# Assessment of the Nutrients in the Leachate and the Groundwater Quality for Drinking and Farming around the Nkolfoulou Landfill in Yaoundé, Cameroon

Authors: Gilbert Feuyit; John Ngolui Lambi; Estella Njoyim-Tamungang; Samuel Laminsi
Journal: Journal of Chemistry
 (2019)

---

## Abstract

This study focuses on the assessment of the nutrients in the leachate and the groundwater quality around the Nkolfoulou landfill in Yaoundé known in French as “Centre de Traitement de Déchets (CTD).” Landfilling generates leachate that can pollute groundwater. Leachate along with groundwater samples (n=1+13) was collected in January (long dry season) and May (long wet season) 2014 and explored for various parameters including pH, temperature, EC, turbidity, TDS, TA, TSS, TH, BOD5, COD, Na+, K+, Mg2+, Ca2+, NH4+, NO3−, Cl−, F−, SO42−, PO43−, HCO3−, and colour using standard methods. In the leachate samples, values of TSS (700.2 and 130.2 mg/L), BOD5 (140 mg/L), COD (1350 and 1750 mg/L), NH4+ (82.50 and 39.51 mg/L), NO3− (159.32 and 74.82 mg/L), and Cl− (702.69 and 345.50 mg/L) exceeded the Cameroonian standards for effluent discharge. All the values of pH and some values of turbidity (4.55 and 4.50 NTU) and NH4+ (0.51 and 0.73 mg/L) in the groundwater samples violated the Cameroonian standards for drinking water. Based on the water quality index (WQI), an average of 11.53% of groundwater samples was improper for drinking in both seasons. Based on the parameters assessed, all the samples complied with the standard set for irrigation, poultry, and livestock. The hazard quotient (HQ) and the hazard index (HI) of NO3− and F− for children and adults were <1, and hence, the increased non-cancer risks due to these ions through the drinking of groundwater was low. From the statistical analysis, the Nkolfoulou landfill may not be the main source of major ions to the nearby groundwater.


---

## Body

## 1. Introduction

Groundwater is important in potable water supply, livestock, and crops production. Many people in Africa rely on groundwater for drinking [1]. But waste disposal negatively impacts the quality of groundwater [2]. Solid wastes are prevalently managed by landfilling [3] because it is the simplest and the cheapest technique of waste management [4]. Landfilling generates leachate which is heavily loaded with nutrients such as Na+, K+, Mg2+, Ca2+, NH4+, NO3−, F−, Cl−, SO42−, PO43−, and HCO3− [5–9]. Many scientific reports emphasize that groundwater close to a landfill is often polluted via leachate [10–13]. Nutrients at an elevated concentration in water render it unsuitable for human and animal health and for farming. For example, high levels of Ca2+ and Mg2+ in water are responsible for its hardness. Hard water requires more soap for cleansing and can form scale deposits on domestic appliances, while drinking water containing excessive levels of SO42− could result in a purgative effect [14]. Ingestion of nitrate and fluoride beyond the threshold level can cause, respectively, blue-baby syndrome in bottle-fed infants [14, 15] and skeletal fluorosis in human beings in general [14, 16–18].In Yaoundé, the capital city of Cameroon, municipal solid wastes have been landfilled in Nkolfoulou since 1989. The Nkolfoulou landfill which was then in a bush far away from the city is now surrounded by habitations. The landfill generates an average of 450 m3/day of leachate, out of which only 54 m3 is collected [19]. The uncollected leachate can percolate the soil to pollute nearby groundwater sources. The study area is partly covered by a water distribution network. Besides, the increasing need for water has resulted in frequent pipe-borne water shortage, thus, putting a stress on the population. To tackle this issue more efficiently, many people around the Nkolfoulou landfill have resorted to digging wells or boreholes in their premises. The water abstracted from these wells and boreholes is quite clean and odourless, allowing the people to use it for different purposes without any prior treatment. This practice is unacceptable since water that appears clean may contain harmful microbes and chemicals [17]. Relevant information on the nutrient status of groundwater in the vicinity of landfills in Cameroon is lacking. This is why the present study is aimed at assessing the nutrients in the leachate and the groundwater quality around the Nkolfoulou landfill.


## 2. Materials and Methods

### 2.1. Study Site Description

Yaoundé, the capital city of Cameroon, locally called “Ngola,” sprawls over 304 km2. It is ranked as the second most populated town in Cameroon with about 2.5 million inhabitants. It is located at an altitude of about 750 m and lies between longitudes 11°20′and11°40′E and between latitudes 3°45′and4°00′N. It has an annual mean rainfall of 1520 ± 268 mm and a mean temperature of 24.4 ± 0.5°C from 1984 to 2008 [20]. Yaoundé has a tropical climate consisting of two rainy seasons (March–June and September–November) and two dry seasons (December–February and July-August). The bed rock of the study area comprises migmatites, migmatitic gneisses, banded gneisses, and mica schists [21].Figure1 displays the map of the study area which consists of the neighborhoods of the Nkolfoulou landfill. The Nkolfoulou landfill is situated at 16 km from Yaoundé centre and is surrounded by Nkolfoulou I and II and Nsan villages. It covers a total land area of about 45 ha [22]. The site specification of groundwater samples in the study area is displayed in Table 1.Figure 1
Map of the study area showing the sampling sites.Table 1
Site specification of groundwater samples.
Sample code
TW
GPS coordinates
Depth (m)
DLE (m)
Longitude
Latitude
GW
1
HDW
11
°
34
′
07.6
″
03
°
55
′
28.3
″
18
111.4
GW
2
DW
11
°
34
′
18.0
″
03
°
55
′
22.4
″
80
329.4
GW
3
HDW
11
°
34
′
24.3
″
03
°
55
′
26.0
″
27
132.5
GW
4
HDW
11
°
34
′
29.1
″
03
°
55
′
27.4
″
20
192.9
GW
5
HDW
11
°
34
′
28.4
″
03
°
55
′
30.6
″
26
154.0
GW
6
HDW
11
°
34
′
35.8
″
03
°
55
′
30.0
″
25
381.7
GW
7
HDW
11
°
34
′
49.4
″
03
°
55
′
25.9
″
21
810.3
GW
8
DW
11
°
34
′
42.8
″
03
°
55
′
47.0
″
87
618.6
GW
9
HDW
11
°
34
′
28.8
″
03
°
55
′
59.0
″
23
331.8
GW
10
HDW
11
°
34
′
23.0
″
03
°
55
′
59.5
″
15
196.4
GW
11
HDW
11
°
34
′
2.7
″
03
°
55
′
45.4
″
8
64.0
GW
12
DW
11
°
34
′
0.3
″
03
°
55
′
49.3
″
82
178.2
GW
13
HDW
11
°
33
′
59.7
″
03
°
55
′
44.0
″
12
97.2
GW = groundwater; TW = type of well; HDW = hand-dug well; DW = drilled well; DLE = distance from the landfill edge.


### 2.2. Sampling Procedure

Thirteen (13) groundwater samples and one (01) sample of leachate not stored by the HYSACAM company were collected in 2014 in January, during the long dry season, and in May, during the long wet season. Since the landfill is equipped with leachate collectors, we were more interested in the unstored leachate that flows outside the landfill. For ion analysis, water and leachate were sampled and filtered in situ through a clean 0.45μm filter paper in 500 mL polyethylene bottles previously washed with deionized water. The samples were kept in a cooler during transportation from the field to the laboratory, stored in a refrigerator at 4°C, and analyzed within 48 hours.


### 2.3. Physicochemical Parameter Analysis

All the reagents utilized were of analytical (AnalaR) grade. Parameters such as temperature, electrical conductivity (EC), pH, and total dissolved solids (TDS) were measured in situ using a multiparameter HANNA HI 9811-5. Total suspended solids (TSS) were determined following the AFNOR method NF EN 872 [23], while total alkalinity (TA) and biocarbonate (HCO3−) were determined by titration as outlined in the AFNOR method NF EN ISO 9963-1 [24]. The turbidity was determined using a turbidity meter model ORBECO-HELIGE 966. Chemical oxygen demand (COD) was determined by digestion following the standard method 5220B [25], while biochemical oxygen demand after 5 days (BOD5) was assessed as specified by Rodier et al. [26]. The colour was determined in the laboratory by the colorimetric method using the ORCHIDIS standard colorimetric comparator réf.1pco15p220. The last three parameters were assessed only in leachate samples.The concentration of anions and cations was determined, respectively, employing models ICS1100 and ICS90 liquid-phase ion chromatographic (IC) single-column system at room temperature. All samples and eluents were filtered through a filter paper (0.45μm) before injection into the IC system. Water samples having higher electrical conductivity were diluted appropriately with distilled water before being analyzed. The chromatograph was computer monitored using a CHROMELEON CM 6.80 SR software.The anionsF−, Cl−, NO3−, PO43−, and SO42− were separated on an AS12A IonPac separating column (4 × 200 mm) with an AG12A guard column (4 × 50 mm) and detected after suppression with an ASRS300 IonPac 4 mm anion electrical self-regenerating suppressor. The anions were eluted using the eluent (2.7 mM Na2CO3 + 0.3 mM NaHCO3) at a flow rate of 1 mL/min. A sample volume of 100 μL was injected and run for 15 minutes. The cycle time was 15 minutes per analysis.The cationsNa+, NH4+, K+, Mg2+, and Ca2+ were separated on a CS12A IonPac separating column (4 × 250 mm) with a CG-12A IonPac guard column and detected after suppression with a CSRS300 IonPac 4 mm cation electrical self-regenerating suppressor. The cations were eluted with 22 mM H2SO4 as eluent at a flow rate of 1 mL/minute. The injection volume was 50 μL, while the run time was set to 15 minutes, and the cycle time was 15 minutes per analysis.The normalized inorganic charge balance (NICB) was computed to check the accuracy of the results using the following equation [13], and the calculated NICB was within ±5%:(1)NICB=∑cations−∑anions∑cations+∑anions×100.In equation (1), the concentration of cations and anions are in meq/L. The total hardness (TH) was computed using the following equation [27]:(2)TH=2.497Ca2++4.115Mg2+.In equation (2), Ca2+ and Mg2+ are in mg/L. Water quality index (WQI) was determined by using the following equation [28]:(3)WQI=∑qiwi∑wi.The quality rating scaleqi for each parameter was computed as follows:(4)qi=100×vi−vosi−vo,where Vi is the estimated concentration of the ith parameter in the analyzed water, Vo is the ideal value of this parameter in pure water (Vo  = 0, except for pH = 7.0), and Si is the maximum limit of the ith parameter. The unit weight, Wi, for each parameter is computed as follows:(5)wi=ksi,where k = constant of proportionality and can be computed as(6)k=1∑1/Si.The increased non-carcinogenic risks due to nitrate and fluorite were evaluated by calculating the hazard quotient (HQ) and the resulting hazard index (HI). HQ was computed from equation (7), while ADD was computed using equation (8) [29]:(7)HQ=ADDRfD,where ADD represents the mean daily dose of a pollutant ingested from drinking water (mg/kg/day) and RfD is the reference dose for non-carcinogenic risk. The RfD for nitrate is 1.6 mg/kg/day while that for fluorite is 0.06 mg/kg/day. AAD is computed using the following equation:(8)ADD=C×IR×EF×EDBW×AT,where C represents the concentration of a particular pollutant in groundwater (mg/L), IR is the water ingestion rate (L/day), BW is the body weight (kg), EF is the exposure frequency (days/year) (EF = 365 days per year), ED is the exposure duration (year) (ED = 70 years), and AT is the average exposure time (days) (AT = 70×365 days)). Thus, from equation (8),(9)EF×EDAT=1,and equation (8) becomes(10)ADD=C×IRBW.In this study, the IR for adults and children is 2 and 1 L/day, respectively, whereas the BW for adults and children is 60 and 18 kg.The resulting hazard index (HI) due to exposure to many non-carcinogenic substances was calculated from the following equation [29, 30]:(11)HI=∑i=1nHQi,where i…n are the non-carcinogenic substances and HQi is the hazard quotient for the ith substance.Sodium adsorption ratio (SAR) was computed using the following equation withNa+ and Mg2+ in meq/L:(12)SAR=Na+Na++Mg2+/2.The Stiff and Piper plots were generated using DIAGRAMME 5.1 software. The geographical coordinates of the selected sampling points were recorded using a Geographical Positioning System (GPS) Magellan Triton-300. These coordinates were loaded in ArcGIS 10 software in order to draw the map of the study area and to evaluate the distances between the border of the landfill and the monitoring sites.


### 2.4. Data Analysis

Statistical processing of the data fort-test and correlation matrix was carried out using the Statistical Package for Social Sciences (SPSS) 23.0.


## 2.1. Study Site Description

Yaoundé, the capital city of Cameroon, locally called “Ngola,” sprawls over 304 km2. It is ranked as the second most populated town in Cameroon with about 2.5 million inhabitants. It is located at an altitude of about 750 m and lies between longitudes 11°20′and11°40′E and between latitudes 3°45′and4°00′N. It has an annual mean rainfall of 1520 ± 268 mm and a mean temperature of 24.4 ± 0.5°C from 1984 to 2008 [20]. Yaoundé has a tropical climate consisting of two rainy seasons (March–June and September–November) and two dry seasons (December–February and July-August). The bed rock of the study area comprises migmatites, migmatitic gneisses, banded gneisses, and mica schists [21].Figure1 displays the map of the study area which consists of the neighborhoods of the Nkolfoulou landfill. The Nkolfoulou landfill is situated at 16 km from Yaoundé centre and is surrounded by Nkolfoulou I and II and Nsan villages. It covers a total land area of about 45 ha [22]. The site specification of groundwater samples in the study area is displayed in Table 1.Figure 1
Map of the study area showing the sampling sites.Table 1
Site specification of groundwater samples.
Sample code
TW
GPS coordinates
Depth (m)
DLE (m)
Longitude
Latitude
GW
1
HDW
11
°
34
′
07.6
″
03
°
55
′
28.3
″
18
111.4
GW
2
DW
11
°
34
′
18.0
″
03
°
55
′
22.4
″
80
329.4
GW
3
HDW
11
°
34
′
24.3
″
03
°
55
′
26.0
″
27
132.5
GW
4
HDW
11
°
34
′
29.1
″
03
°
55
′
27.4
″
20
192.9
GW
5
HDW
11
°
34
′
28.4
″
03
°
55
′
30.6
″
26
154.0
GW
6
HDW
11
°
34
′
35.8
″
03
°
55
′
30.0
″
25
381.7
GW
7
HDW
11
°
34
′
49.4
″
03
°
55
′
25.9
″
21
810.3
GW
8
DW
11
°
34
′
42.8
″
03
°
55
′
47.0
″
87
618.6
GW
9
HDW
11
°
34
′
28.8
″
03
°
55
′
59.0
″
23
331.8
GW
10
HDW
11
°
34
′
23.0
″
03
°
55
′
59.5
″
15
196.4
GW
11
HDW
11
°
34
′
2.7
″
03
°
55
′
45.4
″
8
64.0
GW
12
DW
11
°
34
′
0.3
″
03
°
55
′
49.3
″
82
178.2
GW
13
HDW
11
°
33
′
59.7
″
03
°
55
′
44.0
″
12
97.2
GW = groundwater; TW = type of well; HDW = hand-dug well; DW = drilled well; DLE = distance from the landfill edge.


