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ISSN: 0973-4945; CODEN ECJHAO
E-Journal of Chemistry
http://www.e-journals.net 2010, 7(3), 861-869
Groundwater Quality of Southeastern
MATINI LAURENT and MOUTOU JOSEPH MARIE
Department of Exact Sciences,
E.N.S., Marien NGOUABI University, B.P 69 Brazzaville, Congo.
Received 2 October 2009; Accepted 1 December 2009
Abstract: The groundwater in southeastern Brazzaville (Congo) was analyzed for
their fluoride contents and others related parameters in rainy season. The fluoride
contents in water samples (wells and spring) can be gather in three classes in the
study area: low, optimal, high. Fluoride concentration in water samples presents a
low significant correlation with Ca2+. This suggests that fluoride in the groundwater
come from fluoride-bearing minerals such as CaF2 (fluorite). Maps were drawn to
show the geographical distribution of EC, Ca2+, Mg2+and F-. Factor analysis and
cluster analysis were applied to the dataset. Factor analysis resulted in four factors
explained 76.90% of the total groundwater quality variance. Factor 1 (hardness of
the groundwater) includes total hardness, the concentration of K+, Ca2+ and pH.
Factor 2 (low mineralization of the groundwater) includes concentrations of TDS,
Cl-, SO42- and EC. Factor 3 (anthropogenic activities with the impact of agricultural
fertilizers, farming activities, domestic wastewater, septic tanks) includes
concentrations of Na+ and NO3-. Factor 4 (weathering of calcium minerals)
includes concentrations of F-. For cluster analysis, Wards method and the
Euclidean distance were used. The findings of the cluster analysis are presented in
the form of dendrogram of the well water sites (cases). The discriminating
parameters between clusters have been highlighted from the Student test. In
majority, they are in accordance with those highlighted by factor analysis.
Keywords: Fluoride, Groundwater, Sandstone aquifer, Factor analysis, t-Test.
Fluoride is of interest, because of its effects on human health. Even small quantity of
fluoride (< 0.7 mg/L) has beneficial effects to the teeth by hardening the enamel and
reducing the incidence of dental caries1. Excessive intake of fluoride (>1.5 mg/L) results in
dental and skeletal fluorosis2. Unlike many others elements, a large quantity of fluoride is
ingested from drinking water and food. Many studies have reported that fluoride is one of
the most undesired elements present in the underground water extracted for drinking3-5
862 MATINI LAURENT et al.
Fluoride build-up in water is controlled by many factors like aquifer geology, contact
times with fluoride-bearing minerals, agricultural fertilizers and climate. Fluoride mainly
occurs in groundwater through fluoride-rich minerals, such as fluorite (CaF2), fluorapatite
Ca5F(PO4)3, apatite Ca5(PO4)3(F, OH, Cl). It derives from dissolution of these minerals in
the rocks and soils through which water interacts.
The present study has been designed for the first time on the concentration of fluoride in
groundwater in Southeastern Brazzaville, Congo, which provides baseline data for taking
appropriate management measures to reduce the intensity of health disorders.
The study area
The study area is located between 151353 - 151410 East longitude and 4157.2 to
41528.8 South latitude. The area is in the equatorial climate zone, with two seasons: rainy
season (October to May) and dry season (June to September). Temperature in rainy season varies
from 25 C to 36 C, while it is between 18 C and 24 C in dry season. The mean annual rainfall
is 1470 mm. The vegetation is of savanna type (Loutetia demeusi) and presents a formation to
sparse gramineous carpet with a shrubby layer of hymenocardia acida. The soils of the area are
sandy and have been derived from Tertiary Silicate Sandstones of the Inkisi Serial. They are
ferralitic and acid. Aquifer is shallow. Generally, the depth of wells does not exceed 2 m. The
main natural recharge to groundwater is from precipitation (rainfall). Farming activities are
present around some well water sites and also agricultural activities near the River Mfilou.
