Prepared in cooperation with the 

Jackson Utility Division 
Hydrology of the Jackson, Tennessee, 

Area and Delineation of Areas 

Contributing Ground Water to 

the Jackson Well Fields 

By ZELDA CHAPMAN BAILEY 

U.S. Geological Survey 

Water-Resources Investigations Report 92-4146 

Prepared in cooperation with the 

Jackson Utility Division 

Nashville, Tennessee 

1993 
U.S. DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, Jr., Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

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

District Chief 

U.S. Geological Survey 

810 Broadway, Suite 500 

Nashville, Tennessee 37203 

U.S. Geological Survey 

Books and Open-File Reports Section 

Federal Center 

Box 25425 

Denver, Colorado 80225 
CONTENTS 

Abstract ............................................................. 

Introduction ........................................................... 

Purposeandscope.. .................................................. 

Approach ......................................................... 

Acknowledgments .................................................... 

Description of study area .................................................. 

Geography and climate ................................................. 

Geology .......................................................... 

Landuse ......................................................... 

Wateruse ......................................................... 

Streamflow characteristics ............................................... 

Hydrologic system ...................................................... 

Hydraulic characteristics of aquifers ......................................... 

Ground- and surface-water interaction ........................................ 

Arealrecharge ...................................................... 

Water-level fluctuations ................................................ 

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

Ground-water flow model .................................................. 

Model assumptions ................................................... 

Conceptual model .................................................... 

Model grid and boundaries .............................................. 

Simulation of sources and sinks of water ...................................... 

Model calibration .................................................... 

Model limitations and sensitivity analysis ...................................... 

Pumping simulations .................................................. 

Areas contributing water to the well fields ........................................ 

Configuration of ground-water flow to the well fields .............................. 

NorthWellField .................................................... 

South Well Field ..................................................... 

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

Selected references ...................................................... 

FIGURES 

l-5. Maps showing: 

1. Studyarea .................................................. 

2. Location of data-collection sites and pumped wells .......................... 

3. Surficial geology .............................................. 

4. Saturated thickness of the Memphis Sand, April 1989 ........................ 

5. Thickness of the Fort Pillow Sand .................................... 

6. Hydrogeologic sections .............................................. 

7. Map showing land use .............................................. 

8-l 1. Graphs showing: 

8. Average annual pumping rates from the well fields, 1971-89 ................... 

9. Discharge of the South Fork Forked Deer River at Jackson, Tennessee ............. 

10. Flow duration of the Middle and South Forks Forked Deer River ................ 

11. Water levels in observation wells and precipitation at the Jackson Agricultural 

Experiment Station ............................................. 

12. Map showing configuration of the water table in April 1989 and general directions 

of ground-water flow ............................................... 

13. Representation of aquifer layers in the digital model ............................ 

Page 

1 

2 

2 

2 

4 

4 

4 

4 

9 

11 

11 

13 

13 

14 

15 

16 

17 

17 

17 

19 

19 

21 

24 

26 

29 

37 

37 

43 

43 

43 

53 

3 

5 

6 

7 

8 

9 

10 

12 

12 

14 

16 

18 

19 

Contents iii 
Page 

14-16. Maps showing: 

14. Finite-difference grid for the digital flow model ........................... 

15. Categories of relative recharge rates ................................... 

16. Model-calculated water levels in layer 3 and measured water levels ............... 

17. Diagram showing distribution of water-budget components among the 

layers of the digital flow model ......................................... 

18-22. Graphs showing: 

18. Sensitivity of the digital flow model to adjustments in recharge .................. 

19. Sensitivity of the digital flow model to adjustments in hydraulic 

conductivity of aquifers .......................................... 

20. Changes in root mean square error of simulated water levels with 

respect to simultaneous changes in recharge and aquifer hydraulic 

conductivity using constant-flux boundary conditions ........................ 

21. Sensitivity of the digital flow model to adjustments in vertical 

conductance between layers ........................................ 

22. Sensitivity of the digital flow model to adjustments in hydraulic 

conductivity of streambeds ........................................ 

23-25. Maps showing simulated drawdown in layer 3 for: 

23. Pumping plan 1 with constant-flux boundaries ............................ 

24. Pumping plan 2 with constant-flux boundaries ............................ 

25. Pumping plan 3 with constant-flux boundaries ............................ 

26-29. Maps showing simulated particle-flow pathlines and 5-year time-of-travel 

capture zones for: 

26. The calibrated model ............................................ 

27. Pumping plan 1 ............................................... 

28. Pumping plan 2 ............................................... 

29. Pumping plan 3 ............................................... 

30. Hydrologic sections through the North and South Well Fields showing 

increments of 1 year of travel time for 5 years along pathlines 

to a single pumped well for pumping plan 2 ................................. 

31-34. Maps showing increments of 1 year of travel time for 5 years along 

pathlines to individual wells in the North Well Field for: 

31. The calibrated model ............................................ 

32. Pumping plan 1 ............................................... 

33. Pumpingplan ............................................... 

34. Pumpingplan ............................................... 

35-38. Maps showing increments of 1 year of travel time for 5 years along pathlines 

to individual wells in the South Well Field for: 

35. The calibrated model ............................................ 

36. Pumping plan 1 ............................................... 

37. Pumping plan 2 ............................................... 

38. Pumping plan 3 ............................................... 

TABLES 

1. Landuse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

2. Average annual ground-water use from the Memphis and Fort Pillow Sands 

in the Jackson area, 1989 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . 

3. Estimated hydraulic characteristics of the Memphis Sand and Fort Pillow 

Sand in or near Madison County . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

20 

23 

25 

27 

29 

30 

31 

32 

32 

34 

35 

36 

38 

39 

40 

41 

42 

44 

45 

46 

47 

48 

49 

50 

51 

11 

11 

13 

iv Hydrology of the Jackson, Tennessee, area and delineation 

of areas contributing ground water to the Jackson Well Fields 
Page 

4. Discharges and ground-water gains and losses along segments of the Middle 

and South Forks Forked Deer River, April 24 through 26, 1989 . . . . . . . . , . . . . . . . . . . . . . . . 15 

5. Steady-state ground-water budget for the calibrated model and pumping 

plans for the Jackson area . . , . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . 26 

6. Maximum simulated drawdown in the North and South Well Fields for constanthead and constant-flux boundary conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 

CONVERSION FACTOR, VERTICAL DATUM, AND TRANSMISSIVITY 

Multiply BY To obtain 

inch (in) 

foot (ft) 

mile (mi) 

square mile (mi’) 

acre 

foot per day (ftld) 

inch per year (in/yr) 

foot squared per day (tY/d) 

cubic foot per day (V/d) 

cubic foot per second (ft’ls) 

gallon per day (gal/d) 

million gallons per day (Mgal/d) 

25.4 millimeter 

0.3048 meter 

1.609 kilometer 

2.590 square kilometer 

0.4047 hectare 

0.3048 meter per day 

2.54 centimeter per day 

0.0929 meter squared per day 

0.02832 cubic meter per day 

0.02832 cubic meter per second 

3.785 liter per day 

0.04381 cubic meter per second 

Temperature in degrees Fahrenheit (“F) can be converted to degree Celsius (“C) as follows: “C = 5/9(“F-32) 

Sen level: In this report “sea level” refers to the National Geodetic Vertical Datum of 1929--a geodetic datum derived from a 

genera1 adjustment of the first-order level nets of both the United States and Canada, formerly called Sea Level Datum of 1929. 

Transmissivify: In this report transmissivity is expressed as foot squared per day (ft2/d)--The standard unit for transmissivity (T) 

is cubic foot per day per square foot times foot of aquifer thickness [(A’/d)/ll*]ft of cubic meter per day per square meter times 

meter of aquifer thickness [(m’/d)/mqm. These mathematical expressions reduce to foot squared per day (A*/d) or meter squared 

per day (m*/d). 

Contents v 
Hydrology of the Jackson, Tennessee, Area and 

Delineation of Areas Contributing Ground Water 

to the Jackson Well Fields 

By Zelda Chapman Bailey 

Abstract 

A comprehensive hydrologic investigation of 

the Jackson area in Madison County, Tennessee, was conducted to provide information for 

the development of a wellhead-protection 

program for two municipal well fields. The 

136-square-mile study area is between the 

Middle Fork Forked Deer and South Fork 

Forked Deer Rivers and includes the city of 

Jackson. 

The formations that underlie and crop out in 

the study area, in descending order, are the 

Memphis Sand, Fort Pillow Sand, and Porters 

Creek Clay. The saturated thickness of the 

Memphis Sand ranges from 0 to 270 feet; the 

Fort Pillow Sand, from 0 to 180 feet. The 

Porters Creek Clay, which ranges from 130 to 

320 feet thick, separates a deeper formation, the 

McNairy Sand, from the shallower units. 

Estimates by other investigators of hydraulic 

conductivity for the Memphis Sand range from 

80 to 202 feet per day. Estimates of transmissivity of the Memphis Sand range from 2,700 to 

33,000 feet squared per day. Estimates of 

hydraulic conductivity for the Fort Pillow Sand 

range from 68 to 167 feet per day, and estimates of transmissivity of that unit range from 

6,700 to 10,050 feet squared per day. 

A finite-difference, ground-water flow 

model was calibrated to steady-state hydrologic 

conditions of April 1989, and was used to 

simulate hypothetical pumping plans for the 

North and South Well Fields. The aquifers 

were represented as three layers in the model to 

simulate the ground-water flow system. Layer 

1 is the saturated part of the Memphis Sand; 

layer 2 is the upper half of the Fort Pillow 

Sand; and layer 3 is the lower half of the Fort 

Pillow Sand. 

The steady-state water budget of the simulated system showed that more than half of the 

inflow to the ground-water system is underflow 

from the model boundaries. Most of this inflow 

is discharged as seepage to the rivers and to 

pumping wells. Slightly less than half of the 

inflow is from areal recharge and recharge from 

streams. About 75 percent of the discharge 

from the system is into the streams, lakes, and 

out of the model area through a small quantity 

of ground-water underflow. The remaining 

25 percent is discharge to pumping wells. 

