Using the IRWQIGT Index to Determine Toxicity Levels in Groundwater Resources: A Case Study of Semnan Province

The objective of the present descriptive-analytic study was to estimate the toxicity level of the groundwater resources in the Province of Semnan using the IRWQIGT index and its zoning via GIS. The experiments were conducted over the period from October 2013 to October 2014during which time monthly samples were taken from the 41 wells that supply drinking water to the cities and towns in the Province. All the samples were subjected to lab analyses at Semnan Water and Wastewater Laboratory where such chemical parameters as Arsenic, Phenol, Mercury, Detergents, Cadmium, Lead, Chromium, Cyanide, Iron, Magnesium, and TPH were determined according to the procedures of Standard Methods (2008). The measuerments were subsequently used to calculate the groundwater toxicity level index (IRWQIGT). Finally, a zoning map of the IRWQIGT index for Semnan Province was prepared using GIS. Results showed that the IRWQIGT index in Semnan Province ranged between 96.54 and 98.2, indicating an excellent water quality. The lowest (96.585) and highest (98.076) values of IRWQIGT were recorded in the cities of Sorkheh and Mahdishahr, respectively, and that the values for all the parameters were in the standard range. These results indicate that water of excellent quality is available in all the cities in the province so that no toxicity treatment is required.