Geochemical assessment of groundwater samples from hand-dug wells within the vicinity of Aba-Eku dumpsite was carried out for domestic and irrigation purposes. Ten groundwater samples were collected both in dry season and wet season for analysis of physico-chemical parameters: pH, EC, TDS, The results of the analyses showed the groundwater samples to be within limits of WHO/NSDWQ. However, higher values of concentrations of the chemical constituents were noticed in well 5 nearer to the landfill. Interpretation of Piper diagram showed CaHCO 3 to be dominant in the area. Alkaline earth metals and weak acids are dominant cations and anions over the alkalis and strong acids in both sessions. Groundwater in the study area is of hard, fresh and alkaline nature. Assessment for irrigation purpose showed that most of the water samples were suitable for irrigation purpose except in a few locations.
The quality of water is of vital importance to mankind since it is directly linked with human health. The quality of groundwater is equally important to its quantity due to the suitability of water for various purposes ranging from drinking, domestic, industrial and agricultural purposes all over the world [
Several researchers have identified contamination plumes from disposal sites [
The present study was carried out for both dry and wet seasons from hand-dug wells bordering Aba-Eku landfill for better understanding of spatial and seasonal distribution of hydrogeochemical constituents of groundwater as well as its suitability for domestic and irrigation purposes.
Ibadan lies approximately within the square of longitudes 3˚35'E and 4˚10'E and latitude 7˚20'N and 7˚40'N. The study area, Aba Eku located within Ibadan metropolis and located on longitude 3˚59'009''E and 3˚59'973''E and latitude 7˚19'270''N and 7˚19'843''N. The dumpsite is bothered by residential buildings. The study area falls within the humid and subhumid tropical climate of southwestern Nigeria with a mean annual rainfall of about 1230 mm and mean maximum temperature of 32˚C. Relief in Ibadan is gently undulating and ranges between 200 - 234 m (above mean sea level). Aba-Eku landfill is one of the four designated open dumpsites managed and maintained by Oyo State Waste Management Authority. It was opened in 1998 and is still active till date. It is located along Ijebu Igbo road covering an area of approximately 10 hecatares.
Geologically, the study area lies within the basement complex rock (
Ten groundwater samples were collected during March and August 2013 at ten different locations from hand- dug wells around the dumpsite (
lene Diamine Tetra Acetic Acid (EDTA) titration method using Eriochrome black-T as an indicator. The analytical data can be used for the classification of water for various purposes and their percentage compliance with the World Health Organization (WHO) as well as Nigerian Standard for Driking Water Quality (NSDWQ).
Maximum and minimum concentrations of major ions present in the water samples and their percentage compliance with WHO and NSDWQ limits for both dry and wet seasons are as shown in
