Int. Journal of Advances in Remote Sensing and GIS, Vol. 4, No. 1, 2015
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Research article
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ISSN 2277 – 9450
Geological and hydrogeomorphological control on iron-arsenic
contamination in groundwater in part of Gangetic plain, India
Pandey A. C 1, Suraj Kumar Singh1, DipankarSaha2
1
Centre for Land Resource Management, Central University of Jharkhand, Brambe, India
2
Central Ground Water Board, Ministry of Water Resources, Patna, India
Abstract: A study in parts of Bihar state in the middle Ganga plain was carried out to determine arsenic
contamination in groundwater. Inter-relationship of various chemical constituents of groundwater in
relation to the hydro-geomorphology and geology of the region was studied. Remote sensing based
hydrogeomorphological map derived through visual interpretation technique was performed. The
chemical parameters data was analyzed graphically as well as by generating correlation matrix in order
to establish relationships between various groundwater chemical parameters. The chemical parameters
taken into consideration include calcium, magnesium, PH, TDS, chloride, sulphate, nitrate, flouride,
iron, total hardness as CaCo3 and arsenic along with electric conductivity as the one physical parameter.
Study revealed that in relation to hydrogeomorphology, most of the Arsenic contamination has been
concentrated in the areas of deep and shallow flood plain. This clearly depicts occurrence of arsenic
minerals in and around the areas of paleochannels of the shifting Ganga river. Arsenic is present in
Holocene deposits and shallow aquifer within the depth of 50-60 meters below ground where sand beds
are susceptible for arsenic contamination. The correlation of Arsenic with calcium, magnesium, PH,
TDS, chloride, sulphate, nitrate, flouride, total hardness as CaCo3, electric conductivity was insignificant
whereas a positive correlation with iron.
Keywords: Arsenic in groundwater, hydrogeomorphology, Remote sensing, GIS, Correlation matrix
1. Introduction
The Ganga basin, the largest geomorphic element in the Indian sub-continent was itself formed as a
result of the collision between Indian and Eurasian plates (Dewey and Bird, 1970; Sinha et al., 2005).
The interaction between three forcing factors namely tectonics, climate, and glacio-eustasy sea level
related base level changes have been proposed to be variously responsible for the evolution of the valley
and floodplain architecture in different parts of the Ganga Plains (Burbank et al., 2003; Goodbred, 2003;
Tandon et al., 2006).
Arsenic is a toxic heavy element and carcinogenic in nature. Inorganic arsenic generally exists in two
predominant oxidation states, arsenite (NaAsO2) and arsenate (Na2HAsO4), both of which are toxic to
man and plants. Inorganic arsenic is always considered a potent human carcinogen, associated with
increased risk for cancer of the skin, lungs, urinary bladder, liver and kidney (IARC, 1987). In
Bangladesh and India (West Bengal), alluvial Gangetic aquifers used for public water supply are polluted
with naturally occurring arsenic, which adversely affects the health of millions of people (Nickson, et
al., 1998). However, the most widespread arsenic contamination is detected in the Bhagirathi–Ganga
---------------------------*Corresponding author (Email: [email protected])
Received on September 2015; Accepted on October 2015; Published on November, 2015
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Geological and hydrogeomorphological control on iron-arsenic contamination in groundwater in part of Gangetic plain, India
delta, covering eastern part of West Bengal, India and Bangladesh, affecting 40 million inhabitants
(Mandal, et al., 1996; Nickson, et al., 1998).
In India, Bangladesh, and some other countries, the upper permissible limit of arsenic in potable water
is 0.05 µg/l (Mukherjee, et al., 2006). However, WHO (1993) has recommended guideline of 0.01 mg/l,
which has been endorsed by Bureau of Indian Standards (BIS 2003) in the groundwater. Extensive
groundwater arsenic pollution affects low-lying Bengal Delta, covering southern parts of West Bengal
(India) and major parts of Bangladesh (Mandal, et al., 1996; Nickson, et al., 1998; Pal, et al., 2002;
Kinnibugh and Smedley, 2001). Arsenic contamination (>0.05 µg/l) in the upstream regions of Ganga
plain was detected in 2002 (Chakraborty, et al., 2003). It affects different geological domains, which are
virtually free from any industrial, mining or thermal-water activities and represent natural geological
settings (Acharyya, 2000). Arsenic-contaminated aquifers are pervasive within lowland organic-rich,
clayey deltaic sediments in the Bengal basin and locally within similar facies in narrow, entrenched
channels and floodplains within the Middle Ganga plain covering parts of the states in Jharkhand, Bihar
and eastern Uttar Pradesh (Acharyya, 2005). The Middle Ganga Plain represents an active depositional
basin and one of the important repositories of Quaternary sediments.
