THE IN-SITU MEASUREMENT OF TEMPERATURE AND SPECIFIC CONDCUTANCE OF GROUND WATER IN PUERTO RICO

摘要

Between 2003 and 2008 the author, while working for the U.S. Geological Survey, (USGS) made about 300 in-situ measurements of ground-water temperature and specific conductance at 39 non-pumping observation wells located throughout Puerto Rico. All the data is on the Internet. The data were collected by digital equipment with a 30.5 m cable between the sensor and the display. The purpose of this study is to determine the variation of repeat measurements of in-situ ground-water temperature and specific conductance in Puerto Rico. The data were also compared with average air temperature data from the National Weather Service (NWS) to see if there is any evidence of geothermal heat in the aquifers of Puerto Rico. Most of the ground-water data were collected 28 m below land surface. Prior to this study ground-water temperature data were collected with glass analog thermometers only after the water had been pumped to the surface. The temperature of the water changes as it is pumped to the surface. The average standard deviation of repeat measurements of water temperature and specific conductance are 0.22 °C and 378 uS/cm, respectively. The NWS has average air temperature data for 43 stations in Puerto Rico. The warmest average air temperature is 27.2 °C in Guayama, Puerto Rico. In this study of 39 observation wells there are nine whose average is more than two standard deviations warmer than the warmest air temperature station. All of these warm stations are located in a triangle whose corners are Ponce, Salinas, and Caguas. In this triangle the percentage of warm stations is 60 percent. The warmest observation well is Constancia 3 in Ponce at 29.4 °C. The most likely explanation for these stations being warmer than the average air temperature is geothermal heat. At 29 °C this is not enough geothermal heat to be used for power production but it does give us insights into the ground-water flow system of the area. Compared to cooler areas, aquifers affected by geothermal heat have water that flows slower, deeper, and with lower flux rates.