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EVALUATION OF GROUNDWATER QUALITY CHARACTERISTICS NEAR TWO WASTE SITES IN IBADAN AND LAGOS, NIGERIA
A. IKEM1∗, O. OSIBANJO2, M. K. C. SRIDHAR3 and A. SOBANDE4 1 Environmental Engineering Program, Department of Chemical Engineering, Tuskegee University, AL 36088, U.S.A.; 2 Department of Chemistry, University of Ibadan, Ibadan, Nigeria; 3 Department of Public Health and Preventive Medicine, University of Ibadan, Ibadan, Nigeria; 4 Environmental
Consultants, 7273 Bennell Drive, Reynoldsburg, OH 43068, U.S.A. (∗ author for correspondence, e-mail: [email protected], fax: (334) 727 8942)
(Received 12 October 2000; accepted 9 February 2002)
Abstract. Two industrial and highly populated cities namely Ibadan and Lagos, both located in Southwestern Nigeria have urban migration problems and resource limitations. As a result, the de- velopment of residential areas near waste sites and the indiscriminate dumping of municipal waste are common in both cities. Orita-Aperin and Oworonsoki neighborhoods in Ibadan and Lagos, re- spectively, both located near a waste site were studied. The two areas relied on the wells as sources of drinking water hence poor drinking water quality may have health consequences. A total of 51 groundwater samples (30 wells in Ibadan and 21 wells in Lagos) were monitored seasonally for two years in Ibadan and a year in Lagos. Results from this study revealed that some of the ground- water quality constituents determined exceeded the World Health Organization (WHO) standards for drinking water irrespective of source of pollution. Some of the groundwater samples were poor in quality in terms of pH, conductivity, total dissolved solids, chloride, nitrate, ammonia, COD, Al, Cd, Cr, Fe, Pb, Ni and total coliforms recorded. Thus, groundwater from some of these private wells requires further purification to ensure its fitness for human consumption. F-test, one-way parametric analysis of variance (ANOVA), Mann-Whitney ‘T’ test and Kruskal-Wallis H-test applied to upgradi- ent and downgradient concentrations suggest impact of the waste sites on groundwater quality. The Mann-Whitney test only suggests that the downgradient values of Fe (Ibadan: dry season (1), sulfate (Ibadan: rainy season (2) and pH (Lagos: dry season (2) were significant at 5% level of significance. For Ibadan wells, the Kruskal-Wallis test showed that variances of specific conductivity, dissolved solids, and chloride for Ibadan upgradient and downgradient values were unequal. Also variances of specific conductivity and dissolved solids for upgradient and downgradient values in Lagos were unequal at 5% level of significance. Three downgradient wells in Lagos and four downgradient wells in Ibadan had significant impact due to leachate migration into drinking wells.
Keywords: downgradient, groundwater, leachate, sediment, soil, upgradient, waste sites, water qual- ity constituents, wells
1. Introduction
The impact of leachates on groundwater and other water resources has attracted a lot of attention worldwide because of its overwhelming environmental significance. Leachate migrations from waste sites or landfills and the release of pollutants from sediment (under certain conditions) pose a high risk to groundwater resource if not
Water, Air, and Soil Pollution 140: 307–333, 2002. © 2002 Kluwer Academic Publishers. Printed in the Netherlands.
308 A. IKEM ET AL.
adequately managed. Their impact on groundwater continues to raise concern and have become the subject of recent and past investigations (Ahmed and Sulaiman, 2001; Fatta et al., 1999; Kjelsen et al., 1998; Bjerg et al., 1995; Robinson and Gronow, 1992; Cariera and Masciopinto, 1998; Loizidou and Kapetanios, 1993; Gallorini et al., 1993; Khan et al., 1990; Kunkle and Shade, 1976).
Empirical investigations (Fatta et al., 1999; Bjerg et al., 1995; Loizidou and Kapetanios, 1993) as well as modeling techniques (McCreanor and Reinhart, 2000; Lee et al., 1997; Syriopolou and Koussis, 1987; Koussis et al., 1989; Ostendorf et al., 1984) have been used to assess the pollution of groundwater by leachate from a landfill. Mathematical models have the advantage of being able to predict different scenarios without involving tedious and time-consuming experimentation. However, these models and their predictions have to be tested and verified with field studies. In this study, field investigations, which involved the collection and analyses of samples, were used to generate groundwater quality data for two cities with severe potential pollution problems.
1.1. STATISTICAL APPROACHES FOR EVALUATING GROUNDWATER DATA
Several statistical methods have been used for analyzing and evaluating ground- water-monitoring data. The procedures include the students’ t-test (Montgomery and Loftis, 1987), alternatives to student’s t-test (US EPA, 1988; Doctor et al., 1986; Splitstone, 1989), graphical tools and non-parametric methods (Goodman, 1987; Fisher, 1989; Hensel, 1987; Hirsch and Slack, 1984). Water quality data are usually analyzed with parametric statistical procedures requiring the normality assumption for accuracy of their attained significance levels. However, the data are typically non-normally distributed. When parametric procedures are applied to non-normal data, the powers of parametric procedures are low and their results may be in error (Hensel, 1987; McBean and Rovers, 1998).
