The state of t he poor solid waste management in Port Harcourt, Rivers State, Nigeria is poor and has now reached an alarming proportion. Wastes are frequently dumped along the streets, in the gutters and informal waste dumps, which has been linked to several environmental, safety and public health impacts including the blockage of gutters, nuisance odours, surface and groundwater pollution, air emissions of carbon dioxide and methane and soil contamination. Waste dumps have also been implicated in road traffic obstructions and accidents. The Rivers State environmental sanitation and waste management authorities are at loss on how to best handle the wastes sustainably. In this study, we used an integrated risk based approach (IRBA) to assess and recommend management strategies for Eneka waste dump. The risk index was computed from the summation of the product of the sensitivity of the variable studied and their respective weights of their attributes. The Eneka dumpsite had a total risk index score 452.3 which corresponded to moderate hazard potential, suggesting that the dumpsite require immediate rehabilitation and conversion to a landfill.
Solid waste management has remained an intractable environmental sanitation problem in Nigeria. This problem has manifested in the form of piles of indiscriminately disposed heaps of uncovered waste and illegal dumpsites along major roads and at street corners in cities and urban areas. This problem is compounded by the rapid urbanization and population growth which has led to the generation of enormous quantities of solid waste which are often discarded by open dumping. Rushbroke describes open dumping of municipal solid waste (MSW) as a primitive stage of waste disposal, practiced by three fourths of countries and territories round the world Open dumps are the major causes of environmental degradation and public health concerns in many developing countries including Nigeria. These waste dumps may contain a mixture of general waste and toxic, infectious or radioactive wastes and are susceptible to burning and exposure to scavengers. There are a number of major risks and impacts of the dumpsites on the environment. For instance, air pollution from open burning, due to emission of green house gases such as methane and carbon dioxide; the air emissions and leachates generated as a result of decomposition of waste may contaminate air, surface and groundwater sources; fire hazards and explosions cause public health risks as well. The emission of greenhouse gases, rats and fly infestation and nuisance effects are among the health and environmental impacts of poor solid waste management. In addition, scattering of wastes by wind and scavenging by birds, animals and waste pickers creates aesthetic nuisance. Malodour emanating due to the degradation of the waste in the dumpsite has nuisance effect and decreases the economic and social values in the locality. In many dumpsites, the waste is directly increasing global concern over the public health impacts attributed to environmental pollution, inparticular, the environmental quality and human health risks associated with the waste dumps. The World Health Organization estimated that about a quarter of the diseases facing mankind today occur due to prolonged exposure to environmental pollution. Unfortunately there seems to be no clear cut guidelines at the national or state levels on how to deal with these dumpsites in a sustainable manner, particularly in the developing where ironically the burden of environmental pollution seems to be highest. It is suggested that the first task would be to decide on one of three options: if the dumpsite should be closed, remediated or rehabilitated. To determine whether to rehabilitate and close or remediate, upgrade and operate a dumpsite may require an environmental impact assessments studies (EIAs) including consultation with the interested and affected parties, specifically the adjacent communities. In countries like Nigeria where the number of existing dumpsites (both legal and illegal) are many, economic considerations of the evaluation process must be taken into consideration in recommending a suitable approach or methodology. Assessing the relative health and environment hazards posed by the dumpsites existing throughout the developing countries could help prioritize, plan and initiate dumpsite rehabilitation.
At present there are hardly any documented experiences with the use of risk based approaches for the management of dumpsites in Nigeria. The need for a risk based tool that is suited to the peculiarities of a developing country and that has been tested and proven to be useful, scientifically sound and easy to apply is therefore urgently required, give the number of waste dumps in Nigeria and the march towards the achievement of vision 20-20-20 (the vision of the Nigerian state to become one of the twentieth largest economies in the world by the year 2020). The lack of effective waste management strategy is a potential threat to achieving sustainable development in Nigeria. Studies that would bring about strategies to manage these wastes are urgently needed. Hence, the purpose of this study is to provide a scientific assessment of Eneka dumpsite, using an integrated risk based approach (IRBA) developed by Kurian, et al. that would enable a decision to be taken on the management of the site.
