New techniques for evaluating water and contaminant exchange at the groundwater-surface water interface

Coastal landfills and hazardous waste sites pose a potential environmental threat to surface water bodies through the exchange of groundwater-borne contaminants. To address this issue, we have developed and tested new techniques for identifying potential areas of groundwater impingement into surface waters, as well as techniques for quantifying the flow rates and contaminant levels of groundwater at the surface water interface. To identify potential areas where groundwater is entering the surface water, we have developed the Trident Probe, a simple direct-push system equipped with temperature, conductivity and water sampling probes. Contrast in temperature and conductivity between surface water and groundwater are used to determine likely areas of groundwater impingement. The water-sampling probe can then be used to collect samples for detailed chemical characterization of contaminants. Once areas are identified, groundwater exchange rates and contaminant fluxes can be directly quantified using a seepage meter system that incorporates continuous flow monitoring and water sampling capabilities. The seepage meters are placed at the sediment-water interface for a period of 1-4 days and record a record of the water flow across the interface. A programmable sampling system is then used to collect the seepage water samples for subsequent chemical analysis. Recent results from sites in San Diego Bay, CA show that groundwater migration can be an important process in contaminant mobility at the interface between surface water and sediment.