Non-parametric methods have been found to be more accurate for analyses of environmental data especially groundwater data (Hensel, 1987). The fundamental characteristic of non-parametric tests is that the ranks are utilized instead of data values (McBean and Rovers, 1998). Ranking process for the analysis of environ- mental data has been adjudged to be over 95% more powerful than parametric tests (NCASI, 1985). A non-parametric approach is advantageous because the statistics are valid for all data distributions (NCASI, 1985; Goodman, 1987; Doctor et al., 1986), are easily computed and non-detect or less than values can be incorporated in the data analysis (Doctor et al., 1986; Hensel, 1987).
In this study, parametric and non-parametric procedures were used to assess the homogeneity of variances of upgradient (background) and downgradient (down- hill) concentrations of wells studied. Also further statistical comparisons between downgradient and upgradient concentrations that had unequal variances were made to identify wells that were contaminated.
GROUNDWATER QUALITY CHARACTERISTICS NEAR TWO WASTE SITES IN NIGERIA 309
1.2. BACKGROUND AND AIM OF STUDY
Nigeria is the largest country on the West coast of Africa with an estimated popu- lation of 123.9 million with about 43% of the populace currently living in cities or urban areas (World Bank, 2000a). The rate of urbanization in Nigeria is alarming and the major cities are growing at rates between 10–15% per annum and medium cities at about 7–10%. The siting and development of residential quarters near waste sites are common due to shortage of building land to cope with the increasing rate of migration and consequent population explosion. Environmental problems arising from the improper disposal of solid and liquid wastes near residential areas, poor wastes collection and handling, poor access roads, and the poor state of phys- ical infrastructure especially in big cities like Ibadan and Lagos affect the quality of life.
In Nigeria’s two major cities, Ibadan and Lagos, potable water from the water supply boards are inadequate for the teeming population and fears of drinking water contamination of municipal waters is high since water treatment and distribution is facing many problems. According to the World Bank (2000b), only 39% of people that live in cities have improved water source. Thus, a large percentage of the population of the neighborhoods studied (over 70%) depends on groundwater from their private wells as their main source of quality drinking water. Therefore, it became necessary to ascertain the water quality of these areas since poor water quality may have an adverse health impact. Groundwater quality characteristics near waste sites or landfills have been reported in the literature but similar studies in Nigeria are scarce or lacking.
Against the background information described above, the aims of this invest- igation were: (1) to assess the groundwater qualities near the two sites located in Ibadan and Lagos by comparing water quality data with World Health Or- ganization (WHO) drinking water standards, (2) to characterize the refuse, waste soils, sediments, surface waters and most importantly the speciation of metals on the two sites because of their environmental implications, and (3) to apply two non-parametric procedures namely; the Mann-Whitney and Kruskal-Wallis tests to selected sampled wells that served as upgradient and downgradient wells to assess if the leachates emanating from the waste sites had impact on groundwater quality.
2. Materials and Methods
2.1. DESCRIPTION OF STUDY AREAS
The Ibadan waste site (longitude 6◦01′56′′E to 6◦01′57′′E and latitude 8◦14′11′′N to 8◦14′13′′N) is in Orita-Aperin, a residential area located within Ibadan City, Nigeria. The Ibadan sampling locations is presented in Figure 1a. The Ibadan waste site has been in use since the 1950s and is now abandoned due to legal prohibition of waste discharge on the site. However, illegal local dumping of mostly market
310 A. IKEM ET AL.
Figure 1a. Map of Ibadan sampling locations.
GROUNDWATER QUALITY CHARACTERISTICS NEAR TWO WASTE SITES IN NIGERIA 311
wastes is still continuing on one edge of the site irrespective of the ban. The stream, which runs beside the waste site on the Northeastern boundary, carries pollutants along its path and empties into other water resources. Geologically, Ibadan area is located within the basement complex and the rock is largely crystalline in structure. It consists of banded gneiss and biotite gneiss and groundwater flow within this system is through fractures.
The Lagos waste site (longitude 3◦22′E to 3◦23′E and latitude 6◦33′N to 6◦34′N) is in Oworonsoki area on the northeastern part of Lagos. The sampling locations near the Lagos waste site are presented in Figure 1b. On the eastern side of the Oworonsoki area is the Lagos lagoon. The eastern and northern areas of the site were swamps prior to the land filling and subsequent siting of residential properties beside the waste site. A 10 m wide channel that runs beside the waste site helps in the transport and redistribution of pollutants. The waste site is surrounded by industrial lands to the west, residential to the southeast and northeast and a swamp to the north. The composition of the waste received at this site is estimated to be 80% domestic including market wastes and 20% industrial waste. Since 1977, over 344 000 tonnes of waste have been deposited on this site (Lagos Waste Disposal Board, 1991) and dumping of toxic, hazardous and liquid wastes on the waste site have not been reported. Geologically, the Lagos area is made of sedimentary deposits that are largely alluvial and flow of materials and pollutants is through pores.
2.2. METHODOLOGY
2.2.1. Quality Assurance All chemicals used were of reagent grade and ultra pure deionized water was used throughout the experimentation. Washing procedures, sampling container types, chain-of-custody procedures, sampling for general parameters and heavymetals de- terminations, sample holding times and preservation techniques conform to stand- ard methods for water and wastewater analysis (APHA, 1985). Procedural blanks, reagent blanks, preparation of standard solutions under clean laboratory environ- ment, calibration of the Perkin-Elmer 2382 atomic absorption spectrophotometer (AAS) using certified standards and the analyses of calibrated standards after 15 samples to ensure that the instrument remained calibrated were some of the meas- ures taken during the experimentation. Recovery studies for the metals analyzed using the AAS ranged between 87 and 98% and percent error for the cation-anion balances of all the water quality results were within ±20%.
