Tertiary sediments are unconsolidated sandstones, grits with mudstone band and sand with layers of clay.
Quaternary sediments are recent deltaic sands, mangrove swamps and alluvium near the coast. The state is located
on sedimentary rock mainly of sand and alluvium. The major soil groups are juvenile, organic- hydromorphic and
ferrallitic soils.
The population of the city is expected to grow at the annual rate of 4 per cent, reaching 24 million people by 2015
(UN-HABITAT, 2006). Then it is expected to rank third among the world’s cities. According to Kofoworola
(2007), approximately 4 million tonnes of municipal solid waste (MSW) are generated annually in Lagos,
including approximately 0.5 million of untreated industrial waste. Wastewater treatment in Lagos is almost nonexisting.
Also, the sewage system of the city is poor, the only conventional sewerage system is in the metropolitan
area of Lagos, Victoria Island. Due to inadequate sewerage, much of the excreta and sullage disposed of by the
drainage of rainwater through open ditches. During the dry season, when the flushing action of rainfall does not
exist, drainage channels become blocked with solids, creating stagnant ponds of contaminated water.