The pH values of groundwater range from 6.69 to 7.59 and 6.51 to 7.06 during dry and wet seasons respectively. The pH values during both seasons fall within the WHO and NSDWQ permissible range of 6.5 - 8.5. Fifty percentage of analyzed samples have pH values below 7.0 during dry season while this increase to 80% during wet season. This indicates that there is more dissolution of pollutants during the rainy season. The total Hardness (TH) values during dry and wet seasons ranged from 08 to 288 mg/L and from 132 to 446 mg/L respectively. Based on [
Well | Distance to landfill (m) | Depth to water table (m) (Dry) | Depth to water table (m) (Wet) | Depth to bottom (m) |
---|---|---|---|---|
1. | 110.00 | 5.90 | 4.00 | 7.30 |
2. | 30.00 | 6.60 | 4.30 | 13.40 |
3. | 50.00 | 5.50 | 3.30 | 10.90 |
4. | 50.00 | 6.40 | 2.50 | 10.90 |
5. | 20.00 | 3.00 | 3.50 | 5.40 |
6. | 350.00 | 2.50 | 2.40 | 5.40 |
7. | 360.00 | 5.50 | 3.60 | 6.00 |
8. | 360.00 | 4.30 | 2.90 | 7.30 |
9. | 170.00 | 4.30 | 2.60 | 7.00 |
10. | 200.00 | 0.90 | 1.50 | 4.20 |
while 10% falls under “Hard” class during the dry season. During wet season of sample collection, none falls under “soft” class of hardness, 10% fall under “moderate” class, 70% fall under “Hard” class while the remaining 20% fall under “very hard” class. The chloride ion concentration values ranged from 17 to 106 mg/L and 10 to 120 mg/L during dry and wet seasons respectively and these were found to lie within the permissible level of 250 mg/L. The nitrate values during dry season ranged from 1.4 to 4.8 mg/L. However, during wet season, it ranged from 0 to 3.3 mg/L. Unpolluted natural water usually contains only minute quantities of nitrate. The groundwater samples in both seasons have their nitrate values lie below the limit of 50 mg/L by WHO and
Parameters | Range (Dry) | Percent compliance | Range (Wet) | Percent compliance | [ | ||
---|---|---|---|---|---|---|---|
Min | Max | Min | Max | ||||
pH | 6.69 | 7.59 | 100 | 6.51 | 7.06 | 100 | 6.5 - 8.5 |
EC | 148 | 784 | 100 | 202 | 539 | 100 | 1000 |
TDS | 74 | 392 | 100 | 1000 | 268 | 100 | 500 |
Cl− | 17 | 106 | 100 | 10 | 120 | 100 | 250 |
122 | 366 | 100 | 146.4 | 414.8 | 100 | 1000 | |
60 | 180 | 90 | 72 | 204 | 70 | 120 | |
TH | 08 | 288 | 90 | 132 | 446 | 10 | 150 |
Na+ | 08 | 40 | 100 | 11 | 26 | 100 | 200 |
K+ | 0 | 5 | 100 | 1 | 4 | 100 | 55 |
1.36 | 4.81 | 100 | 0 | 3.27 | 100 | 50 | |
Ca2+ | 0.12 | 5.87 | 100 | 1.62 | 15.09 | 100 | 75 |
Mg2+ | 0.43 | 14.78 | 100 | 4.18 | 26.2 | 100 | 50 |
13.39 | 144.03 | 100 | 10.32 | 75.32 | 100 | 250 |
Sample | pH | EC | TDS | Cl− | TH | Na+ | K+ | Mg2+ | Ca2+ | |||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Dry | Wet | Dry | Wet | Dry | Wet | Dry | Wet | Dry | Wet | Dry | Wet | Dry | Wet | Dry | Wet | Dry | Wet | Dry | Wet | Dry | Wet | Dry | Wet | Dry | Wet | |
S1 | 7.2 | 7.0 | 207 | 244 | 103 | 122 | 25 | 19 | 170.8 | 414.8 | 84 | 204 | 74 | 170 | 17 | 13 | 2 | 1 | 19.56 | 27.10 | 1.9 | 0 | 7.71 | 5.95 | 2.97 | 1.62 |
S2 | 7.1 | 6.9 | 381 | 511 | 190 | 254 | 68 | 41.5 | 170.8 | 195.2 | 84 | 96 | 78 | 320 | 30 | 26 | 1 | 1 | 15.65 | 12.10 | 1.6 | 0 | 5.59 | 15.63 | 0.79 | 2.80 |
S3 | 6.7 | 6.5 | 227 | 253 | 113 | 130 | 20 | 13 | 219.6 | 195.2 | 108 | 96 | 84 | 222 | 15 | 12 | 1 | 2 | 14.19 | 10.65 | 1.6 | 0 | 9.32 | 11.93 | 2.02 | 6.27 |
