Study On Evolution Of Water Quality And Impact Of Oil Development In The Malian River Basin Of Longdong Loess Plateau

With economic development and social progress, water resources must be a valuable resource in arid and semi arid area. Groundwater, as a component of total water resources, plays an important role in te development of Qingyang basin because of its sTablele quality and quantity. In recent years, due to the unreasonable development and utilization of water resources, lead to the degradation of water quality in the area, endangers future water exploitation and limits the supply of poTablele fresh water. Therefore, to utilize and protect valuable water resources effectively and predict the change in water environments, it is necessary to understand the impact of oil industry on water resources and its evolution wnder natural water circulation processes.Based on the analysis of regional hydrogeological conditions, climate characteristics, characteristics of oil development and the emission in Qingyang County, Huanxian, and surrounding areas of Dongzhiyuan, the various anions and cations content are measured for hydrogeochemical interpretation and model esTablelishmentin underlying surface area.The groundwater recharge and evolution characteristics are affected by the interaction between water and rock, while the fuzzy mathematics combined with the use of surface water chemistry are applied to reveal the evolution of surface water qualitatively and quantitatively.Furthermore, the impact of oil development on the local water resources is identified. The results showed that: The surface water salts (TDS) evolutes decreased salinity from north to southwest, from the minimum value near the southwest Zhao Jiachuan 390mg/L, greatly increasing of the salinity from the transition to the bridge north of Hongde to 7965mg/L. The ion changes were more severe of 150km away from Shancheng, and change slowly from 150km to 300km. Using the method of fuzzy mathematics, the results of surface water environment quality evaluation show that most areas of Wangwan and Han Jiachuan Bay Bridge are polluted, where the proportion of V class water accounted for 0.877 and 0.874, on the contrary, Fengjiadong, the proportion of I class water accounted for 0.693 as the better water quality. According to the monitoring of Quzi, Hanjiawan and Ningxian, as a result that before 2000 years, petrolwum and metal poullutants is more evident, after 2000 years, oil and metal pollutants decreases significantly, COD and potassium permanganate index increased significantly.The groundwater salts (TDS) evolutes from the minimum value near the southwest Xiansheng 230mg/L, greatly increasing of the salinity from the transition to the north of Huanxian 7965mg/L. Across the whole aquifer, groundwater evolves gradually from SO42--HCO3--Cl--Na+-Ca2+type water in Huanxian to more ineralized Cl--HCO3--SO42--Na+-Ca2+type water in Qingcheng, and then becomes HCO3--Ca2+-Na+ type water in Dongzhiyuan. From the diagram by plotting of ion relationship, can be seen in Dongzhiyuan, ion content were lower and had no obvious law, but in Qingcheng and Huanxian, all ions increased by Cl- except HCO3-. The geochemical inverse model confirmed that proposed water-rock interactions can occur in this system. The chemical composition of the water is strongly influenced by evaporation of shallow groundwater, dolomite and gypsum, aragonite dissolved into the water, anhydrite precipitation from solution. Meanwhile, in Dongzhiyuan, aragonite, calcite, dolomite gypsum and other substances have experienced varying degrees of precipition except anhydrite and halite.Since the discovery of oil in 1996, as the oil-rich, a lot of oil production led to a high water consumption, causing a certain amount of pollution and waste. It has a serious impact on the groundwater and lasts a long time in case of abnormal emissions but has little effect under normal circumstances. The wastewater mainly from the company of Qinghua, and the company put them into Malian river directly causing serious problems. Dongzhiyuan area as the main areas of agricultural production, heavy use of fertilizers has adverse impact on groundwater. Connecting the groundwater resources and their facts of expoitation and utilization, aiming for the main problems and contradictions in the exploitation and utilization of groundwater were esTablelished with the guide of groundwater system theory and the angle of sustainable supply, regional social and economic development and ecologic recycle. In order to form the sustainable management systems of groundwater resources, the higher efficient management systems and running mechanisms and a series of laws should be establelished.