A GIS-based Assessment of Drinking Quality of Lordegan Plain Groundwater using a GWQI Index

Groundwater quality index (GWQI) is a one of important index to assessment of groundwater quality. The aim of this study was to assess the drinking quality of Lordegan aquifer using a GWQI (groundwater quality index) within a GIS framework. To do this, 97 wells were sampled and pH, Electrical Conductance (EC), Total Dissolved Solids (TDS), Total Suspended Solids (TSS), Turbidity (Tu), Ca2, Mg2,Na,K, Cl-HCO3- , SO42- , NO32- and PO42- were measured. Each parameter was mapped using inverse distance weight method. Each map was difference-normalized and then converted to a rank map. Mean value of a rank map was assumed to be the weight of the corresponding parameter which subsequently were employed in a mathematical expression to obtain GWQI. Mean GWQI of 83 indicates a relatively good quality of water in Lordegan aquifer. GWQI map indicates drinking quality decreases southwest towards the north that may be attributed to the existence of agricultural activities, municipal effluent and gypsum formations present in north of the plain. Map removal sensitivity analysis indicated that TSS, turbidity and to some extent Na were important water parameters, which therefore, must be monitored with greater accuracy and more frequently.