U.S. DEPARTMENT OF THE INTERIOR

U.S. GEOLOGICAL SURVEY

Prepared in cooperation with the

MISSISSIPPI DEPARTMENT OF ENVIRONMENTAL QUALITY
OFFICE OF POLLUTION CONTROL
MISSISSIPPI DEPARTMENT OF AGRICULTURE AND COMMERCE

WATER-RESOURCES INVESTIGATIONS REPORT 93-4129
Location, geology, slope, diagrammatic section, and report text SHEET 1 OF 2

Moreland, R.S., and O'Hara, C.G., 1993, Susceptibility of major aquifers to surface contamination—

Holmes, Humphreys, Issaquena, Sharkey, Washington, and Yazoo Counties, Mississippi

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33°30"

33°30"

USS. Geological Survey

Jackson, Mississippi 39269

91°

Physiography from Stephenson and others, 1928

5 MILES

15 KILONETERS

Geology modified from Bicker, 1969

gi

For additional information write to:

100 W. Capitol Street, Suite 710

EXPLANATION

[sur nis
[EM Norte CENTRAL HILLS
[ !4ckson prairies

[__] LONGLEAF PINE HILLS

Figure 1.—Location and physiography.

Base from U. S. Geological Survey digital data, 1:100,000, 1982, 1984
Lambert Conformal Conic Projection
Standard parallels 33° and 45°, central meridian 90°00"

OLIGOCENE AQUIFER SYSTEM
OUTCROP AREA

Figure 2.--Geology and aquifer outcrop areas.

HB Mssissirt ALLUVIAL PLAIN

MISSISSIPPI RIVER ALLUVIAL AQUIFER OUTCROP AREA

MISSISSIPPI RIVER ALLUVIAL AQUIFER OUTCROP AREA

EXPLANATION
SLOPE OF THE LAND SURFACE, IN PERCENT

me

SPARTA AQUIFER
OUTCROP AREA

COCKFIELD AQUIFER OUTCROP AREA

EXPLANATION

[MM quaTernary ALLUVIUM
HB vickspurc Group
[Forest Hit FORMATION
HB vazoo cray

GE cockFiEL ForMATION

[BB cook MounTaIN FORMATION
[__] SPARTA SAND

( zpua cay

[°_] QuaTERNARY LOESS

SPARTA AQUIFER
OUTCROP AREA

mm
| av

AREAS NOT EVALUATED

Figure 4.--Slope of the land for outcrop areas of major aquifers.

INTRODUCTION

Ground water is one of Mississippi’s most important
natural resources. The Mississippi Department of
Environmental Quality, Office of Pollution Control,
and the Mississippi Department of Agriculture and
Commerce are developing a program to protect the
aquifers in Mississippi from contamination from
surface sources. The U.S. Geological Survey, in
cooperation with these two agencies, is conducting a
series of studies to delineate the outcrop areas of the
major aquifers in Mississippi and those parts of the
outcrop areas that are susceptible to contamination
from surface sources.

Purpose and Scope

This report summarizes selected  surface-
contamination-susceptibility factors for major aquifers
in Holmes, Humphreys, Issaquena, Sharkey,
Washington, and Yazoo Counties (fig. 1).
Susceptibility evaluations were performed by
integrating data sets describing geologic, hydrologic,
physiographic, and cultural data using a vector based
geographic information system (GIS).

Two primary guidelines were established during the
initial stages of the study. The first guideline is that the
study is to address the relative ease by which surface
contaminants might enter the saturated zone. Predicting
the transport and disposition of contaminants after
reaching the saturated zone was beyond the scope of the
study.

The second guideline is to assume that only the parts
of the aquifer that are unconfined are susceptible to
surface contamination. These areas generally coincide
with the outcrop areas of the geologic units which make
up each aquifer. The confined parts of aquifers have a
layer of relatively impermeable material between the
aquifer and the surface and were not evaluated.

Location and Physical Features of the Study Area

The study area, located in west-central Mississippi,
covers about 3,800 square miles and had a total
population of about 136,000 people in 1990 (U.S.
Bureau of the Census, 1991). Major cities in the study
area include Belzoni, Greenville, Lexington,
Mayersville, Rolling Fork, and Yazoo City (fig. 1).
Parts of five physiographic districts are included in the
study area. The Mississippi Alluvial Plain district is a
broad, flat, gently sloping plain formed by the
Mississippi River and its tributaries (Stephenson and
others, 1928). The Bluff Hills district is characterized
by pronounced hills with steep slopes, narrow ridges,
and narrow intervening valleys, formed on loess
deposits along the eastern edge of the Mississippi
Alluvial Plain. The North Central Hills district is a
hilly to moderately irregular upland shaped by stream
erosion. The Jackson Prairies district is a relatively
narrow strip of gently rolling land with many small
prairie-like tracts. The Longleaf Pine Hills district is an
area of rolling to moderately rugged hills.

