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This study aims at assessing the hydro-geochemical
characteristics of deep boreholes in Port Harcourt, Nigeria.
Hydro-geochemical investigations were carried out both in
the field and the laboratory. Groundwater samples from
boreholes in the area were analyzed for various physico-chemical
parameters using standard methods. StatistiXL 1.5 which is
an add-in to Microsoft Excel, was used for performing the
hierarchical cluster analysis (HCA). The HCA was used to
explore and reveal natural groupings or clusters within the
physico-chemical variables that would otherwise not be
apparent. The determination of spatial variance
equality/homogeneity in means of the physico-chemical
parameters was made with the single factor/one-way analysis
of variance and further plots of group means was made with
means plots. The physico-chemical parameters for the deep
boreholes show the following range: Temp. 0C (27.02 –
29.03), pH (4.28 – 7.72), EC (350.60 – 618.20µS/cm), TDS
(122.70 – 381.31mg/l), TSS (BDL – 35.00mg/l), Hardness (2.50
– 36.00mg/l), Cl- (115.00 – 410.00mg/l), Eh (123.22 –
196.00mV), SO42- 48.00 – 90.10mg/l), Fe (0.020 0.820mg/l),
Salinity (12.00 – 355.00mg/l), NO3- (0.201 – 6.300mg/l),
HCO3- (6.701 – 54.011mg/l), Ca2+ (3.000 – 7.633mg/l), Na+
(0.834 – 3.400mg/l), Mg2+ (0.445 – 5.677mg/l), K+ (0.220 –
0.555mg/l), PO42- (0.030 – 0.732mg/l), Mn2+ (0.011 –
0.727mg/l), F- (0.411 – 2.310mg/l), SiO2 (0.55 – 4.94mg/l),
Zn2+ (0.14 – 0.60mg/l), Cu2+ (0.01 -006mg/l), Pb (0.01 –
0.06mg/l) and Br- (12.50 – 79.70mg/l). Generally, for the
deep boreholes the water is soft on account of the hardness
values recorded (2.50 – 36.00mg/l). The study also reveals
saltwater contamination in the area as EC, TDS, salinity as
well as chloride contents in some boreholes are high. This
shows saltwater encroachment at those locations. This is
probably due to the closeness of these locations to the sea.
Therefore, saltwater-freshwater interface should be
delineated in the area. The test of homogeneity in mean
variance of the physico-chemical properties of groundwater
samples across the sampling locations for the boreholes
revealed significant heterogeneity {F(32, 51) > FCrit
(3.87)} at P>0.05. A further post-hoc structure detection of
group means using means plots revealed that salinity
(82.00), Eh (143.00), TDS (22.30), Cl (300.00) and EC
(513.00) were most responsible for the observed
heterogeneity in all sampling locations. The
hydro-geochemical interpretation presented here strongly
illustrates that rational plans for long-term and
sustainable management of the aquifer systems cannot be
based simply on regulatory water quality targets, which are
focused on current anthropogenic causes of water quality
degradation (e.g. in relation to saline intrusion or
industrial contaminants). Although recent management effort
may have an influence on the quality of the aquifer (e.g. in
relation to the dynamic movement of freshwater),
palaeo-hydrogeological events, perhaps resulted in the
presence of relict saline components in the aquifer isolated
from their original sea water source.
Keywords:
Groundwater quality, borehole, hydro-geochemistry, saltwater
intrusion, contamination
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