A qualidade das águas subterrâneas da cidade de Salvaterra, Marajó - Pará

Abstract

The present study verified the quality of groundwater in the city of Salvaterra located in the island of Marajó-Pará. The registration of 20 wells (18 tubular and 2 amazons) was carried out in five neighborhoods of the region (Caju, Centro, Paes de Carvalho, Marabá and Coqueirinho) In order to present results about the hydrogeological characteristics, physicochemical and microbiological analyzes, the samples were collected in two seasonal periods, being in the months of April (rainy period) and November (less rainy period). The main objective of this research was to outline an overview of the groundwater situation of the 20 registered wells used by the population of Salvaterra. The hydrogeological characterization of the study area was based on the descriptive analysis of four wells with 80 meters of depth of COSANPA. The results obtained were a lithologic composite profile, a composite lithologic section, a three dimensional model of hydroestratigraphy, a section composed of the geometric aspects of aquifers, two static level diagrams and two three dimensional models of seasonality. To determine the groundwater quality, the following parameters were analyzed: temperature, pH, electrical conductivity, turbidity, total dissolved solids, dissolved oxygen, total hardness, alkalinity, ammonia, nitrate, chloride, iron, fecal coliforms and total coliforms. For the analysis of the COSANPA water treatment system, free chlorine was included. The results obtained were compared with the potability standards, according to Ministry of Health Ordinance nº 2.914. For the interpretation of the results, 12 charts of variation of values and 12 maps of isovalues and isoteores were elaborated in the seasonal periods. The pH was considered acid with maximum value of 5.9. The hardness presented soft, moderate and hard degrees in the CaCO3 composition of the groundwater. The chemical contaminations presented in the nitrate values reached 74% of the contaminated wells in the rainy season and the iron values with high concentrations in the COSANPA wells up to 3.5 mg/L. The microbiological contaminations were manifested by the presence of fecal coliforms (Escherichia coli) and total coliforms. During the rainy season, the presence of Escherichia coli was detected in 63% of the wells studied and 89% in total coliforms. In the less rainy period, Escherichia coli and total coliforms were present in 21% and 47% of the wells respectively. The results of these analyzes confirm a higher degree of contamination of nitrate, and of fecal and total coliforms of these groundwater, prevailing in greater amounts of the rainy season.