Surface drainage in the North Central Hills and
Jackson Prairies districts is southward to the Big Black
River. In the Bluff Hills and Mississippi Alluvial Plain
districts, surface drainage is south and west to the
Yazoo and Sunflower Rivers.

Description of Major Aquifers

The major aquifers that were evaluated for their
potential to contamination from surface sources are the
Mississippi River alluvial, Cockfield, and Sparta
aquifers (fig. 2). These aquifers consist of sediments of
Tertiary to Quaternary age in the East Gulf Coastal
Plain (table 1). A small part of the Oligocene aquifer
system is present in the southern part of the study area.
The Oligocene aquifer system is composed of the
Byram, Glendon, Marianna, Mint Spring, and Forest
Hill Formations, which consist of beds of clay, marl,
limestone, and sand that range in thickness from 100 to
200 feet. Because of the limited areal extent of the
Oligocene aquifer system, and because only small
supplies of water are withdrawn from it, the Oligocene
aquifer system was not considered to be a major aquifer
in the study area and was not evaluated. The Meridian-
upper Wilcox aquifer is a source of drinking water in
the study area but does not crop out in the study area
and was not evaluated.

WEST
a .
&
$s é = MISSISSIPPI
$e SS RIVER
€ 3 ALLUVIUM

EAST

SPARTA SAND

Figure 3.--Diagrammatic section showing geologic units in the study area.

leakage from the Mississippi River alluvial aquifer
where it overlies the Cockfield (Hosman and others,
1968). Regional ground-water movement generally is
westward (Spiers, 1977).

Sparta Aquifer

The Sparta aquifer consists of sediments in the
Sparta Sand of Eocene age. The Sparta Sand consists of
two or three thick beds of rounded, well-sorted, quartz
sand separated by beds of clay (Gandl, 1982). The
Sparta Sand dips to the west at about 20 feet per mile.

The Sparta aquifer ranges in thickness from 100 to
400 feet. Its recharge area generally coincides with the
outcrop area of the Sparta Sand and extends across the
northeastern part of the study area (fig. 2). The Cook
Mountain Formation forms an upper confining unit, and
the Zilpha Clay forms a lower confining unit (fig. 3). In
the western part of the study area, the Sparta aquifer is
overlain by, but not in contact with, the Mississippi
River alluvial aquifer.

Direct infiltration of precipitation on the outcrop is
one of the primary sources of recharge to the Sparta
aquifer (Hosman and others, 1968). Lesser amounts of
recharge are from leakage from the Mississippi River
alluvial aquifer where it overlies the Sparta and from
streams during high stages. Regional ground-water
movement generally is to the west (Newcome, 1976).

FACTORS AFFECTING
SUSCEPTIBILITY TO
CONTAMINATION

The relative susceptibility of major aquifers to
surface contamination was evaluated on the basis of six
factors: unsaturated zone media, aquifer media, slope of
the land surface, depth to water table, soil permeability,
and land use/land cover. These factors are summarized
in table 2 and table 3. This method of factor analysis to
determine the susceptibility of aquifers to surface
contamination follows the basic principles introduced
by Aller and others (1985). A GIS was used to integrate
digital spatial data sets describing these factors.

Contamination potential ratings for each factor were
determined by multiplying the variable rating by the
fixed weight for that factor (tables 2 and 3). Weights
and ratings for the factors are based on their effect on a
contaminant’s ability to reach the saturated zone.
Higher values for weights or ratings indicate a greater
contamination potential.

Contamination potential ratings for aquifer media,
unsaturated zone media, and soil permeability were
based on the material’s ability to conduct water
(hydraulic conductance) to the aquifer. Because water
entering an aquifer from the surface must first pass
through the soil zone, unsaturated zone, and finally the
aquifer material, these three factors were combined into
one series conductance factor. Because series hydraulic

Table 1.--Geologic units and major aquifers in the study area
[Modified from Slack and Darden, 1991]

System Series Group

Principal aquifer or

logic unit amie

Holocene and
Pleistocene

‘Quaternary

Mississippi River
alluvium

Mississippi River
alluvial aquifer

Pleistocene

Loess
Terrace deposits

(Oligocene

Vicksburg Group [Marianna

Byram
Formation
[Glendon
Formation
[Oligocene
Formation aquifer system
Mint Spring
Formation

Tertiary

Forest Hill
Formation

Jackson Group

Yazoo Clay
/Moodys Branch
Formation

Eocene

(Cockfield
Formation
[Cook Mountain
Formation
Sparta Sand
Zilpha Clay
Winona Sand )Winona-
Tallahatta aquifer

[Cockfield aquifer

Sparta aquifer

Tallahatta
Formation

Mississippi River Alluvial Aquifer

The Mississippi River alluvial aquifer (fig. 2)
consists of the Mississippi River alluvium--primarily
clay, silt, sand, and gravel of Quaternary age. The
alluvium grades upward from gravel and coarse sand to
medium or fine sand to clay. The upper part of the
alluvium generally consists of clay of variable
thickness. The coarse lower sediments (sands and
gravels that comprise the alluvial aquifer) tend to be
thickest in the center of the alluvial plain and thinner
toward the periphery of the alluvial plain.