S4 | 6.8 | 6.7 | 240 | 315 | 120 | 156 | 25 | 19.5 | 219.6 | 244 | 108 | 120 | 90 | 266 | 15 | 15 | 1 | 1 | 13.39 | 12.42 | 1.4 | 0.4 | 7.05 | 10.67 | 1.73 | 9.40 |
S5 | 6.7 | 6.9 | 784 | 539 | 392 | 268 | 106 | 120 | 366 | 390.4 | 180 | 192 | 288 | 446 | 40 | 24 | 5 | 4 | 144.03 | 75.32 | 2.8 | 0.2 | 14.78 | 26.24 | 5.87 | 15.09 |
S6 | 6.9 | 7.1 | 231 | 233 | 115 | 116 | 25 | 16 | 170.8 | 219.6 | 84 | 108 | 08 | 154 | 18 | 16 | 1 | 1 | 15.00 | 15.32 | 1.5 | 0.2 | 2.69 | 5.08 | 0.94 | 5.58 |
S7 | 7.3 | 6.8 | 176 | 237 | 88 | 118 | 25 | 17 | 146.4 | 195.2 | 72 | 96 | 26 | 132 | 13 | 17 | 0 | 1 | 14.19 | 24.52 | 2.8 | 3.3 | 0.43 | 4.18 | 0.12 | 2.22 |
S8 | 7.6 | 6.9 | 245 | 255 | 122 | 126 | 17 | 10 | 195.2 | 268.4 | 96 | 132 | 98 | 208 | 12 | 13 | 1 | 1 | 26.94 | 10.32 | 4.0 | 0.3 | 4.15 | 5.88 | 3.93 | 11.33 |
S9 | 6.9 | 6.8 | 263 | 229 | 131 | 113 | 26 | 15.5 | 219.6 | 195.2 | 108 | 96 | 116 | 216 | 12 | 12 | 1 | 1 | 42.42 | 22.26 | 1.9 | 0 | 12.31 | 11.28 | 4.17 | 7.53 |
S10 | 7.1 | 6.5 | 148 | 202 | 74 | 100 | 19 | 16 | 122 | 146.4 | 60 | 72 | 60 | 174 | 8 | 11 | 1 | 1 | 26.13 | 21.77 | 4.8 | 1.2 | 4.36 | 8.87 | 0.59 | 3.47 |
NSDWQ. The values of sulphate ions in the groundwater samples ranged from 13.4 to 144 mg/L during dry season and 10.3 to 75.3 mg/L during wet season. However, sulphate lie below 200 mg/L according to WHO and NSDWQ limit. The Na+ and K+ values ranged from 08 to 40 mg/L and 0 to 5 mg/L during dry season and lie below the limits set by WHO and NSDWQ. During wet season, Na+ and K+ values ranged from 11 to 26 mg/L and 01 to 4 mg/L respectively. The low pottassium concentrations in both seasons compared to Na+ concentration may be due to the resistant of potassium minerals to decomposition by weathering process. Also its low concentration in natural water is as a consequence of its tendency to be fixed by clay minerals and participate in the formation of secondary minerals.
The Ca2+ and Mg2+ concentration values during dry and wet seasons ranged from 0.1 to 5.9 mg/L; 0.4 to 14.8 mg/L and 1.6 to 15.1 mg/L; 4.2 to 26.2 mg/L respectively.
The EC values range from 148 μS/cm to 784 μS/cm during dry season and 202 μS/cm to 539 μS/cm during wet season. The TDS values lie within the WHO and NSDWQ limits. The TDS values in both seasons showed that all the water samples irrespective of the season belong to “freshwater” class based on [
The abundance of major ions in groundwater during both seasons is in the following order: Na+ > Mg2+ > Ca2+ > K+ and
The degree of a linear association between any two analyzed parameters measured by Pearson’s Correlation coefficient for both dry and wet seasons are presented in
Hydrochemical concept can help to elucidate the mechanism of flow and transport in groundwater systems [
Good quality irrigation water is essential for proper growth of crop plants. Groundwater suitability for irrigation purpose in this study was assessed using various irrigation parameters. The irrigation parameters are Sodium Adsorption Ratio (SAR), Percentage Sodium (%Na), Residual Sodium BiCarbonate (RSBC), Magnessium Ratio (MAR), Kelly’s Ratio (KR) and Permeability Index (PI). The results of these irrigation parameters in both seasons are presented in
Wilcox (1948) classified groundwater for irrigation purposes based on %Na and Electrical conductivity.
