GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 29-1
Presentation Time: 9:00 AM-5:30 PM


KIRKENDALL, Alyssa Blaise, Geology, University of Texas at San Antonio, 1 UTSA Circle, San Antonio, TX 78249, SCHINDEL, Geary M., Aquifer Management, Edwards Aquifer Authority, 900 E. Quincy, San Antonio, TX 78215 and GAO, Yongli, Center for Water Research, Department of Geological Sciences, University of Texas at San Antonio, San Antonio, TX 78249

Dye tracing can help researchers determine where a hazardous spill might travel through the water, and determine the interconnectedness of streams, springs, and underground conduits. This thesis tested the effectiveness of common eluents used to extract fluorescent dye absorbed by activated charcoal used in dye tracing. The objective was to test laboratory methods of dye extraction from charcoal to determine the reliability of charcoal and processing methods for use in dye tracing. Two hypotheses were formulated and tested: 1) charcoal use in dye tracing is an effective and reliable method for obtaining data; and 2) eluted dye samples can be stored for at least one month with minimal change in concentration.

Elution solutions for charcoal vary widely across literature, so there are no standard practices for this technique. Field work and laboratory testing were performed in order to better understand some of these eluents and how they affect the dye elution process. The eluents tested were solutions of 2-propanol and sodium hydroxide (Eluent A), 2-propanol, aqua ammonia, and potassium hydroxide (Eluent B), and 2-propanol with potassium hydroxide (Eluent C).

A preliminary tracer test was performed between Cave Without a Name and Joe’s Diet Cave near Boerne in Kendall County, Texas using uranine dye. Samples were taken using both charcoal packets, automatic water samplers, and hand samples. The results found a flow velocity of approximately 0.11 miles/day between the two caves. This value agreed with a previous study.

Based on the data collected from the laboratory analysis, it was concluded that the extraction of dye from charcoal is a finnicky process, and cannot be completely relied on to determine whether dye was detected in a specific location. It was also determined that long-term storage of samples of elutant with dye should be avoided, due to potential significant changes in the dye concentration. For future work, it is recommended that the adsorption rate of charcoal is tested, and that unfiltered spring water be used to mimic actual field conditions. Different experimental designs should be tested to determine if the method used for this thesis was adequate, or if a different design should be used.