Chemical parameters
The mean values for major ionic constituents are below the permissible limit of WHO (2011) standard, except for NO3−. Statistical summary of the results (Table 2) showed that in wet and dry seasons, the relative abundance of major cations present in groundwater is of the order Ca2+ > Na+ > Mg2+ > K+. During the wet season, anionic constituents within the groundwater samples occur in the descending order NO3− > HCO3− > Cl− > SO42−, while they are present within the order NO3− > Cl− > SO42− > HCO3− during the dry season. This suggests that concentration of NO3− in the groundwater is highest during both seasons, which are likely due to contributions from anthropogenic inputs like the application of fertilizer and inappropriate waste disposal within the study area. Further, HCO3− is the second highest concentration due to the infiltrating rainwater during the wet season and hence least during the dry season. However within the dry season, the effect of evaporation resulted in the high concentration of Cl−.
The concentration of Na+ is highest amongst the cations and this could impart a salty taste on the groundwater by combining with Cl− (Ramesh and Elango 2011; Sarath-Prasanth et al. 2012). Na+ is present within the range from 8.62 to 182.10 mg/l, with a mean value of 34.72 mg/l for the wet season samples. During the dry season, Na+ ranged from 3.42 to 206.70 mg/l, with mean concentration of 27.54 mg/l. K+ was found to occur within the range of 2.07 to 98.85 mg/l, with mean of 11.58 mg/l for the wet season. K+ dry season samples ranged from 1.50 to 28.46 mg/l and a mean of 5.85 mg/l. The values of Ca2+ were found to be present within the range 14.42 to 183.30 mg/l with mean of 51.36 mg/l for the wet season samples analyzed. During the dry season, the range of Ca2+ was 4.39 to 123.20 mg/l, and a mean of 27.64 mg/l. Very high Ca2+ in groundwater can cause abdominal ailment, encrustation and scaling (Saranth-Prasanth et al. 2012). The concentration of Mg2+ present for the wet season samples ranged from 2.52 to 51.41 mg/l, with mean of 14.29 mg/l. In dry season, Mg2+ ranged from 1.42 to 59.40 mg/l, with a mean of 11.60 mg/l. Ca2+ and Mg2+ in groundwater is as a result of rock-water interaction which has led to the dissolution of the more soluble calcium in subsurface through weathering and ion exchange processes.
Of the anions present, the concentration of Cl− in groundwater during the wet season ranged from 0.00 to 266.00 mg/l, with a mean of 34.34 mg/l. In the dry season however, Cl− ranged from 0.00 to 265.00 mg/l, with a mean of 34.44 mg/l. NO3− concentration during the wet season ranged from 0.00 to 318.00 mg/l and a mean of 76.28 mg/l, while the range obtained during dry season occur from 0.00 to 502.00 mg/l with a mean of 55.84 mg/l. Excess Cl− in water may indicate a tracer for groundwater contamination (Loizidou and Kapetanios 1993), while NO3− may indicate anthropogenic influences (Edet 2016). SO42+ in groundwater from the study area during the wet season ranged from 0.00 to 119.00 mg/l and mean of 15.31 mg/l. In the dry season, SO42 ranged from 0.00 to 108.00 mg/l, with mean of 10.87 mg/l. The concentration level of HCO3− ranged from 0.27 to 180.00 mg/l, with a mean value of 59.18 mg/l in wet season. However in the dry season, the concentration of HCO3− ranged 0.67 and 6.93 mg/l, with mean value of 2.18 mg/l. The concentration SO42+ and HCO3− are within the acceptable standard for drinking water according to WHO (2011) in most of the samples, aside from some locations during the wet season where they exceed the permissible limits.
Correlation matrix
Correlation measures how well one variable predicts the other (Bahar and Reza 2010; Adamu et al. 2021). The matrix obtained at 95% confidence limit during the study for both wet and dry season samples are hereby presented (Table 3). The Table 3 revealed that pH and HCO3− show poor correlation with EC, TDS, Na+, K+, Ca2+, Mg2+, Cl−, SO42− and NO3− in both wet and dry seasons. This could be attributed to dissolution of the basement rocks which releases more HCO3− into solution, while the resulting pH of groundwater increasingly tends towards a weak acid. Also during wet season, Mg2+ showed a strong positive correlation with EC and TDS; Na+ showed strong positive correlation with K+, Cl−, SO42− and NO3−, while K+ showed a strong positive correlation with Ca2+, Mg2+, Cl−, SO42− and NO3.