The Mississippi River alluvial aquifer ranges in
thickness from 50 feet to more than 150 feet. The
aquifer unconformably overlies the Sparta and
Cockfield aquifers (fig. 3). A discontinuous clay layer
partially impedes downward movement of water
between the Mississippi River alluvial aquifer and the
underlying aquifers. Where the clay layer is absent, the
Mississippi River alluvial aquifer and the underlying
aquifers are hydraulically connected.

According to Boswell and others (1968), recharge to
the Mississippi River alluvial aquifer is primarily
through direct infiltration of precipitation from the
surface with lesser amounts coming from streams,
runoff from adjacent highlands, and inflow from
underlying aquifers. However, results of aquifer
simulation studies by Sumner and Wasson (1990)
indicate that direct infiltration of precipitation from the
surface is a less important source of recharge to this
aquifer than recharge from streams and lakes and runoff
from adjacent highlands. Although not completely
understood, recharge to the Mississippi River alluvial
aquifer probably involves all of these sources. Regional
movement of water in the Mississippi River alluvial
aquifer is considered to have two components: a north-
to-south component along the center of the aquifer, and
a component from the edges of the aquifer toward the
center (Sumner and Wasson, 1990).

Cockfield Aquifer

The Cockfield aquifer consists of sediments in the
Cockfield Formation of Eocene age. The Cockfield
Formation generally consists of beds of fine to medium
sand, sandy carbonaceous clay, and thin beds of lignite
(Spiers, 1977). The Cockfield Formation dips to the
southwest at about 20 to 30 feet per mile.

The Cockfield aquifer ranges in thickness from 50
to 400 feet. Its recharge area generally coincides with
the outcrop area of the Cockfield Formation and
extends across the eastern part of the study area (fig. 2).
The Yazoo Clay, where it is present, forms an upper
confining unit, and the Cook Mountain Formation
forms a lower confining unit to the Cockfield
Formation (fig. 3). In the western part of the study area,
the Cockfield aquifer is overlain by the Mississippi
River alluvial aquifer. In the study area, almost all
recharge to the Cockfield aquifer is from precipitation
on the outcrop of the Cockfield Formation and from

conductance is combined as a harmonic mean sum, the
following formula was used to determine the combined
contamination potential (McDonald and Harbaugh,
1984):

URT = URS + 1/RU + V/RA q@
where

RT = combined contamination potential rating for
soil permeability, unsaturated zone media, and
aquifer media,

RS = contamination potential rating for soil
permeability factor,

RU = contamination potential rating for unsaturated
zone media factor, and

RA = contamination potential rating for aquifer
media factor.

The resultant combined contamination potential
(RT) was normalized to 130 to give the appropriate
weight to the combined rating for the three factors. The
final contamination potential rating is the sum of the
land use/land cover, slope of the land surface, depth to
water, and the normalized combined contamination
potential rating for soil permeability, unsaturated zone
media, and aquifer media factors from equation 1.

Finally, categories of relative susceptibility were
established and mapped for each aquifer (fig. 8). These
categories are based on a percentage of the possible
total sum of contamination potential ratings for each
factor. These categories, in increasing rank of relative

susceptibility, are as follows:
Relative
Percent of
y 5 susceptibility
possible total rating
sible total ratin; oy
Less than 10 1
10-33 2
33-66 5
66-90 4
More than 90 2)

The numerical values derived from the application
of the rating system have no quantitative implication.
The relative susceptibility categories are intended only
to provide a comparison of contamination risks for
different aquifers or parts of the same aquifer.

Geology

Geologic data (Bicker, 1969) were used to
determine the aquifer and unsaturated zone media and
the boundaries of the aquifer’s recharge areas. Aquifer
media were derived from the lithology of the geologic
units that make up each aquifer. The unsaturated zone
media generally were the same as the aquifer media,
except in areas where different geologic units overlie
those making up the aquifer. The boundaries of the
recharge areas were based on the outcrop areas of the
geologic units that form each aquifer (fig. 2).

Aquifer and unsaturated zone media ratings (table 2)
are based on the permeability of the materials which
make up the aquifer and unsaturated zone. Coarse-
grained materials have a high contamination potential
rating because they are more transmissive to water, and
attenuation (chemical change) of contaminants is less
effective in coarse- than in fine-grained materials. The
aquifer media rating assigned to the Mississippi River
alluvial aquifer was 21 because of the predominantly
gravel and sand lithology. With the exception of parts
of the aquifer overlain by the alluvial apron, a highly
permeable alluvial fan deposit forming on the eastern
edge of the aquifer along the bluff hills, the unsaturated
zone media rating assigned to the Mississippi River
alluvial aquifer was 25. Although the predominant
lithology of the unsaturated zone is clay and silty clay,
which would have a maximum unsaturated zone media
rating of 15, the unsaturated zone media rating was
increased to 25 to account for the discontinuous nature
of this clay layer. The unsaturated zone media rating
assigned for parts of the aquifer overlain by the alluvial
apron was 45 because of the highly permeable nature of
these deposits and the absence of the upper silty clay
layer.

at a scale of 1:250,000 (U.S. Geological Survey, 1986)
and are based on the land use and land cover
classification system developed by Anderson and
others (1976). This is a multilevel classification system
wherein each successive level is a more detailed
characterization of land use and land cover description
(table 3). Level II categories were used for the
susceptibility evaluations, but because of the detailed
nature of level II categories, only level I categories are
shown for each aquifer”s outcrop area (fig. 7).

