MINERALOGICAL AND ENVIRONMENTAL INVESTIGATIONS OF SANDS FROM PIÑONES, PUERTO RICO

Sands can be used as environmental media for constructed wetlands, runoff filtration media for parking lots, and general water treatment. Identifying sands near the point of use is economically desirable. Piñones, Puerto Rico is a high volume destination in the north eastern greater San Juan metropolitan area with extensive beach areas. This is an attractive area for residential and commercial properties however it is also prone to storm and hurricane impacts. Some damage from Hurricane Maria ( 2017) is still clearly evident. As Piñones experiences redevelopment and infrastructure improvements in the future, there will be a demand to use economical and ecological geotechnical materials in an environmentally responsible manner. The coastal sands may be a resource that could be used in some applications. Concerns exist however as natural sands may contain undesirable minerals such as sulfides or oxides that may contain toxic metals that could be released under different conditions. As a preliminary investigation for feasibility of use in geotechnical applications, sands from the berm and dune environments were sampled to initially evaluate these local sources for use in geotechnical and environmental applications. Grain size characteristics for berm, and dune samples have dominant modes of 742 µm, and 360 µm respectively. Small pelecypod fossils occurring in the berm in part account for the difference in grain size. Light microscopy data indicate that approximately 90% of grains are carbonate and are dominantly shell fragments and approximately 10% of grains are quartz. These particles exist in a variety of states of micritization. Intraparticle porosity varies from approximately 29% to 60%. Scanning electron microscopy data indicate grains have a variety of irregular shapes and surface roughness that are interpreted to be a function of the extent of transport and biological origin. Reflective spectroscopy measurements are consistent with observed mineralogy with absorption features being 1434 nm, 1920 nm, 2327 nm. Applications involving long term mechanical stability likely have some risk owing to the soluble nature of naturally occurring beach sands. The solubility of the carbonates may mitigate lower pH of sewage and the surface characteristics may slow transport of pollutants and promote microbial films.