United States Region 4 Environmental Protection 345 Courtland Street, NE EPA904/6-88-001 Agency Atlanta, GA 30365 October 1988 APPLICATION OF DYE-TRACING TECHNIQUES FOR DETERMINING SOLUTE-TRANSPORT CHARACTERISTICS OF GROUND WATER IN KARST TERRANES COVER: Ground-water flow routes and pollutant dispersal in the Horse Cave and Cave City area, Kentucky, just east of Mammoth Cave National Park. Dye-tracing and mapping of the potentio- metric surface (the water table) has made it possible to determine: 1) the boundaries of ground-water basins, 2) the flow-routing of sewage effluent discharged into the aquifer, 3) the flow-routing of other of pollutants that might be dis- charged into the aquifer anywhere else in the map area, and 4) the recharge area of springs. Reliable monitoring for pollu- tants here and in most karst terranes can only be done at springs, wells drilled to intercept known cave streams, wells known to become turbid after heavy rains, and wells drilled on photo-lineaments -- but only if each site proposed for moni- toring has been shown by dye-tracing to drain from the site to be monitored. (reproduced from: Quinlan, James F., Special problems of groundwater monitoring in karst terranes, in Neilsen, David M., and Quinlan, James, F., eds., Symposium on Standards Development for Groundwater and Vadose Zone Moni- toring Investigations. American Society for Testing and Materials, Special Technical Paper, 1988. (in press) UNITED STATES ENVIRONMENTAL PROTECTION AGENCY REGION IV 345 COURTLAND STREET ATLANTA, GEORGIA 30365 Application Of Dye-Tracing Techniques For Determining Solute-Transport Characteristics Of Ground Water In Karst Terranes Prepared By U.S. Environmental Protection Agency Ground-Water Protection Branch Region IV - Atlanta, Georgia and U.S. Geological Survey Water Resources Division Kentucky District Louisville, Kentucky Approximately 20% of the United States is underlain by karst aquifers. This approximation includes roughly 50% of both Kentucky and Tennessee, substantial portions of northern Georgia and Alabama, and parts of other Region IV states. The prevalence of karst aquifers in the southeast, the common use of karst aquifers as drinking water sources and the vulner- ability of these aquifers to contamination highlighted the need to provide a mechanism to assist in ground-water management and protection in karst terranes. In an attempt to meet this need, the U.S. Environmental Protection Agency (EPA) - Region IV and the Kentucky District of the U.S. Geological Survey (USGS), have been cooperating to document the applica- tion of dye tracing techniques and concepts to ground-water protection in karst aquifers. I am pleased to announce that these efforts have resulted in the preparation of this manual, entitled, “Application Of Dye-Tracing Techniques For Determining Solute-Transport Characteristics Of Ground Water In Karst Terranes.” The information presented herein should be viewed as another analytical “tool” to assist in the management and protection of karst water supplies. Regional Administrator APPLICATION OF DYE-TRACING TECHNIQUES FOR DETERMINING SOLUTE-TRANSPORT CHARACTERISTICS OF GROUND WATER IN KARST TERRANES by D.S. Mull, T.D. Liebermann, J.L. Smoot, and L.H. Woosley, Jr., of the U.S. Geological Survey Water Resources Division Louisville, Kentucky EPA Project Officer Ronald J. Mikulak Ground-Water Protection Branch Region IV, U.S. Environmental Protection Agency Atlanta, Georgia 30365 FOREWORD The dawning of the “Age of Environmental Awareness” has been accompanied by great advances in the study of karst hydrology -- its methodology, results, and understanding. This manual is another of those advances. It describes a clever application to subsurface streams of empirical techniques for study of surface streams. It makes possible a good approximation of the time of travel, peak concentration, and flow duration of harmful contami- nants accidentally spilled into many karst aquifers and flowing to a spring or well, and it does so for various discharge condi- tions. As such, these techniques for analysis and interpretation of dye-recovery curves are powerful, useful tools for the protec- tion of water supplies. These techniques are an important complement to those essential for delineation of wellheads and springheads. For karst terranes characterized by conduit-flow, such delineation can only be done by dye-tracing, preferably guided by inferences from good potentiometric maps. Interpretation of dye-recovery curves can yield much informa- tion about the nature of groundwater flow in a karst aquifer and the structure of its conduit system, as shown in this manual, by Maloszewski and Zuber (1985), Zuber (1986), Gaspar (1987), Smart (1988), and other investigators. Similarly, much can be learned from interpretation of flood-discharge hydrography of springs, as shown by Wilcock (1968), Brown (1972), Sara (1977), Podobnik (1987), White (1988, p. 183-186), Meiman et al. (1988), and