The presence of arsenic in natural water is related to the process of leaching from the arsenic containing
source rocks and sediments (Robertson, 1989). The arsenic contamination affecting the shallow aquifers
has created a serious problem to groundwater-based drinking water supply system, particularly in the
rural and semi-urban areas in the affected parts of Middle Ganga Plain in India. Chemical quality plays
a significant role in groundwater resource management in Bihar state as the entire drinking- and a major
part of irrigation consumption is extracted from Quaternary aquifers (Saha, 2007).It is suggested that
the non-point source of geogenic arsenic occurs mostly in Holocene sediments (∼70 m) and probably
mobilized by redox reaction (Saha, 1991, 2009; Bhattacharya, et al., 1997, McArthur, et al., 2001).
2. Study area
The area under investigation comprises of two districts in the southern Bihar plains. It is located between
83° 46' 28'' E to 84° 51' 10'' E longitude and 25° 44' 48'' N to 25° 9' 37'' N latitude, covering a total area
of 4074 km2. The area is drained by rivers Ganga, Son and their tributaries (Figure 1). The direction of
flow of Son river is from south to north whereas Ganga flows in east to west direction. The area
comprised of fertile flat land and is highly prone to floods during the monsoon period. The Quaternary
alluvium deposits cover the entire region with depth of alluvium ranging from few hundred meters to
more than 500 m.
3. Methodology and data used
Satellite data acquired by the LANDSAT, Enhanced Thematic Mapper sensor (ETM+) which provide a
resolution of 30 m in multispectral mode were used to delineate various thematic layers. Survey of India
(SOI) topographical maps on 1:50,000 were used as ancillary data for georeferencing of satellite images
and preparation of base maps. A holistic study on arsenic contamination requires understanding of interrelationship of various chemical constituents of groundwater samples, in relation to the hydrogeomorphology and geology of a region. In order to demarcate the Arsenic zone in the study area, a
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Geological and hydrogeomorphological control on iron-arsenic contamination in groundwater in part of Gangetic plain, India
multi-parametric dataset comprising remote sensing based hydrogeomorphological map, geological
maps from Geological Survey of India and topographic maps from SOI was used.
Figure 1: Location map of the study area showing LANDSAT ETM+ satellite image of the area
exhibiting waterlogging areas in shade of black color whereas agriculture and fallow lands appear
in red and white color tones respectively.
When utilizing spatial data from diverse sources, it is required that all dataset should accurately spatially
overlap with each other. This requires georeferencing of all the maps to a common projection system.
Ground control points were uniformly selected all over the image where location can be easily and
clearly identified and precisely located. Image-to-map transformation is performed using first order
polynomial transformation. The chemical parameters data obtained from Central Ground Water Board
(CGWB) were analyzed graphically as well as by generating correlation matrix in order to establish
relationships between various groundwater chemical parameters. A total number of 5776 samples of
ground water were collected by CGWB from different tube wells, covering various districts of Buxar
and Bhojpur in Bihar state. The chemical parameters of ground water samples were tested in laboratory,
and the same was used in the present study. The chemical parameters taken into consideration include
calcium, magnesium, PH, TDS, chloride, sulphate, nitrate, flouride, iron, total hardness as CaCo3 and
arsenic, whereas electric conductivity was the only physical parameter. The relationship of various
ground water chemicals parameters with Arsenic in various geologic and geomorphic units was
analyzed.
4. Results and discussion
In the present study, visual interpretation of LANSAT ETM+ FCC image acquired on 30 October 2006
was carried out for mapping hydrogeomorphologically significant landforms based on various elements
of satellite image interpretation like tone, texture, shape, pattern, drainage, and association. The
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Geological and hydrogeomorphological control on iron-arsenic contamination in groundwater in part of Gangetic plain, India
concentration of chemical and physical parameters of ground water samples was observed individually
as well as spatially, with special significance to the geomorphic units. Based on geomorphological
characteristics the region can be categorized into Alluvial Plain Shallow, Alluvial Plain Deep, Flood
Plain Shallow and Flood Plain Deep (figure 2). A number of paleochannels and oxbow lakes also exist
in the area. All these units were demarcated while preparing hydrogeomorphological map.
Geologically the area has been divided into two major units i.e. Older Alluvium and Newer Alluvium.
These units comprises of Hajipur (oldest), Vaishali (middle), and Diara (youngest) Formations with an
age group of Late Pleistocene-Early Holocene, Middle-Late Holocene, and Late Holocene respectively
and mainly consists of sand, silt, and clay with caliche nodules. Hajipur Formation is the oldest
depositional land unit in the alluvial landscape of Son-Ganga basin and occupies the highest altitude in
the alluvial valley. This surface has a gently northward master slope as evidenced from the general trend
of major drainage channels. The sediments comprising this unit consist of an alternation of sand, silt,
and clay, and degree of oxidation and compaction is high. The uniformity of subsurface granular zone
is disrupted due to the presence of long stretches of inliers of meta sedimentary and gneissic rocks in
ENE-WSW direction.
