USING THE CORRELATION BETWEEN GROUND-WATER LEVELS AND TEMPERATURE TO STUDY THE VULNERABILITY OF AQUIFERS IN PUERTO RICO

Hourly data for 12 to 18 months from 33 non-pumping observation wells were used to study the correlation between depth-to-water and temperature in Puerto Rico. The data were collected by the author when he was an employee of the United States Geological Survey Caribbean Water Science Center. The author retired in 2008 and the data are used with permission. In many hydrogeologic environments rain is colder than ambient conditions. If the rain reaches the observation well quickly then there will be a correlation between depth-to-water and temperature. If the water reaches the observation well slowly then it will have warmed to ambient conditions and the water level will rise independently of the temperature. Areas with a high correlation between ground-water level and temperature are areas where the recharge from rain can quickly reach the aquifer and are more vulnerable to contamination from the surface than areas where there they are not correlated. The hypothesis is that in Puerto Rico, the karst North Coast Limestone aquifer will on average have a higher Pearson correlation coefficient between depth-to-water and temperature than non-karst aquifers. The hypothesis is not proven. In the karst North Coast Limestone aquifer, the average Pearson correlation coefficient between depth-to-water and temperature is larger than in non-karst aquifers but the intraaquifer variability is large enough to prevent the results from being statistically significant. The two areas in the karst North Coast Limestone aquifer that have the highest correlation between water level and temperature and thus the highest risk of surficial contamination are in the adjoining municipios of Quebradillas-Camuy and Manatí-Vega Baja. Fifteen percent of the observation wells in this study are mixed and have periods of high correlation between temperature and depth-to-water and periods of no correlation. This pattern could be caused by construction defects that allow the rainwater to flow down the annular spacing and into the aquifer. The author recommends that the government of Puerto Rico initiate a program to identify and plug thousands of unused water wells on the island.