Table 3
Correlation matrix for the analyzed samples during the wet and dry seasons
WET SEASON SAMPLES | Parameters | pH | E.C. | TDS | Na+ | K+ | Ca2+ | Mg2+ | Cl− | SO42− | NO3− | HCO3− |
pH | 1.00 | | | | | | | | | | |
E.C. | 0.20 | 1.00 | | | | | | | | | |
TDS | 0.18 | 0.99 | 1.00 | | | | | | | | |
Na+ | 0.16 | 0.04 | 0.06 | 1.00y | | | | | | | |
K+ | -0.16 | 0.39 | 0.40 | 0.53 | 1.00 | | | | | | |
Ca2+ | -0.11 | 0.23 | 0.23 | 0.42 | 0.66 | 1.00 | | | | | |
Mg2+ | 0.12 | 0.58 | 0.57 | 0.34 | 0.64 | 0.59 | 1.00 | | | | |
Cl− | 0.05 | 0.30 | 0.30 | 0.76 | 0.66 | 0.50 | 0.64 | 1.00 | | | |
SO42− | -0.05 | 0.37 | 0.39 | 0.66 | 0.90 | 0.63 | 0.64 | 0.77 | 1.00 | | |
NO3− | 0.03 | 0.31 | 0.31 | 0.58 | 0.74 | 0.56 | 0.76 | 0.78 | 0.75 | 1.00 | |
HCO3− | 0.07 | 0.01 | 0.02 | 0.16 | 0.27 | 0.21 | 0.22 | 0.31 | 0.32 | 0.30 | 1.00 |
DRY SEASON SAMPLES | pH | 1.00 | | | | | | | | | | |
E.C. | 0.18 | 1.00 | | | | | | | | | |
TDS | 0.16 | 0.98 | 1.00 | | | | | | | | |
Na+ | 0.05 | 0.83 | 0.75 | 1.00 | | | | | | | |
K+ | -0.07 | 0.65 | 0.59 | 0.68 | 1.00 | | | | | | |
Ca2+ | 0.22 | 0.74 | 0.72 | 0.78 | 0.82 | 1.00 | | | | | |
Mg2+ | 0.07 | 0.80 | 0.76 | 0.78 | 0.87 | 0.91 | 1.00 | | | | |
Cl− | -0.01 | 0.79 | 0.73 | 0.93 | 0.69 | 0.73 | 0.82 | 1.00 | | | |
SO42− | 0.16 | 0.87 | 0.79 | 0.93 | 0.73 | 0.88 | 0.80 | 0.81 | 1.00 | | |
NO3− | -0.04 | 0.60 | 0.50 | 0.71 | 0.85 | 0.83 | 0.84 | 0.74 | 0.74 | 1.00 | |
HCO3− | 0.19 | 0.27 | 0.24 | 0.24 | 0.12 | 0.26 | 0.07 | 0.08 | 0.34 | 0.11 | 1.00 |
Na+ showed strong positive correlation with K+, Ca2+, Mg2+, Cl−, SO42−, NO3− and HCO3−; EC and TDS show strong positive correlation with Na+, K+, Ca2+, Mg2+, Cl−, SO42−and NO3− in the dry season. Most of the ionic constituents are released into the solution phase during the process of weathering and may be responsible in the chemical break-down of mineral such as feldspars, pyroxenes and amphiboles that are present in the basement rocks under the existing pH condition, and therefore ion-exchange may be take place.
It was observed that NO3− showed strong positive correlation with all the major ionic constituents during wet and dry seasons except HCO3−. Thus, it suggests there are anthropogenic contributions that may arise from agricultural practices (fertilizer and pesticide application), improper disposal of refuse and even indiscriminate open defecation dominant within the study area. These may impact on the chemistry the groundwater over time.
Groundwater suitability for agriculture
According to Alam (2014), hydrochemical changes may be introduced through the dissolution of mineral constituents of a particular salt which are capable of causing an adverse impact on the plant growth. One of such that impairs groundwater quality for irrigation and agricultural purposes is sodium, and it can be measured in-terms of salinity hazard and sodium hazard (Alagbe 2006, Al-Shaibani 2008 and Edet 2016). Irrigation water quality indices computed for the study during the wet and dry seasons are presented (Tables 6), while a summary of the results were further presented (Table 7).