Contamination potential ratings for each land-use
area are based on the relative contamination risk of
anthropogenic and natural activities occurring in that
area as well as hydrologic properties particular to each
area. Because land-use activities influence ground-
water contamination risk, this factor was assigned a
weight of 5. Whenever possible, documented cases of
the relation between ground-water contamination
potential and land-use practice were used to support the
rating assigned to each category.

Urban or Built-Up Land

The urban or built-up land category consists of any
land that is intensively used and much of which is
covered by structures. Included in this category are the
residential, commercial and services; industrial;
transportation, communications, and utilities; mixed
urban or built-up land; and other urban or built-up land
level I categories (table 3).

The residential category was assigned a
contamination potential rating of 6. Sources of
contamination in the residential category include septic
tanks, sanitary sewers, and lawn fertilizers and
chemicals. Septic tanks are a major source of
contamination in this category (J.L. Crawford,
Mississippi Department of Pollution Control, oral
commun., 1992). Improved drainage in residential areas
can increase runoff and decrease direct infiltration from
the surface, thereby decreasing contamination risk
(Becker, 1990).

The commercial and services category was assigned
a contamination potential rating of 7. Although
improved drainage and increased percentage of
impervious surface area decrease direct infiltration of
precipitation, some commercial operations use
hazardous materials that could pose a threat to ground-
water quality. A major source of contamination in this
category is underground tanks used for storing
petroleum products at gasoline stations.

The industrial category was assigned a
contamination potential rating of 10. Many activities in
industrial areas may lead to ground-water
contamination. A study conducted in southern

Table 2.--Contamination susceptibility factors
[>, greater than; <, less than; modified from Aller and others, 1985]

‘Contamination
Factor Weight Divisions potential rating
(CPR)
Unsaturated zone media 5 Gravel #10
‘Sand and gravel 19
Sand 69
Interbedded sand and clay 58
Massive sandstone and limestone 37
Clay 13
Aquifer media 3 Gravel 8:10
Sand and gravel re)
Sand 69
Interbedded sand and clay 58
Limestone 46
Massive sandstone and limestone 37
Slope (percent) 3 0-2 10
26 9
612 5
12-18 3
>18 1
Depth to water table 5 05 10
(feet) 5-15 9
15-30 7
30-50 5
50-75 3
>15 1
Soil permeability 5 <0.20 14
(inches per hour) 02-06 47
>0.60 8-10
The aquifer media rating assigned to the Cockfield Mississippi and Louisiana determined _that

aquifer was 21 because the predominant lithology is
fine- to medium-grained sand. Unsaturated zone media
ratings for the Cockfield aquifer varied depending on
overlying units. Where only the Cockfield Formation
was present, the unsaturated zone rating was 35 because
of the predominantly sandy lithology. Parts of the
aquifer that were overlain by the loess, a highly
permeable deposit, were assigned an unsaturated zone
rating of 50. Parts of the aquifer which were overlain
by outliers of the Yazoo Clay, a relatively impermeable
unit, were assigned an unsaturated zone media rating of
10.

The aquifer media rating assigned to the Sparta
aquifer was 21 because of the predominant fine sand
lithology. In most areas, the unsaturated zone media
rating assigned to the Sparta aquifer was 21; however,
where the aquifer is overlain by the Cook Mountain
Formation (a unit with relatively low permeability), a
rating of 15 was assigned.

Slope of the Land Surface

Data sets describing the percent slope of the land
surface were created from 1-degree digital elevation
models (DEM’s) (U.S. Geological Survey, 1970a,
1970b, 1973, 1979). DEM’s are regular arrays of land-
surface elevations. Each array is a block, 1 degree of
latitude by 1 degree of longitude, with an elevation
every 3 arc-seconds (about 250 feet). Elevations are
reported to the nearest meter (U.S. Geological Survey,
1987). The GIS was used to create an approximation of
the land surface from this array of elevations. This
approximation of land surface, called a triangular
irregular network (TIN), is a series of irregularly
shaped triangles where elevation data are stored at the
corner of each triangle. The GIS then used the three
elevations to calculate the slope of each triangle. Using
a TIN to approximate a three-dimensional surface
results in the angular shapes of the slope polygons in
figure 4.

