Long-term observations on the influence of groundwater level variations on BTEX concentrations in groundwater

A long-term study on natural attenuation and remediation in soil and groundwater at the former military base Schäferhof-Süd (Niedersachsen) was performed at a former gasoline filling station. At this locality, a large residual source of benzene, toluene, ethylbenzene, xylenes (BTEX) and additional petroleum hydrocarbons is present in the soil. BTEX-concentrations in the groundwater and their correlation with groundwater level variations were monitored for three years. Within the monitoring period, a very dry summer was recorded, which caused the groundwater level to drop by 1.7 m and the BTEX concentrations to increase from 240 µg/l to 1300 µg/l at the site of contamination. The microbial degradation of BTEX was documented by data on consumption of electron acceptors (oxygen, nitrate or sulphate) and production of reduced products (Fe(II), methane). The degradation is further supported by the detection of metabolites. Therefore, the increasing BTEX concentrations were not a consequence of limited biological degradation.