An active dumpsite in Lagos Southwestern Nigeria was monitored to test the efficiency of natural attenuation in the reduction of contaminants by determining biogeochemical and engineering properties of soils and groundwater within and around the site. From the Casagrande Plasticity Chart, the soil can be classified as clay or silts of intermediate to high plasticity, thickness of the unsaturated zone is between 10-20m, and permeability is low between 1.96x10-5 and 41.8x10-5 m/s. The appropriate microorganisms such as bacteria, viruses and fungi which are required for natural attenuation were naturally present. Nutrients such as calcium, copper, magnesium, manganese, potassium, sodium, and zinc as well as electron donor (Organic carbon) and electron acceptor (oxygen, nitrate, sulphate, iron) were also present in various amount for effective natural attenuation processes. All the parameters analysed in water samples were within Environmental protection agency standard except Fe, Na, Cl, NO3, Al, Ba, Ni, Total Bacteria and Total Fungi. Phenol and Total viral count were not detected in the two boreholes but they showed values as high as 10000MPN/100ml and 230CFU/100ml, respectively in leachates. The concentrations of contaminants in the soils were very high and inversely proportional to depth.