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POTENTIAL SOURCES OF SALINE POTENTIAL SOURCES OF SALINE GROUNDWATER IN THE MISSISSIPPI GROUNDWATER IN THE MISSISSIPPI RIVER VALLEY ALLUVIAL AQUIFER -RIVER VALLEY ALLUVIAL AQUIFER -
SOUTHEASTERN ARKANSAS SOUTHEASTERN ARKANSAS
CHRIS KING, P.G.CHRIS KING, P.G.
Agriculture in southeastern Agriculture in southeastern ArkansasArkansas
Irrigation of row crops (rice, soybeans, Irrigation of row crops (rice, soybeans, cotton) and aquaculture (catfish) results in cotton) and aquaculture (catfish) results in intensive use of alluvial aquiferintensive use of alluvial aquifer
Mississippi River Valley alluvial aquifer is Mississippi River Valley alluvial aquifer is the source of 97% of groundwater usedthe source of 97% of groundwater used
Isolated areas in Ashley, Desha, and Isolated areas in Ashley, Desha, and Chicot Counties have >100 mg/L ClChicot Counties have >100 mg/L Cl
Many areas with high Cl and TDS Many areas with high Cl and TDS concentrations are less than 5 miles in concentrations are less than 5 miles in diameterdiameter
Large area of the alluvial aquifer in Chicot Large area of the alluvial aquifer in Chicot County contains TDS concentrations County contains TDS concentrations exceeding 1,000 mg/Lexceeding 1,000 mg/L
Numerous studies have been done, Numerous studies have been done, however no clear explanation as to originhowever no clear explanation as to origin
FIGURE 2 - HIGH TDS AREAS OF SOUTHEAST ARKANSAS – NORTHEAST LOUISIANAHUFF AND BONCK, 1993
AREA II
AREA I(Kresse, 2008)
(Kresse, 2008)
Cl concentrations >70 mg/L are unsuitable Cl concentrations >70 mg/L are unsuitable for rice plantsfor rice plants
Elevated Na levels are associated with Elevated Na levels are associated with higher salinity groundwaterhigher salinity groundwater
High Na in irrigation water results in High Na in irrigation water results in deterioration of soil structure (flocculation) deterioration of soil structure (flocculation) and decreased permeabilityand decreased permeability
Structural Features of the Lower Structural Features of the Lower Mississippi ValleyMississippi Valley
Mississippi Embayment is dominant Mississippi Embayment is dominant structural feature in this areastructural feature in this area
Represents northern arm of the Gulf Represents northern arm of the Gulf Coastal Plain sediment wedge of Tertiary Coastal Plain sediment wedge of Tertiary and Quaternary depositsand Quaternary deposits
The wedge of sediments thickens The wedge of sediments thickens tremendously south of a line of marginal tremendously south of a line of marginal faults in southern Arkansasfaults in southern Arkansas
The study area is located between the The study area is located between the South Arkansas and Pickens-Gilbertown South Arkansas and Pickens-Gilbertown fault zonesfault zones
Between these fault zones is a large gap Between these fault zones is a large gap where marginal faults haven’t been mappedwhere marginal faults haven’t been mapped
Two structural features in this area are the Two structural features in this area are the Monroe Uplift and Desha BasinMonroe Uplift and Desha Basin
FORMATION OF THE MISSISSIPPI FORMATION OF THE MISSISSIPPI EMBAYMENTEMBAYMENT
Late in the Precambrian Era (>600 mya), rifting occurs along eastern Arkansas as continents drift apart
Guccione, M.J., 1993
Formation of the Mississippi Formation of the Mississippi EmbaymentEmbayment
Late Cretaceous rifting and structural Late Cretaceous rifting and structural downwarping of fractured Paleozoic rocks downwarping of fractured Paleozoic rocks produced a southward plunging synclineproduced a southward plunging syncline
The axis of the syncline approximates the The axis of the syncline approximates the present course of the Mississippi Riverpresent course of the Mississippi River
EARLY TERTIARY PERIOD
