Book Section
Tracer testing in the Edwards Aquifer
Johnson, S., Schindel, G.M., and Van Brahana, J.
Record Number:
5393
Year:
2019
Journal:
Geological Society of America Memoir
Pages:
283-292
Volume:
215
Editor:
Sharp, J.M., Jr., Green, R.T., and Schindel, G.M.
Book Title:
The Edwards Aquifer: The past, present, and future of a vital water resource
Abstract:
Tracer testing is established as one of the best techniques for determining groundwater
velocities and identifying groundwater flow directions in karstic systems. It has
been employed in the Edwards (Balcones Fault Zone) Aquifer since the mid-1980s.
Nontoxic, fluorescent organic dyes are most commonly used because they are comparatively
inexpensive, relatively easily accessible, detectable at low concentrations,
and not harmful to organisms that use or dwell in the aquifer or its springs. Tracer
tests provide empirical evidence that is difficult to obtain any other way. Tracer tests
have shown rapid groundwater velocities in the contributing, recharge, and artesian
zones. Groundwater velocities were found to range from 915 to 9150 m/d in the
Barton Springs segment of the aquifer; 1–3600 m/d in the San Marcos Springs area;
300–640 m/d near Comal Springs; 13 to >5300 m/d in San Antonio/northern Bexar
County; and 1–1367 m/d in Kinney County, Texas. Tracer testing has shown: (1) preferential
flow paths are conduit-dominated; (2) in places, there is a hydraulic connection
with the underlying Glen Rose Formation; (3) large offsets on faults are not
barriers to flow; and (4) portions of the aquifer act as separate pools.
Times Cited:
2