## 2.2. Sampling Procedure

Thirteen (13) groundwater samples and one (01) sample of leachate not stored by the HYSACAM company were collected in 2014 in January, during the long dry season, and in May, during the long wet season. Since the landfill is equipped with leachate collectors, we were more interested in the unstored leachate that flows outside the landfill. For ion analysis, water and leachate were sampled and filtered in situ through a clean 0.45μm filter paper in 500 mL polyethylene bottles previously washed with deionized water. The samples were kept in a cooler during transportation from the field to the laboratory, stored in a refrigerator at 4°C, and analyzed within 48 hours.


## 2.3. Physicochemical Parameter Analysis

All the reagents utilized were of analytical (AnalaR) grade. Parameters such as temperature, electrical conductivity (EC), pH, and total dissolved solids (TDS) were measured in situ using a multiparameter HANNA HI 9811-5. Total suspended solids (TSS) were determined following the AFNOR method NF EN 872 [23], while total alkalinity (TA) and biocarbonate (HCO3−) were determined by titration as outlined in the AFNOR method NF EN ISO 9963-1 [24]. The turbidity was determined using a turbidity meter model ORBECO-HELIGE 966. Chemical oxygen demand (COD) was determined by digestion following the standard method 5220B [25], while biochemical oxygen demand after 5 days (BOD5) was assessed as specified by Rodier et al. [26]. The colour was determined in the laboratory by the colorimetric method using the ORCHIDIS standard colorimetric comparator réf.1pco15p220. The last three parameters were assessed only in leachate samples.The concentration of anions and cations was determined, respectively, employing models ICS1100 and ICS90 liquid-phase ion chromatographic (IC) single-column system at room temperature. All samples and eluents were filtered through a filter paper (0.45μm) before injection into the IC system. Water samples having higher electrical conductivity were diluted appropriately with distilled water before being analyzed. The chromatograph was computer monitored using a CHROMELEON CM 6.80 SR software.The anionsF−, Cl−, NO3−, PO43−, and SO42− were separated on an AS12A IonPac separating column (4 × 200 mm) with an AG12A guard column (4 × 50 mm) and detected after suppression with an ASRS300 IonPac 4 mm anion electrical self-regenerating suppressor. The anions were eluted using the eluent (2.7 mM Na2CO3 + 0.3 mM NaHCO3) at a flow rate of 1 mL/min. A sample volume of 100 μL was injected and run for 15 minutes. The cycle time was 15 minutes per analysis.The cationsNa+, NH4+, K+, Mg2+, and Ca2+ were separated on a CS12A IonPac separating column (4 × 250 mm) with a CG-12A IonPac guard column and detected after suppression with a CSRS300 IonPac 4 mm cation electrical self-regenerating suppressor. The cations were eluted with 22 mM H2SO4 as eluent at a flow rate of 1 mL/minute. The injection volume was 50 μL, while the run time was set to 15 minutes, and the cycle time was 15 minutes per analysis.The normalized inorganic charge balance (NICB) was computed to check the accuracy of the results using the following equation [13], and the calculated NICB was within ±5%:(1)NICB=∑cations−∑anions∑cations+∑anions×100.In equation (1), the concentration of cations and anions are in meq/L. The total hardness (TH) was computed using the following equation [27]:(2)TH=2.497Ca2++4.115Mg2+.In equation (2), Ca2+ and Mg2+ are in mg/L. Water quality index (WQI) was determined by using the following equation [28]:(3)WQI=∑qiwi∑wi.The quality rating scaleqi for each parameter was computed as follows:(4)qi=100×vi−vosi−vo,where Vi is the estimated concentration of the ith parameter in the analyzed water, Vo is the ideal value of this parameter in pure water (Vo  = 0, except for pH = 7.0), and Si is the maximum limit of the ith parameter. The unit weight, Wi, for each parameter is computed as follows:(5)wi=ksi,where k = constant of proportionality and can be computed as(6)k=1∑1/Si.The increased non-carcinogenic risks due to nitrate and fluorite were evaluated by calculating the hazard quotient (HQ) and the resulting hazard index (HI). HQ was computed from equation (7), while ADD was computed using equation (8) [29]:(7)HQ=ADDRfD,where ADD represents the mean daily dose of a pollutant ingested from drinking water (mg/kg/day) and RfD is the reference dose for non-carcinogenic risk. The RfD for nitrate is 1.6 mg/kg/day while that for fluorite is 0.06 mg/kg/day. AAD is computed using the following equation:(8)ADD=C×IR×EF×EDBW×AT,where C represents the concentration of a particular pollutant in groundwater (mg/L), IR is the water ingestion rate (L/day), BW is the body weight (kg), EF is the exposure frequency (days/year) (EF = 365 days per year), ED is the exposure duration (year) (ED = 70 years), and AT is the average exposure time (days) (AT = 70×365 days)). Thus, from equation (8),(9)EF×EDAT=1,and equation (8) becomes(10)ADD=C×IRBW.In this study, the IR for adults and children is 2 and 1 L/day, respectively, whereas the BW for adults and children is 60 and 18 kg.The resulting hazard index (HI) due to exposure to many non-carcinogenic substances was calculated from the following equation [29, 30]:(11)HI=∑i=1nHQi,where i…n are the non-carcinogenic substances and HQi is the hazard quotient for the ith substance.Sodium adsorption ratio (SAR) was computed using the following equation withNa+ and Mg2+ in meq/L:(12)SAR=Na+Na++Mg2+/2.The Stiff and Piper plots were generated using DIAGRAMME 5.1 software. The geographical coordinates of the selected sampling points were recorded using a Geographical Positioning System (GPS) Magellan Triton-300. These coordinates were loaded in ArcGIS 10 software in order to draw the map of the study area and to evaluate the distances between the border of the landfill and the monitoring sites.


## 2.4. Data Analysis

Statistical processing of the data fort-test and correlation matrix was carried out using the Statistical Package for Social Sciences (SPSS) 23.0.


## 3. Results and Discussion

### 3.1. Physicochemical Quality of Leachate

The physicochemical quality of the leachate is reported in Table2. From the long dry season to the long wet season, the pH and temperature fell slightly from 8.9 to 8.2 and 26.7 to 26.2°C, respectively. The pH remained within the safe range of 6.0−9.0, while the temperature dropped below the safe limit of 30°C set by MINEP [31] for effluent discharge. A similar pH value of 8.1 was found in leachate from Taiwan [32]. The pH values obtained indicate that the leachate samples were from an old cell since old leachate is characterized by a pH > 7.5 [33].Table 2
Physicochemical characteristics of the leachate from the Nkolfoulou landfill.
Parameter
Sampling period
Mean
SD
Percent decrease or increase (%)
Cameroonian effluent limits [31]
Long dry season
Long wet season
T (°C)
26.7
26.2
26.5
0.4
−1.87
30
pH
8.9
8.2
8.6
0.5
−8.54
6.0
−
9.0
EC (μS/cm)
23400
17500
20450
4172
−25.21
—
TDS (mg/L)
7800
7000
7400
566
−10.26
—
TSS (mg/L)
70.2
130.2
100.2
42.4
85.47
50
Turbidity (NTU)
14.2
21.3
17.8
5.0
50.0
—
TH (mg/L)
424.56
349.64
387.10
52.97
−17.65
—
TA (mg·CaCO3/L)
748.04
558.09
653.06
134.31
−25.39
—
BOD
5 (mg·O2/L)
100
140
120
29
40.00
100
COD (mg·O2/L)
1350
1750
1550
283
29.63
200
BOD
5/COD
0.07
0.08
0.08
0.00
8.00
—
Na
+ (mg/L)
465.24
200.62
332.93
187.11
−56.88
—
K
+ (mg/L)
350.75
231.45
291.10
84.36
−34.01
—
Mg
2
+ (mg/L)
75.23
60.13
67.68
10.68
−20.07
—
Ca
2
+ (mg/L)
45.96
40.86
43.41
3.61
−11.10
—
NH
4
+ (mg/L)
82.5
39.51
61.01
30.40
−52.11
0.1
NO
3
− (mg/L)
159.32
74.82
117.07
59.75
−53.04
20
Cl
− (mg/L)
702.69
345.50
524.10
252.57
−50.83
50
F
− (mg/L)
3.48
2.50
2.99
0.69
−28.16
—
PO
4
3
−
mg/L
ND
ND
—
—
—
3
SO
4
2
−
mg/L
50.24
10.60
30.42
28.03
−78.90
—
HCO
3
− (mg/L)
923.50
689.00
806.25
165.82
−25.39
—
Colour (mg/L pt-Co)
5208.33
4654.75
4931.54
391.44
−10.63
—
Appearance
Dark-brown
Brown
—
—
—
Colourless
Odour
Pungent
Pungent
—
—
—
Odourles
ND = not detected; SD = standard deviation.During the long dry and long wet seasons, respectively, the values ofBOD5 (100; 140 mg·O2/L), COD (1,350; 1,750 mg·O2/L), and TSS (70.2; 130.2 mg/L) were all found to be higher than the regulatory limits for the effluent discharge set by MINEP [31] (Table 2). During this same period, leachate had a biodegradability ratio (BOD5/COD) of 0.07 and 0.08, respectively. This implies that the leachate was from an old cell since a ratio of BOD5/COD < 0.1 is typical of leachate from an old landfill (>10 years) [7, 33]. Again, during this same period, the concentration of NH4+ (82.5; 39.51 mg/L), NO3− (159.32; 74.82 mg/L), and Cl− (702.69; 345.50 mg/L) was all superior to the safe limits for effluent discharge stated by MINEP [31] (Table 2). Ammonia-nitrogen in leachate may originate from the catabolism of protein-rich compounds [7, 34, 35]. NH4+ is produced during ammonification [35] and can thereafter be partially transformed into NO3− by the anaerobic ammonium oxidation process (ANAMMOX) as shown in equation (13). It can also be transformed into NO3− under aerobic conditions through nitrification [35], while leachate stagnates or flows on the ground:(13)NH4++1.26NO2−+0.085CO2+0.02H+⟶N2+0.017H++0.24NO3−+1.95H2OPO43− was not detected in any of the seasons, while SO42− concentration dropped from 50.24 to 10.60 mg/L. SO42− found in leachate may be the result of the oxidation of H2S [36], while the absence of PO43− might be due to its coprecipitation by Mg2+ and NH4+ to form magnesium ammonium phosphate (MAP) hexahydrate known as struvite as shown in the following equation [37]:(14)Mg2++PO43−+NH4++6H2O⟶MgNH4PO4.6H2OIn both seasons, leachate had a dark-brownish colour ranging from 5208.33 to 4654.75 mg/L Pt-Co with an offensive pungent smell. In a similar study [38], the values were in the range of 955–15.142 mg/L Pt-Co for an old leachate. The dark brown colour of the leachate may be due to the presence of FeS and PbS formed, respectively, by the reaction of iron and lead with hydrogen sulfide. It may also be due to the presence of MnO resulting from the oxidation of manganese in air. The pungent odour of the leachate is attributable to the presence of either NH3, H2S, CH3SH, and volatile fatty acids (VFAs) or putrescine and cadaverine from the putrefaction of wastes from the abattoirs.Comparatively, the average physicochemical characteristics of the leachate samples collected in this work from the Nkolfoulou landfill differ from those observed elsewhere (Table3). This may be due to the differences in waste composition, meteorological conditions, waste age, and landfilling technology [6, 7]. As observed in Table 3, all comparable parameters were in the typical range stated by Christensen et al. [6] except for TSS which was much lower, more likely as a result of the soil type on which the leachate leaks or runs.Table 3
Landfill leachate characteristics of other countries in comparison with the present study.
Parameter
Typical range [6]
Country (landfill site)
India (Jamalpur) [39]
Spain (Marbella) [40]
Nigeria (Aba-Eku) [41]
Cameroon (Nkolfoulou) (this study)
T (°C)
—
—
22.2
—
26.5
pH
4.5
−
9
9.8
8.21
8.21
8.6
EC (μS/cm)
2,500−35,000
—
24195
2466
20450
TDS (mg/L)
—
6563
—
—
7400
TSS (mg/L)
2,000−60,000
7695
—
144.94
100.2
Turbidity (NTU)
—
79
—
—
17.8
TH (mg/L)
—
638
—
—
387.10
TA (mg·CaCO3/L)
—
—
8789.3
—
653.06
BOD
5 (mg·O2/L)
20−57,000
495
—
—
120
COD (mg·O2/L)
140−152,000
2535
—
57.63
1550
BOD
5
/
COD
0.02−0.80
0.19
—
—
0.08
Na
+ (mg/L)
70−7,700
—
2768.1
—
332.93
K
+ (mg/L)
50−3,700
—
1553
—
291.10
Mg
2
+ (mg/L)
30−15,000
—
189.2
83.55
67.68
Ca
2
+ (mg/L)
10.0−7,200
—
148.6
86.4
43.41
NH
4
+ (mg/L)
—
—
3248.7
3.55
61.01
NO
3
− (mg/L)
—
18.6
555.7
12.37
117.07
Cl
− (mg/L)
150−4,500
1836
4652.7
597.98
524.10
F
− (mg/L)
—
—
—
—
2.99
PO
4
3
− (mg/L)
—
—
—
ND
ND
SO
4
2
− (mg/L)
8.0−7,750
65.1
419.2
118.86
30.42
HCO
3
− (mg/L)
610−7,320
—
—
—
806.25
Colour (mg/L Pt-Co)
—
—
—
—
4931.54
Appearance
—
Brownish
—
—
Dark brownish
Odour
—
Sewage smell
—
—
Pungent
ND = not detected.Seasonal variation of the levels of nutrients as well as the pH, EC, TDS, TA, TH, and colour exhibited a decreasing trend with percent decrease ranging from−1.87% (EC) to −78.90% (SO42−) in going from the long dry season to the long wet season. This decrease is attributable to the dilution of leachate by runoff or rain water. In contrast, the increase in TSS and turbidity as well as BOD5 and COD in the long wet season could be due to runoff that brings solid particles and organic matter to the leachate. Seasonal variation in major ion concentrations is illustrated by the Stiff diagram (Figure 2) in which the shapes of polygons differ from season to season implying that the leachate composition varies according to the season. In the leachate samples, the trends in the cation concentrations were in the order Na+ > K+ > NH4+ > Mg2+ > Ca2+ in the long dry season and Na+ > K+ > Mg2+ > Ca2+ > NH4+ in the long wet season while that of the anions was HCO3− > Cl− > NO3− > SO42− > F− > PO43− in both seasons.Figure 2
Stiff plot of landfill leachate quality.


