Assessment and Modeling of Groundwater Flow and Nitrate Contamination within Coastal Karst Aquifer of Puerto Rico

摘要

Karst aquifers, capable of store and transmit large amount of water, are the main source of drinking water in many regions worldwide. Their excessive permeability leads to enhanced vulnerability to contamination accordingly. In the first section of this study, a comprehensive overview of hydrological processes and concepts, assessment methods and governing equations regarding groundwater flow and contaminant transport in karst aquifers is presented. Moreover, surface water and groundwater interaction and recent groundwater remediation techniques in karst terrains are discussed. Due to the complexity of karst aquifers, different approaches are developed by researchers for investigating and predicting karst processes and groundwater behavior. Modeling techniques are among the most beneficial and powerful methods for assessing groundwater flow and contaminant transport in karst aquifers, as hydrogeological systems with complicated and unpredictable behavior. Hence, several modeling approaches, are reviewed and assessed. Moreover, associated research works conducted for northern Puerto Rico are discussed to complement ongoing hydrogeologic investigations in this island.;In the second section, groundwater Nitrate contamination, as a result of agricultural, industrial and urban development, is assessed for north-central part of Puerto Rico. Using collected field samples and historical data, a Nitrate fate and transport simulation was conducted using MODFLOW and MT3D models. The calculated results of the regional-scale simulation showed high correlation with observed values and hence, the calibrated model was used for prediction purposes. Using land cover data and by assessing agricultural development trend in the island, spatiotemporal pattern of groundwater Nitrate concentration was predicted for the next two decades. It was predicted that agricultural activities will rise dramatically after economic damages of Hurricane Maria and this will negatively impact the groundwater quality. Based on the model prediction results, recommended management plans for each municipality were presented for the use of policy makers and authorities.