Figure 2: Hydrogeomorphological map of the study area.
The Hajipur Formation is followed by the Vaishali Formation to the north which constitutes the older
flood plain deposits of the Ganga. This land unit comprised of a number of landform viz, levee,
abandoned channels is characterized by overlapping alteration of fine sand to silt with thin levees of
clay in the flood plain area. The Vaishali Formation is followed to the north by the youngest Diara
Formation, which occupy the lowest altitude. The surfacial sediments of Diara Formation are
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Geological and hydrogeomorphological control on iron-arsenic contamination in groundwater in part of Gangetic plain, India
represented by unoxidized fine sand and silt with minor amounts of gravel and comprise an alternating
sequence of medium to fine sand and silt with occasionally clay. Figure 3 clearly depict that arsenic
contamination points is mostly concentrated in the Vaishali formation.
Figure 3: Arsenic contaminated points overlaid over geological map of the study area.
In relation to hydrogeomorphology, most of the Arsenic contamination has been concentrated in the
areas of flood plain, deep and shallow. This clearly depicts occurrence of arsenic minerals in and around
the areas of paleochannels of the shifting river. It has been observed that the concentration of chemicals
such as magnesium, calcium, sulphate, chloride, TDS have shown a gradual decline from alluvial plain
shallow to Flood plain deep. This could have been caused due to the high intensity of recurrent floods
in these areas which washed away the deposited minerals and thus resulted in the lower concentration
compared to the alluvial plains. The concentration of arsenic increases in the Newer Alluvium as
compared with the Older Alluvium primarily due to intensive leaching of arsenic from sediments in the
active flood plain area. The arsenic and iron data were converted into database files and were attached
to their respective coordinates in GIS environment using the IDW interpolation technique. IDW
interpolation technique was applied to analyze the spatial pattern and variability in arsenic and iron
levels (figure 4 and 5). Interpolation permits representation of point data in a continuous spatial domain
and therefore helps in understanding the spatial variability of the phenomenon (Gao, 1995). The IDW
method is selected in the present study as it is one of the standard spatial interpolation procedures in
geographic information science (Burrough and McDonnell, 1986). The interpolated maps clearly depicts
that the arsenic has a positive correlation with iron and mostly concentrated in the areas of flood plain,
deep and shallow. Correlation matrix is the most common and useful statistics used to compute a
correlation between two variables. A correlation is a single number that describes the degree of
relationship between two variables (Pathak, et al., 2013). In the present study to understand the influence
of groundwater chemistry on arsenic contamination, Pearson’s correlation (r) between arsenic and other
hydrochemical parameters was determined for those 5776 groundwater samples from different blocks
where the arsenic contamination was found. The correlation of arsenic with calcium, magnesium, PH,
TDS, chloride, sulphate, nitrate, flouride, total hardness as CaCo3andelectric conductivity was found to
be insignificant. The correlation of Arsenic was significant with iron as shown in Table 1.
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Geological and hydrogeomorphological control on iron-arsenic contamination in groundwater in part of Gangetic plain, India
Figure 4: Iron concentration overlaid over geomorphological map.
Figure 5: Arsenic contaminated zones overlaid on geomorphological map
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Geological and hydrogeomorphological control on iron-arsenic contamination in groundwater in part of Gangetic plain, India
Table 1: Correlation Matrix of Groundwater Chemicals in Bhojpur, Buxar Districts of Bihar
5. Conclusion
The upper part of the newer alluvial deposits, underlying active flood-prone areas bordering the Ganga
river is affected by high incidence of arsenic contamination (>50 ppb) in groundwater. The occurrence
of arsenic in ground water depends on the local geology, hydrology and geo-chemical characteristic of
the aquifer materials. Furthermore organic content in sediments as well as the land use pattern may also
be important factors controlling the natural mobility of arsenic in alluvial aquifers. Arsenic is present in
Holocene deposits and shallow aquifer within the depth of 50-60 meters below ground where sand beds
are susceptible for arsenic contamination. It is significant that possibility of Arsenic contamination may
be less at deeper level and deeper aquifer zone with clay free horizons which may be explored for better
ground water prospect. Presence of clay zone indicates the possibility of Arsenic contamination in the
iron rich clay layer present under reducing environment and covered by waterlogging in the area, which
may induce arsenic contamination in groundwater. The upper aquifer may suffer large fluctuation in
water table and thus get contaminated fast. The gradual increase in clay content upward from sand
through kankar indicate a dynamic flood plain depositional environment in earlier phase and clam
depositional environment in abundant channel in the recent geological past which caused accumulation
of arsenic minerals enrichment in the sediments causing groundwater contamination.
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