Contamination potential ratings for the slope
category are based on the assumption that runoff
decreases and infiltration increases in areas of low
slopes. Areas with steeper slopes have a lower
contamination potential rating because of increased
runoff and decreased infiltration of water into the
aquifer.

Depth to Water Table

Maps of the depth to the water table in the outcrop
area of each aquifer were created from 1-degree DEM’s
and digitized potentiometric maps for each aquifer.
Potentiometric-surface elevation data for the
Mississippi River alluvial aquifer were obtained from
Goldsmith (1993); the Sparta aquifer from Darden
(1987); and the Cockfield aquifer from Darden (1986).
Data were processed by digitally sampling the land-
surface elevation and the potentiometric-surface
elevation every 1,500 feet, and calculating the
difference between the two surfaces (the land-surface
elevation minus the potentiometric-surface elevation) at
each sampled point. The difference between each
surface at each sampling point represents the depth to
water at that point. Depth to water is mapped for each
aquifer outcrop area in figure 5.

Contamination potential ratings for depth to water
are based on the distance a contaminant would have to
travel before reaching the saturated zone. Areas with
shallow depths to the water table have a high
contamination potential rating because there is less time
for attenuation of contaminants by soil materials.

Soil Permeability

Data sets describing soil permeability were provided
by the U.S. Soil Conservation Service (SCS). The soil
layer generally is the uppermost part of the unsaturated
zone characterized by significant biological activity.
Each soil type was assigned permeability values
obtained from the SCS county report series (Morris,
1961; Powell and others, 1959; Scott and Carter, 1962;
Scott and others, 1975; Wynn and others, 1961). Soil
permeability is mapped for each aquifer in figure 6.

Contamination potential ratings for soil
permeability are based on the capacity of the soil to
transmit water. The contamination potential rating
increases as soil permeability increases because water
moves more rapidly and allows less time for
biodegradation, sorption, and volatilization.

Land Use/Land Cover

Land-use maps were created from Geographic
Information Retrieval and Analysis System (GIRAS)
data sets (U.S. Geological Survey, 1978a, 1978b,
1980a, 1980b). These data sets generally are compiled

concentrations of most contaminants were higher in
industrial land-use areas than in forested and in mixed
agricultural and forested areas (Strickland and others,
1987).

The transportation, communications, and utilities
category was assigned a contamination potential rating
of 7. Many activities common to this category, such as
producing, processing, treating, and transporting oil,
gas, and electricity, have the potential to contaminate
ground-water supplies.

Because of its relatively limited areal extent and
ambiguous description, the mixed urban or built-up
land category was assigned the same contamination
potential rating as the dominant surrounding land-use
category. For example, if an area classified as mixed
urban or built-up land was surrounded by land
classified as residential, such an area would have a
contamination potential rating of 6 (table 3).

The other urban or built-up land category was
assigned a contamination potential rating of 4. Most
activities taking place on such land pose little or no
threat to ground-water quality.

regime. Included in the forest land category are the
deciduous forest land, evergreen forest land, and mixed
forest land level II categories.

Because of the similar hydrologic and
anthropogenic properties of the forest land level Il
categories, the same contamination potential rating (4)
was assigned to each level II category. A study in
southern Mississippi and Louisiana determined that
ground-water samples from forested land-use areas had
consistently lower concentrations of analyzed
constituents than samples from mixed agricultural-
forest land and industrial land use areas (Strickland and
others, 1987).

Water

The water category includes any land that is
continually covered by water. To be included, if these
areas are linear they must be at least 1/8 mile wide and
if extended they must cover at least 40 acres (Anderson
and others, 1976). Many of the water bodies in
Mississippi do not meet this requirement and were
mapped with the dominant surrounding land-use
category. Included in the water category are the streams
and canals; lakes; reservoirs; and bays and estuaries
level II categories.

All of the level II water categories were assigned a
contamination potential rating of 8 because surface-
water bodies generally are hydraulically connected with
local ground-water systems and contamination of a
surface-water body could lead to ground-water
contamination.

Wetlands

The wetlands category includes any land where the
water table is at, near, or above the land surface for a
significant part of most years. Aquatic or hydrophytic
vegetation usually is established, although some areas
may not be vegetated. Included in the wetlands
category are the forested and nonforested wetland level
TI categories.

Because of the similar hydrologic and
anthropogenic properties of each wetland level II
category the same contamination potential rating (8)
was assigned to each level II category. Wetlands
generally are hydraulically connected to local ground-
water systems, and contamination of a wetland could
Jead to ground-water contamination.

Barren Land

The barren Jand category consists of any land with
limited ability to support life and in which less than
one-third of the area has vegetation or other cover.
Level II categories included in the barren land category
are sandy areas other than beaches; strip mines,
quarries, and gravel pits; transitional areas; and mixed
barren land.

Strip mines, quarries, and gravel pits were assigned
a contamination potential rating of 8. Pits resulting
from mineral extraction commonly intercept the water
table and provide direct contact between ground water
and near surface activities. Because of their limited
areal extent, the sandy areas other than beaches,
transitional areas, and mixed barren land categories
were assigned the same contamination potential rating
as the dominant surrounding land-use category.

