Assessing the Extent of
Saltwater Intrusion in the
Aquifer System of
Southern Baldwin County,
Alabama
Dorina Murgulet
The University of Alabama
OUTLINE
1) Introduction
• Objectives
• Site description and background
information
2) Methodology
3) Results
4) Discussions and conclusions
Introduction
Objectives:

determine the extent and severity of saltwater
intrusion in the aquifers underlying southern
Baldwin County, Alabama using the most
recently collected geochemical, geological and
hydrogeological information.

Provide the current state of regional and local
groundwater flow for the study area.

Collect and compile information to develop a
detailed groundwater model of Southern Baldwin
County.
Location of the study area and surveyed
groundwater wells per aquifer system
Hydrogeologic Cross Section of
Southern Baldwin County, Alabama
Gillett et al., 2000
GillettB.etGillett
al., 2000
Source:
et al.,2000
The Hydrologic System
Is a complex interaction between water
and the physical environment.
 The area is bordered for the most part by
brackish to saline bay and coastal waters.
 Losses from the freshwater zones are by
diffusion into the surrounding subsurface
saline waters, by spring discharge, by ET,
and by water-well production.

Southern Baldwin County with the Fastest Growth
Rates, 2000-2003
Study Area
Baldwin County
has one of the highest
population increases in
Alabama, second only to Shelby
County.
L ULC and Agriculture Area , 2001
·
0
Legend
Agriculture
Bays, estuares, and ponds
Legend
Urban,
Residential, and other build-up land
Agriculture
Prarie
Bays, estuares, and ponds
4
8
Kilometers
12
Major types of land use:
agriculture, recreation
and tourism, seafood
industries, and
urbanization.
The economy of the
county is based
primarily on: agriculture,
tourism, fishery, and
seafood processing
industries.
Dry bare
soil
Urban,
Residential,
and other build-up land
Sand and beaches
Prarie
Evergreen
Forest
Dry bare soil
Pine
SandPlantation
and beaches
Upland
Forest
Evergreen
Forest
Nonforested
vegetated wetland
Pine Plantation
Unharvested
Upland Forestagriculture land
Agriculture=41.94% of
total area
Increase in Agriculture and
Urban LULC from 1987 to 2001
Agriculture
700.00
Agriculture
increase =
14.5%
Urban
increase =
1.1%
600.00
Area (km2)
500.00
400.00
300.00
200.00
Urban
100.00
0.00
agriculture
urban
LULC
2001
1987
Background Information

With increasing development and tourism in
these regions both ground water resources and
environmentally sensitive areas such as coastal
wetlands and ecological coastal habitats will be
at risk.

Unsustainable ground water extraction or aquifer
overdevelopment may lead to the incursion of
salt water into freshwater aquifer zones, shifting
the natural freshwater/salt water interface further
inland.
Methodology
Methodology

The existence of the saltwater/freshwater
interface is distinguished by the presence of
water with high Salinity, Chloride and TDS
concentrations into the freshwater aquifers.

The presence of the principal seawater ions
such as: chloride and sodium, increase water
conductivity.

Thus, water quality in coastal environments can
be determined by measures of fluid conductivity.
Methodology

The ArcGIS was used to compile the geospatial
data, to record and map well locations, well
depths, hydrogeological information, and
concentration data collected from fieldwork and
to generate the final contamination and
groundwater potential surface and general flow
direction maps.

For more confidence, the output maps were
compared with output maps developed from
interpolation of same data using Surfer and
compared with the actual concentrations and
water levels
Results
Aquifer zone A1:
a) Chloride concentration map. b) Salinity concentration map c) TDS
concentration map. d) Groundwater potential surface
Aquifer zone A2
a) Chloride concentration map. b) Salinity concentration map. c) TDS
concentration map. d) Groundwater potential surface.
Aquifer zone A3
a) Chloride concentration map. b) Salinity concentration map. c) TDS
concentration map. d) Groundwater potential surface.
40
2
R = 0.2158
35
30
25
20
15
10
5
0
0
50
100
Salinity vs Chloride Concentrations
(impacted areas)
Salinity concentrations (ppm)
Chloride
concentrations (ppm)
Chloride
concentrations (ppm)
Salinity vs Chloride Concentrations (non-impacted
areas)
45
6000
5000
4000
R2 = 0.9708
3000
2000
1000
0
0
1000
2000
3000
4000
5000
Salinity concentrations (ppm)
6000
Salinity vs TDS Concentrations
(non-impacted areas)
R2 = 0.3127
150
100
50
0
0
10
20
30
40
Salinity vs TDS Concentrations
(impacted areas)
Chloride concentrations (ppm)
TDS concentrations (ppm)
TDS concentrations
(ppm)
200
16000
14000
12000
10000
8000
6000
R2 = 0.6622
4000
2000
0
0
2000
4000
Chloride concentrations (ppm)
6000
Chloride vs Conductivity (non-impacted
areas)
R2 = 0.3017
200
150
100
50
0
0
5
10
15
20
25
Chloride concentrations (ppm)
Chloride vs Conductivity (impacted areas)
16000
Conductivity (μS)
Conductivity (μS)
250
14000
12000
R2 = 0.9615
10000
8000
6000
4000
2000
0
0
1000
2000
3000
4000
Chloride concentrations (ppm)
5000
6000
Binary Masking Method


