Data Exploration:Characterization of the

Groundwater resources of the Leona Aquifer

Lloyd Hemphill

December 3, 2002

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.

Geologic Background

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.

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.

Topography of the Leona Formation

• Northwest to Southeast slope: 0.002 or 0.12 degrees.

• Very Flat!

•Inverted topography.

Wells in Caldwell County, TX

Nitrate in the Leona Aquifer (1946)

•MCL is 44.27 mg/l as Nitrate

•Note the Nitrate hotspot near Lockhart

Nitrate in Wilcox Group Wells (1946)

•Note the Nitrate hotspot near Lockhart.

Chloride in the Leona Aquifer (1946)

•Secondary MCL is 250 mg/l.

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)

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.

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)

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.

Questions?