The calibrated model was modified to 

simulate the effects on the ground-water system 

of three hypothetical pumping plans that 

increased pumping from the North Well Field to 

up to 20 million gallons per day, and from the 

South Well Field, to up to 15 million gallons 

per day. Maximum drawdown resulting from 

the 20 million-gallons-per-day rate of simulated 

pumping was 44.7 feet in a node containing a 

pumping well, and maximum drawdown over an 

extended area was about 38 feet. up to 

34 percent of ground-water seepage to streams 

in the calibrated model was intercepted by 

pumping in the simulations. A maximum of 

9 percent more water was induced through 

model boundaries. 

Abstract 1 
A particle-tracking program, MODPATH, 

was used to delineate areas contributing water to 

the North and South Well Fields for the calibrated model and the three pumping simulations, and to estimate distances for different 

times-of-travel to the wells. The size of the 

area contributing water to the North Well Field, 

defined by the 5-year time-of-travel capture 

zone, is about 0.8 by 1.8 miles for the calibrated model and pumping plan 1. The size of the 

area for pumping plan 2 is 1.1 by 2.0 miles 

and, for pumping plan 3, 1.6 by 2.2 miles. The 

range of distance for l-year time-of-travel to 

individual wells is 200 to 800 feet for the 

calibrated model and plan 1, and 350 to 

950 feet for plans 2 and 3. 

The size of the area contributing water to 

the South Well Field, defined by the 5-year 

time-of-travel capture zone, is about 0.8 by 

1.4 miles for the calibrated model. The size of 

the area for pumping plans 1 and 3 is 1.6 by 

2.2 miles and, for pumping plan 2, 1.1 by 

1.7 miles. The range of distance for l-year 

time-of-travel to individual wells is 120 to 

530 feet for the calibrated model, 670 to 

1,300 feet for pumping plans 1 and 3, and 260 

to 850 feet for pumping plan 2. 

INTRODUCTION 

The U.S. Geological Survey (USGS), in cooperation with the Jackson Utility Division (JUD), 

conducted a comprehensive investigation of the 

hydrogeology of the Jackson area in Madison County, Tennessee. This cooperative effort is a continuation of a pilot investigation of the Jackson area that 

provided preliminary information and analyses for 

the development of a wellhead-protection program 

for two municipal well fields proshears and others, 

1991). The pilot investigation included a preliminary assessment of the local hydrogeology, groundwater quality, and potential sources of contamination. The purpose of the comprehensive investigation was to describe the hydrology of the Jackson 

area to the extent that the JUD can identify potential 

short- and long-term threats to the quality of ground 

water, and can use this information in the develop2 Hydrology of the Jackson, Tennessee, area and delineation 

of areas contributing ground water to the Jackson Well Fields 

ment of appropriate and timely strategies to protect 

municipal supplies. This information will assist 

JUD in making decisions about the protection and 

management of ground-water resources. 

The 136-m? study area (fig. 1) is oriented 

northeast to southwest, parallel to the outcrops of 

major aquifers, and includes most of the area of the 

pilot investigation. The northeastern extent of the 

study area is the Middle Fork Forked Deer River, 

and the southwestern extent is about 1 mile south of 

the South Fork Forked Deer River. A short segment of the North Fork of the South Fork is included in the study area. These tributaries of the Forked 

Deer River will be referred to for brevity in this 

report as the Middle, North, and South Forks. The 

northwestern boundary of the area is 3.5 miles from 

the North Well Field, and the southeastern boundary 

approximates the eastern edge of the outcrop of a 

major aquifer, the Fort Pillow Sand. 

Purpose and Scope 

This report describes the results of a comprehensive hydrologic investigation that was completed 

in 1990. The objectives were to (1) map the lithology and geometry of the aquifers and confining units 

in greater detail than previously available, (2) map 

the configurations of the water table and potentiometric surfaces, (3) determine directions of groundwater flow, (4) delineate areas of ground-water 

recharge and discharge, (5) evaluate effects of 

hypothetical increases in pumping from the well 

fields, (6) delineate areas contributing ground water 

to municipal wells, and (7) estimate times-of-travel 

for advective transport of solutes to municipal weIIs. 

Data collection for stratigraphic and water-level 

information was limited to existing well logs and 

wells. 

Approach 

Subsurface geometry and lithology of the major 

geologic units have been mapped on a regional scale 

by other investigators (Parks and Carmichael, 1989, 

199Oc). Local refinements for the study area were 

made by using 126 drillers’ logs and borehole 

geophysical logs. The drillers’ logs were selected 

from records in the State files on the basis of complete stratigraphic information. The geophysical 
Figure

1 . Study area .

Introduction3
logs were collected from deep wells by the USGS 

during previous investigations. 

Locations and quantities of water discharged to 

streams by industries or sewage treatment plants, 

and locations and rates of commercial, industrial, 

and municipal pumping were identified (fig. 2). 

Water levels were measured in 53 domestic, commercial, and municipal wells from April 24 

through 25, 1989, and elevations of the wells were 

estimated from topographic contours. Stream 

discharge was measured or estimated at the same 

time at 79 sites along all the forks of the Forked 

Deer River and their tributaries (fig. 2). 

Mean annual precipitation for the period 1941 to 

1980 was 49.9 inches (National Climatic Data 

Center, National Oceanic and Atmospheric Administration, written commun., 1988). Rain characteristically falls throughout the year. Mean monthly 

precipitation ranges from about 2.5 inches in October to about 5.4 inches in April. 

A finite-difference, ground-water flow model 

was calibrated to hydrologic conditions of April 

1989 and was used to simulate hypothetical pumping 

plans. A particle-tracking analysis was used to 

delineate areas contributing water to wells in the 

municipal well fields and to estimate distances for 

different times-of-travel to the wells. 

Acknowledgments 

The author thanks the Tennessee Department of 

Environment and Conservation (TDEC), Division of 

Systems and Procedures, for providing extensive 

drillers’ log data. Appreciation also is expressed to 

the staff of the Jackson Utility Division who located 

wells for water-level measurement and assisted in 

the field data collection, and to the businesses and 

homeowners who graciously allowed their wells to 

be measured. Without their support, much of the 

data needed for this investigation could not have 

been collected. 

DESCRIPTION OF STUDY AREA 

Geography and Climate 

The area of investigation is in the West Tennessee Plain of the Coastal Plain physiographic province 

(Miller, 1974, p. 7). Total relief is about 280 feet. 

The lowest elevation, 320 feet above sea level, is 

where the South Fork leaves the study area and the 

highest elevation, about 540 feet, is along the 

drainage divide between the Middle and South 

Forks. The summit of one hill along the divide 

stands at nearly 600 feet above sea level. 

The geologic units that are of hydrologic interest 

in the study area include, from youngest to oldest, 

the Memphis Sand, Fort Pillow Sand (fig. 3), and 

Porters Creek Clay. In the northwestern part, 

comprising about half the study area, the Memphis 

Sand is overlain by loess, and in most of the remaining area, by Pleistocene fluvial deposits (fig. 3); 

however, these deposits are not saturated. The 

principal aquifers, the Memphis and Fort Pillow 

Sands, contain clay lenses of considerable thickness 

and area1 extent. The Memphis Sand consists 

primarily of fine to very coarse sand and silt and 

clay. The Fort Pillow Sand consists primarily of 

fine to very coarse sand and minor clay. The 

saturated thickness of the Memphis Sand ranges 

from 0 to 270 feet (fig. 4). The Fort Pillow Sand in 

most of the area ranges from 0 to 180 feet thick, 

although the thickness in an area in the southern part 

of the study area, near the boundary of the model, 

is as much as 230 feet (fig. 5). Erosional remnants 

of the Flour Island Formation, which confines the 

Fort Pillow Sand to the west, may be present in the 

western part of the study area, but no evidence was 

found on drillers logs. The Porters Creek Clay, 

which ranges from 130 to 320 feet thick, separates 

a deeper formation, the McNairy Sand, from the 

shallower units. The bottom of the Porters Creek 

Clay was not mapped, but was estimated on the 

hydrogeologic sections (fig. 6) using an average 

thickness of 225 feet. All units thin from northwest 

to southeast and dip to the northwest at 20 to 

50 ft/mi. 

4 Hydrology of the Jackson, Tennessee, area and delineation 

of areas contributing ground water to the Jackson Well Fields 

Geology 

TDEC and USGS files and records were 

searched for stratigraphic information on existing 

wells. More than 900 wells in the study area were 

inventoried by the USGS prior to 1960; however, no 

stratigraphic data were collected. Few of the more 

than 3,100 wells in the TDEC files provided stratigraphic information. Data for all deep wells for 
Figure 2. Location of data-collection sites and pumped wells.

Description of study area 5
Figure 3. Surficial geology.

EA
Figure 4. Saturated thickness of the Memphis Sand, April 1989.

Description of study area 7
Figure 5. Thickness of the Fort Pillow Sand .
Land Use

Figure 6. Hydrogeologic sections . (Traces of sections shown on figure 3 .)

which stratigraphic data were available and data for

selected shallow wells, a total of 129 wells, were

used in this investigation to refine the larger scale

geologic maps of other investigators (Miller and

others, 1966; Parks, 1968a-c ; Parks and Carmichael,

1989, 1990c) .

Land use is divided into five general categories:

agricultural, urban, wetlands, forest, and disturbed

(table 1). The distribution of these categories is

shown on figure 7 only for the area included in the

active-model area. The principal land use is agricul

tural. Urban areas include the city of Jackson and

surrounding residential subdivisions, industrialized

areas, and major highways . Wetlands include

forested and nonforested wetlands and open water.

Disturbed land includes land that has been cleared

for construction, quarry operations, or landfills .

Description of study area 9
Figure 7 . Land use.
Table 1 . Land use

Water Use

The primary sources of ground water in the area

are the Memphis Sand and Fort Pillow Sand . A

total of about 16.0 Mgal/d is pumped from these

aquifers in the study area during 1989 (table 2) .

