Influence of Urbanization on Groundwater Chemistry at Lanzhou Valley Basin in China

With the rapid development of the economy, urbanization and industrialization gradually become an important driving force of groundwater chemical evolution. In this study, Lanzhou City, which is one of the biggest industrial cities in northwest China, was selected to investigate the impacts of city development on groundwater quality. Several hydrochemical methods together with principal component analysis (PCA) were used for the hydrochemistry evolution characteristics and sensitive factors of groundwater chemistry in different urban functional areas of Lanzhou City. The results show that 96% of the groundwater in the study area cannot meet the groundwater quality standards of China. The main factors affecting the quality are SO42-, TDS, total hardness, Mg2+ and Na+. Urbanization and industrialization lead to further deterioration of the already naturally high TDS groundwater. NO3-, Cl- and NH4+ are the characteristic factors of human input sources for commercial residential areas; total Fe and NO3- are the characteristic factors of new urban areas in the urban-rural junction; and SO42-, NO3-, Cl-, Total Fe, Mn2+, F-, I-, Pb2+, Cr6+ and As3+ are the characteristic factors of industrial areas. Domestic sewage infiltration and manure infiltration are the main driving factors of groundwater quality deterioration in commercial residential areas. Nitrate fertilizer infiltration and sewage irrigation are the main factors leading to the increase in nitrate nitrogen in groundwater in the new urban area. Industrial wastewater leakage and organic pollution that promote the dissolution of minerals in the aquifer (the dissolution of fluorine-containing minerals and reductive dissolution of iron manganese oxides) are the main driving factors for the deterioration of groundwater quality in the petrochemical industrial area.