The sodium in irrigation water in usually denoted as %Na and can be determined using the formula:
where the quantities are expressed in Meq/L. The classification of analyzed water samples is shown in
Salinity: Electrical conductivity (EC) is a measure of the amount of dissolved salts present in groundwater samples. EC is a good measure of salinity hazard to crops as it reflects the TDS in groundwater [
TDS mg/L | Class | % compliance |
---|---|---|
0 - 1000 | Freshwater | 100 |
1000 - 10,000 | Brackish | - |
10,000 - 100,000 | Saline water | - |
>100,000 | Brine | - |
pH | EC | TDS | Cl− | Bicarbonate | Hardness | Carbonate | Na+ | K+ | Mg2+ | Ca2+ | |||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
pH | 1 | ||||||||||||
EC | −0.446 | 1 | |||||||||||
TDS | −0.447 | 1.000(**) | 1 | ||||||||||
Cl− | −0.419 | 0.955(**) | 0.955(**) | 1 | |||||||||
Bicarbonate | −0.551 | 0.886(**) | 0.886(**) | 0.730(*) | 1 | ||||||||
Hardness | −0.423 | 0.903(**) | 0.903(**) | 0.787(**) | 0.922(**) | 1 | |||||||
Carbonate | −0.551 | 0.886(**) | 0.886(**) | 0.730(*) | 1.000(**) | 0.922(**) | 1 | ||||||
−0.400 | 0.917(**) | 0.917(**) | 0.815(**) | 0.867(**) | 0.935(**) | 0.867(**) | 1 | ||||||
0.471 | −0.060 | −0.059 | −0.089 | −0.185 | 0.102 | −0.185 | 0.187 | 1 | |||||
Na+ | −0.425 | 0.923(**) | 0.922(**) | 0.966(**) | 0.716(*) | 0.703(*) | 0.716(*) | 0.719(*) | −0.264 | 1 | |||
K+ | −0.460 | 0.897(**) | 0.897(**) | 0.808(**) | 0.847(**) | 0.900(**) | 0.847(**) | 0.924(**) | 0.043 | 0.782(**) | 1 | ||
Mg2+ | −0.646(*) | 0.670(*) | 0.670(*) | 0.547 | 0.818(**) | 0.834(**) | 0.818(**) | 0.710(*) | −0.216 | 0.500 | 0.733(*) | 1 | |
Ca2+ | −0.175 | 0.665(*) | 0.664(*) | 0.462 | 0.815(**) | 0.842(**) | 0.815(**) | 0.764(*) | 0.053 | 0.424 | 0.751(*) | 0.807(**) | 1 |
**Correlation is significant at the 0.01 level (2-tailed). *Correlation is significant at the 0.05 level (2-tailed).
pH | EC | TDS | Cl− | Hardness | Na+ | K+ | Mg2+ | Ca2+ | |||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
pH | 1 | ||||||||||||
EC | 0.224 | 1 | |||||||||||
TDS | 0.217 | 1.000(**) | 1 | ||||||||||
Cl− | 0.181 | 0.836(**) | 0.836(**) | 1 | |||||||||
0.551 | 0.351 | 0.351 | 0.535 | 1 | |||||||||
0.551 | 0.351 | 0.351 | 0.535 | 1.000(**) | 1 | ||||||||
Hardness | 0.051 | 0.916(**) | 0.916(**) | 0.882(**) | 0.396 | 0.396 | 1 | ||||||
0.163 | 0.548 | 0.546 | 0.906(**) | 0.613 | 0.613 | 0.650(*) | 1 | ||||||
−0.272 | −0.276 | −0.279 | −0.156 | −0.318 | −0.318 | −0.417 | 0.019 | 1 | |||||
Na+ | 0.369 | 0.923(**) | 0.921(**) | 0.725(*) | 0.225 | 0.225 | 0.713(*) | 0.451 | −0.038 | 1 | |||
K+ | −0.045 | 0.630 | 0.636(*) | 0.894(**) | 0.494 | 0.494 | 0.782(**) | 0.856(**) | −0.184 | 0.453 | 1 | ||
Mg2+ | −0.075 | 0.850(**) | 0.852(**) | 0.896(**) | 0.314 | 0.314 | 0.962(**) | 0.716(*) | −0.369 | 0.644(*) | 0.844(**) | 1 | |
Ca2+ | 0.023 | 0.406 | 0.402 | 0.579 | 0.346 | 0.346 | 0.667(*) | 0.504 | −0.348 | 0.180 | 0.668(*) | 0.593 | 1 |
