Leachate and Groundwater Quality in Lagos State, Nigeria

By Adedoyin Lasisi
June 2011

The Author is the Principal Environmental/Scientific Officer in the Office of Environmental Services at the Ministry of the Environment, Alausa, Ikeja, Lagos, Nigeria.
Note: This paper was presented at an in-house seminar for officers of Lagos State Environmental Protection Agency, the views expressed are solely those of the author and do not necessarily represent the opinion of the government.

Abstract
Water as a gift of nature is generally believed to have no enemy. Despite the abundance of fresh water on the earth, many regions are in deep crisis of water shortage due to there being polluted by human activities, or the ever increasing demand by industrialization and high population growth. Thus, groundwater is the alternative source of fresh water in areas where surface water is polluted or particularly in arid and semi-arid region of the world. However, the ground water that is presently rely on is generally been grossly polluted by various sources e.g. solid waste
Waste is defined as any substance or object discarded for any reason, whether part or all and such substance may be recycled e.g. rubbish, trash, scraps, tiles, bottles, cans, papers, chemicals, slugs, machine parts, scrap metals etc. Once waste is deposited at the landfill (dumpsite) pollution can arise from the migration of both gas and leachate. There are three broad types of contaminants present in leachates that can pollute groundwater and subsequently affects public health. These are hazardous chemicals, conventional and non-conventional contaminates.
The cost of cleaning up groundwater contaminated by Municipal Solid Waste landfill leachates require large sum of money and technology, which are presently not available in our society. Thus it is important that efforts are geared towards preventing pollution that will arise from leachate.

Introduction

Water as a gift of nature is generally believed to have no enemy. However, water is very essential to the well being of man, animals and plants. Of all the earth ’s essential elements that support life water is the second most important after air. Amazingly, a mere 3 per cent of the world’s water is fresh, not salty. Out of this, 95% of the fresh water is locked up in glacier and ice caps or in the underground aquifer thus leaving 1 percent that is readily accessible to human kind. Basically, the total do not amount of water on earth do not increases nor decreases, as the amount on earth now is all there had been. This is because the water in and around the world endlessly circulates from the oceans to the atmosphere, to the land; into the river and back to the ocean again. Moreover, despite the abundance of fresh water on the earth, many regions are in deep crisis of water shortage due to there being polluted by human activities, or the ever increasing demand by industrialization and high population growth. Thus, groundwater is the alternative source of fresh water in areas where surface water is polluted or particularly in arid and semi-arid region of the world.

Groundwater

Groundwater is a resource of global importance, particularly in areas where access to surface water is limited. Groundwater resources include shallow and deep rechargeable aquifers that are connected to rivers; streams or seas while non-renewable aquifers or fossil water are those that may have been created by age. Groundwater makes up about 95 percent of the world ’s supply of fresh water excluding fresh water in global ice. Groundwater may in this case be directly fed through seepage from run off.

Furthermore, groundwater may be fed from the soil surface by an impervious stratum but in general, the water is deeper lying. However, alluvial groundwater presents a special case; where ground water is located in alluvial soil close to a river. Thus, the quality of the river water directly influences the quality of such ground water. Also, the characteristics of groundwater depend on the geological nature of the terrain, which in turn determine the composition of the water. This is constantly in contact with the ground in which it stagnates or circulates leading to equilibrium between the composition of the soil and that of the water. Water that circulates in a sandy organitic substratum is acidic and has few minerals. While water that circulates in limestone contain bicarbonate thus making it alkaline. This water is usually characterized by weak turbidity, constant temperature, chemical composition, and an almost absence of oxygen. However, confined groundwaters, especially one circulating in kast terrain usually appear turbid with various pollutants. Generally, groundwaters are often very poor microbiologically and also contain iron, manganese, fluoride, sulphide, etc in concentrations that exceed the standards for drinking water. This is due to the composition of the groundwater where the water is store.

Lagos Ground Water

Nigeria is subdivided into nine different hydrogeological basins. Lagos is located within the Delta basin within which water table aquifers are abundant. In Lagos, there is substantial report of four aquifers horizon, which are made up of alternating sequence of sands and clays. In some area, the medium is coarse sand layer, which occurs below the superficial laterite. This contains high yielding aquifer with a free water table within which predominantly lateral ground water movement occurs. Also, there are reports that vertical groundwater flow appears to occur across the clay in relatively small (aquifer). The upper and lower aquifer units have been identified as local water sources. However, additional significant aquifers are generally encountered between 80 and 100m and at about 600m below ground.

The first shallow aquifer sediment is used for very small private domestic supplies, while the second and third aquifer (coastal plains sands) provides substantial quantities of water for public water supply, industry and private supplies. The fourth aquifer is the deep and highly productive Abeokuta formation that is only accessable by selected few. The provision of water supply relates differently to groundwater, since it is frequently an important source for both the municipal water company, typically operating a few high yielding wells or well fields and for the private individuals. However, the concern of public and private water industries is the decreasing availability and deteriorating quality and quantity of ground water. Today groundwaters are polluted by various sources that include petroleum products, septic tanks, landfill leachate etc.

