ارزیابی اثرات نواحی صنعتی بر کیفیت منابع آب زیرزمینی با استفاده از مدل DRASTIC

Introduction
Today, industrial units have become industrial complexes and towns and are expanding rapidly. In most of these areas, comprehensive and appropriate studies have not been conducted from the perspective of land use planning, therefore environmental parameters such as proper distance from aquifers or other water sources such as wells, springs and aqueducts and proper privacy have not been studied. Also, most of the wastewater of industrial will being injected directly into the ground through absorption wells without treatment, and consequently, it will pollute the groundwater sources. Therefore, knowing the status of groundwater vulnerability is one of the important principles in groundwater resource management. Vulnerability The possibility of groundwater pollution is a qualitative concept and cannot be measured and must be deduced from other information that can be measured. Various methods have been proposed for groundwater vulnerability. Overlap methods combine the parameters that control the movement of pollutants from the ground to the saturated area and determine an index called the vulnerability index in different parts of an area. One of the most widely used and well-known methods is the DRASTIC model overlap index (Rouhi et al., 2017). In Najafabad city, due to having an arid and semi-arid climate and providing most of the water needs from groundwater resources, attention to the vulnerability of groundwater resources is essential. On the other hand, in the study area, the presence of land uses such as Alavijeh city, Alavijeh industrial town and agricultural land use on the aquifer increases the probability of point and non-point source pollution entering the aquifer environment and its vulnerability. Therefore, in this study, the vulnerability of the aquifer was investigated using the correct model to be informed of its status, the necessary measures are taken.
Research method
• Scope of the study Alavijeh industrial town is located at km 70 of Isfahan-Alavijeh road and the closest residential area to this option is Alavijeh city, 2 km east of it (Figure 1). The existing Alavijeh industrial town with an area of 200 hectares, due to its location in Najafabad city, has greatly contributed to the economy of this city.
• DRASTIC model
It is the numerical ranking model of the US Environmental Protection Agency and the American Water Wells Association to assess the strength of groundwater vulnerability. This model consists of seven measurable and effective hydrological characteristics in the transfer of pollution to groundwater, including groundwater depth, artificial recharge, aquifer, soil environment, slope, unsaturated zone constituents and electrical conductivity. These layers are provided in the GIS environment (Rahman et al., 2021). To determine the relative importance of each layer, according to the importance of the impact on the pollution of the groundwater system, a relative weight of 1-5 is considered. In this model, the ranks of each of the hydrological characteristics are assigned a rank based on their impact on vulnerability. At the end, seven prepared layers are stacked and the final layer of groundwater vulnerability is obtained.
Conclusion
• Assess the risk of aquifer vulnerability
Alavijeh industrial town is located in the study area of Morchekhort and Zayandehrood grade 4 basin. The wells in the study area are of smallholder type and have been drilled mainly for agricultural purposes. Based on the analysis of groundwater level curves in the area, the maximum groundwater level is 2135 meters, which gradually decreases to the east of the groundwater level and reaches at least 1805 meters (average: 1971 meters). It is also the direction of groundwater flow in the region, from northwest to southeast. According to the Piscopo method, the artificial recharge index is ranked 3rd and 6th in the industrial town. The constituents of the aquifer environment have a score of 4 (sand particles with clay (50%) with conglomerate) and the unsaturated area has a score of 3 (sand, rubble and clay). Due to the granulation and characteristics of sediments between the surface and groundwater, the presence of fine-textured materials such as clay and loam reduces the ability to transfer contaminants from the soil surface to groundwater. Therefore, the probability of migration and transfer of pollutants in the area to groundwater has been moderate to low. On the other hand, due to the low slope of the area, the contact time of surface water and pollutants with the ground surface is increased and there is a greater chance of infiltration, which increases the vulnerability in the area. In general, the Drastic index is in the range of 23-230. In the study area, this index was obtained between 50-130.Aquifer vulnerability was divided into 2 zones of low and medium vulnerability. As shown in Figure 1, about 30% of Alavijeh industrial town is located on the aquifer and the western part of the industrial town has a higher potential for vulnerability than the eastern part. In the western part of the study area, the aquifer in the western part is more vulnerable due to the higher rank of aquifer nutrition and soil environment.
Due to the establishment of metal, non-metallic and textile industries up to grade 5 in the industrial town, wastewater pollution caused by the activities of these industries, if environmental standards are not observed and discharged to absorption wells can cause severe groundwater pollution. It is noteworthy that the existing town has more than 80% of the units connected to the town's treatment plant system and 20% of the remaining units are not connected to the treatment plant system. These units have either pre-treated, purified and recycled water in the production process and a number of units are also used absorbing wells and not connected to the wastewater treatment system. However, it is necessary to require all units to connect to the industrial town treatment plant to prevent the transfer of contaminant load to groundwater sources. Another land use in the study area that can increase the vulnerability of the aquifer is the presence of the city of Alavijeh on the aquifer, which is located two kilometers from the industrial town of Alavijeh. Although the city is in a low vulnerability zone, it does not have a treatment plant and sewage is discharged to absorption wells. Also, the area around this city and the industrial town are covered with agricultural lands and gardens, and agricultural lands are located on the aquifer, which in case of excessive use of pesticides and chemical fertilizers, especially nitrate fertilizer, pollution of groundwater sources will occur.