The Taua river drainage basin occupies an area of 404.57 km ² and it is located in the northeastern of Para state. The basin area covers part of the municipalities of Santo Antonio do Taua, Santa Barbara do Para, Santa Isabel do Para and Castanhal. This works aims the hydrogeological characterization of the Taua river basin based on the groundwater quality analysis and on the division of the area into tectonic blocks in order to identify the aquifers recharge areas. It was collected groundwater samples from 25 wells during the drought (November/2012) and rainy seasons (February/2013). For the water quality analysis were performed the following physic-chemical parameters: pH, chloride, sulfate, sodium, potassium, magnesium, calcium, hardness, conductivity and nitrogen compounds (ammonium, nitrite and nitrate). In the drought period, the concentration of ions analyzed was within the permitted by ordinance 2914/11 of the Health Ministry. However, it was observed a significant increase in the concentrations of most ions, especially the nitrogen compounds. The consumption of waters with nitrate concentrations above 10 mg/L presents a risk to human health. The increase in nitrate concentration is related in part to the nitrification reactions in which the ammonia is oxidized and form nitrate. Human activities such as the use of fertilizers in agriculture, animal breeding and release of sewage and the poor construction of cesspits are the main causes of contamination of the unconfined aquifer. Unconsolidated sediments and sandy lithology facilitate the infiltration of these contaminants in the soil until they reach the aquifers. It was identified three areas of direct recharge and four discharge areas of the unconfined aquifer. The area of the Taua river basin was compartmentalized by faults of NE-SW and NW-SE in 11 morphotectonic blocks. The boundaries of these blocks consist of groundwater circulation zones, since the vertical displacements caused by faults can promote communication between the shallow aquifer and other aquifers.
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