130
B. M. J. K. Balasooriya et al.
part of Jaffna peninsula (it is underlain by Miocene limestone formations), and eastern part is dominated by sandy regosols on recent beach and dune sands (Panabokke
and Perera 2005). Sandy regosols support a different type of aquifer. Therefore, quality of the groundwater obtained from shallow coastal aquifers is different compared
to the karstic aquifers (Panabokke 2007). Shallow aquifers on coastal sands are freshwater bulbs floating on saline water and recharge mainly from the 3 to 4 months of
rain received from north to eastern monsoon (Chandrajith et al. 2014). Deep confined aquifers located within sedimentary limestone and sandstone formations of the
north–western and northern coastal plains, and they are relatively deep and have a
relatively high recharge rate (Panabokke and Perera 2005). However, a few alluvial
aquifers are also found in the area. Alluvial aquifers are associated with alluvial landforms such as coastal and inland rivers and inland valleys. Deeper and larger alluvial
aquifers are associated with Mahaweli ganga, Kirindi oya, Kelani ganga, Daduru oya,
etc. (Panabokke and Perera 2005). Metamorphic hard rock regions cover around 80%
of the island and weathered and fractured crystalline rocks bear water (Panabokke
and Perera 2005). However, groundwater potential in the hard rock regions is limited.
South–western lateritic aquifers confined to the wet zone of Sri Lanka (Panabokke
and Perera 2005). It has considerably high water holding capacity due to its vascular nature, and this aquifer is relatively shallow. In the meantime, the water level is
rapidly fluctuating in response to the precipitation patterns (Panabokke and Perera
2005). Overexploitation and contamination tremendously pressurize these aquifers
(Villholth and Rajasooriyar 2010). Lateritic aquifers, alluvial aquifers and coastal
sand aquifers have comparatively higher recharge rate due to their shallow nature
(Panabokke 2007; Villholth and Rajasooriyar 2010). Further, they receive freshwater
frequently, and hence, mineral ion concentration is lower. In contrast, shallow nature
makes them contaminate easily by anthropogenic pollutants dissolved in rainwater
runoffs (Villholth and Rajasooriyar 2010). Therefore, depending on the aquifers in
which they are located, groundwater wells located in dry and intermediate zones
are grouped into either cluster 1 or 2. Since several types of aquifers are available in
adjacent areas, clear boundaries with different groundwater quality controlled by soil
distribution or climatic condition are not identifiable in Sri Lanka. However, groundwater in wet zone is generally similar in quality hence clustering under cluster 2 only.
Furthermore, relatively high precipitation and associated recharge may govern the
water quality in the wet zone of Sri Lanka. Most of the heavy metal ions are proven to
be entered into the surface and groundwater due to anthropogenic activities (Tchounwou et al. 2012; Azizullah et al. 2011). In agreement with that, higher concentrations
of above metal ions were observed in districts such as Colombo, Kandy, Gampaha,
Kalutara, Nuwaraeliya and Galle (Fig. 5.1) those are considered as highly urbanized
and industrialized districts in Sri Lanka. Further, all these districts are located in wet
zone of Sri Lanka, which receives plenty of rainfall during north–western monsoon.
Water quality parameters retained in the backward stepwise DA are fluoride,
EC, sulphate, nitrate, sodium, magnesium, chromium, nickel, arsenic and cadmium.
Among them, nitrate, chromium, nickel, arsenic and cadmium are identified as
anthropogenic pollutants (Leung and Jiao 2006; Wongsasuluk et al. 2014), while
B. M. J. K. Balasooriya et al.
part of Jaffna peninsula (it is underlain by Miocene limestone formations), and eastern part is dominated by sandy regosols on recent beach and dune sands (Panabokke
and Perera 2005). Sandy regosols support a different type of aquifer. Therefore, quality of the groundwater obtained from shallow coastal aquifers is different compared
to the karstic aquifers (Panabokke 2007). Shallow aquifers on coastal sands are freshwater bulbs floating on saline water and recharge mainly from the 3 to 4 months of
rain received from north to eastern monsoon (Chandrajith et al. 2014). Deep confined aquifers located within sedimentary limestone and sandstone formations of the
north–western and northern coastal plains, and they are relatively deep and have a
relatively high recharge rate (Panabokke and Perera 2005). However, a few alluvial
aquifers are also found in the area. Alluvial aquifers are associated with alluvial landforms such as coastal and inland rivers and inland valleys. Deeper and larger alluvial
aquifers are associated with Mahaweli ganga, Kirindi oya, Kelani ganga, Daduru oya,
etc. (Panabokke and Perera 2005). Metamorphic hard rock regions cover around 80%
of the island and weathered and fractured crystalline rocks bear water (Panabokke
and Perera 2005). However, groundwater potential in the hard rock regions is limited.
South–western lateritic aquifers confined to the wet zone of Sri Lanka (Panabokke
and Perera 2005). It has considerably high water holding capacity due to its vascular nature, and this aquifer is relatively shallow. In the meantime, the water level is
rapidly fluctuating in response to the precipitation patterns (Panabokke and Perera
2005). Overexploitation and contamination tremendously pressurize these aquifers
(Villholth and Rajasooriyar 2010). Lateritic aquifers, alluvial aquifers and coastal
sand aquifers have comparatively higher recharge rate due to their shallow nature
(Panabokke 2007; Villholth and Rajasooriyar 2010). Further, they receive freshwater
frequently, and hence, mineral ion concentration is lower. In contrast, shallow nature
makes them contaminate easily by anthropogenic pollutants dissolved in rainwater
runoffs (Villholth and Rajasooriyar 2010). Therefore, depending on the aquifers in
which they are located, groundwater wells located in dry and intermediate zones
are grouped into either cluster 1 or 2. Since several types of aquifers are available in
adjacent areas, clear boundaries with different groundwater quality controlled by soil
distribution or climatic condition are not identifiable in Sri Lanka. However, groundwater in wet zone is generally similar in quality hence clustering under cluster 2 only.
Furthermore, relatively high precipitation and associated recharge may govern the
water quality in the wet zone of Sri Lanka. Most of the heavy metal ions are proven to
be entered into the surface and groundwater due to anthropogenic activities (Tchounwou et al. 2012; Azizullah et al. 2011). In agreement with that, higher concentrations
of above metal ions were observed in districts such as Colombo, Kandy, Gampaha,
Kalutara, Nuwaraeliya and Galle (Fig. 5.1) those are considered as highly urbanized
and industrialized districts in Sri Lanka. Further, all these districts are located in wet
zone of Sri Lanka, which receives plenty of rainfall during north–western monsoon.
Water quality parameters retained in the backward stepwise DA are fluoride,
EC, sulphate, nitrate, sodium, magnesium, chromium, nickel, arsenic and cadmium.
Among them, nitrate, chromium, nickel, arsenic and cadmium are identified as
anthropogenic pollutants (Leung and Jiao 2006; Wongsasuluk et al. 2014), while