# Groundwater Contamination by Gas Stations in Two Eastern Amazonian Towns (Northern Brazil)
## 3 Results  
A total of 150 water samples were collected during each sampling period over the course of the present study between 2020 and 2024 (Table 1). Only 7 of the 150 samples were contaminated with BTEX. A total of 15 samples were collected in December 2020 (rainy season). The first three samples were obtained from the area adjacent to two gas stations in Tracuateua. In Augusto Correa, a further 12 samples were collected from four gas stations for the evaluation of potential contamination by BTEX. All the concentrations were below the QL in all the samples collected in this first session. None of the samples from this period can be considered to have been contaminated in excess. A total of 45 samples were collected in 2021 (from both study towns) in March (rainy season, 15 samples), July (the rainy-dry transition, 15 samples), and October 2021 (dry season, 15 samples), although all the samples were below the QL for any BTEX compound in the combined GC/MS. Once again, contamination was not confirmed in any of the samples according to the MVAs of the Brazilian Health Ministry [36]. In the fifth sampling session (15 samples, January 2022, rainy season), toluene (2.10 \(\mu\)g L\({}^{-1}\)) was detected by GC/MS in 1 sample, A07, from gas station P14 (1\({}^{\circ}\)01\({}^{\prime}\)33.01\({}^{\prime\prime}\) S, 46\({}^{\circ}\)38\({}^{\prime}\)48.06\({}^{\prime\prime}\) W) in Augusto Correa. This sample was above the QL, but contamination was not confirmed \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Period**} & \multicolumn{3}{c}{**Number of Samples Collected in:**} \\ \cline{2-4}  & **Augusto Correa** & **Tracuateua** & **Number of Samples in Which BTEX Were Detected** \\ \hline December 2020 & 12 & 3 & - \\ (rainy season) & 12 & 3 & - \\ March 2021 & 12 & 3 & - \\ (rainy season) & 12 & 3 & - \\ July 2021 & 12 & 3 & - \\ (rainy-dry season) & 12 & 3 & - \\ October 2021 & 12 & 3 & - \\ (dry season) & 12 & 3 & 1 \\ January 2022 & 12 & 3 & 1 \\ (rainy season) & 12 & 3 & 5 \\ (rainy-dry season) & 12 & 3 & 1 \\ November 2022 & 12 & 3 & 1 \\ (dry season) & 12 & 3 & - \\ August 2023 & 12 & 3 & - \\ (dry season) & 12 & 3 & - \\ March 2024 & 12 & 3 & - \\ (rainy season) & 12 & 3 & - \\ Total & 120 & 30 & 7 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of the samples of underground water collected in the towns of Augusto Correa and Tracuateua, in northeastern Para, Brazil, and the occurrence of contamination with BTEX. in terms of the MVA defined by Brazilian legislation [36]. BTEX were not detected in any of the other samples collected from the two study towns during this season. In Tracuateua, during the sixth sampling session (12 samples collected) in July 2022 (rainy-dry transition), 2 samples, A24 (0.141 \(\mathrm{\SIUnitSymbolMicro\text{$\mu$g L}}^{-1}\)) and A25 (0.167 \(\mathrm{\SIUnitSymbolMicro\text{$\mu$g L}}^{-1}\)), from gas station P12 contained toluene (Table 2). Neither of these samples exceeded the maximum values permitted by the Brazilian legislation [36]. Three of the samples collected in Augusto Correa (sample A06 from gas station P14, and samples A10 and A11 from station P15, July 2022) had toluene concentrations that were above the QL, between 0.14 \(\mathrm{\SIUnitSymbolMicro\text{$\mu$g L}}^{-1}\) and 0.236 \(\mathrm{\SIUnitSymbolMicro\text{$\mu$g L}}^{-1}\) (Table 3). None of the samples collected in Augusto Correa during this period exceeded the permitted thresholds for any of these substances [36]. In the seventh sampling session (15 samples, November 2022, dry season), toluene (0.664 \(\mathrm{\SIUnitSymbolMicro\text{$\mu$g L}}^{-1}\)) was detected by GC/MS in a single sample, A06, from a residence near gas station P14 (1\({}^{\circ}\)01\({}^{\prime}\)32.84\({}^{\prime\prime}\) S, 46\({}^{\circ}\)38\({}^{\prime}\)48.59\({}^{\prime\prime}\) W) in Augusto Correa. This sample was above the QL but below the Brazilian legal MVA [36].