2.2.2. Refuse Characterization, Soil and Sediment Analyses Refuse disposed on the Ibadan and Lagos waste sites were collected randomly into long polythene bags and transported to the laboratory. To ascertain the per- centage compositions of the waste types, known weights of the refuse samples were sorted and weighed. Waste soils and sediment samples near the sites were
312 A. IKEM ET AL.
Figure 1b. Map of Lagos sampling locations.
GROUNDWATER QUALITY CHARACTERISTICS NEAR TWO WASTE SITES IN NIGERIA 313
collected randomly into polythene bags with a plastic scoop at a depth of 0–15 cm. The samples were transported to the laboratory and then air-dried in the open at normal room temperature. The pH of the soil and sediment were measured in water with a 1:2.5 soil/solution ratio after equilibration for 30 min (McLean, 1982). Particle size distribution was by pipette method (Day, 1965), organic carbon (%) was by Walkley-Black method (Jackson, 1957), sulfate was by turbidimetry with BaCl2 (IITA, 1979; APHA, 1985), phosphate by ascorbic acid method (IITA, 1979; APHA, 1985), nitrate determination was by phenoldisulphonic acid method (Taras, 1950) and ammonia was by nesslerization (HMSO, 1972).
2.2.3. Metal Speciation The main objective of the speciation analysis was to determine the concentrations of metals bound to the different soil and sediment fractions through chemical extraction schemes. Measurement of the metal fractions and their distribution in the soils and sediments collected will provide information on the pollution risks especially the mobility of toxic metals into groundwater and surface waters. Heavy metals are not biodegradable and they can accumulate in the food chain. Exposures to heavy metals can cause significant health problems in man and animals (Under- wood, 1971). A wide variety of single and sequential techniques are available in the literature for the analysis of metals in soils and sediments using different extracting solutions (Pérez Cid et al., 2001; Maiz et al., 2000; Schramel et al., 2000; Singh et al., 1998; Kersten and Förstner, 1995; Lake et al., 1984; Hall, 1991) but the most applied procedure in the literature is that of Tessier et al. (1979). Sequential extraction procedures provide differentiation between several association forms of metals with the soil and sediment components (Maiz et al., 2000; Kersten and Förstner, 1995; Lake et al., 1984).
Most schemes generally seek to use extractants in decreasing order of pH (Kersten and Förstner, 1995). The method by Hall (1991) was employed to determine the partitioning of metals of environmental significance in soil and sediment fractions. In brief, extraction with 0.1 M hydroxylamine hydrochloride (NH2OH·HCl; pH: 2) is supposed to remove manganese compounds, exchangeable cations, carbonate-bound metals, and in general easily reducible species. Extrac- tion with acidified 30% hydrogen peroxide (H2O2; pH: 2.5) is supposed to remove oxidizable and organically bound species.
Organically bound metals represent those forms that may be complexed, che- lated or adsorbed to organic matter in addition to components of living cells, their exudates and a spectrum of degradation by-products. Extraction with 0.5 M HCl is supposed to distinguish between residual (i.e. metals associated with rock frag- ments) and non-residual (i.e. indicates contribution of human activities to total metals) metals. 0.5 M HCl is able to remove all metals that include those extracted by the 0.1 M NH2OH·HCl and part of the residual species. Concentrated nitric acid was used to estimate total metals. It is known to attack all solid phases of soil/sediment (Valin and Morse, 1982). Residual metals are largely stable because
314 A. IKEM ET AL.
they are embedded in the crystalline structure of the soil/sediment. They contain primary and secondary minerals, which may hold trace metals within their crystal structure. Residual metals are usually not released in solution over a reasonable time span under the conditions normally encountered in nature (Tessier et al., 1979).
The air-dried soil and sediment samples were sieved into 45 – <100 µm, 100 – <180 µm, 180 – <1600 µm and ≥1600 µm particle sizes with a sieve made of stainless steel (Manufactured by Endecotts Limited, London). To study the effect of grain size on the distribution of metals in the soil/sediment and also to study the speciation of metals in their various forms, extractions using the four extracting solutions (concentrated nitric acid, 0.5 M Hydrochloric acid, 0.1 M hydroxylamine hydrochloride, 30% hydrogen peroxide) were conducted on each of the soil and sediment fractions. Nitric acid digestion was conducted by heating 2 g of sample with 15 mL of concentrated nitric acid in a Teflon beaker for 2 hr at 100 ◦C. Digest was filtered with Whatman No. 541. The 0.5 M HCl digestion was carried out by the addition of 30 mL of 0.5 M HCl to 1.5 g of sample in a stoppered flask. Contents were shaken on a mechanical shaker for 12 hours after which mix- tures were filtered. 0.1 M hydroxylamine hydrochloride digestion also followed the procedure used in the hydrochloric acid digestion except that hydroxylamine hydrochloride (pH: 2) was used in place of HCl. In the hydrogen peroxide diges- tion, aliquots (20 mL) of 30% (H2O2; pH: 2.5) were added in small quantities to 1.5 g of sample until frothing stopped. The mixtures were then shaken for 12 hr in loosely stoppered flasks and then filtered. The concentrations of Ca, Mg, K, Na, Mn, Fe, Cu, Zn, Cr, Pb, Co and Cd in filtered samples were then determined using Perkin-Elmer 2382 AAS.
