data exploration: characterization of the groundwater resources of the leona aquifer lloyd hemphill...
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Data Exploration:Characterization of the
Groundwater resources of the Leona Aquifer
Lloyd Hemphill
December 3, 2002
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Introduction•Why should shallow alluvial aquifers be studied?
Convenient source of groundwater..
Abundant worldwide.
Recharge areas for deeper aquifers.
Easily contaminated.
• The Pleistocene age Leona Formation is a prime example.
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Geologic Background
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GoalsUse GIS to:
•Gather data in a useable format.
•Assess extent of existing data in space and time.
•Examine the spatial changes in water quality in the Leona Aquifer.
•Create a map to aid in locating wells.
•Compare water quality in the Leona Aquifer to surrounding aquifers.
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Data Included in Geodatabase
• National Elevation Dataset DEM for San Marcos Basin.
• USGS HUC for San Marcos Basin.• River reach data.• TX-DOT .DGN of Highways for Caldwell Co.• TWDB well data: Well locations, water levels,
and water quality.
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Topography of the Leona Formation
• Northwest to Southeast slope: 0.002 or 0.12 degrees.
• Very Flat!
•Inverted topography.
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Wells in Caldwell County, TX
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Nitrate in the Leona Aquifer (1946)
•MCL is 44.27 mg/l as Nitrate
•Note the Nitrate hotspot near Lockhart
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Nitrate in Wilcox Group Wells (1946)
•Note the Nitrate hotspot near Lockhart.
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Chloride in the Leona Aquifer (1946)
•Secondary MCL is 250 mg/l.
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Chloride Concentration Changes in Lockhart, TX
Cl in Well 6703801
20
40
60
80
100
120
140
1943 1945 1947 1949 1951
Co
nc
en
tra
tio
n (
mg
/l)
Cl in well 6703802
0
200
400
600
800
1000
1200
1942 1944 1946 1948 1950 1952
Co
nce
ntr
atio
n (
mg
/l)
Cl in Well 6703803
0
100
200
300
400
500
600
700
1935 1945 1955 1965 1975
Co
nce
ntr
atio
n (
mg
/l)
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Water Table Elevation in the Leona Aquifer (1964)
•Hydraulic gradient is very small: 0.0027 (0.15 degrees).
•Groundwater flow is to the southwest and toward the margins of the formation.
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Water Level Change in the Leona Aquifer
Water Level Change In Well #6703703
560.0562.0564.0566.0568.0570.0572.0574.0576.0
1/24/41 10/3/54 6/11/68 2/18/82 10/28/95Wate
r T
ab
le E
levati
on
(F
t)
Water Level Change In Well #6702502
596.0
598.0
600.0
602.0
604.0
606.0
608.0
610.0
12/20/62 9/15/65 6/11/68 3/8/71 12/2/73 8/28/76 5/25/79 2/18/82 11/14/84 8/11/87
Wate
r T
ab
le E
levati
on
(F
t)
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Future Work
• Add digital geologic map to geodatabase.
• Compare water level change and precipitation data.
• Examine land use to determine possible sources of NO3 and Cl.
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Questions?