Table 6
Computed groundwater indices for agriculture use
Wet season | Dry season |
Sample ID | TH | %Na | SAR | MH | RSC | PI | Sample ID | TH | %Na | SAR | MH | RSC | PI |
KW01 | 113.44 | 50.82 | 2.08 | 43.54 | -0.17 | 57.05 | KD01 | 4.11 | 36.81 | 0.79 | 30.00 | -1.33 | 43.23 |
KW02 | 361.93 | 18.06 | 0.68 | 47.88 | 2.41 | 34.56 | KD02 | 18.05 | 40.52 | 2.10 | 55.83 | -5.31 | 40.38 |
KW03 | 47.25 | 43.71 | 0.99 | 23.85 | -0.49 | 47.61 | KD03 | 2.39 | 52.65 | 1.26 | 43.08 | -0.72 | 62.32 |
KW04 | 73.63 | 51.92 | 1.75 | 47.31 | 2.87 | 108.24 | KD04 | 5.06 | 53.86 | 1.94 | 42.14 | -1.56 | 57.83 |
KW05 | 182.16 | 25.35 | 0.77 | 50.76 | 0.19 | 29.98 | KD05 | 6.87 | 35.21 | 0.92 | 63.07 | -1.94 | 35.82 |
KW06 | 104.30 | 25.42 | 0.62 | 37.54 | -0.49 | 29.21 | KD06 | 35.40 | 26.40 | 1.37 | 44.28 | -11.00 | 24.01 |
KW07 | 448.00 | 29.34 | 1.10 | 47.20 | -0.46 | 22.50 | KD07 | 1.37 | 37.02 | 0.48 | 28.90 | -0.41 | 65.52 |
KW08 | 75.16 | 28.49 | 0.61 | 22.05 | 1.13 | 95.04 | KD08 | 5.65 | 34.25 | 0.95 | 19.59 | -1.89 | 43.51 |
KW09 | 103.16 | 27.16 | 0.70 | 25.99 | -0.98 | 30.06 | KD09 | 23.95 | 22.87 | 0.94 | 50.71 | -7.20 | 21.87 |
KW10 | 396.88 | 28.36 | 1.49 | 49.12 | -0.04 | 30.11 | KD10 | 4.52 | 42.91 | 1.23 | 18.17 | -1.60 | 45.87 |
KW11 | 90.36 | 40.37 | 1.16 | 20.62 | -1.05 | 42.26 | KD11 | 10.41 | 37.07 | 1.28 | 62.83 | -2.94 | 38.35 |
KW12 | 200.89 | 23.53 | 0.71 | 56.00 | 3.10 | 52.23 | KD12 | 2.91 | 44.26 | 1.01 | 34.31 | -0.94 | 50.00 |
KW13 | 93.40 | 69.90 | 4.40 | 13.96 | -0.08 | 87.84 | KD13 | 2.32 | 39.58 | 0.64 | 34.21 | -0.73 | 47.75 |
KW14 | 123.72 | 60.89 | 3.37 | 13.66 | -1.77 | 63.04 | KD14 | 1.64 | 57.27 | 1.28 | 36.80 | -0.48 | 74.46 |
KW15 | 58.19 | 39.86 | 0.93 | 17.81 | -0.73 | 45.82 | KD15 | 1.84 | 43.00 | 0.80 | 18.66 | -0.63 | 57.00 |
KW16 | 214.50 | 27.36 | 1.02 | 26.77 | 0.63 | 53.77 | KD16 | 2.91 | 45.57 | 1.02 | 42.94 | -0.87 | 55.79 |
KW17 | 116.17 | 34.69 | 1.00 | 28.29 | 1.94 | 82.19 | KD17 | 1.81 | 49.94 | 0.37 | 54.87 | -0.49 | 56.32 |
KW18 | 71.74 | 41.15 | 1.07 | 37.78 | -0.33 | 44.46 | KD18 | 4.90 | 29.67 | 0.65 | 24.32 | -1.66 | 34.11 |
KW19 | 80.83 | 28.62 | 0.42 | 20.30 | -0.24 | 61.47 | KD19 | 4.30 | 21.33 | 0.35 | 20.62 | -1.49 | 26.74 |
KW20 | 215.19 | 18.38 | 0.58 | 14.26 | -1.77 | 38.71 | KD20 | 4.96 | 30.88 | 0.69 | 37.72 | -1.53 | 39.41 |
KW21 | 509.69 | 12.82 | 0.58 | 10.27 | -7.61 | 17.47 | KD21 | 5.48 | 28.72 | 0.65 | 37.78 | -1.73 | 33.13 |
KW22 | 127.39 | 26.55 | 0.70 | 37.87 | 0.00 | 47.27 | KD22 | 9.15 | 32.96 | 1.05 | 43.34 | -2.85 | 33.58 |
KW23 | 156.68 | 28.73 | 0.89 | 29.38 | -0.31 | 49.64 | KD23 | 1.64 | 44.32 | 0.69 | 54.56 | -0.47 | 52.52 |
KW24 | 107.43 | 22.81 | 0.47 | 30.51 | -0.05 | 52.16 | KD24 | 3.82 | 12.91 | 0.17 | 8.04 | -1.42 | 20.02 |