2.2.4. Leachate, Groundwater and Surface Water Analysis Leachate samples were collected by installing polythene containers at crucial points and groundwater sampling was by baling using clean glass bottle. Sampling was conducted from October to April (dry season) and from May to September (rainy season) for two years in Ibadan and for a year in Lagos. All the 51 shallow dug wells monitored in Ibadan and Lagos were within 500 m to the respective waste sites. The nearest well (less than 5 m) to the waste site was recorded in Ibadan. Procedures for sample collection, determination of some general parameters and trace metals conform to standard methods procedures (APHA, 1985). Microbiolo- gical analysis (total coliforms count) was by the most probable method (HMSO, 1956). Physico-chemical parameters determined include pH, specific conductivity, dissolved solids, chloride, nitrate, ammonia, sulfate, COD, phosphate, nutrients, and some trace metals. Digests of leachate, groundwater and surface water samples were filtered and aspirated into Perkin-Elmer 2382 AAS for metals determination.
GROUNDWATER QUALITY CHARACTERISTICS NEAR TWO WASTE SITES IN NIGERIA 315
2.2.5. Statistical Analysis of Analytical Data To test the impact of leachate emanating from the waste site on groundwater qual- ity, two parametric and two non-parametric procedures were employed. Analysis of variance using F-test, one-way parametric ANOVA, Mann-Whitney ‘T’ statistic (Fuch, 1990) and Kruskal-Wallis H-test (McBean and Rovers, 1998) was conduc- ted on selected upgradient and downgradient concentrations to find if variances between upgradient and downgradient concentrations were homogenous. Two up- gradient (background) and eight downgradient (downhill) wells were selected near the Ibadan site while three upgradient and ten downgradient wells were also selec- ted near the Lagos site after eliminating wells affected by other obvious sources of pollution such as septic tanks and wastewater discharges. The Mann-Whitney ‘T’ and the Kruskal-Wallis tests involved ranking of all observed concentrations jointly to remove skewness and non- normality in the environmental data collected. To as- sess the equality of variance between upgradient and downgradient concentrations of selected wells at 5% level of significance, the null hypothesis was either accepted or rejected by comparing calculated values to the critical values. Further data ana- lysis was conducted using Kruskal-Wallis H-test to ascertain which downgradient wells were contaminated by comparing the differences between the average ranks of each downgradient and upgradient well (the average ranks of two upgradient wells in Ibadan and three upgradient wells in Lagos were used).
3. Results and Discussion
3.1. REFUSE COMPOSITION, SOIL AND SEDIMENT TYPES
Analysis of fresh refuse composition of the Ibadan waste site showed that 78% consisted of vegetable matter, 10% paper, 5% metals, 3% plastics, 2% glass and 2% textiles. Also, the Lagos refuse is made up of 59% vegetable matter, 17% paper, 2% textiles, 12% plastics, 8% metals and 2% glass. According to the USDA soil texture triangle (US EPA, 1991), the waste dump soil types for Ibadan and Lagos were sandy loam and loamy sand, respectively. Average values (standard deviations in parenthesis) of the soil, sediment, surface water, leachate and groundwater analyses results for Ibadan and Lagos are presented in Tables I and II, respectively.
3.2. LEACHATE COMPOSITION
Leachates collected from Ibadan and Lagos sites had appreciable levels of dis- solved solids, chloride, ammonia, COD, Pb, Fe, Cu, and Mn (Tables I and II). Average pH values for the leachate samples were between pH 7–8. Dumping of lead acid car batteries and metal scraps at the two waste sites is the likely source of Pb and Fe, respectively. The Ibadan and Lagos leachate results posted lower values of specific conductivity, dissolved solids, chloride, TOC and NH4-N in most cases
316 A. IKEM ET AL.
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318 A. IKEM ET AL.
when compared to leachate values of four Danish landfills and the Compton Bas- sett landfill in U.K. (Jensen and Christensen, 1999; Robinson and Gronow, 1992). However, the level of iron, lead and copper obtained for Ibadan and Lagos leachate samples were higher than the corresponding Danish leachate values. The dissolved solids and ammonium values in this study were also lower than the corresponding leachate values posted for a landfill in Athens area, Greece (Loizidou and Ka- petanios, 1993). In addition, leachate values of COD and chloride in this study were within the range or below the published values for leachate samples collected in England (Robinson et al., 1982), Germany (Ehrig, 1983), U.S.A. (Fang, 1995), Finland (Niininen et al., 1995), and Brazil (Vendrame and Pinho, 1997). The values of both chloride and COD in mg L−1 with the COD values in parenthesis for five countries is as follows: England: 70–2777 (66–11 600), Germany: 2119 (3000– 22 000), U.S.A.: 50–2400 (800–50 000), Finland: 1–600 (52–5200) and Brazil: 275–1949 (90—2000).
3.3. GROUNDWATER AND SURFACE WATER QUALITIES
Classification and comparison of Ibadan and Lagos groundwater quality data ir- respective of source of pollution, with WHO drinking water standards (WHO, 1991a, b) are presented in Tables III and IV, respectively. The comparison revealed that some of the samples were polluted with Al, Pb, Cd, Fe, Cr, Ni, and all samples had total coliforms greater than zero. Some Ibadan wells were polluted with am- monia due to seepage from sewage tanks into drinking wells. The presence of total coliforms (Rutter et al., 2000) and toxic elements (US EPA, 1998; WHO, 1991a, b) at above their respective water quality guidelines can lead to various health problems in humans. Children are known to be more susceptible to expos- ures than adults due to their behaviors, greater gastrointestinal absorption and a lower threshold for adverse effects (Patriarca et al., 2000; Cambra and Alonso, 1995).