The McNairy Sand is not used extensively as a local

source of water, but several flowing wells tap that

aquifer . Some of these wells flow freely at a rate of

about 300 gal/min .

Table 2. Average annual ground-water use from the

Memphis and Fort Pillow Sands in the Jackson area,

1989

The JUD supplies water to customers in Madison

County from two well fields in Jackson (figs . 1-2).

Prior to 1980 all of the water, as much as 9 Mgal/d,

was pumped from the South Well Field. Since

1980, as much as 85 percent of the municipal supply

has been pumped from the North Well Field (fig . 8).

Average annual withdrawal in 1989 was 8 .7 Mgal/d

from the North Well Field, and 1 .6 Mgal/d from the

South Well Field (table 2) . Average pumpage for

the week in April 1989 when water levels and

stream discharges were measured was 9.2 Mgal/d

for the North Well Field and 2.2 Mgal/d for the

South Well Field (Danny Lester, JUD, written

commun., 1989).

Average total industrial pumpage from 33 wells

in the Jackson area is about 5 Mgal/d (table 2) .

Domestic wells provide water for many county

residents and a few wells supply commercial enterprises ; however, withdrawal from these wells, about

0 .7 Mgal/d, is minor compared to withdrawals from

municipal and industrial wells .

Strearnflow Characteristics

The Middle, South, and North Forks are the

major drains for most of Madison County (fig . 1),

and their channels have been ditched and straightened . Wetlands predominate in the flood plains of

the North and South Forks (fig . 7). The uplands

between the rivers are dissected by tributaries that

are dry most of the year.

A continuous-record streamflow-gaging station

was operated on the South Fork at Jackson (fig . 1)

from August 1929 through September 1973 and the

station was reactivated in May 1988 (fig . 9). The

drainage area of the stream upstream of the station

is 495 miZ. Average flow for 44 years of record

(1929-73) was 705 ft/s or 19.34 in/yr (U.S . Geological Survey, 1974, p . 141) . Maximum discharge for

the period was 43,600 ft'/s, and minimum was

67 ft/s.

A continuous-record streamflow-gaging station on

the Middle Fork was operated near Alamo (fig . 1,

location map), about 16 miles downstream from the

study area, from August 1929 through September

1973 . The drainage area of the stream upstream of

the station is 369 miZ . Average flow for 44 years of

Description of study area 11
Figure 8. Average annual pumping rates from the well fields, 1971-89. (Danny Lester, Jackson Utility Division,

written commun., 1989.)

Seepage

measured

Figure 9 . Discharge of the South Fork Forked Deer River at Jackson, Tennessee.
record (1929-73) was 521 ft'/s or 19 .17 in/yr (U.S .

Geological Survey, 1974, p. 142). Maximum

discharge for the period was 34,300 ft'/s, and

minimum was 68 ft'/s .

HYDROLOGIC SYSTEM

Hydraulic Characteristics of Aquifers

Average hydraulic conductivity, transmissivity,

and storage coefficient of the Memphis Sand and

Fort Pillow Sand in Madison County have been

estimated (table 3) by Hosman and others (1968,

p. 8, 9, and 21) and by Moore (1965, pl. 7). Parks

and Carmichael (1990c) reported estimates of

transmissivity and storage coefficient from a regional

study of the Memphis Sand. The values were

estimated from tests in a small number of wells and

applied to large areas, so hydraulic characteristics of

the aquifers in any specific location may vary

considerably from these estimates . Previous investigations in the Jackson area provided estimates of

hydraulic conductivity and transmissivity for both

the Memphis Sand and the Fort Pillow Sand

(Nuzman, C .E., consultant for Layne Central Company, Inc ., written commun., 1977; Groundwater

Management, Inc ., written commun., 1987) .

Estimates of hydraulic conductivity for the Memphis Sand range from 80 to 202 ft/d, transmissivity

from 2,700 to 33,000 ft2/d, and storage coefficient

from 0.0001 to 0.011 . Two estimates of hydraulic

conductivity for the Fort Pillow Sand are 68 and

167 ft/d, and estimates of transmissivity, 6,700 and

10,050 ft'/d . The only estimate of storage coefficient is 0.0015 . The range of porosity for unconsolidated sand aquifers of the type found in the study

area is between 20 and 50 percent (Freeze and

Cherry, 1979, p . 37).

Table 3 . Estimated hydraulic characteristics of the Memphis Sand and Fort Pillow Sand in or near Madison County

Hydrologic system 1 3
Ground- and Surface-Water Interaction

Base-flow measurements and flow-duration curves

were used to study the hydraulic connection between

ground water and surface water. Discharge measurements or estimates of streamflow were made at

79 sites (fig . 2) during base-flow conditions from

April 24 through 26, 1989. During the discharge

measurements, flow at the gage on the South Fork

(fig . 1 ; fig . 2, site SF-3) was equivalent to about the

60-percent flow duration (figs. 9 and 10). A number of the smaller tributaries were dry, and are typically dry except for short periods after significant

Figure 10. Flow duration of the Middle and South Forks Forked Deer River.

rainfall . Ground-water gains and losses were calculated for the segments of the Middle and South

Forks within the study area (table 4), and overall,

both streams were gaining ground water . The

seepage rate for the Middle Fork was 7.6 ft?/s per

mile of stream channel, and for the South Fork,

2.8 fels per mile of stream channel. Seepage rates

also were calculated for three segments of the South

Fork (fig . 2, SF-4 to SF-3, SF-3 to SF-2, SF-2 to

SF-1), and the rates were -2.4, 8 .9, and 2.7 ft'/s per

mile of stream channel, respectively ("-" indicates

loss of streamflow to the ground-water system).
Table 4. Discharges and ground-water gains and losses

along segments of the Middle and South Forks Forked

Deer River, April 24 through 26, 1989

11f, Middle Fork ; SF, South Fork ; tr, tnbutaryl

Flow-duration curves were plotted for the Middle

and South Forks (fig . 10) . The shape of a flowduration curve is determined by hydrologic and

geologic characteristics of the drainage basin. A

steep slope on the curve indicates a highly variable

stream whose flow is mainly from direct runoff. A

steep slope at the lower end of the curve indicates a

negligible amount of perennial storage in the basin;

a flat slope indicates a large amount of storage

(Searcy, 1959, p . 22). The storage may be shallow

ground water or in wetlands or ponds along the river

channel.

The flow-duration curves for the Middle Fork

near Alamo and the South Fork at Jackson (fig . 10)

are relatively flat and are especially flattened on the

lower end, which indicates a large amount of perennial storage capacity that allows slow drainage of

water to the streams . This configuration is typical

of low gradient streams having wide, marshy flood

plains .

Areal Recharge

Nearly all areal recharge to the aquifers is from

precipitation during November through April .

During the growing season, May through October,

nearly all precipitation is transpired and little, if any,

recharge percolates to the ground-water system

(Moore, 1965) . A recharge rate of 9.5 in/yr to the

Coastal Plain within the Tennessee River basin was

estimated from the 1968 water year hydrograph at

the Big Sandy River at Bruceton (Zurawski, 1978,

p. 9). The drainage basin of that river is adjacent to

Madison County, and recharge in that basin is

probably representative of the recharge characteris

tics of the aquifers in the Jackson area. The two

aquifers that crop out in the Big Sandy River basin

are the Cretaceous McNairy and Coffee Sands . The

McNairy Sand is the deep aquifer in Madison

County.

Recharge rates can be estimated from seepage

data, which would represent the period in which the

data were collected, and from continuous-record

streamflow data, which would represent average

annual recharge. Areal recharge rates were calculated from seepage measured during the base-flow

investigation in April 1989. Streamflow at the gage

on the South Fork was at about 60-percent flow

duration (fig . 10), which is slightly lower than

average flow. Recharge rates over the areas drained

by the stream segments were 8.1 in/yr for the

Middle Fork (38-mil drainage area) and 2 .6 in/yr for

the South Fork (116-mil drainage area) . The calculated rate for the South Fork is probably small

because of ground-water interception by pumping

wells. If these losses to pumping wells, about

17 Mgal/d, are added back into the seepage, calculated recharge would be at least 5.7 in/yr.

Graphical hydrograph-separation techniques

(Pettijohn and Henning, 1979, and Ronald A. Sloto,

U.S . Geological Survey, written commun., 1989)

were applied to data from the continuous-record

streamflow-gaging stations on the Middle Fork near

Alamo and the South Fork at Jackson to determine

Hydrologic system 1 5
average aquifer discharge, which can be equated to

average annual recharge to the ground-water system .

Although the station at Jackson is in the study area,

the station near Alamo records data from an area

more geologically similar to that of the study area .

The average rates of recharge calculated for the gage

at Jackson for the years 1966 through 1970, which

represent years of average rainfall (fig . 11), range

from 6.7 to 8.0 in/yr. The rate calculated for the

station near Alamo for the same years ranges from

5.6 to 6.7 in/yr . The ranges of averages resulted

from three different graphical techniques for both

water years and calendar years. The range of areal

recharge rates from all the estimating methods is 5.6

to 9 .5 in/yr.

Water-Level Fluctuations

Seasonal ground-water fluctuations are related to

recharge, natural discharge to streams, evapotranspiration, and the effects of pumping. Natural

seasonal fluctuations are related to seasonal changes

in precipitation, evapotranspiration, and thus, to

changes in recharge. Fluctuations of about the same

magnitude from year to year are indicative of a

ground-water system at long-term steady state, in

which recharge and discharge are about equal on an

annual basis.

Long-term, water-level records are available for

two observation wells in Madison County (fig . 1) .

Figure 11 . Water levels in observation wells and precipitation at the Jackson Agricultural Experiment Station (location

of Md :N wells shown on figure 1) .
Well Md:N-1 is in the McNairy Sand, and 

Md:G-45, near the South Well Field, is in the Fort 

Pillow Sand. The hydrograph of well Md:N-1 

shows natural seasonal fluctuations (fig. ll), which 

indicates that the deep aquifer is at steady state and 

is unaffected by pumping. A downward trend in 

water levels, the effects of pumping, are superimposed on seasonal fluctuations in well Md:G-45. 