**Correlation is significant at the 0.01 level (2-tailed). *Correlation is significant at the 0.05 level (2-tailed).
activity of plants and this interferes with the absorption of water and nutrients from the soil [
Sodium adsorption ratio (SAR): This is a better measurement of sodium hazard present in water. SAR gives an idea about the adsorption of Na+ in water by soil. It is an important parameter that is used to evaluate the suitablity of water for irrigation purpose because it is a measure of sodium hazard to crops. SAR is defined by [
Sample | SAR | % Na | Soluble sodium % | RSBC | MAR | KR | PI |
---|---|---|---|---|---|---|---|
S1 | 1.17509 | 46.74 | 49.96 | 2.651 | 81.16 | 0.93 | 157.6 |
S2 | 2595057 | 71.06 | 72.47 | 2.761 | 92.27 | 2.58 | 164.5 |
S3 | 0.984607 | 41.92 | 43.60 | 3.499 | 88.48 | 0.74 | 116.7 |
S4 | 1.122305 | 48.18 | 50.11 | 3.513 | 87.11 | 0.97 | 192.1 |
S5 | 1.995426 | 51.36 | 55.14 | 5.706 | 80.65 | 1.14 | 128.5 |
S6 | 2.131056 | 72.57 | 74.97 | 2.753 | 82.59 | 2.90 | 233.2 |
S7 | 3.89887 | 93.08 | 93.08 | 2.394 | 85.72 | 13.45 | 348.2 |
S8 | 1.002734 | 47.88 | 50.28 | 3.003 | 63.65 | 0.96 | 217.2 |
S9 | 0.66455 | 29.29 | 30.75 | 3.392 | 83.14 | 0.42 | 137.7 |
S10 | 0.786052 | 45.43 | 48.82 | 1.971 | 92.60 | 0.88 | 238.1 |
Sample | SAR | % Na | Soluble sodium % | RSBC | MAR | KR | PI |
---|---|---|---|---|---|---|---|
S1 | 1.05190 | 48.37 | 50.59 | 6.719 | 85.96 | 0.97 | 277.8 |
S2 | 1.33033 | 43.48 | 44.48 | 3.060 | 90.29 | 0.78 | 113.4 |
S3 | 0.64523 | 27.74 | 30.45 | 2.886 | 76.01 | 0.39 | 126.2 |
S4 | 0.79125 | 32.02 | 33.30 | 3.530 | 65.39 | 0.48 | 131.9 |
S5 | 0.86010 | 25.51 | 28.04 | 5.645 | 74.32 | 0.35 | 89.7 |
S6 | 1.17394 | 48.84 | 50.66 | 3.321 | 60.31 | 0.99 | 185.4 |
S7 | 1.54259 | 60.37 | 62.50 | 3.089 | 75.81 | 1.61 | 211.0 |
S8 | 0.77792 | 34.33 | 35.90 | 3.834 | 46.35 | 0.53 | 164.4 |
S9 | 0.64327 | 27.98 | 29.38 | 2.823 | 71.37 | 0.39 | 125.6 |
S10 | 0.70786 | 33.76 | 35.59 | 2.227 | 81.03 | 0.52 | 145.8 |
Water class | % Na | % during dry season | % during wet season |
---|---|---|---|
Excellent | <20 | - | - |
Good | 20 - 40 | 10% | 60% |
Permissible | 40 - 60 | 60% | 30% |
Doubtful | 60 - 80 | 20% | 10% |
Unsuitable | >80 | 10% | - |
where the concentrations are in Meq/L.