Water quality constituents’ values were higher during the rainy period due to increased mobility of ions. Analysis of variances (F-test) at 95% confidence level between the rainy season and dry season data for Lagos samples suggests signi- ficant variations of total alkalinity, bicarbonate, total hardness, sulfate, ammonia, COD, Al, Mn, Ca and Cu. Also, analysis of variances (F-test) at 95% confid- ence level between the rainy season and dry season data for Ibadan groundwater samples suggests significant variations of pH, chloride, sulfate, nitrate, ammonia, phosphates, COD, Mg, K, Na, Mn, Cu, and Ni.
The concentrations of some metals in the surface water samples from both sites exceeded the WHO stipulated guidelines for drinking water and the mean background dissolved metal concentrations in African rivers values (CIFA, 1994). The reported mean background dissolved metal concentrations in African rivers in µg L−1 were as follows: Cd (0.02), Pb (3), Cu (7), Zn (20), Mn (7), and Fe (4).
GROUNDWATER QUALITY CHARACTERISTICS NEAR TWO WASTE SITES IN NIGERIA 319
TABLE III
Classification of Ibadan groundwater quality data and comparison with guidelines
Parameter Classification Comparison with WHO classification guidelines (% Samples)
Rainy season Dry season
1. Total alkalinity <100 mg L−1 50 50 100–200 mg L−1 40 36.7
>200 mg L−1 10 13.3 2. Sulfate 0–20 mg L−1 40 60 250 mg L−
>20–40 mg L−1 53.3 26.7 >40 mg L−1 6.7 13.3
>250 mg L−1 0 0 3. NH+4 <0.38 mg L
−1 10 20 0.39–1.15 mg L−1 46.7 23.3
>1.15 mg L−1 43.3 56.7 4. COD <3.8 mg L−1 (good) 56.6 100
381–7.5 mg L−1 (fair) 26.7 0 >7.5 mg L−1 (poor ) 16.7 0
5. Total hardness 0–30 mg L−1 3.3 3.3 31–60 mg L−1 20 20 61–120 mg L−1 46.7 46.7
121–180 mg L−1 26.7 20 >180 mg L−1 3.3 10
6. Al >0.2 mg L−1 20 60 0.2 mg L−1 7. Cd >3 µg L−1 97.7 70 3 µg L−1 8. Cr >50 µg L−1 0 66.7 50 µg L−1 9. Cu >1.5 mg L−1 0 0 1.5 mg L−1
10. Fe >2.5 mg L−1 10 10 2.5 mg L−1 11. Pb >10 µg L−1 36.7 56.7 10 µg L−1 12. Mn >0.5 mg l L−1 3.3 0 0.5 mg L−1 13. Ni >15 µg L−1 26.7 96.7 15 µg L−1 14. Na >200 mg L−1 0 0 200 mg L−1 15. Chloride >250 mg L−1 0 3.3 250 mg L−1 16. Nitrate >50 mg L−1 0 3.3 50 mg L−1 17. Total dissolved solids >500 mg L−1 13.3 13.3 500 mg L−1 18. Specific conductivity <500 µS cm−1 36.7 50
500–1000 µS cm−1 60 40 >1000–1700 µS cm−1 3.3 10
19. TOC >3.0 mg L−1 40 13.3 20. pH <6.5 16.7 30
pH >8.5 0 0 21. Total coliforms >Zero 100 100
Number of Samples analyzed each season: 30.
320 A. IKEM ET AL.
TABLE IV
Classification of Lagos groundwater quality data and comparison with guidelines
Parameter Classification Comparison with WHO
classification guidelines
(% Samples)
Rainy season Dry season
1. Total alkalinity <100 mg L−1 95.2 100 100–200 mg L−1 4.8 0
>200 mg L−1 0 0 2. Sulfate 0–20 mg L−1 85.8 100 250 mg L−1
>20–40 mg L−1 13.2 0 >40 mg L−1 1 0
>250 mg L−1 0 0 3. Ammonium (NH+4 ) <0.38 mg L
−1 85.7 57.1 0.39–1.15 mg L−1 9.5 33.3
>1.15 mg L−1 4.8 9.5 4. COD <3.8 mg L−1 (good) 90.5 100
3.81–7.5 mg L−1 (fair) 4.8 0 >7.5 mg L−1 (poor) 4.8 0
5. Total hardness 0–30 mg L−1 61.9 71.4 31–60 mg L−1 33.3 28.6 61–120 mg L−1 4.8 0
121–180 mg L−1 0 0 <180 mg L−1 0 0
6. Al >0.2 mg L−1 71.4 4.8 0.2 mg L−1 7. Cd >3 µg L−1 14.3 33.3 3 µg L−1 8. Cr >50 µg L−1 9.5 28.6 50 µg L−1 9. Na >200 mg L−1 0 0 200 mg L−1
10. Fe >2.5 mg L−1 28.6 19.1 2.5 mg L−1 11. Pb >10 µg L−1 38.1 8.1 10 µg L−1 12. Ni >15 µg L−1 9.5 52.4 15 µg L−1 13. pH <6.5 85.7 81 6.5–8.5
pH >8.5 0 0
14. Mn >0.5 mg L−1 0 0 15. Cu >1.5 mg L−1 0 0 16. Nitrate >50 mg L−1 0 0 17. Chloride >250 mg L−1 0 0 18. Total dissolved solids >500 mg L−1 0 0 19. Specific conductivity >500 µS cm−1 0 0 20. TOC >3.0 mg L−1 0 9.5 21. Total coliforms >Zero 100 100
Number of samples analyzed each season: 21.
