FINDING GROUNDWATER-CONTAMINANT PLUMES USING MEASUREMENTS IN DISCHARGE ZONES

Subsurface heterogeneities make it difficult to predict concentrations, arrival times and discharge locations of groundwater-contaminant plumes. Although monitoring wells may appear to be serving their intended purposes, there is growing evidence that methods used to examing groundwater-surface water interaction can support traditional land-based (e.g. drilling) approaches, and that the information generated can enhance plume monitoring. This is because the groundwater-surface water interface can permit both areal reconnaissance and quantitative measurements of groundwater flow systems.

Semi-quantitative methods are towed bottom contact probes (towed slowly along the sediment water interface and measureing electrical conductivity and gamma radiation) and thermal probes (inserted a few tens of centimeters below the interface).

Quantitative methods are mini-piezometers (permanent, temporary or portable; used to measure hydraulic gradient, hydraulic conductivity and porewater concentration); seepage meters (used to measure water flux directly and in combination with piezometers providing vertical hydraulic conductivity); tracer studies; and manual coring for stratigraphic and geochemical information near the interface.

Cross checking of information from these methods can provide a level of confidence that is seldom possible from the information based on conventional hydrogeological methods.