KW25 | 182.21 | 16.54 | 0.47 | 25.30 | -0.20 | 44.37 | KD25 | 4.24 | 19.91 | 0.32 | 24.88 | -1.45 | 22.63 |
KW26 | 292.17 | 17.06 | 0.57 | 22.97 | -2.24 | 28.38 | KD26 | 2.14 | 45.67 | 0.81 | 63.93 | -0.58 | 57.30 |
KW27 | 126.29 | 25.92 | 0.69 | 25.89 | -0.82 | 42.51 | KD27 | 2.63 | 39.03 | 0.67 | 48.12 | -0.79 | 43.88 |
KW28 | 65.50 | 29.76 | 0.54 | 32.28 | 0.52 | 81.75 | KD28 | 14.19 | 31.66 | 1.37 | 32.60 | -4.63 | 34.66 |
KW29 | 578.84 | 30.17 | 1.03 | 30.56 | -2.08 | 28.69 | KD29 | 2.32 | 44.63 | 0.84 | 37.85 | -0.73 | 50.50 |
KW30 | 93.60 | 28.27 | 0.66 | 18.54 | -1.17 | 28.22 | KD30 | 30.40 | 50.09 | 4.13 | 43.82 | -9.43 | 50.03 |
KW31 | 423.56 | 53.09 | 3.85 | 25.90 | -1.98 | 57.16 | KD31 | 7.78 | 30.54 | 0.96 | 23.83 | -2.66 | 34.57 |
KW32 | 147.00 | 33.29 | 1.13 | 30.02 | -1.11 | 37.61 | - | - | - | - | - | - | - |
Table 7
Irrigation water quality classes for groundwater in the study area
Indices | Units | Class range | Classification | No. of samples | Percentage, % |
Wet | Dry | Wet | Dry |
Electrical Conductivity, E.C. | µS/cm | < 250 | Excellent | 16 | 3 | 50 | 10 |
250 − 750 | Good | 11 | 18 | 34 | 58 |
750–2000 | Permissible | 5 | 8 | 16 | 26 |
2000–3000 | Doubtful | - | 2 | - | 6 |
> 3000 | Unsuitable | - | - | - | - |
Total Hardness, TH | meq/l | < 75 | Soft | 32 | 31 | 100 | 100 |
75–150 | Moderately hard | - | - | - | - |
150–300 | Hard | - | - | - | - |
> 300 | Very Hard | - | - | - | - |
Sodium Absorption Ratio, SAR | - | < 10 | Excellent | 32 | 31 | 100 | 100 |
10–18 | Good | - | - | - | - |
18–26 | Doubtful | - | - | - | - |
> 300 | Unsuitable | - | - | - | - |
Percent Sodium, %Na | % | < 20 | Excellent | 5 | 2 | 16 | 6 |
20–40 | Good | 19 | 16 | 59 | 52 |
40–60 | Permissible | 6 | 13 | 19 | 42 |
60–80 | Doubtful | 2 | - | 6 | - |
> 80 | Unsuitable | - | - | - | - |
Magnesium Hazard, MH | % | < 50 | Suitable | 30 | 24 | 94 | 77 |
> 50 | Unsuitable | 2 | 7 | 6 | 23 |
Residual Sodium Carbonate, RSC | meq/l | < 1.25 | Good | 28 | 31 | 88 | 100 |
1.25–2.50 | Doubtful | 2 | - | 6 | - |
> 2.50 | Unsuitable | 2 | - | 6 | - |
Permeability Index, PI | % | > 75 | Suitable | 5 | - | 16 | - |
75 − 25 | Moderate | 25 | 27 | 78 | 87 |
< 25 | Not Suitable | 2 | 4 | 6 | 13 |
Electrical Conductivity (EC)
EC is a method of determining the salt content of irrigation water. The higher the EC, the greater is its salt content. The wet season data computed for EC showed the following classification; excellent (50%), good (34%), permissible (16%), while in the dry season they were; excellent (10%), good (58%), permissible (26%) and doubtful (6%) for agriculture (Table 7). Therefore on the basis of EC obtained the study area, the groundwater are largely suitable for irrigation, except few locations in the dry season where it is doubtful.
