Environmental Engineering Reference
In-Depth Information
GPS is used to map the location of each sampling well and finally the results were
taken to the GIS for further analysis. The field work included water level measure-
ments, well inventory and collection of water samples from tube wells and the study of
geological and geomorphological features of the area in general. The pre-monsoon
water samples were collected during September 2009 and the post-monsoon water
samples were collected during April 2010. The groundwater samples were analyzed, as
per the procedure of American Public Health Association (APHA
1995
) and suggested
precautions were taken to avoid contamination. The various parameters determined
were: pH, total hardness (TH), chloride (Cl
−
), nitrate (NO
3
−
) and fluoride (F
−
). pH was
determined by pH meter; TH, Cl
−
by titrimetry; F
−
and NO
3
−
were determined by using
ion selective electrode (Orion 4 star ion meter, Model: pH/ISE). The location of each
well was taken into the GIS environment and the results of each parameter analysed
was added to the concerned wells. Spatial analyst, an extended module of Arc GIS 9.3
was used to find out the spatiotemporal behaviour of the fluoride parameters.
Results and Discussion
Chemical Analysis
Fluoride concentration in natural waters depends on several factors such as temperature,
pH, presence or absence of ion complexes or precipitation of ions and colloids, solubil-
ity of fluorine-bearing minerals, anion exchange capacity of aquifer materials, the size
and type of geological formations through which the water flows and the time water is
in contact with a particular formation (Apambire et al.
1997
). The concentration of fluo-
ride in groundwaters is principally governed by the climate, the composition of host
rock, and the hydrogeology. Areas of semiarid climate, crystalline rocks and alkaline
soils are mainly affected (Handa
1975b
). High fluoride concentrations in groundwater
suggest that favourable conditions exists for the dissolution of fluoride bearing minerals
present in the granite and gneissic rocks in the study area. Fluoride bearing minerals
occupy the joints, fractures, faults and vertical openings in the gneissic and granitic
formations which are the oldest geological formations in Anantapur and have under-
gone maximum weathering (Subba Rao
2003
). Granitic rocks are known to contain a
relatively large proportion of fluorine minerals (Edmunds and Smedley
2005
). Fluorite,
the main mineral that controls the geochemistry of fluoride in most environments is
found in significant amounts in granite, granite gneisses and pegmatite (Deshmukh
et al.
1995
; Rama Rao
1982
; UNICEF
2008
; Mamatha and Sudhakar Rao
2010
).
The results of analyzed chemical and statistical parameters including minimum,
maximum, mean and standard deviation are given in Table
1
. Understanding the qual-
ity of ground water is an important aspect because it is the main factor determining its
suitability for drinking, domestic, agricultural and industrial purposes. The pH values
of ground water range from 7 to 8.6 with an average of 7.98 during September 2009,
with a mean of 8 indicating an alkaline condition which favours the solubility of fluo-
ride-bearing minerals. In acidic medium (acidic pH), fluoride is adsorbed in clay; how-
ever, in alkaline medium it is desorbed, and thus alkaline pH is more favourable for
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