The slight l.eveling of the downward trend of the 

hydrograph of Md:G-45 in the late 1960’s and early 

1970’s (fig. 11) may indicate that the aquifer was 

approaching equilibrium with the pumpage. 

No continuous water-level records are available 

for either well field; however, JUD has measured 

each pumped well annually since 1981. Water 

levels from a representative pumped well in the 

South Well Field (fig. 11, well 10) show that water 

levels fluctuated from year to year after 1983, but 

show no significant sustained decline. Water levels 

from a representative pumped well in the North Well 

Field (fig. 11, well 5) show that water levels declined sharply from the onset of pumping through 

1984, but the rate of decline after that year was less. 

Measurements from all the pumped wells in the 

North Well Field showed high water levels in 1986 

(fig. 1 l), which may have been related to conditions 

at the time the wells were measured that were not 

representative of average conditions for 1986. 

Water levels in the South Well Field may still be 

recovering and readjusting to an equilibrium as a 

result of decreased pumpage; however, the trend is 

slight. Pumpage from the South Well Field has 

remained relatively constant since 1982. Similarly, 

water levels in the North Well Field are probably 

still declining and equilibrating to pumpage; however, that trend also is believed to be slight. Therefore, the system is considered to be near steady state 

in the area of the well fields and at steady state in 

most of the study area. 

Ground-Water Flow 

The Memphis and Fort Pillow Sands function as 

a single aquifer, although clay lenses locally act as 

confining units. The McNairy Sand is hydraulically 

separated from this aquifer by the Porters Creek 

Clay. 

Ground-water flow is generally from the eastnortheast toward the major streams. Flow is diverted locally toward major pumping centers. The 

water table is generally below the tributaries in the 

central part of the area, and the tributaries have little 

effect on the ground-water system except to contribute recharge after rainfall events. 

The natural ground-water divide would be 

expected to bisect the area between the Middle and 

South Forks, coinciding with the surface-water 

divide. However, pumping in the North Well Field 

and at a major industrial center along the divide, has 

caused the ground-water divide to move northward 

toward the Middle Fork (fig. 12). 

GROUND-WATER FLOW MODEL 

Model Assumptions 

The finite-difference model of McDonald and 

Harbaugh (1988) was used to simulate threedimensional ground-water flow in the sand aquifers. 

The following simplifications and assumptions were 

made to simulate the hydrologic system: 

1. The Memphis Sand is unconfined; the Fort 

Pillow Sand is confined over most of the area, 

but is unconfined where it crops out. 

2. The bottom of the model is specified as the top of 

the Porters Creek Clay, which is assumed to be 

a no-flow boundary. 

3. On a regional scale, each aquifer is homogeneous . 

4. Flow in the aquifers is horizontal; flow (leakage) 

between the aquifers, whether divided by clay or 

not, is vertical. 

5. The regional ground-water system is at steady 

state; however, this assumption may not be valid 

in the area of the well fields. 

Ground-water flow model 17 
Figure 12. Configuration of the water table in April 1989 and general directions of ground-water flow.
Conceptual Model

The aquifers were divided into three layers to

simulate the ground-water flow system (fig . 13).

Layer 1 is the saturated Memphis Sand; layer 2 is

the upper half of the Fort Pillow Sand; and layer 3

is the lower half of the Fort Pillow Sand. The

layers, particularly layers 2 and 3, are not necessarily hydraulically distinct aquifers, but were divided to

allow greater accuracy in particle-tracking analysis .

Layer 1, a water-table aquifer, does not extend to

the southeastern part of the model, where the Memphis Sand pinches out. Layer 2 is simulated as

confined beneath the Memphis Sand and as a watertable aquifer in the southeastern part of the modeled

area where the upper part of the Fort Pillow Sand

crops out. Layer 3 also is simulated as confined

over most of the modeled area and unconfined in the

outcrop area. Alluvium covering the outcrop area of

the Porters Creek Clay is included in layer 3 .

Model Grid and Boundaries

The model grid is an 11 .8- by 11 .5-mile rectangle and includes the entire study area; however, only

92 .9 mil are active in the model. The model is

discretized into a matrix of 88 by 96 grid blocks

(fig . 14). The grid blocks are variably dimensioned

to accommodate more detail in the well fields and to

separate pumped wells into individual grid blocks

Figure 13. Representation of aquifer layers in the digital model (along rows 40 and 71, figure 14).

Ground-water flow model 19
Figure 14. Finite-difference grid for the digital flow model.
The dimensions of the smallest grid blocks, located 

in the South Well Field, are 300 by 250 feet and the 

largest grid blocks, at the boundaries, are 1,200 by 

1,800 feet. 

The upper boundary of the model is the water 

table, and the lower boundary is the top of the 

Porters Creek Clay, which subcrops beneath the 

alluvium in the river valley of the North and South 

Forks (figs.. 6 and 13). The northern boundary of 

the active model area follows the course of the 

Middle Fork, which is simulated as a headdependent flux (river node) boundary in layer 1 

(fig. 14). No ground water is assumed to flow 

beneath the river across this boundary, and the 

effects of simulated pumping, because of the 

distance to the pumping centers, should not extend 

beyond the Middle Fork. The northern boundary in 

layers 2 and 3 is a no-flow boundary. 

The west-northwestern boundary (a surface-water 

divide) is assumed to correspond closely to a 

ground-water divide and is simulated as a no-flow 

boundary except where the South Fork flows out of 

the modeled area. Underflow in this area is simulated with a constant-head node (fig. 14) in each of 

the three layers. 

The south-southwestern boundary was extended 

about a mile south of the South Fork to accommodate the potential effects of simulated pumping from 

the South Well Field and industrial pumping in the 

area. This boundary is a general-head boundary 

(fig. 14) in all three layers. The general-head 

boundary allows ground-water inflow or outflow to 

fluctuate based on the difference between a specified 

head outside the model and a model-calculated head 

at the model boundary (McDonald and Harbaugh, 

1988, p. 11-l). 

Conductances (c), in feet squared per day, 

between the specified heads and each general-head 

boundary node in the model were calculated by: 

67, 

where K is average hydraulic conductivity of the 

aquifer between the specified head and 

the model boundary, in feet per day; 

A is the area of the vertical face of the boundary 

node (width X depth), in square feet; and 

L is the distance from the specified head to the 

model boundary, in feet. 

The distance between the boundary head and 

model boundary (L) was 3,000 feet. Hydraulic 

conductivity (K) was 200 ft/d for layer 1 and 

170 ft/d for layers 2 and 3, which are the highest 

values estimated by other investigators (table 3). 

The head specified for the southern part of the 

south-southwestern boundary was 360 feet above sea 

level, which was derived from a projection outside 

the modeled area of the 360-foot water-level 

contour. Where the 360-foot contour is inside the 

model boundary, the specified head was 370 feet 

(fig. 12). This boundary condition was specified for 

all three layers. 

The eastern boundary, a surface-water divide, is 

simulated as a no-flow boundary along the northern 

two-thirds, except for a small area of constant head 

to allow inflow to the modeled area (fig. 14). 

Although a surface-water divide can be assumed to 

be a ground-water divide, flow is probably induced 

(fig. 12) into the study area by pumping. The 

southern third of the eastern boundary, which cuts 

across the flood plain of the North and South Forks, 

is specified as a constant-head boundary, which 

allows simulations of underflow in this area. 

Simulation of Sources and Sinks of Water 

Average pumping rates for 18 municipal wells 

and 14 commercial or industrial wells were included 

in the model (fig. 2). Pumping rates for the JUD 

wells were calculated based on pumping rates during 

a week in April 1989: 9.2 Mgal/d for the North 

Well Field and 2.2 Mgal/d for the South Well Field. 

Not all wells are pumped every day, so the average 

pumping rate for some of the wells is lower than the 

actual withdrawal rate. However, for steady-state 

conditions, the lower rate (compared to wells 

pumped every day) is more representative of the 

average stress on the system than the actual pumping 

Ground-water flow model 21 
rate when a well is pumped intermittently. Pumping 

was applied to the layer in which most of the well 

screen is open. 

The recharge rates calculated from seepage data 

and hydrograph-separation techniques represent areal 

averages, but local recharge is dependent on geology, topography, and land use. Local recharge rates 

were determined by assigning relative rankings to 

soil type (which is a product of geology and topography) and land use. Soils have been classified into 

hydrologic soil groupings that represent similar 

runoff potential from rainfall (U.S. Department of 

Agriculture, 1978, p. 35-40). Three groups are 

represented in the study area: soils having a moderate infiltration rate, a slow rate, and a very slow 

rate. Land use also was divided into three groups of 

similar runoff potential: urban and disturbed land 

having the highest runoff potential (and lowest 

recharge potential), forest and wetlands having 

intermediate runoff potential, and agriculture having 

the lowest runoff potential and highest recharge 

potential. The relative rankings of soil and land use 

were combined to create five categories of relative 

recharge rates (fig. 15). The volume of water 

resulting from average areal recharge of 8 in/yr was 

applied to the model area and the percent of 

recharge to each grid block was calculated based on 

the relative recharge for that block. The resulting 

recharge rates assigned to the grid blocks ranges 

from 3.4 to 10.3 in/yr. Recharge was applied to the 

uppermost active layer for any particular node. 

Recharge was not applied to nodes simulating rivers, 

lakes, or constant heads. 

The rivers, tributaries, and lakes were simulated 

as river nodes connected to the water table (fig. 14). 

Conductance (c), in feet squared per day, used to 

simulate leakage to and from river nodes, was 

calculated by: 

where K is vertical hydraulic conductivity of the 

streambed, in feet per day; 

A is the area of the river within the node, in 

square feet; and 

b is the streambed thickness, in feet. 

Thickness of the streambeds was assumed to be 

1 foot to simplify calculations; a vertical hydraulic 

conductivity of 1 ft/d was used initially for all 

streams. These initial values could be changed 

during calibration if simulated seepage to the streams 

did not approximate measured seepage. The streambed bottom within each river node is the elevation of 

the stream on a topographic map, and stream stage 

was calculated for each node using depth of water 

measured in April 1989. 