Total hardness (TH):
Depending on the concentration of Ca2+ against Mg2+, TH was computed to determine the salinity level of the groundwater in the study area. High concentration of Ca2+ against Mg2+ causes water hardness which affects the water quality to crops (Bucks et al. 2009). The obtained values for the wet season ranged from 47.25 to 578.84 meq/l with mean of 186.91 meq/l, while they are ranged from 1.37 to 35.40 meq.l with a mean of 7.39 meq/l in the dry season (Table 6). The values obtained for TH during the wet and dry season revealed that 100% of groundwater samples analyzed are classified as ‘soft water’, since its hardness is < 75 meq/l (Table 7). Hence groundwater within the study area during wet and dry season in terms of TH is suitable for domestic and industrial purposes, in agreement with Gopinath et al. (2015).
Percent sodium (%Na):
Sodium through ion-exchange process replaces calcium in the soil, thus destroying the soil structure and thereby reducing its permeability (Subba-Rao 2006). This may affects the soil drainage and consequently may lead to low yield and reduction of plant growth. Values of %Na obtained revealed that groundwater within Keffi and its environs were found to be suitable for irrigation purposes except at two locations; KW13 (69.90%) and KW14 (60.89%) during the wet season (Table 6). Wet season data computed for %Na showed the following classes; excellent (16%), good (59%), permissible (19%) and doubtful (6%). The dry season %Na data computed showed that groundwater samples were classified as follows; excellent (6%), good (52%) and permissible (42%) for irrigation and agriculture in general (Table 7).
A plot of %Na against EC (Fig. 3) reveals that majority of the groundwater samples are ‘very good to good’ for agricultural purposes. This accounts for 91 and 71% of the analyzed samples during the wet and dry seasons respectively. About 9% and 23% of the wet and dry season samples respectively were ‘good to permissible’ water class for irrigation. Groundwater in the dry season was ‘doubtful to unsuitable’ for irrigation purposes in only about 6% of samples. There is similarity in the trend observed for both seasons, and it may be attributed to geological factors, soil types, sample size, anthropogenic activities and climatic factors, to mention but a few.
Sodium Absorption Ratio (SAR):
SAR is directly related to the absorption of sodium by soils, and is used to assess the groundwater suitability for irrigation. Seasonal SAR values estimated showed that wet season ranged from 0.42 to 4.40 meq/l with mean of 1.16 meq/l, while they are ranged from 0.17 to 4.13 meq.l with a mean of 1.02 meq/l in the dry season (Table 6). During the wet and dry season, 100% of the groundwater samples analyzed were classified as ‘excellent water’ respectively, suitable for agricultural use because all the values for SAR < 10 (Table 7).
A plot of SAR against EC (salinity hazard) during both seasons, indicates that groundwater from the study area were ‘low sodium hazard’ type except for one sample in the dry season sample that is ‘medium sodium hazard’ type (Fig. 4). The wet season groundwater samples were classified for suitability in agriculture as thus; C1S1 indicative of low salinity hazard - low sodium hazard (47%), C2S1 interpreted as medium salinity hazard - low sodium hazard (38%) and C3S1 representing high salinity hazard – low sodium hazard (15%). However in the dry season, they are classified as; C2S1 indicating medium salinity hazard - low sodium hazard (58%), C3S1 is interpreted to have high salinity hazard - low sodium hazard (29%), C1S1 indicates low salinity hazard - low sodium hazard (10%) and C4S2 is interpreted as very high salinity hazard - medium sodium hazard (3%). Therefore, the study has revealed that groundwater within Keffi and its environs in-terms of suitability for agricultural use are classified as moderate to good (Table 8).
