Environmental Effects of Groundwater Development in Xuzhou City, China

摘要

Xuzhou City is located in the most northwestern portion of Jiangsu Province, P. R. China. Karst groundwater in the Ordovician and Cambrian Limestone aquifers is the main source of water supply. There are 527 wells in urban areas to exploit the karst groundwater, yielding up to 35 000 m3 per day. After 1978, urbanization and industrialization of Xuzhou City have continued at a greatly accelerated pace; the population increased from 670 700 (1978) to 1 645 500 (2002), its GDP from 0.71 × 109＄ to 42.7×109＄ and the urban area from 184 km2 to 1,038 km2 (built-up city area from 41.3 km2 to 81.9 km2). The volume of karst groundwater withdrawal increased yearly before the opera- tion of a supply plant of surface water in 1992, from 3.85×107 m3 (1978) to 1.34×108 m3 (1991) and now maintained at 0.1×109 m3 (2002). Intensive overexploitation of karst groundwater has caused a continuous descending of the piezo- metric level and the area of the depression cone increases year after year. These changes have increased the vulnerabil- ity of the karst groundwater system and have induced environmental problems such as depletion of water resources, water quality deterioration, groundwater contamination and karst collapse. The largest buried depth of karst groundwa- ter is up to 100 m in the dry season in some areas, while 66 exhausted wells have been abandoned. A change in the thickness of the unsaturated zone due to the drawdown of the piezometric level has caused a change of the chemical en- vironment which has an impact on the physical state and major chemical compositions in groundwater. The contents of Ca2+, Mg2+, NO3-, SO42– and Cl– in karst groundwater has increased significantly, total hardness (CaCO3 content) rises annually in most pumping wells and exceeds the Standard of Drinking Water of P.R. China. Point source pollution and belt-like pollution along the rivers has caused water quality deterioration. The sudden loss of buoyant support due to rapid drawdown of the piezometric level has induced 7 karst collapses to form 17 pits and has caused an estimated US$10 million economic loss. These problems have influenced the quality of development in the city.