Moreover, the most significant impact on groundwater quality arises from the contamination from landfill leachate. Landfill leachates are a more intractable problem as, even if they can be collected effectively; sophisticated treatment is needed before they can be discharged into the environment. However, landfill leachates collection and treatment is not available in all landfills in Lagos. Thus, leachates contamination is probably inevitable.

Landfill Leachates

Waste is defined as any substance or object discarded for any reason, whether part or all and such substance may be recycled e.g. rubbish, trash, scraps, tiles, bottles, cans, papers, chemicals, slugs, machine parts, scrap metals etc. Once waste is deposited at the landfill (dumpsite) pollution can arise from the migration of both gas and leachate. However, gas problem have become increasingly high over the years. The management of gases from landfill sites can be controlled through the installation of engineered gas extraction system. This engineering control system is not in use in any of the dumpsite (landfill) present in Lagos. Thus, landfill gases still constitute a great problem.

On the other hand, landfill leachates are a more intractable problem. Leachate is the name given to grossly polluted liquid that can emerge from land filled decomposed waste mass. Also, it can be said to be liquids that results from water collecting contaminates as it trickles through agricultural, pesticides or fertilizers wastes. It is important to recognize that the deposition of almost any waste to landfill (dumpsites) will give rise to leachate whose chemistry is not in equilibrium with the chemistry of the surrounding environment thus resulting in pollution.

Numerous physico-chemical and biological processes govern the generation of leachates. The pioneer investigation that provided the basis for a scientific understanding of these processes was conducted in Manchester in 1931-34 by Jones and Owen and subsequent studies by Farquahar et al.,(1972) and Rees (1980).The rate of leachate generation is affected by various factors which include the age of the refuse, waste density, water content, humidity, rainfall etc.Water acts as transport medium for bacteria and for their nutrients and waste products. Thus, the lack of moisture will reduce degradation rates and will result in a landfill producing gas and leachate at a slower rate but over a much longer period of time.

The decomposition of waste takes place by the action of microbes within the waste mass. The decomposition of waste takes place in three stages; thermal stage, acetogenic stage and methogenic stage. In the first stage, aerobic organisms present in the waste attack the degradable waste. In the presence of oxygen in entrapped air, to form more simple organic compounds, carbon dioxide and water. Heat is then generated and aerobic organisms multiply.

The second stage commences when all the oxygen is consumed or displaced by carbon dioxide. The degradation processes is then taken over by organism that can thrive in either the presences or absent of oxygen. The organisms brake down the large organic molecules present in food, paper and similar waste into more simple compounds such as hydrogen, ammonia, water, carbon dioxide and organic acid. During this acetogenic stage, carbon dioxide concentration can reach a maximum of 90% but usually achieve about 50% of gas generated.

In the third and final anaerobic or methogenic stage, species of methane forming organisms multiply and brake down organic acids to form methane gas and other products. The water-soluble degradation products from these biological processes, together with other soluble components in waste such as, the rusting of metals items will be present in leachates. The composition of leachate varies from landfills to landfills. However, based on the compilation of Lee and Jones (1993) who presented the compilation of information from the literature on chemical composition of municipal landfill leachate as detailed in Table 1 below:

Table 1 · Chemical Composition of Municipal Landfill Leachate
Parameter Typical Concentration Average Range
BOD1,000 – 30,00010,500
COD1,000 – 50,00015,500
TOC700 – 10,0003,500
Tva (as acetic acid)70 – 28,000NA
Total Kjeldah N2(as N)10 – 500500
Nitrate (as N)0.1 – 104
Ammonia (as N)100 – 400300
Total Phosphate (Po4)0.5 – 5030
Orthophosphate (Po4)1.0 – 6022
Total alkalinity500 – 10,0003,600
Total Hardness500 – 10,0004,200
Total Solids3,000 – 50,00016,000
Total Dissolved/Solids1,000 – 20,00011,000
Specific Conductance (Mhos/cm)2,000 – 8,0006,700
PH5 – 7.56.3
Calcium100 – 3,0001,000
Magnesium30 – 500700
Sodium200 – 1,500700
Chloride1,000 – 2,000380
Sulphate10 – 1,0000.9
Chromium (total)0.05 – 20.05
Copper0.02 – 10.5
Lead0.1 – 10.5
Nickel10 – 1,000430
Zinc0.5 – 3021
Methane gas60%
Carbon dioxide40%
All values are in mg/l except as noted   NA - Not available.

Dumpsite Management in Lagos

In Lagos, the last decade have seen considerable changes in the management of dumpsites. At the inception of Lagos Waste Management Authority as Lagos State Refuse Disposal Board in 1977, there were five existing dumpsites within Lagos metropolis namely; pelewura (Adeniji Adele), Gbagada, Isolo, Achakpo and Ojota. These sites were open swamps that are progressively reclaimed with refuse. The dumping of waste is done without proper planning programme for leachate or landfill gas thus putting the populace at the risk of environmental problem.

