Electromagnetic Survey (GEM-2) for Monitoring of an Open Dumpsite in Sri Lanka

Open dumping of municipal solid waste creates series of environmental and social problems. Monitoring of dumpsites is important in deciding and designing the mitigation measures to reduce the risk. Direct and continuous monitoring of dumpsite is difficult and requires time, money and labour for both sample collection and laboratory analysis. Geophysical methods such as electromagnetic (EM) technique can be used for subsurface investigation rapidly without in-situ drilling and sampling. GEM-2 is a Multi-frequency, handheld EM sensor. This produces EM waves at pre-set multi frequencies and receives secondary EM waves from eddy current of substrate depending on the apparent electrical conductivity (ECa) of the substrate. Thus ECa of the underneath substrate can be mapped. An open dumpsite in Udapaltha Pradeshiya Sabha, Central province, Sri Lanka was surveyed using GEM-2 and validated with field measurement. For validation, waste samples were collected up to 30 cm depth and electrical conductivity (EC) was measured at the laboratory and ECa was calculated. Spatial and temporal variation of ECa and delineation were clearly depicted in maps produced by GEM-2. Maximum reported ECa in Old-bottom and New-top of dump site were 88 mS/m and 180 mS/m, respectively. Measured ECa and EM surveyed ECa were correlated with simple linear regression. Best correlations were obtained at Old-bottom with 93 kHz wave length while 85 kHz for New-top. It can be concluded that EM survey is a powerful technique for dumpsite monitoring with cautious interpretation.