The static water level varies from 0 m to 44.5 m in the dry season and from 0 m to 32.3 m in the wet season (Table 3). These values are within the range of those recorded by Edet (2014), which varied from less than 4 m to 70 m. Though not all the wells were monitored in both seasons, the higher level in the wet season is an indication of higher recharge from precipitation. Water table contours were closer packed in some areas than others and did not show any definite flow pattern (Fig. 2). This is an indication of the heterogeneous nature of the aquifer system. This may arise majorly from the presence of aquitard systems, as their presence commonly increases the complexity of flow paths and they are capable of deflecting flows and controlling boundaries between flow systems at local, intermediate, and regional scales (Cherry et al., 2006).
Table 3
Fluctuation in static water level between dry and wet seasons
Location | Static Water Level with respect to Ground Surface (m) |
Dry Season | Wet Season | Change in Static Water Level |
MW1 | 12.80 | 12.68 | 0.12 |
MW2 | 15.85 | 15.80 | 0.05 |
MW3 | 11.50 | 11.22 | 0.28 |
MW4 | - | 3.78 | - |
MW4A | 10.96 | 10.65 | 0.31 |
MW4B | - | 6.50 | - |
MW5 | 0 | 0 | 0 |
MW6 | - | 3.73 | - |
MW6A | - | 3.20 | - |
MW6B | 3.50 | 3.20 | 0.30 |
MW7 | 44.50 | - | - |
MW8 | 25.30 | - | - |
MW9 | 25.85 | 25.80 | 0.05 |
MW10 | 23.2 | 22.76 | 0.44 |
MW11 | 15.60 | 15.25 | 0.35 |
MW12 | 32.50 | 32.30 | 0.20 |
MW12B | - | 28.41 | - |
MW13 | - | 18.60 | - |
Average | 20.142 | 14.258 | |
The results of the bacteriological analysis of the water samples are presented in Table 4. The total bacterial counts for all samples were quite high in groundwater, ranging from 70 Cfu/100 ml in location 14BH to 63000 Cfu/100 ml in location 20BH and from 1500 Cfu/100 ml in location 25BH to 21000 Cfu/100 ml in location 22BH in the dry and wet seasons, respectively.
Table 4
Results of microbial analysis of water sample
Sample ID | Total bacterial count (cfu/100ml) | Total Coliform bacterial count (cfu/100ml) | Total Salmonella /shigella count (cfu/100ml) | Total feacal coliform count (cfu/100ml) | Total Vibrio cholera count (cfu/100ml) | Total Escherichia coli count (cfu/100ml) | Temp. oC | pH | TDS mg/l |
Groundwater dry |
3BH | 300 | 0 | 50 | 0 | 0 | 0 | 26.35 | 4.05 | 57.0 |
4BH | 260 | 30 | 0 | 0 | 0 | 0 | 26.45 | 3.75 | 69.5 |
5BH | 550 | 100 | 100 | 100 | 0 | 0 | 26.45 | 3.65 | 64.5 |
6BH | 410 | 0 | 0 | 260 | 0 | 0 | 26.4 | 4.65 | 55.5 |
7BH | 250 | 100 | 0 | 120 | 0 | 0 | 26.4 | 4.0 | 36.5 |
8BH | 100 | 0 | 0 | 0 | 0 | 0 | 26.45 | 4.85 | 41.0 |
9BH | 110 | 0 | 0 | 50 | 0 | 0 | 26.5 | 5.10 | 78.5 |
11BH | 300 | 0 | 0 | 0 | 0 | 0 | 26.4 | 3.35 | 40.0 |
12BH | 710 | 0 | 0 | 0 | 0 | 0 | 26.4 | 4.05 | 31.5 |
14BH | 70 | 0 | 0 | 0 | 0 | 0 | 26.55 | 4.55 | 19.5 |
15BH | 500 | 100 | 0 | 0 | 0 | 0 | 27.75 | 5.05 | 46.0 |
19BH | 1100 | 60 | 350 | 80 | * | 0 | 27.15 | 5.07 | 56.0 |
20BH | 63000 | 600 | 220 | 80 | * | 0 | 26.85 | 4.9 | 43.0 |
Mean | 5204.62 | 76.15 | 55.38 | 53.08 | 0 | 0 | 26.62 | 4.39 | 49.68 |
