Source of Nitrate Contamination of the Upper Aquifer in the Manatí-Vega Baja Area Assessed

Contamination of ground-water in the Manatí-Vega Baja area with nitrates resulted in the closure of several public water-supply wells in 1989.  As a result of this, the U.S. Geological Survey (USGS) in cooperation with the Puerto Rico Environmental Quality Board (PREQB) conducted a ground-water resources assessment to define the principal sources of this contaminant.

The results obtained indicate that the use of fertilizers in pineapple crops and the disposal of domestic waste-water through septic tanks constitute the most important sources of nitrates in the area.  The potential load of nitrates from these two sources to the part of the aquifer with drainage to Laguna Tortuguero was estimated at 264,000 and 51,000 kilograms of nitrogen per year, respectively.  However, although the potential nitrate load from fertilizer use is several orders of magnitude higher than that from septic tanks, it is possible that less than 10 percent is reaching the aquifer with most of the nitrates contained in the zone between the land surface and the water-table which is 230 feet thick in the study area.

The report "Assessment of Nitrate Contamination of the Upper Aquifer in the Manatí-Vega Baja Area, Puerto Rico" by Carlos Conde-Costas and Fernando Gómez-Gómez, is available at the USGS office located in Guaynabo, Puerto Rico.

As the nation's largest water, earth and biological science, and civilian mapping agency, the USGS works in cooperation with more than 2,000 organizations across the country to provide reliable, impartial scientific information to resource managers, planners, and other customers.  This information is gathered in every state by USGS scientists to minimize the loss of life and property from natural disasters, contribute to the sound conservation and the economic and physical development of the nation's natural resources, and enhance the quality of life by monitoring water, biological, energy, and mineral resources.

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