MATERIALS AND METHODS
Description of the Study Site
The Eneka Dumpsite: Eneka dumpsite is situated west of the City of Port Harcourt, along Igwuruta/Eneka road on Longitude 7°02’33.18”E and Latitude 4°53’32.82”N. The neighbouring settlements to Eneka town include Rumuokwurushi/Elimgbu in the North, Igwuruta in the south and Rumuduru town (in Oroigwe) in the east. The nearest building to the dumpsite has a distance of about 500m though initially the area was a thick bush and has been earmarked by the state government as an industrial area. The site is about 200 m in length and 425 m width tapering to about 130 m along Igwuruta/Eneka highway. The site is currently used for the disposal of domestic non hazardous waste mainly kitchen waste from offices, operational and residential locations and wastes arising from estate management activities, including but not limited to garbage (cardboard/paper), garden waste, food, plastics, metals (tins/ cans) and trash.
Risk Assessment: The Risk Index (RI) of the site was calculated using the following formula
Wi – Weightage of the ith variable ranging from 0 – 1000 Si – Sensitive index of the ith variable ranging from 0-1 RI – Risk Index variable from 0 – 1000
The RI for Eneka waste dump was computed based on the attributes presented in Table 1 while the criteria for categorizing the nature of the risk is shown Table 2.
Table 1: Attributable Weightage and Sensitivity
S/ N Attribute Attribute Weightage 0.0-0.25 0.25-0.50 0.5-0.75 0.75-1.0
1 Site Specific Criteria
1 Distance from nearest water supply source (m) 69 >5000 2500-5000 1000-2500 <1000
2 Dept of filling of waste(m) 64 20
3 Area of the dumpsite (Ha) 61 20
4 Ground water dept (m) 54 >20 10- 20 3 – 10 25 10-.25 5 – .10 20 10 – .20 5 – .10 <5
9 Distance from surface water body(m) 41 8000 1500 – 8000 500 -1500 50 30 – 50 15 – 30 0 – 15
11 Life of the site for future use (years) 36 20
12 Type of waste (MSW/HW) 30 100% MSW 75% MSW 50% MSSW >50% HW
+ 25% HW + 50% HW
13 Total Quantity of waste at site(t) 30 105 -106 > 106
14 Quantity of waste disposed (t/day) 24 1000
15 Distance to the nearest village in the predominant wind (m) 21 >1000 600 -1000 300 -600 100 30 -100 10 – 30 <10
17 Annual rainfall (cm/yr) 11 250
18 Distance from the city(km) 7 >20 10 -.20 5 -.10 <5
19 Public Acceptance 7 No public Accepts dump Accepts Accepts dump
concerns rehabilitation dump closure closure and
20 Ambient Air Quality CH4 % 3 0.1
0.05 – 0.1 > 0.1
II – Related to characteristics of waste at dumpsite
21 Hazardous contents in waste % 71 30
22 Biodegradable fraction of waste at site 66 30 20 -30 10 -.20 <10
24 Moisture of waste at site 26 40
III Related to Leachaete Quality
25 BOD of leachate Mg/L 36 100
26 COD of leachate Mg/L 19 500
27 TDS of leachate Mg/L 13 4000
Source: Kurian, et al.
Table 2: Criteria for hazard evaluation based on the hazard potential index
SI.No Overall Score Hazard Evaluation Recommended Action
1 750 – 1000 Very High Close the dump with no more land filling in the area
Take Remedial action to mitigate the impacts
2 600 -749 High Close the dump with no more land filling in the area
Remediation is optional
3 450 -599 Moderate Immediate Rehabilitation of the dumpsite into sustainable landfill
4 300 -499 Low Rehabilitate the dumpsite into Sustainable Landfill in a phased manner
5 <300 Very Low Potential Site for future Landfill
Source: Kurian, et al. 
RESULTS AND DISCUSSIONS
The Eneka dump area is located in a seasonally flooded area (Figures 1 and 2). The waste dump is located though at the outskirt of the city, some residential areas are close to the site and the site is located along one of the roads entering the city. The groundwater of the area is relatively shallow. The permeability and porosity of the soil of the area is high [5, 6]. The site is flooded most part of the year and the rainfall in the area exceeds 2500mm per annum. The aquifers are mostly unconfined. The result of the risk based assessment is presented in Table 3. The Eneka dumpsite had a total risk index score 452.3 (Table 3) which correspond to moderate hazard potential, meaning that immediate rehabilitation of the dumpsite into sustainable landfill is required (Table 2). The wastes generation in Port Harcourt was projected to 210,934, 304, 477 and 352,853 tonnes per annum in 1982, 1990 and 2000 respectively. Ayotamuno and Gobo estimated the solid waste generation rates in Port Harcourt to be 1.25 kg per person per day, whereas Ibiebele reported a more conservative estimate of 0.22 kg per person per day.