GROUNDWATER QUALITY CHARACTERISTICS NEAR TWO WASTE SITES IN NIGERIA 321
3.4. SOIL AND SEDIMENT FRACTIONATION RESULTS
Sediments are chemical sinks and under favorable condition toxic metals can be remobilized into the aquatic environment. Samples of soil and sediment fractions treated with each of the four extractants separately to study the effect of grain size or particle size on the distribution of metals revealed increased concentrations of metals with decreasing grain size. Zhang et al. (1990) also reported similar pattern for the –2 µm sediment fraction. Variation in behavior of elements with grain size have been investigated and they are largely attributed to differences in their relative potential for sorption on to clay minerals, hydrous oxides and organic matter sur- faces, all of which tend to be concentrated in the smaller grain sizes (Sager, 1992; Schoer, 1985).
Extractions with each of the four extractants on separate samples of the fractions also showed that concentrated nitric acid extracted more metals irrespective of particle size followed by 0.5 M HCl but both results were comparable in some cases. With respect to nitric acid extraction and 45 – <100 µm fraction, 0.5 M HCl extracted between 42–98% (combined average of 81%) and 21–96% (combined average of 63%) of elements determined in Ibadan soil and sediment fractions, re- spectively. Similarly, 0.5 M HCl extracted between 54–97% (combined average of 73%) and between 9–97% (combined average of 64%) of elements determined in Lagos soil and sediment fractions, respectively. Concentrated nitric acid is known to attack all solid phases, which includes the residual and non-residual phases of soil/sediment fractions. However, it does not dissolve all silicates completely but destroys organic matter, dissolves precipitated and adsorbed metals, and leach out a certain amount of metals from the silicate lattice (Hall, 1991). The 0.5 M HCl extraction result was comparable because it was able to attack the silicate lattice of the soil to some degree but not as much as concentrated nitric acid with more acid strength and extracting power (Pickering, 1981). Also leaching of metals with dilute HCl is reported to be always effective due to the dissolution of Fe phases, or sulphides, or release from clay minerals (Sager, 1992).
Na, K, Ca, Mg, and Fe levels in the waste soils were abundant from the high values reported (Ikem, 1996). The average values in µg g−1 for the 0.5 M HCl extractions of the 45 – <100 µm fraction of Ibadan soil and sediment were as follows with sediment values in parenthesis:
Ca [33600 (20165)], Mg [6967 (4094)], K [13479 (5363)], Na [3270 (2454)], Mn [1422 (1949)], Fe [15170 (27560)], Cu [434 (433)], Zn [2687 (2019)], Cr [25.8 (33.5)], Pb [718 (814)], Co [45 (88)], and Cd [11 (9)]. Similarly, the Lagos values in µg g−1 for the 0.5 M HCl extractions of the 45 – <100 µm fractions were as follows with sediment values in parenthesis: Ca [23617 (7807)], Mg [5640 (1986)], K [6466 (2541)], Na [2410 (697)], Mn [2757 (919)], Fe [70298 (29911)], Cu [367 (417)], Zn [10163 (1889)], Cr [46.7 (34.7)], Pb [2115 (900.7)], Co [135 (83)], and Cd [18.3 (12)].
322 A. IKEM ET AL.
0.5 M HCl extracted more metals than 0.1 M NH2OH·HCl. The percentages ex- tracted by 0.1 M NH2OH·HCl as compared to the 0.5 M HCl extraction for Ibadan soil and sediment fractions (45 – <100 µm) were Mn (26–37%), Fe (0–1.9%), Cu (0.2–1.6%), Cr (0–0%), Zn (0.8–20%), and Pb (0–0%), Co (69–84%), and Cd (50–75%). Similarly, the percentages of metals extracted by 0.1 M NH2OH·HCl with respect to the 0.5 M HCl extraction for the Lagos soil and sediment fractions (45 – <100 µm) were Mn (25.7–61.4%), Fe (0–1.4%), Cu (0.9–1.1%), Cr (14.6– 32%), Zn (15–59.4%), and Pb (0–0.3%), Co (31–37%), and Cd (9.1–33%). 0.1 M NH2OH·HCl has low acid strength and therefore low extracting power compared to the 0.5 M HCl extractant. Cu may require strong acid medium to effect release in to solution (Hall, 1991) and the leaching of Cr may be low due to the strong affinity of Fe containing Mn phase that provides adsorbing sites for Cr (Sager, 1992).
The 30% H2O2 extractions were also low compared to the 0.5 M HCl extrac- tions. Analysis of variance at 95% confidence interval suggests that there was a significant difference between the results of the two extractants. The levels of Pb and Fe in all the 30% H2O2 extractions were below their respective detection limits suggesting that they were present in the soil/sediment as in inorganic species. Chromium was also not detected in the soils from both sites using 30% H2O2. The levels of Pb and Cr for the 30% H2O2 and 0.1 M-hydroxylamine hydrochloride extractions were also low compared to the 0.5 M HCl extraction result. The low H2O2 and hydroxylamine hydrochloride extractions result suggests that they did not exist to a large extent as organically bound metals or as easily reducible species. Generally, the efficiency of the extractions is in the order: Concentrated HNO3 > 0.5 M HCl > 0.1 M NH2OH·HCl > 30% H2O2 Since 0.5 M HCl extractions were comparable to concentrated nitric acid extractions and also due to the low results of the 0.1 M NH2OH·HCl and 30% H2O2 extractions, most of the metals prob- ably were loosely held and they existed largely in form of exchangeable metals, carbonate bound metals, and as oxides and hydroxides (Ikem, 1996).
