At the Incukalns district of Latvia, two gravels pits from 1956 until 1981 were filled up by liquid sulphuric goudron (mixture of sulphure acids, oil products and other hazardous substances). These dump sites were informatively named as the Northern and Southern pools. During sixty years, the pools are polluting groundwater that moves towards the Gauja river. Waste from the pools will be excavated in the near future. However, the contaminant plumes will continue their movement. Scientists of Riga Technical University have modelled mobility of contaminants, especially, of surface active substances. It was found out that the contaminant plumes of the Northern and Southern pools will reach the Gauja river after about 25 and 76 years (since 2015), accordingly. Luckily, the inflow of contaminants will have no real influence on the quality of river water, because its flow is much stronger than of the contaminated groundwater flow from the pools. This feature encourages development of cost effective remediation methods that will be based on interception of contaminated groundwater that without treatment can be discharged into the river. Without help of the methods, self-purification of the area contaminated by the Northern plume will take about 100 years.