**2.1 Site location and pollution source**

Karst aquifer investigated is located in the Northern China Plain. Karst aquifers provided averagely 25.8×104 m3/d to urban public water supplies from 1981 to 2008 (Liu, 2010). As illustrated in the Fig.1, the karst water is in a relatively confined groundwater system unit and its east and west boundaries are coal seam water-resisting layers and the south and north are groundwater watershed. The karst groundwater system is composed several *relatively independent aquifers. The CCl4 pollution occurs in the* southern Qiligou water-bearing basin.

Fig. 1. *Hydro-geological zonation of the karst groundwater system in the city*

According to monitoring data obtained in November, 2000, it has been contaminated with CCl4 in Qiligou water-bearing basin. The pollution source is a pesticide plant which produced a pesticide that used CCl4 as a solvent and it has used more than 42 tons of CCl4 in the past ten years. This plant is located at hill slope in southwestern recharge area of the karst aquifer (Fig. 2). However, emergency measures were taken in 2001, including closing the pesticide plant and intensive pumping from heavily polluted wells. Untill May 2001, carbon tetrachloride was found in 53 wells (contaminated area is about 17.3 km2). The highest CCl4 concentration in karst water was over 3900 μg/L in a water supply well approximately 465m away from the pesticide plant. The concentration in Chinese standards for drinking water quality is lower than 2μg/L (GB5749-2006) (China's Ministry of Heatlth, 2006). Since then, the contaminated wells have not been used for dinking water. While, some lightly contaminated wells have been pumping for *agricultural and industrial production.*

Fig. 2. View of the pesticide plant and its wastewater drainage