Since some of the metals existed as mostly exchangeable metals, carbonate bound metals, and as oxides and hydroxides, they may be potentially bioavailable for remobilization into the aquatic system under suitable condition. However, the average pH (pH 8.5–9.1) of the soil and sediments studied would not favor the re- mobilization of metals into groundwater or the surface waters near the waste sites. It has been reported that leaching of metals is significant at low pH or under acidic condition. Acidification leads to the mobilization of cations in exchange for H+. The order reported for some elements is as follows: Na > K > Ca > Mg > Mn > Fe > Al. Concerning the mobility of metals in soils, the water solubility of Fe, Mn, Zn, Co, and Cd increases with deceasing pH (Sager, 1992). Mobility of metals in soils and sediments are affected by a variety of factors (Sager, 1992; Petruzzelli, 1990) such as the type of interactive processes in soil (sorption, desorption, precipitation, etc.) and the characteristics of the soil involved (pH, amount of organic matter, type and content of clay, available surfaces, etc.). The study of metals distribution in soils and sediments may suffer inadequacies due to the errors (e.g. effect of air
GROUNDWATER QUALITY CHARACTERISTICS NEAR TWO WASTE SITES IN NIGERIA 323
Figure 2a. Upgradient and downgradient concentrations of dissolved solids in Ibadan.
and oven drying, freezing, evaporation, time delays before analysis, etc.) that may occur during sample handling and analyses (Kersten and Förstner, 1995). Ibadan sediments were polluted with respect to Zn and Pb metals when compared to values for African unpolluted inland water sediments (CIFA, 1994). Similarly, the Lagos sediment samples were polluted with respect to Zn, Cd, Cu and Pb. The reported mean metal concentrations in African unpolluted inland water sediments in µg g−1 dry weight were as follows: Hg (0.05–0.3), Cd (0.11), Pb (19), Cu (33), Zn (95), Mn (770), and Fe (41000).
3.5. UPGRADIENT AND DOWNGRADIENT CONCENTRATIONS OF SELECTED WELLS COMPARED
Pictorial comparison of upgradient and downgradient concentrations of dissolved solids, conductivity, sulfate, chloride, Na, K, Fe and COD for Ibadan and La- gos suggests possible impact of the sites on groundwater. Figures 2a–b and 3a–b presents the upgradient and downgradient dissolved solids and chloride values for Ibadan and Lagos. In Ibadan, well number 28 (a downgradient well and less than 5 m from the waste site) had dissolved solids (Figure 2a) and chloride (Figure 2b) maximum values of 861 mg L−1 and 314.9 mg L−1, respectively. Chloride is known to be a good indicator of pollution and well number 28 had significant impact from the waste site judging from the chloride and dissolved solids values. The chloride and dissolved solids values for well 28 were above their respective WHO drinking water standards. In Ibadan, the difference in chloride values between some upgradient and downgradient wells were up to 100 mg L−1. Also the differences in dissolved solids concentrations were as much as 400 mg L−1. Judging by the
324 A. IKEM ET AL.
Figure 2b. Upgradient and downgradient concentrations of chloride in Ibadan.
Figure 3a. Upgradient and downgradient concentrations of dissolved solids in Lagos.
GROUNDWATER QUALITY CHARACTERISTICS NEAR TWO WASTE SITES IN NIGERIA 325
Figure 3b. Upgradient and downgradient concentrations of chloride in Lagos.
concentrations of dissolved solids and chloride near the Lagos site, the impact of the waste site on the wells was less significant. The dissolved solids concentration decreased by 0.81 mg L−1 while that of chloride decreased by 0.67 mg L−1 from the waste site to the wells. The highest chloride value reported in Lagos was about 100 mg L−1 and this was below the WHO stipulated guideline for drinking wa- ter. Also, the dissolved solids concentrations recorded for Lagos upgradient and downgradient wells were all below the WHO standards for drinking water.
Comparison of some water quality constituents of wells within 10 m and >10 m from the Ibadan waste site and wells within 20 m and >20 m from the Lagos waste site through parametric analysis of variance (F-test) suggests significant variations of conductivity, dissolved solids, chloride, ammonia and COD at 95% confidence level. Also one-way ANOVA applied on the data obtained at different sampling periods at Ibadan suggests statistically significant difference in variances between upgradient and downgradient data at 95% confidence level. Significant variations were observed for pH, specific conductivity, dissolved solids, chloride, and sulfate for Ibadan wells. One-way parametric ANOVA on the Lagos data suggests that variances of pH, specific conductivity, dissolved solids, chloride, sulfate, nitrate, ammonia, and COD were statistically different at 95% confidence level. However, the one-way parametric ANOVA is deficient because it mixes both upgradient and downgradient wells and as such could not provide information on the wells that were contaminated. Confirmation of where the differences existed was not conduc- ted using Bonferroni t-statistic since parametric procedures have been adjudged to be less accurate than non-parametric procedures.
