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.

When the underground storage tanks of gas stations leak fuel, the underlying substrate and groundwater may be contaminated by the monoaromatic hydrocarbons Benzene, Toluene, Ethylbenzene, and Xylene (BTEX). In this preliminary study, we used Ground Penetrating Radar (GPR) to detect possible plumes of contamination by hydrocarbons in the subsurface of gas stations in the Amazonian town of Bragança. The findings of this survey were complemented with Gas Chromatography/Mass Spectrometry (GC/MS), which was used to diagnose the presence of BTEX in water samples collected from the gas stations. At two stations, low electromagnetic signal reflections, which are caused by the lower permittivity of the gas vapor relative to water, were recorded in the vadose zone. Four water samples collected from the gas stations and local residences contained toluene, xylene or benzene. Toluene was detected in three of these samples, two from December 2017 (0.26 and 0.13 µg L− 1), and one from December 2018 (10.390 µg L− 1). Xylene was found in two samples from December 2017 (0.46 and 0.34 µg L− 1), while benzene was detected in one sample from December 2018 (0.558 µg L− 1). None of these samples exceeded the Detection Limit (DL) for any of the other BTEX compounds, and none of the other 20 samples collected were above the DL for any BTEX. According to Brazilian legislation for BTEX in drinking water, none of the samples collected in the study were considered unusable as a source of drinking water. The fact that BTEX were only recorded during the dry season indicates the natural attenuation of these compounds through their biodegradation in the subsurface, in particular during the rainy season. The integrated approach adopted in the present study produced satisfactory results for the study of contamination in the subsurface of the gas stations surveyed.