The composition of the wastes at Eneka dump site includes both degradable (paper wastes, food and agricultural wastes, sewage etc) and non biodegradable wastes (plastics, nylon, aluminium and other metal containing substances) (Figures 1 and 2). The composition of solid wastes found in other cities includes papers and cartons, food remnants, glass and bottles, plastic and polythene, tin and metals, ashes and dust, textile and rags, aluminium and other minerals. Vegetation remains are forms a large part of the most waste dump. On average, the MSW from Port Harcourt consisted of 66.6% volatile solids, 13.5% fixed solids, 19.1% liquid and 0.8% other components. The average biodegradability fraction is 0.807, with a carbon-to-nitrogen ratio of 27:1. The energy content of the refuse was 7.25 MJ/kg. In a related study, the percentage composition of wastes from Port Harcourt consist of organic biodegrable wastes (38.6%), glass (23.%), metals (10.8%), textiles (6.4%), wood wastes (7.6%), sludge (5.6%), expired chemicals and waste drugs (2.1%). Ajao and Anurigwo reported the following composition in tonnes per year; putrescible wastes (108,000), non hazardous wastes (35,500), hazardous wastes (125), non hazardous sludge (1,000) and hazardous sludge (13,600).
Fig. 1: View of Eneka dumpsite from the front
Fig. 2: Truck disposing waste at Eneka dumpsite
Table 3: Risk index worksheet for Eneka dumpsite
Attribute Attribute Sensitivity
S/N Attributes Weightage measurement Index Score
1 Distance from nearest water supply source (m) 69 <1000 0.75 51.75
2 Dept of filling of waste(m) 64 <3 0.125 8
3 Area of the dumpsite (Ha) 61 <5 0.125 7.625
4 Ground water dept (m) 54 6 0.625 33.75
5 Permeability of soil (1x106cm/s) 54 0.1-0.2 X106 0.3 16.2
6 Ground water Quality 50 Potable if no alternative 0.625 31.25
7 Distance to critical habitats such as wetlands and reserved forests (Km) 46 <3km 0.625 28.75
8 Distance to the nearest airport (km) 46 20 0.25 11.5
9 Distance from surface water body(m) 41 <3km 0.25 10.25
10 Type of underlying soil (% clay) 41 40 0.25 10.25
11 Life of the site for future use (years) 36 10 0.5 18
12 Type of waste (MSW/HW) 30 MSW 0.1 3
13 Total Quantity of waste at site(t) 30 12 X 106 0.75 22.5
14 Quantity of waste disposed (t/day) 24 125 0.125 3
15 Distance to the nearest village in the predominant wind (m) 21 500 0.75 15.75
16 Flood proneness (flood period in years) 16 5 0.75 12
17 Annual rainfall (cm/yr) 11 253 1 11
18 Distance from the city(km) 7 3 1 7
19 Public Acceptance 7 Accepts dump rehabilitation 0.5 3.5
20 Ambient Air Quality CH4 % 3 0.05 0.125 0.03
21 Hazardous contents in waste % 71 5 0.01 0.71
22 Biodegradable fraction of waste at site 66 60 0.75 49.5
23 Age of filling (years) 58 12 0.75 43.5
24 Moisture of waste at site 26 30 0.75 19.5
25 BOD of leachate mg/L 36 24 – 120 0.5 18
26 COD of leachate mg/L 19 200-1400 0.5 9.5
27 TDS of leachate mg/L 13 100-3000 0.5 6.5
It is ironical, that Port Harcourt, which used to be known as the ‘Garden City of Nigeria’ because of her neatness is now overwhelmed by the presence of MSW, which is disposed indiscriminately in the streets and disused borrow pits, which are now referred to as waste dumps. According to Ayotamuno and Gobo, the presence of piles of refuse dotting the entire city may have now turned Port Harcourt rather to a "garbage city". Wastes have been indiscriminately dumped in the city especially at street corners and gutters, which have resulted in the blockage of gutters and also obstructing traffic. Ogu has reported that the cause of solid waste problems in Nigeria is obviously due to rapid urbanization with its attendant increase in the generation of solid wastes and that many municipal and local government authorities are unable to manage the situation. Studies of some dump sites in South Eastern Nigeria showed that the dumpsites served as conventional "landfills"; as they received all sorts of wastes which were neither sorted out nor controlled. The dumpsites have variable ages, located on voids, gullies, river banks, borrow pits and swampy areas, which provide breeding grounds for disease vectors and pose significant dangers to human health and environment .
