SMALL-SCALE SPATIAL VARIATION OF WATER QUALITY WITHIN THE MISSISSIPPI RIVER VALLEY ALLUVIAL AQUIFER...
Transcript of SMALL-SCALE SPATIAL VARIATION OF WATER QUALITY WITHIN THE MISSISSIPPI RIVER VALLEY ALLUVIAL AQUIFER...
SMALL-SCALE SPATIAL SMALL-SCALE SPATIAL VARIATION OF WATER QUALITY VARIATION OF WATER QUALITY WITHIN THE MISSISSIPPI RIVER WITHIN THE MISSISSIPPI RIVER
VALLEY ALLUVIAL AQUIFER VALLEY ALLUVIAL AQUIFER ARKANSAS, USAARKANSAS, USA
SMALL-SCALE SPATIAL SMALL-SCALE SPATIAL VARIATION OF WATER QUALITY VARIATION OF WATER QUALITY WITHIN THE MISSISSIPPI RIVER WITHIN THE MISSISSIPPI RIVER
VALLEY ALLUVIAL AQUIFER VALLEY ALLUVIAL AQUIFER ARKANSAS, USAARKANSAS, USA
Ken SteeleKen Steele11, Tim Kresse, Tim Kresse22 and Ralph Davis and Ralph Davis11
11Department of Geosciences, University of Department of Geosciences, University of Arkansas, Fayetteville Arkansas, Fayetteville 22Water Division, Arkansas Water Division, Arkansas
Dep.t of Environmental Quality, Little RockDep.t of Environmental Quality, Little Rock
OBJECTIVEOBJECTIVE
To ascertain spatial variability of major ion concentrations on small scale within the alluvial
aquifer in Arkansas
To ascertain spatial variability of major ion concentrations on small scale within the alluvial
aquifer in Arkansas
Pulaski County
ARKANSAS
CountyWoodruff
CountyMonroe
Alluvial
Aquifer
U S A
Alluvial Aquifer
Composition
Sand, silt, clay grades downward to sand and gravel (~ 45 m thick)
Discontinuous lenses of clay, silt or sandy silt
Overlying unit (6 m thick) composed of fine silt and clay
Mineralogical heterogeneity
Rainfall1270 mm annually but little recharge during summer
Yield 3,785 to 11,355 liters per minute
Site Descriptions
Site Site CropsCropsSoil Mapping Soil Mapping
UnitUnitReliefRelief
mm
Well DepthsWell Depths
mm
Water DepthWater Depth
mm
PulaskiPulaski
CountyCounty
Soybean
Vegetables
Keo & Rilla –well drained
Perry – clayey ~ 0.45
Shallow 9 - 10
Deep 24 – 30
Shallow 7-9
Deep ~ 8
MonroeMonroe
CountyCountySoybean
RiceFoley & Dundee-
poorly drained
~ 0.3 Shallow 8 - 9
Deep 30 - 34
Shallow 4 - 5
Deep ~ 5
WoodruffWoodruff
CountyCountySoybean
Dubbs –permeable
Amagon-more clay
~ 0.3Shallow 9 -15
Deep 24 - 30
Shallow ~ 6
Depth ft P-X P-Y P-Z
Depth ft M-Y M-Z M-R
0-5 silt silt sand 0-2 sand
5-10silt
claysilt
claysand
2-4clay silt sand
10-15
clay clay sand
clay clay4-6
clay clay sand
15-20 sand silt silt 6-8 sand sand sand20-22 sand sand sand 8-10 sand silt sand22-14 sand sand sand 10-12 sand sand sand
12-14 sand sand sand14-16 sand sand16-18 sand18-20 sand
Pulaski County Site Monroe County Site
Monroe County 3 shallow monitoring wells
3 deep irrigation wells Pulaski County
3 shallow monitoring wells 1 domestic well
3 deep irrigation wellsMonitoring wells 20 - 212 m apart
Irrigation wells 1.3 km apart
Irrigation wells 0.8 km from monitoring wells
Woodruff County 4 monitoring wells
1 domestic well
Sample Collection
SiteShallow