Dry stream reaches were simulated as drains 

(fig. 14) that can gain water from the ground-water 

system, but cannot contribute recharge to the ground 

water. Elevation of the drains is the elevation of the 

stream channel obtained from topographic maps. 

Conductance of the drain bottoms was calculated in 

the same manner as conductance for river nodes. 

Conductance for lakebeds was calculated in the 

same manner as conductance for river nodes. Lakesurface elevations and depths were estimated from 

topographic maps. 

Transmissivity for each layer was calculated 

from a uniform value of hydraulic conductivity and 

the variable thickness of the layer. The initial 

hydraulic conductivity of layer 1 was 200 e/d, and 

of layers 2 and 3, 170 ft/d, which are the highest 

values estimated by other investigators (table 3). 

Initial transmissivity of layer 1 ranged from 2,000 to 

54,000 fY/d; and for layers 2 and 3, from 1,700 to 

19,550 ft’ld. 

Leakage between model layers was simulated by 

vertical conductance. Because the layers were 

assumed to be hydraulically well connected and not 

separated by confining material, vertical conductance 

between layers was calculated using the aquifer 

properties. Vertical conductance is calculated within 

the model using values of vertical leakance 

(McDonald and Harbaugh, 1988, p. 5-11). Vertical 

Ieakance, in feet per day per foot, between adjacent 

layers was calculated by: 

Vertical leakmce = 

2Ga% 

KL,brc+Kkbh’ 

22 Hydrology of the Jackson, Tennessee, area and delineation 

of areas contributing ground water to the Jackson Well Fields 
Figure 15. Categories of relative recharge rates .

Ground-water flow model 23
where K is vertical hydraulic conductivity, in feet 

per day; 

b is thickness, in feet; 

La is the uppermost layer; and 

Lc is the lowermost layer. 

In order to calculate the largest reasonable 

vertical conductance between model layers for initial 

runs, the highest estimated hydraulic-conductivity 

values for the Memphis and Fort Pillow Sands (200 

and 170 ft/d, respectively) were used to calculate 

leakance values at each grid block. Initial verticalleakance values between layers 1 and 2 ranged from 

0.9 to 58.1 (ft/d)/fi, and between layers 2 and 3, 1.6 

to 6.8 (ft/d)/ft. Vertical conductance between layers 

varied areally because thickness of each layer varied 

(producing the ranges of vertical leakance) and 

because areas of grid blocks varied. 

Model Calibration 

The ground-water flow model was calibrated to 

water levels in 46 of the 53 wells measured in April 

1989, and to ground-water seepage to streams 

measured at the same time. The overall system is 

assumed to be at steady state because long-term 

water levels seem to be approaching equilibrium, 

although the assumption of steady-state conditions in 

the area of the well fields may not be valid. 

Hydraulic conductivity for all layers, vertical leakante between layers, recharge, and conductivity of 

the streambeds were varied during the calibration 

process to maximize matches between simulated- and 

measured-head values and simulated and measured 

seepage to streams. 

Initial values of aquifer hydraulic conductivity 

were reduced by 0.5 to 100 ft/d for the Memphis 

Sand and 85 ft/d for the Fort Pillow Sand. These 

reductions are reasonable because the initial values 

were the maximum estimated values. Initial verticalconductance values were reduced by an order of 

magnitude. This reduction also is reasonable 

because the highest calculated values of aquifer 

hydraulic conductivity were used as initial values, 

and because vertical hydraulic conductivity of 

aquifers of this type is commonly one-tenth the 

horizontal conductivity (Freeze and Cherry, 1979, 

p. 32). Aquifer hydraulic conductivity, used to 

calculate initial conductance values for the generalhead boundaries, also was reduced by one-half. 

The initial value of hydraulic conductivity for all 

streambeds and lakes was 1 ft/d but the following 

changes were made during calibration: Conductivity 

of lakes was reduced to 0.0001 ft/d, which is a 

reasonable reduction because of siltation of lake 

bottoms. Conductivity of the Middle Fork was 

reduced to 0.5 ft/d, and of the South and North 

Forks, to 0.05 ft/d. Conductivity of all tributaries 

was increased to 5 ft/d, because fine sediment 

accumulation is less likely in the tributaries. 

Measured heads and ground-water seepage to 

streams were relatively well matched. Sixty-three 

percent of the 46 comparison-head values were 

matched within +5 feet, and 87 percent within 

f 10 feet. The model-calculated potentiometric 

surface is shown only for layer 3 (fig. 16) because 

layer 3 shows the full extent of the modeled area. 

Measured-head values are shown for the 46 comparison wells. Although these wells are distributed 

among all three layers, simulated vertical gradients 

between the layers are small, and water-level configurations are similar for layers 1 and 2. 

Model simulated seepage to the Middle Fork was 

10.9 ft% compared to half of the measured seepage 

of 11.3 ff/s. The model simulated only half the 

measured seepage (table 4) because the river is a 

model boundary and simulated seepage is contributed from only one side. Simulated seepage to the 

measured reach of the South Fork was 22.0 ff/s 

compared to measured seepage of 21.9 ft% 

(table 4). 

Components of the steady-state water budget of 

the simulated system are summarized in table 5. 

More than half of the source of water to the groundwater system in the calibrated model is inflow 

through the boundaries. Most of this inflow is lost 

through seepage to the river and nearby pumping. 

Slightly less than half of the source of water is from 

areal recharge and recharge from streams. About 

75 percent of the discharge from the system is into 

the streams, lakes, and out of the model area 

through a small quantity of ground-water underflow. 

The remaining 25 percent is discharge from pumping 

wells. 

Net vertical leakage between model layers is 

nostly flow from layers 1 and 3 into layer 2, 

because most of the pumpage is from layer 2 

(fig. 17). A total of 62 ft3/s leaks into layer 2 and 

24 Hydrology of the Jackson, Tennessee, srea and delineation 

of areas contributing ground water to the Jackson Well Fields 
Figure 16. Model-calculated water levels in layer 3 and measured water levels .

Ground-water flow model 25
Table 5. Steady-state ground-water budget for the calibrated model and pumping plans for the Jackson area

[CH, constant head ; CF, constant fluxr

45.1 ft'/s leaks from layer 2 to the other two layers,

leaving a net gain to layer 2 of 16.9 fe/s . The net

flow of water through vertical leakage from layers 1

and 3 is 10.5 and 6.4 ft'/s, respectively .

Model Limitations and Sensitivity Analysis

The accuracy of the calibrated model in simulating the ground-water flow system is limited by

several factors:

1 . Ground-water levels for calibration were accurately measured, but elevation above sea level of

those water levels was estimated from topo

graphic maps . The error could be in the range

of ± 10 feet .

26 Hydrology of the Jackson, Tennessee, area and delineation

of areas contributing ground water to the Jackson Well Fields

2. Water levels were measured primarily in

pumped wells.

3 . No piezometers were available to measure

vertical gradients.

4. Few wells at hydrologic boundaries were available for measurement.

5. The assumption of steady-state conditions is

probably valid regionally, but not necessarily in

the areas of the well fields .

6. Several combinations of aquifer characteristics

in the simulations produced similar matches to

measured heads and seepage to streams. The

combination accepted for the calibrated model is

nonunique and the existing data do not provide

adequate criteria for selecting the best solution .
Figure 17. Distribution of water-budget components among the layers of the digital flow model.

Ground-water flow model 27
The lack of adequate data to determine a more 

unique set of aquifer characteristics increases the 

possibility of inaccurate delineation of areas contributing water to the pumped wells and misleading 

results from simulation of hypothetical pumping. 

However, model sensitivity analyses can indicate the 

characteristics that are the most critical to an accurate simulation and assist in evaluating the reliability 

of model results. 

The response of the model to adjustments in 

recharge, hydraulic conductivity of the layers, 

vertical conductance between layers, and hydraulic 

conductivity of the streambeds was evaluated using 

sensitivity analyses. Hydraulic conductivity of all 

layers was adjusted by the same multiple for each 

sensitivity test (rather than each layer being adjusted 

individually while the other two layers were held 

constant). Both leakage layers and hydraulic conductivity of all the streambeds were varied by the 

same multiple for each test. For each adjustment, a 

sensitivity test was made for both constant-head and 

constant-flux boundary conditions. The flux values 

were determined by model-calculated fluxes at the 

constant-head nodes. 

Differences between measured and simulated 

water levels were used as indicators of the sensitivity 

of the model to adjustments of a variable. The root 

mean square error (RMSE) is a measure of the 

overall difference between measured and simulated 

water levels. Lower RMSE values indicate better 

matches to measured water levels. RMSE, in feet, 

was calculated for measured and simulated water 

levels using the equation: 

1 N 

c (h”-hf)* 

RMSE = 

i=l 

N ’ 

where N is the number of observations (46); 

him is the measured water level, in feet; and 

hp is the calculated water level, in feet. 

RMSE was plotted for each adjustment in a variable 

to display the range of sensitivity. 

The overall RMSE for all layers in the calibrated 

steady-state model is 11.6 feet because not all 

measured water levels were exactly matched. The 

RMSE of individual layers is: 15.6 feet for layer 1, 

6.1 feet for layer 2, and 5.3 feet for layer 3. 

Average head difference between simulated and 

measured heads for the model was -0.2 foot and the 

standard deviation is 11.6 feet. Calibrated heads 

were slightly lower overall than measured heads. In 

the following discussions, references to RMSE are 

to the value for all layers. 

Areal recharge was adjusted from 0.5 to 2 times 

(4 to 16 in/yr) the calibrated value. Adjustments 

between about 7 and 10 in/yr produced minor 

changes in RMSE (fig. 18) or in seepage. The 

RMSE was slightly lower using 9 in/yr. A range of 

recharge from 8 to 10 in/yr produced net seepage to 

the Middle and South Forks that was within f5 percent of measured seepage. This range was within 

the measurement error of the disharge measurements . 

The model was sensitive to adjustments in 

hydraulic conductivity of the layers (fig. 19), 

particularly for constant-flux boundary conditions. 

