Data and Shapefiles for the Potentiometric Surface of the South Coast Aquifer and Hydrologic Conditions in the Santa Isabel area, Puerto Rico, March-April 2014

A groundwater-level survey and reconnaissance of the hydrologic conditions in the coastal alluvial plain of southern Puerto Rico was conducted by the U.S. Geological Survey, in cooperation with the Puerto Rico Department of Natural and Environmental Resources. The objective of the field survey was to delineate the potentiometric surface of the coastal alluvial aquifer between the Rio Descalabrado to the west and the Rio Jueyes to the east of the town of Santa isabel. The field survey took place from March 31 to April 17, 2014, and included measuring groundwater levels at 55 wells, groundwater specific conductance at 8 wells, estimating groundwater withdrawal rates at 34 active production wells, and measuring instantaneous streamflow at 15 locations in streams and irrigation canals. instantaneous streamflow measurements were made at selected sites along the Rio Coamo, Rio Descalabrado, Rio Canas, and the Canal de Juana Diaz to evaluate ground and surface-water interactions during the synoptic survey.
A potentiometric surface map of the coastal alluvial aquifer was created from the survey data to indicate the directions of groundwater flow in the aquifer. The potentiometric contours were drawn using water-level data collected at wells during the dry season, from March 31 to April 17. Measured values of the potentiometric surface ranged from -22.8 to 185.4 feet above mean sea level in the alluvial deposits of the south coastal plain.
The total rate of groundwater withdrawal for public supply was 5.74 million gallons per day and was calculated using meter readings of instantaneous discharge from 10 production well. During the survey, groundwater withdrawals for irrigation totaled 5.59 million gallons per day; these withdrawal rates were estimated using data obtained from 24 active wells in the study area.
Groundwater specific conductance values measured during the study at observation wells ranged from 411 to 1,332 microsiemens per centimeter at 25 degrees Celsius. Results of the study indicate a cone of depression has formed in the coastal alluvial aquifer near the center of the study area, where the potentiometric surface is below mean sea level. in the long-term, this feature could result in saline-water intrusion and an increase in concentrations of total dissolved solids.