Investigation of groundwater quality changes in Varamin Plain of Tehran

Assessing the quality of water resources, especially drinking water resources, has been of great importance in recent years, along with the per capita reduction of available water resources. Water quality index for drinking and irrigation expresses the total quality of water through a single number at a specific time and place based on various water quality parameters. In this study, the quality of water resources in Varamin Plain was studied using water quality index (WQI) over a period of 10 years.

Varamin plain is located 45 km southwest of Tehran and at an altitude of approximately 1000 meters above sea level. Its alluvial plain area is about 138,000 ha, of which more than 50,000 ha are agricultural lands. In this research, data from 35 qualitative data samples including pH, total dissolved solids (TDS), EC, Calcium, Potassium, Sodium, Magnesium, Bicarbonate, Chlorine and Sulfate have been studied. Also, using Pearson correlation, the relationship and the effect of the parameters on each other were investigated. These samples were prepared from different parts of Varamin Plain in a period of 10 years (2008-2018) and the concentration of parameters affecting the quality of groundwater resources was investigated. In this study, ArcGIS 10.5 software was used to prepare spatial distribution maps and SPSS software was used for statistical analysis.

According to the WQI in 2008, 51.42% of the region has inadequate water, which in 2018 has decreased to 45%. Also, calcium, sodium and chlorine have a positive and significant correlation with TDS. According to the spatial distribution map of Varamin Plain in 2018, it has more area with suitable quality, while the southern and southwestern part of the region, despite improving the water quality of the region, still have unsuitable quality for drinking. The WQI spatial distribution maps show that the area percent of good class of WQI in 2018 has increased compared to 2008. In both years, the southern and southwestern regions are in poor condition. The high concentration of TDS and EC in some places was due to land use change, wastewater discharge, ecogeomorphological factors, as well as over-extraction of groundwater resources. Good quality range in 2008 is in the central areas, which in 2018, these areas include most of the central and eastern regions.

In general, the results of this study showed that currently the values of a number of effective parameters in determining the quality of groundwater resources such as TDS and EC in most sampled areas and also the pH value in some sampled areas of Varamin Plain has exceeded the standards. In addition, groundwater quality has slightly improved during the study period (2008-2018). Thus, considering the widespread impact of human factors on reducing the quality of groundwater resources in Varamin Plain and the severe rate of groundwater abstraction, careful study of illegal wells in the region, quality protection of groundwater resources and management of exploitation wells and the use of appropriate irrigation systems, proper harvesting as well as proper drainage of agricultural lands is essential in future plans.