The range of conductivity tested was from 50 to 

500 ft/d for the Memphis Sand and from 43 to 

425 ft/d for the Fort Pillow Sand. Head matches 

were improved slightly by using 0.8 times (80 and 

68 ft/d) the calibrated values, but the calibrated 

values were the only ones that produced seepage to 

the Middle and South Forks within +5 percent of 

measured seepage. 

When results of the sensitivity tests for recharge 

and hydraulic conductivity were compared (fig. 20), 

a narrow range of optimal values for the two parameters (within the 11-foot RMSE contour) was 

observed. Although measured heads could be 

matched better overall by using higher recharge and 

lower hydraulic conductivity values, seepage to 

streams did not match as well in that range (fig. 20). 

This comparison also showed that, although the 

model was not a unique combination of values for 

aquifer characteristics, the range of values that 

would produce a unique model is small. 

The model was insensitive to the tested range of 

vertical conductance between model layers (fig. 21). 

Changes in the vertical conductance from 0.1 to 10 

times the calibrated value resulted in only small 

changes in the RMSE. The model failed to reach a 

solution when values beyond the range of those 

28 Hydrology of the Jackson, Tennessee, area and delineation 

of ereee contributing ground water to the Jackson Well Fields 
Figure 18. Sensitivity of the digital flow model to adjustments in recharge .

shown in figure 21 were tested . Seepage to streams

was little affected by adjustments in vertical

conductance.

Hydraulic conductivity of the streambeds was

adjusted between 0.1 and 50 times the calibrated

values (fig . 22) . The model was insensitive to

adjustments between 0.5 and 10 times the calibrated

values . Conductivity values from about 2 to 5 times

the calibrated values produced slightly lower RMSE,

but the calibrated values were the only ones that

produced seepage to the Middle and South Forks

within ±5 percent of measured seepage.

Sensitivity analyses confirm that a range of

values for all of the hydraulic characteristics of the

aquifers would produce similar model results and

that the calibrated model was a nonunique combination of aquifer characteristics . However, the

acceptable ranges of areal recharge and hydraulic

conductivity of the aquifers, the two hydraulic

characteristics that the model is most sensitive to,

Pumping Simulations

were relatively small. The calibrated model was

considered the best combination ofhydraulic characteristics to produce reasonable results from pumping

simulations and from particle-tracking analyses . No

significant improvements were indicated by the

sensitivity analyses .

The calibrated model was modified to simulate

the effects on the ground-water system of three

hypothetical pumping plans suggested by JUD.

Only steady-state conditions were simulated because

the main consideration was the determination of a

final water-level distribution under simulated stress,

not the time to reach that point. Following are

descriptions of the three plans :

1 . Average pumping rates of 10 Mgal/d for the

South Well Field and 10 Mgal/d for the North

Well Field.

Ground-water flow model 29
Figure 19. Sensitivity of the digital flow model to

adjustments in hydraulic conductivity of aquifers.

30 Hydrology of the Jackson, Tennessee, area and delineation

of areas contributing ground water to the Jackson Well Fields

2. Average pumping rates of 5 Mgal/d for the

South Well Field and 15 Mgal/d for the North

Well Field.

3 . Average pumping rates of 10 Mgal/d for the

South Well Field and 20 Mgal/d for the North

Well Field.

Each pumping plan was simulated with (1)

constant-head boundary conditions, which maximize

ground-water flow into the system and minimize

drawdown, and (2) constant-flux boundary conditions, which limit ground-water flow into the system

to the rate calculated by the calibrated model and

maximize drawdown. These two extremes of

boundary conditions represent endpoints for simulated model results, and reasonable results of the

pumping schemes were within these endpoints. The

constant-flux conditions produced the most conservative simulation results, and were, therefore, the

conditions shown on the figures and discussed in this

section.

Pumping in the calibrated model was increased

for pumping plan 1 in some of the seven wells in the

North Well Field to a total of 10 Mgal/d, and

pumpage from each of the eleven wells in the South

Well Field was increased by about 4.5 times the

calibrated rate to a total of 10 Mgal/d.

Three hypothetical wells pumping from layer 2

were added to the seven existing wells of the North

Well Field for pumping plan 2. Pumpage in the

original seven wells was altered slightly to total

9.9 Mgal/d and each of the additional wells was

pumped 1 .7 Mgal/d. Total pumpage from the North

Well Field was 15 Mgal/d. Pumpage from each

well in the South Well Field was increased by about

2 .2 times the calibrated pumping rate to a total of

5 Mgal/d.

Four more hypothetical wells pumping from

layer 2 were added to the North Well Field for

pumping plan 3. Total withdrawal for the original

seven wells was adjusted to 9 .2 Mgal/d, and each of

the seven additional wells was pumped 1.54 Mgal/d.

Total pumpage from the North Well Field was

20 Mgal/d. Pumpage from the South Well Field

(10 Mgal/d) was the same as for pumping plan 1.

The water-level configuration in the calibrated

model was the datum used for calculating drawdown. Configurations of drawdown for the three
recharge and aquifer hydraulic conductivity using constant-flux boundary conditions .

Figure 20. Changes in root mean square error of simulated water levels with respect to simultaneous changes in

Ground-water flow model 31
Figure 22. Sensitivity of the digital flow model to adjustments in hydraulic conductivity of streambeds .
pumping plans are shown (figs. 23-25) only for

simulations with constant-flux boundary conditions,

because these boundary conditions show the worst

case and the configuration for constant-head boundaries was nearly the same as for constant-flux

boundaries . Only layer 3 is shown on the figures

because layers 1 and 2 do not cover the entire

modeled area and because the configuration of

drawdown was similar for all the layers . Drawdown

in the nodes containing pumping wells is slightly

greater for constant-flux boundary conditions than

for constant head (table 6). Drawdown from pumping in the South Well Field dewaters the Memphis

Sand (layer 1) in that area in all the pumping simulations. The Memphis Sand is thin in that area and

the well field is at the edge of the outcrop of the

Fort Pillow Sand .

Table 6. Maximum simulated drawdown in the North

and South Well Fields for constant-head and constantflux boundary conditions

[CH, constant head ; CF, constant flux]

Drawdown resulting from simulated pumping in

plan 1 (fig . 23) was concentrated around the South

Well Field, because pumping there was increased by

about 4 .5 times the rate in the calibrated model .

Maximum drawdown was 40 .7 feet in a node containing a pumping well, but maximum drawdown

over an extended area was about 32 feet. Pumping

in the North Well Field was increased only slightly,

and resulting simulated drawdown was small (up to

6 feet) .

Drawdown in the South Well Field resulting

from simulated pumping in plan 2 (fig. 24) was less,

because pumping increases were more moderate.

Pumping in the South Well Field was increased by

2.2 times the rate in the calibrated model, and

pumpage in the North Well Field was increased by

1 .6 times . Maximum drawdown is 27 .3 feet in a

node in the North Well Field containing a pumping

well, and maximum drawdown over an extended

area is about 22 feet. Maximum drawdown in the

South Well Field is 14.1 feet.

Drawdown resulting from simulated pumping in

plan 3 (fig . 25) was the greatest, both locally and in

areal extent. Pumping in the South Well Field was

increased by 4.5 times the rate in the calibrated

model, and pumping in the North Well Field was

increased by 2.2 times. Maximum drawdown in a

node containing a pumping well in the North Well

Field was 39.4 feet. Maximum drawdown was

44 .7 feet in the South Well Field in a node containing a pumping well, and maximum drawdown over

an extended area was about 38 feet.

Simulated drawdown in the pumping simulations, particularly plans 2 and 3 for the North Well

Field, may be somewhat greater than actual draw

down would be because the extent of the cones of

depression reaches the no-flow boundaries . In

reality, some water would be induced across those

boundaries . Simulated drawdown near the South

Well Field for plans 1 and 3 may be somewhat

underestimated because the model continues to

simulate a source of water from the South Fork and

the general-head boundary on the opposite side of

the river.

The primary sources of water for additional

pumping for the pumping plans were ground water

intercepted before reaching the streams and addi

tional water induced through the boundaries

(table 5) . Up to 34 percent of ground-water seepage

to streams in the calibrated model was intercepted in

the pumping simulations . In the constant-head

simulations, up to 8 percent more water was induced

through the general-head boundary and up to 5 percent more through the constant-head boundaries. In

the constant-flux simulations, up to 9 percent more

water was induced through the general-head boundaries, but no more could be induced through the

constant-flux boundary.

Ground-water flow model 33
Figure 23. Simulated drawdown in layer 3 for pumping plan 1 with constant-flux boundaries .
Figure 24. Simulated drawdown in layer 3 for pumping plan 2 with constant-flux boundaries .

Ground-water flow model 35
36 Hydrology of the Jackson, Tennessee, area and delineation

of areas contributing ground water to the Jackson Well Fields

Figure 25. Simulated drawdown in layer 3 for pumping plan 3 with constant-flux boundaries.
AREAS CONTRIBUTING WATER TO THE WELL 

FIELDS 

A particle-tracking program (Pollock, 1989) was 

used to delineate areas contributing water to the 

North and South Well Fields for prescribed pumping 

conditions, and to estimate distances for different 

times-of-travel to the wells. The particle-tracking 

program (MODPATH) uses the results from steadystate model simulations to delineate pathlines of 

ground-water flow and the position of particles at 

specified times. Particle tracking is based on advective transport only and cannot be used to compute 

solute concentrations in ground water. 

Particle-tracking analyses were done for the calibrated model (April 1989 hydrologic conditions) and 

the three pumping plans using constant-flux boundary conditions. Particles were tracked backward 

from the well fields to delineate the configuration of 

areas contributing water to wells. Tracking was 

accomplished by placing a total of six particles on 

the cell faces of nodes containing each pumping 

well; that is, one particle was placed on each cell 

face. Travel times are based on velocities calculated 

in the model, assuming 30-percent porosity for the 

aquifers (Freeze and Cherry, 1979, p. 37). Use of 

a different porosity value would affect travel time, 

but would not affect the configuration of pathlines. 

