A hydrogeological impact survey on the largest onshore oil field in Brazil: physicochemical and total petroleum hydrocarbon (TPH) analyses in the south of Japaratuba River Basin, Sergipe

The Japaratuba River Basin is one of the most important hydrogeological units in terms of water demand in the state of Sergipe, Brazil. Due to its poorly developed water supply plan, oil exploration and agricultural industries, the Japaratuba River Basin is susceptible to considerable environmental stress. Emphasis is given to the area of the Campo de Carmopolis which, being the largest onshore oil field in Brazil, represents the greatest agent of environmental pollution in the area. The aim of this study is to characterise the contaminants present in surface water and groundwater of the southern part of Japaratuba River Basin region which is proximal to Carmopolis Oil field. We performed physicochemical and total petroleum hydrocarbons (TPH) analyses in ten water samples from the southernmost part of the basin. To better characterise the hydrogeological systems, 27 physicochemical parameters were analysed: potential of hydrogen (pH), colour, turbidity, electrical conductivity (EC), hardness, acidity, alkalinity, iron (Fe), nitrate (NO3-), nitrite (NO2-), ammonia (NH3), chloride (Cl-), phosphorus (P), fluoride (F-), sulphate (SO42-), bromate (BrO3-), calcium (Ca2+), magnesium (Mg2+), potassium (K+), sodium (Na+) bicarbonate (HCO3-), carbonate (CO32-), aluminium (Al3+), manganese (Mn2+), total dissolved solids (TDS), chlorite (ClO2-) and glyphosate. The results identified concentrations above Brazil's maximum permitted value (MPV) for TPH in two samples, and at least four samples presented values that do not meet the potability standards established by Brazilian federal legislation (Portaria de Consolidacao No 5, 2017). This enforces the need for more robust remediation and mitigation methods on the contaminated sites, since the local population relies solely on these water resources and poor management would lead to health hazards and socioeconomic impacts. Continuous monitoring of sampled locations along with an increase in sampling mesh are also recommended.