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Joseph W. Troester

Publications and source records attributed to Joseph W. Troester.

3 recordsLinked to original sources
USGS1999

Geochemistry and hydrogeologic framework of the saline-freshwater interface and the calculation of net recharge in the Dorado area, north-central Puerto Rico

The upper aquifer near Dorado, Puerto Rico, is a major source of water for both public and private supply. The aquifer is composed of portions of the Aguada Limestone, Aymam6n Limestone, and adjacent permeable portions of unconsolidated deposits. As water moves through the aquifer it changes from a calcium-bicarbonate type water in the upgradient portions of the aquifer to a sodium-chloride type water in the downgradient portions of the aquifer near the coast. Pumping from the aquifer for industrial use and public supply has lowered the water table to near sea level in some areas, causing saline intrusion to be a concern. The saline-freshwater interface was located by drilling and borehole geophysics. Drilling and borehole geophysics helped locate the lower limit of the aquifer. The saline-freshwater interface is narrow close to the coast and thickens with distance from the coast. Ground-water hydrographs in the study area were simulated with a deterministic model that allows net recharge to be calculated from precipitation data and ground water level data. Calculated net recharge rates ranged from 160 millimeters per year in 1995 at the Santa Rosa well site to 260 millimeters per year in 1996 at the Maguayo well site.

Water-Resources Investigations Report↗
USGS1995

Surface electromagnetic geophysical exploration of the ground-water resources of Isla de Mona, Puerto Rico, a caribbean carbonate island

Two electromagnetic surface geophysical techniques were used to explore the ground-water resources of Isla de Mona, Puerto Rico—a 55-square-kilometer island located between Puerto Rico and Hispañiola, Isla de Mona is a tectonically uplifted carbonate plateau of Neogene age that has an average elevation of about 50 meters above mean sea level. This plateau is bounded by vertical cliffs except on the southwest where there is a narrow, 3-square-kilometer coastal plain. The coastal plain is composed of Quaternary carbonate deposits, and has a maximum elevation of less than 10 meters above mean sea level. No large-scale surface-water features are found on the plateau or on the coastal plain. To better understand the aquifer characteristics of the island, terrain conductivity and transient electromagnetic data were collected on the coastal plain and on the plateau. Computer programs were used to analyze quantitatively the electromagnetic data. Geoelectric models were produced to approximate the depth below land surface of the saline-freshwater interface underlying both the coastal plain and the plateau. Because the geophysical methods could not discern the water-table, it was assumed that it was near sea level. The thickness of the freshwater lens was estimated by subtracting the elevation of the land surface above mean sea level from the depth to the saline-freshwater interface as determined from the geophysical data. Results from the geophysical methods and water-level observations indicate that a freshwater lens with a maximum thickness of about 10 meters exists under the coastal plain. This lens thins towards the ocean, and it also thins away from the ocean toward the plateau. The model produced from the transient electromagnetic data indicates that the freshwater lens under the plateau has a maximum thickness of about 14 meters, which is a much thinner lens than previously estimated. A freshwater lens thickness of 14 meters is similar to direct measurements by divers in Cueva de Agua at Punta los Ingleses (located on the southeast coast), and observations by divers of freshwater seeps into the ocean at depths of 8 to 10 meters along the north coast cliffs after a major rainstorm. Ground-water flow in the coastal plain appears to be radial from the center of the freshwater mound. At the intersection between the coastal plain and the plateau, the flow is parallel to the coastline. The direction of flow on the rest of the plateau could not be determined accurately with the available data.

Carbonates and Evaporites↗