Results of the particle-tracking analyses are displayed for the calibrated model and the three pumping plans in two ways: (1) A general configuration 

of areas contributing water to the municipal well 

fields and other major pumping centers for the entire 

area and the definition of a 5-year time-of-travel 

capture zone (figs. 26-29), and (2) a detailed display 

of pathlines from individual wells in the North and 

South Well Fields showing increments of 1 year of 

travel time along each pathline for a total of 5 years 

(figs. 31-34). Flow lines along representative 

hydrologic sections through the well fields also were 

plotted for pumping plan 2 for increments of 1 year 

of travel time for 5 years (fig. 30). 

Although details within the well fields are 

obscured by the density of pathlines on the figures 

showing the entire modeled area, the general configuration of contributing areas is evident. If fewer 

pathlines were shown, which would more clearly 

show the pumping center, or if the contributing 

areas were more generalized, then the configuration 

of the overall contributing areas would be less 

accurately displayed. Therefore, information shown 

on figures 26 through 29 is meant to display a 

generalized pattern, and the details of pathlines and 

travel times are shown on subsequent figures of each 

well field. 

Configuration of Ground-Water Flow to the 

Well Fields 

The area contributing water to the municipal 

well fields and to other major pumping centers 

(commercial and industrial) for the entire modeled 

area for the calibrated model (fig. 26) were generally separate and distinct. Flow pathlines, calculated 

by MODPATH, that emanate from the pumping 

wells define the contributing areas for each pumping 

center. Water was drawn to the wells primarily 

from upgradient source areas. As pumping in the 

North and South Well Fields was changed for each 

of the pumping plans (figs. 27-29), changes in the 

contributing areas occurred due to interactions 

between the pumping centers. A point along each 

flow line was calculated to delineate the distance 

from which water particles would take 5 years to 

reach the well fields. These points (figs. 26-29), if 

connected, would define a 5-year time-of-travel 

capture zone around each pumping center. Particles 

upgradient from the 5-year demarcation would take 

longer than 5 years to travel to the wells, and 

particles closer to the pumping centers would take a 

shorter time. 

The configuration of the flow pathlines and 

resulting contributing areas for the calibrated model 

and pumping plan 1 probably are not affected by 

simulation of the western boundary as a no-flow 

boundary. However, the configuration for pumping 

plans 2 and 3 may be affected by the boundary 

condition. The boundary, as simulated, eliminated 

the capture of any ground water from the west and 

forced water into the contributing areas that may not 

be realistic. The configuration of the 5-year time-oftravel capture zone may not be as significantly 

affected as the western part of the contributing area 

(figs. 28-29). 

Time-of-travel locations and pathlines that were 

used to delineate the contributing areas and capture 

Areas contributing water to the well fields 37 
38 Hydrology of the Jackson, Tennessee, area and delineation

of areas contributing ground water to the Jackson Well Fields

Figure 26 . Simulated particle-flow pathlines and 5-year time-of-travel capture zones for the calibrated model.
Figure 27 . Simulated particle-flow pathlines and 5-year time-of-travel capture zones for pumping plan 1 .

Areas contributing water to the well fields 39
40 Hydrology of the Jackson, Tennessee, area and delineation

of areas contributing ground water to the Jackson Well Fields

Figure 28. Simulated particle-flow pathlines and 5-year time-of-travel capture zones for pumping plan 2.
Figure 29 . Simulated particle-flow pathlines and 5-year time-of-travel capture zones for pumping plan 3 .

Areas contributing water to the well fields 41
Figure 30. Hydrologic sections through the North and South Well Fields showing increments of 1 year of travel time for 5 years along pathlines to

a single pumped well for pumping plan 2. (Lines of section shown on figure 28.)
zones were projected to the surface of layer 1 to 

construct a map view. Therefore, the locations of 

the capture zone on the surface does not necessarily 

indicate that a particle reaching the well originated 

at that surface location. This concept is illustrated 

by showing the pathlines as they appear in a hydrologic section (fig. 30). The time-of-travel indicators 

(fig. 30) show the distance along the pathlines from 

which particles would, in increments of 1 year, 

reach the well. Particles introduced to a flowpath 

from a source at a great distance from the well 

might take many years to reach the well, but, if not 

attenuated, could eventually affect the well. The 

sections illustrate that, although any potential sources 

of contaminants particles near the wells should be of 

immediate concern, sources far from the wells along 

flow pathlines should not be ignored. 

Pathlines that were used to delineate the contributing areas and capture zones for the calibrated 

model and pumping simulations for the whole 

modeled area (figs. 26-29) are shown on figures 31 

through 38 to demonstrate flow to individual wells 

in more detail for the North and South Well Fields. 

Increments of travel time were increased to l-year 

intervals to show the distances from which particles 

reach the wells. The following discussions focus on 

flow pathlines and times-of-travel to individual wells 

in each well field. 

North Well Field 

The configuration of flow pathlines and 

contributing areas for the North Well Field for the 

calibrated model and pumping plan 1 were nearly 

identical (figs. 31-32). Pumping in plan 1 was 

slightly greater than in the calibrated model, so 

water was drawn from slightly farther downgradient. 

The size of the 5-year time-of-travel capture zone is 

about 0.8 by 1.8 miles for the calibrated model and 

plan 1. The pathlines and contributing areas for 

pumping plans 2 and 3 are similar, but water was 

drawn from a farther distance to the east in plan 3 

because of the locations of the four additional 

pumping wells (figs. 33-34). The 5year time-oftravel capture zone for plan 2 was about 1.1 by 

2.0 miles and for plan 3, about 1.6 by 2.2 miles. 

The range of distance for l-year time-of-travel 

to individual wells was 200 to 800 feet for the 

calibrated model and plan 1, and 350 to 950 feet for 

plans 2 and 3. 

South Well Field 

The configuration of flow pathlines and 

contributing area were different between the calibrated model and the three pumping plans for the 

South Well Field (figs. 35-38). Actual pumping was 

much less in the calibrated model than in the hypothetical pumping simulations. Nearly all the water 

to wells in the calibrated model came from upgradient, and flow to each of the two clusters of wells 

in the well field was separate (fig. 35). The size of 

the 5-year time-of-travel capture zone, for the 

eastern cluster, was 0.5 by 0.7 mile, and for the 

western cluster, 0.7 by 0.8 mile. The size of the 

capture zone for the entire well field, was about 0.8 

by 1.4 miles. 

The configurations for plans 1 and 3 were 

nearly identical because hypothetical pumping was 

the same for the South Well Field (figs. 36, 38). 

The slight differences were caused by different 

pumping rates in the North Well Field. The size of 

the 5-year time-of-travel capture zone around the 

well field was about 1.6 by 2.2 miles. 

The size of the 5-year time-of-travel capture 

zone around the well field for pumping plan 2 was 

1.1 by 1.7 miles (fig. 37). Pumping from all three 

plans draws water from the opposite side of the 

South Fork and would result in streamflow 

reduction. Simulated seepage to the measured 

segments of the South Fork was reduced by 5.1, 

4.2, and 9.5 V/s, for plans 1, 2, and 3, respectively, compared to calibrated seepage (22 ff/s). 

The range of distance for l-year time-of-travel 

to individual wells was 120 to 530 feet for the 

calibrated model, 670 to 1,300 feet for plans 1 and 

3, and 260 to 850 feet for plan 2. 

SUMMARY AND CONCLUSIONS 

The Jackson Utility Division supplies water to 

customers in Madison County, Tennessee, from two 

well fields in Jackson. Prior to 1980 all of the 

water, as much as 8.5 Mgal/d, was pumped from 

the South Well Field. Since 1980, as much as 

85 percent of the municipal supply has been pumped 

Summary and conclusions 43 
Figure 31 . Increments of 1 year of travel time for 5 years along pathlines to individual wells in the North Well Field

for the calibrated model.

44 Hydrology of the Jackson, Tennessee, area and delineation

of areas contributing ground water to the Jackson Well Fields
Figure 32. Increments of 1 year of travel time for 5 years along pathlines to individual wells in the North Well Field

for pumping plan 1 .

Summary and conclusions 45
Figure 33. Increments of 1 year of travel time for 5 years along pathlines to individual wells in the North Well Field

for pumping plan 2 .

46 Hydrology of the Jackson, Tennessee, area and delineation

of areas contributing ground water to the Jackson Well Fields
Figure 34. Increments of 1 year of travel time for 5 years along pathlines to individual wells in the North Well Field

for pumping plan 3.

Summary and conclusions 47
Figure 35. Increments of 1 year of travel time for 5 years along pathlines to individual wells in the South Well Field for the calibrated model.
WO Figure

36. Increments of1 year of travel time for5 years along pathlines to individual wells in the South Well Field for pumping plan

1 .
85

Figure 37. Increments of 1 year of travel time for 5 years along pathlines to individual wells in the South Well Field for pumping plan 2 .
Figure 38. Increments of 1 year of travel time for 5 years along pathlines to individual wells in the South Well Field for pumping plan 3 .

J
from the North Well Field. Average pumpage from 

the North Well Field for a week in April 1989 was 

9.2 Mgal/d, and from the South Well Field, 

2.2 Mgal/d. 

The geologic units of interest that crop out in 

the Jackson area include the Memphis Sand and Fort 

Pillow Sand, the principal aquifers in the area, and 

the Porters Creek Clay, the underlying confining 

unit. The saturated thickness of the Memphis Sand 

ranges from 0 to 270 feet; the Fort Pillow Sand, 

from 0 to 180 feet. The Porters Creek Clay, which 

ranges from 130 to 320 feet thick, separates a 

deeper formation, the McNairy Sand, from the 

shallower units. All units thin from northwest to 

southeast and dip to the northwest at 20 to 50 ft/mi. 

The Memphis and Fort Pillow Sands function as 

a single aquifer, although clay lenses are probably 

locally confining. The McNairy Sand is hydraulically separated from the shallow aquifers by the 

Porters Creek Clay. The natural ground-water 

divide would be expected to bisect the area between 

the Middle and South Forks Forked Deer River, but 

pumping in the North Well Field and at a major 

industrial center along the divide has caused the 

ground-water divide to move northward toward the 

Middle Fork. Ground-water flow is generally from 

the east-northeast and toward the major streams. 