oth- ers. An unstated, implicit assumption made by the authors of this manual in their analysis of dye-recovery curves is that flow is from a single input to a single output. This is a reasonable assumption in many karst terranes, but there are five other sig- nificant types of karst networks, those with: 1. One or more additional unknown inputs; 2. One or more additional unknown outputs; 3. Both one or more additional unknown inputs and outputs; 4. Distributary flow to multiple outlets; 5. Cutarounds and braided passages. (A cutaround is a pas- sage bifurcation in which flow diverges from and then con- verges to the main conduit. The flow routes rejoin one another, but one of them is longer and/or less hydraulic- ally efficient than the other. Where convergence occurs, a second pulse, lagging behind the initial pulse, is formed in the main conduit.) The first three types of karst network are illustrated and discussed by Brown and Ford (1971), Brown (1972), and Gaspar (1987). If flow in an aquifer is through the first type, pre- dictions based on the procedures recommended in this manual will be accurate. If flow is through the second or third types, the accuracy of the predictions will tend to be inversely proportion- al to the amount of dye diverted to unknown discharge points. Distributary flow is a subtype of the second and third types of iii network; it is common in karsts of the Midwestern United States. Flow through cutarounds and braided passages induces bimodal- ity and polymodality in dye-recovery curves, as illustrated and discussed by Gaspar (1987) and Smart (1988). If such curves de- part significantly from those for a relatively simple system like that described in this manual, the accuracy of predictions in the fifth type of network will be inversely proportional to the time between the maxima and will also be affected by the number of maxima and the extent to which they are similar to the greatest maximum. Another factor that influences the shape of a dye-recovery curve is the extent to which tracer penetrates the bedrock matrix deeply enough to be influenced by adjacent fractures (Maloszewski and Zuber, 1985; Zuber, 1986). Such penetration is strongly in- fluenced by the porosity of the matrix and is inversely propor- tional to the flow velocity; matrix penetration by tracer can affect both the duration of a test and the shape of its dye- recovery curve. A karst aquifer may or may not lend itself to the dye- recovery analysis proposed in this manual. But one will not find out -- or determine the type of karst network present -- until and unless dye-tests are run and interpreted. Results of the dye-recovery analysis are vital for wellhead and springhead pro- tection, especially if flow is through a relatively simple con- duit system like that studied by the authors. It was the intention of the authors to only briefly summarize a few principles and descriptions of karst hydrology and geomor- phology; more would be beyond the intended scope of this manual. For a fuller discussion of these topics the reader is referred to the recent excellent textbook by White (1988). Similarly, and although there are much data and unique information on dye-trac- ing in this manual, the reader desiring a comprehensive how-to (and how-not-to) handbook on various dye-tracing techniques and instrumentation is referred to the enchiridion by Aley et al. (1989) . Flow velocities in karst aquifers may be tens of thousands to many millions of times faster than flow in granular aquifers. Therefore, it would be prudent for managers of water supplies in karst terranes to have the recharge areas for their springs and wells delineated and to have dye-recovery analysis done for the sites most susceptible to accidental spills of harmful contami- nants. They should do so before it is too late. Although dye- injection immediately after a spill can sometimes be used to monitor the probable arrival time of pollutants, the tracing necessary for applying the dye-recovery analysis described in this manual can only be done before the spill occurs. Dye-tracing, like neurosurgery, can be done by anyone. But when either is needed, it is judicious and most cost-efficient to iv have it done by experienced professionals, those who have already made the numerous mistakes associated with learning or those who have trained under the tutelage of an expert and learned to avoid numerous procedural errors that could have economically and physically fatal consequences. The analytical technique for dye-recovery analysis described in this manual is best applied to systems similar to the rela- tively simple but common one studied by the authors. According- ly, their approach should be widely applicable. When combined with basin delineation by dye-tracing, the two techniques repre- sent the best pre-spill hydrologic preparations available for spill-response in karst terranes. Their technique is a signifi- cant advance in the evaluation of karst aquifers.