### 3.2. Groundwater Quality

The physicochemical quality of groundwater in both seasons is displayed in Tables4 and 5. During the long dry season, the groundwater temperatures were in the range 23.3−23.6°C (mean 23.5°C), while during the long wet season, the range was 23.0−23.5°C (mean 23.3°C). All the temperature values for both seasons were lower than 25°C, which is the standard limit according to Cameroonian regulations [42] for drinking water.Table 4
Physicochemical characteristics of groundwater in the long dry season.
Parameter
Sampling point
Mean
SD
GW
1
GW
2
GW
3
GW
4
GW
5
GW
6
GW
7
GW
8
GW
9
GW
10
GW
11
GW
12
GW
13
T (°C)
23.5
23.4
23.5
23.4
23.6
23.5
23.3
23.4
23.4
23.5
23.4
23.5
23.5
23.5
0.08
pH
5.8
6.1
5.3
5.6
5.4
5.3
5.2
5.2
5.4
5.6
5.9
6.0
5.9
5.6
0.32
EC (μS/cm)
100
100
40
30
110
90
30
30
130
100
80
30
100
75
37
TDS (mg/L)
40
40
20
10
50
40
10
10
60
40
40
10
40
32
17
Turbidity (NTU)
8.3
0.7
1.3
1.3
12.6
0.9
9.4
0.7
3.2
2.2
4.6
0.8
3.3
3.8
3.9
TSS (mg/L)
59.43
5.00
9.29
9.29
90.00
6.43
67.14
5.00
22.86
15.71
32.5
7.00
23.21
27.14
27.75
TH (mg/L)
26.00
24.09
26.89
33.64
34.21
21.51
16.42
39.45
49.16
36.84
16.02
32.61
22.01
29.14
9.61
TA (mg·CaCO3/L)
33.3
23.8
29.3
28.5
38.0
19.0
28.5
36.1
90.3
47.6
19.0
33.3
23.8
34.7
18.5
Na
+ (mg/L)
2.54
2.42
1.90
0.48
0.48
0.53
6.97
2.67
22.83
5.66
1.84
2.59
1.93
4.07
5.95
K
+ (mg/L)
2.29
1.86
1.52
1.55
2.70
0.70
3.90
2.58
5.71
2.60
2.01
2.71
1.88
2.46
1.24
Mg
2
+ (mg/L)
2.87
3.03
1.12
0.66
3.80
0.20
2.34
3.40
6.05
0.61
2.35
3.36
2.27
2.47
1.59
Ca
2
+ (mg/L)
5.69
4.65
8.92
12.39
7.43
8.29
2.72
10.19
9.71
13.75
2.54
7.52
5.07
7.61
3.44
NH
4
+ (mg/L)
0.12
0.03
0.02
ND
0.02
0.02
0.51
0.22
0.26
0.05
0.07
0.29
0.08
0.14
0.15
NO
3
− (mg/L)
0.63
1.27
3.04
4.25
3.57
2.53
7.18
3.77
11.76
3.02
2.38
2.06
3.41
3.76
2.88
F
− (mg/L)
0.04
0.06
0.03
0.04
0.05
0.03
0.02
0.05
0.03
0.03
0.07
0.05
0.08
0.04
0.02
Cl
− (mg/L)
0.22
0.67
0.51
0.42
0.34
0.52
0.45
1.80
0.95
3.72
1.26
1.81
0.53
1.02
0.97
SO
4
2
− (mg/L)
0.17
3.26
1.21
1.77
0.73
0.48
0.87
3.22
0.24
0.61
0.87
1.61
1.54
1.28
1.01
PO
4
3
− (mg/L)
ND
0.03
ND
ND
ND
0.01
0.02
ND
ND
ND
ND
ND
ND
0.02
0.01
HCO
3
− (mg/L)
40.6
29.0
35.7
34.8
46.4
23.2
34.8
44.0
110.1
58.0
23.2
40.6
29.0
42.3
22.6
WQI
69.27
14.40
19.02
16.61
87.59
17.10
114.50
36.65
53.44
26.39
43.43
40.16
36.92
44.27
30.28
SAR
0.22
0.21
0.16
0.04
0.04
0.05
0.75
0.18
1.41
0.41
0.20
0.20
0.18
0.31
0.38
ND = not detected; SD = standard deviation.Table 5
Physicochemical characteristics of groundwater in the long wet season.
Parameter
Sampling point
Mean
SD
GW
1
GW
2
GW
3
GW
4
GW
5
GW
6
GW
7
GW
8
GW
9
GW
10
GW
11
GW
12
GW
13
T (°C)
23.1
23.0
23.4
23.3
23.5
23.0
23.3
23.3
23.2
23.4
23.5
23.0
23.4
23.3
0.2
pH
6.1
6.2
5.8
5.9
6.1
6.2
6.4
6.1
6.3
5.9
6.4
6.3
6.1
6.1
0.2
EC (μS/cm)
30
80
50
40
30
50
30
20
150
50
50
30
50
51
34
TDS (mg/L)
10
40
20
10
10
20
10
10
70
200
20
10
20
35
53
Turbidity (NTU)
8.23
0.7
1.4
1.2
14.53
1.1
7.45
0.7
4.6
2.1
6.31
0.8
2.38
3.96
4.16
TSS (mg/L)
58.79
5.00
10.00
8.57
103.79
7.86
53.21
5.00
32.86
15.00
45.07
7.00
17.00
28.40
29.63
TH (mg/L)
24.73
20.37
34.21
44.90
42.16
23.02
13.80
22.75
31.91
31.12
11.14
22.53
14.40
25.93
10.47
TA (mg·CaCO3/L)
28.5
23.8
38.0
53.3
42.8
23.8
19.0
23.8
35.0
33.3
14.3
27.5
19.0
29.39
10.86
Na
+ (mg/L)
0.85
1.32
2.31
0.97
1.26
1.03
1.56
1.06
0.03
0.90
1.26
1.31
1.42
1.18
0.51
K
+ (mg/L)
2.11
1.63
2,65
8.44
2.86
1.23
1.20
1.50
1.27
1.41
1.75
2.41
1.45
2.30
1.93
Mg
2
+ (mg/L)
4.06
2.29
1.90
1.36
4.58
0.55
2.03
0.61
0.73
1.55
1.83
2.28
2.01
1.98
1.20
Ca
2
+ (mg/L)
3.21
4.38
10.57
15.74
9.34
8.32
2.18
8.11
11.58
9.90
1.45
5.26
2.45
7.11
4.34
NH
4
+ (mg/L)
0.50
ND
0.73
0.40
0.10
0.03
0.31
ND
0.02
0.14
ND
0.06
0.05
0.23
0.24
NO
3
− (mg/L)
1.03
0.16
3.51
7.97
4.77
3.44
1.96
1.36
0.07
1.46
0.63
1.27
2.10
2.29
2.19
F
− (mg/L)
0.03
0.06
0.05
0.10
0.06
0.04
0.01
0.02
0.03
0.02
0.03
0.03
0.05
0.04
0.02
Cl
− (mg/L)
0.37
0.21
0.85
0.91
0.51
0.72
0.31
0.73
0.15
0.39
0.37
0.55
0.32
0.49
0.24
SO
4
2
− (mg/L)
0.25
1.97
1.24
3.60
1.08
0.79
0.11
0.3
0.03
0.21
0.07
0.35
0.14
0.78
1.02
PO
4
3
− (mg/L)
ND
ND
0.02
ND
0.01
0.03
0.01
ND
0.02
0.01
ND
ND
ND
0.02
0.01
HCO
3
− (mg/L)
34.8
29.0
46.4
64.96
52.2
29.0
23.2
29.0
42.7
40.6
17.4
33.5
23.2
35.84
13.24
WQI
103.16
11.53
86.59
56.59
104.08
15.50
78.13
9.98
35.00
32.28
42.69
16.21
26.22
47.53
34.66
SAR
0.07
0.13
0.17
0.06
0.08
0.09
0.18
0.10
0.00
0.07
0.16
0.12
0.16
0.11
0.05
ND = not detected; SD = standard deviation.The pH of groundwater samples varied from 5.2 to 6.1 (mean 5.6) during the long dry season and 5.8 to 6.4 (mean 6.1) during the long wet season. These pH ranges are lower than7.02−7.85 recorded by Mor et al. [8] for groundwater around a landfill in Delhi (India). For both seasons, the pH values were outside the safe ranges of 6.5–9.5, 6.5–8.5, and 6.5–9.0 set, respectively, by EU [43], EPA [18], and Cameroonian standards [42] (Table 6) for drinking water.Table 6
Water guidelines for drinking and agricultural uses.
Parameter
Guidelines for drinking water
EU [43]
EPA [18]
MINDIC [42]
WHO [14]
T (°C)
—
—
25
—
pH
6.5−9.5
6.5−8.5
6.5−9.0
—
EC (μS/cm)
2,500
—
1,000
—
TDS (mg/L)
—
500
—
1,000
Turbidity (NTU)
—
—
2
1
γ
TSS (mg/L)
—
—
1,500
—
TH (mg/L)
—
—
—
—
TA (mg·CaCO3/L)
—
—
—
—
Na
+ (mg/L)
200
—
150
200
∗
K
+ (mg/L)
—
—
12
—
Mg
2
+ (mg/L)
—
—
50
—
Ca
2
+ (mg/L)
—
—
—
100
−
300
∗
NH
4
+ (mg/L)
0.5
—
0.5
35
∗
NO
3
− (mg/L)
50
45
50
50
F
− (mg/L)
1.5
4
0.7
1.5
Cl
− (mg/L)
250
250
200
250
∗
SO
4
2
− (mg/L)
250
—
250
250
∗
PO
4
3
− (mg/L)
—
—
—
—
HCO
3
− (mg/L)
—
—
—
—
γDisinfection effectiveness; ∗taste consideration.During the long dry and long wet seasons, the EC values were, respectively, in the range 30–130μS/cm (mean 76 μS/cm) and 20–150 μS/cm (mean 49 μS/cm), while the TDS values were in the range 10–60 mg/L (mean 32 mg/L) and 10–70 mg/L (mean 21 mg/L). As can be observed, the EC and TDS values are several folds lower than 12,745 μS/cm and 9,895 mg/L, respectively, as reported by El-Salam and Abu-Zuid [11] for groundwater near a landfill in Alexandria (Egypt). With respect to drinking water, the EC and TDS values complied with the standards set by regulatory bodies [14, 18, 42, 43] (Table 6).During the long dry and long wet seasons, the turbidity values registered were, respectively, between 0.70 and 12.60 NTU (mean 4.55 NTU) and 0.70 and 14.5 NTU (mean 4.50 NTU), whereas the TSS values were between 5.00 and 90.00 mg/L (average 32.44 mg/L) and 5.00 and 103.79 mg/L (average 31.89 mg/L). Comparatively, Han et al. [44] reported high values in the range 0.1−17.2 NTU in groundwater near a landfill at Zhoukou (China). All the recorded TSS values were lower than the recommended maximum limit set by MINDIC for drinking water [42] (Table 6). In the long dry season, GW2, GW6, GW8, and GW12 wells representing 30.76% of the samples and GW2, GW8, and GW12 wells in the long wet season representing 23.07% of the samples had turbidity less than 1 NTU which is within the standard limit for drinking water disinfection effectiveness laid down by WHO [14]. Higher turbidity can seriously interfere with the efficiency of disinfection by providing protection for organisms [14].During the long dry and long wet seasons, the TH values increased, respectively, from 16.02 to 49.16 mg/L (average 26.14 mg/L) and 11.14 to 44.90 mg/L (average 25.93 mg/L), while the TA values increased from 19.02 to 90.28 mg/L (mean 34.66 mg/L) and 14.27 to 53.27 mg/L (mean 29.39 mg/L). These TH and TA values were, respectively, lower than those of296−1388 mg/L and 230−734 mg/L recorded by Mor et al. [8] for groundwater near the Gazipur landfill (India).During the long dry season, the concentration ofNa+, K+, Mg2+, and Ca2+ fluctuated, respectively, between 0.48 and 22.83 mg/L (mean 4.07 mg/L), 0.70 and 5.71 mg/L (mean 2.46 mg/L), 0.20 and 6.05 mg/L (mean 2.47 mg/L), and 2.54 and 13.75 mg/L (mean 7.61 mg/L) while in the long wet season, they ranged from 0.03 to 2.31 mg/L (mean 1.18 mg/L), 1.20 to 8.44 mg/L (mean 2.30 mg/L), 0.55 to 4.58 mg/L (mean 1.98 mg/L), and 1.45 to 15.74 mg/L (mean 7.11 mg/L), respectively. The average values of Na+, K+, Mg2+, and Ca2+ obtained in this work are lower than 23.75, 11.17, 84.6, and 360 mg/L, respectively, reported by Singh et al. [45] for groundwater around the Pirana landfill in Ahmedabad (India). In this study, all the concentrations of Na+ obtained were many folds lower than the maximum limits stated by the regulatory bodies [14, 42, 43] for drinking water (Table 6). In both seasons, the levels of K+ and Mg2+ were lower than the permissible limits laid down by MINDIC [42] for drinking water (Table 6).In the long dry and long wet seasons, theNH4+ levels were observed, respectively, between ND (non detected) and 0.51 mg/L (mean 0.14 mg/L) and ND and 0.73 mg/L (mean 0.23 mg/L), while the NO3− values varied from 0.63 to 11.76 mg/L (mean 3.76 mg/L) and 0.07 to 7.97 mg/L (mean 2.29 mg/L). Comparatively, high values of NH4+ in the range ND–4.3 mg/L were reported by Mor et al. [8] for groundwater near the Gazipur landfill in India, while, for NO3−, a mean value of 49.90 mg/L higher than those found in this study was recorded by Singh et al. [45] for groundwater at the vicinity of the Pirana landfill also in India. In the study area, the NH4+ in the groundwater might have originated from the leachate or leaked from the septic tank. The NH4+ values registered in the long dry season at GW7 (0.51 mg/L) and in the long wet season at GW3 (0.73 mg/L) exceeded both the EU [43] and MINDIC [42] standards for drinking water (Table 6). However, it has been recently substantiated that the additional exposure to NH4+ from water in the concentration range of 0.5−5 mg/L is negligible and thus does not pose a risk to human health [46]. NH4+ in drinking water may have resulted from the protonation of NH3 given the acidic nature (pH < 6.5) of the water. The values of NO3− in both seasons were lower than the threshold set by EU [43], EPA [18], and MINDIC [42] for drinking water (Table 6).During the long dry season, theF−, Cl− and SO42− values were, respectively, between 0.02 and 0.08 mg/L (average 0.04 mg/L), 0.22 and 3.72 mg/L (average 1.02 mg/L), and 0.17 and 3.26 mg/L (average 1.28 mg/L), while in the long wet season, they were, respectively, between 0.01 and 0.10 mg/L (mean 0.04 mg/L), 0.15 and 0.91 mg/L (mean 0.49 mg/L), and 0.03 and 3.60 (mean 0.78 mg/L). The mean average values of F−, Cl−, and SO42− are, respectively, several orders of magnitude lower than 0.67, 253.94, and 96.94 mg/L recorded by Pujari and Deshpande [47] for groundwater around a landfill in Nagpur (India). As far as F−, Cl−, and SO42− were concerned, groundwater sources were fit for drinking for both seasons since their concentrations were lower than the prescribed limits set by EU [43], EPA [18], MINDIC [42], and WHO [14] (Table 6).PO
4
3
− was barely detected in the three wells (GW2, GW6, and GW7) during the long dry season and in six wells (GW3, GW5, GW6, GW7, GW9, and GW10) during the long wet season with concentrations ranging slightly from 0.01 to 0.03 mg/L in both seasons. The concentrations of HCO3− increased from 23.20 to 110.10 (mean 42.26 mg/L) in the long dry season and from 17.40 to 64.96 mg/L (mean 35.84 mg/L) in the long wet season. The mean values of PO43− and HCO3− are, respectively, lower than 0.29 mg/L and 391.8 mg/L reported for groundwater around the Pirana landfill in Ahmedabad (India) [45]. PO43− was not detected in the leachate samples, so its occurrence in some groundwater samples in the study area may be attributed to anthropogenic activities such as domestic waste discharge and agriculture. In groundwater, HCO3− may have originated from the dissolution of atmospheric CO2 and carbonate minerals [8] or from sulfate reduction of organic compounds in the aquifer as represented in the following equation [48]:(15)2CH2O+SO42−⟶H2S+2HCO3−According to Piper’s diagram [49] (Figure 3), the hydrochemical facies of groundwater in the study area were of the Ca-Mg-HCO3− (84.62%) and Na-K-HCO3− (15.38%) types in the long dry season, while in the long wet season, all the groundwater samples were of the Ca-Mg-HCO3− type (100%).Figure 3
Piper diagram showing the hydrochemical composition of groundwater around the Nkolfoulou landfill: (a) long dry season; (b) long wet season.
(a)
(b)


