The invention relates to a process for removing a contaminant from groundwater wherein it is not necessary for groundwater to be extracted from the soil. To that end, the process according to the invention comprises the following steps: a) a biologically active layer (2) is applied on or in the soil b) the contaminated groundwater is contacted with the biologically active layer (2). The contaminant is converted in the biologically active layer. The biologically active layer (2) may be applied discontinuously. The contaminated groundwater may be contacted with the biologically active layer with the aid of for example a gas.