Table 8
A summary of groundwater suitability for agricultural use
Class | Number | Percent (%) | Water quality |
---|
Wet | Dry | Wet | Dry |
---|
C1S1 | 15 | 3 | 48.39 | 9.38 | Good |
C1S2 | - | - | - | - | Moderate |
C1S3 | - | - | - | - | Poor |
C1S4 | - | - | - | - | Very poor |
C2S1 | 12 | 18 | 38.71 | 56.25 | Good |
C2S2 | - | - | - | - | Moderate |
C2S3 | - | - | - | - | Poor |
C2S4 | - | - | - | - | Very poor |
C3S1 | 5 | 9 | 16.13 | 28.13 | Good |
C3S2 | - | - | - | - | Moderate |
C3S3 | - | - | - | - | Poor |
C3S4 | - | - | - | - | Very poor |
C4S1 | - | - | - | - | Good |
C4S2 | - | 1 | - | 3.13 | Moderate |
C4S3 | - | - | - | - | Poor |
C4S4 | - | - | - | - | Very poor |
Magnesium Hazard (MH):
MH is the measure of how much alkaline the groundwater contains. Also, it creates a more alkaline soil during equilibrium reactions thereby reducing the soil quality and crop yield (Paliwal 1972 and Haritash et al. 2014). Groundwater with MH < 50% have no adverse effect on crop yield and if MH > 50%, the water is unsuitable for agricultural purpose. From the study, wet season groundwater samples reveal that 94% are suitable, while only 6% were unsuitable for irrigation and other agricultural uses. Further, the dry season samples have revealed that 77% are suitable, while 23% of the groundwater samples were classified as unsuitable for irrigation within the study area. Furthermore, seasonal SAR values estimated showed that wet season ranged from 10.27 to 56.00 meq/l with mean of 30.13 meq/l, while they are ranged from 8.04 to 63.93 meq.l with a mean of 38.12 meq/l in the dry season (Table 6).
Residual Sodium Carbonate (RSC):
RSC assesses when groundwater it is imparted by excess concentration of HCO3− + CO32− over Ca2+ and Mg2+. This is because Ca2+ and Mg2+ may precipitate as water in the soil becomes more concentrated with these ions. Thus is precipitates calcite from solution in the soil, and thereby increasing sodium in solution resulting in soil dispersion. This is unsuitable for irrigation and other agricultural purposes (Emerson and Bakker 1973). Bi-carbonate hazard in the water samples were investigated in-terms of the RSC (Tables 6 and 7), and wet season samples were classified for irrigation and other agricultural purposes thus; ‘good’ (88%), ‘doubtful’ (6%) and ‘unsuitable’ (6%). However during the dry season, 100% of the groundwater samples classified as ‘good’ on the basis of RSC for irrigation and agricultural purposes. Seasonal RSC values estimated showed that wet season ranged from − 7.61 to 3.10 meq/l with mean of -0.42 meq/l, while they are ranged from − 11.00 to -0.41 meq.l with a mean of -2.31 meq/l in the dry season (Table 6). Therefore, groundwater from Keffi and its environs based on the RSC are suitable for irrigation and other agricultural purposes during the wet and dry season.
Permeability Index (PI):
Soil permeability may be affected by pro-long use of irrigation water as it is influenced by Na+, Ca2+, Mg2+, and HCO3− contents of the soil (Doneen 1964), The concentration of ions like Na+ may become high in groundwater, such that it begins to exchange for Ca2+ and Mg2+. This process tends to adversely affect the permeability of soils after long-term irrigation practice. According to Saleh et al. (1999), it results in poor drainage of soils, including insufficient air and water circulation. Seasonal values showed that wet season ranged from 17.47 to 108.24 meq/l with mean of 49.11 meq/l, while they are ranged from 20.02 to 74.46 meq.l with a mean of 43.65 meq/l in the dry season (Table 6). Based on the values of PI computed from the groundwater samples, the wet season data were classified as; ‘suitable’ (16%), ‘moderate’ (78%), ‘not suitable’ (6%), while in the dry season they were classified as; ‘moderate’ (87%) and ‘not suitable’ (13%) for agricultural purposes. The slight increase during the dry season may be attributed to increase in the concentration of Na+ in groundwater that is readily available during ion-exchange processes with the Ca2+ and Mg2+ present.