CHEMICAL STUDIES OF GROUND WATER AND ITS SUITABILITY FOR IRRIGATION

Abstract

An investigation was carried out to assess the quality of 75 water samples of which 68 samples were groundwater and 7 were from surface sources collected from Dinajpur Sadar. The chemical analyses results were used to determine the hydrogeochemical processes of differentions for their suitability for irrigation and drinking water samples were analysed for pH, electrical conductivity (EC), cations (Ca**, Mg**, Na*, K*, Zn?*, Cu’*, Mn** and Fe**), anions (CO3”, HCO;3, NO;3, S04”, PO, and Cl) and TDS (total dissolved solids). Several variables were compated such as SAR (sodium adsorption ratio), SSP (soluble sodium percentage), RSC (residual sodium carbonate), permeability index (PI), Kelly's ratio, potential salinity, Gibbs ratio and hardness to evaluate the suitability of groundwater supply for specific uses. The pH values indicated that the waters were mostly acidic in nature. From the geochemical results, it has been found both the cations and anions varied in the groundwater. The average values of Mg and Cl was 2.22 meq L” and 1.84 meqL'. Among the chemical budget of ions, Mg and Cl were found to be the most predominant ions. The average value of Ca, Na, K and HCO3 were 1.65 meq Cs 2.10 meq L”, 0.05 meq L"!, and 3.06 meq L" respectively. The above values of these samples were safe limit for crop production. The intense agricultural activities may be an important factor for the higher NO3 concentration in these aquifers. The mean values of TDS and SAR were 165.8 mg L’! and 1.58. As per TDS all the waters were excellent and SAR indicated the excellent category for irrigation purpose. Based on SSP all waters were excellent classes. In respect to hardness, water had moderately hard to very hard class. Based on the total hardness, most ground waters are moderately hard. All waters were free from RSC and belong to the suitable category. According to EC and SAR the most dominant class is Cl-S1. The major ion concentrations are below the acceptable level for drinking water. The salinity hazard is low thus, there is less chances to increase of toxic salt concentrations. Other micronutrient like Fe, Zn, Mn and Cu were within the safe limits for irrigating all types of agricultural crops. Some samples had high concentration of Fe and Mn that exceeded the drinking standard. Other ions likes Cl, Cu, Zn and SO, were within the safe limit. Regarding cation and anion constituents, groundwater is suitable for irrigation, purposes except of few wells.