Abstract
Chunnakam aquifer is the main lime stone aquifer of Jaffna Peninsula. This study focused on characterization of Chunnakam aquifer for its suitability for irrigation. Groundwater samples were collected from wells to represent different uses such as domestic, domestic with home garden, public wells and farm wells during January to April 2011. Important chemical parameters, namely electrical conductivity (EC), chloride, calcium, magnesium, carbonate, bicarbonate, sulfate, sodium and potassium were determined in water samples from 44 wells. Sodium percentage, Sodium adsorption ratio (SAR), and residual Sodium Carbonate (RSC) levels were calculated using standard equations to map the spatial variation of irrigation water quality of the aquifer using GIS. Groundwater was classified based on Chadha diagram and US salinity diagram. Two major hydro chemical facies Ca-Mg-Cl-SO<sub>4</sub> and Na-Cl-SO<sub>4 </sub>were identified using Chadha diagram. Accordingly, it indicates permanent hardness and salinity problems. Based on EC, 16 % of the monitored wells showed good quality and 16 % showed unsuitable water for irrigation. Based on sodium percentage, 7 % has excellent and 23 % has doubtful irrigation water quality. However, according to SAR and RSC values, most of the wells have water good for irrigation. US salinity hazard diagram showed, 16 % as medium salinity and low alkali hazard. These groundwater sources can be used to irrigate all types of soils with little danger of increasing exchangeable sodium in soil. However, 2 % of the wells are not suitable for irrigation due to very high salinity and sodium hazard. <em>Tropical Agricultural Research Vol. 23 (3): 237-248 (2012)</em> DOI: <a href="http://dx.doi.org/10.4038/tar.v23i3.4661">http://dx.doi.org/10.4038/tar.v23i3.4661</a>
Highlights
The population of the Jaffna Peninsula depends entirely on groundwater resources to meet all of their water requirements
Classification of the groundwater based on chemical facies
Such water has permanent hardness and does not deposit residual sodium carbonate in irrigation use. Another 32 % of the groundwater samples fall in the field of 7 which belongs to Na+-Cl--SO42- hydro-chemical facies and represents Na+-dominant Cl- type, or Cl--dominant Na+ -type waters
Summary
The population of the Jaffna Peninsula depends entirely on groundwater resources to meet all of their water requirements. The Jaffna Peninsula has four main types of aquifer system namely Chunnakam (Valikamam area), Thenmaradchi, Vadamaradchi and Kayts (Puvaneswaran, 1986). Limestone is the main aquifer in the Jaffna Peninsula. The low salinity groundwater lenses that constitute the Jaffna Peninsula aquifer system are the only sources of drinking water for the Peninsula. Freshwater lenses supply a large proportion of supplementary irrigation water in the Peninsula (Punthakey & Nimal, 2006). Groundwater is an extremely valuable resource in the Peninsula and pollution of groundwater is a matter of serious concern
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