Twenty seven samples of wells water and one sample of spring water were collected in three
times in rainy season (from March 25 to April 5, 2007) from the study area. They were analyzed
for pH, electrical conductivity (EC), total dissolved solids (TDS), total hardness (TH as CaCO3),
, K+, Cl
- and following standard methods
6. The ratio Ca
was also computed for all the groundwater samples. STATISTICA 7.1 software was used to
perform factor and cluster analyses. Factor analysis was used to understand the correlation
structure of collected data and identified most important factors contributing the data structure7.
The data were standardized to produce a normal distribution of all variables8, whose mean and
variance were set to zero and one respectively. The factor extraction was performed, using the
method of principal components. Kaiser criterion9, which retains only the factors with
eigenvalues greater than 1, was applied. The proportion of variance in all the groundwater
parameters accounted for each factor was obtained by dividing the factors eigenvalue by the
number of parameters. Interpretation of groundwater quality was facilitated, using the
varimax rotation, which is a standard rotation method. Cluster analysis is also another data
that was used to classify entities or objects, with similar properties into
groups called clusters. Objects within the clusters are similar, while objects in different
clusters are dissimilar. This exploratory method enables to discover the data structure not
only among observations, but also among variables. In this study, the Wards clustering
method and the Euclidean distance was used as a similarity measure.
Results and Discussion
Table 1 presents the chemical composition of groundwater samples in the study area. It is
observed that the pH in all the groundwater samples ranges from 3.85 to 6.08, with a mean
of 5.22, indicating an acidic environment. The pH values are below the prescribed limits of
6.5-8.5 for drinking. The results show that electrical conductivity is varied between
75 S/cm and 431.20 S/cm, with a mean of 235.51 S/cm (at 25 C), indicating the
Groundwater Quality of Southeastern Brazzaville 863
groundwater is slightly mineralized (Table 1). Wells, P6 and P14 located in northwestern
and well P23 located in southern parts of the study area, presented in Figure 1, show the
higher electrical conductivity value, which is attributable to the influence of domestic
526250 526300 526350 526400 526450 526500
Figure 1. Contour map of EC (in S/cm) in the wells water and spring water.
The TDS, which is an indicative parameter to assess the degree of water quality, is
below 230 mg/L in the water samples. This is, within the recommended limit of 500
mg/L for drinking purpose2. The TA ranges from 5 to 84.98 mg/L (mean of 26.21 mg/L).
The TH in the groundwater samples is in the range of 5 to 60 mg/L (mean of 29.32
mg/L) and indicates that the water belong to the soft category11
. The concentration
(mg/L) of calcium, magnesium, sodium, potassium, chloride, sulfate and nitrate is in the
range of 4 to 30, 5 to 14, 1.13 to 36.25, 2 to 12, 5.4 to 44.0, 2 to 11, and 0.25 to 23.20
mg/L with a mean of 16.03, 8.5, 10.81, 5.28, 20.24, 7.79 and 1.86 mg/L, respectively.
Compared to WHO2, the concentration of the parameters quoted above are below the safe
limit of 100, 150, 200, 200, 250, 200 and 50 mg/L for drinking, respectively. Since the
chloride-rich minerals are not found in the study area, the higher concentrations of
chloride in the groundwater could be caused by pollution sources such of domestic
wastewater and septic tanks.
Table 1. Hydrochemical parameters of groundwaters in the study area.
Code pH EC TDS TA TH Ca2+
Na K+ Cl
S 3.90 93.92 49.88 40.00 5 4 12 2.53 3.2 19.53 2 48.80 0.42 0.56 0.20 P1 3.98 251.20 133.00 5.00 20 12 10 9.84 5.8 32.23 7 6.10 0.29 1.08 0.72
P2 4.00 104.92 55.54 5.00 10 8 12 17.43 2.0 18.10 4 6.10 0.19 3.90 0.40
P3 4.22 100.84 53.46 30.00 15 6 13 8.49 3.1 12.35 7 36.60 0.37 0.