Integrated Geophysical and Geochemical Methods for Environmental Assessment of Municipal Dumpsite System

Leachate originating from open

refuse dumpsite systems can be delineated through an integration of qualitative

and quantitative methods. This study was designed to examine extent of leachate

and pollution from one of the numerous open refuse dumpsites in Lagos

metropolis. Qualitative assessment was determined using electrical resistivity

tomography (ERT), vertical electrical sounding (VES) and induced polarization

geophysical methods. Both ERT and VES methods revealed persistent low

resistivity (1 - 20 Ωm) of leachate to the depth above 35 m. The two methods were projected to produce

3-D view of the site which shows a NW-SE flow pattern of the leachate and

possibly, the groundwater. IP values observed over the polluted zone was -2.9 - 8 ms, indicating a sandy layer. Quantitative assessment was achieved

by analysis of geochemical substances in the water samples taken from wells and

boreholes in the precinct of the dumpsite. Here, we examine the macroelements,

salts (sulphates, nitrates and chlorides), heavy metals, radioactive metals contents

and physical parameters of the water samples. The analyses reveal the presence

of these substances in the water and their strong correlations justified the

provenance as the same. As part of the quantitative evaluation, physical

parameters (pH, TDS, DO, salinity, total hardness, turbidity, electrical

conductivity EC and temperature) of the water samples were also determined. The

samples pH plotted in the acidic domain unsuitable for human consumption.

Leachate flow direction was generated from the decreasing concentration of

measured parameters (geochemical elements and physicals properties) in NW-SE

direction which agrees with similar flow pattern deduced from ERT results.