Surface water dry |
1SW | 700 | 210 | 0 | 50 | 0 | 0 | 26.52 | 5.35 | 31.5 |
2SW | 340 | 120 | 100 | 0 | 0 | 0 | 26.51 | 5.45 | 76.0 |
10SW | 250 | 0 | 100 | 0 | 0 | 10 | 26.35 | 3.55 | 20.5 |
18SW | 370 | 80 | 50 | 0 | * | 0 | 27.05 | 5.31 | 7.0 |
Mean | 415 | 102.5 | 62.5 | 12.5 | 0 | 2.5 | 26.61 | 4.92 | 33.75 |
Groundwater wet |
3BH | 17000 | 560 | 2400 | 10 | 70 | 0 | 27.05 | 4.05 | 68.0 |
5BH | 8400 | 210 | 150 | 0 | 0 | 0 | 26.35 | 4.7 | 70.15 |
6BH | 5400 | 240 | 50 | 12 | 0 | 60 | 27.10 | 4.5 | 42.0 |
7BH | 7000 | 160 | 80 | 20 | 100 | 30 | 27.02 | 5.15 | 38.5 |
8BH | 7900 | 800 | 120 | 0 | 400 | 0 | 26.21 | 4.7 | 28.0 |
9BH | 16000 | 180 | 2000 | 340 | 700 | 300 | 27.0 | 5.5 | 10.0 |
11BH | 20000 | 420 | 1700 | 0 | 0 | 0 | 26.1 | 3.85 | 68.5 |
12BH | 10000 | 720 | 5000 | 0 | 5000 | 0 | 27.03 | 5.05 | 41.05 |
14BH | 9200 | 110 | 300 | 0 | 0 | 0 | 26.15 | 5.25 | 60.5 |
15BH | 11000 | 2200 | 1200 | 20 | 0 | 50 | 26.15 | 5.3 | 93.05 |
21BH | 14000 | 550 | 1500 | 30 | 70 | 60 | 27.4 | 4.7 | 30.0 |
22BH | 21000 | 1100 | 1400 | 10 | 300 | 21 | 26.65 | 5.55 | 28.0 |
23BH | 6000 | 140 | 0 | 0 | 280 | 0 | 27.2 | 5.02 | 45.5 |
24BH | 7300 | 80 | 290 | 0 | 0 | 0 | 27.2 | 5.05 | 45.5 |
25BH | 1500 | 0 | 11 | 0 | 0 | 0 | 28.2 | 6.1 | 10 |
26BH | 4000 | 10 | 10 | 0 | 0 | 0 | 27.14 | 6.25 | 30.5 |
Mean | 10356.25 | 467.5 | 1013.19 | 27.63 | 432.5 | 32.56 | 26.8 | 5.05 | 44.33 |
Surface water wet |
1SW | 25000 | 510 | 130 | 10 | 40 | 30 | 27.05 | 6.75 | 30.0 |
2SW | 2000 | 600 | 280 | 0 | 400 | 0 | 26.07 | 6.55 | 40.5 |
10SW | 10000 | 900 | 1600 | 0 | 100 | 0 | 26.3 | 4.95 | 28.5 |
Mean | 12333.33 | 670 | 670 | 3.33 | 180 | 10 | 26.47 | 6.083 | 33 |
SON | | 10 | 0 | 0 | 0 | 0 | | | |
EPA | | 100 | 0 | 0 | 0 | 0 | | | |
The total coliform bacterial count ranged from 0 Cfu/100ml in locations (3BH, 6BH, 8BH, 9BH, 11BH, 12BH, and 14BH) to 600 Cfu/100ml in location 20BH and from 0 Cfu/100ml in location 25BH to 2200 in location 15BH during the dry and wet seasons, respectively. The total salmonella/shigella count in the dry season ranged from 0 Cfu/100ml in locations (4BH, 6BH, 8BH, 9BH, 11BH, 12BH, 14BH, and 15BH) to 350 Cfu/100ml at location 19BH and from 0 Cfu/100ml at location 23BH to 5000 Cfu/100ml at location 12BH in the wet season. The total fecal coliform count ranged from 0 Cfu/100ml in locations (3BH, 4BH, 11BH, 12BH, 14BH, and 15BH) to 260 Cfu/100ml at location 6BH in the dry season and from 0 Cfu/100ml in locations (5BH, 8BH, 11BH, 12BH, 14BH, 23BH, 24BH, 25BH, and 26BH) to 340Cfu/100ml at location 9BH in the wet season. The total vibrio cholera was not recorded in the dry season samples but ranged from 0 Cfu/100ml in locations (5BH, 6BH, 11BH, 14BH, 15BH, 24BH, 25BH, and 26BH) to 500 Cfu/100ml in location 12BH in the wet season. Also, the total Escherichia coli (E. coli) was not recorded in the dry season groundwater samples but ranged from 0Cfu/100ml in locations (3BH, 5BH, 8BH, 11BH, 12BH, 14BH, 23BH, 24BH, 25BH, and 26BH) to 300Cfu/100ml at location 9BH in the wet season.