Studies have shown that MSW dumps in Nigeria are a source of heavy metal pollution and constitute a nuisance and create a breeding ground for pests and diseases. Results of physical, chemical and biological analysis of raw water from boreholes collected close to refuse dumps shows that these wastes produce leachates that percolates into the groundwater. Preliminary results of microbiological analysis of the groundwater and surface runoff indicates higher population of pathogenic microorganisms in both surface and groundwater within and around the dump site compared to background values (Ohimain, unpublished data). According to Ogbonda, et al., waste dumps are unsanitary and destroy the aesthetic appeal of the environment. They harbor flies, fleas, mosquitoes, rats and other disease vectors. Some of the diseases carried by rodents and insect vectors include Lassa fever, malaria, filariasis, yellow fever, etc. These waste areas provide food, water and habitats and breeding areas for these disease-carrying agents. Results of laboratory analysis of leachates from waste dump in Port Harcourt showed that the total heavy metal content was 175.8 mg/l as against 3.0 mg/l permissible level. This is quite hazardous because heavy metals are known to be non biodegradable; they rather accumulate along the food chain because domestic and wild animals are known to commonly forage on abandoned wastes. Studies carried out by Anoliefo, et al. shows that leachates from waste dump has made the soil within and around the dump to become toxic. Other studies revealed that the wastes from this and similar dumps in Nigeria have contaminated groundwater and other drinking water sources.
The proliferation of uncontrolled solid waste dumpsites in Nigeria has become a major public health concern. Solid waste poses various threats to public health and adversely affects flora and fauna as well as the environment especially when it is not appropriately collected and disposed. Some of the health problems associated with poor water quality arising from inadequate waste disposal and waste-management practices include typhoid fever, diarrhoea, cholera, hepatitis, hook worm infestation, skin diseases, malaria, etc]. In a study carried out to investigate the heath impacts of solid wastes on waste handling workers in Port Harcourt, showed that heavy metals were higher in the blood of these workers compared to those not exposed to solid wastes. There was also a higher incident of malaria parasitaemia in the solid waste workers. The deterioration of the urban environment resulting from abandoned solid waste heaps in neighbourhoods and public places, coupled with the apparent inability of the city authorities to respond effectively to the challenge, necessitated the search for other options. Hence this study is focused on the use of risk based methods.
Solid waste abounds in Nigeria and due to lack of better means of managing them; they are freely disposed along the streets causing environmental, safety and health impacts. Some municipal wastes are also dumped into makeshift waste dumpsites that are poorly managed. The Government and her agencies are at a loss on how to better manage these waste pits. Using the waste dump at Eneka as a case study, an integrated risk based approach (IRBA) study was carried. The study showed that Eneka dumpsite had a total risk index score 452.3 which corresponded to moderate hazard potential, suggesting that the dumpsite require immediate rehabilitation and conversion to a landfill. The study demonstrates the importance of IRBA in making decision on the management of waste dump facilities in Nigeria.
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UNEP, 2006. Environmental Pollution and Impacts on Public Health: Implications of the Dandora Municipal Dumping Site in Nairobi, Kenya. Urban Environment Unit. UNEP. Kenya.
4. Kurian, J., S. Esakku, R. Nagendran and C. Visvanathan, 2005. A decision making tool for dumpsite rehabilitation in developing countries. Proceedings of Sardinia 2005, Tenth International Waste Management and Landfill Symposium. S. Margherita di Pula, Cagliari, Italy; 3-7 October 2005).