Groundwater quality and underground flow in southern Amazon, Brazil

Abstract

The aim of this study was to evaluate the physical, chemical and microbiological groundwater parameters as well as the mapping of groundwater flow in an urban area of Presidente Médici county in Rondônia State, Southern Amazon. The water samples were collected in 11 wells in April and June of 2017, which corresponds to the dry season in the studied region. Groundwater was acidic, with a large range of nutrients concentration, low turbidity and presence of fecal coliforms in most sampled wells. The parameters that were in disagreement with Consolidation Ordinance No 05/2017/MS and CONAMA no 396/08 Resolution, were pH, turbidity, total coliforms, Escherichia coli, and nitrate. Regarding the microbiological parameter, most of the sampling sites were in disagreement with the established by the legislation that it recommends to be absent in 100mL, when it is destined for human consumption. Densities found were higher than 112,000UFC/100mL for total coliforms and higher than 56,000UFC/100mL for Escherichia coli. The pH ranged from 4.1 to 6.4, and the turbidity showed a maximum value of 6.7 uT. The nitrate concentrations were above the established level (10 mg.L-1) in April in 72.7%, and in June 50% of the wells, with a maximum of 48.5 mg.L-1. The study of the direction of the underground flow demonstrated the predominance of the flow towards the nearest river, as well as potential contributors of microbiological influences. The results indicate contamination of the groundwater by domestic sewage, being proved by the presence of coliforms and nitrate, being the water unfit for human consumption without adequate treatment.