عنوان مقاله [English]
Groundwater quality is one of the important aspects of hydrogeochemistry, which describes the chemical characteristics and the local distribution of various chemical component of the water for various purposes such as drinking, agriculture and industry Therefore, contamination of these sources can be prevented by timely qualitative examination (Alley, 1993). Chemical composition of groundwater and surface water to depond on natural factors such as geology, topography, meteorology, hydrogeology, biology, precipitation and equilibrium between evaporation and precipitation salts and also seasonal changes in runoff volume and type of runoff, air conditioning (Gibbs,1970; Eilers et al., 1992; Bartram and Balance, 1996; Fernandez et al., 2009)).
The Lordegan plain aquifer was located in south of Chaharmahal and Bakhtiari province. this area is part of Folded zagrous zone that is very important point of water and agricalture. many years ago, quality of watre , in tis area was good but now it is change by agricalture, withdrawal more, use the contaminent and influence geology nformation .In 1976 and 1977, water company, was studied by digging a well. Ostovari et al. (2012) investigated the groundwater quality of Lordegan plain using GWQI index. He believes that water quality is decreasing from the southwest to the north, and factors such as intensive agricultural centers and wastewater treatment plants have led to a decrease in water quality. Also, in statistical studies of Lordegan groundwater quality index by Ostovari et al. (2017), water quality has been divided into low and weak categories. Ahankoub et al. (2021) have studied the defects of geological formations on the quality of Khanmirza aquifer. geology formation including salt , saandstone, limestone,. thes unites contamnated the water and decress its quality .she attributes the decrease in groundwater quality to the involvement of these formations. Unfortunately, there are high drop in groundwater levels due to the uncontrolled abstraction of groundwater storage in recent years. The purpose of this study was to present of the hydro-climatological, geological and hydrogeological properties.
Material and Method
In this study, we were studied hydrochemical data of the ten-year of 283 wells, 69 springs and 9 aqueducts. Also, we were taken samples from 10 wells during wet and dry seasons of 2018 and 2019. Then were measured pH, temperature and electrical conductivity. Other geochemical parameters were measured in the laboratory of Chaharmahal and Bakhtiari Regional Water Company. Then we were prepared map of changes of qualitative by Arc Gis10.1 software, Excel, Piper, sholler and Wilcox diagrams. Finally, we were interpretation all of data for aquifer hydrochemical condition.
Discussion and Results
Lordegan plain aquifer is a free alluvial aquifer that has alluvial thickness varies from 20 to 85 meters. Bed rocks is marl and heights around the plain is include Gachsaran and Asmari Formations, in the eastern parts of the plain. Also, in some parts, Bakhtiari Formation has been present in a scattered manner, which has played a significant role in the storage and quality of aquifer groundwater. Also, Pliocene conglomerate due to the presence of fractures, seams and cracks has played an important role in rainfall absorption and in some cases, while having a suitable construction location, has led to the formation of small reservoirs. Long-time discharge statistics (after extension and reconstruction) are estimated at 94.6 million cubic meters at the station and the average of the river discharge volume at the station is 67.17 million cubic meters in the recent 10-year. Depth data indicates the maximum depth of groundwater in the southern areas of the aquifer of the dry period of October 2018 and minimum depth in the central areas of the aquifer. The study of groundwater in different parts of the plain indicates the highest values of decline in the southern regions of the plain from October 1989 to October 2018. Also groundwater level has dropped by about -0.07 meters. The hydrograph diagram was indicates the decrease of groundwater level during the last 26 years, which is equal to 13.13 meters. The Schuler diagram indicates good and acceptable quality for groundwater drinking. Also, Wilcox diagram (Wilcox, 1995) was shown the groundwater quality of this aquifer for agricultural. In this diagram, electrical conductivity and sodium absorption ratio (SAR) are the effective parameters. Piper diagram was shown facies and type of water in different parts of the plain (PIPER, 1944).
Lordegan plain aquifer in the south of Chaharmahal and Bakhtiari province is folded in the Zagros structural zone and is located under the Semirom zone. Geostructurally, the NW-SE folds in this zone form regular anticlines and synclines. Evidence of Dena fault function at the end of the Neogene and the location of Lower Paleozoic rocks on the Bakhtiari conglomerate and the cutting of ancient alluvial deposits by Quaternary alluviums. Lordegan aquifer is a free alluvial aquifer with an area of 67.2 square kilometers with maximum depth in the southern parts and minimum depth in the central parts, which is located inside the Asmari calcareous formations and passes through the conglomerate formations and is adjacent to evaporitic formations. Geophysical data indicate changes in aquifer depth from 22 to 85 meters. In this study, 10-year period data along with sampling during wet and dry period of 1397-1398 from 10 wells have been used. Hydrographic data indicate a decrease of 0.49 m and a decrease in volume of 0.66 million cubic meters of aquifer volume. Hydrogeochemical data indicate the good quality of aquifer groundwater for drinking and C2S1 grade for agricultural use. In the piper diagram, water type is in the range of magnesium bicarbonate. Also, the chemistry of Lordegan aquifer indicates an increase in water salinity over time. The lithology of the region, the solubility of minerals and rocks in the region, the tectonic state, and the drought of recent years are among the effective factors in reducing the water quality of the Lordegan plain aquifer. Lordegan plain aquifer is a free aquifer with a variable depth of 22-85 meters, which has maximum depth in the southern areas and minimum depth in the central areas of the aquifer. The groundwater flow in the study area is from the southern to the central and northwestern of the plain. Improper withdrawal of water and drought have led to groundwater depletion in the region. The greatest groundwater depletion has occurred in the southern and southeastern parts of the plain. The groundwater level of Lordegan plain has decreased -0.49 meters during year 2018-2019 which has led to a volume decrease of -0.66 m3. The average change of groundwater level, annually for a period of 30 years, has been about -0.44 meters per year (-13.13 meters), which has reduced the average annual reservoir volume by 0.59 million cubic meters per year has been mentioned during the thirty-year period. Hydrogeochemical data indicate to groundwater good quality for drinking and C2S1 category for agricultural.