DISCOVERING RELATIONSHIPS BETWEEN SURFACE AND GROUNDWATER VELOCITIES THROUGH DYE TRACING IN FAYETTE CO, KY

In mature karst regions, water may flow through sizeable subsurface conduits, expediting flow to surficial karst springs. The Middle-Ordovician karst of Lexington, Kentucky is an example of this type of environment, providing opportunities for geologists to study water flow.

We performed a dye trace in a single karst drainage basin in southwest Lexington, the primary objective of which was to compare surface-water velocities to groundwater velocities. Important locations within the study area include (1) the Campbell House sinkhole, (2) McConnell Springs, and (3) Preston Cave Spring.

Data were collected using activated charcoal dye receptors (CDRs) and water grab samples. Eosine (Acid Red 87) was injected into the Campbell House sinkhole during high-flow conditions on September 30, 2015. CDRs and grab samples were collected downstream at McConnell Springs (1.9 km) and Preston’s Cave Spring (3.2 km) over a period of two weeks. Sampling intervals for grab samples were every three hours the first day, and were gradually reduced to one sample per day. CDR samples were taken once per day and gradually reduced to every other day.

Dye appeared on October 1, 2015 (six hours after injection) at McConnell Springs, and peaked three hours later. Calculated conduit velocity between the Campbell House sinkhole and McConnell Springs was 5.95 cm/sec (0.133 mph), compared to 76 cm/sec (1.7 mph) for surface-water flow at McConnell Springs, making surface-water velocity approximately 13-times faster than conduit velocity. Although surface-water flow is faster than conduit flow, it is well-understood in karst geology that water flowing through karst conduits is often orders of magnitude faster than water flowing through granular material. This study is a contributory step in understanding conduit-flow velocities in the Lexington area during high-flow conditions.