Flow is diverted locally toward major pumping 

centers. 

Previous investigations in the Jackson area 

produced estimates of hydraulic conductivity and 

transmissivity for the Memphis Sand and the Fort 

Pillow Sand. Estimates of hydraulic conductivity for 

the Memphis Sand ranged from 80 to 202 fi/d, 

transmissivity from 2,700 to 33,000 ft’/d, and 

storage coefficient from 0.0001 to 0.011. Estimates 

of hydraulic conductivity for the Fort Pillow Sand 

range from 68 to 167 ft/d, transmissivity from 6,700 

to 10,050 ft*/d. The only estimate of storage coefftcient is 0.0015. 

Areal recharge rates were calculated from 

seepage measured during the base-flow investigation 

in April 1989 and from graphical hydrographseparation techniques that were applied to data from 

two continuous-record streamflow-gaging stations. 

Calculated rates ranged from 5.6 to 8.1 in/yr. An 

estimate of areal recharge for an adjacent drainage 

basin was 9.5 inlyr. 

A finite-difference ground-water flow model was 

used to simulate the threedimensional, steady-state 

flow system in the sand aquifers. The model uses 

three layers to simulate the ground-water flow 

system. Layer 1 was the saturated Memphis Sand; 

layer 2 was the upper half of the Fort Pillow Sand; 

and layer 3 was the lower half of the Fort Pillow 

Sand. The model was calibrated to water levels in 

46 wells measured in April 1989 and to groundwater seepage to streams measured at the same time. 

Simulated heads and groundwater seepage to 

streams matched measured values relatively well, 

A nonunique combination of values for aquifer 

characteristics comprised the calibrated model; however, the ranges of the most sensitive characteristics 

were shown to be small. The calibrated model is 

considered the best combination of hydraulic characteristics for pumping simulations and for particletracking analyses because no significant improvements were indicated by the sensitivity analyses. 

The aquifer characteristics and boundary conditions 

in the calibrated model should produce reasonable 

results from hypothetical pumping simulations and 

from particle-tracking analyses. 

The steady-state water budget of the simulated 

system showed that more than half of the inflow to 

the ground-water system was underflow into the 

valley of the South Fork Forked Deer River. Most 

of this inflow was discharged as seepage to the river 

and nearby pumping. Slightly less than half of the 

inflow was from areal recharge and recharge from 

streams. About 75 percent of the discharge from the 

system is into the streams, lakes, and out of the 

model area through a small quantity of ground-water 

underflow. The remaining 25 percent was discharged to pumping wells. 

The calibrated model was modified to simulate 

the effects on the ground-water system of three 

hypothetical pumping plans. Pumpage in the calibrated model was increased for pumping plan 1 in 

the North Well Field to a total of 10 Mgal/d, and 

pumpage from the South Well Field was increased 

to a total of 10 Mgal/d. For pumping plan 2, 

pumpage in the North Well Field was 15 MgaUd, 

and pumpage in the South Well Field was 5 Mgal/d. 

For pumping plan 3, total pumpage from the North 

Well Field was 20 Mgal/d, and from the South Well 

Field, 10 Mgal/d. 

52 Hydrology of the Jackson, Tennessee, area and delineation 

of areas contributing ground water to the Jackson Well Fields 
Drawdown resulting from simulated pumping in 

plan 1 was concentrated around the South Well 

Field. Maximum drawdown was 40.7 feet in a node 

containing a pumping well, but maximum drawdown 

over an extended area was about 32 feet. Drawdown resulting from simulated pumping in plan 2 

was less, because pumping increases were more 

moderate. Maximum drawdown was 27.3 feet in a 

node containing a pumping well in the North Well 

Field, and maximum drawdown over an extended 

area was about 22 feet. Drawdown resulting from 

simulated pumping in plan 3 was the greatest, both 

locally and in area1 extent. Maximum drawdown 

was 44.7 feet in a node containing a pumping well 

in the South Well Field, and maximum drawdown 

over an extended area was about 38 feet. 

A particle-tracking post-processor program, 

MODPATH, was used to delineate areas contributing water (capture zone) to the North and South 

Well Fields for the calibrated model and the three 

pumping simulations, and to estimate times-of-travel 

from recharge areas to the wells. Flow paths to the 

well fields and to other pumping wells (commercial 

and industrial) for the entire area for the calibrated 

model were generally separate and distinct. Water 

to all the wells was drawn primarily from upgradient source areas. 

The size of the S-year time-of-travel capture 

zone for the North Well Field was about 0.8 by 

1.8 miles for the calibrated model and plan 1. The 

size of the capture zone for plan 2 was 1.1 by 

2.0 miles and for plan 3, 1.6 by 2.2 miles. The 

range of distance for l-year time-of-travel to individual wells was 200 to 800 feet for the calibrated 

model and plan 1, and 350 to 950 feet for plans 2 

and 3. 

The size of the 5-year time-of-travel capture 

zone for the South Well Field, was about 0.78 by 

1.4 miles for the calibrated model. The size of the 

capture zone for pumping plans 1 and 3 was 1.6 by 

2.2 miles, and for pumping plan 2, 1.1 by 

1.7 miles. The range of distance for l-year time-oftravel to individual wells was 120 to 530 feet for the 

calibrated model, 670 to 1,300 feet for plans 1 and 

3, and 260 to 850 feet for plan 2. 

Summary and conclusions 53 
SELECTED REFERENCES 

Broshears, R.E., Connell, J.F., and Short, N.C., 

1991, A pilot study for delineation of areas contributing water to wellfields at Jackson, Tennessee: U.S. Geological Survey Water-Resources 

Investigations Report 89-4201, 32 p. 

Freeze, R.A., and Cherry, J.A., 1979, Groundwater: Englewood Cliffs, N.J., Prentice-Hall, 

Inc., 604 p. 

Hosman, R.L., Long, A.T., and Lambert, T.W., 

1968, Tertiary aquifers in the Mississippi 

embayment: U.S. Geological Survey Professional Paper 448-D, 29 p. 

Hutson, S.S., 1988, Estimated use of water in 

Tennessee, 1985: U.S. Geological Survey OpenFile Report 88-348, 1 sheet. 

McDonald, M.G., and Harbaugh, A.W., 1988, A 

modular three-dimensional, finite-difference, 

ground-water flow model: Techniques of 

Water-Resources Investigations of the U.S. 

Geological Survey, Book 6, Chapter Al. 

Miller, R.A., 1974, The geologic history of Tennessee: Tennessee Division of Geology Bulletin, 

74, 63 p. 

Miller, R.A., Hardeman, W.D., and Fullerton, 

D.S., 1966, Geologic map of Tennessee, west 

sheet: Tennessee Division of Geology, scale 

1:250,000, 1 sheet. 

Moore, G.K., 1965, Geology and hydrology of the 

Claiborne Group in Western Tennessee: U.S. 

Geological Survey Water-Supply Paper 1809-F, 

44 p. 

Nyman, D.J., and Moore, G.K., 1963, Summary of 

the ground-water resources of Madison County, 

Tennessee: Tennessee Division of Water Resources Hydrologic Atlas No. 1, 9 p. 

Parks, W.S., 1968a, Geologic map of the Beech 

Bluff quadrangle, Tennessee: Tennessee Division of Geology, GM 446-SW, scale 1:24,000, 

1 sheet. 

-1968b, Geologic map of the Claybrook quadrangle, Tennessee: Tennessee Division of 

Geology, GM 446~NW, scale 1:24,000,1 sheet. 

-1968c, Geologic map of the Jackson south 

quadrangle, Tennessee: Tennessee Division of 

Geology, GM 43%SE, scale 1:24,000, 1 sheet. 

Parks, W.S., and Carmichael, J.K., 1989, Geology 

and ground-water resources of the Fort Pillow 

Sand in western Tennessee: U.S. Geological 

Survey Water-Resources Investigations Report 

89-4120, 20 p. 

-1990a, Altitude of potentiometric surface, fall 

1985, and historic water-level changes in the 

Fort Pillow aquifer in western Tennessee: U.S. 

Geological Survey Water-Resources Investigations Report 89-4048, 8 p. 

-1990b, Altitude of potentiometric surface, fall 

1985, and historic water-level changes in the 

Memphis aquifer in western Tennessee: U.S. 

Geological Survey Water-Resources Investigations Report 88-4180, 8 p. 

-199Oc, Geology and ground-water resources of 

the Memphis Sand in western Tennessee: U.S. 

Geological Survey Water-Resources Investigations Report 88-4182, 30 p. 

Pettijohn, W.A., and Henning, Roger, 1979, Preliminary estimate of ground-water recharge 

rates, related streamflow and water quality in 

Ohio: Ohio State University Water Resources 

Center Project Completion Report Number 552, 

323 p. 

Pollock, D.W., 1989, Documentation of computer 

programs to compute and display pathlines using 

results from the U.S. Geological Survey modular three-dimensional ground-water flow model: 

U.S. Geological Survey Open-File Report 

89-381, 188 p. 

Searcy, J.K., 1959, Flow-duration curves: U.S. 

Geological Survey Water-Supply Paper 1542-A, 

33 p. 

U.S. Department of Agriculture, 1978, Soil survey 

of Madison County, Tennessee: U.S. Department of Agriculture Soil Conservation Service, 

51 p. 

U.S. Geological Survey, 1973, Land use and land 

cover 1973, Blytheville, Alabama; Tennessee; 

Alabama; Missouri: U.S. Geological Survey 

Open-File Report 77-101-1, 1 sheet. 

-1974, Water-resources data for Tennessee: U.S. 

Geological Survey Water Data Report, 222 p. 

Zurawski, Ann, 1978, Summary appraisals of the 

Nation’s ground-water resources, Tennessee 

Region: U.S. Geological Survey Professional 

Paper 813-L, 35 p. 

54 Hydrology of the Jackson, Tennessee, eree and delineation 

of erees contributing ground water to the Jackson Well Fields ‘USGPO 1993750~232/800X3