FATE OF DNAPLS IN EOGENETIC KARST AQUIFERS: THE CASE OF NORTHERN PUERTO RICO

Eogenetic kart aquifers have developed in carbonate rocks that have not undergone deep burial and are under active meteoritic diagenesis. In addition to well-developed conduit networks, these aquifers have significant primary porosity and permeability. As a result, contaminant fate and transport processes are influenced by combined conduit- and diffuse-flow transport mechanisms. In such systems, conduits can convey non-aqueous contaminants rapidly to potential-exposure discharge points (e.g., springs). They can also covey contaminants to diffuse-flow zones, where they can be trapped for later release. This work employs historical groundwater contamination data of chlorinated volatile organic compounds (CVOCs) to assess the fate of dense non-aqueous phase liquids (DNAPLs) that have entered the eogenetic karst aquifer of northern Puerto Rico. Data analysis indicates that a significant fraction of the DNAPLs are stored in the underground system, where they are slowly released by dissolution and desorption into flowing groundwater. As a result, groundwater shows continued level of contamination over long periods of times. The long-term source of contamination, combined with high variability of flow dynamics in the system, give rise to an extended spatial distribution of contaminants beyond the demarked sources of contamination.