KARST, CONTAMINATION AND PUBLIC HEALTH: MEETING AT THE EXPOSURE POINT

The vulnerability of karst aquifers to contamination is an often-mentioned statement. Although contaminants can be readily introduced to karst systems via sinkholes and then rapidly transmitted, the physical heterogeneity of the aquifers compounds the difficulty in predicting contaminant outcomes. Knowing or predicting those outcomes at the exposure point – where humans and ecosystems encounter the water – is a critical step in assessing contaminant impacts and potential threats. A conceptual model for contaminant transport in karst systems must incorporate both aquifer and contaminant characteristics. The following factors are critical in karst aquifers: the potential for contaminant sorption onto sediments with associated deposition and transport; dilution of background concentrations during storm events; introduction of surface contaminants with storm events; the presence of physical traps that may limit movement of non-aqueous phase liquids (NAPLs); changes with hydraulic conditions; phreatic vs. vadose conditions; and transformation reactions within the aquifer. The chemical characteristics of the compounds, such as solubility, polarity, polarizability, volatility, acid-base characteristics, and NAPL density, are well known for most common contaminants but the implications for karst aquifers are not always considered. Understanding exposure point concentrations requires that the karst hydrogeology and the contaminant behavior models be integrated. Recent advances in this integration include the use multi-tracer studies for transport comparisons and in-situ reaction experiments. This talk will present a preliminary integrated conceptual model and review some recent advances on this topic.