The total bacteria count in the surface water ranged from 340 CFU/100ml at location 2SW to 700 CFU/100ml at location 1SW in the dry season and from 2000 CFU/100ml at location 2SW to 25000 CFU/100ml at location 1SW in the wet season. The total coliform bacterial count ranged from 0 Cfu/100ml at location 10 SW to 210 Cfu/100ml at location 2SW in the dry season and from 510 Cfu/100ml at location 1SW to 900 Cfu/100ml at location 10SW in the wet season. The total salmonella/shigella count ranged from 0 Cfu/100ml at location 1SW to 100Cfu/100ml at locations (2SW & 10SW) in the dry season and from 130Cfu/100ml at location 1SW to 1600Cfu/100ml at location 10SW in the wet season. The total fecal coliform count ranged from 0 Cfu/100ml at locations (2SW & 10SW) to 50 Cfu/100ml at location 1SW in the dry season and from 0 Cfu/100ml at locations (2SW & 10SW) in the wet season. While the total vibrio cholera was not recorded in the dry season samples, it ranged from 40 Cfu/100ml at location 1SW to 400 Cfu/100ml at location 2SW. And the total E. coli count of 10Cfu/100ml was recorded only at location 10SW in the dry season and ranged from 0 Cfu/100ml at locations (10SW & 2SW) to 30 Cfu/100ml at location 1SW in the wet season.
The isolation of some bacteria pathogens capable of causing waterborne diseases such as salmonella typhi (typhoid fever), salmonella paratyphi (paratyphoid), shigella spp. (bacillary dysentery), E. coli, and vibrio cholera (cholera) is an indication of recent contamination by human and animal feces (Mohan, 2010; EPA, 2002). The results generally show that a strong relationship exists between microbial concentrations in groundwater and rainfall. A higher concentration was recorded in the wet season compared to the dry season samples in both control points and around the dumpsite (Figs. 3 and 4), suggesting that runoff is a significant factor in the temporal distribution of the bacteria in the area, as some indicator organisms are associated with particles transported by runoff (George et al., 2004). However, the concentration of the microbial indicators was higher around the dumpsite compared to the control points, indicating that the dumpsite leachate contributes to the concentration of the indicator organisms in the area.
A comparison between the concentration of the indicator organisms in the different boreholes and their distance from the center of the dumpsite and static water level was made. The results did not show any definite pattern, but rather wells located downstream of the dump (20BH, 19BH, and 7BH) had higher diversity and microbial concentration compared to those closer but upstream (4BH and 3BH). Three locations with higher microbial concentration but further away from the dumpsite and upstream were boreholes with poorly protected well heads (15BH, 9BH, and 5BH) (Fig. 5). The same pattern was observed in the wet season samples (Fig. 6). This pattern suggests that the most important factors affecting well vulnerability to microbial contamination were those relating to the location of the wells relative to groundwater flow with respect to the dumpsite, activities around the wells, and well head protection. These factors show greater influence compared to the well's distance from the dumpsite.