Salinity Distribution of Groundwater in Trincomalee Coastal Region
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Date
2013
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Uva Wellassa University of Sri Lanka
Abstract
Groundwater is the prime source for people living in dry zone of Sri Lanka, especially
duringdry season for their drinking, domestic and agricultural activities. Groundwater has been
exploited from earliest times in Sri Lanka mainly for domestic use and where readily available
for irrigation as well. Almost 80% of the rural population in Sri Lanka relies on groundwater for
their domestic needs today, because of its excellent natural quality and sustained availability
throughout the year (Panabokke, 2007). Groundwater is frequently contaminated due to
anthropogenic activities. However, some natural phenomena too are responsible for making
groundwater unsuitable for drinking. Seawater intrusion is one such prominent process of
groundwater contamination.
This study focuses on seawater intrusion of groundwater regime along a 22 km long coastal
region of Trincomalee, fromKinniya to Nilaweli by evaluating the salinity distribution of
groundwater. Groundwater plays a significant role as the major source of freshwater for
Trincomalee district during the dry season. The main aquifer type in Trincomalee coastal region
is called ‘shallow aquifer in coastal sand’. This aquifer is well marked in Nilaweliarea (Water
Resources Board 1999-2001). People consuming water from the wells near the sea are highly
affected by the salt (saline) water and undesirable properties of the water. Seawater intrusion
has not only been affecting the groundwater, but also has changed the soil condition making it
unsuitable for agricultural uses. Therefore, most of the farming lands are converted into fallow
lands. After the tsunami in 2004 seawater intrusion has exacerbated more than the past.
Therefore, seawater intrusion becomes a serious issue and has to be controlled for the future
demands both water and land resources. Seawater mainly consists of cations like sodium,
magnesium, calcium and major anion known chloride, which induce salinity and high el ectrical
conductivity.Therefore, measuring the conductivity of groundwater may help identify any
saltwater intrusion.
Methodology
Initially, existing data including aquifer types, geology and topography were studied with the
help of previous researches and monitoring carried out in the area. Wells were selected along a
profile perpendicular to the coastal region until the electric conductivity (EC) value became
very low close to the drinking water standards. Water samples were collected in plastic bottles
and capped tightly for subsequent laboratory analysis. Finally, 32 shallow well samples were
selected for chemical analysis from the area of 22 km coastal belt from Kinniya to Nilaweli.
Well locations were identified using GPS. On the spot measurement for EC of the water
samples was carried out with Orion 3 Star EC meter. Water samples were analysed for Cl by
using Silver Nitrate Titration method. Na was determined by Varian SpectrAA AAS facility
available at the Uva Wellassa University. Spatial distribution of the chemical and physical
parameters in the groundwater was plotted and interpolated using Inverse Distance Weighted
method aided by ArcGIS 9.3 software to visualize the data.
Description
Keywords
Mineral Sciences, Mineral, Science and Technology, Waste Water Treatment, Water quality, Water Chemistry