3 major marine transgressions (sea level rises) in Mississippi Embayment:
• Sediments deposited in streams, swamps, and shallow coastal environments
• Deposition of sand and clay, with lignite coal accumulation in swamps
Source: National Geographic
LATE TERTIARY PERIOD
- Sea level much lower
- Ancestral Mississippi River forms in a well-defined but narrow and shallow valley
Source: National Geographic
Quaternary Period (<1.6 MYA)Quaternary Period (<1.6 MYA)
Several major glacial periods provide massive amounts Several major glacial periods provide massive amounts of coarse sediment to the lower Mississippi Valley:of coarse sediment to the lower Mississippi Valley:
Mississippi River is a braided stream flowing in a Mississippi River is a braided stream flowing in a wide, shallow valleywide, shallow valley
Sand and gravel deposited in a series of channels Sand and gravel deposited in a series of channels that migrate across the valleythat migrate across the valley
Periodic wind storms blow fine sand and silt out of Periodic wind storms blow fine sand and silt out of channels (deposited in dunes and ridges)channels (deposited in dunes and ridges)
Mississippi River erodes Tertiary sediments Mississippi River erodes Tertiary sediments on west of Crowley’s Ridge, Ohio River on on west of Crowley’s Ridge, Ohio River on the eastthe east
Eventually the Mississippi River cuts through Eventually the Mississippi River cuts through Crowley’s Ridge near Cairo, IllinoisCrowley’s Ridge near Cairo, Illinois
Approximately 10,000 years ago glaciation Approximately 10,000 years ago glaciation ends, Mississippi switches from a braided to ends, Mississippi switches from a braided to meandering streammeandering stream
MISSISSIPPI RIVER VALLEY ALLUVIAL AQUIFERMISSISSIPPI RIVER VALLEY ALLUVIAL AQUIFER
Quaternary alluvial deposits adjacent to Mississippi Quaternary alluvial deposits adjacent to Mississippi River:River:
- Clay and silt serves as a semi-confining unit above- Clay and silt serves as a semi-confining unit above
- Sand and gravel in middle to lower part of alluvium- Sand and gravel in middle to lower part of alluvium
Sands and gravels function as the Mississippi Sands and gravels function as the Mississippi Alluvial Valley AquiferAlluvial Valley Aquifer
Beneath gravel are Tertiary age Jackson and Claiborne Group:
• Top of formation represents an unconformity (erosion surface)
• Deposited in coastal environment
• Low-permeability clays, silts, and highly permeably sands
• Deposits occur as discontinuous lenses with variable thicknesses
FIGURE 1 – CROSS-SECTION THROUGH THE ALLUVIAL AQUIFERIN ASHLEY AND CHICOT COUNTIES
From: Gonthier and Mahon, 1992
TERTIARY DEPOSITS
ALLUVIAL AQUIFER
UPPER CONFINING UNIT
CROSS-SECTION OF ALLUVIAL AQUIFER(WEST-EAST THROUGH CENTRAL ASHLEY & CHICOT COUNTIES)
MRVA CONFINING UNIT
TERTIARY AGE DEPOSITS
MRVA AQUIFER
BASAL GRAVEL
Gonthier, G.J. and Mahon, G.L., 1992
The Tertiary Age Jackson Group and underlying The Tertiary Age Jackson Group and underlying Cockfield and Cook Mountian Formations are Cockfield and Cook Mountian Formations are sometimes referred to as the “upper Claiborne sometimes referred to as the “upper Claiborne and Jackson Group undifferentiated”and Jackson Group undifferentiated”
FIGURE 5 - GEOLOGIC CROSS SECTION THROUGH SOUTHEASTERN ARKANSAS
From Fitzpatrick, D.J., 1985
Difficult to distinguish w/Discontinuous sand beds
Approx. 2800’ - Cretaceous
RechargeRecharge
The alluvial aquifer is confined from above The alluvial aquifer is confined from above where the overlying clay and silt is thick and where the overlying clay and silt is thick and continuouscontinuous
Most recharge occurs from infiltration in point Most recharge occurs from infiltration in point bar deposits and along major streams during bar deposits and along major streams during high stages.high stages.
