Tracing Groundwater Flowpaths in the Vicinity of San Marcos Springs, Texas August 2012 Report No. 12-0& TRACING GROUNDWATER FLOWPATHS IN THE VICINITY OF SAN MARCOS SPRINGS, TEXAS Compiled by: Steve Johnson1, Geary Schindel1, George Veni2, Nico Hauwert3, Brian Hunt4, Brian Smith4, and Marcus Gary1 1Edwards Aquifer Authority, 1615 N. St. Mary’s St., San Antonio, Texas 78215 2Executive Director, National Cave and Karst Research Institute, Carlsbad, New Mexico 3City of Austin Watershed Protection and Development Review Department, Austin, Texas 4Barton Springs Edwards Aquifer Conservation District, Austin, Texas August 2012 1615 N. St. Mary’s Street San Antonio, Texas 78215 http://www.edwardsaquifer.org ii CONTENTS EXECUTIVE SUMMARY................................................................................................................................... 1 Purpose ................................................................................................................................................... 1 Scope of Investigation ............................................................................................................................. 1 Findings of Investigations........................................................................................................................ 1 INTRODUCTION......................................................................................................................................... 2 Purpose and Scope................................................................................................................................. 2 Geologic Setting of the Edwards Aquifer................................................................................................. 2 Hydrogeology .......................................................................................................................................... 6 PREVIOUS STUDIES ....................................................................................................................................... 8 METHODOLOGY............................................................................................................................................ 10 Groundwater Tracers (Dyes)................................................................................................................. 10 Sample Collection................................................................................................................................. 11 Water Samples (Grab Sample, Autosampler)................................................................................. 12 Charcoal Receptors ........................................................................................................................ 12 Preparation and Analyses of Samples.................................................................................................. 13 EAA Analysis................................................................................................................................... 13 OUL Analysis................................................................................................................................... 13 Quality Control....................................................................................................................................... 14 Dye Standards, Duplicate and Replicate Samples, and Rinsate Samples for the EAA Laboratory ...... 15 Duplicate Samples .......................................................................................................................... 15 Detection Limits..................................................................................................................................... 15 Positive Dye-Recovery Interpretation.............................................................................................. 15 EAA Laboratory............................................................................................................................... 15 OUL................................................................................................................................................. 16 Breakthrough Curves............................................................................................................................. 16 TRACER TESTS............................................................................................................................................. 17 Testing Phases...................................................................................................................................... 17 Southwest of San Marcos Springs Traces: Ezell’s Cave and Primer’s Fissure (2002, 2004, 2005)............................................................................................................................. 17 Purpose........................................................................................................................................... 17 Setting............................................................................................................................................. 19 Injections......................................................................................................................................... 21 September 2002 Results................................................................................................................. 22 January 2004 Tracer-Test Results .................................................................................................. 22 July 2004 and July 2005 Tracer-Test Results ................................................................................. 31 Comparison of the Southwestern Tracer Tests...................................................................................... 37 West of San Marcos Springs Traces: Windy Cave and Dakota Ranch Cave (2005)...................... 37 Purpose........................................................................................................................................... 37 Setting............................................................................................................................................. 37 Injections......................................................................................................................................... 39 Results............................................................................................................................................ 39 Blanco River Tracer Tests: Bull Pasture Sink, Halifax Creek, and Johnson Swallet ............................. 44 Purpose........................................................................................................................................... 44 Setting of the Blanco River Tracer Tests......................................................................................... 44 Injection Site Selection for the Blanco River Tracer Test ................................................................ 46 iii Pre-Injection Preparation and Monitoring........................................................................................48 Injections......................................................................................................................................... 49 Results............................................................................................................................................ 50 Northern Tracer Tests: Fritz’s Cave (2008), Sink Creek (2009), and TSU Cooling Tower Leak Test (2009)............................................................................................61 Purpose........................................................................................................................................... 61 Injections......................................................................................................................................... 62 Setting of Sink Creek ...................................................................................................................... 62 Setting of Fritz’s Cave..................................................................................................................... 62 Setting of the TSU Cooling Tower................................................................................................... 62 Results of Fritz’s Cave Injections.................................................................................................... 63 Results of Sink Creek Dam #3 and TSU Cooling Tower Injections................................................. 68 Northern Traces: Rattlesnake Cave (2004, 2009), Hageman’s Well (2005) ......................................... 73 Purpose........................................................................................................................................... 73 Setting............................................................................................................................................. 73 Injections......................................................................................................................................... 74 Results of 2004 Injection................................................................................................................. 74 Results of 2009 Injection................................................................................................................. 78 Fern Bank Spring Tracer Test: Four-Hole