The output concentration grid layers for each of
the three parameters (Cl- , salinity and TDS)
were reclassified using the binary masking
method.
Through this process critical areas such as those
that exceed Cl- concentrations of 250 mg/l,
salinity concentrations of 500 mg/l and TDS
concentrations of 500 mg/l. were reclassified as
1 and all other areas that include concentrations
within the limits were reclassified as 0.
Contamination maps by aquifer zones: a) Aquifer
zone A1; b) Aquifer zone A2; c) Aquifer zone A3
Potential causes of the groundwater seawater
contamination in southern Baldwin County:
Increasing development associated with
overdevelopment of the aquifer system.
 Aquifer hydrogeologic properties.
 Salt water infiltration from the surface from
different sources.
 Periods of low recharge from the surface
due to low precipitation rates.

Hydrogeologic Properties
• The transmissivity of the
Miocene-Pliocene
aquifer system of
Baldwin County,
was estimated to range
from 700 to 5,400 ft²/day
( Robinson et al., 1996)
• The storage coefficients
were estimated as
ranging from 0.00014 to
0.00115 (Walter and
Kidd 1979).
PRECIPITATION and RECHARGE



Rain is the primary source of recharge to
groundwater,
Precipitation, throughout southern Baldwin County
averages about 162.56 cm/ year (USGS, 1936 to
2005).
Data collected from three stations for the year of
2006, indicated that the annual-mean precipitation
reported is appreciatively uniform throughout
Baldwin County with a range from 44.6024 cm/year
in Robertsdale to 50.3428 cm/year in Bay Minette
(data from USGS, 2006).
Annual Precipitation Rates (cm)
Annual-Average Precipitation from Three Different
Sites Located in Baldwin County, Alabama
300
300
250
250
200
200
150
150
2006 annual precipitation
rate = 45 cm
100
100
50
50
Bay Minette
Fairhope
Roberstdale
0
0
60 9 63 9 66 9 69 9 72 9 75 9 78 9 81 9 84 9 87 9 90 9 93 9 96 9 99 0 02 0 05 0 08
19
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
Years
Discussions and conclusions:
• The compilation of data into a user-friendly GIS
database allowed for useful graphical
visualizations, data interpretation, data analyses,
and current assessments of groundwater quality
and availability for the region.
• Examination of the Cl-, salinity and TDS
parameters revealed the Gulf of Mexico as the
source of saltwater intrusion.
Discussions and conclusions:
• For aquifer A1, the elevated salinity, chloride, and TDS
concentrations may be the result of a combination of both
saltwater intrusion and surface contamination.
• Aquifer zone A2 is vulnerable to saltwater intrusion,
particularly in areas where wells are in close proximity to
the Gulf of Mexico. Saltwater contamination of aquifer
zone A2 might be the result of aquifer overdevelopment
and infiltration from aquifer A1.
• It appears that aquifer zone A3 is less vulnerable to
saltwater intrusion however this does not mean that
saltwater intrusion has not occurred in the aquifer zone.
Discussions and conclusions:
N
Not at scale
S
REFFERENCES

Dowling, C.B.; Poreda, R.J.; and Carey, A.E. 2004, Ground Water Discharge and Nitrate
Flux to the Gulf of Mexico, Ground Water, v.3, no.3, p. 401-417.

Chandler, R.V.; Moore, J.D.; and Gillett, B. 1985, Ground-Water Chemistry and Salt-Water
Encroachment, Baldwin County, Alabama: Geological Survey of Alabama Bulletin 126. pp.
16, 17, 53, 54, 78-80, 84-86.

Gillett, B.; Raymond, D.E.; Moore, J.D.; and Tew, B.H. 2000, Hydrogeology and
Vulnerability to Contamination of Major Aquifers in Alabama: Area 13: Geological Survey of
Alabama Circular 199A.

Kidd, R.E. 1988, Hydrogeology and Water-Supply Potential of the Water-Table Aquifer on
Dauphin Island: United States Geological Survey Water-Resources Investigation Report
87-4283.

Kopaska-Merkel, D. and Moore, J.D. 2000, Water in Alabama: Geological Survey of
Alabama Circular 122O.

Speiran, G.K., Hamilton, P.A., and Woodside, M.D. 1997, Natural Processes for Managing
Nitrate in Ground Water Discharge to Chesapeake Bay and Other Surface Waters: More
than Forest Buffers, United States Geological Survey, Report FS-178-97.
Acknowledgments
Funding: Alabama Department of Conservation
and Natural Resources ADCNR
Thanks:
My Committee members: Dr. Geoffrey R. Tick,
Dr. Chunmiao Zheng, Dr. Rona Donahoe, Dr.
Andrew Goodliffe, and Dr. Christian Langevin.
•
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•
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•
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To people of Baldwin County
Enid Probst (ADEM)
Blakney Gillett, Marlon Cook, and others (GSA)
Weeks Bay Reserve
Joe Kington
Valeriu Murgulet