Abstract:
This work is the study of the risk of groundwater and surface water pollution of the 136.98 km2 Kombolcha
area (Eastern Amhara, Ethiopia). The Kombolcha city is in a state of progressive population growth,
uncontrolled urbanization, and industrialization as well as agricultural activities, which are all potential
sources of surface and groundwater pollution in the area. The main objectives of the present study are
identifying the major pollution source in the area, study the groundwater quality and identify its pollution
level of groundwater, as well as aquifer vulnerability to contaminants in the area. To achieve this,
hydrogeochemical analysis, groundwater heavy metal and water level contour mapping, geospatial data
analysis, ion ratio, correlation matrix, principal component analysis, Heavy metal Pollution Index (HPI),
Water Quality Index (WQI), and DRASTIC modeling methodologies were employed. A total of 36
samples had been collected and assessed for major physicochemical variables and heavy metals. The
samples have been gathered from groundwater, surface water, spring, and effluent which are spatially
distributed throughout the area. Hydrogeochemical methods showed groundwater mineralization due to
(1) silicate weathering, (2) cation exchange processes, and (3) anthropogenic sources (i.e., contaminated
discharge of sulphate, carbonate, and trace metal effluents).
The study result revealed that major cations and anions dominating the area are Ca2+ >Na+ > Mg2+ >K+,
and HCO3- >SO42- > Cl- > NO3- respectively. And also, for heavy metals the concentration of Fe> Mn
>Pb> Cr> Cd. The study also showed that the water in the study area is evolved from Ca-HCO3 to different
types of water via geogenic evolution (rock-water interaction) and anthropogenic factors. Chloro-alkaline
indices resulted for CAI-I and CAI-II (68.8%), showed Ca2+ and Mg2+ exchange in groundwater with Na+
and K+ in an aquifer, confirmed for cation exchanging. In groundwater samples the mean concentration
of iron, manganese, lead, cadmium, and chromium were above the drinking water limits prescribed by the
World Health organization standards. Multivariate statistical analyses revealed that the release of these
heavy metals into the groundwater system is primarily influenced by anthropogenic inputs than natural
processes. Based on the result of DRASTIC modeling, the aquifer close to the center of the city is
moderately vulnerable, and areas close to the Borkena River are highly vulnerable. Following the results
of the combined assessments based on WQI and HPI, the study showed that the groundwater samples in
the proximity of industrial sites and surface waters are polluted by factories effluent and uncontrolled
waste disposal due to urbanization. Generally, the study result is believed to give directions for
groundwater management options