An estimated net recharge of 0.5 in/yr occurs by An estimated net recharge of 0.5 in/yr occurs by upward flow through the base of the aquifer from upward flow through the base of the aquifer from Tertiary and Cretaceous age aquifersTertiary and Cretaceous age aquifers
Groundwater Flow in Alluvial Groundwater Flow in Alluvial AquiferAquifer
Flow within the alluvial aquifer is in the Flow within the alluvial aquifer is in the direction of hydraulic gradient, south-direction of hydraulic gradient, south-southeastsoutheast
Intense pumping for irrigation creates local Intense pumping for irrigation creates local hydraulic gradients, capable of causing hydraulic gradients, capable of causing plume migrationplume migration
FIGURE 9 – POTENIOMETRIC SURFACE OF THE MISSISSIPPI RIVER VALLEY ALLUVIAL AQUIFER, SPRING 2004
From: Schrader, T.P., 2006
Lower Confining UnitLower Confining Unit
Thinning of the Cockfield surface through Thinning of the Cockfield surface through channel erosion has occurred in southern channel erosion has occurred in southern Chicot CountyChicot County
Upward flow from below is possible in Upward flow from below is possible in areas where the Cockfield is thin or absentareas where the Cockfield is thin or absent
Saltwater may flow from southern Chicot Saltwater may flow from southern Chicot County into Louisiana via a fluvial channel County into Louisiana via a fluvial channel eroded into the surface of the Cockfield eroded into the surface of the Cockfield Fm.Fm.
FIGURE 8 - SURFACE OF TERTIARY JACKSON FORMATION WITH TDS CONCENTRATIONS FROM ALLUVIAL AQUIFER PLOTTED
From: Huff and Bonck, 1993
Regional Flow ModelRegional Flow ModelHuff and Bonck, 1993Huff and Bonck, 1993
Precipitation falling on the outcrop areas west of Precipitation falling on the outcrop areas west of the Mississippi Alluvial Plain flows eastward and the Mississippi Alluvial Plain flows eastward and downgradient through the Sparta and deeper downgradient through the Sparta and deeper Carrizo-Wilcox aquifersCarrizo-Wilcox aquifers
Deeply circulating groundwater comes into Deeply circulating groundwater comes into contact with waters with TDS concentrations of contact with waters with TDS concentrations of 3,000 to >10,000 mg/L3,000 to >10,000 mg/L
Upward flow occurs further east and may enter Upward flow occurs further east and may enter the alluvial aquifer from below where the lower the alluvial aquifer from below where the lower confining unit has been erodedconfining unit has been eroded
Generalized section showing regional geology and hydrology in the Mississippi River Alluvial Plain
From: Huff and Bonck, 1993
Regional Flow ModelRegional Flow ModelMason, P.G., 2001Mason, P.G., 2001
The linear NW to SE trend of the Desha Basin The linear NW to SE trend of the Desha Basin may have at first been a preferential pathway for may have at first been a preferential pathway for flow into the Cockfield, but where the syncline flow into the Cockfield, but where the syncline closed to the southeast, flow may have been closed to the southeast, flow may have been restricted, trapping Cl-rich watersrestricted, trapping Cl-rich waters
The Midway group has a dip of approximately 25 The Midway group has a dip of approximately 25 feet per mile toward the axis of the Desha Basinfeet per mile toward the axis of the Desha Basin
Very little deep-aquifer data is available for Very little deep-aquifer data is available for southeastern Arkansassoutheastern Arkansas
Bedinger and Reed, 1961. Bedinger and Reed, 1961. Water Resources Circular No. 6, Geology and Ground-Water Resources Circular No. 6, Geology and Ground-
water Resources of Desha and Lincoln Counties, Arkansaswater Resources of Desha and Lincoln Counties, Arkansas
““The bottom of the Sparta sand marks the The bottom of the Sparta sand marks the maximum depth at which fresh water can maximum depth at which fresh water can be obtained.”be obtained.”
