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Nitrate concentrations exceeding the maximum contaminant level of 10 milligrams per liter (mg/L) permitted by the Puerto Rico Department of Health at public-water supply wells have been documented at wells in the Manat�-Vega Baja area by G�mez-G�mez and Guzm�n-R�os (1982); Guzm�n-R�os and Qui�ones-M�rquez (1984); and Rom�n-M�s and Ramos-Gin�s (1988). Between 1988 and 1990, nitrate concentrations equal to or exceeding 10 mg/L were detected at three public-water supply wells in the area (Puerto Rico Environmental Quality Board, 1992). The findings led to the closure of these wells, resulting in a production loss of 3,900 m3/d. The use of fertilizers in pineapple fields (the main agricultural activity), septic tanks, livestock facilities discharges, and illegal dump sites were suggested as the most probable causes of the high nitrate concentrations detected at the affected public water-supply wells (Puerto Rico Environmental Quality Board, 1992)......
Conclusions
The results of the study indicate that the portion of the upper aquifer with nitrate concentrations close to or above 10 milligrams per liter is contained primarly within the Laguna Tortuguero ground-water drainage basin. Sources of nitrate in the study area are derived primarily from fertilizer used in the cultivation of pineapples and from septic tank effluents from rural communities. On an areal unit basis the maximum potential nitrate load from agricultural land under pineapple cultivation (760 kg-N/(ha-yr)) is about four times that of rural communities without sewerage connections (200 kg-N/(ha-yr)). The total nitrate load estimated in domestic wastewater discharge at un-sewered communities may reach the upper aquifer according to mass balance calculations. In addition, the mass balance calculations indicate that much of the un-accounted nitrate load from fertilizer use at the pineapple farms (550 kg-N/(ha-yr)) is probably in transient storage within the vadose zone since only about 45 kg-N/(ha-yr) is accounted in the upper aquifer.
This is a very comprehensive and informative report - well worth reading in its entirety
Conclusions
The results of the study indicate that the portion of the upper aquifer with nitrate concentrations close to or above 10 milligrams per liter is contained primarly within the Laguna Tortuguero ground-water drainage basin. Sources of nitrate in the study area are derived primarily from fertilizer used in the cultivation of pineapples and from septic tank effluents from rural communities. On an areal unit basis the maximum potential nitrate load from agricultural land under pineapple cultivation (760 kg-N/(ha-yr)) is about four times that of rural communities without sewerage connections (200 kg-N/(ha-yr)). The total nitrate load estimated in domestic wastewater discharge at un-sewered communities may reach the upper aquifer according to mass balance calculations. In addition, the mass balance calculations indicate that much of the un-accounted nitrate load from fertilizer use at the pineapple farms (550 kg-N/(ha-yr)) is probably in transient storage within the vadose zone since only about 45 kg-N/(ha-yr) is accounted in the upper aquifer.
This is a very comprehensive and informative report - well worth reading in its entirety