### 3.3. Statistical Correlation

The correlation matrices for 19 measured variables during the long dry and long wet seasons are illustrated in Table7. The perfect positive correlation between TSS and turbidity (r = 1, p≤0.01) in both seasons means that they have exactly the same contributor which could be mud brought in by the infiltrating rain water. The strong positive correlation between EC and TDS (r = 0.98, p≤0.01) in the dry season signifies that they have nearly the same contributors (the dissolved ions). At the 0.05 p level, a significant negative correlation was observed only between the temperature and NH4+ (r =  −0.57) in the long dry season, while for the long wet season, it was registered between pH and NH4+ (r =  −0.57), between pH and Ca2+ (r =  −0.62), between pH and Cl− (r =  −0.58), and between pH and HCO3− (r =  −0.66) indicating the opposing distribution of these pair variables. In both seasons, the depth of the wells exhibited no significant correlation with any of the variables in the matrices except for SO42− with a significant positive correlation (r = 0.78, p≤0.01) in the long dry season. In the long dry season, there was a significant positive correlation between pH and F− (r = 0.68), Na+ and Mg2+ (r = 0.64), NH4+ and K+ (r = 0.68), and Mg2+ and HCO3− (r = 0.66) at the 0.05 p level, while at the 0.01 p level, there was a significant positive correlation between Na+ and K+ (r = 0.89), Na+ and NO3− (r = 0.87), Na+ and HCO3− (r = 0.91), K+ and Mg2+ (r = 0.78), K+ and NO3− (r = 0.83), K+ and HCO3− (r = 0.84), and NO3− and HCO3− (r = 0.77).Table 7
Correlation matrix.
pH
T
EC
TDS
TSS
Turbidity
Na
+
NH
4
+
K
+
Mg
2
+
Ca
2
+
F
−
Cl
−
NO
3
−
PO
4
3
−
SO
4
2
−
HCO
3
−
Depth
Distance
LDS
pH
1
T
0.12
1
EC
0.231
0.372
1
TDS
0.17
0.369
0.984
∗∗
1
TSS
−0.185
0.170
0.251
0.262
1
Turbidity
−0.187
0.167
0.256
0.267
1.00
∗∗
1
Na
+
−0.219
−0.349
0.374
0.397
0.006
0.007
1
NH
4
+
−0.257
−
0.572
∗
−0.35
−0.363
0.235
0.23
0.463
1
K
+
−0.223
−0.349
0.219
0.231
0.306
0.304
0.891
∗∗
0.677
∗
1
Mg
2
+
0.066
−0.106
0.332
0.349
0.282
0.279
0.642
∗
0.430
0
.
779
∗∗
1
Ca
2
+
−0.323
0.254
−0.06
−0.081
−0.417
−0.418
0.139
−0.311
−0.001
−0.219
1
F
−
0.678
∗
0.169
0.183
0.167
−0.084
−0.081
−0.361
−0.324
−0.299
0.157
−0.404
1
Cl
−
0.074
0.048
−0.018
−0.052
−0.354
−0.356
0.128
0.041
0.131
−0.119
0.500
−0.073
1
NO
3
−
−0.494
−0.435
0.13
0.178
0.115
0.117
0.870
∗∗
0.516
0.829
∗∗
0.513
0.148
−0.403
−0.054
1
PO
4
3
−
0.121
−0.469
0.005
−0.046
−0.022
−0.021
−0.038
0.201
−0.048
−0.045
−0.449
−0.087
−0.237
−0.056
1
SO
4
2
−
0.214
−0.29
−0.409
−0.461
−0.484
−0.484
−0.32
−0.051
−0.255
0.033
0.004
0.419
0.065
−0.270
0.372
1
HCO
3
−
−0.253
−0.051
0.409
0.423
0.043
0.041
0.910
∗∗
0.273
0.843
∗∗
0.655
∗
0.424
−0.368
0.246
0.771
∗∗
−0.282
−0.314
1
Depth
0.159
−0.11
−0.359
−0.402
−0.415
−0.422
−0.118
0.201
−0.014
0.296
0.049
0.150
0.180
−0.214
0.309
0.779
∗∗
−0.057
1
Distance
−
0.582
∗
−
0.654
∗
−0.371
−0.395
0.05
0.05
0.243
0.701
∗∗
0.349
0.113
−0.098
−0.458
−0.012
0.420
0.520
0.259
0.073
0.321
1
LWS
pH
1
T
−0.263
1
EC
0.192
−0.169
1
TDS
−0.287
0.148
0.315
1
TSS
0.25
0.413
−0.129
−0.177
1
Turbidity
0.246
0.417
−0.127
−0.175
1.00
∗∗
1
Na
+
−0.264
0.251
−0.537
−0.322
−0.078
−0.079
1
NH
4
+
−
0.574
∗
0.141
−0.247
−0.147
0.058
0.060
0.466
1
K
+
−0.459
0.115
−0.191
−0.224
−0.083
−0.083
0.013
0.392
1
Mg
2
+
−0.036
0.149
−0.349
−0.217
0.747
∗∗
0.744
∗∗
0.217
0.265
0.049
1
Ca
2
+
−0.621∗
0.085
0.239
0.241
−0.202
−0.200
−0.254
0.237
0.610
∗
−0.300
1
F
−
−0.473
0.045
0.02
−0.265
−0.090
−0.088
0.103
0.213
0.815
∗∗
0.133
0.518
1
Cl
−
−
0.584
∗
0.083
−0.503
−0.294
−0.310
−0.310
0.379
0.431
0.593
∗
−0.211
0.560
∗
0.429
1
NO
3
−
−0.537
0.258
−0.354
−0.252
0.065
0.067
0.208
0.405
0.833
∗∗
0.07
0.626
∗
0.748
∗∗
0.736
∗∗
1
PO
4
3
−
−0.080
−0.096
0.374
0.178
−0.007
−0.005
−0.043
0.12
−0.257
−0.326
0.371
−0.131
0.153
0.105
1
SO
4
2
−
−0.480
−0.091
−0.064
−0.196
−0.226
−0.224
0.136
0.302
0.853
∗∗
0.001
0.583
∗
0.903
∗∗
0.524
0.741
∗∗
−0.120
1
HCO
3
−
−
0.656
∗
0.142
0.073
0.100
0.091
0.092
−0.129
0.441
0.760
∗∗
0.151
0.879
∗∗
0.663
∗
0.487
0.728
∗∗
0.142
0.677
∗
1
Depth
0.124
−0.519
−0.122
−0.200
−0.410
−0.415
0.075
−0.317
−0.111
−0.125
−0.041
−0.076
0.106
−0.271
−0.303
0.092
−0.126
1
Distance
0.358
−0.200
−0.059
−0.106
−0.079
−0.077
−0.045
−0.146
−0.263
−0.381
−0.080
−0.428
−0.054
−0.138
0.174
−0.146
−0.273
0.321
1
LDS = long dry season; LWS = long wet season.∗Correlation is significant at the 0.05 level; ∗∗correlation is significant at the 0.01 level.In the long wet season, there was a significant positive correlation betweenK+ and Ca2+ (r = 0.61), K− and Cl− (r = 0.59), Ca2+ and Cl− (r = 0.56), Ca2+ and NO3− (r = 0.63), Ca2+ and SO42− (r = 0.58), F− and HCO3− (r = 0.66), and SO42− and HCO3− (r = 0.68) at the 0.05 p level, whereas at the 0.01 p level, there was a significant positive correlation between Mg2+ and TSS (r = 0.75), Mg2+ and turbidity (r = 0.74), K+ and F− (r = 0.82), K+ and NO3− (r = 0.83), K+ and SO42− (r = 0.85), K+ and HCO3− (r = 0.76), Ca2+ and HCO3− (r = 0.88), F− and NO3− (r = 0.75), F− and SO42− (r = 0.90), Cl− and NO3− (r = 0.74), NO3− and SO42− (r = 0.74), and NO3− and HCO3− (r = 0.73).The distance between the wells and the landfill barely exhibited significant negative correlation with pH (r =  −0.58, p≤0.05) and temperature (r =  −0.65, p≤0.05), implying that the landfill may not be the main source of the major ions in the nearby groundwater. The strong positive correlations observed between the various ions in both seasons imply that they may have common sources (weathering of rocks, septic tanks, pit latrines, domestic effluent, and agricultural activities), which contribute to the ion input in the groundwater in the area.


### 3.4. Seasonal Variation of Groundwater Quality

Although thet-test is usually applied on larger sample sizes, it can be used for small sample sizes (N≤5), as long as the effect sample size is large [50]. The t-test was performed to check the significance of the seasonal variation of the mean value of the parameters assessed. Results of this test are summarized in Table 8. The resulting p values were compared with the significance level, α = 0.05. The seasonal variation of parameters was statistically significant only for pH (p≤0.001), T (temperature) (p=0.004), and EC (p=0.021) (Table 8), whereas it was insignificant for the remaining data pairs representing 84.21% as p>α. It can therefore be inferred that the change in groundwater quality from the dry season to the wet season was generally insignificant within a 95% confidence limit.Table 8
Student’st-test.
Paired variable
N
Descriptive statistics
Paired differences
t
df
p value
Dry season
Wet season
95% confidence interval of the difference
Mean (SD)
Mean (SD)
Lower
Upper
pH (d)-pH (w)
13
5.592 (0.317)
6.139 (0.189)
−0.752
−0.340
−5.781
12
0.000
T (d)-T (w)
13
26.454 (0.078)
26.262 (0.185)
0.075
0.309
3.584
12
0.004
EC (d)-EC (w)
13
74.615 (36.882)
50.769 (33.531)
4.337
43.356
2.663
12
0.021
TDS (d)-TDS (w)
13
31.539 (17.246)
34.615 (52.538)
−32.925
26.771
−0.225
12
0.826
TSS (d)-TSS (w)
13
27.143 (27.748)
28.396 (29.632)
−5.749
3.243
−0.607
12
0.555
Turb (d)-turb (w)
13
3.792 (3.894)
3.962 (4.160)
−0.797
0.459
−0.587
12
0.568
TH (d)-TH (w)
13
29.142 (9.608)
25.926 (10.472)
−2.093
8.525
1.320
12
0.211
TA (d)-TA (w)
13
34.654 (18.509)
29.392 (10.856)
−5.748
16.271
1.041
12
0.318
Na
+ (d)-Na+ (w)
13
4.065 (5.949)
1.175 (0.510)
−0.906
6.685
1.659
12
0.123
NH
4
+ (d)-NH4+ (w)
13
0.130 (0.150)
0.180 (0.234)
−0.224
0.124
−0.626
12
0.543
K
+ (d)-K+ (w)
13
2.462 (1.243)
2.301 (1.926)
−1.386
1.709
0.227
12
0.824
Mg
2
+(d)-Mg2+(w)
13
2.466 (1.594)
1.983 (1.203)
−0.611
1.577
0.962
12
0.355
Ca
2
+ (d)-Ca2+ (w)
13
7.605 (3.444)
7.115 (4.338)
−0.824
1.805
0.813
12
0.432
F
− (d)-F− (w)
13
0.045 (0.018)
0.041 (0.024)
−0.012
0.020
0.534
12
0.603
Cl
− (d)-Cl− (w)
13
1.015 (0.968)
0.492 (0.244)
−0.091
1.138
1.857
12
0.088
NO
3
− (d)-NO3− (w)
13
3.759 (2.879)
2.287 (2.194)
−0.783
3.727
1.423
12
0.180
PO
4
3
− (d)-PO43− (w)
13
0.005 (0.010)
0.008 (0.010)
−0.011
0.005
−0.805
12
0.436
SO
4
2
− (d)-SO42−(w)
13
1.275 (1.006)
0.780 (1.025)
−0.192
1.183
1.569
12
0.143
HCO
3
− (d)-HCO3− (w)
13
42.264 (22.562)
35.843 (13.239)
−6.993
19.835
1.043
12
0.318
d = dry season; w = wet season; turb = turbidity. Bolded figures indicate significant difference.In the groundwater samples, the order of abundance of cations wasCa2+ > Na+ > Mg2+ > K+ > NH4+ in the long dry season and Ca2+ > K+ > Mg2+ > Na+ > NH4+ in the long wet season while that of anions was HCO3− > NO3− > SO42− > Cl− > F− > PO43− in both seasons.


### 3.5. Drinking Water Suitability Based on TDS, TH, and WQI

Following the classification of van der Aa [51] of drinking water based on TDS (Table 9), apart from the GW5 and GW9 wells in the long dry season and the GW9 and GW10 wells in the long wet season, the remaining wells, representing 84.61% of the samples in both seasons, had very low mineral concentrations. According to the same classification, 15.38% of the samples in the long dry season (GW5 and GW9) and in the long wet season (GW9 and GW10) had low mineral concentrations.Table 9
Classification of drinking water based on TDS, TH, and WQI.
Parameter
Range
Description
TDS (mg/L) [51]
<
50
Very low mineral c
50
−
500
Low mineral c
500−1,500
Intermediate mineral c
>1,500
High mineral c
TH mg/L [52]
<
75
Soft
75
−
150
Moderately hard
150
−
300
Hard
>
300
Very hard
WQI [53]
0
−
25
Excellent water quality
26
−
50
Good water quality
51
−
75
Poor water quality
76
−
100
Very poor water quality
>
100
Unsuitable for drinking
c = concentration.According to the classification of Crittenden et al. [52] based on TH (Table 9), all (100%) the samples were “soft” in both seasons.Using the Cameroonian standards [42], the weighted arithmetic water quality index (WQI) in the present study was calculated with 13 parameters, namely, pH, temperature, EC, TSS, turbidity, Na+, K+, NH4+, Mg2+, NO3−, F−, Cl−, and SO42−. The values of WQI obtained in this study ranged from 14.40 to 114.50 (mean 44.27) in the long dry season (Table 4) and from 9.98 to 104.08 (mean 47.53) in the long wet season (Table 5). Employing the classification of Chatterjee and Raziuddin [53] of drinking water based on WQI (Table 9), out of the 13 samples, 30.76% (GW2, GW3, GW4, and GW6) had excellent water quality, 38.46% (GW8, GW10, GW11, GW12, and GW13) had good water quality, 15.38% (GW1 and GW9) had poor water quality, 7.69% (GW5) had very poor water quality, and 7.69% (GW7) was unsuitable for drinking in the long dry season. In the long wet season, out of the 13 samples, 30.76% (GW2, GW6, GW8, and GW12) had excellent water quality, 30.76% (GW9, GW10, GW11, and GW13) had good water quality, 7.69% (GW4) had poor water quality, 15.38% (GW3 and GW7) had very poor water quality, and 15.38% (GW1 and GW5) were unsuitable for drinking. It should be noted that WQI may have been underestimated since some pollutants such as heavy metals (As, Cd, Hg, and Pb) which may be present were not considered.