SUSCEPTIBILITY OF MAJOR
AQUIFERS TO SURFACE
CONTAMINATION

Relative susceptibility (to contamination from
surface sources) categories range from 1 to 5 for the
aquifer outcrop areas. The Mississippi River alluvial
aquifer outcrop has the smallest percent area rated
within susceptibility category 4; the Cockfield aquifer
outcrop has the largest percent area rated within
susceptibility category 4 (table 4). For the three
aquifers, the combined aquifer outcrop areas rated
within susceptibility categories 1 and 5 are less than 1
percent of the total area. These areas are not mapped
(fig. 8) because they are too small to be discerned at the
map scale used.

Mississippi River Alluvial Aquifer

Less than 1 percent of the Mississippi River alluvial
aquifer outcrop area rated within susceptibility category
5; 35 percent rated within susceptibility category 4; 62
percent rated within susceptibility category 3; 2 percent
rated within susceptibility category 2; and less than 1
percent rated within susceptibility category 1 (table 4).
Aquifer outcrop areas rated within susceptibility
category 4 (fig. 8) generally are located along larger
streams and rivers where depths to water are lower,
where soil permeability is higher on the natural levees
which have formed along the larger waterways, and
where the predominant land use is agricultural. Factors
most contributing to areas rated within susceptibility
category 3 for the Mississippi River alluvial aquifer are
the relatively impermeable unsaturated zone material
and low soil permeabilities. Areas rated within
susceptibility category 2 generally are located where
the land use type is not agricultural.

Table 3.--Land use/land cover categories and ratings

[--, indicates areas were merged with adjacent areas; CPR, contamination potential rating;
modified from Anderson and others, 1976]

Land use categories General description —
Level I Level Il or example
Urban or built-up land Residential High and low density residential areas 6
‘Commercial and services Land used for the sale of goods and 7
services
Industrial Land used for the manufacture of 10
products
‘Transportation, communications and utilities Roads, railways, utility lines, airports, docks 7
Mixed urban or built-up land ‘More than one-third intermixture of two or more -
urban/built-up level HI categories
Other urban or built-up land Parks, cemeteries, 200s, levees 4
Agricultural land Cropland and pasture Land used to cultivate crops and livestock 10
Orchards, groves, vineyards, nurseries, and Land used to cultivate fruits, nuts, trees -
ornamental horticultural areas
Confined feeding operations Stock yards, feed lots, chicken houses 10
‘Other agricultural land Ponds, field roads, out buildings -
Forest land Deciduous forest land Predominately deciduous trees present 4
Evergreen forest land Predominately evergreen trees present 4
Mixed forest land More or less equal numbers of deciduous and 4
evergreen trees present
Water Streams and canals Streams, canals, unimpounded linear water bodies 8
Lakes Natural impoundments 8
Reservoirs Artificial impoundments 8
Wetlands Forested wetland Wetlands dominated by woody vegetation 8-10
Nonforested wetland ‘Wetlands dominated by herbaceous vegetation or 8-10
nonvegetated
Barren land Sandy areas other than beaches Sand bars usually in rivers and streams -
Strip mines, quarries, and gravel pits Lands undergoing surface mineral extraction 8
‘Transitional areas Areas changing from one category to another -
Mixed barren land Mixture of barren land categories; no category -
‘occupies more than two-thirds total area
Agricultural Land Cockfield Aquifer

The agricultural land-use category consists of any
land used for the production of food or fiber. Included
in this category are: cropland and pasture; confined
feeding operations, orchards, groves, vineyards,
nurseries, and ornamental horticulture operations; and
other agricultural land level II categories.

The cropland and pasture category was assigned a
contamination potential rating of 10 because of the
large amount of agricultural chemicals used in the
cultivation of crops. Insecticides, herbicides, fertilizers,
and other chemicals, when accompanied by irrigation
and/or precipitation, present a high potential for
affecting ground-water quality.

The confined feeding operations category was
assigned a contamination potential rating of 10. The
high concentration of livestock produces a build-up of
waste that has the potential to degrade ground-water
quality (Anderson and others, 1976).

Because of their small areal extent, the other
agricultural land and the orchards, groves, vineyards,
nurseries and ornamental horticultural categories were
assigned the same contamination potential rating as the
dominant surrounding land-use category. For example,
an other agricultural land area surrounded by cropland
and pasture would have a contamination potential
rating of 10.

Forest Land

The forest land category includes any land with a
tree-crown areal density of 10 percent or more, which is
stocked with trees capable of producing timber or other
wood products, which influence the climate or water

About 43 percent of the Cockfield aquifer outcrop
area rated within susceptibility category 4; 57 percent
rated within susceptibility category 3; and less than 1
percent rated within susceptibility categories 2 and 1
(table 4). Areas rated within susceptibility category 4
are located mostly in the eastern part of the outcrop (fig.
8). Factors most influencing areas rated within
susceptibility category 4 in the eastern part of the
outcrop include high soil permeability, shallow depths
to water, low slopes, and agricultural land use. Areas in
the western part of the outcrop rated within
susceptibility category 3 due to steep slopes, great
depths to water, and land use being primarily forested
Tand.

