CHARACTERIZATION OF PUERTO RICAN CARBONATE SANDS FOR SUBSURFACE FLOW CONSTRUCTED WETLANDS (SFCW) CONSTRUCTION AND WATER FILTRATION

Carbonate sands have been explored for their potential functionality as reactive media for geotechnologial applications, specifically within the context of developing subsurface flow constructed wetlands (SFCWs). Developing efficient SFCWs is particularly important in the Caribbean, a region at risk of high intensity tropical storm activity. Specifically, the porosity and textural characteristics of this media can work to support water filtration and flood mitigation of stormwater. Detailed studies of carbonate sand properties are therefore needed to assess which types of carbonate sand are best suited to certain applications within SFCW systems. Twenty sand samples were collected from four beach locations in southwestern Puerto Rico (Boquerón berm and shore, Buyé berm and shore). Samples were characterized for their grain size, textural diversity, mineralogical properties, and chemical compositions via light microscopy, scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), inductively coupled plasma mass spectrometry (ICP-MS), and reflective spectroscopy methods. Grain size analysis indicates that Boquerón sand has an average grain size of ~568 µm and Buyé sand has an average grain size of ~418 µm. Digital imaging revealed variable mineralogy (e.g., quartz, amphibole), morphological diversity, and variations in intragranular porosity. From a biological perspective, forams were dominant with a lesser amount of gastropods and echinoderms; however, many fragments were difficult to identify due to natural degradation. SEM-EDS documented variable chemical compositions of silicate mineral grains and biological skeletal grains. Within the context of potential elements of environmental concern, results from bulk sample ICP-MS chemical analysis across all four locations yielded the following averages: 5 ppm for V, 5 ppm for Pb, and 17 ppm for Cr. Reflective spectroscopy documented absorption features at 1440 nm, 1935 nm, and 2330 nm across each location type. Results suggest that the Buyé shore sand may be best for potential geotechnology applications due to its relatively finer grain size and intragranular porosity, which is ideal for filtration.