### 3.6. Non-Cancer Risks Assessment

The non-cancer health risk on human health is evaluated through the calculation of the hazard quotient (HQ) and the hazard index (HI) assuming that HQ or HI > 1 signifies an acceptable level [54]. In this study, two age groups, namely, children and adults were considered for the calculation of HQ and HI of nitrate and fluorite. The HQ and HI values are depicted in Table 10. As it can be seen in Table 10, all the values of HQ and HI were <1, implying that the increased non-cancer risks due to nitrate and fluorite through the drinking of the groundwater from the study area were low. Nevertheless, a close perusal of Table 10 shows that the mean value of HI for children was about 1.6 times higher than that of HI for adults in both seasons.Table 10
Non-carcinogenic health risk assessment of water for children and adults via ingestion.
Season
Sample ID
Children
Adults
HQ
NO
3
−
HQ
F
−
HI
HQ
NO
3
−
HQ
F
−
HI
Long dry season
GW
1
4.94
E
−
03
3.70
E
−
02
4.20
E
−
02
2.96
E
−
03
2.22
E
−
02
2.52
E
−
02
GW
2
9.96
E
−
03
5.56
E
−
02
6.55
E
−
02
5.97
E
−
03
3.33
E
−
02
3.93
E
−
02
GW
3
2.38
E
−
02
2.78
E
−
02
5.16
E
−
02
1.43
E
−
02
1.67
E
−
02
3.10
E
−
02
GW
4
3.33
E
−
02
3.70
E
−
02
7.04
E
−
02
2.00
E
−
02
2.22
E
−
02
4.22
E
−
02
GW
5
2.80
E
−
02
4.63
E
−
02
7.43
E
−
02
1.68
E
−
02
2.78
E
−
02
4.46
E
−
02
GW
6
1.98
E
−
02
2.78
E
−
02
4.76
E
−
02
1.19
E
−
02
1.67
E
−
02
2.86
E
−
02
GW
7
5.63
E
−
02
1.85
E
−
02
7.48
E
−
02
3.38
E
−
02
1.11
E
−
02
4.49
E
−
02
GW
8
2.96
E
−
02
4.81
E
−
02
7.77
E
−
02
1.77
E
−
02
2.89
E
−
02
4.66
E
−
02
GW
9
9.22
E
−
02
2.78
E
−
02
1.20
E
−
01
5.53
E
−
02
1.67
E
−
02
7.20
E
−
02
GW
10
2.37
E
−
02
2.78
E
−
02
5.15
E
−
02
1.42
E
−
02
1.67
E
−
02
3.09
E
−
02
GW
11
1.87
E
−
02
6.48
E
−
02
8.35
E
−
02
1.12
E
−
02
3.89
E
−
02
5.01
E
−
02
GW
12
1.61
E
−
02
4.70
E
−
02
6.32
E
−
02
9.68
E
−
03
2.82
E
−
02
3.79
E
−
02
GW
13
2.67
E
−
02
7.41
E
−
02
1.01
E
−
01
1.60
E
−
02
4.44
E
−
02
6.05
E
−
02
Mean
2.95
E
−
02
4.15
E
−
02
7.10
E
−
02
1.77
E
−
02
2.49
E
−
02
4.26
E
−
02
Long wet season
GW
1
8.08
E
−
03
2.78
E
−
02
3.59
E
−
02
4.85
E
−
03
1.67
E
−
02
2.15
E
−
02
GW
2
1.25
E
−
03
5.56
E
−
02
5.68
E
−
02
7.53
E
−
04
3.33
E
−
02
3.41
E
−
02
GW
3
2.75
E
−
02
4.63
E
−
02
7.38
E
−
02
1.65
E
−
02
2.78
E
−
02
4.43
E
−
02
GW
4
6.25
E
−
02
9.07
E
−
02
1.53
E
−
01
3.75
E
−
02
5.44
E
−
02
9.19
E
−
02
GW
5
3.74
E
−
02
5.56
E
−
02
9.30
E
−
02
2.24
E
−
02
3.33
E
−
02
5.58
E
−
02
GW
6
2.70
E
−
02
3.70
E
−
02
6.40
E
−
02
1.62
E
−
02
2.22
E
−
02
3.84
E
−
02
GW
7
1.54
E
−
02
9.26
E
−
03
2.46
E
−
02
9.22
E
−
03
5.56
E
−
03
1.48
E
−
02
GW
8
1.07
E
−
02
1.85
E
−
02
2.92
E
−
02
6.40
E
−
03
1.11
E
−
02
1.75
E
−
02
GW
9
5.49
E
−
04
2.78
E
−
02
2.83
E
−
02
3.29
E
−
04
1.67
E
−
02
1.70
E
−
02
GW
10
1.14
E
−
02
1.85
E
−
02
3.00
E
−
02
6.87
E
−
03
1.11
E
−
02
1.80
E
−
02
GW
11
4.94
E
−
03
2.78
E
−
02
3.27
E
−
02
2.96
E
−
03
1.67
E
−
02
1.96
E
−
02
GW
12
9.96
E
−
03
2.78
E
−
02
3.77
E
−
02
5.97
E
−
03
1.67
E
−
02
2.26
E
−
02
GW
13
1.65
E
−
02
4.63
E
−
02
6.28
E
−
02
9.88
E
−
03
2.78
E
−
02
3.77
E
−
02
Mean
1.79
E
−
02
3.76
E
−
02
5.55
E
−
02
1.08
E
−
02
2.26
E
−
02
3.33
E
−
02


### 3.7. Suitability of Water for Agricultural Uses Based on SAR, EC, TDS, pH, TDS, and TSS

In the long dry season, SAR varied from 0.04 to 1.41 (mean 0.31) (Table4), while in the long wet season, it ranged from 0.00 to 0.18 (mean 0.11) (Table 5). All the SAR values of the water samples from the study area in both seasons were less than 10 and were, thus, graded as excellent for irrigation according to the classification of Richards [55] (Table 11).Table 11
Classification of water based on irrigation water quality parameters.
Parameter
Range
Description
SAR [55]
<10
Low (excellent)
10
−
18
Medium (good)
18
−
26
High (doubtful)
>26
Very high (unsuitable)
EC (μS/cm) [55]
0
−
250
Low (excellent quality)
251
−
750
Medium (good quality)
751−2,250
High (permissible quality)
>2,250
Very high (unfair)
TDS (mg/L) [51]
<1,000
Nonsaline
1,000−3,000
Slightly saline
3,000−10,000
Moderately saline
>10,000
Very salineSalty water in terms of TDS and EC reduces the yield of crops [56]. According to Richards [55] and van der Aa [51] classifications of water for irrigation based, respectively, on EC and TDS (Table 11), all (100%) the water samples were graded, respectively, as excellent quality and nonsaline for both seasons.According to Pescod’s classification [57] (Table 12), all (100%) the water samples had no restriction on their use in localized drip irrigation in both seasons with respect to pH and TDS. Following the same classification concerning TSS, 76.92% of the samples (GW2, GW3, GW4, GW6, GW8, GW9, GW10, GW11, GW12, and GW13) had no restriction on their use in localized drip irrigation in both seasons. 23.08% of groundwater samples (GW1, GW5, and GW7) had slight to moderate restriction on their use in localized drip irrigation in the long dry season, while 15.38% (GW1 and GW7) and 7.69% (GW5) of groundwater samples had, respectively, slight to moderate restriction and severe restriction on their use in localized drip irrigation in the long wet season. In addition, the acidic nature of groundwater from the study area imposes, for its transport, pipes that can withstand acid corrosion such as polyvinyl chloride (PVC) or polytetrafluoroethylene (PTFE) pipes.Table 12
Influence of water quality on clogging problems in the localized (drip) irrigation system [57].
Parameter
Range
Degree of restriction
pH
<7
None
7.0
−
8.0
Slight to moderate
>8.0
Severe
TDS (mg/L)
<500
None
500−2,000
Slight to moderate
<2,000
Severe
TSS (mg/L)
<50
None
50
−
100
Slight to moderate
>100
Severe


### 3.8. Suitability of Water for Poultry and Livestock Based on EC

Water with high salt content may cause temporary diarrhoea in livestock not accustomed to it, watery droppings in poultry, increased mortality, and decreased growth, especially in turkeys [56]. Following the classification of Ayes and Westcot [56] of water for poultry and livestock uses based on EC, all (100%) the water samples in this study were categorized as excellent for both seasons (Table 13).Table 13
Classification of water for poultry and livestock uses based on EC [56].
EC (μS/cm)
Description
Poultry
Livestock
<
1500
Excellent
Excellent
1,500−5,000
Very satisfactory
Very satisfactory
5,000−8,000
Unfit
Satisfactory
8,000−11,000
Unfit
Limited use
11,000−16,000
Unfit
Very limited use
>16,000
Not recommended
Not recommended


### 3.9. Suitability of Water for Cattle Rearing Based onNO3− and TDS

Water with high levels ofNO3− and TDS may be hazardous to cattle [58]. According to Higgins’ classification [58] of water for cattle based on these parameters, all (100%) the water samples in this study were declared safe for cattle rearing in both seasons (Table 14).Table 14
Classification of drinking water for cattle based onNO3− and TDS [58].
Parameter
Range
Description
NO
3
− (mg/L)
0
−
44
Safe
45
−
132
Safe with restrictions
133
−
220
Harmful
221
−
660
Risk of death
>661
Unsafe
TDS (mg/L)
<1,000
Safe
1,000−2,999
May cause mild diarrhoea
3,000−4,999
May cause diarrhoea
5,000−6,999
Unsafe to lactating or Pregnant cattle
7,000−10,000
Health problems
>10,000
Unsafe


## 3.1. Physicochemical Quality of Leachate

The physicochemical quality of the leachate is reported in Table2. From the long dry season to the long wet season, the pH and temperature fell slightly from 8.9 to 8.2 and 26.7 to 26.2°C, respectively. The pH remained within the safe range of 6.0−9.0, while the temperature dropped below the safe limit of 30°C set by MINEP [31] for effluent discharge. A similar pH value of 8.1 was found in leachate from Taiwan [32]. The pH values obtained indicate that the leachate samples were from an old cell since old leachate is characterized by a pH > 7.5 [33].Table 2
Physicochemical characteristics of the leachate from the Nkolfoulou landfill.
Parameter
Sampling period
Mean
SD
Percent decrease or increase (%)
Cameroonian effluent limits [31]
Long dry season
Long wet season
T (°C)
26.7
26.2
26.5
0.4
−1.87
30
pH
8.9
8.2
8.6
0.5
−8.54
6.0
−
9.0
EC (μS/cm)
23400
17500
20450
4172
−25.21
—
TDS (mg/L)
7800
7000
7400
566
−10.26
—
TSS (mg/L)
70.2
130.2
100.2
42.4
85.47
50
Turbidity (NTU)
14.2
21.3
17.8
5.0
50.0
—
TH (mg/L)
424.56
349.64
387.10
52.97
−17.65
—
TA (mg·CaCO3/L)
748.04
558.09
653.06
134.31
−25.39
—
BOD
5 (mg·O2/L)
100
140
120
29
40.00
100
COD (mg·O2/L)
1350
1750
1550
283
29.63
200
BOD
5/COD
0.07
0.08
0.08
0.00
8.00
—
Na
+ (mg/L)
465.24
200.62
332.93
187.11
−56.88
—
K
+ (mg/L)
350.75
231.45
291.10
84.36
−34.01
—
Mg
2
+ (mg/L)
75.23
60.13
67.68
10.68
−20.07
—
Ca
2
+ (mg/L)
45.96
40.86
43.41
3.61
−11.10
—
NH
4
+ (mg/L)
82.5
39.51
61.01
30.40
−52.11
0.1
NO
3
− (mg/L)
159.32
74.82
117.07
59.75
−53.04
20
Cl
− (mg/L)
702.69
345.50
524.10
252.57
−50.83
50
F
− (mg/L)
3.48
2.50
2.99
0.69
−28.16
—
PO
4
3
−
mg/L
ND
ND
—
—
—
3
SO
4
2
−
mg/L
50.24
10.60
30.42
28.03
−78.90
—
HCO
3
− (mg/L)
923.50
689.00
806.25
165.82
−25.39
—
Colour (mg/L pt-Co)
5208.33
4654.75
4931.54
391.44
−10.63
—
Appearance
Dark-brown
Brown
—
—
—
Colourless
Odour
Pungent
Pungent
—
—
—
Odourles
ND = not detected; SD = standard deviation.During the long dry and long wet seasons, respectively, the values ofBOD5 (100; 140 mg·O2/L), COD (1,350; 1,750 mg·O2/L), and TSS (70.2; 130.2 mg/L) were all found to be higher than the regulatory limits for the effluent discharge set by MINEP [31] (Table 2). During this same period, leachate had a biodegradability ratio (BOD5/COD) of 0.07 and 0.08, respectively. This implies that the leachate was from an old cell since a ratio of BOD5/COD < 0.1 is typical of leachate from an old landfill (>10 years) [7, 33]. Again, during this same period, the concentration of NH4+ (82.5; 39.51 mg/L), NO3− (159.32; 74.82 mg/L), and Cl− (702.69; 345.50 mg/L) was all superior to the safe limits for effluent discharge stated by MINEP [31] (Table 2). Ammonia-nitrogen in leachate may originate from the catabolism of protein-rich compounds [7, 34, 35]. NH4+ is produced during ammonification [35] and can thereafter be partially transformed into NO3− by the anaerobic ammonium oxidation process (ANAMMOX) as shown in equation (13). It can also be transformed into NO3− under aerobic conditions through nitrification [35], while leachate stagnates or flows on the ground:(13)NH4++1.26NO2−+0.085CO2+0.02H+⟶N2+0.017H++0.24NO3−+1.95H2OPO43− was not detected in any of the seasons, while SO42− concentration dropped from 50.24 to 10.60 mg/L. SO42− found in leachate may be the result of the oxidation of H2S [36], while the absence of PO43− might be due to its coprecipitation by Mg2+ and NH4+ to form magnesium ammonium phosphate (MAP) hexahydrate known as struvite as shown in the following equation [37]:(14)Mg2++PO43−+NH4++6H2O⟶MgNH4PO4.6H2OIn both seasons, leachate had a dark-brownish colour ranging from 5208.33 to 4654.75 mg/L Pt-Co with an offensive pungent smell. In a similar study [38], the values were in the range of 955–15.142 mg/L Pt-Co for an old leachate. The dark brown colour of the leachate may be due to the presence of FeS and PbS formed, respectively, by the reaction of iron and lead with hydrogen sulfide. It may also be due to the presence of MnO resulting from the oxidation of manganese in air. The pungent odour of the leachate is attributable to the presence of either NH3, H2S, CH3SH, and volatile fatty acids (VFAs) or putrescine and cadaverine from the putrefaction of wastes from the abattoirs.Comparatively, the average physicochemical characteristics of the leachate samples collected in this work from the Nkolfoulou landfill differ from those observed elsewhere (Table3). This may be due to the differences in waste composition, meteorological conditions, waste age, and landfilling technology [6, 7]. As observed in Table 3, all comparable parameters were in the typical range stated by Christensen et al. [6] except for TSS which was much lower, more likely as a result of the soil type on which the leachate leaks or runs.Table 3
Landfill leachate characteristics of other countries in comparison with the present study.
Parameter
Typical range [6]
Country (landfill site)
India (Jamalpur) [39]
Spain (Marbella) [40]
Nigeria (Aba-Eku) [41]
Cameroon (Nkolfoulou) (this study)
T (°C)
—
—
22.2
—
26.5
pH
4.5
−
9
9.8
8.21
8.21
8.6
EC (μS/cm)
2,500−35,000
—
24195
2466
20450
TDS (mg/L)
—
6563
—
—
7400
TSS (mg/L)
2,000−60,000
7695
—
144.94
100.2
Turbidity (NTU)
—
79
—
—
17.8
TH (mg/L)
—
638
—
—
387.10
TA (mg·CaCO3/L)
—
—
8789.3
—
653.06
BOD
5 (mg·O2/L)
20−57,000
495
—
—
120
COD (mg·O2/L)
140−152,000
2535
—
57.63
1550
BOD
5
/
COD
0.02−0.80
0.19
—
—
0.08
Na
+ (mg/L)
70−7,700
—
2768.1
—
332.93
K
+ (mg/L)
50−3,700
—
1553
—
291.10
Mg
2
+ (mg/L)
30−15,000
—
189.2
83.55
67.68
Ca
2
+ (mg/L)
10.0−7,200
—
148.6
86.4
43.41
NH
4
+ (mg/L)
—
—
3248.7
3.55
61.01
NO
3
− (mg/L)
—
18.6
555.7
12.37
117.07
Cl
− (mg/L)
150−4,500
1836
4652.7
597.98
524.10
F
− (mg/L)
—
—
—
—
2.99
PO
4
3
− (mg/L)
—
—
—
ND
ND
SO
4
2
− (mg/L)
8.0−7,750
65.1
419.2
118.86
30.42
HCO
3
− (mg/L)
610−7,320
—
—
—
806.25
Colour (mg/L Pt-Co)
—
—
—
—
4931.54
Appearance
—
Brownish
—
—
Dark brownish
Odour
—
Sewage smell
—
—
Pungent
ND = not detected.Seasonal variation of the levels of nutrients as well as the pH, EC, TDS, TA, TH, and colour exhibited a decreasing trend with percent decrease ranging from−1.87% (EC) to −78.90% (SO42−) in going from the long dry season to the long wet season. This decrease is attributable to the dilution of leachate by runoff or rain water. In contrast, the increase in TSS and turbidity as well as BOD5 and COD in the long wet season could be due to runoff that brings solid particles and organic matter to the leachate. Seasonal variation in major ion concentrations is illustrated by the Stiff diagram (Figure 2) in which the shapes of polygons differ from season to season implying that the leachate composition varies according to the season. In the leachate samples, the trends in the cation concentrations were in the order Na+ > K+ > NH4+ > Mg2+ > Ca2+ in the long dry season and Na+ > K+ > Mg2+ > Ca2+ > NH4+ in the long wet season while that of the anions was HCO3− > Cl− > NO3− > SO42− > F− > PO43− in both seasons.Figure 2
Stiff plot of landfill leachate quality.