Sparta Aquifer

About 41 percent of the Sparta aquifer outcrop area
rated within susceptibility category 4; 58 percent rated
within susceptibility category 3; 1 percent rated within
susceptibility category 2; and less than 1 percent rated
within susceptibility category 1 (table 4). Areas which
are rated within susceptibility category 3 for the Sparta
aquifer are located in the central and eastern parts of the
outcrop (fig. 8). Factors most influencing areas rated
within susceptibility category 3 for the Sparta aquifer
include shallow depths to the water table and low
slopes. These areas are located primarily along stream
valleys. Areas rated within susceptibility category 2
generally are located where slopes are steep (away from
stream valleys) and the water table is deep.

SUMMARY

The relative susceptibility of the Mississippi River
alluvial, Cockfield, and Sparta aquifers in west-central
Mississippi to contamination from surface sources was
determined by analyzing six factors: unsaturated zone
media, aquifer media, soil permeability, slope of the
land surface, depth to water table, and land use/land
cover. A geographic information system was used to
integrate digital spatial data sets describing these
factors to rate the susceptibility of unconfined parts of
these aquifers to contamination from surface sources.
Areas were rated within one of five categories in
increasing rank of relative susceptibility to
contamination from surface sources.

SELECTED REFERENCES

Aller, Linda, Bennett, Truman, Lehr, J.H., and Petty, R.J., 1985,
DRASTIC: A standardized system for evaluating ground
water pollution potential using hydrogeologic settings:
U.S. Environmental Protection Agency /600/2-85/018,
163 p.

Anderson, J.R., Hardy, E.E., Roach, J.T., and Witmer, R.E.,
1976, A land use and land cover classification system for
use with remote sensor data: U.S. Geological Survey
Professional Paper 964, 28 p.

Becker, L.D., 1990, Simulation of flood hydrographs for small
basins in Missouri: U.S. Geological Survey Water-
Resources Investigations Report 90-4045, 40 p.

Bettandorff, J.M., and Leake, S.A., 1976, Water for industrial
and agricultural development in Attala, Holmes,
Humphreys, Issaquena, Sharkey, and Yazoo Counties,
Mississippi: Mississippi Research and Development
Center Bulletin, 68 p.

Bicker, A.R., Jr, 1969, Geologic map of Mississippi:
Mississippi Geological Survey Map, 1 sheet, 1:500,000.

Boswell, E.H., Cushing, EM., and Hosman, R.L., 1968,
Quaternary aquifers in the Mississippi embayment, with a
discussion of Quality of water by H.G. Jeffery: US.
Geological Survey Professional Paper 448-E, 15 p.

Cushing, E.M., Boswell, E.H., and Hosman, R.L., 1964, General
geology of the Mississippi embayment: U.S. Geological
Survey Professional Paper 448-B, 28 p.

Cushing, EM., and others, 1970, Availability of water in the
Mississippi Embayment: U.S. Geological Survey
Professional Paper 448-A, 13 p.

Dalsin, G. 8, The Mississippi River valley alluvial aquifer
in Mississippi: U.S. Geological Survey Water-Resources
Investigations Report 78-106, 1 sheet.

Darden, Daphne, 1986, Potentiometric map of the Cockfield
aquifer in Mississippi, fall 1984: U.S. Geological Survey
Water-Resources Investigations Report 86-4042, | sheet.

1987, Potentiometric map of the Sparta aquifer system in
Mississippi, fall 1984: U.S. Geological Survey Water-
Resources Investigations Report 86-4206, 1 sheet.

Gandl, L.A., 1982, Characterization of aquifers designated as
potential drinking-water sources in Mississippi: U.S.
Geological Survey Water-Resources Investigations Open-
File Report 81-550, 90 p.

Goldsmith, G.D.S., 1993, Potentiometric-surface map, October
through December 1988, and water-level change map,
1983-88, of the Mississippi River alluvial aquifer in
northwestern Mississippi: U.S. Geological Survey Water-
Resources Investigations Report 92-4176, 1 sheet.

Hosman, R.L., Long, A.T., Lambert, T.W., and others, 1968,
Tertiary aquifers in the Mississippi embayment, with
discussions of Quality of the water by H.C. Jeffery: U.S.
Geological Survey Professional Paper 448-D, 29 p.

McDonald, M.G., and Harbaugh, A.W., 1984, A modular three-
dimensional finite-difference ground-water flow model:
U. S. Geological Survey Open-File Report 83-875, 528 p.

Morris, W.M.,1961, Soil survey of Washington County,
Mississippi: U.S. Department of Agriculture Series 1959,
no. 3, 57 p.

