Assessing Ground Water and Surface Water Interaction Through Tracer Observation

Abstract

In many cases the ability to determine and quantify groundwater and surface water interaction based upon hydraulic observations is an arduous task. The task is further complicated by possible transient interactions that can obscure chemical leakage signals observed in the groundwater system. The impetus of this paper is to provide an introduction to two studies where groundwater is being recharged from surface water sources on a relatively fast time of travel . The two test cases demonstrate the research plan for identifying groundwater-surface water interaction in an unconsolidated semi - confined aquifer and a karst setting. The study identifies emerging techniques and hypothesis testing for determination of groundwater under the direct influence of surface water and the potential role of these techniques in possib le quantification of the flux . The tracer techniques used in the research include geochemical testing, tritium/3 -helium, and microbiological molecular techniques. These inter -disciplinary studies are currently underway and this paper will provide a summary of the methodology, preliminary data and interpretation of the variant signals observable in a groundwater system from surface water interaction. Background and Purpose The purpose of the study described in this paper is to evaluate the potential role of environmental tracer tools for grou ndwater and surface water interaction. It should be noted that the study is a part of an evaluation of two ongoing studies with complimentary objectives. The two cases presented herein represent two hydrogeologic end members: 1) a typical coastal plain a quifer setting with known localized leakage and 2) a karst dominated system with suspected rapid flow paths, see Figure 1. The study is currently underway for the site in the coast plain aquifer setting and the data presented herein represents some of the preliminary data and findings. The research is in the planning phase for the karst dominated system and the discussion presented has focused on the experimental design with insights regarding the potential technology transfer and outcomes. Groundwater and Surface Water Interaction The role and scale of groundwater and surface water interaction is complex and difficult to assess with the data typically at hand. These interactions may be of interest due to the impact on river ecology (Sear et al. 1999; Wood et al 2000), to better