## 3.2. Groundwater Quality

The physicochemical quality of groundwater in both seasons is displayed in Tables4 and 5. During the long dry season, the groundwater temperatures were in the range 23.3−23.6°C (mean 23.5°C), while during the long wet season, the range was 23.0−23.5°C (mean 23.3°C). All the temperature values for both seasons were lower than 25°C, which is the standard limit according to Cameroonian regulations [42] for drinking water.Table 4
Physicochemical characteristics of groundwater in the long dry season.
Parameter
Sampling point
Mean
SD
GW
1
GW
2
GW
3
GW
4
GW
5
GW
6
GW
7
GW
8
GW
9
GW
10
GW
11
GW
12
GW
13
T (°C)
23.5
23.4
23.5
23.4
23.6
23.5
23.3
23.4
23.4
23.5
23.4
23.5
23.5
23.5
0.08
pH
5.8
6.1
5.3
5.6
5.4
5.3
5.2
5.2
5.4
5.6
5.9
6.0
5.9
5.6
0.32
EC (μS/cm)
100
100
40
30
110
90
30
30
130
100
80
30
100
75
37
TDS (mg/L)
40
40
20
10
50
40
10
10
60
40
40
10
40
32
17
Turbidity (NTU)
8.3
0.7
1.3
1.3
12.6
0.9
9.4
0.7
3.2
2.2
4.6
0.8
3.3
3.8
3.9
TSS (mg/L)
59.43
5.00
9.29
9.29
90.00
6.43
67.14
5.00
22.86
15.71
32.5
7.00
23.21
27.14
27.75
TH (mg/L)
26.00
24.09
26.89
33.64
34.21
21.51
16.42
39.45
49.16
36.84
16.02
32.61
22.01
29.14
9.61
TA (mg·CaCO3/L)
33.3
23.8
29.3
28.5
38.0
19.0
28.5
36.1
90.3
47.6
19.0
33.3
23.8
34.7
18.5
Na
+ (mg/L)
2.54
2.42
1.90
0.48
0.48
0.53
6.97
2.67
22.83
5.66
1.84
2.59
1.93
4.07
5.95
K
+ (mg/L)
2.29
1.86
1.52
1.55
2.70
0.70
3.90
2.58
5.71
2.60
2.01
2.71
1.88
2.46
1.24
Mg
2
+ (mg/L)
2.87
3.03
1.12
0.66
3.80
0.20
2.34
3.40
6.05
0.61
2.35
3.36
2.27
2.47
1.59
Ca
2
+ (mg/L)
5.69
4.65
8.92
12.39
7.43
8.29
2.72
10.19
9.71
13.75
2.54
7.52
5.07
7.61
3.44
NH
4
+ (mg/L)
0.12
0.03
0.02
ND
0.02
0.02
0.51
0.22
0.26
0.05
0.07
0.29
0.08
0.14
0.15
NO
3
− (mg/L)
0.63
1.27
3.04
4.25
3.57
2.53
7.18
3.77
11.76
3.02
2.38
2.06
3.41
3.76
2.88
F
− (mg/L)
0.04
0.06
0.03
0.04
0.05
0.03
0.02
0.05
0.03
0.03
0.07
0.05
0.08
0.04
0.02
Cl
− (mg/L)
0.22
0.67
0.51
0.42
0.34
0.52
0.45
1.80
0.95
3.72
1.26
1.81
0.53
1.02
0.97
SO
4
2
− (mg/L)
0.17
3.26
1.21
1.77
0.73
0.48
0.87
3.22
0.24
0.61
0.87
1.61
1.54
1.28
1.01
PO
4
3
− (mg/L)
ND
0.03
ND
ND
ND
0.01
0.02
ND
ND
ND
ND
ND
ND
0.02
0.01
HCO
3
− (mg/L)
40.6
29.0
35.7
34.8
46.4
23.2
34.8
44.0
110.1
58.0
23.2
40.6
29.0
42.3
22.6
WQI
69.27
14.40
19.02
16.61
87.59
17.10
114.50
36.65
53.44
26.39
43.43
40.16
36.92
44.27
30.28
SAR
0.22
0.21
0.16
0.04
0.04
0.05
0.75
0.18
1.41
0.41
0.20
0.20
0.18
0.31
0.38
ND = not detected; SD = standard deviation.Table 5
Physicochemical characteristics of groundwater in the long wet season.
Parameter
Sampling point
Mean
SD
GW
1
GW
2
GW
3
GW
4
GW
5
GW
6
GW
7
GW
8
GW
9
GW
10
GW
11
GW
12
GW
13
T (°C)
23.1
23.0
23.4
23.3
23.5
23.0
23.3
23.3
23.2
23.4
23.5
23.0
23.4
23.3
0.2
pH
6.1
6.2
5.8
5.9
6.1
6.2
6.4
6.1
6.3
5.9
6.4
6.3
6.1
6.1
0.2
EC (μS/cm)
30
80
50
40
30
50
30
20
150
50
50
30
50
51
34
TDS (mg/L)
10
40
20
10
10
20
10
10
70
200
20
10
20
35
53
Turbidity (NTU)
8.23
0.7
1.4
1.2
14.53
1.1
7.45
0.7
4.6
2.1
6.31
0.8
2.38
3.96
4.16
TSS (mg/L)
58.79
5.00
10.00
8.57
103.79
7.86
53.21
5.00
32.86
15.00
45.07
7.00
17.00
28.40
29.63
TH (mg/L)
24.73
20.37
34.21
44.90
42.16
23.02
13.80
22.75
31.91
31.12
11.14
22.53
14.40
25.93
10.47
TA (mg·CaCO3/L)
28.5
23.8
38.0
53.3
42.8
23.8
19.0
23.8
35.0
33.3
14.3
27.5
19.0
29.39
10.86
Na
+ (mg/L)
0.85
1.32
2.31
0.97
1.26
1.03
1.56
1.06
0.03
0.90
1.26
1.31
1.42
1.18
0.51
K
+ (mg/L)
2.11
1.63
2,65
8.44
2.86
1.23
1.20
1.50
1.27
1.41
1.75
2.41
1.45
2.30
1.93
Mg
2
+ (mg/L)
4.06
2.29
1.90
1.36
4.58
0.55
2.03
0.61
0.73
1.55
1.83
2.28
2.01
1.98
1.20
Ca
2
+ (mg/L)
3.21
4.38
10.57
15.74
9.34
8.32
2.18
8.11
11.58
9.90
1.45
5.26
2.45
7.11
4.34
NH
4
+ (mg/L)
0.50
ND
0.73
0.40
0.10
0.03
0.31
ND
0.02
0.14
ND
0.06
0.05
0.23
0.24
NO
3
− (mg/L)
1.03
0.16
3.51
7.97
4.77
3.44
1.96
1.36
0.07
1.46
0.63
1.27
2.10
2.29
2.19
F
− (mg/L)
0.03
0.06
0.05
0.10
0.06
0.04
0.01
0.02
0.03
0.02
0.03
0.03
0.05
0.04
0.02
Cl
− (mg/L)
0.37
0.21
0.85
0.91
0.51
0.72
0.31
0.73
0.15
0.39
0.37
0.55
0.32
0.49
0.24
SO
4
2
− (mg/L)
0.25
1.97
1.24
3.60
1.08
0.79
0.11
0.3
0.03
0.21
0.07
0.35
0.14
0.78
1.02
PO
4
3
− (mg/L)
ND
ND
0.02
ND
0.01
0.03
0.01
ND
0.02
0.01
ND
ND
ND
0.02
0.01
HCO
3
− (mg/L)
34.8
29.0
46.4
64.96
52.2
29.0
23.2
29.0
42.7
40.6
17.4
33.5
23.2
35.84
13.24
WQI
103.16
11.53
86.59
56.59
104.08
15.50
78.13
9.98
35.00
32.28
42.69
16.21
26.22
47.53
34.66
SAR
0.07
0.13
0.17
0.06
0.08
0.09
0.18
0.10
0.00
0.07
0.16
0.12
0.16
0.11
0.05
ND = not detected; SD = standard deviation.The pH of groundwater samples varied from 5.2 to 6.1 (mean 5.6) during the long dry season and 5.8 to 6.4 (mean 6.1) during the long wet season. These pH ranges are lower than7.02−7.85 recorded by Mor et al. [8] for groundwater around a landfill in Delhi (India). For both seasons, the pH values were outside the safe ranges of 6.5–9.5, 6.5–8.5, and 6.5–9.0 set, respectively, by EU [43], EPA [18], and Cameroonian standards [42] (Table 6) for drinking water.Table 6
Water guidelines for drinking and agricultural uses.
Parameter
Guidelines for drinking water
EU [43]
EPA [18]
MINDIC [42]
WHO [14]
T (°C)
—
—
25
—
pH
6.5−9.5
6.5−8.5
6.5−9.0
—
EC (μS/cm)
2,500
—
1,000
—
TDS (mg/L)
—
500
—
1,000
Turbidity (NTU)
—
—
2
1
γ
TSS (mg/L)
—
—
1,500
—
TH (mg/L)
—
—
—
—
TA (mg·CaCO3/L)
—
—
—
—
Na
+ (mg/L)
200
—
150
200
∗
K
+ (mg/L)
—
—
12
—
Mg
2
+ (mg/L)
—
—
50
—
Ca
2
+ (mg/L)
—
—
—
100
−
300
∗
NH
4
+ (mg/L)
0.5
—
0.5
35
∗
NO
3
− (mg/L)
50
45
50
50
F
− (mg/L)
1.5
4
0.7
1.5
Cl
− (mg/L)
250
250
200
250
∗
SO
4
2
− (mg/L)
250
—
250
250
∗
PO
4
3
− (mg/L)
—
—
—
—
HCO
3
− (mg/L)
—
—
—
—
γDisinfection effectiveness; ∗taste consideration.During the long dry and long wet seasons, the EC values were, respectively, in the range 30–130μS/cm (mean 76 μS/cm) and 20–150 μS/cm (mean 49 μS/cm), while the TDS values were in the range 10–60 mg/L (mean 32 mg/L) and 10–70 mg/L (mean 21 mg/L). As can be observed, the EC and TDS values are several folds lower than 12,745 μS/cm and 9,895 mg/L, respectively, as reported by El-Salam and Abu-Zuid [11] for groundwater near a landfill in Alexandria (Egypt). With respect to drinking water, the EC and TDS values complied with the standards set by regulatory bodies [14, 18, 42, 43] (Table 6).During the long dry and long wet seasons, the turbidity values registered were, respectively, between 0.70 and 12.60 NTU (mean 4.55 NTU) and 0.70 and 14.5 NTU (mean 4.50 NTU), whereas the TSS values were between 5.00 and 90.00 mg/L (average 32.44 mg/L) and 5.00 and 103.79 mg/L (average 31.89 mg/L). Comparatively, Han et al. [44] reported high values in the range 0.1−17.2 NTU in groundwater near a landfill at Zhoukou (China). All the recorded TSS values were lower than the recommended maximum limit set by MINDIC for drinking water [42] (Table 6). In the long dry season, GW2, GW6, GW8, and GW12 wells representing 30.76% of the samples and GW2, GW8, and GW12 wells in the long wet season representing 23.07% of the samples had turbidity less than 1 NTU which is within the standard limit for drinking water disinfection effectiveness laid down by WHO [14]. Higher turbidity can seriously interfere with the efficiency of disinfection by providing protection for organisms [14].During the long dry and long wet seasons, the TH values increased, respectively, from 16.02 to 49.16 mg/L (average 26.14 mg/L) and 11.14 to 44.90 mg/L (average 25.93 mg/L), while the TA values increased from 19.02 to 90.28 mg/L (mean 34.66 mg/L) and 14.27 to 53.27 mg/L (mean 29.39 mg/L). These TH and TA values were, respectively, lower than those of296−1388 mg/L and 230−734 mg/L recorded by Mor et al. [8] for groundwater near the Gazipur landfill (India).During the long dry season, the concentration ofNa+, K+, Mg2+, and Ca2+ fluctuated, respectively, between 0.48 and 22.83 mg/L (mean 4.07 mg/L), 0.70 and 5.71 mg/L (mean 2.46 mg/L), 0.20 and 6.05 mg/L (mean 2.47 mg/L), and 2.54 and 13.75 mg/L (mean 7.61 mg/L) while in the long wet season, they ranged from 0.03 to 2.31 mg/L (mean 1.18 mg/L), 1.20 to 8.44 mg/L (mean 2.30 mg/L), 0.55 to 4.58 mg/L (mean 1.98 mg/L), and 1.45 to 15.74 mg/L (mean 7.11 mg/L), respectively. The average values of Na+, K+, Mg2+, and Ca2+ obtained in this work are lower than 23.75, 11.17, 84.6, and 360 mg/L, respectively, reported by Singh et al. [45] for groundwater around the Pirana landfill in Ahmedabad (India). In this study, all the concentrations of Na+ obtained were many folds lower than the maximum limits stated by the regulatory bodies [14, 42, 43] for drinking water (Table 6). In both seasons, the levels of K+ and Mg2+ were lower than the permissible limits laid down by MINDIC [42] for drinking water (Table 6).In the long dry and long wet seasons, theNH4+ levels were observed, respectively, between ND (non detected) and 0.51 mg/L (mean 0.14 mg/L) and ND and 0.73 mg/L (mean 0.23 mg/L), while the NO3− values varied from 0.63 to 11.76 mg/L (mean 3.76 mg/L) and 0.07 to 7.97 mg/L (mean 2.29 mg/L). Comparatively, high values of NH4+ in the range ND–4.3 mg/L were reported by Mor et al. [8] for groundwater near the Gazipur landfill in India, while, for NO3−, a mean value of 49.90 mg/L higher than those found in this study was recorded by Singh et al. [45] for groundwater at the vicinity of the Pirana landfill also in India. In the study area, the NH4+ in the groundwater might have originated from the leachate or leaked from the septic tank. The NH4+ values registered in the long dry season at GW7 (0.51 mg/L) and in the long wet season at GW3 (0.73 mg/L) exceeded both the EU [43] and MINDIC [42] standards for drinking water (Table 6). However, it has been recently substantiated that the additional exposure to NH4+ from water in the concentration range of 0.5−5 mg/L is negligible and thus does not pose a risk to human health [46]. NH4+ in drinking water may have resulted from the protonation of NH3 given the acidic nature (pH < 6.5) of the water. The values of NO3− in both seasons were lower than the threshold set by EU [43], EPA [18], and MINDIC [42] for drinking water (Table 6).During the long dry season, theF−, Cl− and SO42− values were, respectively, between 0.02 and 0.08 mg/L (average 0.04 mg/L), 0.22 and 3.72 mg/L (average 1.02 mg/L), and 0.17 and 3.26 mg/L (average 1.28 mg/L), while in the long wet season, they were, respectively, between 0.01 and 0.10 mg/L (mean 0.04 mg/L), 0.15 and 0.91 mg/L (mean 0.49 mg/L), and 0.03 and 3.60 (mean 0.78 mg/L). The mean average values of F−, Cl−, and SO42− are, respectively, several orders of magnitude lower than 0.67, 253.94, and 96.94 mg/L recorded by Pujari and Deshpande [47] for groundwater around a landfill in Nagpur (India). As far as F−, Cl−, and SO42− were concerned, groundwater sources were fit for drinking for both seasons since their concentrations were lower than the prescribed limits set by EU [43], EPA [18], MINDIC [42], and WHO [14] (Table 6).PO
4
3
− was barely detected in the three wells (GW2, GW6, and GW7) during the long dry season and in six wells (GW3, GW5, GW6, GW7, GW9, and GW10) during the long wet season with concentrations ranging slightly from 0.01 to 0.03 mg/L in both seasons. The concentrations of HCO3− increased from 23.20 to 110.10 (mean 42.26 mg/L) in the long dry season and from 17.40 to 64.96 mg/L (mean 35.84 mg/L) in the long wet season. The mean values of PO43− and HCO3− are, respectively, lower than 0.29 mg/L and 391.8 mg/L reported for groundwater around the Pirana landfill in Ahmedabad (India) [45]. PO43− was not detected in the leachate samples, so its occurrence in some groundwater samples in the study area may be attributed to anthropogenic activities such as domestic waste discharge and agriculture. In groundwater, HCO3− may have originated from the dissolution of atmospheric CO2 and carbonate minerals [8] or from sulfate reduction of organic compounds in the aquifer as represented in the following equation [48]:(15)2CH2O+SO42−⟶H2S+2HCO3−According to Piper’s diagram [49] (Figure 3), the hydrochemical facies of groundwater in the study area were of the Ca-Mg-HCO3− (84.62%) and Na-K-HCO3− (15.38%) types in the long dry season, while in the long wet season, all the groundwater samples were of the Ca-Mg-HCO3− type (100%).Figure 3
Piper diagram showing the hydrochemical composition of groundwater around the Nkolfoulou landfill: (a) long dry season; (b) long wet season.
(a)
(b)


