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Groundwater discharge to an irrigation pond

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Groundwater Quality Monitoring Project

Project Number: MJ00D7V
Project Chief: José M. Rodríguez
Cooperator: Department of Natural and Environmental Resources
Period of Project: FY 2011-2013

Introduction

Groundwater is one of the most valuable natural resources of Puerto Rico. In 2010, aquifers in Puerto Rico provided approximately 125 million gallons per day (Mgal/d) (Molina, written communication, 2013), equivalent to 17 percent of the total freshwater withdrawals on the island. Principal aquifers in Puerto Rico (figure 1) include the North Coast Limestone Aquifer System (NCLAS) and the South Coast aquifer. During 2010, the NCLAS provided 42.1 Mgal/d distributed as 81 percent for public supply, 12 percent for agriculture, 5 percent for industrial uses, and 1 percent for domestic self-supplied and mining. The South Coast aquifer provided 36.4 Mgal/d in 2010, distributed as 63 percent for public supply, 33 percent for agriculture, 2 percent for thermoelectric power water use, and 1 percent for industrial and mining uses.

Gaining understanding of the potential groundwater quality trends could significantly influence future environmental policies and management strategies related to its use. Previous studies indicate increasing trends of dissolved solids concentrations in groundwater from areas of the NCLAS (Gómez-Gómez, 2008) and the South Coast aquifer (Rodríguez and Gómez-Gómez, 2008). Aquifer overdraft can cause the thinning of the freshwater lens and consequently saline-water encroachment and degradation of groundwater quality. Relatively high nitrate concentrations were also reported in groundwater from areas of the NCLAS (Conde-Costas and Gómez-Gómez, 1999) and the South Coast aquifer (Rodríguez, 2006, and 2013). In some areas dissolved solids and nitrate concentrations were above the secondary maximum contaminant level (SMCL) and maximum contaminant level (MCL), respectively, for drinking water established by the United States Environmental Protection Agency.

In 2011, the U.S. Geological Survey (USGS), in cooperation with the Puerto Rico Department of Natural and Environmental Resources, began the Groundwater Quality Monitoring Project to obtain and analyze groundwater quality data at selected areas of Puerto Rico. Data collected indicated dissolved solids concentrations above the SMCL in groundwater samples collected from wells in the upper aquifer of the NCLAS in the Vega Alta, Vega Baja, Manatí, Barceloneta, and Arecibo areas. Also, nitrate concentrations in groundwater above the MCL for drinking water were detected in the Manatí and Hatillo areas. Collected data also indicated dissolved solids concentrations above the SMCL in groundwater samples collected from wells in the South Coast aquifer at Salinas, Santa Isabel, and Ponce. Nitrate concentrations in groundwater above the MCL for drinking water were detected during 2011 in the Salinas and Santa Isabel areas.

To view maps presenting the location of sampled wells in the upper aquifer of the NCLAS and the South Coast aquifer, click the area of interest. To view the figures and tables presenting the results of the chemical analysis from the samples collected, click the dot that represents a sampled well location. If you need more information on how to interpret the figures, please refer to the online report titled "Groundwater-Quality Survey of the South Coast Aquifer of Puerto Rico, April 2 through May 30, 2007". (http://pubs.usgs.gov/sim/3092)

Groundwater Quality Monitoring Project sampling sites

Figure 1. Groundwater Quality Monitoring Project sampling sites in the upper aquifer of the North Coast Limestone Aquifer System and the South Coast Aquifer of Puerto Rico


References


Conde-Costas, C., and Gómez-Gómez, F., 2008, Assessment of nitrate contamination of the upper aquifer in the Manatí-Vega Baja area, Puerto Rico,: U.S. Geological Survey Water-Resources Investigations Report 99-4040, 43 p.

Gómez-Gómez, F., 2008, Estimation of the Change in Freshwater Volume in the North Coast Limestone Upper Aquifer of Puerto Rico in the Río Grande de Manatí-Río de la Plata Area between 1960 and 1990 and Implications on Public-Supply Water Availability: U.S. Geological Survey Scientific Investigations Report 2007-5194, 24 p.

Rodríguez, J.M., 2013, Evaluation of Groundwater Quality and Selected Hydrologic Conditions in the South Coast Aquifer, Santa Isabel Area, Puerto Rico, 2008–09: U.S. Geological Survey Scientific Investigations Report 2012-5254, 36 p.

Rodríguez, J.M., 2006, Evaluation of hydrologic conditions and nitrate concentrations in the Río Nigua de Salinas alluvial fan aquifer, Salinas, Puerto Rico, 2002-03: U.S. Geological Survey Scientific Investigations Report 2006-5062, 38 p.

Rodríguez, J.M., and Gómez-Gómez, F., 2008, Groundwater-Quality Survey of the South Coast Aquifer of Puerto Rico, April 2 through May 30, 2007:U.S. Geological Survey Scientific Investigations Map 3092, 1 sheet: Online Only

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