Geologic and hydrologic data collected at test well NC-5, Barceloneta, Puerto Rico

Abstract

Test well NC-5 was drilled in the municipality of Barceloneta, as part of a study of the aquifers in the Northern Coastal Province of Puerto Rico. The total depth of the well was 2,564 feet. Hydrologic and geologic data collected during drilling included continuous core, water-quality data, head measurements, geophysical logs, and estimates of well yields from the water-bearing zones. Detailed petrological and microfaunal analyses of the core were made to determine the mineralogical content, ages, and paleoenvironments of deposition. The core recovered from test well NC-5 indicated that the well penetrated five formations of middle Tertiary age: the Aymamdn Limestone, the Los Puertos Limestone, the Cibao Formation (including the Montebello Limestone Member), the Lares Limestone, and the San Sebastian Formation. Five hydrogeologic units were encountered in NC-5: three aquifers and two confining units. The uppermost unit is a water-table aquifer and contains the Aymamon Limestone, Los Puertos Limestone, and the uppermost strata of the Cibao Formation. The entire water-table aquifer contains freshwater. Two confining units and a lower artesian aquifer of local extent, occur in the informally named upper member of the Cibao Formation. The underlying artesian aquifer is composed of the lowermost beds of the upper member of the Cibao Formation, the Montebello Limestone Member of the Cibao Formation, and the Lares Limestone. INTRODUCTION The Northern Coastal Province in Puerto Rico is part of a coastward-thickening wedge of platform carbonates and minor clastic rocks of Oligocene to Holocene age. Extensive dissolution of limestone has created excellent examples of humid tropical karst landforms. Flanking the central mountains of Cretaceous and early Tertiary age, this wedge sequence extends from Aguada, in the western part of the island, to Loiza 30 miles east of San Juan, and underlies an area of approximately 700 square miles. 1 U.S. Geological Survey, Water Resources Division, San Juan, Puerto Rico. 2 Department of Geology, University of New Orleans, New Orleans, Lousiana. 1 Limited geologic and hydrologic data are available for the, subsurface coastal areas of northern Puerto Rico. As part of a cooperative study between the U.S. Geological Suivey and the Puerto Rico Department of Natural Resources, fifteen test wells were drilled (fig. 1) to better understand the geologic and hydrologic characteristics of the aquifers and confining units of the Northern Coastal Province (Torres-Gonzdlez and Wolansky, 1984). Purpose and Scope This report presents the geologic and hydrologic data coi municipality of Barceloneta, north-central Puerto Rico (figs. 1 lected at test well NC-5, drilled in 1986 in the and 2). The data include water levels, aquifer thickness, lithology, and water-quality data for the major aquifeis identified at this site. These data will aid the correlation of major north coast hydrogeologic and geologic unit$ (fig. 3) and help quantify the direction and rate of ground-water flow in the Northern Coastal Province. The drilling and coring program was designed to allow the continuous collection of core samples for geologic, hydrogeologic, and paleontologic analysis. Geophysical logs were) made to help describe and define major geologic and hydrologic units. Water-level measurements were made and Water-quality samples were collected from discrete water-bearing zones. Location of Study Area The municipality of Barceloneta is located in the north-central part of Puerto Rico, approximately 35 miles west of San Juan. The well is located about one-quarter of a mi|e south of Highway 2, along Highway 140 near Cruce Davila (fig. 2). The land surface altitude at the well site is| 312 feet above mean sea level. DATA-COLLECTION METHODS Drilling and Well-Construction Methods Test well NC-5 was drilled to a depth of 2,564 feet bdlow land surface. The well was drilled by a hydraulically driven, reverse air drill that uses air under pressure. The drill stem consisted of 20-foot sections of threaded, seamless, double-walled pipe. As drilling progressed, air was forced under high pressure through the annulus between the two walls of the drill stem, forcing formation water and core samples up the center of the drill stem. Cores and water were ejected from the inner pipe into a ilarge cyclone container that served as a sample collector. Test well NC-5 was cased with 2.5 inch diameter casing from land surface to a depth of 1,070 feet below land surface. From 1,070 to 2,564 feet, the well is uncased. A construction diagram for test well NC-5 is shown on figure 4.