Investigation of Qualitative and Quantitative Changes of Groundwater Resources in Mahvalat Plain

In order to investigate of Mahvalat plain aquifer in Khorasan Razavi, quantitative changes (with completion of questionnaire and periodic data of groundwater level) and qualitative changes (with sampling and chemical analysis) of groundwater resources Has been studied. The analysis of periodic data of groundwater level in a 14-year period (1994-1995 to 2007-2008), showed that the Average drop of groundwater level has been annually 1.35 m. The data analysis of questionnaires showed that the total annual depletion by wells and Qanats is 254 MCM, the annual recharge of basin is 157 MCM and the annual reservoir deficit is 97 MCM. Chemical analysis of 48 water samples from wells and 3 water samples from Qanats showed that the water quality has reduced from the northeastern plain to margins. In terms of classifying the quality of groundwater for agricultural purposes by Wilcox, 5.88% of samples in Class C3-S1, 19.61% of samples in Class C3-S2, 9.80% of samples in class C4-S2, 23.53% of samples in class C4-S3 and 41.18% of samples were placed in class C4-S4. According to this method, 74.51 percent of groundwater samples are not suitable for agriculture.