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Significance: Karst groundwater systems are important freshwater resources for human consumption and ecological integrity. This work advances fundamental knowledge of the fate and transport processes controlling the temporal and spatial paths of contaminants in karst system. The outcomes of the proposed research will improve the ability of scientists and engineers to assess the migration of contaminants in karst ground-water systems and, ultimately, predict and minimize the potential for exposure of these pollutants to humans and ecosystems.
The project studies the fate and transport of Superfund-related organic contaminants and the processes controlling their mobility, persistence, distribution, and paths toward potential exposures and/or remediation zones in karst groundwater systems. The project’s specific aims are directed at characterizing fate and transport processes and concentration distributions of contaminants in karst groundwater systems typified by variable conduit and/or diffusion dominated flow, as those found in northern Puerto Rico. This region is the focal area of PROTECT’s work to study exposure to Superfund hazardous chemicals and their potential contribution to high rates of preterm birth in Puerto Rico, which are the highest among U.S. jurisdictions. The project focuses on chlorinated volatile organic compounds (CVOCs) and phthalates as model contaminants because they are ubiquitous and have been shown to have potential health impacts.
Karst groundwater systems, which provide over 40% of the groundwater used for drinking in the U.S., develop in soluble rocks, such as limestone and dolomites. Flow in these systems may occur through fractures, conduits, and the rock matrix. In such systems, conduits can concentrate water and contaminants from direct sources and/or diffuse flow and convey them rapidly to potential-exposure discharge points such as springs. They can also convey contaminants to “trapping” diffuse-flow zones, which can result in long-term storage and subsequent release of contaminants. This project is developing the ability to assess and predict contaminant transport and potential exposure to contaminants in these types of aquifers. This is essential to understand and prevent health effects stemming from contaminants in the groundwater.
Project 4 uses experimental data and field measurements to characterize, quantify, and statistically model spatiotemporal contaminant distributions and transport properties. Fundamental knowledge developed from hydraulic and transport experiments in laboratory-scale models will be integrated into field-scale measurements and tracer tests through the use of geostatistical methods.
Thousands of sample historical records from hundreds of wells have been collected, compiled, categorized, and analyzed for CVOCs and phthalates. In addition, groundwater and tap water samples are collected throughout the study area. Analysis of historical contamination patterns in the karst region of northern Puerto Rico (Padilla et al. 2011) shows significant contaminant distribution beyond the demarcated sources of contamination and a strong capacity of the karst groundwater system to store and slowly release contamination. Historical data show that groundwater sources in the north coast of Puerto Rico have been contaminated for over 40 years. CVOCs are among the most frequently detected contaminants in groundwater, with over 50% of all samples and 70% of all sampled wells showing detection. Current field sampling show continued presence of CVOCs and phthalates in groundwater and tap water, which indicates that contamination remains in the groundwater in the area long after major sources have been controlled. Phthalates, including di-2-ethylhexyl phthalate (DEHP), dibutyl phthalate (DBP) and diethyl phthalate (DEP), are detected in groundwater to a lesser degree than CVOCs, but show much greater detection in tap water, indicating additional sources of contamination. Comparison of CVOC in groundwater and tap water samples suggest that groundwater contamination is reaching drinking water sources and is a potential mode of exposure.
Ingrid Padilla, Project Leader
Associate Professor in Environmental and Water Resources Engineering, Department of Civil Engineering and Surveying, University of Puerto Rico at Mayaguez
Raul Macchiavelli, Investigator
Professor, Department of Crops and Agroenvironmental Sciences, Agronomy & Soils, University of Puerto Rico at Mayagüez
Dorothy Vesper, Investigator
Associate Professor, Geology, West Virginia University
Perla Torres, Laboratory Analyst
Civil Engineering, University of Puerto Rico at Mayaguez