monitoring and domestic wells
Deep irrigation
wells
Monroe
Pulaski
counties
June 24-25 2002
August 11-12, 2002August 11-12
2002
Woodruff
County June 18
1996None
Monroe County
Shallow Monitoring wells ~ 30 feet deep
Deep Wells ~ 100 feet
SmallSmall
scalescale
00 500500
FeetFeet
SepticSeptic tanktank
PulaskiPulaski
CountyCounty
MonroeMonroe
CountyCounty
Monitoring Monitoring WellWell
Monroe County Monroe County Pig penPig pen
14.45
Monroe County
High SOHigh SO44, ,
Cl, and Cl, and NONO33
0
5
10
15
20
25
30
35
40
0 10 20 30 40
Recharge Cl mg/L
No
n-r
ech
arg
e C
l m
g/L
TemporalTemporal
Spatial Spatial VariationVariation
Plots of recharge versus non-recharge periods ion concentrations allow simultaneous comparison of spatial and temporal variations
Recharge Conditions
Wells assigned recharge or non-recharge conditions based on:
• Typical recharge period (October – June)
Septic tank effluent and Irrigation return flow recharge not likely
• Best scientific judgment based on:
Rainfall Ground water levels
0
10
20
30
40
50
60
70
0 20 40 60 80
Recharge SO4
No
n-r
ech
arg
e S
O4
Monroe-SPulaski-SMonroe-DPulaski-DWoodruff-S
0
5
10
15
20
25
30
35
40
0 10 20 30 40
Recharge Cl mg/L
No
n-r
ec
ha
rge
C
l m
g/L
Monroe-SPulaski-SMonroe-DPulaski-DWoodruff-S
0
50
100
150
200
250
300
350
400
450
0 50 100 150 200 250 300 350 400 450
Recharge HCO3 mg/L
No
n-r
ech
arg
e H
CO
3 m
g/L
Monroe-S
Pulaski-S
Monroe-D
Pulaski-D
Woodruff-S
max/minmax/min
MM P P WW
Shallow Shallow 1.9 1.6 4.11.9 1.6 4.1
Deep Deep 1.91.9 1.7 1.7
max/minmax/min
MM P P WW
Shallow Shallow 3.7 4.9 4.43.7 4.9 4.4
Deep Deep 1.41.4 4.7 4.7
max/minmax/min
M M P W P W
Shallow Shallow 3.7 4.9 4.43.7 4.9 4.4
Deep Deep 1.41.4 4.7 4.7
0
10
20
30
40
50
60
70
80
0 10 20 30 40 50 60 70 80
Recharge Ca mg/L
Non
-rec
harg
e C
a m
g/L
Monroe-S
Pulaski-S
Monroe-D
Pulaski-D
Woodruff-S
0
10
20
30
40
50
60
70
0 10 20 30 40 50 60 70
Recharge Na mg/L
Non
-rec
harg
e N
a m
g/L
Monroe-SPulaski-SMonroe-DPulaski-DWoodruff-S
0
5
10
15
20
25
30
0 10 20 30
Recharge Mg mg/L
No
n-r
ech
arg
e M
g m
g/L
Monroe-S
Pulaski-SMonroe-D
Pulaski-DWoodruff-S
0
1
2
3
4
5
0 1 2 3 4 5
Recharge K mg/L
Non
-rec
harg
e K
mg/
L
Monroe-SPulaski-SMonroe-DPulaski-DWoodruff-S
max/min max/min
M P WM P W
Shallow Shallow 5.3 1.8 3.55.3 1.8 3.5
Deep Deep 2.02.0 -- --
max/minmax/min
MM P P W W
Shallow Shallow 2.9 1.6 4.52.9 1.6 4.5
Deep Deep 2.02.0 -- --
max/minmax/min
MM P P W W
Shallow Shallow 2.9 1.7 >6.72.9 1.7 >6.7
Deep Deep 1.51.5 1.3 1.3
max/minmax/min
M P WM P W
Shallow Shallow ---- 5.4 5.4 -- --
Deep Deep -- -- -- -- -- --
0
2
4
6
8
10
12
14
0 0.5 1 1.5 2(Ca+Mg)/HCO3 meq
(Na+
K)/
Cl
meq
Monroe-NPulaski-NM Wells NP Wells NMonroe - RPulaski - RWoodruff-S
All points to the left are shifted to the right within the acceptable
ratio zone when Na+K are added to Ca+Mg
These two points are moved to the left within the acceptable ratio zone
when SO4 is substracted
from Ca+Mg.