In view of this, the state government under the World Bank Assisted Project package of 1988 commissioned a consultant for the development of landfill sites for the state. The project gave rise to sites such as Olusosun, Abule-egba, and Solus. The Olusosun landfill site is about 42 hectares in size with a life span of 35 years receives an average of 1.2 million tones of waste annually. The Abule-Egba (Oke -odo) landfill is about 3.0 hectares. While Solus is about 3.0 hectares. It must be noted that Pelewura, Gbagada, Isolo, Achakpo and Ojota have been closed down to waste disposal operations.

With the existing landfills sites, the average tonnage of solid waste disposed weekly in the state is estimated to be 17000 metric tones, while the recorded dailywaste generation rate is about 0.5kg per capita. However, with the composition of a still active landfill in Lagos and the climatic condition of the state, the leachate generation is expected to be high.
According to Ikem (1996), the table below represent the composition of an active landfill site in Lagos.

Table 2 · Composition of an Active Landfill Site in Lagos
Material Percentage
Vegetation59 %
Paper17 %
Textiles2 %
Plastic12 %
Metals8 %
Glass2 %
Total100 %

From the above values it can be noted that the percentage of decomposable materials is greater than the less decomposable materials. Moreover, it is worthy of note that some other factors that contribute to the leachate generation include: the mean annual rainfall in Lagos is 1620.59mm, which varies from place to place. Generally, relative humidity is very high in Lagos being in a tropical region with relative humidity ranges from76% to 80.5%. The morning hours recorded annuals average of 90% while 13:00 hours has annual mean of 71%. The average moisture content of Lagos waste is estimated to be 36.8%. (Lasisi K.S.A., 2001). With this state of climatic condition leachate generation in Lagos is expected to be high.

Table 3 · Typical Composition of Leachate from Existing Landfills in Lagos State
Parameter Olushosun Solus Abule-Egba
Temperature (°C)34.2037.4031.20
PH7.308.407.78
TSS104999709.408983.64
TDS28733543.803639.24
TS1772613252.2012622.88
Chloride13191389.001177.20
Sulphate582321728
Nitrate3.527.6076.71
Phosphate0.030.261.26
Lead0.540.500.10
Magnesium60.9853.1764.63
Iron8.0110.5910.89
Copper0.100.100.20
Calcium13.5914.7511.69
Mercury1.002.102.30
Cadmium0.010.010.01
Arsenic0.590.604.21
Nickel0.040.020.31
Dissolved Oxygen2.342.333.15
*Mean of five samples
All results in mg/l except as noted
Source: Lasisi K.S.A,(2001)

Groundwater Pollution by Leachate

There is a common misconception that since the materials placed in landfills are basically household wastes, they are relatively ‘safe ’ and are not likely to adversely affect public health and groundwater quality. However, one need only to consider the proposition of drinking the ooze that developed at the bottom of a garbage can or water used to clean garbage disposal plastics to understand that it is not desirable to have solid waste leachate in water considered desirable for potable use. Yet this is what happens when leachate from municipal solid waste landfill is allowed to contaminate water that is or could be used for domestic supply.

The USEPA estimates that there are about 55,000 landfills in the United State with 75% of which are polluting groundwater. If this is happing in the US where there is a groundwater-monitoring programme, then only God knows the quantity of leachates that are presently polluting groundwater in Lagos with high water table.

As reported, there are three broad types of contaminants present in leachates that can pollute groundwater and subsequently affects public health. These are hazardous chemicals, conventional and non-conventional contaminates. Gintautass et. al, (1992) reported the present of Phenoxyalkanoic acid herbicide in leachate, which had not been previously reported. In a study trip to the existing landfills in Lagos, it is not surprising to note the present of cans and container of herbicides, germicides and other materials in the landfills. Belevi and Baccini (1989) estimated that unlined landfills in a fairly wet climate will hazardous chemical, such as, lead at concentration above drinking water standards for several thousands years.

Presently, automobile waste oil with its elevated heavy metals and hydrocarbons are routinely thrown into household trash. Also, various types of batteries, such as, mercury, nickel and cadmium based are presently been disposed off in landfill in Lagos. Also, the disposal of burned out fluorescent tubes used for home or commercial lighting also eventually finds its way to the groundwater.

How You Can Help

Conclusion

The removal of contaminants from contaminated landfill is generally difficult. It involves the use of many methods, such as, air stripping, bioremediation, ion exchange demineralization or reverse osmosis, activated carbon colums etc. This means that the cost of cleaning up groundwater contaminated by municipal solid waste landfill leachates require large sum of money and technology, which are presently not available in our society. Even if they are cleaned up they cannot be relied upon to provide safe drinking water supply. In this view, the US EPA in 1999 concluded that once a water supply well has been contaminated by MSW leachates, the well has to be abandoned as source of potable water supply. Thus, there is need for the development of a leachate-monitoring program, which must include routine measurement of a wide variety of chemicals that are known or suspected to be present in the landfill that can be measured at very low concentration.

More than 90% of the contaminates present in landfill leachate are not identified or quantified; their public health implication are unknown. The efficacy of groundwater “remediation”-treatment methods in removing such contaminants to “safe” levels cannot be determined. Thus, prevention and monitoring is the only option. We must be wise, groundwater resources is becoming the only available sources of water supply.

References

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