500’
Sea Level
U.S. GEOLOGICAL SURVEY HYDROLOGIC INVESTIGATIONS ATLAS HA-309“Geohydrology of the Coastal Plain Aquifers of Arkansas”
Chemistry of Alluvial Aquifer Chemistry of Alluvial Aquifer GroundwaterGroundwater
Chemical constituents in groundwater vary Chemical constituents in groundwater vary widely across the Mississippi alluvial plainwidely across the Mississippi alluvial plain
In Arkansas rainwater, virtually all of the In Arkansas rainwater, virtually all of the Na, Cl, and Mg originate from seawaterNa, Cl, and Mg originate from seawater
Evapotranspiration alone can theoretically Evapotranspiration alone can theoretically produce TDS near 100 mg/Lproduce TDS near 100 mg/L
Cation exchange occurs in clays of the Cation exchange occurs in clays of the unsaturated zoneunsaturated zone
Kresse and Fazio, 2002Kresse and Fazio, 2002
Chemistry of Alluvial Aquifer Chemistry of Alluvial Aquifer Groundwater (cont.)Groundwater (cont.)
From Fitzpatrick, D.J., 1985
4 MILES
FIGURE 10 – NORTH-SOUTH TRENDING BAND OF ELEVATED CHLORIDE CONCENTRATIONS IN CHICOT COUNTY
Mixing from another source can Mixing from another source can produce waters with TDS >350 mg/Lproduce waters with TDS >350 mg/L
Poor quality water sources cited include:Poor quality water sources cited include:- De-watering of clay lenses/confining units De-watering of clay lenses/confining units
storing ancestral waterstoring ancestral water- Upward recharge from Tertiary and older Upward recharge from Tertiary and older
aquifers along faults or updipaquifers along faults or updip- Irrigation returns flows along with high Irrigation returns flows along with high
evapotranspiration and ion exchange in evapotranspiration and ion exchange in the soil zonethe soil zone
- Recharge from rivers- Recharge from rivers
Areas further within the alluvial Areas further within the alluvial aquifer flow system have higher aquifer flow system have higher
TDS concentrations due to TDS concentrations due to increased residence timeincreased residence time
As recharge enters the flow path near the As recharge enters the flow path near the fall line, it picks up calcium in the soil zonefall line, it picks up calcium in the soil zone
More calcium, along with other dissolved More calcium, along with other dissolved constituents, are picked up along the flow constituents, are picked up along the flow path during rock-water interactionpath during rock-water interaction
Cooper, C.D., 2002
SPECIFIC CONDUCTANCE IN THE ALLUVIAL AQUIFER VERSUS WATER LEVELS
Cooper, C.D., Wilson, A.D., Davis, R.K., and Steele, K.F., 2001
Hypotheses that may explain Hypotheses that may explain spatial variations in concentrations spatial variations in concentrations
of specific chemical parametersof specific chemical parameters
Movement of water from deeper Tertiary Movement of water from deeper Tertiary and older units either along faults or updipand older units either along faults or updip
De-watering of clay lenses/confining units De-watering of clay lenses/confining units that may be storing connate paleo-waters that may be storing connate paleo-waters of differing chemistry through increased of differing chemistry through increased pumpingpumping
Cooper, C.D., 2002
GROUNDWATER WITHDRAWALSGROUNDWATER WITHDRAWALS
Increased pumping of groundwater for Increased pumping of groundwater for irrigation is the most significant irrigation is the most significant development in southern Arkansasdevelopment in southern Arkansas
When the rate of groundwater withdrawal When the rate of groundwater withdrawal is sufficient to strongly influence flow, is sufficient to strongly influence flow, areas of higher salinity may increase in areas of higher salinity may increase in extent or migrateextent or migrate
Spatial distributions of Spatial distributions of hydrochemical variations do not hydrochemical variations do not suggest that increased pumping suggest that increased pumping has modified the geochemistry of has modified the geochemistry of the alluvial and Sparta aquifersthe alluvial and Sparta aquifers
Cooper, C.D., 2002
Kresse, 1999.Kresse, 1999. “Ground-water Resources and Water Quality in the “Ground-water Resources and Water Quality in the Vicinity of the Pine Bluff Municipal Area – Jefferson Vicinity of the Pine Bluff Municipal Area – Jefferson
County, Arkansas.”County, Arkansas.”
Water Quality in the Sparta, Cockfield, Water Quality in the Sparta, Cockfield, and alluvial aquifers of Jefferson and alluvial aquifers of Jefferson County do not show evidence of County do not show evidence of increases in major cations and anions increases in major cations and anions when compared to historical data.when compared to historical data.
