Evaluation of As, Zn, Cr and Mn concentrations in groundwater resources of Razan plain and preparation of zoning map using GIS

Iran is located in the dry and semi dry zone of the world and almost 90% of its drinking water requirement is supplied from groundwater resources. Considering the increase of pollution and decline of groundwater resources quality due to agricultural and industrial activities and urban development, this study was conducted to evaluate As, Zn, Cr and Mn concentrations in groundwater resources of Razan plain and to prepare the zoning map during spring and summer in 2012. For this purpose, samples were randomly collected from 20 wells across the plain, and pH and temperature parameters were measured in situ. Concentration of heavy metals in groundwater samples was cited by Atomic Emission device after laboratory preparations. The results showed that the mean concentrations of As, Zn, Cr and Mn in the samples were respectively 5.86±0.69, 30.28±3.42, 0.044±0.005, and 3.69±0.40 ppb in spring and respectively 6.83±0.68, 34.50±3.11, 0.046±0.006 and 4.50±0.51 ppb in summer. Moreover, comparison of heavy metals mean concentrations with WHO permissible limits showed that they were lower than standard levels. The results from comparison of variations in heavy metals mean concentration in two seasons revealed the lack of meaningful difference (p<0.05). The determined correlation between pH, water temperature and heavy metals mean concentration accumulated in the samples indicated no correlation between parameters and heavy metals accumulated concentration. Although the groundwater resources in Razan plain are not currently over polluted with heavy metals, long-term and excessive use of agricultural inputs as well as construction of polluting industries can threaten the groundwater resources of this area in addition to bearing some irretrievable consequences.