Tracer Studies Conducted Nearly Two Decades Apart Elucidate Groundwater Movement Through a Karst Aquifer in the Frederick Valley of Maryland

Abstract

A pair of groundwater tracer studies at a single karst test site were completed 18 years apart. The results of these studies have provided evidence of both relatively rapid advective transport via conduits and an extreme capacity for dye storage and retardation. The tracer results, coupled with other subsurface investigation data, are used to develop a conceptual model for groundwater movement through this karst aquifer in the Frederick Valley of Maryland, as well as identify implications for remediation. Three fluorescent tracer dyes used in the initial study were detected in several background monitoring locations established for the second study conducted 18 years later; demonstrating the persistence of these dyes in the aquifer. One of these dyes was not detected during the original study, providing useful information regarding flow and transport in the aquifer. At some of these sampling locations, at least one of the dyes was degraded, and would have gone undetected without the use of activated carbon samplers. Lastly, even though relatively rapid first detections occurred during both studies (as compared to non-karst groundwater systems) the majority of injected dye mass remained in the aquifer after the studies were completed. This suggests that the aquifer has a large capacity to store contaminants and that low levels of contaminants can be expected to persist in groundwater discharged from springs for a long period of time.

Improving the detection of fluorescent tracer dyes in groundwater investigations

“…White, Aley, Cobb, Weikel, and Beeman () published on extensive tracer studies conducted in a karst area with gentle topography and numerous monitoring wells and springs that were sampled. The tracer dye sampling was focused on an area about 3.5 km long by 1.8 km wide.…”

“…Both are "real-world" cases where contaminants of concern exist, where effective remediation efforts are needed, and where data resulting from groundwater tracing investigations were relied upon to identify flow paths and receptor sites as accurately and completely as possible. White, Aley, Cobb, Weikel, and Beeman (2015) published on extensive tracer studies conducted in a karst area with gentle topography and numerous monitoring wells and springs that were sampled. The…”