Building of a shopping center was planed in Riga city, Latvia. Unfortunately, the center was located in the former dump site place where the about eight meters thick waste body contained an irregular mixture of oil products, Phenols, Detergents and metals: Copper, Lead and Chromium. These dissolved in groundwater contaminants entered the nearby lake and dich. It was found out that cleaning of the place was not time and cost effective. It was necessary to reduce the concentration of these pollutants before they entered the both surface water objects [1]. To find the proper walls for reduction of the contaminated groundwater concentration, the local hydrogeological model (HM) was built. The model size was 800m×800m, the plane approximation step was 1.0m. The model contained 11 layers. Therefore, the spatial HM grid contained 7.04×106 nodes. The Groundwater Vistas program was used to run HM [2]. The regional data for HM were provided by the HM of Latvia LAMO4 [3]. It was found out that immobilization of the contamination body by using an enclosing impermeable wall was not practicable, because the valid wall must cover there the 37m thick sand layer. The shallow wall cannot stop the contaminated groundwater flow [4]. Results of modelling proved that to reduce the contaminant concentration, the permeable reactive wall that cleans groundwater must be established before the lake. No wall is necessary for protecting the ditch, because the polluted groundwater flows along the ditch. Results of modelling may be useful for specialists dealing with using impermeable and reactive walls for reducing effects of contaminated groundwater.