Hydrochemical evoluation, groundwater quality and aspects of the vulnerability of the Barreiras
Aquifer System in Pirangi River Basin / RN
Pirangi River Basin; Barreiras Aquifer System; Hydrochemical Analysis; Vulnerability Analysis.
The Pirangi River Basin, located in the Metropolitan Region of Natal, has an area of 436 km2, which is composed of the sub-basins of the Pitimbu, Taborda and Pium rivers. The occurrence of the Barreiras Aquifer in the region has given the area great hydrogeological importance, because the waters of the Barreiras Aquifer are essential for supplying the urban and rural populations and industrial and agricultural development of the region. In addition, urban development without proper planning of the city of Parnamirim/RN, present in the study area, requires not only an evaluation of the problems generated, but also adequate measures to protect natural resources, especially groundwater. The present work is linked to the project of the FINEP / CNPq - CT - Hidro Network (Potentials and definition of groundwater management strategies of the Parnamirim/RN region) and aims to hydrochemically evaluate the waters of the Barreiras Aquifer System in the Basin Pirangi River, allowing to classify the waters according to hydrogeochemical facies, to orient the use according to the quality of the waters and to discuss aspects of the vulnerability of the aquifer in the region. From the registration of 30 tubular wells, samples were collected (november 2017) and the following parameters were analyzed: pH, electrical conductivity, total dissolved solids and sodium, potassium, calciummagnesium, iron, chloride, bicarbonate, sulfate and nitrate ions. From the results of the chemical analyzes, isovalues maps were elaborated, besides plotting the data in the diagrams of Piper, Durov Expandido and Stiff. Vulnerability analysis was performed using the GOD method. In general, the waters of the Barreiras Aquifer in the study area are characterized as slightly acidic and of low salinity, covering mixed chlorinated waters (43.33%), sodium chloride (36.67%), magnesium chlorate (6.67%), mixed bicarbonates (6.67%) and calcium bicarbonates (3.33%). Contamination of groundwater by nitrate was identified in 30% of the samples, with emphasis on the more urbanized regions. The analysis of the isovalent maps revealed that despite the influence of the underground flow on the hydrogeochemical variations of the groundwater in the study area, other factors must be considered in this analysis, such as the influence of urban effluents, agricultural activities and climatic variations. The vulnerability analysis identified the northern portion of the study area as being of low vulnerability. The areas of medium vulnerability extend to the south and part of the west. Four zones of high vulnerability were also identified: one in the western portion, along the rivers (characterized as effluents) and two smaller areas, in the eastern and northeast portions