326 A. IKEM ET AL.
Non-parametric procedures (Mann-Whitney ‘T’ test and Kruskal-Wallis H-test) were then applied to upgradient and downgradient wells to further evaluate leachate impact on groundwater quality. Applying the Mann-Whitney ‘T’ test to ranked analytical data, it was found that upgradient concentrations of almost all the water quality constituents analyzed except iron, sulfate, and pH did not differ signific- antly with downgradient concentrations at 95% confidence level. Thus, the null hypothesis that the downgradient values of Fe, sulfate and pH were the same as the upgradient values were rejected at 95% confidence level. The average Fe levels for upgradient and downgradient wells were 0.12 and 1.07 mg L−1, respectively. The average sulfate concentrations for upgradient and downgradient wells were 4.2 and 27.3 mg L−1, respectively. The average pH values for upgradient wells and downgradient wells were 6.13 and 5.59, respectively.
The Kruskal-Wallis H-statistic conducted revealed that variances of pH, specific conductivity, dissolved solids, and chloride for Ibadan upgradient and downgradi- ent wells were significantly different at 5% level of significance. Similarly, the Lagos upgradient and downgradient wells showed significant variation in vari- ances of only specific conductivity and dissolved solids at 5% level of significance. To ascertain specific wells that had significant contamination, further comparison of average rank of background wells (average rank of selected upgradient wells was used as background value) and each downgradient wells were conducted on parameters that had unequal variance in the Kruskal-Wallis H-test. From the test, downgradient wells DG6, DG8 and DG9 in Lagos had significant contamination from dissolved solids. Similarly, downgradient wells DG1, DG2, DG 23 and DG 28 in Ibadan also had significant contamination from dissolved solids and chloride intrusion. Sulfate was also significant for DG1, DG2 and DG28 in Ibadan. In a sim- ilar study in Malaysia (Ahmed and Sulaiman, 2001), downstream borehole values of electrical conductivity, sodium, potassium, chloride, hardness, phosphate and nitrite were higher than the corresponding upstream borehole values. Also the de- gree of contamination of the underground water quality in the Athens area, Greece increased with decreasing distance from the landfill (Loizidou and Kapetanios, 1993).
More detailed work especially on the geology of the two sites is imperative but the hydrochemical maps obtained for the Lagos dissolved solids (Figure 4a) and chloride (Figure 4b) concentrations over the sampling periods showed values below the WHO standards for drinking water. The effect of the Lagos waste site on the wells may not manifest immediately but may take years to cause significant damage to the aquifer. Deeper aquifers of the two sites may be at risk from possible contamination since most of the drinking wells studied were shallow and vertical migration of pollutants may be more significant than horizontal flow. The Lagos and Ibadan sampled areas are both located in elevated zones relative to the waste sites. Thus, the low migration of materials over time towards the wells probably may be due to the low hydraulic gradient from the waste site to the wells. The leachate emanating from the Lagos waste site is largely westward and in opposite
GROUNDWATER QUALITY CHARACTERISTICS NEAR TWO WASTE SITES IN NIGERIA 327
Figure 4a. Dissolved solid distribution for Lagos sampled area.
direction to the wells. Elevations and water level measurements of sampling points (Figure 5) near the Ibadan waste site suggested a groundwater dominant flow pat- tern moving largely towards the west and also in the northwest direction. This also suggested a low migration of pollutants towards the wells especially on the eastern and northeastern side of the Ibadan waste site.
4. Conclusions
The analytical results of the 51 wells monitored in this study irrespective of source of pollution, revealed that groundwater from these private wells requires further purification to ensure their suitability for human consumption because the levels of some of the water quality parameters exceeded the WHO guidelines for drink- ing water. This study also revealed that nutrients and trace metals in the soils and sediments from the two sites were mostly in form of exchangeable metals, carbonate bound metals, and as oxides and hydroxides. These metals are largely of anthropogenic sources from the extractions conducted. The leaching of trace metals
328 A. IKEM ET AL.
Figure 4b. Chloride distribution for Lagos sampled area.
into groundwater will be enhanced under favorable conditions such as low pH and high hydraulic gradient from the waste site towards the wells studied. However, the high pH (pH 8.5–9.1) condition of the soils and sediments (Tables I and II) and the low hydraulic gradient from the waste sites to the wells monitored may have posed limitation on the leaching of toxic metals into groundwater. Based on the statistical analysis of selected wells, three downgradient wells in Lagos and four downgradient wells in Ibadan were significantly impacted by leachate migration during the sampling seasons.
These areas need to be independently studied over time to fully evaluate the environmental impact of the waste sites on the water resources and the health of citizens in the two neighborhoods. The results of this study indicate the need for en- vironmental education, adequate regulations and proper management of the waste sites by the Nigerian government. Well owners were educated on the implications of inadequate well protection from storm water/runoffs and siting wells near waste sites or septic tanks. Waste dumping on both sites by companies and individuals
GROUNDWATER QUALITY CHARACTERISTICS NEAR TWO WASTE SITES IN NIGERIA 329
Figure 5. Elevation and dominant flow pattern near Ibadan waste site.
is now prohibited and the sites are gradually being reclaimed. The Federal gov- ernment of Nigeria has set up the States and Federal Environmental Protection Agencies (FEPA) to help protect the Nigerian environment from pollution in gen- eral. Some of the measures already in place to help curtail the disastrous effects of leachate migration into groundwater include laws on discharge and disposal of wastes especially industrial wastes; new and better designed waste sites in Lagos and Ibadan cities; and drinking water guidelines for Nigeria. A huge water project to help provide drinking water to a larger population of Lagos metropolis was recently undertaken.
330 A. IKEM ET AL.
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