## 3.3. Statistical Correlation

The correlation matrices for 19 measured variables during the long dry and long wet seasons are illustrated in Table7. The perfect positive correlation between TSS and turbidity (r = 1, p≤0.01) in both seasons means that they have exactly the same contributor which could be mud brought in by the infiltrating rain water. The strong positive correlation between EC and TDS (r = 0.98, p≤0.01) in the dry season signifies that they have nearly the same contributors (the dissolved ions). At the 0.05 p level, a significant negative correlation was observed only between the temperature and NH4+ (r =  −0.57) in the long dry season, while for the long wet season, it was registered between pH and NH4+ (r =  −0.57), between pH and Ca2+ (r =  −0.62), between pH and Cl− (r =  −0.58), and between pH and HCO3− (r =  −0.66) indicating the opposing distribution of these pair variables. In both seasons, the depth of the wells exhibited no significant correlation with any of the variables in the matrices except for SO42− with a significant positive correlation (r = 0.78, p≤0.01) in the long dry season. In the long dry season, there was a significant positive correlation between pH and F− (r = 0.68), Na+ and Mg2+ (r = 0.64), NH4+ and K+ (r = 0.68), and Mg2+ and HCO3− (r = 0.66) at the 0.05 p level, while at the 0.01 p level, there was a significant positive correlation between Na+ and K+ (r = 0.89), Na+ and NO3− (r = 0.87), Na+ and HCO3− (r = 0.91), K+ and Mg2+ (r = 0.78), K+ and NO3− (r = 0.83), K+ and HCO3− (r = 0.84), and NO3− and HCO3− (r = 0.77).Table 7
Correlation matrix.
pH
T
EC
TDS
TSS
Turbidity
Na
+
NH
4
+
K
+
Mg
2
+
Ca
2
+
F
−
Cl
−
NO
3
−
PO
4
3
−
SO
4
2
−
HCO
3
−
Depth
Distance
LDS
pH
1
T
0.12
1
EC
0.231
0.372
1
TDS
0.17
0.369
0.984
∗∗
1
TSS
−0.185
0.170
0.251
0.262
1
Turbidity
−0.187
0.167
0.256
0.267
1.00
∗∗
1
Na
+
−0.219
−0.349
0.374
0.397
0.006
0.007
1
NH
4
+
−0.257
−
0.572
∗
−0.35
−0.363
0.235
0.23
0.463
1
K
+
−0.223
−0.349
0.219
0.231
0.306
0.304
0.891
∗∗
0.677
∗
1
Mg
2
+
0.066
−0.106
0.332
0.349
0.282
0.279
0.642
∗
0.430
0
.
779
∗∗
1
Ca
2
+
−0.323
0.254
−0.06
−0.081
−0.417
−0.418
0.139
−0.311
−0.001
−0.219
1
F
−
0.678
∗
0.169
0.183
0.167
−0.084
−0.081
−0.361
−0.324
−0.299
0.157
−0.404
1
Cl
−
0.074
0.048
−0.018
−0.052
−0.354
−0.356
0.128
0.041
0.131
−0.119
0.500
−0.073
1
NO
3
−
−0.494
−0.435
0.13
0.178
0.115
0.117
0.870
∗∗
0.516
0.829
∗∗
0.513
0.148
−0.403
−0.054
1
PO
4
3
−
0.121
−0.469
0.005
−0.046
−0.022
−0.021
−0.038
0.201
−0.048
−0.045
−0.449
−0.087
−0.237
−0.056
1
SO
4
2
−
0.214
−0.29
−0.409
−0.461
−0.484
−0.484
−0.32
−0.051
−0.255
0.033
0.004
0.419
0.065
−0.270
0.372
1
HCO
3
−
−0.253
−0.051
0.409
0.423
0.043
0.041
0.910
∗∗
0.273
0.843
∗∗
0.655
∗
0.424
−0.368
0.246
0.771
∗∗
−0.282
−0.314
1
Depth
0.159
−0.11
−0.359
−0.402
−0.415
−0.422
−0.118
0.201
−0.014
0.296
0.049
0.150
0.180
−0.214
0.309
0.779
∗∗
−0.057
1
Distance
−
0.582
∗
−
0.654
∗
−0.371
−0.395
0.05
0.05
0.243
0.701
∗∗
0.349
0.113
−0.098
−0.458
−0.012
0.420
0.520
0.259
0.073
0.321
1
LWS
pH
1
T
−0.263
1
EC
0.192
−0.169
1
TDS
−0.287
0.148
0.315
1
TSS
0.25
0.413
−0.129
−0.177
1
Turbidity
0.246
0.417
−0.127
−0.175
1.00
∗∗
1
Na
+
−0.264
0.251
−0.537
−0.322
−0.078
−0.079
1
NH
4
+
−
0.574
∗
0.141
−0.247
−0.147
0.058
0.060
0.466
1
K
+
−0.459
0.115
−0.191
−0.224
−0.083
−0.083
0.013
0.392
1
Mg
2
+
−0.036
0.149
−0.349
−0.217
0.747
∗∗
0.744
∗∗
0.217
0.265
0.049
1
Ca
2
+
−0.621∗
0.085
0.239
0.241
−0.202
−0.200
−0.254
0.237
0.610
∗
−0.300
1
F
−
−0.473
0.045
0.02
−0.265
−0.090
−0.088
0.103
0.213
0.815
∗∗
0.133
0.518
1
Cl
−
−
0.584
∗
0.083
−0.503
−0.294
−0.310
−0.310
0.379
0.431
0.593
∗
−0.211
0.560
∗
0.429
1
NO
3
−
−0.537
0.258
−0.354
−0.252
0.065
0.067
0.208
0.405
0.833
∗∗
0.07
0.626
∗
0.748
∗∗
0.736
∗∗
1
PO
4
3
−
−0.080
−0.096
0.374
0.178
−0.007
−0.005
−0.043
0.12
−0.257
−0.326
0.371
−0.131
0.153
0.105
1
SO
4
2
−
−0.480
−0.091
−0.064
−0.196
−0.226
−0.224
0.136
0.302
0.853
∗∗
0.001
0.583
∗
0.903
∗∗
0.524
0.741
∗∗
−0.120
1
HCO
3
−
−
0.656
∗
0.142
0.073
0.100
0.091
0.092
−0.129
0.441
0.760
∗∗
0.151
0.879
∗∗
0.663
∗
0.487
0.728
∗∗
0.142
0.677
∗
1
Depth
0.124
−0.519
−0.122
−0.200
−0.410
−0.415
0.075
−0.317
−0.111
−0.125
−0.041
−0.076
0.106
−0.271
−0.303
0.092
−0.126
1
Distance
0.358
−0.200
−0.059
−0.106
−0.079
−0.077
−0.045
−0.146
−0.263
−0.381
−0.080
−0.428
−0.054
−0.138
0.174
−0.146
−0.273
0.321
1
LDS = long dry season; LWS = long wet season.∗Correlation is significant at the 0.05 level; ∗∗correlation is significant at the 0.01 level.In the long wet season, there was a significant positive correlation betweenK+ and Ca2+ (r = 0.61), K− and Cl− (r = 0.59), Ca2+ and Cl− (r = 0.56), Ca2+ and NO3− (r = 0.63), Ca2+ and SO42− (r = 0.58), F− and HCO3− (r = 0.66), and SO42− and HCO3− (r = 0.68) at the 0.05 p level, whereas at the 0.01 p level, there was a significant positive correlation between Mg2+ and TSS (r = 0.75), Mg2+ and turbidity (r = 0.74), K+ and F− (r = 0.82), K+ and NO3− (r = 0.83), K+ and SO42− (r = 0.85), K+ and HCO3− (r = 0.76), Ca2+ and HCO3− (r = 0.88), F− and NO3− (r = 0.75), F− and SO42− (r = 0.90), Cl− and NO3− (r = 0.74), NO3− and SO42− (r = 0.74), and NO3− and HCO3− (r = 0.73).The distance between the wells and the landfill barely exhibited significant negative correlation with pH (r =  −0.58, p≤0.05) and temperature (r =  −0.65, p≤0.05), implying that the landfill may not be the main source of the major ions in the nearby groundwater. The strong positive correlations observed between the various ions in both seasons imply that they may have common sources (weathering of rocks, septic tanks, pit latrines, domestic effluent, and agricultural activities), which contribute to the ion input in the groundwater in the area.


