pumpage was located in northeastern Jefferson Parish where the best 

combination of low chloride concentration (less than 250 mg/L chloride) and 

relatively low color (less than 100 platinum-cobalt units) was available. 

Pumpage was located as far as possible from areas underlain by saltwater to 

decrease the rate of encroachment and maximize the time required for saltwater 

to reach the well fields.

32
Results of simulations indicate average ground-water velocities will 

increase at the present freshwater-saltwater interface near Kenner from the 

present velocity of 65 ft/yr to a maximum of 200 ft/yr with an additional 50 

Mgal/d withdrawal for 1 year. Simulation results also indicate the freshwater-saltwater interface located about 4 mi south of the pumping nodes will 

begin to move northward between 150 to 500 ft/yr. Short pumping periods, 7 

days and 30 days at 25 Mgal/d, will have little effect on the movement of the 

freshwater-saltwater interface. However, if additional pumpage of 25 Mgal/d 

is continued for 20 years, the freshwater-saltwater interface would encroach 

northward about 0.9 mi. The maximum rate of northward encroachment, 500 

ft/yr, would occur during the additional pumpage of 50 Mgal/d for 1 year. 

Simulation results indicate maximum water-level declines from 57 to 166 ft 

will occur at hypothetical well fields. Simulation results also indicate 

vertical leakage of saltwater through overlying and underlying clays into 

freshwater areas of the Gonzales-New Orleans aquifer in northern Jefferson 

Parish may increase with additional pumpage.

SELECTED REFERENCES

Cardwell, G.T., Forbes, M.J., Jr., and Gaydos, M.W., 1967, Water resources of 

the Lake Pontchartrain area, Louisiana: Louisiana Department of Conservation and Louisiana Department of Public Works Water Resources Bulletin 

12, 105 p.

Cardwell, G.T., Rollo, J.R., and Long, R.A, 1963, Basic ground-water data for 

the Mississippi River parishes south of Baton Rouge, Louisiana: Louisiana Department of Public Works, 5 p.

Dial, D.C., 1983, Ground-water data for the Mississippi River parishes in the 

Greater New Orleans area, Louisiana: Louisiana Department of Transportation and Development, Office of Public Works Water Resources Basic 

Records Report No. 11, 47 p.

Dial, D.C., and Kilburn, Chabot, 1980, Ground-water resources of the Gramercy 

area, Louisiana: Louisiana Department of Transportation and Development, 

Office of Public Works Technical Report no. 24, 39 p.

Dial, D.C., and Sumner, D.M., 1989 [in press], Geohydrology and simulated 

effects of pumpage on the New Orleans aquifer system at New Orleans, 

Louisiana: Louisiana Department of Transportation and Development Water 

Resources Technical Report no. 46.

Eddards, M.L., Kister, L.R., and Scarcia, Glenn, 1956, Water resources of the 

New Orleans area, Louisiana: U.S. Geological Survey Circular 374, 41 p.

Hem, J.D., 1985, Study and interpretation of the chemical characteristics of 

natural water: U.S. Geological Survey Water-Supply Paper 2254, 225 p.

Hosman, R.L., 1972 [1973], Ground-water resources of the Norco area, Louisiana: Louisiana Department of Conservation and Louisiana Department of 

Public Works Water Resources Bulletin 18, 61 p.

33
Kazmann, R.G., and Heath, M.M., 1968, Land subsidence related to ground water 

offtake: Transaction-Gulf Coast Association of Geological Societies, v. 

XVIII, p. 108-113.

McDonald, M.G., and Harbaugh, A.W., 1984, A modular three-dimensional finitedifference ground-water flow model: U.S. Geological Survey Open-File 

Report 83-875, 528 p.

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report, EPA.R3.733.033, 594 p.

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annual summary, Louisiana 1982: U.S. Department of Commerce, NQAA, v. 

89, no. 13, 23 p.

Rollo, J.R., 1966, Ground-water resources of the Greater New Orleans area,

Louisiana: Louisiana Department of Conservation and Louisiana Department 

of Public Works Water Resources Bulletin 9, 69 p.

Saucier, R.T., 1963, Recent geomorphic history of the Pontchartrain Basin, 

Louisiana, pt. A of U.S. Gulf Coastal Studies Technical Report no. 16: 

Louisiana State University Coastal Studies Institute Contribution 63-2, 

114 p.

Snowden, J.O., Siirmons, W.B., Traughber, E.B., and Stephens, R.W., 1977, 

Differential subsidence of marshland peat as a geologic hazard in the 

Greater New Orleans area, Louisiana: Transactions Gulf Coast Association 

of Geological Societies, v. 27, 11 p.

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water regulations: Federal Register, v. 40, no. 248, Wednesday, Dec. 24, 

1975, part IV, p. 59566-59587.

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Protection Agency, Washington, D.C., 256 p.

Whiteman, C.D., Jr., 1979, Saltwater encroachment in the "600-foot" and

11 1,500-foot" sands of the Baton Rouge area, Louisiana, 1966-78, including 

a discussion of saltwater in other sands: Louisiana Department of 

Transportation and Development, Office of Public Works Water Resources 

Technical Report no. 19, 49 p.

 1980, Measuring local subsidence with extensometers in the Baton Rouge 

area, Louisiana, 1975-79, Louisiana Department of Transportation and 

Development, Office of Public Works Water Resources Technical Report no. 

20, 18 p.

34