Water class | EC values | % during dry season | % during wet season |
---|---|---|---|
Excellent | <250 | 70% | 50% |
Good | 250 - 750 | 30% | 50% |
Permissible | 750 - 2000 | - | - |
Doubtful | 2000 - 3000 | - | - |
Unsuitable | >3000 | - | - |
High value of SAR means that sodium in water may replace Ca2+ and Mg2+ ions in the soil thereby causing potential damage to the soil structure and affect availability of water to crop [
Permeability Index (PI): The PI values also indicate the suitability of groundwater for irrigation purpose. The influencing constituents for PI values are total dissolved solid, Sodium bicarbonate and the soil type. It is defined as follows [
where the concentrations are in Meq/L.
From
Soluble sodium percentage (SSP): This is an important factor for studying sodium hazards. Sodium has the potential of reacting with soil thereby reducing its permeability and supports little or no plant growth [
where the concentrations are in meq/L.
Based on SSP values, 70% of analyzed water samples belong to “Excellent” class while 30% belong to “Good to Permissible” class during dry season. In wet season, 90% of analyzed water samples fall under “Excellent” class while only 10% falls under “Good to Permissible” class (
Residual Sodium BiCarbonate (RSBC): The concentration of bicarbonate and carbonate in water influences the suitability of water for irrigation purpose. Land irrigated with high RSBC water becomes infertile due to deposition of sodium carbonate [
where ions are expressed in Meq/L.
During dry season, 80% of water samples fall under “Fair” category while 20% falls under “Good” category. During wet season, the percentage of groundwater samples under “Fair” class has increased to 90% while the remaining 10% falls under “Good” category for irrigation purpose. The classification of groundwater based on RSBC value is shown in
Kelly’s Ratio: Kelly’s ratio is calculated by the numerical formula [
KR values of 1 or <1 is an indication of good quality water for irrigation purpose while KR of >1 is unsuitable
Water class | Alkalinity hazard | SAR values | % during dry season | % during wet season |
---|---|---|---|---|
Excellent | S1 | <10 | 100 | 100 |
Good | S2 | 10 - 18 | - | - |
Doubtful | S3 | 18 - 26 | - | - |
Unsuitable | S4 | >26 | - | - |
Water class | PI values | % during dry season | % during wet season |
---|---|---|---|
Excellent | >75 | 100 | 100 |
Good to permissible | 75 - 25 | - | - |
Doubtful to unsuitable | <25 | - | - |
Water class | SSP values | % during dry season | % during wet season |
---|---|---|---|
Excellent | <60 | 70 | 90 |
Good to permissible | 60 - 75 | 30 | 10 |
Doubtful to unsuitable | >75 | - | - |
Water class | RSBC values | % during dry season | % during wet season |
---|---|---|---|
Excellent | <1.25 | - | - |
Good to permissible | 1.25 - 2.5 | 20 | 10 |
Doubtful to unsuitable | >2.5 | 80 | 90 |
for agricultural purpose due to alkali hazard [
Total Dissolved Solids (TDS): The TDS concentrations in the groundwater surrounding Aba-Eku dumpsite during dry season range from 74 to 392 mg/L and 100 to 268 mg/L during wet season. Based on classification of irrigation water with respect to TDS [
The major ions in groundwater samples were found to be within the permissible limits of WHO and NSDWQ, thus suitable for domestic purpose. However, water from location 5 showed higher values of concentration of most parameters than other locations due to its nearness to the landfill. Generally, the groundwater quality of the study area in both seasons based on the interpretation of hydrochemical analyses is hard, fresh and alkaline in nature. The dominant groundwater type in both seasons was CaHCO3 type. Alkaline earth (Ca2+ and Mg2+) exceeds alkalis (Na+ and K+) and weak acids (
Range of KR | Water class | % during dry season | % during wet season |
---|---|---|---|
<1 or 1 | Good | 60 | 90 |
>1 | Unsuitable | 40 | 10 |
samples will neither cause salinity hazards nor have adverse effects on the soil properties and thus suitable for irrigation needs.
The authors are grateful to the Institute of Food Security, Environmental Resources and Agricultural Research (IFSERAR) of Federal University of Agriculture, Abeokuta (FUNAAB), Nigeria for funding part of this research work through research grant no: FUNAAB/IFSERAR/IRG100.