Spatial and Temporal Characteristics of Carbon Tetrachloride Pollution in a Karst Aquifer

The karst aquifer in a northern city of China was polluted by carbon tetrachloride (CCl₄). The pollution characteristics was studied by four years´ monitoring CCl₄ concentration of the karst groundwater in 15 typical wells and analysis of the CCl₄ content in 206 soil samples from 17 boreholes in polluted source area. The CCl₄ pollution plume is distributed as a belt-dumbbell form. Two polluted centers are located at the southern pollution source sub-area and the northern artificial discharge sub-area respectively. 95.4% polluted wells are laid in Ordovician limestone aquifer. In general, CCl₄ concentration of groundwater in all wells decreased in recent years and inside a year the CT concentration during the period of August to October was much higher. The CCl₄ polluted the karst aquifer by directly seeping of wastewater in the pesticide plant area, flowing into the aquifer through bare section of limestone in effluent ditch, and leaking under ditch by soil. The heterogeneity of water-bearing media and artificial exploitation control the CCl₄ diffusion and the CCl₄ plume is similar with the groundwater flow field.