Calcite-richCalcite-rich
unitunit
Clay-richClay-rich units
Clay-richClay-rich
unitunit
Non-rechargeNon-recharge
period waterperiod water
tabletable
RechargeRecharge
period waterperiod water
tabletable
RechargeRecharge
period waterperiod water
tabletable
Sandy siltSandy silt
Sandy siltSandy silt
WellsWells
CONCLUSIONSCONCLUSIONS
• There is prevalent and extensive small-There is prevalent and extensive small-scale spatial variation of ion scale spatial variation of ion concentrationsconcentrations
• There is temporal variation for Ca, Mg, There is temporal variation for Ca, Mg, Na, SONa, SO44, HCO, HCO33
• Significant cation exchange occurs for Significant cation exchange occurs for Ca and Na (and some for Mg and K)Ca and Na (and some for Mg and K)
• Deep wells may or may not have ion Deep wells may or may not have ion concentrations greater than shallow concentrations greater than shallow wellswells
CONCLUSIONS (continued)CONCLUSIONS (continued)
• Spatial variation of water quality is attributed Spatial variation of water quality is attributed to:to:–discontinuous sand, silt and clay lenses discontinuous sand, silt and clay lenses
with heterogeneous mineralogywith heterogeneous mineralogy–differences in residence timedifferences in residence time
–lower water tables can allow fine-grained lower water tables can allow fine-grained sediment units to de-water thus increasing sediment units to de-water thus increasing ion concentrationsion concentrations
• Temporal variation is caused by:Temporal variation is caused by:
–fluctuating water tables that can fluctuating water tables that can change flow pathschange flow paths
SUMMARYSUMMARY
Complex physical and mineralogical Complex physical and mineralogical heterogeneity of the alluvial aquifer heterogeneity of the alluvial aquifer sediments and varying recharge sediments and varying recharge cause significant variability of the cause significant variability of the ground-water chemistryground-water chemistry
0
5
10
15
20
25
30
35
40
0 10 20 30 40
Recharge Cl mg/L
No
n-r
ech
arg
e C
l m
g/L
Monroe-SPulaski-SMonroe-D
Pulaski-DWoodruff-S
max/minmax/min
MM P W P W
Shallow Shallow 6.8 3.6 4.36.8 3.6 4.3
Deep Deep 1.31.3 -- --
0
10
20
30
40
50
60
70
0 10 20 30 40 50 60 70
Recharge SO4
No
n-r
ech
arg
e S
O4
Monroe-SPulaski-SMonroe-DPulaski-DWoodruff-S
max/minmax/min
MM P P WW
Shallow Shallow 3.7 4.9 4.43.7 4.9 4.4
Deep Deep 1.41.4 4.7 4.7
0
50
100
150
200
250
300
350
400
450
0 50 100 150 200 250 300 350 400 450
Recharge HCO3 mg/L
No
n-r
ec
ha
rge
H
CO
3 m
g/L
Monroe-S
Pulaski-S
Monroe-D
Pulaski-D
Woodruff-S
max/minmax/min
MM P P WW
Shallow Shallow 1.9 1.6 4.11.9 1.6 4.1
Deep Deep 1.91.9 1.7 1.7
0
10
20
30
40
50
60
70
80
0 10 20 30 40 50 60 70 80
Recharge Ca mg/L
No
n-r
ech
arg
e C
a m
g/L
Monroe-SPulaski-SMonroe-DPulaski-DWoodruff-S
max/minmax/min
MM P W P W
Shallow Shallow 2.9 1.6 4.52.9 1.6 4.5
Deep Deep 2.02.0 -- --
0
10
20
30
40
50
60
70
0 10 20 30 40 50 60 70
Recharge Na mg/L
No
n-r
ech
arg
e N
a m
g/L
Monroe-S
Pulaski-S
Monroe-D
Pulaski-D
Woodruff-S
max/minmax/min
MM P P WW
Shallow Shallow 5.3 1.8 3.55.3 1.8 3.5
Deep Deep 2.02.0 -- --
0
5
10
15
20
25
30
0 5 10 15 20 25 30
Recharge Mg mg/L
No
n-r
ech
arg
e M
g m
g/L
Monroe-SPulaski-SMonroe-DPulaski-DWoodruff-S
max/minmax/min
MM P P WW
Shallow Shallow 2.9 1.7 >6.72.9 1.7 >6.7
Deep Deep 1.51.5 1.3 1.3
0
1
2
3
4
5
0 1 2 3 4 5
Recharge K mg/L
No
n-r
ech
arg
e K
mg
/LMonroe-SPulaski-SMonroe-DPulaski-DWoodruff-S
max/minmax/min
MM P P WW
Shallow Shallow ---- 5.4 5.4 ----
Deep Deep -- -- -- -- ----