Median TDS values for the Sparta Median TDS values for the Sparta aquifer were within 1 mg/L from the aquifer were within 1 mg/L from the early 1950’s to 1999, despite a large early 1950’s to 1999, despite a large cone of depression which developed cone of depression which developed resulting in water levels dropping resulting in water levels dropping approximately 250 feetapproximately 250 feet
Chicot CountyChicot County
An area of high TDS concentrations is An area of high TDS concentrations is located near a major magnetic anomalylocated near a major magnetic anomaly
Suggests upward transport of saline fluids Suggests upward transport of saline fluids via fault(s) from a deeper aquifervia fault(s) from a deeper aquifer
Areas of localized faultingAreas of localized faulting
High Cl concentrations are found in an High Cl concentrations are found in an area 5 miles north of Greenville, area 5 miles north of Greenville, Mississippi in the Cockfield aquiferMississippi in the Cockfield aquifer
This area is also known for anomalously This area is also known for anomalously high hydraulic gradients and pH, which high hydraulic gradients and pH, which suggests the presence of faultingsuggests the presence of faulting
Mason, P.G., 2001
Deep wells in southern ArkansasDeep wells in southern Arkansas
Very few wells draw from aquifers below the Very few wells draw from aquifers below the SpartaSparta
Below the Sparta and Wilcox Formation is the Below the Sparta and Wilcox Formation is the thick Midway shale, a major barrier to fluid flowthick Midway shale, a major barrier to fluid flow
Below the Tertiary section is a thick sequence of Below the Tertiary section is a thick sequence of carbonatescarbonates
Near the center of the Monroe Uplift these Near the center of the Monroe Uplift these carbonates form productive Cretaceous and carbonates form productive Cretaceous and Jurassic petroleum reservoirsJurassic petroleum reservoirs
FIGURE 3 - STRUCTURAL FEATURES OF THE LOWER MISSISSIPPI RIVER VALLEY
Kresse and Fazio, 2002
DESHA BASIN
OIL & GAS TEST WELLS IN SOUTHEASTERN ARKANSAS
As of 2008, AOGC database lists 116 wells having been drilled in Ashley County; 39 in Chicot County
Many are at least 5,000 feet deepArkansas Geological Survey
Pathways for intrusion of deeper Pathways for intrusion of deeper saline groundwater into alluvial saline groundwater into alluvial
aquiferaquifer
Direct or indirect migration along a deep faultDirect or indirect migration along a deep fault
Upward flow from below where the Cockfield/Jackson Upward flow from below where the Cockfield/Jackson confining unit is thinconfining unit is thin
Dewatering of clay lenses or confining unitsDewatering of clay lenses or confining units
Upward movement from underlying Sparta due to high Upward movement from underlying Sparta due to high pumping rates in alluvial aquifer (Cl concentrations in parts pumping rates in alluvial aquifer (Cl concentrations in parts of Sparta aquifer are not as high as those in overlying of Sparta aquifer are not as high as those in overlying Cockfield aquifer)Cockfield aquifer)
Movement through abandoned oil and gas test holesMovement through abandoned oil and gas test holes
MOSTACCEPTEDSCENARIOS
Areas for further researchAreas for further research
Geochemical modeling of existing dataGeochemical modeling of existing data
Collection of site-specific data from areas with elevated Cl Collection of site-specific data from areas with elevated Cl concentrations:concentrations:
- Coring and analysis of saturated and unsaturated zone- Coring and analysis of saturated and unsaturated zone- Sample wells over a growing season for trends- Sample wells over a growing season for trends- Monitor water levels in the same wells over time- Monitor water levels in the same wells over time- Examine local and regional soil types- Examine local and regional soil types
REFERENCESREFERENCES
Armstrong, O.P., 2005, “An Overview of Mississippi Embayment Petroleum Potential of NE Arkansas,” unpublished online report.
Bedinger, M.S. and Reed, J.E., 1961, “Geology and Ground-Water Resources of Desha and Lincoln Counties, Arkansas,” Water Resources Circular No. 6, Arkansas Geological and Conservation Commission.