## 3.4. Seasonal Variation of Groundwater Quality

Although thet-test is usually applied on larger sample sizes, it can be used for small sample sizes (N≤5), as long as the effect sample size is large [50]. The t-test was performed to check the significance of the seasonal variation of the mean value of the parameters assessed. Results of this test are summarized in Table 8. The resulting p values were compared with the significance level, α = 0.05. The seasonal variation of parameters was statistically significant only for pH (p≤0.001), T (temperature) (p=0.004), and EC (p=0.021) (Table 8), whereas it was insignificant for the remaining data pairs representing 84.21% as p>α. It can therefore be inferred that the change in groundwater quality from the dry season to the wet season was generally insignificant within a 95% confidence limit.Table 8
Student’st-test.
Paired variable
N
Descriptive statistics
Paired differences
t
df
p value
Dry season
Wet season
95% confidence interval of the difference
Mean (SD)
Mean (SD)
Lower
Upper
pH (d)-pH (w)
13
5.592 (0.317)
6.139 (0.189)
−0.752
−0.340
−5.781
12
0.000
T (d)-T (w)
13
26.454 (0.078)
26.262 (0.185)
0.075
0.309
3.584
12
0.004
EC (d)-EC (w)
13
74.615 (36.882)
50.769 (33.531)
4.337
43.356
2.663
12
0.021
TDS (d)-TDS (w)
13
31.539 (17.246)
34.615 (52.538)
−32.925
26.771
−0.225
12
0.826
TSS (d)-TSS (w)
13
27.143 (27.748)
28.396 (29.632)
−5.749
3.243
−0.607
12
0.555
Turb (d)-turb (w)
13
3.792 (3.894)
3.962 (4.160)
−0.797
0.459
−0.587
12
0.568
TH (d)-TH (w)
13
29.142 (9.608)
25.926 (10.472)
−2.093
8.525
1.320
12
0.211
TA (d)-TA (w)
13
34.654 (18.509)
29.392 (10.856)
−5.748
16.271
1.041
12
0.318
Na
+ (d)-Na+ (w)
13
4.065 (5.949)
1.175 (0.510)
−0.906
6.685
1.659
12
0.123
NH
4
+ (d)-NH4+ (w)
13
0.130 (0.150)
0.180 (0.234)
−0.224
0.124
−0.626
12
0.543
K
+ (d)-K+ (w)
13
2.462 (1.243)
2.301 (1.926)
−1.386
1.709
0.227
12
0.824
Mg
2
+(d)-Mg2+(w)
13
2.466 (1.594)
1.983 (1.203)
−0.611
1.577
0.962
12
0.355
Ca
2
+ (d)-Ca2+ (w)
13
7.605 (3.444)
7.115 (4.338)
−0.824
1.805
0.813
12
0.432
F
− (d)-F− (w)
13
0.045 (0.018)
0.041 (0.024)
−0.012
0.020
0.534
12
0.603
Cl
− (d)-Cl− (w)
13
1.015 (0.968)
0.492 (0.244)
−0.091
1.138
1.857
12
0.088
NO
3
− (d)-NO3− (w)
13
3.759 (2.879)
2.287 (2.194)
−0.783
3.727
1.423
12
0.180
PO
4
3
− (d)-PO43− (w)
13
0.005 (0.010)
0.008 (0.010)
−0.011
0.005
−0.805
12
0.436
SO
4
2
− (d)-SO42−(w)
13
1.275 (1.006)
0.780 (1.025)
−0.192
1.183
1.569
12
0.143
HCO
3
− (d)-HCO3− (w)
13
42.264 (22.562)
35.843 (13.239)
−6.993
19.835
1.043
12
0.318
d = dry season; w = wet season; turb = turbidity. Bolded figures indicate significant difference.In the groundwater samples, the order of abundance of cations wasCa2+ > Na+ > Mg2+ > K+ > NH4+ in the long dry season and Ca2+ > K+ > Mg2+ > Na+ > NH4+ in the long wet season while that of anions was HCO3− > NO3− > SO42− > Cl− > F− > PO43− in both seasons.


## 3.5. Drinking Water Suitability Based on TDS, TH, and WQI

Following the classification of van der Aa [51] of drinking water based on TDS (Table 9), apart from the GW5 and GW9 wells in the long dry season and the GW9 and GW10 wells in the long wet season, the remaining wells, representing 84.61% of the samples in both seasons, had very low mineral concentrations. According to the same classification, 15.38% of the samples in the long dry season (GW5 and GW9) and in the long wet season (GW9 and GW10) had low mineral concentrations.Table 9
Classification of drinking water based on TDS, TH, and WQI.
Parameter
Range
Description
TDS (mg/L) [51]
<
50
Very low mineral c
50
−
500
Low mineral c
500−1,500
Intermediate mineral c
>1,500
High mineral c
TH mg/L [52]
<
75
Soft
75
−
150
Moderately hard
150
−
300
Hard
>
300
Very hard
WQI [53]
0
−
25
Excellent water quality
26
−
50
Good water quality
51
−
75
Poor water quality
76
−
100
Very poor water quality
>
100
Unsuitable for drinking
c = concentration.According to the classification of Crittenden et al. [52] based on TH (Table 9), all (100%) the samples were “soft” in both seasons.Using the Cameroonian standards [42], the weighted arithmetic water quality index (WQI) in the present study was calculated with 13 parameters, namely, pH, temperature, EC, TSS, turbidity, Na+, K+, NH4+, Mg2+, NO3−, F−, Cl−, and SO42−. The values of WQI obtained in this study ranged from 14.40 to 114.50 (mean 44.27) in the long dry season (Table 4) and from 9.98 to 104.08 (mean 47.53) in the long wet season (Table 5). Employing the classification of Chatterjee and Raziuddin [53] of drinking water based on WQI (Table 9), out of the 13 samples, 30.76% (GW2, GW3, GW4, and GW6) had excellent water quality, 38.46% (GW8, GW10, GW11, GW12, and GW13) had good water quality, 15.38% (GW1 and GW9) had poor water quality, 7.69% (GW5) had very poor water quality, and 7.69% (GW7) was unsuitable for drinking in the long dry season. In the long wet season, out of the 13 samples, 30.76% (GW2, GW6, GW8, and GW12) had excellent water quality, 30.76% (GW9, GW10, GW11, and GW13) had good water quality, 7.69% (GW4) had poor water quality, 15.38% (GW3 and GW7) had very poor water quality, and 15.38% (GW1 and GW5) were unsuitable for drinking. It should be noted that WQI may have been underestimated since some pollutants such as heavy metals (As, Cd, Hg, and Pb) which may be present were not considered.


## 3.6. Non-Cancer Risks Assessment

The non-cancer health risk on human health is evaluated through the calculation of the hazard quotient (HQ) and the hazard index (HI) assuming that HQ or HI > 1 signifies an acceptable level [54]. In this study, two age groups, namely, children and adults were considered for the calculation of HQ and HI of nitrate and fluorite. The HQ and HI values are depicted in Table 10. As it can be seen in Table 10, all the values of HQ and HI were <1, implying that the increased non-cancer risks due to nitrate and fluorite through the drinking of the groundwater from the study area were low. Nevertheless, a close perusal of Table 10 shows that the mean value of HI for children was about 1.6 times higher than that of HI for adults in both seasons.Table 10
Non-carcinogenic health risk assessment of water for children and adults via ingestion.
Season
Sample ID
Children
Adults
HQ
NO
3
−
HQ
F
−
HI
HQ
NO
3
−
HQ
F
−
HI
Long dry season
GW
1
4.94
E
−
03
3.70
E
−
02
4.20
E
−
02
2.96
E
−
03
2.22
E
−
02
2.52
E
−
02
GW
2
9.96
E
−
03
5.56
E
−
02
6.55
E
−
02
5.97
E
−
03
3.33
E
−
02
3.93
E
−
02
GW
3
2.38
E
−
02
2.78
E
−
02
5.16
E
−
02
1.43
E
−
02
1.67
E
−
02
3.10
E
−
02
GW
4
3.33
E
−
02
3.70
E
−
02
7.04
E
−
02
2.00
E
−
02
2.22
E
−
02
4.22
E
−
02
GW
5
2.80
E
−
02
4.63
E
−
02
7.43
E
−
02
1.68
E
−
02
2.78
E
−
02
4.46
E
−
02
GW
6
1.98
E
−
02
2.78
E
−
02
4.76
E
−
02
1.19
E
−
02
1.67
E
−
02
2.86
E
−
02
GW
7
5.63
E
−
02
1.85
E
−
02
7.48
E
−
02
3.38
E
−
02
1.11
E
−
02
4.49
E
−
02
GW
8
2.96
E
−
02
4.81
E
−
02
7.77
E
−
02
1.77
E
−
02
2.89
E
−
02
4.66
E
−
02
GW
9
9.22
E
−
02
2.78
E
−
02
1.20
E
−
01
5.53
E
−
02
1.67
E
−
02
7.20
E
−
02
GW
10
2.37
E
−
02
2.78
E
−
02
5.15
E
−
02
1.42
E
−
02
1.67
E
−
02
3.09
E
−
02
GW
11
1.87
E
−
02
6.48
E
−
02
8.35
E
−
02
1.12
E
−
02
3.89
E
−
02
5.01
E
−
02
GW
12
1.61
E
−
02
4.70
E
−
02
6.32
E
−
02
9.68
E
−
03
2.82
E
−
02
3.79
E
−
02
GW
13
2.67
E
−
02
7.41
E
−
02
1.01
E
−
01
1.60
E
−
02
4.44
E
−
02
6.05
E
−
02
Mean
2.95
E
−
02
4.15
E
−
02
7.10
E
−
02
1.77
E
−
02
2.49
E
−
02
4.26
E
−
02
Long wet season
GW
1
8.08
E
−
03
2.78
E
−
02
3.59
E
−
02
4.85
E
−
03
1.67
E
−
02
2.15
E
−
02
GW
2
1.25
E
−
03
5.56
E
−
02
5.68
E
−
02
7.53
E
−
04
3.33
E
−
02
3.41
E
−
02
GW
3
2.75
E
−
02
4.63
E
−
02
7.38
E
−
02
1.65
E
−
02
2.78
E
−
02
4.43
E
−
02
GW
4
6.25
E
−
02
9.07
E
−
02
1.53
E
−
01
3.75
E
−
02
5.44
E
−
02
9.19
E
−
02
GW
5
3.74
E
−
02
5.56
E
−
02
9.30
E
−
02
2.24
E
−
02
3.33
E
−
02
5.58
E
−
02
GW
6
2.70
E
−
02
3.70
E
−
02
6.40
E
−
02
1.62
E
−
02
2.22
E
−
02
3.84
E
−
02
GW
7
1.54
E
−
02
9.26
E
−
03
2.46
E
−
02
9.22
E
−
03
5.56
E
−
03
1.48
E
−
02
GW
8
1.07
E
−
02
1.85
E
−
02
2.92
E
−
02
6.40
E
−
03
1.11
E
−
02
1.75
E
−
02
GW
9
5.49
E
−
04
2.78
E
−
02
2.83
E
−
02
3.29
E
−
04
1.67
E
−
02
1.70
E
−
02
GW
10
1.14
E
−
02
1.85
E
−
02
3.00
E
−
02
6.87
E
−
03
1.11
E
−
02
1.80
E
−
02
GW
11
4.94
E
−
03
2.78
E
−
02
3.27
E
−
02
2.96
E
−
03
1.67
E
−
02
1.96
E
−
02
GW
12
9.96
E
−
03
2.78
E
−
02
3.77
E
−
02
5.97
E
−
03
1.67
E
−
02
2.26
E
−
02
GW
13
1.65
E
−
02
4.63
E
−
02
6.28
E
−
02
9.88
E
−
03
2.78
E
−
02
3.77
E
−
02
Mean
1.79
E
−
02
3.76
E
−
02
5.55
E
−
02
1.08
E
−
02
2.26
E
−
02
3.33
E
−
02


## 3.7. Suitability of Water for Agricultural Uses Based on SAR, EC, TDS, pH, TDS, and TSS

In the long dry season, SAR varied from 0.04 to 1.41 (mean 0.31) (Table4), while in the long wet season, it ranged from 0.00 to 0.18 (mean 0.11) (Table 5). All the SAR values of the water samples from the study area in both seasons were less than 10 and were, thus, graded as excellent for irrigation according to the classification of Richards [55] (Table 11).Table 11
Classification of water based on irrigation water quality parameters.
Parameter
Range
Description
SAR [55]
<10
Low (excellent)
10
−
18
Medium (good)
18
−
26
High (doubtful)
>26
Very high (unsuitable)
EC (μS/cm) [55]
0
−
250
Low (excellent quality)
251
−
750
Medium (good quality)
751−2,250
High (permissible quality)
>2,250
Very high (unfair)
TDS (mg/L) [51]
<1,000
Nonsaline
1,000−3,000
Slightly saline
3,000−10,000
Moderately saline
>10,000
Very salineSalty water in terms of TDS and EC reduces the yield of crops [56]. According to Richards [55] and van der Aa [51] classifications of water for irrigation based, respectively, on EC and TDS (Table 11), all (100%) the water samples were graded, respectively, as excellent quality and nonsaline for both seasons.According to Pescod’s classification [57] (Table 12), all (100%) the water samples had no restriction on their use in localized drip irrigation in both seasons with respect to pH and TDS. Following the same classification concerning TSS, 76.92% of the samples (GW2, GW3, GW4, GW6, GW8, GW9, GW10, GW11, GW12, and GW13) had no restriction on their use in localized drip irrigation in both seasons. 23.08% of groundwater samples (GW1, GW5, and GW7) had slight to moderate restriction on their use in localized drip irrigation in the long dry season, while 15.38% (GW1 and GW7) and 7.69% (GW5) of groundwater samples had, respectively, slight to moderate restriction and severe restriction on their use in localized drip irrigation in the long wet season. In addition, the acidic nature of groundwater from the study area imposes, for its transport, pipes that can withstand acid corrosion such as polyvinyl chloride (PVC) or polytetrafluoroethylene (PTFE) pipes.Table 12
Influence of water quality on clogging problems in the localized (drip) irrigation system [57].
Parameter
Range
Degree of restriction
pH
<7
None
7.0
−
8.0
Slight to moderate
>8.0
Severe
TDS (mg/L)
<500
None
500−2,000
Slight to moderate
<2,000
Severe
TSS (mg/L)
<50
None
50
−
100
Slight to moderate
>100
Severe


## 3.8. Suitability of Water for Poultry and Livestock Based on EC

Water with high salt content may cause temporary diarrhoea in livestock not accustomed to it, watery droppings in poultry, increased mortality, and decreased growth, especially in turkeys [56]. Following the classification of Ayes and Westcot [56] of water for poultry and livestock uses based on EC, all (100%) the water samples in this study were categorized as excellent for both seasons (Table 13).Table 13
Classification of water for poultry and livestock uses based on EC [56].
EC (μS/cm)
Description
Poultry
Livestock
<
1500
Excellent
Excellent
1,500−5,000
Very satisfactory
Very satisfactory
5,000−8,000
Unfit
Satisfactory
8,000−11,000
Unfit
Limited use
11,000−16,000
Unfit
Very limited use
>16,000
Not recommended
Not recommended


## 3.9. Suitability of Water for Cattle Rearing Based onNO3− and TDS

Water with high levels ofNO3− and TDS may be hazardous to cattle [58]. According to Higgins’ classification [58] of water for cattle based on these parameters, all (100%) the water samples in this study were declared safe for cattle rearing in both seasons (Table 14).Table 14
Classification of drinking water for cattle based onNO3− and TDS [58].
Parameter
Range
Description
NO
3
− (mg/L)
0
−
44
Safe
45
−
132
Safe with restrictions
133
−
220
Harmful
221
−
660
Risk of death
>661
Unsafe
TDS (mg/L)
<1,000
Safe
1,000−2,999
May cause mild diarrhoea
3,000−4,999
May cause diarrhoea
5,000−6,999
Unsafe to lactating or Pregnant cattle
7,000−10,000
Health problems
>10,000
Unsafe


## 4. Conclusion and Recommendations

The objectives of this study were the assessment of nutrients in the leachate from the Nkolfoulou landfill and the evaluation of groundwater quality within its vicinity. 72.73% of the parameters were found in the leachate at levels higher than the Cameroonian standards for effluent discharge while 27.27% complied with these standards. It is, therefore, imperative that the leachate be collected and properly treated before being released to the environment. About 88.47% of the groundwater samples was found to be suitable for drinking, while all the water samples (100%) were judged fit for livestock and irrigation in both seasons. Based on the statistical analysis, major ions present in the groundwater may not be directly associated with leachate percolation. They may rather have been derived from community settlements adjacent to the study area, agricultural practices, and rock weathering. The increased non-cancer risks due to nitrate and fluorite through the drinking of groundwater from the study area was low. Despite the relatively good state of groundwater assessed, further investigations are recommended for the assessment of heavy metals, phthalate esters, pathogens, and emerging pollutants.



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*Source: 6362134-2019-02-03.xml*