CHARACTERIZATION OF SANDS FROM PLAYA LAS GOLONDRINAS IN ISABELA, PUERTO RICO FOR APPLICATIONS IN ENVIRONMENTAL GEOTECHNOLOGIES

Although commonly associated with groundwater resources, sand is an important medium in geotechnical engineering. Because naturally occurring sands are suited for their given environment, they are efficient media for subsurface flow constructed wetlands (SFCWs) in their native region. Furthermore, utilizing local sands for SFCWs is less expensive and lower maintenance than acquiring crushed or manufactured media. Nevertheless, natural sands may contain unwanted materials, including sulfides or oxides with toxic metal contaminants. To determine the utility of sands in geotechnical applications, several analytical approaches are useful: grain size analysis, scanning electron microscopy (SEM), light microscopy, and reflective spectroscopy. These techniques were applied to sands from Playa Las Golondrinas in Isabela, Puerto Rico collected from the shoreface, berm, and dune. Grain size characteristics for shoreface, berm, and dune samples vary with respective dominant average modes of 462 μm, 326 μm, and 462 μm, classifying them as medium-sized. SEM data reveal higher concentrations of silica in both the berm and dune samples, while the shore samples contain more carbonate minerals. Other abundant elements include potassium, calcium, oxygen, and aluminum. Size, shape, and texture vary among particles. When viewed under an optical microscope, thin sections include forams and echinoderms, indicating heterogeneity. Common silicate minerals identified in thin sections include quartz, plagioclase, and lesser amounts of amphibole. Reflective spectroscopy measurements indicate that sands within each type are relatively uniform with major common adsorption features being 475 nm, 1415 nm, 2300 nm, and 1930 nm. Analysis of sands from Playa Las Golondrinas in Isabela, Puerto Rico indicates their potential in the use of sand filtration, SFCWs, and reactive media owing to their grain size characteristics and composition. This study provides constraints for further investigation of pollutant remediation such as bacterial removal, nutrient attenuation, and metal sorption. Sands show promise for environmental geotechnology development.