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Reassessment of the Georgetown limestone as a hydrogeologic unit of the Edwards Aquifer, Georgetown area, Texas

Water-Resources Investigations Report 88-4190

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Abstract

A reassessment of the uppermost geologic unit of the Edwards aquifer, the Georgetown Limestone, to determine if it should continue to be classified as a unit of the Edwards aquifer, was conducted in the Georgetown area using (1) data from six surveys of streamflow gains and losses and groundwater levels, (2) aquifer tests at three clusters of test wells, and (3) variation in water quality characteristics to indicate groundwater circulation. The surveys did not show a pattern of corresponding streamflow gains and losses with positive (upward) and negative (downward) head differentials, respectively, between the main water-bearing zone of the Edwards aquifer and the streams. A consistent and corresponding pattern was shown only for the subreach containing Berry Springs. The aquifer tests consisted of ' slug ' test analyses to determine the transmissive characteristics of the Georgetown Limestone and produced hydraulic conductivity values ranging from 1.4 x 10 to the minus eighth power to 2.8 x 10 the the ninth power centimeters/sec at four of the six test wells. The other two test wells did not produce data suitable for conventional aquifer-test analysis. An analysis of the water quality characteristics indicates that the Edwards Limestone and the stream have a significant hydraulic connection but the groundwater circulation between the Edwards Limestone and the Georgetown Limestone is very limited. The only area, where a high degree of hydraulic connection between the main water bearing zone of the Edwards aquifer and the streams was found, is near the updip limits of the Georgetown where a nearby fault occurs and where major springs have developed. These findings indicate that the Georgetown Limestone does not function as a unit of the Edwards aquifer but as a regional confining bed with localized avenues that allow flow to and from the underlying Edwards aquifer. (USGS)

Additional Publication Details

Publication type:
Report
Publication Subtype:
USGS Numbered Series
Title:
Reassessment of the Georgetown limestone as a hydrogeologic unit of the Edwards Aquifer, Georgetown area, Texas
Series title:
Water-Resources Investigations Report
Series number:
88-4190
Edition:
-
Year Published:
1988
Language:
ENGLISH
Publisher:
U.S. Geological Survey,
Description:
v, 49 p. :ill., maps ;28 cm.