Evaluation of the contamination of the subsurface and groundwater by monoaromatic hydrocarbons in an eastern Amazonian town in northern Brazil

Abstract

The present study evaluated the contamination by monoaromatic hydrocarbons (BTEX: benzene, toluene, ethylbenzene, and xylene) of the subsurface of gas stations and adjacent residences in the Amazonian town of Bragança, in northern Brazil. We combined the ground penetrating radar (GPR) geophysical tool, to detect possible plumes of contamination by BTEX, with gas chromatography (GC) and mass spectrometry (MS), which were used to diagnose the presence of BTEX in water samples obtained from boreholes located within the study area. The GPR identified low-amplitude reflections in the vadose zone of two gas stations, whose attenuation near the surface was due to the low permittivity recorded in the radargrams, which may have been caused by the reduced permittivity of the hydrocarbons (gas vapor) in comparison with water. The GC–MS identified benzene, toluene, ethylbenzene and/or xylene in 13 water samples (19.7% of the samples collected). Only three of the samples contained two contaminants, invariably toluene and xylene, whereas all the others contained only a single BTEX. Toluene and xylene were the BTEX compounds found most frequently in the samples. However, none of the samples collected in the study exceeded the threshold established by Brazilian legislation for BTEXs in drinking water. The integrated application of GPR and CG-MS produced satisfactory results for the diagnosis of the contamination of the subsurface of the gas stations surveyed in the present study.

Groundwater Contamination by Gas Stations in Two Eastern Amazonian Towns (Northern Brazil)

“…Ref. [67] evaluated the occurrence of BTEX contamination in the subsoil of gas stations and adjacent residences in the eastern Amazonian town of Bragança, combining groundpenetrating radar (GPR) with GC/MS. That study identified the presence of the BTEX contaminants benzene, toluene, ethylbenzene, and/or xylene in 13 of the samples of underground water (19.7% of the total) and found evidence of the possible existence of plumes of BTEX contamination in the subsurface of the gas stations, confirming that leaks in the storage tanks were the source of the contamination.…”

“…Even so, it is important to consider that even a minimal level of contamination serves as a warning call, which highlights the need for continued monitoring. Further research is also needed to identify the source of the contamination of the subsurface in the two study towns, using, for example, geophysical tools, which have been shown to be highly effective for the identification of underground plumes of BTEX contamination, contributing to the verification of possible sources of contamination, e.g., [66,67].…”

Application of the Ground Penetrating Radar (GPR) and Electromagnetic (EM34-3) Geophysical Tools and Sedimentology for the Evaluation of the Subsurface of Sites Earmarked for Aquaculture Ponds in the Amazon Region of Northern Brazil

“…Geophysical tools are one other valuable option for the description of the quality of soils. This technology is non-invasive, non-destructive, and has excellent spatio-temporal resolution (e.g., [22][23][24]), and can provide valuable information on the characteristics of the subsoil, including its lithology, stratigraphy, bedrock, water table, and the presence of depressions, faults, and fractures (e.g., [25][26][27][28][29][30][31][32][33][34][35][36][37][38]).…”

“…The data were also edited, with spatial resampling and interpolation being applied to the traces. The data processing involved the following steps (e.g., [25][26][27][28][29][30][31][32][33][34][35][36][37][61][62][63][64]): static correction of zero-time, gain, time filtering (1D), and spatial filtering (2D), that is, background removal and moving average trace subtraction. The hyperbole overlap method was used for the time-depth conversion, by obtaining a propagation velocity of 0.092 m/ns.…”