Geographically, the largest region in Puerto Rico is the volcanic interior, or central mountain range. This region covers 59% of the area of Puerto Rico, or 1,992 square miles. The subterranean water resources available in this region come from fractured rocks of volcanic origin and from the abundance of alluvial valleys.
Most of the central mountain range is formed of rocks of volcanic origin. The tectonic movement the island experiences helps to deform and intensely fracture the majority of the volcanic rocks that form the region. The geographic size of the fractured volcanic rocks contributes to the development of characteristics that favor subterranean bodies of water. Among the factors that contribute to the high capacity for underground water storage are the density of the fractures, sedimentation in the fractures, the environment in which the volcanic rock formed, mineralization, the degradation of the rocks and the size of the saturated area. The most abundant accumulations of subterranean water are found in zones with fractures from geological faults.
The alluvial aquifers in the interior of Puerto Rico are found in the valleys of Aibonito, Cayey and Caguas-Juncos, although there are other alluvial deposits of smaller size. The main alluvial aquifers feed the major rivers in the region.
The Caguas to Juncos alluvial aquifer is the most important in the interior of Puerto Rico. Located in the east-central part of the island, it covers most of the urban zone of Caguas. The aquifer, which extends the length of the municipalities of Caguas and Juncos and includes sectors of Gurabo, covers an area of 35.1 square miles. The aquifer formed from the accumulation of sedimentary deposits carried from the central mountain range by the Gurabo and Grande de Loíza rivers. Although this aquifer is capable of producing significant quantities of water, the extraction of water has been substantially reduced due to contamination by industrial solvents. The wells that produce the most are located in the Autoridad de Acueductos y Alcantarillados (AAA) pumping centers in the Bairoa and Las Catalinas sectors in Caguas, the urban area of Gurabo in Gurabo, and at the Experimental Station near Juncos.
The Cayey aquifer is lesser in importance and capacity, in comparison to the other alluvial valleys of Puerto Rico. Located at the headwaters of La Plata River, the alluvial valley that forms the aquifer covers an area of approximately 3.2 square miles in the Cayey plain. The alluvium was carried to the plain from the slopes of the Cayey range by La Plata River and its tributaries. The alluvium rests on rocks of volcanic origin. Although the thickness of the alluvium is insignificant, it acts as a channel for the water that infiltrates the decomposed and fractured materials.
The Cidra aquifer is located in the east-central part of the island and has an area of 0.44 square miles. This alluvial aquifer formed from the accumulation of sedimentary deposits from the Sabana and Bayamón Rivers, although subterranean water from fractures in the volcanic rocks on the perimeter of the Cidra Reservoir also contributes to it. Most of the wells are located close to the reservoir because most of the water that feeds them comes from the reservoir itself. This infiltration of surface water results in marginal water quality with high concentrations of nitrogen and phosphorous, which limits its use or requires treatment to remove these nutrients.
Author: Sigfredo Torres González
Published: August 27, 2014.
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