Comparision of Birjand Plain Aquifer Chromium Monitoring Network Using Principal Component Analysis (PCA) and Entropy Theory

In order to efficiently and effectively manage groundwater resources, it is very important to determine the important points for sampling in terms of reducing the sample size and saving cost and time. In this study, the main chrome monitoring network of Birjand plain aquifer was designed using principal component analysis method and entropy theory, which is a practical method in evaluating quality monitoring systems. For this purpose, 25 aquifers of Birjand plain with a statistical length of 5 yr (2015-2019) were surveyed. In the study area, the average annual chromium (hexavalent) of groundwater was studied using principal component analysis technique and entropy theory to determine the effective sampling wells in the aquifer of this plain. The results showed that out of 25 wells in the study area, 15 wells can be introduced as groundwater chromium index wells of Birjand plain aquifer having a good distribution in the area that can play an important role in reducing sampling costs. Moreover, in order to consider the time factor in the changes, this method was performed in two time periods of 2 and 3 yr. The results showed that in the period of 2 yr (2015-2016), 19 wells were selected as effective wells, while the number reduced to 17 wells in the period of 3 yr (2017-2019). Entropy theory showed that all wells in the region are of equal importance in monitoring network design.