From introduction: The purpose of this report is to summarize available information concerning iron-ore resources in the United States in order to provide a general background for understanding and appraising the present status of this basic commodity.

From introduction: The North Coast Limestone area is one of the two most important ground-water provinces of Puerto Rico--the other being the South Coast Alluvial aquifer. The investigation of the water resources of the South Coast has progressed to the point that at this time (mid-1971) an electric-analog model of the area is being prepared. The hydrology of the North Coast Limestones, however, was never investigated as a whole before this investigation, and, therefore, this study was designed to assess the most important hydrolic features of the area.

Abstract: Lajas Valley is plagued with problems of salinity and waterlogging the soils. Use of brackish (500 milligrams per liter) irrigation compounded ground water for the problem until an irrigation-drainage system was constructed in 1955. Lajas is an alluvium-filled limestone highlands. The alluvium, mostly clay and as much 300 feet (90 meters) thick, contains brackish ground water except in the recharge areas located along the foothills...Results from a digital model show that a network of discharge wells could alleviate waterlogging of the soils in the artesian area.

From purpose and study: The principal objectives of this study were as follows: (1) to determine the existing water-quality conditions in Lago Loiza as reflected by the principal chemical, physical, biological and bacteriological characteristics in the lake and its tributaries. (2) To estimate the reservoir's water budget during the study period, including the contributions from the tributaries and other sources. (3) Estimation of the reservoir's overall nitrogen and phosphorus budget, including the principal sources and sinks of these nutrients. (4) Definition of the sedimentation rate in the reservoir.

From introduction: This report summarizes the results of the study in the Manati-Barceloneta area. The study includes an analysis of the availability of water from both surface and ground-water sources, and water quality. The major focus of the study was the alluvial valley of Rio Grande de Manati north of Highway 2. Areas outside of the valley were included as necessary only to the degree in which these influence the local hydrology.

From introduction: This report presents observed data on the interlagoon and ocean exchange of the flows of water, sediment, and selected chemicals for a tidal cycle in January 1974.

From introduction: A post-drought analysis of the sources of water supply for the metropolitan area indicated a need for better knowledge of the ground-water resources. A study was implemented through the cooperative water-resources investigation program between Commonwealth agencies of Puerto Rico and the U.S. Geological Survey.

Abstract: The principal chemical, physical and biological characteristics, as well as the hydrology of Laguna Tortuguero, Puerto Rico, were studied from 1974-75. The lagoon, with and area of 2.24 square kilometers and a volume of about 2.68 million cubic meters, contains about 5 percent of seawater. Drainage through a canal on the north side averages 0.64 cubic meters per second per day, flushing the lagoon about 7.5 times per year. Chloride and sodium are the principal ions in the water, ranging from 300 to 700 mg/L and 150 to 400 mg/L, respectively. Among the nutrients, nitrogen averages about 1.7 milligrams per liter, exceeding phosphorus in a weight ratio of 170:1. About 10 percent of the nitrogen and 40 percent of the phosphorus entering the lagoon is retained. The bottom sediments, with a volume of about 4.5 million cubic meters, average 0.8 and 0.014 percent nitrogen and phosphorus, respectively.

This report used "annual peak-discharge records at fifty sites with five or more years of record" to determine individual site frequency curves. It includes several maps.

This report presents an analysis of "three limestone aquifers on the north coast of Puerto Rico west of the RÍo de la Plata" using "analog modeling techniques."

Abstract: Laguna La Torrecilla, Laguna de Pinones, Laguna San Jose, and Laguna del Condado, in the San Juan, Puerto Rico area, are located within a metropolitan area of more than 1 million people. Bathymetric maps made during the study, in 1973, showed that Lagunas La Torrecilla, San Jose, and del Condado have been modified by dredging and filling; whereas, Laguna de Pinones has remained in a near natural state. Laguna La Torrecilla has been dredged to a depth, in places, of about 18 metres, and Lagunas San Jose and del Condado, in places to about 11 meters. Dredging in the San Juan lagoons has been harmful, beneficial, and in a few instances has had little or no noticeable effect on the water quality. Usually, dredging in the connecting canals has been beneficial if the water entering the lagoons through the canals was of better quality than the water in the lagoon. Dredging in the mouths of lagoons has been beneficial; whereas, filling or blocking the mouths has been harmful.

From abstract: A statistical summary of the available continuous and once-daily discharge, specific-conductance, dissolved oxygen, temperature, and pH data collected at NASQAN stations during the 1973-81 water years and documentation of the period of record on which the statistical calculations were based are presented.