CHARACTERIZATION OF CARBONATE SANDS FROM TWO DIFFERENT LOCATIONS IN PUERTO RICO FOR GEOTECHNOLOGY DEVELOPMENT

Carbonate sands have been explored for use as reactive media for use in geotechnology such as constructed subsurface wetlands previously in other settings in the Caribbean. Potential advantages of using carbonate sands are the comparatively higher porosity and microtextures that are likely conducive to increasing effective porosity for retardation of bacteria and pollutants. However, there are aspects of knowledge of carbonate sands that require further development. One issue in using carbonate sands is understanding the variability of mineralogy and grain size. To better assess the variability of these sands, an investigation was conducted on ten berm sands and ten shore sands collected from two locations (Boquerón and Buyé) in Puerto Rico utilizing grain size, scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), light microscopy, and reflective spectroscopy methods. Thin sections were analyzed under polarized light microscopy using digital capture. Imaging indicates a high degree of morphological variation, variable mineralogy, as well as variations in intragranular porosity. An unexpected level of particle diversity within these samples was observed, with a wide range of benthic skeletal grains present. Forams are commonly dominant with lesser amounts of gastropods. Sands from both locations were primarily categorized as slightly gravelly sand; Buyé sands had an average mode of 381μm, while Boquerón sands had an average mode of 516.8 μm. SEM-EDS analysis of the samples showed a diversity of granular surface porosity, chemical composition, and morphology. Multiple images demonstrate the diversity of internal porosity textures and skeletal grains. Major elements identified amongst the samples from both locations include Ca, Mg, Si, and O, while minor elements include Fe, Al, Na, and K. A single hackly fractured anthropogenic Cu-Zn alloy particle was observed in Buyé shore sand. Reflective spectroscopy suggests that the sands are uniform among each setting type with common absorption features being 1440 nm, 1935 nm, and 2330 nm. Sands from both sites show promise for environmental geotechnology development. Detailed investigations of remediation of bacterial transport and removal as well as nutrient attenuation are warranted.