RESUMOO monitoramento das águas subterrâneas no Estado de São Paulo tem detectado concentrações anômalas de nitrato em amostras de água do Sistema Aquífero Bauru em poços tubulares situados nas áreas urbanas de inúmeros municípios do interior paulista. Diante deste cenário, o Instituto Geológico, juntamente com outras instituições, está desenvolvendo um projeto para avaliar as tendências de distribuição das concentrações desse contaminante nas águas subterrâneas, ao longo do tempo e espaço, frente aos padrões de ocupação urbana. Uma das áreas de estudo compreende a cidade de Marília, onde o Sistema Aquífero Bauru é representado pelos aquíferos Marília (superior) e Adamantina (inferior). As atividades realizadas compreenderam o cadastro de poços, tratamento estatístico dos dados hidroquímicos pré-existentes e avaliação entre possíveis relações das concentrações de nitrato observadas com a expansão urbana ao longo das últimas décadas. Os resultados obtidos indicaram que as maiores concentrações de nitrato (até 16,9 mg/L N-NO 3 -) ocorrem nas áreas com ocupação urbana mais antiga e em poços com profundidades até 150 m. Isto sugere que a contaminação está relacionada aos sistemas de esgotamento sanitário (fossas antigas e vazamentos na rede coletora de esgotos) e ocorre predominantemente no Aquífero Marília. As porções mais profundas deste aquífero são menos permeáveis devido à cimentação carbonática, o que limita a movimentação desse contaminante para o Aquífero Adamantina, evidenciado pela qualidade da água dos poços mais profundos, que apresentaram baixas concentrações de nitrato, em geral, inferiores a 3,0 mg/L N-NO 3 -.Palavras-chave: Sistema Aquífero Bauru; nitrato; água subterrânea; ocupação urbana. ABSTRACTAnomalous nitrate concentrations have been detected in the Bauru Aquifer System by groundwater monitoring wells located at the urban areas of many cities throughout the State of São Paulo. Focusing on this problem, the Geological Institute, together with other institutions, is developing a project to evaluate the trends of nitrate concentration in groundwater over time and space related to urban development. One of the study areas comprises the Marília municipality, where the Bauru Aquifer System is composed of the Marília and Adamantina aquifer units. The activities conducted include: record of drilling wells, statistical treatment of previous hydrochemical data and evaluation of urban expansion over the last decades. The results indicate that the highest nitrate concentrations (up to 16.9 mg/L N-NO 3 -) occur in older urban areas and in drilling wells up to 150 m in depth. This indicates that the contamination is probably related to the sewage system (old septic tanks and sewer network leakage) and that it occurs mainly in the Marília Aquifer. The deepest parts of the aquifer are less permeable due to carbonate cementation, which restricts the percolation of this contaminant into the Adamantina Aquifer. It is evidenced by the groundwater quality of the deepest wells, which showed low nitrate concentratio...

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The aim of this study is to investigate groundwater contamination caused by septic tank, which infiltrates domestic effluent into a sandy-alluvial unconfined aquifer at Parque Ecológico do Tietê (São Paulo, Brasil). The methodology used is based on chemical analysis of 68 shallow monitoring wells (up to 5.0 deep) installed at 50x50m area. Some chemical parameters as nitrate, nitrite, ammonium, chloride, pH, Eh, electric conductivity and dissolved oxygen have been measured fortnightly using portable equipaments. Major ions and nitrogen compounds (organic-N, ammonia, ammonium, nitrite, nitrate) have been analysed monthly. This detailed monitoring program has allowed to identify three different geochemical zones, according to predominance of nitrogen species: organic-N, ammonium and nitrate. Following the groundwater flux, it is also possible to verify a decrease in the pH values. From chloride concentration variation and eletric conductivity, the dispersion of the plume was calculated. Fast contaminant concentration variations have been attributed to the rapid aquifer recharge that provokes deformation into the streamtubes geometry.

This study follows the geochemistry of nitrogen in a Cretaceous and unconfined sedimentary aquifer in the city of Urânia (Brazil) over 20 years. Although the sewer network was built in the 1970s, the nitrate contamination problem (>45 mg/L-NO3−) persists to this day. The oldest urbanization areas located in the north of the city initially used cesspits for wastewater and currently present the highest nitrate concentrations (>120 mg/L-NO3−), with the plume reaching the deeper aquifer portions (up to 100 m). The contamination is not as dramatic in the south part of the city, where urbanization including installation of the sewage network with PVC pipes that are more resistant to leak than the old ceramic networks occurred after 1985. Based on the constructive well profiles, three hydrogeochemical zones were established: shallow (<20 m deep), with average nitrate of 63 mg/L-NO3−; intermediate (20–60 m), with 30 mg/L-NO3−; and deep (>60 m), with 17 mg/L-NO3−. The current total nitrate mass in the aquifer exceeds 731 kg-NO3−. Numerical flow (Modflow) and transport (MT3D) model scenarios support the hypothesis that the nitrate contamination is caused by substantial infiltration of nitrogen through the cesspits until the 1970s, but after the 1990s, leaks from the sewer network should be responsible for the maintenance of the recently observed high concentrations of nitrate.