Superfund Research Program

Effect of Extreme Weather on Potential Exposure of Contaminant Mixtures in Karst Water Systems

Project Leader: Ingrid Y. Padilla (University of Puerto Rico at Mayaguez)
Co-Investigators: Damian E. Helbling (Cornell University), Philip Larese-Casanova, Raul Macchiavelli (University of Puerto Rico at Mayaguez), Dorothy Vesper (West Virginia University)
Grant Number: P42ES017198
Funding Period: 2010-2025

Project-Specific Links

Final Progress Reports

Year:   2019  2013 

Studies and Results

The Dynamic Transport and Exposure Pathways of Contaminants in Karst Groundwater Systems project has continued to generate a tremendous amount of environmental data and information used in the analysis of historical contamination and potential exposure patterns in the karst region of northern Puerto Rico. Over 6,600 sample historical records spanning in over 1,280 groundwater sites have been collected, compiled, categorized, and analyzed for chlorinated volatile organic compounds (CVOCs) and phthalates. The project has also established 17 groundwater monitoring stations for continuous measurements over historically wet and dry periods. In collaboration with the Human Subjects and SamplingCore and Discovery of Xenobiotics Associated with Preterm Birth project, the Dynamic Transport and Exposure Pathways of Contaminants in Karst Groundwater Systems project collected and analyzed 125 tap water samples from residences of the birth cohort participants to assess potential relationships between environmental contaminants and biomarkers found in human subjects.

Analysis of the groundwater contamination data shows distinct spatial and temporal patterns that vary for different contaminants. CVOCs are frequently found beyond sources of contamination throughout the entire study area, but major areas with carbon tetrachloride (CT), trichloroethylene (TCE), and tetrachloroethylene (PCE) are associated with superfund sites. The widespread presence of trichloromethane (TCM) and dichloromethane (DCM) in groundwater, however, shows weak association with major sources of contamination. On average, historical concentrations of TCE, PCE, CT, and DCM are above maximum concentration levels (MCLs). Total CVOC concentrations show decreasing tendencies with time, mainly because the reductions in concentration near the major centers of contamination and remedial activities. Temporal distributions of individual CVOC species show, however, that concentrations are increasing in several areas distant from the source, even after over 30 years of remediation. Changes in temporal distribution of major CVOC contaminants vary spatially, indicating high heterogeneity of the fate and transport processes in the karst system. Phthalates, including Di(2-ethylhexyl) phthalate (DEHP); dibutyl phthalate (DBP), and diethyl phthalate (DEP), are also detected in the study area, although to a much lesser extent than CVOCs. DEHP is still the most frequently detected phthalate in groundwater, and its spatial distribution tends to be associated with major contamination sites. Phthalate concentration distributions do not show a trend with time, suggesting discontinuous, but dynamic sources of contamination.

Current field sampling and analysis shows continued detection of CVOC and phthalates in groundwater and tap water. Except for TCM, CVOC concentrations tend to be higher in groundwater and lower in tap water. Phthalates on, the hand, are most frequently detected in tap water than groundwater. Differences in the distribution of specific contaminants between groundwater and tap water reflect variability in the sources of contaminants, mixing patterns, and degradation pathways. PCE is the most frequently detected CVOC in groundwater, whereas TCM is the most frequently CVOC found in tap water. For the phthalates, DEHP is most frequently detected in tap water, whereas DBP is most frequently detected in groundwater. Current measurement efforts also show that concentrations and detection frequencies of CVOC and phthalates vary for different hydrogeologic conditions, but the variations depend on the contaminant. Laboratory-scale transport experiments using tracers and aqueous TCE have generated spatially distributed fate and transport parameters. Results show that velocity and dispersion parameters are associated with regions of preferential flow paths and their magnitude and distribution are highly influenced by flow regimes. Some regions show bimodal concentrations distributions (two concentration peaks) indicating the presence of multiple interconnected preferential flow regions. TCE shows significant retardation and mass transfer limitations with respect to conservative tracers.

Previous work in this project developed hydrogel bead tracers to mimic the transport of non-aqueous phase liquids in karst aquifers. Field transport experiments at the Buckeye Creek Cave, West Virginia, show that the beads can be used as tracers in karst environments, but they require enhanced detection capabilities. Work during this funding period focused on the development an optical method for the detection of florescent hydrogel beads. The method applies enhance imagery at temporal frames to general pixel-intensity data representing the concentration of hydrogel beads.

Significance

Providing over 40% of the groundwater used for drinking in United States, karst systems supply important freshwater resources. These systems are highly vulnerable to contamination and close to 25% of Superfund sites are in karst regions. The outcomes of the research conducted by Dr. Padilla and her research team improve the ability to assess the migration of contaminants in karst groundwater and, ultimately, predict and minimize the potential for exposure of these pollutants.