Newcome, Roy, Jr., The Sparta aquifer system in Mississippi:
U.S. Geological Survey Water-Resources Investigations
Report 76-7, 3 sheets.

Powell, J.C., Cole, W.A., Scott, F.T., Wynn, A.H., and Pitts, JJ.,
1959, Soil survey of Humphreys County, Mississippi: U.S.
Department of Agriculture Series 1954, no. 4, 38 p.

Scott, F.T., and Carter, R-C., 1962, Soil survey of Sharkey
County, Mississippi: U.S. Department of Agriculture
Series 1959, no. 3, 36 p.

Scott, F.T., Walton, L.B., Nail, E.E., and McGehee, V.H., 1975,
Soil survey of Yazoo County, Mississippi: U.S.
Department of Agriculture, 51 p.

Slack, L.J., and Darden, Daphne, 1991, Summary of aquifer tests
in Mississippi, June 1942 through May 1988: U.S.
Geological Survey Water-Resources Investigations Report
90-4155, 40 p.

Spiers, C.A., 1977, The Cockfield aquifer in Mississippi: U.S.
Geological Survey Water-Resources Investigations Report
71-17, 3 sheets.

Stephenson, L.W., Logan, W.N., and Waring, G.A., 1928,
Ground-water resources of Mississippi, with a discussion
of The chemical character of the waters by C.S. Howard:
U.S. Geological Survey Water-Supply Paper 576, 515 p.

Strickland, D.J., Fendick, R.B., Jr., Bednar, G.A., and Everett,
DE., 1987, A reconnaissance study to relate land use and
ground-water quality in the Gulf Coastal Plain of Louisiana
and Mississippi: U.S. Geological Survey Water-Resources
Investigations Report 86-4325, 20 p.

Sumner, D.M., and Wasson, B.E., 1990, Geohydrology and
simulated effects of large ground-water withdrawals on the
Mississippi River alluvial aquifer in northwestern
Mississippi: U.S. Geological Survey Water-Supply Paper
2292, 60 p.

U.S. Bureau of the Census, 1991, Census of populations housing,
1990: Public Law 94-171 Data for Mississippi [machine-
readable data files], prepared by the Bureau of the Census-
-Washington, D.C.

US. Geological Survey, 1970a, Meridian, Mississippi digital
elevation model, scale 1:250,000.
1970b, West Point, Mississippi digital elevation model,
scale 1:250,000.

1973, Jackson, Mississippi digital elevation model, scale
1:250,000.

______1978a, Land use and land cover, Greenwood, Mississippi;
Arkansas; Louisiana: digital geographic information
retrieval and analysis system format, scale 1:250,000.
1978b, Land use and land cover, Jackson, Mississippi;
Louisiana: digital geographic information retrieval and
analysis system format, scale 1:250,000.

1979, Greenwood, Mississippi digital elevation model:
scale 1:250,000.

_____1980a, Land use and land cover, 1972-74 West Point,
Mississippi; Alabama: digital geographic information
retrieval and analysis system format, scale 1:250,000.
1980b, Land use and land cover, 1972-75 Meridian,
Mississippi; Alabama: digital geographic information
retrieval and analysis system format, scale 1:250,000.
1986, Land use and land cover digital data from
1:250,000- and 1:100,000-scale maps: National Mapping
Program Technical Instructions Data Users Guide 4, 36 p.
1987, Digital elevation models: National Mapping
Program Technical Instructions Data Users Guide 5, 38 p.

‘Wynn, A.H., Morris, W.M., Scott, F.T., and Walton, L.B., 1961,
Soil survey of Issaquena County, Mississippi: U.S.
Department of Agriculture Series 1959, no. 2, 42 p.

CONVERSION FACTORS AND
VERTICAL DATUM

Multiply By To obtain
inch 2.54 centimeter
inch per hour 2.54 centimeter per hour
foot 0.3048 meter
mile 1.609 kilometer
square mile 259) square kilometer
foot per mile 0.018939 meter per kilometer
foot per day 0.3048 meter per day

Sea Level: In this report, “sea level” refers to the
National Geodetic Vertical Datum of 1929 (NGVD of
1929)—a 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.

Table 4.--Relative susceptibility category of major aquifers to surface contamination
[Values are percent surface area of the aquifer’s outcrop area,
values are rounded and may not total 100 percent]

Category
Aquifer name 1 2, 3h 4 5
Mississippi Less than 1 2 62 oe) Less than 1
River
alluvial aquifer
Cockfield Lessthan1 Less than 1 57 43 0
aquifer
Sparta aquifer Less than 1 1 58 41 0

Susceptibility of Major Aquifers to Surface Contamination--

Holmes, Humphreys, Issaquena, Sharkey, Washington, and Yazoo
Counties, Mississippi

By

RICHARD S. MORELAND AND CHARLES G. O’HARA

1993

Copies of this report can be purchased from:

U.S. Geological Survey

Earth Science Information Center
Open-File Reports Section

Box 25286, MS 517

Denver Federal Center

Denver, CO 80225