UPDATES ON ENVIRONMENTAL GEOTECHNOLOGY DEVELOPMENT THROUGH THE CHARACTERIZATION OF SANDS FROM PLAYA LAS GOLONDRINAS IN ISABELA, PUERTO RICO

This investigation compared shoreface, berm, and dune sands collected from Playa Las Golondrinas in Isabela, Puerto Rico for potential use in water filtration systems. Sand is a valuable resource for geotechnology due to its filtration properties and accessibility. Using sand as a filtering medium proximal to where it naturally occurs promotes the use of native materials in restoration efforts, while also eliminating costs associated with transporting or importing non-native materials. Specifically, sand can be used in subsurface flow-constructed wetlands (SFCWs), a type of water filtration geotechnology that maximizes efficiency and minimizes maintenance requirements. However, naturally occurring sands also have the potential to contain sulfides or oxides with potentially high toxic metal concentrations (e.g., As, Cr). If natural sands are used in SFCWs, they must be comprehensively characterized for their physicochemical properties to determine their viability. Characterization in this study includes grain size analysis, scanning electron microscopy (SEM), and polarized light microscopy. Grain size characterization determined medium-sized averages of 462 μm, 326 μm, and 462 μm, for shoreface, berm, and dune, respectively. From SEM data, the berm and dune samples contained higher quartz concentrations while the shore samples were carbonate-dominant. Polarized light microscopy images of thin sections documented the presence of forams and echinoderms with silicate minerals: quartz, plagioclase, and minor amphibole. Although the three types of sand shared similar physicochemical properties, the berm sand would likely be the most effective for water filtration due to its grain size characteristics and mineralogical composition. Additional characterization of natural sands for use in SFCWs will involve metal sorption assessments, nutrient attenuation, bacterial removal, and the addition of a carbon source to optimize filtering capacity. The results of this work will contribute to ongoing efforts that investigate sustainable approaches to SFCW construction.