Fitzpatrick, D.J., 1985, “Occurrence of Saltwater in the Alluvial Aquifer in the Boeuf-Tensas Basin, Arkansas,” U.S. Geological Survey Water-Resources InvestigationReport 85-4029.
Cooper, C.D., 2002, “Spatial Characterization of Hydrochemistry for the Alluvial and Sparta Aquifers of the Grand Prairie Region, Eastern Arkansas,” University of ArkansasM.S. Thesis.
Cooper, C.D., Wilson, A.D., Davis, R.K., and Steele, K.F., 2001, “Hydrochemical Characterization for the Alluvial and Sparta Aquifers of Eastern and South-Central Arkansas:Final Data Report,” University of Arkansas and Arkansas Water Resources Center.
Cox, R.T., Larsen, D., Forman, S.L., Woods, J., Morat, J., and Galluzzi, J., 2004, “Preliminary Assessment of Sand Blows in the Southern Mississippi Embayment,” Bulletin ofthe Seismological Society of America, Vol. 94, No. 3, pp. 1125-1142.
Greene, B.G., “Shrimp Culture in Low-Salinity Water in Arkansas,” USDA-ARS unpublished technical presentation, date unknown.
Gonthier, G.J. and Mahon, G.L., 1992, “Thickness of the Mississippi River Valley Confining Unit, Eastern Arkansas,” U.S. Geological Survey Water-Resources InvestigationsReport 92-4121.
Guccione, M.J., 1993, “Geologic History of Arkansas Through Time and Space,” University of Arkansas with funding by the National Science Foundation, 63 pp.
Hosman, R.L., 1969, “Geohydrology of the Coastal Plain Aquifers of Arkansas,” U.S. Geological Survey Hydrologic Investigations Atlas HA-309.
Hosman, R.L., 1996, “Regional Stratigraphy and Subsurface Geology of Cenozoic Deposits, Gulf Coastal Plain, South-Central United States,” U.S. Geological SurveyProfessional Paper1416-G.
Huff, G.F., and Bonck, J.P., 1993, “Saltwater in shallow aquifers in east central and northeastern Louisiana and southeastern Arkansas.” U.S. Geological Survey Open FileReport 93-494.
Kresse, T.M., 2008, “Occurrence, Distribution, and Source of Elevated Chlorides in the Mississippi River Valley Alluvial Aquifer in Southeastern Arkansas,” 2008 South-Central Geological Society of America Annual Meeting Abstracts with Programs.
Kresse, T.M. and Fazio, J.A., 2002, “Pesticides, Water Quality and Geochemical Evolution of Ground Water in the Alluvial Aquifer, Bayou Bartholomew Watershed, Arkansas,” Arkansas Department of Environmental Quality Water Quality Report WQ02-05-1.
Mason, P.G., 2001, “Monitored Salinity and Water Levels in the Cockfield Aquifer, Washington County, Mississippi,” Mississippi Department of Environmental Quality, Hydrologic Investigations Report 2001-1.
Reed, T.B., 2004, “Status of Water Levels and Selected Water-Quality Conditions in the Mississippi River Valley Alluvial Aquifer in Eastern Arkansas, 2002,” U.S. Geological Survey Scientific Investigations Report 2004-5129.
Schrader, T.P., 2006, “Status of Water Levels and Selected Water-Quality Conditions in the Mississippi River Valley Alluvial Aquifer in Eastern Arkansas, 2004,” U.S. Geological Survey Scientific Investigations Report 2006-5128.
U.S. Geological Survey Fact Sheet FS-041-02, 2002, “The Mississippi River Alluvial Aquifer in Arkansas: A Sustainable Water Resource?”
U.S. Geological Survey Fact Sheet 2005-3008, 2005, “Ground-Water Models of the Alluvial and Sparta Aquifers: Management Tools for a Sustainable Resource.”
Zachry, D.L, Steele, K.F., Wood, L.J., and Johnston, D.H., “Stratigraphy and Hydrology of Upper Cretaceous and Tertiary Strata, Columbia and Union Counties, Arkansas,” University of Arkansas, 1986.