Pavements, foundations and underground constructions face many geotechnical problems related to wastewater leakage into underlying soils. The chemical processes between soil particles and chemical constitutive of wastewater change the soil engineering properties into undesirable properties. The effect of wastewater seepage on the consolidation process of contaminated clayey soil was investigated and presented in this paper. A series of consolidation tests was carried out on naturally polluted undisturbed soil samples at variant exposure period of wastewater. Soil samples were taken over a period of time from tested holes of a ground sewage tank. This tank is used to collect and discharge the wastewater from dewelling buildings. The results show harmful effects of wastewater from dewelling buildings. The results show harmful effects of wastewater seepage on consolidation parameters and deformational behavior of consolidated clayey soil.