The use of fluorescent tracers as a groundwater investigation tool Presented by: Geary M. Schindel, P.G. Chief Technical Officer Edwards Aquifer Authority San Antonio, Texas

Fluorescent Dyes: Cheap to purchase ($20 - $50 per pound) Low cost analysis ($15 - $25 per analysis) Low detectability (10 - 20 ppt) Non-toxic compounds

Fluorescent Dyes: Determine Groundwater Flowpaths Evaluate geologic controls Time of Travel Relative Vulnerability of Groundwater Resources Aquifer assimilative capacity

Can be field labor intensive Fluorescent Dyes: Can be field labor intensive Requires identification of recharge and discharge points Collection and analysis of samples Requires knowledge and experience with tracer test design COMAL SPRINGS SHOWING MONITORING POINTS, WELLS, AND INJECTION POINTS LCRA WELL PANTHER CANYON WELL

Breakthrough Curves at Landa Lake Outlet Comal Springs Discharge (366 - 352 cfs) Eosine From Panther Canyon Well Uranine from LCRA Well DYE BREAKTHROUGH CURVES FOR EOSINE AND URANINE NOTE DYE BREAKDOWN FROM LIGHT EXPOSURE DURING DAY AS DYE CROSSES LANDA LAKE Uranine results indicate photodegradation of dye as it crosses Landa Lake

Geologic Map Dolomitic Travel time - 3 miles per day Basal Nodular Cyclic & Marine

One well-designed tracer test, properly done, and correctly interpreted, is worth a 1000 expert opinions . . . or 100 computer simulations of groundwater flow Dr. James F. Quinlan Tracer tests will change your conceptual understanding of groundwater flow – towards reality Dr. E. Calvin Alexander,