Navegando por Autor "OLIVEIRA, Beatriz Pinheiro Pantoja de"

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Hidroquímica e caracterização isotópica (87sr/86sr) dos sistemas aquíferos Barreiras e Pirabas nos municípios de São Francisco do Pará e Igarapé-Açu, nordeste do Pará.
(Universidade Federal do Pará, 2019-08-16) OLIVEIRA, Beatriz Pinheiro Pantoja de; GALARZA TORO, Marco Antonio
The northern region of Brazil is privileged in water resources, both superficial and underground. Recently the use of groundwater has increased, since it can be captured in the place of consumption. In the northeastern meso-region of Pará, the volume of hydrogeological data is concentrated in the metropolitan region of the capital Belém, which has a mixed supply system, that is, with surface water (Guamá River) and groundwater. However, in the other municipalities, such as those in this study, that the water supply system is made entirely by groundwater. Thus, it is very necessary, any and all surveys that contribute for a better knowledge of the underground resources which serves the northeastern state of Pará. The main aquifers in this context are: the Pirabas System - SP (carbonate host rock), Barreiras System - SB (siliciclastic host rock). Previous studies have shown, through hydrogeochemistry and isotope geochemistry (87Sr/86Sr), the interaction between these two important underground reservoirs, and they showed a hydraulic connection through faults and fractures, resulting from the neotectonic present in NE of Pará. Thus, in this work, groundwater is studied in the municipalities of São Francisco do Pará and Igarapé Açu, in the period of fifteen months, following the seasonality of this region, in order to investigate interactions that the aquifers may present during recharge periods. From a screening of the Groundwater System (SIAGAS) and logistic campaigns, 9 wells were selected, being 5 shallow (~ 30 to 60 m) and 4 deep (~ 80 to 135 m). The campaigns took place from October 2017 until January 2019, three collections in the dry period and three in the rainy season. Physical-chemical measurements were taken in the field, such as temperature, pH, electrical conductivity. The hydrochemical analyzes were performed in the Laboratory of Hydrochemistry of the Institute of Geosciences, being determined the total alkalinity by the titration method, the silica and the total iron by the spectrophotometric method; the chromatographic analyzes were performed at the Eletronorte Analytical Laboratory, and the concentrations measured by chromatography of the ions Ca2+, Mg2+, Na2+, K+, Cl-, SO42-, NO3-, F-. The concentration of Sr2+ was obtained in the ICP-MS (ICap-Q) and the 87Sr/86Sr isotopic ratio in the ICP-MS (Neptune) of the Geochronology Laboratory of the Federal University of Pará (Pará-Iso). The results were submitted to statistical treatments to show correlations and grouping of elements. The physical-chemical parameters of the aquifer systems did not show significant variations during the hydrological cycle. The mean temperature varied from 27.6 to 27.4°C, the conductivity from 28 to 154 μS/cm, and the pH from 4.0-5.5 (SB) and 6.0-7.2 (SP). The concentrations of Fe (t) (mg / L) ranged from 0.0 to 2.2 (SB) and 0.0 to 3.3; SiO2 (mg / L) 0.8 to 13.6 (SB) 5.4 to 21.0 (SP); HCO3- (mg / L) 0.0 to 9.0 (SB) and from 0.0 to 81.3 (SP). The concentrations of ions had results (in mg / L) as Na+1.78 at 22.15 (SB) and 2.34 at 7.29 (SP); K+ 0.14 to 1.81 (SB) and 1.05 to 1.58 (SP); Mg+2 20.34 to 0.99 (SB) and 1.49 to 3.81 (SP); Ca+2.07 to 3.22 (SB) and 12.26 to 26.93 (SP); Cl- 3.18 to 37.24 (SB) and 3.71 to 16.88 (SP); NO3 - 0.10 to 10.33 (SB) and 0.00 and 1.20 (SP); SO4 2-0.94 to 12.17 (SB) and 1.84 to 6.62 (SP); F- 0.00 to 0.02 (SB) and 0.05 to 0.11 (SP) and, Sr2+0.006 to 0.018 (SB) and 0.045 to 0.146 (SP). From the Piper diagram, it was verified that in the Barreiras aquifer predominates the Na-Cl facies and acid pH, on average 4.7, with contribution of meteoric and / or anthropogenic water, a factor that increases the vulnerability of the aquifer; and the water of the Pirabas aquifer, predominates Ca-Mg-HCO3 facies and pH above 6.0 on average, being strongly influenced by the dissolution of the carbonate, the aquifer has a confined regime, a factor that reduces its vulnerability to contamination. The Stiff diagram indicates that substrates in interaction with water are sandstone, shale, limestone and dolomite. Metals that may be toxic and cumulative to human health were not detected at significant levels. The 87Sr/86Sr isotopic ratio of each sample had a linear trend over time, and the individual samples showed little variation in their isotopic ratios. According to the obtained isotopic ratio values, three aquifers are separated: the Lower Pirabas which remains in the dry and rainy periods between 0.709138 and 0.709333, as well as the Upper Pirabas remained between 0.710413 and 0.711013; the Barreiras Aquifer demonstrated a differentiated variation in the rainy season, evidencing a small interaction with rainwater, and values were between 0.710687 and 0.714903. The multivariate statistical treatment (PCA), along with the 87Sr/86Sr vs. 1/Sr have shown that the Aquifers behave independently. Regarding the wells, although they have been prepared to avoid contamination, the maintenance of these wells is somewhat unsatisfactory, so that at some collection points there are indications contamination by anthropic action. In the northeast of the State of Pará, the upper contact of the Pirabas Formation with the Barreiras Formation is quite discussed, and varies along the Bragantina Platform. There are works that describe as discordant contact, or as a faciological interdigitation and still, those that defend local variations. In this case study, the lenticular complexity of these aquifers, which are interspersed with impermeable layers, impede hydraulic communication, which explains the geochemical diversification of the water and the confined type aquifer behavior.