Determining the spread of aromatic oil compounds caused by gasoline leakage in the northern parts of the Shazand plain and the role of the cone of depression in developing contamination plume

Nowadays, groundwater pollution, especially the pollutants realized from petroleum refineries and petrochemical complexes, in which the pollution potential of leakage is more possible is one of the main concerns of humanity. In the present research, the northern parts of Shazand plain, Arak province, an area with concentrated industrial units, have been selected as a case study to investigate the oil contaminant caused by the leakage of gasoline at the upstream of well No. 7 in Shazand plain. After stopping the pollution leakage, in order to determine the pollution status, a number of points were selected to drill monitoring wells along the flow direction and two rounds of sampling in August and March 2019 were conducted. The results of analyzed samples revealed that the pollution is gasoline type. Also, the absence of pollution in some of the monitoring wells indicated that the pollution did not spread so much in the monitoring wells MW5, MW6, PB3, and MW4 with concentrations of 7121.5, 3820.7,1046, 257 µg/l and in well No. 7 (260.8 µg/l) as well. In fact, during the period of leakage, the plume progressed downstream of the plain, in about 10 hectares, but the development of a depression cone due to the over-extraction of this well has prevented its further spread of it. Given the aquifer storage coefficient and the depth of groundwater, it has been estimated that about 365000 cubic meters of the aquifer are polluted by the oil contamination.