Pollution vulnerability and health risk assessment of groundwater around an engineering landfill in Lagos Nigeria

(2017) 58 68 iscientic.org. 59 www.bosaljournals/chemint/ editorci@bosaljournals.com INTRODUCTION Good and sound management of municipal solid wastes (MSW) is of major environmental interests across the world. Dumpsite (an engineering landfill) pollution has been identified as one of the major threats of groundwater resources (Singh et al. 2008) Osibanjo and Majolagbe (2012) conducted a study on the influence on land use pattern in Lagos, confirming solid wastes as the worst of various sources of pollution threatening the groundwater quality. The amount of municipal solid wastes generated globally is projected to increase to 27 billion tons by the year 2050 (MOE, 2009) out of which Lagos, Nigeria generate 12,370 tons of MSW/day (LAWMA, 2011) Solid wastes are of different origin: industrial (this contains much more toxic pollutants, trace metals and organic Ikem et al. 2002) domestic, Agricultural and street sweep. Improper method and practice, as well as non challance towards waste disposal, affect quality of life, creating problems in public health and environment (Ravikumar, 2009) particularly in developing countries. The inefficient and inadequate law (legislation) guiding disposal methods practiced by relevant agencies is another major setback in the handling of municipal solid wastes (Nema, 2004) The process and facilities involved in the storage, collection, sorting, transportation, treatment and disposal of wastes vary from one nation and regions to another. Cultural awareness and belief, organizational abilities, level of technical knowhow and government wastes management policies are some other factors influencing world of MSW disposal practices. Historically, dumpsite remains the simplest, the most cost effective and common method of organized wastes disposal around the world (Wikipedia, 2013) In most developing countries of low and medium income, almost 100% of the wastes generated goes to dumpsite (Longe and Balogun,2010) 90% of the MSW from India are disposed unscientifically (TETRI, 1998) more than 75% of solid wastes generated in more than half member states of European Union are sent to dumpsite EEA,2005) and 138 million tons of 251 million tons of MSW generated in USA was landfilled as well as 82.9% of the wastes were dump sited in Ireland (EHS,2005) There have been several classifications of dumpsite by various countries based on different parameters such as type of wastes deposits, types of liner used and the construction design of the dumpsite. Dumpsite is however, generally grouped into open dumpsite, controlled dumpsite (an engineering landfill) and Sanitary dumpsite (an engineered landfill) Sanitary dumpsites are highly engineered containment system, where wastes is Isolated from the environment. This environmental friendly landfill system involves full or partial hydrogeological isolation, formal engineering preparation, permanent controls and planned waste emplacements and coverings (Kerry et al. 2007; UN Habitat, 2010; Majolagbe et al. 2011) However, the best wastes disposal facility still in practice in many developing nations like Nigeria is controlled dumpsite (engineering landfill) which is an intermediate stage between open dump and sanitary dumpsite. The engineering landfill (controlled dumpsite) option does not isolate the immediate environment from impact of pollutant emanating from dumpsite, hence the need to constantly monitor the environment especially the groundwater. Various techniques have been extensively used in groundwater quality assessment and monitoring. These techniques include: modeling (Magnus et al. 2011) geophysical method (Adepelumi et al. 2008; Adegbola et al. 2012) and the use of water quality indices (Srinivas and Nageswararao, 2013) However, the application of computer based approach (modeling) is now gaining popularity among researchers (Ojuri and Bankole, 2013).The modelling options have provided solutions to some of the limitation in the aforementioned techniques. This study is therefore designed to use a model (modified DRASTIC model) to evaluate potential groundwater vulnerability to pollution from Solous dumpsite in Lagos, Nigeria and the associated health risk.  Description of study area The Solous dumpsite is a controlled dumpsite (engineering landfill) situated within the longitude 3o26 E to 3o25 E and latitude 6o56N to 6o57 N in Igando, Alimosho Local Government Area of Lagos state (Figure 1.0) It started operations in the year 1991 with a projected lifespan of between 5 and 6 years. However, it has been serving for more than twenty (20) years. It is dubbed as Solous 1, as three other relatively newer and smaller refuse dumpsites have been opened very close to the old one (Solous 1) It receives about 4000 tons of waste per day and covers an area of about 5 hectares of land with a waste depth of about 9 m and has reached over 70% of its full capacity (Aboyade, 2004) The dumpsite is surrounded by residential areas, an abattoir and a small fast shrinking Oba stream, located about 2.5 km east ward of the dumpsite. Sampling, chemical and microbiological analyses Forty (40) water samples were collected from twenty different wells around Solous dumpsite bimonthly, for two consecutive years and analysed for various physicochemical parameters using standard procedures. Ten (10) groundwater samples were also collected for microbiogical analysis following standard procedures.